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Anodic oxidation based on PbO2 anode has been demonstrated as the feasible approach for the decontamination of organic pollutants; however, the performance of this process is hindered by its ordinary electrochemical activity and relatively low stability. In this study, we fabricated an efficient Ti/TiO2-RNTs/Sb-SnO2/PbO2-ND electrode with electrochemically reduced TiO2 nanotubes as the interlayer and nano-diamond as the dopant. As compared with other electrodes, the constructed Ti/TiO2-RNTs/Sb-SnO2/PbO2-ND exhibited higher oxygen evolution overpotential, larger active area and less charge transfer resistance. Thus, the average current efficiency of 30% could be attained at 120 min with TiO2-NTs/Sb-SnO2/PbO2, which was 1.5 times higher in comparison with the typical Ti/Sb-SnO2/PbO2 electrode. It was found that the removal efficiency of COD could be increased from 49% to 69% after 120 min treatment in the presence of 10 mM Cl−1 in the electrolyte. After 6 h of electrolysis, 74% of TOC was removed and 31% and 22% of initial N was transformed into NH4+ and NO3− ions, respectively. And oxalic acid, glyoxylic acid, malonic acid and acetic acid were identified quantitatively as the intermediate products. Finally, it was estimated that the accelerated service life of Ti/TiO2-RNTs/Sb-SnO2/PbO2-ND electrode was approximately three times of Ti/Sb-SnO2/PbO2 electrode. Generally, this study is of great interest for the engineering community to design an efficient electrode material for the wastewater treatment.

It has already been known that oxidative degradation of organochlorine (e.g. chlorophenols) is accompanied by de novo formation of new polychlorinated compounds, however, whether the similar scenario can happen during decomposition of iodine-containing pollutants is completely unknown. Here degradation of two iodinated X-ray contrast media (ICM), iomeprol and iohexol, by sulfate radical generated through Co(II)-mediated activation of peroxymonosulfate (PMS) was investigated. The influencing parameters, such as the initial concentrations of PMS and Co(II), the initial solution pH and natural water constituents were examined. The pseudo-first-order rate constant of iomeprol in the PMS/Co(II) system is more than twice of iohexol, with values of 7.7 × 10−2 and 3.5 × 10−2 min−1, respectively, indicating that iomeprol seems more susceptible to radicals attack than iohexol. The bimolecular rate constants for reaction of sulfate radical (SO4•−) with ICM were determined to be 1.8 × 1010 M−1 s−1 and 7.9 × 109 M−1 s−1 for iomeprol and iohexol, respectively. The low degrees of mineralization and identification of iodinated intermediates of iomeprol and iohexol indicate that the degradation of iomeprol and iohexol in the Co/PMS system were incomplete. A de novo formation of new polyiodinated compounds would not happen because most of released inorganic iodine were ultimately oxidized to iodate (IO3−), rather than the reactive iodinated agents. Based on the identified byproducts and quantum chemical calculation, eight main transformation pathways are proposed for the degradation of iomeprol and iohexol as follows: (a) deiodination; (b) hydrogen abstraction; (c) amide hydrolysis; (d) amino oxidation; (e) hydroxyl substituent; (f) transformed alkyl aromatic amides to aromatic carbamoyl; (g) dehydration; (h) oxidized primary alcohol groups to carboxyl groups.

4-(2-Methoxyethyl) phenol (MEP) is an significant methoxypheolic compound, which has been shown to play an important role in the formation of secondary organic aerosols(SOA). The present work focuses on the gas-phase oxidation mechanism and kinetics of MEP and OH radical by the density functional theory (DFT). Energetically favourable reaction channels and feasible products were identified. The initial reactions of MEP with OH radical have two different channels: OH addition and H abstraction. Subsequent reaction schemes of main intermediates in the presence of O2 and NOx are investigated using quantum chemical methods at M06-2X/6-311++G(3df,2p)//M06-2X/6-311+G(d,p) level. Ketene, Phenyldiketones and nitrophenol compounds are demonstrated to be possible oxidation products. The total rate constant(1.69×10-11 cm3 molecule-1 s-1) and individual rate constant are calculated using the traditional transition state (TST) theory at 298K and 1atm. The lifetime of MEP is estimated to be 16.4 hours, which provides a comprehensive explanation for atmospheric oxidation pathway of MEP and shows MEP would be removed by OH radical in the atmosphere.

The mechanism and kinetic for the reaction of Pyrrole + O(3P) has been investigated using CCSD(T)//M06-2X method with multichannel RRKM-TST calculation. On the triplet surface, four product channels corresponding to α-C-addition, β-C-addition, N-addition and direct H-abstraction have been characterized for the first time. The rate constants and branching ratios for twelve product channels are calculated. It is predicted that the total rate coefficients vary with temperature, and exhibit strong positive temperature dependence. Moreover, the total rate coefficients are independence pressure. On the singlet surface, the atomic oxygen can easily add to the C C double bond or the N atom of Pyrrole forming intermediate s-IM1or s-IM2; both approaches were found to be barrierless. It is indicated that the singlet reaction exhibits a marked difference from the triplet reaction. This calculation is useful to simulate experimental investigations of the Pyrrole + O reaction in the singlet surface.

Mechanisms and channels of the C2H5O2 + ClO reaction in atmosphere were investigated using quantum chemistry method, i.e., CCSD(T)/6-311++G(2d,2p)//B3LYP/6-311++G(d,p) levels of theory. Our result indicates that the title reaction occurs on both the singlet and triplet potential energy surfaces (PESs). Kinetically, C2H5O3Cl and C2H5O + ClOO on the singlet PES were dominant in atmosphere; while other products including CH3CHO2 + HOCl, CH3CHO + HOClO, and CH3CHO + HClO2 make minor contributions to overall reaction due to high barriers and unstable formations. Moreover, time-dependent density functional theory (TDDFT) calculation on the vertical excitation energy implies that C2H5O3Cl will photolyze under the sunlight.

2,2′,4,4′,5,5′-hexabrominated diphenyl ether (BDE-153) and its OH radical addition products are considered potentially harmful to ecological systems. Therefore, the oxidation reactions mechanisms of BDE-153 initiated by OH radical, the reaction kinetics and the ecotoxicity of BDE-153 assessment in the gas and the aqueous phase were investigated using quantum chemical methods. It is more feasible for the OH radical to add at the nonbromine substituted carbon atoms of the aromatic ring in the BDE-153 molecule to create OH addition intermediates. The secondary reactions involving OH addition intermediates in the presence of O2/NO would generate preferred tribromophenol and OH-addition products. Most of the transformation products are still toxic to aquatic organisms. The total and individual rate constants were evaluated by using the KiSThelP program in a suitable temperature range (198–338 K) and a pressure of 1 atm. At 298 K and 1 atm, the total rate constants in atmosphere and wastewater are 2.90 × 10-13 cm3 molecule-1 s−1 and 9.61 × 106 M−1 s−1, and the half-lives are 39.9 days and 72.1–7.21 × 1010 s, respectively. The implicit and explicit solvent models were used to examine the solvent effect on the total reaction. These results clarify the transformation mechanism, atmospheric fate, and ecotoxicity of BDE-153 in advanced oxidation processes. The calculations provided a basis for designing experimental and industrial applications of BDE-153.

Singlet and triplet potential energy surfaces for the CH3O2 with H reaction have been investigated computationally to propose the reaction mechanisms and possible products. On the singlet PES, addition-dissociation was located. At 3.65 Torr with He as bath gas, the formation of CH2O + H2O channel is dominated at the whole temperature range. Furthermore, the predicted rate constants for k CH 2 O + H 2 O at 298 K 3.65 Torr of He agree well with the available experimental values. The pathways on the triplet PES will not compete with the pathways on the singlet PES in kinetically.

Catalytic dehydration and dehydrogenation reactions of ethanol have been investigated systematically using the ab initio quantum chemistry methods The catalysts include water, hydrogen peroxide, formic acid, phosphoric acid, hydrogen fluoride, ammonia, and ethanol itself. Moreover, a few clusters of water and ethanol were considered to simulate the catalytic mechanisms in supercritical water and supercritical ethanol. The barriers for both dehydration and dehydrogenation can be reduced significantly in the presence of the catalysts. It is revealed that the selectivity of the catalytic dehydration and dehydrogenation depends on the acidity and basicity of the catalysts and the sizes of the clusters. The acidic catalyst prefers dehydration while the basic catalysts tend to promote dehydrogenation more effectively. The calculated water-dimer catalysis mechanism supports the experimental results of the selective oxidation of ethanol in the supercritical water. It is suggested that the solvent- and catalyst-free self-oxidation of the supercritical ethanol could be an important mechanism for the selective dehydrogenation of ethanol on the theoretical point of view.

Methyl iodine (CH3I) and carbon tetrachloride (CCl4) are both important volatile precursors for atmospheric ozone destruction. CH3I and CCl4 can act as halogen bond donors to form molecular complexes with atmospheric organic species, such as 2,5-dihydrofuran, tetrahydrofuran, and acetone. This study characterized the halogen bonds in the CH3I and CCl4 complexes using matrix isolation infrared spectroscopy and density functional theory calculations. With the combination of vibrational frequencies in spectra and the calculated interaction energies, frequencies and atoms-in-molecules analyses, we confirmed the formation of halogen-bonded complexes. CH3I as a halogen-bond donor is comparable or slightly weaker than CCl4, and furans involving ether oxygens are better halogen acceptors than acetone. The results help to understand the possibilities of formation of atmospheric molecular complexes that may influence the atmospheric chemical activities and enhance the aerosol formation.

The mechanism of the reaction of Methylidyne Radical (CH) with acetaldehyde (CH 3 CHO) has been investigated using CBS-QB3//B3LYP/aug-cc-pVTZ method. The initial CH + CH 3 CHO reaction is a barrierless process, forming a linear intermediate, CH 3 CHOCH, which can be converted into several products. The microscopic mechanism recommended by the present study not only identifies the products observed by previous experimental studies but also explains the isotopic effects (CH/CCD) observed experimentally. In view of the calculated energies, C 2 H 5 + CO is the most exothermic product pair, additionally, the energy barrier of this product channel is the lowest. Concerning the hydrogen elimination channel, acrolein (CH 2 CHCHO) and methylketene (CH 3 CHCO) are preferable co-products. Furthermore, a new product channel, C 2 H 3 + CH 2 O, has been discovered.

Using BMC-CCSD//B3LYP/6-311G(d,p) levels of theory, the mechanisms and kinetics of the OH + (CH3)2NNH2 reaction in atmosphere were investigated theoretically. The result indicates that both H-abstraction and substitution mechanisms are located, and the former one is dominant. Moreover, the product of (CH3)2NNH + H2O is more favorable than CH3N(CH2)NH2 + H2O in the H-abstraction mechanism. The calculated total rate constant shows negative temperature dependence below 500 K. It is in accordance with experimental study that slightly negative temperature dependence was found between 254 and 633 K. Moreover, the calculated rate constant shows significance variational effect from 200 to 3000 K, and methyl substitution effect plays an important role in the OH + (CH3)nNH2−nNH2 (n = 0,1 and 2) reactions.

The mechanism and kinetics for the O( 3 P) + CH 3 CH CHCN reaction has been investigated firstly. The BHandHLYP and M05-2X methods were employed to obtain the initial geometries. The triplet/singlet potential energy surfaces (PESs) were constructed with high-level BMC-CCSD method. The conventional transition-state theory (CTST) and multichannel RRKM theory were employed to calculate the total and individual rate constants over a wide range of temperatures under high-pressure limit. Our computed rates agree well with the available experimental results. The yield of IM1 is 0.9–0.5 from 200 to 1000 K, and the construction of h-P1(OH + CH 2 CHCHCN) is 0.42 at 2000 K under high-pressure limit. The yields of the predicted decomposition products P1(CH 3 + HCOHCCN), P2(HCCN + CH 3 CHO) and P3(H + CH 3 COHCCN) at 298 K and 1 atom are 0.81, 0.07, and 0.09, respectively.

In order to understand the thiophene with hydroxyl reaction mechanism and kinetics, we carried out a detailed potential energy surface (PES) on the title reaction at the M06-2X/6-311++G(d,p) and G3(MP2) (single-point) levels. Two possible reaction mechanisms including addition-elimination and H-abstract were revealed. The hydrogen abstraction of thiophene by OH produces H 2 O along with the 2-thienyl (h-P1) or 3-thienyl (h-P2) radicals via a barrier of 7.9 and 2.2 kcal/mol, respectively. The addition of OH to the carbon atoms of the thiophene ring (at either α or β reaction sites) proceeds to intermediates IM1 and IM2 via barrier of 3.4 and 4.7 kcal/mol, and then decompose to the final products, respectively. Multichannel RRKM calculations have been carried out for the total and individual rate constants for all the channels over a wide range of temperatures and pressures. At atmospheric pressure with Ar, N 2 and He as bath gases, IM1 formed by collisional stabilization is dominated at T ⩽ 600 K, whereas P1 produced by addition/elimination pathway are the major products at the temperatures between 700 and 1000 K; the direct hydrogen abstraction leading to H 2 O with 3-thienyl (h-P2) plays an important role at higher temperatures.

Using QCISD(T)//B3LYP methods, mechanisms and pathways of the atmospheric C 2 H 5 O 2 + IO reaction was investigated theoretically. The result indicates that the title reaction proceeds on both singlet and triplet potential energy surfaces. It is speculated that C 2 H 5 O + IOO, CH 3 CHO + HIO 2 , CH 3 CHO + HOIO and CH 3 CHO 2 + HOI are dominant for the C 2 H 5 O 2 + IO reaction in the atmosphere. While other products including CH 3 CHO + HOOI, C 2 H 5 O + OIO, C 2 H 5 OIO + O( 3 P), C 2 H 5 OOI + O( 3 P), and C 2 H 5 OI + O 2 are of no importances due to high barriers or unstable products. Moreover, comparisons suggest that halogen and alkyl substitution effects play minor significance in the relative stability of R O 3 X isomers ( R = H, CH 3 , C 2 H 5 ; X = Cl, Br, I).

In this work, using quantum chemistry methods the reactions of Hg and HgO with six organics including methane (CH4), benzene (C6H6), methanol (CH3OH), formaldehyde (HCHO), formic acid (HCOOH) and phenol (C6H5OH) in sludge incineration were investigated. The computational result indicates that Hg reacts with six organics via insertion mechanism to form CH3HgH, CH3OHgH, CH3HgOH, HHgCH2OH, HCOHgH, H2CHgO, HHgCOOH, HOCHHgO, HCOOHgH, HCOHgOH, C6H5HgH, C6H5OHgH, C6H5HgOH, and m-, o-, p-HHgC6H4OH. However, all barriers involved are extremely high and all products are rather unstable, therefore, Hg will be discharged as elements into fuel gas. With extra oxygen supplied Hg could be oxidized to HgO firstly; subsequently, CH3OHgOH, HCOHgOH, HOCOHgOH, C6H5HgOH and o-HOHgC6H4-OH were formed when HgO reacts with above above organics. The corresponding barriers are lower and all products are much more stable, indicating these Hg-contained organic compounds would be generated readily in incineration of sludge. Therefore it is presumed that in presence of oxygen Hg is more active to react with organics in sludge incineration.

The kinetics and mechanisms of the CH2FO2/CHF2O2 with ClO reactions have been investigated firstly by using the quantum chemical method. The single and triplet potential energy surfaces (PESs) of these two reactions have been obtained by using the BMC−CCSD method based on the geometries obtained at the B3LYP/6−311++G(d,p) level. For the CH2FO2 with ClO reaction, three activated intermediates, IM1 (CH2FOOOCl), IM2 (CH2FOOClO), and IM3 (CH2FOClO2) are generated along the reaction path, and then dissociate to various products. The similar production pathways are investigated for the CHF2O2 with ClO reaction. It should be noted that the isomerization of IM3 (CH2FOClO2) and the 1,3-Cl shift from IM1 (CH2FOOOCl) pathways were not found for the CH2FO2 with ClO reaction. The rate constants for the dominant product pathways are predicted by RRKM-TST theories. The major production pathway is the generation of IM1 (CH2FOOOCl)/IM1 (CHF2OOOCl) at 200−1200 K, and the generation of P1 (CHFO + HO2 +Cl)/P1 (CF2O + HO2 + Cl) by H-migration/elimination become dominant at higher temperatures for the CH2FO2/CHF2O2 + ClO reactions, respectively. The atmospheric lifetimes of CH2FO2 and CHF2O2 in ClO are around 11.38 and 8.65 h, respectively. Furthermore, on the basis of the analysis of the kinetics of all channels through which the addition and abstraction reactions proceed, we expect that the competitive power of reaction channels may vary with experimental conditions for the title reaction. The present study may be helpful for probing the mechanisms of the title reaction and understanding the halogen chemistry.

In this work, feasible mechanisms and pathways of the C2H5O2 + BrO reaction in the atmosphere were investigated using quantum chemistry methods, i.e., QCISD(T)/6-311++G(2df,2p)//B3LYP/6-311++G(2df,2p) levels of theory. Our result indicates that the title reaction occurs on both the singlet and triplet potential energy surfaces (PESs). Kinetically, singlet C2H5O3Br and C2H5O2BrO were dominant products under the atmospheric conditions below 300 K. CH3CHO2 + HOBr, CH3CHO + HOBrO, and CH3CHO + HBrO2 are feasible to a certain extent thermodynamically. Because of high energy barriers, all products formed on the triplet PES are negligible. Moreover, time-dependent density functional theory (TDDFT) calculation implies that C2H5O3Br and C2H5O2BrO will photolyze under the sunlight.

The hydroxyl radical, as the most important oxidant, controls the removal of some volatile organic compounds (VOCs) in the atmosphere. In this work, the atmospheric oxidation processes of acrylic acid by OH radical have been investigated by density functional theory (DFT). The energetic routes of the reaction of CH2CHCOOH with OH radical have been calculated accurately at the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level. It is implicated that the oxidation has five elementary reaction pathways mostly hinging on how hydroxyl radical approaches to the carbon skeleton of acrylic acid. The atmospheric degradation mechanisms of the CH2CHCOOH by OH radical are the formation of reactive intermediates IM1 and IM2. Meanwhile, the further oxidation mechanisms of IM1 and IM2 by O3 and NO are also investigated. The rate coefficients have been computed using tight transition state theory of the variflex code. The calculated rate coefficient is 2.3 × 10−11 cm3 molecule−1 s−1 at standard pressure and 298 K, which is very close to the laboratory data (1.75 ± 0.47 × 10−11 cm3 molecule−1 s−1). Moreover, the atmospheric lifetime of acrylic acid is about 6 h at 298 K and 1 atm, implying that the fast sinks of acrylic acid by hydroxyl radical.

Helical structures play essential roles in biological systems and the potential physical and chemical properties. The single-stranded and double-stranded supramolecular helical chains are found in six achiral β-alanine-inorganic-acid (β-AIA) compounds and one achiral β-alanine-organic-acid (β-AOA) compound. The supramolecular helical models of those β-alanine-acid compounds are classified into four types. And, the law of supramolecular assembly of helical chains in β-alanine-acid compounds is also summarized.

The potential-energy surfaces of the amino radical (NH2) with IO reaction have been studied at the CCSD(T)/cc-pVTZ//MP2/6-311++G(d,p) level. Two kinds of pathways are revealed, namely H-abstraction...