Design and optimization of chitosan–polyethylenimine encapsulated aluminum–palladium layered double hydroxide for efficient paraquat herbicide adsorption via Box–Behnken approach

The AlPd-LDH/CS-PEI hydrogel beads was created by embedding aluminum–palladium layered double hydroxide (AlPd-LDH) within a chitosan/polyethylenimine (CS-PEI) framework, utilizing epichlorohydrin as a cross-linking agent. These composite hydrogel beads were intended for the active capture of the cationic herbicide paraquat (PQ²⁺). A complete assessment of the structural and surface belongings of the adsorbent was conducted through various techniques, including PXRD, XPS, FESEM, EDX, FT-IR, and nitrogen adsorption–desorption isotherm. The study exposed a mesoporous architecture considered by a surface area measuring 57.54 m²/g. To investigate the adsorption process, batch tests were achieved, examining the belongings of pH, temperature, dosage, and initial paraquat concentration. Kinetic studies indicated that the adsorption method adhered to pseudo-second-order kinetics, while the equilibrium data fit the Langmuir isotherm model, which signifies monolayer adsorption. The calculated adsorption energy (34.58 kJ/mol) and thermodynamic limits (ΔG°, ΔH°, and ΔS°) indicate that the procedure is spontaneous and endothermic. An examination of the thermodynamic belongings reveals notable communications among the adsorbent and the adsorbate. These interactions primarily stem from physical forces such as electrostatic attractions, pore filling, π–π stacking, and hydrogen bonding, as opposed to covalent or coordinative chemical bonds. These results shed light on the favorable and reversible adsorption appearances of PQ²⁺ onto the hydrogel beads. Furthermore, optimization techniques, including Box–Behnken design (BBD) and response surface methodology (RSM), significantly enhanced adsorption efficacy, highlighting the potential of this composite for water purification requests.