Gel-Phase Reduction of Graphene Oxide Coatings by L-Ascorbic Acid ^†

Reduced graphene oxide (r-GO) has physical–chemical properties like graphene and therefore it can be used for most graphene-based technological applications. r-GO is produced by chemical or thermal reduction of graphene oxide (GO). GO is a highly water-soluble organic compound that can be easily processed in the form of aqueous/alcoholic ink to produce thick self-standing films (i.e., GO paper) or thin coatings supported on a variety of substrates (e.g., polymers, cellulose, glass, silicon, etc.). The best GO reduction technique depends on the substrate chemical/thermal stability, and in the case of thermally unstable substrates (e.g., cellulose), the chemical approach is mandatory. However, traditional reductants, like hydrazine and phenyl-hydrazine, are highly active and therefore detrimental for the substrate. Among the mild reducing agents, L-ascorbic acid (L-aa), a green chemical reductant, has been widely investigated for GO reduction in aqueous solutions. Here, L-aa has been used to convert a GO gel-phase to r-GO by (i) swelling the GO phase with hot water, in order to allow L-aa permeation inside its lamellar structures by diffusion; and (ii) periodically restoring the reductant on the GO layer surface. According to the morphological–structural characterization (SEM, FT-IR, etc.), the proposed approach allowed GO conversion to r-GO, preserving a thin GO interfacial layer essential for a good adhesion.