Synthesis, inhibition behavior and recycling of Fe3O4@ZnAl-MoO4 LDH nanocomposite inhibitor

The nanocomposite corrosion inhibitor with MoO 4 2− intercalated ZnAl-LDH coating on the Fe 3 O 4 surface was synthesized by ion exchange methods. The morphology, structure and magnetic properties of the composite were characterized by transmission electron microscope, X-ray diffraction, Fourier transform infrared spectra and vibrating sample magnetometer . The release behavior of MoO 4 2− and corrosion inhibition of the sample under “NO MF” (without external magnetic field) and “MF ON” modes (under external magnetic field) were measured by UV–vis spectroscopy, electrochemical tests and scanning electron microscopy. Calcination the composite after release test and redispersing the sintered products in Na 2 MoO 4 solution, the composite was regenerated. The results show that the superparamagnetic nanocomposite inhibitor Fe 3 O 4 @MoO 4 -LDH presents well-defined core-shell structure. The release test revealed that for “NO MF” mode the release of MoO 4 2− from Fe 3 O 4 @MoO 4 -LDH displayed smaller t 0.5 (Time to reach half release equilibrium) of 4.25min and shorter time (3 h) to reach equilibrium with high release amount of 71.95% for 0.5  g/L nanocomposite. Under “MF ON” mode the release rate is slower with longer t 0.5 (from 26.40min to 1.60 h for 0.5  g/L to 4.0  g/L nanocomposite, respectively), thus realizing sustained release up to 12 h. At the same time, the release amount decreases and the release time prolongs with the concentration increasing. Correspondingly, the MoO 4 2− has a long-term excellent corrosion inhibition effect over 71.96% at 24 h on Q235 steel. For “NO MF”, the release route mainly contains the interlayer intraparticle diffusion between the LDH layers and interparticle diffusion among the outer LDH. While for “MF ON” mode, the diffusion between magnetic particles of corrosion inhibitor becomes important. The reconstructed inhibitor still maintains excellent superparamagnetic properties and high corrosion inhibition efficiency, up to 64.84% after five cycles.