Photocatalytic activity of monolithic TiO₂-SiO₂ composite aerogels obtained by ambient drying for degrading oily wastewater

TiO₂-SiO₂ composite aerogels with different contents of SiO₂ were synthesized through a sol-gel route with tetrabutyl titanate and tetraethyl orthosilicate as the raw materials. In combination with solution aging and pinhole drying processes, monolithic TiO₂-SiO₂ composite aerogels were prepared via ambient drying, and their microstructure and the physicochemical properties were studied by scanning electron microscopy, BET method and X-ray diffraction analysis. It is found that the composite aerogels have low density, high specific surface area and show uniform element distribution of Ti and Si. With the increase of SiO₂ content, the density of the composite aerogels decreases gradually, the specific surface area and the porosity increase, and the phase transition temperature to anatase rises. By calcination at high temperature, the composite aerogels change into anatase structure. The photocatalytic properties of the calcined samples were investigated by degradation experiments of the aqueous emulsion of crude oil from the Bohai Sea. The experimental results show that the photocatalytic degradation efficiency of the calcined sample increases with the mole fraction of SiO₂ increasing till 30%, but it decreases when the mole fraction of SiO₂ is above 30%. The best photocatalytic performance is acquired when the calcined sample contains 30% SiO₂, with the catalytic degradation efficiency for 90 min being up to 95%.