Oxidation Regime Research Articles

Enantio-Recognition and Charge Transfer Complex Formation Involving Tetrathiafulvalene-Appended Chiral 1,2-Cyclohexane-Diamine: An Integrated Experimental and Theoretical Study.

In this work, we exploit the electronic features of tetrathiafulvalene (TTF) as a backbone in synthesizing chiral derivatives. The aim is to make use of TTF's well-known and unique redox and semiconducting properties in the fields of enantio-selective recognition and chiral charge transfer (CT) complex preparation, with the ultimate objective of obtaining devices with various potential applications, ranging from plasmonics to quantum computing. In particular, both cyclohexane-bis (TTF-amide)-based enantiomers 1-(S,S) and 1-(R,R), stable under an oxidation regime, have been selected, and under these conditions, the electrochemical enantiospecific response of the four possible systems, coming from the combination with L- and D-tartaric acid, respectively, was tested. The 1:tartaric acid adducts show lower oxidation potentials than the pristine 1, together with clear enantio-discrimination demonstrated by sizeable potential differences in the range of 29-46 mV between the diastereomeric adducts. Because the oxidation potential of 1 suggests the possibility of the formation of CT complexes, impedance and FT-IR spectra were recorded to confirm this hypothesis in the case of the CT complex 1:I2. The experimental results obtained through the FT-IR analysis were also compared with the theoretical results deriving from the DFT-based calculations.

High temperature oxidation regime transitions in hafnium carbide

AbstractUnderstanding the oxidation behavior of hafnium carbide is crucial to its application in extreme environments. In this work, the transition in high‐temperature oxidation kinetics regimes in hafnium carbide is explained based on phase equilibria considerations supported by observed changes in oxide scale microstructure evolution associated with different transformation pathways. Below, a composition‐dependent critical temperature and oxygen pressure, hafnium carbide first transforms to an amorphous material with nominal composition HfO2C followed by phase separation into carbon and hafnia domains. Subsequently, gaseous transport through a nanometric pore network formed by oxidative removal of phase‐separated carbon becomes rate‐limiting. Above this critical point, the oxidation sequence involves a direct transformation from hafnium carbide to hafnia and gaseous products, leading to dissimilar scale morphologies responsible for the reported transition from gaseous to solid‐state diffusion‐limited oxidation regimes at ultra‐high temperatures.

Modeling and simulation of a novel chemical process for clean hydrogen and power generation

The present work aims to develop a novel chemical process for clean hydrogen and power production and simulate it accordingly through a unique thermodynamic equilibrium model. This particular process is based on a partial oxidation of hydrogen sulfide (H2S) at superadiabatic conditions to study its respective chemical products. The simulation of superadiabatic partial oxidation of H2S is developed through the present model for the first time in the Aspen Plus. The process is further studied by varying different operating variables with an overall goal of optimizing the H2S conversion into hydrogen. The developed model predicts a satisfactory H2 production flow rate coupled with a low-sulfur dioxide (SO2) output within the superadiabatic partial oxidation regime at an operating pressure below 0.5 bar. The H2S conversion into H2 is then found to be 23.48 % at 0.25 bar. The overall energy and exergy efficiencies of the system are found to be 87.51 % and 70.08 % respectively. The dissociation of H2S in the presence of stoichiometric air results in elemental sulfur and hydrogen production rates of 0.0019 kg/s and 0.0012 kg/s, respectively.

Myofibrillar protein hydrolysis under hydroxyl radical oxidative stress: Structural changes and their impacts on binding to selected aldehydes

In this study, a hydroxyl radical oxidation system was established to simulate the oxidation process in fermented meat products. This system was employed to examine the structural changes in myofibrillar proteins (MPs) resulting from tryptic hydrolysis after a hydroxyl radical oxidative regime. The effect of these changes on the ability of MPs to bind selected aldehydes (3-methyl butanal, pentanal, hexanal, and heptanal) was also investigated. Moderate oxidation (H2O2 ≤ 1.0 mM) unfolded the structure of MPs, facilitating trypsin-mediated hydrolysis and increasing their binding capacity for the four selected aldehydes. However, excessive oxidation (H2O2 ≥ 2.5 mM) led to cross-linking and aggregation of MPs, inhibiting trypsin-mediated hydrolysis. The oxidised MPs had the best binding capacity for heptanal. The interaction of the oxidised trypsin-hydrolysed MPs with heptanal was driven by hydrophobic interactions. The binding of heptanal affected the structure of the oxidised trypsin-hydrolysed MPs and reduced their α-helix content.

Reliable calibration and validation of phenomenological and hybrid models of high-cell-density fed-batch cultures subject to metabolic overflow

Fed-batch cultures are the preferred operation mode for industrial bioprocesses requiring high cellular densities. Avoids accumulation of major fermentation by-products due to metabolic overflow, increasing process productivity. Reproducible operation at high cell densities is challenging (>100 gDCW/L), which has precluded rigorous model evaluation. Here, we evaluated three phenomenological models and proposed a novel hybrid model including a neural network. For this task, we generated highly reproducible fed-batch datasets of a recombinant yeast growing under oxidative, oxygen-limited, and respiro-fermentative metabolic regimes. The models were reliably calibrated using a systematic workflow based on pre-and post-regression diagnostics. Compared to the best-performing phenomenological model, the hybrid model substantially improved performance by 3.6- and 1.7-fold in the training and test data, respectively. This study illustrates how hybrid modeling approaches can advance our description of complex bioprocesses that could support more efficient operation strategies.

Oxidation Mechanism and Surface Characterization of Pyrolytic Graphite in Simulated Air for Pyrochemical Reprocessing Application

Accidental air ingress into the containment chamber of pyrochemical reprocessing of spent nuclear fuels can cause severe oxidation of graphite components. Pyrolytic graphite (PyG) coating on conventional high-density graphite (HDG) is proposed for protection against oxidation, molten salt, and molten metal corrosion. The aim of the present study is to evaluate the thermal stability and kinetic parameters and propose a suitable oxidation mechanism of PyG under simulated air using thermogravimetry analysis (TGA). In dynamic oxidation, a linear increase in the oxidation onset, peak, and burnout temperature is observed for PyG synthesized at increasing pyrolysis temperature from 1200 to 2400°C except for 1400°C. The isothermal oxidation study showed a similar trend i.e., a decrease in the linear oxidation rate constant value for any given isotherm with increasing pyrolysis. The Arrhenius plot showed two-stage oxidation regimes operating between 600 to 1000°C. In regime-I, between 600 to ∼800°C controlled by surface chemical reaction kinetics, the activation energy is measured between 100-200 kJ.mol−1. The graphite-oxygen reaction initiates and propagates preferentially along the prismatic planes at the sample edges, where the dangling bonds of stacked graphite layer structures are exposed. In regime-II operating above ∼800°C, the surface reaction rate is infinitely faster, and the diffusional mass transport becomes a rate-limiting factor. In this regime, the graphite-oxygen initiates by pore formation on defective reactive sites on the bulk surface and propagates by pore-widening and pore-coalescence mechanism. The observed differences in the oxidation rates for different pyrolysis PyG attributed to its intrinsic material properties are investigated. This work provides new insights into the oxidation mechanism of the PyG during accidental air ingress in a pyrochemical reprocessing plant.

Abstract 2471 Supercharged Heme: Unmasking a New Regime of Aromatic Oxidation by an Emergent Superfamily

Abstract 2471 Supercharged Heme: Unmasking a New Regime of Aromatic Oxidation by an Emergent Superfamily

Fractional adaptive observer for variable structure high cell density fed-batch cultures

This paper presents the design and application of a fractional order asymptotic adaptive observer coupled to an adaptive controller for the robust operation of high-cell density cultures in fed-batch mode. The control goal is to maximize biomass productivity by controlling the culture’s estimated specific growth rate. Since the specific growth rate cannot be measured, a fractional order asymptotic adaptive observer is proposed, based on the equivalent integer order asymptotic observer proposed before. Simulations are performed to validate the observer and controller, under the assumption that the system is in the oxidative regime under aerobic conditions. Obtained results show that, in close loop operation, the fractional adaptive observer behaves better than the integer order observer in the presence of measurement noise. For fractional orders of the observer in the range α G [0.6,0.8], it was observed a 51.71% increase in biomass concentration, compared to the biomass obtained with the classic integer-order observer. Furthermore, the controlled system reaches very low ethanol concentrations (< 1 grams per liter), which is desirable in this process.

The New Parthian Inscription from New Nisa

The article publishes a fragment of a ceramic vessel with a Parthian inscription preserved on it, discovered in 2012 at the site of New Nisa (Turkmenistan), approximately 120 m northeast of Tower XIII, and currently kept in a private collection in Russia. A small sherd (maximum dimensions 73×45 mm) 5–8 mm thick is most likely a fragment of a jug covered with white engobe. It is possible that, judging by the color of the engobe and the shard in the fracture, as well as the use of a high-temperature oxidative firing regime, the jug was made not in Parthyene, but in Margiana. A one-line inscription written in black paint or ink, of which only nine characters have come down to us, is located on the outside of the vessel, apparently on its hangers. The surviving part of the inscription reads ](y/z) ZNH ʻL wt(?)[. Its translation reads: “[The vessel] is for Vat...” It is possible that the name of the owner of the jug read as Wtpn (*Vātapāna) – “having the protection of the wind(-god)”, known from an Aramaic inscription from Persepolis. Judging by the fact that there is no hint of cursive in the inscription – each letter is written separately, it can be dated in the same way as the entire body of documents from Old Nisa, i.e. e second half of the 2nd – end of the 1st centuries BC.

Understanding the effect of char oxidation on wood temperature profiles for varying heating and oxygen conditions

The use of mass timber framing as a sustainable material, particularly in high-rise buildings, requires detailed structural fire performance calculations. Thermal models describing only the solid phase are cost-effective alternatives to provide information to structural behavior models. Their accuracy depends on an adequate description of drying, pyrolysis, charring and eventually flaming phenomena. While in recent years there have been considerable contributions to the development of such models, there are still open questions. This work proposes a thermal model which incorporates char oxidation, describing both the kinetic- and diffusion-controlled regimes. The model was used to replicate two sets of experimental results which used standard fire calorimeters to study the ignition of thick wood specimens within a range of incident heat fluxes and oxygen concentrations, respectively. The model yields adequate temperature predictions in the early heating stages, but fails to replicate the behavior at later stages, when the effect of the surface combustion is noticeable. In terms of mass loss rates, a poorer performance is observed. To change from one oxidation regime to another, a Damköhler number is proposed, based on char oxidation reaction rates. It is found that for compartment fire conditions, char oxidation will mostly occur develop under diffusion-controlled conditions.

On the Mechanism of Sulfur Dioxide Oxidation in Cloud Droplets

Data from field experiments on the dynamics of SO2 oxidation in cloud droplets are presented. The rapid oxidation of SO2 by molecular oxygen observed in experiments is attributed here to the catalytic action of a pair of manganese and iron ions in droplets. Their inhomogeneous effect by the drop-size distribution, attributed in experiments only to the leaching of ions of these metals from coarse particles of mineral dust is also due to the transition of the oxidation reaction into a branched mode. The results obtained indicate that the branched regime of catalytic oxidation of SO2 detected in cloud droplets should be considered as a new and significant source of sulfates in the atmosphere. This process must be taken into account when considering both the budget of sulfates in the global atmosphere and their impact on the climate.

Synergetic Effects of Isoprene and HOx on Biogenic New Particle Formation

AbstractNew particle formation (NPF) has been observed at various locations, but NPF does not occur in isoprene‐dominant forests. Recent laboratory studies were conducted to understand the role of isoprene in biogenic NPF, and these studies show that isoprene can suppress biogenic NPF, with contradicting theories. To reconcile these discrepancies, we conducted flow tube experiments of biogenic nucleation under a wide range of isoprene over monoterpene carbon ratios (R) and oxidant conditions (OH vs. ozone). Our results show isoprene either suppresses or enhances biogenic NPF, depending on R and oxidation regimes, demonstrating the synergetic effects of isoprene and HOx (OH and HO2) on biogenic NPF. Whereas the suppression of NPF by isoprene is due to the product suppression effects of monoterpene dimers (C20), RO2 + HO2 termination reactions also play important roles in suppressing the dimer formation, another likely process to suppress NPF in the atmosphere.

Efficacy and mechanism of peroxymonosulfate activation by single-atom transition metal catalysts for the oxidation of organic pollutants: Experimental validation and theoretical calculation

Single-atom catalysts can activate peroxymonosulfate (PMS) to enhance its oxidation of organic pollutants in water treatment. We synthesized a series of carbon-supported single-atom transition metal catalysts (MnN@C, FeN@C, CoN@C, NiN@C, and CuN@C) with similar compositions and structures. Their catalytic activity toward PMS activation and oxidation mechanisms were investigated using acid orange 7 (AO7) as a model pollutant. The degradation rate (min−1·mol−1·g·m−2) of AO7 followed order: FeN@C/PMS (7.576 × 103) > MnN@C/PMS (5.104 × 103) > CoN@C/PMS (1.919 × 103) ≫ NiN@C/PMS (0.058 × 103) > CuN@C/PMS (0.035 × 103). Electron transfer mediated by surface-activated PMS was found to be the main regime of AO7 oxidation in the catalytic systems. Density functional theory calculations indicated that the degradation of AO7 was promoted by the intense adsorption of PMS and the electron transfer between AO7 and the surface-activated PMS on the catalyst. The cleavage of the naphthalene ring and the azo group was the primary degradation pathway. The toxicity of the products was significantly reduced. This research provides valuable findings for preparing highly efficient single-atom transition metal catalysts for PMS-based degradation of toxic and refractory organic pollutants from water.

Catalytic oxidation of acetone and ethanol on a platinum wire

The current-voltage characteristics of a thin long platinum wire in air with acetone or ethanol small admixtures were obtained. Using the quadratic dependence of platinum resistance on temperature, the temperature-current dependences for the wire were calculated. At concentrations of combustible gas vapors above a certain value, these dependences show a hysteresis character. Using the assumption of acetone and ethanol complete oxidation on platinum, as a catalyst, and the first order of the oxidation reaction, temperature-current dependences was analysised. The temperature difference between the high and low-temperature stationary regimes of catalytic oxidation on the wire makes it possible to estimate the admixture concentration. As a result, the experimental dependence of the critical current value by catalytic ignition and extinction gas mixture on platinum on the admixture concentration was constructed. With its analytical description, it is possible to fairly accurately estimate the apparent values ​​of the activation energy and the pre-exponential multiplier for the oxidation reaction in a wide temperature range. A method of determining the kinetic parameters for the oxidation reaction based on the experimentally found parameters of degeneracy critical conditions is proposed.

Effect of oxygen blowing on the competitive removal rate of silicon and iron from molten copper

The effect of blown oxygen on the competitive removal of impurities from liquid copper was investigated at 1673 K. Silicon and iron, which are the dominant impurities in molten copper, are clearly separated into the slag by oxygen blowing. Since the area of the reaction site for impurities’ oxidation was found to be one of the most influential aspects, the interfacial area for both cases of top-blowing and bottom blowing was carefully estimated by considering bubbles and cavity formation. The removal rate of the impurities in competitive oxidation regime could be theoretically analyzed. By a comparison of the apparent rate constant obtained from the oxidation experiments with that was theoretically calculated, the present kinetic model based on liquid phase mass transfer of impurities could be verified to be valid for the understanding the competitive removal of the impurities from liquid copper.

Insights into the reaction pathways of platinum dissolution and oxidation during electrochemical processes

Recent studies have shown the limits of passivity of the platinum electrode. Since it is an important benchmarked electrode for various catalysis reactions and a vital counter electrode, it is essential to understand the mechanism of leaching of the platinum electrode. This report studies the electrochemically driven oxidation and leaching of platinum using a combined theoretical and experimental framework. With insights from electrochemistry, surface enhanced Raman spectroscopy, and electrochemically driven reactive MD, different regimes of chemisorption, surface oxidation, and 3D oxide formation are uncovered that directly affect leaching of individual Pt2+(H2O)4 molecules.

Cs-Symmetric, Peripherally Fluorinated Boron Subphthalocyanine–Subnaphthalocyanine Hybrids: Shedding New Light on Their Fundamental Photophysical Properties and Their Functionality as Optoelectronic Materials

Hybridization of boron subphthalocyanine (BsubPc) and boron subnaphthalocyanine (BsubNc) has been modestly explored in the past, and was therefore carried out herein to access a subclass of these chromophores denoted as Ra-FxBsub(Pc3–p-Ncp) hybrids, where Ra is the axial halide substituent (axial chloride, Cl-, or axial fluoride, F-), x = 8, and p = 1. These chromophores were targeted as new candidate materials for organic electronic applications due to their Cs symmetry, in-plane dipole moment, and unique photophysical properties. Cl-/F- F8Bsub(Pc2-Nc1) hybrids were compared to Cl-/F- F8BsubPc hybrids, which are analogous compounds with an identical number of peripheral fluorine atoms but lower degree of π-conjugation. Upon photoexcitation of dilute toluene solutions and doped thin films with polystyrene as a nonemissive host, F8Bsub(Pc2-Nc1) hybrids exhibited distinctively broad absorption spectra and narrow emission profiles with red-shifted peak photoluminescence wavelengths in the 618–623 nm region compared to F8BsubPc hybrids (581–584 nm). Electroluminescence properties were probed in simple solution-cast organic light-emitting diodes (OLEDs) in which all four hybrids were diluted within an F8BT emissive polymer host. Upon electronic excitation, electroluminescence (EL) of Cs-symmetric hybrids followed the same trends as photoluminescence (PL), with OLED devices displaying narrow EL in the orange region (588–592 nm) for F8BsubPc hybrids and in the near-red region for F8Bsub(Pc2-Nc1) hybrids (627–632 nm). The photophysical processes important to OLEDs moderately improved with less π-conjugation in the periphery of the Cs-symmetric hybrids [F8Bsub(Pc2-Nc1) vs F8BsubPc; EQEMax: 0.099% vs 0.129%; luminance: 500 cd/m2 vs 1000 cd/m2 at maximum current density; relative PL quantum yields (QYs) ≈ 17–22% vs ≈ 35–44%]. Electrochemical data showed that Cs symmetry introduces reversibility or quasi-reversibility in the oxidation regime at potentials >1 V, and peripheral fluorination enables reversibility in the reduction process. Overall, F8Bsub(Pc2-Nc1) hybrids embody several unique physical characteristics into one: broad absorption spectra (full width at half-maximum height, FWHMsolabs = 53–55 nm, FWHMfilmabs = 71 nm), narrow near-red electroluminescence (FWHMOLEDEL = 33 nm), and photoluminescence (FWHMsolPL = 25–26 nm, FWHMfilmPL = 32 nm) emission, small energy band gaps (1.95–1.96 eV), high extinction coefficients (ε ≈ (5.65–6.16) × 104 M–1 cm–1), and dual electrochemical versatility. These results provide new physical insights into the material properties of Cs-symmetric macrocycles and advance the consideration of F8Bsub(Pc2-Nc1) and F8BsubPc hybrids for optoelectronic applications.

Impact of flow velocity on the heterogeneous reaction of SO2 over Fe2O3

Flow velocity, potentially linked to dry deposition velocity and wind speed parameters, show non-marginal significance in the heterogeneous oxidation of SO2 on α-Fe2O3 particles. Our uptake measurement results produce lab-based evidence that an increase in flow velocity can potentially strengthen SO2 uptake capability over α-Fe2O3 by nearly one order of magnitude within the range of considered reaction conditions. Additionally, specimen analysis of surface S-containing products indicates a distinct SO2 oxidation regime, shifting from the heterogeneous reaction mediated by active sites under low flow velocity and low RH to an aqueous-like multiphase-dominated pathway under high flow velocity and high RH. An attempt was further made to link this experimental parameter to dry deposition velocity regulated by wind force in the atmosphere. This work highlights the significance of flow velocity in triggering fast sulfate production concerning dust chemistry.

Phenomena and mechanism of local oxidation microlithography of 4H–SiC via electrochemical jet anodisation

Local oxidation microlithography (LOM) of 4H–SiC wafers based on the spatial confinement of electrochemical oxidation inside a microelectrolyte jet, namely, electrochemical jet anodisation (EJA), is presented. EJA enables selective growth of the oxide layer on a micro-scale local area with no masks because the anodic reaction occurs exclusively in the jet-substrate interaction area. The shape and height profile of the oxide layer were highly dependent on the anodising conditions. The change in the current density resulted in two distinct oxidation regimes, leading to the formation of either Gaussian-type or doughnut-shaped oxide spots. The oxide growth mechanism was revealed by SEM, AFM and XTEM characterisation of the oxide at the micro/nanoscale. A flat oxide layer with uniform thickness was obtained by applying parametric control. Following a chemical etching process, microstructures were readily created at the patterned oxide locations, demonstrating EJA as a potential lithography technique for microfabrication.

Enhanced Degradation of Antibiotic by Peroxydisulfate Catalysis with CuO@CNT: Simultaneous 1O2 Oxidation and Electron-Transfer Regime.

The nonradical process in the peroxydisulfate (PDS) oxidation system is a promising method for antibiotic removal in water. In this study, CuO@CNT was successfully synthesized by a facile approach to catalyze PDS. The removal efficiency of the antibiotic sulfamethoxazole (SMX) was 90.6% in 50 min, and the stoichiometric efficiency (ΔSMX/ΔPDS) was 0.402. The very different degradation efficiency of common organic contaminants revealed the selective oxidation of the surveyed system. The process of 1O2 oxidation and the electron-transfer regime was exhibited by chemical quenching tests, electron paramagnetic resonance (EPR) determination, a UV–vis spectrophotometer, X-ray photoelectron spectroscopy (XPS) detection, and cyclic voltammetry (CV) measurements. Sustainable catalysis was promoted by the circulation between the surface electron-rich centers of Cu(II) and Cu(III). Dissolved oxygen (DO) and a metastable Cu(III) intermediate contributed to the generation of 1O2. Still, a portion of SMX was removed by the mildly activated PDS. Moreover, the influence factors (pH, dosage, water matrix) were examined, and suppressions were acceptable by common anions and real water. Distinguished from the radical process, unique intermediate products were ascertained via the theoretical calculation and liquid chromatography–mass spectrometry (LC-MS) detection. Furthermore, CuO@CNT showed a satisfactory activation ability in the cycling experiments. Overall, this study developed CNT to be a supporter of CuO, unveiled the mechanism of catalysis, and evaluated the application potential of the nonradical process.