Template-assisted ordering of Pb nanoparticles prepared from molecular-level colloidal processing

Abstract

Lead nanoparticles ranging from 10–200 nm were prepared by reacting [Pb{N(SiMe 3) 2} 2] with the reducing agent tert-butoxy alane, [H 2Al(O tBu)] 2, in non-aqueous media. By this reaction, Pb nuclei on the molecular scale can be produced imparting a high regularity of shape and size to the resulting nanoparticles. The amino-alkoxo-alane {[(Me 3Si) 2N][ tBuO]Al-H} 2 is formed as the main molecular by-product. The molecular structure of this amino-alkoxo-alane was determined by single crystal X-ray diffraction techniques revealing a centro-symmetric molecule with a central Al 2O 2 ring (Al–O = 1.848(1) Å) to which tert-butyl (on oxygen) and hexamethyldisilazyl and hydrogen atoms (on aluminium) are bonded. Coloured sols of lead particles were obtained using donor solvents containing N, S and O atoms. The optical absorption spectra of colloids obtained at different concentrations of the starting materials indicate that the colour change (yellow – orange – burgundy red) is related to the particle size and/or the aggregation of particles in more concentrated solutions. The particles are nanoscopic and can be redispersed after a short ultrasonic treatment. This phase-separation is related to the nature of Pb-ligand interactions and to the aggregation of particles in the colloidal solution. Particle growth and inter-particle aggregation were observed by electron microscopy studies and absorption spectra of lead particles present in different solutions. A variation of concentration of lead clusters present in the colloids shows a shift in the absorption spectra related to plasmon–plasmon interaction typically observed in the aggregates of metal nanoparticles. Porous anodic alumina membranes were filled with lead nanoparticles either by vacuum-induced infiltration of lead particles or by reduction of the Pb(II) precursor within the pores. The latter approach proved to be more successful in obtaining Pb/Al 2O 3 composites. The chemical composition and morphology of Pb particles in colloidal solutions and those present in and on the porous alumina membrane were investigated by XRD, FT–IR, SEM and TEM analysis. To cite this article: M. Veith et al., C. R. Chimie 7 (2004).