Chemical Transformations of Anisotropic Platelets and Spherical Nanocrystals

Covalently Functionalized MoS2 Initiated Gelation of Hydrogels for Flexible Strain Sensing

Transition metal dichalcogenides (TMDs), with superior mechanical and electrical conductivity, are one of the most promising two-dimensional materials for creating a generation of intelligent and flexible electronic devices. However, due to the high van der Waals and electrostatic attraction, TMD nanomaterials tend to aggregate in dispersants to achieve a stable state, thus severely limiting their further applications. Surface chemical modification is a common strategy for improving the dispersity of TMD nanomaterials; however, there are still constraints such as limited functionalization methods, low grafting rate, and difficult practice application. Thus, it is challenging to develop innovative surface modification systems. Herein, we covalently modify an olefin molecule on surface-inert MoS₂, and the modified MoS₂ can be used as not only a catalyst for hydrogel polymerization, but also a cross-linker in the hydrogel network. Specifically, allyl is covalently grafted onto chemically exfoliated MoS₂, and this modified MoS₂ can be uniformly dispersed in polar solvents (such as acetone, N,N-dimethylformamide, and ethanol), remaining stable for more than 2 weeks. The allyl-modified MoS₂ can catalyze the polymerization of polyacrylamide hydrogel and then integrate in the network, which increases the tensile strength of the composite hydrogel. The flexible sensor based on the composite hydrogel exhibits an ideal operating range of 600% and a quick response time of 150 ms. At the same time, the flexible device can also track the massive axial stretching movements of human joints, making it a reliable option for the next wave of wearable sensing technology.

2D FeP Nanoframe Superlattices via Space-Confined Topochemical Transformation

Self-assembled nanocrystal superlattices represent an emergent class of designer materials with potentially programmable functionalities. The ability to construct hierarchically structured nanocrystal superlattices with tailored geometry and porosity is critical for extending their applications. Here, 2D superlattices comprising monolayer FeP nanoframes are synthesized through a space-confined topochemical transformation approach induced by the Kirkendall effect, using carbon-coated Fe₃ O₄ nanocube superlattices as a precursor. The particle shape and the close-packed nature of Fe₃ O₄ nanocubes as well as the interconnected carbon layer network contribute to the topochemical transformation process. The resulting 2D FeP nanoframe superlattices possess several unique and advantageous structural features that are unavailable in conventional 3D nanocrystal superlattices, which make them particularly attractive for catalytic applications. As a proof of concept, such 2D FeP nanoframe superlattices are harnessed as highly efficient and durable electrocatalysts for the hydrogen evolution reaction, the performance of which is superior to that of most FeP-based catalysts reported previously. This topochemical transformation approach is scalable and general, representing a new route of designing hierarchical superlattices with highly open features that cannot be accessible by traditional self-assembly methods.