Thiolate-Protected Palladium Nanoparticles Revisited: New Insights into their Chemistry and Crystalline Structure

CORTHEY, G.; CASILLAS, G.; OLMOS-ASAR, J.; MARISCAL, M. M.; MEJIA-ROSALES, S.; PONCE, A.; PICONE, A. L.; RUBERT, A. A.; BENITEZ, G. A.; ZELAYA, E.; JOSE-YAMACAN, M.; SALVAREZZA, R. C.; FONTICELLI, M. H.

Mount Holyoke College, South Hadley, MA,

Conferencia; Gordon Research Conference on Noble Metal Nanoparticles.; 2012

Among noble metal nanoparticles (NPs), thiolate-protected Au NPs have been deeply studied in the last 18 years by different research groups of diverse fields, from physics to medicine. The chemical composition of these particles is well known [1] and the geometric structure of some kinds of them was determined by X-ray diffraction (XRD) [2,3]. Although the mechanisms involved in the synthesis of these NPs were supposed to be completely understood, recent experimental results have proposed alternative final products [4] or intermediates [5] for NPs prepared by the one- or two-phase Brust-Schiffrin methods, respectively. Moreover, it still remains the question about the validity of the model proposed for thiolate-protected Au NPs on the basis of XRD, for NPs produced by other methods or self-assembled monolayers (SAMs) of thiolates on Au(111) [1]. The case of thiolate-protected Pd NPs is even more complicated because the chemical composition and structure of these particles and even of SAMs of thiolates on bulk Pd surfaces were not extensively studied as in the case of Au. Although it was proposed, based on strong experimental data, that SAMs of thiolates on bulk Pd surfaces and Pd NPs are composed by a mixed interface of palladium sulfide and thiolates [6?9], several works have neglected these results and these surfaces have been described as similar to Au ones [10,11]. Recently, we have reported a detailed study on the chemical composition of alkanethiolate-protected Pd NPs on the basis of data obtained by a multi-technique approach [12]. The results for Pd NPs obtained by different synthetic routes are consistent with NPs composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. The chemical nature of these particles is very similar to that of alkanethiolate-modified bulk Pd surfaces. In this work we will discuss the results on the chemistry of Pd NPs in relation to their crystalline structure. We have studied the influence of two different capping agents (alkanethiols and alkyl amines) on the crystalline structure of the NPs, by means of aberration-corrected high-resolution transmission electron microscopy (HRTEM), aberration-corrected scanning TEM (STEM) and image simulations. We have also studied the radiation-induced damage on these particles by the electron beam, and its effect on the images recorded. It was clearly observed that the crystallinity of the particles is largely affected by the capping agent: while alkyl amine-protected Pd NPs present a crystalline structure, it was not possible to distinguish lattice fringes in any of the images of thiolate-protected Pd NPs. Computer Simulations using state-of-the-art semi-empirical potentials were performed to validate the experimental findings. In general terms, excellent agreement was found. Although some similar results were already observed with different capping molecules [13], as far as we know, the interpretation of these observations in relation to the chemical nature of the particles have not been reported. References: 1. Pensa, E.; Cortés, E.; Corthey, G.; Carro, P.; Vericat, C.; Fonticelli, M. H.; Benítez, G.; Rubert, A. A.; Salvarezza, R. C. Acc. Chem. Res. 2012, DOI: 10.1021/ar200260p. 2. Jadzinsky, P. D.; Calero, G.; Ackerson, C. J.; Bushnell, D. A.; Kornberg, R. D. Science 2007, 318, 430?433. 3. Heaven, M. W.; Dass, A.; White, P. S.; Holt, K. M.; Murray, R. W. J. Am. Chem. Soc. 2008, 130, 3754?3755. 4. Corthey, G.; Giovanetti, L. J.; Ramallo-López, J. M.; Zelaya, E.; Rubert, A. A.; Benitez, G. A.; Requejo, F. G.; Fonticelli, M. H.; Salvarezza, R. C. ACS Nano 2010, 4, 3413?3421. 5. Goulet, P. J. G.; Lennox, R. B. J. Am. Chem. Soc. 2010, 132, 9582?9584. 6. Love, J. C.; Wolfe, D. B.; Haasch, R.; Chabinyc, M. L.; Paul, K. E.; Whitesides, G. M.; Nuzzo, R. G. J. Am. Chem. Soc. 2003, 125, 2597?2609. 7. Corthey, G.; Rubert, A. A.; Benitez, G. A.; Fonticelli, M. H.; Salvarezza, R. C. J. Phys. Chem. C 2009, 113, 6735?6742. 8. Carro, P.; Corthey, G.; Rubert, A. A.; Benitez, G. A.; Fonticelli, M. H.; Salvarezza, R. C. Langmuir 2010, 26, 14655?14662. 9. Murayama, H.; Ichikuni, N.; Negishi, Y.; Nagata, T.; Tsukuda, T. Chem. Phys. Lett. 2003, 376, 26?32. 10. Marshall, S. T.; O?Brien, M.; Oetter, B.; Corpuz, A.; Richards, R. M.; Schwartz, D. K.; Medlin, J. W. Nat. Mat. 2010, 9, 853?858. 11. Majumder, C. Langmuir 2008, 24, 10838?10842. 12. Corthey, G.; Rubert, A. A.; Picone, A. L.; Casillas, G.; Giovanetti, L. J.; Ramallo-Lopez, J. M.; Zelaya, E.; Benitez, G. A.; Requejo, F. G.; Jose-Yacaman, M.; Salvarezza, R. C.; Fonticelli, M. H. J. Phys. Chem. C 2012, DOI: 10.1021/jp301531n. 13. Liu, Y.; Wang, C.; Wei, Y.; Zhu, L.; Li, D.; Jiang, J. S.; Markovic, N. M.; Stamenkovic, V. R.; Sun, S. Nano Lett. 2011, 11, 1614?1617.