Ion-driven exfoliation of two-dimensional ZIF-L sheets via phosphate intercalation for advanced epoxy anti-corrosive coatings

Abstract

The development of corrosion inhibitor-loaded zeolitic imidazolate framework-8 (ZIF-8) on two-dimensional (2D) materials has shown significant potential in corrosion protection. However, practical limitations such as the agglomeration of 2D sheets and the use of volatile organic solvents like methanol in ZIF-8 synthesis hinder broader application. Herein, 2D leaf-like zeolitic imidazolate frameworks (ZIF-L), which integrate the advantages of 2D materials and metal-organic frameworks, were synthesized in water media. Afterwards, phosphate anions (hydrated size = 3.39 Å) were intercalated into the interlayer spacing of ZIF-L (3.97 Å), yielding phosphate-modified ZIF-L (PZIF). This modification promoted ligand exchange by removing free 2-methylimidazole between layers and induced exfoliation of ZIF-L sheets, reducing the sheet thickness from ~ 190 nm to 100–110 nm. While the original crystalline structure was partially preserved, the formation of new zinc phosphate phases was observed. Electrochemical impedance spectroscopy revealed superior corrosion inhibition of PZIF in saline environments, with steel samples immersed in PZIF extract solution exhibiting a total resistance of 24,648 Ω.cm2, 10-fold and 20-fold higher than those in ZIF-L extract and blank NaCl solution. Furthermore, PZIF-incorporated epoxy coatings demonstrated long-term protection, maintaining a low-frequency impedance of 1011 Ω.cm2 after more than 10 months immersion in NaCl solution.