Combined DFT and IR evidence on metastable-equilibrium adsorption of arsenate on TiO2 surfaces.

Adsorption of arsenate on TiO(2) surfaces under the same total mass and thermodynamic conditions reached to different final equilibrium states when the reaction was conducted through different pathways. The microscopic structure for equilibrium adsorption samples were significantly affected by the way arsenate was added to the TiO(2) suspension (e.g. 1-batch or multi-batch). The As-OTi asymmetric stretching vibration of 3-batch samples shifted to lower wavenumbers by 15 cm(-1) than that of 1-batch samples. Combined analysis of ATR-FTIR spectroscopy and DFT calculation indicated that the change of reaction pathway altered the ratio of double-corner complex to single-corner complex and, hence, the real equilibrium state that is a mixture of the two surface complexes.