A novel strategy of post defect modification (PDM) for synthesizing hydrophobic FA-UiO-66-CF3 with enhanced n-hexane vapor adsorption capacity under humidity

Volatile organic compounds (VOCs) are hard to recover due to the existence of large amounts of water vapor in practical conditions by adsorption method. Given the abundant functional groups of metal-organic frameworks (MOFs), especially –NH2 group, which can be easily functionalized to solve this problem. However, their pore apertures of the modified MOFs are constricted after post synthesis modification (PSM), leading to unsatisfied adsorption capacity under high humidity. In this work, we proposed a novel strategy of post defect modification (PDM) to synthesize high-performance hydrophobic MOFs for improving adsorption performance under humidity. Originally, the defect-rich UiO-66-NH2 was prepared by using different monocarboxylic acids (MA). In particular, the sample FA-UiO-66-NH2, obtained by the addition of formic acid (FA), exhibited strong n-hexane vapor adsorption ability (198 mg·g−1), which was 97% larger than the non-defective UiO-66-NH2. Afterwards, the defect-engineered FA-UiO-66-NH2 was decorated with –CF3 groups for improving its hydrophobicity, which showed superhydrophobicity with a water contact angle (WCA) of 151.6° and decreased (60%) water vapor adsorption capacity. Dynamic competitive adsorption experiments also indicated that the FA-UiO-66-CF3 sample is more superior competitive adsorption performances for n-hexane vapor than water vapor. Furthermore, we provide a novel strategy for constructing defect-engineered and functionalized MOFs, which will expand their application fields.