Enhanced Hydrogen Evolution Catalysis of Pentlandite due to the Increases in Coordination Number and Sulfur Vacancy during Cubic-Hexagonal Phase Transition.

The search for new phases is an important direction in materials science. The phase transition of sulfides results in significant changes in catalytic performance, such as MoS2 and WS2 . Cubic pentlandite [cPn, (Fe, Ni)9 S8 ] can be a functional material in batteries, solar cells, and catalytic fields. However, no report about the material properties of other phases of pentlandite exists. In this study, the unit-cell parameters of a new phase of pentlandite, sulfur-vacancy enriched hexagonal pentlandite (hPn), and the phase boundary between cPn and hPn are determined for the first time. Compared to cPn, the hPn shows a high coordination number, more sulfur vacancies, and high conductivity, which result in significantly higher hydrogen evolution performance of hPn than that of cPn and make the non-nano rock catalyst hPn superior to other most known nanosulfide catalysts. The increase of sulfur vacancies during phase transition provides a new approach to designing functional materials.

Active pathways of anaerobic methane oxidization in deep-sea cold seeps of the South China Sea.

IMPORTANCE: Cold seeps occur in continental margins worldwide and are deep-sea oases. Anaerobic oxidation of methane is an important microbial process in the cold seeps and plays an important role in regulating methane content. This study elucidates the diversity and potential activities of major microbial groups in dependent anaerobic methane oxidation and sulfate-dependent anaerobic methane oxidation processes and provides direct evidence for the occurrence of nitrate-/nitrite-dependent anaerobic methane oxidation (Nr-/N-DAMO) as a previously overlooked microbial methane sink in the hydrate-bearing sediments of the South China Sea. This study provides direct evidence for occurrence of Nr-/N-DAMO as an important methane sink in the deep-sea cold seeps.

Oldhamite: a new link in upper mantle for C-O-S-Ca cycles and an indicator for planetary habitability.

In the solar system, oldhamite (CaS) is generally considered to be formed by the condensation of solar nebula gas. Enstatite chondrites, one of the most important repositories of oldhamite, are believed to be representative of the material that formed Earth. Thus, the formation mechanism and the evolution process of oldhamite are of great significance to the deep understanding of the solar nebula, meteorites, the origin of Earth, and the C-O-S-Ca cycles of Earth. Until now, oldhamite has not been reported to occur in mantle rock. However, here we show the formation of oldhamite through the reaction between sulfide-bearing orthopyroxenite and molten CaCO3 at 1.5 GPa/1510 K, 0.5 GPa/1320 K, and 0.3 GPa/1273 K. Importantly, this reaction occurs at oxygen fugacities within the range of upper-mantle conditions, six orders of magnitude higher than that of the solar nebula mechanism. Oldhamite is easily oxidized to CaSO4 or hydrolysed to produce calcium hydroxide. Low oxygen fugacity of magma, extremely low oxygen content of the atmosphere, and the lack of a large amount of liquid water on the celestial body's surface are necessary for the widespread existence of oldhamite on the surface of a celestial body otherwise, anhydrite or gypsum will exist in large quantities. Oldhamites may exist in the upper mantle beneath mid-ocean ridges. Additionally, oldhamites may have been a contributing factor to the early Earth's atmospheric hypoxia environment, and the transient existence of oldhamites during the interaction between reducing sulfur-bearing magma and carbonate could have had an impact on the changes in atmospheric composition during the Permian-Triassic Boundary.

Catalytic supercritical water oxidation of o-chloroaniline over Ru/rGO: Reaction variables, conversion pathways and nitrogen distribution.

To ascertain the reaction variables on o-chloroaniline (o-ClA) mineralization, total nitrogen (TN) removal rate, and N-species distribution, o-ClA was subjected to catalytic supercritical water oxidation (CSCWO) in a fused quartz tube reactor (FQTR). The findings demonstrated that when the temperature, reaction time, and excess oxidant were 400 °C, 90 min, and 150%, respectively, the mineralization rate of o-ClA could reach more than 95%. Moreover, potential degradation pathways of o-ClA in supercritical water oxidation (SCWO) was proposed according to the GC-MS results. TN removal rate is significantly impacted by Ru/rGO, despite the fact that its catalytic effect on the mineralization of o-ClA was not particularly noteworthy. Compared with no catalyst, the TN removal rate of o-ClA obviously increased from 44.1% to 90.3% at 400 °C, 10 wt% Ru loading, 90 min and 200% excess oxidant. In addition, N-species distribution in SCWO and CSCWO were also investigated. Results indicated that the Ru/rGO catalyst could accelerate the oxidation of ammonia-N and convert it to nitrate-N, promoting N2 generation. Finally, the possible N transformation pathway in CSCWO of o-ClA was proposed. As a result, this work offers fundamental information about o-ClA catalytic oxidation removal in the SCWO process.

In situ observations of tungsten speciation and partitioning behavior during fluid exsolution from granitic melt.

Most economically important tungsten (W) deposits are of magmatic-hydrothermal origin. The species and partitioning of W during fluid exsolution, considered to be the controlling factors for the formation of ore deposits, are thus of great significance to investigate. However, this issue has not been well addressed mainly due to the significant difference in reported partition coefficients (e.g., from strongly incompatible to strongly compatible) between fluid and melt (DWfluid/melt). Here, we used an in situ Raman spectroscopic approach to describe the W speciation, and to quantitatively determine the Dfluid/melt of individual and total W species in granite melts and coexisting Na2WO4 solutions at elevated temperatures (T; 700-800 °C) and pressures (P; 0.35-1.08 GPa). Results show that WO42- and HWO4- are predominant W species, and the fractions of these two species are similar in melt and coexisting fluid. The partitioning behaviors of WO42- and HWO4- are comparable, exhibiting strong enrichment in the fluid. The total DWfluid/melt ranges from 8.6 to 37.1. Specifically, DWfluid/melt decreases with rising T-P, indicating that shallow exsolution favors enrichment of W in evolved fluids. Furthermore, Rayleigh fractionation modeling based on the obtained DWfluid/melt data was used to describe the fluid exsolution processes. Our results strongly support that fluid exsolution can serve as an important mechanism to generate W-rich ore-forming fluids. This study also indicates that in situ approach can be used to further investigate the geochemical behavior of ore-forming elements during the magmatic-hydrothermal transition, especially for rare metals associated with granite and pegmatite.

Determination of H2 Densities Over a Wide Range of Temperatures and Pressures Based on the Spectroscopic Characterization of Raman Vibrational Bands.

Raman spectroscopy is a powerful method for determining the densities of gas species in fluid inclusions, especially for H2-bearing inclusions in which the microthermometry approach is difficult to apply. The relationships between Raman peak position and H2 density have been recorded in several previous studies. However, systematic discrepancies exist among these studies. In this study, the Raman spectral parameters (peak position, width, and intensity) of the vibrational bands of H2 (Q1(0), Q1(1), Q1(2), and Q1(3)) were systematically measured at temperatures from 25 to 400 °C and pressures up to 150 MPa using a high-pressure optical cell. The variation in each parameter as a function of H2 density was discussed. Several calibration polynomials derived from the measured peak positions and peak widths of these vibrational bands and the peak intensity ratios of Q1(1) to Q1(n = 0, 2, 3) were established to determine H2 densities up to 0.062 g/cm3 at 25 °C. For natural fluid inclusions, the peak position of the Q1(1) band is the best choice for density determination mainly because (i) Raman spectra derived from fluid inclusions are not always of applicable qualities and the strongest intensity Q1(1) band could be obtained easier than others, and (ii) the peak position is insensitive to instrumental factors. The relationship between the peak position of Q1(1) band and density can be represented by ΔQ1(1) = 90,246.070 × ρ4 - 5471.203 × ρ3 + 770.944 × ρ2- 41.038 × ρ (r2 = 0.999), where ρ is the density of H2 in g/cm3; ΔQ1(1) (cm-1) is the difference between the obtained peak position of Q1(1) band of H2 and the known peak position of Q1(1) band of H2 at near-zero density. This polynomial is independent of instrumental factors and can be applied in any laboratory, as long as the peak position of H2 with a near-zero density is known. The effects of temperature on the relationship between these spectral parameters and H2 density were also examined.

Crystallization Behavior of the Hydrogen Sulfide Hydrate Formed in Microcapillaries.

There are no reports on the hydrogen sulfide hydrate growth process and morphology in micropores due to the toxicity of hydrogen sulfide. In this study, the experimental measurements and dissociation enthalpies were provided to assess the effect of the microcapillary silica tube size on hydrogen sulfide hydrate dissociation conditions. To simulate micropore sediments, the H2S hydrate growth processes and morphologies at different supercooling temperatures were observed in this study. The dissociation temperature depression of the hydrate crystal in the microcapillary was less than 0.001 °C, which shows that the stability of the hydrate is less affected by the microcapillary pore used in this study. The mass transfer from the gas phase to the liquid phase is easily blocked when the hydrogen sulfide hydrate shell covers the gas-water meniscus, causing the growth of the gas hydrate to be inhibited. The hydrate crystal morphology can be divided into fibrous, needle-like crystals and dendritic crystals when ΔT sub > 12.7; the hydrate crystal morphology can be categorized as dendritic crystals and columnar crystals when ΔT sub = 7.9-8.9, and the hydrate crystals can form polyhedral crystals when ΔT sub = 7.9-8.9. Additionally, a new "bridging effect" that a hollow crystal which was filled with the gas phase can connect with two separated gas phases was found at low supercooling temperature.

Effects of Vitrinite in Low-Rank Coal on the Structure and Combustion Reactivity of Pyrolysis Chars.

Pyrolysis is a highly promising technology for the efficient utilization of low-rank coal. The structure of coal plays an important role in its utilization. In this paper, the evolution of the char structure during heat treatment (200-800 °C) of Naomaohu coal and its different vitrinite-rich fractions was studied. The functional group structure, aromatic ring structure, and crystallite size of chars were determined by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD) spectroscopy, respectively. The results indicated that minerals inhibit the condensation reaction of aromatic rings during pyrolysis. The high vitrinite content in coal is conducive to the formation of larger char crystallite average sizes (L a). The relationship between L a (1.69-3.10 nm) and the Raman band area ratio A (GR+VL+VR)/A D or A D/A all was established. In addition, the combustion performance and kinetics of chars were also investigated. The results showed that the char from high contents of the liptinite fraction has lower combustion reactivity, and demineralization treatment has significantly reduced the combustion reactivity of char.

A new type of hydrothermal diamond-anvil cell with cooling system.

A new type of hydrothermal diamond-anvil cell (HDAC-VII) and its accompanied cooling system were designed. The design of HDAC-VII in which the three posts work simultaneously as guideposts and screw posts greatly shortened the horizontal size of HDAC compared with older types. It provides more open space and shorter distance to analyze and observe the sample chamber from side access. Moreover, four ports were used to connect the upper and lower spaces between windows and anvils, so mixed gas (Ar + H2) can pass through both of them. In the heating experiments, the mixed gas prevents diamond anvils and other parts from being oxidized as well as cooling the observing windows. Dry gas can be passed through those spaces during cooling, preventing condensation on the table faces of anvils and the observing windows. The cooling system can cool the sample chamber to -170 °C with an accuracy of ±0.5 °C by using a nitrogen stream cooled through a stainless steel coil immersed in a liquid nitrogen Dewar. The heating rates while reheating a frozen sample can be controlled to be 0.1 °C/min with a temperature fluctuation of 0.1 °C. These improvements extend the HDAC applications especially in low temperature conditions. For example, (1) we measured the salinities of NaCl-H2O loaded in the sample chamber, (2) we observed the ice I and VI-melting process and correspondingly calculated the density of water in the sample chamber, and (3) we performed lepidolite crystallization in an aqueous solution with 10 wt. % NaCl to simulate its natural forming conditions.

Raman spectroscopic technique towards understanding the degradation of phenol by sodium persulfate in hot compressed water.

Degradation of phenol by sodium persulfate (SPS) in hot compressed water (HCW) was investigated in a lab-built fused quartz tube reactor (FQTR) coupled with Raman spectroscopy system. The species of S2O82-, SO42-, HSO4-, SO32- and HSO3- in the reaction system were qualitatively and quantitatively analyzed by Raman spectroscopy. The hydrothermal stability of phenol and SPS at different temperature and the degradation of phenol by SPS were also studied. The results indicated that phenol was not stable in aqueous solution above 200 °C, and that only SO42- was generated in the hydrolysis of SPS at temperatures below 50 °C, and SO42- and HSO4- were generated at higher temperatures. The maximum conversion rate (90.93%) and mineralization efficiency (38.88%) of phenol by SPS was obtained at reaction temperature of 300 °C with 180 min reaction time. During the degradation of phenol by SPS, HSO4- was the main product and S∗ (not detected by Raman spectroscopy) exhibits a positive correlation with temperature. In addition, a degradation pathway of phenol by SPS was proposed. The degradation data for the kinetic analysis indicated that the reaction followed pseudo first-order kinetics, and the reaction rate constants (ks) were given as k50 °C = 0.0083 min-1, k100°C = 0.0197 min-1, k200 °C = 0.0498 min-1, k300 °C = 0.0619 min-1 and k400°C = 0.0505 min-1 at 30 min reaction. Moreover, the activation energy (12.580 kJ mol-1), the enthalpy change (9.064 kJ mol-1) and the entropy change (-222.104 J mol-1) of the reaction were also calculated.

High Hydrostatic Pressure Inducible Trimethylamine N-Oxide Reductase Improves the Pressure Tolerance of Piezosensitive Bacteria Vibrio fluvialis.

High hydrostatic pressure (HHP) exerts severe effects on cellular processes including impaired cell division, abolished motility and affected enzymatic activities. Transcriptomic and proteomic analyses showed that bacteria switch the expression of genes involved in multiple energy metabolism pathways to cope with HHP. We sought evidence of a changing bacterial metabolism by supplying appropriate substrates that might have beneficial effects on the bacterial lifestyle at elevated pressure. We isolated a piezosensitive marine bacterium Vibrio fluvialis strain QY27 from the South China Sea. When trimethylamine N-oxide (TMAO) was used as an electron acceptor for energy metabolism, QY27 exhibited a piezophilic-like phenotype with an optimal growth at 30 MPa. Raman spectrometry and biochemistry analyses revealed that both the efficiency of the TMAO metabolism and the activity of the TMAO reductase increased under high pressure conditions. Among the two genes coding for TMAO reductase catalytic subunits, the expression level and enzymatic activity of TorA was up-regulated by elevated pressure. Furthermore, a genetic interference assay with the CRISPR-dCas9 system demonstrated that TorA is essential for underpinning the improved pressure tolerance of QY27. We extended the study to Vibrio fluvialis type strain ATCC33809 and observed the same phenotype of TMAO-metabolism improved the pressure tolerance. These results provide compelling evidence for the determinant role of metabolism in the adaption of bacteria to the deep-sea ecosystems with HHP.

An improved hydrothermal diamond anvil cell.

A new type of HDAC-V hydrothermal diamond anvil cell (HDAC-VT) has been designed to meet the demands of X-ray research including X-Ray Fluorescence, X-ray Absorption Spectroscopy, and small angle X-ray scattering. The earlier version of HDAC-V that offered a large rectangular solid angle used two posts and two driver screws on both sides of a rectangular body. The new version HDAC-VT in a triangular shape has two alternative guide systems, either three posts inserted into bushings suitable for small anvil faces or linear ball bearings suitable for large anvil faces. The HDAC-VT having three driver screws offers the advantage of greater control and stability even though it sacrifices some of the size of solid angle. The greater control allows better sealing of samples, while greater stability results in longer survival for anvils and ceramic parts. This improved design retains several beneficial features of the original HDAC-V as well. These include the small collar that surrounds the heater and sample chamber forming an Ar + H2 gas chamber to protect diamonds and their heating parts from being oxidized. Three linear ball bearings, when used, fit to the three posts prevent seizing that can result from deterioration of lubricant at high temperatures. Positioning the posts and bearings outside of the gas chamber as in HDAC-V also prevents seizing and possible deformation due to overheating. In order to control the heating rate precisely with computer software, we use Linkam T95 and have replaced the Linkam 1400XY heating stage with the HDAC-VT allowing the HDAC to be heated to 950 °C at a rate from 0.01 °C/min to 50 °C/min. We have used the HDAC-VT and Linkam T95 to observe in situ nucleation and growth of zabuyelite in aqueous fluid and to homogenize melt inclusions in quartz from three porphyry deposits in Shanxi, China.

Raman Spectroscopic Observations of the Ion Association between Mg(2+) and SO4(2-) in MgSO4-Saturated Droplets at Temperatures of ≤380 °C.

Liquid­liquid phase separation was observed in aqueous MgSO4 solutions with excess H2SO4 at elevated temperatures; the aqueous MgSO4/H2SO4 solutions separated into MgSO4-rich droplets (fluid F1) and a MgSO4-poor phase (fluid F2) during heating. The phase separation temperature increases with SO4(2­)/Mg2+ ratio at a constant MgSO4 concentration. At a MgSO4/H2SO4 ratio of 5, the liquid­liquid phase separation temperature decreases with an increase in MgSO4 concentration up to ∼1.0 mol/kg and then increases at higher concentrations, showing a typical macroscale property of polymer solutions with a lower critical solution temperature (LCST) of ∼271.4 °C. In situ Raman spectroscopic analyses show that the MgSO4 concentration in fluid F1 increases with an increase in temperature, whereas that in fluid F2 decreases with an increase in temperature. In addition, HSO4(­), which does not readily form complexes with Mg(2+), tends to accumulate in fluid F2. Analyses of the v1(SO4(2­)) bands confirmed the presence of four-sulfate species of unassociated SO4(2­) (∼980 cm(­1)), contact ion pairs (CIPs; ∼995 cm(­1)), and triple ion pairs (TIPs; ∼1005 cm(­1)) in aqueous solution, and more complex ion pair chain structure (∼1020 cm(­1)) in fluid F1. Comparison of the sulfate species in fluids F1 and F2 at 280 °C suggests that SO4(2­) in fluid F2 is less associated with Mg(2+). On the basis of in situ visual and Raman spectroscopic observations, we suggest that the formation of the complex Mg(2+)­SO4(2­) ion association might be responsible for the liquid­liquid phase separation. In addition, Raman spectroscopic analyses of the OH stretching bands indicate that the hydrogen bonding in fluid F1 is stronger than that in fluid F2, which might be ascribed to the increasing probability of collision of H2O with Mg(2+) and SO4(2­) in fluid F1.

Containment of fluid samples in the hydrothermal diamond-anvil cell without the use of metal gaskets: performance and advantages for in situ analysis.

Metal gaskets (Re, Ir, Inconel, or stainless steel) normally used to contain fluid samples in the hydrothermal diamond-anvil cell (HDAC) are sometimes undesirable due to possible contamination and to gasket deformation at high pressures and temperatures resulting in nonisochoric behavior. Furthermore, in x-ray spectroscopic experiments, metal gaskets may attenuate the incident x-ray beam and emitted fluorescence x-rays, and the interaction of scattered radiation with the gasket may produce fluorescence that interferes with the x-ray spectrum of the sample. New arrangements and procedures were tested for the operation of the HDAC without using the metal gaskets. Distilled, de-ionized water was loaded into the sample chamber, a laser-milled recess 300 microm in diameter and approximately 50 microm deep centered in the 1.0 mm face of the lower diamond anvil, and sealed by pressing the top diamond anvil face directly against the lower one without a metal gasket in between. A maximum sample pressure of 202 MPa at 617 degrees C was maintained for a duration of 10 min without evidence of leakage. A small change in fluid density was observed in one experiment where the sample was held at 266 MPa at 708 degrees C for 10 min. The gasketless HDAC was also employed in x-ray absorption spectroscopy experiments, where, in addition to the sample chamber in the lower diamond, two grooves were milled at a 90 degrees angle to each other around the sample chamber to minimize the attenuation of incident and fluorescent x rays. With a minimum distance between the sample chamber and the grooves of 80 microm, a pressure of 76 MPa at 500 degrees C was maintained for 2 h with no change in the original fluid density.

Synchrotron x-ray spectroscopy of EuHNO3 aqueous solutions at high temperatures and pressures and Nb-bearing silicate melt phases coexisting with hydrothermal fluids using a modified hydrothermal diamond anvil cell and rail assembly.

A modified hydrothermal diamond anvil cell (HDAC) rail assembly has been constructed for making synchrotron x-ray absorption spectroscopy, x-ray fluorescence, and x-ray mapping measurements on fluids or solid phases in contact with hydrothermal fluids up to approximately 900 degrees C and 700 MPa. The diamond anvils of the HDAC are modified by laser milling grooves or holes, for the reduction of attenuation of incident and fluorescent x rays and sample cavities. The modified HDAC rail assembly has flexibility in design for measurement of light elements at low concentrations or heavy elements at trace levels in the sample and the capability to probe minute individual phases of a multiphase fluid-based system using focused x-ray microbeam. The supporting rail allows for uniform translation of the HDAC, rotation and tilt stages, and a focusing mirror, which is used to illuminate the sample for visual observation using a microscope, relative to the direction of the incident x-ray beam. A structure study of Eu(III) aqua ion behavior in high-temperature aqueous solutions and a study of Nb partitioning and coordination in a silicate melt in contact with a hydrothermal fluid are described as applications utilizing the modified HDAC rail assembly.

Determination of epsomite-hexahydrite equilibria by the humidity-buffer technique at 0.1 MPa with implications for phase equilibria in the system MgSO4-H2O.

Epsomite (MgSO(4).7H(2)O) and hexahydrite (MgSO(4).6H(2)O) are common minerals found in marine evaporite deposits, in saline lakes as precipitates, in weathering zones of coal and metallic deposits, in some soils and their efflorescences, and possibly on the surface of Europa as evaporite deposits. Thermodynamic properties of these two minerals reported in the literature are in poor agreement. In this study, epsomite-hexahydrite equilibria were determined along four humidity-buffer curves at 0.1 MPa and between 25 and 45 degrees C. Results obtained for the reaction epsomite = hexahydrite + H(2)O, as demonstrated by very tight reversals along each humidity buffer, can be represented by ln K(+/- 0.012) = 20.001 - 7182.07/T, where K is the equilibrium constant, and T is temperature in Kelvin. The derived standard Gibbs free energy of reaction is 10.13 +/- 0.07 kJ/mol, which is essentially the same value as that calculated from vapor pressure measurements reported in the literature. However, this value is at least 0.8 kJ/mol lower than those calculated from the data derived mostly from calorimetric measurements.