Selective removal of chloride ions by bismuth electrode in capacitive deionization

A review of chloride ions removal from high chloride industrial wastewater: Sources, hazards, and mechanisms

To reduce metal pipe corrosion, improve product quality, and meet zero liquid discharge (ZLD) criteria, managing chloride ion concentrations in industrial wastewaters from metallurgical and chemical sectors has become increasingly important. This review provides detailed information on the sources, concentration levels, and deleterious effects of chloride ions in representative industrial wastewaters, and also summarizes and discusses various chloride ion removal techniques, including precipitation, ion exchange, physical separation, and advanced oxidation (AOPs). Among these, AOPs are particularly promising due to their ability to couple with other technologies and the diversity of their auxiliary technologies. The development of dechlorination electrode materials by electro-adsorption (CDI) can be inspired by the electrode materials used in chloride ion battery (CIB). This review also provides insights into exploring the effective combination of multiple chloride removal mechanisms, as well as the development of environmentally friendly composite materials. This review provides a theoretical basis and development direction for the effective treatment and secondary utilization of chlorine-containing industrial wastewater in the future.

Advanced capacitive deionization for ion selective separation: Insights into mechanism over a functional classification

Due to the diversity and variability of harmful ions in polluted water bodies, the selective removal and separation for specific ions is of great significance in water purification and resource processes. Capacitive deionization (CDI), an emerging desalination technology, shows great potential to selectively remove harmful ionic pollutants and further recover valuable ions because of the simple operation and low energy consumption. Researchers have done a lot of work to investigate ion selectivity utilizing CDI, including both theoretical and experimental studies. Nevertheless, in the investigation of selective mechanisms, phenomena where carbon materials exhibit entirely opposite selectivity require further analysis. Furthermore, there is a need to summarize the specific chemical reaction mechanisms, including the formation of hydrogen bonds, complexation reactions, and ligand exchanges, within selective electrodes, which have not been thoroughly examined in detail previously. In order to fill these gaps, in this review, we summarized the recent progress of CDI technologies for ion selective separation, and explored the selective separation mechanism of CDI from three aspects: selective physical adsorption, specific chemical reaction, and the utilization of selective barriers. Additionally, this review analyzes in detail the formation process of chemical bonds and ion conversion pathways when ions interact with electrode materials. Finally, some significant development prospects and challenges were offered for the future selective CDI systems. We believe the review will provide new insights for researchers in the field of ion selective separation.

Interfacial assembled porous bismuthene/Ti3C2Tx MXene heterostructure for highly efficient capacitive deionization

Capacitive deionization (CDI) is perceived as a promising technology for freshwater production owing to its environmentally friendly nature and low energy consumption. To date, the development of high-performance electrode materials represents the foremost challenge for CDI technology. In this work, the porous bismuthene/MXene (P-Bi-ene/MXene) heterostructure was synthesized using a simple interfacial self-assembly method with two-dimensional (2D) bismuthene and Ti3C2Tx MXene. Within the P-Bi-ene/MXene heterostructure, the porous structure can increase the active site and facilitate ion transport. Simultaneously, MXene effectively enhances the conductivity of the heterostructure, resulting in accelerating electron transport. Due to these attributes, the P-Bi-ene/MXene heterostructure demonstrates high desalination capacity (90.0 mg/g), fast desalination rate, and good cycling performance. The simple self-assembly strategy between 2D/2D materials described herein may offer inspirations for the synthesis of innovative electrode materials with high performance.

Strong interface coupling boosting hierarchical bismuth embedded carbon hybrid for high-performance capacitive deionization

Capacitive deionization (CDI) is regarded as a promising desalination technology owing to its low cost and environmental friendliness. However, the lack of high-performance electrode materials remains a challenge in CDI. Herein, the hierarchical bismuth-embedded carbon (Bi@C) hybrid with strong interface coupling was prepared through facile solvothermal and annealing strategy. The hierarchical structure with strong interface coupling between the bismuth and carbon matrix afforded abundant active sites for chloridion (Cl^-) capture, improved electrons/ions transfer and the stability of the Bi@C hybrid. As a result of these advantages, the Bi@C hybrid showed a high salt adsorption capacity (75.3 mg/g under 1.2 V), salt adsorption rate and good stability, making it a promising electrode material for CDI. Furthermore, the desalination mechanism of the Bi@C hybrid was elucidated through various characterizations. Therefore, this work provides valuable insights for the design of high-performance bismuth-based electrode materials for CDI.

Removal of high concentration of chloride ions by electrocoagulation using aluminium electrode

Wastewater containing a high concentration of chloride ions (Cl^- ions) generated in industrial production will corrode equipment and pipelines and cause environmental problems. At present, systematic research on Cl^- removal by electrocoagulation is scarce. To study the Cl^- removal mechanism, process parameters (current density and plate spacing), and the influence of coexisting ions on the removal of Cl^- in electrocoagulation, we use aluminum (Al) as the sacrificial anode, combined with physical characterization and density functional theory (DFT) to study Cl^- removal by electrocoagulation. The result showed that the use of electrocoagulation technology to remove Cl^- can reduce the concentration of Cl^- in an aqueous solution below 250 ppm, meeting the Cl^- emission standard. The mechanism of Cl^- removal is mainly co-precipitation and electrostatic adsorption by forming chlorine-containing metal hydroxyl complexes. The current density and plate spacing affect the Cl^- removal effect and operation cost. As a coexisting cation, magnesium ion (Mg²⁺) promotes the removal of Cl^-, while calcium ion (Ca²⁺) inhibits it. Fluoride ion (F^-), sulfate (SO₄^2-), and nitrate (NO₃^-) as coexisting anions affect the removal of Cl^- ions through competitive reaction. This work provides a theoretical basis for the industrialization of Cl^- removal by electrocoagulation.

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Selective Ion Removal by Capacitive Deionization (CDI)-Based Technologies

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.

Removal of chloride from water and wastewater: Removal mechanisms and recent trends

Increased chloride concentration can cause salinization, which has become a serious and widespread environmental problem nowadays. This review aims at providing comprehensive and state-of-the-art knowledge and insights of technologies for chloride removal. Mechanisms for chloride removal mainly include chemical precipitation, adsorption, oxidation and membrane separation. In chemical precipitation, chloride removal by forming CuCl, AgCl, BiOCl and Friedel's salt. Adsorbents used in chloride removal mainly include ion exchangers, bimetal oxides and carbon-based electrodes. Oxidation for chloride removal contains ozone-based, electrochemical and sulfate radical-based oxidation. Membrane separation for chloride removal consists of diffusion dialysis, nanofiltration, reverse osmosis and electrodialysis. In this review, we specifically proposed the factors that affect chloride removal process and the corresponding strategies for improving removal efficiency. In the last section, the remaining challenges of method explorations and material developments were stated to provide guidelines for future development of chloride removal technologies.

The Performance and Mechanism of a Mg-Al Double-Layer Oxide in Chloride ion Removal from an Aqueous Solution

The increasing threat of chloride ions (Cl-) has led researchers to explore efficient removal technologies. Sewage treatment with a double-layer hydroxide/oxide (LDH/LDO) is receiving increasing attention. In this work, Mg-Al LDO adsorbents were produced by the calcination of the Mg-Al LDH precursor, which was constituted by improved coprecipitation. The influence of calcination temperature, calcination time, adsorbent dosage, Cl- initial concentration, contact time, and adsorption temperature on Cl- elimination was investigated systematically. The experimental results showed that a better porous structure endowed the Mg-Al LDO with outstanding adsorption properties for Cl-. The adsorption process was well matched to the pseudo-second-order kinetics model and the Freundlich model. Under optimal conditions, more than 97% of the Cl- could be eliminated. Moreover, the removal efficiency was greater than 90% even after 11 adsorption-desorption cycles. It was found that the electrostatic interaction between Cl- and the positively charged Mg-Al LDO laminate, coupled with the reconstruction of the layer structure, was what dominated the Cl- removal process.

Electrochemical Driven Phase Segregation Enabled Dual-Ion Removal Battery Deionization Electrode

Battery deionization (BDI) offers a powerful platform for integrating water treatment and energy conversion. Exploring novel BDI electrode materials with high energy storage capacity and high efficiency for both cations and anions removal is the key to advancing the BDI technique. Herein, we report the first BDI electrode material capable of simultaneously removing Cl^- (58.4 mg g^-1) and Na⁺ (8.7 mg g^-1) in water with a reversible capacity of 160 mAh g^-1. In situ powder X-ray diffraction (PXRD) unravels that the dual-ion removal capability is attributed to a novel reversible electrochemical driven phase segregation reaction mechanism between NaBi₃O₄Cl₂ and the in situ formed metallic Bi. The unique dual-ion storage capability demonstrated with the NaBi₃O₄Cl₂ electrode indicates that exploring electrochemical reversible phase segregation electrode material holds great promise for advancing the BDI electrode for future desalination techniques and aqueous rechargeable battery systems.