From Silver Plates to Spherical Nanoparticles: Snapshots of Microwave-Assisted Polyol Synthesis

Abstract

The fabrication of silver nanoparticles (Ag NPs) with different sizes by microwave (MW)-assisted synthesis is presented. The fast heating of the MW technique, combined with the possibility to thermally quench the reactions, enabled us to capture snapshots of nucleation and growth processes difficult to accomplish in other techniques. The Ag NPs were synthesized using poly(vinylpyrrolidone) (PVP) through a polyol approach. The effects of the reaction time, the reaction temperatures, and the silver precursor concentration were investigated. The influence of agitation, the PVP concentration, and the initial conditions of the silver precursor was also studied. It is found that at very short reaction times and at low temperatures, polyhedral plates are formed with sizes ca. 300 nm and large polydispersity. However, by increasing the time or the temperature, a size and shape refinement is observed resulting in 10 nm spherical NPs with low polydispersity. Mechanistic insights are provided based on the observations extracted from transmission electron microscopy (TEM) and ultraviolet−visible spectroscopy (UV−vis). A formation mechanism starting from kinetically favored silver polyhedral plates to thermodynamically favored spherical nanoparticles is proposed. Understanding these effects allowed us to control the particle size and the tuning of Ag NPs ondemand. Moreover, the reproducibility and scalability of the process and the long-term stability of the NPs in aqueous solutions are demonstrated. Finally, we provide a recommendation regarding the use of fresh PVP as a capping and stabilizing agent.

Ezetimibe-Loaded Nanostructured Lipid Carrier Based Formulation Ameliorates Hyperlipidaemia in an Experimental Model of High Fat Diet

“…It was also concluded that EZE is molecularly dispersed in the lipid matrix, indicating its reduction in crystallinity as the peak intensity of the drug was found to be reduced as shown in Figure 4 . It was also reported earlier that the shift of the peak and reduction in peak height whether in lipid or drug can be attributed to the matrix which was composed of the mixture of lipids [ 32 , 33 ].…”

“…According to work done by Proetto et al, particles at some locations may begin to coalesce over time, owing to electron-beam induced impairment [ 32 ]. Additionally, Torras et al, stated that the loss of discrete particles might be attributed to higher temperatures [ 33 ]. We assume, this could be due to the slight melding of particle surfaces, for instance during the cooling phase of the nanoemulsion.…”

Silver nanoparticles: synthesis, characterisation and biomedical applications

“…These silver nanoparticles were spherical and non-agglomerated [ 21 ]. Recently, it has been demonstrated that the polyol process produces spherical nanoparticles with different sizes under laser ablation [ 17 , 22 ]. To examine the effects of laser wavelength on the particle size, silver nanoparticles were synthesised through ablation with different lasers and it was noticed that decrease in laser wavelength reduced the average diameter of particles from 29 to 12 nm [ 23 ].…”

Modeling, design, and synthesis of gram-scale monodispersed silver nanoparticles using microwave-assisted polyol process for metamaterial applications

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“…The MW-assisted synthesis can be scaled up to accelerate the commercialization of the NPs. Using the MW-assisted polyol method, Torras and Roig [20] could improve the yield of NP production to 61%, obtaining 1 mg of silver per batch. Following a similar approach, Helmlinger et al [31] obtained 20 mg of Ag per batch, corresponding to a yield beyond 98%.…”