Reaction temperature and solvent conditions affect the phase transition and
morphology of metal chalcogenides. With increasing temperature, NiSe 2 nanocrystals prepared through solvothermal-reduction at low temperatures transform
from an initial filament to a final octahedron [115]. In different solvents, the wellcrystallized nickel selenides obtained, such as NiSe 2 , Ni 0:85 Se and Ni 3 Se 2 , showed
different morphologies [116]. The synthesis of NiS, using en and hydrazine hydrate as solvent, resulted in a rod-like nanocrystalline product, whereas spherical
nanoparticles were obtained in aqueous ammonia [117]. Two different phases of a(hexagonal, P6 3 /mmc) and b-(rhombohedral, R3m) NiS nanocrystals were obtained
by hydrazine reduction of NiCl 2 Á6H 2 O in the presence of sulfur at 110
C in ethanol and pyridine, respectively [118].
The metastable b- and g-MnS crystallites were obtained at about 200
C in tetrahydrofuran and benzene, whereas in water, ammonia liquor, en, the metastable
phases converted to the stable phase of a-MnS [119]. However, only the stable
phase of a-MnSe can be obtained by solvothermal reaction at 190
C in en [120].
In the solvothermal synthesis of the I–III–VI 2 ternary compound semiconductors, organic amines are normally used as solvents for the reactants and as ligands to form metal complexes. In the reaction system InCl 3 Á4H 2 O, CuCl 2 Á2H 2 O
and elemental selenium at 180
C, CuInSe 2 nanowhiskers with widths of 3–6 nm
and lengths of 30–80 nm were prepared in en, whereas in diethylamine and pyridine, the product was only spherical nanoparticles [121]. Therefore, bidentate ligands may be more effective than monodentate ligands for directional growth of
chalcogenide nanocrystals. Nanorods of CuME 2 (M ¼ In or Ga, E ¼ S or Se) were
also prepared by elemental reactions in en at 200–280
C [122, 123]. From a stoichiometric mixture of the single-molecule precursors M(S 2 CNEt 2 ) 3 (M ¼ In, Cu,
Ag), nanorods of MInS 2 (M ¼ Cu or Ag) were prepared by removing the thione
groups with en solvent at 195
C [124]. Nanocrystalline AgGaS 2 and AgInS 2 with
particle sizes ranging from 5 to 12 nm were prepared by reacting AgCl, sulfur,
elemental gallium or indium in en at 180–230
C [125].
Some other ternary chalcogenides have also been prepared by the solvothermal
method, such as Cu 5:5 FeS 6:5 nanotubes [126], AgBiS 2 nanowhiskers [127],
Cu 2 SnS 3 [128], Cu 2 SnSe 4 [129], CuSbS 2 and Ag 3 SbS 3 [130] nanoparticles.
7.7
Room Temperature Synthesis of Nanomaterials
Room-temperature synthesis of nanomaterials can be realized by designing suitable reactions under some special solution conditions, or with the assistance of
additional energy supplies such as g-ray irradiation and ultrasound.
Traditionally, selenides have been synthesized at high temperature (>500
C) by
solid-state reaction [131] or self-propagating synthesis [132]. A high-energy ball
milling method at room temperature has also been used [133], however, the product quality was difficult to control. In liquid ammonia, a low-temperature route to
selenides was developed [134]. Organometallic precursors have been used to obtain
7 Solvothermal Synthesis of Non-Oxide Nanomaterials
198
morphology of metal chalcogenides. With increasing temperature, NiSe 2 nanocrystals prepared through solvothermal-reduction at low temperatures transform
from an initial filament to a final octahedron [115]. In different solvents, the wellcrystallized nickel selenides obtained, such as NiSe 2 , Ni 0:85 Se and Ni 3 Se 2 , showed
different morphologies [116]. The synthesis of NiS, using en and hydrazine hydrate as solvent, resulted in a rod-like nanocrystalline product, whereas spherical
nanoparticles were obtained in aqueous ammonia [117]. Two different phases of a(hexagonal, P6 3 /mmc) and b-(rhombohedral, R3m) NiS nanocrystals were obtained
by hydrazine reduction of NiCl 2 Á6H 2 O in the presence of sulfur at 110
C in ethanol and pyridine, respectively [118].
The metastable b- and g-MnS crystallites were obtained at about 200
C in tetrahydrofuran and benzene, whereas in water, ammonia liquor, en, the metastable
phases converted to the stable phase of a-MnS [119]. However, only the stable
phase of a-MnSe can be obtained by solvothermal reaction at 190
C in en [120].
In the solvothermal synthesis of the I–III–VI 2 ternary compound semiconductors, organic amines are normally used as solvents for the reactants and as ligands to form metal complexes. In the reaction system InCl 3 Á4H 2 O, CuCl 2 Á2H 2 O
and elemental selenium at 180
C, CuInSe 2 nanowhiskers with widths of 3–6 nm
and lengths of 30–80 nm were prepared in en, whereas in diethylamine and pyridine, the product was only spherical nanoparticles [121]. Therefore, bidentate ligands may be more effective than monodentate ligands for directional growth of
chalcogenide nanocrystals. Nanorods of CuME 2 (M ¼ In or Ga, E ¼ S or Se) were
also prepared by elemental reactions in en at 200–280
C [122, 123]. From a stoichiometric mixture of the single-molecule precursors M(S 2 CNEt 2 ) 3 (M ¼ In, Cu,
Ag), nanorods of MInS 2 (M ¼ Cu or Ag) were prepared by removing the thione
groups with en solvent at 195
C [124]. Nanocrystalline AgGaS 2 and AgInS 2 with
particle sizes ranging from 5 to 12 nm were prepared by reacting AgCl, sulfur,
elemental gallium or indium in en at 180–230
C [125].
Some other ternary chalcogenides have also been prepared by the solvothermal
method, such as Cu 5:5 FeS 6:5 nanotubes [126], AgBiS 2 nanowhiskers [127],
Cu 2 SnS 3 [128], Cu 2 SnSe 4 [129], CuSbS 2 and Ag 3 SbS 3 [130] nanoparticles.
7.7
Room Temperature Synthesis of Nanomaterials
Room-temperature synthesis of nanomaterials can be realized by designing suitable reactions under some special solution conditions, or with the assistance of
additional energy supplies such as g-ray irradiation and ultrasound.
Traditionally, selenides have been synthesized at high temperature (>500
C) by
solid-state reaction [131] or self-propagating synthesis [132]. A high-energy ball
milling method at room temperature has also been used [133], however, the product quality was difficult to control. In liquid ammonia, a low-temperature route to
selenides was developed [134]. Organometallic precursors have been used to obtain
7 Solvothermal Synthesis of Non-Oxide Nanomaterials
198