In situ assembled MIL-101(Cr) composite functionalized with chitosan and tannic acid as an efficient adsorbent for...

The uncontrolled release of lead (Pb²⁺) into water bodies presents a major risk to both environmental integrity and human health, owing to its high toxicity, long-term stability, and tendency to accumulate in living organisms. Addressing this challenge, the present study reports the synthesis of a novel, eco-compatible bioinorganic composite-Chitosan-Tannic Acid@MIL-101(Cr) (CS-TA@MIL-101)-designed for efficient Pb²⁺ adsorption from aqueous media. The composite integrates the high surface area of MIL-101(Cr) with the functional versatility of chitosan and tannic acid via in situ self-assembly. Characterization by FTIR, XRD, SEM, TGA, and BET confirmed the formation of a stable, hierarchically porous material with a surface area of 884.8 ± 3.6 m²/g, pore volume of 0.58 ± 0.02 cm³/g, and dual micro-/mesoporosity. Batch experiments demonstrated a maximum Pb²⁺ adsorption capacity of 317.6 ± 1.9 mg/g and removal efficiency of 98.88 ± 0.7%. Kinetic data fit both nonlinear and linear pseudo-second-order (PSO) models with R² = 0.998/0.997 and RMSE = 0.78/1.03, indicating a chemisorption mechanism. Isothermal studies followed the Langmuir model with R² = 0.999/0.998 and RMSE = 0.93/1.08, suggesting monolayer adsorption. Thermodynamic analysis confirmed spontaneous and endothermic behavior (ΔH° = 85.84 ± 2.74 kJ/mol). After undergoing six regeneration cycles, the composite maintained an efficiency of 90.24 ± 0.6%, highlighting its strong reusability and suitability for long-term, eco-friendly water purification efforts.