Photocatalytic hydrogen production over mixed Cd Zn sulfide catalysts promoted with nickel or nickel phosphide
Abstract Photocatalytic production of hydrogen has been investigated over irradiated aqueous dispersions of mixed Cd Zn sulfide catalysts (CZS) promoted with nickel or nickel phosphide in the presence of sulfide/sulfite ions as sacrificial electron donors. The CZS composites were prepared by a co precipitation method followed by calcination in air at temperatures in the range of 300 to 600 degC. It has been found that heat treatment at 500 degC results in materials with increased activity for H2 evolution, which is attributed to the formation of the Zn0.78Cd0.22S phase. Photocatalytic performance of CZS(500) is further improved following addition of small amounts of Ni or Ni2P on the photocatalyst surface. The activity of the optimized materials, loaded with 0.05 wt. Ni or 0.25 wt. Ni2P, exhibit similar activity with a Pt promoted CZS(500) catalyst, and is one order of magnitude higher than that of the reference TiO2 catalyst of the same platinum loading (0.25 wt. Pt) Results of long term stability tests show that the 0.25%Ni2P/CZS(500) catalyst is very stable in the presence of S2 /SO32 ions in solution, with cadmium leaching not exceeding 0.1% after 65 h under irradiation. Experiments performed with the use of low (or negative) cost waste materials, such as real wastewater resulting from film printing processes or glycerol solutions, demonstrate that the 0.25%Ni2P/CZS(500) photocatalyst exhibits stable H2 evolution even in the absence of S2 /SO32 ions and has the potential to be used as a solar light responsive photocatalyst for practical applications.