A ladder-type organic molecule with pseudocapacitive properties enabling superior electrochemical desalination†

Abstract

The availability of clean water is fundamental for maintaining sustainable environments and human ecosystems. Capacitive deionization offers a cost-effective, environmentally friendly, and energy-efficient solution to meet the rising demand for clean water. Electrode materials based on pseudocapacitive adsorption have attracted significant attention in capacitive deionization due to their relatively high desalination capacity. In this study, a novel organic compound, PTQN, is introduced, featuring a ladder-type structure enriched with imine-based active sites, specifically designed for capacitive deionization. This advanced molecular design imparts the PTQN compound with exceptional pseudocapacitive properties, enhanced electron delocalization, and superior structural stability, which are supported by both experimental results and theoretical analyses. As an electrode, PTQN exhibits a high pseudocapacitive capacitance of 238.26 F g⁻¹ and demonstrates excellent long-term stability, retaining approximately 100 percent of its capacitance after 5000 cycles in NaCl solution. The involvement of PTQN active sites in the Na⁺ electrosorption process was further elucidated using theoretical calculations and ex situ characterization. Moreover, a hybrid capacitive deionization (HCDI) device employing the PTQN electrode exhibited an impressive salt removal capacity of 61.55 mg g⁻¹, a rapid average removal rate of 2.05 mg g⁻¹ min⁻¹, and consistent regeneration performance (∼97.04 percent after 50 cycles), demonstrating its potential for capacitive deionization systems. Furthermore, the PTQN electrode displayed superior removal efficiency for tetracycline. This work contributes to the rational design of organic materials for the development of advanced electrochemical desalination systems.