Gas-phase Conditions Research Articles

Supercritical CO2-Stable Cementing Materials Based on Vinyl Ester Resin for Maintaining Wellbore Integrity.

Ensuring long-term wellbore integrity is critical for carbon dioxide geological storage. Ordinary Portland cement (PC) is usually used for wellbore primary cementing and plug operation, and set cement is easily corroded by acidic fluids, such as carbon dioxide, in underground high-temperature and high-pressure (HTHP) environments, resulting in a decrease in the mechanical properties and an increase in permeability. In order to achieve long-term wellbore integrity in a CO2-rich environment This study introduces materials such as thermosetting vinyl ester resin (TSR), filler composite resin (FCR), and low-cost resin cement (RC). Corrosion experiments were conducted using four materials in 28 days under supercritical carbon dioxide gas and water phase conditions of 60 °C and 10 MPa. The samples were characterized through mechanical property testing machines, core permeability measuring instruments, FTIR, XRD, and SEM. The results proved that after corrosion, PC mechanical properties decreased, the permeability increased, and the microscopic composition and morphology changed greatly. Penetrating corrosion occurs in the sample in the gas phase environment, and propulsive corrosion from outside to inside occurs in the water phase environment. However, TSR, FCR, and RC materials all maintain excellent resistance to carbon dioxide corrosion in gas and water environments. They have higher compressive strength and extremely low permeability compared to ordinary Portland cement. These three materials' compressive strengths can be maintained around 131, 99, and 58 MPa, and permeability can be stabilized at <6 × 10-7, <6 × 10-7, and 0.16 mD levels. In summary, the above three materials all show better performance than ordinary Portland cement and are promising alternative materials that can be used in primary cementing and plug operations of carbon dioxide geological storage wells.

Electric Field-assisted Photocatalytic Reduction of Carbon Dioxide over Titanium Dioxide: Influence of the Type and Strength of Electric Field

This study focuses on investigating the sole impact of an external electric field on the photocatalytic activity of TiO2-based materials. Typically, built-in electric fields are used to efficiently separate free energy carriers and improve the photocatalytic performance of semiconductors. The creation of such field requires modifications to the photocatalyst that alter various properties such as adsorption and optical characteristics. These modifications make it challenging to isolate and interpret the promotion effect associated with the electric field alone. The investigations were carried out in the gas-phase conditions in a specially constructed reactor equipped with two electrodes connected to a high – voltage that provides a field strength of up to 5.7·103 V/cm. The results showed that the effect of electric field promotion varied significantly depending on the properties of titanium dioxide, such as structure, adsorption, and presence of impurities. The strength and the type (direct or alternating current) of the electric field also played a determining role. The greatest promoting effect was observed for rutile, the photocatalytic activity of which under an electric field increased threefold in the process of reduction of CO2 with water vapor.Graphical

Supercritical carbon dioxide likely served as a prebiotic source of methanethiol in primordial ocean hydrothermal systems

Abiotic synthesis of methanethiol through CO2 reduction is a presumptive initiation reaction of protometabolism in primordial ocean hydrothermal systems. However, reported artificial means of methanethiol production indicate the necessity of gas-phase condition, rather than aqueous-phase setting, for this prebiotic reaction to occur. Here we show that, under supercritical CO2 with a geochemically feasible concentration of hydrogen, up to 7.9% conversion of hydrogen sulfide to methanethiol is attained through a 14-day reaction at 200 °C on molybdenum sulfide catalyst deposited in a carbonate-NaCl solution. On the present ocean floor, discharges of liquid/supercritical CO2 occasionally occur in close vicinity to hydrothermal vents. Geological records of ancient seafloor suggest prevalence of such CO2 fluxes associated with hydrothermal activities. Our experimental results link these facts with the protometabolism scenario, leading to the possibility that the generation and transportation of methanethiol through the subseafloor CO2 fluxes constituted the beginning step of protometabolism in primordial ocean hydrothermal systems. Thus, the supply of supercritical-CO2-derived materials likely assisted the chemical evolution of life in combination with the known geochemical processes at the vent-ocean interface.

Elucidating the Photophysics and Nonlinear Optical Properties of a Novel Azo Prototype for Possible Photonic Applications: A Quantum Chemical Analysis.

The photophysics and nonlinear optical responses of a novel nitrothiazol-methoxyphenol molecule were investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods with the polarizable continuum model to take the solvent effect into account. Special attention is paid to the description of the lowest absorption band, characterized as a strong π → π* state in the visible region of the spectrum. The TD-DFT emission spectrum analysis reveals a significant Stokes shift of more than 120 nm for the π → π* state in gas phase condition. The results show a great influence of the solvent polarity on the nonlinear optical (NLO) response of the molecule. Specifically, the second harmonic generation hyperpolarizability β(-2ω; ω, ω) shows a large variation from gas to aqueous solvent (82 × 10-30 to 162 × 10-30 esu), exhibiting notably higher values than those reported for standard compounds such as urea (0.34 × 10-30 esu) and p-nitroaniline (6.42 × 10-30 esu). Furthermore, a two-photon absorption analysis indicates a large cross-section (δ2PA = 77 GM) with superior performance compared to several dyes. These results make the molecule quite interesting for nonlinear optics.

Electron-driven processes in enantiomeric forms of glutamic acid initiated by low-energy resonance electron attachment.

Low-energy (0-14eV) resonance electron interaction and fragment species produced by dissociative electron attachment (DEA) for enantiomeric forms of glutamic acid (Glu) are studied under gas-phase conditions by means of DEA spectroscopy and density functional theory calculations. Contrary to a series of amino acids studied earlier employing the DEA technique, the most abundant species are not associated with the elimination of a hydrogen atom from the parent molecular negative ion. Besides this less intense closed-shell [Glu - H]- fragment, only two mass-selected negative ions, [Glu - 19]- and [Glu - 76]-, are detected within the same electron energy region, with the yield maximum observed at around 0.9eV. This value matches well the energy of vertical electron attachment into the lowest normally empty π* COOH molecular orbital of Glu located at 0.88eV according to the present B3LYP/6-31G(d) calculations. Although the detection of asymmetric DEA properties a priori is not accessible under the present experimental conditions, "chirality non-conservation" can be associated with some decay channels. Evidently, the measured spectra for the L- and D-forms are found to be identical, the results, nevertheless, being of interest for the forthcoming experiments utilizing spin-polarized electron beam as a chiral factor in the framework of conventional DEA technique.

Unveiling 5-fluorouracil anti-cancer drug encapsulation within pristine and silver-doped boron, aluminum, and gallium nitride nanotubes: A DFT investigation for advancing nanomedicine

Nanomaterials represent a promising frontier in drug delivery systems for combating cancer, offering precise targeting of tumour cells. This study delves into the encapsulation capabilities of 5-fluorouracil (5-FU) on pristine armchair (6,6) single-wall boron-, aluminium-, and gallium-nitride nanotubes (BNNT, AlNNT, GaNNT), both in their natural state and doped with silver (Ag) atoms under gas phase and water solution conditions. Employing density functional theory calculations at the M06-2X level, we scrutinise the geometric stabilities, encapsulation efficiencies, and electronic interactions between 5-FU molecules and NNTs. Our results reveal that a shorter distance between the drug and nanotube cavity enhances encapsulation ability and solubility while facilitating larger charge transfers, especially within Ag-doped NNTs. The Ag doping significantly augments the reactivity of NNTs towards 5-FU molecules, with thermodynamic analyses indicating exothermic and spontaneous interactions with Ag-doped NNTs. The decapsulation of 5-FU from Ag-BNNT, Ag-AlNNT, and Ag-GaNNT necessitates recovery time 6.42E+00, 3.21E+05, and 2.19E−04 s, with corresponding adsorption energies of −38.70, −49.52, and −28.42 kcal/mol, respectively. Electronic analyses demonstrate notable changes in states’ energy gap and density post-5-FU encapsulation in Ag-doped NNTs, suggesting enhanced sensitivity. Moreover, our investigation delves into topological features, molecular stability, bond strength, and intermolecular interactions using various analytical techniques, including MEPs, ELF maps, NBO, QTAIM, Hirshfeld surface, and RDG analyses. These comprehensive findings underscore the potential of Ag-doped NNTs as promising components for drug delivery systems and biosensors in nanomedicine applications, particularly in sensing and catalytic functions for 5-FU molecule encapsulation and detection.

Oxidation of benzene with N2O on ZSM-5 zeolite: A comparison of gas-phase and supercritical conditions

The catalytic oxidation of benzene with nitrous oxide (N2O) over ZSM-5 zeolite has been carried out in a continuous-flow reactor under supercritical conditions and compared with the results of the gas-phase reaction. Aromatic substrates and nitrous oxide under the conditions of supercritical experiments (300–435 °C, 6.0–18.0 MPa) are both reagents and the supercritical medium. It has been established that the productivity of the supercritical oxidation of benzene into phenol significantly exceeds the productivity of the gas-phase process owing to the limited reversible deactivation of the catalyst under supercritical conditions and the in situ removal of the coke precursors by the dense reaction medium. In addition, it has been demonstrated that a successful in situ regeneration of the deactivated oxidation catalyst can be carried out during the transition from gas-phase reaction conditions to supercritical conditions in one experiment.

Glycyrrhetinic acid interaction with solvated and free electrons studied by the CIDNP and dissociative electron attachment techniques.

Electron transfer plays a crucial role in living systems, including the generation of reactive oxygen species (ROS). Oxygen acts as the terminal electron acceptor in the respiratory chains of aerobic organisms as well as in some photoinduced processes followed by the formation of ROS. This is why the participation of exogenous antioxidants in electron transfer processes in living systems is of particular interest. In the present study, using chemically induced dynamic nuclear polarization (CIDNP) and dissociative electron attachment (DEA) techniques, we have elucidated the affinity of solvated and free electrons to glycyrrhetinic acid (GA)-the aglicon of glycyrrhizin (the main active component of Licorice root). CIDNP is a powerful instrument to study the mechanisms of electron transfer reactions in solution, but the DEA technique shows its effectiveness in gas phase processes. For CIDNP experiments, the photoionization of the dianion of 5-sulfosalicylic acid (HSSA2-) was used as a model reaction of solvated electron generation. DEA experiments testify that GA molecules are even better electron acceptors than molecular oxygen, at least under gas-phase conditions. In addition, the effect of the solvent on the energetics of the reactants is discussed.

Electronic and Nonlinear Optical Properties of B(III)-Submonoazaporphyrin-π-Diimide Compounds: A Density Functional Theory Study.

Three hypothetical complexes were designed using diimides (PMDI, NTCDI, and PTCDI) as the acceptor unit and B(III)-submonoazaporphyrin (1) as the donor unit. These complexes have smaller HOMO-LUMO energy gaps (3.39-3.96 eV) than pristine 1 (6.61 eV). Further, the energy gap can be tuned by changing the number of benzene rings of these diimides. Remarkably, these proposed complexes possess considerable first hyperpolarizabilities (β0) (4865-6921 a.u.), and the regularity of the β0 values remained the same in the gas phase and toluene solvent conditions. There is an inverse relationship between the energy gap and the polarizability/first hyperpolarizability. In addition, absorption spectra, frontier molecular orbitals, and hole electron distributions were obtained using time-dependent density functional theory calculations to emphasize the relationship between structure and properties. Ultraviolet-Visible absorption spectra reveals that all complexes show satisfying IR working regions. Further analysis of the first hyperpolarizability density reveals the nature of the excellent NLO properties of the studied systems. This study can provide valuable insights for the development of potential high-performance NLO molecules.

Reaction Mechanisms and Production of Hydrogen and Acetic Acid from Aqueous Ethanol Using a Rn-Sn/TiO2 Catalyst in a Continuous Flow Reactor

The catalytic reforming of bioethanol can produce green hydrogen (H2) and acetic acid (AcOH). In the present study, the conversion of aqueous ethanol (EtOH) over 4 wt%Ru-4 wt%Sn/TiO2 in a flow reactor was investigated at different temperatures at 0.1 MPa or at various pressures at 260 °C. The ethanol conversion was rather slow in liquid water, while the reactivity increased significantly when water was evaporated. Under gas-phase conditions at 0.1 MPa, the conversion rate increased with increasing reaction temperature, but the AcOH yield and H2 purity decreased due to by-production of CH4, CO, and CO2. The CH4 and CO generated by fragmentation of acetaldehyde (AA), an intermediate, were suppressed by increasing reaction pressure, although the formation of CH4 and CO2 generated from AcOH was pressure independent. Thus, the highest-pressure conditions in steam at a given reaction temperature are preferred for the production of pure H2. The initial step, EtOH → AA, was the rate-determining reaction, and the model experiments using AA as a substrate showed that the Cannizzaro reaction of two AA molecules to form EtOH and AcOH occurred preferentially. This oxidation system was confirmed to be effective at EtOH concentrations of up to 500 g/L in water.

The Magnesium Dication and Water Synergistically Promote the Protonolysis of Two of the B-C Bonds in the Tetraphenylborate Anion.

Analytes are sampled from both solution phase and gas-phase environments during the ESI process, and thus, the mass spectrum that is measured can reflect both solution and gas-phase conditions. In the gas-phase regime, ion-molecule reactions can influence the types of ions that are observed. Herein, the synergistic effects of a Lewis acid (Mg2+) and background water are shown to lead to protonolysis of two of the B-C bonds of the tetraphenylborate ion in the gas phase, giving rise to different ions at different reaction times in ESI-MS/MS experiments in a linear ion trap mass spectrometer. At short reaction times (1 ms), the expected adduct [Mg(BPh4)]+ is observed. At 10 ms, [(HO)Mg(BPh3)]+ and [(HO)2Mg(BPh2)]+ are observed. At 100 ms, the water adducts [(HO)2Mg(BPh2)(H2O)]+ and [(HO)2Mg(BPh2)(H2O)2]+ appear, and these become the dominant ions at longer reaction times. DFT calculations provide a plausible explanation as to why only [(HO)Mg(BPh3)]+ and [(HO)2Mg(BPh2)]+ but not [(HO)3Mg(BPh)]+ are observed.

Urocanic acid as a novel scaffold for next-gen nature-inspired sunscreens: II. Time-resolved spectroscopy under solution conditions.

In recent years the use of synthetic UV filters in commercial skincare formulations has come under considerable scrutiny. Urocanic acid is a naturally occurring UV filter that could serve as a scaffold for developing next-generation biomimetic UV filters. We have carried out time-resolved electronic and vibrational absorption studies on urocanic acid and modified variants in various solvents on timescales spanning eighteen orders of magnitude; from femtoseconds to hours. In combination with quantum chemical calculations these provide vital insight into the photochemical and photophysical properties of urocanic acid and how these are tuned by substitutions and solvents. Moreover, they solve the hitherto conundrum of the wavelength dependence of the photochemistry of trans-urocanic acid in an aqueous environment. Crucially, these studies - together with the accompanying article that reports high-resolution laser spectroscopic studies performed under isolated gas-phase conditions (https://doi.org/10.1039/D4CP02087A) open novel avenues for a rational design of urocanic acid-based UV filters.

Comparative kinetic study of formic acid decomposition for hydrogen production in supercritical water and gas phase: Effect of water catalysis

Formic acid is attracting increasing attention due to is important role for hydrogen production in different practical scenarios. This work presents a comparative kinetic study of formic acid decomposition in supercritical water (SCW) and gas phase. At first, the decomposition of formic acid in SCW was investigated at a pressure of 25.0 MPa, temperatures of 773–848 K and residence times of 2.1–8.5 s in an isothermal flow reactor. Hydrogen and carbon dioxide were found to be the major gaseous products, indicating that decarboxylation was the predominant reaction pathway. A detailed kinetic model was developed with consideration of water catalysis and was used to interpret the present data as well as data from literature. For gas-phase conditions, the kinetics of formic acid decomposition were well characterized by analyzing different types of experimental data in literature. The Machado model was proved to provide satisfactory description of the kinetic behavior of formic acid decomposition. Based on the developed models, a comparative kinetic analysis was further conducted to explore the differences of characteristics of formic acid decomposition under the two conditions. Water catalysis effectively reduced the onset temperature and facilitated the reaction rate for formic acid decomposition in SCW. Finally, the catalytic mechanism of water was elucidated in detail.

Elementary processes triggered in curcumin molecule by gas-phase resonance electron attachment and by photoexcitation in solution.

Electron-driven processes in isolated curcumin (CUR) molecules are studied by means of dissociative electron attachment (DEA) spectroscopy under gas-phase conditions. Elementary photostimulated reactions initiated in CUR molecules under UV irradiation are studied using the chemically induced dynamic nuclear polarization method in an acetonitrile solvent. Density functional theory is applied to elucidate the energetics of fragmentation of CUR by low-energy (0-15eV) resonance electron attachment and to characterize various CUR radical forms. The adiabatic electron affinity of CUR molecule is experimentally estimated to be about 1eV. An extra electron attachment to the π1* LUMO and π2* molecular orbitals is responsible for the most intense DEA signals observed at thermal electron energy. The most abundant long-lived (hundreds of micro- to milliseconds) molecular negative ions CUR- are detected not only at the thermal energy of incident electrons but also at 0.6eV, which is due to the formation of the π3* and π4* temporary negative ion states predicted to lie around 1eV. Proton-assisted electron transfer between CUR molecules is registered under UV irradiation. The formation of both radical-anions and radical-cations of CUR is found to be more favorable in its enol form. The present findings shed some light on the elementary processes triggered in CUR by electrons and photons and, therefore, can be useful to understand the molecular mechanisms responsible for a variety of biological effects produced by CUR.

Effect of Protonation on the Molecular Structure of Adenosine 5'-Triphosphate: A Combined Theoretical and Near Edge X-ray Absorption Fine Structure Study.

The present work combines the near edge X-ray absorption mass spectrometry of a protonated adenosine 5'-triphosphate (ATP) molecule isolated in an ion trap with (time-dependent) density functional theory calculations. Our study unravels the effect of protonation on the ATP structure and its spectral properties, providing structure-property relationships at atomistic resolution for protonated ATP (ATPH) isolated in the gas-phase conditions. On the other hand, the present C and N K-edge X-ray absorption spectra of isolated ATPH appear closely like those previously reported for solvated ATP at low pH. Therefore, the present work should be relevant for further investigation and modeling of structure-function properties of protonated adenine and ATP in complex biological environments.

Molecular insights into the corrosion inhibition mechanism of omeprazole and tinidazole: a theoretical investigation

ABSTRACT In many studies published in recent years, corrosion scientists proved that various drug molecules can exhibit high inhibition performance against the corrosion of metal surfaces and alloys. This study presents the adsorption behaviour and inhibition mechanism of Omeprazole and Tinidazole on steel surface in gas phase and aqueous acidic conditions using quantum chemical calculations and molecular dynamics simulations. Well-known quantum chemical parameters such as EHOMO, ELUMO, energy gaps, dipole moment, global hardness, softness, electrophilicity, electrodonating power, electroaccepting power and the fraction of electron transfer, were calculated to understand the corrosion inhibition properties and interactions with the steel surface of the studied molecules. Fukui indices analysis was performed to identify the local reactivities of the molecules. Additionally, Monte Carlo simulations were used to determine the optimal adsorption configuration of the inhibitors onto a Fe (1 1 0) surface. The study's findings provide valuable insights into preventing corrosion of steel surfaces in aqueous acidic environments. The theoretical data obtained was evaluated in terms of Maximum Hardness, Minimum Polarizability and Minimum Electrophilicity Principles.

A density functional theory study of the molecular structure, reactivity, and spectroscopic properties of 2-(2-mercaptophenyl)-1-azaazulene tautomers and rotamers

Five stable tautomer and rotamers of the 2-(2-Mercaptophenyl)-1-azaazulene (thiol, thione, R1, R2, and R3) molecules were studied using density functional theory (DFT). The geometries of the studied tautomer and rotamers were fully optimized at the B3LYP/6-31G(d,p) level. Thermodynamic calculations were performed at M06-2X/6-311G++(2d,2p) and ωB97XD/6-311G++(2d,2p) in the gas phase and ethanol solution conditions modeled by the solvation model based on density (SMD). The kinetic constant of tautomer and rotamers conversion was calculated in the temperature range 270–320 K using variational transition state theory (VTST) accompanied by one-dimensional wigner tunneling correction. Energy refinement at CCSD(T)/6–311++G(2d,2p) in the gas phase has been calculated. All the studied DFT methods qualitatively give similar tautomer stability orders in the gas phase. The ethanol solvent causes some reordering of the relative stability of 2-(2-Mercaptophenyl)-1-azaazulene conformers. The transition states for the 2-(2-Mercaptophenyl)-1-azaazulene tautomerization and rotamerization processes were also determined. The reactivity, electric dipole moment, and spectroscopic properties of the studied tautomer and rotamers were computed. The hyper-Rayleigh scattering (βHRS), and depolarization ratio (DR) exhibited promising optical properties when nonlinear optical properties were calculated.

Dissociative electron attachment to 1- and 9-chloroanthracene in the gas phase

Dissociative electron attachment (DEA) to 1-chloroanthracene and 9-chloroanthracene was investigated under gas-phase conditions. In both compounds, the elimination of the chlorine anion is the dominant channel for the dissociation of molecular negative ions (NIs). The second most intense channel leads to the formation of molecular anions (Mˉ). The autodetachment lifetime of Mˉ was measured to be about 170 μs for both compounds. The widths of the Mˉ peaks indicate that molecular anions are formed via two resonances: at thermal electron energies and through a shape resonance at the energy of ∼0.5 eV. Adiabatic electron affinities were estimated in the framework of the simple Arrhenius model to be 0.86 eV for both molecules, the values being close to the theoretical predictions by DFT method of 0.90 eV and 0.93 eV for 1-chloroanthracene and 9-chloroanthracene respectively. Metastable negative ions are observed in the DEA spectra of both molecules, which testifies that the elimination of chlorine anions from molecular NIs appears on a time scale of several microseconds.

Development of a detailed kinetic model for high-pressure ethanol oxidation in gas phase and supercritical water

The present study aims to develop a detailed chemical kinetic model for high-pressure ethanol oxidation in the gas phase and supercritical water (SCW). Kinetic parameters for key elementary reactions involving HO2 and CH3OO radicals were updated, deriving from a careful analysis of ignition delay data or analogy. The model performance is validated comprehensively by comparison to a wide variety of recent experimental data from both gas-phase and SCW conditions. The model predicted ignition delay times and speciation measurements (15–60 bar) in the gas phase fairly well. Additionally, the model showed satisfactory performance in reproducing the species concentration profiles at SCW conditions. A comparative kinetic analysis was further conducted to investigate the characteristic differences and similarities of ethanol oxidation at the two conditions. The results indicated SCW lowered the onset temperature for ethanol ignition and facilitated the ethanol oxidation rate, but did not introduce additional oxidation pathways.

Neutron Imaging Experiments to Study Mass Transport in Commercial Titanium Felt Porous Transport Layers

In this work, neutron imaging was used to visualize and study invasion phenomena in fibrous porous transport layers (PTLs) of titanium felt under different flow conditions of gas and liquid phase. The experiments were realized with flow cells that contained a gas and a liquid flow channel separated by PTLs with different thicknesses and pore size distributions. The invasion can be characterized by counter-current flow of water and air with joint imbibition and drainage processes. The dynamics were visualized with neutron radiography with a local resolution of 6.5 μm and a temporal resolution of 0.1 s. Individual static gas-liquid distributions were additionally studied by neutron tomography, with a local resolution of 22 μm and an exposure time of 1.5 s per image (projections: 800/360°). It is shown and discussed that the invasion occurred in continuously repeated imbibition/drainage cycles with frequencies depending on the flow conditions and the PTL structure as well. The change of the PTL saturation with air or water appeared almost independent from the specific PTL structure and the breakthrough of the gas phase occurred at almost constant positions.