Solvent-Free Preparation of Closely Packed MoS2 Nanoscrolls for Improved Photosensitivity

Spontaneous formation of MoS2 nanoscrolls from flat monolayers with sulfur vacancies: a molecular dynamics investigation

The unique physical properties exhibited by one-dimensional nanoscrolls assembled from nanosheets have propelled them into the spotlight of two-dimensional materials research. However, the self-scrolling mechanism of transition metal dichalcogenides has not been unveiled with an appropriate theoretical approach. In this paper, we systematically investigate the spontaneous formation of MoS2 nanoscrolls from flat monolayers by molecular dynamics simulations based on a reactive force field. The sulfur vacancies on one side break the atomic symmetry and the reconstruction acts as the driving force for the curling of the flat nanoribbon. If sulfur vacancies are arranged in a line, clear bending angles of the nanoribbon can be obtained and the angle relies on the direction of the line vacancy. With random sulfur vacancies on the top, spontaneous curling and a time-dependent scrolling process of the nanoribbon can be observed. The interplay between dangling bonds and van der Waals (vdW) interactions plays a pivotal role in the formation process of MoS2 nanoscrolls. With an increasing density of sulfur vacancies, the curvature of the nanoscrolls increases. Meanwhile, the scrolling rate accelerates and the time required for the formation of vdW structures decreases. These results provide theoretical insights into the fabrication of nanoscrolls and pave avenues for tailoring nanoscrolls with different morphologies.

Transition Metal Dichalcogenides Nanoscrolls: Preparation and Applications

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) nanosheets have shown extensive applications due to their excellent physical and chemical properties. However, the low light absorption efficiency limits their application in optoelectronics. By rolling up 2D TMDCs nanosheets, the one-dimensional (1D) TMDCs nanoscrolls are formed with spiral tubular structure, tunable interlayer spacing, and opening ends. Due to the increased thickness of the scroll structure, the light absorption is enhanced. Meanwhile, the rapid electron transportation is confined along the 1D structure. Therefore, the TMDCs nanoscrolls show improved optoelectronic performance compared to 2D nanosheets. In addition, the high specific surface area and active edge site from the bending strain of the basal plane make them promising materials for catalytic reaction. Thus, the TMDCs nanoscrolls have attracted intensive attention in recent years. In this review, the structure of TMDCs nanoscrolls is first demonstrated and followed by various preparation methods of the TMDCs nanoscrolls. Afterwards, the applications of TMDCs nanoscrolls in the fields of photodetection, hydrogen evolution reaction, and gas sensing are discussed.

Recent Advances in Rolling 2D TMDs Nanosheets into 1D TMDs Nanotubes/Nanoscrolls

Transition metal dichalcogenides (TMDs) van der Waals (vdW) 1D heterostructures are recently synthesized from 2D nanosheets, which open up new opportunities for potential applications in electronic and optoelectronic devices. The most recent and promising strategies in regards to forming 1D TMDs nanotubes (NTs) or nanoscrolls (NSs) in this review article as well as their heterostructures that are produced from 2D TMDs are summarized. In order to improve the functionality of ultrathin 1D TMDs that are coaxially combined with boron nitride nanotubes and single-walled carbon nanotubes. 1D heterostructured devices perform better than 2D TMD nanosheets when the two devices are compared. The photovoltaic effect in WS₂ or MoS₂ NTs without a junction may exceed the Shockley-Queisser limit for the above-band-gap photovoltage generation. Photoelectrochemical hydrogen evolution is accelerated when monolayer WS₂ or MoS₂ NSs are incorporated into a heterojunction. In addition, the photovoltaic performance of the WSe₂ /MoS₂  NSs junction is superior to that of the performance of MoS₂ NSs. The summary of the current research about 1D TMDs can be used in a variety of ways, which assists in the development of new types of nanoscale optoelectronic devices. Finally, it also summarizes the current challenges and prospects.

Direct Synthesis of MoS2 Nanosheets in Reduced Graphene Oxide Nanoscroll for Enhanced Photodetection

Due to their unique tubular and spiral structure, graphene and graphene oxide nanoscrolls (GONS) have shown extensive applications in various fields. However, it is still a challenge to improve the optoelectronic application of graphene and GONS because of the zero bandgap of graphene. Herein, ammonium tetrathiomolybdate ((NH₄)₂MoS₄) was firstly wrapped into the ((NH₄)₂MoS₄@GONS) by molecular combing the mixture of (NH₄)₂MoS₄ and GO solution on hydrophobic substrate. After thermal annealing, the (NH₄)₂MoS₄ and GO were converted to MoS₂ nanosheets and reduced GO (RGO) simultaneously, and, thus, the MoS₂@RGONS was obtained. Raman spectroscopy and high-resolution transmission electron microscopy were used to confirm the formation of MoS₂ nanosheets among the RGONS. The amount of MoS₂ wrapped in RGONS increased with the increasing height of GONS, which is confirmed by the atomic force microscopy and Raman spectroscopy. The as-prepared MoS₂@RGONS showed much better photoresponse than the RGONS under visible light. The photocurrent-to-dark current ratios of photodetectors based on MoS₂@RGONS are ~570, 360 and 140 under blue, red and green lasers, respectively, which are 81, 144 and 35 times of the photodetectors based on RGONS. Moreover, the MoS₂@RGONS-based photodetector exhibited good power-dependent photoresponse. Our work indicates that the MoS₂@RGONS is expected to be a promising material in the fields of optoelectronic devices and flexible electronics.