Highly Efficient Capacitive Removal of Heavy Metal Ions from Wastewater via In Situ π–π Stacking Covalent Organic Frameworks on Graphene Oxide Sheets

Capacitive deionization (CDI) is a promising technology for heavy metal wastewater purification but is limited by traditional carbon or Faradaic materials with low adsorption capacity, slow ion diffusion, poor selectivity, and inferior long-term cycling stability. Covalent organic frameworks (COFs) are recognized as highly anticipated porous materials, enable the construction of a stationary framework with superior structural properties, and provide numerous pores for ion transport in CDI applications. Herein, we synthesized a Schiff-based polymerized TOB-DAQ COF uniformly coated on graphene oxide (GO) sheets by a solvent-thermal in situ self-assembly strategy, leveraging π-π stacking interactions. These synthesized materials exhibit high efficiency and selectivity for heavy metal ion removal in complex and high-salinity solutions, enabled by their abundant active sites, rapid ion diffusion, and enhanced specific capacity. Crucially, conjoint material structural characterization and computational analysis of the electrostatic potential energy and adsorption energy barriers within the expanded framework elucidate the synergistic removal mechanism. This mechanism is attributed to central pore adsorption and carbonyl oxygen (-C═O) complexation. This study demonstrates the potential of COF materials to advance CDI-based wastewater treatment.