Reduction of graphene oxide with substituted borohydrides

Abstract

The emergence of graphene as a next-generation material promises enhanced improvement in various fields of materials science. So far, the oxidation of graphite to graphite oxide and consequent reduction to chemically reduced graphene oxide is the most relevant method towards large scale production of graphene materials. Our long-standing aim in the investigation of reductive chemical reactions on graphene surfaces is to evaluate standard, well documented organic synthetic reactions with well-known mechanisms. Sodium borohydride is one of the most common reductants to reduce graphene oxide to chemically reduced graphene oxide, and is only one of the very few with a well-known mechanism. It is well-known in synthetic chemistry that the reducing strength of borohydrides can be fine-tuned by alternating their substituents. This knowledge has not yet been applied to the reduction of graphene oxides. Herein, we expand on the scope for reduction of graphene oxides using various derivatives of borohydrides, specifically sodium cyanoborohydride and sodium triacetoxyborohydride, and investigate the extents of reduction conferred by these variations with comparison to sodium borohydride. The reduced graphenes were characterized by high resolution X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry analyses. Our findings highlighted that sodium triacetoxyborohydride is inclined to react unfavourably with graphene oxide, thus resulting in a graphene material with an almost similar electrochemical characteristic to its precursor. On the other hand, sodium cyanoborohydride conferred obvious reductive effects but was still less effective when compared to sodium borohydride. Our findings bring a deeper understanding of the effects of organo-boron substituents on the extent of graphene oxide reduction. This would allow for potential tailoring of the graphene properties for various applications.