The Evolution Research Of Three-dimensional Structures And Conductivity Of Graphite During Forming Graphenen

Graphite oxide was prepared via modified Hummers method. Different oxidation level’s graphite oxidation products were prepared by changing the amount of KMn O4. A series of different oxidation level’s graphene oxide dispertion were gained after the graphite oxidation products were ultrasonic stripped in the alkaline aqueous solution. Then the graphene oxide membranes were gained through the vacuum filtration. Reduction graphene oxide was prepared from the graphene oxide dispertion via the chemical reduction(choosing the hydrazine hydrate as reductant), the hydrazine hydrate dosage was changed in the chemical reduction, therefore gaining a series of different reduction degree’s RGO samples. Reduction graphene oxide were prepared by chemical reduction、hydrothermal reduction and roast reduction methods, the evolution of micro appearance 、 structural characters and electrical properties were study compared. In view of the structural layer and conductivity of products are destroyed in oxidation-reduction process. High-quality graphene was prepared by directly stripping graphite method. SEM、 AFM、 FT-IT、 XRD、 XPS、UV-vis 、 Raman are adopted to characterize the products’ micro appearance 、 spectroscopy characteristics 、 the oxygen-containing functional groups’ evolution 、 three-dimensional structures and conductivity of the products.The study demonstrates that in the process which graphite forms the graphite intercalation compounds, sulfuric acid molecule and polar hydrogen sulfate ions are inserted into the graphite structure interlayer, π conjugate system of original graphite is destroyed, carbon-carbon bond length increases, the interplanar spacing( d1 0 0、 d110) ⊥ the a-b axis increase, conductivity decreases and randomness increases.With the increase of the KMn O4 dosage, the product’s graphite intercalation compound phase transforms into the graphite oxide phase gradually, oxygen-containing functional groups such as C-OH、 C-O-C substitute sulfuric acid molecule and polar hydrogen sulfate ions. And, during the initial phase of oxygen-containing functional groups’ inserting, the carbon layer plane is stretched, and d100 decreases slightly, and d110 increases. During the following oxidation process, the contents of C-OH keep increasing slightly while the d100、d11 0 keep increasing. But, when the contents of KMn O4 are too many, the randomness of products increases, the contents of defect increase, d001 、 d10 0 and d110 all decrease. During the whole oxidation process, the contents of oxygen-containing functional groups such as C-O-C are becoming more and more. They affect the π electronic. And π conjugate system is destroyed gradually, the sample’s band gap width is becoming larger and larger, the electronic mobility decreases, and conductivity is becoming poorer and poorer.Ultrasonic stripping is adopted to graphite oxide in the alkaline aqueous solution, therefore gaining graphene oxide at the monolayer dispersion state. The lamella’s thickness is about 1.4nm; With its own nanometer effect, the monolayer graphene oxide shows that the carbon-carbon bond decreases and d100、 d11 0 are a little smaller than that of graphite oxide of oxidation level; During the film-forming stage, with the hydrogen bond force, graphene oxide’s lamella stacks again ⊥ the c axis, forming the ordered structure. And, in the XRD pattern it shows graphite oxide’s character diffraction peak.After the chemical reduction, graphene oxide’s oxygen-containing functional groups mostly disappear, the products shows the transparent yarn appearance, and the monolayer ’s thickness distributes between 0.8-1.3nm. Besides, while the hydrazine hydrate’s dosage increasing, the reduction effect increases and the monolayer ’s thickness decrease; The residual oxygen-containing functional groups which are on the small piece diameter’s RGO carbon layer plane affect each other, the products agglomerate and the randomness increases. After the hydrothermal treatment, RGO sheet intertwines to three-dimensional network structure. Under the air atmosphere, reduction treatment is adopted to graphene oxide film via calcination. Then the superficial oxygen-containing functional groups gradually decrease and disappear, π conjugate system gradually recovers, the stucture defects and degree of disorder gradually increase, and the microcrystal’s lateral dimension gradually decreases; as for the graphene oxide film of the ordered two-dimensional lamination aggregate, the loss of the interlayer water molecules and the oxygen-containing functional groups results in the decreasing of the interlayer spacing during the reduction of heating, maintaining the ordering of two-dimensional lamination aggregate and showing the characteristic of evolution towards the graphite structure. In the study comparative, it found that the oxygen containing functional groups of graphene oxide by hydrothermal reduction treatment remove more thoroughly, the conductivity is better.Although after the reduction the contents of oxygen-containing functional groups decrease, π conjugate system recovers, the conductivity increases, and it will result in the increasing of the sample defects and disordered degree. Compared with three kinds of RGO prepared by oxidation- reduction methods, the crystallite average size is bigger, the content of defect is less, conductivity more excellent that grphene was prepared by direct stripping graphite, but the prepared graphene is only a few monolayer. Key words : Graphite; Graphene; Oxidation-Reduction;...