Nanopore Volume Research Articles

Influence of inherent mineral matrix on the geochemical reactions and pore structure evolution from shale oxidative dissolution

Oxidant stimulation presents a promising avenue for enhancing fluid mobility in shale reservoirs with ultra-low permeability and porosity. However, the effect of diverse minerals, major components of shale, on geochemical reactions and associated microstructures still warrants further exploration. In this study, we employed acid demineralization followed by oxidant stimulation to explore the impact of carbonate and silicate minerals on shale oxidative dissolution, considering both geochemical reactions and pore structures. Combined with artificial neural network (ANN) modeling, the dominance of shale composition on pore structures variation was further elucidated. Results demonstrated effective removal of carbonate and silicates minerals following treatment with HCl and HF acids. Interestingly, while silicate minerals exhibited greater mass loss in response to all oxidant stimulations, carbonate minerals only contributed to mass loss induced by Na2S2O8. Integration of X-ray diffraction, Fourier transform infrared spectroscopy, water chemistry and total organic content analysis revealed mineral- and oxidant-dependent geochemical reactions within the stimulation process. These included preferential dissolution of K-feldspar, dedolomitization accompanied by different precipitates, and transformation from quartz to albite, among other conventional reactions. The alteration in mineral and organic matter composition also induced variation in shale nanopores structures, resulting in increased specific surface area, nanopore volume, and average pore diameter induced by acid treatment, while the effects of oxidants varied. To better understand the relationship between shale composition and micropore structure, an ANN model was established to quantify this underlying connection, emphasizing the significant role of carbonate, chlorite, pyrite, and organic matter in shale oxidative dissolution. Our study provides further evidence for the influence of minerals on shale oxidative dissolution, offering insights for the engineering application of oxidant stimulation in shale gas extraction.

Detection of aldehydes from degradation of lipid nanoparticle formulations using a hierarchically-organized nanopore electrochemical biosensor

Degradation of ionizable lipids in mRNA-based vaccines was recently found to deactivate the payload, demanding rigorous monitoring of impurities in lipid nanoparticle (LNP) formulations. However, parallel screening for lipid degradation in customized delivery systems for next-generation therapeutics maintains a challenging and unsolved problem. Here, we describe a nanopore electrochemical sensor to detect ppb-levels of aldehydes arising from lipid degradation in LNP formulations that can be deployed in massively parallel fashion. Specifically, we combine nanopore electrodes with a block copolymer (BCP) membrane capable of hydrophobic gating of analyte transport between the bulk solution and the nanopore volume. By incorporating aldehyde dehydrogenase (ALDH), enzymatic oxidation of aldehydes generates NADH to enable ultrasensitive voltammetric detection with limits-of-detection (LOD) down to 1.2 ppb. Sensor utility was demonstrated by detecting degradation of N-oxidized SM-102, the ionizable lipid in Moderna's SpikeVax™ vaccine, in mRNA-1273 LNP formulation. This work should be of significant use in the pharmaceutical industry, paving the way for automated on-line quality assessments of next-generation therapeutics.

Molecular Simulation of the Impact of Defects on Electrolyte Intrusion in Zeolites.

We have investigated through molecular simulation the intrusion of electrolytes in two representative pure-silica zeolites, silicalite-1 and chabazite, in which point defects were introduced in varying amounts. We distinguish between two types of defects, considering either "weak" or "strong" silanol nest defects, resulting in different hydration behaviors. In the presence of weak defects, the hydration process occurs through a homogeneous nucleation process, while with strong defects, we observe an initial adsorption followed by a filling of the nanoporous volume at a higher pressure. However, we show that electrolytes do not penetrate the zeolites, and these defects appear to have only marginal influence on the thermodynamics of electrolyte intrusion. While replacing pure water by the electrolyte solution shifts the intrusion pressure toward higher values because of the drop of water saturation vapor pressure, an increase in hydrophilicity of the framework due to point defects has the opposite effect, showing that controlling the amount of defects in zeolites is crucial for storage energy applications.

Microstructure changes induced by adsorption/desorption of low rank coals and its desorption hysteresis mechanism

Adsorption/desorption behavior and its hysteresis phenomenon of coalbed methane (CBM) make a critical contribution to estimate CBM recovery. Hence, to investigate the adsorption/desorption mechanism of low rank coals, this study compared the adsorption/desorption characteristics of methane in different rank coals through isotherm adsorption/desorption experiments and then analyzed the changes in microstructure before and after adsorption/desorption. Thus, the coupling relationship among chemical structure, nanopores and gas adsorption/desorption and the desorption hysteresis mechanism for low rank coals were revealed. Results show that the isosteric adsorption heat and desorption hysteresis coefficient present a decreasing first and then increasing trend with coalification from isotherm adsorption/desorption curves and thermodynamic characteristics. Specially, for low rank coals, as the degree of thermal evolution increases, the desorption hysteresis coefficient increases from 0.27 to 0.39 during low metamorphism stage. Then, compared the nanopore structure distribution and microcrystalline structure characteristics before and after adsorption/desorption, methane adsorption/desorption behavior not only promotes the pore expansion effect of ultra-micropores, but also leads to a swelling effect of basic structure unit (BSU). Furthermore, it can be found that as the BSU increases, the specific surface area (SSA) and pore volume (PV) of nanopores in coal increase, which directly controls the adsorption space. Meanwhile, the adsorption/desorption behavior can also induce the BSU swelling to change nanopore structure distribution, especially micropores and ultra-micropores. Finally, concerning desorption hysteresis effect, its esssence can actually be explained by the energy difference and microstructure. All these findings would provide the theorical guidance for CBM development in low rank coals.

Fracture of Fe95Ni5 Alloys with Gradient-Grained Structure under Uniaxial Tension

The fracture behavior of single- (fcc) and two-phase (fcc + bcc) Fe95Ni5 samples with gradient-grained structure, under uniaxial tension, was analyzed via molecular dynamics simulation. The study revealed that fracture initiation and propagation is always associated with grain boundaries. The fracture process develops in three stages. In the first stage, nanopores are formed in the boundaries of coarse grains. The total volume of nanopores at this stage increases slowly due to the formation of new nanopores. The second stage is characterized by a rapid increase in the total nanopore volume due to the formation of nanopores, their growth along the grain boundaries, and their coalescence. At the third stage, the total nanopore volume increases linearly with deformation due to the growth of the largest nanopores. Fracture of two-phase samples begins at higher strains compared to a single-phase sample. With an increase in the volume fraction of bcc lamellae in the original sample, the number of nanopores at the third stage of fracture decreases and tends to one.

Effect of litho-facies on nano-pore structure of continental shale in shuinan formation of Jiaolai Basin

Continental shale lithofacies has an important influence on nano-pore structure? However, nano-pore distribution heterogeneity (NDH) in continental shale lithofacies is not well documented. Continental shale was collected from the Shuinan Formation in the Jiaolai Basin, and the shale lithofacies of all samples are identified based on the mineralogical composition and TOC content. Nano-pore size distributions are characterized by LPN2 and CO2GA tests. Then, micro-pore (0.3∼2 nm) and meso-pore (2∼100 nm) distribution heterogeneity of different facies are discussed by single and multi-fractal model. Finally, the pore structure mechanism in shale lithofacies is clarified, and the results are as follows. The lithofacies of all shale samples are classified into three types, (A) calcareous shale lithofacies is characterized by the higher siliceous minerals and highest TOC content; (B) Calcareous/siliceous mixed shale lithofacies is characterized by middle TOC content; (C) Siliceous shale lithofacies is characterized by higher clay minerals and lowest TOC content. Micro- and meso-pore volume and A shale lithofacies NDH is much lower than that of B and C, which indicates that the lithofacies type has a great influence on the nano-pore structure. Felsic mineral and TOC content has a weak negative correlation with nano-pore structure, and there is a linear relationship between clay mineral content and nano-pore volume, indicating that clay mineral content is the main factor that can affect nano-pore structure. Moreover, fractal characteristics of the nitrogen desorption curve have been proved, and there are obvious differences in the fractal values of adsorption and desorption curves among those different lithofacies. Single fractal dimension D1 derived from LPN2 and CO2GA tests has a linear correlation with the multifractal parameter D-10-D0, which shows that a lower pore volume of pore diameter determines NDH variation. In conclusion, siliceous rich shale can provide a larger pore volume and specific surface area, and it acts as the dominant lithofacies for shale gas drainage in the study area.

Reservoir Characteristics and Gas Content of Black Shale of Wufeng-Longmaxi Formation in Qianjiang Area, Southeast Chongqing, China

The shale gas exploration in Changning, Weiyuan, Fuling Jiaoshiba, and other areas has achieved great success in the Sichuan Basin, and the basin margin of the Sichuan Basin will be an important target in the future. In view of the lack of understanding of shale gas reservoir characteristics of the basin margin area of the Sichuan Basin, this paper conducts a study on reservoir characteristics and gas-bearing properties of this area using qualitative and quantitative techniques. The results show that the thickness of the black shale reservoir in the Qianjiang area is up to 33 m, the kerogen sapropelic type (I) is dominant, and Ro ranges from 2.2 wt% to 3.39 wt%. The mineral composition is relatively complex, mainly composed of quartz and clay minerals. Quartz content is in the range between 9.4 wt% and 79 wt% ( average = 47.48 wt % ), while clay content is in the range between 10.02 wt% and 43.6 wt% ( average = 29.41 wt % ). There are various types of reservoir spaces, mainly including organic pores dominated by matrix pores, intergranular and intragranular pores, intergranular and intragranular dissolution pores, secondary dissolution pores, and microfractures, among which organic pores are the main pore types. The pore volume of nanopores is 0.009897-0.017177 cm3/g ( average = 0.01304 c m 3 / g ), and the specific surface area ranges from 12.1 m2/g to 35.1 m2/g ( average = 20.47 m 2 / g ). Micropores and mesopores are the main pore sizes for the development of organic pores. Quartz particles promote the development of reservoir space, while clay minerals are not conducive to the development of pores. The total gas content ranges from 0.5 m3/t to 4.43 m3/t ( average = 1.69 m 3 / t ). Its enrichment is controlled by many factors. The increase of organic matter abundance is the material basis for shale gas enrichment. The development of organic pores provides high-quality storage space for shale gas preservation. The development of different mineral components restricts the enrichment of shale gas.

Effect of Petroleum Generation and Retention on Nanopore Structure Change in Laminated and Massive Shales-Insights from Hydrous Pyrolysis of Lacustrine Source Rocks from the Permian Lucaogou Formation.

The lacustrine shale of the Middle Permian Lucaogou Formation in the Jimusar Sag is the principal prospective unconventional target in the Junggar Basin. The effect of petroleum generation and retention on nanopore structure change during thermal maturity in lacustrine shale is still unclear. In this study, two laminated and two massive shale samples from the Permian Lucaogou Formation were selected to study this change by closed hydrous pyrolysis. The pyrolysis temperatures were 295, 320, 345, 370, and 400 °C, which cover from the mature to the post-mature stage. Total organic carbon (TOC), Rock-Eval, and low-pressure N2 adsorption tests on pyrolyzed shale samples before and after extractable organic matter (EOM) extraction were conducted systematically. The results indicate that (1) the petroleum generation on nanopore structure change is in stages. The peak nanopore volume expanding stage is the late oil window (R o = 0.9-1.35%). At the post-mature stage (R o > 1.35%), the mesopore volume decreased and the majority of the nanopore space is from macropores. (2) The presence of EOM decreased both mesopores and macropores in the peak oil window. (3) The organic-rich laminated shale generated more macropores than massive shale with increasing thermal maturity. The results of this study shed light on the dynamic effect of laminae fabric, petroleum generation, and retention on shale nanopore structure change across the oil window.

Structure and energetics of hydrogen bonding networks in dilute HOD/H2O solutions confined in silica nanopores

Nanoconfinement in silica nanopores strengthens hydrogen bonds near surfaces, and weakens hydrogen bonds in nanopore volume away from the surfaces.

Multiscale Pore Structure Evolution of Longmaxi Shale Induced by Acid Treatment

SummaryHydraulic fracturing to generate complex fracture networks is essential for shale reservoir development. However, the recovery of shale oil and gas is still low due to various engineering and geological factors. Acid treatment has been approved as a potential approach to enhance stimulated reservoir volume (SRV) by changing petrophysical and mechanical properties. Understanding the multiscale pore structure evolution behind the macro-performance change is critical in the application of acid treatment in shale reservoirs. In this study, cylindrical and powder shale samples from the Longmaxi formation are treated with 15 wt% hydrochloric acid (HCl) for 10 days. Before and after acid treatment, X-ray computed tomography (CT) and N2 adsorption techniques are used to characterize shale pore structure at microscale and nanoscale, respectively. Combined with the determination of variations in chemical compositions of shale samples and acid solutions, the mechanism of multiscale pore structure evolution induced by acid treatment is discussed. The N2 adsorption results uncover a considerable increase in volume and size of nanopores. All the nanopores increase in carbonate-rich shale, whereas the micropores and mesopores undergo a decrease in clay-rich shale. Reconstructed 3D CT images reveal the generation of large volumes of microscale pores and fractures, which leads to an increase in porosity of about 9%. The pore structure evolution in shale due to acid treatment is controlled by both mineralogy and microstructure. These findings demonstrate the promise of acid treatment for enhanced SRV and long-term productivity of shale oil and gas reservoirs in China.

Apparent diffusion coefficient for adsorption-controlled gas transport in nanoporous media

We present an apparent diffusion coefficient derived from a diffusion-based mass conservation equation for single-component gas transport in nanoporous media. Multiple transport and storage mechanisms have been considered, including Knudsen diffusion and viscous flow for the free phase and surface diffusion and multilayer adsorption for the sorbed phase. The real gas effect, confinement effect, and dynamic adsorption layer thickness are also considered. A pore-scale simplified local density method is utilized to obtain sorbed phase properties, such as volume fraction, concentration, and adsorption isotherm. The developed apparent diffusion coefficient is applied to investigate the effects of fluid–solid attraction, fluid–solid species, and pore sizes on the gas diffusion and adsorption in nanoporous media. The results reveal that the sorbed phase occupies a significant volume of nanopores, and the entire pore space becomes sorbed-phase volume in pores with diameters ≤ 2 nm. The total mass transport in these pores is dominated by surface diffusion, and free-phase diffusion contribution increases as the pore size increases. Furthermore, in strong adsorption systems such as CO2-coal, the apparent diffusion coefficient is up to two orders of magnitude smaller than in weak adsorption systems (e.g., N2-coal and CH4-coal). This is attributed to the reduced free-phase volume fraction and increasing adsorption capacity. The proposed apparent diffusion coefficient can be used in the diffusion-based models for gas transport in nanoporous media.

Pore Structure in Shale Tested by Low Pressure N2 Adsorption Experiments: Mechanism, Geological Control and Application

The N2 adsorption experiment is one of the most important methods for characterizing the pore structure of shale, as it covers the major pore size range present in such sediments. The goal of this work is to better understand both the mechanisms and application of low-pressure nitrogen adsorption experiments in pore structure characterization. To achieve this, the N2 adsorption molecular simulation method, low-pressure N2 adsorption experiments, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and a total of 196 shale samples from the Wufeng–Longmaxi formations in the Sichuan basin have been employed in this study. Based on the analytical data and the simulations, two parameters, the connectivity index and the large pore volume index, are proposed. These parameters are defined as the connectivity of the pore system and the volume of large nanopores (>10 nm) respectively, and they are calculated based on the N2 adsorption and desorption isotherms. The experimental results showed that TOC content and clay minerals are the key factors controlling surface area and pore volume. However, in different shale wells and different substrata (divided based on graptolite zonation), the relative influences of TOC content and clay minerals on pore structure differ. In three of the six wells, TOC content is the key factor controlling surface area and pore volume. In contrast, clay minerals in samples from the W202 well are the key factors controlling pore volume, and with an increase in the clay mineral content, the pore volume increases linearly. When the carbonate content exceeds 50%, the pore volume decreases with an increase in carbonate content, and this may be because in the diagenetic process, carbonate cement fills the pores. It is also found that with increasing TOC content the connectivity index increases and SEM images also illustrate that organic pores have better connectivity. Furthermore, the connectivity index increases as quartz content increases. The large pore volume index increases with quartz content from 0 to 40% and decreases as quartz increases from 40% to 100%. By comparing the pore structure of shale in the same substrata of different shale gas wells, it was found that tectonic location significantly affects the surface area and pore volume of shale samples. The shale samples from wells that are located in broad tectonic zones, far from large-scale faults and overpressure zones, have larger pore volumes and surface areas. On the contrary, the shale samples from shale gas wells that are located in the anticline region with strong tectonic extrusion zones or near large-scale faults have relatively low pore volumes and surface areas. By employing large numbers of shale samples and analyzing N2 adsorption mechanism in shale, this study has expanded the application of N2 adsorption experiment in shale and clarifies the effects of sedimentary factors and tectonic factors on pore structure.

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.

Nanopore Structure and Origin of Lower Permian Transitional Shale, Eastern Ordos Basin, China

Nanopores in the shale play a vital role in methane adsorption, and their structural characteristics and origins are of great significance for revealing the mechanism of methane adsorption, desorption, and diffusion. In this paper, through low-temperature ashing and low-pressure gas adsorption experiments, the nanopore structure of original shales and ashed shales was quantitatively characterized, and the nanopore origins in the transitional shale of lower Permian in eastern Ordos Basin were analyzed. The results show that the pore volume (PV) and specific surface area (SSA) of nanopores in transitional shale reservoirs are 0.0217–0.0449 cm3/g and 13.91–51.20 m2/g, respectively. The average contribution rates of micropores (<2 nm), mesopores (2–50 nm), and macropores (50–100 nm) to PV are 18.78, 72.26, and 8.96%, respectively, and the average contribution rates to SSA are 66.19, 33.10, and 0.71%, respectively. In addition, it is found that the average contribution rates of inorganic minerals and organic matter to the SSA of micropores are 55.9 and 44.1%, respectively, and the average contribution rates to the SSA of mesopores are 92.3 and 7.7%, respectively. Combining the adsorption properties of the main clay minerals and kerogen in shale, it is concluded that organic pores control the adsorption of methane with an absolute advantage in transitional shales. It is of great significance to understand the mechanism of methane occurrence, desorption, and diffusion in shales by clarifying the origins of multiscale pores.

The effect of oil extraction on porosity and methane adsorption for dry and moisture-equilibrated shales

The porosity and methane adsorption capacity of shale used to estimate gas in place (GIP) are affected both by moisture and oil residing in the pore structure, as well as oil naturally present from maturation, which can include contaminant drilling mud fluids used for drilling. To demonstrate the impact of extractable oil on methane adsorption capacity for both dry and moisture-equilibrated shales, two overmature shales from China (SH1, SH2) and two lower mature shales from UK (BS3, GH4) have been investigated. The oils extracted from the overmature shales (<0.5 wt% TOC) are in low yield and arise from oil-based drilling mud, while the much higher yields from the lower maturity UK shales (1.1–2.5 wt% TOC) is mainly from oil generated by maturation. After extraction, minimal changes (<5%) in total nanopore volume (<100 nm) were observed for the dry over mature shales, but significant increases (95 and 176%) were observed for the dry lower maturity shales. More than 60% of the extracted oil resides in micro and mesopores, and removal could unblock the micropore necks and enlarge the accessible meso and macropore volume. Moisture contents are lower for extracted shales, with reductions of 7–37% observed. Methane equilibrium adsorption capacities increased after oil extraction for both the dry and wet shales, especially for lower maturity shales, where increases were over 200% for the wet shales. Henry’s Law was used to show that there were not significant amounts of dissolved methane in oils for the dry shales. Extracting oil from shales prior to determining the porosity and methane adsorption capacity can lead to the GIP being over-estimated for moisture equilibrated shales, particularly for oil-window shales where an overestimation of 22% was obtained for the shale investigated in this study. These findings provide a better understanding of the combined impacts of residual oil and water on GIP and avoid its overestimation.

Effects of spodumene flotation tailings as aggregates on mechanical properties of cement mortar

This work explored the use of spodumene flotation tailings (SFT) as an aggregate used in cement mortar to mitigate their environmental impact. The principal phase compositions of SFT were quartz (Qtz), feldspar (Fsp) and muscovite (Ms). So, the effects of variations in the particle size of Qtz, and mineral additives, Ms and Fsp, on the compressive strength and hydration products were examined. Ms additives imparted the lowest compressive strength. Finer Qtz aggregates (4000–106 µm) reduced the nano-pore volume, and Ms increased the nano-pore width of cement mortar. In addition, fewer hydration products, and poor crystallinity of both ettringite (Aft) and portlandite resulted in a decrease in the compressive strength of the cement mortar, eventually. Therefore, increasing the particle size or optimisation of the mineral composition of SFT could provide a facile route to improving the mechanical properties of cement mortars.

Preparation and characterization of low-κ polyhedral oligomeric silsesquioxane/polyimide hybrid films

A series of Polyimide (PI)/Phenyl-POSS (POSS) hybrid films with low dielectric constants and excellent comprehensive properties have been successfully prepared via physical blend methods by incorporating different proportions of POSS into the polyimide precursors (Pyromellitic dianhydride- 4, 4′-Diaminodiphenyl ether). An appropriate amount of POSS doping can effectively improve the optical and dielectric properties of hybrid films due to the contribution of POSS with hollow, cage-like molecular structure to weakening intermolecular charge transfer complexation and increasing nanopore volume fraction in hybrid films. Instead, excessive amount of POSS doping can reduce dielectric properties due to the interface polarization effect induced by POSS agglomeration. When the doping amount is 15%, the highest light transmission reaches to 84.5%. When the doping amount is 25%, the dielectric properties have been are best improved. The dielectric constant and loss at 104 Hz are reduced to 2.37 and 0.0018 respectively. However, the mechanical properties decrease in response to the increase of POSS content, because POSS molecular dispersing in the folded molecular chains hinders the interaction of molecular chains PI matrix. The correlation between the dielectric properties of PI/POSS films and their nonopore volume fraction has been explained with the help of positron lifetime spectra.

Effect of Pt Loading Percentage on Carbon Blacks with Large Interior Nanopore Volume on the Performance and Durability of Polymer Electrolyte Fuel Cells

Achieving high performance and durability at low Pt loads is an important challenge for polymer electrolyte fuel cells (PEFCs). We investigated the effect of catalyst Pt loading percentage (wt % Pt) on the performance and durability of an ultrahigh surface area carbon black (CB) with a large nanopore volume using morphological observations, nitrogen adsorption, and electrochemical performance measurements. The ratio of the surface areas of Pt on the interior and exterior surfaces of the CB affects the penetration of the ionomer into the nanosized pores. When the exterior Pt surface area is larger than that of the interior, the oxygen diffusion resistance in the ionomer increases and the performance deteriorates due to the thick covering of the ionomer on the exterior Pt. Based on durability testing that combines startup, shutdown, and galvanostatic load cycling, the main deterioration factors are dependent upon the Pt interparticle distance and the thickness of the catalyst layer, which vary with the wt % Pt. The advanced characterization and optimization of the various wt % Pt on an ultrahigh surface area CB, combined with the extensive performance and durability testing, have provided an unprecedented understanding of the reaction sites, mass transport characteristics, and stability, which are crucial for their practical application in PEFCs.

Actively Controllable Solid-Phase Microextraction in a Hierarchically Organized Block Copolymer-Nanopore Electrode Array Sensor for Charge-Selective Detection of Bacterial Metabolites.

Pseudomonas aeruginosa produces a number of phenazine metabolites, including pyocyanin (PYO), phenazine-1-carboxamide (PCN), and phenazine-1-carboxylic acid (PCA). Among these, PYO has been most widely studied as a biomarker of P. aeruginosa infection. However, despite its broad-spectrum antibiotic properties and its role as a precursor in the biosynthetic route leading to other secondary phenazines, PCA has attracted less attention, partially due to its relatively low concentration and interference from other highly abundant phenazines. This challenge is addressed here by constructing a hierarchically organized nanostructure consisting of a pH-responsive block copolymer (BCP) membrane with nanopore electrode arrays (NEAs) filled with gold nanoparticles (AuNPs) to separate and detect PCA in bacterial environments. The BCP@NEA strategy is designed such that adjusting the pH of the bacterial medium to 4.5, which is above the pKa of PCA but below the pKa of PYO and PCN, ensures that PCA is negatively charged and can be selectively transported across the BCP membrane. At pH 4.5, only PCA is transported into the AuNP-filled NEAs, while PYO and PCN are blocked. Structural characterization illustrates the rigorous spatial segregation of the AuNPs in the NEA nanopore volume, allowing PCA secreted from P. aeruginosa to be quantitatively determined as a function of incubation time using square-wave voltammetry and surface-enhanced Raman spectroscopy. The strategy proposed in this study can be extended by changing the nature of the hydrophilic block and subsequently applied to detect other redox-active metabolites at a low concentration in complex biological samples and, thus, help understand metabolism in microbial communities.

Exploring the coupling relationship between hydrocarbon generation of continental shale and nanopore structure evolution\u2014A case study of Shahejie formation in Bohai Bay Basin

The nano-scale pore structure of shale is closely related to the self-generated and self-accumulated shale oil and gas. The Bohai Bay Basin is a crucial oil-bearing basin in eastern China, and the Paleogene Shahejie Formation is the most important source rock section in this area. In order to study the internal relationship between hydrocarbon generation evolution and pore structure characteristics of source rocks, we conducted hydrocarbon generation simulation tests with a closed gold tube system, and heated up original rocks from Shahejie Formation in Laizhou Bay Sag, southern Bohai Bay Basin, from 290 °C to 440°C at different heating rates. Besides, we carried out low-temperature N2 adsorption experiments on sample residues, and measured their pore structure characteristic parameters. The results show that with the increase of simulated temperature, the specific surface area and pore volume of nano-pores below 10 nm (which are mainly organic pores) decrease first and then increase, while those of nano-pores above 10 nm increase all the way. The evolution trend of total specific surface area and pore volume is mainly controlled by pores below 10 nm which are mainly organic pores, especially micropores below 2 nm. There are two main factors affecting the development of inorganic pores: (1) Dissolution of organic acids produced by pyrolysis of organic matter in hydrocarbon-generation evolution; (2) Deformation of crystal structure of mineral components under the combined action of temperature and pressure. The experimental results at different heating rates demonstrate that rapid settlement under geological conditions is not conducive to the development of nano-pores, especially micro-pores composed of organic pores.