Adsorption kinetics, isotherm, and thermodynamics studies of phytochemical-assisted synthesized ZnO nanoparticles for the removal of selected heavy metals from abattoir wastewater

Abstract

This study explores the green synthesis and adsorption capacity of zinc oxide nanoparticles (ZnO NPs) for the degradation of heavy metals (Cr, Cu, Pb, and Cd) from abattoir wastewater. ZnO NPs were synthesized by the Piliostigma thonningii leaf extract-mediated synthesis as reducing and stabilizing agents. Confirmation of crystalline wurtzite ZnO formation with particle sizes between 37–54 nm and a surface area of 32.54 m²/g was confirmed by characterization. The nanoparticles exhibited extensive metal adsorption with 87.22% (Cr), 86.82% (Pb), and 86.33% (Cu) removal efficiencies under optimized conditions. Adsorption kinetics followed the Langmuir isotherm with the maximum capacities for adsorption of 91.25, 88.57, 85.92, and 82.34 mg/g for Cr, Pb, Cu, and Cd, respectively, suggesting monolayer adsorption. Kinetic data fitted the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Thermodynamic analysis reported that the process was endothermic and spontaneous, and it enhanced adsorption with increasing temperature. The results indicate that green-synthesized ZnO NPs are viable, green adsorbents for the removal of heavy metals from Abattoir effluents. • Green ZnO nanoparticles synthesized using Piliostigma thonningii leaf extract. • Crystalline wurtzite ZnO formed with particle sizes of 37–54 nm and 32.54 m²/g surface area. • High removal efficiencies achieved for Cr (87.22%), Pb (86.82%), and Cu (86.33%). • Langmuir isotherm showed monolayer adsorption with capacities up to 91.25 mg/g. • Pseudo-second-order kinetics indicated chemisorption as the dominant mechanism. • Adsorption was spontaneous and endothermic, improving at elevated temperatures. • Green-synthesized ZnO NPs demonstrated strong potential for abattoir wastewater treatment.

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