Mechanism of O2-accelerated sonolysis of bisphenol A

The effects of dissolved gases on the sonochemical degradation of bisphenol A (BPA) were studied at a frequency of 500 kHz. BPA degradation rate increased in the order O(2)>Ar>air>N(2). The rate constant for oxygen (2.6 h(-1)) was approximately two fold higher than that for argon (1.2 h(-1)). A primary intermediate (2,3-dihydro-2-methylbenzofuran), a typical intermediate of BPA formed during attack by OH radicals, was detected only in the presence of oxygen, revealing that a different reaction path was responsible for the enhancement of decomposition.     

Ultrasonic frequency effects on the removal of Microcystis aeruginosa

Algae bloom in source water causes high chemical consumption and deteriorates water quality in waterworks. This paper studied the ultrasonic removal of Microcystis aeruginosa. The results showed that algae cells could be effectively removed by sonication and gas vesicle collapse was the main mechanism. The ultrasonic algae removal followed the first order reaction with a rate constant of 0.023 min(-1) (80 W, 80 kHz). Higher ultrasound frequency benefited algae removal; the algae removal rate constant was 0.114 min(-1) at 1320 kHz and 0.0224 min(-1) at 20 kHz (80 W). Higher ultrasound power also accelerated algae removal; the algae removal rate constant was 0.023 min(-1) at 80 W and 0.007 min(-1) at 32 W (80 kHz). However, high ultrasound power and long irradiation caused microcystins to increase. 80 W, 80 kHz sonication for 5 min increased the extracellular microcystins concentration from 0.87 microg/L to 3.11 microg/L. Sound frequency had little impact on the microcystins release. The chlorophyll a concentration initially decreased and then stabilized after 5 min of sonication.     

Frequency effect on the sonochemical remediation of alachlor

The effect of ultrasonic frequency on the sonodegradation of alachlor is described. The rate observed for the destruction of alachlor is approximately 25 times faster at 300 kHz under argon saturation than at 20 kHz under comparable acoustic input energy. The effect of variation of a number of extrinsic parameters such as dissolved gases, radical scavengers and hydroxyl radical promoters is also explored. Argon-saturated solutions display an enhancement in rate by a factor of two compared to either oxygen- or air-saturated solutions upon sonication at 300 kHz. The principal ultrasonic degradation products have been determined in air, argon, and oxygen. The products results primarily from cleavage of the N-methoxymethyl unit when sonication occurs in argon and air. Oxygen addition has been observed when the saturating gas is oxygen. The nature of the active site for reactivity of alachlor is discussed.     

Ultrasonic destruction of bisphenol-A: the operating parameters

Degradation of bisphenol-A (BPA) by ultrasonic irradiation at 300 kHz was investigated at varying substrate concentrations, pH, hydroxyl radical scavengers and sparge gases. It was found that increases in BPA initial concentration slowed down the reaction rate, but enhanced the sonochemical product yield. Both the rate of reaction and the product yield were adversely affected by pH elevation above the neutral level. The degree of BPA decay was fastest in the presence of air due to the formation of acids and excess radicals, and slowed down as the gas was replaced by argon and oxygen. The impact of large concentrations of hydroxyl radical scavengers such as carbonate and t-butanol was to decrease the rate of degradation, particularly when the scavenger concentration was considerably larger than that of BPA, and the deceleration was more remarkable in the presence of t-butanol than in that of carbonate.     

Concomitant degradation of bisphenol A during ultrasonication and Fenton oxidation and production of biofertilizer from wastewater sludge

Degradation of bisphenol A (BPA), an endocrine disruptor, from wastewater sludge (WWS) has attracted great interest recently. In the present study, the effects of different pre-treatment methods, including ultrasonication (US), Fenton's oxidation (FO) and ferro-sonication (FS) was assessed in terms of increase in solubilization of WWS and simultaneous degradation of BPA. Among US, FO and FS pre-treatment, higher suspended solids (SS), volatile suspended solids (VSS), chemical oxygen demand (COD) and soluble organic carbon (SOC) solubilization (39.7%, 51.2%, 64.5% and 17.6%, respectively) was observed during a ferro-sonication pre-treatment process carried out for 180 min, resulting in higher degradation of BPA (82.7%). In addition, the effect of rheological parameters (viscosity and particle size) and zeta potential on the degradation of BPA in raw and different pre-treated sludges were also investigated. The results showed that a decrease in viscosity and particle size and an increase in zeta potential resulted in higher degradation of BPA. BPA degradation by laccases produced by Sinorhizobium meliloti in raw and pre-treated sludge was also determined. Higher activity of laccases (207.9 U L(-1)) was observed in ferro-sonicated pre-treated sludge (180 min ultrasonic time), resulting in higher removal of BPA (0.083 μg g(-1)), suggesting concomitant biological degradation of BPA.     

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.     

Adsorption kinetics of 4-chlorophenol onto granular activated carbon in the presence of high frequency ultrasound

This work describes the results of investigations carried out to examine the adsorption kinetics of 4-chlorophenol (4-CP) from aqueous solution containing tert-butyl alcohol (10%, v/v) onto granular activated carbon (GAC) in the presence of ultrasound of different high frequencies (516, 800 and 1660 kHz) and acoustic powers (15.2, 21.5, 31.1 and 38.3 W). The main objective of this study is to describe the mechanism of ultrasound-assisted adsorption rather than the enhancement of adsorption capacity. Sonochemical degradation of 4-CP was studied in the absence and presence of tert-butyl alcohol. The sonolysis of 4-CP is effectively inhibited by the addition of tert-butyl alcohol (10%, v/v) and very little 4-CP degradation occurs, indicating that little or no pyrolysis of the compound occurs. Without addition of tert-butyl alcohol, after 300 min and at 1660 kHz, the removal of 4-CP in the presence of ultrasound for an acoustic power of 38.3 W was nearly total (99%), but in the conventional method only 60% was eliminated. In this case, the removal of 4-CP by GAC in the ultrasound-assisted technique is due to both adsorption and ultrasonic degradation, but the removal by simple stirring is only due to adsorption, which makes a direct comparison unacceptable. In order to distinguish sonochemical degradation and adsorption of 4-CP onto GAC and to make an exact and practical comparison of the adsorption in the absence and presence of ultrasound, kinetic adsorption experiments were conducted using aqueous solution containing 10% (v/v) tert-butyl alcohol. The obtained results show that both adsorption rate and adsorbed amount were significantly enhanced and improved in the presence of ultrasound for all the studied frequencies and powers. The enhancement of adsorption is favored by increasing ultrasonic power. Adsorption kinetic data were modeled using the liquid-film mass transfer equation and intraparticle diffusion model. The values of the intraparticle diffusion coefficient obtained in the presence of ultrasound are greater than that obtained in the absence of ultrasound. In the initial period of adsorption, where external mass transfer is assumed to predominate, liquid-film mass transfer coefficients significantly increased by the assistance of ultrasound. These results indicate that ultrasound enhances the mass transport in the pores as well as across the boundary layer. This effect increased with increasing ultrasonic power for the three studied frequencies. The average order for the studied ultrasonic waves according to the initial adsorption rate, the intraparticle diffusion coefficient and the liquid-film mass transfer coefficient is 516 kHz>800 kHz>1660 kHz.     

Effect of potassium monopersulfate (oxone) and operating parameters on sonochemical degradation of cationic dye in an aqueous solution

In this study, removal of Cresol Red (CR), a cationic triphenylmethane dye, by 300 kHz ultrasound was investigated. The effect of additive such as potassium monopersulfate (oxone) was studied. Additionally, sonolytic degradation of CR was investigated at varying power and initial pH. RC can be readily eliminated by the ultrasound process. The obtained results showed that. Sonochemical degradation of CR was strongly affected by ultrasonic power and pH. The degradation rate of the dye increased substantially with increasing ultrasonic power in the range of 20–80 W. This improvement could be explained by the increase in the number of active cavitation bubbles. The significant degradation was achieved in acidic conditions (pH = 2) where the color removal was 99% higher than those observed in higher pH aqueous solutions. The ultrasonic degradation of dye was enhanced by potassium monopersulfate (oxone) addition. It was found that the degradation of the dye was accelerated with increased concentrations of oxone for a reaction time of 75 min.     

Direct sonication of acetic acid in aqueous solutions

Sonochemical oxidation has a promising future in the area of waste water treatment as one of the advanced oxidation methods. In this study, direct ultrasonic degradation of acetic acid was investigated in low powers (0.1-0.4 W) and in a frequency range of 30-100 kHz. An ultrasonic transducer was used for sonication. The results showed that there was an optimum frequency at 60 kHz for direct sonication of acetic acid and degradation rate increased up to a power of 0.2 W and then it decreased. Sonochemistry is associated with the bubble of cavitation which depends on the sound pressure field and nature of molecule. Therefore, the frequency and intensity have to be optimized for the minimization of energy requirement during waste water treatment with ultrasound.     

超声波降解溴苯:操作参数与环境因素的影响

本文考察了用超声波降解水中溴苯的动力学与脱卤效应,并研究了重要的操作参数如强度与饱和气体,以及环境干扰因素如悬浮物、地表水其他杂质的影响。结果表明,超声波可以有效地处理溴苯,在20kHz,7.5W／cm2下一级反应常数达0.044／min,脱卤效率达58％。本研究范围内,声强度越高,反应越快。氧气和氩气下降解速率高于空气下。超声降解不受地表水中杂质、纳米级微粒、无机颗粒的影响,但有机悬浮物能在一定程度上干扰溴苯的超声降解。     

Baeyer-Villiger oxidation of cyclohexanone to epsilon-caprolactone in airlift sonochemical reactor

Baeyer-Villiger oxidation of cyclohexanone to epsilon-caprolactone was studied in a new type reactor--the airlift loop sonochemical reactor. The reactor plays a synergistic effect of sonochemsity and higher oxygen transfer rate. The influences of ultrasound intensity, reaction temperature, the molar ratio of benzaldehyde to cyclohexanone and oxygen gas flow rate on the conversion and selectivity of cyclohexanone were investigated and discussed. Under ultrasound, the amount of benzaldehyde can be reduced from 75% to 67%. Ultrasound not only intensified the rates of reactions but also increased the yield of product. The optimized operation conditions are listed as follows: the reaction temperature is 30 degrees C, the molar ratio of cyclohexanone to benzaldehyde is 1:2, the oxygen gas flow rate is 1.15 cm s(-1), and ultrasonic irradiations 2h at 40 kHz, 2.25 W cm(-2). Under the optimum operation conditions, the average molar yield of epsilon-caprolactone comes up to 87.7%.     

The effect of pH on sonochemical degradation of hydrazine

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1 and 1.0 mmol/L was investigated as a function of pH under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the hydrazine degradation depended greatly upon pH under the ultrasonic irradiation condition, while it did not take place over the whole pH range (0.8-9) under the stirring condition. The hydrazine degradation was suppressed by the addition of tertial butyl alcohol (t-BuOH) known as a scavenger of OH radicals. This result suggested that OH radicals played an important role in the hydrazine degradation. The pH dependence of the hydrazine degradation was discussed in terms of a dissociating form of hydrazine depending upon pH and the effect of OH radicals.     

PEG6000溶液超声化学反应机理的初步研究

采用不同电功率的超声波处理了聚乙二醇(PEG6000)溶液。凝胶渗透色谱(GPC)分析超声处理后的PEG溶液发现,当超声电功率超过250W时,PEG分子量随超声波作用强度的增大而减少,随超声波作用时间的延长而增大;在电功率超过250W超声波作用下,傅立叶红外光谱(FT-IR)分析表明,组成PEG的单体没有明显改变,但是,羟基含量分析表明,PEG固体样品中的羟基含量有所减少。结合实验结果,根据高分子化学、有机化学和超声化学中相关理论对PEG超声化学反应机理进行了探讨,认为:当超声波作用于PEG溶液时,同时存在有PEG的缩水聚合反应和自由基降解反应,当频率为20-25kHz、电功率为250-600W的超声作用于PEG6000溶液时,缩水聚合反应占主导地位。     

Individual and combined effects of ultrasound, ozone and UV irradiation: a case study with textile dyes

Comparative degradation of azo dyes by 520 kHz ultrasonic irradiation and its combinations with ozone and/or ultraviolet light (UV) was investigated using a probe dye C.I. Acid Orange 7. Operation parameters such as ultrasonic power density, ozone flow, UV intensity, and type and injection mode of the bubbling gas were optimized based on the rate of absorption decay in the visible and UV bands as estimated by regression analysis of absorption-time data. At equivalent initial dye concentrations and contact times, individual effects of UV irradiation, ultrasound and ozone were "no effect", "bleaching", and "bleaching/organic carbon degradation", respectively. UV irradiation, however, was found to induce a catalytic effect when applied in combination with either ultrasound or ozone schemes; and the overall degradation process was most rapid under simultaneous operation of the three in the presence of a continuous flow of a gas mixture made of argon and oxygen. The synergy observed in combined schemes was attributed to enhanced ozone diffusion by mechanical effects of ultrasound, and the photolysis of ultrasound-generated H(2)O(2) to produce hydroxyl radicals.     

Effect of coal ash on hydrazine degradation under stirring and ultrasonic irradiation conditions

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1-5.0 mmol/L was investigated as a function of amount of coal ash (0.0-5.0 wt%) under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the rate of decrease in the hydrazine concentration depended upon an amount of coal ash under the stirring and ultrasonic irradiation condition. It was considered under the stirring condition that hydrazine was adsorbed and degraded partly on coal ash. Furthermore, the sonochemically formed OH radicals were more effective in the hydrazine degradation than stirring condition in the presence of an intermediate amount of coal ash (0.6-2.4 wt%), whereas the effect of OH radicals disappeared in the presence of coal ash more than 2.4 wt%.     

Propargylation of indene-1,3-dione under a new phase-transfer catalyst combined with ultrasonication – A kinetic study

In the present study, kinetics of synthesis of 2,2-di(prop-2-ynyl)-1H-indene-1,3(2H)-dione was successfully carried out by propargylation of indene-1,3-dione with propargyl bromide using aqueous potassium hydroxide and catalyzed by a newly synthesized phase-transfer catalyst viz., N-benzyl-N-ethyl-N-isopropylpropan-2-ammonium bromide, PTC under ultrasonic (40 kHz, 300 W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40 kHz, 300 W) in a batch reactor, it shows that the overall reaction rate can be greatly enhanced with ultrasound irradiation than without ultrasound.     

Numerical simulations and electrochemical experiments of the mass transfer of microvias electroforming under ultrasonic agitation

This paper explores the mass transfer mechanism of microvias electroforming under ultrasonic agitation by numerical simulations and electrochemical experiments. Firstly, the velocity distribution of electroforming solution inside the microvias under ultrasound treatment is simulated by COMSOL Multiphysics software. The ultrasonic frequency is that of 120 kHz. The ultrasonic powers are 100 W, 200 W, 300 W and 400 W, respectively. The simulation results indicate that the mean liquid velocity inside the microvias increases with the increasing of acoustic power. In addition, under a certain ultrasonic power, the mean liquid velocity will decrease with increasing the distance between microvias and transducer, the aspect ratio of microvias and the distance between cathode and central position. Secondly, electrochemical experiments are presented to investigate the effect of ultrasonic agitation on the electrode kinetics of microvias electroforming. It is found that ultrasonic treatment decreases the thickness of diffusion layer, increases the limiting diffusion current densities and further enhances the mass transfer of microvias electroforming. Compared with the silent condition, the diffusion layer thicknesses with the acoustic power of 100 W, 200 W, 300 W, 400 W are decreased by 50.0%, 64.1%, 69.3% and 74.5%, respectively. Finally, according to the results above, the 200 × 200 metal micro-column array structures are fabricated by ultrasonic electroforming under the condition of 120 kHz and 200 W. The metal micro-column is 250 μm high and has a diameter of 80 μm. The results show that ultrasonic electroforming can enhance the mass transfer of microvias electroforming, and further solve the problem of porous structure in electroforming layer. This work contributes to expanding the application of ultrasonic agitation in the microvias electroforming.     

Regeneration of granular activated carbon using ultrasound

To evaluate the feasibility of ultrasonic regeneration of granular activated carbon (GAC), desorption of trichloroethylene (TCE) from GAC by ultrasound was investigated at 20 kHz. About 64% of TCE was desorbed from 5 g of GAC loaded with 6.5 mg TCE for 1 h in ultrasonic field and TCE desorbed to liquid phase were rapidly degraded by ultrasound. 34-43% of stoichiometrically calculated chloride, final degradation product of TCE, was observed in liquid phase during ultrasonic treatment. However, there was desorption limitation at 20 kHz ultrasound. Despite of prolonged ultrasonic irradiation, desorption efficiency of TCE did not exceed critical value. And also, the higher percentage of TCE was desorbed when a sample of 2 mg TCE/4 g GAC was treated ultrasonically than that of 2 mg TCE/g GAC under the same experimental conditions. These results indicate that desorption of TCE by 20 kHz ultrasound occurred mainly at a nearby surface of GAC. In conclusion, the ultrasonic regeneration showed a possibility as an alternative to chemical and thermal regenerations of GAC.     

Oxygen-induced concurrent ultrasonic degradation of volatile and non-volatile aromatic compounds

Acoustic cavitation, induced by ultrasound, can be used to eliminate organic pollutants from water. This type of ultrasonic treatment of polluted water can be grouped with those generally referred to as advanced oxidative processes since it involves hydroxyl radicals. In this case these highly active species are generated from the dissociation of water and oxygen dissociation caused by cavitation bubble collapse. The cavitation induced degradation rates of organic compounds in water are mainly linked to their vapor pressure and solubility and here we will further explore these links by examining the degradation of a mixture of two materials with different physical properties, chlorobenzene and 4-chlorophenol. The results obtained when a dilute solution of a mixture of these compounds saturated with argon is subjected to sonication at 300 kHz, parallels previous observations achieved in an aerated aqueous medium at 500 kHz. The two compounds exhibit sequential degradation with the more volatile chlorobenzene entering the cavitation bubble and being destroyed first. The 4-chlorophenol degradation occurs subsequently only when the chlorobenzene has been completely destroyed. The two compounds exhibit different behavior when sonicated in water saturated with oxygen. Under these conditions the two compounds are degraded simultaneously, a remarkable result for which two explanations can be proposed, both of which are based on the formation of additional OH radical species: The ability to produce conditions for the simultaneous elimination of two organic compounds by the use of oxygen is of great importance in the developing field of ultrasonic water treatment.     

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.