Contribution Of Hydroxyl Radicals Research Articles

Oxidation of selected fluoroquinolones by ferrate(VI) in water: Kinetics, mechanism, effects of constituents, and reaction pathways

In this work, the oxidation of gatifloxacin (GAT), fleroxacin (FLE) and enoxacin (ENO) in aqueous solution by ferrate (Fe(VI)) was systemically investigated. Weak alkaline and high oxidant doses were favorable for the reaction. The pseudosecond-order rate constants were 0.18055, 0.29162, and 0.05476 L/(mg·min), and the activation energies were 25.13, 15.25, and 11.30 kJ/mol at pH = 8.00 and n(Fe(VI)):n(GAT) = 30:1, n(Fe(VI)):n(FLE) = 20:1, n(Fe(VI)):n(ENO) = 40:1 and a temperature of 25 °C. The maximum degradation rates of the GAT, FLE and ENO were 96.72%, 98.48% and 94.12%, respectively, well simulated by Response Surface Methodology. During the oxidation, the contribution of hydroxyl radicals (HO•) varied with time, whereas the final contribution was approximately 20% at 30 min. The removal efficiency was inhibited by anions by less than 10%, and cations by less than 25%, and significantly inhibited by high concentrations of humic acid. Moreover, two or three dominant reaction pathways were predicted, and the ring cleavages of quinolone and piperazine were mainly achieved through decarboxylation, demethlation and hydroxylation, and some pathways ended up with monocyclic chemicals, which were harmless to aquatic animals and plants. Theoretical calculations further proved that the reactions between FeO4− and neutral fluoroquinolone antibiotics were the major reactions. This work illustrates that Fe(VI) can efficiently remove fluoroquinolone antibiotics (FQs) in aqueous environments, and the results may contribute to the treatment of wastewater containing trace antibiotics and Fe(VI) chemistry.

Facile solvothermal synthesis of Exfoliated-Corrugated g-C3N4@BiOBr heterojunction for fast visible light Photocatalyst: A structural and optical study

A novel and versatile strategy to increase the photoreactivity (PR) of catalytic systems is to modulate the coupling between two dimensional (2D) semiconductors. Herein, a 2D heterojunction of graphitic carbon nitride (g-C3N4) and bismuth oxobromide (BiOBr), g-C3N4@BiOBr, was carefully synthesized by a solvothermal method at different molar ratios. The optical, morphological, structural, and electronic properties were characterized for the heterojunction and compared with pure 2D BiOBr and g-C3N4. The photocatalytic degradation kinetics of rhodamine B showed that the molar composition (1:2) of g-C3N4@BiOBr produces the largest activity under visible light. Radical scavenger studies showed that the (1:2) heterojunction in an oxygen-saturated environment induces superoxide and hole radicals that actively participate in the photodegradation, while the contribution of hydroxyl radicals is negligible. The optimized PR derives from the perfect coupling between (001) crystalline planes of BiOBr with (002) planes of g-C3N4as evidenced by HRTEM and XRD.To prove the photocatalytic efficiency, tests were carried out on the degradation of different dyes, their reuse cycles, and the degradation capacity of emerging contaminants, particularly for the antibiotic sulfadiazine, obtaining excellent promising results for the development of future commercial applications for the treatment of wastewater.

Efficiency and mechanism of the degradation of ciprofloxacin by the oxidation of peroxymonosulfate under the catalysis of a Fe3O4/N co-doped sludge biochar

A novel and recyclable composite material, Fe3O4/N co-doped sludge biochar (FNBC), was developed from original sludge biochar (BC) and found to have excellent stability and superior catalytic capacity during the ciprofloxacin (CIP) degradation under the action of peroxymonosulfate (PMS). In the FNBC/PMS system, an approximately complete removal of CIP was achieved within 60 min under the condition of 1.0 g/L FNBC, 3.0 mM PMS, and 20 mg/L CIP, which was about 2.08 times of that in BC/PMS system (48.01%). Besides, FNBC/PMS system could effectively remove CIP under the influence of wide pH (2.0–10.0) or inorganic ions compared with BC/PMS system. Moreover, it was found that there were radical produced under the effect of Fe element, defects, functional groups, pyridinic N and pyrrolic N and non-radical caused by graphitic N, carbon atoms next to the iron atoms and better adsorption capacity in the FNBC/PMS system. It was observed that the contribution of hydroxyl radical (•OH), sulfate radical (SO4•−) and singlet oxygen (1O2), which were the main reactive oxygen species, during the CIP degradation, were 75.80%, 11.49% and 10.26%, respectively. Furthermore, total organic carbon (TOC) variation was analyzed and the degradation pathway of CIP was speculated. The application of this material could combine the recycling of sludge with the effective degradation of refractory organic pollutant, providing an environmentally friendly and economic method.

Degradation of antiviral drug acyclovir by thermal activated persulfate process: Kinetics study and modeling

Pharmaceutical and personal care products (PPCPs) pose a great threat to water environment security. In this study, acyclovir (ACV) was efficiently degraded by thermally activated persulfate (TAP) system. The ACV degradation increased with rising reaction temperature and persulfate dosage. With the existence of inorganic anions and humic acid, ACV removal was retarded to varying degrees. Under strong alkaline condition, it was observed that the degradation of ACV was significantly inhibited. In addition, Kintecus software was employed to simulate ACV removal and achieved a good fit with the experimental results. The contribution rates of main reactive radicals under acidic, neutral, and alkaline conditions were investigated, and the contribution of hydroxyl radical (⋅OH) increased significantly under alkaline condition. The main active species were identified as sulfate radical (SO4⋅-) and ⋅OH through quenching experiment, and the second-order reaction rate constants of SO4⋅- and ∙OH reacted with ACV were calculated to be 9.17 × 109 M−1 s−1 and 2.74 × 109 M−1 s−1, respectively. The main degradation pathways included addition of free radicals, oxidation of branch chain and ring opening. The acute and chronic toxicity of intermediates to organisms predicted by ECOSAR were significantly reduced compared with that of ACV.

Performance and mechanism of the pyrite-kerogen complexes oxidation with H2O2 at low temperature during shale stimulation: An experimental and modeling study

Pyrite and organic matter (OM) paly important role during rock chemical weathering and shale gas exploitation, the oxidation of which by O2 is widely recognized. But the performance and mechanism of pyrite and kerogen oxidizing with H2O2 during shale gas production are not well understood, and the impact of carbonates and clays on the oxidation process is still not known. In this study, the performance of the gas bearing carbonate-rich shale oxidation with 15 wt% H2O2 at low temperature was firstly explored. The total oxidation-dissolution capacity of the studied shale with H2O2 at room temperature was less than 5%, which is significantly poorer than shale richness in silicates. To unravel the underlying mechanisms leading to the divergent oxidation dissolution of shale with different compositions, pyrite-kerogen complexes were isolated from shale and batch experiments between individual key components including pyrite/kerogen/carbonates/clays and H2O2 were performed. On the basis of mechanistic understanding, kinetic models of the pure components reaction with H2O2 were also developed. Results show that pyrite is preferentially oxidized by H2O2 when compared to kerogen, and possesses a reaction rate 1–3 orders of magnitude larger than kerogen at different pyrite/kerogen mass ratio. Pyrite can induce the Fenton-like reactions to promote kerogen oxidation. The contribution of hydroxyl radicals on the oxidation of kerogen was about 22% for pyrite-kerogen complex with a pyrite/kerogen mass ratio of 1.65. Existence of calcite can buffer the solution pH to a circumneutral condition and induce the precipitation of Fe(III)-(oxy)hydroxides and anhydrite on the surface of the pyrite-kerogen complexes, thus to limit the generation of hydroxyl radicals and encapsulate the pyrite-kerogen complex, so as to inhibit the oxidation of these reduced components. This finding presents new insight into the mechanisms of H2O2-based oxidation stimulation of shale and provides guidance for the optimization of fracturing recipe.

Removal of gaseous toluene by nonthermal plasma coupled with wet scrubber containing Fe2+

A non-thermal plasma with a wet scrubber (NTP + WS) was used to degrade gaseous toluene. Compared with the NTP + WS/H2O system, the toluene and by-product ozone removal efficiencies were increased by 10% and 85% in the NTP + WS/Fe2+ system, respectively. For 60 ppm toluene degradation, the maximum mineralization rate (MR) of toluene (61%) was obtained, at the optimum Fe2+ concentration of 50 mg/L. During catalytic oxidation, the removal efficiency of toluene was limited by its solubility in WS systems. In addition, decreased Fe2+ concentration and accumulation of organics led to the system deactivation. The EPR and quenching experiments verified the presence and contribution of hydroxyl radicals (4.6%) and superoxide radicals (3.8%) to the removal efficiency of toluene. Based on the radicals and intermediates detected in the gas and liquid phases, a degradation mechanism for toluene in the NTP + WS/Fe2+ system was proposed.

Establishment of a Method for Investigating Direct and Indirect Actions of Ionizing Radiation Using Scavenger-free Plasmid DNA.

In this study, an improved method using scavenger-free plasmid DNA was established to accurately determine yields of DNA damage induced by direct and indirect actions of ionizing radiation. The scavenger-free plasmid DNA was obtained by dialysis over 5-7 days, and the DNA solvent was replaced with phosphate buffer to completely remove impurities, which could be scavengers of radicals produced as a result of water radiolysis. DNA samples of films and dilute aqueous solutions were used to separately evaluate contributions of the direct and indirect actions of X rays (150-160 kVp). The irradiated DNA was analyzed by agarose gel electrophoresis to quantify strand-break yields. The yields of single-strand breaks (SSBs), n(SSB), were determined to be (6.5 ± 2.0) × 10-10 and (3.1 ± 0.9) × 10-7 SSBs/Gy/Da for the film and solution samples, respectively, showing a significant contribution of hydroxyl radicals (•OH) compared with direct energy depositions from ionizing radiation to DNA. As observed in SSBs, the yields of double-strand breaks (DSBs), n(DSB), were (5.6 ± 1.1) × 10-11 and (1.3 ± 0.2) × 10-8 DSBs/Gy/Da for the film and solution samples, respectively. The yield ratio of DSBs to SSBs, that is, n(DSB)/n(SSB), was 0.091 ± 0.026 for the film samples, while it was much lower for the solution samples (0.045 ± 0.010), indicating that direct actions result in more localized strand breaks relative to indirect actions. Base excision repair enzymes, namely, endonuclease III (Nth) and formamidopyrimidine-DNA glycosylase (Fpg), were utilized after irradiations to convert base lesions and apurinic/apyrimidinic (AP) sites into strand breaks. The amounts of Nth and Fpg for the conversion were optimized to a few units per µg of DNA, although the optimal concentrations can differ among conditions.

Comparative study on heterogeneous and homogeneous catalytic ozonation efficiency in micropollutants' removal

Abstract Catalytic ozonation was applied for the removal of small concentrations (4 μM) of micropollutants benzotriazole, carbamazepine, p-CBA from aqueous solutions at pH 7. These compounds present different physicochemical characteristics and different kinetic rate constants, when reacting with ozone or hydroxyl radicals in the ranges of <0.15–3 × 105, 5.2 × 109, and 8.8 × 109 M−1s−1, respectively. Calcite was used as heterogeneous catalyst and its catalytic activity evaluated, by applying (and optimized) different experimental conditions (i.e., pH, temperature, ozone concentration), concerning the removal efficiency of p-CBA. Study of micropollutants' removal showed all examined organic compounds can be sufficiently removed by application of catalytic ozonation either by use of calcite, or by presence of Co(II) or Fe(II) (applied as homogeneous catalysts), while the optimum catalyst between them was found to be calcite. Carbamazepine with kO3 = 3 × 105 M−1s−1 can be easily removed, even by application of single ozonation, while benzotriazole and p-CBA resulted in 50% and 68.2% higher removal after application of catalytic ozonation within 3 min of oxidation reaction, due to acceleration of hydroxyl radicals' production by presence of calcite in the ozonation system. The contribution of hydroxyl radicals in removal of all three micropollutants was evaluated by extraction of Rct and f•OH parameters.

Advanced oxidation mechanism of UV photolysis of electrochemically generated free bromine

ABSTRACT In recent times, some researchers have successfully demonstrated the efficacy of UV photolysis of electrochemically generate free chlorine (UV/electro-chlorine) as for an advanced oxidation process. Since bromine as well as chlorine is an element belonging to halogen, it is expected that UV photolysis of electrochemically generated free bromine (UV/electro-bromine) also shows an advanced oxidation effect. To elucidate the feasibility of UV/electro-bromine system, its advanced oxidation mechanism was investigated using radical probes of 1,4-dioxane and nitrobenzene. In contrast to the UV/electro-chlorine system, the advanced oxidation effect of UV/electro-bromine system was inhibited under acidic conditions due to the accumulation of photochemically inert Br2. The most abundant radical in UV/electro-bromine system was dibromine radical anion (Br2˙−) and the second-order reaction rate constant of Br2˙− with 1,4-dioxane was estimated to be 2.4 × 105 M−1 s−1. As a result of the abundance and the reactivity of Br2˙−, it was the main contributor to 1,4-dioxane degradation. On the other hand, nitrobenzene was mainly decomposed by direct UV photolysis because Br2˙− does not react with nitrobenzene. The contribution of hydroxyl radical (HO˙) to 1,4-dioxane degradation was much lower than that of Br2˙− because its concentration was 4–5 order of magnitude lower than that of Br2˙−. However, the HO˙ concentration elevated with a decrease in the concentration of bromide ion (Br−). Consequently, the reactivity of Br2˙− with pollutants and the Br− concentration have critical impacts on the advanced oxidation performance of UV/electro-bromine system.

Microbubble ozonation of the antioxidant butylated hydroxytoluene: Degradation kinetics and toxicity reduction

Butylated hydroxytoluene (BHT) is recognized as a crucial pollutant in aquatic environments, but efforts to achieve its complete removal are without success. The aim of this study was to investigate the degradation efficiency of BHT in water using ozone microbubbles (OMB), coupled with toxicity change assessment at sub-lethal BHT concentrations (0.34, 0.45 and 0.90 μM) based on oxidative stress biomarkers in Daphnia magna. The efficiency of OMB on ozone gas mass transfer was assessed and the contribution of hydroxyl radicals (·OH) in the degradation of BHT was determined using p-chlorobenzoic acid (pCBA) probe compound and a ·OH radical scavenger (sodium carbonate, Na2CO3). The ozone gas mass transfer coefficient (kLa = 1.02 × 10−2 s−1) was much larger than the ozone self-decomposition rate (kd = 8 × 10−4 s−1) implying little influence of self-decomposing ozone in the volumetric ozone transfer during OMB generation. Generally, OMB improved ozone gas mass transfer (1.3–19-fold) relative to conventional ozone techniques, while indirect reaction of BHT with ·OH was dominant (82%) over the direct reaction with molecular ozone. Addition of 15, 25 and 35 mM Na2CO3 reduced BHT degradation by 30, 50 and 65%, respectively, indicating the significance of ·OH in the degradation of BHT. Increase in initial BHT concentration correspondingly reduced its removal rate by OMB possibly due to increase in metabolites produced during ozonation. Post BHT treatment exposure tests recorded significant (p < 0.05) reductions in oxidative stress (according to enzyme activities changes) in D. magna compared to pretreatment tests, demonstrating the effectiveness of OMB in detoxification of BHT. Overall, the results of the study indicate that OMB is extremely efficient in complete degradation of BHT in water and, consequently, significantly (p < 0.05) reducing its toxicity.

Exploiting water contaminants: In-situ electrochemical generation of ferrates using ambient raw water iron (Fe2+)

Many complexities arise when applying conventional water treatment processes to small and remote systems. A significant challenge is the difficulty and impracticality of supplying chemicals needed for oxidation processes. A burgeoning, yet currently under-utilised, type of treatment are electrochemical technologies, which are receiving considerable research attention and innovation at present. In particular, through the advancement of high oxygen overpotential electrodes, the ability to synthesise highly oxidative chemical species under circumneutral pH conditions has become possible. In this study, the generation of highly oxidative iron-based species, specifically ferrate (Fe6+), has been explored utilising a boron-doped diamond (BDD) electrode and low concentrations of Fe2+ typically found in raw water, thereby eliminating the chemical supply chain required for conventional oxidation processes. Electrochemical ferrate generation experiments were performed in a batch-recycle configuration and were found to be mass transfer limited, whereby the rate-limiting step was the diffusion of Fe2+ to the electrode surface. This was evidenced by very little variation in ferrate generation at the three current densities tested, specifically 3.1 ± 0.2, 2.6 ± 0.2 and 3.3 ± 0.2 μM were generated at 10, 40 and 80 mA/cm2, respectively. Measured Fe6+ concentrations correlated well with those predicted by a mathematical process model, which assumed a completely mass transport limited process. While cyclic voltammetry confirmed ferrate generation by direct oxidation at the BDD surface, the contribution of hydroxyl radicals was indicated by the presence and absence of methanol, an OH scavenger, with ferrate generation decreased by greater than 50 % with methanol, compared to non-scavenged experiments. The results provide one of the first quantitative studies regarding the oxidation mechanisms of ferrate generation by electro-oxidation, and the first example of ferrate generation at circumneutral pH from Fe2+ at levels representative of raw water.

Theoretical and experimental investigation of the mechanism of the catalytic ozonation process by using a manganese-based catalyst

ABSTRACT The mechanisms of heterogeneous catalytic ozonation using a manganese catalyst have been studied in this work. The effects of catalyst, pH and the radical scavengers on the degradation of a model pollutant (i.e. phenol) were evaluated. The contribution of hydroxyl radicals and molecular ozone on the oxidation of phenol was studied for both homogeneous and heterogeneous systems. It was observed that the contribution of hydroxyl radial was 11–44% at pH 3–9. The heterogeneous catalyst may pose a rather complex mechanism as compared to homogenous catalyst. In presence of manganese catalyst, the decomposition ozone is very fast and generates more hydroxyl radicals. This helps the rapid oxidation of phenol at a wide range of pH 3–9. The surface of the catalyst undergoes multiple oxidation reaction and plays the major role in generation of the hydroxyl radicals. A considerable amount of phenol degradation was observed even at low catalyst dose (i.e. 0.5 g L−1). The effect of catalyst on the ozone mass transfer in water was also studied in this work. It was observed that, the overall performance of the phenol degradation is dependent on both chemical reaction due to catalytic action and gas–liquid mass transfer rate.

Tartaric acid enhanced CuFe2O4-catalyzed heterogeneous photo-Fenton-like degradation of methylene blue

CuFe2O4 particles were obtained by sol-gel process and characterized by XRD, SEM and EDS. The effects of tartaric acid (TA) on the degradation of methylene blue (MB) were studied in the presence of CuFe2O4 and H2O2 under light irradiation. The results showed that introducing TA enhanced MB decolorization rate from 52.0% to 92.1% within 80 min. The contribution of superoxide anions (O2−) was only 10% and the contribution of hydroxyl radical (OH) was around 88%. For H2O2-CuFe2O4-photo system, in the presence (or absence) of TA, the dynamic change of OH suggested that the addition of TA could promote the generation of hydroxyl radicals. The enhanced effect of TA in TA-H2O2-CuFe2O4-photo system could be attributed to its own structure and the dissolved metal ions of the catalyst surface. In addition, a reasonable mechanism for the complex system was elucidated.

Enhanced removal of lomefloxacin based on peroxymonosulfate activation by Co3O4/δ-FeOOH composite

In the present study, a novel Co3O4/δ-FeOOH composite was successfully fabricated. Subsequently, we measured its crystal structure, morphology, and surface area. After this, the Co3O4/δ-FeOOH composite was applied to activate peroxymonosulfate (PMS) for lomefloxacin (LOM, a type of fluoroquinolones) degradation. Compared with pure Co3O4 and δ-FeOOH, Co3O4/δ-FeOOH composite exhibited the best efficiency towards LOM degradation, in which the removal of LOM (>82%) and first order reaction kinetic rate constant (kapp = 0.064 min−1) were achieved after 25 min reaction with 0.25 g·L−1 Co3O4/δ-FeOOH, 0.49 mM PMS, and 10 mg·L−1 (28.5 μM) LOM at initial pH 6.08. Next, we considered the concentration of catalyst, PMS and the effect of pH on LOM degradation. The results showed that the increase of PMS and catalyst was beneficial for the degradation of LOM. Moreover, the highest degradation efficiency of LOM was achieved under neutral conditions, which was due to the minimum repulsive force between the PMS and the catalyst. In addition, active radical scavenging experiment was performed and it was found that the contribution of hydroxyl radicals was greater than that of sulfate radicals. Subsequently, possible reaction mechanism was proposed. What’s more, possible degradation intermediates in Co3O4/δ-FeOOH system were determined and five decomposition pathways were proposed. Meanwhile, activated sludge inhibition experiment was carried out to evaluate the variation of toxicity of the LOM and its degradation intermediates in the oxidation process. Overall, this work provided a new strategy for the practical application of sulfate radicals-based advanced oxidation processes (SR-AOPs) in wastewater treatment.

The efficiency and mechanism in a novel electro-Fenton process assisted by anodic photocatalysis on advanced treatment of coal gasification wastewater

A novel dual-chamber photo-electrochemical oxidation system with Fe@Fe2O3/CF cathode was constructed bycombining cathodic electro-Fenton and anodic photocatalysis for advanced treatment of biologically pretreated coal gasification wastewater (CGW). In the electro-Fenton cathode chamber, maximal chemical oxygen demand (COD) removal efficiency of 84.2% was arrived within 120 min at current density 10 mA/cm2, initial pH 3 and air flow rate 0.4 L/min for its initial concentration of 200 mg/L. Correspondingly, the effluent concentration of COD, BOD5, TOC and total phenols were 31.5, 3.9, 8.4 and 13.8 mg/L respectively, satisfying the stringent wastewater discharge standard. Moreover, the H2O2 concentration change and wastewater acute toxicity were analyzed. Furthermore, a reasonable degradation mechanism was proposed based on the contribution of hydroxyl radicals (OH), and thus degradation pathway of phenol as typical pollutant was also speculated. The integrated system is confirmed to be high-effective and stable, and thus it is a potentially promising alternative for treatment toxic refractory industrial wastewater.

Significant enhancement of micropollutant photocatalytic degradation using a TiO2 nanotube array photoanode based photocatalytic fuel cell

This study evaluated the application of a membrane-free photocatalytic fuel cell composed of a TiO2 nanotube array photoanode and a Cu cathode, i.e. TNA-Cu PFC system, for micropollutant removal from water. Significantly enhanced removal of a commonly present aqueous micropollutant 4-chloro-2-methylphenoxyacetic acid (MCPA) was obtained in this TNA-Cu PFC system: the TNA-Cu PFC system achieved better MCPA degradation compared to the conventional photocatalytic method using the same catalyst. In the TNA-Cu PFC system, the MCPA degradation was largely promoted under acidic conditions, indicating this as an important operational condition. The enhancement of MCPA degradation in the TNA-Cu PFC system involved better e−/h+ separation and generation of other oxidants: in conventional photocatalytic process, hydroxyl radicals in liquid phase contributed to 93.7% MCPA degradation while only 2.4% MCPA degradation was mediated by other oxidants like O2−, H2O2, HO2; for MCPA degradation in the TNA-Cu PFC system, the contribution of hydroxyl radicals in the liquid phase decreased to 83.6%, while contribution of other oxidants like O2−, H2O2, HO2 increased to 15.3%. This change in MCPA degradation mechanisms was confirmed via degradation intermediates analysis by LC-MS/MS. The study on the effect of electrolyte concentration suggests that when operated under acidic conditions, addition of electrolyte is not required. The TNA-Cu PFC system was shown to work well in the presence of up to 15 mg/L natural organic matter (originating from two large rivers), high amounts of common inorganic ions, and even in WWTP effluent. The TNA-Cu PFC system also exhibited relatively good stability after several cycles of repeated use. The obtained results demonstrated that this is an adequate system for micropollutant removal from water at various places in the water cycle, i.e. as polisher of WWTP effluents before discharge or for cleaning intake water before producing drinking water.

Photo‐activated periodate in homogeneous degradation and mineralization of quinoline: Optimization, kinetic, and energy consumption

Aqueous solutions of quinoline (Qu) were treated with photo‐activated potassium periodate (UV/KPI) process. A low consumption, cylindrical photo‐reactor was employed for this purpose. Either KPI oxidant or UV irradiation alone had little effect in Qu degradation; however, the combined UV/KPI process leads to significant degradation and mineralization. Experiments were conducted based on central composite design (CCD) methodology. The established optimized conditions for treatment of 40 mg L−1 of the substrate were [KPI] = 695.5 mg L−1, pH = 4.3 and T = 35.6 °C. Under these conditions, 96.5% degradation and 71.5% mineralization were obtained after 70 min operations. A quadratic equation predicts the variation of degradation efficiency as a function of the influencing parameters. To investigate about the involved species, tert‐butyl alcohol was used as radical scavenger and it was found that the contribution of hydroxyl radical was about 73.1%. Kinetic study revealed that Qu degradation was a pseudo first‐order reaction and the corresponding activation energy was determined. Meanwhile, the required irradiation energy for one order of magnitude degradation was estimated as 3.13 kWh m−3. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1621–1627, 2017

Investigation on the Kinetics of Heterogeneous Catalytic Ozone Decomposition in Aqueous Solution over Composite Iron-Manganese Silicate Oxide

ABSTRACTThe kinetics of heterogeneous catalytic ozone decomposition in aqueous solution over composite iron-manganese silicate oxide (FMSO) was investigated. Results showed that the presence of FMSO significantly accelerated the ozone decomposition rate from 0.022 (without FMSO) to 0.101 min−1. The effects of inorganic anions and solution pH indicated that surface hydroxyl groups on FMSO were the active sites for catalyzing ozone decomposition and neutral charge surface seemed to show the highest catalytic performance. Tert-butanol inhibition experiments demonstrated that FMSO effectively accelerated the transformation rate of ozone into hydroxyl radicals. The contribution of hydroxyl radicals on ozone decomposition with and without FMSO was subsequently determined.

Contribution of hydroxyl radicals to the degradation of Acid Orange 7 by fly ash under ultrasonic irradiation

Ultrasonic irradiation (US) alone usually has comparatively low ultrasonic degradation efficiency for limited organic pollutants. In this research, fly ash, an industrial waste from thermal power plant, was used to assist ultrasonic degradation of Acid Orange 7, a common dye pollutant. The decolorization efficiency within 60 min by US alone, fly ash adsorption alone and the combined process were of 3.8, 41.5, and 76.7%, respectively. The contribution of hydroxyl radicals was investigated systematically by indirect iso-propanol quenching method. Although more dyes were degraded by hydroxyl radicals in fly ash-assisted US than in US alone, the contribution percentage of hydroxyl radicals in the former system was much lower than that in the latter system, being 24.8 and 53.4%, respectively. The results showed that pH had significant impact on the degradation efficiency of dye due to its influence on generation of hydroxyl radicals. The coexistence of chloride, sulfate, and nitrate anions inhibited the contribution of hydroxyl radicals. In comparison to fly ash, diatomite and tourmaline were capable of facilitating the generation of more OH radicals, while kaoline actually reduced the contribution percentage of hydroxyl radicals.

Aspects of decontamination of ivermectin and praziquantel from environmental waters using advanced oxidation technology

Recently performed environmental risk assessments of ivermectin demonstrated the need to complete the information regarding the fate of ivermectin in environment. There is also a lack of information concerning the fate and stability of praziquantel.The forced degradation study and photocatalytic degradation pathways in aqueous TiO2 suspensions of the two anthelmintics ivermectin and praziquantel were investigated and compared. The degradation efficiency increased for both compounds with the increase in the TiO2 concentration from 0.25 to 2.00 g L−1, and then remained constant. The estimated k-values were from 0.36 h−1 to 0.64 h−1 for IVE and from 0.29 h−1 to 0.47 h−1 for PZQ, respectively. The degradation rate was not significantly impacted by the change of the pH value (pH 3, 5, 7, and 9) at 2.0 g L−1 of TiO2.The photo degradation was about 90% for both compounds after 5 h of irradiation and it was significantly inhibited in the presence of iodide anion and isopropyl alcohol, which indicated, that hydroxyl radicals as well as holes contributed to the degradation of both anthelmintics. The contribution of hydroxyl radicals and holes was 92.1% for IVE and 93.2% for PZQ, respectively.Photocatalytic process of ivermectin resulted in three degradation intermediates; another two were formed during acidic and basic hydrolysis. Praziquantel underwent degradation to six degradation intermediates; four of them were formed under photocatalytic irradiation. The intermediates were identified using UHPLC-MS/MS.UV/TiO2 photolysis has been found as an effective advanced oxidation technology for the decontamination of ivermectin and praziquantel.