Few aspects of semiconductor photocatalysis for water purification

Abstract

In this thesis, water purification by semiconductor photocatalysis is considered. In the first part, removal of arsenic (As) from water and wastewater was investigated systematically. Adsorption of As(III) and As(V) on different brands of TiO2 at different pH, photocatalytic reduction of As(V) and As(III) to elemental As, and photocatalytic oxidation of As(III) to As(V) were studied extensively. As kinetic rate of photocatalytic oxidation of As(III) to As(V) is very first and adsorption of As(V) is stronger than As(III) on TiO2, the most viable option to remove arsenic from water and wastewater was found to be photocatalytic oxidation of As(III) to As(V) followed by subsequent adsorption of As(V) on TiO2. Effect of many process parameters such as initial concentration, catalyst loading, light intensity, pH, different brands of TiO2, presence of Fe(III), etc. were studied to determine mechanism of oxidation process and optimal parameter values. In second part of this study, a new photocatalytic reactor, namely Taylor Vortex Reactor (TVR), is developed that creates unsteady Taylor Couette flow in between two co-axial cylinders by recirculating fluids form bulk to the inner cylinder wall, which is coated with TiO2. Systematic experimental investigation for degradation of three different organic compounds was carried out. The effect of Reynolds number and optimal catalyst loading on degradation of the three model compounds were compared for slurry and fixed catalyst system. Experimental results show that photocatalytic reaction in fixed bed system is mass transfer controlled, which could be reduced by Taylor-Couette flow.