Photocatalytic Ozonation Process Research Articles

Photocatalytic ozonation of pesticides in a fixed bed flow through UVA-LED photoreactor

In this study, a fixed bed flow through UVA-LED photoreactor was used to compare the efficiency of ozone, photocatalysis and photocatalysis-ozone degradation, and mineralization of two pure pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), and a commercial one, Killex®. For the degradation of the parent compounds, ozone-based processes were more effective. While for mineralization, photocatalytic processes were more effective. Photocatalytic ozonation was the most efficient process for both the degradation and mineralization of the parent compounds. The degradation rates and mineralization by photocatalytic ozonation were higher than the summation of the corresponding rates by ozonation and photocatalysis, indicating a symbiotic relationship.Overall, the photocatalytic ozonation process with the fixed bed TiO2 reduces the time needed for the degradation and mineralization of the pesticides, reduces the costs of powder catalyst separation and overcomes the reduced efficiency of immobilized catalysts, which makes the process quite attractive for practical applications.

High performance of magnetic BiFeO 3 nanoparticle-mediated photocatalytic ozonation for wastewater decontamination

Abstract In this paper, bismuth ferrite (BiFeO3) magnetic nanoparticles were used as visible light photocatalyst in the photocatalytic ozonation coupling system. It was successfully synthesized by thermal decomposition of a glyoxylate complex. The as-prepared photocatalyst was characterized by XRD, FT-IR, SEM, TEM, UV–Vis DRS and vibrating sample magnetometer. The magnetic hysteresis loop demonstrated that BiFeO3 possessed certain magnetization. Oxalic acid (OA) and norfloxacin (NFX) were selected as target pollutants for photocatalytic ozonation reactions to evaluate the catalytic ability of BiFeO3. The pseudo-first-order kinetic rate constants of degrading OA and NFX removal in O3/Vis/BiFeO3 at given time are 5.48 and 1.65 times as great as the sum of that when using Vis/BiFeO3 and O3, respectively. This enhancement was due to a synergy between photocatalysis and ozonation triggered by BiFeO3. In O3/Vis/BiFeO3 process, the photo-generated electrons produced on BiFeO3 could be trapped by ozone and reaction with them. Subsequently, the improved yield of hydroxyl radicals enhanced the degradation efficiency of organics. In addition, the stability and reusability of BiFeO3 in photocatalytic ozonation process were examined in this work.

Nanostructured CeO2 as catalysts for different AOPs based in the application of ozone and simulated solar radiation

Two CeO2 catalysts with different morphology (nanocubes and nanorods) were synthetized by hydrothermal treatment, characterized by TEM, XRD, N2 adsorption-desorption isotherms, XPS and DR-UV–vis spectroscopy and examined for different AOPs (photocatalytic oxidation, catalytic and photocatalytic ozonation) using simulated solar radiation (λ>300nm) or visible radiation (λ>390nm) from a Xe lamp, and DEET as target compound. Neither significant DEET removal nor mineralization was achieved by solar photocatalysis and the catalysts did not show an important beneficial effect during catalytic ozonation. The best results were obtained in photocatalytic ozonation process being nanorods more active under visible radiation according to its lower band gap energy whereas nanocubes presented the highest intrinsic photocatalytic activity under visible and solar radiation. Photocatalytic ozonation of DEET with CeO2 catalysts proceeds through a complex reaction mechanism that involves at least ozone-direct reaction that triggers a radical chain mechanism, indirect ozone reactions, ozone photolytic and photocatalytic decomposition and hydrogen peroxide formation-decomposition.

Development of kinetic models for photocatalytic ozonation of phenazopyridine on TiO2 nanoparticles thin film in a mixed semi-batch photoreactor

The degradation of phenazopyridine hydrochloride (PhP), an analgesic pharmaceutical, through photocatalytic ozonation process was modeled using three types of kinetic approaches. The experiments were performed using a semi-batch photoreactor where TiO2 nanoparticles thin film was coated on ceramic plates irradiated by UV-A light in the proximity of ozone. The surface morphology, topography and roughness of the bare and TiO2 coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The photocatalytic ozonation kinetic characteristics were experimentally investigated under the different operational parameters including pH, PhP initial concentration, ozone inlet flow rate, light intensity, ozone and oxygen dissolved concentrations. It was found that the pseudo-first-order rate constant (kapp) decreased with increase in the initial PhP concentration and increased with increasing ozone inlet flow rate solution pH and light intensity. Based on the generally accepted intrinsic elementary reactions for photocatalytic ozonation process, a novel kinetic model was proposed and validated for predicting PhP removal efficiency. The developed kinetic model explicitly explains the dependency of the apparent kinetic constant on PhP initial concentration, light intensity, ozone and oxygen dissolved concentrations. A good agreement among the predicted values of PhP removal efficiency using the developed model with experimental results was observed (R2=0.987, MSE=0.0011 and MAE=0.0290). In order to profoundly evaluate and compare the accuracy of the proposed intrinsic kinetic model, an empirical kinetic model as function of main functional parameters and an artificial neural network model (ANN) by 3-layer feed-forward back propagation network with topology 5:14:1 were developed. The performance of the three models was compared based on the error functions and analysis of variance (ANOVA). Comparison based on the errors function demonstrated that the experimental data were fitted reasonably well by all the three proposed models with an adequate accuracy. Also, ANOVA results showed that there is no significant discrepancy among the predicted values of the three proposed models, implying that the kinetic model have been developed based on the proper specification of the intrinsic reactions occurred in the process.

Photocatalytic ozonation of oxalic acid by g-C 3 N 4 /graphene composites under simulated solar irradiation

Abstract Graphitic carbon nitride (g-C 3 N 4 )–reduced graphene oxide (rGO) nanocomposites were synthesized successfully by grinding a mixture of melamine and graphene oxide (GO) with different weight ratios, followed by calcination at 550 °C under flowing nitrogen atmosphere. Photoluminescence (PL) analysis was performed to investigate the efficiency of charge separation in g-C 3 N 4 –rGO composite. The result showed that the intensity of emission peak for g-C 3 N 4 –rGO composite is much lower than pure g-C 3 N 4 . The activity of g-C 3 N 4 –rGO composite in photocatalysis and photocatalytic ozonation process was evaluated by degradation of oxalic acid (OA) under simulated solar light irradiation. The results demonstrated that the degradation rate of OA with g-C 3 N 4 –rGO composite was significantly improved compared with pure g-C 3 N 4 in both process. This enhancement was due to the hetero-junction built between rGO and g-C 3 N 4 . Furthermore, during photocatalytic ozonation process, g-C 3 N 4 –rGO composite could trigger a synergistic effect between photocatalysis and ozonation. This study indicated that the metal-free g-C 3 N 4 –rGO nanocomposite showed high solar-light activity in photocatalytic ozonation process, which makes them promising materials for further applications in wastewater treatment.

Fast mineralization and detoxification of amoxicillin and diclofenac by photocatalytic ozonation and application to an urban wastewater

The degradation of two organic pollutants (amoxicillin and diclofenac) in 0.1 mM aqueous solutions was studied by using advanced oxidation processes, namely ozonation, photolysis, photolytic ozonation, photocatalysis and photocatalytic ozonation. Diclofenac was degraded quickly under direct photolysis by artificial light (medium-pressure vapor arc, λexc > 300 nm), while amoxicillin remained very stable. In the presence of ozone, regardless of the type of process, complete degradation of both organic pollutants was observed in less than 20 min. Photolysis or ozonation on their own led to modest values of total organic carbon (TOC) removal (<6% or 41%, respectively in 180 min), while for photocatalysis (no ozone present) a significant fraction of nonoxidizable compounds remained in the treated water (∼15% after 180 min). In the case of photolytic ozonation, the kinetics of TOC removal was slow.In contrast, a relatively fast and complete mineralization of amoxicillin and diclofenac (30 and 120 min, respectively) was achieved when applying the photocatalytic ozonation process. The absence of toxicity of the treated waters was confirmed by growth inhibition assays using two different microorganisms, Escherichia coli and Staphylococcus aureus. Photocatalytic ozonation was also applied to an urban wastewater spiked with both amoxicillin and diclofenac. The parent pollutants were easily oxidized, but the TOC removal was only as much as 68%, mainly due to the persistent presence of oxamic acid in the treated sample. The same treatment allowed the effective degradation of a wide group of micropollutants (pesticides, pharmaceuticals, hormones and an industrial compound) detected in non-spiked urban wastewater.

Removal of emerging contaminants from municipal WWTP secondary effluents by solar photocatalytic ozonation. A pilot-scale study

Ozonation, solar photocatalytic oxidation and a combination of both systems (i.e., solar photocatalytic ozonation) have been studied to treat a secondary effluent from a municipal wastewater treatment plant containing a selection of six emerging contaminants (acetaminophen, antipyrine, bisphenol A, caffeine, metoprolol and testosterone). Fe(III), Fenton reagent and TiO2 were used in photocatalytic experiments, which were conducted in a pilot-scale compound parabolic collector photo-reactor using solar radiation as energy source. Emerging contaminants (0.2mgL−1 each), at pH 3, were completely removed by photo-Fenton and single ozonation in 90 and 25min, respectively. Moreover, solar photocatalytic ozonation treatments (Fe(III)/O3/light and Fe(III)/H2O2/O3/light systems) were able to completely remove the ECs in about 20min with UV doses of 2–6kJL−1. However, the organic matter mineralization level achieved was limited (<35% TOC removal) even after the application of solar photocatalytic ozonation, for which an enhanced generation of hydroxyl radicals was measured in experiments carried out in the presence of the hydroxyl radical probe p-chlorobenzoic acid. Daphnia magna bioassays were used to test toxicity of samples before and after their treatment, showing that samples subjected to solar photocatalytic ozonation were less toxic (% inhibition <15%) than the mixture of emerging contaminants in the secondary effluent (% inhibition about 25%). Finally, a simplified estimation of operating costs shows some solar photocatalytic ozonation processes advantageous over the solar photo-Fenton system.

G-C3N4-triggered super synergy between photocatalysis and ozonation attributed to promoted [rad]OH generation

We coupled g-C3N4 or chlorine modified g-C3N4 (Cl/g-C3N4) photocatalysis with ozonation for mineralization of oxalic acid (OA) under visible light. g-C3N4 and Cl/g-C3N4 could trigger a super synergy between photocatalysis and ozonation, with a coupling coefficient at 17.8 and 9.9, respectively. The great gap of redox potential between the conduction band of g-C3N4 and ozone greatly benefitted electrons captured by ozone molecules, and thus promoted charge separation and ozone self-decomposition into a growing number of hydroxyl radicals in a photocatalytic ozonation process. Besides, the influence of chlorine modification on g-C3N4 to photocatalysis and photocatalytic ozonation was also clearly stated.

Photocatalytic ozonation of phenazopyridine using TiO2 nanoparticles coated on ceramic plates: mechanistic studies, degradation intermediates and ecotoxicological assessments

Removal of phenazopyridine (PhP), an analgesic drug, from water with different oxidation processes including photocatalysis, ozonation and photocatalytic ozonation was studied. The experiments were conducted using a semi-batch reactor where TiO2 nanoparticles were immobilized on ceramic plates irradiated by UV-A light in the proximity of oxygen and/or ozone. The surface morphology, topography and roughness of the bare and TiO2-coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Comparing the processes of photocatalysis, ozonation and photocatalytic ozonation revealed that using photocatalytic ozonation led to the highest efficiency (85% at 35min) in PhP removal. The influence of pH, PhP initial concentration and ozone gas flow rate on the removal of PhP was investigated in both individual and combined processes. The presence of synergy was investigated under various operational parameters. The mechanism of photocatalytic ozonation process was investigated in the presence of various reactive oxygen species (ROS) scavengers. The main intermediate products of PhP produced in ozonation and photocatalytic ozonation processes were verified by the GC–MS technique. The chronic phytotoxicity of PhP and its intermediate compounds formed in ozonation and photocatalytic ozonation was evaluated using aquatic species Spirodela polyrrhiza (S. polyrrhiza). It was found that the photocatalytic ozonation process, in contrast to the single ozonation process, can efficiently reduce the phytotoxicity of the PhP from aqueous solutions.

Monitoring simultaneous photocatalytic-ozonation of mixture of pharmaceuticals in the presence of immobilized TiO2 nanoparticles using MCR-ALS: Identification of intermediates and multi-response optimization approach

The present study has focused on the degradation of a mixture of three pharmaceuticals, i.e. methyldopa (MDP), nalidixic acid (NAD) and famotidine (FAM) which were quantified simultaneously during photocatalytic-ozonation process. The experiments were conducted in a semi-batch reactor where TiO2 nanoparticles (crystallites mean size 8nm) were immobilized on ceramic plates irradiated by UV-A light in the proximity of oxygen and/or ozone. The surface morphology and roughness of the bare and TiO2-coated ceramic plates were analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). An analytical methodology was successfully developed based on both recording ultraviolet–visible (UV–Vis) spectra during the degradation process and a data analysis using multivariate curve resolution with alternating least squares (MCR-ALS). This methodology enabled the researchers to obtain the concentration and spectral profiles of the chemical compounds which were involved in the process. A central composite design was used to study the effect of several factors on multiple responses namely MDP removal (Y1), NAD removal (Y2) and FAM removal (Y3) in the simultaneous photocatalytic-ozonation of these pharmaceuticals. A multi-response optimization procedure based on global desirability of the factors was used to simultaneously maximize Y1, Y2 and Y3. The results of the global desirability revealed that 8mg/L MAD, 8mg/L NAD, 8mg/L FAM, 6L/h ozone flow rate and a 30min-reaction time were the best conditions under which the optimized values of various responses were Y1=95.03%, Y2=84.93% and Y3=99.15%. Also, the intermediate products of pharmaceuticals generated in the photocatalytic-ozonation process were identified by gas chromatography coupled to mass spectrometry.

Enhanced removal of dichloroacetonitrile from drinking water by the combination of solar-photocatalysis and ozonation

In this study, the photocatalytic ozonation process using either UV lamps with a wavelength close to a solar wavelength (UVsolar) or natural solar light was established to study the effects of the major operating parameters on the removal of a toxic disinfection by-product (DBP), dichloroacetonitrile (DCAN), from drinking water. Based on the test results of a bench system, the UVsolar/TiO2/O3 process had the highest DCAN-removal rate among the advanced oxidation processes (AOPs). The optimal TiO2 and ozone doses were 1gL−1 and 1.13gL−1h−1, respectively, while room temperature (20°C) produced the highest rate constant in the kinetic tests. The kinetic rate constants linearly increased when the UVsolar intensity increased in the range 4.6–25Wm−2; however, it increased less at intensities higher than 25Wm−2. The test results of the outdoor system showed that the solar/TiO2/O3 process provided complete removal of DCAN that was two times faster and had about 4.6 times higher energy efficiency than with solar/TiO2. As a green oxidation technique, solar photocatalytic ozonation could be a good alternative for treating recalcitrant and toxic organic pollutants, because it has high oxidation potential and low energy consumption compared to conventional AOPs.

Chlortetracycline degradation by photocatalytic ozonation in the aqueous phase: mineralization and the effects on biodegradability

Chlortetracycline (CTC) is a hazardous material in aquatic environments. This study was focused on optimization of photocatalytic ozonation processes for removal of CTC from wastewater at pH 2.2 and 7.0. In this study, the tested processes for CTC removal were arranged from the least efficient to the most efficient as: UV, UV/TiO2, O3, O3/UV and O3/UV/TiO2. Ozonation efficiency was due to ozone affinity for electron-rich sites on the CTC molecule. In the O3/UV and O3/UV/TiO2 processes, efficiency was increased by the photolysis of CTC and generation of •OH. At pH 7.0, all the processes were more efficient for CTC degradation than at pH 2.2 due to CTC speciation, ozone decay to •OH and the attractions between ionized CTC and TiO2 particles. UV/O3 at pH 7.0 showed an additive effect while other combination processes showed a synergistic effect that resulted in higher rates of reactions than the sums of individual reaction rates. The TOC removal ranged from 8% to 41% after one hour of reaction, with the above-mentioned order of efficiency. The biodegradability increased rapidly during the early minutes of the reaction. A reaction time of 10–15 min was sufficient for near maximum biodegradability, making these processes good pretreatments for the biological processes.

복합 파라볼라형(CPC) 모듈을 이용한 태양광/촉매/오존 공정에서 초기 pH 변화에 따른 디클로로아세토니트릴 제거 속도에 관한 연구

이 연구에서는 디클로로아세토니트릴을 제거하는데 태양광/촉매/오존 공정에서 적정 pH 조건을 찾기 위해 각각 pH 3, 6.5, 10 조건에서 제거속도를 알아보았다. 태양광/촉매/오존 공정에서 각각의 pH 조건(3, 6.5, 10)에서 4시간 동안의 DCAN 제거율을 알아본 결과 각각 43.8, 91.1, 98.2%로 pH 10 조건에서 가장 높은 제거속도를 보였다. 그 원인은 디클로로아세토니트릴의 자체 분해와 오존의 분해 메커니즘의 변화 때문이었다. pH 6.5 조건에서도 91.1%로 높은 제거율을 보이는데 그 원인은 디클로로아세토니트릴의 촉매 흡착량 증가로 촉매표면에서의 전도대의 전자와 오존의 반응으로 인해 흡착된 디클로로아세토니트릴이 분해되기 때문이다. pH 3 조건에서는 디클로로아세토니트릴의 촉매 흡착이나 오존의 반응 메커니즘 변화로 인한 제거속도 향상 효과가 없기 때문에 제거속도가 가장 저조한 현상을 보였다. In this study, we investigated to reaction rate of dichloroacetonitrile(DCAN) in each pH(3, 6.5, 10) using heterogeneous photocatalytic ozonation in order to determine optimal pH in photocatalytic ozonation (solar/<TEX>$TiO_2/O_3$</TEX>) process. The results, showed that DCAN was removed at pH of 3, 6.5, and 10 within 4h, and that the corresponding removal rates were 43.8, 91.1, 98.2%, respectively, in the solar/<TEX>$TiO_2/O_3$</TEX> process. The highest reaction rate was observed at pH 10. These results could be attributed to the self-decomposition of DCAN and the change in the mechanism of the ozone process. Besides, pH 6.5 also achieved a high degradation rate(91.1%) which is due to DCAN adsorbed onto the catalyst surface and reacted with radicals(<TEX>${\cdot}OH$</TEX>) generated by the reaction between ozone and electron(<TEX>$e^-$</TEX>) released from the conduction band of catalyst. The lowest degradation rate was observed at pH 3 due to absence of adsorption and no change in ozone reaction mechanisms.

TiO 2 and Fe (III) photocatalytic ozonation processes of a mixture of emergent contaminants of water

A mixture of three emergent contaminants: testosterone (TST), bisphenol A (BPA) and acetaminophen (AAP) has been treated with different photocatalytic oxidation systems. Homogeneous catalysts as Fe(III) alone or complexed with oxalate or citrate ions, heterogeneous catalysts as titania, and oxidants such as hydrogen peroxide and/or ozone have been used to constitute the oxidation systems. For the radiation type, black light lamps mainly emitting at 365 nm have been used. The effects of pH (3 and 6.5) have been investigated due to the importance of this variable both in ozone and Fe(III) systems. Removal of initial compounds and mineralization (total organic carbon: TOC) were followed among other parameters. For the initial compounds removal ozonation alone, in many cases, allows the highest elimination rates, regardless of the presence or absence of UVA light and catalyst. For mineralization, however, ozone photocatalytic processes clearly leads to the highest oxidation rates.

Removal of Orange II Dye in Water by Visible Light Assisted Photocatalytic Ozonation Using Bi2O3and Au/Bi2O3Nanorods

This paper presents the results of visible light assisted photocatalytic ozonation and other related oxidation processes for the removal of Orange II dye from water using Bi2O3 and Au/Bi2O3 nanorods prepared using microwave irradiation which was found effective compared to Bi2O3 particles prepared by conventional heat treatment method at 90 °C. Particularly, in the photocatalytic ozonation using Au/Bi2O3 nanorods, a fourfold increase in the rate was observed as compared to that in the absence of Au/Bi2O3. This is because tuning semiconductor materials into nanosize could create high quantum confinement of electron and hole to increase the illumination efficiency. In addition, the deposition of nanomaterial can also be employed to enhance the mechanical strength of devices. That is, deposited Au nanoparticles act as electron traps to impede electron/hole recombination.

A study on synergistic effect of photocatalytic ozonation for carbaryl degradation

The combination of UVA radiation and ozone, in the presence of titanium dioxide, has been investigated as a potential destructive technology for the treatment of pesticide wastewaters. The contribution of single ozonation (O 3), photolytic ozonation (O 3/UV), and photocatalysis (TiO 2/UV) to degradation of carbaryl, a carbamate pesticide is assessed and compared with that of combined photocatalytic ozonation process (TiO 2/UV/O 3). For 40 mg/L of carbaryl (500 mL) at pH 6 and with 0.28 g/h of ozone and 1 g/L of TiO 2, 92% COD reduction was achieved in 180 min. Under this experimental condition, 76.5% TOC removal and increase of BOD 5/COD ratio to 0.38 was also observed. The synergistic effect occurs in the combined photocatalytic ozonation process which is proved by the significant improvement in the mineralization rate constant (0.09 min –1) when compared with the sum of mineralization rate constant of photocatalysis and ozonation (0.05 min –1). Further synergistic effect was noticed at acidic and neutral pH, but synergism was lost at alkaline pH due to faster self decomposition of ozone.

Degradation of Pesticide by Photocatalytic Ozonation Process and Study of Synergistic Effect by Comparison with Photocatalysis and UV/Ozonation Processes

AbstractSynergistic effect of TiO

Comparison between photocatalytic ozonation and other oxidation processes for the removal of phenols from water

AbstractPhotocatalytic ozonation (1O3 + VUV + TiO2), ozonation (O3), catalytic ozonation (O3 + TiO2), ozone photolysis (O3 + VUV), photocatalysis (TiO2 + VUV) and photolysis (VUV) have been compared in terms of formation of intermediates, extent of, mineralization (TOC, COD, chloride, nitrate) and kinetics in the aqueous treatment of three phenols (phenol, p‐chlorophenol and p‐nitrophenol). In all cases, photocatalytic ozonation led to lower degradation times for chemical oxygen demand and total organic carbon removal. Intermediates formed were similar in the different oxidation systems with some exceptions. They can be classified into three different types: polyphenols (resorcinol, catechol, hydroquinone), unsaturated carboxylic acids (maleic and fumaric acids) and saturated carboxylic acids (glyoxylic, formic and oxalic acids). First order kinetic equations have been checked for the oxidation processes studied in the case of the parent compound. Rate constants of these systems have also been calculated. Copyright © 2005 Society of Chemical Industry

Novel effects of TiO2 photocatalytic ozonation on control of postharvest fungal spoilage of kiwifruit

Abstract Novel effects of TiO2 photocatalytic ozonation (a combination of TiO2 photocatalytic oxidation and ozonation) were investigated for the control of postharvest storage rots in kiwifruit and on the decomposition of residual fungicides. The TiO2 photocatalytic ozonation process synergistically degraded organic compounds and inhibited conidial germination of the fungal pathogen, when compared to a single treatment of ozonation or TiO2 photocatalytic oxidation. TiO2 photocatalytic ozonation was not effective in controlling latent infections in kiwifruit tissue, but apparently retarded the disease development during cold storage. It also effectively degraded the fungicide flusilazole commonly used for disease control in Korea. These findings suggest that TiO2 photocatalytic ozonation can be a very attractive method for postharvest disease control of kiwifruit with an emphasis on food safety.