Optimized Pore Structure Research Articles

Investigation and Preparation of the Plastering Mortar for Autoclaved Aerated Blocks Walls

The increase in the use of aerated concrete blocks (AAB) in construction walls has increased the demand for specialized plastering mortar, which should have the characteristics of high water retention, low water absorption, low thermal conductivity and high toughness. This study scrutinized the potential of expanded and vitrified small ball (EVSB) and expanded perlite as lightweight aggregates, and the beneficial effect of a modifying additive based on a mixture of ethylene-vinyl acetate (EVA), hydroxypropyl methylcellulose (HPMC) and fibers has been proved. The dry density, consistency, water absorption, mechanical strength, pore characteristics and micro morphology of the plaster mortar were evaluated. It is manifested by enhanced toughness, reduced dry density, and optimized pore structure characteristics. The relationship between mass water absorption and freeze-thaw cycle resistance is established, which shows that when the mass water absorption is 20%, the mortar exhibits better freeze resistance. After 25 freeze-thaw cycle tests, the mass loss was 0.26% and the strength loss was 1.41%. Through the comparison of test results, a new composition of plastering mortar is provided: cement: fly ash: water: heavy calcium carbonate: quartz sand: EVSB: EVA: HPMC (100,000 mPa·s): fiber = 70: 30: 76: 12: 250: 24: 2: 0.3: 0.2.

Regulation of the mesopore proportion of porous carbon for optimizing the performance of electric double layer capacitors

So far, there are still some difficulties in controlling the pore structure of porous carbon materials. Exploring the relationship between the structure and electrochemical behavior of porous carbon through optimizing pore structure is of great significance for its application in the field of energy storage.Here, we employ the interpenetrating polymer networks as the precursor to prepare ultra-microporous carbon with a pore diameter of 0.6 nm, and regulate the mesoporous content by chemical activation. The relationship between mesoporosity and electrochemical performance was studied. In our experimental results, the optimized sample has a mesoporous ratio of 55.1% and the specific surface area of 2453 m2g−1. As electrode material, its specific capacity reaches 247F g−1with excellent cycle performance. As the symmetric device, its specific energy reached 17.75Wh kg−1.

On the Porous Structuring using Unit Cells

This study presents the characteristics of the eleven commonly used porous structures. The structures are designed using ten different unit cells. Some of the unit cells consist of free-form surfaces (e.g., triply periodic minimal surface). Some of them are straightforward in design (e.g., honeycomb structure). Some of them have a hybrid structure. The 3D CAD models of the structures are created using commercially available CAD software. The finite element analysis is conducted for each structure to know how it behaves under a static load. The structures are also manufactured using a 3D printer to confirm the manufacturability of them. It is found that some of the structures are easy to manufacture, and some are not. Particularly, metal-alloy-printed structures need a minimal thickness. However, the structures’ printed or virtual models are evaluated by determining their respective mass, production cost, production time, Mises stress, and surface area. Using the values of mass, production time and cost, Mises stress, and surface area, the optimal structure is identified. Thus, the outcomes of this study can help identify the optimal porous structure for a given purpose.

Effect of optimized pore structure on sealing performance of drilling sealing materials in coal mine

To enhance the drilling sealing material's performance, SiO2, sodium silicate, and styrene-acrylic emulsion are selected to optimize the pore structure. Through the uniaxial compression experiment, NMR, SEM, and combined with fractal theory, each substance's influence on the pore structure and physical strength of the sealing material is analyzed qualitatively and quantitatively. The results show that the synergistic effect of styrene-acrylic emulsion and SiO2 on cement performance improvement is better than that of a single substance. The porosity of the optimized material decreases by more than 13.49%, and the peak stress of uniaxial compression is increased by more than 18.08%. Besides, the styrene-acrylic emulsion can improve the material's elastic modulus and enhance the material's ability to resist harmful external factors. Sodium silicate can hinder the optimization effect of SiO2 and styrene-acrylic emulsion. Compared with ordinary cement, the peak stress of materials containing these three substances is reduced by 3.05%, and the porosity is decreased only by 0.73%. Comparing the fractal dimension of each material, SiO2 and styrene-acrylic emulsion increases the total pore fractal dimension (Dw) and the percolation pore fractal dimension (Ds) of the material. The fractal dimension has a positive linear correlation with the porosity, which indicates that the pore structure of the material is optimized, and the pore connectivity is reduced.

Optimization Strategies of Preparation of Biomass-Derived Carbon Electrocatalyst for Boosting Oxygen Reduction Reaction: A Minireview

Oxygen reduction reaction (ORR) has attracted considerable attention for clean energy conversion technologies to reduce traditional fossil fuel consumption and greenhouse gas emissions. Although platinum (Pt) metal is currently used as an electrocatalyst to accelerate sluggish ORR kinetics, the scarce resource and high cost still restrict its further scale-up applications. In this regard, biomass-derived carbon electrocatalysts have been widely adopted for ORR electrocatalysis in recent years owing to their tunable physical/chemical properties and cost-effective precursors. In this minireview, recent advances of the optimization strategies in biomass-derived carbon electrocatalysts towards ORR have been summarized, mainly focusing on the optimization of pore structure and active site. Besides, some current challenges and future perspectives of biomass-derived carbon as high-performance electrocatalysts for ORR have been also discussed in detail. Hopefully, this minireview will afford a guideline for better design of biomass-derived carbon electrocatalysts for ORR-related applications.

Boosting electrochemical performance of activated carbon by tuning effective pores and synergistic effects of active species

Clean energy conversion/storage techniques have become increasingly significant because of the increasing energy consumption. Regarding practical applications like zinc-air batteries and supercapacitors, electrode materials are essential and often require both porous networks and active species to enhance their electrochemical performance. Nitrogen-doped porous carbon (NPC) is a kind of promising material, which provides efficient active sites and large surface areas for energy conversion/storage applications. However, rational modulation of properties for maximizing NPC performance is still a challenge. Herein, a promising NPC material derived from natural biomass is successfully synthesized by following a stepwise preparation method. Physisorption and X-ray photoelectron spectroscopy (XPS) analyses demonstrate both pore structures and nitrogen species of the NPC have been delicately tuned. The optimized sample NPC-800-m exhibits excellent performance in both oxygen reduction reaction (ORR) and three-electrode supercapacitor measurement. Moreover, the homemade zinc-air battery and symmetric supercapacitor assembled with NPC-800-m also display outstanding energy and power density as well as durable stability. Density functional theory (DFT) calculations further confirm the synergistic effects among graphitic, pyridinic and pyrrolic nitrogen. The existence of multispecies of nitrogen combined with the optimized pore structure is the key to the high electrochemical performance for NPC-800-m. This work not only provides feasible and green synthetic methodology but also offers original insights into the effective pores and the synergistic effects of different nitrogen species in the NPC materials.

Topology-Dependent Alkane Diffusion in Zirconium Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) can be designed for chemical applications by modulating the size and shape of intracrystalline pores through selection of their nodes and linkers. Zirconium nodes with variable connectivity to organic linkers allow for a broad range of topological nets that have diverse pore structures even for a consistent set of linkers. Identifying an optimal pore structure for a given application, however, is complicated by the large material space of possible MOFs. In this work, molecular dynamics simulations were used to determine how a MOF's topology affects the diffusion of propane and isobutane over the full range of loadings and to understand how MOFs can be tuned to reduce transport limitations for applications in separations and catalysis. High-throughput simulation techniques were employed to efficiently calculate loading-dependent diffusivities in 38 MOFs. The results show that topologies with higher node connectivity have reduced alkane diffusivities compared to topologies with lower node connectivity. Molecular siting techniques were used to elucidate how the pore structures in different topologies affect adsorbate diffusivities.

Isoreticular Microporous Metal–Organic Frameworks for Carbon Dioxide Capture

The isoreticular principle has been applied to construct two copper metal-organic framework (MOF) analogues with different porosities for the adsorptive capture of CO2 from N2 and CH4 at 1 atm and 298 K. By using a 4-substituted isophthalate linker with a bulky nitro group, the microporous MOF [Cu(BDC-NO2)(DMF)] (UTSA-93 or CuBDC-NO2; H2BDC-NO2 = 4-nitroisophthalic acid and DMF = N,N'-dimethylformamide) has been synthesized with mot topology, showing a compact pore structure with a size of 6.0 × 7.0 Å2 in contrast to that of 6.9 × 8.5 Å2 in the prototypical MOF with a bromo group. The optimized pore structure allows the nitro-functionalized MOF to capture CO2 with a higher capacity of about 2.40 mmol g-1 under ambient conditions, in contrast to 1.08 mmol g-1 in the bromo-functionalized analogue. The adsorption selectivity of CuBDC-NO2-a for a CO2/N2 (15:85) mixture (28) under ambient conditions is also higher than that of the bromo-substituted prototype (25) and comparable with those of several MOF materials. Moreover, dynamic breakthrough experiments of the nitro-functionalized MOF have been performed to illustrate its separation potential toward a CO2/N2 mixture.

Simulation of forced convective heat transfer in Kelvin cells with optimized skeletons

The optimization of pore structure for metal foam is a feasible method for reducing the pressure drop and improving the overall heat transfer performance, especially at high velocity. In this regard, the optimized Kelvin cell with elliptical skeletons with a cross-section ratio of the long axis to the short axis (b/a) of 1.0, 1.4, and 2.0 are considered to evaluate the effects of b/a on the pressure drop and the heat transfer coefficient (HTC). The results indicate that both the pressure drop and HTC decrease with an increase in b/a. However, the pressure drop reduces more significantly. For instance, as b/a increases from 1.0 to 2.0, the pressure drop and the volumetric HTC at 90 m/s decrease by 98.5% and 6.3%, respectively. Therefore, the value of the volumetric area goodness factor (which considers both the effect of heat transfer coefficient and pressure drop on the overall heat transfer performance) jv/fof the sample with b/a = 2.0 is 86.7% higher than the sample with b/a = 1.0 at 90 m/s. As the velocity increases, the effect of b/a on the overall heat transfer performance increases. Compared with the cylindrical skeleton velocity distribution and pressure drop, the elliptical skeletons lead to a more uniform velocity distribution and reduce pressure drop significantly; nevertheless, the temperature distributions barely change. Moreover, the elliptical skeleton increases the specific surface area. Therefore, the jv/fof the elliptical skeleton significantly improves. This study provides a new direction for the design of novel metal foams with excellent overall heat transfer performance for heat transfer devices.

Porosity and hydrophilicity modulated quaternary ammonium-based sorbents for CO2 capture

Quaternary ammonium (QA)-based polymeric sorbents are known to be effective for CO2 capture, especially from ultradilute streams like air. In this work, we address two major challenges in QA sorbent design for application in moisture-swing processes, porosity control and hydrophilicity modulation. Facilely substituting porous CO2-active components for non-porous ones can enhance the sorption kinetics by 4-fold compared to the state-of-art, and micro–mesoporous structures are identified as optimal porous structures. A method to modulate the hydrophilicity of QA-based sorbents is developed using controlled radical polymerization, incorporating fluorine-containing monomers. The CO2 sorption capacity and the tolerance towards moisture are simultaneously enhanced via adjustment of the structure and the content of fluorine-containing blocks. We postulate that porosity and hydrophilicity optimization can make QA-based sorbents adaptive to deployment of scalable moisture-swing processes in varied and complex atmospheric circumstances.

Utilization of barium slag to improve chloride-binding ability of cement-based material

In this study, barium slag (BS) was utilized as a supplementary cementitious material (SCM) to improve the chloride-binding ability of cement pastes. Hardened paste specimens with 0–30% BS content were prepared, and the chloride binding rate (CBR) was evaluated. The compressive strength was tested, and the hydration heat was assessed. The mechanism behind was investigated by XRD, TGA, NMR, EDS, and MIP analyses. The results showed that 10–30% BS greatly promoted the CBR of the cement-BS system. The reasons were demonstrated in three angles: a) the physical resistance of ion-migration was enhanced because of the optimized pore structures; b) the chemically combined chloride was significantly strengthened because the formation of Friedel’s salt in hardened pastes was facilitated; c) the physically adsorbed chloride was reduced because less amount of C–S–H gel was generated. These inferences provided one innovative way of utilizing BS in the Portland cement system and might provide useful experience in promoting the chloride-binding ability of cementitious materials.

Influence of pore size optimization in catalyst layer on the mechanism of oxygen transport resistance in PEMFCs

In PEMFC, the oxygen transport resistance severely hinders the cell from achieving high performance. In this paper, pore-forming agent was used to optimize the pore size distribution of the catalyst layer (CL), and to study its effect on the mechanism of oxygen transport resistance, including molecular diffusion resistance, Knudsen diffusion resistance, and local O2 resistance in CL. The results showed that with the pore formation the cell performance had a significant improvement at high current density, mainly due to its better oxygen transport properties, especially under low platinum conditions. The addition of pore-forming agent moved the pore diameter toward a larger pore diameter with a range from 70 to 100 nm, and also obtaining a higher cumulative pore volume. It was found that the increase of the cumulative pore volume and larger pore size were conducive to the diffusion of oxygen molecules in CL, and the resistance caused by which was the dominant part in total transport resistance. Further tests indicated that the improvement of molecular diffusion resistance was much larger than that of Knudsen diffusion resistance in the catalyst layer after pore formed. In addition, the optimized pore structure will also get a higher number of effective pores, which resulted in an increased effective area of the ionomer on the Pt surface. The higher effective area of the ionomer was particularly beneficial for the reduction of local O2 resistance with low Pt loading.

Encapsulation of Se into Hierarchically Porous Carbon Microspheres with Optimized Pore Structure for Advanced Na-Se and K-Se Batteries.

Sodium-selenium (Na-Se) and potassium-selenium (K-Se) batteries have emerged as promising energy storage systems with high energy density and low cost. However, major issues such as huge Se volume changes, polyselenide shuttling, and low Se loading need to be overcome. Although many strategies have been developed to resolve these issues, the relationship between the carbon host pore structure and electrochemical performance of Se has not been studied extensively. Here, the effect of the carbon host pore structure on the electrochemical performance of Na-Se and K-Se batteries is investigated. N, S-co-doped hierarchically porous carbon microspheres with different pore structures that can incorporate a large amount of amorphous Se (∼60 wt %) are synthesized by spray pyrolysis and subsequent chemical activation at different temperatures. By optimizing the amount of micropore volume and micropore-to-mesopore ratio, high reversible capacity and cycling stability are achieved for the Se cathode. The optimized cathode delivers a reversible capacity of 445 mA h g-1 after 400 cycles at 0.5C for Na-Se batteries and 436 mA h g-1 after 120 cycles at 0.2C for K-Se batteries. This study marks the importance of developing conductive carbon matrices with delicately designed pore structures for advanced alkali metal-chalcogen battery systems.

An Ultramicroporous Metal-Organic Framework for High Sieving Separation of Propylene from Propane.

Highly selective adsorptive separation of olefin/paraffin through porous materials can produce high purity olefins in a much more energy-efficient way than the traditional cryogenic distillation. Here we report an ultramicroporous cobalt gallate metal-organic framework (Co-gallate) for the highly selective sieving separation of propylene/propane at ambient conditions. This material possesses optimal pore structure for the exact confinement of propylene molecules while excluding the slightly large propane molecules, as clearly demonstrated in the neutron diffraction crystal structure of Co-gallate⊃0.38C3D6. Its high separation performance has been confirmed by the gas sorption isotherms and column breakthrough experiments to produce the high purity of propylene (97.7%) with a high dynamic separation productivity of 36.4 cm3 cm-3 under ambient conditions. The gas adsorption measurement, pore size distribution, and crystallographic and modeling studies comprehensively support the high sieving C3H6/C3H8 separation in this MOF material. It is stable under different environments, providing its potential for the industrial propylene purification.

Effect of diameter of multi-walled carbon nanotubes on mechanical properties and microstructure of the cement-based materials

This paper is intended to investigate the effects of multi-walled carbon nanotubes (MWCNTs) with different inner diameters on the mechanical properties (flexural strength and compressive strength) and microstructures of cement-based materials. Three kinds of multi-walled carbon nanotubes (MWCNTs) with diameter of 10–20 nm, 20–40 nm and 40–60 nm were ready to reinforce cement-based materials. And each batch incorporated 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt% MWCNTs by cement weight. To obtain a uniform distribution of MWCNTs in the cement-based materials, the effects of ultrasonic dispersion time and intensity on the properties of MWCNTs cement-based materials were studied. In addition, the relationships between mechanical properties, porosity and diameter of MWCNTs were investigated. Experimental results showed that the improvements of flexural strength and compressive strength of cement-based materials were altered by increasing the diameter of MWCNTs. Microstructure analysis by SEM and MIP tests indicated that MWCNTs with diameter of 10–20 nm have the best effect on optimizing pore structure. The results of this study were useful to determine the diameter and content of MWCNTs required for optimum pore structure and maximum strength enhancement of cement-based materials.

Cold start capability and durability of electrospun catalyst layer for proton exchange membrane fuel cell

The electrospun catalyst layer (E-spun CL) was found capable of improving both catalyst performance and durability under normal temperature operations. In this work, we first explored the reasons for this improvement, and then systematically compared the cold start capability and durability of E-spun CL with that of the commercial electro-sprayed catalyst layer (E-sprayed CL). Improved performance under normal temperature operations for E-spun CL was attributed to the optimized pore structure, which resulted in less mass transport losses. E-spun CL exhibited a better cold start capability in terms of more condensed product water due to longer survival time, possibly caused by the lower freezing probability of super-cooled water in micro-pores. After enduring several cold start tests, less performance and structural deterioration were observed for E-spun CL, mainly resulting from the high mechanical flexibility of porous nanofiber structure.

In-situ template cooperated with urea to construct pectin-derived hierarchical porous carbon with optimized pore structure for supercapacitor

Pectin as a functional biopolymer has been successfully exploited to produce N/O co-doped 3D carbon architecture with hierarchical pores. A simple and novel in-situ template combining with KOH activation method is utilized to prepare porous carbon using calcium acetate as the template source and urea as a dopant. The in-situ CaCO3 template, activation temperature and urea additive have a significant influence on the morphology, pore structure and performance of porous carbon. The high specific surface area of NHPC-700 (2928 m2g − 1) and its suitable micropore/mesopores ratio are helpful to promote specific capacitance and rate performance. The NHPC-700 possesses the high specific capacitance of 338 F g − 1 at 1 A g − 1 and the excellent capacitance retention of 83% from 1 A g − 1 to 50 A g − 1. Furthermore, the NHPC-700 symmetric supercapacitor shows an energy density of 22.4 Wh kg−1 at 880 W kg−1 in 1 M Na2SO4. The efficient use of pectin to synthesize functionalized hierarchical porous carbon materials has a broad development prospect.

Pore structure optimization of electrospun PTFE nanofiber membrane and its application in membrane emulsification

Polytetrafluoroethylene (PTFE) nanofiber membranes with a kind of novel circular pore structure were fabricated in our study. Firstly, PTFE/PVA spinning solution was electrospun into precursor nanofiber membrane, during which, poly(tetrafluoroethylene-hexafluoropropylene) (FEP) aqueous dispersion was introduced by electrostatic spraying aiming to optimize the original fibrous network pore structure of electrospinning. After which, the prepared precursor nanofiber membranes were sintered, and PTFE nanofiber membranes were finally obtained. Effects of FEP contents on PTFE nanofiber membranes’ structure and performance were investigated, respectively. From the morphology observation, it was found that the PTFE nanofiber membrane’s pore structure gradually transformed from fibrous network to circular pore due to the melting of FEP resins. Owing to the excellent under-oil hydrophobicity and the uniform circular pore structure, the obtained PTFE nanofiber membranes were utilized in membrane emulsification (ME) process to prepared water in oil (W/O) emulsion. Compared with the conventional mechanical stirring method, the W/O emulsion prepared by ME process showed not only more uniform water droplet size (about 270 nm), but also more stable and higher production efficiency.

Development of calcium phosphate/calcium sulfate biphasic biomedical material with hyaluronic acid containing collagenase and simvastatin for vital pulp therapy

ObjectiveIn vital pulp therapy (VPT), a barrier is created with appropriate capping to protect the remaining pulp and thus maintain pulp vitality. Here, we evaluated the feasibility of a biphasic calcium phosphate cement (CPC)–calcium sulfate hemihydrate (CSH) biomaterial containing simvastatin (Sim) and collagenase (Col) for VPT. MethodsCombinations of varying CPC and CSH concentrations were analyzed for their handling properties and setting times, with their structures observed through scanning electron microscopy–energy dispersive X-ray spectrometry (SEM-EDS). Drug release patterns of simvastatin and collagenase combined with CPC–CSH (CPC–CSH–Sim–Col) were also analyzed, followed by biocompatibility and bioactivity tests on human dental pulp stem cells (hDPSCs) and in vivo animal study in canine models; the in vivo results were obtained through microcomputed tomography and histological analysis. ResultsThe results revealed that 70 wt% CPC (CPC7) with 30 wt% CSH (CSH3) exhibited optimal setting time and porous structure for clinical use. The cell viability and cytotoxicity analysis demonstrated that CPC7–CSH3 with or without simvastatin or collagenase did not injure hDPSCs. In vivo, the CPC7–CSH3–Sim–Col induced dentin bridge formation. SignificanceCPC7–CSH3–Sim–Col in this study has great potential as a VPT biomaterial to enhance the dentin bridge formation.

Fabrication and performance of a stable micro/nano composite electret filter for effective PM2.5 capture

Airborne particulate matter (PM) pollution has raised serious concerns over both the global climate and public health. Therefore, there is an urgent need for air filters of high-efficiency and energy-saving. Pore structure optimization and electret enhancement are feasible means to improve their filtration performance. Herein, a novel sandwich-structured electret composite filter with a low pressure drop and robust filtration stability was successfully designed and fabricated. The composite filter was composed of fluffy PS microfibers with large electric resistivity and high porosity, and PAN nanofibers with high polarity and small pore size. Benefiting from the fluffy structure constructed by electrospinning at the right humidity, the tortuous pore channels created by the appropriate mixing of microfibers and nanofibers, and the abundant static charges generated by the hybrid of polar and nonpolar polymer materials, the PS/PAN/PS composite filter possessed a high filtration efficiency of 99.96% for particles of 0.30 μm, a low pressure drop of 54 Pa and a satisfactory quality factor value of 0.1449 Pa−1 at an airflow velocity of 5.3 cm/s. In particular, the composite filter exhibited better electret stability and PM2.5 loading performance than the commercial ones, which guarantees its long-term storage and usage.