Nature-inspired synthesis of silver microparticles using lemongrass extract for highly efficient removal of chromium and lead from industrial waste water

ABSTRACT The silver microparticles were prepared using an aqueous extract of Cymbopogon citratus (lemongrass) by a green synthesis approach, where Ag+ ions were reduced to Ag0, leading to the formation of microparticles. The synthesized adsorbents possessed numerous surface functionalities (OH, C–O, and C = C). The highest removal rate of 94.3% was achieved for Pb(II) through batch adsorption experiments at a pH level of 4, a contact duration of 13 min, and an adsorbent dose of 50 mg/100 ml. Furthermore, Cr(III) showed 92.6% adsorption at pH 5, and a contact time of 15. The efficiency of the adsorption procedure was well indicated by the Freundlich isotherm model, as evidenced by the coefficient of determination (R2) for lead and chromium heavy metals surpassing 0.99427 and 0.99547, respectively. The kinetic data demonstrated the best fit with pseudo-first order in all experimental concentrations, exhibiting physical adsorption as the rate-limiting step. The thermodynamic research describes the current procedures as spontaneous and endothermic, where Gibbs free energy (ΔGo), enthalpy change (ΔHo), and entropy change (ΔSo) were −5243.35 kJmol−1, 12.45 kJmol−1, and 22.138 kJmol−1 for lead and −7922.71 kJmol−1, 15.43 kJmol−1, and 25.21 kJmol−1 for Cr(III), respectively.