Isopropoxy Tetramethyl Dioxaborolane on TiO2: Reaction Pathway and Formation of a Visible-Light-Sensitive Photocatalyst

Borate toxicity is a concern in agriculture since a high level of borates may likely exist in irrigation water systems. In this research, transmission infrared spectroscopy and X-ray photoelectron spectroscopy are employed to study the thermal and photochemical reactions of isopropoxy tetramethyl dioxaborolane (ITDB) on TiO 2 , with the aid of density functional theory calculations. In addition, the possibility for the formation of a boron-modified TiO 2 (B/TiO 2 ) surface, using ITDB as the boron source, is explored and the photocatalytic activity of the B/TiO 2 is tested. After adsorption of ITDB on TiO 2 at 35 °C and heating the surface to a temperature higher than ∼200 °C in a vacuum, the surface is found to be covered with both the organic components of OC(CH 3 ) 2 -C(CH 3 ) 2 O and OCH(CH 3 ) 2 and the inorganic components of (TiO 2 )BO and Ti-B-O. The organic intermediates can be further thermally transformed into pinacolone and acetone; however, the inorganic parts exist at 400 °C, forming a boron-modified surface. The thermal decomposition of ITDB is proposed to be initiated by breaking one B-O bond, forming -OC(CH 3 ) 2 -C(CH 3 ) 2 O-B-OCH(CH 3 ) 2 on the surface. In the case of photoreaction, the ITDB on TiO 2 decomposes under photoirradiation at 325 nm to form acetone. The boron-modified TiO 2 surface can absorb visible light, likely due to the presence of new states in the band gap, and shows a photocatalytical activity in degrading methylene blue, under 500 nm irradiation in air.