5.1 Chemical Precipitation Method
81
in 23 mL deionized water to prepare an oxidant solution B was added dropwise to
the mixture A in a 300 mL beaker. The polymerization proceeded at 25 °C and was
stirred for 24 h. The resultant samples were collected by filtration and then washed
with Soxhlet extractor, water, and ethanol were used as medium, respectively, to
remove the oxidant, MO, and oligomers. Finally, the PPy powder was dried in a
vacuum oven at 60 °C for 12 h.
Meanwhile, Li et al. prepared 3D flower-like Ni/Co-LDHs microspheres and
explored the synthetic mechanism of the LDHs microspheres (Li et al. 2016). They
took reactant concentrations, reaction time, and pH into consideration. At the beginning, Ni
2+ /Co
2+ reacted with OH
− to generate nickel/cobalt hydroxide monomer
nuclei and then formed the original nanoparticles (step I). The fresh nanoparticles
tended to aggregate and produce larger particles because of the existence of high
surface energy from nanoscale. Here, a slow but steady reaction rate was sharply
controlled by the slow-released OH
− adjusting agent of NH 4 Cl and NaOH in the
solution, resulting in the separation of nucleation and growth. That was fatal factor
for synthesizing high-quality crystal (step II). As continued to aggregate, the generated particles underwent dehydration process due to hydroxylation reaction (step III).
Next, they continued to crystallize along c-axis and develop into the petal-like high
crystalline LDHs nanosheets (step IV). Finally, because of Ostwald ripening, the
self-assembly occurred and resulted in the obtained coordination nanosheets further
reacted to a stable Ni/Co-LDHs flower-like microsphere structure (step V). All things
considered, it can be seen that this facile but effective strategy can efficiently control
the structure of Ni/Co-LDHs by varying the reaction condition, employed to prepare
other LDHs nano/micro materials.
At the end of this portion, what we want to introduce is the application of
metal oxide frameworks (MOFs) (Yang et al. 2017). As known, MOFs, a category of highly porous materials, have attracted researchers’ attention a lot since
1990s (Li et al. 1999). Facing two intrinsic problems of MOFs (insufficient mechanical/chemical stability and low electrochemical conductivity), researchers took
measures to enhance the pseudocapacitance of MOFs by doping metal oxides into
the system with Chemical Precipitation Method. In the report, as starting materials, MOF-manganese hexacyanoferrate hydrate (MHCF) nanocubes had an obvious
change that manganese in the framework reacted to manganese oxides (2016a, b).
MHCF nanocubes were synthesized via a simple chemical precipitation method.
Besides, MHCF was dissolved in the mixed solvent system with 10 mL C 2 H 5 OH
and 15 mL H 2 O under stirring to get a homogeneous solution. At the same time,
NH 4 F was dissolved in distilled water. Then, the obtained NH 4 F solution was added
to the MHCF solution. Subsequently, the obtained mixture was stirred for 20 min
and then the product was obtained after being washed. As shown in Fig. 5.1e–g, the
nanoflower modified the surface of each individual MHCF cubes evenly.
81
in 23 mL deionized water to prepare an oxidant solution B was added dropwise to
the mixture A in a 300 mL beaker. The polymerization proceeded at 25 °C and was
stirred for 24 h. The resultant samples were collected by filtration and then washed
with Soxhlet extractor, water, and ethanol were used as medium, respectively, to
remove the oxidant, MO, and oligomers. Finally, the PPy powder was dried in a
vacuum oven at 60 °C for 12 h.
Meanwhile, Li et al. prepared 3D flower-like Ni/Co-LDHs microspheres and
explored the synthetic mechanism of the LDHs microspheres (Li et al. 2016). They
took reactant concentrations, reaction time, and pH into consideration. At the beginning, Ni
2+ /Co
2+ reacted with OH
− to generate nickel/cobalt hydroxide monomer
nuclei and then formed the original nanoparticles (step I). The fresh nanoparticles
tended to aggregate and produce larger particles because of the existence of high
surface energy from nanoscale. Here, a slow but steady reaction rate was sharply
controlled by the slow-released OH
− adjusting agent of NH 4 Cl and NaOH in the
solution, resulting in the separation of nucleation and growth. That was fatal factor
for synthesizing high-quality crystal (step II). As continued to aggregate, the generated particles underwent dehydration process due to hydroxylation reaction (step III).
Next, they continued to crystallize along c-axis and develop into the petal-like high
crystalline LDHs nanosheets (step IV). Finally, because of Ostwald ripening, the
self-assembly occurred and resulted in the obtained coordination nanosheets further
reacted to a stable Ni/Co-LDHs flower-like microsphere structure (step V). All things
considered, it can be seen that this facile but effective strategy can efficiently control
the structure of Ni/Co-LDHs by varying the reaction condition, employed to prepare
other LDHs nano/micro materials.
At the end of this portion, what we want to introduce is the application of
metal oxide frameworks (MOFs) (Yang et al. 2017). As known, MOFs, a category of highly porous materials, have attracted researchers’ attention a lot since
1990s (Li et al. 1999). Facing two intrinsic problems of MOFs (insufficient mechanical/chemical stability and low electrochemical conductivity), researchers took
measures to enhance the pseudocapacitance of MOFs by doping metal oxides into
the system with Chemical Precipitation Method. In the report, as starting materials, MOF-manganese hexacyanoferrate hydrate (MHCF) nanocubes had an obvious
change that manganese in the framework reacted to manganese oxides (2016a, b).
MHCF nanocubes were synthesized via a simple chemical precipitation method.
Besides, MHCF was dissolved in the mixed solvent system with 10 mL C 2 H 5 OH
and 15 mL H 2 O under stirring to get a homogeneous solution. At the same time,
NH 4 F was dissolved in distilled water. Then, the obtained NH 4 F solution was added
to the MHCF solution. Subsequently, the obtained mixture was stirred for 20 min
and then the product was obtained after being washed. As shown in Fig. 5.1e–g, the
nanoflower modified the surface of each individual MHCF cubes evenly.