Synthesis and Reduction of Copper-Coagulated, Graphene Oxide, Free-Standing Thin Films

Abstract

As a two-dimensional material, graphene has attracted great interest among the research groups and the industry due to its exceptional electrical, optical and mechanical properties. Currently, the primary methods for mass production of graphene are focused on the solution-processable chemical redox reaction. The oxidation of graphite introduces a large amount of oxygen functional groups attached onto its basal plane or edges, which makes graphene oxide (GO) sheets hydrophilic to form stable dispersions. However, the starting material graphite gradually becomes an insulator during the oxidation process as a part of planar sp2- hybridized geometry transformed to distorted sp3-hybridized geometry, which decreases the electrical conductivity. As a result, the reduction of GO is essential to recover graphene-like electrical conductivity for practical applications. In addition, the hydrophilic property of GO sheets allows coagulation of divalent metal ions in GO. These ions attach onto the GO basal plane and interact with functional groups resulting in GO/metal ion hybrid thin films with excellent electrical conductivity after reduction. In this work, the effect of coagulation of GO using copper ions (Cu2+) on optical and electrical properties of graphene oxide and reduced graphene oxide is studied. Two different reduction schemes were examined: direct, low-temperature annealing in vacuum and laser reduction of GO and GO-Copper films. This study includes the preparation of GO and GO-Cu stable dispersions, the fabrication of free standing thin films using a doctor blade process, the GO reduction, and the structural and electrical conductivity characterization of the resulting materials. Structural studies involved Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy/ Electron dispersive spectroscopy (SEM/EDS). A four-point probe measurement was used to examine film electrical resistivity.