MIL-88A grown in-situ on graphitic carbon nitride (g-C3N4) as a novel sorbent: Synthesis,characterization, and high-performance of tetracycline removal and mechanism

The extensive and accumulative use of tetracycline (TC) in the environment has become a serious problem. In this study, MIL-88A/g-C₃N₄ micro-nano particles were successfully prepared through a simple, low-cost, one-step hydrothermal method for TC adsorption in water. At a pH of 7.0, the maximum adsorption capacity (154.51 mg·g^?1) of MIL-88A/g-C₃N₄ is reached at room temperature. Owing to its porous structure and large pore size (>2.06 nm) of MIL-88A/g-C₃N₄, TC can be adsorbed on both external and internal surfaces. Kinetic and thermodynamic studies have shown that the pseudo-second-order kinetic and the Langmuir-Freundlich model can be used to describe the adsorption process, which is a spontaneous endothermic process. The mechanism study reveals that the TC adsorption process by MIL-88A/g-C₃N₄ is mainly through electrostatic interaction and the ion exchange of COOH and NH₂ groups on MIL-88A/g-C₃N₄ to TC. After simple pickling and water washing, MIL-88A/g-C₃N₄ can still reach 83.1% of the original adsorption capacity after five cycles, which proves that MIL-88A/g-C₃N₄ can be a promising adsorbent.