Micropore Volume Research Articles

Nitrogen doping in carbon xerogels via ammonia pyrolysis: A case study

Nitrogen-doped carbon xerogels (CXNs) were carbonized across a range of temperatures (400 °C–800 °C) using sol-gel derived resorcinol-formaldehyde xerogel to elucidate their structural evolution during carbonization in ammonia. The investigation extensively probed chemical and structural changes in CXNs at varying carbonization temperatures, employing analytical methods such as X-ray photoelectron spectroscopy, infrared spectroscopy, and energy-dispersive X-ray spectroscopy. These findings were thoroughly compared with the local structure derived from total X-ray scattering and Raman spectroscopy. The results showed a transformation in the local ordering and chemical structure of CXNs, characterized by a reduction in oxidation sites, expansion of C sp2 network structures, leading to the growth of aromatic domains, and the incorporation of nitrogen into the carbon backbone structure. Pyrolysis in ammonia notably influenced the textural structure, resulting in a partial loss of mesopores and an increased micropore volume.

(Nanocarbons Division Poster Award, 3rd Place) Investigating the Impact of Reaction and Carbonization Variables on ZIF-67 and Its Energy Storage Properties

Metal-organic frameworks (MOFs), with their exceptional properties such as high surface area, well-defined pores, and diverse chemical functionalities, have garnered widespread attention in scientific and industrial domains [1-2]. Among these, zeolitic imidazolate frameworks (ZIFs), known for their chemical and thermal stability, are extensively explored for applications ranging from catalysis and gas adsorption to electronic devices and sensors.By employing a novel hydrothermal method in aqueous solutions at room temperature, ZIF-67 nanocrystals were successfully synthesized, eliminating the need for toxic organic solvents and reducing overall costs. The resulting materials demonstrated notable efficiency in energy storage. To address the increasing demand for scalable synthesis methods, the study investigated the impact of reaction scale, reaction time, and reaction mixture dilution on the yield, morphology, and molecular structure of ZIF-67. The optimized conditions increased the production yield to 83%, surpassing the reported 75%. The subsequent carbonization process under three different regimes (800 °C, 800 °C with 3h ramp, 900 °C) resulted in materials exhibiting promising energy storage capabilities, with capacitance values reaching 81 F g−1 at a low sweep rate of 5 mV s−1. The carbonization yield showed a decrease with increasing carbonization time and temperature, and capacitance values were influenced by the presence of cobalt in the material.A slightly higher specific surface area of sample C-800 is reflected in the slightly higher capacitance values over all sweep rates indicating that specific surface area plays a role in the behavior of here synthesized materials. Capacitance is invariant at higher sweep rates (above 20mV s-1) which can be an indication that a part of the material surface, at macro- and mesopores, is highly responsive and highly conductive. At lower sweep rates micropores become available, due to prolonged time for ion insertion, which increases the capacitance that is unavailable at higher sweep rates. The highest percentage rise in capacitance is also seen in sample C-800 as its micropore volume, 40% of its total volume, is the highest among the samples investigated.Specifically, considering only the carbon part, the specific capacitance reached 176 F g−1, comparable to literature values for MOF-derived carbons [3]. The study suggests that dissolution of cobalt could enhance the material's capacitance behavior, opening avenues for further improvement in energy storage applications. This transformative approach addresses challenges associated with escalating energy demands and showcases the potential of ZIF-67-derived materials in electrochemical applications.AcknowledgementThis research was supported by the Science Fund of the Republic of Serbia, grant number 7750219, Advanced Conducting Polymer-Based Materials for Electrochemical Energy Conversion and Storage, Sensors and Environmental Protection-AdConPolyMat (IDEAS programme)

A Deep Dive into the Study of Nitrogen-Doped Carbons As Electrocatalysts for the Oxygen Reduction Reaction Via a Design of Experiments Approach

Porous nitrogen (N)-doped carbons derived from earth-abundant precursors and exhibiting tunable properties hold promise as low-cost, high-performance electrode materials for energy storage and conversion applications. As metal-free electrocatalysts for the oxygen reduction reaction (ORR) at the cathode in hydrogen fuel cells, N-doped carbons have shown selectivity and performance rivaling that of Pt/C. Alternatively, other N-doped carbons have also demonstrated low overpotentials and high selectivity for the 2-electron pathway of the ORR for the production of hydrogen peroxide. The activity and selectivity of these doped carbons are thought to result from their N-content, N-motifs, and/or porosity. However, the extent to which each of these variables impacts electrocatalytic ORR performance and whether there is an interactive effect between N-content, porous structure, etc. remains unclear. Herein, by implementing a design of experiments approach, the synthesis-structure-function relationship for N-doped carbons prepared via molten salt templating was elucidated to reveal how synthetic handles tune material properties which, in turn, determine electrocatalytic performance. Specifically, the wt% of N precursor and the synthesis temperature were found to have the most significant effect on the N-content and N-motif composition of the resulting N-doped carbons. Regarding porosity, larger surface areas and micropore volumes were realized for the carbons prepared with a larger wt% of N precursor. It was found that surface areas upwards of 300 m2/g were required to see any substantial activity (e.g. half-wave potential greater than 0.7 V vs RHE, effective electron transfer number > 3.4). Only after a threshold surface area was achieved were effects from N-content and N-motifs notable on performance and selectivity.

Controlling the structure of nitrogen-doped zeolite-templated carbon for CO2 capture based on the synthesis conditions

The surface chemistry and the textural properties of nitrogen-doped zeolite-templated carbon materials (N-ZTC) are decisive for their functionality in CO2 capture. This study analyses how the synthesis conditions affect the structure, formation of N-containing functional groups, thermal stability and CO2 capture of N-ZTC in comparison with nitrogen-free ZTC. Faujasite as a hard template and chemical vapour depositions (CVD) with propene and acetonitrile were used for the synthesis of ZTC and N-ZTC, respectively. XRD, SEM, N2 and CO2 sorption, XPS and TG/DSC analyses showed that the structural ordering and microporous volume in N-ZTC increases with increasing synthesis temperature. Conversely, at higher temperatures, the content of basic pyridinic groups in N-ZTC decreases in favour of stable graphitic nitrogen. The Lewis acid−base interaction of CO2 with the pyridinic groups provides the highest adsorption heats, the highest affinity for CO2 compared to N2 and enhances CO2/N2 selectivity (CO2/N2 selectivities of 127, 95, 89, and 66 for N-ZTC750°C, N-ZTC800°C, N-ZTC850°C and ZTC, respectively). The maximum adsorption capacity was achieved for N-ZTC800°C still yielding a high content of basic groups and a larger micropore volume compared to N-ZTC750°C. The decisive factor for the selectivity is thus the presence of basic centers attainable in N-ZTC at a lower synthesis temperature. The maximum adsorption capacity is associated with a large microporous volume and basic centers in N-ZTC synthesized at medium temperatures. The energy of CO2 adsorption by Lewis acid−base interactions and well-developed micropores are decisive for high selectivity and large adsorption capacity for efficient CO2 capture using N-ZTC materials.

Solid residues after gasification of agricultural residues as scalable and economical CO2 adsorption materials

Economical CO2 adsorbents are gaining significant attention as viable solutions to combat climate change. This research assessed the CO2 adsorption potential of solid residues following the gasification of bagasse (SR-Bagasse), bamboo (SR-Bamboo), and rice husk (SR-Rice husk) in various systems in Vietnam and Cambodia. Among these residues, SR-Bagasse showed the highest CO2 adsorption capacity, followed by SR-Bamboo, while SR-Rice husk exhibited moderate performance. The CO2 adsorption capacity at 25 °C with 100 % CO2 flow varied from 6 % to 9.5 % of the adsorbent's weight. Under flue gas conditions (15 % CO2 and 85 % N2), the adsorption capacity ranged from 2 % to 5 %. Additionally, these chars demonstrated significant recyclability with 90 % of initial adsorption capacity retained after 30 cycles, making them comparable to several advanced CO2 adsorbents studied previously. The highest performance of SR-Bagasse could be attributed to its substantial microporous and ultra-microporous volumes, with micropores serving as both CO2 adsorption sites and conduits to ultra-micropores. This study's findings emphasize the potential for integrating energy production with the development of economical and scalable CO2 adsorbents for industrial use.

Valorization of sponge iron industrial waste into iron-modified zeolite X for ciprofloxacin removal: a multi-parameter optimization study.

Ciprofloxacin (CIP), a commonly used antibiotic, is frequently detected in water bodies and the natural environment. The profound health consequences of CIP have led to growing attention focusing on environmental concerns. Adsorption is highly preferred because of its adaptability and remarkable efficiency in removing CIP. Therefore, the current work focuses on synthesizing an eco-friendly and economical adsorbent for removing CIP. The work aims to remove CIP using zeolite X (ZX), synthesized from dolochar, and subsequently modified ZX into iron-modified zeolite X (FeZX) via ion exchange. The synthesized FeZX had a crystallinity of 82.701%, an average pore size of 5.917 nm, a micropore volume of 0.298 cc/g, a micropore area of 451.807 m2/g, and a total surface area of 478.521 m2/g. The effect of parameters such as initial CIPconcentration, pH, contact period, adsorbent dosage, and iron dosage was analyzed in the batch adsorption studies of CIP using ZX and FeZX. CIP removal of 37.786% was achieved using ZX; hence, the adsorption parameters were optimized to maximize the CIP removal using response surface methodology (RSM), specifically Box-Behnken Design (BBD) using FeZX. Maximum removal of 97.974% was achieved under optimum conditions of 8.06 pH, contact period of 59.422 min, CIP concentration of 17.117 mg/L, and adsorbent dosage of 0.478 g/L. Freundlich isotherm and pseudo-second-order kinetic models werethe most accurate representations of the experimental data. The findings indicatethe significance of using this iron-modified mesoporous zeolite as an adsorbent for efficiently treating CIP wastewater.

Multifunctional CaO template promotes the synthesis of natural N-doped hierarchical porous carbon for supercapacitors

N-doped porous carbon with reasonable pore size distribution is conducive to improving low specific capacitance and low ion transport efficiency. Natural N-doped hierarchical porous carbon (NNHPC) was synthesized by microwave-assisted heating using kapok tree and chlorella vulgaris as raw materials. CaO was used as a template to extend the pore channels and simultaneously enhance the retention of N atoms in NNHPC. The pyrolysis properties of the samples and surface functional groups of NNHPC were analyzed, revealing that CaO enhanced the creation of nitrogenous compounds in the coke by inhibiting protein nitrogen decomposition. It led to a 74.45 % increase in N atom retention. When the addition ratio of CaO to biomass is 1:10, the optimal sample NNHPC-1CaO exhibits the highest specific surface area (SSA) of 3117.73 m2/g, accompanied by a microporous volume of 0.71 cm3/g. Therefore, NNHPC-1CaO exhibits the highest specific capacitance of 429.18 F/g, which still achieves excellent rate performance with 69.53 % at 20 A/g. The symmetric supercapacitor achieves a best energy density of 11.01 Wh/kg at 125 W/kg.

Co-regulating the pore structure and surface chemistry of sludge-based biochar for high–performance deodorization of gaseous dimethyl disulfide

A straightforward and eco-friendly preparation method for porous sludge biochar (SBA-3) was developed to deodorize gaseous dimethyl disulfide (DMDS) using ion exchange to adjust micropore structures coupled with carboxyl functionalization. Compared with the unmodified sludge biochar SBA-1 and SBA-2 treated with ion exchange, the pore size of SBA-3 decreased accompanied with increasing specific surface area and micropore volume. The Brunauer–Emmett–Teller (BET) specific surface area and micropore volume were 176.35 m2 g−1 and 0.0314 cm³ g−1, which were 2.02 and 1.71-fold larger than those of SBA-2, as well as 20.60 and 78.5-fold larger than those of SBA-1, respectively. Meanwhile, the amount of –COOH on the surface of SBA-3 increased from 0.425 to 1.123 mmol g−1, which was 2.64-fold larger than that of SBA-1. The adsorption behavior between DMDS and SBA-3 could be well described by the quasi-second-order kinetic model and Langmuir isotherm model. The maximum monolayer adsorption capacity was 35.12 mg g−1 at 303 K. Thermodynamic and DFT calculations indicated that the adsorption of DMDS on SBA-3 was exothermic with the deodorization mechanisms involving pore filling and chemisorption.

CHARACTERISATION OF EGG WHITE-IMPREGNATED ACTIVATED CARBON FOR CO2 ADSORPTION APPLICATION

In this study egg white was used as a source of natural amino acids to modify the surface properties of palm shell activated carbon towards enhancing its CO2 capture performance. A simple impregnation method was employed for this purpose. Characterisation analysis was performed on the egg white-impregnated activated carbon to examine any changes on its surface properties prior to CO2 adsorption test. The modified adsorbent showed high thermal stability below 300°C and comprised of new amide functional group. Furthermore, the modified adsorbent exhibited 31% higher breakthrough time and maintained its CO2 adsorption capacity at 0.3 mmol/g in comparison to raw activated carbon, regardless of the reduction of surface area and micropore volume by 17% and 18% respectively. These findings provide evidence on the prospect of egg white-impregnated activated carbon for CO2 adsorption application which could pave the way for a new generation of affordable and eco-friendly adsorbents.

Pore evolution and reaction mechanism of coal under the combination of chemical activation and autothermal oxidation

Aiming at the limitation problems such as limited scope, high cost and energy consumption of coal bed penetration enhancement technology by traditional physical and chemical methods, a coal seam methane penetration enhancement method based on the combined action of chemical activation and auto thermal oxidation is proposed from the idea of utilizing the in-situ energy of the coal body. In this paper, N2 and CO2 adsorption, XPS and FTIR methods are used to study the pore structure evolution law and the change characteristics of the reactive structure of coal matrix under the effect of chemically activated autothermal oxidation. The synergistic microporous pore volume of chemical activation and auto thermal oxidation was 48.91 cm3/g−1 × 10-3, which was 28.96 % and 22.7 % higher than chemical activation and auto thermal oxidation respectively; The microporous specific surface area was 162.7 m2/g, which was 38 % and 26.6 % higher than chemical activation and auto thermal oxidation respectively. Activated coals expand and merge holes to a deeper degree after oxidative warming, and the complexity of the pore structure in the coal decreases; Highly reactive radicals in coal pores substantially promote the oxidation of coal structure, enhance the aromatic polymerization reaction of activated coal, and improve the maturity and aromaticity of activated coal, and the oxygen-containing functional groups in activated coal are negatively correlated with the oxidation temperature. The results of this study reveal the potential of the auto thermal oxidation-driven penetration enhancement method under chemical activation for coal seam gas penetration enhancement and extraction.

Effect of Tectonic Deformation on the Pore System and Methane Adsorption of Anthracite Coal.

Tectonic deformation significantly alters the physical structure of coals, holding great importance to the coal mining industry and coalbed methane. In this study, eight anthracite coal samples with varying degrees of deformation were collected to investigate the effects of tectonic deformation on the pore system and CH4 adsorption of anthracite coals. In addition, low-temperature gas adsorption (N2 and CO2), Raman spectroscopy, and CH4 isothermal experiments were performed. The results revealed that coal samples with higher degrees of deformation exhibited larger ratios of D-band intensity to G-band intensity (I D/I G), indicating increased molecular defects induced by tectonic deformation. As the deformation degree of the coal samples increased, the mesopore volume increased from 0.00044 cm3/g (primary coal) to 0.0019 cm3/g (scaly coal). Conversely, the micropore volume tended to decrease with the increasing deformation degree of the coal samples. Moreover, the impact of deformation degree on the CH4 adsorption capacity of anthracite coals was complex. With the deformation degree increasing, the Langmuir volume initially decreased from 32.0 to 24.55 cm3/g and then rose to 30.14 cm3/g. This complexity arose from the differential effects of tectonic deformation on various pore types, where micropores and mesopores collectively determined the CH4 adsorption capacity of anthracite coals. This study analyzed the influence of tectonic deformation on the pore structure and CH4 adsorption capacity at the molecular level, providing valuable insights for evaluating the in situ CH4 content in anthracite coal seams.

Innovative green preparation of activated carbon by combining microwave pyrolysis and self-activation: Pyrolysis behavior, carbon characteristics and arsenic adsorption properties

Self-activation technology offers an eco-friendly strategy to produce activated carbons. This research attempted to enhance the production efficiency of self-activation by introducing microwave heating. Activated carbons were prepared as arsenic adsorbents from bamboo shoot shells (BSS) by combining microwave pyrolysis and self-activation. Microwave pyrolysis showed a faster thermal decomposition rate and lower pyrolysis temperature range than conventional pyrolysis, and H2O and CO2 from pyrolysis acted as activator. Besides, the prediction models of specific surface area (SSA), micropore volume (MPV) and As(V) adsorption capacity (qe) with high accuracy were established using response surface methodology. Based on the qe values, the optimum preparation condition was 1018 °C for 39 min under a microwave power of 1625 W. The activated carbon exhibited satisfactory As(V) adsorption capacity of 4.79 mg/g, with a total pore volume of 0.702 cm3/g and a SSA of 1330 m2/g. This work significantly improved self-activation technology's production efficiency and reduced the arsenic adsorbent's production cost. Furthermore, it also provided a promising strategy for green preparation of activated carbons from biomass resources.

Effect of hot isostatic pressing on stress-rupture crack growth of a single-crystal nickel-based superalloy

The solution-treated second-generation single crystal (SX) superalloys underwent hot isostatic pressing (HIP) at 1316 °C and 105 MPa for varying durations. This study investigates the effect of HIP on micropores and stress-rupture behavior under conditions of 980 °C and 250 MPa. The results illustrate that the application of HIP treatment significantly reduces the porosity and volume of micropores, thereby increasing the rupture life of the alloys. With the disappearance of micropores, the crack initiation site shifts from the micropores to the γ/γʹ interface, resulting in reduced crack dimensions and decelerated propagation. Consequently, the smaller size of cracks in HIPed specimens slow down fracture. Nonetheless, the crack propagation pattern remains consistent: cracks expand perpendicular to the stress axis, connecting with cracks at other heights via secondary cracks along the <112> direction.

Multi-fractal characteristics of pore system in deep organic-rich shales of the Wufeng-Longmaxi formation in the Sichuan Basin and their geological significance

The heterogeneity of pore system of deep shale reservoir determines the occurrence, enrichment and migration behavior of shale gas within shales. In this study, multi-fractal analysis was applied to analyze CO2 and N2 adsorption data for obtaining multi-fractal parameters including Hurst index and multi-fractal spectrum (D5--D5+) of the deep Wufeng-Longmaxi shales collected from the Sichuan Basin, China, in order to study the connectivity and heterogeneity of micropore pores and meso-macropores as well as their influencing factors. The results showed that pore system of the Wufeng-Longmaxi deep shale exhibits distinct multifractal nature. There exists significant differences in the pore volume (PV) of micropores (&amp;lt;2 nm), mesopore (2–50 nm), and macropore (&amp;gt;50 nm) across different shale lithofacies due to their differences in TOC content and mineral composition. The heterogeneity and connectivity of micropores and meso-macropores within deep shales in the Sichuan Basin are controlled by multiple factors including shale lithofacies, burial depth, and pressure coefficients. Notably, siliceous shale (SL) and calcareous/argillaecous siliceous shale (C/ASL), known as sweet spot for current shale gas exploitation, exhibits characteristics such as relative low micropore connectivity, high micropore heterogeneity, high micropore PV and low meso-macropore connectivity. These suggest that isolated pressure-sealing compartment is easier formed within the overpressured SL and C/ASL. Thus, pressure in these shales is less likely to release during the Yanshanian-Xishanian tectonic uplift process, favoring the preservation of organic matter (OM) pores and residual interparticle pores, which is conducive to the accumulation of deep shale gas dominated by free gas.

Production of activated carbons from Quercus cerris acorn shell under various experiment conditions, and their characterizations

Due to the high porosities, large surface areas, insolubilities in solutions, and unique structural and morphological structures, porous materials are utilized in various application areas such as energy conversion and storage, wastewater treatment, adsorption, catalysis and photocatalysis. In this study, activated carbons (QCACs), one type of porous materials, were synthesized from Quercus cerris acorn shells by using ZnCl2 chemical activation under various production conditions. The effects of carbonization temperature, carbonization period, and impregnation ratios on the yields, surface areas, pore developments, and N2 adsorption–desorption isotherms of activated carbons obtained were investigated in detail. The highest surface area (1751.61 m2/g) was reached when utilized at the impregnation ratio of 2.0 at 500 ℃ for 90 min. The total pore volume of QCAC increased with increasing impregnation ratio, however the micropore volume of QCAC reduced. It was found from the pore distribution data that QCACs contained mostly narrow mesopores and a little amount of micropores. Also, N2 adsorption–desorption isotherm data revealed that QCACs produced under different conditions were usually mesopore structures, and the pores were narrow slit-shaped. Moreover, the data provided from SEM, FTIR, Boehm titration, and elemental analysis gave more characterization information about QCACs synthesized.

Microwave pyrolysis-prepared engineering carbons from corn cobs and red mombin seeds towards xylene adsorption

High-quality biochars/activated carbons were prepared, optimizing individual parameters of energetically-save microwave pyrolysis (raw material loading - 20 vs. 60 g, nitrogen atmosphere - flow vs. batch, ZnCl2 activation) from two agricultural wastes - corn cobs, red mombin seeds. Most promising carbons were examined for gaseous xylene adsorption and showed higher sorption capacity (∼250–475 mgxylene· g−1) than commercial carbon (∼214 mgxylene· g−1). ZnCl2 activation of both raw materials reduces the fixed carbon content and increases volatiles in activated carbon, suggesting microwave pyrolysis of activated feedstock should take 25 min. While biochars are microporous materials with inhomogeneous low-surface mesopore/macropore network, activated carbons are highly microporous-mesoporous. ZnCl2 activation of both raw materials contributes to formation of extensive high-surface mesopore network (with pore-size < 20 nm) and enlargement of micropore-size, but does not affect the micropore volume. ZnCl2 activation increases H2 and decreases CH4 production. Microwave pyrolysis of larger raw material loading with ZnCl2 leads to CO2 increase. Best xylene adsorption capacity (475 mgxylene· g−1) was determined for activated carbon produced from 60 g loading of corn cobs in batch nitrogen atmosphere, showing the largest micropore volume, lowest surface polarity and medium rate of graphitization. Large micropore volume, low surface polarity and high rate of graphitization of carbon are xylene sorption capacity-determining factors.

Structural and Electrochemical Evolution of Water Hyacinth-Derived Activated Carbon with Gamma Pretreatment for Supercapacitor Applications.

This study introduces a gamma pretreatment of water hyacinth powder for activated carbon (AC) production with improved electrochemical properties for supercapacitor applications. The structural and morphological changes of post-irradiation were meticulously analyzed using scanning electron microscopy (SEM), Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS). The pretreatment significantly modifies the pore structure and reduces the particle size of the resulting activated carbon (WHAC). Nitrogen adsorption-desorption isotherms indicated a substantial increase in micropore volume with escalating doses of gamma irradiation. Electrochemically, the activated carbon produced from pretreated WH at 100 kGy exhibited a marked increase in specific capacitance, reaching 257.82 F g-1, a notable improvement over the 95.35 F g-1 of its untreated counterpart, while maintaining 99.40% capacitance after 7000 cycles. These findings suggest that gamma-pretreated biomasses are promising precursors for fabricating high-performance supercapacitor electrodes, offering a viable and environmentally friendly alternative for energy storage technology development.

Long‐Term Performance on Drought Mitigation of Soil Slope Through Bio‐Approach of MICP: Evidence and Insight from Both Field and Laboratory Tests

AbstractDrought is a serious global environmental issue that causes water resource scarcity and threatens agriculture and food supplements. This study aims to investigate the long‐term performance of an eco‐friendly technique‐microbial induced carbonate precipitation (MICP) on drought mitigation at field and laboratory scales. Seven in‐situ slopes treated with different MICP rounds and cementation solution concentrations were subjected to 16‐month weathering. Tests were conducted to evaluate the evaporation characteristics, water retention capacity, and CaCO3 distribution. Laboratory soil samples were further prepared to provide evidence related to underlying weathering mechanisms. The results show that MICP has a time‐dependent performance on drought mitigation. After MICP treatment, soil performs a remarkable evaporation suppression ability and the evaporation rate can decrease by 50%. This is attributed to the soluble salts which increase soil water retention capability and dense hard crust which inhibits water vapor migration into the atmosphere. However, the soluble salts and crust are sensitive to weathering thus leading to degradation of MICP. Suffering 16‐month weathering, the MICP‐induced CaCO3 decreases by more than 60%. The evaporation rate of soil increases with MICP rounds and cementation solution concentrations and can reach nearly two times of untreated soil. MICP‐treated field soil exhibits weaker water retention capacity than untreated soil because MICP alters soil microstructure which expands macropores and decreases volume of micropores. Connected macropores act as favorable evaporation channels and accelerate evaporation. To ensure MICP long‐term effects, periodical treatments are necessary. The most effective MICP treatment scheme is four to six treatment rounds and 1.0 M cementation solution.

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).

Enhancing the catalytic performance of H-ZSM-5 in bio n-butanol dehydration by zeolite crystal engineering

NH4F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5’s, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH4F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes.