GAMMA-IRRADIATION: AN ALTERNATIVE METHOD TO ANCHOR ORGANOSILANE ON SILICA SURFACE

Hybrid materials are an important new family of amorphous solids in which organic and inorganic constituents are enclosed in a unique composite material. Silica is the ubiquitous inorganic platform used in systems designed for catalysis, separation, filtration, sensing, optoelectronics and environmental technology. The versatility of the silica is due to bulk silica properties as morphology, particle size, shape and porosity jointly to the number of surface silanol groups that are the active groups in the grafting process. The incorporation of single or multiple organic functional groups onto inorganic supports leads to hybrid organic-inorganic materials with tailored physicochemical properties. Generally, the surface modification of pre-formed inorganic materials is obtained through vapor-phase deposition or solution methods. 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. In solution methods, the grafting reaction is mediated by physisorbed water in a hydrolysis step of the haloalkylsilane. 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. It is well-known that gamma-irradiation exerts complex effects both on silica. Radiation damage imparted to silica by gamma-rays includes oxygen vacancies formed through knock-on processes, trapping of a hole at oxygen-deficient centers and transformation of pre-existing Si-H, Si-OH, Si-X centers. In short, 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 organosilane by gamma-rays should generate 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 organosilane by ionizing radiation, we expect to obtain an organically-modified silica surface. The aim of the present work is to explore the possibility of obtaining organosilane-modified silica by gamma- irradiation. We study the silica grafting process using different alkoxy-propylsilanes precursors with general formula (CH3CH2O)3Si-CH2CH2CH2X where X = H, Cl, NH2 . We investigate the grafting efficiency of the gamma-irradiation processes and subsequently compare it with the efficiency of thermal grafting. The properties of gamma-grafted hybrid materials are investigated by ATR FT-IR analysis, elemental analysis and thermogravimetric analysis.