Sonochemical Processes Research Articles

Sono-Fenton oxidation of formic acid/formate ions in an aqueous solution: From an experimental design to the mechanistic modeling

In order to establish an efficient oxidation process for the mineralization of a model wastewater containing formate species, the effects of some operating parameters such as Fenton reagent dosages and volume of the treated system were observed during the treatment by the ultrasonic assisted Fenton and modified Fenton processes. The mineralization kinetics was also examined based on the experimental data. The overall mineralization kinetics was found to be in the accordance with the first-order reaction kinetics. The results obtained within this work indicate an efficient mineralization, achieved by studied sonochemical oxidation processes. With the appropriate combination of operating parameters it is reasonable to expect a mineralization extent of 94%, corresponding to the complete degradation of formate species with the consequent formation and the degradation of oxalic acid in the system. The detailed mathematical model describing the ongoing process in the studies batch system was developed on the basis of a mechanistic reaction scheme, given in the frame of this work. The model has been validated, pointing at the significance of the assumed reactions and the accuracy of the corresponding rate constants.

Study of photochemical and sonochemical processes efficiency for degradation of dyes in aqueous solution

The degradation of two commercially available dyestuffs (C.I. Reactive Black 5 and C.I. Disperse Orange 25) by ultraviolet radiation (UV), ultrasonic irradiation (US), UV/H2O2 and US/H2O2 processes was investigated in a laboratory-scale batch photoreactor equipped with a 55 W immersed-type low-pressure mercury vapor lamp and a sonoreactor with low frequency (42 kHz) plate type transducer at 170 W of acoustic power. The toxicity was also evaluated in acute toxicity studies using Daphnia magna. Results showed that color removal efficiencies by US and US/H2O2 processes were negligible for both dyes. Almost complete disappearance of Reactive Black 5 (97.9%) in UV/H2O2 process was possible after 5 min of irradiation. The maximum color removal efficiency of Disperse Orange 25 after 10 min of irradiation, however, was only 9.2% and reached a maximum value of 41% after 120 min of irradiation. Pseudo-first order kinetics with respect to dyestuffs concentrations was found to fit all the experimental data. The results clearly showed that both dyes examined were toxic to D. magna and resulted in quite low LC50 values.

Sonophotochemical Degradation of Bisphenol A with Solid Catalysts

In order to investigate the degradation of bisphenol A (BPA) solution under sono, photo, sonocatalytic, photocatalytic and sonophotocatalytic processes, the BPA concentration and the total organic carbon (TOC) concentration were analyzed. The degradation rate of BPA was higher at high frequency (1 MHz) than at low frequency (300 kHz). At high frequency the acoustic period is shorter, and a high H2O2 concentration is therefore produced in aqueous solutions, which can enhance the degradation rate. The degradation rates of BPA were 0.0060, 0.0258, and 0.0451 min-1 under the sonocatalytic (1 MHz), photocatalytic and sonophotocatalytic processes respectively. The combined system of the sonochemical and photocatalytic processes can enhance the degradation rate of BPA compared with individual processes (sono and photocatalytic processes). The order of degradation of BPA (CuO>ZnO≈TiO2) and TOC (TiO2>ZnO>CuO) differed for each of the three types of catalysts. The separation characteristics of catalysts were dissimilar for each of the two frequencies.

A calorimetric study of energy conversion efficiency of a sonochemical reactor at 500 kHz for organic solvents

It would seem that the economic viability is yet to be established for a great number of sonochemical processes, owning to their perfectible ultrasonic equipments. Industrial scale sonoreactors may become more important as a result of mastering the parameters with influence on their energy balance. This work related the solvent type to the energy efficiency as the first step of a complex study aiming to assess the energy balance of sonochemical reactors at 500 kHz. Quantitative measurements of ultrasonic power for water and 10 pure organic solvents were performed by calorimetry for a cylindrically shaped sonochemical reactor with a bottom mounted vibrating plate. It was found that the ultrasonic power is strongly related to the solvent, the energy conversion for organic liquids is half from that of water and there is a drop in energy efficiency for filling levels up to 250 mm organic solvents. Surface tension, viscosity and vapor pressure influence the energy conversion for organic solvents, but it is difficult explain these findings based on physical properties of solvents alone. The apparent intensity of the atomization process shows a good agreement with the experimentally determined values for energy conversion for water and the solvent group studied here. This study revealed that to attain the same ultrasonic power level, more electrical energy is need for organic solvents as compared to water. The energy balance equation has been defined based on these findings by considering an energy term for atomization.

Novel sulfation of curdlan assisted by ultrasonication

This study carried out a novel sulfation process on curdlan. Results document that sulfation of the polysaccharide was more effective with the assistance of ultrasonication. Ultrasonication significantly increased the DS value of samples by almost fourfold (from about 0.030 to 0.115). Evaluation of the extent of sulfation has been made using FTIR, 1H NMR, 13C NMR and SEC. Both FTIR and 1H NMR spectra confirmed the occurrence of sulfation. The combined effect of ultrasonication and acid resulted in relatively small molecular weights (e.g., sample 360_360: MW ∼49.0 kDa), as opposed to curdlan (MW ∼807 kDa). This work contributes to better understanding of the molecular mechanism governing the sonochemical processes of polysaccharide modification with improved physicochemical properties, and potential biomedical application.

Ultrasonic Surface Modification of Electronics Materials

The electronics industry has always had a requirement for a range of metallised dielectric materials to form the conductive tracks used in many electronic products. It is essential that there is excellent adhesion between the dielectric material and the metal or other conductive track since without this failure of the device can occur. Surface modification of the substrate is one way to achieve good adhesion. Traditional wet chemical methods of surface modification employed in electronic manufacturing tend to be very cost effective but use hazardous, oxidizing, corrosive chemistry operate at elevated temperatures (high energy requirements) and require copious rinsing (high water usage). With the introduction of stricter health and safety and environmental legislation it is essential that ‘greener’ methods of surface modification are investigated. A study is currently being carried out evaluating sonochemical surface modification processes on a range of materials used in electronic manufacturing. This work has already shown that some materials can be surface modified using ultrasound through water. However, process times are still relatively long (30–60 minutes) and for the technique to become commercially viable they must be significantly reduced. One way to increase the ultrasonic intensity is to change the solvent and ‘solvent swell’ in a traditional surface modification process that can dramatically improve the adhesion of metal deposited on that material and a number of solvents have been screened. The efficacy of the whole process has been determined using methods such as scanning electron microscopy, contact angle measurements and the determination of adhesion of the plated metal.

Potential applications of sonochemistry in spent nuclear fuel reprocessing: A short review

The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitric acid medium. In order to minimize the volume of radioactive waste it seems interesting to generate the reactive species in situ in such solutions using ultrasonic irradiation without addition of salt-forming reagents. This review summarizes for the first time the versatile sonochemical processes with uranium, neptunium and plutonium in homogeneous nitric acid solutions and heterogeneous systems. The dissolution of refractory solids, ultrasonically driven liquid–liquid extraction and the sonochemical degradation of the volatile products of organic solvent radiolysis issued from PUREX process are considered. Also the guidelines for required further work to ensure successful application of the studied processes at industrial scale are discussed.

Influence of a high-intensity ultrasonic field on the removal of natural organic compounds from water

Organic compounds, which are considered water pollutants, have the ability to react with chlorine or other oxidants leading to the formation of products which pose a significant threat to human health. Humic substances play an important role in the formation of disinfection by-products. Therefore, the removal of organic compounds in the process of water treatment is of great importance. The application of ultrasound initiates a number of physicochemical processes in water which can be used in water treatment technologies, e.g. coagulation or adsorption. These methods, as well as the ion-exchange process, are applied in order to remove organic contaminants. With reference to the theoretical fundamentals of ultrasound, some sonochemical processes can result in a decrease in the content of color organic compounds in water. Increasing the intensity of ultrasonic field enhances the occurrence of sonochemical processes including the destruction of high-molecular organic compounds or the oxidation reactions with...

Sonochemistry and Sonoluminescence under Simultaneous High- and Low-Frequency Irradiation

Sonoluminescence emission, sonochemiluminescence from luminol and the sonochemical yield of hydrogen peroxide were studied under a dual frequency field combining low-frequency (20 kHz) and high-frequency (355 kHz) ultrasound. Under certain conditions it was found that a synergistic enhancement of both sonoluminescence and sonochemical processes could be attained. Ultrasound parameters including pulsing conditions and sonication time were found to sensitively influence the efficiency of the dual-frequency mode operation. Possible mechanisms responsible for the dual-frequency effects are discussed.

The research on the possibility of ultrasound field application in iron removal of water

The paper describes the preliminary researches on the influence of the ultrasounds of diversified intensity (22 and 24 kHz) on the content iron compounds in water. For the researches, variable operational parameters were used, such as: the vibration amplitude and the exposure time (1–5 min). The substrate was: distilled water and natural river water of intensive colour, prepared by iron Fe(II) compounds (iron ammonium-sulphate). The effect of ultrasounds was researched as a result of the influence of sonochemical oxidation processes and ultrasound coagulation on iron in the ionized form (of ions Fe 2+) and on iron–organic complexes in the lowionized or colloidal form. The share of sonochemical and coagulation processes depends on the parameters determining the ultrasounds intensity. The effects of the iron removal were researched at the low and high intensity determining the strain of cavitation processes. As a result, the changes of iron content (Fe 2+, Fe 3+, Fe og) and the colour of water exposed to ultrasound field of variable parameters were presented. The effectiveness of the researched processes was analysed from the point of view of the possibility of determinate intensity ultrasound usage as an unconventional method of the removal of iron from water.

Modelling of sonochemical processes in water treatment

The mechanisms and kinetics of the sonochemical degradation of organic molecules in water are relatively complex since several parameters such as physicochemical properties, substrate concentration, water matrix, reactor geometry, ultrasound properties (frequency, power, emission system) all typically affect the process. In this work, simple kinetic models were used to predict the degradation of 2-chlorophenol and sodium dodecylbenzene sulphonate in aqueous solutions and verified against experimental data taken from previous studies. A pseudo-first order kinetic expression can adequately describe the degradation of the phenolic substrate, while a heterogeneous model based on the Langmuir-Hinshelwood equation is suitable for the surfactant degradation.

Ultrasonic Evidence of Hydrophobic Interactions. Effect of Ultrasound on Benzoin Condensation and Some Other Reactions in Aqueous Ethanol

The kinetics of KCN-catalyzed benzoin condensation of benzaldehyde in water and ethanol-water binary mixtures was investigated both under ultrasound at 22 kHz and without sonication. Thermodynamic activation parameters were calculated from kinetic data obtained at 35, 50, and 65 degrees C. Evidence that ultrasound can retard reactions is reported and hence a direct proof that sonochemical processes occur in the bulk solution. Former results and literature data for ester hydrolyses and tert-butyl chloride solvolysis are involved in the discussion. A quantitative relationship between sonication effects and the hydrophobicity of reagents is presented for the first time. Ultrasound affects hydrophobic interactions with the solvent, which are not manifested in conventional kinetics. When it suppresses the stabilization of the encounter complexes between reagents, sonication hinders the reaction but accelerates it when it perturbs the hydrophobic stabilization of the ground state of a reagent.

Sonochemistry on primordial Earth – Its potential role in prebiotic molecular evolution

Sonochemical processes are known to occur in nature and have occurred ever since there was liquid water on Earth. We advance a hypothesis that complex carbonaceous compounds, the probable precursors of life, were produced from simple primordial molecules by sonochemical processes in breaking waves of primordial seas or oceans. Our calculations show that these processes were much more common on Earth than other pathways, suggested for the formation of prebiotic complex carbonaceous compounds. The high occurrence rate of sonochemical events in breaking sea waves and the qualitative difference between sonochemical processes and other shock phenomena might have enabled formation of a variety of complex carbonaceous compounds, including amino acids, nucleotides and nucleosides, the precursors of RNA or DNA.

Impact of ultrasound on hydrophobic interactions in solutions: Ultrasonic retardation of benzoin condensation

Kinetics of the benzoin condensation of benzaldehyde in presence of KCN as the catalyst in water and in ethanol–water binary solutions were investigated without sonication and under ultrasound at 22 kHz. A statistically significant 20% decrease of the rate was observed in water. The retardation effect of ultrasound gradually decreases up to 45 wt% ethanol content. We report an evidence of ultrasonic retardation of reactions and thereby a direct evidence for sonochemical processes in the bulk solution. Ultrasound can disturb solvation of the species in the solution. If breaking down the stabilization of the encounter complexes between the reagents, sonication hinders the reaction while perturbation of the solvent-stabilization of the reagents accelerates the reaction.

A review of methods for synthesis of nanostructured metals with emphasis on iron compounds

AbstractSynthesis of metal nanoparticles with specific properties is a newly established research area attracting a great deal of attention. Several methods have been put forward for synthesis of these materials, namely chemical vapor condensation, arc discharge, hydrogen plasma—metal reaction, and laser pyrolysis in the vapor phase, microemulsion, hydrothermal, sol-gel, sonochemical, and microbial processes taking place in the liquid phase, and ball milling carried out in the solid phase.The properties of metal nanoparticles depend largely on their synthesis procedures. In this paper the fundamentals, advantages, and disadvantages of each synthesis method are discussed.

Synthesis of gold/magnetic iron oxide composite nanoparticles for biomedical applications with good dispersibility

Composite nanoparticles consisting of gold and magnetic iron oxide were synthesized in an aqueous solution system by sonochemical and radiochemical processes. Small Au nanoparticles were immobilized on the surface of the iron oxide nanoparticles. Removal of the excess polymers in the solution leads to the good dispersibility of the composite nanoparticles. The composite nanoparticles are expected as a type of nanocarrier for biomedical applications.

The Sonochemical Insertion of Nanomaterials into Mesostructures

AbstractFor Abstract see ChemInform Abstract in Full Text.

Fe(III)-Enhanced Sonochemical Degradation Of Methylene Blue In Aqueous Solution

The sonochemical degradation rate of Methylene Blue (MB) is markedly increased in the presence of Fe(Ill), a rather inexpensive reagent for the application of sonochemistry to wastewater treatment. The effect of Fe(lll) is due to a sonochemically induced Fenton reaction, where both reactants (Fe(ll) and H2O2) are sonochemically synthesized. Hydroperoxide/superoxide, generated upon sonochemical processes in aerated solution, is a key species involved in both Fe(lll) reduction to Fe(ll) and in the production of H2O2. The Fenton reaction between Fe(ll) and H2O2 then produces hydroxyl radicals, enhancing the degradation of MB. A further enhancement of the degradation of the substrate in the presence of Fe(lll) takes place upon addition of H2O2, which is likely to favor the Fenton process. Interestingly, H2O2 alone, in the absence of Fe(lll), has a very limited effect on the sonochemical degradation rate.

Sonochemical degradation of polycyclic aromatic sulfur hydrocarbons (PASHs) in aqueous solutions exemplified by benzothiophene

The degradation of polycyclic aromatic sulfur hydrocarbons (PASHs) in aqueous solutions due to sonochemical processes was studied. Benzothiophene (BT), and dibenzothiophene (DBT) in addition to two polycyclic aromatic hydrocarbons, namely phenanthrene (Phe) and naphthalene (Nap) were compared. Results showed that all polycyclic aromatic compounds were decomposed rapidly following a pseudo‐first‐order kinetics upon ultrasonic irradiation in aqueous solutions. The rate constant increased with increasing pH and decreased with increasing initial benzothiophene concentration. Whereas, for temperature, the rate increased with temperature up to 50°C then decreased upon further increase in temperature above 50°C. Hydroxybenzothiophenes, dihydroxy‐benzothiophenes, and benzothiophene‐dione were identified as major intermediates. Also evolution of carbon dioxide and sulfite was observed. Hydroxyl radicals play the major role in the decomposition of PASHs. The toxicity of sonochemically treated solutions was evaluated by monitoring the respiration rate of E. coli. Results indicate that a sonochemically treated benzothiophene sample improved the respiration rate of E. coli compared to an untreated sample.

The Sonochemical Insertion of Nanomaterials into Mesostructures

Ultrasound radiation has been recently used for the synthesis of mesoporous materials (MSPM). The main advantages are manifested in the short preparation time and thicker walls leading to a more hydrothermally stable structure.1 This preparation method has already been reviewed.2 The discovery of MSP materials led immediately to the development of many experimental methods for the deposition of materials, especially catalytic materials, into the mesopores. Impregnation, thermal spreading, ion adsorption, and the most recent method3 in which colloidal gold solution is premixed with the precursors for the preparation of the MSPM, are among the methods used for the insertion of materials into the mesopores. Sonochemistry was also employed for this purpose. We will outline in this article the use of the sonochemical processes for the insertion of nanomaterials into the pores of MSPM. We will explain how this process is conducted, to what extent the materials are deposited in the pores and what is the mechanism for the insertion. An example will be given for the preparation of Ru/MSP TiO2 and its application as a catalyst in the wet air oxidation of succinic acid and acetic acid, which often appear as the ultimate intermediates in oxidation of many organic pollutants.