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.