Organophosphorus modified hollow bimetallic organic frameworks: Effective adsorption and catalytic charring of pyrolytic volatiles

Up to now, hollow metal organic frameworks (MOFs) usually possess a single metal element, and the size and shape of hollow structure cannot be reasonably tuned. In this work, novel organophosphorus modified hollow bimetallic organic frameworks (W-Zr-MOF-DOPO) are successful synthesized. Briefly, zirconium-based MOFs octahedron is first prepared according to a modified method, then hollow bimetallic MOFs are obtained by etching with WO42− under acidic condition, and organophosphorus is grafted onto it by the Kabachnik-Fields reaction. Inspiringly, the particle size of zirconium-based MOFs can be adjusted by the adding of acetic acid, thus acquiring hollow MOFs with controllable interior channels. The as obtained material is employed to reduce the fire risk of epoxy resin (EP), in which the hierarchical pores and metals can effectively facilitate the adsorption and catalytic charring of pyrolytic volatiles. Moreover, the P element of organophosphorus acts both in the condensed and gas phases, endowing EP with excellent thermal stability, fire retardancy and smoke suppression. The results indicate that the limiting oxygen index value of W-Zr-MOF-DOPO/EP composite increases from 24.6% (pure EP) to 32.2% and it can pass UL-94 V-0 rating when the additive amount is only 3 wt%. Especially, the total smoke production (14.5 m2) and peak heat release rate (403 kW m−2) of W-Zr-MOF-DOPO/EP composite decrease by up to 36% and 58%, respectively, compared with pure EP. Therefore, this work draws novel inspirations for the rational design of polymer composites with high fire retardancy and smoke suppression performance.