Direct Synthesis and Characterization of High Titanium-Loading Hexagonal Mesostructured Silica Thin Films

Abstract

High titanium-loading hexagonal mesostructured silica thin films (Ti-HMSTF) have been successfully synthesized by carefully controlling two factors. One is the hydrolysis and condensation reaction of titanium alkoxide and the other is the aging condition of as-made Ti/Si mixed thin films. The former was controlled by adding acetylacetone (AcAc) as a Ti chelating agent. Regarding the latter, aging under a hydrothermal water vapor ambient environment was found to be effective in synthesizing Ti-HMSTFs with well-defined mesostructures. The maximum molar ratio of Ti/Si in the Ti-HMSTF materials attained a value of 0.3 (referred to as Ti-HMSTF-0.3) for the as-made films. These materials were subjected to a specific hydrothermal aging process, which was prepared from a precursor solution containing AcAc with the molar ratio AcAc/Ti=1. Small angle X-ray diffractometry (SA-XRD) and transmission electron microscopy (TEM) demonstrated that Ti-HMSTF-0.3 had a highly ordered 2-dimensional hexagonal mesostructure. This 2D hexagonal mesostructure was thermally stable even after the removal of the triblock copolymer template by calcination at 450°C for 4 h. Moreover, small amounts of TiO2 anatase nanocrystals with a size of about 3 nm were formed in the calcined Ti-HMSTF-0.3. O(1s) X-ray photoelectron spectroscopy (XPS) analysis indicated that the incorporation of titanium into the HMSTF was through the Si–O–Ti bonds. The Ti(2p) XPS showed that the binding energy of the titanium in HMSTF decreased with increasing Ti loading.