The thermolysis behavior of Ag/PAMAMs nanocomposites
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- Peng, Z., Zhang, J., Sun, X. et al. Colloid Polym Sci (2009) 287: 609. doi:10.1007/s00396-009-2015-2
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Ag/polyamidoamine (PAMAM) nanocomposites were produced by photoreduction of relevant metallic salts in different generations of PAMAM (PAMAMs) methanol solutions under room temperature and ambient pressure. The obtained Ag nanoparticles were quite uniform in size with a diameter of about 15 nm. Thermogravimetric analysis (TGA) results showed that the amount of Ag nanoparticles could well affect the thermal stability of PAMAMs. As the mass ratio of Ag nanoparticles to PAMAMs increased, the weight-losing ratios decreased. Meanwhile, TGA curves also indicated that the thermal behavior of Ag/PAMAMs was greatly different in the two stages of low (130~280 °C) and high temperature (280~450 °C) range; the loading of Ag nanoparticles mainly influences the thermal stability of PAMAMs in high temperature region (280~450 °C). Moreover, the multistage decomposition profile of derivative thermal gravimetry curves suggested that there might contain some intermediate Ag/PAMAMs type of composites.
The properties of nano- or microscale sizes of metals are size-dependent and can be simply tuned by changing the dimension . Recently, people found that polymer embedding represents a simple but effective way to use mesoscopic properties of nano-sized metals because polymer/metal nanoparticle composites are very useful for functional applications , of which silver polymer nanocomposites have a lot of novel properties and have many potential applications in the areas of heterogeneous catalysts, antibacterial agent and health-care products [3, 4], and so on. There are many polymer-embedding methods [5–8] to synthesize silver polymer nanocomposites, such as chemical reduction  and photoreduction [10–12].
High generations of dendritic polyamidoamines (PAMAMs) have a dramatic structure because they exhibit densely packed near-spherical topologies with many cavities in nanometer sizes , and the cavities can act as nanoscale templates to produce metal nanoparticles [14–17].
In this paper, Ag nanoparticles were successfully prepared by amino-terminated dendritic PAMAMs acting as monodispersed templates. And, the thermal behavior of Ag/PAMAMs nanocomposites was investigated by virtue of thermal gravimetry (TG)-derivative thermal gravimetry (DTG) techniques in detail.
Ethylenediamine, methanol, and silver nitrate are analytically pure and used as received, while acrylic acid ester was used after being purified by distillation.
G1-G5 PAMAM was synthesized by the reaction to ethylenediamine with acrylic acid ester in methanol according to the literature .
The morphology of the Ag/PAMAMs nanocomposites were observed on a Hitachi Model H-800 transmission electron microscope. Samples for transmission electron microscopy (TEM) observation were prepared by ultrasonic dispersion in methanol for 30 min, followed by dipping copper 400-mesh carrier grids covered with carbon-coated Formvar films into the dispersions.
Thermogravimetric analysis (TGA) data for the PAMAMs and composites were taken on 851e TGA/SDTA (Mettler-Toledo, Switzerland) at a heating rate of 10 °C/min in argon atmosphere.
Synthesis of Ag/PAMAM nanocomposites
Ag/PAMAMs nanocomposites were produced by photoreduction of silver nitrate in PAMAM methanol solutions under room temperature and ambient pressure. Different amount of silver nitrate (gram mass, (a) 0 g; (b) 0.32 g; (c) 0.64 g; (d) 1.08 g; (e) 1.44 g; (f) 1.60 g) and PAMAMs (10.0 g) were dissolved in methanol (100 mL), respectively. These solutions were respectively put into four-necked flasks equipped with mechanical stirrer and nitrogen inlet, then the silver nitrate methanol solutions were slowly added into the flasks within 2 h. The mixture was continuously stirred under a nitrogen atmosphere for 3 h; it was pale yellow. Later, the mixture was irradiated under ultraviolet light lamp (180 W) for 3 h; the color of mixtures became dark, and some dark suspension appeared. Subsequently, the mixed solutions were filtrated with a buchner filter after ultraviolet irradiation. It was found that the limpidity filter liquor did not turn turbid when the filter liquor was titrated by dilute hydrochloric acid., so silver nitrate in the solutions was considered to be completely photoreduced at the moment.
Whereafter, the mixtures were volatilized in rotary vacuum evaporator at 40 °Cfor 5 h. Then it was dried in a vacuum drying oven at 50 °C for 24 h. Finally, the brown products (the gram mass: (a) 10.00 g; (b) 10.20 g; (c) 10.40 g; (d) 10.60 g; (e) 10.80 g; (f) 11.00 g; in the series of nanocomposites, the mass ratio of Ag nanoparticles to PAMAMs is: (a) 0:10; (b) 0.2:10; (c) 0.4:10; (d) 0.6:10; (e) 0.8:10; (f) 1.0:10.) were collected.
Results and discussion
It shows that the Ag nanoparticles in different generations of PAMAM are near-spherical and quite uniform in size with a diameter of 15 nm. So it can be concluded that PAMAMs can be considered as a good template to prepare silver nanoparticles.
The weight-losing ratio of Ag-PAMAMs composites with different mass ratio of Ag nanoparticles to PAMAMs at different stages
The numbers of generations
The mass ratio
The total weight-losing ratio (%)
The weight-losing ratio (%)
The ratio (%) of the losing PANAM to the total PANAM weight
The ratio of the losing PANAM at two temperature stages
All of the DTG curves of PAMAMs have two large peaks between 200 and 320 °C, while the DTG curves of Ag/PAMAMs nanocomposites have more than two peaks; it may indicate the formation of some different intermediate Ag+/PAMAM type  of composites in the thermolysis process. As the loading of Ag nanoparticles increase, in all curves a main inflexion about 175 °C occur, which corresponds to the initial stage of thermolysis of PAMAMs, it shows that the appearance of Ag nanoparticles can accelerate the initial thermolysis of PAMAMs. At the same time, the two large peaks of PAMAMs shift to the lower temperature, which proves that the weight-losing ratio at the lower temperature stage will increase in the total weight-losing ratio when the loading of Ag nanoparticles increases.
In this work, Ag/PAMAMs nanocomposites with different mass ratio of Ag nanoparticles to different generations of PAMAM were synthesized successfully. It is found that the amount of Ag nanoparticles could efficiently affect the thermal stabilities of PAMAMs. As the mass ratio of Ag nanoparticles increased, the weight-losing ratio decreased, and the proportion of weight-losing ratio of the lower temperature stage to the higher temperature increased, which has shown that the loading of Ag nanoparticles could well improve the thermal stabilities of PAMAMs in the higher temperature region (280~450 °C). Moreover, the multistage decomposition profile of DTG is observed. It can be concluded that the Ag/PAMAMs nanocomposites with higher silver loading might contain some intermediate Ag/PAMAMs type of composite.
This program is financially supported by Natural Science Foundation of Hebei Province (E200800440).