HCl-Etched ZIF-9-Derived Carbon with Modulated Pore Architecture Featuring Superior Capacitive Deionization and Multifunctional Water Contaminant Elimination

Abstract Pore engineering plays a decisive role in governing the water desalination and contaminant treatment performance of metal–organic framework (MOF)-derived carbons. Herein, hierarchical porous carbons with tunable architectures are prepared through the pyrolysis of ZIF-9 followed by controllable hydrochloric acid etching. The acid treatment reopens blocked pore channels, effectively increases the surface area, and generates abundant accessible active sites, thereby accelerating ionic diffusion and enhancing interfacial adsorption. As a result, the etched carbons exhibit markedly enhanced capacitive deionization (CDI) performance relative to their pristine counterparts, delivering higher salt adsorption capacity, faster ionic migration rate, and superior cyclic stability. Experimental results confirm that 24 h of HCl etching is optimal, which enhances interfacial adsorption while preserving the structural integrity of the carbon skeleton. More importantly, the optimized electrode achieves simultaneous removal of inorganic salts, tetracycline, and heavy metal ions, overcoming the single-function limitation of conventional CDI systems. Theoretical calculations confirm that the synergy between pore-assisted physical diffusion and active-site-dominated chemical adsorption endows the material with excellent multifunctional purification performance. This work elucidates the structure–activity relationship of etching conditions, pore evolution, and water-treatment performance and provides a facile and scalable strategy for the rational design of multifunctional carbon electrodes for complex wastewater remediation.