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Capacitive deionization-based technologies such as flow electrode capacitive deionization (FCDI) have shown great promise for desalination and resource recovery, but simultaneous desalination and resource recovery using one FCDI device has thus far received minimal attention. In this study, a novel four-chamber FCDI coupled with a monovalent cation exchange membrane (MCEM) was proposed to realize simultaneous desalination (including water softening) and ammonia-rich solution production from coal gasification gray water (CGGW). The results showed that under optimal conditions, up to 91.2 ± 0.1 % ammonia nitrogen, 88.9 ± 1.0 % Ca2+, and 92.6 ± 5.5 % total organic carbon of real CGGW were removed by the desalination chamber. Furthermore, NH 4 + passed through the MCEM and entered the recovery chamber, while Ca2+ was effectively blocked from entering the recovery chamber by MCEM. Thus, a multipurpose ammonia-rich solution with purity of 98.0 % was obtained. The process was superior since two typical FCDI cells are needed to realize water softening and recover ammonia-rich solutions. The mechanistic insights into the proposed four-chamber FCDI coupled with MCEM can be expanded to other simultaneous desalination, ion separation and recovery processes. Thus, the four-chamber FCDI is a promising technology for simultaneous desalination and resource recovery with the advantages of being chemical-free, capital efficient and operable. [Display omitted] • A novel four-chamber FCDI was proposed to treat CGGW. • Simultaneous water softening and selective ammonia nitrogen recovery were realized. • The separation of NH 4 + /Ca2+ was realized by a monovalent cation exchange membrane. • Up to 91.2 % ammonia nitrogen, 88.9 % Ca2+, and 92.6 % TOC of real CGGW were removed. • The purity of the obtained ammonia-rich solution reached 98.0 %. [ABSTRACT FROM AUTHOR]

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

Faradic capacitive deionization (FDI), as an emerging research branch of capacitive deionization (CDI), has shown its great potential to relieve global water stress owing to its high desalination capacity/efficiency, flexible scale, and zero secondary pollution characteristics. However, the slow desalination kinetics and poor cyclic stability of the anion-capturing electrode of current FDI systems greatly limit its practical application. Herein, we proposed a strategy of interweaving FeOOH nanospindle inside the 3D network structure of carbon nanofiber aerogel to construct a 3D network structure (CNFAs@FeOOH) and further used it as a chloride capture electrode for FDI. As a result, the FDI system equipped with CNFAs@FeOOH enjoys excellent desalination performance with an ultrahigh desalination rate of up to 0.33 mg g−1 s−1. More importantly, the CNFAs@FeOOH-based FDI system enjoys excellent cycling stability with no significant decrease in 100 cycles and only 17.85 % decrease in 200 cycles. Carbon nanofiber aerogel interweaved FeOOH was introduced as chloride-insertion electrodes for faradic capacitive deionization, achieving durable and fast desalination. [Display omitted] • Carbon nanofiber aerogel interweaved FeOOH (CNFAs@FeOOH) was used as the anode of faradic capacitive deionization (FDI). • The 3D network structure of CNFAs@FeOOH prevents aggregation between FeOOH and enables rapid charge/electron transfer. • The open porous structure of CNFAs@FeOOH allows flow-through water mode to accelerate mass transfer. • The CNFAs@FeOOH-based FDI system displays an ultrahigh desalination rate with excellent long-term stability. [ABSTRACT FROM AUTHOR]

Flow electrode capacitive deionization (FCDI) is a new ion removal technology with sustainable deionization performance. However, the interface resistance has a significant impact on ions migration in FCDI. We therefore introduced a novel FCDI device that incorporated a layer of carbon felt as an "ionic capacitor" between the flow electrode and the ion exchange membrane, termed CF-FCDI. Mechanism exploration results revealed that the addition of carbon felt reduced device resistance, shorten electron transfer pathways, improved charge efficiency, and increased ion migration rate. Experimental results demonstrated that the improved CF-FCDI device achieved 44 % higher desalination rate compared to traditional device. In addition, long term operation experiments confirmed the stability of CF-FCDI device, highlighting its potential as a viable desalination solution. The findings of this study provided valuable insights for further development of FCDI and offered a promising solution for its applications such as seawater desalination. [ABSTRACT FROM AUTHOR]

As water scarcity intensifies, the quest for developing sophisticated electrode materials with adjustable configurations, complex structures, and developed desalination performance garners important interest. Prussian Blue (PB) and its analogs (PBAs), owing to their cost-effectiveness, uncomplicated synthesis, innate open framework, and modifiable composition, have elicited considerable recognition. Herein, the paper provides a comprehensive overview and analysis of the advances made in capacitive deionization electrodes based on PB and PBAs. It commences by detailing the synthesis techniques, post-treatment processes, and derivatives of standard PBs and PBAs. Subsequent sections propose strategies to minimize auxiliary reactions in electrochemical processes, encompassing structural design, protective coatings, substitution, and the confinement effect. Subsequently, emphasis is placed on structures that have potential as electrode materials in applications such as desalination, heavy metal removal, resource recovery, and water softening. A summary of current achievements in the field is provided, alongside a critique of prevailing limitations and emergent challenges. As advancements in electrode materials continue to unfold, it aims to stimulate innovative ideas for utilizing PB and PBAs in environmental research, thereby catalyzing additional investigation into the desalination area. [Display omitted] • The preparation methods of advanced PB/PBAs electrode are discussed in depth. • The versatile applications of PB/PBAs electrode are discussed extensively. • The future orientation development of PB/PBAs in CDI is provided. [ABSTRACT FROM AUTHOR]

Energy-efficient and low-cost desalination of water continues to be a problem that society is facing. With the advances in nanotechnology, a variety of nanopore membranes have emerged for desalination. In particular, YX 2 nanopores (Y W, Mo, etc. and X = S, Se, Te, etc.) have been considered as promising membranes for water purification. In this work, we used a combination of high-throughput molecular dynamics simulations and machine learning to reveal the nanopore mass transfer mechanism and rationally design the YX 2 nanopore. The pore size and the charge of the pore mouth were found to be the main factors affecting water permeation and salt rejection, as discovered through the machine learning study. The physical-chemical analysis provides us with a deep understanding of the charge-governed mechanism on the desalination performance of YX 2 nanopores. It revealed that YX 2 nanopores with a conical shape and minimized pore charges could be ideal candidates for excellent desalination performance. Based on this, we designed the YX 2 pore with a specific charge distribution, which could achieve high water permeation with high salt rejection. Therefore, the combination of machine learning and high-throughput computation methods could aid in designing materials with excellent performance for desalination. • A combination of high-throughput computational and machine learning is developed • YX 2 nanopores with a conical shape and minimized pore charges could be ideal candidates for excellent desalination performance. • The importantance of pore size and the charge of the pore mouth were explored on affecting water permeation and salt rejection [ABSTRACT FROM AUTHOR]

Manganese dioxide (MnO 2) has been recognized for its high theoretical capacitance. Recent advancements highlight the potential of modulating the spin state of Mn to elevate charge transfer kinetics. Nonetheless, the specific relationship between Mn spin distribution and desalination efficacy, alongside the underlying mechanism, remains elusive. This study introduces the novel concept of half-disturbed spin desalination, elucidating its complex mechanism via the strategic induction of oxygen vacancies on the MnO 2 surface. Theoretical analyses reveal that electron transfer from the O p y (up) and p z (up) to the Mn d z 2 (up) orbitals alters MnO 2 's spin state from a symmetric low spin to an asymmetric high spin configuration. This transition disrupts spin up symmetry, bolstering dynamic processes and diminishing the ion diffusion energy barrier. Consequently, oxygen vacancy-enriched MnO 2 (V O -MnO 2) demonstrates an enhanced specific capacitance of 289 F g−1 at 1 A g−1. Remarkably, in the hybrid capacitive deionization (HCDI) process, it achieves a superior salt adsorption capacity (SAC) of 56.5 mg g−1 and a salt adsorption rate (SAR) of 2.5 mg g−1 min−1. This research pioneers the correlation between spin desalination mechanisms and spin state applications, paving the way for novel applications across diverse fields. [Display omitted] • V O -MnO 2 was synthesized by a simple method utilizing NaBH 4 as a reducing agent. • O vacancies cause electron flow from the O p y (up) and p z (up) to the Mn d z 2 (up). • The orbital rearrangement causes a shift from a low spin to high spin state in Mn. • V O -MnO 2 displays superior desalination performance. [ABSTRACT FROM AUTHOR]

Flexible devices have shown great application potential in portable and miniaturized devices. However, work on flexible electrodes for capacitive deionization (CDI) has not been well developed due to the issues of desalination property, processability, and availability under actual bending conditions. Herein, we constructed a kind of flexible lamellar MXene membrane by assembling Ti 3 C 2 T x sheets with both crumpled and perforated structures and studied their desalination performance in conventional planar and bent configurations. The crumpled and perforated features in Ti 3 C 2 T x (C-P-TC) nanosheets could optimize the in-plane and out-of-plane diffusion channels of the stacked samples, respectively, effectively improving the accessibility of membranes. As a result, the desalination performance of such C-P-TC electrodes was superior to that of those assembled from crumpled or perforated sheets alone. Significantly, this flexible C-P-TC electrode still showed excellent performance at real bend deformation, which possessed not only almost the same CDI capacity as the traditional planar configuration but also good cycling stability. This work not merely proposes an alternative strategy to improve the CDI performance of lamellar MXene electrodes by regulating the nanostructures of channels but also confirms their effective deionization ability under real bent state, greatly facilitating the potential use of flexible electrodes in miniaturized CDI devices. [Display omitted] • MXene sheets with crumpled and perforated structures are used to assemble membranes. • These lamellar membranes have abundant diffusion channels and well flexibility. • The membrane electrodes possess superior capacitive deionization performance. • Such flexible electrodes have excellent deionization ability under real bent state. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a potentially cost-effective method of desalinating brackish groundwaters though the technology has not yet been widely utilised for this particular application. Silicon (Si) is a common element in groundwaters which may cause problems due to its tendency to induce severe fouling of equipment used for water treatment. In this study we focus on the impacts of the presence of Si on the performance of CDI. A systematic evaluation procedure is proposed, which is used to distinguish the "dynamic" and residual Si scaling and the impacts of these types of fouling on desalination performance. Results show that Si has minimal influence on CDI performance within low concentration ranges (<0.5 mM). Sorption of deprotonated silicic acid species is largely avoided in CDI, which contributes to sustaining the removal of major ions and stable operation of the system. However, at high concentrations of Si (>2.0 mM), scaling was observed to form on the electrode surface, leading to noticeable deterioration in CDI electrode performance. The presence of ion exchange membrane in CDI (i.e. , membrane CDI or MCDI) can significantly alleviate Si scaling of the desalination system. Results of this study clearly demonstrate the scaling behavior of CDI and its derivatives when dealing with Si-laden water matrices, providing insights into the design and maintenance of CDI systems in practical applications. [Display omitted] • Impact of presence of Si on the performance of CDI and MCDI systems examined. • Si has minimal impact on CDI and MCDI performance at low concentrations (<0.5 mM). • Significant deterioration in CDI performance at Si concentrations >2 mM. • Presence of membranes in MCDI mitigates impact of Si, even at concentrations >2 mM. [ABSTRACT FROM AUTHOR]

The utilization of solar-driven interfacial desalination is widely regarded as a promising technological approach for mitigating the global water crisis. Existing solar interface evaporators often face limitations such as salt accumulation and oil waste liquid interference, impeding water supply channels and the efficient escape of interface water vapor, consequently diminishing the evaporation rate. This study proposes a novel approach by synthesizing a monolithic structure composed of carbon nanotubes (CNTs) and vertically arranged Al 2 O 3 fibers which are embedded in cellulose skeleton, achieved through the thermally induced phase separation (TIPS) method. The resulting hierarchically porous monolith exhibits high steam generation rate, remarkable superhydrophilic properties and underwater superoleophobicity, rendering it highly effective in salt tolerance and resistance against oil pollution. In particular, highly oriented Al 2 O 3 fibers form multiple thermal localization arrays and steam dissipation channels，complemented by interconnected hydrophilic skeleton that achieved strong synergy, enabling a stable and high evaporation rate of 1.98 kg m−2 h−1 and 2.06 kg m−2 h−1 in high salt concentration (10 wt%) seawater and oil-in-water (O/W) emulsion, respectively. This work contributes to the ongoing efforts in advancing next-generation solar vapor generators, aiming to enhance the sustainability and efficiency of freshwater production in response to the global water crisis. • A composite monolith doped with CNTs/Al 2 O 3 fibers was fabricated. • The capillary microchannels around Al 2 O 3 fibers guarantee efficient mass transfer. • The CNTs/highly oriented Al 2 O 3 fiber arrays synergistically facilitate evaporation. • The salt resistance and underwater superoleophobicity were concurrently enhanced. [ABSTRACT FROM AUTHOR]

The escalating global population growth, the aspiration for improved living standards, environmental concerns, and the rising focus on circular economy frameworks have collectively emphasized the imperative to recover resources such as nutrients, water, and energy. Despite the notable advantages and technological capabilities of capacitive deionization (CDI) systems, their potential remains largely untapped. This comprehensive review aims to synthesize and analyze the progress made in CDI systems for nutrient recovery. It concentrates on two vital wastewater nutrients: nitrogen (N) and phosphorus (P). The study explores both conventional and advanced CDI systems, including CDI, membrane capacitive deionization (MCDI), flow electrode capacitive deionization (FCDI), and hybrid capacitive deionization (HCDI). In three key areas, a detailed framework for recovering nitrogen, phosphorus, and both is provided: (1) process optimization, (2) innovative cell design, and (3) process development for effectively integrating CDI with complementary techniques, enabling simultaneous ion recovery and the production of value-added products. Additionally, future perspectives on CDI development and expansion for nutrient recovery are discussed in this review with an emphasis on aligning these efforts with circular economy goals. [Display omitted] • Faradic materials boost CDI for nutrient recovery. • Optimizing parameters crucial for high-efficiency nutrient recovery in CDI • CDI opens a highly efficient path for circular economy development. • CDI exhibits high ammonia recovery potential. • Combined N and P recovery shows cost-effective potential. [ABSTRACT FROM AUTHOR]

As food production dominates global freshwater consumption and nutrient discharge regulation tightens, the performance of novel technologies at applied scale needs to be studied to optimize water use and minimize environmental impact. Water reuse and the nutrient recovery from greenhouse wastewater were assessed utilizing one-pass capacitive electrodialysis (CED) at a pilot scale (19.32 m2 membrane area, 1–4 m3/day capacity), employing carbon-based electrodes. CED was optimized for key parameters, including applied voltage, cross-flow velocity, staging, water recovery, and varying feed concentrations. High-quality greenhouse irrigation water (conductivity<0.2 mS/cm and Na+ < 0.1 mmol/L) was produced, meeting specified guidelines. Na+ was retained less compared to Ca2+ and Mg2+ (86 % ± 4 %, 97 % ± 2 %, and 98 % ± 3 % removal, respectively) and nutrients concentration factors for K+, NO 3 − and PO 4 3− reached up to 2.3 (596 ± 5 mg/L), 2.7 (1330 ± 20 mg/L), and 1.9 (130 ± 2 mg/L), respectively. There was no significant improvement in ion removal for all feed compositions beyond 12 V and 80 % water recovery. CED's specific energy consumption (SEC) with optimized parameters was 4-fold lower than the modeled RO system, and lower than previous electrodialysis studies. The highest SEC obtained was 0.24 kWh/m3. These findings suggest that CED is a promising technology for the greenhouse horticulture sector, aiding the move toward zero liquid discharge. • Pilot-scale CED is efficient for resource recovery from greenhouse wastewater. • Irrigation water with conductivity <0.2 mS/cm and Na+ < 0.1 mmol/L was achieved. • Optimal operation at 12 V, 80 % recovery, 5.12 cm/s flow velocity and 2-stack staging. • Nutrient showed concentration factors of K+ (2.3), NO 3 − (2.7), and PO 4 3− (1.9). • CED's energy consumption was 4-fold lower than RO. [ABSTRACT FROM AUTHOR]

Flow electrodes, which are integral to flow-electrode capacitive mixing (F-CapMix), primarily consist of activated carbon (AC), conductive additive and an aqueous electrolyte with a salt. For the better performance of F-CapMix, the AC must have a high surface area and excellent electrical conductivity to facilitate efficient charge percolation and electron transport between the AC particles within the flow electrode. In this study, nitrogen-doped activated carbon (N-doped AC) was synthesized through a straightforward process involving the heating of a mixture of raw AC and melamine in a covered container. The resulting N-doped AC powder exhibited an average of 20 % higher electrical conductivity than raw AC powder without sacrificing the surface area (AC: 2284.7 m2/g vs N-doped AC: 2125.6 m2/g) owing to the incorporation of graphitic nitrogen and oxidized nitrogen into the raw AC surface. The surface characteristics of N-doped AC were found to be similar to those of raw AC. Electrochemical impedance spectroscopy analysis of F-CapMix utilizing N-doped AC in the flow electrode revealed reduced resistance and increased capacitance, leading to an enhancement in power density from 0.706 to 0.828 W/m2. Consequently, integrating N-doped AC into the flow electrode can contribute to the improved performance of F-CapMix. [Display omitted] • N-doped AC exhibited an average of 20 % higher electrical conductivity than raw AC. • Surface area, and pore size and volume of N-doped AC were similar to those of raw AC. • Integrating N-doped AC into flow electrode improves the performance of F-CapMix. [ABSTRACT FROM AUTHOR]

This study focused on removing salts and nutrients (nitrogen and phosphorus) from tertiary treated urban wastewater by capacitive deionization. The performance of a pilot-scale radial capacitive deionizer subjected to varying feed flow rates during the purification stage and constant flow rates during the reject stage was evaluated. This operational strategy aimed to maximize the water recovery rates of the system, with electrical adjustments being made proportionally to the water recovery rate. Lower hydraulic loads resulted in the radial capacitive deionizer removing more ions from the sewage, albeit with higher specific energy consumption. Optimal operational conditions reduced conductivity by 92.8 %, with a specific energy consumption of 2.17 kWhm−3. Significant removals of ammonium, nitrite, nitrate, and orthophosphate ions were observed, with average specie reductions of up to 84, 91.4, 100, and 60.5 %, respectively. Higher rates of treated water recovery resulted in lower ion removal reduction and energy consumption. The limiting step of the process referred to ion desorption, requiring the correct adjustment of the time lapse, flow rate, and applied electrical voltage to ensure the efficiency of the subsequent purification stage. A loss of efficiency was observed when the process was run continuously, thus emphasizing the strategic significance of capacitor rinsing during the rejection phase across multiple subsequent treatment cycles. • Significant removals of NH 4 +, NO 2 −, NO 3 −, and PO 4 3− from the effluent were observed. • The lower the hydraulic loads, the higher the removing rates of ions from the sewage. • The best ions removals were achieved with the higher specific energy consumption. • The limiting step of the process was the ion desorption during capacitor rinsing. [ABSTRACT FROM AUTHOR]

The innovative design of collector is a top priority to drive the advancement of flow electrode capacitive deionization (FCDI) technology. Currently, the majority of FCDI research has concentrated on the implementation and modification of carbon-based flow electrode materials, while ignoring the effect of the current collector in FCDI. In this study, a 3D-FCDI configuration with porous titanium foam as the collector is designed, and rectorite (Rec) is used as the flow electrode in 3D-FCDI. Thanks to the porous structure of the 3D current collector, the collision opportunities of electrons with the Rec particles are increased and the long-distance migration of electrons in the conventional graphite collector is overcome, thus improving the system conductivity. The Rec exhibits good electrode dispersion, desalination rate, and energy consumption at low cost. In addition, the ASAR of Rec can be achieved by adjusting the electrode concentration (5 wt%), electrode flow rate (25 mL min−1) and operating voltage (1.8 V) to 11.43 μg cm−2 min−1. This study demonstrates the capability of 3D-FCDI configuration to advance the creation and implementation of FCDI. [Display omitted] • A 3D-FCDI configuration with porous titanium foam as the current collector is designed. • Collision opportunities of electrons and 3D-FCDI conductivity are increased. • Rectorite exhibits good desalination rate, and energy consumption at low cost. • 3D-FCDI is very conducive to the industrial application of FCDI technology. [ABSTRACT FROM AUTHOR]

Remarkable progress has been achieved to enhance the performance of electrochemical desalination technologies. Desalination batteries are promising due to their ability to simultaneously desalinate water and generate energy. A typical desalination battery consists of rechargeable high-capacity Na- and Cl-storage electrodes that remove ions during charging and release them during discharging. This technology works at low voltages and does not require chemicals, high-pressure pumps, or thermal heaters. Despite the existence of studies focusing on desalination batteries, a notable research gap persists regarding the assessment of performance characteristics, comparison of the various desalination battery designs, evaluation of energy consumption, and the exploration of the potential and limitations of desalination batteries. This highlights the need for a comprehensive review to address these key aspects. The goal of this work was to address these points by shedding light on the fundamentals, principles, and main findings related to desalination batteries to-date. Four main types of desalination batteries are surveyed: membrane-free, rocking chair, redox flow, and metal-air. Emphasis is given on energy considerations, as the energy consumption of desalination technologies has been a significant challenge for decades. Finally, research directions for further desalination battery developments are discussed related to both challenges and opportunities in the field. [Display omitted] • A critical review of desalination batteries • Comparative advantages of battery-based desalination over capacitive deionization • Comprehensive investigation of different desalination battery types • Energy consumption analysis in desalination batteries • Comparison of desalination batteries with state-of-the-art desalination technologies [ABSTRACT FROM AUTHOR]

Composite electrode materials for removing paraquat from contaminated water were synthesized by loading aluminium oxide (Al 2 O 3) onto activated carbon (AC) via co-precipitation method. The composite properties were investigated by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy. Capacitive deionization batch experiments compared the electrosorption of paraquat herbicide by the composite electrode and the pristine activated carbon. The performance of the composite electrodes showed that the removal efficiency and adsorption capacity depend on the aluminium oxide loading, applied potential, flow rate, and charging time. At 1.2 V, a flow rate of 15 mL/min, a charging time of 3 h and 20 mg/L PQ initial concentration, the composite electrode (AC/Al 2 O 3 -1:1) demonstrated a removal efficiency, electrosorption capacity, and energy consumption of 95.5 %, 1.27 mg/g, and 0.055 kWh/m3, respectively, compared to 62 %, 0.83 mg/g, and 0.11 kWh/m3 for the unmodified AC. The presences of other ions/pollutants were found to have negligible interference on PQ pesticide removal as the removal efficiency and electrosorption capacity of the AC/Al 2 O 3 -1:1 composite in both artificial (95.5 %, 1.27 mg/g) and natural water (87.5 % 1.17 mg/g). The study confirmed that composite electrode can reused several times, as there was no significant decrease in its regeneration efficiency even after multiple cycles. • Drinking water with pesticides can result in severe health problems. • Capacitive deionization (CDI) is a promising method for pesticide removal. • Presence of different ions and other contaminants does not affect the removal of PQ • Aluminium oxide-modified carbon composite is a promising CDI electrode material for paraquat removal. • Surface modification of activated carbon with aluninium oxide minimizes energy consumption. [ABSTRACT FROM AUTHOR]

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

Capacitive Deionization (CDI), a burgeoning desalination technology, effectively removes ionic species from aqueous solutions. One-dimensional (1D) electrospinning nanomaterial electrodes present unique opportunities for the enhancement of CDI performance, resulting in increased salt removal capacities and energy-efficient desalination for high-salinity streams. The review begins by elaborating on electrospinning principles, along with parameter considerations influencing said technology. We discuss post-electrospinning treatments such as carbonization, hydrothermal methods, and surface modifications, explicating their resultant impact on the structural, compositional, and morphological attributes of the nanocomposite fabrics synthesized through electrospinning. Progressing further, the analysis categorizes CDI cell architectures and introduces performance assessment metrics for CDI. Moreover, it presents an exploration of the multifarious applications of electrospinning nanomaterials in diverse industrial sectors. These applications incorporate the removal of heavy metals, resource recovery, and water disinfection processes. The potential benefits in these areas appear promising, signifying the requirement for further research toward optimizing the design of electrospinning nanomaterial electrodes to suit these specific purposes more effectively. Lastly, we delineate the existing challenges and potential research avenues, aiming to provide strategic guidance for future inquiries. The evolution of electrospinning nanomaterial electrode technologies could shed light on the emerging CDI research frontier and engender further environmental exploration. [Display omitted] • This paper reviews the growths in 1D electrospinning nanomaterials for CDI. • The post-electrospinning treatments of advanced electrode are discussed in depth. • The versatile applications of capacitive deionization are discussed extensively. • It provides a new perspective for the progress of 1D electrospinning electrode. [ABSTRACT FROM AUTHOR]

While MnO 2 has been identified as a potent agent in the desalination process, its efficacy is significantly impeded by its inherent poor electrical conductivity and substantial ion diffusion barriers. By orchestrating an interfacial electron bridge within the MnO 2 /g-C 3 N 4 heterostructure, reinforced through N p z -Mn d z 2 orbital hybridization, we have managed to significantly boost both SAC and SAR in the HCDI process. The reinforced N p z -Mn d z 2 orbital hybridization triggers a substantial electron transition from g-C 3 N 4 to MnO 2 , culminating in a high Mn d z 2 electron occupancy. Further analysis reveals the formation of a Mn N chemical bond at the MnO 2 /g-C 3 N 4 interface, operating as an essential electron transfer bridge from g-C 3 N 4 to MnO 2. This process concurrently initiates a rise in the Mn d z 2 orbital energy level, equipping the Mn d z 2 electron with superior redox activity. With these enhancements, the manufactured MnO 2 /g-C 3 N 4 exhibits exemplary performance, boasting an improved SAC of 68 mg g−1 and SAR of 3.6 mg g−1 min−1 with a decreased energy consumption of 0.7224 kWh kg−1 at 1.2 V. This innovative work offers an unconventional roadmap for activating electron redox activity and thereby accelerating charge transfer in transition metal oxides. [Display omitted] • A MnO 2 /g-C 3 N 4 heterostructure with strong interfacial coupling was fabricated. • MnO 2 /g-C 3 N 4 heterostructure displays reinforced N p z -Mn d z 2 orbital hybridization. • High Mn d z 2 electron occupancy accelerates the charge transfer. • High salt adsorption capacity and fast salt adsorption rate were achieved. [ABSTRACT FROM AUTHOR]

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

Photovoltaic (PV) systems are considered as a support unit and eco-friendly energy source for the desalination system. If the surface of the desalination plant is covered by PV cells, it is possible to produce self energized desalination plants. Capacitive deionization (CDI) is a water purification technology known for its reduced energetic footprint. The cells are supplied with Direct current (DC) power which makes the application of the PV panels logically intuitive. Conventional existing PV maximum power point trackers (MPPT) are similar to each other in hardware as electrically DC modulated and operated, but different in software. Through different algorithms, existing PV power trackers aims battery charging or grid-tie exportation as application. In this study, a new power tracking using the water flow control is presented as an adapted solution for water desalination using the solar power. The developed algorithm is based on Maximum Salt Adsorption Tracking (MSAT). The proposed algorithm shows a comparative performance as other tracking algorithms under varying radiations. Besides, MSAT brings considerable lower costs by eliminating the need of any storage unit and any DC to DC converters. The developed controller is described in detail and comparative simulated/experimental analysis and performance evaluation are presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Membrane scaling is an enormous challenge in the desalination of hypersaline water using membrane distillation (MD). In this study, vacuum membrane distillation (VMD) was employed for brackish water treatment, with an emphasis on scaling mechanisms and mitigation strategies. Four methods, including deionized water, hydrochloric acid, and acetic acid, ultrasonication, were utilized for membrane cleaning. The cleaning efficiency was assessed through a comprehensive analysis of residual foulant layers. It was determined that mineral scaling constituted the primary fouling mechanism, and a minor amount of organic fouling was present at the interface between scaling-scaling and scale-membrane. Calcium and magnesium carbonate were the primary scaling components observed in brackish water desalination, appearing as needle-like and block crystals. Notably, CaCO 3 predominantly existed as the aragonite crystal structure. Ultrasonication and deionized water demonstrated limited effectiveness due to the alkaline nature of the scaling. Conversely, the application of dynamic hydrochloric acid and acetic acid treatments resulted in a significant reduction in scaling, with acetic acid demonstrating superior efficacy in removing carbonate scaling. The results presented in this study can provide valuable theoretical guidance for the treatment of brackish water using membrane desalination techniques. • Fouling mechanism of VMD in brackish water treatment was revealed. • Aragonite was the leading crystal polymorph for scaling. • Acetic acid demonstrates promise for carbonate scaling mitigation. [ABSTRACT FROM AUTHOR]

Efficient recovery of valuable resources from wastewater has emerged as a critical challenge in the era of carbon neutral society. Capacitive deionization (CDI) has been employed in electrochemical lithium recovery (ELR) processes based on selective Li+ intercalation to LiMn 2 O 4 (LMO). We herein propose a four-step constant voltage operation (forward/zero/reverse/zero) of bifunctional hybrid CDI to produce deionized water as well as Li+-rich concentrate within a cycle. Especially, selective Li+ enrichment was possible without influent replacement since adsorption of competing ions and liberation of Li+ could occur simultaneously. This unique performance was enabled by composite electrodes on capacitive activated carbon cloth (ACC) impregnated with redox-active materials; LMO@ACC and Ag@ACC. Together with material characterization and electroanalysis on the composite electrodes, deionization (step 1; forward voltage) and Li+ enrichment (step 3; reverse voltage) by assembled LMO@ACC//Ag@ACC cell were evaluated by single pass experiments with binary NaCl and LiCl solution (10 mM each). Besides, a multi-stage operation with internal recycle confirmed long-term stability and continuous increase of Li purity for practical implementation. The advanced bifunctional CDI (ELR coupled with water treatment) paved a way to advance the resource recycle from wastewater. [Display omitted] • Hybrid CDI electrodes were fabricated by impregnating LMO and Ag on ACC. • Four-step constant voltage operation with composite electrodes enabled selective desorption. • Bifunctional CDI-ELR system produced deionized water and Li+-rich brine within a cycle. • Extended electrochemical Li+ recovery was stable under variable feed compositions. [ABSTRACT FROM AUTHOR]

Intercalation host compounds (IHC) are promising for selective ion removal from water. Recent theoretical developments have suggested that electrochemical desalination with IHC (nickel hexacyanoferrate (NiHCF)) electrodes could separate K+ and Na+ by a factor of 160. However, the experiments only produce a selectivity of around 3. In this work, we derive theory and a finite-element (FEM) model to investigate the origins of time-dependent selectivity suppression. The first results show that ion starvation can severely limit selectivity. Surprisingly, we also find that operations at low state-of-charge produce theoretical selectivity of 600, which is way above what was previously thought to be the theoretical maximum. Also surprising is that the main cause of low selectivity is that the constant-current overpotential disproportionally favors the adsorption of the ion that is less selected in the equilibrium state. By implementing short charging cycles near the depleted state with rest periods at the ends, we raised the time-dependent selectivity from 3 to 450. Even higher output selectivity could be achieved by combining IHC cathodes with membrane-less carbon anodes. In conclusion, the insights and methods derived here could enable highly selective ion removal at the device level for a wide class of IHC materials. [Display omitted] • Theory and finite-element (FEM) model of intercalation selectivity suppression • Discovered optimal theoretical selectivity of 600 for K+ and Na+ in NiHCF • Charging overpotential causes selectivity suppression. • Improved operations raised the time-dependent selectivity from 3 to 450. • Even higher output selectivity with IHC cathodes and membrane-less anodes [ABSTRACT FROM AUTHOR]

The increasing demand for efficient and sustainable solutions in the field of energy storage and water desalination has sparked research in the development of supercapacitors and capacitive deionization (CDI) cells. This study presents a scalable and eco-friendly process for the preparation of N-doped polyhedral macrotube carbon arrays with a multihole cross-sectional profile. These arrays were synthesized from lotus stems (N-ALS) through carbonization at 500 °C and activation at 700 °C. The resulting material offers a high density of adsorption sites and good conductivity, making it suitable for use as electrodes in both supercapacitors and CDI cells. The N-ALS electrodes exhibit a high specific capacitance of 221.34 F g−1 at a scan rate of 2 mV s−1 and excellent cycling stability, as well as a salt adsorption capacity (SAC) of 26.07 mg g−1 at an applied voltage of 1.4 V and 85 % retention after 50 desalination-regeneration cycles in CDI cells, outperforming traditional activated carbon electrodes. • The environmentally friendly, N-doped porous biochars has been successfully prepared through a facile and efficient method. • N-ALS has better electrochemical performance, higher desalination efficiency and good recycling in CDI cells. • This study provides feasibility for the application of CDI in metallurgical wastewater treatment. [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]

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

Defect engineering has emerged as an effective approach for modulating the electronic structure and physicochemical properties of carbon materials. Porous carbon materials with abundant defects are regarded as prospective electrode materials for capacitive deionization. Nevertheless, constructing defect-rich carbon materials and revealing the relationship between desalination capacity and intrinsic defects remains a daunting challenge. Herein, the defect-rich interconnected hierarchical porous carbon (IHPC) was fabricated via sol-gel method to form a supramolecular hydrogel containing highly dispersed K+ using coal, polyvinylpyrrolidone, and KOH as raw materials, followed by homogeneous activation. The spectroscopic studies coupled with density functional theory calculations demonstrate that the introduction of intrinsic defects can optimize the distribution of electron density to promote charge transfer, thereby enhancing saline ions adsorption. The plentiful adsorption sites, robust charge transfer kinetics and rapid ion diffusion derived from the multiple advantageous characteristics of IHPC facilitate a high desalination capacity of 31.25 mg g−1 in 800 mg L−1 NaCl solution. Meanwhile, it also presented excellent desalination performances in KCl (31.42 mg g−1), CaCl 2 (29.55 mg g−1), and MgCl 2 (26.65 mg g−1) solutions. The higher desalination capacity, rapid salt adsorption rate as well as outstanding cycling stability rank the IHPC as a potential candidate for capacitive deionization applications. • Defect-rich interconnected hierarchical porous carbons (IHPC) were prepared by homogeneous activation strategy. • Interconnecting hierarchical porous structures and abundant defects provide an abundance of adsorption sites. • The IHPC electrode reveals superior desalination capacity of 31.25 mg g−1 and high stability. [ABSTRACT FROM AUTHOR]

Rocking-chair capacitive deionization (CDI), in combination with commercially available ion-exchange membranes, was evaluated for the feasibility of recovering phosphate. Here, contrary to the typical ion-selective adsorption methods in CDI, we aim to isolate and recover phosphate via a rejection mode. We have successfully removed 80 % of chloride from a binary solution containing equimolar concentrations of chloride and monovalent phosphate, while retaining virtually 100 % of phosphate. Further studies have revealed that ≥90 % of chloride can be removed while sacrificing as little as 15–20 % of the original phosphate concentration. To optimize the electrochemical ion separation process, we have studied several different working potentials, flowrates, and cycle times in these experiments. Moreover, we have observed similar selectivity results for both carbon-based and intercalation electrodes (Prussian blue analogues, PBAs) in a direct comparison. Within the constraints of the testing parameters, both systems exhibit no pronounced differences, with PBAs marginally outperforming carbon-based electrodes in terms of total chloride removed (94 % vs. 92 %). However, during the early stages of a desalination run, the carbon-based system revealed a minor edge on the ion separation performance compared to the PBA system. [Display omitted] • Alternative method of phosphate recovery via rejection mode. • Effect of potential, flowrate, and cycling time on phosphate recovery. • At 80 % of chloride removal, virtually 100 % of phosphate remains. • CDI system tested with two different types of electrodes. [ABSTRACT FROM AUTHOR]

Flow-electrode capacitive deionization (FCDI) couples flow electrode and ion exchange membrane to bridge the technical bottleneck of limited adsorption capacity and long-term continuous operation of traditional CDI technology. After nearly a decade of extensive research, FCDI technology has made positive progress in the research of charge transport theory and operation mechanism, material development, and engineering applications, and has shown good application prospects. This paper summarizes and compares the mechanism, energy consumption and cost of FCDI technology with other deionization technologies (including Reverse Osmosis, Electrodialysis, Multi-stage Flash and Fixed Capacitive deionization). Furthermore, we introduce the flow electrode materials (including carbon materials and faraday materials) and the application of FCDI in the environmental field (including desalination, resource recovery and contaminant removal). Finally, the possible problems of FCDI technology (such as expansion design, energy recovery and technology coupling) are presented and the main challenges in the future full-scale applications are presented. [Display omitted] • Comprehensive review of recent advances in flow-electrode capacitive deionization (FCDI); • Critical energy and economic analysis in comparison with existing desalination technologies; • The recent development of flow electrode materials was summarized; • The environmental application of FCDI was summarized; • Future perspective and challenges for FCDI were carried out. [ABSTRACT FROM AUTHOR]

Faradaic deionization (FDI) is an emerging water treatment technology based on electrodes able to remove ionic species from water by charge transfer reactions. It is a young and promising technology that has attracted much attention due to its large capacity to store ions and the high selectivity of the faradaic electrode materials. This study reviews published papers on FDI from different angles: data mining, bibliometric and machine learning. Metrics such as annual growth rate, most important journals, relevant authors, collaborations maps, sentiment and subjectivity analysis, similarity and clustering analysis were performed. The results indicated that the strong interest in FDI really started in 2016, China is the most active country in FDI, and Desalination is the most important journal publishing FDI articles. The word cloud method showed that the most preferred adopted words are deionization, capacitive, electrode, material. Sentiment analysis results indicated that most of the researchers are optimistic about FDI technology. The title similarity method revealed that FDI researchers were successful in proposing unique and appropriate titles. The clustering approach stressed that FDI literature is concentrated on electrode material production, desalination application, lithium recovery and comparison with CDI. [Display omitted] • Faradaic Deionization (FDI) dataset includes 170 papers downloaded from Scopus. • Annual growth rate of FDI research based on published articles is 55.12 %. • Desalination , J. Mat. Chem. and ACS Appl. Mater. Inter. are the core sources of FDI. • China and the USA are the most active countries on FDI research. • Deionization , capacitive and desalination are frequent words in FDI articles titles. [ABSTRACT FROM AUTHOR]

The form of the energy input for widely investigated desalination technologies include thermal energy (distillation), mechanical work (reverse osmosis) or electrical energy (electrodialysis and capacitive deionization). We here propose and characterize an electrodialysis-type desalination cell which is driven instead by spontaneous redox reactions occurring at electrodes. Thus, this system utilizes solely a chemical energy input to perform desalination, and requires no electricity input, instead producing electricity while desalinating. With our custom-built prototype system based on high performance zinc-bromine chemistry, we demonstrate the desalination of feedwater with an initial salinity of ~30 g/L while simultaneously generating up to 23.5 kWh of electricity per m3 of desalted water. Further, we show our prototype cell can recover up to 85% of the input chemical energy as electricity during operation without needing a recovery device. The net energy usage, defined as chemical energy input minus electricity output, was measured to be 3.9 kWh/m3 when desalting to near-zero concentration at 2 mA/cm2 with our first-generation cell. Our proposed concept decouples reactant production from its usage in the cell, and we show that this decoupling can potentially lead to net negative operating costs when low-cost reactants are employed. • A desalination system requiring solely chemical energy input • Outputs both desalted water and electricity simultaneously • Device achieves electricity generation of up to 23.5 kWh/m3 of desalted water. • Chemical energy usage as low as 3.9 kWh/m3 at 2 mA/cm2 generated current [ABSTRACT FROM AUTHOR]

Electrode materials for capacitive deionization (CDI), an energy efficient method for desalination, were developed in this work. Waste-tire derived carbon (TC) coated with polyaniline was used to form a carbon polymer composite (CPC). CPC was used as an electrode in CDI configurations to determine the salt adsorption capability of the material. Chemical treatment of TC with KOH led to an enhancement in surface area to 952 m2/g and microporosity in the sub-2-nm range. This unique microstructure is considered to be beneficial for effective ion uptake in CDI applications. The capacitance of the electrodes was further enhanced through surface coating with polyaniline, resulting in a specific capacitance of 168.2 F/g. In batch cell testing with 1.2 V applied potential, the salt adsorption capacity (SAC), measured in mg of salt adsorbed per gram of active material, in a 1500–1700 ppm KCl solution was measured at 14.2 mg/g. Scale-up of the process with ionic-membrane-assisted CDI (MCDI) led to improvement in SAC at 18.9 mg/g. Further, cycling tests revealed that the electrodes had comparable or better longevity compared to other CDI materials, retaining >92.8% charging capacity after 300 cycles. High adsorption capacities for other salts such as LiCl, NaCl, MgCl 2 and CaCl 2 have been found. Process flow chart depicting starting tire material, chemical treatments and coatings, electrode preparation, and electrode use in CDI that leads to purified water products. Unlabelled Image • Carbon recovered from waste tire rubber. • Carbon has been coated with polyaniline to form composites. • Composite materials are used as CDI electrodes. • High adsorption capacities for LiCl, NaCl, KCl, MgCl 2 and CaCl 2 achieved. • 300 cycles with >92.8% charging capacity observed. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a promising technique for water treatment and desalination. To enable high CDI performance, the electrode materials should possess high surface area, conductivity, hydrophilicity, and cycling stability. Here, we report the design and construction of a hierarchical porous composite of N-doped hollow mesoporous carbon sphere and holey graphene hydrogel with in-plane pores, i.e. , N-HMCS/HGH composite, for high-performance CDI. The N-HMCS/HGH composite shows a three-dimensional (3D), hierarchical porous structure with a specific surface area of 337.7 m2 g−1, high conductivity, and high hydrophilicity. With these structural characteristics, the optimized N-HMCS/HGH electrode exhibits a large specific capacitance (226.5 F g−1) in 0.5 M NaCl solution to ensure a large electrosorption capacity of 17.8 and 32 mg g−1 in a feeding NaCl solution with initial concentration of 500 and 2500 mg L−1, respectively. Upon 35 CDI-regeneration cycles, the electrosorption capacity of the N-HMCS/HGH electrode shows no obvious attenuation, exhibiting excellent cycling stability. These results indicate that the hierarchical N-HMCS/HGH composite shows great potential for practical application. Unlabelled Image • N-HMCS/HGH composite with a high specific surface area was prepared. • Its HGH matrix endows high conductivity avoiding the use of electrode binder. • N-doping further improves the hydrophilicity of the composite. • The composite delivers a large capacitance for remarkable electrosorption capacity. [ABSTRACT FROM AUTHOR]

Pollution of water and limited availability of freshwater are the major environmental issues faced globally in the present era. Capacitive deionization, a potential water treatment technique based on electrochemistry, has gained huge recognition in the last decade owing to the facile ions' expulsion from sewage water, along with the benefits of being eco-friendly, reduced cost, decreased consumption of energy, and effortless renewal of electrode. Similarly, electrosorption emerged as a replacement technique to traditional adsorption techniques because of the generation of compound electrodes with flexible surface features, porous in nature, certainty, and the capability to execute electrochemical reactions. Extensive advancement has been witnessed in both capacitive deionization and electrosorption with their various electrodes. The scientific developments are assisted with distinct applications of these techniques. Thus, the current review paper has provided an elaborate description of the capacitive deionization and electrosorption methods with various electrode materials, highlighting polymer, membrane, and bio electrodes. The review paper has also delivered detailed explanations for the treatment of waste water which includes desalination, and expulsion of heavy metals and organic compounds, individually for capacitive deionization and electrosorption techniques. This review paper would be of great benefit in nurturing these technologies to evolve into a challenging alternative to get along with other water treatment problems. [Display omitted] • The versatile applications of capacitive deionization and electrosorption are discussed extensively. • Principles and mechanisms for both capacitive deionization and electrosorption are explained in detail. • Various electrode materials, along with bio electrodes, are given special emphasis. • The operational parameters for the effective functioning of capacitive deionization and electrosorption are detailed. • Challenges and future directions for empirical applications of capacitive deionization and electrosorption are explored. [ABSTRACT FROM AUTHOR]

The functionalized utilization of lignin is attracting more and more attention. In this paper, we report a 3D interconnected foamy carbon material with highly open pore structure. The carbon foam is synthesized by depolymerization reforming strategy. The foamy carbon has a deep internal pore channels and exhibits an enhanced electrosorption capacity. The highest desalination of the foamy carbon reaches 30.2 mg·g−1 in 500 mg·L−1 NaCl at 1.2 V with adsorption rate of 3.75 mg/g/min. Meanwhile, the optimal electrode PDLC-1 shows good regeneration capacity. Our work provides a usable way for the preparation of lignin-derived carbon foam with high-performance of capacitive deionization. • Depolymerization-reforming lignin regulates its agglomeration behavior. • An efficient strategy to prepare carbon foam with highly open porous structures. • The ultra-high electrosorption performance and cycle stability are observed. [ABSTRACT FROM AUTHOR]

Flow electrode capacitive deionization (FCDI) is a newly developed salt removal technology that overcomes the limitations of conventional CDI by eliminating the need for a discharging process, thus achieving much higher desalination capacity and a continuous desalination operation. In this study, we aimed to achieve selective and continuous sodium recovery from Na+/Ca2+ mixtures through FCDI by utilizing polymer multilayer functionalized cation-exchange membranes (CEM). A layer-by-layer method was used to deposit polymer multilayers consisting of PAH (poly allylamine hydrochloride) and PSS (poly styrene sulfonate) on the CEM. Changes in the concentration of feed electrolyte, number of coated polymer layers, and type of outermost layer were investigated in terms of their effect on the selective ion separation. The functionalized CEM switches from a divalent ion affinity to a monovalent ion affinity due to their different ion sizes and charge densities. As the number of polymer layers increased, the selectivity of Na+/Ca2+ increased, reaching up to 3.26 from 0.16 for pristine CEM. We believe that our approach can provide insight into the selective recovery of valuable materials including lithium-ion battery recycling, the recovery of noble metals, and the separation of toxic ions using the FCDI system. [Display omitted] • Selective ion recovery was realized by FCDI using a functionalized membrane. • PAH/PSS polymer multilayers were successfully deposited onto an ion exchange membrane. • The multilayer coating changed the affinity of the FCDI system from divalent to monovalent. • Na/Ca selectivity increased from 0.16 to 3.26 as a result of multilayer coating. [ABSTRACT FROM AUTHOR]

Thin-film composite (TFC) membrane capable of superior permeability contributes to the industrial implementation of forward osmosis (FO) technology, but it is plagued with some bottlenecks including the unsatisfactory selectivity. Herein, the surfactant-induced intervention in interfacial polymerization was performed by incorporating hexadecyltrimethylammonium toluene-p-sulphonate (CTAT) into the amine aqueous solution for developing the highly-permeable TFC membrane with exceptional selectivity. The effect of CTAT incorporation on the physicochemical properties of polyamide (PA) layer was systemically investigated by conventional characterizations, so as to unravel the mechanism for the improved performance of resultant TFC-FO membrane. Besides, three typical surfactants of Tween 80, sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium chloride (CTAC) were also introduced and studied contrastively for comparison. Amongst the fabricated membranes, the optimized TFC-CTAT membrane achieves the improved water fluxes (J V) of 31.8 and 21.7 L.m-2.h−1 accompanied with the reduced specific reverse salt fluxes (J S /J V) of 0.05 and 0.04 g·L−1 in active layer facing the draw solution (AL-DS) and active layer facing the feed solution (AL-FS) orientations respectively, using 1 M NaCl solution and deionized water as draw and feed solutions. Therefore, this work provides a new perspective for constructing TFC-FO membrane with high perm-selectivity by employing suitable surfactant at the relatively low concentrations. [Display omitted] • CTAT-induced intervention in interfacial polymerization (IP) was verified. • Effect of CTAT contents on the formation of polyamide layer were studied. • Incorporation of CTAT during IP leads to a uniform and dense polyamide layer. • Resultant TFC-FO membranes show improved water flux and reduced reverse salt flux. [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]

A model that can be used to predict the performance of Membrane Capacitive Deionization (MCDI), including current efficiency, flowrate of the product water, water recovery and energy consumption is established in this work. The model was developed using a Response Surface Model approach that considers the influence of influent conductivity, flowrate passing by the electrodes and applied current on MCDI system performance rather than relying on electrochemical principles or the description of the intrinsic properties of the carbon electrodes and ion exchange membranes. In the scenarios tested here, flowrate contributes the most towards MCDI performance. The appropriateness of using NaCl for an MCDI performance model is confirmed. The model can be applied to extensive applications with two examples detailed here including a small town potable application of 100 m3/day with influent water of 2000 μS/cm and an industrial wastewater application of 1000 m3/day with influent water of 4000 μS/cm. A costing model is developed and applied to the two scenarios with the optimised levelized cost of water (LCOW) found to be US$0.74/m3 for the small town and US$1.08/m3 to US$1.41/m3 for the industrial wastewater (product water quality dependent). By maximising the production rate, the LCOW can be minimised. The model presented here can be applied to a wide range of applications or used as a framework for efficient performance modelling of other MCDI configurations. [Display omitted] • A framework for a simplified MCDI performance model developed. • MCDI performance model based on influent conductivity, flowrate and applied current. • Levelized cost of water (LCOW) of US$0.74/m3 for MCDI treated potable supply. • LCOW can be minimised by maximising MCDI production rate. [ABSTRACT FROM AUTHOR]

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

Abstract 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]

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

Abstract Capacitive deionization (CDI) is an emerging desalination technique by utilizing the electrosorption of porous electrodes. Thus far, only linear concentration profiles in bulk electrolyte between the electrodes have been observed, during ion charging (ion depletion) or ion discharging (ion enrichment). This so-called linear ion concentration polarization (ICP) can be predicted by the simple convective-diffusion model. In this study, we demonstrate that capacitive charging can induce nonlinear concentration profiles in the electrolyte. To visualize nonlinear ICP dynamics, a miniaturized CDI platform is developed to observe in situ ion concentration profiles. Determined by the ion flux mismatching of electrosorption and bulk ion transport, we discovered four ICP regimes in CDI – steady, linear ICP, delayed-nonlinear ICP, and nonlinear ICP. We directly observed the signatures of nonlinear ICP: i) flat depletion zone with extremely low ion concentration, and ii) corresponding exponential current drop. Based on this observation, two scaling models are formulated to predict i) when the nonlinear ICP occurs, and ii) the propagation speed of the flat depletion zone. To the best of our knowledge, this is the first microscopic characterization of ICP in CDI systems, and it firmly establishes the existence of nonlinear ion transport dynamics in CDI's bulk electrolyte. Highlights • Miniaturized CDI platform is presented to visualize in situ ion concentration profiles. • The linear and nonlinear ICP dynamics in the bulk electrolyte are discovered. • Each ICP regime has unique concentration profile and current-time response. • Nonlinear ICP shows flat, propagating depletion zone and dual exponential current drop. • We formulate scaling laws for predicting ICP regimes and nonlinear zone propagation. [ABSTRACT FROM AUTHOR]

Abstract Capacitive deionization (CDI), which is based on the electrosorption of ions by porous electrodes, is an emerging technology for brackish water desalination. Understanding the key drivers of energy consumption in CDI and benchmarking CDI with reverse osmosis (RO), the current state-of-the-art for brackish and seawater desalination, is crucial to guide the future development of desalination technologies. In this study, we develop system-scale models to analyze the energy consumption and energy efficiency of CDI and RO over a wide range of material properties and operating conditions. Using our models, we explore how the energetic performance of CDI and RO compare as a function of feed salinity, water recovery, salt rejection, and average water flux, which is normalized by electrode and membrane area in CDI and RO, respectively. Our analysis shows that RO is significantly more energy efficient than CDI, particularly when targeting higher salinity feed streams and higher salt rejection values. For brackish water with a salt concentration of 2000 mg L−1, achieving 50% water recovery and 75% salt rejection, with an average water flux of 10 L m−2 h−1 using CDI requires a specific energy consumption of 0.85 kWh m−3, more than eight times that of RO (0.09 kWh m−3). Importantly, our results also indicate that current efforts to improve electrode materials can only marginally reduce the energy consumption of CDI. We conclude with a discussion highlighting other important factors, such as capital cost, electrode stability, and membrane fouling, which affect the efficacy of CDI and RO for low-salinity desalination. Graphical abstract Unlabelled Image Highlights • RO is significantly more energy efficient than CDI for brackish water desalination. • Novel simplified CDI circuit model can predict key aspects of energetic performance. • Development of CDI electrode materials will marginally improve energy efficiency. • CDI cannot compete with RO on the basis of both energy consumption and capital cost. [ABSTRACT FROM AUTHOR]

Abstract Capacitive deionization is a water desalination technology in which ions are stored in electrodes in an electrochemical cell construction, connected to an external circuit, to remove ions present in water from various sources. Conventionally, carbon has been the choice of material for the electrodes due to its low cost, low contact resistance and high specific surface area, electronic conductivity, and ion mobility within pores. The ions in the water are stored at the pore walls of these electrodes in an electrical double layer. However, alternative electrode materials, with a different mechanism for ion and charge storage, referred to as ion intercalation, have been fabricated and studied as well. The salt adsorption performance exhibited by these materials is in most cases higher than that of carbon electrodes. This work traces the evolution of the study of redox activity in these intercalation materials and provides a chronological description of major developments in the field of Capacitive Deionization (CDI) with intercalation electrodes. In addition, some insights into the cell architecture and operation parameters are provided and we present our outlook of future developments in the field of intercalation materials for CDI. Highlights • Water desalination by capacitive deionization highly promising with novel intercalation materials • A full chronology is provided of the literature on CDI with intercalation materials • The timeline starts from 50 years ago and illustrates a rapid development in research interests in this field • Birds-eye view provided on insights and outlook for the use of intercalation materials in capacitive deionization [ABSTRACT FROM AUTHOR]

Abstract Research into desalination of groundwaters for agricultural application in Australia has previously focused on the viability of large scale reverse osmosis plants. Capacitive Deionization (CDI) is an alternative method of desalination that has been demonstrated to be effective for desalting moderately saline (brackish) waters in pilot studies and can be powered using photovoltaics. Using a farm scale economic model coupled to a CDI performance model, potentially viable agricultural applications for CDI have been identified with variation in crop type and CDI configuration enabling optimisation. Scenarios for grapes, oranges, almonds, apples and tomatoes were modelled with maximum internal rates of return (IRR) and annualised profits (AUD$/ha/yr) determined. Groundwater bore salinity thresholds above which the regime is not feasible were found to be 4.2 dS/m for grapes, 5.5 dS/m for oranges, 4.4 dS/m for almonds, 14 dS/m for apples and 8.5 dS/m for tomatoes for a 60 ha crop with an investment period of 10 years. Costing of CDI desalinated water was scenario dependent with a large portion falling below AUD$1/kL. CDI desalination was found to be economically feasible for a range of scenarios and should be explored further as an option to assist with global water and food security concerns. Highlights • Capacitive Deionization (CDI) is economically viable for irrigated agriculture. • Bore salinity thresholds range from 4.2 to 14 dS/m for fruit, nuts and tomatoes. • Cost of CDI desalinated water is now below AUD$1/kL (scenario dependent). • Crop regime for use of brackish groundwater optimised. [ABSTRACT FROM AUTHOR]

Abstract The objective of this study is to understand the effects of operating conditions and cathode parameters on the salt removal performance of hybrid capacitive deionization systems (HCDI). Hence, the effects of half cycle length, flow rate, cathode thickness, and conductive additive loading in the cathode are systematically investigated. Hydrothermally synthesized α-MnO 2 was selected as the active material in the cathode. Desalination results indicate notable dependence of HCDI performance on the investigated parameters. For instance, increasing half cycle length increases the salt adsorption capacity (SAC) by ~58% but decreases the peak salt adsorption rate (PSAR) by ~28%. On the other hand, increasing the flow rate leads to an increase of the SAC and PSAR by ~25% and ~115%, respectively. Increase in the cathode thickness also showed a notable decay in performance with 43% drop in SAC. The amount of conductive additive in the cathode was also investigated to observe the impact of electrical conductivity on the CDI performance. Salt adsorption capacity and rate of HCDI systems containing identical active materials show strong dependence on the operation conditions and cathode parameters, which suggests a necessity of developing an understanding of the impact of these conditions on the system performance. Graphical abstract Unlabelled Image Highlights • Rate performance of the HCDI setup strongly depends on the applied flow rate. • Effective delivery of ions to the electrodes strongly depends on the flow rate. • Increasing half cycle length, increases SAC at the expense of ASAR. • Efficient utilization of electrodes strongly depends on electronic conductivity. • Contribution of conductive additives to SAC is negligibly small. [ABSTRACT FROM AUTHOR]