Sonoluminescence of aqueous solutions of sulfuric acid and sulfur dioxide

Sonoluminescence (SL) of aqueous solutions of sulfuric acid and sulfur dioxide enhances with an increase in their concentration and reaches a maximum at 16 and 0.05 mol L^–1, respectively. The further increase in the concentration of these substances decreases the SL intensity. The SL spectra of the solutions have a broad maximum at 450 nm. Excited SO₂ molecules formed in sulfuric acid due to sonolysis are luminescence emitters. The proposed mechanism of bright SL in these systems is based on the energy transfer from the electron-excited sonolysis products to the SO₂ molecules in cavitation bubbles.     

Multibubble sonoluminescence of Tb3+ ion in aqueous solutions of dimethyl sulfoxide

The intensity and spectra of multibubble sonoluminescence of TbCl₃ solutions in water-DMSO mixtures saturated with air and argon are studied. The spectra represent the superposition of the characteristic glow of Tb³⁺ ions and the continuum of emission of electronically excited products of solvent sonolysis (with H₂O*, OH*, and SO₂* as main emitters). Abnormal action of DMSO and sulfur dioxide on the characteristic luminescence of Tb³⁺ ions during sonolysis of aqueous solutions is revealed. These additives enhance the sonoluminescence of water to different extent, quench the sonoluminescence of Tb³⁺, and differently influence the photoluminescence quantum yield of this ion (DMSO acts as activator, whereas SO₂ acts as quencher). Sulfur dioxide quenches the sonoluminescence of Tb3+ much more efficiently than the photoluminescence of Tb³⁺. The abnormal effect of DMSO on sonoluminescence is most probably due to the quenching action of sulfur dioxide formed during sonolysis of DMSO on Tb³⁺* ions in cavitation bubbles.     

Multibubble sonoluminescence of europium(III) chloride in heavy water

A weak glow in the region of the Eu³⁺ photoluminescence spectrum was detected against the background of the continuum of the solvent emission during multibubble sonolysis of air- or argon-saturated EuCl₃ solutions (0.1 mol L⁻¹) in heavy water. No characteristic sonoluminescence of the europium ion in aqueous solutions was observed earlier. Possible reasons for the low yield of Eu³⁺ sonoluminescence compared with other lanthanide ions (Ln³⁺) are discussed and the influence of europium on the spectrum of the solvent continuum related, in particular, to quenching of the electron-excited sonolysis products H₂O* (D₂O*) and Eu³⁺* in electron transfer reactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1793–1796, September, 2008.     

Multibubble sonolysis and sonoluminescence in molten elementary sulfur and sulfur—styrene mixture

The effect of saturation with argon, as well as styrene and iodine additives on the temperature dependence of multibubble sonoluminescence intensity in molten sulfur at 120–230 °C was studied. The shape of the temperature dependence with a maximum at 170–200 °C is determined by the viscosity variations related to the changes in the molecular structure of molten elemental sulfur. At high temperatures, cyclooctasulfane (S₈) molecules break to radical products, which then undergo polymerization that can be slowed down by the additives. Sulfurization of styrene during sonolysis of a sulfur—styrene mixture resulting in products of the thiophene series was detected. Unlike thermal sulfurization that affords 2,5-diphenylthiophene as a major product, sonochemical sulfurization results mainly in 2,4-diphenylthiophene. The mechanism of 2,4-diphenylthiophene formation initiated by the reaction of styrene molecules with S⁺ ions produced upon fragmentation of S₈ within cavitation bubbles is proposed. The glow of electronically excited S⁺* ions is responsible for the band with a maximum at 560 nm in the sonoluminescence spectrum of molten sulfur, which is suppressed by the styrene additive.     

TRLFS study on the speciation of uranium in seepage water and pore water of heavy metal contaminated soil

In situ leaching of uranium ores with sulfuric acid during active uranium mining activity on the Gessenheap has caused longstanding environmental problems of acid mine drainage and elevated concentrations of uranium. To study there remediation measures the test site Gessenwiese, a recultivated former uranium mining heap near Ronnenburg/East Thuringia/Germany, was installed as a part of a research program of the Friedrich-Schiller University Jena to study, among other techniques, the phytoremediation capacity of native and selected plants towards uranium. In the first step the uranium speciation in surface seepage and soil pore waters from Gessenwiese, ranging in pH from 3.2 to 4.0, were studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Both types of water samples showed mono-exponential luminescence decay, indicating the presence of only one major species. The detected emission bands were found at 477.5, 491.8, 513.0, 537.2, 562.3, and 590.7 nm in case of the surface water samples, and were found at 477.2, 493.2, 513.8, 537.0, 562.4, and 590.0 nm in case of the soil water samples. These characteristic peak maxima together with the observed mono-exponential decay indicated that the uranium speciation in the seepage and soil pore waters is dominated by the uranium (VI) sulfate species UO₂SO_4(aq). Due to the presence of luminescence quenchers in the natural water samples the measured luminescence lifetimes of the UO₂SO_4(aq) species of 1.0–2.6 μs were reduced in comparison to pure uranium sulfate solutions, which show a luminescence lifetime of 4.7 μs. These results convincingly show that in the pH range of 3.2–4.0 TRLFS is a suitable and very useful technique to study the uranium speciation in naturally occurring water samples.     

Extraction of moderate oxidation state technetium species between 30 % tri-n-butyl phosphate and H2SO4/HNO3

The extraction of technetium species at oxidation state lower than +7 has been examined in sulfuric and sulfuric/nitric acid solutions using UV–Vis spectroscopy and optically transparent thin layer cell (RVC-OTTLE). Soluble Tc(III), TcO²⁺ and [Tc₂O₂]³⁺ species with absorption bands at 420–450, 400, and 502 nm, respectively, were detected as products of pertechnetates electroreduction. The distribution ratios of ⁹⁹Tc with lower than +VII oxidation state ionic species between 4 M H₂SO₄ and 30 % TBP/kerosene were found and are significantly lower than for TcO₄ ^? in the same solution.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.     

Proton mobility in complex [RhL4Cl2]HSO4 · nH2SO4 · mH2O salts (L = Py, γ-picoline)

The method of deposition from solutions was used to synthesize [RhL ₄Cl₂]HSO₄ · nH₂SO₄ · mH₂O complex salts (L = Py, γ-picoline), n ≈ 0.5−0.6, m ≈ 5−6. According to the data of X-ray phase analysis, the crystal structure of these salts is formed by layers of cations separated by layers consisting of anions molecules of sulfuric acid and water connected through a system of hydrogen bonds. Calorimetric methods were used to study phase transitions and the range of thermal stability of salts. The method of ¹H NMR spectroscopy discovered that protons within the {HSO₄⁻ · nH₂SO₄ · mH₂O} subsystem featured enhanced conductivity. Conductivity studies showed that trans-[RhL ₄Cl₂]HSO₄ · nH₂SO₄ · mH₂O samples had high proton conductivity.     

The surface characteristics of polycrystalline cobalt electrooxidised in sulfuric acid solutions

The oxidation of cobalt electrodes has been carried out by means of cyclic voltammetry and coulometry under controlled potential in sulfuric acid solutions of different concentrations. The electrochemical scanning tunneling microscope/scanning tunneling microscope (ECSTM/STM) systems constructed by the authors and scanning electron microscopy (SEM) with the SEM-EDX system of surface analysis of the elements have been used. The procedure applied in this work made it possible to observe the fragments of the same surface by means of SEM and ECSTM/STM. The most typical images for a polycrystalline Co electrode with a ±10% accuracy at the scales of 4800 nm × 4800 nm and 100 nm × 100 nm are presented and the results are discussed. In a diluted electrolyte (0.1 M), irregular forms of a stable cobalt oxide with Co:O ratio ∼1:1 appear. Unreproducible results have been obtained in a 1.0 M H₂SO₄ solution. Compact and relatively regular layers of cobalt oxide of the same ratio have been obtained in 0.1 M H₂SO₄, as well as in 10.0 M sulfuric acid solution, under controlled oxidation potential at the passivation range. Received: 6 January 1999 / Accepted: 5 May 1999     

Solubility in the systems Rb2SO4-H2SO4-H2O and Cs2SO4-H2SO4-H2O at 25°

Conclusions The solubility of rubidium and cesium sulfates in aqueous solutions of sulfuric acid was studied at 25°. Rubidium sulfate forms the compounds 3Rb₂SO₄· H₂SO₄, Rb₂SO₄ · H₂SO₄, Rb₂SO₄·3H₂SO₄ and Rb₂SO₄·7H₂SO₄ with sulfuric acid, while cesium sulfate forms the compounds Cs₂SO₄·H₂SO₄; Cs₂SO₄·3H₂SO₄ and Cs₂SO₄ · 7H₂SO₄.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1166–1170, June, 1968.     

The characteristics of the nanosized η-TiO2 polymorph

The nanosized η-TiO₂ polymorph was prepared by the hydrolysis of titanyl sulfate (TiO)SO₄ · xH₂SO₄ · yH₂O. η-TiO₂ was studied by X-ray diffraction, X-ray photoelectron spectroscopy, IR spectroscopy, and Raman spectroscopy. Characteristic X-ray data and distinguishing Raman spectrum features were found for η-TiO₂,. The surface of η-TiO₂ samples contained adsorbed OH⁻ particles and water molecules or water molecules of crystal hydrates. The free specific surface area of samples with crystallite sizes of L = 50 (4) and 60 (5) ? was S = 10.17 (9) and 15.6 (1) m²/g. The characteristics of samples with η-TiO₂ were favorable for their use as photocatalysts and adsorbents.     

Demetallation of α,β,γ,δ-tetrakis(p-sulfophenyl) porphiniron(III) in mineral acid–alcohol–water media

Demetallation rates of α,β,γ,δ-tetrakis(p-sulfophenyl)porphiniron(III) in hydrochloric acid–ethanol–water, perchloric acid–ethanol–water, and sulfuric acid–alcohol–water media were determined. For a given acidity value H₀ the order of the rates for the three acids was HCl > H₂SO₄ > HClO₄. This is also the order for complex formation between acid anion and iron(III). Consequently ligands as well as protons are involved in the breaking of bonds between the metal and the porphyrin leading to the formation of the activated complex. The log k values for HCl and HClO₄ media were not linearly related to the Hammett acidity function as they were for sulfuric acid–ethanol–water media. The average ΔH? and ΔS?values for the HCl media were 18.4 ± 1.4 kcal/mol and ? 19 ± 3 cal K mol, respectively, in very close agreement with those for H₂SO₄ media despite the difference in H ₀ dependence. For H₂SO₄–alcohol–water media the order of the rates was butanol > propanol > ethanol with little difference between isomeric alcohols.     

Synthesis of Poly(<Emphasis Type="Italic">o</Emphasis>-anisidine)/H<Subscript>2</Subscript>SO<Subscript>4</Subscript> Film for the Development of Glucose Biosensor

The poly(o-anisidine)–sulfuric acid–glucose oxidase (POA–H₂SO₄–GOx) electrode has been investigated in the present work. Platinum electrode was used for the synthesis of poly (o-anisidine)–sulfuric acid (POA–H₂SO₄) film using galvanostatic method with 0.2 M o-anisidine, 1.0 M H₂SO₄ solution, 1.0 pH and 2 mA/cm² applied current density. The synthesized film was characterized using electrochemical technique, conductivity measurement, UV–visible spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. GO_X was immobilized on synthesized POA–H₂SO₄ film by cross-linking via glutaraldehyde in phosphate and acetate buffer. The Michaelis–Menten constant ( K_\textm￠K_{\text{m}}^\prime ) was determined for the immobilized enzyme. The glucose oxidase electrode shows the maximum current response at pH 5.5 and potential 0.6 V. The sensitivity of POA–H₂SO₄–GO_X electrode in phosphate and acetate buffer has been recorded. The results of this study reveal that the phosphate buffer gives fast response as compared to acetate buffer in amperometric measurements.     

A theoretical study of the H2SO4+H2O → HSO4 −+H3O+ reaction at the surface of aqueous aerosols

The surface region of sulfate aerosols (supercooled aqueous concentrated sulfuric acid solutions) is the likely site of a number of important heterogeneous reactions in various locations in the atmosphere, but the surface region ionic composition is not known. As a first step in exploring this issue, the first acid ionization reaction for sulfuric acid, H₂SO₄ + H₂O HSO₄^– + H₃O⁺, is studied via electronic structure calculations at the Hartree–Fock level on an H₂SO₄ molecule embedded in the surface region of a cluster containing 33 water molecules. An initial H₂SO₄ configuration is selected which could produce H₃O⁺ readily available for heterogeneous reactions, but which involves reduced solvation and is consistent with no dangling OH bonds for H₂SO₄. It is found that at 0 K and with zero-point energy included, the proton transfer is endothermic by 3.4 kcal/mol. This result is discussed in the context of reactions on sulfate aerosol surfaces and, further, more complex calculations.Contribution to the Jacopo Tomasi Honorary Issue     

Extraction of uranium (VI) from sulfuric acid solution with TOPO

The extraction of uranium(VI) from sulfuric acid medium with tri-octylphosphine oxide (TOPO) in n-heptane was studied. Accompanied with the increase in the concentration of H₂SO₄, the distribution coefficient of uranium(VI) increased in the region of dilute sulfuric acid. When the concentration of H₂SO₄ surpassed 3.5 mol·dm⁻³, the distribution coefficient of uranium(VI) was at maximum. This result was due to the competition extraction between uranium(VI) and H₂SO₄. From the data, the composition of extracted species and the equilibrium constant of extraction reaction have been evaluated, which were (TOPOH)₂UO₂(SO₄)₂ (TOPO) and 10^7.6±0.15, respectively.     

Isotopic effects on the time-dependences of 420 nm ice luminescence excited by UV light

The kinetics of the 420 nm luminescence emitted from H₂O and D₂O polycrystalline Ih ices have been studied over the 77 to 162 K temperature range. In the case of both H₂O and D₂O ices, it was found that the luminescence rise and decay curves consisted of two luminescence components, and superimposing two first-order curves with different rate constants gave the best fit to the decay and rise curves. The mean lifetimes of the two luminescence components were 1.08 ± 0.03 s and 2.47 ± 0.03 s. The rate constants were found to have negligible temperature dependences, which led to activation energies well below those obtained for either activation-limited processes or even diffusion-limited processes. Furthermore, it was found that the luminescence kinetics were not affected by isotopic substitution of D for H in the ice lattice. These observations suggest that the rate-determining step in the mechanism for the production of the luminescence is a slow (probably spinforbidden) electronic transition that can occur at two different rates due to the presence of two different types of trapping sites in the ice lattice. A possible candidate for the electronic transition is the ⁴Σ → X ²Π transition of excited OH^. radicals and not the previously suggested and ubiquitous A ²Σ⁺ → X ²Π transition of this species. Published in Russian in Kinetika i Kataliz 2006, Vol. 47, No. 5, pp. 709–721. This text was submitted by the authors in English.     

Sonochemiluminescence of aromatic hydrocarbons

Multibubble sonoluminescence of water and a series of aromatic hydrocarbons, viz., benzene, toluene, ethylbenzene, and m-xylene (at 25 °C), and a naphthalene melt (at 110–120 °C) was studied. An analysis of the influence of oxygen and argon on the sonoluminescence intensity and the luminescence spectra of these liquid compounds, as well as the effect of additives of ionol, ethanol, and 9,10-dibromoanthracene on m-xylene sonoluminescence, showed that a considerable contribution to the sonoluminescence of aromatic hydrocarbons is made by chemiluminescence reactions associated with their oxidation. This sonochemiluminescence is observed in both the gas phase of cavitation bubbles and the bulk solution where luminescence is retained for a long time after ultrasonication switching-off (the initial intensity of the residual chemiluminescence is up to 10% of the luminescence intensity during sonolysis). As for thermoinitiated oxidation, the afterglow of m-xylene contains the radical and molecular components.     

The chemiluminescence of rare earth elements in sulfuric acid

It has been found that solutions of oxides of the rare earth elements (REE) in sulfuric acid exhibit chemiluminescence in the visible and ultraviolet ranges on interaction with the products of the electrolysis of H₂SO₄. Analysis of the luminescence fading curve shows that the process leading to deexcitation obeys a bimolecular law and its linear anamorphosis can be represented on coordinates I^–1/2 and t. The problem of the possible mechanism of the process involving the participation of S*O_4– ion-radicals is examined. A comparison is made with the known luminescence of the REEs, and possible explanations are put forward for the chemiluminescence of those REEs which are generally assumed to exhibit no luminescence.     

Effect of the structure of frozen solutions of H2SO4 on radiothermoluminescence

A pronounced effect of structural heterogeneity (cracks) of glass-like solutions of 4.9M H₂SO₄ on their radiothermoluminescence (RTL) was found. In perfect glasses one RTL peak was observed at 115 K. Additional luminescence peaks appeared at 165, 195, and 240 K in glasses having cracks. The effect observed was explained by elevated thermal stability of the SO₄ ^– radical stabilized on the surface of sulfuric acid crystal hydrates: H₂SO₄ · 4H₂O and H₂SO₄· 6.5H₂O.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1566–1568, June, 1996.