Sequestration of aqueous-bound cadmium ions using ZnO nanoparticle synthesized from <i>Ocimum gratissimum</i> leaf extract: kinetic, isotherm, and thermodynamics studies

Nanoparticles (NPs) have found numerous applications in various areas of science, technology, engineering, and mathematics (STEM), including drug delivery, quality control, environmental assessment, and diagnostics. This is primarily because of its environmentally friendly nature and cost-effectiveness. In recent times, NPs have been explored for metal remediation over traditional methods. ZnONPs were produced successfully from <i>Ocimum gratissimum</i> (OG) leaf extract (ZnONP-OG) and characterized using SEM-EDX, XRD, BET, and FTIR. The potency and optimal clean-up conditions for aqueous-bound Cd were investigated using the batch-type adsorption process. The optimal cleanup conditions were observed at a contact time of 15 min, temperature of 303 K, adsorbent dose of 0.5 g, initial concentration of 25 mg/L, and pH of 11. Optimum removal percentage of >93% was observed, and the experimental data best fitted the Langmuir isotherm model (R²:0.999) and the pseudo-second order kinetic model (R²:0.99). Thermodynamic studies revealed a spontaneous and exothermic sorption process for the uptake of Cd from aqueous solutions onto the ZnONP-OG. Overall, the results demonstrated that the ZnONPs synthesized from OG were effective in decontaminating Cd from aqueous solutions and could serve as a potent and cheap substitute compared to conventional adsorbents.