Continuous hydrogen production activity over finely dispersed Ag2O/TiO2 catalysts from methanol:water mixtures under solar irradiation: A structure–activity correlation

Ag2O/TiO2 catalysts with varying amounts of Ag2O 0.5, 1, 2, and 5 wt% loadings are prepared by impregnation method and Ag/TiO2 catalyst is prepared by photo deposition method. These catalysts are characterized by XRD, SEM-EDAX, DRS, XPS and TEM techniques. DRS studies clearly showing the expanded photo response of TiO2 into visible region on impregnation of Ag+ ions on surface layers of TiO2 due to the increased number of energy states created by the silver ions in TiO2 surface lattice. TEM images are showing the fine dispersion of silver particles on TiO2 surface. XPS of Ag2O/TiO2 calcined and used catalysts along with Ag2O/TiO2 reduced and Ag/TiO2 photo deposited catalysts are compared and the binding energy values of Ti 2p, O1s and Ag 3d are confirming that silver ions are in interaction with TiO2 in Ag2O/TiO2 calcined catalysts. EDAX analysis supports the presence of silver species on the surface layers of TiO2. Photocatalytic hydrogen production activity studies are conducted over Ag2O/TiO2, Ag2O/TiO2 reduced and Ag/TiO2 photo deposited catalysts in pure water and methanol:water mixtures under solar irradiation. Maximum hydrogen production of 145 μmoles/h is observed on 0.5wt% Ag2O/TiO2 catalyst in pure water and the maximum hydrogen production of 3350 μmoles/h is observed on 1wt% Ag2O/TiO2 catalyst in methanol:water mixtures. Whereas Ag2O/TiO2 reduced and Ag/TiO2 photo deposited catalysts are not showing any hydrogen production activity either in water or in methanol:water mixtures under solar irradiation. Based on the XPS, DRS, TEM, SEM-EDAX studies and the hydrogen production activity on these catalysts, a structure–activity correlation has been proposed wherein the interacted Ag+ ions on the surface layers of TiO2 are playing an important role in maintaining the hydrogen production activity under solar irradiation.