Porous adaptive luminescent metal cages enable sensitive detection and efficient adsorption of PFCAs

On September 28, 2022, Professor Chi Xiaodong’s research group at Huazhong University of Science and Technology and Professor Jonathan L. Sessler’s research group at the University of Texas at Austin published an article entitled “Porous Adaptive Luminescent Metallacage for the Detection and Removal of Perfluoroalkyl” in the journal Chem Carboxylic Acid” research results.

The research group prepared a porous adaptive light-emitting metal-organic cage to achieve highly sensitive rapid detection and efficient adsorption of perfluoroalkyl carboxylic acid pollutants (PFCAs). The corresponding authors of the paper are Chi Xiaodong and Jonathan L. Sessler; The first author is He Yanlei.

The problem of water pollution has become one of the most pressing environmental problems in the world. Perfluoroalkyl substances and polyfluoroalkyl substances, such as perfluoroalkyl carboxylic acids (PFCAs), are widely used in various consumer and industrial applications such as semiconductors, electronics, leather surface treatment agents, fire-fighting foams, non-stick pans, textiles, paper and coatings due to their unique physical and chemical properties (oil resistance, water resistance, high temperature resistance and chemical resistance). However, due to their widespread global use, environmental durability and bioaccumulation, PFCAs pollution is very common and affects drinking water, surface water, livestock and agricultural products around the world. This persistent environmental pollution is worrying because long-term exposure to even low levels of these compounds can have negative health effects such as thyroid disease, liver damage, high cholesterol, reduced immune response, and multiple cancers. Therefore, there is an urgent need to develop methods that enable rapid and sensitive detection and efficient removal of PFCAs. Most of the current methods used for the detection of PFCAs require sophisticated instrumentation and complex operations, while the low-cost, easy-to-operate spectral rules are limited by low sensitivity. In addition, due to the high bond energy of C-F bonds, the degradation of PFCAs is also very difficult, and new toxic by-products will be generated. Adsorption is a more effective method for purifying polluted water sources. However, the specific adsorption performance of traditional adsorbents for PFCAs is poor, and it also lacks the ability to achieve real-time detection and efficient adsorption of PFCAs in the same system. Therefore, it is of great significance to design and synthesize adsorption materials that have selective recognition of PFCAs, while achieving highly sensitive detection and specific adsorption.

In this work, Chi Xiaodong’s research group based on the research of non-porous adaptive crystalline materials in the early stage (J. Am. Chem. Soc. 2021, 143, 18849;J. Am. Chem. Soc. 2022, 144, 133), by preparing a porous adaptive luminescent metal cage (Zn-Cage), to achieve high sensitivity and selectivity detection and adsorption of PFCAs (guests) in contaminated water. When metal cages are exposed to PFCAs, the fluorescence signal of the metal cages exhibits varying degrees of fluorescence attenuation depending on the concentration of PFCAs and allows them to be monitored with detection limits (LODs) as low as 57 nM. Further combined with the smartphone app, PFCAs concentrations can be detected in real time quickly and easily by reading the RGB values displayed in the app. In addition, through the monocrystalline structure of the subject and guest between the metal cage and different PFCA objects, it can be found that the metal cage can adaptively change the body accumulation method according to the size of different guest molecules to achieve rapid capture of target molecules, and the capture of guest molecules mainly relies on the hydrogen bond interaction between the guest molecules and the subject.

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Figure 1: Chemical structure detection and separation of PFCAs by Zn-Cage.

Figure 2: Schematic diagram of the single crystal structure and object-induced adaptive structural transformation of PFHxA@Zn-Cage, PFOA@Zn-Cage and PFBA@Zn-Cage.

Figure 3: PFCAs calibration curve based on fluorescence titration and selective detection of PFCAs

Figure 4: Study of the adsorption properties of PFCAs by Zn-Cage.

In addition to enabling rapid and sensitive detection of PFCAs, the porous adaptive metal cage (Zn-Cage) can also remove representative PFCAs such as heptafluorobutyric acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorohexanoic acid (PFOA), and perfluorocapric acid (PFDA) from simulated contaminated water samples with high adsorption efficiency. Further research results show that as the PFCA carbon chain grows, the better the adsorption effect of metal cages on PFCA.

In general, this work will provide new research ideas for improving the detection and removal of PFCAs, and provide a promising method for adaptive fluorescent crystalline materials for the detection and adsorption of pollutants, which is expected to provide new enlightenment and breakthroughs for the development of new supramolecular crystalline materials in synthetic chemistry, energy materials, separation science and other fields. The research was supported by the National Natural Science Foundation of China and other funds. (Source: Science Network)

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