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[Display omitted] • A NF/Mn 2 CoO 4 @MoO 2 electrode was prepared for Pb2+-targeted removal via CDI technology. • SCR of the electrode relies on preferential adsorption and sluggish desorption for Pb2+. • Synergistic effects of Mn 2 CoO 4 and MoO 2 are beneficial for Pb2+ capacitive removal. • Theoretical calculations confirm SCR is due to stronger bonding between Pb2+ and MoO 2. • Electrodepositing loaded MoO 2 onto NF/Mn 2 CoO 4 for 60 min achieved optimum capacitance. To achieve targeted removal of Pb2+ from industrial wastewater, a NF/Mn 2 CoO 4 @MoO 2 composite electrode, synthesised using the hydrothermal method combined with electrodeposition technology, was employed to construct an asymmetric capacitive deionization (CDI) system to selectively electro-adsorb and desorb Pb2+ ions. The electrode exhibited pseudocapacitive characteristics in solutions containing Pb2+, facilitating rapid and reversible redox reactions. The asymmetric CDI system, utilising graphite paper as the positive electrode and NF/Mn 2 CoO 4 @MoO 2 as the negative electrode, displayed exceptional adsorption performance at 1.4 V for 1 h, decreasing the Pb2+ concentration from 50 ppm to 4 ppb, achieving an adsorption capacity of 156.24 mg g−1, and displaying outstanding cyclic stability. Moreover, the electrode demonstrated preferential adsorption of Pb2+ in mixed solutions containing multiple heavy metal ions, with relative removal coefficients of 4.48 − 19.86 compared with other ions. Analysis of the adsorption mechanism indicated that during the adsorption process, Pb2+ was embedded between MoO 2 layers, disrupting the electron cloud symmetry and triggering an oxidation reaction. Octahedral MoO 2 then lost electrons and transformed into tetrahedral [MoO 4 ]2-, forming PbMoO 4 with embedded Pb2+ between the layers, and achieving effective removal of Pb2+ with high selectivity. Molecular dynamics simulations and density functional theory (DFT) calculations confirmed the high selectivity of the prepared electrode for Pb2+ ions based on stronger binding of Pb2+ to MoO 2 than other ions. The electrode has application potential for the capacitive removal of Pb2+ from industrial effluent through CDI technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • BiOCl/MXene composite was synthesized via a hydrothermal reaction. • The effect of MXene on the morphology of BiOCl was studied. • PDDA was used to adjust the electronegativity of the MXene surface. • PDDA modified BiOCl/MXene has high dichlorination ability and cycling stability. • Capacitive deionization (CDI) was simulated using COMSOL Multiphysics. Currently, chloride ions in industrial water limits its reuse when extending the circulating water cycle. Therefore, it is necessary to remove Cl− to ensure its effective reuse. Considering the development of new materials for efficient electrochemical chloride removal is a key issue limiting the development of capacitive deionization technology for chlorine removal. In this study, BiOCl was grown in situ on the surface of V-MXene, and then a nanoflower-like BiOCl/MXene composite was synthesized by utilizing the properties of MXene as a structure-directing agent to modulate the morphology, which exhibits superior pore structure and specific capacitance. The poly (diallyl dimethylammonium) (PDDA) modification improved the materials' specific capacitance and reduced energy consumption for dichlorination. The optimal BMP-10 exhibited superior performance for dichlorination, the maximum dichlorination capacity and rate were 161.64 mg g−1 and 2.20 mg g−1 min−1. We found that MXene has excellent properties for exfoliation and morphology modulation of layered materials. Additionally, the electrical properties have an important influence on the electrochemical removal of chloride ions. Here we successfully synthesized an efficient electrode material with unique morphological structure for CDI dichlorination and provided ideas for structure-directing agents and electrical modulation in material design for electrochemical dichlorination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemical techniques for uranium extraction from water were reviewed. • The strengths, limitations, applicability of each method were evaluated. • The fouling of membranes and electrodes is a main challenge. • Environmental and economic considerations are discussed. Electrochemical removal of uranium from water is an emerging topic that addresses the treatment of drinking water, remediation of contaminated sites, and mining from seawater. Electrochemical strategies compare favorably to conventional processes, such as adsorption and coagulation/flocculation, with advantages in speed and efficiency, materials regeneration, uranium recovery, and recycling. This review assesses all published work on electrochemical techniques for uranium extraction from water, including capacitive deionization (electrosorption), electrodeposition, electrodialysis, and electrocoagulation. This work compares these approaches with conventional techniques and discusses their applicability in different use cases. Environmental and economic considerations are discussed, as well as the current outlook and opportunities for engagement in this emerging field. [ABSTRACT FROM AUTHOR]

• K 2 FeO 4 is first utilized for the solid-phase oxidation of pitch by a high-energy ball mill. • The solid-phase reaction mechanism involving in oxidation and condensation was revealed. • Advanced pitch-based porous carbon (H-CBPF) was prepared by a solid–liquid synergistic strategy. • The synergistic effect improves both the porous geometric configuration and O content of H-CBPF. • H-CBPF delivers an excellent salt adsorption capacity and a superior charge efficiency. To address limited desalination capacity and insufficient charge efficiency for carbon materials in capacitive deionization (CDI), a solid–liquid synergistic oxidation strategy of potassium pertechnetate (VI) for pitch was proposed to construct porous carbon with a reasonable pore structure and high reactive surface. On the one hand, K 2 FeO 4 is first utilized for the solid-phase oxidation (SPO) of pitch by a high-energy ball mill, introducing rich oxygen-containing groups such as ether bonds. Meanwhile, dehydro-condensation reactions occurred during SPO, resulting in the formation of the oxidized pitch with a high degree of condensation. Importantly, the pyrolysis yield of the oxidized pitch is as high as 46.9 % at 800 °C, almost twice that of the pristine pitch, meaning that the oxidized pitch with high polymer degree and rich C-O bridge bonds facilitates the carbon fixation and emission reduction during carbonization. On the other hand, the self-oxidation of K 2 FeO 4 in aqueous solution forms bifunctional activators (KOH and Fe(OH) 3) for the preparation of pitch-based porous carbon. Benefiting from the crosslinking structure of oxidized pitch and the multi-effective activation, the prepared porous carbon (H-CBPF) exhibits a robust layered stacking topology with a high surface area and oxygen content. Thereby, it can deliver an excellent salt adsorption capacity (SAC) of 22.1 mg g−1 with an average desalination rate of 1.89 mg g−1 min−1 and a high charge efficiency of 85 % at 1.2 V in 500 mg L-1 NaCl solution. This work opens up a green and economical route for the preparation of pitch-derived porous carbon for high-performance CDI. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel active unit Sb with electrically driven redox reaction with F- is reported. • The antimony active sites initiate the Faradaic-induced pseudocapacitive behavior. • The N-rich carbon laminar framework endows rapid ion diffusion and electron transfer. • The SNTPC2 electrode exhibit a superior F- removal capacity of 178.58 mg g−1. • This system performs excellent selectivity towards F- and outstanding recyclability. Fluoride (F-) contamination has become a pressing environmental concern owing to its extensive origins and severe toxicity. Capacitive deionization (CDI) emerges as a promising technique for efficient defluorination, with the development of electrode materials being pivotal to its efficiency. Herein, we present a novel design of Sb-decorated N-rich carbon composites (SNTPCs) for the formation of a hybrid capacitive engine that integrates Faradaic-induced pseudocapacitance and electrical double layer capacitance, enabling efficient F- electrosorption. This approach features a distinctive N-rich carbonaceous laminar framework that not only guarantees rapid ion diffusion and electron transfer but also provides a dense electrical double layer for F- storage. The Sb sites are electrically stimulated to release the intrinsic affinity with F-, forming the Faradaic Sb-F bonds. The SNTPC2 electrode exhibits the exceptional saturation removal capability and dynamic electrosorption capacity for defluorination, reaching 178.58 and 34.77 mg F/g at 1.2 V respectively, which exceeds most reported F- capture electrodes. It also demonstrates excellent selectivity towards F- in complex conditions and exhibits effectiveness across a wide range of pH values. Additionally, the utilized electrode performs outstanding regeneration performance after 20 consecutive cycles. This study provides innovative perspectives for the effective elimination of fluoride pollution in aquatic environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • The sandwich structure NPC/NiMn-LDH/MXene is elaborately designed for Cl- capture. • The NPC/NiMn-LDH/MXene electrode presents optimized Cl- diffusion kinetics. • The NPC/NiMn-LDH/MXene//NPC cell showcases exceptional Cl- removal performance. • DFT results validate NPC/NiMn-LDH/MXene facilitates interfacial charge transfer. Layered double hydroxides (LDHs) have been recognized as prospective two-dimensional capacitive deionization (CDI) faradaic materials for Cl- capture, offering tunable interlayer distance, high anion exchange capacity, and reversible ion intercalation/deintercalation ability. However, the self-stacking tendency, poor electrical conductivity, and undesired stability of LDHs nanosheets severely impede ion migration and active sites accessibility, leading to unsatisfactory CDI performance. Herein, we present an elaborately designed three-dimensional sandwich structural composite N-doped porous carbon spheres/NiMn-layered double hydroxide/MXene (NPC/NiMn-LDH/MXene) to efficiently capture Cl- as the CDI anode. In this assembly, MXene not only ensures excellent electrical conductivity for rapid ion transfer but also serves as a robust substrate for the uniform dispersion of NiMn-LDH nanosheets. Moreover, NiMn-LDH effectively inhibits the agglomeration of MXene and provides substantial storage capacity for ion accommodation. The conductive intermedium NPC establishes interconnected conductive channels, enriching accessible charge transport pathways, resulting in an accelerated ion diffusion kinetics. Accordingly, the NPC/NiMn-LDH/MXene electrode demonstrated predominant specific capacitance (265 F g-1), lower ion transfer resistance, and an optimized Cl- diffusion coefficient (7.95 × 10-17 cm2 s−1). In an asymmetrical CDI cell assembly, the NPC/NiMn-LDH/MXene//NPC cell delivered outstanding Cl- removal capacity (43.5 mg g−1), swift salt removal rate (12.5 mg g−1 min−1), efficient energy utilization (0.183 kWh kg−1-NaCl), and remarkable cyclic adsorption/desorption stability (89.6 % retention rate). Additionally, density functional theory (DFT) calculations validated that the sandwich construction of NPC/NiMn-LDH/MXene facilitated interfacial charge transfer from NPC and MXene to NiMn-LDH, accelerated ion transfer rate, and reduced ion migration energy, resulting in accessible ion diffusion kinetics and smooth Cl- shuttle. This unique approach enriches ion transfer pathways by leveraging the distinctive structural characteristics of faradaic materials, providing valuable insights for further developments in CDI technology. [ABSTRACT FROM AUTHOR]

• A novel capacitive deionization with a three-phase architecture (T-CDI) was proposed. • Cathodic oxygen reduction was enhanced in T-CDI without affecting desalination. • SAC value and H 2 O 2 generation were 14.91 mg/g and 25.55 mg/L, respectively. • Simultaneous desalination and organics control was achieved by T-CDI/UV. • Applicability of T-CDI in long-term operation was investigated. Cathodic oxygen reduction, as a Faradaic side reaction, has been proven to be thermodynamically favorable for H 2 O 2 generation in capacitive deionization (CDI), which may provide a greener manner for organics control alongside desalination. However, the low levels of dissolved oxygen (DO) in saline water and its potential Faradaic degradation of carbon-based electrodes limit the H 2 O 2 generation in the conventional CDI (C-CDI). Herein, a novel three-phase CDI architecture (T-CDI) was proposed to simultaneously achieve stable desalination and supplementary H 2 O 2 generation. Unlike C-CDI architecture, T-CDI was open-ended at the cathode side, where porous nickel foam was used as current collector and air diffusion layer. Accordingly, a stable gas–liquid-solid three-phase interface was created inside the cathode, thus enhancing the diffusion and utilization of atmospheric air and preventing the damaging effects of excessive DO on the electrode. A stable electrosorption and electrocatalysis performance for T-CDI was obtained by regulating electrode hydrophilic-hydrophobic properties, comparing with other CDI configurations, and altering operating conditions. The salt adsorption capacity and H 2 O 2 accumulative concentration were 14.91 mg/g and 25.55 mg/L, respectively. Furthermore, the simultaneous desalination and organics control in T-CDI were investigated with the assistance of UV irradiation (T-CDI/UV). When treating NaCl and sulfamethazine (SMR) mixture solution, T-CDI/UV significantly reduced the irreversible electrode organic fouling and improved the desalination stability. Additionally, the potentially hazardous SMR was effectively removed alongside desalination. Finally, the long-term operation of T-CDI demonstrated that the generated H 2 O 2 cannot induce an additional substantial deterioration in desalination stability. The techno-economic assessment showed T-CDI was economically competitive compared with C-CDI. This study provides insights into the synergy of non-Faradaic and Faradaic processes and further diversifies the application of CDI in water treatment. [ABSTRACT FROM AUTHOR]

Bithmush-impregnated carbon nanofiber aerogel with a rational "multi-layer protection" shell was unprecendently prepared and used as chloride chloride-capturing electrode to trigger fast and ultra-durable faradic capacitive deionization. [Display omitted] • Bi nanoclusters impregnated carbon nanofiber aerogel (Bi NCs@CNFAs) was prepared. • Bi NCs@CNFAs was unprecedently introduced in faradic capacitive deionization (FDI). • The multi-layer protection design could prevent structural changes of Bi NCs@CNFAs. • The ultrasmall and even distributed Bi nanoclusters enable fast pseudo-capacitance. • The desalination rate/durability of our FDI outperforms most reported systems. Faradic-based capacitive deionization (FDI) has been recognized as one of the most promising technologies to solve the freshwater crisis, yet was hindered mostly by the relatively low desalination rate and sluggish long-term stability of its anode materials. Through careful analysis, the origin of the slow desalination rate was determined to be the faradic diffusion and mass transfer, while the poor cycling stability could be originated from the volumetric expansion of the redox-active material as well as structural damage caused by the uneven stress during multicycle operation. Herein, we developed a Bi nanocluster (NCs) embedded in carbon nanofiber aerogels (Bi NCs@CNFAs) nanostructure as chloride-capturing electrodes for FDI. The essence of this work lies in the design of the "multi-layer protection" shell that could not only limit the volumetric expansion of the Bi NCs (inner protection layer) but also alleviate the stress caused by potential structure changes (outer buffer layer). As a result, the Bi NCs@CNFAs-based FDI display ultra-fast desalination kinetics (0.524 mg g−1 s−1) with remarkable long-term stability (only 8 % reduction over 250 cycles), significantly outperformed the highest value reported in the literature so far. This study is interesting because it exemplifies the significance of problem-driven strategy (nanocluster-induced surface-driven capacitance to address slow desalination kinetics; rigid carbon shell to suppress the volumetric expansion of Bi NCs; CNFAs scaffold to address potential structural damage and aggregation) to improve the desalination performance of FDI, which could further motivate advancements of highly effective desalination systems in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • LVP@2C exhibited a maximum Li+ adsorption capacity of 25.8 mg g−1 in 200 mg L−1 of Li+ ion solution. • The LVP@2C maintained a high retention rate of 78 % even after 50 cycles. • The selectivity coefficient of LVP@2C is 444.7 and 351.2 at Mg/Li ratios of 1:5 and Na/Li ratios of 1:15. • The LVP@2C displayed excellent lithium extraction performance in natural Tibet salt lake brine. • The Li+ adsorption and desorption behavior is due to V reversible synergistic valence transitions. Recently, with the rapid development of lithium-ion batteries and electric vehicles, the demand for lithium resources in the world has undoubtedly greatly intensified. Based on the advantages of high selectivity and low energy consumption, capacitive deionization (CDI) technology is well-suited for the selective extraction of lithium resources from salt lakes. Herein, carbon-coated Li 3 V 2 (PO 4) 3 (LVP@C) is developed as a cathode electrode for the first time by using a hybrid CDI device to selectively extract Li+ ions from salt lake brine, due to its high theoretical capacity and excellent cycling capacity. The electrochemical (de)intercalation mechanism of Li+ ions in the LVP@C has been evaluated by electrochemical, X-ray photoelectron spectroscopy (XPS), and in-situ X-ray diffraction (XRD) techniques, demonstrating a reversible transition of the V valence state during electrosorption/desorption based on Faradaic redox reaction. The optimized LVP@2C delivers a maximum Li+ electrosorption capacity of 25.8 mg g−1, and still maintains a high retention of 78 % even after 50 cycles. The LVP@2C has lithium selectivity coefficients of 444.7 and 351.2 at high Mg-Li ratios of 1:5 and high Na-Li ratios of 1:15. Density Functional Theory (DFT) calculations further reveal that the selective electrosorption mechanism in the LVP@2C electrode is mostly ascribed to the smaller hydrated ionic radius and lower ionic diffusion energy barrier of Li+ ions in comparison with Mg2+ ions. Finally, the effectiveness evaluation of the lithium selective extraction from the brine of a natural salt lake in Tibet indicates that the LVP@2C has highly selective electrosorption of lithium (α (Li/Mg) = 187.50, α (Li/K) = 136.11, α (Li/Na) = 116.88, α (Li/Ca) = 4.92) and can serve as a potential electrode for the extraction of lithium from salt lake brine. [ABSTRACT FROM AUTHOR]

[Display omitted] • The development history of capacitive deionization for defluorination is introduced. • Recent advances of electrode materials have been classified and reviewed. • Defluorination mechanisms have been summarized. • Challenges for engineering applications are presented. • Future perspectives on defluorination by capacitive deionization are provided. The combined need for advanced treatment of fluoridated water and low-energy technologies has inspired researchers to develop more efficient and green methods of fluoride removal. Capacitive deionization (CDI), a novel water treatment technology, has garnered significant attention in the defluorination field due to its exceptional ion selectivity. Recent decades, CDI has achieved remarkable advancements in electrode materials, F− storage mechanisms, and the potential for engineering applications in the realm of F− removal. However, there has been a lack of reviews that highlight design strategies for electrode materials in terms of fluoride ion properties in water and provide insights into key factors for designing CDI structures with excellent performance and promise for scale applications. Herein, starting from the background of fluorine pollution in surface water, and the selective removal of fluorine heavily relies on the crucial role played by electrode materials. Accordingly, all kinds of defluorinated electrode materials are reviewed. Secondly, the defluorination mechanism is summarized especially the distinctions among these processes. Additionally, the challenges existing in the promotion of CDI defluorination to large-scale applications are firstly analyzed in depth. Finally, future research opportunities and prospects by CDI for defluorination are proposed. In summary, CDI shows great potential for removing fluoride ions from water, offering a fresh approach to sustainable water resource management and environmental protection. [ABSTRACT FROM AUTHOR]

[Display omitted] • NiCoAl-LDH nanosheet arrays were vertically assembled on the surface of MXene. • Conductive CNT developed tighter bridge connections between LDH nanosheet arrays. • The nanoarray structure further exposed active sites and improved ion storage. • The splendid desalination capability and remarkable stability were acquired. Layered double hydroxide (LDH) is considered as an attractive capacitive deionization (CDI) faradic material for anion (such as Cl−) capture due to its excellent anion storage capacity, highly reversible anion (de)insertion and superior chemical stability. Nevertheless, the self-stacking property and poor conductivity of LDH lead to undesirable CDI performance. Herein, the CNT@NiCoAl-LDH@MXene heterostructure with three-dimensional (3D) interconnected network was rationally designed with MXene as the conductive substrate for the uniform and vertical growth of NiCoAl-LDH nanosheet arrays and CNT as the conductive bridge for fast electron transfer. Strong chemical bonding interactions were formed at the interface of this heterostructure, creating tighter and more stable interconnections. Moreover, the specific surface area of this unique arrays structure is 4.28 and 8.62 times that of NiCoAl-LDH and MXene, respectively, effectively suppressing the aggregation of layered materials and providing more exposed active sites. Therefore, the obtained CNT@NiCoAl-LDH@MXene electrode exhibits prominent specific capacitance (179 F g−1), decreased equivalent series and transfer resistance, increased ion diffusion rate and splendid electrochemical stability (capacitance retention rate of 107.5 % after 1500 GCD cycles). Consequently, as employed for Cl− intercalation anode coupled with AC cathode for CDI, the CNT@NiCoAl-LDH@MXene//AC cell exhibited excellent Cl− removal capacity (79.5 mg g−1), higher charge efficiency (88.4 %), lower energy consumption (0.62 kWh kg−1-NaCl) and exceptional desalination capacity retention rate (96.4 % after 40 adsorption/desorption cycles). This work provides an excellent anode material selection for the enhancement of CDI performance and valuable insights for the design of 3D interconnected network heterostructure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various morphologies of core–shell tungsten oxide@carbon composite electrodes were synthesized. • The urchin-like W 18 O 49 @C HCDI cathode achieved high SAC of 32.25 mg g−1 at 1.2 V. • Excellent cycling stability over 200 cycles with negligible metal leaching was displayed. • Such core@carbon shell structure with particular morphology provides inspirations for future research. W 18 O 49 has been considered as a promising candidate for electrochemical applications, but it suffers from unsatisfactory electrical conductivity, low specific surface area, poor structural stability, and the corresponding morphology dependent capacitive deionization (CDI) performance has not been reported. Herein, we explored the novel composites of various morphologies of W 18 O 49 encapsulated by a carbon shell (W 18 O 49 @C) as hybrid capacitive deionization (HCDI) cathode for water desalination. The as-obtained W 18 O 49 @C exhibited unique structures, allowing synergistic effects of ion intercalation and electric-double-layer capacitance, fast ion penetration, rapid electron transfer, and dissolution prevention of the active core materials. Among the three morphologies of W 18 O 49 @C, urchin-like W 18 O 49 @C (UWC) presented appropriate pore size distribution, the largest specific surface area and specific capacitance, the highest degree of graphitization and carbon content, consequently achieving excellent desalination capacity. Furthermore, an outstanding cycling stability over 200 cycles as well as a high charge efficiency and a low energy consumption were displayed for the UWC electrode. This study illustrates the great promise of urchin-like core–shell tungsten oxide@carbon composite in HCDI and paves a way for rational design of highly efficient and stable electrode materials for water desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesoporous NCS were synthesized by controlled self-assembly method. • NCS enriched with nitrogen-doped active sites and interconnected framework. • NCS-900 exhibited an ultra-high electrosorption capacity of 149.35 mg/g for NO 3 – at 1.2 V. • A novel stirring CDI was used to accelerate the ion mass transfer rate. Nitrate contamination in the water environment has become an increasingly serious problem. Capacitive deionization (CDI), an emerging electrochemical water treatment technique, possesses a promising potential for efficient nitrate removal. Herein, we prepared nitrogen-doped carbon spheres (NCS) by controlled self-assembly using nano-SiO 2 as a sacrificial template and constructed a novel stirring CDI (SCDI) using NCS as nitrate capture electrodes. The interconnected framework and controllable mesoporous structure of NCS-900 enhance the transfer and diffusion of nitrate ions. In addition, the defects caused by the nitrogen-doped increase the active sites of NCS-900, resulting in outstanding specific capacitive properties. SCDI system promotes mass transfer and allows them to be more uniformly distributed in solution. As a consequence, the concentration of ions near the electrode is elevated, which enhances the removal capacity and reaction rate of the process. Importantly, the SCDI system using NCS-900 as the electrode achieved an ultrahigh nitrate electrosorption capacity of 149.35 mg/g with a rapid removal rate of 7.46 mg/g/min at 1.2 V condition in 5 mM NaNO 3 solution, which was much higher than that of reported nitrate capture electrodes. The superior nitrate removal performance can be ascribed to the synergy between the novel electrode material NCS with high adsorption capacity and the reaction device SCDI with improved system dynamics. In addition, the stability and selectivity of nitrate electrosorption were maintained well in the comprehensive conditions and actual sewage. This work opens a new path for efficient nitrate removal by CDI technology. [ABSTRACT FROM AUTHOR]

• A system based on membrane rejection and electrochemical technique was developed. • MIL-101 endowed the mixed matrix membranes (MMMs) with phosphate adsorption capacity. • MMMs of capacitive deionization capacity was prepared with porous carbon cloth. • The conductive MMM performed both high selectivity and permeability. The great potential of ultrafiltration (UF) membranes for phosphate rejection has been challenged by the selectivity-permeability trade-off. Here, we propose a filtration system based on a novel dual-layer UF mixed matrix membrane (MMM) with a capacity for capacitive deionization (CDI), which was fabricated by incorporating NH 2 -MIL-101 into a polyethersulfone (PES) polymer matrix and the in-situ combination of carbon cloth (CC). The MMM exhibited an improved porosity of 85.52%, a declined water contact angle of 53.25°, and a 5.7% increase in water permeability in comparison to those of the PES membrane due to the hydrophilic and mesoporous NH 2 -MIL-101 particles. While incorporating the CC provided the non-conductive PES polymer with high electroconductivity. As an electrode, the CC/MMM exhibited a relatively high permeance of 424.63 L/h MPa m2, good antifouling performance, and remarkable phosphate rejection that reached 100% during the 2-h filtration period in the electrically-enhanced dead-end filtration cell. The removal capacity of the cell exceeded 22.51% and 74.0% for the energized CC/PES membrane and uncharged CC/MMM, respectively, due to the superior phosphate adsorption ability of NH 2 -MIL-101 and enhanced deionization capacity due to the electric field. UF MMM separation coupled with the electrochemical technique exhibited great potential to enhance the selective rejection of phosphate ions at low levels, while maintaining high membrane permeability and shortening the treatment time required by the CDI technique. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Capacitive deionization (CDI) has emerged as a promising way to obtain freshwater. • Nitrogen-doped mesostructured carbon nanocrystals (NMCs) are useful for CDI. • NMCs show a high nitrogen content and large accessible surface area. • NMCs exhibit a high salt adsorption capacity of 20.63 mg g−1. • The salt adsorption capacity is much higher than for the typical AC benchmarks. Abstract Capacitive deionization (CDI) has emerged as a promising way to obtain freshwater from saline water, but its implementation is in its infancy and remains challenging due to the low salt adsorption capacity (SAC) of commonly used activated carbons (ACs). It is thus desirable to develop carbon electrodes that can exceed the performance of ACs benchmarks. In this work, nitrogen-doped mesostructured carbon nanocrystals (NMCs) have been developed by direct carbonization of highly ordered mesostructured polymers. Due to their mesoporous structure, high N content and large surface area, NMCs exhibit a maximum SAC of 20.63 mg g−1. This state-of-the-art carbon electrode largely surpasses common ACs. This work demonstrates the significance of the material synthetic chemistry and the importance of nanostructuring carbon materials for CDI applications. [ABSTRACT FROM AUTHOR]

Highlights • The feasibility of perchlorate selective removal by batch-mode CDI was investigated. • A one-dimensional CDI process model was developed to describe the process. • A favorably strong preferential adsorption of ClO 4 − over Cl− was observed. Abstract Capacitive deionization (CDI) has attracted increasing attention over the past decade for the facile removal of ions from aqueous solutions. Nowadays, CDI is rapidly growing and evolving, and has been applied in many aspects. One important application field is water remediation, i.e., removing ionic contaminants of concern from water. Herein, we investigated the feasibility of perchlorate removal from brackish waters by batch-mode CDI technology. Effects of various operating parameters on dynamic electrosorption processes of both perchlorate and chloride were examined. Meanwhile, a one-dimensional CDI process model for dual-anions was developed to quantitatively describe the electrosorption kinetics of perchlorate and chloride, and an excellent agreement between the modeling results and the experimental data was observed. Experimental results revealed a favorably strong preferential adsorption of ClO 4 − over Cl− in the studied CDI system under various conditions. Moreover, only slight discrepancy between adsorption-desorption cycles was found, demonstrating the good regeneration of electrodes and operational stability of the CDI cell. Finally, the scale-up studies indicated that the CDI stack with multiple pairs of electrodes could achieve a much more superior ion removal performance than the CDI cell with only one pair of electrodes. To conclude, these results showed that the CDI system was effective for perchlorate selective removal in the presence of other major ions and had potential in treatment of perchlorate-contaminated brackish water. [ABSTRACT FROM AUTHOR]

Highlights • Selective removal of lead ions against calcium and magnesium ions is demonstrated. • CEM leads to a high lead removal rate but inability to discharge lead ions. • AEM-CDI shows improved selective removal of lead and enhanced lead discharge. Abstract Capacitive deionization (CDI) is a rising technology as a low-energy-consumption and low-cost option for water purifications and treatments; however, selective removal of heavy metal ions has been rarely reported. In this study, the impacts of ion-exchange membranes on the selective removal of lead ions (Pb2+) by CDI are investigated with a single-pass model. Both cation-exchange membrane (CEM) and anion-exchange membrane (AEM) demonstrate improved Pb2+ removal efficiencies. The presence of CEM retards discharge of adsorbed Pb2+, which eliminates the selectivity of removing Pb2+ against other cations (such as Ca2+ and Mg2+); in contrast, without the CEM, the CDI cell with only the AEM (called AEM-CDI) exhibits enhanced discharge efficiency and retains the selectivity of removing Pb2+ against Ca2+ and Mg2+. More importantly, the AEM-CDI presents improved Pb2+ discharge efficiency when applying inverted voltages, which is not possible in the membrane-free CDI because desorbed ions can be re-adsorbed to the counter electrode. In addition, surface modification for porous carbon with functional groups to enhance the affinity between Pb2+ and electrode surface is expected to further improve the selectivity of removing Pb2+ against other cations, thereby showing very promising potential in purification of drinking water. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CDI concept was applied for the HSS removal from amine solutions. • Mesoporous and well-ordered interconnected network of CNTs-Si-Ag was obtained along with the active sites. • The HSS removal capacity of CNTs-Si-Ag electrodes attained 21.5 mg g−1. Abstract The presence of heat stable salts (HSS) in the gas sweetening absorption columns reduces the absorption capacity of the amine solutions. For the first time, the capacitive deionization (CDI) technique is used to clean the MDEA solutions from HSS. For this purpose, the hybrid material (CNTs-Si-Ag) was synthesized by using the sol–gel process followed by chemical reduction. This hybrid material was then utilized as CDI electrode material in order to remove the HSS from the lean amine solutions. TEM and SEM confirmed the well-ordered interconnected porous network containing silanized CNTs (carbon nanotubes) along with silver (Ag) nanoparticles. Nitrogen adsorption–desorption analysis and electrochemical studies (EIS and CV) evidenced the substantial conductivity, porosity, surface area and specific capacitance of the prepared material. The specific capacitance of the hybrid material was found to be 149.1 F g−1 at 10 mV s−1 heralding substantial electrosorption capacity for the removal of HSS. The continuous CDI experiments showed that the highest SAC of the newly prepared electrode is 21.5 mg g−1 with maximum ASAR of 0.17 mg g−1 min−1 under 1.0 V and the lowest SAC is 17.3 mg g−1 with ASAR of 0.12 mg g−1 min−1 under 0.8 V. This work introduced the CDI as a potential technique that can be used to clean amine solutions advantaged with its low maintenance, easy operation and environment friendliness. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbons are promising materials for applications in capacitive deionization, electrosorption and aqueous ion separation, as nitrogen atoms doped into a carbon matrix are active for the selective capture of metal ions. However, much remains unknown about the preferential interaction behavior between metal ions and nitrogen-containing active sites, which retards the development of high-performance capacitive materials for practical applications. Here, we developed two types of nitrogen-doped carbon: pyridinic N-dominated graphene (N-6-G) and pyrrolic N-dominated graphene (N-5-G). The pyridinic-N was found to prefer binding “hard” ions (H + and Na + ), while pyrrolic-N showed enhanced performance in capturing “soft” ions (Pb 2+ ). Compared to pristine reduced graphene oxide, the specific capacitance of N-6-G in Na 2 SO 4 electrolyte increased by 50.0% (239.7 F g −1 ), while an increase of only 22.1% was found for N-5-G (195.2 F g −1 ), which demonstrate the superior capture capacity of pyridinic N toward Na + . However, for the electrosorption of Pb 2+ ion, the maximum adsorption capacity per surface area of N-5-G was 2.43 mg m −2 , which is 3.3 times as high as N-6-G (0.73 mg m −2 ). Furthermore, the distribution coefficient (K d ) value of N-5-G is ∼50 times higher than N-6-G. It is proposed that soft-soft and hard-hard interactions exist between nitrogen-containing groups and metal ions. These findings set a new benchmark for the capture of aqueous metal ions and suggest the great potential of N-doped carbon for challenging toxic metal pollution issues. [ABSTRACT FROM AUTHOR]

[Display omitted] • Charging time plays a decisive role in CDI performance improvement. • UQ analysis quantitively provides guidance for CDI optimization. • The pore distribution and connectivity are highlighted. Capacitive deionization (CDI) is considered to be one of the most promising technologies to deionize water with low/medium concentration. Great attention has been paid to improve its performance by optimizing electrode architectures and operation conditions. However, no guidelines are built for developing such strategies due to the nonlinear impact of the parameters concerning electrodes and operations. Therefore, our work quantitatively reveals the influence of some key parameters involving electrode characteristics, operation conditions and ion properties using the statistical analysis based on uncertainty quantification. We find the porosity solely has a small influence on all the performance metrics. But the pore might play a significant role by the pore size distribution and connectivity that greatly determine the effective diffusion coefficient of salt ions. The high diffusion coefficient obviously raises the salt adsorption by facilitating ion transport, which also reduces the energy consumption while most of the consumed energy could even be recovered. The current exerts an opposite influence by shortening the charging period in the constant current (CC) mode. The salt concentration in the inflow water increases the adsorption capacity but decreases the removal efficiency. The decreased removal efficiency requires less external energy, enabling the usage of CDI as an economic pre-treatment unit. We highlight the ion transport resistance and its influence on CDI performance by acting upon charging time in the CC mode. We also suggest the application of the constant voltage mode to the low-salinity wastewater instead of the CC mode due to the high resistance. Our work addressed the importance of proper electrode and operation condition for high desalination performance and energy efficiency. [ABSTRACT FROM AUTHOR]

A novel system combining photocatalysis and capacitive deionization (CDI) was proposed and used to efficiently remove the total Cr from the aqueous solution for the first time. MIL-53(Fe) with wide visible-light absorption was successfully prepared by a simple solvothermal method, and applied as positive photoelectrode material of the photocatalysis-CDI system (PCS) to convert Cr(VI) to Cr(III). Active carbon was used as negative electrode material to absorb Cr(III). An enhanced removal of Cr(VI) can be obtained by applying visible light irradiation and 1.3 V direct current (DC) voltage simultaneously and the Cr(VI) removal can reach a maximum value of 81.6%, much higher than those under individual 1.3 V DC voltage (39.4%) or visible light irradiation (54.2%), demonstrating the synergistic effect from CDI and photocatalysis. More importantly, effective removal of the total Cr with high removal ratio (72.2%) can be achieved, which is difficult to be realized using current other technologies. The strategy in this work provides a promising method for the complete removal of high-valence heavy metal ions. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a promising candidate for the removal of nitrate (NO 3 − ) from water, but the concentrated waste water inevitably produced in the electrode regeneration process would cause secondary pollution. In the present study, a Pd/NiAl-LMO film electrode was successfully prepared and used as an innovative NO 3 − electro-sorption/reduction electrode. Metallic Pd nanoparticles were uniformly doped into NiAl-LMO nanosheets, which created a loose porous nanostructure for NO 3 − electro-sorption and enabled catalytic activity for NO 3 − electro-reduction. Doping Pd nanoparticles into NiAl-LMO improved electron transport in the film electrode. The Pd/NiAl-LMO film electrode possessed larger specific capacitance and lower ion diffusion resistance than the pristine NiAl-LMO electrode. NO 3 − was electro-adsorbed by the Pd/NiAl-LMO electrode with concomitant reconstruction of the original hydrotalcite structure by the intercalation of NO 3 − , then the adsorbed NO 3 − was electro-reduced to N 2 by atomic H∗ during the electrode regeneration process. Our study provides not only a novel CDI electrode but also a new concept for a CDI process to achieve a more environmentally friendly outcome. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) has been a promising technique to obtain fresh water by electrosorption of charged ionic species in seawater/brackish water. Its performance is highly dependent on the physical and chemical properties of CDI electrode materials. Herein, N-doped porous carbon (NPC) with a N content of 1.66 at.% was fabricated using soybean shell as starting material by a facile pyrolysis approach with the assistance of KHCO 3 in N 2 atmosphere. The as-prepared NPC with porous structure and high surface area (1036.2 m 2  g −1 ) was further functionalized with sulfonic groups in an aryl diazonium salt solution to obtain sulfonyl functionalized NPC (S-NPC) with a surface area of 844.0 m 2  g −1 . S-NPC as cathode material was assembled into an asymmetric CDI device with aminated activated carbon (A-AC) as anode material, exhibiting superior CDI performance with an adsorption capacity of 15.5 mg g −1 and an average adsorption rate of 0.44 mg g −1  min −1 in 40 mg L −1 NaCl solution at an applied voltage of 1.2 V. As a proof of concept study, such configured CDI device was also powered for the first time by a Zn-air battery made from NPC with an open-circuit voltage of 1.28 V owing to N doping in soybean shell derived porous carbon with superior oxygen reduction reaction (ORR) activity, delivering an impressive CDI performance with an adsorption capacity of 15.8 mg g −1 and an average adsorption rate of 0.37 mg g −1  min −1 in 40 mg L −1 NaCl solution. This superior CDI performance can be due to S-NPC with high surface area, porous structure and surface rich negative charges resulted from sulfonyl functionalization, favourable for adsorption active sites exposure and mass transport of Na + ions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Capacitive deionization enables membrane- and chemical-free boron removal. • Reversing discharge polarity enhances boron removal by capacitive deionization. • Order-of-magnitude enhancement of boron electrosorption per charge. • Single-pass separation process meeting WHO recommendations is demonstrated. • Low energy consumption of 0.2 kWh per m3. Increasing global water stress motivates a growing interest in seawater desalination by reverse osmosis. Boron is typically weakly removed by reverse osmosis membranes at seawater pH, necessitating expensive post-processes such as caustic agent dosing of the permeate followed by additional filtration steps. It has been previously demonstrated that membraneless capacitive deionization can enable chemical-free boron removal from reverse osmosis permeate, with basic design rules established. However, the level of boron electrosorption per cell charge was limited to ∼0.5 µmol/g, a level too low for practical applications. We here explore, both theoretically and experimentally, methods to enhance boron removal by capacitive deionization. We found that reversing the polarity of the applied voltage during the discharge step resulted in an order of magnitude increase in boron electrosorption to nearly 4 µmol/g with promising energy consumption of 0.2 kW⋅h/m3. The promise of these results is highlighted when compared with recently-developed boron electrosorption cells requiring bipolar membranes, which demonstrate similar boron removal of 4.35 µmol/g but with much higher energy consumption of 18.3 kW⋅h/m3 while incurring significant membrane costs. Overall, we demonstrate for the first time that membrane- and chemical-free electrochemical technologies can remove sufficient boron from RO permeate in a single pass, significantly enhancing its potential to provide energy- and cost-efficient boron removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preparation process of the CDI electrode is simplified. • Laser-induced graphene (LIG) can be directly used as a CDI electrode. • LIG electrode is modified by one-step electrodeposition of Co 4 S 3. • The LIG6/Co 4 S 3 -15 presents a high adsorption capacity of 2702.79 mg g−1. • UO 2 2+ adsorption is attributed to the synergistic action of EDLs and pseudocapacitance. It has been proved that capacitive deionization (CDI) technology possesses a significant potential for uranium capture. However, the CDI performance has been limited by the complex preparation process of the electrodes and the poor adhesion between electrode materials and collectors. Here we combine the laser-induced graphene (LIG) and the electrodeposition to develop the LIG/cobalt sulfide (LIG/Co 4 S 3) electrodes with good adsorption performance. The obtained LIG6/Co 4 S 3 -15 electrode has both electrical double layers (EDLs) and pseudocapacitance properties, with a specific capacitance of 24.27 F g−1, which is 1.82 times higher than that of LIG6 (13.36 F g−1). The LIG6/Co 4 S 3 -15 electrode exhibited a high adsorption capacity of 2702.79 mg g−1. The advantages of this electrode preparation method are mainly attributed to the synergistic effect of the following aspects: (i) simplified graphene preparation by avoiding wet chemistry and post-treatment steps; (ii) simplified tedious electrode preparation such as electrode slurry distribution and sheet coating; (iii) the three-dimensional structure of LIG provides not only the conductive network but also the site for Co 4 S 3 nanosheet growth, thus avoiding nanosheet aggregation. The abundant pore structure of the conductive graphene substrate and the layered structure of the Co 4 S 3 nanosheets enable the LIG6/Co 4 S 3 -15 electrode with fast charge/ion transport, high hydrophilicity and superior pseudocapacitance, allowing uranyl (UO 2 2+) to be firstly electrosorbed, then physicochemically adsorbed, and finally electrocatalytically reduced/deposited onto the electrode. This study will offer a simple and environmentally friendly method for the synthesis of electrodes and provide a reference for the design of efficient electroadsorption materials. [ABSTRACT FROM AUTHOR]

• NiHCF/MXene was prepared via in situ close packing of NiHCF on MXene nano-stacking. • NiHCF/MXene exhibits 3D charge transfer pathway with unique vertical charge transfer. • NiHCF/MXene exhibits both excellent desalination capacity and high desalination rate. Prussian blue analogues (PBAs), as a kind of metal–organic framework–like materials, has attracted great attention in capacitive deionization (CDI) field due to excellent redox activity, but its desalination performance, especially its desalination rate, is greatly limited due to its poor electrical conductivity. Hybridization of PBAs with MXene can potentially solve this problem, but still remains intrinsic limitation, such as poor vertical charge transfer between nano-sheets. Herein, we engineered a three-dimensional (3D) charge transfer pathway in nickel hexacyanoferrate (NiHCF)/MXene through in situ close packing of NiHCF nanoparticles on MXene nano-stacking by electrostatic attraction. Compared to charge transfer mode in two-dimensional (2D) nano-sheets, 3D MXene nano-stacking can not only have excellent conductivity like MXene to provide horizonal charge transfer pathway alongside nano-sheets, but also possess unique vertical charge transfer pathway between nano-sheets. As a result, the NiHCF/MXene exhibits a superior desalination performance with a high desalination capacity of 30 mg g−1, ultrahigh desalination rate of 9.5 mg g−1 min−1 and good cycling stability over 30 cycles. This work demonstrates an effective way to address the poor CDI performance of nickel hexacyanoferrate nanoparticles by employing 3D MXene nano-stacking as charge transfer support, and is of significance to be applied for other nanoparticle materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A capacitive deionization and electro-oxidation (CDI-EO) hybrid system was developed. • CDI-EO highly effectively removed heavy metal ions and organics from synthetic wastewater. • Heavy metals were removed via cathodic electrosorption and electrodeposition. • The organic dye was degraded via direct and indirect oxidation at the anode. • CDI-EO exhibited good stability and high energy efficiency in treating the actual wastewater. Capacitive deionization is an appealing technology to remove and recover heavy metal ions from wastewater. However, the co-existing organic pollutants in actual wastewater greatly inhibit its practical application, by causing electrodes fouling and deterioration issues. Herein, a novel system combing the capacitive deionization and electro-oxidation (CDI-EO) processes in a single apparatus was developed for simultaneous removal of heavy metals and organics. This hybrid system consists of a carbon-coated graphite paper as the cathode for heavy metals removal, and a RuO 2 -IrO 2 protected titanium plate as the anode for organics degradation. The synthetic and actual textile wastewater were both treated to explore the purification mechanisms and evaluate the system stability. When copper (Cu2+) or Acid Orange 7 (AO7) was present individually in the synthetic wastewater, the CDI-EO cell achieved 83% and 91% of removal efficiencies, respectively, at an applied current density of 5 mA/cm2. When Cu2+ and AO7 were mixed, their removal efficiencies still maintained at 80% and 89%, respectively, with little mutual interference. Cu2+ ions were removed through cathodic electrosorption and electrodeposition. By reversing the electrode polarities at 3 V for 30 min, over 71% of the deposited Cu was re-dissolved for potential recovery, with the cathode re-generation. Active chlorine species were identified as the predominant oxidants generated by the anode for AO7 degradation, and a possible degradation pathway was determined. Cycling tests indicated that the CDI-EO system exhibited good stability and reliable pollutants removal. It performed equally well when treating the actual textile wastewater collected from an industrial park. The energy consumption of the CDI-EO system for textile wastewater treatment was 4.66 kWh/m3-wastewater, which is much lower than that of other advanced oxidation processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modified carbon black (CB) by O 2 plasma technology for improving CDI capacity. • The effect and mechanism of plasma modified CB (PCB) to improve CDI were explored. • PCB improved the salt removal performance 6.9 times that of the original CB (OCB) • PCB can be applied to improve CDI of various active materials. • PCB has universal applicability in purifying brine, heavy metals and radionuclides. Previous research on capacitive deionization (CDI) mainly focuses on electrode active materials, while the research on conductive additive and their modification for improving CDI performance are rarely reported. In this work, we mainly investigate the effect and mechanism of oxygen (O 2) plasma-modified carbon black (PCB) to enhance CDI performance. The CB treated with O 2 plasma at 100 W for 10 min (CB-100 W-10 min) was assembled with activated carbon (AC) to form a CB-100 W-10 min/AC electrode with excellent desalination performance (32.54 mg g−1), 6.9 times that of the original CB/AC electrode (OCB/AC, 4.91 mg g−1). The roles of the specific surface area, hydrophilicity, electrical conductivity, and specific capacitance of CB in enhancing the performance of CDI were explored, and the interaction mechanism between H 2 O molecules and CB was investigated using molecular dynamics (MD) simulations. The advantages of PCB are mainly attributed to the synergy of the following aspects: (i) The excellent three-dimensional network structure acts as a "bridge" between activated carbon and increases the contact sites for allowing more PCB and AC to participate in the electrosorption process; (ii) Shorter electron transmission paths and more electron transmission channels between PCB and AC promote the electrosorption rate; (iii) High surface roughness and oxygen-containing functional groups of PCB boost hydrophilicity and dispersibility. Interestingly, we found that PCB possesses universal applicability in the enhancement of deionization performance of various active materials for purification of brine, heavy metals and radionuclides. This work unprecedentedly applies plasma technology to the modification of conductive additive, providing new ideas for material modification and improvement of CDI technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-doped porous carbon is synthesized via a dual-salt template approach. • The carbon exhibits high ion adsorption capacity and ultrafast adsorption rate. • Ion adsorption proceeds via electrocapacitive and pseudocapacitive mechanisms. • The electrocapacitive mechanism plays a dominant role in the ion adsorption. Porous carbon materials hold tremendous potential for capacitive deionization (CDI). However, realizing high specific surface area (SSA), suitable pore size distribution, and hierarchical porosity in carbons with facile and sustainable techniques is still challenging. In this work, we prepare hierarchical porous carbons (HPCs) with high SSA, abundant pore structures, and N-self doping via a versatile and sustainable modified salt-template approach. The optimized electrode gives a high SSA of 1639.9 m2/g, a large pore volume (2.7 cm3/g), and hierarchical porous structures (micro-meso-macro pores). For applications, the symmetric CDI electrode assembly delivers a salt adsorption capacity (SAC) of up to 17.67 mg/g in a 500 mg/L NaCl at 1.2 V together with ultrafast salt adsorption kinetics. We systematically study their associated desalination mechanism by combining several electrochemical experiments with the in-situ Raman spectroscopy technique, which revealed that the total salt storage is from the synergistic effect of both electrical double-layer (EDL) storage and pseudocapacitive mechanisms, with the EDL storage being dominant. This work paves the way to design economical and eco-friendly porous carbon materials for high-performance CDI desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • The terephthalic acid intercalated carbon nanotube composite was developed for phosphate removal by CDI. • ZnZr-COOH/CNT electrode showed greatest phosphate adsorption capacity. • Phosphate adsorption occurred via the electrostatic attraction, inner sphere complexation and coordination exchange. • The energy consumption of CDI dephosphorization was sixteenth of that of chemical phosphate removal process. The discharge of phosphate from sewage water can lead to water eutrophication and endanger the aquatic ecosystem. Capacitive deionization (CDI) has displayed great potential for salt removal and nutrient recovery due to its excellent performance such as environmental friendliness and energy efficient. In this study, the terephthalic acid intercalated carbon nanotube composite material (ZnZr-COOH/CNT) was developed as an anode and its selective removal of phosphate in CDI was investigated. At a applied voltage of 1.2 V, ZnZr-COOH/CNT electrode exhibited great adsorption capacity of phosphate with low concentration (∼10 mg/L) at a wide range of pH (3 – 10), with the equilibrium concentration as low as 0.3 mg/L which was less than the national first-class emission standard (0.5 mg/L). Moreover, the adsorption of phosphate by ZnZr-COOH/CNT composite electrode was mildly disturbed by the coexisting ions (Cl−, NO 3 –, SO 4 2− and HCO 3 –). X-ray Photoelectron Spectroscopy (XPS) analysis indicated that the zirconium and zinc were coordinated with phosphate to form inner sphere complex, and the hydrogen bond was formed between the hydroxyl group of phosphate and the carboxyl group of electrode material, which enhanced the selective adsorption of phosphate. Furthermore, the energy consumption of CDI dephosphorization was calculated as low as 0.0075 kWh/g P and 0.043 kWh/m3 water at 1.2 V. This study was expected to provide the potential electrode materials and theoretical basis for the application of CDI dephosphorization. [ABSTRACT FROM AUTHOR]

• An in-depth overview of MXene applied to capacitive deionisation for desalination. • Performances of MXene are compared to current best performing faradaic electrodes. • MXene salt desalination mechanisms and its stability in water are addressed. • Challenges and prospects of MXene capacitive deionisation are highlighted. Due to the continually growing world population, water desalination has played a vital role for many countries with a shortage of clean water services. A relevant process for brackish water desalination is capacitive deionization (CDI) with the potential of producing clean water via low energy consumption electrochemical interactions. Due to the recent availability of layered and nanostructured materials to fabricate faradaic electrodes acting as pseudocapacitors to increase the salts' storage capacity, CDI-like desalination methods have gained renewed interest. As a way of improving the desalination performance and energy efficiency of CDI, faradaic deionization (FDI) based on faradaic electrodes such as Ti-MXene (Ti 3 C 2 T x) have been proposed for brackish water desalination. This paper provides a review of the theoretical and experimental framework underpinning CDI and FDI using MXene as electrodes, discussing the actual unique role of MXene in CDI-like desalination methods and its prospects. We will examine MXene's current achievements in the broader area of faradaic and hybrid capacitive deionization if compared with other materials and with various architectures and determine the research gaps in the use of MXene for these applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Waste pomelo peel converted into a novel adsorbent for use in CDI. • Removal of Pb and Cu ions strongly enhanced by functionalizing with pyrrolic-N. • Strong selectivity of Pb2+ from water containing multiple competing ions. • Easy regeneration of adsorbent on no loss in performance over 300 cycles. Water is not only a valuable resource that is needed to sustain life, but also an essential ingredient in many engineering processes, which unavoidably leads to large volumes of water being contaminated. To achieve safe discharge and also recover valuable "pollutants", better performing sorbents are needed to rapidly and efficiently decontaminate water while generating minimal secondary wastes. Bio-sorbents derived from pomelo peel were functionalized with pyrrolic-N (BNC-5 electrode) and pyridinic-N (BNC-6 electrode) to enhance electroadsorption and selectivity of Pb2+ and Cu2+. The interaction between soft acid ions (Pb2+) and soft base sites (pyrrolic-N) contributed to a strong chemisorption that elevated the electroadsorption capacity to 2.0 mmol g−1 for Pb2+ at an applied voltage of 1.2 V. With fast removal kinetics (0.077 g mg−1 min−1 of Pb2+), the BNC-5 sorbent performed comparably to other N-doped sorbents prepared using graphene. The large adsorption–desorption hysteresis of BNC-5 in responding to the applied electric voltage confirmed the nature of chemisorption. The results showed only 32.4% of the adsorbed ions being desorbed from the sorbent by reducing the applied voltage to 0 V, but reached almost complete desorption (98.5% of adsorbed ions) at –0.8 V. When operated in adsorption–desorption cycle mode, BNC-5 after ∼ 400 cycles maintained a capacity retention ≥ 80%. After 400 cycles, the electrode capacity was almost fully restored (98.7%) by only mild chemical washing (0.1 M HNO 3) of the sorbent and the cycling performance maintained. The study demonstrated the robustness of the sorbent over 1200 cycles and hence the potential to successfully convert waste into high-performance materials for large-scale remediation strategies of contaminated wastewater using CDI. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fungal hypha activated carbon pad (FhACPad) is a promising electrode for desalination. • FhACPad is a freestanding electrode readily prepared from the fungus suspension for CDI. • The continuous and porous structure of FhACPad facilitates both electron and ion transfer. • FhACPad with hierarchical pores exhibits a high desalination capacity of 35.6 mg NaCl /g. Capacitive deionization (CDI) is an emerging technology for water desalination, especially low-salinity water. Freestanding porous carbon-based electrodes with rapid electron transfer rate and effective ion diffusion features are desired to achieve high desalination performance. Here, a porous carbon pad derived from the fungal hyphae of Aspergillus niger was prepared as a precursor of the electrode. After carbonization and activation, the intertwined and hierarchical porous structure of the fungal hypha pad was well-preserved, producing a freestanding fungal hypha activated carbon pad (FhACPad) electrode for MCDI. The interconnected carbon fibers and open pore structure of the FhACPad yielded an electrode with high electrical conductivity and rapid ion transport properties. The novel FhACPad exhibited a gravimetric salt adsorption capacity of 35.6 ± 2.3 mg NaCl /g with an average desalination rate of 1.2 mg NaCl /g electrode /min from a 585 mg/L NaCl aqueous solution at a cell voltage of 1.2 V and a flow rate of 1 mL/min. As a result, the FhACPad outperformed conventional powdered activated carbon (PAC) electrodes and the most recently reported porous carbon electrodes under similar desalination conditions. This work also provides insights into the structure-performance relationships of CDI electrodes and shows a great potential of fungal biomass-derived porous carbon electrodes for high-performance MCDI applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developed a carbonized MIP-202/MXene (CMM) for selective electrosorption of U(VI). • MXene provides pseudocapacitance/intercalation effect and conductive base. • Two composite structures were observed during preparation of CMMs. • The CMM electrode exhibited excellent adsorption capacity and selectivity for U(Ⅵ). As the key element in the nuclear industry, uranium (U) has been widely concerned for its stable acquisition and efficient recycling. Capacitive deionization (CDI), which known as a seawater desalination technology, has shown great potential for uranium-adsorption. However, the poor selectivity restricts the application of CDI in uranium extraction. In this work, a carbonized MIP-202/MXene (CMM) composite was developed for highly efficient selective electrosorption of U(VI) from multi-ionic water. The uniformly decorated MIP-202 can prevent MXene from aggregation and provide rich pore structures, large specific surface area and additional nitrogen source for the efficient electrosorption of U(VI). With the addition of MXene nanosheets, a conductive network was introduced into the CMM and improved mechanical robustness of material to facilitate rapid charge transfer at the interface. As a result, the CMM electrode exhibited a maximum adsorption capacity of 582.46 mg g−1 calculated from Langmuir model and a removal ratio of 89.1% at 1.2 V in UO 2 2+ solution. The selectivity adsorption of CMM for UO 2 2+ can reach 92.3% when treated with multi-ionic solution. Besides, there is an interesting fact that the decreased ratio of added MXene can got a higher adsorption capacity, which may cause by the two composite structures formed when the mixing ratio changed. Overall, the excellent conductivity, high adsorption capacity and selectivity make CMM a promising electrode in CDI for efficient extraction of uranium from water. [ABSTRACT FROM AUTHOR]

A self-supported MoS 2 /CoS 2 @TiO 2 nanotube (TNT) hybrid electrode was fabricated by an in-situ hydrothermal process-assisted growth strategy, which achieved a significantly high gravimetric Na+ adsorption capacity and excellent regeneration performance. It also demonstrated amazing removal efficiencies close to 90% for various heavy metal ions (i.e., Fe3+, Cr3+, Cd2+, Pb2+, Cu2+ and Ni2+), revealing its great potential for wastewater purification. [Display omitted] • A self-supported MoS 2 /CoS 2 @TNT hybrid electrode was constructed. • The electrode achieved a gravimetric Na+ adsorption capacity of 44.22 mg g−1. • The electrode exhibited excellent regeneration performance and removal rates. • The electrode also realized removal efficiencies up to 90% for heavy metal ions. Recently, the rational design and construction of graphene-like layered transition-metal disulfides (TMDs) with chemical and physical superiorities to act as capacitive desalination (CDI) electrodes for water purification have attracted increasing interest worldwide. Herein, an advanced self-supported MoS 2 /CoS 2 @TiO 2 nanotube (TNT) hybrid electrode was grown on a TNT scaffold by a hydrothermal process-assisted in-situ growth strategy, and an asymmetric CDI cell was constructed with the as-fabricated MoS 2 /CoS 2 @TNT and commercial AC electrodes as cathode and anode, respectively. Benefiting from the effective structural feature (i.e., fully open nanosheet-assembled flowers and hierarchical pore alignment) and synergy effect of metal-like CoS 2 , state-of-the-art MoS 2 and TNTs with an efficient charge "superhighway", the MoS 2 /CoS 2 @TNT electrode achieved a significantly high gravimetric Na+ adsorption capacity of 44.22 mg g−1 in a 600 mg L−1 NaCl solution at 1.2 V. Moreover, the hybrid electrode possessed excellent regeneration performance with a capacity retention of nearly 100% even after 20 cycles. Most notably, such electrode also demonstrated amazing removal efficiencies close to 90% for various heavy metal ions (i.e., Fe3+, Cr3+, Cd2+, Pb2+, Cu2+ and Ni2+), revealing its great potential for wastewater purification. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crude glycerol from biodiesel was used to obtain a new sustainable activated carbon. • The polyglycerol activated carbon electrodes successfully desalinate brackish water. • Operation within the potential stability window ensured the long-term stability. • Asymmetric configurations (CDI) and MCDI improved the charging efficiency. • The best stable desalination performance was achieved using the membrane CDI at 1.6 V. Capacitive deionization (CDI) is a promising electrochemical technology for water desalination that can contribute to reducing water scarcity. At the same time, appropriate routes for the disposal or reuse of liquid wastes are also a major current concern. Based on the water-waste nexus concept, this work demonstrates that crude glycerol from biodiesel plants can be successfully used to obtain a new sustainable activated carbon. After polymerization, the crude glycerol was carbonized and activated to obtain polyglycerol activated carbon (PGAC), which was employed as an electrode for CDI desalination of brackish water. Evaluation was made of the electrode performance and stability over cycles of electrosorption/desorption, using different cell configurations (symmetric, asymmetric, and membrane CDI) and cell voltages (E cell). It was observed that maintaining the potential of zero charge of the negative and positive electrodes outside their working domains during the cycles enabled minimization of that part of the applied potential deviated to co-ion repulsion, consequently improving the salt adsorption capacity (SAC) and charge efficiency (Q E). Furthermore, maintaining the potential of the positive electrode below the oxidation potential by controlling the applied E cell could ensure electrode stability. The best desalination performance using the PGAC electrode was achieved using the membrane CDI configuration (at 1.6 V), resulting in stable SAC (∼ 27.1 mg g−1) and Q E (∼100%) over 50 cycles. The low cost and high SAC and Q E values suggested that the PGAC electrode could be considered a potential candidate for use in CDI desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ion removal performance of FCDI was greatly enhanced via cathodic iodide redox couple. • A similar positive effect noticed during desorption upon polarity reversal. • The system exhibited a stable behavior over multi-cycle consecutive runs. • The approach holds great promise in treatment of iodide-containing saline wastewater. Flow-electrode capacitive deionization (FCDI) is attracting growing attention owing to its advantages such as effective ion removal capacity and easy management of the electrodes. Optimization of the flow-electrode comprising carbon materials and aqueous electrolyte is always a research hotspot aimed at improving FCDI performance. Herein, we innovatively introduced appropriate amount of KI 3 into the cathodic flow-electrode to provide a highly efficient means of enhancing FCDI desalination performance with a stable behavior in salt electrosorption and desorption over multi-cycle consecutive runs. The accelerated salt removal rate originated from the reversible redox reaction of I 3 −/I− and the maintenance of the electro-neutrality of the global electrolyte. Although possible minor release or leakage of I−/I 3 − through the cation-exchange membrane and into the treated water occurred, which makes the proposed approach not quite suitable for potable water production, we demonstrated that this system has great application prospects in treatment of iodide-containing saline wastewater without causing secondary pollution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simultaneous and precise recovery of lithium and boron from salt lake brine. • Capacitive deionization with oxygen vacancy-rich CoP-graphene aerogel as electrode. • Adsorption capacity of Li+ and B(OH) 4 − is 37 mg/g and 70 mg/g (Mg/Li = 24, Cl/B = 70) • A good and stable performance of CDI system with >92% of recovery after 10 cycles. • Synergy of oxygen vacancy, hydrophilicity, P-metal interaction and low resistance. Lithium and boron recovery from salt lake brine is highly important for resource utilization and environmental risk reduction, particularly as an alternative source of the critical raw lithium materials for lithium ion batteries. This study develops a novel capacitive deionization (CDI) method to simultaneously and precisely extract Li+ and B(OH) 4 − ions from salt lake brine with high Mg/Li ratio. Using oxygen vacancy-rich CoP/Co 3 O 4 -graphene aerogel (GA/CoP/Co 3 O 4) as the bifunctional anode and cathode, the effective adsorption capacity of Li+ and B(OH) 4 − ions reached 37 mg/g and 70 mg/g, respectively at the Mg/Li ratio of 24:1 and Cl/B ratio of 70:1. The excellent selectivity and efficiency could be attributed to the synergistic effect of rich oxygen vacancy, better hydrophilicity, flexible P-metal interaction and low internal resistance. The CDI system also has a good and stable performance of electrochemical adsorption-desorption, reaching >92% of recovery after 10 cycles. This paper provides a green and efficient method for recovery of valuable elements from salt lake brine and reduction of environmental risk. [ABSTRACT FROM AUTHOR]

[Display omitted] Ion electrosorption in sub-nanometer carbon micropores enables ion separation. • Studies ion selectivity in nanoconfinement applying online chemical monitoring. • Ion selectivity based on pore size effect, charge effect, and desolvation energy effect. • Observed ion sieving effect and the influence on ion selectivity. Subnanometer pores of carbon discriminate against ions based on their size. Capitalizing on such nuanced differences enables ion separation via charge/discharge cycling during ion electrosorption. Different ion uptake capacities in aqueous media with multiple, competing ions are also of high importance to understand capacitive deionization of surface water or industrial process water. In our experiments, we observed divalent cations sieving in pores smaller than 0.6 nm. By applying this phenomenon, a desalination cell with online concentration monitoring was used to study the ion-selectivity. We concluded that in pores below 0.6 nm, divalent Mg2+ and Ca2+ are entirely blocked, and the K+ over Na+ selectivity corresponds with their size ratio. Larger micropores show a preference for divalent cations with higher charge numbers. In both materials, a dynamic monovalent cation and divalent cation replacement dependent on the potential variation is observed. [ABSTRACT FROM AUTHOR]

• MoS 2 /NOMC electrode exhibited an electrosorption capacity of 28.82 mg/g. • Porous architecture of electrodes facilitated the desalination performance. • Increased conductivity and hydrophilicity were beneficial to the CDI process. • Capacitive and diffusion-controlled processes contributed to electrosorption. • A good regeneration property of MoS 2 /NOMC was demonstrated. Capacitive deionization (CDI) is a promising technology for seawater and brackish water desalination but still suffers from several drawbacks, such as low electrosorption capacity and less efficient desalination performance. In this study, MoS 2 /NOMC (nitrogen-doped highly ordered mesoporous carbon) composite with enhanced hydrophilicity, conductivity and capacitance was successfully synthesized by a hydrothermal process. The MoS 2 /NOMC electrodes showed efficient desalination performances with an electrosorption capacity of 28.82 mg/g at 1.6 V in 250 mg/L NaCl solution and a maximum electrosorption capacity of 30.49 mg/g based on Langmuir fitting. The mechanism of the enhanced desalination performance of MoS 2 /NOMC electrodes was explored through the characterization of the contributions of the capacitor-controlled (electrical double layer capacitor without charge transfer) and diffusion-controlled processes (charge transfer with N-doping of NOMC as well as the various oxidation states (from + 2 to + 6) of molybdenum atoms (Mo) in MoS 2). Capacitor-controlled process played a major role (with the contribution of 73.17%) for the improved desalination performances of MoS 2 /NOMC electrodes compared to the diffusion-controlled process (with the contribution of 26.83%). In addition, MoS 2 /NOMC electrodes showed an excellent regeneration performance, indicating the potential of MoS 2 /NOMC composite as a promising CDI electrode material. [ABSTRACT FROM AUTHOR]

Cellulose fibers extracted from facial tissue paper were used as a porous carbon substrate to coat exfoliated two-dimensional Ti 3 C 2 T x MXene nanosheets in order to prepare unique CLF@Ti 3 C 2 T x nanostructures composites. The designed CLF@Ti 3 C 2 T x material was assembled in symmetric capacitive deionization cell, which showed the desalination capacity of 35 mg·g−1, with good cycling stability. Inspired by the conventional chemical gilding process, the proposed low-cost synthesis strategy and innovative design open a new way to develop MXene-carbon based electrodes for CDI water desalination. • 2D Ti 3 C 2 T x nanosheets@CLF core-shell structures are prepared by chemical gilding. • CLF@Ti 3 C 2 T x electrodes are used in symmetric CDI cell for water desalination. • Pseudo-capacitance-effect is induced by ultrathin 2D Ti 3 C 2 T x NSs shell. • Ti 3 C 2 T x NSs coating on CLF significantly improved the overall CDI performance. • CLF@Ti 3 C 2 T x shows salt absorption capacity (SAC) 35 mg·g−1. We introduce a novel and facile synthesis strategy to design 2D MXene (Ti 3 C 2 T x) nanosheets (NSs) coated cellulose fibers (CLF) based 3D nanostructures (CLF@Ti 3 C 2 T x) to overcome the drawbacks of co-ion expulsion in carbon-based, commonly used CDI electrodes and restacking of MXene NSs due to van der Waals forces in the pure MXene based electrodes. CLF extracted from facial tissue paper were used as a porous carbon core-substrate to coat shell of exfoliated two-dimensional (2D) Ti 3 C 2 T x NSs in order to prepare unique CLF@Ti 3 C 2 T x nanostructures composite by an improved dip-coating method. After appropriate structural and chemical characterization, the designed CLF@Ti 3 C 2 T x material was assembled in symmetric capacitive deionization (CDI) cell as an active electrode and the electrochemical properties and desalination capacity were studied in detail. Interestingly, the CLF@Ti 3 C 2 T x based active electrodes displayed good specific capacitance of 142 F·g−1 in 1 M sodium chloride electrolyte, and high salt adsorption capacitance of 35 mg·g−1 compared with the pure MXene and carbon-based electrodes at an applied voltage of 1.2 V, with considerable cycling stability of 10 cycles. Inspired by the conventional chemical gilding process, the proposed unique and low-cost synthesis strategy and unique design open a new way to develop MXene-carbon based composite nanostructures for CDI and energy storage applications. [ABSTRACT FROM AUTHOR]

• Floriform WO 3 /C electrode were developed for electrosorption of U(VI) from water. • The charge/discharge process of WO 3 /C primarily belongs to capacitive controlled behavior. • WO 3 /C electrodes achieve a maximum U(VI) electrosorption capacity of 449.9 mg g−1 at 1.2 V. • Electrosorption of U(VI) is credited to synergistic effect of EDLs and pseudocapacitance from WO 3 /C. Decontamination and recovery of uranium(VI) [U(VI)] from radioactive wastewater is vital to sustainable nuclear power production and reclamation of radioactive waste. As a promising technology of water treatment, capacitive deionization for adsorption of U(VI) started to attract attention. Herein, for the first time, a floriform WO 3 /C composite was developed as a pseudocapacitive electrode material for electrosorption of U(VI) from water. The as-prepared WO 3 /C composite was constructed from dozens of 2D nanosheets with a thin amorphous carbon layer, resulting in uniform flower-like particles with hierarchical nanostructure and superior open pore network. The charge/discharge process of WO 3 /C was demonstrated as prominent capacitive controlled behavior by quantization of capacitance contributions. As a result, the WO 3 /C electrodes achieved a maximum U(VI) electrosorption capacity of 449.9 mg g−1 at 1.2 V and good cycling stability after consecutive adsorption-desorption, which is superior to the conventional physical adsorption processes. The superior CDI performance of the WO 3 /C electrode is credited to the synergistic effect of EDLs and pseudocapacitance based on the combination of WO 3 and carbon layer with hierarchical nanostructure. Overall, the facile preparation strategy, the superior electrosorption performances, and the high cycling stability, endow the floriform WO 3 /C electrodes to be a promising electrode material for electrosorption of U(VI) from wastewater. [ABSTRACT FROM AUTHOR]

• CPT-IC-CDI-IX process was proposed to eliminate ions association and remove heavy metals from HTPW. • Desalination target was determined via calculation of ion association constant. • Ni(II) (Co(II)) in HTPW were decreased from 262 (15.1) mg/L to 0.0412 (0.0279) mg/L. • TDS was significantly decreased from 176 g/L to 9.6 g/L achieving Na 2 SO 4 recovery. A hybrid process of coprecipitation-induced crystallization-capacitive deionization-ion exchange (CPT-IC-CDI-IX) was developed for heavy metals removal from the hypersaline ternary precursor wastewater (HTPW), containing Ni(II) (262 mg/L), Co(II) (15.1 mg/L), Mn(II) (20.5 mg/L) and a great deal of total dissolved solids (TDS, in the main form of Na 2 SO 4 , 176 g/L). After coprecipitation (CPT) on basis of solubility product theory, the residues of Ni(II), Co(II) and Mn(II) in filtrate of primary sedimentation (FPS) were reduced to 1.25, 0.90 and 0.10 mg/L, respectively, suggesting that CPT was propitious for reutilization of heavy metals. The salinity was a key factor affecting heavy metal removal. Based on calculation of ionic association constant, HTPW should be desalted to below 10 g/L for eliminating the association effect between salt anions and trace heavy metal ions. Hence, 3 °C-induced crystallization (IC) was applied in desalination referring to theoretical crystallization temperature with recovery of Na 2 SO 4. TDS in FPS was obviously removed from 191 to 68.7 g/L, while Ni(II) and Co(II) were decreased to 0.401 and 0.228 mg/L, respectively. A self-made capacitive deionization (CDI) stack followed the IC unit for deep Na 2 SO 4 removal to 9.60 g/L. After eliminating ionic association effect, Ni(II) and Co(II) were further removed by ion exchange achieving the levels of 0.0412 and 0.0279 mg/L, respectively, which were below the emission standards of Ni(II) (0.5 mg/L) and Co(II) (0.1 mg/L). The heavy metals in HTPW can be efficiently removed from hypersaline wastewater by the hybrid technique with lower operating cost. [ABSTRACT FROM AUTHOR]

• CDI was applied for nitrate removal from synthetic domestic wastewater. • Concentrated nitrate stream was obtained during CDI regeneration. • CDI operational parameters were investigated. • Effect of PVDF on AC electrode was estimated. Capacitive deionization (CDI), an emerging technology, has attracted attention recently and has been applied for various purposes. Herein, we investigated the application of a CDI system using activated carbon (AC) electrodes for nitrate removal and recovery in the scope of domestic wastewater treatment. The electrochemical behavior and structural parameters of AC electrodes were investigated as a part of this work. CDI electrodes were fabricated from microporous activated carbon, and the specific surface area of the electrode material was 210 m2/g. The negative effect of polymeric binder on the AC electrodes performance was observed as well. The specific capacitance of the fabricated AC electrodes at 40 mV/s scan rate was 0.5 F/g and 19 F/g for 1 and 1000 mM electrolyte (NH 4 NO 3), respectively. The CDI performance was examined as a function of flow rate (2, 4, 9, 14 mL/min), applied voltage (0.6, 0.8, 1.0, 1.2 V), and initial nitrate concentration (10, 25, 50, 70 mg/L) in single-pass (SP) mode. Regeneration performance and recovery efficiency of the CDI cell were observed during 5 subsequent operational cycles. The recovery efficiency of nitrate ions from low salinity water was 21%, while the electrosorption capacity of 5.5 mg/g and removal efficiency of 48% was achieved. Presence of the competitive ions in the tested solution resulted in a slight decrease (~10%) of nitrate removal efficiency. [ABSTRACT FROM AUTHOR]