Study on the strengthening mechanism of graphene-FeTCPP MOF on the corrosion resistance of steel bars in alkaline environment

Abstract

Reinforced concretes are the primary materials in coastal and offshore engineering. In the strong alkaline environment of concrete, steel bars are passivated spontaneously. However, concrete carbonization and Cl− in marine environments negatively affects the passivation process of steel bars and the durability of passivation films. Considering the anodic passivation is coupled with cathodic oxygen reduction reaction (ORR) and they form the current circuit, in this paper, we propose that the passivation process would be encouraged by the catalyzed ORR. The prepared ORR catalytic agent, graphene-iron meso-tetra(4-carboxyphenyl)porphine metal-organic framework (G-FeTCPP MOF), is characterized by UV-VIS, FT-IR, XRD, XPS, SEM, TEM and TGA. G-FeTCPP MOF could be directly doped into concrete during construction to promote passivation of steel bars. G-FeTCPP MOF exhibits significant ORR catalytic activity by reducing the reaction activation energy and driving the more efficient 4-electron pathways. The passivation of steel bars is facilitated by catalytic ORR which depletes the electrons released by coupled anodic passivation. It is the first innovation point. Another newly discovered function of G-FeTCPP MOF is to hinder the generation, migration and accumulation of crystal defects (interspaceal ferrous ions, iron ions vacancy, oxygen ions vacancy and iron atomic vacancy) by forming the adsorption film outside the passivation film. It is manifested as the optimization effect on the crystal structure of passivation film which is the greatest innovation of this paper.