Low-cost pathways to synthesize silica-smectite clay-based composites

Abstract

Abstract The present study aimed at using rice husk as a natural silica precursor in the fabrication of silica-smectite composites. A local smectite clay was respectively mixed with 1) silica sludge from rice husk ashes after an acid treatment, 2) an aqueous sodium silicate solution from alkaline dissolution of silica sludge and 3) a nanosilica powder obtained after hydroxylation/polymerisation of a sodium silicate solution. Products from the three different synthesis pathways were investigated by XRD, infrared spectrometry, SEM/EDX and BET specific surface measurement. They show a heterogeneous morphology where the distribution of silica particles in the clay matrix change with each synthesis pathway. For silica sludge synthesis pathway, a predominated three-dimensional-like structure with a phyllosilicate matrix skeleton was obtained. For the pathway using a silicate solution, we obtained an amorphous compound having a limited intergranular cohesion and containing silicate agglomerates that are intercalated between clay sheets. It is different for the nanosilica reinforced pathway that led to a packed morphology with a regular distribution of silica phases in the clay matrix. In all the synthesized composites, we observe the occurrence of amorphous silica phases that favours both the existence of porosity and the presence of chemically active sites. Consequently, obtained products are potential multifunctional materials.