Electrophysical properties of In2O3-and WO3-based gas-sensitive semiconducting films as sensors for unsymmetrical dimethylhydrazine in air

Some n-type semiconductor metal oxide sensors based on WO₃ and In₂O₃ were studied in detecting unsymmetrical dimethylhydrazine (UDMH) vapors. The sensors are highly sensitive to the presence of UDMH vapors in air at concentrations equal to or lower than the MPC. They have short response and relaxation times in detecting UDMH vapors in air. It was found that, when ammonia was present in air in concentrations comparable to those of UDMH, it did not affect the electrophysical properties of the semiconductor sensors.     

Sol–gel derived mesoporous Pt and Cr-doped WO<Subscript>3</Subscript> thin films: the role played by mesoporosity and metal doping in enhancing the gas sensing properties

Mesoporous Cr or Pt-doped WO₃ thin films to be employed as ammonia gas sensors were prepared by a fast one-step sol–gel procedure, based on the use of triblock copolymer as templating agent. The obtained films were constituted by aggregates of interconnected WO₃ nanocrystals (20–50 nm) separated by mesopores with dimensions ranging between 2 and 15 nm. The doping metals, Pt and Cr, resulted differently hosted in the WO₃ mesoporous matrix. Chromium is homogeneously dispersed in the oxide matrix, mainly as Cr(III) and Cr(V) centers, as revealed by EPR spectroscopy; instead platinum segregated as Pt (0) nanoparticles (4 nm) mainly included inside the WO₃ nanocrystals. The semiconductor layers containing Pt nanoclusters revealed, upon exposure to NH₃, remarkable electrical responses, much higher than Cr-doped and undoped layers, particularly at low ammonia concentration (6.2 ppm). This behavior was attributed to the presence of Pt nanoparticles segregated inside the semiconductor matrix, which act as catalysts of the N–H bond cleavage, decreasing the activation barrier in the ammonia dissociation. The role of the mesoporous structure in influencing the chemisorption and the gas diffusion in the WO₃ matrix appeared less decisive than the electronic differences between the two examined doping metals. The overall results suggest that a careful combination between mesoporous architecture and metal doping can really promote the electrical response of WO₃ toward ammonia.     

The anodic dissolution of chalcocite in an ammoniacal environment

Presented is the proposed model for the mechanism of anodic oxidation of the semiconductor mineral chalcocite in an ammoniacal environment. The kinetic parameters of the process α_a, k_s, j₀⁰, the formal potential and the electrochemical order of the reaction in relation to ammonia are given.     

Surfactant‐Free Nonaqueous Synthesis of Plasmonic Molybdenum Oxide Nanosheets with Enhanced Catalytic Activity for Hydrogen Generation from Ammonia Borane under Visible Light

Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth‐abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface‐capping agents in their synthetic procedures. To fulfill this, a facile non‐aqueous procedure was employed to prepare well‐defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO_3‐x nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near‐infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen‐generation activity of ammonia borane under visible light irradiation.     

Direct analysis of ultra-trace semiconductor gas by inductively coupled plasma mass spectrometry coupled with gas to particle conversion-gas exchange technique

An inductively coupled plasma mass spectrometry (ICPMS) coupled with gas to particle conversion-gas exchange technique was applied to the direct analysis of ultra-trace semiconductor gas in ambient air. The ultra-trace semiconductor gases such as arsine (AsH₃) and phosphine (PH₃) were converted to particles by reaction with ozone (O₃) and ammonia (NH₃) gases within a gas to particle conversion device (GPD). The converted particles were directly introduced and measured by ICPMS through a gas exchange device (GED), which could penetrate the particles as well as exchange to Ar from either non-reacted gases such as an air or remaining gases of O₃ and NH₃. The particle size distribution of converted particles was measured by scanning mobility particle sizer (SMPS) and the results supported the elucidation of particle agglomeration between the particle converted from semiconductor gas and the particle of ammonium nitrate (NH₄NO₃) which was produced as major particle in GPD. Stable time-resolved signals from AsH₃ and PH₃ in air were obtained by GPD-GED-ICPMS with continuous gas introduction; however, the slightly larger fluctuation, which could be due to the ionization fluctuation of particles in ICP, was observed compared to that of metal carbonyl gas in Ar introduced directly into ICPMS. The linear regression lines were obtained and the limits of detection (LODs) of 1.5 pL L⁻¹ and 2.4 nL L⁻¹ for AsH₃ and PH₃, respectively, were estimated. Since these LODs revealed sufficiently lower values than the measurement concentrations required from semiconductor industry such as 0.5 nL L⁻¹ and 30 nL L⁻¹ for AsH₃ and PH₃, respectively, the GPD-GED-ICPMS could be useful for direct and high sensitive analysis of ultra-trace semiconductor gas in air.     

Defect induced nickel,nitrogen-codoped mesoporous TiO2 microspheres with enhanced visible light photocatalytic activity

Nickel, nitrogen-codoped mesoporous TiO₂ microspheres (Ni–N–TiO₂) with high surface area, and an effective direct band gap energy of ∼2.58 eV. Nickel sulfate used as the Ni source and ammonia gas as the N source here. The efficiency of the as-prepared samples was investigated by monitoring the degradation of Rhodamine B under visible light irradiation. The experimental results indicate that Ni-doped mesoporous TiO₂ microspheres show higher photocatalytic activity than mesoporous TiO₂ microspheres under visible light irradiation. It mainly due to that the electron trap level (Ni²⁺/Ni⁺) promoting the separation of charge carriers and the oxygen vacancies inducing the visible light absorption. In addition, Ni–N–TiO₂ shows enhanced activity compared with Ni–TiO₂. Codopants and dopants are found to be uniformly distributed in TiO₂ matrix. Among the all samples the 0.5% molar quantity of Ni dopant and 500 °C 2 h nitriding condition gives the highest photocatalytic activity. The treatment of ammonia gas on Ni–TiO₂ sample induced oxygen vancancies, substitutional and interstitial N. A suitable treatment by ammonia gas also promote separation of charge carriers and the absorption of visible light. The active species generated in the photocatalytic system were also investigated. The strategy presented here gives a promising route towards the development of a metal and non-metal codoped semiconductor materials for applied photocatalysis and related applications.     

Synthesis, Characterization, Photoluminescence and Photocatalytic Properties of CeO2 Nanoparticles by the Sonochemical Method

Uniform CeO₂ nanoparticles were synthesized via a facile sonochemical reaction between ceric ammonium nitrate and ammonia. Nanoparticles were synthesized via a surfactant free reaction at room temperature in solvent of water. Products were characterized using X-ray diffraction, scanning electron microscopy, photoluminescence (PL) spectroscopy, and energy dispersive X-ray analysis. The effect of different parameters such as precursor, power of pulsation, surfactant and reaction time on the morphology of the products was investigated. It was found that the as-obtained CeO₂ nanoparticles exhibit a strong PL peak at 381 nm at room temperature that can be ascribed to the high level transition in the CeO₂ semiconductor. The photocatalytic behavior of CeO₂ nanoparticles was evaluated using the degradation of a methyl orange aqueous solution under ultraviolet light irradiation. The results show that CeO₂ nanoparticles are promising materials with excellent performance in photocatalytic applications.     

Room Temperature Ferromagnetism in Ga1-xHoxN (x=0.0 and 0.05) Diluted Magnetic Semiconductor Thin Films

Holmium doped GaN diluted magnetic semiconductor thin films have been prepared by thermal evaporation technique and subsequent ammonia annealing. X-ray diffraction mea-surements reveal all peaks belong to the purely hexagonal wurtzite structure. Surface mor-phology and composition analysis were carried out by scanning electron microscopy and energy dispersive spectroscopy respectively. The room temperature ferromagnetic proper-ties of Ga_1-xHo_xN(x=0.0, 0.05) films were analyzed using vibrating sample magnetometer at room temperature. Magnetic measurements showed that the undoped films (i.e. GaN) exhibited diamagnetic behavior, while the Ho-doped (Ga_0.95Ho_0.05N) film exhibited a ferro-magnetic behavior.     

Synthesis and electrical properties of CuBr<Subscript>2</Subscript> complexes with 1,10-phenanthroline monohydrate

Using 1,10-phenanthroline monohydrate and CuBr₂ in molar ratios of 1:1 and 2:1, in CH₃OH/H₂O (ϕ_r = 1:1), the complexes [(phen)CuBr₂]₂, (I), and {[(phen)₂CuBr]Br·H₂O}, (II), have been prepared. The hydrogen bondings and aqua bridges between coordinated and noncoordinated bromides of II have been observed by XRD. Complex II has a triclinic crystal structure with distorted trigonal bipyramidal coordination geometry. Possibilities of ligand exchange with hydroxide or ammonia have been examined in both complexes. While the mononuclear complex II is stable in a refluxed ammonia solution and the complex {[phen)₂CuBr]Br·3H₂O}, (IV), trihydrate of II, is obtained; the binuclear complex I reacts with the ammonia solution to replace one of its bromides in the subunits with hydroxide to give {[(phen)₂Cu₂Br₂(OH)₂]·4H₂O}, (III). Structural and electrical properties of the complexes have been investigated by elemental analysis, vibrational and electronic spectroscopy, mass spectrometry, TGA, XRD and the four-point probe method. The temperature coefficients of resistivity and the activation energies of the complexes have also been obtained. All complexes behave as intrinsic semiconductor in the temperature range of 310–440 K.     

Ammonia oxidation to nitrogen mediated by electrogenerated active chlorine on Ti/PtOx-IrO2

The electrochemical oxidation of ammonia (NH₃ and/or NH₄⁺) in the presence of chloride was investigated on a Ti/PtO_x–IrO₂ electrode. It was shown that ammonia is effectively removed from solution via electrogenerated active chlorine. Based on mass balances, nitrogen is postulated to be the main product of ammonia electrolysis. In the bulk, the concentration of chloramines was low. This could be explained by the fact that the oxidation of ammonia takes place close to the electrode surface where an excess of chlorine relative to ammonia is ensured during the process. This results in the oxidation of ammonia to N₂ and in a local pH decrease. As a result, chloramines were decomposed in the proximity of the electrode prior to diffusing into the bulk.     

Pretreatment of wastepaper and pulp mill sludge by aqueous ammonia and hydrogen peroxide

Pretreatment of two different softwood-based lignocellulosic wastes (newsprint and Kraft pulp mill sludge) was investigated. Pretreatment was done by aqueous ammonia and hydrogen peroxide (H₂O₂), two delignifying reagents that are environmentally benign. Three different treatment schemes were employed: aqueous ammonia alone (ammonia recycled percolation [ARP]), mixed stream of aqueous ammonia and H₂O₂ and successive treatment with H₂O₂ and aqueous ammonia. In all cases there was a substantial degree of delignification ranging from 30 to 50%. About half of the hemicellulose sugars were dissolved into the process effluent. Retention of cellulose after pretreatment varied from 85 to 100% for newspaper feedstock and from 77 to 85% for the pulp mill sludge. After treatment with aqueous ammonia alone (ARP), the digestibility of newspaper and the pulp mill sludge was improved only by 5% (from 40 to 45% for the former and from 68 to 73% for the latter), despite a substantial degree of delignification occurring after the ARP process. The lign in content thus did not correlate with the digestibility for these substrates. Simultaneous treatment with H₂O₂ and aqueous ammonia did not bring about any significant improvement in the digestibility over that of the ARP. A succcessive treatment by H₂O₂ and ARP showed the most promise because it improved the digestibility of the newspaper from 41 to 75%, a level comparable to that of α-cellulose.     

Zinc Tetracyanoplatinate: A Reversible Luminescence-Based Ammonia Sensor

ZnPt(CN)₄ was shown to be an effective material for ammonia sensing, and can be synthesized using either solution or mechanochemical methods. A combination of luminescence and Raman spectroscopy revealed that multiple species are involved in the reaction between ammonia and ZnPt(CN)₄. The crystal structure of one of these species, Zn(NH₃)₂Zn(NH₃)₃(Pt(CN)₄)₂, was elucidated. Detection of ammonia vapor down to 50 ppm in air was accomplished by monitoring the luminescence spectrum. The reaction between ZnPt(CN)₄ and ammonia vapor is reversible, and can be cycled multiple times by either flowing air over the material or heating. ZnPt(CN)₄ also has a relatively high thermal stability, decomposing only when heated above 420 °C.     

Zirconia prepared from UIO-66 as a support of Ru catalyst for ammonia synthesis

The development of effective Ru catalyst for ammonia synthesis is of important practical value and scientific significance because of the wide application of ammonia as a fertilizer and its promising applications in the renewable energy. Generally, ZrO₂ was regarded as an inferior support for Ru catalyst used in ammonia synthesis. Here we prepare ZrO₂ with monoclinic phase and carbon species from ZrCl₄ following the preparation route of UiO-66 as well as ammonia treatment. Owing to the presence of a larger amount of hydrogen adsorption as well as the easier desorption of hydrogen species, the ill effect of hydrogen species on the nitrogen adsorption-desorption and ammonia synthesis can be effectively alleviated. The resulting ZrO₂-supported Ru catalyst showed 4 times higher ammonia synthesis activity than the conventional Ru/ZrO₂ obtained from zirconium nitrate.     

Synthesis of ammonia from natural gas at atmospheric pressure with doped ceria–Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>–K<Subscript>3</Subscript>PO<Subscript>4</Subscript> composite electrolyte and its proton conductivity at intermediate temperature

A new type of oxide–salt composite electrolyte, yttrium doped ceria YDC–Ca₃(PO₄)₂–K₃PO₄, was developed and demonstrated for its promising use for ammonia synthesis. Using this composite electrolyte, ammonia was synthesized from nitrogen and natural gas at atmospheric pressure in the solid-state proton conducting cell reactor, and the optimal condition for ammonia production was determined . The evolved rate of ammonia is up to 6.95×10⁻⁹ mol s⁻¹ cm⁻².     

Enhanced ammonia oxidation on BDD induced by inhibition of oxygen evolution reaction

Electrochemical oxidation of ammonia (NH₃ and NH₄ ⁺ ) on boron-doped diamond (BDD) electrode was studied using differential electrochemical mass-spectrometry (DEMS) and chronoamperometry. Electro-oxidation of ammonia induces inhibition of the oxygen evolution reaction (OER) due to adsorption of the ammonia oxidation products on the BDD surface. The inhibition of the OER enhances ammonia electro-oxidation, which becomes the main reaction. The amino radicals, formed during ammonia oxidation, trigger a reaction chain in which molecular oxygen dissolved in solution is involved in the ammonia electro-oxidation. Nitrogen, nitrous oxide, and nitrogen dioxide were detected as the ammonia oxidation products, with nitrogen being the main gaseous product of the oxidation.     

Electrochemical behavior of ammonia at Ni/Ni(OH)2 electrode

The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)₂ electrode prepared by potential cycling of a Ni electrode in 1 M NaClO₄. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH₃ rather than ${\text{NH}}_4^{+}$ is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)₂ is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule.     

Co-SrTiO3上光催化分解水制氢的性能研究

氢能在使用过程中不会给环境带来任何污染,是未来最理想的能源。但目前的氢气生产方法能耗较高,同时伴随着严重的环境污染,显然不适合大规模生产能源用氢气。洁净化生产氢气方法的开发备受世人的关注,吸引了大量的科研人员从事这方面的研究。其中以半导体氧化物为催化剂,光催化分解水制氢被认为是最有前途的方法。经过几十年的努力,取得了很大的进步,先后开发出在紫外光照射下可以将蒸馏水分解为氢气和氧气的光催化剂,如TiO2犤1犦、SrTiO3犤2犦、Na2Ti6O13犤3犦、BaTi4O9犤4犦、K2La2Ti3O10犤5犦、K4Nb6O17犤6犦、ZrO2犤7犦等;可见…     

Metal oxide semiconductor sensors for determination of reactive gas impurities in air

Characteristics of metal oxide semiconductor sensors intended for measuring O₃, NO _x , Cl₂, C1O₂, and HCl microconcentrations were discussed. Specific features of detection of these microimpurities with semiconductor sensors were determined. The size of signal generated by sensors with WO₃-, ZnO-, and In₂O₃-based sensing layers was examined in relation to the O₃, NO _x , Cl₂, C1O₂, and HCl concentration. The sensitivities exhibited by the semiconductor sensors with respect to target impurities make them suitable for measuring their maximum permissible concentrations in sanitary zones and for monitoring background ozone level in atmosphere. Examples of application of gas analyzers based on semiconductor sensors in determination of gas impurities in the open atmosphere were given.     

The determination of ammonia in flue gas from the selective catalytic reduction of nitric oxide with ammonia

The emission of NO_x from coal-fired boilers can be limited by means of the selective catalytic reduction of NO_x with ammonia. The amounts of unreacted ammonia downstream should be low to avoid processing and environmental problems. Continuous measurement of the ammonia in the flue gas is needed. The determination of ammonia and flue gas sampling techniques are discussed. Measurements of ammonia in exhausts of a laboratory reactor and of a pilot plant for the selective catalytic reduction of NO_x with ammonia are presented. Ammonia was determined by mass spectrometry and chemiluminescence in the gas phase, and by spectrophotometric (Nessler and Berthollet reactions) or potentiometry in aqueous solution, in low (<5 μl l^?1) and high (<1000 μl l^?1) concentration ranges.     

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH₃)NH₂BH₃, was synthesized by treatment of LiNH₂BH₃ with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at ?20 °C crystallizes in the orthorhombic space group Pbca with lattice parameters of a=9.711(4), b=8.7027(5), c=7.1999(1) Å, and V=608.51 ų. The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH₃)NH₂BH₃ is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40–70 °C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 °C, which represents a significant advantage over LiNH₂BH₃. It has been found that the formation of the coordination bond between ammonia and Li⁺ in LiNH₂BH₃ plays a crucial role in promoting the combination of hydridic B? H bonds and protic N? H bonds, leading to dehydrogenation at low temperature.