Visible-light active doped titania for water purification: nitrogen and silver doping

IWA Publishing
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Nanotechnology for Water and Wastewater Treatment, 2013, 1, pp. 189 - 208
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Photocatalysis over semiconductors, mainly Ti02, has been employed and extensively studied over the past few decades (Malato et aI., 2009). The so-called "first generation photocatalYSIS" are characterised by their photoexcitation limited to the UV region of the solar spectrum. Nevertheless, many photocatalysts showed outstanding performance in decomposing a large number of pollutants of water and air. A number of water pollutants belong to the family of biorecalcitrant pollutants (non-biodegradable) and these include pharmaceutical and personal care products, industrial wastes, and a large number of pesticides/herbicides. Many of the emerging pollutants are resistant to conventional water treatment processes, noxious to the environment and some are classified as endoctine disrupting agents. The removal of non-biodegradable pollutants from wastewater poses a serious challenge for the water industry. Generally, advanced oxidation processes (AOP) are employed to achieve this goal. Heterogeneous photocatalysis, as part of AOP, is sometimes adopted as a tool to eliminate these contaminants. However, the high cost associated with the use of photocatalysis to treat such compounds has always been a disadvantage for its large-scale adoption in treatment processes. The high cost is mainly associated with: (1) the energy consumed for the UV light irradiation of the photocatalyst, (2) the energy required for the separation of the photocatalyst particles from water. A total of 40% of the solar light reaching the lithosphere is visible light, whereas UV light accounts only for 5% of the total solar radiation. The development of new photocatalysts that can effectively harvest visible light is crucial for making this technology viable in the waler treatment industry. The use of "second-generation riOz photocatalysts" to harvest visible light from solar energy is gaining popularity (Anpo, 1997). Most of the research involving the use of second generation TiOz photocatalysts has focused on energy conversion and solar cell applications (Yuan et aI., 2006). However, interest is increasing in their potential for treating water pollutants (ChatteIjee & Dasgupta, 2005; Malato et al., 2009; Rehman et al., 2009). In particular, the large surface areas of nanoparticulate Ti02 materials make them particularly interesting in this regard. In addition, the ability to introduce dopants into the Ti02 stmcture allows the optical properties of the nanomaterials to be manipulated. In this chapter, doped second generation Ti02 photocatalysts are reviewed in the context of water pollutant treatment.
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