TiO2 nanocrystals grafted on macroporous silica: A novel hybrid organic–inorganic sol–gel approach for the synthesis of highly photoactive composite material

TiO2–SiO2 composite materials with photocatalytic properties similar to those of slurry powdered TiO2 is obtained by a novel sol–gel synthetic strategy involving the hydrolysis/condensation of TMOS assisted by PEG as templating agent and the grafting of preformed titania nanocrystals onto the macropore walls of the silica matrix. In order to anchor TiO2 particles to the surface of SiO2, avoiding their embedding into silica matrix, functionalization with carboxylic acid or amine derivatives was carried out. The functionalization induces the confinement of titania nanocrystals in PEG, during the silica formation, and allows their dispersion on the silica surface. TiO2–SiO2 materials exhibit high thermal and chemical stability and a photocatalytic activity in the phenol mineralization comparable to that of powder TiO2 in slurry (half degradation time 120 min). These results suggest that the immobilization procedure here reported provides high accessibility of the catalyst active sites preserving the functional properties of the photoactive catalyst.