Fourier transform infrared spectroscopy has been employed to study the adsorption and reactions of N,N-dimethylformamide (DMF) and dimethylamine (DMA) on powdered TiO 2 . DMF can be adsorbed in molecular form with the carbonyl interacting with the surface Lewis site (Ti 4+ ) or in dissociative form of OCN(CH 3 ) 2 . Theoretical adsorption study of rutile (110) points out that the C* and O atoms of OC*N(CH 3 ) 2 are bonded at a two-foldcoordinated O site and a five-fold-coordinated Ti site, respectively. The thermal products of DMF/TiO 2 are found to be CO and DMA. Photochemical reaction of DMF on TiO 2 in O 2 generates CO 2 , HCOO, and NCO. O 2 participates in the reaction with its oxygen atoms incorporated into the three products. DMA can be adsorbed in molecular form and imine species on TiO 2 . Photoirradiation of DMA/TiO 2 in O 2 generates CO 2 , HCOO, NCO, and imine species. Interestingly, DMF and OCN(CH 3 ) 2 are produced after postirradiation thermal treatment of DMA on TiO 2 , possibly from the reaction between residual DMA and HCOO photoproduct.
Acetone is generated upon mesityl oxide (MO) adsorption on TiO2 at 35°C. Water plays an important role in promoting MO decomposition to form acetone. It is suggested that diacetone alcohol plays a role in the transformation of MO to acetone. The thermal reaction of pinacol on TiO2 mainly produces pinacolone at a temperature higher than 100°C. However, acetone is mainly formed in the photocatalytic decomposition of pinacol on TiO2 in O2. Pinacolone is thermally transformed into 2,3‐dimethyl‐1,3‐butadiene in the absence of O2 and into pivalate in the presence of O2. Both the reactions of pinacolone occur above 200°C.
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 TiO2, with the aid
of density functional theory calculations. In addition, the possibility
for the formation of a boron-modified TiO2 (B/TiO2) surface, using ITDB as the boron source, is explored and the photocatalytic
activity of the B/TiO2 is tested. After adsorption of ITDB
on TiO2 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(CH3)2–C(CH3)2O and OCH(CH3)2 and the inorganic components of (TiO2)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(CH3)2–C(CH3)2O–B–OCH(CH3)2 on the surface. In the case of photoreaction,
the ITDB on TiO2 decomposes under photoirradiation at 325
nm to form acetone. The boron-modified TiO2 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.
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