Preparation of magnetic core-shell Fe3O4@MBT-LDH composite and its application as an effective inhibitor for carbon steel

The core-shell structural Fe3O4@MBT-LDH was synthesized via the ion exchange method, with MBT (2-mercaptobenzothiazole) inhibitor ions intercalated lamellar ZnAlCe-LDH attaching closely to the Fe3O4 microspheres surface. The morphology, composition, structure, and magnetic properties of the composite were measured by transmission electron microscope, X-ray diffraction, Fourier transform infrared spectra, and vibrating sample magnetometer. The release behavior of MBT ions and corrosion inhibition performance of the Fe3O4@MBT-LDH under “no MF” (without an external magnetic field) and “MF ON” modes (under an external magnetic field) were measured by UV–vis spectroscopy, electrochemical tests, scanning electron microscopy, and X-ray photoelectron spectrometer (XPS). Calcinating the composite after the release test and redispersing the sintered products in MBT ions-containing solution, the composite was reestablished. Results showed that the Fe3O4@MBT-LDH possessed moderate MBT loadings amount (12.0%) and presented strong superparamagnetic properties with saturation magnetization (Ms) of 27.6 emu⋅g−1. The release behavior of the MBT− from the composite was sustainable and could be further slowed down by using an external magnetic field with changing the release mechanism. The release curve reached equilibrium with a longer time of 48 h and a lower release amount of 57.0% under MF ON mode than that of no MF mode with a time of 7 h and a release amount of 74.7%. The Fe3O4@MBT-LDH owned a good and long-term protection performance for Q235 carbon steel with maximum corrosion inhibition efficiency (ηe) of up to 93.30%. As a promising controlled-release inhibitor, it could be recycled and regenerated by simple treatment, still having high ηe higher than 80% and excellent magnetic properties with Ms of 21.47 emu⋅g−1 after five cycles. The corrosion mechanism for carbon steel was further analyzed by quantum chemical calculations and molecular dynamics simulation.