| 1The surface structure and properties of visible light driven ZnS-CdS/SiO2photocatalysts for hydrogen generationZnS-CdS/SiO2complex photocatalysts were prepared by co-precipitation method using Na2S and H2S as sulfur source, respectively. The resulting photocatalysts were characterized by HRTEM, XPS, and XRD techniques. The effects of sulfur sources on the surface structure of photocatalysts and their photocatalytic activities for H2production were investigated. Results showed that the ZnS-CdS could be deposited on SiO2efficiently when Na2S was used as sulfur source, as compared with H2S source, and had a surface structure with a CdS core and ZnS shell. Also, the surface structure was varied with the contents of ZnS-CdS and pH values of solution. The loading amounts of ZnS-CdS had significantly influence on the activities and existed an optimum value. It was found that when H2S was used for preparing photocatalysts, the interaction between ZnS-CdS and SiO2increased with the increase of pH values of solution, which facilitated the deposition of ZnS-CdS and promoted the activity for hydrogen generation.2Studies on photocatalytic hydrogen production relating to the surface functional groups’modulation of polymer-modified Pt/ZnS-CdS/SiO2The hydrophilic-OH group and aromatic benzene ring were modified to the surface of synthetic Pt/ZnS-CdS/SiO2complex photocatalyst through acrylate resin and epoxy resin. Then the particles were calcined in atmosphere and hydrogen at different temperature respectively. The photocatalytic hydrogen-producing activity of the resulting photocatalysts was investigated. The results showed that modification and heat treatment resulted in the decrease of catalyst activity by different degrees. The XRD results showed that the characteristic peaks of ZnS and CdS were not changed after modification, but its crystalline changed from cubic-type CdS and hexagonal-type ZnS into hexagonal-type CdS and α-ZnS after heat treatment in air, while the hexagonal structure solid solution Zn0.5Cd0.5S was formed between cubic-type CdS and hexagonal-type ZnS in hydrogen. The heat treatment of unmodified catalysts in both air and hydrogen led to the same phase transformation. HRTEM results showed that the catalyst’s average diameter reduced from18nm to6nm after surface modification, while the surface structure of a CdS core and ZnS shell was not changed. UV-Vis DRS results showed that the light absorption of the compound semiconductor materials enhanced after modification and heat treatment in the range of450to800nm. The absorption edge of the catalyst red shifted from480nm to520nm after heat treatment at500℃in air, while its blue shift from480nm to420nm in hydrogen treatment was observed. Despite the interface-modified catalysts’ photoabsorption performance were improved, the hydroxyl absorption was enhanced after modification, and the characteristic absorption of benzene ring appeared. IR results showed that these functional groups had significant difference after heat treatment. Some oxygen containing functional groups desorbed and the hydroxyl absorption was enhanced when the sample was underwent heat treatment in air, while the absorption of oxygen containing functions such as C-O and C-O-C were enhanced in hydrogen treatment. These changes were also confirmed by TG-DTA results. The decrease of hydrogen-producing activity may be attributed to the reduction of the reaction system’s dispersion and separation efficiency of photogenerated charges, both of which were caused by the reduction of the surface hydroxyl groups. The oxygen containing functional groups on the catalyst surface occupied the catalytic active sites and reduced the particles’dispersion in aqueous solution. |
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