Titanium oxide particles were treated using six organophosphorus compounds chosen as model coupling molecules: phenylphosphonic and diphenylphosphinic acids, their ethyl esters, and their trimethylsilyl esters. The ability of all of these coupling molecules to modify the surface of the TiO2 particles was demonstrated by elemental analysis, thermogravimetric analysis, and nitrogen adsorption. The bonding modes on the surface were investigated by means of diffuse reflectance IR Fourier transform (DRIFT) and 31P solid-state MAS NMR spectroscopy. Upon irradiation in water, a marked trend to the photooxidative degradation of the anchored organophosphorus groups was evidenced, especially in the case of phosphinate groups.

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Phosphonic acids are increasingly being used for controlling surface and interface properties in hybrid or composite materials, (opto)electronic devices and in the synthesis of nanomaterials. In this perspective article, a concise survey of phosphonate coupling molecules is first presented, including details on their coordination chemistry, their use in the surface modification of inorganic substrates with self-assembled monolayers, and the analytical techniques available to characterize their environment in nanomaterials. Then, some of their recent applications in the development of organic electronic devices, photovoltaic cells, biomaterials, biosensors, supported catalysts and sorbents, corrosion inhibitors, and nanostructured composite materials, are presented. In the last part of the article, a brief overview of recent progress in the use of phosphonate ligands for the preparation of molecular nanomaterials like metal organic frameworks and functionalized polyoxometalates is given.

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.

The surfaces of alumina particles were modified by grafting with phenylphosphonic acid and its organic-soluble ester derivatives (diethyl phenylphosphonate and bis(trimethylsilyl) phenylphosphonate). Solid-state 31 P NMR spectroscopy indicated that in aqueous media the formation of bulk aluminium phosphonate phases could be avoided by using phenylphosphonic acid at pH 6. The formation of such phases was detected in organic media in the presence of phenylphosphonic acid or its silyl ester. On the other hand the use of the dialkyl ester derivative in organic media allowed controlled grafting, excluding the formation of phosphonate phases even under prolonged heating. Alternatively a two-step sol-gel process was carried out, which involved first the nonhydrolytic condensation between aluminium alkoxide and phenylphosphonic acid (or the parent bis(trimethylsilyl) ester), then the hydrolysis-condensation of the remaining Al-OR groups. 31 P and 27 Al NMR spectroscopy proved the homogeneity of the solids obtained, even for P/Al ratios as high as 1.

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Titanium oxide/phenylphosphonate hybrids were prepared by a two-step sol-gel processing, involving first the nonhydrolytic condensation between titanium isopropoxide and phenylphosphonic acid (or the parent bis(trimethylsilyl)ester), followed by the hydrolysiscondensation of the remaining alkoxide groups. Partial hydrolysis led to the formation of Ti 4 (µ 3 -O)(µ 2 -O i Pr) 3 (O i Pr) 5 (PhPO 3 ) 3 ; the potential use of this intermediate compound as a single-source precursor was explored. The composition, thermal stability, and structure of the hybrid xerogels were investigated using EDX, TGA, XRD, FTIR, and 31 P, 13 C, and 29 Si MAS NMR. The compositional and structural stability of the hybrids was investigated over a wide pH domain.