Energy level matching for efficient charge transfer in Ag doped - Ag modified TiO2 for enhanced visible light photocatalytic activity

The combined approach of bulk doping and surface modification seems to be rational wherein, the dopant acts as visible light absorber and the surface grafted ion acts as co-catalyst to trap the photo-excited electron. Recently, it was established that if the doped energy levels are similar to the surface energy levels, charge transfer from these doped states to the surface states is enhanced based on the concept of energy level matching. Silver (Ag), whose doped and modified levels are almost similar must exhibit this concept of energy level matching and in fact, a combination of doping and surface modification, i.e. Ag-doped Ag-modified TiO2 gave better results when compared to individually doped or modified samples. Upon photocatalyst excitation, the photo-generated electrons in the TiO2 valence band are excited to the dopant Ag 4d states (0.76 eV below the conduction band) from where they are further transferred to the surface states of Ag and later consumed for the reduction of oxygen through multi-electron reduction leading to an enhancement in the photocatalytic activity. The photocatalysts prepared by this concept of energy level matching have been tested for various self-cleaning applications like decomposition of acetaldehyde and degradation of methylene blue under visible-light illumination. (C) 2019 Elsevier B.V. All rights reserved.