Synthesis of Hierarchical-Porous Fluorinated Metal-Organic Frameworks with Superior Toluene Adsorption Properties

Constructing metal-organic frameworks (MOFs) with high volatile organic compounds (VOCs) adsorption capacity and excellent water resistance remain challenging. Herein, a monocarboxylic acid-assisted mixed ligands strategy was designed to synthesize a novel fluorinated MOFs, MIL-53 (Al). The monocarboxylic acid promoted crystallization and produced abundant crystal defects, which increased pore volume. Moreover, the competitive coordination between tetrafluoroterephthalic acid and 1,4-dicarboxybenzene was moderated by monocarboxylic modulators, significantly improving the hydrophobicity. The toluene uptake of the optimal sample reached 254.85 mg g(-1) under humid conditions, increased by 33.56 % of MIL-53(Al), and the Q(Wet)/Q(Dry) (the ratio of adsorption quality under wet to adsorption quality under dry) was 0.92, remarkably surpassing that of origin MIL-53 (0.72). The recycle experiment showed superior reusability with no performance degradation after 10 recycle under RH=50 % (relative humidity). The adsorptive kinetic and thermodynamic analysis proves that the adsorption process is controlled by surface mono-layer adsorption and pore diffusion. The fluorine group affects the internal diffusion, which weakens the transfer rate. This strategy opens a new prospect of obtaining hierarchical functional MOFs for meeting the VOCs uptake under the practical application.

Automated summary

A novel fluorinated metal-organic framework (MOFs), MIL-53(Al), with high VOCs adsorption capacity and excellent water resistance was successfully synthesized using a monocarboxylic acid-assisted mixed ligands strategy. The results showed that the toluene uptake of the material under humid conditions was significantly improved compared to the original material, and the adsorption quality ratio was remarkably higher. The material also exhibited superior reusability and the adsorption process was controlled by surface mono-layer adsorption and pore diffusion.