Optical, Vibrational, and Structural Properties of MoS₂ Nanoparticles Obtained by Exfoliation and Fragmentation via Ultrasound Cavitation in Isopropyl Alcohol

Abstract

Thin sheets and small MoS 2 nanoparticles have been obtained by exfoliation/fragmentation processes via intense ultrasound cavitation in isopropyl alcohol (IPA). The formation mechanism, the structure (in terms of size, presence of defects, lattice periodicity) and the optical and vibrational properties of the obtained materials have been investigated by means of atomic force (AFM) and high-resolution transmission electron (HRTEM) microscopies and UV−visible near infrared (UV−vis−NIR) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies. Fast-Fourier transform (FFT) analyses of HRTEM images have provided a simple and powerful tool to better evidentiate defective situations on extended and regular regions of exfoliated MoS 2 nanosheets with large lateral dimensions. The transparent ultracentrifuged portion of MoS 2 in IPA is characterized by size and height distributions peaking at about 6 and 1.5 nm, respectively, a fact which is indicative of very high fragmentation and very reduced stacking. The evolution of the UV−vis−NIR and DRIFT spectra upon increasing sonication time and ultracentrifugation give unprecedented information on the optical properties of nanoparticles, on the vibrational properties of surface species, and on the lattice modes of virgin and fragmented material. It is also demonstrated that the extensive layer fragmentation due to the cavitation field is associated with rupture of MoSMo bonds and subsequent exposure of coordinatively and chemically unsaturated Mo and S species. These chemically unsaturated species readily react with the IPA solvent and with atmospheric oxygen with the predominant formation of surface hydroxyl, alkyl, and, to a lesser extent, oxidized species like sulfate and carbonylic and carboxylate groups. Hence, it is concluded that the edges formed by layers breaking in the IPA solution are fully functionalized. This spectroscopic study is made possible by the complete absence of adsorbed IPA, which being a low boiling solvent can be easily removed from MoS 2 and does not interfere in the DRIFT measurements. The transparent fraction containing the fragmented particles can be used for blending MoS 2 nanoparticles with high surface area materials. This process is favored by the volatile character of IPA, which can be easily removed from the ultrasonicated material. This makes the proposed method fully suitable to prepare MoS 2 -based hybrid composite materials by simple impregnation of high surface area supports.

Modification of Deposited, Size-Selected MoS2 Nanoclusters by Sulphur Addition: An Aberration-Corrected STEM Study

“…Figure 2c shows a single crystalline MoS 2 cluster with a single set of diffraction spots corresponding to the (100) plane with 0.26 nm spacing. The regular honeycomb pattern shown here originates from the atomic arrangements of Mo and S atoms, which is in agreement with the TEM studies on the MoS 2 nanoparticles made by other methods, e.g., CVD and exfoliation [33,34]. The intensity profile shows this cluster consists of two, non-identical hexagonal layers; the brighter region in the middle has a bi-layered structure with mono-layer structures on both sides.…”

One Batch Exfoliation and Assembly of Two-Dimensional Transition Metal Dichalcogenide Nanosheets Using Electrophoretic Deposition

“…The correlation between solution absorbance and suspension concentration allow for the estimation of sedimentation rate by the change in absorbance over time. 31 From the data in Figure 7d it is evident that suspensions in ACN sediment at a substantially greater rate than in NMP and that WS 2 and MoSe 2 demonstrate significant sedimentation over the 2 minute deposition period compared with NMP. We find that the magnitude of change in sticking factor values is directly related to the degree of sedimentation with more heavily sedimenting particles producing smaller sticking factor values.…”

Synthesis of MoS 2 nanoparticles using MoO 3 nanobelts as precursor via a PVP-assisted hydrothermal method

“…Meanwhile, MoS 2 nanomaterials with various morphologies such as open-ended nanotubes [9], hollow nanospheres [2], flower-like microspheres [10], nanorods [11] and nanoparticles [12] have been reported. Among various morphologies, MoS 2 nanoparticles are promising due to their distinct physicochemical properties different from bulk materials.…”

“…It has been found that MoS 2 nanoparticles show excellent shock-absorbing performance under a very high shock wave pressure [13] and ultra-low friction and wear [14]. In addition, MoS 2 nanoparticles exhibit enhanced catalytic [3], electronic [15] as well as optical [12] properties. As a result, it is essential to synthesize MoS 2 with a nanoparticle morphology in a controlled manner.…”