A novel hybrid sol–gel method for the synthesis of highly porous silica employing hyperbranched poly(ethyleneimine) as a reactive template

Abstract

A novel hybrid sol–gel templating route employing hyperbranched polymers for the production of nanostructured silica with tailored porosity and high specific surface area values is proposed based on the use of hyperbranched poly(ethyleneimine) both as a reactive template and as a macromolecular “porogen”. The procedure developed involves dissolution of hyperbranched poly(ethyleneimine), PEI, of two different molecular weights (5,000 and 25,000), in N,N-dimethylformamide or chloroform serving as solvents of different polarity and addition of 3-(triethoxysilyl)propyl isocyanate as a silica precursor which is also reactive towards PEI’s amino groups. The obtained triethoxysilyl functionalized macromolecules after hydrolysis and subsequent polycondensation reactions lead to the formation of a novel silica network architecture. By firing this hybrid material a silica powder of nanoporous structure and advanced textural properties is obtained. Synthetic reactions are monitored by FTIR spectroscopy, while the silica network formed after firing is characterized by TGA, low and wide-angle XRD, TEM and N2 adsorption techniques. The influence of several parameters, i.e., molecular weight of PEI, PEI/silica precursor molar ratio and solvent polarity on silica’s porosity is studied. Depending on the synthesis conditions, this novel templating route proved effective for the successful imprinting of mesoporous cavities into silica structure. In this way, nanostructures with tailor-made properties were obtained exhibiting specific surface area values varying from ∼600 to 1100m2/g and pore diameters up to around 5nm.