Effect of LDHs-ALA on steel corrosion in chloride-rich simulated concrete pore solution: experimental and DFT studies

Seeking green and efficient anti-rust anion is beneficial to promote the development and application of layered double hydroxides (LDHs) corrosion inhibitor. This paper explores the feasibility of alanine (ALA) as interlayer anion of LDHs and the corrosion inhibition mechanism of LDHs-ALA via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electrochemical tests, chloride equilibrium isotherm, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) simulations. The results show that LDHs-ALA can be synthesized using calcination-rehydration method. The binding energy (EB) of LDHs-ALA is more positive than that of LDHs-Cl, implying chloride ion can be captured by LDHs-ALA. The chloride capture behavior of LDHsALA conforms to the Langmuir isotherm as following equation: qe = 0.073Ce/(1 + 0.02Ce). The released ALAcan be adsorbed on Fe (100) surface and increase the Fe2+/Fe3+ ratio of passive film by forming Fe-O bond. Moreover, the pre-adsorption of ALA- on Fe (100) surface weakens the interaction between Cl 3p orbital and Fe 3d orbital, increasing the adsorption energy of Cl- on the Fe (100) surface and lengthening the Fe-Cl bond. Therefore, LDHs-ALA has a high inhibition efficiency up to 99.7%.