Continuous Ultrasonic Irradiation Research Articles

Polymorph control by designed ultrasound application strategy: The role of molecular self-assembly

Molecular self-assembly plays a vital role in the nucleation process and sometimes determines the nucleation outcomes. In this study, ultrasound technology was applied to control polymorph nucleation. For the first time, different ultrasonic application methods based on the nucleation mechanisms have been proposed. For PZA-water and DHB-toluene systems that the molecular self-assembly in solution resembles the synthon in crystal structure, ultrasound pretreatment strategy was conducted to break the original molecular interactions to alter the nucleated form. When the solute molecular self-associates can’t give sufficient information to predict the nucleated polymorph like INA-ethanol system, the method of introducing continuous ultrasonic irradiation in the nucleation stage was applied. The induction of ultrasound during nucleation process can break the original interactions firstly by shear forces and accelerate the occurrence of nucleation to avoid the reorientation and rearrangement of solute molecules. These strategies were proved to be effective in polymorph control and have a degree of applicability.

Enzyme-free saccharification of cellulose to glucose using ultrasonic welding

• Ultrasonic welding can decompose cellulose in a short time. • No enzymes or catalysts are required for cellulose degradation. • The present method can be applied to the process of producing bioethanol from nonedible biomass. Ultrasonic welding is a processing technology that can instantly fuse and join thermoplastic resins by applying minute amounts of ultrasonic vibration and pressure. The present study demonstrates that the frictional force or pressure caused by ultrasonic welding can cause cellulose decomposition without a saccharifying enzyme or catalysts. Ultrasonic waves of 19.5 kHz were irradiated downward on samples using a horn-type transducer. The cellulose specimens were composed of 15 – 105 stacked sheets of filter paper with high cellulose content, a sheet of cotton, and a sheet of hemp. The high frictional forces resulting from direct contact of cellulose with the ultrasonic horn tips decomposed the saccharides within a short time to produce glucose. Cellulose is decomposed into glucose through hydrolysis in an enzyme-free environment by ultrasonic irradiation, but then it is further decomposed into 5-hydroxymethylfurfural, furfural, and other compounds via a dehydration reaction caused by an increase in temperature of the reaction field from continuous ultrasonic irradiation. Glucose could be obtained from the cellulose without using an enzyme through ultrasonic welding. The result of decomposing cellulose, cotton, and hemp by this method revealed that a yield of 1.2% glucose could be obtained by decomposing filter paper.

Continuous and pulsed ultrasound pectin extraction from navel orange peels

Pectin is a valuable product (up to 30 $kg−1) that makes-up 20–30% of an orange’s peel. The commercial extraction is lengthy (up to 6h) and energy intensive as it requires heating aqueous solutions (60–100 °C). Ultrasound speeds up the extraction process reducing processing time by macroscopic and microscopic mixing by acoustic cavitation. We adopted an ultrasonic horn to deliver a rated power of 500W at amplitudes of 20%, 40%, and 60% with and without pulsation to extract pectin from waste orange peels. These correspond to power densities of 0.08Wml−1, 0.16Wml−1 and 0.24Wml−1, respectively. The extractions operated at a pH of either 2 or 3. The experimental data agree with the fitted values from the statistical model (R2=95.5%). The model confirms our predictions that yield increases with amplitude/power density and decreasing pH. The highest yield was (11%) at a pH of 2 and with continuous ultrasonic irradiation at a power density of 0.24Wml−1. There is only a 1.3% difference between this datum and pulse ultrasound mode (1 s on/1 s off) at the same conditions — a Student’s t test confirmed that there was no significant difference in yield between continuous and pulse mode. However, pulsing is more efficient in that it consumes less than half the energy of continuous operation (80kJ vs. 190kJ).

Ultrasound‐Controlled Chiral Separation of Four Amino Acids and 2,2,2‐Trifluoro‐1‐(9‐anthryl)ethanol

Chiral separation of 4‐hydroxyphenylglycine, phenylglycine, tryptophan, methionine, and 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol (TFAE) was performed under ultrasound reduction at room temperature and high temperature (50 °C). At high temperature (50 °C), both α and Rs were improved slightly under ultrasound reduction as compared to those under non‐ultrasonic and ultrasonic irradiation (50 watt/L) conditions. Even at low temperatures, the largest α was observed under ultrasound reduction conditions, except in the case of methionine. However, at low temperature, Rs was reduced under ultrasound (50 watt/L) irradiation, but was improved under ultrasound reduction rather than under the continuous ultrasonic irradiation. Similar to the fact that gradient elution (based on solvent polarity) can improve α , ultrasound reduction can improve α and Rs. Ultrasound reduction is demonstrated to aid the rapid separation of chiral compounds with improved resolution, especially, at high temperatures. Although chromatographic separation using ultrasound has been rarely dealt with until now, ultrasound can be used as an external field in chromatography.

Enhanced coagulation by high-frequency ultrasound in Microcystis aeruginosa-laden water: Strategies and mechanisms

Ultrasonic treatment has attracted much attention because of its physical and chemical effects that are distinct from those of chemical agents. In particularly, high-frequency ultrasound is known as an effective method because the theoretical resonance frequency of the gas vesicles in Microcystis aeruginosa is in the high frequency range (>100 kHz), which causes gas vesicles collapse and changes the settleability of the algal cells. In this work, the effects of the ultrasonic frequency, acoustic power density and duration on enhancing coagulation to remove turbidity in algae-laden water were studied. In order to explain the mechanism, the morphology of algae cells, the changes in extracellular organic substances, the zeta potential and the formation of hydroxyl radicals were analyzed systematically. Finally, Zeta potentials and flocs morphology after adding PAC were investigated to verify the mechanism. The results showed that the frequency exhibited fewer effects than power and duration on coagulation. SEM images showed that there were more severe cellular damages at 430 and 740 kHz than other frequencies. Sonication could cause the collapse of gas vesicle inside the cell, which was due to the instantaneous high pressure generated by the ultrasonic cavitation instead of the resonance. Furthermore, sonication would result in an increase in proteins in extracellular organic matter (EOM) with continuous ultrasonic irradiation, indicating that a small amount of proteins could promote coagulation and that the accumulation of proteins would inhibit coagulation. Free radical content testing showed that the production of excessive free radicals was often accompanied by a deterioration of the coagulation. The proper mechanical effects were the main mechanism of ultrasonic enhanced coagulation. Thus, it was recommended that the appropriate ultrasonic condition was the one that resulted in a small amount of protein leakage and little generation of free radicals, which occurred at 740 kHz and 0.02 W/mL in approximately 5 min, and would significantly enhance the turbidity removal rate in algae-containing water from approximately 80–90%.

Ultrasound membrane hybrid processes for dairy wastewater treatment: pilot-scale analysis

Novel wastewater treatments are necessary to effectively decrease the organic load of dairy wastewater before disposal. In this work the feasibility of a hybrid process of membrane filtration combined with ultrasonication to decrease organic load was investigated. The efficiency of the advanced hybrid process that simultaneously applies ultrasonic irradiation and pressure-driven membrane ultrafiltration was examined. Polyethersulfone ultrafiltration membranes with 20 and 50 kDa molecular weight cut-off were tested. The effects of the continuous and half intermittent ultrasonic irradiation during the ultrafiltration were compared. Ultrafiltration fluxes, chemical oxygen demand retentions and membrane, pore fouling and polarization layer resistances were analyzed in a combined process. Furthermore, mass transfer coefficients, fouling coefficients and concentrations on membrane surface were also calculated and compared. The results showed that the best correlation were achieved by plotting the cake filtration model, but the other models also have given relatively good correlations using gradual pore blocking and intermediate filtration models. For this reason the membrane filtration ultrasonication should be further investigated for future applications.

Effects of ultrasonic irradiation on crystallization and structural properties of EMT-type zeolite nanocrystals

Synthesis of EMT zeolite nanocrystals from rice husk ash biomass (RHA) under continuous ultrasonic irradiation is reported. The aging, nucleation and crystallization stages of EMT zeolite in the system were monitored at ambient temperature, and compared with the conventional hydrothermal method. It was found that ultrasonic wave induced rapid crystal growth of the nanosized EMT zeolite. Complete crystallization of EMT nanocrystals was achieved within 24 h which was much faster than conventional hydrothermal synthesis (36 h). Furthermore, XRD and TEM analyses revealed that more nuclei were formed during the nucleation stage, allowing the preparation of smaller zeolite nanocrystals with high crystallinity. The results also showed that sonocrystallization produced EMT zeolite with high yield (ca. 80%). The ultrasound-prepared EMT nanocrystals were also found to have high porosity and high hydrophilicity, making the material promising for water sorption applications including vapor sensing, heat pump and adsorption technologies.

Pulsed ultrasound assisted dehydration of waste oil

A method to aid the separation of the oil phase from waste oil emulsion of refineries had been developed by using a pulsed ultrasonic irradiation technology. Compared with conventional continuous ultrasonic irradiation, it is found that pulsed ultrasonic irradiation is much better to make water drop coalescence and hence dehydration of waste oil. The effects of ultrasonic irradiation parameters on waste oil dehydration are further discussed. The orthogonal experiment is also designed to investigate the degrees of influence of ultrasonic parameters and the optimal technological conditions. Under the optimal experimental conditions, the water content of waste oil is decreased from 65% to 8%, which thereby satisfies the requirements of refineries on the water content of waste oil after treatment (<10%).

Ultrasound-Mediated Microbubble Destruction Increases Renal Interstitial Capillary Permeability in Early Diabetic Nephropathy Rats

Diabetic nephropathy (DN) is defined as persistent proteinuria corresponding to a urinary albumin excretion rate >300 μg/mg in the absence of other non-diabetic renal diseases. The aim of this study was to determine if ultrasound (US)-mediated microbubble (MB) destruction could increase renal interstitial capillary permeability in early DN rats. Diabetes was induced with streptozotocin. DN rats presented with mild micro-albuminuria 30 d after onset of diabetes. DN rats (N = 120) were divided into four groups that received Evans blue (EB) followed by: (i) no treatment (control group); (ii) continuous ultrasonic irradiation for 5 min (frequency = 7.00 MHz, mechanical index = 0.9, peak rarefactional pressure = 2.38 MPa: US group); (iii) microbubble injection (0.05 mL/kg: MB group); and (iv) both ultrasound and microbubble injection (US + MB group). Another 8 DN rats were subjected to ultrasound and microbubbles and then injected with EB after 24 h (recovery group). EB content, EB extravasation and E-selectin mRNA and protein expression significantly increased, and interstitial capillary walls became discontinuous in the US + MB group. Neither hemorrhage nor necrosis was observed on renal histology. Urine samples were collected 24 h post-treatment. There was no hematuria, and the urinary albumin excretion rate did not increase after ultrasound-microbubble interaction detected by urinalysis. EB content returned to the control group level after 24 h, as assessed for the recovery group. In conclusion, ultrasound-mediated microbubble destruction locally increased renal interstitial capillary permeability in DN rats, and should be considered a therapy for enhancing drug and gene delivery to the kidney in the future.

Optimization of ultrasound-assisted ultrafiltration of Radix astragalus extracts with hollow fiber membrane using response surface methodology

Response surface methodology (RSM) with a central composite rotatable design (CCRD) was employed to optimize the process of ultrasound-assisted ultrafiltration (UF) for Radix astragalus mixtures. The effects and mutual interaction of several parameters, namely ultrasonic power, ultrasonic irradiation mode, trans-membrane pressure (TMP) and temperature, on fouling degree (Y1) and process duration (Y2) were investigated simultaneously. The analysis of variance (ANOVA) demonstrates that the second order polynomial regression models were appropriate and significant, with R2 of 0.9820 and 0.9581 for Y1 and Y2, respectively. The study also shows that TMP is the most significant factor, followed by the temperature, ultrasonic power and irradiation mode. The desirability function approach was used to find the optimum conditions to minimize fouling degree and process duration simultaneously. The optimum conditions were found to be at ultrasonic power of 120W, continuous ultrasonic irradiation mode, TMP of 0.60bar and temperature of 20°C. The predicted responses are 40.2% for fouling degree and 57min for process duration, which are in good agreement with the results obtained from the confirmation experiments, valued about 38.5–43% and 53–58min respectively. The results indicate that the regression models are adequate and RSM is an efficient optimization tool for multi-responses and multi-variables study.

Inhibition of barnacle cyprid settlement using low frequency and intensity ultrasound

Low frequency, low intensity ultrasound was demonstrated as an effective inhibitor of barnacle cyprid settlement. When the same substratum vibration amplitude (10.05 nm) and acoustic pressure (5 kPa) were applied, ultrasound at a frequency of 23 kHz significantly reduced cyprid settlement. The mechanism appeared to differ from the ultrasonic cavitation induced inhibition previously reported as no increased mortality was observed, and no change in the exploratory behaviour of cyprids was observed when they were exposed to this continuous ultrasonic irradiation regime. The application of ultrasound treatment in an intermittent mode of ‘5 min on and 20 min off’ at 20–25 kHz and at the low intensity of 5 kPa produced the same effect as the continuous application of 23 kHz. This energy efficient approach to the use of low frequency, low intensity ultrasound may present a promising and efficient strategy regarding irradiation treatment for antifouling applications.

Application of propidium monoazide-qPCR to evaluate the ultrasonic inactivation of Escherichia coli O157:H7 in fresh-cut vegetable wash water

The efficacy of sanitizing technologies in produce or in vegetable wash water is generally evaluated by plate count in selective media. This procedure is time consuming and can lead to misinterpretations because environmental conditions and sanitizing processes may affect bacterial growth or culturable capability. Thus, the aim of this study was to determine the applicability of a propidium monoazide real-time PCR (PMA-qPCR) method to monitor the inactivation by ultrasound treatment of foodborne bacteria in fresh-cut vegetable wash water. To this aim, lettuce wash water was artificially inoculated with Escherichia coli O157:H7 (106 CFU/mL) and treated by means of a continuous ultrasonic irradiation with a power density of 0.280 kW/L. Quantification data obtained by PMA-qPCR and plate counts were statistically similar during the viability reduction of 99.996% which corresponds to 4.4 log reductions. Further reductions of E. coli O157:H7 were not detected by the PMA-qPCR method due to the limit of detection of this technique (20 CFU/mL). Inactivation data obtained by both techniques successfully fitted a linear model, giving no significant differences in kinetic parameters. These results indicate that the PMA-qPCR method is a suitable technique for evaluating ultrasonic disinfection of vegetable wash water, being able to distinguish between live and dead bacteria.

Continuous crystallization of adipic acid with ultrasound

The application of a novel continuous cooling crystallization system coupled with ultrasound technology to crystallize adipic acid from an aqueous solution was investigated. Both continuous ultrasound irradiation and silent (control) regimes were used in order to elucidate the effects of unstable cavitation on the duration of the transient period, steady state operating conditions, crystal habit, and particle size distribution. The results reveal that under continuous ultrasonic irradiation the steady state particle size distribution is achieved after shorter times, with a consistent reduction of the steady state supersaturation resulting in increased product yields relative to silent continuous crystallization experiments. Continuous crystallization with ultrasonic irradiation results in significantly smaller crystal sizes, reduced agglomeration and an improved habit of crystals. Furthermore, the influence of mean residence time using continuous ultrasound produces a smaller change in particle size and size distribution. Finally, the experiments reveal a noticeable reduction of the fouling on non-cooling surfaces and underline the need for intermittent discharge to prevent classification on withdrawal product.

Study of ultrasound-promoted, lipase-catalyzed synthesis of fructose ester

The effect of low energy ultrasound in biochemistry and biotechnology has attracted great attention in recent years. It can enhance substrate dissolution and improve mass transfer within and outside of a cell, both of which are beneficial to the synthesis of fructose ester. Here we describe the experimental study of the effect of ultrasounds of different intensity on the lipase-catalyzed synthesis of fructose ester in the solvent butanone. The results were compared with control reactions performed with no ultrasound. High performance liquid chromatography (HPLC) and thin layer chromatography (TLC) were used for qualitative and quantitative analyses. The results show the following: 1) the concentration of mono-ester and diester increased with the reaction time, either with or without ultrasonic irradiation. Low energy ultrasound accelerated the reaction due to the effect of ultrasonic steady cavitations, and high energy ultrasound was not beneficial to the reaction. 2) The application of ultrasound played an important role in our lipase-catalyzed reaction. It decreased reaction time as compared to a reaction without ultrasound that resulted in the same yield, increased reaction rate, and enhanced the amount of fructose ester produced. When the frequency was 10 kHz and sound intensity was 0.16 W·m−2, the concentration of ester was twofold more than without ultrasonic irradiation after a reaction time of up to 12 h. With the proper ultrasonic parameters, the overall concentration of production appeared to increase exponentially with the reaction time. 3) Ultrasound had little effect on the initial reaction rate, and continuous ultrasonic irradiation was favorable for the reaction. The longer the reaction continued, the more obvious the effects of the ultrasound became in our experiments.

Decolorization of textile azo dyes by ultrasonication and microbial removal

The textile industry involves several processes that generate large quantities of wastewaters. Remediation by a combination of various physical, chemical, and biological techniques of these effluents is required due to their complexity and bioresistance. Ultrasonication is an advanced oxidation process used to degrade organic compounds. It has the potential for use in environmental remediation due to the formation of highly concentrated oxidizing species. In this study, the decolorization of Reactive Red 2 (RR2), Reactive Blue 4 (RB4), and Basic Yellow 2 (BY2) was studied first by continuous ultrasonic irradiation at 20 kHz and second microbially ( Rhodotorula mucilaginosa). After the ultrasonic/microbial step by step applications, the highest decolorization yield was 93% in the sample with RR2 at 50 mg/L initial dye and 6 g/L cell concentrations. The lowest dye removal yield was 25% for about 100 mg/L initial BY2 and 4 g/L cell concentrations.

Influence of the mean scattering free-path on the temperature field

To avoid injuries caused by excessive heating during a therapeutic ultrasound treatment it is important to know the application time required to bring tissue to a reference temperature. Heating is assumed to be associated to ultrasonic absorption by tissues. However, it must be pointed that ultrasonic waves are scattered by heterogeneous media such as tissues. This leads to an increase in the average wave free-path and, consequently, to an extra ultrasonic absorption, which influences directly the thermal field and the correct determination of the thermal dose. To evaluate this phenomenon we analyzed the thermal field generated in silicone-based phantoms, with different percentages of graphite powder, subjected to continuous ultrasonic irradiation at therapeutic levels (0.5, 1.0 and 2.0 W/cm2 at 1.0 MHz). The phantoms had thermocouples inserted at four depths. Just to exemplify, we observed that the smaller temperature increase was 3∘C (compared to a phantom with no scatterers) with a phantom loaded with 0.25% graphite, after irradiated with 0.5 W/cm2 for 2 min. Thus temperature increase, due to the effect of ultrasonic scattering, must not be neglected but, on the contrary, should be taken into account, at least for certain treatments.

Fabrication of single-crystal ZnO nanorods and ZnS nanotubes through a simple ultrasonic chemical solution method

A simple and rapid method has been developed for the preparation of rod-like ZnO nanocrystals via ultrasonic irradiation. The as-synthesized ZnO nanocrystals were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods had an average diameter of 15–70 nm that varied from the ultrasonic operation mode. The results showed that Zn powder played an important role in the synthesis of ZnO nanorods. Through adding a sulfur source in the reaction system, ZnO/ZnS nanocables and ZnS nanotubes could be obtained with continuous ultrasonic irradiation. The formation mechanism of ZnS nanotubes could be attributed to the Kirkendall effect.

Effects of Sparging Gas Properties and Substrate Size on Enzymatic Hydrolysis of Waste Paper in an Ultrasonic External Loop Airlift

AbstractOffice paper shredded into various sizes was used as a model substrate for waste paper in the present work, aimed at developing an efficient utilization for waste cellulosics. The enzymatic hydrolysis of the office paper was carried out in an external loop airlift bubble column reactor equipped with an ultrasonic horn system, by sparging with water‐saturated or unsaturated gas. The enhanced hydrolysis was characterized by a two‐stage time course when either water‐unsaturated air or nitrogen was bubbled into the reaction suspension in the airlift reactor, without ultrasonic irradiation. In contrast, a much lower enhanced effect was observed when either saturated air or nitrogen was employed. The total sugar productivity with sparging by either saturated air or nitrogen was lower than in the case of sparging by unsaturated gas. This was ascribed to a shear stress acting on the surface of the paper in the gas sparging section in the riser. The critical superficial gas velocity for complete circulation of the substrate was reduced as its size was decreased. The smaller paper size for sparging with unsaturated air resulted in a more enhanced hydrolysis with a more remarkable two‐stage time course. In the case of sparging with saturated air, the continuous ultrasonic irradiation was effective for enhancing the enzymatic hydrolysis. The time courses of the glucose and total sugar concentrations were successfully analyzed and simulated, based on the kinetic model proposed previously. The variation in the paper size, sparging gas humidity and ultrasonic irradiation exerted an effect on the apparent rate constant and ultimate total sugar concentration, but had no effect on the apparent Michaelis, competitive inhibition and equilibrium constants.

Electroless Nickel Plating under Continuous Ultrasonic Irradiation to Fabricate a Near-Field Probe Whose Metal Coat Decreases in Thickness toward the Tip

This paper describes a size-dependent electroless plating method to fabricate a new type of probe with a locally decreasing thickness of metal and a tiny tip size for a combined high resolution shear-force and near-field optical microscope. In this method, the tip size and decreasing thickness profile, which affect the resolution capabilities of the microscopes, are controlled by adding a continuous ultrasonic wave with a frequency of 1 MHz to a nickel plating bath. The probe with a tip radius of curvature of 25 nm was successfully fabricated at an ultrasonic power density of 1.6 W cm−2, its metal thickness gradually decreased from 850 to 20 nm toward the distal tip.

Enhancing sonochemical activity in aqueous media using power-modulated pulsed ultrasound: an initial study

Relatively little is known about the effects of pulsed ultrasound on the facilitation of chemical reactivity. Previous studies have indicated that sonochemistry using pulses is generally less effective than continuous ultrasonic irradiation. However, the pulse trains employed were such that the peak power of the pulses was the same as the maximum power used in continuous irradiation. As a result, less acoustic energy was transmitted to the solutions over the same period of time. The effectiveness of ultrasound when the pulse is adjusted so that the same amount of acoustic energy is input compared to continuous irradiation over a given time has not been previously explored. In this study we have embarked on an examination of the efficacy of power-modulated pulsed (PMP) sonochemistry. Specifically, we have explored the effects of pulse type and pulse frequency on the oxidation of potassium iodide and the degradation of acid orange, a common industrial colorant. A rate increase by a factor of three was observed compared with continuous irradiation under conditions of equivalent acoustic input power.