Synthesis and characterization of reduced graphene oxide-based composites

Abstract

Graphene, a new class of two-dimensional crystalline material, has shown remarkable electronic, mechanical and thermal properties and great importance in the fundamental research and practical applications. Therefore, graphene is desirable for preparation of composites by mixing it with various metal or semiconductor nanostructures. In order to obtain graphene-based composites with well control of the composite morphology and properties, several methods have been designed and conducted. First, graphene oxide (GO) and reduced graphene oxide (rGO) have been prepared by a modified Hummers method and the hydrazine reduction process, respectively. Through various characterization techniques, their structures and properties have been investigated. The conductive rGO films are fabricated by reduction of spin-coated GO films. By varying the solution volume in the spin-coating process, the film thickness can be adjusted and hence the film transmittance and sheet resistance can be controlled. Second, Cu/rGO nanostructured composites have been synthesized through the electrochemical deposition method. The chronoamperometry has been applied to study the Cu nucleation modes on rGO. This work shows that the Cu nucleation, morphology and density on rGO films can be altered by changing the deposition conditions, such as deposition potential, electrolyte concentration and pH. Third, ZnO/rGO composites have also been obtained through the electrochemical method. The morphology of ZnO is dependent on the thickness of rGO film and the deposition potential. The thicker rGO film and higher deposition potential is beneficial for the growth of crystalline ZnO nanorods. Moreover, a hybrid solar cell using ZnO nanorods deposited on annealed rGO film has been fabricated as a conceptual application, producing a power conversion efficiency of 0.31%. Fourth, the Cu2O/rGO composites obtained by the electrochemical deposition have been explored as well. By changing the pH value of electrolyte, Cu2O with different morphologies and semiconducting behaviors can be deposited on rGO. In order to improve the n-type conducting behavior of Cu2O, chlorine has been electrochemically doped into the Cu2O/rGO composites. The amount of chlorine precursor (CuCl2) in the electrolyte has two-sided effects on the doping of Cl-Cu2O/rGO composites as it determines donor concentration and simultaneously affects the surface coverage of Cu2O crystals on the rGO electrode. Finally, solution processing approach has been chosen for the synthesis of bifunctional Fe3O4-Pt/rGO composite. The as-synthesized composite possesses the magnetic property of Fe3O4 nanoparticles and the catalytic property of Pt nanoparticles. By varying the amount of iron and platinum precursors, the nanoparticle density on rGO sheets can be adjusted. In addition, the Fe3O4-Pt/rGO composite can catalyze the reduction of methylene blue and be recycled within 1 min by applying an external magnetic field for at least 16 times.