Synthesis Of Carbon Nano-hybrid Materials For Energy Storage And Photoelectric Conversion Applications

Graphene, a two-dimensional (2D) form of carbon atoms with a hexagonal lattice structure has attracted enormous research interest since it first use in 2004. Graphene is a zero band-gap semiconductor material, its unique structure and these outstanding properties qualify graphene as one of the most important materials for a wide range of applications in electronics devices, gas sensor, energy storage and hybrid materials. To promote the photoelectronic application, is one of the reasons for the huge increase in the number of research projects aimed at functionalization of graphene, meanwhile, there is another way to get a strong photoluminescence carbon material by gradual cutting graphene, so-called carbon dots (C dots).The main purpose of this thesis is to design, synthesize and modify carbon nano-hybrid materials for energy storage and photoelectronic response application. We developed new method for functional nano-materials based on graphene and C dots and study their applications in photonics, energy storage and photoelectrochemical. The main nano-hybrid materials include free radical promoted conversion of graphite oxide, small organic molecules covalently functionalized graphene composite, C dots/CdS nano-hybrid thin films and small organic molecules covalently functionalized white-light emitting C dots. The obtained carbon nano-hybrid materials were characterized to explore their potential applications in the fields like lithium ion battery, supercapacitor and photocatalysis.The main results in this thesis are listed as follows:1. The preparation of chemically modified graphene (CMG) generally involves reduction of graphite oxide (GO) using various reducing reagents. We report a free radical promoted synthesis of CMG, which does not require any conventional reductant. We demonstrated that the phenyl free radical can efficiently promote the conversion of GO into CMG under mild condition, and produces phenyl functionalized CMG. This pseudo "reduction" process is attributed to a free radical mediated elimination of the surface-attached oxygen-containing functionalities. This work illustrates a new strategy for preparing CMG that is alternative to the conventional means of chemical reduction. Furthermore, the phenyl functionalized graphene shows excellent performance as electrode materials for lithium battery applications.2. We have prepared the photoactive graphenes by functionalization using ruthenium complex, and studied its photocatalysis and supercapacitor applications. Phenanthroline (P-NH2) was synthesized successfully and subsequently immobilized on graphene oxide through amide bond to obtain G-P composite. The G-RuP composite was synthesized through complexation ruthenium bipyridine to G-P. We can confirm that the organic molecules were functionalized onto graphene oxide by UV-vis, FTIR, SEM and TEM etc. The G-RuP exhibits obvious photoelectrochemical response under visible light irradiation, indicating that the photogenerated electron-hole can separate effectively. We synthesized the tetrahydroquinoline products using G-RuP as a photocatalyst, and compare with traditional photocatalyst RuP. We also tested the supercapacitive properties of G-RuP and G-P, which demonstrated that the RuP molecule can improve the supercapacitor performance.3. We report a facile layer-by-layer method to fabricate uniform C dots/CdS heterojunction films via electrophoretic and sequential chemical bath deposition method, and studied its photoelectrochemical and photocatalytic applications. Because no ligands are used, the strategy facilitates the formation of intimate interfacial contact beneficial for charge separation and transfer, which can lead to a high photocurrent density of 2.6 mA/cm2. In addition, the electron donor-acceptor heterojunction can expedite charge separation and effectively suppress electron-hole pair recombination, eventually contributing to enhanced photoelectrochemical and/or photocatalytic efficiency of the system. As a proof-of-concept, the hybrid films manifested themselves as efficient visible-light-driven photocatalyst when applied for reduction of nitro-benzene derivatives in aqueous phase under low power irradiation. Our findings thus establish a new frontier on the rational design and fabrication of well-controlled hybrid films with built-in heterojunctions for solar light conversion.4. We adopt a simple thermal polymerization method to produce N-doped C dots and synthesized C dots composite (N-C dots-RuP) through covalantly attach RuP molecules. We characterized the surface morphology and optical properties by AFM, SEM, XRD, Raman, FTIR and UV-vis. The N-C dots-RuP exhibits extraordinary properties in solubility and photoluminescence. The N-C dots-RuP emits white light under 365nm irradiation, which provides a new material for the preparation of white LED devices.