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Synthesis, Characterization, Photocatalytic Activity of Visible-Light-Responsive Photocatalysts BiOxCly/BiOmBrn by Controlled Hydrothermal Method
Abstract
Bismuth oxyhalide and its composite belong to a new family of visible light driven photocatalysts and attract more and more attention because of their interesting structures dependent on the photocatalytic performance arisen from their layered structures interleaved with [Bi2O2] slabs and double halogen atoms slabs. An effective and simple strategy to improve the photocatalytic activity of a photocatalyst is the construction of a heterostructure, as the heterojunction has great potential in tuning the desired electronic properties of the composite photocatalysts and efficiently separating the photogenerated electron-hole pairs. This is the first report that a series of BiOxCly/BiOmBrn heterojunctions are prepared using controlled hydrothermal methods. The compositions and morphologies of BiOxCly/BiOmBrn could be controlled by adjusting some growth parameters, including reaction pH, time, and temperature. The products are characterized by XRD, SEM-EDS, HR-TEM, DR-UV, BET, CL, and HR-XPS.
... A simple and facile hydrolysis method at 60 • C at neutral pH was used to fabricate BiOX 0.5 X ′ 0.5 (X and X' = Cl, Br, I; and X∕ =X ′ ). Therefore, as far as our approach optical and morphological properties as-fabricated catalysts have been modified Singh et al., 2018;Dutta et al., 2019;Lofrano et al., 2016;Chen et al., 2014;Huang et al., 2014;Jiang et al., 2015a;Ma et al., 2017)- Singh et al., 2018;Dutta et al., 2019;Lofrano et al., 2016;Chen et al., 2014;Huang et al., 2014;Jiang et al., 2015a;Ma et al., 2017). Due to the inclusion of quercetin in inner coupled oxyhalides, multiple interfaces were formed which increased the photocatalytic efficiency of the as-fabricated catalyst. ...
... A simple and facile hydrolysis method at 60 • C at neutral pH was used to fabricate BiOX 0.5 X ′ 0.5 (X and X' = Cl, Br, I; and X∕ =X ′ ). Therefore, as far as our approach optical and morphological properties as-fabricated catalysts have been modified Singh et al., 2018;Dutta et al., 2019;Lofrano et al., 2016;Chen et al., 2014;Huang et al., 2014;Jiang et al., 2015a;Ma et al., 2017)- Singh et al., 2018;Dutta et al., 2019;Lofrano et al., 2016;Chen et al., 2014;Huang et al., 2014;Jiang et al., 2015a;Ma et al., 2017). Due to the inclusion of quercetin in inner coupled oxyhalides, multiple interfaces were formed which increased the photocatalytic efficiency of the as-fabricated catalyst. ...
The nanostructured, inner-coupled Bismuth oxyhalides (BiOX0.5X′0.5; X, X’ = Cl, Br, I; X≠X′) heterostructures were prepared using Quercetin (Q) as a sensitizer. The present study revealed the tuning of the band properties of as-prepared catalysts. The catalysts were characterized using various characterization techniques for evaluating the superior photocatalytic efficiency and a better understanding of elemental interactions at interfaces formed in the heterojunction. The material (BiOCl0.5Br0.5-Q) reflected higher degradation of MO (about 99.85%) and BPA (98.34%) under visible light irradiation than BiOCl0.5I0.5-Q and BiOBr0.5I0.5-Q. A total of 90.45 percent of total organic carbon in BPA was removed after visible light irradiation on BiOCl0.5Br0.5-Q. The many-fold increase in activity is attributed to the formation of multiple interfaces between halides, conjugated π-electrons and multiple –OH groups of quercetin. The boost in degradation efficiency can be attributed to the higher surface area, 2-D nanostructure, inhibited electron-hole recombination, and appropriate band-gap of the heterostructure. Photo-response of BiOCl0.5Br0.5-Q is higher compared to BiOCl0.5I0.5-Q and BiOBr0.5I0.5-Q, indicating better light absorption properties and charge separation efficiency in BiOCl0.5Br0.5-Q due to band edge position. First-principles Density Functional Theory (DFT) based calculations have also provided an insightful understanding of the interface formation, physical mechanism, and superior photocatalytic performance of BiOCl0.5Br0.5-Q heterostructure over other samples.
... The Bi 4f peaks of MoS 2 /Bi 2 O 3 catalyst was shown at 158.56 and 163.87 eV, which indicated the existence of Bi and the shifting of these peaks towards higher binding energy specifies partially reduced form of trivalent Bi (3Àx)þ by simple autoclave hydrothermal method. Similar results were observed in previous reports of Yongsheng et al. [38], S. T. Huang et al. [49], and Chen et al. [50], described the higher binding energy shift would be attributed to the substoichiometric forms of Bi and the low oxidation state, that resulted in the formation of oxygen vacancy in the crystal lattice. Fig. 4d shows the asymmetric profile, which can be deconvoluted into three binding energy peaks it might be at 532.6, 531.3 and 529.9 eV. ...
... The Oxygen signal at 532.6 eV promotes photocatalytic activity by trapping photoinduced electron-hole pairs [56]. Finally, it is important to notify that the Mo 3d and Bi 4f XPS peaks of MoS 2 /Bi 2 O 3 heterojunction catalyst were evidently shifted towards higher binding energy ( Fig. 4a and b) compared to that of the pristine MoS 2 and Bi 2 O 3 , which indicate the interaction between MoS 2 and Bi 2 O 3 in Z-scheme MoS 2 /Bi 2 O 3 heterojunction catalyst [49]. Further, this interaction would promote the transfer of charge carriers, thereby enhancing the photocatalytic performance and stability. ...
An oxygen-vacancy rich, bismuth oxide (Bi2O3) based MoS2/Bi2O3 Z-scheme heterojunction catalyst (2-BO-MS) was prepared in an autoclave hydrothermal method using ethanol and water. The performance of MoS2/Bi2O3 catalyst was examined for photocatalytic hydrogen evolution, photoelectrochemical activity, and crystal violet (CV) dye degradation by comparing with pristine Bi2O3 and MoS2. The hydrogen evolution performances of 2-BO-MS catalyst exhibited 3075.21 μmol g⁻¹ h⁻¹, which is 7.18 times higher than that of MoS2 (428.14 μmol g⁻¹ h⁻¹). The XPS, XRD and HRTEM analyses covered that the superior photocatalytic performance of 2-BO-MS catalyst might have stemmed out due to the existence of oxygen vacancies, enhanced strong interfacial interaction between MoS2 and Bi2O3 and specific surface area. The in-depth investigation has been performed for MoS2/Bi2O3 Z-scheme heterojunction using several characterization techniques. Moreover, the photocatalytic mechanism for hydrogen evolution and photodegradation were proposed based on trapping experiment results. This results acquired using MoS2/Bi2O3 Z-scheme heterojunction would be stepping stone for developing heterojunction catalyst towards attaining outstanding photocatalytic activity.
... Over a decade, the evolution of nanotechnology has led to the discovery of materials with unique physicochemical properties [4] and has a wide range of applications from nanoelectronics (sensors, NEMS, and fabrication) to nanomedicine (drug delivery, artificial implants) [5]. Metallic and semiconductor nanomaterials are effective materials for catalytic/photocatalytic degradation of dyes in the aquatic environment [6][7][8][9][10][11][12][13][14][15][16][17]. Owing to their unique properties, nanomaterials made dye degradation more effective due to their high surface to volume ratio. ...
... Reducing the power of SeNPs was increased by the presence of extract. Using the electron relay effect [16,42,43], SeNPs act as an acceptor of electrons from the extract and as a donor of electrons for methylene blue. Therefore, the extract is acting as a catalyst for the oxidationreduction reaction. ...
The aquatic environment is contaminated with methylene blue (MB) due to increasing industrial activity which causes health hazard for both humans and animals. In the present study, we report a cost-effective, environmentally friendly, rapid green synthesis method for fluorescent selenium nanoparticles (SeNPs) using Ficus benghalensis leaf extract. The biogenic SeNPs were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS), and photoluminescence spectroscopy (PL). The size distribution profile of SeNPs was found to be 45–95 nm, and the average size was found at 64.03 nm by DLS and SEM study. X-ray diffraction (XRD) of the sample suggests that the synthesized selenium is polycrystalline in nature. As-synthesized SeNPs were used for the photocatalytic degradation of MB in the aquatic environment. The degradation reached 57.63% in 40 min with a rate constant of 0.02162 s−1.
... However, the dissociation of structural bonds of the dye affects the groups like chromophore and auxochromes from the molecular structure indicating decolourization of MB dye [65]. In our study, owing to the electron relay effect, SeNPs act as an acceptor as well as a donor of electrons for MB, hence SeNPs are a catalyst for oxidation-reduction reaction [48,66]. The reduction in central ring of MB indicates the elimination of n→π* electronic transition and its conjugative structure which subsequently leading with the formation of colourless MB and time-dependent shift of absorption peaks. ...
Biogenic synthesis of nanoparticles has been established as an environmentally benign and sustainable approach. This study emphasizes biosynthesis of selenium nanoparticles (SeNPs) utilizing leaf extract of Nyctanthes arbor-tritis L., well known for its abundant bioactive compounds. Various analytical techniques were employed for characterization of synthesized SeNPs. X-ray diffraction (XRD) spectroscopy confirmed the crystalline structure and revealed the average crystalline size of SeNPs to be 44.57 nm. Additionally, UV–Vis spectroscopy confirmed successful synthesis of SeNPs by validating the surface plasmon resonance (SPR) properties of SeNPs. FTIR analysis data revealed different bonds and their corresponding functional groups responsible for the synthesis and stability of synthesized SeNPs. DLS and zeta analysis revealed that 116.5 nm sized SeNPs were stable in nature. Furthermore, field emission scanning electron microscopy (FE-SEM) validated the spherical morphology of SeNPs with a size range of 60–80 nm. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) determined the concentration of SeNPs in the obtained colloidal solution. Antioxidant activity of synthesized SeNPs was evaluated employing DPPH and H2O2 assay, revealed that the synthesized SeNPs were effective antioxidant agent. Additionally, antimicrobial potential was evaluated against a panel of Gram-positive and Gram-negative bacteria and found to be effective at higher concentration of SeNPs. SeNPs also exhibited strong anti-biofilm activity while evaluated against various biofilm producing bacteria like Escherichia coli,Staphylococcus epidermidis and Klebsiella pneumonia. The cytotoxicity of the bio-synthesized SeNPs was evaluated against HEK 293 cell line, exhibited minimal toxicity even at concentration 100 μg/mL with 65% viable cells. SeNPs has also been evaluated for dye degradation which has indicated excellent photocatalytic activity of synthesized SeNPs. The experimental data obtained altogether demonstrated that synthesized SeNPs exhibited significant antimicrobial and anti-biofilm activity against various pathogens, and also showed significant antioxidant and photocatalytic efficiency.
... Furthermore, such additional techniques required to treat the secondary pollutants enhances the cost of remediation. 16,17 Photocatalysis is a method used to degrade organic compounds found in waste water by mineralizing them into simplest compounds like H 2 O, CO 2 , etc. Nano photocatalysts have been studied extensively since they have favorable combination of electronic structure, light absorption properties; charge DOI: https://doi.org/10.36503/chcmj Volume 9, Number 1 transport characteristics, etc. 18,19 Among the di erent kinds of photocatalysts, the prominent nanocatalysts extensively used are TiO 2 , ZnO, SnO 2 , etc. [20][21][22][23] However, reports about the usage of CaCO 3 Nps as photocatalyst against the degra-dation of organic pollutant are scarce. ...
Background: The problem associated with the textile industries are the direct discharge of coloring chemicals into water body that causes threat to the aquatic lives.
... Bismuth oxyhalides (BiOX, X = Cl, Br, or I) are among many semiconductors that have gained attention recently due to their stability, easiness in band gap tailoring, and high photocatalytic activity [16][17][18][19]. Among the oxyhalides, bismuth oxychloride (BiOCl) is regarded as one of the ideal photocatalysts because it is inexpensive, non-toxic, and has strong redox ability under visible light irradiation [20][21][22]. The Van der Waals forces between Cl atoms interlaced the internal layer structure of this ternary layered oxide, which can offer sufficient capacity to allow separation of the photogenerated charge carriers [23][24][25][26]. ...
In this work, BiOCl, 0.5%, 1%, and 5% Nb2O5/BiOCl (NBO/BCl) composite were prepared by a facile co-precipitation method. The synthesized materials were characterized using various characterization techniques such as XRD, FTIR, Raman, UV–Vis DRS, PL, BET, and TEM. The XRD confirms the formation of NBO/BCl composite with no impurities detected. The FT-IR results revealed the successful formation of the NBO/BCl composite, where both functional groups belonging to BiOCl and NBO/BCl were present. The TEM showed that BiOCl and 1% NBO/BCl have irregular nanoplate-like morphology with an average thickness of 22 and 18 nm, respectively. The photocatalytic degradation performance of the BiOCl and NBO/BCl composites was evaluated by degrading Rhodamine B (RhB) dye under visible light irradiation. Among all of the photocatalysts, 1% NBO/BCl showed the highest photocatalytic activity in which it degraded 96.7% of RhB dye in 120 min under visible light irradiation. Furthermore, the photoelectrochemical response of BiOCl and NBO/BCl composites was investigated by linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. The LSV and EIS analysis of NBO/BCl showed enhanced response when exposed to visible light compared to dark conditions. The significant improvement in the photocatalytic and photoelectrochemical performance of NBO/BCl composite was attributed to the synergistic effects of the NBO/BCl which enhanced light absorption abilities and charge carrier transfer making it easier for charge separation by lowering the recombination rate.
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... To date, scholar has been widely probed a new visible-light photocatalyst, BiOX (X = Cl, Br, I) has gained more consideration in research, due to stability, suitable bandgap, superior photocatalytic activity, high surface area, optical properties and environmentally -friendly nature ( Di et al., 2013 ;Xia et al., 2014 ;Li et al., 2016Li et al., , 2020Li et al., , 2014Siao et al., 2018Siao et al., , 2019Lee et al., 2019 ;Chen et al., 2018Chen et al., , 2014Lin et al., 2016 ;Huang et al., 2014 ;Yu et al., 2015). All the BiOX compounds belongs to multi-component oxyhalides family that have a similar layered structure and high catalytic activity, which is possess of halogen atoms [X] between the double slabs of [Bi 2 O 2 ] 2 + ( Xia et al., 2016 ). ...
Photocatalytic degradation was considered as a best strategy for the removal of antibiotic drug pollutants from wastewater. The photocatalyst of ABC (Ag2CO3/BiOBr/CdS) composite synthesized by hydrothermal and precipitation method. The ABC composite used to investigate the degradation activity of tetracycline (TC) under visible light irradiation. The physicochemical characterization methods (e.g. scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), ultraviolet visible spectroscopy (UV), photoluminescence (PL) and time resolved photoluminescence (TRPL) clearly indicate that the composite has been construct successfully that enhances the widened visible light absorption, induces charge transfer and separation efficiency of electron - hole pairs. The photocatalytic activity of all samples was examined through photodegradation of tetracycline in aqueous medium. The photocatalytic degradation rate of ABC catalyst could eliminate 98.79% of TC in 70 min, which is about 1.5 times that of Ag2CO3, 1.28 times that of BiOBr and 1.1 times that of BC catalyst, respectively. The role of operation parameters like, TC concentration, catalyst dosage and initial pH on TC degradation activity were studied. Quenching experiment was demonstrated that ·OH and O2·- were played a key role during the photocatalysis process that was evidently proved in electron paramagnetic resonance (EPR) experiment. In addition, the catalyst showed good activity perceived in reusability and stability test due to the synergistic effect between its components. The mechanism of degradation of TC in ABC composite was proposed based on the detailed analysis. The current study will give an efficient and recyclable photocatalyst for antibiotic aqueous pollutant removal.
... A proposed MG dye degradation mechanism is represented by Figure 13. superoxide and hydroxyl radicals started to degrade via radical mechanism [51]. Importantly, it has been identified by previous studies that the degradation of MG dye is mainly occurring due to the superoxide ions and consequently a harmful dye is changed into harmless products. ...
The present study demonstrates the crucial role of agave americana extract in enhancing the optical properties of zinc oxide (ZnO) through thermal treatment method. Various analytical and surface science techniques have been used to identify the morphology, crystalline structure, chemical composition, and optical properties, including scanning electron microscopy (SEM), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray spectroscopy (EDS) and UV-visible spectroscopy techniques. The physical studies revealed the transformation of ZnO nanorods into nanosheets upon addition of an optimized amount of agave americana extract, which induced large amount of amorphous carbon deposited onto ZnO nanostructures as confirmed by HRTEM analysis. The use of increasing amount of americana extract has significantly reduced the average crystallite size of ZnO nanostructures. The resultant hybrid system of C@ZnO has produced a significant effect on the ultraviolet light-assisted photodegradation of malachite green (MG) dye. The photocatalyst dose was fixed at 10 mg for each study whereas the amount of agave americana extract and MG dye concentration are varied. The functionality of hybrid system was greatly enhanced when the amount of agave americana extract increased while dye concentration kept at lower level. Ultimately, almost 100% degradation efficiency was achieved via the prepared hybrid material, revealing combined contribution from synergy, stabilization of ZnO due to excess of carbon together with the high charge separation rate. The obtained results suggest that the driving role of agave americana extract for surface modification of photocatalyst can be considered for other nanostructured photocatalysts.
... The textile dyeing and finishing industry discharges a large quantity of industrial waste that contains numerous chemically toxic pigments and dyes into bodies of water, which results in their pollution and causes serious harm to humans and the natural environment [1]. Traditional industrial wastewater treatment methods include coagulation and biological treatment; however, industrial wastewater treated using these methods does not meet discharge standards. ...
This study used a three-dimensional (3D) printing process to develop the Ag/AgCl/TiO2 coupled photocatalyst with a specific surface area of 748 mm²/g. We examined the catalytic capability of this photocatalyst in degrading methyl blue (MB) dye and sterilizing Escherichia coli as well as the durability and reliability of its continuous use. A TiO2 module was constructed through fused filament fabrication (FFF), and the adopted 3D printing filament was composed of anatase TiO2 nanoparticles, stearic acid, wax, and a plasticizer. The green compact of the TiO2 module was subjected to solvent debinding, thermal debinding, and sintering to obtain a fundamental structure that was subsequently coupled with AgCl through a precipitation reaction. Ultraviolet radiation was used for the photoreduction to obtain the Ag/AgCl/TiO2 coupled photocatalyst coupling module. This photocatalyst can effectively degrade MB dye and disinfect E. coli. The degradation of MB dye and sterilization of E. coli were conducted under visible and ultraviolet light. The degradation of MB dye by the Ag/AgCl/TiO2 coupled photocatalyst was a first-order reaction. In addition, this coupled photocatalyst could retain its MB dye degradation rate (95%) for five cycles. E. coli was sterilized using the prepared photocatalytic module in a 120-min test, and this sterilization phenomenon could be presented as a hyperbolic reaction. The photocatalytic module manufactured in this study through FFF could efficiently degrade pollutants in water, and its durability and reliability after repeated use have been approved.
... Thousands of chemicals are used in the textile dyeing industry, and the waste is a source of water contamination around the world. According to a World Bank report, approximately 17%-20% of industrial waste comes from the textile dyeing and finishing industries, and some of the ingredients are toxic to the environment, harming the environmental [1]. Of these, azo dye (Orange II) is environmentally persistent and must be effectively treated before being released into a natural water body. ...
An advanced three-dimensional printing process for producing the Ag/AgCl/TiO2-coupled photocatalyst was developed and tested for its stability and degradability in relation to azo dye (Orange II) and bacteria (Escherichia coli). The TiO2 structure is produced through fused filament fabrication (FFF) with filaments of thermoplastic material, which is composed of TiO2 anatase nanoparticles, high density polyethylene (HDPE), stearic acid, wax, and plasticizer. The TiO2 structure is then solvent degreased, thermal degreased, and sintered to become a fundamental structure to couple the AgCl particles through an ion exchange process. Following the photoreduction of UV radiation, a Ag/AgCl/TiO2-coupled photocatalyst is formed. In our experiments, this photocatalyst effectively degraded Orange II dye and sterilized E. coli. The degradation of Orange II dye and E. coli was performed under visible and ultraviolet light irradiation. The degradation kinetics of Orange II dye was a first-order reaction, with the degradability (94%) persisting for five cycles. The sterilization of E. coli was accomplished within 120 min, and the degradation kinetics were characteristic of a hyperbolic reaction. The photocatalytic module fabricated through FFF not only exhibited the ability to degrade contaminants in water but also exhibited durability and reliability after repeated use.
... The textile dyeing and nishing industry discharges a large quantity of industrial waste that contains numerous chemically toxic pigments and dyes into bodies of water, which results in their pollution and causes serious harm to humans and the natural environment [1]. Traditional industrial wastewater treatment methods include coagulation and biological treatment; however, industrial wastewater treated using these methods does not meet discharge standards. ...
This study used a three-dimensional (3D) printing process to develop a Ag/AgCl/TiO 2 coupled photocatalyst with a large specific surface area. We examined the catalytic ability of this photocatalyst in methyl blue dye degradation and Escherichia coli sterilization as well as the reliability of its repeated use. A TiO 2 module was constructed of fuse filament [through fused filament fabrication (FFF)], and the adopted 3D printing filament was composed of anatase (TiO 2 ) nanoparticles, stearic acid, wax, and a plasticizer. The green compact of the TiO 2 module was subjected to solvent debinding, thermal debinding, and sintering to obtain a basic structure that was subsequently coupled with AgCl through a precipitation reaction. Ultraviolet radiation was used for the photoreduction of the coupled product to obtain a Ag/AgCl/TiO 2 photocatalyst coupling module. This photocatalyst can effectively degrade methylene blue (MB) dye and disinfect E. coli . The degradation of MB dye and sterilization of E. coli were conducted under visible and ultraviolet light. The degradation of MB dye by Ag/AgCl/TiO 2 was a first-order reaction. In addition, this catalyst could retain its MB dye degradation rate (95%) for five cycles. E. coli was sterilized using the prepared photocatalyst in a 120-min test, and this sterilization was a hyperbolic reaction. The photocatalytic module manufactured in this study through FFF can degrade pollutants in water has durability and retains reliability after repeated use.
... Recently, the development of bismuth oxyhalides (BiOX; X = Br, I, Cl), has gained prodigious consideration due to their appealing physicochemical properties, high chemical stability, decent visible light photocatalytic activity and appropriate bandgap, which makes BiOX an excellent photocatalyst [38][39][40][41][42][43] . BiOX (X = Cl, Br, I) are currently being explored and improved for effective performance under visible-natural light for photocatalytic degradation of harmful organic compounds in air and water [44][45][46][47][48][49] . ...
Silver oxide loaded bismuth oxybromide (Ag2O/BiOBr) nanocomposite was synthesized using high efficiency solution-based method. The as-prepared samples were characterized by different analytical techniques. The synthesized nanoparticles were then evaluated for antimicrobial efficacy on opportunistic human pathogenic bacteria viz. Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium, Klebsiella pneumonia, Aeromonas salmonicida. In the experiments, all the five strains were treated with BiOBr and Ag2O/BiOBr, in a concentration ranging from 0.5 mg/mL to 2.0 mg/mL and Ag2O/BiOBr was found to be highly effective. The minimum inhibitory concentration (MIC) and minimum bactericidal activity (MBC) of Ag2O/BiOBr was 0.5 mg/mL and 1 mg/mL against E. coli, Salmonella typhimurium and Klebsiella pneumonia, 1 mg/mL and 1.5 mg/mL against Pseudomonas aeruginosa, and Aeromonas salmonicida, respectively. Only 2 hours of exposure to different concentration of Ag2O/BiOBr nanocomposites completely inhibited the growth of all the tested bacterial strains showing an effective dose dependent inhibition of bacterial growth in a short time period. The results showed the potential bactericidal activity of as synthesized Ag2O/BiOBr, which could be an alternative to the conventional antimicrobial agents currently used and a perspective for the application of nano-silver with antibiotics to improve antimicrobial activity.
... From these atomic structures, the monoclinic scheelite BiVO 4 (m-BiVO 4 ) exhibits the optimum photoinduced activity for visible light radiations and has the coloristic dimension at much upper-level as compared to the other two crystalline forms [12,13]. It is well known that the crystal structure of BiVO 4 is intimately depended on engaged preparation methods [7,14,15]. The tetragonal BiVO 4 is generally obtained at a low temperature from aqueous precipitation, while the m-BiVO 4 can be obtained by many ways, including aqueous route, solid-state reaction, sono-chemical method, solgel method, co-precipitation, chemical bath deposition and hydrothermal treatment [5,16,17]. ...
... From these atomic structures, the monoclinic scheelite BiVO 4 (m-BiVO 4 ) exhibits the optimum photoinduced activity for visible light radiations and has the coloristic dimension at much upper-level as compared to the other two crystalline forms [12,13]. It is well known that the crystal structure of BiVO 4 is intimately depended on engaged preparation methods [7,14,15]. The tetragonal BiVO 4 is generally obtained at a low temperature from aqueous precipitation, while the m-BiVO 4 can be obtained by many ways, including aqueous route, solid-state reaction, sono-chemical method, solgel method, co-precipitation, chemical bath deposition and hydrothermal treatment [5,16,17]. ...
Highly crystalline bismuth vanadate (BiVO4) powder was prepared by a template-free hydrothermal method under different pH (~ 2, 3, 5, 8, 11) reaction conditions and characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, Brunauer–Emmett–Teller surface area, photoluminescence, and electron spin resonance techniques. It was found that variation in pH of the precursor solution can influence morphology, structure and, consequently, photocatalytic efficiency of obtained products. The spherical BiVO4 nanoparticles were obtained at pH 2 and 3, nanorods at pH 5 and 8, whereas nanoplates were obtained at pH 11. Among the different pH-based BiVO4 samples, the one prepared at pH ~ 11 (BiVO4-11) exhibited surface area 102.74 m2/g and degraded the dye solution completely within 90 min. Therefore, pH-controlled hydrothermal reaction can be useful to synthesize nanostructures with different morphologies efficiently for the enhanced photocatalytic degradation of pollutant under visible light.
... Moreover, the availability of superoxide anion radical has been hypothersised to result in formation of hydroxyl radicals by Equations 13 -18 [71,89]. These equations shows that there are numerous ROSs that can be generated and they all result in generation of hydroxyl radicals. ...
The escalation of pharmaceutical products development and sales in the last few decades have raised concerns about their effect on the environment, particularly water and consequently their removal from wastewater. Composites of cobalt oxide (Co3O4) and bismuth oxyiodide (BiOI) were synthesised and evaluated for degradation of ibuprofen (IBU) and effect of trimethoprim (TMP) under visible light irradiation. The properties of the as synthesised composites were evaluated using different techniques such as FTIR, SEM, TEM, XRD, BET, TGA, UV-Vis and PL. The self-assembled direct Z-scheme heterojunction showed high photocatalytic activity for degradation of ibuprofen (97.02 %) after adding 2 mg of TMP. TOC reduction of 85.68 ± 2.22 % at pH 11.3 was also calculated. The enhanced photocatalytic activity of the Z-scheme heterojunction was attributed to strong visible light absorption properties of the catalyst and improved separation of photoexcited charge carriers resulting from the built-in electric field formed between the BiOI microspheres and the Co3O4 wormy epitaxy established after equilibrium Fermi level was reached. The Z-scheme heterojunction is a promising material for the removal of pharmaceuticals in aquatic effluents.
Background
Considerable research efforts have been dedicated to comprehensively evaluate the electrochemical and photocatalytic properties of newly synthesized metal sulfides.
Aims
This research aims to determine the viability of using metal sulfide, MnS 2 :Ni 9 S 8 :Co 3 S 4 thin film with excellent energy retention capacities and amazing photocatalytic activities.
Materials & Methods
Single source precursor method was utilized for the synthesis of metal sulfide. Furthermore, deposition of thin film was performed through physical vapour deposition route. Detailed characterization was done by using UV‐visible spectrophotometry, Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffraction crystallography and X‐ray photoelectron spectroscopy. Electrochemical investigation was done through cyclic and linear sweep voltammetry while competence of the thin film in degrading various environmental pollutants, including crystal violet dye, fuberidazole and phenol, was evaluated by photocatalytic degradation.
Results & Discussion
A crystallite size of 47 nm with 86.5% crystallinity was found along with a 3.4 eV bandgap energy. Round‐edged cubical structures in the composite were seen. X‐ray photoelectron spectroscopy revealed core level peaks of Mn 2p, Ni 2p, Co 2p and S 2p. A specific capacitance of 590 Fg ⁻¹ was observed from the electrochemical analysis showing the presence of electroactive sites that allow for effective electrochemical processes. After 60 minutes of exposure to the thin film, phenol showed the slowest rate of degradation, whereas crystal violet and fuberidazole showed significant percentages of deterioration.
Conclusion
The findings highlight MnS 2 :Ni 9 S 8 :Co 3 S 4 thin film's adaptability as viable compound for addressing the critical concerns of storing energy, production, and environmental cleanup. These significant findings highlight the versatility of tri‐metal sulfide thin films, opening up avenues for further research and technological advancements.
Semiconductor based photocatalysts have been an efficient technology for water and wastewater remediation, addressing the concepts of green chemistry and sustainable development. Owing to narrow and suitable band structure, BiOBr is a promising candidate for efficient wastewater treatment via photocatalysis. Enhancement of photocatalytic properties can be obtained by various techniques like doping, element rich strategy, facet engineering, and defect control. This review primarily focuses on the band engineering of single BiOBr, its binary, ternary composites and their applications in degradation of hazardous pollutants in wastewater. Moreover, current challenges and future perspectives were discussed along with concluding comments.
In this study, reduced graphene oxide (rGO)/BiOCl catalysts with visible light response capacity were synthesized in-situ using a mild and facile hydrothermal method. rGO/BiOCl photocatalysts were studied by specific surface area analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflection spectroscopy (UV–Vis DRS) techniques. In light of the excellent electrical conductivity of rGO and surface modification of rGO, the photogenerated carriers separation efficiency of rGO/BiOCl is remarkably improved. The experiments results reveal that BiOCl with rGO modification holds higher photocatalytic activity than the single BiOCl. Moreover, the highest photocatalytic activity is obtained when the mass ratio of rGO and BiOCl is 2%. Under visible light irradiation, compared with the single BiOCl, activity of the 2% rGO/BiOCl sample toward destruction of tetracycline (TC) and rhodamine B (RhB) increases by 49.8 and 6.8 times, respectively. The 2% rGO/BiOCl catalyst also shows enhanced degradation activity for perfluorooctanoic acid (PFOA), trichloroacetic acid (TCA) and perfluorooctane sulfonic acid (PFOS) under UV light irradiation. Considering the above experimental observations, photocatalytic enhancement mechanism for rGO/BiOCl photocatalyst was reasonably elaborated.
An advanced three-dimensional printing process for producing the silver clusters/ Silver(I) chloride/titanium dioxide-coupled photocatalyst was developed and tested for its stability and degradability in relation to azo dye (Orange II) and bacteria (Escherichia coli). The titanium dioxide structure is produced through fused filament fabrication (FFF) with filaments of thermoplastic material, which is composed of titanium dioxide anatase nanoparticles, high density polyethylene (HDPE), stearic acid, wax, and plasticizer. The TiO2 structure is then solvent degreased, thermal degreased, and sintered to become a fundamental structure to couple the AgCl particles through an ion exchange process. Following the photoreduction of UV radiation, a silver clusters/Silver(I) chloride/titanium dioxide-coupled photocatalyst is formed. In our experiments, the degradation of Orange II dye and E. coli was performed under visible and ultraviolet light irradiation. The degradation kinetics of Orange II dye was a first-order reaction, with the degradability (94%) persisting for five cycles. The sterilization of E. coli was accomplished within 120 min, and the degradation kinetics were characteristic of a hyperbolic reaction. The photocatalytic module prepared through FFF not only exhibited the ability to degrade contaminants in water but also exhibited durability and reliability after repeated use.
The construction of heterojunction composites using suitable semiconductor materials is an effective method for the removal of organic pollutants from wastewater. Herein, Bi4O7/Cu-BiOCl nanocomposites were synthesized by hydrothermal and calcination methods as photocatalysts. The morphology, structure, and optical properties of the composites were characterized by SEM, XRD, EDX, FT-IR, DRS, and PL related techniques. Results show that Cu-BiOCl was tightly loaded on the surface of Bi4O7, and the heterojunction was successfully formed between them. The photocatalytic activity of the composites was evaluated by the degradation of tetracycline (TC) under visible light irradiation. It was found that Bi4O7/Cu-BiOCl-2 exhibit excellent photodegradation performance than that of single-phase materials, and the photodegradation efficiency of TC could reach 91% in short time (60 min). Meanwhile, Bi4O7/Cu-BiOCl-2 composite showed high stability and degradation efficiency in simulation experiments with different water sources and inorganic anions doping. The possible degradation pathways were investigated by LC-MS and 3D EEM, and the mechanism was studied using capture experiments and electron spin resonance. Thus, this work provides a new approach for the design of bismuth-based heterojunction photocatalysts.
Nanosheets of Bi2SiO5/Bi4Si3O12 composite material was prepared by a one-step hydrothermal method with HNO3 solution as the solvent. In the same hydrothermal condition, the nanosheets of Bi2SiO5 and hollow spherical of Bi4Si3O12 were prepared by substituting HNO3 solution with ethylene glycol and benzyl alcohol as solvent, respectively. The obtained materials were characterized by the XRD, XPS, SEM, TEM, BET, UV–vis spectroscopy and PL. The Bi2SiO5, Bi2SiO5/Bi4Si3O12 and Bi4Si3O12 photocatalysts were applied to remove 17α-ethynylestradiol(EE2), and the EE2 removal rates were 47.6%, 99.4% and 25.4% after 12 min of UV-light irradiation, respectively. Photocatalytic activity of Bi2SiO5/Bi4Si3O12was better than that of Bi2SiO5 and Bi4Si3O12, because that heterojunction of Bi2SiO5/Bi4Si3O12 had the matching band structure between Bi2SiO5 and Bi4Si3O12, the carrier separation efficiency and transport efficiency were improved. The Bi2SiO5/Bi4Si3O12 shows the highest reaction rate, which is 9.69, 26.41, 27.29 and 124.96 times higher than that of Bi2SiO5, Bi4Si3O12, P25 and EE2 photolysis, respectively. The effects of pH value and photocatalyst dosage were optimized for removing EE2 in water. The possible photocatalytic mechanism was proposed based on the trapping photocatalytic experiments and the energy band positions. Surprisingly, the Bi2SiO5/Bi4Si3O12 photocatalyst had specific adsorption performance on EE2 comparing to BPA due to the EE2 has stronger hydrophobicity than BPA, while it can photodegrade both EE2 and bisphenol A (BPA). Results in this work provide new insights for controlled synthesized the Bi2SiO5, Bi2SiO5/Bi4Si3O12 and Bi4Si3O12 only by changing the solvent in hydrothermal process. The Bi2SiO5/Bi4Si3O12 possess a synergistic effect of adsorption and photocatalysis for hydrophobic organic molecules, which indicates that it can be used as an efficient material for removing hydrophobic molecules. Meanwhile, Bi2SiO5/Bi4Si3O12 composite was considered a promising photocatalyst for removing all kinds of Endocrine Disrupting Chemicals (EDCs) organic pollutants.
Assessing the interaction between microbes and nanocatalysts for finding an inclusive, proactive and deep understanding of nanoparticles-based toxicity is vital for discovering their broad range of applications. Palladium based photocatalysts owing to their unique fundamental characteristics and brilliant physicochemical potential have gained immense interest in environment remediation as disinfection system. In the present study, we report synthesis of a novel palladium nanoparticles decorated bismuth oxybromide (Pd/BiOBr) nanostructures using an energy efficient solution-based method, having excellent photocatalytic antibacterial action. The synthesized nanomaterials was thoroughly characterized using various analytical techniques. The photocatalytic antibacterial efficiency of Pd/BiOBr was evaluated against some common pathogenic strains of Gram-positive and Gram-negative bacteria (Pseudomonas fluorescens, Pseudomonas aeruginosa, Escherichia coli, Aeromonas salmonicida, Salmonella typhimurium, Klebsiella pneumoniae, Bacillus subtilis). In our results Pd/BiOBr showed excellent photocatalytic disinfection efficacy with > 99.9% bacterial inactivation. A very low concentration of Pd/BiOBr (0.5 µg/mL) effectively inhibited the bacterial growth in response to just 2 h of visible light irradiation, while 1 µg/mL of Pd/BiOBr completely killed all the tested bacterial strains proving their magnificent bactericidal potential. The developed materials with exceptional antibacterial broad range efficiency can be used in different photocatalytic disinfection systems including water purification systems, biofilm exclusion and combating differential antibiotic resistance.
The proper design of interfacial contact of heterojunction photocatalyst plays an important role in the transfer/separation of interfacial charge carriers. The Z-type photocatalyst can reduce the recombination of photogenerated electron-hole pairs and retain the original redox ability. Here, KBiO3/g-C3N4 Z-scheme heterojunction photocatalysts were facile synthesized by mixing and programmed heating. Compared to pure g-C3N4 and KBiO3, the photocatalytic performance of the obtained photocatalyst on the photo-oxidative degradation of crystal violet and phenol was improved significantly. The apparent rate constants of degrading CV (Crystal Violet) and phenol were 0.15493 min⁻¹ and 0.02057 min⁻¹, which were 10 times and 4 times that of pure KBiO3, respectively. The formation mechanism of KBiO3/C3N4 Z-type heterojunction was investigated by experiments and DFT calculations. The result shows that the improvement of photo-degradation performance was attributed to the internal electric field formed by the Z-scheme photo-catalyst, which leads to the enhancement of visible light absorption and the blocking effect of light-induced electron-hole recombination.
Heterojunction g-C3N4@BiOBr/BiOI photocatalytic membrane was prepared through electrospinning technology and hydrothermal reaction. Structural characterization confirmed that red algae-like porous graphite carbon nitride (g-C3N4) and bismuth oxyhalide (BiOX) were uniformly supported on SiO2 fibrous membrane. The g-C3N4@BiOBr/BiOI heterojunction membrane exhibits efficient photoactivity degradation of organic pollutants (drug residue) under visible light irradiation, which could remove 100% tetracycline (TC) within 120 min. The main reason for improving the performance is that the red algae-like porous g-C3N4 and BiOX form a heterojunction, which reduces the electron-hole recombination and enhances the electron-hole separation efficiency. This result has great potential in future research on the degradation of organic pollutants.
Development of low-cost, nontoxic, highly efficient performance photocatalyst for water pollution control engineering is critical for environmental remediation. In this contribution, a direct Z-scheme heterojunction based on C quantum dot (CQDs), bismuth oxybromide (BiOBr) and bulk graphitic carbon nitride (g-C3N4, CN) (CQDs-BiOBr/CN composite) with outstanding photocatalytic activity and good reusability is successfully fabricated though a hydrothermal procedure for cefixime antibiotic photodegradation. In particular, the CQDs-BiOBr/CN composite possess the best cefixime degradation effect, the degradation rate is about 92.82% within 120 min. The enhancement photocatalytic activity of CQDs-BiOBr/CN can be ascribed to the improved light-harvest ability, the excellent adsorption performance, the efficient charge transportation and separation capability. A possible degradation pathway of cefixime is proposed base on HPLC-MS. Toxicity experiments demonstrate that the antibiotic activity of cefixime is effectively deactivated after degradation process, and which is no toxic effect for Rye seeds in deionized water. The CQDs-BiOBr/CN also displays the excellent photoactivation activity towards Escherichia coli (E. coli). Reactive-species-trapping experiments show that hydroxyl radical (⋅OH) and superoxide radical (⋅O2⁻) are the active reactive species in the photodegradation process. The CQDs-BiOBr/CN composite demonstrate an effective potential practical application in antibiotic pollutants degradation from wastewater.
Photocatalysis acts as an important role in controlling wastewater purification. However, it is still a huge challenge to obtain highly‐efficient visible light driven photocatalysts. Herein, flower‐like BiOBr microparticles with splendid photocatalytic activities are developed. The electronic structure of BiOBr host is explored via the first‐principles density function theory. Besides, the impact of some external factors on the photocatalytic properties of BiOBr compounds is studied. In comparison, the flower‐like BiOBr microparticles have the best photocatalytic behaviors and they can degrade RhB within 10 min with a high K value of 0.498. Moreover, via using heat treatment, the light harvest ability and phase structure of flower‐like BiOBr microparticles are hardly altered, while their photocatalytic capacity is tailored due to the modified specific surface area and pore volume as well as the diverse charge separation efficiency. Furthermore, through altering the pH value of solvent, the resultant compounds exhibit totally different photocatalytic behaviors, and these products achieved at pH = 7 exhibit the best properties. Additionally, the designed photocatalysts have excellent recyclability and the photocatalytic mechanism is determined by h+, ·O2−, and ·OH. These achievements imply that the flower‐like BiOBr microparticles are promising candidates for visible light driven photocatalysts to realize wastewater purification. Flower‐like BiOBr microparticles with splendid visible light driven photocatalytic activity are promising photocatalysts for wastewater purification.
Photo-responsive ZnS nanostructures (ZnSM1 and ZnSM2) were synthesized using 3-mercaptopropionic acid (MPA) and polyvinylpyrrolidone (PVP) capping agents respectively via reflux method. Capped photocatalysts hold unique optical properties such as absorption in visible region, multi band gap values and surface defects. Interestingly, structural analysis revealed that nanorods and nanospheres were formed with MPA and PVP whereas randomly arranged particles were formed without using any capping agent (ZnSUC). The successful passivation of
–COOH (1549cm⁻¹ and 1357cm⁻¹) in case of ZnSM1 whereas –CH2 (1284cm⁻¹) and C-N stretching (1429cm⁻¹) for ZnSM2 was determined by FT-IR studies. Owing to effective charge separation, 1D structure, suitable band gap energies and higher surface area (252m²g⁻¹), ZnSM1 exhibited enhanced photocatalytic activity towards crystal violet degradation (CV, 93%) under UV light which was about two folds higher than standard ZnS. Under sunlight, uncapped ZnS nanoparticles (ZnSUC and std. ZnS) showed minor activity in comparison to capped ZnSM1 (88%) and ZnSM2 (77%). Moreover, 2-nitrophenol (NP) was also degraded to 83% with ZnSM1 under natural light without using any other reducing agent under solar irradiations. Thus, present work provides more insights to understand the outstanding activity of ZnS nanomaterials towards organic pollutants beyond UV region without metal deposition.
In this work, a Z-scheme heterojunction of BiOIO3/MIL-88B was constructed via two steps solvothermal method. Various characterization techniques showed that this Z-scheme heterojunction is an effective strategy to promote spatial charge separation, and the catalytic performance was evaluated by degrading simulated organic pollutants. Herein, the BiOIO3/MIL-88B composites exhibited an exceptional removal rate for Reactive Blue 19 and tetracycline hydrochloride (TC) under visible light irradiation, which was approximately 3.28 and 4.22 times higher than the pristine BiOIO3, respectively. Additionally, the analysis of photocatalysis mechanism showed that the active species ·O2⁻ and ·OH could strongly affect the degradation of tetracycline hydrochloride (TC) in the studied system. Furthermore, the degradation process of TC was tracked and detected by identifying intermediates produced in the reaction system. It is anticipated that this research can deepen the understanding of BiOIO3/MIL-88B heterojunction structure to remove organic contaminants and provide a strategy for applying photocatalytic technology in the practical industry.
The first systematic synthesis of bismuth oxychloride/bismuth oxybromide/graphitic carbon nitride (BiOxCly/BiOmBrn/g-C3N4) nano-composites used a controlled hydrothermal method. The structure, morphology and characteristic of BiOxCly/BiOmBrn/g-C3N4 photocatalyst were measured by XRD, UV–vis-DRS, FT-IR, FE-TEM, FE-SEM-EDS, PL, BET, HR-XPS and EPR. Under visible light irradiation, the photodegradation activity was evaluated for the decolorization of crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) in aqueous solution. The catalytic performance showed that, when using sample BB2C1-4-250-30 wt% g-C3N4 composite as a photocatalyst, the best reaction-rate-constant (k) was 0.071 h⁻¹. It was 1.5 times higher than the k value of BB2C1-4-250 as a photocatalyst. From the scavenging effect of various scavengers, the results of EPR showed that reactive OH was the main scavenger, while O2⁻, h⁺ and ¹O2 were the second scavenger in CV degradation. In this study, a possible photodegradation mechanism was proposed and discussed. In this work, our method of BiOxCly/BiOmBrn/g-C3N4 preparation could be used for future mass production and the BiOxCly/BiOmBrn/g-C3N4 composite materials could be applied to the environmental pollution control in future.
Designing efficient photocatalysts is essential for improving photocatalytic performance. Separation efficiency of photogenerated carriers is one of the key factors affecting photocatalytic performance. Combining the construction of two-dimensional materials with elemental doping can further improve the separation of photogenerated carriers. As expected, the performance of the samples produced by Fe and Cu co-doping was superior to that of pure BiOBr and mono-doped samples, with significant improvements in the photocatalytic degradation of both rhodamine B and tetracycline. The dopant of excess metal element atoms can form impurity energy levels in the forbidden band that effectively facilitate the separation and migration of photogenerated carriers. Meanwhile, the thin-layer two-dimensional structure can effectively shorten the bulk charge carrier transmission distance and improve the transmission efficiency. This study not only provides a simple, green and low-cost method for combining iron and copper into composites materials at same time but also confirmed that the photocatalytic performance of BiOBr was strongly influenced by different Fe and Cu contents.
Perfluorooctanoic acid (PFOA), which is an emerging contaminant, has received extensive attention in recent times due to its high toxicity and environmental risk. In this study, BiOI supported on Zn-Al hydrotalcite (BOI0.04-BHZA) was calcined at 400 ℃ to obtain flower-shaped Bi5O7I/ZnO n-n heterojunction microspheres for the photocatalytic degradation of PFOA under visible light irradiation. The samples were characterized by X-ray diffraction, Fourier transform infrared, UV–vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Compared with BOI (k1 = 0.0044 h⁻¹), BHZA (k2 = 0.0054 h⁻¹), and BOI0.04-BHZA (k3 = 0.0073 h⁻¹), the degradation rate constant of Bi5O7I/ZnO n-n heterojunction microspheres (k4 = 0.013 h⁻¹) increased by 2.9, 2.4, and 1.8 times, respectively. Approximately 91% of PFOA was degraded after 6 h of irradiation. The excellent photocatalytic performance was ascribed to the Bi5O7I/ZnO n-n heterojunction formed by calcination, which enlarged the photoresponse to the visible light region and increased the separation efficiency of electron-hole pairs. Moreover, the degradation pathway of PFOA was investigated using high-performance liquid chromatography-mass spectrometry and ion chromatography assisted by density functional theory calculations. The results demonstrated that the carboxylic groups of PFOA was vulnerable to attack by the photoproduction hole. The formed unstable perfluoroheptyl radicals transformed into shorter chain perfluorocarboxylic acids by the elimination of CF2 units. It was expected that this Bi5O7I/ZnO n-n heterojunction photocatalyst would be a promising candidate for PFOA treatment.
As an indispensable energy source, ammonia plays an essential role in agriculture and various industries. Given that the current ammonia production is still dominated by the energy-intensive and high carbon footprint Haber-Bosch process, photocatalytic nitrogen fixation represents a low-energy consuming and sustainable approach to generate ammonia. Heterostructured photocatalysts are hybrid materials composed of semiconductor materials containing interfaces that make full use of the unique superiorities of the constituents and synergistic effects between them. These promising photocatalysts have superior performances and substantial potential in photocatalytic reduction of nitrogen. In this review, a wide spectrum of recently developed heterostructured photocatalysts for nitrogen fixation to ammonia are evaluated. The fundamentals of solar-to-ammonia conversion, basic principles of various heterojunction photocatalysts and modification strategies are systematically reviewed. Finally, a brief summary and perspectives on the ongoing challenges and directions for future development of nitrogen photofixation catalysts are also provided.
As typical persistent organic pollutants, polybrominated diphenyl ethers (PBDEs) have aroused high environmental concern due to their toxicity and recalcitrant degradation. Herein, the photocatalytic decabromodiphenyl ether (BDE209) removal performance was evaluated firstly on facet-dependent BiOCl with oxygen vacancies under irradiation (>360 nm). The results revealed that BDE209 was rapidly debrominated on {001} BiOCl with a reaction rate 4.4 times greater than that on {010} BiOCl under oxygen-free environment. Such a degradation order is completely opposite to that of Rhodamine B (RhB) degradation. This enhanced reduction is mainly attributed to the abundant oxygen vacancies on {001} facet of BiOCl, which act as adsorption sites for BDE209 to achieve C-Br bond activation efficiently. Meanwhile, debrominated products via meta-position have the highest proportion than that via ortho- and para-position in the first step. Therefore, a position-selective multi-electrons reduction mechanism is hypothesized. This study provides a new sight on C-X bond activation of halogenated aromatics by inducing oxygen vacancies on specific facets.
A photocatalyst which consists of zero-dimension (0D) ZnFe2O4 (ZFO) and two-dimension (2D) Fe-doped g-C3N4 (Fe-CN) has been prepared successfully through a facile solvothermal method. The Fe doping into g-C3N4 lattice has been identified by both the infrared (IR) and X-ray photoelectron spectra (XPS), respectively. Introducing Fe into CN extends the spectral response to 700 nm while ZFO serves as a near infrared (NIR) photosensitizer of the Fe-CN component. The formation of Fe-CN heterostructure not only contributes to visible light absorption but also promotes the separation of photo-generated electron-hole pairs. Furthermore, the density functional theory (DFT) calculation indicated that the N2 molecules prefer to be adsorbed onto the Fe sites with a reduced potential barrier for N2 fixation. More importantly, the Fe atoms doped into the CN lattice acted as the reaction sites for accelerating photocatalytic N2 fixation reaction, which was also demonstrated by DFT. These factors lead to a high photocatalytic NH4⁺ generation rate of 25.3 mg·g⁻¹·h⁻¹ under a full-spectrum irradiation, which is much higher than the value (4.4 mg·g⁻¹·h⁻¹) of pure CN catalysts. This research might provide a novel approach for rationally designing full-spectrum-response N2 fixation photocatalyst.
Simultaneously integrating heterogeneous interface and element doping into BiOCl crystals is a promising strategy to promote the visible-light-driven photocatalytic activity. Here we demonstrated a facile solvothermal route for one-pot coupling Bi nanodots with Ta-doped BiOCl nanosheets (denoted as Ta-BiOCl/Bi). This Ta-BiOCl/Bi sample presented a remarkable catalytic performance toward the visible-light-driven degradation of Rhodamine B and tetracycline solution than those of the Ta-BiOCl, BiOCl/Bi and BiOCl photocatalysts. The enhanced photocatalytic mechanism can be proposed as follows. Both Ta dopant level in energy band structure of BiOCl and LSPR effect of Bi species were beneficial to increasing the visible light absorption, and the formation of heterogeneous interface between Ta-BiOCl and Bi was responsibility for accelerating the separation of charge carriers. This work might arouse in-depth investigations on the development of novel one-pot strategy for the synthesis of high-active BiOX (X = Cl, Br and I)-based photocatalysts.
In this paper, a novel BiOI/Bi2WO6 heterojunction photocatalyst that responds to visible light was synthesized by hydrothermal method. The photocatalyst is a flower-like layered microsphere structure composed of many nanosheets. The influence of the molar ratio of BiOI and Bi2WO6 on heterojunction photocatalyst activity was investigated, compared with pure BiOI and pure Bi2WO6, BiOI/Bi2WO6 which formed heterojunctions showed higher photocatalytic activity, among which BiOI/Bi2WO6(2,1) had the highest photocatalytic activity for phenol. Five cycles of photocatalytic experiments, it was found that the photocatalytic performance of the sample did not significantly reduced, indicating that the photocatalyst has good stability and reusability. In addition, the enhancement mechanism of photocatalytic activity was explored, and it was proved that hole was the main active substance, and the enhancement of photocatalytic activity was mainly since the generated electrons and holes are separated in the two semiconductor materials, inhibiting their recombination. This study provides a new idea and method for visible light degradation of organic pollutants.
Ultrathin 2D Bi3O4Cl nanosheets are promising photocatalysts for photocatalytic organic pollutions degradation, and tailoring the electronic structure by non-metal element doping of Bi3O4Cl is an important strategy to increase its photocatalytic activity. However, the role of doped non-metal atoms on charge carriers separation and light absorption has not been understood in depth. Here, the B-doped Bi3O4Cl ultrathin nanosheets are fabricated via a solvothermal way, which increase solar absorption and electron-hole separation of Bi3O4Cl. The products are characterized by FE-SEM, TEM, AFM, indicating that B-doped Bi3O4Cl are 3.87 nm thick nanosheets. And UV–Vis-DRS, XPS, PL and density functional theory show that the doped B atoms play multiple roles in facilitating photocatalytic performance: (1) inducing midgap states to immensely expand the light response region up from 450 nm to 557 nm; (2) acting as the electron capture centers to accelerate charge carries separation. The ESR technology shows that B-doped Bi3O4Cl can produce more O2– and OH radicals. As a result, the B-doped sample achieves a high-efficient photocatalytic bisphenol A and ciprofloxacin degradation, 3-fold and 2.1-fold higher than pure Bi3O4Cl, respectively. This work presents new opinions into the design of photocatalyst and confirms the role of electronic structure modulation on tuning catalytic activity.
In this study, the use of calcined eggshell (CE) as an adsorbent in removing Victoria Blue R (VBR) dyestuff from the solution medium was investigated. For this purpose, pH, interaction time, adsorbate concentration, amount of adsorbent, and salt effect parameters were studied to determine the appropriate adsorption conditions. The highest adsorption yield was obtained in pH 2, 2.0 g/L adsorbent and a stirring time of 5 minutes. 97% of the dye was removed under optimum adsorption conditions. The results obtained from the experimental studies showed that the adsorption mechanism is compatible with the pseudo-second-order kinetic model and the Langmuir isotherm model. SEM and IR analyses were performed for the characterization of calcined eggshells (CE).
An ecofriendly and cheap photocatalyst is crucial for realizing practical photocatalysis applications. Many inorganic materials have modular structures in which individual units are responsible for different functions. [Bi2O2]²⁺ slabs with an α-PbO-type structure and simple halide layers are effective spacers in some layered functional materials. Previous reports have mainly discussed electronic reasons for the different photocatalytic activities of layered PbBiO2X-type materials (X = Cl, Br, I). To the best of our knowledge, nanocomposite semiconductors consisting of PbBiO2I/g-C3N4 have not been reported in the literature. In this study, PbBiO2X/g-C3N4 composites were isolated and characterized by FE-SEM-EDS, XRD, HR-XPS, TEM, PL, BET, FT-IR, and UV-vis-DRS. By degrading crystal violet (CV) and 2-hydroxybenzoic acid (HBA) in an aqueous solution under visible-light irradiation, the photocatalytic activities of PbBiO2I/g-C3N4 are discussed further. In particular, the catalytic performance illustrates the best reaction rate constants of 0.3259 h⁻¹ using the PbBiO2I/g-C3N4 composite as the photocatalysts; these are 13.7 and 9.1 times higher than those of PbBiO2I and g-C3N4, respectively. The quenching effects of different scavenger results demonstrate that reactive O2•⁻ plays the major role and •OH, h⁺, and ¹O2 play the minor role in CV degradation.
Perfluorooctanoic acid (PFOA), a widely used compound, is harmful to the environment and human health. In this study, a facile one pot solvothermal method of integrating BiOCl with Zn-Al hydrotalcite to form spherical-shaped BiOCl/Zn-Al hydrotalcite (B-BHZA) sample is reported. The characteristics and main factors affecting photocatalytic PFOA and photocatalytic mechanism of BiOCl/Zn-Al hydrotalcite (B-BHZA) are systematically investigated. It is found that spherical-shaped B-BHZA possesses abundant defects and a larger surface area of 64.4 m² g⁻¹. The factors affecting photocatalytic removal PFOA (e.g., time, pH, initial concentration and dosage) are investigated by modeling the 3D surface response. The removal rate of PFOA is over 90% in 6 h under UV light at an optimal pH of 2, an initial concentration of 500 μg/L and a dose of dosage 0.5 g/L. The main mechanism occurs by photo-generated h⁺ oxidation and synergistic effects from the photocatalysis process. Though investigating the intermediates of PFOA degradation and F-, a possibility was proposed that h⁺ initiated the rapidly decarboxylation of PFOA. The unstable perfluoroheptyl group is formatted and further conversed to short chain perfluorocarboxylic acid. This study provides a new insight for the preparation of highly efficient photocatalysts to the treatment of halogenated compounds in UV system.
In this research work, CuO nanostructures were synthesized using atmospheric pressure microplasma (AMP) electrochemical process. The synthesized CuO nanostructures were characterized by various techniques such as X-ray diffractometer (XRD), scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectrometer, and UV-Vis spectrometer. XRD pattern showed that CuO has a monoclinic structure. Morphological analysis revealed that the shapes of nanostructures were sheet like. FTIR spectra confirmed the presence of the Cu–O stretching bond. Optical properties were studied by UV-Vis spectrometer. The bandgap was found to be 2.54 eV. The synthesized nanostructures were also employed for photodegradation of organic dyes such as methyl orange and rhodamine B under solar irradiation. It was observed that the percentage removal for both the dyes increased with increasing contact time and a significant removal was attained after a time of 80 min. The obtained results were confirmed by isotherm and kinetic studies. The dye adsorption data were fitted well to Temkin isotherm, while the adsorption process was well described by pseudo-first-order and intraparticle diffusion kinetics. These results would be extremely helpful for environmental applications regarding the removal of dyes from aqueous solutions as wastewater remediation.
Cocatalysts play an important role in increasing the photogenerated electron-hole separation rate of catalytic materials. Here, we selected a novel 2D material Ti3C2Tx (Tx = –OH, –O) as a cocatalyst and synthesized BiOCl/Ti3C2Tx (named as BT-n n = 0, 0.5, 1.0, 2.0, 4.0) composite materials by electrostatic self-assembly. We carefully characterized the structure, morphology and photoelectric performance of the composites, finding that we successfully synthesized 2D/2D BiOCl/Ti3C2Tx materials. The photocatalytic performance of the composites was evaluated by degradation of p-nitrophenol as a pollutant under simulated illumination. Among the composites obtained, BT-2.0 showed the best photocatalytic performance; specifically, its removal rate reached 97.86% and its degradation rate was about 3.3 times that of BT-0. Free radicals in the photocatalytic process were tested by electron paramagnetic resonance, which showed that superoxide radicals and holes are the most active free radicals in the system due to the higher photogenerated electron separation efficiency of BT-2.0. Therefore, constructing a heterojunction with Ti3C2Tx as a cocatalyst can improve the photocatalytic activity of BiOCl, which may provide new insights into the selection of novel co-catalytic materials in the field of photocatalysis.
It still is difficult issue to exploit the efficient photocatalysts that can response broad solar spectrum from visible to near-infrared (NIR) region. Herein, the H-TiO2/BiOCl heterojunctions are constructed firstly by a facile solvothermal method. The transfer and separation efficiency of charge carriers are improved distinctly owing to the modification effects of H-TiO2 nanoparticles on the surface of BiOCl flower spheres. Compared to BiOCl and H-TiO2, H-TiO2/BiOCl heterojunctions remarkably exhibit the enhanced photocatalytic activity for degrading tetracycline hydrochloride (TC-HCl) and methyl orange (MO) dye under the visible and NIR light, respectively. Moreover, we discuss the effect of H-TiO2/BiOCl heterojunction on the physical and photoelectrochemical properties, as well as the possible produced intermediates and degradation mechanism of TC-HCl in detail.
The three quasi-binary phase systems BiOX–BiOY (X, Y = Cl, Br, I) have been investigated by X-ray powder methods. No quaternary phases were found in the three systems. BiOCl–BiOBr and BiOBr–BiOI form systems of unlimited mutual solubility. BiOCl–BiOI is a system of limited solubility at the iodine-rich side. In the BiOBr–BiOI system a strong deviation from Vegard's rule is observed with respect to one of the lattice parameters. A few methods to quantify such a deviation are briefly discussed and a possible explanation for the strong deviation in the BiOBr–BiOI system is proposed. Error calculations have been performed to estimate uncertainties in the concentration parameter x of the investigated mixtures. The crystal structure of BiOI has been re-determined by single crystal structure analysis.
Bi2O2CO3/BiOI composites were fabricated at room temperature for the first time by a facile method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (UV–vis DRS), and nitrogen adsorption–desorption techniques were employed to characterize the physiochemical properties of the composites. The photocatalytic activities of Bi2O2CO3, BiOI, and Bi2O2CO3/BiOI were evaluated through the photocleaning of wastewater which contained rhodamine-B, methylene blue, crystal violet, or a mixture of them under visible-light irradiation (λ ≥ 420 nm). The photocatalytic activity of Bi2O2CO3/BiOI is much higher than that of its components. Moreover, the composite shows good photostability and recyclability. The excellent catalytic efficiency of the Bi2O2CO3/BiOI composite is deduced closely related to Bi2O2CO3/BiOI heterojunctions whose presence is generally regarded to be a favorable factor for the separation of photogenerated electrons and holes. Moreover, ·OH was found to be the main active species for the photocatalytic interactions. The catalyst shows potential application in the treatment of dye-containing wastewater.
Background
The discharge of wastewater that contains high concentrations of reactive dyes is a well-known problem associated with dyestuff activities. In recent years, semiconductor photocatalysis has become more and more attractive and important since it has a great potential to contribute to such environmental problems. One of the most important aspects of environmental photocatalysis is in the selection of semiconductor materials like ZnO and TiO2, which are close to being two of the ideal photocatalysts in several respects. For example, they are relatively inexpensive, and they provide photo-generated holes with high oxidizing power due to their wide band gap energy. In this work, nanostructural ZnO film on the Zn foil of the Alkaline-Manganese Dioxide-Zinc Cell was fabricated to degrade EV dye. The major innovation of this paper is to obtain the degradation mechanism of ethyl violet dyes resulting from the HPLC-PDA-ESI-MS analyses.
Results
The fabrication of ZnO nanostructures on zinc foils with a simple solution-based corrosion strategy and the synthesis, characterization, application, and implication of Zn would be reported in this study. Other objectives of this research are to identify the reaction intermediates and to understand the detailed degradation mechanism of EV dye, as model compound of triphenylmethane dye, with active Zn metal, by HPLC-ESI-MS and GC-MS.
Conclusions
ZnO nanostructure/Zn-foils had an excellent potential for future applications on the photocatalytic degradation of the organic dye in the environmental remediation. The intermediates of the degradation process were separated and characterized by the HPLC-PDA-ESI-MS and GC-MS, and twenty-six intermediates were characterized in this study. Based on the variation of the amount of intermediates, possible degradation pathways for the decolorization of dyes are also proposed and discussed.
This paper presents a study on the efficiency and mechanisms underlying the photo-catalytic degradation of crystal violet (CV) using nano-cubic barium titanate (BaTiO3). This study used P25-TiO2 as a starting material for the synthesis of BaTiO3, due to of its low cost, stability, and nontoxicity, compared with titanium alkoxide. The BaTiO3 was first synthesized using the autoclave hydrothermal method under alkaline condition with P25-TiO2 and Ba(OH)2·8H2O as starting materials, using various NaOH concentrations, reaction durations, and reaction temperatures. The characterization of the resulting BaTiO3 was confirmed by SEM-EDS, powder XRD, HR-XPS, FT-IR, DR-UV, and BET. The band gap of nanocubic BaTiO3 is estimated to be 2.93–3.05 eV and the lower band gap has a positive effect on photocatalytic activity. The photo-degradation efficiency of CV dye by BaTiO3 was measured under UV light irradiation with various pH reaction media in dark room conditions for comparison. Degradation intermediates were separated using HPLC-PDA-ESI/MS to identify the possible mechanism involved in photo-degradation according to variations in the concentration ratio of intermediates during the course of the reaction.
BiOI thin film via chemical vapor transport: Photocatalytic activity, durability, selectivity and mechanism a b s t r a c t BiOI thin film (BiOI TF) was prepared via a low temperature chemical vapor transport (CVT) route for the first time, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, fast-Fourier transform pattern and UV–vis diffuse reflectance. As-synthesized BiOI thin film was composed of high symmetrical BiOI nanosheets with dominant exposed {0 0 1} facets. It displayed better photocatalytic activity, durability and selectivity than benchmark P25 TiO 2 thin film and the origin come from the layered structure and good photoelectrochemical performance, CVT immobilization, the 100% terminal oxygen atoms of {0 0 1} facets, respectively. At end, the photocatalytic mechanism with O 2 • − production was studied.
TiO2-based nanosheet (TNS) was prepared by the alkaline hydrothermal treatment of P25, which was characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD) and nitrogen adsorption–desorption measurement. Its adsorption and regeneration properties for removal of high-chroma crystal violet (CV) were systematically investigated. The prepared TNS has much higher specific surface area of 207 m2/g and exhibits much stronger adsorption for CV than the raw material P25. The maximum adsorption capacity of TNS as determined from the Langmuir isotherm is 56.3 mg/g. The enhancement of adsorption capacity is ascribed to the increasing of specific surface area and surface hydroxyl groups, which can provide much more adsorption sites and stronger electrostatic attraction. It was further found that H2O2 can produce a synergetic photocatalytic degradation effect with TNS under UV–Vis irradiation, and the regeneration of TNS was effectively achieved by H2O2-assisted photocatalytic degradation process. The good reusability of prepared TNS in the cyclic adsorption–regeneration experiments indicates that it may be useful for dealing with dye wastewater.
This study employed HPLC–PDA–ESI–MS analysis to characterize the mechanisms underlying the degradation of ethyl violet dyes. A nanostructural ZnO film was fabricated on the surface of the Zn foil of Alkaline-Manganese dioxide–Zinc Cells through a simple oxidation reaction in aqueous solution at room temperature. Our results indicate that the ZnO nanostructure/Zn-foil has outstanding potential for future applications in the photocatalytic degradation of organic dyes. The nanostructural polycrystalline ZnO was characterized using XRD, SEM, and XPS. To identify the underlying mechanism involved in ZnO/Zn-assisted degradation of EV dye, we separated and characterized 26 intermediates using HPLC–PDA–ESI–MS and GC–MS. Specifics related to the quantities of the intermediates provide an indication of possible degradation pathways associated with the decolorization of EV dyes.
A nanocrystalline bismuth tungstate (Bi2WO6) with sheets morphology was successfully prepared by hydrothermal method and characterized by the field emission scanning electron microscopy with the energy dispersive X-ray spectrometer (FE-SEM-EDS), the X-ray diffractometer (XRD), and the high resolution X-ray photoelectron spectroscopy (HR-XPS). At alkaline condition, having pH 9, Bi(NO3)3·5H2O and H2WO4 as the starting materials, the reaction mixture was kept at 160 °C for 24 h, 48 h and 72 h to produce a high yield of Bi2WO6 with flower-like architecture. Moreover, the binding energy shift of Bi element was clearly observed, proposing that Bi(+3−x) formal oxidation state could most probably be attributed to the substoichiometric forms of Bi at outer site of the particles, and the formation of the low oxidation state resulted in oxygen vacancy in the crystal surface. The photocatalytic activities of the as-synthesized catalysts were evaluated by the photodegradation of crystal violet (CV) dye, while the nineteen intermediates were separated and characterized by the HPLC-PDA–ESI-MS techniques. The results demonstrated that the N-de-methylation degradation and the oxidative degradation of the CV dye took place during the degradation process. Based on these products, the probable degradation mechanisms were further proposed and discussed.
BiOCl/BiOBr uniform flower-like composite photocatalysts had been successfully synthesized through a one-pot ethylene glycol (EG)-assisted solvothermal process in the presence of 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl) and 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) reactable ionic liquids. Their structures, morphology, and optical properties were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). The DRS analysis and high photocurrent suggested that BiOCl/BiOBr possessed absorption under visible light and was a benefit for the efficient generation and separation of the electron–hole pairs. Photocatalytic activity experiment proved that BiOCl/BiOBr composites exhibited higher photocatalytic activity than single BiOCl and BiOBr for the degradation of rhodamine B (RhB) under visible light (λ > 400 nm). A possible photocatalytic mechanism based on the relative band positions of BiOCl and BiOBr had been proposed.
In this study we demonstrate that Bi3O4Br is a superior visible light driven photocatalyst for the decomposition and mineralization of a typical chlorinated phenol derivative sodium pentachlorophenate. It could remove more than 92% of sodium pentachlorophenate with concentration of 40 mg/L under visible light irradiation from 500 W Xe-lamp with a 420 nm cut off filter in 15 min, accompanying with 80% of mineralization. Density functional theory (DFT) calculation and systematical characterization reveal that high efficient visible light driven sodium pentachlorophenate removal with Bi3O4Br could be attributed to effective separation and transfer of photoinduced charge carriers in Bi3O4Br with narrower band gap and more negative conduction band position, which favors the photogenerated electrons trapping with molecular oxygen to produce O2−. The O2− radicals could not only inhibit the recombination of photoinduced charge carriers, but also benefit the dechlorination of chlorinated phenol derivative. The visible light induced degradation pathway of sodium pentachlorophenate was carefully investigated with high performance gas chromatography–mass spectrometry. This study provides a new photocatalyst for chlorinated phenol derivative removal with solar light.
In this study, a facile and effective method to modify the photocatalytic performance of a bismuth oxy-bromide (BiOBr) semiconductor through the fabrication of a heterojunction with a hydrated bismuth oxide (BHO) is reported. The new yBiOBr-(1 − y)BHO heterojunction, synthesized by a simple hydrothermal method, exhibits a high photocatalytic activity under visible light irradiation for the photodegradation of typical organic pollutants in water, such as Rhodamine B (RhB) and acetophenone (AP). Both the individual BiOBr and BHO components show very low photocatalytic efficiency. Furthermore, the unique photo-catalytic performance of the new hybrid material was demonstrated through the uphill photocatalytic reaction that involves the oxidation of potassium iodide (KI) to triiodide. The remarkable photocatalytic activity of the coupled system is directly related to the effectual charge carrier separation due to the formation of the heterostructure. 0.9BiOBr-0.1BHO shows a higher photocatalytic activity as compared with other members of the same family, 0.8BiOCl-0.2BHO and 0.8BiOI-0.2BHO, which is directly ascribed to a synergistic effect of the energy band-gap structure and flow of charge carriers through the heterojunction, surface area, and light absorbance. In comparison with TiO 2 (Degussa P25), the new composite material demonstrated 10.7 times higher activity in removing aqueous RhB under visible light (λ ≥ 420 nm) irradiation. Study of the photocatalytic mechanism proves that the degradation of RhB under visible light irradiation over the as-prepared 0.9BiOBr-0.1BHO is mainly via a direct hole oxidation mechanism and superoxide oxidation pathways. The resulting yBiOBr-(1 − y)BHO composites exhibit high photocatalytic and thermal stabilities and are very promising photocatalysts for degradation of organic pollutants in water and for other applications.
A novel heterojunction photocatalyst BiOI/BiOBr was synthesized by a simple modified deposition–precipitation method. Several characterization tools including XRD, SEM, HRTEM and UV–vis DRS were employed to study the phase structures, morphologies and optical properties of the samples. BiOI/BiOBr exhibited higher photocatalytic activity than single BiOI and BiOBr for the degradation of methyl orange (MO) under visible light (λ>420nm). This result can be due to the formation of the heterojunction between BiOI and BiOBr, which can separate photogenerated carriers efficiently. The photocatalytic mechanism study demonstrates that O2− and h+ are the main reactive species while OH can be negligible.
A new family of BiO(ClxBr1−x) photocatalysts have been synthesized by a hydrothermal method. The photocatalytic activity of the new material was measured on the degradation of Rhodamine B (RhB) and Acetophenone (AP) and photooxidation of potassium iodide in water under UV–vis and visible light (λ≥420nm) irradiations. In comparison to Degussa P25, the new photoactive material with x=0.5 demonstrated 3 times higher rate in removing aqueous RhB under visible light irradiation. A morphology, chemical composition and crystalline structure of BiO(ClxBr1−x) were characterized using scanning electron microscopy and powder X-ray diffraction. The values of their unit cell parameters depend on Cl/Br ratio and they change according to the Vegard's law.
The Bi-based oxychloride Bi4NbO8Cl with a layered structure was studied as a novel efficient photocatalyst. The compound prepared by a solid state reaction method has a band gap of 2.38 eV. It possesses an excellent visible-light-response ability. The visible-light-driven photocatalytic activities for degrading methyl orange (MO) over different catalysts follow the decreasing order of Bi4NbO8Cl > Bi3O4Cl > anatase TiO2, different from the order found under UV light illumination (Bi3O4Cl > anatase TiO2 > Bi4NbO8Cl). The dispersion of Pt over Bi4NbO8Cl leads to an obvious increase in photocatalytic performance, to about 1.5 times higher. The polarizing fields in NbO6 and BiO8 local structures, as well as the internal electrical fields between [Bi2O2] and [Cl] slabs, are considered to be useful for the efficient separation of electron–hole pairs upon photoexcitation.
A new class of oxyhalide photocatalysts xBiOBr–(1−x)BiOI prepared by a soft chemical method were characterized by X-ray diffraction and UV–Vis diffuse reflectance spectra. They are all visible-light-responsive materials with the bandgaps ranging from 1.92 to 2.91eV. Methyl orange (MO) photocatalytic degradation experiments showed that BiOBr possessed a higher photocatalytic activity than P25 (TiO2) under UV illumination and iodine-modified BiOBr exhibited high photocatlytic activities under visible-light irradiation. The high photocatalytic activity is in close relation with the deep valance band edge position and the internal electric fields between [Bi2O2] slabs and halogen anionic slabs.
The morphology-controlled fabrication of nano-/microstructured functional materials has opened up new possibilities to enhance their physical and chemical properties and remains a great challenge. This work represents a one-pot template-free fabrication and growth mechanism of novel rose-like uniform (BiO)2CO3 hierarchical hollow microspheres, which are self-assembled by single-crystal nanosheets. The observation of time-dependent evolution of crystal structure and morphology revealed that the growth mechanism of such a novel structure might involve a unique multistep pathway. First, an amorphous particle was formed during a nucleation and aggregation process. Then, the intermediate (BiO)4CO3(OH)2 of embryonic stacked buds with attached particles were produced due to Ostwald ripening. The driving force for the formation of such embryonic structure is the intrinsic dipole field introduced by the nanosheets as a result of selective adsorption of the citrate ions on some polar surfaces of the nanoparticles. Subsequently, all the particles were consumed and (BiO)4CO3(OH)2 crystals started to transform to (BiO)2CO3 phase by means of repeated reaction-dissolution-recrystallization process in a homocentric layer-by-layer growth style, where carbonate ions substituted OH− groups. Monodisperse buds were then generated and the size of the hollow in the center becomes smaller to reduce surface energy. Finally, all (BiO)4CO3(OH)2 transformed to (BiO)2CO3 phase and uniform monodisperse (BiO)2CO3 roses were produced through layers splitting driven by the OH− group deintercalating from the interlayer spaces of (BiO)4CO3(OH)2. More interestingly, the novel (BiO)2CO3 microspheres exhibited outstanding activities under both UV and visible light irradiation for indoor NO removal, far exceeding that of commercial P25, synthetic C-doped TiO2 and (BiO)2CO3 with particle morphology due to the special hierarchical morphology and band gap structure.
Photoinduced electron transfer (PET) from excited probes attached to proteins is of considerable current interest. Photochemical processes following 532nm excitation of triphenyl methane dye, crystal violet (CV+) bound to a protein, bovine serum albumin (BSA), have been investigated in picosecond (ps) to microseconds (μs) time scales by flash photolysis technique. The excited singlet state lifetime of CV+ is found to be increased to ∼130ps as compared to ∼1–5ps for the unbound dye in low viscosity solvents. From flash photolysis studies in microsecond region, transient absorption in the region ∼650nm is observed which is attributed to the dication radical CV2+ formed by electron transfer from 3CV+∗ to BSA, contrary to electron transfer from BSA to the excited dye as proposed in a recent report. Supporting spectral evidence for the electron transfer from 3CV+∗ to BSA is obtained from pulse radiolysis studies.
The efficiency of a coupled photocatalytic-biological system for removing crystal violet (CV) from an aqueous solution was assessed. Initial experiments demonstrated that the optimal operating parameters for the photoreactor were a 1.5-h reaction time, pH 7.0, and a 2.0-min retention time. Under these conditions, the photocatalytic reaction reduced the toxicity of the CV solution by 94%. Subsequent evaluation of the performance and characteristics of the coupled photocatalytic-biological system in terms of CV removal revealed that the coupled system successfully removed and efficiently mineralized CV in a semi-continuous mode when the CV concentration was <150mgL(-1). Based on our analysis of the degradation products, CV degradation in this coupled system involved stepwise demethylation and aromatic ring opening. Phylogenetic analysis of the bioreactor effluent showed that the predominant phyla were Proteobacteria, followed by Bacteroidetes and Actinobacteria, suggesting that this coupled system is conducive for such processes as demethylation, aromatic ring opening, carbon oxidation, and nitrification. These results were verified in a GC-MS analysis. To our knowledge, this is the first report on CV removal using a coupled system.
Visible light induced degradation of the textile diazo dye Naphthol Blue Black (NBB) has been carried out on TiO2 semiconductor nanoparticles. Diffuse reflectance transient absorption and FTIR techniques have been used to elucidate the mechanistic details of the dye degradation. The failure of the dye to degrade on insulator surfaces such as Al2O3 or in the absence of oxygen further highlights the importance of semiconducting properties of support material in controlling the surface photochemical processes. The primary event following visible light excitation is the charge injection from the excited dye molecule into the conduction band of the semiconductor TiO2, producing the dye cation radical. This was confirmed by diffuse reflectance laser flash photolysis. The surface-adsorbed oxygen plays an important role in scavenging photogenerated electrons, thus preventing the recombination between the dye cation radical and photoinjected electrons. Diffuse reflectance FTIR study facilitated identification of reaction intermediates and end products of dye degradation. By comparison with the degradation products from other azo dyes such as Chromotrope 2B and Chromotrope 2R we conclude that the NBB is degraded to a colorless naphthaquinone-like end product.
The ZnO-mediated photocatalysis process has been successfully applied to degradation of Acid Blue 1 (AB1) dye pollutants. To obtain a better understanding, the mechanistic details of this ZnO-assisted photodegradation of the AB1 dye with low Watt UV irradiation, a large number of the photodegradation intermediates were separated, identified, and characterized by the HPLC−PDA−ESI−MS and GC−MS techniques. The degradation progresses through competitive reactions such as N-de-ethylation, destruction of the conjugated structure, hydroxylation on the benzene ring, hydroxylation on sulfonylated benzene ring, and substitution. The probable photodegradation pathways were proposed and discussed.
In this work, we demonstrated the EG-assisted solvothermal synthesis of 3-D microspherical BiOBr architectures assembled by nanosheets. The morphology and compositional characteristics of the 3-D architectures were investigated by various microscopy techniques. The possible formation mechanism for the architectures was discussed. The band gap of the obtained BiOBr materials was estimated to be 2.54 eV by UV–vis. The specific surface area and porosity of the BiOBr 3-D architectures also were investigated by using nitrogen adsorption and desorption isotherms. Because of the narrow bandgap and the novel 3-D micro-/nanostructure, the BiOBr architectures show a more excellent photocatalytic activity under visible light irradiation than the BiOBr bulk plates. Several possible reasons for the higher photocatalytic activity have been taken into consideration. In addition, the photocatalyst is stable during the reaction and can be used repeatedly.
In this article, for the first time, two-dimensional (2D) single-crystalline bismuth oxyhalides (BiOX, X = Cl, Br) micro- and nanostructures, such as nanoplates, nanosheets, and microsheets, were synthesized in a large scale by a simple wet chemistry approach of hydrogen peroxide (H2O2) direct oxidation of bulk metal bismuth (Bi) particles in a mixed solution followed by a hydrothermal treatment, instead of previous coprecipitation of Bi salts route. The in-plane size and thickness of the 2D products can be conveniently tailored by varying the temperature and the concentrations of the Bi precursor. The products were characterized by a range of methods, such as X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission microscopy, energy-dispersive X-ray spectroscopy, selected area electron diffraction, thermogravimetric analysis, Fourier transform infrared spectra, and UV−vis diffuse reflectance spectra. The BiOBr nanoplates, nanosheets, and microsheets have also been selectively synthesized via a similar route. The formation process investigation revealed that under hydrothermal treatment the spherical Bi oxhydrohalide nanopariticles could be side-by-side self-assembled to form Bi oxyhalide nanoplates by increasing the in-plane size, and nanosheets could be piled up to form Bi oxyhalide thick microsheets by increasing the thickness. The UV−vis diffuse reflectance spectra revealed that the estimated band gap energies were about 3.5, 3.3, 2.3, and 2.1 eV for BiOCl nanoplates, BiOCl micro- and nanosheets, BiOBr nanoplates, and BiOBr micro- and nanosheets, respectively. It is expected that the present study could be extended to facile, large-scale synthesis of various multicomponent 2D inorganic micro- and nanostructures, which would have better performances than the corresponding spherical nanoparticles and would be the new members in the family of advanced functional inorganic materials well-applied in industry.
A facile approach of layer-by-layer depositing and hydrolysis of FeCl(3) is developed to fabricate 3D-ordered Fe(2)O(3) film. The 3D-ordered Fe(2)O(3) film was characterized by SEM, XRD, and DRUV-vis. It has 3D-ordered interconnecting macropores (340 nm) with nanocrystalline hematite Fe(2)O(3) walls (27.2 nm). The 3D-ordered macroporous nanocrystalline Fe(2)O(3) film exhibits 2,4 times larger photocatalytic activity for the photodegradation of dye in the presence of H(2)O(2) under visible irradiation than the nanocrystalline alpha-Fe(2)O(3) film without macropores and very good photostability. The much higher photocatalytic activity of the 3D-ordered macroporous nanocrystalline Fe(2)O(3) film than that of the reference Fe(2)O(3) film is attributed to the unique nanostructure and architecture of the 3D-ordered Fe(2)O(3) film, which result in the much greater light harvesting efficiency and efficient mass transport in the former than in the latter due to the existence of 3D-ordered interconnecting macropores. The effect of photonic stop band on the photocatalytic activity of the 3D-ordered Fe(2)O(3) film was studied by angle-dependent solid-state photodegradation experiments with monochromatic irradiation. A slow photon enhancement of photocatalytic activity was achieved by adjusting the red edge of the photonic stop band of the 3D-ordered Fe(2)O(3) film close to the electronic bandgap of Fe(2)O(3). The photodegradation mechanism of crystal violet on the 3D-ordered Fe(2)O(3) photocatalyst in the presence or absence of H(2)O(2) was discussed.
Photostable 3D-ordered titania hybrid photocatalyst with the core/shell structure of dye-containing polymer/titania was prepared by layer-by-layer coating of adsorption and hydrolysis of Ti(OBu)(4) on fluorescent polystyrene microspheres (YG), in which a sensitized dye of fluorescein isothiocyanate with a strong absorption in the visible light region of 400-500 nm is fixed. Photocatalytic tests show that the nanostructured titania hybrid photocatalyst exhibited efficient and stable photocatalytic activity for the photodegradation of crystal violet (CV) under visible light irradiation. The titania hybrid photocatalyst was characterized by UV-visible spectroscopy, SEM, TEM, XRD, photoluminescence (PL), time-resolved fluorescence, and electrochemical measurement. The characterization results show that the dye in YG spheres acts as a sensitizer for titania. By absorbing a visible photon it is promoted to an excited electronic state YG*, from which an electron can be injected into the conduction band of titania on the interface of YG spheres and titania shell. The electron subsequently induces the generation of active oxygen species, which result in the degradation of CV. The produced YG(+) radical cation can react with CV to realize the recycling of the photosensitized dye. The photodegradation of CV on TiO2-YG undergoes two competitive mechanisms: N-demethylation and destruction of the conjugated structure. The N-demethylation process predominates during the initial irradiation period. Later, the process of ring rupture is significant. It is evidenced that the N-didemethylated intermediate and the N-tridemethylated intermediate of CV undergo a direct cleavage of their conjugated structures.
Hierarchical macro-/mesoporous titania is prepared without the addition of templates or auxiliary additives at room temperature by the simple dropwise addition of tetrabutyl titanate to pure water, and then calcined at various temperatures. The products are characterized by X-ray diffraction, N 2-adsorption-desorption analysis, scanning electron microscopy, and the corresponding photocatalytic activity is evaluated by measuring the photocatalytic oxidation of acetone in air. The results reveal that hierarchical macro-/mesoporous structures of titania can spontaneously form by self-assembly in alkoxide-water solutions in the absence of organic templates or auxiliary additives. The calcination temperature has a strong effect on the structures and photocatalytic activity of the prepared titania. At 300 °C, the calcined sample shows the highest photocatalytic activity. At 400 and 500 °C, the photocatalytic activity slightly decreases. When the calcination temperature is higher than 500 °C, the photocatalytic activity greatly decreases because of the destruction of the hierarchical macro-/mesoporous structure of the titania and the drastic decrease of specific surface area. The hierarchically macro-/mesostructured titania network with open and accessible pores is well-preserved after calcination at 500 °C, indicating especially high thermal stability. The macroporous channel structures are even preserved after calcination at 800 °C, This hierarchical macro-/mesostructured titania is significant because of its potential applications in photocatalysis, catalysis, solar-cell, separation, and purification processes.
Bismuth titanate (Bi12TiO20) nanoparticles with spherical structures and good dispersion were synthesized hydrothermally using C6H13BiN2O7·H2O and TiCl3 in the presence of polyethylene glycol (PEG). Only 2 h of hydrothermal process was needed which means the whole process of preparation was a less power consumption. X-ray diffraction (XRD) proved that the samples were in pure cubic phase. UV–vis diffuse reflection spectra showed the band gap of Bi12TiO20 is about 2.65 eV. Brunauer–Emmett–Teller (BET) analysis showed that the Bi12TiO20 samples have higher surface areas. Visible-light-induced photodegradation of acid orange 7 (AO7) on Bi12TiO20 was investigated. It was found that Bi12TiO20-assisted photocatalytic degradation of AO7 occurs via two processes: the photocatalytic process of Bi12TiO20 semiconductor and the photosensitized process of AO7. Photocatalytic experiments in the presence of N2 and the radical scavenger suggested that OH and O2− are two main active species in the whole degradation process.Graphical abstractResearch highlights▶ Synthesiaing Bi12TiO20 nanoparticles within 2 h hydrothermal treatment. ▶ Bi12TiO20 has spherical structures with good dispersion and high BET surface area. ▶ Bi12TiO20 has a high activity under visible light irradiation. ▶ The photocatalytic mechanisms were identified.
Organic dye degradation was achieved via direct oxidation by bismuth silver oxide coupled with visible light photocatalysis by sodium bismuthate. Crystal violet dye decomposition by each reagent proceeded via two distinct pathways, each involving different active oxygen species. A comparison of each treatment method alone and in combination demonstrated that using the combined methods in sequence achieved a higher degree of degradation, and especially mineralization, than that obtained using either method alone. In the combined process direct oxidation acts as a pretreatment to rapidly bleach the dye solution which substantially facilitates subsequent visible light photocatalytic processes. The integrated sequential direct oxidation and visible light photocatalysis are complementary manifesting a > 100% increase in TOC removal, compared to either isolated method. The combined process is proposed as a novel and effective technology based on one primary material, sodium bismuthate, for treating wastewaters contaminated by high concentrations of organic dyes.
A novel class of heterojunctioned bismuth oxyhalide photocatalysts yBiO(ClxBr1-x)-(1 - y)BHO (bismuth oxide hydrate) has been prepared by a simple hydrothermal method. The new materials are highly efficient under visible light irradiation (lambda >= 420 nm) for the degradation of Rhodamine B (RhB), Acetophenone (AP) and photooxidation of iodide. Even though BHO shows very low photocatalytic efficiency, its combination with BiO(Cl0.5Br0.5) Provides exceptional high photocatalytic activity due to more effective photo-excited electron-hole separation by the heterojunction semiconductor. The relationship between BHO amounts and the photocatalytic activities was investigated. Compared to Degussa P25 the composite with x=0.5 and y = 0.9 demonstrated 14.6 times higher activity in removing aqueous RhB under visible light irradiation. The possible photodegradation mechanism was studied by the examination of different active species through adding appropriate scavengers. Furthermore, the photogenerated charge transfer process was proposed based on the bands positions of BiO(Cl0.5Br0.5) and BHO. After five cycles, the catalyst did not exhibit any significant loss of photocatalytic activity, confirming the photocatalyst is essentially stable. The excellent activity and photostability reveal that yBiO(ClxBr1-x)-(1 - y)BHO is a promising visible-light-responsive photocatalyst.
Ferroelectric Bi 4 Ti 3 O 12 ceramics have been prepared by the method of reactive sintering. The ceramics exhibit good ferroelectric properties with a remanent polarization Pr=5.5×10-2 C/m 2 and a coercive field Ec=3 MV/m. High resolution x-ray photoelectron spectra of the atomic constituents of Bi 4 Ti 3 O 12 were recorded. The obtained results indicate that oxygen vacancies are preferentially sited in the vicinity of Bi ions, in the Bi 2 O 2 layers. © 1998 American Institute of Physics.
This research represents a highly enhanced visible light photocatalytic removal of 450 ppb level of nitric oxide (NO) in air by utilizing flower-like hierarchical porous BiOI/BiOCl composites synthesized by a room temperature template free method for the first time. The facile synthesis method avoids high temperature treatment, use of organic precursors and production of undesirable organic byproducts during synthesis process. The result indicated that the as-prepared BiOI/BiOCl composites samples were solid solution and were self-assembled hierarchically with single-crystal nanoplates. The aggregation of the self-assembled nanoplates resulted in the formation of 3D hierarchical porous architecture containing tri-model mesopores. The coupling to BiOI with BiOCl led to down-lowered valence band (VB) and up-lifted conduction band (CB) in contrast to BiOI, making the composites suitable for visible light excitation. The BiOI/BiOCl composites samples exhibited highly enhanced visible light photocatalytic activity for removal of NO in air due to the large surface areas and pore volume, hierarchical structure and modified band structure, exceeding that of P25, BiOI, C-doped TiO(2) and Bi(2)WO(6). This research results could provide a cost-effective approach for the synthesis of porous hierarchical materials and enhancement of photocatalyst performance for environmental and energetic applications owing to its low cost and easy scaling up.
Many synthetic dyes in industrial wastewaters are resistant to degradation in conventional biological treatment process. Decolorization of eight synthetic dyes including azo, anthraquinone, metal complex and indigo were examined in white-rot fungal cultures and by fungal peroxidase-catalysed oxidation. The dyes were not decolorized by manganese-dependent peroxidase (MnP) while above 80% color was removed by ligninase-catalysed oxidation. Dye decolorization rate increased linearly with ligninase doses. Compared with fungal cultures in which ligninase was detected, partially purified ligninase showed a consistent and higher extent of dye decolorization with other essential components being provided such as veratryl alcohol, hydrogen peroxide and acidic pH (3.5–5). Veratryl alcohol had a critical concentration level above which no further effect on dye decolorization was observed. Depending on the influence of H2O2 on dye decolorization, the eight dyes can be divided into two groups; one had an optimum H2O2 concentration and the other showed increased decolorization with high H2O2 doses. Dye concentration had a negative effect on decolorization rate in general. The dye concentration above which the negative effect was observed varied from 10 to 125 mg/L, depending on individual dye structure. These results indicate that a highly efficient bioprocess using white-rot fungi to remove color from industrial effluents should produce ligninase, H2O2, veratryl alcohol continuously and coordinately under acidic condition and controlled back-mixing flow of wastewater.