Novel Morphology-Controlled Magnetic Hollow Mesoporous Fe₃O₄ Nanocarriers for Inhibitor Release

Hollow mesoporous Fe₃O₄ microspheres are attractive as corrosion inhibitor carriers for their structural stability, and strong superparamagnetic properties. Here, the morphology-controlled magnetic hollow mesoporous Fe₃O₄ nanocarriers (MHMNs) with saturation magnetization of ca. 77 emu/g were fabricated by self-template etching route. Serial characterization results showed that the sample (MHMNs-7.0), obtained by etching MHMNs with 7.0 mg/mL of the oxalic acid solution, presented the largest cavity volume and a rich pore structure, which promotes its high loading capacity of 77.6% for 2-mercaptobenzothiazole (MBT) inhibitor. The resulting material could be used as the carrier for loading various types of inhibitors, e.g., MBT, Ce³⁺, benzotriazole (BTA), and under negative vacuum treatment. The release behavior of the obtained composite inhibitors was detected by UV-vis spectroscopy, and the inhibition behavior of the composite inhibitors for mild steel in 3.5% NaCl solution was evaluated by electrochemical impedance spectroscopy and immersion tests. The results showed that all of the as-obtained composites presented magnetic-controlled release properties and good inhibition performance. Without the external magnetic field (no MF mode), the release of MBT from MHMNs-7.0/MBT mainly involved Fickian diffusion. Under the application of a magnetic field (MF ON mode), the release behavior was dominated by a swelling mechanism, Fickian diffusion, and diffusion between magnetic particles. The nanocomposite inhibitor had good inhibition efficiency for carbon steel in 3.5% NaCl solution with a maximum of 93.66%, and its continuous release properties enabled it to exhibit long-term corrosion inhibition performance.