M/TiO2 (M = Fe, Co, Ni, Cu, Zn) catalysts for photocatalytic hydrogen production under UV and visible light irradiation

Abstract

In order to improve the photocatalytic response of TiO₂ to UV and visible light for hydrogen photoproduction, low cost M/TiO₂ semiconductor catalysts were prepared by the impregnation method of five different first row transition metals (M = Fe, Co, Ni, Cu or Zn) on a commercial titania support. The maximum hydrogen production efficiency was achieved for the Cu/TiO₂ photocatalyst, with ∼5000 and ∼220 μmol h⁻¹ g⁻¹ H₂ production rates for UV and visible irradiation, respectively. Ni/TiO₂ and Co/TiO₂ also showed a significant photocatalytic activity when UV light was used. The best performing catalyst, Cu/TiO₂, was characterized by TEM and XPS measurements. The data showed that Cu was highly dispersed over the TiO₂ support and the copper species existed as both reduced Cu⁰/Cu⁺ and oxidized Cu²⁺ on TiO₂. Besides, during the hydrogen production reaction, the reduced Cu was partially oxidized to Cu²⁺ by the transfer of photogenerated holes under UV or visible light irradiation. With UV and visible lamps, the H₂ production rates were higher than those obtained with non-impregnated TiO₂ by factors of 16 and 3, respectively. These results demonstrated that a Cu/TiO₂ photocatalyst could be considered a promising low-cost alternative to the well-known Pt/TiO₂ system for hydrogen production, making the Cu-based catalyst an ideal cost-effective candidate for this reaction.