Enhancing capacitive deionization with element-doped carbon nanotube electrodes for selective uranium ion removal

Modeling multicomponent ion transport to investigate selective ion removal in electrodialysis

Abstract

Capacitive deionization (CDI) removes ions from solution using charged electrodes. CDI has demonstrated significant energy savings compared with reverse osmosis for removal of salt from brackish water. By tailoring electrode properties such as pore morphology and surface functionality, as well as cell operating parameters, selective separation of ions can be achieved (e.g., selective absorption of nitrate in the presence of chloride and sulfate ions). The selective removal of toxic ions from otherwise potable water has the potential to dramatically reduce the cost of water treatment. Here, we will present the latest work from Lawrence Livermore National Laboratory on selective ion removal using our unique flow-through electrode CDI platform, including the development of a multi-scale model (FE + QMD) to help elucidate the mechanism(s) for ion selectivity in CDI. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Faradic capacitive deionization (FCDI) for desalination and ion removal from wastewater

The pollution of toxic heavy metals is becoming an increasingly important issue in environmental remediation because these metals are harmful to the ecological environment and human health. Highly efficient selective removal of heavy metal ions is a huge challenge for wastewater purification. Here, highly efficient selective capacitive removal (SCR) of heavy metal ions from complex wastewater over Lewis base sites of S-doped Fe-N-C cathodes was originally performed via an electro-adsorption process. The SCR efficiency of heavy metal ions can reach 99% in a binary mixed solution [NaCl (100 ppm) and metal nitrate (10 ppm)]. Even the SCR efficiency of heavy metal ions in a mixed solution containing NaCl (100 ppm) and multicomponent metal nitrates (10 ppm for each) can approach 99%. Meanwhile, the electrode also demonstrated excellent cycle performance. It has been demonstrated that the doping of S can not only enhance the activity of Fe-N sites and improve the removal ability of heavy metal ions but also combine with heavy metal ions by forming covalent bonds of S- clusters on Lewis bases. This work demonstrates a prospective way for the selective removal of heavy metal ions in wastewater.

Severe freshwater shortages and global pollution make selective removal of target ions from solutions of great significance for water purification and resource recovery. Capacitive deionization (CDI) removes charged ions and molecules from water by applying a low applied electric field across the electrodes and has received much attention due to its lower energy consumption and sustainability. Its application field has been expanding in the past few years. In this paper, we report an overview of the current status of selective ion removal in CDI. This paper also discusses the prospects of selective CDI, including desalination, water softening, heavy metal removal and recovery, nutrient removal, and other common ion removal techniques. The insights from this review will inform the implementation of CDI technology.

The selective removal and recovery of silver ions from an aqueous solution is necessary, owing to the toxicity, persistency, and recoverable value. Herein, we first reported that silver ions could be selectively removed from an acidic solution by utilizing redox-active covalent organic framework (COF) materials as an adsorbent, resulting in the loading of Ag nanoparticles (NPs) with a narrow size distribution onto the framework simultaneously. The redox-active COF not only showed promising performance in adsorbing silver ions but also had a high selectivity at a low pH value. Subsequently, it was found that the N sites of amine groups within the framework took responsibility for the Ag NP generation after the systematic investigation on the redox adsorption mechanism. Furthermore, the recycled Ag@COF materials could be further used as new adsorbents to remove Hg(II) ions from water via NPs as a "bridge", exhibiting ultrahigh atomic utilization (>100%). Accordingly, this work not only provides a novel insight for the use of redox-active COF in the removal of metal ions but also opens a new field for designing of functionalized COF for their potential application in diverse areas.

Advances and challenges in capacitive deionization: Materials, architectures, and selective ion removal

As global temperatures rise & water consumption increases, freshwater is becoming a scarce commodity. Selective removal of ions is a burgeoning area of research for ion harvesting & water infrastructure, but traditional desalination techniques are not capable of selective removal. In this work, hybrid capacitive deionization is presented as a low energy, efficient solution to the water crisis using one-dimensional (1D) & two-dimensional (2D) advanced intercalation compounds that are studied for selectivity. 1D tunnel manganese oxide (TuMO) nanowires displaying a highly controllable rectangular tunnel size, which can be used for ion removal, are synthesized, formulated into electrodes, and studied in single-ion and multi-ion solutions for the first time. It is observed that in single-ion solutions, smaller tunnels prefer ions with a smaller size. In mixed solutions, however, the charge of the ions plays a more critical role. TuMO electrodes show preference toward removal of the Mg²⁺ & Ca²⁺ ions, which is attributed to higher mobility of doubly charged ions in water. The removal of singly charged Li⁺ & K⁺ ions is suppressed in the mixed solutions, which is likely caused by a charge screening mechanism. Finally, binderless 2D MXene electrodes are implemented without traditional current collector materials, as MXene itself acts as the current collector. MXene electrodes are studied in NaCl solutions, and a salt adsorption capacity of 39.1 mg g-1 of NaCl is reported for bi-stacked electrodes. This research sheds light on the ion dynamics between redox active electrode materials & ionic species in mixed solutions & has far reaching impacts for the next generation of HCDI for selective ion removal.

Electrochemically activated layered manganese oxide for selective removal of calcium and magnesium ions in hybrid capacitive deionization

Selective ion removal and antibacterial activity of silver-doped multi-walled carbon nanotube / polyphenylsulfone nanocomposite membranes

Capacitive deionization (CDI) is an emerging technology capable of selective removal of ions from water. While many studies have reported chemically tailored electrodes for selective ion removal, the selective removal of divalent cations (i.e., hardness) over monovalent cations can simply be achieved using membrane CDI (MCDI) equipped with ion exchange membranes (IEMs). In this study, we use both experimental and modeling approaches to systematically investigate the selective removal of Ca2+ over Na+. Specifically, the impacts of current density, hydraulic retention time, and feed composition on the selectivity of Ca2+ over Na+ were investigated. The results from our study suggest a universal correlation between the ratio of molar fluxes and the ratio of spacer channel ion concentrations, regardless of operating conditions and feed composition. Our analysis also reveals inherent and universal trade-off relationships between selectivity and the Ca2+ removal rate and between selectivity and the degree of Ca2+ removal. This fundamental understanding of the mechanism of selective ion removal in MCDI can also be applied to flow-electrode CDI processes that employ IEMs.

Redox flow deionization using Prussian blue and functionalized ion exchange membrane for enhanced selective ion recovery

Recent advances and future challenges in selective removal of calcium and magnesium ions with capacitive deionization

Selective electrosorption of heavy metal ions from wastewater with S-doped hierarchical porous carbon derived from waste Camellia oleifera shell