Photocatalytic decolorization and degradation of Congo Red on innovative crosslinked chitosan/nano-CdS composite catalyst under visible light irradiation

The crosslinked chitosan/nano-CdS (CS/n-CdS) composite catalyst prepared by simulating bio-mineralization process was extensively characterized by FT-IR spectra, XRD, SEM, TEM and TGA. An azo dye, Congo Red (CR), was used as model pollutant to study its photocatalytic activity under visible light irradiation. The influences of catalyst amount, initial CR concentrations, pH of the reaction solution and different anions on CR decolorization and degradation reaction kinetics were investigated. Results of characterization indicated the successful formation of hexagonal phase of CdS on raw chitosan under mild conditions. The photocatalytic degradation was found to follow a pseudo-first-order kinetics according to Langmuir–Hinshelwood (L–H) model. The dye could be decolorized more efficiently in acidic media than alkaline media. The presence of NO3− accelerated evidently the degradation of CR, while the other chosen anions (Br−, SO42− and Cl−) had an inhibitory effect on the decolorization of CR, of which the inhibitory effect of Cl− was the most pronounced. UV–vis spectra were analyzed to indicate that degradation of CR in the solution was the break up of the NN bonds and degradation of aromatic fragment in this reaction system. The recycling experiments confirmed the relative stability of the catalyst.