Capillary Electrophoresis Separation Of Nanomaterials

Graphene, as a two-dimensional nanomaterial, is composed of single layer ofsp2-hybridized carbon atoms in a hexagonal lattice. Since its discovery in2004, graphenehas attracted a lot of attention not only for fundamental studies but also for potentialapplications due to its unique physical, chemical and electrical characteristics. Because ofthe high charge mobility, crystal quality, easily patterned nanometer scale and theatomically precision properties, graphene has been regarded as an excellent candidate forthe non-silicon-based materials for the next generation of field effect transistors or otherelectronic devices.In addition to electronic applications, graphene also has tremendous potential in materialfield. As a conductive, transparent, and ultrathin material, graphene can be used todeveloping photovoltaics devices. Graphene has been used to research on various micro-and nanodevices or as building blocks for new composite materials. Graphene has alsobeen used for the fabrication of chemically modified electrodes, the preparation ofchemical power sources, catalyst and medicinal matrices, and gas sensors.At present, the synthesis methods of graphene are maked up by physical methods andchemical methods, such as micromechanical cleavage, epitaxial growth, chemical vapordeposition and the reduction of graphene oxide. Graphene is mostly polydisperse withdifferent sizes and thickness and easily aggregate due to the-interaction between pieces.Thus, the preparation of highly dispersed and size-controlled graphene is of greatimportance for the application in fabrication of nano or micro electronic devices.Micromechanical cleavage of bulk graphite used to prepare graphene nanosheets is tediousand difficult to control the sizes of graphene sheets. Dialysis and ultrafiltration of GO orgraphene suspension can not obtain graphene pieces with high resolution in sizedistribution. So to develop a separation technique for GO or graphene with high resolutionis a vital step to prepare highly dispersed and size-controlled graphene pieces, which willfacilitate fabrication of the corresponding nano-or micro-devices. In this work, suspended graphene oxide were separated by capillary electrophoresis andthe fractionations were collected onto a platform driven by a motor and subjected tofollowing characterization including Raman spectroscopy, atomic force microscopy （AFM）and transmission electron microscopy （TEM）. Thin-layer and mono dispersed GO sheetswere obtained after CE separation and a CE separation model was suggested. Separation ofGO with high resolution is of great significance for fabrication of chemical or physical GOor graphene micro-or nano-devices. The main points of this thesis are as follows:1. High resolution separation of graphene oxide by Capillary ElectrophoresisSeparation and purification of graphene oxide （GO） prepared from chemical oxidationof flake graphite and ultra-sonication by capillary electrophoresis （CE） was demonstrated.CE showed the ability to provide high-resolution separations of GO fractionations withbaseline separation. The GO fractionations after CE were collected for Ramanspectroscopy, atomic force microscopy and transmission electron microscopy charact-erizations. GO nanoparticles （unexfoliated GO） or stacking of GO sheets migrated towardanode, while the thin-layer GO sheets migrated toward the cathode. Therefore, it need toperform CE twice with reversed electric field to achieve a full separation of GO. Thisseparation method was suggested to be based on the thicknesses of the GO sheets and aseparation model was proposed. This study might be valuable for fabrication of GO orgraphene micro-or nano-device with controlled thickness.2. Electrophoresis of Graphene Oxide by Vertical Electric FieldIn this work, we proposed a novel method to separate graphene oxide （GO） by freesolution electrophoresis in the vertical electric filed. The migration of graphene oxide inthe vertical electric filed is differet from the conventional electrophoresis with the horiz-ontal electric filed. In the end, graphene oxide solution was separation into three layers.The most of graphene oxide in the first layer were thin and large, while the fractionationsin the third layer were mostly unexfoliated GO or graphite. The fractionations in the threelayers were also different in the electrochemistry property. Their difference in the structureand nature needs to be further studied.3. Separation of gold nanoparticles by Capillary Electrophoresis In this work, we studied the electrophoretic behavior of gold nanoparticles in differentrunning electrolytes, including the buffer solution of Na₂SO₄-NaOH （pH10.8） and ofNa₂SO₄-Na₃cit （pH7.1）. In the end of separation, we obtained two electrophoretic zones（smooth and with spikes） in the Capillary electropherogram, which were attributed tocolloidal and suspended particles with the approximately same size. The effects of dete-ction wavelength, injection time, electric field strength and the running electrolytes werestudied.