Photocatalysis by Nanoparticles of Titanium Dioxide

1 downloads 0 Views 568KB Size Report
of these contaminants using conventional water treatment processes has ..... Brookite and anatase are metastable and transform exothermally and irreversibly to.
Materials Science Forum Vol. 764 (2013) pp 130-150 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.764.130

Photocatalysis by Nanoparticles of Titanium Dioxide for Drinking Water Purification: A Conceptual and State-of-Art Review Jatinder Kumar*, Ajay Bansal Department of Chemical Engineering Dr B R Ambedkar National Institute of Technology Jalandhar-144011, Punjab, India E-mail: [email protected] Keywords: Titanium dioxide, photocatalytic degradation.

photocatalysis,

decontamination,

photocatalytic

properties,

Abstract. To overcome the water pollution problems, and to meet stringent environmental regulations, scientist and researchers have been focusing on the development of new water purification processes. One such group of new technologies is advanced oxidation processes (AOPs). Among the AOPs, titanium dioxide photocatalysis has been widely studied on lab scale by the researchers for decontamination of drinking water. In the present chapter, a conceptual as well as state-of-art review of titanium dioxide photocatalysis for water purification has been discussed. Introduction Water is one of the most important resources for human being, as well as animal and plants in the world. With rapid development of science and technology, many industries such as chemical, petrochemical, textile and food etc. are set up worldwide and these industries discharge polluted water leading to contamination of natural water resources. The contamination of drinking water sources with harmful organic substances has been recognized as a major problem worldwide. Among many contaminants, pesticides, pharmaceuticals, and personal care products are now frequently found in water resources and outflows from sewage treatment plants [1-6]. The removal of these contaminants using conventional water treatment processes has been shown to be very difficult; therefore, an increasing number of new treatment technologies are being developed and evaluated. One such group of technologies is advanced oxidation processes (AOPs) [7-8]. The AOPs can completely mineralize the contaminants to CO2, H2O and mineral acids. The majority of AOPs involve the generation of significant amounts of the hydroxyl radicals ( ), which is very effective, nonselective oxidizing agent in aqueous solution. It is the second of the most violent oxidants, and can attack virtually all organic compounds. It reacts 106-1012 times more rapidly than alternative oxidants such as ozone. Many AOPs involve UV radiation energy as an important step in synthesis of HO• radicals, because UV energy, often, appreciably increases the reaction rate of AOPs in comparison with the same technology in the absence of illumination. AOPs based on usage of UV radiation, are called photochemical AOPs [9]. Some of the photochemical AOPs and ozonation based AOPs are shortly described below. H2O2/UV process: Hydrogen peroxide (H2O2) is a weak acid and a powerful oxidant. H2O2 has been widely used in the removal of low levels of pollutants from wastewaters (chlorine, nitrites, sulphites, hypochlorites) and as a disinfectant. However, low reaction rates make its use in the treatment of high levels of All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 220.227.41.253-29/04/13,13:11:19)

Materials Science Forum Vol. 764

131

refractory pollutants ineffective. The oxidizing power of H2O2 can be sensibly improved by cleavage of O-O bond, generating HO• radicals. The mechanism most commonly accepted for the photolysis of H2O2 is the cleavage of the molecule into hydroxyl radicals with a quantum yield of two HO• radicals formed per quantum of radiation absorbed (1). Wavelengths lower than 280 nm must be used to efficiently cleave the O-O bond in H2O2. The rate of photolysis of aqueous H2O2 has been found to be pH dependent, and increases when more alkaline conditions are used. H2O2 + hν → 2HO•

(1)

The use of H2O2 as an oxidant brings a number of advantages in comparison to other methods of chemical or photochemical water treatment; commercial availability of the oxidant, thermal stability and storage on-site, infinite solubility in water and simple operation procedure. On the contrary, there are also some obstacles. The rate of oxidation of the contaminant is limited by the rate of formation of hydroxyl radicals, and H2O2 has a small molar absorption coefficient. Photolysis: The photolysis of water molecules by VUV radiation leads to the formation of hydrogen atoms and hydroxyl radicals as major primary species (2). In addition, small amounts of hydrated electrons (eˉaq) are generated which are immediately trapped by dissolved molecular oxygen for the formation of superoxide radical anions (O2•ˉ). Similarly, hydrogen atoms are immediately transformed into hydroperoxyl radicals (HO2•) by fast reaction with dissolved O2 [10]. In aerated solutions, HO2• and O2•ˉ are rapidly generated from the primary active species (3 and 4). The generated oxidants (HO•, HO2• and O2•ˉ) and reductants (H•, eˉaq, HO2• and O2•ˉ) make possible simultaneous reductions and oxidations in the chemical system. H2O + hν →



O2 + H• →

2

O2 + eˉaq →

2

(H+ + eˉaq) + HO•

(2)



(3)

ˉ

(4)



The important advantage of VUV process is that there is no need for additional chemicals or catalysts besides water. The drawbacks of VUV process are (i) expensive, requirement of transparent reactor material (special quartz glass), and (ii) that absorption of radiation occurs in very thin film of treated solution due to high absorption coefficients of water and organic pollutants at λ below 190 nm. Ozone based AOPs: Ozonation is widely and successfully applied for many types of oxidative water treatments. For water treatment processes ozone is typically produced on-line in an ozone generator fed with dried air or oxygen. To transfer the ozone into the aqueous phase, the ozone-containing gas is diffused into the water via porous plates or turbine-type diffusers located at the bottom of contact equipment. Ozone reacts with reactants primarily with its terminal electrophilic O-atoms. The most often

132

Photocatalytic Materials & Surfaces for Environmental Cleanup III

described types of reactions of aqueous ozone are electron-transfer reactions, for example reaction between hydroperoxide anion (HO2ˉ) and ozone (5), and oxygen-atom transfer reactions, for example reaction between hydroxide anion (HOˉ) and ozone (6) •

HO2ˉ + O3 →

2

HOˉ + O3 →



+ O3ˉ

(5)

+ O2

(6)

Ozone molecule is not stable in aqueous solution. By reactions with HOˉ, or solutes or reactions on surfaces such as on activated carbon, some ozone is consumed, and often transformed into products such as hydrogen peroxide (H2O2) or HO2•. The UV irradiation of the aqueous solution accelerates the decomposition of ozone, generating different reactive oxygen species including H 2O2 and HO• radicals. If the aqueous ozone is exposed to UV radiation of a wavelength below 310 nm, it is very efficiently photolysed to form an excited O atom which adds to H2O forming H2O2 (7 and 8). O3 + hν ( pHzpc conditions, while anionic electron donors and acceptors will be favoured at pH < pHzpc. TiOH + H+ → Ti

2+

TiOH + OHˉ → Ti ˉ + H2O

(35) (36)

Like most photoreactions, photocatalytic reactions are not dramatically sensitive to minor variations in temperature. Thus, the potentially temperature-dependent steps, such as adsorption, desorption, surface migration, and rearrangement do not appear to be rate determining in this case [56]. There are two regimes of the photocatalytic reaction with respect to the UV-photon flux. They comprise a first-order regime for fluxes up to about 25 mW cm-2 in laboratory experiments and a half-order regime for higher intensities. In the former regime, the eˉ/h+ pairs are consumed more rapidly by chemical reactions than by recombination reactions, whereas in the half-order regime, the recombination is dominant. Methods of improving the performance of TiO2 photocatalysis The researchres are continuously trying to improve the structural, electronic and photocatalytic characteristics of TiO2 for its efficient use in pollutant degradation. There are various methods mentioned in the literature which have been utilized to improve the performance of TiO2 photocatalysis. A brief review of those methods is summarized below.

142

Photocatalytic Materials & Surfaces for Environmental Cleanup III

Morphological aspects: A large surface area can be determining factor in certain photodegradation reactions, as a large amount of adsorbed molecules promotes the reaction rate. However, powders with large surface area are usually associated with low crystallinity and large number of crystalline defects, which favour the recombination of electrons and holes leading to a poor photoactivity [57].A balance between surface area and crystallinity must be found in order to obtain the highest photoactivity. Particle size is an important parameter for photocatalytic efficiency, since the predominant way of electron/hole recombination may be different depending on the particle size [44]. It is well known that in the nanometer-size range, physical and chemical properties of titania are modified. Small variations in particle diameters lead to great modifications in the surface/bulk ratio, thus modifying the significance of electron-hole recombination. When the crystallite dimension of a semiconductor particle falls below a critical radius of approximately 10 nm, the photoactivity decreases because of enhancement in recombination rate of electrons and holes. Doping: When a small amount of a noble metal is doped into the TiO2, the electrons and holes produced by the light irradiation are retained on the noble metal and TiO2 semiconductor, respectively because the noble metal trap the electrons, which limit the recombination of the electrons and photo holes, and thus improve the reactivity of the photo catalyst. However, through this approach, the large band gap of TiO2 is not significantly reduced. Doping of TiO2 with precious metal (Pt), metal oxides such as ZnO, Fe2O3 and inorganic components such as N for extended visible light activities has been successfully conducted [58-59]. A recent preliminary investigation by a team of researchers revealed a significant enhancement of visible light activity (up to 60-70% absorbance) by doping a combination of N and C or silver into TiO2 in a nano sol-gel system. Many researchers had already reported that photo catalysts with visible light activity have only achieved light absorbance at < 30%. Doping of TiO2 with various metal ions may improve its photoactivity because of enhancement in light absorption capability, adsorption capacity, and interfacial charge transfer rate [37].

Fig. 5. Effect of metal coating on photocatalytic process.

Materials Science Forum Vol. 764

143

Metal coating: If the redox potential of the metal is higher than that of TiO2, electrons are removed from the TiO2 particles in the vicinity of each metal particle. This results in decrease in electron/hole recombination, as well as to an efficient charge separation [60]. As a consequence of the improved separation of electrons and holes, metal deposition on the TiO2 surface enhances photocatalytic reactions by accelerating the transfer of electrons to dissolved O2 (Fig. 5). Photodeposition is the most commonly used technique in obtaining metal deposits on TiO2 and involves the reduction of metal ions by CB electrons, while the anodic process is represented by the oxidation of water by VB holes. The deposition of metals can be either beneficial or detrimental for photocatalytic degradation in aqueous solution, depending on an amount of loaded metal, chemical nature of the pollutant, and chemical nature of the metal [61]. Photocatlytic treatment of persistent organic pollutants (POPs) Photocatalytic process based on TiO2 is mostly known for oxidation of wide range of organic compounds. This process has attracted an immense attention over the past few years for treatment of organic compounds due to its intriguing advantages over the other processes. Complete mineralization of organic pollutants and the usage of atmospheric oxygen as oxidant are the main advantage of this process. From the aspect of economic considerations, TiO2 photocatalysis has to be cost-effective in capital costs, recurring operation as well as maintenance costs in order to make this approach to be a realistic competitor to other technologies. Alfano et al. [62] had compared several economic analyses done by different research groups and summarized that the treatment cost would strongly depend on the type of waste stream, the desired mode of the plant operation, the design of the photoreactor, and the reliable experimental data that obtained under actual operating conditions. When comparing with the conventional treatment methods, in any event, the cost of chemical disposal such as hazardous by-products and spent adsorbent in an environment friendly means must be included. The first complete mineralisation of an organic compound in water by photocatalysis was reported in 1983 by Pruden and Ollis [63]. Since then, thousands of scientific papers have been published regarding the photocatalytic elimination of organic and inorganic compounds. Photocatalytic oxidation of organic compounds is of considerable interest for environmental applications and in particular for the control and eventual destruction of hazardous wastes. The complete mineralization to CO2, H2O, and associated inorganic components such as HCl, HBr, SO42ˉ, NO3ˉ, of a variety of hydrocarbons via heterogeneous photooxidation on TiO2 has been reported. The general classes of compounds that have been degraded, although not necessarily completely mineralized by semiconductor photocatalysis include alkanes (Methane, isobutene, pentane, heptanes, n-dodecane and cyclohexane etc.), haloalkanes (Chloromethane, tetrachloroethane, dibromoethane, trichloroethane and fluorochloromethane etc.), aliphatic alcohols (Methanol, isopropanol, cyclobutanol, glucose and sucrose), carboxylic acids (Formic, oxalic, malic, benzoic, salicyclic, phthalic, butanoic, 4-aminobenzoic and p-hydroxybenzoic acid), alkenes (Propene and cyclohexene etc.), aromatics (benzene and naphthalene etc.), haloaromatics (Chlorobenzene and bromobenzene etc.), haloalkenes (Hexafluoropentene, perchloroethene, 1,2-dichloroethylene etc.), nitrohaloaromatics (dichloronitrobenzene etc.), phenolic compounds (Phenol, 4-chlorophenol, 4fluorophenol and pentachlorophenol etc.), amides (Benzamide etc.), polymers (polyethylene and

144

Photocatalytic Materials & Surfaces for Environmental Cleanup III

PVC etc.), surfactants (Sodium dodecylsulphate, polyethylene glycol, trimethyl phosphate, tetrabutyleammonium phosphate etc.), herbicides (Methyl viologen, atrazine, propetryne, prometon and bentazon etc.), pesticides (Parathion, lindane, DDT and tetrachlovinphos etc.) and dyes (Methylene blue, methyl orange, rhodamine B and amaranth etc.) [19, 37, 64]. Potable water applications In recent years scarcity of safe drinking water has become a significant challenge to the existence of many communities throughout the world with the Middle East and Southern Europe experiencing particular problems. In addition to different harmful microorganisms in polluted water, cyanotoxins present serious problems to the water industry as existing technologies are not always effective in the removal of such compounds. TiO2 photocatalysis has been proven to be rather effective in removal of a wide range of chemicals and microbiological pathogens from potable water supplies [64]. Humic acids are naturally occuring compounds and must be removed prior to the distribution of water since not only they colour the water, but may solubilise pesticides. The effectiveness of TiO2 photocatalysis has been confirmed by different researchers [65]. Cyanobacterial toxins produced and released by cyanobacteria in freshwater around the world are well documented [66]. Microcystins are the most common of the cyanobacterial toxins found in water, as well as being the ones most often responsible for poisoning animals and humans. Lawton et al. (1999) [66] reported a rapid photocatalytic degradation of microcystin to 7 UV-detectable compounds, 6 of which did not undergo further degradation. Anyway, photocatalytic process removed any residual toxicity from the water together with potential tumour promoting activity. Modern research in the field aimed at supplying microbe-free water has placed particular emphasis on minimization of costs. To date, numerous studies have been carried out demonstrating the germicidal effects of TiO2 photocatalysis [67]. Some authors suggest that the cell membrane is the primary site of attack by reactive HO• radicals [68].They reported results that can be explained by peroxidation of the polyunsaturated phospholipid component of the lipid cell membrane leading to a loss of essential cell functions, e.g., respiratory activity, and in the end, to cell death. Problems in commercialization of photocatalysis Titanium dioxide photocatalysis is an emerging and promising advance oxidation process for air and water purification [21, 69-70]. More than 1200 different organic pollutants have been reportedly as degraded using this technology [19, 21, 70-71]. Despite the many advantages of photocatalysis and the extensive laboratory research done in this field, there are still some factors that hinder the development of large scale photocatalytic oxidation reactors for commercial water treatment. Lack of proper modeling and simulation tools for predicting and analyzing the performance of fullscale systems, and therefore lack of adequate design, scale-up and optimization strategies, is among the key factors restricting the development of commercial water treatment systems utilizing this technology. The modeling, simulation, design, scale-up and optimization of photocatalytic reactors/processes is a tough task because it involves hydrodynamics, mass transfer, chemical reaction and irradiance simultaneously along with other conventional reactor complications such as reactant catalyst contact time, temperature control, and catalyst installation. Commercialization of photocatalysis technology for water purification is the focus of research these days.

Materials Science Forum Vol. 764

145

The use of traditional UV irradiation sources such as mercury vapor lamp is also one of the important factors posing hindrance to the commercial development of photocatalytic technology. The problems in using the conventional UV irradiation source include low life time, power instability, low photonic efficiency, and use of hazardous mercury metal, etc. The use of solar light is an alternate to the UV irradiation, but it needs large installation area. Moreover, the efficiency of the solar process depends upon intensity, direction and availability of the solar light. Now a day, researchers are working on the use of ultraviolet light emitting diodes (UV-LEDs) as source of UV light to overcome the drawbacks of conventional UV irradiation sources. UV-LEDs are new, safer, non-hazardous, longer life time and energy efficient source of UV light [72-73]. Summary Photocatalysis by nanoparticles of titanium dioxide has been widely studied on lab scale by the researchers for decontamination of drinking water. One of the major advantages of this technology lies in its capability to completely mineralize the pollutants into harmless compounds (carbon dioxide, water and mineral acids) without producing any other waste streams in addition to the inactivation of pathogens including protozoa and viruses. A lot of work has been done to improve the performance of titanium dioxide photocatalysis. Despite the many advantages of titanium dioxide photocatalysis and extensive lab research done in this field, there has been very little work done for commercial or industrial use of this technology so far. The major reason for the same is lack of modeling & simulation tools, and scale-up strategies for the development of this technology for commercial use. Commercialization of photocatalysis technology for water purification is the focus of research these days. An overview has been presented in the present chapter on the conceptual as well as state-of-art aspects of titanium dioxide photocatalysis. The potential applications of this technology, for drinking water purification, strongly depend on the future development of the photocatalytic engineering. References [1]

Ternes, T., 1998. Occurrence of drugs in German sewage treatment plants and rivers. Water Research, 32, 3245–3260.

[2]

Kolpin, D. W., Furlong, E. T., Meyer, M. T., Thurman, E., Zaugg, S. D., Buxton, L. B., 2002. Pharmaceuticals, hormones, and other organic wastewater contaminants in U.S. streams, 1999–2000: A national reconnaissance. Environmental Science and Technology, 36, 1202–1211.

[3]

Boyd, G. R., Reemtsma, H., Grimm, D. A., Mitra, S., 2003. Pharmaceuticals and personalcare products (PPCPs) in surface and treated waters of Louisiana, USA and Ontario, Canada. Science of the Total Environment, 311, 135–149.

[4]

Jasim, S. Y., Irabell, A., Yang, P., Ahmed, S., Schweitzer, L. 2006. Presence of pharmaceuticals and pesticides in Detroit river water and the effect of Ozone on removal. Ozone: Science & Engineering, 28, 415–423.

146

Photocatalytic Materials & Surfaces for Environmental Cleanup III

[5]

Na, T., Fang, Z., Zhanqi, G., Cheng, Z., Ming, S., 2006. The status of pesticide residues in the drinking water sources in Meiliangwan bay, Taihu lake of China. Environmental Monitoring and Assessment, 123, 351–370.

[6]

Pasternak, J., 2006. Agricultural pesticide residues in farm ditches of the lower Fraser Valley, British Columbia, Canada. Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 41, 647–669.

[7]

Oppenlander, T., 2004. Photochemical purification of water and air. Weinheim, Wiley– VCH.

[8]

Poyatos, J., Munio, M., Almecija, M., Torres, J., Hontoria, E., Osorio, F., 2009. Advanced oxidation processes for wastewater treatment: state of the art. Water, Air and Soil Pollution , 205, 187–204.

[9]

Legrini, O., Oliveros, E., Braun, M., 1993. Photochemical processes for water treatment. Chemical Reviews, 93, 671-698.

[10]

Oppenlander T. 2003. Photochemical purification of water and air. Advanced oxidation processes (AOPs): principles, reaction mechanisms, reactor concepts. Weinheim, WileyVCH.

[11]

Kisch, H., 1989. What is Photocatalysis, in photocatalysis: Fundamentals and applications, ed by N. Serpone and E. Pelizzetti, 1-7. New York, Wiley.

[12]

Fenton H. J. J., 1894. Oxidation of tartaric acid in the presence of iron. Journal of Chemical Society, 65, 899-901.

[13]

Litter, M. I., 1999. Heterogeneous photocatalysis: Transitiion metal ions in photocatalytic systems. Applied Catalysis B: Environmental, 23, 89-114.

[14]

Mills, A., Davies, R. H., Worsley, D. 1993. Water purification by semiconductor photocatalysis. Chemical Society Reviews, 22, 417–425.

[15]

Matthews, R. W., 1988. Kinetics of photocatalytic oxidation of organic solutes over titanium dioxide. Journal of Catalysis, 111, 264–272.

[16]

Linsebigler, A. L., Lu, G., Yates, J. T., 1995. Photocatalysis on TiO2 surfaces: Principles, mechanisms, and selected results. Chemical Reviews, 95, 735–758.

[17]

Minero, C., Pelizzetti, E., Malato, S., Blanco, J., 1996. Large solar plant photocatalytic water decontamination: Degradation of atrazine. Solar Energy, 56, 411-419.

[18]

Ollis, D. F., Pelizzetti, E., Serpone, N., 1989. Heterogeneous photocatalysis in environment: Application to water purification. In photocatalysis: Fundamentals and applications, ed by N. Serpone and E. Pelizzetti, Willey Interscience, New York, 603-637.

[19]

Mills, A., Hunte, S. L., 1997. An overview of semiconductor photocatalysis. Journal of Photochemistry and Photobiology A: Chemistry, 108, 1–35.

[20]

Carraway, E. R., Hoffmann, A. J., Hoffmann, M. R., 1994. Photocatalytic oxidation of organic acids on quantum-sized semiconductor colloids. Environmental Science and Technology, 28, 786-793.

Materials Science Forum Vol. 764

147

[21]

Hoffmann, M. R., Martin, S. T., Choi W., Bahnemannt, D. W., 1995. Environmental applications of semiconductor photocatalysis. Chemical Reviews, 95, 69–96.

[22]

Khalil, L. B., Mourad, W. E., Rophael, M. W., 1998. Photocatalytic reduction of environmental pollutant Cr (VI) over some semiconductors under UV/visible light illumination. Applied Catalysis B: Environmental, 17, 267-273.

[23]

Ohno, T., Tsubota, T., Toyofuku, M., Inaba, R., 2004. Photocatalytic activity of a TiO2 photocatalyst doped with C4+ and S4+ ions have a rutile phase under visible light. Catalysis Letters, 98, 255-258.

[24]

Fox, M. A., Dulay, M. T., 1993. Heterogeneous Photocatalysis. Chemical Reviews, 93, 341–357.

[25]

Davis, A. P., Huang, C, P., 1991. The photocatalytic oxidation of sulfur-containing organic compounds using cadmium sulfide and the effect on CdS photocorrosion. Water Research, 25, 1273-1278.

[26]

Reutergardh, L. B., Iangphasuk, M., 1997. Photocatalytic decolorization of reactive Azo dye: A comparison between TiO2 and CdS Photocatalysis. Chemosphere, 35, 585- 596.

[27]

Deng, N. S., Wu, F., Luo, F., Xiao, M., 1998. Ferric citrate-induced photodegradation of dyes in aqueous solution. Chemosphere, 36, 3101-3112.

[28]

Bahnemann, D. W., Kholuiskaya, S. N., Dillert, R., Kulak A. I., Kokorin, A. I., 2002. Photodestruction of dichloroacetic acid catalyzed by nano-sized TiO2 particles. Applied Catalysis B: Environmental, 36, 161-169.

[29]

Arabatzis, I. M., Antonaraki, S., Stergiopoulos, T., Hiskia, A., Papaconstantinou, E., Bernard, M. C., Falaras, P., 2002. Preparation, characterization and photocatalytic activity of nanocrystalline thin film TiO2 catalysts towards 3,5-dichlorophenol degradation. Journal of Photochemistry and Photobiology A: Chemistry, 149, 237-245.

[30]

Turchi, C. S., Ollis, D. F., 1989. Mixed reactant photocatalysis : Intermediates and mutual rate inhibition. Journal of Catalysis, 119, 483- 496.

[31]

Pelizzetti, E., Minero, C., Maurino, V., Sclafani, A., Hidaka, H., Serpone, N., 1993. Photocatalytic degradation of nonylphenol ethoxylated surfactants. Environmental Science and Technology, 23, 1380-1385.

[32]

Matthews, R. W., 1984. Hydroxylation reactions induced by near-ultraviolet photocatalysis of aqueous titanium dioxide suspensions. Journal of the Chemical Society, Faraday Transactions, 80, 457-471.

[33]

Turchi, C. S., Ollis, D, F., 1990. Photocatalytic degradation of organic water contaminants: Mechanisms involving hydroxyl radical attack. Journal of Catalysis, 122, 178-192.

[34]

Serpone, N., Sauve, G., Koch, R., Tahiri, H., Pichat, P., Piccinini, P., Pelizzetti, E., Hidaka, H., 1996. Standadization protocol of process efficiencies and activation parameters in heterogeneous photocatalysis: Relative photonic efficiencies. Journal of Photochemistry and Photobiology A: Chemistry, 106, 191-203.

148

Photocatalytic Materials & Surfaces for Environmental Cleanup III

[35]

Augugliaro, V., Davi, E., Palmisano, L., Schiavello, M., Sclafani, A., 1990. Influence of hydrogen peroxide on the kinetics of phenol photodegradation in aqueous titanium dioxide dispersion. Applied Catalysis, 65, 101-116.

[36]

Sclafani, A., Herrmann, J, M., 1996. Comparison of the photoelectronic and photocatalytic activities of various anatase and rutile forms of titania in pure liquid organic phases and in aqueous solution. Journal of Physical Chemistry, 100, 13655-13661.

[37]

Carp, O., Huisman, C. L., Reller, A., 2004. Induced reactivity of titanium dioxide. Progress in Solid State Chemistry, 32, 33-177.

[38]

Fujishima, A., Rao, T. N., Tryk, D. A., 2000. Titanium dioxide photocatalysis. Journal of. Photochemistry and Photobiology C: Photochemistry Reviews. 1, 1-21.

[39]

Cheng, H., Ma, J., Zhao, Z., Qi, L., 1995. Hydrothermal preparation of uniform nanosize rutile and anatase particles. Chemistry of Materials, 7, 663-671.

[40]

So, W. W., Park, S. B., Kim, K. J., Shin, C. H., Moon, S. J., 2001. The crystalline phase stability of titania particles prepared at room temperature by the sol-gel method. Journal of Materials Science, 36, 4299-4305.

[41]

Xu, T., Song, C., Liu, Y., Han, G., 2006. Band structures of TiO2 doped with N, C and B. Journal of Zhejiang University Science B, 7, 299–303.

[42]

Corma, A., 1997. From microporous to mesoporous molecular sieve materials and their use in catalysis, Chemical Reviews, 97, 2373-2419.

[43]

Yin, H., Wada, Y., Kitamura, T., Kambe, S., Murasawa, S., Mori, H., Sakata, T., Yanagida, S., 2001. Hydrothermal synthesis of nanosized anatase and rutile TiO2 using amorphous phase TiO2, Journal of Materials Chemistry, 11, 1694-1703.

[44]

Zhang, Z. B., Wang, C. C., Zakaria, R., Ying, J. Y., 1998. Role of particle size in nanocrystalline TiO2 based photocatalysts. Journal of Physical Chemistry B, 102, 1087110878.

[45]

Xu, Z., Shang, J., Liu, C., Kang, C., Guo, H., Du, Y., 1999. The preparation and characterization of TiO2 ultrafine particles. Material Science and Engineering: B, 56, 211216.

[46]

Maira, A. J., Yeung, K. L., Lee, C. Y., Yue, P. L., Chan, C. K., 2000. Size effect in gasphase photo-oxidation of trichloroethylene using nanometer-sized TiO2 catalysts. Journal of Catalysis, 192, 185-196.

[47]

Almquist, C. B., Biswas, P., 2002. Role of synthesis method and particle size of nanostructures TiO2 on its photoactivity. Journal of Catalysis, 212, 145-156.

[48]

Hoffman, A. J., Yee, H., Mills, G., Hoffmann, M. R., 1992. Photoinitiated polymerization of methyl methacrylate using Q-sized zinc oxide colloids. Journal of Physical Chemistry, 96, 5540-5546.

[49]

Giuseppe, P. L., Langford, C. H., Vichova, J., Vleck, A., 1993. Photochemistry and picosecond absorption spectra of aqueous suspensions of a polycrystalline titaniumdioxide optically transparent in the visible spectrum. Journal of Photochemistry and Photobiology A: Chemistry, 75, 67-75.

Materials Science Forum Vol. 764

149

[50]

Wang, C. C., Zhang, Z., Ying, J. Y., 1997. Photocatalytic decomposition of alogenated organics over nanocrystalline titania. Nanostructured Materials, 90, 583-586.

[51]

Dijkstra, M. F., Panneman, H. J., Winkelman, J. G., Kelly, J. J., Beenackers, A. A., 2002. Modeling the photocatalytic degradation of formic acid in a reactor with immobilized catalyst. Chemical Engineering Science, 57, 4895–4907.

[52]

Al-Ekabi, H., De Mayo, P., 1986. Surface Photochemistry: On the Mechanism of the Semiconductor Photoinduced Valence Isomerization of Hexamethyl-Dewar Benzene to Hexamethylbenzene. Journal of Physical Chemistry, 90, 4075-4080.

[53]

Cunningham, J., Srijaranci, S. J., 1991. Sensitized photo-oxidations of dissolved alcohols in homogenous and heterogeneous systems Part 2. TiO2-sensitized hotodehydrogenations of benzyl alcohol. Journal of Photochemistry and Photobiology A: Chemistry, 58, 361-371.

[54]

Martin, S. T., Herrmann, H., Choi, W., Hoffmann, M. R., 1994. Time-resolved microwave conductivity. Part1-TiO2 photoreactivity and size quantization. Journal of the Chemical Society, Faraday Transactions, 90, 3315-3323.

[55]

Peill, N. J., Hoffmann, M. R., 1998. Mathematical model of photocatalytic fiber-optic cable reactor for heterogeneous photocatalysis. Environmental Science and Technology, 32, 398404.

[56]

Haque, M. M., Muneer, M., Bahnemann, D. W., 2006. Semiconductor-mediated photocatalyzed degradation of a herbicide derivative, chlorotoluron, in aqueous suspensions. Environmental Science and Technology, 40, 4765-4770.

[57]

Saaduon, L., Ayllon, J. A., Jimenez. Becerril, J., Peral, J., Domenech, X., Rodriguez., Clemente, R., 1999. 1, 2-diolates of titanium as suitable precursors for the preparation of photoactive high surface titania. Applied Catalysis B: Environmental, 21, 269-277.

[58]

Chen, D., Ray, A. K., 1999. Photocatalytic kinetics of phenol and its derivatives over UV irradiated TiO2. Applied Catalysis B: Environmental, 23, 143-147.

[59]

Sriprang, N., Kaewchinda, D., Kennedy1, J. D., Milne, S. J., 2000. Processing and sol chemistry of a triol-based sol–gel route for preparing lead zirconate titanate thin films. Journal of American Ceramic Society, 83, 1914-1920.

[60]

Yoshiya, K., Shin-ya, M., Hiroshi, K., Bunsho, O., 2002. Design, preparation and characterization of highly active metal oxide photocatalysts. In: Photocatalysis: science and technology. Kaneko, M., Okura, I., (eds.). Berlin Heidelberg New York, Springer-Verlag: 29-49.

[61]

Hu, C., Tang, Y., Jiang, Z., Hao, Z., Tang, H., Wong, P. K., 2003. Characterization and photocatalytic activity of noble-metal-supported surface TiO2/SiO2. Applied Catalysis A: General, 253, 389-369.

[62]

Alfano, O. M., Bahnemann, D., Cassano, A. E., Dillert, R., Goslich, R., 2000. Photocatalysis in water environments using artificial and solar light. Catalysis Today, 58, 199-230.

[63]

Pruden, A. L., Ollis, D. F., 1983. Degradation of chloroform by photoassisted heterogeneous catalysis in dilute aqueous suspensions of TiO2. Environmental Science and Technology, 17, 628-631.

150

Photocatalytic Materials & Surfaces for Environmental Cleanup III

[64]

Robertson, K. J., Bahnemann, D. W., Robertson, J. M. C., Wood F., 2005. Photocatalytic detoxification of water and air. In: Environmental photochemistry. Part II. Boule, P., Bahnemann, D. W., Robertson P. (eds.). Berlin Heidelberg, Springer-Verlag, 367-423.

[65]

Wiszniowski, J., Robert, D., Surmacz., Gorska, J., Miksch, K., Malato, S., Weber, J. V., 2004. Solar photocatalytic degradation of humic acids as a model of organic compounds of landfill leachate in pilot-plant experiments: influence of inorganic salts. Applied Catalysis B: Environmental, 33, 127-137.

[66]

Lawton, L. A., Robertson, P. K. J., Cornish, B. J. P. A., Jaspars, M., 1999. Detoxification of microcystins (cyanobacterial hepatotoxins) using TiO2 photocatalytic oxidation. Environmental Science and Technology, 33, 771-775.

[67]

Sichel C., Blanco J., Malato S. Fernández-Ibáñez P., 2007. Effects of experimental conditions on E. coli survival during solar photocatalytic water disinfection. Journal of Photochemistry and Photobiology A: Chemistry, 189, 239-246.

[68]

Maness P.-C., Smolinski S., Blake D.M., Huang Z., Wolfrum E.J., Jacoby W.A. 1999. Bactericidal activity of photocatalytic TiO reaction: toward an understanding of its killing mechanism. Applied and Environmental Microbiology, 265, 4094-4098.

[69]

Ollis, D. F., Turchi, C., 1990. Heterogeneous photocatalysis for water purification: contaminant mineralization kinetics and elementary reactor analysis. Environmental Progress, 9, 229–234.

[70]

Herrmann, J., 2005. Heterogeneous photocatalysis: State of the art and present applications. Topics in Catalysis, 34, 49–65.

[71]

Fujishima, A., Zhang, X., 2006. Titanium dioxide photocatalysis: Present situation and future approaches. Comptes Rendus Chimie , 9, 750–760.

[72]

Natarajan T. S., Thomas M., Natarajan, K., Bajaj, H. C., Tayade, R. J., 2011. Study on UVLED/TiO2 process for degradation of Rhodamine B dye. Chemical Engineering Journal, 169,126–134.

[73]

Natarajan, T. S., Natarajan, K., Bajaj, H. C., Tayade, R. J., 2011. Energy Efficient UV-LED source and TiO2 nanotube array-based reactor for photocatalytic application. Industrial & Engineering Chemistry Research, 50, 7753-7762.