Yushi MITA
Effects of metal ion substitution on the photocatalytic activity of metal oxides fot water splitting reaction
Kazunori SATO
The production of hydrogen, being a clean energy source, from water by photocatalysts is among important issues for solving energy crisis and CO2-related environmental problems caused by fossil fuel. In aiming at understanding of the photocatalysis-enhancing factors that are closely associated with the photocatalytic activity, the effects of metal ion substitution on the activity of metal oxide photocatalysts for water splitting were investigated in the present study. A part of Ga3+ metal ions in MgGa2O4 with d10 electronic structure was replaced by In3+ metal ion. The sample was prepared by solid state reaction of MgO, In2O3 and Ga2O3 in air at 1573 K for 16 h, on which fine RuO2 particle were loaded as a co-catalysts by an impregnation-oxidation method. The photocatalytic activity of RuO2/ MgGa2-xInxO4 increased with increasing x, passed thorough a maximum x=0.08, and decreased with further x addition. The highest activity was 6-fold lager than that RuO2/MgGa2O4. The Raman spectra showed that the replacement of Ga3+ by In3+ in MgGa2O4 caused a shift of a peak due to A1g stretching vibration, indicating the distortion of a GaO6 octahedron, which was considered to be responsible for activity enhancement. The DFT calculation showed that the replacement by In3+ increased mobility of photoexcited electrons by the contribution of In5s5p band to the conduction band, and the In3+ replacement also affected the electronic states. In conclusion, the method of partially replacing core metal ions by other metal ions is useful for the activation of metal oxide photocatalysts for water splitting reaction
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