Silica–titania composite aerogels were synthesized via ambient pressure drying by using water glass and titanium tetrachloride as raw materials. The influences of heat-treatment at different temperature with different heating rate on the microstructure and properties of the composite aerogels were investigated by differential thermal analyzer, Fourier transform infrared spectrometer, X-ray diffraction, nitrogen adsorption–desorption, scanning electron microscope and transmission electron microscope analysis. The results indicate that the silica–titania composite aerogels heat-treated at 250 °C exhibited highest specific surface area, pore volume and average pore diameter. When the heat-treatment temperature was higher than 450 °C, the –CH3 groups on the surface of silica–titania composite aerogels would transform into –OH groups gradually, and in the meantime, the composite aerogels network structure would be destroyed gradually and the crystallinity of TiO2 would be improved with the increase of heat-treatment temperature. Particularly, heat-treatment at temperatures above 750 °C would cause serious damage to the network structure of the composite aerogels. The adsorption/photocatalytic activity experiments showed that the composite aerogels heat-treated at 550 °C exhibit highest darkroom adsorption efficiency, and the 650 °C-heat-treated samples exhibited highest efficiency for removing the Rhodamine B from water. 相似文献
The first catalytic asymmetric construction of the cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindole scaffold with potential bioactivity has been developed via chiral phosphoric acid‐catalyzed enantioselective addition reactions of cyclic enaminones to isatin‐derived imines, which afforded a series of cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindoles in high yields and excellent enantioselectivities (up to 99% yield, 97% ee). The investigation of the reaction mechanism suggested that it was facilitated by a dual hydrogen‐bonding activation mode between the two substrates and the chiral phosphoric acid. Besides, this method could be utilized for a large‐scale synthesis with maintained enantioselectivity. This approach will not only offer a useful method for enantioselective construction of the cyclic enaminone‐based 3‐substituted 3‐amino‐2‐oxindole scaffold, but also enrich the research on catalytic asymmetric addition reactions of isatin‐derived imines by using electron‐rich olefins as nucleophiles. More importantly, a preliminary evaluation on the cytotoxicity of some selected products revealed that two of the enantio‐pure compounds exhibited moderate to strong cytotoxicity to A549, 786‐0, ECA109 and BT474 cancer cell lines.