Photocatalytic performance of silver TiO2: Role of electronic energy levels

Nano-sized silver deposits on the surface of Degussa P25 TiO2 (Ag-DP25) particles act as sites of electron accumulation where the reduction of adsorbed species takes place. Electrons can be transferred from Degussa P25 TiO2 (DP25) to Ag particles because of the difference in the work functions of the two materials. The efficiency of the electron transfer depends on the size and the distribution of metal deposits. A significant photocatalytic oxidation enhancement by metal deposit will only be observed if the metal deposits play a more dominant role than just increasing the life time of charge carriers. The properties of metal deposits like, loaded amount, oxidation state of the deposit and its size will influence the performance. Further, a decrease in band-gap in DP25 and Ag-DP25 was observed due to the carbide ion substitution for the oxide ion in TiO2. Such unintentional carbon incorporation is expected mostly in combustion synthesized materials. Silver metal deposits and unintentional incorporation of the carbon shows the beneficial effect by specific mechanism in the photocatalytic degradation of Congo Red (CR).