| Abstract
| - Tetragonal lead tungstate, PbWO4, consisting of a WO4 tetrahedron showed high and stable photocatalyticactivity for the overall splitting of water, producing a stoichiometric quantity of H2 and O2 under UV irradiationwhen loading RuO2 on the metal oxide. The activity was found to strongly depend on the preparationtemperature of PbWO4. In the temperature range 773−1273 K, a maximum appeared at around 1023 and 973K when prepared in air and under a N2 atmosphere, respectively. X-ray diffraction analysis and SEM observationshowed that high activity was achieved with a combination of crystallized PbWO4 with a high dispersion ofRuO2 particles. The DFT calculation for PbWO4 with the d10s2-d0 electronic configuration showed that thetop of the valence band (HOMO) was composed of hybridized O 2p + Pb 6s orbitals, while the bottom ofthe conduction band (LUMO) consisted of hybridized W 5d + O 2p + Pb 6p orbitals. Considerable dispersionwas observed for both the conduction and valence bands, which differed from the small dispersion observedfor the photocatalytically inactive CaWO4 with a similar crystal structure. Photoexcited electrons and holeswith 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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