Precisely Tailor the Longitudinal Localized Surface Plasmon Resonance of Gold Nanorods by Mild Oxidation with NaNO2

In this work, we introduce a new method to precisely tailor the longitudinal localized surface plasmon resonance (LLSPR) wavelengths of gold nanorods (GNRs) through the use of NaNO₂ as the oxidant. The effects of the concentrations of NaNO₂, NH₄Br and HCl on the reaction kinetics were investigated separately. To prepare GNRs with desired LLSPR wavelengths, equations were derived and were proved to be able to guide the tailoring of the LLSPR wavelengths through carefully tuning either the amount of NaNO₂ or the reaction time. TEM characterizations performed on two representative sets of GNRs show that the GNRs obtained exhibited shortened lengths but unchanged diameter with good monodispersity. In particular, GNRs with targeted LLSPR at 800 nm, 750 nm, 700 nm and 650 nm were successfully synthesized with relative errors of only 1 %～5 %. This method shall promote more applications of GNRs and may advance the synthesis of other metal nanoparticles.     

Determination of plutonium in environmental samples by controlled valence in aniion exchange

The title method was successfully used for collecting^239,249Pu from 200 litres of seawater by coprecipitation with 16 g FeSO₄·7H₂O under redcing conditions witout filtering. The plutonium is leached by concentrate HNO₃+HCl from the coprecipitate and the solid particles. The precipitate is heated at 400°C and digested in aqua regia. Na₂SO₃ and NaNO₂ have been applied to obtain the Pu⁴⁺ valence state in 0.5–1N HNO₃ for different samples. Plutonium and thorium are coadsorbed on anionic resin from 8N HNO₃. The column is eluted with 8N HNO₃ containing fresh NaNO₂ to keep the Pu⁴⁺ state for uranium decontaination. The system of the column is changed from 8N HNO₃ to concentrated HCl with 50 ml concentrated HCl containing a few milligrams of NaNO₂. Furtheer decontaimination of torium was achieved by elution with concentrated HCl instead of 9N HCl. The plutonium is successfully stripped by H₂O, NaOH, 2N HNO₃ and 0.5N HNO₃ containign 0.01M NaNO₃. The chemica yield of plutonium for a 2001 seawate sample is 60–80%. The resolution of the electroplated thin source is very good.     

Selective synthesis of functionalized pyrazoles from 5-amino-1H-pyrazole-4-carbaldehydes with sodium nitrite: 5-Amino-4-nitrosopyrazoles and pyrazole-4-carbaldehydes

A novel and efficient redox reaction was developed to react 5-amino-1H-pyrazole-4-carbaldehyde with sodium nitrite (NaNO₂) in an acidic solution (HCl/MeOH) to generate 5-amino-4-nitrosopyrazole, pyrazole-4-carbaldehyde, or diazenylpyrazole selectively. The results showed that 5-amino-4-nitrosopyrazoles were formed as the major product in the diluted acidic solution (≤2 N HCl in MeOH solution) through redox, formylation, and nitrosation reactions of NaNO₂. Intriguingly, pyrazole-4-carbaldehyde was the main product under 6 N HCl in MeOH solution.     

Kinetics and mechanism of trichloroisocyanuric acid/NaNO2-triggered nitration of aromatic compounds under acid-free and Vilsmeier-Haack conditions

Kinetics and mechanism of nitration of aromatic compounds using trichloroisocyanuric acid (TCCA)/NaNO₂, TCCA-N,N-dimethyl formamide (TCCA-DMF)/NaNO₂, and TCCA-N,N-dimethyl acetamide (TCCA-DMA)/NaNO₂ under acid-free and Vilsmeier-Haack conditions. Reactions followed second-order kinetics with a first-order dependence on [Phenol] and [Nitrating agent] ([TCCA], [(TCCA-DMF)], or [(TCCA-DMA)] >> [NaNO₂]). Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, but did not fit well into the Hammett's theory of linear free energy relationship or its modified forms like Brown-Okamoto or Yukawa-Tsuno equations. Rate data were analyzed by Charton's multiple linear regression analysis. Isokinetic temperature (β) values, obtained from Exner's theory for different protocols, are 403.7 K (TCCA-NaNO₂), 365.8 K (TCCA-DMF)/NaNO₂, and 358 K (TCCA-DMA)/NaNO₂. These values are far above the experimental temperature range (303-323 K), indicating that the enthalpy factors are probably more important in controlling the reaction.     

A study on combustion behaviour of carbon-sulphur-sodium nitrate mixtures

The effect of substitution of KNO₃ by NaNO₃ in black powder has been studied by DSC, TG/DTG and FTIR emission spectroscopy. Unlike KNO₃, there is no visible exothermic reaction between S and NaNO₃, immediately after the melting of NaNO₃. Instead a minor exothermic reaction is observed at higher temperature between melted NaNO₃ and adsorbed S on carbon. However, there is an increase in such reaction, when carbon black instead of charcoal is used. Infrared spectra show that CO₂ and Na₂SO₄ are major gaseous and solid products respectively. This shows that the combustion of ternary mixtures in air is different from that in N₂, with slower heating rate, in DSC or TG apparatus.

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Zusammenfassung Mittels DSC, TG/DTG und FTIR Emissionsspektroskopie wurde der Effekt des Ersatzes von KNO₃ gegen NaNO₃ in Sprengpulver untersucht. Im Gegensatz zu KNO₃ gibt es unmittelbar nach dem Schmelzen von NaNO₃ keine wahrnehmbare exotherme Reaktion zwischen S und NaNO₃. Dafür wurde bei höheren Temperaturen eine geringe exotherme Reaktion zwischen geschmolzenem NaNO₃ und an C adsorbiertem S beobachtet. Unabhängig davon werden Reaktionen begünstigt, in denen man anstelle von Holzkohle Ruß verwendet. IR-Spektren zeigen, daß die hauptsächlichen gasförmigen und festen Produkte CO₂ bzw. Na₂SO₄ sind. Dies zeigt, daß sich die Verbrennung ternärer Gemische in Luft von der in Stickstoff unterscheidet.

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We thank the Procurement Executive, Ministry of Defence for the support of this research.     

GC determination of volatile organoiodine and organobromine compounds in Arctic seawater and air samples

Summary During September 1992 seawater and air samples were collected on Spitzbergen, Norway, and the concentrations of volatile organoiodine and organobromine compounds of biogenic origin were determined by a GC system supplied with a capillary column and an electron capture detector. A purge and trap technique was used to isolate the organohalogen compounds from the seawater samples, whereas the air samples were collected by an adsorption tube filled with Carbosieve S-III. The iodinated compounds CH₃I, CH₂I₂, CH₂C1I, CH₃CH₂CH₂I and CH₃CHICH₃ were determined in Arctic seawater and air samples with mean concentrations in the range of (0.3–6.2) ng/l and (0.7–2) pptv, respectively. This is the first time that 1- and 2-propyl iodide could be analysed both in atmospheric samples and in seawater samples of the Arctic. CH₂Br₂, CHBr₃, CH₂BrCl, CHBrCl₂ and CHBr₂Cl were determined as biogenic brominated methanes in mean concentrations of (0.1–164) ng/l and (0.1–0.5) pptv in seawater and air samples, respectively. The highest concentrations in seawater samples were found for CH₂I₂ and CHBr₃, respectively, whereas in air samples the most abundant iodinated compound was CH₃I and the most abundant brominated compounds with equal mean concentrations were CH₂Br₂ and CHBr₃. Significant differences were found in the seawater concentration from the middle of the fjord and the shore site, compared with samples from a field of algae. In all cases the concentration was higher for the samples from the field of algae with an especially high excess by a factor of 4–9 for CH₂I₂ and CHBr₃. This result shows that algae are an important biological species in the polar region for the production of these halogenated substances. Whereas the brominated compounds in seawater samples correlate well with each other, CH₃I or any other iodinated compound does not correlate with the bromomethanes. This indicates a different biogenic mechanism for their formation. Under certain preconditions the annual flux from the Arctic Ocean to the atmosphere could be calculated for CH₃I to be 4×10⁹ g, for CHBr₃ to be 5.4×10¹⁰ g, which is an essential contribution to the total global budget of these important atmospheric trace gases.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Experimental determination and prediction of the vapor pressure of some binary and quaternary aqueous solutions of alkaline nitrites and nitrates

Vapor pressure of H₂O + NaNO₃ and H₂O + NaNO₂ solutions were measured with static method from 298.1 to 353.1 K in a range of salt mass fractions between 0.05 and 0.50. As well, the vapor pressure was determined for quaternary mixtures LiNO₃ + NaNO₃ + KNO₃ + H₂O (salt mass ratio 53:5:42) and LiNO₃ + KNO₃ + NaNO₂ + H₂O (salt mass ratio 53:35:12) from 313.1 to 353.1 K and total salt mass fraction of 0.30, 0.40 and 0.50. The experimental vapor pressure data of binary systems were correlated with the temperature and the liquid-phase composition using an analytical polynomial equation. The capability of the electrolyte non-random two liquid model (Electrolyte-NRTL) to predict the vapor–liquid equilibrium was evaluated by comparing predicted and experimental data of the mixtures studied in this work.     

Nitrosation of salts of 1-hydroxyimino-2,2-dinitro-1-R-ethanes,a novel method for the preparation of isomeric 3(4)-nitro-4(3)-R-furoxans

A novel general method for the synthesis of isomeric 3(4)-nitro-4(3)-R-furoxans is developed. 3-Nitro isomers were obtained by reaction of hydroximoyl chlorides with dinitromethane sodium salt followed by conversion of the resulting 1-substituted 1-hydroxyimino-2,2-dinitroethanes into dipotassium (or disodium salts) and their subsequent nitrosation with NaNO₂ in AcOH or with N₂O₄. Thermal isomerization of 3-nitro isomers afforded 4-nitro isomers were prepared in high yields.     

Hydrolysis and chemical speciation of (C2H5)2Sn2+, (C2H5)3Sn+ and (C3H7)3Sn+ in aqueous media simulating the major composition of natural waters

The hydrolysis of (C₂H₅)₂Sn²⁺, (C₂H₅)₃Sn⁺ and (n‐C₃H₇)₃Sn⁺ has been studied, by potentiometric measurements ([H⁺]‐glass electrode), in NaNO₃, NaCl, NaCl/Na₂SO₄ mixtures and in a synthetic seawater (SSWE), as an ionic medium simulating the major composition of natural seawater, at different ionic strengths (0 ≤ I ≤ 5 mol dm^?3) and salinities (15 ≤ S ≤ 45), and at t = 25 °C. Five hydrolytic species for (C₂H₅)₂Sn²⁺, three for (C₂H₅)₃Sn⁺ and two for (C₃H₇)₃Sn⁺ are found. Interactions with the anion components of SSWE, considered as single‐salt seawater, are determined by means of a complex formation model. A predictive equation for the calculation of unknown hydrolysis constants of trialkyltin(IV) cations, such as tributyltin(IV), in NaNO₃, NaCl, and SSWE media at different ionic strengths is proposed. Equilibrium constants obtained are also used to determine the interaction parameters of Pitzer equations. Copyright © 2001 John Wiley & Sons, Ltd.     

Micelle-assisted cerium(IV) oxidation of <Emphasis Type="SmallCaps">L</Emphasis>-sorbose in aqueous sulfuric acid

Spectrophotometric kinetic technique has been used to investigate the effect of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) surfactants on the redox reaction of cerium(IV)+l-sorbose in aqueous sulfuric acid media. The anionic SDS has no effect, whereas the reaction rate increases in the presence of cationic CTAB, which is due to favorable conditions provide by the cationic micelles. The reaction rate decreases with [H₂SO₄], and no acid-dependent path has been observed. At constant [H₂SO₄], the rate of the reaction is dependent on the first powers of the l-sorbose and cerium(IV) concentrations. The CTAB-assisted reaction is retarded by addition of electrolytes (Na₂SO₄, NaNO₃, and NaCl), which is attributed to the competition between electrolyte anions and cerium(IV)-sulfato species. Bromide ion (of CTAB or externally added in the form of NaBr) is not oxidized by the cerium(IV) (as a main or side reaction).     

Transport of NaNO3 solutions across an activated composite membrane: electrochemical and chemical surface characterizations

Electrochemical characterization of two different samples of an activated membrane, which consists of a polymeric support containing different amounts of Di-(2-ethylhexyl) phosphoric acid as a carrier, was made by measuring the electrical resistance, salt diffusion and membrane potential for the activated membranes and the polymeric support in contact with NaNO₃ solutions. Transport parameters such as the ion transport numbers and concentration of fixed charge in the membrane, salt and ionic permeabilities at different NaNO₃ concentrations were obtained. A comparison of the different electrochemical parameters obtained with both activated membranes and the polymeric support shows how the carrier affects the transport of NaNO₃ solutions across the activated membranes. On the other hand, chemical composition of the membrane surfaces as a function of the amount of carrier was determined by X-ray photoelectron spectroscopy technique, which also allows an envisagement of the chemical bonding between the carrier and the membrane top layer (polyamide).     

Determination of asulam by fast stopped-flow chemiluminescence inhibition of luminol/peroxidase

An efficient, sensitive and fast stopped-flow method has been developed to determine asulam in water, based on its inhibition effect on the horseradish peroxidase-luminol-hydrogen peroxide chemiluminescence reaction, (HRP-luminol-H₂O₂). Ultra fast data acquisition (0.20 s) facilitates excellent selectivity because no interferences from concomitants in the matrix act in such short time scale. The precision as repeatability (expressed as relative standard deviation, n = 10) was 0.4% at a 40 pM level. The detection limit was 1.5 pM (0.35 ng/L) and 7.15 pM in pure and raw water, respectively. The calibration data over the range 5-60 pM present a correlation coefficient of r = 0.9993. The proposed method has been applied to determine asulam in water samples by using solid-phase extraction (SPE). Mean recovery value was 98.1 ± 2% at 50 pM level.     

Phase Diagram of the NaNO<Subscript>2</Subscript>—KNO<Subscript>3</Subscript> System in the 0 to 1 Molar Fraction Range of Concentrations of KNO<Subscript>3</Subscript>

The temperature dependence of the phase composition of KNO₃—NaNO₂ mixtures in the 0 to 1 molar fraction range of concentrations of KNO₃ is investigated. A phase diagram of the KNO₃—NaNO₂ binary system in the range of concentrations from 0 to 1 molar fractions of KNO₃ is drawn on the basis of DTA results. The composition of the eutectic mixture and its melting temperature is determined experimentally.     

Identification of Superoxide O2- during Thermal Decomposition of Molten KNO3-NaNO2-NaNO3 Salt by Electron Paramagnetic Resonance and UV-Vis Absorption Spectroscopy

On account of excellent thermal physical properties, molten nitrates/nitrites salt has been widely employed in heat transfer and thermal storage industry, especially in concentrated solar power system. The thermal stability study of molten nitrate/nitrite salt is of great importance for this system, and the decomposition mechanism is the most complicated part of it. The oxide species O₂^2- and O₂^- were considered as intermediates in molten KNO₃-NaNO₃ while hard to been detected in high temperature molten salt due to their trace concentration and low stability. In this work, the homemade in situ high temperature UVVis instrument and a commercial electron paramagnetic resonance were utilized to supply evidence for the formation of superoxide during a slow decomposition process of heat transfer salt (HTS, 53 wt% KNO₃/40 wt% NaNO₂/7 wt% NaNO₃). It is found that the superoxide is more easily generated from molten NaNO₂ compared to NaNO₃, and it has an absorption band at 420-440 nm in HTS which red shifts as temperature increases. The band is assigned to charge-transfer transition in NaO₂ or KO₂, responsible for the yellow color of the molten nitrate/nitrite salt. Furthermore, the UV absorption bands of molten NaNO₂ and NaNO₃ are also obtained and compared with that of HTS.     

Silica-supported perchloric acid and potassium bisulfate as reusable green catalysts for nitration of aromatics under solvent-free microwave conditions

Silica-supported perchloric acid and bisulfate (SiO₂/HClO₄ and SiO₂/KHSO₄) have been developed as reusable green catalysts for nitration of aromatic compounds using NaNO₂ in acetonitrile medium under conventional and solvent-free microwave conditions. The reaction times under microwave irradiation are significantly shorter than conventional method even though the yields obtained in microwave-assisted reactions are comparable with those obtained under reflux conditions.     

Stereospecificity in the transformation of α-aminoacids into fluoroacids

In the reaction of α-aminoacids with excess NaNO₂ in polyhydrogen fluoridepyridine, stereospecific substitution(i.e. retention of configuration) is observed with C₆H₁₁CH₂CHNH₂COOH, while a stereospecific rearrangment occurs in the case of phenylalanine.     

Differential scanning calorimetry of sodium and potassium nitrates and nitrites

Differential scanning calorimetry (DSC) experiments were performed with NaNO₃, KNO₃, (Na,K)NO₃, NaNO₂ and KNO₂ over the temperature range 350–990 K. Endothermic peaks, indicative of decomposition reactions, were observed to occur in the single salts above their melting points. The equimolar mixture of sodium and potassium nitrate did not decompose in the temperature range specified. The nitrites began to decompose at 800±10 K. Sodium nitrate began to decompose at 840±10 K and potassium nitrate began to decompose at 820±20 K. These results were compared with previously reported differential thermal analysis investigations of NaNO₃ and KNO₃.     

Synthesis of alkaline-earth metal tungstates in melts of [NaNO3-M(NO3)2]eut-Na2WO4 (M = Ca, Sr, Ba) systems

Alkaline-earth metal tungstates are synthesized in NaNO₃-M(NO₃)₂ (M = Ca, Sr, Ba) eutectic melts. The synthesis is based on the exchange reaction of calcium, strontium, or barium nitrate with sodium tungstate.     

Large volume preconcentration and purification for determining the240Pu/<Superscript>239</Superscript>Pu isotopic ratio and <Superscript>238</Superscript>Pu/<Superscript>239+240</Superscript>Pu alpha-activity ratio in seawater

Summary The present paper describes a new analytical method for determining the ²⁴⁰Pu/²³⁹Pu isotopic ratio and ²³⁸Pu/^239+240Pu α -activity ratio in seawater, both of which are important parameters for determining Pu sources in the ocean. Plutonium isotopes were preconcentrated from a large volume of seawater (4700-10800 liter) by solid phase extraction using MnO₂-impregnated fibers and eluted into 3M HCl. After the elution, the Pu species of all oxidation states were converted to Pu(IV) using NaNO₂, purified by solvent extraction using thenoyltrifluoroacetone (TTA)-benzene, and concentrated in 5 ml of 0.2M HNO₂. The ²⁴⁰Pu/²³⁹Pu and ²³⁸Pu/^239+240Pu ratios in the 5-ml final solution were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and α-spectrometry, respectively. A pg level of Pu, which was a sufficiently large amount for the determination, was obtained by the solid phase extraction. Through the redox conversion and solvent extraction, the Pu species, such as Pu(III), Pu(IV) and Pu(VI), were collected at a high recovery of 96±2% (n=3) despite the presence of large amounts of Mn, and interfering ²³⁸U (3.3 μg^. l^-1in seawater) was effectively removed with a decontamination factor of 1.7·10⁷. The accuracy of the method for the ²⁴⁰Pu/²³⁹Pu ratio was verified using reference materials of seawater and a terrestrial soil sample. The present technique was applied to the determination of the ²⁴⁰Pu/²³⁹Pu and ²³⁸Pu/^239+240Pu ratios in coastal and oceanic water.