One-step biomimetic construction of bio-based, robust and superhydrophobic coatings for simultaneously enhancing the surface functionality and passive fire-proof of steel structures

In contemporary application, the conflict between optimal fire resistance and adequate surface functionality in conventional coatings for steel structures became increasingly prominent. Aimed at addressing the critical challenge associated with steel materials, the introduction of multifunctional coatings emerged as an effective and practical strategy. Limited by the restricted requirement from environment and ecology, the renewable fillers and clean materials aroused more and more attention in preparing the fire-retardant coatings with multiple surface functionality on steel structures. Bio-inspired by natural phenomena, super-hydrophobic coatings were constructed on steel structures via an one-step spraying method that the combination of as-prepared phytic acid/ZIF-8 hybrids (S-MPA@ZIF-8), titanium dioxide (TiO₂) and epoxy resin/silicone resin (EP/SR) was involved in the coatings. These components were expected to act as flame retardants, fillers and adhesive, respectively. The composite coatings could achieve the excellent water repellency, self-cleaning and anti-icing ability with water contact angle (WCA) of 162.3°±1° and water sliding angle (WSA) of 3°±0.2°, which were ascribed to the formation of adequate surface roughness with low surface energy. The superhydrophobic composite coatings maintained the superhydrophobicity even after 5 m abrasion distance and 250 tape peeling cycles owing to the native rigidity of TiO₂. Based on the chemical stability of SR, the water repellency of as-prepared coatings was exhibited after immersing in acid/alkaline solution for 24 h and undergoing 6 plasma etching cycles. This indicated that the superhydrophobic coatings possessed the remarkable mechanical durability, chemical stability, and weather resistance. Accorded with the charring ability of S-MPA@ZIF-8 and the reinforcing effect of TiO₂, the equilibrium backside temperature of coated steel structure during flame impact tests was as low as 203.2 °C, suggesting the excellent fire resistance of as-prepared coatings. In a nutshell, this study provided a viable, clean and effective strategy for enhancing the surface functionality and fire resistance, which was expected to raise the application value of steel structures in fields of aerospace industry, construction and buildings.