Synthesis of Lateral Size-Controlled Monolayer 1H-MoS₂@Oleylamine as Supercapacitor Electrodes.

A new wet chemistry approach, based on the hot-injection-thermolytic decomposition of the single-source precursor [Mo₂O₂S₂(S₂COEt)₂] in oleylamine, is described for the production of nanodimensional 1H-MoS₂@oleylamine. High quality freestanding MoS₂ nanosheets capped with oleylamine have been prepared and subjected to detailed compositional analyses for the first time. The selection of the appropriate reaction temperatures (200-325°C) in the simple yet robust procedure allows control of the lateral nanosheet dimensions which range from 4.5 to 11.5 nm, as 1H-MoS₂@oleylamine entities which maintain a consistent chemical composition (MoS₂·oleylamine_0.28-0.33). This work provides the first example of atomic resolution STEM imaging of these fine-scale nanosheet materials, providing new insights into their morphology and demonstrating that those freestanding MoS₂ nanosheets are pure, highly crystalline, randomly oriented monolayers. The 1H-MoS₂@oleylamine samples were analyzed by attenuated total reflectance FT-infrared spectroscopy (ATR-FTIR), transmission electron microscope (TEM) imaging, aberration corrected scanning transmission electron microscope (STEM) imaging, energy dispersive X-ray (EDX) spectrum imaging, powder X-ray diffractometry (p-XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. Composite materials of the as-synthesized MoS₂ nanosheets and exfoliated graphene were then used to construct coin-cell supercapacitor electrodes with a specific capacitance of 50 mF/cm², demonstrating its utility as an energy storage material.