Functionalization and surface chemistry of nanoparticles

Organized Mesoporous Silicas (SMO) have many interesting properties (large specific area, narrow size distribution of pores). Their regular porosity (size and arrangement) should make it possible favoring narrow distributions of size and spatial dispersion of nanoparticles formed inside. Our objective is to obtain gauged metal particles dispersed within mesoporous silica matrices of MCM41 or SBA15 types. Metal cobalt particles were generated starting from molecular precursors like metal carbonyl or cobalt soaps, introduced in-situ during the synthesis of the silica or by post-synthesis impregnation or grafting.

Organometallic precursors as metal clusters constitute a calibrated source of metal ions. For instance, bimetallic clusters of composition Pd2Mo2(h5-C5H5)2(m3-CO)2(m2-CO)4 (PR3)2 (R = ethyl or phenyl) were incorporated by impregnation from solution into two different silica matrices, amorphous xerogels and ordered SBA-15.1 With both matrices, a suitable thermal treatment afforded nanoparticles of a new bimetallic phosphide. Although nanoparticles of composition PdxMoyP, isostructural with Mo3P, were formed in both matrices, they were more uniformly distributed in the  de type SBA-15 framework and showed a narrower size distribution. The samples have been characterized by powder XRD, chemical analysis, FT-IR spectroscopy, and TEM ; electron tomography (3D TEM) was used to locate precisely the nanoparticles inside the silica.

Another example concerns the synthesis of well dispersed cobalt phosphide nanoparticles (NPs) in SBA-15 mesoporous silica by wet impregnation of the molecular cluster [Co4(CO)10(l-dppa)] (1) (dppa = HN(PPh2)2). The thermal activation of the silica impregnated precursor under a H2/N2 (5/95 %) stream at different temperatures to form NPs was studied and it was found that the size of the latter is limited in the 5.5–6.5 nm range by the size of the pores. The porosity and the structure of the mesoporous silica supports were analyzed by N2 adsorption/desorption and small-angle X-ray diffraction. The nanoparticles were characterized by wideangle X-ray diffraction, transmission electron microscopy in conventional and scanning modes, electron tomography, energy-dispersive X-ray spectroscopy, and magnetic measurements. Cobalt phosphide NPs of few nanometers were efficiently observed in the pores of SBA-15 by STEM observations and 3D tomography. We also show that magnetic impurities can be washed away by HCl solution.

Structure of the molecular cluster precursor [Co4(CO)10(µ-dppa)] and electron tomography analysis of the NPs inside the pores of SBA15.

References

Grosshans-Viéles, S.; Croizat, P.; Paillaud, J. L.; Braunstein, P.; Ersen, O.; Rosé, J.; Lebeau, B.; Rabu, P.; Estournès, C., Molecular Clusters in Mesoporous Materials as Precursors to Nanoparticles of a New Lacunar Ternary Compound Pd x Mo y P. Journal of Cluster Science 2008, 19 (1), 73-88.

(a) Buchwalter, P.; Rosé, J.; Lebeau, B.; Ersen, O.; Girleanu, M.; Rabu, P.; Braunstein, P.; Paillaud, J.-L., Characterization of cobalt phosphide nanoparticles derived from molecular clusters in mesoporous silica. J Nanopart Res 2013, 15 (12), 1-21; (b) Buchwalter, P.; Rosé, J.; Lebeau, B.; Rabu, P.; Braunstein, P.; Paillaud, J.-L., Stoichiometric molecular single source precursors to cobalt phosphides. Inorganica Chimica Acta 2014, 409, Part B (0), 330-341.