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The continuous population growth and drying up the freshwater reservoirs around the world are increasing the demand for fresh water. Therefore, there is an urgent need to explore newer technologies able to purify water on large scales for human usage. Capacitive deionization is one of the most promising approaches to generate fresh water by the removal of salt ions from brackish water. In this work, we prepared three different capacitive deionization electrodes using carbonized palm tree fronds (PFC). These PFC activation was achieved using CO2 at 900°C. To generate the deionization electrodes, PFC activated carbon was combined with either polyaniline (PANI), MnO2, or both (PFC‐PANI, PFC‐MnO2, and PFC‐MnO2‐PANI). The MnO2 and PANI provided additional functionality and enhanced electrical conductivity, which resulted in much higher Na+ and Cl− ions adsorption. The BET surface area of PFC‐MnO2‐PANI was estimated to be 208.56 m2/g, which is approximately three times that of PCF‐PANI and PFC‐MnO2 alone. The morphological analysis showed that the PANI and MnO2 nanorods were well dispersed throughout the PFC network. Although PANI and MnO2 is largely embedded inside the PFC network, some remnants are visible on the surface of the electrodes. The cyclic voltammetry (CV) curves showed capacitive behavior of all electrodes in which PFC‐MnO2‐PANI showed highest specific capacitance of 84 F/g, while the PFC‐MnO2 and PFC‐PANI showed 42 and 43 F/g, respectively. Owing to its enhanced functionality and CV characteristics, the PFC‐MnO2‐PANI showed maximum salt adsorption capacity of 10.5 mg/g in contrast to 3.72 and 5.64 mg/g for PFC‐MnO2 and PFC‐PANI, respectively. Moreover, the measured contact angle for PFC‐MnO2‐PANI was ~51°, which indicates the hydrophilic nature of electrode that improved ions adsorption. Practitioner Points: Date tree fronds were converted into mesopores carbon using CO2 as activation agent.Three composites were prepared with PANI, MnO2, and date palm fronds activated carbon (PFC‐MnO2, PFC‐MnO2‐PANI, and PFC‐PANI).Surface area, pore profile, surface morphology, electrochemical behavior, desalination performance, and hydrophilicity of all the electrodes were investigated.The PFC‐MnO2‐PANI showed maximum salt adsorption capacity of 10.5 mg/g in contrast to 3.72 and 5.64 mg/g for PFC‐MnO2 and PFC‐PANI, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient CuHCF/C electrode was prepared for Cu2+ removal by CDI. • CuHCF/C achieved high Cu2+ adsorption capacity of 134.47 mg g−1 at low applied voltage of 0.8 V. • CuHCF/C manifested excellent Cu2+ selectivity in multi-ion coexisting solution. • The mechanism of removing Cu2+ by Faradaic pseudocapacitance was explained. 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 CuSO 4 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. [ABSTRACT FROM AUTHOR]

The radioactive pollution caused by uranium containing wastewater generated during the nuclear fuel cycle seriously threatens human health and environmental safety. The electrosorption (or capacitive deionization, CDI) separation of U(VI) from wastewater has the advantages of high efficiency, low energy consumption, convenient operation, and no secondary pollution, making it a promising new separation technology. By combining double layer capacitive materials with pseudo capacitive materials, the specific capacitance and ion storage capacity of the composites can be significantly improved, thereby improving the electrosorption performance. This work used natural biomass as raw material to prepare hierarchical porous biocarbon through high-temperature pyrolysis and chemical activation, and then it was incorporated with hydrothermally synthesized α-MnO 2 nanofibers to obtain novel composites (BC/α-MnO 2) with high hybrid capacitance for U(VI) removal in CDI. The electrochemical characteristics of the composites and their electrosorption performances for U (VI) were respectively investigated in a three electrode system and a CDI device. The results suggested that BC/α-MnO 2 exhibited an ideal capacitive behavior, and theoretical calculations indicated the synergistic effect of capacitive and diffusion control processes on ion storage. Among different BC/α-MnO 2 electrodes, BC/α-MnO 2 -2 had the highest specific capacitance (130.48 F/g) and also the highest adsorption capacity for U (VI) (280.20 mg/g at 0.9 V and pH 4.0). The isotherms and kinetics of U (VI) electrosorption were consistent with the Langmuir and PFO models, respectively. The electrosorption mechanism was mainly related to the contribution of pseudocapacitance and EDL adsorption. Overall, BC/α-MnO 2 -2 exhibited ideal electrochemical properties and excellent electrsorption performance for U (VI) (high electrosorption capacity, fast kinetic rate, and good cycling stability), facile fabrication and environmentally friendly, and thus it has promising application in CDI treatment of radioactive wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesoporous polydopamine (mPDA) was coated on the surface of leaf-like zeolitic imidazolate frameworks (ZIFL). • mPDA layer effectively mitigate backbone collapse of ZIFL during pyrolysis. • ZIFL@mPDA derived carbon possess hierarchical pore structures along with carbon nanotubes. • The structural and compositional merits enable ZIFL@mPDA derived carbon excellent desalination performance. The onstruction of novel porous carbon materials for efficient desalination is crucial but remains challenging for capacitive deionization (CDI) development. Herein, a micelle-assisted strategy was raised to coat mesoporous polydopamine (mPDA) on the surface of two-dimensional (2D) leaf-like zeolitic imidazolate frameworks (ZIFL) followed by confinement pyrolysis. The introduction of the mPDA layer can not only mitigate the backbone collapse of ZIFL during pyrolysis to build a favorable porous environment for efficient ion transport and diffusion, but also induce explosive growth of carbon nanotubes (CNTs) to improve the electron conductivity. As expected, the derivative ZIFL@mPDA-C possessed a high desalination capacity of 41.9 mg g−1 in 500 mg L-1 NaCl solution at an operating voltage of 1.2 V. In particular, the retention ratio of the desalination capacity of ZIFL@mPDA-C was about 100 % after 50 consecutive adsorption-desorption cycles, while its leaf-like morphology and hierarchical pore structures were well preserved. This study highlights the importance of rationally designed structures and components for the performance breakthrough of carbon-based CDI electrode materials. [ABSTRACT FROM AUTHOR]

• The impact of doping nitrogen is calculated for combining fluoride. • The spherical La-MOFs are pyrolytic to use as electrode material to demonstrate the function of nitrogen. • The La-N-C-800°C is used for electrosorption of fluoride. • The mechanism has been studied by density functional theory calculation and experiments. Fluoride is an important pollutant in wastewater, and adsorption is an effective way to remove fluoride. Because nitrogen plays an important role in adsorbent materials, computational models were developed to understand the changes in work function resulting from nitrogen doping. La-N-C-800°C, was prepared by pyrolyzing La-MOF-NH 2 to verify the influence on the performance of removing fluoride by electrosorption. Material and electrochemical performance tests were performed to characterize La-N-C-800°C. Adsorption kinetics, adsorption thermodynamics, initial concentrations, pH, and ions competition were investigated using La-N-C-800°C for fluoride removal. In addition, density functional theory was applied to evaluate the function of nitrogen. When nitrogen atoms were added, the density of states, partial density of states, populations, and different orbits of charge were calculated to discover deep changes. Nitrogen strengthened the carbon structure and La 2 O 3 structure to remove fluoride. In addition, nitrogen can also act as an adsorption site in the carbon structure. These results provide design ideas for improving the performance of adsorbent materials by doping elements. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Flexible free-standing hierarchical SnS 2 @NC hybrid electrode was fabricated. • The hollow structure alleviates volume expansion and facilitates ion diffusion. • A high electrosorption capacity and a rapid salt adsorption rate were achieved. • Work function-driven interfacial electron transfer accelerates reaction kinetics. Constructing pseudocapacitive electrodes with high specific capacities is indispensable for increasing the large-scale application of capacitive deionization (CDI). However, the insufficient CDI rate and cycling performance of pseudocapacitive-based electrodes have led to a decline in their use due to the corresponding volumetric expansion and contraction that occurs during long-term CDI processes. Herein, hierarchical porous SnS 2 nanoflakes are encapsulated inside an N -doped carbon (NC) matrix to achieve efficient CDI. Benefiting from the synergistic properties of the pseudocapacitive SnS 2 nanoflakes and few-layered N -doped carbon, the heterogeneous interface simultaneously provides more available vigorous sites and demonstrates rapid charge-transfer kinetics, resulting in a superior desalination capability (49.86 mg g−1 at 1.2 V), rapid desalination rate (1.66 mg g−1 min−1) and better cyclic stability. Computational research reveals a work function-induced surface charge redistribution of the SnS 2 @NC heterojunction, which can lead to an auspicious surface electronic structure that reduces the adsorption energy to improve the diffusion kinetics toward sodium adsorption. This work contributes to providing a thoughtful understanding of the interface engineering between transition metal dichalcogenides and NC to construct high-performance CDI electrode materials for further industrialization. [ABSTRACT FROM AUTHOR]

Recent years have seen the emergence of capacitive deionization (CDI) as a promising desalination technique for converting sea and wastewater into potable water, due to its energy efficiency and eco‐friendly nature. However, its low salt removal capacity and parasitic reactions have limited its effectiveness. As a result, the development of porous carbon nanomaterials as electrode materials have been explored, while taking into account of material characteristics such as morphology, wettability, high conductivity, chemical robustness, cyclic stability, specific surface area, and ease of production. To tackle the parasitic reaction issue, membrane capacitive deionization (mCDI) was proposed which utilizes ion‐exchange membranes coupled to the electrode. Fabrication techniques along with the experimental parameters used to evaluate the desalination performance of different materials are discussed in this review to provide an overview of improvements made for CDI and mCDI desalination purposes [ABSTRACT FROM AUTHOR]

Recent years have seen the emergence of capacitive deionization (CDI) as a promising desalination technique for converting sea and wastewater into potable water, due to its energy efficiency and eco‐friendly nature. However, its low salt removal capacity and parasitic reactions have limited its effectiveness. As a result, the development of porous carbon nanomaterials as electrode materials have been explored, while taking into account of material characteristics such as morphology, wettability, high conductivity, chemical robustness, cyclic stability, specific surface area, and ease of production. To tackle the parasitic reaction issue, membrane capacitive deionization (mCDI) was proposed which utilizes ion‐exchange membranes coupled to the electrode. Fabrication techniques along with the experimental parameters used to evaluate the desalination performance of different materials are discussed in this review to provide an overview of improvements made for CDI and mCDI desalination purposes [ABSTRACT FROM AUTHOR]

[Display omitted] Porous carbon materials have been regarded as a promising alternative to activated carbon for desalination via capacitive deionization (CDI) due to refined architectures and functionalities. However, it is still challenging to obtain a controlled hierarchical pore structure and considerable nitrogen-doped content by convenient method. Herein, nitrogen-doped hierarchical porous carbon foams (NHCFs) with different microstructural features, nitrogen contents and nitrogen species were successfully fabricated via a stepwise pyrolysis carbonization strategy using easily available melamine foam. Due to the synergistic effect of hierarchical porous structure and doped nitrogen, the optimized NHCF sample carbonized at 800℃ (NHCF-800) exhibited a maximum desalination capacity of 30.1 mg g−1 at the optimal operating parameters (500 mg/L NaCl solution, 1.2 V) and an excellent regeneration performance after 50 continuous adsorption–desorption cycles. Furthermore, density functional theory (DFT) was also conducted to elaborate the disparity of sodium adsorption energy among the nitrogen species for in-depth understanding, and it mainly benefits from the ascendency of the pyrrolic-N and pyridinic-N over the graphitic-N dopant. This work paves the way of rational regulation of nitrogen-doped process and hierarchical porous structure carbon as CDI electrode materials for desalination. [ABSTRACT FROM AUTHOR]

Environmental protection associated with renewable energy is among the most critical challenges for translational ion‐capture based on capacitive storage of ions in electrical double layers at the interface of electrode and electrolyte. Electric double‐layer capacitance with charge induction and faradaic pseudo‐capacitance with charge transfer classifies the capacitance of the electrochemical interface. The electrochemical interface in most energy technologies involves porous and pseudocapacitive redox materials that offer varying degrees of electrolyte confinement. In this review, we discuss the factors affecting water desalination, such as the effect of nanopores for ion capture, the ion sieving effect, the effect of hydration energy, and hydration radius in the carbon sub‐nanometer pore. Moreover, the surface phenomena of electrodes, including carbon corrosion, and the potential of zero charge to control the oxidation of carbon electrodes are explained along with protection mechanisms. The various capacitive deionization (CDI) operations and the corresponding electrochemical cell technologies are briefly introduced, including the significance of double‐layer charging materials with faradaic intercalation, which suffer less from co‐ion expulsion. Finally, we revisit the effects of various nanoarchitectures and the construction of capacitive deionization electrodes for clean water technology. [ABSTRACT FROM AUTHOR]

Water resources are the basis for human survival and development. However, human beings face severe challenges of water pollution and freshwater shortage. With the critical advantages of low energy consumption, high efficiency, low cost, green and pollution-free, and renewable electrodes, capacitive deionization (CDI) has become an up-and-coming water treatment technology. After decades of development, the application of CDI has expanded from seawater desalination to many fields. However, the existing literature still needs a comprehensive overview of the multi-functional application of CDI technology in water treatment. Therefore, our work critically reviewed the latest research progress of CDI in water treatment to meet the technical requirements of various application fields. This paper first summarizes the various applications of CDI in water treatment, focusing on CDI's representative research results in heavy metal removal, organic contaminants removal, water softening, phosphate and nitrate removal, and water disinfection. In addition, we also discussed the latest research progress of energy recovery and energy consumption assessment for the CDI process. Finally, this paper discusses the challenges and future opportunities facing CDI technology. [ABSTRACT FROM AUTHOR]

Constructing faradaic electrode with superior desalination performance is important for expanding the applications of capacitive deionization (CDI). Herein, a simple one‐step alkalized treatment for in situ synthesis of 1D TiO2 nanowires on the surface of 2D Ti3C2 nanosheets, forming a Ti3C2‐MXene partially derived hierarchical 1D/2D TiO2/Ti3C2 heterostructure as the cathode electrode is reported. Cross‐linked TiO2 nanowires on the surface help avoid layer stacking while acting as the protective layer against contact of internal Ti3C2 with dissolved oxygen in water. The inner Ti3C2 MXene nanosheets cross over the TiO2 nanowires can provide abundant active adsorption sites and short ion/electron diffusion pathways.. Density functional theory calculations demonstrated that Ti3C2 can consecutively inject electrons into TiO2, indicating the high electrochemical activity of the TiO2/Ti3C2. Benefiting from the 1D/2D hierarchical structure and synergistic effect of TiO2 and Ti3C2, TiO2/Ti3C2 heterostructure presents a favorable hybrid CDI performance, with a superior desalination capacity (75.62 mg g−1), fast salt adsorption rate (1.3 mg g−1 min−1), and satisfactory cycling stability, which is better than that of most published MXene‐based electrodes. This study provides a feasible partial derivative strategy for construction of a hierarchical 1D/2D heterostructure to overcome the restrictions of 2D MXene nanosheets in CDI. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a promising and cost-effective technology that is currently being widely explored for removing dissolved ions from saline water. This research developed materials based on activated carbon (AC) materials modified with zinc oxide (ZnO) nanorods and used them as high-performance CDI electrodes for water desalination. The as-prepared electrodes were characterized by cyclic voltammetry, and their physical properties were studied through SEM and XRD. ZnO-coated AC electrodes revealed a better specific absorption capacity (SAC) and an average salt adsorption rate (ASAR) compared to pristine AC, specifically with values of 123.66 mg/g and 5.06 mg/g/min, respectively. The desalination process was conducted using a 0.4 M sodium chloride (NaCl) solution with flow rates from 45 mL/min to 105 mL/min under an applied potential of 1.2 V. Furthermore, the energy efficiency of the desalination process, the specific energy consumption (SEC), and the maximum and minimum of the effluent solution concentration were quantified using thermodynamic energy efficiency (TEE). Finally, this work suggested that AC/ZnO material has the potential to be utilized as a CDI electrode for the desalination of saline water. [ABSTRACT FROM AUTHOR]

Copper ions (Cu2+) disposed to the environment at massive scale pose severe threat to human health and waste of resource. Electrochemical deionization (EDI) which captures ions by electrical field is a promising technique for water purification. However, the removal capacity and selectivity toward Cu2+ are unsatisfying, yet the recycling of the captured copper in EDI systems is yet to be explored. Herein, an efficient electrochemical copper pump (ECP) that can deliver Cu2+ from dilute brackish water into much more concentrated solutions is constructed using carbon nanosheets for the first time, which works based on reversible electrosorption and electrodeposition. The trade‐off between the removal capacity and reversibility is mediated by the operation voltage. The ECP exhibits a removal capacity of 702.5 mg g−1 toward Cu2+ and a high selectivity coefficient of 64 for Cu2+/Na+ in the presence of multiple cations; both are the highest reported to date. The energy consumption of 1.79 Wh g–1 is among the lowest for EDI of copper. More importantly, the Cu species captured can be released into a 20‐fold higher concentrated solution. Such a high performance is attributed to the optimal potential distribution between the two electrodes that allows reversible electrodeposition and efficient electrosorption. [ABSTRACT FROM AUTHOR]

[Display omitted] Capacitive deionization (CDI) technologies have the potential to become cost-competitive alternatives to reverse osmosis for the treatment of brackish waters. In this study, we report our findings on the effect of co-ion sorption and faradaic side reactions on our ion exchange resin functionalized desalination electrodes which passively capture salt and reject it upon charging. This system, which we previously reported on and refer to as electrically regenerated ion exchange (ERI), avoids the use of expensive ion exchange membranes in an effort to save costs. Surprisingly, we find that, compared to a reference CDI system, ERI electrodes capture salt most effectively at low applied voltages (0.5 mg/cm3 at 0.8 V). Both CDI and ERI systems also seem to suffer from co-ion sorption effects which negatively impact salt adsorption. However, Faradaic side reactions at higher voltages (1 V and 1.2 V) which we track via pH measurements, serve as a detriment to CDI but seem to facilitate the functionality of ERI. [ABSTRACT FROM AUTHOR]

Recently, the rational design and development of efficient faradaic deionization electrodes with high theoretical capacitance, natural abundance, and attractive conductivity have shown great promise for outstanding capacitive deionization (CDI)‐based desalination applications. Herein, the construction of novel FeOOH hybrid heterostructures with Na and Cl dopants (e.g., Na‐FeOOH and Cl‐FeOOH) via a robust hydrothermal strategy is reported, and an asymmetric CDI cell (Na‐FeOOH//Cl‐FeOOH) comprising Na‐FeOOH and Cl‐FeOOH working as the cathode and anode, respectively, is assembled. The multiple coupling effects of the specific structural features (e.g., enriched porosity, hierarchical pore alignment, and highly open crystalline framework), enhanced electrochemical conductivity, and optimized ion‐transfer property endow the FeOOH hybrid electrode with improved electrochemical performance. Impressively, the Na‐FeOOH//Cl‐FeOOH cell demonstrates a superior salt adsorption capacity (SACNaCl) of 35.12 mg g−1 in a 500 mg L−1 NaCl solution, a faster removal rate, and remarkable cycling stability. Moreover, the pseudocapacitive removal mechanism from the synergetic contribution of the Na‐FeOOH cathode and Cl‐FeOOH anode account for the significant desalination promotion of the Na‐FeOOH//Cl‐FeOOH cell. [ABSTRACT FROM AUTHOR]

The growing demand for rare earth elements (REEs) necessitates cheap and environmentally friendly technologies for REEs recovery. Herein, we fabricated a pyrrolic-N doped activated carbon electrode (PPyN-AC) via two facile steps of in-situ polymerization of pyrrole monomers and further carbonization. Capacitive deionization (CDI) using PPyN-AC as electrodes is the first time applied for REEs capture from aqueous solution. PPyN-AC possesses a high N doping rate (9.55 at.%) and excellent capacitance (128.98 F/g). The CDI flow-by tests shows that the electrosorption capacity of La(III) by PPyN-AC electrode was 23.66 mg/g within 25 min at optimal conditions. The rapid and efficient La(III) electrosorption performance is attributed to the pyrrole-N configuration in the carbon matrix. Beyond that, the PPyN-AC electrode could selectively capture La(III) from a quaternary-component system of La(III), Fe(III), Ca(II) and Na(I) in aqueous solution. The REE selectivity mechanism, which involves the ionic charge, hydrated radii of metal ions, and hard-soft Lewis acid-base principle, was proposed. Overall, this work demonstrates a new efficient approach for the selective recovery of REEs from aqueous solution with minimal land and energy demands. The study reported a straight route to prepare pyrrolic-N doped AC serving as capacitive deionization electrode for the recovery of REEs from wastewater. The proposed PPyN-AC electrode exhibits excellent selectivity toward La(III) in the presence of competitive ions. [Display omitted] • Capacitive deionization (CDI) system for REEs recovery is first proposed. • CDI realized 23.66 mg/g La(III) uptake within 25 min by PPyN-AC electrode. • PPyN-AC selectively electrosorbed La(III) from a mixture of La–Fe–Ca–Na. • The pyrrole-N configuration contributes in the selective capture of REEs. [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]

• A balanced discussion on the technological requirements of NASICONs. • Comparison of cost of NASICON and carbon-based materials. • The performances of NASICON materials. • The methods to enhance the performance of NASICON materials. • NASICON materials for sodium ion battery can be applied in CDI. The world is suffering from water shortage and the hope relies on the desalination of salty water. Several technologies are available for desalination such as reverse osmosis and electrodialysis. However, the application of these technologies in desalination is limited by the higher energy consumption, high investment and maintenance costs. Capacitive deionization (CDI), an up-coming technology at an infant stage is able to supplement the dwindling freshwater resources and provide water to the population. The performance of CDI is directly affected by the electrode materials. Since its inception carbon has been the principal electrode materials for CDI technology. However, low salt removal capacity due to inaccessibility of nanopores and ejection of co-ions hinder the application of carbon materials. Battery materials have been developed as an alternative to accompany carbon materials. Specifically, sodium superionic conductor (NASICON) materials have been used in brackish water desalination by CDI due to having the diffusion channels forming a three dimensional open structure and availability at low cost. However, the NASICON materials have not yet applied in the desalination of water with high salinity such as sea water. This paper reviews the present status of NASICON materials as CDI electrode materials and fairly compares it with carbon materials. It further compares the cost of NASICON and carbon materials, highlights the possibility of NASICON to desalinate high ionic strength solutions such as seawater. Moreover, the paper, discuss the methods which can be used to enhance the salt removal capacity of NASICON materials and provide examples of NASICON materials in the field of energy storage that can be borrowed and used in CDI. From the analysis of this work, NASICON materials are great companion of the carbon materials, are cost effective and are promising for the desalination of sea water. [ABSTRACT FROM AUTHOR]

• Ag@CN was prepared using a porous carbon nanocage for packaging Ag nanoparticles. • Porous carbon nanocages act as a "molecular grid" to protect the Ag nanoparticle and allow Cl− transport. • Ag@CN shows an excellent dichlorination capacity of 110.0 mg·g−1. • Ag@CN electrode decreased slightly by 7.14 % after 100 cycles at 10 mv s−1. Selective dechlorination is the key to solving the pollution problem of saline wastewater and achieving resource recovery, which is a major challenge for existing treatment methods. The recent development of capacitive deionization (CDI) based on the Ag@carbon electrode exhibits highly selective Cl− removal; however, its industrialization still poses a significant challenge due to the agglomeration and subsequent falling of Ag nanoparticles in the electrochemical field. In this work, we proposed a new physical confinement strategy based on carbon nanocage that can suppress the migration and agglomeration behavior of Ag nanoparticles. Firstly, a controllable construction of porous carbon nanocages on the surface of Ag nanoparticles was realized by the Ag+/H 2 O 2 synergistic oxidation-carbonization process, significantly inhibiting the migration and agglomeration of Ag nanoparticles in the Ag@carbon electrode. The Cl− removal capacity fluctuated around 110.0 mg·g−1 in 100 CDI cycles, exhibiting an excellent stability. Meanwhile, the high Cl−/SO 4 2− selectivity coefficient (89.0) promised the efficiently selective separation of Cl− ions from saline wastewater. In particular, the migration and agglomeration of Ag species in the carbon matrix was mainly attributed to the mutual attraction-recrystallization of Ag nanoparticles in the electrochemical field. Consequently, our study provides significant support for the industrial application of Ag@carbon electrodes and fundamentally solves the problem of saline wastewater pollution. [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]

This study focused on removing salts and nutrients (nitrogen and phosphorus) from tertiary treated urban wastewater by capacitive deionization. The performance of a pilot-scale radial capacitive deionizer subjected to varying feed flow rates during the purification stage and constant flow rates during the reject stage was evaluated. This operational strategy aimed to maximize the water recovery rates of the system, with electrical adjustments being made proportionally to the water recovery rate. Lower hydraulic loads resulted in the radial capacitive deionizer removing more ions from the sewage, albeit with higher specific energy consumption. Optimal operational conditions reduced conductivity by 92.8 %, with a specific energy consumption of 2.17 kWhm−3. Significant removals of ammonium, nitrite, nitrate, and orthophosphate ions were observed, with average specie reductions of up to 84, 91.4, 100, and 60.5 %, respectively. Higher rates of treated water recovery resulted in lower ion removal reduction and energy consumption. The limiting step of the process referred to ion desorption, requiring the correct adjustment of the time lapse, flow rate, and applied electrical voltage to ensure the efficiency of the subsequent purification stage. A loss of efficiency was observed when the process was run continuously, thus emphasizing the strategic significance of capacitor rinsing during the rejection phase across multiple subsequent treatment cycles. • Significant removals of NH 4 +, NO 2 −, NO 3 −, and PO 4 3− from the effluent were observed. • The lower the hydraulic loads, the higher the removing rates of ions from the sewage. • The best ions removals were achieved with the higher specific energy consumption. • The limiting step of the process was the ion desorption during capacitor rinsing. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive review to highlight the application of 3D faradic materials in CDI field is presented. • The desalination performances of non-3D faradic electrodes and 3D faradic electrodes are systematically compared. • The perspective of 3D faradic materials is discussed to provide guidelines for future CDI development. To address the water scarcity issue, capacitive deionization (CDI) as a burgeoning desalination technology for removing different ions from sea and wastewater have been intensively explored. However, the low salt adsorption capacity and poor cycling stability of widely used carbon materials are difficult to fulfill the demand of practical CDI application, while the non-three-dimensional (non-3D) faradic electrode materials manifest the drawbacks of low specific capacitance and dissolution loss of metal ions, which severely limit their CDI application. Notably, three-dimensional (3D) faradic materials usually possess higher desalination capacity and better cycling stability than carbon materials and non-3D faradic materials, due to their wide ion diffusion channels and versatile structure, which are highly promising for achieving practical CDI application. However, few review papers have specifically focused on the limitations and advantages of 3D faradic materials in CDI field. In this review, a comprehensive insight into 3D faradic materials in terms of the solutions of limitations and corresponding desalination performance (via comparing with the desalination performance of non-3D faradic materials) is provided and the development prospect of 3D faradic materials is also expounded. [ABSTRACT FROM AUTHOR]

• CEM showed a greater advantage over AEM in improving coulombic efficiency. • Low charge efficiency was mainly attributed to co-ion repulsion. • A single IEM cannot effectively suppress co-ion repulsion. • The energy consumption and the desorption efficiency need to be a trade-off. Four different configurations of capacitive deionization (CDI) were assembled to comparatively investigate the contribution of different ion exchange membranes (IEMs), including anion exchange membrane (AEM) and cation exchange membrane (CEM), to the enhancement of desalination performance. The results showed that the low charge efficiency of membrane-free biochar-based CDI system was mainly attributed to co-ion repulsion rather than Faraday reactions, and a single IEM was not effective in suppressing the co-ion repulsion effect thereby exhibiting a similar low charge efficiency. Compared with AEM, CEM was more beneficial for high coulombic efficiency by restraining the oxygen reduction reactions. In addition, the electrosorption and desorption behaviors of the biochar-based membrane capacitive deionization (MCDI) under different operating conditions were explored. The results showed that zero voltage desorption (ZVD) was unfavorable to the desorption capacity of the electrode, especially in high concentration solutions, the reverse voltage desorption (RVD) led to higher desorption efficiency but required higher energy consumption. Therefore, energy consumption and regeneration efficiency need to be a trade-off in practical applications to realize energy saving and efficient desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Fe-N-C material can be used as the electrode material for CDI to remove copper ions. • The Fe-N-C material has abundant Fe 3 N and Fe 4 N active sites. • Fe-N-C has high selectivity for the electro-adsorption removal of copper ions. • Ion exchange and ion binding promote the removal of copper ions. In the current research, the resource recovery technology for Cu-containing wastewater from electroplating is still a difficult problem. Capacitive deionization technology (CDI) has received widespread attention for its strengths of convenient operation, low cost, and environmentally friendly. In this paper, Fe-N-C was prepared as the electrode material for the treatment of Cu-containing wastewater by capacitive deionization technology through one-pot thermal method. The optimum treatment conditions of Fe-N-C for Cu-containing wastewater were voltage equal to 1 V, pH = 5, and the inlet flow rate was 5 mL/min. The electro-adsorption capacity of a single Cu-containing solution of 400 mg/L could reach 389.4 mg/g. Meanwhile, by carrying out ion competition experiments on five cations, namely Zn2+, Na+, Mg2+, K+, and Cu2+, which demonstrated Fe-N-C had a significant selectivity for the electro-adsorption removal of Cu2+. Theoretical calculations revealed that Fe 3 N and Fe 4 N were more dominant for Cu2+ adsorption energy and more binding for competing ions in the monovalent state, but had less practical effect on Cu2+ adsorption. The morphology of the Fe-N-C was analyzed in more depth by X-ray photoelectron spectroscopy (XPS) and other characterization methods. Combined with density functional calculations, Cu would not only displace with Fe in Fe X N to form a more stable Cu X N structure, but also combine with Fe X N to form a Cu-Fe X N structure. This is conducive to accelerating the application of CDI to recover Cu2+ from heavy metal wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparation of NC-Co(PO 3) 2 adopted facile gas-solidified phosphating strategy. • NC-Co(PO 3) 2 electrode was used for the first time in the field of CDI. • NC-Co(PO 3) 2 showed better electrosorption capacity of 95.41 mg g−1. • NC-Co(PO 3) 2 had excellent selectivity in various ion-competitive environments. • Real copper-containing wastewater confirmed the great potential of NC-Co(PO 3) 2. The increasing amount of heavy metal copper ions (Cu2+) in industrial emissions, poses a serious threat to human health, biological environment, and resource scarcity. Capacitive deionization (CDI) is considered as a green and efficient method for desalination. It is crucial to develop high-performance electrodes for efficient operation of CDI that go beyond conventional carbon and yield considerable environmental benefits. Here, metal organic frameworks (MOFs) derived carbon-loaded cobalt metaphosphate (NC-Co(PO 3) 2) was prepared by low-temperature gas–solid phosphating for Cu2+ removal as CDI electrode for the first time. NC-Co(PO 3) 2 demonstrated superior electrode structure and function due to the synergistic effects of electric double layer coupling P-O bonds, the binding tendency of metaphosphate groups with Cu2+, and interfacial redox reactions induced by the labile valence state of cobalt. The optimal electrosorption capacity of NC-Co(PO 3) 2 was 95.41 mg g−1 at 1 V in 50 mL Cu2+ solution with splendid cyclic regeneration capability. Moreover, NC-Co(PO 3) 2 exhibited excellent selectivity and outstanding electrosorption performance in the presence of multiple coexisting ions and this CDI system realized the purification of actual copper-containing wastewater. A series of characterizations further revealed the specific mechanism of Cu2+ in adsorption–desorption process. Our finding strongly supported NC-Co(PO 3) 2 electrode can extend the CDI platform's capability for effectively removing and retrieving Cu2+ from wastewater. [ABSTRACT FROM AUTHOR]

• Theoretical capacitive ion-exchange mechanism is validated in a CDI pilot plant. • Mechanism for modifying mono and divalent cation concentrations was explained. • Solution with lower conductivity and SAR values were consistently produced. • R Mg/Na > 5–6 and water production rate of 0.5–0.8 L m−2 h−1 were achieved. • Robustness of the mechanism was confirmed in long-term cycling. Soil salinization poses a significant challenge to agricultural activities. To address this, the agricultural industry seeks an irrigation water solution that reduces both ionic conductivity and sodium adsorption rate (SAR), thereby diminishing the risks of soil sodification and fostering sustainable crop production. Capacitive deionization (CDI) is an attractive electrochemical technology to advance this search. Recently, a one-dimensional transient CDI model unveiled a capacitive ion-exchange mechanism presenting the potential to adjust the treated water composition by modifying monovalent and divalent cation concentrations, thereby influencing the SAR index. This behavior would be achieved by using electrodes rich in surface functional groups able to efficiently capture divalent cations during conditioning and releasing them during charging while capturing monovalent ions. Beyond the theoretical modelling, the current experimental research demonstrates, for the first time, the effectiveness of the capacitive ion-exchange mechanism in a CDI pilot plant using real water samples spiked with solutions containing specific mono and divalent ions. Electrosorption experiments and computational modeling, specifically Density-Functional Theory (DFT), were used along with the analysis of the surface functional groups present in the electrodes to describe the capacitive ion-exchange phenomenon and validate the steps involved on it, highlighting the conditioning as a critical step. Various operational and flow modes confirm the versatility of CDI technology, achieving separation factors (R Mg/Na) of 5–6 in batch, raising production from 0.5 to 0.8 L m−2 h−1 (batch) to 8.0–8.1 L m−2 h−1 when using single pass although reducing R Mg/Na to 2. The reliability of the CDI technology in reducing SAR was also successfully tested with different influent compositions, including magnesium and calcium. Finally, the robustness of the capacitive ion-exchange mechanism was validated by a second CDI laboratory 9-cell stack cycled over 350 cycles. Our results confirm the reported theoretical model and expands the conclusions through the experiments in a pilot plant showing direct implications for employing CDI in agricultural applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Faradic capacitive deionization (FDI), as an emerging research branch of capacitive deionization (CDI), has shown its great potential to relieve global water stress owing to its high desalination capacity/efficiency, flexible scale, and zero secondary pollution characteristics. However, the slow desalination kinetics and poor cyclic stability of the anion-capturing electrode of current FDI systems greatly limit its practical application. Herein, we proposed a strategy of interweaving FeOOH nanospindle inside the 3D network structure of carbon nanofiber aerogel to construct a 3D network structure (CNFAs@FeOOH) and further used it as a chloride capture electrode for FDI. As a result, the FDI system equipped with CNFAs@FeOOH enjoys excellent desalination performance with an ultrahigh desalination rate of up to 0.33 mg g−1 s−1. More importantly, the CNFAs@FeOOH-based FDI system enjoys excellent cycling stability with no significant decrease in 100 cycles and only 17.85 % decrease in 200 cycles. Carbon nanofiber aerogel interweaved FeOOH was introduced as chloride-insertion electrodes for faradic capacitive deionization, achieving durable and fast desalination. [Display omitted] • Carbon nanofiber aerogel interweaved FeOOH (CNFAs@FeOOH) was used as the anode of faradic capacitive deionization (FDI). • The 3D network structure of CNFAs@FeOOH prevents aggregation between FeOOH and enables rapid charge/electron transfer. • The open porous structure of CNFAs@FeOOH allows flow-through water mode to accelerate mass transfer. • The CNFAs@FeOOH-based FDI system displays an ultrahigh desalination rate with excellent long-term stability. [ABSTRACT FROM AUTHOR]

Sugarcane bagasse is one of the most common Vietnamese agricultural waste, which possesses a large percentage of cellulose, making it an abundant and environmentally friendly source for the fabrication of cellulose carbon aerogel. Herein, waste sugarcane bagasse was used to synthesize cellulose aerogel using different crosslinking agents such as urea, polyvinyl alcohol (PVA) and sodium alginate (SA). The 3D porous network of cellulose aerogels was constructed by intermolecular hydrogen bonding, which was confirmed by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption/desorption. Among the three cellulose aerogel samples, cellulose – SA aerogel (SB-CA-SA) has low density of 0.04 g m−3 and high porosity of 97.38%, leading to high surface area of 497.9 m2 g−1 with 55.67% micropores of activated carbon aerogel (SB-ACCA-SA). The salt adsorption capacity was high (17.87 mg g−1), which can be further enhanced to 31.40 mg g−1 with the addition of CNT. Moreover, the desalination process using the SB-ACCA-SA-CNT electrode was stable even after 50 cycles. The results show the great combination of cellulose from waste sugarcane bagasse with sodium alginate and carbon nanotubes in the fabrication of carbon materials as the CDI-utilized electrodes with high desalination capability and good durability. [Display omitted] • For the first time the effect of different crosslinking agents on the fabrication of carbon aerogel was investigated. • The fabricated carbon aerogel consisted of micro- and mesopores, with low density, high porosity, and high surface area. • SB-ACCA-SA and SB-ACCA-SA-CNT electrodes exhibited high SAC value of 17.84 mg g−1, and 31.40 mg g−1, respectively. • The desalination process using the SB-ACCA-SA-CNT electrode was stable even after 50 cycles. [ABSTRACT FROM AUTHOR]

Freshwater reserves are being polluted every day due to the industrial revolution. Man-made activities have adverse effects upon the ecosystem. It is thus the hour of need to explore newer technologies to save and purify water for the growing human population. Capacitive deionization (CDI) is being considered as an emerging technique for removal of excess ions to produce potable water including desalination. Herein, cost-effective activated carbon incorporated with carbon nanotubes (CNT) was used as a freestanding electrode. Further, the desalination efficiency of the designed electrodes was tuned by varying binder concentration, i.e., polyvinylidene difluoride (PVDF) in the activated carbon powder and CNT mixture. PVDF concentration of 5, 7.5, 10, and 12.5 wt% was selected to optimize the freestanding electrode formation and further applied for desalination of water. PVDF content affected the surface morphology, specific surface area, and functional groups of the freestanding electrodes. Moreover, the electrical conductivity and specific surface area changed with PVDF concentration, which ultimately affected the desalination capacity using the freestanding electrodes. This study paves the way to produce cost effective carbon-based freestanding electrodes for capacitive deionization and other applications including battery electrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • NO 2 – oxidation and sorption on oxyhydroxides was studied at constant potential. • NiOOH played a rule of diffusive capacitance effective in NO 2 – oxidation. • Adsorption capacity of Ni/CoOOH composite was facilitated by carbon support. • Langmuir model assessed NO 2 – monolayer capacity under given electrode potentials. • NiCo/AC had synergist effect on NO 2 – eliminated. The composite electrode of NiCo oxide supported by porous carbon was synthesized for nitrite oxidation and nitrate electro-sorption. The crystal structure and chemical state of the Co and Ni oxyhydroxides which were precipitated on loofah-derived activated carbon (AC) using hypochlorite were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and BET surface area. The voltammetry showed that the redox couple of Co(II)/Co(III) and Ni(II)/Ni(III) as the mediator catalytically transferred the electrons of NO 2 –/NO 3 –; the Ni site had a relatively high transfer coefficient and diffusive current, while the Co site was better in the capacitive removal of the nitrite and nitrate compounds. A batch electrolysis of nitrite ions was operated under constant anodic potential mode (0 to + 1.5 V vs. Ag/AgCl) to assess the performance of the composite electrodes. The adsorption capacity of NiCo/AC (Ni = 5% and Co = 5% on AC by weight) was 23.5 mg-N g−1, which was twice that of AC substrate (7.5 mg-N g−1), based on a multilayer adsorption model. The steady-state kinetics of the consecutive reaction were derived to determine the rate steps of the electrochemical oxidation of NO 2 – and adsorption of NO 3 –. [ABSTRACT FROM AUTHOR]

The carbonization of 2-methylimidazole zinc salt (ZIF-8) in a nitrogen atmosphere to obtain ZIF-8-derived porous carbon (ZDPC) was explored. ZDPC and activated carbon (AC) were applied to prepare composite electrodes, which were used in capacitive deionization (CDI) for the treatment of vanadium-containing solutions. After carbonization at 950 °C, ZDPC has a high specific surface of 1043.12 m2 g−1, an average pore diameter of 1.73 nm, and a high specific electrochemical capacitance of 156.89 F g−1. It was found that the electrosorption capacity of the ZDPC/AC composite electrode for V(V) was 77.27 mg g−1. The adsorption of V(V) onto ZDPC/AC composite electrodes conforms to the Langmuir isotherm adsorption model, indicating that V(V) is adsorbed as a monolayer on the electrodes. The pseudo-first-order kinetic model fits better toward the adsorption processes of V(V), which shows that the adsorption process is dominated by physical adsorption. The high capacitive adsorption performance of the ZDPC/AC composite electrode proves the huge potential application of ZDPC in the field of capacitive adsorption for metals. [ABSTRACT FROM AUTHOR]

Anion driven Rocking-chair Capacitive Deionization system with flow-through electrode was built for the first time based on the design of high-performance bismuth oxychloride coated carbon foam electrode. [Display omitted] • Anion-driven Flowthrough Rockingchair Capacitive Deionization (AFT-RCDI) was built. • BiOCl coated carbon foams were fabricated and used as the electrode for AFT-RCDI. • The AFT-RCDI displays excellent desalination performance with superior stability. Rocking-chair capacitive deionization (RCDI), as the next generation technique of capacitive deionization, has thrived to be one of the most promising strategies in the desalination community, yet was hindered mostly by its relatively low desalination rate and stability. Motivated by the goal of simultaneously enhancing the desalination rate and structural stability of the electrode, this paper reports an anion-driven flow-through RCDI (AFT-RCDI) system equipped with BiOCl nanostructure coated carbon sponge (CS@BiOCl for short; its backbone is derived from commercially available melamine foam with minimum capital cost) as the flow-through electrode. Owning to the rational design of the composite electrode material with minimum charge transfer resistance and ultrahigh structure stability as well as the superior flow-through cell architecture, the AFT-RCDI displays excellent desalination performance (desalination capacity up to 107.33 mg g−1; desalination rate up to 0.53 mg g-1s−1) with superior long-term stability (91.75% desalination capacity remained after 30 cycles). This work provides a new thought of coupling anion capturing electrode with flow-through cell architecture and employing a low-cost CS@BiOCl electrode with commercially available backbone material, which could shed light on the further development of low-cost electrochemical desalination systems. [ABSTRACT FROM AUTHOR]

Environmental pollution requires advanced methods and materials to clean drinking water. In particular, 2D transition metal carbides, named MXenes, display unique properties such as specific surface area, surface functional groups, conductivity, and antibacterial effects. Here, we review the applications of MXenes for water purification, and the factors controlling the efficiency of MXenes. We present the history of MXenes and focus on applications for adsorption, capacitive deionization, membranes, and catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • The investigation focuses on the impact of the stability of electrodes within CDI. • It unpacks novel advances arising from diverse engineering strategies. • The review evaluates scientific barriers and opportunities around electrode stability. Capacitive deionization (CDI), an emerging desalination technique, harnesses porous carbon electrodes to eliminate ions via electrosorption. Despite its promise, CDI systems encounter persistent obstacles, chiefly the deterioration of carbon electrode efficiency over repetitive sorption/desorption cycles stemming largely from surface oxidation and corrosion. Herein, the review systematically investigates the pressing challenges impinging on electrode stability in CDI systems, including anodic oxidation reactions, cathodic reduction reactions, large volume changes, irreversible electrochemical reactions, and electrode fouling. Their detrimental impact on seawater desalination remains central. Diverging, it unpacks novel advances arising from diverse engineering strategies like surface, defect, interface, and structural engineering. Though nascent, these demonstrate immense potential to significantly strengthen CDI electrodes critical for water purification. In closing, the review evaluates scientific barriers and untapped opportunities around electrode stability, offering clear future outlooks for the expanding research area. It provokes consideration of questions whose answers could profoundly advance CDI technology. By broadly surveying the CDI landscape, the review seeks to catalyze rapid innovation in CDI electrode engineering. [ABSTRACT FROM AUTHOR]

As water scarcity intensifies, the quest for developing sophisticated electrode materials with adjustable configurations, complex structures, and developed desalination performance garners important interest. Prussian Blue (PB) and its analogs (PBAs), owing to their cost-effectiveness, uncomplicated synthesis, innate open framework, and modifiable composition, have elicited considerable recognition. Herein, the paper provides a comprehensive overview and analysis of the advances made in capacitive deionization electrodes based on PB and PBAs. It commences by detailing the synthesis techniques, post-treatment processes, and derivatives of standard PBs and PBAs. Subsequent sections propose strategies to minimize auxiliary reactions in electrochemical processes, encompassing structural design, protective coatings, substitution, and the confinement effect. Subsequently, emphasis is placed on structures that have potential as electrode materials in applications such as desalination, heavy metal removal, resource recovery, and water softening. A summary of current achievements in the field is provided, alongside a critique of prevailing limitations and emergent challenges. As advancements in electrode materials continue to unfold, it aims to stimulate innovative ideas for utilizing PB and PBAs in environmental research, thereby catalyzing additional investigation into the desalination area. [Display omitted] • The preparation methods of advanced PB/PBAs electrode are discussed in depth. • The versatile applications of PB/PBAs electrode are discussed extensively. • The future orientation development of PB/PBAs in CDI is provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile dual physico-chemical activation strategy is proposed. • The synthesized NPHPC possesses high specific surface area, pore volume, specific capacitance and excellent hydrophilicity. • The NPHPC delivered a splendid desalination capacity and good cycling stability. The preparation of heteroatom-doped hierarchical porous carbons (HPCs) possessing both high-performance and cost-effective is advantageous for the advancement of capacitive deionization (CDI). Biomass, which is abundant and inexpensive, has been widely utilized as a precursor for carbon electrodes. However, the simple pyrolysis of a single biomass typically leads to insufficient porosity with narrow surface area, along with poor wettability and conductivity, thereby resulting in limited desalination performance. Therefore, we employ ammonium dihydrogen phosphate (NH 4 H 2 PO 4) and potassium carbonate (K 2 CO 3) as chemical and physical activators, respectively, to co-activate lotus petiole (LP) for the preparation of N/P co-doped hierarchical porous carbon (NPHPC). In comparison with conventional single K 2 CO 3 activation, NPHPC prepared through dual physico-chemical activation exhibits exceptional specific surface area (S BET , 2170.00 m2/g), excellent pore volume (V pore , 1.16 cm3/g), outstanding mesoporosity (V meso /V pore , 72.41 %), superior hydrophilic performance (contact angle: 39°), high specific capacitance (221.86F/g), moderate N-doping (3.1 %) and P-doping (0.4 %). When assembled for desalination, the synthesized materials demonstrate a fabulous electroadsorption capacity of 21.85 mg/g together with notable cycling stability, highlighting their excellent application prospects. In summary, this work presents innovative ideas in proposing a facile synthesis of high-performance heteroatom-doped HPCs for CDI desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrode material with efficient and selective phosphate adsorption was developed. • ZnFe-PANI/CNT electrode exhibited remarkable capacitive behavior and charge storage capacity. • ZnFe-PANI/CNT had excellent phosphate adsorption capacity over a wide parameters range. • The high phosphate removal rate was maintained after 10th regeneration processes. Capacitive deionization technology possesses puissant competitiveness in the field of water treatment due to its low cost and high efficiency. In this study, polyaniline (PANI) doped and carboxyl intercalated metal hydroxide composite (ZnFe-PANI/CNT) was developed by a simple co-precipitation method, and used as anode electrode for phosphate removal in sewage. The results show that ZnFe-PANI/CNT electrode can efficiently remove phosphate at concentration of 2–10 mg/L at a wide range of pH (3–10) by electric double layer capacitive adsorption and pseudocapacitive adsorption. The concentration of phosphate in the effluent was as low as 0.095 mg/L, and the coexisting anions (Cl−, NO 3 −, SO 4 2− and HCO 3 −) hardly inhibited the phosphate adsorption by ZnFe-PANI/CNT composite electrode. In addition, under the optimal phosphate adsorption conditions (pH = 7 and applied voltage of 1.2 V), the energy consumption of CDI system was calculated as low as 0.00274 kWh/g P and 0.017 kWh/m3 water, realizing the expectation of low cost and high efficiency operation. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D MXene expanded and functionalized by S and N doping. • Combination of pyrrolic-N and C=S shows stronger adsorption affinity to Pd2+. • DFT calculations elucidated the selectivity mechanism of S/N-MXene towards Pd2+. • Pd2+ ions were extracted from 0.5 mM and enriched to 120 mM. This work prepared a sulfur/nitrogen co-doped MXene (S/N-MXene) electrode material via a facile hydrothermal method. The electrode material has been specifically designed to recover palladium(II) from wastewater. Numerous S/N-containing functional groups were introduced into the MXene by S and N co-doping, with the contents optimized for the preferential recovery of Pd(II). These functional groups acted as pillars to expand the interlayer spacing of MXene, facilitating Pd2+ diffusion between MXene layers and enhancing accessibility to the anchor sites (–OH groups and heteroatom functional groups). The S/N-MXene electrode exhibited a high recovery capacity of 2.92 mmol g−1, high recovery efficiency of 96.4 % in 15 min and good long-term cycling performance with greater than 80 % capacity retained after 260 cycles. The S/N-MXene electrode showed preferential adsorption of Pd2+ from wastewater. The adsorption mechanism was elucidated through density functional theory (DFT) calculations showing that the downward shift of the p -band center of the MXene-OH groups induced by pyrrolic-N and -C=S in S/N-MXene (compared to single doping with S or N) favours enhancement of the soft ion-soft ion interactions. Furthermore, the adsorbed Pd2+ on the S/N-MXene electrode could be enriched by simple reversing of the applied voltage to strip the ions from the sorbent, thus avoiding the need to use harsh chemicals for regeneration and minimizing the amount of secondary waste. [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]

The innovative design of collector is a top priority to drive the advancement of flow electrode capacitive deionization (FCDI) technology. Currently, the majority of FCDI research has concentrated on the implementation and modification of carbon-based flow electrode materials, while ignoring the effect of the current collector in FCDI. In this study, a 3D-FCDI configuration with porous titanium foam as the collector is designed, and rectorite (Rec) is used as the flow electrode in 3D-FCDI. Thanks to the porous structure of the 3D current collector, the collision opportunities of electrons with the Rec particles are increased and the long-distance migration of electrons in the conventional graphite collector is overcome, thus improving the system conductivity. The Rec exhibits good electrode dispersion, desalination rate, and energy consumption at low cost. In addition, the ASAR of Rec can be achieved by adjusting the electrode concentration (5 wt%), electrode flow rate (25 mL min−1) and operating voltage (1.8 V) to 11.43 μg cm−2 min−1. This study demonstrates the capability of 3D-FCDI configuration to advance the creation and implementation of FCDI. [Display omitted] • A 3D-FCDI configuration with porous titanium foam as the current collector is designed. • Collision opportunities of electrons and 3D-FCDI conductivity are increased. • Rectorite exhibits good desalination rate, and energy consumption at low cost. • 3D-FCDI is very conducive to the industrial application of FCDI technology. [ABSTRACT FROM AUTHOR]

Remarkable progress has been achieved to enhance the performance of electrochemical desalination technologies. Desalination batteries are promising due to their ability to simultaneously desalinate water and generate energy. A typical desalination battery consists of rechargeable high-capacity Na- and Cl-storage electrodes that remove ions during charging and release them during discharging. This technology works at low voltages and does not require chemicals, high-pressure pumps, or thermal heaters. Despite the existence of studies focusing on desalination batteries, a notable research gap persists regarding the assessment of performance characteristics, comparison of the various desalination battery designs, evaluation of energy consumption, and the exploration of the potential and limitations of desalination batteries. This highlights the need for a comprehensive review to address these key aspects. The goal of this work was to address these points by shedding light on the fundamentals, principles, and main findings related to desalination batteries to-date. Four main types of desalination batteries are surveyed: membrane-free, rocking chair, redox flow, and metal-air. Emphasis is given on energy considerations, as the energy consumption of desalination technologies has been a significant challenge for decades. Finally, research directions for further desalination battery developments are discussed related to both challenges and opportunities in the field. [Display omitted] • A critical review of desalination batteries • Comparative advantages of battery-based desalination over capacitive deionization • Comprehensive investigation of different desalination battery types • Energy consumption analysis in desalination batteries • Comparison of desalination batteries with state-of-the-art desalination technologies [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a high-performance, low-energy consumption, and environmentally friendly water treatment technology with a broad application prospect in heavy metal removal. Selecting electrode materials with high capacitance and low resistance is essential for improving CDI's desalting efficiency. This article discusses the utilization of sugarcane bagasse (C-N-X) and the production procedures of CDI materials. The unique 3D cross-linked structure of C-N-X provides excellent mass transfer properties and significant advantages in capacitance and conductivity. The results of X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectrometer (FTIR) show that bagasse biochar with graphene-like structure and abundant functional groups provides active sites for Cu2+ removal. In this paper, C-N-X is first used as CDI electrode material to remove Cu2+. Electrochemical tests show that the specific capacitance of C-N-X is still stable at about 47 F g−1, and the removal capacity of Cu2+ (25 mg L−1) reaches 66.79 mg g−1 within 4 h after 700 cycles. The experimental results and DFT calculations confirm the adsorption selectivity of C-N-700 for Cu2+. [Display omitted] [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]

Composite electrode materials for removing paraquat from contaminated water were synthesized by loading aluminium oxide (Al 2 O 3) onto activated carbon (AC) via co-precipitation method. The composite properties were investigated by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Capacitive deionization batch experiments compared the electrosorption of paraquat herbicide by the composite electrode and the pristine activated carbon. The performance of the composite electrodes showed that the removal efficiency and adsorption capacity depend on the aluminium oxide loading, applied potential, flow rate, and charging time. At 1.2 V, a flow rate of 15 mL/min, a charging time of 3 h and 20 mg/L PQ initial concentration, the composite electrode (AC/Al 2 O 3 -1:1) demonstrated a removal efficiency, electrosorption capacity, and energy consumption of 95.5 %, 1.27 mg/g, and 0.055 kWh/m3, respectively, compared to 62 %, 0.83 mg/g, and 0.11 kWh/m3 for the unmodified AC. The presences of other ions/pollutants were found to have negligible interference on PQ pesticide removal as the removal efficiency and electrosorption capacity of the AC/Al 2 O 3 -1:1 composite in both artificial (95.5 %, 1.27 mg/g) and natural water (87.5 % 1.17 mg/g). The study confirmed that composite electrode can reused several times, as there was no significant decrease in its regeneration efficiency even after multiple cycles. • Drinking water with pesticides can result in severe health problems. • Capacitive deionization (CDI) is a promising method for pesticide removal. • Presence of different ions and other contaminants does not affect the removal of PQ • Aluminium oxide-modified carbon composite is a promising CDI electrode material for paraquat removal. • Surface modification of activated carbon with aluninium oxide minimizes energy consumption. [ABSTRACT FROM AUTHOR]

Capacitive Deionization (CDI) technology achieves ion immobilization through a reversible electrochemical process, gradually emerging as a substitute for conventional desalination techniques due to its simplicity, efficiency, and energy-saving advantages. Materials design has played a pivotal role in the continuous refinement and development of the CDI theoretical framework, with substantial efforts directed towards the design of high-performance novel electrode materials. Among them, Covalent Organic Frameworks (COFs) have been explored as exceptionally promising candidates. COFs represent a burgeoning class of porous crystalline materials, characterized by pronounced intrinsic features encompassing high tunability, highly ordered pore structures, elevated surface areas, and an abundance of functional sites. Consequently, it becomes more facile to tailor channels with facile ion transport and immobilization, facilitating the seamless integration of ion-selective electrochemical redox-active sites. This ultimately fulfills the design objectives for CDI materials. This comprehensive review aims to systematically and comprehensively explore the underlying design fundamentals, principles and frontiers of COFs materials for CDI. Specifically, discussions encompass the three major research challenges of enhancing intrinsic conductivity, suppressing co-ion effects and Faradaic side reactions, and delving into mechanistic studies. These insights provide valuable guidance for the future design of sustainable, high-performance, and ion-selective capacitive deionization electrode materials. [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] • Dual cation titanosilicate(DTS) was utilized in CDI to capture Cs+ and Sr2+. • By applying −1.2 V, the DTS electrode exhibits a high adsorption capacity. • DTS electrode showed rapid kinetics over 95 % of adsorption capacity within 30 min. • It provides a high selectivity of 5x103 mL/g in 10000-fold Na concentrated solution. • It was regenerated by applying + 2.0 V and its structural integrity remains intact. The utilization of ion intercalate capacitive deionization technology is garnering attention as an electrified water treatment method. This study proposes a capacitive deionization technology incorporating Dual-cation TitanoSilicate (DTS) to enable efficient electro-sorption/desorption of radioactive ions Cs and Sr. The synthesized DTS possesses a robust structure, high selectivity for Cs and Sr, and substantial adsorption capacity, incorporating redox-active titanium. Employing DTS as an active material in the electrode demonstrated a high adsorption capacity (186 mg Cs/g, 177 mg Sr/g) and rapid adsorption kinetics, reaching maximum capacity within 30 min, even in environments with a tenfold excess of competing ions. Furthermore, our system exhibited stable performance over 5 cycles of adsorption/desorption, and post-desorption analyses confirmed the durable structure stability without significant alterations. This study highlights the feasibility of CDI technology utilizing DTS for cesium and strontium removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu-MOF serves as a template for porous carbon production. • PVP introduces N-doping to reduce particle size, providing more active sites. • MWCNTs offer conductive networks to facilitate electrons and ions transportation. • EDLs and pseudocapacitance contribute to the enhanced electrosorption efficiency. When applying Capacitive Deionization (CDI) for water desalination, discovering effective techniques to attract more salt ions poses significant challenges. Herein, a 3D porous carbonized MOF-199@PVP/MWCNTs (CMPC) composite for enhanced electrosorption of U(VI) in water had been developed. Further investigation revealed that the incorporation of polyvinylpyrrolidone (PVP) enabled the CMPC composite to maintain its distinctive octahedral porous structure and rich N-doping to reduce particle size, providing more active sites. Additionally, the interpenetrating of multi-walled carbon nanotubes (MWCNTs) had formed a localized conductive network, further enhancing its properties. As a result, the CMPC electrode had been demonstrated a remarkable removal ratio of 95.2 % with the uptake electroadsorption capacity of 410.3 mg g−1 for UO 2 2+ aqueous solution (1.2 V). The exceptional CDI efficiency achieved by the CMPC electrode is attributed to the collaborative influence of electrochemical double layers (EDLs) and pseudocapacitance derived from the unique assembly of MOF-199, PVP, and MWCNTs. Besides, the results of the experiments on the effect of ionic strength showed that the electrosorption ratio still remained at 80.1 % when 60 mg/L NaNO 3 was added to the UO 2 2+ solution. And the removal performance of U(VI) remained over 85.7 % even after five CDI cycles. Overall, CMPC is a highly prospective electrode material in CDI for efficient extraction of uranium from water. [ABSTRACT FROM AUTHOR]