A bio-inspired strategy using hydrophobic bacterial EPS for the design of ZIF-8-based anti-corrosion coatings with secondary sealing function

Abstract

Developing sustainable corrosion-resistant coatings remains a key challenge for protecting metals in marine environments. Here, we report a bio-inspired hybrid coating that integrates naturally hydrophobic soluble extracellular polymeric substances (s-EPS) derived from marine Bacillus subtilis with the metal-organic framework ZIF-8. The s-EPS@ZIF-8 composite is formed through electrostatic attraction and coordination between Zn²⁺ nodes of ZIF-8 and the functional groups (-COOH, -OH, -NH₂) of s-EPS, enabling a uniform and compact organic-inorganic network. The hydrophobicity of s-EPS originates from amphiphilic protein components such as BslA and the molecular rearrangement that exposes hydrophobic domains during film formation. This synergy produces a dense superhydrophobic layer on X70 carbon steel with a water contact angle of 131.7^°. Structural and chemical analyses confirm coherent incorporation of s-EPS within the ZIF-8 framework without compromising its crystallinity. Electrochemical tests reveal superior corrosion resistance, with inhibition efficiencies of 94.54 % after 2 days and 94.84 % after 30 days in artificial seawater. The coating functions via a cooperative formation-stabilisation-reinforcement mechanism, providing durable, self-reinforcing barrier protection. This strategy demonstrates the potential of combining naturally hydrophobic marine biopolymers with MOF frameworks for sustainable, high-performance anticorrosion coatings in marine environments.