Mineralization of anionic dyes over visible light responsive Cd(x)Zn(y)S–Nb2O5 heterostructured photocatalysts

Abstract

A novel, Cd_xZn_yS–Nb₂O₅ heterostructured photocatalyst is found to have enhanced photocatalytic activity for the degradation and mineralization of a variety of anionic dyes such as acid violet 7, methyl orange and indigo carmine compared to its single phase constituents. This composite catalyst exhibits adsorption enhanced photocatalytic activity and it is found to degrade relatively high concentrations of AV 7 solution (120 ppm) in nearly 45 min using a fluorescent lamp as a source of light (UV < 3%), which has not been reported so far. In this composite system, Cd_xZn_yS exists as a solid solution and both phases, Cd_xZn_yS and Nb₂O₅ exist in a dispersed state. The composite system exhibits improved visible light absorption compared to pure CdS. Photoluminescence and time resolved fluorescence studies indicate an increased lifetime for the photogenerated charge carriers in the composite compared to CdS and Nb₂O₅. The improved activity of the composite is attributed to increased lifetime of the charge carriers as well as to the increased adsorption of the dyes on the composite catalysts. A slight, gradual decrease in the photocatalytic activity is observed during repeated cycles of degradation experiment but the catalyst regains its activity after heat treatment. Based on the experiments with different quenchers, it is concluded that the photogenerated holes play a significant role in the degradation reaction.