Adsorptive performance of SPE via modified POM biochar for Pb(II) and tetracycline with concurrent antimicrobial action

This study developed a novel, eco-friendly solid-phase extraction (SPE) sorbent, modified pomegranate biochar (POM), from the agricultural waste of pomegranate peel for the efficient removal of toxic lead (Pb(II)) and the tetracycline (TC) antibiotic from aqueous solutions. Synthesized POM was comprehensively characterized using (SEM, TEM, FT-IR, and XRD) and confirmed POM’s hierarchical core-shell nanostructure, enriched surface functional groups. Optimized SPE conditions using POM achieved maximum adsorption capacities of 3900 ± 71 (RSD = 1.8%, n = 3) µmol/g for Pb(II) at (pH 7, 20 s microwave-assisted) and 87.6% ± 0.18 (RSD = 0.001%, n = 3) removal for TC at (pH 4, 30 min shaking). while PO achieved (2000 ± 71 (RSD = 2.8%, n = 3) µmol/g Pb(II); and 45.9% ± 1.8 (RSD = 0.03%, n = 3) TC removal). Although the pseudo-second-order (PSO) model accurately describes the kinetic data for Pb(II) adsorption on POM and PO, this alone does not prove a chemisorption mechanism. In general, the thermodynamic parameters, especially ΔH°, have proved that the primary mechanism is physisorption; nevertheless, the excellent fit to the PSO model suggests that the adsorption process may incorporate certain characteristics of chemisorption or that the rate-limiting step involves the sharing or exchange of electrons. While TC obeys the pseudo-first order model, indicating a physisorption mechanism for both POM and PO. Additionally, the Langmuir model provides the best fit for both POM and PO with Pb(II) and TC, indicating the formation of a monolayer on the adsorbent surface. Efficient desorption used 1 M HCl for Pb(II) (98.7% recovery) and acidified methanol (1:1 v/v HCl: methanol) for TC (99.3% recovery). The Limit of Detection (LOD) and limit of quantification (LOQ) for TC were 1.725 ppm and 5.227 ppm, while Pb(II) ions were 16.27 ppm and 50.06 ppm, respectively. The thermodynamic parameters for the adsorption of Pb(II) and TC onto both POM and PO confirm a spontaneous and endothermic process driven by an increase in entropy. POM also exhibited antibacterial activity comparable to that of a standard antibiotic, particularly against Gram-negative bacteria (E. coli and P. aeruginosa).