Microhydration of oxalic acid leading to dissociation

The effect of microhydration on the simplest dicarboxylic acid, namely oxalic acid, leading to the dissociation of its proton, is studied using first principle-based electronic structure calculations. The geometry of the hydrated clusters of oxalic acid considering up to seven water molecules is determined at ωB97X-D/aug-cc-pVDZ level of theory. Solvent stabilisation and interaction energy parameters are calculated applying CCSD(T) level of theory. The calculated free energy of formation shows that the hydrated oxalic acid clusters are stable only at low temperature and pressure. Though the solvent stabilisation energy increases linearly with an increase in the size of the hydrated cluster, the calculated interaction energy, acidic O–H bond dipole moment and hydrogen bond energy show characteristic features of ion pair formation. The spectral manifestation of the weakening hydroxyl bond is observed as red shift in its stretching frequency. A rigid potential energy scan, altering the dissociating O–H bond length of the oxalic acid molecule, shows an energy barrier for acid to water proton transfer in all cases except hepta-hydrate of oxalic acid, where a barrier-less proton transfer occurs. The number of water molecules (n) needed for dissociation of oxalic acid molecule is consistent with the value obtained from recently reported emperical correlation between n and pKa.     

Ultrasonic degradation of butadiene, styrene and their copolymers

Ultrasonic degradation of commercially important polymers, styrene-butadiene (SBR) rubber, acrylonitrile-butadiene (NBR) rubber, styrene-acrylonitrile (SAN), polybutadiene rubber and polystyrene were investigated. The molecular weight distributions were measured using gel permeation chromatography (GPC). A model based on continuous distribution kinetics approach was used to study the time evolution of molecular weight distribution for these polymers during degradation. The effect of solvent properties and ultrasound intensity on the degradation of SBR rubber was investigated using different pure solvents and mixed solvents of varying volatility and different ultrasonic intensities.     

Sonolytic degradation of acetic acid in aqueous solutions

In this work, ultrasonic degradation of acetic acid, which is one of the most resistant carboxylic acids to oxidize, was investigated. The effects of parameters such as ultrasonic power, initial concentration, addition of NaCl or several oxides were studied on the degradation of acetic acid. Acetic acid was sonicated indirectly using an ultrasonic bath with 40 kHz. It was observed that degradation degree increased with decreasing power and initial concentration and with increasing NaCl concentration. Initial degradation degree was enhanced with addition of zeolite and SiO(2).     

Ultrasonic study of nitric acid

I.IntroductionBymeansofu1trasonicwavesthedynamicspecificpropertiesofmolecu1esinmediacouldbeapprehended.Fromthe195ostol96osacousticiansstudiedmo1ecu1aracousticandthermodynamicspecificpropertiesof1iquidsandmixtureswithgreate.th.siasm['-'],andkeptonbringto1ighttheirreportsofrc1evantstudiesinthe1astten-oddyearsl'-'l.overrecentyearstheauthorhasbeenengagedinthemeasurementandstudyofsoundve-locityofsevera1chemica1so1utionsinassociationwithu1trasonicmeasurementstudyofthecon-centrationofsolutionsproduce…     

Tracer studies of anodic films formed on aluminium in malonic and oxalic acids

Using a tungsten-containing layer, incorporated into sputtering-deposited aluminium, as a tracer, the growth of porous anodic films in malonic and oxalic acid electrolytes has been investigated using transmission electron microscopy, Rutherford backscattering spectroscopy and nuclear reaction analysis. Comparisons were also made with films formed in phosphoric acid electrolyte, which have been studied previously. The findings reveal a distortion of the tracer layer within the barrier region of the porous films, evident as a lagging of the tracer beneath the pores relative to that in the adjacent cell wall region. Further, the films are significantly thicker than the layer of metal consumed during anodizing and display smooth-sided pores. The anodizing behaviours are consistent with a major role for field-assisted flow of film material within the barrier layer in the development of the pores.     

Effect of heat treatment on the structure of incorporated oxalate species and photoluminescent properties of porous alumina films formed in oxalic acid

The present work focuses on the use of IR spectroscopy and photoluminescence spectral measurements for studying the treatment temperature effect on the compositional and luminescent properties of oxalic acid alumina films. In line with the recent researches we have also found that heat treatment of porous alumina films formed in oxalic acid leads to considerable changes in their photoluminescence properties: upon annealing the intensity of photoluminescence (PL) increases reaching a maximum at the temperature of around 500 °C and then decreases. IR spectra of as-grown and heat-treated films have proved that PL emission in the anodic alumina films is related with the state of ‘structural’ oxalate species incorporated in the oxide lattice. These results allowed us to conclude that PL behavior of oxalic acid alumina films can be explained through the concept of variations in the bonding molecular orbitals of incorporated oxalate species including σ- and π-bonds.     

Ultrasonic degradation of Rhodamine B in the presence of hydrogen peroxide and some metal oxide

In this research, degradation of Rodamine B in the presence of (hydrogen peroxide), (hydrogen peroxide + ultrasound), (hydrogen peroxide + aluminum oxide), (hydrogen peroxide + aluminum oxide + ultrasound with different ultrasound power), (hydrogen peroxide + iron oxide) and (hydrogen peroxide + iron oxide + ultrasound with different ultrasound power) were investigated at 25 °C. The apparent rate constants for the examined systems were calculated by pseudo-first-order kinetics. The results indicate that the rate of degradation was accelerated by ultrasound. The rate of degradation was increased by increasing power ultrasound. The efficiency of the (hydrogen peroxide + iron oxide + ultrasound) system for degradation of Rodamine B was higher than the others examined.     

高温高压下草酸脱羧反应中的拉曼光谱研究

应用水热金刚石压腔结合拉曼光谱技术研究了高温高压下草酸溶液的热稳定,使用拉曼光谱对其脱羧反应及产物进行监测。结果表明低温升温过程中,草酸的拉曼谱图中各个特征振动峰没有发生变化,随着温度的继续升高,其特征振动峰逐渐变弱。达到一定温度后,羧基的拉曼特征峰消失,草酸发生脱羧反应:C2H2O4—2CO2+H2生成CO2和H2。高温高压下草酸发生热分解的温度压力之间呈线性关系,其线性回归方程为P(MPa)=12.839 T(K)-5 953.7,R2=0.99。草酸脱羧反应的摩尔体积变化与温度压力的关系为ΔV(cm-3.mol-1)=16.69-0.002P(MPa)+0.005 2T(K),R2=0.99。     

Ultrasound-assisted anodization of aluminum in oxalic acid

Porous anodic alumina is an important nanoscale template for fabrication of various nanostructures. We report a new ultrasound-assisted anodization process in oxalic acid. Under the continuous irradiation of ultrasound, the one-step-anodized sample has a smooth and clean surface, and two-step-anodization brings ordered porous anodic alumina with higher growth rate of 52 μm/h. The ultrasound applied during the anodization can clean the surface and enhance the nanopore growth since it can accelerate the oxide dissolving on the electrolyte/oxide interface. The ultrasound-assisted anodization may be utilized for other anodizations.     

Ultrasonic absorption studies in solutions of ortho and para hydroxy benzoic acid in dioxan

Ultrasonic absorption was measured in ortho and para hydroxy benzoic acid (OHBA and PHBA) in dioxan at room temperature for various solute concentrations. The variation of ultrasonic absorption in both solutions with the solute concentration showed two maxima, one at lower solute concentration and the other at higher solute concentration. The first maximum is explained as due to formation of hydrogen bonds between the O-H groups of OHBA and PHBA molecules and the oxygen of dioxan molecules and the second maximum as due to the COOH group of the OHBA/PHBA molecules and oxygen of dioxan molecules. In both systems the measured absorption is explained on the basis of Hall’s two-state model.     

Sonochemical processes for the degradation of antibiotics in aqueous solutions: A review

Antibiotic residues in water are general health and environmental risks due to the antibiotic-resistance phenomenon. Sonication has been included among the advanced oxidation processes (AOPs) used to remove recalcitrant contaminants in aquatic environments. Sonochemical processes have shown substantial advantages, including cleanliness, safety, energy savings and either negligible or no secondary pollution. This review provides a wide overview of the different protocols and degradation mechanisms for antibiotics that either use sonication alone or in hybrid processes, such as sonication with catalysts, Fenton and Fenton-like processes, photolysis, ozonation, etc.     

Preparation of zinc tungstate nanomaterial and its sonocatalytic degradation of meloxicam as a novel sonocatalyst in aqueous solution

Zinc tungstate (ZnWO₄) was previously used as a photocatalyst. In this paper, for the first time as an sonocatalyst, the performance of ZnWO₄ for sonocatalytic degradation of meloxicam (MEL) under ultrasonic irradiation were studied. Firstly, ZnWO₄ nanomaterials were synthesized at different acidity (pH = 5, 6, 7, 8, 9) via the hydrothermal method. Utilizing SEM, XRD and EDS techniques to characterize composition and morphology of each product, the same crystal forms, but different morphologies (nano-sheet, nano-microspheres or nano-rod) of ZnWO₄ could be obtained. Secondly, the sonocatalytic activities of ZnWO₄ on degradation of MEL were studied. It was found that the degradation ratio varied with the synthetic pH values, with ZnWO₄ under synthetic pH = 6 exhibiting the best sonocatalytic performance (75.7%). While being synthesized at this pH value, ZnWO₄ nano-microspheres had the largest BET surface area (27.068 m²/g), the smallest particle size (40–60 nm) so as to provide more active sites on its surface, which were able to produce more reactive oxygen species (ROS) and holes under ultrasonic irradiation. These ROS and holes had a positive effect on the degradation of MEL into CO₂, H₂O and inorganic. Thirdly, various influential factors including ultrasonic power intensity, ultrasonic time, catalyst addition dosage, initial concentration of MEL solution and reusability of catalyst were also explored. Under the condition of 10 mg/L MEL concentration, 20 mg catalyst dosage, 120 min irradiation time, 0.278 W/cm² ultrasonic power intensity, the degradation ratio on MEL reached 75.7%. Finally, the presence of hydroxyl radical (OH) and singlet molecular oxygen (¹O₂) in the reaction was confirmed by adding ROS scavenger. The experimental results suggested that ZnWO₄ nanoparticle could be used not only as an effective photocatalyst, but also, under the condition of ultrasonic irradiation, a promising sonocatalyst for degradation of organic pollutants in aqueous media.     

Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19

The decoloration of reactive dye C.I. Reactive Blue 19 (RB 19) using combined ultrasound with the Fenton process has been investigated. The effect of varying the concentrations of hydrogen peroxide and iron sulfate, initial pH, ultrasonic power, initial dye concentration and dissolved gas on the decoloration and degradation efficiencies was measured. Calibration of the ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using the Fricke dosimeter and degradations were carried out with a 20 kHz probe type transducer at 2, 4, 6 and 8 W cm⁻² of acoustic intensity at 15, 25, 50 and 75 mg L⁻¹ initial dye concentrations. First order rate kinetics was observed. It was found that while the degradation rate due to ultrasound alone was slow, sonication significantly accelerated the Fenton reaction. While the results were similar to those reported for other dyes, the effects occurred at lower concentrations. The rate and extent of decoloration of RB 19 increased with rising hydrogen peroxide concentration, ultrasonic powers and iron sulfate concentration but decreased with increasing dye concentration. An optimum pH value of pH = 3.5 was found. The rate of decoloration was higher when dissolved oxygen was present as compared with nitrogen and argon confirming the solution phase mechanism of the degradation.     

Improvement of sonochemical degradation of Brilliant blue R in water using periodate ions: Implication of iodine radicals in the oxidation process

In this paper, the effect of periodate (IO₄⁻) on the ultrasonic degradation at 300 kHz of Brilliant Blue R (BBR), an organic dye pollutant, was investigated. The experiments were realized in the absence and presence of periodate for various operating conditions including initial solution pH (2–8) and delivered ultrasonic power (20–80 W). It was found that periodate greatly enhanced the sonochemical degradation of BBR. The degradation rate increased significantly with increasing IO₄⁻ concentration up to 10 mM and decreased afterward. With 10 mM of periodate, the degradation rate was 2.4-fold higher than that with ultrasound alone. The chemical probes experiments showed that periodate activation into free radicals (IO₃, IO₄ and OH) takes place by sonolysis and iodine radicals contribute significantly in the oxidation process. It was found that the periodate-enhanced effect was strongly experimental parameters dependent. The advantageous effect of periodate increased significantly with decreasing power and the best enhancing effect was obtained for the lowest power. Correspondingly, the periodate-enhanced effect increased with pH increase in the range 2–8 and it was more remarkable at near alkaline condition (pH 8). A reaction scheme for periodate sonolysis was proposed, for the first time, discussed and then used for interpreting the obtained results.     

Ultrasonic degradation kinetics and isomerization of 3- and 4-O-caffeoylquinic acid at various pH: The protective effects of ascorbic acid and epigallocatechin gallate on their stability

Caffeoylquinic acids are existed in many plant species with various biological and pharmacological activities. 3-O-caffeoylquinic acid and 4-O-caffeoylquinic acid are two isomers of caffeoylquinic acids, which may be degraded and transformed to their isomers in processing. The present paper found that the stability of 3- and 4-O-caffeoylquinic acid had decreased with the increasing solution alkalinity. 3-O-caffeoylquinic acid was more stable than 4-O-caffeoylquinic acid at the same condition. During degradation, 3- and 4-O-caffeoylquinic acid were partially converted to their isomers. Additionally, ultrasonic effects on the degradation and isomerization of 3- and 4-O-caffeoylquinic acid at different pH were studied. Ultrasound facilitated the degradation and isomerization of these compounds. The degradation kinetics were described by the Weibull equation. The protective effect of ascorbic acid and epigallocatechin gallate were also explored. Ascorbic acid and epigallocatechin gallate could alleviate the degradation of 3- and 4-O-caffeoylquinic acid under certain conditions.     

Ultrasonic monitoring of malolactic fermentation in red wines

The progress of malolactic fermentation in red wines has been monitored by using ultrasonic techniques. The evolution of ultrasonic velocity of a tone burst 1 MHz longitudinal wave was measured, analyzed and compared to those parameters of oenological interest obtained simultaneously by analytical methods. Semi-industrial tanks were used during measurements pretending to be in real industrial conditions. Results showed that the ultrasonic velocity mainly changes as a result of the conversion by lactic acid bacteria of malic acid into lactic acid and CO₂. Overall, the present study has demonstrated the potential of the ultrasonic technique in monitoring the malolactic fermentation process.     

Ultrasonic-assisted ozone degradation of organic pollutants in industrial sulfuric acid

In this work, a combination of ozone (O₃) and ultrasound (US) has been firstly used to decolorize black concentrated sulfuric acid with high organic content. The effect of different reaction factors on the transparency, extent of decolorization, H₂SO₄ mass fraction, and organic pollutants removal is studied. In addition, the systematic interaction between ultrasound and ozone on the decolorization process is reviewed through comparative experiments of O₃, US and US/O₃. A sulfuric acid product that meets the requirements for first-class products in national standards, with an extent of decolorization of 74.07%, transparency of 70 mm, and a mass fraction of 98.04%, is obtained under the optimized conditions. Under the same conditions, it has been established that the treatment time can be saved by 25% using the US/O₃ process compared to using O₃. Further, the production of oxidative free radicals (•OH) in a concentrated sulfuric acid system is enhanced using the US/O₃ process compared with O₃. In addition, the degree of effectiveness of different oxidizing components on the decolorization process is revealed by adding different free radical shielding agents when the US/O₃ process is used.     

Ultrasonic irradiation effects on electrochemical synthesis of ZnO nanostructures

In the present article, electrochemical synthesis of ZnO nanostructures in presence of ultrasonic irradiation is investigated. The ultrasonic bath use for synthesis is calibrated using hydrophone method so that its frequency and acoustic power were obtained. From the results of the experimentation the role of ultrasonic irradiation in synthesis of ZnO nanoparticles is discussed. Diameter of the ZnO nanoparticles produced in the electrolyte was compared and investigated in absence and presence of the ultrasonic irradiation utilizing UV–visible photo-spectrometer. Then electrodeposited ZnO layer on the ITO glass as cathode’s surface in absence and presence of the ultrasonic irradiation were studied by UV–visible photo-spectrometer and field emission scanning electron microscopy (FE-SEM) and the results were compared. FE-SEM micrographs show, higher growth of nanosheets on the cathode electrode in presence of ultrasonic irradiation. Experiment shows synthesis of ZnO nanoparticles in presence of the ultrasonic irradiation happen 10 times faster.     

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 1 mM 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. 0.1 mM 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.