Dye-modification effects on water splitting activity of GaN:ZnO photocatalyst

Photocatalytic water splitting activities of GaN:ZnO modified with various porphyrins were investigated. Tetraphenylporphyrinato-chromium(III) chloride (Cr-TPPCl) showed the most positive effect on the photocatalytic activity of GaN:ZnO, and worked without decomposition in the photocatalytic water splitting for 24 h. Fluorescence spectra measurements revealed that photoluminescence intensity of GaN:ZnO was decreased by Cr-TPPCl modification and by loading RhO_X and NiO cocatalysts. It suggests that charge or energy transfer occurs from GaN:ZnO to Cr-TPPCl and from Cr-TPPCl to RhO_X-NiO cocatalysts. Fluorescence lifetime measurement showed electron transfer occurred from GaN:ZnO to Cr-TPPCl, and thus artificial photosynthetic water splitting was achieved on GaN:ZnO photocatalyst modified with various porphyrins under visible light. The apparent quantum efficiency of the dye-modified GaN:ZnO photocatalyst (RhO_X (0.1 wt%), NiO (0.1 wt%)/Dye (0.5 wt%)/IrO ₂ (0.1 wt%)-GaN:ZnO) was 2.73% at 410 nm.