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Limononic acid (3-isopropenyl-6-oxoheptanoic acid, LA), as an important precursor of secondary organic aerosols (SOA), has attracted extensive attention in the field of atmospheric chemistry. However, its microscopic oxidation mechanism is still unclear. In this study, the density functional theory calculations were conducted to study the oxidation mechanism of LA by ·OH in aqueous phase. The results show that the reactions of hydroxylation are more likely to occur than the dehydrogenation reaction, because of the lower free energy barrier (2.3–5.4 kcal mol−1). At 298 K, the total rate constant of the reaction initiated by ·OH is 1.06 × 1010 M−1 s−1, which fits the experimental value well. Among all reactions, the hydroxylation reaction in C 9 site of LA is the most favorable pathway, and the corresponding hydroxylation intermediate (IM4) can react with ·OH, H 2 O, dissolved O 2 , and HO 2 ·. Three important tropospheric free radicals (R·, RO· and RO 2 ·) are generated during the subsequent reaction process. Meanwhile alcohols, ketones, aldehydes, and oxidized acids can be formed in the overall reaction scheme. These products are the precursor for the formation of SOA, and this transformation process will increase the O/C ratio of aqueous phase SOA. This study has an important significance for understanding the oxidation mechanism of monoterpenoids in the atmospheric aqueous phase. [Display omitted] • OH-addition reaction of C 9 site is more like to occur of LA. • The intermediate can react with ·OH, H 2 O, dissolved O 2 , and HO 2. • Three important tropospheric free radicals (R·, RO· and RO 2 ·) are generated during the reaction process. • The transformation process will increase the O/C ratio of aqueous phase SOA. [ABSTRACT FROM AUTHOR]

Diclofenac (DCF) is a widely used non-steroidal anti-inflammatory drug, which has attracted more and more attention due to its biotoxicity and refractory degradation. The objective of this study was to systematically analysis the transformation mechanisms, kinetics and toxicity of DCF initiated by •OH and SO 4 •– in persulfate oxidation process. In this study, the degradation mechanism of DCF has been performed by density functional theory (DFT) methods, and the toxicity of the by-products was studied by computational toxicology. The results show that the reactivity of benzylic position of DCF is higher than that of chlorinated aromatic ring, indicating •OH and SO 4 •– are more likely to react in benzylic position. By comparing the initiation reactions of •OH and SO 4 •–, it was found that •OH-initiations were the predominant pathway in the degradation process. The kinetic calculations show that the degradation rate constants were positively correlated with temperature. Furthermore, the calculated toxicological results indicate that the toxicity level of most products is reduced, but the hydrolysates remain toxic and deserve more attention for the degradation by-products of DCF. The comprehensive theoretical study is helpful to reveal the microscopic mechanism of DCF transformation and AOP-wastewater remediation. [Display omitted] • The degradation mechanisms of DCF by •OH and SO 4 •‾ in aquatic environment were studied by theoretical calculation methods. • The rate constants of DCF with •OH and SO 4 •‾ were calculated. • High temperature is more favorable for the initial degradation of DCF. • The eco-toxicity of degradation by-products decreased, but hydrolysates remain toxic. [ABSTRACT FROM AUTHOR]

In this paper, the degradation mechanism and eco-toxicity assessment of bisphenol S (BPS) was studied in the aqueous environment based on the heterogeneous activation of peroxymonosulfate (PMS) through spinel tricobalt tetraoxide (Co 3 O 4) catalyst using density functional theory (DFT) and computational toxicology methods. The result indicates that (100) and (311) surfaces have the higher proportion of bivalent cobalt, the increase of charge transfer, negative adsorption energy, and the lower surface energy. They can more effectively promote the decomposition of PMS to generate reactive oxide species. When generated oxidants react with BPS, HO•-addition reaction at the ortho -C atom-sites plays a dominant role in the system Co 3 O 4 /PMS. The presence of SO 4 •-, HO•, and O 2 promotes the formation of transformation intermediates and products. The formation pathways of important experimental intermediates hydroquinone, p -hydroxybenzenesulfonic acid, and 3, 4-dihydroxybenzenesulfonic acid are identified. And, some hydroxylation products that are not identified in the experiment are determined. The eco-toxicity evaluation shows that most of the decomposition products are completely harmless or significantly reduced compared to BPS. This study not only provides insights into the degradation mechanism of BPS in Co 3 O 4 /PMS system, but also is expected to be a guide for further experimental research and the design and optimization of the activated catalysts in sulfate radical-based advanced oxidation technologies. [Display omitted] • Co 3 O 4 (100) and (311) surfaces are more effectively promote the PMS decomposition. • The most reactive-site of BPS is the ortho -C atom. • OH.•-initiated plays a dominant role in the degradation process of BPS, not SO 4 •-. • Hydroquinone and p-hydroxybenzenesulfonic acid are important intermediates. • Compared with BPS, most decomposition products are harmless or reduced. [ABSTRACT FROM AUTHOR]

2,6-Di-tert-butyl-hydroxytotulene (BHT), as a significant synthetic phenolic antioxidant (SPA), has received increasing attention in the environmental field. In the present study, the BHT is confirmed to be mainly distributed in the liquid phase in the environment base on the Aspen PLUS simulation results. The mechanism and kinetics of BHT transformation initiated by OH radicals were conducted in aquatic environment using density functional theory (DFT) method. Briefly, seven initiation reactions and three detailed transformation pathways of BHT were reported. The H atoms in the t-butyl and methyl group were found more favorable to be abstracted. The C1 site of the BHT was susceptible to addition by OH radicals. Rate constants of different initial reactions were calculated and they were inhibited by temperature rise. Meanwhile, the acute and chronic toxicities of BHT and its metabolites were evaluated at three different trophic levels using the ECOSAR program. During the degradation process, the toxicities of these metabolites gradually decreased, but the toxicities of the final product 2,6-di-tert-butyl-2,5-cyclohexadien-1,4-dione (BHT-Q) were significantly increased. These results could help to reveal the transformation mechanism and risk assessment of BHT in aquatic environment, and further design the experimental and industrial applications of SPAs. Image 1 • Aspen PLUS simulation was used to clarify that more than 90% of the BHT in the environment exist in liquid phase. • This study demonstrated that BHT was more easily oxidized on p-methyl group to generate metabolites. • The product BHT-Q has strong toxicity to aquatic ecosystem. BHT is easily oxidized by OH radicals in aquatic environment to form BHT-CHO, BHT-Q and other metabolites that are more harmful to the aquatic environment. [ABSTRACT FROM AUTHOR]

Terbutaline (TBL, an β-agonists pharmaceuticals) is one of the pharmaceuticals and personal care products (PPCPs), which has caused many environmental concerns due to its eco-toxicological effects in aquatic environment. In this research, density functional theory (DFT) and quantitative structure–activity relationships (QSARs) toxicity methods were performed to systematically elucidate the transformation mechanisms and ecological risk of TBL degraded by •OH and O 3. By analyzing the structure and electronic properties of TBL, the •OH-addition, H-abstraction, single electron transfer and 1, 3-cycloaddition ozonation degradation pathways were mainly investigated. The lowest energy barriers of •OH and O 3 initiated reactions in the degradation process were 7.33 and 18.49 kcal mol−1 respectively, which indicated that the •OH degradation process was more likely to occur than O 3 induced reactions from a thermodynamic perspective. The kinetic rate constants of O 3 and •OH at 298 K were calculated as 7.58 M−1 s−1 and 1.02 × 109 M−1 s−1, respectively. Furthermore, the subsequent intermediates could further transform into hydroxylation substitutes, glyoxylic acid and ketoaldehyde by-products. Based on toxicity assessments, parent reactant TBL can exhibit harmful acute and chronic toxicity to daphnid (identified by LC 50 33.2 mg L−1 and ChV 2.34 mg L−1). The toxicity of most of the degradation products was reduced to harmless level compared with the parent reactant TBL. This work provided a molecular level understanding for evaluating the contribution of O 3 and •OH to the removal of TBL from wastewater by theoretical calculations. [Display omitted] • The degradation mechanisms of terbutaline by.•OH and O 3 in aquatic environment were studied by theoretical calculation methods. • The main degradation mechanism was proposed as an.•OH-addition reaction on the C1 site of aromatic ring of terbutaline. • The calculated total rate constants of.•OH and O 3 -initiated reaction were 1.02 × 109 M−1 s−1 and 7.58 M−1 s−1 during the degradation of terbutaline at 298K. • The eco-toxicity of degradation by-products were changed compared by terbutaline. [ABSTRACT FROM AUTHOR]

In this paper, density-functional theory (DFT) was employed to investigate the reaction mechanism of SO 2 and NO 2 and the important role of intermediate N 2 O 4 formation. In addition, the effect of pure particulate surface (TiO 2) and particulate surface containing other atmospheric components (H 2 O, NH 3 and SO 4 2−) on the conversion of SO 2 and NO 2 to sulfate also was analyzed. The detailed information that intermediate N 2 O 4 acts as the oxidant was demonstrated in this oxidation reaction of SO 2 and NO 2 (as a rate-determining step). The pure particulate surface (TiO 2) has hardly effect on the oxidation process of SO 2 and N 2 O 4. Whereas, different amounts of H 2 O and NH 3 molecules as well as SO 4 2−, contained on the particulate surface, can effectively reduce the activation energy of oxidation step. And, the optimal process is that SO 2 is oxidized by cis-ONONO 2 with the energy barrier of 4.54 kcal/mol when one NH 3 molecule and one H 2 O molecule are contained on the TiO 2 (101) surface. When more H 2 O molecules are contained on particulate surface, SO 2 tends to form HSO 3 − first. However, HSO 3 − is more difficult to be further oxidized by asy-ONONO 2 than SO 2. This study gains more insight into the contribution of SO 2 and NO 2 to haze and the potential impact of atmospheric constituents (including H 2 O/NH 3 /TiO 2 and SO 4 2−/TiO 2) on the formation sulfate. Image 1 • Asy-ONONO 2 acted as oxidant is easily contained on the particulate surface. • The oxidation of SO 2 and asy-ONONO 2 is easy than HSO 3 −. • The oxidation step of SO 2 and N 2 O 4 is the rate-determining step. • Pure particulate surface has hardly effect on the rate-determining step. • Particulate containing H 2 O, NH 3 and SO 4 2− promote the reaction of SO 2 and N 2 O 4. [ABSTRACT FROM AUTHOR]

The important role of reactive chlorine species (RCS) in electrochemical system has been widely concerned for water disinfection recently. In this study, we built an electrochemical system using carbon nanotube as cathode and oxide precursor (Ti/SnO 2 –Sb 2 O 5 –IrO 2) as anode, where RCS was produced from Cl−. This system was used to degrade nitrogen contaminants, i.e. NO 3 − and 4-nitrophenol. Optimization of the reaction conditions was carried out by a treatment of inorganic nitrogen contaminant NO 3 − and the optimal condition of the electrochemical system was determined at U = 5.5 V, and pH = 10 with a Cl− concentration of 2000 mg L−1, and the removal efficiency of NO 3 − can reach up to 60.6% in 150 min. Under the optimal condition, a common nitrogenous organic pollutant, 4-nitrophenol was treated and a removal efficiency of nearly 100% in 90 min. To investigate the detailed degradation mechanism in the applied electrochemical system, a combined method of products identification and density functional theory (DFT) calculation was employed. It concluded that Cl radicals' generation was stimulated was stimulated by the OH radicals after adding Cl− into the electrochemical system. These two radicals jointly promoted the transformation of 4-nitrophenol resulting in the formation of more toxic organic and inorganic substances. In addition, a conversion of organic nitro group to amino group leading to the formation of 4-aminophenol was found and explained by the indirect reduction theory. Image 1 • 4-Nitrophenol can be converted into NO 3 −, NO 2 −, NH 4 + and other inorganic nitrogen. • Adding chloride ions inhibits the formation of NH 4 + transformed from 4-nitrophenol. • The mechanism of converting a nitro group into an amino group is elucidated. • The toxicity of chlorine-containing transformation products of 4-nitrophenol is enhanced. [ABSTRACT FROM AUTHOR]