Adsorption CO2 on the perfect and oxygen vacancy defect surfaces of anatase TiO2 and its photocatalytic mechanism of conversion to CO

The adsorption energies for physisorption and the most stable chemisorption of CO₂ on the neutral charge of perfect anatase [TiO₂] (0 0 1) are −9.03 and −24.66 kcal/mol on the spin-unpolarized and −12.98 and −26.19 kcal/mol on the spin-polarized surface. The small activation barriers of 1.67 kcal/mol on the spin-unpolarized surface and of 6.66 kcal/mol on the spin-unpolarized surface were obtained. The adsorption mechanism of CO₂ on the oxygen vacancy defect [TiO₂ + V_O] surface of anatase TiO₂ using density functional theory calculations was investigated. The energetically preferred conversion of CO₂ to CO was found either on the spin-unpolarized or spin-polarized surfaces of oxygen vacancy defect surface [TiO₂ + V_O] as photocatalyst.     

Molecular structures of 8,8′-dithioureido-2,2′-binaphthalene derivatives and their anions recognition: an ONIOM investigation

The structures of 8,8′-bis(3-phenylthioureidomethyl)-2,2′-binaphthalene (1), 8,8′-bis(3-butylthioureidomethyl)-2,2′-binaphthalene (2) and their complexes with anionic guests such as carboxylate ions (acetate, oxalate, malonate, succinate, glutarate, adipate, pimelate, suberate, and azelate), inorganic oxygen-containing anions (nitrate, sulfate, bicarbonate, hydrogen phosphate, and dihydrogen phosphate), and halide ions (fluoride, chloride, and bromide) were obtained using the ONIOM approach. The binding abilities of receptors 1 and 2 to anionic species in terms of binding energy, thermodynamic properties, and selectivity coefficient were obtained at the ONIOM(B3LYP/6-31G(d):AM1) and BSSE-corrected B3LYP/6-31G(d)//ONIOM(B3LYP/6-31G(d):AM1) levels of theory. The multipoint hydrogen bonding between receptors (either the receptor 1 or 2) and anionic guests were found. The hydrogen phosphate is the most preferable ion to bind with either the receptor 1 or 2.     

First principles theoretical study of the hole-assisted conversion of CO to CO2 on the anatase TiO2(101) surface

First principles density functional theory calculations were carried out to investigate the adsorption and oxidation of CO on the positively charged (101) surface of anatase, as well as the desorption of CO(2) from it. We find that the energy gain on adsorption covers the activation energy required for the oxidation, while the energy gain on the latter is sufficient for the desorption of CO(2), leaving an oxygen vacancy behind. Molecular dynamics simulations indicate that the process can be spontaneous at room temperature. The oxidation process described here happens only in the presence of the hole. The possibility of a photocatalytic cycle is discussed assuming electron scavenging by oxygen.