Characteristics Of Nanopores Research Articles

Influence of the Dielectric Constant on the Ionic Current Rectification of Bipolar Nanopores.

In this paper, we investigate how the dielectric constant, ϵ, of an electrolyte solvent influences the current rectification characteristics of bipolar nanopores. It is well recognized that bipolar nanopores with two oppositely charged regions rectify current when exposed to an alternating electric potential difference. Here, we consider dilute electrolytes with NaCl only and with a mixture of NaCl and charged nanoparticles. These systems are studied using two levels of description, all-atom explicit water molecular dynamics (MD) simulations and coarse-grained implicit solvent MD simulations. The charge density and electric potential profiles and current-voltage relationship predicted by the implicit solvent simulations with ϵ = 11.3 show good agreement with the predictions from the explicit water simulations. Under nonequilibrium conditions, the predictions of the implicit solvent simulations with a dielectric constant closer to the one of bulk water are significantly different from the predictions obtained with the explicit water model. These findings are closely aligned with experimental data on the dielectric constant of water when confined to nanometric spaces, which suggests that ϵ decreases significantly compared to its value in the bulk. Moreover, the largest electric current rectification is observed in systems containing nanoparticles when ϵ = 78.8. Using enhanced sampling, we have shown that this larger rectification arises from the presence of a significantly deeper minimum in the free energy of the system with a larger ϵ, and when a negative voltage bias is applied. Since implicit solvent models and mean-field continuum theories are often used to design Janus membranes based on bipolar nanopores, this work highlights the importance of properly accounting for the effects of confinement on the dielectric constant of the electrolyte solvent. The results presented here indicate that the dielectric constant in implicit solvent simulations may be used as an adjustable parameter to approximately account for the effects of nanometric confinement on aqueous electrolyte solvents.

Initial Occurrence State and Movability Evaluation of the Gulong Shale Oil Reservoir, Songliao Basin

The Qing-1 layer of the Gulong Depression in the northern Songliao Basin is a liquid-rich shale oil reservoir that has the characteristics of nanopores, high maturity, high gas/oil ratio (GOR), etc. The production performance of wells in the Gulong shale oil reservoir shows the characteristics of “single gas production followed by oil-gas production”. It is difficult to analyze the initial occurrence state and movability of fluid in the shale nanopores using conventional methods. In this study, a comprehensive method, including phase behavior analysis, physical experiments, and molecular simulation, was established to analyze the initial occurrence state and movability of fluid in the Gulong shale oil reservoir. The phase state of the fluid was calculated by the equation of state (EOS), considering nano-confinement effects, and the initial occurrence state was quantitatively evaluated by combining two-dimensional nuclear magnetic resonance (NMR) and molecular dynamics simulation. The movable fluid saturation was quantitatively determined by centrifugal experiments. The results show that the condensate gas state was in small pores, while the volatile oil state was in large pores. The occurrence states of oil were mainly adsorbed oil and free oil. The proportion of adsorbed oil in inorganic pores was about 24.4%, while the proportion of absorbed oil in organic pores was about 57.8%. Based on the cutoff value of T2 before and after the centrifuged laboratory experiments, the movable limit of oil was determined to be 4.5 nm, and the movable fluid saturation was about 11%. The research method proposed in this study has important guiding significance for the initial occurrence state and movability evaluation of similar liquid-rich shale reservoirs.

Correction to "Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China"

Correction to "Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China"

Nanopore electrochemical sensors for emerging hazardous pollutants detection

Nanopore electrochemical sensors have been developed to detect various emerging pollutants at the single-molecule level with high sensitivity and specificity due to their high resolution in past three decades, which is of great significance for emerging hazardous pollutants control. Electrochemical detection methods based on nanopore technology are primarily divided into two categories: resistive-pulse and rectification sensing. The main detection mechanism of the resistive-pulse method is based on the volume exclusion effect generated when the analyte enters through the nanopore, and it involves three primary detection strategies. The first approach involves nanopore technology for direct pollutant detection, where pollutant structure and concentration information is assessed based on nanopore-generated ionic current's blockade strength, duration, and frequency. The second strategy relies on weak intermolecular interactions when direct detection of pollutants is challenging. Molecular probes interact with target molecules to enhance detection sensitivity and achieve specific recognition. The third strategy is based on the biological/chemical reaction of pollutant molecules, through indirect detection method to achieve specific detection of target pollutant molecules. Additionally, relies on changes in surface charge polarity or nanopore spatial structure induced by the analyte molecules to achieve the detection of target molecules within the nanopore. This work demonstrates the research progress achieved in the application of nanopore electrochemical sensing technology to high-sensitivity detection of hazardous pollutants, utilizing the unique confined spatial characteristics of nanopores, combined with biorecognition techniques and principles of electrochemical reactions.

Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China

Fractal Characteristics of Nanopores and Their Controlling Factors of the Lower Cambrian Shale in the Western Hubei Area, South China

Fractal and Multifractal Characteristics of Nanopores and their Controlling Factors in Marine–Continental Transitional Shales and their Kerogens from Qinshui Basin, Northern China

Fractal and Multifractal Characteristics of Nanopores and their Controlling Factors in Marine–Continental Transitional Shales and their Kerogens from Qinshui Basin, Northern China

Evolution of anthracite nanopores with CO2 adsorption at different pressures by synchrotron radiation small angle X-ray scattering

As a porous medium, coal has a strong adsorption capacity for CO2. Nanopore is the main adsorption space of coal reservoir. To study the evolutionary characteristics of nanopores in coals with CO2 adsorption, in situ small angle X-ray scattering experiments of anthracite at different CO2 adsorption pressures were carried out. The change of scattering intensity ratio RI in nanopores with different sizes were analyzed. The porosity, specific surface area and average aperture were quantitatively characterized. The research shows that the 5 nm pores is more susceptible to higher CO2 pressure, while the scattering phenomenon in the 15 nm pores changes most obviously at lower CO2 pressure. The deformation sensitivity of 35–75 nm pores to CO2 adsorption is consistent. The scattering data in anthracite show a positive Porod deviation. CO2 will become dense with increasing pressure, and its filling of nanopores makes some scattering phenomena become invisible to X-ray. There will be a new boundary between dense CO2 and free CO2, which affects the fluctuation of electron density between two-phase systems. There is a positive correlation between the Porod deviation of the scattering data and the CO2 pressure. In the process of CO2 adsorption, the dynamic deformation of anthracite nanopores is obvious, resulting in synchronous changes of porosity and specific surface area. CO2 adsorption pressure is negatively correlated with porosity and specific surface area, but positively correlated with the average aperture. The decrease of CO2 pressure leads to the gradual recovery of nanopore deformation. However, at different evolution stages of the same CO2 pressure, the porosity, specific surface area and average aperture of anthracite are inconsistent. Irreversible damage to anthracite nanopores is produced with CO2 adsorption. The evolution of nanopores is the result of the superposition of CO2 compression and adsorption.

Which 2D Material is Better for DNA Detection: Graphene, MoS2, or MXene?

Despite much research on characterizing 2D materials for DNA detection with nanopore technology, a thorough comparison between the performance of different 2D materials is currently lacking. In this work, using extensive molecular dynamics simulations, we compare nanoporous graphene, MoS2 and titanium carbide MXene (Ti3C2) for their DNA detection performance and sensitivity. The ionic current and residence time of DNA are characterized in each nanoporous materials by performing hundreds of simulations. We devised two statistical measures including the Kolmogorov-Smirnov test and the absolute pairwise difference to compare the performance of nanopores. We found that graphene nanopore is the most sensitive membrane for distinguishing DNA bases. The MoS2 is capable of distinguishing the A and T bases from the C and G bases better than graphene and MXene. Physisorption and the orientation of DNA in nanopores are further investigated to provide molecular insight into the performance characteristics of different nanopores.

Study on Pore Structure of Shale Reservoir by Low Temperature Nitrogen Adsorption Method

Shale gas is one of the most actively explored unconventional sources of natural gas. There are several types of pores in the shale reservoir, and their structural characteristics are complex. Evaluating the characteristics of the shale pore structure is the basis for understanding the shale reservoir performance and the oil and gas migration mechanism. In this paper, the micro- and nanopores of shale samples from the Yanchang Formation, Hunan basin, are studied by applying the low-temperature nitrogen adsorption method. Several pore structure parameters such as the specific surface area, the pore volume, and the pore size distribution of the analyzed samples are calculated. The predominant characteristics of nanopores that influence hydrocarbon accumulation and control the development of pores are discussed. The results indicate that the shale reservoir rocks from the study area are mainly mesoporous with an average pore size distribution between 2 and 50 nm. A small number of micropores (less than 2 nm) and macropores (more than 50 nm) are also present in the pore network. The development of micropores and mesopores in the shale samples is associated with organic matter content, while the development of macropores is linked to clay minerals content. Total organic carbon (TOC) content is the key element to control the nanopore volume and the specific surface area of the reservoir rocks from the study area. At the same time, the organic matter-enriched pore network also provides extensive space for the accumulation of shale gas.

Fast prediction of methane adsorption in shale nanopores using kinetic theory and machine learning algorithm

Understanding the gas adsorption behavior in shale nanopores is essential for the reservoir estimation and performance prediction of shale gas, which is still unclear considering the complexity of geological environment and nanoporous structure of shale. In general, traditional methods based on experiments and molecular dynamics (MD) simulations are always expensive and time consuming. In this work, a machine learning (ML) framework to predict the methane adsorption behavior in shale nanopores is constructed from the microscopic and kinetic theory perspectives, where three novel parameters related to potential energy distribution (PED) are proposed to represent the methane adsorption characteristics of shale slit nanopores. Machine learning algorithm based on the uniformly constructed dataset is introduced to realize fast and accurate prediction of methane adsorption behavior, which is well validated by typical inorganic and organic models. Moreover, the application of the proposed ML model to predict the adsorption behavior of methane in different geological conditions (e.g., pressure and temperature) is performed, indicating its feasibility to predict the gas adsorption behavior in shale nanopores with ultra-fast computation speed, that would be beneficial for the exploitation and development of shale gas reservoirs. The insights gained in this work is also instructive for the prediction of nano-confined fluid behavior under complex environmental factors.

Differences in the distribution and occurrence phases of pore water in various nanopores of marine-terrestrial transitional shales in the Yangquan area of the northeast Qinshui Basin, China

Shale gas reservoirs generally contain pore water that affects their gas-bearing properties; however, the differences in the water-bearing characteristics of various shale nanopores remain unclear, especially for marine-terrestrial transitional shales. This study collected a set of fresh shale core samples from the marine-terrestrial transitional strata of the Qinshui Basin and investigated the distribution and occurrence phase of pore water in nanopores with diverse pore widths (micropores and non-micropores) and pore types (organic-matter hosted (OM) and inorganic-matter hosted (IM) pores). The results indicate that an average of 12.98% of the pore water is stored in the OM pores and featured by monolayer adsorption on the OM micropore surfaces, while the OM non-micropores are free of pore water. An average of 87.02% of the pore water is stored in the IM pores, 47.01% and 37.17% of the pore water exhibits monomolecular adsorption on the surfaces of IM micropores and non-micropores, respectively, and the rest of the pore water adsorbs on the two types of IM pore surfaces forming double-molecular or multiple-molecular layers. The pore water takes up the majority of the IM micropore structures and the IM non-micropore surfaces; however, it only occupies a few of the OM micropore structures and fails to occupy the OM non-micropore structures. For the studied shales under as-received conditions, 39.24% of the pore surface areas and 65.99% of the pore volumes are effective for storing shale gas. The effective pore surfaces are predominantly determined by the OM pores, while the effective pore volumes are contributed equivalently from the IM and OM pores. Therefore, the adsorbed gas of the shales is mainly stored in the OM pores, while the IM pores may only contain half of the total free gas.

Single‐Molecule Frequency Fingerprint for Ion Interaction Networks in a Confined Nanopore

AbstractThe transport of molecules and ions through biological nanopores is governed by interaction networks among restricted ions, transported molecules, and residue moieties at pore inner walls. However, identification of such weak ion fluctuations from only few tens of ions inside nanopore is hard to achieve owing to electrochemical measurement limitations. Here, we developed an advanced frequency method to achieve qualitative and spectral analysis of ion interaction networks inside a nanopore. The peak frequency fm reveals the dissociation rate between nanopore and ions; the peak amplitude am depicts the amount of combined ions with the nanopore after interaction equilibrium. A mathematical model for single‐molecule frequency fingerprint achieved the prediction of interaction characteristics of mutant nanopores. This single‐molecule frequency fingerprint is important for classification, characterization, and prediction of synergetic interaction networks inside nanoconfinement.

Single-Molecule Frequency Fingerprint for Ion Interaction Networks in a Confined Nanopore.

The transport of molecules and ions through biological nanopores is governed by interaction networks among restricted ions, transported molecules, and residue moieties at pore inner walls. However, identification of such weak ion fluctuations from only few tens of ions inside nanopore is hard to achieve owing to electrochemical measurement limitations. Here, we developed an advanced frequency method to achieve qualitative and spectral analysis of ion interaction networks inside a nanopore. The peak frequency fm reveals the dissociation rate between nanopore and ions; the peak amplitude am depicts the amount of combined ions with the nanopore after interaction equilibrium. A mathematical model for single-molecule frequency fingerprint achieved the prediction of interaction characteristics of mutant nanopores. This single-molecule frequency fingerprint is important for classification, characterization, and prediction of synergetic interaction networks inside nanoconfinement.

Fractal and multifractal characteristics of shale nanopores

Shale pore structure is an important factor in shale adsorption and percolation. To better characterize the pore structure of shales, this paper selects 24 shale core samples for high-pressure mercury intrusion (HPMI) test, and fractal theory and multifractal theory are applied to analyze the pore structures of shale nanopores. The fractal dimensions using different fractal models and the multifractal parameters are calculated from mercury intrusion capillary pressure (MICP). The correlations between fractal/multifractal parameters and shale nanopore structures are analyzed. The study reveals that the fractal dimension calculated from 3D capillary model can be used as an index for evaluating complex of shale nanopores. The fractal dimension increases with the increase of displacement pressure and homogeneity coefficient and decreases with the increase of the permeability and pore-throat radius. The multifractal analysis shows that shale nanopores have multifractal characteristics, and multifractal parameters can reflect the size, concentration, and asymmetry of pore size distribution (PSD). The PSD of shales are similar when they have similar multifractal parameters (Δα,Δf,α0,α1,α2). The information dimension D1 and correlation dimension D2 are positively correlated to the sizes of shale nanopores, and with the decreasing information dimension D1, the pore size distributes more contributed. Besides, the information dimension D1 has a strong and negative correlation with the fractal dimension derived from 3D capillary model.

Major Understanding and Innovation, Challenges and Potential analysis of Shale Gas Exploration and Development in China

Affected by the success of shale gas development in North America, the Chinese government and major oil and gas producers accurately grasped the development trend of shale gas industry, promoted the pilot tests and introduced policies effectively. In 2018, shale gas production in China was 1.53×1010m3. A total of 1000 horizontal wells were drilled. There are some major understanding and innovation achieved, such as stratigraphic division scheme, development characteristics of nanopores, causes of high TOC(Total Organic Carbon) in black shale. The Challenges are discussed. The endowment of shale gas resource is relatively poor. Some key technologies and equipment encounter “bottleneck” and there is poor external environment for development. At last, the paper analyses the development potentials of shale gas in China. The shale gas resources are rich, and shale gas will be the main contributor to the growth of China’s natural gas production. The next step is need to speed up exploration and development, and to increase reserves and production quickly. Also, it is necessary to insist on innovation, offer on-site services, guidance and support, thus providing technical support for realizing new historic leaps of shale gas in China.

Assessment of 1/f noise associated with nanopores fabricated through chemically tuned controlled dielectric breakdown.

Recently, we developed a fabrication method-chemically-tuned controlled dielectric breakdown (CT-CDB)-that produces nanopores (through thin silicon nitride membranes) surpassing legacy drawbacks associated with solid-state nanopores (SSNs). However, the noise characteristics of CT-CDB nanopores are largely unexplored. In this work, we investigated the 1/f noise of CT-CDB nanopores of varying solution pH, electrolyte type, electrolyte concentration, applied voltage, and pore diameter. Our findings indicate that the bulk Hooge parameter (αb ) is about an order of magnitude greater than SSNs fabricated by transmission electron microscopy (TEM) while the surface Hooge parameter (αs ) is ∼3 order magnitude greater. Theαs of CT-CDB nanopores was ∼5 orders of magnitude greater than theirαb , which suggests that the surface contribution plays a dominant role in 1/f noise. Experiments with DNA exhibited increasing capture rates with pH up to pH ∼8 followed by a drop at pH ∼9 perhaps due to the onset of electroosmotic force acting against the electrophoretic force. The1/f noise was also measured for several electrolytes and LiCl was found to outperform NaCl, KCl, RbCl, and CsCl. The 1/f noise was found to increase with the increasing electrolyte concentration and pore diameter. Taken together, the findings of this work suggest the pH approximate 7-8 range to be optimal for DNA sensing with CT-CDB nanopores.

Distribution Characteristics of Nanopores and Discriminant Characteristics of Sedimentary Environment of the Longmaxi Formation in the Southern Sichuan Basin.

Shale contains a large number of nanopores. The nanopores control the reservoir structure. The formation of nanopores in shale is closely related to the sedimentary environment. The palaeosedimentary structural background determines the provenance and sedimentary diagenesis of mud shale during shale deposition, refines the palaeo-shale and palaeo-sedimentary-tectonic environments of the Longmaxi Formation in the southern Sichuan Basin by elemental geochemical means, and determines the palaeo-deposition of the Longmaxi Formation. The tectonic setting and a numerical simulation method are used to explore the sedimentary tectonic evolution characteristics of the Longmaxi Formation. The results show that the parent rock of the Longmaxi Formation is relatively enriched with light rare earth elements, and the distribution of heavy rare earth elements is relatively stable. The vertical direction shows a trend of increasing from the bottom of the formation to the top of the formation, showing a mixed genesis; the tectonic setting is a passive continental margin, and the active continental margin is the main margin.

The Gas Content Characteristics of Nanopores Developed in a Normal Pressure Shale Gas Reservoir in Southeast Chongqing, Sichuan Basin, China.

To evaluate the gas content characteristics of nanopores developed in a normal pressure shale gas reservoir, the Py1 well in southeast Chongqing was selected as a case study. A series of experiments was performed to analyze the total organic carbon content, porosity and gas content using core material samples of the Longmaxi Shale from the Py1 well. The results show that the adsorbed gas and free gas content in the nanopores developed in the Py1 well in the normal pressure shale gas reservoir range from 0.46-2.24 m₃/t and 0.27-0.83 m₃/t, with average values of 1.38 m₃/t and 0.50 m₃/t, respectively. The adsorbed gas is dominant in the shale gas reservoir, accounting for 53.05-88.23% of the total gas with an average value of 71.43%. The Gas Research Institute (GRI) porosity and adsorbed gas content increase with increasing total organic carbon content. The adsorbed gas and free gas contents both increase with increasing porosity value, and the rate of increase in the adsorbed gas content with porosity is larger than that of free gas. Compared with the other five shale reservoirs in America, the Lower Silurian Longmaxi Shale in the Py1 well developed nanopores but without overpressure, which is not favorable for shale gas enrichment.

Investigation on the Structure and Fractal Characteristics of Nanopores in High-Rank Coal: Implications for the Methane Adsorption Capacity.

The structure and fractal characteristics of nanopores of high-rank coal were investigated using an approach that integrates N₂ adsorption and field emission scanning electron microscopy (FE-SEM). The results indicated that the high-rank coal of the Shanxi Formation has a complex pore-fracture network composed of organic matter pores, mineral-related pores, and microfractures. The pore type of high-rank coal tends to be complicated, and the main pore types are inkbottle pores and open pores, which are more conducive to methane enrichment. The Ro,max has a negative relationship with the total pore volume. In addition, the ash and inertinite contents show a positive correlation with the average pore size (APS), while the fixed carbon content exhibits a negative relationship with the APS. The pore structure of high-rank coal is controlled not only by the degree of metamorphism but also by coal composition, which leads to the variation in pore structure becoming more complicated. With the increase in coal metamorphism, high-rank coal with high amounts of fixed carbon content generally possesses a higher irregularity in pore structure. No obvious relationship was observed between D₂ and the coal components, which indicates that the pore structure, ash content, moisture content and other factors controlled by the metamorphism of coal have different effects on D₂ that lead to this inapparent relationship. A negative relationship exists between adsorption volume and D1, which indicates that the high irregularity of the pore structure is not conducive to methane absorption and that no obvious correlation exists between the adsorption volume and D₂. In the high-rank coal, the high D1 value represents the complexity and heterogeneity of the pore structure and represents a low adsorption affinity for methane molecules; in addition, D₂ has no effect on the methane adsorption capacity.

Fractal Characteristics and Its Controlling Factors of Nanopore of Coal from Shanxi Province, North China.

Much attention has been recently paid to the Carboniferous-Permian coal-bearing strata in Shanxi Province, now the largest producing coalbed methane field in China. In this study, a comprehensive approach of mercury injection, low-temperature liquid nitrogen adsorption, and permeability experiments was adopted to investigate the structure and fractal characteristics of nanopores in the Carboniferous-Permian coal (with 0.77%˜3.04% Ro,ran). Based on the fractal model, two fractal dimensions D1 and D₂ corresponding to diffusion pore (<65 nm) and seepage pore (pore size ≥65 nm), respectively, were calculated, and the relationships between the fractal dimensions with the pore structure parameters and permeability are discussed here. The results indicate that the studied coal samples have good fractal characteristics and that the calculated linear correlation coefficients are higher than 0.80. The fractal dimension D1 of the diffusion pores ranges from 2.3777 to 2.4624, with an average of 2.4173, while the fractal dimension D₂ of the seepage pores is between 2.5844 and 2.6256, with an average of 2.5990. The fractal dimensions D1 of the diffusion pores increases with an increase in the BET specific surface area, vitrinite content, and Ro,ran while it decreases with an increase in the permeability, and has a weak correlation with the total pore volume. The correlation coefficients R² for the fractal dimension D₂ of the seepage pores, pore parameters, permeability, and maceral composition ranges from 0.0357 to 0.2551. These results indicate that uncertain relationships exist among these parameters.