Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: A review of fundamentals, progress and problems

Abstract
Even though heterogeneous photocatalysis appeared in many forms, photodegradation of organic pollutants has recently been the most widely investigated. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its cost effectiveness, inert nature and photostability. Extensive literature analysis has shown many possibilities of improving the efficiency of photodecomposition over titania by combining the photoprocess with either physical or chemical operations. The resulting combined processes revealed a flexible line of action for wastewater treatment technologies. The choice of treatment method usually depends upon the composition of the wastewater. However, a lot more is needed from engineering design and modelling for successful application of the laboratory scale techniques to large-scale operation. The present review paper seeks to offer an overview of the dramatic trend in the use of the TiO2 photocatalyst for remediation and decontamination of wastewater, report the recent work done, important achievements and problems.

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Enhanced photocatalytic disinfection of microorganisms

In this article, palladium modification and silver modification were used as examples to demonstrate the disinfection effects on microorganisms in aqueous environment of photocatalytic transition-metal-ion-modified nitrogen-doped titanium oxide (TiON/M) materials. Transition metal ion modification was applied to TiON to take advantage of the coupling between transition metal ion addition and TiON semiconductor matrix under visible light illumination. The coupling promotes the separation of electron and hole pairs produced by photon excitation, thus it could reduce the intrinsic charge carrier recombination from anion-doping, which largely limits the photoactivity of TiON under visible light illumination. Large enhancements on the hydroxyl radical production and the photocatalytic disinfection efficiency on microorganisms under visible light illumination were observed for TiON with both palladium and silver modifications. The superior photocatalytic performance under visible light illumination suggests that the transition metal ion modification is an effective approach to reduce the massive charge carrier recombination from anion-doping and to enhance the photocatalytic performance of anion-doped TiO2. The resulting photocatalytic materials have the potential for a wide range of environmental applications.

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