High-Field ¹⁷O MAS NMR Investigation of Phosphonic Acid Monolayers on Titania

Abstract

High-field 17O MAS NMR was used to investigate the binding of self-assembled monolayers of 17O-enriched phosphonic acids deposited on a titania anatase support. The spectra were recorded at two different magnetic fields (9.4 and 17.6 T), to improve the reliability of the simulations of the different resonances. The spectra recorded at 17.6 T offer an excellent resolution between the different oxygen sites, PO, P−O−H, and P−O−Ti, thus greatly facilitating their quantification. The data reported here give direct evidence of the extensive formation of Ti−O−P bonds in the surface modification of titania by phosphonic acids. The presence of residual PO and P−O−H sites indicates the presence of several different binding modes in phosphonic acid monolayers. The chemical shift of P−O−Ti sites is consistent with bridging (as opposed to chelating) modes.

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

“…This is due to the strong specific interaction between the organophosphonic acid and the surface. For the reaction of PAs with the surface, the P-OH group will bind to and/or react with the surface hydroxyl groups, while the phosphoryl group can coordinate with Lewis acid sites on TiO2 [13]. As a result, the PA can graft to the surface with different binding modes: mono-, bi-and tridentate.…”

Modification of Nanocrystalline TiO2 with Phosphonate‐ and Bis(phosphonate)‐Bearing Macrocyclic Complexes: Sorption and Stability Studies

“…This nonequivalency could originate from different hapticity of the sorbate; mono-, [29] di-, [30] and tridentate [21] adsorption modes of phosphonate on the TiO 2 surface have been described in the literature as well as their coexistence in one material. [28] The slow energy-demanding transition between the mentioned binding modes leads to stronger sorbate-sorbent interactions. It could explain the slower desorption of phosphonate incubated at higher temperatures.…”

“…[26,27] The description of the interaction between a phosphonic acid group and the surface of TiO 2 on a molecular level involves several possible modes of adsorption. [28] Tridentate, bidentate, and monodentate adsorption modes may be present depending on the number of Ti-O-P bonds formed by one phosphonate group. In the case of di-and monodentate adsorption modes, the remaining phosphonate oxygen atom(s) may form hydrogen bond(s) with either surface hydroxy groups or with other phosphonate groups.…”

“…Interpretation of experimental data and identification of participating binding modes is complicated, and the results reported in the literature may appear contradictory. [21,[28][29][30][31][32][33] Although considerable effort has been devoted to the description of the sorption on a molecular level (i.e., mechanism of absorption and modes of binding), limited attention has been paid to the description of the adsorption from a macroscopic point of view in terms of adsorption capacity, [34] hydrolytic stability (i.e., desorption), [22,25,[35][36][37][38][39] and their relation to the reaction conditions used during the sorption process. [33] Whereas the mode of adsorption is important for theoretical studies, the macroscopic behavior of sorbates (in terms of adsorbed amounts and stability of the adsorbed layer against degrading/washing) is of crucial importance for practical applications of such surface-modified materials.…”

Grafted 2‐chloroethylphosphonic acid on inorganic supports used as flame retardant for unsaturated polyester resins

“…The grafting of TiO 2 [27,28] and Al 2 O 3 particles, [29][30][31] was achieved by treating a suspension of particles at room temperature with an aqueous solution of phosphonic or phosphinic acids. In the case of TiO 2 , the pH was adjusted to 3.5, to be far from pH 5.9, the value of zero-charge state for TiO 2 , so that electrostatic repulsive forces due to charged surface sites acted between the particles, giving unaggregated suspensions [32].…”