Ultrasonic effects on electroorganic processes--Part 20. Photocatalytic oxidation of aliphatic alcohols in aqueous suspension of TiO2 powder

Ultrasonic effects in a suspension system were examined using the photocatalytic oxidation of 2-propanol to acetone and of ethanol to acetaldehyde in the aqueous suspension of TiO2 powder as a model reaction. The formation rate of acetone was significantly increased under ultrasonic irradiation. The oxidation reaction under ultrasonic irradiation was affected in a different manner from that in silence by reaction conditions such as ultrasonic power, stirring speed, amount of TiO2, concentration of 2-propanol, and pretreatment of the TiO2 powder. Furthermore, it was also observed that the particle size of the TiO2 photocatalyst powder was increased due to the particle agglomeration by ultrasonic irradiation, and consequently it was suggested that ultrasound activates the surface of the catalyst. These results are discussed on the basis of not only the activation of the photocatalyst but also ultrasonic enhancement of mass transport of 2-propanol molecules.     

Ultrasonic-assisted Dunlop method for natural rubber latex foam production: Effects of irradiation time on morphology and physico-mechanical properties of the foam

An ultrasonic-assisted technique was first introduced for the production of natural rubber latex foam (NRLF). The flexible elastomeric foam was formed by a liquid–solid state transformation in an aqueous media. The aim of the current research was to provide a novel strategy for fabricating NRLF using ultrasonication and the Dunlop method, as well as to simultaneously utilize irradiation events to achieve the desired foam properties. NRLFs were exposed to ultrasonication at 25 kHz at the beginning of the gelling process. The effects of irradiation times of 0, 1, 3, 5 and 7 min on the morphology, foaming behaviors, physical properties and mechanical performance of NRLFs were investigated. The results revealed that using ultrasonic irradiation, unfoamed regions and a bimodal structure, which seem to be microstructural defects in conventional NRLF, could be completely eliminated. However, excessive irradiation times of 5 min and longer appeared to affect the physico-mechanical properties of the foams in terms of transient cavitation and the unfavorable physicochemical effects of ultrasonic vibrations. As a result, the optimal ultrasonic irradiation time was found to be 3 min. Using this irradiation duration, a foam with the suitable microcellular structure achieved the most desirable properties, such as its expansion ratio (7-fold increase), foam porosity (85.7%), compression recoverability (98.7%), and tensile strength (307.3 kPa). Moreover, the foam still maintained its characteristic soft nature (hardness less than 100 N) with an indentation hardness of 71.9 N. Therefore, ultrasonic treatment introduced to the conventional Dunlop method is a potentially feasible technique since it improves the morphology and the physico-mechanical properties of NRLFs.     

Solubilisation of micellar casein powders by high-power ultrasound

High protein milk ingredients, such as micellar casein powder (MCP), exhibit poor solubility upon reconstitution in water, particularly after long-time storage. In this study, ultrasonication (20 kHz, power density of 0.75 W/ml) was used to improve the solubility of aged MCP powders. For all the MCP powders (concentration varying from 0.5 to 5%, and storage of MCP at 50 °C for up to 10 days) it was found that short time ultrasonication (2.5 min) reduced the size of the protein particles from >30 μm to ∼0.1 μm, as measured by light scattering. This resulted in an improvement of solubility (>95%) for all the MCP powders. Cryo-electron microscopy and small x-ray angle scattering showed that the MCP powders dissolved into particles with morphologies and internal structure similar to native casein micelles in bovine milk. SDS-PAGE and RP-HLPC showed that ultrasonication did not affect the molecular weight of the individual casein molecules. Compared to overhead stirring using a 4-blade stirrer, ultrasonication required less than 10 times the drawn electrical energy density to achieve a particle size 10 times smaller.     

The ex-situ and in-situ ultrasonic assisted oxidation of corn starch: A comparative study

The objective of this study was to evaluate the differences in ex-situ (starch treated by ultrasonication and oxidation sequentially, U-OS) and in-situ (starch treated by ultrasonication and oxidation simultaneously, UOS) ultrasonic assisted oxidation process of corn starch, which were studied in contrast to the traditional oxidized starches (OS). Fourier-transform infrared spectra confirmed the successful oxidation of all modified starches samples. In comparison to the OS, the carboxyl contents of U-OS and UOS increased by 56% and 112%, respectively. The same increase trend was also found for the carbonyl contents. The significance raise was attributed to the great increase of pores and specific surface areas in the starch granule after ultrasonic irradiation which promoted the penetration of the sodium hypochlorite into the starch granules with higher chances for chemical reactions. SEM and pore size distribution characterizations further verified this result. However, the method of in-situ ultrasonic assisted oxidation can simultaneously accelerate the increase of pores and the penetration process. Consequently, the starches with higher oxidation degree can be more efficiently prepared by the strategy of in-situ ultrasonic assisted oxidation.     

Ultrasonic-assisted sol-gel method of preparation of TiO2 nano-particles: characterization, properties and 4-chlorophenol removal application

Nano-size TiO2 photocatalysts were prepared by sol-gel and ultrasonic-assisted sol-gel methods using two different sources of ultrasonicator, i.e., a bath type and tip type. The physicochemical characteristics of the catalysts were investigated by BET, XRD and TEM analyses and the photocatalytic properties of the TiO2 catalysts prepared by three different methods were compared. The intrinsic and extrinsic properties of TiO2, such as the particle size, surface area, pore-volume, pore-diameter, crystallinity as well as anatase, rutile and brookite phase ratios, could be controlled by the ultrasonic-assisted sol-gel method. During this preparation method, the effect of such important operating variables as the ultrasonic irradiation time, power density, the ultrasonic sources (bath-type and tip-type), magnetic stirring during synthesis, initial temperatures and size of the reactors are discussed here. It was found that each of the parameters played a significant role in controlling the properties of the TiO2 nano-particles. Among the three different methods, TiO2 photocatalysts prepared by ultrasonic (tip-US) assisted sol-gel possessed the smallest particle size, highest surface area and highest pore-volume than the catalysts prepared by the other two methods. 4-Chlorophenol was used as a pollutant to observe the photocatalytic degradation ability of the prepared photocatalysts and the TiO2 catalysts prepared by the bath-US ultrasonic-assisted sol-gel method were shown to be the most highly active. This is due to their high surface area and high pore-diameter. This study clearly demonstrates the importance and advantages of ultrasonication in the modification and improvement of the photocatalytic properties of mesoporous nano-size TiO2 particles.     

Physical and chemical characteristics of ultrasonically-prepared water-in-diesel fuel: Effects of ultrasonic horn position and water content

An ultrasonic technique was applied to preparation of two-phase water-in-oil (W/O) emulsified fuel of water/diesel oil/surfactant. In this study, an ultrasonic apparatus with a 28 kHz rod horn was used. The influence of the horn tip position during ultrasonic treatment, sonication time and water content (5 or 10 vol%) on the emulsion stability, viscosity, water droplet size and water surface area of emulsion fuels prepared by ultrasonication was investigated. The emulsion stability of ultrasonically-prepared fuel significantly depended on the horn tip position during ultrasonic irradiation. It was found that the change in the stability with the horn tip position was partly related to that in the ultrasonic power estimated by calorimetry. Emulsion stability, viscosity and sum of water droplets surface area increased and water droplet size decreased with an increase in sonication time, and they approached each limiting value in the longer time. The maximum values of the viscosity and water surface area increased with water content, while the limiting values of the emulsion stability and water droplet size were almost independent of water content. During ultrasonication of water/diesel oil mixture, the hydrogen and methane were identified and the cracking of hydrocarbon components in the diesel oil occurred. The combustion characteristics of ultrasonically-prepared emulsion fuel were studied and compared with those of diesel oil. The soot and NOx emissions during combustion of the emulsified fuel with higher water contents were significantly reduced compared with those during combustion of diesel oil.     

Preparation of Daidzein microparticles through liquid antisolvent precipitation under ultrasonication

In this study, daidzein microparticles (DMP) were prepared using an improved ultrasound-assisted antisolvent precipitation method. Preliminary experiments were conducted using six single-factor experiments, and principal component analysis (PCA) was adopted to obtain the three staple elements of the ultrasonic power, solution concentration, and nozzle diameter. The response surface Box-Behnken (BBD) design was used to optimize the level of the above factors. The optimal preparation conditions of the DMP were obtained as follows: the flow rate was 4 mL/min, the concentration of the daidzein solution was 16 mg/mL, the ratio of antisolvent to solvent (liquid-to-liquid ratio) was 9, the nozzle diameter was 300 μm, the ultrasonic power was 180 W (665 W/L), and the system speed was 760 r/min. The minimum average particle size of DMP was 181 ± 2 nm. The properties of daidzein particles before and after preparation were analyzed via scanning electron microscopy, X-ray diffraction analysis, Differential scanning calorimetry and Fourier transform infrared spectroscopy, no obvious change in its chemical structure was observed, but crystallinity was reduced. Compared with daidzein powder, DMP has a higher solubility and stronger antioxidant capacity. The above results indicate that the improved method of ultrasonication combined with antisolvent can reduce the size of daidzein particles and has a great potential in practical production.     

Green fabrication and characterization of debranched starch nanoparticles via ultrasonication combined with recrystallization

With recent advances in nanotechnology, debranched starch nanoparticle (DBS-NP) materials have attracted considerable interest from the fields of functional food, biomedicine, and material science, thanks to their small size, biodegradability, biocompatibility, sustainability, and non-hazardous effects on health and the environment. In this study, DBS-NP was fabricated using an eco-friendly method involving ultrasonication combined with recrystallization. The effects of ultrasonication and recrystallization times on the morphology, particle size, and crystal structure of the DBS-NPs were systematically investigated. Compared with the DBS-NPs prepared using ultrasonication treatment only, the DBS-NPs formed using ultrasonication combined with recrystallization were uniform in size and well distributed in aqueous solution. Moreover, the maximum encapsulation efficiency and loading capacity of the epigallocatechin gallate (EGCG) in the DBS-NPs with ultrasonication treatment reached 88.35% and 22.75%, respectively. The particle sizes of the EGCG@DBS-NP were more stable at a neutral pH (7.4) than at an acidic pH (2.1). The EGCG in the EGCG@DBS-NP displayed excellent radical scavenging activity and antibacterial effects, and cell assays demonstrated that the EGCG@DBS-NP was non-toxic and highly biocompatible.     

Identification of the Dispersion Behavior of Surface Treated Nanoscale Powders

The stability of highly acidic metal oxide surface treatments on rutile titanium dioxide nanopowders (40 nm nominal particle size) is examined. Dispersions are characterized in terms of their sedimentation behavior and light scattering pattern. Using elliptically polarized light scattering (EPLS), agglomerates are identified as fractal structures and size analysis is performed according to the measured fractal dimension. The effect of ultrasonication on agglomerate size and structure (compactness) is quantified for tungsten oxide and molybdenum oxide surface treatments, as well as untreated titanium oxide. Surface treatments are shown to increase dispersion stability, as witnessed by the decreased size of large agglomerates and sedimentation behavior. The EPLS fractal studies, combined with ultrasonication analysis, reveals information of agglomerate shapes, primary particle bonds and structures, and agglomerate growth mechanisms.     

Effect of amplitude and frequency of ultrasonic irradiation on morphological characteristics control of calcium carbonate

We have previously reported on the morphological control of calcium carbonate by changing synthetic conditions such as temperature, pH and degree of supersaturation in liquid reaction. The present study reports the effect of amplitude and frequency of ultrasonic irradiation on the particle size of calcium carbonate using a horn type ultrasonic apparatus at two different frequencies. The calcium carbonate precipitated by mechanical stirring had a particle size of about 20 μm. By contrast, the particle size of vaterite formed under ultrasonic irradiation was about 2 μm, with a specific surface area of 25–30 m²/g. The major polymorph of calcium carbonate formed by ultrasonic irradiation was vaterite with some calcite present. For 40 kHz ultrasonic irradiation, the specific surface area of the calcium carbonate increased with increasing amplitude. The particle size of vaterite formed at this frequency was about 2 μm, and its distribution was sharper than that obtained at 20 kHz. The mode diameter of the synthesized vaterite was found to decrease with increasing amplitude at 40 kHz.     

Ultrasound stimulated production of a fibrinolytic enzyme

The present study is aimed at enhanced production of a fibrinolytic enzyme from Bacillus sphaericus MTCC 3672 under ultrasonic stimulation. Various process parameters viz; irradiation at different growth phases, ultrasonication power, irradiation duration, duty cycle and multiple irradiation were studied for enhancement of fibrinolytic enzyme productivity. The optimum conditions were found as follows, irradiation of ultrasonic waves to fermentation broth at 12 h of growth phase with 25 kHz frequency, 160 W ultrasound power, 20% duty cycle for 5 min. The productivity of fibrinolytic enzyme was increased 1.82-fold from 110 to 201 U/mL compared with the non sonicated control fermentation. Drop in glucose concentration from 0.41% to 0.12% w/v in ultrasonicated batch implies that, ultrasonication increases the cell permeability, improves substrate intake and progresses metabolism of microbial cell. Microscopic images before and after ultrasonic stimulation clearly signifies the impact of duty cycle on decreasing biomass concentration. However, environmental scanning electron micrograph does not show any cell lysis at optimum ultrasonic irradiation. Offshoots of our results will contribute to fulfill the demand of enhancement of microbial therapeutic enzyme productivity, through ultrasonication stimulation.     

Sonochemical coating of magnetite nanoparticles with silica

Magnetite nanoparticles were coated with silica through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) under ultrasonic irradiation. The ultrasonic irradiation was used to prevent the agglomeration of the magnetite particles and accelerate the hydrolysis and condensation of TEOS. TEM, DLS, XRF, VSM, TG and sedimentation test were used to characterize the silica-coated magnetite particles. The dispersibility of silica-coated magnetite particles in aqueous solution was improved significantly and the agglomerate particle size was decreased to 110 nm. It was found that the agglomerate particle size of silica-coated magnetite particles was mainly decided by the coating temperature and the pH value in the silica-coating process. The weight ratio of silica in silica-coated magnetite particles was mainly decided by the pH value in the silica-coating process. The dispersibility of silica-coated magnetite particles was mainly decided by the agglomerate particle size of the suspension. The oxidation of magnetite particles in air was limited through the coated silica. The magnetism of silica-coated magnetite particles decreased slightly after silica-coating.     

Sonoelectrochemical Synthesis of Nano Zinc (II) Complexes with 9-Anthracenecarboxylic Acid: Effect of Current Density and Study of their Photophysical Properties

A new zinc complex, [Zn (9-AC)₂] (1) (9-AC = 9-anthracenecarboxylic acid), was prepared via conventional electrochemical method in a fast and facile process and fully characterized by ¹H NMR, ¹³C NMR, IR spectroscopy and elemental analysis. The nano structures of the same compound were successfully produced by a facile and environment-friendly sonoelectrochemical route at different current densities (0.5, 1.2, 1.8, 2.5 and 3.5 mA/cm²). The new nano-structure particles were characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analysis. Thermal stability of single crystal and nano-size samples of the prepared compound was studied by thermogravimetric and differential thermal analysis. The comparison of the effect of current density without and with ultrasonic irradiation on particle size has been investigated in convectional electrochemical and sonoelectrochemical method respectively. The results showed that using ultrasonic irradiation with increasing the current density lead to decrease the particle sizes unlike conventional electrochemical method. In other words, when the current density increase from 0.5 to 3.5 mA/cm², in sonoelectrochemical method, the particle sizes decrease from 100 to 48 nm while, in convectional electrochemical method, the particle sizes increase from 400 to 1200 nm and possible explanation offered. Photoluminescence properties of the nano-structured and crystalline bulk of the prepared complex at room temperature in the solid state have been investigated in detail. The results indicate that the size of the complex particles has an important effect on their optical properties.     

Effect of combined ultrasonic and enzymatic extraction technique on the quality of noni (Morinda citrifolia L.) juice

In order to obtain noni juice with high yield and good quality, the effect of combined extraction technique of enzymatic treatment (EZ) and ultrasonication (US) on the overall quality of noni juice was investigated. Moreover, the extraction performance of the EZ-US combined extraction technique was compared with that of EZ-based extraction and the US-based extraction. Response surface methodology (RSM) was designed to optimize the parameters of ultrasonic treatment, by taking consideration of the extraction efficiency, quality parameters and bioactive ingredients of noni juice. The results indicated that combined ultrasonic and enzymatic treatment achieved a synergistic effect on promoting the quality of noni juice. The maximum juice yield of 67.95 % was obtained under ultrasonication for 10 min at 600 W after enzymatic treatment (EZU). In addition, EZU-treated juice exhibited the highest contents of total phenolic and flavonoid, which were 148.19 ± 2.53 mg gallic acid/100 mL and 47.19 ± 1.22 mg rutin/100 mL, respectively, thus contributing to better antioxidant activity. Moreover, the EZU treatment significantly reduced the particle size of noni juice, and improved its suspension stability and rheological properties. FTIR results indicated that the treatments did not bring major changes in the chemical structure and the functional groups of compounds in noni juice. Therefore, EZU treatment can be successfully applied to the extraction of noni juice with better nutritional properties and overall quality.     

Role of Ag ions on the structural evolution of nano ZnO clusters synthesized through ultrasonication and their optical properties

ZnO powder doped with 0.84 at wt.% of silver has been synthesized through continuous and pulsed mode sonication method. The particle size was found to be 57(±1)nm and 44(±1)nm for continuous and pulsed mode powder, respectively. Contraction along 'c' axis has been observed for Ag doped powders. The surface area measured for pulsed mode powder was found to be twice that of continuous mode powder. Photoluminescence spectra of pulsed mode ZnO:Ag powder show new emission band at 608 nm. This has been attributed to silver atoms sitting on the surface of ZnO nano rods. Structure of the nano rods observed in both the samples was found to be different and this has been attributed to the presence of silver on the surface of the nano rods. The structural evolution during the process of sonication has been explained in the light of Ag ion reduction in the local high concentration region during ultrasonication.     

Structural and functional changes in ultrasonicated bovine serum albumin solutions

Effects of high-intensity ultrasonication on functional and structural properties of aqueous bovine serum albumin (BSA) solutions were investigated. The functional properties of BSA were altered by ultrasonication. Surface activity of BSA increased. Minimal changes were observed in the global structure of BSA but surface charge increased particularly at basic pH values (e.g. pH>9). While dynamic light scattering measurements indicated that the particle size increased up to 3.4 times after 90 min of sonication, no significant increase in the oligomeric state of BSA using blue native PAGE was observed. The amount of free sulfhydryl groups in BSA after 90 min of sonication decreased. The increased particle size and decreased number of free sylfhydryl groups may be attributed to formation of protein aggregates. Surface hydrophobicity increased and circular dichroism spectroscopy and FTIR analysis indicated changes in the secondary structure of BSA. We hypothesize that mechanical, thermal and chemical effects of ultrasonication resulted in structural changes in BSA that altered the functional properties of the macromolecule which may be attributed to the formation of an ultrasonically induced state that differs from a thermally, mechanically or solvent induced state.     

Ultrasonic pretreatment of corn slurry for saccharification: A comparison of batch and continuous systems

The effects of ultrasound on corn slurry saccharification yield and particle size distribution was studied in both batch and continuous-flow ultrasonic systems operating at a frequency of 20 kHz. Ground corn slurry (28% w/v) was prepared and sonicated in batches at various amplitudes (192–320 μm_{peak-to-peak (p–p)}) for 20 or 40 s using a catenoidal horn. Continuous flow experiments were conducted by pumping corn slurry at various flow rates (10–28 l/min) through an ultrasonic reactor at constant amplitude of 12 μm_p–p. The reactor was equipped with a donut shaped horn. After ultrasonic treatment, commercial alpha- and gluco-amylases (STARGEN^TM 001) were added to the samples, and liquefaction and saccharification proceeded for 3 h. The sonicated samples were found to yield 2–3 times more reducing sugars than unsonicated controls. Although the continuous flow treatments released less reducing sugar compared to the batch systems, the continuous flow process was more energy efficient. The reduction of particle size due to sonication was approximately proportional to the dissipated ultrasonic energy regardless of the type of system used. Scanning electron microscopy (SEM) images were also used to observe the disruption of corn particles after sonication. Overall, the study suggests that both batch and continuous ultrasonication enhanced saccharification yields and reduced the particle size of corn slurry. However, due to the large volume involve in full scale processes, an ultrasonic continuous system is recommended.     

Ultrasonication an intensifying tool for preparation of stable nanofluids and study the time influence on distinct properties of graphene nanofluids – A systematic overview

Optimum ultrasonication time will lead to the better performance for heat transfer in addition to preparation methods and thermal properties of the nanofluids. Nano particles are dispersed in base fluids like water (water-based fluids), glycols (glycol base fluids) &oils at different mass or volume fraction by using different preparation techniques. Significant preparation technique can enhance the stability, effects various parameters & thermo-physical properties of fluids. Agglomeration of the dispersed nano particles will lead to declined thermal performance, thermal conductivity, and viscosity. For better dispersion and breaking down the clusters, Ultrasonication method is the highly influential approach. Sonication hour is unique for different nano fluids depending on their response to several considerations. In this review, systematic investigations showing effect on various physical and thermal properties based on ultrasonication/ sonication time are illustrated. In this analysis it is found that increased power or time of ideal sonication increases the dispersion, leading to higher stable fluids, decreased particle size, higher thermal conductivity, and lower viscosity values. Employing the ultrasonic probe is substantially more effective than ultrasonic bath devices. Low ultrasonication power and time provides best outcome. Various sonication time periods by various research are summarized with respect to the different thermophysical properties. This is first review explaining sonication period influence on thermophysical properties of graphene nanofluids.     

Improvement in properties of coal water slurry by combined use of new additive and ultrasonic irradiation

Coal water slurry (CWS) was prepared with a newly developed additive from naphthalene oil. The effects of ultrasonic irradiation on coal particle size distribution (PSD), adsorption behavior of additive in coal particles and the characteristics of CWS were investigated. Results showed that ultrasonic irradiation led to a higher proportion of fine coal in CWS and increased the saturated adsorption amount of additive in coal particles. In addition, the rheological behavior and static stability of CWS irradiated by ultrasonic wave were remarkably improved. The changes on viscosity of CWS containing 1% and 2% additive are qualitatively different with the increasing sonication time studied. The reason for the different effect of sonication time on CWS viscosity is presented in this study.     

Investigation on transition crystal of ordinary rutile TiO2 powder and its sonocatalytic activity

The transition crystal TiO(2) sonocatalyst was prepared utilizing the method of ultrasonic irradiation in hydrogen peroxide solution. The sonocatalytic activity of the transition crystal TiO(2) powder was validated through the degradation of methyl orange in aqueous solution by ultrasonic irradiation. The results show that the sonocatalytic activity of the transition crystal TiO(2) powder is obviously higher than that of pure rutile and anatase TiO(2) powders as well as mixed rutile and anatase TiO(2) powders according to the proportion of corresponding transition crystal TiO(2) catalyst. The degradation ratio of methyl orange in the presence of the transition crystal TiO(2) catalyst surpasses 75% within 80 min ultrasonic irradiation, while the degradation ratios are 55.93%, 51.68% and 40.88%, respectively, for rutile, mixed and anatase TiO(2) powders.