Facile preparation and size-dependent photocatalytic activity of Cu_2O nanocrystals modified titania for hydrogen evolution

摘要

Degussa TiO_2 powder (P25) with Cu_2O nanocrystals of different sizes deposited on the surface were prepared by a facile ethanol-induced deposition followed with a calcination process at 350 ℃ and characterized by XRD, XPS, HRTEM and UV-Vis diffuse reflectance spectra, respectively. In our protocol, Cu_2O nanocrystals is formed by reducing Cu(Ⅱ) with the ethanol adsorbed on the surface of P25. The absorption edge as well as photocatalytic activity for H_2 evolution are closely related to the size of the Cu_2O nanocrystals depending on the Cu content in the as-prepared composites. The 0.9 mol% Cu_2O/TiO_2 composite with ca. 4 nm Cu_2O nanocrystals exhibits the highest photocatalytic H_2 evolution rate of 318 μmol h~1 under the illumination of simulant solar light and an apparent quantum efficiency of 28.6% at 365 nm, 397 times higher than that of P25. This enhancement is mainly attributed to the quantum confinement effect of quantum-sized Cu_2O nanocrystals (q-Cu_2O), which can upgrade the conduction band bottom of q-Cu_2O, and thus facilitates the effective separation of photogenerated charge carriers to enhance the photocatalytic activity. The results provided here not only offers a green and simple way for depositing q-Cu_2O on the surfaces of P25 to get the photocatalyst with an excellent photocatalytic activity for H_2 evolution, but also sheds a new insight for the fabrication of efficient p-n heterojunctions for the separation of electron-hole pairs by quantum confinement effect.