Mechanochemical reaction using weak acid salts enables dispersion and exfoliation of nanomaterials in polar solvents

Nanomaterials, such as carbon nanotubes, graphene, and various types of nanosheets, form aggregates in dry powder due to attractive van der Walls forces. To bring out their unique properties, dispersion of the nanomaterial in solid or liquid is essential. However, the dispersion media for these materials are limited; the surface tension of liquid should be as close as possible to that of the nanomaterial. This limitation restricts the effective usage of nanomaterials. Here, we find that nanomaterials are easily dispersed or exfoliated in water and low-boiling point solvents after simple pretreatment. Pulverization of nanomaterials induces many dangling bonds at the newly created edge, and these active species react with weak acid salts. In polar solvent, the bonded salts are dissociated and enhance the negative charging of nanomaterials. The enhanced electric charging prevents the aggregation or restacking of nanosheets even in typically incompatible solvent such as water and alcohol. The functionalized powder can be easily exfoliated, giving more than 20% yield of nanosheets after only 5 min of sonication.