Kinetic and equilibrium investigation of the lead (II) adsorption via orange peel and lemon peel: realistic adsorption design for poly(limonene) framework

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A laboratory investigation was performed to regulate the physicochemical attributes—geomorphological and organizational, kinetic estates, and purposeful groups—of orange ( Citrus × sinensis) and lemon ( Citrus × limon) with a view toward a prospective adsorbent of toxic lead ions from aquatic solution. Outcomes demonstrated that optimal requirements for the Pb (II) removal are a preliminary concentration of 50 mg/L, an adsorbent mass of 0.2 g, and 6 and 4.4 as pH for orange peel and lemon peel, respectively. The investigational statistics were discussed via Freundlich, Langmuir, and D–R isotherm. Equilibrium statistics matched appropriately via Langmuir typical with a qmax of 16.76 mg/g for orange peel and 76.92 mg/g for lemon peel. The kinetic adsorption process was inspected and was adequately accomplished via a second-order equivalence. The characterization of lemon peel and orange peel was examined with a scanning electron microscope, Vis-IR spectroscopy, and GC-mass. The Pb(II) adsorption spontaneity onto orange peel is enhanced by enhancing temperature. The positive ∆ H° (53.76 kJ/mol) estimate implies an endothermic system. The positive ∆ S° (180.41 J/mol) estimate implies an enhanced randomness on the solid/liquid periphery during adsorption. In the case of lemon peel, the Pb(II) adsorption spontaneity is reduced by temperature. The negative ∆ H° (−32.71 kJ/mol) estimate implied an exothermic adsorption nature. The ∆ S° parameter was (−70.17 J/mol.K) for lemon peel, indicating that the Pb(II) in the bulk phase was more disorderly. Scanning electron microscopy exhibits a distinctive development in the adsorbent surface. The removal efficiency reached 92.34 and 90.4 for lemon peel and orange peel, respectively, at 0.2 mol/L KOH. Molecular electrostatic potential, frontier molecular orbital, and the density of states analysis were conducted to investigate the important active sites on the adsorption.