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Excessive phosphorus discharge causes water eutrophication and disturbs the homeostasis of aquatic ecosystems. Capacitive deionization (CDI) has been proven to be a more energy-efficient and environmentally friendly technology for removing phosphorus. Raw carbon (Raw C) electrodes are widely used in CDI. However, the phosphorus removal capacity of most unmodified Raw C still needs to be enhanced. Therefore, the Fe, N-co-doped carbon prepared in this study was expected to further improve the phosphorus removal performance. Herein, the optimal electrode with 5% Fe (FeNC) had an approximately 2.7 times higher adsorption capacity than Raw C. At a low concentration (5 mg P/L), FeNC exhibited a high maximum removal capacity of 4.28 mg P/g. Under reversed voltage, the phosphorus was easily desorbed by deionized water. Ion competition studies showed that coexisting ions adversely affected phosphorus adsorption onto FeNC in the order SO42- > NO3- > Cl-. Furthermore, the energy consumption of FeNC was calculated to be as low as 0.0069 kWh/g P and 0.023 kWh/m3 water under 1.2 V. More importantly, phosphorus removal by FeNC during CDI was demonstrated in simulated natural water from the Jinjiang River (Chengdu, China). This study indicated that FeNC is expected to be a potential electrode for CDI dephosphorization. [ABSTRACT FROM AUTHOR]

Anodic electrodeposition was used to synthesize a composite electrode of nanostructured manganese dioxide/carbon fiber (CF) galvanostatically. Different characterization results of the nanostructured MnO2 were obtained by varying the H2SO4 concentration and the current density. Field emission scanning electron microscopy, X‐ray diffraction, and atomic force microscopy were utilized to characterize the prepared composite electrodes. The best conditions were: 0.3 mA cm−2 current density and 0.64 M H2SO4 concentration. The electrosorption performance of the MnO2/CF electrode prepared under the best conditions was tested by way of its chromium(VI) ion adsorption from a simulated solution. The applied voltage, pH, and ionic strength affect the efficiency of Cr(VI) ion removal. The highest chromium removal efficiency was 99.98 %, achieved at pH 2, a cell voltage of 4.6 V, and a NaCl concentration of 1 g L−1. [ABSTRACT FROM AUTHOR]

Biochar derived from lignocellulosic biomass has been used as a low-cost adsorbent in wastewater treatment applications. Due to its rich porous structure and good electrical conductivity, biochar can be used as a cost-effective electrode material for capacitive deionization of water. In this work, willow biochar was prepared through carbonization of shrub willow chips, activated with potassium hydroxide, and loaded with manganese dioxide (WBC-K-MnO2 nanocomposite). The prepared materials were used to electrochemically adsorb Pb2+ from aqueous solutions. Under the applied potential of 1.0 V, the WBC-K-MnO2 electrode exhibited a high Pb2+ specific electrosorption capacity (23.3 mg/g) as compared to raw willow biochar (4.0 mg/g) and activated willow biochar (9.2 mg/g). KOH activation followed by MnO2 loading on the surface of raw biochar enhanced its BET surface area (178.7 m2/g) and mesoporous volume ratio (42.1%). Moreover, the WBC-K-MnO2 nanocomposite exhibited the highest specific capacitance value of 234.3 F/g at a scan rate of 5 mV/s. The electrosorption isotherms and kinetic data were well explained by the Freundlich and pseudo-second order models, respectively. The WBC-K-MnO2 electrode demonstrated excellent reusability with a Pb2+ electrosorption efficiency of 76.3% after 15 cycles. Thus, the WBC-K-MnO2 nanocomposite can serve as a promising candidate for capacitive deionization of heavy metal contaminated water. [ABSTRACT FROM AUTHOR]

The present study investigates the removal of glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos herbicides from their 5 × 10–5 M aqueous solutions onto activated carbon cloth by adsorption and electrosorption. Analysis of these highly polar herbicides was achieved by UV–visible absorbance measurements, after derivatization with 9-fluorenylmethyloxycarbonyl chloride. The limit of quantification values of glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos were 1.06 × 10–6 mol L−1, 1.38 × 10–6 mol L−1, 1.32 × 10–6 mol L−1 and 1.08 × 10–6 mol L−1, respectively. Glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos were removed from their aqueous solutions with higher efficiencies by means of electrosorption (78.2%, 94.9%, 82.3% and 97%, respectively) than of open-circuit adsorption (42.5%, 22%, 6.9% and 81.8%, respectively). Experimental kinetic data were fitted to pseudo-first order and pseudo-second order kinetic models. It was determined that pseudo-second order kinetic model represents experimental data better with satisfactory coefficient of determination, r2 (> 0.985) and normalized percent deviation, P (< 5.15) values. Adsorption isotherm data were treated according to Freundlich and Langmuir isotherm models. Based on the r2 (> 0.98) and P (< 5.9) values, it was found that experimental data well fitted to Freundlich isotherm model. Adsorption capacities of activated carbon cloth for glyphosate, glufosinate, aminomethylphosphonic acid and bialaphos, expressed in terms of Freundlich constant, were calculated as 20.31, 118.73, 239.33 and 30.68 mmol g−1, respectively. The results show that the studied ACC can be used in home/business water treatment systems as an adsorbent due to its high adsorption capacity. [ABSTRACT FROM AUTHOR]

Heavy metals are considered a class of contaminant that can accumulate in the food chain and thus must be removed from contaminated media. Heavy metals can be removed by electrocoagulation, electroflotation, electrodialysis, capacitive deionization, and so on. Among the methods to remove heavy metals, capacitive deionization is one of the most attractive methods that can remove heavy metal ions without using a large volume of chemicals and producing a high number of heavy metals containing solid wastes. In this study, after a brief introduction to the mechanism of capacitive deionization, we focus on materials that have been developed as electrodes for heavy metal removal in capacitive deionization and summarize the latest advancements. Finally, with particular emphasis on material design, we provide some further insights in this area. [ABSTRACT FROM AUTHOR]

Environmental context: Naturally occurring arsenic was the likely cause of endemic black foot disease in groundwaters in Taiwan, and levels still exceed Taiwan EPA water quality standards. A method for the clean-up of these groundwaters that is both feasible and environmentally friendly is urgently needed. Oxidation of As(III) as H3AsO3 to the less toxic As(V)− and removal of As in groundwater was performed quantitatively by electrosorption using materials derived from agricultural wastes; this shows that this method has the potential to be a novel, green remediation method. Rationale: Naturally occurring arsenic in the groundwater caused black-foot disease (BFD) in the 1950s on the southwest seashore of Taiwan. Recently, we found that the concentration of arsenic in groundwater taken from currently sealed wells in areas previously affected by BFD remained higher than the Taiwan (EPA) water quality standard. Although clean tap water is available in that area, removal of arsenic from the groundwater is of great importance to expand possible utilisation. Methodology: Removal of arsenic from two old endemic BFD groundwaters with activated carbon (AC) electrodes recycled from agricultural wastes by electrosorption using capacitive deionisation (CDI) processes was studied. A better understanding of arsenic electrochemistry involved in electrosorption was investigated by in situ X-ray absorption near-edge structure spectroscopy. Results: Arsenic removal efficiencies (61–93%) remained high across concentrations (5 and 196 mg/L). A high oxidation rate constant (0.93 h−1) for As(III)0 to As(V)− was found, allowing the electrosorption of As(V)− onto the meso- and micro-pores of the AC CDI electrodes with rate constants of 0.021 and 0.0013 h−1, respectively. Removal of arsenic from contaminated groundwater for drinking water was achieved with six CDI reactors in series. Moreover, in the presence of other ions (such as Na+, Mg2+ and Ca2+), 60–73% of As(III)0 and As(V)− ions were removed from the groundwaters by electrosorption. Discussion: We have developed an engineering-feasible method for converting As(III)0 to less toxic As(V)−, enabling its removal by electrosorption, which demonstrates the feasibility for green remediation of BFD waters as well as other arsenic-contaminated groundwaters. Environmental context. Naturally occurring arsenic was the likely cause of endemic black foot disease in groundwaters in Taiwan, and levels still exceed Taiwan EPA water quality standards. A method for the clean-up of these groundwaters that is both feasible and environmentally friendly is urgently needed. Oxidation of As(III) as H3AsO3 to the less toxic As(V)− and removal of As in groundwater was performed quantitatively by electrosorption using materials derived from agricultural wastes; this shows that this method has the potential to be a novel, green remediation method. [ABSTRACT FROM AUTHOR]

As a kind of common nitrogen pollutants, ammonia seriously pollutes water and soil environments and threatens human health. The treatment of water contaminated with ammonia was carried out in an electrochemical-adsorption system (ECAS). This paper discusses the capacity, kinetics, and mechanism of ammonia electrosorption, which is accurately described by a pseudo-first-order model, indicating that physical adsorption is the dominating mechanism. A high adsorption capacity of 4.086 mg N/g was attributed to the formation of a large number of adsorption sites and the highly acidic nature of dealumination of zeolites during electrolysis. Fast directional migration of ammonia in the electric field weakened the negative effect of boundary layer on adsorption and accelerated adsorption procedure. Brunauer, Emmett, and Teller measurements and scanning electron microscopy indicated that the formation of new channels and surface erosion, which resulted in a large surface area and pore volume of zeolites and a low resistance towards ion migration. As a whole, this study achieved efficient ammonia removal without the addition of chemical reagents to avoid secondary pollution. [ABSTRACT FROM AUTHOR]

• Novel Fe-CoS 2 @NC with elevated specific area and pore size are designed and fabricated. • Electrosorption of Yb(III) by Fe-CoS 2 @NC and Fe-CoS 2 is comparatively studied. • Electrosorption mechanism mainly depends on electric double layers and pseudo-capacitance. • Fe-CoS 2 @NC is successfully recycled for successive 5 times with less than 2% degradation. In this study, the novel Fe-doped CoS 2 @nitrogen-doped carbon (Fe-CoS 2 @NC) composites were manufactured and investigated as the capacitive deionization (CDI) electrode materials for electrosorption of Yb(III). The as-prepared materials were characterized with X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, N 2 adsorption–desorption test with Brunauer-Emmett-Teller method, Raman spectroscopy, and X-ray photoelectron spectroscopy. The electrochemical tests, including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy, revealed that Fe-CoS 2 @NC exhibited the better electrochemical performance with a specific capacitance of 58.41 F g−1 than Fe-CoS 2 @0.5NC and Fe-CoS 2. The electrosorption results demonstrated that Fe-CoS 2 @NC possessed the Yb(III) uptake of 129.4 mg·g−1 within 60 min at a voltage of 1.2 V and a flow rate of 20 mL·min−1. After five successive sorption–desorption cycles, the electrosorption efficiency of Fe-CoS 2 @NC remained at 98 %, exhibiting the robust durability for future industrial application. Furthermore, Fe-CoS 2 @NC also showed the favorable electrosorption performance towards various rare earth ions, especially for heavy rare earth ions. The mechanism analysis indicated that the impressive electrosorption performance is attributed to the synergistic contribution by the electric double layers of carbonaceous matrix and the pseudo-capacitance that induced by the redox reactions of Fe atom. [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]

The aim of this study is the use of a new conducting composite material which was prepared from an agricultural byproduct "olive pomace (OP)" and a polymer "polyaniline doped with a chlorhydric acid (PANI-HCl) and used for the fabrication of electrode, which was then used as substrate for the recovery of chromium hexavalent to an aqueous solution through chemical adsorption and electrosorption tests. We used the spectral analysis techniques such as FT-IR to characterize the material as well as scanning electron microscopy (SEM) to show that the PANI was successfully attached to OP. We carried out adsorption in batch system and electrosorption tests in acid medium within an electrochemical cell at a potential of +800 mV imposed and we compared the recovery with chemical adsorption at open circuit under the same conditions. For batch adsorption tests of Cr (VI) on olive pomace, PANI-HCl and the composites material prepared; the effect of several parameters such as the contact time, and the pH of the solution were studied. For the électrosorption tests, the results demonstrated that the electrosorption capacity of Cr (VI) is superior to the adsorption, which is due to the excellent electrical conductivity and mechanical properties of OP/PANI composite electrode. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is notable for its ability to perform low–energy desalination of brackish water and selective separation/recovery of salt and metal ions. However, redox side–reactions at porous carbon electrodes, such as the formation of weakly–acidic, oxygen–containing surface groups, limit ion electrosorption into double layers and electrode lifespan. In this study, we employ porous electrode theory to investigate the coupled effects of transport, electrosorption, redox reactions, and acid/base surface chemistry in practical flow through electrode (FTE) CDI cells, and we develop an efficient numerical solver that allows us to perform full–cell simulations over numerous charging/discharging cycles. We verify that our high fidelity model's predictions agree with analytical solutions in the limit of small voltage perturbations, and we demonstrate the significance of accurately capturing interplay between pH dynamics and surface chemistry. Our simulations demonstrate that anodic oxidation in FTE CDI is substantially inhomogeneous in space and in time, exhibiting cyclic protonation/deprotonation of surface groups and traveling, shock–like pH fronts. Moreover, we uncover connections between microscopic behavior and macroscopic performance parameters, demonstrating that this theoretical and numerical approach may substantially benefit the practical design optimization of CDI cells. • Multiple coupled reaction and transport phenomena are responsible for CDI degradation. • Efficient numerical methods allow full–cell simulations of CDI over multiple cycles. • Performance degradation is highly sensitive to accurate modeling of pH in electrodes. • Electrode oxidation exhibits substantial spatial and temporal inhomogeneity. [ABSTRACT FROM AUTHOR]

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

Capacitive deionization (CDI) technology holds great potential for rapid and efficient uranyl ion removal from wastewater. However, the related electrode materials still have much room for research. Herein, chitosan/phytic acid complexes were anchored on polypyrrole nanotubes (CS/PA-PPy) to fabricate the electrode for the electrosorption of uranyl ions (UO 2 2+). In this system, polypyrrole nanotubes provided specific channels for ion and electron diffusion, and chitosan/phytic acid complexes offered selective sites for UO 2 2+ binding. The results demonstrated that CS/PA-PPy via electrosorption showed faster kinetics and higher uranium uptake than those via physicochemical adsorption. The maximum adsorption capacity toward UO 2 2+ via electrosorption (1.2 V) could reach 799.3 mg g−1, which was higher than most of the reported CDI electrodes. Electrochemical measurements and experimental characterizations showed that the electrosorption of UO 2 2+ by CS/PA-PPy was a synergistic effect of capacitive process and physicochemical adsorption, in which the capacitive mechanism involved the formation of an electric double layer from hollow polypyrrole nanotubes, whereas the coordination of phosphate, amino and hydroxyl groups with UO 2 2+ was attributed to physicochemical adsorption. With the rational design of material, along with its excellent uranium removal performance, this work exhibited a novel and potential composite electrode for uranium capture via CDI from wastewater. Chitosan/phytic acid complexes were anchored on polypyrrole nanotubes to fabricate capacitive deionization electrode for the removal of uranyl ions from wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • MBiC@tE achieves an efficient F- electrosorption capacity of 37.9 mg F - gelectrode-1. • Fluoride was removed by the synergistic roles during capacitive control process. • Bismuth active units induced Faradaic redox reaction and increased pseudocapacitance. • The complex carbon framework ensured electrical double layer capacitance. • Insights into the phase transition of bismuth during the electrosorption. Remediation of fluoride in groundwater through electrosorption to cope with its high charge density and the smallest anion radius remains a promising strategy. Composite carbon materials obtained by calcining metal–organic frameworks contribute to the performance of conventional fluoride electrosorption systems. This study provides a redox-active electrode (MBiC@tE) that incorporates the Faradaic ion trapping effect for fluoride removal. Under potential control, MBiC@tE reversibly traps/releases fluoride anions from the aqueous solution through the combined roles of Faradaic pseudocapacitance and electrical double layer capacitance, with an electrosorption capacity of approximately 37.9 mg F - g electrode -1. The target contaminant anions are directly involved in the Faradaic reaction on the bismuth sites, with the formation of Bi-F bond excited by an electric field, thus resulting in the removal of fluoride as a consequence of the generation of insoluble substance (BiF 3). Furthermore, as expected (Bi 0 + 3F- ⇌ BiF 3 + 3e-), the working electrode exhibits good reversibility and maintains a high fluoride removal capacity even after multiple cycles. This study presents a comprehensive elucidation on the synergistic roles of Faradaic effect and electrical double layer capacitance induced by the electric field, and offers profound insights into the phase transition of bismuth and its affinity for fluoride during the electrosorption. [ABSTRACT FROM AUTHOR]

• Electrodeposition nanofabrication of carboxylated carbon nanotubes/α-MnO 2 nanorods/ polypyrrole electrodes for U(VI) electrosorption. • The obtained electrode provides high hybrid specific capacitance, good conductivity and hydrophilicity. • Electrosorption mechanism is dominated by hybrid capacitive adsorption and complexation. • CMP-0.10 presents highest specific capacitance and best U(VI) electrosorption performance. The uranium-containing wastewater resourced from the nuclear fuel cycle presents serious harm to human health and ecological environment. Herein, carboxylated carbon nanotubes/α-MnO 2 nanorods/polypyrrole (CMP) composite as high hybrid capacitance (EDL and pseudocapacitance) electrodes with good electrosorption performance for U(VI) were nanofabricated by the electrodeposition of polypyrrole (PPy) on the surface of carboxylated carbon nanotubes/α-MnO 2 nanorods composites using potentiostatic method. The morphology and structure characteristics, electrochemical properties and electrosorption U(VI) properties of the CNT/α-MnO 2 /PPy composites were systematically investigated. The results show that among the CMP composites obtained at different pyrrole concentrations, CMP-0.10 has the highest specific capacitance (366.97F/g), and its electrosorption performance is also the best, which is due to its well balanced porous structure and high hybrid capacitance which favors U(VI) ions transfer and storage. Cyclic voltammetry (CV) curves with obvious redox peaks were observed at low sweep speeds, indicating its hybrid capacitance behavior of CMP composites in which the capacitance contribution can be quantified. The electrosorption experiments were performed in a capacitive deionaiztion (CDI) system in which different factors (voltage, pH, U(VI) concentration and contact time, etc.) on the electrosorption of U(VI) were investigated, which shows that high U(VI) removal could be achieved at a wide pH range. The theoretical simulation using different models shows the best fit of the Langmuir model for the electrosorption isotherms and PFO model for the kinetics. The U(VI) electrosorption capacity reaches 339.45 mg/g at 0.9 V and pH 4.5 for CMP-0.10, which is much higher that achieved at 0.0 V. The facile fabrication, excellent electrochemical and electrosorption performance as well as good cycling stability for the CMP composites highlight their potential application in radioactive wastewater treatment. [ABSTRACT FROM AUTHOR]

One of the main steps in the biotechnological production of chemical building blocks, such as, e.g. bio‐based succinic acid which is used for lubricants, cosmetics, food, and pharmaceuticals, is the isolation and purification of the target molecule. A new approach to isolate charged, bio‐based chemicals is by electrosorption onto carbon surfaces. In contrast to ion exchange, electrosorption does not require additional chemicals for elution and regeneration. However, while the electrosorption of inorganic salts is well understood and in commercial use, the knowledge about electrosorption of weak organic acids including the strong implications of the pH‐dependent dissociation and their affinity towards physical adsorption must be expanded. Here, we show a detailed discussion of the main pH‐dependent effects determining the achievable charge efficiencies and capacities. An explicit set of equations allows the fast prediction of the named key figures for constant voltage and constant current operation. The calculated and experimental results obtained for the electrosorption of maleic acid show that the potential‐free adsorption of differently protonated forms of the organic acid play a dominating role in the process. At pH 8 and a voltage threshold of 1.3 V, charge efficiencies of 25% and capacities around 40 mmol/kg could be reached for a constant current experiment. While this capacity is clearly below that of ion exchange resins, the required carbon materials are inexpensive and energy costs are only about 0.013 €/mol. Therefore, we anticipate that electrosorption has the potential to become an interesting alternative to conventional unit operations for the isolation of charged target molecules. [ABSTRACT FROM AUTHOR]

BACKGROUND: Electrosorption efficiency for uranyl ion (UO22+) capture is low in acid solution due to the adverse effect caused by protons. This requires novel electrodes effective at acid conditions for UO22+ electrosorption in highly acidic industrial effluents such as spent nuclear fuel treatment. RESULTS: In the current study, UO22+ electrosorption was conducted using an amidoxime‐modified carbon paper (CP‐AO) electrode. The effects of voltage and frequency, pH, UO22+ initial concentration, and competing ions on UO22+ electrosorption were investigated. The reusability and electrochemical properties of the CP‐AO electrode were studied. The experimental results showed that the current CP‐AO electrode worked well in acidic conditiona (pH = 3) with a square wave periodic voltage (SWPV, −4 V, 1000 Hz), and outperformed a previously used carbon felt‐based electrode. The CP‐AO electrode showed considerable selectivity toward UO22+ in the presence of competitive ions. After seven rounds of continuous electrosorption–desorption, the CP‐AO electrode still showed good UO22+ uptake efficiency. The electrosorption mechanisms were studied in‐depth based on experimental and characterization results. The electrosorption of UO22+ by the CP‐AO electrode was due mainly to the electric field force moving UO22+ to the surface of the electrode, leading to electrodeposition of uranium compounds and the formation of electrically neutral substances. CONCLUSIONS: The results indicated that based on SWPV electrosorption the CP‐AO could be a desirable treatment approach for acidic uranium‐containing wastewater with promising practical applications. [ABSTRACT FROM AUTHOR]

In this paper, polyphosphazene was synthesized as precursors using benzene-1,4-diboronic acid and hexachlorocyclotriphosphazene (HCCP) by a simple one-step ultrasonic method. Furthermore, B, N, and P co-doped carbon materials containing phosphate functional groups (denoted as BNPCs-PO4) was obtained by the carbonization and functionalization of precursors at high temperature. Through the structural characterization and the investigation of electrochemical and electrosorption properties, it can be proved that BNPCs-PO4 has excellent porous structure and electrosorption properties with the maximum electrosorption capacity of 750 ± 40 mg/g for U(VI) and the equilibrium time of 24 min. The optimal pH and applied potential for electrosorption were 5.0 and 0.9 V, respectively. Meanwhile, it also showed high selectivity under the coexistence of multiple metal ions and excellent recyclability after six cycles. The results showed the introduction of heteroatoms improved the electrosorption properties of carbon materials and BNPCs-PO4 can be utilized as electrode for the removal of U(VI) in aqueous solution. [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]

[Display omitted] • Novel edge-N doped hierarchical carbons were firstly reported for P electrosorption. • The edge-N strategy endowed more accessible active centers and conductive efficiency. • The LNPC900 electrode showed a superior phosphate removal capacity of 533.06 mg g−1. • The system performed well in natural water purification with low P concentration. • The coupling of electrical capacitance and chemical interactions were achieved. Achieving high-efficiency removal of phosphate has been an urgent issue to combat eutrophication and meet ever-stricter emission standards. Electro-assisted adsorption, a mild electrochemical technology, demonstrated great potential for wastewater treatment owing to the merits of considerable removal performance, facile operation, and energy efficiency. Exploring and boosting the properties of electrode materials is exceedingly vital for technological advancement. In this study, the novel edge-N decorated La-doped hierarchical carbon composites (LNPCs) were developed via in-situ nucleation and one-pot pyrolysis strategy as phosphate capture electrodes. The LNPC900 electrode exhibited an ultrahigh phosphate removal capability of 533.06 mg PO 4 3- g−1 at 1.2 V, surpassing most of the reported electrode materials. Furthermore, this electrochemical system also performed well in the purification of natural river water with low phosphate concentration, where the treated concentration was below the first-class emission standard in China (0.5 mg P L−1). Comprehensive analysis and theoretical calculations indicate that the synergistic property of edge-N and small graphitic carbon nanodomains ensured more accessible active centers and conductive efficiency. The superb phosphate removal capability mainly originated from the coupling contribution of the electrical double layer capacitance, ligand exchange, and electrostatic attraction. This study possesses insight into the theoretical basis for the practical application of phosphate electrosorption and provides a new level of the technology. [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]

[Display omitted] The wastewater polluted by high concentrations of aqueous hexavalent chromium (Cr(VI)) has serious adverse effects on ecological environment and human health. As a burgeoning, environmental-friendly, and promising wastewater treatment technology, capacitive deionization (CDI) process for efficient removal of aqueous Cr(VI) needs to be investigated. In this work, pseudocapacitive NiFe-layered double hydroxide/ polypyrrole (NiFe-LDH/PPy, denoted as NiFe/PPy) electrode was synthesized by the in-situ polymerization of PPy on the NiFe-LDH surface. Results of characterizations manifested that NiFe/PPy had the chain spherical structure of PPy. In particular, excellent PPy provides effective reversible capacitance and ion diffusion and improves the conductivity and pseudocapacitance performance of NiFe-LDH. Then, the NiFe/PPy anode and activated carbon (AC) cathode were assembled into the CDI cell for capacitive removal of high concentrations of aqueous Cr(VI). In 20 mL/min of flow velocity, 1.2 V, and 100 mL 100 mg/L of Cr(VI) solution, the Cr(VI) electrosorption capacity and removal ratio attained to 47.95 mg/g and 95.89%, respectively. The electrosorption of Cr(VI) slightly decreased under the common competing anions of Cl−, NO 3 −, SO 4 2−, HCO 3 −, and CO 3 2−. Based on Langmuir isotherm model, the maximum theoretical removal capacity of NiFe/PPy for Cr(VI) was 111 mg/g. The electrostatic attraction, reduction, and surface complexation played primary roles in the CDI system of NiFe/PPy//AC asymmetric electrodes. The outstanding electrosorption performance makes this CDI system have a favorable application prospect in the actual wastewater treatment containing high concentrations of Cr(VI). [ABSTRACT FROM AUTHOR]

• An efficient method is presented for the recovery of In3+ from acidic solution. • The activated carbon electrode shows good capability for electrosorption of In3+. • The recovery of In3+ is mainly based on electrical double-layer charging. • In3+ ions are preferentially electrosorbed in a competitive environment. High-efficiency recycling technology for endangered elements effectively mitigates the risk of resource shortages and promises the sustainability of supply chains, which is significant to the industry. In this study, an activated carbon (AC)-based capacitive deionization (CDI) for the selective electrosorption and recovery of indium ions (In3+) from acidic aqueous solution is proposed. The effects of applied voltage, pH, and initial concentration of indium were investigated to optimize the operation parameters for In3+ electrosorption. The results of cyclic voltammetry and the galvanostatic charge/discharge measurements indicate that the AC electrode shows good capability for the electrosorption of In3+ based on electrical double-layer capacitance. As demonstrated, In3+ can be successfully removed by CDI without deposition when the pH < 4, as confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The deionization capacity of In3+ is 7.95 mg/g with an energy consumption of 0.84 kWh/mol in single-pass mode CDI with an initial concentration of 50 mg/L (pH = 3) at 1.2 V. However, the removal of In3+ is affected by the solution pH since hydrogen ions (H+) compete for electrosorption. Note that In3+ ions with high valence are preferentially electrosorbed on the electrode surface over H+ ions, exhibiting a selectivity coefficient of 2.12. Herein, in the charging step, a large number of H+ ions in solution are rapidly electrosorbed onto the electrode, while these H+ ions are gradually replaced by a small number of In3+ ions in solution. Therefore, this electrosorption process shows great potential for effectively recovering indium ions from acidic aqueous solutions. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) technology has excelled in water treatment areas such as brackish water desalination, hard water softening and pollution ion removal. However, the poor performance of the electrodes used in CDI cell construction continues to limit its practical application. In this work, we used chitosan mixed with potassium hydroxide (KOH) and simply carbonized to synthesize porous carbon electrode materials (CTS-850) with excellent material and electrochemical performance, and achieve high adsorption capacity and fast adsorption rate in a variety of salt solutions. The material characterization of CTS-850 displayed super large specific surface area (>2300 cm3 g−1), pore volume and excellent nitrogen doping. Electrochemical characterization showed excellent specific capacitance, good conductivity and cycle performance. In CDI experiments, we explored the removal efficiency of electrodes carbonized under different temperatures in single and mixed solution systems, and the CTS-850 electrode had an ultra-high adsorption capacity of 47 mg g-1 and a fast adsorption rate of 6.7 mg g-1 min-1 in 15 mM synthetic municipal wastewater (～1750 mg L-1). In addition, we discussed the relationship between high adsorption capacity, fast adsorption rate and material properties. Our work is expected to provide guidance for the synthesis of higher performance CDI electrode materials. [ABSTRACT FROM AUTHOR]

This study aims to investigate the feasibility of desalinating secondary effluent from a domestic wastewater treatment plant (DWTP) using membrane capacitive deionization (MCDI) for reclamation purposes. The desalination performance of a MCDI stack with 10 pairs of 20 cm × 20 cm activated carbon electrodes was evaluated in single-pass mode. As evidenced, the MCDI stack outperformed the capacitive deionization stack. The water quality characteristics of the inflows and product water were also analyzed. Our results revealed that MCDI can effectively remove undesired ions such as calcium and nitrate from the DWTP effluent for water reclamation. In particular, the solution conductivity of the product water was observed to be as low as 1.27 μS/cm. Removal of the ions was easily performed by the electrostatic field-assisted deionization process. The use of MCDI for low-salinity wastewater reclamation demonstrated favorable energy performance with a low volumetric energy input and a molar energy input of 0.12 kWh/m3 and 0.03 kWh/mole, respectively; and the energy efficiency of this system is expected to be further improved by energy recovery or incorporation of energy-producing processes. These results are indicative of the benefits of using MCDI as part of the treatment processes for the reclamation of wastewater with low salinity. • A scale-up MCDI system was developed to desalinate secondary effluent. • Ion-exchange membranes help to improve desalination and energy performance. • Removal efficiencies of 83% for TDS and 92% for water hardness were achieved. • The energy performance and implications of the MCDI system were addressed. • MCDI is an energy efficient process for reclamation of wastewater with low salinity. [ABSTRACT FROM AUTHOR]

A pulse electrosorption reaction device was constructed， in which the pulse-switching power supply was used to replace the DC stabilized power supply adopted in the traditional electro-adsorption， and the activated carbon powder was used as the adsorbent material to prepare the electrode plate. The removal rates of NO3-N and NH3-N in the simulated wastewater using pulse electrosorption method and direct current adsorption method were compared and results show that the removal rate of the pulse electrosorption method is higher within 60min.Taking the removal rate of NO3-N as the index， the effects of duty cycle and frequency on nitrogen removal rate were also studied. The results show that the removal rate of NO3-N is the highest when the duty cycle is 50% and the frequency is 104Hz. [ABSTRACT FROM AUTHOR]

The adsorption phenomenon on surfaces is investigated both with and without the presence of an external electric field. A simple interpretation of the adsorption coefficient and desorption time, as they appear in Langmuir's isotherm model, is presented. A model for electrosorption is proposed, which explicitly takes into account the applied external voltage and the reaction field resulting from the adsorbed charges. Both saturation, stemming from the finite density of adsorption sites, and non-saturation regimes are considered. The case of a system in contact with a reservoir of particles is also analyzed for its experimental importance. The model's validity is assessed by analyzing experimental data published by several research groups. A comparative study of the proposed model is conducted in relation to the commonly used pseudo-first and pseudo-second order models. Unlike the latter models, the proposed model allows for the assessment of the impact of the external voltage on the model parameters. The model takes into account ion generation resulting from electrolysis phenomena. [Display omitted] [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]

The discharge of effluents containing radionuclides has a detrimental impact on the ecological environment, emphasizing the importance of recovering U(VI) from nuclear wastewater to safeguard the environment. Electrosorption has emerged as a viable technique for the extraction of uranium from radioactive solutions. Herein, we propose a facile strategy utilizing ultrasonication to fabricate a novel sulfonated carbon material (HCCMs-SO 3 H) co-doped with B, N, and P atoms. The incorporation of sulfonate groups and doping heteratoms in HCCMs-SO 3 H significantly enhanced its electrosorption capacity for uranium, yielding an impressive capacity of 626.37 mg/g at 0.9 V. This enhancement in electrosorption ability is attributed to the synergistic effects of sulfonate groups and the presence of B, N, and P atoms in the carbon matrix. Furthermore, HCCMs-SO 3 H exhibited excellent recoverability and selectivity towards uranium, endowing it a promising material for uranium extraction from uranium-containing solutions. Its high electrosorption capacity, coupled with favorable recoverability and selectivity, positioned HCCMs-SO 3 H as a potential candidate for efficient and environmentally friendly uranium recovery processes. 1. A novel sulfonated carbon material (HCCMs-SO 3 H) co-doped with B, N, and P atoms was successfully fabricated; 2. The incorporation of sulfonate groups and doping heteratoms in HCCMs-SO 3 H significantly enhanced its electrosorption capacity for uranium; 3. The maximum electrosorption capacity reached 626.37 mg/g at −0.9v and the optimum pH value was 5.5; 4. HCCMs-SO 3 H electrode exhibited excellent recoverability and selectivity towards uranium; 5. The high electrosorption capacity, coupled with favorable recoverability and selectivity, positioned HCCMs-SO 3 H as a potential candidate for efficient and environmentally friendly uranium recovery processes. [Display omitted] • HCCMs-SO 3 H electrode was successfully synthesized. • The maximum electrosorption capacity reached 626.37 mg/g at −0.9 v and the optimum pH value was 5.5. • The excellent selectivity and regeneration performance is demonstrated. • The modified sulfonic acid group and co-doped B,N,P atoms contributed to the electrosorption capacity of U(VI). [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemical separation for sustainable formate recovery. • Scaling up selective formate separation using electrochemical flow cell. • Optimization of operating conditions using response surface methodology. • Flow rate has the most significant effect on total cycle charge efficiency. • The selectivity of formate ions reached 6.2 in the presence of excess perchlorate electrolyte. Selective ion separation is a fundamental challenge with applications ranging from the manufacturing of pharmaceuticals & industrial salts to water desalination. In particular, the separation of formate, a primary product of electrochemical carbon dioxide reduction, has attracted attention not only to reduce carbon emissions and energy costs but to provide new routes to value-added chemicals. In the present study, selective formate separation from an aqueous solution is demonstrated using an electrochemical flow cell with symmetric redox-active polyvinyl ferrocene electrodes. An electrosorption system equipped with an electrosorption cell, inline conductivity, and pH sensors was constructed to provide real-time measurements of the formate adsorption performance in continuous flow mode while varying operating conditions such as the flow rate, cell voltage, and electrolyte concentration. These parameters were optimized using a Box–Behnken experimental design to improve the formate adsorption selectivity. The flow cell results showed a selectivity higher than 6.0 toward the removal of formate in an electrolyte containing a 30-fold excess of perchlorate under optimal operation conditions (i.e., 0.5 mL/min flow rate, 1.0 V, and 15 mM electrolyte concentration). The performance of the flow cell was also tested using a solution that contained different liquid CO 2 reduction products, and formate separation was achieved. The results suggest that the proper design of the electrochemical cell and efficient operation of the flow platform pave the way for scaling up the technology for selective formate separation. [ABSTRACT FROM AUTHOR]

Lithium extraction from the solution in low Li+ concentration by an energy-saving and high-efficiency method is still a challenge. Herein, a novel hollow porous LiMn 2 O 4 (H-LMO) with highly active site was proposed to enhance the extraction performance of Li+. Based on the established hollow porous structure, the H-LMO film electrode (H-LMOE) exhibits excellent lithium electrosorption performance and stability. Under the current density of 0.5 C, the electrosorption capacity of Li+ could reach 31.52 mg/g, the separation coefficient of Li+/Mg2+ was 581.67, and the energy consumption was as low as 0.49 Wh/mol Li. This unique structural strengthening mechanism made H-LMOE maintain a good Li+ extraction performance even in a solution of low Li+ concentration. The Li+ electrosorption capacity of H-LMOE was 2.13 times that of T-LMOE in a 60 mg/L Li+ solution, while the specific energy consumption of the H-LMOE was 15.78% lower than that of the traditional-LiMn 2 O 4 film electrode (T-LMOE). Even in a 10 mg/L Li+ solution, the electrosorption capacity of H-LMOE was 21.48 mg/g, which was 10.0% higher than that of T-LMOE. Moreover, after 50 recycling processes, the final electrosorption capacity of the H-LMOE was about 25.0% higher than that of the T-LMOE. • We supplemented the XPS of H-LMO electrode after 50 cycles of Li+ adsorption. • We supplemented the discussion about the difference between electro-adsorption and chemical adsorption in Introduction. • We supplemented and corrected the data and formatting errors in the manuscript. [ABSTRACT FROM AUTHOR]

Water electrolysis can hinder the operation of capacitive deionization (CDI) and membrane CDI (MCDI). This study is aimed at investigating the overpotential limits of CDI and MCDI (OP-MCDI) for water electrolysis and desalination performance. For sodium chloride concentrations of ~28,460 ppm, MCDI with mesoporous carbon electrodes could be operated at up to 2.4 V without water electrolysis, and the salt-adsorption capacity of the OP-MCDI system at 2.4 V was about two times greater than that of the MCDI at 1.2 V. This study offers an opportunity to extend the applicability of conventional CDI and MCDI systems for desalination of low-salinity solutions. [ABSTRACT FROM AUTHOR]

Membrane capacitive deionization (MCDI) is an emerging technology for effective removal of charged pollutants from the water sources including domestic wastewater. In this work, a lab-scale MCDI system was employed to investigate its feasibility for effective phosphorus removal from domestic wastewater. The effect of phosphate equilibrium reactions on the ion sorption behaviour was studied in sodium phosphate buffer solution at typical pH range maintained in a real domestic raw wastewater effluent (between 6.5 and 8.5). The results demonstrated that phosphate equilibrium system has positive impact on the degree of inorganic phosphorus (P) adsorption capacity in aqueous solution. In addition, the ion selectivity of P over other co-existing anions (Cl-, SO²4-) were experimentally studied using a synthetic wastewater solution. And it was found that the preferential electrosorption sequence of the competitive anions is: Cl- > SO²4- > P. while the initial ion concentration order in the synthetic feed solution is: Cl- (1.90mM) > P(0.40mM) > SO²4- (0.32mM). The experiments with diverse operating conditions revealed that the optimal adsorption of inorganic phosphorus over chloride and sulphate can be achieved in some extent with slower flow rates and higher applied potentials (less than 1.23 V). [ABSTRACT FROM AUTHOR]

• This work demonstrates the suitability of MCDI for P removal from wastewater. • The fundamental behavior of P removal in MCDI was systematically investigated. • Phosphate equilibrium has a significant impact on the degree of P adsorption capacity. • P removal was hampered by the other competition anions present in wastewater. • P removal performance was improved by adjusting pH of wastewater and operating conditions. Membrane capacitive deionization (MCDI) is an emerging technology for effective removal of charged pollutants from the water sources including domestic wastewater. In this work, a lab-scale MCDI system was employed to investigate its feasibility for effective phosphorus removal from domestic wastewater. The effect of phosphate equilibrium reactions on the ion sorption behaviour was studied in sodium phosphate buffer solution at typical pH range maintained in a real domestic raw wastewater effluent (between 6.5 and 8.5). The results demonstrated that phosphate equilibrium system has positive impact on the degree of inorganic phosphorus (P) adsorption capacity in aqueous solution. In addition, the ion selectivity of P over other co-existing anions (C l - , S O 4 2 -) were experimentally studied using a synthetic wastewater solution. And it was found that the preferential electrosorption sequence of the competitive anions is: C l - > S O 4 2 - > P, while the initial ion concentration order in the synthetic feed solution is: C l - 1.90 m M > P (0.40 m M) > S O 4 2 - (0.32 m M). The experiments with diverse operating conditions revealed that the optimal adsorption of inorganic phosphorus over chloride and sulphate can be achieved in some extent with slower flow rates and higher applied potentials (less than 1.23 V). [ABSTRACT FROM AUTHOR]

Abstract Carbon aerogels (CAs) with different microstructure were prepared via ambient pressure drying for capacitive deionization (CDI) of NaCl solution. The activated CAs exhibit a hierarchical porous structure, whose micro-, meso- and macropore size distribution can be varied with the molar ratio of resorcinol to catalyst (R/C). Desalination experiments illustrate that CA electrode with R/C of 200 shows the maximum salt adsorption capacity (SAC) of 10.34 mg/g at a working voltage of 1.5 V. It is found that electrosorption capacity of CA electrodes dose not only depend on the micro-porosity for large surface area but also the mesopores who provide transport channels. A positive-negative alternate adsorption (PNAA) method by alternating the polarity of voltage applied on the electrodes was developed to enhance the desalination capacity. The ultimate SAC of CA electrode with R/C of 200 is 25.45 mg/g, which is more than twice of the adsorption amount for the single adsorption. This method makes full use of the pores of the CAs and provides a further enhancing capacity for CA CDI. Graphical abstract Unlabelled Image Highlights • Carbon aerogel electrodes with different nanostructure are prepared. • Wider transport channel reduces the rates of adsorption and desorption. • A positive-negative alternate adsorption method is adopted for the first time. • A high electrosorption capacity of 25.45 mg/g is obtained. • The mechanism of PNAA inside electrode pores is proposed. [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]

Abstract Electrochemical oxidation is an effective mean to degrade non-biodegradable organics from the contaminated waters. However, its current efficiency is very low for the low-concentration organic pollutants treatment. In this work, combining with the outstanding adsorption property of CNT and the effective electrocatalytic oxidation performance of β-PbO 2 , we constructed novel layer-by-layer carbon nanotube/PbO 2 anodes (CNT/PbO 2 -3, CNT/PbO 2 -4 and CNT/PbO 2 -5) with high adsorbability to enhance the electrochemical degradation efficiency of low-concentration sodium pentachlorophenate (PCP Na). In electrochemical oxidation tests, the PCP-Na was rapidly enriched in the CNT/PbO 2 film through adsorption/electrosorption and then efficiently degraded in site. The removal efficiency of low-concentration PCP-Na (5 mg/L) on CNT/PbO 2 -4 reached 73.8% after only 5 min of electrolysis, whereas that on pure PbO 2 was only 9.9%. To further clarify the mechanism of improvement of PCP-Na removal on CNT/PbO 2 -4 anode, the generation capacity of·OH radicals, oxygen evolution overpotential, voltammetric charge quantity, interface resistance, and specific surface area of CNT/PbO 2 -4 anode were also assessed and compared with those of other three anodes. Results showed that, in addition to the synergistic effect of adsorption/electrosorption and electrocatalysis, the more active sites, smaller electron transfer resistance and higher direct oxidation capacity of CNT/PbO 2 -4 anode also contributed to improving degradation rate of PCP-Na on CNT/PbO 2 -4 anode. Additionally the electrochemical degradation pathway of PCP-Na was also proposed based on the gas chromatography-mass spectrometry analysis. Finally, CNT/PbO 2 -4 electrode exhibited longer accelerated lifetime of 116 h than pure PbO 2 electrode (91 h). Thus, these findings provide a new anode to improve the removal of low-concentration organic pollutants through combining electrochemical oxidation and adsorption/electrosorption processes. Graphical abstract Image 1 Highlights • A novel layer-by-layer CNT/PbO 2 anode was fabricated. • The degradation efficiency of PCP-Na on CNT/PbO 2 anode was obviously improved. • The low-concentration PCP-Na was enriched on the surface CNT/PbO 2 anode. • Adsorption/electrosorption and electrocatalysis were combined. [ABSTRACT FROM AUTHOR]

Abstract In this work, we report the use of pseudocapacitive RuO 2 in a porous carbon-based substrate as a composite electrode for high-performance capacitive deionization (CDI). RuO 2 was electrodeposited onto inexpensive activated carbon (AC) via cyclic voltammetry to optimize the composite electrode (denoted as RuO 2 (20)-AC) fabrication. The electrochemical measurements indicate that the composite electrode with a specific surface area of 576 m2/g and hydrophilicity yields an improved specific capacitance and good cycling stability. The notably enhanced performance is attributed to the presence of RuO 2 , which allows rapid Faradaic charge-transfer reactions as well as pseudocapacitive charge storage. These results confirm that incorporating RuO 2 onto an AC electrode effectively reduces the electrical resistance and enhances the charge efficiency. Furthermore, batch-mode CDI experiments were conducted at 1.2 V in a 5 mM NaCl solution. As evidenced, the RuO 2 (20)-AC composite has a promising salt adsorption capacity of 11.26 mg/g, which is 3.7-fold higher than that of pristine AC. Therefore, using the RuO 2 (20)-AC composite as the cathode, an enhanced desalination performance can be achieved through a mixed capacitive-Faradaic process, resulting from two removal mechanisms of capacitive electrosorption and pseudocapacitive redox reactions. This work provides an efficient strategy to utilize RuO 2 on porous carbon-based substrates to improve CDI performance. Highlights • RuO 2 /activated carbon composite electrodes were prepared for CDI. • Electrodeposited RuO 2 showed good pseudocapacitive charge storage. • The metallic conductivity of RuO 2 ensures rapid ion transport. • The composite had a superior salt electrosorption capacity. • The combination of capacitive electrosorption and Faradaic reactions enhanced the CDI performance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The NiCoAl-MMOs electrodes showed outstanding performance in CDI. • Maximum electrosorption capacity of NiCoAl-MMOs electrodes was 108.8 mg NaCl/g. • Concomitants reconstruction of LDHs occurred during electrosorption process. • Intercalation of anions into NiCoAl-MMOs was enhanced by electric field. Abstract The ternary-component NiCoAl-mixed metal oxides (NiCoAl-MMOs), which are expected to have a high capacitance, were successfully prepared as film electrode for capacitive deionization (CDI). Hexagonal NiCoAl-MMOs nanoplatelets with a lateral size between 250 and 400 nm densely covered the surface of the nickel foam substrate. With the optimal Ni/Co/Al ratio (1.5:1.5:1), NiCoAl-MMOs displayed a more well-distributed surface, better crystallinity, and higher specific surface area, while the Ni/Co/Al ratio of 1.5:1.5:1 was also optimal for the NiCoAl-MMOs film electrodes to achieve maximum capacitance of 1167 F/g. The NiCoAl-MMOs film electrodes possessed ideal pseudocapacitive behavior and good capacitive reversibility, and showed outstanding performance in CDI from the concomitant reconstruction of the layered double hydroxides by intercalating anions. The desalination capacity of the NiCoAl-MMOs film electrodes was 108.8 mg NaCl/g, which was significantly higher than that of binary-component NiAl-MMOs and carbon-based electrodes. The NiCoAl-MMOs electrodes were quickly regenerated by reversing the voltage, with a desorption rate of 81.36%. The electrosorption capacity was about 2.5 times higher than that of adsorption without bias, indicating that the intercalation of ions into NiCoAl-MMOs nanoplatelets was enhanced by applying an electric field. NiCoAl-MMOs showed great promise as a CDI electrode in desalination. [ABSTRACT FROM AUTHOR]

Global demand for lithium (Li) resources has dramatically increased due to the demand for clean energy, especially the large-scale usage of lithium-ion batteries in electric vehicles. Membrane capacitive deionization (MCDI) is an energy and cost-efficient electrochemical technology at the forefront of Li extraction from natural resources such as brine and seawater. In this study, we designed high-performance MCDI electrodes by compositing Li+ intercalation redox-active Prussian blue (PB) nanoparticles with highly conductive porous activated carbon (AC) matrix for the selective extraction of Li+. Herein, we prepared a series of PB-anchored AC composites (AC/PB) containing different percentages (20%, 40%, 60%, and 80%) of PB by weight (AC/PB-20%, AC/PB-40%, AC/PB-60%, and AC/PB-80%, respectively). The AC/PB-20% electrode with uniformly anchored PB nanoparticles over AC matrix enhanced the number of active sites for electrochemical reaction, promoted electron/ion transport paths, and facilitated abundant channels for the reversible insertion/de-insertion of Li+ by PB, which resulted in stronger current response, higher specific capacitance (159 F g−1), and reduced interfacial resistance for the transport of Li+ and electrons. An asymmetric MCDI cell assembled with AC/PB-20% as cathode and AC as anode (AC//AC-PB20%) displayed outstanding Li+ electrosorption capacity of 24.42 mg g−1 and a mean salt removal rate of 2.71 mg g min−1 in 5 mM LiCl aqueous solution at 1.4 V with high cyclic stability. After 50 electrosorption-desorption cycles, 95.11% of the initial electrosorption capacity was retained, reflecting its good electrochemical stability. The described strategy demonstrates the potential benefits of compositing intercalation pseudo capacitive redox material with Faradaic materials for the design of advanced MCDI electrodes for real-life Li+ extraction applications. [Display omitted] • Redox-active PB intercalation material with AC for efficient Li+ extraction. • AC facilitate electron and Li + transport to redox-active sites of PB. • AC/PB exhibit high specific capacitance (159 F g−1) and rapid Li+ diffusion. • Excellent Li + extraction of 24.42 mg g−1 in Asymmetric AC//AC/PB-20 MCDI cell. • Excellent cyclic stability and Li + retention of 95.11% even after 50 cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • State of the art in electrosorption of organic compounds (EOC) critically reviewed. • EOC shows promise against poorly adsorbable, highly polar, and ionized pollutants. • Enhanced adsorption and active control of ad-/desorption by electric potential. • Insightful performance parameters proposed to unify rapidly growing EOC research. • EOC application for on-site regenerable adsorbers and in treatment trains discussed. The widespread contamination of water resources with emerging organic contaminants necessitates the development of sustainable and cost-effective water treatment technologies. Adsorption, as a widely used water remediation process, is hampered by severe performance limitations against ionic and hydrophilic organic contaminants. In addition, no facile on-site regeneration techniques are available. Electrosorption of organic compounds (EOC) is a promising alternative to not only improve adsorption performance, but also to facilitate adsorbent regeneration by green electricity. The number of studies on EOC has grown exponentially over the past decades. There are numerous examples showing that applied electric potentials can significantly enhance the adsorption affinity, capacity, and kinetics of conductive carbon adsorbents. However, whether these effects are specific to certain compound classes or more generally applicable remains unclear as well as the optimal criteria for designing EOC processes. Therefore, we critically evaluated the current state of the art of EOC in terms of active control of adsorption and desorption processes and the achievable effects for ionic and neutral organic compounds. Through a detailed consideration of compound speciation and surface chemistry of electrode materials, we derive mechanistic insights into the EOC process and discuss differences between electrosorption of inorganic and organic compounds. We provide definitions and propose insightful performance parameters to unify the rapidly growing EOC research. Potential application scenarios and future research directions are discussed. Overall, EOC is less likely to be a one-fits-all solution for removing contaminants, but adds a valuable tool especially for the hydrophilic and ionic organic contaminants that challenge conventional adsorption processes. [ABSTRACT FROM AUTHOR]

The available fresh water resources have been polluted by rapid industrialization and urbanization. Several techniques have been developed and practiced for the treatment of wastewater, including physical, thermal, chemical, membrane-based and electrochemical techniques. Still the efficient and effective technique for the wastewater treatment is challenging for researchers over the years. The capacitive deionization (CDI) is an environmentally friendly technology for water purification (desalination) with substantial scope, which works on the principle of electrical double layer (EDL). In this case, salt ions are electrostatically adsorbed on the surface of electrode material. Porous carbon with optimized pore size, hierarchal pore structure and high surface area is preferred for CDI. Herein, we report the detailed study of microporous carbon derived from Zeolitic Imidazolate Framework-67 (PC-ZIF-67) and its application as electrode material in CDI. This setup has been utilized for the removal of monovalent cations (Na+ and K+) and divalent cation (Ca2+) along with heavy metal- lead (Pb2+) from water. The PC-ZIF-67 exhibits typical truncated cubic morphology with microporosity and high gravimetric surface area of 532 m2/g. The as-synthesized PC-ZIF-67 offers salt adsorption capacity (SAC) of 28.1, 30.6, 50.9 mg/g for the removal of Na+, K+ and Ca2+, respectively. Moreover, PC-ZIF-67 shows SAC of 117.2 mg/g for the removal of Pb2+, which is higher than other saline cations. The mechanism of Pb2+ removal is attributed to the electrostatic and π- π interaction between the surface of PC-ZIF-67 and Pb2+. Further, the material displays good cyclic stability during the removal of each cation, retaining 90% of SAC after ten adsorption-desorption cycles. The selectivity of cations is studied by mixed salt electrosorption experiment revealing that there is higher selectivity of PC-ZIF-67 electrode towards divalent cations as compared to monovalent cations. The SAC values have been validated by matching with theoretical adsorption model isotherms. This work promotes future utilization of MOF-derived porous carbon for the effective removal of dissolved Na+, K+, Ca2+ and Pb2+ from aqueous source using CDI. [Display omitted] • Microporous carbon with SSA of 532 m2/g is derived from ZIF-67 (PC-ZIF-67). • Heavy metal- lead (Pb2+) along with Na+, K+, Ca2+ are effectively removed. • High SAC of 117.2 mg/g for the removal of Pb2+. • Good cyclic stability retaining 90 % of SAC after ten adsorption-desorption cycles. • PC-ZIF-67 shows more selectivity towards divalent cations as compared to monovalent cations. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging electrochemical desalination technique for the energy- efficient removal of dissolved ions from aqueous solution. This is a first research attempt which describes the influence of dye molecules on capacitive deionization of salt solution. In this regard, a CDI flow cell has been fabricated and tested in order to scrutinize the electrosorptive removal of three different dye molecules such as amido black 10B (AB) (acidic dye), eosin yellow (EY) (neutral dye) and methyl violet (MV) (basic dye) from synthetic aqueous solutions. The electrosorption capacitance was analyzed by cyclic voltammetry cell and CDI flow cell using activated carbon cloth (ACC) electrodes with 1 cm 2 and 24 cm 2 surface areas respectively. The capacitance values of 106 and 99 F/g correspondingly were obtained for a steady-state CV and CDI flow cell with 50 mM Na 2 SO 4 electrolyte solution. In addition to this, the dye removal efficiency was also examined by a CDI flow cell for the solution containing 10 ppm of dye and 500 ppm of Na 2 SO 4 . The experimental results substantiate that EY exhibits strong adsorption during charging and strong desorption during discharge cycle when compared with other two dye molecules (AB & MV). Conclusively, electrosorption of dye molecules at the carbon cloth electrodes surface was found in the following order: EY > AB > MV. [ABSTRACT FROM AUTHOR]

Abstract: Lignin‐derived carbon is introduced as a promising electrode material for water desalination by using capacitive deionization (CDI). Lignin is a low‐cost precursor that is obtained from the cellulose and ethanol industries, and we used carbonization and subsequent KOH activation to obtain highly porous carbon. CDI cells with a pair of lignin‐derived carbon electrodes presented an initially high salt adsorption capacity but rapidly lost their beneficial desalination performance. To capitalize on the high porosity of lignin‐derived carbon and to stabilize the CDI performance, we then used asymmetric electrode configurations. By using electrodes of the same material but with different thicknesses, the desalination performance was stabilized through reduction of the potential at the positive electrode. To enhance the desalination capacity further, we used cell configurations with different materials for the positive and negative electrodes. The best performance was achieved by a cell with lignin‐derived carbon as a negative electrode and commercial activated carbon as a positive electrode. Thereby, a maximum desalination capacity of 18.5 mg g−1 was obtained with charge efficiency over 80 % and excellent performance retention over 100 cycles. The improvements were related to the difference in the potential of zero charge between the electrodes. Our work shows that an asymmetric cell configuration is a powerful tool to adapt otherwise inappropriate CDI electrode materials. [ABSTRACT FROM AUTHOR]

Asymmetrical capacitive deionization (A-CDI) is expected to be a promising desalination technique with high salt removal capacity. In this work, the novel A-CDI are proposed where the negative and positive electrode are Na 4 Ti 9 O 20 (NTO) and activated carbon (AC), respectively. Basically, the NTO nanotubes with the specific surface area of 142.43 m 2 /g have been prepared by hydrothermal reaction. The electrochemical test shows that the specific capacitance of optimum NTO electrode can reach 120.45 F/g in 1 M Na 2 SO 4 solution with the scan rate of 1 mV/s by employing three-electrodes method. Moreover, the electrosorption capacity of AC/NTO asymmetrical electrodes is approach to 23.35 mg/g in NaCl solution with an initial concentration of 250 ppm. To improve the conductivity of NTO, reduced graphene oxide (rGO) is proposed to couple with NTO, named as rGO@NTO, to constitute the AC/rGO@NTO A-CDI. As a result, the AC/rGO@NTO A-CDI exhibited an ultrahigh desalination capacity of 41.8 mg/g in NaCl solution with an initial concentration of 250 ppm under 1.4 V, which is almost twice higher than that of AC/NTO electrodes and the highest value among all reported data anywhere. Besides, the charge efficiency of AC/rGO@NTO approaches to 1, implying the co-ions impaction has been successfully restricted. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an upcoming technique that can replace existing processes for removing and recuperating metal ions from dilute industrial waste waters. CDI removes ions via electrosorption on to its electrode surfaces, the efficiency of which is a function of CDI electrode properties that progressively change during continued operation. As such a need exists to develop a model to predict CDI performance over elongated periods which is independent of electrode properties and has negligible error values. By applying a first order non-linear dynamic model (FONDM) with inputs independent of the electrode characteristics, we propose a universal model that can predict CDI ion adsorption capacity with changes in applied potential, flow rate and electrolyte temperature to within 5% of the experimentally obtained results. The model was verified using activated carbon cloth (ACC) as a test electrode and aqueous sodium chloride solution as electrolyte, with a good prediction for ion electrosorption efficiency and time dependent electrosorption dynamics. The simplicity of the model makes it easy to adapt for various applications and in the development of intelligent control systems for CDI units in practical settings. [ABSTRACT FROM AUTHOR]

In an attempt to improve the capacitive deionization (CDI) performance and develop an efficient CDI electrode material, the effect of carbon characteristics on CDI was investigated. Activated carbon (AC) and ordered mesoporous carbon (OMC) materials synthesized by template method were used for the electrode manufacture. The capacitive deionization performance of AC and OMC based electrodes was investigated and compared. We found that when the specific surface areas of AC materials increased from 712 to 1347 m 2 /g, the electrosorption capacities of AC electrodes increased slightly from 9.43 to 10.14 mg/g. The characteristics of OMC materials can be optimized by the adjustment of the mesoporous silica beads template proportion, resulting in a maximum average pore size of 11.35 nm and total pore volume of 2.101 cm 3 /g. The optimum electrosorption capacity obtained with OMC4 electrode was 10.83 mg/g, which was not only higher than that of AC electrodes, but obviously higher than the values of most carbon-based electrodes in other studies. In conclusion, these results provide important insights into the effect of carbon characteristics on capacitive deionization and suggest that OMC synthesized by template method could be a promising carbon material for the CDI electrode manufacture. [ABSTRACT FROM AUTHOR]

In this study, the desalination performance of Capacitive Deionization (CDI) and Membrane Capacitive Deionization (MCDI) was studied for a wide range of salt compositions. The comprehensive data collection for monovalent and divalent ions used in this work enabled us to understand better the competitive electrosorption of these ions both with and without ion-exchange membranes (IEMs). As expected, MCDI showed an enhanced salt adsorption and charge efficiency in comparison with CDI. However, the different electrosorption behavior of the former reveals that ion transport through the IEMs is a significant rate-controlling step in the desalination process. A sharper desorption peak is observed for divalent ions in MCDI, which can be attributed to a portion of these ions being temporarily stored within the IEMs, thus they are the first to leave the cell upon discharge. In addition to salt concentration, we monitored the pH of the effluent stream in CDI and MCDI and discuss the potential causes of these fluctuations. The dramatic pH change over one adsorption and desorption cycle in CDI (pH range of 3.5–10.5) can be problematic in a feed water containing components prone to scaling. The pH change, however, was much more limited in the case of MCDI for all salts. [ABSTRACT FROM AUTHOR]