Effect of dye-metal complexation on photocatalytic decomposition of the dyes on TiO2 under visible irradiation

The photocatalytic degradation of dyes (Acid Chrome Blue K (ACBK) and Alizarin Red (AR)) with strong complexation ability was investigated in the presence of metal ions under visible light irradiation. It was found that, at low dye-metal ratio, the photodegradation of ACBK was markedly inhibited by the addition of high oxidative potential Cu2+. However, at high dye-metal ratio, the presence of Cu2+ enhanced the photodegradation of ACBK. The negtive effect of Cu2+ on the photodegradation of AR was observed for all dyemetal ratios. The relative chemical inert Zn2+ tended to enhance the photodegradation of both anionic dyes. The mechanism underlying the different effect of Cu2+ was discussed from the different roles of surface-adsorbed and dye-coordinated Cu2+ in the photodegradation of dyes.