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

[Display omitted] • The roles of specific N-containing groups on HCHO removal were comprehensively studied. • The ACN-600 exhibited the superior HCHO adsorption capacity (16.37 mg/g). • DFT calculation results indicated that pyrrolic-N exhibited the highest HCHO adsorption energy (−32.83 kJ/mol). • Pyridinic-N could trigger the Cannizzaro-type disproportionation reaction. Inserting nitrogen (N) heteroatoms into the carbonaceous adsorbents has been confirmed to be one of efficient strategies for enhancing HCHO removal. However, the essential promotion mechanisms of specific N-containing groups (such as pyridinic-N, pyrrolic-N, and quaternary-N) remain blurred. Herein, a series of N-doped activated carbons were prepared by annealing the melamine impregnated activated carbons at 600–900 °C and used for HCHO elimination. It manifested that the HCHO elimination performance of samples was remarkably improved after N-doping and their HCHO adsorption capacities were in the order of ACN-600 (16.37 mg/g) > ACN-750 (9.87 mg/g) > ACN-900 (7.28 mg/g) > AC (5.09 mg/g). DFT calculation results revealed that there existed stronger attractive noncovalent interactions between pyrrolic-N doped carbon and HCHO due to the formation of stronger H-bonds. Therefore, the HCHO physisorption energy on pyrrolic-N doped carbon was the highest (−32.83 kJ/mol). Compared with the single physisorption mechanism of previous studies, the in-situ DRIFTS results manifested that the pyridinic-N atom (as a typical strong Lewis base) could trigger the Cannizzaro-type disproportionation reaction, which would transform toxic HCHO into relatively less toxic methanol and formic acid. Benefiting from the dual enhanced mechanisms of attractive noncovalent interactions and Cannizzaro-type disproportionation reaction, the ACN-600 manifested excellent HCHO removal performance. This study not only intrinsically discloses the promotion mechanism of specific N-containing groups on HCHO removal at molecular level but also provides guidelines for rational design and development of carbonaceous materials for effective HCHO elimination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual cation titanosilicate(DTS) was utilized in CDI to capture Cs+ and Sr2+. • By applying −1.2 V, the DTS electrode exhibits a high adsorption capacity. • DTS electrode showed rapid kinetics over 95 % of adsorption capacity within 30 min. • It provides a high selectivity of 5x103 mL/g in 10000-fold Na concentrated solution. • It was regenerated by applying + 2.0 V and its structural integrity remains intact. The utilization of ion intercalate capacitive deionization technology is garnering attention as an electrified water treatment method. This study proposes a capacitive deionization technology incorporating Dual-cation TitanoSilicate (DTS) to enable efficient electro-sorption/desorption of radioactive ions Cs and Sr. The synthesized DTS possesses a robust structure, high selectivity for Cs and Sr, and substantial adsorption capacity, incorporating redox-active titanium. Employing DTS as an active material in the electrode demonstrated a high adsorption capacity (186 mg Cs/g, 177 mg Sr/g) and rapid adsorption kinetics, reaching maximum capacity within 30 min, even in environments with a tenfold excess of competing ions. Furthermore, our system exhibited stable performance over 5 cycles of adsorption/desorption, and post-desorption analyses confirmed the durable structure stability without significant alterations. This study highlights the feasibility of CDI technology utilizing DTS for cesium and strontium removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • 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] • Defective MoS 2 electrode exhibited highly efficient and selective lead(II) adsorption. • Removal efficiency at initial concentration from 1 to 100 mg/L can reach ∼ 100 % • Adsorption capacity and removal efficiency were enhanced almost 8 folds after applying voltage. • Introduction of defects strengthened chemicalsorption and electrosorption. • A complete lead(II) desorption and reusability of electrodes can be achieved. Developing method for efficient lead(II) removal from aqueous solutions over a wide concentration range is urgent but challenging. In this work, defective molybdenum disulfide (MoS 2) was served as electrode coating to capture lead(II) over a wide range from aqueous solution via chemisorption and electrosorption coupling (CEC) process. The distinct adsorption behaviors of lead(II) on defective MoS 2 electrode were theoretically and experimentally investigated. In a wide concentration range (1 ∼ 100 mg/L), the removal efficiency of lead(II) from aqueous solutions can be close to ∼ 100 %. Adsorption capacities for lead(II) removal at initial concentration of 8.37 and 18.71 mg/L were 64.99 and 159.98 mg/g, respectively. After applying voltage, adsorption capacity and removal efficiency were enhanced almost 8 folds due to strengthened migration of ions, electrostatic interaction and electric double layer. Besides, lead(II) was completely desorbed from defective MoS 2 electrode within 60 min, and defective MoS 2 electrode by CEC process maintained excellent regeneration ability even after 10 cycles. Defective MoS 2 electrode has shown superior properties for lead(II) removal, such as (i) great specific capacitance and (ii) low charge transfer resistance toward the enhanced adsorption capacity and diffusion for lead(II) in the electrical double layer, compared with MoS 2. Extensive computations and characterizations of defective MoS 2 -lead(II) interaction demonstrated that the active unsaturated S sites were indispensable for lead(II) adsorption, which was beneficial for chemisorption. Based on the strong interaction with lead(II), defective MoS 2 electrode showed high-selectivity lead(II) adsorption with co-existence metal ions. Overall, defective MoS 2 as electrode coating by CEC has a great potential for the practical application in removing heavy metal ions from aquatic environment. [ABSTRACT FROM AUTHOR]

Based on the electro-negativity and structural characteristics of CR, a novel copper-organic framework (Cu-MOF) was synthesized with unique cage topology and cation network. The Cu-MOF exhibited efficient and targeted adsorption, separation and recovery characteristics for CR. The DFT calculation and two-dimensional correlation spectroscopy analysis further revealed that the energy distribution in CR adsorption was dominated by electrostatic interactions, followed by π-π stacking and van der Waals interactions. [Display omitted] • A novel Cu-MOF with caged topology and cation framework was synthesized for Congo Red (CR) specific-adsorption. • The Cu-MOF exhibited the efficient performance with the maximal adsorption capacity of 119.76 mg/g. • The Cu-MOF realized the separation, purification and recovery of the CR from mixed dyes. • Mechanism revealed the adsorption was spontaneous and exothermic with monolayer diffusion. • DFT and 2D-COS analysis clarified the adsorption was generated through electronic interaction and π-π stacking. Metal-organic frameworks (MOFs) with a three-dimensional (3D) caged structure and charged networks are promising adsorbents for separation and purification applications. However, it is a challenge to synthesize the MOFs in crystalline structures with a targeted ability of efficiently removing and reutilizing the individual diazo dye from sewage. Here, we report the synthesis of a novel copper-organic framework (Cu-MOF) with a 3D caged stucture and cationic networks using CuCl 2 and a triazole ligand (methyl-1H-1,2,4-triazole-3-carboxylate MTC). The novel Cu-MOF exhibited highly efficient and targeted adsorption, separation and recovery characteristics for Congo Red (CR). Specifically, the maximal adsorption capacity was 119.76 mg·g−1, and the adsorbed CR can be efficiently released in NaCl-DMF solution with a recovery rate of almost 100%. After suffered from three adsorption–desorption cycles, the Cu-MOF could still reach a adsorption rate of >85% and maintain an intact skeleton structure. The batch-equilibrium experiment combined with density functional theory calculation further revealed that the adsorption process was spontaneous and exothermic, following the pseudo-second-order kinetic equation with monolayer diffusion. The specific adsorption of Cu-MOF for CR was precisely generated through electronic interaction with the –NH 2 and -SO 3 groups, exhibiting the adsorption energies of −2.16 eV and −2.04 eV, respectively. The two-dimensional correlation spectroscopy analysis comfirmed that the energy distribution in CR adsorption was dominated by electrostatic interactions, followed by π-π stacking and van der Waals interactions. In summary, our work not only presents a promising strategy for the targeted separation and purification of CR from wastewater, but also contributes to the design of highly efficient MOF-adsorbents for other organic pollutants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitric acid oxidation promotes moderate dissociation of petroleum pitch. • Preparation Multi cavity Carbon Microsheets by using NaCl and Modified pitch. • Multi cavity carbon microsheets have excellent NO 3 – removal performance of CDI. • DFT calculations indicate carbon cavity is beneficial for NO 3 – electron enrichment. Capacities deionization (CDI) denitrification technology has attracted considerable attention, and electrode materials with nitrate adsorption properties have become a research hotspot. In this study, a multi cavity carbon microsheets (MCCM-5) was prepared using a hard template method and low-cost nitrated pitch as a carbon source. The results of the electrosorption experiments showed that the material had an excellent capacity of NaNO 3 (45 mg g−1). Furthermore, although the actual specific surface area and specific capacitance of MCCM-5 are lower than those of hierarchical porous carbon materials (HPCM-1), MCCM-5 exhibit lower diffusion and charge-transfer resistances, resulting in a better denitrification performance. The adsorption capacity of MCCM-5 for NaNO 3 was twice that HPCM-1 and 11.8 times that of commercial activated carbon, which is superior to the material properties reported thus far. Our analysis indicated that the material combined the advantages of both a layered structure and hierarchical pores. First, the uniformly distributed hierarchical pores in the layered structure enhanced the ion concentration potential. Second, the layered structure provided good ion diffusion channels, thereby increasing the effective adsorption area of the material. DFT calculation shows that the carbon cavity structure enriched in the material shows a stronger adsorption capacity for NO 3 –, which can promote the electron transfer process during NO 3 – adsorption. This study shows that a precise regulation of the carbon material structure can be achieved by adjusting the size of the template material and carbonization conditions to obtain a higher adsorption capacity and provides a new idea for the structural optimization of electrode materials. [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]

[Display omitted] • EDTA grafted MXene was designed and fabricated as CDI electrode for treating simulant nuclear wastewater. • EDTA grafted MXene demonstrates high selectivity of Cs+ from concentrated HNO 3 solutions. • Cs+ can be concentrated to form an enriched waste stream that can be further utilized or disposed as a small waste package. • Stripping of adsorbed Cs+ by simple reverse of applied voltage led to easy regeneration with outstanding performance over 320 cycles. A capacitive deionization (CDI) electrode comprising ethylenediamine triacetic acid (EDTA) and 2D MXene (EDTA-MXene) is fabricated to separate Cs+ from strongly acidic process water. The method provides new direction for an advanced aqueous recycle process to separate fission products from spent fuel liquor. Grafting EDTA on MXene has no detrimental effect on its structure but does diversify the modes of ion interaction and increase the number of binding sites. The composite CDI electrode has a Cs+ adsorption capacity of 2.07 mmol g−1 at 1.2 V with 97.3% removal efficiency within 15 min. Step-wise adsorption and desorption cycling of the electrode highlights the chemisorption effect of EDTA which immobilizes the ions as the applied voltage is lowered, although almost all ions can be stripped by reversing the voltage to −1.4 V and without the need for chemical treatment. The EDTA-MXene electrode demonstrates outstanding cyclic performance with a capacity retention of >80% after 320 cycles. Furthermore, the electrode maintains its performance in strongly acidic solution, removing 0.66 mmol g−1 Cs+ at 1.2 V, as well as being stable after immersing in 3 mol L−1 HNO 3 for 7 days. Through continuous cycling it is possible to enrich the Cs+ into a highly concentrated solution for element recovery or safe disposal. The EDTA-MXene material is robust and maintains good performance in harsh chemical environments, levering its multiple binding sites to successfully isolate Cs+ from strongly acidic solutions and in the presence of competing ions, Sr2+ and Ce(IV). [ABSTRACT FROM AUTHOR]

As an indispensable element in the field of nuclear energy, uranium (U (VI)) is widely concerned because it is abundant and easy to obtain from seawater. Herein, we report a promising dual-template strategy to prepare heteroatom-doped carbon materials with hierarchical micro−/ meso −/macroporous from low-cost biomass precursors. The carbon materials with hierarchical porosity nitrogen/oxygen are synthesized through freeze-drying, high-temperature thermal treatment and subsequent HF etching treatment by in-situ growth of SiO 2 on the precursor with ethyl silicate as silicon source and introduction of ZnCl 2 as hard template and starch/ammonia as carbon and nitrogen source. Based on the advantages of three-dimensional interconnected hierarchical porous heteroatom doping, the electrosorption capacity reaches 67.25 mg/g, and the removal efficiency is as high as 98.45%, when the initial UO 2 (NO 3) 2 concentration is 80 mg/L in capacitive deionization. The isothermal adsorption of nitrogen doped hierarchical porous carbon (NHPC) is consistent with the Langmuir model, with a maximum electrosorption capacity of 152.43 mg/g, good cycle stability and high charge efficiency (energy consumption is only 0.77 kg-U kWh−1). Fascinatingly, the initial UO 2 (NO 3) 2 concentration is 80 mg/L and it also has a high adsorption capacity in 3.5 wt% NaCl solution, and the U (VI) removal efficiency could reach 42.5% after 8 h of continuous adsorption, with high selectivity. The prepared adsorbent NHPC shows good selectivity for U (VI) in the solution of 11 metal ions co-existing, and the effective selectivity K d value of U (VI) is 1620.84 mL/g. Finally, X-ray photoelectron spectroscopy analysis reveals that in addition to Coulomb interaction and chelation during the adsorption process, there is also a synergistic effect of the conversion of U (VI) to UO 2 under electric drive to improve the adsorption capacity of U (VI). • Dual-template synthesis of biomass-derived hierarchical porous heteroatom-doped carbon materials. • The removal efficiency of the NHPC electrode for U (VI) in 3.5 wt% NaCl solution is 42.5%. • The synergistic effect between UO 2 2+ and NHPC through coulomb interaction and reduction reaction makes it selective for UO 2 2+. [ABSTRACT FROM AUTHOR]

[Display omitted] • A low-carbon strategy was proposed for discarded mask recycling. • High Cr(VI) removal (358.68 mg g−1) was achieved using low-cost CPM/PDA/PPy. • Excellent desalination performance was obtained via capacitive deionization. • It has shown excellent reusability in Cr(VI) adsorption and desalination. The global mask consumption has been exacerbated because of the coronavirus disease 2019 (COVID-19) pandemic. Simultaneously, the traditional mask disposal methods (incineration and landfill) have caused serious environmental pollution and waste of resources. Herein, a simple and green mass-production method has been proposed to recycle carbon protective mask (CPM) into the carbon protective mask/polydopamine/polypyrrole (CPM/PDA/PPy) composite by in situ polymerization of PPy. The CPM/PDA/PPy composite was used for the removal of Cr(VI) and salt ions to produce clean water. The synergistic effect of PPy and the CPM improved the removal capability of Cr(VI). The CPM/PDA/PPy composite provided high adsorption capacity (358.68 mg g−1) and economic value (811.42 mg $−1). Consequently, the CPM/PDA/PPy (cathode) was combined with MnO 2 (anode) for desalination in CDI cells, demonstrated excellent desalination capacity (26.65 mg g−1) and ultrafast salt adsorption rate (6.96 mg g−1 min−1), which was higher than conventional CDI cells. Our work proposes a new low-carbon strategy to recycle discarded masks and demonstrates their utilization in Cr(VI) removal and seawater desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • The universal low carbon mass loading was used in capacitive deionization (CDI) for efficient deionized (DI) water production. • Partial desalination performance weakened with increasing carbon mass loading. • CDI cells using YEC-8–5.81 as electrodes produced DI water with a low conductivity of 1.89 μS/cm. • Carbons with a suitable micro- meso pore distribution and high specific capacitance may be a better choice. • 82.2% DI water recovery was achieved under stopped flow (SF) discharge mode. High-purity deionized (DI) water can be widely used in high-end manufacturing fields, but its efficient and energy-saving production is a huge challenge. Here, simple carbon mass loading control was developed for efficient DI water production via advanced capacitive deionization (CDI). Supercapacitor carbon (YEC-8) electrodes with diverse mass loading of 2.50, 5.81, 12.63 and 24.72 mg/cm2 were prepared for desalination. As expected, YEC-8–2.50 acquired the optimal CDI performance. High mass loading of 12.63 and 24.72 mg/cm2 not only caused an overt property drop but also serious wasted materials. Competitively, YEC-8–5.81 achieved a similar volumetric adsorption capacity (VAC) to YEC-8–2.50 as well as made up for the lack of total mass of YEC-8–2.50 and the resultant solution conductivity was as low as 1.89 μS/cm (grade III DI water). This strategy has been successfully extended to other carbon materials and carbons with suitable micro- meso pore distribution and high specific capacitance may be a better choice. Besides, the reverse effect of acetylene black (AB) mass on desalination was verified. To gain a high water recovery (W R), stopped flow (SF) discharge was introduced and realized a high W R of 82.2 %. Meanwhile, cycling tests indicated its splendid cycling stability. This study provides a universal direction for using low mass loading strategy for efficient DI water production. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • A pilot-scale MCDI system was designed for ammonia recovery from municipal wastewater. • Different working conditions were optimized for ammonia recovery. • Competitive adsorption between Ca2+, Mg2+ and NH 4 + were discussed. • The MCDI system showed high stability in long-term operation. • MCDI showed preferential electrosorption of NH 4 + in short adsorption periods. With the depletion of energy, renovation of wastewater has attracted wide attention around the world, among which the recovery of ammonia has also been an ongoing topic. Membrane capacitive deionization (MCDI) has emerged as a promising technology for nutrient removal and recovery. However, limitations of both scale-up and treatment of practical wastewater still restrict its real application. This study aims to investigate the feasibility of ammonia removal from real wastewater by MCDI on a pilot scale. The MCDI module used in this study was expanded to a 2-unit facility (15 pairs of electrodes per unit). Firstly, synthetic wastewater was used as feed water to optimize different kinds of operating parameters, including applied voltage (0–2.5 V), flow rate (7–30 L/h), and initial concentration (20–100 mg/L). Further experiments investigated the competitive adsorption performance under complex inflow conditions. Results indicated that the presence of co-existing cations significantly reduced the removal efficiency and adsorption capacity of ammonia. With the same inflow concentration, the removal efficiency of NH 4 +, Mg2+, and Ca2+ was 39.12 ± 5.31%, 47.56 ± 2.68%, and 33.33 ± 1.90% respectively. The interplay of initial ion concentration, charge valence, and hydrated radii led to the different electro-sorption performances. Subsequently, practical municipal wastewater after the up-concentration of organics was used as feed water to evaluate the feasibility of the pilot-scale MCDI. Under the optimized condition, a long-term experiment was carried out for 15-day to deal with actual wastewater. Besides, ion removal performance, the energy consumption, and desorption efficiency were also analyzed. The system maintains a stable removal efficiency for all cations, with low energy consumption (1.16 kWh/m3) and high desorption efficiency (around 90%). Overall, the results of this study posed the MCDI process as a potential approach to ammonia removal and recovery from municipal wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • HBC was synthesized via a "sacrifice template" method and applied in CDI. • The salt adsorption capacity was 28.06 mg g−1, the ASAR was 1.56 mg g−1 min−1. • Hollow bowl-like structure and N-doped 3D carbon reached high ion removal capacity. As a bright technology for desalinating brackish water, the desalination ability of capacitive deionization (CDI) has been limited by the electrode materials. However, it was still a challenge to adjust the construction of CDI electrode material to improve the salt removal ability. Here, nitrogen-doped hollow bowl-like carbon (HBC) has been successfully constructed in ZIF-8 by facile templating approaches. Physical measurements displayed that HBC had a hollow bowl-like structure, a certain number of nitrogen-containing groups and high specific surface area (1244 m2 g−1). These unique features made HBC have high capacitance (210.7F g−1), remarkable cycle stability and low charge transfer resistance in electrochemical double layer capacitors, indicating its promising application in CDI desalination. Due to the abundant ion accumulation active sites and rapid ion diffusion of HBC materials, provided by unique characteristics of regular hollow bowl-like structure, microporous dominated structure, interconnected channels and nano-scale wall thickness, HBC showed high salt removal ability of 28.06 mg g−1 with 1.2 V in 0.5 g L-1 NaCl solution. Besides, HBC exhibited excellent average salt ion adsorption rate (1.56 mg g−1 min−1) and initial salt adsorption capacity of 90% after 20 cycles. [ABSTRACT FROM AUTHOR]

• Adsorption mechanisms were found to be both ion exchange and surface adsorption. • The isotherms were better fitted using Freundlich model. • KZTS-NS showed fast kinetics and high adsorption capacity and selectivity for Co2+. • A DF of Co2+ as high as 1176 was obtained in tap water using a CTA-F-MF process. The removal of radioactive Co2+ from aqueous solutions is a critical issue because it is highly toxic and hazardous to humans. Metal sulfides are promising materials for the removal of toxic ions; however, studies on the adsorption of Co2+ by this class of adsorbents as well as their adsorption mechanisms and practical application in complex natural water matrixes are limited. To fill this knowledge gap, in this study, a layered K/Zn/Sn/S metal sulfide nanosheet (KZTS-NS) was employed as an adsorbent for Co2+ removal from aqueous solutions. Besides ion exchange, the mechanism of surface adsorption by forming a Zn 0.76 Co 0.24 S composite was found when initial Co2+ concentration was higher than 20 mg/L, which was reported for the first time in layered metal sulfides. The Co2+ adsorption performance of KZTS-NS was systematically studied using batch methods in deionized water, including isotherms, kinetics, influential factors, and selectivity. The results indicated that KZTS-NS exhibited a high adsorption capacity, rapid kinetics, and strong selectivity in a wide pH range. Furthermore, tap water was used as a complex natural water matrix, and the practical application of KZTS-NS in a bench-scale countercurrent two-stage adsorption-flocculation-microfiltration (CTA-F-MF) process for Co2+ removal from tap water matrix was demonstrated. The CTA-F-MF process significantly enhanced the performance of the adsorbent, thereby achieving ultrahigh Co2+ removal (decontamination factor of up to 1176). This study not only provides a new insight into the adsorption of Co2+ by layered metal sulfides, but also forms the basis to enable the practical application of metal sulfides in the field of radioactive wastewater treatment. [ABSTRACT FROM AUTHOR]

• Porous carbon nanoflakes were prepared by carbonizing xylose with KHCO 3. • Porous carbon nanoflakes exhibited a satisfactory salt adsorption capacity. • Porous carbon nanoflakes have great potential for large-scale application. Capacitive deionization (CDI) works by using the electrical double layer on various materials including nanoporous carbons to separate ions from saline water. To help realize industrial application, there has been an increasing interest in the exploration of carbon materials from low cost, eco-friendly and abundant biomass for CDI to align with the demands of sustainable development strategies. Herein we report pyrolysis of xylose with KHCO 3 to prepare hierarchically porous carbon nanoflakes which display a satisfactory salt adsorption capacity of 16.29 mg g−1. This novel strategy can design highly efficient carbon materials from naturally-developed biomass materials with its low preparation cost, environmentally friendliness and superior desalination performance. Our xylose-derived hierarchically porous carbon nanoflakes are promising for potential industrial application for CDI. [ABSTRACT FROM AUTHOR]

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

• A biocharcoal-based electrode was used to improve Cl− and Cr3+ removal. • The adsorption and regeneration performance of the KOBC15 were analyzed and evaluated. • Optimization of operation parameters for the CDI system was performed. Red oak biocharcoal, a novel electrode material that is inexpensive and highly conductive, was used for capacitive deionization (CDI) to simultaneously remove Cl− and Cr3+ from leather processing wastewater. The results showed that both the carbonization temperature and time played important roles in reducing the resistivity (ρ) of biocharcoal. Additionally, at 1000 °C and 3 h, the ρ value was reduced from 4.68 to 1.19 Ω·cm after the addition of Fe 2 O 3. KOH impregnation enhanced the desalination capacity of the biocharcoal electrodes by increasing the specific surface area and hydrophilicity. Under the optimal operating parameters (voltage of 1.8 V, flow rate of 10 ml/min and electrode spacing of 2 mm), the KOBC15 electrode exhibited a maximum adsorption capacity of 13.79 mg/g. After 10 cycles of CDI system operation, the removal rates of Cl− and Cr3+ reached 86.7% and 100%, respectively, in simulated leather processing wastewater. This work provides new ideas and methods for the treatment of high-salinity wastewater. [ABSTRACT FROM AUTHOR]