Sustainable Mesoporous Silica Nanoparticles from Groundnut Shells for High-Efficiency Cr(VI) Removal

The increasing concentrations of toxic hexavalent chromium [Cr(VI)] in aquatic systems pose a major threat to human health and the environment, necessitating the development of high-performance, reasonably priced, and environmentally friendly adsorbents. Mesoporous silica nanoparticles (SiNPs) were synthesized from groundnut shell waste via alkaline extraction followed by acid precipitation, yielding 21 %. Amorphous, mesoporous silica with a high surface area (84.61 m² g–1) and a large number of silanol groups was confirmed by characterization (XRD, FTIR, SEM–EDS, and BET). Batch adsorption experiments revealed that the maximum Cr(VI) removal efficiency reached 92 % at pH 4, with an optimum equilibrium adsorption capacity (qₑ) of 4.5955 mg g–1. The process followed pseudo-second-order kinetics (R2 = 0.99) and the Freundlich isotherm model (R2 = 0.9826), indicating chemisorption. Surface complexation was confirmed by post-adsorption analyses, demonstrating the effectiveness the SiNPs as environmentally friendly adsorbents for wastewater treatment.