Overall splitting of water by RuO2-loaded PbWO4 photocatalyst with d10s2-d0 configuration

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 H-2 and O-2 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 N-2 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 d(10)s(2)-d(0) 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 d(10)s(2) electronic configuration in photocatalysis has been elucidated.