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Rapid continuous microwave-assisted synthesis of silver nanoparticles to achieve very high productivity and full yield: from mechanistic study to optimal fabrication strategy.

Dzido G, Markowski P, Małachowska-Jutsz A, Prusik K, Jarzębski AB - J Nanopart Res (2015)

Bottom Line: Systematic studies of silver nanoparticle synthesis in a continuous-flow single-mode microwave reactor using polyol process were performed, revealing that the synthesis is exceptionally effective to give very small metal particles at full reaction yield and very high productivity.Owing to its much higher reactivity, silver acetate was shown to be far superior substrate for the synthesis of small (10-20 nm) spherical silver nanoparticles within a few seconds.The performed studies indicate an optimal strategy for the high-yield fabrication of metal particles using polyol method.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering and Process Design, Faculty of Chemistry, Silesian University of Technology, Ks. M. Strzody 7, 44-100 Gliwice, Poland.

ABSTRACT

Systematic studies of silver nanoparticle synthesis in a continuous-flow single-mode microwave reactor using polyol process were performed, revealing that the synthesis is exceptionally effective to give very small metal particles at full reaction yield and very high productivity. Inlet concentration of silver nitrate or silver acetate, applied as metal precursors, varied between 10 and 50 mM, and flow rates ranged from 0.635 to 2.5 dm(3)/h, to give 3-24 s reaction time. Owing to its much higher reactivity, silver acetate was shown to be far superior substrate for the synthesis of small (10-20 nm) spherical silver nanoparticles within a few seconds. Its restricted solubility in ethylene glycol, applied as the solvent and reducing agent, appeared to be vital for effective separation of the stage of particle growth from its nucleation to enable rapid synthesis of small particles in a highly loaded system. This was not possible to obtain using silver nitrate. All the observations could perfectly be explained by a classical LaMer-Dinegar model of NPs' formation, but taking into account also nonisothermal character of the continuous-flow process and acetate dissolution in the reaction system. The performed studies indicate an optimal strategy for the high-yield fabrication of metal particles using polyol method.

No MeSH data available.


Related in: MedlinePlus

Particle size distributions histograms (by DLS) and UV–Vis spectra of samples produced with 10 mM (T4, T5) and 50 mM (T13, T14) Ag-acetate inlet content
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Related In: Results  -  Collection


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Fig5: Particle size distributions histograms (by DLS) and UV–Vis spectra of samples produced with 10 mM (T4, T5) and 50 mM (T13, T14) Ag-acetate inlet content

Mentions: However, a more plausible explanation, perfectly in accordance with LMD model, which we propose herein, is that these bimodal size distributions of NPs directly stem from a nonisothermal nature of the realized continuous-flow process, and hence, the presence of two distinct regimes of particle formation prevailing in central and exit sections of the reactor. In the region of low and medium temperatures, the rate of substrate reduction is low and hence the concentration of species generated by the reaction of reduction and hydrolysis cannot easily reach a supersaturation level, needed for nucleation (Fivet and Brayner 2013). This facilitates their attachment to few particles already present in the system, ending up in the synthesis of large particles, as predicted by LMD model. The second regime, which prevails in a high-temperature (center and/or outlet) region, features very fast rate of substrate reduction and rapid increase in the concentration of final species to the value exceeding a critical supersaturation, i.e., nucleation level. In effect, it triggers very fast nucleation, which immediately lowers concentration below that of nucleation. If the concentration of final species remains higher than the saturation level, then a slow growth of particles follows. This mechanisms results in the formation of small particles, also seen in the PSD patterns (Fig. 4), in agreement with the LMD model predictions (Blosi et al. 2011; Fivet and Brayner 2013). Clearly, this picture is obscured by both temperature- and MW-stimulated particle oscillations which facilitate coalescence and aggregation of smaller particles into larger ones. However, on the whole, this portrayal is also supported by a larger amount of bigger NPs obtained at longer reaction time, under otherwise identical conditions (cf. T9 and T10 in Fig. 4). As already pointed out, Ag-acetate appeared to be much more reactive than Ag-nitrate, and hence very small particles, of less than 10 nm, could be obtained in just 3 s at full reaction yield, and even at the exit temperature of 150 °C. However, closer analyses of the PSD (hydrodynamic diameter by DLS) patterns showed that again the trends observed are in good agreement with the predictions of LMD model. At low inlet concentrations (10 mM) and under very vigorous microwave heating, to achieve the exit temperature of 150 °C in just 3 s, particles with size distribution ranging from 5 to 10 nm were synthesized at full reaction yield and with a minute content of those <5 nm (T17, data not shown), a clear sign of very rapid nucleation. If a MW power supply was reduced by half (T18, 6 s), still narrower PSD pattern was achieved, with a majority of particle sizes being in the range of 3–4 nm (by DLS, data not shown). Clearly, too powerful irradiation (short reaction time) appears to be detrimental for the formation of uniform particles. We ascribe it to both the MW-induced oscillations and collisions, ending up in the aggregation of very fine particles (of 2–3 nm) to give those 5–8 nm in size, However, also to vigorous, repeated multiple-step dissolution and crystallization phenomena. They disrupt a dynamic equilibrium between reduction, nucleation, and growth, deemed to be critical for the synthesis of uniform particles (Blosi et al. 2011). All these experiments were performed using K25 PVP as a capping agent. When K30 PVP was applied, PSDs appeared to be somewhat wider (cf. T4 Fig. 5), which points to the importance of effective capping in the rapid synthesis of NPs. Worth noting is that application of PVP with even shorter chain (Mw 8 kDa) had no appreciable effect on particle sizes. Surprisingly enough, at lower power input, and hence longer reaction times (T5, 12 s and T6, 24 s), particles with bi- (T5, Fig. 5) and even tri-size (T7) distributions in the range of 8–80 nm were obtained (not shown), when PVP with a longer chain (K30), and hence less capping ability, was applied. We believe that the mechanism of particle formations is exactly the same as that discussed above for Ag-nitrate system, but owing to much higher reactivity of silver acetate–EG system, the particles were considerably smaller. In this respect, it is noteworthy that low temperature (90 °C, T3) synthesis in the same time resulted in the formation of particles with a narrow PSD, similar to that corresponding to larger particles seen in the bimodal distributions of T5 and T6, in good agreement with the observations made for T9 and T10 (Fig. 4).Fig. 5


Rapid continuous microwave-assisted synthesis of silver nanoparticles to achieve very high productivity and full yield: from mechanistic study to optimal fabrication strategy.

Dzido G, Markowski P, Małachowska-Jutsz A, Prusik K, Jarzębski AB - J Nanopart Res (2015)

Particle size distributions histograms (by DLS) and UV–Vis spectra of samples produced with 10 mM (T4, T5) and 50 mM (T13, T14) Ag-acetate inlet content
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4300398&req=5

Fig5: Particle size distributions histograms (by DLS) and UV–Vis spectra of samples produced with 10 mM (T4, T5) and 50 mM (T13, T14) Ag-acetate inlet content
Mentions: However, a more plausible explanation, perfectly in accordance with LMD model, which we propose herein, is that these bimodal size distributions of NPs directly stem from a nonisothermal nature of the realized continuous-flow process, and hence, the presence of two distinct regimes of particle formation prevailing in central and exit sections of the reactor. In the region of low and medium temperatures, the rate of substrate reduction is low and hence the concentration of species generated by the reaction of reduction and hydrolysis cannot easily reach a supersaturation level, needed for nucleation (Fivet and Brayner 2013). This facilitates their attachment to few particles already present in the system, ending up in the synthesis of large particles, as predicted by LMD model. The second regime, which prevails in a high-temperature (center and/or outlet) region, features very fast rate of substrate reduction and rapid increase in the concentration of final species to the value exceeding a critical supersaturation, i.e., nucleation level. In effect, it triggers very fast nucleation, which immediately lowers concentration below that of nucleation. If the concentration of final species remains higher than the saturation level, then a slow growth of particles follows. This mechanisms results in the formation of small particles, also seen in the PSD patterns (Fig. 4), in agreement with the LMD model predictions (Blosi et al. 2011; Fivet and Brayner 2013). Clearly, this picture is obscured by both temperature- and MW-stimulated particle oscillations which facilitate coalescence and aggregation of smaller particles into larger ones. However, on the whole, this portrayal is also supported by a larger amount of bigger NPs obtained at longer reaction time, under otherwise identical conditions (cf. T9 and T10 in Fig. 4). As already pointed out, Ag-acetate appeared to be much more reactive than Ag-nitrate, and hence very small particles, of less than 10 nm, could be obtained in just 3 s at full reaction yield, and even at the exit temperature of 150 °C. However, closer analyses of the PSD (hydrodynamic diameter by DLS) patterns showed that again the trends observed are in good agreement with the predictions of LMD model. At low inlet concentrations (10 mM) and under very vigorous microwave heating, to achieve the exit temperature of 150 °C in just 3 s, particles with size distribution ranging from 5 to 10 nm were synthesized at full reaction yield and with a minute content of those <5 nm (T17, data not shown), a clear sign of very rapid nucleation. If a MW power supply was reduced by half (T18, 6 s), still narrower PSD pattern was achieved, with a majority of particle sizes being in the range of 3–4 nm (by DLS, data not shown). Clearly, too powerful irradiation (short reaction time) appears to be detrimental for the formation of uniform particles. We ascribe it to both the MW-induced oscillations and collisions, ending up in the aggregation of very fine particles (of 2–3 nm) to give those 5–8 nm in size, However, also to vigorous, repeated multiple-step dissolution and crystallization phenomena. They disrupt a dynamic equilibrium between reduction, nucleation, and growth, deemed to be critical for the synthesis of uniform particles (Blosi et al. 2011). All these experiments were performed using K25 PVP as a capping agent. When K30 PVP was applied, PSDs appeared to be somewhat wider (cf. T4 Fig. 5), which points to the importance of effective capping in the rapid synthesis of NPs. Worth noting is that application of PVP with even shorter chain (Mw 8 kDa) had no appreciable effect on particle sizes. Surprisingly enough, at lower power input, and hence longer reaction times (T5, 12 s and T6, 24 s), particles with bi- (T5, Fig. 5) and even tri-size (T7) distributions in the range of 8–80 nm were obtained (not shown), when PVP with a longer chain (K30), and hence less capping ability, was applied. We believe that the mechanism of particle formations is exactly the same as that discussed above for Ag-nitrate system, but owing to much higher reactivity of silver acetate–EG system, the particles were considerably smaller. In this respect, it is noteworthy that low temperature (90 °C, T3) synthesis in the same time resulted in the formation of particles with a narrow PSD, similar to that corresponding to larger particles seen in the bimodal distributions of T5 and T6, in good agreement with the observations made for T9 and T10 (Fig. 4).Fig. 5

Bottom Line: Systematic studies of silver nanoparticle synthesis in a continuous-flow single-mode microwave reactor using polyol process were performed, revealing that the synthesis is exceptionally effective to give very small metal particles at full reaction yield and very high productivity.Owing to its much higher reactivity, silver acetate was shown to be far superior substrate for the synthesis of small (10-20 nm) spherical silver nanoparticles within a few seconds.The performed studies indicate an optimal strategy for the high-yield fabrication of metal particles using polyol method.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical Engineering and Process Design, Faculty of Chemistry, Silesian University of Technology, Ks. M. Strzody 7, 44-100 Gliwice, Poland.

ABSTRACT

Systematic studies of silver nanoparticle synthesis in a continuous-flow single-mode microwave reactor using polyol process were performed, revealing that the synthesis is exceptionally effective to give very small metal particles at full reaction yield and very high productivity. Inlet concentration of silver nitrate or silver acetate, applied as metal precursors, varied between 10 and 50 mM, and flow rates ranged from 0.635 to 2.5 dm(3)/h, to give 3-24 s reaction time. Owing to its much higher reactivity, silver acetate was shown to be far superior substrate for the synthesis of small (10-20 nm) spherical silver nanoparticles within a few seconds. Its restricted solubility in ethylene glycol, applied as the solvent and reducing agent, appeared to be vital for effective separation of the stage of particle growth from its nucleation to enable rapid synthesis of small particles in a highly loaded system. This was not possible to obtain using silver nitrate. All the observations could perfectly be explained by a classical LaMer-Dinegar model of NPs' formation, but taking into account also nonisothermal character of the continuous-flow process and acetate dissolution in the reaction system. The performed studies indicate an optimal strategy for the high-yield fabrication of metal particles using polyol method.

No MeSH data available.


Related in: MedlinePlus