Sonocatalytic degradation of methylene blue with TiO2 pellets in water

A series of experiments were carried out to study the degradation of methylene blue by the irradiation of ultrasound onto TiO(2) in aqueous solution. A statistically significant decrease in the concentration of methylene blue was observed after 60 min irradiation. While the reduction was 22% of the initial concentration without H(2)O(2), addition of H(2)O(2) significantly enhanced the degradation of methylene blue for the TiO(2) containing system (85% reduction of the initial concentration). The addition of H(2)O(2) had no effect on the methylene blue degradation when the system contained Al(2)O(3). The degradation ratio of methylene blue was dependent on the amount of TiO(2) and also the specific surface area of TiO(2) in the solution. The effects of radical scavenging agents on the degradation of methylene blue were also investigated for the system with TiO(2). It was found that the radical scavenging agents dimethyl sulfoxide (DMSO), methanol, and mannitol suppressed the degradation, with DMSO being the most effective. The effect of pH on the degradation of methylene blue was further investigated. An U-shaped change in the concentration of methylene blue in the presence of TiO(2) was observed along with the change in pH values (pH 3-12), and the highest degradation ratio was observed at around pH 7. In conclusion, ultrasound irradiation of TiO(2) in aqueous solution resulted in significant generation of hydroxyl radicals, and this process may have potential for the treatment of organic dyes in wastewater.     

Investigation on the sonocatalytic degradation of acid red B in the presence of nanometer TiO2 catalysts and comparison of catalytic activities of anatase and rutile TiO2 powders

Here, the nanometer anatase and rutile titanium dioxide (TiO(2)) powders were introduced to act as the sonocatalysts during the ultrasonic degradation of azo dye-acid red B which was chosen as model compound. The ultrasound of low power was used as an irradiation source to induce TiO(2) particles performing catalytic activity. It was found that the processes of sonocatalytic degradation were different between nanometer anatase TiO(2) and nanometer rutile TiO(2). For nanometer anatase TiO(2) catalyst, the acid red B was mainly oxidated by the holes on the surface of nanometer anatase TiO(2) particles, so that the decolorization and degradation happened at the same time. For the nanometer rutile TiO(2) catalyst, the acid red B was mainly oxidated by the *OH radicals from the ultrasonic cavitation, so that the decolorization of azo bond takes place primarily, and then the degradation of naphthyl ring does. The intermediates of acid red B in the presence of nanometer anatase and rutile TiO(2) powders have been monitored by UV-vis spectra and high performance liquid chromatography (HPLC), respectively. All experiments indicated that the degradation effect of acid red B in the presence of nanometer anatase TiO(2) powder was obviously better than that in the presence of nanometer rutile TiO(2) powder. Hence, the method of sonocatalytic degradation for organic pollutants in the presence of nanometer anatase TiO(2) powder is expected to be promising as an advisable choice for the treatment of organic wastewaters in future.     

Sonophotocatalytic degradation of methyl orange by nano-sized Ag/TiO2 particles in aqueous solutions

Sonophotocatalytic behaviour of methyl orange (MeO) in aqueous solution illuminated by light generated by a xenon lamp was investigated. For all three kinds of photocatalysts: Degussa P25 (75% anatase, 25% rutile, with a surface area of 55.07 m(2)/g), Yili TiO(2) (mainly anatase, with a surface area of 10.45 m(2)/g) and Ag/TiO(2) (silver loaded on Yili TiO(2)), the degradation followed pseudo-first order kinetics. The results showed a synergistic effect between sonolysis and photocatalysis. Some parameters affecting the sonophotocatalytic degradation of MeO with nanoparticles Ag/TiO(2) were determined. The results indicated that the degradation ratio of MeO increased with the increase of ultrasonic power. An optimum 60 mg/L of Ag/TiO(2) added to relatively low concentrations of MeO was proved to have the most effective degradation efficiency. The study on the effects of hydroxyl radical (*OH) scavengers (i.e. mannitol and dimethyl sulfoxide) on the MeO degradation indicated that *OH radicals played an important role during MeO degradation, which enhanced MeO to be completely decomposed.     

Sonocatalytic performance of Tb7O12/TiO2 composite under ultrasonic irradiation

A Tb(7)O(12)/TiO(2) composite was successfully synthesized through a hydrolysis-calcination process. The Tb(7)O(12)/TiO(2) composite catalyst was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy, UV-Vis absorption/reflection spectroscopy, and X-ray diffraction (XRD). The heterogeneous sonocatalytic oxidation of amaranth in water, containing dispersed pure TiO(2) and Tb(7)O(12)/TiO(2) composite, was investigated under ultrasonic irradiation. The activity of the Tb(7)O(12)/TiO(2) catalyst is higher than that of pure TiO(2) during the sonodegradation of amaranth. The enhanced sonocatalytic activity of the composite may be attributed to the increase in charge separation efficiency and the presence of surface acidity.     

Application of salicylic acid dosimetry to evaluate hydrodynamic cavitation as an advanced oxidation process

The generation of OH* radicals inside hydrodynamic cavitation bubbles was monitored using a salicylic acid dosimeter. The reaction of this scavenger with OH* produces 2,5-dihydroxybenzoic acid (2,5-DHB) and, to a lesser degree, 2,3-DHB. The former, is a specific reaction product that can be determined with a very high sensitivity using HPLC-IF. This method has been applied to study the influence of the flow-rate and the solution pH for a given cavitation chamber geometry. The salicylic dosimetry has proven especially suitable for the characteristic time scales of hydrodynamic cavitation (higher than those of ultrasonic cavitation), which usually gives rise to recombination of radicals before they can reach the liquid-phase. Working at low pH the hydrophobic salicylic acid migrates to the gas-liquid interface and reacts with the OH* radicals, increasing the trapping efficiency of the dosimeter. Hydrodynamic cavitation works as a very low frequency sonochemical reactor, and therefore its potential as an Advanced Oxidation Process might be limited to reactions at the gas-liquid interface and inner bubble (i.e. with volatiles and/or hydrophobic substances).     

Spectroscopic investigation on the sonodynamic activity of Safranine T to bovine serum albumin damage

In this paper, the Safranine T (ST) was used as sonosensitive compound to study the sonodynamic damage to bovine serum albumin (BSA) under ultrasonic irradiation using fluorescence and UV–vis spectroscopy. The experimental results revealed the obvious synergetic effect of Safranine T (ST) and ultrasonic irradiation during the damage of BSA molecules. In addition, some influencing factors such as ultrasonic irradiation time, Safranine T (ST) concentration, pH value and ionic strength on the sonodynamic damage of BSA molecules were also considered. Finally, the generation of reactive oxygen species (ROS) in sonodynamic process was estimated by the method of Oxidation-Extraction Photometry (OEP). Meanwhile, several radical scavengers were used to determine the kind of generated ROS. Experiments showed that under ultrasonic irradiation the Safranine T (ST) can generate several kinds of ROS at the same time, at least including singlet oxygen (¹O₂) and hydroxyl radicals (OH).     

Spectroscopic study on the sonodynamic and sonocatalytic damage of anthraquinone derivants to bovine serum albumin under ultrasonic irradiation

In this work, three anthraquinone derivants (Alizarin: 1,2-dihydroxy-9, 10-anthraquinone, Alizarin–DA: 1,2-dihydroxy-9, 10-anthraquinone-3-aminomethyl-N, N-diacetic acid and Alizarin–DA–Fe: 1,2-dihydroxy-9, 10-anthraquinone-3-aminomethyl-N, N-diacetate-Ferrous(III)) were used to study the sonodynamic and sonocatalytic damage of bovine serum albumin (BSA) molecules according to the hyperchromic effect of UV–vis spectra and quenching effect of intrinsic fluorescence. Meanwhile, some influencing factors such as ultrasonic irradiation time, anthraquinone derivants concentration and ionic strength on the damage of BSA molecules were also considered. The results show that the synergetic effect of anthraquinone derivants and ultrasonic irradiation can efficiently damage the BSA molecules. Finally, some special radical scavengers were used to determine the kind of generated reactive oxygen species (ROS) in the presence of three anthraquinone derivants under ultrasonic irradiation. The results show that the ROS, at least, including singlet oxygen (¹O₂) and hydroxyl radicals (OH) are generated during the sonodynamic and sonocatalytic processes. It is wished that this paper could offer some valuable references for the application of anthraquinone derivants in sonodynamic therapy (SDT) and sonocatalytic therapy (SCT) for tumor treatment.     

Ultrasonic effects on electroorganic processes--Part 20. Photocatalytic oxidation of aliphatic alcohols in aqueous suspension of TiO2 powder

Ultrasonic effects in a suspension system were examined using the photocatalytic oxidation of 2-propanol to acetone and of ethanol to acetaldehyde in the aqueous suspension of TiO2 powder as a model reaction. The formation rate of acetone was significantly increased under ultrasonic irradiation. The oxidation reaction under ultrasonic irradiation was affected in a different manner from that in silence by reaction conditions such as ultrasonic power, stirring speed, amount of TiO2, concentration of 2-propanol, and pretreatment of the TiO2 powder. Furthermore, it was also observed that the particle size of the TiO2 photocatalyst powder was increased due to the particle agglomeration by ultrasonic irradiation, and consequently it was suggested that ultrasound activates the surface of the catalyst. These results are discussed on the basis of not only the activation of the photocatalyst but also ultrasonic enhancement of mass transport of 2-propanol molecules.     

光谱法研究纳米二氧化硅(SiO_2)催化超声波照射对牛血清白蛋白(BSA)的损伤

利用紫外-可见(Uv-Vis)光谱和荧光光谱研究了超声波照射激活纳米二氧化硅(SiO2)粒子对牛血清白蛋白(BSA)分子的损伤,并考查了超声波照射时间、纳米SiO2粉末加入量、溶液酸度和超声波照射功率等因素对BSA分子损伤程度的影响.结果表明,对于体系温度为(37.0±0.2)℃和浓度为1.0×10-5mol·-1的BSA溶液,UV-Vis光谱显示,随着超声波照射时间,纳米SiO2粉末加入量,溶液pH值和照射功率的增大呈现出越来越明显的增色效应.然而,BSA溶液的荧光光谱却随着上述因素的增大呈现出越来越明显的猝灭现象.此外,还初步探讨了超声波照射激活纳米siO2粒子对BSA分子损伤的机理,认为是声致发光或高热激发使纳米siO2粒子产生·OH自由基,进而损伤溶液中的BSA分子.这一研究结果对声催化方法应用于临床治疗肿瘤以及纳米药物的开发具有一定的指导意义.     

A combination of ultrasound and inorganic catalyst: removal of 2-chlorophenol from aqueous solution

Removal of 2-chlorophenol by ultrasonic waves (sonolysis), inorganic catalyst, and a combination of the two processes was tested and compared with each technique. In sonolysis, 2-chlorophenol mostly degraded indirectly in the bulk of solution by the radicals produced in the cavitation process. In catalyst treatment, the removal was performed in the presence of Al2O3, TiO2 and CuO. The highest removal was achieved in the presence of TiO2 for this pollutant. In the combined method an enhancement was observed for the removal of 2-chlorophenol. This could be attributed primarily to the continuous cleaning and chemical activation of the catalyst by acoustic cavitation. The mass transfer between the liquid phase and the catalyst and also the surface area of the catalyst are accelerated by the ultrasonic waves. The removal of 2-chlorophenol was performed under different intensities of irradiation, temperatures and quantities of catalyst. Some experiments were conducted in the presence of a Fenton reagent. In kinetic point of view, the removal of pollutant showed a pseudo-first order behavior. The combined method had a higher rate coefficient than sonolysis and catalyst treatment individually. Under some conditions, the presence of ultrasound has increased the rate coefficient of removal to about 10 times that in the absence of ultrasound.     

Spectroscopic investigation on the sonodynamic activity of amsacrine (AMSA) to bovine serum albumin (BSA) damage

The sonodynamic damage of bovine serum albumin (BSA) under ultrasonic irradiation in the presence of amsacrine (AMSA) was studied by hyperchromic effect of UV-vis spectra and quenching effect of intrinsic fluorescence. In addition, several influencing factors such as ultrasonic irradiation time, AMSA concentration, system acidity and ionic strength about the damage of BSA molecules were reviewed. The results showed that the damage degree was obviously enhanced with the increase of ultrasonic irradiation time and AMSA concentration, but it was only slightly increased with the increase of solution pH value and ionic strength. Furthermore, the binding and damaging sites to BSA molecules were estimated by synchronous fluorescence spectra. The different chances to damage tryptophan (Trp) and tyrosine (Tyr) residues were found through the ratios of synchronous fluorescence quenching (R_SFQ). At last, the generation of reactive oxygen species (ROS) in sonodynamic process was estimated by the method of oxidation-extraction Spectrometry (OES). And then, several radical scavengers were used to determine the kind of ROS, which includes singlet oxygen (¹O₂) and hydroxyl radicals (·OH). Perhaps, the result would bring a certain guiding significance to use sonosensitive drugs in the fields of tumor treatment.     

Ultrasonically initiated emulsion polymerization of styrene in the presence of Fe2+

Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of Fe(2+). The addition of a small amount of Fe(2+) markedly enhanced the polymerization rate of styrene. In the presence of 50 microM Fe(2+), the conversion of monomer in the reaction time of 60 min was 2.4 times as high as that in the absence of Fe(2+). The increase in the polymerization rate was due to higher concentration of hydroxyl (*OH) radicals generated via Fenton reaction of Fe(2+) with hydrogen peroxide (H(2)O(2)), which was proved by a lower amount of H(2)O(2) in Fe(2+) aqueous solution compared with that in pure water during ultrasonic irradiation. However, the addition of excessive Fe(2+) had no further accelerating effect on the polymerization rate due to the reduction of *OH radicals by Fe(2+). So it is an effective way to add an appropriate amount of Fe(2+) to accelerate ultrasonically initiated emulsion polymerization of styrene.     

Spatiotemporal measurement using L-band ESR-CT system for water sonolysis in the presence of 1-Hydroxy-2,2,5,5-tetramethyl-3-imidazoline-3-oxide

When using ESR to measure the radicals generated by ultrasound, it is necessary to extract a solution and place it in the ESR system. To avoid this process, we incorporated an ultrasonic reaction cell in an L-band ESR-CT system, producing a system that allows the detection of the concentration of radicals during ultrasonic irradiation. This system was used to measure the time and space dependences of OH radicals generated by ultrasonic irradiation. When a 10 ml aqueous solution of 1-hydroxy-2,2,5,5-tetramethyl-3-imidazoline-3-oxide (HTIO) was irradiated with ultrasound, it was found that the generation of radicals was clearly shown in a CT image after a period of 10 min. It was also found that continued irradiation resulted in an increased concentration of radicals. In addition to this system, an X-band ESR system was also used to measure the concentration of OH radicals generated, and the results of both systems were then compared. Both results are very similar, showing that the proposed system, which was realized by incorporating an ultrasonic irradiation cell in the L-band ESR-CT system, operated properly. Because this system allows the measurement of sonochemical reactions in an opaque cell or an opaque solution such as blood and industrial wastewater, it is a very useful measurement system for achieving the applying of sonochemistry to the medical engineering field.     

Complete mineralization of propyzamide in aqueous solution containing TiO2 particles and H2O2 by the simultaneous irradiation of light and ultrasonic waves

Environmental problems arise from the pollution of ground water and soil by propyzamide, 3,5-dichloro-N-(3-methyl-1-butyn-3-yl) benzamide, which is a popular herbicide. To decompose propyzamide, aqueous solutions containing propyzamide and TiO2 particles was irradiated by light. The photocatalytic decomposition was accelerated when the solution temperature and pH were high. The temperature dependence was due to the adsorption processes of propyzamide on the TiO2 particles. The decomposition was further promoted by addition of H2O2 because of its effective electron-trapping and generated *OH which was available to decompose propyzamide. Although no propyzamide was detected in the solution after the irradiation time of about 20 min, the decomposed intermediate compounds still remained. In order to mineralize completely propyzamide, simultaneous irradiation by light and ultrasonic waves was carried out. The hybrid effect of the irradiation by light and ultrasonic waves in conjunction with H2O2 was first confirmed to achieve the complete mineralization of propyzamide.     

Effect of coal ash on hydrazine degradation under stirring and ultrasonic irradiation conditions

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1-5.0 mmol/L was investigated as a function of amount of coal ash (0.0-5.0 wt%) under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the rate of decrease in the hydrazine concentration depended upon an amount of coal ash under the stirring and ultrasonic irradiation condition. It was considered under the stirring condition that hydrazine was adsorbed and degraded partly on coal ash. Furthermore, the sonochemically formed OH radicals were more effective in the hydrazine degradation than stirring condition in the presence of an intermediate amount of coal ash (0.6-2.4 wt%), whereas the effect of OH radicals disappeared in the presence of coal ash more than 2.4 wt%.     

Synthesis and sonocatalytic property of rod-shape Sr(OH)2·8H2O

A novel rod-shape sonocatalyst Sr(OH)₂·8H₂O was prepared by a facile precipitation method, and characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and UV–vis absorption spectroscopy. Comparative sonocatalytic degradation experiments were carried out in different conditions under ultrasonic irradiation by using rhodamine B (RhB) as the model substrate, indicating that Sr(OH)₂·8H₂O was highly sonocatalytic. Total organic carbon experiment demonstrated Sr(OH)₂·8H₂O with mass mineralization of organic carbon. The effects of catalyst amount, initial RhB concentration and ultrasonic energy of degradation were investigated, and the sonocatalyst could be reused 5 times without significant loss of activity. Furthermore, the potent degrading capability was ascribed to ultrasonic cavitation producing flash light/energy which generated radicals (e.g., OH) with high oxidation activity.     

Investigation on transition crystal of ordinary rutile TiO2 powder and its sonocatalytic activity

The transition crystal TiO(2) sonocatalyst was prepared utilizing the method of ultrasonic irradiation in hydrogen peroxide solution. The sonocatalytic activity of the transition crystal TiO(2) powder was validated through the degradation of methyl orange in aqueous solution by ultrasonic irradiation. The results show that the sonocatalytic activity of the transition crystal TiO(2) powder is obviously higher than that of pure rutile and anatase TiO(2) powders as well as mixed rutile and anatase TiO(2) powders according to the proportion of corresponding transition crystal TiO(2) catalyst. The degradation ratio of methyl orange in the presence of the transition crystal TiO(2) catalyst surpasses 75% within 80 min ultrasonic irradiation, while the degradation ratios are 55.93%, 51.68% and 40.88%, respectively, for rutile, mixed and anatase TiO(2) powders.     

Inactivation of Escherichia coli by ultrasonic irradiation

Ultrasonic inactivation of Escherichia coli XL1-Blue has been investigated by high-intensity ultrasonic waves from horn type sonicator (27.5 kHz) utilizing the "squeeze-film effect". The amplitude of the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The inactivation of the E. coli cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant gradually increased with increasing amplitude of the vibration face and showed rapid increase above 3 microm (p-p). In contrast, the H2O2 formation was not observed below 3 microm (p-p), indicating that the ultrasonic shock wave might be more important than indirect effect of OH radicals formed by ultrasonic cavitation in this system. The optimal thickness of the squeeze film was determined as 2 mm for the E. coli inactivation. More than 99% of E. coli cells was inactivated within 180-s sonication at the amplitude of 3 microm (p-p) and 2 mm of the thickness of the squeeze film.     

The effect of ultrasound upon the oxidation of thiosulphate on stainless steel and platinum electrodes

Ultrasound was found to increase the oxidation peak current and hence the decomposition rate of thiosulphate 50-fold compared to silent conditions. The effects of the ultrasonic frequency (20 and 38 kHz) and power upon the electrochemical oxidation of thiosulphate in aqueous KCl (1 mol dm-3) at stationary stainless steel and platinum electrodes were studied chronoamperometrically and potentiostatically (at various scan rates). No sigmoidal-shaped voltammograms were observed for the redox couple S4O6(2-)/S2O3(2-) in the presence of ultrasound. However, application of ultrasound to this redox couple provided an increase in the oxidation peak current at the frequencies employed, the magnitude of which varied with concentration, scan rate and ultrasonic power. Under sonication at 20 and 38 kHz, the oxidation peak potential shifted anodically with increasing ultrasonic power. This anodic shift in potential may be due to the formation of hydroxyl radicals, changes in electrode surface composition and complex adsorption phenomena. The large increase in oxidation peak currents and the rates of decomposition of thiosulphate, in the presence of ultrasound, are explained in terms of enhanced mass transfer at the electrode due to cavitation and acoustic streaming together with microstreaming coupled with adsorption phenomena. It is also shown that changes in macroscopic temperature throughout the experiment are insufficient to cause the observed enhanced diffusion.     

Kinetics of ultrasonic degradation of phenol in the presence of TiO2 particles

The degradation of phenol by ultrasonic irradiation in the presence of TiO2 was investigated in complete darkness. The effects of amount of TiO2 and the combination of TiO2 addition with gas (air or oxygen) supply on the degradation kinetics of phenol and the formation of the reaction products were examined. The degradation rate of phenol increased with the amount of TiO2. As the dissolved oxygen concentration increased by supplying oxygen, the degradation rate of phenol also increased. A kinetic model for the disappearance of phenol was proposed. The model takes into account the OH radical formation by direct water degradation, indirect degradation by oxygen atom and indirect degradation by TiO2 catalysis. The calculated results explained well the fact that a higher amount of TiO2 and dissolved oxygen concentration gave faster disappearance rate.