В работе проведено исследование структурных, оптических и электронных свойств графитоподобного нитрида углерода (g-C3N4), синтезированных методом пиролиза мочевины при температурах 450–600°С. Метод функционала плотности использован для подтверждения выводов, основанных на экспериментальных данных. Был выполнен анализ литературных данных по g-C3N4, были рассмотрены структурные особенности получаемого материала и их оптическое поглощение. Также приведено описание используемых экспериментальных методов и математическое описание используемого метода моделирования – теории функционала плотности. Структура синтезированных образцов g-C3N4 определена по спектрам рентгеновской дифракции и ИК поглощения. Оптическое поглощение образцов исследованы по спектрам диффузного отражения, преобразованным в соответствии с теорией Кубелки-Мунка, оценка ширины энергетической щели для прямых и непрямых оптических переходов проводилась по методу Тауца. Была установлена линейная зависимость параметров кристаллической решетки и ширины щели от температуры синтеза. Для подтверждения экспериментальных результатов было проведено моделирование возможных структур g-C3N4 методом функционала плотности в пакете Quantum ESPRESSO. Была проведена оптимизация положений атомов для различных модельных структур, рассчитаны ИК спектры и зонные структуры электронных состояний. / In this work we investigated structural, optical and electrical properties of graphitic carbon nitride (g-C3N4) synthesized by thermal treatment of urea at 450– 600°C. Density functional theory calculations were performed to support suggestions based on experimental data. Available research data for g-C3N4 was studied, with interest in structural and absorption properties of the material. Additionally, the experimental methods and theory behind DFT-calculations were described. We determined the structure of g-C3N4 samples based on XRD and IR spectra. Optical absorption was investigated using diffuse reflectance spectra transformed with Kubelka-Munk function. Energy band gap was evaluated with Tauc plot for direct and indirect optical transitions. We show that crystal lattice parameters and band gap linearly depend on the synthesis temperature. To further prove our assumptions based on experimental data we also performed DFT-calculations for g-C3N4 in Quantum ESPRESSO software package. We calculated IR spectra and electronic band structures for models of each sample.

Les médicaments traditionnels à base de plantes (tradimédicaments) sont très utilisés par les populations africaines. Mais leur qualité est difficile à maîtriser, car ce sont des mélanges complexes de plusieurs drogues végétales ou des préparations à base de drogues végétales d’origine souvent inconnue et/ou très variable. Le profil chromatographique des métabolites phytochimiques constitue un outil important pour l’évaluation de la qualité de ces produits.L'objectif de ce travail est de proposer un protocole de préparation des échantillons et d’établissement de profil par chromatographie liquide et chromatographie en phase gazeuse des métabolites apolaires, pour l’évaluation de la qualité des médicaments traditionnels à base de plantes.La méthodologie est basée sur le traitement chimiométrique des profils chromatographiques des métabolites apolaires issus de différents lots de feuilles de Combretum micranthum et Mitracarpus scaber.Le profilage métabolique s’est effectué par chromatographie liquide sur Carbone Graphite Poreux en milieu non-aqueux et par chromatographie en phase gazeuse à haute température, couplées à la spectrométrie de masse, après extraction au dichlorométhane et élimination de la chlorophylle adsorbée sur charbon actif.L'analyse chimiométrique des données utilisant l’analyse PLS-discriminante avec ou sans correction orthogonale du signal, appliquée aux profils chromatographiques des feuilles de Combretum micranthum et Mitracarpus scaber, a montré de faibles différences entre les lots de chaque drogue végétale, et une différenciation claire des deux drogues végétales.Les deux méthodes d'analyse par chromatographie liquide et chromatographie en phase gazeuse permettent de détecter la plupart des métabolites secondaires apolaires bioactifs ou non déjà identifiés dans les feuilles des deux espèces. / The traditional herbal medicines are widely used by African people. But their quality control is difficult, because they are complex mixtures of several herbal drugs or herbal drugs preparations. Their origin is often unknown and/or highly variable. The chromatographic profile of phytochemical metabolites is an important tool for quality assessment of these products.The objective of this work is to propose a protocol for sample preparation and liquid chromatographic and gas chromatographic profiling of non-polar metabolites for quality assessment of africain traditional herbal medicinal products.The methodology is based on the chemometric treatment of chromatographic profiles of non-polar metabolites from different batches of leaves of Combretum micranthum and Mitracarpus scaber.Metabolic profiling is carried out by non-aqueous liquid chromatography on Porous Graphitic Carbon and by high temperature gas chromatography, coupled with mass spectrometry, after extraction with dichloromethane and removal of chlorophyll adsorbed on activated charcoal.The chemometric data analysis using PLS-discriminant analysis with or without orthogonal signal correction applied to the chromatographic profiles of leaves of Combretum micranthum and Mitracarpus scaber showed small differences between batches of each herbal drug, and a clear differentiation two herbal drugs.Both analyses by liquid chromatography and gas chromatography methods detect most non-polar metabolites bioactive or/not already identified in the leaves of both species.

<p>In this thesis, porous graphitic carbon (PGC) has been used as packing material in packed capillary liquid chromatography. The unique chromatographic properties of PGC has been studied in some detail and applied to different analytical challenges using both electrospray ionization-mass spectrometry (ESI-MS) and ultra violet (UV) absorbance detection. </p><p>The crucial importance of disengaging the conductive PGC chromatographic separation media from the high voltage mass spectrometric interface has been shown. In the absence of a grounded point between the column and ESI emitter, a current through the column was present, and changed retention behaviors for 3-O-methyl-DOPA and tyrosine were observed. An alteration of the chromatographic properties was also seen when PGC was chemically oxidized with permanganate, possibly due to an oxidation of the few surface groups present on the PGC material. </p><p>The dynamic adsorption of the chiral selector lasalocid onto the PGC support resulted in a useful and stable chiral stationary phase. Extraordinary enantioselectivity was observed for 1-(1-naphthyl)ethylamine, and enantioseparation was also achieved for other amines, amino acids, acids and alcohols. </p><p>Finally, a new strategy for separation of small biologically active compounds in plasma and brain tissue has been developed. With PGC as stationary phase it was possible to utilize a mobile phase of high content of organic modifier, without the addition of ion-pairing agents, and still selectively separate the analytes. </p>

In this thesis, porous graphitic carbon (PGC) has been used as packing material in packed capillary liquid chromatography. The unique chromatographic properties of PGC has been studied in some detail and applied to different analytical challenges using both electrospray ionization-mass spectrometry (ESI-MS) and ultra violet (UV) absorbance detection. The crucial importance of disengaging the conductive PGC chromatographic separation media from the high voltage mass spectrometric interface has been shown. In the absence of a grounded point between the column and ESI emitter, a current through the column was present, and changed retention behaviors for 3-O-methyl-DOPA and tyrosine were observed. An alteration of the chromatographic properties was also seen when PGC was chemically oxidized with permanganate, possibly due to an oxidation of the few surface groups present on the PGC material. The dynamic adsorption of the chiral selector lasalocid onto the PGC support resulted in a useful and stable chiral stationary phase. Extraordinary enantioselectivity was observed for 1-(1-naphthyl)ethylamine, and enantioseparation was also achieved for other amines, amino acids, acids and alcohols. Finally, a new strategy for separation of small biologically active compounds in plasma and brain tissue has been developed. With PGC as stationary phase it was possible to utilize a mobile phase of high content of organic modifier, without the addition of ion-pairing agents, and still selectively separate the analytes.