Local structure and photocatalytic activity of B2O3–SiO2/TiO2 ternary mixed oxides prepared by sol–gel method

Abstract

The local structure and the photoactivity of B2O3–SiO2/TiO2 ternary mixed oxides (SiO2 content was fixed as 30at.% with respect to TiO2) was investigated by using XRD, FT-IR, BET, UV-vis spectra, and electron paramagnetic resonance (EPR) measurement. In FT-IR analysis, boron was incorporated into the framework of titania matrix with replacing TiOSi with SiOB or TiOB bonds. Also, paramagnetic species such as O− and Ti3+ defects were formed by the boron incorporation. In SiO2/TiO2 mixed oxides, a blue shift in the light absorption band was observed due to the quantization of band structure. All B2O3–SiO2/TiO2 samples had pure anatase phase and no rutile phase was formed even though the calcination temperature was over 900°C. Incorporating boron oxides of more than 10% enlarges the grain size of anatase phase and causes a red shift of the light absorption spectrum. The surface area was monotonically decreased with increasing the content of boron content. As a result, the photoactivity of B2O3–SiO2/TiO2 ternary mixed oxides was greatly influenced by the content of boron oxide. The highest photoactivity (gmoles/minl) was obtained when the boron content was 5% and seven times higher than that of silica/titania binary mixed oxide. In addition, the specific photoactivity (gmoles/m2l) was maximum still at 5%. It was concluded that the large reduction of surface area, the change of band structure, and more formation of bulk Ti3+ sites are responsible for the deterioration in the photoactivity of B2O3–SiO2/TiO2 ternary mixed oxides when the content of boron is over 10%, although their crystallinity was enhanced by increasing the calcination temperature with keeping anatase phase.