A Convenient Synthesis of Silylated Silica Xerogels

Abstract

Treated silica xerogels with controlled porosity and surface area were prepared by the in situ treatment of hydrogels with hexamethyldisiloxane or alkylchlorosilanes in the presence of isopropyl alcohol. The resulting hydrogels were hydrophobic and readily transferred to nonpolar organic solvents upon contact. The surface area and porosity of the xerogel were controlled by varying the pH, time, and temperature used to polymerize the hydrogel prior to treatment. In general, the surface area decreased with increases in aging time or temperature, whereas the total pore volume and pore size increased. Silylation of the hydrogel in the aqueous phase retains the structure of the hydrogel and permits isolation with minimum structure collapse. By using this technique, silylated xerogels with surface areas ranging from 200 to >700 m2/g and pore volumes of 1.5 to 3.8 cm3/g were obtained.

Silylating Agents Grafted onto Silica Derived from Leached Chrysotile

“…Infrared spectroscopy was used as a tool to provide information on the total or partial use of silanol groups bonded to the original leached chrysotile for the new inorganic structure and to clarify the effect caused by the immobilization of organic groups on the surface. The bands were assigned on the basis of previous studies on silica gel after anchoring a series of silylating agents (22)(23)(24)(25).…”

“…A broad band assigned to the Si-O-Si symmetric stretching mode was observed at 1088 cm −1 . The spectrum relating to the precursor silica shows the band at 955 cm −1 , which is identified as the terminal Si-OH deformation band due to the presence of this group bonded on the silica surface, and another band associated to δSi-O is located at 463 cm −1 (22)(23)(24)(25). These series of bands suggest that the inorganic structure is consistent with siloxane groups in the bulk and silanol moieties at the surface, as was similarly observed for chromatographic silica gel.…”

Direct Measurement of Microporosity and Molecular Accessibility in Stöber Spheres by Adsorption Isotherms

“…A plausible mechanism would be pore coarsening, through which dissolution and re-deposition of silica, preferentially at convex surfaces (Ostwald ripening), would lead to gradual increase of the average pore size. 79 Indeed, pore coarsening during aging is known in microporous systems such as gels 35,80 and membranes 81 . Future studies should confirm this proposition.…”

Influence of Chemical Conditions on the Nanoporous Structure of Silicate Aerogels

“…“Ambient-pressure drying” techniques can be applied on a large scale for industrial purposes. Many studies have synthesized water glass based aerogels using an ambient pressure drying method [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. However, the transparency of such aerogels is still lower than that of aerogels produced under high pressure [ 37 ].…”