Ultrasonic cavitation induced water in vegetable oil emulsion droplets--a simple and easy technique to synthesize manganese zinc ferrite nanocrystals with improved magnetization

A hand-powered microfluidic system for portable and low-waste sample discretization

In this work, we present a simple and equipment-free system for discretizing samples into tens of thousands of discrete volumes in tens of seconds. Unlike conventional sample discretization systems that require bulky syringe pumps, pressure controllers, or vacuum equipment, our system requires only a sheet of water-soluble film, a hand-operated syringe, and a microfluidic device containing a high-density microchamber array. In this system, the water-soluble film seals the device inlet to form a closed channel-chamber system, while the syringe is used to create a vacuum in the closed system. Benefitting from the high negative pressure created by syringe-vacuum and the dissolution-triggered gating mechanism of the sealing water-soluble film, the aqueous sample loaded into the device inlet can be rapidly partitioned into tens of thousands of isolated chambers without the need for any expensive pumping systems. We demonstrated the utility of this system by exploiting it for digital PCR. We believe that this simple discretization system will find broad applications, such as in digital bioassays, single-cell analysis, and point-of-care diagnostics.

Sonochemical dosimetry: A comparative study of Weissler, Fricke and terephthalic acid methods

Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO2 in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH, the reason for a very low OH yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.

Impact of sonochemical synthesis condition on the structural and physical properties of MnFe2O4 spinel ferrite nanoparticles

Herein, we report sonochemical synthesis of MnFe₂O₄ spinel ferrite nanoparticles using UZ SONOPULS HD 2070 Ultrasonic homogenizer (frequency: 20 kHz and power: 70 W). The sonication time and percentage amplitude of ultrasonic power input cause appreciable changes in the structural, cation distribution and physical properties of MnFe₂O₄ nanoparticles. The average crystallite size of synthesized MnFe₂O₄ nanoparticles was increased with increase of sonication time and percentage amplitude of ultrasonic power input. The occupational formula by X-ray photoelectron spectroscopy for prepared spinel ferrite nanoparticles was (Mn_0.29Fe_0.42)[Mn_0.71Fe_1.58]O₄ and (Mn_0.28Fe_0.54) [Mn_0.72Fe_1.46]O₄ at sonication time 20 min and 80 min, respectively. The value of the saturation magnetization was increased from 1.9 emu/g to 52.5 emu/g with increase of sonication time 20 min to 80 min at constant 50% amplitude of ultrasonic power input, whereas, it was increased from 30.2 emu/g to 59.4 emu/g with increase of the percentage amplitude of ultrasonic power input at constant sonication time 60 min. The highest value of dielectric constant (ε') was 499 at 1 kHz for nanoparticles at sonication time 20 min, whereas, ac conductivity was 368 × 10^-9 S/cm at 1 kHz for spinel ferrite nanoparticles at sonication time 20 min. The demonstrated controllable physical characteristics over sonication time and percentage amplitude of ultrasonic power input are a key step to design spinel ferrite material of desired properties for specific application. The investigation of microwave operating frequency suggest that these prepared spinel ferrite nanoparticles are potential candidate for fabrication of devices at high frequency applications.

On-Demand Sonochemical Synthesis of Ultrasmall and Magic-Size CdSe Quantum Dots in Single-Phase and Emulsion Systems

The sonochemical synthesis of CdSe quantum dots (QDs) in a single-liquid bulk phase and in an emulsion-based system is presented. Reactions utilized cadmium oleate and trioctylphosphine selenide precursors and were monitored as a function of sonication time under controlled temperature conditions to isolate the effects of cavitation from those of bulk temperature changes. QD synthesis was found to be slow in the single-phase liquid system (i.e., 1-octadecene) but greatly accelerated in the dispersed system (i.e., emulsions of 1-octadecene in ethylene glycol). It is hypothesized that the emulsion system increases the cavitation efficiency while also delivering acoustic energy in closer proximity to the precursor molecules. The capacity of CdSe production in the emulsion system was found to be 3.8 g/(L h), which is comparable to the typical hot-injection synthesis of CdSe QDs and can likely be further optimized. While the single-phase solvent system was found to produce ultrasmall QDs that exhibit broadband white-light emission, the emulsion system was found to produce well-defined magic-size clusters (MSCs) with photoluminescence quantum yield as high as 34%. Differences in synthesis rate and product properties from the emulsion and single-phase systems were probed by X-ray diffraction, electron microscopy, UV-visible (vis) and photoluminescence spectroscopy, and small-angle X-ray scattering (SAXS). Finally, precise temporal control of the QD synthesis was demonstrated via on-off cycling of the ultrasound waves.

Sonochemical synthesis of Gd3+ doped CoFe2O4 spinel ferrite nanoparticles and its physical properties

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe_2-xGd_xO₄; x=0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd³⁺ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe_2-xGd_xO₄ nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd³⁺ substitution in CoFe₂O₄ nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd³⁺ doped cobalt ferrite (CoFe_2-xGd_xO₄; x=0.20) exhibit enhanced dielectric constant (277 at 100Hz) and ac conductivity (20.2×10^-9S/cm at 100Hz). The modulus spectroscopy demonstrated the impact of Gd³⁺ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd³⁺ substitution from 234.32Oe (x=0.00) to 12.60Oe (x=0.05) and further increases from 12.60Oe (x=0.05) to 68.62Oe (x=0.20). Moreover, saturation magnetization decreases with Gd³⁺ substitution from 40.19emu/g (x=0.00) to 21.58emu/g (x=0.20). This work demonstrates that the grain size and cation distribution in Gd³⁺ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications.

Synergistic effects of ultrasonication and ethanol washing in controlling the stoichiometry, phase-purity and morphology of rare-earth doped ceria nanoparticles

Over a period of last thirty years, use of ethanol has been historically reported for obtaining nanopowders with low agglomeration for various oxide systems. In addition to these benefits, we show for the first time that treatments in ethanol medium coupled with an ultrasonication step can impart crucial additional advantages in controlling the phase purity and stoichiometry/composition for such systems. This is an important issue especially for any complex multicationic oxide nanoparticles system and hence we selected one of the most popular catalyst systems of doped-ceria (CeO₂) nanoparticles with very high (50%) level of rare-earth (lanthanum) doping for this case study. The effect of an ultrasonication combined ethanol treatment was compared with the other solvent media (pure water and ethanol) without ultrasonication. The underlying mechanism for this process involves lowering the deprotonation rate in ethanol medium which eventually reduces the condensation of the individual metal oxides while the ultrasonication ensures the reproducibility of the synthesis by providing a homogeneous colloidal solution for each washing stages. This novel modification in synthesis of nanoparticles aims to provide meaningful solutions in optimising the phase, composition and morphology of multicationic complex system of nanocrystals.

Evaluation of short cycles of ultrasound application in nanoemulsions to obtain nanocapsules

Ultrasound is widely used in several chemical reactions and other process, including production of nanocapsules by in situ polymerization. In this work, the main objective was to evaluate the impacts and viability of successive ultrasound application in nanoemulsions to obtain nanocapsules. Initiator potassium persulfate (KPS) concentration, number of ultrasound cycles and reaction time influences on polymerization efficiency and droplet size were evaluated. This work revealed the successful in situ production of nanocapsules using successive shorts cycles of ultrasound. Number of cycles was the only parameter that not exerted significant influence in polymerization yield. Particle size decay was observed in all nanoemulsions after the first ultrasound application, the same was not observed in further cycles. Gravimetric assessment showed remarkable increase of monomer conversion, indicating that once started polymerization continued at least until 28 days after ultrasound application. Concluding, ultrasound short cycles can be used with no harm to formulation, if carefully performed and, furthermore is a potential cost-effective route for polymerization reactions.

A new method for the synthesis of LiNi1/3Co1/3Mn1/3O2 from waste lithium ion batteries

Re-synthesis of a new cathode material from waste LIBS using citric acid as a leaching agent and complexing agent.

Sonochemical synthesis of mesoporous ZrFe2O5 and its application for degradation of recalcitrant pollutants

In this paper, we have reported the sonochemical synthesis and characterization of zirconium ferrite (ZrFe₂O₅), and its use as a catalyst in advanced oxidation processes (AOPs) using decolorization/degradation of textile dyes as model processes.

Emulsification by high frequency ultrasound using piezoelectric transducer: formation and stability of emulsifier free emulsion

Emulsifier free emulsion was developed with a new patented technique for food and cosmetic applications. This emulsification process dispersed oil droplets in water without any emulsifier. Emulsions were prepared with different vegetable oil ratios 5%, 10% and 15% (v/v) using high frequency ultrasounds generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. The emulsion was prepared with various emulsification times between 0 and 10h. Oil droplets size was measured by laser granulometry. The pH variation was monitored; electrophoretic mobility and conductivity variation were measured using Zêtasizer equipment during emulsification process. The results revealed that oil droplets average size decreased significantly (p<0.05) during the first 6h of emulsification process and that from 160 to 1 μm for emulsions with 5%, 10% and from 400 to 29 μm for emulsion with 15% of initial oil ratio. For all tested oil ratios, pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH(-) at oil/water interface leading to droplets stability in the emulsion. The conductivity of emulsions showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH(-) structure. They constitute a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil.

Ultrasound-assisted/biosurfactant-templated size-tunable synthesis of nano-calcium sulfate with controllable crystal morphology

Nano-sized crystals of alpha calcium sulfate hemihydrate (α-HH) with considerable morphology-dependent properties find promising applications in the clinical fields as a cementitious material. Towards this end, ultrasound-assisted rhamnolipid and surfactin biosurfactant-template route is explored to control the morphology and aspect ratio of nano-CaSO4 by adjusting the mass ratio of rhamnolipid/H2O, surfactin/H2O and rhamnolipid/surfactin. The change in the molar ratio of [SO4(2-)]:[Ca(2+)] results in modification in variable morphology and size of nano-CaSO4 including long, short rods and nanoplates. With increase in the rhamnolipid/H2O ratio from 1.3 to 4.5, the crystal length decreases from 3 μm to 600 nm with the corresponding aspect ratio reduced sharply from 10 to 3. Similarly, the crystal morphology gradually changes from submicrometer-sized long rod to hexagonal plate, and then plate-like appearance with increase in surfactin concentration. The preferential adsorption of rhamnolipid on the side facets and surfactin on the top facets contributes to the morphology control. The process using 50% amplitude with a power input of 45.5 W was found to be the most ideal as observed from the high yields and lower average l/w aspect ratio, leading to more than 94% energy savings as compared to that utilized by the conventional process. As a morphology and crystal habit modifier, effects of Mg(2+) and K(+) ions on α-HH growth were investigated to find an optimal composition of solution for α-HH preparation. Mg(2+) ions apparently show an accelerating effect on the α-HH growth; however, the nucleation of α-HH is probably retarded by K(+) ions. Thus, the present work is a simple, versatile, highly efficient approach to controlling the morphology of α-HH and thereby, offers more opportunities for α-HH multiple applications.

Forming double layer-encapsulated quantum dots for bio-imaging and cell targeting

We report a simple and effective approach for the preparation of double layer-encapsulated quantum dots (DL-Qdots) composed of alkyl-capping ligands to interdigitate with hydrophobic, protective agents on the surface of AgInS(2)/ZnS quantum dots (Qdots), which allow phase transfer of hydrophobic Qdots from the organic phase into the aqueous phase. The alkyl-capping ligands consist of a hydrophobic, aliphatic chain and different functional terminal groups (e.g., carboxyl, amine, hydroxyl, and thiol groups) that can serve as reactive sites to chemically couple with other materials. The resulting DL-Qdots bearing various functional groups retain good fluorescence properties and show excellent solubility as well as stability over a range of pH in the aqueous phase. Cytotoxicity studies of DL-Qdots bearing carboxyl groups (DL-Qdots-COOH) were carried out against human cervical (HeLa) cancer cells to elicit no apparent toxicity even at high concentrations of 300 μg mL(-1) and 24 h of incubation. To demonstrate their potential biomedical application, DL-Qdots-COOH were further conjugated with folate for staining in HeLa, human liver carcinoma (HepG2), and human breast (MCF-7) cancer cells. Confocal imaging characterization revealed that folate-conjugated DL-Qdots could target most specifically and effectively HeLa cells via folate receptor-mediated targeted delivery compared to HepG2 and MCF-7 cells. The generality and simplicity of this newly developed strategy can possibly be extended to a large variety of hydrophobic Qdots and nanocrystals whose surface protective agents have a long aliphatic chain.