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The design and synthesis of high‐performance and economical carbon electrodes play a critical role in developing energy‐efficient water desalination technologies. As a sustainable approach, low‐cost and abundant biomass materials are promising candidates to prepare porous carbon for capacitive deionization. In this study, binder‐free porous carbon sheets are successfully prepared using natural balsa, pine, and basswood by thermal carbonization and treated by chemical activation. The carbon electrode materials converted from balsa and pine exhibit a comparable salt adsorption performance by capacitive deionization due to the extensive surface area, substantial electrical property, and superior hydrophilic performance. The following activation treatment of the balsa‐converted carbon further enhances the surface and electrical properties and benefits the desalination performance. The salt adsorption capacity of the activated balsa electrode exhibits 12.45 mg g−1. Additionally, 19.52 mg g−1 Pb2+ and 20.06 mg g−1 Cr3+ heavy metal adsorption capacity is also observed with the activated balsa electrode in 100 mg L−1 PbCl2 and 50 mg L−1 CrCl3, respectively. To the best of authors' knowledge, this is the highest NaCl adsorption capacity performance reported thus far by using pure wood converted carbon as the electrode, and these promising results indicate that activated balsa is an extraordinary material for water desalination. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an efficient new technology that can be used to remove charged pollutants. However, differences in the electrode selectivity for different ions limit its further application. Therefore, the electrosorption behavior and selectivity of four anions in a CDI system with activated carbon electrodes were investigated using mixed solutions. The results showed that the adsorption capacities and selectivities of the anions varied due to differences in their hydration energy and valence. The preferential electrosorption order was as follows: NO3− > Cl− > SO24− > phosphate (P). In addition, the competitive mechanism between different anions and P was studied. P competed with SO24− the most for electrosorption sites due to their spatial similarity. However, because the NO3− adsorption capacity was the highest, P had the lowest electrosorption selection coefficient when it coexisted with NO. Finally, the mechanism of the electrosorption selectivity was verified. The results indicated that the electrosorption selectivity of P was improved by decreasing the voltage to weaken the competition between P and other anions for sites and by adjusting the pH to optimize the hydration energy and electronegativity of P. This research may provide readers with a deeper understanding of electrosorption selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amidoxime-modified g-C 3 N 4 electrode was hydrothermally synthesized. • Th(IV) electrosorption was studied by varying voltage, time, and concentration. • Maximum adsorption capacity was 275.74 mg.g−1 at – 1.0 V within 30 min. • Chemisorption and double-layer charging occurred with AX/g-C 3 N 4 in electrosorption. • The electrosorption occurs via the abundant of N and O redox sites of AX/g-C 3 N 4. Electrosorption is a technique that combines electrical and adsorption processes and has been established to displace Th(IV) from aqueous solutions. The present study successfully synthesised a novel electrode, where graphitic carbon nitride was modified with amidoxime amidoxime groups (g-C 3 N 4 /AX) via the hydrothermal method. The batch experiments conducted in this study revealed that the g-C 3 N 4 /AX electrode possessed a favourable thorium adsorption capacity of 275.74 mg.g−1 and a swift elimination equilibrium of within 30 min. Furthermore, the removal efficiency at − 1.0 V (84.46 %) of the electrode was almost threefold greater than the removal efficiency at open circuit potential (24.09 %). The results were due to the free electrical charges on the g-C 3 N 4 /AX electrode, which induced the electrical driving force and facilitated the adsorption of Th(IV) ions onto the g-C 3 N 4 /AX surface. The shifted bands from the Fourier transform-infrared (FT-IR) spectrum post-electrosorption demonstrated a substantial complexation of Th(IV) with the amine groups of amidoxime and g-C 3 N 4. A significant transference in energy band peaks was also observed during the XPS assessment, indicating that the electrosorption process included oxygen (O), carbon (C), and nitrogen (N) species. In the practical real wastewater involving rare earth residue, which contains Ce, La, Nd and Pr ions, g-C 3 N 4 /AX exhibited good capabilities in selectively adsorbing Th(IV). The electrode synthesised in this study also exhibited the ability to regenerate with a reasonable ∼ 80 % removal ratio after five runs. The results indicated that the amidoxime-modified graphitic carbon nitride electrode demonstrated a good potential in removing thorium from aqueous solutions via electrosorption applications. [ABSTRACT FROM AUTHOR]

Membrane capacitive deionization (MCDI) is a modification of capacitive deionization (CDI) using ion-exchange membranes (IEM) in front of the electrodes. Electrode properties, especially the specific surface area, are known to be strongly related with desalination performance in CDI, but the effects of other properties in MCDI are not fully understood. The objective of this study was to investigate the effect of hydrophilicity in activated carbon electrodes on desalination performance in MCDI. Two types of activated carbon (P60 and YS-2) whose specific surface areas were similar were used as electrode materials, but they had different hydrophilicity (i.e., P60 was originally hydrophobic and YS-2 was relatively hydrophilic due to its nitrogen-containing surface chemistry). These hydrophilic electrodes (either the electrode itself or modified with polydopamine (PDA)) led to an increase in the salt adsorption capacity (SAC) in MCDI because they facilitated the access of both ions and water molecules into the electrode pores. In particular, the SAC of the P60 electrode displayed a large increase to almost reach that of the YS-2 electrode due to the improved hydrophilicity with PDA modification and the insignificant effects of PDA modification on an already hydrophilic YS-2 electrode. Additionally, PDA-modified IEM in MCDI reduced the SAC as a result of the additional insulating PDA layer with little changes in hydrophilicity. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) technology has shown practicality and cost-effectiveness for water desalination. However, electrode development remains a major challenge. Carbon electrodes, commonly used in CDI, have limited adsorption capacity, necessitating the improvement of their physicochemical and electrochemical properties. To address these limitations, Faradaic electrodes based on the redox process have emerged as an alternative. Faradaic reactions in CDI systems offer benefits such as pseudocapacitive/intercalation effects and the development of charged species. Different types of Faradaic reactions include anodic oxidation reactions (to be avoided in CDI), cathodic oxygen reduction reactions, and Faradaic ion storage processes involving intercalation effects. Faradaic electrodes exhibit higher ion storage capacity due to their redox reactions and have been produced in various forms, expanding the range of available CDI electrodes. This indicates a promising future for Faradaic materials in CDI technology. The review highlights recent strategies in the development of capacitive and Faradaic electrode materials for CDI, along with progress in material synthesis and its impact on desalination. The review also introduces approaches to address complexities in defining optimal electrode parameters and achieve material optimization in electrochemical desalination. Overall, advancements in material development for electrochemical desalination processes are overviewed. [Display omitted] • Electrochemical desalination of seawater/brine was reviewed. • A wide range of electrode material design has been analyzed. • Faradaic redox reactions in CDI were represented. • The performances of various electrode materials have been summarized and compared. • Future challenges in the field of CDI have been discussed. [ABSTRACT FROM AUTHOR]

Abstract Herein, combined with the outstanding adsorption ability of flower-like MoS 2 with ultra-thin nanosheets and the good electrical conductivity of reduced graphene oxide (rGO), a sensitive and anti-interference electrochemical sensing interface for the analysis of Pb(II) was constructed by using MoS 2 /rGO nanocomposite modified glassy carbon electrode (MoS 2 /rGO-GCE). The stripping behavior of Pb(II) was estimated using square wave anodic stripping voltammetry (SWASV), a high sensitivity of 50.80 μA μM−1 was achieved, and the limit of detection (LOD) was determined to be 0.005 μM (3σ method). The reasons for the excellent electrochemical performance of MoS 2 /rGO-GCE toward Pb(II) is that the excellent adsorption capacity and electrical conductivity, and the redox reaction of Pb(II) occurs directly on the surface of the MoS 2 /rGO nanocomposite. Moreover, series interference experiments were systematically conducted, the sensitivity of Pb(II) has no obvious change in the presence of other coexist heavy metal ions. In addition, an intriguing interference phenomenon between Pb(II) and Cu(II) was found. When Cu(II) exists in the solution, two stripping peaks of Pb(II) were observed, this phenomenon can be explained that the form of Pb Cu alloy or intermetallic compounds during the preconcentration process. Further experiments indicated that the proposed method has good stability and reproducibility. Finally, the accurate detection result of Pb(II) in wastewater sample gathered from Wangxiaoying wastewater treatment plant were obtained. Graphical abstract On the basis of the excellent adsorption capacity and good electrical conductivity of MoS 2 /rGO nanocomposite, Pb(II) can be first adsorbed on the surface of MoS 2 /rGO nanocomposite, and the redox reaction of Pb(II) would occur on the surface of MoS 2 /rGO nanocomposite in situ, so a high sensitive and anti-interference electrochemical sensing Pb(II) was realized. Image 1 Highlights • High sensitive and anti-interference electrochemical sensing Pb(II) was realized using MoS 2 /rGO-GCE. • Excellent adsorption capacity enhances sensing performance was revealed by stripping voltammetry and XPS analysis. • The redox reaction of Pb(II) would occur on the surface of MoS 2 /rGO nanocomposite in situ. • An interesting phenomenon of interference was observed on the detection of Pb(II) in the presence of Cu(II). • The proposed method was successfully utilized to detect Pb(II) in wastewater sample. [ABSTRACT FROM AUTHOR]

A method for operating membrane capacitive deionization (MCDI) systems without electrode reactions at a high cell potential was studied. The charge supplied to the cell was controlled to suppress Faradaic reactions. The maximum allowable charge (MAC) that can be supplied to a carbon electrode without electrode reactions was measured to be 58 C/g. Adsorption experiments were conducted while supplying a charge of 55 C/g (95% of the MAC value) in constant-current (CC) and constant-voltage (CV) mode. The cell potential increased to 1.42 V in CC (1.43–4.29 mA/cm2) mode, but the concentration and pH of the effluent were kept constant. In addition, the effluent pH was stable in CV (1.25–2.0 V) mode. The salt adsorption capacities and charge efficiencies were approximately 15.5 mg/g and 92%, respectively, regardless of the current densities and cell potentials applied to the cell. With increasing cell potential, the concentration polarization in the feed stream was intensified, resulting in an increase in cell resistance. It was thought that electrode reactions did not occur at a high cell potential because of the high voltage drop due to the cell resistance. The higher the cell potential (or current density) is, the faster the desalination rate in MCDI operation. It is expected that this operation method applying the MAC concept will contribute to the stable operation of MCDI systems and an improvement in desalination performance. Image 1 • A stable operation method for MCDI systems at high cell potentials was proposed. • Faradaic reactions were suppressed by controlling the charge supplied to the cell. • The MCDI desalination performance was stable regardless of cell potential. • The voltage drop due to cell resistance increased with increasing cell potential. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Electrosorption performance of activated carbons was examined for the desalination. • The effect of pore structure on capacitive characteristics was investigated. • High specific capacitance suggested high salt adsorption capacity. • CDI Ragone provided comprehensive view on desalination capacity and rate. • Single-pass mode CDI was desirable to estimate desalination performance. Abstract In the present work, the electrosorption performance of activated carbon-base capacitive deionization (CDI) was evaluated by batch and single-pass mode experiments. Two commercial activated carbon electrodes with raw materials of coal (AC1) and wood (AC2) were selected and their physical and electrochemical characteristics were determined by Brunauer–Emmett–Teller (BET) and cyclic voltammetry experiments. The results indicated that micropores and mesopores are well-balanced in both AC1 and AC2. The specific surface of AC1 (940 m2/g) was higher than that of AC2 (662 m2/g), and the AC1 showed a higher specific capacitance from cyclic voltammetry curves. CDI characteristics could be determined from the batch-mode and single-pass experiment, both AC1 and AC2 showed good electrosorption performance. The batch-mode, however, can only serve as evaluation of basic CDI performance. As evidenced in single-pass experiments with 2 mM NaCl at 1.0 V, AC1 exhibited a higher salt adsorption capacity of 5.08 mg/g-carbon than that of AC2 (2.39 mg/g-carbon). The CDI Ragone plot from single-pass experiments was further used as a functional tool to provide the key performance indicators: salt adsorption capacity and mean deionization rate. In the CDI Ragone plot, AC1 appeared towards the top and right side, showing that AC1 was more well-developed than AC2. In addition, the impact of pore structure on electrosorption performance was clearly observed. Overall, this study can provide a fundamental basis for understanding the estimation of CDI performance. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an energy efficient desalination method which is founded on the simple mechanism of ion attraction and repulsion by charged electrodes. One of the main challenges in implementation of this method in industrial scale is the synthesis of an optimum electrode material. Carbon gel is known to be one of the most promising candidates for the electrode material of CDI. Among different types of carbon gels, carbon xerogels have much lower costs of synthesis due to subcritical drying method used at the expense of reducing the porosity and specific capacitance. Here, we optimize carbon xerogel fabrication parameters using response surface methodology (RSM), in order to achieve maximum capacitance. Specifically, we focus our attention on investigation the effect of (i) the pH of initial RF solution, (ii) Reactant to liquid ratio of RF solution, and (iii) Pyrolysis temperature of dried carbon gel. Through our methodology, we show that with the choice of pH = 6.25, R/L = 30%, and PT = 736°C, an optimum capacitance of 42.26 F/g can be achieved. We then use this electrode in our FCDI cell and demonstrate that we can desalinate up to 87.7% a solution containing 1 g/L NaCl whit salt adsorption capacity of 7 mg/gelectrode. [ABSTRACT FROM AUTHOR]

Abstract A new standard metric has been developed to express the actual adsorption capacity of the carbon electrode in consideration of the electrode reactions. The adsorption experiments were carried out by changing the cell potentials (0.6–1.6 V) in the MCDI unit cell. The point at which the electrode reactions occur was determined from the change in instantaneous charge efficiency during the adsorption process. Then, the total charge supplied to the carbon electrode at this point was defined as the maximum allowable charge (MAC). The MAC values were constant at 59 C/g irrespective of cell potentials. In addition, the salt adsorption capacity (S A C M A C ) and the charge efficiency at MAC were approximately 16 mg/g and 91%, respectively, regardless of the cell potentials. Furthermore, the equivalent circuit analysis for the MCDI cell revealed that Faradaic reactions rarely occur at the MAC. The MAC is the maximum charge that can be supplied to the carbon electrode without electrode reactions. It is also unaffected by the cell components and operating conditions of the MCDI cell. Therefore, the MAC is expected to be a useful metric to objectively express the actual adsorption capacity of the carbon electrode. Graphical abstract Image 1 Highlights • The total charge supplied until Faradaic reactions occurred is defined as MAC. • The MAC values of the carbon electrode were constant regardless of the cell potentials. • The desalination performances at MAC were constant irrespective of the cell potentials. • MAC can be a useful metric to describe the adsorption capacity of carbon electrodes. [ABSTRACT FROM AUTHOR]

The resin-activated carbon composite (RAC) electrodes were fabricated and applied in capacitive deionization for recovery of V(V) from complex vanadium solution. The adsorption capacity of the RAC electrode for V(V) is extremely low and the reduction of V(V) is significant in low pH solution, but the adsorbed V(V) on the electrode increases obviously and the reduction of V(V) gradually diminishes with the rise of pH. However, as the pH is increased to 10, the adsorbed V(V) on the RAC electrode declines. The higher applied potential is beneficial to the adsorption of V(V) and 1.0 V is appropriate for the adsorption. The impurities ions (Al, P and Si) are mainly adsorbed in the electric double layers on the RAC electrode and V(V) is dominantly adsorbed by the resins in the electrode. The adsorbed impurity ions can be easily removed by diluted H 2 SO 4 and V(V) can be effectively eluted by 10% NaOH solution. The vanadium-bearing eluent can be recycled to recover and enrich vanadium from the complex solution. The performance of the RAC electrode keeps stable during the cyclic operation. This study may provide a promising and novel method for the recovery and separation of metals from aqueous solution. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a promising technology for the desalination of brackish water due to its potentially high energy efficiency and its relatively low costs. One of the most challenging issues limiting current CDI cell performance is poor cycling stability. CDI can show highly reproducible salt adsorption capacities (SACs) for hundreds of cycles in oxygen-free electrolyte, but by contrast poor stability when oxygen is present due to a gradual oxidation of the carbon anode. This oxidation leads to increased concentration of oxygen-containing surface functional groups within the micropores of the carbon anode, increasing parasitic co-ion current and decreasing SAC. In this work, activated carbon (AC) was chemically modified with titania to achieve additional catalytic activity for oxygen-reduction reactions on the electrodes, preventing oxygen from participating in carbon oxidation. Using this approach, we show that the SAC can be increased and the cycling stability prolonged in electrochemically highly demanding oxygen-saturated saline media (5 mM NaCl). The electrochemical oxygen reduction reaction (ORR) occurring in our CDI cell was evaluated by the number of electron transfers during charging and discharging. It was found that, depending on the amount of titania, different ORR pathways take place. A loading of 15 mass% titania presents the best CDI performance and also demonstrates a favorable three-electron transfer ORR. [ABSTRACT FROM AUTHOR]

Energy-efficient desalination technologies are needed to address the growing requirements of potable water owing to population increase, industrial development, and increasing energy cost. Capacitive deionization (CDI) technique is receiving attention because it offers an energy-efficient method of removing dissolved salts by electro-adsorption. The technique has been explored for ground water with total dissolved solids (TDS) of 500–1,500 mg/l, typical of rural areas in India. We have therefore undertaken development of a test cell and report its use for electro-sorption of dissolved ions in groundwater. The active material used is mesoporous carbon aerogel having surface area ~2,000 m2/g, developed in house. The carbon aerogel-based electrodes have shown high salt adsorption capacity of 8.4 mg/g with NaCl electrolyte. CDI cell modules of 500 ml capacity with eight-electrode stack have been used in single and multiple stages, depending on the ground water TDS. Water having salt concentration of 1,500 mg/l was treated to achieve output of ~238 mg/l with power consumption ~0.5 kWh/m3. The low power requirement, chemical free regeneration, and applicability for the ground water make this system of potential interest for addressing the issue of potable water in rural and remote areas. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) has been considered as the most promising and environmentally friendly electrical desalination technology owing to its low energy consumption and no secondary pollution. CDI is based on the principle of electric double layer for salt ion adsorption, but the existence of co-ions repulsion reduce the charge efficiency, leading to the low salt adsorption capacity. To prevent the intrinsic "co-ion effect" inside the porous carbon electrodes, membrane capacitive deionization (MCDI) by applying an ion-exchange membrane (IEM) to the surface of electrode is of increasing interest. However, MCDI brings various resistances, such as the internal and interface resistances of membrane, as well as the contact resistance between membrane and carbon electrode. More recently, by integrating "membrane" with carbon electrode without the introduction of free-standing IEM, integrated-MCDI has shown great merits to enhance counter-ion selectivity of electrode and decrease resistance, resulting in improving adsorption rate and reducing energy consumption. In this review, the preparation methods of innovative electrodes, the working mechanisms and performances of integrated-MCDIs, and the advanced advantages are summarized. It is hoped that this work will provide insight into integrated-MCDI and shed light on the future direction of water desalination based on CDI technology. [Display omitted] • Integrated-MCDI has been developed without using free-standing IEM on electrode. • Integrated-MCDI outperforms MCDI on energy consumption, cost, and kinetic rate. • Integrated-MCDI has the potential of anti-organic pollution and ion-selective removal. • Review summarized current status of integrated-MCDI for water desalination. • The mechanisms of integrated-MCDI with different fabrication methods are analyzed. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging technology in brackish water desalination. Several types of CDI electrodes have been fabricated and tested throughout the years and most, if not all, require hours of CDI performance testing to assess their capability. In this study, a model was created to predict the salt adsorption capacity of different carbon-based CDI electrodes. Random forest, a statistical classification method, was utilized in the making of the model. Based on the results, the generated models had high accuracy and precision in estimating the salt adsorption capacity, representing R2 values mostly over 0.9. Furthermore, feature importance analysis showed that specific capacitance at higher scan rates can reduce the performance of the model. Therefore, it is recommended that low scan rate specific capacitance be used in creating any kind of CDI model. This study also illustrated that a universal model is possible for CDI with a minor sacrifice in precision. Depending on the goal of the end user, individual and universal models can be used in the prediction of salt adsorption capacity of various CDI electrodes. • The SAC of different CDI electrodes was predicted by the RF model. • Carbon electrodes doped with heteroatom and metal/metal-heteroatom were examined. • Variable importance of operational condition and electrode property was explored. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ppy grafted CMC carbon aerogels are applied in CDI for the first time. • Ppy/CA-2 shows excellent electrochemical and electrosorption performance. • The salt adsorption capacity of Ppy/CA-2 reaches 34.03 mg g−1. • Ppy could capture Cl− via surface redox reaction during CDI. Capacitive deionization (CDI) has been identified as a prospective desalination technology. There has been increasing interest in the exploration of electrodes with high electrochemical properties and salt adsorption capacity. Here, polypyrrole (Ppy)/CA electrodes were prepared by grafting Ppy on carbon aerogel (CA) via in-situ polymerization and applied in CDI desalination. Compared with CA, the Ppy/CA samples display higher specific capacitance, lower charge transfer resistance as well as enhanced ion diffusion rate. Particularly, Ppy/CA shows enhanced pseudocapacitance generation and the synergistic effect of the diffusion-controlled dominating process and capacitive process by Ppy introduction, conducive to the desalination performance. The optimal Ppy/CA-2 CDI system exhibits high adsorption capacity (34.03 mg g−1 with 500 mg L−1 solution), fast salt adsorption rate (0.053 mg g−1 s−1 with 500 mg L−1 solution) together with reasonable long-term stability. The outstanding desalination performance is principally on account of the positively charged nitrogen atoms of Ppy could capture Cl− well through the surface redox reaction in CDI and the most positively charged nitrogen in Ppy/CA-2 contribute its best adsorption capacity. The simple preparation method, excellent electrochemical properties, outstanding adsorption performance, and good cycling stability render Ppy/CA-2 a potential CDI electrode material. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cyclic voltammetry (CV) measurements were performed for the MCDI cell. • The potential of minimum charge (PMC) of the MCDI cell was measured as −0.22 V. • The desorption rate was not significantly affected by the desorption potential. • The water splitting reaction occurred at a desorption potential below the PMC value. • The optimal desorption potential was equivalent to the PMC value for stable and effective operation of the MCDI cell. The optimal desorption potential (DP) for maximizing the salt adsorption capacity of a carbon electrode while maintaining the stable operation of a membrane capacitive deionization (MCDI) cell was studied. Cyclic voltammetry (CV) measurements were performed for the MCDI unit cell. Additionally, the adsorption and desorption characteristics of the MCDI cell were analyzed while changing the DP. The potential at which the charges of the carbon electrode become the minimum was defined as the potential of minimum charge (PMC). The PMC value was measured as −0.22 V from the cyclic voltammogram. In addition, as the cell potential increased, the adsorption capacity of the carbon electrode increased. However, the effect of the DP on the desorption rate was negligible. In DPs below the PMC value, all adsorbed ions were desorbed, but the effluent pH rapidly decreased due to the occurrence of a water splitting reaction at the interface between the carbon electrode and the ion exchange membrane. When the DP was set as greater than the PMC value, some ions remained on the carbon electrode, resulting in a decrease in the amount of adsorbed ions during the subsequent adsorption process. When the DP was equivalent to the PMC value, the adsorption capacity of the carbon electrode was maximally utilized, and the pH of the effluent was maintained in a stable state. [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]

• Freundlich model can well describe the phosphate electroadsorption behavior. • CDI electroadsorption is an endothermic process according to thermodynamics. • pH was determined by water electrolysis and forms transformation of phosphate. • Surface charge can reflect the amount of ions adsorbed by GCS model. The advanced treatment for phosphate (P) has been focused on in the wastewater treatment field in recent years. Developing an innovative P removal technology with high efficiency, low cost, and low energy consumption has become an imperative requirement. Capacitive deionization (CDI) is an emerging environmentally friendly technology for removing charged ions from aqueous solutions. In this study, we investigated the performances of P removal by CDI with homemade activated carbon electrodes. Furthermore, kinetics, thermodynamics and the equilibrium Gouy-Chapman-Stern (GCS) double-layer model were studied to reveal the mechanism of P adsorption. It was observed that the adsorption capacity was positively correlated with the voltage. The pH first increased and then decreased during the adsorption because of water electrolysis and forms transformation of phosphate. The experimental results were validated by pseudo-first-order adsorption kinetics and Freundlich isotherms. The adsorption rate increased with increasing temperature, voltage, and concentration. The adsorption capacity decreased with increasing temperature, and the maximum adsorption capacity was 8.53 mg/g. Thermodynamic analysis confirmed that the electrosorption of P on the activated carbon electrode was an endothermic process, and the high temperature was conducive to reducing the adsorption potential of P on the activated carbon electrode. The theoretical results of the double layer model were in agreement with the experimental data, which showed that the ion adsorption can be reflected by surface charge. This study can help to understand the adsorption mechanism of P on activated carbon electrodes and provide a theoretical basis for the application of P removal by CDI. [ABSTRACT FROM AUTHOR]