On the Mechanism of Phase Transfer Catalysis in Brust–Schiffrin Synthesis of Metal Nanoparticles

Abstract

The two-phase Brust-Schiffrin method (BSM) is used to synthesize highly stable nanoparticles of noble metals. A phase transfer catalyst (PTC) is used to bring in aqueous phase soluble precursors into the organic phase to enable particle synthesis there. Two different mechanisms for phase transfer are advanced in the literature. The first mechanism considers PTC to bring in an aqueous phase soluble precursor by complexing with it. The second mechanism considers the ionic species to be contained in inverse micelles of PTC, with a water core inside. A comprehensive experimental study involving measurement of interfacial tension, viscosity, water content by Karl-Fischer titration, static light scattering, (1)H NMR, and small-angle X-ray scattering is reported in this work to establish that the phase transfer catalyst tetraoctylammonium bromide transfers ions by complexing with them, instead of encapsulating them in inverse micelles. The findings have implications for particle synthesis in two-phase methods such as BSM and their modification to produce more monodispersed particles.

Mechanistic Insights into the Formation of Dodecanethiolate-Stabilized Magnetic Iridium Nanoparticles: Thiosulfate vs Thiol Ligands

“…34 Later, however, Kumar et al have shown that the same shifts resulted from the ion-pair complex formation without the presence of an inverse micelle of tetraoctylammonium. 35,36 On the basis of the latter hypothesis, our NMR data support the formation of an ion-pair complex of tetra- n -octylammonium with IrX 6 2– . The interaction between the positively charged quaternary ammonium nitrogen and IrX 6 2– was the primary reason for the upfield shifts of both αC H 2 -N peaks and βC H 2 -CH 2 -N peaks of tetra- n -octylammonium salts.…”

Novel kinetics model for third-liquid phase-transfer catalysis system of the “complex” carbanion: Competitive role between catalytic cycles

“…With the increase of the cation volume, a c is enlarged and the charge is more ''naked'', leading to higher reactivity of the carbanion ion-pair. Additionally, the content of water and the solvation effect for OPA in the organic phase decrease with increasing lipophilicity of the cation [46]. Therefore, the presentation of log k 2l with ClogV for all quaternary ammonium cations shows a high correlation coefficient with the straight line.…”

The Structure of Gold-Nanoparticle Networks Cross-Linked by Di- and Multifunctional RAFT Oligomers

“…In addition to this originally introduced approach were the AuNPs are modified with an alkanethiol in situ, it is also possible to conduct the synthesis in the absence of thiols (ex situ approach). While the exact mechanism of the latter is still a topic of research, 31 it is known that it leads to AuNPs with weakly chemisorbed phasetransfer catalyst (most commonly tetraoctylammonium bromide (TOAB)) on their surfaces. 32 TOAB can be easily substituted by competitive ligands, 33 which renders TOABcapped AuNPs ideal candidates as building units in grafting reactions with functional (macro)molecules that may be used to interconnect these primary particles resulting in nanoparticle superstructures.…”