Adsorption modes of 1,3-thiazol-2-amine on the TiO2 (001) and (101) anatase surfaces

Density functional theory (DFT) method, considering periodic boundary conditions (PBC) and full geometry optimization, was used to study the adsorption of different tautomers of 1,3-thiazol-2-amine on TiO2 (101) and (001) anatase surfaces. The optimized structures of the tautomers on the surface and their corresponding adsorption energies (Ead) were determined. The tautomers were adsorbed on the surfaces mostly through the interaction between Ti atom on the surface and the lone electron pairs of their N, N3, and S atoms. The adsorption of tautomers through their N sites on the surfaces was more favorable compared to N3 and S sites. The adsorption of tautomers on (001) surface was more favorable than their adsorption on (101) surface. The adsorption of 1,3-thiazol-2-amine decreased the band gap of TiO2 which is favorable for solar cells. Comparison of the calculated total density of states (TDOS) of TiO2 + adsorbate with that of bare TiO2 showed the presence of the extra peaks in first band gap of TiO2 in the valence region which increased the conductivity of the surface. Also, for the adsorption of some tautomers, extra states were seen in the second band gap of TiO2 between the valence and conduction band of TiO2. The adsorption of the tautomers shifted the TDOS of the surface to the lower energy compared to the bare surface and caused a negative shift in the TiO2 Fermi level. The effect of solvent on the adsorption of the tautomers on the surfaces was also studied.