Photocatalytic water splitting using modified GaN:ZnO solid solution under visible light: long-time operation and regeneration of activity.

Overall water splitting using GaN:ZnO solid solution photocatalyst modified with Rh(2-y)Cr(y)O(3) nanoparticles as H(2) evolution cocatalysts under visible light (400 < λ < 500 nm) was examined with respect to long-term durability and regeneration of photocatalytic activity. The rate of visible light water splitting remained unchanged for 3 months (2160 h), producing H(2) and O(2) continuously at a stoichiometric amount. After 6 months of operation, a 50% loss of the initial activity occurred. Regeneration treatment of deactivated catalysts was attempted by reloading the Rh(2-y)Cr(y)O(3) cocatalyst. The degree of activity regeneration depended on the reloading amount. Up to 80% of the initial activity for H(2) evolution could be recovered under optimal treatment conditions. It was also found that deactivation of GaN:ZnO was suppressed to some extent by prior coloading of an O(2) evolution cocatalyst, which helped to suppress oxidative decomposition of GaN:ZnO by valence band holes, thereby improving the durability.