Size-Controlled Synthesis of Monodispersed Silver Nanoparticles Capped by Long-Chain Alkyl Carboxylates from Silver Carboxylate and Tertiary Amine

Abstract

Monodispersed silver nanoparticles capped by long-chain alkyl carboxylates were prepared by the reaction of silver carboxylate with tertiary amine at 80 degrees C for 2 h. This approach is a unique, size-controlled synthetic method for the large-scale preparation of silver nanoparticles. Long-chain alkyl carboxylate derived from a precursor acts as a stabilizer to avoid the aggregation of silver nanoparticles and to control particle size. In addition, amine plays an important role both as a reagent to form a thermally unstable, amine-coordinated intermediate, bis(amine)silver(I) carboxylate, and as a mild reducing agent for the intermediate to produce nanoparticles at a low temperature. The silver core and carboxylate-capping ligand of silver nanoparticles were characterized by various techniques such as transmission electron microscopy, optical absorption spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, gas chromatograph mass spectroscopy, and thermogravimetric and differential thermal analysis. The diameter of the nanoparticles can be strongly influenced by the alkyl chain length and the structure of the carboxylate. The average diameters of the silver nanoparticles were controlled to less than 5 nm in the case of silver carboxylate with a single alkyl chain length of 13 or 17 carbon atoms. On the contrary, the average diameters of silver nanoparticles became large and polydisperse in the case of silver carboxylate with a chain length of 7 carbon atoms or a branched chain. In comparing triethylamine with trioctylamine, there was no obvious effect to regulate the size distribution of the nanoparticles because they could not function as a capping ligand of the nanoparticles due to their weak coordination to silver. In addition, the heat treatment of silver nanoparticles in solution rather than in the solid state was effective for the growth of particles while maintaining narrow size distributions.

A Facile Synthetic Method of Silver Nanoparticles with a Continuous Size Range from sub-10 nm to 40 nm

“…Interestingly, the reducing agents had an apparent effect on the size of Ag NPs because Nakamoto et al reported that the types of amines had negligible effect. 28 They attempted several types of tertiary alkyamines and primary amines. None affected the size and size distribution of the NPs except for n-octylamine.…”

“…[20][21][22][23][24][25] Nakamoto et al reported the synthesis of Ag NPs from the decomposition of a specially designed coordinated compound. [26][27][28][29] The Ag NPs were prepared by the reduction of Ag(I) carboxylates with a reducing agent, triethylamine, under mild conditions, e.g. 80 o C. 26 The size (from 2.7 nm to 4.4 nm) of the Ag NPs was strongly affected by the alkyl chain length of the carboxylate, while the reducing agent and other reaction conditions had a negligible effect.…”

“…80 o C. 26 The size (from 2.7 nm to 4.4 nm) of the Ag NPs was strongly affected by the alkyl chain length of the carboxylate, while the reducing agent and other reaction conditions had a negligible effect. 28 Although it is a facile method for producing monodisperse Ag NPs, the size range is too narrow (almost all the high-quality NPs were in the sub-10 nm size regime). In their later report, large NPs could be prepared using short chain length or branched carboxylates.…”

“…However, the synthesized NPs had a broad size distribution. 27,28 Considering the demand for Ag NPs of various sizes with a narrow distribution in printable electronics, it is important to advance this synthetic method to the 10 ~ 50 nm region.…”

Mechanism of Organogel Formation from Mixed-Ligand Silver (I) Carboxylates

“…34 It has been often reported that Ag nanoparticles have been obtained through the decomposition of Ag(I) complexes in the presence of reductants such as triethylamine. [35][36][37][38] They have also been observed in some other solvents, such as DMSO, CHCl 3 and DMF. Chlorobenzene, with both aromatic and reducing properties, formed a yellowish, clear gel indicating the production of Ag nanoparticles within the gel.…”