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.

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MoS2/TNTs composites have been obtained by impregnation of titanate nanotubes (TNTs) with a centrifuged solution of nanosized MoS2 particles in isopropyl alcohol (IPA). The characterization has been performed by combining UV-vis-NIR, Raman, AFM, and HRTEM analyses, before and after impregnation. HRTEM images show that the contact between single-layer MoS2 nanoparticles and the support is efficient, so justifying the decoration concept. The volatility of IPA solvent allows the preparation of composites at low temperature and free of carbonaceous impurities. MoS2 nanoparticles have strong excitonic transitions, which are only slightly shifted with respect to the bulk because of quantum size effects. Concentrations of MoS2, less than 0.1 wt %, are enough to induce strong absorption in the visible. Photodegradation of methylene blue (MB) has been performed on TNTs and MoS2/TNTs to verify the effect of the presence of MoS2. The first layer of adsorbed MB is consumed first, followed by clustered MB in the second and more external layers. The presence of low concentrated MoS2 nanoparticles does not substantially alter the photocatalytic properties of TNTs. This result is due to poor overlapping between the high frequency of MoS2 C, D excitonic transitions and the TNTs band gap transition.