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Capacitive deionization (CDI) is proposed as a thermodynamically effective desalination method for treating non‐potable water with a low‐salt concentrator to address the growing need for clean drinking water. MXenes, 2D transition metal carbides derived from Mn+1AXn (n = 1, 2, 3, or 4) bulk phases, are an intriguing class of crystalline materials with unique physicochemical properties. However, a significant challenge for their practical use is the degradation and phase transition experienced by MXene flakes when exposed to aqueous conditions. Several strategies for improving MXene stability are proposed, including combining it with porous materials such as carbon and metal–organic frameworks (MOFs). In addition to ZIFs, antioxidants with amine functional groups are used to stabilize MXene. Additionally, amine‐functionalized MXenes exhibit improved resistance to oxidation caused by water, enabling them to maintain their dispersity in aqueous solutions at room temperature. The produced A‐ZIF@MXene electrode represents high desalination performance with the highest salt adsorption capacity up to 80.3 mg g−1 in 1000 mg L−1 The NaCl solution reserve more than 99% of its initial capacity in 50 cycles to the synergism of its surface amine groups, high hydrophilicity, and distinctive hierarchical porous structure. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a promising and cost-effective technology that is currently being widely explored for removing dissolved ions from saline water. This research developed materials based on activated carbon (AC) materials modified with zinc oxide (ZnO) nanorods and used them as high-performance CDI electrodes for water desalination. The as-prepared electrodes were characterized by cyclic voltammetry, and their physical properties were studied through SEM and XRD. ZnO-coated AC electrodes revealed a better specific absorption capacity (SAC) and an average salt adsorption rate (ASAR) compared to pristine AC, specifically with values of 123.66 mg/g and 5.06 mg/g/min, respectively. The desalination process was conducted using a 0.4 M sodium chloride (NaCl) solution with flow rates from 45 mL/min to 105 mL/min under an applied potential of 1.2 V. Furthermore, the energy efficiency of the desalination process, the specific energy consumption (SEC), and the maximum and minimum of the effluent solution concentration were quantified using thermodynamic energy efficiency (TEE). Finally, this work suggested that AC/ZnO material has the potential to be utilized as a CDI electrode for the desalination of saline water. [ABSTRACT FROM AUTHOR]

The zirconium-based metal–organic framework (MOF) (UiO-66)/bamboo carbon (BC) composite with chitosan was prepared using hydrothermal and impregnation methods and used for capacitive desalination (CDI) and disinfection of water. The results showed that these composites had fast ion exchange and charge transfer properties. During the CDI process, these composites' electrodes exhibited good cycle stability, electrosorption capacity (4.25 mg/g) and excellent bactericidal effect. These carbon-based composites electrodes' bactericidal rate for Escherichia coli could reach 99.99% within 20 minutes; therefore, they had good performance and were a good choice for high-performance deionization applications. [ABSTRACT FROM AUTHOR]

• Activated carbon derived from agriculture by-products obtain high surface area, high porosity, and low density. • Deionization efficiency of CDI, MCDI, and FCDI reached 80–90 % and water recovery rate 90 %. • The roller, spray coating, and mill ball grinding are useful to fabricate electrodes for industry applications. • The adsorption capacities of AC and AC-modified electrodes were 25–40 mg/g. • Life span and deionization efficiency of the flow electrode are higher than electrode plate. Capacitive deionization (CDI), membrane capacitive deionization (MCDI), and flow capacitive deionization (FCDI) are emerging technologies applied to remove ions from brackish water or saline wastewater based on electrode double layer (EDL) mechanisms. The electrode itself can be seen as the most important factor that determines the deionization efficiency of the CDI system. Electrode fabrication using activated carbon derived from agriculture byproducts is a useful solution to decrease cost, restrict environmental pollution, and enable agriculture waste recovery. In this review, the primary parameter's impact on activated carbon (AC) and the electrode fabrication process from the agriculture byproducts is detailed in a discussion to find the most optimal conditions. With excellent characteristics for the activated carbon such as a surface area of up to 2500 m2/g, it can be used to fabricate electrodes that have a high adsorption capacity of approximately 25 mg/g, able to be advanced to 40 mg/g with a modified AC. It can achieve a cycle performance of 95–97 %. The deionization efficiency of the CDI, MCDI, and FCDI systems can be up to 90 % with an input salt concentration from 2000 to 3000 mg/L where the water recovery ratio achieved is 50–90 %, alongside a salt rejection rate of about 7–75 %. AC can be modified to increase its special properties such as surface area, conductivity, and ion selectivity using different methods. The drawbacks and challenges of the CDI technology are also mentioned along with useful solutions such as electrode coating techniques using an anilox roller and a spray, for use in industry applications. [Display omitted] [ABSTRACT FROM AUTHOR]

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

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]

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

Abstract In the growing field of capacitive deionization (CDI), a number of performance metrics have emerged to describe the desalination process. Unfortunately, the separation conditions under which these metrics are measured are often not specified, resulting in optimal performance at minimal removal. Here we outline a system of performance metrics and reporting conditions that resolves this issue. Our proposed system is based on volumetric energy consumption (Wh/m3) and throughput productivity (L/h/m2) reported for a specific average concentration reduction, water recovery, and feed salinity. To facilitate and rationalize comparisons between devices, materials, and operation modes, we propose a nominal standard separation of removing 5 mM from a 20 mM NaCl feed solution at 50% water recovery. We propose this particular separation as a standard, but emphasize that the rationale presented here applies irrespective of separation details. Using our proposed separation, we compare the desalination performance of a flow-through electrode (fte-CDI) cell and a flow between membrane (fb-MCDI) device, showing how significantly different systems can be compared in terms of generally desirable desalination characteristics. In general, we find that performance analysis must be considered carefully so to not allow for ambiguous separation conditions or the maximization of one metric at the expense of another. Additionally, for context and clarity, we discuss a number of important underlying performance indicators and cell characteristics that are not performance measures in and of themselves but can be examined to better understand differences in performance. Graphical abstract Image 1 Highlights • The separation conditions must be controlled to compare desalination performance. • Separation conditions include water recovery, concentration reduction, and feed salinity. • Desalination performance is captured by throughput (L/h/size) and energy use (Wh/m3). [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an electrochemical ion removal technique that could offer a lower energy or more selective alternative to reverse osmosis for water treatment applications. Over a dozen CDI cell architectures have been developed, but few studies have directly compared these designs for performance metrics such as ion adsorption rate and energy efficiency. Two of the most popular cell architectures include flow-by CDI, in which a feed stream flows parallel to two charged porous electrodes, and flow-through electrode CDI, in which the feed stream flows perpendicular to the electrodes. In this study, flow-by and flow-through CDI architectures were compared using commercially available electrode materials. Experimentally observed salt adsorption capacity (SAC), average salt adsorption rate (ASAR), and charge efficiency (Λ) was then compared to theoretical models over a range of voltage conditions (0.2–1.2 V), charge cycle times (1–60 min), and flow rates (10–30 mL min - 1 ). Cell architecture affected the SAC, ASAR, Λ, electrode stability, and oxidation rates for a given electrode material. Flow-by CDI tended to have higher SAC and better charge efficiency than flow-through CDI, yet flow-through CDI demonstrated a higher ASAR, particularly for shorter half-cycle times. [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]

[Display omitted] • Survey on biowaste material derived activated carbon (BMDAC) electrodes in CDI. • Applications of BMDAC electrodes for removal of pollutant ions are explained. • Systematic tabulation on BMDAC electrodes performance and parameters is presented. Capacitive deionization (CDI) is water desalination process used to remove pollutant ions and water purification. In present review contains current status biowaste material derived activated carbon (BMDAC) electrodes for pollutant ion removal using CDI. This review systematically present the fundamental about CDI, application of CDI, discusses the numerous BMDAC material, comparative tabulation on current status removal of pollutants ion using BMDAC electrodes by CDI and a future scope in present area. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is a novel technology that has been successfully utilized for many water treatment/purification applications. In many cases, the CDI technology has shown increased efficiency compared to the other contemporary technologies. There have been some recent developments in this field that have enhanced the overall adsorption capacity and thus performance of CDI. Different types of carbon electrodes, such as conventional and latest forms of porous-carbon and graphene based electrodes have been used in the CDI technology. This has facilitated mass transfer in the form of adsorption of salt ions onto modified electrodes and increased the effectiveness of CDI operations. This paper aims to assess the overall state of the CDI technology and review basic concepts, saturation-regeneration of CDI electrodes, and various types of materials used for electrodes. In addition, this article reviews the recent progress made in electrode surface modifications by metals or metal oxides, membrane, polymer, organics and other compounds that have resulted in increased efficiency of ion extraction from the water. The evaluation of past and present published research on use of low-cost carbon forms as CDI electrodes to reduce the overall cost and eliminate the need of regeneration of saturated electrodes is also a part of the article. [ABSTRACT FROM AUTHOR]

Here we detail a previously unappreciated loss mechanism inherent to capacitive deionization (CDI) cycling operation that has a substantial role determining performance. This mechanism reflects the fact that desalinated water inside a cell is partially lost to re-salination if desorption is carried out immediately after adsorption. We describe such effects by a parameter called the flow efficiency, and show that this efficiency is distinct from and yet multiplicative with other highly-studied adsorption efficiencies. Flow losses can be minimized by flowing more feed solution through the cell during desalination; however, this also results in less effluent concentration reduction. While the rationale outlined here is applicable to all CDI cell architectures that rely on cycling, we validate our model with a flow-through electrode CDI device operated in constant-current mode. We find excellent agreement between flow efficiency model predictions and experimental results, thus giving researchers simple equations by which they can estimate this distinct loss process for their operation. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) offers an affordable technology for the reduction of salt concentrations in brackish water. However, there are still drawbacks concerning electrode capacity and energy consumption, compared to other well-established technologies such as reverse osmosis or electrodialysis. This study investigates high-adsorption electrodes based on polyaniline-activated carbon, applying different configurations (symmetric and asymmetric electrodes, and membrane CDI) to optimize electrosorption capacity and energy consumption. A new approach called OSR (optimized salt removal) is proposed, based on simultaneous analysis of the electrosorption capacity and the adsorption/desorption kinetics. This technique was used to evaluate different electrode configurations. The best performance was obtained using MCDI, which improved the electrode capacity from 14.9 to 20.0 mg g −1 , while reducing the specific energy consumption by 21%. It was demonstrated that the performance of the electrode depended on both the specific adsorption capacity ( SAC ) and the electrosorption/desorption kinetics. Fitting the electrosorption and desorption curves using a pseudo-first order kinetic model and applying the OSR method showed that the best desalination was achieved using MCDI at 1.2 V. This configuration did not present the highest SAC or the fastest electrosorption/desorption kinetics, but a good balance was obtained between these two variables. [ABSTRACT FROM AUTHOR]

The aim of present study is simultaneous and individual removal of chromium (VI) (Cr(VI)) and fluoride (F) ions with activated carbon (AC) electrode by capacitive deionization (CDI). Capacitive deionization is recently developing and worldwide attracted technique due to less energy consumption and eco-friendly in use. AC electrode was fabricated and further it characterized by SEM, EDS, and cyclic voltammetry. The maximum electrosorptive removal of Cr(VI) and F were found to 97.1% and 94.20% for 10 mg/L binary feed at optimized flow rate 16 mL/min and 1.2 V. Effective regeneration electrode was observed after electrosoprtion of Cr(VI) and F. In mono component modeling Redlich Peterson model and Freundlich isotherm model were found best agreement with experimental results of Cr(VI) and F electrosorption. Non Modified R–P model and Extended Freundlich model among six applied multicomponent isotherm models found to good correlation with the experimental data for both Cr(VI) and F electrosorption. Pseudo first order kinetic model found good agreement experimental data for both Cr(VI) and F electrosorption. Thus CDI process could be used for simultaneous electrosorptive removal of low concentrated Cr(VI) and F binary feed system. [ABSTRACT FROM AUTHOR]

Experiments were conducted to develop a statistical model which describes the relation between operating parameters and capacitive deionization performance for the removal of Ni(II) ion using multi-walled carbon nanotubes (MCNT) electrodes. The $$R^{2}$$ value of 0.84 in regression analysis represents that the statistical model reproduced the data well. The factors for pH ( $$a = 0.242$$ ), applied voltage ( $$b = 0.619$$ ) and retention time ( $$c = 0.504$$ ) in the statistical model revealed the significance of each parameter. The effect of initial Ni(II) concentration is best described by Langmuir isotherm. Kinetic study showed that pseudo-first-order equation fitted the data well. Modeling the performance with operating parameters for the removal of Ni(II) using MCNT electrodes is feasible, and results can be used for practical engineering applications. [ABSTRACT FROM AUTHOR]

Water desalination is a method to deal with water shortage that today considered as a way to meet the growing human demand. Obtaining freshwater at low cost guarantees the stability of the desalination method. Capacitive Deionization (CDI) method is a new technology for deionization of water with saline properties, the least energy, and environmental pollution. In this paper, an Artificial Neural Network (ANN) model was developed to estimate the amount of water produced by the CDI method based on experimental data. The backpropagation Multi-Layer Perceptron (MLP) model with Adam (Adaptive Moment Estimation) learning algorithm with two hidden layers was used. To evaluate performance, RMSE, MAE, MSE and R2 mathematical indices were used. The input layer had three variables that include the amount of initial solution concentration, the flow rate, and the amount of voltage applied to the cell. The output layer had a neuron as the amount of percentage of water desalination. For estimating the amount of salt removal percentage, the ANN modeling method was acceptable. The amount of correlation coefficient between experimental laboratory data and data estimated by ANN for training data was equal to 0.972. The overall correlation coefficient was 0.90 that for estimating the amount of salt removal percentage by CDI method is acceptable. The RMSE values for testing and training data were 0.008 and 0.003, respectively. In the statistical study of the effect of variables, it was found that by CDI method the initial concentration of salt has an inverse relationship with the amount of salt removed from water. Also, the amount of applied voltage has a direct relationship and the amount of feed rate has an inverse relationship with the amount of salt removed from water. • Predicting and modeling of salt removal percentage by CDI method using ANNs based on experimental data. • Applying the MLP model which is combined with Adam's learning algorithm considering different operating conditions. • Presenting a new hybrid modeling method by combining artificial intelligence strategies for the CDI method. [ABSTRACT FROM AUTHOR]

The unequal distribution of the water resources warrants a search for more energy efficient water treatment technologies. In this regard, capacitive deionization (CDI) could play a leading role particularly in the case of brackish water desalination. In this work, inexpensive materials that are commercially available were investigated for being used as electrodes in CDI. After physical and electrochemical evaluation, activated carbon (AC) demonstrated superior performance compared to the different fabrics tested. Hereafter, a factorial design of experiments was used to investigate the effect of cell potential, mass of AC ( m AC ), carbon black, and interparticle porosity on ion removal, charge efficiency and energy consumption. The results showed that neither carbon black nor macroporosity had a single effect on electrode performance. An interaction effect of macroporosity and m AC was found to be beneficial in terms of ion electrosorption for thick electrodes. An additional evaluation concerning the role of electrode thickness revealed that an increase in thickness translated into an increase in the total salt removed and a reduction in ion removal per mass of electrode. In addition, while electrosorption kinetics were found to be independent of the AC thickness, slow desorption kinetics were detected for the thicker electrodes. [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]

A promising electrode material, manganese dioxide (MnO 2), has been widely studied for capacitive deionization (CDI) desalination and recently researched for heavy metal removal. However, there are significant differences in the performance of MnO 2 in applications for heavy metal removal and desalination. In this paper, the mechanism for different electrochemical processes of Cd2+/Na+ ions on MnO 2 electrodes was comprehensively studied. MD simulations show that the diffusion performance of Cd2+ is much slower than that of Na+ in the presence of CdCl−, leading to a lower adsorption rate of Cd2+. Of the two ion storage mechanisms (capacitive and diffusion-controlled progress), capacitance contributions provided 65.6% of the total in the Na+ electrolyte, while diffusion-controlled progress contributed 55.2% in the Cd2+ electrolyte. For diffusion, tunnelling is the main storage mechanism for Na+; instead, Cd2+ undergoes a sequential surface redox process: (1) the combination of Cd2+ and O atoms from Mn-O-Mn results in the transition from Mn4+ to Mn3+, and (2) the H substitution reaction on Mn-O-H is generated from (1). Therefore, the adsorption capacity of Cd2+ is closely related to the chemical state of MnO 2 on the surface, which results in worse cycling stability than Na+. • The presence of CdCl+ reduces the migration of Cd2+ on the electrode surface. • Different faradaic processes are responsible for differences in the adsorption of Cd2+ and Na+. • The surface redox mechanism for Cd2+ in MnO 2 involves two processes. • The results of this study provide significant insights into the cation storage mechanism of MnO 2. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an emerging technology for the energy-efficient and cost-effective removal of ions from salt water by electrosorption. To further enhance the capacitive deionization performance, sugarcane bagasse biowastes are used as raw materials to synthesize biomass-derived electrodes via microwave carbonization and activation assisted with potassium hydroxide in the flows of carbon dioxide, which has the advantages of reducing preparation time and saving energy. Experimentally, the effect of microwave power (500–800 W) has been studied on the morphology, the ratios of mesoporosity in the biocarbons and their corresponding desalination performance of CDI. Accordingly, the biocarbons which are activated at 700 W of microwave irradiation under carbon dioxide atmosphere (denoted as SB-CO 2 –700) possess the higher fraction of mesopore to total pore volume (ca. 64.1%) with surface area (764 m2 g−1). By using cyclic voltammetry, the specific capacitance of SB-CO 2 –700 is calculated to be ca. 123 F g−1 at 5 mV s−1. With the superior properties (greater fraction of mesopore to total pore volume, reasonable surface area and hierarchical porosity), the electrosorption capacity of SB-CO 2 –700 samples is estimated to be 11.4 mg g−1 in 10 mM of NaCl solution at 1.2 V. These low-cost biowastes-derived hierarchically porous carbons prepared by time and energy saving route may provide a potential electrode for CDI applications. • Synthesis of biocarbons from bagasse was done by microwave-aided carbonization and activation. • The pore structure can be developed by adjusting microwave power in the presence of CO 2 and KOH. • The superior CDI capacity may be due to the higher V meso /V total , S BET and hierarchical pore. • The surpassing performance and cost-effectiveness enable biocarbons practical applications. [ABSTRACT FROM AUTHOR]

• The electrosorption capacity of AC electrodes is enhanced by nitric acid treatment. • The high salt removal of AC is due to the presence of oxygen containing groups. • The asymmetric electrode cell produced DI water with the conductivity of 1.6 μS/cm. • Nitric acid treated activated carbon is a promising electrode material for CDI. The deionized water (DI) of high purity standards is used in several industrial processes to manufacture products and technologies for high end applications. Currently, DI water is produced by either reverse osmosis or continuous electrodeionization systems, however; both of them are facing several limitations. Therefore there is an urgent need for the alternative technologies for DI water production. This study investigated suitability of producing DI water by using capacitive deionization (CDI) with nitric acid treated activated carbon electrodes (NTAC). Activated carbon (AC) was etched in nitric acid solution to introduce various oxygen functional groups on its surface. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to confirm the increased surface oxygen containing groups on AC after nitric acid treatment that enhanced its salt adsorption capacity. CDI experiments were conducted using water solution of 12.0 μS/cm as a result DI water with the conductivity of 1.6 μS/cm (DI water grade III, according to International Organization of Standards) was produced. Also, electrochemical tests revealed good capacitive behavior due to improved conductivity with NTAC having highest specific capacitance of 381.7 F/g compared to 106.6 F/g of AC electrode. This study provides an insight of the electrosorption performance of materials in desalination of solutions of low ionic strength. [ABSTRACT FROM AUTHOR]