316
9 Electrosynthesis of Nanostructures Without a Coating …
The structure of the nanoparticles was in accord with their composition. When
iron was the majority component, the X-ray diffractograms differed from that of
magnetite and maghemite to a negligible extent only. However, when Mn and Zn
were the major metallic element in the particles, the diffraction lines could be found
nearly at the same position as for the corresponding MeFe 2 O 4 ferrite. Magnetic
properties of the particles were similar to the corresponding ferrites, whereas some
difference was found in their saturation magnetization and remanence values as
compared to their bulk counterparts. Due to the small particle size, some samples
were superparamagnetic.
9.3 Electrochemically Assisted Synthesis of Miscellaneous
Non-metallic Nanoparticles
ZnO nanoparticles were synthesized in a similar manner as iron oxide nanoparticles.
Concerning the formation of ZnO and its stability in comparison with Zn(OH) 2 ,
Chap. 8.3.2 already gave abundant information. In both works reported here [60,
61], Zn
2+ ions originated from the anode reaction of the sacrificial Zn electrode.
The supporting electrolytes were totally different in the synthesis methods applied.
While oxalic acid proved to be suitable in spite of its high buffering ability due to
the step-wise acidic dissociation [60], tetrabutyl ammonium bromide could act as
both supporting electrolyte and stabilizer [61]. The variation of the solvent revealed
the flexibility of the precipitation-based ZnO synthesis method, as shown in Fig. 9.4.
Pure ethanol as solvent led to a porous structure with nearly spherical grains. As
the water content of the solvent was increased, the porosity as measured by the
specific surface area strongly decreased, the grain size increased and the shape of
the particles became more and more rhombohedral. In parallel to the morphological
change, Zn(OH) 2 also appeared beside ZnO in the deposit when the solvent was
pure water. The ZnO structure was highly conformal to the wurtzite structure with a
good crystallinity as shown by the X-ray diffractograms. TEM images revealed that
the grains having a diameter of a few hundred nm were made of nearly spherical
grains of 25–30 nm. This subgrain structure may indicate that the particles primarily
produced in the precipitation reaction correspond to the spherical subgarins and the
larger particles formed as a result of the seizure of the primarily formed particles.
In the synthesis of CuS particles [62], the products of the electrode reactions are
Cu
2+ at the sacrificial Cu anode and OH
– ions at the cathode. The peculiar feature
of this synthesis mode is that the hydroxide ions produced on the cathode are not a
reactant but a catalyst. The solution component that provides sulphur for the formation of CuS is the thiosulfate ion whose decomposition is facilitated by two other
components of the solution. One of these components is the hydroxide ion produced
at the cathode, and the other is the thioglycerol which is also a solution component
which is nonreactive but act as a catalyst. At relatively large thioglycerol concentration (0.1 M), the primary reaction product is a metastable form of CuS with 8–12 nm
9 Electrosynthesis of Nanostructures Without a Coating …
The structure of the nanoparticles was in accord with their composition. When
iron was the majority component, the X-ray diffractograms differed from that of
magnetite and maghemite to a negligible extent only. However, when Mn and Zn
were the major metallic element in the particles, the diffraction lines could be found
nearly at the same position as for the corresponding MeFe 2 O 4 ferrite. Magnetic
properties of the particles were similar to the corresponding ferrites, whereas some
difference was found in their saturation magnetization and remanence values as
compared to their bulk counterparts. Due to the small particle size, some samples
were superparamagnetic.
9.3 Electrochemically Assisted Synthesis of Miscellaneous
Non-metallic Nanoparticles
ZnO nanoparticles were synthesized in a similar manner as iron oxide nanoparticles.
Concerning the formation of ZnO and its stability in comparison with Zn(OH) 2 ,
Chap. 8.3.2 already gave abundant information. In both works reported here [60,
61], Zn
2+ ions originated from the anode reaction of the sacrificial Zn electrode.
The supporting electrolytes were totally different in the synthesis methods applied.
While oxalic acid proved to be suitable in spite of its high buffering ability due to
the step-wise acidic dissociation [60], tetrabutyl ammonium bromide could act as
both supporting electrolyte and stabilizer [61]. The variation of the solvent revealed
the flexibility of the precipitation-based ZnO synthesis method, as shown in Fig. 9.4.
Pure ethanol as solvent led to a porous structure with nearly spherical grains. As
the water content of the solvent was increased, the porosity as measured by the
specific surface area strongly decreased, the grain size increased and the shape of
the particles became more and more rhombohedral. In parallel to the morphological
change, Zn(OH) 2 also appeared beside ZnO in the deposit when the solvent was
pure water. The ZnO structure was highly conformal to the wurtzite structure with a
good crystallinity as shown by the X-ray diffractograms. TEM images revealed that
the grains having a diameter of a few hundred nm were made of nearly spherical
grains of 25–30 nm. This subgrain structure may indicate that the particles primarily
produced in the precipitation reaction correspond to the spherical subgarins and the
larger particles formed as a result of the seizure of the primarily formed particles.
In the synthesis of CuS particles [62], the products of the electrode reactions are
Cu
2+ at the sacrificial Cu anode and OH
– ions at the cathode. The peculiar feature
of this synthesis mode is that the hydroxide ions produced on the cathode are not a
reactant but a catalyst. The solution component that provides sulphur for the formation of CuS is the thiosulfate ion whose decomposition is facilitated by two other
components of the solution. One of these components is the hydroxide ion produced
at the cathode, and the other is the thioglycerol which is also a solution component
which is nonreactive but act as a catalyst. At relatively large thioglycerol concentration (0.1 M), the primary reaction product is a metastable form of CuS with 8–12 nm