Design, Preparation And Properties Of Graphene-semiconductor Nanocomposite

Graphene, due to its unique structure as a single layer of carbon atoms in a honeycomb lattice, has exceptional physical and chemical properties such as high surface area and carrier mobility, good transparency, strong Young’s modulus and excellent thermal conductivity, which make it a very promising candidate in various applications. In addition to the pristine graphene, a variety of graphene-based nanocomposites have also been proposed to realize the multifunction of nanocomposite as well as to investigate the interaction between the graphene and other materials. Actually, various of binary nanocomposites including "graphene-semiconductor","graphene-magnetic","graphene-metal" and even ternary nanocomposite have been synthesized successfully and utilized widely for energy generation and storage, sensor, photocatalyst, drug delivery, and photodetector.This dissertation is focused on the fundamental problems and the pivotal techniques for the design, synthesis, performance and application of the graphene-based nanocomposite, and its contents are introduced briefly as following.In chapter one, we first reviewed the structure, properties, synthesis strategies and existing challenges of the graphene and its nanocomposite, then we presented the backround and the motivation of our research.In chapter two, we produced a linker-free connected reduced graphene oxide/CdSe Nanoparticles (Graphene-CdSe) nanocomposite by directly anchoring CdSe NPs onto R-GO. The nanocomposite was provided with tunable morphology and well charge transfer character. We constructed a high-performance photodetector device based on the Graphene-CdSe nanocomposite. The device can be utilized in various areas with high photosensitivity, fast response speed (rising edge:≤250μs and decreasing edge:～500μs) and high stability. Moreover, both of the excellent photoresponse performance and the photoluminance quenching of this nanocomposite have well been interpreted with the fast charge transfer behavior between CdSe and graphene.In chapter three, we succeeded in designing and synthesizing of a ternary nanocomposite of Graphene-TiO2-Fe3O4(GTF), which can be used as a low-cost, re-collectable, and stable photocatalyst for degradation of organic dyes. GTF showed excellent combination of three materials:i) TiO2NPs as a semiconductor photocatalyst to degrade the dye; ii) Graphene as an effective electron pathway to suppress the charge recombination in TiO2and enhance its photocatalytic activity; and in) Fe3O4NPs as a magnetic material for the magnetic separation. The result showed that the RGO can shunt most of photo-generated electrons from the TiO2NPs and thus decrease the opportunity of electron transfer to the Fe3O4NPs and suppress the photo-dissolution of Fe3O4NPs effectively, making the structure and properties of GTF more stable. Furthermore, the GTF nanocomposite works well in different pH environment and is capable to eliminating the mixture of various dyes. It can even be used under the illumination of the sunshine. These abilities make GTF an excellent candidate in the treatment of organic polluted water.In chapter four, we investigated the charge separation and the transport properties of graphene-CdSe nanocomposite. Athough anchored with CdSe NPs, the dominating transport mechanism of the nanocomposite still preserves the behavior of two-dimensional variable range hopping (VRH). It was found that the photoinduced carriers in CdSe nanoparticles could transfer rapidly into the graphene and resulted in the increase of conductance of nanocomposite with the incident light intensity. When the incident light is weak or at the low temperature, the dependence of the photocurrent on the incident light intensity demonstrates a linear behavior. This is because the various defects in the nanocomposite trap or annihilate the photocarriers dominantly in this case. However, as the incident light increases, the process of direct recombination between the photoinduced electrons and holes increases gradually. As a consequence, the dependence of the photocurrent on the incident light intensity becomes a sublinear.In chapter five, we prospected the existing challenges as well as the opportunities for the furture researches of the graphene-based nanocomposites.