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Energy shortage severely impedes the advancement of human society and economy. The vigorous development of nuclear energy is a viable solution to address this issue. The escalating depletion of uranium resources necessitates prioritizing the selective extraction of uranyl from seawater and wastewater to ensure the prosperity of nuclear power. A bismuth-based MOF, CAU-17, was synthesized by the one-step solvothermal method for targeted selection of uranyl in the first time. The uranium adsorption tests demonstrated that CAU-17 exhibited a high adsorption capacity of 421.9 mg g−1 (T = 25 °C, pH = 7), exceptional selectivity, outstanding salt tolerance, and favorable stability with 83.6 % of the initial capacity retained after 5 cycles. Through the utilization of XPS and theoretical calculations, it was elucidated that the carboxyl oxygen that connects the Bi played a pivotal role in the binding process between CAU-17 and uranium ions, with bismuth acting as an electron regulator through its bridging effect with carboxyl oxygen. This work not only presents an exceptional uranium adsorption material but also elucidates the role of core metal atoms in MOFs during the binding to uranium process, thereby offering a novel perspective for future advancements in MOFs-based adsorbents. [Display omitted] • A bismuth-based MOF, CAU-17, was synthesized by the one-step solvothermal method for targeted selection of uranyl. • CAU-17 exhibited a high adsorption capacity (421.9 mg g-1), outstanding salt tolerance, and favorable stability with 83.6% of the initial capacity retained after 5 cycles • CAU-17 formed a complex coordination with uranium through carboxyl oxygen atoms while bismuth played a role in charge regulation. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) holds great promise for phosphorus adsorption and recovery from wastewater, while current electrodes exhibit poor salt adsorption capacity (SAC) and selectivity due to co-ion effect and interference of co-existed ions with high concentration. Herein, to overcome these issues, a facile route was proposed to prepare a covalent organic framework-membrane coating electrode (COF-MCE) by depositing polyvinyl alcohol/polyethyleneimine membrane onto activated carbon fiber (ACF) followed by the in-situ growth of COF-LZU1. Compared to ACF and MCE, COF-MCE, with abundant functional groups and specific sites, facilitated electrical double layer (EDL)-based adsorption and induced hydrogen-bond interaction with phosphorus, contributing to a higher SAC of phosphorus (10.5 mg/g) in treating 1 mM NaH 2 PO 4. When treating different mixtures of NaH 2 PO 4 /NaCl, NaH 2 PO 4 /NaNO 3 , and NaH 2 PO 4 /Na 2 SO 4 with molar ratio of 1:5, COF-MCE exhibited the high phosphorus selectivity of 3.62, 5.98 and 7.01, respectively, which was attributed to the synergistic effects of EDL-based adsorption, hydrogen-bond and pseudocapacitance. Desorption experiments revealed that high reversal voltage and alkaline condition can weaken the hydrogen-bond interaction and strengthen the electrostatic repulsion between COF-MCE and phosphorus, thus improving the desorption and recovery of phosphorus. These findings confirmed the high potential of COF-MCE in the effective electrosorption and recovery of phosphorus from wastewater. • COF-MCE was prepared by casting followed by in-situ growth of COF powders. • Inhibited co-ion effect and enhanced EDL formation led to superb P adsorption. • Hydrogen-bond and redox-reaction interaction contributed to high selectivity for P. • A reversal voltage and high pH weakened the interaction and favored P recovery. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) technology represents a potent approach towards energy-efficient and sustainable access to potable water, with minimal environmental impact. However, the ion removal capacity of CDI systems remains inadequate for desalination of saline water. Herein, mesopore-enhanced graphene foam with modified hydrophilicity via O 2 -plasma treatment (MGFP) is proposed for ultrahigh CDI. This developed MGFP encompasses abundant mesopores, outstanding electrical conductivity and good hydrophilicity, enabling fast ions migration, efficient solution/pores contact and high adsorption capacity. As such, MGEP delivers a high specific capacitance of 156.64 F g−1 at 1 mV s−1, and a maximum salt adsorption capacity (SAC) up to 40.76 mg g−1 (1000 mg L−1, 1.2 V), much higher than most of the CDI systems leveraging the carbon-based materials. What's more, MGFP can be employed in the treatment of wastewaters containing various heavy metals, with the SAC of 89.96, 83.38, and 91.80 mg g−1, as for CuCl 2 , CoCl 2 , and NiCl 2 (1000 mg L−1, 1.6 V), respectively. This well-developed MGFP undoubtedly presents a promising material platform within the CDI system, effectively tackling the pressing concern of water scarcity. Mesopore-enhanced MGFPs electrodes with modified hydrophilicity have been successfully proposed for ultrahigh CDI performance. MGFP exhibits abundant mesopores, outstanding electrical conductivity and good hydrophilicity, enabling fast ions migration, efficient solution/pores contact and high adsorption capacity. As a result, MGEP delivers a maximum salt adsorption capacity (SAC) up to 40.76 mg g−1 (1000 mg L−1, 1.2 V), and demonstrate the SACs of 96.69, 83.38 and 91.80 mg g−1 when treating heavy metal salt wastewater containing CuCl 2 , CoCl 2 and NiCl 2 , respectively. [Display omitted] • High performance capacitive deionization with Mesopore-enhanced graphene electrodes with modified hydrophilicity. • The interaction mechanism of the modified material in solution for Na+ was investigated. • The highest salt adsorption capacity of NaCl during CDI was 40.76 mg g–1. • MGFP3 showed great potential in treating wastewater containing CuCl 2 , CoCl 2 and NiCl 2 with high SACs. [ABSTRACT FROM AUTHOR]

With the continuous development of the global society, people's demand for lithium is increasing. Recovering valuable lithium from waste lithium-ion batteries and fly ash is essential for environmental protection and energy saving. We have developed a new imprinted capacitance deionization technology (N@Li+-IPDI), which can selectively recover lithium ion from acidic solution (pH = 2) under complex environment. The recovery capacity of N@Li+-IPDI electrode material was up to 20.26 mg/g. Separation of Li+ from Na+, K+, and Al3+ was achieved based on the size effect. Separation from Mg2+ was due to the higher hydration energy of Mg2+ (1940 kJ/mol) than Li+ (510 kJ/mol). After 5 regeneration cycles, recovery effect of N@Li+-IPDI was 93.42 % of original. Through density functional theory (DFT) modeling, bond length of Li+-O was 2.04–2.05 Å, and adsorption energy of 2H12C4-Li+ (−33.66 Kcal/mol) was the largest among the five ions. In addition, energy and structure of deprotonation process were studied, and the energy required for deprotonation was 6.33 kJ/mol, which was the reason Li+ adsorption is difficult in acidic environment. This research provides a new green ion recovery technology with excellent selectivity, high adsorption and conductivity for Li+ recovery in acid solution, to meet the challenge of growing demand for lithium. [Display omitted] • Ion imprinting technology and capacitive deionization technology are combined. • The maximum adsorption capacity of the N@Li+-IPDI is up to 20.26 mg/g under pH = 2. • Crown ether protonation was effectively overcome under electric field. • Adsorption energy of Li+ (−33.66 Kcal/mol) was the largest among cations. • The energy required for deprotonation was 6.33 kJ/mol. [ABSTRACT FROM AUTHOR]

Abstract Capacitive deionization (CDI) has emerged as an attractive approach for desalination and water treatment for its high energy efficiency, low cost, and easy regeneration. Here, we report the preparation and application of villiform carbon fiber paper (v-CFP) as the current collector for CDI device with high areal electrosorption capacity. The v-CFP was prepared by thermal annealing and subsequent O 2 plasma etching of the commercial pristine carbon fiber paper (p-CFP). With greatly improved surface area and hydrophilicity, the v-CFP itself showed an areal capacitance as high as 0.70 F·cm−2 in 0.5 M NaCl solution, and delivered an areal electrosorption capacity up to 122 and 400 mg·m−2 when feeding a NaCl solution with initial concentration of 50 and 3500 mg·L−1, respectively. Upon loading with additional electrode materials (EMs), e.g., graphene hydrogel, activated carbon, carbon nanotubes, and porous carbon spheres, the v-CFP/EM electrodes exhibited further improved areal electrosorption capacities, generally outperforming the corresponding p-CFP/EM electrodes by >2 times. Our studies demonstrate that proper surface treatment can largely improve the capacitance of the commonly used p-CFP current collector, making it greatly attractive in CDI devices. Graphical abstract Unlabelled Image Highlights • Annealing and O 2 plasma can improve the surface area and hydrophilicity of p-CFP. • The resultant v-CFP itself exhibits a high areal electroadsorption capacity. • The electrosorption capacity of v-CFP/AEM is higher 2 times that of p-CFP/AEM. • v-CFP has great potential as a new current collector in CDI device. [ABSTRACT FROM AUTHOR]

Abstract The ion exchange membrane (IEM) is a key component that helps achieve good performance in membrane capacitive deionization (MCDI). However, systematic researches have been limitedly conducted regarding the effect of IEM characteristics on MCDI performance. The aim of this study is to investigate the effects of the characteristics of the cation exchange membrane (CEM) on MCDI performance. Salt adsorption capacity (SAC), maximum average deionization rate (MADR), and charge efficiency were chosen to demonstrate MCDI performances. Only MADR was significantly affected by CEM characteristics. Additionally, MADR showed a positive relationship with the transport number divided by total electrical resistance (R 2 = 0.83). Therefore, CEM should have a high transport number and low electrical resistance for fast rate-capable MCDI. The correlations between CEM characteristics and MCDI performances revealed through this study are expected to further develop high-performance MCDI. Highlights • Cation exchange membrane (CEM) properties for membrane CDI (MCDI) were examined. • Tested performance of MCDI were capacity, rate, and efficiency. • Among them, the rate performance was the most sensitive to CEM properties. • CEM with high transport number and low resistance showed good rate performance. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) have great application potential in capacitive deionization (CDI), which can selectively extract ions from water with high charge efficiency and low contamination. Previous studies have found that cationic segregation of TMOs has adverse effects on their electrochemical performance, but its effect on CDI remains unclear. Herein, we demonstrate for the first time that Ca2+ segregation provides more sites for F− adsorption by synthesizing Ca 2 Mn 3 O 8 for CDI selective defluorination. The Ca 2 Mn 3 O 8 material has a graded porous structure, low charge transfer resistance, high specific capacitance (255.64 F/g, 1 mV/s, 0.5 M NaF solution) and good charge/discharge reversibility (about 100 % charge specific capacity retention after 50 cycles). Moreover, Ca 2 Mn 3 O 8 has a high specific adsorption capacity (SAC) for NaF (1419.07 μmol/g) and excellent cyclic stability (capacity retention rate is 96.69 % after 100 cycles). The Ca2+ segregation from lattice to surface provides more sites for F− adsorption and greatly shortens ion transport paths. Density functional theory (DFT) calculation further suggests that the adsorption energy of Ca 2 Mn 3 O 8 for F− is much greater than that of Cl−. As a result, the removal rate of F− by Ca 2 Mn 3 O 8 in mixed solutions is up to 20 times higher than that of Cl−. [Display omitted] • It is proved that cationic segregation on the surface provides additional sites for ion adsorption. • Ca 2 Mn 3 O 8 electrode delivers outstanding fluoride removal performance and cycle stability. • Ca 2 Mn 3 O 8 electrode is much more selective for F− than for Cl−. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an electrochemical ion removal technique that could offer a lower energy or more selective alternative to reverse osmosis for water treatment applications. Over a dozen CDI cell architectures have been developed, but few studies have directly compared these designs for performance metrics such as ion adsorption rate and energy efficiency. Two of the most popular cell architectures include flow-by CDI, in which a feed stream flows parallel to two charged porous electrodes, and flow-through electrode CDI, in which the feed stream flows perpendicular to the electrodes. In this study, flow-by and flow-through CDI architectures were compared using commercially available electrode materials. Experimentally observed salt adsorption capacity (SAC), average salt adsorption rate (ASAR), and charge efficiency (Λ) was then compared to theoretical models over a range of voltage conditions (0.2–1.2 V), charge cycle times (1–60 min), and flow rates (10–30 mL min - 1 ). Cell architecture affected the SAC, ASAR, Λ, electrode stability, and oxidation rates for a given electrode material. Flow-by CDI tended to have higher SAC and better charge efficiency than flow-through CDI, yet flow-through CDI demonstrated a higher ASAR, particularly for shorter half-cycle times. [ABSTRACT FROM AUTHOR]

Desalination technologies can increase potable water supplies worldwide. One possible approach, capacitive deionization (CDI), could prove optimal for brackish water treatment. At present, CDI development has largely focused on increasing salt adsorption capacity and desalination rates of materials and devices. In addition to these metrics, ultimately, optimizing salt rejection and throughput will be essential. In this work, we present a framework for the design of flow-between CDI cells for maximum salt rejection. We developed a model that is dependent on device specific parameters (system volume, flow rate, inlet and outlet water quality), to generalize the design of a cell for any given requirement. We showed that decreasing the advection-diffusion Péclet number and increasing the aspect ratio of the electrode compared to the channel space yield the highest salt rejection. In addition, tuning the cycle frequency time for salt rejection instead of complete electrode charging can yield faster water production rates and optimal salt rejection. These modeling results were validated through experimental prototypes that made use of vertically-aligned carbon nanotube (VA-CNT) electrodes. This framework to maximize salt rejection can be extended to a multitude of porous electrodes used in flow-between CDI devices. [ABSTRACT FROM AUTHOR]

Prussian blue analogue (PBA) as a typical Faraday electrode material has important application value in capacitive deionization (CDI) for its rigid open framework and unique ion storage properties. But poor electrical conductivity and deformation of crystal structure during the desalination process restrict its development. To enhance the stability of PBA and provide rapid charge transfer, a new composite hollow core-shell polyaniline-encapsuled Ni-Prussian blue analogue (H-NP@PANI) is constructed. Experiments illustrate that PANI formed an omnidirectional uniform and highly conductive layer on the crystal surface, which tremendously improved the electrochemical capacity of H-NP@PANI (242.24 F·g−1). In constant voltage mode, the adsorption capacity of AC║H-NP@PANI cell is 35.86 mg·g−1, which was the highest to H-NP (20.82 mg·g−1) and pure Ni-PBA (16.08 mg·g−1). The retention rate remains 96.1 % after 50 cycles. XRD tests show that superior cycle stability is due to the hollow structure and buffer space provided by PANI shell, which can effectively inhibit the degree of crystal transformation. Furthermore, DFT calculation confirms the existence of a highly stable tight electron coupling between H-NP and PANI, and the electron aggregation center around Fe atom facilitates the Fe3+/Fe2+ redox cycle. Hence, this work can provide a feasible strategy for designing stable and efficient electrodes. [Display omitted] • Hollow core-shell PANI-encapsuled Ni-PBA (H-NP@PANI) with omni-directional conductive layer was constructed. • H-NP@PANI electrode showed superior electrochemical performance with high specific capacity of 242.24 F·g-1. • H-NP@PANI electrode had remarkable desalination performance of 35.86 mg·g-1 with superior desalination cycle stability. • Both DFT calculation and experimental analysis revealed the synergistic effect between PANI shell and H-NP in CDI process. [ABSTRACT FROM AUTHOR]

Fluorine pollution has been recognized as one of the major problems of global concern. Metal-organic frameworks (MOFs), as potential fluoride adsorbents, possess unique chemical reactivity and broad functionalities. However, their application is restricted by instability in fluoride or acid/base solution and difficult separation. Here, lotus flower-like Al/N-doped porous carbon composite was prepared by a simple pyrolysis method using Al-based MOF as a precursor and used for capacitive deionization (CDI) defluorination. Through pyrolysis, MOF-derived carbon not only obtained a larger specific surface area and N-rich structure, but also possessed multiple F− capture sites. These carbon substrate enabled the metal centers to be uniformly dispersed and contributed to enhanced electrical conductivity and chemical stability of electrode material. Through the CDI defluorination system, F− migrate rapidly with the aid of the electric field and was captured under the synergistic effect of metal sites and carbon substrate. According to the Langmuir isotherm, the maximum F− removal capacity was 76.28 mg g−1 at 1.2 V, and the adsorption kinetics followed pseudo-second-order model. The electroenhanced adsorption method exhibits high adsorption capacity and selectivity for F− due to combining the advantages of adsorbent adsorption and electrosorption, which already exceeds the capacities of most electrode material. [Display omitted] • MOF-derived Al/N-doped porous carbon composite (AlNC) is firstly proposed in Capacitive deionization defluorination. • The F− removal capacity reached 76.28 mg g-1 at 1.2 V. • Presented a possible mechanism for the elctrosorption of F- on AlNC. [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]

Given that carbon-based electrodes suffer from poor long-term stabilities and limited desalination capacity, the optimized charge storage mechanism used for improving desalination performance remains requisite. In this work, the KC-pre-intercalated carbon nanosheets (PCNs) with abundant conjugated carbonyl groups were designed via a one-step smelting method for the first time as a novel intercalation electrode in the symmetric capacitive deionization. Interestingly, below 500 mg/L, the physical electrical double-layer mechanism is mainly influential. Benefitting from the proposed dynamic intercalation mechanism, a remarkable ion removal capacity of 1.65 g g−1 and impressive cyclability of 300 cycles (97.96%) were observed in the high salt concentrations (>1000 mg/L) and simulated seawater system rather than pure NaCl solution. The ultrahigh adsorption capacity and prominent cycling stability make the PCNs-based device rank top three among these of all the symmetric CDI systems reported in the literatures so far. The Na+ ions are intercalated in the enlarged interlayer spacing without a host structure deformation, thus offering a high ion removal rate (2.04 mg g−1 min−1) and a low energy consumption (0.28 Wh g−1). Our work exemplifies the importance of engineering conjugated carbonyl groups and pre-intercalated structure to capacitive deionization for brine. [Display omitted] • A novel dynamic intercalation mechanism leads to a remarkable SAC of 1.65 g g−1 in the simulated seawater system. • Pre-intercalation carbon nanosheets deliver superior SAC (40.72 mg g−1) as well as life-span (300 cycles) in 500 mg/L NaCl. • Engineering conjugated carbonyl groups and pre-intercalated structure to capacitive deionization. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an electrochemically controlled desalination technology based on applying a non-faradaic process in the electrical double layer region. Because CDI performance is affected by the type of operational mode, this study examined salt adsorption capacity (deionization capacity) and energy consumption of two CDI operational modes, constant voltage (CV) and constant current (CC). The use of higher cell voltage in CV mode resulted in faster salt adsorption under a given charging time due to stronger electrostatic attraction than CC mode. However, despite of the faster salt adsorption of CV mode, CC mode showed much lower energy consumption than CV mode by 26%–30% as an identical electrical charge was consumed or an identical amount of ion removal was considered. This lower energy consumption is due to the overall lower cell voltage used in CC mode than in CV mode. This study suggests that better salt adsorption capacity and energy consumption in CDI operation may be achieved by applying appropriate CV and CC modes. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) technology is a high-efficiency, energy-saving, green and environmentally friendly new water treatment technology, which will have potential in the field of low-salinity seawater desalination. Current carbon-based electrode materials have limited desalination capacity and rate due to insufficient ion-accessible specific surface area and slow ion transmission rate. Here, we demonstrate layered porous carbon (CHPC) derived from Chitosan, colloidal SiO 2 and polytetrafluoroethylene (PTFE) mixed carbonization for efficient CDI desalination. CHPC has abundant macropores that are connected with mesopores. This layered porous structure enables CHPC to have a faster ion migration rate. The salt removal capacity of CHPC reaches 26.5 ± 1.5 mg/g, and the average adsorption rate is 8.8 ± 0.5 mg/g/min, which are about 1.6 and 10 times than that of commercial activated carbon, respectively. In addition, CHPC has extremely strong anti-interference performance against organic macromolecules, which could maintain more than 95% adsorption capacity after 30 cycles. Our work helps to promote the practical application of hierarchical porous structures based on typical biomass in large-capacity and fast-rate CDI desalination technology. [Display omitted] • CHPC forms a macroporous-mesoporous hierarchical carbon network framework through a multi-step etching reaction. • CHPC achieves an ultra-fast adsorption efficiency of 8.8 ± 0.5 mg/g/min due to fast ion/electron transport. • CHPC has excellent cycle stability and resistance to interference from macromolecular substances. [ABSTRACT FROM AUTHOR]

Activated-carbon-electrodes are widely used in capacitive deionization (CDI). However, the desalination capacity of most activated carbons remains to be improved, which makes it necessary to explore activated carbons with special structure and improved desalination capacity. In this context, we studied the desalination performance of super activated carbons with ultra-high total pore volume (V Tot). This carbon showed a salt adsorption capacity of 27.2 mg/g in 500 mg/L NaCl solution at 1.2 V, which ranked among the highest value ever reported for activated carbons. The high adsorption capacity was due to the large V Tot caused by the abundant presence of both micropores and mesopores in the material. The adsorption capacity of the carbon after 10 adsorption-desorption cycles (saturated adsorption capacity) was as high as 67.6 mg/g, which was dominated by V Tot and water contact angle. The sample also showed excellent desalination rate and superior charge efficiency (76.5%). This study indicated that superior desalination performance could be obtained by using super activated carbon with high pore volume as a CDI electrode material. [Display omitted] • SAC with high pore volume (AC-P-CO 2) showed excellent desalination performance. • The salt adsorption capacity of AC-P-CO 2 was 27.2 mg/g. • The salt adsorption capacity ranked among the highest values for activated carbons. • The salt adsorption capacity after 10 cycles of AC-P-CO 2 was 67.6 mg/g. • AC-P-CO 2 showed superior desalination rate and charge efficiency (76.5%). [ABSTRACT FROM AUTHOR]

A promising electrode material, manganese dioxide (MnO 2), has been widely studied for capacitive deionization (CDI) desalination and recently researched for heavy metal removal. However, there are significant differences in the performance of MnO 2 in applications for heavy metal removal and desalination. In this paper, the mechanism for different electrochemical processes of Cd2+/Na+ ions on MnO 2 electrodes was comprehensively studied. MD simulations show that the diffusion performance of Cd2+ is much slower than that of Na+ in the presence of CdCl−, leading to a lower adsorption rate of Cd2+. Of the two ion storage mechanisms (capacitive and diffusion-controlled progress), capacitance contributions provided 65.6% of the total in the Na+ electrolyte, while diffusion-controlled progress contributed 55.2% in the Cd2+ electrolyte. For diffusion, tunnelling is the main storage mechanism for Na+; instead, Cd2+ undergoes a sequential surface redox process: (1) the combination of Cd2+ and O atoms from Mn-O-Mn results in the transition from Mn4+ to Mn3+, and (2) the H substitution reaction on Mn-O-H is generated from (1). Therefore, the adsorption capacity of Cd2+ is closely related to the chemical state of MnO 2 on the surface, which results in worse cycling stability than Na+. • The presence of CdCl+ reduces the migration of Cd2+ on the electrode surface. • Different faradaic processes are responsible for differences in the adsorption of Cd2+ and Na+. • The surface redox mechanism for Cd2+ in MnO 2 involves two processes. • The results of this study provide significant insights into the cation storage mechanism of MnO 2. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) has aroused significant concern for its application in treating low-concentration brackish water. However, some carbonaceous materials suffer from the limited salt adsorption capacity (SAC), sluggish adsorption kinetics, and inferior selectivity to particular ions. Hence, we develop the well-dispersed few-layered two-dimensional pseudocapacitive material MoS 2 connected with a robust 3D conductive architecture constructed by carbon nanotubes (CNT) and carbon spheres (CS) (MoS 2 @CNT-CS). The enhanced dispersibility and expanded interlayer of MoS 2 nanosheets provide sufficient faradic effective sites for ion storage and transfer, while the interlaced carbonaceous network affords improved hydrophilicity, convenient electron transport path, and low charge transfer resistance for fast charge transportation and permeation. Therefore, the asymmetric hybrid CDI cell (CNT-CS for anode and MoS 2 @CNT-CS for cathode) delivers a prominent SAC (25.35 mg g−1), fast SAR (3.9 mg g−1 min−1), enhanced desalination kinetics, and favorable cycling stability. In addition, the specific ion selectivity of MoS 2 @CNT-CS electrode was evaluated systematically in the equimolar multi-salt solutions, and a selectivity order of Ca2+ > Na+ > Mg2+ > K+ was obtained. The molecular dynamic (MD) calculation provides the lowest intercalation energy for Ca2+ (−2.55 eV), further confirming the strong interaction and preferable pseudocapacitive deionization of MoS 2 @CNT-CS electrode to Ca2+ over other cations. [Display omitted] • Few-layered MoS 2 is dispersed in a robust 3D carbonaceous CNT-CS architecture. • MoS 2 @CNT-CS has improved active sites, conductivity, and hydrophilicity. • MoS 2 @CNT-CS electrode shows a prominent salt adsorption capacity and rate. • MoS 2 @CNT-CS has an ion selectivity of Ca2+ > Na+ > Mg2+ > K+. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) has aroused significant concern for its application in treating low-concentration brackish water. However, some carbonaceous materials suffer from the limited salt adsorption capacity (SAC), sluggish adsorption kinetics, and inferior selectivity to particular ions. Hence, we develop the well-dispersed few-layered two-dimensional pseudocapacitive material MoS 2 connected with a robust 3D conductive architecture constructed by carbon nanotubes (CNT) and carbon spheres (CS) (MoS 2 @CNT-CS). The enhanced dispersibility and expanded interlayer of MoS 2 nanosheets provide sufficient faradic effective sites for ion storage and transfer, while the interlaced carbonaceous network affords improved hydrophilicity, convenient electron transport path, and low charge transfer resistance for fast charge transportation and permeation. Therefore, the asymmetric hybrid CDI cell (CNT-CS for anode and MoS 2 @CNT-CS for cathode) delivers a prominent SAC (25.35 mg g−1), fast SAR (3.9 mg g−1 min−1), enhanced desalination kinetics, and favorable cycling stability. In addition, the specific ion selectivity of MoS 2 @CNT-CS electrode was evaluated systematically in the equimolar multi-salt solutions, and a selectivity order of Ca2+ > Na+ > Mg2+ > K+ was obtained. The molecular dynamic (MD) calculation provides the lowest intercalation energy for Ca2+ (−2.55 eV), further confirming the strong interaction and preferable pseudocapacitive deionization of MoS 2 @CNT-CS electrode to Ca2+ over other cations. [Display omitted] • Few-layered MoS 2 is dispersed in a robust 3D carbonaceous CNT-CS architecture. • MoS 2 @CNT-CS has improved active sites, conductivity, and hydrophilicity. • MoS 2 @CNT-CS electrode shows a prominent salt adsorption capacity and rate. • MoS 2 @CNT-CS has an ion selectivity of Ca2+ > Na+ > Mg2+ > K+. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a feasible low-cost desalination technique for low-to-medium (brackish) salinity water. However, cycling stability and regeneration of the CDI electrodes are the bottlenecks hindering the practical application of the technology on large scale. Oxidation of the electrodes during the sequential adsorption-desorption processes is one of the most challenging problems hindering their long-term cycling performance. Herein, we demonstrated the ability to design and fabricate exceptionally stable CDI electrodes via a one-pot pyrolysis protocol. The optimized pyrolysis of nitrogen‑carbon precursors at different temperatures enabled the fabrication of carbon materials with a controlled amount nitrogen dopant (NDCs) with exceptional cycling stability. The NDCs showed high specific capacitance and dual meso /microporous structures with high salt adsorption capacity (SAC), reaching 26.5 mg·g−1 in a single-pass desalination mode. Moreover, all NDC electrodes exhibited exceptional desalination stability performance over 150 successive charging/discharging cycles with 100% retention in aerated and deaerated solutions under harsh 1.4 V as the charging voltage. Moreover, all NDCs cells demonstrated charge efficiencies in the range from ~40 to 60%. The potential of zero charge (PZC) was determined for the tested NDC electrodes to elucidate their oxidation resistance (EOR). The electrodes exhibited a minimal shift in potential after the entire desalination stability tests, revealing minor electrode oxidation. The performance of our NDC-electrodes was compared against that of the commercially available activated carbon (AC) under the same experimental conditions, with the latter showing a server decrease in the SAC retention within the first few cycles. [Display omitted] • Synthesis of meso/microporous carbon electrodes with a controlled nitrogen content • The electrodes showed a salt adsorption capacity of 26.5 mg·g−1 in a single-pass desalination mode. • The electrodes showed exceptional cycling stability over 150 successive cycles. • The electrodes showed 100% retention in aerated and deaerated solutions under harsh 1.4 V. • The potential of zero charge (PZC) showed very high oxidation resistance. [ABSTRACT FROM AUTHOR]

Rocking-chair capacitive deionization (RCDI) is a semi-continuous desalination technology, however, suffering from issues pertaining to effluent salinity and pH. We thoroughly investigated the composition evolution and pH-related behavior in RCDI and disclosed the underlying causes for quality decay. RCDI concomitantly produces two streams: the desalted cathodic effluent becomes basic, whereas the brine anodic stream becomes acidic. These pH-related species deteriorate the outflow quality and distort conductivity profiles. Under variation in dissolved oxygen and potential distribution, we verified the carbon oxidation and oxygen evolution reactions as causes for the acidic anode and oxygen reduction as the cause for the basic cathode. Faradaic reactions and resultant pH fluctuation were exacerbated with increasing charging voltages, even at 0.9 V, whereas they were negligibly affected by the resembling potential distribution at different flowrates. To improve pH stability and water recovery, we integrated the ion exchange and flowrate adjustment procedures; consequently, water recovery increased to 71.43% and pH was stabilized at 5–6.5 for over 80 cycles, with significant adsorption capacity enhancement owing to the ion exchange with pH-related species. Thus, with a better understanding of pH-related behaviors, RCDI can be optimized and extended more specifically for demands such as acid/base production and resource enrichment. • RCDI with semi-continuity and high capacity was thoroughly investigated. • Evolution of pH and mechanism for performance variation was disclosed fundamentally. • The effect of voltage and flowrates on pH and RCDI behavior was expounded. • Facile modification for stable outflow composition and high efficiency were proposed. [ABSTRACT FROM AUTHOR]

Electrosorptive desalination is a very simple and appealing approach to satisfy the increasing demand for drinking water. The large-scale application of this technology calls for the development of easy-to-produce, cheap and highly performing electrode materials and for the identification and tailoring of their most influential properties, as well. Here, biosynthesised bacterial cellulose is used as a carbon precursor for the production of three-dimensional nanostructures endowed with hierarchically porous architecture and different density and type of intrinsic and hetero-atom induced lattice defects. The produced materials exhibit unprecedented desalination capacities for carbon-based electrodes. At an initial concentration of 585 mg L−1 (10 mmol L−1), they are able to remove from 55 to 79 mg g−1 of salt; as the initial concentration rises to 11.7 g L−1 (200 mmol L−1), their salt adsorption capacity reaches values ranging between 1.03 and 1.35 g g−1. The results of the thorough material characterisation by complementary techniques evidence that the relative amount of oxygenated surface functional species enhancing the electrode wettability play a crucial role at lower NaCl concentrations, whereas the availability of active non- sp 2 defect sites for adsorption is mainly influential at higher salt concentrations. • Bacterial-cellulose (BC) is biosynthesised by using Gluconacetobacter medellinensis as a strain. • By carbonising BC, microporous nanocarbons with different amount and type of defects are produced. • BC-derived nanocarbons are tested as electrodes for the capacitive deionization of water. • The BC-based electrodes remove 55–79 mg g−1 of NaCl from a solution with a 585 mg L−1 initial concentration. • The C network defectiveness plays a key role in the electrode capacitive and electrosorptive behaviour. [ABSTRACT FROM AUTHOR]

Introduction of new nanomaterials with conductivity, salt adsorption capacity (SAC) and rate (SAR) exceeding that of carbon electrodes may greatly improve capacitive deionization of water. However, those materials show a different electrochemical behavior, which must be studied and optimized for practical use. Here, effects of operating conditions on desalination performance of pre-conditioned Ti 3 C 2 T x -MXene-based electrodes in a symmetric membrane capacitive deionization (MCDI) system were investigated. Specifically, influences of discharge potential, half-cycle length (HCL), and flow rate were systematically studied. Results showed different degrees of performance dependence on operating conditions. For instance, lower discharge potentials increased SAC and SAR by 152%. However, longer HCL increased SAC by 32% while decreasing SAR by 54%. Finally, faster flow rates decreased both SAC and SAR by 20%. Desalination performances of symmetric pre-conditioned MXene and activated carbon cloth (ACC) electrodes were gravimetrically and volumetrically compared in MCDI system. Pre-conditioned MXene electrodes gravimetrically performed 30% lower than ACC due to their notably higher density. Yet, pre-conditioned MXene electrodes volumetrically outperformed ACC by 162%. Results suggest that although MXenes offer high electrochemical activity and hydrophilicity, making them promising candidates for CDI applications, the strong dependence of desalination performance of MXenes on operating conditions requires in-depth understanding and warrants further research. Unlabelled Image • Pre-conditioned MXene outperforms ACC by 162% due to bulk volume ion storage. • Pre-conditioned MXene MCDI system has shown steady SAC for 100 cycles. • Lower discharge potentials enable more effective ion deintercalation. • Improved ion deintercalation leads to up to 152% increase in SAC and SAR. • Longer half-cycle length increases SAC by 32% and decreases SAR by 54%. [ABSTRACT FROM AUTHOR]