Molecular aspects of solid silica formation

Abstract Raman spectroscopy indicates distinct differences between the molecular constitutions of amorphous silicas solidified from aqueous solutions at acidic and basic conditions which might have implications on the synthesis and properties of zeolites, mesostructured silicas and silica gels. The Q n connectivities of [SiO 4 ] tetrahedra in the primary nanoparticles, which determine the ultimate molecular structure of gels, seem rarely to depend on the concentration, elemental composition, or molecular constitution of the dissolved alkaline silicate ingredients. Experimental and computational evidence support a surprisingly large volume of Q ° silica monomers in many acid-set gels. Because of a good spectral resolution both in liquid and solid phases, robust and mobile instrumentation, low cost and ease of use, Raman spectroscopy is a preferred noninvasive analytical technique that allows one to follow in situ the complex solidification process of silicates. However, we found that FTIR spectroscopy is better suited in some cases, for example for studying the TEOS based synthesis of (Me 4 N) 8 Si 8 O 20 × 65H 2 O, a starting material for the designed synthesis of double four ring (D4R) based nano structures.