Photocatalytic treatment of 4-chlorophenol in aqueous ZnO suspensions: intermediates, influence of dosage and inorganic anions

Photocatalytic Dye Degradation from Textile Wastewater: A Review

The elimination of dyes discharged from industrial wastewater into water bodies is crucial due to its detrimental effects on aquatic organisms and potential carcinogenic impact on human health. Various methods are employed for dye removal, but they often fall short in completely degrading the dyes and generating large amounts of suspended solids. Hence, there is a critical need for an efficient process that can achieve complete dye degradation with minimal waste emission. Among traditional water treatment approaches, photocatalysis stands out as a promising method for degrading diverse toxic and organic pollutants present in wastewater. In this review, the heterogeneous photocatalysis process is well explained for dye removal. This comprehensive review not only provides insightful illumination on the classification of dyes but also thoroughly explains various dye removal methods and the underlying mechanisms of photocatalysis. Furthermore, factors which effect the activity of the photocatalysis process are also explained in detail. Likewise, we categorized the heterogeneous photocatalyst in three generations and observed their activity for dye removal. This review also addresses the challenges and effectiveness of this promising field. Its primary aim is to offer a comprehensive overview of the photocatalytic degradation of pollution and to explore its potential for further future applications.

Degradation and metagenomic analysis of 4-chlorophenol utilizing multiple metal tolerant bacterial consortium

Chlorophenols are persistent environmental pollutants used in synthesizing dyes, drugs, pesticides, and other industrial products. The chlorophenols released from these processes seriously threaten the environment and human health. The present study describes 4-chlorophenol (4-CP) degradation activity and metagenome structure of a bacterial consortium enriched in a 4-CP-containing medium. The consortium utilized 4-CP as a single carbon source at a wide pH range, temperature, and in the presence of heavy metals. The immobilized consortium retained its degradation capacity for an extended period. The 4-aminoantipyrine colorimetric analysis revealed complete mineralization of 4-CP up to 200 mg/L concentration and followed the zero-order kinetics. The addition of glycerol and yeast extract enhanced the degradation efficiency. The consortium showed both ortho- and meta-cleavage activity of catechol dioxygenase. Whole genome sequence (WGS) analysis revealed the microbial compositions and functional genes related to xenobiotic degradation pathways. The identified genes were mapped on the KEGG database to construct the 4-CP degradation pathway. The results exhibited the high potential of the consortium for bioremediation of 4-CP contaminated sites. To our knowledge, this is the first report on WGS analysis of a 4-CP degrading bacterial consortium.

Photocatalytic degradation of metronidazole and oxytetracycline by novel l-Arginine (C, N codoped)-TiO2/g-C3N4: RSM optimization, photodegradation mechanism, biodegradability evaluation

Removal of Metronidazole (MNZ) and Oxytetracycline (OTC) from wastewater by the prepared (C, N codoped)-TiO₂/g-C₃N₄ (Graphitic carbon nitride) was examined. l-Arginine (C, N codoped)-TiO₂ and l-Arginine (C, N codoped)-TiO₂/g-C₃N₄ photocatalysts were successfully synthesized through the sol-gel method, and optimal ratio of l-arginine:TiO₂, as well as l-arginine/TiO₂:g-C₃N₄, was determined by a kinetic study of photodegradation process. The maximum photocatalytic removal rate (0.065 min^-1 for MNZ removal) was observed using 1% l-Arginine-TiO₂/g-C₃N₄ (1:1) under visible light illumination, 2.2 and 6.5 times greater than those of 1% l-Arginine-TiO₂ and pure TiO₂, respectively. l-Arginine (1%)-TiO₂/g-C₃N₄ (1:1) (co-doped-TCN) was investigated using X-ray diffraction analysis (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), Photo-luminescence (PL), and Differential Reflectance Spectroscopy (DRS) as the best-performing photocatalyst. Response surface methodology (RSM) was used to study the effect of co-doped-TCN dosage (0.5-1.0 g/L), pH of simulated wastewater (4-10), initial concentration of MNZ and OTC (50-100 mg/L), and irradiation time (30-90 min for MNZ and 20-40 min for OTC) on removal efficiency of the antibiotics. Also, their optimum values were determined by RSM. The treated pharmaceutical wastewater showed high biodegradability features with 5-day biological oxygen demand/chemical oxygen demand (BOD₅/COD) of 0.51 and 0.46 after 40 and 100 min reaction for OTC and MNZ, respectively. The order of reactive species responsible for the photodegradation of pollutants was •O₂^─> •OH > h⁺>¹O₂. The effect of inorganic anions showed that all anions decreased the removal efficiency of both antibiotics in order of NO₃^─> Cl^─ >SO₄^2─>HPO₄^2─ >HCO₃^─ for MNZ and NO₃^─> SO₄^2─ > Cl^─ >HPO₄^2─ >HCO₃^─ for OTC. Also, introducing different oxidants improved the photocatalytic removal efficiency with the order of H₂O₂>K₂S₂O₈> KBrO₃.

Fabrication of an in situ-grown TiO2 nanowire thin film and its enhanced photocatalytic activity

TiO₂ is a promising photocatalyst used in practical environmental remediation. TiO₂ photocatalysts are usually implemented in two forms: suspended powder and immobilized thin films. A simple technique for fabricating TiO₂ thin film photocatalyst was developed in this work. The fabricated TiO₂ thin film photocatalyst featured a homogeneous nanowire layer grown in situ on the parent Ti plate. The optimized fabrication protocol was to soak the ultrasonically cleaned and acid-washed Ti plate in 30% H₂O₂ solution containing 3.2 mM melamine and 0.29 M HNO₃ at 80 °C for 72 h and then anneal at 450 °C for 1 h. TiO₂ nanowires with uniform diameters were homogeneously arrayed on the Ti plate surface. The thickness of the TiO₂ nanowire array layer was 1.5 μm. The pore properties of the TiO₂ thin film were close to those of P25. The band gap of the fabricated photocatalyst was 3.14 eV. The photocatalytic activity of the fabricated photocatalyst toward 10 mg/L RhB and 1 mg/L CBZ demonstrated greater than 60% degradation under 2 h UVC irradiation. The RhB and CBZ degradation efficiencies remained at a good level after 5 consecutive cycles. Mechanical wearing, such as 2 min sonication, will not lead to significant suppression of the photocatalytic activity. Photocatalytic RhB and CBZ degradation using the fabricated photocatalyst favored an acidic > alkaline > neutral environment. The presence of Cl^- slightly suppressed the photocatalytic degradation kinetics. However, RhB and CBZ photocatalytic degradation kinetics were promoted in the copresence of SO₄^2- or NO₃^-.

Photocatalytic Degradation of Methylene Blue Using N-Doped ZnO/Carbon Dot (N-ZnO/CD) Nanocomposites Derived from Organic Soybean

This study reports on successful synthesis of carbon dots (CDs), nitrogen-doped zinc oxide (N-ZnO), and N-ZnO/CD nanocomposites as photocatalysts for degradation of methylene blue. The first part was the synthesis of CDs utilizing a precursor from soybean and ethylenediamine as a dopant by a hydrothermal method. The second part was the synthesis of N-ZnO with urea as the nitrogen dopant carried out by a calcination method in a furnace at 500 °C for 2 h in an N2 atmosphere (5 °C min-1). The third part was the synthesis of N-ZnO/CD nanocomposites. The characteristics of CDs, N-ZnO, and N-ZnO/CD nanocomposites were analyzed through Fourier transform infrared (FTIR), UV-vis absorbance, photoluminescence (PL), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), thermal gravimetry analysis (TGA), field-emission scanning electron microscopy energy-dispersive spectroscopy (FESEM EDS), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis. Based on the HR-TEM analysis, the CDs had a spherical shape with an average particle size of 4.249 nm. Meanwhile, based on the XRD and HR-TEM characterization, the N-ZnO and N-ZnO/CD nanocomposites have wurtzite hexagonal structures. The materials of N-ZnO and N-ZnO/CD show increased adsorption in the visible light region and low energy gap E g. The E g values of N-ZnO and N-ZnO/CDs were found to be 2.95 and 2.81 eV, respectively, whereas the surface area (S BET) values 3.827 m2 g-1 (N-ZnO) and 3.757 m2 g-1(N-ZnO/CDs) belonged to the microporous structure. In the last part, the photocatalysts of CDs, N-ZnO, and N-ZnO/CD nanocomposites were used for degradation of MB (10 ppm) under UV-B light irradiation pH = 7.04 (neutral) for 60 min at room temperature. The N-ZnO/CD nanocomposites showed a photodegradation efficiency of 83.4% with a kinetic rate of 0.0299 min-1 higher than N-ZnO and CDs. The XRD analysis and FESEM EDS of the N-ZnO/CDs before and after three cycles confirm the stability of the photocatalyst with an MB degradation of 58.2%. These results have clearly shown that the N-ZnO/CD nanocomposites could be used as an ideal photocatalytic material for the decolorization of organic compounds in wastewater.

Insight into the LED-assisted deposition of platinum nanoparticles on the titania surface: understanding the effect of LEDs

This paper proposes a novel LED-assisted deposition of platinum nanoparticles on the titania surface. For the first time, this process was supported by a UV-LED solution. We used two light sources with different wavelengths (λmax = 365 and 395 nm), and power (P = 1, 5, and 10 W) because the photodeposition process based on LEDs has not been defined. The TiO2-Pt material was discovered to be nano-crystalline anatase particles with nano-platinum particles deposited on the surface of titanium dioxide. Furthermore, the luminescence intensity decreased when Pt was added to TiO2, indicating that charge carrier recombination was reduced. The spectra matching of the photocatalyst and LED reactor was performed for the first time in this work. We proposed a convenient LED reactor that focused light in the range of 350-450 nm, allowing us to effectively use photo-oxidative properties of TiO2-Pt materials in the process of removing 4-chlorophenol. In the presented work, the LED light source plays a dual role. They first induce the platinum photodeposition process, before becoming an important component of tailored photoreactors, which is an important innovative aspect of this research.

An Evaluation of the Kinetic Properties Controlling the Combined Chemical and Biological Treatment of Toxic Recalcitrant Organic Compounds from Aqueous Solution

Due to their high toxicity, propensity for cancer, teratogenicity, mutagenicity, and genotoxicity, hazardous water-soluble phenolic compounds must be controlled immediately. In this study, a model was created to simulate the degradation of harmful recalcitrant organic compounds in a combined chemical and biological treatment system. The parameter estimations with inhibition coefficient (Haldane model) and without inhibition coefficient (Michaelis-Menten model) were assessed over a wide range of initial concentrations using the Monod-like model. The kinetic parameters were optimized using AQUASIM 2.0 software. At a 50 mgL−1 feed concentration of 4-chlorophenol, removal efficiencies of more than 98% were attained under these circumstances. The primary kinetic parameters were identified and their values models were validated using the fitted parameter values that reached a good degree of agreement (R2 = 0.998). We may better comprehend and make use of the complex phenolic compounds’ biodegradation processes, such as progress optimization and scale-up, by understanding the mechanisms of substrate interaction and the new kinetic models that have been provided in this work.

Combining Ultraviolet Photolysis with In-Situ Electrochemical Oxidation for Degrading Sulfonamides in Wastewater

Ultraviolet photolysis (UVC, 254 nm) was coupled with an electrochemical oxidation process to degrade three kinds of veterinary sulfonamide (sulfamethazine [SMZ] tablets, sulfamonomethoxine [SMM] tablets, and compound sulfamethoxazole [SMX] tablets). The treatment was applied using a flat ceramic microfiltration membrane to study the effects of photocatalysts. The effectiveness of degradation of the three sulfonamides was evaluated under different conditions. Dissolved oxygen was provided via aeration, but this resulted in a large decrease in the degradation effectiveness due to the inhibition of free chlorine electrogeneration. The photocatalysts had no promotional effect on sulfonamide removal from wastewater due to reduced UV penetration. Because of the different distribution coefficients of sulfonamides, UV irradiation had different effects on different sulfonamide species. For SMZ and SMM, anionic species exhibited a higher degradation rate, whereas for SMX, degradation was most effective for neutral species. In addition, the free chlorine yield increased as the pH increased. Free chlorine conversion reactions occurred under UV irradiation, with the reactions possibly restrained by sulfonamides. Reactive chlorine species promoted SMM degradation. Compared to UV irradiation or electrochemical oxidation alone, the UV/in-situ electrochemical oxidation process was more effective and is suitable for treating real wastewater under various environmental pH levels.

The In Situ Hydrothermal and Microwave Syntheses of Zinc Oxides for Functional Cement Composites

This study presents the results of research on cement mortars amended with two zinc oxides obtained by two different methods: hydrothermal ZnO-H and microwave ZnO-M. Our work indicates that, in contrast to spherical ZnO-H, ZnO-M was characterized by a columnar particle habit with a BET surface area of 8 m2/g, which was four times higher than that obtained for hydrothermally obtained zinc oxide. In addition, ZnO-M induced much better antimicrobial resistance, which was also reported in cement mortar with this oxide. Both zinc oxides showed very good photocatalytic properties, as demonstrated by the 4-chlorophenol degradation test. The reaction efficiency was high, reaching the level of 90%. However, zinc oxides significantly delayed the cement binder setting: ZnO-H by 430 min and ZnO-M by 380 min. This in turn affected the increments in compressive strength of the produced mortars. No significant change in compressive strength was observed on the first day of setting, while significant changes in the strengths of mortars with both zinc oxides were observed later after 7 and 28 days of hardening. As of these times, the compressive strengths were about 13-15.5% and 12-13% higher than the corresponding values for the reference mortar, respectively, for ZnO-H and ZnO-M. There were no significant changes in plasticity and flexural strength of mortars amended with both zinc oxides.

Efficient degradation of clofibric acid by heterogeneous catalytic ozonation using CoFe2O4 catalyst in water

CoFe₂O₄ (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O₃ process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O₃ process were dramatically enhanced in comparison with those under the O₃ system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (^•OH), especially superoxide radicals (O₂^•-), singlet oxygen (¹O₂), and hydrogen peroxide (H₂O₂) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O₃ can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Photocatalytic Applications of Fe–Ag Co-Doped TiO2 Nanoparticles in Removal of Flumioxazin Pesticide Residues in Water

Fe–Ag co-doped TiO2 nanoparticles (NPs) were prepared as a photocatalyst using a precipitation method for the removal of flumioxazin pesticide residues in water. The analytical method was validated with specificity, linearity, recovery, precision, the limit of quantification, and detection limit. Linearity was determined by different known concentrations of standard solutions. Detection limit was identified as the lowest concentration resulting in a 3-fold response to baseline noise. Photolytic and photocatalytic studies were conducted in borosil glass bottles under sunlight at a single fortification level (1.0 μg/mL) in Milli-Q water with various pH values (pH 4.0, 7.0, and 9.0). The optimum catalyst concentration recommended for complete degradation was found to be 50 mg/L under sunlight. The HPLC-UV method was used to determine flumioxazin residues in water, and the rate constant, DT50, and DT90 values were calculated from the data obtained. The photolytic results do not indicate a significant residue loss due to adsorption. Fe–Ag co-doped TiO2 NPs are an outstanding decontaminating catalyst in various water samples.

Tailoring of bismuth vanadate impregnated on molybdenum/graphene oxide sheets for sensitive detection of environmental pollutants 2, 4, 6 trichlorophenol

In the present work, we reported a one pot simple colloidal-gel synthesis of molybdenum bismuth vanadate (MoBiVO₄). The charge transfer property of MoBiVO₄ was improved by developing a composite with graphene oxide (GO) through sonochemical technique. The optical and morphological analysis revealed that successful formation of GO-MoBiVO₄ composite without any other filth. As prepared composite was used to modify the superficial surface of glassy carbon electrode (GO-MoBiVO₄/GCE) and applied for the selective detection of environmental pollutant 2, 4, 6 trichrlorophenol (TCP). The electron channeling capability of GO with molybdenum bismuth vanadate possessed a superior electrochemical response in cyclic voltammetry (CV), whereas bare GCE and other modified electrodes provided an inferior response with lower current response. The differential pulse voltammetry (DPV) response of TCP at GO-MoBiVO₄/GCE outcomes with low level detection of 0.4 nM and higher sensitivity of 2.49 μA μM^-1 cm^-2 with wider linear response 0.199-17.83 μM. Furthermore, the proposed sensor applied in practicability analysis and the results indicates GO-MoBiVO₄/GCE prominent towards electrochemical detection of TCP.

Photodegradation of Pharmaceutical and Personal Care Products (PPCPs) and Antibacterial Activity in Water by Transition Metals

The intensity of emerging pollutants such as pharmaceuticals and personal care products (PPCPs) in the aquatic and terrestrial environment is a major source of concern to researchers. The current conventional methods of wastewater treatment plants are considered not efficient enough in the complete removal of the recalcitrant contaminants from water. The use of modified transition metals in visible responsive synthesis to degrade PPCPs and other pollutants (organic and inorganic) is considered as a developing green chemistry and sustainable technology. Hence, this review presents the state-of-the-art discussion on the novel photodegradation of PPCPs, and antibacterial activities of transition metal-modified magnetite materials for wastewater treatment, and suggested directions for the future. Transition metal-modified magnetite nanostructured photocatalysis is identified as one of the best candidates employed in advanced oxidation processes (AOPs) for wastewater treatment and has been found to efficiently destroy bacterial spores and effectively remove recalcitrant pollutants in water. Therefore, this article hopes to contribute scientific knowledge along with existing ones on advanced mechanisms and technology used in wastewater treatment.

The photocatalytic destruction of cinnamic acid and cinnamyl alcohol: Mechanism and the effect of aqueous ions

Cinnamic acid was chosen as an exemplar molecule to study the effect of potential contaminants on the kinetics and mechanism of the photocatalytic destruction of hydrocarbons in aqueous solutions. We identify the principal intermediates in the photocatalytic reaction of the acid and corresponding alcohol, and propose a mechanism that explains the presence of these species. The impact of two likely contaminants of aqueous systems, sulfate and chloride ions were also studied. Whereas sulfate ions inhibit the degradation reaction at all concentrations, chloride ions, up to a concentration of 0.5 M, accelerate the removal of cinnamic acid from solution by a factor of 1.6. However, although cinnamic acid is removed, the pathway to complete oxidation is blocked by the chloride, with the acid being converted (in the presence of oxygen) into new products including acetophenone, 2-chloroacetophenone, 1-(2-chlorophenyl)ethenone and 1,2-dibenzoylethane. We speculate that the formation of these products involves chlorine radicals formed from the reaction of chloride ions with the photoinduced holes at the catalyst surface. Interestingly, we have shown that the 1-(2-chlorophenyl)ethenone and 1,2-dibenzoylethane products form from 2-chloroacetophenone when irradiated with 365 nm light in the absence of the catalyst. The formation of potentially dangerous side products in this reaction suggest that the practical implementation of the photocatalytic purification of contaminated water needs to considered very carefully if chlorides are likely to be present.

A comprehensive study on the application of FeNi3@SiO2@ZnO magnetic nanocomposites as a novel photo-catalyst for degradation of tamoxifen in the presence of simulated sunlight

Pharmaceutical compounds at trace concentrations are found in the environment, especially in drinking water and food, posing significant negative effects on humans as well as on animals. This paper aimed to examine the diagnostic catalytic properties and efficacy of a novel synthesized photocatalyst, namely FeNi₃@SiO₂@ZnO magnetic nanocomposite, for the removal of tamoxifen (TMX) from wastewater under simulated sunlight. According to the results, it was found that TMX was completely degraded operating under optimized conditions (i.e. pH = 7, catalyst dose = 0.01 g/L, initial TMX concentration = 20 mg/L and reaction time = 60 min). The reaction kinetics of TMX degradation followed a pseudo-first order kinetics model. The final by-products from the TMX photodegradation were water, carbon dioxide, acetic acid, nitroacetic acid methyl ester, 2-methyl-2-pentenal, and 4-methyl-2-pentanol. In addition, the synthesized photocatalyst could successfully performed five consecutive photodegradation cycles. The obtained results revealed that the synthesized FeNi₃@SiO₂@ZnO magnetic nanocomposite holds a great potential to be applied as a photocatalyst for the degradation of TMX on an industrial scale.

Highly Sensitive Determination of 2,4,6-Trichlorophenol by Using a Novel SiO2@MIPIL Fluorescence Sensor with a Double Recognition Functional Monomer

A novel SiO₂@ MIPIL fluorescence sensor for the highly sensitive detection of 2,4,6-trichlorophenol was prepared by using surface molecularly imprinting technology with SiO₂ microspheres as carriers and 3,3'-(anthracene-9,10-diylbis(methylene))bis(1-vinyl-1H-imidazole-3-ium) chloride as a double recognition fluorescence functional monomer. The prepared molecularly imprinted polymer (SiO₂@MIPIL) was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, laser confocal microscopy, and nuclear magnetic resonance. Compared with the polymer obtained via bulk polymerization (MIPIL), the surface molecularly imprinted polymer (SiO₂@MIPIL) has a better linear range (0.1-50 nM), lower detection limit (89 pM), and shorter detection time (approximately 1.5 min). The fluorescence sensor also shows good specificity, high sensitivity, good stability, and reusability. Satisfactory results were obtained when using this sensor in industrial wastewater and spiked environmental water.

Solar light harvest: modified d-block metals in photocatalysis

With solar light, modified d-block metal photocatalysts are useful in areas where electricity is insufficient, with its chemical stability during the photocatalytic process, and its low-cost and nontoxicity.

The practical utility of the synthesis FeNi3@SiO2@TiO2 magnetic nanoparticles as an efficient photocatalyst for the humic acid degradation

Humic acid (HA) compounds in drinking water and wastewater disinfection processes are viewed as precursors of highly toxic, carcinogenic, and mutagenic disinfection by-product chemicals. In recent times, these compounds have gained considerable attention of scientists for their successful removal from aqueous solutions to permissible limits. To achieve this aim, the present study investigated, for the first time, the photocatalytical performance of the synthesis FeNi₃@SiO₂@TiO₂ nanoparticles for the HA degradation under different environmental conditions. The photocatalytic reactions were performed using ultraviolet (UV) radiation, whose intensity was fixed at 2500 μW/cm² throughout the experimental study. The characterization study performed, using specific diagnostic techniques, revealed the presence of several good morphological, magnetic, and catalytic specifications of the synthesized nanoparticles. The use of the simplified form of the Langmuir-Hinshelwood equation sufficiently describes the experimental data of the HA kinetic degradation, as it shows a high coefficient of regression values. Furthermore, the complete HA degradation was reached under conditions of pH = 3; initial HA concentration = 10 mg/L; FeNi₃@SiO₂@TiO₂ nanoparticles dosage = 0.01 g/L; and reaction time >30 min. Thus, the results obtained from this research suggested that the catalyst of FeNi₃@SiO₂@TiO₂ nanoparticles was an attractive, novel, and effective agent, which could be used for the degradation of HA in the photocatalytic processes.

Facile synthesis of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) nanosheets for DFT supported visible photocatalysis of 2-Chlorophenol

Visible light active g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) ternary composite nanosheets were fabricated by facile co-precipitation routes. The density functional theory (DFT) computations investigated changes in geometry and electronic character of g-C3N4 with CeO2 and Fe3O4 addition. Chemical and surface characterizations were explored with XRD, XPS, SEM, TEM, PL, DRS and Raman measurements. DRS and PL spectroscopy evidenced the energy band gap tailoring from 2.68 eV for bulk g-C3N4 and 2.92 eV for CeO2 to 2.45 eV for the ternary nanocomposite. Efficient electron/hole pair separation, increase in red-ox species and high exploitation of solar spectrum due to band gap tailoring lead to higher degradation efficiency of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01). Superior sun light photocatalytic breakdown of 2-Chlorophenol was observed with g-C3N4 having CeO2 loading up to 5 wt%. In case of ternary nanocomposites deposition of 1 wt% Fe3O4 over g-C3N4/CeO2 binary composite not only showed increment in visible light catalysis as predicted by the DFT studies, but also facilitated magnetic recovery. The g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) nanosheets showed complete mineralization of 25 mg.L-1 2-CP(aq) within 180 min exposure to visible portion of sun light and retained its high activity for 3 consecutive reuse cycles. The free radical scavenging showed superoxide ions and holes played a significant role compared to hydroxyl free radicals while chromatographic studies helped establish the 2-CP degradation mechanism. The kinetics investigations revealed 2.55 and 4.04 times increased rate of reactions compared to pristine Fe3O4 and CeO2, showing highest rate constant value of 18.2 × 10-3 min-1 for the ternary nanocomposite. We present very persuasive results that can be beneficial for exploration of further potential of g-C3N4(0.94)/CeO2(0.05)/Fe3O4(0.01) in advance wastewater treatment systems.

Insights into the rapid elimination of antibiotics from aqueous media by tunable C3N4 photocatalysts: Effects of dopant amount, co-existing ions and reactive oxygen species

Conventional photocatalytic nanomaterials are not environmentally sustainable since these are usually produced from scarce mineral and metal precursors. Moreover, high pollutant removal efficiencies by conventional photocatalysts are only attained after several hours of reaction with light. In this study, novel visible light-active photocatalysts were synthesized from environment-friendly carbon precursors and applied for the rapid degradation of sulfamethoxazole (SMX) in aqueous solutions. The photocatalysts were prepared via the co-pyrolysis of urea with varying doping temperature and dopant amount. These variations played a vital role in improving the performance of the photocatalysts and resulted in up to >99% SMX removal within 45 min of visible light irradiation. Characterization of the photocatalysts showed that potassium and iodine dopants were responsible in the red shift and broadening of the light absorption spectrum to the visible region. In addition, the band gap energy narrowed by 0.23 eV resulting in faster charge transfer but slower recombination of the photo-generated electron and hole pairs. Effects of varying concentrations of inorganic salts (NO₃^-, SO₄^2-, Cl^-, PO₄^3-) on SMX removal were also examined. Lastly, the mechanism of SMX photodegradation was elucidated.

Evaluation of photocatalytic fuel cell (PFC) for electricity production and simultaneous degradation of methyl green in synthetic and real greywater effluents

Recycling of alternative water sources particularly greywater and recovery of energy from wastewater are gaining momentum due to clean water scarcity and energy crisis. In this study, the photocatalytic fuel cell (PFC) employing ZnO/Zn photoanode and CuO/Cu photocathode was successfully designed for effective greywater recycling as well as energy recovery. The photoelectrodes were analyzed using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and fourier transform infrared (FTIR) spectroscopy. The PFC performance in terms of electricity generation and parallel methyl green (MG) degradation were evaluated under operating parameters such as electrolyte type, initial MG concentration and solution pH. The results showed that the addition of Na₂SO₄ electrolyte, MG concentration of 40 mg L^-1 and solution pH of 5.2 improved the short circuit current density (J_sc) and power density (P_max) in the as-constructed PFC. Such a system also afforded highest MG and chemical oxygen demand (COD) removal efficiencies after 4 h of irradiation. The photoanodes used in this study demonstrated great recyclability after four repetition tests. The COD removal was reduced to some extents when the PFC treatment was tested in the real greywater under optimal conditions. Various greywater quality parameters including ammoniacal nitrogen (NH₃-N), turbidity, pH and biochemical oxygen demand (BOD₅) were also monitored. The phytotoxicity experiments via Vigna radiate seeds indicated a reduction in the phytotoxicity.

Enhanced Photocatalytic Activity of Titania by Co-Doping with Mo and W

Various W and Mo co-doped titanium dioxide (TiO2) materials were obtained through the EISA (Evaporation-Induced Self-Assembly) method and then tested as photocatalysts in the degradation of 4-chlorophenol. The synthesized materials were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy (RS), N2 physisorption, UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results showed that the W-Mo-TiO2 catalysts have a high surface area of about 191 m2/g, and the presence of an anatase crystalline phase. The co-doped materials exhibited smaller crystallite sizes than those with one dopant, since the crystallinity is inhibited by the presence of both species. In addition, tungsten and molybdenum dopants are distributed and are incorporated into the anatase structure of TiO2, due to changes in red parameters and lattice expansion. Under our experimental conditions, the co-doped TiO2 catalyst presented 46% more 4-chlorophenol degradation than Degussa P25. The incorporation of two dopant cations in titania improved its photocatalytic performance, which was attributed to a cooperative effect by decreasing the recombination of photogenerated charges, high radiation absorption capacity, high surface areas, and low crystallinity. When TiO2 is co-doped with the same amount of both cations (1 wt.%), the highest degradation and mineralization (97% and 74%, respectively) is achieved. Quinones were the main intermediates in the 4-chlorophenol oxidation by W-Mo-TiO2 and 1,2,4-benzenetriol was incompletely degraded.

Photoactive ZnO Materials for Solar Light-Induced CuxO-ZnO Catalyst Preparation

In this work, the solar light-induced redox photoactivity of ZnO semiconductor material was used to prepare Cu_xO-ZnO composite catalysts at room temperature with a control of the chemical state of the copper oxide phase. Cu₂^(I)O-ZnO and Cu^(II)O-ZnO composite catalysts were prepared by using Cu(acac)₂ in tetrahydrofuran-water and Cu(NO₃)₂ in water as metallic precursor, respectively. Prior to the implementation of the photon-assisted synthesis method, the most efficient photoactive ZnO material was selected from among different ZnO materials prepared by the low temperature polyol and precipitation methods with carbonates and carbamates as precipitation agents. The photocatalytic degradation of the 4-chlorophenol compound in water under simulated solar light was taken as a model reaction. The ZnO support materials were characterized by X-ray diffraction (XRD), surface area and porosimetry measurements, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the synthesis method strongly influenced their photoactivity in terms of 4-chlorophenol degradation and of total organic carbon removal. The most photoactive ZnO material was prepared by precipitation with carbonates and calcined at 300 °C, benefitting from a high specific surface area and a small mean crystallite size for achieving a complete 4-chlorophenol mineralization within 70 min of reaction, with minimum Zn²⁺ released to the solution. Besides thermal catalysis applications, this work has opened a new route for the facile synthesis of Cu₂O-ZnO heterojunction photocatalysts that could take place under solar light of the heterojunction built between the p-type semi-conductor Cu₂O with direct visible light band gap and the ZnO semiconductor phase.

Photostability Issues in Pharmaceutical Dosage Forms and Photostabilization

Photodegradation is one of the major pathways of the degradation of drugs. Some therapeutic agents and excipients are highly sensitive to light and undergo significant degradation, challenging the quality and the stability of the final product. The adequate knowledge of photodegradation mechanisms and kinetics of photosensitive therapeutic entities or excipients is a pivotal aspect in the product development phase. Hence, various pharmaceutical regulatory agencies, across the world, mandated the industries to assess the photodegradation of pharmaceutical products from manufacturing stage till storage, as per the guidelines given in the International Conference on Harmonization (ICH). Recently, numerous formulation and/or manufacturing strategies has been investigated for preventing the photodegradation and enhancing the photostability of photolabile components in the pharmaceutical dosage forms. The primary focus of this review is to discuss various photodegradation mechanisms, rate kinetics, and the factors that influence the rate of photodegradation. We also discuss light-induced degradation of photosensitive lipids and polymers. We conclude with a brief note on different approaches to improve the photostability of photosensitive products.

Hierarchical Design of CuS Architectures for Visible Light Photocatalysis of 4-Chlorophenol

Hydrothermal-assisted CuS hierarchical architectures were grown in the presence of anionic sulfur sources, and the investigation of their degradation efficiency for a pesticide 4-chlorophenol (4-CP) under visible light irradiation was carried out. The dissociation of S^2- from the sulfur compound governs the nucleation of CuS followed by a specific pattern of growth to produce different morphologies. The self-assembled covellite spherical CuS flower architecture assembles in the presence of thiourea and exhibits the highest photodegradation activity. The open architecture of ∼2.3 μm spherical CuS flowers consisting of a ∼100 nm thick sheet encompasses a comparatively high surface area and particle growth along the (110) plane that facilitates more active sites for catalytic activity enhancement. The catalyst loading for 4-CP degradation has been optimized, and a detailed trapping mechanism has been explored.

Antibacterial properties of F-doped ZnO visible light photocatalyst

Nanocrystalline ZnO photocatalysts were prepared by a sol-gel method and modified with fluorine to improve their photocatalytic anti-bacterial activity in visible light. Pathogenic bacteria such as Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) were employed to evaluate the antimicrobial properties of synthesized materials. The interaction with biological systems was assessed by analysis of the antibacterial properties of bacteria suspended in 2% (w/w) powder solutions. The F-doping was found to be effective against S. aureus (99.99% antibacterial activity) and E. coli (99.87% antibacterial activity) when irradiated with visible light. Production of reactive oxygen species is one of the major factors that negatively impact bacterial growth. In addition, the nanosize of the ZnO particles can also be toxic to microorganisms. The small size and high surface-to-volume ratio of the ZnO nanoparticles are believed to play a role in enhancing antimicrobial activity.

Recent developments of zinc oxide based photocatalyst in water treatment technology: A review

Today, a major issue about water pollution is the residual dyes from different sources (e.g., textile industries, paper and pulp industries, dye and dye intermediates industries, pharmaceutical industries, tannery and craft bleaching industries, etc.), and a wide variety of persistent organic pollutants have been introduced into our natural water resources or wastewater treatment systems. In fact, it is highly toxic and hazardous to the living organism; thus, the removal of these organic contaminants prior to discharge into the environment is essential. Varieties of techniques have been employed to degrade those organic contaminants and advanced heterogeneous photocatalysis involving zinc oxide (ZnO) photocatalyst appears to be one of the most promising technology. In recent years, ZnO photocatalyst have attracted much attention due to their extraordinary characteristics. The high efficiency of ZnO photocatalyst in heterogeneous photocatalysis reaction requires a suitable architecture that minimizes electron loss during excitation state and maximizes photon absorption. In order to further improve the immigration of photo-induced charge carriers during excitation state, considerable effort has to be exerted to further improve the heterogeneous photocatalysis under UV/visible/solar illumination. Lately, interesting and unique features of metal doping or binary oxide photocatalyst system have gained much attention and became favourite research matter among various groups of scientists. It was noted that the properties of this metal doping or binary oxide photocatalyst system primarily depend on the nature of the preparation method and the role of optimum dopants content incorporated into the ZnO photocatalyst. Therefore, this paper presents a critical review of recent achievements in the modification of ZnO photocatalyst for organic contaminants degradation.

Pd nanoparticles supported on amino-functionalized magnetic mesoporous silica nanotubes: a highly selective catalyst for the catalytic hydrodechlorination reaction

Highly dispersed Pd nanoparticles supported on amine-functionalized magnetic mesoporous silica nanotubes are prepared. This catalyst exhibits remarkable catalytic performance for the HDC reaction.

Immobilization of self-assembled pre-dispersed nano-TiO2 onto montmorillonite and its photocatalytic activity

The immobilization of pre-dispersed TiO2 colloids onto the external surface of the clay mineral montmorillonite (Mt) was accomplished and regulated via a self-assembly method employing the cationic surfactant cetyltrimethylammonium bromide (CTAB). The role of CTAB in the synthesis process was investigated by preparing a series of TiO2-CTAB-Mt composites (TCM) with various CTAB doses. The results indicated that a uniform and continuous TiO2 film was deposited on the external surface of montmorillonite in the composite synthesized with 0.1 wt.% of CTAB, and the TCM nano-composites showed much higher values for specific surface area, average pore size and pore volume than the raw montmorillonite clay. Then, the formed TCM materials were applied in photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous solution. The degradation efficiency reached as high as 94.7%. Based on the degradation intermediates benezoquinone, fumaric acid and oxalic acid identified by LC-MS analysis, a mechanism for the photocatalytic oxidation of 2,4-DCP on TiO2/Mt nano-composites is proposed.

Simple Response Surface Methodology: Investigation on Advance Photocatalytic Oxidation of 4-Chlorophenoxyacetic Acid Using UV-Active ZnO Photocatalyst

The performance of advance photocatalytic degradation of 4-chlorophenoxyacetic acid (4-CPA) strongly depends on photocatalyst dosage, initial concentration and initial pH. In the present study, a simple response surface methodology (RSM) was applied to investigate the interaction between these three independent factors. Thus, the photocatalytic degradation of 4-CPA in aqueous medium assisted by ultraviolet-active ZnO photocatalyst was systematically investigated. This study aims to determine the optimum processing parameters to maximize 4-CPA degradation. Based on the results obtained, it was found that a maximum of 91% of 4-CPA was successfully degraded under optimal conditions (0.02 g ZnO dosage, 20.00 mg/L of 4-CPA and pH 7.71). All the experimental data showed good agreement with the predicted results obtained from statistical analysis.