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.

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Fourier transform infrared spectroscopy was employed to study the thermal and photochemical reactions of melamine ((H 2 N) 3 (C 3 N 3 )) on TiO 2. Also tested was the adsorption of urea, cyanamide (H 2 N-C≡N), dicyandiamide ((H 2 N) 2 C=N-C≡N) and cyanuric acid ((OH) 3 (C 3 N 3 )) for identifying possible reaction intermediates. It was found that the thermal decomposition of melamine starts with N-H bond scission, possibly forming the intermediates such as (H 2 N) 2 (C 3 N 3 )NH-and (H 2 N)(C 3 N 3 ) (NH) 2 -. Further loss of hydrogen atoms and ring-opening from these intermediates lead to the formation of -NCO (isocyanate) and -N 3 (azide) on the surface. The TiO 2 -mediated photochemical reaction of melamine proceeds via different mechanism, forming dicyandiamide. These thermal and photochemical reaction pathways of melamine on TiO 2 are reported for the first time. They are different from previous studies showing the processes of polymerization, and substitution of NH 2 by OH to form cyanuric acid and urea.

Cyanuric acid is often found to be the end product in the hydrolysis of waste melamine and in the TiO2-mediated photocatalytic decomposition of s-triazine-containing compounds used as herbicides or dyes. The photocatalytically recalcitrant nature of cyanuric acid on TiO2 may be closely related to its adsorption properties, including the tautomeric forms present on the surfaces and their bonding structures, which remain to be determined. In this paper, we present the optimized adsorption structures of the four tautomeric isomers (triketo, diketo, monoketo, and triol) of cyanuric acid on a model rutile-TiO2(110) surface and their vibrational absorptions. Experimentally, the adsorption structures of cyanuric acid and chloride on powdered TiO2 are analyzed on the basis of the theoretically obtained, characteristic infrared information. Cyanuric acid on TiO2 at 35 °C exists in triketo and hydroxylated forms, but the diketo becomes the predominant form on the surface at 250 °C, being bonded to a titanium site via one of its carbonyl groups and with a N-H···O hydrogen bonding interaction. Hydroxylation of cyanuric chloride occurs as it is adsorbed on TiO2 at 35 °C. Upon being heated to 200 °C, the surface is mainly covered with the diketo form of cyanuric acid after the adsorption of cyanuric chloride.

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.