OH Radical Yield Research Articles

Increase of OH radical yields due to the decomposition of hydrogen peroxide by gold nanoparticles under X-ray irradiation.

We elucidate the decomposition mechanism of hydrogen peroxide, which is formed by water radiolysis, by gold nanoparticles (GNPs) under X-ray irradiation. The variations in yields of hydrogen peroxide generated in the presence of GNPs are evaluated using the Ghormley technique. The increase of yields of OH radicals has been quantified using Ampliflu® Red solutions. Almost all hydrogen peroxide generated by irradiation of <25 Gy is decomposed by GNPs, while the yield of OH radicals increases by 1.6 times. The amount of OH radicals thus obtained is almost equivalent to that of the decomposed hydrogen peroxide. The decomposition of hydrogen peroxide is an essential reaction to produce additional OH radicals efficiently in the vicinity of GNPs.

Estimation of vanadium removal from calcification roasting-acid leaching tailings using ultrasonic-H2C2O4 synergistic technology

Metal vanadium smelting produces roasting-acid leaching tailings containing approximately 1% vanadium residue, making it challenging to store and recycle these waste tailings in an environmentally friendly manner. To address this issue, a clean method called ultrasonic-enhanced oxalic acid complexation was proposed in this study for efficient removal of residual vanadium. Under the optimal conditions, the removal rate of vanadium and the decomposition rate of oxalic acid reached 86.88% and 23.6%. An in-depth analysis on the experimental results in combination with thermodynamics found a virtuous cycle chain induced by ultrasonic cavitation. Ultrasonic waves facilitated the decomposition of oxalic acid, producing more CO2 to supplement the limited cavitation bubble nucleuses. Consequently, the cavitation effect was strengthened, leading to an increased yield of OH radicals. This resulted in a continuous improvement in the oxidation environment. Furthermore, the enhanced virtuous cycle generated by ultrasonic cavitation produced powerful microjets that facilitated the stripping and dispersion of mineral particles. Overall, the oxalic acid-ultrasonic leaching technique offers a clean and efficient technology for separating vanadium.

Atmospheric photooxidation and ozonolysis of sabinene: reaction rate coefficients, product yields, and chemical budget of radicals

Abstract. The oxidation of sabinene by the hydroxyl radical (OH) and ozone (O3) was investigated under atmospherically relevant conditions in the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric Photochemistry In a Large Reaction Chamber) at Forschungszentrum Jülich, Germany. The rate coefficients of the reactions of sabinene with OH and with O3 were determined. The temperature dependence between 284 to 340 K of the rate coefficient of the reaction of sabinene with OH, kSAB+OH, was measured for the first time using an OH reactivity instrument, resulting in an Arrhenius expression of (1.67 ± 0.16) × 10−11 × exp((575 ± 30)/T) cm3 s−1. The values agree with those determined in chamber experiments in this work and reported in the literature for ∼ 298 K within the uncertainties of measurements. The ozonolysis reaction rate coefficient of sabinene (kSAB+O3) determined in chamber experiments at a temperature of (278 ± 2) K is (3.4 ± 0.8) × 10−17 cm3 s−1, which is 58 % lower than the value reported in the literature for room temperature. The measurement of products from the oxidation of sabinene by OH resulted in an acetone yield of (21 ± 15) %, a formaldehyde yield of (46 ± 25) %, and a sabinaketone yield of (18 ± 16) %. All yields determined in the chamber experiments agree well with values from previous laboratory studies within their uncertainties. In addition, the formaldehyde yield determined in this study is consistent with that predicted by the sabinene OH-oxidation mechanism which was devised from quantum chemical calculations by Wang and Wang (2018), whereas the acetone yield is about 15 % higher than that predicted by the mechanism. In the ozonolysis experiments, the analysis of product measurements results in an acetone yield of (5 ± 2) %, a formaldehyde yield of (48 ± 15) %, a sabinaketone yield of (31 ± 15) %, and an OH radical yield of (26 ± 29) %. The OH radical yield is lower than expected from the theoretical mechanism in Wang and Wang (2017), but the value still agrees within the uncertainty. An analysis of the chemical budget of OH radicals was performed for the chamber experiments. The analysis reveals that the destruction rate of the OH radical matches the production rate of OH, suggesting that there is no significant missing OH source for example from isomerization reactions of peroxy radicals for the experimental conditions in this work.

Effective reinforcement ozone oxidation degradation of N,N-dimethylformamide with cobalt doping micro electrolysis composite

Here we report a novel cobalt doping iron carbon micro electrolysis composite Fe-Co-AC (FCA) that exhibits excellent catalytic performance for the remove of N,N-Dimethylformamide (DMF). The catalytic effects of FCA micro electrolysis (ME), only ozone oxidation (O3), and micro electrolysis synergetic ozonation (ME-O3) on the degradation of DMF were carried out. The results proved that the ME-O3 could obtain high •OH radical yield, showing eminent catalytic efficiency. This is attributed that Co doping optimizes the electron transport path in the material, improves the micro electrolysis synergetic catalytic ozonation performance. Additionally, the relative contribution of reactive oxygen species (ROS) and related reactions were qualitatively evaluated, and the reaction mechanism of ROS generation and pollutant removal was explored. According to the conversion of organic nitrogen and the detection of intermediate, the possible degradation paths of DMF were speculated. The column experiments showed that the ME-O3 process has a certain potential in practical application.

Highly-visible-light-driven photocatalysts based on terbium(III) complexes with tetraselenidoantimonate and polyamine mixed ligands

Terbium(III) complexes with anionic selenidoantimonate ligand, [H2tepa][{Tb(tepa)(SbSe4)}2(μ-OH)2] (1) (tepa = tetraethylenepentamine), and [Tb(peha)(SbSe4)]2 (2) (peha = pentaethylenehexamine), were prepared by solvothermal methods in tepa and peha solvents, respectively. The tetrahedral [SbSe4]3− anion coordinated to the Tb3+ ion with a monodentate coordination mode in compound 1, and a bidentate chelating mode in compound 2. Under Xe light irradiation, complexes 1 and 2 exhibited effective photocurrent response with steady current densities of 21.03, and 10.77 μA/cm2, respectively. 1 and 2 were photocatalytically active in the degradation of the organic dye methylene blue in aqueous solution at room temperature. Compound 1 exhibited higher photocatalytic activity than 2 in the degradation due to its stronger photocurrent intensities. The ∙OH radicals and h+ holes were the major reactive substances in the degradation. The in-built redox cycle of Tb(III)/Tb(IV) pair could effectively prompt the h+ hole and ∙OH radical yield, and photocatalytic activities were enhanced.

Degradation of carbamazepine by high-voltage direct current gas-liquid plasma with the addition of H2O2 and Fe2.

Carbamazepine (CBZ) is a typical psychotropic pharmaceutical which is one of the most commonly detected persistent pharmaceuticals in the environment. The degradation of CBZ in the aqueous solution was studied by a direct current (DC) gas-liquid phase discharge plasma combined with different catalysts (H2O2 or Fe2+) in this study. The concentrations of reactive species (H2O2, O3, and NO3-) and •OH radical yield in the liquid were measured during the discharge process. The various parameters that affect the degradation of CBZ, such as discharge powers, initial concentrations, initial pH values, and addition of catalysts, were investigated. The energy efficiency was 25.2mg·kW-1·h-1 at 35.7W, and the discharge power at 35.7W was selected to achieve the optimal balance on the degradation effect and energy efficiency. Both acidic and alkaline solution conditions were conducive to promoting the degradation of CBZ. Both H2O2 and Fe2+ at low concentration (10-100mg/L of Fe2+, 0.05-2.0mmol/L of H2O2) were observed contributing to the improvement of the CBZ degradation rate, while the promotional effect of CBZ degradation was weakened even inhibition would occur at high concentrations (100-200mg/L of Fe2+, 2.0-5.0mmol/L of H2O2). The degradation rate of CBZ was up to 99.1%, and the total organic carbon (TOC) removal efficiency of CBZ was up to 67.1% in the plasma/Fe2+ (100mg/L) system at 48min, which suggested that high degradation rate and mineralization efficiency on CBZ could be achieved by employing Fe2+ as a catalyst. Based on the intermediate products identified by Ultra Performance Liquid Chromatography Tandem Mass Spectrometry (UPLC-MS), the possible degradation pathways were proposed. Finally, the growth inhibition assay with Escherichia coli (E. coli) showed that the toxicity of plasma/Fe2+-treated CBZ solution decreased and a relatively low solution toxicity could be achieved. Thus, the plasma/catalyst could be an effective technology for the degradation of pharmaceuticals in aqueous solutions.

CH2 + O2: reaction mechanism, biradical and zwitterionic character, and formation of CH2OO, the simplest Criegee intermediate.

The singlet and triplet potential surfaces for the title reaction were investigated using the CBS-QB3 level of theory. The wave functions for some species exhibited multireference character and required the CASPT2/6-31+G(d,p) and CASPT2/aug-cc-pVTZ levels of theory to obtain accurate relative energies. A Natural Bond Orbital Analysis showed that triplet 3CH2OO (the simplest Criegee intermediate) and 3CH2O2 (dioxirane) have mostly polar biradical character, while singlet 1CH2OO has some zwitterionic character and a planar structure. Canonical variational transition state theory (CVTST) and master equation simulations were used to analyze the reaction system. CVTST predicts that the rate constant for reaction of 1CH2 + 3O2 is more than ten times as fast as the reaction of 3CH2 (X3B1) + 3O2 and the ratio remains almost independent of temperature from 900 K to 3000 K. The master equation simulations predict that at low pressures the 1CH2O + 3O product set is dominant at all temperatures and the primary yield of OH radicals is negligible below 600 K, due to competition with other primary reactions in this complex system.

Insight into the impact of excluding mass transport, heat exchange and chemical reactions heat on the sonochemical bubble yield: Bubble size-dependency

Numerical simulations have been performed on a range of ambient bubble radii, in order to reveal the effect of mass transport, heat exchange and chemical reactions heat on the chemical bubble yield of single acoustic bubble. The results of each of these energy mechanisms were compared to the normal model in which all these processes (mass transport, thermal conduction, and reactions heat) are taken into account. This theoretical work was carried out for various frequencies (f: 200, 355, 515 and 1000 kHz) and different acoustic amplitudes (PA: 1.5, 2 and 3 atm). The effect of thermal conduction was found to be of a great importance within the bubble internal energy balance, where the higher rates of production (for all acoustic amplitudes and wave frequencies) are observed for this model (without heat exchange). Similarly, the ignorance of the chemical reactions heat (model without reactions heat) shows the weight of this process into the bubble internal energy, where the yield of the main species (OH, H, O and H2) for this model was accelerated notably compared to the complete model for the acoustic amplitudes greater than 1.5 atm (for f = 500 kHz). However, the lowest production rates were registered for the model without mass transport compared to the normal model, for the acoustic amplitudes greater than 1.5 atm (f = 500 kHz). This is observed even when the temperature inside bubble for this model is greater than those retrieved for the other models. On the other hand, it has been shown that, at the acoustic amplitude of 1.5 atm, the maximal production rates of the main species (OH, H, O and H2) for all the adopted models appear at the same optimum ambient-bubble size (R0 ~ 3, 2.5 and 2 µm for, respectively, 355, 500 and 1000 kHz). For PA = 2 and 3 atm (f = 500 kHz), the range of the maximal yield of OH radicals is observed at the range of R0 where the production of OH, O and H2 is the lowest, which corresponds to the bubble temperature at around 5500 K. The maximal production rate of H, O and H2 is shifted toward the range of ambient bubble radii corresponding to the bubble temperatures greater than 5500 K. The ambient bubble radius of the maximal response (maximal production rate) is shifted toward the smaller bubble sizes when the acoustic amplitude (wave frequency is fixed) or the ultrasound frequency (acoustic power is fixed) is increased. In addition, it is observed that the increase of wave frequency or the acoustic amplitude decrease cause the range of active bubbles to be narrowed (scenario observation for the four investigated models).

The oxidation mechanism of gas-phase ozonolysis of limonene in the atmosphere.

Limonene with endo- and exo-double bonds is a significant monoterpene in the atmosphere and has high reactivity towards O3. We investigated the atmospheric oxidation mechanism of limonene ozonolysis using a high level quantum chemistry calculation coupled with RRKM-ME kinetic simulation. The additions of O3 can take place at both the endo- and exo-double bonds with a branching ratio of 0.87 : 0.13, forming four major highly energized CIs* (named Syn-2a*, Syn-2b*, Anti-2b* and Anti-2c*) with the relative higher fractions of 0.21 : 0.35 : 0.27 : 0.11. A yield of 4% for Limona-ketone was obtained as well. For the unimolecular isomerization pathways of limonene + O3 → POZs → CIs* → SOZ, VHP, or dioxirane, five, one, or none of the internal rotations are treated as hindered internal rotors for CIs*. We obtained percentages of 0.59 : 0.18 : 0.14 in total for separate isomerization routes in the formation of VHPs, dioxirane and SOZs from CIs* using the fourth-order Runge-Kutta method. Additionally, a yield of ∼5% was acquired for stabilized CIs compiling the fractions of different addition routes. About ∼10% of stabilized Anti-2b would isomerize to VHP and 90% would isomerize to SOZs. Isomerization to VHPs dominates the fate of stabilized Syn-2a, Syn-2b and Anti-2c. The overall yield of OH radicals was 0.61. Our study suggested a yield of 0.17 for stabilized SOZs and 0.18 for dioxirane, although both their fates are ambiguous.

Quantification of hydroxyl radicals in photocatalysis and acoustic cavitation: Utility of coumarin as a chemical probe

• Probe based total OH quantification is unlikely but frequently reported. • Uncertainty of total OH make it an unsuitable performance indicator. • Fate of OH was deconstructed to identify a suitable performance indicator. • OH utilised by the probe [P] is a suitable process specific performance indicator. • Performance of acoustic cavitation and photocatalysis was compared based on [P]. In-situ hydroxyl radical production is a characteristic of advanced oxidation processes (AOPs) and its quantification is crucial for assessing the performance of these processes. Direct OH quantification is however unlikely due to their high reactivity and short life-time (~10 −6 s). Therefore, chemical probes (like coumarin) are often used to indirectly quantify OH radicals. The resulting hydroxylated products of these probe molecules are relatively stable and detectable (like 7-hydroxycoumarin; 7OHC); their concentration is usually related to the OH radical concentration. Reported literature suggests the use of a constant fraction (6.1%) as the yield of 7OHC from total OH radicals generated (δ). This was originally determined from γ-irradiation studies of coumarin and translated across to other AOPs. It is however highly unlikely that this fraction is same across other AOPs. To address this gap and as a means of comparing AOPs, in the present work, we used coumarin as a probe to quantify 7OHC during acoustic cavitation (AC) and photocatalysis (PC) and determined the OH radical yields. Since δ cannot be determined directly, an alternative and simple means of comparison based on the amount of OH radicals utilised for desired reactions i.e., hydroxylation was exploited. Based on the proposed means of comparison, it was determined that OH radicals utilised by the probe was higher for PC than AC by ~ 25 times under the considered process operating conditions. The presented results will be useful for researchers and engineers interested in quantifying hydroxyl radicals and optimising AOPs.

Physical and chemical characterization of shock-induced cavitation

A strong impact on a water surface induces a shock wave propagation with a significant pressure variation leading to cavitation bubble formation. A new shock induced cavitation reactor described in this work was characterized by physical and chemical techniques. Water hammer model verification with Joukowsky approach allowed to determine the wave speed propagation and gas fraction in water submitted to shock. These values were used for frequency analysis and compared with direct bubble visualization in order to estimate the influence of the experimental parameters on the shock-induced cavitation. Thereby, the shock wave contains a broad spectrum as decomposed into frequencies. This multi-frequency nature induces heterogeneous bubbles with calculated radii of 0.01 to 3.5 mm and observed radii of 0.01 to 2.8 mm depending on experimental conditions (initial pressure, impact height, gas atmosphere). For the first time, the formation of hydroxyl radicals was proven under impact-induced cavitation. The concentration of radicals increases with increasing number of successive impacts, reaching ca. 1.3 µmol.L−1 after 500 impacts in the presence of 20% O2-Ar as saturating gas. Radical generation seems to be relatively independent of the impact height but strongly depend on the type of gas saturating water, being substantially lower in the presence of air. Moreover, radical generation increases when decreasing the initial pressure and depends on the frequency at which water is impacted by the piston. Nevertheless, yield of OH radicals during shock-induced cavitation remains much lower than that produced by power ultrasound.

Water radiolysis with thermal neutrons, fast neutrons and contamination γ rays in the accelerator based thermal neutron field: Time dependence of hydroxyl radical yields

Radiation chemical yields (G value) of OH radicals created in the accelerator-based neutron field are evaluated using coumarin-3-carboxilic acid (C3CA) solution to understand the role of the indirect action induced by radiations emitted as a result of 10B(n,α)7Li reactions for boron neutron capture therapy. The G values for ionizing radiations emitted as a result of 10B(n,α)7Li reactions, the contamination (ionizing) radiations (i.e., fast neutrons and γ rays) in the accelerator-based neutron field are discriminately assessed. We have followed the recombination process of OH radicals by adjusting the concentration of C3CA solution from 0.5 to 20 mM. The G values for ionizing radiations emitted as a result of 10B(n,α)7Li reactions are the lowest ones. This finding indicates that the indirect action induced by 10B(n,α)7Li reactions is not effective to kill tissues. In comparison to this, a significant influence would be expected by the contamination (ionizing) radiations not only on cancer tissues but also on healthy tissues.

Formation Rate and Energy Yield of Hydroxyl Radicals in Water under the Action of Gas-Discharge Plasma

The kinetics of hydroxyl radical formation in water under the action of a pulsed discharge in vapor-gas bubbles formed near the surface of a graphite electrode immersed into water is studied. The reaction of potassium hexacyanoferrate(II) oxidation is used to determine the concentration and formation rate of OH radicals in the liquid phase. The power dissipated in the discharge is estimated from measurements of the time dependences of the current through the discharge cell, the voltage applied to the electrodes, and the integrated intensity of the discharge radiation. The yields of OH radicals per 100 eV of the energy applied to the plasma are calculated. It is found that, with an increase in power from 13 to 100 W, the rate of radical generation increases within the range of (2.8–34.8) × 10–7 mol/(L s). The radical yield weakly depends on power and is equal to 0.12 ± 0.03 particles/100 eV.

Pd-MnO2 nanoparticles/TiO2 nanotube arrays (NTAs) photo-electrodes photo-catalytic properties and their ability of degrading Rhodamine B under visible light

Pd-MnO2/TiO2 nanotube arrays (NTAs) photo-electrodes were successfully fabricated via anodization and electro deposition subsequently; the obtained Pd-MnO2/TiO2 NTAs photo electrodes were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and characterized accordingly. Moreover, the light harvesting and absorption properties were investigated via ultraviolet–visible diffuse reflectance spectrum (DRS); photo degradation efficiency was investigated via analyzing the photo catalytic degradation of Rhodamine B under visible illumination (xenon light). The performed analyses illustrated that Pd-MnO2 codoped particles were successfully deposited onto the surface of the TiO2 nanotube arrays; DRS results showed significant improvement in visible light absorption which was between 400 and 700nm. Finally, the photo catalytic degradation efficiency results of the designated organic pollutant (Rhodamine B) illustrated a superior photocatalytic (PC) efficiency of approximately 95% compared to the bare TiO2 NTAs, which only exhibited a photo catalytic degradation efficiency of approximately 61%, thus it indicated the significant enhancement of the light absorption properties of fabricated photo electrodes and their yield of OH radicals.

Hydroxyl radical yields in the Fenton process under various pH, ligand concentrations and hydrogen peroxide/Fe(II) ratios

The Fenton process, one of several advanced oxidation processes, describes the reaction of Fe(II) with hydrogen peroxide. Fe(II) is oxidized to Fe(III) that reacts with hydrogen peroxide to Fe(II) and again initiates the Fenton reaction. In the course of the reactions reactive species, e.g. hydroxyl radicals, are formed. Conditions such as pH, ligand concentrations and the hydrogen peroxide/Fe(II) ratio may influence the OH radical yield. It could be shown that at pH < 2.7 and >3.5 the OH radical yield decreases significantly. Two ligands were investigated, pyrophosphate and sulfate. It was found that pyrophosphate forms a complex with Fe(III) that does not react with hydrogen peroxide and thus, the Fenton reaction is terminated and the OH radical yields do not further increase. The influence of sulfate is not as strong as that of pyrophosphate. The OH radical yield is decreased when sulfate is added but even at higher concentrations the Fenton reaction is not terminated.

Modeling the effect of carbon-dioxide gas on cavitation

One of the controlling parameters of the physical and chemical effects produced by acoustic cavitation is the use of dissolved gas as it affects the temperature and pressure obtained at cavity collapse and, the reactions happening in a bubble. It also enhances the nucleation rates by decreasing the threshold required for cavitation by providing dissolved gas nuclei. The present study looks into the effect of carbon dioxide gas on cavitation using a diffusion limited model. The model couples the dynamics of a single bubble with 11 chemical reactions involving 8 reactive species. The effect of mass transport (diffusion of water vapor and radical species) and heat transport (by conduction) is included in the model. Simulations were carried out for different initial compositions of an Ar-CO2− bubble and the results were compared with an experimental study reported in the earlier literature. The results have indicated that intensity of collapse decreases with an increase in CO2 composition in the bubble thereby decreasing the yield of the oxidizing radicals like OH. This is due to the lower polytropic coefficient and higher specific heat of CO2 compared to that of argon. Also, the bubbles grows to a larger extent with an increase in the dissolved CO2 concentration thereby accommodating higher amounts of water vapor and ultimately decreasing the temperature obtained at collapse. Simulations were done for a bubble containing a mole fraction of 95% Ar and 5% CO2 at different values of driving frequencies (213, 355, 647 and 1000kHz) and driving pressure amplitudes (3.22, 5, 7.5 and 10bar). Higher production rate of OH radicals was predicted at a lower driving frequency, for a given driving pressure amplitude and it increased with an increase in the driving pressure amplitude. At a given driving pressure amplitude, the yield of OH radicals decreased with an increase in the CO2 concentration in the bubble for all the driving frequencies used in the simulations.

Ozonation of pyridine and other N-heterocyclic aromatic compounds: Kinetics, stoichiometry, identification of products and elucidation of pathways

Pyridine, pyridazine, pyrimidine and pyrazine were investigated in their reaction with ozone. These compounds are archetypes for heterocyclic aromatic amines, a structural unit that is often present in pharmaceuticals, pesticides and dyestuffs (e.g., enoxacin, pyrazineamide or pyrimethamine). The investigated target compounds react with ozone with rate constants ranging from 0.37 to 57 M−1 s−1, hampering their degradation during ozonation. In OH radical scavenged systems the reaction of ozone with pyridine and pyridazine is characterized by high transformation (per ozone consumed) of 55 and 54%, respectively. In non scavenged system the transformation drops to 52 and 12%, respectively. However, in the reaction of pyrimidine and pyrazine with ozone this is reversed. Here, in an OH radical scavenged system the compound transformation is much lower (2.1 and 14%, respectively) than in non scavenged one (22 and 25%, respectively). This is confirmed by corresponding high N-oxide formation in the ozonation of pyridine and pyridazine, but probably low formation in the reaction of pyrimidine and pyrazine with ozone. With respect to reaction mechanisms, it is suggested that ozone adduct formation at nitrogen is the primary step in the ozonation of pyridine and pyridazine. On the contrary, ozone adduct formation to the aromatic ring seems to occur especially in the ozonation of pyrimidine as inferred from hydrogen peroxide yield. However, also OH radical reactions are supposed processes in the case of pyrimidine and in particular for pyrazine, albeit negligible OH radical yields are obtained. The low compound transformation in OH radical scavenged system can prove this. As a result of negligible OH radical yields in all cases (less than 6%) electron transfer as primary reaction pathway plays a subordinate role.

Influence of dissolved gases on sonochemistry and sonoluminescence in a flow reactor

In the present work, the influence of gas addition is investigated on both sonoluminescence (SL) and radical formation at 47 and 248kHz. The frequencies chosen in this study generate two distinct bubble types, allowing to generalize the conclusions for other ultrasonic reactors. In this case, 47kHz provides transient bubbles, while stable ones dominate at 248kHz. For both bubble types, the hydroxyl radical and SL yield under gas addition followed the sequence: Ar>Air>N2>>CO2. A comprehensive interpretation is given for these results, based on a combination of thermal gas properties, chemical reactions occurring within the cavitation bubble, and the amount of bubbles. Furthermore, in the cases where argon, air and nitrogen were bubbled, a reasonable correlation existed between the OH-radical yield and the SL signal, being most pronounced under stable cavitation at 248kHz. Presuming that SL and OH originate from different bubble populations, the results indicate that both populations respond similarly to a change in acoustic power and dissolved gas. Consequently, in the presence of non-volatile pollutants that do not quench SL, sonoluminescence can be used as an online tool to qualitatively monitor radical formation.

Preparation and electrochemical property of TiO2/Nano-graphite composite anode for electro-catalytic degradation of ceftriaxone sodium

Titanium dioxide/Nano-graphite (TiO2/Nano-G) composite was synthesized by a sol-gel method and TiO2/Nano-G electrode was prepared in hot-press approach. The composite was characterized by X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR), scanning electrons microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrochemical performance of the TiO2/Nano-G anode electrode was investigated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electro-catalytic performance was evaluated by the yield of OH radicals, degradation of methyl orange and ceftriaxone sodium. The results demonstrated that TiO2 nanoparticles were dispersed on the surface and interlamination of the Nano-G uniformly, TiO2/Nano-G electrode owned higher electro-catalytic oxidation activity and stability than Nano-G electrode. Degradation rate of ceftriaxone sodium within 120min by TiO2(40)/Nano-G electrode was 97.7%. And OH radicals given by TiO2/Nano-G electrode was higher than that of Nano-G electrode and DSA (Ti/IrO2-RuO2) electrode. The excellent electro-catalytic performance could be ascribed to the admirable conductive property of the Nano-G and more production of OH offered by TiO2(40)/Nano-G electrode.

Influence of Seasonal Variation of Water Temperature and Dissolved Organic Matter on Ozone and OH Radical Reaction Kinetics During Ozonation of a Lake Water

ABSTRACTThis study used key description parameters of the ozonation process in lake water samples over a 1-year period to better understand the influence of seasonal variations in water quality such as water temperature and dissolved organic matter on ozone decomposition and OH radical formation and reaction kinetics. The parameters were the initial ozone demand (IOD), ozone decay rate constant after the IOD (ksec), ratio of OH radical exposure to the ozone exposure (RCt), and ratio of ozone consumption to the OH radial exposure multiplied by the second-order rate constant for the reaction of the OH radical with an OH radical probe compound (Ω). The seasonal variations in water quality had the most significant influence on RCt (39–64%), followed by ksec (35–38%), Ω (27–34%), and IOD (11–25%) for the raw lake water and sand-filtered water in which the numbers inside parentheses indicate the percent standard deviation of the measured values for 1 year. For the oligotrophic-type lake water, the seasonal variation in water temperature (6–26 °C) had the most significant influence on the ksec, RCt, and Ω. The Ω was newly found to be inversely related with water temperature, possibly due to the temperature-dependent OH radical yield from ozone decomposition. This implies that the OH radical oxidation capacity during ozonation can be significantly influenced by the temperature due to the varying ozone decomposition rate and the intrinsic OH radical yield. This study also demonstrated the Ω is a useful, alternative parameter to the RCt for describing or predicting OH radical exposure from ozone consumption especially when the ozone decay is rapid or varies over time such as the initial ozonation phase of natural water or wastewater where a considerable OH radical exposure takes place.