Dual-functional two-dimensional covalent organic frameworks for water sensing and harvesting

Abstract

Two-dimensional covalent organic frameworks (2D COFs) with both water detection and adsorption properties are highly attractive for both basic research and applied research. Herein, we constructed hydrazone-linked Pythz-COF and urea-linked Pyurea-COF based on the building block 1,3,6,8-tetrakis(p-formylphenyl)pyrene (Py). The COFs presented high surface area and good chemical/thermal stabilities, as well as a significant fluorescence quenching response to trace water in organic solvents. The detection limit of water sensing in acetonitrile was as low as 0.09% for Pythz-COF and 0.02% for Pyurea-COF, and the COFs maintained good crystallinity and detection efficiency after at least five cycles. In addition, the COFs showed high atmospheric water harvesting capacity with the maximum water uptake of 83.2 wt% at RH = 90% for Pythz-COF. Both COFs are moisture-stable and easily regenerated. The outstanding sensing behavior and water storage capacity of the COFs give them great prospects in future applications for efficient water detection and adsorption.