Circular Economy-Driven Synthesis of SBA-15 Mesoporous Silica from Sugar Cane Husk Ash for Environmental and Catalytic Applications

Abstract

A circular economy seeks to retain waste streams in productive use rather than dispose of them. Sugarcane bagasse ash (SCBA), a combustion residue generated in sugar and ethanol mills, is produced at large scale and contains substantial amorphous silica. This study investigates the conversion of SCBA into SBA-15 mesoporous silica within a circular-economy framework. SCBA was pretreated using conventional HCl/NaOH and greener citric acid (CA), L-cysteine (Lcys), and TPAH routes, followed by P123-templated sol-gel synthesis. The resulting materials were characterized by XRD, FTIR, BET, BJH, SEM, TEM, TGA, and EDS and evaluated for brilliant green dye adsorption and biodiesel production from waste sunflower oil. SCBA-derived SBA-15 exhibited BET surface areas of 18–466 m²/g and pore diameters of 3.12–15.6 nm, depending on pretreatment. CA-500 and Lcys-500 produced larger pores (14.9–15.6 nm) than HCl treatment (3.12 nm), but retained higher carbon contents (6.73–48.83 wt%). HCl-derived SBA-15 achieved the highest dye removal (55.1%; 5.51 mg/g), whereas Lcys-500 gave the highest FAME yield (5.60%). Circularity assessment indicated strong waste-prevention and renewable-feedstock benefits but limitations associated with chemicals, energy, and template recovery. Standardized pretreatment, template recovery, and life-cycle costing remain priorities for achieving greater circularity.