Showing papers on "Membrane published in 2022"

Catalytic Membranes and Membrane Reactors

Abstract: Introduction. Catalytic Membrane Separation Processes. Pervaporation Membrane Reactors. Membrane Bioreactors. Modelling of Membrane Reactors. Economic and Technical Feasibility Issues of Membrane Reactor Processes. Conclusions. Index.

Tailored design of nanofiltration membranes for water treatment based on synthesis–property–performance relationships

Abstract: Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

Rational design of mixed-matrix metal-organic framework membranes for molecular separations

Abstract: Conventional separation technologies to separate valuable commodities are energy intensive, consuming 15% of the worldwide energy. Mixed-matrix membranes, combining processable polymers and selective adsorbents, offer the potential to deploy adsorbent distinct separation properties into processable matrix. We report the rational design and construction of a highly efficient, mixed-matrix metal-organic framework membrane based on three interlocked criteria: (i) a fluorinated metal-organic framework, AlFFIVE-1-Ni, as a molecular sieve adsorbent that selectively enhances hydrogen sulfide and carbon dioxide diffusion while excluding methane; (ii) tailoring crystal morphology into nanosheets with maximally exposed (001) facets; and (iii) in-plane alignment of (001) nanosheets in polymer matrix and attainment of [001]-oriented membrane. The membrane demonstrated exceptionally high hydrogen sulfide and carbon dioxide separation from natural gas under practical working conditions. This approach offers great potential to translate other key adsorbents into processable matrix. Description Mixed-matrix membranes using nanosheets Selective adsorbents can show enhanced separation of components from mixed-gas streams, but these materials can often be difficult to fabricate into large-scale, robust membranes. Datta et al. report the synthesis and characterization of a mixed-matrix membrane. They first describe the synthesis of sheets of the metal organic framework (MOF) material AlFFIVE-1-Ni. By using nanosheets instead of the more commonly synthesized MOF nanoparticles, the authors were able to achieve much better alignment, loading fractions up to 60%, and better polymer-MOF compatibility when embedding the MOF nanosheets into a polymer matrix. These mixed-matrix membranes exhibited improved carbon dioxide and methane selectivity relative to many other comparable ones, as well as the ability to remove hydrogen sulfide. —MSL High loading of metal organic framework materials enables efficient upgrading of natural gas by removing carbon dioxide and hydrogen sulfide.

Zr-MOF Nanoflower Sensor and Its Mixed-Matrix Membrane for Highly Sensitive Nitroaromatics Detection

Abstract: A new luminescent metal-organic framework nanoflower material CJLU-1 (Zr6(3-O)4(3-OH)4(OH)6(TCA)2(H2O)6) (H3TCA= tri-carboxylic acids 4,4′,4″-nitrilotribenzoic acid) have been realized for the highly sensitive sensing of nitroaromatic molecules with fast response. CJLU-1 consists...

Anion-Exchange Membrane Water Electrolyzers

Abstract: This Review provides an overview of the emerging concepts of catalysts, membranes, and membrane electrode assemblies (MEAs) for water electrolyzers with anion-exchange membranes (AEMs), also known as zero-gap alkaline water electrolyzers. Much of the recent progress is due to improvements in materials chemistry, MEA designs, and optimized operation conditions. Research on anion-exchange polymers (AEPs) has focused on the cationic head/backbone/side-chain structures and key properties such as ionic conductivity and alkaline stability. Several approaches, such as cross-linking, microphase, and organic/inorganic composites, have been proposed to improve the anion-exchange performance and the chemical and mechanical stability of AEMs. Numerous AEMs now exceed values of 0.1 S/cm (at 60–80 °C), although the stability specifically at temperatures exceeding 60 °C needs further enhancement. The oxygen evolution reaction (OER) is still a limiting factor. An analysis of thin-layer OER data suggests that NiFe-type catalysts have the highest activity. There is debate on the active-site mechanism of the NiFe catalysts, and their long-term stability needs to be understood. Addition of Co to NiFe increases the conductivity of these catalysts. The same analysis for the hydrogen evolution reaction (HER) shows carbon-supported Pt to be dominating, although PtNi alloys and clusters of Ni(OH)2 on Pt show competitive activities. Recent advances in forming and embedding well-dispersed Ru nanoparticles on functionalized high-surface-area carbon supports show promising HER activities. However, the stability of these catalysts under actual AEMWE operating conditions needs to be proven. The field is advancing rapidly but could benefit through the adaptation of new in situ techniques, standardized evaluation protocols for AEMWE conditions, and innovative catalyst-structure designs. Nevertheless, single AEM water electrolyzer cells have been operated for several thousand hours at temperatures and current densities as high as 60 °C and 1 A/cm2, respectively.

Double‐Defense Design of Super‐Anti‐Fouling Membranes for Oil/Water Emulsion Separation

Abstract: Oil fouling threatens the water flux stability of membranes for oil/water separation. Simple hydrophilic modification fights for an opportunity to prevent oil contamination but fails to eliminate severe water flux decline. In essence, a “single‐defense” mechanism is insufficient to build a potent barrier against accumulated cake layer under a filtration environment. This work reports a “double‐defense” design by integrating hydrophilic polymer brushes and hydrogel layer on oil/water separation membranes for desired anti‐oil‐fouling property, where a poly(vinylidene fluoride) porous membrane is first covered by a layer of poly(hydroxyethyl methylacrylate) hydrogel and then controllably grafted with poly(sulfobetaine) brushes. The spatially hierarchical structure establishes a highly covered “double‐defense” barrier for the membrane surface to efficiently repel oil adhesion and the formation of an accumulated cake layer. When separating various surfactant‐stabilized oil‐in‐water emulsions, the permeating flux displays a nearly zero decline throughout the whole filtration period. Most importantly, the permeating flux of the membrane is almost the same when filtrating pure water and filtrating oil‐in‐water emulsions, which is difficult to be achieved by the general membranes, indicating that the membrane has excellent anti‐oil‐fouling property superior to the currently reported membranes.

Fuel cells with an operational range of –20 °C to 200 °C enabled by phosphoric acid-doped intrinsically ultramicroporous membranes

Abstract: Conventional proton exchange membrane fuel cells (PEMFCs) operate within narrow temperature ranges. Typically, they are run at either 80‒90 °C using fully humidified perfluorosulfonic acid membranes, or at 140‒180 °C using non-humidified phosphoric acid (PA)-doped membranes, to avoid water condensation-induced PA leaching. However, the ability to function over a broader range of temperature and humidity could simplify heat and water management, thus reducing costs. Here we present PA-doped intrinsically ultramicroporous membranes constructed from rigid, high free volume, Tröger’s base-derived polymers, which allow operation from −20 to 200 °C. Membranes with an average ultramicropore radius of 3.3 Å show a syphoning effect that allows high retention of PA even under highly humidified conditions and present more than three orders of magnitude higher proton conductivity retention than conventional dense PA-doped polybenzimidazole membranes. The resulting PA-doped PEMFCs display 95% peak power density retention after 150 start-up/shut-down cycles at 15 °C and can accomplish over 100 cycles, even at −20 °C. Most proton exchange membrane fuel cells are designed to operate within a temperature range of a few tens of degrees, but functioning in a broader range of conditions could be advantageous. Here the authors use ultramicroporous, phosphoric acid-doped membranes that allow fuel cell operation from −20 °C to 200 °C.

Hydrogel-based strong and fast actuators by electroosmotic turgor pressure

Abstract: Hydrogels are promising as materials for soft actuators because of qualities such as softness, transparency, and responsiveness to stimuli. However, weak and slow actuations remain challenging as a result of low modulus and osmosis-driven slow water diffusion, respectively. We used turgor pressure and electroosmosis to realize a strong and fast hydrogel-based actuator. A turgor actuator fabricated with a gel confined by a selectively permeable membrane can retain a high osmotic pressure that drives gel swelling; thus, our actuator exerts large stress [0.73 megapascals (MPa) in 96 minutes (min)] with a 1.16 cubic centimeters of hydrogel. With the accelerated water transport caused by electroosmosis, the gel swells rapidly, enhancing the actuation speed (0.79 MPa in 9 min). Our strategies enable a soft hydrogel to break a brick and construct underwater structures within a few minutes. Description Wrap it up Conventional stimuli-responsive hydrogel actuators generally suffer from weak actuation force and slow response speed because of the osmotic-driven actuation mechanism. They are also limited in how much pressure they can endure and will collapse or shatter if pushed too hard. Na et al. significantly increased the actuation stress of a hydrogel wrapping the gel in a relatively stiff but flexible semipermeable membrane, which confined the transverse deformation (see the Perspective by Jiang and Song). This effect is similar to the turgor pressure seen in biological cells. The actuation speed can also be enhanced by adding the electrolyte into the water solution and applying an electric field, which reduces the actuation time from hours to minutes. —MSL A selectively permeable membrane can enhance the strength and actuation speed of a hydrogel actuator.

Fuel cells with an operational range of –20 °C to 200 °C enabled by phosphoric acid-doped intrinsically ultramicroporous membranes

Abstract: Conventional proton exchange membrane fuel cells (PEMFCs) operate within narrow temperature ranges. Typically, they are run at either 80‒90 °C using fully humidified perfluorosulfonic acid membranes, or at 140‒180 °C using non-humidified phosphoric acid (PA)-doped membranes, to avoid water condensation-induced PA leaching. However, the ability to function over a broader range of temperature and humidity could simplify heat and water management, thus reducing costs. Here we present PA-doped intrinsically ultramicroporous membranes constructed from rigid, high free volume, Tröger’s base-derived polymers, which allow operation from −20 to 200 °C. Membranes with an average ultramicropore radius of 3.3 Å show a syphoning effect that allows high retention of PA even under highly humidified conditions and present more than three orders of magnitude higher proton conductivity retention than conventional dense PA-doped polybenzimidazole membranes. The resulting PA-doped PEMFCs display 95% peak power density retention after 150 start-up/shut-down cycles at 15 °C and can accomplish over 100 cycles, even at −20 °C. Most proton exchange membrane fuel cells are designed to operate within a temperature range of a few tens of degrees, but functioning in a broader range of conditions could be advantageous. Here the authors use ultramicroporous, phosphoric acid-doped membranes that allow fuel cell operation from −20 °C to 200 °C.

Recent Progress in Protective Membranes Fabricated via Electrospinning: Advanced Materials, Biomimetic Structures, and Functional Applications

Abstract: Electrospinning is a significant micro/nanofiber processing technology and has been rapidly developing in the past 2 decades. It has several applications, including advanced sensing, intelligent manufacturing, and high-efficiency catalysis. Here, multifunctional protective membranes fabricated via electrospinning in terms of novel material design, construction of novel structures, and various protection requirements in different environments are reviewed. To achieve excellent comprehensive properties, such as, high water vapor transmission, high hydrostatic pressure, optimal mechanical property, and air permeability, combinations of novel materials containing nondegradable/degradable materials and functional structures inspired by nature have been investigated for decades. Currently, research is mainly focused on conventional protective membranes with multifunctional properties, such as, anti-UV, antibacterial, and electromagnetic-shielding functions. However, important aspects, such as, the properties of electrospun monofilaments, development of "green electrospinning solutions" with high solid content, and approaches for enhancing adhesion between hydrophilic and hydrophobic layers are not considered. Based on this systematic review, the development of electrospinning for protective membranes is discussed, the existing gaps in research are discussed, and solutions for the development of technology are proposed. This review will assist in promoting the diversified development of protective membranes and is of great significance for fabricating advanced materials for intelligent protection.

A smart and responsive crystalline porous organic cage membrane with switchable pore apertures for graded molecular sieving

Abstract: Membranes with high selectivity offer an attractive route to molecular separations, where technologies such as distillation and chromatography are energy intensive. However, it remains challenging to fine tune the structure and porosity in membranes, particularly to separate molecules of similar size. Here, we report a process for producing composite membranes that comprise crystalline porous organic cage films fabricated by interfacial synthesis on a polyacrylonitrile support. These membranes exhibit ultrafast solvent permeance and high rejection of organic dyes with molecular weights over 600 g mol-1. The crystalline cage film is dynamic, and its pore aperture can be switched in methanol to generate larger pores that provide increased methanol permeance and higher molecular weight cut-offs (1,400 g mol-1). By varying the water/methanol ratio, the film can be switched between two phases that have different selectivities, such that a single, 'smart' crystalline membrane can perform graded molecular sieving. We exemplify this by separating three organic dyes in a single-stage, single-membrane process.

General synthesis of ultrafine metal oxide/reduced graphene oxide nanocomposites for ultrahigh-flux nanofiltration membrane

Abstract: Abstract Graphene-based membranes have great potential to revolutionize nanofiltration technology, but achieving high solute rejections at high water flux remains extremely challenging. Herein, a family of ultrafine metal oxide/reduced graphene oxide (rGO) nanocomposites are synthesized through a heterogenous nucleation and diffusion-controlled growth process for dye nanofiltration. The synthesis is based on the utilization of oxygen functional groups on GO surface as preferential active sites for heterogeneous nucleation, leading to the formation of sub-3 nm size, monodispersing as well as high-density loading of metal oxide nanoparticles. The anchored ultrafine nanoparticles could inhibit the wrinkling of the rGO nanosheet, forming highly stable colloidal solutions for the solution processing fabrication of nanofiltration membranes. By functioning as pillars, the nanoparticles remarkably increase both vertical interlayer spacing and lateral tortuous paths of the rGO membranes, offering a water permeability of 225 L m −2 h −1 bar −1 and selectivity up to 98% in the size-exclusion separation of methyl blue.