Flexible ultrathin Nitrogen-Doped carbon mediates the surface charge redistribution of a hierarchical tin disulfide nanoflake electrode for efficient capacitive deionization

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

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.

Interface gypsum deposition in flow-electrode CDI treating brackish water: Impacts and mechanisms

Flow-electrode capacitive deionization (FCDI) is a promising electrically driven technology for brackish water desalination, but it suffers from scaling issues in the concentrate chamber when treating brackish water with high levels of SO42- and Ca2+. In addition, how the key components (e.g., flow electrodes, spacer and ion exchange membranes) induce scaling in the concentrate chamber remains poorly understood. Therefore, this study systematically investigated the roles of the FCDI's components playing in the scaling process. Results showed substantial pressure loss in the concentrate chamber, which increased by 108% due to the scaling. The characterization results revealed that the scale attached to the surface of the spacer and membranes was gypsum. Gypsum crystallization experiments highlighted the crucial role of the cation exchange membrane and spacer in the heterogeneous nucleation process, which significantly shortened the induction time compared to the homogeneous nucleation process. The surface properties, such as the surface energy and surface charge, were found closely related to gypsum nucleation. In summary, the results of this work pave the way for understanding the gypsum nucleation process in FCDI continuously desalinating brackish hard water, potentially aiding in scaling removal and system optimization for broader environmental applications.

Efficient unsymmetric disulfide formation by molecular-scale tailoring of ortho-polyquinone-based polymer photocatalyst

Disulfide bonds, especially unsymmetric disulfide bonds, have important applications in bioactivity and drug molecules, but the synthesis of unsymmetric disulfide bonds remains challenging due to efficiency and selectivity issues. Herein, this work utilizes anthraquinone (AQ) and cyclictriphosphonononitrile through a nucleophilic substitution reaction to synthesize an organic polymer (ANTH-AMI) that incorporates an ortho-polyquinone (o-polyquinone) redox center. The anthraquinone molecule functions as a redox center, capable of accepting photoinduced electrons and subsequently transferring them to initiate an electron-coupled hydrogenation reaction (AQ to AQH). Moreover, the proximity of the o-polyquinone redox sites facilitates the catalysis of unsymmetric disulfide bond formation. Consequently, the ANTH-AMI photocatalysts demonstrate exceptional yields (up to 82 %), substrate versatility, cycling stability, and scalable preparation in promoting unsymmetric coupling reactions of thiol. This work offers a solution for designing organic polymer photocatalysts with adjacent multiple redox centers for cross-coupling reactions.

Copper hexacyanoferrate/carbon sheet combination with high selectivity and capacity for copper removal by pseudocapacitance

The efficient capture of copper ions (Cu2+) in wastewater has dual significance in pollution control and resource recovery. Prussian blue analog (PBA)-based pseudocapacitive materials with open frameworks and abundant metal sites have attracted considerable attention as capacitive deionization (CDI) electrodes for copper removal. In this study, the efficiency of copper hexacyanoferrate (CuHCF) as CDI electrode for Cu2+ treating was evaluated for the first time upon the successful synthesis of copper hexacyanoferrate/carbon sheet combination (CuHCF/C) by introducing carbon sheet as conductive substrate. CuHCF/C exhibited significant pseudocapacitance and high specific capacitance (52.92 F g-1) through the intercalation, deintercalation, and coupling of Cu+/Cu2+ and Fe2+/Fe3+ redox pairs. At 0.8 an applied voltage and CuSO4 feed liquid concentration of 100 mg L-1, the salt adsorption capacity was 134.47 mg g-1 higher than those of most reported electrodes. Moreover, CuHCF/C demonstrated excellent Cu2+ selectivity in multi-ion coexisting solutions and in actual wastewater experiments. Density functional theory (DFT) calculations were employed to elucidate the mechanism. This study not only reveals the essence of Cu2+ deionization by PBAs pseudocapacitance with promising potential applications but also provides a new strategy for selecting efficient CDI electrodes for Cu2+ removal.