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Zheng Y, Yang J, Li M, Zhu Y, Liang J, Yu D, Wang Z, Pei J. Mechanistic insight into the degradation of sulfadiazine by electro-Fenton system: Role of different reactive species. J Hazard Mater 2024; 469:134063. [PMID: 38508112 DOI: 10.1016/j.jhazmat.2024.134063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 03/08/2024] [Accepted: 03/16/2024] [Indexed: 03/22/2024]
Abstract
Sulfadiazine (SDZ), a widely used effective antibiotic, is resistant to conventional biological treatment, which is concerning since untreated SDZ discharge can pose a significant environmental risk. Electro-Fenton (EF) technology is a promising advanced oxidation technology for efficiently removing SDZ. However, due to the limitations of traditional experimental methods, there is a lack of in-depth study on the mechanism of ·OH-dominated SDZ degradation in EF process. In this study, an EF system was established for SDZ degradation and the transformation products (TPs) were detected by mass spectrometry. Dynamic thermodynamic, kinetic and wave function analysis of reactants, transition states and intermediates were proposed by density functional theory calculations, which was applied to elucidate the underlying mechanism of SDZ degradation. Experimental results showed that amino, benzene, and pyrimidine sites in SDZ were oxidized by ·OH, producing TPs through hydrogen abstraction and addition reactions. ·OH was kinetically more likely to attack SDZ- than SDZ. Fe(IV) dominated the single-electron transfer oxidation reaction of SDZ, and the formed organic radicals can spontaneously generate the de-SO2 product via Smiles rearrangement. Toxicity experiments showed the toxicity of SDZ and TPs can be greatly reduced. The results of this study promote the understanding of SDZ degradation mechanism in-depth. ENVIRONMENTAL IMPLICATION: Sulfadiazine (SDZ) is one of the antibiotics widely used around the world. However, it has posed a significant environmental risk due to its overuse and cannot be efficiently removed by traditional treatment methods. The lack of in-depth study on SDZ degradation mechanism under reactive species limits the improvement of SDZ degradation efficiency. Therefore, this work focused on SDZ degradation mechanism in-depth under electro-Fenton system through reactive species investigation, mass spectrometry analysis, and theoretical calculation. The results in this study can provide a theoretical basis for improving the SDZ degradation efficiency which will contribute to solving SDZ pollution problems.
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Affiliation(s)
- Yanshi Zheng
- School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China; Sino-Spain Joint Laboratory for Agricultural Environment Emerging Contaminants of Zhejiang Province, School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China
| | - Jinyan Yang
- School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China; Sino-Spain Joint Laboratory for Agricultural Environment Emerging Contaminants of Zhejiang Province, School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China
| | - Mei Li
- School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China; Sino-Spain Joint Laboratory for Agricultural Environment Emerging Contaminants of Zhejiang Province, School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China
| | - Yingshi Zhu
- Office of Scitech Research, Zhejiang Environment Technology Co., Ltd., Hangzhou 311100, People's Republic of China; Key Laboratory of Biomass Chemical Engineering of Ministry of Education, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Jiayu Liang
- School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China; Sino-Spain Joint Laboratory for Agricultural Environment Emerging Contaminants of Zhejiang Province, School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China
| | - Dehai Yu
- State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, People's Republic of China
| | - Ziyao Wang
- State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, People's Republic of China
| | - Jianchuan Pei
- School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China; Sino-Spain Joint Laboratory for Agricultural Environment Emerging Contaminants of Zhejiang Province, School of Environment and Resources, Zhejiang A&F University, Hangzhou 311300, People's Republic of China.
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Li Y, Zhang RM, Xu X. Theoretical Kinetics studies of isoprene peroxy radical chemistry: The fate of Z-δ-(4-OH, 1-OO)-ISOPOO radical. Ecotoxicol Environ Saf 2023; 266:115553. [PMID: 37839188 DOI: 10.1016/j.ecoenv.2023.115553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 09/19/2023] [Accepted: 10/05/2023] [Indexed: 10/17/2023]
Abstract
The OH radical recycling mechanism in isoprene oxidation is one of the most exciting topics in atmospheric chemistry, and the corresponding studies expand our understanding of oxidation mechanisms of volatile organic compounds in the troposphere and provide reliable evidence to improve and develop conventional atmospheric models. In this work, we performed a detailed theoretical kinetics study on the Z-δ-(4-OH, 1-OO)-ISOPOO radical chemistry, which is proposed as the heart of OH recycling in isoprene oxidation. With the full consideration of its accumulation and consumption channels, we studied and discussed the fate of Z-δ-(4-OH, 1-OO)-ISOPOO radical by solving the energy-resolved master equation over a broad range of conditions, including not only room temperatures but also high temperatures of a forest fire or low temperatures and pressures of the upper troposphere. We found non-negligible pressure dependence of its fate at combustion temperatures (up to two orders of magnitude) and demonstrated the significance of both the multi-structural torsional anharmonicity and tunneling for accurately calculating kinetics of the studied system. More interestingly, the tunneling effect on the phenomenological rate constants of the H-shift reaction channel is also found to be pressure-dependent due to the competition with the O2 loss reaction. In addition, our time evolution calculations revealed a two-stage behavior of critical species in this reaction system and estimated the shortest half-lives for the Z-δ-(4-OH, 1-OO)-ISOPOO radical at various temperatures, pressures and altitudes. This detailed kinetics study of Z-δ-(4-OH, 1-OO)-ISOPOO radical chemistry offers a typical example to deeply understand the core mechanism of OH recycling pathways in isoprene oxidation, and provides valuable insights for promoting the development of relevant atmospheric models.
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Affiliation(s)
- Yan Li
- Center for Combustion Energy, Department of Energy and Power Engineering, and Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China
| | - Rui Ming Zhang
- Center for Combustion Energy, Department of Energy and Power Engineering, and Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China
| | - Xuefei Xu
- Center for Combustion Energy, Department of Energy and Power Engineering, and Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, China.
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Li Z, Zhang W, Chen Z, Ren Z, Ning S, Li M. A kinetics mechanism of NO X formation and reduction based on density functional theory. Sci Total Environ 2023; 867:161519. [PMID: 36639002 DOI: 10.1016/j.scitotenv.2023.161519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Revised: 12/26/2022] [Accepted: 01/06/2023] [Indexed: 06/17/2023]
Abstract
NOX are serious pollutants emitted during combustion, which are greatly harmful to human health and the environment. However, previous studies have not accurately elucidated the NOX conversion mechanism in complicated combustion reactions. To reveal the micro-chemical mechanism of NOX conversion and obtain accurate kinetics data, advanced quantum chemistry methods are employed in this study to systematically explore the pathways of NOX formation and reduction, and determine the new rate coefficients. An energy barrier analysis revealed that during NOX formation (N2 → N2O → NO→NO2), NO is primarily produced by a sequence of reactions (N2 + O → N2O → NO) rather than the traditional reaction (O + N2 → NO+N). Meanwhile, NO2 formation (NO→NO2) largely depends on the O and HO2 radicals, while the active O atom can promote both the formation and destruction of NO2. During NOX reduction (NO2 → NO→N2O → N2), NO2 reduction (NO2 → NO) is closely related to H, CO, and O, whereas CO plays a critical role in NO2 destruction. However, NO reduction (NO→N2O) is unfavourable because of a high energy barrier, while N2O reduction (N2O → N2) is strongly affected by the O atom instead of CO. HONO is mainly formed when NO2 reacts with the HO2 and H radicals, and when NO reacts with OH radicals; thus, HONO consumption largely depends on OH and H radicals. Based on the transition state theory, we obtained new kinetic parameters for NOX conversion, which supplement and correct critical kinetics data obtained from the current NOX model. Performance assessment of the proposed NOX kinetic mechanism reveals that it can improve the existing NOX kinetic mode, which is in good agreement with experimental data.
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Affiliation(s)
- Zehong Li
- Yunnan Key Laboratory of Internal Combustion Engine, Kunming University of Science and Technology, Kunming 650500, China
| | - Wei Zhang
- Yunnan Key Laboratory of Internal Combustion Engine, Kunming University of Science and Technology, Kunming 650500, China.
| | - Zhaohui Chen
- Yunnan Key Laboratory of Internal Combustion Engine, Kunming University of Science and Technology, Kunming 650500, China
| | - Zhaoying Ren
- Faculty of Foreign Languages and Cultures, Kunming University of Science and Technology, Kunming 650500, China
| | - Shuo Ning
- Yunnan Key Laboratory of Internal Combustion Engine, Kunming University of Science and Technology, Kunming 650500, China
| | - Mengting Li
- Yunnan Key Laboratory of Internal Combustion Engine, Kunming University of Science and Technology, Kunming 650500, China
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Marković Z, Komolkin AV, Egorov AV, Milenković D, Jeremić S. Alizarin as a potential protector of proteins against damage caused by hydroperoxyl radical. Chem Biol Interact 2023; 373:110395. [PMID: 36758887 DOI: 10.1016/j.cbi.2023.110395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 01/30/2023] [Accepted: 02/06/2023] [Indexed: 02/10/2023]
Abstract
Alizarin is a natural anthraquinone molecule with moderate antioxidative capacity. Some earlier investigations indicated that it can inhibit osteosarcoma and breast carcinoma cell proliferation by inhibiting of phosphorylation process of ERK protein (extracellular signal-regulated kinases). Several mechanisms of deactivation of one of the most reactive oxygen species, hydroperoxyl radical, by alizarin are estimated: hydrogen atom abstraction (HAA), radical adduct formation (RAF), and single electron transfer (SET). The plausibility of those mechanisms is estimated using density functional theory. The obtained results indicated HAA as the only thermodynamically plausible mechanism. For that purpose, two possible mechanistic pathways for hydrogen atom abstraction are studied in detail: hydrogen atom transfer (HAT) and proton-coupled electron transfer (PCET). Water and benzene are used as models of solvents with opposite polarity. To examine the difference between HAT and PCET is used kinetical approach based on the Transition state theory (TST) and determined rate constants (k). Important data used for a distinction between HAT and PCET mechanisms are obtained by applying the Quantum Theory of Atoms in Molecules (QTAIM), and by the analysis of single occupied molecular orbitals (SOMOs) in transition states for two examined mechanisms. The molecular docking analysis and molecular dynamic are used to predict the most probable positions of binding of alizarin to the sequence of ApoB-100 protein, a protein component of plasma low-density lipoproteins (LDL). It is found that alizarin links the nitrated polypeptide forming the π-π interactions with the amino acids Phenylalanine and Nitrotyrosine. The ability of alizarin to scavenge hydroperoxyl radical when it is in a sandwich structure between the polypeptide and radical species, as the operative reaction mechanism, is not significantly changed concerning its antioxidant capacity in the absence of polypeptide. Therefore, alizarin can protect the polypeptide from harmful hydroperoxyl radical attack, positioning itself between the polypeptide chain and the reactive oxygen species.
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Affiliation(s)
- Zoran Marković
- Institute for Information Technologies, Department of Science, University of Kragujevac, Jovana Cvijića bb, 34000, Kragujevac, Serbia; Department of Natural Science and Mathematics, State University of Novi Pazar, Serbia.
| | - Andrei V Komolkin
- Faculty of Physics, Department of Nuclear-Physics Research Methods, St. Petersburg State University, Saint Petersburg, Russia
| | - Andrei V Egorov
- Faculty of Physics, Department of Nuclear-Physics Research Methods, St. Petersburg State University, Saint Petersburg, Russia
| | - Dejan Milenković
- Institute for Information Technologies, Department of Science, University of Kragujevac, Jovana Cvijića bb, 34000, Kragujevac, Serbia
| | - Svetlana Jeremić
- Department of Natural Science and Mathematics, State University of Novi Pazar, Serbia.
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Huang R, Cao H, Huang T, Li H, Tang Q, Wang L, Zheng X. Effects of environmental factors on the fleroxacin photodegradation with the identification of reaction pathways. Chemosphere 2022; 308:136373. [PMID: 36113649 DOI: 10.1016/j.chemosphere.2022.136373] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2022] [Revised: 08/19/2022] [Accepted: 09/05/2022] [Indexed: 06/15/2023]
Abstract
The abuse of fluoroquinolones (FQs) antibiotics leads to bacterial resistance and environmental pollution, so it is of great significance to verify the decomposition mechanism for eliminating antibiotic efficiently and conveniently. The effects of various environmental factors and the fleroxacin (FLE) photodegradation mechanisms were investigated by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS), UV-Vis absorption spectroscopy, fluorescence spectroscopy and quantum chemical calculation. Six possible photodegradation reaction paths on T1 (excited triplet state) were proposed and simulated. The departure of the piperazine ring and the substitution of F atom at C-6 position by OH group were determined as the main reactions based on the reaction rates and energy barriers of each path. The multi-pathway reactions resulted in the fastest photodegradation rates of FLE at pH 6-7 than other pH conditions. NaN3 would promote FLE photodegradation by inhibiting the reverse reaction of the separation process of F atom at C-8 and the generation of biphenyl molecules, which was a novel and distinctive phenomenon in this report. ·OH would rapidly combine with the free radicals generated in photolysis processes and made a great contribution to FLE photodegradation. Ca2+, Mg2+ and Ba2+ could stabilize the carboxyl group to impede the photo-competitive process of the decarboxylation reaction, while NO3- could generate reactive oxygen species to promote photodegradation.
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Affiliation(s)
- Ruisi Huang
- College of Environmental and Chemical Engineering, Dalian University, Dalian, 116622, China
| | - Hongyu Cao
- College of Life Science and Biotechnology, Dalian University, Dalian, 116622, China; Liaoning Key Laboratory of Bio-Organic Chemistry, Dalian University, Dalian, 116622, China.
| | - Ting Huang
- College of Environmental and Chemical Engineering, Dalian University, Dalian, 116622, China
| | - Hongjiang Li
- College of Environmental and Chemical Engineering, Dalian University, Dalian, 116622, China.
| | - Qian Tang
- College of Life Science and Biotechnology, Dalian University, Dalian, 116622, China; Liaoning Key Laboratory of Bio-Organic Chemistry, Dalian University, Dalian, 116622, China
| | - Lihao Wang
- College of Environmental and Chemical Engineering, Dalian University, Dalian, 116622, China
| | - Xuefang Zheng
- College of Environmental and Chemical Engineering, Dalian University, Dalian, 116622, China; Liaoning Key Laboratory of Bio-Organic Chemistry, Dalian University, Dalian, 116622, China.
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Mousavi SE, Younesi H, Bahramifar N, Tamunaidu P, Karimi-Maleh H. A novel route to the synthesis of α-Fe2O3@C@SiO2/TiO2 nanocomposite from the metal-organic framework as a photocatalyst for water treatment. Chemosphere 2022; 297:133992. [PMID: 35247450 DOI: 10.1016/j.chemosphere.2022.133992] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 02/03/2022] [Accepted: 02/11/2022] [Indexed: 06/14/2023]
Abstract
In this study, an attempt was made to synthesize metal-organic frameworks (MOFs) based magnetic iron particles as photocatalysts for textile dye wastewater. Improvement strategy was a novel two-step dry method without using conventional methods to eliminate the consumption of chemical reagents. First, the heterogeneous photocatalyst of Fe-MOFs derived magnetic carbon nanocomposite with carboxylic acid surface functional groups (Fe@C-COOH) was achieved. Next, the α-Fe2O3@C@SiO2/TiO2 was successfully synthesized followed by a sol-gel method to coat the SiO2 shell and a solvothermal method to coat the surface of the intermediate TiO2 particles. The as-synthesized nanocomposite materials were characterized and physicochemical analytical equipment. Further, the investigation on magnetic photocatalytic nanocomposite α-Fe2O3@C@SiO2/TiO2 performance of dye degradation and photocatalytic activity on Reactive yellow 145 (RY145), using as an indicator was conducted. The as-synthesized nanocomposite particles were characterized using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), X-ray energy dispersive spectroscopy (EDX), and scanning electron microscopy (SEM) techniques. The structural characterization of the as-synthesized materials proved that these methods generate oxygen-containing functional groups, such as, -OH, -CO, and -COOH, which increases the polarity and hydrophilicity of the photocatalyst. The photocatalytic oxidation of RY145 dye under UVc light was discussed by the apparent first-order reaction rate and the kinetic model of the Langmuir-Hinshelwood followed a better fitting. The optimal performance of the composite is at pH = 2, 15 mg/100 mL of photocatalyst dose, 150 mg/L concentration of the dye RY145 at 25 °C temperature under UVc lamp irradiation for 90 min, and with the apparent reaction rate constant was 0.0165 min-1. The thermodynamic analysis of activation parameters computed by the Eyring model and based on transition state theory (TST), an endothermic reaction with a positive value for Δ‡Ho (50.16 kJ mol-1) and a negative value for Δ‡So (-153 J/mol K) both contribute toward achieving positive values for Δ‡Go and a nonspontaneous process. The proposed α-Fe2O3@C@SiO2/TiO2 demonstrated a high capability of photocatalytic degradation up to 97% after five successive cycles at the optimal condition compared to that of Fe3O4@C (18.74%) and Fe@C-COOH (77.9%) without reusability.
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Affiliation(s)
- Seyedeh Elaheh Mousavi
- Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, B.O. Box 46414-356, Tehran, Iran
| | - Habibollah Younesi
- Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, B.O. Box 46414-356, Tehran, Iran.
| | - Nader Bahramifar
- Department of Environmental Science, Faculty of Natural Resources, Tarbiat Modares University, B.O. Box 46414-356, Tehran, Iran
| | - Pramila Tamunaidu
- Malaysia-Japan Advanced Research Centre, Malaysia Japan International Institute of Technology, Universiti Teknologi Malaysia, 84600, Pagoh, Johor, Malaysia
| | - Hassan Karimi-Maleh
- School of Resources and Environment, University of Electronics Science and Technology of China (UESTC), 611731, China; Department of Chemical Engineering and Energy, Quchan University of Technology, Quchan, Iran; Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, 2028 Johannesburg, P.O. Box 17011, South Africa.
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Pfeffermann J, Goessweiner-Mohr N, Pohl P. The energetic barrier to single-file water flow through narrow channels. Biophys Rev 2021; 13:913-23. [PMID: 35035593 DOI: 10.1007/s12551-021-00875-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Accepted: 10/26/2021] [Indexed: 10/30/2022] Open
Abstract
Various nanoscopic channels of roughly equal diameter and length facilitate single-file diffusion at vastly different rates. The underlying variance of the energetic barriers to transport is poorly understood. First, water partitioning into channels so narrow that individual molecules cannot overtake each other incurs an energetic penalty. Corresponding estimates vary widely depending on how the sacrifice of two out of four hydrogen bonds is accounted for. Second, entropy differences between luminal and bulk water may arise: additional degrees of freedom caused by dangling OH-bonds increase entropy. At the same time, long-range dipolar water interactions decrease entropy. Here, we dissect different contributions to Gibbs free energy of activation, ΔG ‡, for single-file water transport through narrow channels by analyzing experimental results from water permeability measurements on both bare lipid bilayers and biological water channels that (i) consider unstirred layer effects and (ii) adequately count the channels in reconstitution experiments. First, the functional relationship between water permeabilities and Arrhenius activation energies indicates negligible differences between the entropies of intraluminal water and bulk water. Second, we calculate ΔG ‡ from unitary water channel permeabilities using transition state theory. Plotting ΔG ‡ as a function of the number of H-bond donating or accepting pore-lining residues results in a 0.1 kcal/mol contribution per residue. The resulting upper limit for partial water dehydration amounts to 2 kcal/mol. In the framework of biomimicry, our analysis provides valuable insights for the design of synthetic water channels. It thus may aid in the urgent endeavor towards combating global water scarcity.
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Khan MY, So S, da Silva G. Decomposition kinetics of perfluorinated sulfonic acids. Chemosphere 2020; 238:124615. [PMID: 31454742 DOI: 10.1016/j.chemosphere.2019.124615] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 08/16/2019] [Accepted: 08/17/2019] [Indexed: 05/28/2023]
Abstract
Perfluorooctanesulfonic acid (PFOS) is a widespread and persistent pollutant of concern to human health and the environment. Although incineration is often used to treat material contaminated with PFOS and related per- and polyfluoroalkyl substances (PFAS), little is known about the precise chemical mechanism for the thermal decomposition of these substances of concern. Here, we present the first study of the thermal decomposition kinetics of PFOS and related perfluorinated acids, using computational chemistry and reaction rate theory methods. We discover that the preferred channel for PFOS decomposition is via an α-sultone that spontaneously decomposes to form perfluorooctanal and SO2. At 1000 K the halflife for PFOS is predicted to be 0.2 s, decreasing sharply as temperature increases further. These results show that the acid headgroup in PFOS can be efficiently destroyed in incinerators operating at relatively modest temperatures. The new insights provided into the exact decomposition mechanism and kinetics of PFOS will help to improve remediation technologies actively under development.
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Affiliation(s)
- M Yasir Khan
- Department of Chemical Engineering, University of Melbourne, Victoria, 3010, Australia
| | - Sui So
- Department of Chemical Engineering, University of Melbourne, Victoria, 3010, Australia
| | - Gabriel da Silva
- Department of Chemical Engineering, University of Melbourne, Victoria, 3010, Australia.
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Sarıkaya Y, Önal M, Pekdemir AD. Application of diffusion and transition state theories on the carburizing of steel AISI 316 by annealing in uranium carbide powder. Heliyon 2019; 5:e02305. [PMID: 31485518 DOI: 10.1016/j.heliyon.2019.e02305] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Revised: 04/19/2019] [Accepted: 08/09/2019] [Indexed: 11/25/2022] Open
Abstract
The steel specimens were tempered in contact with uranium carbide powder by sodium bonding at 500, 600, 700, and 800 °C for 1000h. Carburizing zone of the specimens was determined by measuring of microhardness which is taken as a kinetic variable instead of the corresponding carbon content. Arrhenius equation was determined for the diffusion of carbon atoms in the steel by using the solution of Fick's second law. Temperature dependency of the activation enthalpy, Gibbs energy, and entropy was calculated from the transition state theory by an assumption that the carburizing occurs over an activated complex. Kinetic and thermodynamic for formation an activated complex were discussed depending on the obtained numerical values.
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Abstract
Recent studies have found an unusual way of dissociation in formaldehyde. It can be characterized by a hydrogen atom that separates from the molecule, but instead of dissociating immediately it roams around the molecule for a considerable amount of time and extracts another hydrogen atom from the molecule prior to dissociation. This phenomenon has been coined roaming and has since been reported in the dissociation of a number of other molecules. In this paper we investigate roaming in Chesnavich's CH 4 + model. During dissociation the free hydrogen must pass through three phase space bottleneck for the classical motion, that can be shown to exist due to unstable periodic orbits. None of these orbits is associated with saddle points of the potential energy surface and hence related to transition states in the usual sense. We explain how the intricate phase space geometry influences the shape and intersections of invariant manifolds that form separatrices, and establish the impact of these phase space structures on residence times and rotation numbers. Ultimately we use this knowledge to attribute the roaming phenomenon to particular heteroclinic intersections.
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Affiliation(s)
- Vladimír Krajňák
- Johann Bernoulli Institute, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
- Present Address: School of Mathematics, University of Bristol, University Walk, Bristol, BS8 1TW UK
| | - Holger Waalkens
- Johann Bernoulli Institute, University of Groningen, Nijenborgh 9, 9747 AG Groningen, The Netherlands
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Abstract
We present a theoretical study on the detailed mechanism and kinetics of the H + HCN → H + HNC process. The potential energy surface was calculated at the complete basis set quantum chemical method, CBS-QB3. The vibrational frequencies and geometries for four isomers (H 2CN, cis-HCNH, trans-HCNH, CNH 2), and seven saddle points (TSn where n = 1 - 7) are very important and must be considered during the process of formation of the HNC in the reaction were calculated at the B3LYP/6-311G(2d,d,p) level, within CBS-QB3 method. Three different pathways (PW1, PW2, and PW3) were analyzed and the results from the potential energy surface calculations were used to solve the master equation. The results were employed to calculate the thermal rate constant and pathways branching ratio of the title reaction over the temperature range of 300 up to 3000 K. The rate constants for reaction H + HCN → H + HNC were fitted by the modified Arrhenius expressions. Our calculations indicate that the formation of the HNC preferentially occurs via formation of cis-HCNH, the fitted expression is k P W2(T) = 9.98 × 10-22 T 2.41 exp(-7.62 kcal.mol-1/R T) while the predicted overall rate constant k O v e r a l l (T) = 9.45 × 10-21 T 2.15 exp(-8.56 kcal.mol-1/R T) in cm 3 molecule -1 s -1. Graphical Abstract (a) Potential energy surface, (b) thermal rate constants as a function of temperature and
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Affiliation(s)
- Eberth Correa
- Universidade de Brasília, Campus do Gama, Gama, Brasília, DF, CEP 72444-240, Brazil
| | - Washington Barbosa da Silva
- Instituto Federal de Educação, Ciência e Tecnologia de Goiás, Campus de Luziânia, Luziânia, GO, CEP 72811-580, Brazil
| | - Patricia R P Barreto
- Laboratório Associado de Plasma - LAP, Instituto Nacional de Pesquisas Espaciais - INPE/MCT, CP515, São José dos Campos, São José, SP, CEP 12247-970, Brazil
| | - Alessandra F Albernaz
- Instituto de Física, Universidade Brasília, CP04455, Brasília, DF, CEP 70919-970, Brazil.
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Abstract
This article is an essay that discusses the concepts underlying the application of modern transition state theory to reactions in enzymes. Issues covered include the potential of mean force, the quantization of vibrations, the free energy of activation, and transmission coefficients to account for nonequilibrium effect, recrossing, and tunneling.
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Affiliation(s)
- Donald G Truhlar
- Department of Chemistry, Chemical Theory Center, and Supercomputing Institute, University of Minnesota, 207 Pleasant St. SE, Minneapolis, MN 55455, United States.
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Sedev R. The molecular-kinetic approach to wetting dynamics: Achievements and limitations. Adv Colloid Interface Sci 2015; 222:661-9. [PMID: 25449187 DOI: 10.1016/j.cis.2014.09.008] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 09/24/2014] [Accepted: 09/24/2014] [Indexed: 11/19/2022]
Abstract
The molecular-kinetic theory (MKT) of dynamic wetting was formulated almost 50 years ago. It explains the dependence of the dynamic contact angle on the speed of a moving meniscus by estimating the non-hydrodynamic dissipation in the contact line. Over the years it has been refined to account explicitly for the influence of (bulk) fluid viscosity and it has been applied successfully to both solid-liquid-vapour and solid-liquid-liquid systems. The free energy barrier for surface diffusion has been related to the energy of adhesion. The MKT provides a qualitative explanation for most effects in dynamic wetting. The theory is simple, flexible, and it is widely used to rationalize the physics of wetting dynamics and fit experimental data (dynamic contact angle versus contact line speed). The MKT predicts an intermediate wettability as optimal for high-speed coating as well as the maximum speeds of wetting and dewetting. Nevertheless, the values of the molecular parameters derived from experimental data tend to be scattered and not particularly reliable. This review outlines the main achievements and limitations of the MKT and highlights some common cases of misinterpretation.
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Affiliation(s)
- Rossen Sedev
- Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia.
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