XAFS studies on the local structures of Ti-HMS mesoporous molecular sieves and their photocatalytic properties

Various Ti-containing HMS mesoporous molecular sieves having high surface areas and pore volumes have been prepared at ambient temperature. The Ti-HMS samples exhibited a well-defined XRD pattern of typical hexagonal lattice. UV-vis and XAFS spectra for the calcined forms of Ti-HMS indicated that the Ti ions are tetrahedrally coordinated in the framework of HMS for the samples of Ti-HMS(1) and Ti-HMS(2), while at least a fraction of Ti-oxides in Ti-HMS(10) is in octahedral coordination. UV irradiation of the Ti-HMS catalysts in the presence of NO was found to lead to the decomposition of NO to form N₂, O₂, and N₂O at 273 K with different yields and product distributions. The photocatalytic performance of Ti-oxides appears to be completely modified by their incorporation structure and reaction environment. High efficiency and selectivity for the formation of N₂ and O₂ in the photocatalytic decomposition of NO was achieved with the Ti-HMS(1) having highly dispersed isolated tetrahedral titanium oxide species, while the reactivity decreased with an increase in the Ti content.