Reaction Of OH Radicals Research Articles

Fast Peroxy Radical Isomerization and OH Recycling in the Reaction of OH Radicals with Dimethyl Sulfide.

Dimethyl sulfide (DMS), produced by marine organisms, represents the most abundant, biogenic sulfur emission into the Earth's atmosphere. The gas-phase degradation of DMS is mainly initiated by the reaction with the OH radical forming first CH3SCH2O2 radicals from the dominant H-abstraction channel. It is experimentally shown that these peroxy radicals undergo a two-step isomerization process finally forming a product consistent with the formula HOOCH2SCHO. The isomerization process is accompanied by OH recycling. The rate-limiting first isomerization step, CH3SCH2O2 → CH2SCH2OOH, followed by O2 addition, proceeds with k = (0.23 ± 0.12) s-1 at 295 ± 2 K. Competing bimolecular CH3SCH2O2 reactions with NO, HO2, or RO2 radicals are less important for trace-gas conditions over the oceans. Results of atmospheric chemistry simulations demonstrate the predominance (≥95%) of CH3SCH2O2 isomerization. The rapid peroxy radical isomerization, not yet considered in models, substantially changes the understanding of DMS's degradation processes in the atmosphere.

Atmospheric oxidation mechansim of polychlorinated biphenyls (PCBs) initiated by OH radicals

Long-range atmospheric transport (LRAT) is the main route for circulating polychlorinated biphenyls (PCBs) from sources to sinks. In the atmosphere, PCBs containing six and less chlorine substitutions exist mainly as vapour, which can be oxidized by OH radical. Here, using quantum chemistry and transition state theory, we calculated the rate coefficients for reactions of OH radical with selected PCBs. The predicted rate coefficients agree with the available experimental values within a factor of 3. Calculations show that all PCBs considered here are persistent with their half-lives longer than 24 h. Reactions of PCBs with OH radical start with OH addition to the phenyl rings, forming PCB-n-OH adducts. Fate of biphenyl-n-OH (BP-n-OH, n = 2, 3, 4) adducts in the atmosphere is investigated. Calculations show that these radical adducts react similarly to benzene-OH adducts, forming hydroxybiphenyl (HO-BP) as main product and bicyclic radicals as minor products in their reaction with O2. Effective rates of reaction with O2 in the atmosphere are relatively slow, ∼1400, ∼45000, and ∼800 s−1 for BP-2-OH, BP-3-OH, and BP-4-OH, respectively. This suggests considerable reactions between BP-n-OH adducts and NO2, forming nitrobiphenyls. The bicyclic radicals from BP-n-OH + O2 would further transform to highly oxidized products as observed in a previous study. PCB-OH adducts react similarly as BP-n-OH radicals. For the three PCB-OH radicals considered here, their reactions with O2 also form HO-PCBs and bicyclic radicals.

Kinetic and Theoretical Study of the Atmospheric Aqueous-Phase Reactions of OH Radicals with Methoxyphenolic Compounds.

Methoxyphenols, which are emitted through biomass burning, are an important species in atmospheric chemistry. In the present study, temperature-dependent aqueous-phase OH radical reactions of six methoxyphenols and two related phenols have been investigated through laser flash photolysis and the density functional theory. The rate constants obtained were in a range of (1.1-1.9) × 1010 L mol-1 s-1 with k(3-MC) > k(Cre) ≈ k(Syr) ≈ k(MEP) > k(Res) > k(3-MP) > k(2-EP) ≈ k(2-MP). We derived the parameters of these reactions from the obtained T-dependent rate constants and found a mean Arrhenius activation energy of 16.9 kJ mol-1. The diffusion rate constants were calculated for each case and compared to the measured ones. Generally, the rate constants are found to be close to fully diffusion-controlled (kdiff = (1.4-1.5) × 1010 L mol-1 s-1 for all reactions). A structure-function relationship was established through the measurement result, which could be used for predicting unknown rate constants of other phenolic compounds. All of these findings are expected to enhance the predictive capabilities of models, such as the chemical aqueous-phase radical mechanism.

The oxidation decomposition mechanisms of HFO-1336mzz(Z) as an environmentally friendly refrigerant in O2/H2O environment

A series of ReaxFF-MD simulations are employed to illuminate the oxidation mechanism of HFO-1336mzz(Z) as an environmentally friendly refrigerant in O2/H2O environment. The results showed that H2O molecule has a significant impact on the HFO-1336mzz(Z) oxidation reactions and promotes the rate of HFO-1336mzz(Z) oxidation decomposition. H2O molecule can react with H and O radicals to form OH radical and will provide more H atoms to combine with F radicals to generate HF molecule. The OH radical plays a crucial role in the HFO-1336mzz(Z) oxidation reactions because the reactivity of OH radical. CO2, COF2 and HF are dominant products and the other radicals COF, O, F, CF3 and CO2F have a significant impact on the HFO-1336mzz(Z) oxidation reactions. The chemical equations of HFO-1336mzz(Z) oxidation in different conditions are presented to expound the comprehensive oxidation mechanism.

Characterization of the chemical activity of a pulsed corona discharge above water

A pulsed corona discharge above liquid combined with ozonation has been investigated for the degradation of organic pollutants in water, as well as regarding the generation of several oxidizing species: ozone in gas phase, hydrogen peroxide and hydroxyl radicals in the liquid. A considerable improvement in the energy efficiency for organic compounds removal has been observed when reducing the width of the discharge pulses. This finding was correlated with the efficient formation of oxidizing species in case of short pulses. Recycling of the effluent gas from the plasma also enhances contaminants degradation. This was mainly attributed to an in situ peroxone process, i.e. the reaction between plasma-generated O3 and H2O2, forming highly reactive OH radicals, largely responsible for organic compounds degradation. This assumption is supported by the decline in O3 and H2O2 concentrations and simultaneous increase in OH concentration detected in plasma-ozonation experiments as compared to results obtained with plasma alone.

Formation of two centre three electron bond by hydroxyl radical induced reaction of thiocoumarin: evidence from experimental and theoretical studies

Radiation chemical studies of thioesculetin (1), a thioketone derivative of coumarin, were performed by both pulse radiolysis technique and DFT calculations. Hydroxyl (•OH) radical reaction with 1 resulted transients absorbing at 320, 360 and 500 nm. To identify the nature of the transients, the reaction was studied with specific one-electron oxidant (N3•) radical, where 360 nm band was absent. The transient absorption at 500 nm was concentration-dependent. The overall impression for •OH radical reaction was that the transient absorbing at 320, 360 and 500 nm was due to sulphur centred monomer radical, hydroxysulfuranyl and dimer radical of 1 respectively. The equilibrium constant between the monomer to dimer radical was 3.75 × 104 M−1. From the transients’ redox nature, it was observed that 57 and 24% of •OH radical yielded to oxidising and reducing products respectively. Further, the product analysis by HPLC suggested that the dimer radical disproportionate to esculetin and thioesculetin. DFT energy calculation for all the possible transients revealed that dimer radical has the lowest energy. The HOMO of 1 and its monomer radical suggested that the electron density was localised on the sulphur atom. The bond length between the two sulphur atoms in dimer radical was 2.88 Å which was less than the van der Waals distance. Bond order between the two sulphur atoms was 0.55, suggesting that the bond was two centre three electron (2c–3e). From TD-DFT calculation, the electronic transition of dimer radical was at 479 nm which was in close agreement with the experimental value. The nature of the electronic transition was σ → σ* from a 2c − 3e bond.

Rate Constants for the Reactions of OH Radicals with the ( E)/( Z) Isomers of CFCl=CFCl and ( E)-CHF=CHF.

The rate constants for the OH radical reactions with halogenated ethenes were investigated experimentally and computationally. The rate constants for the reactions of OH radicals with ( E)-CFCl=CFCl ( k1), ( Z)-CFCl=CFCl ( k2), and ( E)-CHF=CHF ( k3) were measured using flash and laser photolysis methods. The temporal profile of the OH radical was monitored by a laser-induced fluorescence technique. Kinetic measurements were carried out over the temperature range of 250-430 K. Arrhenius rate constants were determined to be k1 = (1.67 ± 0.06) × 10-12·exp[(140 ± 10) K/ T], k2 = (1.75 ± 0.04) × 10-12·exp[(140 ± 10) K/ T], and k3 = (3.99 ± 0.15) × 10-12·exp[(260 ± 10) K/ T] cm3 molecule-1 s-1. The quoted uncertainties are 95% confidence levels and do not include systematic errors. Infrared absorption spectra were measured at room temperature. The atmospheric lifetimes and the global warming potentials of ( E)-CFCl=CFCl, ( Z)-CFCl=CFCl, and ( E)-CHF=CHF were estimated to be 4.3, 4.2, and 1.2 days and 0.035, 0.036, and 0.0056, respectively. The ozone depletion potentials of ( E)-CFCl=CFCl and ( Z)-CFCl=CFCl were determined to be 0.00011 and 0.00010, respectively. The photochemical ozone creation potentials of the halogenated ethenes were less than 1/4 that of ethene. In addition, the ( E)/( Z) differences in the energy and IR spectra of the CFCl=CFCl and CHF=CHF molecules were computationally examined. The reactivities of these halogenated ethenes toward OH radicals were investigated through the combination of DFT and ab initio computations. The rate constants calculated for the OH radical reactions of these halogenated ethenes showed reasonable agreement with the experimentally determined values. Our computational results for the CFCl=CFCl and CHF=CHF ( E)/( Z) isomeric pairs indicated that the rate constants toward OH radicals are larger for the higher-energy geometrical isomers than for the lower-energy counterparts.

Rate Coefficients for the Gas-Phase Reaction of ( E)- and ( Z)-CF3CF═CFCF3 with the OH Radical and Cl-Atom.

The rate coefficients, k, for the gas-phase reaction of the OH radical and Cl-atom with ( E)- and ( Z)-CF3CF═CFCF3 were measured using a relative rate technique over a range of temperature (240-375 K) and bath gas pressure (50-630 Torr, He). The obtained rate coefficients were found to be independent of pressure under these conditions. The obtained rate coefficients for the reaction of Cl-atom with ( E)- and ( Z)-CF3CF═CFCF3 at 296 K were k1(296 K) = (7.23 ± 0.3) × 10-12 cm3 molecule-1 s-1 and k2(296 K) = (6.70 ± 0.3) × 10-12 cm3 molecule-1 s-1, respectively, with the temperature dependence described by the Arrhenius expressions: k1( T) = (3.47 ± 0.35) × 10-12 exp[(210 ± 25)/ T] cm3 molecule-1 s-1 and k2( T) = (3.37 ± 0.35) × 10-12 exp[(199 ± 25)/ T] cm3 molecule-1 s-1. The rate coefficients for the OH radical reaction with ( E)- and ( Z)-CF3CF═CFCF3 were found to be k3(296-375 K) = (4.34 ± 0.45) × 10-13 cm3 molecule-1 s-1 and k4(296-375 K) = (3.30 ± 0.35) × 10-13 cm3 molecule-1 s-1, respectively. The quoted rate coefficient uncertainties are 2σ (95% confidence level) and include estimated systematic errors. The rate coefficients for the reaction of OH with a mixture of the two stereoisomers were determined using a pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) technique for comparison with previous kinetic measurements using stereoisomer mixtures. The effective rate coefficient for the 0.7/0.3 ( E)/( Z) stereoisomer sample was found to be nearly independent of temperature over the range 222-375 K with a value of (4.47 ± 0.36) × 10-13 cm3 molecule-1 s-1. The atmospheric lifetimes for ( E)- and ( Z)-CF3CF═CFCF3 due to OH-reactive loss are estimated to be 25 and 35 days, respectively. The lifetime-corrected radiative efficiencies (W m-2 ppb-1) and 100 year time horizon global warming potentials derived in this work are 0.05 and 1.2 for ( E)-CF3CF═CFCF3 and 0.13 and 4.1 for ( Z)-CF3CF═CFCF3. The photochemical ozone creation potentials for ( E)- and ( Z)-CF3CF═CFCF3 are estimated to be 2.5 and 2.1, respectively.

The mechanism and kinetics of the gas-phase reactions of OH radicals with O,O-diethyl methylphosphonothioate, (C2H5O)2P(S)CH3: Theoretical investigations

In this research, the kinetics of bimolecular reaction of O,O-diethyl methylphosphonothioate (DEMPT) with OH radical is investigated theoretically. First, the mechanism of the reaction of OH radical with DEMPT is explored some by well-tested density functional methods. Next, the rate constants for different reaction pathways are calculated by statistical rate theories. The results are compared with available experimental data. The present calculations reveal that in the most favorable reaction pathway, the reaction proceed through a relatively deep complex due to the hemi-bond between OH radical and sulphur atom of DEMPT leading to the product (C2H5O)(OH)P(S)CH3+C2H5O. Other product channels have minor contribution to overall reaction rate. The present theoretical rate coefficients are in accord with the available empirical data. Based on the predicted rate coefficients, the tropospheric lifetime of DEMPT is estimated to be about 50 min.

Modeling of a DBD plasma reactor for porous soil remediation

A Dielectric Barrier Discharge (DBD) plasma multiscale simulator has been developed, addressing key mechanisms of soil remediation with characteristic time scales ranging from nanoseconds to minutes in a hierarchical approach. The simulated microscopic DBD plasma processes were linked to the macroscopic remediation modeling through the local species concentrations. A complex, 100 species-based reaction set was implemented in the plasma simulator for the calculation of the concentrations of highly reactive species produced in pertinent operational conditions. These species concentrations were extracted from the microscopic plasma process in the nanoseconds time scale, and introduced as source terms for the solution of the macroscopic problem. In addition, an effective mobility term was introduced to capture the structure effect of the soil medium on the plasma process. The momentum, mass, and energy transport phenomena were modeled and used to predict the degradation rate of atrazine pollutant as a function of specific key reactive molecules, namely, O3 and OH radicals. The activity of these species was examined under different working scenarios, providing valuable information for the remediation process. A wide range of flow rate scenarios were examined, showing that the air velocity influences the remediation process significantly. Another case study involved the application of several sandy soil materials with varying porosity and permeability values, and assessed their impact on the degradation rate. This model analysis was accompanied with experimental data, which were used as reference and validation points for the numerical investigation. Improved operational conditions for the DBD reactor were suggested for the case of atrazine degradation.

Laser-induced fluorescence of the CHFCHO radical and reaction of OH radicals with halogenated ethylenes.

A new laser-induced fluorescence spectrum of the 2-fluorovinoxy (CHFCHO) radical was first observed around 335 nm. The radical was produced in the reaction of an OH radical with 1,2-difluoroethylene (CHF=CHF). A single weak band was observed, which was assigned to the 00 0 band of the B̃-X̃ transition of the trans-CHFCHO radical. The B̃←X̃ electronic transition energy (T0) for trans-CHFCHO was 29 871 cm-1, which was just 3 cm-1 lower than that of its isomer, the 1-fluorovinoxy (CH2CFO) radical. The fluorescence lifetime at 29 871 cm-1 was shorter than 20 ns. This means that strong predissociation is probable at v' = 0 in the excited B̃ state of trans-CHFCHO. From an analysis of the dispersed fluorescence spectrum, some of the vibrational frequencies can be assigned for the ground electronic state: ν3 = 1557 cm-1 (C-O stretch), ν7 = 1162 cm-1 (C-C stretch), and ν8 = 541 cm-1 (CCO bend). These vibrational assignments were supported by ab initio calculations. The structure of the C-C-O skeleton and the spectroscopic character of trans-CHFCHO were close to those of CHClCHO and CH2CHO than those of CH2CFO. For the reaction of CH2=CHF with O(3P), the formation of both the regioisomeric radicals, i.e., 1- and 2-fluorovinoxy radicals, was confirmed. The regioselectivity of the oxygen atom added to the double bond of monofluoroethylene is discussed.

Photo-Oxidation Reaction Kinetics and Mechanistics of 4-Hydroxy-2-butanone with Cl Atoms and OH Radicals in the Gas Phase.

The temperature-dependent rate coefficients for the gas-phase reaction of 4-hydroxy-2-butanone (4H2BN) with Cl atoms and OH radicals were explored experimentally using relative rate technique and computational methods. The concentrations of the reactants as well as products were followed using gas chromatography (GC) with the flame ionization detector, GC/mass spectrometry, and GC/infrared spectroscopy as analytical techniques. Formaldehyde was obtained as the major product during the title reaction. The kinetics of 4H2BN with Cl atoms and OH radicals were measured over the temperature range of 298-363 K at 760 Torr in the N2 atmosphere using C3H8, C2H4, isopropanol, and n-propanol as reference compounds. The temperature-dependent rate coefficients for the reaction of 4H2BN with Cl atoms and OH radicals were obtained as kExpt( T) = [(1.52 ± 0.86) × 10-26] T5 exp[(2474 ± 450)/ T] cm3 molecule-1 s-1 and kexpt( T) = [(2.09 ± 0.24) × 10-12] exp[-(409 ± 15)/ T] cm3 molecule-1 s-1, respectively. Theoretical calculations were carried out at the M062X/6-31G(d,p) and M06-2X/6-31+G(d,p) level of theories, and the rate coefficients for H abstraction reactions were evaluated using the canonical variational transition state theory with the inclusion of small-curvature tunneling correction over the temperature range of 200-400 K. The rate coefficients obtained over the studied temperature range were used to fit the data, and the Arrhenius expression was obtained to be kCl(Theory) (200-400 K) = (6.10 × 10-25) T4.42 exp(2397/ T) cm3 molecule-1 s-1, kOH(Theory) (200-400 K) = (1.13 × 10-19) T2.27 exp(1505/ T) cm3 molecule-1 s-1, respectively, for the reactions of Cl atoms and OH radicals with 4H2BN. The possible reaction mechanism proposed based on the obtained products for the title reaction, thermochemistry, branching ratios, and atmospheric implications and cumulative lifetime of 4H2BN were also explored in this study.

Seasonal variations of NPAHs and OPAHs in PM2.5 at heavily polluted urban and suburban sites in North China: Concentrations, molecular compositions, cancer risk assessments and sources

16 nitrated polycyclic aromatic hydrocarbons (NPAHs) and 5 oxygenated polycyclic aromatic hydrocarbons (OPAHs) in PM2.5 at two locations in Northern China were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). Sampling was conducted at an urban site in Shandong University in Jinan (SDU) and a suburban site in Qixingtai in Jinan (QXT) in March, June, September and December in 2016. Overall, the concentrations of NPAHs and OPAHs were higher at SDU (1.88 and 9.49 ng/m3, respectively) than QXT (1.57 and 6.90 ng/m3, respectively), and the NPAHs and OPAHs concentrations were significantly higher during the winter than the other seasons at both sites. The incremental lifetime cancer risk (ILCR) values were lower than 10−6 for all sites, seasons and age groups (ranging between 1.85E-08 and 2.56E-07), so there was no risk of carcinogenesis due to exposure to these pollutants. Total cancer risk at SDU was higher than QXT and NPAHs have the highest carcinogenic risk for adults aged from 30 to 70 years. The positive matrix factorization (PMF) results revealed that coal/biomass combustion, diesel vehicle emissions, gasoline vehicle emissions and secondary formation were the main sources of NPAHs and OPAHs at SDU and QXT. Coal/biomass combustion contributed more in spring, autumn and winter; diesel vehicle emission contributed the most in summer; secondary formation made greatest contributions in winter; the contributions of gasoline vehicle emission were similar in summer, autumn and winter. Diagnostic ratios clearly demonstrated that secondary formation is more active in winter than in other seasons, and the reactions of PAHs and OH radical were the dominant secondary formation pathway at both SDU and QXT. In addition, the potential source contribution function (PSCF) identified that the Beijing-Tianjin-Hebei region, Shandong province, Bohai Sea, Yellow Sea, Anhui province and Henan province were the main source regions of NPAHs and OPAHs in Jinan.

Can a single water molecule catalyze the OH+CH2CH2 and OH+CH2O reactions?

The reaction of OH radicals with ethylene (CH2CH2) and formaldehyde (CH2O) molecules with and without water have been investigated using ab initio/DFT potential energy surfaces (PESs) at CCSD(T)/aug-cc-pVTZ//BHandHLYP//aug-cc-pVTZ levels of theory. The rate coefficients for the bimolecular reaction pathways OH + CH2X···H2O (X = CH2, O) and CH2X + H2O⋯HO were calculated using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) correction. The kinetic results show that OH radical adds to C=C bond in CH2CH2, and abstract the hydrogen atoms from CH2O, similar to its isoelectronic analogous OH + CH2NH (+H2O) reaction. The catalytic effect of a single water molecule on OH + CH2X (X = CH2, O) reaction system shows that the initial water complexation step is essential in the rate coefficients calculation. The calculated rate coefficient for the OH + CH2CH2(+H2O) reaction at 300K is 6 × 10−16 cm3 molecule−1 s−1 and for OH + CH2O(+H2O) reaction at 300K is 8.1 × 10−14 cm3 molecule−1 s−1. The rate coefficient for OH + CH2CH2(+H2O) reaction is at least two orders of magnitude smaller than OH + CH2NH(+H2O) reaction (at 300K is 5.1 × 10−14 cm3 molecule−1 s−1) and rate coefficient for OH + CH2O reaction is in good agreement with OH + CH2NH reaction. In general, the rate coefficients for OH + CH2X (X = CH2, O)⋯H2O and for CH2X + H2O⋯HO reactions are ∼3–4 orders of magnitude smaller than reaction without water molecule. Our results predict that catalytic effect of single water molecule on OH + CH2CH2 and OH + CH2O reactions can make a negligible contribution to the gas phase removal of CH2CH2 and CH2O by OH radicals because the dominated water-assisted process depends parametrically on water concentration. As a result, the overall reaction rate coefficients are smaller. The present results provide a better understanding of gas phase catalytic effect of a water molecule on the most important atmospheric and combustion reaction prototypes.

Oxidation reaction mechanism and kinetics between OH radicals and alkyl-substituted aliphatic thiols: OH-addition pathways

Kinetic rate constants for the oxidation reactions of OH radicals with CH3SH (1), C2H5SH (2), n-C3H7SH (3) and iso-C3H7SH (4) under inert conditions (Ar) over the temperature range 252−430 K have been studied using the CBS-QB3 composite method. Kinetic rate constants under atmospheric pressure and in the fall-off regime have been estimated using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Comparison with experiment confirms that in the OH-addition pathways 1−4 leading to the related products, the first bimolecular reaction step has effective negative activation energies around −2.61 to 3.70 kcal mol−1. Effective rate coefficients have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a result of the negative activation energies, pressures larger than 104 bar would be required to restore to some extent the validity of this approximation for all the channels. By comparison with experimental data, all our calculations for both the OH-addition and H-abstraction reaction pathways indicate that from a kinetic viewpoint and in line with the computed reaction energy barriers, the most favourable process is the OH-addition pathway to n-C3H7SH to yield the [ n-C3H7SH−OH]• species, whereas under thermodynamic control of the bimolecular reactions (R−SH+OH•), the most abundant product derived from the H-abstraction pathway will be the [ n-C3H7 S•+H2O] species.

Kinetics and mechanisms of the gas-phase reactions of OH radicals with three C15 alkanes

The reaction constants and products for the reactions of OH radicals with different C15 alkanes, were determined by using Proton-Transfer-Reaction Mass Spectrum (PTR-MS) in the smog chamber. Rate coefficients (in units of 10−11 cm3 molecule−1 s−1) k1(pentadecane) = 1.72 ± 0.18,k2(2,6,10-trimethyldodecane) = 1.90 ± 0.20, k3(nonylcyclohexane) = 2.09 ± 0.22 were first obtained by the relative rate method using toluene and m-xylene as reference compounds at (298 ± 1)K and atmospheric pressure. In addition, the products of these reactions were measured by PTR-MS simultaneously. The results show that the major gas phase products observed in the OH radicals reactions were aldehydes and ketones for C15 alkanes. The possible reaction mechanisms were speculated and the atmospheric implications were also discussed.

Layered double hydroxide derived ultrathin 2D Ni-V mixed metal oxide as a robust peroxidase mimic

Herein, we first show that layered double hydroxide derived ultrathin 2D Ni-V mixed metal oxide (MMO) nanosheets with thickness of sub-10 nm exhibit an robust peroxidase (POx) mimic activity, accelerating H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a color reaction. The effect of varying the Ni/V molar ratio and heating temperature on the POx mimic activity and physicochemical properties of Ni-V MMOs has also been investigated in detail. Ni-V MMO is composed of NiO and Ni3V2O8 and under optimized conditions, Ni3V2O8 nanoparticles with particle size of sub-5 nm are well dispersed on the 2D NiO nanosheet matrix. Ni-V MMO with a Ni/V molar ratio of 3:1 calcinated at 400 °C shows best POx mimic activity. The catalytic mechanism was analyzed by electron spin resonance spectroscopy, which suggested that the enzyme mimic activities of Ni-V MMO originated from the decomposition of H2O2 to generate reactive OH radicals. Kinetic analysis indicates typical Michaelis-Menten catalytic behavior. The findings were used to design a colorimetric assay for H2O2, best measured at 652 nm. The method has a linear response in the 10–100 mM H2O2 concentration range, with a 5.7 mM detection limit. Benefitting from the high dispersibility and high specific surface area of the ultrathin 2D nanosheets, the method is well reproducible. It’s also easily performed and highly specific. The current work can provide new strategies to construct novel LDH derived nanoenzymes for biosensor, biotechnology, and biomedicine.

Rate constants and vibrational distributions for water‐forming reactions of OH and OD radicals with thioacetic acid, 1,2‐ethanedithiol and tert‐butanethiol

AbstractReactions of OH and OD radicals with CH3C(O)SH, HSCH2CH2SH, and (CH3)3CSH were studied at 298 K in a fast‐flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10−11 cm3 molecule−1 s−1 for the OD + CH3C(O)SH reaction and (3.8 ± 0.7) × 10−11 cm3 molecule−1 s−1 for the OD + HSCH2CH2SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H2S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C2H5)2S reference reaction, the rate constant for the OD + (CH3)3CSH reaction was estimated to be (3.6 ± 0.7) × 10−11 cm3 molecule−1 s−1. Vibrational distributions of the H2O and HOD molecules from the title reactions are typical for H‐atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.

Rate coefficients for reactions of OH radicals with CH3D, CH2D2, CHD3, and CD4

AbstractFourier transform infrared (FTIR) smog chamber techniques were used to investigate the atmospheric chemistry of the isotopologues of methane. Relative rate measurements were performed to determine the kinetics of the reaction of the isotopologues of methane with OH radicals in cm3 molecule−1 s−1 units: k(CH3D + OH) = (5.19 ± 0.90) × 10−15, k(CH2D2 + OH) = (4.11 ± 0.74) × 10−15, k(CHD3 + OH) = (2.14 ± 0.43) × 10−15, and k(CD4 + OH) = (1.17 ± 0.19) × 10−15 in 700 Torr of air diluent at 296 ± 2 K. Using the determined OH rate coefficients, the atmospheric lifetimes for CH4–xDx (x = 1–4) were estimated to be 6.1, 7.7, 14.8, and 27.0 years, respectively. The results are discussed in relation to previous measurements of these rate coefficients.

Co-oxidation effects and mechanisms between sludge and alcohols (methanol, ethanol and isopropanol) in supercritical water

Sludge is a by-product of wastewater treatment process with high organic and nitrogen contents. Supercritical water oxidation (SCWO) rates of refractory species in sludge might be accelerated by reactive alcohols, which is referred to as a co-oxidation phenomenon. In this work, influences of three typical reactive alcohols (methanol, ethanol and isopropanol) on TOC and of NH3–N removal rates of sludge by SCWO were analyzed and their co-oxidation products were characterized by GC–MS, FT–IR, EDS and TG–DTG methods. Additionally, to capture the nature of co-oxidation, HO2 and OH radicals released by alcohols were theoretically compared with detailed chemical kinetics models using the Chemkin Software. The results show that methanol, ethanol and isopropanol all exhibited co-oxidation accelerated effects on TOC and NH3–N removal rates of sludge. One reason was that alcohols provided reactive HO2 and OH radicals. The other reason was that adding alcohols not only prevented forming recalcitrant products (non-nitrogen and nitrogen aromatic compounds) but also encouraged producing reactive products (non-nitrogen open chain compounds). Ethanol offered the best co-oxidation promotion effects on the removal of TOC and NH3–N in the liquid products and also gave the lowest organic contents in the solid products, followed by isopropanol and methanol. This order was consistent with the difficulty of how the alcohols themselves could be oxidized in supercritical water since ethanol could support the highest amount of HO2 radicals for sludge in the shortest time.