Synthesis of micro porous barium nitrate with improved ignition reliability as a reliable pyrotechnic oxidant

Pure barium nitrate is one of the most widely used oxidizing materials in the field of pyrotechnics. The ignition reliability of compositions based on this material is not very high and needs to be improved. In the present work, modified barium nitrate with micro porous structure has been synthesized using three different vesicants to make it more reliable as a pyrotechnic oxidant. Two pyrotechnic compositions were formulated by using pure and modified barium nitrate as oxidant and micro sized aluminum powder was used as a fuel. The ignition temperature of both the compositions was determined using differential thermal analysis. The composition formulated with the modified oxidizer ignited at lower temperatures as compared to the one formulated with pure barium nitrate depicting an improvement in the ignition behavior. SEM results show that the modified barium nitrate has obvious pores of the order of few micrometers. Bulk density of the modified oxidizer decreased due to the development of micro pores. Crystallite size of the barium nitrate also decreased after the modification.     

甲酸存在下硝酸根在二氧化钛表面光催化还原成氨

用甲酸作空穴清除剂,研究了ＴｉＯ２水悬浮体系中硝酸根光催化还原氨的反应。与草酸作空穴清除剂相比,甲酸加速硝酸根的还原更显著。研究了硝酸根和甲酸根的浓度效应及ｐＨ效应。实验结果表明,硝酸根在ＴｉＯ２表面的吸附是加附是加速该光催化还原反应的重要因素。     

An amperometric nitrate reductase-phenosafranin electrode: kinetic aspects and analytical applications

The enzyme-catalysed reduction of nitrate was studied utilising Aspergillus niger nitrate reductase (NR) and phenosafranin in solution as the enzyme regenerator, working at lower potentials than that of the more common methyl viologen mediator. Cyclic voltammograms when enzyme, phenosafranin and substrate were together put in evidence the enzyme-catalysed reduction of nitrate, although with a relatively slow kinetics. From slope values not dependent on mediator concentration, the apparent Michaelis-Menten constant was evaluated. Analytical parameters for the enzyme-modified electrode in the presence of phenosafranin for the determination of nitrate content in water were assessed, including a recovery assay for nitrate added to a river water sample. The stability of the electrode was checked.     

The effect of arsenate,and of transitioń-metal ions,on the precipitation of phosphate as ammonium 12-molybdophosphate

The radionuclides phosphorus-32, arsenic-74, iron-59 and molybdenum-99 were used to determine the effect-of arsenate and some transition-metal ions on the precipitation of phosphorus as ammonium 12-molybdophosphate. Under the conditions necessary for the quantitative precipitation of phosphorus, arsenic is also precipitated by ammonium molybdate. The presence of iron(III) nitrate inhibits the precipitation of phosphorus and, particularly, arsenic, although the precipitates contain more molybdenum, and are heavier, than when iron is absent. Chromium (111) nitrate, nickel(II) nitrate and manganese(II) nitrate do not inhibit the precipitation of phosphorus and arsenic to the same extent as iron (III) nitrate.     

二维离子色谱法测定精己二酸中痕量硝酸根离子

建立二维离子色谱法测定精己二酸中痕量硝酸根离子含量的方法。第一维采用去离子水作为流动相,经过Ion Pac ICE–AS1色谱柱将精己二酸中的硝酸根离子和己二酸进行预分离,分离出来的硝酸根富集于Ion Pac TAC–ULP1浓缩柱上。以淋洗液发生器产生的不同质量浓度的氢氧化钾溶液作为淋洗液,将富集柱上的硝酸根淋洗下来,经第二维Ion Pac AS17–C色谱柱进行分离,以抑制型电导检测器测定硝酸根离子的含量。精己二酸中硝酸根离子的质量浓度在2.0~50.0μg/L范围内与其色谱峰面积呈良好线性,线性相关系数r20.999,检出限为0.10μg/L,测定结果的相对标准偏差小于1.5%(n=7),加标回收率为98.0%~105.0%。该方法操作简单,灵敏度、准确度高,选择性好,能够准确测定精己二酸中痕量硝酸根离子的含量。     

Selective synthesis of ZIFs from zinc and nickel nitrate solution for photocatalytic H2O2 production

Hydrogen peroxide (H₂O₂) is one of the most promising, green, and effective oxidants that can be used in different applications. In this study, zeolitic imidazolate frameworks (ZIFs), consisting of organic ligands and metal sites, were selectively prepared from zinc or nickel nitrate solutions for use in photocatalytic H₂O₂ production. High concentrations of zinc nitrate solution provided more metal sites to coordinate with 2-methylimidazole, producing ZIF-8 with larger particle size, whereas low zinc nitrate concentrations resulted in more interconnected N–H⋯N hydrogen bonds, forming 2D-layered ZIF-L, with smaller particle size. Various concentrations of zinc and nickel nitrate solutions produced ZIFs that exhibited ZIF-8 or ZIF-L topology, with bandgap energies of 5.45 and 4.85 eV, respectively. These samples could serve as promising photocatalyst for the successful production of H₂O₂ under Xenon lamp irradiation.     

Seasonal and water column trends of the relative role of nitrate and nitrite as *OH sources in surface waters

Based on literature data of sunlight spectrum, photolysis quantum yields, and absorption spectra, the relative role of nitrite and nitrate as *OH sources in surface waters was assessed, and its dependence on the season and the depth of the water column studied. In the majority of surface water samples (river, lake and seawater) nitrite is expected to play a more important role as *OH source compared to nitrate, in spite of the usually lower [NO2(-)] values. Interestingly, under the hypothesis of a constant ratio of the concentrations of nitrate and nitrite (to be corrected later on for the actual concentration ratio in a given sample), the relative role of nitrite compared to nitrate would be minimum in summer, at noon, in the surface layer of natural waters. Any decrease in the sunlight intensity that can be experienced in the natural environment (different season than summer, water column absorption, time of the day other than the solar noon), with its associated influence on the sunlight spectrum, would increase the relative role of nitrite compared to nitrate.     

An inexpensive,selective procedure for oxidizing α‐methyl to α‐formyl pyrroles pavel bobal

α‐Methylpyrroles are converted to α‐formyl by sodium bromate in aqueous methanol in ～60% yield. Adding 1% ceric ammonium nitrate as a co‐oxidant brings the isolated yields of synthetically useful 2‐formylpyrroles 2a‐d up to ～70%, or close to those found when using only the considerably more expensive ceric ammonium nitrate as oxidant.     

Chemometric approach to the optimisation of LC-FL and GC-MS methods for the determination of nitrite and nitrate in some biological,food and environmental samples

Gas chromatography–mass spectrometry (GC-MS) method and a liquid chromatography–fluorescence (LC-FL) detection method using experimental design and optimisation approach were improved for the quantitative determination of nitrite and nitrate in biological, food and environmental samples. The obtained recoveries of nitrite and nitrate ions from samples based on both GC-MS and LC-FL results ranged from 98.5% to 98.9% for nitrite and 97.9% to 98.4% for nitrate. The precision of these methods, as indicated by the relative standard deviations (RSDs), was within the range from 2.4% to 3.6% for nitrite and 2.5% to 3.8% for nitrate, respectively. The limits of detection of nitrite and nitrate ions from samples based on GC-MS and LC-FL results ranged from 0.01 to 0.14 ng L^?1 for nitrite and 0.02 to 0.71 ng L^?1 for nitrate, respectively. The optimised isolation procedure by central composite design was successfully applied to real samples. The results revealed that the proposed procedure combined with GC-MS and LC-FL techniques is more sensitive, reliable and selective compared to the other methods available for the precise determination of trace levels of nitrite and nitrate in biological, food and environmental samples.     

Nitrate ion-selective sensor based on electrochemically prepared conducting polypyrrole films

Nitrate-doped polypyrrole (PPy) films on a glassy carbon substrate have been prepared electrochemically in aqueous, acetonitrile, and propylene carbonate solutions for use as nitrate sensors. Lithium nitrate, sodium nitrate, nitric acid, tetraethylammonium p-toluene sulfonate (TS), and tetradodecylammonium nitrate (TDN) were employed as electrolytes. The effect of dibutylphthalate (DBP) as a plasticizer on the sensitivity and lifetime of PPy film sensors was also investigated. A Nernstian behavior with a slope of 56.9 m V/decade over 0.1–7.4 × 10⁻⁵ M NO and a detection limit of 4.7 × 10⁻⁵ M were observed for the polymer sensor prepared in acetonitrile solution containing lithium nitrate and 15% plasticizer (DBP). A lifetime of more than 6 months for this PPy film electrode was obtained.     

FTIR spectroscopy combined with quantum chemical calculations to investigate adsorbed nitrate on aluminium oxide surfaces in the presence and absence of co-adsorbed water

Surface reactions of nitrogen oxides with aluminium oxide particles result in the formation of adsorbed nitrate. Specifically, when alpha-Al(2)O(3) and gamma-Al(2)O(3) particles are exposed to gas-phase NO(2) and HNO(3) adsorbed nitrate forms on the surface. In this study, Fourier transform infrared (FTIR) spectroscopy is combined with quantum chemical calculations to further our understanding of the adsorbed nitrate product on aluminium oxide particle surfaces in the presence and absence of co-adsorbed water at 296 K. FTIR spectra of adsorbed nitrate on alpha-Al(2)O(3) and gamma-Al(2)O(3) particles are interpreted using calculated vibrational frequencies of nitrate coordinated to binuclear Al oxide cluster models. Comparison of the calculated and experimental vibrational frequencies of adsorbed nitrate establishes different modes of coordination (monodentate, bidentate and bridging) of the nitrate ion to the surface in the absence of adsorbed water. In the presence of co-adsorbed water, the nitrate ion becomes fully solvated, as shown by a comparison of the experimental nitrate infrared spectra as a function of relative humidity with the calculated nitrate vibrational frequencies for binuclear Al cluster compounds which contain both coordinated nitrate ions and water molecules. These calculations also suggest that adsorbed water can displace nitrate from direct coordination to the surface, leading to an outer-sphere nitrate adsorption complex as well as an inner-sphere complex. Furthermore, the relative humidity dependence of the spectra suggest that water does not evenly wet the surface even at high relative humidity, as there are open or bare surface sites where nitrate ions are not solvated. Besides adsorbed mondendate, bidendate, bridging and solvated nitrate, the presence of ion bound nitrate ion, partially solvated nitrate, molecular nitric acid, hydronium ion and H(3)O(+):NO(3)(-) ion pairs on the oxide surface are also discussed.     

Preparation and Electrochemical Properties of the Pd-modified Cu Electrode for Nitrate Reduction in Water

The reduction of nitrate has gained renewed attention due to environmental problems like overfertilization and the increasing costs of purification of drinking water. The usual techniques (e.g. ion-exchange and biofiltration) have some disadvantages1. So …     

Fabrication of Redox‐Mediator Supported Potentiometric Nitrate Biosensor with Nitrate Reductase

Fabrication of a more superior nitrate potentiometric biosensor than previously achieved with NaR and NADH has been accomplished by co‐entrapment of redox mediators and NaR into polypyrrole (PPy) film during galvanostatic polymerization of pyrrole. The replacement of NADH with redox mediators such as thionin acetate (ThAc), safranin (Saf), and azure A (AzA) gave more sensitive potentiometric responses, better minimum detectable concentration, linear concentration range and response time for nitrate than possible with NADH. The co‐entrapment of ThAc, Saf, AzA and methyl viologen (MV) with NaR into PPy films also improved the Nernstian behavior of the electrode process beyond the capability of the PPy‐NaR‐NADH biosensor. Substantial reduction in volume and quantity of cofactor/mediator and, hence cost, was achieved by the replacement of NADH with a redox mediator. Only 50 μM of AzA was required to form a PPy‐NaR‐AzA biosensor which gave the most sensitive potentiometric response for nitrate, achieving a minimum detectable concentration of 10 μM, a linear concentration range of 50–5000 μM and a response time of 2–4 s.     

Nitrate and ammonium ion-selective electrodes as sensors. I. In bacterial growth curves for isolation of nitrate and nitrite reductases from Escherichia coli

Ammonium and nitrate ion-selective electrodes were applied as sensors in bacterial growth curves for the isolation of nitrate and nitrite reductase. A nitrate ion-selective electrode was used as a successful new technique for the assay of nitrate reductase activity: the decrease in nitrate concentration was followed continuously. Likewise, an ammonium ion-selective electrode was used to follow the increase in ammonium ion concentration. Excellent agreement with spectrophotometric procedures ( < 5%) was obtained.     

Pronounced sponge-like nanostructure in propylammonium nitrate

The bulk structure of the ionic liquid propylammonium nitrate (PAN) has been determined using neutron diffraction. Empirical potential structure refinement (EPSR) fits to the data show that PAN self-assembles into a quasi-periodic bicontinuous nanostructure reminiscent of an amphiphile L(3)-sponge phase. Atomic detail on the ion arrangements around the propylammonium cation and nitrate anion yields evidence of hydrogen bonding between ammonium and nitrate groups and of strong alkyl chain aggregation and interdigitation. The resultant amphiphilic PAN nanostructure is more pronounced than that previously determined for ethylammonium nitrate (EAN) or ethanolammonium nitrate (EtAN).     

Buchbesprechungen

The effect of the solubility of insoluble lead chromate in the formation ofLiesegang rings has been studied. Rings are less closely packed as the solubility of lead chromate is increased with the increasing acidity of the medium. For the same concentration of potassium dichromate diffusing in the agar agar gels containing solutions of lead nitrate, it is observed that rings become more close as lead nitrate solution is diluted, a fact which is usually not observed in theLiesegang ring formation of different substances.     

A fluorescent nitrate sensing system using a reaction cartridge and titanium trichloride

A simple and highly sensitive cartridge type nitrate sensing system was developed using titanium trichloride (TiCl(3)) in hydrochloric acid to reduce nitrate to ammonium ion. The system primarily consisted of a nitrate reduction section using titanium trichloride and an ammonia detection section. The nitrate was reduced in a simply made cartridge equipped with filter units and the resulting ammonium ion solution was directly introduced into a flow injection system, where it was neutralized to ammonia and allowed to react with o-phthalaldehyde (OPA). The isoindole thus formed was detected by virtue of its fluorescence, allowing quantitation of the nitrate in the initial sample. Our sensing system has a detection limit of 0.01 mg l(-1) and a dynamic linear range from 0.05 to 2.5 mg l(-1) with response times of less than 5 min for the entire procedure. The system had a relative standard deviation (RSD) of less than 2.56% after more than 30 consecutive measurements of 0.5 mg l(-1) NO(3)(-). The system is unaffected by FeCl(3), Na(2)SO(4) and NaCl at concentrations of 200 mg l(-1) or by biological oxygen demand (BOD) values as high as 110 mg O l(-1). The effects of reaction time and titanium trichloride concentration were also investigated. Furthermore, several river water samples were examined.     

Catalytic Activity of the Oxide Catalysts Based on Ni<Subscript>0.75</Subscript>Co<Subscript>2.25</Subscript>O<Subscript>4</Subscript> Modified with Cesium Cations in a Reaction of N<Subscript>2</Subscript>O Decomposition

The Ni_0.75Co_2.25O₄ catalysts were prepared by a coprecipitation method and modified with cesium cations by impregnation with a solution of cesium nitrate or cesium nitrate with citric acid and ethylene glycol additives (the Pechini method). The catalysts obtained were investigated by X-ray diffraction analysis, the BET method, X-ray photoelectron spectroscopy, temperature-programmed reduction, and the temperatureprogrammed desorption of oxygen. The activity of the samples in a reaction of nitrous oxide decomposition was determined at temperatures of 200–300°C, in particular, in the presence of oxygen and water in the reaction mixture. It was found that the use of the Pechini method for supporting Cs makes it possible to obtain a more active catalyst, as compared with that prepared by impregnation with cesium nitrate, at the same cesium content (~2%) of the samples.     

Cu2+ ions as a paramagnetic probe to study the surface chemical modification process of layered double hydroxides and hydroxide salts with nitrate and carboxylate anions

A layered zinc hydroxide nitrate (Zn5(OH)8(NO3)2.2H2O) and a layered double hydroxide (Zn/Al-NO3) were synthesized by coprecipitation and doped with different amounts of Cu2+ (0.2, 1, and 10 mol%), as paramagnetic probe. Although the literature reports that the nitrate ion is free (with D3h symmetry) between the layers of these two structures, the FTIR spectra of two zinc hydroxide nitrate samples show the C2v symmetry for the nitrate ion, whereas the g ||/A || value in the EPR spectra of Cu2+ is high. This fact suggests bonding of some nitrate ions to the layers of the zinc hydroxide nitrate. The zinc hydroxide nitrate was used as matrix in the intercalation reaction with benzoate, o-chlorobenzoate, and o-iodobenzoate ions. FTIR spectra confirm the ionic exchange reaction and the EPR spectroscopy reveals bonding of the organic ions to the inorganic layers of the zinc hydroxide nitrate, while the layered double hydroxides show only exchange reactions.