Detailed Investigation into the Preparation of Graphene Oxide by Dichromate Oxidation

Abstract

Graphene oxide (GO) can be prepared using numerous protocols including the well‐known Hummers method that relies on potassium permanganate as the oxidizing agent. Given the widespread use of GO and its many applications, a better understanding of the mechanisms of chemical oxidation is highly desirable including research into alternative oxidizing agents. Limited work has so far been carried out into using potassium dichromate as an oxidizing agent and the chemical structure of GO prepared by dichromate oxidation remains unclear. Here we present a full structural characterization of GO prepared by dichromate oxidation and we investigate its thermal stability. Furthermore, the previously reported preparation protocol is optimized by reducing the reaction time from 5 days to 20 hours and showing that sodium nitrate is not needed in the reaction mixture. Contrary to previous reports, we show that the GO material produced by dichromate oxidation is highly oxidized if thermal annealing is avoided. Compared to traditional GO, larger amounts of carboxylic acid groups are found which constitutes a major advantage for chemical processing and applications in materials chemistry.

Graphene Oxide Chemistry Management via the Use of KMnO4/K2Cr2O7 Oxidizing Agents

“…The synthesis of the GO samples was carried out according to a method based on the Hummers [ 32 ] and Rosillo-Lopez [ 36 ] methods. For the oxidation of graphite, a mixture of KMnO 4 /K 2 Cr 2 O 7 oxidizing agents in a different ratio was used.…”

“…The proportion of each oxidizing agent in the mixture was determined in accordance with the proportion of the amount required for the complete oxidation of graphite. It is known [ 32 , 36 ] that the complete oxidation of 1 g of graphite requires 3 g of KMnO 4 or 7.5 g of K 2 Cr 2 O 7 . According to our synthesis method, if the KMnO 4 /K 2 Cr 2 O 7 ratio is 20:80, then the KMnO 4 fraction was calculated as 20 wt.% of 3 g, and the K 2 Cr 2 O 7 fraction as 80 wt.% of 7.5 g. Thus, the complete oxidation of such a sample requires 0.6 g of KMnO 4 and 6 g K 2 Cr 2 O 7 .…”

“…Then, K 2 Cr 2 O 7 was slowly added and kept under stirring for 5 days at room temperature. In 2018, Martin Rosillo-Lopez and Christoph G. Salzmann [ 36 ] presented an optimized technique for oxidizing graphite with K 2 Cr 2 O 7 . The authors reduced the reaction time from 5 days to 20 h, and also showed that sodium nitrate does not affect the reaction.…”