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1.
A detailed study of the geometry, aromatic character, electronic and magnetic properties for a series of positively charged N-doped polycyclic aromatic hydrocarbons (PAHs) was performed. Magnetic properties of the examined molecules were analyzed by means of the magnetically induced current density calculated using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method. The comparative study of the local aromaticity of the studied molecules was performed using several different indices: energy effect (ef), harmonic oscillator model of aromaticity (HOMA) index, six centre delocalization index (SCI) and nucleus independent chemical shifts (NICS). The presence of N-atoms in the inner rings was found to cause a planarity distortion in the studied N-doped systems. The geometric changes and charged nature of the studied N-doped systems do not significantly influence the current density and the local aromaticity distribution in comparison with the corresponding parent benzenoid hydrocarbons. The present study demonstrates how quantum chemical calculations can be used for rational design of novel PAHs and for fine tuning of their properties.  相似文献   
2.
A novel solid-phase microextraction coating of phosphorous-containing titanium oxide composite was developed using titanium fiber as a support and a titanium source by hydrothermal oxidation in a phosphoric acid solution containing hydrogen peroxide. The morphology of the fiber coatings was controlled by the conditions of the hydrothermal oxidation reaction. The oriented nanofiber coating was employed to extract several types of representative aromatic analytes. The experimental results demonstrated that the as-prepared fiber exhibited excellent extraction efficiency toward polycyclic aromatic hydrocarbons. Combined with high-performance liquid chromatography with ultraviolet detection, main extraction conditions were optimized, including pH, ionic strength, extraction temperature, stirring rate, extraction time and desorption time. The established method presented good linearity from 0.05 to 200 μg/L with limit of detection ranging from 0.012 to 0.126 μg/L. This convenient and green procedure was suitable for the selective extraction and determination of typical polycyclic aromatic hydrocarbons in environmental water samples. The relative recoveries of 85.8–112% were obtained for the determination of target polycyclic aromatic hydrocarbons in water samples spiked with 5.0 and 15.0 μg/L. Moreover, the as-prepared fiber showed at least 210 extraction/desorption cycles due to its high mechanical and chemical stability.  相似文献   
3.
This review critically evaluates the plastic accumulation challenges and their environmental (primarily) and human (secondarily) impacts. It also emphasizes on their degradation and fragmentation phenomena under marine conditions. In addition, it takes into account the leachability of the various chemical substances (additives) embedded in plastic products to improve their polymeric properties and extend their life. Regardless of their effectiveness in enhancing the polymeric function of plastic products, these additives can potentially contaminate air, soil, food, and water. Several findings have shown that, regardless of their types and sizes, plastics can be degraded and/or fragmented under marine conditions. Therefore, the estimation of fragmentation and degradation rates via a reliable developed model is required to better understand the marine environmental status. The main parameter, which is responsible for initiating the fragmentation of plastics, is sunlight/UV radiation. Yet, UV- radiation alone is not enough to fragment some plastic polymer types under marine conditions, additional factors are needed such as mechanical abrasion. It should be also mentioned that most current studies on plastic degradation and fragmentation centered on the primary stages of degradation. Thus, further studies are needed to better understand these phenomena and to identify their fate and environmental effects.  相似文献   
4.
采用阳极氧化法在镍钛合金(NiTi)纤维上原位生长了双金属氧化物纳米孔(NiTiONPs)涂层,通过扫描电镜(SEM)和能谱(EDS)考察了电解质组成和电压对形貌的影响。将NiTiONPs涂层的NiTi纤维与高效液相色谱-紫外检测器联用,研究了4种典型芳香分析物的萃取性能。结果表明,富含TiO2的NiTiONPs涂层对多环芳烃(PAHs)具有良好的萃取效率,尤其对苯并[a]芘的萃取选择性优于市售聚二甲基硅氧烷纤维和聚丙烯酸酯纤维。在优化条件下,PAHs的线性范围为0.05~200μg/L,相关系数均大于0.999,检出限为0.012~0.134μg/L。对单支纤维日内和日间分析的相对标准偏差(RSDs)分别为4.0%~5.5%和6.0%~6.8%,使用分批组装的5支纤维分析的RSDs为6.4%~7.6%。实际水样分析的加标回收率为84.5%~111.5%。所制备NiTi纤维至少可重复使用250次以上,重现性好。  相似文献   
5.
A solid‐phase microextraction coupled with gas chromatography and mass spectrometry method has been developed for the determination of ten nitrated polycyclic aromatic hydrocarbons in water samples. Five different kinds of commerical fibers were used to compare the extraction efficiency, including 65 μm polydimethylsiloxane/divinylbenzene, 100 μm polydimethylsiloxane, 30 μm polydimethylsiloxane, 7 μm polydimethylsiloxane, and 85 μm polyacrylate fibers. Five factors were also selected to optimize conditions, including extraction temperature, time, stirring speed, salt concentration, and headspace volume. Taguchi design was applied to design the experiments and obtain the best parameters. The results show that 65 μm polydimethylsiloxane/divinylbenzene fiber directly immersed into aqueous solution for 35 min at 55°C with a constant stirring rate of 1150 rpm were the optimal conditions. Under these conditions, the limits of quantification were 0.007–0.063 μg/L, and the relative standard deviation based on six replicates ranged from 2.8 to 9.5%. The spiked recoveries ranged from 69.1 to 110.1%. Intra‐ and inter day relative standard deviations at three concentration levels were less than 12%, and the recoveries were 66.4–111.5%. The proposed method is reliable for analyzing nitrated polycyclic aromatic hydrocarbons in different water samples.  相似文献   
6.
2,3-Naphthalenediol on superelectrophilic activation with aluminium halides smoothly reacts with benzene to give 4-((3-phenyl-1H-inden-1-yl)methyl)benzene-1,2-diol, which in turn undergoes intramolecular cyclization to form 5,10-methano-5-phenyldibenzo[a,d]cycloheptane-2,3-diol. The mechanistic aspects of these unusual transformations are discussed.  相似文献   
7.
Efficient conversion of lignin to aromatic hydrocarbons via depolymerization and subsequent hydrodeoxygenation is important. Previously, we found that NbOx species played a key role in the activation and cleavage of C–O bonds in lignin and its model compounds. In this study, commercial niobic acid (HY-340), niobium phosphate (NbPO-CBMM) and lab-made layered niobium oxide (Nb2O5-Layer) were chosen as supports to study the effect of Brönsted and Lewis acids on the activation of C–O bonds in lignin conversion. A variety of Ru-loaded, Nb-based catalysts with different Ru particle sizes were prepared and applied to the conversion of p-cresol. The results show that all the Ru/Nb-based catalysts produce high mole yields of C7–C9 hydrocarbons (82.3–99.1%). What's more, Ru/Nb2O5-Layer affords the best mole yield of C7–C9 hydrocarbons and selectivity for C7–C9 aromatic hydrocarbons, of up to 99.1% and 88.0%, respectively. Moreover, it was found that Lewis acid sites play important roles in the depolymerization of enzymatic lignin into phenolic monomers and the cleavage of the C–O bond of phenols. Additionally, the electronic state and particle size of Ru are significant factors which influence the selectivity for aromatic hydrocarbons. A partial positive charge on the metallic Ru surface and a smaller Ru particle size are beneficial in improving the selectivity for aromatic hydrocarbons.  相似文献   
8.
Nano‐molybdenum trioxide was prepared from nano‐molybdenum disulfide by simple firing in muffle furnace. Nano‐molybdenum trioxide was used as the extraction coating on the stainless steel wire. Four wires were filled in a polyetheretherketone tube to get an extraction tube. The tube was connected to the six‐port valve of a high performance liquid chromatograph, and the online analysis system was constructed. Extraction selectivity of the tube for different types of compounds, including polycyclic aromatic hydrocarbons, plasticizers, estrogens, anilines and neonicotinoids, was studied. Good enrichment ability for polycyclic aromatic hydrocarbons, but the extraction efficiency of others was not satisfactory. Using eight polycyclic aromatic hydrocarbons as the targets, an analytical method was established after optimizing main factors such as sampling volume, sampling rate, methanol content, and desorption time. The established method exhibited wide linear range to 0.016–20.00 μg/L and low limits of detection to 0.005 μg/L, and the enrichment factors can be up to 2443. The method was applied to the detection of trace polycyclic aromatic hydrocarbons in tap water and river water, and a good recovery was obtained. The tube showed good durability and chemical stability, and it still remained good extraction effect after more than 140 run.  相似文献   
9.
Endophytic fungi were isolated from red alga Asparagopsis taxiformis - Falkenbergia stage, collected from the Brazilian coast, and were identified as Annulohypoxylon stygium (AT-03) and A. yungensis (AT-06) based on their macro/micromorphological and molecular features. Bioassay-guided fractionation of the EtOAc extract from laboratory cultures of both strains yielded known compounds pyrogallol from A. stygium, (3R)-scytalone and (3R,4R)-4-hydroxy-scytalone from A. yungensis. Pyrogallol was active against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli strains. An inactive fraction from A. stygium afforded two additional compounds, (3R,4R)-3,4,5-trihydroxy-1-tetralone and tyrosol. Optically active compounds had their stereochemistry determined by circular dichroism (CD) spectroscopy.  相似文献   
10.
For the last decades, the hydrogen-abstraction−acetylene-addition (HACA) mechanism has been widely invoked to rationalize the high-temperature synthesis of PAHs as detected in carbonaceous meteorites (CM) and proposed to exist in the interstellar medium (ISM). By unravelling the chemistry of the 9-phenanthrenyl radical ([C14H9].) with vinylacetylene (C4H4), we present the first compelling evidence of a barrier-less pathway leading to a prototype tetracyclic PAH – triphenylene (C18H12) – via an unconventional hydrogen abstraction–vinylacetylene addition (HAVA) mechanism operational at temperatures as low as 10 K. The barrier-less, exoergic nature of the reaction reveals HAVA as a versatile reaction mechanism that may drive molecular mass growth processes to PAHs and even two-dimensional, graphene-type nanostructures in cold environments in deep space thus leading to a better understanding of the carbon chemistry in our universe through the untangling of elementary reactions on the most fundamental level.  相似文献   
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