Synthesis and characterization of silica xerogel and aerogel from rice husk ash and pulverized beach sand via sol-gel route

Abstract

The high cost and toxicity associated with the use of orthosilicates as silica precursors drive growing interest in an environmentally friendly and cost - efficient natural silica source. Rice husk (a biomass) and beach sand are both natural and non - toxic and the extraction of silica from each using sodium hydroxide makes the process green for the production of nanosilica gels (xerogel and aerogel) via the sol – gel route. The gels from the ash of rice husk and pulverized beach sand were dried by the use of a laboratory oven and supercritical extraction methods. The structures of the gels were studied through X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), X - ray fluorescence (XRF) spectroscopy and Fourier transform infrared (FTIR) spectroscopic analyses. XRF spectroscopy revealed silicon in its oxide form as the prominent element with low levels of trace elements concentrations. XRD results showed the crystalline nature of the prepared silica. TEM images confirmed the crystalline and nanometric structures of the streak - free xerogel and aerogel. SAED confirmed that the gels were polycrystalline with no streaks. SEM monographs showed varied globes of fine surfaces indicating the high level of purity of the gels. FTIR showed the absorption peaks of the silanol-OH bond and Si-O-Si vibration, confirming the gels as nanometric structures. The high yield, crystalline nature, purity and crystallographic features of the produced silica suggest rice husk ash and pulverized beach sand as alternative silica sources for the production of silica gels nanoparticles with potential applications in biomedical field, nanofiltration and as additive for improving the strength of materials.