Fabricating epoxy composite coating having self-healing/barrier anti-corrosion functions utilizing ion-exchange/pH-sensitive phosphate-doped ZIF8 MOF decorated Zn-Al-LDH nano-layers

Recently, the development of epoxy composite coatings with smart anti-corrosion features has been considered in many studies. Using inhibitor-loaded nanocarriers, i.e., layered double hydroxides (LDH) and metal-organic frameworks (MOFs) has attracted recent attention. In this work, the hybrid LDH@ZIF8 was constructed and applied in the epoxy coating as a dual-functional nanocarrier. In this study, firstly, LDH nano-size lamellar was synthesized followed by surface modification with nano-porous ZIF8 3D structures. Afterward, to provide further corrosion inhibition properties, phosphate ions were doped and the resultant particles were introduced into the epoxy coating. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD) analysis were utilized to characterize the nanoparticles and they were a good indicator to prove the successful surface modification. Via inductively coupled plasma (ICP), the inhibitor pH/ion-responsive release (i.e., PO43− anions, Zn2+ cations) ability at various pHs was screened. Electrochemical measurements proved the inhibitive action of the phosphate-doped LDH@ZIF8 structures in the solution state (75.99 % inhibition index). EIS results revealed that after incorporating the phosphate-doped LDH@ZIF8 nano-hybrid into the epoxy coating its barrier properties were significantly improved (impedance values>1010 Ω.cm2). Besides, the phosphate-doped LDH@ZIF8 filled epoxy (with artificial scratch) showed about 57 % self-healing index. The adhesion bond durability was significantly improved after the addition of phosphate-doped LDH@ZIF8. About 69 % improvement in the wet adhesion (pull-off test) and 73 % reduction of cathodic delamination diameter (CD test) were recorded for the epoxy coating loaded with phosphate-doped LDH@ZIF8 compared to the blank epoxy. Generally, using phosphate-doped LDH@ZIF8, both barrier and active corrosion protection properties of the epoxy coating were significantly improved, and compared to similar works reported in literature better anti-corrosion durability was reached.