Synthesis of hydrophilic and hydrophobic xerogels with superior properties using sodium silicate.

Highly porous hydrophilic and hydrophobic silica xerogels were synthesized by surface modification of silica hydrogels at ambient pressure drying. The silica hydrogels were prepared by a sol–gel polymerization of an inexpensive silica precursor (sodium silicate) under atmospheric conditions. In order to minimize shrinkage due to drying, the hydrogel surface was modified using trimethylchlorosilane (TMCS) in the presence of ethanol/n-hexane solution before ambient pressure drying (APD). Properties of the final product were investigated using Field-Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric and Differential Analysis (TG–DTA), and nitrogen physisorption studies. The final product was observed to have an extremely high specific surface area (783 m2/g) and a large cumulative pore volume (2.74 cm3/g). Highly porous hydrophilic xerogels were obtained after heat-treating the modified xerogels. At temperatures above 450 °C the surface alkyl groups (—CH3) were significantly oxidized and, consequently, the properties of the resulting xerogels were altered. Products obtained via the proposed inexpensive approach have superior properties and the method exploits an inexpensive silica source (sodium silicate). Thus it is feasible for large-scale economic industrial production. [ABSTRACT FROM AUTHOR]