The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully ...active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy.
Porous organic polymers were used as photosystems to deliver a constant production rate for the CO2 to formate reduction for several days. Their photoactivation pathway is presented, including an ultrafast electronic energy transfer from the photosensitizer to the catalyst as evidenced by time‐resolved spectroscopy and quantum mechanical calculations.
Oxidation of finely divided molybdenum sulfide in ambient air has been studied for air exposure times from 10 min to 1 year to clarify the nature of the reaction products and the mechanistic steps. ...At the initial steps, for air exposure times from several minutes to several hours, rapid oxidation of MoS2 edges occurs with simultaneous formation of hydroxyl species and surface disulfide S2 2– moieties as attested by 1H NMR, X-ray photoelectron spectra, and temperature-programmed reduction. Prolonged air exposure of MoS2 nanodispersions leads to deep oxidation. According to the results of X-ray absorption spectroscopy, UV–visible, and electron paramagnetic resonance spectroscopies, the main oxidation products are soluble paramagnetic molybdenum blue species and sulfuric acid. As shown by EXAS fitting, the major product is oxo-bridged dimolybdenyl Mo(V, VI) species. Ambient moisture plays an important role in the oxidation process as it contributes to the formation of sulfuric acid which leads to liquescence of the material and to deep oxidation without formation of a protective passivation layer.
Gas oils (GOs) analysis is essential for production process control, in order to meet quality standards, to render these products safer for the environment, and to support research for alternative ...fuels. GOs quantitative analysis can be commonly achieved by employing two-dimensional comprehensive gas chromatography with flame ionization detection (GC × GC-FID) in combination with identification templates. However, in order to perform quantification for families which coelute in GC × GC analysis (e.g., naphthenes/olefins or polynaphthenes/monoaromatics), prefractionation of gas oil before GC × GC analysis is necessary. Recent introduction of the vacuum ultraviolet (VUV) detector has offered new possibilities in GOs analysis, as this detector can discern between the majority of hydrocarbon families thus possibly rendering the gas oil prefractionation unnecessary. Additionally, it can perform quantification according to Beer–Lambert’s law provided that VUV relative response factors (RRFs) are known. The purpose of this work is to report, for the first time, VUV RRFs for numerous hydrocarbons in GOs (∼160) according to their family and their carbon number, permitting to perform their direct quantification without the necessity of GO prefractionation. VUV RRFs were measured by using a GC × GC-VUV/FID dual detection setup in which FID was employed as a quantitative reference. In order to obtain VUV RRFs representative for any gas oil, a set of 14 GOs with different origins was employed. Both VUV RRFs averaged in the 125–240 nm range and spectral VUV RRFs (reference spectra) were obtained. It was demonstrated that VUV RRFs were similar between employed GOs allowing their universal use. Obtained RRFs were used to perform hydrocarbons quantification for a light cycle oil (LCO) by GC × GC-VUV, with olefins and naphthenes being quantified through spectral decomposition. Good comparability with results obtained by prefractionation was observed demonstrating the great interest of the GC × GC-VUV approach for the detailed and rapid analysis of hydrocarbons in gas oils.
Various everyday areas such as agriculture, wood industry, and wastewater treatment yield residual biowastes in large amounts that can be utilised for the purpose of sustainability and circular ...economy. Depending on the type of biowaste, they can be used to extract valuable chemicals or converted into alternative fuels. However, for efficient valorisation, these processes need to be monitored, for which thorough chemical characterisation can be highly beneficial. For this aim, two-dimensional (2D) chromatography can be favourable, as it has a higher peak capacity and sensitivity than one-dimensional (1D) chromatography. Therefore, here we review the studies published since 2010 involving gas chromatography (GC) or liquid chromatography (LC) as one of the dimensions.
For the first time, we present the 2D chromatographic characterisation of various biowastes valorised for different purposes (chemical, fuels), together with future prospects and challenges. The aspects related to the 2D chromatographic analysis of polar, poorly volatile, and thermally unstable compounds are highlighted. In addition, it is demonstrated how different 2D setups can be applied for monitoring the biowaste conversion processes.
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•Overview of 2D GC and 2D LC chromatography applied for the analysis of biowastes published since 2010.•Strengths and limitations of the 2D chromatography techniques.•2D plots applied for the monitoring of valorisation processes.•Technical aspects regarding the analysis of polar, poorly volatile, and thermally unstable compounds.
Gas chromatography vacuum ultraviolet spectroscopy: A review Lelevic, Aleksandra; Souchon, Vincent; Moreaud, Maxime ...
Journal of separation science,
January 2020, 2020-Jan, 2020-01-00, 20200101, 2020-01, Letnik:
43, Številka:
1
Journal Article
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Accelerated technological progress and increased complexity of interrogated matrices imposes a demand for fast, powerful, and resolutive analysis techniques. Gas chromatography has been for a long ...time a ‘go‐to’ technique for the analysis of mixtures of volatile and semi‐volatile compounds. Coupling of the several dimensions of gas chromatography separation has allowed to access a realm of improved separations in the terms of increased separation power and detection sensitivity. Especially comprehensive separations offer an insight into detailed sample composition for complex samples. Combining these advanced separation techniques with an informative detection system such as vacuum ultraviolet spectroscopy is therefore of great interest. Almost all molecules absorb the vacuum ultraviolet radiation and have distinct spectral features with compound classes exhibiting spectral signature similarities. Spectral information can be ‘filtered’ to extract the response in the most informative spectral ranges. Developed algorithms allow spectral mixture estimation of coeluting species. Vacuum ultraviolet detector follows Beer–Lambert law, with the possibility of calibrationless quantitation. The purpose of this article is to provide an overview of the features and specificities of gas chromatography–vacuum ultraviolet spectroscopy coupling which has gained interest since the recent introduction of a commercial vacuum ultraviolet detector. Potentials and limitations, relevant theoretical considerations, recent advances and applications are explored.
•Quantitative performance of forward fill/flush modulation is investigated in detail.•Parameters influencing efficiency of the modulation are delineated.•Relation between modulated peak shape and ...analyte quantitation is explored.•Role of the modulation fill and flush distances is explored through appropriate calculations.
GC × GC is an advanced separation technique allowing to achieve quantitative and qualitative characterization of complex samples. In order to perform two-dimensional separation, the system must provide suitable peak modulation which will direct short impulses of first column flow towards the second column. Forward fill/ flush differential flow modulation is a cost effective and no cryogen requiring approach which allows modulation over a wide range of analytes with very different boiling points. However, optimization of the flow modulation process can be difficult to understand and quantification performance might be compromised if the parameters of the modulation process are not properly set. Modulated peak shape can be a good indication of the efficiency of the modulation process, however it is not sufficient to guarantee good quantification. Different average velocities in the beginning and the end of the thermally programmed GC run may cause different efficiency of the modulation process in various parts of the chromatogram. The purpose of this work is to investigate quantitative performance of the forward/fill flush modulation and delineate parameters that determine the effectiveness of the modulation process and its ability to properly reflect the quantitative composition of the investigated sample.
Insight into the composition of middle distillates is essential to meet the requirements for product quality but also in terms of complying with ever more stringent environmental regulations. A newly ...introduced vacuum ultraviolet absorbance detector (VUV) possesses both quantitative and qualitative abilities and is amenable to hyphenation with comprehensive two-dimensional gas chromatography (GC×GC). It has good selectivity for hydrocarbon species and permits their differentiation even if they are not chromatographically separated. In this study, quantification of hydrocarbons in 14 gas oils coming from different origins was performed to evaluate the benefits of GC×GC-VUV for the analysis of middle distillates. Coelutions between hydrocarbon families were investigated and spectral decomposition was carried out for quantification of coeluted hydrocarbon families. Quantification obtained with GC×GC-VUV was compared with conventional techniques such as GC×GC-FID with prefractionation, MS method based on ASTM D2425, UV spectroscopic analysis, and bromine number. In general, good comparability was obtained between GC×GC-VUV and all the different techniques for major hydrocarbon families, however with a gain in time and/or information when using GC×GC-VUV. This demonstrates that GC×GC-VUV can be considered as a relevant tool for the detailed analysis of middle distillates, regardless of their origin.
Comprehensive two‐dimensional gas chromatography with vacuum ultraviolet detection results in sizable data for which noise and baseline drift ought to be corrected. As the data is acquired from ...multiple channels, preprocessing steps have to be applied to the data from all channels while being robust and rather fast with respect to the significant size of the data. In this study, we have described advanced data preprocessing techniques for such data which were not available in the existing commercial software solutions and which were dedicated primarily to noise and baseline correction. Noise reduction was performed on both the spectral and the time dimension. For the baseline correction, a morphological approach based on iterated convolutions and rectifier operations was proposed. On the spectral dimension, much less noisy and reliable spectra were obtained. From a quantitative point of view, mentioned preprocessing steps significantly improved the signal‐to‐noise ratio for the analyte detection (circa six times in this study). These preprocessing methods were integrated into the plugim! platform (https://www.plugim.fr/).
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