Eco-friendly synthesized g-C3N4/[B]ZSM-5 zeolite nanocomposites as smart fillers for epoxy coatings with excellent anticorrosion, self-healing, and hydrophobic performance

In this study, we design a novel borosilicate zeolite/g-C₃N₄ (GCN) composite loaded with Zn²⁺ ions to synergistically enhance barrier protection and active corrosion inhibition. Borosilicate zeolite (B) with a high Si/B molar ratio was synthesized via the hydrothermal method and subsequently composited with g-C₃N₄ (GCN) through thermal condensation and in situ polymerization using melamine as a precursor. Among the synthesized nanocomposites, B-53.1 %GCN (containing 53.1 wt% GCN, as determined by thermogravimetric analysis (TGA)) was selected as a novel nanofiller for epoxy-based coatings. Additionally, B, GCN, and B-53.1 %GCN were loaded with Zn²⁺ ions (denoted as B-Zn, GCN-Zn, and B-53.1 %GCN-Zn) leveraging the cation exchange capability of zeolites and electrostatic interactions with nitrogen in GCN. The release of Zn²⁺ ions in 3.5 wt% NaCl solution was tracked over 48 h, while electrochemical impedance spectroscopy (EIS) confirmed the formation of a protective film on steel. Tafel (potentiodynamic) polarization tests after 48 h of immersion revealed that B-53.1 % GCN-Zn exhibited the highest corrosion inhibition efficiency (80.2 %) by simultaneously suppressing anodic and cathodic reactions. Epoxy (EP) coatings containing 0.5 wt% of the synthesized fillers (with/without Zn²⁺) were investigated for their barrier properties using EIS, salt spray, and cathodic delamination tests. The EP/B-53.1 % GCN and EP/B-53.1 % GCN-Zn coatings demonstrated superior anti-corrosion performance, with |Z|₁₀ₘ_Hz values 813 and 912 times greater than bare epoxy after 202 days of immersion, respectively. Furthermore, scratched coatings immersed in 3.5 wt% NaCl exhibited self-healing behavior, as evidenced by increased R_t(total)(R_coat(c) +R_{charge transfer(ct)}) values for EP/B-Zn and EP/B-53.1 %GCN-Zn compared to unmodified epoxy.