Efficient exfoliation of layered materials by waste liquor

Based on their unique material properties, two-dimensional (2D) nanomaterials such as graphene, molybdenum disulfide (MoS₂), and boron nitride (BN) have been attracting increased research interest. The potential of 2D materials, in the form of nanoplatelets that are used as new materials, will be important to both nanomaterials and advanced materials. Water is usually considered to be the ideal dispersed medium, and the essential hydrophobicity and limitations to mass production of 2D nanoplatelets have become quite serious obstacles to their usage in various fields. In this paper, pulping black liquor was used as dispersant, with high concentration of lignin to get single- and few-layered nanoplatelets. The whole process required only the high-shear mixing of 2D layered materials and pulping waste liquor. This method was not only simple and efficient but also environmentally friendly and resource-recycling. Moreover, the fabricated single- or few-layered nanoplatelets possessed good solubility in aqueous solution due to their edge functionalization, and could be well dispersed in water at concentrations (10 mg ml^-1 for graphene, 6.3 mg ml^-1 for MoS₂, and 6.0 mg ml^-1 for BN) which were much higher than that of other methods. The dispersions of graphene, MoS₂, and BN nanosheets were highly stable over several months, which allowed us to easily prepare graphene, MoS₂, and BN films through simple vacuum filtration or spraying. These results indicated that pulping black liquor can be used as a material or reagent, and the mass production of 2D material is possible in a simple and fast method.