OH Yield Research Articles

Thermal and Vibrationally Activated Decomposition of the syn-CH3CHOO Criegee Intermediate

The full reaction pathway between the syn-CH3CHOO Criegee Intermediate via vinyl hydroxyperoxide (VHP) to CH2COH+OH is followed for vibrationally excited and thermally prepared reactants. Reactivity along the entire pathway was characterized from an aggregate of more than 10 μs of reactive MD simulations using energy functions with accuracies at the Møller–Plesset second order level of theory. Reaction times for OH elimination are on the nanosecond time scale, and the energy dependence of the rates is consistent with experiments in the jet. The actual rates depend on the O–O dissociation energy (DeOO = 31.5 kcal/mol at the MP2/aug-cc-pVTZ level or DeOO = 23.5 kcal/mol closer to earlier CASPT2 calculations). Also, the initial preparation of the reactants influences both the VHP formation/OH elimination rates and the OH yields. For most conditions with initial vibrational excitation 80% or more of syn-CH3CHOO progress to OH elimination on the 5 ns time scale. However, for internally cold conformational ensembles generated at low temperature (50 K) only 20% to 30% of VHP eliminate OH on the 5 ns time scale which increases to 55% to 67% depending on excitation energy from simulations on the 15 ns time scale. For thermal preparation of syn-CH3CHOO, which is relevant in the atmosphere, 35% of the trajectories lead to OH-elimination within 1 ns. This compares with experimentally reported yields of 24% to 64% in a collisional environment. The estimated thermal rate at 300 K is 103 s–1, extrapolated from results at 500 to 900 K, is consistent with the experimentally measured rate of 182 ± 66 s–1.

Enhanced degradation of micropollutants over iron-based electro-Fenton catalyst: Cobalt as an electron modulator in mesochannels and mechanism insight

Heterogeneous electro-Fenton (hetero-EF) process is an emerging alternative for effective oxidation of recalcitrant micropollutants, but it is hampered by limited hydroxyl radical (•OH) generation and low stability on the iron-based cathodes. Herein, we demonstrate an enhanced hetero-EF performance via modulation of iron electronic structure in an ordered mesoporous carbon (OMC). By tuning the cobalt incorporation, the highly-dispersed iron-cobalt (FeCo) nanoalloys in mesochannels (Fe0.5Co0.5@OMC) show a 3-fold increase in •OH yield compared with Fe@OMC, achieving degradation efficiency with 92% of sulfamethazine (SMT) and 99% of rhodamine B (RhB), and the corresponding total organic carbon (TOC) removal with 66% of SMT and 85% of RhB within 2 h in neutral pH, respectively. Experimental results and density functional theory (DFT) calculations demonstrate that iron incorporated with cobalt reduces energy barrier for facile generation of H2O2 and •OH from O2 through direct electron transfer, along with decreased overpotential. Meanwhile, cobalt doping promotes H2O2 decomposition by accelerated Fe(II)/Fe(III) cycle and Co(II)/Co(III) redox. Furthermore, spatially confined and half-embedded structure endows the nanocatalyst (8 nm) excellent durability within a wide pH value range and good stability in cycle tests. A plausible reaction mechanism and degradation pathway for SMT are proposed. Moreover, the superiority of Fe0.5Co0.5@OMC cathode is maintained in simulated wastewater, suggesting an enormous potential in practical wastewater treatment.

In situ Irradiated XPS Investigation on S-Scheme TiO2 @ZnIn2 S4 Photocatalyst for Efficient Photocatalytic CO2 Reduction.

Reasonable design of efficient hierarchical photocatalysts has gained significant attention. Herein, a step-scheme (S-scheme) core-shell TiO2 @ZnIn2 S4 heterojunction is designed for photocatalytic CO2 reduction. The optimized sample exhibits much higher CO2 photoreduction conversion rates (the sum yield of CO, CH3 OH, and CH4 ) than the blank control, i.e., ZnIn2 S4 and TiO2 . The improved photocatalytic performance can be attributed to the inhibited recombination of photogenerated charge carriers induced by S-scheme heterojunction. The improvement is also attributed to the large specific surface areas and abundant active sites. Meanwhile, S-scheme photogenerated charge transfer mechanism is testified by in situ irradiated X-ray photoelectron spectroscopy, work function calculation, and electron paramagnetic resonance measurements. This work provides an effective strategy for designing highly efficient heterojunction photocatalysts for conversion of solar fuels.

Atmospheric photooxidation and ozonolysis of Δ<sup>3</sup>-carene and 3-caronaldehyde: rate constants and product yields

Abstract. The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Δ3-carene with OH and O3 and of the reaction of caronaldehyde with OH were determined to be (8.0±0.5)×10-11 cm3 s−1 at 304 K, (4.4±0.2)×10-17 cm3 s−1 at 300 K and (4.6±1.6)×10-11 cm3 s−1 at 300 K, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be 0.30±0.05 and 0.06±0.02, respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02. The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Δ3-carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx=OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the chamber experiments. In an OH-free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.

Combustion chemistry of ammonia/hydrogen mixtures: Jet-stirred reactor measurements and comprehensive kinetic modeling

To investigate the oxidation of ammonia (NH3)/hydrogen (H2) mixtures at intermediate temperatures, this work has implemented jet-stirred reactor (JSR) oxidation experiments of NH3/H2 mixtures at atmospheric pressure and over 800-1280 K. The H2 content in the NH3/H2 mixtures is varied from zero to 70 vol% at equivalence ratios of 0.25 and 1.0. Species identification and quantification are achieved by using Fourier-transform infrared (FTIR) spectroscopy. A kinetic model for pure NH3 and NH3/H2 mixtures is also developed for this research, and validated against the present experimental data for pure NH3 and NH3/H2 mixtures, as well as those for pure NH3, H2/NO, H2/N2O, NH3/NO, NH3/NO2 and NH3/H2 mixtures in literature. The model basically captures the experimental data obtained here, as well as in literature. Both measured and predicted results from this work show that H2 blending enhances the oxidation reactivity of NH3. Based on the model analysis, under the present experimental conditions, NH3 + H = NH2 + H2 proceeds in its reverse direction with increasing H2 content. The H atom produced is able to combine with O2 to produce either O and OH via a chain-branching reaction, or to yield HO2 through a chain-propagation reaction. HO2 is an important radical under the present intermediate-temperature conditions, which can convert NH2 to OH via NH2 + HO2 = H2NO + OH; H2NO is then able to convert H to NH2 and OH. In this reaction sequence, NH2 and H2NO are chain carriers, converting HO2 and H to two OH radicals. Since the OH radical is the dominant radical to consume NH3 under the present conditions, the enhanced OH yield via H + O2 = O + OH, NH2 + HO2 = H2NO + OH and H2NO + H = NH2 +OH, with increasing H2 content, promotes the consumption of NH3. For NOx formation, non-monotonous trends are observed by increasing the content of H2 at the 99% conversion of NH3. These trends are determined by the competition between the dilution effects and the chemical effects of H2 addition. Nitrogen related radicals, such as NH2, NH and N, decrease as H2 increases, and this dilution effect reduces NOx formation. For chemical effects, the yields of oxygenated radicals, such as O, OH and HO2, are enhanced with increasing H2 content, which results in enhancing effects on NO formation. For N2O formation, the enhanced oxygenated radicals (O, OH and HO2) suppress its formation, while the enhanced NO promotes its formation.

The oxidative immobilization of phosphonate by simulated solar light mediated peroxi-coagulation process sustained by the iron-air fuel cell

Phosphonates are an important type of phosphorus-containing compounds and is of primary concern due to its eutrophication potential. Herein, we achieved simultaneously oxidative immobilization of phosphorus from ethylene diamine tetra (methylene phosphonic acid) (EDTMP) in the simulated solar light mediated peroxi-coagulation process sustained by the iron-air fuel cell (IAFC). The integration of simulated solar light irradiation with IAFC could enhance the oxidation capacity, yield of iron ions and power density output. The highest total phosphorus (TP) removal efficiency (approximately 100%) could be obtained at pH 4.0 owing to the synergistic action of coprecipitation and oxidation of EDTMP to orthophosphate (o-PO4), accompanying the optimum power density of 2459 mW m−2 at 2086 mA m−2. The OH mediated oxidation and photodegradation of Fe(III)-EDTMP complex via ligand-to-metal charge transfer reaction worked together to transform EDTMP into o-PO4. In the precipitate, the immobilized phosphorus existed mainly in the forms of organic phosphorus and o-PO4. The presence of oxalic and citric acid enhanced the yield of OH, but the formation of soluble Fe(III)-carboxylate complexes negatively affected the TP removal due to the decreased precipitation capacity. Contrastly, the observed decrease in TP removal caused by humic acid was ascribed to its scavenging effect toward OH. In general, this study proposed an energy efficient and environmental friendly approach for mitigating the potential risk of phosphonates to environmental safety.

Effect of phosphate on peroxymonosulfate activation: Accelerating generation of sulfate radical and underlying mechanism

Effect of phosphate on pollutant removal was widely investigated in various peroxumonosulfate-based advanced oxidation processes (AOPs) but the role of phosphate was controversial. Many studies also used phosphate as buffer in PMS-based AOPs. This study shows that phosphate promoted PMS activation for pollutants removal. Therefore, PMS activation capacity of some strategies may be overestimated when conducted in the phosphate buffer. Importantly, the results of radical quenching tests, radical probes and reaction stoichiometries indicated that the yields of SO4− was elevated by the presence of phosphate and linearly depended on phosphate concentration, while the yields of OH remained constant. Density Functional Theory (DFT) calculation confirmed that PO43− and HPO42− could efficiently break OO bond of PMS, promoting the generation of SO4− for contaminants decomposition. These results illuminated the role of phosphate in AOPs utilizing PMS and uncovered the underlying mechanism of PMS activation by phosphate.

Constructing Electron Levers in Perovskite Nanocrystals to Regulate the Local Electron Density for Intensive Chemodynamic Therapy.

The local electron density of an atom is one key factor that determines its chemical properties. Regulating electron density can promote the atom's reactivity and so reduce the reaction activation energy, which is highly desired in many chemical applications. Herein, we report an intra-crystalline electron lever strategy, which can regulate the electron density of reaction centre atoms via manipulating ambient lattice states, for Fenton activity improvement. Typically, with the assistance of ultrasound, the Mn4+ -O-Fe3+ bond in BiFe0.97 Mn0.03 O3 perovskite nanocrystals can drive valence electrons and free electrons to accumulate on Fe atoms by a polarization electric field originated from the designed lattice strain. The increase of electron density significantly improves the catalytic activity of Fe, decreasing the activation energy of BiFe0.97 Mn0.03 O3 -mediated Fenton reaction by 52.55 %, and increasing the . OH yield by 9.21-fold. This study provides a new way to understand the sono-Fenton chemistry, and the increased . OH production enables a highly effective chemodynamic therapy.

Constructing Electron Levers in Perovskite Nanocrystals to Regulate the Local Electron Density for Intensive Chemodynamic Therapy

AbstractThe local electron density of an atom is one key factor that determines its chemical properties. Regulating electron density can promote the atom's reactivity and so reduce the reaction activation energy, which is highly desired in many chemical applications. Herein, we report an intra‐crystalline electron lever strategy, which can regulate the electron density of reaction centre atoms via manipulating ambient lattice states, for Fenton activity improvement. Typically, with the assistance of ultrasound, the Mn4+−O−Fe3+ bond in BiFe0.97Mn0.03O3 perovskite nanocrystals can drive valence electrons and free electrons to accumulate on Fe atoms by a polarization electric field originated from the designed lattice strain. The increase of electron density significantly improves the catalytic activity of Fe, decreasing the activation energy of BiFe0.97Mn0.03O3‐mediated Fenton reaction by 52.55 %, and increasing the .OH yield by 9.21‐fold. This study provides a new way to understand the sono‐Fenton chemistry, and the increased .OH production enables a highly effective chemodynamic therapy.

Eradication of solid tumors by chemodynamic theranostics with H2O2-catalyzed hydroxyl radical burst.

Activatable theranostics, integrating high diagnostic accuracy and significant therapeutic effect, holds great potential for personalized cancer treatments; however, their chemodynamic modality is rarely exploited. Herein, we report a new in situ activatable chemodynamic theranostics PAsc/Fe@Cy7QB to specifically recognize and eradicate cancer cells with H2O2-catalyzed hydroxyl radical (•OH) burst cascade.Methods: The nanomicelles PAsc/Fe@Cy7QB were constructed by self-assembly of acid-responsive copolymers incorporating ascorbates and acid-sensitive Schiff base-Fe2+ complexes as well as H2O2-responsive adjuvant Cy7QB.Results: Upon systematic delivery of PAsc/Fe@Cy7QB into cancer cells, the acidic microenvironment triggered disassembly of the nanomicelles. The released Fe2+ catalyzed the oxidation of ascorbate monoanion (AscH-) to efficiently produce H2O2. The released H2O2, together with the endogenous H2O2, could be converted into highly active •OH via the Fenton reaction, resulting in enhanced Fe-mediated T1 magnetic resonance imaging (MRI). The synchronously released Cy7QB was activated by H2O2 to produce a glutathione (GSH)-scavenger quinone methide to boost the •OH yield and recover the Cy7 dye for fluorescence and photoacoustic imaging.Conclusion: The biodegradable PAsc/Fe@Cy7QB designed for tumor-selective multimodal imaging and high therapeutic effect provides an exemplary paradigm for precise chemodynamic theranostic.

Sonochemical dosimetry: A comparative study of Weissler, Fricke and terephthalic acid methods

Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO2 in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH, the reason for a very low OH yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.

Physical interpretation of a pulsed atmospheric pressure plasma jet following parametric study of the UV–to–NIR emission

In the present report, an atmospheric pressure plasma jet is sustained in a helium channel by high square wave unipolar voltage. The gas flow rate and the square wave features (amplitude, frequency, and duty cycle) are varied over a wide range, while the plasma ultraviolet to near infrared emission is recorded. The plasma emission pattern, the propagation dynamics of the involved ionization fronts, the relative density of critical excited species, and the rotational and vibrational temperatures of neutral and ionic species are measured. An optimum operational window is found corresponding to a helium flow rate of 2 slm, a pulse amplitude of 7.5 kV, a pulse repetition rate of 10 kHz, and a pulse duty cycle of 5%–7%. Under these conditions, a plasma jet length close to 45 mm and a gas temperature close to 325 K are obtained, while a high yield of OH, N2(SPS), N2+(FNS), N2(FPS), He*, O*, and NOγ is achieved. The results are found to be in good agreement with the bibliography and motivate a consideration on the involved physical mechanisms. The plasma jet propagation with respect to the reactive species production is discussed based on the local electric field variation over the high voltage pulse width.

Tertiary Amine-Ethylene Glycol Based Tandem CO2 Capture and Hydrogenation to Methanol: Direct Utilization of Post-Combustion CO2.

Carbon dioxide capture using tertiary amines in ethylene glycol solvent was performed under ambient conditions. Subsequently, the CO2 captured as alkyl carbonate salts was successfully hydrogenated to methanol, in the presence of H2 gas and Ru-Macho-BH catalyst. A comprehensive series of tertiary amines were selected for the integrated capture and conversion process. While most of these amines were effective for CO2 capture, tetramethylethylenediamine (TMEDA) and tetramethylbutanediamine (TMBDA) provided the best CH3 OH yields. Deactivation of the base due to side reactions was significantly minimized and substantial base regeneration was observed. The proposed system was also highly efficient for CO2 capture from a gas mixture containing 10 % CO2 , as found in flue gases, followed by tandem conversion to CH3 OH. We postulate that such high boiling tertiary amine-glycol systems as dual capture and hydrogenation solvents are promising for the realization of a sustainable and carbon-neutral methanol economy in a scalable process.

Fuel, thermal and surface properties of microwave-pyrolyzed biochars depend on feedstock type and pyrolysis temperature

We evaluated the fuel, thermal and surface properties of twelve biochars produced from three lignocellulosic (canola straw, sawdust, wheat straw) and one non-lignocellulosic feedstock (manure pellet) pyrolyzed at three temperatures using a microwave. Regardless of feedstock type, increasing pyrolysis temperature progressively reduced the abundance of -OH functional group and yield, but increased pH and thermal stability of biochar. Gross calorific values (GCV), carbon stability, and degree of aromaticity of biochars derived from lignocellulosic feedstocks increased with increasing temperature due to decreased elemental oxygen content. However, high ash content in the non-lignocellulosic feedstock retarded its thermal degradation, producing biochars with low GCV. The specific surface area of biochars was low, with the highest value of 43 m2 g−1 achieved for sawdust biochar produced at 500 °C. We conclude that the fuel, thermal, and surface properties of the biochars were dependent on the feedstock type and pyrolysis temperature.

Mutual Interactions between Reduced Fe-Bearing Clay Minerals and Humic Acids under Dark, Oxygenated Conditions: Hydroxyl Radical Generation and Humic Acid Transformation.

Hydroxyl radicals (·OH) exert a strong impact on the carbon cycle due to their nonselective and highly oxidizing nature. Reduced iron-containing clay minerals (RIC) are one of the major contributors to the formation of ·OH in dark environments, but their interactions with humic acids (HA) are poorly known. Here, we investigate the mutual interactions between RIC and HA under dark and oxygenated conditions. HA decreased the oxidation rate of structural Fe(II) in RIC but significantly promoted the ·OH yield. HA dissolved a fraction of Fe(II) from RIC to form an aqueous Fe(II)-HA complex. ·OH were generated through both heterogeneous (through oxidation of structural Fe(II)) and homogeneous pathways (through oxidation of aqueous Fe(II)-HA species). RIC-mediated ·OH production by providing H2O2 to react with Fe(II)-HA and electrons to regenerate Fe(II)-HA. This highly efficient homogeneous pathway was responsible for increased ·OH yield. Abundant ·OH significantly decreased the molecular size, bleached chromophores, and increased the oxygen-containing functional groups of HA. These molecular changes of HA resembled photochemical transformation of HA. The mutual interaction between RIC and HA in dark and redox-fluctuating environments provides a new pathway for fast turnover of recalcitrant organic matters in clay- and HA-rich ecosystems such as tropical forest soils and tidal marsh sediments.

A novel method Hybrid Photo-electrocatalytic Oxidation for the treatment of 3,4-dimethyaniline wastewater: Degradation mechanism and synergistic effect

3,4-dimethyl-aniline is a stubborn organic matter and widely appears in many industrial wastewaters. A novel method Hybrid Photo-electrocatalytic Oxidation (HPECO) combining Photocatalytic Oxidation (PCO) with Electrocatalytic Oxidation (ECO) was established to treat it. The removal efficiencies were compared among HPECO, PCO and ECO systems and the result suggested HPECO was 2.45 and 1.14 times higher than the sum of other two systems for 3,4-DMA and TOC removals, separately. Furthermore, a three-stage mechanism was proposed in HPECO process by cyclic voltammetry, ESR and quantitative determination of HClO and a whole degradation pathway was deduced by GC–MS. In the first stages, HClO attacked the side chains of 3,4-DMA and oxidized it into 3,4-dimethylphenol, 2-amino-6-methylbenzoic acid and 1,2,4-benzoic acid. In the last two stages, these intermediates were further degraded until mineralization, under the co-oxidation of chlorine radical species (CRS) and OH. In addition, synergistic effect was studied with generating reason and controlling factors. UV irradiation and applied voltage could increase the yields of OH and CRS. Electrochemical process could also accelerate the production of OH through O2 evolution reaction. The existence of OH could facilitate the transform of 3,4-DMA into the intermediates containing COOH groups, which provided the bridge substances for CRS and HClO to achieve the rapid selective oxidation. The further investigation found that synergistic effect was positively correlated with current density and negative correlated with pH and UV power. Finally, pharmaceutical wastewater was treated with this novel method and it can be successfully removed to meet the Chinese national sewage discharge standard after 30 h degradation.

Acetonyl Peroxy and Hydro Peroxy Self- and Cross-Reactions: Kinetics, Mechanism, and Chaperone Enhancement from the Perspective of the Hydroxyl Radical Product.

Pulsed laser photolysis coupled with infrared (IR) wavelength modulation spectroscopy and ultraviolet (UV) absorption spectroscopy was used to study the kinetics and branching fractions for the acetonyl peroxy (CH3C(O)CH2O2) self-reaction and its reaction with hydro peroxy (HO2) at a temperature of 298 K and pressure of 100 Torr. Near-IR and mid-IR lasers simultaneously monitored HO2 and hydroxyl, OH, respectively, while UV absorption measurements monitored the CH3C(O)CH2O2 concentrations. The overall rate constant for the reaction between CH3C(O)CH2O2 and HO2 was found to be (5.5 ± 0.5) × 10-12 cm3 molecule-1 s-1, and the branching fraction for OH yield from this reaction was directly measured as 0.30 ± 0.04. The CH3C(O)CH2O2 self-reaction rate constant was measured to be (4.8 ± 0.8) × 10-12 cm3 molecule-1 s-1, and the branching fraction for alkoxy formation was inferred from secondary chemistry as 0.33 ± 0.13. An increase in the rate of the HO2 self-reaction was also observed as a function of acetone (CH3C(O)CH3) concentration which is interpreted as a chaperone effect, resulting from hydrogen-bond complexation between HO2 and CH3C(O)CH3. The chaperone enhancement coefficient for CH3C(O)CH3 was determined to be kA″ = (4.0 ± 0.2) × 10-29 cm6 molecule-2 s-1, and the equilibrium constant for HO2·CH3C(O)CH3 complex formation was found to be Kc(R14) = (2.0 ± 0.89) × 10-18 cm3 molecule-1; from these values, the rate constant for the HO2 + HO2·CH3C(O)CH3 reaction was estimated to be (2 ± 1) × 10-11 cm3 molecule-1 s-1. Results from UV absorption cross-section measurements of CH3C(O)CH2O2 and prompt OH radical yields arising from possible oxidation of the CH3C(O)CH3-derived alkyl radical are also discussed. Using theoretical methods, no likely pathways for the observed prompt OH radical formation have been found and the prompt OH radical yields thus remain unexplained.

The mechanism of Metal-H2O2 complex immobilized on MCM-48 and enhanced electron transfer for effective peroxone ozonation of sulfamethazine

In the peroxone process (O3/H2O2), OH yield ratio with respect to O3 consumption was low due to the competition experiments. Singular effectiveness of CoCe as a supporting ligand in the interface of ozone-H2O2-catalysts and related complexes formed on catalysts enhanced the electron transfer between ozone chain reaction and various chemical state of Ce/Co. A computationally determined stereochemical structure corroborated that the CoCe synergistic effect led to the region around Co atom (electron donor) with low Gibbs free energy to form OH. Meanwhile, reactive oxygen species (ROSs) were tend to attack the sites with very negative natural population charge or high frontier electron density (FED) values of sulfamethazine (SMT) by LC–MS/MS and density functional theory (DFT) calculations. Benefiting from the unique superoxide complexes and synergetic effect of CoCe, the Co10Ce10@MCM-48 catalysts showed superior performance of SMT mineralization (64.1 %, 120 min), which resolved the low-efficient ROSs generation in bare peroxone reaction.

Sonozonation (sonication/ozonation) for the degradation of organic contaminants - A review.

Ozonation (OZ) is an important advanced oxidation process to purify water and wastewater. Because of the lower solubility and instability of ozone (O3), selective oxidation and dependence on pH value, the industrial applications of OZ have been hindered by the following disadvantages: incomplete removal of pollutants, lower mineralization efficiency and the formation of toxic by-products. Meanwhile, OZ seems to have higher processing costs than other technologies. To improve the treatment efficiency and O3 utilization, several combined processes, such as H2O2/O3, UV/O3, and Cavitation/O3, have been explored, while the combined method of ultrasonication (US) with OZ is a promising treatment technology with a complex physicochemical mechanism. In US alone, the sonolysis of water molecules can produce more powerful unselective oxidant hydroxyl radicals (OH), and directly cause the sonochemical pyrolysis of volatile pollutants. In US/OZ, US can promote the mass transfer of O3, and also drive the chemical conversion of O3 to enhance the formation of OH. Various layouts of US/OZ devices and the interactive effects of US/OZ (synergism or antagonism) on the degradation of various organics are illustrated in this review. The main factors, including US frequency, pH value, and radical scavengers, significantly affect the mass transfer and decomposition of O3, the formation of OH and H2O2, the degradation rates of organics and the removal efficiencies of COD and TOC (mineralization). As a result, US can significantly increase the yield of OH, thereby improving the degradation efficiency and mineralization of refractory organics. However, US also enhances the decomposition of ozone, thereby reducing the concentration of O3 in water and impairing the efficiency of selective oxidation with O3 molecules.

Porous Z-scheme MnO2/Mn-modified alkalinized g-C3N4 heterojunction with excellent Fenton-like photocatalytic activity for efficient degradation of pharmaceutical pollutants

A porous Z-scheme MnO2/Mn-modified alkalinized g-C3N4 catalyst (MnO2/CNK-OH-Mn) was fabricated by calcination-impregnation method. MnO2/CNK-OH-Mn exhibited higher Fenton-like photocatalytic activity in degrading tetracycline than pure g-C3N4 and alkalinized g-C3N4. The optimal MnO2/CNK-OH-Mn15% showed the highest catalytic activity with 96.7% tetracycline removal and 74.9% total organic carbon (TOC) removal efficiency due to the enhanced reactive oxygen species generation. The tetracycline degradation process followed two pathways, and the formation of NO3– further revealed deep mineralization of tetracycline to inorganic substance during the photocatalytic degradation. The highest •OH yield of MnO2/CNK-OH-Mn15% was attributable to synergism of surface grafted hydroxyl groups, Z-scheme charge transfer and H2O2 activation via redox cycles of Mn(IV)/Mn(III)/Mn(II). The Fenton-like photocatalytic mechanism of Z-scheme MnO2/CNK-OH-Mn was presented. Moreover, MnO2/CNK-OH-Mn15% can effectively dispose of pharmaceutical wastewater with 77.1% chemical oxygen demand (COD) removal.