Nanopore Size Research Articles

Mobility of Dissolved Gases in Smectites under Saturated Conditions: Effects of Pore Size, Gas Types, Temperature, and Surface Interaction

In a nuclear waste repository, the corrosion of metals and the degradation of the organic material in the waste matrix can generate significant amounts of gases. These gases should be able to migrate through the multibarrier system to prevent a potential pressure build-up that could lead to a loss of barrier integrity. Smectite mineral particles form a tortuous pore network consisting of larger interparticle pores and narrow interlayer pores between the platelets of the smectite minerals. These pores are normally saturated with water, so one of the most important mechanisms for the transport of gases is diffusion. The diffusion of gases through the interparticle porosity depends on the distribution of gas molecules in the water-rich phase, their self-diffusion coefficients, and the tortuosity of the pore space. Classical molecular dynamics simulations were applied to study the mobility of gases (CO2, H2, CH4, He, and Ar) in Na-montmorillonite (Na-MMT) under saturated conditions. The simulations were used to estimate the gas diffusion coefficient (D) in saturated Na-MMT as a function of nanopore size and temperature. The temperature dependence of the diffusion coefficient was expressed by the Arrhenius equation for the activation energy (Ea). The predicted D values of gases were found to be sensitive to the pore size as the D values gradually increase with increasing pore size and asymptotically converge to the gas diffusion coefficient in bulk water. This behavior is also observed in the self-diffusion coefficients of water in Na-MMT. In general, H2 and He exhibit higher D values than Ar, CO2, and CH4. The predicted Ea values indicate that the confinement affects the activation energy. This effect is due to the structuring of the water molecules near the clay surface, which is more pronounced in the first two layers of water near the surface and decreases thereafter. Atomic density profiles and radial distribution functions obtained from the simulations show that the interaction of the gas with the liquid and the clay surface influences mobility. The obtained diffusion coefficient for different gases and slit pore size were parameterized with a single empirical relationship, which can be applied to macroscopic simulations of gas transport.

Preparation and Hardened Performance of Bentonite-Induced Porous Magnesium Oxysulfate Cement Paste.

Porous magnesium oxysulfate (MOS) cement pastes were successfully fabricated by injecting presaturated bentonite into modified MOS cement paste. Their pore structure and hardened performance were investigated. The results indicated that the 20MgO-MgSO4·7H2O-18H2O system modified by citric acid (C6H8O7⋅H2O) and ethylene diamine tetraacetic acid was suitable to fabricate porous MOS cement paste. Bentonite slurry led to significant refinement of pores, generating nanosized pores in MOS cement pastes. When volume replacement of bentonite slurry in MOS cement paste rose between 0 and 60%, pore size corresponding to the peak in the pore size distribution curve of MOS cement-based materials decreased from 180.0 nm to 22.8 nm and then increased to 163.0 nm, and the porosity linearly increased from 21.1% to 58.1%. These small pores caused the successful preparation of porous MOS cement paste with dry bulk density of 760–1650 kg/m3, compressive strength of 7.8–69.8 MPa, and thermal conductivity of 0.25–0.85 W/(m·K).

Fabrication of a three-level hierarchically porous silver via GASAR and dealloying processes and its catalytic behavior for formaldehyde oxidation

• Three-level hierarchically porous silver (THPS) are prepared by dealloying GASAR porous Mg 82.43 Ag 17.57 alloy. • Selective dissolution of Mg atoms in α-Mg and Mg 54 Ag 17 forms the submicron- and nano- pores. • Nanopore size and morphology can be controlled by adjusting the variety of dealloying solution. • The THPS-2 sample with fine granular ligaments has better catalytic performance for formaldehyde. Hierarchically porous materials, which have significant potential for applications in catalysis and biotechnology, is limited by complicated synthesis steps and expensive pore-former. Herein, a new type of three-level hierarchically porous silver (THPS) comprises oriented micron pores, submicron pores and inter-connected nanopores was fabricated by dealloying GASAR porous Mg 82.43 Ag 17.57 eutectic alloy. Firstly, the porous Mg 82.43 Ag 17.57 eutectic alloy with micron pore was made by GASAR technique. This porous alloy was then subjected to dealloying treatment, and the submicron pores were gradually formed in the matrix. Meanwhile, the dissolution of Mg atoms and the diffusion and rearrangement of Ag atoms in the acid solutions were resulting in formation of the nanopores. Furthermore, the results of the catalytic performance for formaldehyde showed that those of THPS with granular-like nanopores has better performance, which is attributed to the efficient mass transfer of micron- and submicron pores and the high specific surface area afforded by the nanopores.

Environmental noise reduction for tunable resistive pulse sensing of extracellular vesicles.

Extracellular vesicles (EVs) bearing biomolecules from parental cells can represent a novel source of disease biomarkers and are under intensive study for their clinical potential. Tunable resistive pulse sensing (TRPS) quantifies the magnitude of a small ionic resistive pulse current to determine the size, concentration, and zeta potential of EVs. Environmental noise is a common limiting factor that affects the precision of sensing devices. TRPS is particularly vulnerable to environmental noise, including both mechanical and electrical. The upper detection limit of the TRPS relies on the physical size of the elastomeric tunable nanopore. The lower limit relies on the electrical signal-to-noise ratio. Guided by simulation, we designed an external device to suppress environmental noise for TRPS measurement. Both mechanical and electrical environmental noise reductions were observed after using the shield. The study also validated the noise reduction function of the shield by quantifying EVs from different cell origins. Detection of EVs smaller than 200 nm was improved by using the shield; which was reported challenging for conventional quantification methods. The study highlighted a feasible approach to solve environmental noise challenges for TRPS based EV quantification.

Mechanically Induced Nanoscale Architecture Endows a Titanium Carbide MXene Electrode with Integrated High Areal and Volumetric Capacitance.

Complete utilization of electrochemically active materials while maintaining the high areal/volumetric packing density is a goal to be achieved in miniaturized supercapacitor devices, which therefore display both high volumetric and areal energy density. Although critical, it is usually challenging to achieve this goal by optimizing the electrode architecture. Dense packing of active materials maximizes the volumetric capacitance butalso results in sluggish diffusion of the electrolyte. Structurization of the electrode by forming large pores creates a pathway for electrolyte penetration but reduces the volumetric energy density. Here, densified electrodes with hierarchical porous architecture at the nanoscale are reported, which provide an alternative solution. Worm-like expanded titanium carbide MXene powders are produced in highly viscous reaction media and assembled by mechanical compression. The expanded morphology of the MXene powders translates into a buckling microstructure in the electrodes, resulting in 28.2 ± 4.1% porosity mainly in the form of nanosized pores. At the sub-nanometer scale, the diffusion of electrolytes is enhanced in interlayer space of the bended lattice with pillared intercalants. These hierarchical structural features lead to both high areal and volumetric capacitance (11.4Fcm-2 coupled with 770Fcm-3 ) in hundred-micrometers-thick electrodes, which inspires the design of high-performance electrochemical energy storage devices.

Lithofacies and its controls on the organic matter-hosted pores in the Cambrian gas-rich Niutitang shale in upper Yangtze Plate, China

The organic-rich shale in the Lower Cambrian Niutitang Formation (Є1n) has great gas resources potential in south China but have no commercial gas production achieved yet. The EYY1 well is the first well located at the eastern edge of the upper Yangtze plate to obtain success in commercial gas production in the Niutitang Formation, providing a rare case for better understanding gas enrichment mechanism in the Niutitang shale. By observation of cores and thin sections, bulk rock X-ray diffraction mineral analysis, the Niutitang shale is classified into three kinds of organic-rich lithofacies: calcareous shale (CS), siliceous shale (SS) and transitional shale (TS). The organic matter (OM) and OM-hosted pore in different lithofacies were examined by using scanning electron microscope (SEM) with argon-ion polishing sample treating, accompanied by energy spectrum test and SEM image analysis. The results show that: (1) Shale lithofacies control the organic matter type and development degree of organic matter-hosted pores (OMPs). (2) CS have plenty of depositional organic matter (DOM) in which nano-micron sized OMPs are poorly developed with surface porosity ranges between 3.05% and 9.08%. Siliceous and transitional shale have more migrated organic matter (MOM), which possess more sponge-like nano-sized pores with surface porosities range of 10.7%–31.5%. The pore development degree and gas content of siliceous shale is higher than that of transitional and calcareous shale. (3) Organic matter abundance (TOC content), type, and mineral composition also have important constrain on OMPs development. TOC has a positive correlation to the OMPs, whereas TOC 4 wt% or so is a balance point between the influence of organic matter content and formation compaction on pore development, higher TOC cannot prevent the pore from collapsing due to compaction in this region. The OMPs associated with or adjacent to clay minerals in siliceous shale are more developed, which indicate clay minerals which have positive effects on the adsorption of organic matter and the formation and preservation of OMPs.

Gas Separation Membranes with Atom-Thick Nanopores: The Potential of Nanoporous Single-Layer Graphene.

Gas separation is one of the most important industrial processes and is poised to take a larger role in the transition to renewable energy, e.g., carbon capture and hydrogen purification. Conventional gas separation processes involving cryogenic distillation, solvents, and sorbents are energy intensive, and as a result, the energy footprint of gas separations in the chemical industry is extraordinarily high. This has motivated fundamental research toward the development of novel materials for high-performance membranes to improve the energy efficiency of gas separation. These novel materials are expected to overcome the intrinsic limitations of the conventional membrane material, i.e., polymers, where a longstanding trade-off between the separation selectivity and the permeance has motivated research into nanoporous materials as the selective layer for the membranes. In this context, atom-thick materials such as nanoporous single-layer graphene constitute the ultimate limit for the selective layer. Gas transport from atom-thick nanopores is extremely fast, dependent primarily on the energy barrier that the gas molecule experiences in translocating the nanopore. Consequently, the difference in the energy barriers for two gas molecules determines the gas pair selectivity. In this Account, we summarize the development in the field of nanoporous single-layer graphene membranes for gas separation. We start by discussing the mechanism for gas transport across atom-thick nanopores, which then yields the crucial design elements needed to achieve high-performance membranes: (i) nanopores with an adequate electron-density gap to sieve the desired gas component (e.g., smaller than 0.289, 0.33, 0.346, 0.362, and 0.38 nm for H2, CO2, O2, N2, and CH4, respectively), (ii) narrow pore size distribution to limit the nonselective effusive transport from the tail end of the distribution, and (iii) high density of selective pores. We discuss and compare the state-of-the-art bottom-up and top-down routes for the synthesis of nanoporous graphene films. Mechanistic insights and parameters controlling the size, distribution, and density of nanopores are discussed. Fundamental insights are provided into the reaction of ozone with graphene, which has been successfully used by our group to develop membranes with record-high carbon capture performance. Postsynthetic modifications, which allow the tuning of the transport by (i) tailoring the relative contributions of adsorbed-phase and gas-phase transport, (ii) competitive adsorption, and (iii) molecular cutoff adjustment, are discussed. Finally, we discuss practical aspects that are crucial in successfully preparing practical membranes using atom-thick materials as the selective layer, allowing the eventual scale-up of these membranes. Crack- and tear-free preparation of membranes is discussed using the approach of mechanical reinforcement of graphene with nanoporous carbon and polymers, which led to the first reports of millimeter- and centimeter-scale gas-sieving membranes in the year 2018 and 2021, respectively. We conclude with insights and perspectives highlighting the key scientific and technological gaps that must be addressed in the future research.

Modeling pyramidal silicon nanopores with effective ion transport

While the electrical models of the membrane-based solid-state nanopores have been well established, silicon-based pyramidal nanopores cannot apply these models due to two distinctive features. One is its 35.3° half cone angle, which brings additional resistance to the moving ions inside the nanopore. The other is its rectangular entrance, which makes calculating the access conductance challenging. Here, we proposed and validated an effective transport model (ETM) for silicon-based pyramidal nanopores by introducing effective conductivity. The impact of half cone angle can be described equivalently using a reduced diffusion coefficient (effective diffusion coefficient). Because the decrease of diffusion coefficient results in a smaller conductivity, effective conductivity is used for the calculation of bulk conductance in ETM. In the classical model, intrinsic conductivity is used. We used the top-down fabrication method for generating the pyramidal silicon nanopores to test the proposed model. Compared with the large error (≥25% in most cases) when using the classical model, the error of ETM in predicting conductance is less than 15%. We also found that the ETM is applicable when the ratio of excess ion concentration and bulk ion concentration is smaller than 0.2. At last, it is proved that ETM can estimate the tip size of pyramidal silicon nanopore. We believe the ETM would provide an improved method for evaluating the pyramidal silicon nanopores.

Manufacturing 3D nano-porous architecture for boron-doped diamond film to efficient abatement of organic pollutant: Synergistic effect of hydroxyl radical and sulfate radical

Electrochemical advanced oxidation process (EAOP) has caught increasing attention in purification of organic wastewater. However, its degradation performance is chiefly relevant to electrode micro-structure and radical species. Herein, the three-dimensional (3D) nano-porous boron-doped diamond (BDD) film with controllable nano-pore size is tailored for enhancing the production of hydroxyl radical (•OH) and activating sulfate to sulfate radical (SO4•-) in EAOP. The nano-porous BDD film favors interconnected porous structure, channel-like pores with size ranged from 10 nm to 1 μm, highly improved electron-transfer rate and large oxygen evolution potential (>2.0 V). It is effective for elimination of p-nitrophenol (PNP) with pseudo first-order kinetics rate of 1.14 × 10-2 min−1 and remove rate of 92.43 % after 180 min. The indirect oxidation is the dominant mechanism of PNP degradation. Benefited from enhanced active surface area and fast mass diffusion based on 3D interconnected porous channel, the generation of •OH increases from 1.41 mM to 2.20 mM after 180 min, which not only eliminates polymer intermediate, but also signally stimulates the degradation efficiency. Additionally, SO4•- is produced by activation of sulfate on the nano-porous BDD film, resulting in the 79.58 % of remove rate of chemical oxygen demand in Na2SO4 which is higher than that in NaNO3 (55.20 %). Oxidation of PNP with radical quenchers is conducted and PNP remove rate slightly decreases with addition of ethanol compared to that in presence of tert-butanol, indicating both •OH and SO4•- contribute to the oxidation of PNP but •OH is more important. Based on intermediate characterization, it’s found that detachment of nitro, abstraction of hydrogen atom, cleavage of aromatic ring and decarboxylation reactions rapidly occur and effectively accelerate the mineralization of organic pollutant. This study enriches the EAOP application of nano-grade porous BDD film and broadens the aspect of designing porous electrode in the environment fields.

Improved mechanical strength and thermal resistance of porous SiC ceramics with gradient pore sizes

Thermal insulation applications of porous SiC ceramics require low thermal conductivity and high mechanical strength. However, low thermal conductivity and high mechanical strength possess a trade-off relationship, because improving the mechanical strength requires decreasing the porosity, which increases the thermal conductivity. In this study, we established a new strategy for improving both the mechanical strengths and thermal resistances of porous SiC ceramics with micron-sized pores by applying a double-layer coating with successively decreasing pore sizes (submicron- and nano-sized pores). This resulted in a unique gradient pore structure. The double-layer coating increased the flexural strengths and decreased the thermal conductivities of the porous SiC ceramics by 24–70 % and 29–49 % depending on the porosity (48–62 %), improving both their mechanical strengths and thermal resistances. This strategy may be applicable to other porous ceramics for thermal insulation applications.

Effects of curing time on the pore structure evolution and fracture behavior of CAC bonded alumina-spinel castables

The present work investigated the pore structure evolution and fracture behavior of calcium aluminate cement (CAC)-bonded alumina-spinel castables treated at 110 and 1600 °C after curing at 25 °C for 1 day and 3 days. The pore structure and fracture behavior were characterized by mercury intrusion combined with micro-CT scanning and a wedge splitting test coupled with acoustic emission, respectively. The results showed that the hydration degree was enhanced by extending the curing time, and more hydrates were conducive to the generation of complex pore structures after drying. In comparison, the heat treatment at 1600 °C resulted in a substantial reduction in nano-sized pores, the 3 d sample obtained developed and complex micro-sized pores than 1 d sample. Therefore, specimens cured for 3 d had better hot modulus of rupture (HMOR) and thermal shock resistance compared to those cured for 1 d, which could be attributed to the induced tortuous microcrack propagation within the matrix and along the aggregate-matrix interfaces.

Bridging confined phase behavior of CH[formula omitted]-CO[formula omitted] binary systems across scales

Phase behavior of confined fluids may deviate significantly from that of the bulk fluid due to the fluid–wall interactions being a significant portion of all intermolecular interactions under confinement. Despite recent advancements in understanding confined phase behavior of pure fluids, confined phase behavior of mixtures remains an understudied topic. In this work, we examine the confined phase behavior of a CH4-CO2 binary system by combining Monte Carlo (MC) simulations, a cubic equation of state (EoS), and the lattice Boltzmann method (LBM). First, the effects of confinement on density and phase distribution in nano-size pores are established using Gibbs Ensemble MC calculations, which produce precise results of liquid and vapor confined pressures and account for the modification of the phase change location. By comparing the phase envelopes of bulk and confined mixtures at a fixed temperature, it is observed that the phase envelopes shrink with reductions in pore size. Based on this observation, we extend a modified Peng–Robinson EoS, which was originally developed for pure fluids under confinement, to mixtures via van-der-Waals-type mixing rules and by accounting for shifts in the critical properties of confined CH4-CO2. The resulting phase envelopes are in good agreement with the MC data. In addition, a local density model is used in combination with the confined EoS to calculate adsorption isotherms of CH4-CO2 mixtures and to characterize the behavior of confined matter in nanopores. Finally, we incorporate this EoS in a multicomponent multiphase LBM that uses a pseudopotential model to represent intermolecular forces. This workflow utilizes multiscale simulation techniques to bridge the behavior of multicomponent systems across scales and to shed light on the confined phase behavior of CH4-CO2 binary systems.

Analysis of micropore size distribution using Dubinin's theory of volume filling - Effect of particle size on pore characterization of organic-rich Indian shales

Micropores play a significant role in adsorption and are abundant in a shale pore structure. The influence of particle size on pore structure parameters, especially micropores, is a subject of primary interest for shale gas characterisation. In this work, a total of 6 samples with varying mineralogical and organic content are selected from 2 Indian sedimentary basins, Cambay and Krishna-Godavari. Selected samples were crushed to different particle sizes 500-425 μm (M1), 425-250 μm (M2), 250-150 μm (M3), and 150-75 μm (M4) and low pressure N2 and CO2 adsorption experiments at 77 K and 273 K were performed on them. Through these experiments, it was observed that, with crushing of samples to smaller particle sizes low-pressure N2 adsorption tend to show higher values for total pore volume and average pore diameter. The mean difference over all samples for average pore diameter between M4 and M1 particle size is closer to 1 nm. Similarly, the mean difference over all samples for total pore volume between M4 and M1 particle sizes of all samples is 0.005 cc/g, which is almost closer to their micropore volumes. Such inconsistencies in measurements can lead to serious errors in shale gas exploration. Further, the low pressure N2 experiments indicated that M4 particle size samples show higher values of pore structure parameters, and low pressure CO2 experiments show that M3 particle size shows higher micropore volumes. For further understanding of nano-sized pore contributions, micropore size distributions of the samples have been constructed using Stoeckli pore size distribution function. From these distributions and other analysis, it was concluded that the smallest particle size overestimates the pore structure parameters and M3 particle size is optimum for both low pressure N2 and CO2 adsorption.

Vapor-liquid phase equilibrium of n-pentane in quartz nanopores by grand canonical Monte Carlo calculation

As the main basis for calculating other physical property data, the critical temperature and pressure of fluid are important parameters in the process of oil and gas field development. In unconventional reservoirs, crude oil fluid generally exists in nanopores. The interaction between fluid molecules and the pore wall leads to the deviation of fluid properties. Pore size is an important parameter affecting the phase state of reservoir fluid. The phase state laws of alkanes in different nanopore sizes are quite different. We studied the effect of the pore size of quartz nanopores on the vapor–liquid phase equilibrium using the grand canonical Monte Carlo method. The quantitative relationship between the nanopore size and the adsorption amount, density profile, and phase diagram of n-pentane was obtained, and its micromechanism was analyzed. The results showed that the critical temperature and critical pressure of n-pentane increased with an increase in the nanopore size. The critical temperature was consistent with the bulk phase after the pore size reached 10 nm, and the critical pressure could be treated with the bulk phase after the pore size reached 30 nm. The van der Waals force between the fluid and the pore wall was the main factor leading to the phase change of the system. These findings suggest that the aperture of nanopores was significant for alkane phase change, which might provide a reference for understanding the phase transformation law behavior of alkanes in nanopores of tight reservoirs.

New insight into electrochemical denitrification using a self-organized nanoporous VO-Co3O4/Co cathode: Plasma-assistant oxygen vacancies catalyzed efficient nitrate reduction

A novel self-organized nanoporous VO-Co3O4/Co cathode was prepared via anodization and plasma treatment and obtained a significant nitrate reduction efficiency. In the anodization, an oxide layer with the nano-sized pore structure initially grew in-situ on the Co substrate and showed a better surface area. Subsequently, He-plasma increased surface oxygen vacancies (VO) from 24 % to 57 %. Electrons in vacancies were charged into empty eg orbital of low-spin Co3+(Oh, octahedral) and firstly generated high-spin Co2+(Oh) with the configuration of t2g6eg1, accounting for 71.7 % of cobalt species. Accordingly, two original mechanisms (Vo-catalyzed and Co2+(Oh)-catalyzed) were concluded in this study. Oxygen vacancies increased the charge intensity and served as absorption sites in nitrate reduction. Meanwhile, massive Co2+(Oh) provided electrons in the eg orbital with a higher energy state and mediated the faster electron transfer through a Co2+–Co3+–Co2+ redox cycle, compared with Co2+ (Td, tetrahedral). Ultimately, a faster reaction kinetic of 0.0220 min−1 was achieved by VO-Co3O4 than other cathodes e.g., Co3O4 (0.0150 min−1). Such VO-Co3O4/Co cathode-based denitrification strategy displayed great advantages in engineering application and completely removed 90 % of TN from actual wastewater.

In-depth investigation of pore structure and fracture behavior of CAC bonded alumina-spinel castables treated at 110 ∼ 1600 °C

An in-depth investigation of pore structure evolution and corresponding fracture behavior of calcium aluminate cement (CAC) bonded alumina-spinel castables treated at 110–1600 °C has been carried out by taking the respective advantages of mercury intrusion and micro-CT scanning, wedge splitting test and acoustic emission, respectively. The results showed that the complexity of nano-sized and submicron-sized pores increased from 110 to 800 °C, and then decreased gradually from 800 to 1600 °C due to the dehydration of hydrates and formation of C12A7, CA, CA2, and CA6 phases. In comparison, the complexity of the pores above 1 μm increased with the ascent of treating temperatures. Consequently, the heat treatment resulted in deterioration of “toughness” owing to the vanish of majority of nano-sized and submicron-sized pores and the subsequent formation of strong ceramic bonding. The fractal dimension of pore structure presented positive correlation with “toughness” of castables, where higher fractal dimension standed for higher frature energy consumption within matrix caused by tortuous crack propagation paths.

Construction of 3D Ordered Honeycomb Films with Controllable Pores as Efficient Catalytic Supports

AbstractThe facile construction of 3D porous film using the breath figure technique is critically important in diverse practical applications. However, the discovery of easy synthetic methods and preparation of stimuli‐responsive 3D ordered nano‐/micro‐architectures remain challenging. Herein, the promotive breath figure technique is presented to construct 3D honeycomb porous films on curved substrates using an azobenzene‐containing copolymer. The nanopore size of honeycomb structure decreases gradually with the increase of surface curvature, due to the different solvent drying speeds. Upon irradiation with directional linear polarization light, the round‐shaped nanopores are converted into rectangular‐ and rhombic‐shaped nanopores under different polarization directions. Moreover, these porous films are employed as substrates to load various metal nanoparticles, successfully preparing the nanocomposites. The catalytic capacity of both control and these nanocomposites are evaluated using the NaBH4‐mediated reduction reaction from 4‐nitrophenol to 4‐aminophenol. Compared to the control and nonporous films, the porous films with smaller nanopores exhibit larger catalytic activity. Additionally, UV irradiation upon the nanocomposites promotes the catalytic action, due to the change in surface hydrophilicity caused by the photoisomerization of azobenzene. Recyclable use of nanocomposites demonstrates the high stability. This research provides an innovative strategy to prepare 3D curved porous films for potential on catalysis.

Defect‐Induced Effects in Nanomaterials

Defect‐Induced Effects in Nanomaterials

Occurrence Regularity of Methane Gas Molecules in Composite Nanopores: A Molecular Simulation Study

Abstract To understand the occurrence regularity of methane gas molecules in composite nanopores, the effects of temperature, pressure, size of nanopore, and burial depth on the occurrence state of methane were studied theoretically by using the grand canonical Monte Carlo and molecular dynamic simulation methods. By comparing the results available in the literature, the reasons for the difference in the occurrence states of methane molecules in nanopores were analyzed, and a reasonable occurrence regularity of methane was proposed, which provides corresponding suggestions for the actual exploitation of shale gas. The results indicated that the methane gas molecules existed in nanopore only in the adsorption and transition states under different environmental conditions. They were preferentially adsorbed at the strong adsorption sites on the nanopore surface to form a stable adsorption layer. After the adsorption layer reached saturation, a transition layer with higher density than that of bulk methane was formed at the nanopore center. The total adsorption capacity of methane decreased gradually with an increase in the internal temperature of shale reservoirs and increased with an increase in nanopore size. In addition, the average amount of methane stored in the nanopore increased at a deeper burial depth. The occurrence state of methane under different pressure ranges was controlled under different action mechanisms. Under low pressure (P<20 MPa), the adsorption of methane molecules was controlled by the number of strong adsorption sites on the nanopore surface, where the density peak intensity of the adsorption layer increased with the pressure. However, under high pressure (P>20 MPa), the adsorption was controlled by the diffusion process of methane molecules in the organic matter layer, where both the adsorption and transition layers reached the saturation state, and excessive methane molecules diffused deeper into the kerogen layer. The approach to effectively improve the recovery efficiency was to inject water or carbon dioxide into the shale reservoir where the water or carbon dioxide molecules occupy strong adsorption positions than the methane molecules adsorbed originally under the competitive adsorption effect, and the adsorbed methane molecules were transformed to a free state.

(Digital Presentation) Synergistic Effect of Cobalt and Nitrogen on the Spent Coffee Grounds Derived Carbon As an Efficient Catalyst for Alkaline Hydrogen Evolution

Due to global electricity demand and ecological issues, eco-friendly and sustainable energy resource is becoming a hot topic in energy production and future economic development. On this point, efficient catalytic materials for electrochemical hydrogen evolution reaction (HER) are crucial in the research area. HER in alkaline medium has several advantages, including its lower vapor pressure, which helps produce pure hydrogen gas and provides better stability than acidic medium to metal contents by reducing catalyst’s corrosion. Primarily, carbon-based electrocatalytic materials such as hetero-atomic-doped carbon, transition metal-doped carbon, and co-doped carbon show off an effective HER performance. Because it has a large surface area, good chemical stability, it is inexpensive and earth-abundant.Additionally, spent coffee grounds (SCG) contain a high amount of carbohydrates, melanoidins, and lipids that are given a possibility to be suitable carbon precursors for carbon catalyst synthesis. Moreover, SCG is becoming an environmental issue that produces many tons of waste worldwide each year due to the proliferation of global coffee consumption.Here, we present cobalt nanoparticles embedded on nitrogen (N)-doped carbon catalyst, synthesized from SCG. Initially, SCG-derived nanoporous carbon was obtained by pyrolysis under high temperatures with KOH and urea. After that, carbon materials were functionalized with cobalt and nitrogen with the simple method.Cobalt-embedded N-doped carbon catalyst has a high surface area and highly distributed nano-sized pores. Polarization measurement, Tafel plot, electrochemical impedance spectroscopy, chronopotentiometry, and cyclovoltammetry have tested the electrochemical performance. Even though the catalyst contained a negligible amount of cobalt (0.56 at. %), HER catalytic activity in alkaline medium has better resulted than non-functionalized carbon catalysts and was comparable to higher activity benchmark electrocatalysts such as RuO2 and 20% Pt/C. Also, experimental results demonstrate that excellent long-term stability for the alkaline hydrogen evolution. So, synergistic effects of cobalt nanoparticles content and N-doping on the SCG-derived carbon were indicated for efficient catalyst in the alkaline hydrogen evolution application.