Enhanced Uranium Extraction via Charge Dynamics and Interfacial Polarization in MoS2/GO Heterojunction Electrodes

The removal of uranyl ions (UO2 2+) from water is challenging due to their chemical stability, low concentrations, complex water matrix, and technical limitations in extraction and separation. Herein, a novel molybdenum disulfide/graphene oxide heterojunction (MoS2/GO-H) is developed, serving as an effective electrode for capacitive deionization (CDI). By combining the inherent advantages of electroadsorption and electrocatalysis, an innovative electroadsorption-electrocatalysis system (EES) strategy is introduced. This system utilizes interface polarization at the MoS2 and GO interface, creating an additional electric field that significantly influences carrier behavior. The MoS2/GO-H electrode, with its extraordinary adsorption capacity of 805.57 mg g-1 under optimal conditions, effectively treated uranium-laden wastewater from a mine, achieving over 90% removal efficiency despite the presence of numerous competing ions at concentrations significantly higher than UO2 2+. Employing density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, it is found that the MoS2/GO-H total charge density at the Fermi level, enhanced by interfacial polarization, surpasses that of separate MoS2 and GO, markedly boosting conductivity and electrocatalytic effectiveness.

Activated Carbon Aerogel as an Electrode with High Specific Capacitance for Capacitive Deionization

In this study, carbon aerogels (CAs) were synthesized by the sol-gel method, using environmentally friendly glucose as a precursor, and then they were further activated with potassium hydroxide (KOH) to obtain activated carbon aerogels (ACAs). After the activation, the electrochemical performance of the ACAs was significantly improved, and the specific capacitance increased from 19.70 F·g−1 to 111.89 F·g−1. Moreover, the ACAs showed a stronger hydrophilicity with the contact angle of 118.54° compared with CAs (69.31°). When used as an electrode for capacitive deionization (CDI), the ACAs had not only a better diffuse electric double layer behavior, but also a lower charge transfer resistance and intrinsic resistance. Thus, the ACA electrode had a faster CDI desalination rate and a higher desalination capacity. The unit adsorption capacity is three times larger than that of the CA electrode. In the desalination experiment of 100 mg·L−1 sodium chloride (NaCl) solution using a CDI device based on the ACA electrode, the optimal electrode spacing was 2 mm, the voltage was 1.4 V, and the flow rate was 30 mL·min−1. When the NaCl concentration was 500 mg·L−1, the unit adsorption capacity of the ACA electrode reached 26.12 mg·g−1, much higher than that which has been reported in many literatures. The desalination process followed the Langmuir model, and the electro-sorption of the NaCl was a single layer adsorption process. In addition, the ACA electrode exhibited a good regeneration performance and cycle stability.

Recent Progresses in Adsorption Mechanism, Architectures, Electrode Materials and Applications for Advanced Electrosorption System: A Review

As an advanced strategy for water treatment, electrosorb technology has attracted extensive attention in the fields of seawater desalination and water pollution treatment due to the advantages of low consumption, environmental protection, simplicity and easy regeneration. In this work, the related adsorption mechanism, primary architectures, electrode materials, and applications of different electrosorption systems were reviewed. In addition, the developments for advanced electrosorb technology were also summarized and prospected.

Freestanding Activated Carbon Nanocomposite Electrodes for Capacitive Deionization of Water

Freshwater reserves are being polluted every day due to the industrial revolution. Man-made activities have adverse effects upon the ecosystem. It is thus the hour of need to explore newer technologies to save and purify water for the growing human population. Capacitive deionization (CDI) is being considered as an emerging technique for removal of excess ions to produce potable water including desalination. Herein, cost-effective activated carbon incorporated with carbon nanotubes (CNT) was used as a freestanding electrode. Further, the desalination efficiency of the designed electrodes was tuned by varying binder concentration, i.e., polyvinylidene difluoride (PVDF) in the activated carbon powder and CNT mixture. PVDF concentration of 5, 7.5, 10, and 12.5 wt% was selected to optimize the freestanding electrode formation and further applied for desalination of water. PVDF content affected the surface morphology, specific surface area, and functional groups of the freestanding electrodes. Moreover, the electrical conductivity and specific surface area changed with PVDF concentration, which ultimately affected the desalination capacity using the freestanding electrodes. This study paves the way to produce cost effective carbon-based freestanding electrodes for capacitive deionization and other applications including battery electrodes.

Experimental and theoretical study of a new CDI device for the treatment of desulfurization wastewater

According to the characteristics of desulfurization wastewater, A new capacitive deionization (CDI) device was designed to study the desalination characteristics of desulfurization wastewater in this paper. The experiments investigated the desalination efficiency under different conditions which find that the best desalination efficiency is achieved at a voltage of 1.2V, pH=11 and 50°C. Besides, ion adsorption is more favorable under acidic and alkaline conditions. The anion and cation removal performance experiments showed that the order of cation removal is Mg²⁺>Na⁺>Ca²⁺>K⁺ and the order of anion removal is Cl^->CO₃^2->NO₃^->SO₄^2->HCO₃^-. The mechanism of CDI was studied and analyzed by the isothermal adsorption model and COMSOL simulation software. It was found that the Freundlich model and Redlich-Peterson model have a good fit with the experimental results. The experiments show that the CDI device has excellent stability. CDI device was used to treat actual desulfurization wastewater. Furthermore, the study provides theoretical support for the industrial application of CDI for desulfurization wastewater treatment in the future. Graphical abstract.

Microscopic mechanism about the selective adsorption of Cr(VI) from salt solution on nitrogen-doped carbon aerogel microsphere pyrolysis products

A series of nitrogen-doped carbon aerogels (NCAs) were obtained through phase reaction polymerization and different carbonization temperatures to enhance adsorption efficacy of hexavalent chromium (Cr[VI]) from wastewater significantly. Factors that influence adsorption properties of carbon aerogel microspheres toward Cr(VI), such as pH, adsorbent content, initial Cr(VI) concentrations, and coexisting anion, were investigated. Three isotherm (Langmuir, Freundlich, and Sips) and three kinetic (pseudofirst-order, pseudosecond-order, and Elovich) models were used to interpret the adsorption process. The adsorption capacity of Cr(VI) reached 180.62 mg·g^-1, which was superior to that of most aerogel adsorbents. In addition to the adsorption effect, the XPS results also showed that N-containing groups on the NCA surface reduce the adsorbed Cr(VI) to the less toxic Cr(III). The prepared sorbent demonstrates a negligible loss in adsorption capacity after 6 cycles. NCAs show acceptable application prospects in selective removal of Cr(VI) ions.

Tio2 and carbon nanotubes composites modify capacitive deionization anodes to improve the dechlorination efficiency in desulfurization wastewater

A new capacitive deionization (CDI) technology was used to remove Cl^- from desulfurization wastewater. TiO₂ and carbon nanotubes (CNTs) were combined with N-methyl pyrrolidone (NMP) to form composites by a solvothermal method in which it is coated onto the CDI anode to improve dechlorination efficiency (DE). The morphology, surface area, wettability, crystal structure and chemical composition of the TiO₂/CNTs were characterized. They showed good hydrophilicity (contact angle: 85.9°), high specific surface area (96.68 m²/g) and high specific capacitance (87.6 F/g). The experimental results illustrated that the best DE was achieved by the composites (60%T/C) under 1.2 V with the maximum electrosorption capacity toward 6.5 mg/g, and the TiO₂/CNTs composites had excellent stability. Adsorption kinetics analysis was explored and analyzed. Furthermore, TiO₂/CNTs composites exhibited excellent DE in actual desulfurization wastewater. The catalysis and adsorption mechanisms of the TiO₂/CNTs anode were discussed in detail. This study provides a new direction for the application of TiO₂/CNTs composites as adsorption materials of CDI in the Cl^- of desulfurization wastewater.

Efficient sucrose-derived mesoporous carbon sphere electrodes with enhanced hydrophilicity for water capacitive deionization at low cell voltages

Mesoporous carbon spheres synthesized by a hard template approach. Low contact angle and better hydrophilicity. MCS electrodes can desalinate water at a low cell voltage of 0.8 V.

Low-Frequency Impedance-Based Cell Discrimination Considering Ion Transport Model in Cell Suspension

Low-frequency impedance-based (LFI) cell discrimination as a novel non-destructive and non-invasive cell discrimination is proposed. LFI cell discrimination discriminates the cell type by considering an ion transport model in cell suspension. Ion transport model in cell suspension is constructed on the basis of Fick's laws of diffusion in the extracellular region under ion permeability P which represents the characteristics of cell type. P is achieved using the ion transport model equation through an iterative curve fitting to an ion concentration in extracellular region obtained from low-frequency impedance which is assumed to be linearly related to the ion concentration in extracellular region. In experiment, the electrical impedance spectra from the frequency of 200 kHz to 2.0 MHz are measured over time during producing ions from intracellular region to extracellular one in cell suspension using an impedance analyzer and an interdigitated array electrode system. As a target cell type, two different cell types based on Medical Research Council 5 (MRC-5), which are different in intracellular component are used. The curve fitting is performed for the low-frequency impedance at 200 kHz at which impedance reflects the ion concentration in extracellular region in order to obtain P of each cell type. As a result, each cell type has its own P. The proposed LFI cell discrimination successfully discriminates the cell type.

Enhanced capacitive performance by improving the graphitized structure in carbon aerogel microspheres

Herein, good electrical conductivity and high specific surface area carbon aerogel (CA) microspheres were synthesized by a facile and economical route using a high temperature carbonization and CO₂ activation method. The electroconductive graphitized structure of the CA microspheres could be easily improved by increasing the carbonization temperature. Then the CA microspheres were activated with CO₂ to increase the specific surface area of the electrode material for electric double layer capacitors (EDLC). The sample carbonized at 1500 °C for 0.5 h and CO₂ activated at 950 °C for 8 h showed an acceptable specific surface area and excellent cycle performance and rate capability for EDLC: 98% of the initial value of the capacitance was retained after 10 000 cycles, a specific capacitance of 121 F g⁻¹ at 0.2 A g⁻¹ and 101 F g⁻¹ at 2 A g⁻¹.

Carbon aerogels (CAs) microspheres with good electrical conductivity and high specific surface area were synthesized by high temperature carbonization and CO₂ activation method, which exhibit an enhanced capacitive performance in supercapacitors.

Removal of heavy metal ions by capacitive deionization: Effect of surface modification on ions adsorption

Activated carbon cloth (ACC) coated with zinc oxide (ZnO) nanoparticles (NPs) have been used as electrodes in flow-by capacitive deionization (CDI) system. Aqueous solution of individual Pb²⁺ and Cd²⁺ ions and mixed Pb²⁺ and Cd²⁺ ions were used as test contaminant in CDI system to study the effect of surface modification upon ions removal efficiency. Due to the aggregated structure of ZnO NPs on ACC surface, the modified ACC electrodes develop the additional surface area as well as dielectric barrier therefore resulting in higher specific capacitance. In addition, coating with ZnO NPs effectively reduced physical adsorption whereby enhanced the ions adsorption rate and capacity during electrosorption process. Upon incorporating with ZnO NPs, the electrosorption efficiency was enhanced from 17% to 33% for Pb²⁺, from 21% to 29% for Cd²⁺ and from 21% to 35% for mixed Pb²⁺ and Cd²⁺ ions. The power consumption of individual ions and mixed ions removal process for ACC and ZnO NPs modified ACC were also discussed. Furthermore, used ACC electrodes surfaces were examined using photoelectron spectroscopy (XPS) and results were also conferred. The CDI ACC electrodes with ZnO NPs showed a promising and an effective way for heavy metal removal applications.

Frontiers of carbon materials as capacitive deionization electrodes

Carbon materials are widely used as capacitive deionization (CDI) electrodes due to their high specific surface area (SSA), superior conductivity, and better stability, including activated carbon, carbon aerogels, carbon nanotubes and graphene.

Electrosorptive removal of salt ions from water by membrane capacitive deionization (MCDI): characterization, adsorption equilibrium, and kinetics

Capacitive deionization (CDI) was demonstrated to be an affordable technology for reduction of salt concentrations in brackish water. In this study, a novel membrane capacitive deionization (MCDI) cell was assembled by incorporating ion exchange membranes into the CDI cell which was built with high-adsorption electrodes based on ordered mesoporous carbon. The synthesized mesoporous carbon electrode was fully characterized. The simultaneous analysis of the electrosorption capacity and adsorption/desorption kinetics was evaluated by using real power plant desulfurization wastewater. The ordered mesoporous carbon was favorable for salt ion electrosorption, and the best performance was obtained by using MCDI which improved the removal efficiency of total dissolved solids (TDSs) from 65 to 82%. The total hardness and alkalinity of the effluent after treatment could meet the requirement of water quality standard for industries. Langmuir isotherm and pseudo-first-order kinetic models were found to be in best agreement with experimental results of salt ion electrosorption. The selective transport of ions between the electrode surface and bulk solution due to the ion exchange membranes resulted in a better desalination performance of MCDI. The results presented in this paper could be used for developing new electrode materials of MCDI for desalination from water.

Ethylenediamine-Catalyzed Preparation of Nitrogen-Doped Hierarchically Porous Carbon Aerogel under Hypersaline Condition for High-Performance Supercapacitors and Organic Solvent Absorbents

The simple and cost-efficient preparation of high-performance nitrogen-doped carbon aerogel (N-CA) for supercapacitors and other applications is still a big challenge. In this work, we have presented a facile strategy to synthesize hierarchically porous N-CA, which is based on solvothermal polymerization of phenol and formaldehyde under hypersaline condition with ethylenediamine (EDA) functioning as both a catalyst and a nitrogen precursor. Benefited from the catalytic effect of EDA on the polymerization, the obtained N-CA has a predominant amount of micropores (micropore ratio: 52%) with large specific surface area (1201.1 m²·g^-1). In addition, nitrogen doping brings N-CA enhanced wettability and reduced electrochemical impedance. Therefore, the N-CA electrode shows high specific capacitance (426 F·g^-1 at 1 A·g^-1 in 0.5 M H₂SO₄) and excellent cycling stability (104% capacitance retention after 10,000 cycles) in three-electrode systems. Besides, a high energy density of 32.42 Wh·kg^-1 at 800 W·kg^-1 can be achieved by symmetric supercapacitor based on the N-CA electrodes, showing its promising application for energy storage. Furthermore, N-CA also exhibits good capacity and long recyclability in the absorption of organic solvents.

Ambient Pressure-Dried Graphene–Composite Carbon Aerogel for Capacitive Deionization

Capacitive deionization (CDI) technology possessing excellent desalination performance and energy efficiency is currently being widely studied in seawater desalination. In this work, the graphene–composite carbon aerogels (GCCAs) easily prepared by an ambient pressure drying method served as electrodes to remove salt ions in aqueous solution by CDI. The microstructure of the obtained GCCAs was found to depend on the component content in the precursor solution, and could be controlled through varying the mass ratio of resorcinol and formaldehyde to graphene oxide (RF/GO). The surface characteristics and microstructure of GCCAs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In addition, the electrochemical tests and CDI experiments of GCCA electrodes were conducted in NaCl solution. Thanks to the reasonable pore structure and highly conductive network, GCCA-150 achieved the best salt adsorption capacity of 26.9 mg/g and 18.9 mg/g in NaCl solutions with concentrations of 500 mg/L and 250 mg/L, respectively.

ZIF-67 derived Co3O4/carbon aerogel composite for supercapacitor electrodes

We report carbon aerogels with a 3D hierarchical porous structure as a backbone to support nanoporous Co₃O₄ derived from ZIF-67 for supercapacitors.