Hydrothermal Technology for Nanotechnology—A Technology for Processing of Advanced Materials - Hydrothermal Technology - page 628

from dendrite to compact crystals were investigated during the evolution of the
reaction system from nonequilibrium to quasi-equilibrium conditions. Here, the
strong shape anisotropy of the Ni nanotube has influenced the formation of Ag
dendritic nanostructures. When a poly - vinyl pyrrolidone (PVP) surfactant was
used, the nanostructures were replaced by bulk or compact particles. Figures 10.6
and 10.7 show the characteristic photographs of Ag nanocrystals and Ag compact
crystals [50] .
Several magnetic nanoparticles have been reported in the literature. Xie et al. [52]
and Liu et al. [55] have reported the hydrothermal synthesis of cobalt nanorods and
nanobelts with and without surfactants. When a microemulsion was used, cobalt
nanorods with hcp structures have been obtained at 90 C, with an average particle
size of 10 nm diameter and 260 nm length [55] . Similarly, Co-nanobelts via a
surfactant-assisted hydrothermal reduction process at 160 C for 20 h have been
reported by Xie et al. [52] . Liu et al. [56] have reported a complex surfactant-assisted
hydrothermal route to ferromagnetic nickel nanobelts at about 110 C in 24 h. These
Ni-nanobelts show remarkably enhanced ferromagnetic properties. Here the key fac-
tors in the preparation of these Ni-nanobelts are the pre-formation of the Ni complex
Ni(C 4 H 2 O 6 ) 2 2 , the presence of surfactant sodium dodecylebenzene sulfonate (SDBS-
Spectral Database for Organic Compounds), and the selective use of the reducing
agent NaH 2 PO 2 . Such an approach can be extended to the hydrothermal preparation
of nanobelts of several other transitional metals and their alloys.
Niu et al. [57] have prepared Ni Cu alloy nanocrystallites at low temperatures
under hydrothermal conditions. These nanoscale metallic alloys such as CuNi,
Figure 10.6 TEM images of Ag dendrites.
Source: Photographs Courtesy Prof. Y.T. Qian.