Catalytic Charring Meets Toxic Gas Conversion: Multifunctional Montmorillonite Hybrids for Sustainable Fire Protection of Paperboard

To address the critical safety hazards of inherent flammability and highly toxic smoke emission from cellulose-based materials, this study developed a composite flame-retardant system by synthesizing ammonium phytate supported on bimetallic Cu/Ce-modified montmorillonite (AP/Cu/Ce-MMT). Through interlayer intercalation of ammonium phytate and anchoring of Cu−Ce oxides in Ca-montmorillonite, the system increased the limiting oxygen index (LOI) of flame-retardant paperboards from 24.2% to 28.2% and delayed ignition time by 18 s in an alcohol-lamp open-flame test. Cone calorimetry revealed a 27.8% reduction in the second peak heat release rate (P 2 HRR), 38.33% decrease in total smoke production (TSP), and 23.1% suppression in CO yield, while increasing char residue yield from 10.47% to 22.18%. This performance is reinforced by MMT lamellae forming covalent P−O−Si bonds and graphitized carbon networks, gas-phase radical quenching where PO·/PO 2 · radicals scavenge H·/OH· radicals, and catalytic oxidation converting toxic CO to CO 2 through Cu + /Ce 3+ redox cycles on Cu/Ce-MMT surfaces, enabled by oxygen vacancy mobility. Density functional theory (DFT) calculations further reveal that the CuO/CeO 2 heterointerface facilitates electron transfer, enhancing CO adsorption and promoting oxygen vacancy formation, providing atomic-scale evidence for the enhanced catalytic oxidation. This study presents a strategy for developing green lignocellulosic composites that combine high flame retardancy with low smoke toxicity, providing a viable approach for designing safer biobased materials.