Influence of CuO catalyst in the nanoscale range on SnO2 surface for H2S gas sensing applications

The dispersal of CuO catalyst on the surface of the semiconducting SnO₂ film is found to be of vital importance for improving the sensitivity and the response speed of a SnO₂ gas sensor for H₂S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical technique using a reverse micelle method involving the reduction of Cu(NO₃)₂ by NaBH₄ exhibited significant improvement in the gas sensing characteristics of SnO₂ films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H₂S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity (S = 2.06 × 10³) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO₂ allows effective removal of excess adsorbed oxygen from the uncovered SnO₂ surface due to spill over of hydrogen dissociated from the H₂S-CuO interaction.     

The preparation and desulfurization of nano-size ZnO by a matrix-assisted method for the removal of low concentration of sulfur compounds

Zinc oxide (ZnO) nano-particles have been synthesized by a matrix-assisted method with various precursors. An activated carbon was used as a matrix and zinc acetate, zinc nitrate, and zinc chloride were selected as precursors. The ZnO nano-particles appeared to be either spherical or elliptical shapes when zinc acetate and zinc nitrate were used as precursors, while those particles became irregular in their shapes when zinc chloride was used as a precursor. The products were characterized by using TGA, XRD, BET, TEM and SEM. A nano-size ZnO was formulated for the effective removal of a very low concentration of sulfur compounds (H₂S, COS) contained in a gasified fuel gas and their reactivity was also investigated in this study. Zinc acetate was the best precursor for the formulation of the ZnO nano-particles in the experiment. The size of the formulated ZnO nano-particles was in the range of 10–30 nm and its surface area was about 40.7 m²/g. From TGA (thermal gravity analysis) test, it was found that its sulfur capacity was about 9.27 g S/100 g-sorbent for H₂S and 0.56 g S/100 g-sorbent for COS and its initial sulfur absorption rates with H₂S and COS absorption were about 257.5 mg S/min · 100 g-sorbent and 15.6 mg S/min · 100 g-sorbent, respectively. Their reactivity increased as their sizes became smaller and their surface areas of the sorbents were larger. Most prepared nano-size ZnO showed an excellent performance for the removal of not only H₂S but also COS.     

An investigation of paddle wheel Cu2(μ2-O2CCH3)4 for gas molecule adsorptions

Metal organic frameworks (MOFs) have been well-known and extensively researched due to the high storage /good selectivity for gas molecules. Herein, the structures and electron paramagnetic resonance (EPR) spectra for dicopper paddle wheel MOF compound (Cu₂(µ₂-O₂CCH₃)₄ with various gas molecule are theoretically investigated by density functional theory (DFT) calculations. The adsorption energies and isotherms (including pure gas molecules and the mixed ones) are calculated for the gas molecules interacting with the unsaturated Cu₂(µ₂-O₂CCH₃)₄. Both quantities exhibit the roughly consistent orders (e.g. H₂S?>?NH₃?>?CO₂?>?CO?>?H₂O?>?N₂?>?NO?>?H₂ for isotherms and H₂S?>?NH₃?>?N₂?>?CO₂?>?NO?>?H₂O?>?H₂?>?CO for adsorption energies), possibly suggesting that this material may act as a potential adsorbent of these gas molecules. The catalytic property of Cu₂(µ₂-O₂CCH₃)₄ for oxidation of CO and NO into non-toxic molecules and splitting of H₂O into H₂ and O₂ in the solvent condition are uniformly discussed. Simulation of Grand Canonical Monte Carlo (GCMC) in MS 8.0 and calculations in Langmuir model reveal that Cu₂(µ₂-O₂CCH₃)₄ has good selectivity for CH₄ in natural gas (CH₄/CO₂/N₂) and SO₂ in fog (SO₂/NO/NO₂/H₂O/O₂), which would exhibit potential environmentally friendly applications.     

Coumarin-based Fluorescent Probes for H2S Detection

Although hydrogen sulfide (H₂S) has been known as a toxic gas with unpleasant rotten egg smell, the correlation between H₂S and physiological processes has attracted scientists to develop brand new methods to monitor such a gaseous molecule in vitro and in vivo. Herein, we described a couple of coumarin-based fluorescent probes (1a and 1b) that can be activated by reduction of azide to amine in the presence of H₂S. It should be emphasized that probe 1b demonstrated high selectivity and sensitivity for H₂S over other relevant reactive sulfur species in vitro, as well as identified exogenous H₂S in living cells.     

Direct Radiometric Measurement of Vapor-Liquid Equilibria: Hydrogen Sulfide-Diethanolamine

Direct radiometric measurements of the vapor concentration of H₂S in equilibrium with aqueous diethanolamine absorbing solution were made using ³⁵S-labeled H₂S. A thin-window Geiger-Müller tube viewed the gas phase only, while the absorbing solution was held in another part of the reaction flask. The equilibrium data were measured at H₂S partial pressures below 0.01 mm Hg; the agreement with published results obtained by chemical analysis was good. The radiometric results were obtained very rapidly; a test run with seven data points took about two hours to complete. The results were applied to processes for reducing H₂S concentrations in petroleum refinery fuel gases needed to meet tightening air pollution requirements.     

Immobilization of RuS2 Nanoparticles Prepared in Reverse Micellar System onto Thiol-Modified Polystyrene Particles and their Photocatalytic Properties

RuS₂ nanoparticles, smaller than 3 nm in diameter, were prepared by H₂S gas injection into the AOT/isooctane reverse micellar solution containing RuCl₃ aqueous solution. The nanoparticle size was found to be independent of the W_o (water content) value of the reverse micellar system, as shown by TEM observation. The recovery and immobilization of the RuS₂ nanoparticles from reverse micelles onto thiol-modified polystyrene particles (PSt-SH) were successfully carried out, by the addition of PSt-SH into the reverse micellar solution under conditions of mild stirring. The resulting composites, PSt-RuS₂, showed photocatalytic activity for H₂ generation form aqueous solution containing 2-propanol and Na₂SO₃ as sacrificial electron donors.     

Photoacoustic system for on-line process monitoring of hydrogen sulfide (H2S) concentration in natural gas streams

A dual-channel hydrogen sulfide (H₂S) concentration measuring system based on photoacoustic spectroscopy is described. The system uses a single-mode, fiber-coupled, room-temperature-operated, telecommunication-type diode laser with a wavelength of 1574.5 nm and an output optical power of 40 mW and two identical resonant photoacoustic cells to achieve minimum detectable H₂S concentration at 0.5 ppm (3σ) in both measured natural gas streams. The instrument features excellent long-term stability and unattended automatic on-line monitoring even when operated in harsh industrial environments. The potentially deteriorating effect of temporal variation in the natural gas composition was successfully suppressed by applying a spectral baseline correction method and by introducing an additional measurement phase with measurement of a reference gas from which the H₂S has been removed. Various tests of the instrument demonstrate its reliable performance and suitability for process-control application. PACS 82.80.Kq; 42.62.Fi; 07.07.Df     

A chemical strategy to control the shape of oxide nanoparticles

A new strategy, epoxide-assisted precipitation route presented in this work, allows the shape control synthesis of Co₃O₄ nanoparticles. The shape of the nanoparticles is determined by the nature of the precursor cobalt salts (Co(NO₃)₂ · 6H₂O, CoCl₂ · 6H₂O) used for the preparation of the particles. The different reaction dynamics of the two salts in ethanolic and aqueous solutions with propylene oxide result in precursor particles with different structures, which lead to the formation of oxide nanoparticles with different shapes during the heat treatment. Spherical particles of about 20 nm are obtained from the ethanolic solution of Co(NO₃)₂ · 6H₂O; cubic-shaped particles of about 30 nm can be prepared from the ethanolic solution of CoCl₂ · 6H₂O; whereas platelet-like particles of more than 100 nm are synthesized from the aqueous solution of the mixture of Co(NO₃)₂ · 6H₂O and CoCl₂ · 6H₂O.     

HITEMP, the high-temperature molecular spectroscopic database

A new molecular spectroscopic database for high-temperature modeling of the spectra of molecules in the gas phase is described. This database, called HITEMP, is analogous to the HITRAN database but encompasses many more bands and transitions than HITRAN for the absorbers H₂O, CO₂, CO, NO, and OH. HITEMP provides users with a powerful tool for a great many applications: astrophysics, planetary and stellar atmospheres, industrial processes, surveillance, non-local thermodynamic equilibrium problems, and investigating molecular interactions, to name a few. The sources and implementation of the spectroscopic parameters incorporated into HITEMP are discussed.     

Performance of non-thermal DBD plasma reactor during the removal of hydrogen sulfide

Destruction of hydrogen sulfide using dielectric barrier discharge plasma in a coaxial cylindrical reactor was carried out at atmospheric pressure and room temperature. Three types of DBD reactor were compared in terms of specific energy density (SED), equivalent capacitances of the gap (Cg) and the dielectric barrier (Cd), energy yield (EY), and H₂S decomposition. In addition, byproducts during the decomposition of H₂S and destruction mechanism were also investigated. SED for all the reactors depended almost linearly on the voltage. In general, Cg decreased with increasing voltage and with the existence of pellet material, while Cd displayed the opposite trend. The removal efficiency of H₂S increased substantially with increasing AC frequency and applied voltage. Longer gas residence times also contributed to higher H₂S removal efficiency. The choice of pellet material was an important factor influencing the H₂S removal. The reactor filled with ceramic Raschig rings had the best H₂S removal performance, with an EY of 7.30 g/kWh. The likely main products in the outlet effluent were H₂O, SO₂, and SO₃.     

Sodium affinity of caffeine and adenine: the effect of microsolvation and electrostatic field of solvent on the sodium affinity

The sodium affinity (SA) of caffeine (CAF), adenine (AD) and their microsolvated clusters containing one X molecule (CAF-X and AD-X; X = H₂O, NH₃, H₂S and HF) has been calculated in the gas phase and water, separately. The density functional theory (DFT) employing CAM-B3LYP functional has been used for all of the calculations in this work. The solvent was modelled by the polarised continuum model (PCM) which considers the electrostatic field of solvent on solute. The calculated SA of [CAF-X] and [AD-X] was higher than that of CAF and AD in the gas phase, respectively, which showed that the microsolvation of molecules in the gas phase could be used for changing the tendency of molecules for binding to Na⁺. Also, it was observed that the electrostatic effect of solvent decreases the SA of the species compared to the gas phase, considerably. The symmetry adapted perturbation theory (SAPT) calculations were also used to interpret the change in the SA of CAF and AD due to the clustering with one X molecule in the gas phase. In addition, there is a detailed study on the position of Na⁺ relative to AD and CAF structures in different conditions including gas phase, microsolvation and electrostatic field of solvent in this work.     

BeH2(X1Σ+g)与H2S(X1A1)分子的结构与解析势能函数

运用单双取代二次组态相关(QCISD)方法,在6-311++G(3df,3pd)基组水平上,对BeH₂和H₂S分子的结构进行了优化计算,得到基态BeH₂分子的稳定结构为D_∞h构型,电子态为X¹Σ⁺_g,平衡核间距R_BeH=0.13268nm,R_{关键词： 2}')" href="#">BeH₂ 2S')" href="#">H₂S Murrell-Sorbie函数 多体项展式理论 解析势能函数     

Flame structure studies of rich ethylene-oxygen-argon mixtures doped with CO2, or with NH3, or with H2O

Structures of several premixed ethylene-oxygen-argon rich flat flames burning at 50 mbar have been established by using molecular beam mass spectrometry in order to investigate the effect of CO₂, or NH₃, or H₂O addition on species concentration profiles. The aim of this study is to examine the eventual changes of profiles of detected hydrocarbon intermediates which could be considered as soot precursors (C₂H₂, C₄H₂, C₅H₄, C₅H₆, C₆H₂, C₆H₄, C₆H₆, C₇H₈, C₆H₆O, C₈H₆, C₈H₈, C₉H₈ and C₁₀H₈). The comparative study has been achieved on four flames with an equivalence ratio (f) of 2.50: one without any additive (F2.50), one with 15% of CO₂ replacing the same quantity of argon (F2.50C), one with 3.3% of NH₃ in partial replacement of argon (F2.50N) and one with 13% of H₂O in replacement of the same quantity of argon (F2.50H). The four flat flames have similar final flame temperatures (1800 K).CO₂, or NH₃, or H₂O addition to the fresh gas inlet causes a shift downstream of the flame front and thus flame inhibition. Endothermic processes CO₂ + H = CO + OH and H₂O + H = H₂ + OH are responsible of the reduction of the hydrocarbon intermediates in the CO₂ and H₂O added flames through the supplementary formation of hydroxyl radicals. It has been demonstrated that such processes begin to play at the end of the flame front and becomes more efficient in the burnt gases region.The replacement of some Ar by NH₃ is responsible only for a slight decrease of the maximum mole fraction of C₂H₂, but NH₃ becomes much more efficient for C₄H₂ and C₅ to C₁₀ species. Moreover, the efficiency of NH₃ as a reducing agent of C₅ to C₁₀ intermediates is larger than that of CO₂ and H₂O for equal quantities added.     

Theoretical study of chemi- and physisorption processes of H2 molecules on a (1 0 0) surface of silver

A model system consisting of a cluster of 13 Ag atoms and n (n = 1, 2, 3) H₂ molecules has been used to study, by ab initio methods, the structural and energetic characteristics of the chemi- and physisorption processes of H₂ on a (1 0 0) surface of silver. The dissociative chemisorption of a first H₂ molecule is analyzed in terms of hydrides formation and it is shown that several electronic states are interacting in the vicinity of the activation barrier leading to complex electronic processes. The energy of the physisorption interaction of the first H₂ molecule for different orientations and that of further H₂ molecules coming directly on top of the first chemisorbed one are determined with highly correlated wavefunctions. As for the (H₂)_nCu₁₃ system, already studied with similar approaches, it is found for the (H₂)_nAg₁₃ system that the physisorption energy of the second layer is enhanced by a factor close to two compared to that of the first layer due to dipolar interactions with the polarized surface. The physisorption energy of the third and further layers tends to the van der Waals H₂/H₂ interaction energy.     

On the interplay of chemical and physical processes during the combustion of aluminum in water vapor

A model is considered, and the results of numerical calculations of the dynamics of the combustion of pre-prepared gas mixtures of Al and H₂O under adiabatic conditions are presented. The formation of the condensed phase is modeled taking into account the homogeneous nucleation of Al₂O₃ molecules and the processes of condensation, evaporation, and coagulation. The time dependences of the gas composition of the system, the concentration of aerosol particles, and their size distribution during the process are simulated. Details of the mechanism of the interplay of the gas-phase reactions and the formation of aerosol particles during aluminum combustion are discussed.     

Effect of additives for higher removal rate in lithium niobate chemical mechanical planarization

High roughness and a greater number of defects were created by lithium niobate (LN; LiNbO₃) processes such as traditional grinding and mechanical polishing (MP), should be decreased for manufacturing LN device. Therefore, an alternative process for gaining defect-free and smooth surface is needed. Chemical mechanical planarization (CMP) is suitable method in the LN process because it uses a combination approach consisting of chemical and mechanical effects. First of all, we investigated the LN CMP process using commercial slurry by changing various process conditions such as down pressure and relative velocity. However, the LN CMP process time using commercial slurry was long to gain a smooth surface because of lower material removal rate (MRR). So, to improve the material removal rate (MRR), the effects of additives such as oxidizer (hydrogen peroxide; H₂O₂) and complexing agent (citric acid; C₆H₈O₇) in a potassium hydroxide (KOH) based slurry, were investigated. The manufactured slurry consisting of H₂O₂-citric acid in the KOH based slurry shows that the MRR of the H₂O₂ at 2 wt% and the citric acid at 0.06 M was higher than the MRR for other conditions.     

H_2+He流体混合物在部分离解区的物态方程

H2+He流体混合物在高温高压下由于氢的离解化学反应形成由H2,H,He三种粒子构成的混合体系,此时粒子间的相互作用较为复杂,离解能也会由于粒子间的这种复杂相互作用而降低.本文利用自洽流体变分理论来研究部分离解区H2+He流体混合物的高温高压物态方程,模型考虑了各种粒子间的相互作用及由温致和压致效应引起的离解能降低的自洽变分修正,并通过自洽流体变分过程对非理想的离解平衡方程求解得到粒子数密度分布,进而对自由能求导获得体系的热力学状态参量.计算结果与已有的冲击波实验数据、蒙特卡罗模拟及其他理论计算进行了比较.     

Adsorption and diffusion behaviors of H2, H2S,NH3, CO and H2O gases molecules on MoO3 monolayer: A DFT study

Molybdenum trioxide (MoO₃) with α-phase is a promising material for gas sensing because of its high sensitivity, fast response and thermodynamic stability. To probe the mechanism of superior gas detection ability of MoO₃ monolayer, the adsorption and diffusion of H₂, H₂S, NH₃, CO and H₂O molecules on two-dimensional (2D) MoO₃ layer are studied via density functional theory (DFT) calculations. Based on calculated adsorption energies, density of states, charge transfer, diffusion barriers and diffusion coefficient, MoO₃ shows a superior sensitive and fast response to H₂ and H₂S than CO, NH₃, H₂O, which is consistent with experimental conclusions. Moreover, the response of MoO₃ to H₂S and H₂ will be obviously enhanced at high gas concentration, and the incorporation of H₂ and H₂S results in an obvious increasing in DOS near Fermi level. Our analysis provides a conceptual foundation for future design of MoO₃-based gas sensing materials.