Physical–Chemical Properties of Magnetite Nanoparticles Doped …
549
the following conditions, the pH values are gradually increased from 4.8 to 5.8 and
from 4.8 to 5.5 at the initial c(Au
3+ ) 0.5 and 1 mg/dm
3 , respectively. At the same time,
the increase in the initial c(Au
3+ ) up to 3–10 mg/dm
3 the total iron concentrations are
increased to 6–12 mg/dm
3 and get stability (curves 3–5). Whereas the final pH values
equal to 5.5 in all cases, but the increase in the time of phase formation process up
to 24 h and more may increase the final values of hydrogen ion exponent. Generally,
pH index insignificantly depended on the quantity of aurichlorohydric acid added
into the work solutions. Whereas the pH value equaled 7.4 at the initial c(Au
3+ ) =
1 mg/dm
3 , it decreased to 6.7at c(Au
3+ ) = 10 mg/dm
3 , and the enhancement of the
HAuCl 4 quantity did not give rise to the acidification of the work solutions. Such
dependence well correlates with the property of the rotation–corrosion dispergation
system steady (stationary) state to average out the pH of the dispersion medium to
7–9 in a wide range of initial values [15]. So, the formation of the nanoparticles runs
out within a few hours of the contact of the steel surface with aurum-bearing water
solutions. Hence, at the initial c(Au
3+ ) > 3 mg/dm
3 , the system gets stability in 3–5 h.
3.3 The Morphology of the Nanostructures Formed
on the Steel Surface Contacting with AgNO 3 and HAuCl 4
Solutions
The morphology of the composite structures formed on the steel surface that was
contacted with water solutions containing noble metal aquaforms is present in Fig. 6.
The surface structures formed at c(Ag
+ ) = 5 mg/dm
3 are shown in Fig. 6a, b, and
at c(Ag
+ ) = 15 mg/dm
3 , corresponding, in Fig. 6c, d. The structures obtained at
c(Au
3+ ) = 20 mg/dm
3 are present in Fig. 6e, f. Independent of the precious metal
concentrations, the obtained nanocomposites form aggregates that are distinguished
by homogeneity and spherical or plate-like shapes. The size of individual aggregate
lies in the range from 50 to 200 nm. But in all cases, the formation of big associates
included more than ten aggregates clearly seen on the SEM images.
At the same time, the formation of the sore and shell type nanoparticles takes place
in the water solution contacted with the steel surface. We can see the spherical particles of the following composites in Fig. 7a (Fe 3 O 4 and Ag
0 ) and Fig. 7b (Fe 3 O 4 and
Au
0 ). Drying-out of the corresponding sol drops leads to obtain the film that included
individual particles (Fig. 7c, d). In general, the particle size is 10–40 nm, but in the
case of polynuclear growth of the nanocomposites, the particle size increased to 150–
200 nm. Usually, the bi-phase system was formed in the sol composition included
Fe 3 O 4 and Ag
0 and lepidocrocite (Fig. 7e, f)) when the argentum concentration in
the initial solution was relatively small (3–5 mg/dm
3 ).
549
the following conditions, the pH values are gradually increased from 4.8 to 5.8 and
from 4.8 to 5.5 at the initial c(Au
3+ ) 0.5 and 1 mg/dm
3 , respectively. At the same time,
the increase in the initial c(Au
3+ ) up to 3–10 mg/dm
3 the total iron concentrations are
increased to 6–12 mg/dm
3 and get stability (curves 3–5). Whereas the final pH values
equal to 5.5 in all cases, but the increase in the time of phase formation process up
to 24 h and more may increase the final values of hydrogen ion exponent. Generally,
pH index insignificantly depended on the quantity of aurichlorohydric acid added
into the work solutions. Whereas the pH value equaled 7.4 at the initial c(Au
3+ ) =
1 mg/dm
3 , it decreased to 6.7at c(Au
3+ ) = 10 mg/dm
3 , and the enhancement of the
HAuCl 4 quantity did not give rise to the acidification of the work solutions. Such
dependence well correlates with the property of the rotation–corrosion dispergation
system steady (stationary) state to average out the pH of the dispersion medium to
7–9 in a wide range of initial values [15]. So, the formation of the nanoparticles runs
out within a few hours of the contact of the steel surface with aurum-bearing water
solutions. Hence, at the initial c(Au
3+ ) > 3 mg/dm
3 , the system gets stability in 3–5 h.
3.3 The Morphology of the Nanostructures Formed
on the Steel Surface Contacting with AgNO 3 and HAuCl 4
Solutions
The morphology of the composite structures formed on the steel surface that was
contacted with water solutions containing noble metal aquaforms is present in Fig. 6.
The surface structures formed at c(Ag
+ ) = 5 mg/dm
3 are shown in Fig. 6a, b, and
at c(Ag
+ ) = 15 mg/dm
3 , corresponding, in Fig. 6c, d. The structures obtained at
c(Au
3+ ) = 20 mg/dm
3 are present in Fig. 6e, f. Independent of the precious metal
concentrations, the obtained nanocomposites form aggregates that are distinguished
by homogeneity and spherical or plate-like shapes. The size of individual aggregate
lies in the range from 50 to 200 nm. But in all cases, the formation of big associates
included more than ten aggregates clearly seen on the SEM images.
At the same time, the formation of the sore and shell type nanoparticles takes place
in the water solution contacted with the steel surface. We can see the spherical particles of the following composites in Fig. 7a (Fe 3 O 4 and Ag
0 ) and Fig. 7b (Fe 3 O 4 and
Au
0 ). Drying-out of the corresponding sol drops leads to obtain the film that included
individual particles (Fig. 7c, d). In general, the particle size is 10–40 nm, but in the
case of polynuclear growth of the nanocomposites, the particle size increased to 150–
200 nm. Usually, the bi-phase system was formed in the sol composition included
Fe 3 O 4 and Ag
0 and lepidocrocite (Fig. 7e, f)) when the argentum concentration in
the initial solution was relatively small (3–5 mg/dm
3 ).