Diphylleia Grayi-Inspired Intelligent Temperature-Responsive Transparent Nanofiber Membranes

Nanofiber membranes(NFMs) have become attractive candidates for next-generation flexible transparent materials due to their exceptional flexibility and breathability. However, improving the transmittance of NFMs is a great challenge due to the enormous reflection and incredibly poor transmission generated by the nanofiber-air interface. In this research, we report a general strategy for the preparation of flexible temperature-responsive transparent(TRT) membranes,which achieves a rapid transformation of NFMs from opaque to highly transparent under a narrow temperature window. In this process, the phase change material eicosane is coated on the surface of the polyurethane nanofibers by electrospray technology. When the temperature rises to 37 ℃, eicosane rapidly completes the phase transition and establishes the light transmission path between the nanofibers, preventing light loss from reflection at the nanofiber-air interface. The resulting TRT membrane exhibits high transmittance(> 90%), and fast response(5 s). This study achieves the first TRT transition of NFMs, offering a general strategy for building highly transparent nanofiber materials, shaping the future of next-generation intelligent temperature monitoring, anti-counterfeiting measures, and other high-performance devices.

Two-dimensional material separation membranes for renewable energy purification, storage, and conversion

The current energy crisis has prompted the development of new energy sources and energy storage/conversion devices. Membranes, as the key component, not only provide enormous separation potential for energy purification but also guarantee stable and high-efficiency operation for rechargeable batteries and fuel cells. Remarkably, two-dimensional(2D) material separation membranes have attracted intense attention on their excellent performance in energy field applications, owing to high mechanical/chemical stability, low mass transport resistance, strict sizeexclusion, and abundant modifiable functional groups. In this review, we concentrate on the recent progress of 2D membrane and introduce 2D membranes based on graphene oxide(GO), MXenes, 2D MOFs, 2D COFs, and 2D zeolite nanosheets, which are applied in membrane separation(H2 collection and biofuel purification) and battery separators(vanadium flow battery, Li–S battery, and fuel cell). The mass transport mechanism, selectivity mechanism, and modification methods of these 2D membranes are stated in brief, mainly focusing on interlayer dominant membranes(GO and MXenes) and pore dominant membranes(MOFs, COFs, and zeolite nanosheets). In conclusion, we highlight the challenges and outlooks of applying 2D membranes in energy fields.

Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry, but challenged in some cases. Compared with conventional separation technologies, pervaporation is quite promising in terms of its economical, energy-saving, and eco-friendly advantages. However, this technique has not been used in industry for separating aromatic/aliphatic mixtures yet. One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory. Membrane material is an important factor that affects the separation performance. This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade. Explored pristine polymers and their hybrid materials(as hybrid membranes) are summarized to highlight their nature and separation performance. We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.

Additional Mass: Orthotropic Membrane Material with Four Sides Fixed in Air Flow

When the membrane material in the air field vibrates, it will drive the movement of the surrounding air. The aerodynamic force generated by the moving air will act on the membrane material in turn, resulting in the change of dynamic characteristics such as membrane vibration frequency. In this paper, the additional air mass produced by membrane vibration in air is studied. Firstly, under the assumption that the incoming flow is uniform and incompressible ideal potential flow, the additional air mass acting on the surface is derived by using the thin airfoil theory and potential flow theory respectively. Then, according to the first law of thermodynamics and the principle of aeroelasticity, the analytical expression of the additional air mass is derived. Finally, through a specific example, the variation of the additional air mass with the membrane material parameters and pretension, as well as the influence of the aerodynamic force on the vibration frequency and amplitude of the membrane is obtained.

Processing and Properties of Flexible Hot Gas Sealing Materials for Ceramic Membrane

Ceramic membranes are effective to reduce PM2.5 emission when used for hot flue gas filtration.The properties of the sealing material play a decisive role infiltration efficiency.However,there are few studies on sealing materials for hot flue gas filtration above 700 ℃.This investigation was performed to develop flexible sealing materials which can be used for a long time at high temperatures.In order to obtain sufficient mechanical strength and continuous flexibility,three kinds of binders were selected as coating binders.The sealing materials based on high silica fiber fabric and aluminum silicate fiber fabric were successfully prepared.The effect of aging on mechanical properties and microstructural characteristics of the composites subjected to coating had been investigated by XRD,SEM and EDS.The results show that waterborne polyurethane (WPU) is a suitable coating binder for the sealing materials,which can be used for a long time at 1 000 ℃ and 700 ℃,respectively,without significant decrease in strength.However,the other two binders,aluminum dihydrogen phosphate and aluminum chromium phosphate will weaken the flexibility,resulting in frangibility and reducing sealing performance.The developed composites possess required thermo-stability and desired mechanical strength as flexible sealing materials,indicating their strong application possibility in hot flue gas filtration.

Preparation of Cellulose Acetate Butyrate Porous Micro/Nanofibrous Membranes and Their Properties

Cellulose acetate butyrate(CAB)is a cellulose ester that is commonly used in applications such as coatings and leather brighteners.However,its appearance in a fibrous form is rarely reported.CAB porous micro/nanofibrous membranes with a large number of nanopores on the fiber surface were successfully prepared by electrospinning with dichloromethane(DCM)/acetone(AC)as the mixed solvent.Apparent morphology,porosity,moisture permeability,air permeability,static water contact angles,and thermal conductivity of the fibrous membranes were investigated at different spinning voltages.The results showed that with the increase of the spinning voltage,the average fiber diameter of the CAB porous micro/nanofibrous membranes gradually decreased and the fiber diameter distribution was more uniform.When the spinning voltage reached 40 kV,the porosity reached 91.38%,the moisture permeability was up to 7430 g/(m^(2)·d),the air permeability was up to 36.289 mm/s,the static water contact angle was up to 145.0°,while the thermal conductivity of the fibrous membranes reached 0.030 W/(m·K).The material can be applied as thermal-insulation,waterproof and moisture-permeable membranes.

A Research on the Air Permeability of High Polymer Materials Used to Produce Sports Clothing Fabrics

Composite fabrics based on Polytetrafluoroethylene(PTFE)polymer displays several notable properties.They are waterproof,windproof,permeable to moisture and thermally insulating at the same time.In the present study,PTFE fibers are used as raw material to make fiber membranes.The film is formed by crisscrossing interconnected fiber filaments and the related air permeability:tensile creep characteristics and other properties are tested.The results show that the pore size,thickness,and porosity of the film itself can affect the moisture permeability of the film.The water pressure resistance of the selected fabric is 8.5 kPa,and the moisture permeability is 7038 g/(m^(2)·24 h).

Recent advances on mixed matrix membranes for CO_2 separation

Recent advances on mixed matrix membrane for CO2 separation are reviewed in this paper. To improve CO2 separation performance of polymer membranes, mixed matrix membranes (MMMs) are developed. The concept of MMM is illustrated distinctly. Suitable polymer and inorganic or organic fillers for MMMs are summarized. Possible interface morphologies between polymer and filler, and the effect of interface morphologies on gas transport properties of MMMs are summarized. The methods to improve compatibility between polymer and filler are introduced. There are eight methods including silane coupling, Grignard treatment, incorporation of additive, grafting, in situ polymerization, polydopamine coating, particle fusion approach and polymer functionalization. To achieve higher productivity for industrial application, mixed matrix composite membranes are developed. The recent development on hollow fiber and flat mixed matrix composite membrane is reviewed in detail. Last, the future trend of MMM is forecasted.

Beyond graphene oxides: Emerging 2D molecular sieve membranes for efficient separation☆

Recent decades witnessed the significant progress made in the research field of 2D molecular sieve membranes.In comparison with their 3D counterparts, 2D molecular sieve membranes possessed several unique advantages like significantly reduced membrane thickness(one atom thick in theory) and diversified molecular sieving mechanisms(in-plane pores within nanosheets & interlayer galleries between nanosheets). M. Tsapatsis first carried out pioneering work on fabrication of lamellar ZSM-5 membrane. Since then, diverse 2D materials typically including graphene oxides(GOs) have been fabricated into membranes showing promising prospects in energy-efficient gas separation, pervaporation, desalination and nanofiltration. In addition to GOs, other emerging 2D materials, including 2D zeolites, 2D metal–organic frameworks(MOFs), 2 D covalent-organic frameworks(COFs), layered double hydroxides(LDHs), transition metal dichalcogenides(TMDCs), MXenes(typically Ti3C2TX), graphitic carbon nitrides(typically g-C3N4), hexagonal boron nitride(h-BN) and montmorillonites(MT) are showing intriguing performance in membrane-based separation process. This article summarized the most recent developments in the field of 2D molecular sieve membranes aside from GOs with particular emphasis on their structure–performance relationship and application prospects in industrial separation.

Removal of aqueous phenol compound by vacuum membrane distillation

The effects of feed temperature and pH value on the removal of aqueous phenol wastewater by vacuum membrane distillation process are studied by experiments employing micro porous membranes of poly vinylidene fluoride (PVDF) and ploy tetrafluoro ethylene (PTFE) with nominal average pore sizes 0.22 mm and 0.20 mm, respectively. It is found that the optimal feed temperature for PVDF membrane is 50 ℃; and for PTFE membrane, 60 ℃. The pH value of the feed has little influence on the membrane fluxes and ion rejection ratios, while it influenced considerably on the selectivity. Increase of pH value of the feed is conducive to the increase of selectivity. In the same experimental conditions, PTFE membrane shows better separation performance than PVDF membrane does.

Two-dimensional MXene hollow fiber membrane for divalent ions exclusion from water

Two-dimensional material membranes with fast transport channels and versatile chemical functionality are promising for molecular separation.Herein,for the first time,we reported design and engineering of two-dimensional Ti_(3)C_(2)Tx MXene(called transition metal carbides and nitrides)membranes supported on asymmetric polymeric hollow fiber substrate for water desalination.The membrane morphology,physicochemical properties and ions exclusion performance were systematically investigated.The results demonstrated that surface hydrophilicity and electrostatic repulsion and size sieving effect of interlayer channels synergistically endowed the MXene hollow fiber membrane with fast water permeation and efficient rejection of divalent ions during nanofiltration process.

Membrane Engineering for Green Process Engineering

Green process engineering, which is based on the principles of the process intensification strategy, can provide an important contribution toward achieving industrial sustainable development. Green process engineering refers to innovative equipment and process methods that are expected to bring about substan- tial improvements in chemical and any other manufacturing and processing aspects. It includes decreasing production costs, equipment size, energy consumption, and waste generation, and improving remote con- trol, information fluxes, and process flexibility. Membrane-based technology assists in the pursuit of these principles, and the potential of membrane operations has been widely recognized in the last few years. This work starts by presenting an overview of the membrane operations that are utilized in water treatment and in the production of energy and raw materials. Next, it describes the potential advantages of innovative membrane-based integrated systems. A case study on an integrated membrane system （IMS） for seawa- ter desalination coupled with raw materials production is presented. The aim of this work is to show how membrane systems can contribute to the realization of the goals of zero liquid discharge （ZLD）, total raw materials utilization, and low energy consumption.

Electro-viscoelastic behaviors of circular dielectric elastomer membrane actuator containing concentric rigid inclusion

The time-dependent electro-viscoelastic performance of a circular dielectric elastomer(DE) membrane actuator containing an inclusion is investigated in the context of the nonlinear theory for viscoelastic dielectrics. The membrane, a key part of the actuator, is centrally attached to a rigid inclusion of the radius a, and then connected to a fixed rigid ring of the radius b. When subject to a pressure and a voltage, the membrane inflates into an out-of-plane shape and undergoes an inhomogeneous large deformation. The governing equations for the large deformation are derived by means of non-equilibrium thermodynamics, and viscoelasticity of the membrane is characterized by a rheological spring-dashpot model. In the simulation, effects of the pressure, the voltage, and design parameters on the electromechanical viscoelastic behaviors of the membrane are investigated. Evolutions of the considered variables and profiles of the deformed membrane are obtained numerically and illustrated graphically. The results show that electromechanical loadings and design parameters significantly influence the electro-viscoelastic behaviors of the membrane. The design parameters can be tailored to improve the performance of the membrane. The approach may provide guidelines in designing and optimizing such DE devices.

Smart membranes for biomedical applications

Smart membranes with tunable permeability and selectivity have drawn widespread attention because of their unique biomimetic characteristics.Constructed by incorporating various stimuli-responsive materials into membrane substrates,smart membranes could self-adjust their physical/chemical properties(such as pore size and surface properties)in response to environmental signals such as temperature,pH,light,magnetic field,electric field,redox and specific ions/molecules.Such smart membranes show great prospects in biomedical applications ranging from controlled drug release to bioseparation and tissue engineering.In this review,three controlled release models realized by different designed smart membranes are emphatically introduced,and then smart membranes for biological separation and controlled cell culture are introduced and discussed respectively.At last,the existing challenges of smart membranes for biomedical applications are briefly summarized,and future research topics are suggested.

An asymmetric membrane of polyimide 6FDA-BDAF and its pervaporation desulfurization for n-heptane/thiophene mixtures

Polyimide（PI） is a type of important membrane material. A soluble polymer was synthesized from 4,4′-（hexafluoroisopropylidene） diphthalic anhydride（6FDA） and 2,2-bis[4-（4-aminophenoxy） phenyl] hexafluoropropane（BDAF） by the two-step polymerization method. The polymer was proved to be polyimide 6FDA-BDAF by the Fourier transform infrared（FT-IR）, the 1H-NMR and ^（19）F-NMR spectra. An asymmetric membrane was prepared with the synthesized polyimide 6FDA-BDAF, it was porous in the 50 μm height bulk and dense in a 3–5 μm height surface. The membrane was used to separate n-heptane/thiophene mixtures by pervaporation with sulfur（S） contents from 50 to 900 μg g^（–1）. The total flux was enlarged from 7.96 to 37.61 kg m^（–2） h^（–1） with temperature increasing from 50 to 90°C. The membrane＇s enrichments factor for thiophene were about 3.13 and dependent on the experimental conditions. The experimental results demonstrated that polyimide 6FDA-BDAF would be a potential membrane material for desulfurization and controlled release of the S-containing fertilizer.

Graphene-based membranes for molecular and ionic separations in aqueous environments

Graphene-based laminar materials open up to new applications for molecular and ionic separations in aqueous environments due to the atomic thickness, mechanical strength, chemical stability and other fantastic properties.Recent advances on controlling the structure and chemical functionality of graphene-based membranes can potentially lead to new classes of tools for desalination, dehydration, toxicant rejection, specific ionic separation and so on. The recent developments of graphene-based membranes prepared by using a concept to form interlayer space between graphene sheets and creating nanoscale or sub-nanoscale pores in a graphene lattice, together with their mass-transfer mechanisms and potential applications in aqueous environments are reviewed. A summary and outlook is further provided on the opportunities and challenges in this arising field.This article is expected to address the intricate details of mass transport through two distinct graphene-based membranes in aqueous environment and to optimize the fabrication of graphene-based membranes as a fascinating separation system for a wide range of applications.

A new route of fabricating porous polyimide membranes

A novel experimental route to fabricate porous polyimide membranes （PPMs） with ideal air permeability was reported. The polymer solution layer consisting of the corresponding polyamic acid （PAA）, solvent, and dibutyl phthalate （DBP） with a boiling temperature of 340℃ was treated by a simple process. The polymer solution layer was first treated at a lower temperature （about 150℃）, then the received solid membrane was further imidized at a higher temperature （about 270℃）, and finally, DBP was removed from the membrane at a temperature above its boiling temperature. The final asymmetric polyimide membrane with a dense skin layer was obtained. To improve the air permeability of the polyimide membranes, the polymer solution layer was treated between two substrates. And the PPMs with open pores on both sides are fabricated and the air permeability of the films is improved greatly.

Modification of Nylon Membrane Used for Affinity Adsorption

Nylon membrane was modified by binding with polyhydroxyl-containing materials to increase its hydrophilicity and reduce its nonspecific interaction with proteins. The effect of binding hydrophilic materials on amount of ligand bound-Cibacron Blue F3GA (CBF) was investigated. Experimental data showed that the amount of CBF bound can be increased significantly after binding of hydrophilic materials.

Pore-filling Three-dimensionally Ordered Macroporous Polyimide Composite Proton Conducting Membranes

The silica opal templates were prepared from three silica colloids of different diameters of 230 nm, 500 nm and 1.5 mm by a filtration route. The large-scale stable opal template membranes after sintering the deposited SiO2 opal template can be successfully obtained by optimizing the pH value and NaCl concentration in silica colloidal solutions. The three-dimensionally ordered macroporous（3DOM） polyimide membranes without crack were fabricated by reproducing the structure of silica opal template. We prepared the pore-filling composite proton exchange membranes by filling the 3DOM structure with proton conducting organosilane sol. The result indicates that the composite membranes exhibit higher water uptake than pure filling organosilane gel. The proton conductivity increased with the increasing of pore cell in composite membranes.

Recent Advances on the Development of Functional Materials in Microbial Fuel Cells:From Fundamentals to Challenges and Outlooks

Microbial fuel cells(MFCs),as a sustainable and promising technology to solve both environmental pollution and energy shortage,have captured tremendous attention.The conversion efficiency of chemical energy contained in organic waste or wastewater to electricity via microbial metabolism strongly depends on the performance of each functional unit,including the anode,cathode and separator/membrane used in MFCs.Therefore,significant attention has been paid toward developing advanced functional materials to enhance the performance of each unit or provide new featured functions.This review paper provides a comprehensive review on recent achievements and advances in the modification and development of functional materials for MFC systems,including 1)the development of functional anode materials for enhanced microbial compatibilities as well as electron transfer capabilities,2)the development of cost-effective separators/membranes such as ion exchange membrane,porous membrane,polymer electrolyte membrane and composite membrane,and 3)the development of functional cathode catalysts to decrease the over-potential and enhance the electrocatalytic efficiency for oxygen reduction reaction in order to substitute the common costly Pt catalyst.The challenges and outlooks of functional materials for MFC applications are also discussed.