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Heterostructures composed of two-dimensional (2D) nanosheets and zero-dimensional (0D) nanoparticles (NPs) have attracted increasing attention because of the synergy arising from the coupling interactions between the two mixed-dimensional components. Despite recent advances, it remains a challenge to fabricate 2D/0D heterostructures with clean and accessible surfaces, which is highly desirable for the diversity of catalytic, sensing, and energy storage applications. Herein, we report a generalized methodology that enables the facile assembly of sandwich-like 0D/2D/0D heterostructures with facilitated mass-transport channels and exposed surface active sites. A ligand-exchange strategy with HBF4 is employed to strip off the surface-coating ligands of colloidal NPs, rendering them positively charged and dispersible in polar solvents. This allows subsequent electrostatic assembly of NPs with oppositely charged 2D nanosheets to afford sandwich-like 0D/2D/0D heterostructures. The barely covered surfaces and the advantageous architectures of such sandwich-like 0D/2D/0D heterostructures induce the desired synergistic effect, making them particularly suitable for electrochemical energy storage and conversion. We demonstrate this by employing MXene/NiFe2O4 and MXene/Fe3O4 heterostructures for high-performance electrocatalytic oxygen evolution and supercapacitors, respectively.

A facile and scalable exfoliation approach is developed to prepare large-flake, few-layer MoS2 nanosheets with the assistance of carbon nanotubes (CNTs). CNTs not only facilaite the efficient exfoliation of MoS2 nanosheets, but also benefit their subsequent electrochemical applications for both hydrogen evolution and sodium-ion storage. This CNT-mediated exfoliation approach can be extended to other kinds of 2D materials.

Transition metal dichalcogenides (TMDs) are promising anode materials for sodium-ion batteries (SIBs), but suffer from low rate capability and poor cycling stability. Here, we describe our efforts in designing a unique MoS2-based van der Waals (vdW) superstructure, namely mesoporous MoS2@graphene supraparticles, for realizing unprecedented high-rate, long-life sodium storage. The key to obtaining mesoporous MoS2@graphene vdW supraparticles is the high mass loading of the initially hydrophilic (NH4)2MoS4 precursor into the hydrophobic mesoporous graphene, which is realized through a novel phase-transfer assisted method. Subsequent precursor decomposition confined in ∼11 nm mesopores triggers the epitaxial growth of MoS2 nanosheets featuring a spherically curved geometry and an expanded interlayer spacing. Thanks to the greatly improved electron and ion transport properties enabled by the unique mesoporous vdW superstructure, the resulting MoS2@graphene vdW supraparticles exhibit arguably the best rate performance ever reported.

Recently, iron, nitrogen and sulfur codoped carbon-based materials have gained increasing attention for their synergistic effect towards superior electrocatalytic oxygen reduction performance. To gain insight into the contributions of the heteroatoms, we developed a facile and reproducible method for constructing Fe, N, S-codoped carbon frameworks derived from self-assembled Fe3O4 nanocrystal superlattices. The material constructed by the suggested method exhibited excellent ORR activity with more positive half-wave potential (∼ 0.869 V, vs RHE), higher diffusion-limiting current density (∼ 5.88 mA/cm2) and smaller Tafel slope (45 mV/dec) compared with Fe, N-codoped carbon frameworks and Pt/C. Notably, Fe3O4 nanocrystals served as both the building blocks for constructing carbon frameworks and the source of Fe residues leaving in the frameworks at the same time. By artificially tailoring the doping type and level as well as the homogeneousness of heteroatoms, the results discussed herein prove the importance of each kind of heteroatom in boosting ORR activity. Electronic supplementary material The online version of this article (10.1186/s40580-019-0174-5) contains supplementary material, which is available to authorized users.

Fine-tuning strain and vacancies in 2H-phase transition-metal dichalcogenides, although extremely challenging, is crucial for activating the inert basal plane for boosting the hydrogen evolution reaction (HER). Here, atomically curved 2H-WS2 nanosheets with precisely tunable strain and sulfur vacancies (S-vacancies) along with rich edge sites are synthesized via a one-step approach by harnessing geometric constraints. The approach is based on the confined epitaxy growth of WS2 in ordered mesoporous graphene derived from nanocrystal superlattices. The spherical curvature imposed by the graphitic mesopores enables the generation of uniform strain and S-vacancies in the as-grown WS2 nanosheets, and simultaneous manipulation of these two key parameters can be realized by simply adjusting the pore size. In addition, the formation of unique mesoporous WS2 @graphene van der Waals heterostructures ensures the ready access of active sites. Fine-tuning the WS2 layer number, strain, and S-vacancies enables arguably the best-performing HER 2H-WS2 electrocatalysts ever reported. Density functional theory calculations indicate that compared with strain, S-vacancies play a more critical role in enhancing the HER activity.

Heteroatom doping of carbonaceous materials can effectively modulate their physiochemical properties, providing great potentials to design innovative architectures with enhanced performance for energy-related applications. Herein, we report a versatile molecular-based strategy for the in-situ synthesis of highly-ordered, heteroatom-doped mesoporous carbon frameworks (MCFs). Our approach is based on the transformation of self-assembled superlattices consisting of Fe3O4 nanocrystals (NCs) with desired surface-coating molecular species, which are realized by exploiting versatile surface chemistry of colloidal NCs. By this strategy, various heteroatoms, such as N, B, and S, can be directly incorporated into the simultaneously formed MCFs with a homogeneous distribution. Taking advantage of their highly ordered and interconnected mesoporosity, tunable doping level, and high surface area, such heteroatom-doped MCFs show great promise for energy-related applications. We show that the N-doped MCFs (N-MCFs) exhibit significantly enhanced catalytic activity relative to their undoped counterparts when evaluated as electrocatalyst for oxygen reduction reaction. Likewise, the N-MCFs can also be used as electrode material for constructing supercapacitors with outstanding cycling stability and rate performance. This work offers a surface chemistry approach for the direct synthesis of highly-ordered MCFs containing homogeneously distributed heteroatoms, which are suitable for applications in various energy conversion and storage devices.

Discretely sized semiconductor clusters have attracted considerable attention due to their intriguing optical properties and self-assembly behaviors. While lead halide perovskite nanostructures have been recently intensively explored, few studies have addressed perovskite clusters and their self-assembled superstructures. Here, we report the room-temperature synthesis of sub-2 nm CsPbBr3 clusters and present strong evidence that these ultrasmall perovskite species, obtained under a wide range of reaction conditions, possess a specific size, with optical properties and self-assembly characteristics resembling those of well-known II–VI semiconductor magic-sized clusters. Unlike conventional CsPbBr3 nanocrystals, the as-synthesized CsPbBr3 nanoclusters spontaneously self-assemble into a hexagonally packed columnar mesophase in solution, which can be further converted to single-crystalline CsPbBr3 quantum nanoribbons with bright deep-blue emission at room temperature. Such a conversion of CsPbBr3 nanoclusters to nanoribbons is found to be driven by a ligand-destabilization-induced crystallization and mesophase transition process. Our study will facilitate the investigation of perovskite nanoclusters and offer new possibilities in the low-temperature synthesis of anisotropic perovskite nanostructures.