Regulation of interlayer channels of graphene oxide nanosheets in ultra-thin Pebax mixed-matrix membranes for CO_(2) capture

For the application of carbon capture by membrane process,it is crucial to develop a highly permeable CO_(2)-selective membrane.In this work,we reported an ultra-thin polyether-block-amide(Pebax)mixedmatrix membranes(MMMs)incorporated by graphene oxide(GO),in which the interlayer channels were regulated to optimize the CO_(2)/N_(2) separation performance.Various membrane preparation conditions were systematically investigated on the influence of the membrane structure and separation performance,including the lateral size of GO nanosheets,GO loading,thermal reduction temperature,and time.The results demonstrated that the precisely regulated interlayer channel of GO nanosheets can rapidly provide CO_(2)-selective transport channels due to the synergetic effects of size sieving and preferential adsorption.The GO/Pebax ultra-thin MMMs exhibited CO_(2)/N_(2) selectivity of 72 and CO_(2) permeance of 400 GPU(1 GPU=106 cm^(3)(STP)·cm^(2)·s^(-1)·cmHg^(-1)),providing a promising candidate for CO_(2) capture.

Recent progress on nanomaterial-based electrochemical dissolved oxygen sensors

Dissolved oxygen(DO)usually refers to the amount of oxygen dissolved in water.In the environment,medicine,and fermentation industries,the DO level needs to be accurate and capable of online monitoring to guide the precise control of water quality,clinical treatment,and microbial metabolism.Compared with other analytical methods,the electrochemical strategy is superior in its fast response,low cost,high sensitivity,and portable device.However,an electrochemical DO sensor faces a trade-off between sensitivity and long-term stability,which strongly limits its practical applications.To solve this problem,various advanced nanomaterials have been proposed to promote detection performance owing to their excellent electrocatalysis,conductivity,and chemical stability.Therefore,in this review,we focus on the recent progress of advanced nanomaterial-based electrochemical DO sensors.Through the comparison of the working principles on the main analysis techniques toward DO,the advantages of the electrochemical method are discussed.Emphasis is placed on recently developed nanomaterials that exhibit special characteristics,including nanostructures and preparation routes,to benefit DO determination.Specifically,we also introduce some interesting research on the configuration design of the electrode and device,which is rarely introduced.Then,the different requirements of the electrochemical DO sensors in different application fields are included to provide brief guidance on the selection of appropriate nanomaterials.Finally,the main challenges are evaluated to propose future development prospects and detection strategies for nanomaterial-based electrochemical sensors.

Solar-assisted two-stage catalytic membrane reactor for coupling CO_(2) splitting with methane oxidation reaction

A two-stage catalytic membrane reactor(CMR)that couples CO_(2) splitting with methane oxidation reactions was constructed based on an oxygen-permeable perovskite asymmetric membrane.The asymmetric membrane comprises a dense SrFe_(0.9)Ta_(0.1)O_(3-σ)(SFT)separation layer and a porous Sr_(0.9)(Fe_(0.9)Ta_(0.1))_(0.9)Cu_(0.1)O_(3-σ)(SFTC)catalytic layer.In thefirst stage reactor,a CO_(2) splitting reaction(CDS:2CO_(2)→2CO+O_(2))occurs at the SFTC catalytic layer.Subsequently,the O_(2) product is selectively extracted through the SFT separation layer to the permeated side for the methane combustion reaction(MCR),which provides an extremely low oxygen partial pressure to enhance the oxygen extraction.In the second stage,a Sr_(0.9)(Fe_(0.9)Ta_(0.1))_(0.9)Ni_(0.1)O_(3-σ)(SFTN)catalyst is employed to reform the products derived from MCR.The two-stage CMR design results in a remarkable 35.4%CO_(2) conversion for CDS at 900℃.The two-stage CMR was extended to a hollowfiber configuration combining with solar irradiation.The solar-assisted two-stage CMR can operate stably for over 50 h with a high hydrogen yield of 18.1 mL min^(-1) cm^(-2).These results provide a novel strategy for reducing CO_(2) emissions,suggesting potential avenues for the design of the high-performance CMRs and catalysts based on perovskite oxides in the future.

Influence of water vapor on the separation of volatile organic compound/nitrogen mixture by polydimethylsiloxane membrane

In the industrial treatment of waste volatile organic compound(VOC)streams by membrane technology,a third impurity,generally,water vapor,coexists in the mixture of VOC and nitrogen or air,and can affect membrane performance and the design of the industrial process.This study focused on the investigation of the effect of water vapor on the separation performance of the separation of VOC/water/nitrogen mixtures by a polydimethylsiloxane(PDMS)membrane.Three types of VOCs:water-miscible ethanol,water-semi-miscible butanol,and water-immiscible cyclohexane,were selected for the study.Different operating parameters including,concentration of the feed VOC,feed temperature,and concentration of the feed water were compared for the separation of binary and ternary VOC/nitrogen mixtures.The interaction between the VOC and water was analyzed to explain the transportation mechanism after analyzing the difference in the membrane performance for the separation of binary and ternary mixtures.The results indicated that the interaction between the VOC(or nitrogen)and water is the key factor affecting membrane performance.Water can promote the permeation of hydrophilic VOC but prevent hydrophobic VOC through the membrane for the separation of ternary VOC/water/nitrogen mixtures.These results will provide fundamental insights for the design of the recovery application process for industrial membrane-based VOCs,and also guidance for the investigation of the separation mechanism in vapor permeation.

Manipulation of confined structure in alcohol-permselective pervaporation membranes

Alcohol-permselectivity pervaporation has been arousing increasingly more attention in bioalcohol production due to the advantages of environmental friendliness, low energy consumption and easy coupling with fermentation process. With the intrinsic feature of larger molecules preferentially permeating and the consequent inferiority in selective diffusion, the development of alcohol-permselective membrane is relatively retarded compared with water-permselective membrane. This review presents the prevalent membrane materials utilized for alcohol-permselective pervaporation and emphatically expatiates the representative and important developments in the past five years from the aspect of tuning confined structure in membranes. In particular, the diverse structure tuning methods are described with the classifications of physical structure and chemical structure. The corresponding structure-performance relationships in alcohol-permselective pervaporation membranes are also analyzed to identify the objective of structure optimization. Furthermore, the tentative perspective on the possible future directions of alcohol-permselective pervaporation membrane is briefly presented.

Design and Fabrication of Ceramic Catalytic Membrane Reactors for Green Chemical Engineering Applications

Catalytic membrane reactors(CMRs),which synergistically carry out separations and reactions,are expected to become a green and sustainable technology in chemical engineering.The use of ceramic membranes in CMRs is being widely considered because it permits reactions and separations to be carried out under harsh conditions in terms of both temperature and the chemical environment.This article presents the two most important types of CMRs:those based on dense mixed-conducting membranes for gas separation,and those based on porous ceramic membranes for heterogeneous catalytic processes.New developments in and innovative uses of both types of CMRs over the last decade are presented,along with an overview of our recent work in this field.Membrane reactor design,fabrication,and applications related to energy and environmental areas are highlighted.First,the configuration of membranes and membrane reactors are introduced for each of type of membrane reactor.Next,taking typical catalytic reactions as model systems,the design and optimization of CMRs are illustrated.Finally,challenges and difficulties in the process of industrializing the two types of CMRs are addressed,and a view of the future is outlined.

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.

Natural gas purification by asymmetric membranes: An overview

Natural gas, as a very important source of energy and chemical feedstock, can be used in place of coal to lower net carbon dioxide emissions.Membrane separation technology is an attractive alternative for natural gas purification where the impurities represented by acid gases(CO_(2) and H_(2)S) as well as inert gases(N_(2)) must be removed to meet the transportation and usage specifications. From the economic benefits viewpoint,asymmetric membranes are required for industrial manufacture and applications. This paper aims to review the latest development of various kinds of asymmetric membranes for natural gas purification, mainly focusing on CO_(2) removal from CH_(4), including H_(2)S and N_(2) separation from CH_(4) as well. According to material types, polymeric, inorganic, mixed-matrix and carbon molecular sieve membranes are introduced. The associated fabrication approaches and transport properties are discussed for each kinds of asymmetric membranes. Towards the practical implementation, an emphasis is placed on hollow fiber asymmetric structure for these polymeric, mixed-matrix and carbon molecular sieve membranes.

Polydimethylsiloxane (PDMS) Composite Membrane Fabricated on the Inner Surface of a Ceramic Hollow Fiber: From Single-Channel to Multi-Channel

The fabrication of a separation layer on the inner surface of a hollow fiber (HF) substrate to form an HF composite membrane offers exciting opportunities for industrial applications, although challenges remain. This work reports on the fabrication of a polydimethylsiloxane (PDMS) composite membrane on the inner surface of a single-channel or multi-channel ceramic HF via a proposed coating/crossflow approach. The nanostructures and transport properties of the PDMS HF composite membranes were optimized by controlling the polymer concentration and coating time. The morphology, surface chemistry, interfacial adhesion, and separation performance of the membranes were characterized by fieldemission scanning electron microscope (FE-SEM), attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, the nano-indentation/scratch technique, and pervaporation (PV) recovery of bio-butanol, respectively. The formation mechanism for the deposition of the PDMS layer onto the inner surface of the ceramic HF was studied in detail. The optimized inner surface of the PDMS/ceramic HF composite membranes with a thin and defect-free separation layer exhibited a high flux of ~1800 gm-2h-1 and an excellent separation factor of 35–38 for 1 wt% n-butanol/water mixtures at 60
C. The facile coating/cross-flow methodology proposed here shows great potential for fabricating inner-surface polymer-coated HFs that have broad applications including membranes, adsorbents, composite materials, and more.

Graphene-based membranes for pervaporation processes

Two-dimensional graphene and its derivatives exhibiting distinct physiochemical properties are intriguing building blocks for researchers from a large variety of scientific fields.Assembling graphene-based materials into membrane layers brings great potentials for high-efficiency membrane processes.Particularly,pervaporation by graphene-based membranes has been intensively studied with respect to the membrane design and preparation.This review aims to provide an overview on the graphene-based membranes for pervaporation processes ranged from fabrication to application.Physical or chemical decoration of graphene-based materials is elaborated regarding their effects on the microstructure and performance.The mass transport of pervaporation through graphene-based membranes is introduced,and relevant mechanisms are described.Furthermore,performances of state-of-the-art graphene-based membranes for different pervaporation applications are summarized.Finally,the perspectives of current challenges and future directions are presented.

Graphene oxide membranes supported on the ceramic hollow fibre for efficient H2 recovery

The special channels and intrinsic defects within GO laminates make it a very potential candidate for gas separation in recent years. Herein, the gas separation performance of GO membranes prepared on the surface of ceramicα-Al_2O_3 hollow fibre was investigated systematically. The microstructures of ceramic hollow fibre supported GO membranes were optimized by adjusting operation conditions. And, the GO membrane fabricated at 30 min exhibited great promising H_2 recovery ability from H_2/CO_2 mixture. At room temperature, the H_2 permeance was over 1.00 × 10^(-7)mol·m^(-2)·s^(-1)·Pa^(-1)for both single gas and binary mixture. The corresponding ideal selectivity and mixture separation factor reached around 15 and 10, respectively. In addition, humility, operation temperature, H_2 concentration in the feed and the reproducibility were also studied in this work.

3D Prussian blue/Pt decorated carbon nanofibers based screen-printed microchips for the ultrasensitive hydroquinone biosensing

Nowadays,water pollution has become more serious,greatly affecting human life and healthy.Electrochemical biosensor,a novel and rapid detection technique,plays an important role in the realtime and trace detection of water pollutants.However,the stability and sensitivity of electrochemical biosensors remain a great challenge for practical detections in real samples to the strong interferences derived from complex components and coagulation effects.In this work,we reported a novel threedimensional architecture of Prussian blue nanoparticles(PBNPs)/Pt nanoparticles(PtNPs)composite film,using 3 D interweaved carbon nanofibers as a supporting matrix,for the construction of screenprinted microchips-based biosensor.PtNPs with diameters of-2.5 nm was highly dispersed on the carbon nanofibers(CNFs)to build a 3 D skeleton nanostructure through a solvothermal reduction.Subsequently,uniform PBNPs were in-situ self-assembled on this skeleton to construct a 3 D architecture of PB/Pt-CNF composite film.Due to the synergistic effects derived from this special feature,the as-prepared hydroquinone(HQ)biosensor chips can synchronously promote both surface area and conductivity to greatly enhance the electrocatalysis from enzymatic reaction.This biosensor has exhibited a high sensitivity of 220.28μA·L·mmol^(-1)·cm^(-2) with an ultrawide linear range from 2.5μmol·L^(-1) to 1.45 mmol·L^(-1) at a low potential of 0.15 V,as well as the satisfactory reproducibility and usage stability.Besides,its accuracy was also verified in the assays of real water samples.It is highly expected that the 3 D PB/Pt-CNF based screen-printed microchips will have wide applications in dynamic monitoring and early warning of analytes in the various practical fields.

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.

Preface to Special Issue of Membranes and Membrane Processes based on Confined Mass Transfer

Membrane separation is playing an increasingly critical role indiverse fields as a cost-efficient and energy-economic technology. Ultra-filtration and microfiltration based on the size-sieving mechanismof macroporous media have been clearly elucidated using classicaltheories of mass transfer. However, membrane processes includingpervaporation, gas separation, ion exchange, nanofiltration, reverseosmosis, etc., mainly involve mass transfer in narrow spaces whosesizes are comparable to the free distances of molecules mobility.

Thermoregulatory molecular sieving in crystals

Sub-nanometer channels for the selective recognition of the components in chemical mixtures from others play a crucial role in the adsorption and membrane separation[1].It remains a grand challenge to separate small molecular pairs with minor size/shape difference owing to the undesirable pore structure.

Graphene oxide membrane for molecular separation:challenges and opportunities

氧化石墨烯作为一种典型二维材料具有单原子层厚度和大量含氧官能团,可作为高性能分离膜的理想构筑单元,已成为近年来的研究热点.通过对氧化石墨烯纳米片的有序组装,可构筑亚纳米尺寸的分子传质通道,对水分子、有机小分子、气体分子具有快速选择性透过效应,在水处理、溶剂纯化和气体分离等膜过程展现出优异的分离性能.本文重点分析了近期氧化石墨烯膜的突破性进展,并指出氧化石墨烯膜用于分子分离过程所面临的机遇与挑战.

Cation-diffusion controlled formation of thin graphene oxide composite membranes for efficient ethanol dehydration

Structural manipulation of graphene oxide (GO) building blocks has been widely researched. Concerning GO membranes for separation applications, the validity and maintenance of their microscopic structures in the chemical environment are pivotal for effective separation at the molecular scale. Cationic interactions with both aromatic rings and oxygenated functional groups of GO make metal ions intriguing for physically and chemically structural reinforcement. By filtrating GO suspension through the substrate loaded with cations, stacking o f GO nanosheets and diffusion of cations steadily evolve simultaneously in an aqueous environment without flocculation. Thus, thin and homogeneous GO membrane is obtained. Divalent and monovalent cations were studied regarding their interactions with GO, and the performance of correspondingly functionalized membranes was evaluated. The divalent cation-stabilized membranes have favorable stability in the separation of water/ethanol. This facile fabrication and functionalization method may also be applicable for structure construction of other two-dimensional materials.

Two-Dimensional-Material Membranes:Manipulating the Transport Pathway for Molecular Separation

CONSPECTUS:The discovery of graphene triggers a new era of two-dimensional(2D)materials,which exhibit great potential in condensed matter physics,chemistry,and materials science.Meanwhile,the booming of 2D materials brings new opportunities for the next generation of high-performance(high permeability,selectivity,and stability)separation membranes.Two-dimensional materials with atomic thinness can serve as new building blocks for fabricating ultrathin membranes possessing the ultimate permeation rate.The plane structure with micrometer lateral dimensions provides an excellent platform for the orderly alignment of the nanosheets.Moreover,the apertures of two-dimensional-material membranes(2DMMs),including the in-plane nanopores and interlayer channels,can contribute to the fast and selective transport of small molecules/ions related to molecular separation.Therefore,the emerging 2D materials with various nanostructures,including graphene oxide(GO),zeolite nanosheets,metal−organic framework(MOF)nanosheets,and transition-metal carbides/carbonitrides(MXene),can be assembled into highperformance membranes.Various assembly methods such as filtration,spin coating,and hot dropping have been employed to fabricate 2DMMs,while the processes for separating small molecules/ions tend to demand higher precision,especially in water desalination and gas separation.The nanostructures of 2DMMs and the physicochemical properties of transport pathway need to be finely tuned to meet the requirement.In addition,the stability of 2DMMs,which is critical to the large-scale implementation,must be taken into consideration as well.In this Account,we discuss our recent progress in manipulating molecular transport pathways in 2DMMs by optimizing the assembly behavior of 2D nanosheets,tuning the microstructure of interlayer channels,and controlling the physicochemical properties of the membrane surface.Assembly methods,including vacuum suction assembly,polymer-induced assembly,and external force-driven assembly,have been proposed to construct ordered laminates for molecular transport.The size and chemical structure of interlayer channels were further tailored by strategies such as nanoparticle intercalation,cationic control,and chemical modification.Interestingly,the manipulation of surface properties of 2DMMs was proven to contribute to fast molecular transport through interlayer channels.Moreover,the issues concerning 2DMMs toward practical applications are discussed with an emphasis on the substrate effect,molecular bridge strategy,and preliminary progress in large-scale fabrication.Finally,we conclude this Account with an overview of the remaining challenges and the new opportunities that will be opened up for 2DMMs in molecular separation.

Efficient CO_2/N_2 separation by mixed matrix membrane with amide functionalized porous coordination polymer filler

Mixed matrix membrane used to selective removal of CO2 was considered as an efficient solution to energy and environmental sustainability. In this study, a MMM that consists of amide functionalized porous coordination polymer filler（MIL-53-NH2） was successfully prepared, which sharply promotes the CO2/N2 selectivity from 44（neat polymeric membrane） to 75. Remarkably, the positive effect of amide group and nanochannel of MIL-53-NH2 filler was illustrated by decreased selectivity of the MMM with formic acid modified MIL-53-NH2 filler（MIL-53-NHCOH）.