Effect of key operational factors on decolorization of methyl orange by multi-walled carbon nanotubes (MWCNTs)/TiO2/CdS composite under simulated solar light irradiation

To improve the photocatalytic performance of TiO2, a novel composite of TiO2/CdS nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) was prepared by a sol-gel method. This photocatalyst exhibited a strong photocatalytic activity for the decomposition of methyl orange (MO) in aqueous solution under simulated solar irradiation. The effects of key operational parameters, such as the initial MO concentration, initial pH values, catalyst dosage and the amount of additional H2O2, were systematically studied. The presence of all the anions examined (Cl−, NO3−,SO42−,CO32−andPO43−) had an inhibitory effect on the decolorization of MO. The photocatalyst had good stability, as when it was used for the fifth time, the decolorization efficiency was still about 98.7% after 80 min of irradiation. The simultaneous application of simulated solar and ultrasound irradiation resulted in increased decolorization compared to that achieved by photocatalysis alone. Possible decomposition mechanisms are discussed. The enhanced photocatalytic performance might be attributable to the matched band potentials and the electron transfer between CdS and TiO2 semiconductors. These results showed that the MWCNTs/TiO2/CdS composite prepared in this study was effective and feasible for use in the decolorization of dye-containing wastewater.