Unusual oxygen re-equilibration kinetics of TiO2−δ

Oxygen re-equilibration kinetics, along with the equilibrium conductivity, have been measured on undoped, single-crystal TiO_2−δ, by a four-probe d.c. conductivity relaxation technique, against oxygen partial pressure in the range of − 16 < log(P_O2/atm) ≤ 0 at different temperatures in the range of 1173 ≤ T/K ≤ 1373. The isothermal conductivity varies as σ ∝ P_O2^m with m ≈ − 1/4, − 1/5 and − 1/6 in turn with increasing P_O2 up to 1 atm, suggesting a sequential variation of the majority ionic disorder types from Ti_i to Ti_i to V_O, respectively. Contrary to the conventional knowledge that due to the local (defect) equilibrium postulate there should be one and only one chemical diffusivity or single relaxation time for a binary oxide, the oxygen re-equilibration kinetics has turned out to be twofold with two different relaxation times depending on oxygen activities. This is interpreted as being due to the independent relaxation of each sublattice of TiO₂ in an oxygen activity gradient applied, indicating a failure of local equilibrium during oxygen re-equilibration. From the two different relaxation times the chemical diffusion coefficients of component Ti and O are separately evaluated and subsequently, their self-diffusion coefficients. The latter are found to be in a good agreement with the literature data.     

Theoretical estimation of the temperature and pressure within collapsing acoustical bubbles

Formation of highly reactive species such as OH, H, HO₂ and H₂O₂ due to transient collapse of cavitation bubbles is the primary mechanism of sonochemical reaction. The crucial parameters influencing the formation of radicals are the temperature and pressure achieved in the bubble during the strong collapse. Experimental determinations estimated a temperature of about 5000 K and pressure of several hundreds of MPa within the collapsing bubble. In this theoretical investigation, computer simulations of chemical reactions occurring in an O₂-bubble oscillating in water irradiated by an ultrasonic wave have been performed for diverse combinations of various parameters such as ultrasound frequency (20–1000 kHz), acoustic amplitude (up to 0.3 MPa), static pressure (0.03–0.3 MPa) and liquid temperature (283–333 K). The aim of this series of computations is to correlate the production of OH radicals to the temperature and pressure achieved in the bubble during the strong collapse. The employed model combines the dynamic of bubble collapse in acoustical field with the chemical kinetics of single bubble. The results of the numerical simulations revealed that the main oxidant created in an O₂ bubble is OH radical. The computer simulations clearly showed the existence of an optimum bubble temperature of about 5200 ± 200 K and pressure of about 250 ± 20 MPa. The predicted value of the bubble temperature for the production of OH radicals is in excellent agreement with that furnished by the experiments. The existence of an optimum bubble temperature and pressure in collapsing bubbles results from the competitions between the reactions of production and those of consumption of OH radicals at high temperatures.     

Sensitivity of free radicals production in acoustically driven bubble to the ultrasonic frequency and nature of dissolved gases

Central events of ultrasonic action are the bubbles of cavitation that can be considered as powered microreactors within which high-energy chemistry occurs. This work presents the results of a comprehensive numerical assessment of frequency and saturating gases effects on single bubble sonochemistry. Computer simulations of chemical reactions occurring inside a bubble oscillating in liquid water irradiated by an ultrasonic wave have been performed for a wide range of ultrasonic frequencies (213–1100 kHz) under different saturating gases (O₂, air, N₂ and H₂). For O₂ and H₂ bubbles, 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 air and N₂ bubbles. The numerical simulations have indicated that radicals such as OH, H, HO₂ and O are created in the bubble during the strong collapse. In all cases, hydroxyl radical (OH) is the main oxidant created in the bubble. The production rate of the oxidants decreases as the driving ultrasonic frequency increases. The production rate of OH radical followed the order O₂ > air > N₂ > H₂ and the order becomes more remarkable at higher ultrasonic frequencies. The effect of ultrasonic frequency on single bubble sonochemistry was attributed to its significant impact on the cavitation process whereas the effects of gases were attributed to the nature of the chemistry produced in the bubble at the strong collapse. It was concluded that, in addition to the gas solubility, the nature of the internal bubble chemistry is another parameter of a paramount importance that controls the overall sonochemical activity in aqueous solutions.     

Determination of nitrofurans in feeds based on silver nanoparticle-catalyzed chemiluminescence

A highly sensitive chemiluminescence (CL) method for the determination of nitrofurans (NFs) was developed based on the enhancement of CL intensity of luminol–H₂O₂–NFs system by silver nanoparticles (AgNPs). It was supposed that the oxygen-related radicals of OH and superoxide radical (O₂^?) could be produced when NFs reacted with H₂O₂. Furthermore, the enhancement mechanism was originated from the reinforcer of AgNPs, which could catalyze the generation of the OH radical. Then OH radicals reacted with luminol anion and HO₂^? to form luminol radical (L^?) and O₂^?. The excited state 3-aminophthalate anion was obtained in the reaction of L^? and O₂^?, which was the emitter (luminophor) in the luminol–H₂O₂ CL reaction system and the maximal emission of the CL spectrum was at 425 nm. The experiments of scavenging oxygen-related radicals were done to confirm these reactive oxygen species participated in the CL reaction. The limits of detection (LOD) (S/N=3) were 8×10^?7 g mL^?1 for furacilin, 8×10^?8 g mL^?1 for furantoin, 4×10^?8 g mL^?1 for furazolidone and 2×10^?7 g mL^?1 for furaltadone. The proposed method was successfully applied to the determination of NFs in feeds and pharmaceutical samples.     

Nonstoichiometry of the perovskite-type solid solution La0.9Ca0.1Cr1−yAlyO3−δ

Nonstoichiometry of the perovskite-type solid solutions La_0.9Ca_0.1Cr_1−yAl_yO_3−δ was studied by high-temperature gravimetry under controlled P(O₂) atmospheres of 1–10^− 23 bar at 1073–1273 K. The observed data were described by a regular solution-like model for the randomly distributed defects of V_O¨, Cr_Cr., Ca_La,, and Al_Cr^X. With the increase in y, V_O¨ formation becomes much easier. For y > 0.8, some fraction of Ca_La, becomes surrounded only by Al_Cr^X and V_O¨ remains around such Ca_La, up to high P(O₂) to reduce the maximum oxygen content below 3.000.     

Using pulsed wave ultrasound to evaluate the suitability of hydroxyl radical scavengers in sonochemical systems

Hydroxyl radical (OH) scavengers are commonly used in sonochemistry to probe the site and nature of reaction in aqueous cavitational systems. Using pulsed wave (PW) ultrasound with comparative sonochemistry we evaluated the performance of OH scavengers (i.e., formic acid, carbonic acid, terephthalic acid/terephthalate, iodide, methanesulfonate, benzenesulfonate, and acetic acid/acetate) in a sonochemical system to determine which OH scavengers react only in bulk solution and which OH scavengers interact with cavitation bubbles. The ability of each scavenger to interact with cavitation bubbles was assessed by comparing the pulse enhancement (PE) of 10 μM of a probe compound, carbamazepine (CBZ), in the presence and absence of a scavenger. Based on PE results, acetic acid/acetate appears to scavenge OH in bulk solution, and not interact with cavitation bubbles. Methanesulfonate acts as reaction promoter, increasing rather than inhibiting the degradation of CBZ. For formic acid, carbonic acid, terephthalic acid/terephthalate, benzenesulfonate, and iodide, the PE was significantly decreased compared to in the absence of the scavenger. These scavengers not only quench OH in bulk solution but also affect the cavity interface. The robustness of acetic acid/acetate as a bulk OH scavenger was validated for pH values between 3.5 and 8.9 and acetic acid/acetate concentrations from 0.5 to 0.1 M.     

Synergistic degradation of antibiotic norfloxacin in a novel heterogeneous sonochemical Fe0/tetraphosphate Fenton-like system

In this study, synergistic degradation of antibiotic norfloxacin (NOR) was obtained in a novel sonochemical ultrasound/zero-valent iron/tetraphosphate system (US/ZVI/TPP). Compared to three common organic ligands (EDTA, EDDS, and DTPA), TPP could perform more excellently in activation of O₂ to produce reactive oxidative species (ROS) and lead to efficient Fenton-like oxidative degradation of NOR in the sonochemical in situ chemical oxidation (ISCO) system. An optimized initial condition was obtained as 10 mg/L NOR, 0.3 mM TPP, 1 g/L ZVI and initial pH 7, and the US/ZVI/TPP system would effectively degrade NOR with relative low dosage of ZVI and ligand as well as broad pH work range 3–9. It was found that three ROS (OH, O₂⁻ and H₂O₂) instead of OH only would participate in the NOR degradation, while the in situ generation of H₂O₂ during the series of Fe-TPP reactions should be more critical. Fourteen organic intermediates and four inorganic products were detected during the NOR decomposition, suggesting that two main degradation pathways would occur under OH oxidation via cleavage of the piperazine ring and defluorination of the benzene ring, respectively. Finally, an integrated reaction mechanism in the US/ZVI/TPP system was proposed including solid-liquid interfacial iron corrosion as well as bulk homogenous oxygen activation and Fenton reactions, wherein US would play mechanically and chemically promotional roles. Besides, triple-repeated treatments suggested the relative long-term re-usage of ZVI particles and low effluent dissolved iron (<0.6 mg/L).     

Intramolecular motion in the triptycenegermanyl radical: single crystal EPR study at variable temperature and DFT calculations

X-irradiation of single crystals of Tp–GeH₃ (Tp: triptycene) led to the trapping of the radical Tp–GeH₂. The angular variations of the resulting EPR spectra were recorded at 300 and 77 K. The drastic temperature dependence of the spectra was caused by both a strong anisotropy of the g-tensor and a rotation of the GeH₂ moiety around the C–Ge bond. The determination of the EPR tensors as well as the analysis of this motion required to take the presence of disorder in the crystal into account. In accordance with DFT calculations, Tp–GeH₂ is shown to be pyramidal and to adopt, in its lowest energy structure, a staggered conformation. Rotation around the C–GeH₂ bond is blocked at 90 K and is almost free above 110 K. The experimental barrier, obtained after simulation of the EPR spectra as a function of the rotational correlation time, is equal to 1.3 kcal mol⁻¹, which is slightly inferior to the barrier calculated by DFT (3.6 kcal mol⁻¹). Calculations performed on Tp–CH₃, Tp–GeH₃ and Tp–GeH₂ show that the rotation barrier ΔE_rot around the C–Ge bond drastically decreases by passing from the germane precursor to the germanyl radical and that ΔE_rot increases by passing from the germane to its carbon analogous. Structural parameters involved in these barrier differences are examined.     

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: R_ab, formed by abstraction reactions of the alcohols with sonochemically formed OH radicals or H atoms, and R_py, 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 > R_py > R_ab. 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 Mn²⁺ 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.     

Synthesis,characterization and luminescent property of metal-ion-doped terbium complexes of 2,3-Pyrazinedicarboxylate

Using 2,3-pyrazine dicarboxylate (pzdc^2?) as ligand, a series of new terbium complexes Tb₂L₂(HL)(NO₃)10 H₂O, Tb₂Mg₂L₄(HL)(NO₃)14 H₂O, Tb₂Ca₂L₄(HL)(NO₃)14 H₂O, Tb₂Sr₂L₄(HL)(NO₃)14 H₂O, Tb₂Ba₂L₄(HL)(NO₃)14 H₂O, Tb₂Cd₂L₄(HL)(NO₃)14 H₂O, Tb₂Co₂L₄(HL)(NO₃)14 H₂O, Tb₂Ni₂L₄(HL)(NO₃)14 H₂O and Tb₂Zn₂L₄(HL)(NO₃)14 H₂O (L=pzdc^2-) have been synthesized. The complexes were characterized by elemental analysis, ICP-AES, molar conductivity measurement, TG-DSC analysis, IR spectroscopy and UV absorption spectroscopy. The luminescence spectra, luminescence lifetimes and emission quantum efficiencies of the complexes were measured. The results show that doping alkaline earth metal ions have significantly increased the luminescence intensities and quantum efficiencies of the complexes, and the sequence of the quantum efficiencies of the doped complexes is Ba²⁺>Ca²⁺>Mg²⁺>Sr²⁺. The enhancement of luminescence efficiencies may result from the decrease of the concentration quenching effect of Tb³⁺ ions, intramolecular energy transfer from the ligands coordinated with doped ions to Tb³⁺ ions and the lattice distortion of the complexes. The luminescence efficiencies of the Tb³⁺ ions are also enhanced by doping Cd²⁺ and Zn²⁺ ions. However, the complexes doped with Co²⁺ or Ni²⁺ ions exhibit luminescence quenching, which is caused by the energy consumed by these two ions in the form of d-d electron transitions.     

Efficient sonochemical degradation of perfluorooctanoic acid using periodate

A rapid and efficient treatment method, using periodate (PI) for sonochemical oxidation of persistent and bioaccumulative perfluorooctanoic acid (PFOA) was developed. With an addition of 45 mM PI, 96.5% of PFOA was decomposed with a defluorination efficiency of 95.7% after 120 min of ultrasound (US). The removals of PFOA were augmented with an increase in PI doses. In all the PI + US experimental runs, decomposition efficiencies were essentially similar to those of defluorination, indicating that PFOA was decomposed and mineralized into fluoride ions. Lower solution pHs resulted in an increase in decomposition and defluorination efficiencies of PFOA due to acid-catalyzation. Dissolved oxygen increased the amount of IO₄ radicals produced, which consumed the more effective IO₃ radicals. Consequently, presence of oxygen inhibited the destruction of PFOA. The PFOA degradation rates with different gases sparging are in the following order: nitrogen > air > oxygen. Effects of anions follow the Hofmeister effects on PFOA degradation (i.e., Br⁻ > none ⩾ Cl⁻ > SO₄²⁻). Br⁻ could react with OH to yield radical anion Br₂⁻ that enhances the PFOA degradation. A reaction pathway was also proposed to describe the PI oxidation of PFOA under US irradiation.     

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.     

Sonochemical degradation of ciprofloxacin and ibuprofen in the presence of matrix organic compounds

Ciprofloxacin (CIPRO) and ibuprofen (IBU), a hydrophilic and a hydrophobic compound, respectively, were degraded by ultrasound at the frequencies of 20 and 620 kHz in aqueous solution containing matrix organic compounds. Compared to in its absence, in the presence of terephthalate (TA), a commonly used OH scavenger, CIPRO degradation was inhibited by a factor of 40–1500 depending on the frequency and initial concentration. However, the degradation rates of IBU were only reduced between 30% and 80% with TA present compared to in its absence. Similar to TA, the presence of Suwannee River Fulvic Acid (SRFA) inhibited CIPRO degradation to a greater extent than that of IBU but overall inhibition by SRFA was dramatically less than by TA. Although both TA and SRFA inhibited the degradation of CIPRO and IBU, the mechanisms of inhibition are different. TA reacts with OH in bulk solution and our evidence also indicates that it accumulates on or interacts with cavitation bubbles. On the other hand, SRFA stays in bulk solution, quenching OH and/or associating with the target compounds.     

Infrared diode laser spectroscopy of N212C18O2

The high-resolution infrared spectrum of N₂¹²C¹⁸O₂ has been observed in the ν₃ band (2314 cm^?1) region of ¹²C¹⁸O₂ with diode laser absorption spectroscopy of pulsed molecular beam. The geometry of N₂¹²C¹⁸O₂ is similar to N₂¹²C¹⁶O₂, a T-shaped structure with the nitrogen molecular axis pointing towards the carbon atom. The geometrical parameters of the T-shaped ground-state structure are determined as R_NcmC = 3.7285(5) Å and (90?Θ_NcmCO) = 6.85(3)°. The vibrational band origin of N₂¹²C¹⁸O₂ corresponding to the ν₃ mode of ¹²C¹⁸O₂ shows a shift of 0.52499(10) cm^?1 with respect to that of ¹²C¹⁸O₂.     

Mid-wave infrared liquid crystal shutter for breathalyzer applications

There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic CH stretch absorption bands in CH₃ and CH₂ functional groups in ethanol (CH₃CH₂OH) appear at a wavelength of λ = 3.42 μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ = 3.42 μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ = 3.42 μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of CH bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of CH bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.     

Production of pyrite nanoparticles using high energy planetary ball milling for sonocatalytic degradation of sulfasalazine

Sonocatalytic performance of pyrite nanoparticles was evaluated by the degradation of sulfasalazine (SSZ). Pyrite nanoparticles were produced via a high energy mechanical ball milling (MBM) in different processing time from 2 h to 6 h, in the constant milling speed of 320 rpm. X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR) analysis and Brunauer–Emmett–Teller (BET) confirmed the production of pyrite nanoparticles during 6 h of ball milling with the average size distribution of 20–80 nm. The effects of various operational parameters including pH value, catalyst amount (mg/L), SSZ concentration (mg/L), ultrasonic frequency (kHz) and reaction time on the SSZ removal efficiency were examined. The obtained results showed that the maximum removal efficiency of 97.00% was obtained at pH value of 4, catalyst dosage of 0.5 g/L, SSZ concentration of 10 mg/L and reaction time of 30 min. Experimental results demonstrated that the kinetic of the degradation process can be demonstrated using Langmuir–Hinshelwood (L-H) kinetic model. The effect of different inorganic ions such as Cl⁻, CO₃²⁻ and SO₄²⁻ was investigated on the L-H reaction rate (k_r) and adsorption (K_s) constants. Results showed that the presence of the mentioned ions significantly influenced the L-H constants. The impact of ethanol as a OH radical scavenger and some enhancers including H₂O₂ and K₂S₂O₈ was investigated on the SSZ removal efficiency. Accordingly, the presence of ethanol suppressed SSZ degradation due to the quenching of OH radicals and the addition of K₂S₂O₈ and H₂O₂ increased the SSZ removal efficiency, due to the formation of SO₄⁻ and additional OH radicals, respectively. Under the identical conditions of operating parameters, pyrite nanoparticles maintained their catalytic activity during four consecutive runs.     

Thermal activation and reaction of allyl alcohol on Ni(100)

The thermal chemistry of allyl alcohol (CH₂CHCH₂OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the OH, CC, and CO bonds produces η¹(O)-allyloxy CH₂CHCH₂O_(a), η²(C, C) allyl alcohol (C_(a)H₂C_(a)HCH₂OH), and η³(C, C, O)-alkoxide (C_(a)H₂C_(a)CH₂ O_(a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH₂CHCH₃), 1-propanol (CH₃CH₂CH₂OH), propanal (CH₃CH₂CHO), and combustion and dehydrogenation products (H₂O, H₂, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the η³(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the η²(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.     

Ultrasound (US), Ultraviolet light (UV) and combination (US + UV) assisted semiconductor catalysed degradation of organic pollutants in water: Oscillation in the concentration of hydrogen peroxide formed in situ

Application of Advanced Oxidation Processes (AOP) such as sono, photo and sonophoto catalysis in the purification of polluted water under ambient conditions involve the formation and participation of Reactive Oxygen Species (ROS) like OH, HO₂, O₂⁻, H₂O₂ etc. Among these, H₂O₂ is the most stable and is also a precursor for the reactive free radicals. Current investigations on the ZnO mediated sono, photo and sonophoto catalytic degradation of phenol pollutant in water reveal that H₂O₂ formed in situ cannot be quantitatively correlated with the degradation of the pollutant. The concentration of H₂O₂ formed does not increase corresponding to phenol degradation and reaches a plateau or varies in a wave-like fashion (oscillation) with well defined crests and troughs, indicating concurrent formation and decomposition. The concentration at which decomposition overtakes formation or formation overtakes decomposition is sensitive to the reaction conditions. Direct photolysis of H₂O₂ in the absence of catalyst or the presence of pre-equilibrated (with the adsorption of H₂O₂) catalyst in the absence of light does not lead to the oscillation. The phenomenon is more pronounced in sonocatalysis, the intensity of oscillation being in the order sonocatalysis > photocatalysis ⩾ sonophotocatalysis while the degradation of phenol follows the order sonophotocatalysis > photocatalysis > sonocatalysis > sonolysis > photolysis. In the case of sonocatalysis, the oscillation continues for some more time after discontinuing the US irradiation indicating that the reactive free radicals as well as the trapped electrons and holes which interact with H₂O₂ have longer life time (memory effect).     

Efficient sonoelectrochemical decomposition of sulfamethoxazole adopting common Pt/graphite electrodes: The mechanism and favorable pathways

In this study, efficient degradation of sulfamethoxazole (SMX) with a high synergy factor of 14.7 was demonstrated in a sonoelectrochemical (US-EC) system adopting common Pt and graphite electrodes. It was found that the US-EC system could work effectively at broad pH range of 3–9, but would achieve good performances with appropriate electrochemical conditions at 20 mA/cm² and 0.1 M Na₂SO₄. Both OH attacking and the anode oxidation would be responsible for the SMX degradation in the US-EC system, while the multiple promotional roles of US would be played homogenously and heterogeneously. US could not only effectively accelerate the decomposition of cathode-generated H₂O₂ into OH, but also lead to the enhancement in the heterogeneous reactions on the two electrodes, i.e. the cathode generation of H₂O₂ as well as the anode oxidation of SMX and H₂O/OH⁻. Besides, the US-EC system would decompose SMX molecule via similar and simple pathways, by using either Na₂SO₄ or NaCl electrolytes. It was interesting to note that the US-EC system could successfully avoid the formation of complex chlorinated byproducts that detected in the referring EC system with NaCl. This finding would make the sonoelectrochemical processes favorable in treating practical wastewaters by alleviating the environmental impact of disinfection byproducts.     

Assay of hydroxyl radicals generated by focused ultrasound

Water sonolysis leads to the formation of hydroxyl radicals (OH). Various techniques are used to detect the OH production and thus to assess the level of ultrasound-mediated cavitation generated in vitro. In this study, we used terephthalic acid (TA) as an OH trap. This method is based on the fluorescent properties of hydroxyterephthalic acid (HTA) formed by the reaction of TA with OH and used as an indicator of the degree of inertial cavitation caused.The experimental system is comprised mainly of a focused piezoelectric ultrasound transmitter and a measurement cell containing 1X PBS/TA diluted solution. In the first part, we aimed to characterize the most appropriate experimental conditions (TA dosimeter solution, irradiation time) in order to optimize the resulting HTA fluorescence values. Then, we could determine that the HTA production increased with the level of the cavitation phenomenon caused by the acoustic power from which OH production may be estimated.