High efficiency Pb(II) removal from water using STPP-crosslinked chitosan-muscovite composite

Lead contaminated wastewater poses serious risks to aquatic ecosystems and human health, necessitating the development of efficient, low-cost, and environmentally sustainable remediation technologies. In this study, a sodium tripolyphosphate (STPP)-crosslinked chitosan-muscovite (CSN + MS) composite adsorbent was successfully synthesized and evaluated for Pb 2 ⁺ removal from aqueous solutions. The composite was characterized using FTIR, XRD, TGA, and FESEM analyses, which confirmed the successful incorporation of chitosan into the muscovite matrix along with enhanced structural integrity and thermal stability. Batch adsorption experiments were conducted to assess the effects of pH, adsorbent dosage, initial Pb 2 ⁺ concentration, contact time, and temperature. The adsorption efficiency increased with increasing pH, with optimum adsorption performance observed near neutral pH. Because lead hydroxide precipitation may occur at higher pH values, adsorption studies were evaluated under controlled conditions to minimize precipitation effects. The composite exhibited a high adsorption capacity, with a maximum monolayer capacity of 625 mg g⁻ 1 as predicted by the Langmuir isotherm model (R 2 = 0.997), indicating monolayer adsorption behavior, while the Freundlich model suggested surface heterogeneity. The adsorption mechanism involves electrostatic attraction, ion exchange, and surface complexation through functional groups such as amine, hydroxyl, siloxane, and phosphate. Thermodynamic analysis revealed that the adsorption process is spontaneous and exothermic, demonstrating the strong potential of CSN + MS as an eco-friendly adsorbent.