Unexpected Multi-Step Transformation of AgCuS to AgAuS During Nanoparticle Cation Exchange.

Cation exchange reactions can modify the compositions of colloidal nanoparticles, providing easy access to compounds or nanoparticles that may not be accessible directly. The most common nanoparticle cation exchange reactions replace monovalent cations with divalent cations or vice versa, but some monovalent-to-monovalent exchanges have been reported. Here, we dissect the reaction of as-synthesized AgCuS nanocrystals with Au to form AgAuS, initially hypothesizing that Au could be selective for Cu (rather than for Ag) based on a known Au-for-Cu exchange and the stability of the targeted AgAuS product.

Introducing Porosity into Refractory Molybdenum Boride through Controlled Decomposition of a Metastable Mo-Al-B Precursor.

The high temperatures typically required to synthesize refractory compounds preclude the formation of high-energy morphological features, including nanoscopic pores that are beneficial for applications, such as catalysis, that require higher surface areas. Here, we demonstrate a low-temperature multistep pathway to engineer mesoporosity into a catalytic refractory material. Mesoporous molybdenum boride, α-MoB, forms through the controlled thermal decomposition of nanolaminate-containing sheets of the metastable MAB (metal-aluminum-boron) phase MoAlB and amorphous alumina.

Expanded Tunability of Intraparticle Frameworks in Spherical Heterostructured Nanoparticles through Substoichiometric Partial Cation Exchange.

Partial cation exchange reactions provide a synthetic pathway for rationally constructing heterostructured nanoparticles that incorporate different materials at precise locations. Multiple sequential partial cation exchange reactions can produce libraries of exceptionally complex heterostructured nanoparticles, but the first partial exchange reaction is responsible for defining the intraparticle frameworks that persist throughout and help to direct subsequent exchanges. Here, we studied the partial cation exchange behavior of spherical nanoparticles of roxbyite copper sulfide, CuS, with substoichiometric amounts of Zn.