Bond-breaking Reactions Research Articles

Degradation of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) by ultraviolet activated hydrogen peroxide: Mechanisms, pathways and toxicity assessments

The ubiquity and ecotoxicity of tri (1,3-dichloro-2-propyl) phosphate (TDCPP) in aquatic environments make it essential to develop efficient related treatment techniques. The present research aims to systematically explore the mechanisms and toxicity changes of TDCPP degradation through UV-driven hydrogen peroxide process (UV/H2O2). The results revealed degradation efficiency of TDCPP attained 95 % with 0.5 mM H2O2, corresponding to a reaction rate constant (k) of 0.04919 min−1. Furthermore, three typical chlorinated OPEs (Cl-OPEs) were simultaneously degraded by the UV/H2O2 process, with different degradation efficiencies, according to the following order: TCEP<TDCPP<TCPP. The degradation efficiency was restricted under alkaline condition and the presence of humic acid (HA), nitrate (NO3–), chloride (Cl-), sulfate (SO42-), and dihydrogen phosphate (H2PO4-). A total of 12 intermediates were identified, which were generated through different pathways, including bond breaking, hydroxylation, and oxidation reactions. The Toxicity Estimation Software Tool (T.E.S.T) results demonstrated stronger mutagenicity and developmental toxicity of the TDCPP intermediates than parent compound. According to RNA sequencing results, UV/H2O2-based TDCPP degradation for 20 min and 60 min still had negative effects on Escherichia coli (E. coli). Indeed, the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results further suggested the stronger negative effect (e.g., damaging effects on the cell membrane, energy metabolism, and vitality) of the 20-min oxidation solution on E. coli, followed by those observed in without treatment and 60-min oxidation solution. Therefore, longer oxidation times are required in the UV/H2O2 process to decrease the toxicity of TDCPP.

Thermal decomposition behaviors of adamantane and 1-methyladamantane in oxygen atmosphere: ReaxFF molecular dynamics simulation

High energy density fuels (HEDFs) have garnered considerable interest in the aerospace applications due to their high density and effective heat dissipation capabilities. However, there is still no clear understanding of the pyrolysis and oxidation mechanisms of HEDFs. In this work, a computational strategy based on ReaxFF molecular dynamics reveals dehydrogenation and ring-opening reaction events for adamantane and 1-methyladamantane. A comparative analysis of the initial decomposition behavior, intermediate reaction mechanism, and final product distribution demonstrates that the decay of the reactants is dependent on temperature and oxygen concentration. The main decomposition pathways of adamantane and 1-methyladamantane involve multi-step dehydrogenation and ring opening by the following reaction: i. C10H16 → C10H15 → C7H10 + C3H5, ii. C10H16 → C10H12, iii. C11H18 → C11H16, iv. C11H18 → C11H15 → C2H4 + C9H11. C7H10, C3H5, and C9H11 undergo further bond-breaking reactions to form linear hydrocarbon chains. At low temperatures, C10H16 and C11H18 exhibit a preference for reacting with OH and HO2, accounting for 15 %–35 % of the reactions. At high temperatures, the preferred reaction for C10H16 and C11H18 is with O2, accounting for 33 %–64 % of the reactions. The bridge carbon atom acts as the initial dehydrogenation site for both adamantane and 1-methyladamantane, as well as the active site for ring opening. The decomposition energy barrier for 1-methyladamantane (108.16–130.39 kJ/mol) is lower than that for adamantane (130.72–142.61 kJ/mol). Our findings shed light on the complicated interplay of oxidation of adamantane and 1-methyladamantane.

A Hexaarylbiimidazole‐Terarylene Hybrid: Visible‐to‐NIR‐II Absorption via Sequential Photochromic Reactions

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi‐state photochromism. The biphotochrome hybrid shows four‐state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C–N bond breaking reaction of the HABI in preference to the ring‐closing reaction of the 6π‐electron system in the terarylene unit, leading two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π‐electrocyclization reaction by UV irradiation. The delocalized π‐radical on the closed‐ring form of the terarylene is efficient to enhance the photosensitivity to the NIR‐I and ‐II region. Furthermore, a recombination reaction of radicals between the open‐ and closed‐ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units.

A Hexaarylbiimidazole-Terarylene Hybrid: Visible-to-NIR-II Absorption via Sequential Photochromic Reactions.

A synergetic interaction between two or more photochromic chromophores has a potential to achieve advanced photochemical properties beyond conventional photochromic molecules and to realize photochemical control of complex systems using only a single molecule. Herein, we report a hybrid photochromic molecule consisting of hexaarylbiimidazole (HABI) and terarylene that exhibits multi-state photochromism. The biphotochrome hybrid shows four-state photochromic reaction involving sequentially proceeding photoreactions. The UV or visible light irradiation to the biphotochrome leads to the C-N bond breaking reaction of the HABI in preference to the ring-closing reaction of the 6π-electron system in the terarylene unit, leading to two terarylene radical molecules. The photogenerated terarylene radical further exhibits the 6π-electrocyclization reaction by UV irradiation. The delocalized π-radical on the closed-ring form of the terarylene is efficient to enhance the photosensitivity to the NIR-I and -II region. Furthermore, a recombination reaction of radicals between the open- and closed-ring isomers of terarylene affords an unprecedented photochromic dimer as a structural isomer of the initial molecule. This is a consequence of the sequential hybrid photochromic system involving the HABI and terarylene units.

What Phenomena Happen During Pyrolysis of Plastic? FTIR AND GC-MS Analysis of Pyrolyzed Low Linear Density Polyethylene (LLDPE) Polymer Particles Completed with Bibliometric Research Trend and Pyrolysis Chemical Reaction Mechanism

This research aims to determine the compounds produced from the pyrolyzed Low Linear Density Polyethylene (LLDPE) using Fourier Transform Infrared (FTIR) and Gas Chromatography-Mass Spectroscopy (GC MS). We used pyrolysis of 985 g of 2-mm diameter LLDPE plastic ore at a temperature between 192-194°C for 135 min using a batch reactor (length x width x height = 35 cm x 24 cm x 44 cm) equipped with an outlet connected to two condensers (24°C). To ensure the chemical results, the reactor was connected in series to condensers 1 and 2. The results obtained in condenser 1 were 3 mL of 2-phase liquid with a strong odor. The upper fluid is yellow, and the lower fluid is brown. In condenser 2 (connected directly to condenser 1), 4 mL of yellow single-phase liquid was produced with a strong odor. The liquid obtained from the pyrolysis process was then analyzed by FTIR and GC-MS. FTIR results on both samples showed that the samples contained the functional groups O-H, CH₂, and C=O. The GC-MS results on condenser sample 2 showed that the pyrolysis product contained acetone compounds. This confirmed that pyrolysis caused chemical structural changes in LLDPE due to LLDPE chain bond-breaking reactions, producing many smaller chemical compounds. Additionally, some oxidation happens, which is due to the oxygen content in the reactor. This study provides new insights into the LLDPE pyrolysis mechanism and the physical and chemical properties of the liquid resulting from the pyrolysis process.

Plasma water treatment for PFAS: Study of degradation of perfluorinated substances and their byproducts by using cold atmospheric pressure plasma jet

This study evaluates the effectiveness of non-thermal plasma at atmospheric pressure (NTP APPJ) for treating PFAS - contaminated water in different matrices. Successful removal of several perfluoroalkyl carboxylic acids (PFCAs) (C6 to C4), perfluroalkane sulfonic acids (PFSAs) (C8 to C4) and perfluropolyethers (PFPEs) (GenX and ADONA) PFAS compounds was achieved in laboratory scale experiments. In the deionized water (DW), high removal efficiencies (> 90%) were observed for longer-chain PFAS, PFOS (99.89%), PFHxA (94.61%) and ADONA (94.83%), while shorter- chain compounds had lower removal rates. Real water samples (tap water and synthetic effluent) showed lower overall degradation percentages (8–50%) depending on compound and matrix. Short-chain PFAS displayed around 10% removal in tap water, while PFOS and GenX achieved 50% and 32% removal, respectively. Complex matrix effects influence degradation rates. Byproducts from the plasma treatment were investigated, revealing distinct degradation mechanisms for various PFAS compounds. For PFSAs and PFCAs, degradation involved electron transfer, bond breaking and subsequent reactions. Conversely, ADONA and GenX degradation initiated with ether-group cleavage, followed by additional transformation processes. Plasma-based technology shows potential for degradation of PFAS, especially for newer substitute compounds like ADONA and GenX. However, further research is needed to optimize plasma performance for complete mineralization of PFAS. This study also proposes a degradation mechanism for ADONA, marking a novel investigation into ether-group PFAS degradation with potential implications for further research and understanding toxicological implications.

Nickel perovskite catalysts for ammonia decomposition: DFT calculations and microreaction kinetics

Combining policy guidance, catalyzing ammonia decomposition to produce hydrogen is a new concept for hydrogen energy supply. Alkaline carriers can effectively improve the ammonia decomposition activity on the catalyst by adjusting the dispersion of nickel (Ni) and controlling the size of Ni. However, the activity of Ni-based perovskite catalysts does not seem to be entirely affected by the above factors. Exploring the mechanism of Ni and perovskite alkaline carrier surfaces through theoretical calculations provides deeper theoretical guidance for ammonia (NH3) decomposition. This study uses periodic density functional theory calculation methods to investigate the reaction paths and energy distribution of monomeric ammonia and dimeric ammonia on a nickel-doped barium zirconate (Ni/BaZrO3) catalyst. Molecular dynamics simulations, Bader charge analysis, and density of states assist in understanding the adsorption states of NH3 and the catalytic decomposition mechanism. The energy barriers for N-H bond breaking and nitrogen generation reactions of Ni clusters loaded on the BaZrO3 surface (Ni4/BaZrO3) were compared and analyzed. The results show that Ni/BaZrO3 is more conducive to ammonia decomposition, with a maximum reaction barrier of 0.90 eV. The catalytic activity of the catalyst under oxygen vacancy conditions was further examined. By comparing the mechanisms of dimeric ammonia decomposition on the clean catalyst surface and the oxygen vacancy catalyst surface, it was found that the presence of oxygen vacancies facilitates ammonia decomposition, but Ni doping provides more effective assistance for N-H bond breaking. The rate constant for ammonia decomposition was calculated using transition state theory. This work not only provides theoretical references for the decomposition mechanism of NH3 in Ni-based perovskite materials but also provides kinetic data for the kinetic modeling of NH3 decomposition.

Insights into the pyrolytic coking process of RP-3 fuel from ReaxFF molecular dynamics

Active cooling technology serves as one of the promising and effective methods for addressing the thermal protection strategy for hypersonic aircraft. While the coke generated through pyrolysis, dehydrogenation and coking reactions of fuel will reduce the heat transfer efficiency, even clog the heat exchange channel. In this work, three-component RP-3 aviation fuel was adopted as model compounds to investigate the cracking coking reaction mechanism and explore the method of inhibiting coking. It is found that the three-component RP-3 molecules generate an intermediate system dominated by C2 products through bond breaking, reforming and bimolecular reactions (mainly hydrogen abstraction reactions) under supercritical state, in which the ·H radicals, as represented radicals, play a crucial role in the opening of benzene rings. The coking process is analyzed in details furtherly, and detailed soot formation mechanisms are revealed. Additionally, a suitable “core-shell structure” model is proposed to describe the coke formation process. Meanwhile, it is found that the addition of a small number of addition agents can effectively inhibit the formation of coke and thus prolong the residence time of fuel molecules in the heat transfer channel for the coking process mainly consisted of addition reaction. The study attempts to provide a theoretical basis for the high-temperature pyrolytic coking mechanism of endothermic hydrocarbon fuel, as well as the significance to understanding the inhibition of coke formation.

Insights into the photocatalytic degradation of hydrophobic organic contaminants on the surface of nitrogen doped silica: New findings of the formation of silicon-based substitution products

In this work, nitrogen-doped SiO2 (N-SiO2) was successfully synthesized to develop an “adsorption-photocatalytic degradation” water purification technology to remove hydrophobic organic contaminants (HOCs). As a representative of HOCs, decabromodiphenylethane (DBDPE) could be efficiently degraded under simulated sunlight after adsorption on the surface of N-SiO2. Due to the generation of reactive oxygen species (ROS) and silicon-based radicals, the photodegradation rate of DBDPE on water-SiO2 interface was 1.5-fold higher than that in water. Furthermore, the transformation pathways of DBDPE on N-SiO2 surface were compared with that in water. Bond breaking and debromination reactions were the common pathways, while hydroxylation and silicon-based substitution reactions were the specific transformation pathways for DBDPE on the surface of N-SiO2. Density functional theory (DFT) calculation was used to reveal the generation mechanism of silicon-based radicals and determine the rationality of the involvement of silicon-based radicals in DBDPE transformation. The energy barriers of silicon-based substitution reaction were comparable to that of hydroxylation and debromination reactions, which confirmed the plausibility of the generation of silicon-based substitution products. This study provides an efficient method for the disposal of HOCs, which also gives some new insights into the conversion mechanism of organic pollutants mediated by silicon-based radicals.

Enhanced removal of sulfamethoxazole by Mn(II)/bisulfite in presence of nitrilotriacetic acid: Role of Mn(III)

Currently, the research on bisulfite (BS) activation by Mn(II) is very limited probably because of the low catalytic efficiency of Mn(II). Adding ligands to Mn(II)/BS system is likely to improve the BS activation, but the relative information is very rare. Therefore, the effect of nitrilotriacetic acid (NTA) on Mn(II)/BS system was investigated in this work using sulfamethoxazole (SMX) as the target contaminant. The results showed that the addition of NTA enhanced SMX removal in Mn(Ⅱ)/BS system through forming Mn(Ⅱ/III)-NTA complexes driving Mn(III)/Mn(II) cycle and stabilizing Mn(III). Alcohol scavenging experiments and competitive kinetic experiments indicated that sulfate radical (SO4•−) and hydroxyl radical (HO•) were not the main reactive species in Mn(II)/NTA/BS system. Mn(Ⅲ) was the primary oxidant for SMX elimination in this system and its existence was proved by UV-Vis absorption spectrum of reaction solution. Mn(Ⅱ)/NTA/BS system could greatly degrade SMX in near-neutral conditions, while nearly no SMX removal was observed at pH 3.0. The decrease of dissolved oxygen concentration significantly inhibited BS autocatalytic stage, thus suppressing the removal of SMX. Due to the competitive complexation of HCO3− and FA with NTA for Mn(II), their addition in Mn(Ⅱ)/NTA/BS system obviously inhibited SMX degradation. Four intermediates were detected during SMX degradation in Mn(Ⅱ)/NTA/BS system, and the possible SMX transformation pathways were speculated as N-S bond breaking, hydroxylation, amino oxidation and coupling reaction.

Efficient visible-light photocatalysis of chloramphenicol using novel engineered biochar-based Ti-doped Bi2WO6 composite: Mechanisms, degradation pathways, and applications

A novel engineered biochar (ACB)-based Ti-doped Bi2WO6 composite (Ti-Bi2WO6@ACB) was synthesized via a one-step hydrothermal reaction for the efficient degradation of chloramphenicol (CAP) and extensive environmental applications. Multiple characterization techniques, CAP degradation effects, total organic carbon (TOC) removal, effects of environmental factors, recycling tests, actual wastewater treatment, enhancement strategies, and disinfection effects were systematically evaluated. It was found that Ti-Bi2WO6@ACB is a Ti3+ self-doped TiO2/Bi2WO6/ACB ternary heterogeneous photocatalyst. The introduction of ACB and Ti doping enhanced the elemental composition, oxygen-containing functional groups, defect structure (oxygen vacancies), visible-light absorption, and active sites. Moreover, Ti-Bi2WO6@ACB effectively inhibited the recombination of photogenerated carriers. The removal efficiency of Ti-Bi2WO6@ACB for 50 mg⋅L−1 CAP was 92.44 % at 120 min of irradiation, and the TOC removal rate was 67.72 %, which was significantly higher than that of the control treatment. Ti-Bi2WO6@ACB is reusable and photostable, with approximately 99 % sterilization of Staphylococcus aureus and Escherichia coli within 10 min of light irradiation and 48 h of cultivation. The addition of H2O2, ultrasonication, heating, and blowing air in the system improved the photocatalytic efficiency. The ultrasound enhancement mechanisms are related to the effects of cavitation, microjets, and photocatalysis coupled with sonocatalysis. CAP degradation was dominated by OH, O2−, and h+. The doping of Ti3+/TiO2 generated more defects and O2−, and the ACB acted as a carrier to prevent the agglomeration of TiO2 and Bi2WO6. Further, the degradation process of CAP was documented and the degradation pathways may include hydroxylation addition, methanol denaturation, substitution, C–N bond breaking, oxidation, hydrolysis, and decarboxylation reactions. The research presents fresh insights into the development of high-performance engineered biochar-based composite for environmental detoxification.

Enhanced removal of phenolic compounds by ferrate(VI): Unveiling the Bi(III)-Bi(V) valence cycle with in situ formed bismuth hydroxide as catalyst

The use of 2-hydroxybenzophenone (2-HBP) in personal care products is of great concern due to its potential negative effects on the ecosystem and public health. This paper presents the degradation of 2-HBP by bismuth(III) (Bi3+)-ferrate(VI) (FeVIO42−, Fe(VI)) (Bi3+-Fe(VI) system). Experimental studies at different pH and dosages of Bi3+ and Fe(VI) showed that the Bi3+-Fe(VI) system increased the degradation rate and removal efficiency of 2-HBP compared to Fe(VI) alone. The in situ formed flake-like white flocculent precipitate of Bi(OH)3 showed catalytic performance through the Bi(III)-Bi(V)-Bi(III) valence cycle which was demonstrated through spectroscopic measurements. The hydrogen transfer-mediated reactions between Fe(VI) and Bi(OH)3 as well as subsequent formation of Bi(V) were supported by performing density functional theoretical (DFT) calculations. Seventeen identified transformation products of 2-HBP by Fe(VI) with and without Bi3+ revealed hydroxylation, bond breaking, carboxylation, and polymerization reaction pathways. Significantly, Bi3+ facilitated the polymerization reaction and the dioxygen transfer-mediated hydroxylation reaction pathways. The ions (anions and cations) and humic acids (HA) present in the Bi3+-Fe(VI) system had minimal influence on the removal efficiency of 2-HBP. Reusability tests and use of real water samples as well as toxicity assessments of transformation products unveiled the practical application aspect of the Bi3+-Fe(VI) system. Finally, the results showed that the system exhibits good removal efficiency for all 12 phenolic compounds, indicating theuniversality. The Bi3+-Fe(VI) system may be an easy-to-implement cost-effective method for the catalytic degradation of benzophenones by Fe(VI).

Experimental and computational study on xylan pyrolysis: The pyrolysis mechanism of main branched monosaccharides

The high percentage of branched units with different structures leads to the complex pyrolysis chemistry and product distribution of hemicellulose. In this study, four main branched monosaccharides, i.e., arabinose (Ara), galactose (Gal), galacturonic acid (GacA), and glucuronic acid (GlcA) were employed as typical xylan-based hemicellulose model compounds. The pyrolysis behaviors and mechanisms of these monosaccharides were deeply explored by the combination of pyrolysis experiments and density functional theory (DFT) calculations. Particularly, the roles of structural differences of these monosaccharides were carefully analyzed. Due to the uronic acid group, GacA and GlcA were easier to decompose, having two weightloss peaks with close intensity, and the release of CO2 had greater intensity than Ara and Gal pyrolysis at low temperatures. GlcA with the equatorial hydroxyl group can undergo a special CC bond breaking reaction to depart the C6 uronic acid group to release HCOOH. The fast pyrolysis of these monosaccharides obtained similar product species but distinct relative contents. The structure of an uncertain hydromethyl-furnaose product was identified as 5-(hydroxymethyl)furan-3(2H)-one (5-HMFO) by combined DFT calculations and experimental results. The findings of this work are beneficial to gain a deep understanding of the pyrolysis chemistry of hemicellulose, especially the role of different branches.

Unraveling Multiple Pathways of Electron Donation from Phenolic Moieties in Natural Organic Matter.

Natural organic matter (NOM) exhibits a distinctive electron-donating capacity (EDC) that serves a pivotal role in the redox reactions of contaminants and minerals through the transformation of electron-donating phenolic moieties. However, the ambiguity of the molecular transformation pathways (MTPs) that engender the EDC during NOM oxidation remains a significant issue. Here, MTPs that contribute to EDC were investigated by identifying the oxidized products of phenolic model compounds and NOM samples in direct or mediated electrochemical oxidation (DEO or MEO, respectively) using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It was found that the oxidation of newly formed phenolic-OH (ArOH) and the oxidative coupling reaction of the phenoxy radical are the main MTPs that directly contribute to EDC, in addition to the transformation of hydroquinones to quinones. Notably, the oxidative coupling reaction of ArOH contributed at least 22-42% to the EDC. Ferulic acid-like structures can also directly contribute to EDC by incorporating H2O into their acrylic substituents. Furthermore, the opening of C rings can indirectly attenuate the EDC through structural alterations in the electron-donating process of NOM. Decarboxylation can either weaken or enhance the EDC depending on the structure of the phenolic moieties in NOM. These findings suggest that the EDC of NOM is a comprehensive result of multiple NOM MTPs, involving not only ArOH oxidation but also the addition of H2O to olefinic bonds and bond-breaking reactions. Our work provides molecular evidence that aids in the comprehension of the multiple EDC-associated transformation pathways of NOM.

Photocatalytic degradation of alkyl imidazole ionic liquids by TiO2 nanospheres under simulated solar irradiation: Transformation behavior, DFT calculations and promoting effects of alkali and alkaline earth metal ions

In this study, TiO2 nanospheres prepared by the sol-gel method were found to efficiently catalyze the photodegradation of 1-butyl-2,3-dimethylimidazolium bromide salt ([BMMIm]Br) under simulated solar irradiation through the main attack of hydroxyl radicals (•OH). The promoting effect of alkali metal (Li+→Cs+) and alkaline earth metal ions (Mg2+→Ba2+) was particularly emphasized. In-situ EPR tests showed that the introduction of alkali and alkaline earth metal ions could enhance the formation of •OH thus leading to a 7%−30.3% increase in the degradation efficiency of. [BMMIm]+. Moreover, the removal efficiency of [BMMIm]+ still reached > 96.19% in four real waters. A total of 23 products of [BMMIm]Br were detected, and hydroxyl substitution, bond breaking, direct oxidation and ring opening were considered as the main reactions during the photocatalytic degradation process. The results of toxicity evaluation showed that hydroxylation was a reaction process of increasing toxicity, while the bond breaking reaction had great detoxification capacity for [BMMIm]+. These findings may enhance our understanding on the effects of alkali or alkaline earth metal ions on the photocatalytic activity of TiO2, which could also provide reference for the efficient and green removal of alkylimidazolium ionic liquids in waters.

The mechanism of photothermal catalytic reforming of biomass tar: An exploratory study based on density functional theory

Tar removal is a hot topic in the biomass gasification field. Photothermal catalytic reforming (PCR) is an emerging approach that shows high efficiency, but the mechanism and tar cracking reaction pathway under PCR are still not clear. In this paper, as a widely recognized catalyst that has both thermal and photo-catalysis effects, Ni/TiO2 was investigated and the model was calculated by density functional theory (DFT). Toluene was selected as the model tar compound, and the cracking performances were analyzed in both PCR and conventional heating conditions. It was found that H2O and toluene can be stably adsorbed on the catalyst surface but the adsorption sites are different, which provides support for the comparisons of toluene cracking pathways. The energy barriers of CC bond breaking reactions were calculated and the toluene cracking pathway showed significant changes under PCR, due to the formation of oxygen vacancy and hydroxyl radical. Toluene mainly occurs in the dissociation reaction of methyl group under conventional conditions, but toluene tends to open aromatic ring to form chain hydrocarbons under PCR conditions. It indicates that PCR shows greater activation on the aromatic ring which is crucial for tar cracking. This study confirms the change of the toluene cracking pathway under photothermal conditions by the DFT calculation method and also provides guidance for the optimization of the tar removal process and photothermal catalyst preparation.

Simplification of the combustion mechanism of Jatropha biodiesel surrogate fuel and reaction path analysis

The objectives of this study were to explore the evolution process of the chemical reaction pathways in the combustion of a biodiesel surrogate fuel and to reduce the calculation burden in the numerical simulation of this combustion process due to the complicated mechanism. A mixture of methyl decanoate, methyl 9-decanoate, and n-heptane was selected as the Jatropha biodiesel surrogate fuel. A simplified combustion mechanism of the biodiesel comprising 170 components and 737 reaction components was formed by systematically simplifying 3299 components and 10806 reaction mechanisms using a multistep directed relation graph method, path flux analysis, and sensitivity analysis. The simplified mechanism was compared with the detailed mechanism and experimental data to effectively verify the accuracy of the mechanism. The simplified mechanism could reproduce the detailed mechanism, and the results were in good agreement with the experimental data in terms of the ignition time of a methyl decanoate/air mixture in a shock tube, the concentrations of the components generated in the combustion process of the biodiesel in a jet stirred reactor, and the flame propagation speed of methyl decanoate and n-heptane/air mixture. The rate of production analysis method was used to explore the main reaction pathways and the evolution process of important intermediate components in the Jatropha biodiesel surrogate fuel generated at high and low temperatures. Methyl decanoate and methyl 9-decanoate formed hydrogen peroxide ketone and oxy groups mainly through dehydrogenation, oxygenation, and isomerization at low temperatures. The high-temperature stage mainly involved bond-breaking decomposition reactions, partial dehydrogenation, and isomerization reactions of low-temperature reaction products, resulting in the formation of small molecular products.

UV254 induced sulfamethazine and carbamazepine elimination in the presence of nitrate: Roles of reactive species and generation risk of highly toxic DBPs

This study systematically compared the degradation kinetics, conversion pathways, formation of disinfection by-products (DBPs), and changes in toxicity for sulfamethazine and carbamazepine in UV/nitrate system. Additionally, the study simulated the generation of DBPs in the post-chlorination process after the introduction of bromine ions (Br−). The contributions of UV irradiation, hydroxyl radicals (•OH), and reactive nitrogen species (RNS) to SMT degradation were determined to be 28.70 %, 11.70 %, and 59.60 %, respectively. The contributions of UV irradiation, •OH, and RNS to CBZ degradation were found to be 0.00 %, 96.90 %, and 3.10 %, respectively. A higher dosage of NO3− facilitated the degradation of both SMT and CBZ. Solution pH posed almost no effect on SMT degradation, while acidic conditions favored CBZ removal. The degradation of SMT was found to be slightly promoted at low concentrations of Cl−, while the presence of HCO3− significantly accelerated the degradation. Cl−, as well as HCO3−, retarded the CBZ degradation. Natural organic matter (NOM) as a free radical scavenger and UV irradiation filter posed a substantial inhibitory effect on the degradation of SMT and CBZ. The degradation intermediates and transformation pathways of SMT and CBZ by UV/NO3− system were further elucidated. The results showed that the main reaction pathways were bond-breaking reaction, hydroxylation, and nitration/nitrosation reaction. The acute toxicity of most of the intermediates generated during SMT and CBZ degradation was reduced after UV/NO3− treatment. After treatment of SMT and CBZ in UV/nitrate system, the DBPs generated in subsequent chlorination were mainly trichloromethane and a small amount of nitrogen-containing DBPs. After bromine ions were introduced in UV/NO3− system, a large amount of the originally generated trichloromethane was converted to tribromomethane.

Study on the initial pyrolysis kinetics of strained polycyclic hydrocarbons

Strained polycyclic hydrocarbons are one of the most important classes of high-energy density fuels. In this work, the thermodynamics and initial pyrolysis kinetics of five strained polycyclic hydrocarbons, which are isomers of JP-10 and are linearly aggregates of two cyclopropyl rings and one cyclobutyl ring, were investigated using quantum chemical computations. The initial pyrolysis reactions include ring bond breaking and bridge bond breaking. The ring bond breaking reactions include a diradical pathway which is the direct C-C bond breaking to produce a diradical and an isomerization pathway involving concert bond breaking and H-atom transfer, and the bridge bond breaking reactions lead to two radicals. Our potential energy calculation shows that the ring bond breaking reactions are much more energetically favorable than the bridge bond breaking reactions, which can be neglected in the initial pyrolysis process of strained polycyclic hydrocarbons. The rate constants of the ring bond breaking reactions were computed using variational transition state theory (VTST) or transition state theory (TST). Our calculated results demonstrated that ring bond breaking reactions of the three-membered ring are competitive with that of the four-membered ring. The studied reactions are divided into classes depending on the size of the rings (three- or four-membered ring) and the types of the carbon atoms of the breaking C-C bond (Cs-Cs, Cs-Ct, Ct-Ct and Cq-Cs). Reaction rate rules are established for each class, which are useful for the mechanism generation for analogous strained polycyclic hydrocarbons. Thermodynamic properties including net calorific values per mole, gravimetric net heat of combustion and impulse time of our studied strained polycyclic hydrocarbons are higher than those of JP-10. A comparison of the initial pyrolysis kinetics of our studied strained polycyclic hydrocarbons with the isomer JP-10 indicates that these compounds may be easier to pyrolyze.

Inhibitory mechanisms of ammonia addition on soot formation during n‑decane pyrolysis

Soot formation during the imperfect combustion or pyrolysis of fuels is harmful to engine efficiency·NH3 has been proved to reduce soot emission effectively in flames. In this work, the effect of NH3 addition on soot inhibition during n-decane pyrolysis was systematically investigated from a theoretical principle. The MD simulations indicate that the coking phenomenon is weakened with the NH3 addition. Besides, the NH3 additives make the concentration peak of the dominant gas products lag. Thus, the concentrations of crucial precursors (acetylene and propargyl) are reduced by NH3 addition. Moreover, the NH3 additives can also influence the PAH growth process through the PAHs with N atoms (N-PAHs). Then, the chemical kinetic analysis shows that proper addition of NH3 additives can meet the heat absorption demand of fuel cracking. Furthermore, the mass fractions of PAHs and soot particles decrease with NH3 addition, which is consistent with the results from MD simulations. The formation of the main carbonitride species originates from the reaction of CH3 and C2H5 with NH2 followed by the dehydrogenation or C-C bond breaking reaction. The carbon source directly involved in the formation of soot particle will be reduced and the growth of the soot particle will be inhibited by preventing the formation of the key reactants, such as the acetylene molecule.