The purpose of this investigation is to evaluate the implementation of ultrasound-assisted liquid biphasic flotation (LBF) system for the recovery of natural astaxanthin from Haematococcus pluvialis microalgae. Various operating conditions of ultrasound-assisted LBF systems such as the position of ultrasound horn, mode of ultrasonication (pulse and continuous), amplitude of ultrasonication, air flowrate, duration of air flotation, and mass of H. pluvialis microalgae were evaluated. The effect of ultrasonication on the cellular morphology of microalgae was also assessed using microscopic analysis. Under the optimized operating conditions of UALBF, the maximum recovery yield, extraction efficiency, and partition coefficient of astaxanthin were 95.08 ± 3.02%, 99.74 ± 0.05%, and 185.09 ± 4.78, respectively. In addition, the successful scale-up operation of ultrasound-assisted LBF system verified the practicability of this integrated approach for an effective extraction of natural astaxanthin.
In this study, the effect of the dimensions of the bottom plate and liquid height was investigated for high-frequency sonoreactors under a vertically irradiated system. The dimensions of the bottom plate did not significantly influence sonochemical activity considering power density. However, as the bottom plate was increased in size, the hydroxyl radical generation rate decreased because of a decrease in power density. It is therefore recommended that sonoreactors with bottom-plate dimensions close to those of the ultrasonic transducer module be used. Liquid height had a significant effect on sonochemical activity, but the trend of the activity considering power density changed as the initial pollutant concentration changed. In the case of low initial concentration of As(III) (1 mg/L), the maximum cavitation yield for As(III) oxidation was observed at liquid heights of 150 mm.
The effects of ultrasonic conditions and physicochemical properties on the synergistic degradation in synthetic solution were investigated. A wide range of ultrasound frequencies, including 35, 170, 300, 500 and 700 kHz, and ultrasonic power densities, including 11.3, 22.5 and 31.5 W/L were used. It was revealed that the physical effect of ultrasound plays a major role in synergistic mechanism and 35 kHz was found to be the most effective frequency due to its more vigorous physical effect induced by high implosive energy released from collapse of cavitation bubbles. The highest ultrasonic power density (31.5 W/L) showed the highest synergy index as it increases the number of cavitation bubbles and the energy released when they collapse. The synergy indexes of various substituted phenols under identical condition were investigated. These results were correlated with physicochemical properties, namely octanol-water partition coefficient (Log K OW), water solubility (SW), Henry's law constant (KH) and water diffusivity (DW). Among these parameters, Log K OW and DW were found to have substantial effects on synergy indexes.
Bifunctional electrocatalysts to enable efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for fabricating high performance metal-air batteries and fuel cells. Here, a defect rich nitrogen and sulfur co-doped graphene/iron carbide (NS-GR/Fe3C) nanocomposite as an electrocatalyst for ORR and OER is demonstrated. An ink of NS-GR/Fe3C is developed by homogeneously dispersing the catalyst in a Nafion containing solvent mixture using an ultrasonication bath (Model-DC150H; power - 150 W; frequency - 40 kHz). The ultrasonically prepared ink is used for preparing the electrode for electrochemical studies. In the case of ORR, the positive half-wave potential displayed by NS-GR/Fe3C is 0.859 V (vs. RHE) and for the OER, onset potential is 1.489 V (vs. RHE) with enhanced current density. The optimized NS-GR/Fe3C electrode exhibited excellent ORR/OER bifunctional activities, high methanol tolerance and excellent long-term cycling stability in an alkaline medium. The observed onset potential for NS-GR/Fe3C electrocatalyst is comparable with the commercial noble metal catalyst, thereby revealing one of the best low-cost alternative air-cathode catalysts for the energy conversion and storage application.
In this investigation, sisal fibres were treated with the combination of alkali and high intensity ultrasound (HIU) and their effects on the morphology, thermal properties of fibres and mechanical properties of their reinforced PP composites were studied. FTIR and FE-SEM results confirmed the removal of amorphous materials such as hemicellulose, lignin and other waxy materials after the combined treatments of alkali and ultrasound. X-ray diffraction analysis revealed an increase in the crystallinity of sisal fibres with an increase in the concentration of alkali. Thermogravimetric results revealed that the thermal stability of sisal fibres obtained with the combination of both alkali and ultrasound treatment was increased by 38.5°C as compared to the untreated fibres. Morphology of sisal fibre reinforced composites showed good interfacial interaction between fibres and matrix after the combined treatment. Tensile properties were increased for the combined treated sisal fibres reinforced PP composites as compared to the untreated and pure PP. Tensile modulus and strength increased by more than 50% and 10% respectively as compared to the untreated sisal fibre reinforced composite. It has been found that the combined treatment of alkali and ultrasound is effective and useful to remove the amorphous materials and hence to improve the mechanical and thermal properties.
This study investigates the potential of using small amounts of ionic liquids (IL) to enhance ultrasound-assisted extraction of lipids content from green microalgae. Three imidazolium-based ILs (butyl, octyl and dodecyl), each of them with two anions (bromide and acetate) were tested as additives. Viscosity and surface tension of the ILs aqueous mixtures were analyzed to determine the influence of ILs' anions and alkyl chain length, whereas KI dosimetry experiments were used as an indicator of radicals formation. A key finding suggests that the small addition of ILs improves the ultrasonication either by enhancing the viscosity and reducing the water surface tension, leading to a more powerful acoustic cavitation process or by increasing HO° production likely to oxidize the microalgae cells membranes, and consequently disrupting them on a more efficient manner. KI dosimetry also revealed that long ILs alkyl chain is detrimental. This experimental observation is confirmed thus strengthened as the yield of extracted lipids from green microalgae has shown an incremental trend when the IL concentration also increased. These hypotheses are currently under investigation to spot detailed impact of ILs on cavitation process.
Novel heterostructured β-Bi2O3/Bi2O2CO3 nanoplates (hBN) were synthesized to observe the sonocatalytic degradation of bisphenol A (BPA) (widely used as a model pollutant) under ultrasonic (US) irradiation. Prior to obtaining the hBN, the Bi2O2CO3 micropowder precursor was prepared under hydrothermal conditions and then converted to hBN by increasing the calcination temperature to 300 °C. The synthesized hBN samples were characterized by field emission scanning electron microscope with energy dispersive X-ray analysis (FESEM/EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible spectrophotometer diffuse reflection spectroscopy (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The hBN/US system exhibited greater sonocatalytic activity for the degradation of BPA than the US treatment with the single element bismuth oxide, β-Bi2O3 prepared by annealing the Bi2O2CO3 precursor at 400 °C for 1 h. The US frequency and US power intensity in the hBN/US system were the key operating parameters, which were responsible for the complete degradation of BPA during 6 h of reactions. The degradation efficiency of BPA under the US irradiation was positively correlated with the dose of hBN. Our findings indicate that heterostructured hBN can be used as an efficient sonocatalyst for the catalytic degradation of BPA in water and wastewater treatment.
Glassy carbon particles (millimetric or micrometric sizes) dispersions in water were treated by ultrasound at 20kHz, either in a cylindrical reactor, or in a "Rosette" type reactor, for various time lengths ranging from 3h to 10h. Further separations sedimentation allowed obtaining few nanoparticles of glassy carbon in the supernatant (diameter <200nm). Thought the yield of nanoparticle increased together with the sonication time at high power, it tended to be nil after sonication in the cylindrical reactor. The sonication of glassy carbon micrometric particles in water using "Rosette" instead of cylindrical reactor, allowed preparing at highest yield (1-2wt%), stable suspensions of carbon nanoparticles, easily separated from the sedimented particles. Both sediment and supernatant separated by decantation of the sonicated dispersions were characterized by laser granulometry, scanning electron microscopy, X-ray microanalysis, and Raman and infrared spectroscopies. Their multiscale organization was investigated by transmission electron microscopy as a function of the sonication time. For sonication longer than 10h, these nanoparticles from supernatant (diameter <50nm) are aggregated. Their structures are more disordered than the sediment particles showing typical nanometer-sized aromatic layer arrangement of glassy carbon, with closed mesopores (diameter ∼3nm). Sonication time longer than 5h has induced not only a strong amorphization (subnanometric and disoriented aromatic layer) but also a loss of the mesoporous network nanostructure. These multi-scale organizational changes took place because of both cavitation and shocks between particles, mainly at the particle surface. The sonication in water has induced also chemical effects, leading to an increase in the oxygen content of the irradiated material together with the sonication time.
Sequentially precipitated Mg-promoted nickel-silica catalysts with ageing performed under various ultrasonic intensities were employed to study the catalyst performance in the partial hydrogenation of sunflower oil. Results from various characterisation studies showed that increasing ultrasonic intensity caused a higher degree of hydroxycarbonate erosion and suppressed the formation of Ni silicates and silica support, which improved Ni dispersion, BET surface area and catalyst reducibility. Growth of silica clusters on the catalyst aggregates were observed in the absence of ultrasonication, which explained the higher silica and nickel silicate content on the outer surface of the catalyst particle. Application of ultrasound also altered the electron density of the Ni species, which led to higher activity and enhanced product selectivity for sonicated catalysts. The catalyst synthesised with ultrasonic intensity of 20.78 Wcm-2 achieved 22.6% increase in hydrogenation activity, along with 28.5% decrease in trans-C18:1 yield at IV = 70, thus supporting the feasibility of such technique.
Sonodynamic therapy (SDT) emerges as a promising non-invasive alternative for eradicating malignant tumours. However, its therapeutic efficacy remains limited due to the lack of sonosensitisers with high potency and biosafety. Previously, gold nanorods (AuNRs) have been extensively studied for their applications in photodynamic or photothermal cancer therapy, but their sonosensitising properties are largely unexplored. Here, we reported the applicability of alginate-coated AuNRs (AuNRsALG) with improved biocompatibility profiles as promising nanosonosensitisers for SDT for the first time. AuNRsALG were found stable under ultrasound irradiation (1.0 W/cm2, 5 min) and maintained structural integrity for 3 cycles of irradiation. The exposure of the AuNRsALG to ultrasound irradiation (1.0 W/cm2, 5 min) was shown to enhance the cavitation effect significantly and generate a 3 to 8-fold higher amount of singlet oxygen (1O2) than other reported commercial titanium dioxide nanosonosensitisers. AuNRsALG exerted dose-dependent sonotoxicity on human MDA-MB-231 breast cancer cells in vitro, with ∼ 81% cancer cell killing efficacy at a sub-nanomolar level (IC50 was 0.68 nM) predominantly through apoptosis. The protein expression analysis showed significant DNA damage and downregulation of anti-apoptotic Bcl-2, suggesting AuNRsALG induced cell death through the mitochondrial pathway. The addition of mannitol, a reactive oxygen species (ROS) scavenger, inhibited cancer-killing effect of AuNRsALG-mediated SDT, further verifying that the sonotoxicity of AuNRsALG is driven by the production of ROS. Overall, these results highlight the potential application of AuNRsALG as an effective nanosonosensitising agent in clinical settings.
The current work proposed an alternative ultrasound (US) technology, namely the high-intensity ultrasonic tubular reactor (HUTR) for preparing Pickering emulsions. Using the non-toxic and environmentally friendly cellulose nanocrystal (CNC) as a solid stabilizer, Pickering emulsions were produced using the HUTR and the results showed that Pickering emulsions as small as 1.5 µm can be produced using HUTR at the US power and sonication time of 300 W and 15 min respectively. Additionally, the sizes of Pickering emulsion obtained are found to remain the same upon 30 days of storage. The performance of HUTR in emulsion preparation is compared to conventional US horn system at the same US power. It was observed that the use of HUTR allowed generation of Pickering emulsion that is significantly smaller (around 7.40 μm) and with better droplet size distribution (Coefficient of variation, CV = 31%) as compared to those prepared with US horn method (12.75 µm, CV = 36%). This is owing to the better distribution of cavitation activity in the treatment chamber of HUTR as compared to those in the horn, according to the sonochemiluminescence (SCL) study. From the 30-days storage stability analysis, the CNC-PE prepared using HUTR was found to more stable against droplet coalescence in comparison to those prepared using US horn. Our findings suggested that the HUTR possessed superior Pickering emulsification capacity when compared to conventional US horn. Further work will be necessary to evaluate the feasibility of such intensifying tubular reactor technology for larger scale emulsification and other process intensification applications.
Ultrasound was applied simultaneously with adsorption process in most of the previous studies. However, this method is not practical to treat huge amounts of coloured wastewater effluent. In this study, the efficiency of ultrasound pre-treated peanut husk powder at different power levels (1.5-3.5 W) in dye adsorption with several conditions of initial dye concentration (20-100 mg/L), contact time (0.5-5 h), solution pH (2-8), and dosage (0.1-0.3 g) was studied and compared with ultrasound simultaneous adsorption process and the control. Adsorption efficiency of indirect ultrasound pre-treated peanut husk powder has increased 25.78%, 13.64% and 1.5% compared with the control, ultrasound simultaneous adsorption and direct ultrasound pre-treated sample respectively at 60 mg/L of initial dye concentration. Indirect ultrasound pre-treated sample at 3.5 W has achieved the highest adsorption efficiency of 89.96% at solution pH 8 and 94.83% at 0.3 g dose for 3 h. The surface feature and textural properties of samples were characterized by using scanning electron microscopy and surface characterization analyser. The result indicated that more porous structure was created on the ultrasound pre-treated sample at increasing power levels.
Ultrasound (US) demonstrates remarkable potential in synthesising nanomaterials, particularly nanobiomaterials targeted towards biomedical applications. This review briefly introduces existing top-down and bottom-up approaches for nanomaterials synthesis and their corresponding synthesis mechanisms, followed by the expounding of US-driven nanomaterials synthesis. Subsequently, the pros and cons of sono-nanotechnology and its advances in the synthesis of nanobiomaterials are drawn based on recent works. US-synthesised nanobiomaterials have improved properties and performance over conventional synthesis methods and most essentially eliminate the need for harsh and expensive chemicals. The sonoproduction of different classes and types of nanobiomaterials such as metal and superparamagnetic nanoparticles (NPs), lipid- and carbohydrate-based NPs, protein microspheres, microgels and other nanocomposites are broadly categorised based on the physical and/or chemical effects induced by US. This review ends on a good note and recognises US-driven synthesis as a pragmatic solution to satisfy the growing demand for nanobiomaterials, nonetheless some technical challenges are highlighted.
The aim of this study was to evaluate the effect of ultrasound on the intestinal adherence ability, cell growth, and cholesterol removal ability of parent cells and subsequent passages of Lactobacillus fermentum FTDC 1311. Ultrasound significantly decreased the intestinal adherence ability of treated parent cells compared to that of the control by 11.32% (P<0.05), which may be due to the protein denaturation upon local heating. Growth of treated parent cells also decreased by 4.45% (P<0.05) immediately upon ultrasound (0-4h) and showed an increase (P<0.05) in the viability by 2.18-2.34% during the later stage of fermentation (12-20 h) compared to that of the control. In addition, an increase (P<0.05) in assimilation of cholesterol (>9.74%) was also observed for treated parent cells compared to that of the control, accompanied by increased (P<0.05) incorporation of cholesterol into the cellular membrane. This was supported by the increased ratio of membrane cholesterol:phospholipids (C:P), saturation of cholesterol in the apolar regions, upper phospholipids regions, and polar regions of membrane phospholipids of parent cells compared to that of the control (P<0.05). However, such traits were not inherited by the subsequent passages of treated cells (first, second, and third passages). Our data suggested that ultrasound treatment could be used to improve cholesterol removal ability of parent cells without inducing permanent damage/defects on treated cells of subsequent passages.
This study aimed to evaluate the effect of ultrasound treatment on the cholesterol removing ability of lactobacilli. Viability of lactobacilli cells was significantly increased (P < 0.05) immediately after treatment, but higher intensity of 100 W and longer duration of 3 min was detrimental on cellular viability (P < 0.05). This was attributed to the disruption of membrane lipid bilayer, cell lysis and membrane lipid peroxidation upon ultrasound treatment at higher intensity and duration. Nevertheless, the effect of ultrasound on membrane properties was reversible, as the viability of ultrasound-treated lactobacilli was increased (P < 0.05) after fermentation at 37 °C for 20 h. The removal of cholesterol by ultrasound-treated lactobacilli via assimilation and incorporation of cholesterol into the cellular membrane also increased significantly (P < 0.05) upon treatment, as observed from the increased ratio of membrane C:P. Results from fluorescence anisotropies showed that most of the incorporated cholesterol was saturated in the regions of phospholipids tails, upper phospholipids, and polar heads of the membrane bilayer.
Improving dispersion stability of nanofluids through ultrasonication has been shown to be effective. Determining specific conditions of ultrasonication for a certain nanofluid is necessary. For this purpose, nanofluids of varying nanoparticle concentrations were prepared and studied to find out a suitable and rather mono-dispersed concentration (i.e., 0.5 vol.%, determined through transmission electron microscopy (TEM) analyses). This study aims to report applicable ultrasonication conditions for the dispersion of Al2O3 nanoparticles within H2O through the two-step production method. The prepared samples were ultrasonicated via an ultrasonic horn for 1-5h at two different amplitudes (25% and 50%). The microstructure, particle size distribution (PSD), and zeta potentials were analyzed to investigate the dispersion characteristics. Better particle dispersion, smaller aggregate sizes, and higher zeta potentials were observed at 3 and 5h of ultrasonication duration for the 50% and 25% of sonicator power amplitudes, respectively.
Nanofluids are promising in many fields, including engineering and medicine. Stability deterioration may be a critical constraint for potential applications of nanofluids. Proper ultrasonication can improve the stability, and possibility of the safe use of nanofluids in different applications. In this study, stability properties of TiO2-H2O nanofluid for varying ultrasonication durations were tested. The nanofluids were prepared through two-step method; and electron microscopies, with particle size distribution and zeta potential analyses were conducted for the evaluation of their stability. Results showed the positive impact of ultrasonication on nanofluid dispersion properties up to some extent. Ultrasonication longer than 150min resulted in re-agglomeration of nanoparticles. Therefore, ultrasonication for 150min was the optimum period yielding highest stability. A regression analysis was also done in order to relate the average cluster size and ultrasonication time to zeta potential. It can be concluded that performing analytical imaging and colloidal property evaluation during and after the sample preparation leads to reliable insights.
The ability of sonication phenomena in facilitating separation of azeotropic mixtures presents a promising approach for the development of more intensified and efficient distillation systems than conventional ones. To expedite the much-needed development, a mathematical model of the system based on conservation principles, vapor-liquid equilibrium and sonochemistry was developed in this study. The model that was founded on a single stage vapor-liquid equilibrium system and enhanced with ultrasonic waves was coded using MATLAB simulator and validated with experimental data for ethanol-ethyl acetate mixture. The effects of both ultrasonic frequency and intensity on the relative volatility and azeotropic point were examined, and the optimal conditions were obtained using genetic algorithm. The experimental data validated the model with a reasonable accuracy. The results of this study revealed that the azeotropic point of the mixture can be totally eliminated with the right combination of sonication parameters and this can be utilized in facilitating design efforts towards establishing a workable ultrasonically intensified distillation system.
Palm oil mill effluent (POME) is a highly contaminating wastewater due to its high chemical oxygen demand (COD) and biochemical oxygen demand (BOD). Conventional treatment methods require longer residence time (10-15 days) and higher operating cost. Owing to this, finding a suitable and efficient method for the treatment of POME is crucial. In this investigation, ultrasound cavitation technology has been used as an alternative technique to treat POME. Cavitation is the phenomenon of formation, growth and collapse of bubbles in a liquid. The end process of collapse leads to intense conditions of temperature and pressure and shock waves which assist various physical and chemical transformations. Two different ultrasound systems i.e. ultrasonic bath (37 kHz) and a hexagonal triple frequency ultrasonic reactor (28, 40 and 70 kHz) of 15 L have been used. The results showed a fluctuating COD pattern (in between 45,000 and 60,000 mg/L) while using ultrasound bath alone, whereas a non-fluctuating COD pattern with a final COD of 27,000 mg/L was achieved when hydrogen peroxide was introduced. Similarly for the triple frequency ultrasound reactor, coupling all the three frequencies resulted into a final COD of 41,300 mg/L compared to any other individual or combination of two frequencies. With the possibility of larger and continuous ultrasonic cavitational reactors, it is believed that this could be a promising and a fruitful green process engineering technique for the treatment of POME.
O/W nanoemulsions are isotropic colloidal systems constituted of oil droplets dispersed in continuous aqueous media and stabilised by surfactant molecules. Nanoemulsions hold applications in more widespread technological domains, more crucially in the pharmaceutical industry. Innovative nanoemulsion-based drug delivery system has been suggested as a powerful alternative strategy through the useful means of encapsulating, protecting, and delivering the poorly water-soluble bioactive components. Consequently, there is a need to generate an emulsion with small and consistent droplets. Diverse studies acknowledged that ultrasonic cavitation is a feasible and energy-efficient method in making pharmaceutical-grade nanoemulsions. This method offers more notable improvements in terms of stability with a lower Ostwald ripening rate. Meanwhile, a microstructured reactor, for instance, microchannel, has further been realised as an innovative technology that facilitates combinatorial approaches with the acceleration of reaction, analysis, and measurement. The recent breakthrough that has been achieved is the controlled generation of fine and monodispersed multiple emulsions through microstructured reactors. The small inner dimensions of microchannel display properties such as short diffusion paths and high specific interfacial areas, which increase the mass and heat transfer rates. Hence, the combination of ultrasonic cavitation with microstructures (microchannel) provides process intensification of creating a smaller monodispersed nanoemulsion system. This investigation is vital as it will then facilitate the creation of new nanoemulsion based drug delivery system continuously. Following this, the fabrication of microchannel and setup of its combination with ultrasound was conducted in the generation of O/W nanoemulsion, as well as optimisation to analyse the effect of varied operating parameters on the mean droplet diameter and dispersity of the nanoemulsion generated, besides monitoring the stability of the nanoemulsion. Scanning transmission electron microscopy (STEM) images were also carried out for the droplet size measurements. In short, the outcomes of this study are encouraging, which necessitates further investigations to be carried out to advance a better understanding of coupling microchannel with ultrasound to produce pharmaceutical-grade nanoemulsions.