Spatial distribution of acoustic cavitation bubbles at different ultrasound frequencies.

Images of sonoluminescence, sonophotoluminescence and sonochemiluminescence are recorded in order to semi-quantitatively compare the spatial distribution of the cavitation activity at three different ultrasound frequencies (170 kHz, 440 kHz and 700 kHz) and at various acoustic amplitudes. At all ultrasound frequencies investigated, the sonochemically active cavitation zones are much larger than the cavitation zones where sonoluminescence is observed. Also, the sonochemically active bubbles are observed at relatively lower acoustic amplitudes than that required for sonoluminescence bubbles to appear.

Synthesis of temperature responsive poly(N-isopropylacrylamide) using ultrasound irradiation.

Ultrasound was employed to synthesize poly(N-isopropylacrylamide) [poly(NIPAM)] either as aqueous solutions or microgels in the absence of a chemical initiator. Poly(NIPAM) of different microstructures can be readily prepared via ultrasound irradiation by varying the reaction temperature. At a preparation temperature of 20 degrees C, poly(NIPAM) was formed in aqueous solutions, whereas, at a higher preparation temperature (beyond the lower critical solution temperature of approximately 32 degrees C), poly(NIPAM) microgels were formed.

Combined advanced oxidation processes for the synergistic degradation of ibuprofen in aqueous environments.

Ibuprofen (IBP) is a widely used analgesic and anti-inflammatory drug and has been found as a pollutant in aqueous environments. The sonolytic, photocatalytic and sonophotocatalytic degradations of IBP in the presence of homogeneous (Fe(3+)) and heterogeneous photocatalysts (TiO(2)) were studied. When compared with sonolysis and photocatalysis, a higher degradation rate was observed for sonophotocatalysis in the presence of TiO(2) or Fe(3+) and also a slight synergistic enhancement was found with a synergy index of 1.

Sonophotocatalytic degradation of monocrotophos using TiO2 and Fe3+.

Monocrotophos (MCP) is an organophosphate insecticide that has been found as a pollutant in aqueous environments. The sonolytic, photocatalytic and sonophotocatalytic degradation of MCP in the presence of homogeneous (Fe(3+)) and heterogeneous photocatalysts (TiO(2)) were studied. The photocatalytic degradation rate using TiO(2) was found to be lower than that of sonolysis alone due to the interference of phosphate ions formed as an intermediate product.

Ultrasonic processing of dairy systems in large scale reactors.

High intensity low frequency ultrasound was used to process dairy ingredients to improve functional properties. Based on a number of lab-scale experiments, several experimental parameters were optimised for processing large volumes of whey and casein-based dairy systems in pilot scale ultrasonic reactors. A continuous sonication process at 20 kHz capable of delivering up to 4 kW of power with a flow-through reactor design was used to treat dairy ingredients at flow rates ranging from 200 to 6000 mL/min.

Degradation of orange-G by advanced oxidation processes.

The degradation and mineralization of orange-G (OG) in aqueous solutions by means of ultrasound irradiation at a frequency of 213kHz and its combination with a heterogeneous photocatalyst (TiO(2)) were investigated. The effects of various operational parameters such as, the concentration of the dye and solution pH on the degradation efficiency were studied. The degradation of the dye followed first-order like kinetics under the conditions examined.

Frequency effects during acoustic cavitation in surfactant solutions.

The acoustic cavitation-induced events, multibubble sonoluminescence (MBSL) and initial growth of MBSL have been studied in surfactant solutions and correlated with bubble coalescence data at three different ultrasound frequencies. For an ionic surfactant, both the number of ultrasonic pulses required to reach a steady state MBSL intensity (N(crit)) and the magnitude of this intensity increases to a maximum as the surfactant concentration increases and then falls again. The total bubble volume generated for a fixed sonication time, which is indirectly related to bubble coalescence, similarly falls as surfactant concentration increases and then rises again.

The detection and control of stable and transient acoustic cavitation bubbles.

Acoustic cavitation plays a significant role in many applications that include therapeutic medicine, sonochemsitry and materials processing. The type of cavitation bubbles generated, namely transient or stable (repetitive transient), is important for optimizing the efficiency of these applications. We report on a multibubble sonoluminescence (MBSL)-based experimental technique for the detection and the control of type of cavitation at low and high ultrasound frequencies.

Cavitation activation by dual-frequency ultrasound and shock waves.

High-speed photographic observations of cavitation occurring under a low-frequency (21 kHz) sonotrode tip in the presence of an additional, high-frequency (355 kHz) ultrasound source have been made in water and in dilute aqueous solute solutions. Acoustic emission spectra were measured to support the visual observations. It was seen that a nucleating effect of the high-frequency action on cavitation at the low-frequency sonotrode was highly power dependent, with cavitation being homogenous at low acoustic power and highly localised at high acoustic power.

Sonochemical synthesis of liquid-encapsulated lysozyme microspheres.

Liquid-encapsulated lysozyme microspheres were successfully synthesized using a sonochemical method. The encapsulation of four different liquids, namely, sunflower oil, tetradecane, dodecane and perfluorohexane on the formation, stability and morphology of the lysozyme microspheres was studied. Among the four different liquids used for encapsulation, perfluorohexane-filled microspheres were found to be most stable in the dried state with a narrow size distribution.

Kinetics of the sonophotocatalytic degradation of orange G in presence of Fe(3+).

The degradation and mineralization of orange G (OG) in aqueous solution by means of ultrasound irradiation at a frequency of 213 kHz and its combination with Fe(3+) were investigated. The effect of Fe(3+) concentration on the degradation efficiency was studied. The degradation of the dye followed first-order like kinetics under the conditions examined.

Hot topic: sonication increases the heat stability of whey proteins.

The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat has been an ongoing problem in dairy processing for many decades. This phenomenon can restrict the range of dairy product options and reduce manufacturing efficiencies by limiting the type and extent of heat treatment that can be used. In this report, we outline a novel approach to overcoming this problem.

Bubble population phenomena in sonochemical reactor: II. Estimation of bubble size distribution and its number density by simple coalescence model calculation.

A simple bubble population model, with emphasis on the bubble-bubble coalescence, is proposed. In this model, the bubble size distribution is simulated through the iteration of fundamental bubble population process: generation, dissolution, and coalescence. With this simple modelling, the bubble size distribution experimentally observed by the pulsed laser diffraction method and the void rate obtained by the capillary system at 443kHz were successfully simulated.

Bubble population phenomena in sonochemical reactor: I estimation of bubble size distribution and its number density with pulsed sonication - laser diffraction method.

To characterize the bubble populations (size and its number distribution) in a sonochemical reactor, a simple but powerful technique based on the Fraunhofer laser diffraction (LD) has been proposed. In this method, the acoustic wave disturbance to the laser probe in the sonochemical reaction field was eliminated by the temporal separation using pulsed sonication (pulsed LD). With this relatively simple strategy, the temporal development of the bubble size distribution could be evaluated by pulsed LD.

Simple and efficient sonochemical method for the oxidation of arsenic(III) to arsenic(V).

A simple and efficient sonochemical method has been developed for the oxidation of acutely toxic As(III) to the less toxic As(V). The OH radicals produced during acoustic cavitation readily oxidize As(III) to As(V) in an aqueous environment The effects of various operational parameters of ultrasonication, such as power density and pulse mode, on the oxidation of As(III) were studied. Pulsed sonication showed a profound effect on the oxidation of As(III) to As(V) in comparison to the continuous mode of operation, that consequently reduced the reaction time and energy requirement for the process.

Visible light assisted photocatalytic degradation of acid red 88 using Au-ZnO nanophotocatalysts.

Photocatalytic degradation of acid red 88 (AR88) in aqueous suspensions of Au-ZnO nanoparticles under visible light illumination was studied in order to evaluate various effects of the Au deposition on the ZnO photocatalytic activity. Au-ZnO nanoparticles were prepared by deposition precipitation method and characterized by different analytical techniques. In Au-ZnO system, all gold nanoparticles were tethered on the surface of zinc oxide particles.

Genetic variants on apolipoprotein gene cluster influence triglycerides with a risk of coronary artery disease among Indians.

Apolipoprotein C3 and apolipoprotien A5 are proteins coded from the APOA1/C3/A4/A5 gene cluster. Sst I polymorphism on apolipoprotein C3 and -1131C polymorphism of apolipoprotien A5 are key variants involved in triglyceride metabolism and cause a significant cardio-metabolic risk. Here, we have evaluated these two variants for their roles in coronary artery disease in patients of the Indian population.

Minimising oil droplet size using ultrasonic emulsification.

The efficient production of nanoemulsions, with oil droplet sizes of less than 100nm would facilitate the inclusion of oil soluble bio-active agents into a range of water based foods. Small droplet sizes lead to transparent emulsions so that product appearance is not altered by the addition of an oil phase. In this paper, we demonstrate that it is possible to create remarkably small transparent O/W nanoemulsions with average diameters as low as 40nm from sunflower oil.

Effect of power and frequency on bubble-size distributions in acoustic cavitation.

Acoustic bubble-size distributions have been determined using a pulsed ultrasound method at different ultrasound powers and frequencies. It was observed that the mean bubble size increased with increasing acoustic power and decreased with increasing ultrasound frequency. It was also recognized that the mean size of bubbles emitting sonoluminescence was greater than those producing sonochemiluminescence indicating that the two processes take place in different populations of cavitation bubbles in the system.

Novel one-pot synthesis of magnetite latex nanoparticles by ultrasound irradiation.

A simple and efficacious procedure for the synthesis of magnetite nanoparticles has been achieved via a sonochemical miniemulsion polymerization process. The sonochemically synthesized magnetite encapsulated polymer latex particles exhibit excellent colloidal stability and strong magnetic properties, and are of a size that makes them technologically relevant. This novel method may be readily extended to the preparation of multiple combinations of different polymers and encapsulated materials.

Kinetics and mechanism for the sonochemical degradation of a nonionic surfactant.

The sonolytic degradation of the nonionic surfactant, octaethylene glycol monododecyl ether (C(12)E(8)), has been studied at various initial concentrations below and above its critical micelle concentration (CMC). It has been observed that the degradation rate increases with an increase in the initial concentration of the surfactant until the CMC is reached. Above the CMC an almost constant degradation rate is observed, suggesting that the surfactant in its monomer form is involved in the degradation process.

The pasting properties of sonicated waxy rice starch suspensions.

The effect of sonication on the pasting properties of waxy rice starch solutions (5 wt%) was investigated. It has been found that the functionality of starch granules was significantly influenced by the length of sonication and the solution temperature. A comparison of the pasting behaviour showed that the peak and final viscosities of the starch dispersions sonicated at temperatures near the onset temperature of gelatinisation were lower than those of the non-sonicated dispersions.

Sonochemical synthesis of Au-TiO2 nanoparticles for the sonophotocatalytic degradation of organic pollutants in aqueous environment.

Au-TiO2 photocatalysts were sonochemically prepared by three different procedures and their photocatalytic and sonophotocatalytic efficiencies were evaluated by studying the degradation of a representative organic pollutant, nonylphenol ethoxylate (NPE) surfactant in aqueous solutions. In the first procedure, Au-TiO2 nanoparticles were prepared by depositing sonochemically synthesized gold nanoparticles on Degussa P25 TiO2 by stirring in the absence of an ultrasonic field. In the second procedure, Au nanoparticles were sonochemically synthesized and simultaneously deposited on Degussa P25 TiO2 particles.

Photocatalytic degradation of Acid Red 88 using Au-TiO(2) nanoparticles in aqueous solutions.

Metal loaded semiconductors in general possess greater photocatalytic activity than pure semiconductors. Hence, with an attempt to achieve higher photocatalytic activity, Au-TiO(2) photocatalysts were prepared by deposition-precipitation method and used for the photocatalytic degradation of an azo dye (Acid Red 88; AR88). The materials were characterized by different analytical techniques.

Ultrasonic nebulization in aqueous solutions and the role of interfacial adsorption dynamics in surfactant enrichment.

High-density micron-sized aerosols from liquid surfaces were generated using an ultrasonic (frequency = 1056 kHz) nebulization technique in the absence and presence of a number of surfactants. The surfactants included cationic surfactants, cetylpyridinium chloride and dodecylpyridinium chloride, and anionic surfactants, sodium dodecylbenzenesulfonate and sodium benzenesulfonate. The nebulization process generated aerosols of a narrow size distribution with a number mean diameter of about 3.