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

Reduced graphene oxide (r-GO) has physical-chemical properties like graphene and thereforeit can be used for most graphene-based technological applications. r-GO is produced by chemicalor thermal reduction of graphene oxide (GO). GO is a highly water-soluble organic compound thatcan 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 andtherefore detrimental for the substrate. Among the mild reducing agents, L-ascorbic acid (L-aa), agreen 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 hotwater, in order to allow L-aa permeation inside its lamellar structures by diffusion; and (ii) periodicallyrestoring the reductant on the GO layer surface. According to the morphological-structuralcharacterization (SEM, FT-IR, etc.), the proposed approach allowed GO conversion to r-GO, preservinga thin GO interfacial layer essential for a good adhesion.