Sunlight photocatalytic activity of CdS modified TiO2 loaded on activated carbon fibers

To improve the photocatalytic application performances of TiO2, in this work, firstly CdS modified Degussa P25 TiO2 (CdS/TiO2) composites were prepared by two methods, sol-gel method and precipitation method. Next they, sol-gel-CdS/TiO2 (sg-CdS/TiO2) and precipitation-CdS/TiO2 (pp-CdS/TiO2), were loaded on activated carbon fibers (ACFs) by dip-coating method using the sodium carboxymethyl cellulose as adhesives. The composites were characterized by XRD, UV-vis absorbance spectra, SEM, EDS and BET. The photocatalytic activities under sunlight were investigated by the degradation of methylene blue. The results showed that CdS/TiO2 composites were mainly composed of anatase-TiO2 and little CdS cubic phases. The absorption wavelengths of sg-CdS/TiO2 and pp-CdS/TiO2 composites were extended to 590 nm and 740 nm, respectively. The absorption edge had a pronounced 'red shift'. From EDS analysis, the elemental contents of CdS/TiO2 were mainly Ti and O and a small quantity of S and Cd. CdS/TiO2 loaded on ACFs were in the form of small clusters, but not very uniform; compared with the original ACFs, the surface area and pore volume of CdS/TiO2/ACFs decreased slightly, respectively, while the average pore diameter was not changed. The photodegradation rate of methylene blue under sunlight with CdS/TiO2/ACFs composites was markedly higher than that of P25-TiO2/ACFs, and the effect of pp-CdS/TiO2/ACFs composites was better than that of sg-CdS/TiO2/ACFs, when irradiated for 180 min, and the photodegradation rate of methylene blue reached to 90.1%. The photodegradation kinetics of the methylene blue fitted with the Langmuir-Hinshelwood equation. The apparent reaction rate constants of sg-CdS/TiO2/ACFs and pp-CdS/TiO2 were 0.0105 min−1 and 0.0146 min−1, respectively, which were about 1.3-1.7 times as large as that of P25-TiO2/ACFs.