Preparation of porous materials with ordered hole structure

Mechanical and thermal characterizations of nanoporous two-dimensional boron nitride membranes

Hexagonal boron nitride (h-BN) is a promising 2D material due to its outstanding mechanical and thermal properties. In the present study, we use molecular dynamics simulations to investigate the influence of porosity and temperature on the mechanical characteristics of h-BN based on uniaxial and biaxial tensions. Meanwhile, the progression of the microstructure of h-BN up to fracture is studied in order to clarify its fractures mechanism during the tension process. Our results reveal that depending on the porosity and tensile direction, the phase transition occurs more or less. The strength, and Young's modulus of h-BN membranes reduce as increasing porosity. Due to the presence of the pores, the most substantial stresses will be centred around the pores site in the tensile test. Then the fracture starts on the pore edge and spreads preferentially along the zigzag direction of h-BN. Furthermore, fracture strain, strength, and Young's modulus decrease when the temperature rises. In addition, the non-equilibrium molecular dynamics (NEMD) simulations are performed to investigate the influence of various porosities and temperatures on the thermal conductivity of h-BN membranes. The results reveal that the thermal conductivity is greatly reduced by nanoporous. The higher the porosity, the lower the thermal conductivity. The vibration density of states of h-BN membranes is calculated; the result suggests that the defects might reduce the phonon mean free path because of the high collision of the phonons. These alterations represent the scattering influence of defects on phonons, which reduces phonon life and considerably lowers thermal conductivity. Moreover, the findings also proved that as temperature increases, the intrinsic thermal conductivity of h-BN decreases. The thermal conductivity and mechanical properties of the pristine h-BN thin film are interestingly equivalent in the zigzag and armchair orientations.

Fabrication of porous polymer coating layers with selective wettability on filter papers via the breath figure method and their applications in oil/water separation

A comb-like amphiphilic polymer (PBTF), composed of hydrophobic backbones and hydrophilic side chains, was employed to grow honeycomb coating layers in situ on a filter paper via directly casting a polymer solution and by the subsequent dynamic breath figure (BF) method. Through regulating the hydrophilic polymer side chain density and the solution concentration, a continuous honeycomb coating layer contouring to the filter paper surface profile, in addition to possessing a water contact angle (WCA) as high as 146°, was successfully fabricated. The present study also finds that increasing the hydrophilic side chain density will turn PBTF into a surfactant-like polymer, and thus, endow the PBTF solution with the capacity of numerous micro-nano-sized water droplets, rather than simply stabilizing the ordered water droplet arrays on the surface of the solution. With vast nano-sized water droplets in it, the once transparent PBTF solution changed into a translucent nano-emulsion, which demonstrates a strong Tyndall effect. While casting such nano-emulsion on a filter paper and then subjecting to the BF process, the polymeric solute takes both nano-emulsion intrinsic nano-sized water droplets and solvent evaporation-induced water droplets as templates and self-assembles into a bird-nest-like three-dimensional porous microstructure, which possesses micro-nano-sized communicating pores. By regulating the water content in the nano-emulsion, the bird-nest-like structure can be uniformly formed on the surface of the filter paper, which revealed a WCA of 152°. The coated filter papers possess selective wettability, and meanwhile, maintain the inherent permeability of the substrates, which therefore can be directly utilized as oil/water separation materials.

Site-Selective Wettability Control of Honeycomb Films by UV-O3-Assisted Sol-Gel Coating

Wettability control of porous materials is significant in lateral flow immunoassay, microfluidic systems, microdroplet manipulation, and so on. In this report, formation of metal oxide layers on self-organized polymer honeycomb films to control surface wettability by simple sol-gel coating and UV-O₃ treatment was demonstrated. By the combination of bottom-up and top-down processes, silica thin layers can be formed by retaining their original three-dimensional honeycomb structures. Furthermore, photopatterning of metal oxides on honeycomb films can be achieved by UV irradiation through photomasks. Site-selective wettability control of honeycomb films was realized by patterning silica layers on the surface of the film.

MIL-100(Fe) and its derivatives: from synthesis to application for wastewater decontamination

MIL-100(Fe), an environmental-friendly and water-stable metal-organic framework (MOF), has caught increasing research and application attention in the recent decade. Thanks to its mesoporous structure and eximious surface area, MIL-100(Fe) has been utilized as precursors for synthesizing various porous materials under high thermolysis temperature, which makes the derivatives of MIL-100(Fe) pretty promising candidates for the decontamination of wastewater. Herein, this review systematically summarizes the versatile synthetic methods and conditions for optimizing the properties of MIL-100(Fe) and its derivatives. Then, diverse environmental applications (i.e., adsorption, photocatalysis, and Fenton-like reaction) of MIL-100(Fe) and its derivatives and the corresponding removal mechanisms are detailed in the discussion. Finally, existing knowledge gaps related to fabrications and applications are discussed to close and promote the future development of MIL-100(Fe) and its derivatives toward environmental applications. Graphical abstract.

Honeycomb-like porous chitosan films prepared via phase transition of poly(N-isopropylacrylamide) during water evaporation under ambient conditions

Honeycomb-like porous chitosan (CS) films are attractive tools for developing functional materials for filters, catalyses, adsorbents, biomaterials, etc. A simple method for fabricating honeycomb-like porous CS films without special reagents, facilities, and techniques would make them accessible. Here we introduce an easily available method for fabricating honeycomb-like CS films without a strong acid/base, toxic reagents, or special facilities/techniques. An aqueous solution containing CS and poly(N-isopropylacrylamide) (PNIPAm) was allowed to stand at 25 °C to evaporate water. After 3 days, CS–PNIPAm composite films with homogenously phase-separated PNIPAm particles were obtained. The PNIPAm particles were removed by immersion in methanol, and the resulting films dried under reduced pressure to become honeycomb-like porous CS films. The pore size could be varied in the range of 0.5–3.0 μm by altering the CS concentration and the molecular weight of CS where the pore size was reduced under conditions with stronger interaction between CS molecules. We reveal that the key to success with this system is the decrease of lower critical solution temperature (LCST) of PNIPAm with water evaporation. In addition, we confirmed the removed PNIPAm was recyclable in this system. Furthermore, we found this method was also applicable to alginate. The proposed facile method for fabricating honeycomb-like porous polymeric films could provide various functional porous materials.

A simple method for fabricating honeycomb-like porous chitosan films without special reagents, facilities, and techniques was achieved by using poly(N-isopropylacrylamide).

Nanowire Assemblies for Flexible Electronic Devices: Recent Advances and Perspectives

The fabrication of nanowire (NW)-based flexible electronics including wearable energy storage devices, flexible displays, electrical sensors, and health monitors has received great attention both in fundamental research and market requirements in our daily lives. Other than a disordered state after synthesis, NWs with designed and hierarchical structures would not only optimize the intrinsic performance, but also create new physical and chemical properties, and integration of individual NWs into well-defined structures over large areas is one of the most promising strategies to optimize the performance of NW-based flexible electronics. Here, the recent developments and achievements made in the field of flexible electronics composed of integrated NW structures are presented. The different assembly strategies for the construction of 1D, 2D, and 3D NW assemblies, especially the NW coassembly process for 2D NW assemblies, are comprehensively discussed. The improvements of different NW assemblies on flexible electronics structure and performance are described in detail to elucidate the advantages of well-defined NW assemblies. Finally, a short summary and outlook for future challenges and perspectives in this field are presented.

Adsorption on Nanopores of Different Cross Sections Made by Electron Beam Nanolithography

Adsorption on nanoporous matrices is characterized by a pronounced hysteresis loop in the adsorption isotherm, when the substrate is loaded and unloaded with adsorbate, the origin of which is a matter of immense debate in the literature. In this work, we report a study of argon adsorption at 85 K on nonconnecting nanopores with one end closed to the surrounding where the effects of different pore cross sections fabricated by electron beam lithography (EBL) are investigated. A polymethylmethacrylate (PMMA) resist is deposited on the electrodes of a sensitive quartz crystal microbalance without degradation of the resonance quality factor or the long-term and short-term stabilities of the device even at cryogenic temperatures. Four different pores' cross sections: circular, square, rectangular, and triangular, are produced from EBL, and the isotherms for these pore shapes exhibit pronounced hysteresis loops whose adsorption and desorption branches are nearly vertical and have almost the same slopes. No difference is observed in the hysteresis loops of the isotherms for the pores with triangular and square cross sections, whereas the hysteresis loop for the pore with circular cross sections is much narrower, suggesting that they are more regular than the other pores. All of these observations suggest that the hysteresis behavior resulted mainly from microscopic geometric irregularities present in these porous matrices.

One step fabrication of mesh-reinforced hierarchic perforated microporous honeycomb films with tunable filtering property

Highly ordered porous films whose pore size ranges from submicron to micron scale have always been an extensive area of research due to their broad range of application to photonic crystals, cell culturing scaffolds, filtration and separation membranes, just to name a few. However, the fragile nature of such a functional porous film has hindered its implementation to advanced uses. Inspired by the hierarchic structure in nature which offers both robustness and functionality, we created in a single fabrication step a mesh-reinforced hierarchic perforated honeycomb film with highly ordered micron pores using the breath figure method. By using the elastomer 1,2-polybutadiene as the material for the film in the combination of the mesh grid, the pore size of the obtained film can be tuned upon stretching. Tubular structures made from the mesh-reinforced hierarchic perforated porous honeycomb film with tunable pore size have been demonstrated.

Assembly of Ultrathin Gold Nanowires into Honeycomb Macroporous Pattern Films with High Transparency and Conductivity

Because of its promising properties, honeycomb macroporous pattern (HMP) film has attracted increasing attention. It has been realized in many artificial nanomaterials, but the formation of these HMPs was attributed to templates or polymer/supermolecule/surfactant assistant assembly. Pure metal HMP film has been difficult to produce using a convenient colloidal template-free method. In this report, a unique template-free approach for preparation of Au HMP film with high transparency and conductivity is presented. Ultrathin Au nanowires, considered a linear polymer analogue, are directly assembled into HMP film on various substrates using a traditional static breath figure method. Subsequent chemical cross-linking and oxygen plasma treatment greatly enhance the stability and conductivity of the HMP film. The resulting HMP film exhibits great potential as an ideal candidate for transparent flexible conductive nanodevices.

Integration of Triboluminescent EuD4TEA Crystals to Transparent Polymers: Impact Sensor Application

Lanthanide-based organometallic materials are well-known candidate triboluminescent (TL) materials that can show bright emission when a mechanical force is applied. These materials are usually in the form of crystalline powders, and it is often useful to integrate these samples into a polymer matrix in order to achieve processability, enabling coating from a solution/molten state or fabrication as a complex-shaped matrix. In this work, micrometer-sized europium tetrakis (dibenzoylmethide) triethylammonium (EuD₄TEA) crystals were synthesized and integrated with various transparent polymers (PMMA, PS, PVDF, and PU) using two approaches: (i) blending and (ii) surface impregnation. In the former method, the crystalline particles were molecularly dissolved; therefore, a TL response cannot be achieved. More than 10 wt % TL crystals in the composite is needed to obtain TL signals. However, TL signal was achieved at 2.5 wt % when a composite was prepared by the latter approach. TL intensity shows exponential decay with consecutive mechanical action. The TL emission of PU-based surface impregnated composite expires with long-lived emission, and maximum TL response with respect to applied force was measured between 2.45 and 42.0 N.

Self-assembled porous film with interconnected 3-dimensional structure from 6sPCL-PMPC copolymer

Biodegradable porous films with fibrous frame and good interconnectivity were prepared just by evaporating solvent of 6-arms star-shaped copolymer solution.

Breath Figure Method for Construction of Honeycomb Films

Honeycomb films with various building units, showing potential applications in biological, medical, physicochemical, photoelectric, and many other areas, could be prepared by the breath figure method. The ordered hexagonal structures formed by the breath figure process are related to the building units, solvents, substrates, temperature, humidity, air flow, and other factors. Therefore, by adjusting these factors, the honeycomb structures could be tuned properly. In this review, we summarized the development of the breath figure method of fabricating honeycomb films and the factors of adjusting honeycomb structures. The organic-inorganic hybrid was taken as the example building unit to discuss the preparation, mechanism, properties, and applications of the honeycomb films.

Porous Materials for Hydrolytic Dehydrogenation of Ammonia Borane

Hydrogen storage is still one of the most significant issues hindering the development of a “hydrogen energy economy”. Ammonia borane is notable for its high hydrogen densities. For the material, one of the main challenges is to release efficiently the maximum amount of the stored hydrogen. Hydrolysis reaction is a promising process by which hydrogen can be easily generated from this compound. High purity hydrogen from this compound can be evolved in the presence of solid acid or metal based catalyst. The reaction performance depends on the morphology and/or structure of these materials. In this review, we survey the research on nanostructured materials, especially porous materials for hydrogen generation from hydrolysis of ammonia borane.

Enzymatic Catalysis Combining the Breath Figures and Layer-by-Layer Techniques: Toward the Design of Microreactors

Herein, we report the fabrication of microstructured porous surfaces with controlled enzymatic activity by combining the breath figures and the layer-by-layer techniques. Two different types of porous surfaces were designed based on fluorinated and carboxylated copolymers in combination with PS, using poly(2,3,4,5,6-pentafluorostyrene)-b-polystyrene (PS5F31-b-PS21) and polystyrene-b-poly(acrylic acid) (PS19-b-PAA10) block copolymers, respectively. For comparative purposes, flat surfaces having similar chemistry were obtained by spin-coating. Poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) multilayers incorporating alkaline phosphatase (ALP) were built on these porous surfaces to localize the enzyme both inside and outside of the pores using PS/PS5F31-b-PS21 surfaces and only inside the pores on PS/PS19-b-PAA10 surfaces. A higher catalytic activity of ALP (about three times) was obtained with porous surfaces compared to the flat ones. The catalysis happens specifically inside the holes of PS/PS19-b-PAA10surfaces, where ALP is located. This opens the route for applications in microreactors.

Poly(ethylene oxide) functionalized polyimide-based microporous films to prevent bacterial adhesion

Preventing microbial adhesion onto membranes is a crucial issue that determines the durability of the membrane. In this Research Article, we prepared aromatic polyimides (extensively employed for the elaboration of ultrafiltration membranes) containing PEO branches. Four polyimide-g-PEO copolymers were prepared from 6F dianhydride and a novel aromatic diamine containing PEO-550 side groups. The copolymers were designed to have variable PEO content, and were characterized by their spectroscopic and physical properties. The Breath Figure technique was successfully applied to create an ordered surface topography, where the PEO chains were preferentially located on the surface of the micrometer size holes. These unique features were explored to reduce bacterial adhesion. It was established that surface modified polyimide membranes have a high resistance to biofouling against Staphylococcus aureus. In particular, we observed that an increase of the PEO the content in the copolymer produced a decrease in the bacterial adhesion.

Adsorption in alumina pores open at one and at both ends

We have studied adsorption in regular, self-ordered alumina pores open at both ends or only at one end. The straight, non-connected pores have diameters ranging from 22 to 83 nm, with a relative dispersion below 1% in the pore size. Adsorption isotherms measured in open pores with a torsional microbalance show pronounced hysteresis loops characterized by nearly vertical and parallel adsorption and desorption branches. Blocking one end of the pores with glue has a strong influence on adsorption, as expected from classical macroscopic arguments. However, the experimental measurements show an unexpectedly rich phenomenology dependent on the pore size. For large pores (Dp ≥ 67 nm), the isotherms for closed end pores present much narrower hysteresis loops whose adsorption and desorption boundaries envelop the desorption branches of the isotherms for the corresponding open pores of the same size. The loop for small closed end pores (Dp = 22 nm) is slightly wider than that for open pores while the adsorption branches coincide. For large pores, in contrast, the desorption branches of pores with the same Dp overlap regardless of the pore opening. These observations are in agreement with our grand canonical Monte Carlo (GCMC) simulations for a cylindrical pore model with constrictions, suggesting that the alumina pores could be modeled using a constricted pore model whose adsorption isotherm depends on the ratio of the constriction size to the pore size (Dc/Dp).

Micro/macroporous system: MFI-type zeolite crystals with embedded macropores

Zeolite crystals with an embedded and interconnected macropore system are prepared by using mesoporous silica particles as a silica source and as a sacrificial macroporogen. These novel hierarchical zeolite crystals are expected to reduce diffusion limitations in all zeolite-catalyzed reactions, especially in the transformation of larger molecules like in the catalytic cracking of polymers and the conversion of biomass.

In vitro, ex vivo and in silico mechanistic elucidation of the performance of an optimized porosity-controlled multi-elemental transbuccal system

PURPOSE

To elucidate the mechanisms of construction and performance of a porosity controlled, multi-elemental transbuccal system employing experimental and computational approaches.

METHODS

The production of the formulation was guided through a Box-Benkhen design employing homogenization coupled with lyophilization. The physicochemical and physicomechanical properties of the experimental design formulations were quantified with relevant analytical techniques. The influence of changes in porosity measures on the magnitude of these physical properties were explored mathematically. Furthermore, experimental outputs from the Box-Behnken design formulations were fitted into set limits and optimized using the response surface method. The optimized porosity-controlled formulation was subjected to mechanistic experimental and computational elucidations.

RESULTS

In general, the changes in magnitudes of studied porosity quantities had significant impact on formulation physicochemical and physicomechanical properties. The generation of an optimized formulation validated the stability and accuracy of the Box-Behnken experimental design. Experimental investigations revealed that the construction of this formulation is as a result of non-destructive physical interactions amongst its make-up compounds while its mechanism of performance is anchored mainly upon a gradual collapse of its ordered porous structure. Furthermore, the molecule mechanics simulations quantitatively predicted the molecular interactions inherent to multicomponent matrix formation and the mucoadhesion mechanism.

CONCLUSIONS

The fabrication and performance mechanisms of the porosity-controlled transbuccal system was successfully explored.

Green and low-cost synthesis of PANI–TiO2 nanocomposite mesoporous films for photoelectrochemical water splitting

Green and low-cost synthesis procedure for preparation of PANI/TiO₂ mesoporous nanocomposite films with enhanced photocatalytic performance, thanks to a synergic reaction mechanism between PANI and TiO₂ under UV light irradiation.

A nano-frost array technique to prepare nanoporous PVDF membranes

Frost, the solid deposition of water vapor from humid air, forms on the surface of a solid substrate when its temperature drops below the freezing point of water. In this study, we demonstrate how this natural phenomenon can be applied to develop novel nanoporous materials. The solvent annealing of polyvinylidene fluoride (PVDF) infiltrated into nanopores induced template-directed dewetting thus preparing nanoembossing films. Then, water nanodroplets formed on the cold polymer nanopatterned surfaces following the embossing patterns, similar to dew formation on the ground. Subsequently, the nanodroplets were frozen and then removed by freeze-drying. This nano-frost array technique produced nanoporous PVDF membranes with an average thickness of 250 (± 48) nm. It was revealed that the nanopatterned surface formed by solvent annealing played an important role in achieving a nano-frost array with an adjustable size. Additionally, the freezing process led to significant changes of the PVDF crystallinity and polymorphism. Our results prove that the nano-frost array technique can be broadly used to design ordered nanoporous structures and provide new prospects in nanomaterial fields.

Formation of breath figure arrays in methanol vapor assisted by surface active agents

Breath figure (BF) process is a promising technique for fabricating honeycomb polymer films. It is usually conducted in water vapor. While, in organic vapors only unique polymer can be used to prepare BF arrays as reported in our previous article (Breath Figure in Nonaqueous Vapor. Soft Matter, 2013, 506-514), although new structure features are induced in the film. In this paper, a universal modified BF processing is devised for preparing porous films in methanol vapor with conventional polymers, by adding a small amount of surface active agent into the casting solution, such as siloxane- and fluorine-containing block copolymers. The pores in the PS films prepared with this method are of cylindrical shape with large depth-diameter aspect ratio, and the diameter and depth of pores can be well controlled by the experiment conditions. Based on these results, the formation mechanism of honeycomb structure in methanol vapor is discussed.

Breath figure patterns made easy

In this work, a simple breath figure method was proposed to directly fabricate large-area and ordered honeycomb structures on commercial PMMA substrates or PS Petri dishes without the use of an external polymer solution. The obtained honeycomb structure is indeed part of the substrate, providing the honeycomb layer with enough mechanical stability. The breath figure method in this work for the synthesis of honeycomb structure is extremely simple with scale-up capability to large-area production, which offers new insights into surface engineering with great potential in commercial technologies. For example, using the honeycomb-patterned Petri dishes prepared via this method, cells can be easily separated into divided aggregation, which favors understanding of naturally occurring networks in higher organisms and cell-cell and cell-matrix interactions, and the therapeutic control of genetic circuits.

Porous surface structure fabricated by breath figures that suppresses Pseudomonas aeruginosa biofilm formation

As colonizers of medical-device surfaces, Pseudomonas aeruginosa strains present a serious source of infection and are of major concern. In this study, we fabricated films with porous surfaces by breath figures that disturb mergence by bacterial attachment, thereby impeding biofilm development. Previous studies have shown that microtopography prevents the development of P. aeruginosa biofilms. Accordingly we indented surfaces with patterns of micrometer-sized pores using breath figures at ordinary temperatures and pressures. The antimicrobial effect of surface figures was experimentally investigated by controlling the surface structure. The results suggested that pores of 5-11 μm in diameter effectively inhibit bacterial activity. It appears that biofilm development is precluded by the decreased contact area between the films and bacteria.

Recovery of gold as a type of porous fiber by using biosorption followed by incineration

This study introduces a new process for the recovery of gold in porous fiber form by the incineration of Au-loaded biosorbent fiber from gold-cyanide solutions. For the recovery of gold from such aqueous solutions, polyethylenimine (PEI)-modified bacterial biosorbent fiber (PBBF) and PEI-modified chitosan fiber (PCSF) were developed and used. The maximum uptakes of Au(I) ions were estimated as 421.1 and 251.7 mg/g at pH 5.5 for PBBF and PCSF, respectively. Au-loaded biosorbents were freeze-dried and then incinerated to oxidize their organic constituents while simultaneously obtaining reduced gold. As a result, porous metallic gold fibers were obtained with 60 μm of diameter. Scanning electron microscopic (SEM) analysis and mercury porosimetry revealed the fibers to have 60 μm of diameter and to be highly porous and hollow. The proposed process therefore offers the potential for the efficient recovery of metallic porous gold fibers using combined biosorption and incineration.