Visible light sensitive photocatalyst, delafossite structured α-AgGaO2

Delafossite structured alpha-AgGaO2 powder was successfully synthesized through a cation exchange reaction. alpha-AgGaO2 has a band gap of 2.4 eV, absorbs visible light up to 520 nm, and effectively decomposes 2-propanol to CO2 via acetone by irradiating with either UV light (300-400 nm) or visible light (420-530 nm). The values of the quantum efficiency are similar (ca. 0.6%) under light irradiations with wavelengths of 365, 390, 430, 470, and 510 +/- 10 nm, but steeply decrease with wavelengths longer than 530 +/- 10 nm, which support a 2.4 eV band gap. In contrast, the other polymorph, beta-AgGaO2 powder, which has a band gap of 2.1 eV, shows a negligible activity when irradiating with either UV light or visible light. The higher oxidation activity of alpha-AgGaO2 is probably due to its larger band gap, which is formed at the top of its valence band in a lower energy region as compared to, beta-AgGaO2. Moreover, the first-principle calculations of alpha-AgGaO2 and beta-AgGaO2 clearly indicate that alpha-AgGaO2 has a remarkably larger dispersed valence band as compared to beta-AgGaO2, which is advantageous to the photocatalytic activity due to the efficient hole conduction.