Sonolysis of aqueous 4-nitrophenol at low and high pH

The sonolysis of 4-nitrophenol in argon-saturated aqueous solution has been studied at 321 kHz. In order to evaluate separately the effect of OH radicals that are formed in the cavitational bubble and part of which react in the aqueous phase with this substrate, radiolytic studies in N2O-saturated solutions were carried out for comparison. A detailed product study of the sonolysis of 4-nitrophenol solutions shows that at pH 10, where 4-nitrophenol is deprotonated (pKa = 7.1), its sonolytic degradation is fully accounted for by OH-radical-induced reactions in the aqueous phase. At this pH, the sonolytic yield of H2O2 resulting from OH radical recombination in the solution, measured as a function of the 4-nitrophenol concentration, is reduced in line with the scavenging capacity of the 4-nitrophenolate. In contrast, at pH 4 the formation of H2O2 is already fully suppressed when the solution is 7 x 10(-4) mol dm-3 in 4-nitrophenol, and oxidative-pyrolytic degradation predominates, as exemplified by the large yields of CO and CO2 which are accompanied by a large H2 yield. The basis of this difference in behavior is a hydrophobic enrichment of 4-nitrophenol (which is undissociated at pH 4) at the interface of the cavitational bubble by a factor of about 80. The pH dependence of the yields of the pyrolytic products reflects the hydrolytic equilibrium concentration of 4-nitrophenol. The paper also demonstrates that the complexity of this sonochemical system precludes its use a gauge to determine the temperature in the interior of the cavitational bubble.     

Zur Materialabhängigkeit des Massenschwächwächungskoeffizienten von β-Strahlung

Catalase was desactivated in aqueous solution by irradiation with gamma-rays or ultrasound with nearly equal yields, if the applied doses were related to the response of a chemical dosimeter. The decrease of the enzymatic activity proceeded in parallel to the release of ¹²³iodine from ¹²⁵I-(iodo)-catalase. The same competition kinetics were observed in the radiolytic and sonolytic bleaching of p-nitrosodimethylaniline in the presence of catalase, respectively. It is concluded, that OH-radicals were, responsible for the sonolytic destruction of catalase. Phospholipids exerted a protective effect, which may be useful in the preparation of liposomes as carriers of macromolecules.     

On the gamma-radiolysis of aqueous solutions of cerium(III) - ethylmediamine tetra-acetate

A reinvestigation of the radiolytic behaviour of aqueous solutions of Ce(III)-EDTA (in alkaline medium) has revealed several new features. Earlier mechanism involving OH radicals and molecular hydrogen peroxide is modified regarding the role of the latter and is found to be more consistent with the results. Scavenger studies lend further support to the proposed mechanism of radiolytic degradation.     

OH-radical formation by ultrasound in aqueous solution--Part II: Terephthalate and Fricke dosimetry and the influence of various conditions on the sonolytic yield

Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombination product H2O2 in aqueous solutions under various operating conditions (nature of operating gas, power, frequency, temperature). For example, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321 kHz, and a power of 170 W kg-1, the total yield [G(.OH) + 2 G(H2O2)], equals 16 x 10(-10) mol J-1. This represents the total of .OH that reach the liquid phase from gas phase of the cavitating bubble. The higher the solute concentration, the lower the H2O2 production as more of the OH free radicals are scavenged, in competition with their recombination. Fricke dosimetry, in the absence and presence of Cu2+ ions, shows that the yield of H atom reaching the liquid phase is much lower, with G(H.) of the order of 3 x 10(-10) mol J-1. These sonolytic yields are smaller in solutions that are at the point of gas saturation, and increase to an optimum as the initial sonication-induced degassing and effervescence subsides. The probing of the sonic field has shown that the rate of sonolytic free-radical formation may vary across the sonicated volume depending on frequency and power input.     

Comparison of chemiluminescence methods for analysis of hydrogen peroxide and hydroxyl radicals

Assessment of alpha radiolysis influence on the chemistry of geologically disposed spent fuel demands analytical methods for radiolytic product determination at trace levels. Several chemiluminescence methods for the detection of radiolytic oxidants hydrogen peroxide and hydroxyl radicals are tested. Two of hydrogen peroxide methods use luminol, catalyzed by either μ-peroxidase or hemin, one uses 10-methyl-9-(p-formylphenyl)-acridinium carboxylate trifluoromethanesulfonate and one potassium periodate. All recipes are tested as batch systems in basic conditions. For hydroxyl radical detection luminophores selected are 3-hydroxyphthalic hydrazide and rutin. Both methods are tested as batch systems. The results are compared and the applicability of the methods for near-field dissolution studies is discussed.     

Improved sonolytic hydrolysis of peptides in aqueous solution with addition of 1,4-benzenedithiol

Described here is the sonolytic hydrolysis of peptides achieved by treatment of aqueous solution to which the radical scavenger 1,4-benzenedithiol (1,4-BDT), which has hydrogen donating ability, has been added. Mass spectrometric analysis of the products of sonolytic hydrolysis gave information about amino acid sequence of the peptides without any byproducts. The additive 1,4-BDT improves the sonolytic hydrolysis of peptides in terms of the rate of hydrolysis reaction and the amount of additive required when compared to catechol, a previously reported additive. The sonolytic hydrolysis of peptides differs from both acid hydrolysis and hydrogen atom-induced dissociation named matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD), in characteristics. We propose a mechanistic reaction for the sonolytic hydrolysis of peptides, based on the mechanisms of both acid hydrolysis and MALDI-ISD processes. The sonolytic hydrolysis of peptides upon addition of hydrogen donating radical scavengers can be rationalized via the attachment of a hydrogen atom to the carbonyl oxygen with subsequent hydrolysis.     

Modeling of ultrasonic degradation of non-volatile organic compounds by Langmuir-type kinetics

Sonochemical degradation of phenol (Ph), 4-isopropylphenol (4-IPP) and Rhodamine B (RhB) in aqueous solutions was investigated for a large range of initial concentrations in order to analyze the reaction kinetics. The initial rates of substrate degradation and H₂O₂ formation as a function of initial concentrations were determined. The obtained results show that the degradation rate increases with increasing initial substrate concentration up to a plateau and that the sonolytic destruction occurs mainly through reactions with hydroxyl radicals in the interfacial region of cavitation bubbles. The rate of H₂O₂ formation decreases with increasing substrate concentration and reaches a minimum, followed by almost constant production rate for higher substrate concentrations. Sonolytic degradation data were analyzed by the models of Okitsu et al. [K. Okitsu, K. Iwasaki, Y. Yobiko, H. Bandow, R. Nishimura, Y. Maeda, Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration OH radicals and azo dyes, Ultrason. Sonochem. 12 (2005) 255–262.] and Seprone et al. [N. Serpone, R. Terzian, H. Hidaka, E. Pelizzetti, Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates, J. Phys. Chem. 98 (1994) 2634–2640.] developed on the basis of a Langmuir-type mechanism. The five linearized forms of the Okitsu et al.’s equation as well as the non-linear curve fitting analysis method were discussed. Results show that it is not appropriate to use the coefficient of determination of the linear regression method for comparing the best-fitting. Among the five linear expressions of the Okitsu et al.’s kinetic model, form-2 expression very well represent the degradation data for Ph and 4-IPP. Non-linear curve fitting analysis method was found to be the more appropriate method to determine the model parameters. An excellent representation of the experimental results of sonolytic destruction of RhB was obtained using the Serpone et al.’s model. The Serpone et al.’s model gives a worse fit for the sonolytic degradation data of Ph and 4-IPP. These results indicate that Ph and 4-IPP undergo degradation predominantly at the bubble/solution interface, whereas RhB undergoes degradation at both bubble/solution interface and in the bulk solution.     

Ultrasonic degradation of aqueous carboxymethylcellulose: effect of viscosity, molecular mass, and concentration

It is well established that prolonged exposure of solutions of macromolecules to high-energy ultrasonic waves produces a permanent reduction in viscosity. It is generally agreed as well and also this study proved the hydrodynamic forces to have the primary importance in degradation. According to this study the sonolytic degradation of aqueous carboxymethylcellulose polymer or polymer mixtures is mainly depended on the initial dynamic viscosity of the polymer solution when the dynamic viscosity values are in the area range enabling intense cavitation. The higher was the initial dynamic viscosity the faster was the degradation. When the initial dynamic viscosities of the polymer solutions were similar the sonolytic degradation was dependent on the molecular mass and on the concentration of the polymer. The polymers with high molecular mass or high polymer concentration degraded faster than the polymers having low molecular mass or low polymer concentration. The initial dynamic viscosities were adjusted using polyethyleneglycol.     

Sonochemical and sonophotocatalytic degradation of malachite green: the effect of carbon tetrachloride on reaction rates

A comparative study between the sonolytic, photocatalytic and sonophotocatalytic oxidation processes of aqueous solutions of malachite green was carried out in the presence of carbon tetrachloride, under a low power ultrasonic field (<15 W) and using titanium dioxide as a photocatalyst. The effect of a number of parameters such as ultrasonic intensity, TiO2 crystalline structure and the presence of CCl4 were studied using an inexpensive reactor. Enhanced rates of sonolytic degradation of malachite green in the presence of CCl4 were demonstrated. On the other hand, the simultaneous use of sonolysis and photocatalysis in the presence of CCl4 does not improve the degradation rate of malachite green in comparison with the one obtained using only sonolysis, but it makes possible a faster oxidative degradation of some reaction intermediaries. Finally, in air saturated solutions both processes, the sonolytic and the photocatalytic one, follow a first-order rate law.     

Sonolytic and sonophotolytic degradation of Carbamazepine: Kinetic and mechanisms

An in-depth investigation on the ultrasonic decomposition of Carbamazepine (CBZ), one of the most regularly identified drugs in the environment, was conducted. The effects of diverse variables were evaluated, such as frequency, power, solution pH, initial CBZ concentration and varied inorganic anions. Reaction order was determined on the basis of analyzing reaction kinetics of CBZ degradation. The sonophotolysis and photolysis of CBZ was also examined in this contribution. The influence of water composition on the sonolytic and sonophotolytic elimination of CBZ was analyzed. Additionally, 21 intermediates were identified during sonolytic degradation of CBZ based on LC/ESI-MS/MS analysis, among which two escaped from the detection in previous studies. Possible decay pathways were proposed accordingly. The epoxidation, cleavage of double bond, hydration, hydroxylation, ring contraction and intramolecular cyclization were believed to be involved in sonochemical degradation of CBZ.     

Nonenzymatic glycosylation of human serum albumin: Fluorescence and chemiluminescence behavior

In the present study the progress of the cross-linking reaction between glyceraldehyde (GCA) and human serum albumin (HSA) was followed by monitoring the development of new absorption bands characteristic of the cross-linked product. Generation of electronically excited species (EES) during horseradish peroxidase (HRP)-catalyzed oxidation of glycosylated HSA was followed by measuring direct chemiluminescence. It was found that adducts of HSA with GCA in the presence of HRP are capable of forming EES. The mechanism of EES generation is discussed further on the basis of fluorescence and chemiluminescence measurements. Formation of EES in studied systems thus could be a possible source of free radicals generatedin vivo during age- and diabetes-related complications.     

Sonophotolytic diethyl phthalate (DEP) degradation with UVC or VUV irradiation

This study investigated the degradation of diethyl phthalate (DEP) by sonolytic, photolytic and sonophotolytic processes. Two types of UV lamps, UVC (254 nm) and VUV (185 nm + 254 nm), were combined with ultrasound (283 kHz). The pseudo-first order degradation rate constants were in the order of 10^?1–10^?3 min^?1 depending on the processes. The sonolytic DEP degradation rate increased with increasing applied power. Photolytic or sonophotolytic degradation of DEP when using a VUV lamp appeared to be effective because the photo ?? (UVC/VUV) resulted in a significantly faster degradation than the photo ? (UVC) processes due to the higher photon energy and higher hydroxyl radical generation by homolysis of water by VUV. Significant degradation and mineralization (TOC) of DEP were observed with the combined sonophotolytic processes. Moreover, synergistic effects of 1.68 and 1.23 were exhibited at DEP degradation of the sonophoto I and sonophoto II processes, respectively. This was attributed to the UV-induced dissociation of hydrogen peroxide (H₂O₂) generated by the application of US to hydroxyl radicals. Therefore, US in sonophotolytic processes can play an important role in enhancing DEP degradation. Moreover, the sonophoto ?? process is more effective on the mineralization and biodegradability of DEP.     

Degradation of Acid Blue 25 in aqueous media using 1700 kHz ultrasonic irradiation: ultrasound/Fe(II) and ultrasound/H2O2 combinations

In this work, the sonolytic degradation of an anthraquinonic dye, C.I. Acid Blue 25 (AB25), in aqueous phase using high frequency ultrasound waves (1700 kHz) for an acoustic power of 14 W was investigated. The sonochemical efficiency of the reactor was evaluated by potassium iodide dosimeter, Fricke reaction and hydrogen peroxide production yield. The three investigated methods clearly show the production of oxidizing species during sonication and well reflect the sonochemical effects of high frequency ultrasonic irradiation. The effect of operational conditions such as the initial AB25 concentration, solution temperature and pH on the degradation of AB25 was studied. Additionally, the influence of addition of salts on the degradation of dye was examined. The rate of AB25 degradation was dependent on initial dye concentration, pH and temperature. Addition of salts increased the degradation of dye. Experiments conducted using distilled and natural waters demonstrated that the degradation was more efficient in the natural water compared to distilled water. To increase the efficiency of AB25 degradation, experiments combining ultrasound with Fe(II) or H₂O₂ were conducted. Fe(II) induced the dissociation of ultrasonically produced hydrogen peroxide, leading to additional OH radicals which enhance the degradation of dye. The combination of ultrasound with hydrogen peroxide looks to be a promising option to increase the generation of free radicals. The concentration of hydrogen peroxide plays a crucial role in deciding the extent of enhancement obtained for the combined process. The results of the present work indicate that ultrasound/H₂O₂ and ultrasound/Fe(II) processes are efficient for the degradation of AB25 in aqueous solutions by high frequency ultrasonic irradiation.     

A sensitive chemical procedure for monitoring the radiolytic oxidation of proteins at γ-ray dosages down to 1 Krad

Abstract

The radiolytic degradation of proteins in oxygenated solution is initiated by the attack of OH radicals at a multiplicity of main-chain and side-chain loci to give a wide variety of oxidized protein sites. A major fraction of these oxidation reactions lead to the introduction of reactive carbonyl groups into the protein co-valent structure. With γ-rays the total carbonyl yield correspond to G(>CO)_t ? 1 for a number of different proteins. Outlined here is a sensitive chemical-spectrophotometric procedure for quantitatively monitoring G(>CO)_t over a dose range of interest in radiation biology (1 to 50 Krad). Data obtained with pepsin, α-chymotryps in and β-lactoglobulin are discussed.     

Role of H202 in the radiolysis of B-group vitamins in neutral aqueous solutions. part I. reactions with vitamin radicals produced by oh radical reaction

The radiolytic decomposition of the B-group vitamins in 0.1 mM neutral aqueous solutions has been studied in oxygenated as well as N₂O saturated solutions. In the former G(-Vit) and G(H₂O₂) values suggested the occurrence of reaction between the vitamin radioals and the H₂O₂ formed during radiolysis in the oase of pyridoxin, folic acid and cyanocobalamin. The occurrence of this reaction was directly confirmed in N₂O saturated solutions initially containing hydrogen peroxide. In this case an increased vitamin decomposition and a parallel consumption of the H₂O₂ were observed. Reactivities of different types of radicals with H₂0₂ are discussed.     

Sonolytic degradation of halogenated organic compounds in groundwater: mass transfer effects

Organic pollutants in liquid exposed to acoustic waves behave differently according to their physical and chemical properties. Laboratory batch experiments of sonication for the degradation of trichloroethylene (TCE) and ethylene dibromide (EDB) were carried out in groundwater at 20 kHz, and 12.5 and 35 W/cm(2). A theoretical model for the batch sonication system was derived to examine the mass transfer dependency of the ultrasonic degradation. Experimental results were supported with model predictions suggesting that both liquid phase diffusion coefficient and Henry's law constant are important parameters for the sonolytic degradation of the halogenated organic compounds in groundwater. When compared with the effect of the diffusion coefficient, Henry's constant exerts a greater influence on sonolytic degradation. When Henry's constant exceeds a value of 1 (volume/volume ratio), however, it no longer has much influence on the degradation process. The results also suggest that degradation is enhanced with an increase in ultrasonic power probably due to a greater bubble residence time and the formation of larger bubble at high-energy intensities.     

Sonolytic degradation of volatile pollutants in natural ground water: conclusions from a model study.

In order to evaluate the possibilities of an ultrasound-based cleaning technology, the effects of sonication on pollutants in a contaminated natural ground water were investigated. After the discussion of the results from this model study on the sonolytic degradation of volatile organic compounds, some consequences are reported and the important role of water components is described. Furthermore, the use of sonication as a cleaning technology for polluted water is discussed based on the conclusions from this study.     

Analysis of sonolytic degradation products of azo dye Orange G using liquid chromatography-diode array detection-mass spectrometry

In this paper, seven new sonolytic degradation products of Orange G were found and identified using powerful analytical techniques such as liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS), tandem mass spectrometry (MS/MS), and liquid chromatography with diode-array detection (LC-DAD). Each technique provided complementary information for the degradation products identification. In order to resolve the MS and MS/MS spectra obtained, the separation conditions were optimized. Among them, Orange G was unambiguously identified based on its abundant [M-H](-) ion, [M+H](+) ion, ultra-violet and visible spectra, retention time, and tandem mass spectrometric analysis compared with an authentic standard. The seven new degradation products were tentatively identified based on ultra-violet and visible spectra, [M-H](-) ions, and tandem mass spectrometry. The neutral losses of SO(2), SO(3), N(2) and H(2)O for MS/MS spectra which appear to be characteristic of the negative ion mode were observed. Based on this by-product identification, a possible multi-step degradation scheme is proposed. The analysis results of degradation products reveal that the degradation mechanism proceeds via reductive cleavage of the azo linkage, as well as intermolecular dehydration and desulfonation due to the powerful oxidizing hydroxyl radicals as well as hydrogen radical.     

How do dissolved gases affect the sonochemical process of hydrogen production? An overview of thermodynamic and mechanistic effects – On the “hot spot theory”

Although most of researchers agree on the elementary reactions behind the sonolytic formation of molecular hydrogen (H₂) from water, namely the radical attack of H₂O and H₂O₂ and the free radicals recombination, several recent papers ignore the intervention of the dissolved gas molecules in the kinetic pathways of free radicals, and hence may wrongly assess the effect of dissolved gases on the sonochemical production of hydrogen. One may fairly ask to which extent is it acceptable to ignore the role of the dissolved gas and its eventual decomposition inside the acoustic cavitation bubble? The present opinion paper discusses numerically the ways in which the nature of dissolved gas, i.e., N₂, O₂, Ar and air, may influence the kinetics of sonochemical hydrogen formation. The model evaluates the extent of direct physical effects, i.e., dynamics of bubble oscillation and collapse events if any, against indirect chemical effects, i.e., the chemical reactions of free radicals formation and consequently hydrogen emergence, it demonstrates the improvement in the sonochemical hydrogen production under argon and sheds light on several misinterpretations reported in earlier works, due to wrong assumptions mainly related to initial conditions. The paper also highlights the role of dissolved gases in the nature of created cavitation and hence the eventual bubble population phenomena that may prevent the achievement of the sonochemical activity. This is particularly demonstrated experimentally using a 20 kHz Sinaptec transducer and a Photron SA 5 high speed camera, in the case of CO₂-saturated water where degassing bubbles are formed instead of transient cavitation.     

Removal of dinitrotoluenes and trinitrotoluene from industrial wastewater by ultrasound enhanced with titanium dioxide

Oxidative degradation of dinitrotoluenes (DNTs) and 2,4,6-trinitrotoluene (TNT) in wastewater was conducted using ultrasonic irradiation combined with titanium dioxide (TiO(2)). The batch-wise experiments were carried out to elucidate the influence of various operating parameters on the sonolytic behavior, including power intensity, TiO(2) dosage, acidity of wastewater, reaction temperature and oxygen dosage. It is worthy to note that the nitrotoluene contaminants could be almost completely eliminated by sonochemical oxidation enhanced significantly with the addition of TiO(2) due to the supply of adsorbent and/or excess nuclei. High destruction rate of nitrotoluenes could be achieved by increasing the acidity of wastewater and decreasing the reaction temperature. According to the result given by pyrolysis/gas chromatograph-mass spectrometer (Pyrolysis/GC-MS), it is postulated that DNTs adsorbed on TiO(2) preliminarily undergo denitration pathway to o-mononitrotoluene (MNT) or oxidation pathway to 1,3-dinitrobenzene (DNB), respectively. Further, based on the spectra obtained from GC-MS, it is proposed that DNTs dissolved in wastewater proceed with similar reaction pathways as those adsorbed on TiO(2). Besides, oxidative degradation of 2,4,6-TNT results in the formation of 1,3,5-trinitrobenzene (TNB). Apparently, the sonolytic technique established is promising for direct treatment of wastewater from TNT manufacturing process.