Regulation of Intra-Nanopore Microenvironment in Oxygen-Rich Covalent Organic Frameworks for Enhanced Capacitive Deionization

Capacitive deionization has emerged as a highly promising water treatment technology but is still limited by the low charge efficiency due to the co-ion expulsion effect. The precise modulation of the microenvironment at the electrode interface is crucial for boosting overall performance. In this work, the intra-nanopore microenvironment at oxygen-rich covalent organic frameworks electrode interface is precisely regulated by tuning charge density and hydrophilicity. The incorporation of hydroxyl groups manipulates the electronegativity of the electrode interface, significantly achieving strong adsorption with sodium ions as well as effectively minimizes the co-ions expulsion effect. Besides, the electrode exhibits enhanced hydrophilicity, which promotes more sodium ion transport and enrichment. Consequently, the prepared electrode demonstrates a high salt adsorption capacity of 47.7 mg g⁻¹ and a charge efficiency of 0.87 at a voltage of 1.2 V in a 500 mg L⁻¹ NaCl solution. The superior performance is confirmed to originate from the synergistic mechanism of the coordination ion exchange of hydroxyl and the redox reaction of carbonyl groups. This work offers new insights in establishing a feasible strategy to advance the efficiency and applicability of capacitive deionization and energy-related applications.