Aqueous exfoliation and dispersion of monolayer and bilayer graphene from graphite using sulfated cellulose nanofibrils

Amphiphilic sulfated cellulose nanofibrils were synthesized with yields in excess of 99% by sulfation of dissolving pulp cellulose using chlorosulfonic acid in anhydrous N,N-dimethyl formamide followed by high-speed blending. The sulfation level was stoichiometrically tunable to between 1.48 and 2.23 mmol g-1. The optimized SCNF demonstrated the ability to act as an effective dispersant for graphene produced via exfoliation in aqueous media, allowing for the production of aqueous stabilized graphene with 3.9 +/- 0.3 wt% graphite to graphene conversion and suspended solids comprised of 19.5 +/- 1.5 wt% graphene. Graphene exfoliated with SCNF was observed to consist exclusively of mono- and bilayers, with 42% of sheets being monolayer. Furthermore, it was demonstrated that SCNF defibrillation and graphene exfoliation could be combined into a single one-pot process. High-quality graphene in 42% monolayer and rest in bilayer was efficiently aqueously exfoliated in the presence of amphiphilic sulfated cellulose nanofibrils (SCNFs) or simultaneously with sulfated cellulose.