Oxidized Carbon Species Research Articles

Insights into Photothermocatalytic Dry Reforming of Methane on Ru/La‐Al2O3 using Carbonate Species and Reactive Oxygen Species to Enhance the Fuel Production Rates and Completely Prevent Coking

AbstractPhotothermocatalytic dry reforming of methane (DRM) offers a promising strategy for converting solar energy into fuel. However, the high light intensity required for high fuel production rates and thermodynamically more favorable coking side reactions limit this strategy. Herein, a nanocomposite of La‐doped Al2O3 supporting Ru nanoparticles (NPs) (Ru/La‐Al2O3) is synthesized. At relatively low light intensity (80.2 kW m−2), Ru/La‐Al2O3 obtains high production rates of CO and H2 per gram of Ru (rRu, CO and rRu, H2, 8410.19 and 7181.94 mmol gRu−1 min−1) with light‐to‐fuel efficiency (η, 26.6%), and completely prohibits coking. In striking contrast, the reference catalyst without La doping (Ru/Al2O3) exhibits lower rRu, CO, rRu, H2, η and produces large amounts of coke. The improved photothermocatalytic performance stems from the fact that reactive oxygen species and carbonate species are involved in the oxidation of carbon species (rate‐determining steps of DRM) through two different reaction pathways, which significantly increases catalytic activity and prevents the carbon species from polymerizing into coke. Additionally, light not only enhances the DRM on Ru NPs and the oxidation reaction between carbonate species and carbon species but also promotes the dissociation of CH4 and desorption of H2, which improves the catalytic activity and product selectivity of Ru/La‐Al2O3.

The Geochemical Potential for Metabolic Processes on the Sub-Neptune Exoplanet K2-18b

Quantifying disequilibria is important to understand whether an environment could be habitable. It has been proposed that the exoplanet K2-18b has a hydrogen-rich atmosphere and a water ocean, making it a “hycean world.” The James Webb Space Telescope recently made measurements of methane, CO2, and possibly dimethyl sulfide (DMS) in the atmosphere of this planet. The initial interpretation of these data is that they may support the occurrence of hycean conditions. Here I attempt to take a next step in exploring the prospects for habitability. I use constraints on the abundances of atmospheric gases to calculate how much chemical disequilibrium there could be, assuming that K2-18b is a hycean world. I find that the presence of oxidized carbon species coexisting with abundant H2 (1–1000 bars) at cool to warm (25°C–120°C) conditions creates a strong thermodynamic drive for methanogenesis. More than ∼75 kJ (mol C)−1 of free energy can be released from CO2 hydrogenation. Partially oxidized carbon compounds such as DMS (if present) also have the potential to provide metabolic energy, albeit in smaller quantities. Because of the thermodynamic instability of CO2 under hycean conditions, other reductive reactions of CO2 are likely to be favored, including the synthesis of amino acids. Glycine and alanine synthesis can be energy releasing or at least much less costly on K2–18b than in Earth’s ocean, even when NH3 is scarce but not totally absent. These first bioenergetic calculations for a proposed ocean-bearing exoplanet lay new groundwork for assessing exoplanetary habitability.

Synergetic effect for highly efficient light-driven CO2 reduction by CH4 on Co/Mg-CoAl2O4 promoted by a photoactivation

The utilization of photothermocatalytic dry reforming of methane is shown to be an up-and-coming technology. However, reaching high fuel productivity at a comparatively low light intensity and effectively suppressing the side reactions of coking in the DRM process are still two tough difficulties. Under focused UV–vis–IR irradiation at a relatively low light intensity of 80.5 kW m−2, a nanostructure of Co/Mg-CoAl2O4 possesses excellent photothermocatalytic activity and a light-to-fuel efficiency of 34.2 % and a low carbon deposition rate compared to its reference catalyst without Mg2+ doping (Co/CoAl2O4). The improved photothermocatalytic activity and coking resistance of Co/Mg-CoAl2O4 mainly comes from the synergetic effect, including Mg2+ doping, the active lattice oxygen in CoAl2O4 also participating in the oxidation of carbon species, and strong light absorption properties of the Mg-CoAl2O4. The photoactivation promotes DRM on Co nanoparticles while significantly facilitates the C* oxidation by strongly adsorbed CO2 on doped Mg2+.

Reaction path model of the formation of abiotic immiscible hydrocarbon fluids in subducted carbonated serpentinites, Lanzo Massif (Western Italian Alps)

Fluids generated from subducted slabs participate in the cycling of deep carbon in the crust and upper mantle. In these fluids, aqueous carbon species vary in oxidation state between +IV and -IV depending on whether the fluids are oxidizing or reducing, respectively. Most studies of subduction-zone fluids have focused on oxidized carbon species. However, recent studies of natural samples have demonstrated the occurrence of deep, reducing fluids, generated in both subducted oceanic upper mantle and crustal rocks. CH4-H2-rich fluid inclusions in subducted carbonated serpentinites have demonstrated the existence of abiotic, immiscible, hydrocarbon fluids at upper mantle conditions. To investigate the formation of such immiscible hydrocarbon fluids during the evolution of subducted carbonated serpentinites, we used equilibrium constants from the Deep Earth Water model to carry out predictive chemical mass transfer modeling to simulate the alteration reactions. A novel feature of the models was the inclusion of an immiscible hydrocarbon fluid containing six components (CH4,f,C2H6,f,C3H8,f,isoC4H10,f,CO2,f,H2,f). This feature enabled prediction of the formation of a separate immiscible fluid in equilibrium with aqueous species and minerals.We developed a predictive reaction path model of invasive H2,f reacting with carbonated serpentinites and interstitial aqueous fluids for comparison with the natural samples from the Lanzo Massif, western Italian Alps. Over a range of temperatures and pressures, immiscible hydrocarbon fluids formed in association with altered mineral assemblages. Reaction progress caused the transformation of carbonated serpentinites and the formation of clinopyroxene, brucite, graphite, and hydrocarbon fluids, along with changes of pH, logfO2, and aqueous species. CH4,f was the most abundant hydrocarbon species in all the models. The overall results at 2.0 GPa and 400 to 450 °C were consistent with the natural samples from the Lanzo Massif. Interestingly, large amounts of H2O formed due to oxidation of H2. More hydrocarbons and H2O formed in models with lower fluid/rock mass ratios or with more reactant H2. Models at different pressure and temperature conditions showed similar results with some variation in the relative stabilities of aragonite, graphite and olivine solid solution, and associated differences in mineral sequences, hydrocarbon fluids, values of aqueous species, and the final logfO2 and pH. Our models strongly support the laboratory and field evidence that reduction of carbonated serpentinites by infiltrating H2 fluids can cause the formation of immiscible, abiotic hydrocarbon fluids in subduction zones.

Effective UV–visible-infrared light-driven photothermocatalytic dry reforming of methane on Ni/Ni-MgO caused by a novel synergetic effect and photoactivation

Light-driven photothermocatalytic dry reforming of methane (DRM) is a promising technology which can efficiently convert two greenhouse gases of CO2 and CH4 into fuels and realize effective solar energy storage simultaneously. It is greatly challenging to achieve high fuel production rate with a relatively low light intensity and restrain the coking side-reactions that cause catalyst deactivation. Herein, a novel nanocomposite of Ni nanoparticles (NPs) loaded on Ni-doped MgO (Ni/Ni-MgO) was prepared. Very high production rate (r) of H2 and CO (82.78 mmol min−1 g−1 and 98.05 mmol min−1 g−1) as well as a light-to-fuel efficiency (η, 28.8%) are obtained with concentrated UV–vis IR irradiation at a relatively low light intensity (78.8 kw m−2). Ni/Ni-MgO displays excellent durability due to its very low coking rate of 2.46 × 10−3 gc h−1 g−1catalyst, reduced by 11.6 times as compared to that of a reference sample of Ni NPs loaded on MgO (Ni/MgO). This is attributed to a synergetic effect between Ni NPs and Ni-MgO, in which the active oxygen of Ni-doped MgO participates in the oxidation of carbon species as one of the rate-determining steps of DRM, thus facilitating DRM on Ni NPs and greatly improving coking resistance. A photoactivation is found to greatly reduce activation energy and thus enhances catalytic activity due to the substantial facilitation of carbon oxidation by light irradiation.

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

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

A Novel Synergetic Effect and Photoactivation Lead to Very Effective UV–Visible–Infrared Light‐Driven Photothermocatalytic CO2 Reduction with CH4 on Ni/Ni‐Doped Al2O3

A nanocomposite of Ni nanoparticles (NPs) loaded on Ni‐doped Al2O3 (Ni/Ni‐Al2O3) is prepared. Very effective photothermocatalytic dry reforming of methane (DRM) is acquired by Ni/Ni‐Al2O3 under focused UV–vis–IR illumination with a relatively low light intensity of 80.7 kW m−2. Under focused UV–vis–IR illumination, Ni/Ni‐Al2O3 has high production rates of H2 (, 72.62 mmol g−1 min−1) and CO (rCO, 88.29 mmol g−1 min−1) as well as a large light‐to‐fuel efficiency (η) of 28.0%. Compared with a reference catalyst of Ni NPs loaded on Al2O3 (Ni/Al2O3), the photothermocatalytic activity and η of Ni/Ni‐Al2O3 are enhanced and its photothermocatalytic durability is significantly improved due to its coking rate being dramatically decreased by 42.5 times. This is attributed to a synergistic effect between Ni NPs and Ni‐Al2O3: the active oxygen of Ni‐Al2O3 participates in the oxidation of carbon species as one of decisive steps for DRM, thus not only improving the catalytic activity, but also dramatically promoting coking resistance. It is found that light not only plays a heating role, but also substantially reduces the activation energy of DRM, thus improving the catalytic activity and coking resistance due to the great acceleration of carbon oxidation upon focused illumination (photoactivation).

Thermal and Plasma-Assisted CO2 Methanation over Ru/Zeolite: A Mechanistic Study Using In-Situ Operando FTIR

CO2 methanation is an attractive reaction to convert CO2 into a widespread fuel such as methane, being the combination of catalysts and a dielectric barrier discharge (DBD) plasma responsible for synergistic effects on the catalyst’s performances. In this work, a Ru-based zeolite catalyst, 3Ru/CsUSY, was synthesized by incipient wetness impregnation and characterized by TGA, XRD, H2-TPR, N2 sorption and CO2-TPD. Catalysts were tested under thermal and plasma-assisted CO2 methanation conditions using in-situ operando FTIR, with the aim of comparing the mechanism under both types of catalysis. The incorporation of Ru over the CsUSY zeolite used as support induced a decrease of the textural properties and an increase of the basicity and hydrophobicity, while no zeolite structural damage was observed. Under thermal conditions, a maximum CO2 conversion of 72% and CH4 selectivity above 95% were registered. These promising results were ascribed to the presence of small Ru0 nanoparticles over the support (16 nm), catalyst surface hydrophobicity and the presence of medium-strength basic sites in the catalyst. Under plasma-catalytic conditions, barely studied in similar setups in literature, CO2 was found to be excited by the plasma, facilitating its adsorption on the surface of 3Ru/CsUSY in the form of oxidized carbon species such as formates, aldehydes, carbonates, or carbonyls, which are afterwards progressively hydrogenated to methane. Adsorption and surface reaction of key intermediates, namely formate and aldehydic groups, was observed even on the support alone, an occurrence not reported before for thermal catalysis. Overall, similar reaction mechanisms were proposed for both thermal and plasma-catalysis conditions.

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells.

Silicon (Si)‐based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re‐formation of the solid electrolyte interphase and consumption of active lithium. The pre‐lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si‐based LIB full‐cells and enable their practical implementation. Here, the use of lithium squarate (Li2C4O4) as low‐cost and air‐stable pre‐lithiation additive for a LiNi0.6Mn0.2Co0.2O2 (NMC622)‐based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full‐cells is reported, which grows linearly with the initial amount of Li2C4O4, due to the extra Li+ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre‐lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre‐lithiation additive.

Fate of Carbonates in the Earth’s Mantle (10-136 GPa)

Earth carbon cycle shapes the evolution of our planet and our habitats. As a key region of carbon cycle, subduction zone acts as a sole channel transporting supracrustal carbonate rocks down to the mantle, balancing carbon budget between the Earth’s surface and the interior, and regulating CO2 concentration of the atmosphere. How carbonates evolve at depth is thus, a most fundamental issue in understanding carbon flux and carbon sequestration mechanism in the Earth. This study reviews prominent progresses made in the field of crystal chemistry of carbonates along subduction geotherms. It clearly finds that, in addition to common carbonates in the Earth’s crust, several new polymorphs of carbonates have been discovered to be stable under high-pressure and high-temperature conditions. This opens possibilities for oxidized carbon species in the deep Earth. However, metamorphic decarbonatation and reduction reactions restrict subducting carbonates to the top-mid region of the lower mantle. Specifically, subsolidus decarbonatation in the form of carbonates reacting with silicates has been proposed as an efficient process releasing CO2 from slabs to the mantle. Besides, carbonate reduction in the metal-saturated mantle likely results in generation of super-deep diamonds and a considerable degree of carbon isotope fractionation. Review of these novel findings leads us to consider three issues in the further studies, including 1) searching for new chemical forms of carbon in the mantle, 2) determining the reduction efficiency of carbonates to diamonds and the accompanying carbon isotope fractionation and 3) concerning carbon cycle in subduction of continental crust.

The Influence of Alkanethiols on the Production of Hydrophobic Gold Nanoparticles via Pulsed Laser Ablation in Liquids

The ability to suspend plasmonic metal nanoparticles in apolar environments is an important feat towards harnessing their optical properties for use in amphiphilic biological environments. Pulsed laser Ablation in Liquids (PLAL) is a well-established method for the production of gold nanoparticles (AuNPs) in aqueous environments; however, ablation in organic liquids for the synthesis of hydrophobic AuNPs still has many unknowns, such as the relationship between colloidal stability and the ligand shell. In this study, hydrophobic AuNPs were produced by PLAL of gold in a 1-alkanethiol/n-decane solution and treated with laser fragmentation. Results demonstrate that longer chain length ATs produced particles with a smaller average size; however, there was no strong correlation between alkanethiol (AT) concentration and particle size. Stability was investigated by monitoring the temporal evolution of the extinction spectra which revealed that lower concentrations of AT stabilize the colloids while higher concentrations tend to result in quicker particle aggregation. Furthermore, longer chain length ATs demonstrated improved stability. Additionally, vibrational spectroscopy was employed to examine the AuNP surface chemistry, which pointed to the presence of oxidized carbon species and graphitic carbon.

Oxidative aging of epoxy asphalt

ABSTRACT Oxidative aging is responsible for the irreversible asphalt stiffening and embrittlement leading to asphalt pavements of increased susceptibility to fatigue and thermal cracking. In recent years, various flexible binders have been introduced in asphalt industry to produce long-life pavements and the epoxy asphalt binders are among them. Nevertheless, in-depth understanding of the oxidative aging mechanism of epoxy asphalt binders and binding systems is still needed to enable reliable predictions of material degradation through service life. In this research, the compositional and rheological changes of epoxy asphalt, with and without filler, were analysed by means of Fourier Transform Infrared spectroscopy and Dynamic Shear Rheometer. Especially, kinetics (Arrhenius) parameters of epoxy asphalt have been determined by tracking the chemical composition changes. Oxidation of carbon species in epoxy asphalt is compositional dependent, and low values of activation energy accompany in low values of reaction rate are shown by adding epoxy in asphalt. Furthermore, the epoxy asphalt mastics (binders with filler) have been subjected to rheological testing to evaluate the stiffening effect as oxidation proceeds. Increase of modulus over a wide range of frequencies, decrease of frequency dependency of modulus of epoxy asphalt and shifting of phase angle to lower values are some important observations noticed as well. Overall, oxidation in epoxy asphalt materials occurs slowly yielding to oxygen-resistant binders when epoxy compounds are incorporated in asphalt binders.

The impacts of fossil fuel emission uncertainties and accounting for 3-D chemical CO2 production on inverse natural carbon flux estimates from satellite and in situ data

Atmospheric carbon dioxide (CO2) inversions for estimating natural carbon fluxes typically do not allow for adjustment of fossil fuel CO2 emissions, despite significant uncertainties in emission inventories and inadequacies in the specification of international bunker emissions in inversions. Also, most inversions place CO2 release from fossil fuel combustion and biospheric sources entirely at the surface. However, a non-negligible portion of the emissions actually occurs in the form of reduced carbon species, which are eventually oxidized to CO2 downwind. Omission of this ‘chemical pump’ can result in a significant redistribution of the inferred total carbon fluxes among regions. We assess the impacts of different prescriptions of fossil fuel emissions and accounting for the chemical pump on flux estimation, with a novel aspect of conducting both satellite CO2 observation-based and surface in situ-based inversions. We apply 3-D carbon monoxide (CO) loss rates archived from a state-of-the-art GEOS chemistry and climate model simulation in a forward transport model run to simulate the distribution of CO2 originating from oxidation of carbon species. We also subtract amounts from the prior surface CO2 fluxes that are actually emitted in the form of fossil and biospheric CO, methane, and non-methane volatile organic compounds (VOCs). We find that the posterior large-scale fluxes are generally insensitive to the finer-scale spatial differences between the ODIAC and CDIAC fossil fuel CO2 gridded datasets and assumptions about international bunker emissions. However, accounting for 3-D chemical CO2 production and the surface correction shifts the global carbon sink, e.g. from land to ocean and from the tropics to the north, with a magnitude and even direction that depend on assumptions about the surface correction. A GOSAT satellite-based inversion is more sensitive to the chemical pump than one using in situ observations, exhibiting substantial flux impacts of 0.28, 0.53, and −0.47 Pg C yr−1 over tropical land, global land, and oceans, due to differences in the horizontal and vertical sampling of the two observation types. Overall, the biases from neglecting the chemical pump appear to be minor relative to the flux estimate uncertainties and the differences between the in situ and GOSAT inversions, but their relative importance will grow in the future as observational coverage further increases and satellite retrieval biases decrease.

Hyperosmotic Infusion and Oxidized Surfaces Are Essential for Biofilm Formation of Staphylococcus capitis From the Neonatal Intensive Care Unit.

Staphylococcus capitis is an opportunistic pathogen often implicated in bloodstream infections in the neonatal intensive care unit (NICU). This is assisted by its ability to form biofilms on indwelling central venous catheters (CVC), which are highly resistant to antibiotics and the immune system. We sought to understand the fundamentals of biofilm formation by S. capitis in the NICU, using seventeen clinical isolates including the endemic NRCS-A clone and assessing nine commercial and two modified polystyrene surfaces. S. capitis clinical isolates from the NICU initiated biofilm formation only in response to hyperosmotic conditions, followed by a developmental progression driven by icaADBC expression to establish mature biofilms, with polysaccharide being their major extracellular polymer substance (EPS) matrix component. Physicochemical features of the biomaterial surface, and in particular the level of the element oxygen present on the surface, significantly influenced biofilm development of S. capitis. A lack of highly oxidized carbon species on the surface prevented the immobilization of S. capitis EPS and the formation of mature biofilms. This information provides guidance in regard to the preparation of hyperosmolar total parenteral nutrition and the engineering of CVC surfaces that can minimize the risk of catheter-related bloodstream infections caused by S. capitis in the NICU.

Examining conductivity, current density, and sizings applied to carbon fibers during manufacture and their effect on fiber-to-matrix adhesion in epoxy polymers

This study provides a comprehensive study of carbon fiber surface treatment conditions for epoxy resins. A set of 27 fibers, derived from DowAska precursor, with alterations to manufacturing conditions only occurring at the electrochemical oxidation and sizing bath. Electrolyte (NH4HCO3) conductivity was varied between 8, 16 and 24 μS/cm while oxidative current density was varied between 0.5, 1.0 and 1.5 A/m2. Subsequent to oxidation, fibers were coated with either epoxy, polyamide or polyurethane compatible sizing. This study is the first to consider electrolyte conductivity, oxidative current density and sizing variables simultaneously and links them to interfacial shear strength (IFSS). Extensive chemical, physical and mechanical characterization was conducted to quantify the changes to fiber properties as a result of treatment variation. Results reveal that varying combinations of electrolyte and applied current density not only vary the degree of oxidation on the fiber, but the types of surface chemistry installed (e.g. ratio of COH, CO, and COOH). Somewhat counter-intuitively, at high conductivities and current densities the degree of oxidized carbon species on the fiber surface is decreased. Indeed, this study shows combinations of surface treatment variables which could be used to promote the formation of surface bound functional groups in preference (e.g. phenolic groups in preference to COOH) to enhance interfacial bonding for a given resin. Determination of fiber roughness for all samples showed no statistical difference between samples, suggesting that mechanical interlocking effects do not play a role in the variations in interfacial adhesion observed herein.

The Effect of Iron‐ and Manganese‐Based Oxygen Carriers as Bed Materials in Oxygen Carrier Aided Combustion

Combustion of organic materials in fluidized bed combustion is generally performed using an over‐stoichiometric air‐to‐fuel ratio. Despite excess air in the system, sub‐stoichiometric combustion regions are present in the fluidized bed because of nonperfect mixing of reactants in the system. These regions with oxygen‐deficient combustion contribute to increased levels of nonoxidized or partially oxidized carbon species. To enhance heat transfer and uniform heat distribution in the incineration chamber, an inert fluidized bed material such as silica sand is generally used. Substitution of silica sand in favor of an oxygen carrier could potentially be used to promote oxygen distribution in the incineration chamber. This is referred to as oxygen carrier‐aided combustion. In this work, three alternative bed materials, previously investigated in chemical looping combustion, are investigated and compared with silica sand in over‐ and sub‐stoichiometric combustion. The materials investigated as bed materials are a manganese ore, the mineral ilmenite, and a synthetic material mixture of Fe2O3 on a ZrO2 support. Results show that during combustion using sub‐stoichiometric air‐to‐fuel ratios, the amount of CO in the effluent gases can be reduced using an active bed material compared to inert silica sand.

Chemical Composition of Surface Species in Pyrolyzed Brown Coals and Their Evolution during the Steam Gasification Reaction

In this paper, a detailed study focused on the characterization of the surface chemical species on the Kansk-Achinsk brown coal chars with different inherent mineral matters, calcium, in particular, and on the evolution of chemical species upon steam gasification at a mild temperature of 700 °C was performed by using surface-sensitive X-ray photoelectron spectroscopy , X-ray absorption near edge structure, and other techniques. It was found that the naturally occurring calcium surface species represented highly dispersed carbonate-like forms. Before gasification, they represented aragonite-like species. However, on steam gasification, they readily underwent solid-phase polymorphic transition into a calcite-like form. The main proportion of the surface carbon atoms (68–71%) on all the chars represented sp²-hybridized carbons in the graphene fragments, while the remaining 29–32% accounted for as oxidized carbon species of different configurations. Mainly, sp²-hybridized carbon atoms were found to be sensitive to activation by a calcium catalyst. The conclusion was drawn that these were highly dispersed calcite-like surface species derived from the aragonite-like ones under steam gasification reaction, which could be responsible for the catalytic activation of sp²-hybridized carbon atoms and for the char gasification reactivity.

Transformation of oxytetracycline by redox-active Fe(III)- and Mn(IV)-containing minerals: Processes and mechanisms

Abiotic mechanisms of oxytetracycline degradation by redox-active minerals, Fe(III)-saturated montmorillonite (Fe-SWy) and birnessite (δ-MnO2), were studied to better understand the environmental behavior of tetracycline antibiotics in aqueous systems. Kinetics of dissipation (adsorption, oxidation and formation of transformation products (TPs)), was investigated up to 7 days, and reaction mechanisms were elucidated based on identification of TPs by liquid chromatography mass spectrometry. Oxytetracycline was completely removed from solution by both minerals, however kinetics, TPs and mechanisms were distinct for each mineral. Oxytetracycline oxidation by δ-MnO2 occurred within minutes; 54 identified TPs were detected only in solution, most of them exhibited decreasing levels with time. In contrast, oxytetracycline was completely adsorbed by Fe-SWy, its degradation was slower, only 29 TPs were identified, among them 13 were surface-bound, and most of the TPs accumulated in the system with time. Oxytetracycline transformation by δ-MnO2 involved radicals, as was proven by electrochemical degradation. Reductive dissolution was observed for both minerals. X-ray photoelectron spectroscopy demonstrated accumulation of Fe(II) on Fe-SWy surface, whereas Mn(II) was primarily released from δ-MnO2 surface. Highly oxidized carbon species (i.e., newly formed TPs) were observed on the surface of both minerals interacting with oxytetracycline. This study demonstrates the impact of structure and reactivity of redox-active minerals on removal and decomposition of tetracycline antibiotics in aqueous systems.

Experimental investigation on thermochemical sulfate reduction in the presence of 1-pentanethiol at 200 and 250 °C: Implications for in situ TSR processes occurring in some MVT deposits

Organic sulfur compounds are ubiquitous in natural oil and gas fields and moderate-low temperature sulfide ore deposits. Previous studies have shown that organic sulfur compounds are important in enhancing the rates of thermochemical sulfate reduction (TSR) reactions, but the details of these reaction mechanisms remain unclear. In order to assess the extent of sulfate reduction in the presence of labile sulfur species at temperature conditions near to those where TSR occurs in nature, we conducted a series of experiments using the fused silica capillary capsule (FCSS) method. The tested systems containing labile sulfur species are MgSO4 + 1-pentanethiol (C5H11SH) + 1-octene (C8H16), MgSO4+1-octene (C8H16), MgSO4+1-pentanethiol (C5H11SH), 1-pentanethiol (C5H11SH)+H2O, and MgSO4 + 1-pentanethiol (C5H11SH) + ZnBr2 systems. Our results show that: (1) intermediate oxidized carbon species (ethanol and acetic acid) are formed during TSR simulation experiments when 1-pentanethiol is present; (2) in the presence of ZnBr2, 1-pentanethiol can be oxidized by sulfate to CO2 at 200 °C, which is within the temperature range observed in natural TSR; and (3) the precipitation of sulfide minerals may significantly promote the rate of TSR, indicating that the rates of in situ TSR reactions in ore deposits could be much faster than previously thought. This may be important for understanding the possibility of in situ TSR as a mechanism for the precipitation of metal sulfides in some ore deposits. These findings provide important experimental evidence for understanding the role of organic sulfur compounds in TSR reactions and the pathway of TSR reactions initiated by organic sulfur compounds under natural conditions.

XPS Study of Rare Earth Redox Mediators for Solid-State Supercapacitors

One of the effective approaches to increase the specific energy of a supercapacitor while maintaining a high specific power is to dissolve active redox species, mediators into the liquid[i],[ii],[iii],[iv] and solid-state[v],[vi],[vii], 4 electrolytes in porous electrodes., Because the mediators are completely dispersed into the ion conducting electrolytes at the molecular level, the utilization rate of the active materials can be maximized. In order to further improve the specific energy of the mediator supercapacitor, redox species that receive/give off multiple electrons in a redox reaction were synthesized and used. It has been proven that the specific energy of a supercapacitor is limited by the ion depletion in the electrolyte during charging. In order to minimize the problem, we use so-called “complimentary” mediators in the positive and negative electrodes. In other words, a mediator that releases positive ions is used for the positive electrode and a mediator that releases negative ions is used for the negative electrode. For example, redox mediators in the form KMFe(CN)6 (M: Y, La, Ce, Pr, or Ho) are used in the positive electrode while VOSO4 is used in the negative electrode. Using rare earth metal based mediators, we improved the specific energy by 60% relative to that of our first generation supercapacitor while maintaining the high specific power. Typical cyclic voltammetry curves for supercapacitors with cathode containing KLaFe(CN)6 or K4Fe(CN)6 mediator and anode containing VOSO4 mediator in comparison with that for an active carbon based supercapacitor are shown in Figure 1. The mediator supercapacitor with the rare-earth mediator exhibited higher specific energy (˃40 Wh/kg) relative to the K4Fe(CN)6 mediator, high charge/discharge efficiency (˃99%) and high reversibility (capacity retention ˃ 90% after 10000 cycles). The specific energy is above the theoretical limit that is anticipated for EDLCs (~15 Wh/kg), which corresponds to depletion of ions in the electrolyte.[viii]As the mediators were synthesized in-house, XPS, XRD, and SEM are used to insure the oxidation states and phase purity and reveal the morphology of the mediators. In Figure 2, the Fe 2p XPS spectra for the mediators are similar regardless of the rare-earth element being used. With the Fe 2p3/2binding energy at ~709, Fe is present with an oxidation state of 2+ as one would expect in this type of material. The spectra for the rare-earth elements Y, La, Ce, and Pr (not shown) are consistent with all being present with an oxidation state of 3+. In the case of Ho, we anticipate the oxidization state to be 3+ but it was difficult to confirm due to lack of reference data. The C 1s spectra (not shown) are dominated by a contribution with binding energy near ~285 eV that corresponds to CN and hydrocarbon chemistries and a minor component with binding energy near 289 eV that corresponds to more oxidized carbon species. The XPS spectra of the N1s region are dominated by a major component with binding energy at 398.0 eV that corresponds to the CN chemistry and a minor component with binding energy near ~402 eV which could be attributed to NOx type of species. Additional ex situ and in situ structural characterization after polarization at different states of charge will be used to correlate with performance characteristics in order to explore the critical factors controlling energy, power, and capacity retention. [i]. G. Lota, K. Fic, and E. Frackowiak, Electrochemistry Communications, 12, 38-41 (2011). [ii]. S. T. Senthilkumar, R. K. Selvan, and J. S. Melo, J. Mat. Chem., 1, 12386-12394 (2013). [iii]. B. Akinwolenmiwa, C. Peng, and G. Z. Chen, J. Electrochem. Soc., 162(5), A5054-A5059 (2015). [iv]. J. Lee, S. Choudhury, D. Weingarth, D. Kim, and V. Presser, ACS Appl. Mater. Interfaces, 8, 23676-23687 (2016). [v]. M. Parthasarathy, C. S. Gopinath, and V. K. Pillai, Chem. Mat., 18, 5244-5255 (2006). [vi]. J. Zhou, Y. Yin, A. N. Mansour, and X. Zhou, Electrochem. Solid-State Lett., 14(3), A25-A28 (2011). [vii]. J. Zhou, J. cai, S. Cai, X. Zhou, and A. N. Mansour, J. Power Sources, 196, 10479-10483 (2011) [viii]. J. P. Zheng, J. Electrochem. Soc., 156(7), A500-A505 (2009). Figure 1