Hierarchical assembly of Cu2+-polydopamine and phytic acid functionalized GO with Co-Fe/B nanosheets for improving the fire retardancy of waterborne epoxy coatings

Cu-doped PDA and PA were grafted onto GO to form a P-N-rich barrier (GPCu/PA). • Co-Fe/B nanosheets were grown on GPCu/PA to construct a hierarchical structure. • Multi-metal (Cu, Co, Fe) and boron synergistically enhance char formation and stability. • The hierarchical filler provides physical barrier, radical quenching, and catalytic charring. Water-based intumescent epoxy coatings for steel structures face challenges in simultaneously achieving high-efficiency flame retardancy, smoke suppression, thermal insulation, and long-term environmental durability. In this study, a hierarchical GPCu/PA/Co-Fe/B hybrid flame retardant was developed by sequentially grafting Cu 2+ -chelated polydopamine (PDA) and phytic acid (PA) onto graphene oxide (GO), followed by the in situ growth of Co-Fe/B nanosheets. This ingeniously designed structure integrates the layered barrier effect of GO, the catalytic charring capability of PDA and transition metal species, the phosphorus-promoted expansion effect of PA, and the protective effect of boron-containing compounds. Through these synergistic effects, the hybrid system facilitates the formation of a dense and stable char layer, thereby effectively suppressing heat conduction, oxygen diffusion, and the release of flammable volatiles during combustion. When incorporated into water-based epoxy coatings, just 2 wt% of GPCu/PA/Co-Fe/B significantly improves flame-retardant performance by reducing the back-surface temperature by 36.3%, increasing the char layer expansion height by 244.9%, and enhancing smoke suppression capabilities. The cone calorimeter test further confirmed the reduced heat release, smoke generation, and toxic gas emissions achieved by this coating, demonstrating its outstanding fire safety performance. Additionally, water immersion and UV-accelerated aging tests showed that even after environmental exposure, the coating maintained low water absorption, structural integrity, and flame-retardant properties, indicating excellent durability and weather resistance. This study provides a highly promising strategy for developing multifunctional, tiered flame-retardant systems for durable water-based intumescent coatings designed for fire protection of steel structures. Download: Download high-res image (370KB) Download: Download full-size image