Removal of lead and cadmium ions by single and binary systems using phytogenic magnetic nanoparticles functionalized by 3-marcaptopropanic acid

The present research study is focused on green fabrication of superparamagnetic Phytogenic Magnetic Nanoparticles (PMNPs), and then its surface functionalization with 3-Mercaptopropionic acid (3-MPA). The resulting material (i.e. 3-MPA@PMNPs) characterized by FTIR, powder XRD, SEM, TEM, EDX, VSM, BET and TGA techniques and then further employed for the investigation of the adsorptive removal of lead (Pb²⁺) and cadmium (Cd²⁺) ions from aqueous solutions in single and binary systems. The material showed fastest adsorptive rate (98.23%) for Pb²⁺ and (96.5%) Cd²⁺ within the contact time of 60 min at pH 6.5 in the single system. The experimental data were fitted well to Langmuir isotherm, indicated monolayer adsorption of both metal ions onto 3-MPA@PMNPs and an estimated comparable adsorptive capacity of 68.41 mg·g^-1 (Pb²⁺) and 79.8 mg·g^-1 (Cd²⁺) at pH 6.5. However, kinetic data agreed well with pseudo-second-order model, and indicated that the removal mainly supported chemisorption and/or ion-exchange mechanism. Thermodynamic parameters such as ΔGo°, ΔHo°, and ΔSo°, were -3259.20, 119.35 and 20.73 for Pb²⁺, and -1491.10, 45.441 and 7.87 for Cd²⁺ at temperature 298.15 K, confirmed that adsorption was endothermic, spontaneous and favorable. The material demonstrated higher selectivity of Pb²⁺ and its removal efficiency was (98.20 ±0.3)% in binary system experiments. The material persisted performance up-to seven (07) consecutive treatment cycles without losing their stability and offered comparable fastest magnetic separation (35 s) from aqueous solutions. Therefore, it is recommended that the prepared material can be employed to remove toxic heavy metal ions from water/wastewaters and this "green" method can easily be implemented at large scale in low economy countries.