Introduction: The synthesis of Fe₃O₄ magnetic nanomaterials has been considered due to their potential applications in wastewater treatment. The surface coating agent or stabilizing agent of Fe₃O₄ nanomaterials can significantly affect their properties and final applications. Green synthesis methods are considered as an alternative strategy to avoid the disadvantages of chemical reactions that may involve some toxic chemicals or solvents. In this regard, plants are used as one of the most useful sources for the green synthesis of nanoparticles because they have a wide variety of metabolites that can be used as stabilizing agents. The current research was carried out with the aim of green synthesis of magnetic iron oxide nanoparticles (Fe₃O₄) functionalized with proanthocyanidin and evaluating its application in lead (Pb) ion removal from battery industry wastewater.

Materials and Methods: Hydrophilic nanoparticles of iron oxide (Fe₃O₄) functionalized with proanthocyanidin were synthesized through hydrothermal approach. In order to identify and investigate the properties of the synthesized adsorbent, the obtained Fe₃O₄ nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Wastewater samples were taken from battery industry wastewater for absorption tests. Adsorption experiments were performed continuously and parameters of contact time, adsorbent dose and pH were considered as effective factors on the absorption process. The optimization of absorption tests was done through design expert software based on three parameters with response surface methodology using Box-Behnken. Also, the modeling of adsorption kinetics process using pseudo-first-order and pseudo-second-order kinetics and the degree of conformity of experimental data of adsorption equilibrium with Langmuir and Freundlich adsorption isotherm models were investigated.

Results and Discussion: According to the findings of the SEM image, most of the produced nanoparticles have a spherical structure and tend to form larger masses. TEM image of Fe₃O₄ nanoparticles showed that the average size of these nanoparticles is 47±7.3 nm. The XRD pattern indicated the presence of cubic spinel structure in Fe₃O₄ nanoparticles. Based on the results, the effect of contact time and adsorbent dosage on the Pb adsorption process onto magnetic iron oxide (Fe₃O₄) nanoparticles functionalized with proanthocyanidin was more effective than pH. At high contact time, more adsorbent dosage and in low pH range, Pb removal was done with much higher efficiency. The highest Pb removal efficiency of 93.81% from battery industry wastewater was obtained under optimal conditions of neutral pH (6.5), contact time of 200 minutes and magnetic iron oxide nanoparticles (Fe₃O₄) functionalized with proanthocyanidin dosage to 4 mg/L. The kinetics and isotherm of Pb adsorption on magnetic iron oxide nanoparticles (Fe₃O₄) functionalized with proanthocyanidin were consistent with pseudo-quadratic and Langmuir models, respectively. Therefore, the absorption rate is controlled by chemical interaction and the absorption process is a single layer type.

Conclusion: The results of the present study showed that the iron oxide (Fe₃O₄) magnetic nanoparticle adsorbent functionalized with proanthocyanidin has a good ability to Pb ions removal from the battery industrial wastewater. Due to the affordable cost, simple preparation method and environmentally friendly process, as well as the high efficiency of the adsorbent prepared, it can be used as a suitable alternative to the use of relatively expensive adsorbents such as activated carbon in the removal of heavy metal ions from wastewaters.