ZHOU Peng1,2, ZHAO Chengjian3, DONG Wenping3, LV Gongxuan1
(1. State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China; 2.The College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China;3. Institute of Space Medico Engineering of China, Beijing 100094, China )
Abstract: The hydrophilic -OH group and aromatic benzene ring were modified to the surface of synthetic Pt/ZnS-CdS/SiO2 complex photocatalyst through acrylate resin adhesive and epoxy resin. Then the particles were respectively calcined in atmosphere and hydrogen at different temperature. The photocatalytic hydrogen-producing activity of the resulting photocatalysts was investigated. The results showed that modification and heat treatment made the catalyst’s activity decrease 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 from 18 nm to 6 nm 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 of 450 to 800 nm. The absorption edge of the catalyst red shifted from 480 nm to 520 nm after heat treatment at 500 ℃in air, while it blue shifted from 480 nm to 420 nm in hydrogen. 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 underwent heat treatment in air, while the absorption of oxygen containing functions such as C-O and C-O-C were enhanced in hydrogen. 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 reduce 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.
Key words: Pt/ZnS-CdS/SiO2; polymer-modification; surface functional groups; Photocatalytic hydrogen generation
E-mail: gxlu@lzb.ac.cn
Journal of Molecular Catalysis Vol. 26, Issue 3, 2012,265-275
