Highly size- and shape-controlled synthesis of silver nanoparticles via a templated Tollens reaction.
Bottom Line: The high degree of size- and shape-control of these AgNPs is achieved by the use of triazole sugar ligands scaffolded by a central resorcinol ether core.Both the triazoles and the resorcinol ether core mediate the nucleation, growth, and passivation phases of the preparation of AgNP in the presence of the Tollens reagent as the silver source.Kinetic and (1)H NMR titration data is presented describing the nature of the interactions between the Tollens reagent and these ligands.
Affiliation: Department of Chemistry, University of Leicester, University Road, Leicester, LE1 1RE, UK.Show MeSH
Mentions: Kinetics experiments were then conducted as a function of reducing sugar type (1–3) using the formation of the surface plasmon peak at ∼400 nm as a diagnostic marker of the formation of AgNPs. For each of the sugar triazoles (1–3) investigated, an autocatalytic process was observed (Figure 3). The onset of AgNP@(1) formation was observed at ∼2000 s with an endpoint at 2868 s using the optimized conditions for their formation. A significantly faster reaction rate [onset at ∼1000 s] was observed when D-galactose was used as the silver(I) reductant to form AgNP@D-galactose,4b suggesting that the triazole unit in (1) slows the rate of AgNP@(1) formation. In contrast to the AgNP@(1) and AgNP@D-galactose systems, the reaction kinetics of both AgNP@(2) and AgNP@(3) were significantly faster (Figure 3). Intriguingly, the rate of onset (∼120 s) and the end point (∼588 s) of both AgNP@(2) and AgNP@(3) were virtually identical.4b Thus, based on the kinetic data, an increase in the number of reducing sugars from one (1) to two (2) increases the rate of AgNP formation, however a further increase in the number of reducing sugars from two (2) to four (3) has little effect on the reaction rate. We therefore conclude that the presence of the triazole unit in sugar (1) slows the rate of AgNP@(1) formation relative to the rate of formation of AgNP@D-galactose. The rate of both AgNP@(1) and AgNP@D-galactose formation is significantly slower than AgNP@(2) and AgNP@(3), resulting in the following trend: rate of AgNP formation AgNP(2) ≈AgNP(3) ≫AgNP@D-galactose>AgNP@(1). This trend cannot be rationalized by an increase in only the reducing sugar moieties as the sugar (3) system should exhibit a considerably faster rate relative to sugar (2). We therefore conclude that the resorcinol ether core structure of the sugar triazole (2) is a key determinant in the increased rate of the reaction kinetics relative to (1).
Affiliation: Department of Chemistry, University of Leicester, University Road, Leicester, LE1 1RE, UK.