1 research outputs found
Redox Decomposition of Silver Citrate Complex in Nanoscale Confinement: An Unusual Mechanism of Formation and Growth of Silver Nanoparticles
We demonstrate for the first time
the intrinsic role of nanoconfinement
in facilitating the chemical reduction of metal ion precursors with
a suitable reductant for the synthesis of metal nanoparticles, when
the identical reaction does not occur in bulk solution. Taking the
case of citrate reduction of silver ions under the unusual condition
of [citrate]/[Ag<sup>+</sup>] ≫ 1, it has been observed that
the silver citrate complex, stable in bulk solution, decomposes readily
in confined nanodomains of charged and neutral matrices (ion-exchange
film and porous polystyrene beads), leading to the formation of silver
nanoparticles. The evolution of growth of silver nanoparticles in
the ion-exchange films has been studied using a combination of <sup>110m</sup>Ag radiotracer, small-angle X-ray scattering (SAXS) experiments,
and transmission electron microscopy (TEM). It has been observed that
the nanoconfined redox decomposition of silver citrate complex is
responsible for the formation of Ag seeds, which thereafter catalyze
oxidation of citrate and act as electron sink for subsequent reduction
of silver ions. Because of these parallel processes, the particle
sizes are in the bimodal distribution at some stages of the reaction.
A continuous seeding with parallel growth mechanism has been revealed.
Based on the SAXS data and radiotracer kinetics, the growth mechanism
has been elucidated as a combination of continuous autoreduction of
silver ions on the nanoparticle surfaces and a sudden coalescence
of nanoparticles at a critical number density. However, for a fixed
period of reduction, the size, size distribution, and number density
of thus-formed Ag nanoparticles have been found to be dependent on
physical architecture and chemical composition of the matrix