Photocatalytic degradation of pesticides using TiO2 nanoparticles

The problem of water pollution has been an environmental concern for many years. Numerous researchers are looking for an effective method to solve this issue. Heterogeneous photocatalysis, using a semiconductor as a catalyst, is a promising method for the destruction of water polluting pesticides. This method has been called the Advanced Oxidation Process (AOP) which is one of the techniques for water treatment. Titanium dioxide (TiO2) is the most widely accepted photocatalyst because it is non-toxic, stable to photocorrosion, low cost and can potentially work using sunlight rather than artificial sources of light. When titanium dioxide is illuminated by UV radiation, the absorption of photons of energy is then equal to or greater than its band gap width. This artefact leads to the formation of conduction-band electrons and valence-band holes on the surface of TiO2, which yield hydroxyl radicals, the primary oxidising species needed for the photocatalytic degradation of pollutants. Supercritical water hydrothermal synthesis (ScWHS) is one of novel approaches for nanoparticle manufacture which involves the mixing of an aqueous metal salt stream with a supercritical water stream to produce nano-sized metal oxide particles. The engineering design for the mixing of these two fluids is critical and a novel nozzle reactor has been developed at the University of Nottingham that can produce high quality particles with an excellent control over particle size and particle size distribution. By application of this technique, titanium dioxide (TiO2), in nanoparticle form, was produced and used for the photocatalytic treatment of wastewater. In this thesis, the photocatalytic degradation of the three pesticides - isoproturon, simazine and propazine - was measured using 3 different types of reactors: thin film fixed bed reactor (TFFBR), a stirred reactor, and a fluidised bed photoreactor. Various conditions were used: for example without UVC and UVA illumination, with commercial TiO2, with the synthesised TiO2, without any photocatalyst, low concentration, high concentration, and at different TiO2 concentrations. The optimum TiO2 concentration for the treatment of the three chosen pesticides was equal to 5 g litre-1. The efficiency in decreasing the pesticides concentration of the synthesised TiO2 (from ScWHS technique) with all three types of reactors was lower than that of the commercial titanium dioxide (P-25 TiO2). The fluidised bed reactor appeared to give the highest performance amongst three reactors