Combination Of Photocatalytic Oxidation Research Articles

Examination of Photocatalyzed Chlorophenols for Sequential Photocatalytic-Biological Treatment Optimization

Given the known adverse effect of chlorophenols for the aquatic environments which they can reach, the development of efficient methods both technically and economically to remove them has gained increasing attention over time. The combination of photocatalytic oxidation with biological treatment can lead to high removal efficiencies of chlorophenols, while reducing the costs associated with the need to treat large volumes of aqueous solutions. Therefore, the present paper had as its main objective the identification of the minimum photocatalytic oxidation period during which the aqueous solutions of 4-chlorophenol and 2,4-dichlorophenol can be considered as readily biodegradable. Thus, the results of photocatalytic oxidation and biodegradability tests showed that, regardless of the concentration of chlorophenol and its type, the working solutions become readily biodegradable after up to 120 min of irradiation in ultraviolet light. At this irradiation time, the maximum organic content of the aqueous solution is less than 40%, and the biochemical oxygen demand and chemical oxygen demand (BOD/COD) ratio is much higher than 0.4. The maximum specific heterotrophic growth rate of activated sludge has an average value of 4.221 d−1 for 4-chlorophenol, and 3.126 d−1 for 2,4-dichlorophenol. This irradiation period represents at most half of the total irradiation period necessary for the complete mineralization of the working solutions. The results obtained were correlated with the intermediates identified during the photocatalytic oxidation. It seems that, working solutions initially containing 4-chlorophenol can more easily form readily biodegradable intermediates.

Fouling process and anti-fouling mechanisms of dynamic membrane assisted by photocatalytic oxidation under sub-critical fluxes

Membrane fouling is often considered as a hindrance for the application of microfiltration/ultrafiltration (MF/UF) for drinking water production. A novel process of photocatalytic membrane reactor/dynamic membrane (PMR/DM), operating in a continuous mode under sub-critical flux, was proposed for the mitigation of membrane fouling caused by humic acids (HAs) in water. The mechanism of membrane fouling alleviation with synergistic photocatalytic oxidation and dynamic layer isolating effect was comprehensively investigated from the characterization of foulant evolution responsible for the reversible and irreversible fouling. The results showed that the PMR/DM utilized photocatalytic oxidation to enhance the porosity and hydrophilicity of the fouling layer by converting the high molecular weight (MW) and hydrophobic HA molecules with carboxylic functional groups and aromatic structures into low-MW hydrophilic or transphilic fractions, including tryptophan-like or fulvic-like substances. The fouling layer formed in the PMR/DM by combination of photocatalytic oxidation and DM running at a sub-critical flux of 100 L·h−1·m−2, was more hydrophilic and more porous, resulting in the lowest trans-membrane pressure (TMP) growth rates, as compared to the processes of ceramic membrane (CM), DM and PMR/CM. Meanwhile, the dynamic layer prevented the foulants, particularly the high-MW hydrophobic fractions, from contacting the primary membrane, which enabled the membrane permeability to be restored easily.

Synthesis and characterization of samarium and nitrogen doped TiO2 photocatalysts for photo-degradation of 4-acetamidophenol in combination with hydrodynamic and acoustic cavitation

In the present work, samarium (Sm) and nitrogen (N) doped TiO2 photocatalysts have been synthesized using conventional sol-gel process (CSP) and ultrasound assisted sol-gel process (USP). Detailed characterizations of catalysts have been performed using PL, UV-DRS, XPS, XRD, FTIR, FESEM, and EDX analysis. Photocatalytic activity of the catalysts has also been evaluated for the degradation of 4-Acetamidophenol (4-AMP) using different combinations of ultraviolet (UV) irradiation, hydrodynamic cavitation (HC) and ultrasound (US). Initially, the effects of operating parameters i.e. catalyst dosage, solution pH, and 4-AMP initial concentration on the extent of degradation have been investigated. It was observed that degradation of 4-AMP followed first order reaction kinetics and almost 50% degradation with a degradation rate constant of 4.4 × 10−3 (min−1) was achieved using only photocatalytic oxidation at an optimum TiO2 catalyst loading of 2 g/L and natural pH (6.8). Nearly 60% and 63% degradation were obtained using Sm and N doped TiO2 at the optimized molar ratio of Sm to TiO2 (1.5:1) and N to TiO2 (1:1) respectively. It was also established that combination of photocatalytic oxidation with US and HC yielded synergistic results with extent of degradation as 87% and 91% respectively under optimized conditions in 180 min treatment. Energy efficiency (mg/J) was estimated on the basis of the amount of pollutant degraded per unit energy delivered. The hybrid method of HC and photocatalytic oxidation exhibited higher energy efficiency (9.0 × 10−6 mg/J) which was almost 9 folds higher than the energy efficiency of the sonophotocatalytic process. The degradation by-products formed during the combined treatment of HC and photocatalytic oxidation were identified by LC-MS.

Simultaneous removal of several pharmaceuticals and arsenic on Zn-Fe mixed metal oxides: Combination of photocatalysis and adsorption

A series of ZnFe-MMOs were synthesized by in situ topotactic transformation of ZnFe-LDH precursors, and screened for obtaining an efficient functional material used in the simultaneous removal of pharmaceuticals and arsenic. In a mono-component system, the photodegradation efficiency of ibuprofen with optimal ZnFe-MMOs can reach 95.7% under simulated solar irradiation and the maximum adsorption capacity of arsenic was up to 176.3mg·g−1. In the binary system of ibuprofen and arsenic, the degrading activity of ibuprofen inordinately decreased depending on both the arsenic species and concentrations, while the presence of ibuprofen had no significant impact on arsenic removal. The potential application of ZnFe-MMOs for the simultaneous removal of several pharmaceuticals (ibuprofen, acetaminophen and diclofenac) and arsenic in actual water matrix was also investigated. After 12h, arsenic concentration decreased from 1000 to 1.61μg·L−1 and no pharmaceutical was detected. Possible mechanisms were revealed, indicating that photogenerated h+ was primary reactive species for the photodegradation of ibuprofen, and arsenic species including As(III) and As(V) were removed by the combination of photocatalytic oxidation and surface complexation adsorption. Furthermore, ZnFe-MMOs exhibited good reusability after regeneration, rendering it a promising multi-functional material for the decontamination of polluted water with the coexistent pharmaceuticals and arsenic pollutants.

Photocatalytic organic syntheses using a glass-milled microchip

Abstract Photocatalytic reactions, typically known as difficult to control due to secondary reactions and involvement of multiple radicals, were demonstrated to be controlled well by optimizing the reaction time and the microchip design. The glass-milled microchip has a good resistivity for the organic solutions and withstands multiple usage more than 100 times. The oxidization and reduction reactions were demonstrated and the flow considerably improved the conversion and yield. Furthermore, an imine synthesis was demonstrated as a multi-step reaction by combination of photocatalytic oxidation and reduction reactions.

Biological treatment with fungi of olive mill wastewater pre-treated by photocatalytic oxidation with nanomaterials

Olive mill wastewater (OMW) still is a major environmental problem due to its high chemical oxygen demand (COD) and total phenolic content (TPC), contributing for the high toxicity and recalcitrant nature. Several attempts have been made for developing more efficient treatment processes, but no chemical or biological approaches were found to be totally effective, especially in terms of toxicity reduction. In this context, the main purpose of this study was to investigate the treatability of OMW by the combination of photocatalytic oxidation, using two nanomaterials as catalysts (TiO2 and Fe2O3), with biological degradation by fungi (Pleurotus sajor caju and Phanerochaete chrysosporium). Photocatalytic oxidation was carried out using different systems, nano-TiO2/UV, nano-Fe2O3/UV, nano-TiO2/H2O2/UV and nano-Fe2O3/H2O2/UV. The effectiveness of the treatment was assessed through color (465nm), aromatics (270nm), COD and TPC reductions, as well as by the decrease in toxicity using the bacterium Vibrio fischeri. The chemical treatment with the system nano-TiO2/H2O2/UV promoted 43%, 14%, 38% and 31% reductions in color, aromatics content, COD and TPC, respectively. However no toxicity reduction was observed. The combination with a biological treatment increased the reduction of COD and TPC as well as a reduction in toxicity. The treatment with P. chrysosporium promoted the highest reduction in toxicity, but P. sajor caju was responsible for the best reduction in COD and TPC. However, the biological treatment was more effective when no hydrogen peroxide was used in the pre-treatment.

Application of solar photocatalytic ozonation for the degradation of emerging contaminants in water in a pilot plant

Abstract Aqueous mixtures of six commonly detected emerging contaminants (acetaminophen, antipyrine, bisphenol A, caffeine, metoprolol and testosterone), selected as model compounds, were treated by different solar-driven photochemical processes including photolysis, photocatalytic oxidation with Fe(III) or TiO2, photo-Fenton and single, photolytic and photocatalytic ozonations. Experiments were carried out in a compound parabolic collector photoreactor. It was found that photolysis and photocatalytic oxidation using Fe(III) are not effective for the complete removal of the selected contaminants, while TiO2 photocatalysis, photo-Fenton, single, photolytic and photocatalytic ozonations can rapidly remove them and decrease total organic carbon to some extent. The combination of photocatalytic oxidation and ozonation considerably enhances the system efficiency by reducing the ozone demand and energy requirements to completely remove the contaminants. Results also demonstrate that, at the operational conditions applied in this work, the contaminant removal and mineralization by ozone processes takes place in the slow kinetic regime, therefore the application of the ozone combined processes studied instead of single ozonation is recommended. Kinetic considerations on the application of solar photocatalytic processes for mineralization have been also assessed.

Photocatalysis: Light energy conversion for the oxidation, disinfection, and decomposition of water

The results of many-year studies of the relationship between the physical properties and photocatalytic activity of TiO2 and Pt/TiO2 in photocatalytic purification and disinfection of air and water and water photodecomposition with oxygen evolution are presented. Recommendations are given as to finding the optimal method for platinum supporting on TiO2 to achieve the highest possible catalytic activity. Multisite kinetic models of the gas-phase oxidation of simple organic substances are considered. Methods for regenerating the photocatalyst after its deactivation in the oxidation of sulfur-containing organic substances are suggested. New data are discussed on the acceleration of air purification by the combination of photocatalytic oxidation with atmospheric electric discharges, the addition of gaseous hydrogen peroxide, and oxidation on photocatalysts existing in the aerosol state. As compared to pure TiO2, platinated titanium dioxide has a higher capability for disinfection and complete mineralization of microorganisms. Two promising methods for production of hydrogen from water using solar light are presented.

The Effect of Ozone on the Removal Effectiveness of Photocatalysis on Indoor Gaseous Biogenic Volatile Organic Compounds

In this study, the degradation of d-limonene by photocatalytic oxidation (PCO) (titanium dioxide [TiO2]/ultraviolet [UV]) and by the combination of PCO and ozone (O3) (TiO2/UV/O3) was investigated to evaluate the enhancement effect of O3. The degradation of d-limonene by UV/O3 was also investigated for comparison. The experiments were conducted with a quartz photoreactor under various gas flow rates (600–1600 mL min-1), d-limonene concentrations (0.5–9 parts per million [ppm]), and relative humidity (RH) (20–80%). The d-limonene removal efficiency of TiO2/UV/O3, TiO2/UV, and UV/O3 ranged from 62 to 99%, from 49 to 99%, and from 46 to 75%, respectively. The addition of 120-ppb O3 can enhance the d-limonene removal efficiency of PCO up to 12%. The apparent kinetic parameters (apparent rate constants, k apparent and Langmuir adsorption constants, K apparent) of TiO2/UV and TiO2/UV/O3 reactions obtained from fitting Langmuir–Hinshelwood models are TiO2/UV: k apparent = 1.45 × 10−3 ppm-m sec−1, K apparent = 0.34 ppm−1; TiO2/UV/O3: k apparent = 1.83 × 10−3 ppm-m sec−1, and K apparent = 0.35 ppm−1. When RH was higher than 40%, the residual intermediates yield rates of d-limonene of TiO2/UV/O3, TiO2/UV, and UV/O3 reactions ranged from 0.39 to 0.51 μmol carbon m−2 sec−1, 0.56 to 1.96 μmol carbon m−2 sec−1, and 157 to 177 μmol carbon m−3 sec−1, respectively. In the photocatalytic reaction experiments, the addition of 120-parts per billion (ppb) O3 can reduce the residual intermediates yield rates of d-limonene by up to 1.46 μmol carbon m−2 sec−1. These experimental results showed that O3 can enhance the effectiveness of photo-catalysis on the removal of d-limonene.

Removal of gaseous toluene by the combination of photocatalytic oxidation under complex light irradiation of UV and visible light and biological process

Photocatalysis is a promising technology for treatment of gaseous waste; its disadvantages, however, include causing secondary pollution. Biofiltration has been known as an efficient technology for treatment volatile organic compounds (VOCs) at low cost of maintenance, and produces harmless by-products; its disadvantages, include large volume of bioreactor and slow adaptation to fluctuating concentrations in waste gas. A bench scale system integrated with a photocatalytic oxidation and a biofilter unit for the treatment of gases containing toluene was investigated. The integrated system can effectively oxidize toluene with high removal efficiency. The photocatalytic activity of N-TiO 2/zeolite was evaluated by the decomposition of toluene in air under UV and visible light (VL) illumination. The N-TiO 2/zeolite has more photocatalytic activity under complex light irradiation of UV and visible light for toluene removal than that of pure TiO 2/zeolite under UV or visible light irradiation. N-TiO 2/zeolite was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrum analysis (XPS), Fourier transform infrared spectroscopy (FT-IR), and as-obtained products were identified by means of gas chromatography/mass spectrometry (GC/MS). Results revealed that the photocatalyst was porous and was high photoactive for mineralizing toluene. The high activity can be attributed to the results of the synergetic effects of strong UV and visible light absorption, surface hydroxyl groups. The photocatalytic degradation reaction of toluene with the N-TiO 2/zeolite follows Langmuir–Hinshelwood kinetics. Toluene biodegradation rate matches enzymatic oxidation kinetics model.

Ozone enhanced activity of aqueous titanium dioxide suspensions for photodegradation of 4-chloronitrobenzene

The TiO 2/UV/O 3 process has been employed to remove 4-chloronitrobenzene (4-CNB) and compared to UV/air, O 3, TiO 2/O 3, TiO 2/UV/O 2 and UV/O 3 five parallel oxidation pathways. The reaction activities of these six processes were tested in aqueous using electron paramagnetic resonance (EPR) spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. Moreover, the effects of ozone dosage, catalyst dosage and initial solution pH on the degradation of 4-CNB by TiO 2/UV/O 3 process were also investigated. Results showed that the TiO 2/UV/O 3 is the most efficient process for complete mineralization of 4-CNB since the combination of photocatalytic oxidation with ozone has a synergistic effect. The relative intensity of DMPO- OH follows the order of UV/air < O 3 < TiO 2/O 3 < UV/O 3 < TiO 2/UV/O 2 < TiO 2/UV/O 3. In TiO 2/UV/O 3 process, the ozone and catalyst dosage are found to have a significant impact on the process efficiency whereas initial pH has relatively less effect. Chlorine atoms of 4-CNB are absolutely oxidized to chloride anions when the ozone dosage in the range of 5–18 mg/min, or the catalyst dosage ranging from 1.0 to 2.0 g/L. Part of chloride anions would be further oxidized to chlorate(V) ions if the ozone dosage exceeds 24 mg/min, or the catalyst dosage exceeds 2.0 g/L.