A Systematical Study on Photocatalytic Properties of AgMO2 (M = Al, Ga, In): Effects of Chemical Compositions, Crystal Structures, and Electronic Structures

Four Ag-based semiconductor oxides with visible-light absorption, alpha-AgGaO2, alpha-AgInO2, beta-AgAlO2, and beta-AgGaO2, were prepared to investigate the influences of chemical composition and the crystal structure on the electronic structures and photocatalytic properties of AgMO2 (M = Al, Ga, In). The catalytic efficiencies of these oxides were characterized by testing the photooxidation of gaseous 2-propanol to acetone under visible-light irradiation. The ranking of the activity was alpha-AgGaO2 > beta-AgAlO2 > beta-AgGaO2 > alpha-AgInO2, The electronic structures of these compounds were investigated in terms of density functional theory. These experimental and computational studies of these materials reveal the following: (1) regarding chemical compositions, the conduction bands constructed through hybridization of the Ag 5s5p states with Ga 4s4p states and Al 3s3p states are necessary for promotion of photocatalytic activities under visible light for a-phase and beta-phase, respectively, and (2) regarding crystal structures, the Ag 4d states in the absence of crystal-field splitting in the a-phase are favorable for a well-dispersed valence band that is responsible for higher photocatalytic activity.