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• Structure evolution features of LDHs precursors with pH was investigated. • Role of pH on activating the performance of LDHs type adsorbents was concluded. • Precipitative formation mechanism of LDHs adsorbents was firstly proposed. Aluminum-based adsorbents, simply prepared by eluting the lithium-aluminum layered double hydroxide precursors with deionized water, is the only industrialized adsorbents for selectively separating Li+ from saline brines. Taking the roles of lattice and surface Li+ active sites on its performances into consideration, influence of ending pH modulating on prominently improving the adsorbing capacity and stability of aluminum-based adsorbents prepared by precipitation method is initially investigated. As experimentally evidenced that, the maximum desorption amount of Li+ at the eluting stage should be controlled to around 20 mg/g Li+ rather than thoroughly removed to effectively avoid the topotactic solid-phase transformation from adsorbent to α-Al(OH) 3. As-prepared adsorbents not only has high adsorption capacity up to 8.4 mg/g in 400 ppm LiCl solution, but also owns unique self-healing ability, thus promising the excellent cycling stability. It is firstly proposed that the formation of the layer-structured precursor by precipitation method is well in accordance with the three-step formation mechanism and pH modulating mainly contributes to the anions exchange between solution Cl- and interlayer OH–. This study experimentally proves the importance of pH adjusting for preparing high performance lithium adsorbents by precipitation method, which is very significant and important for effectively extracting lithium resources from the complicated multi-component liquid minerals. [ABSTRACT FROM AUTHOR]

• K 2 FeO 4 is first utilized for the solid-phase oxidation of pitch by a high-energy ball mill. • The solid-phase reaction mechanism involving in oxidation and condensation was revealed. • Advanced pitch-based porous carbon (H-CBPF) was prepared by a solid–liquid synergistic strategy. • The synergistic effect improves both the porous geometric configuration and O content of H-CBPF. • H-CBPF delivers an excellent salt adsorption capacity and a superior charge efficiency. To address limited desalination capacity and insufficient charge efficiency for carbon materials in capacitive deionization (CDI), a solid–liquid synergistic oxidation strategy of potassium pertechnetate (VI) for pitch was proposed to construct porous carbon with a reasonable pore structure and high reactive surface. On the one hand, K 2 FeO 4 is first utilized for the solid-phase oxidation (SPO) of pitch by a high-energy ball mill, introducing rich oxygen-containing groups such as ether bonds. Meanwhile, dehydro-condensation reactions occurred during SPO, resulting in the formation of the oxidized pitch with a high degree of condensation. Importantly, the pyrolysis yield of the oxidized pitch is as high as 46.9 % at 800 °C, almost twice that of the pristine pitch, meaning that the oxidized pitch with high polymer degree and rich C-O bridge bonds facilitates the carbon fixation and emission reduction during carbonization. On the other hand, the self-oxidation of K 2 FeO 4 in aqueous solution forms bifunctional activators (KOH and Fe(OH) 3) for the preparation of pitch-based porous carbon. Benefiting from the crosslinking structure of oxidized pitch and the multi-effective activation, the prepared porous carbon (H-CBPF) exhibits a robust layered stacking topology with a high surface area and oxygen content. Thereby, it can deliver an excellent salt adsorption capacity (SAC) of 22.1 mg g−1 with an average desalination rate of 1.89 mg g−1 min−1 and a high charge efficiency of 85 % at 1.2 V in 500 mg L-1 NaCl solution. This work opens up a green and economical route for the preparation of pitch-derived porous carbon for high-performance CDI. [ABSTRACT FROM AUTHOR]

• A novel capacitive deionization with a three-phase architecture (T-CDI) was proposed. • Cathodic oxygen reduction was enhanced in T-CDI without affecting desalination. • SAC value and H 2 O 2 generation were 14.91 mg/g and 25.55 mg/L, respectively. • Simultaneous desalination and organics control was achieved by T-CDI/UV. • Applicability of T-CDI in long-term operation was investigated. Cathodic oxygen reduction, as a Faradaic side reaction, has been proven to be thermodynamically favorable for H 2 O 2 generation in capacitive deionization (CDI), which may provide a greener manner for organics control alongside desalination. However, the low levels of dissolved oxygen (DO) in saline water and its potential Faradaic degradation of carbon-based electrodes limit the H 2 O 2 generation in the conventional CDI (C-CDI). Herein, a novel three-phase CDI architecture (T-CDI) was proposed to simultaneously achieve stable desalination and supplementary H 2 O 2 generation. Unlike C-CDI architecture, T-CDI was open-ended at the cathode side, where porous nickel foam was used as current collector and air diffusion layer. Accordingly, a stable gas–liquid-solid three-phase interface was created inside the cathode, thus enhancing the diffusion and utilization of atmospheric air and preventing the damaging effects of excessive DO on the electrode. A stable electrosorption and electrocatalysis performance for T-CDI was obtained by regulating electrode hydrophilic-hydrophobic properties, comparing with other CDI configurations, and altering operating conditions. The salt adsorption capacity and H 2 O 2 accumulative concentration were 14.91 mg/g and 25.55 mg/L, respectively. Furthermore, the simultaneous desalination and organics control in T-CDI were investigated with the assistance of UV irradiation (T-CDI/UV). When treating NaCl and sulfamethazine (SMR) mixture solution, T-CDI/UV significantly reduced the irreversible electrode organic fouling and improved the desalination stability. Additionally, the potentially hazardous SMR was effectively removed alongside desalination. Finally, the long-term operation of T-CDI demonstrated that the generated H 2 O 2 cannot induce an additional substantial deterioration in desalination stability. The techno-economic assessment showed T-CDI was economically competitive compared with C-CDI. This study provides insights into the synergy of non-Faradaic and Faradaic processes and further diversifies the application of CDI in water treatment. [ABSTRACT FROM AUTHOR]

• A system based on membrane rejection and electrochemical technique was developed. • MIL-101 endowed the mixed matrix membranes (MMMs) with phosphate adsorption capacity. • MMMs of capacitive deionization capacity was prepared with porous carbon cloth. • The conductive MMM performed both high selectivity and permeability. The great potential of ultrafiltration (UF) membranes for phosphate rejection has been challenged by the selectivity-permeability trade-off. Here, we propose a filtration system based on a novel dual-layer UF mixed matrix membrane (MMM) with a capacity for capacitive deionization (CDI), which was fabricated by incorporating NH 2 -MIL-101 into a polyethersulfone (PES) polymer matrix and the in-situ combination of carbon cloth (CC). The MMM exhibited an improved porosity of 85.52%, a declined water contact angle of 53.25°, and a 5.7% increase in water permeability in comparison to those of the PES membrane due to the hydrophilic and mesoporous NH 2 -MIL-101 particles. While incorporating the CC provided the non-conductive PES polymer with high electroconductivity. As an electrode, the CC/MMM exhibited a relatively high permeance of 424.63 L/h MPa m2, good antifouling performance, and remarkable phosphate rejection that reached 100% during the 2-h filtration period in the electrically-enhanced dead-end filtration cell. The removal capacity of the cell exceeded 22.51% and 74.0% for the energized CC/PES membrane and uncharged CC/MMM, respectively, due to the superior phosphate adsorption ability of NH 2 -MIL-101 and enhanced deionization capacity due to the electric field. UF MMM separation coupled with the electrochemical technique exhibited great potential to enhance the selective rejection of phosphate ions at low levels, while maintaining high membrane permeability and shortening the treatment time required by the CDI technique. [ABSTRACT FROM AUTHOR]

[Display omitted] • Charging time plays a decisive role in CDI performance improvement. • UQ analysis quantitively provides guidance for CDI optimization. • The pore distribution and connectivity are highlighted. Capacitive deionization (CDI) is considered to be one of the most promising technologies to deionize water with low/medium concentration. Great attention has been paid to improve its performance by optimizing electrode architectures and operation conditions. However, no guidelines are built for developing such strategies due to the nonlinear impact of the parameters concerning electrodes and operations. Therefore, our work quantitatively reveals the influence of some key parameters involving electrode characteristics, operation conditions and ion properties using the statistical analysis based on uncertainty quantification. We find the porosity solely has a small influence on all the performance metrics. But the pore might play a significant role by the pore size distribution and connectivity that greatly determine the effective diffusion coefficient of salt ions. The high diffusion coefficient obviously raises the salt adsorption by facilitating ion transport, which also reduces the energy consumption while most of the consumed energy could even be recovered. The current exerts an opposite influence by shortening the charging period in the constant current (CC) mode. The salt concentration in the inflow water increases the adsorption capacity but decreases the removal efficiency. The decreased removal efficiency requires less external energy, enabling the usage of CDI as an economic pre-treatment unit. We highlight the ion transport resistance and its influence on CDI performance by acting upon charging time in the CC mode. We also suggest the application of the constant voltage mode to the low-salinity wastewater instead of the CC mode due to the high resistance. Our work addressed the importance of proper electrode and operation condition for high desalination performance and energy efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen-doped porous carbon is synthesized via a dual-salt template approach. • The carbon exhibits high ion adsorption capacity and ultrafast adsorption rate. • Ion adsorption proceeds via electrocapacitive and pseudocapacitive mechanisms. • The electrocapacitive mechanism plays a dominant role in the ion adsorption. Porous carbon materials hold tremendous potential for capacitive deionization (CDI). However, realizing high specific surface area (SSA), suitable pore size distribution, and hierarchical porosity in carbons with facile and sustainable techniques is still challenging. In this work, we prepare hierarchical porous carbons (HPCs) with high SSA, abundant pore structures, and N-self doping via a versatile and sustainable modified salt-template approach. The optimized electrode gives a high SSA of 1639.9 m2/g, a large pore volume (2.7 cm3/g), and hierarchical porous structures (micro-meso-macro pores). For applications, the symmetric CDI electrode assembly delivers a salt adsorption capacity (SAC) of up to 17.67 mg/g in a 500 mg/L NaCl at 1.2 V together with ultrafast salt adsorption kinetics. We systematically study their associated desalination mechanism by combining several electrochemical experiments with the in-situ Raman spectroscopy technique, which revealed that the total salt storage is from the synergistic effect of both electrical double-layer (EDL) storage and pseudocapacitive mechanisms, with the EDL storage being dominant. This work paves the way to design economical and eco-friendly porous carbon materials for high-performance CDI desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] • S-doped ultra-microporous wood carbon (SUMW) composite was prepared by one-step chemical activation. • We proposed E pzc -based ion-selective electro-adsorption mechanism. • The selective coefficient of SUMW electrode of NO 3 – over SO 4 2− was reached 32, • The adsorption capacity of the designed material reached up to 637 μmol/g. Capacitive deionization (CDI) technology is promising for selective removal of target ions from various sewages. However, the low electro-adsorption capacity and poor selectivity in the complex sewage system highly restrict its practical application. Potential of zero charge (E pzc) is the external circuit applied potential as the electrode material exhibiting no ion electro-adsorption from the electrolyte. Although E pzc shows a great prospect for regulating the electro-adsorption performance of the electrode, how to use it to achieve selective electro-sorption remains challenging. Herein, we demonstrate a Sulphur (S) doped ultra-microporous (∼0.7 nm) free-standing wood carbon electrode by one step chemical activation, which exhibits different E pzc values in nitrate or sulphate solution due to the unique S-doped ultra-microporous structure. Accordingly, a fantastic selectivity for NO 3 – over SO 4 2− (S N O 3 - / SO 4 2 - =32) was achieved as the applied voltage window ranges from 0.12 V (E pzc -NO 3 –) to 0.43 V (E pzc -SO 4 2−). In addition, the adsorption capacity of the designed material reached up to 637 μmol/g, which is much higher than the maximum value ever reported (∼200 μmol/g). 2000 mL Yellow River water was treated by our tandem CDI cell device through recycling charge and discharge ten times. As expected, the concentrations of NO 3 – ions in the Yellow River water were dramatically reduced from 152 mg/L to about ∼ 35 mg/L after treated with the tandem CDI cell device, which demonstrates the excellent practical application prospect. [ABSTRACT FROM AUTHOR]

• The presence of coordinated water was beneficial for ion diffusion within CuHCF. • Chelators and Na+ in precursors reduced zeolitic and/or coordinated water in CuHCF. • Lower water content increased Na+ removal capacity but sacrificed stability. • CuII/CuI redox couple activation increases when controlling chelators in precursors. • Activation of reversible CuII/CuI redox couple contributed to BDI cycling stability. Prussian blue analogues are being explored as electrode materials for electrochemical desalination of saline water in battery-type electrode deionization systems and hybrid capacitive deionization systems due to their open framework crystal structure that provides selective adsorption of multiple cations, high theoretical sodium adsorption capacities, and low costs. However, poor electronic conductivity and instability (dissolution) prevents the use of these materials for long-term desalination applications. To understand how synthesis conditions might improve the properties of copper hexacyanoferrate (CuHCF) powders relative to sodium ion adsorption capacity and cycle life, the co-precipitation process was investigated using multiple common synthesis strategies that included addition of chelators and sodium salts as well as different concentrations and oxidation states of precursors. Smaller crystallite sizes (<35 nm) and lower structural water contents increased the initial sodium removal capacity to 53.2 mAh/g from 40.4 mAh/g (control), but also reduced cycling stability in long-term operation (20–55% retention over 100 cycles). The trade-off in stability is thought to be a consequence of structural water facilitating ion diffusion within the material. Adding chelators as precursors led to a highly reversible CuII/CuI redox couple that increased the stability of the FeIII/FeII redox couple in BDI cycling performance (79.4% retention over 100 cycles). [ABSTRACT FROM AUTHOR]

• A porous nanofiber membrane with dense distribution of La nanorods was prepared. • Exceptional high utilization ratio of La (0.98). • LPS was easily separated from solution. • The LPS can reduce total phosphorus to less than 10 μg/L in natural lake water. • Phosphate was effectively captured in a wide pH range of 4–10. As phosphate is one of the key causes of water eutrophication, its removal from aquatic ecosystems is essential. Adsorption methods have been widely used to remove phosphate from water bodies. However, most of the adsorbents are unstable and difficult to separate from solution. In this paper, we used a simple electrospinning method to prepare a new, well-dispersed, lanthanum (La)-based porous polyacrylonitrile nanofiber (LPS) with more active sites, which improve its phosphate removal efficiency. The maximum phosphate adsorption capacity on LPS was 218.5 mg P/g (La) (50.4 mg P/g). After complete adsorption, the P/La molar ratio on LPS was 0.98. After 48 h of oscillation, the leakage of La from LPS in deionized water was only 74 μg/L, effectively ruling out secondary pollution of the water-body. Moreover, unlike most adsorbents, LPS has the advantage that it can be readily isolated from water. After treatment with LPS, the total phosphorus (TP) of a water sample from Yangzonghai Lake (Yunnan, China) was reduced to 4.2 μg/L, a value lower than the concentration threshold of eutrophication (10 μg/L) set by the United States Environmental Protection Agency (USEPA) and the first category of the surface water environmental quality standard (10 μg/L) set by China for lakes and reservoirs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Developed a carbonized MIP-202/MXene (CMM) for selective electrosorption of U(VI). • MXene provides pseudocapacitance/intercalation effect and conductive base. • Two composite structures were observed during preparation of CMMs. • The CMM electrode exhibited excellent adsorption capacity and selectivity for U(Ⅵ). As the key element in the nuclear industry, uranium (U) has been widely concerned for its stable acquisition and efficient recycling. Capacitive deionization (CDI), which known as a seawater desalination technology, has shown great potential for uranium-adsorption. However, the poor selectivity restricts the application of CDI in uranium extraction. In this work, a carbonized MIP-202/MXene (CMM) composite was developed for highly efficient selective electrosorption of U(VI) from multi-ionic water. The uniformly decorated MIP-202 can prevent MXene from aggregation and provide rich pore structures, large specific surface area and additional nitrogen source for the efficient electrosorption of U(VI). With the addition of MXene nanosheets, a conductive network was introduced into the CMM and improved mechanical robustness of material to facilitate rapid charge transfer at the interface. As a result, the CMM electrode exhibited a maximum adsorption capacity of 582.46 mg g−1 calculated from Langmuir model and a removal ratio of 89.1% at 1.2 V in UO 2 2+ solution. The selectivity adsorption of CMM for UO 2 2+ can reach 92.3% when treated with multi-ionic solution. Besides, there is an interesting fact that the decreased ratio of added MXene can got a higher adsorption capacity, which may cause by the two composite structures formed when the mixing ratio changed. Overall, the excellent conductivity, high adsorption capacity and selectivity make CMM a promising electrode in CDI for efficient extraction of uranium from water. [ABSTRACT FROM AUTHOR]

A self-supported MoS 2 /CoS 2 @TiO 2 nanotube (TNT) hybrid electrode was fabricated by an in-situ hydrothermal process-assisted growth strategy, which achieved a significantly high gravimetric Na+ adsorption capacity and excellent regeneration performance. It also demonstrated amazing removal efficiencies close to 90% for various heavy metal ions (i.e., Fe3+, Cr3+, Cd2+, Pb2+, Cu2+ and Ni2+), revealing its great potential for wastewater purification. [Display omitted] • A self-supported MoS 2 /CoS 2 @TNT hybrid electrode was constructed. • The electrode achieved a gravimetric Na+ adsorption capacity of 44.22 mg g−1. • The electrode exhibited excellent regeneration performance and removal rates. • The electrode also realized removal efficiencies up to 90% for heavy metal ions. Recently, the rational design and construction of graphene-like layered transition-metal disulfides (TMDs) with chemical and physical superiorities to act as capacitive desalination (CDI) electrodes for water purification have attracted increasing interest worldwide. Herein, an advanced self-supported MoS 2 /CoS 2 @TiO 2 nanotube (TNT) hybrid electrode was grown on a TNT scaffold by a hydrothermal process-assisted in-situ growth strategy, and an asymmetric CDI cell was constructed with the as-fabricated MoS 2 /CoS 2 @TNT and commercial AC electrodes as cathode and anode, respectively. Benefiting from the effective structural feature (i.e., fully open nanosheet-assembled flowers and hierarchical pore alignment) and synergy effect of metal-like CoS 2 , state-of-the-art MoS 2 and TNTs with an efficient charge "superhighway", the MoS 2 /CoS 2 @TNT electrode achieved a significantly high gravimetric Na+ adsorption capacity of 44.22 mg g−1 in a 600 mg L−1 NaCl solution at 1.2 V. Moreover, the hybrid electrode possessed excellent regeneration performance with a capacity retention of nearly 100% even after 20 cycles. Most notably, such electrode also demonstrated amazing removal efficiencies close to 90% for various heavy metal ions (i.e., Fe3+, Cr3+, Cd2+, Pb2+, Cu2+ and Ni2+), revealing its great potential for wastewater purification. [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] • 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]

• A novel core-shell LiX@ZIF-8 composite has been constructed. • Single layer showed the highest CO 2 adsorption capacity in highly humid flue gas. • The whole synthesis is conducted in a green, energy-saving and economical way. • LiX@ZIF-8-I could maintain excellent cycle hydrothermal stability in humid flue gas. Decreased adsorption capacity and complicated synthetic procedures with expensive or toxic raw chemicals are two major challenges faced by physical adsorbents for carbon capture in highly humid flue gas. In this study, a novel core-shell composite using LiX with high CO 2 adsorption capacity as core and superior hydrophobic ZIF-8 as shell is proposed. The overall synthesis process is conducted under ambient temperature and pressure by adopting deionized water as green solvent. Experimental results show that the adsorption performance of the core-shell structure is enhanced along with the improvement of hydrophobic performance in highly humid flue gas. The performance of ZIF-8 shells from monolayer to multilayers (up to three layers) are investigated. In particular, LiX@ZIF-8-I with single layer of ZIF-8 exhibit the highest CO 2 adsorption capacity of 1.73 mmol/g in humid flue gas. The monolayered adsorbent not only exhibit superior hydrophobicity and CO 2 adsorption capacity but also maintain excellent hydrothermal stability in humid flue gas over 50 adsorption/desorption cycles, which promote its application to practical in a green, energy-saving and economical way. [ABSTRACT FROM AUTHOR]