Extraction of highly pure silica from rice husk as an agricultural by-product and its application in the production of magnetic mesoporous silica MCM–41

Rice husk is one of the agricultural by-products that is found abundantly around the world. After utilization of its organic matters as a source of energy in the combustion process, the remaining ash is rich in silica, which is a valuable precursor for production of silica materials. In this study, in the first step, the extraction of silica from rice husk was optimized by leaching with four acids of HCl, HNO3, H2SO4, and H3PO4, and in the second and third step, the mesoporous silica MCM–41 and the magnetic mesoporous silica MCM–41 (magMCM–41) were produced by the extracted silica. The produced materials were characterized by the XRF, XRD, FT-IR, N2 adsorption–desorption, VSM (vibrating sample magnetometry), TGA, SEM, and TEM analyses. The results of XRF analysis showed that the silica was extracted by 95.48% purity by leaching with HCl. The XRD and TEM analyses results revealed that the magMCM–41 was produced with a highly ordered hexagonal structure. The results of N2 adsorption–desorption analysis indicated that the magMCM–41 specific surface area, total pore volume, average pore diameter, and wall thickness were 695.7 m2 g−1, 0.65 cm3 g−1, 2.71 nm, and 1.59 nm, respectively. The magnetic property of the magMCM–41 was determined to be 10.61 emu g−1 at optimum conditions by the VSM analysis. The results of TGA analysis proved the thermal stability of the magMCM–41 by low total weight loss of 1.97%.