Controlled Pore Size Research Articles

Accelerating Anhydrous Proton Transport in Covalent Organic Frameworks: Pore Chemistry and its Impacts.

Proton conduction is important in both fundamental research and technological development. Here we report designed synthesis of crystalline porous covalent organic frameworks as a new platform for high-rate anhydrous proton conduction. By developing nanochannels with different topologies as proton pathways and loading neat phosphoric acid to construct robust proton carrier networks in the pores, we found that pore topology is crucial for proton conduction. Its effect on increasing proton conductivity is in an exponential mode other than linear fashion, endowing the materials with exceptional proton conductivities exceeding 10-2 S cm-1 over a broad range of temperature and a low activation energy barrier down to 0.24 eV. Remarkably, the pore size controls conduction mechanism, where mesopores promote proton conduction via a fast-hopping mechanism, while micropores follow a sluggish vehicle process. Notably, decreasing phosphoric acid loading content drastically reduces proton conductivity and greatly increases activation energy barrier, emphasizing the pivotal role of well-developed proton carrier network in proton transport. These findings and insights unveil a new general and transformative guidance for designing porous framework materials and systems for high-rate ion conduction, energy storage, and energy conversion.

E-peroxone with a novel GDE decorated with hydrophobic membrane for the degradation of pyridine: Stability, byproducts and toxicity

E-peroxone process is an emerging electrochemical oxidation process, based on ozone and the in-situ cathodic generation of H2O2, but the stability of cathode is one of the key restraining factors. In this study, we designed a multilayer gas diffusion electrode (GDE) decorated with a commercial hydrophobic membrane for the degradation of pyridine. It was found that a proper control of membrane pore sizes and hot-pressing temperature can significantly promote the GDE stability. Subsequently, key operational parameters of the constructed E-peroxone system were investigated, including the ozone concentration, current density, pH value, electrolyte type and initial concentration of pyridine. The degradation pathways were proposed according to six identified transformation products. The toxicity variation along the degradation progress was evaluated with microbial respiration tests and Toxicity Estimation Software Tool (T.E.S.T.) calculation and an efficient detoxification capacity of E-peroxone was observed. This research provides a theoretical basis and technical support for the development of highly efficient and stable E-peroxone system for the elimination of toxic organic contaminants.

Application of mesoporous silica particles as an additive for controlling rheological, thermal, and filtration properties of water-based fluids

Mesoporous silica particles (MSP) have received increasing interest for various applications because of their unique features such as controlled pore size, low density, high chemical and thermal stability, and high surface area. In this study, MSP was applied as an additive in water-based drilling fluids (WBMs). The effect of MSP on the rheological, thermal, filtration, and structural properties of WBMs was investigated. The results were compared with those of analogous fluids containing conventional nonporous silica particles (SSP). Rheological assays showed shear-thinning and viscoelastic behavior, which were more noticeable for fluids including MSP. It was observed that low concentrations of MSP (0.25 %wt) can achieve the same rheological properties as the fluids with higher SSP content (up to 0.5 %wt). The rheological properties of SSP-containing fluids were not significantly affected by the presence of NaCl or aging tests. The theoretical Herschel–Bulkley model represents the rheological behavior of WBMs. The MSP-based WBMs exhibited better filtration properties before aging. The microstructures of the WBMs were analyzed using Scanning Electron Microscopy (SEM). A homogeneous distribution of SSP in the WBMs was observed, while particle agglomeration was observed in WBMs containing MSP. In addition, surface interactions were studied to elucidate the interactions between particles and fluid constituents. The surface interaction, assessed through ζ-potential and FTIR analysis, revealed that the binding affinities of BT, PAC, and XGD with MSP were augmented compared to their individual values. Based on the experimental results, MSP constitutes a promising alternative as an additive for the design of WBMs.

Impact of nanopores in porous GaN on LED emission based on FDTD simulations

We simulated the light extraction efficiency (LEE) of porous GaN-based InGaN/GaN micrometer-sized light-emitting diodes (μLEDs) emitting within the visible wavelength range using the finite-difference time-domain (FDTD) method. The simulations show that the embedding of a porous GaN layer with 40 % porosity reduces the bottom LEE, while the top side LEE of the μLEDs is increased. In addition, it also exhibits complex scattering properties that affect the microcavity structure of these devices. The LEE and the degree of microcavity structure disruption are related to nanopore size and location. This association weakens with increasing wavelength. Also, a decrease in nanopore size corresponds to a diminished impact on μLED optical properties. Since the porous GaN layer contributes to the deposition of high-quality InGaN, controlling pore size of the porous GaN layer will aid the development of GaN-based red μLEDs and full-color displays.

Nitrogen-enriched nanoporous polytriazine as efficient electrode material for high-performance supercapacitor application in non-aqueous medium with high cyclic stability

Nitrogen-enriched nanoporous polytriazine (NENP) synthesized by conventional heating method possesses a high specific surface area (SABET) of 966 m2 g−1, controlled pore size distribution (1.6, 5, and 8.3 nm) and total pore volume of 2.73 cm3 g−1. The synthesized specimen was utilized as an electrode material for supercapacitor (SC) application in non-aqueous media. The electrodes of NENP were fabricated by two approaches viz., conventional binder-based method and a binder-free electrophoretic deposition (EPD) approach. In case of electrode fabrication by controlled EPD process, the mass of 0.58 mg was obtained as the optimized mass achieved at pH = 2, deposition voltage = 20 V and deposition time = 6 min. The optimized electrodes and tetraethylammonium tetrafluoroborate in adiponitrile (TEA-BF4/ADP) non-aqueous electrolyte were used to fabricate symmetric supercapacitor devices (SC). The SC device, with EPD- based binder-free electrodes, exhibited higher specific capacitance (Csp = 84 F g−1), energy density (Esp = 118.8 Wh kg−1) and power density (Psp = 17 kW kg−1) compared to SC device (49 F g−1, 68.8 Wh kg−1, and 11 kW kg−1 at 0.8 A g−1) fabricated using electrode made from the binder based method. To enhance the SC performance, KI was added as a redox additive to the non-aqueous electrolyte (TEA-BF4/ADP). The SC device, with NENP binder-free electrodes and redox-active nonaqueous electrolyte (TEA-BF4/ADP/KI), achieved the highest Csp, Esp, and Psp (112 F g−1, 150.5 Wh kg−1, and 27 kW kg−1) and demonstrated high cyclic stability (~80.2 % initial capacitance retention after 30,000 cycles, at 5 A g−1).

Functionalized Zr‐MOFs for Enhancing Flame Retardancy and Smoke Suppression Performance on TPU

AbstractMetal‐Organic Framework (MOF) materials can be used as flame‐retardants and smoke suppressants for polymers. As a MOF material, UIO‐66(Zr) possesses higher thermal stability and controllable pore size. In this paper, UIO‐66(Zr), NH2‐UIO‐66(Zr), and SiO2, MWCNT, and GO functionalized NH2‐UIO‐66(Zr) was fabricated to improve the flame retardant and smoke suppression performance of thermoplastic polyurethanes (TPU). The experimental results show that compared with neat TPU (LOI value 19.1 %), 2 % usage of UIO‐66(Zr) and NH2‐UIO‐66(Zr) can endow TPU with 26 % LOI value and vertical combustion rating of V‐1. Moreover, SiO2, MWCNT, and GO functionalized NH2‐UIO‐66(Zr) provide TPU with above 27.8 % LOI value and vertical combustion rating of V‐0. Meanwhile, the CCT results showed that the peak heat release rate and total heat release of TPU‐U5 (added 2 % GO‐modified NH2‐UIO‐66(Zr)) are 299.52 Kw ⋅ m−2 and 68.21 MJ m−2, much lower than that of neat TPU, which are 1180.05 Kw ⋅ m−2and 104.87 MJ m−2, respectively. The TGA, char residue EDS and XRD analysis show that SiO2, MWCNT, and GO functionalized NH2‐UIO‐66(Zr) could generate zirconium metal oxide during the combustion process, which acts as a physical barrier to prevent the TPU matrix by promoting the generation of carbonization layer. The zirconium metal oxide and carbonization layer also can confine flammable gases, which can delay the ignition time and hinder the overflow of gas. In addition, NH2‐UIO‐66(Zr) could generate non‐flammable N2 diluting the concentration of flammable gases. The mechanical properties of TPU composites can maintain more than 87 % of the neat TPU after the addition of 2 % SiO2, MWCNT, and GO functionalized NH2‐UIO‐66(Zr). These results indicate that functionalized Zr‐MOFs composites could act as excellent flame‐retardants in TPU.

Polyoxometalate/MOF-derived MoSe2/(Ni, Co)Se2 for battery-type electrodes of high-performance supercapacitors

Polyoxometalates (POMs), as multinuclear metal oxide clusters, possess natural multi-electron redox properties and high electrical conductivity. However, their susceptibility to leaching and agglomeration limits their application in energy storage. MOF materials provide a solution to the limitation of POMs due to their controllable pore sizes, big surface areas and strong adsorption properties. The synergistic effect between the two components greatly improves the electrochemical properties of the composites. In view of this, PMo12 is encapsulated in ZIF-67 to form PMo12@ZIF-67 by in situ self-assembly, and benefitted from this unique precursor, MoSe2/(Ni, Co)Se2 hollow structures assembled by nanoparticles are synthesized though Ni2+ etching and selenization process. At the same time, the PMo12 content is optimized to get the best performance of 60-MoSe2/(Ni, Co)Se2. In the three-electrode test, the developed 60-MoSe2/(Ni, Co)Se2 electrode material exhibits an excellent specific capacity of 359.9 mA h g−1 at a current density of 1 A g−1, and a capacitance retention rate of 83.7 % after 10,000 cycles. In addition, the asymmetric supercapacitor (ASC) assembled with a positive electrode of 60-MoSe2/(Ni, Co)Se2 and a negative electrode of activated carbon exhibits an excellent energy density of 40.3 W h kg−1 at a power density of 800.9 W kg−1. These superior electrochemical properties are attributed to the unique electronic structure of PMo12, which further demonstrates the feasibility of constructing hollow multicomponent selenides as energy storage materials using PMo12-ZIF-67 as a precursor.

Confinement Effects on Proton Transfer in TiO2 Nanopores from Machine Learning Potential Molecular Dynamics Simulations.

Improved understanding of proton transfer in nanopores is critical for a wide range of emerging applications, yet experimentally probing mechanisms and energetics of this process remains a significant challenge. To help reveal details of this process, we developed and applied a machine learning potential derived from first-principles calculations to examine water reactivity and proton transfer in TiO2 slit-pores. We find that confinement of water within pores smaller than 0.5 nm imposes strong and complex effects on water reactivity and proton transfer. Although the proton transfer mechanism is similar to that at a TiO2 interface with bulk water, confinement reduces the activation energy of this process, leading to more frequent proton transfer events. This enhanced proton transfer stems from the contraction of oxygen-oxygen distances dictated by the interplay between confinement and hydrophilic interactions. Our simulations also highlight the importance of the surface topology, where faster proton transport is found in the direction where a unique arrangement of surface oxygens enables the formation of an ordered water chain. In a broader context, our study demonstrates that proton transfer in hydrophilic nanopores can be enhanced by controlling pore size, surface chemistry, and topology.

Development of PLA/HA porous scaffolds with controlled pore sizes using the combined freeze drying and sucrose leaching technique for bone tissue engineering

The combination of freeze drying and sucrose leaching technique was employed to fabricate PLA/HA scaffolds with controlled pore size. The influence of the HA content and sucrose size on the scaffold properties was investigated. The fabricated scaffolds showed porous properties with a porosity of 44% to 58% and pore size of 461 μm to 688 μm. The results indicated that the scaffolds possessed favorable porous properties, illustrated by good interconnectivity, appropriate pore size, and suitable porosity. These characteristics were crucial for facilitating bone cell growth and promoting the formation of new tissue within the scaffold structure. The compressive modulus of the scaffolds was examined and found to be in the range of 3.35 MPa to 5.75 MPa. Furthermore, the degradation behavior of the scaffolds was studied for 28 days in a Phosphate Buffered Saline solution. The results showed that the degradation rate was varied in the range of 6% to 14%. The water uptake of the scaffolds exhibited a range between 180% and 200%. Enhancement in water uptake was observed with higher HA content and increased sucrose size. Consequently, the scaffolds developed in this study hold promise as optimal candidates for bone tissue engineering applications.

Mesophase pitch-derived porous carbon constructed by template/activation synchronous pore-forming technology for electrochemical energy storage

Porous carbon materials with high specific surface area and wide pore size distribution play a crucial role in the energy storage process. In this paper, a mixed sol-gel system of carbon source, chemical activator and salt template agent was constructed using raw pitch, o-xylene soluble substance and their mesophase as carbon source, NaCl as template agent and KOH as activator. After one step process of high temperature treatment, porous carbon materials with high specific surface area (SBET 1969 m2/g) and wide nanopore distribution (0.4–6 nm) were obtained. The electrochemical properties of the prepared mesophase porous carbon materials were tested. At a charge-discharge rate of 80 mA/g, a specific capacitance of 102.5 F/g can be achieved for porous carbon materials obtained from the o-xylene soluble mesophase, indicating the feasibility of preparing porous carbon electrode materials by o-xylene soluble mesophase. The development of template/activation synchronous pore-forming technology can integrate the advantages of the two kinds of pore-forming technologies, reduce the demand for pore size control in porous carbon materials, and promote the one-step realization of porous carbon materials with high specific surface area, wide pore size distribution and controllable pore size.

Fabrication of high-performance recrystallized silicon carbide ceramic membrane based on particle packing optimization

Overcoming the challenges associated with achieving high uniformity and connectivity of pore channels in ceramic membranes, we designed silicon carbide ceramic membrane derived from the recrystallization process based on the Dinger-Funk equation of the closest-packing model with various grain grading. Furthermore, the effects of particle size distribution on the resulting microstructure and pore architecture of the ceramic membrane was also explored. The findings corroborated the critical importance of raw material particle size distribution in controlling pore size distribution and morphology. After sintering at 1900°C, the silicon carbide ceramic membrane, benefiting from ideal particle packing, exhibited a remarkably uniform pore structure. Notably, the most probable pore size constituted over 70 %, while achieving an open porosity of 51.3 % even without the addition of pore-forming agents. The silicon carbide ceramic membrane also demonstrated exceptional hydrophilicity (water contact angle:∼0°), impressive water permeation (1210 L m−2 h−1·bar−1), coupled with efficient turbidity removal (∼100 %) in carbon black wastewater treatment applications. Additionally, membrane regeneration proved effective using a dilute NaOH solution backwash, achieving a flux recovery efficiency of 98 %. This strategy had directive significance for designing high-performing silicon carbide ceramic membranes.

Design of PVDF hollow fiber membranes with stable crystalline and porous structure by solvent‐free method

AbstractOne of the critical principles of green chemistry and environmental sustainability is to avoid using harmful solvents in chemical processes. In this study, a novel solvent‐free method was employed to prepare poly (vinylidene fluoride) (PVDF) hollow fiber composite membranes with stable crystalline and porous structures. Utilizing the cold‐hot stretching method, the crystalline structure and orientation of PVDF were effectively redesigned, resulting in improved mechanical and penetration properties of the membrane. Additionally, an investigation into the internal crystalline structure of the PVDF hollow fiber membrane was conducted, focusing on crystalline changes induced by ion‐dipole interactions. Results indicated that the addition of neutral ion‐dipole functional particles (N‐P) promoted the conversion of α crystalline to β crystalline, leading to stable β crystalline and controllable pore sizes in the prepared PVDF hollow fiber membrane. Furthermore, the internal crystalline structure significantly contributed to enhancing the membrane's mechanical properties and penetration performance. Notably, a PVDF hollow fiber with high β crystalline content was achieved through 150% cold‐hot stretching and the addition of 20. wt% N‐P further enhanced the β‐crystalline content in the membrane. This study presents a promising approach for reducing solvent consumption and minimizing environmental impact in the field of environment‐friendly membrane fabrication.

Solvothermal Fabrication of Mesoporous Pd Nano-Corals at Mild Temperature for Alkaline Hydrogen Evolution Reaction.

Porous metallic nanomaterials exhibit interesting physical and chemical properties, and are widely used in various fields. Traditional fabrication techniques are limited to metallurgy, sintering, electrodeposition, etc., which limit the control of pore size and distribution, and make it difficult to achieve materials with high surface areas. On the other hand, the chemical preparation of metallic nanoparticles is usually carried out with strong reducing agents or at high temperature, resulting in the formation of dispersed particles which cannot evolve into porous metal. In this study, we reported the simple fabrication of coral-like mesoporous Pd nanomaterial (Pd NC) with a ligament size of 4.1 nm. The fabrication was carried out by simple solvothermal reduction at a mild temperature of 135 °C, without using any templates. The control experiments suggested that tetrabutylammonium bromide (TBAB) played a critical role in the Pd(II) reduction into Pd nanoclusters and their subsequent aggregation to form Pd NC, and another key point for the formation of Pd NC is not to use a strong reducing agent. In alkaline water electrolysis, the Pd NC outperforms the monodisperse Pd NPs and the state-of-the-art Pt (under large potentials) for H2 evolution reaction, probably due to its mesoporous structure and large surface area. This work reports a simple and novel method for producing porous metallic nanomaterials with a high utilization efficiency of metal atoms, and it is expected to contribute to the practical preparation of porous metallic nanomaterials by solvothermal reductions.

Silk Fibroin-Laponite Porous Microspheres as Cell Microcarriers for Osteogenic Differentiation.

Silk fibroin (SF) has garnered significant attention as a natural polymer for fabricating porous scaffolds in various engineering applications. However, the limited osteoinductive property of SF has hindered its efficacy in bone repair applications. In this study, we constructed an SF-based injectable porous microcarrier that is doped with laponite (LAP), containing magnesium ions (Mg2+). The influence of freezing temperatures and concentrations of SF and LAP on the structural parameters of SF-LAP microcarriers was investigated. The SF-LAP microcarrier exhibited a porosity of 76.7 ± 1.2% and a controlled pore size of 24.6 ± 4.0 μm. At the 6 weeks of in vitro degradation test, a mild alkaline level in culture medium containing SF-LAP microcarriers was detected. The release of Mg2+ from the SF-LAP microcarrier was maintained at a concentration within the range of 1.2-2.3 mM during the 6 weeks. The seeded human adipose-derived stem cells in the SF-LAP microcarrier demonstrated a significant enhancement in osteogenic differentiation compared with cells seeded in the pure SF microcarrier, as evidenced by quantitative alkaline phosphatase activity and the expression of osteogenic marker genes. These findings underscore the potential of the SF-LAP microcarrier as an ideal cell carrier in the treatment of bone defects.

Controlling pore size and photothermal layer to improve solar-porous evaporation performance

Controlling pore size and photothermal layer to improve solar-porous evaporation performance

Control of Pore Sizes in Epoxy Monoliths and Applications as Sheet-Type Adhesives in Combination with Conventional Epoxy and Acrylic Adhesives.

Materials with monolithic structures, such as epoxy monoliths, are used for a variety of applications, such as for column fillers in gas chromatography and HPLC, for separators in lithium-ion batteries, and for precursor polymers for monolith adhesion. In this study, we investigated the fabrication of epoxy monoliths using 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (TETRAD-C) as the tetrafunctional epoxy and 4,4'-methylenebis(cyclohexylamine) (BACM) as the amine curing agent to control pore diameters using polyethylene glycols (PEGs) of differing molecular weights as the porogenic agents. We fabricated an epoxy monolith with micron-order pores and high strength levels, and which is suitable for the precursors of composite materials in cases where smaller PEGs are used. We discussed the effects of the porous structures of monoliths on their physical properties, such as tensile strength, elongation, elastic modulus, and glass transition temperatures. For example, epoxy monoliths prepared in the presence of PEGs exhibited an elastic modulus less than 1 GPa at room temperature and Tg values of 175-187 °C, while the epoxy bulk thermoset produced without any porogenic solvent showed a high elastic modulus as 1.8 GPa, which was maintained at high temperatures, and a high Tg of 223 °C. In addition, the unique adhesion characteristics of epoxy monolith sheets are revealed as a result of the combinations made with commercial epoxy and acrylic adhesives. Epoxy monoliths that are combined with conventional adhesives can function as sheet-type adhesives purposed with avoiding problems when only liquid-type adhesives are used.

Sodium lignosulfonate/graphene composites for efficient desalination by incorporating CoS to control pore size

The phenomenon of overlapping double layers due to micropores inhibits capacitive deionization performance, which is improved by increasing the pore size. In this study, a novel ternary composite electrode (sodium lignosulfonate/reduced graphene oxide/cobalt sulfide, LGC) was designed using a two-step hydrothermal method. CoS with high pseudocapacitance modifies sodium lignosulfonate and graphene connected by hydrogen bonding, benefiting from the constitutive steric structure. The electrochemical performance was significantly enhanced, and the desalination capacity substantially improved. The LGC electrode specific capacitance was as high as 354.47 F g−1 at a 1 A g−1 current density. The desalination capacity of the capacitive deionization device comprising LGC and activated carbon in 1 M NaCl electrolyte reached 28.04 mg g−1 at an operating condition of 1.2 V, 7 mL min−1. Additionally, the LGC electrodes degraded naturally post the experiment by simply removing the CoS, suggesting that the LGC composites are promising material for capacitive deionization electrodes.

Innovative membrane technology for water treatment solutions: Current status and future prospects of carbon nanotube membranes

Carbon nanotube (CNT)-based membranes are gaining attention for their unique properties and applications in membrane technology. This review comprehensively explores major types of CNT-based membranes—buckypaper, CNT mixed, and vertically aligned CNT membranes—along with their fabrication methods, pore size control strategies, unique properties, and potential applications. Understanding these aspects will help fully harness the potential of CNT-based membranes in addressing challenges in water treatment and other fields. CNTs offer promise as water treatment membranes due to their ability to enhance performance of existing membranes, overcome trade-offs, exhibit antibacterial properties, and facilitate fast water transport.

Hierarchically porous electrospun carbon nanofiber for high-rate capacitive deionization electrodes

Capacitive deionization (CDI) is a promising technology that has gained interest for the desalination of brackish water. Hierarchically porous carbons are commonly used as electrodes for CDI due to their high surface areas and controlled pore size distributions that maximize ion adsorption capacity and rate. Electrospinning is an effective way of generating carbon nanofibers with high inter-fiber macroporosity that can be further modified to improve surface area, total pore volume, and pore size distribution. This work describes the use of sacrificial mesopore formers in tandem with a micropore etching technique to induce hierarchical porosity in electrospun fibers. Mesopores are formed via the dissolution of silica nanoparticles that are introduced into the fibers during the electrospinning step. After mesopore formation, micropores are etched into the resulting surface through KOH impregnation and thermal activation. This sequential technique creates a hierarchical network of pores from the inherent macroporosity of the fiber network, to the mesopores, and finally micropores to simultaneously maximize surface area and accessibility. Micropore formation is optimized to maximize specific surface area while maintaining physical integrity of the fibers. The combination of mesopores and micropores enables fast ion adsorption rates and capacity. Carbon fiber electrodes fabricated in this method achieve specific surface areas exceeding 1400 m2 g−1, with pore volumes exceeding 1.0 cc g−1. The pore size distributions are highly controlled, with 80 % of total pore volume coming from pores <20 nm in radius. In 500 ppm constant voltage CDI tests, these fiber electrodes obtain a salt adsorption capacity of over 14 mg g−1 at a salt adsorption rate of ∼4 mg g−1 min−1, showcasing the high capacity matched with high rate of these easily fabricated, inexpensive materials.

Fabrication of phosphorylated UiO-66 for efficient selective removal of Pb2+ from acidic wastewater

Metal-organic framework (MOF) materials have emerged as promising candidates for treating heavy metal wastewater because of their controllable pore size, high specific surface area, and abundant active sites. Nevertheless, the currently reported MOFs usually require near-neutral environments (pH = 5–6) to achieve efficient removal of Pb2+ and cannot be applied to acidic environments (pH = 2–3). In this work, the structurally stabilized zirconium-based MOF UiO-66 was chosen as the object of study. Three phosphate ester-based MOFs (UiO-66-(OPO3)X) containing different amounts and spatial positions were designed and prepared by simple chemical modification and used to remove Pb2+. Adsorption experiments showed that they could reach adsorption equilibrium in 30 min with excellent adsorption rate. Owing to the unique ionization ability of the phosphate ester group, UiO-66-(OPO3)X maintains a high removal efficiency of Pb2+ even at pH = 2 and pH = 3. In addition, selectivity and competition experiments demonstrated that UiO-66-(OPO3)X possessed excellent selectivity and anticompetitive ability towards Pb2+.The excellent regeneration performance demonstrates their value for practical application. Moreover, the adsorption mechanism was investigated in detail by experiment combined with density functional theory (DFT).