Structure-stabilizing silanols in amorphous silica with ultra-high specific surface area

Submicron micro-mesoporous spherical silica particles are synthesized. The particles have the form of a sheet of highly hydroxylated silicon-oxygen tetrahedra crumpled into sphere. The structure determines outstanding porosity characteristics of the material synthesized, namely, extremely high specific surface area (SSA) up to similar to 2300 m(2)/g and the pore volume of 0.86 cm(3)/g. The obtained SSA value is almost twice as high as that of previously reported for silica-based materials. A comprehensive study of the particles by thermogravimetric analysis and solid-state nuclear magnetic resonance spectroscopy revealed the concentration of surface hydroxyl groups of 3.5 OH/nm(2) or 11 mmol/g. It is found that surface hydroxyl groups present predominantly in the form of single silanols, which form an H-bonded network and stabilize a delicate silica framework. It is shown that all Si-OH groups are external surface silanols accessible for reaction and/or interaction largely determining the functionality of the material. The hydrothermal stability of the synthesized material is demonstrated. The experiments on vapor-phase adsorption of different substances of various polarity (water, toluene, formic acid) revealed superior sorption capacity (at least two times higher) of the synthesized silica material compared to standard MCM-41-type silica and HY-zeolite. Compared to HY-zeolite sorption of toluene turned out to be even five times higher, which is due to the size of adsorbate molecule. Thus, the obtained silica with improved adsorption properties and a large number of active sites is highly promising for various sensors, separators, catalysts support.