Tin oxide nanocrystals embedded in silica aerogel: Photoluminescence and photocatalysis

Tin oxide nanocrystals were successfully introduced into the mesoporous network of silica aerogels with an aqueous solution deposition process. The success of the tin oxide introduction was evidenced by the drastic reduction in the specific surface area, over 400 m2/g, and pore volume of the resulted SiO2–SnO2 composite aerogels and a shift in nitrogen adsorption–desorption characteristics from type H3 to type H2 hysteresis loop of the type IV isotherm. The crystallinity of the tin oxide nanoparticles was improved and grain size was increased, from 5.5 to 8.5 nm, with increasing the post-reaction thermal treatment temperature. Characterizations of photoluminescence and photocatalysis were performed, and rich photoluminescence emissions were observed. The composite aerogel showed a near band edge emission of the tin oxide nanocrystals at 349 nm and two emission peaks, 318 and 475 nm, attributable to the oxygen deficiency of the silica backbone. Three more emission peaks, 390, 433, 548 nm, were observed, with the 390 nm peak contributed by the oxygen vacancies VO++, the 433 nm peak by the Sn interstitials, and the 548 nm peak by the oxygen vacancies VO+. Photocatalysis performance of the composite aerogel was conducted for photo-degradation of methylene blue and was found achieved by the embedded tin oxide nanocrystals but not by the silica backbone. Products from three thermal treatment temperatures, 400, 500, and 700 °C, were investigated, with those from thermal treatment at or above 500 °C showing better performance in photocatalysis, 73% vs. 62% in conversion, attributable to the better crystallinity realized at or above 500 °C.