Nowadays, nanoparticles with sizes between 2 to 50 nm become more and more popular, because they can be applied in various fields such as materials science, chemistry, catalysis, medicine or biology. In particular nanoparticles with fancy shapes gain a lot of attention, also because of the low-cost synthesis methods. This study is focused on several types of catalytic nanoparticles (NPs), silver nanoparticles synthesized using green chemistry methods and in particular on their morphological and chemical analysis using HR(TEM). Three-dimensional (3D) catalysts [1] being promising for application in fuel cells were studied. These nanoparticles have a dodecahedron shape with Pt skin at the edges and a Ni core, Figure 1(a). When etching away the core, the remaining empty Pt frame offers a much larger active surface compared to spherical nanoparticles. The morphology of these 3D PtNi particles strongly depends on the synthesis parameters allowing fabricating dodecahedrons, Figure 1(a), core-shell or even dendritic structures, Figure 1(b).

SnO₂ nanoparticles are excellent supports for noble metal NPs, as their combination exhibits good catalytic activity towards ethanol oxidation reaction [2]. Various synthesis routes including polyol and microwave assisted methods allowed producing different SnO₂ NPs, Figure 2(a). The break of the C=C bond in the ethanol molecule occurs at the interface between PtRh and SnO₂ particles, Figure 2(b). Therefore their physical contact is imperative for the effectiveness of the catalyst. Structural aspects and chemical analysis by TEM characterization techniques of the PtRh/SnO₂/C catalysts were analyzed.

Green synthesis method using camomile extract was applied to synthesize silver nanoparticles in order to tune their antibacterial properties merging the synergistic effect of camomile and Ag [3]. Scanning transmission electron microscopy (STEM) revealed that camomile extract (CE) consisted of porous globular nanometer sized structures, which were a perfect support for Ag nanoparticles, Figure 3(a). The Ag nanoparticles synthesized with the camomile extract (AgNPs/CE) of 7 nm average size, were uniformly distributed on the CE support, Figure 3(b). The EDX chemical analysis showed that camomile terpenoids, Figure 3(c) act as a capping and reducing agent being adsorbed on the surface of AgNPs/CE, Figure 3(d), enabling their reduction from Ag⁺ and preventing them from agglomeration. Antibacterial tests using four bacteria strains, showed that the AgNPs/CE performed five times better compared to CE and AgNPs/G samples, reducing totally all the bacteria in 2 hours, Figure 4.

References

1. C. Chen, Y. Kang, Z.Huo, Z. Zhu, W. Huang, H.L. Xin, J.D. Snyder, D. Li, J.A. Herron, M. Mavrikakis, M. Chi, K.L. More, Y. Li, N.M. Markovic, G.A. Somorjai, P. Yang, V.R. Stamenkovic, Science 343 (2014) 1339-1343.

1. A. Kowal, M. Li, M. Shao, K. Sasaki, M.B. Vukmirovic, J. Zhang, N.S. Marinkovic, P. Liu, A.I. Frenkel and R.R. Adzic, Nature Materials 9 (2009) 325-330.
2. M. Parlinska-Wojtan, M. Kus-Liskiewicz, J. Depciuch, and O. Sadik submitted to Bioprocess and Biosystems Engineering.

Acknowledgements

We thank the Center for Innovation and Transfer of Natural Sciences and Engineering Knowledge of the University of Rzeszow and the Division of Materials Processing Technology, Management and Computer Techniques in Materials Science, Institute of Engineering Materials and Biomaterials, of the Silesian University of Technology in Poland for using the TEM instruments. Financial support from the Polish National Science Centre (NCN), grant UMO-2014/13/B/ST5/04497 is acknowledged.

Figures:

Figure 1 STEM HAADF images of PtRh: (a) Dodecahedrons; (b) Dendritic nanoparticles.

Figure 2 STEM HAADF images of: (a) SnO2 NPs synthesized using microwave assisted method; (b) PtRh NPs (white, small dots) on SnO2 supports (large, grey islands).

Figure 3 STEM HAADF images of: (a) camomile support with the; (b) Ag NPs on camomile support synthesized using green chemistry method; Corresponding EDX maps of: (c) phosphorus in camomile support; (d) Ag, O and P distribution in Ag NPs/CE.

Figure 4 Percentage of microorganism (S.aureus) reduction after exposition to: AgNPs/G (blue) and AgNPs/CE (green) nanosuspensions.

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