SYNTHESIS OF SILVER NANOPARTICLES IN THE PRESENCE OF HYPERBRANCHED OLIGOMERIC IONIC LIQUID AS THEIR SURFACE STABILIZER

Abstract

A method for synthesis of silver nanoparticles (AgNPs) in the presence of proposed by us protic anionic oligomeric ionic liquid (OIL) of hyperbranched structure as a stabilizer of their surface was developed. Reduction of Ag(I) silver cations was carried out with trisodium citrate in an aqueous environment at temperature of 100°C for an hour. The OIL proposed and used by us as a surface stabilizer of colloidal AgNPs is a product of exhaustive acylation of hyperbranched oligoester polyol of the 3rd generation (contains 32 terminal primary aliphatic hydroxyl groups) with cyclic 2-sulfobenzoic anhydride and subsequent neutralization of the resulting sulfonic compound with N-methylimidazole. The synthesized AgNPs stabilized with the OIL are powders soluble in water that opens up wide possibilities of using the developed AgNPs to obtain nanodisperse systems, in particular hydrosols and nanocomposite functional polymer materials. The formation of «guest-host» type complexes between the OIL and silver ions Ag(I) and the adsorption of carbonyl and ionic (their cationic component) groups on the surface of the formed AgNPs were established by FTIR. According to FTIR data trisodium citrate is also partially adsorbed on the surface of the formed silver nanoparticles and takes part in complex formation. The formation of AgNPs was also confirmed by X-ray analysis. The X-ray diffractograms of the obtained AgNPs show reflections at 38.0, 44.2, 64.4 and 77.3°, which are correspondingly related to (111), (200), (220) and (311) reflections of crystal planes and indicates the formation of silver nanoparticles with a face-centered cubic structure. It should be noted that the intensity of the above-mentioned reflexes increases with an increase in amount of the OIL used in the synthesis that confirms the stabilizing effect of the OIL in relation to the AgNPs and favoring the formation of the last ones due to autoreduction of silver. X-ray data evidences presence of trisodium citrate in the composition of the AgNPs being absorbed on the surface or as the complex with silver ions. The formation of AgNPs is also confirmed by TEM data. The TEM micrograph shows nanosized spherical particles of the «core-shell» type, where according to FTIR and X-ray analys a reduced silver is the core, and the OIL and trisodium citrate forms the shell as a stabilizer. These nanoparticles form swarm-like structures. Analysis of the microphotograph showed that the obtained AgNPs are characterized by a narrow size distribution in the range of 5–10 nm. The synthesized AgNPs stabilized with OIL and trisodium citrate are powders soluble in water, which opens up wide possibilities of their use for obtaining highly dispersed systems, in particular hydrosols and nanocomposite functional polymer materials based on them.