Membrane Capacitive Deionization Research Articles

Efficient lithium extraction using redox-active Prussian blue nanoparticles-anchored activated carbon intercalation electrodes via membrane capacitive deionization

Global demand for lithium (Li) resources has dramatically increased due to the demand for clean energy, especially the large-scale usage of lithium-ion batteries in electric vehicles. Membrane capacitive deionization (MCDI) is an energy and cost-efficient electrochemical technology at the forefront of Li extraction from natural resources such as brine and seawater. In this study, we designed high-performance MCDI electrodes by compositing Li+ intercalation redox-active Prussian blue (PB) nanoparticles with highly conductive porous activated carbon (AC) matrix for the selective extraction of Li+. Herein, we prepared a series of PB-anchored AC composites (AC/PB) containing different percentages (20%, 40%, 60%, and 80%) of PB by weight (AC/PB-20%, AC/PB-40%, AC/PB-60%, and AC/PB-80%, respectively). The AC/PB-20% electrode with uniformly anchored PB nanoparticles over AC matrix enhanced the number of active sites for electrochemical reaction, promoted electron/ion transport paths, and facilitated abundant channels for the reversible insertion/de-insertion of Li+ by PB, which resulted in stronger current response, higher specific capacitance (159 F g−1), and reduced interfacial resistance for the transport of Li+ and electrons. An asymmetric MCDI cell assembled with AC/PB-20% as cathode and AC as anode (AC//AC-PB20%) displayed outstanding Li+ electrosorption capacity of 24.42 mg g−1 and a mean salt removal rate of 2.71 mg g min−1 in 5 mM LiCl aqueous solution at 1.4 V with high cyclic stability. After 50 electrosorption-desorption cycles, 95.11% of the initial electrosorption capacity was retained, reflecting its good electrochemical stability. The described strategy demonstrates the potential benefits of compositing intercalation pseudo capacitive redox material with Faradaic materials for the design of advanced MCDI electrodes for real-life Li+ extraction applications.

Water hyacinth as a green and sustainable material for carbon aerogel electrodes utilized in membrane capacitive deionization

AbstractWater hyacinth is a substantial and quick‐growing plant that can strongly invade and negatively affect the aquatic ecosystem, causing many problems to the water environment by consuming nutrients and oxygen from surface water. However, the hierarchical porous carbon derived from water hyacinth can be employed for the removal of oil spills, heavy metals, or wastewater nutrients. Recently, water‐hyacinth‐derived carbon aerogel has been utilized as electrode for the desalination of brackish water using membrane capacitive deionization (MCDI) technology. In this research, lignocellulose aerogels were synthesized from water hyacinth, which were then pyrolyzed to obtain carbon aerogel and then treated with KOH to acquire activated carbon aerogel, with the corresponding surface area of 51 and 100 m2 g−1. The desalination capacity of the MCDI device was also evaluated using a 200 ppm NaCl feed water solution with an applied potential of 1.2 V. A high salt adsorption capacity value of 14.69 mg g−1 was achieved after 3000 s. These results will lead a new research area of biomass and bio‐waste conversion to fabricate CDI‐utilized carbon aerogel electrodes.

Nanofiltration combined with membrane capacitive deionization for efficient classification and recovery salts from simulated coal chemical industrial wastewater

Achieving water reuse and salt resources recycling in high-salt wastewater from the coal chemical industry is crucial to the sustainable development. However, the current widely used RO (reverse osmosis)-NF (nanofiltration)-crystallizationprocess requires significant energy consumption in the step of heat-driven crystallization. Here, RO-NF-membrane capacitive deionization (MCDI) system was designed for classify and recover salt from high-salt wastewater of coal chemical industry. Sludge-derived biochar with high specific surface area and hierarchical structure was used as the electrode for MCDI. The MCDI cell can stabilize desalination of source water containing NaCl up to 300 mM, i.e., the total dissolved solids (TDS) of 18,000 mg·L−1, which can be applied to the desalination treatment after RO-NF salt separation. Based on the MCDI, a two-channel architecture was designed, in which a concentration channel was constructed between the electrode and the anion exchange membrane, while the desalination channel remains between the anion and cation exchange membrane. Continuous operation of desalination and concentration was achieved by exchanging the inlet and outlet of the concentration and desalination channels during the charging and discharging phases. This work demonstrates that the RO-NF-MCDI system could be a feasible method for classification and recovery salts from coal chemical industrial wastewater.

Bipolar Membrane Capacitive Deionization for pH-Assisted Ionic Separations

Selective ionic separations represent an increasingly important technical area for the strategic interests of the U.S. economy─for example, securing critical minerals and materials and circular economy aspirations that include recovering organic acids from processed biomass. This work disseminates bipolar membrane (BPM) capacitive deionization for selective ionic separations from multicomponent, ionic species mixtures. The selective separations are guided by the Pourbaix diagram and acid–base equilibria principles. BPM capacitive deionization was demonstrated to generate alkaline or acidic process streams depending upon the location of the BPM in the electrochemical cell. The role of system operating parameters, such as the cell voltage, residence time, and feed concentration on effluent stream pH was studied. It was observed that the pH adjustment in BPM-CDI/MCDI (MCDI, membrane capacitive deionization) was more sensitive to the cell voltage when compared to the process stream residence time and salt feed concentration. The BPM-MCDI gave over 6 times higher percentage of copper(II) removal when compared to sodium ion removal from brine mixtures. Finally, BPM-MCDI demonstrated over 40% greater removal for copper ions from brine mixtures and fivefold higher removal for itaconic acid from brine mixtures when benchmarked against a traditional flow-by-MCDI setup.

Electrode Materials for Desalination of Water via Capacitive Deionization.

Recent years have seen the emergence of capacitive deionization (CDI) as a promising desalination technique for converting sea and wastewater into potable water, due to its energy efficiency and eco-friendly nature. However, its low salt removal capacity and parasitic reactions have limited its effectiveness. As a result, the development of porous carbon nanomaterials as electrode materials have been explored, while taking into account of material characteristics such as morphology, wettability, high conductivity, chemical robustness, cyclic stability, specific surface area, and ease of production. To tackle the parasitic reaction issue, membrane capacitive deionization (mCDI) was proposed which utilizes ion-exchange membranes coupled to the electrode. Fabrication techniques along with the experimental parameters used to evaluate the desalination performance of different materials are discussed in this review to provide an overview of improvements made for CDI and mCDI desalination purposes.

Electrode Materials for Desalination of Water via Capacitive Deionization

AbstractRecent years have seen the emergence of capacitive deionization (CDI) as a promising desalination technique for converting sea and wastewater into potable water, due to its energy efficiency and eco‐friendly nature. However, its low salt removal capacity and parasitic reactions have limited its effectiveness. As a result, the development of porous carbon nanomaterials as electrode materials have been explored, while taking into account of material characteristics such as morphology, wettability, high conductivity, chemical robustness, cyclic stability, specific surface area, and ease of production. To tackle the parasitic reaction issue, membrane capacitive deionization (mCDI) was proposed which utilizes ion‐exchange membranes coupled to the electrode. Fabrication techniques along with the experimental parameters used to evaluate the desalination performance of different materials are discussed in this review to provide an overview of improvements made for CDI and mCDI desalination purposes

Explainable deep learning model for membrane capacitive deionization operated under fouling conditions

To avoid fouling problems during operation, membrane capacitive deionization (MCDI) requires proper cleaning processes. In this study, we assessed seven different conditions to investigate the effects of flushing conditions and foulant concentration on the recovery rate of the MCDI salt adsorption capacity. Two representative deep learning models, namely the long short-term memory (LSTM) and temporal fusion transformer (TFT) models, were developed to simulate effluent salt concentrations under fouling conditions. The prediction results obtained using the two models indicated that the TFT model (R2, 0.945–0.993; RMSE, 0.051–0.151) was superior to the LSTM model (R2, 0.631–0.993; RMSE, 0.051–0.740) in terms of performance and applicability. Analyses of the permutation importance and attention weights were performed to evaluate the importance of input variables and the model-training process. The interpretation of the models based on attention scores revealed that the TFT model used the applied voltage and implementation of flushing as important inputs, which contributed to higher prediction accuracy. Thus, the proposed model could be utilized as an interpretable artificial intelligence model in practical applications to improve the efficiency of MCDI operations involving flushing processes.

Photovoltaic powered operational scale Membrane Capacitive Deionization (MCDI) desalination with energy recovery for treated domestic wastewater reuse

An operational scale Membrane Capacitive Deionization (MCDI) desalination system was trialled for water reuse applications in Western NSW, Australia. The 6 electrode module system had an average current efficiency of 74 %, water recovery of 84 % (77 % including pre-treatment) and delivered 1.0 m3/h of treated water with an electrode energy consumption of 0.35 kWh/m3 (including energy recovery) and total energy consumption of 1.28 kWh/m3 (using mains power) or 1.05 kWh/m3 (using photovoltaics to power the electrodes). No performance decline was noted over an operational period of 3 months that included reverse current stopped flow desorption and regular cleaning with sodium hypochlorite. The use of photovoltaics for the electrode power supply enabled an average power saving of 27 %. The inclusion of energy recovery devices on the electrode control system facilitated a 40 % reduction in electrode energy consumption. The system demonstrated that MCDI desalination is a feasible option for treated domestic wastewater reuse and can be easily coupled with photovoltaics supply to the electrodes. As one of the first larger scale MCDI operations, we demonstrate that performance trends found in bench scale studies do translate to larger units, however control constraints of the operational units may require optimisation trade-offs between performance parameters.

Zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon electrode for efficient capacitive deionization defluorination

Excessive fluoride in water is severe harm to human health and has become a global public health problem. However, there is a lack of efficient and affordable defluorination technology, especially for fluoride removal from low concentration F- wastewater. Herein, zinc oxide nanosheet decorated self-supporting hierarchical porous wood carbon (ZnO/HPWC) was prepared as electrode for membrane capacitive deionization (MCDI) and used for defluorination. The used activator of ZnCl2 would not only manufacture hierarchical pore structure of wood carbon, but also allow in-situ vertical growth of uniform ZnO nanosheets on HPWC. A high F- removal (94.52%) was achieved at 5 mg L-1 of F− solution by the ZnO/HPWC-based MCDI, as well as its improved electrosorption capacity (31.25 mgF- g-1ZnO/HPWC). Excellent defluorination performance of ZnO/HPWC was also achieved at real wastewater (F-, 6.25 mg L-1), of which the final F- concentration (1.32 mg L-1) can meet the WHO standard of drinking water (<1.5 mg L-1). The defluorination mechanism was studied and discussed, which proved the high defluorination performance of ZnO/HPWC was due to the chemical interaction between F- and ZnO nanosteets, and diffusion capacitance (pseudocapacitance) offered by ZnO nanosheets dominated over the surface capacitance (electric double layer capacitance) by HPWC.

Predictive performance and costing model for Membrane Capacitive Deionization (MCDI) at operational scale

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.

Electrochemical properties of MCDI-utilized PVA/SSA/GA cation exchange membrane

Membrane capacitive deionization (MCDI), an alternative desalination technology that uses a voltage between two electrodes that are covered with ion-exchange membranes to remove salt, has been drawing a lot of research attention. It has been demonstrated that the desalination performance in terms of salt removal and energy efficiency can be maximized when ion-exchange materials are incorporated on the electrodes in MCDI. In this study, the electrochemical properties of the MCDI electrodes coated with PVA/SSA/GA cation exchange membrane were intensively investigated, specifically the effect of sulfosuccinic acid (SSA) and glutaric anhydride (GA) content in the cross-linking reaction with polyvinyl alcohol (PVA). The presence of SSA in the cation exchange membrane helps improve its conductivity, as proven by the electrochemical measurements via cyclic voltammetry and galvanostatic charge-discharge. As a result, the salt adsorption capacity was also enhanced in the addition of SSA and GA into the PVA chain. The PVA/SSA/GA cation exchange membrane is proved to be an inexpensive, environmentally friendly and suitable candidate to be utilized in the MCDI systems.&#x0D; ® 2022 Journal of Science and Technology - NTTU

Selective lithium extraction from diluted binary solutions using metal-organic frameworks (MOF)-based membrane capacitive deionization (MCDI)

The increasing demand for lithium (Li) calls for exploring efficient and environmental-friendly methods to extract Li from brine. Capacitive deionization (CDI) as an emerging technology is of interest for resource recovery because of its rapid adsorption rate, limited energy consumption, and low environmental impact. However, Na and K in seawater and seawater reverse osmosis (SWRO) brine and Mg and Ca in inland brine challenge the feasibility of selective Li extraction. Herein, CDI was integrated with deposition-coated ZIF-8-PDA membranes to extract Li from binary solutions containing Li and M (M representing Na, K, Mg, and Ca). MCDI tests were conducted under a series of voltages (±0.5 V, ±1.0 V, and ±1.5 V) to investigate the influence of applied potentials on Li extraction performances. The results indicated advantages for Li extraction when coexisting cations were monovalent than divalent. Additionally, a lower voltage of 0.5 V could provide superior Li selectivity, charge efficiency (CE), and energy normalized to Li (ENL) than higher voltages. Especially, Li selectivity of 1.50 and 1.85 was achieved in Li/Na and Li/K feeds under 0.5 V, 37 % and 74 % higher than those under 1.5 V, respectively, illuminating the potential of MCDI for Li extraction from seawater and SWRO brine with low energy input.

Functional anode of membrane capacitive deionization enabled by Cu2+/Cu+ redox couple for simultaneous anions removal and anodic oxidation mitigation

Activated carbon (AC) based conventional capacitive deionization has shown extraordinary promise for energy efficient water treatment, but its capacity and cycle stability are limited by the mechanism of electric double-layer and the oxidation of anode, respectively. Redox electrolytes are proposed as one of the most promising strategies to improve the charge storage capacitance. Here, functional anode enabled by Cu2+/Cu+ redox couple is constructed by adding 10 mM CuCl2 into 100 mM NaCl supporting electrolyte. A membrane capacitive deionization (MCDI) cell with the functional anode and anion exchange membrane, employing a two channel structure is proposed to remove the anions (F−, Cl−) from wastewater. The reverse constant current discharge mode with 1.2 V/−1.2 V cut-off voltage can realize Cu2+/Cu+ redox reaction. The water production rate of the MCDI cell is above 50 % and the Cl− removal capacity is increased by 163 % due to the additional faradaic process. The cell capacity can be maintained above 83 % after 40 cycles. In particular, fast charge balance and redox couple reaction processes of this functional anode could significantly alleviate the oxidation of the anode AC electrode. This work provides new opportunities for developing cost-effective technologies to remove the anions from wastewater.

Voltage control for membrane capacitive de-ionization cell for higher energy efficiency in salt removal

Membrane Capacitive DeIonization (MCDI) cells have proven to be advantageous in water desalination and ions removal. Therefore, the time has come to introduce an alternative water purification technique to reduce the global water shortage. MCDI is known to be environmentally friendly, energy efficient and economical. Besides its reduced energy footprint, recent applications underline the regenerated energy during the desorption phase, which makes the MCDI as a potential cleaner energy source. Thus, a large number of scientific publications addressing problems and enhancing the performance of an MCDI have been published. In this paper, we have developed a simple and inexpensive method to control the adsorption voltage of the cells. So, the ion adsorption/desorption mechanisms of the MCDI will be controlled by a variable charging voltage applied to the cell.The entire response of controlled MCDI integrated model was created and he simulated results were compared with the experimental ones in order to validate the results. Accordingly, the controller parameters were tuned using the genetic algorithm optimization technique, based on the integral time absolute error criterion. Furthermore, the experimental results reveal that the control of the cell had increased the salt retention by 50%, the quantity of removed salt by the energy unit was improved by 10%, and the cell energy ratio from 28% to 32%.

Treatment of Semiconductor Wastewater Containing Tetramethylammonium Hydroxide (TMAH) Using Nanofiltration, Reverse Osmosis, and Membrane Capacitive Deionization

As the semiconductor industry has grown tremendously over the last decades, its environmental impact has become a growing concern, including the withdrawal of fresh water and the generation of harmful wastewater. Tetramethylammonium hydroxide (TMAH), one of the toxic compounds inevitably found in semiconductor wastewater, should be removed before the wastewater is discharged. However, there are few affordable technologies available to remove TMAH from semiconductor wastewater. Therefore, the objective of this study was to compare different treatment options, such as Membrane Capacitive Deionization (MCDI), Reverse Osmosis (RO), and Nanofiltration (NF), for the treatment of semiconductor wastewater containing TMAH. A series of bench-scale experimental setups were conducted to investigate the removal efficiencies of TMAH, TDS, and TOC. The results confirmed that the MCDI process showed its great ability as well as RO to remove them, while the NF could not make a sufficient removal under identical recovery conditions. MCDI showed higher removals of monovalent ions, including TMA+, than divalent ions. Moreover, the removal of TMA+ by MCDI was higher under the basic solution than under both neutral and acidic conditions. These results were the first to demonstrate that MCDI has significant potential for treating semiconductor wastewater that contains TMAH.

A review on recent contributions in the progress of membrane capacitive deionization for desalination and wastewater treatment

A review on recent contributions in the progress of membrane capacitive deionization for desalination and wastewater treatment

New operation method of a membrane capacitive deionization system with a dual-solution mode for improving the desorption rate

A new operation method of a membrane capacitive deionization (MCDI) system with a dual-solution mode was proposed. In this method, the concentration of the solution supplied to the cell was different during the adsorption and desorption processes. After adsorption was performed for the adsorption solution (AS) of 10 mM NaCl, desorption was performed while changing the concentration of the desorption solution (DS) to 10–70 mM. As the DS concentration increased, the discharge rate (desorption rate) linearly increased. The average discharge rates at DSs of 10 and 70 mM are 0.187 and 0.278C/g·s, respectively, which increases by approximately 1.5 times. As the DS concentration increases, the time constant (product of the electrical resistance and capacitance) of the cell decreases, resulting in an increase in the desorption rate. At the end of the desorption process, some DS remained inside the cell, reducing the charge efficiency of the subsequent adsorption process. By changing the flushing time, it was possible to control the charge efficiency and the water recovery.

Effect of activated carbon electrode material characteristics on hardness control performance of membrane capacitive deionization.

Capacitive deionization (CDI) is an electrochemical-based water treatment technology that has attracted attention as an effective hardness-control process. However, few systematic studies have reported the criteria for the selection of suitable electrode materials for membrane capacitive deionization (MCDI) to control hardness. In this study, the effect of electrode material characteristics on the MCDI performance for hardness control was quantitatively analyzed. The results showed that the deionization capacity and the deionization rate were affected by the specific capacitance and BET-specific surface area of the activated carbon electrode. In addition, the deionization rate also showed significant relationship with the BET specific surface area. Furthermore, it was observed that the deionization capacity and the deionization rate have a highly significant relationship with the BET specific surface area divided by the wettability performance expressed as the minimum wetting rate (MWR). These findings highlighted that the electrode material should have a large surface area and good wettability to increase the deionization capacity and the deionization rate of MCDI for hardness control. The results of this study are expected to provide effective criteria for selecting MCDI electrode materials aiming hardness control.

Enhancing desalination rate and water recovery through operational optimization of a membrane capacitive deionization system

Enhancing desalination rate and water recovery through operational optimization of a membrane capacitive deionization system

Implementation and design of an electrical characterization system for membrane capacitive deionization units in water treatment, with teaching purpose

Implementation and design of an electrical characterization system for membrane capacitive deionization units in water treatment, with teaching purpose