Rice Husk Ash as a Sustainable Silica Precursor for the Preparation of Ordered Mesoporous COK-12

Abstract

The use of agricultural residues as functional materials provides an effective way to achieve the goals of dual use of agricultural residues and development of value added products. In this work, rice husk ash (RHA) was investigated as a renewable silica precursor for preparing ordered mesoporous COK-12.  preparation sequence comprised controlled combustion of rice husk, chemical purification of the ash, alkaline dissolution of its silica fraction, change to sodium silicate, and subsequent template-assisted assembly of COK-12 with Pluronic P-123 in a citrate-buffered, near-neutral medium. The resulting solid was examined using X-ray diffraction (XRD), X-ray fluorescence (XRF), N₂ adsorption–desorption analysis, Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM),  energy-dispersive X-ray spectroscopy (EDS/EDX), Barrett–Joyner–Halenda (BJH)/density functional theory (DFT) pore-size analysis, Brunauer–Emmett–Teller (BET) surface-area measurements, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS),  thermogravimetric/differential thermogravimetric analysis (TGA/DTG), and 29Si magic-angle-spinning nuclear magnetic resonance (29Si MAS NMR). Low-angle diffraction and electron microscopy provide complementary evidence for mesoscopic ordering, whereas nitrogen sorption provides quantitative information on accessible surface area, pore volume, and pore dimensions. FTIR, Raman and 29Si MAS NMR provide information concerning the siloxane network and surface silanol groups, whereas XPS and EDX/XRF establish the chemical composition and purity of the material. The work establishes the feasibility of converting an abundant agricultural residue into an ordered mesoporous silica and establishes a sustainable route for producing COK-12 with potential applications in adsorption, catalysis, environmental remediation and energy-related technologies.