Search Results (9)

The fabrication and application of single-site heterogeneous reaction centers are new frontiers in chemistry. Single-site heterogeneous reaction centers are analogous to metal centers in enzymes and transition-metal complexes: they are charged and decorated with ligands and would exhibit superior reactivity and selectivity in chemical conversion. Such high reactivity would also result in significant response, such as a band gap or resistance change, to approaching molecules, which can be used for sensing applications. As a proof of concept, the electronic structure and reaction pathways with NO and NO₂ of Au(I) fragments dispersed on phosphorene (Pene) were investigated with first-principle-based calculations. Atomic-deposited Au atoms on Pene (Au₁-Pene) have hybridized Au states in the bulk band gap of Pene and a decreased band gap of 0.14 eV and would aggregate into clusters. Passivation of the Au hybrid states with -OH and -CH₃ forms thermodynamically plausible HO-Au₁-Pene and H₃C-Au₁-Pene and restores the band gap to that of bulk Pene. Inspired by this, HO-Au₁-Pene and H₃C-Au₁-Pene were examined for detection of NO and NO₂ that would react with -OH and -CH₃, and the resulting decrease of band gap back to that of Au₁-Pene would be measurable. HO-Au₁-Pene and H₃C-Au₁-Pene are highly sensitive to NO and NO₂, and their calculated theoretical sensitivities are all 99.99%. The reaction of NO₂ with HO-Au₁-Pene is endothermic, making the dissociation of product HNO₃ more plausible, while the barriers for the reaction of CH₃-Au₁-Pene with NO and NO₂ are too high for spontaneous detection. Therefore, HO-Au₁-Pene is not eligible for NO₂ sensing and CH₃-Au₁-Pene is not eligible for NO and NO₂ sensing. The calculated energy barrier for the reaction of HO-Au-Pene with NO is 0.36 eV, and the reaction is about thermal neutral, suggesting HO-Au-Pene is highly sensitive for NO sensing and the reaction for NO detection is spontaneous. This work highlights the potential superior sensing performance of transition-metal fragments and their potential for next-generation sensing applications. Full article

We compare enhancements of mesospheric volume mixing ratios of hydroperoxyl radical ${\mathrm{HO}}_2$ and nitric acid ${\mathrm{HNO}}_3$, as well as ozone depletion in the Northern Hemisphere (NH) polar night regions during energetic particle precipitation (EPP) in January of 2005 and 2012. We utilize mesospheric observations of ${\mathrm{HO}}_2$, ${\mathrm{HNO}}_3$, and ozone from the Microwave Limb Sounder (MLS/Aura). During the second half of January 2005 and 2012, the GOES satellite identified strong solar proton events with virtually the same proton flux parameters. Geomagnetic disturbances in January of 2005 were stronger, with Dst decreasing up to 100 nT compared to January 2012 while the Dst drop did not exceed 70 nT. Comparison of observations made with the MLS/Aura shows the highest change of ${\mathrm{HO}}_2$ and ${\mathrm{HNO}}_3$ concentrations and also the deepest ozone destruction at the latitudinal range from ${60}^{\circ }$ NH to ${80}^{\circ }$ NH inside the north polar vortex right after the spike in energetic particle flux registered by GOES satellites. MLS/Aura observations show ${\mathrm{HNO}}_3$ maximum enhancements of about 1.90 ppb and 1.66 ppb around 0.5 hPa (about 55 km) in January 2005 and January 2012, respectively. The ${\mathrm{HO}}_x$ increases lead to short-term ozone destruction in the mesosphere, which is seen in MLS/Aura ozone data. The maximum ${\mathrm{HO}}_2$ enhancement is about 1.05 ppb and 1.62 ppb around 0.046 hPa (about 70 km) after the onset of EPP in the second half of January 2005 and January 2012, respectively. Ozone maximum depletion is observed around 0.02 hPa (about 75 km). Ozone recovery after EPP was much faster in January 2005 than in January 2012. Full article

Green ammonia has become an increasingly popular fuel in recent years because of its combustion process without carbon oxide release. Adding ammonia to methane fuel for co-combustion has become one of the important research topics in the current combustion field. In the present study, the CH₄/NH₃/Air counterflow diffusion flame was taken as the research object, and Chemkin-2019 R3 software was used to explore and analyze the flame extinction limit and chemical kinetics characteristics under different ammonia mixing ratios, initial pressures, and air preheating temperatures. It was obtained that the flame extinction stretch rate was decreased by increasing the NH₃ mole fraction in the CH₄/NH₃ mixed fuel. The increase in pressure or air preheating temperature would accelerate the chemical reaction rate of each component in the combustion process, increase the flame extinction limit, and counteract the “stretching effect” of the flame, thus restraining the flame extinguishing phenomenon. The results of a path analysis show that the formation and consumption of OH had an important influence on flame extinction in the chain reaction. The net reaction rate of OH increases with increasing the initial pressure or air preheating temperature, which leads to an increase in flame intensity, combustion stability, and the extinction limit. Furthermore, the function curve between the reaction influences the RIF factor and the stretch rate of the first-to-ten reactions, affected by the heat release of flame combustion, was drawn and quantitatively analyzed. Eventually, a sensitivity analysis of the flame under different working conditions was completed, which found that promoting the forward reaction R39 H + O₂<=>O + OH also promotes the positive combustion as a whole when the flame was near extinction. The sensitivity coefficient of R39 in the CH₄/NH₃/Air flame increases with the growing initial pressure. The increasing air preheating temperature was capable of switching the reaction of R248 NH₂ + OH<=>NH + H₂O in the CH₄/NH₃/Air flame from an inhibiting reaction to a promoting reaction, while decreasing the sensitivity coefficient of inhibiting the forward reaction R10 O + CH₃<=>H + CH₂O, R88 OH + HO₂<=>O₂ + H₂O, and R271 H + NO + M<=>HNO + M. Thus, the inhibition effect of flame extinction was weakened, and the positive progress of combustion was promoted. Full article

The potential of cold atmospheric plasma (CAP) in biomedical applications has received significant interest, due to its ability to generate reactive oxygen and nitrogen species (RONS). Upon exposure to living cells, CAP triggers alterations in various cellular components, such as the cell membrane. However, the permeation of RONS across nitrated and oxidized membranes remains understudied. To address this gap, we conducted molecular dynamics simulations, to investigate the permeation capabilities of RONS across modified cell membranes. This computational study investigated the translocation processes of less hydrophilic and hydrophilic RONS across the phospholipid bilayer (PLB), with various degrees of oxidation and nitration, and elucidated the impact of RONS on PLB permeability. The simulation results showed that less hydrophilic species, i.e., NO, NO₂, N₂O₄, and O₃, have a higher penetration ability through nitro-oxidized PLB compared to hydrophilic RONS, i.e., HNO₃, s-cis-HONO, s-trans-HONO, H₂O₂, HO₂, and OH. In particular, nitro-oxidation of PLB, induced by, e.g., cold atmospheric plasma, has minimal impact on the penetration of free energy barriers of less hydrophilic species, while it lowers these barriers for hydrophilic RONS, thereby enhancing their translocation across nitro-oxidized PLB. This research contributes to a better understanding of the translocation abilities of RONS in the field of plasma biomedical applications and highlights the need for further analysis of their role in intracellular signaling pathways. Full article

It has been experimentally reported that not only oxidation reactions but also reduction reactions occur in aqueous solutions under ultrasound without any additives. According to the numerical simulations of chemical reactions inside an air or argon bubble in water without any additives under ultrasound, reducing agents produced from the bubbles are $\mathrm{H},{ \mathrm{H}}_2,{ \mathrm{HO}}_2$ (which becomes superoxide anion (${\mathrm{O}}_2^{-}$) in liquid water), $\mathrm{NO}$, and ${\mathrm{HNO}}_2$ (which becomes ${\mathrm{NO}}_2^{-}$ in liquid water). In addition, ${\mathrm{H}}_2{\mathrm{O}}_2$ sometimes works as a reducing agent. As the reduction potentials of $\mathrm{H}$ and ${\mathrm{H}}_2$ (in strongly alkaline solutions for ${\mathrm{H}}_2$) are higher than those of $\mathrm{RCHOH}$ radicals, which are usually used to reduce metal ions, $\mathrm{H}$ and ${\mathrm{H}}_2$ generated from cavitation bubbles are expected to reduce metal ions to produce metal nanoparticles (in strongly alkaline solutions for ${\mathrm{H}}_2$ to work). It is possible that the superoxide anion (${\mathrm{O}}_2^{-}$) also plays some role in the sonochemical reduction of some solutes. In strongly alkaline solutions, hydrated electrons (${\mathrm{e}}^{-}\left(\mathrm{aq}\right)$) formed from $\mathrm{H}$ atoms in liquid water may play an important role in the sonochemical reduction of solutes because the reduction potential is extremely high. The influence of ultrasonic frequency on the amount of $\mathrm{H}$ atoms produced from a cavitation bubble is also discussed. Full article

In this study, we investigated the effect of different radical scavengers on the nitrate and/or nitric acid (NO₃⁻ and/or HNO₃) formation chain in liquid while the dielectric barrier discharge plasma system (DBD) was used for ozone (O₃) generation. The effects of the excess concentration of each scavenger were studied individually. In addition, ultrapure water (UPW), tap water, and surface water samples were examined in the same condition. Due to the absence of scavengers in the UPW, we expected the highest NO₃⁻ formation in this experiment because all active species produced by the DBD system should have formed NO₃⁻. However, the obtained results were unexpected; the highest NO₃⁻ formation was obtained in the tap water at 385 ± 4.6 mg/L. The results can be explained by some compounds in tap water acting as a trap for radicals involved in chain reactions that form NO₃⁻ and/or HNO_3. The second highest result was obtained in the sodium hydroxide solution as 371 ± 4.9 mg/L, since the OH⁻ ions accelerated the decomposition of O₃ to its intermediates such as hydroperoxide (HO₂⁻), ozonide (O₃⁻), and hydroxyl radical (OH^•), and, by increasing radicals in the liquid, more chain reactions can be promoted that lead to the formation of NO₃⁻ and/or HNO₃. On the other hand, the quenching of radicals by scavengers such as carbonate ion and phosphoric acid and/or the long-term stabilization of O₃ as O₃ negatively affected the chain reactions that generate NO₃⁻ and/or HNO₃. Full article

A dispersive solid-phase microextraction (DSPME) sorbent consisting of poly(1,6-hexanediol diacrylate)-based polymer microspheres, with embedded graphene microparticles (poly(HDDA)/graphene), was synthesized by microfluidic emulsification/photopolymerization and characterized by optical microscopy and X-ray fluorescence spectrometry. This sorbent was applied for simple, fast, and sensitive vortex-assisted DSPME of rare earth elements (RREs) in coal fly ash (CFA) leachate, prior to their quantification by inductively coupled plasma mass spectrometry (ICP-MS). Among nine DSPME variables, the Plackett–Burman screening design (PBD), followed by the central composite optimization design (CCD) using the Derringer desirability function (D), identified the eluent type as the most influencing DSPME variable. The optimum conditions with maximum D (0.65) for the chelating agent di-(2-ethylhexyl) phosphoric acid (D2EHPA) amount, the sorbent amount, the eluting solvent, the extraction temperature, the centrifuge speed, the vortexing time, the elution time, the centrifugation time, and pH, were set to 60 μL, 30 mg, 2 M HNO₃, 25 °C, 6000 rpm, 1 min, 1 min, 5 min, and 4.2, respectively. Analytical validation of the DSPME method for 16 REEs (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in CFA leachate samples estimated the detection limits at the low ppt level, the recovery range 43–112%, and relative standard deviation within ± 22%. This method was applied to a water extraction procedure (EP) and acetic acid toxicity characteristic leaching procedure (TCLP) for leachate of CFA, from five different coal-fired thermoelectric power plants. The most abundant REEs in leachate (20 ÷ 1 solid-to-liquid ratio) are Ce, Y, and La, which were found in the range of 22–194 ng/L, 35–105 ng/L, 48–95 ng/L, and 9.6–51 μg/L, 7.3–22 μg/L, 2.4–17 μg/L, for EP and TCLP leachate, respectively. The least present REE in TCLP leachate was Lu (42–125 ng/L), which was not detected in EP leachate. Full article

This work describes the first real developments in radiochemistry around exotic radionuclides at the cyclotron of Orléans focusing on the radiochemistry of two radiometals ¹⁶⁵Er and ⁵²Mn. For these developments, targets were irradiated during 0.5–2 h at a maximum current of 2 µA. All activities have been determined by radiotracer method. The production of ¹⁶⁵Er from a natural Ho target that was irradiated is described. Higher activities of ¹⁶⁵Er were obtained via deuteron irradiation then proton with lower ratio ¹⁶⁵Er/¹⁶⁶Ho (400/1 to 8/1). By using LN2 resin, the separation of adjacent lanthanides was made on various concentrations of HNO₃ (0.3 to 5 M). Weight coefficients (Dw) were defined in a batch test. Then, the first tests of separation on a semi-automated system were made: the ratio ^166+natHo/¹⁶⁵Er in an isolated fraction was significantly reduced (1294 ± 1183 (n = 3)) but the reliability and reproducibility of the system must be improved. Then, a new Cr powder-based target for ⁵²Mn production was designed. Its physical aspects such as mechanics, thermal resistance and porosity have been studied. Dw for various compositions of eluent Ethanol/HCl were evaluated by reducing contact time (1 h) comparative to the literature. A first evaluation of semi-automated separation Cr/Mn has been made. Full article

SO₂ and H₂S are the two most important gas-phase sulfur species emitted by volcanoes, with a global amount from non-explosive emissions of the order 10 Tg-S/yr. These gases are readily oxidized forming SO₄²⁻ aerosols, which effectively scatter the incoming solar radiation and cool the surface. They also perturb atmospheric chemistry by enhancing the NO_x to HNO₃ heterogeneous conversion via hydrolysis on the aerosol surface of N₂O₅ and Br-Cl nitrates. This reduces formation of tropospheric O₃ and the OH to HO₂ ratio, thus limiting the oxidation of CH₄ and increasing its lifetime. In addition to this tropospheric chemistry perturbation, there is also an impact on the NO_x heterogeneous chemistry in the lower stratosphere, due to vertical transport of volcanic SO₂ up to the tropical tropopause layer. Furthermore, the stratospheric O₃ formation and loss, as well as the NO_x budget, may be slightly affected by the additional amount of upward diffused solar radiation and consequent increase of photolysis rates. Two multi-decadal time-slice runs of a climate-chemistry-aerosol model have been designed for studying these chemical-radiative effects. A tropopause mean global net radiative flux change (RF) of −0.23 W·m⁻² is calculated (including direct and indirect aerosol effects) with a 14% increase of the global mean sulfate aerosol optical depth. A 5–15 ppt NO_x decrease is found in the mid-troposphere subtropics and mid-latitudes and also from pole to pole in the lower stratosphere. The tropospheric NO_x perturbation triggers a column O₃ decrease of 0.5–1.5 DU and a 1.1% increase of the CH₄ lifetime. The surface cooling induced by solar radiation scattering by the volcanic aerosols induces a tropospheric stabilization with reduced updraft velocities that produce ice supersaturation conditions in the upper troposphere. A global mean 0.9% decrease of the cirrus ice optical depth is calculated with an indirect RF of −0.08 W·m⁻². Full article