Slit-shaped Pores Research Articles

Exploring the nanobiohybrids of nanodiamonds-functionalized MoAlB@MBene and microalgae synergistic potential for sustainable pharmaceutical removal

Nanobiohybrid systems combine nanomaterials and biological components, creating synergistic platforms for diverse applications. We successfully developed MoAlB@MBene core-shell structure using HCl/H2O2 mixture, transforming the densely packed nanolaminar MoAlB MAB phase into an expanded multilayered MBene’ structure, featuring open slit-shaped pores. EDS and XRF analysis suggested that the voids between the Mo-B layers were due to the removal of approximately one aluminum layer. The etching of the MAB phase also caused a transition in the zeta potential from 1.11 to −3.35. Such characteristics suggest a potential for MBene’ surface functionalization. SEM and EDS confirmed that functionalization with 1.0 wt% fluorescent nanodiamonds (FND) was optimal, and guaranteed uniform distribution of the FND. Functionalization with FND ensured favorable optical properties, including fluorescence in the orange/red region and reduced direct band gap value (from 1.32 eV to 0.54 eV). The presence of FND mitigated the ecotoxicological properties of MoAlB@MBene. We observed sustained proliferation even at a concentration of 500 mg L−1 of the nanocomposite, with toxicity plateauing after 48 h of incubation. Optimization of encapsulation with sodium alginate suggested the best concentration (1.5 wt%) and cross-linking time (10 min), allowing for structural integrity, sphericality, and rapid microalgae growth. The fluorescent nanocomposite within encapsulated microalgae improved the decomposition rate of tetracycline (18 vs 45%) and doxycycline (14 vs 48%), achieving almost threefold enhancement within 24 h. Furthermore, it positively influenced microalgae growth, counteracting pharmaceuticals toxic effects. Altogether, these findings provide insights into developing and maintaining nanobiohybrid systems, incorporating fluorescent nanocomposite and microalgae, combining the knowledge from environmental protection and materials science.

Factors Controlling Differences in Morphology and Fractal Characteristics of Organic Pores of Longmaxi Shale in Southern Sichuan Basin, China

Shale gas is a prospective cleaner energy resource and the exploration and development of shale gas has made breakthroughs in many countries. Structure deformation is one of the main controlling factors of shale gas accumulation and enrichment in complex tectonic areas in southern China. In order to estimate the shale gas capacity of structurally deformed shale reservoirs, it is necessary to understand the systematic evolution of organic pores in the process of structural deformation. In particular, as the main storage space of high-over-mature marine shale reservoirs, the organic matter pore system directly affects the occurrence and migration of shale gas; however, there is a lack of systematic research on the fractal characteristics and deformation mechanism of organic pores under the background of different tectonic stresses. Therefore, to clarify the above issues, modular automated processing system (MAPS) scanning, low-pressure gas adsorption, quantitative evaluation of minerals by scanning (QEMSCAN), and focused ion beam scanning electron microscopy (FIB-SEM) were performed and interpreted with fractal and morphology analyses to investigate the deformation mechanisms and structure of organic pores from different tectonic units in Silurian Longmaxi shale. Results showed that in stress concentration areas such as around veins or high-angle fractures, the organic pore length-width ratio and the fractal dimension are higher, indicating that the pore is more obviously modified by stress. Under different tectonic backgrounds, the shale reservoir in Weiyuan suffered severe denudation and stronger tectonic compression during burial, which means that the organic pores are dominated by long strip pores and slit-shaped pores with high fractal dimension, while the pressure coefficient in Luzhou is high and the structural compression is weak, resulting in suborbicular pores and ink bottle pores with low fractal dimension. The porosity and permeability of different forms of organic pores are also obviously different; the connectivity of honeycomb pores with the smallest fractal dimension is the worst, that of suborbicular organic pores is medium, and that of long strip organic pores with the highest fractal dimension is the best. This study provides more mechanism discussion and case analysis for the microscopic heterogeneity of organic pores in shale reservoirs and also provides a new analysis perspective for the mechanism of shale gas productivity differences in different stress–strain environments.

Characterization of Pore Structure and Fluid Mobility of Shale Reservoirs.

Accompanying the commercial exploitation of shale oil and gas in North America, shale oil has gradually become an important resource, sparking great interest among countries around the world in recent years. In this study, focusing on the Paleogene Shahejie Formation in Bohai Bay (Eastern China), techniques such as CT, nitrogen adsorption, mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) were used to characterize the pore structure and mobility of the shale reservoir. Based on the X-ray CT data, the pore radius of the shale reservoir is in the range 0.5-65 μm, and the pore coordination number is concentrated in the range of 1-4. The shale reservoir is poorly connected. The minimum size of the unit body for establishing the digital core model is 380 μm. Based on the experimental data of nitrogen adsorption and MICP, the pores of shale in the study area are mainly classified as ink-bottle-shaped pores, transition-shaped pores, and flat plate slit-shaped pores. The specific surface area and volume of pores are mainly attributed to meso- and macropores. The movable fluid saturation of shale is distributed from 23.59 to 44.42%, the pore throat radius is distributed from 0.001 to 6 μm, and the lower limit of the movable pore throat radius of shale is distributed between 9.0 and 20.1 nm. The movable fluid porosity is mainly distributed between 0.84 and 4.08%, with an average movable fluid porosity of 2.37%. The findings provide a theoretical basis for the efficient development of shale oil resources.

Molecular Density Fluctuations Control Solubility and Diffusion for Confined Aqueous Hydrogen.

Hydrogen's contribution to a sustainable energy transformation requires intermittent storage technologies, e.g., underground hydrogen storage (UHS). Toward designing UHS sites, atomistic molecular dynamics (MD) simulations are used here to quantify thermodynamic and transport properties for confined aqueous H2. Slit-shaped pores of width 10 and 20 Å are carved out of kaolinite. Within these pores, water yields pronounced hydration layers. Molecular H2 distributes along these hydration layers, yielding solubilities up to ∼25 times those in the bulk. Hydrogen accumulates near the siloxane surface, where water density fluctuates significantly. On the contrary, a dense hydration layer forms on the gibbsite surface, which is, for the most part, depleted of H2. Although confinement reduces water mobility, the diffusion of aqueous H2 increases as the kaolinite pore width decreases, also a consequence of water density fluctuations. These results relate to H2 permeability in underground hydrogen storage sites.

Pore Morphology and Oxidation Behaviour of Deep-Loaded Granular Coal at High Initial Temperatures

ABSTRACT As coal mining proceeds deeper, fragmented coal is subjected to high geostress and elevated thermal environments, causing changes in its micro-physical properties and spontaneous combustion (SC) risks. Deep mining operations entail significant risks of coal fires. In order to investigate the effects of high stress and high thermal environments on the microstructural and physicochemical damage of fragmented coal, and to elucidate the mechanisms influencing oxidation behavior, we conducted experiments including low-temperature nitrogen adsorption, synchronous thermal analysis, and in-situ diffuse reflectance spectroscopy. These experiments aimed to explore the pore morphology and oxidation characteristics of high initial temperature unloading granular coal (HITU-GC) unloading conditions. The results indicate that with increasing initial temperature, characteristic point temperatures initially rise and then decrease, while both the mass loss and heat release during the low-temperature oxidation stage decrease. After pressure-unloading composite treatment, the oxidation process accelerates with more intense reactions, resulting in an overall increase in heat release. The pore shapes of HITU-GC show no significant difference compared to the original coal, mainly comprising non-rigid aggregates of micropores, platy or layered matrix particles, including numerous slit-shaped pores. The coal surface also exhibits ink bottle-shaped pores and cone-shaped pores. Higher pre-oxidation temperatures correlate with higher specific surface areas. Higher stress levels from pressurized unloading correlate with lower specific surface areas. The specific surface area of sample O60-P16 is reduced by 0.879 m2/g compared to sample O60-P0. Pressurized unloading treatment disrupts mesoporous pores. Following thermal environment and pressure-unloading, the coal’s aromatic hydrocarbon content decreases, while the contents of hydroxyl, aliphatic hydrocarbons, and oxygen-containing functional groups (FG) all increase. Sample O60-P4 shows the highest content of active FG. While thermal environments enhance coal oxidation activity, pressure-unloading treatment increases the extent of coal surface fragmentation. The synergistic effect of both significantly increases the SC risk of coal. This study provides a theoretical basis for controlling thermal hazards associated with high-initial-temperature unloading fragmented coal in deep goaf areas.

One-Pot Phyto-Mediated Synthesis of Fe2O3/Fe3O4 Binary Mixed Nanocomposite Efficiently Applied in Wastewater Remediation by Photo-Fenton Reaction

A binary Fe2O3/Fe3O4 mixed nanocomposite was prepared by phyto-mediated avenue to be suited in the photo-Fenton photodegradation of methylene blue (MB) in the presence of H2O2. XRD and SEM analyses illustrated that Fe2O3 nanoparticles of average crystallite size 8.43 nm were successfully mixed with plate-like aggregates of Fe3O4 with a 15.1 nm average crystallite size. Moreover, SEM images showed a porous morphology for the binary Fe2O3/Fe3O4 mixed nanocomposite that is favorable for a photocatalyst. EDX and elemental mapping showed intense iron and oxygen peaks, confirming composite purity and symmetrical distribution. FTIR analysis displayed the distinct Fe-O assignments. Moreover, the isotherm of the developed nanocomposite showed slit-shaped pores in loose particulates within plate-like aggregates and a mesoporous pore-size distribution. Thermal gravimetric analysis (TGA) indicated the high thermal stability of the prepared Fe2O3/Fe3O4 binary nanocomposite. The optical properties illustrated a narrowing in the band gab (Eg = 2.92 eV) that enabled considerable absorption in the visible region of solar light. Suiting the developed binary Fe2O3/Fe3O4 nanocomposite in the photo-Fenton reaction along with H2O2 supplied higher productivity of active oxidizing species and accordingly a higher degradation efficacy of MB. The solar-driven photodegradation reactions were conducted and the estimated rate constants were 0.002, 0.0047, and 0.0143 min−1 when using the Fe2O3/Fe3O4 nanocomposite, pure H2O2, and the Fe2O3/Fe3O4/H2O2 hybrid catalyst, respectively. Therefore, suiting the developed binary Fe2O3/Fe3O4 nanocomposite and H2O2 in photo-Fenton reaction supplied higher productivity of active oxidizing species and accordingly a higher degradation efficacy of MB. After being subjected to four photo-Fenton degradation cycles, the Fe2O3/Fe3O4 nanocomposite catalyst still functioned admirably. Further evaluation of Fe2O3/Fe3O4 nanocomposite in photocatalytic remediation of contaminated water using a mixture of MB and pyronine Y (PY) dyestuffs revealed substantial dye photodegradation efficiencies.

Synthesis of novel collagen-based aerogel with slit-shaped pore structure: Study on its adsorption mechanism on copper ions

In this study, (SA/BHC)@TE aerogel is successfully prepared based on hydrogen bonding between three components, covalent cross-linking between bovine hide collagen (BHC) and tannin extract (TE), and the gelation of sodium alginate (SA). The adsorption properties of (SA/BHC)@TE on Cu(Ⅱ) are systematically analyzed through a combination of simulations and specific experiments. Firstly, DFT simulations are performed to rapidly predict the possibility of interactions among BHC, SA and TE. Then, experiments are performed to indicate that the (SA/BHC)@TE aerogel is endowed with a core–shell structure, a slit-shaped pore structure, and abundant active centers (–OH, –COOH, –NH2 and –CONH–). (SA/BHC)@TE has a maximum removal efficiency of 90.3 % for Cu(Ⅱ). Consequently, (SA/BHC)@TE successfully achieves selective adsorption of specific ions Cu(Ⅱ) from the mixture with a distribution coefficient of 11.12 L/g. It suggests that the adsorption is mainly multilayer adsorption and chemisorption. Furthermore, the FTIR and XPS studies reveal that the adsorption of Cu(Ⅱ) onto (SA/BHC)@TE is the result of the synergistic effect of coordination, ion exchange and electrostatic interaction. In addition, the (SA/BHC)@TE aerogel is easy to separate and recycle. Therefore, this paper has important implications for the development of selective adsorbents for Cu(Ⅱ) as well as for the resource utilization of collagen.

Density and volume of adsorbed methane in key applications for in-situ gas content: Insights from molecular simulation

The evaluation of the in-situ gas content in deep coal seams, potentially containing free gas in saturated-oversaturated reservoirs, holds practical significance for exploration and production compared with shallow undersaturated-saturated reservoirs dominated by adsorbed gas. However, owing to the inherent limitations of volumetric and gravimetric methods, the accurate assessment of adsorbed and free gases faces significant challenges. In this study, based on molecular simulations, we focused on slit-shaped pores to explore the microscopic interaction mechanisms between coal and methane molecules under different pore sizes, temperatures, and pressures. By combining isothermal adsorption and pore structure experiments, the distribution characteristics of the adsorbed phase density (APD) and adsorbed phase volume (APV) were determined. The results showed that, in pores smaller than 1.5 nm, methane exhibited an aggregated state distribution (containing only adsorbed methane) characterized by micropore filling adsorption. In pores larger than 1.5 nm, methane showed a dispersed state distribution (coexistence of adsorbed and free methane) characterized by monolayer adsorption. The APD increased with pressure and decreased with temperature and pore size, whereas the APV remained independent of the pressure and temperature. In the in-situ gas content evaluation, three adsorption models (SL, SDR, and SL + SDR models) considering APV and APD were utilized to describe the methane adsorption behavior. The SDR model considering the APV was consistent with the actual physical properties and molecular simulation results. Traditional correction methods often lead to an overestimation of the adsorbed methane content, and neglecting the APV can result in an overestimation of the free methane content. In summary, the SDR model considering the APV can provide more rigorous scientific support for the refined study of methane occurrence states and gas content distribution.

Physical insights into uranyl diffusion and sorption in bentonite: Theoretical and molecular dynamics study

Mechanistic understanding of diffusion and sorption of radionuclides and metals in clay-based engineered barriers is essential to develop models and define parameters for transport calculations for the safety analysis of disposal systems. Here we studied diffusion of uranyl (UO22+) species in the clay interparticle pore or macropores of bentonite clay by means of molecular dynamics simulation (MDS) for pore sizes ranging from 8.37 to 33.5 nm. The conceptual model of the clay pore system considered diffusion as a combination of pore diffusion (Dp) and surface diffusion DS (i.e. diffusion of adsorbed cations within the electrical double layer of the clay surfaces), from which the apparent diffusion Da was calculated as the weighted sum of Dp and DS, using a weighing factor f calculated as the ratio of adsorbed to total UO22+ in the system. Diffusivities at equilibrium for the largest pore size of 33.5 nm were: Da=7.37×10−10 m2 s−1, Dp=1.14×10−9 m2 s−1, and Ds=1.97×10−13 m2 s−1. The Ds was several orders of magnitude smaller than Dp. This was evident from the much smaller gradient of the mean-square displacement vs time lag curve for the adsorbed species than that of the species in the pore space. We found a remarkable consistency between our theoretical derivation and independent MDS evidence. For the slit-shaped interparticle pore, the retardation factor Rf was found to be the reciprocal of the unabsorbed fraction (Rf=1/1−f) and the capacity factor α was a ratio of the porosity to the unadsorbed fraction (α=ε1−f) or the ratio of the diffusant density in the bulk sample to the corresponding density in the pore solution. MD simulations of diffusion and sorption processes can be applied to other transport related problems at continuum scale, pore scale and molecular scale, such as for improved modelling of global elemental cycles, CO2 geosequestration, or the performance of desalination membranes.

Microscopic pore structure characteristics and controlling factors of marine shale: a case study of Lower Cambrian shales in the Southeastern Guizhou, Upper Yangtze Platform, South China

A systematic study of the pore structure characteristics of Lower Cambrian shales in the southeastern Upper Yangtze Platform, was conducted using organic geochemistry, mineralogy, nitrogen adsorption, physical property analysis, and scanning electron microscopy. The results indicate that: 1) The Total organic carbon (TOC) content shows a strong correlation with quartz and clay minerals. Shales with low TOC content and rich in clay minerals primarily exhibit slit-shaped and narrow slit-like inter-clay particle pores with pore size distribution is dominated by mesopores and macropores. Shales with high TOC content predominantly feature narrow slit-like and ink bottle-shaped pores with pore size distribution dominated by micropores and mesopores. 2) Shale pore structures vary significantly under different gas content and preservation conditions. Shales under favorable preservation conditions exhibit a relatively “high porosity, low permeability, and high gas content” pattern, with well-developed organic pores and a strong pore-permeability correlation. In contrast, shales under unfavorable preservation conditions appear dense, with excessively developed fractures increasing both average pore size and local permeability. The pore-permeability correlation is weak, presenting a relatively “low porosity, high permeability, and low gas content” pattern. 3) TOC content plays a crucial role in controlling pore structure, showing overall positive correlations with pore volume, specific surface area, and porosity, and negative correlations with pore size. High TOC content enhances shale plasticity, resulting in lower pore diameters. Factors such as compaction and unfavorable preservation conditions lead to the shrinkage, collapse, and closure of some narrow pore throats, negatively impacting pore volume, specific surface area, brittleness, and fractal dimension, exhibiting a negative correlation with TOC content. 4) The pore structure of Lower Cambrian shales is complex, with fractal dimensions D1 and D2 exhibiting negative correlations with average pore size and positive correlations with TOC, specific surface area, and total pore volume. A high D1 value indicates well-preserved nanoscale pore surface structures with low complexity, suggesting minimal alteration by external fluids and better shale gas preservation. D1 serves as an indicator for shale gas content and preservation conditions. D2 shows better correlations with various pore structure parameters, making it suitable for characterizing pore structures.

Alginate-based adsorbents with adjustable slit-shaped pore structure for selective removal of copper ions

Adopting effective and efficient techniques for the treatment of heavy metal pollution in water bodies plays an important role in guaranteeing the quality of water and the sustainable development of water resources. In this study, GO, MMT and SA were used as raw materials to compare the adsorption behaviors of three alginate-based adsorbents crosslinked with different valence metal ions (Ca2+, Fe3+ and Zr4+) on Cu(II). The aerogels were based on sodium alginate as the matrix material with unique slit-shaped pore structures formed by stacking effect of sheets and chemical bonding. It was found that the pore structures of the aerogels were denser and more orderly with the increase of the valence states of the crosslinked ions, and the affinity for Cu(II) in planar configuration was stronger. The Zr4+-GMSA aerogel had the maximum adsorption capacity of 126.68 mg/g and the Kd of Cu(II) was up to 50.80 L/g, which exhibited good preferential adsorption performance. The adsorption mechanism of Mn+-GMSA aerogels on Cu(II) was mainly ionic exchange, surface complexation and physical adsorption, which was explored by combining XPS and EDS characterizations of Mn+-GMSA before and after adsorption. This scheme can provide valuable and meaningful contribution to realize the selective recovery of Cu(II).

Permeability Modeling of Pore Shapes, Compaction, Sorption, and Molecular Diffusivity in Unconventional Reservoirs

Summary Shale and ultratight gas reservoirs are multiscale, containing organic matter (OM) and inorganic minerals in multiple pore compartments of different pore shapes and scales. Selecting a suitable model to describe the multiscale transport mechanisms requires a minimum understanding of the inherent pore shape, OM content, typical pore size, and inherent flow regime. Interestingly, during gas production and associated pressure depletion, some mechanisms, such as pore compressibility, pore diffusion, and diffusion of sorbed gas molecules, become significant at lower pressure. In this study, multiscale and multiphysics permeability models are introduced that couple the effects of poroelasticity (especially in slit-shaped pores with <1.0 aspect ratio) and sorbed gas diffusion, Fick diffusion, transition diffusion, or Knudsen diffusion, depending on the pore structural properties at multiscale for shale and ultratight gas applications. Shale here refers to organic-rich low-permeability rock with >1–2 wt% OM, while ultratight gas has negligible organic content with <1.0 wt%. These experimentally and computationally validated models could be combined with Gaussian pressure transient solutions to effectively understand the uncertainty in multiphysics gas permeability in addition to the hydraulic and natural fracture parameters for large-scale flow simulation of hydraulically fractured unconventional reservoirs.

A Dynamic Permeability Model in Shale Matrix after Hydraulic Fracturing: Considering Mineral and Pore Size Distribution, Dynamic Gas Entrapment and Variation in Poromechanics

Traditional research on apparent permeability in shale reservoirs has mainly focussed on effects such as poromechanics and porosity-assisted adsorption layers. However, for a more realistic representation of field conditions, a comprehensive multi-scale and multi-flowing mechanism model, considering the fracturing process, has not been thoroughly explored. To address this research gap, this study introduces an innovative workflow for dynamic permeability assessment. Initially, an accurate description of the pore size distribution (PSD) within three major mineral types in shale is developed using focussed ion beam-scanning electron microscopy (FIB-SEM) and nuclear magnetic resonance (NMR) data. Subsequently, an apparent permeability model is established by combining the PSD data, leading to the derivation of dynamic permeability. Finally, the PSD-related dynamic permeability model is refined by incorporating the effects of imbibition resulting from the fracturing process preceding shale gas production. The developed dynamic permeability model varies with pore and fracture pressures in the shale reservoir. The fracturing process induces water blockage, water-film formation, and water-bridging phenomena in shale, requiring additional pressure inputs to counteract capillary effects in hydrophilic minerals in shale, But also increases the overall permeability from increasing permeability at larger scale pores. Unlike traditional reservoirs, the production process commences when the fracture is depleted to 1–2 MPa exceeds the pore pressure, facilitated by the high concentration of hydrophobic organic matter pores in shale, this phenomenon explains the gas production at the intial production stage. The reduction in adsorption-layer thickness resulting from fracturing impacts permeability on a nano-scale by diminishing surface diffusion and the corresponding slip flow of gas. this phenomenon increases viscous-flow permeability from enlarged flow spacing, but the increased viscous flow does not fully offset the reduction caused by adsorbed-gas diffusion and slip flow. In addition to the phenomena arising from various field conditions, PSD in shale emerges as a crucial factor in determining dynamic permeability. Furthermore, considering the same PSD in shale, under identical pore spacing, the shape factor of slit-like clay minerals significantly influences overall permeability characteristics, much more slit-shaped pores(higher shape factor) reduce the overall permeability. The dynamic permeability-assisted embedded discrete fracture model (EDFM) showed higher accuracy in predicting shale gas production compared to the original model.

Boosting the Initial Coulombic Efficiency of Sustainable Hard Carbon Derived from Polyethylene Terephthalate with Cyclopentyl Methyl Ether As a Co-Solvent for Wide-Temperature Sodium-Ion Batteries

Upcycling plastic waste into value-added products helps to generate cost-effective and sustainable resources towards a circular materials economy and safer ecosystem. The conversion of polyethylene terephthalate (PET) municipal waste via the carbonization process into hard carbon (HC) delivers a high-reversible capacity, low-cost, sustainable anode material for sodium-ion batteries (SIBs). However, the low initial Coulombic efficiency (ICE) is a significant challenge of the HC anode, which should be optimized by electrolyte and interfacial chemistry.1 In conventional carbonate esters-based electrolytes, ethylene carbonate (EC) forms an organic-rich thick SEI layer, soluble on cycling, limiting the cyclic stability. The low-temperature performance is also a significant concern in achieving high capacity, long cyclability, and ICE.2 Herein, HC derived via single-step carbonization at 1000℃ exhibits larger interlayer spacing of 0.379 nm, low surface area (~205 m2g-1), and unique slit-shaped pores with 84% mesoporosity in the structure. PET-HC exhibits a high reversible capacity of 337 mAh g-1 with ICE of just 66%, using EC-PC-based electrolyte. EC-free cyclopentyl methyl ether (CPME) was used due to its weakly solvating and wide temperature solvent.3 CPME-PC-based electrolytes significantly enhanced the ICE value to 74.5% and reversible capacity to 356 mAh g-1 with superior cycling of 91% after 100 cycles at 0.1C rate. The inorganic-rich SEI layer for CPME-PC-based electrolytes results in a thin SEI that improves the ICE and cyclic stability of the anode. The low-temperature performance (up to -20°C) for CPME-PC-based electrolytes showed ~30% added capacity compared to EC-PC-based electrolytes. This work provided an eco-friendly approach to developing hard carbons from plastic trash and offered an effective strategy to replace EC with CPME for low-temperature sodium storage applications. References Shen, L., Shi, S., Roy, S., Yin, X., Liu, W., Zhao, Y., Adv. Funct. Mater. 2021, 31, 2006066. Ramasamy, H. V., Kim, S., Adams, E. J., Rao, H. & Pol, V. G. Chem. Commun. 2022, 58, 5124–5127.Zhang, H., Zeng, Z., Ma, F., Wu, Q., Wang, X., Cheng, S., Xie, J., Angew. Chem. 2023, e202300771. Figure 1

Pore Structure and Fractal Characteristics of the Middle and Upper Permian Dalong and Gufeng Shale Reservoirs, Western Hubei Province, South China

The Middle and Upper Permian Dalong and Gufeng Formations in South China have recently been considered as potential gas-producing shales. However, their pore structure characteristics remain poorly understood. To investigate the pore structure and fractal characteristics of the pores in these two formations, a suite of shale samples from the Dalong and Gufeng Formations in the western Hubei Province, South China were analyzed by multiple techniques, namely, TOC content, X-ray diffraction (XRD) mineralogy analysis, optical microscopy observations, major elemental analysis, field emission-scanning electron microscopy (FE-SEM), and low-pressure gas adsorption measurements (N2 and CO2). The identified major shale lithofacies include siliceous mudstone, carbonaceous mudstone, argillaceous-siliceous mixed mudstone, and calcareous-siliceous mixed mudstone. SEM images show that the dominant pore types include the pores between brittle minerals, slit-shaped pores between clay sheets, and secondary organic matter (OM) pores within solid bitumen. The pore size distribution is dominated by micropores and mesopores (<30 nm), which are the major contributors to total pore volume and surface area for the Dalong and Gufeng Formations. Based on the Frenkel–Halsey–Hill (FHH) method, fractal dimensions (D1, D2) calculated from the nitrogen adsorption data have a range of from 2.489 to 2.772 (D1) and from 2.658 to 2.963 (D2), and are higher in the Gufeng Formation (average TOC = 8.3 wt.%) due to a higher TOC content comparing to the Dalong Formation (average TOC = 6.2 wt.%). The pore development and fractal characteristics are primarily controlled by organic matter (OM), carbonate minerals, and clay minerals for both the Dalong and Gufeng Formations. Shale samples with high TOC content, low carbonate content, and high clay content tend to develop more heterogeneous micropores and mesopores, which is ascribed to the generation of clay-related and OM-hosted pores, along with the destruction of primary pores by pore-filling carbonate cements.

A convenient and user-friendly hydrometallurgical process for preparing porous siliceous adsorbents using ascharite tailings: Mechanism of structural change and evaluation of adsorption properties

Ascharite tailings are discarded by the boron industry due to their low boron content and high magnesium content. Additionally, the large-scale storage of these tailings contributes to resource wastage and environmental pollution. The present study successfully prepared a siliceous adsorbent through the combined use of mechanical and acid activation methods. The tailings underwent acid treatment under mild conditions, leading to the dissolution of magnesium while maintaining the integrity of the silicate framework. This process resulted in the formation of a mesoporous structure primarily composed of slit-shaped pores. The specific surface area reached 234.7 m2 g−1, while the pore volume reached 0.31 cm3 g−1. The maximum adsorption capacity for methylene blue was 0.66 mg m−2 per unit of surface area. The pollutants displayed a flat orientation at equilibrium, with a maximum tilt angle of approximately 53°. The adsorption rate was limited due to the decrease in available adsorption sites. However, mechanical activation increased the density of active silanol sites from 2.76 to 4.34 mg m−2, significantly weakening the shielding effect on other potential sites. Thus, tailings resources can be effectively converted into valuable adsorbent materials using a convenient and controllable hydrometallurgical process.

Methane hydrate formation in slit-shaped pores: Impacts of surface hydrophilicity

Gas hydrate accumulation and hydrate-based gas storage and transportation technology are intimately linked to the formation process of hydrates in the pore space. However, the molecular mechanism underlying this process remains unclear. Here, we employ molecular simulations to investigate methane hydrate formation in surface-modified silica pores, with specific emphasis on the impact of pore surface characteristics. Our results show that under the same thermodynamic conditions, methane hydrate shows no preference towards either the hydrophobic or hydrophilic pore surface, and tends to nucleate in the central part of the hydrophilic slit. It means that whilst the surface properties can impact the dynamics and structure of the molecules on it, thus affecting methane concentration and, as a result, the probability of cage formation, the confinement effect ultimately controls the nucleation process. Furthermore, the pre-filling of the pores with methane can significantly accelerate hydrate formation. This is because methane bubbles adsorbed in the pores can noticeably elevate methane concentration in solution. Moreover, the hydrophobic surface can help with methane dissolution in water, which can both promote the transportation of molecules between methane bubbles and enhance methane hydrate nucleation. This study enhances understanding of the hydrate formation process in pores, which can aid in the design of gas hydrate promoters or inhibitors that meet the demands of hydrate technologies.

Insertion of molecular hydrogen into slit-shaped carbon pores: theoretical study

Insertion of molecular hydrogen into slit-shaped carbon pores: theoretical study

Two-Dimensional PC-SAFT-DFT Adsorption Models for Carbon Slit-Shaped Pores with Surface Energetical Heterogeneity and Geometrical Corrugation

Two-Dimensional PC-SAFT-DFT Adsorption Models for Carbon Slit-Shaped Pores with Surface Energetical Heterogeneity and Geometrical Corrugation

Pore Characteristics, Oil Contents and Factors Influencing Laminated Shale in the First Member of the Qingshankou Formation in the Gulong Sag, Northern Songliao Basin

To clarify the reservoir characteristics of laminated shale, the occurrence mechanism of shale oil and its influencing factors in the Gulong Sag, northern Songliao Basin, are studied to better guide the exploration and development of shale oil there. First, X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) are used to characterize the pore types, pore geneses and factors influencing the pore volume in the study area. Second, the organic matter of the samples is extracted with a mixture of dichloromethane and methanol. Total organic carbon (TOC), nitrogen adsorption and Rock-Eval tests are performed on the samples before and after extraction to reveal the pore size distribution after extraction. The factors influencing free and adsorbed shale oil and the lower limit of pore size are discussed in detail. The results show that interparticle pores (interP pores), intraparticle pores (intraP pores), organic matter pores (OM pores) and microfractures can be found in the laminated shale (Q1) in the Gulong Sag, Songliao Basin, and that the interP pores and intercrystalline pores in clay minerals are the main pores. The FE-SEM results show that the diameters of interP pores vary from several hundred nanometers to several microns, and their morphologies are mainly triangular, strip-shaped or irregular. The morphology of the intercrystalline pores in the clay minerals is generally irregular, depending on the crystal type and arrangement of clay minerals. According to the characteristics of the nitrogen adsorption and desorption curves, the pore morphologies are mainly slit-shaped pores, parallel-plate-shaped pores and ink-bottle-shaped pores. The pore size distribution is mostly bimodal, and the pore volume contribution is the greatest in the pore size range of 10~20 nm. Before and after extraction, the overall characteristics of the pore size distribution change only slightly, but the number of micropores increases significantly. Different minerals have different degrees of influence on the proportions of micropores, mesopores and macropores. Quartz mainly inhibits the formation of micropores, while the overall effect on mesopores and macropores is positive depending on the diagenetic period. Feldspar has a strong positive correlation with the micropore and mesopore proportions but is not highly correlated with the macropore proportions. The influence of the carbonate mineral content on the pore volume is not obvious because of its complex composition. The TOC content and vitrinite reflectance (Ro) are the two most important factors controlling free oil and adsorbed oil, and the contents of mineral components, such as felsic minerals, carbonate minerals and clay minerals, have no obvious correlation with shale oil content. With increasing pore volume, the contents of free oil and adsorbed oil increase, but the proportion of adsorbed oil decreases gradually. The correlation between the specific surface area and adsorbed oil content is poor. At normal temperatures and pressures, the lower limit of the pore diameters that can contain free oil is 4 nm, and the lower limit of the pore diameters that can contain movable oil is 10 nm.