Novel pH-responsive self-healing anti-corrosion coating with high barrier and corrosion inhibitor loading based on reduced graphene oxide loaded zeolite imidazole framework

Abstract

Utilization of self-healing coating is an efficient strategy for protecting metals from corrosion. However, rational design and synthesis of self-healing nanomaterial with excellent barrier property and high loading rate of corrosion inhibitor is still a challenge. Herein, the obvious physical barrier properties of graphene and the self-healing function of zeolite imidazole framework-8 (ZIF-8) was combined (RGO@ZIF) based on the concept of composite coating with "passive barrier" body and "active self-healing" guest. Herein, as a coordination complex, ZIF-8 can store and release inhibitors (2-methylimidazole) through the formation and cleavage of coordination bonds. Moreover, silica was supported on the ZIF surface (RGO@ZIF@SiO2) to compensate for the negative impact of the remaining voids after ZIF decomposition on the barrier properties of the coatings. The UV–vis results proved that ZIF-8 displayed outstanding pH-responsive activities under acidic conditions, and the loading capacity was up to 63.0%. Therefore, ZIF-8 was proposed as a solid corrosion inhibitor, which is expected to provide a new way to improve the loading rate of inhibitors. The EIS results showed that the impedance values of ZIF/EP, RGO@ZIF/EP and RGO@ZIF@SiO2/EP composites coatings increased inversely with the prolongation of immersion time, attributing to their self-healing performance. Besides, the epoxy loaded 0.7% of RGO@ZIF@SiO2 exhibited the higher impedance value than that of other samples in the whole immersion stage, which can be ascribed to the excellent barrier properties. Moreover, the corrosion products and bubbles on the surface of RGO@ZIF@SiO2/EP (0.7%) sample were the least after 200 h of exposure in salt spray test, further proving its best corrosion protection performance.