Mechanistic Study on Graphene Oxidation by KMnO₄ in Solution Phase and Resultant Carbon–Carbon Unzipping

Abstract

We reveal the origins of surface groups on pristine and defective graphene after oxidation with potassium permanganate in aqueous solution. Density functional theory calculations show that the hydroxyl group that is first introduced onto graphene via hydrolysis of permanganate ester plays an important role in the oxidative cutting of graphene. Our results demonstrate that oxidative unzipping of defect-free graphene will occur from the edge and the inner plane simultaneously in terms of comparable maximum barrier heights along these two reaction routes. Divacancy on the defective graphene may accelerate the etching process when the hydroxyl group is introduced at the defect edge. Different from the previous unzipping mechanisms producing graphene flakes with only zigzag edges, our new mechanism involves hydroxyl and both sides of the graphene sheet, which allows richer edge states after oxidative cutting that agree with experimental observations. The detailed molecular insight into the mechanisms for graphene oxidation and fragmentation will be valuable for developing an effective means for graphene manipulation and interpretation of the long-puzzling graphene oxide structure.

Kinetics of Direct Reaction of Vanadate, Chromate, and Permanganate with Graphene Nanoplatelets for Use in Water Purification

“…In this case, the electronic graphene structure should be partially destroyed. DFT calculations by Liu et al showed a 5-ring intermediate before hydrolytic cleavage [53], consistent with pseudo firstorder kinetics. They proposed the oxidation of neighboring carbon atoms as the first step to detach graphene layers from both edges and the inner plane.…”

“…Zhu et al used a redox reaction of rGO and KMnO 4 in a pH-neutral solution under microwave irradiation to prepare graphene/MnO 2 composites for use in supercapacitors [ 52 ]. The theoretical background was provided by Liu and co-workers, who found that hydroxyl groups are introduced into graphene through hydrolysis of permanganate ester, and the oxidative unpacking of defect-free graphene occurs simultaneously from the edge and the inner plane [ 53 ]. Afkhami and Conway studied the adsorption and electrosorption of Cr(VI), Mo(VI), W(VI), V(IV), and V(V) ions from water samples at low temperatures on large-area carbon-tissue electrodes and found an irreversible reduction, except for molybdenum [ 54 ].…”

Carbocatalysts for Enhancing Permanganate Oxidation of Sulfisoxazole

“…With the introduction of GO, blue-shifts from 839 to 843 cm –1 (Figure d) and from 1677 to 1683 cm –1 (Figure f) were observed, respectively (peaks at 839 and 1677 cm –1 were assigned to Mn–O in MnO 4 – , ), ascribed to the interaction between the Mn–O bond and GO. , Besides, a peak at 917 cm –1 emerged in the Mn­(VII)/GO system (Figure d), which was assigned to the Mn­(VII) adsorbed by or complexed with GO. Previous study revealed that Mn­(VII) ions would be bonded to carbocatalysts surface with relatively low adsorption barriers, particularly to the surface oxygen functional groups, based on density functional theory calculations. , Importantly, the adsorption energies of Mn­(VII) onto hydroxyl groups are estimated to be −3.18 eV, which is lower than that of th ecarboxyl group (−1.93 eV) or other sites . Thus, this experimental evidence proved the adsorption or complexing of Mn­(VII) by hydroxyl groups on the GO surface.…”

“…Previous study revealed that Mn(VII) ions would be bonded to carbocatalysts surface with relatively low adsorption barriers, particularly to the surface oxygen functional groups, based on density functional theory calculations. 20,51 Importantly, the adsorption energies of Mn(VII) onto hydroxyl groups are estimated to be −3.18 eV, which is lower than that of th ecarboxyl group (−1.93 eV) or other sites. 20 Thus, this experimental evidence proved the adsorption or complexing of Mn(VII) by hydroxyl groups on the GO surface.…”