Sonolysis Of Water Research Articles

Activation of Ru(bpy)32+ multibubble sonochemiluminescence in alkaline aqueous solutions by a hydrated electron

The sonochemiluminescence in 10−4 M aqueous solutions of Ru(bpy)3Cl2 was studied in the presence of NaOH and KOH (up to 0.4 M). The observed increase in the steady-state emission intensity from Ru(bpy)32+ as compared with the intensity in neutral solutions was attributed to conversion of H resulting from water sonolysis to eaq. As a result, there is a multiple (>106) change in the concentrations of the sonochemical intermediates Ru(bpy)3+ and Ru(bpy)33+. The reduction of the Ru(bpy)33+ ion with H, which is of low efficiency for the formation of the excited *Ru(bpy)32+ ion, is replaced by reduction with hydrated electron, in which *Ru(bpy)32+ is generated in a high yield. The participation of eaq provides a fivefold increase in the sonochemiluminescence intensity in a key disproportionation reaction: Ru(bpy)3+ + Ru(bpy)33+ → Ru(bpy)32+ + *Ru(bpy)32+. It was shown that chemiluminescence from reduction of intermediate Ru(bpy)33+ with the OH− ion does not make a pronounced contribution to the sonochemiluminescence intensity.

Noble metal NPs and nanoalloys by sonochemistry directly processed on nanocarbon and TiN substrates from aqueous solutions

The sonochemical processing of nanomaterials in a solution is well established and has been advantageously used for a variety of nanomaterials and morphologies thereof. In general, high energy and high frequency ultrasound is applied to a solution containing the ionic species of the elements to be reduced as well as a certain amount of reducing chemicals. For further applications such as catalysis washing, filtering, dispersion and mounting on or mixing in a substrate are necessary. A sonochemical processing of nanomaterials directly on a substrate could make all these steps obsolete. Herein we show that noble metal and nanoalloy nanoparticles (NPs) can directly be processed on nanocarbon and titanium nitride surfaces using a simple ultrasound laboratory cleaner in aqueous solutions that are free from any reducing chemicals. The process is demonstrated on Au-NPs and nanoalloys of AuPd and PdPt which form a dense distribution on the substrate surface. To illustrate the catalytic activity of the NPs, the electrocatalytic performance of one AuPd-nanoalloy is demonstrated. The results are discussed in terms of reduction phenomena occurring at the interface between the ultrasonic cavitation and the substrate. We think that these reduction phenomena are mediated by the formation of reducing radicals at the substrate surface that are in turn driven by OH radicals from water sonolysis. Electrochemical current measurement at 0 V seem to support the existence of reducing currents during measurements under chopped ultrasound in an aqueous solution of HAuCl4 in comparison to measurements in water.

Correlations Between the Sonochemical Production Rate of Hydrogen and the Maximum Temperature and Pressure Reached in Acoustic Bubbles

Water sonolysis generates hydrogen through acoustic cavitation. In this work, based on a model for a reactive acoustic bubble, correlations between the sonochemical production of hydrogen and the maximum temperature and pressure reached in the bubble at the violent collapse have been made. The computational analysis has been performed for more than 800 points obtained by combining various cavitation parameters, i.e., frequency, acoustic intensity, liquid temperature, and ambient bubble radius. The simulation results showed that hydrogen production rate progressed linearly with the bubble temperature and pressure rise up to plateaus, which begin at 3500 ± 200 K and 100 ± 10 atm. Analyzing the progress of \(\text {H}^{{\cdot }}\) and \(^{{\cdot }} \)OH (\(\text {H}_{2}\) precursors) as function of bubble temperature and pressure showed very similar evolutions as those obtained for \(\text {H}_{2}\) with the same optimums at 3500 ± 200 K and 100 ± 10 atm. Consequently, in addition to the quench of hydrogen formation at very high bubble temperatures through the reaction \(\text {H}_{2}+\,^{{\cdot }}{\hbox {OH}}\rightarrow \text {H}_{2}\hbox {O}+\text {H}^{{\cdot }}\), the existing optimum temperature and pressure for \(\text {H}_{2}\) production may also be due the hard consumption of their precursors (\(^{{\cdot }}\)OH and \(\text {H}^{{\cdot }})\) above 3500 K and 100 atm.

Improving the adsorption kinetics of ibuprofen on an activated carbon fabric through ultrasound irradiation: Simulation and experimental studies

In order to override the slow adsorption kinetics of micropollutants on an activated carbon fabric (ACF) in water medium, different mixing modes, i.e. orbital stirring (250 rpm), low frequency ultrasonic irradiation with either a 20 kHz probe (volumic power: 80 W/L) or a 38 kHz bath (10 W/L), were compared to promote the adsorption of ibuprofen (4 ppm initial concentration).The used ACF is formed of wowen braids made of three yarns (∼300 µm diameter), each of them being composed of microporous fiber bundles (12.6 µm diameter) and its texture was accurately characterized. The adsorption kinetics were studied in buffered phosphate solution (pH 7.5) on a disk, braids or fiber from the fabric and were simulated by a volume diffusion model. The fitted values of the external mass transfer and the volume diffusion coefficients have demonstrated the limitation of the adsorption kinetics under stirring on the fabric disks and braids by the diffusion step within the yarn in the inter-fiber macroporosity.The 20 kHz sonication coupled to the adsorption on ACF led to the degradation of ibuprofen by OH° radicals issued from water sonolysis but without damaging further the fabric. The low power irradiation at 38 kHz allowed a sharp acceleration of the adsorption kinetics with respect to the one obtained through orbital stirring. This is explained by a fast mobility of the ibuprofen owing to the presence of standing waves and absence of harsh cavitation as compared to 20 kHz probe system, and confirmed by a fitted diffusion coefficient higher than the one of molecular ibuprofen and of two order of magnitude than in stirring conditions.

Sonochemiluminescence in an aqueous solution of Ru(bpy)3Cl2

The sonochemiluminescence spectra of electron-excited ions *[Ru(bpy)3]2+ was registered for the first time during sonolysis of argon saturated aqueous solutions of Ru(bpy)3Cl2 with low concentration. At single-bubble sonolysis, the luminescence band of ruthenium is recorded at a concentration of Ru(bpy)3Cl2 from 10−6 M, and at multibubble from 10−5 M. Possible mechanisms for the appearance of the band of a tris-bipyridyl ruthenium(II) complex on the background of an structureless continuum of water in the spectra of sonoluminescence are analyzed. Based on the results of the comparison of the sonoluminescence spectra of Ru(bpy)3Cl2 aqueous solutions with the sonoluminescence spectra of aqueous solutions of rhodamine B (which has a high quantum yield of photoluminescence) it was established that a possible mechanism of sonophotoluminescence does not play a decisive role in ruthenium sonoluminescence. The effect of radical acceptors (O2, C2H5OH, Cd2+, I−) on ruthenium sonoluminescence is analyzed. The most significant mechanism for the formation of electron-excited ions *[Ru(bpy)3]2+ during sonolysis is the sonochemiluminescence in oxidation-reduction reactions involving [Ru(bpy)3]2+ ions and radical products of sonolysis of water (OH, H, e−aq) in the solution volume.

Characterization and corrosion behavior of graphene oxide-hydroxyapatite composite coating applied by ultrasound-assisted pulse electrodeposition

Abstract Hydroxyapatite (HA) coating reinforced with graphene oxide (GO) had been developed for getting rid of restrictions associated with its brittleness. This study introduced a promising method of ultrasound-assisted pulse electrodeposition to fabricate the GO-HA coating on the anodized heat-treated surface of titanium. The SEM images indicated that the combined effect of employing ultrasonic waves and GO as a second mechanically resistant phase resulted in the formation of a fine and compact microstructure for the HA-based coating. The EDS elemental maps and micro-Raman spectra showed that the ultrasonic power of 60 W was more effective to incorporate the GO sheets into the coating. However, aggressive agitation of electrolyte with increasing the power to 100 W limited the electrocrystallization of HA crystals in some regions of the surface. The results of nanoindentation test demonstrated the highest nano-hardness (3.08 Gpa) and elastic modulus (41.26 Gpa) for the GO-HA coating prepared by the ultrasound-assisted method. The EDS and FTIR analyses revealed that both the GO sheets and highly reactive OH · radicals produced during the water sonolysis had a positive influence on the mineralization of HA phase. In addition, the pore size distribution diagrams calculated from the N 2 adsorption-desorption isotherms indicated a decrease in the pore size of HA crystals for the electro-co-deposited GO-HA sample. Finally, anodizing/heat-treatment process and the incorporation of GO sheets into the coating led to a significant improvement in the corrosion protection of titanium.

Application of sonochemical technique for sustainable surface modification of polyester fibers resulting in durable nano-sonofinishing

In this study firstly we aimed at introducing the effects of ultrasound and sonochemistry in surface modification of polyester fibers. For this purpose, surface modification of polyester fibers was achieved by ultrasound, and contact angle and water spreading time measurements were used to confirm the treatment efficiency. Hydroxylation of terephthalate was occurred by hydroxyl radicals formed during water sonolysis, forming functional groups on polyester surface, as confirmed by XPS analysis, improving the wettability. Creation of hydroxyl groups under sono surface modification was further assessed by dyeing the samples with reactive dye. Secondly, we investigated the durable nano-sono-finishing of polyester fibers by nano TiO2 particles under ultrasonic bath. Washing durability of the sono-synthesized TiO2 nanoparticles was evaluated confirming the effective role of sonochemical technique in polyester surface modification. Thirdly, the self-cleaning activity of sono-synthesized nano TiO2 treated samples toward degradation of Methylene Blue stain was superior to coating of fabric with commercial nano TiO2 using identical procedure.

Generation of ROS mediated by mechanical waves (ultrasound) and its possible applications

The thermal decomposition of 9,10 diphenylanthracene peroxide (DPAO2) generates DPA and a mix of triplet and singlet molecular oxygen. For DPAO2 the efficiency to produce singlet molecular oxygen is 0.35. On the other hand, it has shown that many thermal reactions can be carried out through the interaction of molecules with ultrasound. Ultrasound irradiation can create hydrodynamic stress (sonomechanical process), inertial cavitation (pyrolitic process) and long range effects mediated by radicals or ROS. Sonochemical reactions can be originated by pyrolytic like process, shock mechanical waves, thermal reactions and radical and ROS mediated reactions. Sonolysis of pure water can yield hydrogen or hydroxyl radicals and hydrogen peroxide (ROS). When DPAO2 in 1,4 dioxane solution is treated with 20 or 24kHz and different power intensity the production of molecular singlet oxygen is observed. Specific scavengers like tetracyclone (TC) are used to demonstrate it. The efficiency now is 0.85 showing that the sonochemical process is much more efficient that the thermal one. Another endoperoxide, artemisinin was also studied. Unlike the concept of photosensitizer of photodynamic therapy, in spite of large amount of reported results in literature, the term sonosensitizer and the sonosensitization process are not well defined. We define sonosensitized reaction as one in which a chemical species decompose as consequence of cavitation phenomena producing ROS or other radicals and some other target species does undergo a chemical reaction. The concept could be reach rapidly other peroxides which are now under experimental studies. For artemisinin, an important antimalarian and anticancer drug, was established that ultrasound irradiation increases the effectiveness of the treatment but without any explanation. We show that artemisinin is an endoperoxide and behaves as a sonosensitizer in the sense of our definition.

Toward a new paradigm for sonochemistry: Short review on nonequilibrium plasma observations by means of MBSL spectroscopy in aqueous solutions

This review summarizes recent studies of multibubble sonoluminescence (MBSL) in aqueous media in order to highlight new insights into the origin of the sonochemical activity. The observation of OH(C2Σ+–A2Σ+) emission band and a spectroscopic analysis of OH(A2Σ+–X2Πi) emission band in MBSL of water pre-equilibrated with noble gases revealed the formation of a nonequilibrium plasma inside the collapsing bubble (Te>Tv>Tr, where Te is an electron temperature, Tv is a vibrational temperature and Tr is a rotational (gas) temperature). The Te and Tv estimated using OH(A2Σ+–X2Πi) emission band increase with ultrasonic frequency. In Xe the Tv of OH(A2Σ+) state is much higher than in Ar most probably due to the lower ionization potential of Xe. The MBSL of C2∗ Swan band (d3Πg–a3Πu) measured in aqueous tert-butanol (t-BuOH) solutions correlates with the data obtained for OH(A2Σ+–X2Πi) emission band. Analysis of the gaseous products of t-BuOH sonolysis revealed a significant sonochemical activity even at high t-BuOH concentration when MBSL is totally quenched, indicating that drastic intrabubble conditions (plasma) are not necessarily accompanied by sonoluminescence. The nonequilibrium plasma model of cavitation allows to explain the reverse carbon isotope effect observed during the sonolysis of water in the presence of Ar/CO gas mixture.

Computational engineering study of hydrogen production via ultrasonic cavitation in water

Ultrasonic cavitation, the formation and subsequent collapse of microbubbles, is the unique phenomenon responsible of the production of hydrogen during water sonolysis. This work presents the results of a comprehensive computational study of hydrogen production via acoustic cavitation in water. Computer simulations of chemical reactions occurring inside an ultrasonic cavitation bubble have been performed for a wide range of ultrasonic frequencies (20–1100 kHz) under different saturating gases (Ar and air), various acoustic intensities (0.5–1 W cm−2) and diverse liquid temperatures (20–50 °C). For an Ar bubble, reactions mechanism consisting in 25 reversible chemical reactions were proposed for studying the internal bubble-chemistry whereas 73 reversible reactions were taken into account for an air bubble. The obtained results have indicated that hydrogen (H2) as well as radicals, such as OH, H, HO2 and O, are created in the bubble during the strong collapse. In all cases, H2 is the main molecular product formed in the bubble at appreciable amount. The production rate of H2 decreases significantly as the frequency increases. The production rate of H2 is higher when water is saturated with argon than air and the beneficial effect of argon becomes more remarkable at higher ultrasonic frequencies. The numerical simulation showed the existence of an optimum liquid temperature (∼30 °C) for the production of H2. All the obtained results were analyzed and interpreted basing on the bubble dynamic characteristics.

Sonochemical water splitting in the presence of powdered metal oxides

Kinetics of hydrogen formation was explored as a new chemical dosimeter allowing probing the sonochemical activity of argon-saturated water in the presence of micro- and nano-sized metal oxide particles exhibiting catalytic properties (ThO2, ZrO2, and TiO2). It was shown that the conventional sonochemical dosimeter based on H2O2 formation is hardly applicable in such systems due to catalytic degradation of H2O2 at oxide surface. The study of H2 generation revealed that at low-frequency ultrasound (20kHz) the sonochemical water splitting is greatly improved for all studied metal oxides. The highest efficiency is observed for relatively large micrometric particles of ThO2 which is assigned to ultrasonically-driven particle fragmentation accompanied by mechanochemical water molecule splitting. The nanosized metal oxides do not exhibit particle size reduction under ultrasonic treatment but nevertheless yield higher quantities of H2. The enhancement of sonochemical water splitting in this case is most probably resulting from better bubble nucleation in heterogeneous systems. At high-frequency ultrasound (362kHz), the effect of metal oxide particles results in a combination of nucleation and ultrasound attenuation. In contrast to 20kHz, micrometric particles slowdown the sonolysis of water at 362kHz due to stronger attenuation of ultrasonic waves while smaller particles show a relatively weak and various directional effects.

Ultrasonic activation of oxidation of azo dyes in aqueous solutions

The main tendencies in the oxidation of the azo dye methyl orange during high-frequency ultrasonic treatment in aqueous solutions were studied. It was proven experimentally that the hydroxyl radicals formed during water sonolysis play the critical role in this process. A synergy effect was observed when the combined method for oxidation of methyl orange in the presence of potassium persulfate was used.

Hydrogen Production from Water by Photolysis, Sonolysis and Sonophotolysis with Solid Solutions of Rare Earth, Gallium and Indium Oxides as Heterogeneous Catalysts

In this work, we present the hydrogen production by photolysis, sonolysis and sonophotolysis of water in the presence of newly synthesized solid solutions of rare earth, gallium and indium oxides playing as catalysts. From the experiments of photolysis, we found that the best photocatalyst is the solid solution Y0.8Ga0.2InO3 doped by sulphur atoms. In experiments of sonolysis, we optimized the rate of hydrogen production by changing the amount of water, adding ethanol and tuning the power of our piezoelectric transducer. Finally, we performed sonolysis and sonophotolysis experiments in the presence of S:Y0.8Ga0.2InO3 finding a promising synergistic effect of UV-visible electromagnetic waves and 38 kHz ultrasound waves in producing H2.

Bactericidal Effect of Photolysis of H2O2 in Combination with Sonolysis of Water via Hydroxyl Radical Generation.

The bactericidal effect of hydroxyl radical (·OH) generated by combination of photolysis of hydrogen peroxide (H2O2) and sonolysis of water was examined under the condition in which the yield of ·OH increased additively when H2O2 aqueous solution was concomitantly irradiated with laser and ultrasound. The suspension of Staphylococcus aureus mixed with the different concentrations of H2O2 was irradiated simultaneously with a laser light (wavelength: 405 nm, irradiance: 46 and 91 mW/cm2) and ultrasound (power: 30 w, frequency: 1.65 MHz) at 20 ± 1°C of the water bulk temperature for 2 min. The combination of laser and ultrasound irradiation significantly reduced the viable bacterial count in comparison with the laser irradiation of H2O2 alone. By contrast, the ultrasound irradiation alone exerted almost no bactericidal effect. These results suggested that the combination effect of photolysis of H2O2 and sonolysis of water on bactericidal activity was synergistic. A multi-way analysis of variance also revealed that the interaction of H2O2 concentration, laser power and ultrasound irradiation significantly affected the bactericidal activity. Since the result of oxidative DNA damage evaluation demonstrated that the combination of laser and ultrasound irradiation significantly induced oxidative damage of bacterial DNA in comparison with the laser irradiation of H2O2 alone, it was suggested that the combination effect of photolysis of H2O2 and sonolysis of water on bactericidal activity would be exerted via oxidative damage of cellular components such as DNA.

Critical factors in sonochemical degradation of fumaric acid

The effects of critical factors such as Henry’s Law constant, atmospheric OH rate constant, initial concentration, H2O2, FeSO4 and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H2O2 under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H2O2 under sonication. 0.1mM of fumaric acid suppresses H2O2 formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO4) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.

ChemInform Abstract: Organic Reactions in Water or Biphasic Aqueous Systems under Sonochemical Conditions. A Review on Catalytic Effects

AbstractReview: 35 refs.

Mechanism of the sonochemical production of hydrogen

It has been long recognized that propagation of an ultrasonic wave in water results in hydrogen production. The chemical effects of ultrasound (sonochemistry) originate from acoustic cavitation, that is, the formation, growth and implosive collapse of microscopic bubbles in liquid irradiated by ultrasound wave. Enormous temperatures and pressures are generated within the bubbles at the collapse, making each bubble as a microreactor within which typical flame reactions occur. The combustion in the cavitation bubbles yield species such as OH, H, O, HO2 and others. Although H2 is the most molecular product of water sonolysis, the mechanism of its production is until now not understood and the most reported suggestions are controversial. In this paper, a comprehensive numerical work was carried out, for the first time, to explain the mechanism of ultrasound induced generation of H2 in water. Computer simulations of chemical reactions occurring inside a bubble oscillating in water irradiated by an ultrasonic wave have been performed for different conditions. A kinetics mechanism of 25 reversible chemical reactions was proposed for studying the internal bubble-chemistry. The numerical simulations have evidenced the formation of H2 as well as other products such as O2, H2O2, OH, H, HO2 and O in the bubble during implosion. In all cases, H2 was the main product formed in the bubbles at appreciable amount. Basing on the simulation results and using material balance for hydrogen in the gas and liquid phases, the production rate of H2 in each phase has been quantified. The conclusion was that the main source of H2 production during water sonolysis is the gas phase of the bubbles through the reaction H + OH ↔ H2 + O.

Effect of operational conditions on sonoluminescence and kinetics of H2O2 formation during the sonolysis of water in the presence of Ar/O2 gas mixture

Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204–362kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry allowed to conclude that H2O2 is formed from non-excited OH (X2Π) and HO2 radicals. Finally, it was shown that at the studied conditions the efficiency of ultrasonic degassing is hardly influenced by frequency.

Ultrasound-assisted degradation of methyl orange in a micro reactor

In this study, an aqueous solution containing methyl orange (MO) was indirectly sonicated in a polydimethylsiloxane/glass micro reactor using a 200kHz transducer. A removal efficiency (RE) of about 9% was observed in 90min when 5mgL−1 MO solution was circulated at a flow rate of 0.76mLmin−1 at pH 2 and 20°C. While a lower RE was observed with an increase in solution temperature, an increase in MO concentration, flow rate and acoustic power led to an increase in RE. The addition of 100mgL−1 of CCl4 increased RE by 4% under similar experimental conditions. The mechanism of MO degradation involved sonochemically generated oxidising radicals, which was confirmed by the formation of H2O2 during sonolysis of water and reduction in RE with the addition of a radical scavenger.

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 Mn2+. 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 Mn2+. The optimum irradiation time for the effective synthesis of MnO2 was 13min at pH 2.2, 9min at pH 6.0, 8min at pH 9.3, respectively.