High Salt Adsorption Capacity Research Articles

Pore structure and N/F bifunctional groups in hierarchical porous carbons via spontaneous silica etching for enhanced capacitive deionization performance

This study presents a novel, one-step synthesis of nitrogen and fluorine bifunctional hierarchical porous carbons (HPCs) for capacitive deionization (CDI). The method involves co-gelation of silica and polyvinylidene fluoride, followed by pyrolysis for efficient silica removal. This method eliminates the need for toxic solvents and extensive cleaning steps. Optimized HPCs exhibit a high surface area (1464.71 m2/g) with abundant mesopores. Electrochemical analysis reveals a specific capacitance of 179.5F/g. In the CDI process using 500 mg/L NaCl solution, the HPCs demonstrate exceptional performance with a high salt adsorption capacity (24.61 mg/g) and a fast average adsorption rate (3.69 mg/g/min). This performance is attributed to the combined effects of the hierarchical pore structure facilitating rapid ion adsorption and the N/F bifunctional groups enhancing electrosorption ability. This work offers a one-step, solvent-free method for synthesizing HPCs with superior desalination performance and demonstrates the synergistic effect of pore structure and N/F bifunctional groups.

A green potassium citrate activation strategy via one-step synthesis of 3D porous carbon for capacitive deionization

Capacitive deionization (CDI) shows potential for desalination whereas exploring green and low-cost porous carbon electrodes exhibiting good desalination performance is still challenging. Herein, a green one-step carbonization-activation strategy was developed with carboxymethyl cellulose (CMC) as precursor and potassium citrate as activator to prepare CA(K)/CMC for CDI desalination. Owing to the introduction of potassium citrate, CA(K)/CMC exhibited larger specific surface area, better porous structure, more defects, and richer oxygen content. These improvements effectively accelerated charge transfer and ion transport process in CA(K)/CMC, which significantly increased the specific capacitance of CA(K)/CMC. Owing to the synergistic effect of these above properties, the optimized CA(K)/CMC-1-2 demonstrated high salt adsorption capacity (17.21 mg g−1, 1.2 V, 200 mg/L) and desalination rate (0.023 mg g−1 s−1, 1.2 V, 200 mg/L), and good cycling stability. Density functional theory (DFT) calculations further verified the advantageous characteristics of CA(K)/CMC-1-2 indeed improved ions adsorption. This finding offers new insights for designing green and economical carbon-based electrodes for desalination by CDI.

Heterointerface regulation of covalent organic framework-anchored graphene via a solvent-free strategy for high-performance supercapacitor and hybrid capacitive deionization electrodes.

Covalent organic frameworks (COFs) with customizable geometry and redox centers are an ideal candidate for supercapacitors and hybrid capacitive deionization (HCDI). However, their poor intrinsic conductivity and micropore-dominated pore structures severely impair their electrochemical performance, and the synthesis process using organic solvents brings serious environmental and cost issues. Herein, a 2D redox-active pyrazine-based COF (BAHC-COF) was anchored on the surface of graphene in a solvent-free strategy for heterointerface regulation. The as-prepared BAHC-COF/graphene (BAHCGO) nanohybrid materials possess high-speed charge transport offered by the graphene carrier and accelerated electrolyte ion migration within the BAHC-COF, allowing ions to effectively occupy ion storage sites inside BAHC. As a result, the BAHCGO//activated carbon asymmetric supercapacitor achieves a high energy output of 61.2 W h kg-1 and a satisfactory long-term cycling life. More importantly, BAHCGO-based HCDI possesses a high salt adsorption capacity (SAC) of 67.5 mg g-1 and excellent long-term desalination/regeneration stability. This work accelerates the application of COF-based materials in the fields of energy storage and water treatment.

(Invited) Layered Double Hydroxides with Enhanced Interlayer Space for Electrochemical Energy Storage and Deionization

Layered double hydroxides (LDHs) have been extensively studied as promising functional nanomaterials owing to their excellent electrochemical activity and tunable chemical composition. In this work, we presented a series of investigations on enhanced interlayer space of LDHs for electrochemical energy and deionization.Firstly, using acetate anions (Ac-) as an intercalating element, NiCo-LDH nanosheets arraying on Ni Foam with different amounts of Ac- anions intercalation or volumes of hydrothermal solution were prepared by a simple hydrothermal method. The optimized amount of Ac- anions expanded the interlayer space of LDH nanosheets from 0.8 to 0.94 nm. An ultrahigh specific capacity of 1200 C g-1 at 1 A g-1 (690 C g-1 without Ac- anions), outstanding rate capability of 72.5% at 30 A g-1 and cycle stability of 79.90% after 4500 cycles, which were mainly attributed to the higher interlayer spacing of Ac- anions intercalation.Moreover, CoAl-LDH nanosheets intercalated by sodium dodecyl sulfate (SDS) with an enhanced interlayer spacing from 0.76 to 1.33 nm are synthesized and used as an anode of electrosorption. The enlarged interlayer spacing provides an enhanced ion diffusion channel and improves the utilization of the interlayer electroactive sites, while heat treatment transferring LDHs to layered metal oxides offers additional active oxidation reaction sites to facilitate the electro-sorption rate, contributing to the high salt adsorption capacity (31.78 mg g-1) and average salt adsorption rate (3.75 mg g-1 min-1) at 1.2 V in 500 mg L-1 NaCl solution. In addition, the excellent long-term cycling stability (92.9%) after 40 cycles proves the strong electronic interaction between SDS and the host layer, which is validated by density functional theory calculations later on.In addition, ionic surfactants like SDS and cetyl trimethyl ammonium bromide (CTAB) can be used to modify the morphology of LDH. The original LDH shows microspheres formed by nanorods, and LDH-CTAB is similar, yet more tangled, while LDH-SDS is like micro flowers consisting of interwoven nanosheets. LDH-SDS achieved better electrochemical performance (1003.6 C g-1 at 1 A g-1 and 73.84% after 3500 cycles) than LDHs-CTAB (430.54 C g-1, 57.3%), and both higher than the original LDH (278.5 C g-1, 54.3%), while the electrocatalytic performance like Tafel slope follows an opposite trend owing to the difficulty of bubbles detachment from the nanosheets or nanorods, clearly showing the importance of morphology regulation in the synthesis of nanomaterials.

(Invited) Development and Scale-up of Membrane Capacitive Deionization (MCDI) for Desalination and Water Reuse

Desalination and water reuse are the key solutions to address global water scarcity. It is important to recognize the water-energy interactions and develop energy-efficient technologies to separate ions from brackish water, seawater and reclaimed wastewater. Most recently, membrane capacitive deionization (MCDI), inspired by energy storage devices (e.g., supercapacitors), is a promising desalination technology with several advantages of energy efficiency (TDS < 4000 ppm), high water recovery, less chemical additive, and environmental friendliness. In MCDI, ions are electrostatically captured within highly porous carbon electrodes through the formation of electrical double layer during the charging step, and then released into the solution by discharging the electrodes. By incorporating ion-exchange membranes (IEMs) in front of each electrode, the desalination performance can be significantly improved, achieving high salt adsorption capacity and charge efficiency. Over the past few years, we have made efforts to scale up the MCDI stacks for commercialization purposes, which are composed of 32 pairs of 400 mm × 200 mm activated carbon electrodes. Note that a stop-flow operation is applied in the discharge process to increase the water recovery (> 75%). A pilot-scale study of an MCDI system was performed to reclaim the secondary effluents from a municipal wastewater treatment plant. In addition, MCDI prototypes offer promising engineering opportunities for water recycling in high-tech industries, including reverse osmosis reject and wet scrubbing. Furthermore, we will discuss the challenges and perspectives for the future of MCDI as a cost-efficient, low-energy approach for desalination and resource recovery.

A lamellar chitosan-lignosulfonate/MXene nanocomposite as binder-free electrode for high-performance capacitive deionization

Ti3C2Tx (MXene) is considered as a superior electrode material for capacitive deionization (CDI) due to its high conductivity and two-dimensional structure. However, the electrochemical performance of pristine MXene nanosheets has been significantly impeded by the surface oxidation in the aqueous media and re-stacking caused by van der Waals forces which reduces the ions storage capacity. In this study, the chitosan-lignosulfonate/MXene (CLM) composite was used as a binder-free electrode to enhance the ion storage capacity and long-run cycling stability for hybrid capacitive deionization (HCDI). The chitosan-lignosulfonate nanospheres were able to increase the interlayer spacing between the MXene nanosheets effectively, which has significantly enhanced the ion storage capacity and electrochemical properties of the electrode. The binder-free CLM cathode demonstrated a high salt adsorption capacity of 44.6 mg g−1 and a maximum average salt adsorption rate of 5.8 mg g−1 min−1 at 1.2 V. A high cycling stability above 97 % for 30 cycles was observed. Also, the long-term stability of CLM electrode was studied by X-ray photoelectron spectroscopy (XPS) and the results showed that the CLM electrode was not prone to surface oxidation after 30 cycles. This study can guide future development of high-performance 2D material composite electrodes for enhancing capacitive deionization efficiency.

Pre-oxidized ultramicroporous carbon cloth with ultrahigh volumetric capacity and ultralong lifespan for capacitive desalination

Capacitive deionization is a promising desalination technique to tackle with freshwater scarcity, due to its facile, energy-efficient and eco-friendly operation. Carbon materials are primary electrode materials in capacitive deionization devices; however, their practical applications are limited by the low salt adsorption capacity and poor cycling stability. Here, we report a pre-oxidized strategy to significantly improve the salt adsorption capacity and cycling lifespan of carbon clothes. By the simple pre-oxidation treatment, it creates abundant ultramicropores and a superhydrophilic surface, which lead to a high salt adsorption capacity (31.5 mg g−1 and 13 mg cm−3) in 0.01 M NaCl aqueous solution. Moreover, the surface of each carbon fiber is oxidized, combined with a high mechanical strength, resulting in a stable surface during the cycling process. The retention rate is 74% even after 5000 adsorption/desorption cycles in diluted seawater. This work provides a new avenue to the design of high-performance, low-cost, and durable electrodes for capacitive deionization applications.

NiCu bimetallic metal–organic framework to improve the desalination performance of capacitive deionization

Due to its energy-saving and environment-friendly process without secondary pollutant, capacitive deionization (CDI), which separates the charged ion species from solution by applying external electric energy, provides an alternative desalination technology. Even though carbon-based electrodes have mostly been used so far, they suffer from limited salt removal performance because of insufficient ion uptake capacity and stringent regeneration conditions, which hinder the system from obtaining higher performance and scale-up. The development of a transition metal-based electrode has attracted much attention for emerging electrochemical applications, such as capacitive deionization, due to its unique electrochemical properties. However, synthesizing metal–organic frameworks (MOFs) in aqueous solution with high crystalline structure has been a challenging task. In this study, we used a simple hydrothermal technique to create NiCu–FA in aqueous solution to synthesize crystalline MOF structure. The newly developed NiCu–FA demonstrated high salt adsorption capacity, high salt adsorption rate, and outstanding CDI cycle stability, emphasizing the importance of high surface area with salt-activated transition metal. The high adsorption capacity of 10.55 mg/g could be achieved, which is over 76 % increase, compared to that of the pristine AC electrode 5.98 mg/g. Such enhanced desalination performance results from the synergistic contribution of electric double layer (EDL) capacitance from AC and pseudocapacitive behavior from NiCu–FA, which was confirmed by electrochemical measurements. We believe that our approach can offer a promising candidate for practical CDI application with high desalination performance and high salinity feed source.

High‐Efficient Capacitive Deionization Using Amine‐Functionalized ZIF‐67@ 2D MXene: Toward Ultrahigh Desalination Performance

AbstractCapacitive deionization (CDI) is proposed as a thermodynamically effective desalination method for treating non‐potable water with a low‐salt concentrator to address the growing need for clean drinking water. MXenes, 2D transition metal carbides derived from Mn+1AXn (n = 1, 2, 3, or 4) bulk phases, are an intriguing class of crystalline materials with unique physicochemical properties. However, a significant challenge for their practical use is the degradation and phase transition experienced by MXene flakes when exposed to aqueous conditions. Several strategies for improving MXene stability are proposed, including combining it with porous materials such as carbon and metal–organic frameworks (MOFs). In addition to ZIFs, antioxidants with amine functional groups are used to stabilize MXene. Additionally, amine‐functionalized MXenes exhibit improved resistance to oxidation caused by water, enabling them to maintain their dispersity in aqueous solutions at room temperature. The produced A‐ZIF@MXene electrode represents high desalination performance with the highest salt adsorption capacity up to 80.3 mg g−1 in 1000 mg L−1 The NaCl solution reserve more than 99% of its initial capacity in 50 cycles to the synergism of its surface amine groups, high hydrophilicity, and distinctive hierarchical porous structure.

Water hyacinth as a green and sustainable material for carbon aerogel electrodes utilized in membrane capacitive deionization

AbstractWater hyacinth is a substantial and quick‐growing plant that can strongly invade and negatively affect the aquatic ecosystem, causing many problems to the water environment by consuming nutrients and oxygen from surface water. However, the hierarchical porous carbon derived from water hyacinth can be employed for the removal of oil spills, heavy metals, or wastewater nutrients. Recently, water‐hyacinth‐derived carbon aerogel has been utilized as electrode for the desalination of brackish water using membrane capacitive deionization (MCDI) technology. In this research, lignocellulose aerogels were synthesized from water hyacinth, which were then pyrolyzed to obtain carbon aerogel and then treated with KOH to acquire activated carbon aerogel, with the corresponding surface area of 51 and 100 m2 g−1. The desalination capacity of the MCDI device was also evaluated using a 200 ppm NaCl feed water solution with an applied potential of 1.2 V. A high salt adsorption capacity value of 14.69 mg g−1 was achieved after 3000 s. These results will lead a new research area of biomass and bio‐waste conversion to fabricate CDI‐utilized carbon aerogel electrodes.

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.

Three-dimensional (3D) MnMoO4@g-C3N4/CNT hybrid composite electrode for hybrid capacitive deionization

In this work, a hierarchical three-dimensional MnMoO4@g-C3N4/CNT hybrid ternary composite was developed through the facile hydrothermal method. MnMoO4@g-C3N4/CNT and g-C3N4/CNT electrodes were used as cathode and anode to fabricate the hybrid capacitive deionization (HCDI) system. Manganese molybdate (MnMoO4) rods are uniformly intertwined on the three-dimensional (3D) conductive network structure of graphitic carbon nitride/carbon nanotube (g-C3N4/CNT) heterojunction in the ternary composite. As-obtained electrode materials of MnMoO4@g-C3N4/CNT and g-C3N4/CNT show the specific capacitance of 252.4 and 89.2 Fg−1, respectively, at 1 Ag−1 in 1 M NaCl solution. Mn element in the MnMoO4@g-C3N4/CNT hybrid induces a reversible redox reaction that selectively intercalates/de-intercalates the Na+-ion in the salt solution, yielding a high salt adsorption capacity of 43.6 mg. g−1 at 1.2 V and 1000 ppm NaCl solution medium. In addition, MnMoO4@g-C3N4/CNT //g-C3N4/CNT-based HCDI cell was recycled for 10 cycles. The system reaches the highest SAC of 42.6 mg. g−1 after 10 consecutive charge–discharge cycles with a retention of 91%, indicating the excellent cycling stability of the MnMoO4@g-C3N4/CNT electrode. These results signify that the MnMoO4@g-C3N4/CNT is a promising electrode material, possessing a pseudocapacitive behavior and remarkable desalination ability, which can be a potential new candidate for the HCDI system.

Flexible structural construction of the ternary composite Ni,Co-Prussian blue analogue@MXene/polypyrrole for high-capacity capacitive deionization

Prussian blue analogues (PBAs), as the representative of Faradaic materials, has drawn extensive attention in capacitive deionization (CDI) for unique redox activity, open framework structure, and low-cost synthesis. However, the serious aggregation, low conductivity, and easy structural collapse of PBAs nanoparticles limit the practical application in CDI. Herein, the ternary composite Ni,Co-PBA@MXene/PPy is flexibly constructed by integrating the collective advantages of Ni,Co-PBA, MXene, and PPy. In this configuration, MXene not only provides high conductivity but also acts as the good substrate for the in-situ homogeneous growth of Ni,Co-PBA nanoparticles. Furthermore, Ni,Co-PBA nanoparticles could effectively inhibit the self-stacking of MXene and facilitate fast ion intercalation. And the doping of Co in Ni,Co-PBA promotes the redox process by the pseudocapacitive contribution. Meanwhile, PPy contributes to accelerating ions transport rate and promoting the structural stability of MXene and Ni,Co-PBA. Consequently, the hybrid CDI cell AC//Ni,Co-PBA@MXene/PPy delivers prominent desalination performance with the high salt adsorption capacity (38.7 mg g−1), rapid salt adsorption rate (10 mg g−1 min−1), low energy consumption (0.283 kWh kg−1-NaCl), and outstanding cyclic stability. Most importantly, the Ni,Co-PBA@MXene/PPy electrode can reserve favorable structural integrity by the significant shielding effect of PPy to prevent Ni,Co-PBA from collapse and MXene from being oxidized.

Layered Metal Oxide Nanosheets with Enhanced Interlayer Space for Electrochemical Deionization.

Electrochemical deionization is regarded as one of the promising water treatment technologies. Here, CoAl-layered metal oxide nanosheets intercalated by sodium dodecyl sulfate (SDS) with an enhanced interlayer spacing from 0.76 to 1.33nm are synthesized and used as an anode. The enlarged interlayer spacing provides an enhanced ion-diffusion channel and improves the utilization of the interlayer electroactive sites, while heat treatment, transferring layered double hydroxides to layered metal oxides (LMOs), offers additional active oxidation reaction sites to facilitate the electro-sorption rate, contributing to the high salt adsorption capacity (31.78mgg-1 ) and average salt adsorption rate (3.75mgg-1 min-1 ) at 1.2V in 500mgL-1 NaCl solution. In addition, the excellent long-term cycling stability (92.9%) after 40 cycles proves the strong electronic interaction between SDS and the host layer, which is validated by density functional theory calculations later on. Moreover, the electro-sorption mechanism of LMOs that originated from the reconstruction of the layered structure based on the "memory effect" is revealed according to the X-ray photoelectron spectroscopy peak shifts of Co element. This strategy of expanding the interlayer spacing combined with heat treatment makes LMOs a competitive candidate for electrochemical water deionization.

Preparation of N-Doped Layered Porous Carbon and Its Capacitive Deionization Performance

In this study, N-doped layered porous carbon prepared by the high-temperature solid-state method is used as electrode material. Nano calcium carbonate (CaCO3) (40 nm diameter) is used as the hard template, sucrose (C12H22O11) as the carbon source, and melamine (C3H6N6) as the nitrogen source. The materials prepared at 850 °C, 750 °C, and 650 °C are compared with YP-50F commercial super-activated carbon from Japan Kuraray Company. The electrode material at 850 °C pyrolysis temperature has a higher specific surface area and more pores suitable for ion adsorption. Due to these advantages, the salt adsorption capacity (SAC) of the N-doped layered porous carbon at 850 °C reached 12.56 mg/g at 1.2 V applied DC voltage, 500 mg/L initial solution concentration, and 15 mL/min inlet solution flow rate, which is better than the commercial super activated carbon as a comparison. In addition, it will be demonstrated that the N-doped layered porous carbon at 850 °C has a high salt adsorption capacity CDI performance than YP-50F by studying parameters with different applied voltages and flow rates as well as solution concentrations.

Design of Uniform Hollow Carbon Nanoarchitectures: Different Capacitive Deionization between the Hollow Shell Thickness and Cavity Size.

Carbon-based materials with high capacitance ability and fast electrosorption rate are ideal electrode materials in capacitive deionization (CDI). However, traditional carbon materials have structural limitations in electrochemical and desalination performance due to the low capacitance and poor transmission channel of the prepared electrodes. Therefore, reasonable design of electrode material structure is of great importance for achieving excellent CDI properties. Here, uniform hollow carbon materials with different morphologies (hollow carbon nanospheres, hollow carbon nanorods, hollow carbon nano-pseudoboxes, hollow carbon nano-ellipsoids, hollow carbon nano-capsules, and hollow carbon nano-peanuts) are reasonably designed through multi-step template method and calcination of polymer precursors. Hollow carbon nanospheres and hollow carbon nano-pseudoboxes exhibit better capacitance and higher salt adsorption capacity (SAC) due to their stable carbonaceous structure during calcination. Moreover, the effects of the thickness of the shell and the size of the cavity on the CDI performance are also studied. HCNSs-0.8 with thicker shell (≈20nm) and larger cavity (≈320nm) shows the best SAC value of 23.01mgg-1 due to its large specific surface area (1083.20m2 g-1 ) and rich pore size distribution. These uniform hollow carbon nanoarchitectures with functional properties have potential applications in electrochemistry related fields.

MOF-derived 3D MnO2@graphene/CNT and Ag@graphene/CNT hybrid electrode materials for dual-ion selective pseudocapacitive deionization

In the present study, an asymmetric pseudocapacitive deionization (PCDI) system was fabricated using redox-active electrode materials of three-dimensional (3D) MnO2@graphene/CNT (MGC) and Ag@graphene/CNT (AGC) as cathode and anode, respectively. The asymmetric PCDI system owns a dual-ion capture mechanism, resulting in a high desalination capacity. The 3D MGC and AGC active electrode materials have been derived through a facile two-step method. Initially, the Mn-BTC and Ag-BTC were in situ grown on the 3D r-GO/CNT structure through a hydrothermal process, yielding Mn-BTC@r-GO/CNT and Ag-BTC@r-GO/CNT hybrids. Subsequently, high-temperature annealing of these hybrids leads to respective MGC and AGC hybrid nanocomposites. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis facilities were used to investigate the structure and morphology of the as-prepared hybrid nanocomposites. The as-derived 3D MGC and AGC electrode materials exhibit the high specific capacitance of 496.4 and 206.6 F g−1, respectively, at 1 A g−1 using a 1 M NaCl solution. Furthermore, the MGC (cathode)//AGC (anode) electrode pairs-based PCDI system exhibits remarkable desalination performance with a high salt adsorption capacity of 62.4 mg g−1 and a charge efficiency of 95 % in 1000 ppm NaCl solution at 1.2 V.

Dopant-designed conducting polymers for constructing a high-performance, electrochemical deionization system achieving low energy consumption and long cycle life

Electrochemical deionization (ECDI) systems are attractive desalination devices that achieve relatively high salt adsorption capacity (SAC) with acceptable energy consumption, which can replace or be a promising complement to other desalination techniques. However, most ECDI systems are only suitable for brackish water desalination, and the energy consumption is significantly increased with the salt concentration of brine water without considering their short cycle life. Here a new concept that an ECDI cell constructed with both electrodes of the same conducting polymer (polypyrrole, PPy) shows the high SAC of Faradaic desalination in the brackish water of a wide concentration range and low cell voltages of ion-capturing/ion-releasing, leading to low energy consumption and excellent cycle life, is demonstrated. Anionic dopants of different sizes make PPy films exhibit distinct ion exchange abilities. Trapping large dopants, 4-methylbenzene-sulfonic acid (p-TS), enables the cation-capturing characteristics of the PPy-p-TS electrode, while the free movement of small dopants, perchlorate (ClO4), facilitates the anion exchange capability of the PPy-ClO4 electrode. Moreover, the operation parameters, including charging/discharging time ratio, mass loading ratio of PPy-p-TS/PPy-ClO4, and overall mass loading on two electrodes, are optimized to achieve excellent desalination performance, long cycle life, and the dual function of salt-removal and salt-concentrating. Finally, a three-dimensional ECDI Ragone plot is proposed to judge the performance of all ECDI systems. This work shows the design guidelines for constructing ECDI systems with high desalination capacity, fast deionization rate, low energy consumption, and long cycle life.

Solar reduced graphene oxide decorated with manganese dioxide nanostructures for brackish water desalination using asymmetric capacitive deionization.

Capacitive deionization (CDI) has emerged as a low-cost, reagent-free technique for the desalination of water. This technique is based on the immobilization of dissolved ions on the electrically charged electrodes, by the electrosorption phenomenon. The electrosorption of dissolved ions by using CDI is limited for feed water having a low concentration of salts. To address this problem, we employ an asymmetric capacitive deionization (Asy-CDI) architecture having solar reduced graphene oxide decorated with manganese dioxide nanostructures (SRGO-MnO2 composite). The Asy-CDI possesses an SRGO-MnO2 composite as the cathode and SRGO as the anode with an anion exchange membrane. The cathode formed from the SRGO-MnO2 composite serves the purpose of immobilization of cations, whereas the anode formed from SRGO is responsible for anion removal. The crystal structure, chemical composition and morphology of the as-synthesized SRGO-MnO2 composite electrode materials are characterized by several techniques, confirming that the surface of SRGO is successfully loaded with α-MnO2 nanostructures. The electrochemical characterization reveals a high specific capacitance of the as-synthesized SRGO-MnO2 composite (419.9 F g-1) at 100 mV s-1. The Asy-CDI provides a higher salt adsorption capacity (40.2 mg g-1) compared to Sy-CDI (28.3 mg g-1) with feed water containing a salt concentration of 2000 mg L-1. These results indicate that the Asy-CDI may be employed as an efficient technique for the desalination of high concentration salt water.

The electrosorption behavior of shuttle-like FeP: performance and mechanism.

Owing to its high electrochemical ability, the FeP is envisioned to be the potential electrode for capacitive deionization (CDI) with enhanced performance. However, it suffers from poor cycling stability due to the active redox reaction. In this work, a facile approach has been designed to prepare the mesoporous shuttle-like FeP using MIL-88 as the template. The porous shuttle-like structure not only alleviates the volume expansion of FeP during the desalination/salination process but also promotes ion diffusion dynamics by providing convenient ion diffusion channels. As a result, the FeP electrode has demonstrated a high desalting capacity of 79.09 mg g-1 at 1.2 V. Further, it proves the superior capacitance retention, which maintained 84% of the initial capacity after the cycling. Based on post-characterization, a possible electrosorption mechanism of FeP has been proposed.