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In the past few decades, with the rapid development and wide application of lithium-ion battery, the demand for lithium resources has increased significantly. Lithium resources mainly exist in Salt Lake, so extracting lithium from Salt Lake is of great significance. Since Mg 2+ and Li + have similar ionic radius and chemical property, the main difficulty in extracting lithium from Salt Lake is the separation of Mg 2+ and Li + . Current techniques in the common use of separating Mg 2+ and Li + from Salt Lake mainly include the extraction method, adsorption method, and membrane method. Electrochemical electrode deionization (EEDI), also known as capacitive deionization in its early days, is a promising water desalination technology that has the advantages of environmental friendliness, low cost, low energy consumption, and convenient electrode regeneration. EEDI is primarily used for desalination, but its working principle indicates that it can also be used for element enrichment. Currently, a large number of works have used EEDI for Mg 2+ /Li + separation and Li + enrichment. This work aims to review the research progress of EEDI for lithium extraction, focusing on its working mechanism, key materials (electrode materials or membrane materials), achieved performance, and prospects for future development. This work will help promote the development of EEDI technology in the field of Mg 2+ /Li + separation.

Capacitive deionization (CDI) is a promising technology to satisfy the global need for fresh water, since it can be both economical and sustainable. While two-dimensional transition metal carbides/nitrides (MXenes) exhibit great characteristics for use as CDI electrode materials, their tightly spaced layered structure renders intercalation inefficiency. In this study, the interlayer distance of MXenes is precisely modulated by inserting different quantity of one-dimensional bacterial fibers (BC), forming freestanding MXene/BC composite electrodes. Among the studied samples, MXene/BC-33% electrode with the interlayer spacing of 15.2 Å can achieve an optimized tradeoff among various desalination performance metrics and indicators. The salt adsorption capacity (SAC), the average salt adsorption rate (ASAR), the energy normalized adsorbed salt (ENAS), and the thermodynamic energy efficiency (TEE) of the MXene/BC-33% electrode are improved by 24%, 46%, 13%, and 66% respectively compared with those of pure MXene electrode. While the insertion of BC improves the ion diffusion pathways and facilitates the intercalation kinetics, the desalination performance decreases when the insertion amount of BC exceeds 40%. This is attributed to the overlarge resistance of the composite and the resulting increased energy consumption. This study reveals the desalination performance tradeoffs of MXene-based electrodes with different interlayer distances and also sheds light on the fundamental ion storage mechanisms of intercalation materials in a CDI desalination system.

HighlightsA broad overview of MXenes and MXene-based nanomaterials in desalination is presented.Recent advancement in the synthesis of MXenes for applications in desalination is critically evaluated. Salt removal mechanisms and regeneration capability of MXenes are appraised.Current challenges and future prospect of MXenes in desalination are highlighted. Research directions are provided to safeguard the applications of MXenes in future desalination.MXenes, novel 2D transition metal carbides, have emerged as wonderful nanomaterials and a superlative contestant for a host of applications. The tremendous characteristics of MXenes, i.e., high surface area, high metallic conductivity, ease of functionalization, biocompatibility, activated metallic hydroxide sites, and hydrophilicity, make them the best aspirant for applications in energy storage, catalysis, sensors, electronics, and environmental remediation. Due to their exceptional physicochemical properties and multifarious chemical compositions, MXenes have gained considerable attention for applications in water treatment and desalination in recent times. It is vital to understand the current status of MXene applications in desalination in order to define the roadmap for the development of MXene-based materials and endorse their practical applications in the future. This paper critically reviews the recent advancement in the synthesis of MXenes and MXene-based composites for applications in desalination. The desalination potential of MXenes is portrayed in detail with a focus on ion-sieving membranes, capacitive deionization, and solar desalination. The ion removal mechanism and regeneration ability of MXenes are also summarized to get insight into the process. The key challenges and issues associated with the synthesis and applications of MXenes and MXene-based composites in desalination are highlighted. Lastly, research directions are provided to guarantee the synthesis and applications of MXenes in a more effective way. This review may provide an insight into the applications of MXenes for water desalination in the future.

This study investigates the transport mechanisms of NaCl solution through electroporcelain, a material used to produce high voltage insulators. Utilizing a combination of experimental and computational methods, the modes of transport, primarily the diffusion and osmosis were studied. The experiment consisted of two reservoirs connected by the sample, one filled with NaCl solution and the other with deionized water. Transport parameters, such as osmotic efficiency σ, molar water permeability k, and molar diffusivity D, were obtained from the measured time evolution of pressure difference across the sample. An analysis of the molar flow of water that allows to determine the size of the parts belonging to specific transport mechanism was then performed using these parameters. The results revealed that ∼ 90 % of the total flow is osmotic, while the diffusion contributed to only about 5 % and the Darcy flow to only about 2 % – 5 %.

Another technique for desalination, known as membrane capacitive deionization (MCDI), has been investigated as an alternative. This approach has the potential to lower the voltage that is required, in addition to improving the ability to renew the electrodes. In this study, the desalination effectiveness of capacitive deionization (CDI) was compared to that of MCDI, employing newly produced cellulose acetate ion exchange membranes (IEMs), which were utilized for the very first time in MCDI. As expected, the salt adsorption and charge efficiency of MCDI were shown to be higher than those of CDI. Despite this, the unique electrosorption behavior of the former reveals that ion transport via the IEMs is a crucial rate-controlling step in the desalination process. We monitored the concentration of salt in the CDI and MCDI effluent streams, but we also evaluated the pH of the effluent stream in each of these systems and investigated the factors that may have caused these shifts. The significant change in pH that takes place during one adsorption and desorption cycle in CDI (pH range: 2.3–11.6) may cause problems in feed water that already contains components that are prone to scaling. In the case of MCDI, the fall in pH was only slightly more noticeable. Based on these findings, it appears that CDI and MCDI are promising new desalination techniques that has the potential to be more ecologically friendly and efficient than conventional methods of desalination. MCDI has some advantages over CDI in its higher salt removal efficiency, faster regeneration, and longer lifetime, but it is also more expensive and complex. The best choice for a particular application will depend on the specific requirements.

To address the characteristic that graphene was difficult to disperse in deionized water, four factors including dispersant type, dispersant content, pH value, and ultrasonic time were selected to construct an orthogonal test combined with signal-to-noise ratio (SNR) analysis for exploring the optimal dispersion parameters of graphene. The orthogonal test results and signal-to-noise ratio analysis results showed that dispersant type and pH value had a higher degree of influence on graphene dispersion. Combined with the characterization results of SEM, LS, and Raman spectrometer, it could be determined that a better dispersion effect was obtained when the mixture with 1% of PVP and Triton X-100 was added to the dispersion with a pH value of about 8 and 80-minute ultrasonication was conducted.

Several harmful or valuable ionic species present in seawater, brackish water, and wastewater are amphoteric, weak acids or weak bases, and, thus, their properties depend on local water pH. Effective removal of these species can be challenging for conventional membrane technologies, necessitating chemical dosing of the feedwater to adjust pH. A prominent example is boron, which is considered toxic in high concentrations and often requires additional membrane passes to remove during seawater desalination. Capacitive deionization (CDI) is an emerging membraneless technique for water treatment and desalination, based on electrosorption of salt ions into charging microporous electrodes. CDI cells show strong internally generated pH variations during operation, and, thus, CDI can potentially remove pH-dependent species without chemical dosing. However, development of this technique is inhibited by the complexities inherent to the coupling of pH dynamics and ion properties in a charging CDI cell. Here, we present a theoretical framework predicting the electrosorption of pH-dependent species in flow-through electrode CDI cells. We demonstrate that such a model enables insight into factors affecting species electrosorption and conclude that important design rules for such systems are highly counterintuitive. For example, we show both theoretically and experimentally that for boron removal, the anode should be placed upstream and the cathode downstream, an electrode order that runs counter to the accepted wisdom in the CDI field. Overall, we show that to achieve target separations relying on coupled, complex phenomena, such as in the removal of amphoteric species, a theoretical CDI model is essential.

As a promising desalination technology, capacitive deionization (CDI) have shown practicality and cost-effectiveness in brackish water treatment. Developing more efficient electrode materials is the key to improving salt removal performance. This work reviewed current progress on electrode fabrication in application of CDI. Fundamental principal (e.g. EDL theory and adsorption isotherms) and process factors (e.g. pore distribution, potential, salt type and concentration) of CDI performance were presented first. It was then followed by in-depth discussion and comparison on properties and fabrication technique of different electrodes, including carbon aerogel, activated carbon, carbon nanotubes, graphene and ordered mesoporous carbon. Finally, polyaniline as conductive polymer and its potential application as CDI electrode-enhancing materials were also discussed.

Hydrogels of conducting polymers, particularly poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), provide a promising electrical interface with biological tissues for sensing and stimulation, owing to their favorable electrical and mechanical properties. While existing methods mostly blend PEDOT:PSS with other compositions such as non-conductive polymers, the blending can compromise resultant hydrogels’ mechanical and/or electrical properties. Here, we show that designing interconnected networks of PEDOT:PSS nanofibrils via a simple method can yield high-performance pure PEDOT:PSS hydrogels. The method involves mixing volatile additive dimethyl sulfoxide (DMSO) into aqueous PEDOT:PSS solutions followed by controlled dry-annealing and rehydration. The resultant hydrogels exhibit a set of properties highly desirable for bioelectronic applications, including high electrical conductivity (~20 S cm −1 in PBS, ~40 S cm −1 in deionized water), high stretchability (> 35% strain), low Young’s modulus (~2 MPa), superior mechanical, electrical and electrochemical stability, and tunable isotropic/anisotropic swelling in wet physiological environments. Hydrogels of conducting polymers provide an electrical interface with biological tissues for sensing and stimulation, but currently have compromised mechanical and electrical properties. Here, the authors show a simple method to achieve pure PEDOT:PSS hydrogels that exhibit superior mechanical and electrical properties, stability, and tunable swelling.

The demand for water and energy in today’s developing world is enormous and has become the key to the progress of societies. Many methods have been developed to desalinate water, but energy and environmental constraints have slowed or stopped the growth of many. Capacitive Deionization (CDI) is a very new method that uses porous carbon electrodes with significant potential for low energy desalination. This process is known as deionization by applying a very low voltage of 1.2 volts and removing charged ions and molecules. Using capacitive principles in this method, the absorption phenomenon is facilitated, which is known as capacitive deionization. In the capacitive deionization method, unlike other methods in which water is separated from salt, in this technology, salt, which is a smaller part of this compound, is separated from water and salt solution, which in turn causes less energy consumption. With the advancement of science and the introduction of new porous materials, the use of this method of deionization has increased greatly. Due to the limitations of other methods of desalination, this method has been very popular among researchers and the water desalination industry and needs more scientific research to become more commercial.