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Abstract Image Advances in the synthesis and self-assembly of nanocrystals have enabled researchers to create a plethora of different nanoparticle superlattices. But while many superlattices with complex types of translational order have been realized, rotational order of nanoparticle building blocks within the lattice is more difficult to achieve. Self-assembled superstructures with atomically coherent nanocrystal lattices, which are desirable due to their exceptional electronic and optical properties, have been fabricated only for a few selected systems. Here, we combine experiments with molecular dynamics (MD) simulations to study the self-assembly of heterostructural nanocrystals (HNCs), consisting of a near-spherical quantum dot (QD) host decorated with a small number of epitaxially grown gold nanocrystal (Au NC) “patches”. Self-assembly of these HNCs results in face-centered-cubic (fcc) superlattices with well-defined orientational relationships between the atomic lattices of both QD hosts and Au patches. MD simulations indicate that the observed dual atomic coherence is linked to the number, size, and relative positions of gold patches. This study provides a strategy for the design and fabrication of NC superlattices with large structural complexity and delicate orientational order. 

Using microwave irradiation, PtCo alloy nanoparticles were deposited within a few minutes on COOH‐functionalized MWCNT supports. The obtained catalysts were used for selective hydrogenation of cinnamaldehyde, a reaction whose products are widely used in various fields. In the selective cinnamaldehyde hydrogenation to cinnamyl alcohol, microwave‐prepared catalysts (generically, Pt_xCo_y‐MW) outperformed a catalyst prepared by the conventional method (Pt₁Co₂‐con). The highest selective hydrogenation to cinnamyl alcohol, 89%, was obtained using Pt₁Co₂‐MW, while Pt₁Co₂‐con showed a selectivity of 76%. Characterization results confirmed that the microwave prepared samples had a stronger interaction between Pt and Co than that in the Pt₁Co₂‐con sample. The alloyed Co altered the electronic structure of Pt, leading to favorable adsorption of the C=O bond by the lone‐pair electrons of its oxygen atom. Moreover, the Pt₁Co₂‐MW sample showed neglectable change in catalytic performance (e. g., cinnamaldehyde conversion and selective hydrogenation to cinnamyl alcohol) during recycling experiments.

 

Metal nanoparticles of multi-principal element alloys (MPEA) with a single crystalline phase have been synthesized by flash heating/cooling of nanosized metals encapsulated in micelle vesicles dispersed in an oil phase (e.g., cyclohexane). Flash heating is realized by selective absorption of a microwave pulse in metals to rapidly heat metals into uniform melts. The oil phase barely absorbs microwave and maintains the low temperature, which can rapidly quench the high-temperature metal melts to enable the flash cooling process. The precursor ions of four metals, including Au, Pt, Pd, and Cu, can be simultaneously reduced by hydrazine in the aqueous solution encapsulated in the micelle vesicles. The resulting metals efficiently absorb microwave energy to locally reach a temperature high enough to melt themselves into a uniform mixture. The duration of microwave pulse is crucial to ensure the reduced metals mix uniformly, while the temperature of oil phase is still low to rapidly quench the metals and freeze the single-phase crystalline lattices in alloy nanoparticles. The microwave-enabled flash heating/cooling provides a new method to synthesize single-phase MPEA nanoparticles of many metal combinations when the appropriate water-in-oil micelle systems and the appropriate reduction reactions of metal precursors are available. 

Applications of silicon as a high-performance anode material has been impeded by its low intrinsic conductivity and huge volume expansion (> 300%) during lithiation. To address these problems, nano-Si particles along with conductive coatings and engineered voids are often employed, but this results in high cost anodes. Here, we report a scalable synthesis method that can realize high specific capacity (~800 mAh g-1), ultrafast charge/discharge (at 8 A g-1 Si) and high initial Coulombic efficiency (~90%) with long cycle life (1000 cycles) at the same time. To achieve 1000 cycle stability, micron-sized Si particles are subjected to high-energy ball milling to create nanostructured Si building blocks with nano-channel shaped voids encapsulated inside a nitrogen (N)-doped carbon shell (termed as Si micro-reactor). The nano-channel voids inside a Si micro-reactor not only offer the space to accommodate the volume expansion of Si, but also provide fast pathways for Li ion diffusion into the center of the nanostructured Si core and thus ultrafast charge/discharge capability. The porous N-doped carbon shell helps to improve the conductivity while allowing fast Li ion transport and confining the volume expansion within the Si micro-reactor. Submicron-sized Si micro-reactors with limited specific surface area (35 m2 g-1) afford sufficient electrode/electrolyte interfacial area for fast lithiation/delithiation, leading to the specific capacity ranging from ~800 to 420 mAh g-1 under ultrafast charging conditions (8 A g-1), but not too much interfacial area for surface side reactions and thus high initial coulombic efficiency (~90%). Since Si micro-reactors with superior electrochemical properties are synthesized via an industrially scalable and eco-friendly method, they have the potential for practical applications in the future.