Sustainable Magnetic Nanosilica Composites Derived from Biosilica for Efficient Brackish Water Treatment: Adsorption Performance, Mechanisms, and Regeneration
J. Environ. Nanotechnol., Volume 15, No 2 (June 2026) pp. 110-124
Abstract
Sustainable technologies for brackish water treatment are essential for addressing global freshwater scarcity. In this study, bio-derived magnetic nanosilica composites were synthesized from rice husk ash and integrated with Fe₃O₄ nanoparticles to enable rapid magnetic recovery. Surface functionalization using amine, carboxyl, and chitosan groups was introduced to enhance divalent-ion adsorption. Structural and physicochemical characterizations confirmed the formation of mesoporous nanocomposites with a preserved amorphous silica structure, well-dispersed magnetite nanoparticles, and tunable surface chemistry. Adsorption experiments demonstrated significantly enhanced Ca²⁺ removal by the functionalized composites compared to unmodified nanosilica. The chitosan-functionalized material exhibited the highest adsorption capacity and removal efficiency under neutral pH conditions at a salinity of 1000 mg/L while maintaining strong performance at elevated salinities. Adsorption followed pseudo-second-order kinetics and was well described by the Langmuir isotherm model, indicating monolayer adsorption on homogeneous active sites. Thermodynamic analysis revealed spontaneous and endothermic adsorption behavior. The composites demonstrated excellent regeneration stability by retaining high performance after ten continuous cycles, with magnetic separation efficiency exceeding 98%. Continuous-flow column experiments further confirmed prolonged breakthrough times for the functionalized materials. The combined advantages of bio-derived silica, tailored surface functionalization, and magnetic recoverability provide a sustainable platform for selective hardness removal in complex brackish-water systems.
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