Sugar-Based Natural Deep Eutectic Mixtures as Green Intercalating Solvents for High-Yield Preparation of Stable MoS2 Nanosheets: Application to Electrocatalysis of Hydrogen Evolution Reaction

Wide applicability of nanosized MoS2 in diverse research fields including optoelectronics, biomedicine, energy storage, and conversion is a motivation for investing efforts in green, low-cost, and efficient synthesis of these nanomaterials. To date, various methods for the synthesis of MoS2 nanosheets have been reported, most of which use toxic organic solvents in appreciable amounts. In the present report, we introduced a mechanical exfoliation approach in which bulk MoS2 is converted to two-dimensional nanosheets with a yield as high as 44%. We used sugar-based natural deep eutectic solvents (NADESs) as intercalating solvents and a reusable 5 mL glass syringe as an exfoliation chamber to achieve this purpose. Using the present approach, we were able to tune the thickness, length, and concentration of the nanosheets by changing experimental parameters. Under the optimized experimental conditions and based on their UV-vis absorption spectrum, the average thickness and length of the nanosheets exfoliated by NADES 1 were estimated as 4 and 150 nm, respectively. The nanosheets were mixed phase (2H-1T) with 2H/1T ratio of 1.4. They were electrocatalytically active in hydrogen evolution reaction. We achieved the overpotential of 0.339 V versus reversible hydrogen electrode at the current density of 10 mA/cm(2) and long-term durability in acidic media. Furthermore, the synthesized MoS2 nanosheets were stable in ethanol/water, water, and various cell culture media for a prolonged time. The designed experimental setup in the present report is low-cost and very easy to assemble. Most notably, the use of NADESs as the green exfoliation solvents fulfills the principles of green chemistry as they have no environmental impacts. We believe that owing to the green nature of the solvent, cost efficiency, and the high-yield characteristic of the method, it has the potential to be employed in an industrial scale.