Preparation of 1T′-Phase ReS2xSe2(1-x) (x = 0–1) Nanodots for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction

An Insight into the Phase Transformation of WS2 upon Fluorination

The transformation from semiconducting to metallic phase, accompanied by a structural transition in 2D transition metal dichalcogenides has attracted the attention of the researchers worldwide. The unconventional structural transformation of fluorinated WS₂ (FWS₂ ) into the 1T phase is described. The energy difference between the two phases debugs this transition, as fluorination enhances the stability of 1T FWS₂ and makes it energetically favorable at higher F concentration. Investigation of the electronic and optical nature of FWS₂ is supplemented by possible band structures and bandgap calculations. Magnetic centers in the 1T phase appear in FWS₂ possibly due to the introduction of defect sites. A direct consequence of the phase transition and associated increase in interlayer spacing is a change in friction behavior. Friction force microscopy is used to determine this effect of functionalization accompanied phase transformation.

Recent advances in the field of transition metal dichalcogenides for biomedical applications

Nanosheets of transition metal dichalcogenide (TMDs), the graphene-like two-dimensional (2D) materials, exhibit a unique combination of properties and have attracted enormous research interest for a wide range of applications including catalysis, functional electronics, solid lubrication, photovoltaics, energy materials and most recently in biomedical applications. Their potential for use in biosensors, drug delivery, multimodal imaging, antimicrobial agents and tissue engineering is being actively studied. However, the commercial translation of exfoliated TMDs has been limited due to the low aqueous solubility, non-uniformity, lack of control over the layer thickness, and the long-term colloidal stability of the exfoliated material. There is wide interest in the synthesis and exfoliation of TMDs resulting in the reporting of increasing numbers of new methods and their biomedical applications. The unique physicochemical characteristics of the TMD nanosheets have been exploited to tether them with biological payload to achieve selective localized delivery in vivo. The large surface-to-volume ratio, good cytocompatibility, ease of surface modification, tunable bandgap, strong spin-orbit coupling, and high optical and thermal conversion efficiency of TMD nanosheets make them favorable over traditional nanomaterials for biomedical research. Moreover, the presence of abundant active edge sites on the 2D TMDs makes them suitable for catalytic activities, while the large surface area and the interspace between layers are particularly conducive to ion or small molecule intercalation, making them useful for energy storage applications with rapid redox reaction capabilities. One of the major limitations of the exfoliated TMDs has been their limited colloidal stability in aqueous media. In this review, we summarize the recent advances in the exfoliation and synthesis of single-layered TMDs, their biomedical efficacy in terms of cytotoxicity, combinatorial therapy and diagnostic imaging, as well as antimicrobial activity. We highlight the current challenges in the field and propose strategies for the future.

Preparation and Characterization of Chiral Transition-Metal Dichalcogenide Quantum Dots and Their Enantioselective Catalysis

Two-dimensional transition-metal dichalcogenides (TMDs) had attracted enormous interests owing to their extraordinary optical, physical, and chemical properties. Herein, we prepared for the first time a series of chiral TMD quantum dots (QDs) from MoS₂ and WS₂ bulk crystals by covalent modification with chiral ligands cysteine and penicillamine. The chiral TMD QDs were carefully investigated by spectroscopic and microscopic techniques. Their chiral optical activity was confirmed by distinct circular dichroism signals different to those of the chiral ligands. Interestingly, with the assistance of copper ions, the chiral QDs displayed strong and chiral selective peroxidase-like activity. Up to now, inorganic nanomaterials with peroxidase-like activity were tremendous but seldom examples with enantioselectivity. The enantioselectivity of our chiral TMD QDs toward chiral substrates d- and l-tyrosinol was highly up to 6.77, which was almost the best performance ever reported. The mechanisms of enantioselectivity was further investigated by quartz crystal microbalance assays. We believed that because of the extraordinary electronic and optical properties, the chiral TMD QDs should be useful for nonlinear optical materials, asymmetric catalysis, chiral and biological sensors, and so on.

Edge-Terminated MoS2 Nanoassembled Electrocatalyst via In Situ Hybridization with 3D Carbon Network

Transition metal dichalcogenides, especially MoS₂ , are considered as promising electrocatalysts for hydrogen evolution reaction (HER). Since the physicochemical properties of MoS₂ and electrode morphology are highly sensitive factor for HER performance, designed synthesis is highly pursued. Here, an in situ method to prepare a 3D carbon/MoS₂ hybrid catalyst, motivated by the graphene ribbon synthesis process, is reported. By rational design strategies, the hybrid electrocatalysts with cross-connected porous structure are obtained, and they show a high HER activity even comparable to the state-of-the-art MoS₂ catalyst without appreciable activity loss in long-term operations. Based on various physicochemical techniques, it is demonstrated that the synthetic procedure can effectively guide the formation of active site and 3D structure with a distinctive feature; increased exposure of active sites by decreased domain size and intrinsically high activity through controlling the number of stacking layers. Moreover, the importance of structural properties of the MoS₂ -based catalysts is verified by controlled experiments, validating the effectiveness of the designed synthesis approach.