Spontaneous Decoration of Ultrasmall Pt Nanoparticles on Size-Separated MoS2 Nanosheets

Liquid exfoliation can be considered as a viable approach for the scalable production of 2D materials due to its various benefits, although the polydispersity in the obtained nanosheet size hinders their straightforward incorporation. Size-separation can help alleviate these concerns, however a correlation between nanosheet size and property needs to be established to bring about size-specific applicability. Herein, size-selected aqueous nanosheet dispersions have been obtained via centrifugation-based protocols, and their chemical activity in the spontaneous reduction of chloroplatinic acid is investigated. Growth of ultrasmall Pt nanoparticles was achieved on nanosheet surfaces without a need for reducing agents, and stark differences in the nanoparticle coverage were observed as a function of nanosheet size. Defects in the nanosheets were probed via Raman spectroscopy, and correlated to the observed size-activity. Additionally, the effect of reaction temperature during synthesis was investigated. The electrochemical activity of the ultrasmall Pt nanoparticle decorated MoS2 nanosheets was evaluated for the hydrogen evolution reaction, and enhancement in performance was observed with nanosheet size, and nanoparticle decoration density. These findings shine light on the significance of nanosheet size in controlling spontaneous reduction reactions, and provide a deeper insight to intrinsic properties of liquid exfoliated nanosheets.

Insights into the Solution Processing of Non-van der Waals Boron Carbide

Exfoliation of non-layered materials is crucial to unleash their enormous potential in wide range of applications. However, the presence of strong non-van der Waals interactions in all three dimensions makes exfoliation challenging. Boron carbide (B4C), known for its high hardness, holds great potential for diverse applications. In this work, B4C is exfoliated in 29 solvents to determine its Hansen solubility parameters (HSP) and understand the dispersion stability. The experimentally determined HSP values are 19.6, 15.3 and 15.1 MPa1/2 for dispersive interactions (δD), polar interactions (δP) and hydrogen bonding interactions (δH), respectively. Subsequently, in situ dispersion stability is analyzed qualitatively and quantitatively from the space-time resolved extinction profiles employing an analytical centrifuge. The sedimentation kinetics of B4C dispersions are analyzed using instability index, integral extinction and sedimentation velocity. B4C dispersions in solvents like ϵ-caprolactone, isopropyl alcohol, propylene carbonate and formamide exhibited excellent stability. Additionally, B4C nanosheets are utilized to investigate their field emission properties. These nanosheets exhibit a turn-on electric field of 3.35 V/μm at an emission current density of 1 μA cm-2, and it delivered a large emission current density of ~375 μA cm-2 at an applied electric field of 5.7 V/μm.