O óxido de grafeno (OG), nanomaterial sintetizado a partir do grafite, tem atraído atenção como adsorvente com grande capacidade de remoção de cátions e diversos contaminantes de soluções aquosas, devido a presença dos grupos hidroxila, epóxi, carbonila e carboxila em sua superfície. Este trabalho, visa avaliar o potencial do óxido de grafeno bruto (OG) e de sua forma imobilizada em poli(divinilbenzeno) (PDVB-OG) na remoção de íons de césio de uma solução aquosa sintética. Os experimentos foram realizados em batelada, e foi avaliado a influência do tempo de contato e da concentração inicial de íons de césio. Para descrever a isotermas de equilíbrio foram aplicados os modelos de Langmuir e Freundlich, e a cinética do processo de adsorção, foi avaliada utilizando-se os modelos de pseudo-primeira ordem, pseudo-segunda ordem e difusão intrapartícula. Para prever a espontaneidade do processo de adsorção, foi calculado a energia livre de Gibbs. Nos experimentos de adsorção de íons de césio, o OG e o nanocompósito PDVB-OG, após 30 min. de contato, apresentaram taxa de remoção de 80% e 63% respectivamente. O modelo que melhor descreveu o processo de adsorção, para ambos adsorventes, na faixa de concentração de 30 a 130 mg.L-1, foi o de Langmuir e a capacidade máxima de adsorção calculada foi de 17 mg.g-1 para o OG e de 15 mg.g-1 para o PDVB-OG. Tanto para o OG quanto para o PDVB-OG, o modelo cinético que melhor descreveu o processo foi o de pseudo-segunda ordem e o valor da energia livre de Gibbs determinou que a adsorção dos íons de césio foi espontânea. A matriz polimérica não apresentou capacidade de remoção significativa, evidenciando que a adsorção dos íons césio pelo nanocompósito de PDVB-OG se deve a presença do OG imobilizado. Por outro lado, devido a maior densidade, o PDVB-OG foi facilmente separado da solução por decantação após o experimento de adsorção. Os resultados indicam a capacidade do OG e do nanocompósito PDVB-OG em tratar rejeitos líquidos radioativos, a fim de minimiza-los. / Due to the presence of hydroxyl, epoxy, carbonyl and carboxyl groups on its surface, graphene oxide (GO), synthesized from graphite, has attracted attention as a high adsorbent of cation removal and several contaminants from aqueous solutions. This work aims to evaluate the potential of graphene oxide (GO) and its immobilized form as poly(divinylbenzene) (PDVB-GO) in the removal of cesium ions from a synthetic aqueous solution. The experiments were performed in batch, and the influence of the contact time and the initial concentration of cesium ions were studied. Langmuir and Freundlich models as the equilibrium isotherms, and the kinetics of the adsorption process, pseudo-first order, pseudo-second order and intraparticle diffusion models, were evaluated GO and PDVB-GO, removed after 30 min. of contact time 80% and 63% of cesium ion, respectively for both adsorbents. The maximum adsorption capacities were 17 mg.g-1 for the GO and 15 mg.g-1 for the PDVB-GO. For both GO and PDVB-GO, Langmuir model fitted better in the adsorption process, the Gibbs Free Energy showed that this process for were spontaneous and the kinetic models were the pseudo-second order. As the polymer matrix, PDVB, has no significant removal capacity, the adsorption of the cesium ions by the PDVB-GO nanocomposite is due to the presence of the GO. On the other hand, the PDVB-GO was easily separated from the solution by decantation after the adsorption experiment. The results indicate the ability of the GO and the PDVB-GO nanocomposite to treat radioactive liquid wastes in order to minimize them.

This work focuses on improving the quality of carbon-based core-shell materials for high performance liquid chromatography (HPLC) via the characterization of the core materials, and also the development of chromatographic methods (separations) for them. In the early part of this work, I applied organic synthesis to make uniform, spherical poly(divinylbenzene) (PDVB) microspheres, and then carbonized them to prepare carbon core materials for core-shell particle synthesis. Here, I studied in detail the surface and material properties of these particles with multiple instruments, which allowed me to describe the physical and chemical changes that took place during each treatment. The uniform, spherical carbon core materials greatly improved the efficiency of the previously developed carbon-based core-shell HPLC columns from ca. 70,000 plates per meter (N/m) to ca. 110,000 N/m for various alkyl benzenes. Later, I focused on generating application notes to showcase these mixed-mode HPLC columns. Here, liquid chromatography mass spectrometry (LC-MS) was used for the detection of analytes that lack chromophores for UV detection. In this dissertation, Chapter 1 contains a historical background and theory of HPLC along with a review of the use of carbon-based core-shell materials for elevated pH and temperature applications. Chapter 2 describes the improvement of the efficiency of carbon-based materials for HPLC using carbonized PDVB microspheres as the carbon core material. Chapter 3 is a study on the characterization of carbonized PDVB microspheres with multiple instruments. Chapter 4 describes the separation of cannabinoids using three types of carbon-based mixed-mode HPLC columns. Chapter 5 consists of (i) guidelines for the retention mechanism of the core-shell particles that have been commercialized for chromatography by Diamond Analytics, a US Synthetic Company in Orem, Utah, and (ii) application notes for these columns. Finally, Chapter 6 discusses possible future work.