Formation Of Micropores Research Articles

Enhanced chemical stability and H+/V4+ selectivity of microporous sulfonated polyimide via a triptycene-based crosslinker

Long durability of sulfonated polyimide in vanadium redox flow battery (VRFB) is urgently required to be solved. Herein, we synthesize a triptycene-based crosslinker and use it as chemical crosslinking point to modify a linear sulfonated polyimide for promoting its antioxidative stability. The novel triptycene-based cross-linked sulfonated polyimide (TCSPI-X) membranes featuring covalently crosslinked network display lower water uptake and swelling ratio than the commercial perfluorinated ionomer membrane (Nafion 117) membrane. More importantly, unnoticeable proton conductivity loss is appeared. We speculate this is because of the covalently crosslinking structure provides stable proton transportation channels, and the formation of micropores induced by rigid triptycene unit decrease proton migration resistance. In which, the TCSPI-5 (with 5 % molar triptycene unit) exhibit higher voltage efficiency as compared with the pristine membrane TCSPI-0. Combined with the excellent vanadium ions resistance, the TCSPI-5 reaches energy efficiency of 78 % at the current density of 140 mA cm−2. In addition, TCSPI-5 also shows high oxidation resistance even under strong acid and pentavalent vanadium ions (V5+) conditions. The above results suggest the potential of TCSPI-X membranes in VRFB application.

Photoaging effects on polyethylene microplastics: Structural changes and chlorpyrifos adsorption

Microplastics (MP) are a global concern due to their small size, insolubility in water, and non-degradable nature, and long-term environmental persistence. Weathering processes, such as ultraviolet (UV) radiation, can alter their properties, enhancing their ability to absorb pollutants or release harmful substances, such as pesticides, which is also an environmental concern, thereby complicating their environmental impact and mitigation efforts. This study investigates the impact of UVB-induced photoaging on polyethylene (PE) microplastics and their sorption behavior towards the pesticide chlorpyrifos (CP). PE microplastics were exposed to varying UVB aging durations, leading to significant changes in their physicochemical and morphological properties. The sorption experiments revealed that aged microplastics exhibited increased affinity for CP, with adsorption capacity rising by 17.9% compared to pristine PE. This enhanced adsorption was attributed to the (1) introduction of oxygen-containing functional groups, facilitating the formation of hydrogen bonds between the microplastic surface and surrounding water molecules, thereby contributing to the adsorption of CP; (2) formation of irregular micropores and surface roughness, potentially providing ample sites for pesticide adsorption and (3) reduction in crystallinity from 35% to 30%, which favors the sorption of hydrophobic organic pollutants. Density Functional Theory (DFT) calculations supported these findings by showing changes in the electronic structure of PE that facilitate interactions with CP. These results provide critical insights into the environmental behavior of aged microplastics and their potential to adsorb hazardous chemicals, underscoring the need for further research on the environmental impact of microplastic aging.

Thermodynamic and Kinetic Analysis of TiN Precipitation in Nickel-Based Superalloys During Solidification.

Large TiN inclusions in nickel-based superalloys promote micropore formation, compromising the mechanical properties of the alloys. However, current research lacks a comprehensive coupled model that considers both solute element microsegregation and TiN precipitation specifically in nickel-based superalloys. This study investigated TiN precipitation during the solidification of IN718 alloys through a combined thermodynamic and kinetic approach. A modified Clyne-Kurz model was applied to account for multi-element microsegregation, enabling an integrated analysis of both microsegregation and precipitation processes. The results indicated that solute elements in the molten alloy segregated to varying degrees during solidification. At an initial nitrogen concentration of 25 ppm, TiN inclusions precipitated when the solid fraction reached 0.256, eventually resulting in a total TiN precipitation of 64 ppm by the end of solidification, while residual nitrogen in the liquid phase decreased to 1.3 ppm. Increasing the initial nitrogen concentration from 10 ppm to 40 ppm advanced the onset of TiN precipitation and raised the total amount from 16 ppm to 126 ppm. Further analysis indicated that cooling rates of 0.03 °C/s, 0.06 °C/s, and 0.18 °C/s did not significantly affect the final TiN accumulation.

Printed flexible supercapacitors utilizing composites of MWCNT/MOF ultrathin nanosheets: Exploring 1D/2D structural adjustment

The self-stacking propensity of metal–organic frameworks (MOFs) during synthesis, combined with their intrinsic limitations in electrical conductivity and mechanical stability, constrains their utility as high-capacity energy sources in wearable electronics. Here, we employ a surfactant-assisted method to mitigate the Z-axis stacking of zinc metalloporphyrin organic frameworks (NMOFs), yielding ultrathin two-dimensional (2D) material sheets. By integrating carboxyl multiwalled carbon nanotubes into these nanosheets (denoted as C-NMOF-x), the lamellar structure of MOF is preserved while promoting the formation of rich multistage micropores and continuous conductive channels. This structural refinement remarkably enhances electrochemical properties, including capacitance, electronic conductivity, and cycling stability. Leveraging synergistic interactions, the resulting C-NMOF-4 composite achieves a specific capacitance of 0.152 mAh/g in a three-electrode system at a current density of 1 A/g. Furthermore, the modulated C-NMOF-4 composites are successfully formulated into homogeneous e-inks suitable for dispensing printing, enabling the mass production of flexible micro-supercapacitors (MSCs). Notably, these MSCs maintain 95 % of their capacitance even after 180° bending under wearable conditions. This surface and interface microstructure modulation strategy holds promise for enhancing the synergistic coupling effects of 2D materials and offers new avenues for the application of innovative 2D materials in wearable electronics.

Impact of Asymmetric Microstructure on Ion Transport in Ti3C2Tx Membranes.

Consolidation or densification of low-dimensional MXene materials into membranes can result in the formation of asymmetric membrane structures. Nanostructural (short-range) and microstructural (long-range) heterogeneity can influence mass transport and separation mechanisms. Short-range structural dynamics include the presence of water confined between the 2D layers, while long-range structural properties include the formation of defects, micropores, and mesopores. Herein, it is demonstrated that structural heterogeneity in Ti3C2Tx membranes fabricated via vacuum-assisted filtration significantly affects ion transport. Higher ion permeabilities are achieved when the dense "bottom" side of the membrane, rather than the porous "top" side, faces the feed solution. Characterization of the membrane reveals distinct differences in flake alignment, surface roughness, and porosity across the membrane. The directional dependence on permeability suggests that one region of the membrane experiences stronger internal concentration polarization, potentially suppressing permeability through the porous side of the membrane.

Interface Structure and Properties of Polypropylene/Wood Flour Composites Reinforced with Grafted Polypropylene Compatibilizer

AbstractIn this work, a new compatibilizer, ternary monomer grafted polypropylene (hereafter shorted as: G‐PP), was successfully synthesized by solid phase grafting of maleic anhydride, methyl methacrylate, and butyl‐acrylate onto polypropylene. For all developed polypropylene matrix composites, the prepared G‐PP evidently showed enhancing mechanical properties on PP/wood flour (WF) composites, which is obviously superior to those from maleic anhydride grafted polypropylene (W‐PP) and virgin polypropylene (C‐PP). In particular, the wettability of G‐PP was greatly improved, while the melting temperature and β crystal phase amounts of the WF composites with G‐PP are much higher when compared to that of W‐PP and C‐PP. This can be reasonably explained by the formation of continuous micropores and filaments in WF composites containing G‐PP, as verified by hot stage polarizing optical microscope (POM). Meanwhile, the G‐PP effectively reduced movement of molecular chains of WPC and formed a better interface layer with WF, which contributed to penetrate more deeply and form micro‐crosslinking in the WF layer. We believe that the results reported in this work will increase the added value of polypropylene based wood plastics composites (WPC) and allow WPC to participate in lightweight and environmentally friendly products.

Micropores formation and effects in the magnetization roasting of limonite ore

As an abundant iron ore resource, limonite (mainly composed of goethite, hematite, lepidocrocite and other iron minerals) ore is seldom utilized due to its complex compositions, which has led to it lack mature processing methods. Magnetization roasting and magnetic separation is a promising method to process limonite ore. In this paper, the influence of microscopic pores on the reduction roasting of limonite ore was studied. X-ray diffraction, vibrating sample magnetometry, optical microscope, scanning electron microscopy, and the Brunauer-Emmett-Teller method of surface area analysis were used to study the dehydroxylation mechanism. The results indicated that goethite transformed into hematite, and the crystal structure of partly hematite probably changed when the dehydroxylation temperature increased from 600 °C to 1000 °C, making the sample more magnetic, the saturation magnetization increases significantly from 0.29 to 3.20 A·m2·kg−1. Simultaneously, SEM and BET showed the surface property has a big difference after roasting, more and more pores were generated with the temperature increased, then the specific surface area of the sample decreased from 75.94 to 0.59 m2·g−1. The reduction experiment results showed the dehydroxylation temperature has a significant effect on the reduction efficiency, the reduction time increased from 4 to 12.5 min with the temperature increased. This study has implications for the utilization of limonite ore using magnetization roasting technology.

A Model of Interpolation of Non-thermal Technique with Antibiotics Ameliorates Diffusion within Biofilm and Prediction of its Binding Site through In-silico Approach

This study aims to elucidate the intricate phenomenon of ultrasound-induced antibiotic transport across bacterial membranes, focusing on the synergistic interplay among sonic oscillation, transient retention, and micropore formation within the plasma membrane. A comprehensive approach was undertaken, involving detailed analysis of E. coli biofilms cultivated for 13 and 24 hours and exposed to distinct ultrasonic frequencies (22 and 33 kHz). Antibiotic diffusion assays were meticulously conducted at 15, 30, 45, and 60 minutes at 37°C. Computational exploration was employed to investigate norfloxacin's binding sites on bacterial gyrase through in-silico methods. The investigation revealed a significant fourfold increase in norfloxacin concentration within biofilms under ultrasound insonation compared to non-insonated samples. Sonic oscillation-induced micropore formation and transient retention facilitated complex exchanges of nutrients, waste, and antibiotics, presenting a potential breakthrough in addressing biofilm infections. Computational analysis further enriched mechanistic understanding by unveiling insightful conformational scores (-7.097 and -7.493 kcal/mol) related to norfloxacin's binding sites on bacterial gyrase. This study underscores the potential of ultrasound-enhanced antibiotic transport as a promising strategy for treating biofilm infections, providing novel insights into antibiotic delivery mechanisms.

Effect of peroxide-free and peroxide-based in-office bleaching on the surface and mechanical properties of CAD/CAM esthetic restorative materials.

The study aimed to investigate the influence of H2O2-based and H2O2-free in-office bleaching on the surface and mechanical attributes of CAD/CAM composite blocks. CAD/CAM composite blocks from five different composite materials (CC1, CC2, CC3, CC4, and CC5) were randomly divided into two groups according to bleaching application (H2O2-based and H2O2-free). The surface topography, morphology, nanohardness, elastic modulus, flexural strength, and fracture toughness were measured. A paired and unpaired sample t-tests gauged the effect of pre- and post-bleaching on the substrates. The estimated mean differences (before-after bleaching) suggested an increase in surface roughness for two materials CC2 and CC4, and a significant decrease in nanohardness for material CC4 and in elastic modulus for materials CC2 and CC4 with H2O2-based bleaching, whereas H2O2-free bleaching resulted in changes compatible with no change in these properties. Flexural strength and fracture toughness showed no evidence of changes, irrespective of the bleaching gel used. Scanning electron microscopic analysis revealed erosive effects and micropore formation due to H2O2-based bleaching. H2O2-based bleaching deteriorates the surface of CAD/CAM composite materials while H2O2-free bleaching gel had an insignificant effect on both surface and bulk properties. The clinician should carefully evaluate the potential effects of H2O2-based bleaching on the surface properties of CAD/CAM composites.

One-step utilizing of waste acidic Cu-containing etching solution to prepare hierarchical Cu-ZSM-5 for efficient flue gas Hg0 removal

Developing mercury adsorbents could mitigate environmental risk of mercury pollution. In this study, waste acidic Cu-containing etching solution from PCBs etching industry was utilized for the simultaneous porosity etching and Cu/Cl sites loading to prepare WA-ZSM for Hg0 removal via a one-step method. WA-ZSM synthesized with different waste acid concentrations exhibited over 94 % Hg0 removal efficiency within 60 min. The long-term stability of 5WA-ZSM under 110 μg/m3 Hg0 within 300 min was higher than 90 %. The dealumination process significantly affected the formation of micropores and Cu loading into the pore structure. The EFAl-Al3+ and “Si-O-Cu” structures formed by dealumination greatly enhanced the strong acid sites and the Cu sites improved the medium strong acidity. Isolated [Cu-OH]+ sites and [Cu–O-Cu]2+ sites are the main active sites in Hg0 removal. This method successfully synthesizes low-cost, high-efficiency Hg0 adsorbents using hazardous wastes, presenting a significant advancement in sustainable waste utilization and mercury pollution control.

Exploring the micro-indentation behavior of mortar and aggregate samples exposed to low-power microwave energy

Microwave heating presents a promising approach for repurposing waste concrete aggregates, leveraging its time efficiency and selective heating capabilities for complex materials. This study employs a micro-indentation test to investigate how low-power microwave radiation affects the micromechanical characteristics of recycled mortar-aggregate samples. The changes in properties, such as modulus and hardness under varying microwave exposure times, along with the influence of creep, are examined. The results indicate that with prolonged microwave exposure, the aggregate surface becomes stiffer and harder, a stark contrast to the mortar's weakening, attributed to the increased surface crystallinity of the aggregates as confirmed by X-ray diffraction (XRD) analysis. The mortar's softening is linked to the formation of micro-pores due to moisture evaporation. Additionally, while the aggregate surface showed improved creep modulus post-microwave treatment, the mortar samples displayed the opposite trend. However, both materials maintained a consistent creep recovery rate of about 50 % under different microwave heating conditions. These findings suggest that low-power microwave irradiation can selectively enhance the micromechanical properties of the aggregate surface while diminishing those of mortar, offering valuable insights into the micro-scale constitutive modeling of these materials with potential applications in separating aggregate from mortar in an industrial setting.

Processing and microstructure development of reactive sintered (Ti-Zr-Nb-Hf-Ta)B2 + (Ti-Zr-Nb-Hf-Ta)C high-entropy ceramics

A novel dual-phase (Ti-Zr-Nb-Hf-Ta)B2 + (Ti-Zr-Nb-Hf-Ta)C high-entropy, compositionally complex composite was synthesized by reactive spark plasma sintering using commercial ZrB2, NbB2, HfB2, TaB2 and TiC powders as starting materials. The composite with high density, consists predominantly of boride (∼39.7 vol%) and carbide (∼56.4 vol%) phases and with residual amount of (Hf-Zr)O2. The microstructure is homogenous and relatively fine due to the reaction and solid solution coupling effect with average grain sizes of 3.4 μm and 2.2 μm of the boride and carbide phases, respectively. Large-area SEM analyses confirmed no microcracks or micropore formation and no presence of large grains or clusters. Investigation from micro to nano and atomic level, focused on local chemical composition and spatial distribution of constituent elements, revealed that Ti preferentially dissolves into the boride and all other elements to the carbide phase creating a (Ti0.82Zr0.04Nb0.08Hf0.03Ta0.03)B2 + (Ti0.49Zr0.12Nb0.13Hf0.11Ta0.15)C system. The analysis of grain and phase boundary interfaces revealed a continuous, <1.5 nm wide, segregation of impurity atoms of Fe and Co. Continuous (>20 nm) and atomically flat basal interfacial termination planes (001) decorated with monoatomic Zr enriched layer in the boride phase were observed. Triple points at grain and phase boundaries exhibit metal-rich composition due to impurities from the starting raw powders.

Development of Phase-Separating Microfiber Network Hydrogels to Promote In Vitro Vascularization.

Engineered vascularized tissues in vitro exhibit the potential for transplantation therapy and disease modeling. Despite efforts to design hydrogels as cell culture platforms for in vitro vascularization, development of vascularized tissues recapitulating the natural structures and functions remains difficult due to a poor understanding of the relationships between the matrix microstructures and tube formation of endothelial cells. Herein, we developed microfiber network hydrogels with microporous structures by controlling the liquid-liquid phase separation (LLPS) of proteins and matrix structures in hydrogels. Extracellular matrix protein gelatin was modified with hydrogen-bonding moieties and mixed with hyaluronic acid sodium salt to form microfiber network structures. Gelatin gelation and hyaluronic acid sodium salt dissolution led to the formation of a microporous microfiber network hydrogel formation. Matrix structures of hydrogels were modified by controlling LLPS that affects endothelial cell tube formation. Vascularization was improved using laminin peptides and coculturing with mesenchymal stem cells. Overall, our approach exhibits the potential to induce in vitro vascularization for regenerative medicine and disease modeling applications.

Unravelling the nexus between structure, texture, and acoustic traits of fried chicken nuggets

SummaryTexture is a multi‐parameter attribute and one of the prime quality attributes of fried products. This study explored the nexus between microstructure and texture of fried breaded chicken nuggets. Chicken nuggets were deep‐fat fried (2, 4, 6, and 8 min) in canola oil at different frying temperature (170, 180, and 190 °C). Microstructure and texture of fried samples were assessed by scanning electron microscopy (SEM) and acoustic‐mechanical texture analyser, respectively. Maximum force (Fmax), number of force peaks (NFP), area under force‐deformation plots (FA), sound pressure level (SPL), number of sound peaks (AUX), and area under amplitude‐time curves (SA) were used to describe the textural parameters. Microstructural indices (porosity, number of pores, average pore area, polydispersity index, and average shape factor) were estimated from the SEM images. Results revealed that, both the frying time and temperature were positively correlated with the mechanical (Fmax: 25–55 N, NFP: 05–74 N, FA: 6500–15 000 N.sec) and acoustic (SPL: 88–97 dB, AUX: 650–810 dB, SA: 380–405 dB.sec) parameters. Frying time and temperature significantly (P &lt; 0.05) impacted the formation of micropores in fried chicken nuggets. Crust microporosity showed strong positive correlations (r = 0.82) with the AUX value. The NFP, SPL, and SA of the fried nuggets were significantly (P &lt; 0.05) impacted by the crust microporosity. Crust porosity (10–30%), number of pores (8–400), average pore area (10–4000 μm2), polydispersity index (0.05–0.2), and average shape factor (0.8–1.1) of fried nuggets were significantly (P &lt; 0.05) influenced by both the frying time and temperature. Findings from this study would be useful in quality improvement and process monitoring including modelling of coated fried products.

Evolution of pore structure and diagenetic stages of late Permian shales in the Lower Yangtze Region, South China

This study examines the evolution characteristics of shale pores in the Late Permian Longtan Formation located in the Lower Yangtze region of South China. The complete process of thermal evolution of the samples was achieved through thermal simulation experiments while identifying qualitatively the pore types and their development characteristics using field emission-scanning electron microscope (FE-SEM). Quantitative analysis of pore size distribution was conducted through mercury intrusion capillary pressure (MICP), nitrogen (N2) and carbon dioxide (CO2) adsorption experiments. The paper comprehensively analyzed the pore evolution characteristics and controlling factors of shale in the study area, with an analysis of diagenetic differences. Findings reveal that during the pore evolution process, both morphology and pore size are influenced by thermal maturity. The pore volume is dominated by mesopores and macropores, while the specific surface area is mainly dominated by mesopores and micropores. Thermal evolution promotes the formation of micropores and mesopores but hinders the development of macropores. Moreover, clay minerals transformation and mineral dissolution make certain contributions to the development of micropores. The diagenesis in the study area is controlled primarily by the pyrolysis of organic matter. Pyrite and clay minerals are the first to dissolve, followed by calcite and quartz. Five stages of evolution characterization have been identified from low-mature stage (Ro = 0.88 %) to overmature stage (Ro = 3.35 %) in combination with diagenesis. The development of pore structure and its influencing factors vary across different stages. The influencing factors mainly include hydrocarbon generation from organic matter, compaction, mineral transformation, and dissolution. The process of hydrocarbon generation in organic matter occurs throughout the entire pore evolution process, resulting in the development of numerous micropores and mesopores. Compaction primarily impacts pore development during the early diagenetic stage, causing a substantial transition of primary mineral pores from macropores to mesopores. Mineral transformation and dissolution take place during and after the middle diagenetic stage. The former governs the development of mesopore-sized clay interlayer pores, while the latter primarily generates micropores.

Influence of methane-oxygen coupled gas field on the transformation mechanism of microporosity and active structure of cryogenic pre-oxidized residual coal

Due to the impact of coal seam mining processes and the release of adsorbed gases in residual coal, a mixed gas field of methane and oxygen is formed in the goaf, which affects the oxidation process of the residual coal over a long period. In this study, to explore the low-temperature oxidation mechanism of residual coal in a hypoxic methane-containing environment, Low temperature nitrogen adsorption (LTNA) experiments and Fourier transform infrared spectroscopy (FTIR) were utilized to examine the pore development properties of residual coal and the transformation mechanisms of reactive micro-groups. The results indicate that increases in temperature and methane proportion promote the transition of various pores to larger scales, with 3 % methane inducing the formation of fine micropores, thereby increasing the specific surface area of the coal. High temperatures (80℃，100℃) and increased proportions of oxygen and methane synergistically elevate the fractal dimensions. Methane inhibits the consumption of hydroxyl groups, and a low oxygen concentration (5 %) impedes the gas production from coal oxidation. The presence of both oxygen and methane exhibits a compound effect; the strongest tendency towards spontaneous combustion occur at 1 % methane and 9 % oxygen. The findings provide valuable insights for controlling spontaneous combustion disasters in goafs.

Second phase strengthening and grain boundary segregation effects on the microstructure and properties of (Ce, Y)-TZP-based ceramics prepared by vat photopolymerization

Immediate implant placement (IIP) has garnered significant attention due to its minimally invasive approach and ability to facilitate immediate crown replacement. Nevertheless, challenges persist in processing complex geometries and selecting suitable materials. This study successfully fabricated high-performance, complex-structured (Ce, Y)-TZP-based composite ceramics using vat photopolymerization (VPP) technology, combining second-phase strengthening and grain boundary segregation effects. The incorporation of α-Al2O3 as a secondary phase led to a progressive refinement of (Ce, Y)-TZP grains, with the most favorable grain size achieved at 20 wt% α-Al2O3, reducing the average grain size to 0.75 μm. However, excessive α-Al2O3 content resulted in micropore formation, compromising the material's mechanical performance. At an optimal concentration of 15 wt% α-Al2O3, the composite exhibited superior mechanical properties, including a Vickers hardness of 11.53 ± 0.27 GPa and a flexural strength of 525.5 ± 21.3 MPa. Despite these improvements, some coarse (Ce, Y)-TZP grains persisted within the ceramic matrix. To further enhance grain refinement at lower α-Al2O3 content, a minimal addition of La3+ (0.1 wt%) was introduced, promoting grain boundary segregation and additional grain refinement. This modification reduced the (Ce, Y)-TZP grain size to 0.74 μm, increased hardness to 13.03 ± 0.31 GPa, and elevated flexural strength to 550.4 ± 39.8 MPa, while maintaining excellent material stability.

Research on influence laws of aggregate sizes on pore structures and mechanical characteristics of cement mortar

Aggregate plays an important role in cement-based materials. Evaluating the impact of aggregate gradation on pore structure and mechanical properties will help to optimize the mortar ratio and improve its durability. In this study, artificial sand with 5 different particle sizes was used as aggregate, and the synthetic gradation formed by their coupling was compared. The pore structure distribution of mortar was quantitatively characterized by nuclear magnetic resonance (NMR) technology. Surface-to-volume ratio (SVR) and ρd (aggregate packing density) were used to characterize the aggregate grading characteristics. The correlation between aggregate gradation characteristics and mortar parameters, such as porosity, pore structure fractal dimension, permeability coefficient, and mechanical strength, was analyzed, and a compressive modulus of mortar was established. The results indicate that the pore structure characteristics, K (permeability), and mechanical characteristics of mortar are all influenced by both SVR and ρd. The predominant pores in the mortar are micropores and movable fluid pores, and the addition of 0.1–0.5 mm aggregates reduces the formation of micropores, mesopores, macropores, and movable fluid pores in the mortar. As the number of pores increases, the complexity of the pore structure decreases, leading to higher homogeneity. Moreover, the K shows a strong power function relationship with the total porosity and the total porosity fractal. The compressive strength and Ec (compression modulus) of GM1–6 are significantly higher than those of GM7–9, correlating with the minimum aggregate size and the inherent strength of the aggregates. The regression results of the strength correlation model are significant, and the strength model established based on the porosity of micropores and Ec can accurately predict the compressive strength of mortar.

In Ukrainian

The CMs were obtained in argon in three stages: 1) heating (4 grad/min) to the specified temperature t in the range of 350–825 °С; 2) isothermal exposure 1 h; 3) cooling, washing from alkali and drying. Samples are denoted as CM(t). The CM yield (Y, %) and CMs elemental composition are determined. Based on low-temperature (77 K) nitrogen adsorption-desorption isotherms, integral and differential dependences of the specific surface area SDFT (m2/g) and pore volume V (cm3/g) on the average pore diameter (D, nm) were calculated by 2D-NLDFT-НS method (SAIEUS program). They were used to define volumes of ultramicropores (Vumi), supermicropores (Vsmi) and micropores (Vmi). The total pore volume V was calculated from the nitrogen amount adsorbed at a relative pressure p/p0 ~ 1.0. The S values of ultramicropores (Sumi), supermicropores (Ssmi) and micropores (Smi) were similarly determined. The CM yield was established to decrease linearly (R2 = 0.979) from 70.2 to 45.3 % with an increase in temperature from 350 to 825 °С. The carbon content decreases to a minimum value at 500 °С (72.6 %), and then increases to a maximum value (87.5 %) at 825 °С; the oxygen content changes antibatically. Two temperature regions were identified: region I (≤ 500 °С) of increasing the oxygen content due to reactions in which KOH acts as a donor of O atoms; region II (≥ 500 °C) of dominating the thermal destruction of functional groups (carboxyl, lactone, ester) with the release of CO and CO2, and condensation increasing the size of polyarenes of the CM secondary framework and formsng single Сar-Саr bonds between them. The CM(350) sample was found to contain only mesopores (D ≥ 10 nm) and macropores. An activation temperature increase to 400 °C initiates the additional formation of small-diameter micropores and mesopores. In samples CM(400) - CM(825), the main portion of newly formed pores falls on pores with D ≤ 5 nm. With increasing temperature, the micropores volume increases almost linearly (R2 = 0.992). The Vumi and Vsmi volumes increase up to 600 °C. At higher temperatures the ultramicropores volume decreases due to transforming ultramicropores (D ≤ 0.7 nm) into supermicropores (D = 0.7–2.0 nm). Portion of the ultramicropores volume changes with a maximum (23.9 %) in the CM(600) sample. The SBET specific surface area linearly (R2 = 0.992) increases with temperature up to 1729 m2/g. The SDFT values are close to SBET, but noticeably lower (1514–1530 m2/g) for CM(785)-CM(825). The micropores specific surface area increases to 1415 m2/g, and ultramicropore surface Sumi changes extremely with a maximum (526 m2/g) for the CM(600) sample, which should be expected based on the temperature dependence of the Vumi parameter. The decrease in Sumi values after the maximum is compensated by an increase in the supermicropore surface. Such an effect - the redistribution of pores by size in the microporous range (D ≤ 2 nm) with an increase in the alkaline activation temperature is not described in the literature. The portion of the micropores surface is dominant (92.6–97.0 %) in samples prepared at t ≥ 450 °C. The portion of the ultramicropore surface is maximum (56.3 %) in CM(500). Pores are revealed that do not form at all at 450–750 °C. These are supermicropores (D = 0.96–2.00 nm) and mesopores of small diameters (D = 2.0–2.82 nm). This effect was assumed to be due to the properties of the CM supramolecular framework, which is formed from polyarene fragments of the initial and activated coals having polyarenes with diameters of the same order (1.68–2.54 nm).

Interconnected pyrolysis and activation with in-situ H3PO4 activation of biochar from pear wood chips in a pilot scale dual fluidized bed

Interconnected pyrolysis and activation is a novel technology for combustible gas and biochar production in dual fluidized bed (DFB). The study proposed one-step and two-step methods for pyrolysis and activation of biomass in a pilot scale DFB with capacity of 100 kg/h. Physical and chemical activation occurred simultaneously in DFB system by phosphoric acid (H3PO4) impregnation pretreatment of pear wood chips, and flowing hot flue gas and steam. Stable operating parameters were observed for both methods. The one-step method was superior to the two-step method in terms of the pyrolysis gas quality, biochar pore distribution, micro- and meso-pores structures of biochar, while one-step method reduced the biochar yields. As an activation agent, H3PO4 increased the yields of biochar and pyrolysis gas, promoted formation of micropores and enriched the surface functional groups of biochar with increasing ratio of H3PO4. H3PO4 to biomass ratio of 1:5 reached the maximum biochar yield of 42.3 wt% and highest iodine adsorption value of 648.5 mg/g, increasing by 70.6 % and 90.3 % compared to the biochar without H3PO4 pretreatment, respectively. This DFB system facilitated the diversified use of fluidized beds and the co-production of biochar and product gas with energy saving and CO2 emission reduction.