Controlling the Hierarchical Structures of Molybdenum Disulfide Nanomaterials via Self-Assembly of Supramolecular Polymers in Water

Abstract

Programmed exfoliation of highly crystalline molybdenum disulfide (MoS2) into water-dispersible exfoliated nanosheets with well-tunable structural characteristics was successfully developed using an environmentally benign solvent (water) and a water-soluble cytosine-functionalized supramolecular polymer (Cy-PPG). Herein, we show that MoS2 can be directly dispersed in aqueous solution using ultrasound to obtain dozen-layered MoS2 nanosheets; this process is termed first exfoliation. When Cy-PPG is subsequently incorporated into the MoS2 solution (i.e., second exfoliation), ordered hierarchical lamellar nanostructures form through self-assembly of Cy-PPG on the surface of the metallic 1T and semiconducting 2H phases of the exfoliated MoS2 nanosheets due to the high-affinity interaction between Cy-PPG and MoS2. Furthermore, after second exfoliation, the resulting MoS2/Cy-PPG composites exhibit long-term dispersion stability in water. Broad, tunable MoS2 exfoliation can be achieved by systematically adjusting the content of Cy-PPG within the composites to obtain the desired structural, physical, and conductive performance; these exceedingly rare features offered by programmed exfoliation hold great potential for achievement of high-quality, custom-made MoS2 nanomaterials. Thus, this newly developed system offers a myriad of potential uses for fabrication of fully aqueous solution-processed MoS2-based thin films for optoelectronic and biomedical applications.

Recent Strategies for the Synthesis of Phase-Pure Ultrathin 1T/1T′ Transition Metal Dichalcogenide Nanosheets

“…286 Although the mechanism is specific and complicated, numerous solvents have been used to exfoliate TMD crystals, for example, liquid nitrogen, 287 ammonia, 288 and even polymers. 289 For example, MoS 2 has been exfoliated in two steps, as shown in Figure 15 (f). First, the bulk MoS 2 crystal was ultrasonicated in water to collect thin MoS 2 flakes (E-MoS 2 ).…”

“…Copyright 2017 American Chemical Society. (f) reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

“…However, Jawaid et al discovered that hydroperoxide intermediates generated during exfoliation were vital to stimulate exfoliation via corrosion at reactive edge sites, and that redox additives could be used to facilitate nanosheet exfoliation and, thus, increase yields to over 10% . Although the mechanism is specific and complicated, numerous solvents have been used to exfoliate TMD crystals, for example, liquid nitrogen, ammonia, and even polymers . For example, MoS 2 has been exfoliated in two steps, as shown in Figure (f).…”

“…First, the bulk MoS 2 crystal was ultrasonicated in water to collect thin MoS 2 flakes (E-MoS 2 ). Then, Cy–PPG was added to further exfoliate the E-MoS 2 and stabilize the MoS 2 nanosheet dispersion in water . Similarly, chemical exfoliation could take the advantage of the both exfoliation methods, namely, the bulk crystal is intercalated first and, then, sonicated in solution to complete the whole exfoliation. , …”