Enhanced sonochemical degradation of bisphenol-A by bicarbonate ions

Sonochemical elimination of organic pollutants can take place through two degradation pathways. Molecules with relatively large Henry’s law constants will be incinerated inside the cavitation bubble, while nonvolatile molecules with low Henry’s law constants will be oxidised by the OH ejected from the bubble of cavitation. Taking bisphenol-A as a model pollutant, this study points out an alternate degradation route, mediated by bicarbonate ions, which is significant for the elimination of micro-pollutants at concentrations present in natural waters. In this process, OH radicals react with bicarbonate ions to produce the carbonate radical, which, unlike the OH radical, can migrate towards the bulk of the solution and therefore induce the degradation of the micro-pollutants present in the bulk solution. As a consequence, initial degradation rate is increased by a factor 3.2 at low concentration of bisphenol-A (0.022 μmol l⁻¹) in presence of bicarbonate in water.     

Effectiveness of ultrasound for the destruction of Mycobacterium sp. strain (6PY1)

Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical and chemical effects on microorganisms. The aim of this study was to investigate the effect of ultrasound on the destruction of Mycobacterium strain 6PY1. Ultrasound waves (20 kHz or 612 kHz) were used to treat aqueous suspensions of Mycobacterium at different volumes, initial bacterial concentrations, and power densities. At the same power density and the same exposure time, sonication at high frequency resulted in a lower destruction of Mycobacterium sp. 6PY1 (35.5%) than sonication at low frequency (93%). The percentage of removal was not significantly affected by the volume of the irradiated suspension (150–300 ml) or the initial cell concentration (2.15 × 10⁻³–1.4 × 10⁻² mg protein L⁻¹). At low frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density, with a constant level reached after a certain power density. At high frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density. The mechanism of cell killing was investigated by examining the effects of OH radical scavengers such as sodium carbonate. At high frequency the presence of sodium carbonate suppressed the removal process. However, at low frequency the removal process was not affected, thus indicating that OH radicals have a negligible role in this case. The latter result was supported by ten time’s H₂O₂ production at high frequency greater than that at low frequency.     

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.     

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.     

Peculiarities of electron field emission from ZnO nanocrystals and nanostructured films

ZnO microcrystals and nanocrystals were grown on silicon substrates by condensation from vapour phase. Nanostructured ZnO films were deposited by plasma enhanced metal organic chemical vapour deposition (PEMOCVD). The parameters of field emission, namely form-factor β and work function , were calculated for ZnO structures by the help of the Fowler–Nordheim equation. The work functions from ZnO nanostructured films were evaluated by a comparison method. The density of emission current from ZnO nanostructures reaches 0.6 mA/cm² at electric force F=2.110⁵ V/cm. During repeatable measurements β changes from 5.810⁴ to 2.310⁶ cm⁻¹, indicating improvement of field emission. Obtained values of work functions were 3.7±0.37 eV and 2.9–3.2 eV for ZnO nanostructures and ZnO films respectively.     

Chemiluminescence from NaClO-H2O2 and enhanced by l-cysteine capped Mn-doped ZnS quantum-dots

Water-soluble l-cysteine capped Mn-doped ZnS@Si quantum-dots (QDs), a kind of sensitizer, were synthesized. It was found that this sensitizer could enhance chemiluminescence (CL) signals emitted from interaction of NaClO with H₂O₂ in basic medium. The CL mechanism was studied experimentally by singlet oxygen (¹O₂) quenching method, UV-vis spectra, X-ray photoelectron spectra, transmission electron microscopy studies and ESR spin-trapping spectra. The results demonstrated that the CL enhancement of NaClO-H₂O₂ originate from the catalysis of the sensitizer, which catalyzed the decomposition of H₂O₂, producing reactive intermediates hydroxyl radical (OH) and superoxide anion (O₂⁻). Then the resulting OH reacted with O₂⁻ to form ¹O₂ and oxygen excimer species (¹O₂)₂^?, which rapidly returned to its ground state by passing its energy to the sensitizer through an electron-transfer process. Finally, the sensitizer being in excited state, returned to the ground state through enhanced CL-emission.     

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.     

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.     

A comparative study of coordination between host polymers and Li ions in UV-cured gel polymer electrolytes

Crosslinked gel polymer electrolytes are prepared via free radical photo-polymerization of 1,6-hexanediol diacrylate (HDDA) or tri(ethylene glycol) diacrylate (TEGDA) with 1 M LiClO₄ dissolved in a solvent mixture of ethylene carbonate (EC) and propylene carbonate (PC). TEGDA-based gel polymer electrolytes containing a polar moiety of ethylene oxide exhibit relatively high ionic conductivities over a temperature range from − 15 to 65 °C in comparison to those based on HDDA. The coordination structure between polar moieties of a polymer backbone and Li⁺ ions is examined using a Fourier transform infrared (FT-IR) spectroscopy. The results of FT-IR analyses manifest that the CO and COC groups of TEGDA-based polymer matrix form the complex with Li⁺ ions.     

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.     

Studies of the spin-Hamiltonian parameters, d–d transitions and defect structures for two tetragonal Cu centers in Ba2ZnF6:Cu crystal

Two theoretical methods, the perturbation theory method (PTM) and the complete diagonalization (of energy matrix) method (CDM), are applied to calculate the spin-Hamiltonian parameters (g-factors g, g and hyperfine structure constants A, A, obtained from electron paramagnetic resonance (EPR) spectra) and d–d transitions (obtained from optical spectra) for two tetragonal Cu²⁺ centers in Ba₂ZnF₆:Cu²⁺ crystals. The Cu²⁺(I) ion replaces the Zn²⁺ ion at tetragonally compressed octahedral coordination and has the ground state ²A₁(|d_z²), whereas the Cu²⁺(II) ion is at an interstitial site with a square-planar F⁻coordination and has the ground state ²B₂(|d_x²-y²). The calculated spin-Hamiltonian parameters and d–d transitions from the PTM and CDM coincide and are in reasonable agreement with the experimental values. This suggests that both methods are effective for the theoretical studies of EPR and optical spectral data for 3d⁹ ions in tetragonal symmetry with different ground states. The defect structures of the two Cu²⁺ centers in Ba₂ZnF₆:Cu²⁺ are also estimated.     

Luminescence spectra of Eu ions and interstitial oxygen in PbWO4 crystal

The site-selective excitation and emission spectroscopy, and luminescence decay have been investigated under a pulsed, tunable, narrowband dye laser of the ⁵D₀→⁷F₀ region in the europium ions-doped lead tungstate PbWO₄ (PWO) in single crystal. In as-grown sample, the experimental results show that there is only one ⁷F₀→⁵D₀ excitation transition indicating the only one Eu³⁺ site in PbWO₄ lattices. The sequential annealing treatments were conducted to investigate the effects of oxygen components on the microstructure environments of Eu³⁺ in the lattices. The site distribution of Eu³⁺ was changed by the annealing in air atmosphere, which could create new sites in PWO lattices. Confirmation of interstitial oxygen and interpretations of charge compensation mechanism for the observed new sites were discussed in the context of site-selective excitation and emission spectra. The main Eu³⁺ site is related to the charge compensation by the [(Eu_Pb³⁺)-V″_Pb-(Eu_Pb³⁺)] complex; the other minor new sites after annealing are originated from [(Eu_Pb³⁺)-O″_i-(Eu_Pb³⁺)] defects. Emission spectra excited by 355-laser and RT-Raman spectra were also measured.     

Surface reactions of 2-iodopropane on GaAs(1 0 0)

The surface reactions of 2-iodopropane ((CH₃)₂CHI) on gallium-rich GaAs(1 0 0)-(4 × 1), was studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). CH₃CHICH₃ adsorbs molecularly at 120 K but dissociates below room temperature to form chemisorbed 2-propyl ((CH₃)₂CH) and iodide (I) species. Thermal activation causes desorption of the molecular species at 240 K, and this occurs in competition with the further reactions of the (CH₃)₂CH and I chemisorbed species. Self-coupling of the (CH₃)₂CH results in the formation of 2,3-dimethylbutane ((CH₃)₂CH-CH(CH₃)₂) at 290 K. β-Hydride elimination in (CH₃)₂CH yields gaseous propene (CH₃CHCH₂) at 550 K while reductive elimination reactions of (CH₃)₂CH with surface hydrogen yields propane (CH₃CH₂CH₃) at 560 K. Recombinative desorption of the adsorbed hydrogen as H₂ also occurs at 560 K. We observe that the activation barrier to carbon-carbon bond formation with 2-propyls on GaAs(1 0 0) is much lower than that in our previous investigations involving ethyl and 1,1,1-trifluoroethyl species where the β-elimination process was more facile. The difference in the surface chemistry in the case of 2-propyl species is attributable to its rigid structure resulting from the bonding to the surface via the second carbon atom, which causes the methyl groups to be further away from the surface than in the case of linear ethyl and 1,1,1-trifluoroethyl species. The β-hydride and reductive elimination processes in the adsorbed 2-propyl species thus occurs at higher temperatures, and a consequence of this is that GaI desorption, which is expected to occur in the temperature range 550-560 K becomes suppressed, and the chemisorbed iodine leaves the surface as atomic iodine.     

On the efficiency of water soluble antioxidants

The wide use of high intensity ultrasound (HIU) in modern medicine raises the question of bio-safety. It has been shown that the effect of HIU in biological media may have similarity to the effects of ionizing radiation. Exposure of biological media to HIU field may lead to cavitation phenomenon followed by formation of free radicals such as hydroxyl radical (OH) and the super-oxide ion (O₂-). These are highly reactive species that may cause harmful effects and induce oxidative stress. In the present study we employed electron spin resonance (ESR) spectroscopy together with spin traps to quantify the dynamics of hydroxyl radical formation during exposure to HIU field in the presence of different amounts of six antioxidants. Thus, the efficiency of water-soluble antioxidants, namely Allicin, Melatonin, Deoxyribose, Trolox, Nuphlutine and Hermidin, to suppress accumulation of OH radicals was examined. The results show that among the six, Trolox and Allicin reduce hydroxyl concentration with the highest efficiency.     

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.     

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.     

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.     

Diffusive EPR line width behaviour in two-dimensional Cu(Hippurate)2 4H2O single crystal

X-band EPR measurements were performed at room temperature on layered Cu(Hippurate)₂4H₂O single crystals. Despite the dimeric molecular structure the EPR spectra are characteristic for individual Cu-complexes with square-pyramidal structure and g-factors: g_x=2.045, g_y=2.085 and g_z=2.346. The anticipated zero-field splitting from dimers with S=1 is averaged out by interdimer exchange coupling within the layers. The dimers in adjacent layers are not exchange coupled as we determined from the two-component EPR spectra. Thus, the crystal is an ideal 2D magnetic system and shows a strong spin diffusion effect in the EPR line width. The spin diffusion contribution to the line width is described as P(3cos²Θ−1)² with which is much higher compared to other 2D copper(II) crystals. The background line width is due to dipolar coupling and non-resolved hyperfine structure. Exchange coupling was determined from the exchange narrowing effect as of about 0.1 cm⁻¹.     

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).