Hydrothermal Conditions Research Articles

Rate-and-state friction of epidote gouge under hydrothermal conditions and implications for the stability of subducting faults under greenschist metamorphic conditions

Epidote is a common hydrous mineral present in subduction zones subject to greenschist metamorphic conditions – and potentially an important control on the fault stability-instability transition observed under greenschist facies. We explore controls on this transition through shear experiments on simulated epidote gouge at temperatures of 100–500 °C, effective normal stresses of 100–300 MPa and pore fluid pressures of 30–75 MPa. We use rate-and-state friction to define these controls of temperature, effective stress and pore fluid pressure on gouge stability. Experimental results indicate that the epidote gouge is frictionally strong (μ ∼ 0.73) and the frictional strength is insensitive to variations in temperature or pressure. With increasing temperature, the epidote gouge exhibits a first transition from velocity-strengthening to velocity-weakening at sub-greenschist conditions (T < 100 °C) before transitioning to velocity-strengthening under greenschist metamorphic conditions (T > 300 °C). Elevating the pore fluid pressure or decreasing the effective stress promotes unstable sliding. The transition in gouge rheology at varied temperatures and pressures is explained by the competition between granular flow-induced gouge dilation and pressure solution-induced gouge compaction. Our results demonstrate that the rate-and-state frictional stability of epidote gouges support the potential for a fault stability-instability-stability transition for subduction under greenschist metamorphic conditions.

Unlocking Enhanced Electrochemical Performance of MBene-MoB Through Controlled Aluminum Dissipation from MoAlB.

2D transition metal borides, known as MBenes, have attracted considerable attention due to their exceptional properties. This study explores the feasibility of aluminum (Al) etching from MoAlB using environmentally friendly and sustainable fluoride-free dilute acidic/alkaline solutions at room temperature, revealing its thermodynamic and kinetic viability. Furthermore, it is found that complete removal of Al can be achieved in dilute alkaline reagent under hydrothermal conditions, yielding pristine single/few-layered MBene-MoB for the first time, while acidic solutions result in ≈33% etching rates. XRD refinement, which tracks aluminum removal from 0% to 100%, reveals transient metastable phases of MoAl1-xB (x<0.5) in the initial etching stages, evolving into relatively stable pure Mo2AlB2 structures with 50% Al deficiency, serving as a precursor to MBenes. The subsequent loss of Al results in a 2D MBene-MoB structure. DFT calculations confirm excellent conductivity for MoAlB, MoAl1-xB (x=0-1), and MBene-MoB. Remarkably, MBene-MoB exhibits superior supercapacitor performance with a 4025.60mFcm-2/201.28Fg-1 capacitance. Simulations validate rapid electrolyte diffusion in layered MBene-MoB, contributing significantly to enhanced capacitance. Additionally, in the hydrogen evolution reaction (HER), MBene-MoB demonstrates superior catalytic activity compared to the precursor MoAlB and commercial MoB. Calculations suggest the potential for enhancing HER through surface modulation, considering its suboptimal hydrogen adsorption energy.

Settings Trace elements and garnet formation in a distal skarn zone: a case study of the Rudnik deposit, Central Serbia

The Rudnik Pb-Zn deposit is hosted in skarns and hornfels formed in the late Oligocene by contact metamorphism of limestones, sandstones and shales. Garnets, together with epidote, represent the main non-metallic minerals in the Rudnik skarn. In the distal skarn zone, the garnets are rare and their occurrence is related to the flow path of hydrothermal fluids. To constrain the hydrothermal and physicochemical conditions, in situ elemental SEM-WDS and LA-ICP-MS analyses, and fluid inclusion microthermometric measurements, were made. The Rudnik garnets from the distal skarn zone are predominantly of andradite-grossular composition (Adr39.3–88.9Grs2.9–53.9Alm0.5–10.0), with a small amount of spessartine. Generally, the Fe-rich garnets show a positive Eu anomaly with LREE enrichment and a HREE flat pattern, with homogenization temperatures and salinities of fluid inclusions ranging from 373 to 392°C and from 14.25 to 15.27% NaCl equivalent, respectively. The trace elements and microthermometric properties indicate that the garnets formed at moderately high temperatures, mildly acidic pH levels and increased oxygen fugacity

Global Wetland Methane Emissions From 2001 to 2020: Magnitude, Dynamics and Controls

AbstractThe large uncertainties in estimating CH4 emissions from wetland ecosystems, the leading natural source to the atmosphere, substantially hinder the quantification of the global CH4 budget. This study used the IBIS‐CH4 (Integrated BIosphere Simulator‐Methane) model, a process‐based model integrating microbial mechanisms associated with CH4 production and oxidation processes, to simulate global wetland CH4 emissions from 2001 to 2020. Initially, we employed the IBIS‐CH4 model to evaluate its performance across 26 diverse wetland sites worldwide. The results showed that the magnitude and seasonality of observed CH4 fluxes over various wetland sites were well reproduced. We then used this model to estimate the annual global wetland CH4 emissions from 2001 to 2020, averaging 152.67 Tg CH4 yr−1, with a range of 135.72–167.57 Tg CH4 yr−1. The estimated global wetland CH4 emissions are generally in agreement with the current bottom‐up estimates (117–256 Tg CH4 yr−1) and closely overlap with independent top‐down estimates (139–183 Tg CH4 yr−1). During 2001–2020, the estimated global wetland CH4 emissions initially showed an increasing trend, followed by a decline. The peak of CH4 emissions reached in 2010, coinciding with the peak of wetland area. The majority of global wetland CH4 emissions were concentrated in tropical regions, which exhibited a clear seasonality and had a peak in July. The impact of meteorological factors on wetland CH4 emissions was greater than that of leaf area index, indicating the importance of soil hydrothermal conditions on wetland CH4 emissions.

Prebiotic Synthesis of Microdroplets from Formate over a Bimetallic Cobalt-Nickel Nanomotif.

The hypothesis underlying the abiogenic origin of life suggests that the nonenzymatic synthesis of long-chain fatty acids led to the construction of vesicles for compartmentalization in an early stage during the transition from geochemistry to biochemistry. However, evidence for this theory remains elusive as C5+ carboxylic acids cannot be synthesized using current laboratory simulations. Here, we report the synthesis of long-chain carboxylic acids (C3-C7) with a 42 mmol/gCo+Ni yield and 87.7% selectivity from formate (an intermediate of the acetyl-CoA pathway) over a cobalt-nickel alloy under alkaline hydrothermal conditions and the subsequent formation of microdroplets from organics. Density functional theory (DFT) calculations confirmed that the synergistic effect of the bimetal catalyst is key for catalyzing C-C coupling. Investigations by infrared spectroscopy, electron paramagnetic resonance, and isotope-labeled experiments revealed that HCO* serves as a reaction intermediate and is involved in the subsequent elementary steps for synthesizing long-chain carboxylic acids from formate. Taken together, these findings may help explain how the first protocells emerged geochemically and provide support for the hypothesis of the abiogenic origin of life. The hydrothermal system developed may also be applicable for the sustainable synthesis of long-chain carboxylates from one-carbon substrates using nonnoble metal catalysts.

Hierarchical ultra-thin porous Co3O4 nanosheets derived from mixed phase α- and β-Co(OH)2 for high sensitivity and ppb-level acetone sensing

Addressing the energy loss of carriers during transmission and achieving high sensitivity detection of target gases facilitates the synthesis of trace-level acetone sensors, which is of great significance in the fields of air quality early warning, health monitoring, and industrial safety monitoring. Here, we propose a strategy where, under hydrothermal conditions, the content of mixed-phase α- and β-Co(OH)2 is regulated by varying the protonation level of 2-methylimidazole in different solutions, leading to the formation of porous monocrystalline Co3O4 microflower structure. The microflower is assembled from ultrathin nanosheets, and the 3D-interconnected macroporous and mesoporous structure provides high surface area and gas diffusion channels. The monocrystalline and two-dimensional structures favor high carrier mobility, enhancing the signal-to-noise ratio. Furthermore, the thickness of the Co3O4 nanosheets is less than twice the Debye length, making their electrical properties completely dependent on surface. DFT calculations also indicate that the few layers Co3O4 model is conducive to acetone adsorption. The Co3O4 sensor exhibits exceptional gas sensing performance towards acetone, with favourable sensitivity (16.83 to 10 ppm), selectivity, and stability, as well as an ultra-low practical detection limit of 10 ppb. Rich point defects and line defects play a significant role in improving the surface activity of the sensitive material as well. This research offers a pathway for designing sensors with exceptional gas sensitivity by employing a straightforward method to control the morphology of sensitive materials, combined with defect engineering to enhance sensing activity.

Geospatial variation of granitic soil erodibility along a hydrothermal gradient in the gully region

Gully erosion poses a severe threat to ecological security and economic sustainability globally. Soil erodibility, characterizing the susceptibility to gully erosion, is influenced by hydrothermal conditions that control pedogenic processes, especially for soils derived from the same parent rock. Soil erodibility characteristics in gully erosional areas have been widely investigated, particularly at a pedon scale. However, limited information is available on the regulation pathway of hydrothermal conditions on gully erosion. Therefore, gully erosion distributed in the granite weathering mantle was selected due to its increased density and sediment yield from north to south across subtropical China. To evaluate the impacts of granitic soil erodibility on the spatial distribution of gully erosion, a comprehensive soil erodibility index (CSEI) was constructed. This index integrated various soil erodibility indicators, including mean weight diameter (MWD), soil structural stability index (SSSI), penetration resistance (PR), soil erodibility factor (K-factor), and others. These soil erodibility indicators with inconsistent spatial variation across the study area showed the highest values at the sandy horizon (F=1.72 ∼ 6.53, p < 0.05), indicating the critical role of this horizon to gully erosion. While a consistent increasing trend with the increase of hydrothermal condition was observed, this spatial variation showed a less significant difference statistically. Moreover, the CSEI (0.12 ∼ 0.91) was mainly determined by cementation (R2 = 0.65 ∼ 0.83, p < 0.01) and hydrophysical properties (LL, PL, w) (R2 = 0.64 ∼ 0.69, p < 0.01), especially soil organic matter and free iron and aluminum oxides (R2 = 0.91). Furthermore, hydrothermal conditions indirectly determined the spatial variation of CSEI by altering soil cementation (SPC=0.51) and physical-related properties (SPC= − 0.15). Collectively, hydrothermal conditions determine gully erosion by altering granitic soil erodibility in subtropic China, and this alteration was triggered by an indirect way. The obtained results would facilitate a better understanding of gully erosion mechanisms and more effective gully control strategies.

Isomeric organic ligands directing octamolybdates-linked Copper(II) functionalized complexes as active catalysts in electrochemistry and desulfurization

Two remarkable octamolybdates-based copper-organic complexes, namely, [Cu7(L)4(H2O)7(β-H2Mo8O26)]·7H2O (POM 1) and [Cu6(HX)4(β-Mo8O26)(H2O)6]·3H2O (POM 2) (H3L = 2-(pyridine-4-yl)-1H-imidazole-4,5-dicarboxylic acid; H3X = 2-(pyridine-3-yl)-1H-imidazole-4,5-dicarboxylic acid), were successfully assembled using two isomeric organic ligands under hydrothermal conditions. The two-dimensional metal-organic layers of POMs 1 and 2 were converted into three-dimensional frameworks by hexadentate β-H2Mo8O262− and tetradentate β-Mo8O264− clusters, respectively. The electrocatalytic properties of POM 1 were investigated, revealing its ability to catalyze the reduction of BrO3−, NO2− and H2O2 and the oxidation of ascorbic acid. Notably, POMs 1 and 2 demonstrated exceptional stability in organic solvents and exhibited excellent catalytic performance in oxidative desulfurization. When employed as catalysts for thioanisole oxidation, the conversion rates reached 94.5% after 150 min for POMs 1 and 99.9% after 120 min for POMs 2. In addition, their catalytic performances in model oil remained largely unchanged after five recycling cycles.

Exploring physical and mechanical properties of hydrothermally processed recycled non-sintered dental zirconia wastes

Background and aimThe present investigation explored the potential for recycling residual blocks obtained from the machining processes under hydrothermal conditions. Furthermore, the study examined the recycled samples’ various physical and mechanical properties to assess their viability for further use. Materials and methodsIn this in vitro study, Aman Girbach blocks were collected, half of which underwent a hydrothermal process, while the other half did not. The blocks were then subjected to ball milling. Uniaxial and isostatic pressed blocks were prepared, and 10 samples were obtained from each type of recycled block. These samples were compared to a commercial material, and four groups were formed based on the powder type and pressing method used. The quality control analysis of the recycled samples included assessing particle size distribution, identifying crystalline phases, analyzing color differences, examining microstructure, and evaluating mechanical properties. Statistical tests such as normal distribution calculations (k-s test), one-way ANOVA, Brown-Forsythe, Tukey HSD, and Games-Howell tests were used to compare the four groups and perform pairwise comparisons. ResultsThe flexural strength and density of the control commercial group were significantly higher than the other experimental groups (P = 0.000). Linear shrinkage of recycled isostatic pressed experimental bodies was significantly lower than that of others (P = 0.000). Qualitative evaluation of microstructure and crystalline phase by FESEM and XRD showed no significant difference in grain size and crystalline phase between different groups. ConclusionThe hydrothermal process is a promising way to recycle zirconia ceramic with lower energy consumption. Recycled waste demonstrates potential as a cost-effective and viable option for ceramic prostheses in situations with low to medium stress levels.

Insights into the pore size distribution of amorphous silica membranes using gas permeation activation energies

Silica-based membranes exhibit significant promise for the separation of hydrogen from other larger gas molecules based on size sieving mechanism, particularly when employed in membrane reactors. Nevertheless, the migration of silanol bonds (Si–OH) formed under hydrothermal conditions leads to alterations in pore size, ultimately compromising the performance of the membrane. Therefore, this study focuses on determining the pore size of cobalt-doped silica membranes before and after hydrothermal treatment by the apparent activation energy of gas permeation. The Oscillator model and the effective medium theory are employed to estimate the potential pore size distribution, as well as to calculate the apparent activation energy and permeability. The calculated apparent activation energy is compared with experimental data to identify the most probable pore size distribution, which showed the minimum activation energy error to the experimental value. The calculated permeability based on the identified pore size distribution is in line with experimental permeability, which validated the identified pore size distribution. Since silica-based membrane is generally applied in hydrothermal conditions, our model successfully identifies the changes in pore size of silica-based membranes after hydrothermal treatment. The results demonstrated that hydrothermal treatment significantly impacts the pore size of silica-based membranes. Specifically, 5-membered rings are prevalent in the intact membrane, but after hydrothermal treatment, there is a gradual shift of the pore size distribution towards larger pores, potentially leading to a decrease in sieving performance. This methodology presents a promising approach for determining intriguing pore size information of porous materials.

Sulfur vacancy riched pure 2H phase VS2 for efficient electrocatalytic hydrogen evolution

Vanadium disulfide (VS2), a typical metallic layered transition metal chalcogenide (TMC), has been widely concerned for its high electrical conductivity and reactivity in electrochemical energy storage and conversion applications. The 2H phase VS2 is expected to exhibit high electrocatalytic activity and be more stable for hydrogen evolution reaction (HER) than the 1T phase structure. But at present, there still lacks a facile method to prepare pure 2H phase VS2. Herein, we successfully prepared pure 2H–VS2 through a simple one-step low-temperature hydrothermal method. We have investigated the effect of the hydrothermal reaction conditions (including the proportion of raw materials and hydrothermal reaction temperatures) on the phase composition and microstructure. Under the optimal condition of 140°C-24 h with a vanadium sulfur ratio of 1:5, a nano-flower-like 2H–VS2 material with high crystallinity and rich sulfur vacancy defects was obtained. Leveraging these structural advantages, as a demonstration, the product exhibits excellent electrocatalytic HER activity (with η10 of 181 mV, Tafel slope of 52 mV dec−1, and J0 of 67.9 × 10−3 mA cm−2) and stability (it can continuously produce hydrogen for 20 h at a current density of 50 mA cm−2 with ultra-small increased potential of less than 5 mV). This work provides a new way for constructing atomic vacancy defects in layered TMCs for efficient electrocatalysis and is also expected to promote the research of the basic properties of high phase purity TMCs.

Hydrothermal solidification of siliceous and calcareous wastes into building materials: A generic mix design framework

The presence of inactive components in siliceous and calcareous wastes tends to cause a misunderstanding in their mix design for hydrothermal solidification. The contents of typical reactive elements (i.e. Caact, Siact and Alact) in raw materials are quickly determined by simulating hydrothermal conditions. A generic mix design framework is proposed, which utilizes the molar ratio of Caact/Siact as the controlling parameter. The framework was demonstrated through a series of studies, which involved the production of granular materials using a mixture of clayey soil with slaked lime, as well as the production of compacted cylinders using a mixture of clayey soil with either slaked lime or calcium carbide slag. Experimental results showed that the hydrothermal samples achieved their maximum strength when the molar ratio of Caact/Siact in raw materials approached the theoretical Ca/Si molar ratio (i.e. 0.83) in tobermorite, provided that the molar ratio of Alact/(Alact + Siact) remained below 21%.

Spatial and Temporal Dynamics in Vegetation Greenness and Its Response to Climate Change in the Tarim River Basin, China

Vegetation in ecologically sensitive regions has experienced significant alterations due to global climate change. The underlying mechanisms remain somewhat obscure owing to the spatial heterogeneity of influencing factors, particularly in the Tarim River Basin (TRB) in China. Therefore, this study targets the TRB, analyzing the spatial and temporal dynamics of vegetation greenness and its climatic determinants across multiple spatial scales. Utilizing Normalized Difference Vegetation Index (NDVI) data, vegetation greenness trends over the past 23 years were assessed, with future projections based on the Hurst exponent. Partial correlation and multiple linear regression analyses were employed to correlate NDVI with temperature (TMP), precipitation (PRE), and potential evapotranspiration (PET), elucidating NDVI’s response to climatic variations. Results revealed that from 2000 to 2022, 90.1% of the TRB exhibited an increase in NDVI, with a significant overall trend of 0.032/decade (p &lt; 0.01). The difference in NDVI change across sub-basins and vegetation types highlighted the spatial disparity in greening. Notable greening predominantly occurred near rivers at lower elevations and in extensive cropland areas, with projections indicating continued greening in some regions. Conversely, future trends mainly suggested a shift towards browning, particularly in higher-elevation areas with minimal human influence. From 2000 to 2022, the TRB experienced a gradual increase in TMP, PRE, and PET. The latter two factors were significantly correlated with NDVI, indicating their substantial role in greening. However, vegetation sensitivity to climate change varied across sub-basins, vegetation types, and elevations, likely due to differences in plant characteristics, hydrothermal conditions, and human disturbances. Despite climate change influencing vegetation dynamics in 51.5% of the TRB, its impact accounted for only 25% of the total NDVI trend. These findings enhance the understanding of vegetation ecosystems in arid regions and provide a scientific basis for developing ecological protection strategies in the TRB.

Spatio-temporal variations and multi-scale correlations of climate, water, land, and vegetation resources over the past four decades in the Heihe River Basin

Study regionHeihe River Basin (HRB), Northwest China. Study focusThe study proposes an analytical scheme to identify trend, periodicity, and scale-correlation in climate, water, land, and vegetation resources over the past four decades using multivariate remote sensing data. New hydrological insights for the regionHeat and precipitation resources in the HRB have increased at rates of 14.27℃ yr−1 and 1.26 mm yr−1, respectively. The glacier area has decreased by 47.47 %. Additionally, the increase in upstream precipitation (2.82 mm yr−1) and glacier meltwater effectively replenishes runoff, soil water, and groundwater. The implementation of the ecological water diversion project (EWDP) in 2000 has contributed to enhancing runoff and lake storage capacity. The 9.28 % increase in vegetation cover (including cropland, forest, grassland, and shrubland) indicates an improvement in the hydrothermal conditions of the HRB. Additionally, the magnitude and direction of interactions among various natural resources vary across multiple spatial scales and time scales. The effect of hydrothermal coupling on vegetation is more prominent at the interdecadal scale. Vegetation growth in the upstream area is primarily influenced by thermal condition, while moisture plays a significant role in the midstream and downstream areas. Knowledge from this study contributes to the informed allocation of natural resources and offer policymakers valuable insights to enhance eco-environmental sustainability.

Temperature sensitivity of soil respiration to elevated temperature and nitrogen availability

Plastic film mulching (PFM) and nitrogen (N) fertilization are two important agricultural management methods that are used to enhance crop yields in semi-arid dryland agriculture. However, the impacts of PFM and N fertilization on the temperature sensitivity (Q10) of soil respiration (Rt), particularly its heterotrophic (Rh) and autotrophic (Ra) components, remain unclear. To investigate this, a trenching experiment was carried out between 2019 and 2021 in a rainfed maize-cultivated cropland that had been under cultivation for 7 years. There were four treatments: no PFM and N fertilization (control), full PFM without N fertilization (PFM), 150 kg N ha–1 fertilization without PFM (Nfer), and full PFM with 150 kg N ha–1 fertilization (PFM+Nfer). PFM and N fertilization not only enhanced crop yield and root biomass but also increased soil total respiration (Rt) and its components, due to improved soil hydrothermal conditions with PFM and increased N availability with N fertilization. Soil hydrothermal conditions and root biomass were identified as the most important factors influencing Rh and Ra, respectively. The greater increase in Ra (84 %–212 %) compared to Rh (9 %–29 %) resulted in a decrease in the proportion of Rh in Rt decreasing from 81.2 % in the control to 58 % under the PFM+Nfer treatment. The Rh/Rt ratio decreased in all three treatments compared to the control (p < 0.05). The increase in Rh under PFM led to a decrease in soil organic carbon (SOC) by 17 %. Specifically, the soil labile C content (i.e. LFOC 44 %) decreased more under PFM and PFM+Nfer (p < 0.05) compared to control, but not under the Nfer treatment (p > 0.05). Plastic film mulching increased the Q10 of Rh (p < 0.05) through decrease the content of soil labile C, whereas N fertilization had no effect (p > 0.05). Both PFM and N fertilization increased the Q10 of Ra (p < 0.05) by increasing root biomass. The impact of Ra’s Q10 (0.66) on Rt’s Q10 is greater compared to Rh’s Q10 (0.31). To our knowledge, this is the first long-term field study to examine the response of Rt components and their Q10 to PFM and N fertilization. Our results highlight that soil labile C and root biomass are the determining factors for the Q10 of Rh and Ra, respectively. We emphasize the importance of accurately modeling the temperature responses of Rh and Ra when predicting Rt under climate change scenarios.

Analysis of the yield of spring oats cultivated in a harsh continental climate

Studies of the yield of spring oats for the period 2012–2021 in the conditions of a sharply continental climate in the Kemerovo region have been carried out. The main soils of the steppe zone are leached heavy loamy chernozem, forest-steppe — gray forest. In 2012, the yield of this crop was the lowest — 9.35 kg/ha. The first one reflects the trend of yield dynamics (trend) and is associated with an increase in the general culture of agriculture. The second is caused by fluctuations in weather conditions in each particular year and is depicted as deviations from the trend. It is shown that the yield of spring oats in both steppe and forest-steppe soil-climatic zones tends to slightly increase. The analysis of the data obtained showed that the maximum yield of spring oats was in 2021 — 22.68 kg/ha, and the lowest was in 2012 (9.35 kg/ha). The high fluctuation of oat yield indicates a strong influence of hydrothermal conditions during the growing season of the crop. It was found that the decrease in the growth rate of spring oat yields in the Kemerovo region was in 2015, 2016 and 2018. The maximum growth rate was observed in 2013 — 178.82%. The maximum decrease in the yield growth rate of spring oats occurred in 2016 and 2018 - by -5.31% and -6.68%, respectively. The highest increase in oat yield was observed in 2013 — 78.82%. The absolute content of 1% yield increase was 19.44 c/ha in 2021 compared to 2012.

Conversion of soybean oil under subcritical water conditions into liquid biofuels with low oxygen contents

Although the hydrotreatment of natural triglycerides is a well-established route for producing sustainable aviation fuel and renewable diesel, its high hydrogen consumption is a concern. The hydrothermolysis of natural triglycerides is considered a highly promising alternative route; however, the correlation between process parameters and fuel properties and detailed chemical structures of the produced fuel have not been established. Herein, we investigated the conversion of soybean oil to gasoline-, jet fuel- and diesel-fraction hydrocarbons with low oxygen contents. The properties of fuels produced under various reaction conditions were analyzed comprehensively using simulated distillation, total acid number (TAN), and elemental analysis. Under the optimized reaction conditions of 420 °C, 4.5 MPa, an oil-to-water ratio of 6:1, and reaction time of 10 min, 26 % gasoline-, 62 % jet fuel-, and 90 % diesel-range hydrocarbons with a low oxygen content of 5.1 %, low TAN of 0.04 mg KOH g−1, and high calorific value of 42.7 MJ kg−1 resulted. To elucidate the reaction mechanism, the liquid products produced from soybean oil were analyzed using comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry. In addition, based on the oleic acid conversion under varying hydrothermal conditions, we proposed deoxygenation, cracking, cyclization, and aromatization pathways. The findings of this study present possibilities for producing sustainable biofuels with low oxygen contents for the aviation industry.

Two-episode mineralization in the Haerdaban Pb–Zn deposit, NW China: Insights from sulfide trace elements, in situ S–Pb isotopes, and Rb–Sr geochronology

The Haerdaban Pb–Zn deposit, located in the eastern West Tianshan Orogen, hosts stratiform and vein-type mineralization within Precambrian carbonate rocks. However, there has been limited research on the distinctions and relationships between these two mineralization styles. In this study, we compared trace element distributions, fluid conditions, material sources, and mineralization ages between stratiform and vein-type mineralization and reconstructed a detailed genetic model. Two episodes and four stages of mineralization were identified, including five generations of pyrite and two generations of sphalerite. The sedimentary exhalative episode represents stratiform mineralization including Stage I pyrite–pyrrhotite layers (Py-1, Py-2a, Py-2b, and Py-3) and Stage II sphalerite–galena layers (Sph-1). The magmatic–hydrothermal episode represents vein-type mineralization including Stage III pyrite–quartz–calcite veins (Py-4) and Stage IV sphalerite–galena–quartz–calcite veins (Sph-2). LA–ICP–MS analysis of Se–Co–Ni–As–Ag–Sb–Bi contents in pyrite suggests that Py-1 to Py-3 formed under relatively low temperatures (280 ± 8 °C) and high ƒO2 sedimentary conditions. Py-4 formed under relatively high temperatures (339 ± 18 °C) and low ƒO2 hydrothermal conditions. Variations in Fe–Mn–In–Ga–Ge–Cd–Cu contents in sphalerite indicate that Sph-1 formed under relatively low temperature (211 ± 7 °C), intermediate ƒS2 (logƒS2 = −11.1 ± 0.5), and moderate pH sedimentary exhalative conditions. Sph-2 formed under relatively high temperature (292 ± 5 °C), high ƒS2 (logƒS2 = −7.4 ± 0.2), and low pH hydrothermal conditions. In situ analysis of sulfide S–Pb suggests that ore-forming materials for stratiform mineralization were primarily derived from marine sediments, while those for vein-type mineralization primarily originated from magmatic sources. Sph-1 from stratiform mineralization yielded an Rb–Sr isochron age of 719 ± 16 Ma, while Sph-2 from vein-type mineralization exhibited an Rb–Sr isochron age of 380.3 ± 7.7 Ma. Random Forest classification of trace elements in pyrite and sphalerite predicted that stratiform mineralization is of sedimentary genesis, whereas vein-type mineralization is of magmatic–hydrothermal genesis. Based on our results, we identified a two-episode mineralization history for the Haerdaban Pb–Zn deposit: Neoproterozoic syngenetic sedimentary exhalative mineralization overprinted by Devonian epigenetic magmatic–hydrothermal mineralization. The results of this study highlight the importance of considering multiple geological events in ore-forming processes and will facilitate the exploration of similar deposits in the West Tianshan Orogen.

Research on a harmless treatment method for oily sludge in coal chemical wastewater and the pollutant transformation mechanism of oily sludge during the treatment process

This study developed an ultrasound synergistic subcritical hydrothermal treatment method (U-SHT) to address the challenges posed by the high oil and water content, complex composition, and hazardous nature of oily sludge (OS) generated during the pretreatment of coal chemical wastewater. The study investigated the efficiency of this method for the harmless disposal and resource recovery of OS, and the migration-transformation mechanism of hazardous organic pollutants in OS. The findings revealed that U-SHT achieved a removal efficiency of chemical oxygen demand in OS of 91.16 %, an oil resource recovery efficiency of 96.60 %, and a residual oil rate of 0.28 %, meeting API emission standards. Further research indicated that the solubilizing effect of the surfactant on the oil enhanced the demulsifying effect of ultrasonic cavitation on the emulsified structure of OS, enabling ultrasound to efficiently release and disperse pollutants within OS. This promoted the decomposition and transformation of pollutants under subcritical hydrothermal conditions, with synergistic removal efficiencies for typical pollutants such as long-chain alkanes, polycyclic aromatic hydrocarbons, and phenols reaching 96.61 %, 97.63 %, and 97.76 %, respectively. Economic evaluation indicated that the cost of OS treatment was $29.66/m3, significantly lower than existing methods, demonstrating promising practical application prospects.

Monitoring the dynamics of nanozeolite formation by combined in situ coherent small angle X-ray scattering techniques

Understanding the dynamics of zeolite formation is key to synthesising high-quality zeolitic materials with controllable properties, in order to develop more efficient and performant materials. X-ray photon correlation spectroscopy (XPCS) using coherent X-rays offers new possibilities for in situ observation of nano to micron-scale fluctuation dynamics during crystal growth. An in situ cell, which is capable of collecting time-resolved coherent X-ray scattering data under hydrothermal conditions has been developed and used to study, by in situ XPCS combined with small and wide angle X-ray scattering, zeolite formation and dynamics. Analysis of the results using two-time correlations enables to accurately identify the successive growth and crystallisation steps, revealing the dissolution process of the LTA topology during the SOD growth. This approach opens a powerful new avenue for studying the dynamics of nanomaterials formation, phase transitions and growth processes under in situ conditions that will enable profound insights into the nanoscale synthesis mechanisms.