Computational Study of the Hydrolysis Reactions of the Ground and First Excited Triplet States of Small TiO2 Nanoclusters

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• 作者：Tsang-Hsiu Wang ; Zongtang Fang ; Natalie W. Gist ; Shenggang Li ; David A. Dixon ; James L. Gole
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：May 19, 2011
• 年：2011
• 卷：115
• 期：19
• 页码：9344-9360
• 全文大小：1596K
• 年卷期：v.115,no.19(May 19, 2011)
• ISSN：1932-7455

文摘

Density functional theory and coupled cluster theory are used to study the hydrolysis reactions of (TiO₂)_n (n = 1鈥?) nanoclusters to provide insight into H₂O activation on TiO₂. The singlet鈥搕riplet energy gaps of (TiO₂)_n are predicted to lie between 30 and 65 kcal/mol, depending on the cluster size and structure, consistent with our previous studies. The excitation energies for the various hydroxides, Ti_nO_2n鈥?i>m(OH)_2m (n = 1鈥?, 1 鈮?m 鈮?n) are predicted to be, in general, higher than those for (TiO₂)_n. The partial charge on Ti increases as the Ti 鈺怬 bonds are replaced with the Ti鈥揙H bonds. The Ti鈺怬 and Ti鈥揙 frequencies in the triplet state of (TiO₂)_n and Ti_nO_2n鈥?i>m(OH)_2m are, in general, lower than those in the singlet state. The first H₂O adsorption (physisorption) energies for these TiO₂ nanoclusters are predicted to be 鈭?0 to 鈭?5 kcal/mol for the singlet states and 鈭?0 to 鈭?0 kcal/mol for the triplet states. These physisorption energies depend on the cluster size and the site of adsorption, consistent with existing experimental studies. In general, H₂O prefers to physisorb on the Ti site with one Ti鈺怬 bond and two Ti鈥揙 bonds and at the Ti site with no Ti鈺怬 bond and three Ti鈥揙 bonds. The first hydrolysis (dissociative chemisorption) reaction energies of the TiO₂ nanoclusters are predicted to be 鈭?0 to 鈭?0 kcal/mol for the singlet states and 鈭?5 to 鈭?0 kcal/mol for the triplet states. Both singlet and triplet potential energy surfaces for the hydrolysis are calculated. Our calculations show that H₂O readily reacts with both the singlet and the triplet states of the TiO₂ nanoclusters to form the hydroxides with reaction barriers of 5鈥?6 kcal/mol for the singlet states and 5鈥?6 kcal/mol for the triplet states for the first hydrolysis steps, which are, in general, less than the H₂O complexation energies. Because H₂O splitting to form H₂ and O₂ is a strongly endothermic process by 116 kcal/mol, photocatalytic processes are necessary only in the subsequent steps.