Ni(OH)2 modified CdS nanorods for highly efficient visible-light-driven photocatalytic H2 generation

Abstract

Conventional titania photocatalysts possess good activity and stability, but require near-ultraviolet (UV) irradiation (about 4% of the solar spectrum) for effective photocatalysis, which severely limits their practical applications. Here we report the synthesis of new visible-light-driven Ni(OH)2-modified CdS nanorod-type composite photocatalysts by a simple precipitation method using CdS nanorods as a support and Ni(NO3)2 as a nickel hydroxide precursor. A special emphasis is placed on the effect of Ni(OH)2 content in this composite photocatalyst on the photocatalytic rate of H2 production in triethanolamine aqueous solutions under visible light irradiation. This study shows that the photocatalytic H2-production activity of CdS nanorods is significantly enhanced by modifying them with Ni(OH)2. The optimal Ni(OH)2 loading was found to be 23 mol%, which resulted in a visible-light H2-production rate of 5085 μmol h−1 g−1 corresponding to 28% quantum efficiency (QE) at 420 nm, exceeding that of pure CdS and 1wt% Pt loaded CdS nanorods by a factor of 145 and 1.3 times, respectively. This enhanced photocatalytic H2-production activity was achieved because the potential of Ni2+/Ni (Ni2+ + 2e− = Ni, E° = −0.23 V) is less negative than the conduction band (CB) (−0.7 V) of CdS, meanwhile this potential is more negative than the reduction potential of H+/H2 (2H+ + 2e− = H2, E° = 0.0 V), which favors the transfer of CB electrons from CdS to Ni(OH)2 and the reduction of Ni2+ to Ni0. The role of Ni0 is to help the charge separation and to act as a co-catalyst for water reduction, thus enhancing the photocatalytic H2-production activity. This work not only shows a possibility for the utilization of low cost Ni(OH)2 as a substitute for noble metal Pt in photocatalytic H2-production but also demonstrates its capability for the consumption of the pollutant triethanolamine, used as a sacrificial reagent in this process.