Neutral Species Research Articles

Pyrolysis of mass-selected (V2O5)NO- (N = 1-6) clusters in a high-temperature linear ion trap reactor.

A high-temperature linear ion trap that can stably run up to 873K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V2O5)NO- (N = 1-6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O2 prevailed for the (V2O5)NO- clusters with N = 2-5 at 873K. However, novel dissociation channels involving fragmentation of (V2O5)NO- to small-sized VxOy - anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3-6. Significant variations in branching ratios for different dissociation channels were observed as a function of cluster size. Kinetic studies indicated that the dissociation rates of (V2O5)NO- monotonically increased with the increase in cluster size. The internal energies carried by the (V2O5)NO- clusters at 873K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis.

Antiproliferative Copper(II) Complexes Bearing Mixed Chelating Ligands: Structural Characterization, ROS Scavenging, In Silico Studies, and Anti-Melanoma Activity.

Melanoma is a skin cancer characterized by rapid growth and spread for which current therapies produce both resistance and increased risk of infection. To develop new anti-melanoma biocompatible species, the series of complexes Cu(N-N)(bzac)(X)⋅nH2O (N-N: 1,10-phenanthroline/2,2′-bipyridine, Hbzac: 1-phenyl-1,3-butanedione, X: NO3/ClO4, and n = 0, 1) was studied. Single-crystal X-ray diffraction revealed a mononuclear structure for all complexes. The ability of the complexes to scavenge or trap reactive oxygen species such as O2⋅− and HO⋅ was proved by EPR spectroscopy experiments. All complexes inhibited B16 murine melanoma cells in a dose-dependent and nanomolar range, but the complexes with 1,10-phenanthroline were more active. Moreover, comparative activity on B16 and healthy BJ cells revealed a therapeutic index of 1.27–2.24. Bioinformatic methods were used to calculate the drug-likeness, pharmacokinetic, pharmacogenomic, and pharmacodynamic profiles of the compounds. The results showed that all compounds exhibit drug-likeness features, as well as promising absorption, distribution, metabolism, and excretion (ADME) properties, and no toxicity. The pharmacodynamics results showed that the neutral species appear to be good candidates for antitumor molecular targets (Tyrosyl-DNA phosphodiesterase 1, DNA-(apurinic or apyrimidinic site) lyase or Kruppel-like factor 5). Furthermore, the pharmacogenomic results showed a good affinity of the copper(II) complexes for the human cytochrome. These results recommend complexes bearing 1,10-phenanthroline as good candidates for developing drugs to melanoma alternative treatment.

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

Laser absorption spectroscopy on a transient aluminum plasma generated by excimer laser ablation

Transient Al plasma produced by excimer laser ablation in vacuum was investigated through laser absorption spectroscopy to probe the space-time evolution of neutral species. Spectrally integrating the absorbance, the ground state Al atoms column density was calculated. Typical decreasing trends in time (over a plasma lifetime of about 10 μs) and space (for distances in the range 0.5–8.5 mm from the target surface) were observed. The kinetic temperature of Al ground state species was also estimated from the recorded linewidths, in the assumption of a Doppler broadening mechanism. The resulted values displayed only weak time-fluctuations, while the time-averaged ones showed. a significant drop in few millimeters from the target, similarly to the column density behavior.

Isolation of Elusive Phosphinidene-Chlorotetrylenes: The Heavier Cyanogen Chloride Analogues.

The elusive phosphinidene-chlorotetrylenes, [PGeCl] and [PSiCl] have been stabilized by the hetero-bileptic cyclic alkyl(amino) carbene (cAAC), N-heterocyclic carbene (NHC) ligands, and isolated in the solid state at room temperature as the first neutral monomeric species of this class with the general formulae (L)P-ECl(L') (E=Ge, 3 a-3 c; E=Si, 6; L=cAAC; L'=NHC). Compounds 3 a-3 c have been synthesized by the reaction of cAAC-supported potassium phosphinidenides [cAAC=PK(THF)x ]n (1 a-1 c) with the adduct NHC:→GeCl2 (2). Similarly, compound 6 has been synthesized via reaction of 1 a with NHC:→SiCl2 adduct (4). Compounds 3 a-3 c, and 6 have been structurally characterized by single-crystal X-ray diffraction, NMR spectroscopy and mass spectrometric analysis. DFT calculations revealed that the heteroatom P in 3 bears two lone pairs; the non-bonding pair with 67.8 % of s- and 32 % of p character, whereas the other lone pair is involved in π backdonation to the CcAAC -N π* of cAAC. The Ge atom in 3 contains a lone pair with 80 % of s character, and slightly involved in the π backdonation to CNHC . EDA-NOCV analyses showed that two charged doublet fragments {(cAAC)(NHC)}+ , and {PGeCl}- prefer to form one covalent electron-sharing σ bond, one dative σ bond, one dative π bond, and a charge polarized weak π bond. The covalent electron-sharing σ bond contributes to the major stabilization energy to the total orbital interaction energy of 3, enabling the first successful isolations of this class of compounds (3, 6) in the laboratory.

Reusable nanocomposite-filters for arsenite and arsenate dual real effluents remediation in an up-scaled membrane reactor

A membrane reactor (MR), combining adsorption and membrane separation processes, represents a new hybrid and promising technology for arsenic-contaminated water treatment. This work reports on nanocomposite filters (NCFs) based on poly (vinylidene fluoride-hexafluoropropylene), PVDF-HFP, containing yttrium carbonate (Y2(CO3)3) and magnetite (Fe3O4) to adsorb neutral and anionic species of As(III) and As(V), in an up-scaled membrane reactor. The nano-sorbents and the NCFs were thoroughly characterised concerning morphological and physical-chemical properties. Incorporating the nano-sorbents does not affect the main characteristics of the NCF. Flow rate and pH of the media are the main parameters affecting the adsorption efficiency: lower flow rates and acidic pH are the most favorable conditions for dual As(III) and As(V) adsorption. Y@Fe3O4/PVDF-HFP adsorption follows pseudo-second-order kinetics described by Langmuir isotherm model, reaching maximum absorption capacities of 101.9 and 212.8 mg/g for As(III) and As(V), respectively. In addition, the NCFs proved to be effective for the removal of As(III) and As(V) in treated effluents and easily reactivated and reused without significant efficiency losses. Thus, Y@Fe3O4/PVDF-HFP nanocomposite filters and the designed up-scaled membrane reactor represent a straightforward, efficient, reusable, and low-cost alternative for a continuous treatment process for As(III) and As(V) remediation in real condition effluents sources.

Kinetic modelling of colour and turbidity formation in aqueous solutions of sulphamethoxazole degraded by UV/H2O2

ABSTRACT The oxidation of sulphamethoxazole medicine (SMX) has been studied by means of UV/H2O2 conducting at a controlled pH between 2.0 and 12.0 and oxidant ratios of 500 mol H2O2/mol SMX. It is verified that operating at pH = 2.0 the highest rates of SMX degradation (74%) and loss of aromaticity (64%) are obtained. During the process, a strong brown tint and high turbidity are generated in the water depending on the pH, as it affects the chemical speciation of the dissociable compounds. The colour intensity of the water increases from pH = 2.0 (light brown, 3.5 NTU) to a maximum value at pH = 4.0 (dark brown, 42 NTU), when the neutral SMX species is almost 100%. Under these conditions, the formation of carboxylic acids (acetic and oxalic) and nitrate ion are minor. Conducting at higher pH, hue decreases, obtaining at pH = 12.0 a light yellow water (5 NTU) when the anionic SMX predominates. Thus, the maximum formation of nitrate ion occurs under these conditions. A pseudo-first order kinetic modelling is proposed for the loss of aromaticity and colour and turbidity formation in water, where the kinetic parameters are expressed as a function of the applied pH, being the pseudo-first-order rate constants (min−1): k a r o m = 0.0005 p H 2 − 0.0106 p H + 0.0707 ; k c o l o u r = 0.0011 p H 2 − 0.02 p H + 0.1125 and kNTU = 0.06 min−1.

Pattern of F2-layer peak electron density across African Ionosonde locations and response to solar activity

The diurnal, longitudinal, and latitudinal characteristics of the F2-layer peak electron density (NmF2) at six African stations comprising mid- and equatorial latitudes was investigated. The study covers years of low- (F10.7 = 82.2sfu) and high- (198.6sfu) solar activities. The results revealed that the NmF2 noontime-bite-out was prevalent only in the equatorial latitude. There is latitudinal (geographic) influence on the NmF2 pre-noon and post-noon peak magnitudes at the equatorial locations irrespective of solar activity. The pattern of the NmF2 amplitude during some selected specific time showed that the noontime-12LT, sunset-18LT and midnight-00LT observations are latitudinally inclined, whereas that of the sunrise-06LT is longitudinally-based for both conditions of solar events. Generally, there is a semi-annual asymmetry in the NmF2 monthly pattern with peaks in the equinoctial months. This asymmetry is significant at equatorial latitudes at daytime (06LT/12LT) and nighttime (18LT/00LT) but absent at nighttime of mid-latitudes. The asymmetry feature at the equatorial stations finds its explanation in the ionization anomaly being triggered by the fountain effect mechanism. The NmF2/F10.7 pair correlation (r) presents highest value at 06LT at all equatorial stations for both conditions of solar activity. Generally, r is higher during LSA than during HSA, and finds its explanation in the rate of ionized neutral species and ionospheric electrodynamics. The equatorial noontime bite-out amplitude (bite-outamp) is highest in equinoxes and is latitudinally inclined. We obtained a higher bite-out intensity at the equatorial stations during the HSA than the LSA period by a factor of ≈ 41 %. The importance of thermospheric neutral winds in the large-scale distribution of plasmas was emphasized.

Encroachment order and spatial patterns of broad-leaf tree species in the naturalization of a Cunninghamia lanceolata plantation

The aim of this study was to understand the encroachment order, spatial patterns, interspecific associations, and species diversity of a Cunninghamia lanceolata plantation and to provide context for how to improve the spatial structure of C. lanceolata plantations. We investigated a Guanshan (C. lanceolata) Plantation in the Jiangxi Province. The C. lanceolata plantation was divided into three developmental stages (early, middle and late), with a space-for-time substitution method, according to their diameter at breast height (DBH) measurements. Across these plots, we analyzed encroachment patterns of the species and their interspecific associations with C. lanceolata according to the coordinates of trees in the plot, as well as the variation of species diversity after the encroachment of broad-leaf tree species. Our results show that the encroachment of broad-leaf trees into the C. lanceolata plantation followed a clear successional sequence of tree community assembly: intolerant tree species encroachment first, such as Alniphyllum fortunei and Liquidambar formosana, encroached; neutral tree species then encroachment, such as Daphniphyllum oldhamii and Schima superba, and shade-tolerant tree species encroachment last, such as Castanopsis eyrei and Castanopsis tibetana. Further, the spatial pattern of species establishment differed based upon when they encroached on the plantation. Intolerant and neutral tree species of early and middle developmental stages were distributed randomly. However, intolerant and some shade-tolerant tree species of the late developmental stage were aggregated on a scale of about 0–3 m. In addition, the interspecific associations between broad-leaf species encroachment into the C. lanceolata plantation were mainly negative, among which the most competitive ones were A. fortunei, D. oldhamii and Machilus thunbergii. However, with the development of the community, some species with negative correlations changed to having no correlation with C. lanceolata. We found that species diversity in the plantation gradually increased by nearly-five times from the early to the late developmental stage. Based on our collective results, we conclude that the encroachment and assembly of tree species show obvious order and pattern, which has a strong competitive effect with C. lanceolata in the naturalized plantation. Additionally, the community biodiversity has been significantly improved. Therefore, this successional process is important in the transformation of the C lanceolata plantation and different tree species should be replanted according to C. lanceolata plantation developmental stages with priority given to competitive species, such as A. fortunei, D. oldhamii, and M. thunbergii, so as to promote the C. lanceolata plantation change to C. lanceolata and broadleaf mixed forest.

Effects of deposition precursors of hydrogenated amorphous carbon films on the plasma etching resistance based on mass spectrometer measurements and machine learning analysis

In the growth of hydrogenated amorphous carbon (a-C:H) films by plasma enhanced chemical vapor deposition (PECVD) with H2, CH4 and C3H6 plasma, the gas phase reaction of active species and their contribution to properties of deposited a-C:H film were quantitatively investigated using appearance quadrupole mass spectrometry (QMS) and machine learning. The QMS measurement indicated that two-types of neutral radicals were generated by the dissociation and polymerization of the raw material gasses. A random forest regression model was employed as a prediction model to analyze the correlation between the neutral species and etching rates by molecular oxygen (O2) plasma without any stage bias, which were measured by in-situ ellipsometry. The coefficient of determination (R2), an indicator of the degree of prediction accuracy, was 0.906 and 0.584 for the training and test data, respectively. SHapley Additive exPlanations (SHAP), interpreting the random forest model, were used to quantitatively indicate the contribution of radicals to the etching rate, including their synergistic and secondary effects. They indicated that carbon-rich radicals, such as C3H3 and C5H5, contributed to a decrease in the etching rate, whereas hydrogen-rich radicals, such as CHx (x=1,2,3,4), C2H5, C4H9, and C5H9,11 induced an increase in the etching rate by the O2 plasma. (200 words)

Recent advances in nanoelectrochemistry at the interface between two immiscible electrolyte solutions

The nanoscale interface between two immiscible electrolyte solutions (nanoITIES) is an emerging versatile analytical platform. Analytical advantages of chemical analysis using the nanoITIES include imaging with nanometer spatial resolution, probing fast dynamics with millisecond temporal resolution and fast response times, selectively detecting analytes, probing fundamental chemical processes (e.g., diffusion profiles), and versatile sensing of metal ions, proteins, neurotransmitters, ionic and neutral species, redox-active and non-redox active analytes, etc. We present here a brief theoretical background of the nanoITIES and experimental advances from the past five years. These advances include imaging of nanopores, probing diffusion profiles, biosensing, a new pH modulation mechanism for sensing neutral species, and studying exocytosis from Aplysia californica neurons.

A Global Model Study of Plasma Chemistry and Propulsion Parameters of a Gridded Ion Thruster Using Argon as Propellant

This work reports on the (zero-dimensional) global model study of argon plasma chemistry for a cylindrical thruster based on inductively coupled plasma (ICP) whose output has a system of two grids polarized with each other with direct current potential. The global model developed is based on particle and energy balance equations, where the latter considers both charged and neutral species. Thus, the model allows the determination of the neutral gas temperature. Finally, this study also investigated the role of excited species in plasma chemistry especially in the ions production and its implications for propulsion parameters, such as thrust. For this, the study was carried out in two different scenarios: (1) one taking into account the metastable species Arr and Arp (multi-step ionization), and (2) the other without these species (single-step ionization). Results indicates a distinct behavior of electron temperature with radiofrequency (RF) power for the investigated cases. On the other hand, the gas temperature is almost the same for investigated power range of up to 900 W. Concern propulsion analysis, a thrust of 40 mN at 450 W was verified for case (1), which represents a remarkable thrust value for electric thrusters.

Interactions in coinage-metal/ligand complexes, CM–L, and their cations (CM = Cu, Ag, Au; L = CO, N2 and H2)

The CM–L and CM+–L complexes for the three coinage metals, CM = Cu, Ag and Au interacting with three key ligands, L = CO, N2 and H2, are investigated. Calculations are undertaken using various quantum chemical methods to ascertain the equilibrium geometries and interaction energies; the latter are calculated at the coupled-cluster level of theory, and extrapolated to the basis set limit. Some of the neutral species are found to be particularly challenging, and significant disparity is found in some cases for the geometry and/or harmonic vibrational wavenumbers. In addition, molecular orbital diagrams, atomic charges, and orbital contour plots are presented, in order to gain insight into the interactions occurring in these complexes.

(Keynote) Theoretical Analysis of Electrochemical Stability in a Solid Oxide Cell

In this talk, I will describe a theoretical analysis and modeling of electrochemical stability in solid oxide cells, including solid oxide fuel cell, solid oxide electrolysis, and solid-state batteries. Focus will be on elucidating the origin for the electrochemically driven of phase change and the deposition of neutral species at the interfaces and inside a solid electrolyte.

Computational characterization of capacitive coupled HBr/Cl2/O2 plasma

AbstractA self‐consistent two‐dimensional fluid model was used to study HBr/Cl2/O2 plasma discharge. A comprehensive set of 150 reactions comprising different processes (i.e., dissociation, ionization, and excitation) in tandem with 32 plasma species were considered in the computational model. The results revealed that the plasma reactions were dominated by 11 species (i.e., Cl, Cl+, Cl2+, H, H2, HCl, HCl+, Br, Br+, Br2, and HBr+), where the neutral species outnumbered the charged species. The density of charged species in the plasma reactor followed a bell shaped while the neutral species followed a double humped shaped distribution. The increase in plasma O2 concentration resulted in an initial decrease, followed by a gradual increase in the generation of Cl, Br, H, Cl+, and Br+ in the plasma discharge. A lower/higher concentration of oxygen in the plasma stimulated the densities of neutral/charged species, which facilitated the chemical/physical etching pathway. These findings provide new insights into the type of etching species and their optimization in the HBr/Cl2/O2 plasma discharge, with potential applications in the semiconductor industry.

On the Deposition Process of Ceramic Layer Thin Films for Low-Carbon Steel Pipe Protection.

Ceramic thin films with variable thicknesses have been used in many applications. In order to protect the petroleum transportation pipes against the harmful H2S action, two ceramic materials as thin layers are proposed. In this article, pulsed laser deposition (PLD) of ceramic layers by in situ time-resolved optical techniques is investigated. Two ceramic materials were used as targets and real-time monitoring of the PLD process was realized via ICCD fast camera imaging and optical emission spectroscopy. The space–time displacement of the ceramic emissions was analyzed in order to determine the plasma structure and respective kinetic energies. Spectral-resolved investigation allowed the determination of plasma species individual velocities (in the first case: 43 km/s for C ionic species, 11 km/s for Si, from 25 to 5 km/s for atomic species; in the second case: 32 km/s for C ionic species, 11 km/s for W species, and 15 and 53 km/s for neutral species). SEM and AFM techniques were implemented to analyze the resulting ceramic layers showing homogeneous surfaces with characteristic material droplets. The ablation crater also reveals selective ablation during the deposition process. EDX results show that Al/Si is retained in the thin films similar to the target composition.

The impact of ion mobility coefficients on plasma discharge characteristics

In this paper, the high-accuracy ion mobility coefficient based on the Chapman–Enskog approximation to the solution of the Boltzmann equation for low pressure radio frequency plasma discharges is presented. We employ two-dimensional fluid simulations of the argon filled axisymmetric reactor, where the effect of new ion-kinetics-based fluid closure is compared to theoretical expressions and experimental data. The spatial profiles of plasma composition in the low pressure radio frequency capacitively coupled plasma are presented, which includes the metastable reactions in the simulation. Moreover, inelastic collision integrals terms, due to charge exchange inelastic collisions between ions and neutral species, have been also considered. A Monte Carlo simulation of kinetic ion energy distribution of impinging on the radio frequency powered electrode provides a measure of accuracy of the new transport model. From our simulation, the results that mirror the influence of ion mobility coefficient obtained by the Chapman–Enskog method on plasma physical quantities under different pressures, frequencies, and electrode gaps is in good agreement with experimental measurement results and theoretical expressions.

Hollow cathode enhanced capacitively coupled plasmas in Ar/N2/H2 mixtures and implications for plasma enhanced ALD

Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique gas-phase chemistries and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a hollow cathode enhanced capacitively coupled plasma (HC-CCP) source, a type of plasma source that has seen increasing attention in recent years for PEALD. Ultraviolet to near-infrared spectroscopy as well as spatially resolved Langmuir probe and emissive probe measurements are employed to characterize an HC-CCP plasma source using nitrogen based gas chemistries typical of nitride PEALD processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in HC-CCP systems as a function of applied RF power, gas chemistry, and pressure. In addition, the electron energy distribution function, electron temperature, plasma potential, and plasma density for the same process parameters are examined using an RF compensated Langmuir probe and emissive probe. These measurements indicated that electron temperature (Te), electron density (ne), and plasma potential (Vp) varied significantly over the operating conditions examined with Te varying from 1.5 to 8 eV, Vp varying from 30 to 90 V, and ne varying between 1015 and low 1016 m−3. This wide range of plasma conditions is mediated by a mode transition from a low Te, high ne mode of operation at low pressure (<100 mTorr) to a high Te, low ne mode at higher pressures (>100 mTorr). These operational modes appear analogous to the classical γ and α modes of traditional capacitively coupled plasmas. Atomic N and H densities also vary significantly over the operating conditions examined.

Combining Ultraviolet Photolysis with In-Situ Electrochemical Oxidation for Degrading Sulfonamides in Wastewater

Ultraviolet photolysis (UVC, 254 nm) was coupled with an electrochemical oxidation process to degrade three kinds of veterinary sulfonamide (sulfamethazine [SMZ] tablets, sulfamonomethoxine [SMM] tablets, and compound sulfamethoxazole [SMX] tablets). The treatment was applied using a flat ceramic microfiltration membrane to study the effects of photocatalysts. The effectiveness of degradation of the three sulfonamides was evaluated under different conditions. Dissolved oxygen was provided via aeration, but this resulted in a large decrease in the degradation effectiveness due to the inhibition of free chlorine electrogeneration. The photocatalysts had no promotional effect on sulfonamide removal from wastewater due to reduced UV penetration. Because of the different distribution coefficients of sulfonamides, UV irradiation had different effects on different sulfonamide species. For SMZ and SMM, anionic species exhibited a higher degradation rate, whereas for SMX, degradation was most effective for neutral species. In addition, the free chlorine yield increased as the pH increased. Free chlorine conversion reactions occurred under UV irradiation, with the reactions possibly restrained by sulfonamides. Reactive chlorine species promoted SMM degradation. Compared to UV irradiation or electrochemical oxidation alone, the UV/in-situ electrochemical oxidation process was more effective and is suitable for treating real wastewater under various environmental pH levels.

Plasma reforming for enhanced ammonia-air ignition: A numerical study

Using an in-house 0D plasma chemical solver, this paper investigates the species involved in plasma-assisted reforming of both pure ammonia and stoichiometric ammonia-air mixtures. A nanosecond repetitively pulsed plasma is simulated for dielectric barrier discharge conditions, with reduced electric fields of 180 and 360 Td, energies per pulse of 0.5 and 1 mJ/cm3, and pulse repetition frequencies up to 500 kHz. To show the effect of reforming on combustion performance, the reformates are fed into a neutral species combustion chemistry solver to calculate the ignition delay time at gas-turbine relevant conditions. For a reformed stoichiometric mixture, it is possible to achieve a reduction of two orders of magnitude in ignition delay time. This reduction, however, comes at the cost of lost enthalpy, as ammonia reacts with oxygen to create water. Path flux and sensitivity analyses were performed, and it as found that the two most crucial species in the reformate were H2 and NH2. The presence of NH2 in high concentration also resulted in lower concentrations of NO after ignition, compared to the unreformed mixture. When reforming pure ammonia, the same number of pulses and energy as in the stoichiometric case reduce ignition by one order of magnitude. A higher reduction is possible with more pulses, unlike the stoichiometric reforming case in which ignition is reached during the reforming process, and with no loss of enthalpy due to oxidation. At 200 kHz, a reduction of two orders of magnitude is possible after 1500 pulses. These results support the feasibility of plasma-assisted reforming for the improvement of ammonia combustion characteristics at relevant conditions.