Chitosan-covalent organic framework dual-layer membrane with high efficiency of iodine capture

The main challenge in developing polymer/covalent organic framework (COF) hybrid matrix membrane is to find effective strategies for strongly attaching crystalline COF to the supporting surface as defect-free membrane layers. In this article, we demonstrated for the first time a method for the preparation of a chitosan (CS)/COF mixed matrix dual-layer membrane based on solvothermal synthesis method. A novel surface modification strategy was developed using p-phthalaldehyde as covalent linkers between COF and CS membrane substrate, and then the nitrogen-containing covalent organic framework (NCOF) membrane was further grown in situ on the modified CS membrane substrate utilizing solvothermal synthesis methods. The resultant CS/NCOF dual-layer membrane exhibited highly homogeneous texture due to the excellent compatibility between NCOF crystals and CS matrixes. The combination of NCOF and CS membrane formed a large number of channels in the nitrogen environment, enabling the CS/NCOF dual-layer membrane to have an enhanced iodine uptake capacity up to 3.15 g/g. Furthermore, the CS/NCOF dual-layer membrane could be recycled at least five times while maintaining 95% iodine capture capacity. These properties make the obtained CS/NCOF dual-layer membrane ideal absorbent material for reversible iodine capture. This ingenious dual-layer membrane preparation strategy provides a new avenue to customize synthesis of novel membrane materials for clean energy and environmental remediation. Graphical abstract