Non-covalently functionalized boron nitride by graphene oxide for anticorrosive reinforcement of water-borne epoxy coating

Abstract

Hexagonal boron nitride (h-BN) has great promise for metal corrosion due to its good impermeability to gas and liquid. However, it is difficult for h-BN to disperse in water-borne epoxy (WBE) matrix owing to its nature hydrophobicity. In this work, h-BN was non-covalently modified by graphene oxide (GO) to enhance the compatibility of h-BN for WBE. And the GO/h-BN composite was characterized by transmittance electron microscopy (TEM), Raman spectroscopy, UV–vis absorbance spectroscopy and X-ray photoelectron spectroscopy (XPS). The corrosion protection and barrier performance of GO/h-BN/WBE were evaluated by electrochemical impedance spectroscopy (EIS) and salt spray test, which indicated that the composite coating with 0.3 wt. % GO/h-BN _{(1:1 w/w)} additive exhibited excellent barrier and corrosion protection properties owing to the synergistic impermeable performance of h-BN and GO.

Introduction

Metal corrosion has aroused wide public concern due to the loss of billions of dollars every year and safety problems [1,2]. Metal anticorrosion has achieved though many methods, such as cathodic protection, inhibitor and coatings and so on. Among them, epoxy-based anticorrosive coatings have been considered as an economic and efficient method to protect metal from corrosion [[3], [4], [5]]. However, conventional epoxy-based anticorrosive coatings generally contain enormous amount of volatile organic solvents (VOCs), which is harmful to the environment and human [[6], [7], [8], [9]]. Therefore, the transformation from organic solvent system to more environmentally water-based system is an important subject in the field of coatings. However, during the curing process, the residue of hydrophilic groups and the micropores or microcracks generated by solvent volatilization in the water-borne epoxy (WBE) coatings seriously affect the barrier property of the coating to the corrosive medium [10,11]. Various nanofillers, such as graphene [12], SiO₂ [[13], [14], [15], [16]], MoS₂ [[17], [18], [19]] and so on, are applied to strengthen the corrosion protection of WBE.

The hexagonal boron nitride (h-BN) nanosheet has particular physicochemical characteristics, including outstanding mechanical performance [20,21], electrical insulation [22,23] and barrier property [24,25], which has been drawn great attention. Moreover, h-BN can avoid galvanic corrosion because of its electrical insulating property. Therefore, it has broad application prospects for long-term anti-corrosion of metals [26]. However, the h-BN is inertness and has poor compatibility with WEB matrices, hindering its practical applications in corrosion protection of metal [27,28]. To enhance the dispersion of h-BN in epoxy, diverse methods have been explored [8,27,29,30]. For example, Cui et al. [8] reported the dispersion of h-BN in epoxy resin can be enhanced by carboxylated aniline trimer derivative (CAT⁻). And the composite can significantly strengthen the barrier property of epoxy resin for corrosive medium. Zhang and coworkers [30] also reported that the h-BN modified by poly (dopamine) had excellent compatibility to epoxy resin, and the epoxy composite coatings showed excellent anticorrosion performance. However, these methods of surface modification are very laborious and the dispersants (or intercalators) themselves can’t resist the penetration of H₂O, O₂, and Cl⁻, resulting in modest anticorrosion performance.

The graphene oxide (GO) nanosheet contains various oxygen containing functional groups, which is beneficial for its dispersion in all kinds of solvent [[31], [32], [33], [34]]. Many researchers have shown that GO has potential applications in metal corrosion protection [6,[35], [36], [37], [38], [39], [40]]. For example, Parhizkar et al. [36] reported that GO modified by 3-aminopropyltriethoxysilane can improve the corrosion resistance of epoxy resin. Ramezanzadeh et al. [37] also reported that GO functionalized by -NH₂ group had excellent corrosion protection performance to the mild steel substrates. However, because of the defects in the structure of GO, its composite coatings can’t achieve ideal barrier property to the corrosive medium (H₂O, O₂, and Cl⁻), which can pass through those defects and reach the metal surface for corrosion. Therefore, how to reduce the influence of GO defects on corrosion resistance is a research hotspot.

In our work, a simple and environmentally friendly one-step method has been studied to solve the above problems. The hydrophilic GO was chosen as intercalator to exfoliated h-BN and enhance its dispersion in WBE directly. The π-π interaction between GO and h-BN enables h-BN homogeneously stacks on the surface of GO. The anticorrosive performance of GO/h-BN/WBE composite coatings was measured via electrochemical impedance spectroscopy (EIS) and salt spray test, which indicated that GO/h-BN _{(1:1 w/w)} /WBE composite coating had prominent anti-corrosion properties compared with the pure WBE coating. The homogeneous dispersion of GO/h-BN _{(1:1 w/w)} composite and the synergistic barrier effect of GO and h-BN for the corrosive medium (H₂O, O₂, and Cl⁻) can be used to explain this phenomenon.