Reduction and aggregation of silver and thallium ions in viscous media

Abstract

Radiolytic reduction of silver and thallium ions and the subsequent formation of their clusters have been studied in ethylene glycol and glycerol media and are compared with the parallel processes in aqueous solutions. From the decay of e_sol⁻ at 540 and 580 nm the formation rate constants of Ag⁰ in glycerol and ethylene glycol have been determined to be 5.3 × 10⁸ and 7.2 × 10⁸ dm³ mol⁻¹ s⁻¹, respectively. Rate constants for the reaction of e_sol⁻ with Tl⁺ in glycerol and ethylene glycol were determined to be 3.0 × 10⁸ and 3.6 × 10⁸ dm³ mol⁻¹ s⁻¹, respectively. The surface plasmon absorption band of stable silver clusters obtained by bombardment of electron pulses in glycerol showed an absorption maximum at around 410 nm. Two aggregates of different sizes were stabilized by glycerol upon complete reduction of the silver ions. However, it appears that the viscosity of the medium is not the only criterion for stabilization of small silver nanoparticles. The stability of the nanoparticles was found to be dependent on the dose absorbed by the system. Transmission electron micrograph studies showed the presence of silver nanoparticles having an average size of 20 nm. The growth and reactivity of silver clusters were also studied in the presence of methyl viologen (MV²⁺). The kinetics of formation of silver clusters, produced by the same pulse as in the case of MV˙⁺, confirms the electron transfer from MV˙⁺ to supercritical silver clusters. Electron transfer rates from Tl₂⁺ and Ag⁺ in ethylene glycol and glycerol were determined to be 2.2 × 10⁸ and 5.5 × 10⁷ dm³ mol⁻¹ s⁻¹, respectively.