Degradation of alachlor in aqueous solution by using hydrodynamic cavitation

The degradation of alachlor aqueous solution by using hydrodynamic cavitation was systematically investigated. It was found that alachlor in aqueous solution can be deomposed with swirling jet-induced cavitation. The degradation can be described by a pseudo-first-order kinetics and the degradation rate was found to be 4.90 × 10⁻² min⁻¹. The effects of operating parameters such as fluid pressure, solution temperature, initial concentration of alachlor and medium pH on the degradation rates of alachlor were also discussed. The results showed that the degradation rates of alachlor increased with increasing pressure and decreased with increasing initial concentration. An optimum temperature of 40 °C existed for the degradation rate of alachlor and the degradation rate was also found to be slightly depend on medium pH. Many degradation products formed during the process, and some of them were qualitatively identified by GC–MS.     

Degradation of alachlor in aqueous solution by using hydrodynamic cavitation

Samples of zirconium(IV)iodotungstate have been synthesized under varying mixing order and ratios of aqueous solution of potassium iodate, sodium tungstate and zirconium oxychloride at pH 1. A tentative formula was proposed on the basis of chemical composition, FTIR and thermogravimetric studies. The material shows a capacity of 0.68 meq g⁻¹ (for K⁺) which can be retained up to 200 °C. pH titration data reveal its monofunctional behavior. The distribution coefficient values of metal ions have been determined in various solvent systems. A number of important and analytically difficult quantitative separations of metal ions have been achieved using columns packed with this exchanger. In order to demonstrate practical utility of this material, Hg²⁺ and Pb²⁺ have been selectively separated and determined in the synthetic mixtures. Assay of Al³⁺ and Mg²⁺ in commercial tablets and analysis of lead in the standard reference material have also been attempted.     

瞬态单一声空化气泡的动力学过程及空化发光

1.引言 在1990年,Gaitan[1]发现悬浮在驻波声场中的单一空化气泡能象时钟一样精确地在每个崩溃时刻发出裸眼能看见的光--称之为声致发光.单泡声致发光现象从此引起了众多研究者的浓厚兴趣,很多科学家对其进行了深入而广泛的研究,得到了比较定量的数据,相关的理 论分析也得到快速的进展.     

The role of inertial cavitation in acoustic droplet vaporization

The vaporization of a superheated droplet emulsion into gas bubbles using ultrasound-termed acoustic droplet vaporization (ADV)-has potential therapeutic applications in embolotherapy and drug delivery. The optimization of ADV for therapeutic applications can be enhanced by understanding the physical mechanisms underlying ADV, which are currently not clearly elucidated. Acoustic cavitation is one possible mechanism. This paper investigates the relationship between ADV and inertial cavitation (IC) thresholds (measured as peak rarefactional pressures) by studying parameters that are known to influence the IC threshold. These parameters include bulk fluid properties such as gas saturation, temperature, viscosity, and surface tension; droplet parameters such as degree of superheat, surfactant type, and size; and acoustic properties such as pulse repetition frequency and pulse width. In all cases the ADV threshold occurred at a lower rarefactional pressure than the IC threshold, indicating that the phase transition occurs before IC events. The viscosity and temperature of the bulk fluid are shown to influence both thresholds directly and inversely, respectively. An inverse trend is observed between threshold and diameter for droplets in the 1 to 2.5 µm range. Based on a choice of experimental parameters, it is possible to achieve ADV with or without IC.     

Degradation of trichloroethylene by Fenton reaction in pyrite suspension

Degradation of trichloroethylene (TCE) by Fenton reaction in pyrite suspension was investigated in a closed batch system under various experimental conditions. TCE was oxidatively degraded by OH in the pyrite Fenton system and its degradation kinetics was significantly enhanced by the catalysis of pyrite to form OH by decomposing H(2)O(2). In contrast to an ordinary classic Fenton reaction showing a second-order kinetics, the oxidative degradation of TCE by the pyrite Fenton reaction was properly fitted by a pseudo-first-order rate law. Degradation kinetics of TCE in the pyrite Fenton reaction was significantly influenced by concentrations of pyrite and H(2)O(2) and initial suspension pH. Kinetic rate constant of TCE increased proportionally (0.0030 ± 0.0001-0.1910 ± 0.0078 min(-1)) as the pyrite concentration increased 0.21-12.82 g/L. TCE removal was more than 97%, once H(2)O(2) addition exceeded 125 mM at initial pH 3. The kinetic rate constant also increased (0.0160 ± 0.005-0.0516 ± 0.0029 min(-1)) as H(2)O(2) concentration increased 21-251 mM, however its increase showed a saturation pattern. The kinetic rate constant decreased (0.0516 ± 0.0029-0.0079 ± 0.0021 min(-1)) as initial suspension pH increased 3-11. We did not observe any significant effect of TCE concentration on the degradation kinetics of TCE in the pyrite Fenton reaction as TCE concentration increased.     

Degradation of malachite green in aqueous solution by Fenton process

In this study, advanced oxidation process utilizing Fenton's reagent was investigated for degradation of malachite green (MG). The effects of different reaction parameters such as the initial MG concentration, initial pH, the initial hydrogen peroxide concentration, the initial ferrous concentration and the reaction temperature on the oxidative degradation of MG have been investigated. The optimal reacting conditions were experimentally found to be pH 3.40, initial hydrogen peroxide concentration=0.50mM and initial ferrous concentration=0.10mM for initial MG concentration of 20mg/L at 30 degrees C. Under optimal conditions, 99.25% degradation efficiency of dye in aqueous solution was achieved after 60 min of reaction.     

Hybridization enhancement using cavitation microstreaming

Conventional DNA microarray hybridization relies on diffusion of target to surface-bound probes, and thus is a rate-limited process. In this paper, a micromixing technique based on cavitation microstreaming principle that was developed to accelerate hybridization process is explained. Fluidic experiments showed that air bubbles resting on a solid surface and set into vibration by a sound field generated steady circulatory flows, resulting in global convection flows and, thus, rapid mixing. The time to fully mix dyed solutions in a 50-microL chamber using cavitation microstreaming was significantly reduced from hours (a pure diffusion-based mixing) to 6 s. Cavitation microstreaming was implemented to enhance DNA hybridization in both fluorescence-detection-based and electrochemical-detection-based DNA microarray chips. The former showed that cavitation microstreaming results in up to 5-fold hybridization signal enhancement with significantly improved signal uniformity, as compared to the results obtained in conventional diffusion-based biochips for a given time (2 h). Hybridization kinetics study in the electrochemical detection-based chips showed that acoustic microstreaming results in up to 5-fold kinetics acceleration. Acoustic microstreaming has many advantages over most existing techniques used for hybridization enhancement, including a simple apparatus, ease of implementation, low power consumption (approximately 2 mW), and low cost.     

Fenton试剂降解泥水体系中低浓度DDE

研究了Fenton试剂对底泥-水体系中低浓度DDE的降解作用,探讨了pH、[Fe2^2 ]0、[H2O2]0以及水和泥的质量比(水／泥)等影响因素。结果表明,pH,[Fe^2 ]0以及[H2O2]0的最佳条件值分别为3．0,16mmol／L和400mmol／L,DDE降解率随水／泥比的增大而提高,反应60分钟时DDE的降解率达70％。     

Degradation of methyl tertiary-butyl ether (MTBE) by anodic Fenton treatment

Degradation of MTBE, a common fuel oxygenate, was investigated using anodic Fenton treatment (AFT) and by comparison with classic Fenton treatment (CFT). The AFT system provided an ideal pH environment (2.5-3.5) for the Fenton reaction and utilized gradual delivery of ferrous iron and hydrogen peroxide, which was more efficient than batch CFT to degrade MTBE and its breakdown products. The optimized ratio of ferrous iron to hydrogen peroxide for AFT was determined to be 1:5 (in mmol). Depending on the initial concentration, MTBE was completely degraded by the optimized AFT in 4-8 min. The breakdown products found during the treatment of MTBE were acetone, t-butyl formate, t-butanol, methyl acetate, acetic acid, and formic acid, which were all completely degraded by the optimized AFT in 32 min. Based on the experimental results and other work reported in the literature, degradation mechanisms of MTBE and its breakdown products in AFT and CFT were proposed. Generally, reactions are initiated by H-abstraction by *OH, generating carbon-centered radicals which undergo various reactions including alpha/beta-scission within the radical, combination with oxygen, oxidation by ferric ion, and reduction by ferrous ion before generating the final oxidation products. Radical combination with oxygen (and the reactions thereafter) and radical oxidation by ferric ion are believed to be the most important pathways in the overall fate of the generated radicals, while radical reduction by ferrous ion is the least important. By elucidating the reaction kinetics and mechanisms of MTBE degradation in the anodic Fenton system, this study offers a potential remediation technique for treating MTBE-contaminated wastewater.     

A real-time controller for sustaining thermally relevant acoustic cavitation during ultrasound therapy

A novel method for sustaining inertial cavitation during high-intensity focused ultrasound (HIFU) exposure in an agar-based tissue-mimicking material is presented. Inertial cavitation occurs during HIFU therapy when the local rarefaction pressure exceeds the inertial cavitation threshold of the insonated medium, and is characterized by broadband acoustic emissions which can be easily detected non-invasively using a passive cavitation detector (PCD). Under the right conditions, inertial cavitation has been previously shown to greatly enhance the rate of heat deposition by redistributing part of the energy carried at the fundamental HIFU frequency to higher frequencies, which are more readily absorbed by visco-elastic media such as soft tissue. However, in the absence of any cavitation control, inertial cavitation activity at the focus decays rapidly over a few seconds of exposure because of the combined effects of cavitation nuclei depletion, bubble dissolution, bubble-bubble interactions, increased vapor pressure caused by heating, and focal shielding caused by pre-focal bubble activity. The present work describes the design, validation, and testing of a real-time adaptive controller, with integrated passive localization capabilities, for sustaining inertial cavitation within the focal region of a HIFU transducer by modulation of the HIFU amplitude. Use of the controller in agar gel, originally at room temperature, has enabled therapeutically relevant temperatures in excess of 55°C to be maintained continuously in the focal region for more than 20 s using significantly less acoustic energy than is required to achieve the same temperature rise in the absence of cavitation control.     

Decolourization and mineralization of commercial reactive dyes by using homogeneous and heterogeneous Fenton and UV/Fenton processes

The oxidative decolourization and mineralization of three reactive dyes in separately prepared aqueous solutions C.I. Reactive Yellow 3 (RY3), C.I. Reactive Blue 2 (RB2) and C.I. Reactive Violet 2 (RV2) by using homogeneous and heterogeneous Fenton and UV/Fenton processes have been investigated. The effects of H(2)O(2), Fe(2+) and Fe(0) concentrations, Fe(2+)/H(2)O(2) and Fe(0)/H(2)O(2) molar ratios at pH 3 and T=23+/-1 degrees C have been studied. Optimal operational conditions for the efficient degradation of all three dye solutions (100 mg L(-1)) were found to be Fe(2+)/H(2)O(2)=0.5mM/20mM and Fe(0)/H(2)O(2)=2mM/1mM. The experimental results showed that the homogeneous Fenton process employing UV irradiation was the most effective. By using this process, the high levels of mineralization (78-84%) and decolourization (95-100%) were achieved. Pseudo-first-order degradation rate constants were obtained from the batch experimental data.     

Calcium peroxide (CaO2) for use in modified Fenton chemistry

The use of calcium peroxide (CaO2) powder as a source of H2O2 to promote modified Fenton (MF) chemistry was studied. First, the rate of production and yield of H2O2 from CaO2 dissolving in water at pH 6-9, and 12-13 (i.e., unbuffered CaO2) was measured. The rate of CaO2 dissolution increased as pH decreased, from 62 h for complete dissolution at pH 12-13 to only 4h at pH 6. The yield of H2O2 also increased with decreasing pH, from zero at pH 12-13 to 82% at pH 6. The ability of CaO2 to promote MF oxidation of PCE was demonstrated with a hydroxyl radical (OH) scavenger (2-propanol) at pH 8. The scavenger inhibited PCE oxidation, but 97% of the PCE was oxidized without it. Release of Cl(-) showed that PCE was mineralized. Finally, PCE oxidation was compared with liquid H2O2 (pH 7) and with CaO2 (pH 6, 7, 8, 9). Liquid H2O2 showed the lowest efficiency (mol H2O2 consumed/mol PCE oxidized) and the greatest temperature increase, disproportionation to O2, and PCE volatilization. CaO2 was a more efficient oxidant than liquid H2O2 at all pH values because it only releases H2O2 upon dissolution, reducing the loss to O2 and volatilization. CaO2 performed optimally at pH 8.     

Using acoustic cavitation to enhance chemotherapy of DOX liposomes: experiment in vitro and in vivo

Experiments in vitro and in vivo were designed to investigate tumor growth inhibition of chemotherapeutics-loaded liposomes enhanced by acoustic cavitation. Doxorubicin-loaded liposomes (DOX liposomes) were used in experiments to investigate acoustic cavitation mediated effects on cell viability and chemotherapeutic function. The influence of lingering sensitive period after acoustic cavitation on tumor inhibition was also investigated. Animal experiment was carried out to verify the practicability of this technique in vivo. From experiment results, blank phospholipid-based microbubbles (PBM) combined with ultrasound (US) at intensity below 0.3 W/cm(2) could produce acoustic cavitation which maintained cell viability at high level. Compared with DOX solution, DOX liposomes combined with acoustic cavitation exerted effective tumor inhibition in vitro and in vivo. The lingering sensitive period after acoustic cavitation could also enhance the susceptibility of tumor to chemotherapeutic drugs. DOX liposomes could also exert certain tumor inhibition under preliminary acoustic cavitation. Acoustic cavitation could enhance the absorption efficiency of DOX liposomes, which could be used to reduce DOX adverse effect on normal organs in clinical chemotherapy.     

Toward a reference ultrasonic cavitation vessel: Part 2--investigating the spatial variation and acoustic pressure threshold of inertial cavitation in a 25 kHz ultrasound field

As part of an ongoing project to establish a reference facility for acoustic cavitation at the National Physical Laboratory (NPL), carefully controlled studies on a 25 kHz, 1.8 kW cylindrical vessel are described. Using a patented high-frequency acoustic emission detection method and a sonar hydrophone, results are presented of the spatial variation of inertial acoustic cavitation with increasing peak-negative pressure. Results show that at low operating levels, inertial acoustic cavitation is restricted to, and is strongly localized on, the vessel axis. At intermediate power settings, inertial acoustic cavitation also occurs close to the vessel walls, and at higher settings, a complex spatial variation is seen that is not apparent in measurements of the 25 kHz driving field alone. At selected vessel locations, a systematic investigation of the inertial cavitation threshold is described. This was carried out by making simultaneous measurements of the peak-negative pressures leading to inertial cavitation and the resultant MHz-frequency emissions, and indicates an inertial cavitation threshold of 101 kPa +/- 14% (estimated expanded uncertainty). However, an intermediate threshold at 84 kPa +/- 14% (estimated expanded uncertainty) is also seen. The results are discussed alongside theoretical predictions and recent experimental findings.     

A novel sensor for monitoring acoustic cavitation. Part II: Prototype performance evaluation

For Part I see ibid., vol.50, no.10, p.1342 (2003). This paper describes a series of experimental studies to evaluate the performance of newly developed sensors for monitoring broadband acoustic emissions generated by acoustic cavitation. The prototype sensors are fabricated in the form of hollow, open-ended cylinders, whose inner surface is made from a thin film of piezoelectric polymer acting as a passive acoustic receiver of bandwidth greater than 10 MHz. A 4 mm thick coating of special acoustical absorber forms the outer surface of the sensor. The layer functions as a shield to cavitation events occurring outside the hollow sensor body, allowing megahertz acoustic emissions emanating from within the liquid contained in the sensor to be monitored. Testing of the new sensor concept has been carried out within the cavitating field provided by a commercial ultrasonic cleaning vessel operating at 40 kHz whose power output is rated at 1 kW. It is demonstrated that the prototype cavitation sensors are able to record a systematic increase in the level of the high-frequency acoustic spectrum (>1 MHz) as electrical power to the cleaning vessel is increased. Through careful control of the experimental conditions, reproducibility of the high frequency "energy" associated with the cavitation spectrum was found to be typically /spl plusmn/25%.     

Microdefocusing method for measuring acoustic properties using acoustic microscope

Many papers have been reporting on measuring acoustic properties of materials by acoustic microscopy. In a conventional method of V (z) curve analysis, the phase velocity and the propagation attenuation of a leaky surface acoustic wave (LSAW) are determined from the interference period Deltaz and the slope of the V(z) curve, respectively. For this method it is necessary to measure the V(z) curve for a period several times as long as the interference period Deltaz. Therefore, it is difficult to measure the acoustic properties of a sample with high resolution by the method. In order to overcome these problems, a method called the microdefocusing method is proposed. The method determines the acoustic properties of a sample by analyzing V (z) values measured in the microdefocusing region within an interference period Deltaz near a focal plane. An ultrasonic transducer called the butterfly transducer is proposed to be applied to this microdefocusing method and a digital signal processing procedure is developed to analyze the output of the ultrasonic transducer. Basic experiments are performed to confirm the principles of the new method.     

Microwave assisted catalytic oxidation of p-nitrophenol in aqueous solution using carbon-supported copper catalyst

Carbon-supported copper (Cu/GAC) catalyst was prepared by conventional impregnation method and characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The sizes of Cu particles dispersing on the surface of GAC were 0.3-1.5 microm, which could be penetrated by microwave so that Cu/GAC catalyst could absorb microwave energy effectively. The catalysis of Cu/GAC in microwave assisted catalytic oxidation of p-nitrophenol (PNP) in aqueous solution was investigated through a fixed bed reactor under ambient pressure and continuous flow mode. PNP removal reached 91.8% under optimized conditions, corresponding to 88% of TOC removal. It showed a higher PNP degradation and total organic carbon (TOC) removal for Cu/GAC catalyst than GAC alone, and Cu/GAC catalyst kept on a high catalysis and a good stability for a long time run, which indicated that GAC structure and catalytic capacity were improved by the load of Cu.     

Low-threshold cavitation in water using IR laser pulse trains

The low-temperature cavitational disruption by trains of laser pulses was demonstrated in water. The trains used in the experiment were generated by a Raman laser at a wavelength of 1626 nm. The mean value of the fragmentation threshold energy density per pulse in a train was estimated to be equal to 7.2x10(6) J/m(3). The corresponding amplitude of the negative pressure had the order of 6-7 bars at a temperature jump of only about 2 degrees C. This result opens up prospects for developing precision nonthermal cavitational laser surgery.     

Reduction of cavitation using pseudorandom signals [therapeutic US]

It is known that the scattering of ultrasound by cavitation bubbles reduces the efficiency of treatment by high-intensity focused ultrasound. In the authors' experiments striving to reduce grating lobe levels of annular arrays they observed less microbubble formation at the focus of the transducer when pseudorandom phase-modulated CW signals were used rather than single-frequency CW signals. To confirm this unexpected result, the authors performed an experiment in a solution of luminol which is known to be a cavitation detector. A 5-cm diameter spherical transducer (1.1 MHz center frequency and 0.6 MHz bandwidth), focused at 197 mm was used. The ratio of the sonoluminescence intensity produced by a single-frequency signal to that produced by a pseudorandom phase-modulated signal increased with the intensity of the applied held and attained a value of nearly 50 for an intensity of 4.6 W cm^-2      

Degradation of C.I. Reactive Red 2 through photocatalysis coupled with water jet cavitation

The decolorization of an azo dye, C.I. Reactive Red 2 was investigated using TiO(2) photocatalysis coupled with water jet cavitation. Experiments were performed in a 4.0 L solution under ultraviolet power of 9 W. The effects of TiO(2) loading, initial dye concentration, solution pH, geometry of cavitation tube, and the addition of anions on the degradation of the dye were evaluated. Degradation of the dye followed a pseudo-first order reaction. The photocatalysis coupled with water jet cavitation elevated degradation of the dye by about 136%, showing a synergistic effect compared to the individual photocatalysis and water jet cavitation. The enhancement of photocatalysis by water jet cavitation could be due to the deagglomeration of catalyst particles as well as the better contact between the catalyst surfaces and the reactants. Venturi tube with smaller diameter and shorter length of throat tube favored the dye decolorization. The degradation efficiency was found to increase with decreasing initial concentration and pH. The presence of NO(3)(-) and SO(4)(2-) enhanced the degradation of RR2, while Cl(-), and especially HCO(3)(-) significantly reduced dye decolorization. The results of this study indicated that the coupled photocatalysis and water jet cavitation is effective in degrading dye in wastewater and provides a promising alternative for treatment of dye wastewater at a large scale.