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To improve the spare parts support capacity of civil aircrafts and given the actual lack of evaluation methods at present, the evaluation problem of spare parts support capacity was solved in this study by proposing a multi-attribute decision method based on Type-2 hesitant Pythagorean fuzzy sets and an improved Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). First, the basic definitions of Type-2 hesitant Pythagorean fuzzy sets were given, which were further promoted to Type-n hesitant Pythagorean fuzzy sets, and the basic order relation criterion of Type-2 hesitant Pythagorean fuzzy sets was introduced. Second, a complete evaluation system for spare parts supply support capacity was established with the spare parts of civil aircrafts as the study objects, and each evaluation indicator was introduced in detail. Then, the spare parts support solutions were preferentially sorted using the correlation coefficient formula of Type-2 hesitant Pythagorean fuzzy sets and improved TOPSIS. Finally, the reliability and reasonability of the proposed method were verified through an example calculation and comparative analysis. The experimental results indicate that the proposed method can acquire the evaluation results of spare parts support capacity more scientifically and can be referenced by relevant studies. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the mechanism, thermochemistry and kinetics of the reaction of syn–cis-CH2＝RzCRyC＝O+O− (where Rz, Ry = H, CH3–) unsaturated Criegee intermediates (CIs) with CF3COOH using quantum chemical methods. The rate coefficients for the barrierless reactions were calculated using variable reaction coordinate variational transition state theory (VRC-VTST). For the syn–cis-CH2＝RzCRyC＝O+O− conformation in which conjugated C＝C and C＝O double bonds are aligned with each other, we propose a new pathway for the unidirectional addition of an O＝C–OH molecule (CF3COOH) to the C＝C double bond of syn–cis-CH2＝RzCRyC＝O+O−. The rate coefficient for the 1,4-C＝C addition reaction at 298 K is ∼10−10 to 10−11 cm3 s−1, resulting in the formation of CF3C(O)OCH2CRz＝RyCOOH trifluoroacetate alkyl allyl hydroperoxide (TFAAAH) as a new transitory adduct. It can act as a precursor for the formation of secondary organic aerosols (SOAs). This novel TFAAAH hydroperoxide was identified through a detailed quantum chemical study of the 1,4-addition mechanism and will provide new insights into the significance of the 1,4-addition reaction of unsaturated Cls with trace tropospheric gases on –CRz＝CH2 vinyl carbon atoms. [ABSTRACT FROM AUTHOR]

Recent research on atmospheric particle formation has shown substantial discrepancies between observed and modeled atmospheric sulfate levels. This is because models mostly consider sulfate originating from S O 2 oxidation by •OH radicals in mechanisms catalyzed by solar radiation while ignoring other pathways of non-radical S O 2 oxidation that would substantially alter atmospheric sulfate levels. Herein, we use high-level quantum chemical calculations based on density functional theory and coupled cluster theory to show that monoethanolamine (MEA), a typical alkanolamine pollutant released from C O 2 capture technology, can facilitate the conversion of atmospheric S O 2 to sulfate in a non – •OH – radical oxidation mechanism. The initial process is the MEA-induced S O 2 hydrolysis leading to the formation of H O S O 2 − • M E A H + . The latter entity is thereafter oxidized by ozone ( O 3 ) and nitrogen dioxide ( N O 2 ) to form H S O 4 − • M E A H + , which is an identified stabilizing entity in sulfate-based aerosol formation. Results show that the H O S O 2 − • M E A H + reaction with O 3 is kinetically and thermodynamically more feasible than the reaction with N O 2 . The presence of an additional water molecule further promotes the H O S O 2 − • M E A H + reaction with O 3 , which occurs in a barrierless process, while it instead favors HONO formation in the reaction with N O 2 . The investigated pathway highlights the potential role alkanolamines may play in S O 2 oxidation to sulfate, especially under conditions that are not favorable for •OH production, thereby providing an alternative sulfate source for aerosol modeling. The studied mechanism is not only relevant to sulfate formation and may effectively compete with reactions with sulfur dioxide and hydroxyl radicals under heavily polluted and highly humid conditions such as haze events, but also an important pathway in MEA removal processes. [ABSTRACT FROM AUTHOR]

Organic peroxides (OPs) are an important component of dissolved organic matter (DOM), detected in various aquatic media. Despite their unique functions as redox agents in water ecosystems, the complete mechanisms and factors controlling their transformation are not explicitly established. Here, we evaluate the pH effect on the aqueous-phase reaction of three selected OPs (methyl hydroperoxide (MHP), peracetic acid (PAA) and benzoyl peroxide (BZP)) with dissolved SO2. Results show that due to the presence of hydroperoxyl group in their structures, MHP and PAA preferably form inorganic sulfate and organosulfate (methyl sulfate for MHP and acetyl sulfate for PAA) depending on the pH, while BZP exclusively forms organosulfate (benzoyl sulfate) in the pH range investigated. Moreover, it is seen that the ability for PAA to form inorganic sulfate relative to organosulfate is more pronounced, which is supported by a previous experimental observation. The effective rate constants of the transformation of these peroxides within pH 1 – 10 and 240 K – 340 K ranges exhibit positive pH and temperature dependencies, and BZP is seen to degrade more effectively than MHP and PAA. In addition to the pH impact, it is highlighted that the formation of organic and/or inorganic sulfate strongly depends on the nature of the substituents on the peroxy function. Namely, PAA and BZP are more reactive than MHP, which may be attributed to the electron-withdrawing effects of -C(O)R (R = -CH3 and -C6H5 for PAA and BZP, respectively) substituents that activate the peroxy function. The results further indicate that the aqueous-phase degradation of OPs can adequately drive the change in the chemical composition of DOM, both in terms of organic and inorganic sulfate mass fractions. [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs) can effectively degrade ranitidine, a pharmaceutical that is a typical precursor of nitrosamine dimethylamine (NDMA), an extremely potent human carcinogen. Herein, novel magnetic Ti3C2-based MXene nanosheets decorated with nanoscale zero-valent iron particles (nZVIPs@Ti3C2 nanosheets) were synthesized to boost catalytic peroxymonosulfate (PMS) activation, exhibiting remarkable reactivity and stability for the rapid removal of ranitidine under mild conditions. The response surface methodology (RSM) confirmed that the initial solution pH and PMS dosage were the main factors affecting the heterogeneous oxidation process. The long-lasting catalytic activity was mainly attributed to the rapid charge transfer between dual electron-rich active centers (≡Fe and ≡Ti), with SO4˙− and HO˙ derived from PMS activation being responsible for ranitidine degradation, among which SO4˙− was the major contributor. Density functional theory (DFT) calculations also confirmed that the as-synthesized nZVIPs@Ti3C2 nanosheets provided bi-active centers for PMS activation, and this process triggered a series of thermodynamically favorable reactions. This study demonstrates a recyclable oxidation method for the rapid removal of ranitidine, which may be applicable to the degradation of other challenging pollutants. [ABSTRACT FROM AUTHOR]