Nano-scaled Pores Research Articles

Molecular sieve-like wood achieves efficient chiral catalysis

Molecular sieve catalysts have been adopted in chiral catalytic reactions due to their high specific surface area, nano-scaled pores and effective separation, however, the problems like low utilization ratio of channels, difficult modification, long period and complex preparation, and no economic benefits reduce its widely application. In this paper, natural wood was employed as raw material to preserve the cellulose skeleton rich in poly‑hydroxyl and the multistage porous channels of nanometer, micron and millimeter by simple treatment. A low-cost, high-yield and high-selectivity chiral catalyst could be obtained from wood with chiral catalytic sites. The in situ grafting method retains the well-developed multistage pore structure of wood, enhances the mass transfer and possesses universal applicability to different aldol condensation reactions. The asymmetric reaction of cyclohexanone and p-nitrobenzaldehyde is catalyzed by grafting readily available amino acids such as threonine, with a yield of 82% and selectivity of 57%. Molecular sieve-like wood possesses the advantages of low economic cost and good catalytic performance, which provides a potential possibility to replace traditional molecular sieve catalyst.

Hierarchically Porous Cellulose Membrane via Self‐Assembly Engineering for Ultra High‐Power Thermoelectrical Generation in Natural Convection

AbstractRenewable heat‐to‐power conversion based on thermoelectric strategy holds strong prospect toward clean electricity generation in low‐carbon society, in which its conversion performance is mainly decided by the temperature gradient. However, achieving a high temperature gradient spontaneously throughout the day in natural convection remains a significant challenge. Herein, cost‐effective, sustainable, and hierarchically porous cellulose membrane (HPCM) created through a simple self‐assembly engineering of cellulose molecules is proposed. Such HPCM boasts a unique structure of layered micro‐ and nanoscaled pores with ≈95% porosity, and correspondingly demonstrates >94% solar reflectance and >0.9 mid‐infrared emissivity. As a result, HPCM enables average temperature gradient of 14.5 °C and 76 mV output voltage of thermoelectric module during daytime natural convection, which are 17‐ and 30‐time higher than those of pristine device, respectively. Note that HPCM‐based thermoelectric module consistently generates an average output voltage of 44.2 mV all day. Such modules are seamlessly integrated into thermoelectric arrays to achieve high output voltage of ≈1.5 V and power density of ≈3 W m−2 over 90‐d period. The prepared HPCM marks a significant advancement in environmentally friendly, scalable, and viable thermoelectric conversion to power the low‐carbon society.

The effects of a corrosion product film on the corrosion behavior of Mg-Al alloy with micro-alloying of yttrium in a chloride solution

Micro-alloying Mg alloys with rare earth elements is an economical and promising way to improve their corrosion resistance. It is of great importance to understand their corrosion behavior for designing corrosion-resistant Mg alloys. In this work, Mg-11Al-0.2Y alloy was prepared for exploring its corrosion behavior in 3.5 wt.% neutral NaCl solution. It exhibits a low corrosion current density of 2.3 µA/cm2 after immersion for 1 d due to the formation of a protective surface film containing Al2O3, MgO and Mg(OH)2. However, nano-scaled pores exhibit at the film/matrix interface, which undermines integrity and protectiveness of the surface film after long-term exposure to chloride solution.

Electrochemical Behavior of Nanoporous Gold/Polypyrrole Supercapacitor under Deformation.

Due to the high demand of wearable electronics, flexible supercapacitors have been extensively developed in recent years. Yet, the effect of deformation in the interior electrode material suffered in practical applications on the performance received less attention. Here, we study the electrochemical behavior of macroscopic nanoporous gold/polypyrrole (NPG/PPy) in situ under compression deformation. Dealloying-driven NPG, a network constructed by bi-continuous nano-scaled ligaments and pores, can serve as a compression-tolerant substrate for PPy supercapacitor material. The electrochemical capacitance of NPG/PPy subjected to compression deformation is revealed to decrease at the scan rates and discharge current densities applied in this work. At the same time, the charge transfer resistance of NPG/PPy is found to increase. This electrochemical behavior is due to the locally reduced mass transport of electrolyte caused by the formation of new connections between the neighboring ligaments under the application of compression loads. The fundamental understanding of the effect of deformation on the performance of energy storage materials revealed in this study paves the way for their practical application in wearable devices.

Hydrocarbon mixture and CO2 adsorptions in A nanopore-bulk multiscale system in relation to CO2 enhanced shale gas recovery

Thanks to the continuous depletion of conventional gas reservoirs, shale gas plays an important role to meet the global natural gas demand. The CO2 'huff-n-puff' process has been proven to be an effective method to enhance shale gas recovery and sequestrate CO2. Unlike conventional reservoirs, shale media can contain a significant number of nano-scaled pores and their pore volume can be comparable to that of macropores and fractures in which fluids behave as bulk. While previous works studied the mechanisms of CO2 ‘huff-n-puff’ process in shale gas exploitation, the volume partitioning between nanopores and macropores/fractures is not fully taken into account. In this work, we built a nanopore-bulk multiscale model with varying pore size distributions (PSDs) to study the CO2 'huff-n-puff' process in a constant volume depletion (CVD) setting by using density functional theory (DFT). We found that the volume partitioning effect on adsorption, fluid compositions, hydrocarbon mixture (C1, C2, and C3) recovery is significant in the CO2 'huff-n-puff' process. The majority of hydrocarbon mixtures can be released from micropores and smaller mesopores during the CO2 ‘huff’ and ‘soak’ process, while the average hydrocarbon densities in larger mesopores might increase. During the CO2 ‘huff’ and ‘soak’ process, due to a stronger confinement effect in smaller pores, the PSD case with a higher volume ratio of smaller pores releases fewer hydrocarbons, while stores more CO2 per unit pore volume. Overall, the volume partitioning has a significant effect on hydrocarbon adsorption, compositions, and recovery as well as CO2 storage during the CO2 ‘huff-n-puff’ process in shale gas exploitation and geological CO2 sequestration.

Hierarchical porous carbon heterojunction flake arrays derived from metal organic frameworks and ionic liquid for H2O2 electrochemical detection in cancer tissue

The development of hierarchical nanostructure is demonstrated as an effective strategy to improve catalytic activity and stability of electrocatalysts. Herein, a novel leaf-like hierarchically porous heterojunction flake arrays (FAs), integrated graphitic N-doped carbon (NC) with amorphous B,N-doped carbon (BNC), has been designed and grown on flexible carbon fiber (CF) using metal-organic framework (MOF) FAs and green ionic liquids as precursors. The hierarchical heterojunction structure possesses micro- and nano-scaled pores, large surface areas, and exposed high-density catalytic active sites, which enhances electronic conductivity and offers accessible transport channels for effectively decreasing mass transport resistance. The results of discrete Fourier transform (DFT) calculations and experiments also suggest that the catalytic activity has been promoted by the heterojunction structure through narrowing the banding gap. Consequently, the resultant nanohybrid microelectrode exhibits remarkable electrochemical sensing performance towards H2O2 with a low detection limit of 50 nM, and a high sensitivity of 213 μA×mM-1×cm-2, as well as good anti-interference capability. The practical application of nanohybrid fiber microelectrode has been explored by real-time monitoring H2O2 released from live colon cells and surgically-resected fresh colon cancer tissue, which can provide important information for the identification of different types of cells as well as distinguish cancer cells from normal ones. We believe this research will pave the way towards the development of advanced carbon nanomaterials for application in the fields of electrochemistry, biosensing, and cancer diagnosis.

Potential Transparent Supercapacitor Electrode Materials

Supercapacitor utilizes the nano-scaled pores to increase the surface area indefinitely and shortens the distance between the positive and negative plate, on the account that some larger particles cannot fit into the pores. According to the capacitance equation “capacitance = εrε0 (area/distance),” as the distance decreasing and area increasing, the magnitude of the capacitance is tremendously magnified. A transparent supercapacitor describes a supercapacitor that has a high optical transmittance. If the intensity of light that transmits across the substance is higher than the rate that it is blocked or reflected. The substance possesses a transparency. The flexibility of transparent supercapacitors is another important area of studies. It generalizes a combination of stretchability, bendability, twistibility, or compressibility. In real life, it’s important to obtain the optimal optical transmittance, flexibility, and electrical conductivity for future devices such as smart glasses. These characteristics enable us to develop something more complex and advanced in the future.

Characterization and cytocompatibility of hierarchical porous TiO2 coatings incorporated with calcium and strontium by one-step micro-arc oxidation.

Calcium (Ca) and strontium (Sr) are beneficial for bone reconstruction. This study incorporated Ca and Sr into the TiO2 coatings by one-step micro-arc oxidation (MAO) treatment with CaO and SrO added in tetraborate electrolytes. The structure, composition, hydrophilicity, ion release, and cytocompatibility of the coatings were studied. The coatings combine layered micron-scale pores in various sizes and nano-scaled pores, forming a hierarchical structure. This hierarchical structure is highly porous and super-hydrophilic. The coatings are composed of Ti, O, and B, as well as Ca or Sr. Ca and Sr mainly distribute in the outer layer of the coatings and exist in the forms of carbonates and oxides. The formation of the coatings was discussed. Ca and Sr incorporated into the coatings are readily released into aqueous solutions. The homogeneous surface structure of the coatings leads to an excellent and approximating performance in hydrophilicity, as well as the adhesion and spreading of the human bone marrow-derived mesenchymal stem cells (hBMSCs). The simultaneous incorporation of Ca and Sr incorporation exhibits superior facilitation in the proliferation of hBMSCs compared with single Ca or Sr incorporation. This study shows a promising method to incorporate bioactive elements into the MAO coatings on titanium surfaces.

Formation of Hierarchical Porous Films with Breath-Figures Self-Assembly Performed on Oil-Lubricated Substrates.

Hierarchical honeycomb patterns were manufactured with breath-figures self-assembly by drop-casting on the silicone oil-lubricated glass substrates. Silicone oil promoted spreading of the polymer solution. The process was carried out with industrial grade polystyrene and polystyrene with molecular mass . Both polymers gave rise to patterns, built of micro and nano-scaled pores. The typical diameter of the nanopores was established as 125 nm. The mechanism of the formation of hierarchical patterns was suggested. Ordering of the pores was quantified with the Voronoi tessellations and calculation of the Voronoi entropy. The Voronoi entropy for the large scale pattern was , evidencing the ordering of pores. Measurement of the apparent contact angles evidenced the Cassie-Baxter wetting regime of the porous films.

Hierarchical Nanoporous Copper Architectures via 3D Printing Technique for Highly Efficient Catalysts.

Nanoporous metals represent a class of functional materials with unique bicontinuous open porous structural properties, making them ideal candidates for various catalyst applications. However, the pursuit of nanoporous properties, extremely small pores, and high surface area, results in the restriction of mass transport. Herein, a free-standing hierarchical nanoporous Cu material, prepared by a selective laser melting 3D printing technique and a one-step dealloying process, is presented as a highly efficient electrocatalyst for methanol oxidation. It is demonstrated that the digitally controlled hierarchical structure with macro- and nano-scaled pores can be utilized for promoting and directing mass transport as well as for the enhancement of catalytic properties. This work highlights a facile, low-cost, and alternative strategy for hierarchical nanoporous structure design that can be applied to binary, ternary, and quaternary metal alloys for various functional applications.

Effects of bentonite slurry on air-void structure and properties of foamed concrete

The increase of nano-scaled pores may further improve the thermal insulation properties of foamed concrete. However, air voids in foamed concrete prepared by pre-fabricated foams through surfactant or hydrolyzed protein solutions are commonly above micron level. It becomes a key issue to decrease the air-void sizes and increase the nano-scaled pores in foamed concrete by the modification of pore-forming methods. In this study, gel-like bentonite slurry with solid content of 9.1% was used to replace some of cement and pre-fabricated foams to prepare foamed concrete with dry bulk density of 300 and 600 kg/m3, respectively. Apparent viscosity of the fresh pastes decreased with the increase of bentonite slurry, and the fluidity firstly decreased and then increased. Compressive strength decreased with the increase of bentonite slurry, specially the as-prepared foamed concrete with dry bulk density of 300 kg/m3. Much better thermal insulation properties of the foamed concrete with bentonite slurry could be obtained. Thermal conductivity of the foamed concrete with 50% of bentonite slurry decreased by 29.8% and 15.3% for dry bulk density of 300 kg/m3 and 600 kg/m3, respectively. It is found that the increased pores with nano-scaled sizes in foamed concrete with bentonite slurry could be responsible for the lower thermal conductivity.

Effect of reduction time on the structure and properties of porous graphene

Porous graphene with nanoscaled pores on the sheets was prepared by a carbon thermal reduction method, in which the molybdenum oxide nanoparticles generated from the thermal decomposition of molybdate were used as the etching reagent, and the pores were formed on the surface of the reduced graphene oxide under the conditions of 650 °C and a nitrogen atmosphere. The morphology of pores on the graphene sheets may affect their potential applications in various fields, especially in the enhancement of mass transfer. Previous studies have shown that the reduction temperature and the amount of metal oxide are the key factors affecting the morphology of porous graphene, but in fact the reduction time is a more important affecting factor according to the present study. The results of SEM/TEM showed that a disordered large sheet-like structure with wrinkles was obtained at 120 min in the carbon-thermal reaction. The structural integrity of the PG was further destroyed after the reaction time of 140 min, in which the edge exhibited slightly crush and significant fold. The PG exhibited a hollow rod-like structure at the reaction time of 180 min. FTIR, Raman, XRD, and XPS studies were performed to characterize the morphology of porous graphene prepared at different reduction times.

Carbon nanotube based hybrid nanocarbon foam

Carbon nanotube (CNT) based nanocarbon foams (NFs) and the hybrid nanocarbon foams (HNFs) are fabricated in this work. The NFs are formed by using poly(methyl methacrylate) microspheres as a template to create micro-scaled pores. The cell walls are made of CNT networks with nano-scaled pores. The interconnections among CNTs are secured using graphene and nanographite generated via carbonization of polyacrylonitrile. The resulting NFs are ultra-lightweight, highly elastic, electrically and thermally conductive, and robust in structure. The HNFs are made by infiltrating thermoplastic polymer into the NFs in a controllable procedure. Compared to NFs, the HNFs have much higher strength, same electrical conductivity, and limited increase in density. The compressive strength of the HNF increased more than 50 times while the density was changed less than 10 times due to the polymer infiltration. It is found that the deformed HNFs can recover in both structure and property when they are heated over the glass transition temperature of the infiltrated polymer. Such remarkable healing capability could broaden the applications of the HNFs.

Core-Shell Nanoparticle Coating as an Interfacial Layer for Dendrite-Free Lithium Metal Anodes.

Lithium metal based batteries represent a major challenge and opportunity in enabling a variety of devices requiring high-energy-density storage. However, dendritic lithium growth has limited the practical application of lithium metal anodes. Here we report a nanoporous, flexible and electrochemically stable coating of silica@poly(methyl methacrylate) (SiO2@PMMA) core–shell nanospheres as an interfacial layer on lithium metal anode. This interfacial layer is capable of inhibiting Li dendrite growth while sustaining ionic flux through it, which is attributed to the nanoscaled pores formed among the nanospheres. Enhanced Coulombic efficiencies during lithium charge/discharge cycles have been achieved at various current densities and areal capacities.

Studying Binding, Conformational Transition and Assembly of E. Coli Cytolysin a Pore Forming Toxin by Single Molecule Fluorescence

Pore forming toxins (PFT) belong to a class of bacterial toxin proteins that form nano-scaled pores on target cell's membrane and cause unregulated efflux of ions and biomolecules leading to cell death. They are released in a water-soluble conformation which upon membrane exposure undergoes large structural rearrangement. This membrane bound monomer further oligomerizes and forms of a complete pore. While high resolution structural information of complete pores are available, our understanding of early events of PFT binding and assembly is incomplete owing to the highly dynamic nature of the aforementioned processes. In this study, we use single molecule tracking and spectroscopy to understand the dynamics of Cytolysin A (ClyA), a prototypical α-PFT from E. coli, on lipid bilayer membranes. Binding of ClyA to PEG-cushioned supported bilayer was rapid and reached saturation within a few seconds. Diffusional analysis of particle trajectories showed existence of two discrete mobility states exhibiting ‘fast’ and ‘slow’ motions. Binding of PFT proteins was invariably in the ‘fast’ mobility state that was followed by transitions of the single monomer between the two states. The slow moving population was significantly enhanced in cholesterol containing bilayers. We argue that the change in mobility is a consequence of structural transition to an assembly competent intermediate, the protomer state. Preliminary analysis indicates that cholesterol enhances conformational transition by direct binding to the N-terminus of ClyA leading to stabilization of the protomer-like state. This stabilization directly translates to increased formation of higher order structures at high concentrations of protein as measured by analysis of single molecule photobleaching trajectories of pre-formed ClyA pores. Therefore, we propose a molecular mechanism for selective pore formation in eukaryotic membranes driven by conformational selectivity in the presence of cholesterol.

Characterization of full pore size distribution and its significance to macroscopic physical parameters in tight glutenites

Characterization of microscopic pore structure plays an important role in understanding transport and accumulation mechanism of tight gas accumulation. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) experiments were performed on tight glutenite samples from the Lower Cretaceous Shahezi Formation in the northern Songliao Basin of China in order to gain insight into the microscopic pore structure (e.g., pore types and full pore size distribution), and to discuss the control of full pore structure properties on macroscopic physical parameters. The results show that the tight glutenite samples in this study contain four types of pores: inter-granular pores, dissolution pores, inter-crystalline pores and even some pores associated to micro-fractures. The inter-crystalline pores and inter-granular/dissolution pores can be determined by the surface fractal dimensions and mercury intrusion features because of different pore connectivity. The combination of N2GA and MIP were applied as complementary techniques and revealed that the studied samples have a broad pore size distribution ranging from 2 nm to 200 μm (mainly from 10 nm to 2 μm). Nano-scaled pores become the crucial storage space in tight glutenite samples. A total porosity derived from full pore size distribution curves is between 1.18% and 5.64%, which is closer helium porosity than that originated from N2GA and MIP techniques, respectively. Tight glutenite samples with a greater proportion of small pores (diameter<50 nm) mainly corresponding to inter-crystalline pores always have worse macroscopic physical parameters. However, tight glutenite samples with a greater proportion of large pores (diameter>200 nm) mainly corresponding to inter-granular/dissolution pores always correspond to better macroscopic physical parameters. The development of different pore types controls the macroscopic physical parameters. A series of empirical equations developed from multiple regression analysis between permeability, porosity and pore radius were established in tight glutenite samples. Pore radius corresponding to 15% cumulative pore volume from the combination of N2GA and MIP techniques is the best permeability estimator for tight glutenite samples.

Experimental investigation of the pore structure characteristics of the Garau gas shale formation in the Lurestan Basin, Iran

Gas storage and flow characteristics of shale gas reservoirs are greatly affected by their complex pore structure. These structures contain a wide range of pore size distribution with significant contribution of nanometer scaled pores. In this work an integrated experimental approach including geochemical and mineralogical analysis, Mercury Injection Capillary Pressure (MICP) and helium expansion porosimetry along with nano-scale Field Emission-Scanning Electron Microscopy (FE-SEM) imaging techniques was used to characterize pore structure of Garau formation, a shale gas play recently explored in the western Iran.MICP was used in this study as an acceptable laboratory method to identify pore throat size down to three nanometers. FE-SEM image analysis was also applied for better understanding of distribution, connectivity and nature of sub-micron pore systems. Experimental measurements were made on 23 plugs collected from two depth intervals from two wells in the Garau formation. X-Ray Diffraction mineralogy (XRD) analysis represents that shale samples are calcite rich with low clay contents. The kerogen analysis shows kerogen type II with Total Organic Carbon (TOC) values ranging from 0.41 to 3.18%. The total porosity obtained from helium expansion test, varies between 0.1 and 3.6% under ambient test conditions and between 0.1 and 1.2% under overburden stress test conditions suggesting high stress dependency of the porosity in the studied samples. Based on the MICP test results, the pore throat sizes in the Garau shale samples belong to the mesopores and macropores realm. In addition, two types of pore size distributions are observed in the samples according to their mineralogical compositions. The majority of pores in the first group with high calcite contents are in macro-scale (>50 nm) with the dominant pore radius of around 50 μm, while the dominating pore radii in the second group with illite traces are found to be in the meso-scale (5–50 nm). Furthermore, comparing the MICP and helium porosimetry test results shows that the total porosity of the Garau shale increases with the increase of the meso-scale pore volume. Observations from FE-SEM images were also in good agreement with MICP test results. FE-SEM analysis revealed that pores are located both in the organic matter and inorganic matrix whether in isolated or interconnected types. These observations showed that a portion of kerogen body is occupied by nano-scaled pores with different shapes and sizes; as a result, samples with higher TOC contents and maturity offers generally higher total porosity values.

A general and scalable synthesis approach to porous graphene.

Porous graphene, which features nano-scaled pores on the sheets, is mostly investigated by computational studies. The pores on the graphene sheets may contribute to the improved mass transfer and may show potential applications in many fields. To date, the preparation of porous graphene includes chemical bottom-up approach via the aryl-aryl coupling reaction and physical preparation by high-energy techniques, and is generally conducted on substrates with limited yields. Here we show a general and scalable synthesis method for porous graphene that is developed through the carbothermal reaction between graphene and metal oxide nanoparticles produced from oxometalates or polyoxometalates. The pore formation process is observed in situ with the assistance of an electron beam. Pore engineering on graphene is conducted by controlling the pore size and/or the nitrogen doping on the porous graphene sheets by varying the amount of the oxometalates or polyoxometalates, or using ammonium-containing oxometalates or polyoxometalates.

Influences of saltwater immersion on properties of wood-cellulosic paper.

The saltwater immersion method was developed to inhibit mould growth on flood- or tsunami-damaged paper. Commercially available fine paper used for printing and writing showed decreased tensile indices after saltwater immersion. The salt remaining in the paper tended to increase the moisture content because of the salt deliquescence and moisture in the air. The tensile index was restored by removing salt from the paper. Crystallization and distribution of salt in interfibre pores were also considered to influence interfibre rebonding. The difference in the fibre responses to saltwater depended on the relationship between nano-scaled pores in the fibre walls, osmotic pressure, and the degree of sizing, which resulted in low water retention values. More of the starch applied as a surface sizing agent was dissolved or dispersed during distilled water immersion than saltwater immersion. This loosened the fibre network, which was a factor that decreased the sizing degree of the paper.

Au nanoparticle-built mesoporous films based on co-electrophoresis deposition and selective etching

A simple and facile strategy is presented to fabricate mesoporous Au spherical nanoparticle films based on the combination of co-electrophoresis deposition in the mixed colloidal solutions of Au and Ag and selective etching of the Ag nanoparticles which act as a sacrificial metal. The film is homogeneous in the macroscale but with numerous nanoscaled pores. The film configuration can be easily tuned by the size of Au colloidal nanoparticles and the amount of Ag colloidal solution mixed. Importantly, such structured mesoporous film exhibits strong surface-enhanced Raman scattering activity with good reproducibility and repeatability. Additionally, this study provides a novel method for the controllable construction of other mesoporous films from simple metals to multicomponent hybrids, by using nanoparticles as building blocks.