Desalination Rate Research Articles

MnO2-modified soybean root derived porous carbon with excellent capacity deionization

Developing high-efficient capacitive deionization (CDI) systems with low-cost environmentally friendly electrode materials is one of the most effective ways to address freshwater shortage. Meanwhile, large number of soybean roots are discarded as waste with large production of soybean and contribute to enormous pressure on the environment. In this work, soybean roots are adopted to prepare activate carbon (SRKPC) by a carbonization and KOH activation process. A composite of [email protected]2 with MnO2 nanoparticles supported on SRKPC is synthesized by a low temperature hydrothermal reaction, which exhibits excellent electrochemical properties with high specific capacitance (597.9 F g−1 at 2 mV s−1) and bimode sodium storage characteristics. The dual-mode CDI system based on [email protected]2 delivers an effective desalination performance with a desalination capacity of 42.90 mg g−1, a desalination rate of 2.86 mg g−1 min−1 and relatively good desalination recoverability. Therefore, this work not only exemplifies the simple fabrication of low-cost, environmentally friendly, and efficient dual-mode CDI electrode materials for capacitive desalination, but also provides a sustainable way to turn biomass waste into functional materials.

Pilot Study on the Deep Treatment of Sulfuric-Acid–Titanium-Dioxide Wastewater Using an Ultrafiltration/Reverse Osmosis Process

The production of titanium dioxide via the sulfuric acid process generates large amounts of acidic wastewater. Investigating the possibility of reusing this wastewater after deep treatment can reduce pollutant discharge and conserve water resources. In a pilot study, a dual-membrane method of ultrafiltration (UF) and reverse osmosis (RO) was employed to perform deep treatments of sulfuric-acid–titanium-dioxide wastewater. The findings showed that the multimedia and precision filters reduced the turbidity of water from an external drainage to as low as 0.18 NTU, with a turbidity removal rate of approximately 50%, reaching a maximum of 68%. When the UF effluent had a membrane flux of 70–100 L/m2 h and a water production rate of 85–90%, the SDI15 was <5.0 and the turbidity was <1.0, meeting RO water supply requirements. Additionally, RO achieved a TDS removal rate of >95%, a CODCr removal rate of 85%, and a desalination rate of >98.5%. At a smooth operation system water recovery rate of 50%, the highest system recovery rate obtained was 64%. The water produced via RO adhered to reuse water standards. UF/RO deep treatment of sulfuric-acid–titanium-dioxide production wastewater and its reuse can realize comprehensive wastewater use and conserve water resources.

Comprehensive Electrochemical Impedance Spectroscopy Study of Flow-Electrode Capacitive Deionization Cells.

Flow-electrode capacitive deionization (FCDI) offers infinite ion adsorption for continuous desalination of high-concentration saline water by supplying a flow-electrode to the cell. Although extensive efforts have been made to maximize the desalination rate and efficiency of FCDI cells, the electrochemical properties of these cells are not fully understood. This study investigated the factors affecting the electrochemical properties of FCDI cells containing activated carbon (AC; 1-20 wt %) and various flow rates (6-24 mL/min) for the flow-electrode using electrochemical impedance spectroscopy before and after desalination. Examination of the impedance spectra using the distribution of relaxation time and equivalent circuit fitting analysis revealed three distinctive resistances such as internal, charge transfer, and ion adsorption resistances. The overall impedance decreased significantly after the desalination experiment due to increased ion concentrations in the flow-electrode. The three resistances decreased with increasing concentrations of AC in the flow-electrode due to the extension of electrically connected AC particles that participated in the electrochemical desalination reaction. The ion adsorption resistance decreased significantly due to the flow rate dependence of the impedance spectra. In contrast, the internal and charge transfer resistances were invariant.

Combined removal experiment of multiple impurities from W/O emulsions under high frequency pulsed electric field: Study on laws of desalination, decalcification, and deacidification

AbstractElectrocoalescence is widely used to dehydrate crude oil, but impurities in crude oil are extremely complex, which greatly weaken the effect of dehydration. To understand the coupling law of various impurities, a static demulsification experiment was conducted under a high frequency and high voltage pulsed electric field to investigate the effects of electric field parameters (voltage, frequency, pulse width ratio), emulsification strength, electrocoalescence time, water content, acid value, injection alkali ratio, calcium content, decalcification agent concentration and removal process on desalination, decalcification, and deacidification. The results showed that the desalination and decalcification rates varied synchronously with the electric field parameters and water content. Additionally, the desalination and decalcification rates decreased with the emulsification strength, alkali injection ratio, acid value, and calcium content. Further, they increased first and then decreased with decalcifier concentration. The deacidification rate did not vary with the electric field parameters, but it strengthened with the water content and alkali injection ratio. Conversely, it decreased with the acid value, calcium content, and decalcifier concentration. Additionally, it increased first and then decreased with the emulsification intensity. The best removal procedure is deacidification followed by decalcification. These findings are helpful to achieve the combined removal of various impurities in crude oil.

Modeling of the pressure drop effect using membrane distillation in the desalination process

The desalination process using membrane distillation (MD) has recently attracted wide attention in the last few years around the world. Especially, membranes that have an asymmetric geometry, for their performance to filtrate the salt water and the high salt rejection. In this paper, the Langevin dynamics model was adopted as a simulation method to investigate the transport of salt water through the sloping membrane under a pressure drop. The surface of the used membrane is considered as a hydrophilic sloping surface. Thus, the pressure drop effect on the fluid flux was observed, which leads to attracting the salt water into pores that are randomly distributed. The influence of deposition and accumulation of the ions into pores, the incline angle of the membrane surface, and the thickness of the formed layer on the surface were investigated. In addition, the impact of biofouling is caused by the accumulation and the variation of the fluid velocity as a function of pressure drop values. The obtained results show that the relationship between the fluid velocity and the pressing force is a power law. Moreover, the increase in fluid flow velocity in the porous medium is severe in the earlier time regime, but it becomes almost constant in the second regime. However, the time desalination process increases linearly with the pressure drop. Moreover, the accumulation and deposition of ions into the pores cause a decrease in the water flow through the pores resulting in a higher pressure drop in the less inclined direction. Finally, the influence of deposition and accumulation of the salt phase into the pores on the membrane performance was remarked, resulting in a high desalination rate. The obtained results explain the salt water behavior through a porous membrane, which provides ideas for making a high membrane performance.

Experimental investigation on the performance of air–gap diffusion distillation with foamed ceramics

Air-gap diffusion distillation (AGDD) has been proposed as a novel type of thermal distillation technique, in which the hydrophilic porous media is used as a hot stream channel. Polyvinyl alcohol (PVA) sponge was first selected as the porous medium in our previous reports. To improve the thermal, chemical resistance and mechanical strength of the porous medium, some foamed ceramics (FCs) (alumina, zirconia, and silicon carbide foamed ceramic) are selected as the porous mediums which are used as hot stream channels of AGDD in this work. The effect of different FC materials on performances of AGDD is investigated by experiments. That the influence of FCs with pre-wetting and non-wetting treatments on the performances of AGDD is investigated first. Secondly, the influence of operation and structure parameters on the performances of AGDD and the stability of three FCs in long-term operation are explored. And finally, the performances of AGDD used FCs and PVA sponge are compared. Results show that the FC with pre-wetting treatment can improve the performances of AGDD, and the water production flux can rise to 23.7%, especially for the silicon carbide FC with high pore density. Furthermore, among the three FCs, ZrO2 FC can maintain higher water production flux and desalination rate during long-term operation. The desalination rate of AGDD with three different FCs is higher than 99.1%. The AGDD with FC is ideal for high-temperature and high-flow-rate working fluid environments, whereas the AGDD with PVA is suitable for low-temperature and small-flow-rate working fluid environments. This may be used as a reference for the industry to choose porous material for AGDD.

Multi-physical field simulations of directional seawater freeze-crystallisation under a magnetic field

Ice crystals produced through freeze-desalination of seawater often contain salt pockets that impede the desalination rate. The researchers used phase-field and lattice Boltzmann methods to analyse the influence of magnetic fields on crystal subcooling and the growth law of seawater crystallisation. Results showed that using a DC magnetic field increased the directional growth of ice crystals, leading to a 103.9 % increase in ice crystal area and a 13.05 % reduction in salt pockets compared to no magnetic field. Increasing the strength of the magnetic field improved the overall desalination rate by 25.8 %. The application of an AC magnetic field enhanced the ice crystal area by 37.8 % and the overall desalination rate by 17.0 %, but also increased salt pockets by 11.6 %. The step magnetic field did not affect the crystal area but enhanced the overall desalination rate by 14.3 %. Overall, this study demonstrates the potential for improving the efficiency of freeze desalination by controlling magnetic fields during the sea-ice growth process.

Experimental investigation of freezing desalination using silicon oil for ice production

Because of its potential benefits in lowering process energy consumption, freezing desalination as a seawater desalination method has attracted a lot of attention. However, significant mass loss caused by extensive washing is a fundamental problem preventing the development of freezing desalination technologies. For freezing desalination technology to be widely adopted, the washing process must be eliminated. In this study, a fluid-layer-based method for separating ice is introduced. The density differences between the generated ice and the silicon oil intermediate fluid layer facilitate the separation of the product water without the need of conventional crushing or washing processes. The aim of this work is to study the feasibility and applicability of using silicon oil as an intermediary fluid layer in ice separation during the freezing desalination process. The outcomes show promise for a feasible freezing desalination technique utilizing silicon oil as an intermediate separation layer. It was also observed that as feed salinity decreases, the desalination rate increases. For instance, the distillation rate is 50.89 % and 67.3 % at an initial feed salinity equal 45,000 and 10,000 ppm, respectively. Overall, the initial feed salinity and COP are found to have an impact on specific energy usage.

Nanocomposite substrate-supported nanofiltration membrane for efficient treatment of rare earth wastewater

The incorporation of nanomaterials into the selective layer of nanofiltration membranes can effectively enhance membrane performance. However, the agglomeration of nanoparticles inevitably leads to defects in the membrane PA layer. To address this issue, this paper reports a novel nanocomposite substrate-supported thin-film composite (TFC) nanofiltration membrane with good stability and excellent separation performance. Inorganic two-dimensional O–MoS2 nanosheets were embedded into a polysulfone (PSF) substrate by a non-solvent-induced phase transition method. The PSF/O–MoS2 nanocomposite was used as a support for the interfacial polymerization between piperazine and tricarbonyl chloride. The pore morphology of the nanocomposites changed dramatically as the O–MoS2 content increased. With the optimal content of O–MoS2 in substrates was 0.06 wt%, the pore structure of the substrate changed from a larger irregular bubble pore structure to a finger-like pore structure. The nanocomposite matrix-supported TFC membrane exhibited 1.7 times higher water flux and better salt removal compared to the control membrane. Meanwhile, the obtained nanofiltration membranes showed excellent separation performance in treating simulated rare earth wastewater (P507) containing surfactants with a desalination rate of 97.08%. The desalination rate also reached 95% in a 24- h performance test on real rare earth wastewater (50-fold dilution), demonstrating its great potential for industrial applications. This work also highlights that modification of substrates with functional nanomaterials can provide a versatile approach to enhance the separation performance and stability of TFC membranes.

Hybrid of pyrazine based π-conjugated organic molecule and MXene for hybrid capacitive deionization

In this work, we report a hybrid material of pyrazine based π-conjugated organic molecule, hexaazatrinaphthalene (HATN), and MXene. In this hybrid, MXene serves as a conductive substrate and HATN provides multiple electroactive sites, which are jointly combined to build a unique 3D structure with more ion transport channels for accelerating the charge transfer and ion diffusion rates. The as-obtained HATN/MXene composite displays a superior desalination capacity of 57.5 mg g−1 with an excellent desalination rate of 13.2 mg g−1 min−1 and good long-term stability. This work provides a meaningful guidance for designing and applying organic molecules in capacitive deionization field.

High-performance desalination systems from natural luffa vine: A simple, efficient and environmentally friendly solution for bio-based solar evaporators

In this study, agricultural waste luffa vines (LVs) were used to develop solar evaporators by surface carbonization and KOH treatment combined with freeze-drying method. Scanning electron microscopy (SEM), solar absorption, solar thermal management and salt dissolution tests showed that the water vapor generation rate of a single column of LV-based solar evaporator after surface carbonization was as high as 3.26 kg m−2 h−1 under 1 sun, and its evaporation efficiency (118%) even exceeded the theoretical valve. After 36 h of continuous use, there was almost no salt deposition. Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, thermal conductivity, evaporation enthalpy, and low field nuclear magnetic resonance (LF-NMR) analyses indicated that the high evaporation efficiency of LV-based solar evaporators after surface carbonization was mainly due to high water transport capacity, low water evaporation enthalpy, and high light absorption rate (91%) of LV. The excellent salt-deposition resistance benefitted from the natural multilayered gradient porous structures of LV, forming spontaneous salt backflowing systems. The desalinization rate of LV-based solar evaporators exceeded 99.9%, which was even higher than those of many membrane elements and thermal desalination systems. They also had excellent removal effects on dyes and oily wastewater. After 30 d of continuous soaking, the compressive strength of 2–cm LVs was still 9.4 MPa. KOH-freeze-drying treatment further improved the salt-deposition resistance of LV-based solar evaporators, but reduced their evaporation efficiency and mechanical performance. This work suggests that LVs with carbonized surface have significant potential for development of environmentally friendly biomass solar evaporators with efficient evaporation, excellent resistance to salt deposition, and good durability.

Two-dimensional bimetallic cobalt-copper metal organic framework for improved desalination performance of capacitive deionization

Capacitive deionization (CDI) technology has recently attracted much attention due to its distinct advantages, which include energy efficiency, eco-friendly method, and simple process. Capacitive materials, such as activated carbon, carbon fiber, and carbon aerogel, have mostly been used. However, the conventional carbon-based materials still suffer limitations, such as low electrosorption capacity, slow desalination rate, and insufficient desalination capacity for high saline concentration. Herein, the 2 Dimensional-Cobalt-Copper sulfur linker-based MOF material was prepared by a solvothermal method to develop the performance of electrode material, namely 2D-CoCu sMOF. We applied the synthesized material with porous carbon material (AC) as an electrode material in the CDI desalination system. Owing to the fast and efficient electron transfer in the electrode layer and the lower interfacial resistance between electrode surface and saline electrolyte originating from the redox reactions of MOF structure, 2D − CoCu sMOF exhibited a much higher desalination performance, compared to the pristine AC. CDI experimental results showed that the salt adsorption capacity (SAC) of electrode using 2D − CoCu sMOF was significantly improved from 4.18 to 7.55 mg/g without any changes in the long-term stability test, which was over an 80% increase in desalination performance. This approach provides an effective and simple method for the preparation of MOF-based CDI electrode material, which could have potential for high-performance green technology including desalination applications.

An overlooked soil carbon pool in vegetated coastal ecosystems: National-scale assessment of soil organic carbon stocks in coastal shelter forests of China

Protection and restoration of vegetated coastal ecosystems provide opportunities to mitigate climate change. Coastal shelter forests as one of vegetated coastal ecosystems play vital role on sandy coasts protection, but less attention is paid on their soil organic carbon (OC) sequestration potential. Here, we provide the first national-scale assessment of the soil OC stocks, fractions, sources and accumulation rates from 48 sites of shelter forests and 74 sites of sandy beaches across 22° of latitude in China. We find that, compared with sandy beaches, shelter forest plantation achieves an average soil desalination rate of 92.0 % and reduces the soil pH by 1.3 units. The improved soil quality can facilitate OC sequestration leading to an increase of soil OC stock of 11.8 (0.60–64.2) MgC ha−1 in shelter forests. Particulate OC (POC) is a dominant OC fraction in both sandy beaches and shelter forests, but most sites are >80 % in shelter forests. The low δ13C values and higher C:N ratios, which are more regulated by climate and tree species, together with high POC proportions suggest a substantial contribution of plant-derived OC. Bayesian mixing model indicates that 71.8 (33.5–91.6)% of the soil OC is derived from local plant biomass. We estimate that soil OC stocks in Chinese shelter forests are 20.5 (7.44–79.7) MgC ha−1 and 4.53 ± 0.71 TgC in the top meter, with an accumulation rate of 45.0 (6.90 to 194.1) gC m−2 year−1 and 99.5 ± 44.9 GgC year−1. According to coastal shelter forest afforestation plan, additional 1.72 ± 0.27 TgC with a rate of 37.9 ± 17.1 GgC year−1 can be sequestrated in the future. Our findings suggest that construction of coastal shelter forests can be an effective solution to sequester more soil carbon in coastal ecosystems.

In situ synthesis of ultrasmall NaTi2(PO4)3 nanocube decorated carbon nanofiber network enables ultrafast and superstable rocking-chair capacitive deionization

Faradic-based capacitive deionization (CDI), as an important derivative of conventional CDI, has received wide attention in the desalination community. Yet, oriented from its intrinsic ion storage mechanism, faradic-based CDI has been plagued by several serious issues (e.g., imbalanced ion storage capacity, low desalination rate, and poor cycling stability), which greatly constrained its further development. Herein, we put forward an innovative strategy by using carbon nanofiber-reinforced NaTi2(PO4)3 (eCNF/NTP) as the core material (for Na+-capturing) and further coupling it with rational rocking-chair capacitive deionization (RCDI) cell architecture. Of note, owing to the unique 3D network structure of eCNF/NTP that not only provides sufficient redox-activate sites but also offers a rigid network structure to prevent the potential aggregation during cycling, as well as the rational RCDI symmetric cell architecture to avoid the imbalanced cation and anion storage capacity, the RCDI system equipping with eCNF/NTP electrode displays an excellent desalination performance (desalination capacity: 168.2 mg g−1; desalination rate: 0.46 mg g−1 s−1) with outstanding cycling stability (only 6 % desalination capacity degradation after 80 cycles). This work is interesting because it showcases the critical importance of both delicate material design and rationalized cell architecture in addressing the bottleneck issue of CDI, which could shed light on the future development of other high-performance desalination systems.

A novel UiO-66-NH2/graphene oxide composite thin membrane for retarding membrane wetting in membrane distillation

Membrane distillation (MD) is considered an emerging desalination technology. However, the presence of surfactants allows liquid to penetrate the membrane, resulting in membrane wetting, which hinders the commercialization of MD. In this study, we use very few modified materials to prepare novel Janus thin membranes that immobilize modified materials (graphene oxide (GO) and UiO-66-NH2) on polytetrafluoroethylene (PTFE) hydrophobic base membranes via crosslinkers. The composite thin membrane properties with eight different ratios and contents of GO and UiO-66-NH2 were fabricated and tested by a feed solution of sodium chloride containing a high concentration of sodium dodecyl sulfate. An optimal ratio of Janus membrane with high flux without affecting the effluent water quality was obtained. The Janus membrane exhibited excellent anti-wetting properties compared to the original PTFE membrane. A desalination rate of up to 99.9% was still available even under 48 h of long-term operating conditions by maintaining a flux of approximately 21.2 L/(m2·h). The anti-wetting mechanism of this membrane was further confirmed by the modified XDLVO model. It suggested that the novel Janus membrane could be a highly promising substitute to the MD process for the resource-based treatment of surfactant-containing wastewater, which played an important role in promoting its application.

Soil moisture and salinity dynamics of drip irrigation in saline-alkali soil of Yellow River basin

Soil secondary salinization in the Yellow River Diversion Irrigation Area of Northwest China seriously threatens local agricultural production. Drip irrigation technology is one of the largest contributors to low-yielding saline-alkali land; however, research on the high spatio-temporal scale variability of soil moisture and salinity in drip irrigation is still lacking. Herein, four treatments, CK (flood irrigation, 900 mm), W1 (small volume drip irrigation, 360 mm), W2 (medium volume drip irrigation, 450 mm), and W3 (large volume drip irrigation, 540 mm), were set up to investigate the characteristics and laws of soil moisture and salinity under different irrigation methods. The results showed that the soil moisture of drip irrigation was 5.02%–17.88% (W1), 7.36%–21.06% (W2), and 13.79%–27.88% (W3) higher than that of flood irrigation, resulting in a vertical distribution of soil moisture being low at the top and high at the bottom. Under drip irrigation, the soil salinity formed a desalination zone centered on the drip emitter and this zone gradually expanded to deeper soil with continuous drip irrigation, gradually transforming the soil from surface aggregation type to the bottom accumulation type. The desalination rates of W1, W2, and W3 were 18.46%, 20.84%, and 22.94%, respectively, whereas the salt leaching rate of CK was slower and the salt distribution was not uniform; therefore, the desalination rate was only 5.32%. By precisely controlling the irrigation water volume and flow, drip irrigation significantly reduced surface evaporation and subsurface leakage of water and improved water use efficiency, thus increasing grain yield. Compared with flood irrigation, the yield increase rates of W1, W2, and W3 were 6.6%, 16.18%, and 18.32%, respectively. Therefore, drip irrigation with an appropriate irrigation volume in the saline land in northern Ningxia can improve water saving, salt suppression, and maize yield.

Vertically Aligned Bismuthene Nanosheets on MXene for High-Performance Capacitive Deionization.

Capacitive deionization has been considered as a promising solution to the challenge of freshwater shortage due to its high efficiency, low environmental footprint, and low energy consumption. However, developing advanced electrode materials to improve capacitive deionization performance remains a challenge. Herein, the hierarchical bismuthene nanosheets (Bi-ene NSs)@MXene heterostructure was successfully prepared by combining the Lewis acidic molten salt etching and the galvanic replacement reaction, which achieves the effective utilization of the molten salt etching byproducts (residual copper). The vertically aligned bismuthene nanosheets array evenly in situ grown on the surface of MXene, which not only facilitate ion and electron transport as well as offer abundant active sites but also provide strong interfacial interaction between bismuthene and MXene. Benefiting from the above advantages, the Bi-ene NSs@MXene heterostructure as a promising capacitive deionization electrode material exhibits high desalination capacity (88.2 mg/g at 1.2 V), fast desalination rate, and good long-term cycling performance. Moreover, the mechanisms involved were elaborated by systematical characterizations and density functional theory calculations. This work provides inspirations for the preparation of MXene-based heterostructures and their application for capacitive deionization.

Preparation Janus membrane via polytetrafluoroethylene membrane modification for enhanced performance of vacuum membrane distillation desalination

In this study, we developed novel Janus membranes with multilevel hierarchical structures to prevent membrane pore wetting and enhance the performance for desalination simultaneously. Here, a Janus membrane with multilevel roughness was tailored via a polydopamine (PDA) coating followed by deposition of Fe3O4 nanoparticles and PDA sealing. These novel Janus membranes demonstrated outstanding antiwetting properties and salt rejection performances in comparison to pristine polytetrafluoroethylene (PTFE) membrane. Particularly, the specific flux of Janus membranes was maintained in a relatively stable state (0.6–0.7) after membrane cleaning with pure water, meanwhile, the permeate conductivity was maintained in the range of 0–30 µS/cm with the desalination rate of 99.9% during the vacuum membrane distillation (VMD) tests by using 6.98 wt.% feed solutions, indicating that these Janus membranes (i.e., P/Fe/P-PTFE membrane) can improve the performance for VMD desalination without membrane wetting throughout the test duration. Furthermore, we ascribed these Janus membranes’ superior performances to the coupled effects of super hydrophilicity brought about by PDA layer and self-healing mechanism provided by Fe3O4 nanoparticles. This work highlights the great potential of novel Janus membranes with multilevel hierarchical structures for water reclamation from challenging high-salinity wastewater through VMD.

Temperature-mediated in-situ formation of antimony nanoclusters inside carbon nanofibers for chloride-driven capacitive deionization

Slow desalination kinetics and poor durability constrain the practical application of faradic electrode-directed capacitive deionization (FDI) systems. In view of this, we developed a temperature-mediated in-situ synthesis strategy for fabricating Sb nanoclusters inside carbon nanofibers (Sb NCs@CNF) as Cl− capturing electrodes for high-efficiency FDI. The synthetic strategy allows “temperature-controlled evaporation” of Sb species from the nanofibers, which not only makes the formation of ultrasmall Sb NCs possible but also provides CNF shells to enhance the structural stability and electrical conductivity of Sb NCs. Benefiting from the specific interaction between Sb species and Cl− ions, ultrasmall size, high surface atom ratio of Sb NCs, as well as the protective CNFs shell, the as-fabricated Sb NCs@CNF-based Cl−-driven FDI achieved fast desalination rate (up to 0.24 mg g−1 s−1, through expanding the contribution of surface-controlled capacitance) and excellent cycling stability (only 12.4 % desalination capacity reduction after 30 cycles). In addition to the unprecedented design of Sb NCs-based Cl− capturing electrode materials, this study also provides a paradigm in the temperature-mediated in-situ synthesis of non-coinage MNCs, which may stimulate more research activities in the design and application of carbon-protected MNCs.

Up-shifting the desalination rate limit of capacitive deionization via integrating chloride-capturing Bi nanocluster with flow-through cell architecture

Faradic electrode-directed capacitive deionization (faradic-based CDI) as a green and eco-friendly technique is particularly promising in addressing the freshwater crisis, but its practical applications are plagued by the sluggish desalination kinetic. After deciphering its dynamic desalination process, two rate-determine steps (RDS) are identified, i.e., the ion diffusion inside the faradic electrode (RDS #1) and mass transfer process in the electrolyte (RDS #2). Therefore, we propose a synergetic strategy to upshift the desalination rate limit of faradic-based CDI through the integration of delicate material design with rational cell architecture. Specifically, deploying ultrasmall Bi nanoclusters impregnated carbon nanofibers (Bi NCs@CNF) as chloride-capturing electrodes and constructing a flow-through CDI (FT-CDI) system to accelerate the diffusion process (RDS #1) and shorten the mass transfer pathway (RDS #2), respectively. As expected, Bi NCs@CNF-based FT-CDI performs super-fast desalinization (0.56 mg g−1 s−1) and excellent cyclic stability. Taken together, our study opens an avenue in upshifting the desalination kinetics of faradic-based CDI based on the joint power of both “material design” and “cell architecture”, which may motivate the development of highly-efficient desalination systems.