Ammonia-Induced Size Convergence of Atomically Monodisperse Au₆ Nanoclusters

Developing effective synthetic protocols for atomically monodisperse Au nanoclusters is pivotal to their fundamental science and applications. Here, we present a novel synthetic protocol toward atomically monodisperse [Au₆(PPh₃)₆]²⁺ nanoclusters (abbreviated as Au₆) via ammonia-induced size convergence from polydisperse Au_<i>x</i> (<i>x</i> = 6–11) nanocluster mixture. The analogous ammonia-induced size conversion reactions starting from individually prepared Au₇ and Au₉ nanoclusters to Au₆ were traced by time-dependent ultraviolet–visible absorption and electrospray ionization mass spectra. It is observed that in both cases the size conversion is achieved through gradual release of the ion–molecule complex [NH₄AuPPh₃Cl]⁺ from the larger Au nanoclusters until the formation of thermodynamically stable Au₆ nanoclusters with the stability against the etching reaction. The role of ammonia ions in this size convergence synthesis is to accelerate the depletion of [Au­(PPh₃)]⁺ fragments from the PPh₃-protected Au nanoclusters, by the formation of the stable complex [NH₄AuPPh₃Cl]⁺

A New Three-Dimensional (3D) Multilayer Organic Material: Synthesis, Swelling, Exfoliation, and Application

A novel fully rigid, rod-shaped oligo­(<i>p</i>-benzamide) (OPBA-6) molecule was designed and synthesized, which can be recrystallized into a three-dimensional (3D) multilayer material via an antiparallel molecular packing model. Intermolecular hydrogen bonding and π–π interaction are brought to ensure a strong intralayer interaction, while decoration of layer surface with sulfonic groups promotes water to enter interlayer space and facilitates the swelling and exfoliation of sample. With a simple dispersion in water, the obtained multilayer material can be easily swollen by water without destruction of in-plane morphology and subsequently delaminated into 2D nanosheets with thickness of about 5.38 nm. This achievement may be the first attempt to exfoliate layered organic materials and thus provide a new strategy to prepare 2D organic nanosheets without using any substrates or templates as required by conventional and widely used self-assembly routes. Based on exfoliated nanosheets, poly­(vinyl alcohol) nanocomposites were prepared using a simple water solution processing method. A 64% increase in tensile stress and a 63% improvement in Young’s modulus were achieved by addition of 7 wt % OPBA-6 loading

Unidirectional Thermal Diffusion in Bimetallic Cu@Au Nanoparticles

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using <i>in situ</i> X-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of <i>ca.</i> 7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu–Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics