Rayleigh Instability and Surfactant-Mediated Stabilization of Ultrathin Gold Nanorods

Ultrathin gold nanorods (AuUNRs; diameter ∼2 nm) stabilized by oleylamine (OA) were spheroidized when dispersed in chloroform containing a small amount of OA. Time-resolved optical spectroscopy and TEM analysis indicated that the AuUNRs were gradually shortened with the release of small Au nanospheres (AuNSs) because of Rayleigh instability, followed by transformation into plasmonic AuNSs (diameter >2 nm). The OA surfactants play an essential role in stabilizing the morphology of AuUNRs by suppressing the diffusion of Au surface atoms

Methane Activation in Gold Cation-Exchanged Zeolites: A DFT Study

Activation of methane has attracted a great deal of interest in laboratory chemical synthesis and in large-scale industrial processes. We performed density functional theory studies to investigate the C–H bond breaking of methane on Au⁺ and Au₂⁺ ions in vacuum and inside different types of zeolites. The density functional M06-L and the 6-31G­(d,p) basis set were employed as this level of theory had already been shown to be reasonably accurate and affordable for transition metal systems. We investigated four industrially important catalysts, ZSM-5, FAU, FER, and MCM-22, each with a particular framework topology, with respect to their performance for methane activation. The bicoordinated character of the cationic site in the ZSM-5 structure provides a higher activity than the FAU structure with a 3-fold coordination of its cationic site. The activation energy of the reaction catalyzed by Au-ZSM-5 is lower than the one with the bare Au⁺ cation (13.2 vs 21.3 kcal/mol) because of the structural constraint imposed by the zeolite that leads to an earlier transition state with a high charge difference of the C–H atoms where the bond is broken. It is also found that the activity of Au_<i>n</i>⁺ decreases already with <i>n</i> = 2, due to the shared positive charge. For the zeolites with large pores, Au-MCM-22 provides a higher activity due to the spacious framework of this particular type of zeolite is perfect for stabilizing the transition state structure but not the corresponding adsorption complex. The small and medium pore-sized zeolites, Au-FER and Au-ZSM-5 stabilize both the adsorption complex and the transition states, thus causing the activation energy to remain the same

Wireless Synthesis and Activation of Electrochemiluminescent Thermoresponsive Janus Objects Using Bipolar Electrochemistry

In this work, bipolar electrochemistry (BPE) is used as a dual wireless tool to generate and to activate a thermoresponsive electrochemiluminescent (ECL) Janus object. For the first time, BPE allows regioselective growth of a poly­(<i>N</i>-isopropylacrylamide) (pNIPAM) hydrogel film on one side of a carbon fiber. It is achieved thanks to the local reduction of persulfate ions, which initiate radical polymerization of NIPAM. By controlling the electric field and the time of the bipolar electrochemical reactions, we are able to control the length and the thickness of the deposit. The resulting pNIPAM film is found to be swollen in water at room temperature and collapsed when heated above 32 °C. We further incorporated a covalently attached ruthenium complex luminophore, Ru­(bpy)₃²⁺, in the hydrogel film. In the second time, BPE is used to activate remotely the electrogenerated chemiluminescence (ECL) of the Ru­(bpy)₃²⁺ moieties in the film. We take advantage of the film responsiveness to amplify the ECL signal. Upon collapse of the film, the ECL signal, which is sensitive to the distance between adjacent Ru­(bpy)₃²⁺ centers, is strongly amplified. It is therefore shown that BPE is a versatile tool to generate highly sophisticated materials based on responsive polymers, which could lead to sensitive sensors