Preparation of a Magnetic Molecularly Imprinted Graphene Composite Highly Adsorbent for 4‑Nitrophenol in Aqueous Medium

In this article, a type of magnetic molecularly imprinted graphene composite as a highly efficient adsorbent was prepared by forming a molecularly imprinted sol–gel polymer on the surface of magnetic graphene. The magnetic Fe₃O₄ nanoparticles were first deposited on a graphene sheet to prepare the magnetic graphene (MGR). Using the obtained magnetic graphene as a supporting matrix, 4-nitrophenol (4-NP) as template, phenyltriethoxysilane and tetramethoxysilane as functional monomers, a magnetic molecularly imprinted graphene composite (MGR@MIPs) was subsequently formed after the sol–gel polymerization and extraction of 4-NP. The preparation conditions (concentrations of monomer and template, and reaction time) were optimized. The as-prepared MGR@MIPs was characterized by FTIR, VSM, SEM, and TEM images. Under the optimized conditions, the obtained MGR@MIPs exhibited ultrafast adsorption kinetics (2 min to achieve the equilibrium state), large binding capacity (142 mg/g), and high selectivity toward 4-NP (the imprinting factor α is 4.25). In addition, a high saturation magnetization of MGR@MIPs was demonstrated, which allows easy separation from solution by applying an external magnetic field. Meanwhile, MGR@MIPs can be regenerated and reused in successive six cycles with slight loss in adsorption capacity. Finally, MGR@MIPs was successfully used as a highly adsorbent material for the determination and separation of 4-NP in real samples combining with high-performance liquid chromatography (HPLC)