Large Porosity Research Articles

CV Performance of ZnO-Carbon Nanocomposite Based On ZIF-8 as Lithium-Ion Battery Anode

Compositing between metal oxide and carbon is strategy to improve the performance of lithium-ion battery anode. This is due to the high theoretical capacity of metal oxides, carbon acts as a lithium ion accelerator and supports the structural stability of metal oxides. The advantages of the ZnO-Carbon nanocomposite anode based on ZIF-8 are its large surface area and porosity. The method used is non-solvothermal through precipitation at room temperature. After obtaining ZIF-8 powder, then it was carbonized at temperatures 600°C. The characterization used were SEM, EDS and TEM. The samples also have a porous character with a nano-sized pore radius. Cyclic Voltammetry (CV) was carried out using 3-electrode system. The CV test showed 3 reduction peaks. The first peak indicated the conversion reaction, the second peak indicated the alloying reaction, and the third peak indicated a solid electrolyte interface (SEI) reaction. The highest diffusion coefficient is alloying reaction with 3.65 x 10−8 cm2/s.

Design and optimization of the U-shaped well geothermal systems for heat production performance: A case study from Huangling, China

U-shaped well geothermal systems have obvious advantages in deep geothermal development due to the long heat exchange distance and no fluid leakage. Well layout is a primary optimization target to enhance the heat production performance. However, there is a lack of studies for well location selection and installation configuration considering regional groundwater flow. In this study, a coupled thermo-hydro model considering 1D U-shaped well and 3D reservoirs groundwater flow is proposed for the optimization of U-well geothermal systems. The proposed model is calibrated by the field test of U-shaped well in Huangling, China. First, the U-shaped well geothermal system with multiple injection wells is designed. The feasibility is comprehensively evaluated from the aspects of heat production performance and levelized cost of electricity. Subsequently, the influence of groundwater flow on heat production performance is analyzed in detail, including flow velocity, porosity, aquifer thickness and flow direction. Finally, sensitivity studies of thermal conductivity of cement, wellbore diameter, and injection flow rate are investigated to provide reference for production operations. The results show that the heat production performance of the U-shaped well geothermal system with multiple injection wells are significantly better than the single U-shaped well. And the levelized cost of energy can be reduced by 0.0288 $/kWh compared to the average industrial electricity price in China. The groundwater flow velocity remarkably affects the heat production performance. The large aquifer thickness and porosity contribute to the improvement of the heat production performance of the U-shaped well geothermal system. The U-shaped well with injection wells located in the lower reaches of groundwater flow field has better heat production performance. The research results can provide references for design and optimization of the U-shaped well geothermal systems.

Neochlorogenic Acid Combined with Bone Marrow Mesenchymal Stem Cells Encapsulated into GelMA Hydrogel for Transplantation to Repair Intervertebral Disk Degeneration.

Intervertebral disk degeneration is a common disease with an unknown etiology. Currently, tissue engineering is considered to be an important method for intervertebral disk repair. Although transplanted stem cells may disrupt the repair process because of apoptosis caused by the oxidative microenvironment. Herein, bone marrow mesenchymal stem cell (BMSC) and Neochlorogenic acid (Ncg) were encapsulated into a GelMA hydrogel as a carrier to protect transplanted stem cells. Ncg effectively inhibited the oxidative stress process and reduced the apoptosis rate. A 5% GelMA hydrogel had a large pore size and porosity that provided an enhanced survival space for cells. An in vivo assessment showed that treatment with GelMA + BMSC + Ncg produced greater repair of degenerated intervertebral disks than that found in other model groups. Thus, this study may help contribute to improving stem cell transplantation for treating intervertebral disk degeneration.

Effect of strain rate on compressive behavior and deformation mechanism of CoCrNi medium entropy alloy fabricated via cold spray additive manufacturing

The equiatomic CoCrNi medium entropy alloy (MEA) has shown better mechanical properties than many MEAs and high entropy alloys (HEAs) at room temperatures. However, the mechanical behaviors and deformation mechanisms of CoCrNi MEAs have yet to be studied, especially at different strain rates. In this study, cold spray additive manufacturing (CSAM) was applied to fabricate freestanding CoCrNi deposits. The investigation of compressive behaviors and deformation mechanisms were studied at a low-strain rate of 0.001 s−1 and at a high strain rate ranging from 2300 s−1to 4200 s−1. The as-fabricated sample exhibited refined grains, unfused powders, and large porosity, resulting in limited metallurgical bonding within the bulk CoCrNi deposit and deformed particle interface. Therefore, post-heat treatment at 1350 °C was applied to improve the interparticle bonding and strengthen the as-fabricated CoCrNi deposits. As expected, the annealed deposit significantly improved the ultimate compressive strength (UCS) and strain elongation of the as-fabricated deposits from ∼90 MPa and ∼5% to ∼1400 MPa, and ∼70% at a strain rate of 0.001 s−1. Besides, the annealed samples showed improvement twofold in UCS and ductility of the as-fabricated deposits from ∼67 MPa and ∼8.6% to ∼1266 MPa and ∼34% at a strain rate of 4200 s−1 and 3800 s−1 respectively. The TEM image of the annealed CoCrNi sample showed deformation twining, nano twins, planar slips, and microbands, which are the dominant deformation mechanisms that help to promote the plasticity and the work hardening behavior of this alloy. This work validates the compressive behavior and deformation mechanism of cold-sprayed CoCrNi MEA associated with post-heat treatment at different strain rates.

Exploring How LPBF process parameters impact the interface characteristics of LPBF Inconel 718 deposited on Inconel 718 wrought substrates

This work investigates the interface properties of LPBF Inconel 718 deposited on Inconel 718 wrought substrates fabricated using the laser powder bed fusion (LPBF) technique. The as-printed (S1, S2, S3, and S4) samples were characterized using optical microscopy (OM),scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and micro-hardness techniques.The samples showed the development of a melted interface zone (MIZ) at the wrought substrate-deposition interface for all processing conditions. The developed interface showed a dendritic grain structure, signifying the remelting of the wrought substrate followed by rapid solidification. The MIZ thickness increased with an increase in laser power and scan speed (28.5 % increase in the MIZ thickness with a ∼ 12 % increase in normalized enthalpy). The assessment of the MIZ showed a high-quality interface. However, with an increase in scanning speed, the density of the MIZ decreases owing to increased porosity and lack-of-fusion (LOF) defects. The S1 condition (250 W and 850 mm/s) resulted in a highly dense part with no visible porosity, LOF defects, and a high relative density (∼99.9 %) in the MIZ region. The S4 condition showed the presence of large porosities and LOF defects at the deposition-MIZ interface, signifying an inferior bond between the deposition and substrate. The microstructural characterization of the LPBF-processed and MIZ region showed an increase in the primary dendritic arm spacing (PDAS) with increasing laser power due to a reduced cooling rate. The micro-hardness characterization of the sample shows a decrease in the hardness of the MIZ attributed to the dissolution of strengthening phases due to remelting. The present work outcome demonstrates the effectiveness of the proposed methodology for manufacturing high-quality parts using LPBF technology.

Highly efficient freezing desalination technology: Parameters optimization and model configuration

Seawater desalination has become an available route to reduce the shortage of freshwater resources. Lower energy consumption and suitable operational conditions make freezing crystallization a green technique in the desalination area. Herein, we coupled the sweating intensification with the freezing crystallization to reach a highly efficient desalination performance. Under the trajectory of the freezing temperature and time: 259.15 K and 150 min, the sweating temperature, heating rate, and sweating time: 272.15 K, 0.5 K/min, and 120 min, the desalination ratio exceeds 70 %. Meanwhile, we established the theoretical models to expound the intrinsic correlations of process variables and target parameters, to visualize the impurity migration. Two kinetic models are proposed to analyze temperature effects on the crystal layer growth, sweating melt flow, and inclusion entrapment. Next, the fractal slice model is proposed to describe the complex microstructure of the crystal pillar. The thermal coefficients are deduced based on the fractal theory, where the larger porosity is against thermal conduction. Finally, we discussed the kinetic and porosity effects on the impurity migration and desalination performance, and established a boundary layer model to correlate the separation efficiency with process kinetic and impurity distribution successfully.

A theoretical model for estimating the thermal conductivity of granular geomaterials with low porosity

The thermal conductivity has an important influence on the geotechnical and geoenvironmental engineering. Most existing thermal conductivity models appear to estimate the thermal conductivity of soils samples with large porosity, few of them were proposed to model the thermal conductivity of soil samples with low porosity. In this study, a theoretical model was proposed to estimate the thermal conductivity of unsaturated granular geomaterials with low porosity. Two parameters (i.e., ζ and β) were introduced. The parameter ζ can be applied to control porosity and solid particle shape, while the parameter β can be used to control water content. Mathematical comparison showed that the proposed thermal conductivity model fell within the Wiener bounds. The new model and five thermal conductivity models were evaluated with experimental data, showing that the new model accurately estimates the relationship between thermal conductivity and saturation for granular geomaterials with low porosity.

Synthesis of Superabsorbent Hydrogels with Predefined Geometries and Controlled Swelling Properties for Versatile 3D Cell Culture Scaffolds.

This research presents a simple but general method to prepare water-soluble-polymer-based superabsorbent hydrogels with predefined microscale geometries and controlled swelling properties. Unlike conventional hydrogel preparation methods based on bulk solution-phase cross-linking, poly(vinyl alcohol) is homogeneously mixed with polymer-based cross-linkers in the solution phase and thermally cross-linked in the solid phase after drying; the degree of cross-linking is modulated by controlling the cross-linker concentration, pH, and/or thermal annealing conditions. After the shape definition process, cross-linked films or electrospun nanofibers are treated with sulfuric acid to weaken hydrogen bonds and introduce sulfate functionality in polymer crystallites. The resultant superabsorbent hydrogels exhibit an isotropic expansion of the predefined geometry and tunable swelling properties. Particularly, hydrogel microfibers exhibit excellent optical transparency, good biocompatibility, large porosity, and controlled cell adhesion, leading to versatile 3D cell culture scaffolds that not only support immortalized cell lines and primary neurons but also enable stiffness-modulated cell adhesion studies.

The Impact of HIP Process and Heat Treatment on the Mechanical Behaviour of an Al–Si–Mg Alloy Component

AbstractThis study investigates the effect of hot isostatic pressing (HIPping) on the static and fatigue properties of sand-casting A356 aluminium alloys. HIPping is a method to improve the fatigue properties in aluminium cast material by reducing or eliminating the inner porosities. Investigation of the complex interaction between the microstructural features on mechanical properties before and after the HIPping process was examined using computed tomography and scanning electron microscopy (SEM). Castings generally contain pores and defects that have a detrimental impact on the fatigue properties. The HIPping process closes the porosities in all investigated samples with an increase in density. Without significant defects, the mechanical performance improved in the finer microstructure. However, a considerable variation in the results was found between the different conditions, whereas the coarser microstructure with larger porosities before HIPping showed remarkably reduced results. The high-cycle fatigue-tested samples showed reduced fatigue propagation zone in the coarser microstructure. Moreover, large cleavage areas containing bifilms in the fracture surfaces indicate that the healing process of porosities is inefficient. These porosities are closed but not healed, resulting in a detrimental effect on the static and dynamic properties.

Preparation of Ordered Macroporous ZIF-8-Derived Magnetic Carbon Materials and Its Application for Lipase Immobilization

Metal–organic framework materials (MOFs) and their derivatives are considered ideal immobilization carrier materials because of their large specific surface area, high porosity and excellent structural designability. Among them, ZIF-8 has great potential for immobilization of enzymes due to mild synthesis conditions, and good biocompatibility. However, conventional ZIF-8 crystals have poor separation and recovery efficiency due to their small pore size and poor acid stability, greatly limiting their application in enzyme immobilization and further application. Although the carbonization of ZIF-8 by pyrolysis has been shown to be one of the approaches that can enhance its chemical stability, this still does not effectively solve the problem of the difficulty of recycling. Herein, we developed a strategy of pre-carbonization immersion (immersion in aqueous FeSO4 solution before carbonization) to synthesize ordered macroporous ZIF-8-derived carbon materials with stable ferromagnetism (denoted as CZ-x-M-y, where x denotes the carbonization temperature and y denotes the concentration of the impregnated FeSO4 solution) and used them to immobilize lipases for biodiesel production. XRD analysis showed that the magnetic properties in the materials came from Fe3C species. We found that the magnetic carbon materials obtained by carbonization at 600 °C showed the best immobilization effect, where CZ-600-M-0.3 (using 0.3 mol·L−1 FeSO4 aqueous solution to soak ZIF-8 and carbonized at 600 °C) had the highest enzyme loading of 183.04 mg·g−1, which was 49.7% higher than that of the non-magnetic CZ-600. In addition, CZ-600-M-0.5 maintained the highest enzyme activity, which was 81.9% of the initial activity, after five batches of reuse. The stable magnetic support materials reported in this study have promising potential for the industrial application of immobilized lipase.

Effects of different pre-freezing methods and pressure levels on the pore structure and mechanical properties of microwave-vacuum dried apple

The present study describes the effects of different pre-freezing methods with microwave-vacuum drying (MVD) at different pressure conditions (no vacuum or at 1, 3, or 8 kPa) on the three-dimensional pore structure and mechanical properties of dried apples. Slow-freezing pretreatment and lower pressure conditions were shown to be effective in reducing the drying time in MVD. Slow-frozen MVD samples had large pore sizes and high porosity, especially the mean pore equivalent radii of the slow-frozen MVD samples at 1 and 3 kPa were 153.7 and 138.7 μm, which are comparable to that of the freeze-dried sample (137.7 μm). These structural characteristics were thought to confer low hardness and high crispness in the samples. Principal component analysis revealed that the structural properties of the pores in MVD samples were decided not by the pressure condition, but by the pre-freezing method. Overall, the results showed that the combination of slow-freezing pretreatment with MVD under a lower pressure is advantageous for improving the drying efficiency and the texture of the dried samples. The slow-frozen MVD samples were structurally similar to the freeze-dried samples, but there were some differences in the mechanical properties, suggesting that there are factors other than the pore structure that influence the mechanical properties.

Preparation of Zeolitic Imidazolate Framework and Carbon Nanofiber Composites for Nitrofurazone Detection

Metal–organic frame (MOF) materials may have the advantages of a regular pore structure, large porosity, and large specific surface area, which could provide better catalytic activity, but they have some disadvantages in electrocatalysis. In contrast, carbon nanofibers (CNFs) prepared by electrospinning methods have good conductivity and stability. Therefore, this research aimed to generate MOF/CNFs composite materials to improve the electrochemical properties of MOF materials and apply them to the field of electrochemical sensing. This experiment was based on the preparation of straight unidirectional CNFs by an electrospinning method at 2000 RPM. The original method of preparing zeolitic imidazolate frameworks (ZIF-8) was improved and ZIF-8 was uniformly dispersed on the surface of CNFs to form a ZIF-8/CNF composite with a fiber diameter of about 0.10 to 0.35 µm. The specific surface area of the CNFs was about 42.28 m2/g, while that of the ZIF-8/CNF composite was about 999.82 m2/g. The specific surface area of the ZIF-8/CNF composite was significantly larger than that of CNFs. The GCE/ZIF-8/CNF electrode had an excellent electrochemical reaction, with an oxidation peak at about 216 μA, which proved that the ZIF-8/CNF composite material would have good catalytic activity and excellent electrochemical properties for the detection of nitrofurazone compared to other modified electrodes.

Endosperm structure and Glycemic Index of Japonica Italian rice varieties.

Given that rice serves as a crucial staple food for a significant portion of the global population and with the increasing number of individuals being diagnosed with diabetes, a primary objective in genetic improvement is to identify and cultivate low Glycemic Index (GI) varieties. This must be done while ensuring the preservation of grain quality. 25 Italian rice genotypes were characterized calculating their GI "in vivo" and, together with other 29 Italian and non-Italian genotypes they were studied to evaluate the grain inner structure through Field Emission Scanning Electron Microscopy (FESEM) technique. Using an ad-hoc developed algorithm, morphological features were extracted from the FESEM images, to be then inspected by means of multivariate data analysis methods. Large variability was observed in GI values (49 to 92 with respect to glucose), as well as in endosperm morphological features. According to the percentage of porosity is possible to distinguish approximately among rice varieties having a crystalline grain (< 1.7%), those intended for the preparation of risotto (> 5%), and a third group having intermediate characteristics. Waxy rice varieties were not united by a certain porosity level, but they shared a low starch granules eccentricity. With reference to morphological features, rice varieties with low GI (<55) seem to be characterized by large starch granules and low porosity values. Our data testify the wide variability of Italian rice cultivation giving interesting information for future breeding programs, finding that the structure of the endosperm can be regarded as a specific characteristic of each variety.

Electrospun gel composite electrolyte of solvent-free SiO2 nanofluids coupled polyacrylonitrile nanofibers for high-rate lithium-metal batteries

Composite polymer electrolytes (CPEs) are considered as one of the most promising electrolytes for the next generation of solid-state lithium metal batteries (LMBs) because of their good flexibility, favorable interface contact, easy large-scale processing and improved safety. To address the severe agglomeration of inorganic nanofillers at the high-level loading, a new gel polymer electrolyte (GPE) was fabricated by electrospun membranes adopting polyacrylonitrile (PAN) as the host matrix and solvent-free SiO2 nanofluids (NFs) as nanofillers, presenting low crystallinity, high electrolyte uptake, superior flexibility, and large porosity. The as-prepared PAN/SiO2 GPEs containing 20 % SiO2 NFs show the optimum mechanical and thermal properties, the maximum ionic conductivity (3.44 x 10−4 S cm−1) and Li+ transfer number (0.73), and the widest electrochemical stable window (4.99 V). Benefiting from multiple advantages, the percolated 3D Li+ transport networks are well-established to suppress the electrode polarization and Li dendrite growth. Further, the abundant ester groups on the SiO2 NFs shell and Lewis acid-based sites on SiO2 cores are favored to dissociate lithium salts and produce more free Li+. Accordingly, the assembled solid-state LiFePO4/Li cell exhibits superior cycling stability (132.7 mAh/g after 500 cycles at 3C with a retention of 90.8 %) and rate capability (80.4 mAh/g at 25C) at ambient temperature. This work provides a facile strategy to fabricate GPEs by incorporating solvent-free NFs containing inorganic cores for LMBs with high-rate capability, good cycling stability, and high safety.

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.

PERMEABILITY OF PARTIALLY TO FULLY RANDOMIZED ARRAYS OF SQUARE OBSTACLES: A LATTICE BOLTZMANN APPROACH

Porous media consisting of monodisperse square obstacles were computationally studied using the lattice Boltzmann method in the Darcy regime. Different random arrays of obstacles were generated from the ordered arrays of obstacles using a new algorithm for controlled randomization. The porosity lies in the dilute to moderately dense range of 0.85-0.69. By proper nondimensionalization of the randomization parameter, it was demonstrated that the normalized permeability linearly depends on this parameter within slight randomizations through all porosities. Further randomization breaks the linear dependence, where the normalized permeability undergoes a sharp transition to a plateau at smaller porosities and a continuous transition at larger porosities. The plateau values of the normalized permeability linearly depend on the porosity. Interstitial flow maps show an immediate breakdown of spatial velocity distribution in ordered configurations starting with randomization and manifesting major flow channeling at higher randomizations, which can explain the transition types for permeability.

FRACTAL ANALYSIS FOR PERMEABILITY OF MULTIPLE SHALE GAS TRANSPORT MECHANISMS IN ROUGHENED TREE-LIKE NETWORKS

In this work, a new gas transport model for shale reservoirs is constructed by embedding randomly distributed roughened tree-like bifurcation networks into the matrix porous medium. We constructed apparent permeability models for different shale gas flow mechanisms based on fractal theory, taking into account the effects of relative roughness and surface diffusion. The effects of bifurcation structure parameters as well as shale gas parameters on different apparent permeabilities are systematically analyzed. It is found that the permeability generally shows a decreasing trend with the increase in pore pressure, but the effect on viscous flow is inconsiderable. In addition, larger porosity, fractal dimension and bifurcation levels lead to increased permeability of different mechanisms. Whereas, the increase in the bifurcation levels implies a greater flow resistance, resulting in a decreased permeability. In addition, The relative roughness hinders the development of total permeability but favors surface diffusion permeability. Moreover, larger length ratios and diameter ratios are beneficial to the shale gas flow.

Sustainable versatile chitin aerogels: facile synthesis, structural control and high-efficiency acoustic absorption.

Bio-based materials with excellent acoustic absorption properties are in great demand in architecture, interior, and human settlement applications for efficient noise control. In this study, crayfish shells, a form of kitchen waste, are utilized as the primary material to produce ultralight and multifunctional chitin aerogels, which effectively eliminate noise. Different replacement solvents and freezing rates were employed to regulate the porous structures of chitin aerogels, and their resulting acoustic absorption performance was investigated. Results demonstrate that employing deionized water as the replacement solvent and utilizing a common-freeze mode (frozen via refrigerator at -26 °C) can produce chitin aerogels with larger porosity (96.26%) and apertures, as well as thicker pore walls. This results in superior broadband acoustic absorption performance (with a maximum absorption coefficient reaching 0.99) and higher Young's modulus (28 kPa). Conversely, chitin aerogels solvent-exchanged with tert-butyl alcohol or subjected to quick-freeze mode (frozen via liquid nitrogen) exhibit smaller porosity (92.32% and 94.84%) and apertures, thereby possessing stronger diffuse reflection of visible light (average reflectance of 94.30% and 88.18%), and enhanced low-frequency (500 to 1600 Hz) acoustic absorption properties. Additionally, the acoustic absorption mechanism of fabricated chitin aerogels was predicted using a simple three-parameter analysis Johnson-Champoux-Allard-Lafarge (JCAL) model. This study presents a novel approach to developing multifunctional biomass materials with excellent acoustic absorption properties, which could have a wide range of potential applications.

Strategies for utilizing covalent organic frameworks as host materials for the integration and delivery of bioactives.

Covalent organic frameworks (COFs), a new and developing class of porous framework materials, are considered a type of promising carrier for the integration and delivery of bioactives, which have diverse fascinating merits, such as a large specific surface area, designable and specific porosity, stable and orderly framework structure, and various active sites. However, owing to the significant differences among bioactives (including drugs, proteins, nucleic acid, and exosomes), such as size, structure, and physicochemical properties, the interaction between COFs and bioactives also varies. In this review, we firstly summarize three strategies for the construction of single or hybrid COF-based matrices for the delivery of cargos, including encapsulation, covalent binding, and coordination bonding. Besides, their smart response release behaviors are also categorized. Subsequently, the applications of cargo@COF biocomposites in biomedicine are comprehensively summarized, including tumor therapy, central nervous system (CNS) modulation, biomarker analysis, bioimaging, and anti-bacterial therapy. Finally, the challenges and opportunities in this field are briefly discussed.

Recent progress of electrospun nanofibers as burning dressings.

Burns are a global public health problem, which brings great challenges to public health and the economy. Severe burns often lead to systemic infection, shock, multiple organ failure, and even death. With the increasing demand for the therapeutic effect of burn wounds, traditional dressings have been unable to meet people's needs due to their single function and many side effects. In this context, electrospinning shows a great prospect on the way to open up advanced wound dressings that promote wound repairing and prevent infection. With its large specific surface area, high porosity, and similar to natural extracellular matrix (ECM), electrospun nanofibers can load drugs and accelerate wound healing. It provides a promising solution for the treatment and management of burn wounds. This review article introduces the concept of burn and the types of electrospun nanofibers, then summarizes the polymers used in electrospun nanofiber dressings. Finally, the drugs (plant extracts, small molecule drugs and nanoparticles) loaded with electrospun burn dressings are summarized. Some promising aspects for developing commercial electrospun burn dressings are proposed.