Paracrystalline structure of gold, silver, palladium and platinum nanoparticles

Abstract

Metallic nanoparticles are of great importance because of their unique physical, chemical, antimicrobial, diagnostic, therapeutic, biomedical, sensing, biosensing, catalytic and optical properties. Detailed knowledge of the atomic scale structure of these materials is essential for understanding their activities and for exploiting their potential. This paper reports structural studies of silicasupported silver, gold, palladium and platinum nanoparticles using X-ray diffraction and high-resolution transmission electron microscopy. Electron microscopy observation allowed the determination of nanoparticle sizes, which were estimated to be in the range of 45-470 Å , and their distribution. The obtained histograms exhibit a multimodal distribution of the investigated nanoparticle sizes. The X-ray diffraction data were analyzed using the Rietveld method in the form of Williamson-Hall plots, the PDFgui fitting procedure and model-based simulation. The Williamson-Hall plots provide evidence for the presence of strain in all investigated samples. The PDFgui fitting results indicate that the investigated nanoparticles consist of atomic clusters with different sizes and degrees of disorder as well as slightly different lattice parameters. The detailed structural characterization performed via model-based simulations proves that all samples exhibit a face-centered cubic type structure with paracrystalline distortion. The degree of disorder predicted by the paracrystalline theory is correlated with the sizes of the nanoparticles. The catalytic properties of the investigated noble metals are discussed in relation to their disordered structure. research papers J. Appl. Cryst. (2018). 51, 411-419 Karolina Jurkiewicz et al. Paracrystalline structure of metallic nanoparticles 415 research papers J. Appl. Cryst. (2018). 51, 411-419 Karolina Jurkiewicz et al. Paracrystalline structure of metallic nanoparticles 417 research papers J. Appl. Cryst. (2018). 51, 411-419 Karolina Jurkiewicz et al. Paracrystalline structure of metallic nanoparticles 419

The structure of gold nanoparticles: molecular dynamics modeling and its verification by X-ray diffraction

“…3(a) and 3(b). The existence of vacancies in the interior of the gold NPs can be related to the static disorder suggested by the paracrystalline theory which has been satisfactorily applied to the interpretation of diffraction data for gold NPs (Jurkiewicz et al, 2018). Moreover, the positions of the simulated structure factor peaks are slightly shifted towards lower Q, and consequently the PDF peaks are shifted in the opposite direction, as can be perceived for higher Q and r values.…”

“…Such kinds of disorder can be described in terms of the paracrystalline theory (Jurkiewicz et al, 2018;Hosemann & Bagchi, 1962) in which the network distortion propagates proportionally to the square root of the interatomic distances. The instrumental Q resolution has been taken into account, making the comparison of the simulation results with the experimental data reliable.…”

“…Their atomic structure exhibits paracrystalline-type disorder in which the standard deviation of the interatomic distances, related to the degree of disorder, scales proportionally to the square root of the distance (Jurkiewicz et al, 2018). Their atomic structure exhibits paracrystalline-type disorder in which the standard deviation of the interatomic distances, related to the degree of disorder, scales proportionally to the square root of the distance (Jurkiewicz et al, 2018).…”

“…From the above-cited structural studies of NPs one may conclude that there is a need to develop an approach that offers an alternative to conventional diffraction methods based on the crystallographic formalism. Such an approach has been proposed and discussed in our previous paper (Jurkiewicz et al, 2018) together with other methods cited therein, which allow information about the atomic scale structure, structural defects, strain and lattice distortion to be obtained. In order to analyze the structure of nanomaterials, the formalism of the pair distribution function (PDF) has been revisited.…”

“…It is found that the investigated NPs have approximately spherical shape. Their atomic structure exhibits paracrystalline-type disorder in which the standard deviation of the interatomic distances, related to the degree of disorder, scales proportionally to the square root of the distance (Jurkiewicz et al, 2018). In these modeling studies, disorder has been imposed on the computer-generated models via a generalized Debye-Waller factor consisting of two components: one related to the thermal oscillations and a second describing static disorder in the form described above.…”