Metal oxide nanocluster-modified TiO₂ as solar activated photocatalyst materials

In this review we describe our work on new TiO₂ based photocatalysts. The key concept in our work is to form new composite structures by the modification of rutile and anatase TiO₂ with nanoclusters of metal oxides and our density functional theory (DFT) level simulations are validated by experimental work synthesizing and characterizing surface-modified TiO₂. We use DFT to show that nanoclusters of different metal oxides, TiO₂, SnO/SnO₂, PbO/PbO₂, NiO and CuO can be adsorbed at rutile and anatase surfaces and can induce red shifts in the absorption edge to enable visible light absorption which is the first key requirement for a practical photocatalyst. We furthermore determine the origin of the red shift and discuss the factors influencing this shift and the fate of excited electrons and holes. For p-block metal oxides we show how the oxidation state of Sn and Pb can be used to tune both the magnitude of the red shift and also its mechanism. Finally, aiming to make our models more realistic, we present some new results on the stability of water at rutile and anatase surfaces and the effect of water on oxygen vacancy formation and on nanocluster modification. These nanocluster-modified TiO₂ structures form the basis of a new class of photocatalysts which will be useful in oxidation reactions and with the suitable choice of nanocluster modifier can be applied to CO₂ reduction.