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