Synthesis of a Magnetic ZIF-67-Derived and NaBH4-Modified g-C3N4 Adsorbent for Removal of Tetracycline in Aqueous Solution

Abstract Graphitic carbon nitride (g-C3N4) has attracted significant attention as an adsorbent for antibiotic removal; however, its relatively low specific surface area and poor recyclability limit its practical applications. In our previous work, we synthesized RCN-1-550 by modifying g-C3N4 with NaBH4, which resulted in a significantly higher specific surface area. In this study, we aimed to further improve the adsorption performance and facilitate the recovery of the adsorbent by introducing ZIF-67-derived magnetic components. A magnetic adsorbent, ZIF-67@RCN-1-800, was synthesized by assembling RCN-1-550 with ZIF-67 followed by calcination at 800 °C under a nitrogen atmosphere. The specific surface area of ZIF-67@RCN-1-800 increased by 10.03-fold compared with that of RCN-1-550. At 303 K, with a tetracycline (TC) concentration of 50 mg·L–1 and an adsorbent concentration of 200 mg·L–1, the adsorption process approached equilibrium within approximately 30 min, achieving a removal rate of 91.49% and an adsorption capacity of 228.73 mg·g–1. ZIF-67@RCN-1-800 exhibited near-superparamagnetic behavior with a saturation magnetization of 55.86 emu/g, allowing for easy magnetic separation using an external magnetic field. The adsorbent retained stable adsorption performance after five consecutive adsorption–desorption cycles. These results demonstrate that ZIF-67@RCN-1-800 combines enhanced adsorption performance with rapid magnetic recovery, providing a promising recyclable adsorbent for efficient TC removal from aqueous solutions.