Facet-, composition- and wavelength-dependent photocatalysis of Ag$_{2}$MoO$_{4}$

Faceted $\beta$-Ag$_{2}$MoO$_{4}$ microcrystals are prepared by controlled nucleation and growth in diethylene glycol (DEG) or dimethylsulfoxide (DMSO). Both serve as solvents for the liquid-phase synthesis and surface-active agents for the formation of faceted microcrystals. Due to its reducing properties, truncated $\beta$-Ag$_{2}$MoO$_{4}$@Ag octahedra are obtained in DEG. The synthesis in DMSO allows avoiding the formation of elemental silver and results in $\beta$-Ag$_{2}$MoO$_{4}$ cubes and cuboctahedra. Due to its band gap of 3.2 eV, photocatalytic activation of $\beta$-Ag$_{2}$MoO$_{4}$ is only possible under UV-light. To enable $\beta$-Ag$_{2}$MoO$_{4}$ for absorption of visible light, silver-coated $\beta$-Ag$_{2}$MoO$_{4}$@Ag and Ag$_{2}$(Mo$_{0.95}$Cr$_{0.05}$)O$_{4}$ with partial substitution of [MoO4]$^{2-}$ by [CrO4]$^{2-}$ were prepared, too. The photocatalytic activity of all the faceted microcrystals (truncated octahedra, cubes, cuboctahedra) and compositions ($\beta$-Ag$_{2}$MoO$_{4}$, $\beta$-Ag$_{2}$MoO$_{4}$@Ag, $\beta$-Ag$_{2}$(Mo$_{0.95}$Cr$_{0.05}$)O$_{4}$) is compared with regard to the photocatalytic decomposition of rhodamine B and the influence of the respective faceting, composition and wavelength.