Preparation And Photocatalytic Properties Of Graphene-based Nanocomposites

Photocatalytic semiconductor with single component has many deficiencies,so this thesis modified the semiconductors based on graphene so as to improve their photocatalytic activity.Three kinds of photocatalyst were prepared:(1)TiO2 with different crystal mixture ratio;series of composites with different graphene loading;(2)composite material that graphite like g-C3N4 and graphene co-modified TiO2 with exposed {001} facets;(3)series of sulfide and graphene composite materials.The structure and optical properties of the above samples were characterized by XRD,FESEM,FT-IR,TEM,XPS,LRS,BET and UV-vis DRS.The activity of the catalyst was investigated by degradation of methyl blue(MB)and methyl orange(MO).Various reasons of the composites can improve photocatalytic performance were analysised depthly.The results showed that HCl and CTAB are able to regulate the phase of TiO2.Crystal ligand field theory and Ostwald ripening mechanism can explain the phase transition mechanism.The crystal phase ratio with a continuous change,and there is no third crystal appeared.The photocatalysis experimental results showed that the photocatalytic activity of mixed phase TiO2 was higher than that of single phase TiO2,this is results from the presence of heterojunction in mixed phase TiO2,and generated synergistic effect(mixed crystal effect),improved photocatalytic activity and the separation efficiency of photogenerated electrons and holes.The activity was further improved after mixed phase TiO2 and graphene composited.The TiO2 in the graphite g-C3N4/{001}TiO2/graphene composite is pure anatase,and the exposed percentage was 78.2%.F was adsorpted by the surface of composite materials.The high electronegativity of F was advantageous to the electrons passed from TiO2 and g-C3N4 by O-Ti-F and C-N-F chain to the F and/or graphene.At least two heterogeneous junction interfaces were formed among these three materials,which makes photoproduction carrier transfered effectively.Under ultraviolet light,electronic-hole of TiO2 and g-C3N4 can be separated by F and graphene,and the time of compositing was shortened,so as to improveing the photocatalytic performance.A series of CdxZn1-xS nanospheres with three-dimensional(3D)structure was synthesized by one-pot solvent hot method,The composition of CdxZn1-xS can be regulated by changing the molar ratios of Cd/Zn,and they were composited with graphene successfully.What's more,graphene can obviously alleviate the agglomeration of sulfide nanospheres and effectively restrain the light corrosion phenomenon of sulfides especially ZnS to keep their relatively complete morphology.The photocatalysis experimental results showed that the sample Cd0.5Zn0.5S has best activity.The activity was further improved after they composited with graphene.Graphene was played a key role in the aspect of improving the activity of catalyst.Because of the introduction of graphene,the specific surface area of composite materials hvave increased,and the adsorption of pollutants was enhanced;the separation of e--h+was promoted by good electrical conduction performance of graphene,it make them migrated to the surface.The chance of contacting with contaminants was increased.