Depiction Of Functional Groups On Graphene Oxide Through Oxidation

Graphene oxide(GO)contains a range of oxygen functional groups,such as carboxyl,ketone,epoxy and hydroxyl,which render it a good candidate for use in the optoelectronic nanodevices,catalysis,composites,and drug delivery.Although both experiment and theory research,the precise chemical structure of GO has been the subject of considerable debate over the years,and its real structure remains unknown.Recently,the coexistence of both large unoxidized and oxidized regions on graphene oxide with the high correlation of Oxidation Loci was presented by a possible DFT-based evolution of graphene oxidation by permanganate,which is consistent with experimental observations[Angewandte Chemie International Edition 53,10190(2014)].Here,we study further the starting oxidation process from pristine graphene at one initial time,considering functional groups such as hydroxyl,epoxy,carboxyl,and ketone.Our results show that the beginning of the oxidation loci on pristine graphene is random.However,the oxidation loci at near-edge are more favorable than the ones at near-center.This is confirmed by investigating the oxidation processes with various functional groups and their complex configurations.Especially,the oxidation of graphene oxide with an epoxy and hydroxyl are more easily at the near-edge than the one at the near-center.Additionally,the oxidation of carbons loci prefer to be highly correlated and clustered together,but the clustering degree is not unlimited because of the steric effect originated from neighboring functional groups,including steric attraction between hydroxyl epoxy functional groups,steric repulsion of hydroxyl functional groups and steric hindrance of the epoxy functional groups.Therein,the steric hindrance and repulsion prevent the oxidation loci by deforming the shape of the molecule,and the steric attraction allows the oxidation loci to be clustered.As discussed in above,we have studied the starting oxidation process from pristine graphene at one initial time,the oxidation loci at near-edge are more favorable than the ones at near-center,and functional groups during graphene oxidation prefer to be highly correlated and clustered together.However,the clustering degree of functional groups is limited,due to various steric effects of functional groups.