Influence of the use of rice husk as source of silica on the sol-gel synthesis of bioglass

Among the agro-industrial residues, the rice husk has stood out for presenting contents higher than 90% of silica, the main oxide of bioglass. Thus, the objective of this research was to compare the use of two different sources of silica, tetraethylorthosilicate (TEOS) and rice husk ash (RHA), in the sol-gel synthesis of the bioglass of the SiO2-CaO-Na2O system. For the silica extraction, the rice husk was treated with oxalic acid and calcined at 600 °C. This temperature was determined using thermogravimetry and the calcined powder was analyzed by X-ray diffraction and X-ray fluorescence spectroscopy, proving the achievement of high-purity amorphous silica. In the production of the bioglass, the solution made with the rice husk showed great synthesis efficiency, and the powder calcined was evaluated by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and scanning electron microscopy. FTIR spectra presented characteristic bands of siloxane (Si-O-Si) bonds, which indicated a vitreous network and provided the formation of silanol groups, fundamentals for the growth of the hydroxyapatite layer. The microstructures of the samples were similar, but the sample made from RHA (BRHA) presented porous agglomerates, while the BTEOS had smaller and well-defined particles. The silica obtained from rice husk showed potential to be used in the sol-gel synthesis of bioglass.