Preparation And Characterization Of Hydroxylated Graphene

Graphene with unique two-dimensional crystal structure has excellent mechanical,thermal,optical and electrical properties,making it suitable for field effect transistors,composites,field emitters,chemical sensors,biosensors,hydrogen storage media and transparent conductive electrodes.Aspects have a wide range of applications.However,graphene lacks a sizable band gap width,which greatly limits its application in the field of electronic components.For example,a field effect transistor（FET）made of a graphene material has a low on/off current ratio.Therefore,opening a considerable band gap of graphene is a challenging research direction without destroying the excellent electrical properties of graphene itself.At present,some physical methods have been reported to prepare graphene materials having a certain band gap width.For example,the control of the edge structure,end group and width of the graphene nanoribbons opens the band gap width of the graphene.However,the preparation of graphene having a band gap width by chemical methods still has great difficulty.Graphene contains a large amount of benzene ring structure,and on the other hand,various substitution reactions have been developed to modify the benzene ring without destroying the structure in organic chemistry.If a catalyst and H₂O₂ are used as the oxidant system,the generation of hydroxyl radicals can directly oxidize benzene to phenol.Therefore,we envisaged that these methods can be used to modify graphene to prepare novel graphene derivatives having a complete aromatic ring structure.Based on the above assumptions,we prepared high-quality graphene by liquid-phase ultrasonic stripping.In a solution of pH=3,the FeCl₂ and H₂O₂ react to hydroxyl radicals（·OH）.·OH was bonded to the carbon atoms of graphene.The amount of hydroxyl groups that were attached to the graphene were adjusted by the amount of H₂O₂ added.After that,we designed a set of cyclic reaction separation device,which combines liquid phase stripping and hydroxylation reaction to prepare G-OH by one-step method using graphite as raw material.The prepared G-OH samples were characterized by X-ray photoelectron spectroscopy（XPS）,Ultraviolet–visible spectroscopy（UV-vis）and atomic force microscopy（AFM）.Finally,graphene oxide（GO）was reduced by four reducing agents of vitamin C,glucose,urea and glycine,and the dispersibility of graphene oxide and reduction graphene oxide in water and various organic solvents were studied.The following conclusions were obtained:（1）The G-OH prepared by hydroxylated graphene still had a continuous super large conjugate structure,and the molecular structure symmetry was greatly improved compared with the GO prepared by the improved Hummers method.（2）The G-OH prepared by hydroxylated graphene had a band gap width of semiconductor properties,in the research range,as the hydroxyl group content of the hydroxylated graphene increased,the band gap width also widened.（3）G-OH prepared by graphite one-step method,subjected to atomic force microscopy（AFM）and integrated calculation to obtain a single layer of G-OH more than 40%.In the spherical aberration correction high resolution transmission electron microscope and UV-vis characterization,it was illustrated that the aromatic ring structure of G-OH was changed but still had a high conjugated structure.（4）The G-OH prepared by the one-step graphite method also had a band gap width of semiconductor properties and the band gap value of G-OH was 1.23 eV.（5）Vitamin C,glucose,urea and glycine could reduce GO,respectively.The degree of reduction was:vitamin C>glucose>glycine>urea.Ethylene glycol,DMF and NMP are good solvents for graphene oxide and reduction graphene oxide.