Preparation of Porous TiO₂ Cryogel Fibers through Unidirectional Freezing of Hydrogel Followed by Freeze-Drying

Porous titania cryogel fibers (TCFs) were prepared through the unidirectional freezing and subsequent freeze-drying of titania hydrogels, which were synthesized by sol−gel polymerization of titanium tetraisopropoxide (TTIP) using dialysis. By adjusting the concentrations of TTIP, and using freeze-drying after replacing the water included in the titania hydrogel fibers with tert -butyl alcohol, mesoporous TCFs which maintained their unique fiber morphology were successfully prepared. The as-dried TCFs were transparent, contained anatase structure, and had BET surface areas over 400 m 2 /g. Nitrogen adsorption−desorption measurements, powder X-ray diffractometry (XRD), scanning laser microscopy, and scanning electron microscopy (SEM) were used to characterize the physical properties of TCFs. The effect of heat treatment after freeze-drying on the porous properties and crystal structures of TCFs was examined. It was found that BET surface areas and mesopore volumes of TCFs decrease with the increase in heat treatment temperature. On the other hand, the XRD peak intensity corresponding to anatase structure increases with the increase in heat treatment temperature in the range below 773 K. Photocatalytic decomposition activities of large organic molecules on TCFs was also measured and the results were compared with those from a commercial photocatalyst, Degussa P-25. Moreover, photocatalytic decomposition of methylene blue was examined by using TCF-packed columns.