Abstract
Few-layer nitrogen doped graphene was synthesized originating from graphene oxide functionalized by selective oxygenic functional groups (hydroxyl, carbonyl, carboxyl etc.) under hydrothermal conditions, respectively. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observation evidenced few-layer feature of the graphene oxide. X-ray diffraction (XRD) pattern confirmed phase structure of the graphene oxide and reduced graphene oxide. Nitrogen doping content and bonding configuration of the graphene was determined by X-ray photoelectron spectroscopy (XPS), which indicated that different oxygenic functional groups were evidently different in affecting the nitrogen doping process. Compared with other oxygenic groups, carboxyl group played a crucial role in the initial stage of nitrogen doping while hydroxyls exhibited more evident contribution to the doping process in the late stage of the reaction. Formation of graphitic-like nitrogen species was controlled by a synergistic effect of the involved oxygenic groups (e.g., -COOH, -OH, C-O-C, etc.). The doping mechanism of nitrogen in the graphene was scrutinized. The research in this work may not only contribute to the fundamental understandings of nitrogen doping within graphene but promote the development of producing novel graphene-based devices with designed surface functionalization.
Highlights
Nitrogen doping in graphene has proven to be an effective way in tailoring properties of pristine graphene and extending its applications [1,2,3,4,5,6] because doped nitrogen atoms could modify surface chemical state, crystal structure, as well as electronic structure of graphene
To the best of our knowledge, previous reports were mainly focused on the effect of experimental parameter changes on the nitrogen doping within graphene, and few investigation has been conducted on the influence of oxygenic groups on the graphene surface which may be a non-trivial factor in controlling nitrogen doping process
Designed synthesis of N-doped graphene with different N contents and nitrogen bonding configuration has been successfully obtained under hydrothermal conditions using urea as the nitrogen source
Summary
Nitrogen doping in graphene has proven to be an effective way in tailoring properties of pristine graphene and extending its applications [1,2,3,4,5,6] because doped nitrogen atoms could modify surface chemical state, crystal structure, as well as electronic structure of graphene. For. To the best of our knowledge, previous reports were mainly focused on the effect of experimental parameter changes (temperature, ratio of chemical agents, reaction time) on the nitrogen doping within graphene, and few investigation has been conducted on the influence of oxygenic groups on the graphene surface which may be a non-trivial factor in controlling nitrogen doping process. Graphene oxide has been reported as an intermediate during graphene synthesis by chemical method [15,16] It has abundant functional groups such as epoxide, hydroxyl, phenol carbonyl, and lactone on its basal planes and edges [17], which are often used as precursor for preparing graphene composites or modified graphene [18,19]. Due to different reaction activity among oxygenic groups, functionalizing graphene by selective oxygenic groups may impact content and bonding configuration of nitrogen on the graphene surface [20,21,22]
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