Fabrication of High-Concentration Aqueous Graphene Suspensions Dispersed by Sodium Lignosulfonate and Its Mechanism

Stable aqueous graphene suspensions (AGSs) with high concentration and little defect were prepared through exfoliating from graphite by sonication with the aid of sodium lignosulfonate (SL). The concentration of AGS (C-G) dispersed by the modified SL can reach up to 13.5 g/L at an initial graphite concentration of 200 g/L, which is substantially higher than those reported previously. Four SL fractions with different molecular weight (Mw) and sulfonic acid group prepared by ultrafiltration of a commercial SL were applied to evaluate the dispersing mechanism and the effects of SL molecular structure on the AGS. The maximum concentration of AGS dispersed by the SL fractions increased with the decline of Mw and the ion strength of SL solutions and with the increase of sulfonic acid group. The C-G can be further improved through improving the hydrophobicity of SL by either covalent or noncovalent modification. It was found that the C-G was proportional to the zeta potentials, which suggested that electrostatic repulsion played a crucial role in the dispersion process of AGS. Meanwhile, the obtained high-concentration AGS dispersed by SL is nontoxic, which facilitates it as a promising material for application in the biomedical field.