Monolayer Tantalum Oxide on Mesoporous Silica Substrate

Monolayer Ta2O5 was fabricated on mesoporous silica (SBA-15) substrate by the reaction of Ta(OEt)(5) with surface hydroxyl groups on silica. The monolayer was defined at the saturation amount of Ta(OEt)(5) anchored on SBA-15 surface in a series of increment of the feed amount the precursor, which was confirmed by elemental (inductively coupled plasma-atomic emission, ICP-AE) analysis of the product (Ta2O5/SBA-15). Ta/Si ratio of Ta2O5/SBA-15 with saturated amount of Ta was 0.11-0.12. X-ray photoelectron spectroscopy (XPS) analysis of Ta/Si ratio of a series of samples by using the Ta4f and Si2p signals met agreement with the gradual increase and the saturation at about 0.11-0.12, as well as the local elemental analysis by energy dispersive X-ray spectrometry (EDS) using transmission electron microscopy (TEM). The absorption edge of UV-vis. diffuse reflectance spectra of a series of samples appeared very sharp, decreasing the excitation energy from 5.1 to 4.7 eV by increasing the Ta/Si ratio from 0.01 to 0.11 - 0.12. X-ray absorption near edge fine structure (EXAFS) indicated the inhomogeneous (amorphous) feature of Ta2O5 phase on SBA-15 with Ta octahedral species. The unique surface property of monolayer Ta2O5/SBA-15 was characterized by infrared (IR) spectroscopy and catalytic reactions.