Preparation Of Graphene/Semiconductor Nanocomposites And Their Photocatalytic Performance Of Structure-activity Relationship

Graphene-involved composites have recently attracted great attentions in photocatalysis areas due to their superior catalysis properties.It is widely considered that these added carbon sheets can effectively enhance the photocatalysis activity of semiconductors by improving the light adsorption and the photo-generated charge separation of these as-used semiconductors.Nevertheless,along with the increase of usage of graphene,some inherent negative problems aroused by themselves such as light shield or/and scatting gradually appear,which in return affects the photocatalysis properties of these graphene-involved composites.Thus,in most researches,the photocatalysis activity of these composites is usually optimized just by adjusting the added dosage of graphene.In fact,due to the inadequately utilization of them,these graphene sheets have not yet given full play to their advantages in enhancing photocatalysis activity of semiconductors,the aforementioned side effects have started to be prominent.Accordingly,in the presence of these negative effects,we have reasonably designed the structure of graphene sheets in the TiO2-G composites to make more effectively use of them in photoredox system.Furthermore,noble metal nanoparticles with localized surface plasmon resonance effect have a strong and broad absorption of the sunlight in the visible light region,which is often used to enhance the photocatalytic activity of semiconductors.We intend to load Ag nanoparticles in the TiO2-G matrix,use Ag and graphene as cocatalyst to enhance the photocatalytic performance of TiO2.The dissertation is mainly focused on:(1)Graphene-pasted TiO2 spheres have been prepared successfully by a two-step method,including attaching relatively small graphene oxide sheets onto the surface of the modified TiO2 spheres and the in-situ photocatalysis reduction of these graphene oxide sheets.Since coated almost totally on the surface of TiO2 spheres,these added graphene sheets are utilized more fully in these as-obtained graphene-pasted composites,which possess more interfaces between graphene and TiO2 and can make better use of the irradiated light compared with that of traditional graphene-involved TiO2 composites.As a result,these graphene-pasted TiO2 spheres always display higher photocatalysis activity in both methyl orange dye degradation and 4-nitrophenol reduction than that of control graphene-TiO2 spheres in the case of the same usage of these carbon sheets,which indicates more efficient use of graphene sheets in these graphene-pasted samples in photocatalysis systems.(2)Graphene-pasted TiO2 spheres have been prepared successfully by attaching relatively small graphene oxide sheets onto the surface of the modified TiO2 spheres and the in-situ photocatalysis reduction of these graphene oxide sheets.TiO2-SG-Ag nanocomposite was obtained by loading Ag nanoparticles in the TiO2-SG nanocomposite.The synergetic effect between the Ag nanoparticles and graphene sheets as cocatalyst can efficiently accelerate the separation of photogenerated carriers in the photocatalytic process,improve interfacial charge transfer processes,and thus futher enhanced the photocatalytic activity.