Nitric Acid Vapor Research Articles

A novel aspect of functionalized graphene quantum dots in cytotoxicity studies

Graphene quantum dots (GQDs) represent a new generation of graphene-based nanomaterials with enormous potential for use and development of a variety of biomedical applications. However, up to now little studies have investigated the impact of GQDs on human health in case of exposure. GQDs were synthesized from citric acid as carbon precursor by hydrothermal treatment at 160 °C for 4 h. The synthesized GQDs showed strong blue emission under UV-Irradiation with fluorescence quantum yield of 9.8%. The obtained GQDs were further carbonized, activated and functionalized by nitric acid vapor method. Nitrogen adsorption/desorption isotherms were used to analyze the surface area and porous structures of GQDs. The results revealed that compared to GQDs, the specific surface area of functionalized graphene quantum dots (fGQDs) has been increased from 0.0667 to 2.5747 m2/g and pore structures have been enhanced significantly. The potential cytotoxic effect of GQDs, fGQDs and GO suspensions was evaluated on HFF cell line using MTT assays and flow cytometry method after 24 h incubation. We have for the first time demonstrated that by carbonization, activation and functionalization of GQDs they still showed cytocompatible properties. We observed excellent biocompatibility of GQDs and fGQDs at low concentrations. Moreover, the results suggested that modification of GQDs yields product suspensions with high surface area, enhanced pore volume and loading capacities. Thus, fGQDs represent an attractive candidate for further use in drug delivery systems and bio-imaging application.

A Study on Corrosion Resistance of Electroplated Gold over Nanocrystalline Ni-W for Contact Applications

Highly conductive metal with least corrosion resistance is the most prominent requirement of contact industries. Although deposition of gold over Ni sulfamate is a standard interface for contact and connector applications, the performance of gold over Ni sulfamate has faced several problems such as wear durability, porosity of gold layers and biased corrosion resistance. The deposition of nanocrystalline Ni-W (nc Ni-W) between gold and Ni sulfamate improves the mechanical and surface properties of interfaces. In this work two different types of samples were processed and compared in terms of corrosion. The first sample (Au/NiSO4) was prepared using electroplating of gold, Ni sulfamate and Ni strike over base material of copper alloy with thicknesses of 0.9 µm, 1.9 µm and 0.5 µm respectively. In the second sample (Au/nc Ni-W/NiSO4), all layers of electroplating were same except the addition of 1.8 µm of nanocrystalline Ni-W before deposition of gold. Both samples were passed through the environments of (a) 85% relative humidity at 85oC for 24 hours, (b) 85% relative humidity at 85oC for 96 hours and (c) nitric acid vapors for 60 minutes. The effect on electrical, mechanical and materials properties of samples were investigated before and after passing through these environments using Force Deflection Resistance (FDR), Life-cycle test (LCT), Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-Ray CT scanning. Although Au/NiSO4 is a well-known interface for connector applications [1], the deposition of nc Ni-W between gold and NiSO4 reduces the rate of corrosion because nc Ni-W has a weak tendency for grain boundary segregation and building broader range of accessible grain sizes [2]. There is formation of grain colonies in Ni-W deposit which controls crack propagation and corrosion [3]. The performance of two different interfaces of Au/NiSO4 and Au/nc Ni-W/ NiSO4 against corrosion was tested after electroplating on spring probes. Spring probe is one of the product of Smiths Interconnect which is used for different applications like defense, medical, rail, semiconductor, space etc. [4]. In FDR, the spring force, coefficient of friction and contact resistance was measured under a hysteresis of compression and extension for a travel distance of 0.14 inch. In the case of Au/NiSO4, the difference in compression and extension force at 0.14 inch was 6.1 oz. In the case of Au/nc Ni-W/ NiSO4, this difference was 4.6 oz which means that there is less friction with the deposition of nanocrystalline Ni-W underneath gold. Moreover, the difference in contact resistances was lower in second sample which means that the addition of nc Ni-W enhances the interface of gold and NiSO4. After treatment in humidity from 24 hrs to 96 hrs the difference in compression and extension force at 0.14 inch was increased by 7 oz in first sample but in second sample this difference was only increased by 3.6 oz which means that there is less increase in friction due to the presence of nc Ni-W. In LCT the resistance was measured at a test current of 0.025 amps under a stroke length of 0.09 inch for 10,000 life cycles with a cycle rate of 4 cycles/sec. The rate of increase in resistance with number of cycles was higher in the case of Au/NiSO4 than Au/nc Ni-W/ NiSO4. In first sample, the sticky coefficient was increased from 0 to 25 % after treatment in humidity for 24 hrs and it further increased to 37.5% after keeping in humidity for 96 hrs. The wear off rate and friction reduction of Au/nc Ni-W/ NiSO4 helped in maintaining the sticky coefficient to be constant even after kept in humidity for 96 hrs. The failure of the probes were tested from front and cross section SEM, point and line scan EDS and X-Ray CT scanning. SEM was used to observe mechanical marks and microstructure analysis which explained the reasoning of low wear rate in the case of Au/NiSO4. The failure of the probes was also confirmed from X-Ray CT Scanning in the probes during compression of spring. The complete set of experimental results will be added in the full version of the paper.

Seasonal trends of the stable nitrogen isotope ratio in particulate nitrogen compounds and their gaseous precursors in Akita, Japan

Particulate matter (PM) can have adverse effects on human health. Moreover, because the mechanisms of PM formation and behavior in the atmosphere are notably complicated, to reduce PM concentrations effectively and meet environmental standards, source–receptor relationships must be clearly understood. Stable isotope ratios can be used to detect chemical processes and distinguish sources. In environmental science, especially in research on aerosols, stable isotope ratios have proven to constitute a powerful tool for source identification. However, there are few long-term studies of isotope fractionation during secondary aerosol formation. In this study, stable nitrogen isotope ratios (δ15N) of ammonia gas (NH3), nitrogen dioxide gas (NO2), nitric acid vapor (HNO3), particulate nitrate (NO3−), and ammonium (NH4+) in suspended PM (SPM) were analyzed to investigate seasonal trends and isotope fractionation during aerosol formation for long term sampling in Akita, Japan. The results indicated that δ15N-NH4+ in SPM and δ15N-NH3 gas ranged from 1.3‰ to 38.5‰ (mean 16.1‰) and from −33.6‰ to −0.0‰ (−16.9‰), respectively. Furthermore, δ15N-NO3− (SPM) and δ15N-NO2 and δ15N-HNO3 (gaseous) ranged from −4.6‰ to 4.8‰ (mean −0.5‰), from −8.2‰ to −3.1‰ (−5.4‰), and from −7.5‰ to 2.7‰ (−5.0‰), respectively. The mean annual isotope fractionation factors for transformations from gaseous NH3 to NH4+ in SPM, from gaseous NO2 to gaseous HNO3, and from HNO3 gas to NO3– in SPM in the atmospheric environment were +33.3‰, +0.5‰, and +4.9‰, respectively. Isotope fractionation of NH4+ in SPM was much higher than that of NO3– in SPM. As the chemical reaction from gaseous precursors progressed, δ15N-NO3– in SPM became steadily heavier.

The Role of Graphene‐Based Derivative as Interfacial Layer in Graphene/n‐Si Schottky Barrier Solar Cells

Schottky‐barrier solar cells (SBSCs) represent low‐cost candidates for photovoltaics applications. The engineering of the interface between absorber and front electrode is crucial for reducing the dark current, blocking the majority carriers injected into the electrode, and reducing surface recombination. The presence of tailored interfacial layers between the metal electrode and the semiconductor absorber can improve the cell performance. In this work, the interface of a graphene/n‐type Si SBSC by introducing a graphene‐based derivative (GBD) layer meant to reduce the Schottky‐barrier height (SBH) and ease the charge collection are engineered. The chemical vapor deposition (CVD) parameters are tuned to obtain the two graphene films with different structure and electrical properties: few‐layer graphene (FLG) working as transparent conductive electrode and GBD layer with electron‐blocking and hole‐transporting properties. Test SBSCs are fabricated to evaluate the effect of the introduction of GBD as interlayer into the FLG/n‐Si junction. The GBD layer reduces the recombination at the interface between graphene and n‐Si, and improves the external quantum efficiency (EQE) with optical bias from 50 to 60%. The FLG/GBD/n‐Si cell attains a power conversion efficiency (PCE) of ≈5%, which increase to 6.7% after a doping treatment by nitric acid vapor.

An Efficiency Enhanced Graphene/n-Si Schottky Junction for Solar Cells**Supported by the National Natural Science Foundation of China under Grant Nos 61504113, 61674113 and 51622507, the Natural Science Foundation of Shanxi Province under Grant No 2016011040, the Natural Science Foundation of Fujian Province under Grant No 2018J01567, and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province

A novel and facile oxidation-induced self-doping process of graphene-silicon Schottky junction by nitric acid (HNO3) vapor is reported. The HNO3 oxidation process makes graphene p-type self-doped, and leads to a higher built-in potential and conductivity to enhance charge transfer and to suppress charge carrier recombination at the graphene-silicon Schottky junction. After the HNO3 oxidation process, the open-circuit voltage is increased from the initial value of 0.36V to the maximum value of 0.47V, the short-circuit current is greatly increased from 0.80 μA to 7.71 μA, and the ideality factor is optimized from 4.4 to 1.0. The enhancement of the performance of graphene-Si solar cells may be due to oxidation-induced p-type self-doping of graphene-Si junctions.

High electrical conductivity and oxygen barrier property of polymer-stabilized graphene thin films

Next-generation electronics require mechanical flexibility and durability as well as electrical conductivity. In this report, few-layer graphene and polyelectrolytes were assembled into ultrathin films on flexible plastic substrates by a simple and cost-effective layer-by-layer technique. This technique integrated high electrical conductivity and excellent oxygen barrier property into a single film. These characteristics have been rarely reported for other types of thin films prepared by solution processing. The optical properties, film thickness, and mass of the films were precisely controlled by the number of bilayers. After a brief exposure to nitric acid (HNO3) vapor, the films exhibited much improved electrical conductivity while preserving their other properties. Raman, x-ray photoelectron, and FT-IR spectroscopy proved that the effects of the HNO3 treatment were due to the removal of polymeric components and restricted to the film surface, and not due to the chemical doping of graphene.

Surface modification of silica-graphene nanohybrid as a novel stabilizer for oil-water emulsion

The surface modification of silica-graphene nanohybrid through treatment with a mixture of nitric and sulfuric acid vapors to prepare a novel stabilizer for decalin-water emulsion was investigated. The nanohybrid was prepared through chemical vapor deposition using silica aerogel and acetylene as catalyst and carbon precursor at atmospheric pressure and 600 °C. The physicochemical properties of the modified nanohybrid were characterized by FT-IR, XPS, Raman spectroscopy, and TEM. The surface modification of nanohybrid was at various duration times (24, 48, and 72 hours) to optimize the surface modification conditions. Zeta potential of −39.9 mV revealed that the surface modification of nanohybrid after 72 hours had an excellent stability in aqueous phase due to the presence of exceptional functional groups. The emulsion average droplet size decreased by increasing the nanohybrid concentration. The negative value of the zeta potential showed the proposed nanohybrid can be applied as an appropriate stabilizer for emulsion.

Free energy of formation of a crystal nucleus in incongruent solidification: Implication for modeling the crystallization of aqueous nitric acid droplets in polar stratospheric clouds.

Using the formalism of classical thermodynamics in the framework of the classical nucleation theory, we derive an expression for the reversible work W* of formation of a binary crystal nucleus in a liquid binary solution of non-stoichiometric composition (incongruent crystallization). Applied to the crystallization of aqueous nitric acid droplets, the new expression more adequately takes account of the effects of nitric acid vapor compared to the conventional expression of MacKenzie, Kulmala, Laaksonen, and Vesala (MKLV) [J. Geophys. Res.: Atmos. 102, 19729 (1997)]. The predictions of both MKLV and modified expressions for the average liquid-solid interfacial tension σls of nitric acid dihydrate (NAD) crystals are compared by using existing experimental data on the incongruent crystallization of aqueous nitric acid droplets of composition relevant to polar stratospheric clouds (PSCs). The predictions for σls based on the MKLV expression are higher by about 5% compared to predictions based on our modified expression. This results in similar differences between the predictions of both expressions for the solid-vapor interfacial tension σsv of NAD crystal nuclei. The latter can be obtained by using the method based on the analysis of experimental data on crystal nucleation rates in aqueous nitric acid droplets; it exploits the dominance of the surface-stimulated mode of crystal nucleation in small droplets and its negligibility in large ones. Applying that method to existing experimental data, our expression for the free energy of formation provides an estimate for σsv of NAD in the range ≈92 dyn/cm to ≈100 dyn/cm, while the MKLV expression predicts it in the range ≈95 dyn/cm to ≈105 dyn/cm. The predictions of both expressions for W* become identical for the case of congruent crystallization; this was also demonstrated by applying our method for determining σsv to the nucleation of nitric acid trihydrate crystals in PSC droplets of stoichiometric composition.

Mechanism of Low Temperature Oxidation of 4H-SiC by Nitric Acid Vapor Oxidation Method at 600°C

Oxidation of 4H-SiC proceeds at 600°C by use of nitric acid vapor. The plots of the SiO2 thickness vs. the square root of the oxidation time are linear, indicating that diffusion of oxidizing species is the rate-determining step. The initial oxidation rate of the C-faced surfaces is 3 times higher than that of the Si-faced surfaces. It is found from cross-sectional transmission electron micrography (TEM) measurements that the SiO2 thickness is uniform and steps originating from miss-orientation from the (000−1) direction having 0.25 nm height are present before and after oxidation, showing that oxidation of SiC proceeds only from step-edges along the (−1100) direction for the C-face and the (1−100) direction for the Si-face.

Modelling of carbon nanotube functionalization processes

In the present paper, kinetic regularities of oxidative functionalization of carbon nanotubes in nitric acid vapors are studied. The catalytic effect of transition metal oxide particles on the formation of carboxyl groups is shown. Based on the information about changes in the degree of functionalization and composition of gaseous reaction products, the effective values of the thermal effect of the implemented process are determined. A model of the temperature field of the reaction zone of the gas-phase oxidative functionalization of carbon nanotubes process is proposed, thereby making it possible to determine the structural and mode parameters of the equipment.

ТЕХНОГЕННЫЙ ЭКОЛОГИЧЕСКИЙ РИСК И МЕТРОЛОГИЧЕСКОЕ ОБЕСПЕЧЕНИЕ КАЧЕСТВА НЕФТЕПРОДУКТА

Technogenic pressure in the industrial region, as Kusbass is, despite of taken measures for limitations of harmful substances emissions and stuffi in the atmosphere is continued to grow. The damage is being harmful to all (natural) environment and all living things including humans. This causes the probability of the ecological hazard, i.e. technogenic ecological risk. The present study examines the harmful effects of precipitation in the form of acid rains. It analyzes the factors causing the acid rains intensity in the vicinity of the mining sector. It is noted that fi the acid rains occurrence is caused by industrial explosions in the open casts and harmful emissions from heavy mining trucks. Special laboratory tests of automobile fuel including spectral methods have shown the presence of sub-standard component in the form of sulfur which is greatly exceeded the standard. It infl the air pollution level with sulfur compounds as there is the open cast localization of multi-ton vehicles running on this fuel. On the basis of social-hygienic monitoring of children and adults health and air pollution levels in big industrial centers of Kusbass, causal relationships have been established and the regularities of health disorders formation for population, especially among children, have been determined. In this connection there are opinions about the negative infl on population health who live close to Kuzbass open cast, harmful factors arising due to the fi of the air environment with many chemicals (nitric oxide, sulfur containing compounds like hydrogen sulfi thiophene and its derivatives, acid and average ethers of sulfuric acid, nitric acid vapours and many others) in large quantities.

The Wetting Behavior of Fresh and Aged Soot Studied through Contact Angle Measurements

In this work, contact angle measurements for soot samples collected from a kerosene lantern, wood-burning fireplace, and municipal bus engine exhaust lines are reported. Contact angles for both freshly collected soot and samples treated with various doses of O3 (g), HNO3 (g), and H2SO4 (g) are considered. Use of a literature method has allowed estimation of the enthalpy of immersion (Himm) for the soot samples based on contact angle observed. Contact angles for freshly collected soot were 65 - 110 deg. indicating its hydrophobic nature. Chemical processing of soot usually resulted in smaller contact angles and large increases in immersion enthalpy. However, the dose of ozone, nitric or sulfuric acid vapor required to achieve alteration of the soot surface appeared to be considerably larger than that expected to be experienced by authentic atmospheric samples during the soot particles lifetime. The most significant variability of soot contact angle was observed for the municipal bus exhaust samples, suggesting that combustion chemistry may significantly affect wetting behavior.

Preparation of cleavages of polyethylene naphthalate track membranes for studying with an electron microscope

The possibility of obtaining fracture cleavages of polyethylene naphthalate tracking membrane samples for electron microscope examinations has been investigated. These cleavages allow one to examine the pore channel structure along the whole pore length from one surface to the other. Due to a high radiation and thermal stability of polyethylene naphthalate films, thermal, ultraviolet, and radiation treatment methods applied for obtaining brittle films of such polymers as polyethylene terephthalate, polycarbonate, and polypropylene are unsuitable for them. The treatment of the samples with concentrated nitric acid vapors for 1.5 months makes them brittle. It is possible to obtain good cross-section.

Kinetics of Acid-Catalyzed Dehydration of Cyclic Hemiacetals in Organic Aerosol Particles in Equilibrium with Nitric Acid Vapor.

Previous studies have shown that 1,4-hydroxycarbonyls, which are often major products of the atmospheric oxidation of hydrocarbons, can undergo acid-catalyzed cyclization and dehydration in aerosol particles to form highly reactive unsaturated dihydrofurans. In this study the kinetics of dehydration of cyclic hemiacetals, the rate-limiting step in this process, was investigated in a series of environmental chamber experiments in which secondary organic aerosol (SOA) containing cyclic hemiacetals was formed from the reaction of n-pentadecane with OH radicals in dry air in the presence of HNO3. A particle beam mass spectrometer was used to monitor the formation and dehydration of cyclic hemiacetals in real time, and SOA and HNO3 were quantified in filter samples by gravimetric analysis and ion chromatography. Measured dehydration rate constants increased linearly with increasing concentration of HNO3 in the gas phase and in SOA, corresponding to catalytic rate constants of 0.27 h(-1) ppmv(-1) and 7.0 h(-1) M(-1), respectively. The measured Henry's law constant for partitioning of HNO3 into SOA was 3.7 × 10(4) M atm(-1), ∼25% of the value for dissolution into water, and the acid dissociation constant was estimated to be <8 × 10(-4), at least a factor of 10(4) less than that for HNO3 in water. The results indicate that HNO3 was only weakly dissociated in the SOA and that dehydration of cyclic hemiacetals was catalyzed by molecular HNO3 rather than by H(+). The Henry's law constant and kinetics relationships measured here can be used to improve mechanisms and models of SOA formation from the oxidation of hydrocarbons in dry air in the presence of NOx, which are conditions commonly used in laboratory studies. The fate of cyclic hemiacetals in the atmosphere, where the effects of higher relative humidity, organic/aqueous phase separation, and acid catalysis by molecular H2SO4 and/or H(+) are likely to be important, is discussed.

Modified silver nanowire transparent electrodes with exceptional stability against oxidation

We report an easy method to prepare thin, flexible and transparent electrodes that show enhanced inertness toward oxidation using modified silver nanowires (Ag NWs). Stabilization is achieved through the adsorption of triphenylphosphine (PPh3) onto the Ag NW hybrid dispersions prior to their 2D organization as transparent electrodes on polyethylene terephtalate (PET) films. After 110 days in air (20 °C) under atmospheric conditions, the transmittance of the PET/Ag NW/PPh3 based films is nearly unchanged, while the transmittance of the PET/Ag NW-based films decreases by about 5%. The sheet resistance increases for both materials as time elapses, but the rate of increase is more than four times slower for films stabilized by PPh3. The improved transmittance and conductivity results in a significantly enhanced stability for the figure of merit σdc/σop. This phenomenon is highlighted in highly oxidative nitric acid vapor. The tested stabilized films in such conditions exhibit a decrease to σdc/σop of only 38% after 75 min, whereas conventional materials exhibit a relative loss of 71%. In addition, by contrast to other classes of stabilizers, such as polymer or graphene-based encapsulants, PPh3 does not alter the transparency or conductivity of the modified films. While the present films are made by membrane filtration, the stabilization method could be implemented directly in other liquid processes, including industrially scalable ones.

Combined effect of double antireflection coating and reversible molecular doping on performance of few-layer graphene/n-silicon Schottky barrier solar cells

Few-layer graphene films were grown by chemical vapor deposition and transferred onto n-type crystalline silicon wafers to fabricate graphene/n-silicon Schottky barrier solar cells. In order to increase the power conversion efficiency of such cells the graphene films were doped with nitric acid vapor and an antireflection treatment was implemented to reduce the sunlight reflection on the top of the device. The doping process increased the work function of the graphene film and had a beneficial effect on its conductivity. The deposition of a double antireflection coating led to an external quantum efficiency up to 90% across the visible and near infrared region, the highest ever reported for this type of devices. The combined effect of graphene doping and antireflection treatment allowed to reach a power conversion efficiency of 8.5% exceeding the pristine (undoped and uncoated) device performance by a factor of 4. The optical properties of the antireflection coating were found to be not affected by the exposure to nitric acid vapor and to remain stable over time.

Preparing hydroxyapatite-silicon composite suspensions with homogeneous distribution of multi-walled carbon nano-tubes for electrophoretic coating of NiTi bone implant and their effect on the surface morphology

Preparing a stable suspension is a main step towards the electrophoretically depositing of homogeneous and dense composite coatings on NiTi for its biomedical application. In the present study, different composite suspensions of hydroxyapatite, silicon and multi-walled carbon nano-tubes were prepared using n-butanol and triethanolamine as media and dispersing agent, respectively. Multi-walled carbon nanotubes were first functionalized in the nitric acid vapor for 15h at 175°C, and then mixed into suspensions. Thermal desorption spectroscopy profiles indicate the formation of functional groups on multi-walled carbon nano-tubes. An excellent suspension stability can be achieved for different amounts of triethanolamine. The amount of triethanolamine can be increased by adding a second component to a stable hydroxyapatite suspension due to an electrostatic interaction between components in suspension. The stability of composite suspension is less than that of the hydroxyapatite suspension, due to density differences, which under the gravitational force promote the demixing. The scanning electron microscopy images of the coatings surface show that more dense coatings are developed on NiTi substrate using electrophoretic deposition and sintering at 850°C in the simultaneous presence of silicon and multi-walled carbon nanotubes in the hydroxyapatite coatings. The atomic force microscopy results of the coatings surface represent that composite coatings of hydroxyapatite-20wt.% silicon and hydroxyapatite-20wt.% silicon-1wt.% multi-walled carbon nano-tubes with low zeta potential have rougher surfaces.

Controlled surface functionalization of carbon nanotubes by nitric acid vapors generated from sub-azeotropic solution

Controlled surface modification of nanocarbons is crucial for their use in applications. The paper deals with the functionalization of carbon nanotubes (CNTs) with HNO3 vapors. Sub-azeotropic HNO3 + H2O + Mg(NO3)2 solution is used for the generation of nitric acid vapors. Because this approach allows tuning the HNO3 concentration in the vapor phase, the effect of its variation on the surface chemistry and structural properties of the CNTs is investigated. A combination of analytical techniques is applied to evaluate oxidation extent of the CNT surface, selectivity towards the formation of carboxyl groups compared with other oxygenated functionalities, and CNT integrity. The comparison with liquid-phase functionalization in H2SO4 + HNO3 mixture (1 : 3–3 : 1 v/v), conventionally utilized for oxidizing CNTs, shows that vapor-phase functionalization affords greater surface oxygen uptakes and higher selectivity towards the formation of carboxyl groups, with smaller tube damage; more importantly, it evidences that, regardless of the method and conditions chosen, the selectivity towards carboxyl groups increases linearly with the surface oxygen concentration. The presented results prove that the product of HNO3 concentration in the vapor-phase (25–93 wt%) and vapor-phase functionalization duration (0.5–5 h) controls the surface oxygen concentration. A simple rate model is proposed to account for its increase. Copyright © 2015 John Wiley & Sons, Ltd.

Volatile Emissions of Ammonium Nitrate under Flowing Conditions

AbstractAmmonium nitrate (AN) is an ionic solid commonly used as a fertilizer and in commercial blasting applications. Frequently, AN is mixed with a fuel and used in improvised explosives devices (IEDs). To characterize the low‐volatility components emanating from AN, a sample of AN was sealed inside a stainless steel chamber while a laminar flow of air swept the headspace vapor components into a water impinger or cold‐trap for pre‐concentration and subsequent analysis by ion chromatography (IC). Both collection methods were found to be 100 % efficient for collecting nitric acid vapor, whereas the collection efficiency for ammonia was dependent upon the collection method and, for the water impinging method, additionally upon the vapor concentration, humidity and flow rate. Cold‐trapping efficiency for ammonia was 4 %±2 % across all parameters studied. Water impinging was more efficient (20–70 %), but the efficiency varied according to each of the aforementioned variables. The characteristics of an AN vapor generated from a solid sample were found to vary as the sample approached equilibrium inside the chamber. Initially, large quantities of ammonia were observed, but as a steady state was achieved within the laminar flow and a dynamic equilibrium established, the ratio of ammonia to nitric acid in the effluent vapor dropped, although never becoming equimolar. The ratio was strongly dependent upon humidity.

Surface Chemistry and Thermal Stability in Air of Carbon Nanotubes Functionalised via a Novel Eco-Friendly Approach to HNO3 Vapor Oxidation

Some crucial aspects of the functionalisation of carbon nanotubes by nitric acid vapors are investigated, namely selectivity of the process and thermal stability in air of the functionalised materials. Results obtained by varying duration (0.5–5.0 h) of the conventional treatment with vapors at azeotropic HNO3 concentration are compared with those obtained, for fixed duration (2.0 h), by using sub-azeotropic HNO3+H2O+Mg(NO3)2 solution to generate acid vapors with acid concentration in the range 25–93 wt%, as recently proposed by us. A thorough picture is drawn based on evidences of high-resolution transmission electron microscopy, micro Raman spectroscopy, thermo-gravimetry, derivative thermo-gravimetry, and temperature-programmed desorption systematic analyses.