Quantitation and evaluation of NO2-, NO3-, and H2O2 in the sonolysis of aqueous NaOH solution under air and air-Ar mixture: Effects of solution temperature, ultrasonic power, and ratio of gas mixture.

When an aqueous solution containing dissolved air is sonicated, H2O2, HNO2, and HNO3 are formed. This is a result of the formation of active bubbles with extremely high-temperature and high-pressure. The yields of H2O2, NO2-, and NO3- are representative indexes for understanding the chemical effects of ultrasonic cavitation in water. However, these yields often vary under the acidic conditions caused by sonication. In this study, we measured the yields of H2O2, NO2-, and NO3- in the presence of NaOH, which suppresses the reaction between NO2- and H2O2 and prevents the formation of NO3- in a bulk solution. Therefore, the yields obtained should correspond to the actual yields just after bubble collapse, directly reflecting the chemical effects of the active bubbles themselves. It was confirmed that the yields of NO2- and NO3- decreased, while the ratio of [NO3-] to [NO2-] ([NO3-]/[NO2-] ratio) increased with increasing solution temperature, suggesting that the temperature and pressure in collapsing bubbles decreased with an increase in the solution temperature. Ultrasonic power clearly affected the yields of NO2- and NO3-, but it did not affect the [NO3-]/[NO2-] ratio, suggesting that 1) the quality of the active bubbles did not change largely with increasing ultrasonic power, and 2) the quantity related to the number and/or size of active bubbles increased with increasing ultrasonic power up to a certain power. Additionally, the effects of the ratio of air to Ar on the yields of NO2-, NO3-, and H2O2 were investigated. These yields could be affected not only by the bubble temperature but also by the concentration of reactants and intermediates inside the collapsing bubbles. The chemical reactions are quite complex, but these yields could be valuable analytical tools for understanding the quantity and quality of active bubbles.

Development of a Photometric Method to Measure Molecular Oxygen in Water.

A photometric method to determine molecular oxygen in water was developed. When manganese(II) is oxidized by oxygen under alkaline conditions, the presence of polyphosphate can prevent precipitation due to a coacervate reaction. The oxidized manganese later dissolves in acid to form a pink Mn(III) species, which has a stable UV/vis spectrum. Monitoring of the oxygen concentration based on the absorbance of the pink Mn(III) species at 517 nm showed a strong correlation with both the Winkler method and an optical sensor. As a result, the present method can measure not only dissolved oxygen, but also fine bubbles oxygen in in the water sample with high reliability (0 - 26 mg dm-3, r2 = 0.9995). During this process, no significant interference from nitrite or metal ions was observed. The accuracy of the measurement was steady at high temperatures of the water samples (≤ 363 K).

Sonochemical degradation of surfactants with different charge types: Effect of the critical micelle concentration in the interfacial region of the cavity.

Ionic surfactants tend to accumulate in the interfacial region of ultrasonic cavitation bubbles (cavities) because of their surface active properties and because they are difficult to evaporate in cavitation bubbles owing to their extremely low volatilities. Hence, sonolysis of ionic surfactants is expected to occur in the interfacial region of the cavity. In this study, we performed sonochemical degradation of surfactants with different charge types: anionic, cationic, zwitterionic, and nonionic. We then estimated the degradation rates of the surfactants to clarify the surfactant behavior in the interfacial region of cavitation bubbles. For all of the surfactants investigated, the degradation rate increased with increasing initial bulk concentration and reached a maximum value. The initial bulk concentration to obtain the maximum degradation rate had a positive correlation with the critical micelle concentration (cmc). The initial bulk concentrations of the anionic surfactants were lower than their cmcs, while those of the cationic surfactants were higher than their cmcs. These results can be explained by the negatively charged cavity surface and the effect of the coexisting counterions of the surfactants.

Mechanism for sonochemical reduction of Au(III) in aqueous butanol solution under Ar based on the analysis of gaseous and water-soluble products.

When an aqueous Au(III) solution containing 1-butanol was sonicated under Ar, Au(III) was reduced to Au(0) to form Au particles. This is because various reducing species are formed during sonication, but the reactivity of these species has not yet been evaluated in detail. Therefore, in this study, we analyzed the effects of Au(III) on the rates of the formation of gaseous and water-soluble compounds (CH4, C2H6, C2H4, C2H2, CO, CO2, H2, H2O2, and aldehydes), and the rate of Au(III) reduction as a function of 1-butanol concentration. The following facts were recognized: 1) for Au(III) reduction, the contribution of the radicals formed by the pyrolysis of 1-butanol was higher than that of the secondary radicals formed by the abstraction reactions of 1-butanol with ·OH, 2) ·CH3 and CO acted as reductants, 3) the contribution of ·H to Au(III) reduction was small in the presence of 1-butanol, 4) aldehydes and H2 did not act as reductants, and 5) the types of species that reduced Au(III) changed with 1-butanol concentration.

Synthesis of Au nanorods via autocatalytic growth of Au seeds formed by sonochemical reduction of Au(I): Relation between formation rate and characteristic of Au nanorods.

The sonochemical formation of Au seeds and their autocatalytic growth to Au nanorods were investigated in a one-pot as a function of concentration of HAuCl4, AgNO3, and ascorbic acid (AA). The effects of ultrasonic power and irradiation time were also investigated. In addition, the formation rate of Au nanorods was analyzed by monitoring the extinction at 400 nm by UV-Vis spectroscopy and compared with the growth behavior of Au seeds to nanorods. Most of the reaction conditions affected the yield, size, and shape of Au nanorods formed. It was confirmed that the concentration balance between HAuCl4 and AA was important to proceed the formation of Au seeds and nanorods effectively. The formation rate became faster with increasing AA concentration and dog-bone shaped nanorods were formed at high AA concentration. It was also confirmed a unique phenomenon that the shape of Au nanorods changed even after the completion of the reduction of Au(I) in the case of short-time ultrasonic irradiation for Au seed formation.

Ultrasound Assisted Cascade Extraction of Oil, Vitamin E, and Saccharides from Roselle (Hibiscus Sabdariffa L.) Seeds.

Roselle seeds, a waste biomass of the roselle calyx processing industry, were utilized to recover valuable compounds of oil, vitamin E, and water-soluble saccharides. Firstly, ultrasound-assisted extraction (UAE) and conventional stirring extraction were conducted for saccharide extraction, and the advantage of UAE was confirmed. Secondly, oil, vitamin E, and saccharides extracted from Vietnamese roselle seeds by UAE were analyzed for the first time. Oil of tri-, di-, and mono-glycerides, fatty acids of linoleic-, oleic-, palmitic-, and stearic-acids, vitamin E of γ- and α-tocopherol, and saccharides of sucrose, raffinose, stachyose, etc. were identified, and the amounts of these components were compared with those in other country's roselle seeds. Thirdly, cascade extraction of oil, vitamin E, and saccharides by UAE was investigated with solvents of hexane, hexane:ethyl acetate binary solvent, and water. The results indicated that the order of using solvents was very important for high and selective extraction: the best order to recover oil (almost 100%), vitamin E (95.7%), and saccharides (86.2%) was hexane, and then water.

Facile photo-ultrasonic assisted synthesis of flower-like Pt/N-MoS2 microsphere as an efficient sonophotocatalyst for nitrogen fixation.

Semiconductor photocatalytic technology is a sustainable and less energy consuming one for nitrogen (N2) reduction to produce ammonia (NH3). In this study, flower-like hierarchical N doped MoS2 (N-MoS2) microsphere was synthesized as a photocatalyst by one-step solvothermal method, which was assembled by numerous interleaving nanosheets petals with thin thickness. Besides, Pt nanoparticles were loaded on the surface of N-MoS2 via photo-ultrasonic reduction method. The as-prepared Pt/N-MoS2 photocatalyst exhibited higher N2 fixation ability than that over pure MoS2 and N-MoS2, which can be attributed to that the N doping narrows the band gap, and the Schottky barrier due to the existence of Pt nanoparticles improves the charge transfer and carrier separation. The reduction of N2 with ultrasonic irradiation was also investigated under visible light irradiation to evaluate the sonophotocatalytic activity of the Pt/N-MoS2 microsphere. The results showed that the N2 reduction rate of sonophotocatalysis (133.8 µmol/g(cat)h) was higher than that of sonocatalysis and photocatalysis, which can be ascribed to the synergistic effect of ultrasound and visible light irradiation. The effects of catalyst dosage, ultrasonic power and ultrasonic pulse on the photocatalytic efficiency were also studied. Meanwhile, a possible mechanism for improved sonophotocatalytic performance was also proposed.

Facile photo-ultrasonic assisted reduction for preparation of rGO/Ag2CO3 nanocomposites with enhanced photocatalytic oxidation activity for tetracycline.

Various antibiotics in the aquatic systems have threat the aquatic ecosystem balance and the human health. In this study, a degradation treatment method for tetracycline (TC), one of the commonly used antibiotics, was explored by using novel photocatalysts of rGO/Ag2CO3 under simulated sunlight, because conventional treatment methods are not efficient on the removal of TC. rGO/Ag2CO3 nanocomposites were synthesized via a facile photo-ultrasonic assisted reduction method. More than 90% of TC was removed by 1% (weightrGO/weightcomposites) rGO/Ag2CO3 within 60 min at pH = 4, which was about 1.3 times higher than that of pure Ag2CO3. The cycling experiments indicated that 1% rGO/Ag2CO3 was highly stable and could be reused for at least 5 cycles without significant deactivation to its photocatalytic activity. In addition, the effects of pH, temperature, and dosage amount of 1% rGO/Ag2CO3 on photocatalytic degradation were investigated. Meanwhile, the effect of ultrasonic on the degradation of TC was also investigated. This study can provide a new method for the preparation of smaller nanosized materials and photocatalysts with high activity and stability for its environmental or other applications.

Screening of fatty acids, saccharides, and phytochemicals in Jatropha curcas seed kernel as their trimethylsilyl derivatives using gas chromatography/mass spectrometry.

Jatropha curcas is a multipurpose plant, of which the seed kernel oil (up to 60% content) has been exploited for BDF production. In this report, we explored the various kinds of minor compounds of saccharides, phytochemicals, fatty acids (FAs), and amino acids in the seed kernel using gas chromatography/mass spectrometry (GC/MS) as their trimethylsilyl (TMS) derivatives. The homogenized seed kernels were extracted with methanol, and the extract was distributed into ethyl acetate/water phase. The components of each layer were derivatized with N, O-bis (trimethylsilyl) trifluoroacetamide (BSTFA) and their TMS derivatives were screened by GC/MS analysis. In ethyl acetate layer, the four FAs of palmitic acid, oleic acid, linoleic acid, and stearic acid were identified with total content of 12 wt% in kernel. In addition, the two tocochromanols of γ-tocopherol and γ-tocotrienol, and three phytosterols of campesterol, stigmasterol, and ß-sitosterol were also identified. Meanwhile, as the main saccharide components, di-saccharide of sucrose with content of 3 wt% in kernel, tri-saccharide of raffinose, and sugar alcohol of sorbitol and myo-inositol, were identified in aqueous layer. Furthermore, metabolites of amino acid, and a series of metabolite were also identified. These results suggested that the Jatropha curcas seed kernel can be applied to cascade use for metallic soap, liquid fuel, food and medical supplement, and cosmetics in addition to biodiesel production.

Sonochemistry of aqueous NaAuCl4 solutions with C3-C6 alcohols under a noble gas atmosphere.

The effect of the type of C3-C6 alcohol, solution temperature, and dissolved gas on the rate of Au(III) reduction was investigated in NaAuCl4 aqueous alcohol solution with a 200-kHz ultrasound irradiation system. It was confirmed in the presence of C3-C6 alcohol that more highly hydrophobic alcohols more effectively accumulated at the argon bubble interface region, and the reducing radicals formed here. To avoid changes in the bubble temperature during collapsing bubble, the effects of the solution temperature on the rate of Au(III) reduction and on the rate of formation of the gaseous compounds (CO, CO2, CH4, C2H2, C2H4, C2H6) were investigated in the presence of low concentration (1.0-mM) of 1-hexanol. Both of the rates showed a good relationship with the gas solubility: the amount of dissolved gas at different solution temperatures affected the number of high-temperature bubbles formed. The changes in the concentrations of the gaseous compounds formed from 1-hexanol degradation suggested that CO and the pyrolysis radicals acted as reductants. Finally, the effect of the type of dissolved gas was investigated in the presence of 1.0-mM Au(III) and 1.0-mM 1-hexanol. The rates of 1-hexanol degradation, Au(III) reduction, and gaseous compound formation increased in the order He

Preparation and sonophotocatalytic performance of hierarchical Bi2WO6 structures and effects of various factors on the rate of Rhodamine B degradation.

Hierarchical Bi2WO6 structures with high surface area were prepared in the presence of polyvinylpyrrolidone by using an optimized hydrothermal method. The samples prepared were characterized by X-ray diffraction, field-emission scanning electron microscopy and N2 adsorption-desorption technique. The results of these characterizations showed the formation of the hierarchical Bi2WO6 structures with high surface area (51m2/g). The degradation of Rhodamine B (RhB) with or without visible light was investigated under various experimental conditions to evaluate the sonophotocatalytic activity of the hierarchical Bi2WO6 structures. The result showed that the degradation efficiency was found to be in the following order: sonocatalysis

Mechanism of sonochemical reduction of permanganate to manganese dioxide in aqueous alcohol solutions: Reactivities of reducing species formed by alcohol sonolysis.

The sonochemical reduction of MnO4(-) to MnO2 in aqueous solutions was investigated as a function of alcohol concentration under Ar. The rate of MnO4(-) reduction initially decreased with increasing alcohol concentration, and then increased when the alcohol concentration was increased further. The concentrations at which the reduction rates were minimum depended on the hydrophobic properties of the added alcohols under ultrasonic irradiation. At low concentrations, the alcohols acted as OH radical scavengers; at high concentrations, they acted as reductant precursors: Rab, formed by abstraction reactions of the alcohols with sonochemically formed OH radicals or H atoms, and Rpy, formed by alcohol pyrolysis under ultrasonic irradiation. The results suggest that the reactivity order of the sonochemically formed reducing species with MnO4(-) at pH 7-9 is the sum of H2O2 and H>Rpy>Rab. The peak wavelengths of MnO2 colloidal solutions formed at high 1-butanol concentrations shifted to shorter wavelengths, suggesting the formation of small particles at high 1-butanol concentrations. The rates of sonochemical reduction of MnO2 to Mn(2+) in the presence of 1-butanol were slower than that in the absence of 1-butanol, because the sonochemical formation of H2O2 and H, which act as reductants, was suppressed by 1-butanol in aqueous solutions.

Effects of Na2SO4 or NaCl on sonochemical degradation of phenolic compounds in an aqueous solution under Ar: Positive and negative effects induced by the presence of salts.

Sonochemical degradation of 4-chlorophenol, phenol, catechol and resorcinol was studied under Ar at 200 kHz in the absence and presence of Na2SO4 or NaCl. The rates of sonochemical degradation in the absence of salts decreased in the order 4-chlorophenol>phenol>catechol>resorcinol and this order was in good agreement with the order of log P (partition coefficient) value of each phenolic compound. The effects of salts on the rates of sonochemical degradation consisted of no effect or slight negative or positive effects. We discussed these unclear results based on two viewpoints: one was based on the changes in pseudo hydrophobicity and/or diffusion behavior of phenolic compounds and the other was based on the changes in solubility of Ar gas. The measured log P value of each phenolic compound slightly increased with increasing salt concentration. In addition, the dynamic surface tension for 4-chlorophenol aqueous solution in the absence and presence of Na2SO4 or NaCl suggested that phenolic compounds more easily accumulated at the interface region of bubbles at higher salt concentration. These results indicated that the rates of sonochemical degradation should be enhanced by the addition of salts. On the other hand, the calculated Ar gas solubility was confirmed to decrease with increasing salt concentration. The yield of H2O2 formed in the presence of Na2SO4 or NaCl decreased with increasing salt concentration. These results suggested that sonochemical efficiency decreased with decreasing gas amount in aqueous solution: a negative effect of salts was observed. Because negative and positive effects were induced simultaneously, we concluded that the effects of salts on the rates of sonochemical degradation of phenolic compounds became unclear. The products formed from sonochemical degradation of 4-chlorophenol were also characterized by HPLC analysis. The formation of phenol and 4-chloro-1,3-dihydroxy benzene was confirmed and these concentrations were affected by the presence of salts.

Synthesis of MnO2 nanoparticles from sonochemical reduction of MnO4(-) in water under different pH conditions.

MnO2 was synthesized by sonochemical reduction of MnO4(-) in water under Ar atmosphere at 20°C, where the effects of solution pH on the reduction of MnO4(-) were investigated. The obtained XRD results showed that poor crystallinity δ-MnO2 was formed at pH 2.2, 6.0 and 9.3. When solution pH was increased from 2.2 to 9.3, the morphologies of δ-MnO2 changed from aggregated sheet-like or needle-like structures to spherical nanoparticles and finally to cubic or polyhedron nanoparticles. After further irradiation, MnO2 was readily reduced to Mn(2+). It was confirmed that H2O2 and H atoms formed in the sonolysis of water acted as reductants for both reduction for MnO4(-) to MnO2 and MnO2 to Mn(2+). The optimum irradiation time for the effective synthesis of MnO2 was 13 min at pH 2.2, 9 min at pH 6.0, 8 min at pH 9.3, respectively.

One-pot synthesis of gold nanorods via autocatalytic growth of sonochemically formed gold seeds: the effect of irradiation time on the formation of seeds and nanorods.

A one-pot synthesis for gold nanorods was developed using sonochemical reduction of gold ions in an aqueous solution in the presence of cetyltrimethylammonium bromide, silver nitrate, and ascorbic acid, where we focused on the autocatalytic growth of gold seeds formed by ultrasonic irradiation for short times. In growth experiments with these sonochemically formed gold seeds, sigmoidal shape growth curves were observed, and the induction period before growth began was longer for shorter irradiation times. This result indicated that the number of sonochemically formed gold seeds increased with increasing irradiation time. The average aspect ratio of the gold nanorods produced changed from 2.0 at an irradiation time of 0.5min to 3.6 at 15min. The gold nanorods produced were longer and wider when the irradiation time was shorter.

Ultrasound assisted reduction of graphene oxide to graphene in L-ascorbic acid aqueous solutions: kinetics and effects of various factors on the rate of graphene formation.

The reduction of graphene oxide (GO) to graphene (rGO) was achieved by using 20 kHz ultrasound in L-ascorbic acid (L-AA, reducing agent) aqueous solutions under various experimental conditions. The effects of ultrasound power, ultrasound pulse mode, reaction temperature, pH value and L-AA amount on the rates of rGO formation from GO reduction were investigated. The rates of rGO formation were found to be enhanced under the following conditions: high ultrasound power, long pulse mode, high temperature, high pH value and large amount of L-AA. It was also found that the rGO formation under ultrasound treatment was accelerated in comparison with a conventional mechanical mixing treatment. The pseudo rate and pseudo activation energy (Ea) of rGO formation were determined to discuss the reaction kinetics under both treatment. The Ea value of rGO formation under ultrasound treatment was clearly lower than that obtained under mechanical mixing treatment at the same condition. We proposed that physical effects such as shear forces, microjets and shock waves during acoustic cavitation enhanced the mass transfer and reaction of L-AA with GO to form rGO as well as the change in the surface morphology of GO. In addition, the rates of rGO formation were suggested to be affected by local high temperatures of cavitation bubbles.

Ultrasound assisted production of fatty acid methyl esters from transesterification of triglycerides with methanol in the presence of KOH catalyst: optimization, mechanism and kinetics.

Ultrasound assisted transesterification of triglycerides (TG) with methanol in the presence of KOH catalyst was investigated, where the changes in the reactants and products (diglycerides (DG), monoglycerides (MG), fatty acid methyl esters (FAME) and glycerin (GL)) concentrations were discussed to understand the reaction mechanism and kinetics under ultrasound irradiation. The optimum reaction condition for the FAME production was the concentration of KOH 1.0 wt.%, molar ratio of TG to methanol of 1:6, and irradiation time of 25 min. The rate constants during the TG transesterification with methanol into GL and FAME were estimated by a curve fitting method with simulated curves to the obtained experimental results. The rate constants of [Formula: see text] were estimated to be 0.21, 0.008, 0.23, 0.005, 0.14 and 0.001 L mol(-1)min(-1), respectively. The rate determining step for the TG transesterification with methanol into GL and FAME was the reaction of MG with methanol into GL and FAME.

A two-step continuous ultrasound assisted production of biodiesel fuel from waste cooking oils: a practical and economical approach to produce high quality biodiesel fuel.

A transesterification reaction of waste cooking oils (WCO) with methanol in the presence of a potassium hydroxide catalyst was performed in a continuous ultrasonic reactor of low-frequency 20 kHz with input capacity of 1 kW, in a two-step process. For the first step, the transesterification was carried out with the molar ratio of methanol to WCO of 2.5:1, and the amount of catalyst 0.7 wt.%. The yield of fatty acid methyl esters (FAME) was about 81%. A yield of FAME of around 99% was attained in the second step with the molar ratio of methanol to initial WCO of 1.5:1, and the amount of catalyst 0.3 wt.%. The FAME yield was extremely high even at the short residence time of the reactants in the ultrasonic reactor (less than 1 min for the two steps) at ambient temperature, and the total amount of time required to produce biodiesel was 15h. The quality of the final biodiesel product meets the standards JIS K2390 and EN 14214 for biodiesel fuel.

Ultrasound-assisted production of biodiesel fuel from vegetable oils in a small scale circulation process.

Biodiesel production from canola oil with methanol was performed in the presence of a base-catalyst by a circulation process at room temperature. In this process, the transesterification was accelerated by ultrasonic irradiation of low frequency (20 kHz) with an input capacity of 1 kW. The influences of various parameters on the transesterification reaction, including the amount of catalyst, the molar ratio of methanol to oil and the reaction time, were investigated. The objective of this work was to produce biodiesel satisfying the biodiesel-fuel standards of low energy consumption and material savings. The optimal conditions were: methanol/oil molar ratio of 5:1 and 0.7 wt.% catalyst in oil. Under these conditions, the conversion of triglycerides to fatty acid methyl esters was greater than 99% within the reaction time of 50 min. Crude biodiesel was purified by washing with tap water and drying at 70 degrees C under reduced pressure.

One-pot synthesis of gold nanorods by ultrasonic irradiation: the effect of pH on the shape of the gold nanorods and nanoparticles.

A novel one-pot synthesis method to prepare gold nanorods was developed by using sonochemical reduction of gold ions in aqueous solution. The size of the sonochemically formed gold nanorods was less than 50 nm, and their average aspect ratio decreased with increasing pH of the solution. The aspect ratio measured was 3.0 at pH 3.5, 2.2 at pH 5.0, and 2.1 at pH 6.5. At pH 7.7, irregular shaped gold nanoparticles were formed. At pH 9.8, most of the particles formed had a spherical shape with a smaller particle size than those formed in the lower pH solutions. Based on the obtained results, it was clear that the size and shape of the sonochemically formed gold nanoparticles are dramatically dependent on the pH value of the solution.