Low-Cost Pathways to Synthesize Silica-Smectite Clay-Based Composites

The present study aimed to use 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 ash after an acid treatment, 2) an aqueous sodium silicate solution from the alkaline dissolution of silica sludge, and 3) a nanosilica powder obtained after the hydroxylation/polymerization of a sodium silicate solution. Products from the three different synthetic pathways were investigated by X-ray diffraction; Fourier infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and BET specific surface area (SSA) measurements. All techniques showed a heterogeneous morphology, where the distribution of silica particles in the clay matrix changed with each synthetic pathway. For the silica sludge synthetic pathway, a predominantly three-dimensional-like structure with a phyllosilicate matrix skeleton was obtained. For the pathway using a silicate solution, an amorphous compound with limited intergranular cohesion containing silicate agglomerates intercalated between clay sheets was found. The nanosilica reinforced pathway led to a packed morphology with a regular distribution of silica phases in the clay matrix. In all the synthesized composites, the amorphous silica phase was identified, with a potential higher reactivity and SSA of 228, 257, and 300 m2/g for pathways 1, 2, and 3, respectively. Correspondingly, the microstructure evidenced both an increased porosity and an increase in chemically active sites. Consequently, the obtained products are potential multifunctional materials.