Micro Ammonia Sensor

Abstract

A micro ammonia sensor, consisting of an ISFET covered with a dry membrane which is made from nonactin and substituted poly-γ-methyl-L-glutamate (PMG) is described. The gate output voltage of the micro ammonia sensor increased with NH₄OH addition. The response time of the sensor was 2 min at 30°C, and the sensor exhibited superior selectivity for NH₄ ⁺ compared to a pH sensitive ISFET.     

Optochemical Sensor for Ammonia Based on a Lipophilized pH Indicator in a Hydrophobic Matrix

Abstract

An optical sensor for the determination of ammonia in water based on ion pairing has been investigated. A pH-sensitive dye is immobilized as an ion pair in a silicone matrix. The colour of the dye changes from yellow to blue depending on the concentration of ammonia in the sample solution. This change is reversible. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength.

All measurements were performed with a dual-beam optical meter. The measurement range was from 5.9 × 10^?7 to 1 × 10^?3 M (0.01 to 17 mg/l) in 0.1 M phosphate buffer of pH 8. The detection limit was 10 μg/l. The response times at a flow rate of 2.5 ml/min were 4 min for t₉₀ and 10 min for t₁₀₀ at a change from 41.9 to 82.5 μM ammonia and 12 min for t₉₀ and 48 min for t₁₀₀ at a change from 160 to 0 μM ammonia. The operational lifetime of the ammonia sensor was limited to a period of a few days only. A continuous decrease in baseline signal and relative signal change was observed over the whole measurement. The storage stability was more than 10 months (dry). With respect to possible application of the ammonia sensor to environmental analysis, the influence of pH, typical interferences, such as amines and various detergents on the sensor response was investigated. No interference due to pH was observed in the range from pH 5 to pH 9. With methyl- and ethylamine the response was not completely reversible. The sensor was affected by cationic detergents, but not by anionic or neutral detergents.     

Dielectric Barrier Discharge for Ammonia Production

The leading after-treatment technology for NOx removal process in Diesel engines for stationary and mobile applications is the selective catalytic reduction of oxides of nitrogen [NOx] by ammonia [NH₃]. A novel non-thermal plasma electrode with a needle array in a dielectric barrier discharge reactor, powered by a high frequency neon transformer, is used for the thermal decomposition of solid urea [(NH₂)CO(NH₂)] to produce ammonia. The thermolysis of urea produces iso-cyanic acid [HNCO] as a byproduct, besides ammonia, which can react with water in the gas phase, thus giving carbon dioxide and more ammonia. The presence of water fed before and/or after the plasma reactor was studied to assess its effect on the amount of produced ammonia. Results clearly showed that water fed to the entrance of the reactor can efficiently promote the reaction of iso-cyanic acid to produce ammonia and this result can be improved when air is used as carrier gas for 115 V of input voltage to a neon transformer and with a gas flow rate of 4 L/min.     

Turbidimetric Determination of Ammonia Using 12-Molybdophosphoric Acid

Abstract

A turbidimetric method for the determination of ammonia was developed based on the co-precipitation of ammonium 12-molybdophosphate with thallium(I) 12-molybdophosphate. The analysis is carried out in strongly acidic solution which eliminates possible loss due to volatility and other interferences. Samples containing 0.1 to 3.0 mg of ammonia are conveniently analyzed in 30 minutes with a relative standard deviation 1.7%. A study of the effect of various diverse ions was conducted.     

Analysis of Urea Nitrogen in the Presence of Ammonia Using an Ammonia Gas Sensitive Electrode

Abstract

This report describes a method for the determination of ammonia and urea in raw sewage samples using an Orion Ammonia Gas-Sensing Electrode. Urea is determined by potentiometrically measuring the ammonia produced following exhaustive hydrolysis by urease and subtracting the amount of ammonia present before enzymatic hydrolysis. The recovery of urea from raw sewage samples using the procedure herein described is shown to be nearly Quantitative.     

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.     

Fluorescence Spectrophotometric Determination of Trace Ammonia

Measurement of trace ammonia (or ammonium ion) is important for environmental monitoring. Hiroshi Mikasa et al and Satoshi Sasaki et al had reported the determination of trace ammonia by flow injection analysis based on the reaction of ammonia and o-phthaiadehyde in the presence of 2-mercaptoethanol. The reaction equation is as follows.     

Large-Sized Ammonia Clusters and Solvation Energies of the Proton in Ammonia

The absolute solvation energies (free energies and enthalpies) of the proton in ammonia are used to compute the pK_a of species embedded in ammonia. They are also used to compute the solvation energies of other ions in ammonia. Despite their importance, it is not possible to determine experimentally the solvation energies of the proton in a given solvent. We propose in this work a direct approach to compute the solvation energies of the proton in ammonia from large-sized neutral and protonated ammonia clusters. To undertake this investigation, we performed a geometry optimization of neutral and protonated ammonia 30-mer, 40-mer, and 50 mer to locate stable structures. These structures have been fully optimized at both APFD/6-31++g(d,p) and M06-2X/6-31++g(d,p) levels of theory. An infrared spectroscopic study of these structures has been provided to assess the reliability of our investigation. Using these structures, we have computed the absolute solvation free energy and the absolute solvation enthalpy of the proton in ammonia. It comes out that the absolute solvation free energy of the proton in ammonia is calculated to be −1192 kJ mol^–1, whereas the absolute solvation enthalpy is evaluated to be −1214 kJ mol^–1. © 2019 Wiley Periodicals, Inc.     

Copper-Catalyzed Amination of Aryl Halides with Aqueous Ammonia under Mild Conditions

A Cu(I) generated in situ from CuSO₄·5H₂O/sodium ascorbate catalyzed cross‐coupling reaction of aryl halides with aqueous ammonia for the synthesis of primary aromatic amines has been developed. Key to the success included the application of aqueous ammonia under a homogeneous condition.     

卷烟主流烟气中氨的捕集及其离子色谱法测定

设计了高效的烟气捕集装置,建立了一种稀硫酸吸收、离子色谱法测定的卷烟主流烟气中氨的分析新方法.与早期的比色法、容量法、氨电极法、气相色谱法相比,该方法快速、简便,不需要复杂的样品前处理,完成一次分析只需12 min.检出限为0.005 mg/L,RSD为3.7%,空白加标回收率在87%～102%之间,吸烟加标回收率在98%～106%之间.测定了国内50种主要品牌卷烟,其主流烟气中氨含量范围为6.50～14.22μg/支烟.     

Catalytic Activity for Ammonia Synthesis of Iron Supported Catalysts Prepared from an Acid-modified λ-Al2O3 Method

Iron supported catalysts were prepared by impregnation of several acid-modified λ-Al₂O₃ samples with a K₄[Fe(CN)₆] aqueous solution. A concentration range between 0–20 mmole H⁺ added · g^?1λ-Al₂O₃ was used. The quantitative determination of the acid site and iron contents of the modified λ-Al₂O₃ samples was followed by UV spectrometry and F.A.A.S., respectively. An increasing final iron content of the catalysts with increasing acid site content of the support is observed. The catalytic activity for ammonia synthesis was followed at atmospheric pressure and 593 K (N₂/H₂ = 1/3). An increasing ammonia production per gram of catalyst with increasing protonation of the support was observed in the range 0–8 mmole H⁺ added · g^?1λ-Al₂O₃. The catalytic activity of iron supported catalysts prepared by this method was higher (up to twofold) that of a catalyst prepared by the incipient wetness method.     

Thermodynamic Properties of Ammonia Production from Hydrogenation of Alkali and Alkaline Earth Metal Amides

Thermodynamic properties of alkali and alkaline earth metal amides are critical for their performance in hydrogen storage as well as catalytic ammonia synthesis. In this work, the ammonia equilibrium concentrations of LiNH₂, KNH₂ and Ba(NH₂)₂ at ca.10 bar of hydrogen pressure and different temperatures were measured by using a high-pressure gas-solid reaction system equipped with a conductivity meter. Hydrogenation of KNH₂ gives the highest ammonia equilibrium concentration, followed by Ba(NH₂)₂ and LiNH₂. Based on these data, the entropy and enthalpy changes of the reaction of ANH₂+H₂→AH+NH₃ (A=Li, K, and Ba) were obtained from the van't Hoff equation. These thermodynamic parameters provide important information on the understanding of metal amides in catalytic ammonia synthesis reaction.     

Nickel‐Catalyzed Monoarylation of Ammonia

Structurally diverse (hetero)aryl chloride, bromide, and tosylate electrophiles were employed in the Ni‐catalyzed monoarylation of ammonia, including chemoselective transformations. The employed JosiPhos/[Ni(cod)₂] catalyst system enables the use of commercially available stock solutions of ammonia, or the use of ammonia gas in these reactions, thereby demonstrating the versatility and potential scalability of the reported protocol. Proof‐of‐principle experiments established that air‐stable [(JosiPhos)NiCl₂] precatalysts can be employed successfully in such transformations.     

Towards Green Ammonia Synthesis through Plasma-Driven Nitrogen Oxidation and Catalytic Reduction

Ammonia is an industrial large-volume chemical, with its main application in fertilizer production. It also attracts increasing attention as a green-energy vector. Over the past century, ammonia production has been dominated by the Haber–Bosch process, in which a mixture of nitrogen and hydrogen gas is converted to ammonia at high temperatures and pressures. Haber–Bosch processes with natural gas as the source of hydrogen are responsible for a significant share of the global CO₂ emissions. Processes involving plasma are currently being investigated as an alternative for decentralized ammonia production powered by renewable energy sources. In this work, we present the PNOCRA process (plasma nitrogen oxidation and catalytic reduction to ammonia), combining plasma-assisted nitrogen oxidation and lean NO_x trap technology, adopted from diesel-engine exhaust gas aftertreatment technology. PNOCRA achieves an energy requirement of 4.6 MJ mol⁻¹ NH₃, which is more than four times less than the state-of-the-art plasma-enabled ammonia synthesis from N₂ and H₂ with reasonable yield (>1 %).     

Preparation and Response Properties of Selective Bio-Electrodes Utilizing Polymer Membrane Electrode-Based Ammonia Gas Sensors

Abstract

A new type of potentiometric ammonia gas sensor is employed in the preparation of selective bio-electrodes for urea and glutamine. The bio-electrodes are constructed by immobilizing the enzyme urease and intact porcine kidney cells, respectively, at the surface of a disposable ammonium selective polymer membrane electrode-based ammonia gas sensor. The resulting electrodes have favorable response properties when compared to corresponding devices previously assembled with costly commercial gas sensors. Preliminary studies with the urea electrode demonstrate its usefulness for the rapid determination of urea in serum samples.     

Utilization of Low-grade Iron Ore in Ammonia Decomposition

Due to its cleanliness, fast energy cycle, and convenience of energy conversion, hydrogen has been regarded as the new energy source. Conventional process to produce hydrogen yield large amount of CO as byproduct. Moreover, the hydrogen storage and transportation have become the drawbacks in hydrogen economy. Thus, there has been increased interest in the hydrogen transportation medium as alternatives from the conventional process to produce and transport hydrogen. Ammonia has drawn worldwide attention as the most reliable hydrogen transportation medium. Through the decomposition of ammonia, hydrogen and nitrogen gas were produces as the byproduct without any CO or CO₂ emission. In this experiment, the ore were introduced as the medium for ammonia decomposition. The ore were put into quartz tube reactor and were dehydrated at 400 °C for 1 hour, then hydrogen reduced for 2 hours before and undergone ammonia decomposition at 500-700 °C for 3 hours. The effects of temperature to the % conversion of ammonia decomposition were also studied. Ammonia decomposition at higher temperature gives higher conversion. As seen in the results, the NH₃ conversion decreased with increasing time and the value after 3 hours of reaction increased in the sequence of 500 °C<600 °C< 700 °C. During ammonia decomposition, nitriding of iron occurred. The relation between temperature and the nitriding potential, K_N is also investigated. The purpose of this study is to investigate the utilization of low-grade ore as medium for ammonia decomposition to produce hydrogen.     

Synthesis of Ammonia in a Strong Electric Field Discharge at Ambient Pressure

The plasma synthesis of ammonia has been studied in a nitrogen–hydrogenplasma using a strong electric field discharge at ambient pressure andtemperature. With this method, N₂ and H₂ molecules are ionized anddissociated and a large number of free atoms, ions, and radicals areformed in a nonequilibrium plasma after inelastic collisions. The finalproduct was mainly ammonia, including a small amount of hydrazine. WhenMgO powder, used as a catalyst, was smeared on the surface of the electrodeplates, the yields of ammonia increased about 1.54–1.75 times andreached 5000 ppm (0.5% v/v). In this way, plasma synthesis of ammonia atambient pressure is realized and a new method is provided for inorganicsynthesis, which consumes little energy and simplifies the process.     

Modification of polysulfone membranes 4. Ammonia plasma treatment

The effect of NH₃ and NH₃/Ar plasma on ultrafiltration polysulfone membranes have been studied. Results of contact angle, FTIR-ATR and X-ray photoelectron spectroscopy experiments clearly showed that both plasmas introduced hydrophilic, nitrogen- and oxygen-containing moieties on the polymer surface and that NH₃/Ar plasma was more efficient. That plasma was also more aggressive--signs of strong etching could be seen on the SEM pictures. Redeposition of etched material seemed to take place inside the pores. On the contrary, ammonia plasma was soft and caused cleaning the surface and pores enlargement. Performance of ammonia plasma modified membranes was greatly improved and independent on solution pH. The last observation proved amphoteric character of the surface. NH₃/Ar plasma treatment gave membranes of acidic surface and filtration indices not so good as for ammonia plasma.     

Dilute Ammonia Pretreatment of Sorghum and Its Effectiveness on Enzyme Hydrolysis and Ethanol Fermentation

A new pretreatment technology using dilute ammonium hydroxide was evaluated for ethanol production on sorghum. Sorghum fibers, ammonia, and water at a ratio of 1:0.14:8 were heated to 160 °C and held for 1 h under 140–160 psi pressure. Approximately, 44% lignin and 35% hemicellulose were removed during the process. Hydrolysis of untreated and dilute ammonia pretreated fibers was carried out at 10% dry solids at an enzyme concentration of 60 FPU Spezyme CP and 64 CBU Novozyme 188/g glucan. Cellulose digestibility was higher (84%) for ammonia pretreated sorghum as compared to untreated sorghum (38%). Fermentations with Saccharomyces cerevisiae D₅A resulted in 24 g ethanol /100 g dry biomass for dilute ammonia pretreated sorghum and 9 g ethanol /100 g dry biomass for untreated sorghum.     

Nitrite Electroreduction to Ammonia Promoted by Molecular Carbon Dioxide with Near-unity Faradaic Efficiency

Electrochemical reduction of nitrite (NO₂⁻) offers an energy-efficient route for ammonia (NH₃) synthesis and reduction of the level of nitrite, which is one of the major pollutants in water. However, the near 100 % Faradaic efficiency (FE) has yet to be achieved due to the complicated reduction route with several intermediates. Here, we report that carbon dioxide (CO₂) can enhance the nitrite electroreduction to ammonia on copper nanowire (Cu NW) catalysts. In a broad potential range (−0.7∼−1.3 V vs. RHE), the FE of nitrite to ammonia is close to 100 % with a 3.5-fold increase in activity compared to that obtained without CO_2. In situ Raman spectroscopy and density functional theory (DFT) calculations indicate that CO₂ acts as a catalyst to facilitate the *NO to *N step, which is the rate determining step for ammonia synthesis. The promotion effect of CO₂ can be expanded to electroreduction of other nitro-compounds, such as nitrate to ammonia and nitrobenzene to aniline.