Improved Desalination Performance Research Articles

Improved desalination performance of flow-electrode capacitive deionisation by a novel drop-shape channel

ABSTRACT As an emerging desalination technology, flow-electrode capacitive deionisation (FCDI) has the advantages of theoretically infinite adsorption capacity and applicability to high-concentration brine. However, during the operation of FCDI, the flow electrode in the S-shape channel is prone to sedimentation and clogging the channel. This undesirable phenomenon brings low efficiency and security issues. Therefore, a drop-shape channel was designed for FCDI to improve the flow regime of the flow electrode. The flow simulation of the drop-shape channel was performed to select the appropriate geometry to avoid the formation of the vortex and low-velocity region. The simulation results showed that the streamlined design of the drop-shape channel has insignificant velocity gradients. It significantly reduces the low-velocity region and improves the phenomenon of particle sedimentation. The desalination performance with varieties of electrode flow rate, AC content, and voltage was used to investigate the advantage between S-shape and drop-shape channels. It was found that under the conditions of low flow rate, high AC content, and high voltage, the drop-shape channel FCDI system could still obtain better ASRR and CE.

MXene-enhanced sulfonated TFN nanofiltration membranes for improved desalination performance

MXene, a recently identified 2D nanosheet, has drawn interest due to its potential application in the modification of thin film nanocomposite (TFN) membranes for the production of clean water. This study presents the development of MXene-based sulfonated TFN (STFN) nanofiltration membrane for the desalination application and chlorine resistance. A novel amine monomer approach of combination such as 1-(2-aminoethyl)piperazine (APIP) and 2,5-diaminobenzenesulfonic acid (DABSA) was proposed for the interfacial polymerization. The as-prepared MXene displayed a thin-layer nanoflakes-like structure. The surface morphology of the membrane indicated that the MXene bound well on the sulfonated TFN membrane. The hydrophilicity of the membrane was enhanced significantly in the STFN membrane, and the lower contact angle value was decreased up to 24°. The filtration performance showed that the water flux and salt rejection were improved in both sulfonated thin film composite (STFC) and STFN membranes. STFN membranes achieved a higher rejection of >93 % for Na2SO4 and MgSO4. The antifouling and chlorine resistance were also improved in STFC and STFN membranes. This study would be an insight for the development of novel STFN membranes for desalination applications.

Emerging Frontiers in Multichannel Membrane Capacitive Deionization: Recent Advances and Future Prospects.

Capacitive deionization (CDI) has emerged as a promising desalination technology and recently promoted the development of multichannel membrane capacitive deionization (MC-MCDI). In MC-MCDI, the independent control of multiflow channels, including the feed and electrolyte channels, enables the optimization of electrode operation in various modes, such as concentration gradients and reverse voltage discharge, facilitating semicontinuous operation. Moreover, the integration of redox couples into MC-MCDI has led to advancements in redox-mediated desalination. Specifically, the introduction of redox-active species helps enhance the ion removal efficiency and reduce energy consumption during desalination. This systematic approach, combining principles from CDI and electrodialysis, results in more sustainable and efficient desalination. These advancements have contributed to improved desalination performance and practical feasibility, rendering MC-MCDI an increasingly attractive option for addressing water scarcity challenges. Despite the considerable interest in and potential of this process, there is currently no comprehensive review available that covers the operational features and applications of MC-MCDI. Therefore, this Review provides an overview of recent research progress, focusing on the unique cell configuration, vital operation principles, and potential advantages over conventional CDI. Additionally, innovative applications of MC-MCDI are discussed. The Review concludes with insights into future research directions, potential opportunities in industrial desalination technology, and the fundamental and practical challenges for successful implementation.

Mechanism insight into improved desalination performance and energy efficiency in redox flow deionization with ion exchange resins

In this work, we proposed a concept of redox flow deionization (RFDI) by constructing ion transport channels using ion exchange resins into the redox flow desalination (RFD) cell, and achieved a remarkable reduction of 27.4% in energy consumption and an increase of 24.1% in electrical power output compared to the conventional RFD system at the feed concentration of 1000–5000 mg L−1. Finite element analysis results further revealed the mechanism of RFDI process indicating that the ion exchange resin reduced the cell resistance by forming ions transport channels, which consequently improved the performance of RFDI. As a proof-of-concept application, the RFDI was evaluated for desalination of brackish water, which exhibited a freshwater productivity of 3.85 to 7.79 L m−2 h−1 with energy consumption of 5.39 to 2.31 Wh L–1. What’s more, further modification of the ion transport channels in the RFDI cell could result in even higher brackish water desalination and energy storage performance. The findings of this study have significant implications for addressing global freshwater scarcity and the development of more efficient and sustainable desalination technologies.

Low fouling/scaling double network thin film composite nanofiltration membranes with improved desalination performance

Conventional poly(piperazineamide) [poly(PIP)] thin film composite (TFC) nanofiltration (NF) membranes undergo severe fouling/scaling and -show low barrier towards heavy metal ions and organic solutes. Herein, we report the preparation of double network (DN) TFC NF membranes to address these issues. In situ interfacial polymerization between PIP + poly(2-dimethyl aminoethyl)methacrylate (PDMA) and trimesoyl chloride+activated dihalide provides DN-TFC NF membranes. Formation of DN leads to the lowering of negative charge and narrowing down the pore size distribution of the membranes. PEGylated DN-TFC membranes have been prepared using copolymers of PEG and PDMA to demonstrate the adaptability of this chemistry and to increase the antifouling property. The DN-TFC membranes show water permeance of 7.9–8 L m−2 h−1 bar−1 and higher rejection of MgCl2 (90–94 %), Co2+ (96–98 %) and bisphenol A (91–94 %) as compared to that of the pristine (74 %, 70 % and 80 %) and the reported negatively charged (9–83 %, 60 % and 48–97.6 %) NF membranes. DN-TFC membranes show Na2SO4 rejection of ∼98 %, close to the reported membranes (98–99 %). The fouling and scaling resistant behaviors of the DN-TFC membranes (Flux recovery ratio = 90–94 % and 93–95 %) are greatly enhanced as compared to that of the pristine membrane (∼82 % and 76 %). DN-TFC membranes show great promises for the purification of water.

Insufficient desorption of ions in constant-current membrane capacitive deionization (MCDI): Problems and solutions

Membrane capacitive deionization (MCDI) is a water desalination technology that involves the removal of charged ions from water under an electric field. While constant-current MCDI coupled with stopped-flow during ion discharge is expected to exhibit high water recovery and good performance stability, previous studies have typically been undertaken using NaCl solutions only with limited investigation of MCDI performance using multi-electrolyte solutions. In the present work, the desalination performance of MCDI was evaluated using feed solutions with different levels of hardness. The increase of hardness resulted in the degradation of desalination performance with the desalination time (Δtd), total removed charge, water recovery (WR) and productivity decreasing by 20.5%, 21.8%, 3.8% and 3.2%, respectively. A more serious degradation of WR and productivity would be caused if Δtd decreases further. Analysis of the voltage profiles and effluent ion concentrations reveal that the insufficient desorption of divalent ions at constant-current discharge to 0 V was the principal reason for the degradation of performance. The Δtd and WR can be improved by discharging the cell using a lower current but the productivity decreased by 15.7% on decreasing the discharging current from 161 to 107 mA. Discharging the cell to a negative potential was shown to be a better option with the Δtd, total removed charge, WR and productivity increasing by 27.4%, 23.9%, 3.6% and 5.3%, respectively, when the cell was discharged to a minimum voltage of – 0.3 V. Use of such a method should be feasible for operation of full scale MCDI plants and would be expected to lead to better regeneration of the electrode, improved desalination performance and, potentially, a significant reduction in the need for use of clean-in-place procedures.

Enhancing charge transfer utilizing ternary composite slurry for high-efficient flow-electrode capacitive deionization

Weak contact between activated carbon (AC) particles results in a poor conductivity for the electrode slurry, which limits the improved desalination performance in flow-electrode capacitive deionization (FCDI). Based on the bridging and filling effects of nanoparticles, we report a ternary composite slurry with multi-dimensional sized carbon particles by introducing the carbon nanotubes (CNT) and carbon black (CB) into AC-based slurry, namely AC/(CB + CNT) slurry. Further enhanced electrical conductivity relative to conventional pure AC slurry. By comparison analysis, FCDI system with the ternary carbon composite slurry had a faster average salt removal rate (ASAR) of 1.89 μmol cm−2 min−1 under at 1.2 V in a feed salinity of 2.0 g L−1, which is 3.27 1.92 and 1.46 times that of pure AC, AC/CB and AC/CNT slurry. In long-term operation (1800 min, U = 1.6 V), the AC/(CB + CNT) slurry exhibited a stable ASAR of 4.41 μmol cm−2 min−1 and maintained a charging efficiency (CE) of around 96% and molar energy consumption (Em) of 0.043 kWh mol−1. Electrochemical analysis and computational fluid dynamics (CFD) simulation further confirms that AC/(CB + CNT) slurry enable system with a point-to-line-to-surface connection morphology, which generates a robust charge percolation network with diverse pathway and facilitates the charge transfer. In summary, this study developed a facile strategy for increasing the slurry conductivity to provide a feasible approach in efficient desalination application.

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.

Enhancing the electronic and ionic transport of flow-electrode capacitive deionization by hollow mesoporous carbon nanospheres

Flow-electrode capacitive deionization (FCDI) is a promising desalination technology by virtue of its infinite electrosorption capacity and possible continuous operation. However, FCDI still suffers from the limited electronic and ionic transport of its flow-electrode. Herein, we first employed hollow mesoporous carbon nanospheres (HMCNs) as flow-electrode to improve FCDI desalination performance. To understand the dependence of FCDI performance on the structural properties of flow-electrodes, two other samples, activated carbon (AC) and solid mesoporous carbon nanospheres (SMCNs), were selected for comparison. The results showed that HMCNs flow-electrode exhibited excellent rheological behaviors with good dispersibility and increased viscosity. EIS analysis proved that HMCNs flow-electrode had a decreased electrical resistance and enhanced ion diffusion. As expected, HMCNs exhibited improved desalination performance compared with AC and SMCNs. In particular, at 1.2 V with 10 % mass loading, the average salt removal rate, charge efficiency, and energy consumption reached 0.040 mg/cm2∙min, 92.9 %, and 0.035 kWh/mol, respectively. The excellent desalination performance should be attributed to the structural advantage of HMCNs in electronic and ionic transport. Overall, this study provides insights into the dependence of FCDI performance on the structural properties of flow-electrodes, thereby progressing the FCDI technology in relation to electronic/ionic transport.

Multi-electrode scale-up strategy and parametric investigation of redox-flow desalination systems

Redox flow desalination (RFD) has emerged as a promising energy-efficient and sustainable electrochemical ion separation process for water desalination. Despite the effectiveness of RFD systems for desalination, prior studies have generally focused on fundamental aspects and lab-scale studies; therefore, the practical feasibility and potential for deployment in industry remain unclear. Here, a strategy for scaling-up RFD systems was developed, and the efficacy of RFD for desalination on a larger scale and its practical feasibility for industrial applications were assessed. A new multielectrode stacking strategy employing a carbon electrode and titanium current collector enabled enhanced charge transfer and improved desalination performance without the need for additional channels. This facile strategy of scaling up the RFD remarkably reduces the size of the system compared with unit cell stacking in the conventional electrochemical system. The larger scale RFD system exhibited a salt removal rate of 852 mmol/m2/h and specific energy consumption of 120 kJ/mol (≅0.1 kWh/m3). Multi-parametric optimization was carried out via interactive data visualization by varying the cell voltage, flow rate, number of carbon electrode stacks, and membrane arrangement. The RFD system achieved an energy consumption of 60–80 kJ/mol and removal rate of 200–300 mmol/m2/h. Overall, the feasibility of RFD for water desalination was confirmed through a rational scale-up strategy, comprehensive understanding of the desalination parameters, and techno-economic analysis. Through continued development and further scale-up investigations, we envision the deployment of RFD systems for energy-efficient desalination on the industrial scale as an alternative to conventional electrochemical desalination processes (i.e., electrodialysis and capacitive deionization).

Fabrication of trimethylphosphine-functionalized anion exchange membranes for desalination application via electrodialysis process

The design of conductive, improved durable and selective anion exchange membranes (AEMs) for desalination application via electrodialysis (ED) process is critical for a more sustainable future. This work reports the design of a series of homogeneous trimethylphosphine (TMP)-functionalized anion exchange membranes (AEMs) for desalination application via electrodialysis (ED) process. Physico-chemical characterization and electrochemical performance of the trimethylphosphine-functionalized anion exchange membranes was conducted and the activity found to be tuned by varying the quantity of trimethylphosphine into the membrane architecture. For anion exchange membranes M1 to M4, the ion exchange capacity (IEC) was increased from 1.35 to 2.16 mmol/g, water uptake (WR) from 4.30 to 17.72%, linear expansion ratio (LER) from 3.70 to 12.50% with enhancing the quantity of trimethylphosphine into the polymer architecture. The ionic resistance decreased from 15.14 to 2.61 Ω cm2 with increasing quantities of trimethylphosphine whereas transport number increased from 0.98 to 0.99. The performance of synthesized trimethylphosphine-functionalized anion exchange membranes in desalination of NaCl was evaluated via electrodialysis process (flux of 3.42 mol/m2. h and current efficiency of 64.30%). Results showed that the prepared trimethylphosphine-functionalized membrane (optimum M4) possess improved desalination performance as compared to commercial membrane Neosepta AMX under identical experimental conditions.

Polydopamine-modified HKUST-1 as nanofiller of PPS@PA membrane with well improved desalination performance

In order to improve the permeability and desalination performance of the thin-film nanocomposite (TFN) membranes supported by polyphenylene sulfide ( PPS ), the polydopamine (PDA) modified HKUST-1 (mHKUST-1) nanocomposite materials were added into polyamide ( PA ) functional layer. The mHKUST-1 nanoparticles with good dispersity and chemical compatibility were successfully embedded in PA layer to develop a new negative charged nanofiltration membrane. The optimized PPS/12-mHKUST-1@PA membrane showed an excellent permeability of up to 27.35 L∙m −2 h −1 ∙bar −1 , twice as much as the PPS@PA membranes. Meanwhile, the considerable rejection performance of 91.67% to MgSO 4 and 90.06% to Na 2 SO 4 at 4 bar was mainly up to the repulsive effect of negative charge on membrane surface. Moreover, the PPS/mHKUST-1@PA membranes also has stable filtration performance under long time operation. The results suggested that the membrane modification method in this work have great potential for applications in desalination. • The perfect separation layer by mHKUST-1 nanoparticles combined well with PA layer. • Improving the permeability and desalination performances of TFN membranes significantly. • Negatively charged of TFN membranes surface for the separation of sulfate and hydrochloride.

Electroactive self-polymerized dopamine with improved desalination performance for flow- and fixed- electrodes capacitive deionization

Capacitive deionization (CDI) is an emerging desalination technology with several advantages, including a high energy efficiency and a simple process. In particular, flow electrode CDI (FCDI) shows greatly enhanced salt removal performance by supplying slurry electrodes into a cell, resulting in continuous desalination operation. Along with carbon-based electrodes, Faradaic materials have been widely introduced for FCDI desalination to realize a higher salt removal capacitance. Organic redox-active materials have received significant attention for replacing conventional inorganic electrodes due to their superior characteristics such as cost-effective and eco-friendly properties, light weight, and high theoretical capacity. In this study, dopamine was self-polymerized onto carbon surfaces to provide polydopamine (PDA) grown activated carbons (AC). Strong adhesion property of PDA prevented their dissolution in electrolytes during electrochemical reactions. In addition, it provided a much improved surface wettability and suspension stability. Results showed that the salt adsorption capacity of PDA@AC CDI electrode was significantly enhanced from 6.03 to 10.43 mg/g (a 73% increase). Salt removal rate of an FCDI was also greatly increased from 1.20 to 2.12 mmol/m2s (a 76% increase) for a PDA@AC slurry electrode. The demonstrated approach is expected to open a new door for realizing desalination of a highly saline solution including seawater.

Two-dimensional fractal nanocrystals templating for substantial performance enhancement of polyamide nanofiltration membrane.

In this study, we report the emergence of two-dimensional (2D) branching fractal structures (BFS) in the nanoconfinement between the active and the support layer of a thin-film-composite polyamide (TFC-PA) nanofiltration membrane. These BFS are crystal dendrites of NaCl formed when salts are either added to the piperazine solution during the interfacial polymerization process or introduced to the nascently formed TFC-PA membrane before drying. The NaCl dosing concentration and the curing temperature have an impact on the size of the BFS but not on the fractal dimension (∼1.76). The BFS can be removed from the TFC-PA membranes by simply dissolving the crystal dendrites in deionized water, and the resulting TFC-PA membranes have substantially higher water fluxes (three- to fourfold) without compromised solute rejection. The flux enhancement is believed to be attributable to the distributed reduction in physical binding between the PA active layer and the support layer, caused by the exertion of crystallization pressure when the BFS formed. This reduced physical binding leads to an increase in the effective area for water transport, which, in turn, results in higher water flux. The BFS-templating method, which includes the interesting characteristics of 2D crystal dendrites, represents a facile, low-cost, and highly practical method of enhancing the performance of the TFC-PA nanofiltration membrane without having to alter the existing infrastructure of membrane fabrication.

Facile approach for designing a novel micropatterned antiwetting membrane by utilizing 3D printed molds for improved desalination performance

Membrane wetting in membrane distillation (MD) is a prominent issue during desalination operation, where the interfacial characteristics between the membrane surface and the feed stream are critical. In this study, an antiwetting membrane surface consisting of hierarchical microstructures was explored as a novel concept to understand the wetting behavior during the MD operation. A novel surface-engineered design of an antiwetting polyvinylidene fluoride (PVDF) membrane with micropatterned arrays obtained utilizing a 3D-printed molding phase separation method was thoroughly explored. In a novel introduction to this field, 3D-printed templates with micron-sized pillars in different shapes are used to generate air pockets when imprinted with a polymeric membrane. Additionally, hexadecyltrimethoxysilane was used as a chemical modifier for enhancing the hydrophobic characteristics. Membrane properties were thoroughly analyzed through Fourier-transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy coupled with energy-dispersive X‐ray spectroscopy, and X-ray photoelectron spectroscopy after successful fabrication of the surface and chemically engineered membrane. The chemically modified patterned membrane exhibited a higher contact angle of ~140° and superior antiwetting behavior when compared to that of the plain PVDF membrane. Moreover, the engineered membrane showed superior MD performance in terms of salt rejection and water flux. Therefore, this paper demonstrates a simplistic approach to design a micropatterned functional membrane exhibiting antiwetting and self-cleaning behavior during MD operation.

TiO2 Nanoparticle Filler-Based Mixed-Matrix PES/CA Nanofiltration Membranes for Enhanced Desalination.

Mixed-matrix nanocomposite (PES/CA/PVP) membranes were fabricated for water desalination by incorporating varying amount of titanium dioxide nanoparticles (TiO2 NPs) ranging from 0 and 2 wt. %. Efficient dispersion of nanoparticles within polymeric membranes was achieved using the chemical precipitation method for uniform surface generation, and an asymmetric morphology was achieved via phase inversion method. Finally, membranes were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Thermo Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), porosity and contact angle analysis. FTIR confirmed chemical composition of membranes in terms of polymers (PES/CA/PVP) and TiO2. TGA analysis confirmed an increase in thermal stability of membranes with the increase of TiO2 nanoparticles loading. The addition of TiO2 nanoparticles also resulted in an increase in porous structures due to an increase in mean pore size, as shown by SEM results. An increase in the hydrophilicity of the membranes was observed by increasing the concentration of TiO2 nanoparticles. The present study investigated pristine and mixed-matrix nanocomposite NF membrane performance while filtering a NaCl salt solution at varying concentration range (from 1 to 4 g/Lit 6 bar). The prepared membranes demonstrated significant improvement in water permeability and hydrophilicity. Further, to optimize the water flux and salt rejection, the concentration of Polyvinylpyrrolidone (PVP) was optimized along with TiO2 nanoparticles. Both the water flux and salt rejection of the fabricated membranes were observed to increase with an increase inTiO2 nanoparticles to 2 wt. % loading with optimized PVP concentration, which demonstrated the improved desalination performance of resultant membranes.

Improved Desalination Performance of Polyvinylidene Fluoride Hollow Fiber Membranes by the Intermediate Role of Surfactants

AbstractPolymer hollow fiber membranes (HFMs) are the core or base membranes of various membrane processes (e.g., ultrafiltration and membrane distillation). Preparing polymer HFMs with higher water flux helps improve the efficiency of the membrane processes. Using pore‐forming additives is the commonly used and efficient method to improve the water flux. The current dilemma is that the conventional methods that increase the amounts or the molecular weight of the additives to improve the water flux usually lead to the decrease in membrane mechanical strength. Herein, different from the conventional research strategy, increasing the surfactant surface activity (SA) is first found to deeply promote the core of nonsolvent‐induced phase separation (NIPS) that of the mutual diffusion between water and dopes. As a result, this method distinctly improves the surface porosity (from 0.8% to 9.7%) and optimizes the pore size distribution of polyvinylidene fluoride (PVDF) HFMs. Benefit from these, the water flux of ultrafiltration (3.1‐fold increase, maximally) and direct contact membrane distillation (2.3‐fold increase, maximally) are increased greatly. Moreover, the mechanical strength is not negatively affected due to the additive amount of small molecule surfactants is constant and small (2.0 wt%).

Effect of aminophend/formaldehyde resin polymeric nanospheres as nanofiller on polyamide thin film nanocomposite membranes for reverse osmosis application

Aminophend/formaldehyde resin polymeric nanospheres (APFNSs) synthesized by the sol-gel method with monomers of 3-aminophenol and formaldehyde were used as nanofillers incorporated into polyamide (PA) layers to fabricate thin-film nanocomposite (TFN) membranes via interfacial polymerization of trimesoyl chloride (TMC) and m-phenylenediamine (MPD). Due to the monomer of 3-aminophenol, the APFNSs are rich in hydroxyl and amino groups. Therefore, the APFNSs nanoparticles have good hydrophilicity and can react with TMC, resulting in chemically bonded to polyamide matrix of TFN membrane. The water flux of TFN-As membrane modified by APFNSs nanoparticles is 71.3 L/m2·h nearly twice of the pristine TFC membrane, and the salt rejection all keeps over 96%. TFN-As membranes also exhibit excellent anti-chlorine, anti-fouling and reuse performances. This work demonstrates that aminophend/formaldehyde resin polymeric nanospheres (APFNSs) can be used as a promising nanofiller for developing novel TFN membranes with improved desalination performance.

Surface modification of reverse osmosis membranes by grafting of polyamidoamine dendrimer containing graphene oxide nanosheets for desalination improvement

The use of grafting method by a dendrimer coupling with a nanomaterial in the modification of commercial polyamide reverse osmosis membranes is reported. This study provides the effect of grafting method with a hydrophilic polyamidoamine (PAMAM) dendrimer and graphene oxide (GO) nanosheet to reduce fouling. The response surface method with central composite design (CCD) was used to optimize the input variables of the grafting process, i.e. dendrimer concentration, grafting time and grafting temperature, and the responses of this method included flux, salt retention and antifouling. First, the grafting conditions were optimized and next, different amounts of GO were dispersed in optimum formulation. The modified membranes were tested using humic acid (HA) solution for fouling test and NaCl and NaNO3 solutions for permeability and rejection tests by a cross-flow setup. The results from ATR-FTIR, SEM, AFM, contact angle and zeta potential analyses established successful grafting and modification. The modified PAMAM/GO and PAMAM membranes exhibited less fouling than the commercial reverse osmosis membranes. Among these, the modified membrane with 1.5 wt% PAMAM concentration at 30 °C of grafting temperature and 6 min grafting time with 1 wt% dispersed GO has the least amount of fouling and has the lowest contact angle, the best chlorine resistance; and improved desalination performance in real wastewater treatment.

MXene as a Cation-Selective Cathode Material for Asymmetric Capacitive Deionization.

Capacitive deionization (CDI) has become a promising method to solve the shortage of freshwater resources recently. However, the co-ion expulsion effect obviously hinders electrosorption capacity and charge efficiency of CDI. In this work, an asymmetric CDI cell is assembled in which Na+-intercalated Ti3C2Tx (NaOH-Ti3C2Tx) serves as a cation-selective cathode, while the activated carbon (AC) serves as the anode. The NaOH-Ti3C2Tx with negatively charged surface groups (-OH, -O, and -F) is adopted to weaken the co-ion expulsion effect. Benefited from the synergistic effect of the reduced co-ion expulsion effect and expanded interlayer space, the asymmetric CDI cell achieves a higher electrosorption capacity of 12.19 mg g-1 and a higher charge efficiency of 0.826 compared with the symmetric one composed of AC (4.55 mg g-1 and 0.306) in 100 mg L-1 NaCl solution. High cyclic stability of the as-prepared asymmetric CDI cell is also observed. The improved desalination performance indicates that NaOH-Ti3C2Tx is a promising alternative as cation-selective cathode material for asymmetric CDI cells. The desalination mechanism is discussed in detail to lay the foundation for further improvement of the CDI performance of other 2D materials like MXene.