Reactions of Trimethylindium on TiO2Nanoparticles: Experimental and Computational Study

This article reports the results of an experimental and computational study on the reaction of trimethylindium, In(CH3)3, adsorbed on TiO2 nanoparticle films. Experimentally, Fourier transform infrared (FTIR) spectra have been measured by varying In(CH3)3 dosing pressure, UV irradiation time in the absence and presence of oxygen, and surface annealing temperature on both “clean” and HO-covered TiO2 nanoparticle films. Computationally, adsorption energies, molecular structures, and vibrational frequencies of possible adsorbates have been predicted by first-principles calculations based on the density functional theory (DFT) and the pseudopotential method. Three important reactions involving CH3 elimination, CH4 elimination, and CH3 migration from the adsorbed trimethylindium have been elucidated in detail. CH3 migration is the only exothermic process with the lowest reaction barrier. On the basis of experimental and computational results, the two sharpest peaks at 2979 and 2925 cm-1, detected in the dosage and UV irradiation experiments in the absence of oxygen, are attributable to the asymmetric and symmetric C−H vibrations of methyl groups in In(CH3)3(a) and its derivatives, (H3C)2In(a), H3CIn(a), and H3CO(a). In the UV irradiation experiment in the presence of oxygen, the methyl groups attached to the In atom were quickly oxidized to the methoxy with the C−H vibrations at 2925 and 2822 cm-1 and to the carboxyl group with vibrations at 2888 cm-1 (vs(CH)), 1577 cm-1 (va(OCO)), 1380 cm-1 (δ(CH)), and 1355 cm-1 (vs(OCO)). Finally, from the computed energies with vibrational analysis, the adsorbed structure of the carboxyl group was confirmed to involve two oxygen atoms doubly adsorbed on two surface Ti atoms.