Improved hydrogen production from glycerol photoreforming over sol-gel derived TiO2 coupled with metal oxides

Aiming at improving photocatalytic hydrogen production with TiO2, a series of TiO2 coupled with metal oxide nanoparticles have been prepared by a sol-gel method with a fixed molar ratio in various compositions. The photocatalysts were characterized by surface and bulk techniques (XRD, FESEM, HRTEM etc.) and UV-vis DRS method was employed to understand the optical properties. The as-prepared TiO2 coupled with metal oxide was mainly present as anatase, and the anatase grain sizes were reduced comparing to that in bare TiO2, as evidenced by XRD analysis. By analyzing FESEM and DLS results, aggregations of all samples occurred in both dry powder and water suspension. H2 TPR analysis revealed H2 reduction properties of the samples. Among those, Ag2O-TiO2 presented better dispersion stability in different environmental phases. Improved adsorption of the TiO2 for UV-vis light was confirmed. Photoreforming H2 production was improved by the addition of those metal oxides mainly due to the promotion of heterostructure formation where the generated heterostructures could enhance the separation of electrons and holes under UV-vis light. In particular, Ag2O-TiO2 among the samples exhibited the best hydrogen production activities with the maximum quantum efficiency and light-to-hydrogen energy conversion efficiency of 3.02% and 1.15‰, respectively. Considering the effect of glycerol concentration for photoreforming over Ag2O-TiO2, the obtained hydrogen evolution rate fitted a typical kind of Langmuirian catalytic behavior. Langmuir-Hinshelwood-type kinetic model was employed to calculate the corresponding reaction rate constant and glycerol adsorption constant.