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Academician Ren Yonghua's team made new progress in the research of two-dimensional supramolecular polymer separation membranes
2019-12-28 Source: Polymer Technology

In recent years, membrane separation technology has shown great application prospects in the fields of sewage treatment and desalination, fuel cells, petrochemicals, etc. due to its high separation efficiency and selectivity, and low energy consumption. Two-dimensional porous materials represented by covalent organic framework materials (COFs), because of their controllable porosity and chemical functions, can achieve effective nanoscale separation, which has become a new hope for the preparation of high-performance separation membranes. However, COFs obtained through stable covalent bond synthesis show many inherent disadvantages when forming large-area and structured thin films, such as insolubility, insolubility, disordered orientation, and macroscopic structural defects. These factors cause COFs to fail to address the long-standing "trade-off" challenge between membrane permeability and selectivity.

Aiming at the key problems in the structural design and functionalization of membrane materials, Academician Ren Yonghua's team designed and synthesized a novel honeycomb two-dimensional supramolecular polymer by means of supramolecular self-assembly (Figure 1). Using a simple drop-cast method, the author successfully developed a highly oriented supramolecular assembly composite membrane supported on a polycarbonate filter membrane (Figure 2). Due to its thin thickness, the membrane exhibits a fast penetration speed. In addition, the membrane has a variety of functions, not only for the efficient and selective adsorption of specific precious metal platinum divalent ions, but also for the accurate selection and screening of nanoparticles at sub-nanometer sizes, reflecting the "one membrane for multiple uses" efficacy!

Figure 1. Schematic application of a honeycomb-based two-dimensional supramolecular polymer separation membrane.

Recovery of precious metal platinum from wastewater is a task with both environmental protection and economic value. At present, it is very difficult to achieve high selectivity for platinum because it has some similar chemical properties with other precious metals such as palladium, gold, and silver. The two-dimensional supramolecular polymer prepared by the author was assembled from a positively-charged terpyridine platinum complex, and showed a unique "platinum-platinum" non-covalent bond interaction. ] 2? )会很容易在过滤中被超分子聚合物膜捕获;相反,其他金属离子会非选择性地快速渗透通过膜孔,最终实现对铂的高效分离回收。 It is by virtue of this type of platinum's own interaction and electrostatic attraction that the tetrachloroplatinate anion ([PtCl 4 ] 2? ) Will be easily captured by the supramolecular polymer membrane during filtration; on the contrary, other metal ions will be non-selective It quickly penetrates through the membrane pores, and finally realizes the efficient separation and recovery of platinum.

Figure 2. Photograph (a), scanning electron microscopy image (b), two-dimensional grazing incidence X-ray diffraction image (c), structure schematic (d), and Comparison diagram of adsorption capacity of different metal ions (e).

Based on the above work, the author further explored the separation of the membrane material for different nano-sized particles (Figure 3). Due to the presence of uniform and parallel-oriented nanocavities in the two-dimensional supramolecular polymer, the composite membrane exhibits high dimensional selectivity with a cut-off size of approximately 4.0 nm. In theory, the type of particles that the membrane can separate is unlimited, including quantum dots, precious metals and metal oxides. The authors combined the supramolecular membrane and filtration separation, not only improved the red light emission purity and size monodispersity of the nanoparticles, but also quickly removed smaller magnetic particle adsorbents that were difficult to be captured by the magnet, thus expanding them in many Potential applications in the field.

Figure 3. (a–d) Comparison of electron transmission microscopy images and fluorescence spectra (d) before (a) and after (b) separation and filtration of a supramolecular composite membrane mixed with two different-sized quantum dot colloidal solutions. And scanning electron microscope image (c) of the supramolecular composite membrane after filtration. (E) Rejection rate curve of the supramolecular composite film for quantum dot particles of different sizes. (F) Evaluation of the size of transmission channels in supramolecular composite membranes.

The above related results were published in the Journal of the American Chemical Society (J. Am. Chem. Soc. 2019, 141, 11204–11211) and Angewandte Chemie International Edition (Angew. Chem. Int. Ed. 10.1002 / anie.201913621). . The first author of the thesis is Chen Zhen , a postdoctoral researcher at the Department of Chemistry, The University of Hong Kong, and the corresponding author is Professor Ren Yonghua .

Paper link:

http://pubs.acs.org/doi/abs/10.1021/jacs.9b04397

http://onlinelibrary.wiley.com/doi/abs/10.1002/ange.201913621

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