Quaternized polydimethylaminoethyl methacrylate polymer brushes functionalized magnetic graphene oxide for efficient removal of diclofenac from complex environments: synthesis, adsorption performance, DFT calculation and mechanism

Diclofenac as one of the most widely used anti-inflammatory drugs has been found in various aqueous environments in recent years. In this work, a quaternized polydimethylaminoethyl methacrylate functionalized polydopamine-coated magnetic graphene oxide (denoted MGO@PDA@PDMAEMA*) was prepared for the efficient removal of diclofenac. The polydopamine (PDA) was coated on MGO and then the dopamine derivative containing surface-initiated polymerization initiator was immobilized on the MGO@PDA by controlling the self-polymerization of dopamine and dopamine derivative. Finally, PDMAEMA brushes were grafted onto MGO@PDA by atom transfer radical polymerization, and quaternization by reacting with bromopropane. The morphology and structure of the MGO@PDA@PDMAEMA* are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and vibrating sample magnetometer and Zeta potential analysis. The MGO@PDA@PDMAEMA* exhibits the excellent thermal and chemical stability, high zeta potential (54.74 mV) and magnetic responsivity (36.57 emu·g−1), which can be used as an ideal adsorbent for rapid isolation of targets. The adsorption isotherms and kinetics of diclofenac followed well with the Langmuir model and pseudo-second-order kinetic model, respectively. The maximum saturation adsorption capacity from Langmuir model was 1960.8 mg·g−1 under pH 5 at temperature of 293 K, and the removal rate of diclofenac was more than 90% within half an hour. The adsorption and density functional theory demonstrated that the quaternary ammonium ion on the MGO@PDA@PDMAEMA* was the main electrostatic binding site to diclofenac. More importantly, high removal efficiency of diclofenac in the environmental water confirmed the potential of MGO@PDA@PDMAEMA* as a diclofenac adsorbent.