Overall Splitting of Water by RuO2-Loaded PbWO4 Photocatalyst with d10s2-d0 Configuration
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Abstract
Tetragonal lead tungstate, PbWO4, consisting of a WO4 tetrahedron showed high and stable photocatalytic activity for the overall splitting of water, producing a stoichiometric quantity of H2 and O2 under UV irradiation when loading RuO2 on the metal oxide. The activity was found to strongly depend on the preparation temperature of PbWO4. In the temperature range 773−1273 K, a maximum appeared at around 1023 and 973 K when prepared in air and under a N2 atmosphere, respectively. X-ray diffraction analysis and SEM observation showed that high activity was achieved with a combination of crystallized PbWO4 with a high dispersion of RuO2 particles. The DFT calculation for PbWO4 with the d10s2-d0 electronic configuration showed that the top of the valence band (HOMO) was composed of hybridized O 2p + Pb 6s orbitals, while the bottom of the conduction band (LUMO) consisted of hybridized W 5d + O 2p + Pb 6p orbitals. Considerable dispersion was observed for both the conduction and valence bands, which differed from the small dispersion observed for the photocatalytically inactive CaWO4 with a similar crystal structure. Photoexcited electrons and holes with high mobility were considered to be responsible for the high photocatalytic performance of PbWO4. The useful role of a Pb2+ ion with the d10s2 electronic configuration in photocatalysis has been elucidated.
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