Investigation into the Mechanism and Microstructure of Reaction Intermediates in the Two-Phase Synthesis of Alkanethiol-Capped Silver Nanoparticles

Abstract

To gain better control over the characteristics of the alkanethiol-capped silver nanoparticles (SNP) prepared by the two-phase method, the intermediate stage of this reaction and the structure of the precursor compound were investigated. Samples taken from the intermediate stage of the reaction were analyzed by NMR and vibrational spectroscopy both in solution and after solvent removal. The (1)H NMR chemical shifts of the complexes formed during the phase-transfer step were used to detect any structural changes that occur upon introduction of nonanethiol. Moreover, the presence of silver thiolate was monitored by comparing the FTIR and Raman spectra of silver nonanethiolate with the dried samples. Further insights into the microstructure of the intermediate compounds were sought by characterizing samples differing in molar ratios of tetraoctylammonium bromide (TOAB) to silver nitrate (AgNO3). (13)C solid-state NMR chemical shifts, (13)C relaxation times, and the DSC transitions of these samples revealed a dependence of their phase structure on the initial concentration of the reagents. At least two phases with distinct mobility and conformational ordering of their octyl chains were identified in the samples prepared with excess TOAB, which was associated with the presence of multiple anionic species. The observations regarding the composition of the phase-transfer product were further related to the quality of the resulting nanoparticles. It was demonstrated that a large excess of TOAB, which is commonly used in two-phase methods, can be avoided without compromising the size and dispersity of the silver nanoparticles produced. This modification to the synthetic procedure simplifies the purification of the product, mitigates the propensity of the nanoparticles for aggregation, and facilitates their redispersion.

Facile synthesis of a highly SERS active nanosilver sol using microwaves and its application in the detection of E. coli using Victoria blue B as a molecular probe

“…Nanosilver has the advantage of being low-cost and having a high molar extinction coefficient and excellent optical properties, such as nanosilver aggregates having a low molar extinction coefficient and strong SERS effects. This provides the foundation for its application [1][2][3] and draws great interest to preparing nanosilver, especially stable nanosilver, with new technologies relying on its drastically enhanced properties. Nowadays nanosilver can be synthesized using various methods such as reduction reaction methods, thermal decomposition methods, electrolytic methods and other methods.…”

Contradictory Dual Effects: Organothiols Can Induce Both Silver Nanoparticle Disintegration and Formation under Ambient Conditions

“…8 Organothiols and thiol-containing biomolecules have been utilized in a wide range of AgNP synthesis and applications. [9][10][11][12] They are the most popular capping agents in AgNC synthesis, 4,11,[13][14][15] and the commonly used model molecules in studying AgNP SERS activities. [16][17][18][19] However, current understanding of organothiol interactions with AgNPs and silver ions remains incomplete.…”

“…There are many types of man-made and naturally occurring silver-based nanomaterials including fluorescent-active silver nanoclusters (AgNC) and surface plasmonic resonance (SPR) active silver nanoparticles (AgNPs) − that have been used for biosensing, , chemical catalysis, and solar energy harvesting . Organothiols and thiol-containing biomolecules have been utilized in a wide range of AgNP synthesis and applications. − They are the most popular capping agents in AgNC synthesis ,,− and the commonly used model molecules in studying AgNP SERS activities. − However, current understanding of organothiol interactions with AgNPs and silver ions remains incomplete. As strong chelating agents of silver ion, organothiols and thiol-containing biomolecules can greatly reduce the redox potential of silver, making AgNPs susceptible to oxidative disintegration under ambient conditions .…”