Controllable Synthesis And Properties Of Graphene Oxide-based Inorganic Nanocomposites

Graphene is a crystalline allotrope of carbon with a two-dimensional and hexagonal lattice form that has triggered considerable interests in recent years,owing to its unique physical and chemical properties.Graphene oxide?GO?,synthesized by the oxidation of graphite,also has the two-dimensional and hexagonal lattice form with outstanding thermal,mechanical and optical properties as well as its unique two-dimensional structure and large surface area.Furthermore,it exhibits good solubility and intercalation properties,owing to the presence of the hydrophilic polar groups?hydroxyl,epoxy,carbonyl,and carboxyl groups?on the basal plane and sheet edges.These hydrophilic groups support GO as an ideal building blocks in GO-based nanocomposites.The objective of this dissertation is to controllable synthesis GO-based inorganic nanocomposites with different sizes and properties.The morphologies,structures and properties of these GO-based inorganic nanocomposites were examined.In addition,their applications in the field of photocatalysis,SERS enhancement and electrochemistry were investigated.The main research contents are as follows:Firstly,controllable synthesis of GO-Au.GO-Ag nanocomposites constructed by different size Au,Ag nanoparticles with GO.The size dependences of their properties are investigated.The synthetic procedure involves two steps:First,synthesis of inorganic nanoparticles or colloids with different sizes;Second,mix the inorganic nanoparticles or colloids with GO in a water-n-butylamine system.The n-butylamine intercalates GO sheets,and plays a pivotal role in the reduction of GO and the immobilization of inorganic nanoparticles onto GO sheets.TEM images show that the prepared Ag,Au nanoparticles were monodisperse with uniform size,and random distributed on the GO sheets;UV-vis absorption spectra show that the surface plasmon resonance absorption peak of Au or Ag nanoparticles has obvious red shift with the increase of particle size.Experimental results show that the properties of as-synthesized composites exhibit obvious size dependence.With the increase of the size of Ag nanoparticles,the surface-enhanced Raman scattering?SERS?effect of GO-Ag was significantly increased,and the yield of glyoxal with GO-Au was decreased with the increase of the size of Au nanoparticles.Secondly,a group of Ag/AgBr/GO nanocomposites were successfully prepared by using different carbon chain length of alkyl bromides as halide sources.The results show that the decompositions of AgBr to Ag accelerate when using the short carbon chain of alkyl ammonium bromide.Photocatalytic experiments show that the photocatalytic activities of Ag/AgBr/GO-CTAB and Ag/AgBr/GO-DTAB are higher than those of Ag/AgBr/GO-TBAB and Ag/AgBr/GO-TMAB.Raman scattering studies indicate that these resultant Ag/AgBr/GO nanocomposites can not only enhance the Raman signals of GO,but also be used as surface-enhanced Raman scattering?SERS?substrates to enhance the Raman signals of dye molecules.Owing to the high photocatalytic performance,chemical stability and SERS effect,Ag/AgBr/GO-CTAB and Ag/AgBr/GO-DTAB nanocomposites can be used as the recyclable SERS substrates.Thirdly,inorganic oxide nanoparticles,ceria oxide?CeO₂?,ferric oxide?a-Fe₂O₃?and copper ferrite?CuFe₂O₄?nanoparticles,were prepared by combusting an emulsion contains metal nitrate,ammonium nitrate,oil phase and emulsifier.These oxide nanoparticles were further loaded onto GO sheets.The structures and morphologies of as-synthesized samples were characterized by X-ray diffraction,Transmission electron microscopy,and UV-Vis diffuse reflectance spectroscopy.The results show that CeO₂,a-Fe₂O₃ and CuFe₂O₄ nanoparticle were synthesized successfully with the average diameter of 80 nm,60 nm and 13.5 nm,respectively.The aggregation of oxide nanoparticles was prevented after they were anchored onto GO sheets.The resultant GO-based nanocomposites,GO-CeO₂ and GO-CuFe₂O₄,have very good light response ability under UV and visible light region.About 92.3%and 98.1%of Rhodamine B dyes were photodegraded under mercury lamp light irradiation for 2 h,in the presence of GO-CeO₂ and GO-CuFe₂O₄ pholocatalysts.It indicates that the resultant GO-CeO₂ and GO-CuFe₂O₄ exhibit excellent photocatalytic activity.Additionally,graphene-metal sulfide/selenium quantum dots?QDs?composites?CCG-PbS,CCG-ZnS,CCG-CdS,CCG-MnS,CCG-PbSe,CCG-ZnSe,and CCG-CdSe?were prepared by?-? stacking of pyridine-capped metal sulfide/selenium QDs and chemically converted graphene?CCG?in aqueous solution.CCG sheets disperse stably in water without the assistance of dispersing agents,only by electrostatic repulsion.The aromatic structures of pyridine capped on metal sulfide/selenium QDs make these QDs dispersible in ethanol or water,and further introduce a ?-? stacking interaction between CCG and QDs,and extend the conjugated structure of CCG.The structural details,formation mechanism,and textural properties of the resultant graphene-metal sulfide QDs composites are characterized by X-ray diffraction,UV-vis absorption,electron microscopy,and Raman scattering studies.The CCG-metal sulfide/selenium composites disperse stably in aqueous solution,allowing them to be potentially used in electrochemistry and easy to form filtered films for further research and application.At last,carbon loaded Au/TiO₂ photocatalytic materials were prepared by using carbon fiber?CF?,carbon nanotubes?CNT?and graphene oxide?GO?as carrier,respectively.TiO₂ nanoparticles were loaded on the surface of carbon materials,and then Au nanoparticles were loaded on the TiO₂ layer.The structural details,morphology and properties of carbon loaded Au/TiO₂ were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?and Raman spectroscopy.The photocatalytic performances show about 85%,92%and 95%of Rhodamine B dyes were photodegraded under mercury lamp light irradiation for 2 h,in the presence of Au/TiO₂/CF,Au/TiO₂/CNT and Au/TiO₂/GO photocatalysts.In addition,Raman experiments showed that Au/TiO₂/CF?Au/TiO₂/GO were also excellent surface-enhanced Raman scattering?SERS?substrates.The Au/TiO₂/CF?Au/TiO₂/GO substrates can clean themselves by photodegradation of adsorbates under mercury lamp light irradiation,and be reused for recycling SERS detection.