Anchoring alkylchlorosilanes on silica by gamma-irradiation: an alternative method for surface grafting

The incorporation of single or multiple organic functional groups onto inorganic supports leads to hybrid organic-inorganic materials with tailored physicochemical properties useful in many applications including microelectronics, catalysis, separation processes, molecular recognition and bioengineering. Generall, the surface modification of pre-formed inorganic materials are obtained through vapor-phase deposition or solution methods. Silica is the ubiquitous inorganic platform used in systems designed for catalysis, filtration, sensing and opto-electronic technologies. The vapor phase process is generally performed at high temperature, limiting the silanizing agents to those which have sufficient vapor pressure and high thermal stability. Several physico-chemical phenomena are to be taken into account in the solution approach, namely the affinity of the reactant silane towards silica relative to the solvent, silica hydration, and accessibility of the surface reactive sites as grafting progresses. Alkylhalosilane-functionalized silica are of great interest as starting materials for further chemistry, such as the synthesis of immobilized catalysts or surfacederivatization through click chemistry. 3-chloropropytrietoxylsilane (CPTES) modified silica has been obtained via post-synthetic surface modification of mesoporous silica and also via sol-gel technique. It is well-known that ?-irradiation enhances adsorption and grafting of small molecules and macromolecules on silica, especially through radical and peroxide-based chemistry involving both the silica substrate, and the organic reactants.We have explored the possibility of obtaining chloroorganosilane- modified silica by radiolizing the precursor CPTES in the presence of silica. ?-irradiation exerts complex effects both on silica, and on organosilanes. Both paramagnetic, and diamagnetic (cationic) defects are generated, which account for a higher propensity towards grafting of adsorbed molecules. Furthermore, radical species such as H·, [O], OH· and so forth are developed during irradiation. These may trigger further reactions of radical nature on adsorbed molecules on silica. Besides this silica-mediated effect, direct activation of CPTES by ?-rays should occur similarly to polysiloxanes, generating Si and C radicals that can either be trapped by the solid support, or result in crosslinking reactions. As a result of the combined activation of the silica support and of CPTES by ionizing radiation, we expect to obtain an organically-modified silica surface (Figure) bearing Cl groups for further chemistry. The aim of the present work is to assess the ?-ray-promoted grafting of CPTES-derived moieties onto silica by ATR FT-IR analysis and elemental analysis