Small Mesopores Research Articles

Understanding Multi-Stage Charge Storage on Nanoporous Carbons in Zn-Ion Hybrid Capacitors.

Zn-ion hybrid capacitors (ZIHCs) are promising high-power energy storage devices. However, the underlying charge storage mechanisms, especially the influence of proton storage, remain poorly understood. Herein, the model porous carbons are synthesized having similar specific surface areas (SSAs) and surface chemistry but different pore sizes. They highlight the role of supermicropores and small mesopores (0.86-4nm) enabling a high capacity of 198 mAhg-1 (capacitance of 446 Fg-1), while larger mesopores (4-13nm) significantly enhance cycling stability, exceeding 0.6 million cycles. Electrochemical studies, including EQCM analysis, reveal a 4-stage charge-storage process under cathodic polarization, comprising adsorption and desolvation of hydrated Zn2+ ions, followed by water reduction, catalyzed by Zn2+, and formation of Had. The rising pH leads to the formation of insoluble zinc hydroxysulfate hydrates (ZHS). Depending on the pore architecture, the precipitation of ZHS has different effects on the overall stability of cycling. The study overall: (i) presents a simplified method for pore control in carbon synthesis; (ii) discuss the effect of pore size on charge storage and cycling stability in respect of ZHS formation; (iii) sheds light on the charge storage mechanism indicating the important contribution of cation effect known from electrocatalysis on faradaic charge storage mechanism.

Temperature‐Dependent Synthesis of Robust Ultrathin Cobalt Oxide Nanomesh for Oxygen Evolution Reaction

AbstractA temperature‐dependent annealing methodology has been developed for the synthesis of ultrathin Co3O4 nanomesh that has pores on the basal planes of nanosheets. The high‐temperature annealing resulted in situ exfoliation and etching that created narrow mesopores (3–5.5 nm) on the basal plane. N2 adsorption/desorption and transmission electron microscopy experiments validated the formation of nanomeshes, and the best material (CoNM‐400) was obtained at 400 °C annealing temperature. The CoNM‐400 revealed superior catalytic performance for oxygen evolution reaction with an overpotential of 308 mV, a mass activity of 396.7 A g−1, and a turnover frequency of 6.15 s−1. Electrochemical impedance spectroscopy revealed a minimal charge transfer resistance (4.2 Ω) and pseudoresistance (66.2 Ω), favoring effective electron transport at the electrode/electrolyte interface and improved kinetics for oxygen evolution reaction, respectively. The elevated roughness factor of around 325 underscored the significance of small mesopores in enhancing catalyst–electrolyte interactions and enhancing mass transport inside the material. CoNM‐400 exhibited exceptional stability for 10 days of prolonged electrolysis at a current density of 30 mA cm−2. The stability of the material was due to the presence of narrow mesopores on the basal plane of the ultrathin nanosheets that favored vertical ion penetration and easy O2 release, and the uniformly distributed mesopores served as an efficient buffer to mitigate volume expansion during intense electrocatalysis. The polycrystalline nature of the nanomesh also provided structural robustness to sustain intense electrocatalysis with high gas evolution.

Activated Carbon Synthesized from Nypa fruticans and Areca catechu by Microwave Method as Efficient Adsorbent for the Removal of Chloramphenicol

This work employed the microwave-assisted method to prepare activated carbons from the byproducts of Areca catechu (ACAC) shells and Nypa fruticans (ACNF) nut shells. The results show that the materials have a rough surface like a coral reef and contains the characteristic functional groups such as O-H, C=O, C=C, C-O with an amorphous structure. Surface area and pore size were also evaluated with ACAC of 195.93 m2 g-1 and ACNF of 514.91 m2 g-1. The adsorption isotherms predict the size of the pores as small mesopores. The factors affecting ciprofloxacin adsorption using derived activated carbon were also evaluated. For ACAC, the best optimized adsorption conditions were contact time 90 min, temperature 40 ºC, pH 6, dosage 2 g L-1, concentration 80 mg L-1, whereas for ACNF, the best adsorption conditions were contact time 90 min, temperature 40 ºC, pH 4, dosage 1 g L-1, concentration 80 mg L-1. The results show that activated carbon samples ACAC and ACNF follow the pseudo-second-order (PSO) kinetic model, Elovich kinetic model, Dubinin-Radushkevich (D-R) and Temkin isotherms. The Langmuir model was used to record the maximal adsorption capacities of ACAC and ACNF for ciprofloxacin, which were 57.60 mg g-1 and 67.59 mg g-1, respectively. The adsorption process occurs by diffusion with chemisorption interactions on a homogeneous surface for ACAC and heterogeneous surface for ACNF.

Synergistic Enhancement of Capacitive Performance in Porous Carbon by Phenolic Resin and Boric Acid.

The study of pore structure regulation methods has always been a central focus in enhancing the capacitance performance of porous carbon electrodes in lithium-ion capacitors (LICs). This study proposes a novel approach for the synergistic regulation of the pore structure in porous carbon using phenol-formaldehyde (PF) resin and boric acid (BA). PF and BA are initially dissolved and adsorbed onto porous carbon, followed by hydrothermal treatment and subsequent heat treatment in a N2 atmosphere to obtain the porous carbon materials. The results reveal that adding BA alone has almost no influence on the pore structure, whereas adding PF alone significantly increases the micropores. Furthermore, the simultaneous addition of PF and BA demonstrates a clear synergistic effect. The CO2 and H2O released during the PF pyrolysis contribute to the development of ultramicropores. At the same time, BA facilitates the N2 activation reaction of carbon, enlarging the small mesopores and aiding their transformation into bottlenecked structures. The resulting porous carbon demonstrates an impressive capacitance of 144 F·g-1 at 1 A·g-1 and a capacity retention of 19.44% at 20 A·g-1. This mechanism of B-catalyzed N2-enhanced mesopore formation provides a new avenue for preparing porous carbon materials. This type of porous carbon exhibits promising potential for applications in Li-S battery cathode materials and as catalyst supports.

Mineral composition and pore structure on spontaneous imbibition in tight sandstone reservoirs

The pore structure of tight oil reservoirs is extremely complex, with a wide range of pore sizes, diverse pore types, and well-developed nanopores and throats. Although researchers have conducted in-depth studies on the mechanism of spontaneous imbibition, issues such as low recovery and short imbibition distance have not been well explained. This study characterized the relationship between mineral composition and pore types through XRD and SEM, and combined NMR-C, LF-NMR, and micro-CT to characterize the pore size distribution of tight sandstones. The effects of pore structure characteristics and displaced phase properties on spontaneous imbibition were investigated. Using NMR-C and low-temperature evaporation methods, the proportions of free water and bound water in pores with diameters ranging from 3.33 to 600 nm were quantitatively characterized. The results indicated that the maximum pore size and its proportion were the primary factors influencing permeability, whereas the content of small pores and mesopores played a crucial role in accessing the quality of connectivity. The content of micron-scale pores in the core exhibited a positive correlation with quartz content, whereas the amounts of feldspar and clay minerals were closely associated with the development of nanoscale pores. The proportion of large pores and the viscosity of the displaced phase had the most significant effect on imbibition efficiency, followed by the homogeneity of pore distribution and connectivity. Moreover, the bound water content in nanopores exceeded 50% of the pore volume, which reduced pore size and connectivity during the imbibition process, resulting in a shorter imbibition distance. This study investigated the effect of pore structure and mineral composition on spontaneous imbibition and examined the factors contributing to the limited imbibition distance in tight oil reservoir development. The findings offer new insights and strategies for enhancing recovery in tight oil reservoirs.

Experimental study of supercritical CO2-H2O-coal interactions and the effect on coal spontaneous imbibition characteristics

Experimental study of supercritical CO2-H2O-coal interactions and the effect on coal spontaneous imbibition characteristics

Experimental Research on Behavior of Spontaneous Imbibition and Displacement After Fracturing in Terrestrial Shale Oil Based on Nuclear Magnetic Resonance Measurements

Spontaneous imbibition (SI) effectively enhances oil recovery in shale reservoirs, significantly changing well shut-in and flowback design. This study conducted SI and displacement experiments to simulate the well shut-in and flowback stages so that the mechanism of imbibition and displacement between crude oil and fracture fluid can be discussed. In addition, the relative contribution to oil recovery of different types of pores in various stages and the effect of wettability were determined with low-field nuclear magnetic resonance (LF-NMR) via each sample’s T2 transverse relaxation time at each time. The experimental results show that shale has multiscale pore structure characteristics combined with micropores, small mesopores, and mesopores. During the SI process, crude oil is displaced from micropores by fracture fluid at first, and then a large amount of oil production comes from small mesopores. Oil recovery of water-wet core samples is approximately 40.7%. Oil recovery of oil-wet core samples is about 26%. The wettability significantly affects the imbibition and displacement oil recovery of samples. For the process of SI, oil recovered from small mesopores takes the lead in the complete sample recovery. For the displacement process, oil recovered from small mesopores and mesopores take the lead in the complete sample recovery. After displacement, only 12% of fracture fluid flooded from the samples. This research, demonstrating the imbibition and displacement characteristics of terrestrial shale and several relevant affecting factors, contributes to understanding the fracturing fluid retention mechanism in shale reservoirs and provides crucial theoretical foundations for the development of shale oil reservoirs.

Study on microscopic production characteristics of crude oil in tight reservoirs displaced by CO2-assisted fracturing fluid

The CO2-assisted fracturing fluid displacement technology is of great significance for enhancing oil recovery (EOR) of tight reservoirs, while the characteristics and mechanism of microscopic production for CO2-assisted fracturing fluid are still unclear. In this study, the displacement experiments of fracturing fluid and CO2-assisted fracturing fluid were launched with two various methods, the nuclear magnetic resonance technology (NMR) and high-temperature and -pressure visualization system respectively. The experimental results show that crude oil in mesopores and macropores is mainly displaced by fracturing fluids, and the residual oil is mainly retained in micropores and small pores. CO2-assisted fracturing fluid improved the oil recovery of tight reservoirs, with more crude oil recovered from small pores, mesopores and macropores, and less residual oil content in the form of flake and droplet. This study provides a prospective EOR technology for the efficient development of tight reservoirs.

Gallium Methylene Ga8(CH2)12 on Mesoporous Silica

Gallium methylene Ga8(CH2)12 was grafted onto large‐pore mesoporous silica SBA‐15500 and mesoporous silica MCM‐41500 with smaller mesopores, each thermally pretreated at 500 °C. For comparability reasons, trimethylgallium was employed as a grafting reagent. The hybrid materials Ga8(CH2)12@SBA‐15500, GaMe3@SBA‐15500, Ga8(CH2)12@MCM‐41500 and GaMe3@MCM‐41500 were characterized by ICP‐OES, N2 physisorption, elemental analysis, solid‐state 1H/13C/29Si NMR spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. To gain further insight into potential surface species, the molecular compound Ga8(CH2)12 was treated with excess (eight equivalents) of HOSi(OtBu)3, which gave the dimeric species [GaMe2{OSi(OtBu)3}]2, being isolable also from the reaction of GaMe3 with one equivalent of silanol. The hybrid materials revealed high metal contents and surface species with intact Ga–CH2–Ga linkages as proposed by NMR spectroscopy and their reactivity toward benzophenone.

Self-Templating Synthesis of Mesoporous Carbon Cathode Materials for High-Performance Lithium-Ion Capacitors.

Lithium-ion capacitors (LICs) have attracted considerable interest because of their excellent power and energy densities. However, the development of LICs is limited by the low capacity of the cathode and the kinetics mismatch between the cathode and anode. In this work, mesoporous carbon materials (MCs) with uniform pore sizes were prepared using magnesium citrate as the raw material through a self-templating method. During the carbonization process, MgO nanoparticles generated from magnesium citrate act as a template, resulting in a more orderly pore structure. The resultant MCs demonstrate a high specific surface area of 1673 m2 g-1 and an abundance of small mesopores, which significantly accelerated ion migration within the electrolyte and expedited the formation of electric double layers. Benefiting from these advantages, the MCs cathode demonstrates a high reversible specific capacity, excellent cycling stability, and rate performance. The assembled MCs-based LIC provides a high energy density of 152.2 Wh kg-1 and a high power density of 14.3 kW kg-1. After 5000 cycles, a capacity retention rate of 80 % at the current density of 1 A g-1 is obtained. These results highlight the excellent potential of MCs as a cathode material for LICs.

High removal of volatile organic compounds on hierarchical carbons prepared from agro-industrial waste of banana fruit production for air decontamination.

Activated carbons were prepared from residues from agro-industrial banana production (banana pseudostem) and evaluated in the capture of five different volatile organic compounds (VOCs): dichloromethane, chloroform, ethyl acetate, hexane, and cyclohexane. The biomass was first submitted to a hydrothermal treatment in the presence of KOH or ZnCl2 as activating agents, followed by a dry pyrolysis. This new advance in methodology contributes to producing activated carbons with hierarchical porosity and high surface areas (701-1312 m2g-1), promoting increased interest in managing waste from banana fruit agricultural production. VOC capture studies were performed by thermal analysis, and capture capacities were similar to or higher than those presented in the literature. Higher adsorption capacities were related to the amount of available micropores, and the capture capacity was enhanced by the contribution of small mesopores. As the highest adsorbed amounts of dichloromethane (933mgg-1 at 25°C) were obtained for the material activated with ZnCl2 (1:3), further studies were carried out for this system. The experimental data was fitted using a pseudo-first-order kinetic model. A study was carried out in different atmospheres (He, N2, air), showing that co-adsorption is occurring. Under simulated environmental conditions, the capture capacity decreased slightly at equilibrium, and the new adsorbent was used for up to ten cycles without significantly losing its efficiency, indicating good application in the field.

Rational Design of Mesoporous ZnFe2O4@g-C3N4 Heterojunctions for Environmental Remediation and Hydrogen Evolution.

Mesoporous catalysts with a high specific surface area, accessible pore structures, and appropriate band edges are desirable for optimal charge transfer across the interfaces, suppress electron-hole recombination, and promote redox reactions at the active sites. The present study demonstrates the rational design of mesoporous ZnFe2O4@g-C3N4 magnetic nanocomposites (MNCs) with different pore sizes and pore volumes following a combination of facile thermal itching and thermal impregnation methods. The MNCs preserve the structural, morphological, and physical attributes of their counterparts while ensuring their effectiveness and superior catalytic capabilities. The morphological analysis confirms the successful grafting and confinement of ZnFe2O4 nanoparticles with the polymeric g-C3N4 nanosheets to form heterojunctions with numerous interfaces. The MNCs possess uniformly distributed small mesopores (pore size <4 nm), ample active sites, and a high specific surface area of 62.50 m2/g. The mesoporous ZnFe2O4@g-C3N4 notably improve hydrogen evolution rate and methylene blue dye degradation. The optimal loading weight of ZnFe2O4 is 20 %, in which the MNCs display the highest hydrogen evolution rate of 1752 μmol g-1 h-1 and photo-Fenton dye degradation rate constants of 0.147 min-1, upon solar-light illumination. Furthermore, the photocatalysts demonstrate recyclability over five consecutive cycles, confirming their stability, while easy separation using a simple magnet underscores practical utility.

Engineering porous clay nanoarchitectures from unusual commercial organoclay: Supported manganese oxide as stable catalysts in the total oxidation of volatile organic compounds

Engineering porous clay nanoarchitectures from unusual commercial organoclay: Supported manganese oxide as stable catalysts in the total oxidation of volatile organic compounds

Capacities of sorbents prepared by impregnation of inorganic carriers with PEI using different methods

The study presented here focused on the research of adsorbents for the separation of carbon dioxide from flue gas or other waste gases. Specifically, it focused on the possibility of eliminating the permanent problem with the insufficient resistance of inorganic adsorbents to unwanted – parasitic – adsorption of moisture from the processed gas. Based on the promising data published in recent papers regarding the wet impregnation of adsorbents with branched polyethyleneimine (PEI), four methods for the preparation of PEI-impregnated zeolite were tested. Penetration of the agent into the porous structure of the zeolite was achieved by: applying ultrasound, applying vacuum, combining vacuum and overpressure and boiling off the solvent without further operation. The raw zeolite was characterized by X-ray fluorescence spectrometry and X-ray diffractometry and also subjected to textural analysis. The characterization of the impregnated products mainly included thermogravimetric analysis, textural analysis and organic elemental analysis. In addition to gravimetric screening, the adsorption capacities of raw zeolite and impregnated products were primarily determined using a pressure flow-through apparatus with a fixed bed adsorber. The experimental conditions were determined to be close to real industrial installations: temperature during adsorption 20 and 40 °C, pressure during adsorption 600 kPa and 15% volume fraction of CO2 in the gas. Desorption was carried out by a combination of thermal desorption at 80 °C and vacuum. By reproducing the impregnation procedures from the literature, a PEI loading in the range of 4.1–23.7% was achieved, which is significantly lower than the literature sources state for the same preparation procedures. The measurement of textural properties verified that, depending on the value of PEI loading, there is a gradual reduction of the specific surface area, the total pore volume and the virtual disappearance of micropores and small mesopores. Specifically, at a PEI loading of 4%, the BET surface area decreased compared to the pristine zeolite from 29.4 to 2.9 m2 g–1 and at the same time the total pore volume decreased from 0.13 to 0.02 cm3 g–1, etc. The measurement of capacities did not confirm almost any of the results published in the literature. Without exception, the adsorption capacity decreased with the amount of PEI introduced into the zeolite particles. E.g. if a gas with 80% relative humidity and a content of 15% CO2 was used at a pressure of 600 kPa and a temperature of 40 °C, the capacity (by mass) decreased due to impregnation from 2.4% (for raw zeolite) to 0.8% for the sample with PEI mass fraction of 19%. Tests using dry gas resulted in even more marked deterioration. Thus, one can only partially agree with the literature data in the sense that humidity slightly compensates the negative effect of PEI on capacity. The effect, where the capacity increases with increasing temperature due to the replacement of physical CO2 adsorption by its chemisorption in the PEI layer, was also not confirmed. For example, for the above sample, humidity and pressure, the capacity was 0.9% at 20 °C. The impregnation procedure based on boiling off the solvent turned out to be completely unusable and, despite repeated rigorous attempts to reproduce it, did not lead to a product with a measurable capacity. The results of the study can be summarized in the following sentence. The problem is not that the experiments did not lead to a positive result, but above all the fundamental discrepancy between the published data and the attempts to reproduce them.

Pitch-based spherical activated carbons with small mesopores for CO2 capture

Pitch-based spherical activated carbons with small mesopores for CO2 capture

Pyrolysis combined with KOH activation to turn waste apple pruning branches into high performance electrode materials with multiple energy storage functions

Pyrolysis combined with KOH activation to turn waste apple pruning branches into high performance electrode materials with multiple energy storage functions

A Novel Composite Material UiO-66-Br@MBC for Mercury Removal from Flue Gas: Preparation and Mechanism.

To reduce the mercury content in flue gas from coal-fired power plants and to obtain high-performance, low-cost mercury adsorbents, a novel composite material was prepared by structural design through the in situ growth method. Functionalization treatments such as the modification of functional groups and multilayer loading of polymetallic were conducted. These materials include the MOF material UiO-66 and modified biochar doped with Fe/Ce polymetallic, both of which contain unsaturated metal centrals and oxygen-containing functional groups. On the basis of obtaining the effects of adsorption temperature and composite ratio on the Hg0 removal characteristics, coupling and synergistic mechanisms between the various types of active centers included were investigated by using a variety of characterization and analysis tools. The active adsorption sites and oxidation sites were identified during this process, and the constitutive relationship between the physicochemical properties and the performance of Hg0 removal was established. The temperature-programmed desorption technique, Grand Canonical Monte Carlo simulation, and adsorption kinetic model were employed to reveal the mechanism of Hg0 removal. The results showed that the UiO-66-Br@MBC composite adsorbent possessed an excellent Hg0 removal performance at adsorption temperatures ranging from 50 to 250 °C, and targeted construction of adsorption and oxidation sites while maintaining thermal stability. The Hg0 removal by the composites is the result of both adsorption and oxidation. The micropores and small pore mesopores in the samples provide physical adsorption sites. The modified biochar acts as a carrier to facilitate the full exposure of the central metal zirconium ions, the formation of more active sites, and the process of electron transfer. The doping modification of the Br element can enhance the overall redox ability of the sample, and the introduced Fe and Ce polymetallic ions can work in concert to promote the oxidation process of Hg0. The excellent regulation of the ratio between adsorption and oxidation sites on the surface of the composite material finally led to a significant boost in the samples' capacity to remove Hg0.

Electrodeposition of bismuth, tellurium and bismuth telluride through sub-10 nm mesoporous silica thin films

Templated electrodeposition is an efficient technique for the bottom-up fabrication of nanostructures and can effectively control the size and shape of the electrodeposits. Here, mesoporous silica thin films with highly ordered mesopores and a regular three-dimensional mesostructure were synthesised as templates for electrodeposition. The mesoporous silica films have small mesopores (∼8 nm) and complex mesopore channels (Fmmm mesostructure with the [0 1 0] axis perpendicular to the substrate). Electrodeposition of bismuth, tellurium and bismuth-tellurium was investigated from electrolytes containing [NnBu4][BiCl4], [NnBu4]2[TeCl6] and [NnBu4]Cl dissolved in dry dichloromethane. Top-view SEM images showed Bi, Te and Bi doped-Te nanoparticles in the mesopores and cross-section SEM showed there were a few Te nanowires, in addition to the particle aggregations on the surface. This is a promising observation as it demonstrates the possibility of preparing sub-10 nm nanowires by templated electrodeposition even though the deposits are not uniformly electrodeposited in all the mesopores. EDX shows the deposited Bi-Te nanoparticles were tellurium-rich, XRD shows they were trigonal tellurium (ICSD 65692). A variety of parameters including the choice of pulsed electrodeposition conditions and [NnBu4][BiCl4] concentration (2.25 mM and 3 mM) were investigated in order to control the composition of the deposit. All samples prepared by pulsed electrodeposition showed very low Bi:Te ratio (Bi/Te<0.02), whereas samples deposited for 5 min at −0.6 V achieved high Bi content (Bi/Te=0.49).

Removal of PFOA from water by activated carbon adsorption: Influence of pore structure

Removal of PFOA from water by activated carbon adsorption: Influence of pore structure

Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter?

An improved understanding of preferential solute transport in soil macropores would enable more reliable predictions of the fate of agrochemicals and the protection of water quality in agricultural landscapes. The objective of this study was to investigate how soil organic carbon (SOC) and soil texture shape soil pore structure and thereby determine the susceptibility to preferential transport under steady-state near-saturated flow conditions. To do so, we took intact topsoil samples from an arable field that has large variations in SOC content (1.1–2.7%) and clay content (8–42%). Soil pore structure was quantified by X-ray tomography and soil water retention measurements. Non-reactive solute transport experiments under steady-state near-saturated conditions were carried out at irrigation rates of 2 and 5 mm h−1 to quantify the degree of preferential transport. Near-saturated hydraulic conductivities at pressure heads of −1.3 and −6 cm were also measured using a tension disc infiltrometer. The results showed that larger abundances of small macropores (240–720 µm diameter) and mesopores (5–100 µm diameter) resulted in weaker preferential transport, due to larger hydraulic conductivities in the soil matrix that prevented the activation of water flow and solute transport in large macropores. In particular, the degree of preferential transport was most strongly and negatively correlated with the mesoporosity in the 30–100 µm diameter class. In contrast, the degree of preferential transport was not correlated with connectivity measures (e.g. the percolating fraction and critical pore diameter for the macropore network), probably because i.) the pore space of almost all samples was highly connected, being dominated by one percolating cluster, and ii.) only a part of this percolating macroporosity was active under the near-saturated conditions of the experiment. We also found that the degree of preferential transport was strongly and negatively correlated with clay content, whilst the effects of SOC were not significant. Nevertheless, macroporosity in the 240–720 µm diameter class and mesoporosity were positively correlated with SOC content in our soils and in some previous studies. Therefore, SOC sequestration in arable soils may potentially reduce the risk of preferential transport under near-saturated flow conditions through better developed networks of small macropores and mesopores.