Preparation and Humidity-Sensitive Properties of Graphene Oxide in Different Oxidation Degree

Based on the various oxygenic functional groups and huge specific surface area of graphene oxide,the humidity sensitive properties of graphene oxide with different oxidation degree has been researched.The graphite oxide samples with different oxidation degree were prepared by modified Hummers method.Then the samples were dispersed in water by ultrasonication to form homogeneous graphene oxide dispersions,and the humidity sensing elements of thin graphene oxide film were prepared.Structural and spectral analysis for the experiment process samples were carried out by X-ray diffraction,scanning probe microscopy,infrared spectrum,Raman spectrum and X-ray photo electron emission microscopy.The results shows: the basal spacing of graphite oxide is about 0.9 nm.With the increasing of oxidation degree,diffraction peak of graphite in graphite oxide were gradually disappearing,the crystallite size of graphite phase decreasing,O/C ratio increasing and the degree of oxidation going up.Monolayer graphene oxide with the thickness of 1.3 nm more or less can be dispersed in water.Functional groups of OH,C-O-C,C=O and COOH combine with graphene oxide,and the contents of them gradually increasing with the rising of oxidation degree.The response time of the humidity sensors is about 3 seconds,the sensitivity approaches to 99%.In the relative humidity of 11.3%-93.6%,the resistance of elements significantly reducing with increasing of humidity,logarithmic resistance of graphene oxide elements with higher degree of oxidation is linear with relative humidity.The higher the oxidation degree was,the greater the element′s sensitivity was,the shorter the response time was.