Proportion Of Mesopores Research Articles

Characterization of hybrid organo-silica monoliths for possible application in the gradient elution of peptides.

We characterized thermally polymerized organo-silica hybrid monolithic capillaries to test their applicability in the gradient elution of peptides. We have used a single-pot approach utilizing 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), ethylene dimethacrylate (EDMA), and n-octadecyl methacrylate (ODM) as functional monomers. The organo-silica monolith containing MPTMS and EDMA was compared with the stationary phase prepared by adding ODM to the original polymerization mixture. Column prepared using a three-monomer system provided a lower accessible volume of flow-through pores, a higher proportion of mesopores, and higher efficiency. We utilized isocratic and gradient elution data to predict peak widths in gradient elution. Both protocols provided comparable results and can be used for peptide peak width prediction. However, applying gradient elution data for peak width prediction seems simpler. Finally, we tested the effect of gradient time on achievable peak capacity in the gradient elution of peptides with a column prepared with a three-monomer system providing a higher peak capacity. However, the performance of hybrid organo-silica monolithic stationary phases in gradient elution of peptides must be improved compared to other monolithic stationary phases. The limiting factor is column efficiency in highly aqueous mobile phases, which needs to be focused on.

The main controlling factors of tensile strength in sight of shale reservoir under horizontal bedding: Example of the Lower Paleozoic Niutitang Formation shale from Micangshan, China

Understanding the mechanical characteristics of marine shale during fracturing is essential for shale gas development, and its core scientific problem is what factors in shale control its mechanical properties. The 12 shale samples from the Lower Paleozoic Niutitang Formation in Micangshan are tested for tensile strength and examined using X-ray diffraction, low-field nuclear magnetic resonance (NMR), EA2000 elemental analyzer, and scanning electron microscopy to explore the main controlling factors of shale tensile strength under horizontal bedding conditions. The findings are as follows. (1) The tensile strength of the shale is relatively high, ranging from 10.05 MPa to 20.34 MPa. Quartz is the largest proportion of the shale minerals, accounting for 53.2 wt%–59.0 wt%, followed by anorthose and clay minerals. Total organic carbon (TOC) concentration ranges from 1.7 wt% to 4.1 wt%. (2) NMR results indicate that the pore structure of shale is mainly mesoporous, accounting for 75.76%–88.03%, followed by macropores (12.57%–21.24%) and micropores (0.68%–4.91%). Low-pressure nitrogen adsorption and desorption results indicate that the average pore diameter of shale is 12.58–16.02 nm, which is basically consistent with NMR results. The negative correlation between fractal dimension D2 and tensile strength indicates that the higher the tensile strength of the shale, the lower the complexity of its seepage pores. (3) Micropores occur mainly in clay minerals, whereas quartz indicates positively correlation with mesoporous content. The higher the proportion of mesopores, the lower the tensile strength. This indicates that the mesopores are the main factor controlling the tensile strength, and the quartz content in minerals is a secondary factor restricting the tensile strength. TOC has little controlling action on the tensile strength. This contribution provides a theoretical basis for shale fracturing.

Activated carbon with high mesopore ratio derived from waste Zanthoxylum bungeanum branches by KNO3-assisted H3PO4 staged activation for toluene adsorption.

Waste Zanthoxylum bungeanum branches were used to prepare activated carbon adsorbents with high mesopore ratio by H3PO4 staged activation method with adding KNO3 additive. The prepared activated carbon adsorbents were characterized by SEM, BET, FT-IR, and XRD. The adsorption properties of the prepared activated carbon adsorbents were evaluated by the toluene adsorption/desorption in air. The quasi-first-order, quasi-second-order, and Bangham models were used to fit the obtained toluene adsorption results. The oxidative etching of KNO3 additive improved the pore-forming ability of the H3PO4 activator to enhance the activation pore-forming effects of the selected biomass raw material. The secondary pore-forming effects of K atoms promoted the effective expansion of the pore diameter in the activated carbon preparation process to prepare activated carbon adsorbents with high mesopore proportion. The specific surface area and mesopore proportion of the activated carbon adsorbents prepared by adding KNO3 additive exceeded 1100 m2/g and 71.00%, respectively, and the toluene adsorption capacity exceeded 370.00 mg/g. The rich mesopore structures can effectively reduce the toluene mass transfer resistance, which can promote the corresponding activated carbon adsorbent to be regenerated by low-temperature (40 °C) thermal desorption. The toluene adsorption on the prepared activated carbon adsorbents includes surface adsorption and diffusion in pore structures, and the toluene adsorption mechanism is more consistent with the Bangham kinetic model.

Walnut shell derived N, S co-doped activated carbon for solid-state symmetry supercapacitor device

The kernel of the walnut constitutes a nutrient-dense food source. However, the walnut shell is useless and was thrown away. Therefore, as a small initiative towards waste-to-wealth, herein we developed walnut shell-derived highly porous heteroatom (nitrogen and sulfur) doped activated carbon (NS-WAC) via KOH activation and post-processing treatment by thioacetamide (TAA). The NS-WAC exhibits a high specific surface area (SSA) and various particle size distribution (PSD) involving micropores, mesopores, and macropores, conferring substantial supercapacitor advantages. The NS-WAC possesses a significant proportion of mesopores, which can decrease the ion diffusion path length and improve ion transport efficiency. Hence, NS-WAC demonstrates promising electrochemical performance achieving a high gravimetric specific capacitance of 271.4 Fg−1 at 0.5 Ag−1 in 3 M KOH aqueous electrolyte. Furthermore, the solid-state symmetric supercapacitor (SSC) device exhibited a gravimetric specific capacitance of 52 Fg−1 and volumetric specific capacitance of 74.36F cm−3 at a current density of 0.5 Ag−1. This SSC device also exhibited a gravimetric energy density of 23.4 Wh Kg−1 at a power density of 250 W Kg−1 at a current density of 0.5 Ag−1. It showed superior cycle stability of 91.8% after 10,000 cycles at 5 Ag−1.

Selective Adsorption and Recovery of Silver from Acidic Solution Using Biomass-Derived Sulfur-Doped Porous Carbon.

It is vital to recycle precious metals effectively such as silver from waste sources because of limited natural reserves. Herein, passion fruit (Passiflora edulis Sims) shell-derived S-doped porous carbons (SPCs) were newly synthesized by hydrothermal carbonization and following with activation by KOH/(NH4)2SO4, and the adsorption of Ag+ on SPC under acidic solutions was investigated. It was found that the activator of (NH4)2SO4 can not only introduce the doping of S elements but also increase the proportion of mesopores in the as-prepared SPC. As the active site, the increasing S doping can improve the adsorption of Ag+ on SPC. The kinetic data of Ag+ adsorption by SPC was consistent with the pseudo-second-order kinetic model. The Langmuir isothermal model was used to well fit the Ag+ adsorption isotherms of SPC, and the maximum adsorption capacity of the optimized SPC-3 for Ag+ is up to 115 mg/g in 0.5 mol/L HNO3 solution. SPC-3 showed good selectivity toward Ag+ over diverse competing cations, which is mainly attributed to the strong bonding between Ag+ ions and the sulfur-containing functional groups on the surface of SPC-3 resulting in the formation of Ag2S nanoparticles. The adsorbed Ag could be recovered as an elemental form by a simple calcination. This study provides a new insight into the design of an environmentally friendly and efficient adsorbent for the selective recovery of silver from acidic aqueous media.

Changes in air and liquid permeability properties of loess due to the effect of lead contamination

Heavy metals in landfill leachate are easily adsorbed by soil particles, causing serious threats to human health and surrounding environments. Mining and metallurgy activities are intensive in Northwest China, thereby enlarging threats. The aim of the present study is to enhance our knowledge about the linkage between the microstructural evolution of the loess soil induced by lead contamination and the macro air and liquid permeability properties. A series of air and liquid permeability tests on the uncontaminated and Pb-contaminated loess specimens were conducted. Their air and liquid permeability properties were evaluated on the basis of Darcy’s law and the soil–water retention curves, respectively. The microstructural evolution, when subjected to low and high Pb2+ concentrations, was assessed using scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and zeta potential tests. The intrusion of Pb2+ decreases the absolute zeta potential ζ, which in turn leads to a more distinct agglomerated structure and higher intrinsic permeability. Moreover, the dedolomitization and associated cerussite (PbCO3) precipitation are deemed as the main cause of micropore clogging, whereas the corrosion of the cement between soil particles by H+ shows a good correspondence to an increase in the number of mesopores. With the concentration of Pb2+ increasing from 0 to 2,000 mg/kg, the proportion of micropores decreases from 37.9% to 15.1%, and the proportion of mesopores increases from 17.3% to 53.3%. In addition, the air entry value decreased from 19.5 to 12.8 kPa, indicating that the water retention behavior decreased. The findings highlight the impacts of lead contamination on the microstructure and macro permeability properties and give some design guideposts to heavy metal-contaminated site remediation.

Study of the Microstructure of Coal at Different Temperatures and Quantitative Fractal Characterization.

In order to understand the influence of underground coal fires on coal fractures and pores, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) are combined to study the development of coal pore and fracture under high-temperature treatment and calculate the fractal dimension to analyze the relationship between the development of coal pore and fracture and the fractal dimension. The results show that the volume of pores and fractures of the coal sample (C200) treated at 200 °C (0.1715 mL/g) is greater than that of the coal sample (C400) treated at 400 °C (0.1209 mL/g), and both are greater than the original coal sample (RC) (0.1135 mL/g). The volume increase is mainly due to mesopores and macropores, and the proportions of mesopores and macropores in C200 were 70.15 and 59.97% in C400. The MIP fractal dimension shows a decreasing trend with the increase of temperature, and the connectivity of coal samples improved with the increase of temperature. The changes in volume and three-dimensional fractal dimension of C200 and C400 showed the opposite trend and are related to the different stress of coal matrix at different temperatures. The experimental SEM images confirm that the connectivity of coal fractures and pores improves with the increase of temperature. Based on the SEM experiment, the larger the fractal dimension, the more complex the surface is. The SEM surface fractal dimensions indicate that the surface fractal dimension of C200 is the smallest and that of C400 is the largest, which is consistent with the observations made by SEM. The combination of the two fractal dimensions is used to characterize the self-similarity of coal using the fractal dimension difference. When the temperature increased to 200 °C, the unordered expansion of the coal sample resulted in the largest fractal dimension difference and the lowest self-similarity. When heated to 400 °C, the fractal dimension difference of the coal sample is the smallest, and the microstructure of coal shows a regular groove-like development.

Activation of cellulose with CO2 and/or H2O: Evolution of functionalities of the biochar and environmental impacts

CO2 and H2O are two important activators in production of activated carbon (AC) via physical activation method. They could oxidize the carbonaceous species in biochar or biomass via varied mechanisms and might also impact environments as well as the pore structures and evolution of functionalities of AC in different ways. In this study, the activations of the biochar from pyrolysis of cellulose with H2O, CO2 or mixed H2O/CO2 were performed. The results demonstrated that H2O as an activator led to higher weight loss than that of CO2 during the activation, originating from its higher efficiency for oxidation of the aliphatic structures in biochar to –OH and their further removal via deoxygenation or dehydration. Activation with CO2 made the AC more oxygen-rich, due to the retainment of abundant oxygen-containing functionalities, which suppressed further oxidation of carbon species and led to formation of main micropores. The higher capability of H2O for deoxygenation made the AC more carbon-rich with much more developed pore structures as well as higher proportion of mesopores and thus the superior capability for adsorption of phenol. In addition, during the activation in either CO2 or H2O, the unsaturated aldehyde/ketone and C-O-C structures was thermally more stable than lactones, saturated aliphatic acids and aliphatic aldehydes. The life cycle analysis (LCA) suggested that CO2 activation showed lower impact on environment by reducing emissions and consumption of fossil fuel.

Pore structure characteristics of different lithofacies of the Longmaxi shale, Western Hunan‐Hubei Region, China: Implications for reservoir quality prediction

Lithofacies and micropore characteristics of shale reservoir directly affect the exploration and development of natural gas. To determine the development potential of shales of the Longmaxi Formation in the Western Hunan‐Hubei Region, the lithofacies types and micropore structure characteristics of the Longmaxi Formation shales have been systematically studied in this paper, based on ordinary thin sections, argon ion polishing–scanning electron microscopy, physical property testing, x‐ray diffraction whole‐rock and clay mineral analysis, isothermal nitrogen, and carbon dioxide adsorptions. According to the principle of ‘laminar structure + total organic carbon (TOC) + mineral composition of felsic, clay, and carbonate minerals’, eight types of shale lithofacies were identified. The effective porosity of the Longmaxi shale ranges from 1.8% to 14.4%, with a peak range from 3% to 6%, while the permeability ranges from 0.001 to 1.27 mD, with an average of 0.106 mD. Combined with the isothermal adsorption experiments, the proportion of mesopores is the largest in the Longmaxi shale, followed by macropores and micropores. Moreover, the pore diameters of mesopores are concentrated between 3 and 10 nm, while those of micropores are concentrated between 0.4 and 0.9 nm. The pore volume of shale is most developed when the content of brittle felsic minerals is 50% ~ 75% and the content of clay minerals is 25% ~ 50%, and the TOC content is positively correlated with the pore volume and specific surface area. There are significant differences in the pore development characteristics of different lithofacies. The shale reservoir space analysis indicates that micropores are controlled by TOC content and clay minerals, while the macropores are controlled by depositional intergranular pores, TOC content, and felsic content, as well as diagenetic pyrite mould pores, microfractures pores, and intercrystalline pores. On the other hand, mesopores are related to a mix of depositional and diagenetic factors with dominant contribution of intergranular pores, intercrystalline pores, organic pores, and intergranular shrinkage fractures pores. It is found that the pore development of massive organic‐rich siliceous shale lithofacies has the best reservoir quality, including well‐connected intergranular pores, intercrystalline pores, organic pores, and shrinkage fractures. Therefore, the massive organic‐rich siliceous shale lithofacies is the dominant fine‐grained reservoir lithofacies in the studied area. Based on understating the pore characteristics of different lithofacies, this study can provide a scientific basis for the prediction of favourable sweet spots of shale gas reservoir in the Longmaxi Formation, western Hunan‐Hubei Region.

Mesoscopic Freeze-Thaw Damage Evolution Characteristics of Fractured Sandstone at Different Saturations

To study the effect of saturation on the freeze-thaw damage of fractured rocks in cold regions, five prefabricated oval double-hole red sandstones with different saturations were prepared. Three-dimensional images of rock fractures were obtained by CT technology. The freeze-thaw damage mechanism and critical saturation of the red sandstone were explored through the fracture propagation evolution and quantitative characterization of the pore structure. The experimental results show that the pore size distribution can reflect the complex pore structure. Pores can be divided according to their sizes: small pores, mesopores, and macropores; mesopores account for the largest proportion and more than 70% of the total, and the proportion of mesopores in high-saturation sandstone (90% or 100%) increases under the action of freeze-thaw cycle. This is also accompanied by a small increase in the proportion of macropores. An 80% critical saturation of the sandstone was obtained. In addition, prefabricated cracks make the ice separation mechanism more likely to occur. The low-saturation sandstone mainly damaged the fracture area during freeze-thaw cycles, while the prefabricated cracks provided a good seepage channel for high-saturation sandstone. The corresponding rock bridge area eventually demonstrated a connectivity trend. This study more realistically reflects the freeze-thaw damage of actual rock masses in cold regions and provides a theoretical basis for the prediction of rock mass engineering disasters in cold regions.

Effect of phosphate rock acid insoluble residue on hydration process and mechanical properties of α-hemihydrate gypsum

The application of α-hemihydrate gypsum (α-HH) is limited by several factors, such as a rapid hydration rate, short setting time, poor water resistance, and high cost. Especially because of the high production cost, although α-HH has excellent mechanical strength, it is rarely used in the field of building materials. In this study, based on the composition characteristics of new industrial solid waste (phosphate-rock acid-insoluble residue, PAIR) and to meet the needs of resource utilization, gypsum matrix composites were prepared by adding PAIR to α-HH to solve the problems of short setting time and poor water resistance of gypsum matrix composites and improve the comprehensive properties of α-HH products. The results show that when the different types of pores formed during the hydration of α-HH were filled with inert substances, such as silicon dioxide, insoluble phosphate, and calcium fluoride from PAIR, the proportion of mesopores in the composite products increased, whereas that of harmful macropores decreased. The compressive and flexural softening coefficients of the PAIR/α-HH system with 23% PAIR were the highest at 57.25 and 60.125%, respectively, and the water resistance of the system was improved; when the content of PAIR reaches 35%, the strength of the composite products decreased from 58.125 to 43.8MPa. The HPO42- in PAIR partially replaces the SO42- ion in the dihydrate gypsum (DH) lattice to form a Ca(SO4, HPO4)•2H2O double salt, leading to the production of eutectic phosphorus. Soluble F-, Al3+, Mg2+, and phosphorus-containing substances in PAIR form a variety of complex ions in PAIR/α-HH aqueous solution, which are adsorbed onto the surface of the new DH phase; the crystal morphology changed from thick, long columns to clusters, thin rods, and plates, inhibiting the nucleation and growth of DH and changing its crystal growth rate and crystallization behavior. Therefore, the setting time of gypsum is prolonged; when 35% PAIR was added, the induced nucleation period of the PAIR/α-HH system was prolonged from 40 to 265min, and the final setting time was from 12 to 360min. By mixing solid waste PAIR, while the setting time of α-HH is prolonged, its water resistance is improved, and its mechanical strength is not significantly reduced, reducing the cost. From the perspective of economy and environmental protection, this study is a way to α-HH is widely used in the field of building materials.

Study on the preparation and electrochemical behaviors of histidine-based N-doped hierarchical porous carbon as a supercapacitor material

Hierarchical porous carbon materials can be obtained by etching carbonaceous materials with potassium hydroxide at high temperature. In this work, we chose the environment-friendly biomolecular galactose as the source to prepare carbon materials, histidine as the nitrogen source to improve the surface properties, and potassium hydroxide as the pore-forming agent. A series of carbon precursors were obtained via simultaneous calcination of histidine and galactose with different weight ratios under the nitrogen atmosphere. The porous carbon materials with meso/micro pores were further prepared using KOH as the activation agent. The optimal carbon material G8H1 featured with a large pore volume (1.05 cm3·g−1) and a high proportion of mesopores (Vnonmicro/Vmicro=1.62), large specific surface area (2040.2 m2·g−1), high content oxygen (12.6 at%) and nitrogen (2.32 at%), and good wettability. At three electrode system, G8H1 electrode material showed excellent specific capacitance performance 312 F·g−1 in the 6 M KOH electrolyte when the current density was 0.5 A·g−1. While symmetric supercapacitors were further assembled using 1 M Na2SO4, a capacitance of 85.4 F·g−1 at 0.05 A·g−1 was achieved with a maximal energy density of 38.43 kW·kg−1. Overall, the hierarchical porous carbon materials derived from biomolecules galactose and histidine showed excellent specific capacitance performance, which played a positive role in expanding the raw materials of synthetic carbon materials.

Controllable synthesis of micro-mesoporous Pd@N-doped carbon derived from ZIF@NiCoLDH for enhanced phenol hydrogenation to cyclohexanone

A hollow nitrogen-doped carbon (CN) material, featuring abundant mesopores and high content of graphitic nitrogen, has been synthesized by annealing of the core-shell precursor composed of zeolitic imidazolate framework-67 as core and layered double hydroxides as shell. The proportion of mesopores and nitrogen species in the CN materials significantly vary with the shell thickness of layered double hydroxides in the core-shell precursor by adjusting the etching amount and etching time of nickel nitrate. The as-prepared Pd@CN-1.4–30 catalyst exhibits superior catalytic performance in the hydrogenation of phenol to cyclohexanone, and its turnover frequency (TOF) value is about ten times higher than Pd@CN obtained without the nickel etching, resulting from the abundant mesopores, high graphitic N content, and easy reduction of palladium species. Moreover, Pd@CN-1.4–30 has good reusability during at least six reaction cycles.

Effect of drying-wetting cycles on pore characteristics and mechanical properties of enzyme-induced carbonate precipitation-reinforced sea sand

Enzyme-induced carbonate precipitation (EICP) is an emanating, eco-friendly and potentially sound technique that has presented promise in various geotechnical applications. However, the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting (D-W) cycles is under-explored yet. This study investigates the evolution of mechanical behavior and pore characteristics of EICP-treated sea sand subjected to D-W cycles. The uniaxial compressive strength (UCS) tests, synchrotron radiation micro-computed tomography (micro-CT), and three-dimensional (3D) reconstruction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles. The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis (GRA). Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles. The proportion of mesopores gradually decreases whereas the proportion of macropores increases due to the exfoliated calcium carbonate with increasing number of D-W cycles. The microstructure in EICP-reinforced sea sand was gradually disintegrated, resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched. The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100–1000 μm under the action of D-W cycles. Overall, the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.

Effects of curing temperature on mechanical properties and pore size distribution of cement clay modified by metakaolin and basalt fiber

Owing to the increase in human activities, a large number of construction and maintenance projects in cold regions are facing problems associated with cement soil materials. Undoubtedly, the cement soil structures are inevitably cured at negative temperature conditions. In the present study, the effects of curing temperature and curing age on the unconfined compressive strength (UCS), splitting tensile strength, E50, and failure mode of cement clay modified by metakaolin (CCM) and cement clay modified by metakaolin and basalt fiber (CCMB) were systematically studied. Moreover, the nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) tests were performed to investigate the characteristics of pore size distribution and microstructure of CCM and CCMB specimens at different curing temperatures. Test results indicate that negative curing temperature leads to the increase of peak strain, as well as the decrease in the decline rate of the post-peak stage of stress-strain curves. In addition, the curing age and positive curing temperature contribute to the increase of cement clay strengths, while the incorporation of basalt fiber shows opposite effects on the UCS and splitting tensile strength of CCMB specimens at two curing temperatures. The meso-pores and large-pores will transform into small-pores and micro-pores with the increase of curing age, and the values of total porosity and the proportion of meso-pores and large-pores of specimens at −10 °C curing temperature are higher compared with that at positive curing environment. Furthermore, negative curing temperature inhibits the cement hydration and destroys the bonding effect between basalt fiber and matrix.

Experimental study on the evolution of pore structure of coal samples under freeze–thaw

To investigate the effect of freeze–thaw on damage and pore structure characteristics, some coal samples were freeze-thawed by freeze–thaw test machines. The evolution law of the pore structure of coal samples under freeze–thaw cycles, the porosity, and the bound and free fluid volume of coal samples under freeze–thaw were studied by low nuclear magnetic resonance, the complexity of the pore structure of coal samples under different freeze–thaw cycles was analyzed by fractal dimension, and the influence mechanism of freeze–thaw on the pore structure of coal samples was discussed. The results indicate that: (1) freeze–thaw could damage the pore and fracture structure and reduce the wave velocity of coal samples, and the wave velocity of coal samples after 120 freeze–thaw cycles decreased 66.5% compared with that of before the freeze–thaw cycle. (2) Freeze–thaw can effectively promote the development of pore and fracture. With the increase in freeze–thaw cycles, the proportion of micropores of coal samples decreases, while the proportion of mesopores and macropores gradually increases. (3) The freeze–thaw cycle can promote the increase in the coal sample porosity, and the increment of total, residual, and effective porosity is 3.47%, 1.94%, and 1.53%, respectively, after 120 freeze–thaw. (4) The fractal dimension of total, adsorption, and seepage pore of coal samples all decrease with the increase in freeze–thaw cycles, indicating that liquid nitrogen can reduce the complexity of the pore structure and weaken the heterogeneity of the pore structure.

Study on influencing factors and mechanism of pore compressibility of tight sandstone reservoir—A case study of upper carboniferous in ordos basin

A series of studies were carried out on 11 tight sandstone samples of Upper Carboniferous in Ordos Basin. Firstly, the deposit composition and pore structure characteristics are investigated based on analysis and experiments including cast thin section scanning electron microscope high-pressure mercury intrusion and nuclear magnetic resonance Then, combined with DP-P test, the stress-dependent permeability change and pore compressibility characteristics of sandstone reservoirs were studied to reveal the influencing factors and mechanism of reservoir pore compressibility. The detrital particles of the sandstone reservoir in the study area are mainly quartz (75.8%–89%), followed by fragments (3%–16.1%), and almost no feldspar. The content of interstitial materials is 6.5%–11.2%. The type I reservoirs mainly consist of mesopores and macropores, accounting for 60.57% and 32.84% respectively. Mesopores are dominated in Type II reservoirs, accounting for 78.98% of the total pore volume. There are almost no macropores, while a similar proportion of mesopores, micro mesopores and micropores in the type Ⅲ reservoirs. The study of pore compressibility shows that the pore compressibility coefficient decreases with the increase of effective stress, and the reduction rate shows the two-stage characteristics of rapid in the early stage and slow in the later stage. The pressure turning point is between 3 and 10 MPa. The average pore compressibility coefficient increases from type I to type Ⅲ reservoirs. The compressibility coefficient is directly proportional to the changing rate of the pore volume. The higher the content of rigid detrital particles, quartz and carbonate cement in sandstone, the smaller the pore compressibility coefficient, while the higher the content of ductile components such as soft rock fragments and clay minerals, the greater the pore compression coefficient. The pore-throat structure is closely related to the pore compressibility, reservoirs with low displacement pressure, T2glm value, and large average pore-throat radius show lower compressibility coefficient. In addition, the compressibility coefficient of the reservoir is positively correlated with DL (dimension of large pores such as mesopores and macropores), and negatively correlated with DS (the fractal dimension of micropores and micro mesopores). It is considered the pore compression of sandstone including two stages, viscoplastic destructive deformation of ductile components for the first and then the small-scale non-ideal elastic deformation on rigid particles.

Pore Structure Multifractal Characteristics of Coal Reservoirs in the Central and Eastern Qinshui Basin and Influencing Factors

The heterogeneity of the pore structure of coal reservoirs affects the desorption and diffusion characteristics of coalbed methane, and determining its distribution law is conducive to improving the theory of coalbed methane development. The central and eastern parts of the Qinshui Basin are rich in coalbed methane resources, but the heterogeneity characteristics of the pore structure of coal reservoirs are not clear. NMR has the advantages of being fast, non-destructive and full-scale, and multifractal can describe the self-similarity of NMR T2 curve at different scales so as to analyze the complexity of pore distribution. Based on this, 15 samples with different coal ranks were collected from the central and eastern Qinshui Basin (Ro,max between 1.54 and 2.78%), and quantitative pore characterization experiments such as low-field nuclear magnetic resonance (LF-NMR) and low-temperature liquid nitrogen adsorption (LTN2A) were conducted. Based on multifractal theory, the heterogeneity law of pore structure was quantitatively evaluated, and its influencing factors were elucidated. The results showed that the BJH pore volume of coal samples in the study area ranged from 0.0005–0.0028 cm3/g, with an average of 0.0014 cm3/g, and the BET specific surface area was 0.07–2.52 m2/g, with an average of 0.41 m2/g. The NMR T2 spectrum peaked at 0.1–1, 10–100 and 100–1000 ms, and the spectrum was mostly bimodal or trimodal, indicating that pores of different pore sizes were developed. There were great differences in the pore structure of different coal ranks; high-rank coal was dominated by micropores, and the proportion of mesopores and macropores of medium-rank coal was higher. The pore structure of coal samples showed obvious multifractal characteristics, and the fractal characteristics of the sparse region (low-value information) were more significant; they dominated the pore distribution and had a stronger influence on the distribution of pore space. Pore structure heterogeneity is closely related to the degree of coalification, and with the increase in coalification, it is closely related to coal lithotype and quality, and high mineral and inertinite contents lead to the enhancement of pore structure heterogeneity in coal reservoirs, while Ro,max, Mad and vitrinite group contents have opposite effects. The research results provide theoretical guidance for the subsequent exploration and development of coalbed methane in the region.

Synthesis of hierarchical mesoporous cerium titanate brannerite and uranyl adsorption properties at pH 3.8.

Cerium titanates possessing brannerite structure are produced by employing soft and hard templates via sol-gel processing. Powders synthesized with various hard template sizes and template to brannerite weight ratios are composed of nanoscale 'building blocks' with size ∼20-30 nm and characterized on macro-, nano- and atomic scales. These polycrystalline oxide powders exhibit specific surface area up to ∼100 m2 g-1, pore volume ∼0.4 cm3 g-1, and uranyl adsorption capacity ∼0.221 mmol (53 mg) U per gram powder. Remarkably, the materials possess significant proportion of mesopores with 5-50 nm pores representing 84-98% of total pore volume, which facilitate fast accessibility of the adsorbate to the internal surfaces of the adsorbent with adsorbed uranyl reaching over 70% of the full capacity within 15 min of contact. These mesoporous cerium titanate brannerites synthesized by the soft chemistry route are highly homogenous, stable at least in 2 mol L-1 acidic or basic solution, and may attract attention for other applications like catalysis at high temperature.

Study on CO2 adsorption capacity and kinetic mechanism of CO2 adsorbent prepared from fly ash

The use of fly ash from coal-fired power plants for CO2 adsorption can reduce CO2 emissions and CO2 capture costs while making efficient use of power plant solid waste. In this study, fly ash was used to prepare aerogel support with good microstructure, and the support was impregnated with an incipient wetness impregnation method to make CO2 adsorbent. Adsorption experiments of CO2 adsorbents were carried out in a self-designed small fixed-bed reactor to study the influence of reaction conditions on the adsorption capacity of adsorbents. The results showed that the aerogel support prepared from fly ash had good microscopic properties with specific surface area and specific pore volume were 400 m2/g and 1.9 cm3/g, respectively. The pore structure was uniform, and the proportion of mesopores reached more than 99%. Under the reaction condition of 60 °C reaction temperature, 15% water vapor concentration, 15% CO2 concentration and 500 mL/min total gas flow rate, the maximum adsorption capacity of KA-30 adsorbent was 2.02 mmol/g. Avrami fractional kinetics model was used to calculate the cumulative adsorption capacity to study the adsorption kinetics. Combined with mass transfer kinetic model and deactivation model, the experimental breakthrough curve was fitted to study the adsorption mechanism of the adsorbent.