Search Results (280)

Creep and stress sensitivity can lead to the long-term conductivity degradation of fractures, and this influences the accuracy of long-term productivity predictions in ultra-deep carbonate reservoirs (UDCRs). However, the current models do not consider these two factors. For the long-term conductivity degradation of acid-etched symmetry fractures in UDCRs, a new fracture permeability evolution model incorporating creep and stress sensitivity effects was established. Building upon this, a numerical simulation model for UDCRs was developed for the first time to quantitatively analyze the impacts of creep, stress sensitivity, and production strategies on well productivity. The research revealed that the creep and stress sensitivity characteristics of acid-etched fractures had a significant impact on the well productivity for UDCRs. The larger the creep coefficient and stress sensitivity coefficient, the lower the oil well productivity. The larger the initial reservoir pressure and drawdown pressure, the higher the daily production and cumulative production of the oil well, but the cumulative production growth rate decreased. The cumulative production in the early stage of the released-pressure production was significantly higher than that of the pressure-controlled production, but with the increase in the pressure-controlled time, the cumulative production reversed. When the pressure was controlled for three years, the cumulative production increased by 5952 m³ (38.8%); as the creep coefficient increased, the cumulative production increased by greater than the pressure-released production. This shows that the larger the creep coefficient, the better the effect of controlling pressure production. The research results can provide a theoretical basis and technical support for the efficient development of UDCRs. Full article

This study addresses the efficiency and cost challenges of hydrogen evolution reaction (HER) catalysts in the context of carbon neutrality strategies by employing a synergistic approach that combines cation vacancy anchoring and transition metal doping on two-dimensional (2D) MXenes. Using an in situ LiF/HCl etching process, the aluminum layers in Ti₃AlC₂ were precisely removed, resulting in a few-layer Ti₃C₂T_x MXene with an increased interlayer spacing of 12.3 Å. Doping with the transition metals Fe, Co, Ni, and Cu demonstrated that Fe@Ti₃C₂ provided the optimal HER performance, characterized by an overpotential (η₁₀) of 81 mV at 10 mA cm⁻², a low Tafel slope of 33.03 mV dec⁻¹, and the lowest charge transfer resistance (R_ct = 5.6 Ω cm²). Mechanistic investigations revealed that Fe’s 3d⁶ electrons induce an upward shift in the d-band center of MXene, improving hydrogen adsorption free energy and reducing lattice distortion. This research lays a solid foundation for the design of non-precious metal catalysts using MXenes and highlights future avenues in bimetallic synergy and scalability. Full article

This study synthesized boron-doped diamond (BDD) thin films using hot-filament chemical vapor deposition at different carbon-to-hydrogen (C/H) ratios in the range of 0.3–0.9%. The C/H ratio influence, a key parameter controlling the balance between diamond growth and hydrogen-assisted etching, was systematically investigated while maintaining other deposition parameters constant. Microstructural and electrochemical analysis revealed that increasing the C/H ratio from 0.3% to 0.7% led to a reduction in sp2-bonded carbon and enhanced the crystallinity of the diamond films. The improved conductivity under these conditions can be attributed to effective substitutional boron doping. Notably, the film deposited at a C/H ratio of 0.7% exhibited the highest electrical conductivity and the widest electrochemical potential window (2.88 V), thereby indicating excellent electrochemical stability. By contrast, at a C/H ratio of 0.9%, the excessively supplied carbon degraded the film quality and electrical and electrochemical performance, which was owing to the increased formation of sp² carbon. In addition, this led to an elevated background current and a narrowed potential window. These results reveal that precise control of the C/H ratio is critical for optimizing the BDD electrode performance. Therefore, a C/H ratio of 0.7% provides the most favorable conditions for applications in advanced oxidation processes. Full article

Due to its widespread distribution in industrial, commercial, and residential settings, xylene detection is crucial. In this study, carbon sphere templates and NaHCO₃ etching were used to synergistically prepare WO₃ with uniform macropores, which was then decorated with Au elements. The findings demonstrated that the Au-decorated WO₃-etched sample (WO₃-1%E+Au) had the best sensing performance for 100 ppm xylene (response value: 21.3, optimal operating temperature: 360 °C) and short response/recovery time (1 s/11 s). The etching of NaHCO₃ and the synergistic carbon sphere templates were responsible for the sensing performance, as they enhanced the sample surface’s specific surface area and roughness while also supplying additional active sites. Furthermore, the sensor’s sensitivity and selectivity to xylene were enhanced by the coupling effect and dehydrogenation catalysis of the noble metal Au. The results of this work advance our knowledge of gas-sensing mechanisms and offer guidance for the creation of extremely sensitive and selective xylene gas sensors. Full article

We studied the chemical composition and morphostructural features of micron and submicron-sized particles of native gold in apocarbonate tremolite–diopside skarns of the Ryabinovoye deposit located on the southeastern margin of the Aldan Shield (Far East, Russia). Polished sections of lump ore samples containing native gold were analyzed by scanning electron microscopy in combination with X-ray microanalysis using different modes of visualization and X-ray diffraction methods. Gold particles, clearly visible after etching the surface of some polished sections with acids and partial or complete dissolution of some host minerals, were also examined. Native gold from the studied deposit is of high fineness (above 970‰) and contains (in wt.%) <1.59 Ag and less commonly <0.37 Cu and <0.15 Zn. Native gold is found intergrown with tremolite, diopside, and other magnesian silicates, as well as calcite, fluorite, magnetite, and sphalerite. Rare microinclusions of pyrrhotite, galena, and clinohumite are present in gold grains. It was found that native gold inherits the morphology of tremolite crystals and aggregates, which is determined by the size and shape of the voids bounded by its crystals. Gold localized in the intercrystalline spaces and in the zones of conjugation with remobilized calcite has irregular, lumpy shapes and partially or completely faceted grains with a dense structure. The nature of the localization and distribution of native gold in ores is due to the crystallization of the tremolite component of skarns. Apparently, the processes of gold accumulation are caused by the thermal activation of solid-phase differentiation of the substance of carbonate rocks, in which the processes of destruction of the original minerals and collective recrystallization play a significant role. It is likely that at some gold skarn deposits, carbonate rocks could be the source of gold. Data on the morphology and sizes of native gold segregations, as well as on the intergrown minerals, can be used to improve gold extraction technologies. A specific group of minerals intergrown with native gold in gold skarn deposits can be used as a diagnostic feature in the primary search for placer gold. The obtained results will help to better understand the formation of native gold in apocarbonate tremolite–diopside skarns. Full article

Biochar modification represents an effective approach for enhancing adsorption capacity. In the research, industrial hemp straw-derived biochar was synthesized through hydrothermal carbonization coupled with ultrasound-assisted KOH activation, demonstrating exceptional Pb²⁺ adsorption efficiency. The optimal HBS50-K0.5M exhibited excellent adsorption performance, achieving the maximum adsorption capacity of 345.8 mg/g within 2 h. The etching effect of KOH on the biochar surface increased the O-containing functional groups, which enhanced the adsorption of Pb²⁺. The adsorption kinetics revealed that the adsorption process of Pb²⁺ was aligned with the pseudo-second-order kinetics as well as the Langmuir model. The complexation, ion exchange, π-π interaction, as well as electrostatic interaction participated in the adsorption. This study demonstrates that ultrasound-assisted KOH-activated biochar has great potential for removing Pb²⁺ from wastewater. Full article

Negative temperature environments inhibit bacterial survival in cementitious materials and reduce the self-healing ability of bacteria. To address this challenge, acid-etched alumina hollow spheres are proposed as carriers to encapsulate microorganisms in cementitious materials. The effects of these carriers on the mechanical properties, thermal conductivity, self-healing properties, and self-healing products of specimens after exposure to −20 °C were investigated. Finally, the self-healing mechanism was examined and analyzed. The results demonstrated the effectiveness of the acid-etched hollow microbeads as bacterial carriers. The addition of the alumina hollow spheres participating in the cement hydration reaction enhanced the mechanical properties of the mortar and reduced its thermal conductivity, which supported bacterial survival in the negative temperature environment. Although negative temperature environments may reduce bacterial populations, the hydrolysis of aluminum ions in the alumina hollow spheres during bacterial metabolism resulted in the precipitation of aluminum hydroxide flocs. These flocs adsorbed free calcium carbonate in the pores, converting it into effective calcium carbonate with cementing properties, thus enhancing the crack healing capability of the examined specimens. This microbe-based self-healing strategy, utilizing alumina hollow spheres as bacterial carriers, is anticipated to provide an effective solution for achieving efficient crack self-healing in mortars that is resistant to the detrimental effects of negative temperature conditions. Full article

Supercapacitors (SCs) have garnered significant attention due to their high power density and long cycle life. Among the various electrode materials, carbon materials have emerged as a focal point of research owing to their superior conductivity, stability, and reproducibility. However, the relatively low specific capacitance and specific surface area of carbon materials result in suboptimal electrochemical performance, which seriously hinders their practical applications. This work introduces a straightforward yet effective strategy for constructing hollow nano-cage structures by tannic acid etching of ZIF-8. In this process, tannic acid releases protons that selectively etch the MOF structure, while the residual large molecules adhere to the ZIF-8 surface, stabilizing its framework and preventing structural collapse. Following high-temperature heat treatment, novel hollow nitrogen-doped carbon nano-cage structures (HNCs) are successfully synthesized. Electrochemical tests reveal that the material has a capacity of 349.3 F g⁻¹ at a current density of 0.5 A g⁻¹, and still has a coulombic efficiency of 97.61% as well as a capacity retention of 97.86% after cycling for 10,000 cycles at a current density of 3 A g⁻¹. Therefore, this study provides a novel way to explore the application of carbon materials with excellent electrochemical performance for energy storage. Full article

Amorphous carbon and its heteroatom-doped derivatives often exhibit wrinkled, defective, porous structures, and find wide applications in the fields of energy storage and catalysis. To date, although many methods for preparing doped carbon materials have been reported, the preparation process is relatively complex, and there are still few simple methods available. Therefore, it is necessary to further develop simple and feasible preparation methods. In this study, we employed commercially available manganese disodium ethylenediaminetetraacetate (EDTA-Na₂Mn, serving as both carbon and nitrogen sources) as the precursor. Through thermal decomposition under a nitrogen atmosphere, a nitrogen-doped carbon composite embedded with manganese monoxide (MnO) was initially obtained. Subsequently, hydrochloric acid etching was applied to remove the MnO phases, yielding the final product: nitrogen-doped carbon, denoted as C-N-Mn. Notably, the carbonization and nitrogen-doping processes were simultaneously accomplished during pyrolysis, thereby streamlining the synthesis route for nitrogen-doped carbons. To demonstrate the versatility of this approach, we extended the methodology to two additional metal–organic salts (EDTA-Na₂Zn and EDTA-NaFe), successfully synthesizing nitrogen-doped carbon materials (C-N-Zn and C-M-Fe) in both cases. The phase composition, morphology, microstructure, specific surface area, and pore volume of the products were systematically characterized using X-ray diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption/desorption analysis. These nitrogen-doped carbons exhibit high specific surface areas and tunable pore volumes, suggesting their potential applicability in energy storage systems. Full article

Recently, there has been an increasing emphasis on improving the performance of metal components across various industries, such as automotive, aerospace, electronics, medical devices, and military applications. However, the challenges related to efficient heat generation and transfer in equipment and devices are becoming increasingly critical. A solution to these issues involves the adoption of a metal–composite hybrid structure, designed to efficiently manage heat, while substituting conventional metal components with polymer–carbon composites. In this study, nanopores were formed on the metal surface using an anodization process, serving as the basis for creating 3D-printed polymer/metal hybrid constructions. Various surface treatments, including plasma treatment, mixed electrolyte anodization, and etching, were applied to the metal surface to enhance the bonding strength between the 3D-printed polymer and the aluminum alloy. These processes were essential for developing lightweight polymer/metal hybrid structures utilizing a range of 3D-printed polymer filaments, such as polylactic acid, thermoplastic polyurethane, acrylonitrile butadiene styrene, polypropylene, thermoplastic polyester elastomer, and composite materials composed of polymer and carbon. In particular, the hybrid structures employing polymer–carbon composite materials demonstrated excellent heat dissipation characteristics, attributed to the remarkable conductive properties of carbon fibers. These technologies have the potential to effectively address the device heat problem by facilitating the development of lightweight hybrid structures applicable across various fields, including automotive, mobile electronics, medical devices, and military applications. Full article

Pore–fracture carbonate gas reservoirs exhibit complex pore–throat structures and significant heterogeneity. Formation water can easily migrate along fractures, leading to extensive water-sealed gas accumulation, which severely limits the recovery rate of such reservoirs. To further investigate the water invasion process and the distribution characteristics of water-sealed gas in these reservoirs, a microscopic visualization model was developed using core CT scanning and laser etching technologies, incorporating the actual fracture sizes. The effects of fracture size, fracture density, and permeability heterogeneity on the microscopic distribution of water-sealed gas were analyzed in detail. The results indicate the following findings: (1) Homogeneous fracture size leads to a smaller extent of water-sealed gas accumulation. The ultimate gas saturation in the homogeneous fracture model is 5.79% lower than that in the heterogeneous model. (2) An increase in fracture density helps reduce the volume of water-sealed gas. The ultimate gas saturation in the high-density fracture model is 2.58% lower than in the low-density model. (3) The presence of seepage channels at the reservoir boundary with significant permeability heterogeneity exacerbates the accumulation of water-sealed gas and accelerates water invasion. Full article

A supercapacitor’s energy storage capability is greatly dependent on electrode materials. Layered double hydroxides (LDHs) were extensively studied as battery-type electrodes because of their 2D structure and quick intercalation/deintercalation of electrolyte ions. However, the energy storage capability for pristine LDHs is limited by their large aggregation tendency and poor electrical conductivity. Herein, a novel NiCoMn-LDH/SWCNTs (single-walled carbon nanotubes) composite electrode material, with ultrathin NiCoMn-LDH nanosheets dispersedly grown among the highly conductive networks of SWCNTs, was prepared via a facile zeolitic imidazolate framework-67 (ZIF-67)-derived in situ etching and deposition procedure. The NiCoMn-LDH/SWCNTs electrode demonstrates a specific capacitance as large as 1704.3 F g⁻¹ at 1 A g⁻¹, which is ascribed to its exposure of more active sites than NiCoMn-LDH. Moreover, the assembled NiCoMn-LDH/SWCNTs//BGA (boron-doped graphene aerogel) hybrid supercapacitor exhibits a superior capacitance of 167.9 F g⁻¹ at 1.0 A g⁻¹, an excellent energy density of 45.7 Wh kg⁻¹ with a power density of 700 W kg⁻¹, and an outstanding cyclic stability with 82.3% incipient capacitance maintained when subjected to 5000 charge and discharge cycles at the current density of 10 A g⁻¹, suggesting the significant potential of NiCoMn-LDH/SWCNTs as the electrode material applicable in supercapacitors. Full article

Acid fracturing is a crucial method for reservoir reconstruction in carbonate reservoirs, and the propagation pattern of acid-etched fractures plays a key role in determining the scope of reservoir enhancement and post-fracturing productivity. However, large-scale physical simulations directly using acid solutions in fracturing experiments are limited, and the fracture propagation patterns under acid fracturing remain unclear. To address this gap, in this study, we collected carbonate rock samples from the Majiagou Formation in the Daniudi area, preparing large-scale fracturing specimens with side lengths of 30 cm. The propagation of acid fracturing fractures was investigated using self-developed true-triaxial acid fracturing equipment. Based on post-fracturing fracture morphology and pressure curves, the effects of fracturing fluid type, injection rate, injection mode, and natural fractures (NFs) on acid fracturing fracture propagation were analyzed. The experimental results showed that the acid solution effectively weakens the mechanical properties of the open-hole section, creating multiple mechanical weak points and promoting the initiation of fractures. Pre-fracturing treatment with low-viscosity acid can significantly enhance fracture complexity near the wellbore and expand the near-well stimulation zone. Lowering the injection rate increases the acid solution’s filtration loss into natural fractures, weakening the cementation strength of these fractures and encouraging the formation of complex fracture networks. Furthermore, employing a multi-stage alternating injection of high-viscosity and low-viscosity acids can reduce fracture temperature and acid filtration loss while also enhancing differential etching through viscous fingering. This approach improves the conductivity and conductivity retention of the acid-etched fractures. The results of this study can provide a reference for the acid fracturing stimulation of fractured carbonate reservoirs. Full article

Acid fracturing has become a crucial technology for developing carbonate reservoirs, playing a particularly significant role in enhancing oil and gas recovery. However, the retention and flowback behaviors of residual acid in fractured-vuggy carbonate reservoirs after acid fracturing remain poorly understood, and this uncertainty significantly hinders the efficient development of such reservoirs. In this study, the micro-computed tomography images of carbonate rocks were used to extract actual fracture–vug structures. A microscopic flow model for fractured-vuggy carbonate reservoirs was then designed and fabricated using wet etching techniques. Microfluidic experiments were performed to investigate the invasion and flowback behavior of residual acid within these reservoirs. This study introduces a novel approach by integrating actual fracture-vuggy structures from micro-CT images into a microfluidic model, providing a more realistic representation of fractured-vuggy carbonate reservoirs compared to previous studies that relied on simplified or idealized geometries. Additionally, the invasion coefficient (the ratio of acid invaded area to total pore area) and flowback rate (the proportion of residual acid expelled during flowback) were introduced to quantitatively assess the efficiency of acid invasion and flowback under varying flow rates, viscosities, and the presence or absence of surfactants. The results demonstrate that the invasion coefficient of residual acid increases with the injection rate, while the flowback rate decreases as the injection rate is reduced. A higher viscosity of the oil phase hinders acid invasion and results in slower flowback due to increased flow resistance in the micro model. However, the final flowback rate is higher with a higher viscosity oil phase compared to a lower viscosity phase. The addition of surfactants enhances the efficiency of acid invasion and flowback, increasing the invasion coefficient by up to 5% and the flowback rate by up to 3%. Full article

MXenes, a groundbreaking class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have emerged as highly promising materials for photocatalytic applications due to their unique structural, electrical, and surface properties. These materials are synthesized by selectively etching the A layer from MAX phases, yielding compositions with the general formula M_n+1X_nT_x, where M is a transition metal, X represents carbon or nitrogen, and T_x refers to surface terminations such as ^–OH, ^–O, or ^–F. This review delves into the advanced synthesis techniques of MXenes, including fluoride-free etching and molten salt methods, and explores their potential in photocatalysis for environmental remediation. MXenes exhibit remarkable light absorption capabilities and efficient charge carrier separation, making them highly effective for the photocatalytic degradation of organic pollutants under visible light. Modulating their surface chemistry and bandgap via functional group modifications further enhances their photocatalytic performance. These attributes position MXenes as next-generation materials for sustainable photocatalytic applications, offering significant potential in addressing global environmental challenges. Full article