Synthesis and study of ammonium oxalate sol-gel templated silica gels

Silica tubes and spheres were synthesised in the presence of oxalate ions by the sol-gel method from tetraethylorthosilicate (TEOS) as silica source. The syntheses were carried out in ethanol/water mixtures in the presence of oxalic acid and aqueous ammonia between 0 and 75 °C. TEM images show that the yield and morphology of the silica is influenced by synthesis conditions (temperature, oxalic acid and ammonia concentration, amount of water, length of ageing time, and length of time for TEOS hydrolysis). It was found that tubes, spheres and amorphous silica structures are formed with sizes (length, diameters) determined by the synthesis conditions. Further, once formed these materials can 'dissolve' under the synthesis conditions used.