Generation of porosity in a hybrid organic-inorganic xerogel by chemical treatment

A hybrid xerogel of 1,4-bis(trimethoxysilylethynyl)benzene was prepared by using a sol-gel process. Chemical treatment of this material was performed under mild conditions in order to remove the organic group using fluoride a nion as a catalyst. Experimental procedures were carried out using differen t solvents, acidities and counter-cations in order to modify the nucleophil ic power of F-. Characterization of the residues was done by elemental anal ysis, spectroscopy (Si-29 NMR), thermal analysis, pycnometry, surface area measurement and SAXS. The efficiency of the chemical treatment is related t o the solvation of the F- anion. It was possible to demonstrate that elimin ation of the organic part occurs at the same time as a reorganization of th e silica network. This reorganization is the result of two competitive F--c atalyzed chemical reactions: a redistribution and a polycondensation proces s known in solution and which take place in the solid. These processes acco unt for the textural characteristics of the final material and may efface t he organization of the organic spacers in the hybrid xerogel. These results demonstrate the limitations of silica as a molecular imprinting material a nd open a new approach to porous silica with adjustable pore size.