Unique Porous Structure Research Articles

Lightweight aerogel-like silicon oxycarbide ceramics with directionally honeycomb-like structure for high temperature environments

Ceramic aerogels are considered promising thermal protection materials for their excellent thermal insulation performance and high-temperature stability. Lightweight aerogel-like silicon oxycarbide (SiOC) was prepared from polyhydromethylsiloxane (PHMS) as precursor and divinylbenzene (DVB) as crosslinker through solvothermal, freeze casting/drying and pyrolysis. The aerogel-like SiOC ceramic can achieve a low density of 0.087 g·cm−3 under the optimized mass ratio of DVB:PHMS of 1.5:1, with a directionally honeycomb-like structure induced by cyclohexane ice-crystals during the freeze casting. The unique porous structure endows the aerogel-like SiOC with low effective thermal conductivity (0.051–0.057 W·m−1·K−1) and good compressive strength (0.30–0.34 MPa). Moreover, the aerogel-like SiOC maintains structural and property stability after heat treatment (1400 °C in argon or 800 °C in air) for good thermal stability and oxidation resistance, which sheds light on the preparation of high-performance SiOC thermal insulation materials for high-temperature environments.

Efficient electro-demulsification of O/W emulsions and simultaneous oil removal enabled by a multiscale porous biocarbon electrode

Emulsion wastewater contain substantial amounts of oil and various additives, which pose threats to the environment and human health. Demulsification is a crucial pretreatment stage for wastewater. This study aims to identify a novel electro-demulsification method with high oil removal efficiency and low energy consumption. Modified carbonized birch wood with a unique isotropic multiscale pore structure is used as a self-standing electrode to treat a toluene oil-in-water (O/W) emulsion. The electrode must have a highly porous structure to facilitate efficient water diffusion and oil adsorption. It must also have high electronic conductivity to expedite polarized molecular electrophoresis to realize penetration into the pores and, subsequently, demulsification. Guided by an applied electric field force, polarized O/W droplets are drawn toward the electrode, revealing electrical characteristics distinct from those of polarized organic molecules. This electric field force augments the capture and adhesion of droplets by the electric double layer at the electrode interface. Consequently, adsorbed droplets in close proximity to the electrode rupture due to the combined influence of the electric field force and the electrostatic effects stemming from the electrode's multiscale porous structure. This synergistic action enables demulsification to occur efficiently at low energy consumption levels. This study has revealed that electro-demulsification can effectively treat toluene emulsions stabilized by various surfactants and microemulsion containing toluene. Therefore, this electro-demulsification technology can be further developed for various types of water pollution.

Fe-doped g-C3N4 with duel active sites for ultrafast degradation of organic pollutants via visible-light-driven photo-Fenton reaction: Insight into the performance, kinetics, and mechanism

The photo-Fenton process provides a sustainable and cost-effective strategy for removing refractory organic contaminants in wastewater. Herein, a high-efficient Fe-doped g-C3N4 photocatalyst (Fe@CN10) with a unique 3D porous mesh structure was prepared by one-pot thermal polymerization for ultrafast degradation of azo dyes, antibiotics, and phenolic acids in heterogeneous photo-Fenton systems under visible light irradiation. Fe@CN10 exhibited a synergy between adsorption-degradation processes due to the co-existence of Fe3C and Fe3N active sites. Specifically, Fe3C acted as an adsorption site for pollutant and H2O2 molecules, while Fe3N acted as a photocatalytic active site for the high-efficient degradation of MO. Resultingly, Fe@CN10 showed a photocatalytic degradation rate of MO up to 140.32 mg/L min−1. The dominant ROS contributed to the removal of MO in the photo-Fenton pathway was hydroxyl radical (•OH). Surprisingly, as the key reactive species, singlet oxygen (1O2) generated from superoxide radical (•O2−) also efficiently attacked MO in a photo-self-Fenton pathway. Additionally, sponge/Fe@CN10 was prepared and filled in the continuous flow reactors for nearly 100% degradation of MO over 150 h when treating artificial organic wastewater. This work provided a facile route to prepare highly-active Fe-doped photocatalysts and develop a green photocatalytic system for wastewater treatment in the future.

Constructing gradient reflection and scattering porous framework in composite aerogels for enhanced microwave absorption

Developing high-performance microwave absorption (MA) materials becomes an urgent concern in the field of electromagnetic protection. Constructing porous framework is an efficient approach to MA owing to the abilities of adjusting impedance matching and providing more reflection and scattering paths for electromagnetic waves. Herein, a cellulose nanofibril (CNF)/honeycomb-like carbon-shell encapsulated FeCoNi@C/carbon nanotube (CNT) composite aerogel was fabricated via a facile freeze-drying method. The super-lightweight composites showed a distinctive gradient structure for reflection and scattering inside aerogel pores, micrometer small pores, and nano-fillers on the pore walls. The composite aerogel showed an ideal minimum reflection loss (RLmin) of −43.6 dB and remarkable adjustable effective absorption bandwidth (EAB) of 12.18 GHz due to good impedance matching, unique gradient porous structure, and synergies of multiple loss mechanisms. Therefore, this work will provide a viable strategy to improve the MA capability of absorbers by taking full advantage of constructing gradient reflection and scattering porous structure.

The Synergistic Impact of Crystal Seed and Fluoride Ion in the Synthesis of Silicalite-1 Zeolite in Low-Template Systems.

Silicalite-1 zeolites are widely applied in gas adsorption, catalysis, and separation due to their excellent hydrothermal stability and unique pore structure. However, traditional preparation methods have inherent drawbacks such as high pollution, high cost, etc. Therefore, this work proposed a green and efficient route for preparing Silicalite-1 zeolite by adding NH4F (F/Si = 0.1) and seeds (10 wt%) in a much shorter time (8 h) in a low-template system (TPA+/Si = 0.007). It was found that NH4F is beneficial for inhibiting the formation of SiO2. The S-1 seeds could drastically induce the formation of the zeolite skeleton structure. Noteworthy, the morphology of zeolites was determined by the relative content of NH4F and seeds. The crystal morphology is determined by the higher content of the two substances; however, when the content is similar, the crystal morphology is determined by NH4F. The results showed that simultaneous control of NH4F and seeds can suppress SiO2 formation, can improve the relative crystallinity of products, and can be precisely regulated via the synergistic effect of both in zeolite morphology. This work not only provides new ideas for regulating the morphology of silicate-1 crystals but also offers a new path for industrial large-scale production of low-cost and efficient zeolites.

One-pot synthesis of mechanically robust hierarchical graphene-polyethylene aerogels

Fabricating mechanically robust graphene aerogels (GAs) without compromising their notable features including superelasticity, large surface area, high porosity, and low density is challenging. This work presents a new one-pot strategy based on ambient drying to fabricate a three-dimensional (3D) graphene-polyethylene aerogel (G-PEA) with a unique hierarchical porous structure, in which the highly porous polyethylene is encapsulated by graphene frameworks. The hierarchical G-PEA exhibited substantially enhanced compressive strength while maintaining low density and superelasticity comparable to those of bare GAs. The G-PEAs with 5 wt% PE (G-PEA5) showed a significant improvement (up to 2083 %) in compressive stress compared to bare GAs, which can be attributed to the porous PE support within the GA framework. The G-PEA5 retained 94 % of its compressive stress after 100 compression cycles, which is still higher than that (∼80 %) of bare GAs, and maintained good elastic recovery. The designed hierarchical G-PEAs show great promise in the applications that require outstanding mechanical properties.

Stained Glass Effect in Anodic Aluminum Oxide Formed in Selenic Acid.

A combination of the unique porous structure and physical and chemical properties of anodic aluminum oxide (AAO) makes it widely used in cutting-edge areas of materials science and nanotechnology. Selenic acid electrolyte provides the ability to obtain AAO with low porosity and high optical transparency and thus is promising for the preparation of AAO photonic crystals (PhCs). Here, we show the influence of crystallographic orientation of Al on the electrochemical oxidation rate in 1 M H2SeO4 as well as on the growth rate, porosity, and the effective refractive index of AAO. The cyclic anodization regime is used to prepare AAO PhCs with photonic band gaps, their wavelength positions are used to measure the AAO growth rate. At an anodization voltage of 40-45 V, the growth rate varies by up to 22.6% with crystallographic orientation of Al grains, causing the stained glass effect, which can be seen with the naked eye.

Biomass-derived lightweight SiC aerogels for superior thermal insulation.

Silicon carbide (SiC) aerogels, which possess unique porous structure and high ablation resistance, show great potential as thermal insulation materials, but their wide application is limited by expensive and cumbersome synthetic procedures. Therefore, it is pivotal to develop a facile, versatile, and cost-effective method for producing SiC aerogels. Herein, we have successfully prepared ultra-light SiC nanowire aerogels (SNWAs) boasting remarkably low thermal conductivity, using biomass-derived carbon templates (BCTs) through a direct carbothermal reduction method. The BCTs obtained by simply carbonizing freeze-dried eggplants can serve not only as the carbon sources but also as the templates for the in situ growth of SiC nanowires. The resultant three-dimensional (3D) SNWAs possess various porous structures, incorporating the original micro-sized pores inherited from the eggplant and nano-sized pores constructed from interconnected SiC nanowires. These multi-scale pore structures bestow SNWAs with lower gas-phase heat conduction characteristics. Besides, the numerous stacking faults and heterojunctions present in the SiC nanowires play a key role in obstructing the solid-phase heat transfer and reinforcing the SiC skeleton. As a result, the SNWAs show an exceptionally low thermal conductivity, measuring 0.0149 W m-1 K-1 at room temperature, and maintain this low value (0.0256 W m-1 K-1) even at 500 °C. Remarkably, even after being exposed to air at 1200 °C for 2 h, the SNWAs maintain a low thermal conductivity of 0.0226 W m-1 K-1. Such low-cost and effective preparation of biomass-derived SiC aerogels is anticipated to pave a new avenue for the development of advanced thermal insulators.

Unveiling the deformability of mussel plaque core: the role of pore distribution and hierarchical structure.

The mussel thread-plaque system exhibits strong adhesion and high deformability, allowing it to adhere to various surfaces. While the microstructure of plaques has been thoroughly studied, the effect of their unique porous structure on the high deformability remains unclear. This study first investigated the porous structure of mussel plaque cores using scanning electron microscopy (SEM). Two-dimensional (2D) porous representative volume elements (RVEs) with scaled distribution parameters were generated, and the calibrated phase-field modelling method was applied to analyse the effect of the pore distribution and multi-scale porous structure on the failure mechanism of porous RVEs. The SEM analysis revealed that large-scale pores exhibited a lognormal size distribution and a uniform spatial distribution. Simulations showed that increasing the normalised mean radius value (ū) of the large-scale pore distribution can statistically lead to a decreasing trend in final failure strain, strength and strain energy density but cannot solely determine their values. The interaction between pores can lead to two different failure modes under the same pore distribution: progressive failure mode and sudden failure mode. Additionally, the hierarchical structure of multi-scale porous RVEs can further increase the final failure strain by 40-60% compared to single-scale porous RVEs by reducing stiffness, highlighting the hierarchical structure could be another key factor contributing to the high deformability. These findings deepen our understanding of how the pore distribution and multi-scale porous structure in mussel plaques contribute to their high deformability and affect other mechanical properties, providing valuable insights for the future design of highly deformable biomimetic materials.

Regulation of Macrophage Uptake Through the Bio-nano Interaction Using Surface Functionalized Mesoporous Silica Nanoparticles with Large Radial Pores

Porous nanoparticles, such as mesoporous silica nanoparticles (MSNs), have garnered significant interest for biomedical applications. Recently, MSNs with large radial pores have attracted increased attention because their unique pore structure...

Controllable synthesis of flower-like hierarchical porous TiO2 at room temperature and its affinity application.

Flower-like particles have attracted much attention due to their efficient surface accessible sites and unique hierarchical porous structure. However, their synthesis is usually challenging and requires complex procedures. Herein, we present a simple method for rapid preparation of flower-like hierarchical porous TiO2 (FHP-TiO2) at room temperature for the first time. This method can accurately control the size of FHP-TiO2 from 150 nm to 400 nm by combining co-assembly and Stober reaction. The formation mechanism and influencing factors of FHP-TiO2 were systematically investigated, and its excellent metal oxide affinity was confirmed by theoretical calculations. Due to its hierarchical porous structure, large surface area and high specificity performance, FHP-TiO2 served as an appealing restricted-access adsorbent for specific and efficient enrichment of molecules with phosphate groups in a complex sample matrix, thereby realizing the quantitative analysis of these important biomolecules by coupling with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Moreover, compared with other morphologies (rough surface, and hollow dendritic and mesoporous structure) of TiO2 and flower-like SiO2, FHP-TiO2 showed the best affinity binding ability. This research not only presents a novel approach for tunable room-temperature synthesis of FHP-TiO2 with different sizes, but also expands the application of FHP-TiO2 as an appealing sample-enricher for food safety monitoring and early disease diagnosis.

Antibacterial polylysine-containing hydrogels for hemostatic and wound healing applications: preparation methods, current advances and future perspectives.

The treatment of various types of wounds such as dermal wounds, multidrug resistant bacteria-infected wounds, and chronic diabetic wounds is one of the critical challenges facing healthcare systems. Delayed wound healing can impose a remarkable burden on patients and health care professionals. In this case, given their unique three-dimensional porous structure, biocompatibility, high hydrophilicity, capability to provide a moist environment while absorbing wound exudate, permeability to both gas and oxygen, and tunable mechanical properties, hydrogels with antibacterial function are one of the most promising candidates for wound healing applications. Polylysine is a cationic polymer with the advantages of inherent antibacterial properties, biodegradability, and biocompatibility. Therefore, its utilization to engineer antibacterial hydrogels for accelerating wound healing is of great interest. In this review, we initially discuss polylysine properties, and then focus on the most recent advances in polylysine-containing hydrogels (since 2016) prepared using various chemical and physical crosslinking methods for hemostasis and wound healing applications. Finally, the challenges and future directions in the engineering of these antibacterial hydrogels for wound healing are discussed.

Immobilization of ferrocene and its derivatives within metal-organic frameworks with high loadings toward efficient oxygen evolution reaction.

The use of an appropriate preparation route is the key to immobilize active molecules into a host matrix with high loadings and stability. Herein, we demonstrate a simple and general strategy to immobilize ferrocene and its derivatives into ZIF-8 with high loadings of up to 4.3% Fe content. The unique host pore structure allows for the stabilization of guest molecules and effectively prevents their leaching. As a result, the obtained electrocatalysts exhibit competitive oxygen evolution reaction (OER) catalytic performance. Optimized Fc-CHO/ZIF-8 requires only a low overpotential of 238 mV to achieve 10 mA cm-2, along with a relatively small Tafel slope of 44.4 mV dec-1. This performance is superior to that of commercial IrO2, suggesting its potential application in electrochemical energy conversion.

Synthesis and characterisation of novel metal-organic frameworks (MOFs) based on zirconium and bicinchoninic acid

Metal-organic frameworks (MOFs) are a relatively new class of materials of unique porous structures and exceptional properties. Currently, more than 110,000 types of MOFs have been reported among the countless possibilities. In this study, we have synthesised a novel MOF using zirconium chloride as the metal source and 4,4'-dicarboxy-2,2'-biquinoline (bicinchoninic acid disodium salt) as the linker, which reacted in N,N-Dimethylformamide (DMF) solvent. Three preparation methods were employed to prepare five types of the MOF, and they were compared to optimize the synthesis conditions. The resulting MOFs, named Zr-BADS, were characterised using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), microscopy, and X-ray diffraction (XRD). By incorporating methanol into the preparation solvent, the surface area was increased to 396 m2/g. Additionally, the prepared MOFs exhibited amorphous shapes, with variations in size depending on the synthesis method. This research demonstrates the significance of the preparation method in controlling resulting particles’ properties.

Rational design of conductive metal-organic frameworks and aligned carbon nanofibers for enhancing the performance of flexible supercapacitors.

Carbonaceous materials are attractive active materials for the manufacture of flexible electrochemical double-layer capacitors (EDLCs) because of their high electrical conductivity, large surface area, and inherent resilience against deformation. However, compared to pseudocapacitors, which store electrochemical energy via faradaic redox reactions, EDLCs generally exhibit inferior energy density. One potential approach to addressing this issue is to incorporate highly porous and electrically conductive materials into carbonaceous material-based EDLCs. In this paper, we present a hybrid electrode consisting of a conductive metal-organic framework (c-MOF) with high electrical conductivity and unique porous structure combined with a mat of aligned carbon nanofibers (ACNFs). Its highly ordered structure facilitates electronic/ionic transport, increasing the areal capacitance by up to 3.9 times compared to randomly-oriented carbon nanofibers (RCNFs). An additional increase in areal capacitance (+64%) is achieved by introducing c-MOF (RCNFs: 25.4 mF cm-2; ACNFs: 98.7 mF cm-2; c-MOF/ACNF: 161.8 mF cm-2). Additionally, an ACNF mat exhibits excellent mechanical flexibility and electrochemical reliability, making it highly suitable for the assembly of freestanding flexible supercapacitors. By optimizing the electrochemical performance of c-MOF/ACNF and its suitability for utilization in flexible energy storage systems, this study presents a promising avenue for the practical implementation of c-MOF-based supercapacitors.

Hybrid Pore Formation in Copper Spheres by Gas Entrapment and Oxide Reduction

Solid‐state methods for producing porous metals vary greatly in their approaches and outcomes, and they often result in distinctly different pore sizes and/or characteristics. By combining methods in a hybrid process, it is possible that unique porous structures can be made that are simpler to produce, have improved functional properties, or are otherwise superior to any single approach. For the first time, a combination of gas entrapment and oxide reduction to produce microscale porosity in millimeter‐scale copper spheres created by planetary milling is reported. The milling process entraps Ar in micron to submicron pores within the spheres, which are comprised of a Cu 2 mol% CuO metal matrix composite. Upon heating at 800 °C in an inert atmosphere, the individual spheres expand and form ≈29% closed porosity with an average pore size of 1.5 μm. When those spheres are then reheated to 600 °C in a reducing atmosphere, the porosity is converted to being almost entirely open with an average size of 2.3 μm. In addition to the unique nature of the porosity, the processing of the spheres is unusual in that it is completed after only 90 min of milling.

Batch fabrication and characterization of aligned PAN-based nanofiber membranes for lithium-ion battery separators

Due to their excellent porosity, large specific surface area and unique pore structure, the electrospun nanofiber membranes (NFMs) have been widely studied as separators for high-performance lithium-ion batteries (LIBs). Here, an improved funneling air-jet electrospinning device was proposed to fabricate high-quality aligned polyacrylonitrile (PAN)-based NFMs for LIB separators in large quantities. Its spinning mechanism and effect were studied by combining numerical analysis and experiments. On this basis, the aligned PAN-based NFMs obtained were applied to the LIB separators, and their thermal stability, electrolyte affinity and related electrochemical performance were investigated. The results showed that the properties of aligned PAN separator were better than those of disordered PAN separator, and the addition of polymethyl methacrylate (PMMA) and single-wall carbon nanotubes (SWCNTs) could further improve the separator properties. Finally, the LIB assembled by superposing the aligned PAN/PMMA/SWCNTs NFM and polypropylene (PP) separator as a LIB separator (PAN/PMMA/SWCNTs//PP) had better electrochemical stability, rate and cycling capabilities (capacity retention of 102.81 % after 100 cycles), indicating that PAN/PMMA/SWCNTs//PP was a potential high-performance LIB separator.

Improving Cycle Stability and Kinetics of Rechargeable Al/CO2 Batteries By Functional Cathode Materials

Metal-CO2 batteries have emerged as a promising solution for advancing energy storage technology and sequestering carbon dioxide from ambient air. Aluminum (Al) is an appealing anode material for electrochemical CO2 capture and conversion due to its lower cost and reactivity in comparison to lithium and sodium anode materials, making it safer and more accessible for manufacturing. Its abundance across various regions of the world further adds to Al’s attractiveness. Additionally, Aluminum boasts a high specific energy of 2980A·hour/kg, suggesting that its electrochemical conversion with CO2 can produce large amounts of electrical energy. Previous study shows that Aluminum/CO2 batteries possess a remarkable discharge capability with the introduction of a small amount of oxygen, however, these batteries are not rechargeable.By utilizing a homogeneous iodine-based redox mediator, our group demonstrated that the Al-CO2 battery can achieve reversible discharge and charge with minimal overpotential of 0.05V, reducing stripping/plating overpotentials by 40% across various current rates compared to an unmodified imidazolium-based ionic liquid electrolyte. This is achieved by replacing oxygen gas with aluminum iodide in the electrolyte, which maintains high discharge capacity and enables the battery to be recharged for up to 12 cycles at a 20 mA/gcarbon rate.Examining the discharge and charge rates of different cathode materials was necessary to demonstrate the improvement in cycle stability. By utilizing functional carbon-based materials with increased surface area, heteroatom doping and unique pore structure as the cathode, we demonstrate that the rechargeable Al-CO2 battery can enhance CO2 reduction during the discharge processes, thereby improving reaction kinetics.Higher surface area and porous materials facilitate faster electron transfer during the electrochemical reactions while allowing better CO2 diffusion into the cathode, improving reaction rates.

Rapid Fabrication of Efficient and Stable Microporous Electrodes for Practical Alkaline Water Electrolysis

Efficient and stable electrode is paramount for advancing practical alkaline water electrolysis (AWE) technology. In this study, we employed a rapid and scalable laser texturing process to create microporous nickel electrodes, demonstrating promising catalytic performances for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The alkaline electrolyzer cell (AEL) incorporating laser-textured electrodes (NP-LT30) exhibited a remarkable improvement, with voltage drops exceeding 300 mV under a current density of 1 A cm−1, compared to conventional perforated Ni plate electrodes (NP) based cell. This enhancement resulted from a substantial boost in mass transport, as unveiled by in-situ electrochemical impedance analysis. Of particular note is the unique multi-channel porous structure within the NP-LT30 electrode, enabling rapid mass transport through an innovative convection mode driven by an intermittent bubble eruption (IBE) mechanism, outperforming the traditional convection mode. Furthermore, AEL using NP-LT30 electrodes demonstrated exceptional durability, maintaining performance at 1.0 A cm–2 for an impressive 300 hours. This study highlights the capability of the multi-channel structure within NP-LT30 electrodes to expedite mass transport in practical AWE applications significantly. Moreover, the cost-effective and scalable nature of laser-textured porous electrodes positions them for commercialization, enabling the production of highly efficient electrodes for practical AWE implementation.

Engineering hierarchically porous carbon nanorods electrode materials for high performance zinc ion hybrid supercapacitors

Well-defined carbon materials with tailored unique pore structure are crucial to develop advanced zinc ion hybrid supercapacitors (ZIHCs), but effective synthesis is still a challenge. Herein, hierarchically porous carbon nanorods (HPCNs) are successfully synthesized by Pluronic P123 (PEO20PPO70PEO20) mediated dynamic dual template method that tetraethylsiloxane (TEOS) and sucrose are adopted as silicon (Si) and carbon (C) precursors, respectively. During synthesis, the rod-like organic mesomorphous complexes are generated by self-assembly of cetyltrimethyl ammonium/poly-(acrylic acid) (CTAB/PAA) under the assistance of Pluronic P123 as dynamic soft templates and in-situ formed silica particles as hard templates. The synthesized HPCNs have uniform rod-like morphology, high surface area and notable specific capacity. Furthermore, the HPCNs are activated to afford AHPCNs with enriched micropores and increased surface area of 905 m2 g−1. Consequently, ZIHCs with the AHPCNs as cathode display attractive electrochemical performances including large capacity (157.1 mAh g−1 at 0.1 A g−1), exceptional rate performance (110.3 mAh g−1 at 20 A g−1), high energy density (125.7 Wh kg−1) and power density (16 kW kg−1). Moreover, ZIHCs demonstrated brilliant capacity retention of 100% even after 10,000 cycles at 5 A g−1. Our work presents an effective approach for controllable engineering of hierarchically porous carbon nanorod materials. Meanwhile, it also offers theoretical and technical support to develop advanced zinc ion capacitor energy storage devices.