Effects of atomic Ag on AgBr photocatalyst surfaces: a theoretical survey

Abstract

The electronic states and optical properties of atomic Ag on AgBr photocatalyst surfaces have been investigated using density functional theory plus Hubbard U contributions. Upon the adsorption of Ag on the AgBr surfaces, the adsorbed (110) surface favors a new visible absorption, while a new infrared absorption is largely enhanced for the adsorbed (100) surface. These changes of the absorption spectrum are mainly attributed to the MIGS (metal induced gap states) formed in the energy-gap region of the silver bromide. Moreover, the Ag_ad wave functions mixing with the orbitals of the silver ions of the silver bromide obviously impact on the energy levels of the conduction band bottom. Photoexcitations of the adsorbed (110) surface involve dominant electron transfer from Br to the MIGS and the hybridized orbitals in the whole light absorption region, while the new infrared absorption (>600 nm) is attributed to excitation of states of the Ag_ad and the hybridized orbitals on the adsorbed (100) facet. Consequently, the Ag_ad can effectively reduce the silver bromide photolysis, so as to enhance its stability. Free-energy profiles of water dissociation on these surfaces also indicate that the Ag_ad can effectively improve the photocatalytic activity of silver bromide.