The electrically switched ion exchange (ESIX), as the most promising technique for the efficient extraction of lithium from brine, especially the lithium manganese ion-sieve membrane electrode, possesses the advantages of high selectivity, high adsorption capacity, and high stability. And to enable the simultaneous lithium intercalation and de-intercalation at the cathode and anode, respectively, the selective electrode ought to be delithiated before use. Traditional chemical and electrochemical delithiation and electrochemical techniques consume enormous amounts of reagents and energy, respectively. Thermodynamics and electrochemical analysis indicated that the cathodic reaction induced the high cell voltage, which in turn caused the emitting of toxic gases and high energy consumption. Thus, in this study, a targeted-redox system was adopted to alleviate the above problems. By adding excessive Cu2+ into the cathode compartment, the cell voltages in 5 h reduced from 3 V to about 1.5 V and further reduced to 1.2 V if diluted HCl was also added. With lower cell voltage and higher current density, a higher delithiation rate can be reached (95.83 %). Furthermore, Cu2+ can be regenerated by bubbling O2 under an acidic atmosphere, which enables the re-utilization of the cathodic solution. The targeted electro-redox system can reduce 2980.49 J of the energy consumption compared with the current electrochemical delithiation method, meanwhile, the utilization of cheaper counter electrode makes it economically viable.

The feasibility of using vacuum membrane distillation (VMD) for lithium recovery by concentrating the discharged leachate from spent lithium ion batteries (LIBs) recycling process was evaluated. The performance of VMD was compared with that of direct contact membrane distillation (DCMD) in terms of water flux, concentration rate, membrane wetting, and economic feasibility. VMD achieved a higher volume concentration factor (VCF) of 45 compared to the VCF of 25 achieved by DCMD in the LiCl feed solution. In the Li2SO4 feed solution, VMD and DCMD were concentrated to VCF15 and VCF 17, respectively, before wetting occurred. The stability of the MD process was verified using feed solutions containing nickel and manganese, which are cathode materials that can cause scaling even at low concentrations. Low concentrations of nickel and manganese did not significantly affect the maximum VCF or wetting; however, high concentrations of nickel and manganese affected the stability of the MD process. VMD exhibited a higher flux and 32 % lower thermal energy consumption than DCMD. Furthermore, the expected cost of Li2CO3 production with VMD for leachate concentration was $8.31–10.65/kg. The VMD concentration process is a feasible option for recovering lithium from the discharged leachate from spent LIBs recycling process.

Solar-driven interfacial evaporation technology, a potential method of solving freshwater scarcity without any fossil energy consumption and environmental impact, is limited by its core component of photothermal materials. Herein, we fabricated a cellulose/PVA hydrogel with interconnected pores structure via an in-situ method to improve its working capacity in seawater desalination and wastewater purification. The results show that adding hydroxypropyl cellulose and changing light absorbers (CNTs and Chinese ink) can efficiently regulate the evaporation enthalpy to accelerate the evaporation. Integrating the interconnected pores structure with an indirect water supply can achieve confinement capillarity, i.e., upward water transportation along the inner surface of the porous hydrogel instead of being full of all pores, thus obtaining a sharp increase in evaporation interface. Compared to Chinese ink, CNTs particles exhibit an obvious promotion to the mechanical properties and evaporation capacity. Eventually, the evaporation rate of the hydrogel containing CNTs with optimized structure can reach 3.16 kg m−2 h−1 under 1 sun. Besides, the as-prepared hydrogel has impressive performance in working stability and self-cleaning capacity under harsh environmental conditions, such as high-concentration brine, strong acid, and alkaline solution. The regulation strategy will arouse new inspiration from numerous researchers about designing and manufacturing high-performance solar-driven evaporators.

Membrane distillation (MD) is widely applied to desalination and wastewater treatment processes owing to its low operating pressure, superior rejection efficiency, and low membrane fouling. However, in addition to membrane fouling, MD suffers from temperature polarization (TP). In this study, gold nanoparticles (GNPs) were embedded in MD membranes to improve MD performance through the photothermal effect. Two different techniques (electrospinning and electrospraying) were used to fabricate the photothermal layer and systemically compared. Surface layers with different structures were formed. When irradiated with a continuous 808 nm laser (2 W), the TP coefficient ratios of the two different GNP/PVDF membranes obtained using electrospinning (5.7–8.0 %) and electrospraying (8.2–9.9 %) were higher than that of the virgin PVDF membrane (1.1–3.1 %). Furthermore, with laser irradiation, the organic fouling factors of the GNP-PVDF membranes fabricated via electrospinning and electrospraying decreased from 12.1 ± 3.4 to 9.2 ± 1.4 % and from 48.8 ± 0.5 to 18.3 ± 3.4 %, respectively. Therefore, this study provides a guideline for selecting the appropriate technique for fabricating the photothermal layer on electrospun photothermal MD membranes.

Removing heavy metals from landfill leachate wastewater treatment is an environmental challenge because of its complicated characteristics and composition. Although several chemical and physical processes were developed for landfill wastewater treatment, membrane technologies are still common. Nevertheless, membrane fouling, energy requirements and brine management are drawbacks of membrane technologies. This study proposed a biodegradable, gravity-driven kappa-Carrageenan-vanillin hydrogel for biologically treated leachate wastewater treatment to reduce the treatment cost and brine management problem. The composite hydrogel was synthesized using a facile method, with an average pore size of 2.58 ± 0.5 nm and acts as a water filter with super high flux and excellent rejection for heavy metal ions, divalent ions and other contaminants in the landfill leachate wastewater. The hydrogel filter achieved high rejection for divalent ions from salt feed solutions such as sodium chloride, magnesium sulphate, and copper sulphate. An average rejection of 42 ± 5 % was achieved for sodium chloride, 78 % ± 5 % for copper, 72 % ± 5 % for divalent magnesium ion, and 17 % ± 5 % for sulphate rejection. The hydrogel filter achieved a flux of 27 ± 5 LMH for landfill leachate wastewater with high rejection efficiency for total organic carbon, turbidity, and heavy metal separation. The filtration of the landfill leachate with the hydrogel resulted in a high rejection of total organic carbon (77 ± 3 %), 95 ± 3 % turbidity removal, 73 ± 5 % TDS removal, and 95–97 % colour removal. Heavy metal ions were rejected in the following order: Al (80 ± 3 %) > Ba (88 ± 2 %) > Pb (79 ± 3 %) > Cd (72 ± 3 %). The composite hydrogel filter is inexpensive, reliable, and highly efficient in removing contaminants under gravity filtration, requiring no external energy or high hydraulic pressures and ease of scalability for commercial applications.

The solar interfacial evaporation is considered as an innovate and promising technology to overcome the water scarcity crisis. However, an army of problems are being presented in evaporator applicate on open water, which formats and deposits of salt crystallization at its surface during long-term evaporation and permanents damage causing by wave impact. In this study, a self-floating and durable Janus interfacial solar evaporator (ISE) based on self-healing hydrogel with salt-rejecting was demonstrated for the efficiency production of clean water. Benefiting from the decrease of water evaporation enthalpy in hydrogel-based ISE, water evaporation rates over 2.096 kg·m−2·h−1 and solar efficiency of 85.50 % are attained under 1 sun. Additionally, the evaporator of Janus structure effectively avoids the format and deposition of salt at photothermal layer, exhibiting positive salt-rejecting and purification in various wastewater for long-term evaporation. What is more, the performance and appearance of self-healing hydrogel-based ISE can be easily restored. An encouraging and cheering Janus evaporator was proved via integrating self-healing and damage-tolerant hydrogels for solar desalination and water purification, which exhibits exciting durability and lifetime.

Solar stills have been coupled to several preheating systems to increase their productivity, but never before to a borehole exchanger. In this work, a coaxial type borehole exchanger has been integrated with a single basin solar still. Transient and steady-state heat transfer models are presented to assess the behaviour of the combined system for a four-month winter period corresponding to the Urmia Lake region in Iran. Because ground serves as a heat source during winters and a heat sink during summer, integration with a ground exchanger is seen to increase the solar still's productivity for the winter months, by about 126 % for the considered values of parameters. It is also seen that the steady model over calculates the total distillate collected, by about 7 % for ground exchanger integrated still and underestimates it by about 0.2 % for an independent still, respectively. It is observed that larger inner and smaller outer radius of the ground exchanger are desirable. Further, the water mass flow rate is seen to possess an optimal value at which the still's output gets maximized. This work is proposed to be a first step in analysing the usefulness of extracting geothermal energy via a borehole exchanger for desalination application via a solar still.

Intercalation host compounds (IHC) are promising for selective ion removal from water. Recent theoretical developments have suggested that electrochemical desalination with IHC (nickel hexacyanoferrate (NiHCF)) electrodes could separate K+ and Na+ by a factor of 160. However, the experiments only produce a selectivity of around 3. In this work, we derive theory and a finite-element (FEM) model to investigate the origins of time-dependent selectivity suppression. The first results show that ion starvation can severely limit selectivity. Surprisingly, we also find that operations at low state-of-charge produce theoretical selectivity of 600, which is way above what was previously thought to be the theoretical maximum. Also surprising is that the main cause of low selectivity is that the constant-current overpotential disproportionally favors the adsorption of the ion that is less selected in the equilibrium state. By implementing short charging cycles near the depleted state with rest periods at the ends, we raised the time-dependent selectivity from 3 to 450. Even higher output selectivity could be achieved by combining IHC cathodes with membrane-less carbon anodes. In conclusion, the insights and methods derived here could enable highly selective ion removal at the device level for a wide class of IHC materials.

Thickness reduction of polyamide separation layer played an important role in permeability enhancement of thin film composite (TFC) nanofiltration membrane. However, the practical application of TFC nanofiltration membrane with ultrathin polyamide layer is still a great challenge. Herein, we proposed a strategy for preparing nanofiltration membrane with asymmetric polyamide dual-layer through interfacial polymerization. The top polyamide layer is thin, smooth and dense. The bottom polyamide layer is relatively thick, rough and porous. The thin and dense top polyamide layer enabled membrane with relatively high water permeability (18.5 ± 1 L m−2 h−1 bar−1) and Na2SO4 rejection (97.2 ± 0.8 %) performance. The thick and porous bottom polyamide layer guaranteed membrane stability. This study offers a promising strategy for polyamide composite membrane fabrication with enhanced separation performance.

To avoid structural changes within nanofiltration membranes during operation, pre-compaction of filtration membranes is usually performed. However, even after pre-compaction, the NF270 membrane has previously been shown to display a level of pressure susceptibility in pure water systems, particularly evident at low pressures. For the first time, this study provides experimental evidence for the effect of salinity on the pressure susceptibility of the NF270 membrane. Permeability was shown to decrease with increasing salinity up to 189 mM MgSO4, with the largest reduction (22 %) observed at the lowest MgSO4 concentration (31.49 mM MgSO4). A significant reduction (35 %) in the membrane susceptibility was also observed following the introduction of MgSO4 to a concentration of 31.49 mM. A mathematical expression, developed for pure water systems, was modified to account for salinity effects and fitted the experimental data well for concentrations up to 0.2 M. These results are explained by compaction of the membrane polymer, due to either charge neutralisation at the membrane surface, or electric double layer compression, or both. However, further increases in salinity had no significant effect on membrane susceptibility, suggesting that salt induced membrane compaction occurs at very low concentrations.

Two-dimensional hydroxylated boron nitride (OH-BN) nanosheets were prepared using a new approach of ball milling and monoethanolamine (MEA) assisted sonication. OH-BN/graphene oxide (GO) hybrid nanofiltration membranes were developed for the improvement of the membrane-forming ability of OH-BN nanosheets by π-π interaction between GO and OH-BN nanosheets. The membrane-forming ability of OH-BN nanosheets were improved significantly after the introduction of GO nanosheets, and typical layered structure and enhanced separation performances were achieved for OH-BN/GO hybrid membrane with 40 wt% of GO (OH-BN40GO). OH-BN40GO membrane with a thickness of 500 nm possessed a favorable water permeance of 162.3 L/m2·h·bar and a pleasant rejection rate of 97.7 % for Methyl Blue (MB). Moreover, OH-BN40GO hybrid membrane exhibited an excellent anti-swelling ability in aqueous solution, and kept almost unchanged after soaking in water for 3 months. The flux recovery ratio of OH-BN40GO membrane reached to 85.8 % after BSA contamination and NaClO solution rinse, revealing a suitable anti-fouling property of OH-BN40GO membrane.

Brackish water/seawater reverse osmosis (RO) desalination is a key solution to global freshwater scarcity. However, the water recovery (Rw) in conventional RO desalination plants is limited by the operating pressure (∆P). As a novel staged RO technology, low-salt-rejection RO (LSRRO) can potentially enhance the Rw in the desalination plants. In this study, we perform process modeling and techno-economic analysis to evaluate the viability of upgrading current RO desalination plants with LSRRO. Based on the results from process modeling, in typical brackish water RO (BWRO) and seawater RO (SWRO) desalination plants, adding an LSRRO stage can effectively enhance the Rw by 21 and 53 %, respectively, and the energy efficiencies are not compromised with the enhanced Rw. From techno-economic analysis, upgrading RO desalination plant with LSRRO is highly viable. Specifically, after adding an LSRRO stage in a BWRO plant, the Rw can be enhanced from 71 to 81 % without notably increasing the levelized cost of water (LCOW), and adding an LSRRO stage in the SWRO plant with zero brine discharge can reduce the LCOW by 30 %. The findings in our study highlight the vast potential of adopting LSRRO in brackish water/seawater desalination plants, and shed lights on the design of future desalination plants.

Composite membrane consisting of selective layer and support is the mainstream membrane configuration. Support has drawn increasing attention in recent years. In this work, transport through composite membrane with support pore location distributing randomly was studied based on 2D Voronoi tessellations and the corresponding membrane performance calculation method was developed. For the calculation, firstly, irregular Voronoi regions are transformed into regular polygons with fixed number of edges meanwhile maintaining the region area. Then, the membrane performance can be obtained by combining the computation results of regular support surface pore spatial distribution and random support surface pore spatial distribution formulas. Poisson Voronoi diagrams, one of the most representative Voronoi diagrams, were mainly used to describe the support surface pore spatial distribution. The results indicate the importance of the number of support surface pores, which determines the average area of Voronoi regions. Support surface pores should be as many as possible. Another important conclusion is that a certain randomness of support surface pore structure (size and location) may not exert an influence on the composite membrane performance. That is, when calculating the composite membrane performance, the support surface pore spatial distribution and surface pore size distribution can be considered as being regular.

Membrane distillation provides a promising alternative to supply safe and clean water because of its superiorities over conventional membrane and distillation-based methods. However, it is limited by the thermal energy consumption for feed heating although it can be driven under some specific scenarios by low-cost heat energy such as waste heat and geothermal energy. In addition, temperature polarization (TP) is another key factor that could not be avoided and simultaneously decrease the energy efficiency in MD. Given this, photothermal membrane distillation (PMD) in which light such as solar light provides heat source via photothermal conversion attracts much attention in recent year owing to its capability in meeting higher heat energy consumption and TP in conventional MD. Besides, PMD also shows superiority for developing freshwater-production devices in some developing regions such as remote and rural areas in shortage of infrastructure because it is more suitable for off-grid system design. Various materials with photothermal conversion ability have been integrated into MD to develop PMD membranes in recent years. In this review paper, we focused on the design and performance of these membranes with the reported research results. In addition to materials, we also pay some attention on multi-stage PMD configurations which can effectively increase the photothermal energy efficiency by recovering evaporation latent heat. We also give our perspective in advancing PMD membranes structure and performance in future research.

The increasing demand for efficient and sustainable solutions in the field of energy storage and water desalination has sparked research in the development of supercapacitors and capacitive deionization (CDI) cells. This study presents a scalable and eco-friendly process for the preparation of N-doped polyhedral macrotube carbon arrays with a multihole cross-sectional profile. These arrays were synthesized from lotus stems (N-ALS) through carbonization at 500 °C and activation at 700 °C. The resulting material offers a high density of adsorption sites and good conductivity, making it suitable for use as electrodes in both supercapacitors and CDI cells. The N-ALS electrodes exhibit a high specific capacitance of 221.34 F g−1 at a scan rate of 2 mV s−1 and excellent cycling stability, as well as a salt adsorption capacity (SAC) of 26.07 mg g−1 at an applied voltage of 1.4 V and 85 % retention after 50 desalination-regeneration cycles in CDI cells, outperforming traditional activated carbon electrodes.

Desalinated seawater often represents lack of merit nutrients, unstable and low buffer capacity owing to the fact that various aqueous ions are almost removed. The various re-mineralization processes, such as blending with surface water, chemicals dosing, and minerals dissolution, are commonly used for introduction of merit ions and carbonate alkalinity to desalinated seawater to meet health requirement and to protect water supply facilities from corrosion. This paper discusses the optimization of various re-mineralization processes based on accurate model computation with emphasis on carbonate system model, water stability index, blending model, and mineral surface dissolution model. The accurate model computation investigation justifies the efforts and costs through various re-mineralization processes for achieving narrow water quality criteria.

Molybdenum disulfide (MoS2) layer-stacked membranes have gained considerable attention due to their chemical stability and water permeability in desalination processes. However, molecular transport across slit gaps between edge-to-edge MoS2 nanosheets remains unexplored. It is suspected that edge chemistry in MoS2 slits could be important in the MoS2 desalination membranes. Herein, molecular simulations were performed to investigate water permeation and salt rejection for the MoS2 slits with different edge patterns and slit spacings. It is demonstrated that MoS2 nanoslits could realize high water permeation and efficient ion rejection, in particular, the SS edge slit shows excellent desalination efficiency. The water permeation across MoS2 slits could be attributed to the confined water structures and the surface slips on the edge patterns, both of which are influenced by different surface interactions. The free energy landscapes were simulated to characterize the thermodynamics resistance for ions passing through MoS2 nanoslits. The salt rejection is the combining contributions from the ion hydration interaction and the MoS2 slit interaction, wherein the Coulombic interaction provides the critical influence. Overall, our work will hopefully pave the way for design in applications of MoS2 desalination membranes.

Super-hydrophilic separation membrane has been widely used to treat oily wastewater in production and life. However, the membrane is easily contaminated by oily emulsion and metal ions, which affects the separation flux and efficiency. This study presented a novel approach to prepare super-hydrophilic membranes by intercalating hydroxyapatite with graphene oxide and utilizing vacuum filtration. The membranes were thoroughly characterized using various techniques including FT-IR, XRD, SEM, AFM, and contact angle measurements. The study revealed that the hydroxyapatite's layered petal-like structure, combined with the hydrophilicity and graphene oxide, results in a membrane that is super-hydrophilic and underwater super-hydrophobic. HG-4 membrane had an excellent ability to separate oil-water emulsions (the separation flux reached 1798 L/(m2·h)). In addition, it can maintain good shape after 168 h of exposure to acid, alkali and salt. More importantly, HG-4 can effectively remove metal ions (Fe3+ adsorption effect of 98.34 %) and salt solution (CaCl2 desalination rate of 76.21 %). The proposed hydroxyapatite membrane presents a novel approach for separating oil and water, and holds promising potential for application in this field.

Highly selective and permeable nanofiltration (NF) membranes are desirable for energy-efficient desalination and water treatment. However, the preparation of NF membranes with thinner defect-free selective layers and high separation performance remains challenging. Here a new strategy is reported for designing an NF membrane with a crumpled selective layer using polydopamine-piperazine-halloysite nanotubes (PDP-HNTs) as an interlayer and fabricated through vacuum filtration assisted interfacial polymerization (VFIP) method. Specifically, the PDP-HNTs/piperazine (PIP) dispersion was loaded onto the substrate surface through vacuum filtration, achieving construction of the interlayer and loading of the aqueous phase in one step. The PDP-HNTs interlayer served as a regulator to control the selective layer morphologies by retarding the polymerization reaction, forming an NF membrane with loose and crumpled structures. The resulting membranes display a high performance with the water permeance of 45.3 L m−2 h−1 bar−1, while maintaining a Na2SO4 rejection of 97.1 %. Because of the versatility and simplicity of this strategy, our work provides a new approach for fabricating NF membranes with outstanding separation performance.

The phase inversion technique associated to the Loeb-Sourirajan membranes made possible the creation of membranes in all the range of pressure-driven membrane processes.The present work addresses the synthesis and characterization of CA/SiO2 and CA/SiO2/MOF membranes specific for the removal of the uremic toxins - urea and p-cresil sulfate - from the spent dialysate fluid of haemodialysis. The MOF (Metal Organic Framework) synthesized - UiO2–66(Zr) - is added to casting solutions that differ on the acetone/formamide ratio – CA22, CA22/SiO2, CA34 and CA34/SiO2. The membranes with the higher acetone/formamide ratio, CA22 and CA22/SiO2, have lower hydraulic permeabilities,1.29 Kg/h/m2/bar and 4.1 Kg/h/m2/bar, respectively. The incorporation of UiO2–66(Zr) leads to the increase of their hydraulic permeabilities. This pattern is not verified for the CA34/SiO2 membranes.The molecular weight cut-off for the series of CA22 membranes ranges from 2.9 to 28.3 kDa and for the CA34 series ranges from 8.9 to 35.7 kDa.The incorporation of UiO2–66(Zr) leads to lower rejection coefficients to the two uremic toxins - urea and p-cresil sulfate. In average over the transmembrane pressure range of 0.5–4.0 bar the rejection coefficients are below 5 %.