Solvent-Free Air-Spray Deposition of a Metal-Organic Framework to Develop Fiber Web Composites

Metal-organic framework (MOF)-fiber composites integrate MOF's tunable functionality with flexible fibrous matrices for applications in various areas, including water purification, filtration, gas adsorption, and sensing to catalysis. Conventional techniques for the fabrication of MOF-fiber composites often involve the use of harsh organic solvents and complex time-intensive processing steps and can result in composites with poor MOF adhesion. In our work, we address these challenges by developing a simple and solvent-free air-spray coating method for the fabrication of MOF-fiber web composites. We employ bicomponent nonwovens as our fibrous substrate, consisting of a shell/core structure with polypropylene in the core and poly(ether-block-amide) in the shell. MOF particles, zeolitic imidazolate framework-8 (ZIF-8) and UiO-66-NH₂, are spray-coated onto a nonwoven fabric using compressed air in <1 min, followed by thermal treatment. This results in strong adhesion of MOF particles in the nonwoven matrix as well as fiber fusion, which enhances the mechanical strength of the resulting composites. Fabrication time (<25 min) is significantly lower than conventional methods. By optimizing the shell/core ratio in the fibers and thermal treatment conditions, we achieve surface areas of 66 m²/g for ZIF-8 and 162 m²/g for UiO-66-NH₂ composites, respectively. Finally, ZIF-8 fiber web composite demonstrates >99% removal efficiency of copper ions (Cu(II)) from aqueous solutions, underscoring the applicability for water purification. Beyond ZIF-8 and UiO-66-NH₂, the air-spray coating method is adaptable for other mechanically and thermally stable MOFs and various fibrous and nanofibrous structures. Overall, this work presents a scalable, simple, and solvent-free approach for MOF-fiber composite synthesis with broad applicability.