Synthesis of a Tannin-Immobilized Magnetite/Graphene Oxide Composite for Magnetically Separable and Reusable Arsenic Adsorption

This study proposed a novel method to remove arsenic pollutants using a magnetically separable adsorbent based on a non-toxic biopolymer. We synthesized a tannin-immobilized magnetite/graphene oxide composite (BT–Fe3O4/GO) using tannin extracted from black tea leaves (BT) and a hydrothermal method. Various characterization methods, such as Field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), confirmed the successful synthesis of BT–Fe3O4/GO. The interactions involved in the synthesis were subsequently demonstrated. The maximum adsorption capacity (12.25 mg/g) of BT–Fe3O4/GO was approximately three times higher than that of Fe3O4/GO (3.487 mg/g), which indicated that tannin and Fe3O4 have synergetic adsorption affinities for As (V) ions. The adsorption performance of BT–Fe3O4/GO under acidic conditions was better than that under basic conditions. Based on the experimental results, the possible adsorption mechanisms of BT and Fe3O4 were described. The adsorption capacity of BT–Fe3O4/GO was approximately 80% of that of fresh BT–Fe3O4/GO, even after the third adsorption cycle. Moreover, it retained sufficient magnetic properties to collect the adsorbent after As adsorption. Owing to the synergetic adsorption performance of tannin and Fe3O4, tannin immobilization is a promising removal method for As ions, and BT–Fe3O4/GO is expected to be an alternative adsorbent for As remediation.