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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.

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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.

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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