Layered microporous polymers by solvent knitting method

Abstract

Two-dimensional (2D) nanomaterials, especially 2D organic nanomaterials with unprecedentedly diverse and controlled structure, have attracted decent scientific interest. Among the preparation strategies, the top-down approach is one of the considered low-cost and scalable strategies to obtain 2D organic nanomaterials. However, some factors of their layered counterparts limited the development and potential applications of 2D organic nanomaterials, such as type, stability, and strict synthetic conditions of layered counterparts. We report a class of layered solvent knitting hyper-cross-linked microporous polymers (SHCPs) prepared by improving Friedel-Crafts reaction and using dichloroalkane as an economical solvent, stable electrophilic reagent, and external cross-linker at low temperature, which could be used as layered counterparts to obtain previously unknown 2D SHCP nanosheets by method of ultrasonic-assisted solvent exfoliation. This efficient and low-cost strategy can produce previously unreported microporous organic polymers with layered structure and high surface area and gas storage capacity. The pore structure and surface area of these polymers can be controlled by tuning the chain length of the solvent, the molar ratio of AlCl₃, and the size of monomers. Furthermore, we successfully obtain an unprecedentedly high-surface area HCP material (3002 m² g^-1), which shows decent gas storage capacity (4.82 mmol g^-1 at 273 K and 1.00 bar for CO₂; 12.40 mmol g^-1 at 77.3 K and 1.13 bar for H₂). This finding provides an opportunity for breaking the constraint of former knitting methods and opening up avenues for the design and synthesis of previously unknown layered HCP materials.

Keywords: Friedel-Crafts reaction; Gas storage; High surface area; Hypercrosslinked polymers; Knitting method; Microporous polymer; Naonosheets; Ordered stucture; Two-dimensional.

Scheme 1. Synthesis of polymers and building block structures and layered modeled structure of polymers.

(A) The synthetic pathway to produce the network structure. (B) Molecular structures of the building blocks for the network. (C) The layered model of benzene-based polymer.

Fig. 1. NMR spectra of polymers.

¹³C CP/MAS NMR spectra of polymers. Asterisks denote spinning sidebands.

Fig. 2. HR-TEM data of SHCP-3, SHCP-6, and polymer 3.

The HR-TEM images of SHCP-3 (A and B), SHCP-6 (C and D), and polymer 3 (E and F) [knitted by formaldehyde dimethyl acetal (FDA) as external cross-linker] at different scale bars.

Fig. 3. AFM data of SHCP-3 and SHCP-6 nanosheets.

(A and B) The AFM images and height analysis of SHCP-3 nanosheets on silicon wafer. (C and D) The AFM images and height analysis of SHCP-6 nanosheets on mica wafer.

Fig. 4. Porosity data of polymers.

(A and C) Nitrogen adsorption and desorption isotherms at 77.3 K. (B and D) Pore distribution of pore size distribution calculated using density functional theory (DFT) methods (slit pore models and differential pore volumes). Pore width of polymers. STP, standard temperature and pressure.

Fig. 5. Gas uptake data of polymers.

(A) Volumetric CO₂ adsorption and desorption isotherms up to 1.00 bar at 273.15 K, (B) volumetric CO₂ adsorption and desorption isotherms up to 1.00 bar at 298.15 K, and (C) volumetric H₂ adsorption and desorption isotherms up to 1.13 bar at 77.3 K of polymers. wt %, weight percent.