Gradual Transformation of Ag₂S to Au₂S Nanoparticles by Sequential Cation Exchange Reactions: Binary, Ternary, and Hybrid Compositions

Abstract

Cation exchange reactions have been exploited in the last years as an efficient tool for the controlled chemical modification of pre-made nanocrystals. In this work, the gradual transformation of Ag2S nanocrystals into Au2S analogues is performed by sequential cation exchange reactions that allow for a fine control of the chemical composition, delivering also two intermediate ternary sulfides based exclusively on noble metals. The role of two different surfactants in the reaction medium has been studied: while dodecylamine is favoring the heterogeneous nucleation of metallic Au on the surface of the semiconductor domains in detriment of the cation exchange reaction, the use of tetraoctylammonium bromide turns out to be crucial for the enhancement of the exchange in order to reach full cation substitution, if desired. The presence of Branions in the reaction medium represents an additional tool to modulate the morphology of the final nanocrystals, being either solid or hollow depending on their concentration. The synthetic protocol has been successfully conducted in both spherical and rod-like nanocrystals with identical results, leading to a wide variety of binary, ternary and/or hybrid nanostructures that have been carefully characterized.

Au@HgxCd1-xTe core@shell nanorods by sequential aqueous cation exchange for near-infrared photodetectors

“…What's more, it has been reported that ion exchange could enable the miscibility of Au in Ag-X (X=S, Se, Te) system, which is mainly due to the strong affinity and higher bond energy between Au and X. [56][57] As a result, due to the driving force of CE, the localized CE reaction at the shell surface breaks the balance of Ag + and Te 2-, which causes Au atoms from the core to diffuse into the shell; this leads to formation of a highly crystalline Ag 3 AuTe 2 shell (Figure 3a). For our system, this phenomenon couldn't be initiated without the introduction of trace amount of Cd 2+ ( Figure S6).…”

Cation/Anion Exchange Reactions toward the Syntheses of Upgraded Nanostructures: Principles and Applications

“…Similar gradual CER-enabled transformations from Au-Ag 2 S to Au-Ag 3 AuS 2 were also reported by Figuerola and colleagues with dodecylamine as ligands. 144 By using different precursors and phosphine ligands, the kinetics of CER-facilitated non-epitaxial growth could be regulated, which enabled tunable compositions and morphologies. For example, shape evolution from Au-CdSe core-shell NRs to nanodumbbells was realized by gradual CER with a hydrazine hydrate dispersed selenide precursor, 34 and Au@Sn 2 S 3 and Au@SnS 2 could be tailored by Cd-TBP-and Cd-TOP-induced CER, respectively.…”

Spontaneous Hetero-attachment of Single-Component Colloidal Precursors for the Synthesis of Asymmetric Au–Ag2X (X = S, Se) Heterodimers

“…Thus, it can be concluded that the stabilization of the interface takes place through an interdomain redox reaction at the solid–solid interface followed by atomic diffusion and exchange, occurring only after particle hetero-attachment, leading to the formation of ternary semiconductor phases and metallic alloyed domains. Compared to previous strategies 9 , 26 where more standard molecular precursors are used for the exchange leading to ternary phases (i.e., AuCl 3 instead of Au NPs), the replacement here described occurs exclusively at the interface and can be considered as an intraparticle process: ternary domains grown far apart from the metal–semiconductor interface were never found, suggesting that the solvent is not assisting the replacement through atom diffusion, which is only a solid-phase phenomenon.…”

“…23,24 In the previous publications of our group, gradual cation exchange reactions between gold chloride and silver chalcogenide NPs have been studied. 25,26 The partial exchange of Ag + by Au + cations in the silver chalcogenide lattice entails the formation of ternary phases, a process that is kinetically favored, and thus it occurs fast at room temperature and without the need for additional ligands except for those required to solubilize the gold molecular precursor and stabilize the silver chalcogenide NPs in organic apolar solvents. The easiness of this cation exchange reaction suggests a high stability for the ternary products formed.…”