Synthesis of mesoporous silica materials via nonsurfactant urea-templated sol-gel reactions

Mesoporous silica materials with pore diameters of 2 to 6 nm have been prepared using urea as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate, followed by removing the urea molecules by extraction with methanol or water. Characterization results from nitrogen sorption isotherm, powder X-ray diffraction, and transmission electron microscopy indicate that the materials have large specific surface areas (e.g., 600 m(2)/g) and pore volumes (e.g., 0.8 cm(3)/g) as well as narrow pore size distributions. The mesoporosity is arisen from interconnecting wormlike channels and pores of regular diameters. As the urea concentration is increased, the nitrogen sorption isotherms of the silica matrices transform From the reversible type I to the type IV form with type H2 hysteresis, along with increases in the diameter and volume of the pores.