SYNTHESIS OF VISIBLE LIGHT ACTIVE NANO PHOTOCATALYSTS AND ITS APPLICATION IN TREATMENT AND PRODUCTION OF RENEWABLE ENERGY

Solar photocatalytic reaction systems have been extensively studied for environmental remediation i.e. pollutant degradation in air and water systems and also on energy conversion (hydrogen production and carbon dioxide reduction). Although both applications are based on the same photo induced charge transfer occurring on semiconductor particles, each photocatalytic system (pollutant degradation or hydrogen production) has been practiced separately using different catalytic materials under different experimental conditions. This is because each photocatalytic system is different in the required charge transfer characteristics. The photocatalytic reactions are based on the photo induced charge transfer of the valence band (VB) holes and conduction band (CB) electrons. The degradation of organic pollutants is usually initiated by the transfer of a VB hole or OH radical, which subsequently generates carbon-centered radicals that are further degraded to CO2 and mineral components through a series of radical reactions. In this case, the CB electrons are usually scavenged by dioxygen molecules and the presence of air is essential to achieve the mineralization. On the other hand, the photocatalytic production of hydrogen requires the transfer of two CB electrons to protons and the anoxic condition because O2 preferentially scavenges CB electrons to suppress the formation of hydrogen gas. This means the photocatalytic degradation of organic pollutants is initiated by the single electron transfer under aerated conditions, whereas that for hydrogen production is carried out via two electron transfer in the absence of O2. Because of this reason, the two photocatalytic systems have been practiced separately and combining the two, which is called ?dual function Photocatalysis? i.e. simultaneous production of hydrogen and degradation of pollutants has been a challenging issue. To achieve this goal, the photocatalyst should able to oxidize organic substrates with protons/water and not with O2 as an electron acceptor. In many studies of the photocatalytic production of hydrogen gas, an excess amount of electron donors, e.g. organic acids, alcohols, sulfide/sulfite has been generally used. However, such an approach requiring sacrificial reagents to produce hydrogen is uneconomical and impractical. If organic pollutants present in the system is used instead as electron donors for hydrogen production, the overall process can be cost effective. This research is planned to develop, characterize and test novel visible light active photocatalysts for the dual purpose i.e. treatment of pollutants and production of renewable energy.