A general method for synthesizing heteropore covalent organic framework membranes to rapidly enrich uranyl ions.

Abstract

Heteropore covalent organic framework membranes are predicted to exhibit excellent uranium extraction capabilities due to their combination of rapid transport and strong affinity. However, the growth orientation of covalent organic framework networks is susceptible to disturbance when a supporting substrate is introduced, posing a major challenge to the fabrication of covalent organic framework membranes with well-defined hierarchical pores. Here, a general synthetic method is introduced for the preparation of heteropore covalent organic framework membranes. By pre-coating covalent organic framework nanoparticles onto a nylon substrate, the subsequent covalent organic framework network grows following the orientation of the nanoparticles under solvothermal conditions. This method demonstrates remarkable versatility across a broad range of covalent organic framework systems, including single-pore (with sql net) and dual-pore (with kgm net) networks. Several heteropore covalent organic framework membranes are fabricated with pore sizes ranging from 7.1/26.9 Å to 11.2/34.3 Å and 14.0/42.1 Å. The covalent organic framework membrane with 7.1/26.9 Å dual-pores exhibits the fastest uranyl ion transport rate among all Schiff-base porous membranes, which is 4.3 times faster than that of typical covalent organic framework membranes with single-pore channels. After irradiation treatment, the covalent organic framework membrane enables the conversion of uranium (VI) ions from seawater into insoluble precipitates, which suggests a versatile design paradigm for heteropore covalent organic framework membranes with synthetically engineered functionalities.