Study On The Structure, Band Gap And Molecular Vibrational Spectra Of Graphene Oxide

The i mproved Hummers’ method is successfully used to synthesizegraphene oxide samples, and the structure and nature of relevantproperties were characterized by various means. Based on theexperimental results, the configurations and properties of grapheneoxide mo dels with only epoxy groups, only hydroxyl groups and bothepoxy and hydroxyl groups are investigated by means of the densityfunctional theory first-principles method using a periodic slab model.The system geo metry structures, molecular vibrational spectra,electronic structures and optical absorption spectra of all studiedsyste ms were explored systematically. Thus this thesis reveals thearrangeme nts of functional groups in the diffe rent types of grapheneoxide mo dels and the stability of atomi c structure of graphene oxide.Study results show that the structural orderliness of graphite isreduced and the structure layer is bonded with a large number ofoxygen-containing functional groups, such as hydroxyl group (-OH)and epoxy group (C-O-C) after oxidation. The C/O ratio value of thesaturated preparation products is approxi mately2/1as XPS shows; Theintroduction of oxygen-containing functional groups have causedvarying degrees of da mage on the graphene sheet, making the carbonatoms surface bending and wrinkling under the additional tensioninduced by functional groups. And the hydroxyl functional group on thedestruction of the planar structure is more si gnificant than the epoxyfunctional groups on the destruction of the planar structure. In thegraphene oxide system, it is found that the structure with the functionalgroups located adjacent each other on the both sides of graphene sheethave the highest stability, with respect to other structure models.Besides, the binding energy of graphene oxide struct ure with onlyhydroxyl groups is lower than that of structur e with only epoxy groups.That’s to say that hydroxyl groups are more likely to for m on the carbonatom surface. Electronic band structure of graphene is ve ry sensitive tothe geometric symmetry. When the functional groups are combined with the graphene, the delocalized π electrons of intrinsic graphene arelocalized. Therefore, the functional groups regulate and control theelectronic structure of graphene and electronic structure of system ischanged from a semi-metal with zero band gap to a semiconductor withcertain band gap. The cause of band gap is that the electrons of the O2porbitals are bonding with the electrons of the C2phybrid orbitals,weakening the valence electron state. And the width of band gap isincreased with the increase of oxygen-containing functional groups onthe surface. Calculating Raman spectra further validates arrangement offunctional groups that the structure of oxygen containing functionalgroups is in the ortho position of two sides of the surface. Ra man Gband is generated by the vibration of sp2carbon atoms, and Ra man Dband is not only related to the defects of structure but also associatedwith the oxygen-containing functional groups in the structure. It isproved that the Raman spectrum with a low degree of oxidation looksmuch mor e alike with the experimental results. The calculation resultsof infrared spectra show that the stretching vibration of C-OH islocated in1000~1100c m-1,and the epoxy functional groups of the C-Ostretching vibration is located in1200~1300c m-1, which furtherconfirm t he experimental spectrum that the peak at1095cm-1is causedby the stretching vibration of C-OH, and the peak at1246cm-1is causedby the stretching vibration of C-O in epoxy functional groups.