Effects of divalent metal ion (Mg2+, Zn2+ and Be2+) doping on photocatalytic activity of ruthenium oxide-loaded gallium nitride for water splitting

The effects of divalent metal ion doping on the photocatalytic activity of GaN powder for overall water splitting were studied. The doping of Zn2+, Mg2+ and Be2+ to GaN converted it to be a remarkably active and stable photocatalyst in the presence of RuO2 as a co-catalyst. Both H2 and O2 were produced from the initial stage of UV light illumination, and the ratio of H2 to O2 attained at the stoichiometric ratio of 2.0 at stationary conditions. Main absorption of undoped GaN was at around 390 nm, and a slight shift to longer wavelength occurred with the divalent metal ion-doped GaN. Undoped GaN showed photoluminescence peak due to band gap transition, whereas Zn2+ and Mg2+-doped GaN generated a broad photoluminescence peak having a center at around 450 nm and a tail extending to 600 nm. In RuO2-dispersed Mg2+-doped GaN, with increasing content of Mg in starting materials used for preparation, the activity increased, whereas photoluminescence intensity decreased. The role of divalent metal ion dopants is concluded to produce p-type GaN, which is able to increase the concentration and mobility of holes.