Studies of carbon dots, nanodiamonds, and silica particles: Potential stationary phases for chromatography

Fluorescent carbon dots (C-dots) were synthesized using top-down and bottom-up methods. For the bottom-up method, C-dots were obtained by one-step thermal pyrolysis of citric acid with different passivation reagents. The photoluminescent properties of the synthesized C-dots were compared to those of C-dots prepared without adding a passivation agent and to those of PEG 1500N capped C-dots. Separation by capillary electrophoresis indicated that the synthesized products have different complexity, i. e. some had distinct peaks while others produced broad bands. C-dots produced by top-down method were obtained from carbon fibers and their surface was passivated with different reagents. The luminescent properties of passivated C-dots were studied. Anion exchange (AE)-HPLC was used to study the complexity of the mixture. These studies provided information regarding the relationship between surface passivation and photoluminescent properties.;To separate and purify the C-dots from small fluorescent molecular byproducts, a systematic study of the preparation, separation, and purification of C-dots mixture is presented. Mixture of C-dots and small molecules were produced by hydrothermal reaction of citric acid and amine (EDA or DETA). A trend for the observed fluorescence (i.e., quantum yield) as a function of the precursor-reagent composition (i.e., the ratio of amine to acid precursors) was established for the reaction mixture. The relatively high quantum yields observed were attributed to the production of highly fluorescent small molecules. The separation of highly fluorescent molecular species and C-dots were conducted by dialysis using membranes with different MWCO. HPLC and CE were used as effective tools for analysis and separation of C-dots. Reversed phase HPLC was employed for the separation and analysis of C-dots and molecular fluorophores mixtures. The presence of the highly fluorescent small molecules was proved and its structure was determined by electrospray ionization mass spectrometry.;Nanomaterials have shown potential as separation media. The construct, characterization, and preliminary evaluation of silica-nanodiamonds composite as chromatographic materials for HPLC were explored. Nanodiamond (ND) particles, obtained from detonation soot, were oxidized and/or hydrogenated. Both, the non-hydrogenated and hydrogenated ND particles were coupled to micron-size organo-silica particles. Ultraviolet (UV) radiation and chemical initiators were effective radical initiators for the ND-silica coupling reaction. Commercially available ND primary particles were also coupled to the silica particles. The ND-containing silica particles were packed into columns to study their initial feasibility as adsorbent material for liquid chromatography. The organo-silica particles decorated with hydrogenated NDs showed to possess reversed phase type (i.e., hydrophobic) behavior towards the probe compounds, while silica particles decorated with the non-hydrogenated NDs showed polar (i.e., hydrophilic) interactions, both under liquid chromatographic conditions.;During the development of a strategy to attach carbon nanomaterials (i.e., C-dots) to silica particles, photoluminescent silica particles were prepared. Micron- and submicron-sized silica spheres were prepared by modifying the Stober reaction in which luminescent C-dots were incorporated into the spheres during the silica particle formation process. The luminescent submicron particles can potentially be used as fluorescent probes. They were also packed into a HPLC column and tested for potential chromatographic applications.