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The characterization of electronic defect states of single and double carbon vacancies in graphene sheets using molecular density functional theory
摘要： A detailed picture of the electronic states manifolds of single- and double-vacancy defects in molecular models of graphene based on polycyclic aromatic hydrocarbons (PAHs) is presented. DFT calculations using various density functionals including long-range corrected ones have been performed for pyrene, circumpyrene and 7a,7z-periacene. It has been found for pyrene defect models that DFT results reproduced well the set of closely-spaced singlet and triplet states predicted by the CCSD(T) and previous MRCI + Q calculations, indicating the applicability of DFT for accessing the excited states manifolds also for larger graphene models. For the single-carbon vacancy defect, all structures have a triplet ground state. As expected, in the largest system, 7a,7z-periacene-1C, the lowest lying states are much closer in energy. For all double-vacancy defect structures, a significant rearrangement of the electronic states with increasing size of the sheet is observed. The closed-shell 1Ag state in the smallest systems is destabilised in the extended 7a,7z-periacene system, which has the 3B2u state as the ground state. As observed for the single-vacancy defect, the lowest lying states are closer in energy for the larger systems, since there are more π orbitals close in energy available. For all states, the formation of the bridging bonds for the double vacancy leads to distances shorter than for the single vacancy defect indicating a larger rigidity of the former structure which does not allow stronger distortions.
关键词： polycyclic aromatic hydrocarbons,Excited states,Periacenes,DFT,pyrene
更新于2025-09-19 17:15:36
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Tracking small heterogeneity in binary mixtures of aliphatic and aromatic hydrocarbons: NIR spectroscopic, 2DCOS and MCR-ALS studies
摘要： To our best knowledge, this is the ?rst spectroscopic study of small heterogeneity at a molecular level in binary mixtures of aliphatic and aromatic hydrocarbons. The composition-dependent spectra of benzene/toluene, benzene/n hexane, benzene/cyclohexane, n hexane/n heptane and n hexane/cyclohexane mixtures were recorded by NIR transmission technique in the whole range of mole fractions. A comprehensive exploration of the experimental data was performed by two-dimensional correlation analysis (2DCOS) and chemometric methods. In addition, we calculated excess NIR molar absorption spectra and parameter of ER, which allows for comparison of the degree of deviation from ideality for various mixtures. Our results reveal that all studied mixtures deviate from the ideal mixture. The extent of these deviations is small for the mixtures were both components are aromatic or aliphatic and increases for aromatic/aliphatic mixtures. In addition, molecular shapes have an important effect on the degree of deviation from the ideal mixture. As expected, benzene/n hexane is the most non-ideal mixture, while behavior of n hexane/n heptane and benzene/toluene mixtures is close to the ideal one. Our results suggest that in the mixtures with the largest deviations from ideality are present homoclusters of both components and heteroclusters. The heteroclusters exist in the whole range of compositions, while the homoclusters appears above a certain concentration limit. If both components of the mixture are similar, the molecules with equal probability form the homo- and heteroclusters. In the case of unlike components, the molecules prefer to form the homoclusters. The homoclusters of both components in the mixture are similar as those observed in bulk constituents. This means that deviation from the ideal mixture results from presence of the heteroclusters.
关键词： Aliphatic/aromatic hydrocarbons,NIR,Clustering,MCR-ALS,Binary mixtures,2DCOS,Chemometrics,Excess absorption spectra,Microheterogeneity
更新于2025-09-19 17:15:36
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SERS-based molecularly imprinted plasmonic sensor for highly sensitive PAH detection
摘要： A novel hybrid plasmonic platform based on the synergetic combination of a molecularly imprinted polymer (MIP) thin film with Au nanoparticles (NPs) assemblies, noted as Au@MIP, was developed for surface-enhanced Raman scattering (SERS) spectroscopy recognition of polycyclic aromatic hydrocarbons (PAHs). While the MIP trapped the PAH close to the Au surface, the plasmonic NPs enhanced the molecule Raman signal. The Au@MIP fabrication comprises a two-step procedure, first, the layer-by-layer deposition of Au NPs on glass and their further coating with a uniform MIP thin film. Profilometry analysis demonstrated that the thickness and homogeneity of the MIP film could be finely tailored by tuning different parameters such as prepolymerization time or spin-coating rate. Two different PAH molecules, pyrene or fluoranthene, were used as templates for the fabrication of pyrene- or fluoranthene-based Au@MIP substrates. The use of pyrene or fluoranthene, as a template molecule to fabricate the Au@MIP thin films, enabled its ultradetection in the nM regime with a 100-fold improvement compared with the non-imprinted plasmonic sensors (Au@NIPs). The SERS data analysis allows to estimate the binding constant of the template molecule to the MIP. The selectivity of both pyrene- and fluoranthene-based Au@MIPs was analyzed against three PAHs of different sizes. The results displayed the important role of the template molecule used for the Au@MIPs fabrication in the selectivity of the system. Finally, the practical applicability of pyrene-based Au@MIPs is shown by performing the detection of pyrene in two real samples: creek water and seawater. The design and optimization of this type of plasmonic platform pave the way for the detection of other relevant (bio)molecules in a broad range of fields such as environmental control, food safety or biomedicine.
关键词： Molecularly imprinted polymers,plasmonic sensors,polycyclic aromatic hydrocarbons,SERS,hybrid nanostructures,environmental analysis
更新于2025-09-19 17:13:59
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The Self-Reaction of <i>ortho</i> -Benzyne at High Temperatures Investigated by Infrared and Photoelectron Spectroscopy
摘要： Ortho-benzyne, a Kekulé-type biradical is considered to be a key intermediate in the formation of polycyclic aromatic hydrocarbons (PAH) and soot. In the present work we study the ortho-benzyne self-reactions in a hot micro-reactor and identify the high-temperature products by IR/UV spectroscopy and by photoion mass-selected threshold photoelectron spectroscopy (ms-TPES) in a free jet. Ms-TPES confirms formation of ortho-benzyne as generated from benzocyclobutendione, as well as benzene, biphenylene, diacetylene and acetylene, originating from the reaction o-C6H4 → HCC-CCH + C2H2 , and CH3. PAH molecules like naphthalene, 2-ethynylnaphthalene, fluorene, phenanthrene and triphenylene are identified based on their IR/UV spectra. By comparison with recent computations their formation starting from ortho-benzyne can be readily understood and supports the importance of the biradical addition (1,4-cycloaddition followed by fargmenation) pathway to PAH molecules, recently proposed by Comandini et al.
关键词： photoelectron spectroscopy,Ortho-benzyne,high-temperature reactions,IR/UV spectroscopy,biradical addition,polycyclic aromatic hydrocarbons,PAH,soot
更新于2025-09-10 09:29:36
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Detection of Benzene and Volatile Aromatic Compounds by Molecularly Imprinted Polymer Coated Quartz Crystal Microbalance Sensor
摘要： The detection of benzene and its analogues are important but difficult without using expensive extremely analytical instruments. The present work reports the detection of aromatic hydrocarbons like benzene, toluene and isomers of xylene using quartz crystal microbalance (QCM) sensor. The surface of a silver-coated quartz crystal was coated with a simple solution drop coating method and thermally polymerized in an inert atmosphere for the formation of the sensing film. The polymer was synthesized by copolymerization of the optimum ratio of styrene, divinylbenzene and tung oil at 90°C with template. 1, 2, 3 trimethoxybenzene as template performed most efficiently for all the hydrocarbons. Linear calibration curves were observed for all the vapors in the concentration range between approximately as 1.645 to 2.605 Hz/ppm. For benzene, the sensitivity is 2.605 Hz /ppm which is the highest amongst the reported literature. Thus minimum concentration of benzene that can be detected is 0.98 ppm. The molecularly imprinted polymer structure and surface morphology were analyzed by FTIR spectroscopy, FESEM and AFM. The sensitivity of detection of aromatic molecule in this work by the molecularly imprinted polymer film is found to be the best amongst the reported literatures.
关键词： molecular imprinting technique,thermal polymerization,vegetable oil,Quartz Crystal Microbalance (QCM),aromatic hydrocarbons
更新于2025-09-10 09:29:36
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Impact of molecular structure on secondary organic aerosol formation from aromatic hydrocarbon photooxidation under low NO<sub><i>x</i></sub> conditions
摘要： The molecular structure of volatile organic compounds (VOC) determines their oxidation pathway, directly impacting secondary organic aerosol (SOA) formation. This study comprehensively investigates the impact of molecular structure on SOA formation from the photooxidation of twelve different eight to nine carbon aromatic hydrocarbons under low NOx conditions. The effects of the alkyl substitute number, location, carbon chain length and branching structure on the photooxidation of aromatic hydrocarbons are demonstrated by analyzing SOA yield, chemical composition and physical properties. Aromatic hydrocarbons, categorized into five groups, show a yield order of ortho (o-xylene and o-ethyltoluene) > one substitute (ethylbenzene, propylbenzene and isopropylbenzene) > meta (m-xylene and m-ethyltoluene) > three substitute (trimethylbenzenes) > para (p-xylene and p-ethyltoluene). SOA yields of aromatic hydrocarbon photooxidation do not monotonically decrease when increasing alkyl substitute number. The ortho position promotes SOA formation while the para position suppresses aromatic oxidation and SOA formation. Observed SOA chemical composition and volatility confirm that higher yield is associated with further oxidation. SOA chemical composition also suggests that aromatic oxidation increases with increasing alkyl substitute chain length and branching structure. Further, carbon dilution theory developed by Li et al. (2015a) is extended in this study to serve as a standard method to determine the extent of oxidation of an alkyl substituted aromatic hydrocarbon.
关键词： photooxidation,low NOx conditions,molecular structure,secondary organic aerosol,aromatic hydrocarbons
更新于2025-09-04 15:30:14
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Usage of Cellulose Diacetate as Sorption Material for Fluorescent Analysis of PAH
摘要： Solid-phase matrices made of cellulose diacetate (CDA) as films and fibers were prepared. The CDA film matrices were found to be characterized by a negative value of the surface potential (–32 ± 2 mV) while the fibers had positive ones (+419 ± 1 mV). The possibility of using these matrices as sorption materials for luminescence analysis of polycyclic hydrocarbons in water-ethanol and micellar media is shown. Modification of such polymeric CDA matrices with surfactants of various natures improves their sorptive capacity and hydrocarbon recovery, and increases the sensitivity of luminescent analysis.
关键词： Ethanolic media,Surfactants,Fluorescent analysis,Polycyclic aromatic hydrocarbons,Cellulose diacetate,Aqueous micellar solutions
更新于2025-09-04 15:30:14