Geoscience Reference
In-Depth Information
researchers [58,59]. Here, the hydrogen tetrachloroaurate tetrahydrate was reduced
with sodium borohydride, and mercaptosuccinic acid was used as a stabilizer.
Figure 10.8
shows the TEM micrograph of self-assembled gold nanoparticles.
Similarly, the coating of nanocrystalline films of Cu, Ni, Ag, Au, Pt, Pd, Rh,
etc. on silicon wafers for microelectronics and data storage has been reported
[62]
.
Such an approach has been extended to several other materials like the coating of
nanocrystalline carbon on Si wafers.
Thus, the hydrothermal
solvothermal and hydrothermal-supercritical water offer
unique advantages over the preparation of these metal nanoparticles over other con-
ventional methods. More recently, the researchers are aiming at imitating the deep-
sea hydrothermal conditions in the laboratory to synthesize various metal nanoparti-
cles in the presence of hydrothermal solution and biological molecules, which has
opened up new branches of
science, namely, hydrogeomicrobiology and
geomicrobiology.
10.6.2 Hydrothermal Processing of Carbon Nanoforms
Elemental carbon is known to exist in two well-known polymorphic forms, namely,
graphite (sp
2
hybridized) and diamond (sp
3
hybridized). These two forms of carbon
exist in nature under highly contrasting conditions and possess very different physi-
cal and chemical properties. Besides graphite and diamond, there are reports on
new solid forms of carbon
[63,64]
which have unusual shape and size and are
mainly sp
2
hybridized. They are graphene, CNTs (bucky tubes), fullerenes (bucky
balls),
carbon onions
(bucky onions),
filamentous
carbon, nanocells,
and
Figure 10.8 TEM micrograph of self-
assembled gold nanoparticles.
Source: Photograph courtesy of B.L.
Gersten.
