Solar photocatalytic decolorization of methylene blue in water

In this study, a photocatalytic decolorization system equipped with immobilized TiO2 and illuminated by solar light was used to remove the color of wastewater. To examine the decoloring efficiency of this system, photocatalytic decolorization of an organic dye such as methylene blue was studied as an example. The effects of light source, pH, as well as the initial concentration of dye were also investigated. It was observed that the solution of methylene blue could be almost completely decolorized by the solar light/TiO2 film process while there was about 50% color remaining with solar irradiation only. In addition, it was found that the decoloring efficiency of solution was higher with solar light irradiation than with artificial UV light irradiation, even though the artificial UV light source supplied higher UV intensity at 254 nm. The color removal rate of methylene blue with solar light irradiation was almost twice that of artificial UV light irradiation. This phenomena was mainly attributed to that some visible light range of solar light was useful for exciting the methylene blue molecules adsorbed on TiO2 film, leading to a photosensitization process undergoing and decoloring efficiency promoted. This solar-assisted photocatalytic device showed potential application for decoloring organic dyes in wastewater.     

Photocatalytic degradation of the herbicide erioglaucine in the presence of nanosized titanium dioxide: comparison and modeling of reaction kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm-1 and 0.984 ppm min-1, respectively. In this work, we also compared the reactivity between the commercial TiO2 Degussa P-25 and a rutile TiO2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO2.     

纳米RuO2－TiO2光电催化处理农药废水研究

采用自制的负载型纳米RuO₂－TiO₂光催化剂对农药厂生产废水进行光电催化降解试验。考察了煅烧时间、催化剂用量、光辐照强度、电流密度、废水初始pH值和反应时间对废水COD和色度去除率的影响。结果表明，自制光催化剂光电催化性能显著，最佳光电催化活性是同样降解条件下、同样含量的Degussa P－25 TiO₂的1.38倍，是Ru_0.3Ti_0.7O₂的1.81倍。其COD和色度去除率分别为64.3%和95.2%。     

Comparison of azo dye degradation efficiency using UV/single semiconductor and UV/coupled semiconductor systems

This study examined degradation of azo dyes using photocatalytic oxidation (UV/semiconductor). The model substrates employed in this work were Procion Red MX-5B and Amaranth, while the photocatalysts were TiO2, ZnO, and SnO2. UV-Vis spectrum analysis demonstrated that the band gap energies of TiO2, ZnO, and SnO2 were 3.17, 2.92, and 4.13 eV, respectively. The band gap energy of SnO2 is insufficient to initiate photocatalytic reaction after UV irradiation (365 nm). The reaction rate constants fit a first-order reaction model and the reaction rate constant of Procion Red MX-5B for TiO2+SnO2 (0.31 h-1) is larger than that of TiO2 (0.24 h-1) and SnO2 at pH 10. The difference between the conduction bands of SnO2 and TiO2 enables the former to act as a sink for the photogenerated electrons. Most of the reaction rate constants had higher values at pH 10 than pH 7, and thus the OH attack could be assumed to represent the main reaction in this investigation. The quantities of sulfate and chloride ions released are below stoichiometry during the degradation. Owing to the sulfonate groups of Amaranth exceeding Procion Red MX-5B, Amaranth had larger electrostatic attraction than Procion Red MX-5B with the surface of ZnO, and also had higher adsorption percentage than Procion Red MX-5B on the surface of ZnO. The trend of adsorption is consistent with the reaction rate constant at pH 7, namely Amaranth>Procion Red MX-5B. The sulfate dissociation rate constant of Amaranth in UV/ZnO at pH 7 (0.49 h-1) approaches the overall rate constant (0.53 h-1); therefore, the first step involved in Amaranth can be suggested to the cleavage of the bonds of the C-S in Amaranth, causing sulfate ion formation.     

Photocatalytic oxidation of xenobiotics in water with immobilized TiO2 on agitator

A novel photocatalytic oxidation reactor, using Degussa P-25 TiO2 as a stationary phase with a thickness of 1.5-2.0 um on the blades of agitator, was developed to study the photocatalytic oxidation of xenobiotics. Particularly in this device, separation of photocatalyst from the purified water after oxidation reaction was not necessary, and no other aeration equipment was required to supply oxygen. To examine the efficiency of this device, photocatalytic degradation of xenobiotic organics such as carbofuran was studied as an example. Results indicated that carbofuran could be degraded completely with mineralization efficiency of 20% after 6 hours of oxidation under the imposed conditions. The mineralization rate of carbofuran was found to follow the pseudo-first order reaction kinetics. Moreover, the rate constant of mineralization was found to be proportional to TiO2 film area and the square root of UV light intensity. These results implied the mineralization efficiency of carbofuran could be improved through increasing TiO2 film area and UV light intensity. Accordingly, this novel device showed potential application for degrading xenobiotics in water.     

Fresnel lens to concentrate solar energy for the photocatalytic decoloration and mineralization of orange II in aqueous solution

The decoloration and mineralization of the azo dye orange II under conditions of artificial ultraviolet light and solar energy concentrated by a Fresnel lens in the presence of hydrogen peroxide and TiO(2)-P25 was studied. A comparative study to demonstrate the viability of this solar installation was done to establish if the concentration reached in the focus of the Fresnel lens was enough to improve the photocatalytic degradation reaction. The degradation efficiency was higher when the photolysis was carried out under concentrated solar energy irradiation as compared to UV light source in the presence of an electron acceptor such us H(2)O(2) and the catalyst TiO(2). The effect of hydrogen peroxide, pH and catalyst concentration was also determined. The increase of H(2)O(2) concentration until a critical value (14.7 mM) increased both the solar and artificial UV oxidation reaction rate by generating hydroxyl radicals and inhibiting the (e(-)/h(+)) pair recombination, but the excess of hydrogen peroxide decreases the oxidation rate acting as a radical or hole scavenger and reacting with TiO(2) to form peroxo-compounds, contributing to the inhibition of the reaction. The use of the response surface methodology allowed to fit the optimal values of the parameters pH and catalyst concentration leading to the total solar degradation of orange II. The optimal pH range was 4.5-5.5 close to the zero point charge of TiO(2) depending on surface charge of catalyst and dye ionization state. Dosage of catalyst higher than 1.1 gl(-1) decreases the degradation efficiency due to a decrease of light penetration.     

Kinetic modeling on photooxidative degradation of C.I. Acid Orange 7 in a tubular continuous-flow photoreactor

The decolorization of C.I. Acid Orange 7 (AO7), an anionic monoazo dye of acid class, was investigated using UV radiation in the presence of H2O2 in a tubular continuous-flow photoreactor as a function of oxidant and dye concentrations, reactor length and volumetric flow rate. The removal efficiency of AO7 depends on the operational parameters and increases as the initial concentration of H2O2 is increased but it decreases when the flow rate and initial concentration of AO7 are increased. The decolorization rate follows pseudo-first order kinetic with respect to the dye concentration. A rate equation for decolorization of AO7 was achieved by kinetic modeling. This model allows predicting concentration of AO7 in different photoreactor lengths for different volumetric flow rates and initial concentrations of H2O2 and AO7. The calculated results obtained from kinetic model were in good agreement with experimental data.     

Degradation of azo dye Procion Red MX-5B by photocatalytic oxidation

The photocatalytic oxidation (PCO) of a monoazo dye Procion Red MX-5B under various physico-chemical conditions was investigated. Degradation of the dye by PCO was enhanced by augmentation in UV intensity, titanium dioxide and hydrogen peroxide concentrations but was inhibited by increase in initial dye concentration. The PCO process was affected by pH in a peculiar way. In the presence of 100 mg/l of TiO2 and the absence of H2O2, the highest reaction rate was observed when the initial pH was 10. With 500 mg/l of TiO2 and 10 mM of H2O2, the reaction was the fastest at initial pH of 3-5. The optimal conditions for the degradation of the dye, at an UV intensity of 17 mW/cm2, were determined to be: TiO2 concentration, 500 mg/l; initial H2O2 concentration, 10 mM; initial pH, 5.0. Monitoring of TOC loss showed that the dye was mineralized by 90% within 80 min under these conditions. Nevertheless, the persistence of a low level of TOC indicated that mineralization was not complete and dead-end product(s) which was (were) resistant to PCO might have accumulated.     

Biosorption and biodegradation of Acid Orange 7 by Enterococcus faecalis strain ZL: optimization by response surface methodological approach

Reactive dyes account for one of the major sources of dye wastes in textile effluent. In this study, decolorization of the monoazo dye, Acid Orange 7 (AO7) by the Enterococcus faecalis strain ZL that isolated from a palm oil mill effluent treatment plant has been investigated. Decolorization efficiency of azo dye is greatly affected by the types of nutrients and the size of inoculum used. In this work, one-factor-at-a-time (method and response surface methodology (RSM) was applied to optimize these operational factors and also to study the combined interaction between them. Analysis of AO7 decolorization was done using Fourier transform infrared (FTIR) spectroscopy, desorption study, UV–Vis spectral analysis, field emission scanning electron microscopy (FESEM), and high performance liquid chromatography (HPLC). The optimum condition via RSM for the color removal of AO7 was found to be as follows: yeast extract, 0.1 %?w/v, glycerol concentration of 0.1 %?v/v, and inoculum density of 2.5 %?v/v at initial dye concentration of 100 mg/L at 37 °C. Decolorization efficiency of 98 % was achieved in only 5 h. The kinetic of AO7 decolorization was found to be first order with respect to dye concentration with a k value of 0.87/h. FTIR, desorption study, UV–Vis spectral analysis, FESEM, and HPLC findings indicated that the decolorization of AO7 was mainly due to the biosorption as well as biodegradation of the bacterial cells. In addition, HPLC analyses also showed the formation of sulfanilic acid as a possible degradation product of AO7 under facultative anaerobic condition. This study explored the ability of E. faecalis strain ZL in decolorizing AO7 by biosorption as well as biodegradation process.     

The pH and anion effects on the heterogeneous photocatalytic degradation of o-methylbenzoic acid in TiO2 aqueous suspension

This investigation used UV light of 365 nm and titanium dioxide in aqueous suspension to study the photocatalytic reaction of o-methylbenzoic acid under the influence of pH values, anion additives and the varieties of titanium dioxide. From experimental results, under the condition of 5 g/l TiO2, pH 3 and light intensity of 2.45 mW/cm2, 0.1 mM of o-methylbenzoic acid could be completely decomposed in 2 h. The reaction was faster with lowering pH, and was found to be apparent first-order following Langmuir-Hinshelwood model. In the presence of anion additives, the inhibitive effect of chloride ions was larger than that of sulfate ions under acidic condition for Degussa brand titanium dioxide, but without influence using Janssen brand. Both brands, however, promoted the mineralization of o-methylbenzoic acid (o-MBA).     

Performance of photocatalytic reactors using immobilized TiO2 film for the degradation of phenol and methylene blue dye present in water stream

TiO2 thin film photocatalyst was successfully synthesized and immobilized on glass reactor tube using sol-gel method. The synthesized TiO2 coating was transparent, which enabled the penetration of ultra-violet (UV) light to the catalyst surface. Two photocatalytic reactors with different operating modes were tested: (a) tubular photocatalytic reactor with re-circulation mode and (b) batch photocatalytic reactor. A new proposed TiO2 synthesized film formulation of 1 titanium isopropoxide: 8 isopropanol: 3 acetyl acetone: 1.1 H2O: 0.05 acetic acid (in molar ratio) gave excellent photocatalytic activity for degradation of phenol and methylene blue dye present in the water. The half-life time, t1/2 of photocatalytic degradation of phenol was 56 min at the initial phenol concentration of 1000 microM in the batch reactor. In the tubular photocatalytic reactor, 5 re-circulation passes with residence time of 2.2 min (single pass) degraded 50% of 40-microM methylene blue dye. Initial phenol concentration, presence of hydrogen peroxide, presence of air bubbling and stirring speed as the process variables were studied in the batch reactor. Initial methylene blue concentration, pH value, light intensity and reaction temperature were studied as the process variables in the tubular reactor. The synthesized TiO2 thin film was characterized using SEM, XRD and EDX analysis. A comparative performance between the synthesized TiO2 thin film and commercial TiO2 particles (99% anatase) was evaluated under the same experimental conditions. The TiO2 film was equally active as the TiO2 powder catalyst.     

Photodecomposition of o-cresol by UV-LED/TiO2 process with controlled periodic illumination

This study investigated the effect of controlled periodic illumination on the photonic efficiency and temporal decomposition behavior of o-cresol by UV/TiO2 process in a slurry reactor using light emitting diodes as the light source. Based on the same UV light intensity of 6.7 W m(-2), the calculated photonic efficiencies increased from 1.5% to 6.3% with the decreasing duty cycle from 1.0 to 0.1 possibly ascribed to the decreasing electron-hole recombination. Actually, the calculated photonic efficiency under periodic illumination at sufficiently intermittence was inferior to, but approached, those under continuous illumination at equivalent average UV light intensity. The calculated electric energy per order increased from 32 to 37 k W h m(-3)order(-1) for experiments conducted with the increasing duty cycle from 0.1 to 1.0, and the electric energy consumption decreased significantly due to the lower duty cycle and average UV light intensity. The photocatalytic decomposition of o-cresol with the UV-light emitting diodes light could be well modeled by the Langmuir-Hinshelwood kinetic equation.     

Kinetics of oxidative decolorization and mineralization of Acid Orange 7 by dark and photoassisted Co2+-catalyzed peroxymonosulfate system

A kinetic model was proposed and used to interpret the experimental data for degradation of Acid Orange 7 (AO7) in aqueous solution induced by Co(2+)/peroxymonosulfate (Co/PMS) reagent in terms of both decolorization and mineralization. The pseudo first-order decolorization rate constants are related to [Co(2+)], [PMS], reciprocal of [H(+)] and [AO7](0). Activation energy of the AO7 decolorization process was determined to be 75.7 kJ mol(-1). UV and visible light can accelerate the decolorization and mineralization process due to different mechanisms. In the combined UV/Co/PMS system, UV light can decompose PMS to generate hydroxyl ((*)OH) and sulfate radicals (SO(4)(*-)), while in the Vis/Co/PMS system, excited AO7 molecules can transfer electrons to PMS or Co(3+) and thus accelerate the decomposition of PMS and catalytic cycle of Co(3+)/Co(2+).     

Bactericidal effect of TiO2 photocatalyst on selected food-borne pathogenic bacteria

Titanium dioxide (TiO(2)) photocatalysts have attracted great attention as a material for photocatalytic sterilization in the food and environmental industry. This research aimed to design a new photobioreactor and its application to sterilize selected food borne pathogenic bacteria, Salmonella choleraesuis subsp., Vibrio parahaemolyticus, and Listeria monocytogenes. The photocatalytic reaction was carried out with various TiO(2) concentrations and Ultraviolet (UV) illumination time. A feasible synergistic effect was found that the bactericidal effect of TiO(2) on all bacterial suspension after UV light irradiation was much higher than that of without TiO(2). As the concentration of TiO(2) increased to 1.0 mg/ml, bactericidal effect increased. However, the bactericidal effect was rapidly abbreviated at TiO(2) concentration higher than 1.25 mg/ml to all selected bacteria. UV illumination time affected drastically the viability of all bacteria with different death rate. Similar trends were obtained from S. choleraesuis subsp. and V. parahaemolyticus that their complete killing was achieved after 3 h of illumination. However, L. monocytogenes was more resistant and its death ratio was about 87% at that time.     

Photocatalytic Degradation of the Herbicide Erioglaucine in the Presence of Nanosized Titanium Dioxide: Comparison and Modeling of Reaction Kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO₂ nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO₂ and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO₂, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO₂ system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir–Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm^{? 1} and 0.984 ppm min^{? 1}, respectively. In this work, we also compared the reactivity between the commercial TiO₂ Degussa P-25 and a rutile TiO₂. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO₂ for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO₂ process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO₂.     

外负载Ce-TiO2/活性炭复合体对亚甲基蓝光催化

用超临界流体沉积法处理过的活性炭(AC)为载体,钛酸丁酯为前驱物,硝酸铈为掺杂剂,乙醇为溶剂,制备了外负载TiO2-Ce/Csurf复合材料。在紫外灯照射下,以亚甲基蓝溶液为标准模拟降解物,研究了复合体不同热处理温度、不同浓度、不同亚甲基蓝浓度、不同铈掺杂量以及不同反应温度对光催化性能的影响。结果表明:外负载催化剂的催化性能要高于纯TiO2和体负载催化剂。铈离子掺杂能抑制TiO2晶粒生长,阻碍了TiO2由锐钛矿型向金红石型的转变。当铈离子掺杂量为1.5%,热处理温度为600℃,亚甲基蓝溶液初始浓度为5.5 mg/L,样品浓度为1.5 g/L时,光催化性能最好。     

The evaluation of electrical energy per order (E(Eo)) for photooxidative decolorization of four textile dye solutions by the kinetic model

Photooxidative decolorization of four textile dyestuffs, C.I. Acid Orange 7 (AO7), C.I. Acid Orange 8 (AO8), C.I. Acid Orange 52 (AO52) and C.I. Acid Blue 74 (AB74), by UV/H2O2 was investigated in a laboratory scale photoreactor equipped with a 15 W low pressure mercury vapour lamp. The decolorization of the dyes was found to follow pseudo-first-order kinetics, and hence the figure-of-merit electrical energy per order (E(Eo)) is appropriate for estimating the electrical energy efficiency. The E(Eo) values were found to depend on the concentration of H2O2, concentration and basic structure of the dye. This study shows that these textile dyes can be treated easily and effectively with the UV/H2O2 process with E(Eo) values between 0.4 and 5 kW h m-3 order-1, depending on the initial concentrations of dyes and H2O2. The kinetic model, based on the initial rates of degradation, provided good prediction of the E(Eo) values for a variety of conditions.     

N掺杂TiO2可见光催化降解有机物机理研究

实验研究了掺杂N的TiO2光催化剂在可见光下对有机物的降解机理,研究方法有:加入自由基俘获剂探索对反应速率的影响、有机物降解过程TOC与脱色比较,化学探针法测定了实验中存在的HO.。结果表明,有机物在脱色的同时苯环也在断裂,说明有机物的降解是受无选择性的氧化剂攻击而完成;除亚甲基蓝以外,加入自由基俘获剂对可见光反应速率均有抑制现象,证明自由基的攻击是有机物可见光催化降解的主要途径。分别以二甲基亚砜和水杨酸为分子探针,实验结果证明了光催化反应系统中存在HO.物种,前者与HO.反应形成特定的偶氮结构有机物在425 nm处有吸收,后者与HO.反应生成2,3-二羟基苯甲酸和2,5-二羟基苯甲酸。亚甲基蓝、苯酚和水杨酸经5 h的可见光催化降解后,其TOC分别降低了62.8%、78.9%和96.0%,说明掺杂N的TiO2有较强的可见光催化降解有机物能力。     

N掺杂TiO_2可见光催化降解有机物机理研究

实验研究了掺杂N的TiO2光催化剂在可见光下对有机物的降解机理,研究方法有：加入自由基俘获剂探索对反应速率的影响、有机物降解过程TOC与脱色比较,化学探针法测定了实验中存在的HO.。结果表明,有机物在脱色的同时苯环也在断裂,说明有机物的降解是受无选择性的氧化剂攻击而完成;除亚甲基蓝以外,加入自由基俘获剂对可见光反应速率均有抑制现象,证明自由基的攻击是有机物可见光催化降解的主要途径。分别以二甲基亚砜和水杨酸为分子探针,实验结果证明了光催化反应系统中存在HO.物种,前者与HO.反应形成特定的偶氮结构有机物在425 nm处有吸收,后者与HO.反应生成2,3-二羟基苯甲酸和2,5-二羟基苯甲酸。亚甲基蓝、苯酚和水杨酸经5 h的可见光催化降解后,其TOC分别降低了62.8%、78.9%和96.0%,说明掺杂N的TiO2有较强的可见光催化降解有机物能力。     

The photocatalytic disinfection of urban waste waters

In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptococcus faecalis, have been used as indexes to test disinfection efficiencies. Different experimental parameters have been checked, such as the effect of TiO2, solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO2 at pH 5 in non-air-purged samples.