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Enhanced visible light degradation of indigo carmine dye using conventional and green synthesized TiO2 conjugates with porphyrin
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This study investigates the modification of polyethersulfone (PES) membranes with 1 wt% titanium dioxide (TiO2), zirconium dioxide (ZrO2) and a nanocomposite of TiO2/ZrO2. The aim was to efficiently remove Rhodamine B (RhB) from water using a threefold approach of adsorption, filtration and photodegradation. Among the modified membranes (TiO2, ZrO2 and TiO2/ZrO2), the TiO2/ZrO2-PES nanocomposite membrane showed a better performance in rejection of RhB than other membranes with the rejection efficiency of 96.5%. The TiO2/ZrO2-PES membrane was found to possess a thicker selective layer and reduced mean pore radius, which contributed to its improved rejection. The TiO2/ZrO2 nanocomposite membrane also showed high bulk porosity and a slightly lower contact angle of 69.88° compared to pristine PES with a value of 73°, indicating an improvement in hydrophilicity. Additionally, the TiO2/ZrO2-PES nanocomposite membrane demonstrated a relatively lower surface roughness (Sa) of 8.53 nm, which offers the membrane antifouling properties. The TiO2/ZrO2-PES membrane showed flux recovery ratio (FRR), total fouling (Rt), reversible fouling (Rr) and irreversible fouling (Rir) of 48.0%, 88.7%, 36,8% and 52.9%, respectively. For the photocatalytic degradation performance, the removal efficiency of RhB followed this order TiO2 > TiO2/ZrO2 > ZrO2 (87.6%, 85.7%, 67.8%). The tensile strength and elongation were found to be compromised with the addition of nanoparticles and nanocomposites. This indicates the necessity to further modify and optimise membrane fabrication to achieve improved mechanical strength of the membranes. At low pressure, the overall findings suggest that the TiO2/ZrO2 nanocomposite has the potential to offer significant improvements in membrane performance (water flux) compared to other modifications.
The issue of biofilm formation by microorganisms in household water storage systems is a problem that lowers the efficiency of disinfectants. Antimicrobial photodynamic inactivation (aPDI) is a potential alternative to the current water disinfection methods. It employs a photosensitizer agent that inactivates microbes by absorbing light of a specific wavelength in the presence of molecular oxygen. Although aPDI has been proven in literature to have a wide spectrum of action, effective against resistant microbes and biofilms, it has not been approved for real-life applications yet. Therefore, there is an ongoing search for ideal photosensitizers that can produce sufficient reactive oxygen species for efficient inactivation of microbes and disruption of biofilms in household water storage systems. This review summarises the developments that have been made so far with porphyrin-, expanded porphyrin-, corrole-, and boron dipyrromethene-based photosensitizers. First, the issues with the current water disinfection methods are described, and then aPDI is also described as a possible alternative to the current methods. Emphasis is put on the antimicrobial activities and the solid support materials that the porphyrinoid family members have been incorporated into for potential application in the disinfection of household water and limitation of biofilm formation in water storage systems.
The study presents a breakthrough of a balanced charge separation for heterojunction CuWO4-TiO2 cocatalyst to efficiently enhance visible light photocatalytic degradation of ciprofloxacin (CIP). A solvothermal-synthesized nanopyramid-like CuWO4 semiconductor was assembled before sol–gel treatment with TiO2 precursors to generate CuWO4-TiO2 nanocomposites. The optical, structural, and morphological properties of CuWO4-TiO2 were elucidated using UV–Vis DRS, XRD, FTIR, Raman spectroscopy, and TEM/SEM techniques. The UV–Vis DRS spectroscopy of as-synthesized CuWO4-TiO2 cocatalyst demonstrated enhanced visible light absorbance. The XRD patterns of CuWO4-TiO2 revealed a triclinic phase nanocrystal. The O-Ti–O functionality was confirmed by FTIR spectroscopy. The photoactive bands corresponding to anatase redshift were observed from Raman spectroscopy of CuWO4-TiO2 nanocomposite. The PL studies attributed this redshift to the elevated extra energy bands that aid electron/hole pair charge separation in a co-catalyst heterojunction CuWO4-TiO2 nanocomposite afforded by embedding CuWO4-MOF within TiO2 crystalline. The TEM showed that un-sintered CuWO4.MOF mimicked a pyramidal shape and converted to nanoflakes upon sintering, while TiO2 and CuWO4-TiO2 retained a tetragonal shape. The photocatalytic activity of CuWO4-TiO2 cocatalyst was studied using CIP, as a model pollutant. The innovative design of 5CuWO4-TiO2 charge separation nanocomposite completely degraded 10 mg L−1 CIP solution at pH = 6.31 (natural pH) and 9 under 120 min of sunlight irradiation.
The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron–hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.
Bacterial pathogens remain major contributors to illnesses as they have developed several resistance mechanisms against standard treatments. Innovative porphyrin-quantum dots conjugated materials have great potential in addressing the limitations in the current disinfection methods. The antimicrobial activity of metal-free and In(III) derivative of 4-(15-(4-boronophenyl)-10,20-diphenylporphyrin-5-yl)benzoic acid conjugated to CuInS 2 /ZnS quantum dots is investigated in this study at laboratory-scale experiments under controllable conditions. The conjugate was also immobilized on mesoporous silica for recovery and reusability purposes. Findings of the study were driven by antimicrobial photodynamic inactivation (aPDI) in the presence of a porphyrin and quantum dots. POR(In)-CIS/ZnS QDs-Silica was the best performing conjugate with a singlet quantum yield ( Φ Δ ) of 0.72 and a log reduction of 9.38 and 9.76 against Escherichia coli and S. aureus , respectively.
In this study, two distinct photocatalysts, namely tin(IV)porphyrin-sensitized titanium dioxide nanotubes (SnP-TNTs) and titanium dioxide nanofibers (TNFs), were synthesized and characterized using various spectroscopic techniques. SnP-TNTs were formed through the hydrothermal reaction of NaOH with TiO2 (P-25) nanospheres in the presence of Sn(IV)porphyrin (SnP), resulting in a transformation into Sn(IV)porphyrin-imbedded nanotubes. In contrast, under similar reaction conditions but in the absence of SnP, TiO2 (P-25) nanospheres evolved into nanofibers (TNFs). Comparative analysis revealed that SnP-TNTs exhibited a remarkable enhancement in the visible light photodegradation of model pollutants compared to SnP, TiO2 (P-25), or TNFs. The superior photodegradation activity of SnP-TNTs was primarily attributed to synergistic effects between TiO2 (P-25) and SnP, leading to altered conformational frameworks, increased surface area, enhanced thermo-chemical stability, unique morphology, and outstanding visible light photodegradation of cationic methylene blue dye (MB dye). With a rapid removal rate of 95% within 100 min (rate constant = 0.0277 min−1), SnP-TNTs demonstrated excellent dye degradation capacity, high reusability, and low catalyst loading, positioning them as more efficient than conventional catalysts. This report introduces a novel direction for porphyrin-incorporated catalytic systems, holding significance for future applications in environmental remediation.
In this study, three samples of commercial titanium dioxide nanoparticles (TiO2) in different sizes were used to investigate their effect on the formulation of sunscreen creams. The aim was to evaluate their role in the performance of sunscreens (i.e. SPF, UVAPF, and critical wavelength). Then the particle size of these samples was determined by photon correlation spectroscopy methods. As a result, the size of primary particles was reduced by using milling and homogenization methods at different times. The results showed that the particle size of samples TA, TB, and TC in the ultrasonic homogenizer decreased from 966.4, 2745.8, and 2471.6 nm to 142.6, 254.8, and 262.8 nm, respectively. These particles were used in the pristine formulation. Then the functional characteristics of each formulation were determined by standard methods. TA had the best dispersion in cream compared to other samples due to its smaller size (i.e. 142.6 nm). For each formulation, two important parameters, including pH and TiO2 dosage, were investigated in different states. The results showed that the formulations prepared with TA had the lowest viscosity compared to formulations containing TB and TC. SPSS 17 statistical software analysis of variance showed that the performance of SPF, UVAPF and λc in formulations containing TA had the highest levels. Also, the sample containing TAU with the lowest particle size values had the highest protection against UV rays (SPF). According to the photocatalytic functionality of TiO2, the photodegradation of methylene blue in the presence of each nanoparticle of TiO2 was studied. The results showed that smaller nanoparticles (i.e. TA) had more photocatalytic activity under UV–Vis irradiation during 4 h (TA (22%) > TB (16%) > TC (15%)). The results showed that titanium dioxide can be used as a suitable filter against all types of UVA and UVB rays.
This study presents the spectral characterization of TiO2 nanoparticles (NPs) functionalized with three porphyrin derivatives: 5,10,15,20-(Tetra-4-aminophenyl) porphyrin (TAPP), 5,10,15,20-(Tetra-4-methoxyphenyl) porphyrin (TMPP), and 5,10,15,20-(Tetra-4-carboxyphenyl) porphyrin (TCPP). UV-Vis absorption and Fourier transform infrared spectroscopy–attenuated total reflection (FTIR-ATR) spectroscopic studies of these porphyrins and their complexes with TiO2 NPs were performed. In addition, the efficiency of singlet oxygen generation, the key species in photodynamic therapy, was investigated. UV-Vis absorption spectra of the NPs complexes showed the characteristic bands of porphyrins. These allowed us to determine the loaded porphyrins on TiO2 NPs functionalized with porphyrins. FTIR-ATR revealed the formation of porphyrin-TiO2 complexes, suggesting that porphyrin adsorption on TiO2 may involve the pyrroles in the porphyrin ring, or the radicals of the porphyrin derivative. The quantum yield for singlet oxygen generation by the studied porphyrin complexes with TiO2 was higher compared to bare porphyrins for TAPP and TMPP, while for the TCPP-TiO2 NPs complex, a decrease was observed, but still maintained a good efficiency. The TiO2 NPs conjugates can be promising candidates to be tested in photodynamic therapy in vitro assays.
In the current study, a direct S-scheme titanium dioxide/graphitic carbon nitride (TiO2/g-C3N4) heterojunction structure was fabricated via simultaneous calcination of TiO2 precursors and g-C3N4. Guava leaf extract was utilized as a reductant for TiO2 production through a green synthetic method, and g-C3N4 was prepared by thermal decomposition of melamine. The pristine and nanocomposite photocatalysts were characterized by XRD, FTIR, BET, TGA, HRTEM, UV–vis DRS, and PL to elucidate their physicochemical properties. The photocatalytic activity of synthesized photocatalysts was examined through the degradation of rhodamine B (RhB) and methylene blue (MB) dyes under simulated solar light irradiation. The nanocomposite exhibited commendable photocatalytic performances with 96% degradation efficiency of RhB attained in 120 min and 95% degradation efficiency of MB achieved in 150 min. The enhanced photocatalytic activities were attributable to visible light-harvesting characteristics and the formation of an S-scheme heterojunction system between two catalysts which promotes interfacial charge separation efficiency and longer charge carrier lifespan. After 4 consecutive cycles, the degradation efficiencies of both RhB and MB remained above 85%. According to the trapping experiments, OH· and O2·− radicals were critical in the degradation of RhB, while h⁺ and O2·− radicals were dominant in the degradation of MB. The nanocomposite was also tested for elution of actual water pollutants by combining two dyes, and above 90% degradation efficiencies were achieved for both dyes after 240 min.
Oilfield produced water (OPW) has become a primary environmental concern due to the high concentration of dissolved organic pollutants that lead to bioaccumulation with high toxicity, resistance to biodegradation, carcinogenicity, and the inhibition of reproduction, endocrine, and non-endocrine systems in aquatic biota. Photodegradation using photocatalysts has been considered as a promising technology to sustainably resolve OPW pollutants due to its benefits, including not requiring additional chemicals and producing a harmless compound as the result of pollutant photodegradation. Currently, titanium dioxide (TiO2) has gained great attention as a promising photocatalyst due to its beneficial properties among the other photocatalysts, such as excellent optical and electronic properties, high chemical stability, low cost, non-toxicity, and eco-friendliness. However, the photoactivity of TiO2 is still inhibited because it has a wide band gap and a low quantum field. Hence, the modification approaches for TiO2 can improve its properties in terms of the photocatalytic ability, which would likely boost the charge carrier transfer, prevent the recombination of electrons and holes, and enhance the visible light response. In this review, we provide an overview of several routes for modifying TiO2. The as-improved photocatalytic performance of the modified TiO2 with regard to OPW treatment is reviewed. The stability of modified TiO2 was also studied. The future perspective and challenges in developing the modification of TiO2-based photocatalysts are explained.
Wastewater is produced by numerous dyes producing and dye consuming industries in their process activities especially the textile industry. These effluents become toxic and harmful to the living things and the environment if not properly treated before being discharged to the environment. In recent decades dye wastewater has been becomes a growing water pollution problem because it is one of the most difficult to treat. To put an end to this problem, viable, efficient, and sustainable method of treatment of dye wastewater and color removal needs to be established. Several research papers have been done over the years on various treatment method of dye wastewater with evolving options; this paper is to bring together both the conventional and new methods. Some of the conventional and new methods researched over the years include activated sludge, coagulation, adsorption, membrane separation processes and electrochemical process etc. Although there is currently no uniform standard or method of treatment universally adopted, many countries have put in place allowable limits of composition of dischargeable wastewater. This paper seeks to explore which methods are highly efficient, produces manageable and recyclable waste and a combination/hybrid treatment option of these methods to achieve maximum color removal.
A novel greener methodology is reported for the synthesis of titanium dioxide (TiO 2) nanoparticles (NPs) using gum Arabic (Acacia senegal) and the characterization of the ensuing TiO 2 NPs by various techniques such as X-ray diffraction (XRD), Fourier transform infrared, Raman spectroscopy, scanning electron microscopy−energy dispersive X-ray, transmission electron microscopy (TEM), high resolution-TEM, and UV−visible spectroscopy. The XRD analysis confirmed the formation of TiO 2 NPs in the anatase phase with high crystal purity, while TEM confirmed the size to be 8.9 ± 1.5 nm with a spherical morphology. The electrode for the electrochemical detection of Pb 2+ ions was modified by a carbon paste fabricated using the synthesized TiO 2 NPs. Compared to the bare electrode, the fabricated electrode exhibited improved electro−catalytic activity toward the reduction of Pb 2+ ions. The detection limit, quantification limit, and the sensitivity of the developed electrode were observed by using differential pulse voltammetry to be 506 ppb, 1.68 ppm, and 0.52 ± 0.01 μA μM −1 , respectively. The constructed electrode was tested for the detection of lead content in plastic toys.
Herein, we have reported a new Photon Induced Method (PIM) to the synthesis of enhanced temperature stable anatase phased TiO2 nanoparticles. These TiO2 nanoparticles exhibited an anatase phase even after calcinating at 800 °C for average crystallite size is 9 nm with a bandgap is 2.98 eV, stretching into the visible light region are identified from DRS, and photoluminescence spectroscopic studies. Whereas, the standard and others reported TiO2 has existed a 100% rutile phase at this same temperature. The reversibly improved TiO2 has attained from the PIM method by tuning of oxygen vacancy during the preparation condition. The enhanced methylene blue dye under in the solar-light 100% degradation within 10 min is a very novel report, not reported elsewhere. The obtained pure anatase TiO2 with high chemical reactivity has a great potential for antibacterial, cancer cells kill, photocatalysis and solar energy conversion applications under solar-light irradiation.
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Photodynamic antimicrobial chemotherapy (PACT) and photophysical properties of the photosensitizers are being actively studied as a possible alternative for antimicrobial agents. This study focuses on the application of neutral indium 5-p-carboxyphenyl-10-15-20-(tri-4-pyridyl)porphyrin and cationic indium 5-p-carboxyphenyl-10-15-20-(tris-4-methylpyridyl)-porphyrin triiodide conjugated to 6-mercapo-1-hexanol functionalized Ag/CuFe2O4 magnetic nanoparticles for photo-inactivation of S. aureus bacteria. Comparative studies were done on quaternized and unquaternized indium porphyrin complexes conjugated to Ag/CuFe2O4, where log reduction of 9.27 was obtained for quaternized conjugate and 0.83 for unquaternized conjugate.
Engineered nanomaterials may adversely impact human health and environmental safety by nano–bio–eco interactions not fully understood. Their interaction with biotic and abiotic environments are varied and complicated, ranging from individual species to entire ecosystems. Their behavior, transport, fate, and toxicological profiles in these interactions, addressed in a pioneering study, are subsequently seldom reported. Biological, chemical, and physical dimension properties, the so-called multidimensional characterization, determine interactions. Intermediate species generated in the dynamic process of nanomaterial transformation increase the complexity of assessing nanotoxicity. We review recent progress in understanding these interactions, discuss the challenges of the study, and suggest future research directions.
This paper presents a simple, low cost method of synthesizing TiO2 nanoparticles by sol-gel method, where titanium isopropoxide is used as a starting material. Further, same TiO2 is used to sensitize 2-cyano-3- (4-(7-(5-(4- (diphenylamino) phenyl)-4- octylthiophen-2-yl) benzo[c] [1, 2, 5] thiadiazol-4- yl)phenyl) acrylic acid (RK-1 dye) and Di-tetrabutylammonium cis-bis (isothiocyanato) bis (2,2'-bipyridyl- 4,4'-dicarboxylato) ruthenium(II) (N-719 dye) for light harvesting applications. Anatase structure and average particle size of 7.3 nm were confirmed from XRD pattern. From SEM, it was noticed that particles were of varying size and shape and aggregation with clear porosity. FTIR spectra reveal Ti-O bond corresponding to 483 cm ⁻¹ and from UV-Vis absorption, energy band gap was found to be 3.2 eV. Photocurrent density (J) - photovoltage (V) characteristic of DSSC of different thicknesses of TiO2 were obtained, it was observed that optimum solar energy to electricity conversion efficiency (η) for RK-1 dye and N- 719 dye 4.08 % and 5.12 % with TiO2 thickness of 5.4 μm and 8.6 μm respectively under AM 1.5 irradiation (1000 W/m2) conditions.
To improve the photocatalytic activity of titanium dioxide, a novel nanocomposite was prepared via axial coordination of zinc porphyrin on the semiconducting titanium dioxide surface modified with axial coordinating ligand functionality, pyridine. The obtained product (zinc porphyrin/titanium dioxide) was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, fluorescence, thermogravimetric analysis, and Raman spectroscopic techniques. The photocatalytic performance of the samples was investigated by photodegradation of rhodamine B in aqueous solution. The attached zinc porphyrin on the surface can act as a small bandgap semiconductor to absorb visible light, resulting in the formation of electron–hole separation and an improved photocatalytic activity for the nanocomposite.
Nanotechnology is the creation, manipulation and use of materials at the nanometre size scale (1 to 100 nm). At this size scale there are significant differences in many material properties that are normally not seen in the same materials at larger scales. Although nanoscale materials can be produced using a variety of traditional physical and chemical processes, it is now possible to biologically synthesize materials via environment-friendly green chemistry based techniques. In recent years, the convergence between nanotechnology and biology has created the new field of nanobiotechnology that incorporates the use of biological entities such as actinomycetes algae, bacteria, fungi, viruses, yeasts, and plants in a number of biochemical and biophysical processes. The biological synthesis via nanobiotechnology processes have a significant potential to boost nanoparticles production without the use of harsh, toxic, and expensive chemicals commonly used in conventional physical and chemical processes. The aim of this review is to provide an overview of recent trends in synthesizing nanoparticles via biological entities and their potential applications.
Metallic nanoparticles include both elemental metallic nanoparticles and metal-oxide nanoparticles. Metallic nanoparticles are believed to be the basis of many of the future technological and biomedical innovations of this century. However, it has been shown recently that many of nanosized particles of these materials, not their macro- or microcounterparts, are toxic to living organisms. Thus, there is an urgent need to develop rapid, accurate and efficient testing strategies to assess the potential hazard of these emerging materials. Prevention is always the best strategy to minimize human or environmental exposure to hazardous nanomaterials. Early identification of the potentially hazardous properties of nanomaterials could enable us to design or redesign these materials with less health impact while retaining the main desirable properties. The objective of this chapter is to provide an overview on the relationship between individual physicochemical parameters and biological response after exposure to engineered elemental metallic nanoparticles (with focus on gold and silver) and metal-oxide nanoparticles. Possible mechanisms of observed toxicity, influence of biotic and abiotic factors on particle toxicity, and different biological models (in vitro and in vivo) for studying nanotoxicity are discussed. Doped metal-oxide nanoparticles, new designer products in the recent development of safe nanotechnology application, are also reviewed. Finally, a brief discussion on research gaps and collaboration needed in nano ecotoxicity studies is provided.
Silicon-based nanoparticles were produced by irradiating a single-crystal silicon target with 10.6 μm nanosecond transverse excited atmospheric (TEA) pulsed CO2 laser in de-ionized water. The effects of the laser pulse energies and repetition rate were studied. To reveal the role of thermal effects, a low laser repetition rate has been applied, excluding the interaction of the laser beam with the previously generated cavitation bubble. The analysis of the influence of the laser pulse energies and the laser repetition rate showed that the increase of the laser pulse energies leads to an increase of the nanoparticle size. An explanation of such results was proposed and the importance of the role of the target surface temperature in the ablation process is discussed.
The emergence of resistance against antimicrobial agents by bacteria is a challenge that calls for the development of new antimicrobial technologies. In this study, 5,10,15,20-tetrakis(4-pyridyl) porphyrin (1) and In (III) 5,10,15,20-tetrakis(4-pyridyl) porphyrin (2) conjugated with single-walled carbon nanotubes (SWCNTs), 1-SWCNTs and 2-SWCNTs, respectively, were used to study the photodynamic inactivation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Time-dependent density functional theory (TD-DFT) was used to establish the relationship between structural modifications to the porphyrin core and the resultant bathochromic shift and increase of the Q bands. Introducing a central metal resulted in a blue-shifted spectrum of 2 and more stable MO energies. Additionally, the photosensitizer’s photophysical characteristics were determined. 1-SWCNTs and 2-SWCNTs appear to be more photostable than 1 and 2 due to the single-walled carbon nanotubes. The singlet oxygen quantum yields of 2-SWCNTs and 2 were 0.74 and 0.68, respectively which was higher than that of 1-SWCNTs (0.61). 2-SWCNTs showed the highest log reduction against both E. coli (8.38) and S. aureus (9.76). Both 1-SWCNTs and 2-SWCNTs showed significant photodynamic activity. Hence, they can be recommended as efficient photosensitizers in aPDI.
The World Health Organisation has reported that antimicrobial resistance is one of the top 10 health threats that humanity faces today. Due to this, alternative therapies to the common antimicrobials are being explored and among these is photodynamic antimicrobial chemotherapy, where a combination of light, a photosensitiser and reactive oxygen species can be used to target microbial tissue. In this research, free base, tin (II) and indium (III) tetramethoxyporphyrins photosensitisers are adsorbed onto inorganic titanium dioxide nanofibers in an effort to create reusable fibers that are effective against Staphylococcus aureus. The photodynamic antimicrobial chemotherapy studies indicate that the metalloporphyrin adsorbed nanofibers exhibit good photodynamic antimicrobial activity against Staphylococcus aureus where the Cl2Sn(IV) tetramethoxyporphyrin dyed TiO2 exhibited 100% bacterial inhibition after a 30 min irradiation period.
Organic pollutants are the most critical threats to the health of air and water resources. On this basis, fabricating a photocatalytic acrylic film with dual-use (i.e. removing benzene from air and MB/MO dyes from water) was aimed in this research. For this purpose, waste warm filter cake (WWFC) was used to extract zinc from it. Zinc element was separated from WWFC by a basic leaching method and acidified to prepare zinc oxide nanoparticles. In the following, a simple hydrothermal method was used to increase the surface functionality of the extracted ZnO nanoparticles in order to establish active reaction sites for reaction to silane coupling agent and increase in the holes that were prepared during photo-excitation. Thereafter, the nanoparticles were modified with 3-glycidoxypropyltriethoxysilane (GPTES) at different concentrations. The band gap of the modified nanoparticles decreased from 3.25 to 3.1 eV by surface modification. The photocatalytic performance of ZnO nanoparticles was assessed by degradation of MB and MO aqueous solution (50 ppm) under simulated UV/Visible irradiations. MB and MO were degraded 91 and 60% under UV light and 65 and 50% under visible light after 150 min of irradiation. The photo degradation rate increased after adding carboxy methyl cellulose (CMC) surfactant to methylene blue and adding cocamide-dea (CDE-G) surfactant to methyl orange. The results confirmed that the green surfactants improve the dispersion and surface interaction of the modified nanoparticles in the dyes solution and cause more electron charge transfer which creates effective photocatalytic sites. The prepared nanocomposite films were placed in a photo-reactor to remove gaseous benzene from air under UV/visible irradiation. Gas chromatography (GC) results showed that the modified nanoparticles removed up to 35.25 and 20.34% of benzene from air. Colorimetric analysis (ΔE*) showed that the acrylic film contained modified nanoparticles degraded 91 and 82% of MB, and 85 and 76% of MO under UV/visible lights, respectively. In the end, it can be said that these photocatalytic films are able to remove environmental pollution in air and water.
Antimicrobial resistance is a matter of concern to all biological systems. This work investigates the antimicrobial activity of porphyrins conjugated to pristine graphene quantum dots (pGQDs) through non-covalent linking. A novel In 5,10,15,20-tetrakis[4-(benzyloxy) phenyl] porphyrin (InTBnOPP) was synthesized and fully characterized. The photophysicochemical parameters of H 2 TBnOPP, ZnTBnOPP, InTBnOPP, and their conjugates were investigated. It was found that pGQDs improved the singlet oxygen quantum yield upon conjugation with the porphyrins. pGQDs-InTBnOPP had a higher singlet oxygen quantum yield of 0.80 when compared to all other conjugates. Porphyrins are well-known photosensitizers for photodynamic antimicrobial chemotherapy (PACT); this was also confirmed by pGQDs-ZnTBnOPP and pGQDs-InTBnOPP which completely inhibited both S. aureus and E. coli with log reduction values of 9.42 and 8.59 with an irradiated time of 5 and or 10 min, respectively. The porphyrins alone had significant antibacterial activities. In general, the obtained results demonstrate a good response of these nanoconjugates against Gram (+) and Gram (-) bacteria.
In recent decades, TiO2 nanomaterial photocatalysts for energy and environmental applications have attracted extensive research interest. However, the main bottlenecks are the large bandgap (3–3.2 eV), which limits the amount of light absorption, and the relatively high charge-carrier recombination, which restricts the photocatalytic performance. Fortunately, recent reports indicate that engineering the defects of TiO2 could broaden the photoresponse and promote charge separation efficiency. To further promote the photocatalytic performance of solar energy, it is necessary to summarize the recent progress in defective TiO2 photocatalysts. In this review, various synthesis strategies for defective TiO2, especially black TiO2 nanomaterials, and their applications are summarized. The defect types and characteristics as well as the photocatalytic mechanism are reviewed and discussed in detail. This review is of great significance for environmental remediation and energy production in the field of photocatalysis.
This study is aimed at investigating the influence of different scavenger species of radicals that might possibly be involved in the TiO2/UVA photocatalytic degradation of Indigo Carmine dye. The effect caused by the presence of hydroxyl radicals (1-butanol and 2-propanol), positive holes (h+) (potassium iodide) and singlet oxygen (azide) was studied. Kinetics and optimal degradation conditions were evaluated using a factorial experiment design. The highest pseudo-first-order kinetics (k = 5.22 × 10−2 ± 0.002 and t1/2 = 13.25 ± 0.49 min) was achieved at pH 4.0, 6 mg L−1 of Indigo Carmine dye and 12 mg L−1 of TiO2. Mineralization was not achieved, and direct photolysis was not observed under the studied conditions. Indigo Carmine degradation occurs mainly due to oxidation in the positive hole (h+) followed by singlet oxygen action and on a smaller scale by hydroxyl radical. The use of the aforementioned radical scavengers made it possible to verify the mechanism and kinetics of Indigo Carmine dye through TiO2 heterogeneous photocatalysis.
Two new porphyrins 5,10,15,20-tetra[3-((ethoxycarbonyl)propoxy)phenyl] porphyrin (H2Pp1), 5,10,15,20-tetra[3-((carboxyl)propoxy)phenyl] porphyrin (H2Pp2) and their copper porphyrins (CuPp1, CuPp2) were synthesized and characterized spectroscopically. The corresponding porphyrin/Cu(II) porphyrin-TiO2 nanohybrids (H2Pp1-TiO2, H2Pp2-TiO2, CuPp1-TiO2, CuPp2-TiO2) were then prepared and characterized. These nanohybrids have the same anatase structure as bare TiO2 with BET specific surface area of 117.96–151.76 m² g⁻¹. There exists the heterojunction at the interface of porphyrin/Cu(II) porphyrin and TiO2 within nanoscale. The photocatalytic performances of these nanohybrids were investigated by 4-NP oxidative degradation, as well as reduction to 4-AP. These photocatalysts exhibit high photocatalytic activities compared with bare TiO2 and individual porphyrin/Cu(II) porphyrin. With CuPp2-TiO2 as photocatalyst, the 4-NP degradation can be finished within 25 min, and 4-NP is reduced to 4-AP in 6 min. The main active species are photogenerated hole, hydroxyl radical and superoxide free radical during the photodegradation of 4-NP. The possible photocatalytic Z-scheme mechanism is suggested. In this case, the photogenerated holes from VB of TiO2 and electrons from CB of H2Pp/CuPp are the main drive force for the high photocatalytic activity.
Dye degrading property to exhibit self-cleaning effect in Poly Ethylene Terephthalate (PET) through photocatalytic effect by Metallo porphyrin and TiO2 has been studied in detail. PET has been modified by step wise deposition of anatase TiO2 and Metallo porphyrin (CuTCNPP, NiTCNPP, ZnTCNPP), self-cleaning property of the modified PET has been studied by photo degradation of rhodamine B (RB) by irradiation under visible light and the degrading ability and the efficiency has been monitored using UV-Vis spectral technique by measuring the change in concentration of RB in the PET at different time intervals. Stability of Metallo porphyrin in PET also measured by UV-Vis spectral method. Indicating the porphyrin attached in PET are highly stable after washing the samples with detergent, water even after irradiating under visible light for more than 5 h. The degradation effectiveness found to be in the order of PET/TiO2/ZnTCNPP > PET/TiO2/CuTCNPP > PET/TiO2/NiTCNPP > TiO2 > PET. The modification made in the PET samples were characterized and confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Ultraviolet-visible spectroscopy (UV-Vis), Field emission scanning electron microscope (FESEM) analysis and the prepared Metallo porphyrin has been confirmed through mass analysis.
Green synthesis of nanoparticles via plant extract is a novel method to spread over in the field of nanoscience and nanotechnology. Nanoparticles prepared by biological route are an eco-friendly as well as yields good results than the conventional methods. In this present work we have synthesized TiO2 nanoparticles from Titanium tetra chloride using orange peel extract. The prepared nanoparticles were characterized by different techniques such as powder XRD, field emission electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FT-IR) to determine phase purity, crystallinity, morphology and bonding nature respectively. UV-Visible and photoluminescence (PL) spectra was perceived to identify the optical properties of the nanoparticles. The elemental composition was confirmed by X-ray energy dispersive spectroscopy (EDX). The humidity sensor studies of the nanoparticles were measured at different humidity atmosphere (RH 5% to RH 98%). The response and recovery time and the sensitivity factor Sf were calculated. The antibacterial studies of the nanoparticles reveals good activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Pseudomonuas aeruginosa bacteria respectively.The cytotoxicity of anatase TiO2 NPs was studied in A549 cell lines using MTT assay.Overall results shows that the nanoparticles prepared via biological method exhibits good results compare to nanoparticles prepared by chemical method.
The present work aims at developing an effective technologies in treating such effluents from Indigo Carmine (IC) dye industry through the use of the industrial wastes such as red mud. Red mud, hazardous aluminium industry waste in its activated form using hydrazine sulphate is employed in the removal of the IC dye by batch adsorption operation. The adsorbent is characterized by FESEM, EDX and FTIR methods and found to be potent enough in up-taking the IC dye. However, sensitivity analysis is carried out in identifying the optimum operating conditions at which the ultimate the adsorption capacity of the red mud is found to be 62.6 mg/g with 94.0% overall removal of the IC dye. The adsorption mechanism is analysed by various adsorption isotherm models and the kinetics of the adsorption process is examined. Further, the thermodynamic investigation projected the operation to be spontaneous and endothermic. Regeneration studies indicated the recyclability of the developed adsorbent with % removals not falling below 85.0% even after five regenerations cycles. However, the adsorbent is tested for its reliability by applying it to the water effluents gathered from commercial IC dye polluting industry and found effective enough in its use as a potential adsorbent in water treatment operations.
Keywords: Treated red mud, Indigo Carmine dye, environmental pollution, adsorption, water treatment.
A visible-light sensitized, superhydrophobic, self-cleaning Polyethylene terephthalate (PET) fabric exhibiting photocatalytic dye degrading properties has been prepared by depositing anatase TiO2, porphyrin (TPPS, CuTPPS), and trimethoxy(octadecyl)silane (Si) onto the PET samples. The modified PET fabric showed superhydrophobicity, exhibiting a water contact angle (WCA) of 147° and the ability to photodegrade rhodamine dye (RB), and the dye degradation ability of the modified fabric under visible light was monitored at different time intervals by UV–Vis spectroscopy. The degradation efficiency was found to be in the order PET/TiO2/TPPS > PET/TiO2/TPPS/Si > PET/TiO2/CuTPPS > PET/TiO2/CuTPPS/Si > PET/TiO2 > PET. The photodegradation ability and superhydrophobicity of the modified PET samples in relation to coffee and ketchup stains were examined qualitatively. Due to its superhydrophobicity, water soluble impurities/coffee drops roll off the surface of the modified PET fabrics, resulting in stain-free fabric. The fabrics were characterized by UV–Vis, FESEM, XRD and XPS. The structures of the synthesized porphyrin and TiO2 were confirmed by ¹H NMR spectroscopy and XRD analysis, respectively.
Titanium dioxide nanoparticles were prepared by a simple precipitation method using titanium (IV) isopropoxide as a starting material. The precursor powder was calcined in air at temperatures ranging from 400 to 700 °C. XRD analysis results revealed that the crystallite size and crystallinity of the samples increased with increasing calcination temperature. The morphology and particle size of TiO2 particles were investigated with TEM images and the diameter of the particles was then calculated using the images. It was evident that the calcination temperature had a significant influence on the average particle size since the size increased from 11.3 to 27.4 nm when the temperature was raised from 400 to 700 °C. By extrapolating the graph of (μhv)ⁿ versus photon energy (hv) to the horizontal axis, the energy band gap (Eg) of the calcined TiO2 nanoparticles was in the range of 2.98-3.30 eV. Under UVA irradiation, photodegradation activity of methyl orange had the fastest kinetics as measured by areaction rate constant, k, using the pure anatase TiO2 nanoparticle calcined at 400 °C.
In this study, we synthesized porphyrin dyes and structurally characterized them using ¹H and ¹³C NMR and FT-IR and high-resolution mass spectrometry. By using these porphyrins, new TiO2-porphyrin catalysts (TiO2-PORPC-1, TiO2-PORPC-2, TiO2-PORPC-3 and TiO2-PORPC-4), were prepared and the structures of these catalysts were confirmed by using SEM, TEM, solid-state UV-visible spectroscopy, XPS, FT-IR spectroscopy and EDS analysis. Studies on the photodegradation of methylene blue suggested that our TiO2-porphyrin photocatalysts were more effective for the degradation than bare TiO2-anatase, and furthermore, TiO2-Zn-porphyrins showed better photocatalytic activity than the metal-free TiO2-porphyrins because of their high charge-transfer properties. We evaluated the stability of the TiO2-porphyrins by repeatability test. Finally, we proposed a plausible mechanism for the photocatalytic activity.
Dye effluents released from numerous dye-utilizing industries are harmful towards the environment and living
things. Consequently, existence of dye effluent in environmental water bodies is becoming a growing concern to
environmentalists and civilians. A long term sustainable and efficient dye effluent treatment method should be
established to eliminate this issue. Dye wastewater should be treated first before release to minimize its negative
impacts towards the environment and living things. However, due to lack of information on efficient dye removal
methods, it is difficult to decide on a single technique that resolves the prevailing dye effluent issue.
Therefore, this paper reviews existing research papers on various biological, chemical and physical dye removal
methods to find its efficiency through percentage of dye removal. Although there are numerous existing tried
and tested methods to accomplish dye removal, most of them have a common disadvantage which is the generation
of secondary pollution to the environment. This paper highlights enzyme degradation (biological) and
adsorption (physical) dye removal as these are known as one of the most efficient dye removal techniques these
days. This paper also suggests the usage of a combined adsorbent as it is envisioned that this technique has better
efficiency and is able to remove dyes at a faster rate.
Two novel porphyrins (5,10,15,20-tetra(3-(carboethoxymethyleneoxy)phenyl)porphyrin, H2TEPp and 5,10,15,20-tetra(3-(carboxymethyleneoxy)phenyl)porphyrin, H2TCPp) and their copper(II) porphyrins (CuTEPp, CuTCPp) were synthesized. With these porphyrins, four new porphyrin-sensitized TiO2 nanorod composites (H2TEPp/TiO2, H2TCPp/TiO2, CuTEPp/TiO2, and CuTCPp/TiO2) were prepared and characterized by methods of XRD, SEM, TEM, FT-IR, UV-vis DRS, nitrogen adsorption–desorption and fluorescence spectra. Besides, the photocatalytic activity and stability of the composites were assessed in the degradation of 4-nitrophenol (4-NP). The results indicate that the morphologies and structures of these composites are less influenced by the loaded porphyrins or copper porphyrins compared with the nanorods TiO2 (anatase). The porphyrin or copper porphyrin molecules are confirmed to bond on the surface of TiO2 through carboxyl group, which is beneficial to the electron transfer between porphyrin and TiO2. All composites exhibit enhanced photoactivities compared with the bare TiO2 nanorods. The possible reason is that the recombination of photoproduced electron–hole has been controlled effectively in these composites, which can be seen from their decreased fluorescence emission. The stability results of composites show that they still hold considerable photocatalytic activities after six cycling experiments.
Herein, we report a facile synthetic protocol to grow thin films of Cu(II) tetrakis(4-carboxyphenyl)porphyrin (CuTCPP) metal-organic frameworks (MOF) from a tetrakis(4-carboxyphenyl)porphyrin (H2TCPP) solution and the copper hydroxide (Cu(OH)2) nanoneedle array formed on a Cu substrate at room temperature. The formations of Cu-centered TCPP ligands and crystalline platelet-like Cu MOFs were successfully probed by SEM, XRD, FTIR, UV–vis and XPS. The formation process from Cu(OH)2 was monitored by using SEM images obtained at different reaction times during the first 24 h, thus suggesting the reaction pathway of Cu(OH)2 dissolution followed by the reprecipitation of CuTCPP MOFs at a near surface. In addition, the CuTCPP MOFs exhibited a high specific surface area of 408 m²/g.
Though there are many advantages for the TiO 2 compared to other semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic spectrum (≤ 387.5 nm). As a result, development of visible-light active titanium dioxide is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in the strategies for the visible light activation, origin of visible-light activity, and electronic structure of various visible-light active TiO 2 photocatalysts are discussed in detail. It has also been shown that if appropriate models are used, the theoretical insights can successfully be employed to develop novel catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory and experiments in visible-light induced water splitting, degradation of environmental pollutants, water and air purification and antibacterial applications are also reviewed. Various strategies to identify appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the photocatalytic activity are discussed in detail, and a number of recommendations are also presented.
Tetra(4-carboxyphenyl) porphyrin(TCPP) were chemically sensitized on TiO2 to act as visible light antenna and to modify the photoresponse properties of TiO2 particles, their properties of photo-generated holes and electrons were studied by transient absorption spectroscopes. The time-correlated single-photon counting (TCSPC) technique revealed that the S2-S0 fluorescence intensity of TCPP is enhanced noticeably by TiO2, and the lifetime prolonged. Adsorption and photo degradation of methylene blue (MB) over TCPP-TiO2 were systematically investigated. Moreover the overall picture of electronic relaxation dynamics for TCPP-TiO2 is presented, and the detailed short-time dynamics for visible-light induced catalytic mechanism was discussed. The development of the porphyrin-based photocatalyst provides an alternative approach in harnessing solar visible light and show promising prospect for the treatment of dye pollutants from wastewaters in future industrial application.
A stable metalloporphyrin sensitized TiO2 (Degussa P25) photocatalyst was prepared by using trans-dihydroxo[5,10,15,20-tetraphenylporphyrin]tin(IV) (SnP) as a sensitizer in a simple impregnation process. The solid diffuse reflectance ultraviolet-visible (UV-vis) spectrum of the SnP sensitized TiO2 photocatalyst (SnP-TiO2) indicated that there existed interaction between SnP and TiO2. It was found that SnP-TiO2 exhibited an enhanced visible light photocatalytic activity as compared with that over P25 for the degradation of 4-nitrophenol (4-NP) and methyl orange (MO) in aqueous solutions. The mechanism exploration showed that the degradation of MO and 4-NP experienced two different ways, that is, MO was photodegraded by reactive oxygen species and 4-NP was directly photodegraded by the excited state of SnP. Furthermore, it was found that the loading content of SnP had an important influence on the photocatalytic activity of TiO2. The maximum photocatalytic efficiency was achieved when the contents of SnP were 25 mg and 30 mg per gram TiO2 for MO and 4-NP, respectively. Importantly, SnP-TiO2 was particularly stable and the photocatalytic activity was hardly decreased after being recycled seven times in the presence of oxygen, which could be attributed to the easy reductive regeneration of SnP.
Graphical abstract
The conjugation of Pt nanoparticles with ClGa(III) 5,10,15,20-tetrakis-(4-carboxyphenyl) porphyrin showed greater antimicrobial activity against Staphylococcus aureus, than when the nanoparticles or the porphyrins are used separately and when electrospun into fibers.
Two separate methods were used to prepare a tetra(4-carboxyphenyl)porphyrin (TCPP)-TiO2 composite. In method A TCPP was absorbed onto TiO2 in methanol at room temperature, whilst in method B TCPP was absorbed onto TiO2 in dimethylformamide (DMF) at reflux. Both composites exhibited the same physical and chemical characteristics as shown by FT-IR, SEM and UV–vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of both composites was then determined by HPLC monitoring of the photo-degradation of the pharmaceutical Famotidine under both visible and solar light irradiation. The recyclability of the composites was also examined by recovery of the composite post-reaction, although the absorbed TCPP was found to partially degrade, the recycled composite still exhibited catalytic behaviour. All reactions were monitored by HPLC which revealed that the photodegradation of Famotidine by the TCPP–TiO2 composites does not lead to complete mineralisation, but instead generates a range of intermediates/products. Investigation of these products by LC–MS–MS and DI–MS analysis found that one major degradation product was formed, the S-oxide of Famotidine. The TCPP–TiO2 composites were also screened in the photo-degradation of the pharmaceuticals tamsulosin and solifenacin using the optimised conditions developed for famotidine. However, the composites were found to be ineffective for the photo-catalytic degradation of these compounds, demonstrating that this class of composite are only effective for specific compounds.
Titanium dioxide (TiO 2) nanoparticles with different ratios of anatase to rutile transformation were synthe-sized by the modified sol–gel method. The optical properties were investigated by UV–vis diffuse reflectance spectrophotometry. Phase transformation, crystallinity, and crystal structure of the calcined TiO 2 samples were derived from X-ray diffraction analysis. The morphology and particle size of TiO 2 were characterized by transmission electron microscopy (TEM). The Brunauer, Emmett and Teller (BET) adsorption–desorption of nitrogen gas for specific surface area determination at the temperature of liquid nitrogen was performed on TiO 2 samples. TiO 2 nanoparticles calcined at 400 °C for 3 h possessed the highest specific surface area of 97 m 2 g − 1 . The temperature of anatase to rutile transformation was found between 500 and 600 °C, and then completely transformed to rutile phase at 600 °C. Average particle sizes of the nanoparticles were in the range of 10–50 nm at calcination temperature between 400 and 600 °C. At higher temperature clearly favored particles growth and agglomerates are corresponded to decrease specific surface area. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
Singlet molecular oxygen (1O2), which was produced with a significant yield, was detected from a powder-type TiO2 photocatalyst irradiated with a 355-nm laser pulse by monitoring its near-infrared phosphorescence at 1270 nm. Lifetime measurements for the 1O2 produced at TiO2 (Degussa P25) in various environments, such as in air and in suspensions of H2O, D2O, and ethanol, indicated that quenching takes place mainly at the TiO2 surface in the absence of reactants. Quantum yields for 1O2 generation were measured for ten commercial TiO2 photocatalysts in air and ranged from 0.12 to 0.38, while the lifetimes ranged from 2.0 to 2.5 μs. Since the quenching by the TiO2 surface is quite fast, the formation and decay processes of 1O2 have not been distinguished from the recombination of the photogenerated electron−hole pairs. The values of quantum yield suggest that 1O2 may contribute to the oxidation of some organic molecules at the irradiated TiO2 surface.
The generation of superoxide radical anion O2− from tetra(4-carboxyphenyl)porphyrin (TCPP) adsorbed on TiO2 in DMSO and irradiated by visible light was studied using EPR spectroscopy and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as spin trap. A chemical filter was used to remove light with wave lengths <500 nm. A multiline EPR spectrum was observed, characteristic of a mixture of two adducts, the first corresponding to DMPO–O2− and the second to the so-called nitroxide-like radical. Hyperfine coupling constants determined for the DMPO–O2− adduct are: aN = 14.1 G, aHβ = 10.8 G and aHγ = 1.4 G, and for the nitroxide-like radical adduct aN = 14 G. An increased intensity of the EPR lines corresponding to the nitroxide-like radical adduct was observed under irradiation without chemical filter, which suggests a possible DMPO–O2− decomposition. No singlet oxygen could be detected by EPR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (TEMP) as spin trap and by chemical trapping using anthracene as the trap.