Synthesis of Hybrid Nanomaterials based on Defective Nanocarbons and Their Applications

Department of Energy Engineering(Energy Engineering)Development of hybrid nanomaterials has attracted the intensive interest because of their synergetic effect from the advantages of each nanomaterial in various application. The hybrid nanomaterials based on graphene oxide (GO) and carbon nanoparticles (CDs) have been developed due to their abundant functional groups, large surface area and high conductivity. These nanomaterials is applied for a wide range of applications such as bioimaging, therapy, photocatalyst, electrocatalyst, sensor, and photovoltaic devices. However, tremendous efforts are necessary to develop homogeneous and controlled hybrid nanostructure coupled with the study of the unexpected behavior for the excellent efficiency in various fields. In this regard, this thesis describes the approaches to develop new types of hybrid nanomaterials based on GO and CDs functionalized with organic or inorganic materials. This thesis divides into three parts(1) hybrid nanomaterials based on GO, (2) hybrid nanomaterials based on CDs, and (3) origin of photoluminescence (PL) of nanocarbons. The first part introduces the synthesis of gold (Au) and GO nanocomposite for the reduction of nitroarenes and methanol oxidation. In organic catalyst, GO play an important role as supporting and conducting materials, which results in high concentration of Au nanoparticles loaded on GO and thus high catalytic efficiency. In electrocatalyst, layer-by-layer assembly help to develop the controlled thickness of Au-GO film, which exhibits the excellent electron transfer properties. The second part presents CDs functionalized with organic molecules and metal nanoparticles. CDs have the unique optical and electron transfer properties. When conjugated with polymer and targeting molecules, not only PL intensity but also the targeting efficiency is increased, leading to simultaneously targeted bioimaging and photodynamic therapy. Furthermore, heterodimeric silver-CDs nanostructures are developed by photo-reduction, which possess different interfaces, PL intensity, and SPR effects with respect to the amount of additives. Finally, besides the synthesis of hybrid nanomaterials, origin of PL properties of nanocarbons is demonstrated to extend the applications. First, high PL intensity of dual heteroatom doped CDs is synthesized. To elucidate the origin of the unique properties, the structure analysis, photophysical properties, DFT calculations, and single molecule spectroscopy is carried out. Based on these studies, we found that high PL of CDs is achieved from graphitic structure as well as less oxygen groups and nitrogen traps. Furthermore, hybrid carbon nanosheets show solvent-dependent PL emission in accordance with polarity, because of different energy level by shape-tunable behavior.ope