Processable and robust MoS2 paper chemically cross-linked with polymeric ligands by the coordination of divalent metal ions.

Inorganic graphene analogues (IGAs) are a huge and fascinating family of compounds that have extraordinary electronic, mechanical, and thermal properties. However, one of the largest problems that face the industrial application of IGAs is their poor processability, which has led to a "bottlenecking" in the development of freestanding, large-area, IGA-based thin-film devices. Herein, we report a facile and cost-efficient method to chemically modify IGAs by using their abundant coordination atoms (S, O, and N). Taking MoS2 as an example, we have prepared homogeneous "solution" systems, in which MoS2 nanosheets are chemically cross-linked through a carboxylate-containing polymeric ligand, poly(methyl methacrylate) (PMMA), by copper-ion coordination. Bonding interactions between C=O bonds and sulfur atoms through copper ions were confirmed by various characterization techniques, such as UV/Vis, FTIR, and Raman spectroscopy and XPS. By using our method, freestanding MoS2 paper with significantly improved mechanical properties was obtained, thus laying the basis for the mass production of large-area MoS2-based thin-film devices. Furthermore, copper-ion coordination was also applied to MoS2/PMMA nanocomposites. Direct and strong nanofiller/matrix bonding interactions facilitate efficient load transfer and endow the polymeric nanocomposites with an excellent reinforcement effect. This method may pave a new way to high-strength polymeric nanocomposites with superior frictional properties, flame retardance, and oxidation resistance.