Since the reported visible light driven H2 production of the self-doped TiO2 and black TiO2,[1-3] the enhanced visible light response photocatalyst has attracted more and more attention. However, severe preparation conditions strongly limit it further practical application.
Herein, we developed a simple and facile chemical reduction route to synthesize the colored TiO2 for enhanced solar-driven H2 production. Stable TiO2@TiO2-x core-shell nanocrystals can be prepared via reductant at mild temperature in large scale like 100 grams. The TiO2-x shell thickness can be tuned by reaction time and temperature. The color of TiO2 sample also gradually changes from white to blue and black. The H2 production was investigated under full solar spectrum, it can produce about 0.6 mmol/hour H2 per 0.1 g TiO2@TiO2-x nanocrystals, which is 7 fold better than that of P25 TiO2 nanocrystals. There is a broad absorption band in the visible light region (400-900 nm) for TiO2@TiO2-x, this absorption band results the H2 evolution rate of ~20 micro-mol/hour per 0.1g TiO2@TiO2-x.
XPS investigation implies that the valence band raise with the reduction degree. The Ti3+ signal can be detected through electron paramagnetic resonance (EPR) technique. And then the Ti3+ signal disappears due to too high concentration of oxygen vacancy with the increase of reduction degree. Theoretical calculation shows there is a new vacancy band just below the conduction band. That results in that TiO2@TiO2-x nanocrystals possess a narrow band gap have visible light response for photocatalytic activity.
Acknowledgement. The financial support from the National Natural Science Foundation of China (No. 61176016), Science and Technology Department of Jilin Province (No. 20121801) and Returnee startup fund of Jilin is gratefully acknowledged. Z.S. thanks the support of the “Hundred Talent Program” of CAS, and Innovation and Entrepreneurship Program of Jilin.
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Changchun Institute of Optics, Fine Mechanics and Physics
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