Novel Graphene-based Nanocomposites And Their Enhanced Synergetic Photoelectric Conversion Properties

Graphene, a fascinating two-dimensional layered hexagonal lattice of carbon nanomaterial with atomic thickness, is a more attractive supporting material for nanoobject loading due to its high surface area, fast two-dimensional electron-transfer kinetics, good mechanical strength, and high stability, which has been widely applied in the photoelectric conversion, energy storage, catalysis, biological medicine, and so on. Recently, a unique three-dimensional porous graphene structure has been obtained via hydrothermal reaction, which has high specific surface area and super charge transfer properties can avoid the close stacking of graphene sheets by forming irreversible agglomerates during the assembling and drying process, the limitation the accessible surface areas for electrolyte ion infiltration and the loss of a huge electro-active sites. It means that this novel graphene structure is an ideal prototype to maximize the specific surface area and develop high performance of catalyst and photoelectric device. In this thesis, in order to enhance the photocatalytic properties of wide band gap semiconductors(TiO2 and ZnO), we introduce different sensitive materials to embed in the unique three-dimensional porous graphene structure to extend the range of light absorption, accelerate the charge separation and transmission,as well as increase the restricted reactive sites. Details are shown as follows:1) A novel 3D graphene-based CdS/P25/graphene aerogel is successfully and directly produced by a facile one-step hydrothermal self-assembled approach. We used these CdS/P25/graphene aerogel electrodes in photoelectrochemical studies. The results confirm that the ternary aerogel electrode shows the highest photocatalytic activities, which benefits from superior light-harvesting efficiency, extremely efficient charge separation properties, and superior durability of the material. More importantly,it extends the range of light absorption and facilitates the separation of photogeneration carriers.2) We utilize both the visible absorption of CdS and the excellent electrical properties of graphene to design a new advanced-sunlight-activated photocatalystCdS/ZnO/graphene. Benefiting from the high specific surface area and the flexible sheet-like structure, graphene emerged as an excellent platform on which to load both ZnO and CdS nanoparticles to form CdS/ZnO/graphene ternary composites, which enhanced photoelectrochemical properties, meaning it could solve the disadvantages of ZnO.3) As one of the most investigated functional material in semiconductor photocatalysis, titanium dioxide(TiO2) has been widely used in the fields of environmental pollutant degradation and energy conversion for its non-toxicity,effectiveness, low budget, and chemical stability. However, the photocatalytic activities of titanium dioxide are seriously limited by the photocatalytic sensitivity in the UV region, the fast recombination of photogenerated electronehole pairs and the limited reactive site. So we fabricated a new type of multifunctional 3D MoS2/P25/graphene ternary aerogel by a facile one-step hydrothermal self-assembled approach. The obtained hybrid aerogel exhibit well defined interconnected 3D mesoporous microstructure, superior photoelectrochemical properties and outstanding photo-degration activity under UV irradiation, as an improvement of 6 times of photocurrent(37.45 mA/cm2) at +0.6 V than pure P25, and the photodegradation can be completed within 15 min.