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Modulating the electronic structure of transition metal dichalcogenides (TMDs) via alloying is challenging despite the additional potential applications. In this study, a solvothermal reaction is used to synthesize composition‐tuned ReS2–VS2 (Re1‐xVxS2) alloy nanosheets featuring an expanded interlayer distance. Increasing x induces a phase transition from the semiconducting 1T″ phase ReS2 to the metallic 3R‐stacking 1T phase VS2. Alloying via homogeneous atomic mixing renders the nanosheets more metallic and with less oxidation than VS2. First‐principles calculations consistently predict the 1T″–1T phase transition of the atomically mixed alloy structures. The calculation also suggests that intercalation drives the 3R stacking of 1T phase VS2. The Re1‐xVxS2 nanosheets at x = 0.3–0.8 exhibit enhanced electrocatalytic activity toward water‐splitting hydrogen evolution reaction (HER) in an acid electrolyte. In situ X‐ray absorption fine structure measurements reveal that the metallicity of the alloys is fully retained during HER. The density of states and Gibbs free energy calculations show that alloying increases the metallicity and thus effectively activates the basal S atoms toward the HER, supporting the observed increased HER performance of the alloy nanosheets. [ABSTRACT FROM AUTHOR]

Cobalt oxide nanoparticles (Co3O4-NPs) and cobalt sulfide nanoparticles (Co9S8-NPs) have shown extensive potential in electrochemical sensing, catalysis, specific drug targeting, and resonance imaging. However, Co9S8-NPs have been rarely explored for biomedical applications as compared to their oxide counterparts. Thus, in the current study, biocompatible PEGylated Co9S8-NPs and Co3O4-NPs are explored and compared for biological and photocatalytic properties. PEGylation of both the NPs is achieved using a simple chemical co-precipitation method followed by characterization using UV visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and pH-responsive dispersion study. After thorough characterization, the NPs are evaluated and compared for various biological applications including antibacterial, antifungal, antileishmanial, antioxidant, and biocompatibility as well as photo-catalytic dye degradation studies. Both the NPs have shown excellent biological applications; however, Co9S8-NPs exhibit comparatively better antibacterial, antifungal, and antioxidant properties except antileishmanial potential where Co3O4-NPs show slight superiority. Furthermore, Co3O4-NPs indicate a higher degradation potential of methylene blue (MB) up to 46.93%. In comparison, Co9S8-NPs have a degradation ability of up to 42%, at 20 mg/ml within 3 h, which indicates considerable remediation potential of the NPs. Interestingly, both the NPs exhibit non-hemolytic behavior, thus demonstrating a compatible and bio-safe nature of both the NPs. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides exhibit various stacking polytypes and distinct electronic structures. In this study, first-principles calculations show that chalcogen enrichment induces the phase conversion from 2H to 1T′. Models for Se intercalation and substitution (MoSex and WSex with x > 2) were constructed for the 2H and three stacking polytypes of the 1T′ phase (1T′, 2M, and Td). Se intercalates and substitutes more favorably into the 1T′ polytypes than into the 2H phase. Intercalation in the 1T′ polytypes occurs by forming Se dimers, which is distinct from the Se monomer in the 2H phase. The relative stability predicts that as x increases, the 2H phase undergoes phase conversion preferentially into the 2M phase. On the experimental side, we synthesized Se-rich MoSe2 and WSe2 nanosheets using a colloidal reaction, and confirmed the stacking sequence of the 2M phase using atomic-resolution scanning transmission electron microscopy. The Se-rich 2M phase nanosheets exhibited enhanced electrocatalytic performance in the hydrogen evolution reaction (HER). Gibbs free energy calculations support that excess Se enhances the HER. [ABSTRACT FROM AUTHOR]

The phase control of transition metal dichalcogenides (TMDs) is an intriguing approach for tuning the electronic structure toward extensive applications. In this study, WSe 2 nanosheets synthesized via a colloidal reaction exhibit a phase conversion from semiconducting 2H to metallic 2M under Se-rich growth conditions (i.e., increasing the concentration of Se precursor or lowering the growth temperature). High-resolution scanning transmission electron microscopy images are used to identify the stacking sequence of the 2M phase, which is distinctive from that of the 1T' phase. First-principles calculations employing various Se-rich models (intercalation and substitution) indicated that Se enrichment induces conversion to the 2M phase. The 2M phase WSe 2 nanosheets with the Se excess exhibited enhanced electrocatalytic performance in the hydrogen evolution reaction (HER). In situ X-ray absorption fine structure studies suggested that the excess Se atoms in the 2M phase WSe 2 enhanced the HER catalytic activity, which is supported by the Gibbs free energy (ΔG H* ) of H adsorption and the Fermi abundance function. These results provide an appealing strategy for phase control of TMD catalysts., (© 2023 Wiley-VCH GmbH.)