Micropore Content Research Articles

Preparation and characterization of high performance super activated carbon based on coupled coal/sargassum precursors

High electrochemical performance supercapacitors require activated carbon with high specific surface area, suitable pore size distribution and surface properties, and high electrical conductivity as electrode materials, whereas there exists a trade-off relationship between specific surface area and electrical conductivity, which is not well met by a single type of carbon source. To solve this problem, the coal and sargassum are adopted to obtain the coupling product via co-thermal dissolution, followed by carbonization and KOH activation. The effects of mixing mass ratio and activation temperature on the prepared activated carbon (AC) are investigated using single factor experimental method. The experimental results show that AC1/3-800 has abundant micropore and mesopore content, good pore structure connectivity, high electrical conductivity and good wettability, and superior electrochemical properties compared with other activated carbons prepared in this experiment. Its total specific surface area is up to 2098.5 m2·g−1, the pore volume is up to 1.33 cm3·g−1, the content of mespores with diameter of 6–8 nm is significantly increased, and the pore size distribution is wide and uniform. When the current density increases from 0.1 A·g−1 to 10 A·g−1, the gravimetric capacitance decreases from 219 F·g−1 to 186 F·g−1 with a capacitance retention of 84.9%, the equivalent series resistance is very small, and the rate performance and reversibility of charging and discharging have also been excellent.

Structure and Magnetic Properties of Fe<sub>3</sub>O<sub>4</sub>/C Composites Synthesized from Wheat Straw

The porous structure and magnetic properties of nanostructured Fe3O4/C composites based on wheat straw were investigated in this work. The synthesis was carried out by a one- and two-step method using FeCl3 and ZnCl2 as activating agents. X-ray diffraction methods have shown the presence of an additional phase of magnetite Fe3O4 in both synthesized composites, along with the amorphous carbon phase. Magnetic measurements have shown that the composite synthesized in one step has better magnetic properties, in particular, a higher specific saturation magnetisation. However, the samples of the composite synthesized in two steps are characterised by a higher content of micropores and mesopores, which causes an increase in the specific surface area to 884 m2/g compared to 405 m2/g for the samples synthesized in one step. Based on the dependence of the coercive force on the particle diameter in Fe3O4 dispersions, it was found that the average size of the magnetite particles is ~25 nm for both synthesized magnetoresponsive composites.

Unveiling key impact parameters and mechanistic insights towards activated biochar performance for carbon dioxide reduction

Chemically activated biochar is effective in supercapacitors and water splitting, but low conductivity hinders its application as a carbon support in carbon dioxide reduction reaction (CO2RR). Based on the observed CO2RR performance from potassium hydroxide (KOH)-activated biochar, increased microporosity was hypothesized to enhance the performance, leading to selection of potassium carbonate (K2CO3) for activation. K2CO3 activation at 600℃ increased microporosity significantly, yielding a total Faradaic efficiency of 72%, compared to 60% with KOH at 800℃. Further refinement of thermal ramping rate enriched micropore content, directly boosting FEC to 82%. Additionally, K2CO3′s lower activation temperature could preserve hydroxyl groups to improve ethylene selectivity. These findings demonstrate that optimizing microporosity and surface chemistry is critical for designing activated biochar-based CO2RR electrocatalysts. Despite lower electrical conductivity of activated biochar, selecting the appropriate activating agents and conditions can make it a viable alternative to carbon black-based electrocatalysts.

Mesoporous carbon with extremely low micropore content synthesized from graphene oxide modified with alkali metal nitrates

High-temperature thermal exfoliation is a simple, rapid, and cost-efficient method for transforming graphene oxide (GO) materials into reduced graphene oxide (rGO) materials. In this study, GO materials were dispersed with alkali metal nitrates (MNO3), leading to the preparation of porous rGO materials characterized by high specific surface area (SSA) and pore volume via high-temperature thermal exfoliation. Experimental data indicate that the metal cations of MNO3 tend to react directly with the oxygen functional groups (OFG) of GO, modulating the OFG content. Simultaneously, nitrate anions have preferential interaction with alkali metal ions and adhere to the surface of the GO. The presence of MNO3 on the surface of GO facilitates the thermal exfoliation process and leads to the formation of structures with an extremely high proportion of mesoporous content. The isothermal gas adsorption results show that the exfoliation efficiency of the samples activated with different nitrate salts decreases in the order rGO-KNO3 > rGO-NaNO3 > rGO-LiNO3. Among these samples, rGO modified with KNO3 exhibited the greatest exfoliation efficiency, with a mesopore-to-micropore volume ratio of 22.4, more than 1.7 times that of rGO. Its SSA and pore volume were 359 m2 g−1 and 1.26 cm3 g−1, respectively. These values significantly surpass those of rGO. Our research findings demonstrate that activation with MNO3 significantly increases the SSA and pore volume of the GO material after high-temperature annealing.

Pore Structure Characterization and Fractal Characteristics of Tight Limestone Based on Low-Temperature Nitrogen Adsorption and Nuclear Magnetic Resonance

Pore structure characterization and fractal analysis have great significance for understanding and evaluating tight limestone reservoirs. In this work, the pore structure of tight limestone, low-temperature nitrogen adsorption (LTNA), and low-field nuclear magnetic resonance (NMR) are characterized, and the fractal dimension of the pore structure of tight limestone is discussed based on LTNA and NMR data. The results indicate that the pores of tight limestone have H3 and H4 types, the pore size distribution (PSD) of the H3 type is a wave distribution ranging from 2 to 10 nm, and the PSD of the H4 type is a unimodal distribution ranging from 2 to 10 nm. The transverse relaxation time (T2) spectrum of tight limestone shows a single peak (DF), double peak (SF), and triple peak (TF), and the ranges for the T2 spectra for micropores, mesopores, and macropores are 0.1 to 10 ms, 10 to 100 ms, and greater than 100 ms, respectively. The LTNA fractal dimension of tight limestone (DL) ranges between 2.4446 and 2.7688, with an average of 2.5729, and the NMR fractal dimensions of micropores (DNMR1), mesopores (DNMR2), and macropores (DNMR3) are distributed between 0.3744 and 1.1293, 2.4263 and 2.9395, and 2.6582 and 2.9989, respectively. Moreover, there is a negative correlation between DL and average pore radius, a positive correlation between DL and specific surface area, and a positive correlation between DNMR2 and DNMR3 and micropore content, while DNMR2 and DNMR3 are negatively correlated with the content of mesopores and macropores.

Almond skin derived porous biocarbon nanoarchitectonics with tunable micro and mesoporosity for CO2 adsorption and supercapacitors

The careful selection of carbon precursors for chemical activation is critical in obtaining cost-effective and efficient porous activated biocarbons with multifunctional properties. Herein, we report on utilising almond skin to synthesize porous activated biocarbons via solid-state KOH activation. Through precise manipulation of the impregnation ratio of KOH to the non-porous carbon, a range of materials with intriguing properties including high surface area, large pore volume, tunable micro and mesopores, and surface functionalization with oxygen were synthesized. The optimized material ASPC5-4 displayed an extremely high surface area (3535 m2 g−1), a large pore volume (1.9 cm3 g−1), a high proportion of mesopores (96.5 %) and a notable surface oxygen content (6.93 wt %). These excellent features allowed ASPC5-4 to adsorb a record amount of CO2 at 0 °C/30 bar (39.81 mmol g−1). Another material ASPC5-2 exhibited a high content of micropores and adsorbed 5.92 mmol g−1 of CO2 at 0 °C/1 bar. ASPC5-4 also exhibited great potential as a supercapacitor electrode, displaying a high specific capacitance in both a three-electrode (354 F g−1/0.5 A g−1) and two-electrode (203 F g−1/0.5 A g−1) systems. It also demonstrated high power and energy densities of 638 W kg−1 and 47 W h kg−1, respectively.

Removal of chromium (VI) from aqueous solutions by granular composites based on laponite and alginate ionotropically cross-linked by iron and zirconium ions

The conducted research established the porous structure of the materials through low-temperature nitrogen adsorption. It was demonstrated that the nitrogen sorption isotherms for the investigated samples belong to Type IV with H4 hysteresis associated with bottle-like pores. The specific surface area of the granulated composite samples was determined, ranging from 99 to 111 m2/g. Additionally, it was shown that an increase in iron content in the samples leads to a reduction in micropore content. Active centers on the material's surface, primarily composed of hydroxyl groups, were investigated using infrared spectroscopy. The kinetics of chromium (VI) adsorption were explored, and it was established that the iron-to-zirconium ratio in the reinforcement solutions hardly affects the duration of establishing adsorption equilibrium, which is approximately 60 minutes. Pseudo-first-order and pseudo-second-order models were applied to describe the kinetics of the adsorption process. The dependence of the chromium (VI) removal efficiency on the solution pH was determined. It was demonstrated that the synthesized samples exhibited high adsorption in acidic conditions with a sharp decline when transitioning to neutral and alkaline environments. It was shown that the maximum sorption capacities of the synthesized granulated composite samples significantly depend on the ratio of iron and zirconium ions. One of the most efficient samples is that with 50% Fe and 50% Zr, exhibiting a maximum sorption capacity of 13.29 mol/g at pH 6. The use of Langmuir and Freundlich models allowed establishing the fundamental adsorption properties of the materials.

Grafting EDTA in UiO-66 to modulate the microenvironment of Rh for 1-hexene Hydroformylation

Oriented designing the microenvironment of catalytic sites is essential for understanding catalytic processes. In this work, EDTA was first grafted in UiO-66 and then chelated Rh to obtain an efficient catalyst for 1-hexene hydroformylation reaction. EDTA not only served as a chelation site for Rh immobilization in UiO-66, but also markedly influenced the structure and properties of Rh/UiO-66. The incorporation of EDTA reduced the micropore content and suppressed the formation of heavy products. Moreover, the grafted EDTA regulated the electronic state of Rh effectively to improve the CO and propene adsorption, thus constructing an appropriate microenvironment for hydroformylation. Therefore, EDTA-modified Rh/U-E catalyst exhibited higher aldehydes yield, TOF and stability than Rh/U without EDTA. The dual role of EDTA in anchoring Rh sites and modulating the microenvironment for hydroformylation provides more prospects for designing customized MOFs-based catalysts.

The correlation between the iodine value of coconut shell carbon and their reaction performance for NO2 to NO

AbstractBACKGROUNDThe precise detection of nitrogen dioxide (NO2) requires the conversion of NO2 to nitric oxide (NO) using a molybdenum conversion furnace. Currently, molybdenum wire is utilized as the conversion agent for the molybdenum furnace; however, the high operating temperature of the molybdenum wire can inadvertently convert ammonia (NH3) in industrial exhaust gas to NO, potentially impacting the accuracy of the detection process. Consequently, there is a pressing need to develop low‐temperature conversion agents. The study aims to establish a correlation between the iodine value, which characterizes the liquid‐phase adsorption properties of activated carbon (AC), and its capacity for NO2 conversion, with the potential to provide valuable theoretical insights supporting the development of commercial molybdenum furnace conversion agents.RESULTSThe iodine value of coconut shell carbon (C) is closely related to their reaction performance for NO2‐to‐NO among three samples with different iodine values. AC‐900, AC‐1200 and AC‐1500 exhibited notable NO2‐to‐NO conversion capabilities. Specifically, AC‐900 demonstrated significantly superior reaction performance compared to AC‐1200 and AC‐1500. Under conditions of 175 °C and 1 L min−1, the NO2 conversion rates for AC‐900, AC‐1200 and AC‐1500 were measured at 97.3%, 88.2% and 86.4%, respectively. Furthermore, the evaluation of AC‐1200 and AC‐1500 at different flow rates at 125 °C revealed a decrease in NO2 conversion with increasing gas flow rate. AC‐1200 exhibited better reaction performance compared to AC‐1500.CONCLUSIONThe structure–activity relationship between iodine value of coconut shell C and their NO2‐to‐NO performance is revealed. The capacity of AC to convert NO2 is significantly influenced by the presence of oxygen (O) functional groups and the proportion of micropores. The content of micropores and O‐containing functional groups, especially phenolic hydroxyl groups, decreases with the increase of iodine value, leading to a decrease in the reaction performance of the conversion agent. © 2024 Society of Chemical Industry (SCI).

Influence of carbon structure/porosity on the electrochemical performance in Li–sulfur batteries

The porous structure of three different, commercially available porous carbonaceous materials is investigated by the αS-plot method and by the t-plot method. Subsequently, the electrochemical properties of sulfur-free porous carbon electrodes from inspected materials are studied by cyclic voltammetry. The comparison of double-layer capacitances with the corresponding adsorption isotherms of N2 reveals the role of micropores during the capacitive charging of carbons by Li+. The studied carbons are added to the sulfur cathodes and evaluated. The cyclic voltammograms show no contribution of micropores in the carbon structure to the electrochemical processes taking place in the lithium–sulfur coin cell. The highest specific capacity of 816 mAh/g is observed for material with the lowest content of micropores in the structure (14%). The partially mesoporous and partially microporous (65%) sample and the predominantly microporous one (87%), show specific capacities of 664 mAh/g and 560 mAh/g, respectively. The galvanostatic cycling of lithium–sulfur coin cells with carbonaceous additives reveals that the mesopores and macropores in the carbon structure increase the specific charge capacity of the lithium–sulfur batteries and that the micropores improve the cycling stability of these batteries.Graphical abstract

Development of granular composites based on laponite and Zr/Fe-alginate for effective removal of uranium (VI) from sulfate solutions

The object of research is granular composites based on zirconium-iron alginates and laponite. The task of research is to determine the influence of the Zr:Fe ratio on the structure of granular composites and efficiency of uranium (VI) removal from aqueous solutions. The influence of the zirconium and iron ratio on the parameters of the material's pore structure has been established, particularly on the change in the content of micropores within the matrix. The specific surface area of the materials ranges from 86 to 112 m²/g. The sorption properties of the composites regarding uranium (VI) have been investigated. The impact of the charge of surface groups and the form of uranium (VI) presence in sulfate solutions on their sorption characteristics has been demonstrated. The maximum adsorption capacity reaches 265.1 µmol/g at pH 6. It is shown that an elevated electrolyte content positively affects the efficiency of uranium (VI) removal in neutral and alkaline medium. It has been established that structural changes in the materials occur due to the intensive interaction of iron ions and alginate molecules, resulting in the formation of a dense gel-like structure. The mechanism of uranium (VI) removal is associated with the formation of surface complexes in the presence of electrolytes. The synthesized granulated composites exhibit improved removal efficiency of uranium (VI) under conditions of high mineralization of solutions, making them attractive for potential use as sorbents. The obtained results can be utilized in the development of effective methods for purifying water environments from uranium (VI) in high mineralization conditions, which is a relevant issue in the field of nuclear energy and the removal of radioactive substances from water systems

Further application of the D-A model to evaluate the isothermal CO2 ad/desorption characteristics of coal

The CO2 ad/desorption characteristics is essential for evaluating the effectiveness and suitability of CO2 injection into coal-bed to storage and enhances CH4 recovery (CO2-ECBM). We performed the isothermal CO2 ad/desorption experiments on four different ranks of coal by using the self-developed coal seam high-pressure gas ad/desorption test system in this study. It was found that the isothermal CO2 ad/desorption behavior can be adequately explained by the D-A model, as its parameters can reflect the adsorption capacity, the desorption hysteresis characteristic, and the micropore structure in coal samples. The saturation CO2 adsorption amount (Vmax) for the four coal samples is CC > YW > XLH > HG, showing a “decreasing-increasing-decreasing” trend as the coal rank growth, which is in general consistent with the relation between the total specific surface area, the total micropore volume and the micropore content in coal samples. The difference value in the characteristic adsorption energy (ΔE) in the D-A model can be used as a parameter to quantitatively characterize the hysteresis in the CO2 desorption processes compared to the adsorption processes in coal samples, and the larger ΔE implies the more significant desorption hysteresis. The desorption hysteresis of four coal samples is XLH ≈ HG > YW > CC in order, showing a trend of decreasing first and then increasing as the coal rank growth. The coefficient of structural heterogeneity n reflects the distribution of micropore structure, the larger value of n indicates a higher micropore volume and micropore content in coal. The pore structure is changed by the effect of CO2 ad/desorption, which increases the micropores content in coal, resulting in a larger structural heterogeneity coefficient in the desorption process.

Analyzing Pore Evolution Characteristics in Cementitious Materials Using a Plane Distribution Model

This research aims to analyze the distribution and evolution of pores within the planar structure of cement-based materials. Utilizing digital imaging methods, a model for pore plane distribution was established, and the evolutionary patterns of both total pore numbers and varying pore sizes in cement-based materials were investigated. The research introduced an innovative experimental method for analyzing pore distribution within cement-based planar structures. Additionally, a hybrid method was proposed, combining automated image binarization thresholding with manual comparative analysis, thereby enhancing the feasibility of comparative research. Pores were categorized into four distinct sizes: tiny pores (5–200 μm), small pores (200–500 μm), medium pores (500–1000 μm), and large pores (>1000 μm). Areas with apertures <5 μm were classified as dense areas. The findings indicated that the overall number of pores in cement-based materials increased due to the influence of styrene butadiene latex additives. However, at a 15% dosage, the rate of pore formation reached an inflection point, confirming that various factors, such as styrene butadiene latex, air bubbles, and the cement-based material itself, collectively influenced pore formation. The research also demonstrated that styrene butadiene latex affected the four categorized pore sizes differently. Importantly, a higher latex dosage did not necessarily lead to a proportional increase in pore content. Pore content was influenced by multiple factors and exhibited different distribution patterns. The number of micropores, although relatively small, gradually increased with higher latex dosages, while small and medium pores generally showed an upward trend. At a 10% latex dosage, both small and medium pores reached a turning point in their rate of increase. Large pores also exhibited a general increase, peaking at a latex dosage of 10%. It was confirmed that both the total pore volume and the content of micropores were critical factors in determining the mechanical properties of cementitious materials. Higher porosity and micropore content generally weakened mechanical performance. However, at a small latex dosage, there was an improvement in flexural strength. When the latex dosage reached 15%, the total pore and micropore content declined, resulting in a balanced increase in flexural strength and a mitigated decline in compressive strength. This study offers valuable insights into the evolution of total pore volume and the content of pores of various sizes, providing a theoretical basis for the meticulous selection of additive types and dosages from a microscopic perspective.

Physicochemical characteristics of natural and anthropogenic inorganic and organic solid porous materials: Comprehensive view

Complex textural analyses and ultimate analyses of 23 inorganic and organic solid porous materials of natural and anthropogenic origin have been performed. The type of pores, porosity and pore size distributions are discussed. While Halloysite, Biocalith K and Diatomaceous earth have a balanced distribution of all pores, Clinoptilolite and Kemira have a high micropore content and Montmorillonite contain predominantly mesopores. SH-GC has the highest micro-mesopore content. Natural materials and materials prepared from raw materials have SBET values <50 m2/g, whereas materials on the basis of activated carbon and montmorillonite or pure granulated Fe(OH)3 have SBET > 50 m2/g. The highest porosity values correspond with an extremely high content of macropores in the Eco-Dry Compact and Eco-Dry Plus samples, and in the Wood sawdust samples, where at the same time the presence of the smallest pores is sporadic. The highest micropore values were observed in a sample from the category of aluminosilicates and in samples of activated carbon. Overall, the diverse variability of the properties of these solid porous unconventional materials was revealed, which offers the possibility of wide use for various types of adsorption, both in raw form and after appropriate material treatment. The material is discussed for the suitability of using to remove specific types of pollutants.

Mechanism of the pore and molecular structure evolution of coal exposed to acid mine drainage (AMD)

In the post-extraction epoch, wastewater from mining activities, particularly acid mine drainage (AMD) residing in sulfur-laden coal terrains, assumes a pivotal role in the safety stewardship of decommissioned coal mines. This research aims to investigate the mechanism behind coal characteristic deterioration from prolonged exposure to AMD. Immersion assays were performed on coal samples across pH 2 to 5 to assess the impact of acid mine drainage. Subsequently, the pore and molecular architecture was appraised using microscopic methodologies. Computed Tomography (CT) findings elucidate that post-immersion, the porosity, and fissures proliferated longitudinally along the coal strata, engendering a marked amplification in surface porosity contiguous to pre-existing pores. This escalation in surface porosity was further accentuated in correlation with the intensification of AMD acidity. Nuclear Magnetic Resonance (NMR) data indicated a marginal augmentation in the content of both micropores and macropores within a tepid AMD milieu. However, in a more virulent AMD context, the proportion of micropores diminished, whereas that of macropores and pore throat size (PTS) experienced an upswing, thereby transmuting adsorptive pores into permeable conduits and consequently enhancing coal permeability. Scanning Electron Microscopy (SEM) corroborated the NMR outcomes; as AMD acidity transitioned from mild to severe, the coal matrix manifested many erosive pores, matrix layer disintegration, and an expansion in cleat width. Therefore, the microscopic pore evolution can be succinctly encapsulated as follows: in a mild AMD environment, dissolution of minerals predominates, generating erosive pores, whereas, in a more acidic AMD milieu, the matrix undergoes partial contraction, thereby augmenting pore volume, enhancing permeability, and inducing structural degradation. Additionally, Fourier Transform Infrared Spectroscopy (FTIR) analysis substantiated that AMD compromised the pore architecture and catalyzed the disintegration of coal macromolecules into lower molecular weight constituents. Therefore, AMD degrades coal macromolecules into smaller compounds, heightening matrix layer porosity and impairing coal characteristics. This research yields vital insights for the security and efficient management of abandoned mine excavations.

Induced synthesis of SO2-promoting and H2O-tolerant sorbents for elemental mercury removal from flue gas

In this study, novel S-doped sorbents synthesized via one-step co-pyrolysis of biomass and scrap tires under SO2 atmosphere were developed for elemental mercury (Hg0) removal from coal-fired flue gas. The presence of SO2 could regulate the sulfur species in S-doped sorbents and improve their Hg0 removal performance. Sample characterization exhibited that SO2 activation increased the sulfur content and decreased the carbon content in sorbents due to the occurrence of carbothermal reduction reaction. The specific surface area, pore volume, and micropore content in S-doped sorbents were obviously improved compared with raw sorbents. After SO2 activation, partial inorganic sulfide was converted into sulfur-containing functional groups and more oxygen-containing functional groups were generated on the sorbents. The S-doped sorbents presented more excellent performance for Hg0 removal compared with raw sorbents. The optimal pyrolysis temperature and SO2 concentration in activation atmosphere were 700 °C and 10%, respectively. It was surprising that SO2 facilitated Hg0 removal and the S-doped sorbents showed good water-resistance due to the presence of ZnS. O2 and NO had positive effects on Hg0 removal. A close fitting to the pseudo-second-order model was obtained for the behavior of Hg0 removal over S-doped sorbents. Aliphatic sulfur, sulfoxide, carbonyl and carboxyl/ester groups functioned as active components for Hg0 removal.

Chemical Properties and Breakthrough Adsorption Study of Activated Carbon Derived from Carbon Precursor from Carbide Industry

The residual carbon from the carbide industry in Malaysia has been explored as a precursor in activated carbon (ACs) processing via chemical activation with potassium hydroxide (KOH). The residual carbon from the carbide industry consists of high fixed carbon content and is a sustainable source of raw material, making it a promising precursor for ACs processing. However, the synergy between activation temperature with impregnation ratio has yet to be well explored for precursors from carbide processing. Thus, in the present work, impregnation ratios from 1:1 to 1:5 and temperature for the activation process from 300°C to 700°C were examined in the ACs processing. The impact of these factors was evaluated towards the chemical characteristic of the derived ACs, such as pores and surface morphology, functional groups, and thermal profile. The finding indicated that the ratio of as-received carbon /KOH from 1:1 to 1:5 provided ACs with BET surface areas of 130 – 458 m2 /g and micropores content of 19 – 25.75%. The results suggested that the highest BET surface area in this range of study was 458.15 m2 /g at an activation temperature of 700oC and an impregnation ratio of 1:1. Then the developed ACs were further evaluated in carbon dioxide (CO2) adsorption using breakthrough CO2 adsorption. The breakthrough time and CO2 adsorption rate capacity were calculated as 70 s and 0.175 mmol/g, respectively. This finding indicated that as-received carbon precursors from the carbide industry could be explored as one of the potential materials in ACs development, forming the microporous structure during KOH activation and encouraging the binding of CO2 molecules in CO2 capture.

Experimental study on changes in components and pore characteristics of acidified coal treated by organic solvents

Chemical solvents could change coal components and effectively enhance conductivity of coal reservoir, which is beneficial to efficient methane extraction. Relationship between coal chemical structure parameters and main functional groups variations affected by acidification and tetrahydrofuran (THF) is investigated through infrared spectroscopy tests and curve peak fitting. Meanwhile, variations in fractal dimensionality and pore structure characteristics are studied by adopting low-temperature nitrogen adsorption tests and Frenkel-Halsey-Hill (FHH) fractal model. Main results are: (1) After extracting raw coal and acidified coal using THF with varying concentrations, absorbance of aromatic hydrocarbon –CH surface and aromatic methyl bond become weaker. While the proportion of substituted aromatic hydrocarbons increases in acidified coal than in raw coal. Acidification treatment could reduce strength of C-O-C absorption peak. Proportion of CH2 and CH3 in raw coal decreases with increasing THF concentration, indicating that THF could react with aliphatic structure to reduce CH2 and CH3 content. Extraction with THF dissolves aromatic structure, lowering C = C content in coal to different degrees. (2) Acidification pretreatment could produce more micropores in coal samples. Micropore contents of acidified coal after THF extraction are all lower than coal sample S, while transition pores and mesopores contents are both higher than those in coal sample S. (3) Fractal dimension D1 of raw coal indicates a relatively linear relationship with specific surface area, while the D1 of acidified coal is less correlated with specific surface area. The factor D2 shows a linear relationship with average pore size. After treatment of THF, average pore size of raw coal increases with D2, while that of acidified coal varies in different degrees with uneven distribution of pore sizes.

Highly microporous and mesoporous nanomaterials derived from Agave sisalana waste for supercapacitors

AbstractNanostructured electrodes with large surface area are essential for studying charge storage mechanisms in supercapacitors. Biomass‐based carbonaceous porous electrodes have proven to be good candidates for supercapacitor application. In this study, micropore and mesopore dominated carbon materials derived from Agave sisalana sisal waste were prepared through carbonization and chemical activation with ZnCl2. Scanning electron microscopy, energy‐dispersive X‐ray, transmission electron microscopy, Raman spectroscopy, and X‐ray diffraction studies show that the microstructure and composition of the as‐prepared microporous carbon materials are influenced by adjusting the ZnCl2 to the carbon mass ratio. Sorption studies demonstrated a high Brunauer–Emmett–Teller (BET) surface area of 1464 m2 g−1, type I isotherms for low temperature, type IV at 900 °C, and 99% micropore content in all the samples. The fabricated electrodes exhibited high specific capacitances of 497 F g−1at 5 mV s−1, which is indicative of our carbon materials’ strong potential for use in the production of high‐performance supercapacitors. Specific capacitance increased with increasing micropore surface areas.

Three-dimensional organization of pyrrolo[3,2-b]pyrrole-based triazine framework using nanostructural spherical carbon: enhancing electrochemical performance of materials for supercapacitors

Covalent triazine-based frameworks have attracted much interest recently due to their high surface area and excellent thermal and electrochemical stabilities. This study shows that covalently immobilizing triazine-based structures on spherical carbon nanostructures results in the organization of micro- and mesopores in a three-dimensional manner. We selected the nitrile-functionalized pyrrolo[3,2-b]pyrrole unit to form triazine rings to construct a covalent organic framework. Combining spherical carbon nanostructures with the triazine framework produced a material with unique physicochemical properties, exhibiting the highest specific capacitance value of 638 F g−1 in aqueous acidic solutions. This phenomenon is attributed to many factors. The material exhibits a large surface area, a high content of micropores, a high content of graphitic N, and N-sites with basicity and semi-crystalline character. Thanks to the high structural organization and reproducibility, and remarkably high specific capacitance, these systems are promising materials for use in electrochemistry. For the first time, hybrid systems containing triazine-based frameworks and carbon nano-onions were used as electrodes for supercapacitors.