Synthesis As Well As Optical And Electrical Properties Of Reduced Graphene Oxide And Graphene Oxide/ZnO Hybrid Material

Graphene possesses especial properties including ballistic conductivity, excellentelasticity, outstanding mechanical strength, high surface area, and rapid heterogeneouselectron transfer. Therefore, as a new nanomaterial, graphene is expected to apply forvarious devices, such as field-effect transistors, resonators, transparent anodes,supercapacitor devices, etc. Besides the graphene with only one atomic layer,however, reduced graphene oxide and graphene/nanoparticle hybrid material alsoexhibits aforesaid excellent properties and widely applications, and needs to be paidmore attentions. In addition, the availability of several types of oxygen-containingfunctional groups on the basal plane and the sheet edge allows graphene oxide tointeract with a wide range of organic and inorganic materials in non-covalent,covalent and/or ionic manner so that functional hybrids and composites with unusualproperties can be readily synthesized. Moreover, manipulation of the size, shape,oxygen functional groups and relative fraction of the sp²-hybridized domains ofgraphene oxide by reduction chemistry provides opportunities for tailoring itsoptoelectronic properties. Furthermore, in contrast to pure graphene, reducedgraphene oxide is fluorescent over a broad range of wavelengths. The interactionsbetween reduced graphene oxide and other molecules resulted in photoinducedelectron transfer and significant fluorescence quenching, allowing development of asimple sensor for biomolecules and metal ions. Based on above analysis, in thisdissertation, we have prepared functional reduced graphene oxide and grapheneoxide/ZnO nanoparticles hybrid material using a very simple and straight chemicalreaction, and investigated the electrical and optical properties for reduced graphene oxide, as well as the photoinduced electron transfer properties between grapheneoxide and ZnO. The main results are listed as follows:1. A green route of using a very simple and straightforward chemical reactionultrasonically, under alkaline condition, rather than using hydrazine, is utilized toobtain the hydrophilic reduced graphene oxide sheets, via removing oxygenfunctional groups from graphene oxide and self-repairing the aromatic structure. It isfound that the conductivity for the obtained reduced graphene oxide could be tuned bychanging pH value in alkaline solution, and the current-voltage (I-V) curves for bothgraphene oxide and reduced graphene oxide exhibit nonlinear and slightly asymmetric.Reduced graphene oxide shows a pronounced increase in the electrical conductivity,compared to graphene oxide.2. The luminescent reduced graphene oxide small sheets (average diameter:30⁵0nm) are prepared by using a simple and eco-friendly solvothermal process, andshow an obvious excitation-dependent PL emission as the excitation wavelengthvaries from300to500nm. In particular, under excitation at340nm, a strongest blueemission occurs, whose quantum yield reaches ca.3.2%as Rhodamine B is used as areference. This offers a simple pathway to prepare the luminescent reduced grapheneoxide small sheets. Furthermore, the emission exhibits a good resistance to the changeof pH for the surroundings, which could be beneficial to the practical applications inthe field of optoelectronics, and molecule detection.3. We have developed a hydrothermal method for reduced graphene oxide sheets,having a strong blue emission. Under UV excitation, the reduced graphene oxidesheets show a strong blue emission at440nm. As the pH increases, the intensity ofphotoluminescence decreases after initial increase. We have explored the influence ofdifferent metal ions on fluorescence for reduced graphene oxide, which can be usedfor detecting heavy metal ions such as Pd²⁺, Hg²⁺, and Cd²⁺.4. A hybrid material of graphene oxide sheets beaded with ZnO nanoparticles isprepared. The material extends over several hundred square nanometers, in which theZnO nanoparticles (average diameter (5nm)) evenly disperse on the graphene oxidesheet. Both the surface photovoltage and surface photocurrent intensity for the material are much stronger than those for pure ZnO nanoparticles, meaning that thefree charge carriers can effectively be transferred from ZnO nanoparticles to grapheneoxide sheets. Our research applies a new method for monitoring the photoinducedelectron transfer from an excited ZnO to a graphene oxide.