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[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]

[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]

[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]

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

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

[Display omitted] • Charging activated carbon (AC) tunes adsorption of ionic but not nonionic compounds. • Defunctionalized AC allows better electro-assisted trap&release performance. • Combine surface modification and electric polarization for promoted removal. • Long-term (20 d) stable electro-assisted trap&release with high enrichment effects. • Electro-assisted trap&release promising for on-site AC regeneration. Highly water-soluble, persistent, and mobile organic compounds (PMOCs) are more and more often detected in surface and groundwater, evoking potential threats to the environment and human health. Traditional water treatment strategies, including adsorption by activated carbon materials, fail to efficiently remove PMOCs due to their hydrophilic nature. Electro-assisted sorption processes offer a clean, facile, and promising solution to remove PMOCs on activated carbon-based electrodes and potentially allow an easy on-site sorbent regeneration (trap&release). In this work, the electrosorption of five selected PMOCs, that is, tetrapropylammonium (TPA+), benzyltrimethylammonium (BTMA+), p -tosylate (p -TsO-), p -toluenesulfonamide (p -TSA), and methyl- tert -butyl ether (MTBE), were investigated on two comprehensively characterized activated carbon felt (ACF) types carrying different surface functionalities. Significant enrichment factors in ranges of 102 to 103 for charged PMOCs were expected by our first estimation for electro-assisted trap&release on ACFs in flow systems applying potentials in the range of −0.1 V/+0.6 V vs. SHE for ad-/desorption, respectively. Defunctionalized ACF carrying larger density in surface π-systems and lower O-content promises a higher capability in electrosorption processes than the pristine material in terms of better material stability (tested for 5 cycles over 500 h) and better removal efficiency of ionic PMOCs. To improve ACFs adsorption performance for cationic and anionic PMOCs, permanent chemical surface modification and reversible electric polarization as alternative strategies are compared. Our findings explore future electrode and process design of electrosorption for applications to treat water contaminated by emerging PMOCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ion sorption on EDL and pseudocapacitor was studied at constant potential. • α-MnO 2 was the best in diffusive capacitance among polymorphs. • Effects of ion solvation and valence on sorption of inert ions were studied. • Monolayer capacity as affected by electrode polarity was estimated via Langmuir model. • Isoelectric point of the reversible MnO 2 /AC composite was modified. The capability of manganese dioxide (MnO 2) supported on loofah-derived activated carbon (AC) in the electrosorptive removal of common inert ions was studied in constant potential mode. Four MnO 2 polymorphs were prepared by redox chemical precipitation and characterized by XRD, SEM, BET and XPS. The pseudocapacitance property of the MnO 2 /AC electrode, significantly affected by the surface- and diffusion-controlled charge storage mechanism, was assessed via voltammetry and modified Langmuir adsorption isotherm. Batch electrosorption experiments were then performed at constant potential in the range of −1.5 V to + 1.5 V (vs. Ag/AgCl) using AC and α-MnO 2 /AC electrodes in the presence of common simple electrolytes, including NaNO 3 , Li 2 SO 4 , and Ca(ClO 4) 2. Consequently, the applied working potential (E app) positively affected the ion electrosorption rate and capacity. Faradaic processes occurred on MnO 2 , i.e., Mn(III)/Mn(IV) transition, increased the diffusion capacitance of AC, thus enhancing the first-order rate and monolayer capacity, mainly for the electrosorption of cations. Results showed that ion solvation, controlled by the ionic radius and valence of an ion, which impacted ion intercalation in MnO 2 and affected ion adsorption characteristics. The cation sorption capacity of α-MnO 2 /AC followed the order of Na+ (2.8 × 10-4 mol g−1) > Ca2+ (2.1 × 10-4 mol g−1) > Li+ (0.76 × 10-4 mol g−1) at E app = -1.5 V. The differential capacitance as affected by polarized potential and the shift of zero net charge or IEP toward more positively charging potential further highlighted the contribution of pseudocapacitance to ion adsorption on α-MnO 2 /AC electrode. [ABSTRACT FROM AUTHOR]

[Display omitted] • QRAC electrodes selectively adsorb NO 3 – due to the difference in binding energy. • The selectivity coefficient of QRAC-5 to NO 3 – reaches 2.7 at 0.4 V. • The electrosorption behavior of QRAC depends on physical adsorption and ion exchange adsorption. Nitrate pollution has become an increasingly serious water pollution problem worldwide. Capacitive deionization (CDI) technology is an emerging water treatment technology that can efficiently remove nitrate in water with advantages of simple process, high water recovery rate, low cost and energy consumption. In this work, we engineer a covalently bonded quaternized activated carbon (QRAC) material by silanization and investigate its selective adsorption of nitrate in mixed solution with extended voltage capacitive deionization (eV-CDI) mode. The results show that (1) the QRAC electrodes achieve selective adsorption due to the different adsorption binding energies of the quaternary ammonium group with Cl- and NO 3 –. The selectivity coefficient of QRAC-5 to NO 3 – reaches 2.7 at 0.4 V and the electrosorption capacity is 140% higher than that of AC in 5/5 mM KCl/KNO 3 solution. (2) The electrosorption of QRAC electrodes are dominated by two aspects: physical adsorption by external electric field which occurs in the incipient stage and ion exchange adsorption by quaternary ammonium groups occurring in the following stage. (3) CDI experiments in simulated municipal wastewater show that SO 4 2- had a negative effect on the adsorption capacity of NO 3 –, but QRAC electrode can still achieve separation effect in Cl-/NO 3 – solution system. These results show that covalently bonded quaternized activated carbon can achieve the effective separation and removal of NO 3 – in polluted water, and our work provides new insights into the selective electrosorption of CDI technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polysaccharides-bound porous graphene electrodes were rationally designed. • Oppositely charged groups at cathode and anode weakened the co-ions exclusion effect. • The asymmetrical configuration gave rise to 97.9% removal ratio for U(VI). • The mechanism involves improved EDL, extra micro electric field and complexation. As an energy-saving and facile technology, the potential of capacitive deionization (CDI) starts to surface in enrichment and recovery of uranium (U(VI)) from aqueous solutions. However, co-ion expulsion effect and poor surface wettability of electrode materials limit the eletrosorption performance. Here, polysaccharides xanthan gum (XG)- and chitosan (CS) -bound porous reduced graphene (RGH) electrodes were rationally designed, and then assembled into asymmetrical electrode configuration for U(VI) eletrosorption. Owing to the introduction of polysaccharide binders, the oppositely charged groups on the surface of cathode and anode weaken the co-ions exclusion effect as well as endow their superior surface hydrophilicity and electroconductivity, which facilitates the electrosorption for U(VI). Meanwhile, the negatively charged carboxylate groups could act as extra micro electric fields to attract U(VI) cations, and form stronge complexation between them. As a consequence, asymmetrical polysaccharide-bound RGH configuration gave rise to a larger removal ratio of 97.9% within 4 h at 1.2 V, as well as 2.5 times faster kinetics than symmetrical PVDF-bound RGH electrode configuration. Moreover, the accumulated adsorption capacity in six adsorption–desorption cycles of the former is up to 1413.0 mg g−1, 75% higher than the latter, which is of practical significance and economic benefit for electrosorption application. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemical capture and release of Cd2+ were conducted using Cu-MOF-74. • Selective removal of Cd2+ (>95%) was feasible under Na/Cd ~ 2 × 104 in molar ratio. • Redox of Cu within the MOF enables energy-efficient electrosorption/regeneration. • Excellent electrosorption (>100 mg/g) and regeneration (>90%) were achieved. An electrochemically-assisted wastewater treatment using Faradaic materials offers a promising technique for the selective removal of hazardous substances. Here, we demonstrate the reversible capture and release of cadmium ions in aqueous solutions, using a redox-active metal-organic framework (MOF) electrode. As-synthesized copper-based MOF (Cu-MOF-74; copper 2,5-dihydroxyterephthalate) is a highly attractive candidate for Faradaic electrosorption due to its large surface area, water stability, and redox-active metal nodes. Our work demonstrates the reversible capture and release of Cd2+ ions assisted by the electrochemical redox reaction of Cu2+/Cu+ within the MOF structure. Combined material characterization and electrosorption tests were carried out to determine the operational conditions for maximizing adsorption capacity, energy efficiency, and material stability, thus leading to excellent electrosorption (>100 mg g−1) and regeneration efficiency (>90%). This study demonstrates the feasibility of leveraging MOFs containing redox-active metal nodes for the selective separation of toxic cations, and paves the way for promising future applications of these 3-D porous structures for wastewater treatment and environmental remediation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Charge efficiency is directly related to flow rate and applied voltage. [•] 30–35% Of the energy consumed by CDI is for desorption of co-ions. [•] CDI electrosorption is driven by a physisorption according to thermodynamics. [•] The isotherm results were well represented by the Langmuir model. [Copyright &y& Elsevier]

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

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