High-Speed but Not Magic: Microwave-Assisted Synthesis of Ultra-Small Silver Nanoparticles

Abstract

Reaction procedures have been improved to achieve higher yields and shorter reaction times: one possibility is the usage of microwave reactors. In the literature, this is under discussion, for example, nonthermal effects resulting from the microwave radiation are claimed. Especially for the synthesis of nanomaterials, it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare the syntheses of ultra-small silver nanoparticles via conventional and microwave heating. We employed a versatile one-pot polyol synthesis of poly(acrylic acid)-stabilized silver nanoparticles, which display superior catalytic properties. No microwave-specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering and dynamic light scattering, are revealed. Because of the characteristics of a closed system, microwave reactors give access to elevated temperatures and pressures. Therefore, the speed of particle formation can be increased by a factor of 30 when the reaction temperature is increased from 200 to 250 °C. The particle growth process follows a cluster coalescence mechanism. A postsynthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particle size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A compromise between short reaction times and high yields can be found at a temperature of 250 °C and a corresponding reaction time of 30 s.

Comparative biological effects of spherical noble metal nanoparticles (Rh, Pd, Ag, Pt, Au) with 4–8 nm diameter

“…The generation of small silver nanoparticles (3–6 nm) is often performed only to generate seeds as a precursor for subsequent more complex morphologies, for example, as the core for bimetallic nanoparticles or as a sacrificial core for hollow nanoparticles of a more noble metal like gold [ 71 , 75 – 78 ]. There are many examples of syntheses for silver nanoparticles with a diameter between 5–10 nm [ 71 , 79 – 80 ]. Platinum nanoparticles can be obtained by metal carbonyl-mediated synthesis in organic solvents [ 81 ].…”

Microwave-Driven Synthesis of Iron-Oxide Nanoparticles for Molecular Imaging

“…Among these, polyols are especially popular due to their capability of acting as both a reducing agent and solvent. Saloga et al [95] described a microwave-assisted polyol synthesis of ultra-small AgNPs. In their one-pot reaction, AgNO 3 was used as the Ag source, while poly(acrylic acid) was used as the stabilizing agent, and polyethylene glycol was used as both the solvent and reducing agent.…”

Kinetic monitoring of glutathione-induced silver nanoparticle disintegration

“…23 Briefly, solutions of silver nitrate (833 µL, 0.19 M) and PAA (4.167 mL, 0.03 M) in ethylene glycol were mixed and heated to 200°C for 15 min. The resulting particles were purified by threefold addition of 11.4 mL of water followed by sedimentation.…”