Comparative evaluation of photon-induced water splitting under visible light irradiation using Cd-doped TiO 2 nanoparticles and nanofibers

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Abstract Nanofibrous morphology and the doping technique can overcome the problem of electron/hole fast recombination and improve the activity of such important photocatalysts under visible light irradiation. In this study, nanoparticulate and nanofibrous forms of Cd-doped TiO2 were synthesized with different cadmium contents. For photocatalysts characterization, SEM, (TEM), EDX, and XRD techniques were used. The nanomorphology, cadmium content, and reaction temperature of Cd-doped TiO2 nanostructures were found to strongly affect the hydrogen production rate. Nanofibrous morphology improves the rate of hydrogen evolution by around 2,000 folds over the rate for nanoparticles, due to electron confinement in 0D nanostructures. The average rates of hydrogen production for samples of 0.5 wt% Cd are 0.7 and 16.5 ml/gcat. min for nanoparticles and nanofibers, respectively. We hypothesize that the formation of type II heterostructures between the TiO2 matrix and cadmium nanoparticles is the main reason for the observed enhancement of photocatalytic activity under visible light irradiation. Varying reaction temperature suggests that hydrogen evolution over the proposed catalyst is incompatible with the Arrhenius equation. In particular, reaction temperature was found to have a negative influence on photocatalytic activity. This work shows, for the first time, the prospects for using low-cost Cd as a co-catalyst in photon-induced water splitting and indicates a substantial enhancement in the rate of H2 production when using the Cd-doped TiO2 nanofiber photocatalyst.

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