CDI Process Research Articles

Hydrophilic porous activated biochar with high specific surface area for efficient capacitive deionization

Porous carbon electrode materials were prepared by carbonization and alkali activation from three natural porous biomasses, lotus petiole (LP), sunflower plate (SP), and lotus seedpod (LS). The pore structure, surface characteristics, and electrochemical properties of the three activated biochars were investigated and related to their CDI performance. The results indicated that the three activated biochars were hydrophilic and negatively charged, with a high specific surface area and an abundance of micropores. Due to the best surface wettability, highest specific capacitance, and shortest charge-discharge time, lotus petiole-based activated biochar (LPCK) had the highest electrosorption capacity of 8.67 mg·g−1 and faster desalination rate of 0.24 mg·g−1·min−1. Cyclic voltammetry and adsorption kinetics results indicate that the double-layer electrostatic adsorption mechanism dominated the CDI processes of the three activated biochars. The use of three biomass wastes provides low-cost, eco-friendly, and sustainable materials for the development of CDI electrodes.

Insights into electro-assisted and selective adsorption of U(VI) using hierarchical porous and activated biocarbon from lotus pods/2D-MoS2/polypyrrole composites through capacitive deionization

The current research work involves the fabrication of orderly mesoporous composite materials based on layered molybdenum disulfide, a hierarchical porous biocarbon from Lotus pods electrodeposited with polypyrrole (2D-MoS2/BCL/PPy). The polypyrrole, as a conducting polymer, was electrodeposited in different mole ratios onto Ni foam supported by 2D-MoS2/BCL. The composite materials were analytically characterized by means of FTIR, SEM-EDX, BET, and XRD techniques. The Lotus pod-driven biocarbon exhibited a high surface area. Among different composites, BCL/PPy-3 (electrodeposited with 0.3 M PPy) was found highly efficient in electro-assisted hexavalent uranium recovery via capacitive deionization because of its impressive specific capacitance (Csp) (100.40 F/g) with improved active surface area and admirable total pore volume. These characteristics made BCL/PPy-3 competitive for enhanced hexavalent uranium ion electrosorption. These features were highly conducive to fast electron transfer and better diffusion of hexavalent uranium ions during the CDI process. The exposed S atoms in BCL/PPy-3 showed good coordination and complexing power for hexavalent uranium ions. The BCL/PPy-3 exhibited an inspiring sorption capacity of 417.90 mg/g at pH = 4.5 and applied voltage (−0.9 V), which is better than many other materials used in CDI applications having similar geometry and morphology. During the electrosorption, the composite electrode BCL/PPy-3 offered a small solution resistance (Rs) (0.69 cm2), a minute charge transfer resistance of Rct (1.19 Ω cm2), and a substantial double layer constant phase element (qdl) of (0.0372 S sn/cm2). These features make this composite electrode highly effective for hexavalent uranium ions removal.

Enhanced salt removal performance using nickel hexacyanoferrate/carbon nanotubes as flow cathode in asymmetric flow electrode capacitive deionization

One of the most widely used CDI processes is flow electrode capacitive deionization (FCDI), which is preferred over conventional CDI with static electrode due to its continuous treatment of high-salt wastewater and ability to scale production. However, the discontinuous charge transport network in flow electrodes restricts the improvement of desalination performance. In this study, we prepared nickel hexacyanoferrate and carbon nanotubes composites (NiHCF@CNTs) by a simple ball-milling method and constructed an asymmetric FCDI (AFCDI) system using NiHCF@CNTs and AC as flow cathode and anode, respectively. Then the desalination performance of AFCDI was examined and compared with that of symmetric FCDI system using AC as both flow electrodes under different conditions. The stability was also investigated by a 20-cycle operation test. It was found that AFCDI system showed higher average salt removal rate and lower energy consumption compared with FCDI, owing to the enhancement of charge transport resulting from the couple of high specific capacitance of NiHCF and excellent electrical conductivity of CNTs. Moreover, AFCDI system has stable desalination performance in continuous operation. These results indicate that compositing Faradic materials and CNTs is an effective strategy for improving desalination performance of FCDI.

An insight on the development of functional carbon electrodes from plastic waste for capacitive deionization towards sustainable water reclamation

AbstractCapacitive deionization (CDI) is an emerging electrochemical‐based adsorption system that has a high capability for the water reclamation with future potential towards an energy‐efficient and cost‐effective technique for industrial implementations. However, the higher cost of electrodes and poor performance limit its scale‐up, and there is a need to focus on a cost‐effective electrode towards economic impacts. Among the various waste resources, plastic sources would be the better precursor for carbonization as the plastic‐derived carbon possess enhanced surface properties and high electrochemical stability. Further, the carbonization of plastic products towards electrode minimizes greenhouse gas emissions, maintains environmental sustainability and achieves a dual benefit of circular economy with water reclamation. This paper highlights the overview of CDI, the significance of electrodes in CDI for electrosorption studies, various synthetic routes of plastic‐derived carbon, and its properties that help the researchers to focus on zero waste discharge‐based CDI process.

Chicken feather-derived carbon electrodes for capacitive deionization using poly(vinyl alcohol)-glutaraldehyde as the binder

Abstract Capacitive deionization (CDI) is an emerging technology which is being developed as a promising desalination alternative for charged species from salt water, being electrode materials as key drivers for highly efficient process. Here, we describe synthesis of highly porous activated carbons from chicken feathers using pyrolysis followed by chemical activation with potassium hydroxide in a 1:4 ratio to produce sustainable, scalable, and sustainable carbon electrodes for CDI. Poly (vinyl alcohol) (PVA) was used as binder to modify chicken feather activated carbons (CF-AC), which were subsequently crosslinked with glutaraldehyde (GA) to produce CF-AC-PVA-GA polymers through acetylation reaction. This resulted from improving hydrophilicity of CF-AC-PVA-GA polymers to raise the electrodes' resistance. Prepared materials were characterized using scanning electron microscopy, Fourier transform infrared, X-ray diffraction, Brunauer-Emmett-Teller and cyclic voltammetry. Fabricated CDI electrodes were used to investigate their performance for desalination, and exhibited different electrosorption capacity at different applied potentials. Modified electrodes possessed good stability in shear conditions and CDI process was stable and reproducible around 16 electrosorption cycles. Salt removal capacity of the modified electrodes (CF-AC-PVA-GA) was found to be 3.89 mg g−1. The obtained outcomes offer important considerations of ions electrosorption and help advancing CDI system for water treatment and desalination.

An experimental approach to treat salt and dye contaminated water via capacitive deionization.

This article is intended to provide the versatility of the CDI process for an application covering various pollutants, namely, dye and salt contaminated stream treatment. It was observed that tailoring the base material enhances stated properties revealing proficiency in desalting and dye removal performance. Further, the experimental investigations were performed by modifying the surface of agro-waste developed electrodes to improve the sorption of contaminants over bio-based activated carbon (B-AC). The chemical activation was with potassium hydroxide (KOH-BAC) and phosphoric acid (H3PO4-BAC). The study indicates the best electrochemical and sorption properties with H3PO4-BAC incorporated electrode of the electrode 76.97 F/g specific capacitance. Moreover, these fabricated electrodes were implemented for dye effluent treatment and desalting the concentrated stream from RO reject. It was evaluated that a strong sorption capacity for 18.4 mg/g in the case of salt stream was observed for H3PO4-BAC electrode whereas 0.12 mg/g was reported for dye removal. The equilibrium data was fitted into the isotherm and kinetic model of adsorption. Lastly, the study reveals that the fabricated electrode has huge potential to treat contaminated water.

A Novel Dual-Ion Capacitive Deionization System Design with Ultrahigh Desalination Performance.

Capacitive deionization is an emerging desalination technology with mild operation conditions and high energy efficiency. However, its application is limited due to the low deionization capacity of traditional capacitive electrodes. Herein, we report a novel dual-ion capacitive deionization system with a lithium-ion battery cathode LiMn2O4/C and a sodium-ion battery anode NaTi2(PO4)3/C. Lithium ions could enhance the charge transfer during CDI desalination, while NaTi2(PO4)3/C provided direct intercalation sites for sodium ions. The electrochemical capacities of the battery electrodes fitted well, which was favorable for the optimization of the desalination capacity. The low potential of the redox couple Ti3+/Ti4+ (-0.8 V versus Ag/AgCl) and intercalation/deintercalation behaviors of sodium ions that suppressed hydrogen evolution could enlarge the voltage window of the CDI process to 1.8 V. The novel CDI cell achieved an ultrahigh desalination capacity of 140.03 mg·g-1 at 1.8 V with an initial salinity of 20 mM, revealing a new direction for the CDI performance enhancement.

High-performance pseudocapacitive removal of cadmium via synergistic valence conversion in perovskite-type FeMnO3

Cadmium pollution is a serious threat for the global drink water and natural environment. Herein, a poly-pyrrole coated dual-metal perovskite-type oxide FeMnO3 (PFMO@PPy) was developed firstly as pseudocapacitive cathode for the reversible capture and release of cadmium ions by asymmetry pseudocapacitive deionization (APCDI) technology, extending the library of CDI electrodes. Our work highlighted several points: (i) PFMO@PPy achieved a maximum Cd-removal capacity of 144.6 mg g−1, and maintained the retention rate of 93.4% after 15-cycle CDI process for up to 150 h, far beyond other previous work. (ii) PFMO@PPy showed the superior removal ratio (~90%) under different real water environments such as tap water, lake water and the groundwater. (iii) The superior Cd(II) electrosorption and desorption behavior is ascribed to the reversible synergistic valence conversion (Fe3+/Fe0 and Mn3+/Mn2+), which is confirmed by ex-situ XPS measurement and electrochemical tests. (iv) DFT calculations confirmed the synergistic effect from Mn and Fe elements in perovskite-type bimetallic oxide FeMnO3. This study paves a new way for promising future applications of perovskite-type oxides containing dual Faradic redox-activity for wastewater treatment and environmental remediation.

Resident integration with inpatient clinical documentation improvement: a quality improvement project

BackgroundClinical documentation improvement (CDI) is an increasing part of health system quality and patient care with clinical documentation integrity specialists (CDIS) expanding into daily physician workflow. This integration can be...

(Invited) Separation and Hydrogenation of Ions By Micro-Scale Capacitive-Faradaic Adsorbing Fuel Cells

Capacitive deionization processes are aimed at separation of ions from water and wastewater. Since late 1960-s, when the CDI concept was proposed, the technique was improved via incorporation of ion exchange membranes (MCDI), utilization of slurry electrodes (FCDI) and introduction of one or two battery electrode(s) into the process to enhance the salt adsorption capacity of the cell and to reduce the energy demand of the process. In all these processes the monopolar electrodes must be physically connected to the DC power supply via wires, and cathodes and anodes should be separated to prevent short-circuiting. These and other requirements of CDI processes result in serious drawbacks, limitations and sophisticated design of water treatment reactors.A novel CDI-based method for separation of ions from water and wastewater using micro-scale (10µm – 5 mm) fuel cells is proposed1. The fuel cells comprise activated carbon particles loaded with bi-functional catalyst for hydrogen oxidation and oxygen reduction reactions. Within the proposed process of ions removal, the particles act as the micro-scale capacitive-faradaic adsorbing fuel cells (MS-CF-AFC) which require oxygen and hydrogen gases for adsorption of ions during the water treatment step and desorption of ions in brine production.Within the O2-induced adsorption of anions, thereduction of oxygen on Pt (faradaic electrode of the MS-CF-AFC) results in depletion of electrons from the carbonaceous part (i.e. the capacitive electrode) of the micro-scale fuel cell, which leads to adsorption of anions in the electrical double layer of carbon. The hydrogen oxidation that occurs during the regeneration of the anions-loaded MS-CF-AFCs results in accumulation of electrons in the capacitive electrode and in repulsion of perchlorate ions into the regenerant solution. This way the chemical energy of H2 and O2 is converted by the MS-CF-AFCs into the electrical energy which is utilized for separation of ions. For the separation of cations, the MS-CF-AFCs are powered by the H2 gas during the cationsadsorption step and by the O2 gas in brine production.The O2-induced adsorption of anions (and desorption of cations) results in pH increase in the treated water. Consequently, within the MS-CF-AFC treatment the separated anions are “exchanges” with OH- ions. The rate of the process is faster at lower pH values in the treated water. Higher anions adsorption capacity is achieved at higher O2 pressure. The H2-induced desorption of anions (and adsorption of cations) is accompanied by decrease in the pH. Thus, the cations removal process can be regarded as an exchange of separated cations with the H+ ions. The H2-induced step of the MS-CF-AFC processes is faster at higher pHs, and higher cations removal capacity is obtained at higher H2 pressure. To enhance the salt adsorption capacity of MS-CF-AFCs for anions and cations the activated carbon in the cells can be decorated with appropriate surface groups, e.g., carboxylic and amine groups (respectively).The process was proved for the removal of perchlorate, copper and nitrate ions using pure solutions of NaClO4, KNO3 and CuCl2 salts in deionized water and in groundwater, using batch and packed-bed reactors for two types of platinum loaded (5wt%) MS-CF-AFCs prepared from Lewatit AF5 microporous carbon and a powdered activated charcoal.The main disadvantage of the process described above is its inability to “deactivate” toxic NO3 - and ClO4 - ions as the process only concentrates the pollutant (similarly to the well-known ion-exchange). It was shown that Pt-Cu MS-CF-AFCs are capable to adsorb nitrate ions from water and to reduce them into the N2 gas during the H2-induced step of anions desorption from the MS-CF-AFCs.The proposed MS-CF-AFCs can be performed in batch, continuous stirred (CSTR), fixed-bed and other types of reactors normally applied in adsorptive water treatment processes.Potential advantages of the MS-CF-AFCs process are: (1) the process can be utilized for separation of all types of anions and cations (appropriate carbon modification might be required); (2) the process can be performed in any type of adsorption reactors; (3) desalinating hybrid capacitive-faradaic micro-scale fuel cells do not require any wiring as opposite to CDI, previously proposed desalinating fuel cells and battery electrode desalination processes; (4) the regeneration of the MS-CF-AFCs does not require any concentrated solutions of acids, bases or salts; and (5) the hydrogen required for the process can be produced on-site using hydrogen generators and air can be utilized as the oxygen source.[1] Gendel, Y., Amikam, G., Nativ, P., 2020. Separation of Anions and Cations from Water and Wastewater Using Micro-Scale Capacitive-Faradaic or Pseudocapacitive-Faradaic Adsorbing Fuel Cells. US Provisional Patent Application 62/983,689. Figure 1

A newly synthesized highly stable Ag/N-carbon electrode for enhanced desalination by capacitive deionization

A new Ag@C electrode with Ag–Nx structure was synthesized, which exhibits a high Cl− electrosorption capacity of 75.3 mg g−1 and long-term recycling stability in CDI processes.

Quantitative insight into the effect of ions size and electrodes pores on capacitive deionization performance

In this work, effect of ions size is combined with the influence of pore size to provide a quantitative simulation method to evaluate CDI desalination performance. The method is capable of simulating the equilibrium and dynamic behaviours of the CDI. The simulation provides instructive observations that are important to enhance the current state of the art in CDI research and facilitate its implantation into industrial scale. For example, the desalination performance of CDI for high salinity water can be enhanced by using electrodes with small pore size (less than 2nm), while electrodes with higher pore size performs better for lower salinity water. From design respective it is therefore recommended to use electrodes with different pore sizes for multi-stage CDI process, as the salinity of water will increase from one stage to another. For electrolyte of a given concentration, the specific desalination capacity increases when the pore size becomes smaller till approach a threshold pore size and then dramatically decreases, particularly this is most severe for high salinity water. Therefore, careful and precise design approach for the electrode pore size is crucial. As ions of smaller volume can accumulate more for the same pore size limit, the analysis inspires us an innovative approach: to enhance the CDI performance through reducing the size of ions by weakening the hydration, which has been achieved by employing the electromagnetic wave in our experiments.

Confirmation of The Fouling Phenomena in CDI Process and The Establishment of Its Removal Process Conditions

Confirmation of The Fouling Phenomena in CDI Process and The Establishment of Its Removal Process Conditions

Multifunctional group sulfobutyl ether β-cyclodextrin polymer treated CNT as the cathode for enhanced performance in asymmetric capacitive deionization

In order to enhance the desalting performance of electrode in the capacitive deionization process (CDI), a novel sulfobutyl ether β-cyclodextrin polymer with multi-sulfonic groups and multi-hydroxyl groups (SBE-β-CDP) was successfully synthesized and attached on the surface of carbon nanotubes (CNT) by non-covalent bond. The as-prepared CNT@SBE-β-CDP electrode possesses significantly improved capacitance property and hydrophilicity (60.9 F/g, 65.5°) as compared to the CNT electrode (51.7 F/g, 103.6°), which indicates that the multi-sulfonic groups and multi-hydroxyl groups on the CNT@SBE-β-CDP electrode surface can provide efficient ion transfer pathway by the synergistic effect. The symmetric and asymmetric CDI cells, named as R‖R, R(+)‖R-CDP(−) and R-CDP(+)‖R(−), were assembled with the CNT electrode (R) and CNT@SBE-β-CDP electrode (R-CDP). Based on the electroneutrality principle of electrode, the theoretical analysis about the adsorption process of these CDI cells by balancing the ionic charge, electronic charge and chemical charge in the electrode demonstrates that when the CNT@SBE-β-CDP electrode is used as cathode, the theoretical charge efficiency reaches a maximum in the asymmetric R(+)‖R-CDP(−). In the desalting experiments, the average salt adsorption capacity and charge efficiency for R(+)‖R-CDP(−) (6.37 mg/g, 36.9%) surpass those of R‖R (4.17 mg/g, 25.8%) and R-CDP(+)‖R(−) (3.11 mg/g, 17.3%). These facts confirm the good cation selectivity of CNT@SBE-β-CDP electrode that strengthens the desalting performance of asymmetric CDI process.

The Ratio between the Surface Charge and Electrode's Capacitance as a Fast Tool for Assessing the Charge Efficiency in Capacitive Deionization Processes

This paper suggests an effective approach to evaluate carbon electrodes that can be effective in capacitive de-ionization processes of salty aqueous solutions. The first assessment of any electrode material, before its assembly in a CDI cell, includes its specific capacitance and its electric conductivity among other physical properties. These properties may bring a sense whether the electrode can be suitable for electro-adsorption processes, but can hardly tell about the efficiency of the process which is related to the charge utilization. A new term is discussed - the ratio between the specific capacity of an electrode and the specific charge related to the electrode's surface groups. A close inspection of the amphoteric modified Donnan model of the electric double layer shows that the ratio between the surface charge density and the integral specific capacitance, namely, the overall charge density, of the carbon electrodes is a useful term for predicting the CDI process efficiency. Such a ratio is obtained by regular electrochemical analysis of carbon electrodes and a simple titration of the functional surface groups. For demonstration, electrodes comprising commercial activated carbon cloth were tested in CDI cells. The theoretical calculations were correlated to the performance of their performance in CDI processes.

Facile synthesis of TiO2/ZrO2 nanofibers/nitrogen co-doped activated carbon to enhance the desalination and bacterial inactivation via capacitive deionization

Capacitive deionization, as a second generation electrosorption technique to obtain water, is one of the most promising water desalination technologies. Yet; in order to achieve high CDI performance, a well-designed structure of the electrode materials is needed, and is in high demand. Here, a novel composite nitrogen-TiO2/ZrO2 nanofibers incorporated activated carbon (NACTZ) is synthesized for the first time with enhanced desalination efficiency as well as disinfection performance towards brackish water. Nitrogen and TiO2/ZrO2 nanofibers are used as the support of activated carbon to improve its low capacitance and hydrophobicity, which had dramatically limited its adequacy during the CDI process. Importantly, the as-fabricated NACTZ nanocomposite demonstrates enhanced electrochemical performance with significant specific capacitance of 691.78 F g−1, low internal resistance and good cycling stability. In addition, it offers a high capacitive deionization performance of NACTZ yield with electrosorptive capacity of 3.98 mg g−1, and, good antibacterial effects as well. This work will provide an effective solution for developing highly performance and low-cost design for CDI electrode materials.

Lithium dedicated adsorbent for the preparation of electrodes useful in the ion pumping method

Abstract In this paper, our studies on the extraction of lithium using a new desalination technology are presented. The combination of capacitive deionization with ion pumping batteries resulted in the hybrid CDI process. Hybrid CDI was composed by an electrode prepared from inorganic adsorbents (blended manganese and titanium oxides) and a counter electrode made of activated carbon. The structure and porosity of the adsorbents were investigated by SEM, XRD and BET analyses, while the pore size distribution was calculated according to the QSDFT model. The adsorbent with the best electrochemical performance was manganese oxide with a 5% content of titanium dioxide. It was characterized by enhanced electron conductivity and a structure that offers the highest hybrid CDI adsorption capacity for lithium. This material was used to build a negatively polarized electrode of the hybrid system that allowed ∼36 mg/g sorption capacity for LiCl to be reached. The uptake of KCl and NaCl was 16 mg/g and 11 mg/g, respectively. Additionally, the best adsorbent was characterized by a 2 times smaller consumption of energy needed to extract lithium chloride in comparison to other monovalent salts.

Fabrication of N-doped &SnO2-incorporated activated carbon to enhance desalination and bio-decontamination performance for capacitive deionization

Herein, nitrogen-doped tin oxide intercalated activated carbon nanocomposite (N-AC/SnO2) were prepared using hydrothermal strategy and explored as an electrode for capacitive desalination and disinfection. Although tin oxide (SnO2) has good characteristics, the nitrogen must be carefully considered for modifying the characteristics of the carbonaceous materials to improve the performance as an electrode in the CDI process. The characterization of the proposed materials which investigated by XRD, TEM, FE-SEM, XPS and FT-IR affirmed the formation of the nanocomposite. The electrosorption behavior investigated by electrochemical techniques demonstrates that, compared to the specific capacitance of the AC and AC/SnO2 (207.46 F g−1 and 233.21 F g−1), that of the N-AC/SnO2 is higher at 408.8 F g−1, and N-AC/SnO2 exhibits better electrical conductivity. The CDI performance evaluated by batch mode experiments through an applied voltage of 1.2 V in a 50 mg L−1 NaCl aqueous solution shows that the N-AC/SnO2 electrode introduces a higher electrosorptive capacity of 3.42 mg g−1, an enhanced desalination efficiency of 61.13%, and good antibacterial performance. Overall, the present study demonstrates that N-AC/SnO2 has considerable potential as an electrode material for CDI application.

Functionalization of biomass carbonaceous aerogels and their application as electrode materials for electro-enhanced recovery of metal ions

The CAs/MO hybrid electrodes show an outstanding decontamination capacity of 57.13 mg g−1for Cu(ii) at a low applied voltage of 1.2 V, which was nearly 3 times higher than that of 19.28 mg g−1at an open circuit, which highlights the advantages of the CDI process in decontamination technology.

High capacity and high rate capability of nitrogen-doped porous hollow carbon spheres for capacitive deionization

In this work, nitrogen-doped porous hollow carbon spheres (N-PHCS) were well prepared by using polystyrene (PS) spheres as hard templates and dopamine hydrochloride as carbon and nitrogen sources. Field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate that the N-PHCS have a uniform, spherical and hollow structure. Nitrogen adsorption–desorption analysis shows that the N-PHCS have a high specific area of 512m2/g. X-ray photoelectron spectroscopy result reveals that the nitrogen doping amount is 2.92%. The hollow and porous structure and effective nitrogen doping can contribute to large accessible surface area, efficient ion transport and good conductivity. In the electrochemical tests, we can conclude that the N-PHCS have a high specific capacitance value, a good stability and low inner resistance. The N-PHCS electrodes present a high salt adsorption capacity of 12.95mg/g at a cell voltage of 1.4V with a flow rate of 40mL/min in a 500mg/L NaCl aqueous solution. Moreover, the N-PHCS electrodes show high salt adsorption rate and good regeneration performance in the CDI process. With high surface specific area and effective nitrogen doping, the N-PHCS is promising to the CDI and other electrochemical applications.