Sonolysis of an aqueous mixture of trichloroethylene and chlorobenzene

The effect of the initial concentration on the ultrasonic degradation of two volatile organic compounds trichloroethylene (TCE) and chlorobenzene (CB) was investigated. At higher concentrations, slower sonolysis rates were obtained due to the lowering of the average specific heat ratio gamma of the gas inside the cavitation bubbles. Furthermore, the effect of different concentrations of CB on the sonolysis of 3.34 mM TCE and the effect of different concentrations of TCE on the sonolysis of 3.44 mM CB was examined. The presence of CB lowered the sonolysis rate of TCE, while the sonolysis rate of CB did not decrease by TCE addition. An even higher sonolysis rate was obtained for 3.44 mM CB in the presence of 0.84 mM TCE than without TCE. The explanation for the different effects of both volatile organics on each other's sonolysis rate is thought to be the difference in reaction rate of TCE and CB with the radicals formed during sonolysis. The effect of TCE on the sonolysis rate of CB by lowering the gamma value is compensated by an increased indirect degradation of CB by radicals formed out of TCE. The decreased thermal degradation and the increased indirect radical degradation of CB in the presence of TCE is demonstrated by determining the kinetics of the degradation products styrene and dichlorobenzene.     

Sonolysis of chlorobenzene in aqueous solution: organic intermediates

The ultrasonic degradation of 1.72 mM chlorobenzene was investigated. The sonolysis of chlorobenzene followed first-order kinetics. The influence of the pH of the aqueous solution and the effect of the saturating gás, air or argon, was measured. No pH effect was noticed, and saturation with the monoatomic argon accelerated the degradation. Furthermore, the addition of the radical scavenger benzoate demonstrated that no significant degradation took place in the bulk solution. For air-saturated solutions, the following organic degradation products were identified: methane, acetylene, butenyne, butadiyne, benzene, chlorophenols, phenylacetylene and other chlorinated and non-chlorinated monocyclic and dicyclic hydrocarbons. For argon-saturated solutions, the same products were found, except for the chlorophenols. The presence of the chlorophenols in the case of air-saturation only demonstrated the interaction between the radicals formed and oxygen, and no direct degradation by OH. radicals. The kinetics of several organic degradation products and chloride were determined for the sonolysis of air- and argon-saturated solutions.     

Weak dipolar interaction in solutions: System: Benzene + chlorobenzene and toluene + chlorobenzene

In continuation of our earlier work, excess heats of mixing and volume changes of mixing have been measured for mixtures of chlorobenzene + toluene and chlorobenzene + benzene. The results have been analyzed both in the light of Balescu's theory and our modified approach reported earlier. Analysis shows that our modified approach gives better agreement and the systems should be treated as a mixture of polarizable polar and polarizable non polar molecules.     

Molecular simulation of LiCl aqueous solutions

Non-primitive LiCl aqueous electrolyte solutions were studied at 1.0, 5.0 and 10.0 M concentrations by molecular dynamics simulations. It was observed that the ion hydration structure is progressively lost with increasing concentration. The ions are aggregated in small clusters at C = 1.0 M. However, at this concentration, two large clusters were detected that are an initial step in an aggregation process. At C = 5.0 M, the highly unstable ion clustering seems to correspond to an intermediary state between low concentration states with poor aggregation and states where the ions are highly aggregated, as observed at C = 10.0 M where almost all the ions are clustered in one cluster. This cluster does not present a crystal-like structure. The high solubility of LiCl in aqueous solutions can consequently be explained as a result of the large radii difference between the anion and the cation that results in the instability of the ionic aggregates, which makes the formation of crystal seeds difficult.     

Dielectric behaviour of aqueous CsCl solutions

Complex dielectric permittivity spectra, in the frequency range 10 MHz to 20 GHz are reported for aqueous cesium chloride (CsCl) solutions at 250C using time domain reflectometry technique. The static dielectric constant, relaxation time and conductivity have been determined using nonlinear least squares fit method. From the static dielectric constant, hydration numbers were determined by using measured solutions density at different concentrations.     

Viscosity of aqueous solutions of monocarboxylic acids

An attempt has been undertaken to apply viscosimetric measurements for the examination of incomplete dissociation of symmetric electrolyte solutions. For this purpose precise measurements of the viscosity and density of dilute aqueous solutions of monocarboxylic acids (formic, acetic, propionic and valeric) have been conducted at 298.15 K. Modified Jones–Dole equations have been proposed for incompletely dissociated electrolyte solutions of 1–1 type. The data have been analysed taking into account dimerization of carboxylic acids. The B coefficients for all chemical species in the solution have been determined.     

Sonophotoluminescence from aqueous and non-aqueous solutions

The sonoluminescence generated in air-saturated aqueous and non-aqueous solutions using 515 kHz ultrasound has been used to vibronically excite several fluorescent solutes, namely fluorescein, eosin, pyranine and pyrene. Emission, referred to as 'sonophotoluminescence', was generated in situ with emission spectra that closely matched those obtained by direct photoexcitation of the solutes by an external light source. In the case of pyranine, experiments were also conducted in the presence of the surfactant, sodium dodecyl sulphate (SDS). The presence of 1 mM SDS enhances the sonoluminescence and sonophotoluminescence signals above that seen in pure water by a factor of about 2. Pyrene sonophotoluminescence was observed in ethylene glycol. The emission was quenched by the addition of I-, providing good evidence that emission was from pyrene in bulk solution and not within, or on the surface of cavitation bubbles.     

Sonication of pulp and paper effluent

Final effluent from a pulp and paper kraft mill was exposed to power ultrasound at 357 kHz with the aim of reducing color, turbidity, and chemical oxygen demand (COD). Absorbance measurements showed a bleaching of the effluent at wavelengths above 250 nm, indicating loss of aromatic chromophores. Effluent turbidity also decreased. Surprisingly, there was no observable decrease in COD, within experimental error. This is attributed to the presence of bicarbonate and sulfate ions in the final effluent, which react with hydroxyl radicals and effectively block the oxidation of organics in the effluent. This was demonstrated by sonicating solutions of potassium hydrogen phthalate (KHP) containing chloride, bicarbonate, or sulfate ions, which are the major inorganic ions in the final effluent studied. A solution containing only 2.3 mM KHP showed a 19% reduction in COD after 6 h of sonication. An identical solution with 200 ppm chloride also showed a 19% COD reduction. However, solutions with 700 ppm sulfate and 400 ppm bicarbonate showed COD reductions of 11% and 3%, respectively.     

Multibubble sonoluminescence in aqueous salt solutions

The sonoluminescence from aqueous solutions containing various salts in the concentration range of 0 to 7 M has been examined using 3.5 ms pulses of 515 kHz ultrasound. In almost all cases the sonoluminescence intensity recorded increased with increasing salt level until a critical concentration (in the range of 1-2 M) was reached. At salt levels above the critical concentration the signal intensity decreased sharply with increasing salt concentration. It is not possible to satisfactorily account for the trends in terms of changes in solution viscosity, rate of bubble coalescence, water vapour pressure, air/water interfacial tension or ionic strength. However, a good correlation of the increase in the signal with the extent of gas solubilisation in the solutions with changing salt concentration was observed. Possible reasons for the signal increase with the addition of salts and the marked decrease at high salt concentrations are discussed.     

Sonochemical removal of trihalomethanes from aqueous solutions

In this research, ultrasound irradiation was employed to degrade the trihalomethanes, THMs: CHCl₃, CHBrCl₂, CHBr₂Cl, CHBr₃, and CHI₃. The kinetics reaction rates and removal efficiencies of the THMs compounds, as a sole component in the aqueous solutions, were studied. Batch experiments were conducted at an ultrasonic frequency of 20 kHz and acoustic intensity of 3.75 W/cm². The first-order degradation rate constants and the sonolysis efficiencies followed the decreasing order of CHCl₃ > CHBrCl₂ > CHBr₂Cl > CHBr₃ > CHI₃. Up to 100% of the CHCl₃ was removed, while only 60% of the CHI₃ was sonodegraded, after 180 min sonication. The THMs vapor pressure was found to be the most important parameter affecting the sonodegradation kinetics and efficiency, while the bond dissociation energy and hydrophilic/hydrophobic characteristics of the THMs compounds were found to be of secondary importance.     

Sonoelectrochemical degradation of phenol in aqueous solutions

The sonoelectrochemical degradation of phenol in aqueous solutions with stainless steel electrodes and high-frequency ultrasound (850 kHz) was investigated. A 60% synergetic effect was obtained in the combined reaction system. High concentration of electrolyte (sodium sulfate) and a high electrical voltage are favorable conditions for the degradation of phenol. A nearly complete degradation of phenol was achieved with 4.26 g/L Na₂SO₄ and 30 V electrical voltages at 25 °C in 1 h. The degradation of phenol follows pseudo-first order kinetics. Considering costs and application, the energy efficiency of the reaction system with different reaction conditions was evaluated.     

Optical spectra of aqueous solutions of glutamine-tryptophan associates

The optical density and luminescence ability of aqueous solutions of glutamine-tryptophan depend on the degree of oxidation of the initial dry substances of dipeptide. Glutamine-tryptophan has a high associating ability, which increases if stored. The general form of the optical absorption and luminescence spectra of the associates differs little from the spectra of monomers. Among the spectral-optical symptoms of association of a substance in a solution for glutamine-tryptophan, we discovered the hypochromism and narrowing of the absorption spectra and shortening of the fluorescence lifetime. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 436–439, July–August, 2000.     

Fluorescence of aqueous solutions of commercial humic products

We have studied the spectral luminescence characteristics of aqueous solutions of humic products obtained from different raw material sources, and their behavior as the excitation wavelength increases from 270 nm to 355 nm. We have identified differences in the spectral properties of industrial humic products from coalified materials, lignin-containing organic waste, and humic products from plant raw material (peat, sapropel, vermicompost). We have shown that humic products from plant raw material have spectral properties closer to those for humic substances in natural water or soil than humic products from coalified materials.