Real‐Time Imaging of Nanoscale Redox Reactions over Bimetallic Nanoparticles

The catalytic performance of bimetallic nanoparticles (NPs) strongly depends on their structural and compositional changes under reaction conditions. At the fundamental level, these changes are driven by redox reactions that occur on the surface of the NPs. The degree of complexity in the redox reactions is further amplified in bimetallic NPs because both metals can have their own reactions with the reactant molecules, in addition to any synergistic effects between the metal nanocatalysts and their reducible oxides. Here, the gas phase oxidation and reduction reactions, and the oxidation of carbon monoxide (CO) over Pt–Ni rhombic dodecahedron NPs with segregated Pt frames and Pt–Ni alloy NPs are investigated using in situ gas cell transmission electron microscopy. The real‐time observations show that NiO shell formation and Pt segregation are two important features during the oxidation and reduction of Pt–Ni NPs, respectively. Moreover, the two types of NPs evolved in different ways. By combining high‐resolution imaging, mass spectroscopy, and modeling, it is shown that the evolution of NP morphology and composition during redox reactions plays an important role in controlling the catalytic activity of the NPs.     

Hydrogen-Initiated Synthesis of Indium Antimonide in the Presence of Aluminum Hydride

Fine-particle indium antimonide was prepared by continuously bombarding Sb₂S₃+ In and Sb₂O₃+ InCl₃mixtures with hydrogen atoms in the presence of aluminum hydride. The reaction intermediates were identified by x-ray diffraction.     

Plasmochemical Preparation of Ni-Containing Zeolites

Ni-containing zeolite catalysts were prepared by impregnating a zeolite with a nickel chloride solution, followed by plasmochemical processing. The effects of crystallite size and mechanical-activation time on the activity of the resultant catalysts were studied.     

Detecting SNPs using a synthetic nanopore

We have discovered a voltage threshold for permeation through a synthetic nanopore of dsDNA bound to a restriction enzyme that depends on the sequence. Molecular dynamic simulations reveal that the threshold is associated with a nanonewton force required to rupture the DNA-protein complex. A single mutation in the recognition site for the restriction enzyme, i.e., a single nucleotide polymorphism (SNP), can easily be detected as a change in the threshold voltage. Consequently, by measuring the threshold voltage in a synthetic nanopore, it may be possible to discriminate between two variants of the same gene (alleles) that differ in one base.     

Evolution of Anisotropic Arrow Nanostructures during Controlled Overgrowth

Anisotropic metal nanoparticles (NPs), such as high-aspect-ratio Au nanorods (NRs), play an important role for applications in photocatalysis, sensing, and drug delivery because of their adjustable plasmon resonances. Their performance for these applications can be further improved by fine-tuning their morphologies. Achieving desired NP architectures requires insight into their formation mechanisms. Here, liquid-phase transmission electron microscopy is used to directly follow the overgrowth of Au NR seeds into nanoarrows (NAs) with fourfold symmetric wings along the sides. Adding thiol molecules like L-cysteine to the growth solution can lead to the formation of NAs with periodic prismatic teeth instead of the straight side wings. These observations suggest that this transition is controlled by binding of L-cysteine to the NR surface, which in turn, slows down the metal deposition rate, switching the overgrowth from the kinetically to thermodynamically controlled process. Furthermore, simulations demonstrate that these prismatic teeth enhance the NPs’ plasmonic properties. The study describes how thiol additives control the morphological evolution of metal NPs, which is important for the fabrication of NPs with tailored shapes for a broad range of applications.     

Nanoparticle Interactions Guided by Shape‐Dependent Hydrophobic Forces

Self‐assembly of solvated nanoparticles (NPs) is governed by numerous competing interactions. However, relatively little is known about the time‐dependent mechanisms through which these interactions enable and guide the nanoparticle self‐assembly process. Here, using in situ transmission electron microscopy imaging combined with atomistic modeling, it is shown that the forces governing the self‐assembly of hydrophobic nanoparticles change with the nanoparticle shapes. By comparing how gold nanospheres, nanocubes, nanorods, and nanobipyramids assemble, it is shown that the strength of the hydrophobic interactions depends on the overlap of the hydrophobic regions of the interacting nanoparticle surfaces determined by the nanoparticle shapes. Specifically, this study reveals that, in contrast to spherical nanoparticles, where van der Waals forces play an important role, hydrophobic interactions can be more relevant for nanocubes with flat side faces, where an oriented attachment between the nanocubes is promoted by these interactions. The attachment of nanocubes is observed to proceed in two distinct pathways: nanocubes either: (i) prealign their faces before the attachment, or (ii) first connect through a misaligned (edge‐to‐edge) attachment, followed by a postattachment alignment of their faces. These results have important implications for understanding the interaction dynamics of NPs and provide the framework for the design of future self‐assembled nanomaterials.     

Binary Chiral Nanoparticles Exhibit Amplified Optical Activity and Enhanced Refractive Index Sensitivity

Metallic chiral nanoparticles (CNPs) with a nominal helical pitch (P) of sub‐10 nm contain inherent chirality and are promisingly applied to diverse prominent enantiomer‐related applications. However, the sub‐wavelength P physically results in weak optical activity (OA) to prohibit the development of these applications. Herein, a facile method to amplify the CNPs' OA by alloying the host CNPs with metals through a three‐step layer‐by‐layer glancing angle deposition (GLAD) method is devised. Promoted by the GLAD‐induced heating effect, the solute metallic atoms diffuse into the host CNPs to create binary alloy CNPs. Chiral alloying not only induces the plasmonic OA of the diffused solute and the created alloys but also amplifies that of the host CNPs, generally occurring for alloying Ag CNPs with diverse metals (including Cu, Au, Al, and Fe) and alloying Cu CNPs with Ag. Furthermore, the chiral alloying leads to an enhancement of refractive index sensitivity of the CNPs. The alloy CNPs with amplified plasmonic OA pave the way for potentially developing important chirality‐related applications in the fields of heterogeneous asymmetric catalysis, enantiodifferentiation, enantioseparation, biosensing, and bioimaging.     

Plasmochemical Preparation of NiO–Al2O3Catalysts

NiO–Al₂O₃catalysts were prepared by hydrogen bombardment of aluminum hydroxide impregnated with nickel chloride. After bombardment for 2 h, the material was found to contain nickel aluminum spinel with a heavily distorted structure.