Synthesis, Characterization And Properties Studies Of Alkylated Graphene And Graphene Quantum Dots

Graphene has attracted enormous attention over the past few years due, in part, to the remarkable electrical, mechanical, and thermal properties of this new material. However, low yield and throughput remain limiting factors in producing large quantities of materials needed for many practical applications, such as capacitors, fuel cells, catalysts, and sensors. In addition, graphene materials produced by many reported methods typically have poor dispersibility limiting their processing capabilities. Therefore, a more facile and reliable method for large-scale production of high quality graphene materials, dispersible in water or organic solvents, is still urgently needed. In addition, graphene is a zero-bandgap semiconductor. The absence of a bandgap in graphene constitutes one of the fundamental obstacles that needs to be overcome before exploiting it as a fluorescent material and facilitating its application in nano-optoelectronic devices. There are two main approachs to tune the electronic structure of graphene. The first one is by means of chemical doping or functionalization, and the other one is by cutting it into ribbons and quantum dots. For example, when their sizes are down to ca.10nm, graphene nanoribbons and graphene quantum dots exhibit strong quantum confinement and edge effects, rendering them semiconducting. Due to their unique structure and exceptional properties, graphene and related materials have been studied extensively in recent years.In this dissertation, graphite were reduced by alkali metal in the presence of an aromatic hydrocarbon such as naphthalene in tetrahydrofuran (THF). Efficient exfoliation of graphene sheets occurs as the alkylation reaction gradually propagates from the graphite edges, producing exfoliated and propagatively alkylated graphene sheets (PAGenes). With the solvothermal treatment of PAGenes in organic solvents such as DMF, the decomposition of microsized graphene sheets occured, giving rise to nanosized alkylated graphene quantum dots (AGQDs).This paper consist of four chapters:In the first chapter, we brief review the properties, preparation and potential applications of graphene and graphene quantum dots (GQDs). Our proposal for this dissertation is also described in this part. In the second chapter, we report a facile and scalable synthetic methodof high quality graphene sheets. Graphite materials were efficiently exfoliated by reductive, propagative alkylation. The exfoliated, propagatively alkylated graphene sheets (PAGenes) not only exhibited high solubility in common solvents such as chloroform, water, and N-methyl-pyrrolidone, but also showed electrical conductivity as high as4.1×103S/m, which is5orders of magnitude greater than those of graphene oxides.In the third chapter, we developed a facile and straightforward approach to fabricate alkylated graphene quantum dots (AGQDs) from propagatively alkylated graphene sheets (PAGenes), and show that the PAGenes has an advantage over graphene oxides (GOs) for producing GQDs. In contrast to most GQDs reported so far, the synthesized AGQDs process pH-independent and ultra-bright PL with quantum yield up to65%. The photocatalytic performance of AGQDs-P25nanocomposites was evaluated by the degration of Rhodamine B under visible light. The excellent photocatalytic performance of the complex photocatalysts indicates that the AGQDs could harness the visible spectrum of sunlight for environmental therapy.In the last chapter, we summarized this paper and gave a prospect of follow-up work.