A Brief Review: The Use of L-Ascorbic Acid as a Green Reducing Agent of Graphene Oxide

The reduced form of graphene oxide (r-GO) represents a versatile precursor to obtaingraphene derivatives. Graphene oxide (GO) consists of a layered material based on a carbon skeletonfunctionalized by different oxygen-containing groups, while r-GO is obtained by the almost completeremoval of these oxygen-containing functional groups. The r-GO has mechanical, electrical, andoptical properties quite similar to graphene, thus, it proves to be a convenient 2D material useful formany technological applications. Nowadays, the most important aspects to consider in producingr-GO are: (i) the possibility of obtaining the highest reduction grade; (ii) the possibility of improvingthe dispersion stability of the resulting graphene using surfactants; (iii) the use of environmentallyfriendly and inexpensive reducing agents. Consequently, the availability of effective soft-chemistryapproaches based on a green reducing agent for converting GO to r-GO are strongly needed. Amongthe green reductants, the most suitable is L-ascorbic acid (L-aa). Different studies have revealed thatL-aa can achieve C/O ratio and conductivity values comparable to those obtained by hydrazine,a typical reducing agent. These aspects could promote an effective application strategy, and forthis reason, this review summarizes and analyzes, in some detail, the up-to date literature on thereduction of GO by L-aa. The results are organized according to the two most important approaches,which are the reduction in liquid-phase, and the reduction in gel-phase. Reaction mechanisms anddifferent experimental parameters affecting the processes were also compared.