Dual‐Layer Superamphiphobic/Superhydrophobic‐Oleophilic Nanofibrous Membranes with Unidirectional Oil‐Transport Ability and Strengthened Oil–Water Separation Performance

Thin porous membranes with unidirectional oil‐transport capacity offer great opportunities for intelligent manipulation of oil fluids and development of advanced membrane technologies. However, directional oil‐transport membranes and their unique membrane properties have seldom been reported in research literature. Here, it is proven that a dual‐layer nanofibrous membrane comprising a layer of superamphiphobic nanofibers and a layer of superhydrophobic oleophilic nanofibers has an unexpected directional oil‐transport ability, but is highly superhydrophobic to liquid water. This novel fibrous membrane is prepared by a layered electrospinning technique using poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP), PVDP‐HFP containing well‐dispersed FD‐POSS (fluorinated decyl polyhedral oligomeric silsesquioxanes), and FAS (fluorinated alkyl silane) as materials. The directional oil‐transport is selective only to oil fluids with a surface tension in the range of 23.8–34.0 mN m^–1. By using a mixture of diesel and water, it is further proven that this dual‐layer nanofibrous membrane has a higher diesel–water separation ability than the single‐layer nanofiber membranes. This novel nanofibrous membrane and the incredible oil‐transport ability may lead to the development of intelligent membrane materials and advanced oil–water separation technologies for diverse applications in daily life and industry.     

Template‐Free,Surfactant‐Mediated Orientation of Self‐Assembled Supercrystals of Metal–Organic Framework Particles

Mesoscale self‐assembly of particles into supercrystals is important for the design of functional materials such as photonic and plasmonic crystals. However, while much progress has been made in self‐assembling supercrystals adopting diverse lattices and using different types of particles, controlling their growth orientation on surfaces has received limited success. Most of the latter orientation control has been achieved via templating methods in which lithographic processes are used to form a patterned surface that acts as a template for particle assembly. Herein, a template‐free method to self‐assemble (111)‐, (100)‐, and (110)‐oriented face‐centered cubic supercrystals of the metal–organic framework ZIF‐8 particles by adjusting the amount of surfactant (cetyltrimethylammonium bromide) used is described. It is shown that these supercrystals behave as photonic crystals whose properties depend on their growth orientation. This control on the orientation of the supercrystals dictates the orientation of the composing porous particles that might ultimately facilitate pore orientation on surfaces for designing membranes and sensors.     

Photothermal‐Responsive Microporous Nanosheets Confined Ionic Liquid for Efficient CO2 Separation

2D materials hold promising potential for novel gas separation. However, a lack of in‐plane pores and the randomly stacked interplane channels of these membranes still hinder their separation performance. In this work, ferrocene based‐MOFs (Zr‐Fc MOF) nanosheets, which contain abundant of in‐plane micropores, are synthesized as porous supports to fabricate Zr‐Fc MOF supported ionic liquid membrane (Zr‐Fc‐SILM) for highly efficient CO₂ separation. The micropores of Zr‐Fc MOF nanosheets not only provide extra paths for CO₂ transportation, and thus increase its permeance up to 145.15 GPU, but also endow the Zr‐Fc‐SILM with high selectivity (216.9) of CO₂/N₂ through the nanoconfinement effect, which is almost ten times higher than common porous polymer SILM. Furthermore, based on the photothermal‐responsive properties of Zr‐Fc MOF, the performance is further enhanced (35%) by light irradiation through a photothermal heating process. This provides a brand new way to design light facilitating gas separation membranes.     

Wet‐Chemical Synthesis of Hollow Red‐Phosphorus Nanospheres with Porous Shells as Anodes for High‐Performance Lithium‐Ion and Sodium‐Ion Batteries

Large‐volume‐expansion‐induced material pulverization severely limits the electrochemical performance of red phosphorous (P) for energy‐storage applications. Hollow nanospheres with porous shells are recognized as an ideal structure to resolve these issues. However, a chemical synthetic approach for preparing nanostructured red P is always of great challenge and hollow nanosphere structures of red P have not yet been fabricated. Herein, a wet solvothermal method to successfully fabricate hollow P nanospheres (HPNs) with porous shells via a gas‐bubble‐directed formation mechanism is developed. More importantly, due to the merits of the porous and hollow structures, these HPNs reveal the highest capacities (based on the weight of electrode materials) of 1285.7 mA h g^?1 for lithium‐ion batteries and 1364.7 mA h g^?1 for sodium‐ion batteries at 0.2 C, and excellent long‐cycling performance.     

Ultrathin Dual‐Scale Nano‐ and Microporous Membranes for Vascular Transmigration Models

Selective cellular transmigration across the microvascular endothelium regulates innate and adaptive immune responses, stem cell localization, and cancer cell metastasis. Integration of traditional microporous membranes into microfluidic vascular models permits the rapid assay of transmigration events but suffers from poor reproduction of the cell permeable basement membrane. Current microporous membranes in these systems have large nonporous regions between micropores that inhibit cell communication and nutrient exchange on the basolateral surface reducing their physiological relevance. Here, the use of 100 nm thick continuously nanoporous silicon nitride membranes as a base substrate for lithographic fabrication of 3 µm pores is presented, resulting in a highly porous (≈30%), dual‐scale nano‐ and microporous membrane for use in an improved vascular transmigration model. Ultrathin membranes are patterned using a precision laser writer for cost‐effective, rapid micropore design iterations. The optically transparent dual‐scale membranes enable complete observation of leukocyte egress across a variety of pore densities. A maximal density of ≈14 micropores per cell is discovered beyond which cell–substrate interactions are compromised giving rise to endothelial cell losses under flow. Addition of a subluminal extracellular matrix rescues cell adhesion, allowing for the creation of shear‐primed endothelial barrier models on nearly 30% continuously porous substrates.     

Atom‐by‐Atom Fabrication of Monolayer Molybdenum Membranes

Fabrication of materials in the monolayer regime to acquire fascinating physical properties has attracted enormous interest during the past decade, and remarkable success has been achieved for layered materials adopting weak interlayer van der Waals forces. However, the fabrication of monolayer metal membranes possessing strong intralayer bonding remains elusive. Here, suspended monolayer Mo membranes are fabricated from monolayer MoSe₂ films via selective electron beam (e‐beam) ionization of Se atoms by scanning transmission electron microscopy (STEM). The nucleation and subsequent growth of the Mo membranes are triggered by the formation and aggregation of Se vacancies as seen by atomic resolution sequential STEM imaging. Various novel structural defects and intriguing self‐healing characteristics are unveiled during the growth. In addition, the monolayer Mo membrane is highly robust under the e‐beam irradiation. It is likely that other metal membranes can be fabricated in a similar manner, and these pure metal‐based 2D materials add to the diversity of 2D materials and introduce profound novel physical properties.     

Intrinsic Carbon‐Defect‐Driven Electrocatalytic Reduction of Carbon Dioxide

Heteroatom‐doped carbon catalysts are currently attracting enormous attention due to their excellent performance for the electrocatalytic carbon dioxide reduction reaction (ECRR). However, the origin of the high catalytic activities of doped‐carbon materials remains obscure with the role of intrinsic carbon defects in promoting the ECRR receiving little attention despite the abundance of carbon defects in all carbon‐based catalytic materials. Herein, a positive correlation is reported between the ECRR performance of carbon‐based catalysts and the content of intrinsic carbon defects contained within these catalysts. Further, it is demonstrated that defective porous carbon catalysts containing no active heteroatom dopants also show excellent catalytic performance for ECRR. C K‐edge near edge X‐ray absorption fine structure measurements and density functional theory calculations reveal that sp² defects (octagonal and pentagonal) rather than edge defects are key to the excellent ECRR activity of the defective porous carbon catalysts. This work thus makes an important contribution to the understanding of the origin of the ECRR activity of carbon‐based catalysts, with heteroatom doping perhaps being less important than previously envisaged for achieving a high ECRR performance.     

Controlling Ion‐Transport Selectivity in Gold Nanotubule Membranes

We have developed a new class of synthetic membranes that consist of a porous polymeric support. This support contains an ensemble of gold nanotubules that span the complete thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls, and tubules that have inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. We review in this paper the ion‐transport properties of these Au nanotubule membranes. We will show that these membranes can be cation‐permselective or anion‐permselective, and that the permselectivity can be reversibly switched between these two states. Ion permselectivity can be introduced by two different routes. The first entails chemisorption of an ionizable thiol, e.g., a carboxylated or ammonium‐containing thiol to the Au tubule walls. If the thiol contains both of these functionalities (e.g., the amino acid cysteine), the permselectivity can be reversibly switched by varying the pH of the contacting solution phase. Ion permselectivity can also be introduced by potentiostatically charging the membrane in an electrolyte solution. By applying excess negative charge, cation permselective membranes are obtained, and excess positive charge yields anion permselective membranes. In this case the permselectivity can be reversibly switched by changing the potential applied to the membrane.     

Multiscale analysis method for thermo‐mechanical performance of periodic porous materials with interior surface radiation

This study develops a novel multiscale analysis method to predict thermo‐mechanical performance of periodic porous materials with interior surface radiation. In these materials, thermal radiation effect at microscale has an important impact on the macroscopic temperature and stress field, which is our particular interest in this paper. Firstly, the multiscale asymptotic expansions for computing the dynamic thermo‐mechanical coupling problem, which considers the mutual interaction between temperature and displacement field, are given successively. Then, the corresponding numerical algorithm based on the finite element‐difference method is brought forward in details. Finally, some numerical results are presented to verify the validity and relevancy of the proposed method by comparing it with a direct finite element analysis with detailed numerical models. The comparison shows that the new method is effective and valid for predicting the thermo‐mechanical performance and can capture the microstructure behavior of periodic porous materials exactly.s Copyright © 2015 John Wiley & Sons, Ltd.     

Herstellung von hochporösen,endkonturnahen Titan‐Formkörpern für biomedizinische Anwendungen

Near‐net‐shape manufacturing of highly porous titanium parts for biomedical applications The production of highly porous titanium parts is attractive for biomedical applications. Preferrentially, these parts are produced by powdermetallurgical means using suitable spacer materials. Porosities up to 75 % and well defined pore sizes in the range of 0.1 to 2.0 mm are achieved adjusting the amount and the particle size of the spacer material. Up to now, near‐net‐shape manufacturing of highly porous parts was hindered by the plastic deformation of the sintered network during machining leading to a partial or complete closing of the open porosity. A new manufacturing route is presented, where the shaping is already done in the unsintered state starting from pressed compacts. The stability of the compacts was found to be sufficient to machine the compacts without additional binders. The manufacturing route was successfully applied to the prototype of an acetabular cup. Additionally, some investigations are presented characterizing the highly porous titanium.     

Multiscale Design of Graphyne‐Based Materials for High‐Performance Separation Membranes

By varying the number of acetylenic linkages connecting aromatic rings, a new family of atomically thin graph‐n‐yne materials can be designed and synthesized. Generating immense scientific interest due to its structural diversity and excellent physical properties, graph‐n‐yne has opened new avenues toward numerous promising engineering applications, especially for separation membranes with precise pore sizes. Having these tunable pore sizes in combination with their excellent mechanical strength to withstand high pressures, free‐standing graph‐n‐yne is theoretically posited to be an outstanding membrane material for separating or purifying mixtures of either gases or liquids, rivaling or even dramatically exceeding the capabilities of current, state‐of‐art separation membranes. Computational modeling and simulations play an integral role in the bottom‐up design and characterization of these graph‐n‐yne materials. Thus, here, the state of the art in modeling α‐, β‐, γ‐, δ‐, and 6,6,12‐graphyne nanosheets for synthesizing graph‐2‐yne materials and 3D architectures thereof is discussed. Different synthesis methods are described and a broad overview of computational characterizations of graph‐n‐yne's electrical, chemical, and thermal properties is provided. Furthermore, a series of in‐depth computational studies that delve into the specifics of graph‐n‐yne's mechanical strength and porosity, which confer superior performance for separation and desalination membranes, are reviewed.     

Stress‐Dependent Elastic Properties of Porous Microcracked Ceramics

Although ceramics are considered linear elastic materials, we have observed a non‐linear pseudo‐elastic behavior in porous cellular microcracked ceramics such as β‐eucryptite. This is attributed to the evolution of microstructure in these materials. This behavior is particularly different from that of non‐microcracked ceramics such as silicon carbide. It is shown that in microcracked materials two processes, namely stiffening and softening, always compete when a compressive external load is applied. The first regime is attributed to microcrack closure, and the second to microcracks opening, i.e. to a damage introduced by the applied stress. On the other hand rather a continuous damage is observed in the non‐microcracked case. A comparison has been done between the microscopic (as measured by neutron diffraction) and the macroscopic stress‐strain response. Also, it has been found that at constant load a significant strain relaxation occurs, which has two timescales, possibly driven by the two phenomena quoted above. Indeed, no such relaxation is observed for non‐microcracked SiC. Implications of these findings are discussed.     

Self‐Assembly of Graphene Oxide at Interfaces

Due to its amphiphilic property, graphene oxide (GO) can achieve a variety of nanostructures with different morphologies (for example membranes, hydrogel, crumpled particles, hollow spheres, sack‐cargo particles, Pickering emulsions, and so on) by self‐assembly. The self‐assembly is mostly derived from the self‐concentration of GO sheets at various interfaces, including liquid‐air, liquid‐liquid and liquid‐solid interfaces. This paper gives a comprehensive review of these assembly phenomena of GO at the three types of interfaces, the derived interfacial self‐assembly techniques, and the as‐obtained assembled materials and their properties. The interfacial self‐assembly of GO, enabled by its fantastic features including the amphiphilicity, the negatively charged nature, abundant oxygen‐containing groups and two‐dimensional flexibility, is highlighted as an easy and well‐controlled strategy for the design and preparation of functionalized carbon materials, and the use of self‐assembly for uniform hybridization is addressed for preparing hybrid carbon materials with various functions. A number of new exciting and potential applications are also presented for the assembled GO‐based materials. This contribution concludes with some personal perspectives on future challenges before interfacial self‐assembly may become a major strategy for the application‐targeted design and preparation of functionalized carbon materials.     

Ultrafiltration Membranes with Structure‐Optimized Graphene‐Oxide Coatings for Antifouling Oil/Water Separation

Fouling of ultrafiltration (UF) membranes in oil/water separation is a long‐standing issue and a major economic barrier to their use in a broad range of applications. Currently reported membranes typically show severe fouling, resulting from the strong oil adhesion on the membrane surface and/or oil penetration inside the membranes. This greatly degrades their performance and shortens service lifetime. Here, the use of graphene oxide (GO) as a novel coating material for the fabrication of fully recoverable, UF membranes with desired hierarchical surface roughness is accomplished by a facile vacuum filtration method for antifouling oil/water separation. The combination of ultrathin, “water‐locking” GO coatings with the optimized hierarchical surface roughness, provided by the inherent roughness of the porous supports and the corrugation of the GO coatings, minimizes underwater oil adhesion on the membrane surface. Cyclic membrane performance evaluation tests revealed approximately 100% membrane recovery by facile surface water flushing, establishing their excellent easy‐to‐recover capability. The novel GO functional coatings with optimized hierarchical structures may have broad applications in oil‐polluted environments.     

A discontinuous Galerkin method with plane waves for sound‐absorbing materials

Poro‐elastic materials are commonly used for passive control of noise and vibration and are key to reducing noise emissions in many engineering applications, including the aerospace, automotive and energy industries. More efficient computational models are required to further optimise the use of such materials. In this paper, we present a discontinuous Galerkin method (DGM) with plane waves for poro‐elastic materials using the Biot theory solved in the frequency domain. This approach offers significant gains in computational efficiency and is simple to implement (costly numerical quadratures of highly oscillatory integrals are not needed). It is shown that the Biot equations can be easily cast as a set of conservation equations suitable for the formulation of the wave‐based DGM. A key contribution is a general formulation of boundary conditions as well as coupling conditions between different propagation media. This is particularly important when modelling porous materials as they are generally coupled with other media, such as the surround fluid or an elastic structure. The validation of the method is described first for a simple wave propagating through a porous material, and then for the scattering of an acoustic wave by a porous cylinder. The accuracy, conditioning and computational cost of the method are assessed, and comparison with the standard finite element method is included. It is found that the benefits of the wave‐based DGM are fully realised for the Biot equations and that the numerical model is able to accurately capture both the oscillations and the rapid attenuation of the waves in the porous material. Copyright © 2015 John Wiley & Sons, Ltd.     

Micro‐Macroporous Composite Materials – Preparation Techniques and Selected Applications: A Review

Pores, on several orders of magnitude in size, control the properties of a solid material to a large extent. This is just as true for materials containing pores in the sub‐nanometer range like zeolites as for cellular foam structures with pores of several millimeters in size. All these porous materials have their distinct potential application ranging from heterogeneous catalysis to metal melt filtration. In many cases, the (hierarchical) combination of pores with different size regimes can improve the performance of the respective porous material or can lead to entirely new properties and applications. This review addresses the preparation and properties of microporous‐macroporous composite materials based on cellular foam supports (ceramic, metal, polymer) with a coating of a microporous compound (zeolite, zeotype framework, metal‐organic framework). The manufacturing of these materials can either be performed by dispersion‐based techniques, where the microporous coating is applied from a dispersion onto the cellular support (ex situ), or in situ by crystallization of the microporous compound directly onto the struts of the foam structure. In both cases, the general procedure can be modified by a pretreatment of the cellular support in order to improve the coating layer adherence, the overall amount of deposited material, or to control of the crystal morphology of the microporous compound.

     

Twinned Growth of Metal‐Free,Triazine‐Based Photocatalyst Films as Mixed‐Dimensional (2D/3D) van der Waals Heterostructures

Design and synthesis of ordered, metal‐free layered materials is intrinsically difficult due to the limitations of vapor deposition processes that are used in their making. Mixed‐dimensional (2D/3D) metal‐free van der Waals (vdW) heterostructures based on triazine (C₃N₃) linkers grow as large area, transparent yellow‐orange membranes on copper surfaces from solution. The membranes have an indirect band gap (E _g,opt = 1.91 eV, E _g,elec = 1.84 eV) and are moderately porous (124 m² g^?1). The material consists of a crystalline 2D phase that is fully sp² hybridized and provides structural stability, and an amorphous, porous phase with mixed sp²–sp hybridization. Interestingly, this 2D/3D vdW heterostructure grows in a twinned mechanism from a one‐pot reaction mixture: unprecedented for metal‐free frameworks and a direct consequence of on‐catalyst synthesis. Thanks to the efficient type I heterojunction, electron transfer processes are fundamentally improved and hence, the material is capable of metal‐free, light‐induced hydrogen evolution from water without the need for a noble metal cocatalyst (34 µmol h^?1 g^?1 without Pt). The results highlight that twinned growth mechanisms are observed in the realm of “wet” chemistry, and that they can be used to fabricate otherwise challenging 2D/3D vdW heterostructures with composite properties.     

Programmed Synthesis of Freestanding Graphene Nanomembrane Arrays

Freestanding graphene membranes are unique materials. The combination of atomically thin dimensions, remarkable mechanical robustness, and chemical stability make porous and non‐porous graphene membranes attractive for water purification and various sensing applications. Nanopores in graphene and other 2D materials have been identified as promising devices for next‐generation DNA sequencing based on readout of either transverse DNA base‐gated current or through‐pore ion current. While several ground breaking studies of graphene‐based nanopores for DNA analysis have been reported, all methods to date require a physical transfer of the graphene from its source of production onto an aperture support. The transfer process is slow and often leads to tears in the graphene that render many devices useless for nanopore measurements. In this work, we report a novel scalable approach for site‐directed fabrication of pinhole‐free graphene nanomembranes. Our approach yields high quality few‐layer graphene nanomembranes produced in less than a day using a few steps that do not involve transfer. We highlight the functionality of these graphene devices by measuring DNA translocation through electron‐beam fabricated nanopores in such membranes.     

Plasma Treatment for Nitrogen‐Doped 3D Graphene Framework by a Conductive Matrix with Sulfur for High‐Performance Li–S Batteries

Carbon materials have received considerable attention as host cathode materials for sulfur in lithium–sulfur batteries; N‐doped carbon materials show particularly high electrocatalytic activity. Efforts are made to synthesize N‐doped carbon materials by introducing nitrogen‐rich sources followed by sintering or hydrothermal processes. In the present work, an in situ hollow cathode discharge plasma treatment method is used to prepare 3D porous frameworks based on N‐doped graphene as a potential conductive matrix material. The resulting N‐doped graphene is used to prepare a 3D porous framework with a S content of 90 wt% as a cathode in lithium–sulfur cells, which delivers a specific discharge capacity of 1186 mAh g^?1 at 0.1 C, a coulombic efficiency of 96% after 200 cycles, and a capacity retention of 578 mAh g^?1 at 1.0 C after 1000 cycles. The performance is attributed to the flexible 3D structure and clustering of pyridinic N‐dopants in graphene. The N‐doped graphene shows high electrochemical performance and the flexible 3D porous stable structure accommodates the considerable volume change of the active material during lithium insertion and extraction processes, improving the long‐term electrochemical performance.     

N‐Doped Carbon Nanofibers with Interweaved Nanochannels for High‐Performance Sodium‐Ion Storage

Although graphite materials have been applied as commercial anodes in lithium‐ion batteries (LIBs), there still remain abundant spaces in the development of carbon‐based anode materials for sodium‐ion batteries (SIBs). Herein, an electrospinning route is reported to fabricate nitrogen‐doped carbon nanofibers with interweaved nanochannels (NCNFs‐IWNC) that contain robust interconnected 1D porous channels, produced by removal of a Te nanowire template that is coelectrospun within carbon nanofibers during the electrospinning process. The NCNFs‐IWNC features favorable properties, including a conductive 1D interconnected porous structure, a large specific surface area, expanded interlayer graphite‐like spacing, enriched N‐doped defects and active sites, toward rapid access and transport of electrolyte and electron/sodium ions. Systematic electrochemical studies indicate that the NCNFs‐IWNC exhibits an impressively high rate capability, delivering a capacity of 148 mA h g^?1 at current density of as high as 10 A g^?1, and has an attractively stable performance over 5000 cycles. The practical application of the as‐designed NCNFs‐IWNC for a full SIBs cell is further verified by coupling the NCNFs‐IWNC anode with a FeFe(CN)₆ cathode, which displays a desirable cycle performance, maintaining acapacity of 97 mA h g^?1 over 100 cycles.