Insights into the Photothermal Hydrogen Production from Glycerol Aqueous Solutions over Noble Metal-Free Ti@TiO2 Core-Shell Nanoparticles

Photocatalytic production of hydrogen from renewable sources with platinum group metal-free catalysts is of great importance for environmentally friendly energetics. Herein, Ti@TiO2 core-shell nanoparticles prepared by sonohydrothermal treatment of titanium metal nanoparticles are examined for hydrogen generation from aqueous glycerol solutions under vis/NIR light irradiation. It is shown that photocatalytic reforming of glycerol in the presence of Ti@TiO2 exhibits strong photothermal effect allowing more efficient use of solar energy. Apparent activation energy equal to E-act = 27 +/- 2 kJ mol(-1) indicates that the thermal effect is related to the diffusion of reaction intermediates at catalyst surface rather than to the activation of chemical bonds. The photoexcitation mechanism of Ti@TiO2 particles involves interband transitions in nonplasmonic Ti metal core followed by nonradiative Landau damping. Effective electron-hole separation between Ti core and nanocrystalline TiO2 anatase shell in Ti@TiO2 nanoparticles is confirmed by photoluminescence spectroscopy. In studied system, photothermal hydrogen production is not accompanied by CO2 emission indicating that glycerol is oxidized to glyceric acid without further decarboxylation.