Introduction to Nanotechnology

10.2. CATALYSIS 279
CnHlnfl, which is a hydrocarbon radical obtained by removing a hydrogen atom
from the terminal carbon atom of a straight-chain or normal alkane molecule, with n
ordinarily in the range of 6-20. For example, the hexyl radical with n = 6
is derived from hexane
H H H H H H
H-C-C-C-C-C-C.
H H H H H H
H H H H H H
H-C-C-C-C-C-C-H
H H H H H H
by removing the hydrogen atom on the extreme right, where the dot ‘‘.” on the right
terminal carbon of hexyl indicates the presence of an unpaired electron on the
carbon. To stabilize the metal nanoparticle of the colloid, the N&X molecules
dissociate into their cation NR,f and anion X- parts at the surface of the core, as
illustrated in Fig. 10.22. Metal cores of various diameters from 1.3 to lOnm can be
obtained by varying the transition metal of the core: Ru (1.3 nm), Ir (1.5 nm),
FUI (2.1nm), Pd (2.5nm), Co, Ni, Pt (2.8nm), Fe (3.0nm), Cu (8.3nm), and
Au (10nm). The hydrocarbon chains pointing outward from the core, as shown
in Fig. 10.22, are lipophilic; hence they attract organic solvent molecules, forming
stable dispersions in organic liquids. An analogous colloidal dispersion in water, or a
hydrosol, can be made by attaching an SO, group to the end of one of the
hydrocarbon chains of each NR,f ion to make it hydrophilic or water-attracting, as
shown in Fig. 10.23. This particular metal-stabilizing hydrophilic compound is
called a sulfobetaine.
Figure 10.22. Metallic colloidal particle stabilized by tetraalkylammonium halide NR4X mole-
cules. [From H. Bonnemann and W. Brijoux, in Moser (1996), Chapter 7, p. 173.1