Electromagnetic Field-assisted Preparation Of Graphene Oxide And Its Morphology Regulation

The successful preparation of single layer graphene has caused a big stir in the science world due to its special two dimensional structures,novel physical and chemical properties,and the study on the graphene and its derivatives has attracted great attention.Graphene Oxide,an important derivative of graphene,has widely application value due to its excellent properties such as good hydrophilic,biocompatibility,large specific surface area etc.In addition,at present,reduction of graphene oxide is the mainly method to obtain volume graphene with low cost.So study on preparation of graphene oxide has important scientific and commercial value.Among all the preparation methods,the modified Hummers method is the most commonly used due to its simple,product with good structural integrity.In this method potassium permanganate and sodium nitrate is used for oxidizing agent with concentrated sulfuric acid as solvent and intercalator.Graphite is oxidized to graphite oxide and then exfoliated into graphene oxide.During the reaction,Excessive potassium permanganate is used at a quality ratio of 3-6:1(potassium permanganate:graphite),which leads to wasting and environmental pollution.So it is very important to search for a kind of environmental oxidizer or cut down on potassium permanganate consumption to reduction production cost and emissions,and improve the capacity of work safety.Based on this,study works were carried as follows:1)In this chapter GO was prepared by electromagnetic field assisted Hummers method.Experiments showed the potassium permanganate use efficiency was significantly enhanced by reducing the reaction temperature and introducing alternating electromagnetic field.The self-decomposition rate of potassium permanganate slows down at the low reaction temperature,while the oxidizing reaction is on the rails due to the eddy-curent heating of the alternating electromagnetic field on the graphite.Under the same condition the product has a higher oxidation degree with the alternating electromagnetic field assisted Hummers method,especially a high frequency magnetic field.And the auxiliary effect of electromagnetic field is subdued gradually till out of action when increased the dosage of potassium permanganate.But the auxiliary effect of electromagnetic field Have little effect with a large dosage of potassium permanganate,a quality ratio of 3:1(potassium permanganate:graphite),for example.2)Ozone is the strongest oxidant in the word.But it has poor solubility and decomposes quickly in the concentrated sulphuric acid.The solubility decreases and the decomposition rate increases with the reaction temperature increasing.So in this article,ozone is tried to oxidize graphite under the electromagnetic field.Results show that ozone couldn’t oxide the graphite even if the eddy current effect caused by alternating electromagnetic field could heat the graphite,but it could reoxidize the low oxidation degree of graphite oxide.The GO treated by ozone was used as super capacitor electrode materials after hydrothermal reduction and the specific capacity was improved in certain degree.The capacitance could achieved 314 F/g at a current density of 0.1 A/g and 172 F/g at 10 A/g.3)GO has excellent dispersibility in water due to its abundant oxygen containing groups,and could obtain stable aqueous dispersion conveniently.But it is easy to restack and aggregation during the freeze drying process.In this article,the GO aqueous solution was frozen in the electrostatic field,alternating electric field condition or electrostatic spray granulation,and then freeze drying.It is found that the graphene could curld into a tubular structure with liquid nitrogen as refrigerant whether they(the graphene and the liquid nitrogen)contact or not..Different specific surfa ce areas were obtained with the samples treated by thermal reduction.But the super capacitor performances change little.