Calcium hypochlorite-assisted expanded graphite sheets for efficient Pb2+ and Cd2+ adsorption and box-behnken design analysis

EGS was produced using modified Hummers’ method and characterized using FTIR, SEM, XRD, and BET analysis. Batch adsorption experiments assessed Pb 2+ and Cd 2+ adsorption under different concentrations, contact times, and temperatures. Adsorption mechanisms were analyzed via pseudo-second-order kinetics, Langmuir isotherm, and thermodynamic studies, and Pb 2+ (highly adsorbed) was optimized by Box-Behnken design of the RSM. EGS showed a sheet-like morphology with a pore size of 20.70 nm, surface area: 117.53 m 2 /g, with hydroxyl/oxygen functional groups, confirming the oxidation of graphite. The Langmuir R 2 > Freundlich, Dubinin–Radushkevich and Temkin adsorption isotherms directed monolayer adsorption, following the pseudo-second-order kinetics. due to low Weber-Morris R 2 values, confirmed absences of intra-particle diffusion with chemisorption dominance. The maximum adsorption capacities reached 186.79 mg/g for Pb 2+ and 153.65 mg/g for Cd 2+ at 65 °C, with thermodynamic spontaneity (ΔG < 0) and endothermicity (ΔH > 0). EGS showed higher Pb 2+ affinity, optimized by the Box-Behnken model, proving its effectiveness. EGS could be useful for wastewater treatment.