Progress and prospects of pH-neutral aqueous organic redox flow batteries:Electrolytes and membranes

Aqueous organic redox flow batteries(AORFBs),which exploit the reversible electrochemical reactions of water-soluble organic electrolytes to store electricity,have emerged as an efficient electrochemical energy storage technology for the grid-scale integration of renewable electricity.pH-neutral AORFBs that feature high safety,low corrosivity,and environmental benignity are particularly promising,and their battery performance is significantly impacted by redox-active molecules and ion-exchange membranes(IEMs).Here,representative anolytes and catholytes engineered for use in pH-neutral AORFBs are outlined and summarized,as well as their side reactions that cause irreversible battery capacity fading.In addition,the recent achievements of IEMs for pH-neutral AORFBs are discussed,with a focus on the construction and tuning of ion transport channels.Finally,the critical challenges and potential research opportunities for developing practically relevant pH-neutral AORFBs are presented.

Recent advances in acid-resistant zeolite T membranes for dehydration of organics

Zeolite membranes offer outstanding potentials in separation of many molecular mixtures due to their molecular sieving selectivity and the high thermal and mechanical stability that allow them to operate at harsh conditions.Development of durable and high separation performance membranes with lower fabrication and operation cost are highly demanded for industrial applications. Zeolite T membrane possesses good acid-resistance with excellent hydrophilic properties as compared to NaA zeolite membrane and can be extended to industrial organic dehydrations under an acidic environment. In the present review the research advances in development of zeolite T membranes for the dehydration of organic mixtures in acidic conditions are summarized. Especially the low temperature synthesis, and epitaxial growth of the zeolite membrane with high performance are well addressed, besides emphasis is particularly placed on ensemble synthesis of hollow fiber zeolite T membrane module and its future prospects for industrial separations.

Water-selective hybrid membranes with improved interfacial compatibility from mussel-inspired dopamine-modified alginate and covalent organic frameworks

Hybrid membranes combining the merits of both polymer matrices and fillers have drawn extensive attention. The rational design of polymer–filler interface in hybrid membranes is vitally important for reducing the occurrence of void defects. Herein, imine-type covalent organic frameworks(COFs) were selected as the fillers due to their totally organic nature and multi-functionalities. Mussel-inspired dopamine-modified sodium alginate(Alg DA) was synthesized as the polymer matrix. The dopamine modification significantly improves the Alg DA–COF compatibility,which enhances the COF content up to 50 wt% in the hybrid membranes. The improved interfacial compatibility enhances the membrane separation selectivity. Accordingly, when utilized for dehydration of ethanol/water mixed solution(water concentration of 10 wt%), the hybrid membrane reveals high water concentration of ~98.7 wt% in permeate, and stable permeation flux larger than 1500 g·m-2·h-1. This work might afford useful insights for fabricating hybrid membranes with high separation selectivity by optimizing the polymer–filler interface.

Preparation and Conducting Behavior of Amphibious Organic/Inorganic Hybrid Proton Exchange Membranes Based on Benzyltetrazole

A series of novel amphibious organic/inorganic hybrid proton exchange membranes with H3PO4 doped which could be used under both wet and dry conditions was prepared through a sol-gel process based on acrylated triethoxysilane（A-TES） and benzyltetrazole-modified triethoxysilane（BT-TES）.The dual-curing approach including UV-curing and thermal curing was used to obtain the crosslinked membranes.Polyethylene glycol（400） diacrylate（PEGDA） was used as an oligomer to form the polymeric matrix.The molecular structures of precursors were characterized by 1 H,13 C and 29 Si NMR spectra.The thermogravimetric analysis（TGA） results show that the membranes exhibit acceptable thermal stability for their application at above 200 oC.The differential scanning calorimeter（DSC） determination indicates that the crosslinked membranes with the mass ratios of below 1.6 of BT-TES to A-TES and the same mass of H3PO4 doped as that of A-TES possess the-T g s,and the lowest T g（-28.9 ℃） exists for the membrane with double mass of H3PO4 doped as well.The high proton conductivity in a range of 9.4―17.3 mS/cm with the corresponding water uptake of 19.1%―32.8% of the membranes was detected at 90 oC under wet conditions.Meanwhile,the proton conductivity in a dry environment for the membrane with a mass ratio of 2.4 of BT-TES to A-TES and double H3PO4 loading increases from 4.89×10-2 mS/cm at 30 ℃ to 25.7 mS/cm at 140 ℃.The excellent proton transport ability under both hydrous and anhydrous conditions demonstrates a potential application in the polymer electrolyte membrane fuel cells.

Reducing active layer thickness of polyamide composite membranes using a covalent organic framework interlayer in interfacial polymerization

Polyamide(PA)-based thin-film composite membranes exhibit enormous potential in water purification,owing to their facile fabrication,decent performance and desirable stability.However,the thick PA active layer with high transport resistance from the conventional interfacial polymerization hampers their applications.The controllable fabrication of a thin PA active layer is essential for high separation efficiency but still challenging.Herein,a covalent organic framework TpPa-1 interlayer was firstly deposited on a polyethersulfone(PES)substrate to reduce the thickness of PA active layer in interfacial polymerization.The abundant pores of TpPa-1 increase the local concentration of amine monomers by adsorbing piperazine molecules,while hydrogen bonds between hydrophilic groups of TpPa-1 and piperazine molecules slow down their diffusion rate.Arising from those synergetic effects,the PA active layer is effectively reduced from 200 nm to 120 nm.By optimizing TpPa-1 interlayer and PA active layer,the water flux of resultant membranes can reach 171.35 L·m^-2·h^-1·MPa^-1,which increased by 125.4%compared with PA/PES membranes,while the rejection rates of sodium sulfate and dyes solution remained more than 90%and 99%,respectively.Our strategy may stimulate rational design of ultrathin PA-based nanofiltration membranes with high performances.

ORGANIC PERMSELECTIVE PERVAPORATION CHARACTERISTICS OF POLY(SILYLPROPYNE) AND COPOLYMER DENSE MEMBRANES

An investigation into the organic permselective separation through poly [1-trimethylsilyl-1-propyne] (PTMSP) and (1-trimethylsily 1)-1-(1-penta-methyl-disily 1)-1-propyne copolymer (TMSP-PMDSP) dense membranes was made to gain an insight into the effect of the chemical structure of membrane materials on pervaporation (PV) characteristics. The results show that the copolymer has a higher separation factor alpha(org/water) but with a relatively lower value of flux J(t) (g/m(2).h) than pure PTMSP. This phenomenon may be attributed to the introduction of side chain with large bulk volume in copolymer, which brought about a decrease of excess free volume and the improvement of diffusion selectivity to some extent. With the same molar concentration of organic liquids in feed, THF/water solutions have the highest value of alpha(org/water) as well as J(t) in comparison with ethanol/water, iso-propanol/water and THF/water mixtures.

Occurrence and removal of organic micropollutants in the treatment of landfill leachate by combined anaerobic-membrane bioreactor technology

Organic micropollutants,with high toxicity and environmental concern,are present in the landfill leachate at much lower levels than total organic constituents (chemical oxygen demand (COD),biochemical oxygen demand (BOD),or total organic carbon (TOC)),and few has been known for their behaviors in different treatment processes.In this study,occurrence and removal of 17 organochlorine pesticides (OCPs),16 polycyclic aromatic hydrocarbons (PAHs),and technical 4-nonylphenol (4-NP) in landfill leachate in a comb...

Enrichment of Semi-Volatile Organic Acids from Aqueous Solutions by Multiple-Effect Membrane Distillation

Multiple-effect membrane distillation （MEMD） process for enriching semi-volatile organic acids from their individual aqueous solutions was performed by using a hollow fiber-based air gap membrane distillation （AGMD） module with the function of internal heat recovery. Aqueous solutions of glyoxylic acid, glycolic acid, lactic acid, pyrnvic acid, malonic acid and glutaric acid were used as model feed. For a feed of 1% （mass fraction）, each acid could be enriched for 8--20 times, which depended on the surface tension of the concentrate. The operation performance of MEMD process was characterized by permeation flux J, performance ratio PR and acid rejection rate R. The effects of cold feed-in temperature, heated feed-in temperature, feed-in volumetric flow rate and feed-in concen- tration on MEMD performance were experimentally evaluated. Maximum values of J, PR and R were 4.8 L/（h-m2）, 9.84 and 99.93%, respectively. Moreover, MEMD process demonstrated a fairly good stability in a long-term experiment lasting for 30 d when aqueous solution of 4% （mass fraction） lactic acid was used as a feed.

Remove volatile organic compounds(VOCs) with membrane separation techniques

Membrane separation, a new technology for removing VOCs including pervaporation, vapor permeation, membrane contactor, and membrane bioreactor was presented. Comparing with traditional techniques, these special techniques are an efficient and energy saving technology. Vapor permeation can be applied to recovery of organic solvents from exhaust streams. Membrane contactor could be used for removing or recovering VOCs from air or wastewater. Pervaporation and vapor permeation are viable methods for removing VOCs from wastewater to yield a VOC concentrate which could either be destroyed by conventional means, or be recycled for reuse.

STUDIES ON REVERSE OSMOSIS SEPARATION OF AQUEOUS ORGANIC SOLUTIONS BY PAA/PSF COMPOSITE MEMBRANE

The reverse osmosis (RO) separation of aqueous organic solutions, such as alcohols, amines, aldehydes, acids, ketones, and esters etc., by PAA (polyacrylic acid)/PSF (polysulfone) composite membrane has been studied. It was found that the separation results for aliphatic alcohols, amines and aldehydes are satisfactory, the solute rejection (R-a) and the volume fluxes of solutions (J(V)) for 1000 ppm ethanol, ethylamine and ethyl aldehyde are 66.2%, 61.0%, 84.0% and 0.90 x 10(-6), 0.35 x 10(-6), 0.40 X 10(-6) m(3)/m(2) . s, respectively, at 5.0 MPa and 30 degrees C. R-a increased with increasing molecular weights of alcohols, amines and aldehydes, and the R-a for n-amyl alcohol, n-butylamine and n-butyl aldehyde reached 94.3%, 88.6% and 96.0%, respectively. Satisfactory separation results (R-a > 70%) for ketones, esters, phenols and polyols have been obtained with the PAA/PSF composite membrane. The effect of operating pressure on the properties of reverse osmosis has also been investigated. Analysis of experimental data with Spiegler-Kedem's transport model has been carried out and the membrane constants such as reflection coefficient sigma, solute and hydraulic permeabilities omega and L-p for several organic solutes have been obtained.

Membrane Potentials Across Hybrid Charged Mosaic Membrane in Organic Solutions

Membrane potentials across hybrid charged mosaic membrane in organic solutions were measured. Equilibrium swelling degree （SD） and fixed charge density in both organic solutions and water were also determined. Ethylene glycol, ethanol, n-propanol and glycerol were used as organic solutes; meanwhile 0.001mol-dm^-3 aqueous KCl solution was utilized as a strong electrolyte to measure the electrical difference. Equilibrium swelling degree indicated that it could be affected by the density of organic solutes; while it enhanced with the increasing density of these solutes. The measurement of fixed charge density showed that the membrane had the maximal absolute value in water among these solvents whether for cationic or anionic groups; the difference of dielectric constant between the water and the organic solutes might be responsible for these change trends. It was confirmed that membrane potentials increased with both the increasing concentration of the organic solutions and the elevated pH values. These results demonstrated that the characteristics of the hybrid charged mosaic membrane could be highly impacted by the properties of the organic solutes. A theoretical modal for charged membranes in ternary ion systems of weak electrolyte can be used to explain the above-mentioned phenomena.

Mass transfer model,preparation and applications of zeolite membranes for pervaporation dehydration:A review

Pervaporation(including vapor permeation) is a kind of new membrane separation technology, possessing the advantages of high efficiency, energy saving and convenient operation. It has promising application in the separation and purification of organic solvents. Dehydration is an important step in the production and recovery of organic solvents. Zeolite membranes have attracted wide attention for pervaporation dehydration due to their high separation performance and good thermal/chemical stability. So far, zeolite membranes have been preliminarily industrialized for dehydration of organic solvents. This paper reviews the recent development of zeolite membranes for pervaporation dehydration, including mass transfer models, preparation and applications of zeolite membranes. The review also discusses the current industrial applications of zeolite membranes and their future development in pervaporation.

Engineering Leaf-Like UiO-66-SO3H Membranes for Selective Transport of Cations

Metal–organic frameworks(MOFs)with angstrom-sized pores are promising functional nanomaterials for the fabrication of cation permselective membranes(MOF-CPMs).However,only a few research reports show successful preparation of the MOF-CPMs with good cation separation performance due to several inherent problems in MOFs,such as arduous selfassembly,poor water resistance,and tedious fabrication strategies.Besides,low cation permeation flux due to the absence of the cation permeation assisting functionalities in MOFs is another big issue,which limits their widespread use in membrane technology.Therefore,it is necessary to fabricate functional MOF-CPMs using simplistic strategies to improve cation permeation.In this context,we report a facile in situ smart growth strategy to successfully produce ultrathin(<600 nm)and leaflike UiO-66-SO3H membranes at the surface of anodic alumina oxide.The physicochemical characterizations confirm that sulfonated angstrom-sized ion transport channels exist in the as-prepared UiO-66-SO3H membranes,which accelerate the cation permeation(~3×faster than non-functionalized UiO-66 membrane)and achieve a high ion selectivity(Na^+/Mg^2+>140).The outstanding cation separation performance validates the importance of introducing sulfonic acid groups in MOF-CPMs.

Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination

Aqueous two-phase system features with ultralow interfacial tension and thick interfacial region,affording unique confined space for membrane assembly.Here,for the first time,an aqueous two-phase interfacial assembly method is proposed to fabricate covalent organic framework(COF)membranes.The aqueous solution containing polyethylene glycol and dextran undergoes segregated phase separation into two water-rich phases.By respectively distributing aldehyde and amine monomers into two aqueous phases,a series of COF membranes are fabricated at water-water interface.The resultant membranes exhibit high NaCl rejection of 93.0-93.6% and water permeance reaching 1.7-3.7 L m^(−2) h^(−1) bar^(−1),superior to most water desalination membranes.Interestingly,the interfacial tension is found to have pronounced effect on membrane structures.The appropriate interfacial tension range(0.1-1.0 mN m^(−1))leads to the tight and intact COF membranes.Furthermore,the method is extended to the fabrication of other COF and metal-organic polymer membranes.This work is the first exploitation of fabricating membranes in all-aqueous system,confering a green and generic method for advanced membrane manufacturing.

Engineering HOF‑Based Mixed‑Matrix Membranes for Efficient CO_(2) Separation

Hydrogen-bonded organic frameworks(HOFs)have emerged as a new class of crystalline porous materials,and their application in membrane technology needs to be explored.Herein,for the first time,we demonstrated the utilization of HOF-based mixed-matrix membrane for CO_(2) separation.HOF-21,a unique metallo-hydrogen-bonded organic framework material,was designed and processed into nanofillers via amine modulator,uniformly dispersing with Pebax polymer.Featured with the mix-bonded framework,HOF-21 possessed moderate pore size of 0.35 nm and displayed excellent stability under humid feed gas.The chemical functions of multiple binding sites and continuous hydrogen-bonded network jointly facilitated the mass transport of CO_(2).The resulting HOF-21 mixed-matrix membrane exhibited a permeability above 750 Barrer,a selectivity of~40 for CO_(2)/CH_(4) and~60 for CO_(2)/N_(2),surpassing the 2008 Robeson upper bound.This work enlarges the family of mixed-matrix membranes and lays the foundation for HOF membrane development.

Composite bilayer films with organic compound-triggered bending properties

Organic compounds are widely used in both industry and daily life,and composite bilayer films with organic compound-triggered bending properties are promising for applications of transducers,soft robotics,and so on.Here,a universal and straightforward strategy to generate composite bilayer films with organic compoundtriggered bending properties is demonstrated.The composite bilayer films with organic compound-triggered bending properties are designed with bilayer structures,in which one layer is a porous polymeric membrane with appropriate solubility parameter that matches the value of organic solvents in order to produce prominent affinity to the solvent molecules,and the other layer is reduced graphene oxide membrane stacked on the porous polymeric membrane as an inert layer for restraining the swelling of the polymeric membrane on one side.Guided by matching the solubility parameters between solvent and polymer,a significant bending curvature of 27.3 cm-1 is obtained in acetone vapor.The results in this study will provide valuable guidance for designing and developing functional composite materials with significant organic compound-triggered bending properties.

Membranes for the life sciences and their future roles in medicine

Since the global outbreak of COVID-19,membrane technology for clinical treatments,including extracorporeal membrane oxygenation(ECMO)and protective masks and clothing,has attracted intense research attention for its irreplaceable abilities.Membrane research and applications are now playing an increasingly important role in various fields of life science.In addition to intrinsic properties such as size sieving,dissolution and diffusion,membranes are often endowed with additional functions as cell scaffolds,catalysts or sensors to satisfy the specific requirements of different clinical applications.In this review,we will introduce and discuss state-of-the-art membranes and their respective functions in four typical areas of life science:artificial organs,tissue engineering,in vitro blood diagnosis and medical support.Emphasis will be given to the description of certain specific functions required of membranes in each field to provide guidance for the selection and fabrication of the membrane material.The advantages and disadvantages of these membranes have been compared to indicate further development directions for different clinical applications.Finally,we propose challenges and outlooks for future development.

Research Progress in the Fabrication of Covalent Organic Framework Membranes for Chemical Separations

Membrane technology has become one of the most promising separation technologies for its energy saving, high separation efficiency, environmental friendliness, and economic feasibility. Covalent organic frameworks(COFs) with intrinsically high porosity, controllable pore size, uniform pore size distribution and long-range ordered channel structure, have emerged as next-generation materials to fabricate advanced separation membranes. This feature article summarizes some latest studies in the development of pure COF membranes in our lab, including their fabrication and applications in chemical separations. Finally, current challenges facing high-performance COF separation membranes are discussed.