Microstructural evolution of metatitanic acid with temperature and its photosensitization property

Abstract

Metatitanic acid (MTA) powder was heat-treated up to 800 °C in air, and the resultant evolutions of crystalline phase, specific surface area, and pore size were investigated. MTA loses its weight in two steps; the first one (12.4 %) from 100 to 542 °C and the second one (5.2 %) from 542 to 900 °C. Both of the two stages are due to the elimination of water molecules, while the second-stage weight loss is also associated with the removal of SO4 2− ions present in MTA. As the heating temperature was elevated to 800 °C, the average pore diameter increased from 3.14 to 15.50 nm, while the specific surface area decreased from 377.3 to 54.5 m2/g. The change of these properties was most pronounced from around the temperature at which the second-stage water loss starts (542 °C). The visible-light photosensitization of rhodamine (RhB) dye on the surfaces of a partially de-hydrated MTA (heat-treated at 400 °C) was superior to that of commercial P-25 powder, indicating the potential of the partially de-hydrated mesoporous MTA with high specific surface area for the applications where surface photosensitization is important.