Desalination Applications Research Articles

Partitioning / Self-assembly of Artificial Water Channels - Toward Controlled Permselectivity through Bilayer Membrane.

Artificial water channels (AWCs) have been extensively explored to mimic natural proteins, which enables to effectively transport water while blocking ions. As one of the first AWCs, self-assembled I-quartets (HCx) have showcased high water-permselectivity that can be enhanced by improving their distribution and stability within membrane. The use of long alkyl chains (n>8) is constrained by their low solubility and aggregation. Herein, we considered cycloalkyl moieties, explored for the increase of the solubility favoring enhanced partition and/ for their self-assembly behaviors resulting the formation of effective stable water-channels with increased water permeability in bilayer membranes. This class of cycloalkyl-ureido-ethyl-imidazole amphiphilic (CxUH) channel could serve as a new reference for the effective design of self-assembled artificial water channels, it may give rise to the applications in desalination or in water treatment.

Partitioning / Self‐assembly of Artificial Water Channels – Toward Controlled Permselectivity through Bilayer Membrane

AbstractArtificial water channels (AWCs) have been extensively explored to mimic natural proteins, which enables to effectively transport water while blocking ions. As one of the first AWCs, self‐assembled I‐quartets (HCx) have showcased high water‐permselectivity that can be enhanced by improving their distribution and stability within membrane. The use of long alkyl chains (n>8) is constrained by their low solubility and aggregation. Herein, we considered cycloalkyl moieties, explored for the increase of the solubility favoring enhanced partition and/ for their self‐assembly behaviors resulting the formation of effective stable water‐channels with increased water permeability in bilayer membranes. This class of cycloalkyl‐ureido‐ethyl‐imidazole amphiphilic (CxUH) channel could serve as a new reference for the effective design of self‐assembled artificial water channels, it may give rise to the applications in desalination or in water treatment.

Life After Death: Re‐Purposing End‐of‐Life Supercapacitors for Electrochemical Water Desalination

AbstractThis study explores the potential of re‐purposing end‐of‐life commercial supercapacitors as electrochemical desalination cells, aligning with circular economy principles. A commercial 500‐Farad supercapacitor was disassembled, and its carbon electrodes underwent various degrees of modification. The most straightforward modification involved NaOH‐etching of the aluminum current collector to produce free‐standing carbon films. More advanced modifications included CO2 activation and binder‐added wet processing of the electrodes. When evaluated as electrodes for electrochemical desalination via capacitive deionization of low‐salinity (20 mM) NaCl solutions, the minimally modified NaOH‐etched carbon electrodes achieved an average desalination capacity of 5.8 mg g−1 and a charge efficiency of 80 %. In contrast, the CO2‐activated, wet‐processed electrodes demonstrated an improved desalination capacity of 7.9 mg g−1 and a charge efficiency above 90 % with stable performance over 20 cycles. These findings highlight the feasibility and effectiveness of recycling supercapacitors for sustainable water desalination applications, offering a promising avenue for resource recovery and re‐purposing in pursuing environmental sustainability.

Blend membranes of sulphonated poly(arylene ether sulphone) and sulphonated polybenzimidazole and their characterization for desalination applications

Blend membranes of sulphonated poly(arylene ether sulphone) and sulphonated polybenzimidazole and their characterization for desalination applications

In Situ Growth of Well-Aligned MOF Nanoneedle Arrays into Composite Photothermal Membranes for Solar Desalination.

The solar-driven interfacial evaporation (SDIE) technology serves as a clean and facile approach combining seawater desalination to address water shortage and energy crisis. Recently, porous organic framework materials have aroused great attention, and the development of MOF-based composites with significant performance in photothermal conversion and water activation has become one of the important focuses in this field. In this work, an MOF-based composite photothermal membrane (PON@MOF) was prepared via the in situ growth of metal-organic framework (MOF) nanoneedle arrays induced by a pyridine-based organic polymer nanowire network (PON). The PON@MOF membrane possessed an MOF array layer, a PON-induced layer, and a porous support layer. The PON is rich in coordinated nitrogen atoms for anchoring the metal-ion source, and the main role of the PON layer is to provide favorable nucleation sites and orient in situ growth of well-aligned MOF nanoneedle arrays. With the highly conjugated framework of PON@MOF and the light trapping of the nanoarrays strengthening the photothermal conversion as well as the hydrophilic chemical structure facilitating the decrease of the water evaporation enthalpy, the PON@MOF membrane realizes highly efficient thermal vapor conversion. Under solar irradiation (1.0 kW m-2), PON@MOF demonstrated an evaporation rate of 2.14 kg m-2 h-1 and a solar-to-vapor conversion efficiency of 98.5%. Meanwhile, the PON@MOF membrane has excellent salt resistance and stability, highlighting its potential application in desalination. Overall, this work provides a special idea for the structural design of photothermal composites for solar desalination and freshwater production.

The enhanced performance of NaFe2PO4(SO4)2/C electrode materials in the desalination of brackish water by capacitive deionization

In this study partial substitution of phosphates in Na3Fe2(PO4)3/C (NFP/C) by sulphates to prepare Na2Fe2(PO4)2SO4 (NFP2S/C) and NaFe2PO4(SO4)2/C (NFPS/C) was carried out by dissolution-evaporation method. The idea is to adjust the properties of NFP/C owing to the differences in the inductive effect and sizes of sulphates and phosphates which results the obtained NFPS/C to record excellent electrochemical and desalination performance. Several characterization techniques used to analyse the synthesized materials confirm the successful doping and structure integrity. Electrochemical study reveals NFPS/C to exhibit the highest capacitance of 127.4 F/g when scanned at 10 mV/s. The results show that when the potential of 1.2 V is applied to desalinate 500 mg/L salt solution the salt removal of about 17.3 mg/g is achieved by NFPS/C while NFP/C attaining 9.8 mg/g. The NFPS/C was then tested in the desalination of real Ocean water and promising results obtained. The salt removal performance presented makes the developed materials promising for application in brackish water desalination by capacitive deionization.

Facile fabrication of superhydrophobic carbon-doped nanofibrous mat for solar-driven desalination

Recently, solar-driven localized heating interfacial evaporation for desalination has attracted much attention to draw freshwater from sewage or seawater. However, salt scaling resulted from concentration polarization, as well as the subsequently deterioration of evaporation rate and energy efficiency, are the major obstacles for the application of solar desalination. In this work, carbon-doped nanofibrous mat with photothermal and superhydrophobic properties were facilely fabricated via incorporation of activated carbon (AC) nanoparticles and hydrophobic modification with polydimethylsiloxane (PDMS). The obtained nanofibrous mat exhibited outstanding light absorption (> 93.0%), superhydrophobic characteristics (> 155°) and high porosity (> 82%). Solar-driven evaporation experiments demonstrated that evaporation rate of the nanofibrous mat reached up to 1.2kg·m-2·h-1 with energy efficiency of 82.1%. Moreover, crystal nucleation and growth on the superhydrophobic carbon-doped mat were dramatically suppressed, whose lifespan was prolonged from 4h to as long as 19h with near-saturated NaCl solution as the feedwater. Therefore, the fabricated superhydrophobic carbon-doped nanofibrous mat might find its applications in stable solar-driven evaporation for seawater desalination or wastewater reclamation.

Hofmeister effect induced water activation of hydrogel and its applications for the accelerated solar evaporation in brine

Solar-driven desalination has emerged as a promising approach to address water scarcity caused by the decreasing supply of freshwater. Reducing the enthalpy of water vaporization is crucial for enhancing the efficiency of solar-powered desalination. In this study, inspired by the Hofmeister effect, we developed a highly hydratable network hydrogel evaporator to achieve a superior evaporation rate in brine compared with pure water. The evaporator comprised a carbonized layer as the photothermal layer and a chitosan aerogel hydrogel as the hydratable matrix. The hydrogel exhibited a dramatically reduced vaporization enthalpy of 1397 J/g and a significant evaporation rate of 2.38 kg m−2 h−1 when exposed to seawater. These results demonstrated the superior performance of hydrogel compared with pure water (1.91 kg m−2 h−1). Excellent evaporation rates and outstanding salt resistance ensured efficient coordination for practical long-term desalination applications. Further investigations revealed that the remarkable evaporation performance of the carbonized chitosan (CCS) hydrogel in brine environments was attributed to its hydrability, which was regulated by Cl−. According to the Hofmeister effect, Cl− accelerated the hydration chemistry in CCS and suppressed the associated crystallinity, which resulted in a lower enthalpy of vaporisation owing to a higher amount of intermediate water. With its superior evaporation performance in brine and comprehensive theoretical simulation analysis, this study presents an achievable and economical strategy for simultaneously addressing the water and energy crises.

Prussian Blue-Carbonized wood photothermal composites for efficient solar evaporation and seawater desalination

Freshwater scarcity, exacerbated by environmental pollution, poses a significant global challenge. This study addresses these challenges by developing a Prussian blue/carbonized wood (PB/CW) photothermal composite for solar desalination. The PB/CW composite exhibits enhanced solar absorption and photothermal conversion. The integration of Prussian blue (PB) on the honeycomb structure of wood facilitates efficient water transport and minimizes heat loss, underscoring the composite’s potential in practical solar desalination applications. Under natural sunlight, the PB/CW system achieves an evaporation rate of 4.39 kg m-2h−1, demonstrating its high efficiency in converting solar energy into water evaporation. This work offers a novel and effective approach to designing low-cost, high-efficiency solar evaporators, advancing the field of sustainable desalination technology.

Hierarchical Ti3C2Tx MXene@Honeycomb nanocomposite with high energy efficiency for solar water desalination

The utilization of solar-driven interfacial evaporation holds immense promise in enhancing energy efficiency and establishing sustainable methods for seawater desalination and water purification. While designing the materials to achieve high evaporation efficiency, the tuning of materials with porosity and surface chemistry is very crucial. Novel sustainable materials are of great importance for solar water desalination applications since clean water production is utmost important in the current era. There exists a lack of exploration in modifying the surface wettability states of solar evaporators to expedite the vapor generation rates. In this study, we showcase a hydrophilic Ti3C2Tx MXene-coated carbonized honeycomb (CHC) (Ti3C2Tx MXene@CHC) nanocomposite-based hexagonal-shaped evaporator surface. This is the first-time report on the effective utilization of hierarchical CHC for the preparation of solar absorber comprising of Ti3C2Tx MXene@CHC nanocomposite, particularly for the solar water desalination. The Ti3C2Tx MXene@CHC nanocomposite evaporator achieves an impressive water evaporation rate of 1.6 kg m−2 h−1 with 90% efficiency under 1 sun illumination. The augmented thickness of the water layer in the hydrophilic surface of the Ti3C2Tx MXene@CHC nanocomposite helps in facilitating the rapid escape of water molecules. The relatively elongated contact lines in the hydrophobic region simultaneously ensure substantial water evaporation, significantly enhancing the water desalination process. The Ti3C2Tx MXene@CHC nanocomposite exceeds stringent quality benchmarks, signaling its potential for solar water desalination.

Unlocking desalination’s potential: Harnessing MXene composite for sustainable desalination

Amidst freshwater scarcity, desalination is an effective solution, elevating pure water to a paramount commodity. Researchers actively pursue cost-effective alternatives to traditional desalination methods, with solar steam-based technologies now-a-days. Herein we report the synthesis of hierarchical photothermal absorber consisting of Ti3C2Tx decorated polypropylene fiber (PPF) composite and further used for solar desalination applications. Ensuring system stability amidst temperature fluctuations, pH variations, and mechanical stresses is pivotal for optimal desalination and wastewater treatment performance. Seamless integration of components is imperative to achieve this. Structurally, the Ti3C2Tx MXene@PPF composite evaporator showcases impressive metrics, such as high evaporation rate of 4.63 kg m-2h−1 along with a remarkable solar-evaporation efficiency of 93.48 % when tested under 1 sun illumination. Moreover, the composite absorber exhibits good mechanical stability, exceptional chemical stability even under harsh conditions (such as acid and alkali environments), outstanding salt tolerance and maintained a consistent evaporation rate over extended durations. Also, the absorber achieves good mechanical properties. These findings underscore the Ti3C2Tx MXene@PPF composite evaporator’s potential as a groundbreaking material for solar steam generation, offering high efficiency and cost-effectiveness. Beyond saline water desalination, its salt-preserving attributes and filtration capabilities position it as a promising alternative for wastewater treatment. This study presents an innovative and scalable solar water purification system applicable to a diverse range of water contaminants and manufacture in a cost-effective way.

Salt-resistant MXene-charge gradient hydrogel evaporator with boosted water transport for efficient photothermal desalination

Solar interfacial evaporation represents a highly promising approach for generating potable water from seawater utilizing clean, abundant, and sustainable solar energy. MXene-based materials exhibit outstanding photothermal conversion in desalination applications but face challenges in water transport and salt removal. Here, we introduce an effective MXene-charge gradient hydrogel (MCGH) evaporator that leverages the Donnan effect for salt rejection and internal osmotic pressure for water conveyance. The MCGH evaporator achieved 3.1 kg m−2 h−1 evaporation rate in 3.5 wt% NaCl under 1 sun irradiation. It also operates effectively in concentrated brines, reaching a notable 2.1 kg m−2 h−1 evaporation rate in 20 wt% NaCl solutions. This work introduces a new approach for salt-tolerant MXene photothermal evaporators, holding great promise for sustainable solar desalination applications.

Hydroxy salt induced CoAl-LDH nanosheet composite membrane for pervaporation desalination

Pervaporation is a promising desalination technology. Developing high-performance and stable pervaporation membranes with high continuity structure remains a significant challenge. This study reports the development of a novel layered double hydroxide (LDH) nanosheet composite membrane fabricated using a hydroxyl salt induction method. This approach facilitated the in-situ nucleation and growth of the CoAl-LDH nanosheets on polyvinylidene fluoride (PVDF) substrate, reducing precursor concentration and enhancing preparation efficiency. The resulting cross-compatible architecture closely integrated the dense LDH nanosheet separation layer with the flexible PVDF support. The microstructure and morphology of the hydroxyl salt layer and its transformed CoAl-LDH composite membrane were comprehensively investigated. The optimized membrane was applied for pervaporation desalination (3 wt% NaCl, 50 °C), achieving a high flux of 38.4 kg·m−2·h−1 and exceptional NaCl rejection of 99.9 %. It also demonstrated excellent tolerance to a wide salinity range, maintaining 99.6–99.9 % rejection even at 20 wt% NaCl, while the flux remained stable at 26.7 kg·m−2·h−1. Long-term testing confirmed the consistent separation performance and operational stability, underscoring the great potential of this advanced membrane material for practical pervaporation desalination applications.

Hydrodynamic solar-driven interfacial evaporation - Gone with the flow

Evaporation has been one of the most classic desalination processes on the Earth. When we try to use the power of water flow itself, the evaporation process can perform even better. Here, we report a hydrodynamic solar-driven interfacial evaporation process which water evaporation rate can achieve 6.58 kg·m-2·h-1 (over 100 times higher than natural evaporation). A waterwheel-structure solar interfacial evaporator was designed and assembled by printed filter papers. The evaporator can both rapidly distribute solution on the evaporation interface and be hydraulically driven to rotate continuously to improve the evaporation rate by water flow. The hydrodynamic solar-driven interfacial evaporation process successfully overcomes the problem of slow diffusion of water vapor, but also realizes the day-and-night operation of process and the self-cleaning of salt fouling. Apart from the application in solar desalination, the developed evaporator has great potentials in vapor production and salt recovery for industrial use.

Brine separation with polyamide and polyimine thin film composite nanofiltration membranes obtained from biobased monomers

Thin film composite (TFC) membranes are state-of-the-art membranes that are widely applied in water treatment and seawater desalination. However, these membranes are typically prepared using petrochemical-based monomers and toxic solvents. Herein, plant-based monomers, namely priamine (PA), 2,5-furandicarboxaldehyde (FDA) are used to fabricate green PA–FDA TFC membranes via interfacial polymerization. Additionally, PA was also combined with trimesoyl chloride (TMC) to obtain PA–TMC TFC membranes. The reaction conditions were varied to investigate their effects on membrane morphology and performance. The resultant membranes exhibited smooth surfaces with an average roughness ranging from 15 to 30 nm, and increasing the monomer concentration increased the film thickness. The PA–TMC free-standing films had higher thicknesses (130–300 nm) than the PA–FDA films (36–122 nm). Furthermore, PA–TMC and PA–FDA films were hydrophobic due to the long aliphatic chains of PA. Moreover, PA–TMC membranes demonstrated a water permeance of ∼4 L m−2 h−1 bar−1 with 74% NaCl rejection, while PA–FDA membranes achieved better NaCl rejection (∼80%) but lower water permeance (0.3–4 L m−2 h−1 bar−1). Applied in brine separation, the membranes demonstrated ∼90% divalent ion rejection and only 70% monovalent ion rejection. The proposed plant-based monomer combination provides a steppingstone toward green TFC membrane manufacturing for water treatment and desalination applications.

One-step fabrication of hetero-structured polyethersulfone hollow fiber membranes through surface segregation for pervaporation desalination

Hollow fiber membranes (HFMs) are an ideal configuration for industrial applications of pervaporation desalination (PV) membranes. Currently, the efficient fabrication of PV HFMs is restricted by multi-step post-treatment processes on their outer surfaces to form the selective layer. Herein, we utilized the surface segregation strategy to fabricate a hetero-structured HFM in one step, simultaneously forming the hydrophilic dense outer layer and the porous support layer. During hollow fiber spinning process, the amphiphilic copolymer polyvinylpyrrolidone-polyvinyl acetate (PVP-PVAc) in polyether sulfone (PES) dope solution migrated towards water contacting interface in the coagulation bath and formed the hydrophilic layer by extending hydrophilic segment outwards. This fast in-situ hydrophilization well matched the spinning efficiency. The optimal PVP-PVAc content and phase inversion temperature were investigated and the spinning parameters on the structure and performance of HFMs were studied. The HFMs prepared realized a flux of 26.70 kg m−2 h−1 and the salt rejection of 99.98 %, along with adaptability to solutions with different salinities and excellent anti-organic fouling property. This study may provide a facile method to fabricate HFMs with desirable PV desalination performance and scaling-up potential.

Optimising the effectiveness of osmotic desalination process by using graphene-based nanomaterials

This work examines how graphene-based nanoparticles can be integrated into membranes to improve the effectiveness of water treatment in osmotic desalination processes. This is important since sustainable practices can help address the world's water scarcity. Water treatment, desalination, and resource recovery are areas where osmotic desalination shows great potential. However, membrane performance constraints frequently impede its efficacy. High mechanical strength, superior hydrophilicity, and the ability to lessen internal concentration polarisation are just a few of the remarkable qualities that make graphene-based nanoparticles stand out. In order to increase the membranes' overall functionality, these nanoparticles were created and added to them. Comparing the study to conventional membranes, the main goals were to increase water flux rates and salt ion rejection capacities. It was shown by experimental results that the membranes strengthened with graphene-based nanoparticles performed better. They outperformed conventional membranes in terms of water flow growth and salt ion rejection rates improvement. In order to advance osmotic desalination technologies towards more effective and sustainable water treatment options, this study highlights the revolutionary potential of graphene-based nanoparticles. Graphene-based nanoparticles provide an attractive option for tackling major water issues worldwide by improving membrane characteristics that are essential for osmotic desalination, such as permeability and selectivity. Water management techniques that are environmentally sustainable are supported by their integration into membranes, which also enhances performance metrics. This study opens the door for creative approaches to resource recovery and water treatment by providing important insights into the creation of cutting-edge materials specifically designed for osmotic desalination applications.

Synergistic ionic liquid encapsulated MIL-101 (Cr) metal-organic frameworks for an innovative adsorption desalination system

The transformations of brackish water into freshwater employing porous materials such as metal-organic frameworks (MOFs) show a great potential for a green environment. But the adsorption-based desalination slows down due to slow water adsorption/desorption rates and inadequate water storage capacity in conventional adsorbents. Therefore, the restructuring of porous MOFs increases water storage and transfer rates. This paper presents a comprehensive investigation on the fabrication of ionic liquid encapsulated MIL-101 (Cr) MOFs (metal-organic frameworks), and its interactions with water for desalination applications. Firstly, the pristine MIL-101 (Cr) is encapsulated with various types/amounts of ionic liquids. Next, these MOFs are characterized via SEM (Scanning electron microscope), FTIR (Fourier transform infrared), XRD (X-ray diffraction), TGA (Thermal gravimetric analysis), N2 adsorption techniques. The water adsorption on these MOFs is performed experimentally for a wide temperature (30–80 °C) and pressure (0 < P/Ps < 0.95) ranges. The effects of the size (or type) as well as the encapsulation ratio of ionic liquids on water adsorption behaviors are conducted. Based on the experimentally proven water adsorption (isotherms and kinetics) data, an AD (adsorption desalination) system is modelled and simulated. Finally, the AD performances in terms of the specific daily water production (SDWP) and performance ratio (PR) are parametrically studied with respect to various regeneration temperature (50–80 °C) and cycle times (100 s–1000 s). It is found that by ionic liquid encapsulation, the water uptakes/offtake rates are expedited up to 48% (for adsorption)/55% (for desorption), respectively. In addition, the water transfer (Δq) improves up to 45% more than the parent MIL-101(Cr) MOFs. Furthermore, the SDWP increases from 38 to 56 m3 of water per tonne of MOFs per day at the regeneration temperature of 70 °C. The simulation results also show that the ionic-liquid-encapsulated MIL-101 (Cr) MOFs generates water (>25 m3 water per tonne of IL-MOFs) at the regeneration temperature of 50 °C and is potential for the next generation desalination applications.

Solar/microwave-driven composite membrane evaporation and its application in seawater desalination

Increased economic growth and population expansion has heightened the demand for water resources, leading to escalating levels of water scarcity. Sustainable seawater desalination methods, powered by renewable energy, offer promising solutions to the long-standing global water shortage. This study presents a method for seawater desalination that employs eco-friendly materials. The approach involves utilizing metakaolin-based porous geopolymer (GP) as the base material, and depositing graphene oxide (GO) to create a graphene oxide geopolymer (GOGP) composite membrane. The membrane undergoes in-situ self-reduction to obtain reduced graphene oxide geopolymer (rGOGP). The study examines the composition, microstructure, and water evaporation performance of the composite membrane under both solar/microwave-driven. The results show that, under microwave conditions with a frequency of 2450 MHz and power of 400 W, the evaporation rate can reach up to 4.13 kg·m−2·h−1, doubling the evaporation rate achieved through solar-driven evaporation at an equivalent efficiency level. Furthermore, the evaporation rate of the composite membrane remains consistent when exposed to high-concentration saltwater of 15 wt%. Notably, the removal rates of Na+, K+, Ca2+, and Mg2+ all exceed 99 %, meeting the drinking water requirements established by the World Health Organization. This study provides a novel approach to seawater desalination utilizing environmentally friendly materials and clean energy sources.

High-capacity and high-stability capacitive desalination with dual redox-active MnCo2S4/g-C3N4 heterojunction electrode

Capacitive deionization (CDI) utilizing dual redox-active electrodes has shown significant promise in desalinating low-concentration brackish waters, which is crucial for addressing global freshwater shortages. However, improvements in salt adsorption capacity and long-term operational stability are still required. In this study, we introduce, for the first time, a binary metal sulfide MnCo2S4/g-C3N4 (MCS-CN) heterojunction as a CDI electrode. The innovative integration of dual redox-active centers and heterojunction structures in the MCS-CN composite electrodes underscores their potential for achieving both high capacity and stability in capacitive desalination applications. The microscopic morphology, crystal structure, pore structure, and surface valence properties of the MCS-CN heterojunction composite materials were extensively characterized using various analytical techniques. In-situ X-ray diffraction, refined ex-situ X-ray photoelectron spectroscopy, three-electrode electrochemical analysis, and theoretical calculations were employed to elucidate the electrosorption and desorption mechanisms of sodium ions with the MCS-CN electrodes and to clarify the enhanced desalination performance of the binary metal sulfide-based heterojunction structure. As a result, the optimal MCS-CN-40 electrode exhibited the highest salt removal capacity of 71.64 mg g−1 and maintained stable desalination performance over 100 cycles in a 500 mg L−1 NaCl solution. This innovative approach provides a noval perspective for developing heterojunction electrodes with high redox activity and efficient desalination performance.