Photocatalytic degradation of chlorobenzene using solar and artificial UV radiation

In this work photocatalytic degradation of chlorobenzene has been studied using solar and artificial UV radiations. The effect of pH and the presence of different anions on the degradation of chlorobenzene has been studied for both cases. Chlorobenzene has been found to be a strongly adsorbing and hence rapidly degrading species when subjected to photocatalysis. The effect of pH in the range of 3–10 and the presence of different anions at a concentration of 0.1 mol dm^?3 on the adsorption was studied. Both pH and the presence of anions affect adsorption and the degradation but the overall effect is negligible (<5%). Copyright © 2004 Society of Chemical Industry     

Photocatalytic degradation of phenols in aqueous solution under irradiation of 254 and 185 nm UV light

The photocatalytic decomposition and mineralization of 4-chlorophenol (4-CP), hydroquinone and 4-nitrophenol (4-NP) in aqueous solution were investigated using two kinds of low-pressure mercury lamps: one was UV (ultraviolet) lamp emitting at 254 nm and the other was VUV (vacuum ultraviolet) lamp emitting at both 254 and 185 nm. VUV irradiation led to the most efficient degradation of the organics. Different mechanisms of photocatalysis and photolysis under VUV irradiation were observed. The degradation rate was subjected to the molecular structures of the substrates. 4-CP was easy to be decomposed, while hydroquinone was easy to be mineralized. However 4-NP was difficult to be decomposed or mineralized. VUV was efficient for decomposition of refractory compounds, such as nitrophenols, and the catalyst was efficient for TOC removal.     

Photocatalytic degradation of ethidium bromide over titania in aqueous solutions

The photocatalytic degradation of ethidium bromide (EtBr), a DNA intercalating pollutant, by TiO₂-based catalysts has been analyzed. Three different titanium dioxide samples synthesized by sol–gel within reverse microemulsions at different pH and thermal treatments were characterized and studied for the photocatalytic degradation of EtBr by oxygen in aqueous solutions. A commercial titania, Degussa P25, was also examined as a reference material for comparative purposes. Appreciable differences in the final structural and surface properties of these titania samples are observed which include disparities in the anatase/rutile proportions, optical absorption characteristics, EtBr chemisorption and acid–base properties. EtBr photodegradation results suggest that catalytic acid–base properties are the most relevant to explain EtBr chemisorption and play an important role in their final photocatalytic behaviour. It is stressed that photocatalysis can be an interesting alternative to other chemical or biological methods for mineralization of EtBr diluted in aqueous solutions.     

Photocatalytic and photochemical degradation of aniline using concentrated solar radiation

The photocatalytic and photochemical degradations (PCD) of aniline using concentrated solar radiation were studied. The photochemical reaction takes place on the surface of the catalyst material. Therefore, the adsorption behavior of aniline on the catalyst was also studied. The rates of aniline degradation in the case of the photocatalytic process were compared with the photochemical method. The effects of the presence of anions and cations, which are commonly present in industrial wastewaters, are reported. A plausible explanation for the anomalous behavior of HCO₃^? and CO₃^2? is given. The effect of pH on the PCD of aniline was also studied. Copyright © 2003 Society of Chemical Industry     

纳米TiO_2-UV光催化降解乙酰甲胺磷影响因素的研究

考察了UV-纳米TiO2光催化降解乙酰甲胺磷的可行性,就高压汞灯照射时间及照射方式、催化剂种类及用量、pH值、反应温度、乙酰甲胺磷初始浓度等对光催化降解效率的影响进行了研究,并探索了催化剂的重复利用。结果表明,当添加0.1 g/L的纳米TiO2（德国P25）,乙酰甲胺磷的起始浓度为20 mg/L,温度控制在25℃,反应体系的pH为11时,以高压汞灯持续照射80 min,即可实现对乙酰甲胺磷99.9%的光催化降解。     

Photocatalytic degradation study of diclofenac over aqueous TiO2 suspensions

Diclofenac (2-[2′,6′-(dichlorophenyl)amino]phenylacetic acid) is a non-steroidal anti-inflammatory drug used to treat inflammatory and painful diseases of rheumatic and non-rheumatic origin. The present work deals with the photocatalytic transformation of diclofenac, under simulated solar irradiation using titania suspensions as catalyst, to assess the decomposition of the pharmaceutical compound, to identify intermediates, as well as to elucidate some mechanistic details of the degradation. The variation of TiO₂ amount and initial diclofenac concentration on the reaction rate, were systematically investigated. The use of the response surface methodology allowed to fit the optimal values of the parameters leading to the degradation of the pollutant. Also, a single polynomial expression modeling the reaction was obtained. Photomineralization of the substrate in terms of chlorine ions release was rather a quick process (within 1 h), while the amino moiety is mainly transformed into NH₄⁺ and in a lesser extend into NO₃⁻ ions. Evolution of CO₂ (loss of TOC) was found to occur within 2 h of irradiation. LC/MS was brought to bear in assessing the temporal course of the photocatalyzed process. Based on our findings a tentative degradation pathway is proposed for the photocatalytic degradation of diclofenac based on the formation of hydroxy-derivatives before the complete mineralization of the starting molecule. In addition Microtox bioassay (Vibrio fischeri) was employed in evaluating the ecotoxicity of solutions treated by photocatalysis. Results clearly demonstrate the efficiency of the photocatalytic process in the detoxification of the irradiated solution.     

Photocatalytic degradation of gaseous perchloroethylene in continuous flow reactors: Rate enhancement by chlorine radicals

The degradation of perchloroethylene (PCE) by UV/TiO₂ photocatalysis in gas phase was studied. The degradation efficiency has been compared in different continuous flow reactors: a photocatalytic tangential reactor (PTR) where the air flows tangentially over the catalytic medium and two photocatalytic filtering reactors (PFR) where the air flows through the porous catalytic medium. The degradation rate shows a linear dependence with the concentration of pollutants (up to 350 mg PCE/N m³) for the PTR, but the degradation was negligible for the PFR. The degradation rate was enhanced by accelerating the chlorine radicals’ formation (by adding HCl in catalytic quantity in the air flow or by PCE over-heating). In these conditions, the oxidation rate constant of PCE in the PFR was about five times higher than that in the PTR, although the mass of catalyst involved in the PFR was about 10 times lower and the contact time was about a 1000 times shorter than that of the PTR. Thus, the catalyst is globally more efficiently used in the PFR, as the mass transfer is not limiting. As a result, a degradation mechanism of PCE, involving the generation of free chlorine radicals, as the first limiting step, has been confirmed.     

纳米TiO2-UV光催化降解乙酰甲胺磷影响因素的研究

考察了UV-纳米TiO2光催化降解乙酰甲胺磷的可行性,就高压汞灯照射时间及照射方式、催化剂种类及用量、pH值、反应温度、乙酰甲胺磷初始浓度等对光催化降解效率的影响进行了研究,并探索了催化剂的重复利用。结果表明,当添加0.1 g/L的纳米TiO2(德国P25),乙酰甲胺磷的起始浓度为20 mg/L,温度控制在25℃,反应体系的pH为11时,以高压汞灯持续照射80 min,即可实现对乙酰甲胺磷99.9%的光催化降解。     

Photocatalytic degradation of omethoate using NaY zeolite-supported TiO2

The degradation of omethoate was conducted using H₂O₂ as oxidant, TiO₂ supported on NaY zeolite as photocatalyst and a 300 W lamp as light source. The effect of the calcination temperature of the photocatalyst, the amount of TiO₂ loaded on NaY zeolite, the photocatalyst amount, the pH value and the radiation time on the degradation ratio of omethoate were investigated. The results show that TiO₂/NaY zeolite photocatalyst prepared by sol-gel method had good photocatalysis. The photocatalytic optimum oxidation conditions of omethoate are as follows: the calcination temperature of the photocatalyst is 550°C,the amount of TiO₂ loaded on NaY zeolite is 35.2 wt-%, the amount of photocatalyst is 5 g/L, pH=8 and the radiation time is 180 min. Under these conditions, the removal ratio of omethoate is up to 93%.     

TiO_2光催化降解林可霉素废水的研究

以250W紫外灯作光源,以TiO2为催化剂,研究了林可霉素光催化降解的合适条件.结果表明,在TiO2用量为0.4 g/L,pH为5.0,林可霉素初始质量浓度为60 mg/L,光催化反应90 min的条件下,林可霉素降解率达到100%.掺杂1%(以物质的量计)Cu2+的TiO2复合催化剂,其光催化活性高于纯TiO2.将优化的光催化降解体系用于林可霉素生产厂废水的处理,可实现林可霉素的完全去除.     

Photocatalytic properties of screen-printed titania

Nanocrystalline thin films of important surface roughness and complexity were prepared by screen-printing of commercial TiO₂ powder. The screen-printed titania films were tested in the photocatalytic decomposition reaction of methyl orange under UV light (350 nm). The photocatalytic activity strongly depends on the titania paste components and especially on the presence of a surface modifier (acetyl acetone) combined with a rheology controlling agent (ethyl cellulose). This results in improvement of the paste viscosity and optimization of the films morphology. Experiments under direct full sunlight illumination prove the importance of the screen-printed films for practical applications.     

Photocatalytic activation of TiO2 under visible light using Acid Red 44

The activation of TiO₂ photocatalyst for photocatalysis under the visible light using Acid Red 44 (C₁₀H₇N=NC₁₀H₃(SO₃Na)₂OH) is described. Adjustment of the pH enhanced the photocatalytic activation of TiO₂ in the presence of visible light. This confirms that the adsorption of a dye on TiO₂ surface is an important factor in dye-photosensitization. The differences in the photocatalytic activation mechanism under visible irradiated conditions with that of UV irradiated condition are proposed. The dye-sensitized photocatalysis under visible light was applied to the decomposition of phenol, is a toxic chemical used in industry and frequently discharged into water.     

TIO2-photocatalyzed degradation of phenol and ortho-substituted phenolic compounds

The photocatalytic degradation of phenol, guaiacol, 2-chlorophenol and catechol in aqueous suspensions of TiO₂ under different experimental conditions has been investigated. The photodegradation of the different organics follows a Langmuir–Hinshelwood kinetics, showing rate constants that decrease in the order: guaiacol>2-chlorophenolphenol>catechol. A similar trend is also observed, except for catechol, for the stability of the σ-complexes that may be formed between the aromatic ring and the OH√ radical. From different analytical techniques (HPLC, GC/MS and HPLC/MS), various hydroxylated intermediate compounds have been reported and different mechanisms of degradation of the starting compounds have been proposed. From experiments performed using aqueous solutions containing the four organics, it is observed that the competitive Langmuir–Hinshelwood kinetics for the degradation of each one of the phenolic compounds is obeyed.     

离子对于TiO_2光催化处理废水的影响

废水中一般会有离子存在,而离子对于TiO2光催化作用的影响是非常显著的。对于水体中常见的阳离子、阴离子、高浓度和多种离子共存的影响进行了归纳和分析,其中对于高浓度和多种离子共存的影响进行探讨是较少见报道的。此简述以期为相关研究的拓展提供参考。     

Photocatalytic oxidation of propene at low concentration

The present paper analyses the preparation and characterisation of different titanium dioxide-based photocatalysts for propene oxidation at low concentration. Special attention has been paid to the agglomeration of the photocatalysts in form of pellets, to the study of the effect of introducing some carbonaceous materials into the catalyst composition and to comparison with commercial photocatalysts. Our results show that P25 exhibits the best activity among all the studied materials. However, activity importantly decreases when agglomerating the photocatalysts in form of pellets, either with or without carbon addition. The type of carbon material used in the photocatalyst strongly affects propene activity. Thus, carbon materials combining high surface area and high electric conductivity enhance the photocatalyst performance and photocatalyst pellets have been prepared exceeding the activity of a carbon-containing commercial photocatalyst. The importance of the UV-source has been highlighted, showing the 257.7 nm peak radiation much better results than the 365 nm UV-light. The studied photocatalysts are very interesting for propene oxidation not only because of their high activity, but also because it remains constant for more than 40 h and total mineralization of the oxidised propene to carbon dioxide and water is achieved.     

Dye sensitized artificial photosynthesis in the gas phase over thin and thick TiO2 films under UV and visible light irradiation

Perylene diimide based organic sensitizers capable of electron generation under illumination were used to initiate gas phase photo reduction reactions on TiO₂ thin and thick film surfaces. For comparison [Ru(Bpy)₃]²⁺ dye sensitizers were also studied. The photo reduction of CO₂ was carried out under static conditions in the gas phase. TiO₂ films were coated on hollow glass beads via a sol–gel procedure. Pt was incorporated on the films either by adding the precursor salt in the sol, Pt(in), or by wet impregnation of calcined film with an aqueous solution of the precursor salt, Pt(on). Organic sensitizers were incorporated on the films by wet impregnation of the film from an aqueous solution. Under UV illumination, the methane yields of platinized TiO₂ thin films decreased in the following order: Pt(on)·TiO₂ > Pt(in)·TiO₂ > TiO₂. The presence of organic sensitizers inhibited the catalytic activity of pure and platinized TiO₂ thick films under UV illumination. The relative enhancement of the reaction yields in the presence of the organic sensitizer under visible light illumination depended on the presence of Pt as well as the incorporation method of Pt in the TiO₂ structure. The reaction yields were better when Pt was impregnated on the TiO₂ film than when Pt was incorporated in the Ti sol. On the other hand, pure or platinized TiO₂ under visible light illumination was totally inactive indicating the role of the organic dye in generating catalytically active electrons under visible light.     

Photocatalytic dye degradation using lithium borate-bismuth tungstate glass-ceramics

The disposal of wastewater contaminated with dyes is a prevalent global concern that necessitates the implementation of diverse remediation strategies. There are several methods available for the treatment of wastewater, one of which is photocatalytic treatment. The primary objective of this study is to assess the efficacy of a lithium borate-bismuth tungstate glass-ceramic material (0.7Li₂B₄O₇ - 0.3Bi₂WO₆) in the degradation of methylene blue dye through photocatalysis under visible light irradiation conditions. The glass under consideration was prepared using the conventional melt-quench technique. The characterization of the glass was conducted using X-ray diffraction technique and Raman spectroscopy. Additionally, the glass obtained was subjected to various heat treatments in order to achieve crystallization, as assisted by differential scanning calorimetry as reported. The elemental analysis and morphology of the glass ceramics that were prepared were examined using X-ray photoemission spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). The glass-ceramic sample exhibited a dye degradation efficiency of 73% within a time span of 240 min. The evaluation of the active species involved in degradation is also conducted through the utilisation of a scavenger test. The experiments were conducted multiple times to verify the effectiveness of the prepared glass-ceramic material for water purification purposes.     

Remediation of pesticide contaminated soil using TiO2 mediated by solar light

Heterogeneous photocatalytic degradation of the pesticide Diuron (Nortox, 3-(3,4-dichlorophenyl)-1,1-dimethylurea) was carried under laboratory conditions to evaluate the potential use of this technology for in situ remediation. Soil samples were spiked with three Diuron concentrations (10, 50 and 100 mg kg⁻¹), loaded with catalyst TiO₂ and exposed to solar light (22°S and 47°W, with an averaged intensity of 2 mW cm⁻² measured at 365 nm). Different catalyst loads (0, 0.1, 0.5, 1 and 2% w/w) were tested in Diuron contaminated soil (100 mg kg⁻¹) for up to 120 h of exposure. Both the catalyst and the Diuron concentration show no influence on the kinetics of the pesticide degradation. The effects of water (10% w/w) and Ca(OH)₂ (0.1% w/w) were also evaluated. Water increases the degradation rates, whereas the rise in the pH due to Ca(OH)₂ addition shows no measurable effect on the degradation. The photocatalytic treatment using TiO₂ combined with solar light is shown to be very efficient in the destruction of Diuron in the top 4 cm of contaminated soil, with the degradation rate markedly dependent on the irradiation intensity.     

MoO3改性对二氧化钛光催化性能的影响

通过沉淀-浸渍法,利用TiCl4与（NH4）6Mo7O24.4H2O制备了基于MoO3改性TiO2光催化剂。以亚甲基蓝为模型化合物考察了改性方法与MoO3含量对TiO2光催化性能的影响,并通过XRD、UV、IR对改性前后TiO2的晶体结构与光谱特征进行了表征。结果表明焙烧前MoO3改性能够提高TiO2的光催化性能,且MoO3含量为3%时MoO3/TiO2光催化效果最佳;MoO3改性明显改变了TiO2的吸收光谱特征,但是其晶体结构仍以锐钛相存在。