Layer-by-layer construction of multi-walled carbon nanotubes, zinc oxide, and gold nanoparticles integrated composite electrode for nitrite detection

A novel composite electrode of Au/ZnO/MWCNTs/GC has been constructed for the electrochemical detection of nitrite, where ZnO thin film and Au nanoparticles are electrodeposited through layer-by-layer onto MWCNTs/GC substrate. The resulting electrode is characterized by scanning electron microscopy and energy-dispersed X-ray spectroscopy. Its electrocatalytic activity toward the electro-oxidation of nitrite has been examined and compared to various modified electrodes, including MWCNTs/GC, Au/ZnO/GC, Au/MWCNTs/GC, and ZnO/MWCNTs/GC via cyclic voltammetry. The electrodeposition time for ZnO and the Au loading amount together with the solution pH are investigated to achieve optimal conditions for the electrode fabrication and nitrite detection. Linear relationship between current response and nitrite concentration is observed in the range from 7.8 × 10⁻⁷ to 4.0 × 10⁻⁴ M and the limit of the detection is 4.0 × 10⁻⁷ M (S/N = 3). The influence of various anions and cations on the nitrite detection has been studied. The proposed method is also employed for the determination of nitrite in real samples.     

Oxidation of Nitrites in Mine Waters

A major component in the disinfection cost of mine water is the oxidation of microbiologically formed nitrite ion, which can be effectively oxidized by ozone (at close to the stoichiometric ratio of 3.4 mg O₃ per mg nitrite–snitrogen. The injudicious use of oxidizing disinfectants in the mine water may be implicated n i nitrite ion buildup. Laboratory batch reactor experiments show that 3 to 12 mg Cl₂/L and 3 to 11 mg CIO₂/L can inhibit nitrite ion oxidation by Nitrobacter. This inhibitive effect has not been observed for ozone.     

食品中亚硝酸盐含量的测定

样品经沉淀蛋白质、除去脂肪,在弱酸性溶液中亚硝酸盐与对氨基苯磺酸重氮化后,再与盐酸萘乙二胺偶联生成紫红色的偶氮染料,用分光度法测定。经过校正,亚硝酸盐含量x（ug）与吸光度A之间在λmax=550nm处,具有良好的线性关系,在亚硝酸盐的量为0～25μg／25mL水溶液中,服从朗伯-比耳定律,其线性方程为A=0．0132蜀相关系数r^2=0．9982,利用此方法所测定的当地出售的部分食品中亚硝酸盐的含量均未超过相关标准。用分光光度法测定腌制蔬菜中亚硝酸的含量,方法简单、方便、快捷、实用。     

亚硝酸钠法生产聚合硫酸铁新进展

酸性条件下,以亚硝酸钠为催化剂,以氧气为氧化剂,一步法生产聚合硫酸铁。实践证明:密闭条件下,于350 kg水中投加1 t全铁含量为20%的硫酸亚铁,配以98%浓硫酸的110 kg,以20 kg亚硝酸钠作为催化剂,以10~11 MPa的工业氧气5~6瓶作为氧化剂,55℃下催化氧化硫酸亚铁制备液体聚合硫酸铁可以在3 h内完成反应,生产出符合国家标准的高效净水剂。此生产工艺大大缩短了反应完成时间,提高了生产效率。又因为是密闭条件下反应,也大大减少了亚硝酸钠对环境的污染。是一种制备聚合硫酸铁的理想方案。目前,此工艺已经应用于本公司的实际生产。     

Complex Interplay of Heme-Copper Oxidases with Nitrite and Nitric Oxide

Nitrite and nitric oxide (NO), two active and critical nitrogen oxides linking nitrate to dinitrogen gas in the broad nitrogen biogeochemical cycle, are capable of interacting with redox-sensitive proteins. The interactions of both with heme-copper oxidases (HCOs) serve as the foundation not only for the enzymatic interconversion of nitrogen oxides but also for the inhibitory activity. From extensive studies, we now know that NO interacts with HCOs in a rapid and reversible manner, either competing with oxygen or not. During interconversion, a partially reduced heme/copper center reduces the nitrite ion, producing NO with the heme serving as the reductant and the cupric ion providing a Lewis acid interaction with nitrite. The interaction may lead to the formation of either a relatively stable nitrosyl-derivative of the enzyme reduced or a more labile nitrite-derivative of the enzyme oxidized through two different pathways, resulting in enzyme inhibition. Although nitrite and NO show similar biochemical properties, a growing body of evidence suggests that they are largely treated as distinct molecules by bacterial cells. NO seemingly interacts with all hemoproteins indiscriminately, whereas nitrite shows high specificity to HCOs. Moreover, as biologically active molecules and signal molecules, nitrite and NO directly affect the activity of different enzymes and are perceived by completely different sensing systems, respectively, through which they are linked to different biological processes. Further attempts to reconcile this apparent contradiction could open up possible avenues for the application of these nitrogen oxides in a variety of fields, the pharmaceutical industry in particular.     

Determination of Reaction Rate Constants in a Collimated Beam Setup: The Effect of Water Quality and Water Depth

UV/H₂O₂ processes can be studied using a Collimated Beam (CB) setup. In UV dose calculations, the “water factor” accounts for changes in the irradiation spectrum upon its way through the aqueous solution. Analogous to the “germicidal factor,” the “extinction factor” is introduced, correcting for the fact that resulting compounds will be subjected to an emission spectrum changing over the depth. Using the extinction factor, the fluence-based photolysis and oxidation rate constants of model compounds, as well as the quantum yield for nitrite formation, were found to be independent of the depth of the water layer applied.     

Inhibition of aluminium corrosion in chloride media: an impedance study

Inhibition of the corrosion of pure aluminium by nitrite and chromate anions in near neutral aqueous chloride solution has been studied by electrochemical impedance spectroscopy, keeping the ionic strength constant by addition of potassium sulphate electrolyte. Negative of the chloride pitting potential impedance spectra show that both anions are successful in reducing corrosion through adsorption, nitrite more than chromate. Positive of this value, nitrite becomes ineffective, whereas chromate remains adsorbed and continues to prevent pitting corrosion, probably through its ability to repair defects in the oxide film. Impedance techniques successfully show the qualitative and quantitative differences between the two inhibitors.     

亚硝酸甲酯在甲醇溶剂中的亨利常数测定

在合成气制乙二醇这一新工艺中,亚硝酸甲酯的再生起着至关重要的作用,但关于亚硝酸甲酯的基础物性数据很少,如在甲醇中的亨利常数。由于亚硝酸甲酯的相关物性数据的缺乏,不能用已报道的一些方法进行估算,因此在改进的静态法测定汽液平衡装置上,测定了293.15—323.15 K亚硝酸甲酯在甲醇中的亨利系数。结果表明,温度升高,亨利系数增大,且亚硝酸甲酯在甲醇中的溶解量很小。通过对亨利系数与温度的关联得出普遍意义的表达式,为亚硝酸甲酯再生的研究提供参考。     

Electrocatalytic reduction of nitrite using ferricyanide; Application for its simple and selective determination

The electrocatalytic reduction of nitrite has been studied by ferricyanide at the surface of carbon paste electrode. Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of ferricyanide as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the electrocatalytic ability about 700 mV can be seen and the homogeneous second-order rate constant (k_s) for nitrite coupled catalytically to ferricyanide was calculated 2.75 × 10³ M⁻¹ s⁻¹ by Nicholson-Shain method. Also, electron transfer coefficients (α) for ferricyanide was determined by using various electrochemical approaches such as Tafel plot in the absence and presence of nitrite 0.556 and 0.760, respectively. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00 × 10⁻⁵ to 1.00 × 10⁻³ M. Detection limit has been found to be 2.63 × 10⁻⁵ M (2σ). This method has been applied as a selective, simple and precise method for determination of nitrite in real sample.     

亚硝酸根试纸的开发与研制

本文通过实验确定了一种检测亚硝酸根含量试纸的制备方法。通过实验确定了试纸的材料和显色剂，并对显色剂制备过程中的影响因素进行了分析．实验结果表明：定性中速滤纸可以作为亚硝酸根试纸的材料；含有4-氨基苯磺酰胺和N-1-萘基乙二胺盐酸盐的显色剂A及含有1：1的α-萘胺溶液和对氨基苯磺酸溶液的显色剂B，按1：1混合后可以作为显色剂；通过应用实验表明，亚硝酸根试纸具有体积小、便于携带、检测方便、成本低廉等特点。因此，具有广泛的应用价值和市场开发前景。     

亚硝酸钠含量对乳化炸药生产安全性的影响

硝酸钠中的少量亚硝酸钠对乳化炸药基质具有一定敏化作用和起泡作用,它使乳化炸药基质感度提高,给安全生产带来隐患。选择使用亚硝酸钠含量较低的硝酸钠,可以有效提高乳化炸药生产的本质安全度。     

Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation

Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.     

Effective design of photocatalytic reactors: influence of radiative transfer on their performance

The role of radiative transfer on a photocatalytic reaction occurring in an annular reactor has been investigated by modeling the degradation of chloroform contaminating the processed aqueous stream. From the analysis of the resulting effects it is apparent that the crucial factor in assessing the performance of the reactor is the distribution of radiant energy absorption rate which, in turn, depends on the mass of catalyst and on the way it is dispersed within the reactor. An optimization of the reactor is conceivable through a proper selection of the catalyst dispersion.     

Liquid-liquid mixing for the breakup of accelerating drops

Studies have been made on the fragmentation of liquid metal drops falling through a waterglycerine mixture containing small amounts of nitrogen bubbles owing to the passage of a strong shock wave. The apparent drop volume increased with lime, but neither stripping of small droplets nor misty wake formation was observed in the high-speed photographs. The drop flattened initially into a spherical cap which increased in radius, but remained smooth, within the time period of interest. Hence the Taylor instability is not the principal fragmentation mechanism at these Weber numbers (5-644). Entrainment of liquid into the drop was the cause of breakup, and was postulated to be due to turbulent mixing resulting from vorticity generation near the plane of separation. A hydrodynamic fragmentation model was developed which predicts the rale of drop volume increase reasonably well. The breakup time constant was presented, and drop trajectory can also be predicted from the model.     

催化光度法测定水中微量亚硝酸根

研究了硫酸介质中 ,亚硝酸根离子对溴酸钾氧化中性红褪色的催化效应 ,选择了最佳反应条件。本法测定亚硝酸根的线性范围为 0 .0 0 5 0 .2 4μg·ml-1。方法简便、快速、选择性好 ,不需恒温加热 ,应用于水样中亚硝酸根的测定 ,结果满意。     

表面增强拉曼光谱法快速检测水产品中的孔雀石绿

基于表面增强拉曼光谱技术的便携式拉曼光谱仪运用于水产品养殖、运输过程水样中孔雀石绿的快速测定进行了研究.利用孔雀石绿位于432-437 cm-1,1166-1170 cm-1,1613-1617cm-1的拉曼光谱特征峰及其强度,对孔雀石绿进行定性及半定量的快速测定.检测限为5.0μg/L,常见含氮化合物尿素、亚硝酸钠以...     

Nitrite in soils: accumulation and role in the formation of gaseous N compounds

Nitrite is an intermediary compound formed during nitrification as well as denitrifiication. It occasionally accumulates in soils and drainage water. The nitrite can then undergo transformations to gaseous nitrogen compounds such as NO and NO₂. Soil pH controls the abiotic nitrite decomposition to a large extent. Under acidic conditions(pH <5.5), nitrous acid spontaneously decomposes preferentially to NO and NO₂. Nitrite also undergoes reactions with metallic cations (especially ferrous iron) and with organic matter. As a result of these reactions gaseous compounds such as NO, NO₂, N₂O and CH₃ONO can be formed. Through reaction of nitrite with phenolic compounds nitroand nitrosocompounds can be formed, building up organic N. With normal agricultural practices on slightly acidic soils, the nitrite instability usually does not lead to economically important N losses from soils. However, the compounds formed through its degradation or interaction with other soil constituents are linked to environmental problems such as tropospheric ozone formation, acid rain, the greenhouse effect and the destruction of the stratospheric ozone.     

Influence of the shaping effect on hardness homogeneity by Vickers indentation analysis

In this study, indentation technique (Vickers indentation) has been unconventionally used to evaluate the homogeneity of barium zirconate ceramic samples which have been shaped through different routes. Statistical tools have been used to estimate the correlation which can be established between heterogeneities within the samples and their shaping ways.     

Possible role of nitrite/nitrate redox cycles in N2O decomposition and light-off over Fe-ZSM-5

Surface nitrite/nitrate redox cycles were proposed to explain light-off behavior that was observed during the decomposition of N₂O over Fe-ZSM-5. Further study has demonstrated that while the nitrite/nitrate model can explain the original observations as an isothermal, mechanistic phenomenon, the light-off behavior is thermal, and not a mechanistic effect. Nonetheless, a pathway involving nitrite/nitrate redox cycles appears to be more consistent with experimental observation than the simple two-step pathway involving cation redox cycles. In particular, the nitrite/nitrate pathway can explain the effect of added NO upon the reaction kinetics and the reported isotopic product composition when unlabeled N₂O reacts over an oxygen-labeled catalyst. Further, a nitrite/nitrate pathway is consistent with the steady-state kinetics as well as published thermal desorption and infrared spectroscopic results.     

Carbon steel passivity examined in alkaline solutions: The effect of chloride and nitrite ions

The effect of chloride and nitrite ions on the passivity of steel in alkaline solutions was investigated. Four nitrite dosages were tested, resulting in various nitrite/chloride ratios. The behavior of steel was evaluated on electrodes aged during 1 and 90 days, measuring electrochemical parameters such as the corrosion, pitting and repassivation potentials, the corrosion current density, the weight loss and performing electrochemical impedance spectra. The presence of 0.8 mol l⁻¹ of chloride induced pitting only under polarization and when the chloride/hydroxyl ratio was not less than one. Nitrite ions behave as effective inhibitors of pit propagation for all the concentrations tested (0.2-0.8 mol l⁻¹). A nitrite/chloride ratio of 0.25 induces complete surface repassivation. Nevertheless, at open circuit potential, the high alkalinity guarantees passivation even in the presence of chlorides. In the event that the passive layer is damaged and pitting can be initiated, nitrite ions are effective in inhibiting pit propagation.