Page 621 - Book Hosokawa Nanoparticle Technology Handbook

41 SURFACE MODIFICATION OF INORGANIC NANOPARTICLES BY ORGANIC FUNCTIONAL GROUPS APPLICATIONS
APPLICATION 41

41 SURFACE MODIFICATION OF INORGANIC NANOPARTICLES BY ORGANIC
FUNCTIONAL GROUPS

Nanoparticles are considered as key materials in nanoparticles are synthesized by reducing noble
informational, environmental and medical technolo- metal ions in the presence of thiols [1]. While the
gies. Various methods are proposed to synthesize the reduced noble metal atoms aggregate to form
nanoparticles of metal, metal oxide and organic mate- nanoparticles, thiol molecules attach on the surface
rials. The merits to use nanoparticles in these fields of the nanoparticle to passivate the growing surface
are summarized as below: and minimize the chance to aggregate. The surface
modification by alkanethiol (C H 2n 1 SH) produces
n
(a) We can design new materials with hybridized hydrophobic nanoparticles because SH groups bind
functions by dispersing nanoparticles in a liq- with noble metal atoms and the nanoparticles are
uid or solid. covered with alkyl groups. The modification can be
performed with other molecules that have sulfur
(b) We can reduce resources and costs required to
atoms [2]. The binding energy between noble metals
enable various functions that emerge at surfaces.
and sulfur atoms is not so strong as covalent bonds.
(c) We can bind nanoparticles with biomolecules Based on this nature, we can realize surface modifi-
to enable diagnosis and cure with the minimal cation with two kinds of thiols by dispersing thiol-
invasion. modified noble metal nanoaparticles in a solution
with a different kind of thiol. The exchange reaction
(d) We can fabricate nanostructures with less effort
between the thiol on the nanoparticles and the thiol in
by organizing different kinds of nanoparticles.
solution occurs to produce binary modified noble
(e) We can explore new properties that arise based metal nanoparticles. Most noble metal nanoparticles
on quantum size effects. including gold, silver, copper, palladium, platinum
and nickel can be modified with thiols. Due to its
These merits emerge from the two characters of easy experimental procedure, many researches have
nanoparticles: (1) the new phase of materials that can studied the surface modification of noble metal
mix with solids or liquids to form virtually continuous nanoparticles by thiols.
phases, and (2) the minimum unit of materials that
have defined structure and functions, which arise 2. Organic modification of metal oxide
from the decreased size of nanoparticles itself.
However the decreased size also results in the difficult nanoparticles
handling. We cannot manipulate each nanoparticle
and the nanoparticles tend to aggregate. This nature of Metal oxides have various properties including
nanoparticles prohibits the handling similar to that of electron transport, semiconducting property, ferro-
micrometer-sized particles. magnetism, giant magnetoresistance, luminescence,
These tendencies come from the effects of surface ferroelectric property and catalysis (Table 41.1). In
atoms, which plays dominant role in the dispersion, addition, most oxides are stable even in air and
aggregation and hybridization in the nanometer-sized water. Due to these practical merits, various metal
materials. However, we can exploit this tendency to oxides are used in functional devices. However,
control the behavior of nanoparticles. The surface incorporation of these properties of metal oxides
properties of nanoparticles are possibly changed by into nanoscale devices requires two techniques, that
functional groups on the surface nanoparticles. Based is, synthesis of metal oxide nanoparticles and their
on this idea, we propose the chemical modification of surface modification. So far, few studies have been
the surface of nanoparticles to realize better handling performed to synthesize surface-modified metal
of nanoparticles. In this chapter, we discuss the oxide nanoparticles. We are studying the metal
attachment of organic functional groups on the sur- oxide nanoparticles whose surface is covered by
face of inorganic nanoparticles. organic functional groups. We have developed
simultaneous synthesis and modification of metal
1. Surface-modified noble metal nanoparticles oxide nanoparticles because nanoparticles easily
aggregate together irreversibly. Fig. 41.1 shows our
Sulfur atom has large affinity with noble metals. This method to synthesize surface-modified metal oxide
affinity is used to produce surface-modified noble nanoparticles. During hydrothermal synthesis, the
metal nanoparticles. Thiol-capped noble metal growth of metal oxide nanoparticles proceeds by

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