Preparation of macroporous and mesoporous TiO2 film with various solvents

To investigate the effects of solvents on the microstructure, porous TiO₂ films have been prepared by sol-gel method using hydroxypropyl cellulose as the additive. Ethylene glycol monomethyl ether, propylene glycol monomethyl ether, ethanol, and the mixed solution of half ethylene glycol monomethyl ether and half ethanol were chosen as the solvents. Infrared spectra, scanning electron microscope micrographs, and X-ray diffraction patterns have been studied to characterize the microstructure of the sol and film samples. The results showed that mesoporous TiO₂ films with the pore size around 20 nm, 10 nm and 6 nm were obtained when propylene glycol monomethyl ether, the mixed solution of half ethylene glycol monomethyl ether and half ethanol, and ethanol were used as solvent, respectively. It was found that COC group in the solvent was beneficial to enlarge the pore size, because the oxygen bridge in the COC groups could be pulled out and act with titanoxane polymers. When ethylene glycol monomethyl ether was used as the solvent, macroporous TiO₂ film with pore size around 200 nm was obtained. This can be ascribed to the high enough concentration of effective COC groups of the solvent.