Ion-Selective Transport Promotion Enabled by Angstrom-Scale Nanochannels in Dendrimer-Assembled Polyamide Nanofilm for Efficient Electrodialysis.

The ion permeability and selectivity of membranes are crucial in nanofluidic behavior, impacting industries ranging from traditional to advanced manufacturing. Herein, we demonstrate the engineering of ion-conductive membranes featuring angstrom-scale ion-transport channels by introducing ionic polyamidoamine (PAMAM) dendrimers for ion separation. The exterior quaternary ammonium-rich structure contributes to significant electrostatic charge exclusion due to enhanced local charge density; the interior protoplasmic channels of PAMAM dendrimer are assembled to provide additional degrees of free volume. This facilitates the monovalent ion transfer while maintaining continuity and efficient ion screening. The dendrimer-assembled hybrid membrane achieves high monovalent ion permeance of 2.81 mol m-2 h-1 (K+), reaching excellent mono/multivalent selectivity up to 20.1 (K+/Mg2+) and surpassing the permselectivities of state-of-the-art membranes. Both experimental results and simulating calculations suggest that the impressive ion selectivity arises from the significant disparity in transport energy barrier between mono/multivalent ions, induced by the "exterior-interior" synergistic effects of bifunctional membrane channels.

Ion Resource Recovery via Electrodialysis Fabricated with Poly(Arylene Ether Sulfone)-Based Anion Exchange Membrane in Organic Solvent System.

Ion resource recovery from organic wastewater is beneficial for achieving emission peaks and carbon neutrality targets. Advanced organic solvent-resistant anion exchange membranes (AEMs) for treating organic wastewater via electrodialysis (ED) are of significant interest. Herein, a kind of 3D network AEM based on poly(arylene ether sulfone) cross-linked with a flexible cross-linker (DBH) for ion resource recovery via ED in organic solvent system is reported. Investigations demonstrate that the as-prepared AEMs show excellent dimensional stability in 60% DMSO (aq.), 60% ethanol (aq.), and 60% acetone (aq.), respectively. For example, the optimized AEM shows very low swelling ratios of 1.04-1.10% in the organic solvents. ED desalination ratio can reach 99.1% after exposure of the AEM to organic solvents for 30 days, and remain > 99% in a mixture solution containing organic solvents and 0.5 m NaCl. Additionally, at a current density of 2.5 mA cm-2, the optimized AEM soaked in organic solvents for 30 days shows a high perm-selectivity (Cl-/SO4 2-) of 133.09 (vs 13.11, Neosepta ACS). The superior ED performance is attributed to the stable continuous sub-nanochannels within AEM confirmed by SAXS, rotational energy barriers, etc. This work shows the potential application of cross-linked AEMs for resource recovery in organic wastewater.

An Opportunity for Synergizing Desalination by Membrane Distillation Assisted Reverse-Electrodialysis for Water/Energy Recovery.

Industry, agriculture, and a growing population all have a major impact on the scarcity of clean-water. Desalinating or purifying contaminated water for human use is crucial. The combination of thermal membrane systems can outperform conventional desalination with the help of synergistic management of the water-energy nexus. High energy requirement for desalination is a key challenge for desalination cost and its commercial feasibility. The solution to these problems requires the intermarriage of multidisciplinary approaches such as electrochemistry, chemical, environmental, polymer, and materials science and engineering. The most feasible method for producing high-quality freshwater with a reduced carbon footprint is demanding incorporation of industrial low-grade heat with membrane distillation (MD). More precisely, by using a reverse electrodialysis (RED) setup that is integrated with MD, salinity gradient energy (SGE) may be extracted from highly salinized MD retentate. Integrating MD-RED can significantly increase energy productivity without raising costs. This review provides a comprehensive summary of the prospects, unresolved issues, and developments in this cutting-edge field. In addition, we summarize the distinct physicochemical characteristics of the membranes employed in MD and RED, together with the approaches for integrating them to facilitate effective water recovery and energy conversion from salt gradients and freshwater.

Membrane Design Principles for Ion-Selective Electrodialysis: An Analysis for Li/Mg Separation.

Selective electrodialysis (ED) is a promising membrane-based process to separate Li+ from Mg2+, which is the most critical step for Li extraction from brine lakes. This study theoretically compares the ED-based Li/Mg separation performance of different monovalent selective cation exchange membranes (CEMs) and nanofiltration (NF) membranes at the coupon scale using a unified mass transport model, i.e., a solution-friction model. We demonstrated that monovalent selective CEMs with a dense surface thin film like a polyamide film are more effective in enhancing the Li/Mg separation performance than those with a loose but highly charged thin film. Polyamide film-coated CEMs when used in ED have a performance similar to that of polyamide-based NF membranes when used in NF. NF membranes, when expected to replace monovalent selective CEMs in ED for Li/Mg separation, will require a thin support layer with low tortuosity and high porosity to reduce the internal concentration polarization. The coupon-scale performance analysis and comparison provide new insights into the design of composite membranes used for ED-based selective ion-ion separation.

Enhanced Mono/Divalent Ion Separation via Charged Interlayer Channels in Montmorillonite-Based Membranes.

Efficient mono- and divalent ion separation is pivotal for environmental conservation and energy utilization. Two-dimensional (2D) materials featuring interlayer nanochannels exhibit unique water and ion transport properties, rendering them highly suitable for water treatment membranes. In this work, we incorporated polydopamine/polyethylenimine (PDA/PEI) copolymers into 2D montmorillonite (MMT) nanosheet interlayer channels through electrostatic interactions and bioinspired bonding. A modified laminar structure was formed on the substrate surface via a straightforward vacuum filtration. The electrodialysis experiments reveal that these membranes could achieve monovalent permselectivity of 11.06 and Na+ flux of 2.09 × 10-8 mol cm-2 s-1. The enhanced permselectivity results from the synergistic effect of electrostatic and steric hindrance effect. In addition, the interaction between the PDA/PEI copolymer and the MMT nanosheet ensures the long-term operational stability of the membranes. Theoretical simulations reveal that Na+ has a lower migration energy barrier and higher migration rate for the modified MMT-based membrane compared to Mg2+. This work presents a novel approach for the development of monovalent permselective membranes.

A New Method for Growth Factor Enrichment from Dairy Products by Electrodialysis with Filtration Membranes: The Major Impact of Raw Product Pretreatment.

This study is focused on fractionation of insulin-like growth factor I (IGF-I) and transforming growth factor-ß2 (TGF-ß2) using a new electro-based membrane process calledelectrodialysis with filtration membranes (EDFM). Before EDFM, different pretreatments were tested, and four pH conditions (4.25, 3.85, 3.45, and 3.05) were used during EDFM. It was demonstrated that a 1:1 dilution of defatted colostrum with deionized water to decrease mineral content followed by the preconcentration of GFs by UF is necessary and allow for these compounds to migrate to the recovery compartment during EDFM. MS analyses confirmed the migration, in low quantity, of only α-lactalbumin (α-la) and ß-lactoglobulin (ß-lg) from serocolostrum to the recovery compartment during EDFM. Consequently, the ratio of GFs to total protein in recovery compartment compared to that of feed serocolostrum solution was 60× higher at pH value 3.05, the optimal pH favoring the migration of IGF-I and TGF-ß2. Finally, these optimal conditions were tested on acid whey to also demonstrate the feasibility of the proposed process on one of the main by-products of the cheese industry; the ratio of GFs to total protein was 2.7× higher in recovery compartment than in feed acid whey solution, and only α-la migrated. The technology of GF enrichment for different dairy solutions by combining ultrafiltration and electrodialysis technologies was proposed for the first time.

Comparison of bipolar membrane electrodialysis, electrodialysis metathesis, and bipolar membrane electrodialysis multifunction for the conversion of waste Na2SO4: Process performance and economic analysis.

To convert Na2SO4 into other high-value products (NaOH, H2SO4, and (NH4)2SO4), three types of cell configurations of electrodialysis (ED) were applied (three-compartment bipolar membrane ED (BMED), four-compartment ED metathesis (EDM) and five-compartment bipolar membrane ED multifunction (BMEDM)) and parameters such as average voltage variation, removal ratio of salt, product concentration, conversion rate, ion flux, and energy consumption were calculated and compared. The experimental results and calculations indicated that the overall performance of BMEDM was inferior to that of BMED and EDM. An industrial model was established, which indicated that the net profit from converting Na2SO4 using BMEDM was always higher than that from BMED and EDM. Based on the advantages of low investment (132 $) and energy cost (152 $/t Na2SO4), EDM was applicable to factories with a low output of Na2SO4 (production capacity <45%), whereas BMED (157.3 $/t Na2SO4) and BMED-5 (227.6 $/t Na2SO4) were applicable to factories with a high output of Na2SO4 (production capacity >45%) based on high net profits.

Boosting nutrient recovery from AnMBR effluent by means of electrodialysis technology: Operating parameters assessing.

This work describes a comprehensive assessment of operating parameters of a bench-scale electrodialysis (ED) plant for nutrient concentration from an Anaerobic Membrane BioReactor (AnMBR) effluent. The ED bench-scale plant serves a dual purpose. Firstly, to generate a concentrated stream with a high nutrient content, and secondly, to produce high-quality reclaimed water in the diluted stream, both sourced from real wastewater coming from the effluent of an AnMBR. Two sets of experiments were conducted: 1) short-term experiments to study the effect of some parameters such as the applied current and the type of anionic exchange membrane (AEM), among others, and 2) a long-term experiment to verify the feasibility of the process using the selected parameters. The results showed that ED produced concentrated ammonium and phosphate streams using a 10-cell pair stack with 64 cm2 of unitary effective membrane area, working in galvanostatic mode at 0.24 A, and operating with an Acid-100-OT anionic exchange membrane. Concentrations up to 740 mg/L and 50 mg/L for NH4-N and PO4-P, respectively, were achieved in the concentrated stream along with removal efficiencies of 70% for ammonium and 60% for phosphate in the diluted stream. The average energy consumption was around 0.47 kWh·m-3.

Selective separation of nutrients and volatile fatty acids from food wastes using electrodialysis and membrane contactor for resource valorization.

Transport and selectivity parameters describe the quantity and purity of nutrients and volatile fatty acids (VFAs) separated from fermentation media. However, the complexity of fermentation media and low nutrient concentrations hinder the optimal conditions of such parameters. Exploring technologies to overcome such limitations is crucial for selectively separating VFAs from nutrients in fermented media. The objectives of this study were to investigate the: (1) flux, (2) recovery, (3) concentration factor, and (4) specific energy consumption of nutrients (NH4+, K+, NO3-, and PO43-) and VFAs (acetic, propionic, and butyric acid) via electrodialysis (ED), and (5) selectively separate the VFAs from the nutrients in the ED concentrate using a hydrophobic membrane contactor (HMC). Synthetic feed and real industrial fermented food wastes were used for ED and HMC experiments. The ED consumed 0.395 kWh/kg, recovering 64-95% of the nutrients and VFAs, corresponding to 4.1-9.4 and 0.6-22.1 g/L nutrients and VFAs, respectively. The HMC selectively separated over 94% of VFAs after ED, with <2% nutrients contamination in the final VFA stream. The results suggest that applying HMC after ED can concentrate and selectively separate VFAs from nutrients in fermented food wastes, which can be valorized for bio-based fertilizers and chemical platforms.

Heavy Metal Removal from Aqueous Solutions Using a Customized Bipolar Membrane Electrodialysis Process.

Lack of safe water availability and access to clean water cause a higher risk of infectious diseases and other diseases as well. Heavy metals (HMs) are inorganic pollutants that cause severe threats to humans, animals, and the environment. Therefore, an effective HM removal technology is urgently needed. In the present study, a customized bipolar membrane electrodialysis process was used to remove HMs from aqueous solutions. The impacts of the feed ionic strength, applied electrical potential, and the type and concentration of HMs (Cd2+, Co2+, Cr3+, Cu2+, and Ni2+) on the process performance were investigated. The results showed that feed solution pH changes occurred in four stages: it first decreased linearly before stabilizing in the acidic pH range, followed by an increase and stabilization in the basic range of the pH scale. HM speciation in the basic pH range revealed the presence of anionic HM species. The presence of HMs on anion exchange membranes confirmed the contribution of these membranes for HM removal in the base channels of the process. While no clear trend was seen in the ionic strength solution, the maximum HM removal was observed when 1.5 g/L NaCl was used. The initial HM concentration showed a linear increase in HMs removal of up to 30 mg/L. A similar trend was seen with an increase in the applied electrical potential of up to 15 V. In general, the amount of HMs removed increased in the following order: Cd2+ ˃ Ni2+ ˃ Co2+ ˃ Cu2+ ˃ Cr3+. Under some operational conditions, however, the removed amount of Cu2+, Co2+, and Ni2+ was similar. The mass balance and SEM-EDX results revealed that the removed HMs were sorbed onto the membranes. In conclusion, this process efficiently separates HMs from aqueous solutions. It showed the features of diluate pH adjustment, reduction in the overall stack electrical resistance, and contribution of anion exchange membranes in multivalent cation removal. The mechanisms involved in HMs removal were diffusion and migration from the bulk solution, followed by their sorption on both cation and anion exchange membranes.

Bipolar membrane electrodialysis integrated with in-situ CO2 absorption for simulated seawater concentrate utilization, carbon storage and production of sodium carbonate.

In the context of carbon capture, utilization, and storage, the high-value utilization of carbon storage presents a significant challenge. To address this challenge, this study employed the bipolar membrane electrodialysis integrated with carbon utilization technology to prepare Na2CO3 products using simulated seawater concentrate, achieving simultaneous saline wastewater utilization, carbon storage and high-value production of Na2CO3. The effects of various factors, including concentration of simulated seawater concentrate, current density, CO2 aeration rate, and circulating flow rate of alkali chamber, on the quality of Na2CO3 product, carbon sequestration rate, and energy consumption were investigated. Under the optimal condition, the CO32- concentration in the alkaline chamber reached a maximum of 0.817 mol/L with 98 mol% purity. The resulting carbon fixation rate was 70.50%, with energy consumption for carbon sequestration and product production of 5.7 kWhr/m3 CO2 and 1237.8 kWhr/ton Na2CO3, respectively. This coupling design provides a triple-win outcome promoting waste reduction and efficient utilization of resources.

Simultaneous Manipulation of Membrane Enthalpy and Entropy Barriers towards Superior Ion Separations.

Sub-nanoporous membranes with ion selective transport functions are important for energy utilization, environmental remediation, and fundamental bioinspired engineering. Although mono/multivalent ions can be separated by monovalent ion selective membranes (MISMs), the current theory fails to inspire rapid advances in MISMs. Here, we apply transition state theory (TST) by regulating the enthalpy barrier (ΔH) and entropy barrier (ΔS) for designing next-generation monovalent cation exchange membranes (MCEMs) with great improvement in ion selective separation. Using a molecule-absorbed porous material as an interlayer to construct a denser selective layer can achieve a greater absolute value of ΔS for Li+ and Mg2+ transport, greater ΔH for Mg2+ transport and lower ΔH for Li+ transport. This recorded performance with a Li+/Mg2+ perm-selectivity of 25.50 and a Li+ flux of 1.86 mol ⋅ m-2 ⋅ h-1 surpasses the contemporary "upper bound" plot for Li+/Mg2+ separations. Most importantly, our synthesized MCEM also demonstrates excellent operational stability during the selective electrodialysis (S-ED) processes for realizing scalability in practical applications.

Sustainable Lithium Recovery from Hypersaline Salt-Lakes by Selective Electrodialysis: Transport and Thermodynamics.

Evaporative technology for lithium mining from salt-lakes exacerbates freshwater scarcity and wetland destruction, and suffers from protracted production cycles. Electrodialysis (ED) offers an environmentally benign alternative for continuous lithium extraction and is amenable to renewable energy usage. Salt-lake brines, however, are hypersaline multicomponent mixtures, and the impact of the complex brine-membrane interactions remains poorly understood. Here, we quantify the influence of the solution composition, salinity, and acidity on the counterion selectivity and thermodynamic efficiency of electrodialysis, leveraging 1250 original measurements with salt-lake brines that span four feed salinities, three pH levels, and five current densities. Our experiments reveal that commonly used binary cation solutions, which neglect Na+ and K+ transport, may overestimate the Li+/Mg2+ selectivity by 250% and underpredict the specific energy consumption (SEC) by a factor of 54.8. As a result of the hypersaline conditions, exposure to salt-lake brine weakens the efficacy of Donnan exclusion, amplifying Mg2+ leakage. Higher current densities enhance the Donnan potential across the solution-membrane interface and ameliorate the selectivity degradation with hypersaline brines. However, a steep trade-off between counterion selectivity and thermodynamic efficiency governs ED's performance: a 6.25 times enhancement in Li+/Mg2+ selectivity is accompanied by a 71.6% increase in the SEC. Lastly, our analysis suggests that an industrial-scale ED module can meet existing salt-lake production capacities, while being powered by a photovoltaic farm that utilizes <1% of the salt-flat area.

Precise Cation Separations with Composite Cation-Exchange Membranes: Role of Base Layer Properties.

Separation of specific ions from water could enable recovery and reuse of essential metals and nutrients, but established membrane technologies lack the high-precision selectivity needed to facilitate a circular resource economy. In this work, we investigate whether the cation/cation selectivity of a composite cation-exchange membrane (CEM), or a thin polymer selective layer on top of a CEM, may be limited by the mass transfer resistance of the underlying CEM. In our analysis, we utilize a layer-by-layer technique to modify CEMs with a thin polymer selective layer (∼50 nm) that has previously shown high selectivity toward copper over similarly sized metals. While these composite membranes have a CuCl2/MgCl2 selectivity up to 33 times larger than unmodified CEMs in diffusion dialysis, our estimates suggest that eliminating resistance from the underlying CEM could further increase selectivity twofold. In contrast, the CEM base layer has a smaller effect on the selectivity of these composite membranes in electrodialysis, although these effects could become more pronounced for ultrathin or highly conductive selective layers. Our results highlight that base layer resistance prevents selectivity factors from being comparable across diffusion dialysis and electrodialysis, and CEMs with low resistance are necessary for providing highly precise separations with composite CEMs.

Selective separation of monovalent anions by PPy/pTS membrane electrodes in redox transistor electrodialysis.

Selective separation of nitrate over chloride is crucial for eutrophication mitigation and nitrogen resource recovery but remains a challenge due to their similar ionic radius and the same valence. Herein, a polypyrrole membrane electrode (PME) was fabricated by polymerization of pyrrole (Py) and p-toluenesulfonate (pTS), which was used as a working electrode in redox transistor electrodialysis. The anions in the source solution were first incorporated into the PME at reduction potentials and then released to receiving solution at oxidation potentials. Pulse widths and potentials were optimized to maximize the ion separation performance of PME, resulting in the improvement of NO3-/Cl- separation factor up to 6.93. The ion distributions in various depths of PME indicated that both NO3- and Cl- were incorporated into PME at negative potentials. Then, NO3- was preferentially released from PME at positive potentials, but most Cl- was retained. This was ascribed to the high binding energy between Cl- and PPy/pTS structure, which was 51.4% higher than that between NO3- and PPy/pTS structure. Therefore, the higher transport rate of NO3- in comparison with Cl- was achieved, leading to a high NO3- selectivity over Cl-. This work provides a promising avenue for the selective separation of nitrate over chloride, which may contribute to nitrogen resource recycling and reuse.

Electrodialysis desalination: The impact of solution flowrate (or Reynolds number) on fluid dynamics throughout membrane spacers.

The incorporation of a spacer among membranes has a major influence on fluid dynamics and performance metrics. Spacers create feed channels and operate as turbulence promoters to increase mixing and reduce concentration/temperature polarization effects. However, spacer geometry remains unoptimized, and studies continue to investigate a wide range of commercial and custom-made spacer designs. The in-depth discussion of the present systematic review seeks to discover the influence of Reynolds number or solution flowrate on flow hydrodynamics throughout a spacer-filled channel. A fast-flowing solution sweeping one membrane's surface first, then the neighboring membrane's surface produces good mixing action, which does not happen commonly at laminar solution flowrates. A sufficient flowrate can suppress the polarization layer, which may normally require the utilization of a simple feed channel rather than complex spacer configurations. When a recirculation eddy occurs, it disrupts the continuous flow and effectively curves the linear fluid courses. The higher the flowrate, the better the membrane performance, the higher the critical flux (or recovery rate), and the lower the inherent limitations of spacer design, spacer shadow effect, poor channel hydrodynamics, and high concentration polarization. In fact, critical flow achieves an acceptable balance between improving flow dynamics and reducing the related trade-offs, such as pressure losses and the occurrence of concentration polarization throughout the cell. If the necessary technical flowrate is not used, the real concentration potential for transport is relatively limited at low velocities than would be predicted based on bulk concentrations. Electrodialysis stack therefore may suffer from the dissociation of water molecules. Next studies should consider that applying a higher flowrate results in greater process efficiency, increased mass transfer potential at the membrane interface, and reduced stack thermal and electrical resistance, where pressure drop should always be indicated as a consequence of the spacer and circumstances used, rather than a problem.

Bipolar Membrane Electrodialysis for Direct Conversion of L-Ornithine Monohydrochloride to L-Ornithine.

In this study, bipolar membrane electrodialysis was proposed to directly convert L-ornithine monohydrochloride to L-ornithine. The stack configuration was optimized in the BP-A (BP, bipolar membrane; A, anion exchange membrane) configuration with the Cl- ion migration through the anion exchange membrane rather than the BP-A-C (C, cation exchange membrane) and the BP-C configurations with the L-ornithine+ ion migration through the cation exchange membrane. Both the conversion ratio and current efficiency follow BP-A > BP-A-C > BP-C, and the energy consumption follows BP-A < BP-A-C < BP-C. Additionally, the voltage drop across the membrane stack (two repeating units) and the feed concentration were optimized as 7.5 V and 0.50 mol/L, respectively, due to the low value of the sum of H+ ions leakage (from the acid compartment to the base compartment) and OH- ions migration (from the base compartment to the acid compartment) through the anion exchange membrane. As a result, high conversion ratio (96.1%), high current efficiency (95.5%) and low energy consumption (0.31 kWh/kg L-ornithine) can be achieved. Therefore, bipolar membrane electrodialysis is an efficient, low energy consumption and environmentally friendly method to directly convert L-ornithine monohydrochloride to L-ornithine.

Impact of a Whey Protein Hydrolysate Treated by Electrodialysis with Ultrafiltration Membrane on the Development of Metabolic Syndrome and the Modulation of Gut Microbiota in Mice.

The development of Metabolic Syndrome (MetS) affects a large number of people around the world and represents a major issue in the field of health. Thus, it is important to implement new strategies to reduce its prevalence, and various approaches are currently under development. Recently, an eco-friendly technology named electrodialysis with ultrafiltration membrane (EDUF) was used successfully for the first time at a semi-industrial scale to produce three fractions concentrated in bioactive peptides (BPs) from an enzymatically hydrolyzed whey protein concentrate (WPC): the initial (F1), the final (F2) and the recovery fraction (F3), and it was demonstrated in vitro that F3 exhibited interesting DPP-IV inhibitory effects. Therefore, the present study aimed to evaluate the effect of each fraction on in vivo models of obesity. A daily dose of 312.5 mg/kg was administered to High Fat/High Sucrose diet (HFHS) induced C57BL6/J mice for eight weeks. The physiological parameters of each group and alterations of their gut microbiota by the fractions were assessed. Little effect of the different fractions was demonstrated on the physiological state of the mice, probably due to the digestion process of the BP content. However, there were changes in the gut microbiota composition and functions of mice treated with F3.

Energetic evaluation of phenol wastewater treatment by reverse electrodialysis reactor using different anodes.

Efficient electrode materials are essential to convert salinity gradient energy into oxidative degradation energy and electrical energy by reverse electrodialysis reactor (REDR). In this context, comparative experiments of REDR using different anodes (Ti/IrO2-RuO2, Ti/PbO2 and Ti/Ti4O7) were conducted. The effects of output current and electrode rinse solution (ERS) flowrate on mineralization efficiency and energy output were discussed. Results demonstrated that the COD removal rate(ηCOD) rose almost linearly with output current and ERS flowrate when using Ti/Ti4O7 anode, but excessive operating conditions caused a slow increase or even decrease of ηCOD when using Ti/IrO2-RuO2 or Ti/PbO2 anodes. The order of electrode system potential loss (Eele) for the three anodes was Ti/Ti4O7> Ti/PbO2> Ti/IrO2-RuO2. High Eele was beneficial to ηCOD but had a negative effect on the net output power (Pnet) of REDR. Regardless of the applied anodes, increasing the current and decreasing the ERS flowrate was detrimental to Pnet due to higher Eele. Based on these findings, four energy efficiency parameters were defined to evaluate energy recovery from multiple perspectives by linking energy output with mineralization capacity. They were electrode efficiency (ηele), energy efficiency (EE), general current efficiency (GCE) and energy consumption (EC), respectively. Results showed that REDR with Ti/Ti4O7 anodes and suitable operating conditions achieved the optimal energy indicators and mineralization efficiency, which provided an efficient and economical option for wastewater treatment and energy recovery.

Compressible Ionized Natural 3D Interconnected Loofah Membrane for Salinity Gradient Power Generation.

Large-scale salinity gradient power energy harvesting has generated broad attention in recent years, in which affordable ion-selective membranes (ISMs) are essential for its practical implementation. In this study, for the first time, ISMs derived from natural loofah sponge are reported, which have features of high hydrophilicity, superior ion conductivity, and 3D interconnected long fibers. The permselectivity and ion conductivity of loofah-based anion-selective membranes (ASMs) and cation-selective membranes (CSMs) are designed by chemical modification of the surface functional groups of loofah fibers and followed with compression and the resin filling. The charged nanochannels inside the ISMs are served as ion conductive and selective channels based on the nanofluidic effects and Donnan exclusion. Meanwhile, the unique isotropic structure endows excellent dimensional stability under the NaCl solution for months. When ISMs are used for salinity gradient power generation from the gradient of artificial seawater and river water, the maximum power density is 18.3 mW m-2 . When ten units of loofah-based ISMs are stacked in series, a voltage as high as 1.55 V is achieved. The results highlight the great potential of natural fibers for fabricating affordable, durable, and high performance ISMs, paving a sustainable pathway for developing high-performance, durable, and low-cost salinity gradient power generators.