Abstract:Graphene is the best-studied 2D material available. However, its production is still challenging and the quality depends on the preparation procedure. Now, more than a decade after the outstanding experiments conducted on graphene, the most successful wet-chemical approach to graphene and functionalized graphene is based on the oxidation of graphite. Graphene oxide has been known for more than a century; however, the structure bears variable large amounts of lattice defects that render the development of a con… Show more
“…Raman spectroscopy of a bulk functionalized graphene derivative G (THF) (OH)(H) as a model of GO without σ-defects45. ( a ) Reaction scheme for the hydrogenation and hydroxylation of charged graphenides followed by workup under ambient conditions (O 2 /H 2 O).…”
The verification of a successful covalent functionalization of graphene and related carbon allotropes can easily be carried out by Raman spectroscopy. Nevertheless, the unequivocal assignment and resolution of individual lattice modes associated with the covalent binding of addends was elusive up to now. Here we present an in situ Raman study of a controlled functionalization of potassium intercalated graphite, revealing several new bands appearing in the D-region of the spectrum. The evolution of these bands with increasing degree of functionalization from low to moderate levels provides a basis for the deconvolution of the different components towards quantifying the extent of functionalization. By complementary DFT calculations we were able to identify the vibrational changes in the close proximity of the addend bearing lattice carbon atoms and to assign them to specific Raman modes. The experimental in situ observation of the developing functionalization along with the reoxidation of the intercalated graphite represents an important step towards an improved understanding of the chemistry of graphene.
“…Raman spectroscopy of a bulk functionalized graphene derivative G (THF) (OH)(H) as a model of GO without σ-defects45. ( a ) Reaction scheme for the hydrogenation and hydroxylation of charged graphenides followed by workup under ambient conditions (O 2 /H 2 O).…”
The verification of a successful covalent functionalization of graphene and related carbon allotropes can easily be carried out by Raman spectroscopy. Nevertheless, the unequivocal assignment and resolution of individual lattice modes associated with the covalent binding of addends was elusive up to now. Here we present an in situ Raman study of a controlled functionalization of potassium intercalated graphite, revealing several new bands appearing in the D-region of the spectrum. The evolution of these bands with increasing degree of functionalization from low to moderate levels provides a basis for the deconvolution of the different components towards quantifying the extent of functionalization. By complementary DFT calculations we were able to identify the vibrational changes in the close proximity of the addend bearing lattice carbon atoms and to assign them to specific Raman modes. The experimental in situ observation of the developing functionalization along with the reoxidation of the intercalated graphite represents an important step towards an improved understanding of the chemistry of graphene.
“…EP, therefore, does not cause broadening of the peaks, which indicates a higher concentration of defects 37 . The data seem to lead to the conclusion that the modifications introduced by the electrochemical oxidation are preferentially located on the edges of the GO sheets 38, 39 .Figure 3Raman spectroscopy characterization of the EP coatings compared to coatings obtained via casting. Raman spectra obtained after a baseline correction for coatings on ITO of epGO 0.8 , epGO 1.3 , and cGO.
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New coatings are obtained when graphene oxide is further oxidized at moderate anodic potentials (≤~1.3 V vs. Ag/AgCl). Based on a variety of spectroscopic and electrochemical observations, the coatings are attributed to the direct electropolymerization of graphene oxide sheets via oxidation of the phenol edge groups on graphene. Depending on the applied potential, ether or carboxylic groups are formed. The coatings obtained via further oxidation are characterized by a lower O/C ratio due to decarboxylation and a higher content of C=C bonds. These bonds extend aromatic conjugation into the combined graphene oxide sheets and are responsible for the highly conductive nature of these coatings.
“…This low‐defect type of GO, which we term oxo‐functionalized graphene (oxo‐G), can be converted back to graphene by reductive defunctionalization . As a consequence of a preserved carbon lattice the on‐plane chemistry could be studied . Nevertheless, the question remains, whether other methods can also prevent over‐oxidation of the carbon lattice.…”
Synthesis and studies of graphite oxide started more than 150 years ago and turned into a boom by the measurements of the outstanding physical properties of graphene. A series of preparation protocols emanated trying to optimize the synthesis of graphene oxide in order to obtain a less defective material, as source for graphene. However, over‐oxidation of the carbon framework hampered establishing structure‐property relationships. Here, the fact that two different synthetic methods for graphene oxide preparation lead to very similar types of graphene oxide with a preserved graphene lattice is demonstrated. Either sodium chlorate in nitric acid (similar to Brodie's method) or potassium permanganate in sulfuric acid (similar to Hummers’ method) treatment are possible; however, reaction conditions must be controlled. With a preserved carbon lattice analytical differences between the samples relate to the altered on‐plane functionality. Consequently, terming preparation protocols “according to Brodie's/Hummers’ method” is not sufficient.
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