Synthesis of nanohybrid alcogels of SiO2 and Ni-Cr/Mg-Cr-LDH: study of their rheological and dip coating properties

Silica supported Ni-Cr and Mg-Cr-LDH nanohybrid alcogels were synthesized by a 'soft chemical' nonaqueous sol-gel route using a mixture of metal acetylacetonate and tetraethylorthosilicate (TEOS) precursors. Faster hydrolysis of the alkoxide than the metal acetylacetonates precursors gives an inner SiO2 core around which crystalline LDH sheets are dispersed to give one gel network in an organic medium. These were characterized by XRD, FT-IR, TGA-DTA, particle-size distribution, zeta-potential, SEM, TEM, EDXA, BET surface area and Rheological analysis. The steady shear and dynamic oscillatory measurements showed that the apparent viscosity decreased with shear strain and the complex viscosity decreased with angular frequency indicating the shear thinning behaviour of these nanohybrids. At the linear viscoelastic region (LVE) the storage modulus (G') was greater than the loss modulus (G '') indicating the presence of elastic or gel like behaviour. With the rise of the amount of SiO2 in the nanohybrids the surface area and the negative zeta potentials were found to increase. This helped the dispersibility of the alcogels as well as the formation of thin films over solid surfaces by dip-coating. These findings are expected to be useful in designing crack free catalytic barriers for inorganic membrane applications having transition metal mixed oxide/hydroxide nano-sheets as the active catalyst.