Photocatalytic properties of RuO2-loaded β-Ge3N4 for overall water splitting

Germanium nitride, beta-Ge3N4, is studied as a non-oxide photocatalyst for overall water splitting. Nitridation of GeO2 at 1153 K for 10 h under a flow of NH3 results in the production of well-crystallized beta-Ge3N4 particles with a phenacite structure belonging to the hexagonal crystal system. Although the as-prepared beta-Ge3N4 displays negligible activity for overall water splitting, the material becomes photocatalytically active under ultraviolet (UV) irradiation (lambda > 200 nm) when loaded with RuO2 nanoparticles as H-2 evolution sites. The photocatalytic activity of RuO2-loaded beta-Ge3N4 for overall water splitting is strongly dependent on the reaction conditions. The highest activity is obtained when the reaction is carried out in 1 M H2SO4 aqueous solution. The rates of both H-2 and O-2 evolution decreases as the reaction progresses, attributable to photoreduction of O-2, collapse of the catalyst surface by elusion of Ge cations, and loosened interfacial contact between the beta-Ge3N4 and the loaded RuO2 nanoparticles. Up to 80% of the initial activity can be recovered by calcination of the used catalyst at 673 K in air for 5 h followed by reloading with RuO2.