Processing and Characterization of Nano Silica and Iron Oxide Coated Silica Composites Extracted from Rice Hulls

This study examined the effects of adding iron to rice hulls samples (RHs) on the thermal degradation to prepare nano silica and iron oxide-silica mixtures. Iron is precipitated in different amounts within the RH fibers (as hydroxide) by dipping them in a solution of different concentrations of acidic ferrous sulfate and then immersing it in a dilute ammonia solution. The dry RHs were fired at temperatures between 400 °C and 700 °C in a static or limited air atmosphere. Both weight loss and residual weight are determined to follow its thermal degradation. The products of the RH degradation of silica or iron oxide-silica mixtures were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The surface area, average particle size, and pore diameter of both products were determined. The chemical treatment of RHs before firing accelerates their thermal degradation and leads to obtaining firing products of high purity. Firing RHs in a limited air atmosphere increases thermal degradation and, at the same time, accelerates the catalyst effect of iron on its degradation. Under these conditions, silica and iron oxide bonded silica with an average particle size of 1.31 and 0.07 μm were obtained by firing treated RHs at 600 °C and 500 °C, respectively. Firing in a limited air atmosphere encourages CO 2 to react with burned C to form CO, and iron as an accelerator for this reaction completes its degradation. In contrast, iron oxide remained in the ferrous state. Therefore, the bonding between iron and silica was complete.