Photocatalysis of Titanium Dioxide for Water Disinfection: Challenges and Future Perspectives (original) (raw)
Related papers
Advances in Applied Ceramics, 2012
Water disinfection (removal of microbial agents) using sunlight is an emerging technology, which has the capacity to address the global shortage of drinking water. Therefore, intensive investigations in many laboratories aim to develop photocatalyst for water disinfection. The research is focused on titanium dioxide (TiO 2 ), which is the most promising candidate for high performance photocatalyst able to address the commercial requirements. The present work (Part 1) considers the effect of defect disorder on semiconducting and photocatalytic properties of TiO 2 (rutile) in water disinfection using solar energy. It is shown that photocatalytic properties of TiO 2 in water are closely related to the light induced reactivity of TiO 2 with water leading to the formation of active species, such as OH*, H 2 O 2 and O { 2 , which have the capacity to oxidise microorganisms. It is also shown that the ability of TiO 2 to form the active radicals is closely associated with the presence of point defects in the TiO 2 lattice and the related semiconducting properties. Therefore, photocatalytic properties of TiO 2 may be modified in a controlled manner by changes in its defect disorder. Consequently, defect chemistry may be used as the framework in the development of TiO 2 with controlled properties that are desired for solar water disinfection. The following work (Part 2) considers the structure of bacteria and their reactivity/photoreactivity with TiO 2 in aqueous environments. Both Part 1 and 2 bring together the concepts of TiO 2 photocatalysis and the concepts of microbiology in order to derive the theoretical models that are needed for the development of high performance photocatalysts for solar water disinfection.
A review on the visible light active titanium dioxide photocatalysts for environmental applications
Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
Solar Energy, 2006
Photocatalysis by titanium dioxide (TiO 2), operational in the UV-A domain with a potential use of solar radiation, could be an alternative to conventional water detoxification and disinfection technologies. However, employing the photocatalyst as a suspension or slurry makes the scaling-up of the process difficult, as the TiO 2 has to be removed from the decontaminated water to be reused several times. In this work the photocatalytic activity of different types of TiO 2 catalyst (Degussa P-25, Millennium PC-100 and PC-500, Tayca AMT-100 and AMT-600) in suspension or coated on fibrous web were studied in both decontamination and disinfection experiments at laboratory scale. Gallic acid was chosen as the model pollutant for detoxification experiments and Escherichia coli as the model microorganism for disinfection experiments. The influence of the surface area and other characteristics of TiO 2 are discussed concerning the photocatalytic properties of TiO 2. The role of adsorption is suggested, indicating that the reaction occurs at the TiO 2 surface and not in the solution. Gallic acid degradation kinetics were found to be of the same extent for both TiO 2 suspended and fixed, whereas for the bacterial inactivation efficiency was significantly less important with coated than with suspended TiO 2 .
Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates
Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO.
TiO2 for water treatment: Parameters affecting the kinetics and mechanisms of photocatalysis
Applied Catalysis B: Environmental, 2010
The photocatalytic activity of TiO 2 is the result of an interplay between a considerable number of parameters, e.g., phase composition, electronic structure, particle size, exposed surface area, degree of aggregation, mobility of charge carriers, presence of impurities, amount and kind of defects, adsorption of molecules from gas or aqueous phase, lateral interactions between adsorbed species, nature of solvent, etc. Furthermore, these parameters can be broadly subdivided into those that are intrinsic to the photocatalytic material, and those that are extrinsic being influenced by the surrounding environment and conditions. The specific function and influence of a given feature for the photocatalytic performance of a TiO 2 sample is difficult to characterize since many of the before-mentioned parameters are strongly coupled. For example, while the degree of aggregation could be inherent to a given material, it is also simultaneously influenced by pH. The degree of aggregation can then influence adsorption of molecules, light scattering and photon adsorption, charge carrier dynamics etc. The plurality of variables driving the nature of the photocatalytic activity, presents a challenge when trying to understand the kinetics and mechanisms underlying photocatalytic processes. It is of primary importance to develop a method to understand and control these properties (or at least some of them). In this paper, we also discuss the relevance of quantum-integrated systems in which the local environment where the molecule is adsorbed is different from the "lonely" photocatalyst or the molecule in solution, and could be treated as a whole.
Modified Titanium Dioxide for Photocatalytic Applications
Photocatalysts - Applications and Attributes [Working Title]
Titanium dioxide (TiO 2 ) has been widely used as a photocatalyst in many environmental and energy applications due to its efficient photoactivity, high stability, low cost, and safety to the environment and humans. However, its large band gap energy, ca. 3.2 eV limits its absorption of solar radiation to the UV light range which accounts for only about 5% of the solar spectrum. Furthermore, the photocatalytic activity of TiO 2 is also limited by the rapid recombination of the photogenerated electron-hole pairs. When used in water treatment applications, TiO 2 has a poor affinity toward organic pollutants, especially hydrophobic organic pollutants. Several strategies have been employed to reduce its band gap energy, its electron-hole recombination rates as well as enhance its absorption of organic pollutants. In this chapter, we review some of the most recent works that have employed the doping, decoration, and structural modification of TiO 2 particles for applications in photocatalysis. Additionally, we discuss the effectiveness of these dopants and/or modifiers in enhancing TiO 2 photoactivity as well as some perspective on the future of TiO 2 photocatalysis.
Materials Science in Semiconductor Processing, 2016
During recent years there has been a growing tendency to study new photocatalysts for water and air treatment. To large extent this endeavor is part of a more general effort searching for efficient conversion of solar energy into electricity and into chemical energy stored in hydrogen. Yet, despite the so many man-years invested in this search titanium dioxide is still considered to be the photocatalyst of choice. This paper discusses the current status of research with non-TiO 2 photocatalysts for water decontamination. It suggests that developing of new, highly photoactive photocatalysts for water and air treatment is hindered by a combination of reasons, reflecting the tendency of the scientific community to "search under the streetlight". This includes the overemphasis on bandgap values while overlooking the importance of band positions, the use of dyes as model contaminants under visible light, the ignoring of the importance of transient phenomena, the under-emphasis of the role of surface area and the lack of implementation of theoretical tools in the developing of new photocatalysts. Stepping out of the comfort zone is not only possible but essential.
Influence of water temperature on the photocatalytic activity of titanium dioxide
Reaction Kinetics, Mechanisms and Catalysis, 2012
In this study, it was shown that a possible explanation of increasing photocatalytic activity with temperature may be the fact that with increasing water temperature, the amount of hydroxyl radicals in water also increases, because the ionic product of water increases with an increase in temperature. For measurements of the amount of hydroxyl radicals, the fluorescence technique was used. Terephthalic acid was used as a hydroxyl radical scavenger. After inducing of TiO 2 , positive holes in the valance band may react with OH ions and produce • OH radicals, a strong oxidizing agent.
A Review on TiO 2 Photocatalytic Disinfection of Water with Pathogenic Micro-organisms
During disinfection, the formation of byproducts such as trihalomethanes and other chlorinated byproducts are a major concern. The best alternative to avoid the byproducts formation is photocatalysis. In the past two decades, the studies on photocatalysis have been done using a semiconductor for the treatment of air and water. Among the various semiconductors, TiO 2 is used in various industries as it gives the highest efficiency with the highest stability at a lower cost. This is a powerful process used for disinfecting environment contaminated with pathogenic microorganisms. In this study, a review of previous developments made in the TiO 2 photocatalysis for the disinfection of water contaminated with pathogenic microorganisms is carried out. This paper concludes that TiO 2 photocatalysis can be used in different ways either in suspension or in the form of thin films to disinfect water contaminated with pathogenic microorganisms presenting a potential hazard to animals and human ...