Preparation,Controlled Release Behavior And Inhibition Mechanism Of Magnetic Nanocomposite Inhibitor

Seawater circulating cooling technology has attracted people’s attention for its advantages of rich resources,reducing environmental pollution and saving fresh water resources.The corrosion of common metal equipment carbon steel in circulating cooling seawater is a serious problem that can not be ignored.At present,the multi-functional supported corrosion inhibitors have aroused more attention because it can realize the continuous release of corrosion inhibitor and prolong the protection of carbon steel.In this paper,superparamagnetic ferric oxide（Fe₃O₄）was introduced as magnetic source,and the core-shell structural layered double hydroxides（LDHs）-based magnetic nanocomposite inhibitor,magnetic chitosan（CS）supported inhibitor and hollow mesoporous Fe₃O₄ microspheres supported inhibitor were designed.The composite inhibitor prepared combined the magnetic property and characteristics of nanocontainer,in order to achieve the effect of magnetic controlled release,recycling and efficient corrosion inhibition.（1）Superparamagnetic composite inhibitors Fe₃O₄@Mo O₄-LDHs and Fe₃O₄@MBT-LDHs with core-shell structure were synthesized by ion exchange method.The core-shell structural Fe₃O₄@Zn Al Ce-Mo O₄-LDHs composite inhibitor was prepared by coprecipitation method.The results show that the composite inhibitor has magnetic controlled release property,and the magnetic field slows down the release rate and prolongs the inhibition time.Without magnetic field,the release mechanism is mainly interlayer diffusion of LDHs and the inter particle diffusion of LDHs layer.While under magnetic field,the release mechanism includes the interlayer diffusion of LDHs,the inter particle diffusion of LDHs layer and the diffusion among magnetic nanoparticles.The corrosion inhibition efficiency of the three kinds of composite inhibitors for carbon steel is 78.9%,93.6%and 89.1%respectively,and they still have good corrosion inhibition performance after repeated cycles.（2）Superparamagnetic Fe₃O₄/CS/inhibitors composite corrosion inhibitor with core-shell structure was prepared by ionic gel method,which improves the loading capacity and inhibition efficiency of corrosion inhibitor.When the concentration of chitosan was 2.0 mg/m L,the mass ratio of chitosan to sodium tripolyphosphate was 6and the concentration of sodium tripolyphosphate was 1.50 mg/m L,the loading capacity of Mo O₄^2-and C₆H₅COO^-reached maximum,which was 34.8%and 22.1%,respectively.The composite inhibitor has magnetic controlled release property and the external magnetic field could delay the release behavior of the two kings of inhibitors,which prolonged the release time to 48 h.Without magnetic field,the release of Fe₃O₄/CS/inhibitors is mainly controlled by ion exchange and Fick’s law of diffusion,while the release mechanism under magnetic field mainly includes ion exchange,Fickian diffusion and diffusion among magnetic nanoparticles.The inhibition efficiency of the prepared composite inhibitor Fe₃O₄/CS/inhibitors for carbon steel is up to 95.59%.In addition,three preparation conditions including the concentration of chitosan,the mass ratio of chitosan to sodium tripolyphosphate and the concentration of sodium tripolyphosphate during the fabrication process mainly affect the release behavior of the composite by affecting the release path.（3）Hollow magnetic Fe₃O₄ nanospheres were prepared by solvothermal method,and the superparamagnetic Fe₃O₄/MBT composite inhibitor with core-shell integrated structure was synthesized by loading 2-Mercaptobenzothiazole（MBT）inhibitor into the prepared Fe₃O₄ microspheres via impregnation method,which realizes the multifunctionality of the composite inhibitor.The MBT loading capacity of the composite inhibitor is 55.4%and the composite inhibitor presents the magnetic controlled release performance,when the magnetic field strength is 1350 GS,the release amount was only 10%at release time of 37.66 h.Without magnetic field,the release mechanism is mainly Fick’s law of diffusion and the release mechanism of the inhibitor under magnetic field mode was mainly Fickian diffusion and diffusion among magnetic nanoparticles.The composite inhibitor shows good corrosion inhibition for carbon steel,up to 95.7%and it also has good recycling performance.After five cycles,the inhibitor loading capacity was 45.1%,and the inhibition efficiency was 78.8%.（4）To further improve the loading capacity of hollow Fe₃O₄ microspheres,the obtained Fe₃O₄ microspheres was etched with oxalic acid solution and MBT inhibitor was loaded into the nanospheres by impregnation method.It shows that with the increase of oxalic acid concentration,the cavity and pore size of the nanospheres become larger.When the concentration of oxalic acid was 7.0 mg/m L,the obtained microsphere has the maximal inhibitor loading capacity,which is up to 77.6%.In addition,the release rate of inhibitor from the nanospheres increases with the increase of oxalic acid concentration and the release behaviour shows magnetic controlled release performance.The prepared hollow Fe₃O₄ microspheres can load a variety of inhibitors,such as cerium ion(Ce³⁺),benzotriazole（BTA）and Mo O₄^2-,which all present magnetic controlled release performance and good corrosion inhibition.