Trisodium phosphate-loaded hierarchically ordered meso-nanoporous ZIF-67/ZIF-8 metal-organic frameworks assembled rGO-Zn-Al-LDH: A multi-level pH-triggered nano-vehicle for epoxy coating long-lasting self-repairing/barrier properties improvement

Here, for the first time, a novel mesoporous multi-functional nano-hybrid with high inhibitor absorption/targeted-release capacity was designed via the surface decoration of reduced-graphene oxide (rG) by layered Zn-Al-NO3--LDH (L), and then in situ growth of core-shell (CS) mesoporous ZIF-67 (Z67)/ZIF-8 (Z8) coordinated polymers. The designed rGL-Z67/Z8 CS structures were loaded with Trisodium phosphate (TSP) inhibitor and its multi-functional action for providing a smart anti-corrosion epoxy system was studied in detail. In the solution containing nano-hybrids extract the significantly retarded steel corrosion in the presence of the TSP-loaded rGL-Z67/Z8 structure was proved. Mixed inhibition of the reduction of oxygen/water and Fe dissolution together with a significant degree of inhibition > 90 % were recorded for about 48 h, declaring a strong inhibition index of the designed nano-hybrids. The controlled/pH-triggered inhibitor release activity of the rGL-Z67/Z8 structure was proved by ICP/UV-vis analyses. The scratched TSP-loaded rGL-Z67/Z8 nano-hybrids-filled epoxy systems showed long-lasting self-repairing properties, proving the controlled inhibitor release from LDH and Z67/Z8 structures and the formation of a protective layer over the scratch site. Recording very high impedance, Log | Z|(0.01Hz) > 10(10 )ohm cm(2) and R-f values for the epoxy-containing rGL-Z67/Z8 nano-hybrids proved excellent long-time barrier properties of the coatings. Results depicted that the synergistic corrosion mitigation impact of the rGL-Z67/Z8 came from the excellent barrier action of the rGL structures, LDH-structure effectiveness in capturing Cl--ions, and Z67/Z8 structures controlled damage via pH variation and release of phosphate ions and metal (i.e. zinc and cobalt) ions for a long time. Adhesion investigations showed that the lowest loss of adhesion (49 %) and cathodic delamination diameter (about 10 mm) was recorded for the TSP-loaded rGL-Z67/Z8 filled-epoxy coating.

Automated summary

In this study, a novel mesoporous multi-functional nano-hybrid with high inhibitor absorption and targeted-release capacity was designed, showing significant corrosion inhibition for steel. The nano-hybrids displayed excellent long-time barrier properties in the epoxy system, providing a controlled inhibitor release and self-repairing properties over scratched areas.