TY - JOUR
T1 - Surface chemistry of "unprotected" nanoparticles
T2 - a spectroscopic investigation on colloidal particles
AU - Schrader, Imke
AU - Warneke, Jonas
AU - Neumann, Sarah
AU - Grotheer, Sarah
AU - Swane, Andreas Abildgaard
AU - Kirkensgaard, Jacob Judas Kain
AU - Arenz, Matthias
AU - Kunz, Sebastian
PY - 2015
Y1 - 2015
N2 - The preparation of colloidal nanoparticles in alkaline ethylene glycol is a powerful approach for the preparation of model catalysts and ligand-functionalized nanoparticles. For these systems the term "unprotected" nanoparticles has been established because no strongly binding stabilizers are required to achieve stable colloids. Irrespective of this fact, the particles must be considered as being covered by adsorbates, as otherwise the particles would coalesce and precipitate. The identification of these protecting adsorbate species is however still under debate and is the scope of the present study. "Unprotected" Pt and Ru nanoparticles were characterized by NMR spectroscopy, which does not evidence the presence of any C-H containing species bound to the particle surface. Instead, the colloids were found to be covered by CO, as demonstrated by IR spectroscopy. However, analysis of the stretching mode reveals the presence of a second species. On the basis of the spectroscopic characterization this species is concluded to be OH-, and it is demonstrated that the applied synthesis route results only in stable colloids if OH- is present within the reaction mixture. IR spectroscopy reveals that the CO coverage increases as the NaOH concentration used in the precursor solution is decreased. However, even at the lowest for the synthesis suitable OH- concentration the surface was found to be covered by both species. Finally, the effect of the OH- concentration on the particle size distribution was studied. The maximum was found to shift to larger particle diameters as the OH- concentration is lowered which is accompanied by broadening of the size distribution.
AB - The preparation of colloidal nanoparticles in alkaline ethylene glycol is a powerful approach for the preparation of model catalysts and ligand-functionalized nanoparticles. For these systems the term "unprotected" nanoparticles has been established because no strongly binding stabilizers are required to achieve stable colloids. Irrespective of this fact, the particles must be considered as being covered by adsorbates, as otherwise the particles would coalesce and precipitate. The identification of these protecting adsorbate species is however still under debate and is the scope of the present study. "Unprotected" Pt and Ru nanoparticles were characterized by NMR spectroscopy, which does not evidence the presence of any C-H containing species bound to the particle surface. Instead, the colloids were found to be covered by CO, as demonstrated by IR spectroscopy. However, analysis of the stretching mode reveals the presence of a second species. On the basis of the spectroscopic characterization this species is concluded to be OH-, and it is demonstrated that the applied synthesis route results only in stable colloids if OH- is present within the reaction mixture. IR spectroscopy reveals that the CO coverage increases as the NaOH concentration used in the precursor solution is decreased. However, even at the lowest for the synthesis suitable OH- concentration the surface was found to be covered by both species. Finally, the effect of the OH- concentration on the particle size distribution was studied. The maximum was found to shift to larger particle diameters as the OH- concentration is lowered which is accompanied by broadening of the size distribution.
U2 - 10.1021/acs.jpcc.5b03863
DO - 10.1021/acs.jpcc.5b03863
M3 - Journal article
AN - SCOPUS:84938723602
SN - 1932-7447
VL - 119
SP - 17655
EP - 17661
JO - The Journal of Physical Chemistry Part C
JF - The Journal of Physical Chemistry Part C
IS - 31
ER -