Influence of the gelation and calcination temperatures on physical parameters and photocatalytic activity of mesoporous titania powders synthesized by the nonhydrolytic sol-gel process

Abstract

Titania powders were synthesized by nonhydrolitic sol-gel process starting from titanium(IV)-chloride, titanium(IV)-isopropoxide and carbon-tetrachloride. Gelation was performed in solvothermal conditions, at 140 degrees C or 160 degrees C. The obtained gels were then dried and calcined at 500 degrees C or 750 degrees C. Dry gels and powders obtained by their calcination at 500 degrees C contained only anatase, and the degree of crystallinity increased notably on passing from the dry gels to the powders. The crystallite size of dry gels and powders obtained at 500 degrees C increased slightly with increasing temperature of the gelation. The powder obtained at the higher gelation temperature had a larger specific surface area (52.8 m(2) g(-1)) and a smaller maximum pore diameter (12.3 nm). When the calcination temperature was increased to 750 degrees C, the obtained powders contained both anatase and rutile. The rutile content in the powders is related to the degree of crystallinity of the dry gels: with a lower level of dry gel crystallinity, the rutile content in the powders becomes higher, indicating that the temperature of the anatase - gt rutile transformation decreases with decreasing the size of anatase crystallites. The photocatalytic activity of the powders obtained by gel calcination at 500 degrees C, tested by measuring the photocatalytic degradation of the azo dye CI Reactive orange 16, was sufficiently high and attained the photocatalytic activity of the broadly accepted commercial powder P-25 produced by Degussa. The photocatalytic activity of the powders obtained by calcination at 750 degrees C was low, but showed a tendency to increase with higher anatase content in the powders.