Hierarchically porous metal hydroxide/metal–organic framework composite nanoarchitectures as broad-spectrum adsorbents for toxic chemical filtration

We demonstrate that the hierarchically porous metal hydroxide/metal–organic framework composite nanoarchitectures exhibit broad-spectrum removal activity for three chemically distinct toxic gases, viz. acid gases, base gases, and nitrogen oxides. A facile and general in-situ hydrolysis strategy combined with gentle ambient pressure drying (APD) was utilized to integrate both Zr(OH)4 and Ti(OH)4 with the amino-functionalized MOF-808 xerogel (G808-NH2). The M(OH)4/G808-NH2 xerogel composites manifested 3D crystalline porous networks and substantially hierarchical porosity, with controllable amounts of amorphous M(OH)4 nanoparticles residing at the edge of xerogel particles. Microbreakthrough tests were performed under both dry and moist conditions to evaluate the filtration capabilities of the composites against three representative compounds: SO2, NH3, and NO2. Compared with the pristine G808-NH2 xerogel, the incorporation of M(OH)4 effectively enhanced the broad-spectrum toxic chemical mitigation ability of the material, with the highest SO2, NH3, and NO2 breakthrough uptake reaching 74.5, 55.3, and 394.0 mg/g, respectively. Post-breakthrough characterization confirmed the abundant M-OH groups with diverse binding configurations, alongside the unsaturated M (IV) centers on the surface of M(OH)4 provided extra adsorption sites for irreversible toxic chemical capture besides Van der Waals driven physisorption. The ability to achieve high-capacity adsorption and strong retention for multiple contaminants is of great significance for real-world filtration applications.