MSINDO quantum chemical modeling study of water molecule adsorption at nano-sized anatase TiO2 surfaces

In this work, we studied the adsorption of water molecule onto the (1 0 0), (0 1 0) and (0 0 1) surfaces of nano-sized anatase TiO2 with semiempirical SCF MO method, MSINDO. The anatase TiO2 particles are modeled with free clusters (TiO2)n, where n = 20-80. Whereas, the surfaces have been modeled with two saturated clusters, Ti21O58H32 and Ti36O90H36. The surface lattice fivefold coordinated titanium atoms (Ti5C), which represent the Lewis acid sites, are selected as adsorption centers. We also investigated the effect of TiO2 cluster size on the computed band gap energy. Results reveal that the electronic properties of a cluster in the lowest excited state differ from that of the ground state. Furthermore, the MSINDO band gap energies of 3.68-3.77 eV for the anatase TiO2 are in a fair accordance with other literature data. In agreement with other computational and experimental studies, the dissociated form of water molecule adsorption on anatase TiO2 surfaces is always more stabilized than the molecular form.