Binding modes of phosphonic acid derivatives adsorbed on TiO2 surfaces: Assignments of experimental IR and NMR spectra based on DFT/PBC calculations

Abstract

A DFT study on the adsorption of a series of phosphonic acids (PAs) on the TiO2 anatase (101) and (001) surfaces was performed. The adsorption energies and geometries of the most stable binding modes were compared to literature data and the effect of the inclusion of dispersion forces in the energy calculations was gauged. As the (101) surface is the most exposed surface of TiO2 anatase, the calculated chemical shifts and vibrational frequencies of PAs adsorbed on this surface were compared to experimental 31 P and 17 O NMR and IR data in order to assign the two possible binding modes (mono-and bidentate) to peaks and bands in these spectra; due to the corrugated nature of anatase (101) tridentate binding is not possible on this surface. Analysis of the calculated and experimental 31 P chemical shifts indicates that both monodentate and bidentate binding modes are present. For the reactive (001) surface, the results of the calculations indicate that both bi-and tridentate binding modes are possible. Due to the particular sensitivity of 17 O chemical shifts to hydrogen bonding and solvent effects, the model used is insufficient to assign these spectra at present. Comparison of calculated and experimental IR spectra leads to the conclusion that IR spectroscopy is not suitable for the characterization of the different binding modes of the adsorption complexes.

Aqueous or solvent based surface modification: The influence of the combination solvent – organic functional group on the surface characteristics of titanium dioxide grafted with organophosphonic acids

“…Geometries were optimized until the residual forces were below 0.001 Ry/au; the atoms in the lowest layer of the slab were constrained to their initial bulk positions, while all other layers were allowed to relax. This calculation method was validated in a previous study [16].…”

“…However, also the number of hydroxyl groups is a determining factor for the grafting density. A PA can bind to multiple hydroxyl groups, depending on the binding modes of the PA (mono, bi and tridentate) [16]. Furthermore, not all hydroxyl groups are necessarily available due to steric effects.…”

“…However, assignment of the binding modes is hampered due to the overlap of the P-O stretching region and the bands in the native TiO2 spectrum. Via computational studies the adsorption energies of PA on TiO2 are calculated, as well as the bond distances, 31 P chemical shifts and vibrational frequencies [16]. However, the binding mode is not the only parameter influencing the 31 P chemical shift, it is possible to determine the binding mode by the 31 P chemical shift.…”

Phosphonate‐Mediated Immobilization of Rhodium/Bipyridine Hydrogenation Catalysts

“…These values are in good agreement with previousc alculations. [52] On this basis, the 31 Pc hemical shifts obtained from fits of the experimentals pectra of the supported rhodium/ bipyridine complexes suggest that the monodentate binding mode ci sp redominant (line at ca. 25 ppm).…”

“…[52] On this basis, the 31 Pc hemical shifts obtained from fits of the experimentals pectra of the supported rhodium/ bipyridine complexes suggest that the monodentate binding mode ci sp redominant (line at ca. [52] On this basis, the 31 Pc hemical shifts obtained from fits of the experimentals pectra of the supported rhodium/ bipyridine complexes suggest that the monodentate binding mode ci sp redominant (line at ca.…”