Sustainable economic production of silica nanoparticles from rice husks for adsorptive removal of anionic and cationic dyes

The present study explores a novel microwave-assisted (MW) approach for advancing the sol-gel synthesis of silica nanoparticles from rice husk (RSN) to mitigate methylene blue (MB) and congo red (CR). According to physico-chemical and yield analysis, 50 min of MW calcination produced a high yield of 92 % RSN (RSN50) with a high surface area (208 m2/g). Under optimized conditions, the maximum adsorption capacities of MB and CR on RSN50 were 48.1 mg/g (at pH 5.6, Langmuir model) and 58.5 mg/g (at pH 2, Hills model), respectively. The MB adsorption kinetics on RSN50 followed a pseudo-second-order indicating chemisorption while CR adsorption on RSN50 followed a pseudo-first-order mechanism and positive ΔG signifying non-spontaneity. A regeneration study for 5 consecutive cycles showed retention of % dye removal capacity. The cost assessment showed a profit when compared to commercial silica nanoparticles proposing an efficient, economical, and sustainable substitute for varied applications.