Photocatalytic Ozonation Process Research Articles

Degradation of cefadroxil by photoelectrocatalytic ozonation under visible-light irradiation and single processes

Here, we investigate the degradation of 20 mg L-1 Cefadroxil (CFX) in water using photoelectrocatalytic ozonation (PECO), and compared against its individual processes. A carbon nitrogen-codoped titanium dioxide (CN-TiO2) anode is synthesized using ethylene glycol and ethylenediamine as carbon and nitrogen source, respectively. The X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM) analysis conducted to this material indicate a crystalline phase anatase with irregular morphology formed on the electrode surface; while the diffuse reflectance spectroscopy (DRS) shows a shift in the photoanode absorbance towards the visible region, unlike undoped TiO2 structure. This behavior results from the inclusion of Carbon and Nitrogen species on the CN-TiO2 electrode in weight percentages of 14.5 and 1.61 wt%, respectively, according to Energy Dispersive Spectroscopy (EDS) analysis. The Cefadroxil (CFX) abatement is monitored UV–Vis spectroscopy, high-performance liquid chromatography (HPLC), and total organic carbon (TOC). All techniques reveal that the highest CFX removal occurs with PECO (Photoelectrocatalytic Ozonation) process, decreasing TOC by 57.6% (96% degradation by HPLC) after 90 min of treatment. The main by-products formed from oxidation with the PECO, PCO (Photocatalytic Ozonation) and O3 (Ozonation) systems were acid species presumably corresponding to short chain carboxylic acids. Finally, the germination of lettuce sativa is carried out in water contaminated with the drug, and compared with water treated by PECO and PCO processes, showing that PECO process improves germination by 23.5% on the contaminated sample and 7.4% on the sample treated with PCO. These findings confirm that synergism of oxidation techniques could be a tractable way to resolve the problems related to recalcitrant compounds contained in wastewater.

Insights into the photocatalytic ozonation over Ag2O-ZnO@g-C3N4 composite: Cooperative structure, degradation performance, and synergistic mechanisms

In this work, Ag2O and ZnO modified g-C3N4 (Ag2O-ZnO@CNx) catalysts were fabricated by a simple precipitation-reflux method and employed for visible-light-driven photocatalytic ozonation process towards oxalic acid (OA) degradation. A series of characterizations such as XRD, TEM, XPS, UV–vis DRS, PL, Mott-Schottky were conducted to investigate the impact of loading Ag2O-ZnO on the microstructure and catalytic properties of catalysts. It was noteworthy that the mesoporous and backbone structure did not perceptibly change after doping Ag2O-ZnO to g-C3N4. Moreover, the separation of photogenerated e−−h+ pairs, the mobility of e− transfer, and the photocatalytic ozonation performance were improved with the increase in doping amount of g-C3N4. Amongst, the Ag2O-ZnO@CN0.4 achieved 83.43% of OA removal efficiency and the highest k value (0.0311 min−1), showing an excellent synergistic effect (synergy index η = 10.37) in this coupling system. Moreover, the Ag2O-ZnO@CN0.4 exhibited satisfactory reusability for multiple consecutive cycles (≥5). Through the radical scavenger experiments and ESR spectra, the reactive species including h+, e−, O2•−, 1O2 and •OH were verified to play an important role in PhOx system. Accordingly, an empirical kinetic model was established to predict OA concentration with the given operational parameters. The synergistic mechanism of OA degradation in the PhOx system was also proposed. Overall, the results presented a new insight into the application of PhOx process in water treatment.

Strategy for improving photocatalytic ozonation activity of g-C3N4 by halogen doping for water purification

Feasibility of improving photocatalytic ozonation (PCO) activity of g-C3N4 (CN) by doping halogen (F, Cl, Br and I) was evaluated from the aspect of O3/O2 mass transfer and photogenerated electron (e-) and hole (h+) recombination. All halogen-CN had better activity (F-CN>I-CN>Cl-CN>Br-CN) for degrading ATZ than that of CN. Experimental and theoretical simulations results showed that doping halogen made the electron unevenly distributed and formed hydrophobic sites on CN, narrowed Eg of CN and enlarged e- migration space. The above properties were favorable for enhancing mass transfer of O3/O2 and suppressed e--h+ recombination. Besides, they either upshifted CB (C-I) or downshifted VB (C-F, C-Cl) to enhance the oxidation function of •OH or h+. One-electron reduction (high e- utilization) of O3 was weakened and three-electron reduction (low e- utilization) of O2 was enhanced with decrease of halogen electronegativity. This work provided insights into catalyst design for PCO process.

Development of a Continuous Photo-catalytic/Ozonation System: Application on Amido Black Removal from Water

ABSTRACT A continuous system for photo-catalytic/ozonation was designed at laboratory scale and evaluated for water treatment using Amido Black 10B dye (AB) as a pollutant model. The effect of single ozonation (O3), photolytic ozonation (UV/O3) and combined photocatalytic/ozonation treatment (UV/O3/TiO2) were investigated. TiO2 nanocatalysts films were coated on stainless steel grids (AISI 304) by Atomic Layer Deposition technique (ALD) at 350 °C. An experimental hydrodynamic study of the designed reactor was conducted based on dry and total pressure drop. Three flow regimes were observed by increasing the total pressure drop against gas load factor (Fs). Depollution experiments conducted on the developed reactor showed that reaction rates and efficiency of studied processes were dependent on the studied operational parameters (initial dye concentration, ozone dose, pH). The maximum AB dye ([AB]0 = 100 mg. L−1) conversion efficiency, using the designed (UV/O3/TiO2) system, was about 40.3% of initial TOC and 100% AB color removal was achieved within 10 min at an optimal ozone dose of 132 mg. L−1. A significant improvement in AB removal using UV/TiO2/O3 process (koverall = 0.056 min−1, 40.3%) compared to O3 alone (koverall = 0.032 min−1, 26.87). Results shows also that the addition of tert-butanol (TB), as radical scavenger ([TB] = 0.2 M and 0.4 M), greatly affects the reaction mechanisms of a photocatalytic ozonation process within 5 min of reaction, by decreasing the Amido Black conversion from 99.67% ([TB] = 0 M) to 74.63% and 31.35%, respectively, in presence of 0.2 M and 0.4 M of tert-butanol. The remarkable decrease in AB removal rate observed in the presence of a radical scavenger expresses that there was an obvious enhancement of hydroxyl radical OH• generation due to the synergetic effect between ozone and photocatalytic processes.

MoS2/N-TiO2/Ti mesh plate for visible-light photocatalytic ozonation of naproxen and industrial wastewater: comparative studies and artificial neural network modeling.

This paper presents the results of visible-light assistedphotocatalyticozonation for the degradation of naproxen as a model pharmaceutical pollutant from water using MoS2/N-TiO2 immobilized on a titanium mesh plate in addition to treatment of a real industrial wastewater. The batch studies were performed for naproxen degradation by varying the reaction variables such as ozone flow rate, initial pH and pollutant concertation. It was observed that almost 90% degradation was achieved at pH = 4, ozone flow rate = 3 L min-1 and initial naproxen concentration = 5mg L-1. The catalyst exhibited constant activity even after seven successive cycles. Comparative studies among sorption, ozonation, photocatalysis, catalytic ozonation and photocatalyticozonation revealed that the later process had the highest degradation of pollutant. Moreover, an artificial neural network (ANN) model was developed to simulate the performance of visible-light photocatalytic ozonation in naproxen degradation. The developed ANN model could estimate the visible-light photocatalytic ozonation process under the different experimental conditions. Finally, the applicability of the photocatalyticozonation was successfully approved for industrial wastewater treatment. The results showed that the COD removalefficiency reached 65% within 150min. HIGHLIGHTS: • MoS2/N-TiO2/Ti wassynthesized by the quick electrophoretic deposition method. • The catalyst showed good ability in naproxen degradation via visible-light photocatalytic ozonation. • A three-layer artificial neural network model was developed to predict the naproxen degradation. • Naproxen degradation efficiency through the photocatalytic ozonation was higher than the individual methods. • COD of real wastewater was reduced significantly after thevisible-light photocatalytic ozonation process.

Efficient degradation of tetracycline hydrochloride by photocatalytic ozonation over Bi2WO6

Photocatalytic ozonation technique for wastewater treatment has received much attention for their efficient capability in the mineralization of persistent organic pollutants. In this study, nanostructured Bi2WO6 was prepared by hydrothermal method and applied in the photocatalytic ozonation process for tetracycline hydrochloride (TCH) degradation under simulated solar light irradiation. Bi2WO6 triggered an effective synergy between photocatalysis and ozonation, and it showed a good activity and adaptability in the degradation of organic compounds. Besides, the influence of experimental factors on the total organic carbon removal (including catalyst dosage, ozone concentration, initial pH, reaction temperature and coexisting ions) was also investigated comprehensively. Spin-trapping electron paramagnetic resonance measurements and quenching experiments demonstrated that O2−, OH, 1O2 and h+ contributed to TCH degradation. The possible degradation pathways of TCH were proposed by identifying the intermediates with liquid chromatography-mass spectroscopy.

Synergism in TiO2 photocatalytic ozonation for the removal of dichloroacetic acid and thiacloprid

The synergistic effect of the photocatalytic ozonation process (PH-OZ) using the photocatalyst TiO2 is usually attributed to influences of the physicochemical properties of the catalyst, pollutant type, pH, temperature, O3 concentration, and other factors. It is also often claimed that good adsorption on the TiO2 surface is beneficial for the occurrence of synergism. Herein, we tested these assumptions by using five different commercial TiO2 photocatalysts (P25, PC500, PC100, PC10 and JRC-TiO-6) in three advanced oxidation systems - photocatalysis (O2/TiO2/UV), catalytic ozonation (O3/TiO2) and PH-OZ (O3/TiO2/UV) - for the degradation of two pollutants (dichloroacetic acid - DCAA and thiacloprid) simultaneously present in water. The synergistic effect in PH-OZ was much more pronounced in the case of thiacloprid, a molecule with low adsorption on the surface of the catalyst - in contrast to DCAA with stronger adsorption. The faster kinetics of catalytic ozonation (O3/TiO2) correlated with the higher exposed surface area of TiO2 agglomerates, independent of the (lower) BET surfaces of the primary particles. Nevertheless, DCAA mineralization on the TiO2 surface was much faster than thiacloprid degradation in solution. Therefore, we propose that a high BET surface area of the photocatalyst is crucial for fast surface reactions (DCAA mineralization), while good dispersion - the high exposed surface area of the (small) agglomerates - and charge separation play an important role in photocatalytic degradation or PH-OZ of less adsorbed organic pollutants (thiacloprid).

Fe doped CeO2 nanocubes with the exposure of active (100) facets for photocatalytic ozonation of 4‐chlorophenol under solar irradiation

AbstractBACKGROUNDTo strengthen the treatment efficiency of photocatalytic ozonation, it is necessary to develop a stable bifunctional catalyst active in both processes of photocatalysis and catalytic ozonation.RESULTSA series of Fe doped CeO2 nanocubes with the main exposure of active (100) crystal facets were simply synthesized by a one‐pot hydrothermal method and applied in photocatalytic ozonation for the first time. It was found that doping did not change the morphology of nanocubes but it decreased the crystal size, induced abundant defects of oxygen vacancies and Ce3+, and shifted the optical absorption edge to the visible region. Due to these structure modifications, Fe doped CeO2 nanocubes enhanced the mineralization rate of 4‐chlorophenol by 55.4–74.7% and reduced the formation of carcinogenic bromate by 60.2–85.4%, depending on the doping content. Due to the simultaneous occurrence of photocatalysis, catalytic ozonation, and their synergy in 5%Fe‐CeO2 mediated photocatalytic ozonation under solar irradiation, 4‐chlorophenol almost completely degraded within 9 min, 74.7% of mineralization rate was achieved within 45 min, and the first order kinetics reaction constant reached 2.97 × 10−2·min−1, about 4.1 times that of photo ozonation without any catalysts. Moreover, the introduction of 5%Fe‐CeO2 to the ozonation, photolysis, and photo ozonation decreased the corresponding energy consumption by 60.2%, 84.2%, and 62.5%, respectively.CONCLUSIONIn this study, an efficient and economical Fe doped CeO2 nanocubes‐mediated photocatalytic ozonation process was successfully developed for the refractory organics‐containing wastewater treatment under solar light irradiation. © 2021 Society of Chemical Industry

Investigation of the removal of sulfamethoxazole drug waste from aqueous solutions under the effect of zinc oxide/montmorillonite nanocomposite by photocatalytic ozonation process

Investigation of the removal of sulfamethoxazole drug waste from aqueous solutions under the effect of zinc oxide/montmorillonite nanocomposite by photocatalytic ozonation process

Efficient visible-light photocatalytic ozonation for dye degradation using Fe2O3/MoS2 nanocomposite

ABSTRACT In this study, Fe2O3/MoS2 nanocomposite was fabricated by a simple method and utilized in the visible-light photocatalytic ozonation (PCO) process for the removal of a recalcitrant azo dye, Acid Blue 113. The process was analyzed and optimized by response surface methodology (RSM) based on Box–Behnken design (BBD). Maximum dye removal (99.0%) was achieved at pH = 6.4 using 20 mg of the nanocomposite, 0.2 g l−1 h−1 ozone flow, and 45 min. Application of the PCO process for the treatment of real textile wastewater revealed that the O3/vis light/nanocomposite system is more efficient than the bare catalysts, ozone, and O3/light systems. Kinetic study showed that the PCO process obeyed pseudo-first-order and Langmuir–Hinshelwood models. The as-synthesized Fe2O3/MoS2 nanocatalyst showed high stability in the PCO process with 92% dye degradation after eight repetitive cycles. The results show that the nanocatalyst comprising α-Fe2O3 nanoparticles and MoS2 nanosheets can be efficiently applied in the wastewater treatment by the PCO process.

Photocatalytic ozonation of organic pollutants in wastewater using a flowing through reactor

Photocatalytic ozonation (PCO/O3) process is a promising technology for mineralizing refractory organics in wastewater. In this study, we described an efficient approach to improve the mass-transfer performance of PCO/O3 by using a helical photocatalytic module (HPM) in an annular UVC reactor. Under hydraulic retention time (HRT) of 19 min and influent phenol concentration of 33 mg/L (TOC 26 mg/L), TOC removal of 91.5% was obtained during a PCO/O3 process with HPM, while TOC removal was only 58.1% without HPM (UVC/O3). This flowing through reactor displayed good stability in a continuous test lasting 20 h. The electric energy required to reduce TOC by one order of magnitude per cubic meter of solution was calculated to be 10.23 kWh/(m3 order), which supported that the PCO/O3 process in this flowing through reactor was energy-efficient compared with other processes (24.30–68.75 kWh/(m3 order)). The steel-rolling wastewater after biological treatment was taken as a target. Under the HRT of 57 min and initial COD of 124 mg/L, COD in effluent dropped to 45.8 mg/L and met the discharge standard of pollutants for municipal wastewater treatment plant of China.

Performance of photocatalytic ozonation process for pentachlorophenol (PCP) removal in aqueous solution using graphene-TiO2 nanocomposite (UV/G-TiO2/O3).

The aim of this study was to evaluate the efficiency of photocatalytic ozonation process using graphene-dioxide titanium nanocomposite in removing Pentachlorophenol (PCP) from aqueous solutions. In this study, nanocomposites with graphene to TiO2(G/T) ratios of 1:10 and 1:20 were synthesized by hydrothermal method, and its characteristics were assessed using various analyses, SEM, XRD, FTIR, TEM, BET and TGA. In this process, the effects of parameters including O3 concentration (0.25-1.25mg/L), nanocomposite concentration (50-500mg/L), initial PCP concentration (10-100mg/L), and time (10-60min), were studied. The results showed that PCP removal efficiency was increased by decreasing solute concentration. Increasing nanocomposite dose to 100mg/L was led to an increase in efficiency (99.1%), but then a decreasing trend was observed. Increasing the concentration of ozone, up to specific value, also enhanced the efficiency but then had a negative effect on process efficiency. Furthermore, the optimum ratio of the catalyst was determined to be 1:20. The highest efficiency of the process for initial pentachlorophenol concentration of 100mg/L was obtained 98.82% in optimum conditions (catalyst dose of 100mg/L and 60min). It is concluded that the photocatalytic ozonation process using graphene-dioxide titanium nanocomposite had the highest efficiency in removal and mineralization of PCP.

Degradation of ciprofloxacin by photocatalytic ozonation process under irradiation with UVA: Comparative study, performance and mechanism

The photocatalytic ozonation process (O3/UVA/TiO2) was applied for the removal of ciprofloxacin antibiotic (CIP) from aqueous solutions. The influence of various operational factors such as solution pH, initial pollutant concentration, catalyst content, ozone dose and scavengers was studied on the process. The mineralization, biodegradability, kinetic models, catalyst recyclability, electrical energy consumption and cost estimation of the process were also performed. Various techniques of FE-SEM, EDS, FTIR, XRD and UV–vis were applied to characterize the catalyst. The highest CIP removal (98.5 %) was obtained in ozone and catalyst doses of 0.34 g/h and 1.0 g/L, respectively during 15 min reaction time at pH 9.0. The scavenging experiments approved the contribution of hydroxyl radicals (OH) and superoxide (O2−) as the main active radical species in the process. The competition effect of various anions on the process efficiency was in the order of chloride > carbonate > bicarbonate > sulfate. The process kinetics followed the pseudo-first-order model. The catalyst efficiency was about 95 % of the original one after 6 recycling steps. It can be concluded that the photocatalytic ozonation process (O3/UVA/TiO2), due to the low reaction time and high removal efficiency, can be considered as a suitable and practical technique for the removal of antibiotics from aqueous solutions.

Critical aspects of the stability and catalytic activity of MIL-100(Fe) in different advanced oxidation processes

The Fe-based MOF MIL-100(Fe) has been synthetized and fully characterized by XRD, N2-adsorption-desorption, ATR-FTIR, elemental analysis, WDXRF, XPS, DR-UV-vis, TGA-DTA, and pHPZC. MIL-100(Fe) presented rather good crystallinity and porosity (SBET = 1468 m2 g−1, total pore volume 0.716 cm3 g−1), though some unreacted linker (trimesic acid, TMA) was detected trapped in the structure. Purified MIL-100(Fe), free of unreacted trapped TMA, could be further obtained by some polishing treatments involving ozone, radiation and hydrogen peroxide at different conditions. The stability of the synthesized MIL-100(Fe) was studied in long-term experiments (15 days) at different pH (4–10) in non-buffered and phosphate-buffered ultrapure water, and in secondary effluent samples taken from a municipal wastewater treatment plant. Also, MOF stability was studied under different oxidizing environments through five-cycle experiments reusing the solid. Oxidizing conditions were produced by simulated solar radiation (550 W m−2, 300–800 nm), ozone (doses 0.25–2.0 g O3/g MOF) and/or hydrogen peroxide (doses 0.25–2.5 g H2O2/g MOF). The material showed low stability in the presence of phosphates and, also, at high oxidant doses plus radiation with moderate to high MOF degradation during the treatments. Purified MIL-100(Fe) samples were used as catalysts for the removal of four contaminants of emerging concern (metoprolol, clofibric acid, N,N-diethyl-m-toluamide and ibuprofen) by means of heterogeneous photocatalysis, Fenton-like, photo-Fenton-like, catalytic ozonation and photocatalytic ozonation processes. High catalytic activity in photo-Fenton-like and moderate activity in photocatalytic ozonation processes were attained but still the stability of the materials was questionable because of TMA and iron leaching into the reaction medium. Therefore, although TMA and the organic contaminants could be effectively removed by the advanced oxidation processes studied, bare MIL-100(Fe) is not recommended for water treatment.

Scrutinizing the vital role of various ultraviolet irradiations on the comparative photocatalytic ozonation of albendazole and metronidazole: Integration and synergistic reactions mechanism

Herein, TiO2 nanoparticles were immobilized on the ceramic surface using the sol-gel dip-coating method, which confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Then, a semi-batch reactor containing the prepared ceramic plates, which irradiated by the various UV lights was used for the degradation of the albendazole (ALZ) and metronidazole (MTZ) pharmaceuticals by the photocatalytic ozonation process. The control experiments were performed to compare the photocatalysis, ozonation, photo-ozonation and photocatalytic ozonation processes under the same operational conditions with the UV-A, UV-B and UV-C irradiations. The synergistic effect of photocatalysis and ozonation was observed; moreover, the results revealed that the UV-A/TiO2/O3 had the highest efficiency for the ALZ and MTZ degradation owing to the synergistic heterogeneous reactions (SHRs), which led to more reactive oxygen species (ROS). The MTZ and ALZ degradation were probed by monitoring the dissolved ozone, oxygen and hydrogen peroxide concentrations during the various processes including the UV-A/TiO2/O3 process. The obtained results disclose that the ALZ degradation is lower than the MTZ due to its resistant nature with more direct attacks of the ozone in the bulk solution compared to the MTZ. Furthermore, the various compounds as the holes (h+) and ROS scavengers or ozone solubility enhancers were added to the reaction bulk to investigate the exact mechanism of the photocatalytic-ozonation. Eventually, the degradation intermediates of the pharmaceuticals generated in the photocatalytic-ozonation process were successfully recognized by the Gas chromatography–mass spectrometry (GC–MS) and the possible degradation paths were suggested for the degradation of pollutants considering the responsible ROS in each case.

Photocatalytic ozonation process for degradation of an anthelmintic drug using ceramic coated TiO2 NPs: CFD simulation coupling with kinetic mechanisms

This paper reports numerical usage for modeling and simulation of the mebendazole (MBZ) photocatalytic ozonation in a stirred tank photoreactor by computational fluid dynamics (CFD) method, from mechanistic aspects in the presence of novel method of TiO2 coating ceramic panels. In the first part of the study, TiO2 nanoparticles (NPs) were fixed on the exterior surface of porous ceramic panels by a new modified sol-gel method. The coated surface presented very high stability and durability for 12 runs during a year of the process implementation. The morphological characteristics of the coated and bare panels were scrutinized by SEM and AFM analysis. The evolutional impacts of input parameters such as pH, inlet ozone dosage and initial MBZ concentration on MBZ removal efficiency were experimentally investigated. More than 95% degradation was achieved only after 35min. In the second section, a numerical study of MBZ photocatalytic ozonation has been evaluated by CFD method. Assessment of this process was investigated from two viewpoints: momentum and mass balances. The experimental results revealed a high amount of MBZ elimination in the aforementioned photoreactor. Moreover, CFD modeling simulated the mechanisms of MBZ photocatalytic ozonation. The obtained results described that MBZ degradation has occurred via the two homogenous and heterogeneous pathways in the presence of OH radicals. Briefly, the CFD results confirmed the experimental results from the standpoint of hydrodynamics and various species concentrations.

Application of a photocatalytic ozonation process using TiO2 magnetic nanoparticles for the removal of Ceftazide from aqueous solutions: Evaluation of performance, comparative study and mechanism

The presence of antibiotics in the environment leads to microbial resistance in humans and pathogenic microbes. Given the resistance of antibiotics even after conventional wastewater treatments, the present study is centered on the removal of ceftazide (CFT) from aqueous solutions by the photocatalytic ozonation process using TiO2 magnetic nanoparticles (T-MNPs). The effects of a number of operational parameters such as pH, initial CFT concentration, ozone concentration, reaction time on the degradation of CFT was thoroughly studied by the photocatalytic process. Under the optimum conditions (CFT concentration of 10 mg/L, pH 11, catalyst dosage of 1.0 g/L and ozone flow of 0.22 g/h), the removal efficiency and mineralization of 100 was 75.5 % were obtained for CFT after a 15-min treatment. Following on, the reusability of the photocatalyst was evaluated indicating a 5.8 % drop in the removal performance after six consecutive cycles of use. The mechanism for the degradation of CFT was predominantly governed by the formation of OH radicals. In conclusion, the photocatalytic ozonation process can significantly remove CFT and seems to be a suitable alternative to the others methods used for removal of antibiotics from aqueous solutions.

Kinetic model basis of ozone/light-based advanced oxidation processes: a pseudoempirical approach

Pseudoempirical modeling of the complex photocatalytic ozonation process.

Microwave synthesis of metal-doped ZnS photocatalysts and applications on degrading 4-chlorophenol using heterogeneous photocatalytic ozonation process

Photocatalysts can produce active species in the heterogeneous photocatalytic ozonation (HPO) process, which can efficiently degrade and mineralize organic pollutants. In this study, pristine ZnS and metal-doped (Cu, Ag, Bi, Ga, In) ZnS were synthesized by microwave method. The degradation rate of 4-chlorophenol (4-CP) in HPO process is ranked as Cu/ZnS > Bi/ZnS > Ag/ZnS > In/ZnS > Ga/ZnS > ZnS, which is attributed to the following reasons: (1) the schottky junction formed between ZnS and doped metal can effectively capture electrons as an electron trap, thus inhibiting the recombination of electron-hole pairs; (2) narrow bandgap of Cu/ZnS can enhance electron transport; (3) the valence bands of Ag/ZnS, Bi/ZnS, Ga/ZnS and In/ZnS were more positive than that of pristine ZnS to enhance the oxidization ability of holes. The experimental results showed that the optimal water-intake ozone dose optimal influent ozone dosage was 32 mg/l·min−1 under the optimal initial solution pH of 7. In addition, the possible mechanism of HPO process was proposed and clarified. We believe that metal-doped ZnS has a promising potential to be the photocatalyst for the degradation of organic pollutants.

Highly efficient degradation of perfluorooctanoic acid: An integrated photo-electrocatalytic ozonation and mechanism study

In this work, a novel rGO/BiOCl-mediated photo-electrocatalytic ozonation process integrated from photocatalysis, ozonation and electrocatalysis has been demonstrated, resulting in the PFOA degradation up to 95.4% in 3h from synergistic effects of the efficiently generated h + and OH active species. • A combined photo-electrocatalytic ozonation is developed to remove PFOA up to 95.4%. • Synergistic effects of h + and OH account for the highly efficient PFOA degradation. • The novel rGO/BiOCl catalysts offer high E vb and effective charge-carrier separation. • The degradation intermediates are identified and quantified to unravel the mechanism. Perfluorooctanoic acid (PFOA) is a widely used perfluorinated compound that causes hazards to human health and environment, which is difficult to be removed by biological degradation. In this work, we demonstrate a highly efficient PFOA degradation process integrated from photocatalysis, ozonation and electrocatalysis, with rGO/BiOCl nanocomposites as catalysts. The PFOA removal ratio in 3 h reaches unprecedentedly 95.4%, superior to photocatalytic ozonation (80.5%) and photoelectro-peroxone process (56.1%). The mechanism of the enhanced catalytic activities has been detailedly investigated, which lies in synergistic effects of photo-generated hole (h + ) oxidation from photocatalysis and accelerated OH formation from cathodically generated H 2 O 2 . Through identifying degradation intermediates, it is revealed that decarboxylation of PFOA is rapidly initiated by strongly oxidative h + , forming unstable perfluoroheptyl radicals that are further transformed into shorter-chain perfluorocarboxylic acids by reacting with OH. This strategy will bring new insights into fields of catalysis and other related areas for environmental pollution abatement.