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Highly-efficient Photocatalytic Disinfection of Escherichia coli under Visible Light Using Carbon Supported Vanadium Tetrasulfide Nanocomposites

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... Many different materials can be used as semiconductors for PC such as titanium dioxide (TiO 2 ), zinc oxide (ZnO), magnesium oxide (MgO), calcium oxide (CaO), tin oxide (SnO 2 ), tungsten oxide (WO 3 ), iron oxide (Fe 2 O 3 ) and aluminum oxide (Al 2 O 3 ) [94,97]. In recent years, these semiconductors have been extensively investigated coupled with UV for water disinfection [98][99][100][101][102]. ...
... Different strategies have been developed to enhance the photocatalytic efficiency with the modification of photocatalyst [97] such as mesoporous supports, metal doping, non-metal doping, nanoparticles, semiconductor coupling [106,107]. To overcome these operational problems caused by suspensions of fine powder, catalysts are usually immobilized on different supports such as silica gel [108], alumina [27], activated carbon [109], polymers [88], glasses [106], meshes [110,111] and graphene oxides [100]. ...
... Baogang Zhang et al. [97] examined the photocatalytic disinfection performance of various carbon supported Vanadium tetrasulfide (VS 4 ) nanocomposites based on the bacteria inactivation rate of E. coli as an indicator. Among them, the cost-effective and lattice-structure VS 4 /CP (carbon powder) showed the best disinfection performance for removing E. coli under both simulated visible light (irradiance:100 W m −2 , dose: 18 J cm −2 ) and sunlight (irradiance:~379.2 ...
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Among the critical issues that prevent the reuse of wastewater treatment plants (WWTPs) effluents in a circular economy perspective, the microbiological component plays a key role causing infections and diseases. To date, the use of conventional chemical oxidants (e.g., chlorine) represent the main applied process for wastewater (WW) disinfection following a series of operational advantages. However, toxicity linked to the production of highly dangerous disinfection by-products (DBPs) has been widely demonstrated. Therefore, in recent years, there is an increasing attention to implement sustainable processes, which can simultaneously guarantee the microbiological quality of the WWs treated and the protection of both humans and the environment. This review focuses on treatments based on ultraviolet radiation (UV) alone or in combination with other processes (sonophotolysis, photocatalysis and photoelectrocatalysis with both natural and artificial light) without the dosage of chemical oxidants. The strengths of these technologies and the most significant critical issues are reported. To date, the use of synthetic waters in laboratory tests despite real waters, the capital and operative costs and the limited, or absent, experience of full-scale plant management (especially for UV-based combined processes) represent the main limits to their application on a larger scale. Although further in-depth studies are required to ensure full applicability of UV-based combined processes in WWTPs for reuse of their purified effluents, excellent prospects are presented thanks to an absent environmental impact in terms of DBPs formation and excellent disinfection yields of microorganisms (in most cases higher than 3-log reduction).
... The stability of Cu-VO was similar to BaTiO3@g-C3N4. Zhang et al. [51] and Cai et al. [48] found that the leaching of vanadium in water from VS4/CP was <1%, which was considered stable and safer to use [38]. The leaching of copper and vanadium was less than 2% of 8 mg/L of Cu-VO, indicating that it could be stable and safer for practical use. ...
... The photocatalytic experiments were performed under natural solar light on sunny days [51]. The sky was clear, with slight fluctuations in solar intensity. ...
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In this work, solar-light-active copper–vanadium oxide (Cu-VO) was synthesized by a simple microwave method and characterized by FESEM, EDS, XRD, XPS, UV–Vis/near-infrared (NIR), and FT-IR spectroscopy. Antialgal and dye degradation activities of Cu-VO were investigated against Microcystis aeruginosa and methylene blue dye (MB), respectively. The mechanism of action of Cu-VO was examined regarding the production of hydroxyl radical (˙OH) in the medium and intracellular reactive oxygen species (ROS) in M. aeruginosa. FESEM and XRD analyses of Cu-VO disclosed the formation of monoclinic crystals with an average diameter of 132 nm. EDX and XPS analyses showed the presence of Cu, V, and O atoms on the surface of Cu-VO. Furthermore, FT-IR analysis of Cu-VO exposed the presence of tetrahedral VO4 and octahedral CuO6. Cu-VO effectively reduced the algal growth and degraded methylene blue under solar light. A total of 4 mg/L of Cu-VO was found to be effective for antialgal activity. Cu-VO degraded 93% of MB. The investigation of the mechanism of action of Cu-VO showed that ˙OH mediated antialgal and dye degradation of M. aeruginosa and MB. Cu-VO also triggered the production of intracellular ROS in M. aeruginosa, leading to cell death. Thus, Cu-VO could be an effective catalyst for wastewater treatment.
... Inhibiting intracellular substances (K + ions, DNA, endotoxin, and lipid peroxidation), reducing metabolic activities, and stopping multiplication of bacterial cells have been documented under photoinactivation [4,15,17,18]. Furthermore, discharge of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein from the cells suppressed cellular replication [19][20][21]. Initial attack of nucleic acids by ROS on the sugar/phosphate backbone of both DNA and RNA occurred [22]. ...
... The pyrimidine and purine group of nucleic acids were converted to carbon dioxide, ammonia, and nitrate ions during photocatalytic disinfection [22]. Several studies also proposed that the degradation of nucleic acid and adenosine triphosphate was the main mechanism for photocatalytic inactivation [21,24]. However, the importance of approaches to understand the annihilation mechanism should be focused on the interface of nanostructure/cell-wall microorganism. ...
Article
The mechanism of bacterial damage under visible-light-driven photo-inactivation system was attempted. Atomic force microscopy (AFM) and transmission X-ray microscopy (TXM) were firstly used to identify changes in biophysical properties, such as cellular height, roughness, adhesion, and modulus, and 3D cellular structure of microbial cells under visible-light-responsive N-TiO2 inactivation. Results revealed that the cell adhesion of N-TiO2 occurred immediately upon light irradiation then N-TiO2 particles penetrated the cell membrane, and deformed the cellular structure at the beginning of log phase under photocatalytic inactivation. The destruction of the outer cellular caused leakage of cellular K⁺ and lipid peroxidation, which ultimately brought about severe decrease in cell density. AFM and TXM provided direct observations on interactions between single cell and nano-materials at the nanoscale, which was useful for the early diagnosis of cell damage.
... The COVID-19 pandemic has demonstrated the critical importance of sanitation, hygiene and adequate access to clean water for preventing and containing diseases. Developing economical and effective water disinfection methods is of great significance for human health as well as alleviating clean water scarcity issues Zhang et al., 2018). Conventional water disinfection approaches, including chlorine-based chemical disinfectants, ozone, and ultraviolet (UV), are capable of eliminating a majority of pathogens in water (Xia et al., 2017). ...
... Ozone and UV inactivation methods are much safer, but require more energy consumption. Recently, metal-based photocatalysts, such as titanium dioxide (Fernández-Ibáñez et al., 2015;Cavalcante et al., 2016) and zinc oxide (Masoumbaigi et al., 2014), have been extensively investigated as new disinfectants (Cavalcante et al., 2016;Zhang et al., 2018). However, most metal-containing photocatalysts are activated by UV light irradiation, which is only 4% of the solar spectrum reaching earth surface (McGuigan et al., 2012;Ng et al., 2020). ...
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Graphitic carbon nitride (g-C3N4) as metal-free visible light photocatalyst has recently emerged as a promising candidate for water disinfection. Herein, a nanowire-rich superhydrophilic g-C3N4 film was prepared by a vapor-assisted confined deposition method. With a disinfection efficiency of over 99.99% in 4 h under visible light irradiation, this nanowire-rich g-C3N4 film was found to perform better than conventional g-C3N4 film. Control experiments showed that the disinfection performance of the g-C3N4 film reduced significantly after hydrophobic treatment. The potential disinfection mechanism was investigated through scavenger-quenching experiments, which indicate that H2O2 was the main active specie and played an important role in bacteria inactivation. Due to the metal-free composition and excellent performance, photocatalytic disinfection by nanowire-rich g-C3N4 film would be a promising and cost-effective way for safe drinking water production.
... All the experiments were performed in duplicate. Moreover, to elucidate the main oxidizing agents produced by the CNT-TiO 2 system, isopropanol ( OH quencher) and sodium oxalate (h þ quencher) were employed in the photocatalysis process (i.e., in ultrapure water) (Zhang et al., 2018a). ...
Article
Natural organic matter (NOM) can inhibit the photocatalytic degradation of organic micropollutants (OMPs) through inner filter effect, reactive oxygen species (ROS) scavenging, and competitive adsorption. However, previous studies have focused solely on the bulk properties of NOM and our understanding of the inhibition mechanism by NOM fractions during photocatalytic degradation of OMP is still fragmentary. In this study, five well-characterized different NOM samples (i.e., secondary treated wastewater, river water, and three standard NOM surrogates) were used to elucidate the inhibition mechanisms during photocatalytic degradation of carbamazepine (a model OMP) using TiO2 and its composites with carbon nanotubes (CNT-TiO2) under UVC and solar-light irradiation. The results indicated that terrestrially derived NOM with high aromaticity, a low oxygen/carbon atom ratio, and large molecular weight is the major fraction that participates in ROS scavenging, competitive adsorption, and inner filter effect. Furthermore, the modeling analysis suggested that inner filter effect due to NOM and ROS scavenging was the most influential inhibitory mechanism. In the case of secondary treated wastewater, the presence of high concentrations of inorganic species (e.g., PO43-, Cl-, and NO3-) together with NOM significantly reduced the photocatalytic degradation of carbamazepine. Overall, the methods and the results of this study provide a comprehensive understanding of the effects of NOM fractions on photocatalysis and highlight the need to further consider the interplay between NOM and background inorganic constituents in photocatalytic degradation of OMP.
... In addition, the valence of vanadium in the precipitates was analyzed by XPS (Figure 2d). The sub-band with the peak binding energy of 515.9 eV was identified as V(IV), 35 providing solid evidence that V(V) had been biotransformed to insoluble V(IV) by L. raf finolactis, achieving V(V) detoxification efficiently. Peaks corresponding to V(V) were also detected in the XPS spectrum, due to the easy reoxidation nature of the produced V(IV) in air. ...
Article
Whereas prospects of bioremediation for a vanadium(V) [V(V)]-contaminated environment are widely recognized, reported functional species are extremely limited, with the vast majority of Gram-negative bacteria in Proteobacteria. Herein, the effectiveness of V(V) reduction is proved for the first time by Lactococcus raffinolactis, a Gram-positive bacterium in Firmicutes. The V(V) removal efficiency was 86.5 ± 2.17% during 10-d operation, with an average removal rate of 4.32 ± 0.28 mg/L·d in a citrate-fed system correspondingly. V(V) was bio-reduced to insoluble vanadium(IV) and distributed both inside and outside the cells. Nitrite reductase encoded by gene nirS mainly catalyzed intracellular V(V) reduction, revealing a previously unrecognized pathway. Oxidative stress induced by reactive oxygen species from dissimilatory V(V) reduction was alleviated through strengthened superoxide dismutase and catalase activities. Extracellular polymeric substances with chemically reactive hydroxyl (−OH) and carboxyl (−COO–) groups also contributed to V(V) binding and reduction as well as ROS scavenging. This study can improve the understanding of Gram-positive bacteria for V(V) bio-detoxification and offer microbial resources for bioremediation of a V(V)-polluted environment.
... However, the diffraction among TiC, TiN and Ti(C,N) was difficult to be distinguished due to their extremely similar diffraction angles. The similar phenomenon also existed in the XRD patterns of V tetrasulfide after supported by different carbon materials [34,35]. TiC always combined with TiN to form a solid solution (Ti(C,N)). ...
Article
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Direct reduction–magnetic separation followed by low temperature chlorination was a promising process to comprehensively utilize vanadium–bearing titanomagnetite (VTM). Herein, the conversion of titanium oxides to TiC/TiN/Ti(C,N) is extremely critical. In this study, the carbonization and nitridation of VTM during carbothermal reduction under different atmosphere was investigated. Thermodynamic analysis indicated that the reduction, carbonization and nitridation of VTM was feasible via carbothermal reduction by carbon. Introducing N2 into the reaction system was beneficial to decrease the equilibrium temperature by forming TiN instead of TiC. The experimental results showed that the Fe metallization ratio (MFe/TFe) reached about 100 wt% above 1150 °C regardless of the reduction atmosphere. The maximum carbonization ratio of Ti (TiC/TTi) was 98.55 wt% after roasting at 1300 °C for 2.5 h in Ar atmosphere. The total carbonization and nitridation ratio (TiN/TTi) was 99.55 wt% when reduced at 1300 °C for 2.5 h in N2 atmosphere. The main Ti–bearing phases were reduced and carbonized in the order of ilmenite (FeTiO3)→ ferropseudobrookite (FeTi2O5)→ Fe,Ti,Mg Oxide (Fe0.33Ti0.46Mg0.21)(Ti1.9Mg0.1)O5→ titanium carbide (TiC). TiC was further nitrided to form TiN, which combined with TiC as titanium carbonitride (Ti(C,N)). TiC/TiN/Ti(C,N) granules, with a particle size less than 10 μm, were mainly dispersedly distributed in metallic iron. They also gathered at the edge of metallic iron and part of them existed in the the interval between metallic iron and gangue minerals.
... In the last few decades, 2D TMDC/Os with general chemical formula of AB X (A: transition-metal, B: chalcogen), have been studied extensively in nanotechnology field owing to their unique graphene-like properties, which are composed of a "sandwich" structure of "B-A-B" or "B-A-O" through weak Van der Waals forces [178][179][180]. Prototypical TMDC/Os, MoS2, MoO 2 , MoSe 2 , WO 3-x , and WS 2 are the most extensively explored ones [181,182]. ...
Article
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The marked augment of drug-resistance to traditional antibiotics underlines the crying need for novel replaceable antibacterials. Research advances have revealed the considerable sterilization potential of two-dimension graphene-based nanomaterials. Subsequently, two-dimensional nanomaterials beyond graphene (2D NBG) as novel antibacterials have also demonstrated their power for disinfection due to their unique physicochemical properties and good biocompatibility. Therefore, the exploration of antibacterial mechanisms of 2D NBG is vital to manipulate antibacterials for future applications. Herein, we summarize the recent research progress of 2D NBG-based antibacterial agents, starting with a detailed introduction of the relevant antibacterial mechanisms, including direct contact destruction, oxidative stress, photo-induced antibacterial, control drug/metallic ions releasing, and the multi-mode synergistic antibacterial. Then, the effect of the physicochemical properties of 2D NBG on their antibacterial activities is also discussed. Additionally, a summary of the different kinds of 2D NBG is given, such as transition-metal dichalcogenides/oxides, metal-based compounds, nitride-based nanomaterials, black phosphorus, transition metal carbides, and nitrides. Finally, we rationally analyze the current challenges and new perspectives for future study of more effective antibacterial agents. This review not only can help researchers grasp the current status of 2D NBG antibacterials, but also may catalyze breakthroughs in this fast-growing field.
... The EDS spectrum proved the occurrence of vanadium and chromium in precipitates (Fig. 2b). The high-resolution spectrum of V 2p during XPS analysis with peaks located at 525.2 eV and 517.6 eV (Fig. 2c) was ascribed to V(IV) in forms of VO (OH) 2 [28,29]. Peaks at 586.4 eV and 577.3 eV in high-resolution spectrum of Cr 2p (Fig. 2d) were identified, corresponding to Cr(III) as Cr(OH) 3 [14,30]. ...
Article
Vanadium and chromium co-exist commonly with elevated levels in groundwater at vanadium smelting sites. While bioremediation has been recognized promising for this co-contamination treatment in aquifer, interactions during vanadium (V) [V(V)] and chromium (VI) [Cr(VI)] bio-reductions under autotrophic condition remain largely unknown. In this study, efficient reductions of V(V) and Cr(VI) from synthetic groundwater were realized simultaneously in a continuous flow autotrophic sulfur-based biosystem, with more than 85% overall removals under hydrochemical and hydrodynamic fluctuations during 276-d operation. Soluble Cr(VI) was reduced to insoluble Cr(III) preferentially, while reduction of soluble V(V) to insoluble V(IV) was easily inhibited. Elemental sulfur [S(0)] was bio-oxidized to sulfate. Analyses of carbon isotope, microbial community and metabolic pathway revealed the synergetic mechanisms. Autotrophs (e.g., Sulfuricurvum) utilized energy released from S(0) oxidation to synthesize volatile fatty acids (VFAs), which were consumed by heterotrophic V(V) and/or Cr(VI) reducers (e.g., Geobacter). Functional genes responsible for S(0) oxidation and reduction of V(V) and Cr(VI) were detected. V(V) and Cr(VI) reductions were catalyzed by both cytochrome c and nicotinamide adenine dinucleotide. VFAs were also transformed to glycogen in cells to store energy. Robust remediation strategy is thereby proposed for aquifer co-contaminated by V(V) and Cr(VI).
... The membrane permeability of ONPG increased continuously during the first 60 min of the photocatalytic treatment but did not change significantly afterwards (Fig. 7b). As such, membrane fragmentation (such as pore enlargement or fracture) may occur first in the disinfection process, and the increase in permeability stopped after the membrane becomes seriously damaged (Zhang et al., 2018). The activities of SOD and CAT increased significantly 30 min after light exposure, which reflects the high oxidative stress response of TC-E. coli in the presence of ROS at the beginning of the treatment. ...
... Furthermore, blue precipitates were observed accumulated in BR-1.0 (Fig. S1a, Supporting Information). V 2p core level peaks from XPS analysis for these precipitates showed the sub-band located at around 515.9 eV, which was identified as vanadium (IV) (Fig. 2b) (Zhang et al., 2018b). The electrolyte pH increased slightly from 6.21 ± 0.03 to 7.24 ± 0.11, and the final reduction potential of VO 2+ /VO 2 + calculated from Nernst equation was around 0.803 V. ...
Article
Vanadate contaminant in groundwater receives increasing attentions, but little is known on its biogeochemical transformation with gaseous electron donors. This study investigated bio-reduction of vanadate coupled with anaerobic methane oxidation and its relationship with nitrate reduction. Results showed 95.8 ± 3.1% of 1 mM vanadate was removed within 7 days using methane as the sole electron donor. Tetravalent vanadium compounds were the main reduction products, which precipitated naturally in groundwater environment. The introduction of nitrate inhibited vanadate reduction, though both were reduced in parallel. Accumulations of volatile fatty acids (VFAs) were observed from methane oxidation. Preliminary microbial community structure and metabolite analyses indicated that vanadate was likely reduced via Methylomonas coupled with methane oxidation or through synergistic relationships between methane oxidizing bacteria and heterotrophic vanadate reducers with VFAs served as the intermediates.
... Advanced oxidation processes (AOPs) have been gradually employed to remove CBZ from environment [12][13][14]. Most AOPs are based on the highly reactive hydroxyl radical (HO⋅), which oxidizes almost all organics [15,16]. The Fenton process, involving hydrogen peroxide (H 2 O 2 ) and soluble Fe 2+ , stands out among AOPs to degrade organic pollutants [17,18]. ...
Article
Fenton reaction is an effective method to remove refractory organics such as carbamazepine (CBZ) from water streams. Nevertheless, its application is greatly compromised by extra hydrogen peroxide (H2O2) addition and iron mud accumulation. Herein, Fenton-like process with in situ produced H2O2 by biosynthesized palladium nanoparticles (bioPd-NPs) and natural iron-bearing clay minerals is proposed for CBZ degradation. The bioPd-NPs prepared by Shewanella loihica PV-4 were in the size range of 5-20 nm, which catalyzed the in situ production of H2O2 from formic acid (FA) and oxygen. Then the in situ generated H2O2 underwent Fenton-like reactions with nontronite for CBZ degradation. With bioPd-NPs and nontronite dosage of 1 g/L and FA concentration of 20 mM, the complete CBZ (10 mg/L) degradation was achieved within 60 min. Oxidative radicals such as HO· and H2O2 generated in our constructed system played key roles in CBZ degradation. Intermediates/products identification and theoretical calculation revealed that hydroxylation was the main CBZ degradation pathway. This work provides a promising Fenton-like technology for elimination of CBZ from environment with prevention of additional H2O2 supplementation and excessive iron mud production.
... Particularly, metal oxides with different morphologies and porous structures provide abundant surface area for the high diffusion rate of reactants and separation of charge carriers, thereby increasing photocatalytic activity [10]. Some of the metal chalcogenides with carbon composites were also exhibited tremendous photocatalytic activities [11,12]. Moreover, metal oxides are believed to be environmentally benign materials for the detection and degradation of toxic molecules [13]. ...
Article
Semiconductors with abundant surface areas have received substantial attention in the field of sensors, especially for the specific and sensitive detection of molecules. Eco-friendly synthesis of metal oxides pn junction composite with high specific surface area and its photoelectrochemical monitoring on antibiotics have been reported. The ZnO-Co3O4 pn heterojunction composite has successfully been prepared from a metal-organic framework (MOF) as a template, using benzene tricarboxylic acid (BTC) with a one-step calcination process. In research, obtained nanorods like ZnO-Co3O4 pn heterojunction exhibited high conductivity with excellent stability for the facilitated photocatalytic performance towards the photoelectrochemical detection of sulfadiazine (SDZ). Photo-stability and the optical characteristics of the ZnO-Co3O4 heterojunction composite have been analyzed in photocurrent and UV-visible studies. A mechanism of SDZ signaling has been proposed with appropriate band levels derived by Mott-Schottky analysis. The proposed sensor detects SDZ in the range of 0.005 to 18.5 µM with 1.2 nM as detection limit and exhibits better signaling stability. The applicability of the sensor device has been tested in pork meat, human urine, and river water samples containing SDZ.
... VO(OH) 2 is rather insoluble and strongly adsorbed on particles and then forms stable complexes under the natural pH ( Wehrli and Stumm, 1989 ). XPS analysis was also performed. The V 2p 3/2 and V 2p 1/2 peaks with a binding energy of 517.7 eV and 524.4 eV appeared ( Fig. 2 D), corresponding to V(IV) ( Qiu et al., 2017 ;Zhang et al., 2018b ). This result further confirmed the tetravalent products from V(V) reduction. ...
Article
Although remediation of toxic vanadium (V) [V(V)] pollution can be achieved through either heterotrophic or sulfur-based autotrophic microbial reduction, these processes would require a large amount of organic carbons or generate excessive sulfate. This study reported that by using mixotrophic V(V) bio-reduction with acetate and elemental sulfur [S(0)] as joint electron donors, V(V) removal performance was enhanced due to cooccurrence of heterotrophic and autotrophic activities. Deposited vanadium (IV) was identified as the main reduction product by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Based on 16S rRNA gene amplicon sequencing, qPCR and genus-specific reverse transcription qPCR, it was observed that V(V) was likely detoxified by heterotrophic V(V) reducers (e.g., Syntrophobacter, Spirochaeta and Geobacter). Cytochrome c, intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances were involved in V(V) reduction and binding. Organic metabolites synthesized by autotrophs (e.g., Thioclava) with energy from S(0) oxidation might compensate electron donors for heterotrophic V(V) and sulfate reducers. Less sulfate was accumulated presumably due to activities of sulfur-respiring genera (e.g., Desulfurella). This study demonstrates mixotrophic microbial V(V) reduction can save organic dosage and avoid excessive sulfate accumulation, which will be beneficial to bioremediation of V(V) contamination.
... To further confirm the bacterial membrane damage and cell death, SEM was used according to a protocol reported elsewhere. 22 Briefly, bacterial samples collected before and after SPC were washed and resuspended in NSS. 50 μL of this suspension was transferred onto a clean glass slide, followed by fixing the same using 15% glutaraldehyde and dehydrating using ethanol. ...
Article
Water resources contaminated with antibiotic resistant (ABR) gastrointestinal pathogens pose severe health risk to the society. Unfortunately, the limitations of traditional water treatment methodologies are leading to the evolution and dissemination of ABR microbes. In this aspect, a sonophotocatalytic (SPC) process is demonstrated for the successful disinfection of ABR Salmonella Typhimurium (STm) using Fe-doped ZnO nanoparticles (Fe-ZnO NPs) under visible-LED light. Reactive oxygen species (ROS) produced during SPC contributed to the detrimental effects on the microbe.In general, Information regarding how bacteria modulates their phenotypic attributes during the course of disinfection is largely unknown.Our investigations to understand the effect of sublethal SPC on the expression of various phenotypic features of STm revealed change in virulence and ABR profiles. Sublethal SPC caused STm to adhere more on HCT116 cells whereas the invasion property was substantially reduced. Loss of ABR was recorded after sublethal SPC although the resistance was regained partially after providing nutrient source to the bacteria. A manifestation of morphological transition in STm observed after sublethal SPC from rod to cocci might have resulted in the significant loss of invasiveness and ABR. Further, SPC did not result in any process resistance, making it a good candidate for water disinfection.
... Zhou and co-workers have disinfected E. coli in presence of Ag-3D ordered mesoporous CeO 2 under visible light [24]. PCD of E. coli under visible light using Carbon supported Vanadium Tetrasulfide nanocomposite was reported by Zhang and co-workers [25]. Xin and co-workers have used 3D graphene/AgBr/Ag cascade aerogel for PCD of E. coli [26]. ...
Article
Spread of antibiotic resistant bacteria through water pose severe health risks to society. In this context, a systematic study is reported for photocatalytic removal of multidrug resistant (MDR) Escherichia coli and related genes from water by using Alumina/ZnO heterostructures under visible light. 500 mg/L of the photocatalyst could disinfect ≈106 CFU/mL of target bacteria in water within 240 min of visible light irradiation. Lipid peroxidation, DNA and protein leakage studies have suggested the compromisation of bacterial cell membrane which was further corroborated from electron microscopy images. MDR Escherichia coli has registered a loss of resistance towards fifteen antibiotics with a down-regulation in the antibiotic resistance genes after exposure to photocatalytic process. Proposed process was also validated for disinfection of MDR Staphylococcus haemolyticus and antibiotic susceptible Escherichia coli. Successful disinfection of fecal coliform was achieved in water samples collected from three major rivers and a waste water treatment plant. The in vivo toxicity study of the treated water on mice model has not revealed any remarkable impact on gut health. With high effectiveness in disinfecting bacteria coupled with biocompatibility of the treated water towards animal model may proffer the present technique as a propitious off-grid water disinfection technique for real-world applications.
... In addition, MO could be completely decolorized in the 12%-Ag/ZnO NM degradation system within 35 min when the initial solution pH was 3-10 ( Figure S7). Other researchers also found the same results when Cu-TiO 2 -based NFs were adopted as a photocatalyst for virus removal (Zhang et al 2018). The possible explanation for these results is pH can influence the adsorption of dye molecules onto the catalytic material surface, which is an important step for the photooxidation to occur. ...
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For the efficient disposal of organic pollutants and Escherichia coli (E. coli) in water, Ag-loaded and Pd-loaded ZnO nanofibers (NFs) were prepared through electrospinning (e-spin), followed by the alcohol-thermal method. The NFs were prepared in membrane form to promote their separation, recovery, and reuse in practical applications. The complete decolorizations of three types of dyes (i.e., azo, triarylmethane, and heterocyclic dyes) were observed when the Ag-loaded or Pd-loaded ZnO nanofiber membrane (NFM) was first applied as photocatalyst under 30-min UV irradiation. The characterization of the catalysts and the decolorization performance of dyes both demonstrated that the optimal loading rates of Ag and Pd were 12% and 6%, respectively. Moreover, the 12%-Ag/ZnO NFM displayed excellent recyclability over five cycles than the 6%-Pd/ZnO NFM. The E. coli disinfection test demonstrated that the photocatalytic inactivation rates with the 12%-Pd/ZnO NFM and the 6%-Ag/ZnO NFM were significantly improved under solar or UV irradiation, and hydroxyl radicals (∙OH) was primarily responsible for the antibacterial performance. Therefore, the presented 12%-Ag/ZnO NFM and 6%-Pd/ZnO NFM can be used for the efficient photocatalytic treatment of dyes and E. coli in water.
... Vanadium is a strategic metal and has been widely used in industries due to its superior physicochemical characteristics (Hinwood et al., 2015;Zhang et al., 2018b). The increasing global demand for vanadium promotes intensive mining and smelting activities, however, high amounts of residual vanadium would appear in production water streams and surrounding environment (Yang et al., 2014;Zhang et al., 2019a). ...
Article
Adsorption is widely used in removal of toxic vanadium (V) [V(V)] from water streams, and a fit-for-purpose adsorbent plays a vital role in this process. Herein HZrO@D201, an adsorbent with decoration of nanosized hydrous zirconium oxide (HZrO) on anion exchange resin D201, is fabricated for efficient V(V) removal. Compared to pristine D201, HZrO@D201 excelled in V(V) removal with a maximum adsorption capacity of 118.1 mg/g, due to potential formation of inner sphere complexation between V(V) and HZrO. HZrO@D201 could also functioned well in a wide pH range (3.00 to 9.00) and exhibited outstanding selective V(V) adsorption under the presence of competing anions (chloride, nitrate, sulfate, and phosphate). The adsorption thermodynamics was in accordance with the Langmuir model, while adsorption kinetics followed the Pseudo-Second-Order model. When treating actual vanadium contaminated groundwater from Panzhihua region (China), HZrO@D201 indicated a satisfactory lifespan in the column experiment for V(V) removal (2.41 times longer than D201), and the treated groundwater could meet the vanadium standard of drinking water source in China (less than 50 μg/L). Regeneration of HZrO@D201 was easily achievable with negligible capacity loss. Results from this work suggests a promising application potential of HZrO@D201 in vanadium pollution control.
... Numerous materials have been intensively investigated as water disinfectants such as TiO 2 and zinc oxide (Cavalcante et al., 2016;Zhang et al., 2018). Nonetheless the majority of metal photocatalysts are activated by ultra violet (UV) radiation, this radiation is very limited in solar spectrum that represent only 4% overall the earth, in addition to this, metal photocatalysts produce secondary pollutants due to release of metal ions during the treatment processes (Ng et al., 2020;Zhang et al., 2021aZhang et al., , 2021b. ...
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Herein, green and non-toxic bismuth [email protected] carbon nitride (Bi2S3@g-C3N4) nanosheets (NCs) were firstly synthesized by ultrasonicated-assisted method and characterized with different tool. Bi2S3@g-C3N4 NCs antimicrobial activity tested against three types of microbes. As well the heterostructured Bi2S3@g-C3N4 NCs was investigated for removing dye and hexavalent chromium under visible light and showed high efficiency of photocatalytic oxidation/reduction higher than g-C3N4 alone, attributing to lower recombination photogenerated electron-hole pairs. Bi2S3@g-C3N4 NCs showed high antimicrobial efficiencies against Staphylococcus aureus (S. aureus) as a Gram positive bacterium, Escherichia coli (E. Coli)as a Gram negative bacterium and Candida albicans (C. albicans) and that the disinfection rates are 99.97%, 99.98% and 99.92%, respectively. The core mechanism is that the bacterial membrane could be destroyed by reactive oxygen species. The Bi2S3@g-C3N4 NCs is promising for environmental disinfection including water and public facilities disinfection and solar photocatalytic depollution. Turnover number (TON) and Turnover frequency (TOF) are used as concise assessment indicator for photocatalytic efficiency.
... EDS analysis suggested that the precipitates contained elemental vanadium (Fig. S3b). XPS result identified peak at 515.9 eV in the V 2p high-resolution spectrum corresponding to V(IV) (Fig. 3d), indicating that V(IV) was the main reduction product of V(V) through microbial transformation (Cai et al., 2017;Zhang et al., 2018b). ...
Article
The co-occurrence of toxic pyridine (Pyr) and vanadium (V) oxyanion [V(V)] in aquifer has been of emerging concern. However, interactions between their biogeochemical fates remain poorly characterized, with absence of efficient route to decontamination of this combined pollution. In this work, microbial-driven Pyr degradation coupled to V(V) reduction was demonstrated for the first time. Removal efficiencies of Pyr and V(V) reached 94.8 ± 1.55% and 51.2 ± 0.20% in 72 h operation. The supplementation of co-substrate (glucose) deteriorated Pyr degradation slightly, but significantly promoted V(V) reduction efficiency to 84.5 ± 0.635%. Pyr was mineralized with NH4⁺-N accumulation, while insoluble vanadium (IV) was the major product from V(V) bio-reduction. It was observed that Bacillus and Pseudomonas realized synchronous Pyr and V(V) removals independently. Interspecific synergy between Pyr degraders and V(V) reducers also functioned with addition of co-substrate. V(V) was bio-reduced through alternative electron acceptor pathway conducted by gene nirS encoded nitrite reductase, which was evidenced by gene abundance and enzyme activity. Cytochrome c, nicotinamide adenine dinucleotide and extracellular polymeric substances also contributed to the coupled bioprocess. This work provides new insights into biogeochemical activities of Pyr and V(V), and proposes novel strategy for remediation of their co-contaminated aquifer.
Article
A novel visible light-driven photocatalyst (represented as Mn-CdS/ZCISe/CIS/TiO2) for the inactivation of Escherichia coli (E. coli) was prepared with TiO2 nanowires as support and CuInS2 (CIS), ZnCuInSe (ZCISe) quantum dots (QDs), and Mn-doped CdS (Mn-CdS) nanoparticles (NPs) as sensitizers. The use of CIS, ZCISe QDs and Mn-CdS NPs extends the light harvest region to visible light. The photoelectric conversion efficiency was consequently improved with a photocurrent density of 12.5 mA/cm2, about 60 times that of the pure TiO2 nanowires. The bactericidal efficiency of the photocatalyst was evaluated on the inactivation of E. coli, 96% bacteria in 50 mL 105 colony forming units (CFU)/mL solution were killed within 50 min. Besides the high efficiency, the composite has good stability and satisfactory recycling performance. The antibacterial mechanism was also studied by employing photoluminescence and scavengers of different reactive species, revealing that it was the photo-generated holes to kill the bacterium.
Article
Groundwater vanadium (V) (V(V)) contamination is ubiquitous in vanadium mining/smelting region and development of novel strategy for its remediation is of particular significance. Herein woodchip-sulfur packed biological permeable reactive barrier (bio-PRB) is established towards successful V(V) bio-detoxification. V(V) removal was accelerated under such mixotrophic condition, compared with heterotrophic and autotrophic V(V) reductions. The performance of bio-PRB was relatively steady with V(V) removal efficiency of 68.5-98.2% in fluctuant geochemical and hydrodynamic environments. Microbial community analysis indicated that heterotrophic Geobacter was the main reducer to convert V(V) to insoluble V(IV), by employing organics from woodchip hydrolysis and sulfur anabolism of autotrophs (e.g., Sulfuricurvum and Thiobacillus). V(V) reduction and elemental sulfur oxidation were regulated by genes as omcA, omcB and mtrC and soxB, respectively. The elevated contents of cytochrome c and nicotinamide adenine dinucleotide implied the improved electron transfer, facilitating V(V) reduction. This study provides a cost-effective, robust and sustainable route to V(V)-polluted aquifer remediation.
Article
The effects of bisulfite-activated permanganate technology (PM/BS) as a pre-oxidation process on enhancing Microcystis aeruginosa (M. aeruginosa) removal by post coagulation were investigated. The results demonstrated that pretreatment with PM/BS process effectively promoted the algae removal by coagulation with Al2(SO4)3 as the coagulant and this phenomenon was more obvious with the increase of water hardness. Compared to the sole coagulation, PM/BS pre-oxidation combing with coagulation could neutralize the zeta potential of algal cells effectively, decrease the algal cell size, and lead to the formation of more compact flocs due to the in-situ generated MnO2. The effect of oxidant dosages on algal organic matter (AOM) was also studied and no obvious release of macromolecular substances was observed with the dosage of KMnO4 increasing from 3.0 mg/L to 7.0 mg/L, suggesting the integrity of algal cells at a high KMnO4 dosage. Moreover, PM/BS pre-oxidation could lead to the decrease of most analyzed disinfection by-products (DBPs) at a Al2(SO4)3 dosage of 40.0 mg/L. The algae removal efficiency was also significantly enhanced by PM/BS pre-oxidation in the test using real algae-laden water. This study indicated that PM/BS process might be a potential assistant technology for algae removal by subsequent coagulation.
Article
Effective and environmental water disinfectants are of great importance to address increasing health concerns in drinking water. Hence, in present paper, a highly efficient, recyclable and magnetically separable nanoparticles Ag/AgCl/Fe3O4 was prepared, comprehensively characterized (SEM, TEM, XRD, XPS, UV–vis and PL) and investigated as photocatalytic disinfectants for Escherichia coli K-12 (E. coli K-12). And the Ag/AgCl/Fe3O4 nanocomposites exhibited excellent disinfection performance for eliminating E. coli K-12 under visible light irradiation, with a maximum inactivation rate of 9.1-log at 0.2 g L⁻¹ in 60 min. Consistent disinfection performance was verified with five successive stability tests and reused five times without significant decrease in photocatalytic disinfection. The synergistic effects of Ag/AgCl andFe3O4 in the hybrid could also contribute to the improved photo stability and the reusability towards bacteria inactivation. The potential disinfection mechanism was investigated on the fluorescence assays, Cell morphology (SEM), TOC level and K⁺ leakage, and the results shown that the bacterial cell inactivation begins with the cell wall destruction with the leakage of the cellular components in the present photocatalytic system. Further photochemical investigation indicated that H⁺, OH and H2O2 were the crucial active species. These results demonstrated effectiveness and potential applications for the developed Ag/AgCl/Fe3O4 nanocomposites in waste water disinfection.
Article
Heavy metal complexes with high mobility are widely distributed in wastewater from modern industries, which are more stable and refractory than free heavy metal ions. Their removals from wastewater draw increasing attentions and various technologies have been developed, among which advanced oxidation processes (AOPs) are more effectively and promising. Progresses on five representative types of AOPs, including Fenton (like) oxidation, electrochemical oxidation, photocatalytic oxidation, ozonation and discharge plasma oxidation for heavy metal complexes degradation are summarized in this review. Their rationales, advantages, applications, challenges and prospects are introduced independently. Combinations among these AOPs, such as electrochemical Fenton oxidation and photoelectrocatalytic oxidation, are also comprehensively highlighted. Future efforts should be made to reduce acid requirement and scale up for practical applications of AOPs for heavy metal complex degradation efficiently and cost-effectively.
Article
With the continuous development of the chemical industries, synergistic removal of carbon and nitrogen contaminants has drawn much attention. In this work, a novel strategy for the synergistic removal of methyl orange (MO) and nitrate was developed in a single reactor by combining a TiO2/g-C3N4 nanosheet/graphene photoanode and denitrifying biofilm cathode. Under xenon light illumination, the photocatalytic MO decolorization rate exceeded 90% (the initial concentration of MO was as high as 100 mg·L-1) with a biocathode potential bias of -0.5 V vs Ag/AgCl; additionally, the decolourization rate apparently followed first-order kinetics with a constant of 0.11 ± 0.02 h-1. The improved MO decolourization rate was mainly because the biocathode effectively enhanced the charge separation of the photogenerated charge at the TiO2/g-C3N4 nanosheet/graphene photoanode interface. In the meantime, the effluent nitrate was lower than 1 mg·N·L-1 at a biocathode potential of -0.5 V vs Ag/AgCl. The results indicated that the coupled biocathode-photoanode system could serve the purpose of simultaneously degrading MO and accomplishing nitrate reduction. Considering the sustainability of sunlight and the use of a biocathode, the coupled biocathode-photoanode system is a promising alternative for the simultaneous removal of biorefractory organics and nitrate.
Article
In the drive toward the ever-increasing standards for high-quality drinking water, exploring stable and efficient photocatalysts with excellent visible light (VL) harvesting ability for the photocatalytic water disinfection is still a challenging problem. However, most photocatalysts are solely metal-based or contain at least one metal-containing cocatalyst with detrimental environmental impacts. Here, we show that a novel metal-free 2D heterostructure (BP-CN) composed of black phosphorus (BP) and graphitic carbon nitride (CN) can be used as a VL-driven photocatalyst to achieve highly efficient water disinfection. The activity of BP-CN photocatalyst was about 7 times better compared with that of pure CN for the disinfection of indicator bacteria, with the complete inactivation of bacterial cells (10⁷ cfu·mL⁻¹) within 60 min. The bacterial inactivation mechanism was thoroughly investigated, and hydroxyl radical (OH) and H2O2 were determined to be the major reactive oxygen species (ROSs) for water disinfection. The BP-CN photocatalyst is composed of low-cost and earth-abundant materials and holds great promise in “green” photocatalytic disinfection applications.
Article
Photocatalytic inactivation has been proved to be an effective strategy for controlling biohazards. Herein, the novel Ag deposited phosphorus and sulfur co-doped g-C3N4 (PSCN) composites with different Ag content were constructed via a facile calcination combining with biogenic-reduction method for inactivating Escherichia coli (E. coli). The detailed characterization results indicated that P and S elements were successfully co-doped into g-C3N4 (CN) lattice and Ag nanoparticles (NPs) were evenly deposited on the surface of PSCN with diameter range of 4–20 nm. The Ag/PSCN at depositing amount of 4 wt% (Ag/PSCN-4) achieved the strongest photocatalytic inactivation along with excellent stability, which could completely inactivate 7.0 log cells of E. coli within 60 min of visible light irradiation. This improved bactericidal performance was mainly attributed to the synergistic effects of P-S co-doped together with Ag deposition, which resulted in the increased visible light utilization, the improved separation and transfer efficiency of photo-induced charge carriers. Moreover, active species trapping experiments revealed that the generated superoxide radicals (O2⁻) and holes (h⁺) played the significant roles in photocatalytic inactivation process. Our present work presented a promising and environmentally friendly strategy to enhance the photocatalytic capacities of CN based composites for pathogens inactivation.
Article
In this work, porous defective g-C3N4 ultrathin nanosheets were prepared through thermal condensation of freeze-dried precursor. First-principles density functional theory (DFT) calculations well predicted the role of VN in modulating energy levels and photocatalytic properties. The optimally defective g-C3N4 manifested the better photocatalytic disinfection performance towards E. coli and S. aureus than pristine g-C3N4, respectively. The gradual damaged cell membrane for E. coli and the intimate mechanical constraint for S. aureus was imaged to further decipher the antibacterial behavior. The synergistic effect of enhanced visible light absorption ability, more exposed active sites and improved photogenerated charge separation was responsible for excellent photocatalytic disinfection activity. The photocatalytic disinfection mechanism towards E. coli was explored by electron spinning resonance (EPR), radical scavenger and spectral quantification technology, confirming the major role of h⁺ and O2⁻. This study provides alternative strategy for rational design of effective g-C3N4-based photocatalysts by defective engineering for environmental remediation.
Article
Landfill leachate is a type of complex organic wastewater, which can easily cause serious negative impacts on the human health and ecological environment if disposed improperly. Electrochemical technology provides an efficient approach to effectively reduce the pollutants in landfill leachate. In this review, the electrochemical standalone processes (electrochemical oxidation, electrochemical reduction, electro-coagulation, electro-Fenton process, three-dimensional electrode process, and ion exchange membrane electrochemical process) and the electrochemical integrated processes (electrochemical-advanced oxidation process (AOP) and biological electrochemical process) for landfill leachate treatment are summarized, which include the performance, mechanism, application, existing problems, and improvement schemes such as cost-effectiveness. The main objective of this review is to help researchers understand the characteristics of electrochemical treatment of landfill leachate and to provide a useful reference for the design of the process and reactor for the harmless treatment of landfill leachate.
Chapter
Carbon, well-known from the primordial time, is known as the king of elements, owing to its usefulness and multiplicity in fields such as advanced materials and energy harvesting applications, which is indisputable. Coal is a breakable, ignitable, solid hydrocarbon fuel molded by the decay and modification of flora under high temperature, pressure, and compaction. Due to its origin, coal is a composite and assorted mineral having both organic and inorganic components. Chemical leaching of coal with aid of mineral acid, organic acid, or alkaline solutions helps to lower ash making minerals to a great level. Generally, C-NMR spectroscopy is applied for the identification of carbon atoms in different chemical environments. The transmission electron microscope image of the nanocarbon obtained from coal reveals the formation of graphene structure with hexagonal, spherical, and corn shaped carbon nanotubes. Coal by nature is an abundantly available solid fuel, and delivers most of the power requirements for the living and fiscal advancement of a country.
Article
Photocatalytic disinfection has been regarded as a promising strategy in terms of significantly reducing microbial contamination, in which the activity of photocatalyst mainly depends on UV or visible light, however the effect of full spectrum solar light for photocatalytic disinfection has been rarely considered. Herein, we report a UV–Visible-NIR responsive photocatalyst based on vanadate quantum dots (AgVO3 QDs) interspersed on vacancy-rich BiO2-X (AgVO3/BiO2-X) and achieve highly efficient photocatalytic disinfection for Methicillin-resistant Staphylococcus aureus (MRSA). With our approach, we achieved a 7-log inactivation of bacterial concentration within 30 min, with only a small amount of material (200 μg mL⁻¹) under UV, visible and near-infrared light. The maximum absorption edge of AgVO3/BiO2-X red-shifts from 880 nm to 930 nm, which can be attributed to the inner defective structure and formation of heterostructures, resulting in abundant production of reactive oxygen species (ROS) for bacterial inactivation. DFT calculations confirm the intimate interface contact between BiO2-X and AgVO3, which benefit to the up-conversion photoluminescence properties of AgVO3 QDs and fast interfacial electron transport through the electron tunneling mechanism. In vitro results illustrated that ROS can severely damage the cell wall of bacteria and inhibit its virulence factors, which eventually leading to the death of MRSA. Notably, assessment of wound infection showed that the material was very effective for promoting cell proliferation and differentiation, by phosphorylation of protein kinase B (Akt) signalling pathway in bacterial infection, which shows great potential as a safe, low-cost and efficient multimodal heterostructured photocatalyst in eliminating the microbial contaminated water.
Article
A novel graphene-bridged AgCl/Ag3PO4/rGO photocatalyst with admirable visible-light-driven photocatalytic performance was prepared through a combination of in-situ precipitation and anion-exchange method. The photocatalyst was revealed a well-defined heterostructure in which few-layers rGO sheets are decorated by AgCl and Ag3PO4 nanoparticles. The ternary photocatalyst exhibits excellent photocatalytic activity for the degradation of methylparaben (MPB) and the inactivation of Gram-negative Escherichia coli (E. coli) due to the synergistic effects of AgCl, Ag3PO4 and rGO. Results show that 20 mg•L⁻¹ of MPB or 10⁷ CFU•mL⁻¹ of E. coli can be eliminated in AgCl/Ag3PO4/rGO system within 40 min under visible-light irradiation. Moreover, great stability and reusability were also observed for the ternary photocatalyst. Trapping experiments further confirm that h⁺ is the most important active specie, which indicates the importance of rGO due to its high electron transfer ability. And the possible photocatalytic mechanisms of AgCl/Ag3PO4/rGO in visible light system were finally proposed.
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Electrochemical oxidation (EO) is often used in the advanced treatment of refractory wastewater. However, in a conventional EO process of direct-current (DC) power supply, oxide layers often form on the anodes, which not only hinder the oxidation reaction on them but also cause higher energy consumption. In this paper, a biologically treated leachate (BTL) of municipal solid waste (MSW) was comparably treated by EO with DC (DC–EO), monopulse (MP–EO), and double pulse (DP–EO) power source models in a home-made multi-channel flow reactor. The effects of process parameters of current density (IA), superficial liquid velocity (UL), pulse frequency (fP), duty ratio (RD), and so forth on the removal efficiency of chemical oxygen demand (COD) (RECOD), total organic carbon (TOC) (RETOC), and total nitrogen (TN) (RETN) were investigated simultaneously. Average energy consumption () and organic composition of the treated effluent of DC–EO and MP–EO were also compared comprehensively, and a new mechanism of MP–EO has been proposed accordingly. Under optimal conditions, 2 L of BTL was treated by MP–EO for 180 min, and the RECOD, RETOC, and RETN could reach as high as 80, 30, and 80%, respectively. Compared with DC–EO, the of MP–EO is reduced by 69.27%. Besides, the kinds of organic matter in the treated effluent of MP–EO are reduced from 53 in the BTL to 11, which is much less than in the DC–EO process of 29 kinds. Therefore, the MP–EO process exhibits excellent removal performance of organics and TN and economic prospects in the treatment of refractory organic wastewater.
Chapter
Photocatalysis can be a futuristic process for energy production and environmental remediation applications. It deals with applications such as H2 production from water and biomass; CO2 conversion into hydrocarbon fuels; degradation of various categories of pollutants such as dyes, pharmaceutical pollutants, polymeric pollutants, organic toxic pollutants, and N2 conversion into NH3; heavy metal reduction; antimicrobial activities; etc. However, the key effectiveness of these applications is directly associated with the photocatalytic materials. Therefore, the development of photocatalytic materials with required functionalities is the key in this photocatalysis process. In this direction, the fabrication of photocatalytic materials at nanoscale governs various properties of photocatalysts that include high surface area, rich active sites, dimensional dependent properties, high quantum yield, etc. However, it should also be noted that the control of dimension and morphology at nanoscale could also lead to some negative effects in photocatalysis. For instance, the decrement in particle size could lead to blue shift in the optical properties, i.e., the increment in the bandgap energy. On the other hand, the quantum confinement in the nanoscale materials also helps tuning the band structure of a photocatalyst, which is one of the deciding parameters of the photocatalytic process of the respective photocatalyst. In this context, this chapter discusses the various methods for the synthesis of nanostructured photocatalytic materials and their efficacies in various photocatalytic applications as above listed.
Article
Microbial contamination has globally represented an extreme health risk to human beings. Bacteria, fungi, algae and viruses being minuscule possess excessive ecological toxicity and a wide range of diseases to an aquatic and terrestrial existence Recently, photocatalytic disinfection has acquired ever-growing worldwide attention due to its energy conversion and disinfection potential. Diverse factors such as the type of photocatalytic material employed for the disinfection process and micro-organisms significantly influence the disinfection technique. There are different novel photocatalysts including TiO2, graphitic carbon nitride (g-C3N4), nanocomposites and membranes that have been developed for microbial disinfection in land and water surfaces. Photocatalytic disinfection is majorly dependent on different operational parameters such as photocatalysts dosage, pH, light source, and temperature. Photocatalysts possess antimicrobial properties which might also contribute to the expulsion of micro-organisms from surfaces. Cell membrane degradation mechanism which governs the performance of photocatalytic disinfection is reviewed in detail. The review describes the fundamental mechanism of photocatalytic disinfection. The development of novel photocatalysts for the disinfection of bacteria, fungi, viruses and algae has been reviewed in detail. In addition, different parameters that affect the performance of photocatalytic disinfection are reviewed. Applications of photocatalytic disinfection of microorganisms and future perspectives are discussed.
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In this work, the synthesis, characterization, and photocatalytic activity of iron-doped titanium dioxide nanoparticles (FDT) supported on environmentally benign activated carbon (PAC) has been discussed. The photocatalytic activity of the nanocomposite was investigated for the degradation of Congo red (CR) dye from aqueous solution under visible light (520 nm), and it was observed that 100% degradation for 20 ppm CR solution took place within 60 mins. The experimental data of photodegradation of CR using the FDT/PAC nanocomposite had the highest correlation with Langmuir Hinshelwood model and pseudo-first-order rate kinetics with an apparent rate constant of 0.05341 min−1 and half-life period of 12.97 mins, respectively. The thermodynamics study revealed that the degradation process is exothermic and spontaneous. The effect of interfering ions on the degradation of CR solution was also examined. The photocatalytic antibacterial activity of the nanocomposite was tested against two bacteria pathogens, Escherichia coli and Staphylococcus aureus, and it was found that for the concentration of 105 CFU ml−1, 100% photocatalytic inactivation was achieved for both Escherichia coli in 120 mins and Staphylococcus aureus in 75 mins under visible light irradiation. The total electrical energy consumed and operating cost were measured and the total operating cost was 312.50, 236.74, and 166.67 INR (Indian rupee) for 20 ppm, 60 ppm, and 100 ppm CR dye removal using 0.06 g FDT/PAC nanocomposite, respectively.
Chapter
Fresh fruits and vegetables are susceptible to attack by spoilage and pathogenic microorganisms if not handled correctly during or after harvest. Postharvest disinfection of commodities is a curative operation to inhibit fungal pathogens and human bacterial pathogens and therefore enhance food safety. Deterioration of fruits and vegetables can only be prevented by adopting the inhibition of postharvest pathogens and thus ensuring prolonged storage life. This chapter comprises factual, chemical, and administrative context on some of the essential sanitizers existing for the practice nowadays. These include chlorine, chlorine dioxide, ozone, ethanol, hydrogen peroxide, organic acids, and electrolyzed water. A broad description about postharvest application, disinfection mechanism, and regulatory guidelines of these sanitizers has been given in this chapter. This chapter concludes that disinfectant is a vital tool to reduce postharvest decay in fruits and vegetables. In some conditions, sanitization is a pretreatment to the productive employment of postharvest methodology. This chapter clears the controversial, unjustified, and bad reputation of the use of chemical disinfectants as they leave no or much lesser amounts of remnants of the nonhazardous level. The world may consider the use of chemical disinfectants in an eco-friendly way.
Article
Carbon quantum dots (CQDots), as a sorbent has been decorated via grafting onto polymer matrix (PHQFB) based on 8-hydroxyquinoline (HQ) and biuret using formaldehyde cross-linker for the construction of a novel nanosorbent (CQDots@PHQFB). The assembled material was characterized by different techniques. The SEM image of the prepared CQDots@PHQFB nanosorbent indicated its particle size in the range 17.6-24.1 nm and the average diameter of CQDots@PHQFB is 14.9 nm. The resultant BET pore volume (0.028 cm³ g⁻¹), the mean pore diameter (11.2 nm) and surface area (11.5 m² g⁻¹) were computed. Adsorption studies were accomplished to evaluate the V(V) removal by CQDots@PHQFB nanosorbent from aqueous solution by microwave irradiation technique. CQDots@PHQFB demonstrated excellent adsorption and selectivity for V(V) ions from acidic medium (91.2% for 5 mg L⁻¹) at low pH conditions (pH 1-3). Therefore, three different mechanisms were proposed to account for such high extraction of V(V). The adsorption kinetics of V(V) was approved by the pseudo-second order with of R² (1.0) for both concentrations (5 and 15 mg L⁻¹) Furthermore, The values of qe(cal.) (18.3 mg g⁻¹, 54.3 mg g⁻¹ for 5, 15 mg L⁻¹, respectively), were also confirmed to be very close to qe(exp.) (18.2 mg g⁻¹, 54.2 mg g⁻¹ for 5, 15 mg L⁻¹, respectively), while the equilibrium isotherm results were evaluated by nonlinear models, viz. Langmuir, Freundlich, Liu and Temkin. The maximum capacity of adsorption from the Liu model was found 219.2 mg g⁻¹ at 346 K. the computed parameters of thermodynamic approved endothermic and spontaneous nature of V(V) adsorption onto CQDots@PHQFB nanosorbent. V(V) ions removal values corresponding to 99.3% and 97.7% were achieved from sea water and wastewater, respectively. The collected results affirm that the designed CQDots@PHQFB nanosorbent is an excellent candidate adsorptive uptake of V(V) from aqueous medium. The extraordinary adsorption abilities with higher reusability features for adsorption of inorganic pollutant such as V(V) entrusts this CQDots@PHQFB as a potential economical adsorbent to alleviate water pollution problem.
Thesis
Metal oxynitrides adopting the perovskite structure have shown to be active photocatalysts. In this work we established a route for the synthesis of CaTaO2N, SrTaO2N, BaTaO2N, LaTaON2, EuTaO2N, SrNbO2N, LaNbON2 and LaTiO2N as powders as well as thin films, and an assessment on their photocatalytic activities. Their synthesis was achieved using the polymeric precursor method (Pechini method), which makes use of citric acid and propylene glycol to form a polymeric resin containing the metal cations homogeneously distributed. For the thin film deposition, alumina and quartz substrates were dip-coated into the polymeric gel to form an amorphous oxide precursor film, followed by ammonolysis. Prior to ammonolysis, both, powder and thin film precursors were annealed in air at 800˚C to obtain the oxide precursor. Perovskite oxynitride phases were synthesised in the temperature range of 850-1000 ˚C, a flowing rate of 250 ml min-1 , a heating ramp of 3˚C min-1 and reaction time of 10-54 hours. Phase purity was confirmed by XRD and Rietveld/Le Bail analysis and diffuse reflectance spectra were recorded for each sample. Optical band gaps were calculated from the Tauc plot derived from the Kubelka-Munk function and were found in the range of 1.7-2.4 eV. A cobalt oxide co-catalyst (CoOx) was deposited onto each film by drop casting and the photocatalytic activity was assessed under visible light using dichlorophenolindophenol (DCIP) dye degradation in the presence of a sacrificial oxidant. The light source used was a solar simulator equipped with a 400 nm cut-off filter. The dye degradation test demonstrated photocatalytic activity in all samples except EuTaO2N and BaTaO2N. The three most active samples SrTaO2N, CaTaO2N and SrNbO2N showed initial rate constants of 5.0(1) × 10−4 min−1, 24.3(5) × 10−4 min−1 and 64(5) × 10−4 min−1, respectively. The cocatalyst loading was investigated at nominal surface concentrations of 0.04-0.46 µg cm-2 , however, for all samples, a co-catalyst loading of 0.3 µg cm-2 resulted in being the optimal one, providing an ii equilibrium between sufficient active sites for the degradation to occur without blocking the light from reaching the underlying photocatalyst. The three most active samples SrTaO2N, CaTaO2N and SrNbO2N were assessed on their selfcleaning abilities using the stearic acid test, demonstrating full degradation of an organic contaminant under a visible light source. The protocol for the mineralisation of stearic acid required transparent substrates. In this context, quartz substrates were protected by a layer of Al2O3 deposited via Aerosol-Assisted Chemical Vapour Deposition (AACVD). This method allowed to dip-coat the polymeric gels onto the quartz substrates, preventing side reactions on the perovskite phase with the quartz during the ammonolysis. The pure oxynitride phase was obtained using the conditions optimised for the perovskite oxynitrides deposited onto alumina tiles. For the photocatalytic test, the three samples SrTaO2N, CaTaO2N and SrNbO2N were decorated with 0.3 µg cm-2 cobalt atoms, and the degradation of stearic acid was monitored by FTIR. The rate constants for the mineralisation of the stearic acid were determined and gave values of 14(2) × 10−4 min−1 for SrNbO2N, 8(1) × 10−4 min−1 for SrTaO2 N, and 7.8(6) × 10−4 min−1 for CaTaO2 N. In line with the results from the DCIP dye testing, the SrNbO2N thin film was the most active sample. Finally, we reported a method for the preparation of a materials library using manual inkjet printing and subsequent screening of the photocatalytic activities of the different constituting compositions. This method was applied for the synthesis of a materials library containing nine different compositions of alkaline (Na, K) and alkaline earth (Mg) doped SrNbO2N.
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Copper is known for its bactericidal properties since ancient time. Development of copper nanoparticle (CNP) based antimicrobial products has generated interest in studying their toxicological properties. In this article, we have investigated the ROS (reactive oxygen species)–induced cytotoxicity of colloidal CNPs on MCF-7 human breast cancer cells. To understand the dependence of nanoparticle’s anticancer potential on their per batch yield, three identical sets of CNPs with similar physical properties with hydrodynamic size (11–14 nm) were prepared by chemical reduction method with per batch yield of 0.2 g, 0.3 g, and 0.4 g. Dose-dependent toxicity of as-synthesized (i.e., without any post preparation treatment) CNPs was evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) colorimetric assay for CNP concentrations of 0.001–100 μg/mL. Strong dose-dependent toxicity was observed in all CNPs batches, which was because of the mitochondrial damage in MCF-7. Cytotoxicity in MCF-7 exposed to CNPs was observed due to rupture of cell membrane and shrinkage as well as oxidative stress induced by reactive oxygen species (ROS). IC50 values of CNPs were independent of per batch yield of CNPs. This confirms that increase in CNPs yield from 0.2 to 0.4 g has no negative correlation with their cytotoxic response. The ability to scale up the nanoparticle yield with strong dose-dependent cytotoxicity makes CNPs potential candidate for the development of anticancer drugs. Graphical AbstractAn electrochemical mixed aptamer-antibody sandwich assay based on the aptamer-induced HCR amplification strategy was fabricated for the highly sensitive detection of MUC16. The mixed aptamer-antibody sandwich assay showed acceptable performance of detection range, detection limit, reproducibility, and selectivity.
Article
Multiple synergetic antimicrobial modality (MSAM) platform is a novel approach which has highly advocated recently to meet the challenge of bacterial infection. In this research, we constructed a “Dew-of-Leaf” like hybrid material ([email protected]3C2-BC) with multiple design features that integrated photodynamic, photothermal and silver ion releasing effects. Porphyrinic MOFs (PCN-224) grown on Ti3C2 nanosheets was first filtered onto BC, then nanosilver was sputtered using magnetron sputtering technique. Interestingly, the light-driven singlet oxygen produced by PCN-224 and the heat produced by Ti3C2 not only synergistically enhanced the antibacterial effect, but also promoted the sputtered nanosilver to be degraded to release silver ions, achieving rapid bacterial inactivation and long lasting bacterial inhibition effects. Moreover, after two rounds of bacterial inactivation and 6 months of room environment preservation, an antibacterial inactivation study still demonstrated 99.9999% elimination of Gram-negative Escherichia coli ATCC-8099 and Gram-positive Staphylococcus aureus ATCC-6538 with [email protected]3C2-BC. Taken together, this nanofiber hybrid material permits an effective way to inactivate bacteria rapidly at first and long lasting bacterial inhibition followed, showing great potential for microbial disinfection.
Article
Excessive energy consumption and low reaction efficiency caused by electron cycle rate limitations are bottlenecks in water treatment. Here, we introduce an innovative strategy to overcome this problem via constructing a novel three-dimensional (3D) hybrid of vanadium tetrasulfide cross-linking graphene-like carbon with π electrons (VSO–C(π)), which exhibits excellent performance during refractory pollutant removal based on sustainable electron cycling between hydrogen peroxide (H2O2), dissolved oxygen (DO), and pollutants at the solid–liquid micro-interface. VSO–C(π) is synthesized through an in situ hydrothermal synthesis procedure and characterized via a series of techniques. The cation-π structures are constructed through V–S–C(π) and V–O–C(π) bridges in VSO–C(π), triggering orientable electron transfer from C(π) to the metal V centers and forming a polarized distribution of surface electrons. In the VSO–C(π)/pollutants/DO/H2O2 system, the pollutants act as electron donors to C(π), with the subsequent degradation of pollutants, while DO and H2O2 act as electron acceptors and are activated by reactive oxygen species to further degrade the pollutants at the V centers. This sustainable electron cycling process is responsible for the excellent activity and superior adaptability to pH changes and different salt environments, while also greatly saving resources and reducing energy consumption.
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The inactivation mechanism of pathogenic microorganisms in water needs to be comprehensively explored in order to better guide the development of an effective and green disinfection method for drinking water safety. Here, metal-free modified g-C3N4 was prepared and used to inactivate two typical bacteria (namely, Gram-positive E. coli and Gram-negative S. aureus) in water under visible light from a comparative perspective. These two bacteria could be inactivated in the presence of modified g-C3N4 within 6 h of visible light, but their inactivation kinetics were quite different. E. coli were inactivated slowly in the early disinfection stage and rapidly in the later disinfection stage, whereas S. aureus were inactivated steadily during the entire disinfection process. Moreover, the impacts of important water parameters (pH, salt, temperature, and water matrix) on photocatalytic inactivation of E. coli and S. aureus were also distinct. In addition, scavenger experiments indicated that superoxide radicals played the most important role in E. coli inactivation, while both superoxide and hydroxyl radicals were important for S. aureus inactivation. Quantitative changes in fatty acids, potassium ions, proteins and DNA of the bacterial suspensions suggested that the higher resistance of E. coli in the early inactivation stage could be originated from the difference in the phospholipid repair system in cell membrane structures. This study can provide new insights into research and development of a safe and effective disinfection technology for drinking water.
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Pathogenic microorganism has always been a major threat to human health, which results in infectious diseases and even massive death. In the present study, the solar-light-driven photocatalyst Ag/Ag2O/BiPO4/Bi2WO6 was firstly used for water disinfection. The results showed the Ag/Ag2O/BiPO4/Bi2WO6 composite completely inactivated 7.40 log10 cfu/mL Escherichia coli within only 20 min under light irradiation. The inactivation mechanism was systematically investigated from the antioxidant enzymes, cell membrane, intracellular components and active species involved in the disinfection process. At the early stage of disinfection, the antioxidant system was initiated and increased enzyme activities to fight oxidative attack. Unfortunately, with accumulation of oxidative damage, the activities of antioxidant enzymes were suppressed, leading to deterioration of defense system. After destruction of defense system, cell membrane was destroyed gradually, monitored by K⁺ leakage and microscopic images. Furthermore, severe destruction of cell membrane led to leakage of nucleic acid and proteins, suggesting the irreversible death of bacteria. The photogenerated active species including superoxide radicals and holes played major roles in bactericidal process. In addition, the composite exhibited high adaptability for water disinfection at a wide range of environmental factors including light intensity, temperature, pH and humic acid. The slight release of Ag⁺ (<0.1 mg/L) and high stability of photocatalysts during successive disinfection experiments further implied its great potential for application. This work introduced an efficient solar-light-driven photocatalyst Ag/Ag2O/BiPO4/Bi2WO6, which exhibited a promising prospect for practical application, in hope of providing more useful information for water disinfection.
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Nanotechnology is an uppermost priority area of research in several nations presently because of its enormous capability and financial impact. One of the most promising environmental utilizations of nanotechnology has been in water treatment and remediation where various nanomaterials can purify water by means of several mechanisms inclusive of the adsorption of dyes, heavy metals, and other pollutants, inactivation and removal of pathogens, and conversion of harmful materials into less harmful compounds. To achieve this, nanomaterials have been generated in several shapes, integrated to form different composites and functionalized with active components. Additionally, the nanomaterials have been added to membranes that can assist to improve the water treatment efficiency. In this paper, we have discussed the advantages of nanomaterials in applications such as adsorbents (removal of dyes, heavy metals, pharmaceuticals, and organic contaminants from water), membrane materials, catalytic utilization, and microbial decontamination. We discuss the different carbon-based nanomaterials (carbon nanotubes, graphene, graphene oxide, fullerenes, etc.), and metal and metal-oxide based nanomaterials (zinc-oxide, titanium dioxide, nano zerovalent iron, etc.) for the water treatment application. It can be noted that the nanomaterials have the ability for improving the environmental remediation system. The examination of different studies confirmed that out of the various nanomaterials, graphene and its derivatives (e.g., reduced graphene oxide, graphene oxide, graphene-based metals, and graphene-based metal oxides) with huge surface area and increased purity, outstanding environmental compatibility and selectivity, display high absorption capability as they trap electrons, avoiding their recombination. Additionally, we discussed the negative impacts of nanomaterials such as membrane damage and cell damage to the living beings in the aqueous environment. Acknowledgment of the possible benefits and inadvertent hazards of nanomaterials to the environment is important for pursuing their future advancement.
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Vanadate [V(V)] and phenanthrene (PHE) commonly coexist in groundwater aquifer, posing potential threats to ecological environment and public health. However, little is known about the complicated biogeochemical processes involving microbial V(V) reduction coupled with co-metabolic PHE biodegradation. Herein we demonstrated that synchronous removal of V(V) and PHE could be realized under anaerobic condition. Complete V(V) removal and PHE degradation efficiency of 82.0 ± 0.8% were achieved in 7-d operation in batch experiment. 250-d continuous column experiment implied that hydrochemical condition affected V(V) and PHE removals. V(V) was reduced to insoluble vanadium (IV) and PHE was degraded into small molecule organics (e.g. salicylic acid). Geobacter and Acetobacterium used methanol and intermediates from PHE degradation as electron donors for V(V) reduction. PHE was decomposed by Mycobacterium and Clostridium with methanol as co-metabolic substrate and V(V) as electron acceptor. Genes encoding proteins for V(V) reduction (omcA, omcB and mtrC) and PHE degradation (phnAc) were upregulated. Cytochrome c and nicotinamide adenine dinucleotide promoted electron transfer for V(V) and PHE detoxification. Extracellular polymeric substances could bind V(V) and improve the bioavailability of PHE. Our findings provide a robust strategy for remediation of V(V) and PHE co-contaminated groundwater.
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Metal-organic frameworks (MOFs) are emerging class of porous materials that attracted tremendous attention as eco-friendly photocatalysts. However, poor charge separation in most MOFs largely thwarts their photocatalytic performance. In this work, Materials of Institut Lavoisier-100(Fe) (MIL-100 (Fe)) based on iron mesh was successfully fabricated by in situ growth. MIL-100(Fe) doped with polyaniline, namely MIL-100(Fe)/PANI, were then fabricated by galvanostatic deposition followed by annealing. Compared to pure MIL-100(Fe), MIL-100(Fe)/PANI composites exhibited excellent photocatalytic performances towards Thiamphenicol (TAP) degradation and Escherichia coli (E. Coli.) inactivation. The apparent rate constant, k, for TAP elimination of the MIL-100(Fe)/PANI composites with H2O2 is approximately 3 times as high as that of pure MIL-100(Fe). The electrochemical studies showed enhanced photocatalytic performances, which can be attributed to the electronic conductivity of PANI polymers. Quenching experiments, fluorescent tests and electron paramagnetic resonance (EPR) all suggested ⋅O2⁻, e⁻, ⋅OH and h⁺ as reactive oxidizing species (ROSs) involved in the photocatalytic process, where ⋅OH played the predominant ROSs. The transformation products of TAP were also isolated and characterized by high-resolution mass spectrometry, and transformation pathways of TAP under Vis/MIL-100(Fe)/PANI/H2O2 were tentatively clarified based on involved intermediates. Herein, MOFs conjugated conductive polymers nanocomposites look promising as efficient photocatalysts for organic pollutants degradation and bacteria inactivation. This work could offer novel strategies for the development of heterojunction composites with enhanced photocatalytic performances for better environmental remediation.
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PM2.5 plays a key role in the solar radiation budget and air quality assessments, but observations and historical data are relatively rare for Beijing. Based on the synchronous monitoring of PM2.5 and broadband solar radiation (Rs), a logarithmic function was developed to describe the quantitative relationship between these parameters. This empirical parameterization was employed to calculate Rsn from PM2.5 with normalized mean bias (NMB) −0.09 and calculate PM2.5 concentration from Rsn with NMB −0.12. Our results indicate that this parameterization provides an efficient and straightforward method for estimating PM2.5 from Rs or Rs from PM2.5.
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Objectives The objective of this study was to compare the antibacterial effect of calcium oxide nanoparticles (CONPs) and calcium hydroxide nanoparticles (CHNPs) against Enterococcus faecalis in a dentinal block model. Materials and methods E. faecalis strain JCM 7783 was introduced into dentinal tubules of semicylindrical dentin specimens by centrifugation and incubated for 1 week. Fifty microliters of CONPs or CHNPs was placed on the root canal side of the infected dentin specimens. The specimens were then incubated in aerobic condition at 37 °C and 100 % relative humidity for 1 week. The treated dentin specimens were subjected to fluorescent staining and confocal laser scanning microscopy (CLSM) to analyze the proportions of non-vital and vital bacterial cells inside the dentinal tubules. Scanning electron microscopy (SEM) was used to confirm the effect of the medicaments on the bacteria in the dentinal tubules. Calcium oxide (CO) and calcium hydroxide (CH) were used as controls. Results Based on the CLSM and SEM analyses, CHNPs were more efficient than CONPs in the elimination of the bacteria in the dentinal tubules. CONPs significantly killed more E. faecalis than CO and CH (P < .05). Neither CO nor CH was able to kill the bacteria. Conclusions CHNPs were more effective than CONPs in the elimination of E. faecalis in dentinal tubules. Clinical relevance CHNPs are effective nanoparticles in killing endodontic bacteria present in dentinal tubules. They have potential as an intracanal medicament, which may be beneficial in root canal therapy.
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Bacterial inactivation by magnetic photocatalyst receives increasing interests for the ease recovery and reuse of photocatalysts. This study investigated bacterial inactivation by a magnetic photocatalysts, Fe2O3-AgBr, under the irradiation of a commercially available light emitting diode lamp. The effects of different factors on the inactivation of Escherichia coli were also evaluated, in term of the efficiency in inactivation. The results showed that Fe2O3-AgBr was able to inactivate both Gram negative (E. coli) and Gram positive (Staphylococcus aureus) bacteria. Bacterial inactivation by Fe2O3-AgBr was more favorable under high temperature and alkaline pH. Presence of Ca(2+) promoted the bacterial inactivation while the presence of [Formula: see text] was inhibitory. The mechanisms of photocatalytic bacterial inactivation were systemically studied and the effects of the presence of various specific reactive species scavengers and argon suggest that Fe2O3-AgBr inactivate bacterial cells by the oxidation of H2O2 generated from the photo-generated electron and direct oxidation of photo-generated hole. The detection of different reactive species further supported the proposed mechanisms. The results provide information for the evaluation of bacterial inactivation performance of Fe2O3-AgBr under different conditions. More importantly, bacterial inactivation for five consecutive cycles demonstrated Fe2O3-AgBr exhibited highly stable bactericidal activity and suggest that the magnetic Fe2O3-AgBr has great potential for water disinfection.
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The removal of bacteria from water is a highly important process for drinking water and sanitation systems especially on growing outbreaks of water borne diseases. The aim of this study was to evaluate the water disinfection efficiency of ZnO nanoparticle synthesized by solution combustion method (SCM). The ZnO nanoparticle as a disinfectant was prepared by the SCM. The prepared disinfectant was characterized by scanning electron microscopy (SEM), Xray diffraction (XRD), and Brunauer-Emmett-Teller (BET). The disinfection efficiency of the synthesized ZnO nanoparticle was evaluated using Escherichia coli as an indicator organism by disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests. The results shows that the synthesized ZnO nanoparticle was showed an average size of 15 nm. The MIC and MBC of ZnO nanoparticle were 8 and 16 μg mL-1, respectively. These results suggest that ZnO nanoparticle prepared by SCM could be used as an effective disinfectant, making this approach applicable to water control systems. Keywords: ZnO, Nanoparticle, Disinfection, E. coli, Solution combustion method
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With the exploding interest in transition metal chalcogenides, sulfide minerals containing the dianion S22-, such as pyrite (FeS2), cattierite (CoS2), and vaesite (NiS2) have recently attracted much attention for potential applications in energy conversion and storage devices. However, the synthesis of the patronite structure (VS4, V4+(S22-)2) and its applications have not yet been clearly demonstrated because of experimental difficulties and the existence of nonstoichiometric phases. Herein, we report the synthesis of VS4 using a simple facile hydrothermal method with a graphene oxide (GO) template and the characterization of the resulting material. Tests of various templates such as CNT, pyrene, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and graphite led us to the conclusion that the graphitic layer plays a role in the nucleation during growth of VS4. Furthermore, the VS4/rGO hybrid was proved to be a promising functional material in energy storage devices.
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Development of effective and low-cost disinfection technology is needed to address the problems caused by an outbreak of harmful microorganisms. In this work, an effective photocatalytic removal of Gram-negative bacteria Escherichia coli from aqueous solution was reported by using ZnO nanoparticles under UV light irradiation. The effect of various parameters such as solution pH, ZnO dosage, contact time and initial E. coli concentration were investigated. Maximum photocatalytic disinfection was observed at neutral pH because of the reduced photocatalytic activity of ZnO at low and high pH values originated from either acidic/photochemical corrosion of the catalyst and/or surface passivation with Zn(OH)(2). As the ZnO dosage increased, the photocatalytic disappearance of E. coli was continuously enhanced, but was gradually decreased above 2 g/L of ZnO due to the increased blockage of the incident UV light used. The optimum ZnO dosage was determined as 1 g/L. Photocatalytic removal of E. coli decreased as initial E. coli concentration increased. Three kinetic models (zero-, first- and second-order equations) were used to correlate the experimental data and to determine the kinetic parameters.
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Solar water disinfection (SODIS) has been known for more than 30 years. The technique consists of placing water into transparent plastic or glass containers (normally 2L PET beverage bottles) which are then exposed to the sun. Exposure times vary from 6 to 48h depending on the intensity of sunlight and sensitivity of the pathogens. Its germicidal effect is based on the combined effect of thermal heating of solar light and UV radiation. It has been repeatedly shown to be effective for eliminating microbial pathogens and reduce diarrhoeal morbidity including cholera. Since 1980 much research has been carried out to investigate the mechanisms of solar radiation induced cell death in water and possible enhancement technologies to make it faster and safer. Since SODIS is simple to use and inexpensive, the method has spread throughout the developing world and is in daily use in more than 50 countries in Asia, Latin America, and Africa. More than 5 million people disinfect their drinking water with the solar disinfection (SODIS) technique. This review attempts to revise all relevant knowledge about solar disinfection from microbiological issues, laboratory research, solar testing, up to and including real application studies, limitations, factors influencing adoption of the technique and health impact.
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Copper alloy surfaces are passive antimicrobial sanitizing agents that kill bacteria, fungi, and some viruses. Studies of the mechanism of contact killing in Escherichia coli implicate the membrane as the target, yet the specific component and underlying biochemistry remain unknown. This study explores the hypothesis that nonenzymatic peroxidation of membrane phospholipids is responsible for copper alloy-mediated surface killing. Lipid peroxidation was monitored with the thiobarbituric acid-reactive substances (TBARS) assay. Survival, TBARS levels, and DNA degradation were followed in cells exposed to copper alloy surfaces containing 60 to 99.90% copper or in medium containing CuSO(4). In all cases, TBARS levels increased with copper exposure levels. Cells exposed to the highest copper content alloys, C11000 and C24000, exhibited novel characteristics. TBARS increased immediately at a very rapid rate but peaked at about 30 min. This peak was associated with the period of most rapid killing, loss in membrane integrity, and DNA degradation. DNA degradation is not the primary cause of copper-mediated surface killing. Cells exposed to the 60% copper alloy for 60 min had fully intact genomic DNA but no viable cells. In a fabR mutant strain with increased levels of unsaturated fatty acids, sensitivity to copper alloy surface-mediated killing increased, TBARS levels peaked earlier, and genomic DNA degradation occurred sooner than in the isogenic parental strain. Taken together, these results suggest that copper alloy surface-mediated killing of E. coli is triggered by nonenzymatic oxidative damage of membrane phospholipids that ultimately results in the loss of membrane integrity and cell death.
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We review the principles of ultraviolet (UV) irradiation, the inactivation of infectious agents by UV, and current applications for the control of microorganisms. In particular, wavelengths between 200 and 280 nm (germicidal UV) affect the double-bond stability of adjacent carbon atoms in molecules including pyrimidines, purines and flavin. Thus, UV inactivation of microorganisms results from the formation of dimers in RNA (uracil and cytosine) and DNA (thymine and cytosine). The classic application of UV irradiation is the inactivation of microorganisms in biological safety cabinets. In the food-processing industry, germicidal UV irradiation has shown potential for the surface disinfection of fresh-cut fruit and vegetables. UV treatment of water (potable and wastewater) is increasingly common because the process is effective against a wide range of microorganisms, overdose is not possible, chemical residues or by-products are avoided, and water quality is unaffected. UV has been used to reduce the concentration of airborne microorganisms in limited studies, but the technology will require further development if it is to gain wider application. For bioaerosols, the primary technical challenge is delivery of sufficient UV irradiation to large volumes of air, but the absence of UV inactivation constants for airborne pathogens under a range of environmental conditions (temperature, relative humidity) further compounds the problem.
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ATP, the universal carrier of cell energy, is manufactured from ADP and phosphate by the enzyme ATP synthase using the free energy of an electrochemical gradient of protons (or Na(+)). The proton-motive force consists of two components, the transmembrane proton concentration gradient (delta pH) and the membrane potential. The two components were considered to be not only thermodynamically but also kinetically equivalent, since the chloroplast ATP synthase appeared to operate on delta pH only. Recent experiments demonstrate, however, that the chloroplast ATP synthase, like those of mitochondria and bacteria, requires a membrane potential for ATP synthesis. Hence, the membrane potential and proton gradient are not equivalent under normal operating conditions far from equilibrium. These conclusions are corroborated by the finding that only the membrane potential induces a rotary torque that drives the counter-rotation of the a and c subunits in the F(o) motor of Propionigenium modestum ATP synthase.
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The intracellular level of potassium (K+) in Escherichia coli is regulated through multiple K+ transport systems. Recent data indicate that not all K+ extrusion system(s) have been identified (15). Here we report that the E. coli Na+ (Ca2+)/H+ antiporter ChaA functions as a K+ extrusion system. Cells expressing ChaA mediated K+ efflux against a K+ concentration gradient. E. coli strains lacking the chaA gene were unable to extrude K+ under conditions in which wild-type cells extruded K+. The K+/H+ antiporter activity of ChaA was detected by using inverted membrane vesicles produced using a French press. Physiological growth studies indicated that E. coli uses ChaA to discard excessive K+, which is toxic for these cells. These results suggest that ChaA K+/H+ antiporter activity enables E. coli to adapt to K+ salinity stress and to maintain K+ homeostasis.
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The effectiveness of solar disinfection (SODIS), a low-cost household water treatment method for developing countries, was investigated with flow cytometry and viability stains for the enteric bacterium Escherichia coli. A better understanding of the process of injury or death of E. coli during SODIS could be gained by investigating six different cellular functions, namely: efflux pump activity (Syto 9 plus ethidium bromide), membrane potential [bis-(1,3-dibutylbarbituric acid)trimethine oxonol; DiBAC4(3)], membrane integrity (LIVE/DEAD BacLight), glucose uptake activity (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-d-glucose; 2-NBDG), total ATP concentration (BacTiter-Glo) and culturability (pour-plate method). These variables were measured in E. coli K-12 MG1655 cells that were exposed to either sunlight or artificial UVA light. The inactivation pattern of cellular functions was very similar for both light sources. A UVA light dose (fluence) of <500 kJ m(-2) was enough to lower the proton motive force, such that efflux pump activity and ATP synthesis decreased significantly. The loss of membrane potential, glucose uptake activity and culturability of >80 % of the cells was observed at a fluence of approximately 1500 kJ m(-2), and the cytoplasmic membrane of bacterial cells became permeable at a fluence of >2500 kJ m(-2). Culturable counts of stressed bacteria after anaerobic incubation on sodium pyruvate-supplemented tryptic soy agar closely correlated with the loss of membrane potential. The results strongly suggest that cells exposed to >1500 kJ m(-2) solar UVA (corresponding to 530 W m(-2) global sunlight intensity for 6 h) were no longer able to repair the damage and recover. Our study confirms the lethal effect of SODIS with cultivation-independent methods and gives a detailed picture of the 'agony' of E. coli when it is stressed with sunlight.
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Carbon-based nanomaterials have been widely developed into novel antimicrobial agents because of their high surface-to-volume ratio, extremely high mechanical strength and distinct physicochemical properties. Here, a metal-free photocatalyst graphene oxide/graphitic carbon nitride (GO/g-C3N4) nanocomposite was fabricated through sonication at room temperature and its antibacterial activity against Escherichia coli (E. coli) was investigated. The results demonstrated that the GO/g-C3N4 composite could kill of 97.9% of E. coli after 120 min visible light irradiation at the concentration of 100 µg/mL, which was further confirmed by fluorescent-based cell membrane integrity assay. Additionally, electron spin resonance (ESR) spectra and trapping experiments indicated that the holes produced by photocatalysis were the main active species participating in the photocatalytic sterilization, and scanning electron microscope (SEM) and transmission electron microscopy (TEM) confirmed that the holes could lead to the distortion and rupture of cell membrane and finally cell death. Further photoluminescence (PL) spectra, cyclic voltammetry, photocurrent generation and impedance spectroscopy (EIS) analyses revealed that the introduction of GO promoted the separation and transfer of photogenerated electron-hole pairs of g-C3N4 to produce more h+, which could directly improve the bactericidal ability of GO/g-C3N4. The reusability experiments indicated that the GO/g-C3N4 retained more than 90% of activity after four cycles of use. This study facilitates an in-depth understanding of the mechanism of visible light-driven disinfection and provides an ideal candidate sterilizing agent for treating microbial-contaminated water.
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Photocatalytic decolorization of the dye compounds represents a promising approach for textile wastewater treatment and thus, development of new photocatalysts will be of strong interest. Herein, a novel photocatalyst based on transition metal chalcogenides Vanadium Tetrasulfide (VS4) was prepared via a simple one-step hydrothermal synthesis and the synthesized VS4/carbon powder nanocomposites exhibited excellent photocatalytic decolorization efficiency under visible light irradiation. Significantly higher methyl orange (MO) decolorization rate of 13.4 - 19.8 mg L-1 h-1 was achieved. Reactive species such as •O2−, h+ and e− generated through this photocatalytic process have played the key roles in the decolorization with phthalic acid as a product. The optimal catalyst dosage was determined to be 1.0 g L-1. The decolorization rate was enhanced with the increase of initial MO concentration and an acidic condition favored the degradation. The VS4/carbon powder nanocomposites could maintain the MO decolorization efficiency above 90% in four consecutive reused cycles. The results of this study have collectively demonstrated a promising photocatalyst that encourages further investigation and development for dye decolorization in textile wastewater.
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Photocatalysis has been shown to be effective for the disinfection of water contaminated with pathogenic microorganisms. In order to increase the solar efficiency of photocatalysis on titanium dioxide (TiO2) it is necessary to modify the TiO2 so that visible photons may be utilised in addition to the UV. TiO2 - reduced graphene oxide composites (TiO2-rGO) were prepared by the photocatalytic reduction of exfoliated graphene oxide (GO) using P25 (Evonik-Aeroxide) as the photocatalyst. The composites were tested for the inactivation of E.coli as the model microorganism under UV-Vis and visible only irradiation at relatively low light intensities to help elucidate the mechanism of disinfection. The results showed a 6 log inactivation of E. coli after 120 min of treatment with unmodified TiO2-P25 and the same level of inactivation was achieved after 90 min with TiO2-rGO under UV-Vis irradiation. Under visible irradiation only, the TiO2-rGO gave a 5.3 log inactivation of E.coli following 180 min of treatment whereas the unmodified P25 gave only a 1.7 log-reduction in the same time, similar to that observed in the light control. Using probes, the main reactive oxygen species involved in the disinfection process were determined to be hydrogen peroxide, hydroxyl radicals, and singlet oxygen under UV-Vis irradiation; and only singlet oxygen under visible only irradiation. Scavenger studies were also performed to further elucidate the mechanism of disinfection.
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TiO2/Ag2O heterostructure prepared by a facile in situ precipitation route was used as an effective visible light-driven photocatalyst for degradation of methylene blue (MB) and inactivation of E. coli. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) revealed that Ag2O nanoparticles were well distributed on the surface of TiO2 microspheres. The TiO2/Ag2O composite with optimal mass ratio of TiO2 and Ag2O displayed extremely good photodegradation ability and antibacterial capability under visible light irradiation, which was mainly ascribed to the synergistic effect between Ag2O and TiO2, including highly dispersed smaller Ag2O particles, increased visible light absorption and efficient separation of photo-induced charge carriers. Meanwhile, the roles of the radical species in the photocatalysis process were investigated. Our results showed that the TiO2/Ag2O could be used as a dual functional material in water treatment of removing the organic pollutant and killing the bacterium at the same time.
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Ag@AgI/Bi-BiOI (AABB) three-dimentional (3D) nanoarchitectures, synthesized by solvothermal reaction and photoreduction method, were used as high–effective visible light driven (VLD) photocatalysts for the inactivation of Escherichia coli K–12 (E. coli K–12) and were characterized by TEM, SEM, XRD, BET, XPS and DRS. The prepared 30%AABB exhibited the best bacteria disinfection efficiency, and the quantity of viable bacteria could almost inactivate after being illuminated for 18 min. The enhanced photocatalytic performance can be attributed to the improved separation efficiency of the photogenerated electron–hole pairs because of its multivariant nanoarchitectures with simultaneous electron transfers (Bi → BiOICBM → Ag → AgIVBM). Furthermore, the SEM technology was applied to certify the photocatalytically lethal effect to E. coli K–12 and the rupture of bacterial membranes. In this work, the antibacterial mechanism was studied by employing Photoluminescence (PL), Photoelectrochemical Techniques, Electron Spin Resonance (ESR), and scavengers of different reactive species, revealing the pivotal roles of h⁺, e⁻, and O2⁻ in the photocatalytic process. This study indicated that the fabricated AABB photocatalysts could be potentially utilized to disinfect bacteria in water.
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Solar energy is readily available in most climates and can be used for water purification. However, solar disinfection of drinking water mostly relies on ultraviolet light, which represents only 4% of the total solar energy, and this leads to a slow treatment speed. Therefore, the development of new materials that can harvest visible light for water disinfection, and so speed up solar water purification, is highly desirable. Here we show that few-layered vertically aligned MoS2 (FLV-MoS2) films can be used to harvest the whole spectrum of visible light (∼50% of solar energy) and achieve highly efficient water disinfection. The bandgap of MoS2 was increased from 1.3 to 1.55 eV by decreasing the domain size, which allowed the FLV-MoS2 to generate reactive oxygen species (ROS) for bacterial inactivation in the water. The FLV-MoS2 showed a ∼15 times better log inactivation efficiency of the indicator bacteria compared with that of bulk MoS2, and a much faster inactivation of bacteria under both visible light and sunlight illumination compared with the widely used TiO2. Moreover, by using a 5 nm copper film on top of the FLV-MoS2 as a catalyst to facilitate electron-hole pair separation and promote the generation of ROS, the disinfection rate was increased a further sixfold. With our approach, we achieved water disinfection of >99.999% inactivation of bacteria in 20 min with a small amount of material (1.6 mg l(-1)) under simulated visible light.
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Using fertilizers as draw solutes in forward osmosis (FO) can accomplish wastewater reuse with elimination of recycling draw solute. In this study, three commercial fast-release all-purpose solid fertilizers (F1, F2 and F3) were examined as draw solutes in a submerged FO system for water extraction from either deionized (DI) water or the treated wastewater. Systematic optimizations were conducted to enhance water extraction performance, including operation modes, initial draw concentrations and in-situ chemical fouling control. In the mode of the active layer facing the feed (AL-F or FO), a maximum of 324 mL water was harvested using 1-M F1, which provided 41% of the water need for fertilizer dilution for irrigation. Among the three fertilizers, F1 containing a lower urea content was the most favored because of a higher water extraction and a lower reverse solute flux (RSF) of major nutrients. Using the treated wastewater as a feed solution resulted in a comparable water extraction performance (317 mL) to that of DI water in 72 h and a maximum water flux of 4.2 LMH. Phosphorus accumulation on the feed side was mainly due to the FO membrane solute rejection while total nitrogen and potassium accumulation was mainly due to RSF from the draw solute. Reducing recirculation intensity from 100 to 10 mL min−1 did not obviously decrease water flux but significantly reduced the energy consumption from 1.86 to 0.02 kWh m−3. These results have demonstrated the feasibility of using commercial solid fertilizers as draw solutes for extracting reusable water from wastewater, and challenges such as reverse solute flux will need to be further addressed.
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In photocatalysis, controversy still exists over as whether oxidation proceeds via primary oxidants, such as HO radicals, positive holes, electrons, O2- radicals in the photodegradation process. The contribution of the main active species to the photocatalytic degradation of metoprolol (MET) using a solar simulator with Xenon lamp as irradiation source was examined by using different specific scavengers (formic acid, tert-butyl alcohol, ρ-benzoquinone and oxygen). According to this, we also compared the effect on the generation of active species, in the MET degradation, of two types of TiO2 catalyst having different physical and chemical properties: pure TiO2 and TiO2 doped with 5% B (w/w), both synthesized by sol-gel method. The scavenger study indicates that HO radicals are the dominant reactive species, contributing around 80% and to a lesser extent by the contribution of O2- radicals and holes in systems using TiO2 doped with 5% B (w/w). However, when pure TiO2 was used as catalyst, experiments carried out in ρ-benzoquinone demonstrate that O2- radicals did not participate in the degradation mechanism of MET. Oxygen seems to play an important role during the observed degradation of MET. Additionally, the relation between the intermediates formed during the photocatalytic degradation with TiO2 doped 5% B (w/w) as catalyst, with addition of specific scavengers, was investigated and distinct degradation pathways have been proposed for each active species involved. By-products studies in the presence of scavengers were used as a diagnostic tool for the analysis of the photocatalytic mechanism and it was possible to prove that there is change in the reactions of the degradation process of MET when change the role of any active species generated on the surface of the catalyst.
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Since p-n heterojunction photocatalysts with higher energy facets exposed usually possess greatly enhanced photocatalytic activities than single-phase catalysts, a novel Cu2O octadecahedron/TiO2 quantum dot (Cu2O-O/TiO2-QD) p-n heterojunctions composite was designed and synthesized in this study. Cu2O octadecahedra (Cu2O-O) with {110} facets and {100} facets exposed were synthesized firstly, then highly dispersed TiO2 quantum dots (TiO2-QDs) were loaded on Cu2O-O by the precipitation of TiO2-QDs sol in the presence of absolute ethanol. The morphology, crystal structure, chemical composition, optical properties, photocatalytic activity, and stability of Cu2O-O/TiO2-QD heterojunctions were characterized and investigated. It was found that TiO2-QDs were firmly anchored on Cu2O-O single crystals with good dispersibility. The Cu2O-O/TiO2-QD heterojunctions with partial coverage of TiO2-QDs showed a strong absorbance of visible light and exhibited an effective transfer of photoexcited electrons. The degradation of methyl orange (MO) under visible light irradiation indicated that the photocatalytic activity of Cu2O-O/TiO2-QD heterojunctions was significantly enhanced compared with that of Cu2O-O. This Cu2O-O/TiO2-QD heterojunctions composite exhibited high stability in MO degradation process and after storage in air. The high visible light photocatalytic activity and good stability were attributed to high utilization of light, effective separation of photoexcited electron-hole pairs, and instant scavenging of holes in the unique heterojunction structure.
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Graphene-CdS (G-CdS) nanocomposite was prepared successfully via a two-step solvothermal process, with CdS uniformly dispersed on the graphene nanosheets. The photocatalytic disinfection activity of G-CdS was evaluated, and the result shows that G-CdS exhibited higher inactivation efficiency toward the gram-negative bacterium, Escherichia coli, than pure CdS nanoparticles under visible light irradiation. Exposure to 10. mg of pure CdS resulted in a 1.1-log inactivation after 60. min, but resulted in 5.3-log reduction of viable bacteria when exposure to 10. mg G-CdS under the same illumination conditions. In addition, the impacts of humic acid (HA), a kind of natural organic matter (NOM), on its bactericidal properties have also been determined. G-CdS in the presence of HA (10. mg/L) significantly decreased its toxicity, causing less than 0.4-log inactivation after 60. min. Lipid peroxidation, intercellular ROS generation and antioxidant enzyme activities assays indicate that excess oxidative stress induced by G-CdS suppressed the antioxidant defense system, subsequently affected the normal function of lipid, protein and nucleic acid, and thus resulted in cell death. However, the decreased toxicity of G-CdS in the presence of HA may be attributed to that (1) HA presents a barrier to prevent the physical contact between bacteria cells and G-CdS, which was the first step of toxicity mechanisms; (2) HA acts as an antioxidant to react with any ROS and reduce the toxicity.
Article
Although the identification of effective oxidant species has been extensively studied, yet the subcellular mechanism of bacterial inactivation has never been clearly elucidated in electrochemical disinfection processes. In this study, subcellular mechanism of Escherichia coli inactivation during electrochemical disinfection was revealed in terms of comprehensive factors such as cell morphology, total organic components, K(+) leakage, membrane permeability, lipid peroxidation, membrane potential, membrane proteins, intracellular enzyme, cellular ATP level and DNA. The electrolysis was conducted with boron-doped diamond anode in three electrolytes including chloride, sulfate and phosphate. Results demonstrated that cell inactivation was mainly attributed to damage to the intracellular enzymatic systems in chloride solution. In sulfate solution, certain essential membrane proteins like the K(+) ion transport systems were eliminated. Thus, the pronounced K(+) leakage from cytosol resulted in gradual collapse of the membrane potential, which would hinder the subcellular localization of cell division-related proteins as well as ATP synthesis and thereby lead to the bacterial inactivation. Remarkable lipid peroxidation was observed, while the intracellular damage was negligible. In phosphate solution, the cells sequentially underwent overall destruction as a whole cell with no captured intermediate state, during which the organic components of the cells were mostly subjected to mineralization. This study provided a thorough insight into the bacterial inactivation mechanism on the subcellular level. Copyright © 2015 Elsevier Ltd. All rights reserved.
Article
Since its discovery, little work has been done on the vanadium chalcogenide VS4. Recently, a facile method for synthesizing VS4 was discovered using a graphitic template. Here we show for the first time that template-free VS4 can be synthesized in a hydrothermal reaction by controlling key parameters of the reaction: mainly time, temperature, and pH. The phase and morphology of VS4 materials are tracked carefully using X-ray diffraction (XRD) and scanning electron microscopy (SEM) under each reaction condition. It is found that lower reaction temperatures and longer reaction times are sufficient to form VS4 crystals, while variations in pH do not appear to greatly affect VS4 crystallinity but rather surface area and morphology. By use of optimized reaction parameters, further characterization shows template-free VS4 to be comparable with VS4 templated with graphene oxide. Initial photocatalytic testing of these materials shows that VS4 has the potential to be used in photocatalysis.
Article
This research has been conducted to determine the genotoxicity of nano-Al2O3 towards Pseudomonas putida bacteria using RAPD-PCR method. The results were compared with the impact of the macro form of the compound on DNA. On the basis of RAPD profiles using the primer OPA2, the research demonstrated a mutagenic action of the tested nanocompound. The obtained profiles of RAPD bands are different from the negative control by over 30–9.1%. For the products of PCR carried out using the primer OPA9, genetic similarity indexes relative to the negative control for nano-Al2O3 samples were 80% in all tested concentrations. Regarding the remaining primers, RAPD bands profiles for the samples with the nanocompound and the negative control varied only to a small extent. This study showed a decrease in the genetic stability of DNA (GTS, %) after treatment of the bacteria nano-Al2O3 as compared with the negative control. GTS value for the nano-Al2O3 was 65% (1,000 mg/L). In the remaining concentrations of nano-Al2O3, GTS remained in the range of 75–80%. The results showed that the nano-Al2O3 can induce modifications of the genetic material to a greater extent than the same compounds in the macro form.
Article
VS4/reduced graphene oxide (VS4/rGO) composites are successfully synthesized via a one-step hydrothermal route. Then their photocatalytic activities are examined by water splitting reaction, and the morphology and structure are characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy and thermo gravimetric analysis, respectively. It is shown that graphene accelerates the nucleation during the growth period of VS4. Main product is VS4, not VS2. Monoclinic VS4 particles interact with graphene through chemical action. VS4/rGO composites show excellent photocatalytic water splitting activities under visible-light irradiation. This excellent performance is due to the formation of pi-conjugated structure, which can transmit electrons from S2(p) to graphene rapidly. However, composites with excess graphene show poor dispersion, which leads to the best doping ratio of graphene is 5 wt%. Copyright (c) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.