Phosphonate mesoporous hybrid thin films: Synthesis of organophosphosilane by thiol-ene click chemistry and applications in formation and stabilization of silver nanoparticles

The synthesis of hybrid inorganic organic mesoporous films with pores displaying phosphonic acid functions and their use as template for Ag nanoparticles are presented here. The Photochemical radical thiol - ene addition (PRTEA) was used for the synthesis of organophosphonated thiopropyltrimethoxysilanes with either diethyl allylphosphonate (DEAP) and vinylphosphonic acid (VPA) functionalities, which quantitatively lead to two functionalizing agents with differential reactivities. Phosphonated Hybrid Mesoporous Silica Thin Films with different composition were obtained by incorporating variable amounts of the phosphonated silanes by co-condensation strategy. Structural characterization with electron microscopy, X-ray reflectometry (XRR) and small angle X-ray scattering (SAXS) in transmission mode demonstrated the synthesis of ordered mesoporous phases in all tested compositions. The chemical characteristics of the hybrid films were evaluated by Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) showing the quantitative incorporation of the two silanes. The phosphonic groups present in the hybrid mesoporous silica thin films surface improved the adsorption of Ag (I) ion, acting as complexation sites. Silver nanoparticles (NPs) were afterwards obtained by adsorption/reduction cycles using NaBH4 as reduction agent. The obtained nanocomposites presented well distributed Ag NPs, as demonstrated by electronic microscopy and UV-visible spectroscopy. Moreover, the NPs were highly stable against oxidation when included within the functional oxides, in comparison with the pure oxide counterpart. Both phosphonated functions produced a high Ag (I) and Ag NPs loading, but the different chemistry of the phosphonates had an impact on total loading and stability of the NPs. While the free phosphonic acid presented the largest Ag (I) ion adsorption, higher chemical stability of Ag NPs was achieved for the ester protected phosphonate.