Intelligent water-borne coatings with self-reporting, self-healing, and robust barrier performance for the active corrosion protection of Q235 steels

In this study, we present a facile strategy to construct a smart PN-Zn-MOF-74 nanocontainer-based coating with outstanding triple functions including the barrier effect, as well as self-healing and self-reporting features. Flattened 2D PN-Zn-MOF-74 nanocontainers were synthesized by decorating the hexagonal boron nitride (h-BN) sheets with a polydopamine (PDA) layer, which was employed to interlink the Zn-MOF-74 nanodevices. The composite nanocontainers were then uniformly dispersed in a waterborne epoxy coating (WEC) and coated onto Q235 mild steel surfaces. Thus, as the Fe³⁺ and H⁺ ions were gradually released from the localized corrosion sites, the encapsulated active inhibitors (Zn²⁺ and PDA) in PN-Zn-MOF-74 were exchanged and released promptly to form a robust protective film, coating the micro-damaged sites. The EIS results indicated that PN-Zn-MOF-74 with two inhibitors demonstrated a remarkable active corrosion protection performance, with the |Z|_0.01Hz value increasing from 381 Ω cm² (blank) to 1389 Ω cm² (PN-Zn-MOF-74). However, the cation exchange between Fe³⁺ and Zn²⁺ can collapse the fluorescent Zn-MOF-74 and form a weak fluorescent compound at the damage sites, achieving the self-reporting ability of the coating. In addition, the coating adhesion test and cross-sectional images showed that the presence of PN-Zn-MOF-74 can effectively strengthen the impermeability of the composite coating, guaranteeing its long-lasting barrier properties. The coating demonstrated a higher |Z|_0.01Hz value (4.91 × 10⁹ Ω cm²) despite following 504-h immersion tests, which was over 2 orders of magnitude higher than that of the blank WEC coating. This study provides a simplified and feasible method for augmenting the dependability, practicality, and versatility of anti-corrosion polymer coatings.