Access to small size distributions of nanoparticles by microwave-assisted synthesis. Formation of Agnanoparticles in aqueous carboxymethylcellulose solutions in batch and continuous-flow reactors

Abstract

This article examines the effect(s) of the 2.45-GHz microwave (MW) radiation in the synthesis of silver nanoparticles in aqueous media by reduction of the diaminesilver(I) complex, [Ag(NH₃)₂]⁺, with carboxymethylcellulose (CMC) in both batch-type and continuous-flow reactor systems with a particular emphasis on the characteristics of the microwaves in this process and the size distributions. This microwave thermally-assisted synthesis is compared to a conventional heating (CH) method, both requiring a reaction temperature of 100 °C to produce the nanoparticles, in both cases leading to the formation of silver colloids with different size distributions. Reduction of the diaminesilver(I) precursor complex, [Ag(NH₃)₂]⁺, by CMC depended on the solution temperature. Cooling the reactor during the heating process driven with 390-Watt microwaves (MW-390W/Cool protocol) yielded silver nanoparticles with sizes spanning the range 1–2 nm. By contrast, the size distribution of Ag nanoparticles with 170-Watt microwaves (no cooling; MW-170W protocol) was in the range 1.4–3.6 nm (average size ∼3 nm). The overall results suggest the potential for a scale-up process in the microwave-assisted synthesis of nanoparticles. Based on the present data, a flow-through microwave reactor system is herein proposed for the continuous production of silver nanoparticles. The novel flow reactor system (flow rate, 600 mL min⁻¹) coupled to 1200-Watt microwave radiation generated silver nanoparticles with a size distribution 0.7–2.8 nm (average size ca. 1.5 nm).