Preparation and controlled inhibition behavior of Fe3O4/CS/inhibitors nanocomposite for carbon steel in 3.5% NaCl solution

The superparamagnetic Fe3O4/CS/inhibitor nanocomposite was synthesized by using ionic gel method with Fe3O4 as superparamagnetic core, chitosan as nanocarrier and molybdate (MoO42-) and benzoate (C6H5COO-) working as loaded inhibitors. The morphology, structure and magnetic property of nanocomposite were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and vibrating sample magnetometer. The release behavior of nanocomposite with and without external magnetic field ("no MF" mode and "MF ON" mode) was conducted by UV-vis spectroscopy, and the corrosion inhibition performance of nanocomposite for carbon in 3.5% NaCl solution was investigated by polarization curve and electrochemical impedance spectrum methods. The results show that the obtained Fe3O4 /CS/inhibitors was in a well-defined core-shell structure with MoO42- and C6H5COO- loaded flake-like chitosan shell stacking closely to Fe3O4 surface. Under no MF mode, the release behavior of nanocomposite was mainly ion exchange and Fickian diffusion mechanism. Under MF ON mode, the swelling of polymer chains and diffusion between magnetic nanoparticles were involved apart from the ion exchange and Fickian diffusion mechanism. With the addition of nanocomposite inhibitors in NaCl solution, the charge transfer resistance and inhibition efficiency of steel increased firstly and then decreased with the prolonging of immersion time. The highest inhibition efficiency of nanocomposite inhibitors in NaCl solution under on MF and MF ON mode was located in 30 min and 90 min respectively. The inhibition of nanocomposite for carbon steel in NaCl solution is resulting from the reduction of aggressive Cl- concentration in the solution due to the ion exchange between Cl- ions in solution and MoO42- and C6H5COO- ions in the nanocomposite, and the formation of ferric/ferrous molybdate, ferric/ferrous benzoate and basic ferric benzoate inhibition films on steel. This novel as-prepared composite owns superior loading capacity of inhibitors and its preparation process is especially simple relative to other nanocomposites in previous reported works.