Pd loading, Mn+ (n=1, 2, 3) metal ions doped TiO2 nanosheets for enhanced photocatalytic H2 production and reaction mechanism

Abstract

Pd nanoparticles (NPs) loading, main group metal ions doped TiO 2 nanosheets were prepared by a hydrothermal method, followed by photo-deposition of Pd. The samples were characterized, and their photocatalytic hydrogen production activities were tested in a methanol aqueous solution. The effects of cationic charge, radius and concentration of the doping ions (Na + , K + , Mg 2+ , Al 3+ ) on the photocatalytic activities were investigated systematically. The photocatalytic reaction mechanism was discussed by considering the three aspects: specific surface area, light absorption and charge transfer/separation. The results show that the cation dopings significantly increased the photocatalytic activities of the TiO 2 nanosheets, which may be attributed to the enhanced UV-vis light absorption and accelerated charge transfer/separation of the catalysts. Particularly, the Pd/0.2%K + -TiO 2 possesses the highest photocatalytic H 2 production activity (76.6 μmol h −1 ), which is more than twofold higher than that of the undoped Pd/TiO 2 . The apparent quantum efficiency of hydrogen evolution system reaches 3.0% at 365 nm. The high activity of the Pd/K + -TiO 2 may be attributed to the lower electronegativity of K + , caused by the lower cationic charge or the larger cationic radius, compared to Na + , Mg 2+ and Al 3+ . The doping metal cations with higher electronegativity may compete electrons with H + , which eventually partly depressed the reduction of H + to H 2 . • Pd loading main group metal ions doped TiO 2 nanosheets were synthesized. • Effects of cation charge, radius and content on photocatalytic activity were explored. • Photocatalytic H 2 evolution mechanism was discussed based on experimental results. • 0.2% K + doping increased the H 2 production efficiency by more than two times. • Enhanced light absorption and charge transfer due to M + doping led to higher activity.