Sonochemical decomposition of organic acids in aqueous solution: understanding of molecular behavior during cavitation by the analysis of a heterogeneous reaction kinetics model

Impact of sonication power on the degradation of paracetamol under single- and dual-frequency ultrasound

The effects of sonication power on the ultrasonic cavitation and sonochemistry as well as the degradation of paracetamol were studied and compared for single- and dual-frequency sonoreactors. For the single-frequency sonication, a 500 kHz plate transducer was employed, with three different calorimetric powers of 8.4, 16.7 and 27.9±3.9 W. For the dual-frequency sonication, the plate transducer was perpendicularly coupled with a low-frequency 20 kHz ultrasonic horn, and three calorimetric powers of 27.9, 33.4, 44.6±3.9 W were studied. At all the studied powers, dual-frequency sonication led to a synergistic effect in the degradation of paracetamol, though varying the power of the horn did not affect the degradation rate. A comparison of the degradation data versus the yield of oxidants as well as the overall intensities of sonoluminescence and sonochemiluminescence suggested the degradation is by the action of oxidants near the surface of the bubbles as the major reaction mechanism. Despite the enhancement observed for the degradation, dual-frequency sonication had no significant effect on the yield of either of the oxidants, regardless of the applied power to the horn. In contrast, dual-frequency sonication decreased the overall sonoluminescence and sonochemiluminescence intensities at all powers studied, suggesting that the application of dual-frequency sonication reduces the size of cavitation bubbles. Normal distribution function analysis confirmed dual-frequency sonication resulted in smaller sonoluminescing bubbles, hence the reduction in the sonoluminescence intensity. The increase in degradation rate under DFUS is attributed to the increase in the transfer of paracetamol from the bulk towards the bubbles. As a result, the availability of the pollutant molecules in the vicinity of the bubbles to react with HO• would increase and consequently, the degradation rate would enhance under DFUS.

General analytical solution expressions for analyzing Langmuir-type kinetics of sonochemical degradation of nonvolatile organic contaminants in water

Detailed kinetic studies of the ultrasonic decomposition of contaminants in water are scarce. Most of the work has used a pseudo-first order kinetics law, which is unrealistic. The model based on a Langmuir-type mechanism has been shown to fit the sonolytic decomposition data well, especially by using the non-linear technique. To avoid unrealistic assumptions, general analytical solutions to a time-dependent non-linear Langmuir-type equation may be the appropriate method. In this work, the sonolytic oxidation of organic contaminants, i.e., naphthol blue black and furosemide, in water was analyzed using two general analytical solution expressions of the Langmuir-type kinetics model, which describe the pollutant concentration in water. The validity of the two general analytical solution expressions was tested under a diversity of operating conditions, such as initial substrate concentration and varying ultrasonication frequency and intensity. As the initial substrate concentration increased, the sonolytic oxidation kinetics decreased, while the initial ultrasonic decomposition rate increased and then plateaued. Consequently, a heterogeneous kinetics equation based on a Langmuir-type mechanism can be used to simulate the sono-decomposition process. The decomposition yield increased with increasing sonication intensity and decreasing frequency. The two analytical solution expressions seem to be in excellent agreement with the experimental results of the sonochemical decomposition of the nonvolatile organic contaminants tested for the different operating conditions examined. These expressions provide a valuable tool for the analysis and simulation of advanced sonochemical oxidation processes under various experimental conditions.

Effects of gas saturation and sparging on sonochemical oxidation activity under different liquid level and volume conditions in 300-kHz sonoreactors: Zeroth- and first-order reaction comparison using KI dosimetry and BPA degradation

The sonochemical oxidation activity was investigated for gas saturation and gas sparging under various liquid levels and volumes in 300 kHz sonoreactors. The liquid levels and volumes ranged from 5λ (25 mm, 0.47 L) to 50λ (250 mm, 4.30 L) and two gas mixtures, Ar:O₂ (75:25) and N₂:O₂ (75:25), were used. Two types of reaction kinetics were observed to quantitatively analyze the sonochemical oxidation reactions: zero-order (KI dosimetry: C₀ = 60.2 mM) and first-order (Bisphenol A (BPA) degradation: C₀ = 0.043 mM). The masses of the sonochemical oxidation reactions were calculated and compared rather than the concentrations to more accurately compare the sonochemical oxidation activity under different liquid volume conditions. First, as the liquid level or volume increased for the zero-order reactions, the concentration of I₃^- ions representing the volume-averaged activity decreased substantially for gas saturation owing to the increase in liquid volume. However, gas sparging substantially enhanced sonochemical oxidation activity, and the mass of I₃^- ions representing the total activity remained constant as the liquid level increased from 20λ because of the improved liquid mixing and a shift in the sonochemical active zone. Second, as evidenced by the zero-order reactions, the concentration of BPA decreased considerably as the liquid level or volume increased in the first-order reactions. When gas sparging was used, higher reaction constants were obtained for both gas mixtures, ranging from 40λ to 50λ. However, a comparison of the sonochemical oxidation activity in terms of the degraded mass of BPA was inapplicable as the concentration of BPA decreased substantially and a lack of reactants occurred for the lower liquid level and volume conditions as the irradiation time elapsed. Instead, using the first-order reaction constant, a comparison of the required reaction times for a specific removal efficiency (30%, 60%, and 90%) was proposed. Gas sparging can substantially reduce the reaction time required for a liquid level of 40λ or higher.

Analytical insights into the detoxification process and characterization of a traditional metallopharmaceutical formulation

Metallopharmaceuticals possess unique medicinal properties and have been used since ancient times. In spite of the inclusion of several metals and minerals, there is an increased interest in metallo-drugs for clinical and research purposes because of their immense therapeutic efficiency and non-toxic claim, as they are processed in addition to specific poly herbals. Sivanar Amirtham is one of the traditional metallopharmaceuticals used in Siddha medicine to treat various respiratory diseases and other ailments, including antidote therapy for poisonous bites. The present research work attempted to formulate the metallodrug preparation as per the standard protocols, including the detoxification process of the raw materials, followed by the analytical characterization studies to evaluate the physicochemical properties responsible for the stability, quality, and efficacy. The study included the comparative analysis of the raw materials, processed samples, intermediate samples, finished products, and commercial samples to understand the science involved in detoxification and formulation processing. The appropriate product profile was developed based on analysis of the particle size and surface charge by Zeta sizer, morphology and distribution by SEM-EDAX, functional groups and chemical interactions by FTIR, thermal behavior and stability by TG-DSC, crystallinity by XRD, and elemental composition by XPS. The findings of the research could provide scientific proof of evidence to overcome the limitations of the product owing to the standard quality and safety concern of the metal-mineral constituents, such as mercury, sulphur, and arsenic in the polyherbomineral formulation.

A fundamental study on the degradation of paracetamol under single- and dual-frequency ultrasound

The degradation of paracetamol, a widely found emerging pharmaceutical contaminant, was investigated under a wide range of single-frequency and dual-frequency ultrasonic irradiations. For single-frequency ultrasonic irradiation, plate transducers of 22, 98, 200, 300, 400, 500, 760, 850, 1000, and 2000 kHz were employed and for dual-frequency ultrasonic irradiation, the plate transducers were coupled with a 20 kHz ultrasonic horn in opposing configuration. The sonochemical activity was quantified using two dosimetry methods to measure the yield of HO• and H₂O₂ separately, as well as sonochemiluminescence measurement. Moreover, the severity of the bubble collapses as well as the spatial and size distribution of the cavitation bubbles were evaluated via sonoluminescence measurement. The paracetamol degradation rate was maximised at 850 kHz, in both single and dual-frequency ultrasonic irradiation. A synergistic index higher than 1 was observed for all degrading frequencies (200 - 1000 kHz) under dual-frequency ultrasound irradiation, showing the capability of dual-frequency system for enhancing pollutant degradation. A comparison of the results of degradation, dosimetry, and sonoluminescence intensity measurement revealed the stronger dependency of the degradation on the yield of HO• for both single and dual-frequency systems, which confirms degradation by HO• as the main removal mechanism. However, an enhanced degradation for frequencies higher than 500 kHz was observed despite a lower HO• yield, which could be attributed to the improved mass transfer of hydrophilic compounds at higher frequencies. The sonoluminescence intensity measurements showed that applying dual-frequency ultrasonic irradiation for 200 and 400 kHz made the bubbles larger and less uniform in size, with a portion of which not contributing to the yield of reactive oxidant species, whereas for the rest of the frequencies, dual-frequency ultrasound irradiation made the cavitation bubbles smaller and more uniform, resulting in a linear correlation between the overall sonoluminescence intensity and the yield of reactive oxidant species.

New insight on occurrence of liquid crystal monomers: A class of emerging e-waste pollutants in municipal landfill leachate

Liquid crystal monomers (LCMs) have been proposed as a class of emerging organic pollutants, which were recently detected in indoor dust and sediment samples collected near electronic devices recycling facilities. However, there is a knowledge gap for analytical method, occurrence, and distribution of LCMs in aqueous sample. Herein, a robust method was developed to determine 38 target LCMs in landfill leachate. A combined ultrasonic enhanced liquid-liquid extraction, saponification and silica/florisil packed column purification method achieved recoveries of 76.9~127.1%, 84.5~114.6% and 81.3~104.6% at spiking levels of 2 ng, 10 ng and 50 ng in leachate, respectively. The developed method was validated through determination of target LCMs in leachate samples collected from municipal landfills in Hong Kong (HK) and Shenzhen (SZ), China. There were 23 and 20 LCMs detected in the HK (ΣLCMs=1120 ng/L) and SZ (ΣLCMs=409 ng/L) sample, respectively, with 6 LCMs newly detected in the environment. This study provided the first evidence suggesting that landfill leachate might be a potential sink of LCMs emitted from e-waste. Future study is urged to investigate the potential migration of LCMs from landfill leachate as a point source, and their occurrence, distribution, fate, and ecotoxicological risk in aquatic environments on regional and global scales.

Key Points of Advanced Oxidation Processes (AOPs) for Wastewater, Organic Pollutants and Pharmaceutical Waste Treatment: A Mini Review

Advanced oxidation procedures (AOPs) refer to a variety of technical procedures that produce OH radicals to sufficiently oxidize wastewater, organic pollutant streams, and toxic effluents from industrial, hospital, pharmaceutical and municipal wastes. Through the implementation of such procedures, the (post) treatment of such waste effluents leads to products that are more susceptible to bioremediation, are less toxic and possess less pollutant load. The basic mechanism produces free OH radicals and other reactive species such as superoxide anions, hydrogen peroxide, etc. A basic classification of AOPs is presented in this short review, analyzing the processes of UV/H2O2, Fenton and photo-Fenton, ozone-based (O3) processes, photocatalysis and sonolysis from chemical and equipment points of view to clarify the nature of the reactive species in each AOP and their advantages. Finally, combined AOP implementations are favored through the literature as an efficient solution in addressing the issue of global environmental waste management.

Sonochemical degradation of surfactants with different charge types: Effect of the critical micelle concentration in the interfacial region of the cavity

Ionic surfactants tend to accumulate in the interfacial region of ultrasonic cavitation bubbles (cavities) because of their surface active properties and because they are difficult to evaporate in cavitation bubbles owing to their extremely low volatilities. Hence, sonolysis of ionic surfactants is expected to occur in the interfacial region of the cavity. In this study, we performed sonochemical degradation of surfactants with different charge types: anionic, cationic, zwitterionic, and nonionic. We then estimated the degradation rates of the surfactants to clarify the surfactant behavior in the interfacial region of cavitation bubbles. For all of the surfactants investigated, the degradation rate increased with increasing initial bulk concentration and reached a maximum value. The initial bulk concentration to obtain the maximum degradation rate had a positive correlation with the critical micelle concentration (cmc). The initial bulk concentrations of the anionic surfactants were lower than their cmcs, while those of the cationic surfactants were higher than their cmcs. These results can be explained by the negatively charged cavity surface and the effect of the coexisting counterions of the surfactants.

A review on hybrid techniques for the degradation of organic pollutants in aqueous environment

The creation of the modern world requires many industrial sectors, however, sustainability needs to be considered while developing industries. In particular, organic pollutants generated by many of these industries contaminate the environment leading to health and other issues. Advanced oxidation processes (AOPs) have been introduced to remove organic pollutants present in wastewater. Sonolytic degradation of organic pollutants is considered as one of the AOPs, however, this process has its limitations. In order to overcome the limitations, hybrid techniques involving ultrasound and other AOPs have been developed. That is, ultrasound combined with heterogeneous AOPs (ultrasound/metal ions, ultrasound/metal oxides, and ultrasound/photocatalysis) and homogeneous AOPs (ultrasound/ozone, ultrasound/H₂O₂, and ultrasound/persulfate) for the degradation/mineralization of organic pollutants. This review highlights the advantages of using hybrid techniques involving ultrasound for the degradation of organic pollutants in aqueous solutions.

Influence of ultrasound on the properties of dissolved organic matter with regards to proton and metal ion binding moieties

Ultrasound is widely used in water and wastewater treatment. However, the influence of ultrasound on the composition and structure of dissolved organic matter (DOM) and consequently its behaviors is still unclear. In this study, the changes in proton and metal binding moieties in DOM caused by ultrasound at an environmentally relevant concentration (about 5 mg·L^-1) were investigated using spectrophotometric titrations. The amounts of carboxylic and phenolic-like groups in DOM before and after ultrasound were quantified by the spectral parameter, Dslope_350-400 (the differential slope of the Log-transformed DOM absorbance in the wavelength region of 350-400 nm) in combination with the non-ideal competitive adsorption (NICA) model. The results demonstrate that the concentration of carboxylic-like sites decreased with an increase in the ultrasound intensity at the same reaction time. However, the concentration of phenolic-like sites increased with an increase in the ultrasound intensity in most cases. The amounts of bound metal Ca(II) and Al(III) ions decreased with an increase of the ultrasound intensity due to the reduction of available total binding sites (carboxylic-like and phenolic-like groups) in the DOM after ultrasound. This study provides detailed in-situ information concerning the changes in the properties and behaviors of DOM in ultrasound, which would be useful to understand in more detail and to optimize the utility of ultrasound in water and wastewater treatment.

Synthesis of Nano-Zinc Oxide Loaded on Mesoporous Silica by Coordination Effect and Its Photocatalytic Degradation Property of Methyl Orange

Salicylaldimine-modified mesoporous silica (Sal-MCM-3 and Sal-MCM-9) was prepared through a co-condensation method with different amounts of added salicylaldimine. With the coordination from the salicylaldimine, zinc ions were impregnated on Sal-MCM-3 and Sal-MCM-9. Then, Zn-Sal-MCM-3 and Zn-Sal-MCM-9 were calcined to obtain nano-zinc oxide loaded on mesoporous silica (ZnO-MCM-3 and ZnO-MCM-9). The material structures were systematically studied by Fourier transform infrared spectroscopy (FTIR), N₂ adsorption/desorption measurements, X-ray powder diffraction (XRD), zeta potential, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet diffused reflectance spectrum (UV-vis DRS), and thermogravimetry (TGA). Methyl orange (MO) was used to investigate the photocatalysis behavior of ZnO-MCM-3 and ZnO-MCM-9. The results confirmed that nano ZnO was loaded in the channels as well as the outside surface of mesoporous silica (MCM-41). The modification of salicylaldimine helped MCM-41 to load more nano ZnO on MCM-41. When the modification amount of salicylaldimine was one-ninth and one-third of the mass of the silicon source, respectively, the load of nano ZnO on ZnO-MCM-9 and ZnO-MCM-3 had atomic concentrations of 1.27 and 2.03, respectively. ZnO loaded on ZnO-MCM-9 had a wurtzite structure, while ZnO loaded on ZnO-MCM-3 was not in the same crystalline group. The blocking effect caused by nano ZnO in the channels reduced the orderliness of MCM-41. The photodegradation of MO can be divided in two processes, which are mainly controlled by the surface areas of ZnO-MCM and the loading amount of nano ZnO, respectively. The pseudo-first-order model was more suitable for the photodegradation process.

Kinetic modeling of sonocatalytic degradation of reactive orange 29 in the presence of lanthanide-doped ZnO nanoparticles

The sonocatalytic degradation of reactive orange 29 (RO29) was examined from the reaction kinetics point of view. Sonochemically synthesized lanthanides (Ho³⁺ and Er³⁺)-doped ZnO nanoparticles were utilized as catalyst during the sonocatalytic process. The prepared nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The aqueous RO29 solution was irradiated with a 36kHz ultrasonic bath (150W) for investigation of the degradation kinetics by varying of the initial dye concentration (10-30mg/L) and catalyst dosage (0.25-1g/L). A novel kinetic model was developed and validated for prediction of the RO29 sonocatalytic degradation efficiency using generally accepted intrinsic elementary reactions. The proposed kinetic model clearly demonstrates the dependence of the apparent first-order rate constant on the mentioned operational parameters. The predicted values of degradation efficiency and experimental results were in good agreement with appropriate correlation coefficient (R²>0.945).

Critical factors in sonochemical degradation of fumaric acid

The effects of critical factors such as Henry's Law constant, atmospheric OH rate constant, initial concentration, H2O2, FeSO4 and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H2O2 under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H2O2 under sonication. 0.1 mM of fumaric acid suppresses H2O2 formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO4) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.

Enhancement and inhibition effects of water matrices during the sonochemical degradation of the antibiotic dicloxacillin

The sonochemical degradation of dicloxacillin (DXC) was studied in both synthetic and natural waters. Degradation routes and the effect of experimental conditions such as pH, initial DXC concentration and ultrasonic power were evaluated. Experiments were carried out with a fixed frequency (600kHz). The best performances were achieved using acidic media (pH=3) and high power (60W). The degradation process showed pseudo-first order kinetics as described by the Okitsu model. To evaluate water matrix effects, substrate degradation, in the presence of Fe(2+) and organic compounds such as glucose and 2-propanol, was studied. A significant improvement was achieved with Fe(2+) (1.0mM). Inhibition of the degradation process was observed at a relatively high concentration of 2-propanol (4.9mM), while glucose did not show any effect. Natural water showed an interesting effect: for a low concentration of DXC (6.4μM), an improvement in the degradation process was observed, while at a higher concentration of DXC (0.43mM), degradation was inhibited. Additionally, the extent of degradation of the process was evaluated through the analysis of chemical oxygen demand (COD), antimicrobial activity, total organic carbon (TOC) and biochemical oxygen demand (BOD5). A 30% removal of COD was achieved after the treatment and no change in the TOC was observed. Antimicrobial activity was eliminated after 360min of ultrasonic treatment. After 480min of treatment, a biodegradable solution was obtained.

Ultrasonic degradation of acetaminophen in water: effect of sonochemical parameters and water matrix

This paper deals about the sonochemical water treatment of acetaminophen (ACP, N-acetyl-p-aminophenol or paracetamol), one of the most popular pharmaceutical compounds found in natural and drinking waters. Effect of ultrasonic power (20-60 W), initial ACP concentration (33-1323 μmol L(-1)) and pH (3-12) were evaluated. High ultrasonic powers and, low and natural acidic pH values favored the efficiency of the treatment. Effect of initial substrate concentration showed that the Langmuir-type kinetic model fit well the ACP sonochemical degradation. The influence of organic compounds in the water matrix, at concentrations 10-fold higher than ACP, was also evaluated. The results indicated that only organic compounds having a higher value of the Henry's law constant than the substrate decrease the efficiency of the treatment. On the other hand, ACP degradation in mineral natural water showed to be strongly dependent of the initial substrate concentration. A positive matrix effect was observed at low ACP concentrations (1.65 μmol L(-1)), which was attributed to the presence of bicarbonate ion in solution. However, at relative high ACP concentrations a detrimental effect of matrix components was noticed. Finally, the results indicated that ultrasonic action is able to transform ACP in aliphatic organic compounds that could be subsequently eliminated in a biological system.

Kinetics and mechanism of sonochemical degradation of pharmaceuticals in municipal wastewater

A series of six pharmaceuticals were degraded by continuous wave (CW) and pulsed wave (PW) ultrasound at 205 kHz using deionized water, wastewater effluent, and its isolated organic matter matrices. In deionized water, we observed that hydrophobicity is superior to diffusivity (D(W)) for predicting degradation kinetics. Enhancements in degradation kinetics by the PW mode were greatest for the highest DW (i.e., fluorouracil (5-FU)) and K(OW) (i.e., lovastatin (LOVS)) compounds, indicating that a pharmaceutical with either high diffusivity and low hydrophobicity or low diffusivity and high hydrophobicity benefits from additional time to populate the bubble-water interface during the silent cycle of PW ultrasound. Degradation of 5-FU and LOVS were inhibited by wastewater effluent to a greater extent than the other pharmaceuticals. In addition, a pulse enhancement (PE) for 5-FU and LOVS was not present in wastewater effluent. Irradiating 5-FU and LOVS in hydrophobic (HPO), transphilic (TPI), and hydrophilic (HPI) fractions of effluent organic matter (EfOM) showed that the TPI fraction reduced the PE the most, followed by the HPI and HPO fractions. The smaller size of the TPI over the HPO fraction and higher hydrophobicity of TPI over HPI implicate both size and hydrophobicity of EfOM in hindering degradation of pharmaceuticals.

Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.

Synthesis and sonocatalytic property of rod-shape Sr(OH)2·8H2O

A novel rod-shape sonocatalyst Sr(OH)2·8H2O was prepared by a facile precipitation method, and characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and UV-vis absorption spectroscopy. Comparative sonocatalytic degradation experiments were carried out in different conditions under ultrasonic irradiation by using rhodamine B (RhB) as the model substrate, indicating that Sr(OH)2·8H2O was highly sonocatalytic. Total organic carbon experiment demonstrated Sr(OH)2·8H2O with mass mineralization of organic carbon. The effects of catalyst amount, initial RhB concentration and ultrasonic energy of degradation were investigated, and the sonocatalyst could be reused 5 times without significant loss of activity. Furthermore, the potent degrading capability was ascribed to ultrasonic cavitation producing flash light/energy which generated radicals (e.g., OH) with high oxidation activity.

Sonolytic degradation of butyric acid in aqueous solutions

The sonolytic degradation of butyric acid was investigated in an ultrasonic reactor emitting waves at 850 kHz. The effects of the ultrasonic power, the initial concentration of butyric acid, and the addition of H2O2 were studied on the degradation of butyric acid. In the sonication of butyric acid, degradation degrees as high as 31.5% could be achieved at a power of 31 W, at an initial concentration of 2.8 mM butyric acid with the addition of 0.34 M H2O2 for a sonication time of 5 h. The degradation of butyric acid increased with irradiation time, indicating first order kinetics.

Kinetic investigation on sono-degradation of Reactive Black 5 with core-shell nanocrystal

The experimental data of sonocatalytic degradation of Reactive Black 5 (RB5) as an azo dye by core-shell nanocrystals (CdS-TiO(2)) were applied to the proper kinetic models. In this work, two kinetic models were proposed and fitted properly to the data. In the first one, the heterogeneous reaction was considered similar to the Langmuir-Hinshelwood (L-H) mechanism and the kinetic rate parameters were determined. In this model, short time of sonication with initial concentration changes has been applied and the contribution of the reaction intermediates has been neglected in degradation. Hence, this model may not be valid for longer reaction times where the reaction intermediates effects prevail. In the second one, two first-order reactions in series provided the most convincing rate form for the sonodegradation of dyes adsorbed on the synthesized nanocomposite. In these series reactions, the first step is the conversion of colored dye to colored intermediate, and the second step is the conversion to colorless product(s). The obtained results were in good agreement with the proposed kinetic models. The rate constants of degradation of catalyzed reaction were higher than that obtained without catalyst, solar and UV irradiation.

Sonochemical degradation of cyclic nitroxides in aqueous solution

The sonochemical degradation of eight five- and six-membered nitroxides has been studied by EPR spectroscopy after exposure to ultrasound at a frequency of 354 kHz in argon-saturated aqueous solution. Concentration vs. time profiles do not follow a simple rate law. Octanol/water partition functions have been determined for all eight nitroxides, and an excellent linear correlation has been found between initial decomposition rates and hydrophobicity (log K(octanol/water)). Variation of initial rate with concentration was investigated for one compound (TEMPONE) and is largely consistent with an equilibrium distribution of substrate between bulk solution and the gas/liquid interface.

Comparative study on the process behavior and reaction kinetics in sonocatalytic degradation of organic dyes by powder and nanotubes TiO2

Sonocatalytic degradation of various organic dyes (Congo Red, Reactive Blue 4, Methyl Orange, Rhodamine B and Methylene Blue) catalyzed by powder and nanotubes TiO(2) was studied. Both catalysts were characterized using transmission electron microscope (TEM), surface analyzer, Raman spectroscope and thermal gravimetric analyzer (TGA). Sonocatalytic activity of powder and nanotubes TiO(2) was elucidated based on the degradation of various organic dyes. The former catalyst was favorable for treatment of anionic dyes, while the latter was more beneficial for cationic dyes. Sonocatalytic activity of TiO(2) nanotubes could be up to four times as compared to TiO(2) powder under an ultrasonic power of 100 W and a frequency of 42 kHz. This was associated with the higher surface area and the electrostatic attraction between dye molecules and TiO(2) nanotubes. Fourier transform-infrared spectrometer (FT-IR) was used to identify changes that occurred on the functional group in Rhodamine B molecules and TiO(2) nanotubes after the reaction. Sonocatalytic degradation of Rhodamine B by TiO(2) nanotubes apparently followed the Langmuir-Hinshelwood adsorption kinetic model with surface reaction rate of 1.75 mg/L min. TiO(2) nanotubes were proven for their high potential to be applied in sonocatalytic degradation of organic dyes.

Sonolytic degradation of endocrine disrupting chemical 4-cumylphenol in water

The sonolytic degradation of endocrine disrupting compound 4-cumylphenol (4-CyP) in aqueous solution was investigated. The influence of operating parameters for sonication process such as 4-CyP initial concentration, frequency, power, pH, temperature and saturating gas was examined. The extent of degradation was inversely proportional to the initial substrate concentration. The rate of 4-CyP degradation was frequency dependent. The degradation rate increased proportionally with increasing ultrasonic power from 20 to 100 W and temperature in the range of 20-50°C. The most favorable degradation pH was acidic media. Destruction in the presence of saturating gas follows the order: argon>air>nitrogen. The 4-CyP degradation was inhibited in the presence of nitrogen gas owing to the free radical scavenging effect in vapor phase within the bubbles of cavitation. The ultrasonic degradation of 4-CyP was clearly promoted in the presence of bromide anions and the promoting effect on degradation increased with increasing bromide concentration. At low 4-CyP concentration (0.05 mg L(-1)), bicarbonate ion drastically enhanced the rate of 4-CyP degradation. Experiments conducted using pure and natural water demonstrated that the sonolytic treatment was more efficient in the natural water compared to pure water.

Sonolysis of ciprofloxacin in aqueous solution: influence of operational parameters

Ultrasonic irradiation is a promising technique for the degradation of persistent organic molecules such as pharmaceuticals in wastewater. This paper focuses on the sonolytic degradation of ciprofloxacin (CIP), a fluoroquinolone antibiotic. During a first experiment at 25°C and 544 kHz, the degradation of a 15 mg L(-1) CIP-solution showed a pseudo-first order degradation constant k(1) equal to 0.0067 ± 0.0001 min(-1) (n=3). Experiments with the addition of t-butanol as a radical scavenger showed that reaction with *OH radicals is the main degradation route for ciprofloxacin. Since the production of *OH radicals was the highest at 544 kHz, this was also the most favorable frequency for CIP degradation in comparison with 801 (k(1)=0.0055 min(-1)) and 1081 kHz (k(1)=0.0018 min(-1)). The degradation constant is also strongly dependent on the temperature of the bulk solution. The degradation constant increased significantly with increasing temperature from 0.0055 min(-1) at 15°C to 0.0105 min(-1) at 45°C. According to the Arrhenius law, the apparent activation energy was determined to be 17.5 kJ mol(-1). This suggests that the degradation of CIP is diffusion controlled, as is the case for most radical reactions. A Langmuir-type heterogeneous reaction kinetics model could be used to explain the increasing degradation constant with decreasing initial CIP concentration from 0.0204 min(-1) (C(0)=0.15 mg L(-1)) to 0.0009 min(-1) (C(0)=150 mg L(-1)). According to the model a local reaction zone exists at the interface region of the cavitation bubbles. During bubble oscillation, molecules accumulate in the reaction zone and when the bubble finally collapses, the molecules in the reaction zone can be oxidized by the formed *OH radicals. This means that degradation is limited by the available surface at the interface. The model agreed very well with the experimental data (R(2)=0.975). The pseudo rate constant for decomposition (k(d)) was estimated to be 0.40 μM min(-1) and the modeled equilibrium constant (K) was equal to 0.047 μM(-1).

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 H(2)O(2) 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 H(2)O(2) 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.

Sonochemical decomposition of hydrazine in water: effects of coal ash and pH on the decomposition and adsorption behavior

Sonochemical decomposition of hydrazine in aqueous suspension of coal ash particles was investigated in the different pH solutions. It was clearly found that the initial rate of hydrazine decomposition and adsorption is strongly dependent on the amount of coal ash and pH. At pH1, the amount of the hydrazine adsorption on coal ash was very small and hydrazine was mainly decomposed by ultrasonic irradiation. At pH4, hydrazine was mainly adsorbed on coal ash and not decomposed by ultrasonic irradiation. At pH8, the sonochemical decomposition and the adsorption on coal ash proceeded simultaneously. These results were due to the interactions between the degree of the protonation of hydrazine, the electric charge of coal ash and the amount of OH radicals formed in the sonolysis of water.