HNO3 Vapor Research Articles

Gas-Phase Conversion of Cation-Exchange Resin KU-2×8-M (M = Cs, Ni, Cu, Fe, Nd, U) in a Nitrating Atmosphere

A new approach to the destructive processing of the cation-exchange resin KU-2×8-M (M = Cs, Ni, Cu, Fe, Nd, U) based on its gas-phase treatment in a nitrating atmosphere with subsequent chemical treatment of the conversion products is considered. It is shown that exposure of KU-2×8-M samples (M = Cs, Ni, Cu, Fe, Nd, U) in an HNO3(vapour)-air atmosphere at temperatures of 403-443 K for 8 and 24 h followed by dissolution conversion products in 0.5 mol∙L-1 NaOH and ozonation of the resulting solutions allows e cient utilization of the KU-2×8-M resin (M = Cs, Ni, Cu, Fe, Nd, U).

Thermal-Responsive Conjugated Micropore Polymers for Smart Capture of Volatile Iodine.

The capture of radioiodine is crucial for nuclear security and environmental protection due to its volatility and superior environmental fluidity. Herein, we propose a strategy of "temperature-dependent gate" based on a swellable conjugated microporous polymer (SCMP) to significantly improve the capture of volatile iodine. The SCMP is constructed via the Buchwald-Hartwig coupling reaction of building monomers containing amines. It possesses a hierarchical pore structure with restricted pores, which can be "opened" and "closed" by changing the temperature. By virtue of the thermal-responsive pore structure, it reaches adsorption equilibrium for iodine in 2 h with a capacity of 4.3 g g-1 at 90 °C and retains 92.8% adsorbed iodine at room temperature. The SCMP also exhibits a high adsorption capacity up to 3.5 g g-1 for dissolved iodine within 10 min, as well as good radiation resistance and high selectivity for iodine against moisture, VOCs, and HNO3 vapor. The mechanism is clarified for effective iodine capture and caging based on the relationship between temperature and the pore structure. This work develops not only a strategy to enhance the capture of gaseous and dissolved iodine but also a new adsorption mechanism for iodine capture, which can be extended to the separation and caging of resources or volatile pollutants in other fields.

The Modelling of SiC Gate Oxide Thickness based on Thermal Oxidation Temperatures and Durations for High-Voltage Applications

This research has shown that the oxide thickness for silicon carbide (SiC) based wide materials can be predicted using regression techniques in wet/dry nitrided or wet/dry non-nitrided thermal oxidation process conditions for high voltage applications by employing 2 different regression techniques: Polynomial and linear regression. The R-squared (R2) and Mean Absolute Percentage Error (MAPE) techniques are used to evaluate the regression models. Furthermore, this work investigates and presents a calculation of gate oxide thickness that is correlated to gate voltage ranges for high voltage applications. In this work, the thermal oxidation process environment is classified into 3 different processing conditions: conventional (dry and wet), dry nitrided (NO,N2O), and wet nitrided (HNO3 vapour). The findings from this study showed that wet oxidation combined with nitrided elements can produce thicker and better-quality gate oxide as compared to conventional dry and wet oxidation techniques. The outcome of this work clearly shows that gate oxide thickness may be derived from silicon carbide-based wide-bandgap materials utilizing linear and polynomial approaches using thermal oxidation durations at different temperatures for high-power applications. The regression models and formulations produced in this work are expected to aid the researchers in determining appropriate oxide thickness under practicable process conditions, with the exception of real thermal oxidation process conditions. Hence, the outcome of this work is expected to save the processing time, material, and cost of the power semiconductor device fabrication technology, mainly for high voltage applications. HIGHLIGHTS Regression approaches are being used to determine the oxide thickness (Tox) for SiC-based broad materials in nitrided and non-nitrided thermal oxidation process conditions for high-voltage applications The regression models are assessed using the R-squared (R2) and Mean Absolute Percentage Error (MAPE) approaches The results of this work are anticipated to reduce processing time, material requirements, and manufacturing costs for power semiconductor devices used in high-voltage applications GRAPHICAL ABSTRACT

Designing high efficiency graphite felt electrode via HNO3 vapor activation towards stable vanadium redox flow battery

A new method of preparing nitric acid vapor treated graphite felt for vanadium redox flow battery (VRFB) is developed. This method outperforms traditional impregnation methods in convenience, efficacy and controllability of fabrication process. A sequence reaction mechanism is proposed for nitric acid vapor treated graphite felt reactions occurring at 200 °C. The modified-graphite felt (m-GF) with excellent electrocatalytic redox reversibility toward VO2+/VO2+ and V2+/V3+ redox couples is prepared in the conditions of VHNO3/mpGF=0.45 mL g−1 at 200 °C in 300 min (m-GF-0.45). The nitric acid vapor reaction with graphite felts occurs preferentially on the surface of amorphous carbon and at defect sites in the graphitic structure, yields N2 and carbon-oxygen surface complexes, resulting in a higher double layer capacity (DLC) from 146 μF mg−1 (p-GF) to 1514 μF mg−1 (m-GF-0.45). Thus, the energy efficiency and discharge capacity of m-GF-0.45 electrode increases significantly by 8.7% and 100% at 150 mA cm−2, respectively.

Thermicity of the Decomposition of Oxygen Functional Groups on Cellulose-Derived Chars.

The evolution of oxygen functional groups (OFGs) and the associated thermic effects upon heat treatment up to 800 °C were investigated experimentally as well as by theoretical calculations. A synthetic carbon with a carbonaceous structure close to that of natural chars, yet mineral-free, was derived from cellulose and oxidized by HNO3 vapor at different temperatures and for varied durations in order to generate char samples with different concentrations and distributions of OFGs. The functionalized samples were subjected to calorimetric temperature-programmed desorption measurements in correlation with an extensive effluent gas analysis, thereby focusing on the specific heat effects of individual OFG evolution. Interpretation of the experimental results was aided by density functional theory (DFT) calculations which allowed one to infer the thermal stability of different OFGs and the reaction energy associated with their evolution upon heating. Results showed that, with increasing temperature, H2O was released due to the loss of physisorbed water, the decomposition of clusters bound to carboxylic acids, and condensation reactions. The associated heat uptake amounted to about 100 kJ mol-1. Contrarily, the release of CO2, attributed to the decomposition of condensed acids, carboxylic acids, anhydrides, and lactones, resulted in a heat release of about 40 kJ mol-1. The most strongly pronounced thermic effects were detected for the release of CO, comprising highly exothermic effects due to the decomposition of condensed acids and carbonyls/quinones as well as endothermic effects attributed to anhydrides and phenols/ethers. Notably, anhydrides can be formed during the oxidative treatment as well as during heating by condensation of adjacent carboxylic acids. In the latter case, the two-step decomposition is overall highly exothermic, indicating the associated occurrence of pronounced carbon matrix rearrangements. DFT investigations suggest that these rearrangements not only affect the immediate OFG proximity but also involve several carbon sheets.

Conversion of Secondary C3-C4 Aliphatic Alcohols on Carbon Nanotubes Consolidated by Spark Plasma Sintering.

We analyze how the changes in the dimension of carbon nanomaterial (CNM) affect their catalytic conversion of secondary aliphatic alcohols. Carbon nanotubes (CNTs) consolidated by spark plasma sintering (SPS) were inactive in the conversion of secondary C3-C4 aliphatic alcohols because of the «healing» of defects in carbon structure during SPS. Gas-phase treatment of consolidated CNTs with HNO3 vapors led to their surface oxidation without destruction of the bulk structure of pellets. The oxygen content in consolidated CNTs determined by X-ray photoelectron spectroscopy increased from 11.3 to 14.9 at. % with increasing the oxidation time from 3 to 6 h. Despite the decrease in the specific surface area, the oxidized samples showed enhanced catalytic activity in alcohol conversion because of the increased number of oxygen radicals with unpaired electrons, which was established by electron paramagnetic resonance spectroscopy. We conclude that the structure of CNM determines the content and/or ratio of sp2 and sp3-hybridized carbon atoms in the material. The experimental and literature data demonstrated that sp3-hybridized carbon atoms on the surface are probably the preferable site for catalytic conversion of alcohols.

Optoelectronic properties of (Z)-3-(4-(4,5-diphenyl-1H-imidazole-2-yl)phenyl)-2-phenylacrylonitrile films under acid and thermal environments for tuning OLED emission

A systematic study of changes on optoelectronic properties of (Z)-3-(4-(4,5-diphenyl-1H-imidazole-2-yl)phenyl)-2-phenylacrylonitrile (DPimdPPA) based films owing to treatments with acid or temperature, is reported. The DPimdPPA films treated with vapors of HNO3, HCl, or CH3COOH exhibited a hypsochromic shift up to 70 nm as well as an enhancement in the fluorescence quantum yield. Interestingly, a similar behavior was observed when films were thermally treated at temperatures between 100 °C and 240 °C. XRD studies showed that DPimdPPA in powder form is a polycrystalline material, while the as-deposited films were amorphous. However, the treatments with temperature or acid, induced crystallinity in the films. Studies by atomic force microscopy showed that the induced crystallinity modified the film morphology leading to the formation of agglomerates with needle like shape. These changes in fluorescence were used to tune the emission in OLEDs. Notably, devices with pristine DPimdPPA film as well as treated with HNO3 vapor or heated at 240 °C were prepared. The emission with pristine films was warm white with CIE coordinates (0.45, 0.43); with HNO3 treatment it was green with CIE coordinates (0.28, 0.40) and, when treated at 240 °C the emission was greenish-blue with CIE coordinates (0.35, 0.48). Besides, with the treatments the turn-on voltage decreased, and luminous parameters were enhanced; the maximum luminance was about 5400 cd/m2 while the highest luminance efficiency 5.2 lm/W.

Surface modification of PEDOT: PSS film by chemical vapor texturing process for enhanced organic photovoltaics

Surface modification of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film was performed using chemical vapor texturing process of HNO3 vapor. Textured PEDOT:PSS film exhibits higher root-mean-square roughness of 14.43 nm than pristine PEDOT:PSS film of 11.87 nm with small decrease in thickness. Moreover, approximate one-half reduction of sheet resistance is measured. In correspondence with roughness, increasing optical transmittance in the visible region and reducing water contact angle are explored. The reduction of water contact angle implies that active layer can be deposited on the textured film with better coverage to improve interfacial contact for OPV fabricating process. This improvement facilitates charge transfer in OPV device which causes the increase of short-circuit current density (Jsc) from 7.42 mA/cm2 to 8.01 mA/cm2. The increased Jsc is the major photovoltaic parameter in OPV enhancement. Therefore, the PEDOT:PSS film textured with the chemical vapor texturing process is demonstrated as an efficient rough film for OPV enhancement. Furthermore, the rough film modified using the process could be suggested for applying in several thin-film based devices.

Извлечение никеля из имитаторов пульп никелевого производства в процессе газофазной конверсии

A new approach to Ni removal from simulators of dump waste product of the industrial waste purification of the wet gas-cleaning plant and the copper electrolysis workshop at the Copper Plant (Polar branch PJSC MMC «Norilsk Nickel») is proposed. The method is based on gas-phase treatment of waste product with NOХ, HNO3, or NH3 vapors, followed by dissolution of Ni salt in water. It has been found out that using nitrating media, containing HNO3 (vapor), NOX and H2O (vapor), allowed us to perform the effective leaching of nickel from the pulp simulator volume. A possible disadvantage of the method is a simultaneous leaching of considerable amounts of calcium and sulfur.

Gas-Phase Conversion of Oxide Phases of Lanthanides and Uranium to Water-Soluble Compounds

Gas-phase conversion to water-soluble compounds of individual rare-earth element (REE) (La, Ce, Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm, Lu) oxides and oxide systems (U,Ce)Ox and (U,Nd)Ox in the atmospheres HNO3 (vapor)–air and NOx–H2O (vapor)–air was examined. It was shown that water-soluble compounds are formed in the gas-phase conversion of REE oxides in the atmosphere of both HNO3 vapor and NOx gases. In the case of (U,Ce)Ox in the atmosphere of HNO3 (vapor)–air, water-soluble compounds of uranium are formed, with a part of cerium remaining in the phase of the water-insoluble precipitate. The conversion of (U,Nd)Ox under the same conditions yields water-soluble compounds of both uranium and neodymium. It was found that these gas media can be used in principle to extract uranium from fuel systems containing rare-earth elements.

Electrical properties of nitric acid and DMSO treated PEDOT:PSS/n‐Si hybrid heterostructures for optoelectronic applications

ABSTRACTOrganic/inorganic heterostructures are an emerging and interesting field of research for optoelectronics. In this work, an efficient organic/inorganic hybrid heterojunction between PEDOT:PSS and n‐type Silicon has been fabricated for optoelectronic applications. Samples with varying thickness of PEDOT:PSS were prepared by spin coating technique and the electrical conductivity of organic layers was modified using DMSO as additive. Post fabrication, the hybrid heterostructures were treated with HNO3 vapor so as to enhance the conductivity of the organic layer. Surface treatment with HNO3 was found to lower the roughness of the organic layer and enhance the transparency of the layer. I–V characteristics reveal optimized behavior of HNO3 treated PEDOT:PSS layer with a low Ideality factor (n~3.2) and a barrier height (ΦB) of 0.8 eV. The findings of the study provide a promising efficient method to enhance the electrical and device properties of PEDOT:PSS/n‐Si heterostructures for optoelectronic applications. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48952.

Magnetic properties and vapochromism of a composite on the base of an iron(II) spin crossover complex

A polymeric iron(II) complex, Fe(ATrz)3(NO3)2·nH2O (ATrz = 4-amino-1,2,4-triazole), can be embedded in the polystyrene matrix to form a composite spin crossover material. This composite material can be prepared in the form of films with a thickness of ca. 10–20 μm. The material demonstrates two spin crossover regimes (with and without thermal hysteresis) and reversible switching between these regimes, thermochromic effect (pink – white) and vapochromic behavior in the atmosphere of HCl, NH3, HNO3 and HBr vapors.

1.5 Minute-synthesis of continuous graphene films by chemical vapor deposition on Cu foils rolled in three dimensions

We report a high-productivity chemical vapor deposition (CVD) process of graphene by extending the reaction field to three dimensions (3D) and shortening the CVD time to a few minutes. A large Cu foil (5 × 30 cm2) is rolled up and set in a small reactor (3.4 cm in diameter), and a continuous graphene film is obtained uniformly in a short time (1.5 min) by using C2H4 as a more reactive carbon source than the popular CH4. The graphene transferred onto a quartz glass showed optical transmittances of 94.8–96.7% (550 nm) with sheet resistances of 0.78–1.68 kΩ sq−1 (without doping) and 0.3 kΩ sq−1 (with doping by HNO3 vapor). Compared with the previous reports for fast and/or large-scale CVD, our method realized similarly high productivity of 100 cm2 min−1 based on the CVD time despite of the small reactor, and higher productivity of 0.03 cm2-graphene per cm3-reactor per minute based on the reactor volume and total time for high temperature processing (15 min for heating, 1 min for annealing, and 1.5 min for CVD). The knowledge obtained here on the CVD conditions and packing ratio of Cu foils (0.55 cm2 per cm3-reactor) is reusable for designing large-scale graphene production processes.

Gas-Phase Conversion of Uranium Mononitride in a Nitrating Atmosphere

Gas-phase conversion of UN to water-soluble compounds in NOx-air, NOx-H2O (vapor)-air, or HNO3 (vapor)-air atmosphere (hereinafter, nitrating atmosphere) at temperatures from 298 to 673 K was studied. The use of the oxidizing atmosphere based on NOx gases allows the conversion to be performed at a lower temperature. The process yields both UO3 and hydrates of UO2(NO3)2. The highest conversion of UN to water-soluble compounds, ∼80%, is reached at ∼565 K. In the course of gas-phase conversion in NOx-H2O (vapor)-air and HNO3 (vapor)-air atmospheres, UN transforms into water-soluble compounds (nitrates, hydroxynitrates). The gas-phase conversion of UN in an NOx-H2O (vapor)-air atmosphere occurs less efficiently than that in an HNO3 (vapor)-air atmosphere.

Modified Sorbents Based on BAU-A Activated Carbon and Coarsely Porous Silica Gel for Removing Radionuclides and Nonferrous Metals from Aqueous Solutions

Sorption of radionuclides (90Sr, 90Y, 137Cs, 152Eu) and nonferrous metals (Cu, Ni, Zn, Pb) from aqueous solutions onto granulated sorbents based on coarsely porous silica gel of KSKG and MSKG grades and on BAU-A activated carbon was studied. The granulated sorbents based on coarsely porous silica gel of KSKG and MSKG grades, modified with Cu, Zn, and Ni ferrocyanides, efficiently take up 90Sr and 90Y from distilled water. In tap water, the sorption efficiency for all the sorbents based on KSKG and MSKG does not exceed 70%. The surface of BAU-A was modified by keeping it in a nitrating atmosphere [NOx-air or HNO3 (vapor)-air] at 90–110°C for 4 h, and also by impregnating it with 10 wt % triethanolamine (TEA), triethylenediamine (TEDA), or urea (CH4N2O). The sorbents based on BAU-A activated carbon efficiently take up 90Y (analog of trivalent actinides and lanthanides) and nonferrous metal ions from various aqueous solutions. Modification of BAU-A decreases its sorption capacity for Cu2+, Ni2+, and Zn2+ but increases its sorption capacity for Pb2+.

Gas Phase Conversion of UN and UC in Nitrating Atmosphere

The gas-phase conversion of UN and UC into water-soluble compounds in the atmosphere NOx–H2O (vapor)–air and HNO3 (vapor)–air in the interval 298–423 K was investigated. It is shown that in the gasphase conversion process UN is converted into water-soluble compounds (nitrates, hydroxy nitrates). It is found that the gas-phase conversion of UN in the atmosphere NOx–H2O (vapor)–air is less efficient than in the atmosphere HNO3 (vapor)–air. In the process of gas-phase conversion of UC in a nitrating atmosphere the main products of conversion are uranyl nitrate hydrates. In addition, carbon-containing products are formed and their removal requires ozonation of the solutions formed as a result of contact between water and the products of UC conversion.

Bacterial inactivation by plasma treated water enhanced by reactive nitrogen species

There is a growing body of literature that recognizes the importance of plasma treated water (PTW) for inactivation of microorganism. However, very little attention has been paid to the role of reactive nitrogen species (RNS) in deactivation of bacteria. The aim of this study is to explore the role of RNS in bacterial killing, and to develop a plasma system with increased sterilization efficiency. To increase the concentration of reactive oxygen and nitrogen species (RONS) in solution, we have used vapor systems (DI water/HNO3 at different wt%) combined with plasma using N2 as working gas. The results show that the addition of the vapor system yields higher RONS contents. Furthermore, PTW produced by N2 + 0.5 wt% HNO3 vapor comprises a large amount of both RNS and ROS, while PTW created by N2 + H2O vapor consists of a large amount of ROS, but much less RNS. Interestingly, we observed more deactivation of E. Coli with PTW created by N2 + 0.5 wt% HNO3 vapor plasma as compared to PTW generated by the other plasma systems. This work provides new insight into the role of RNS along with ROS for deactivation of bacteria.

Use of Modified Sorbents Based on Activated Carbon BAU-A for the Extraction of Nonferrous Metals from Aqueous Solutions

The sorption of some nonferrous metals (Cu, Ni, Zn, Pb) from aqueous solutions by granular sorbents based on activated carbon BAU-A has been studied. The surface modification of BAU-A has been conducted by exposing it to a nitrating atmosphere (NOx–air or HNO3 (vapors)–air) at a temperature of 90–110°C for 4 h and impregnating it with 10 wt % of triethanolamine (TEA), tetraethylenediamine (TEDA), or carbamide (CH4N2O). It has been found that modification of BAU-A leads to a decrease in the sorption capacity of this material with respect to Cu2+, Ni2+, and Zn2+ and an increase with respect to Pb2+.

Nanospace-confined preparation of uniform nitrogen-doped graphene quantum dots for highly selective fluorescence dual-function determination of Fe3+ and ascorbic acid.

N-Doped graphene quantum dots (N-GQDs) combine the advantages of N-doped carbon and quantum dot materials, displaying enhanced performance in electrocatalysis, drug delivery, sensing and so on. In this work, novel hydrotropic N-GQDs with controlled size are obtained for the first time via a nanospace-confined preparation strategy, in which HNO3 vapour serves as scissors for quickly cutting the N-doped carbon nanolayer in the confined nanospace of reusable mesoporous molecular sieves. The as-prepared N-GQDs exhibit a uniform lateral size of about 2.4 nm, high photostability and yellow fluorescence, which is strongly quenched upon addition of ferric ions due to the coordination between ferric ions and N/O-rich groups of the N-GQDs surface. Significantly, the fluorescence response to Fe3+ is linear in the 0.5 to 40 μM concentration range and the N-GQDs showed good selectivity and satisfying recovery for ferric ion detection in tap water. Noteworthily, the quenched fluorescence by Fe3+ can be recovered by adding ascorbic acid (AA), which efficiently destroyed the coordination between Fe3+ and N-GQDs. Based on this principle, the N-GQDs were used to successfully construct an AA sensor, exhibiting a wide linearity range (between 0.5 and 90 μM) with a low detection of limit (80 nM at S/N = 3) and better selectivity towards AA compared with other common physiological substances. Finally, the constructed fluorescence sensor was employed successfully for AA determination in fish blood with satisfactory recovery ranging from 95.3 to 106.2%. The results indicate that N-GQDs synthesized by the nanospace-confined strategy are promising in biosensor fabrication.

Evaluation of Thermal Spray Alumina Coatings on Nickel Electrode Connector for Reprocessing Applications

Electro-oxidative dissolution of the spent mixed oxide nuclear fuels with high plutonium content from prototype fast breeder reactor need to be carried out in boiling 11.5 M HNO3. Nickel electrode connectors employed in the electrolyser of the dissolver should possess good corrosion resistance as well as good electrical conductivity. Alumina coating deposited on Ni by plasma spraying was evaluated by electrochemical polarization and impedance experiments in 11.5 M HNO3 at room temperature. In order to improve corrosion resistance, alumina coating relatively denser than plasma spray coating was deposited over Ni by detonation gun (D-gun) spray coating. This alumina coating exhibited a high insulation resistance and the weight loss of alumina coated Ni disc was only 3% compared to 29% for bare Ni disc sample when exposed to the vapour of 11.5 M boiling HNO3 for 12 h. However, coating delamination observed at the alumina/bond coat interface was attributed to the penetration of HNO3 vapour through the pores in the coating. Since alumina coating deposited by D-gun technique over Ni was also found to offer only short-term protection against corrosion due to HNO3 vapour, monolithic dense alumina sleeve fabricated through powder metallurgy route was recommended instead of coating, for better corrosion protection in HNO3 vapour compared to thermal spray coating.