Synthesis of Stable Mesostructured Coupled Semiconductor Thin Films:meso-CdS-TiO_2 and meso-CdSe-TiO_2

摘要

Cd(II) ions can be incorporated into the channels of mesostructured titania films, using the evaporation-induced selfassembly (EISA) approach, up to a record high Cd/Ti mole ratio of 25%. The film samples were obtained by spin or dip coating from a mixture of 1-butanol, [Cd(H_2O)_4](NO_3)_2,HNO_3, and Ti(OC_4H_9)4 and then aging the samples under 50% humidity at 30 ℃(denoted as meso-xCd(II)-yTiO_2). The nitrate ions, from nitric acid and cadmium nitrate, play important roles in the assembly process by coordinating as bidentate and bridged ligands to Cd(II) and Ti(IV) sites, respectively, in the mesostructured titania films. The film samples can be reacted under a H_2S (orH_2Se) gas atmosphere to produce CdS (or CdSe) on the channel surface and/or pore walls. However, the presence of such a large number of nitrate ions in the film samples also yields an extensive amount of nitric acid upon H_2S (or H_2Se) reaction, where the nanoparticles are not stable (they undergo decomposition back to metal ion and H_2S or H_2Se gas). However, this problem can be overcome by further aging the samples at 130 ℃ for a few hours beforeH2S (orH_2Se) reaction. This step removes about 90% of the nitrate ions, eliminates the nitric acid production step, and stabilizes the CdS nanoparticles on the surface and/or walls of the pores of the coupled semiconductor films, denoted as meso-xCdS-yTiO_2. However, the H_2Se reaction, additionally, needs to be carried at lower H_2Se pressures in an N_2 atmosphere to produce stable CdSe nanoparticles on the surface and/or walls of the pores of the films, denoted as meso-xCdSe-yTiO_2. Otherwise, an excessive number of Se_8 particles form in the film samples.