546
O. Lavrynenko et al.
to the Fe–O linkages. The typical bands at 590 and 450 cm
−1 corresponding to the
Fe–O linkages in tetrahedral and octahedral positions of magnetite crystal lattice are
present in spectrum (1) [23]. A band at 1149 cm
−1 points to the presence of oxygen
bridges as well as Fe–OH groups. The bands at 1029, 1164, 759 cm
−1 correspond to
γ-FeOOH and the band at 682 cm
−1 can prove the presence of structural elements
of γ-Fe 2 O 3 . The bands at 674, 628, and 586 cm
−1 are typical for spinel structure and
they characterize the uncoated ferrimagnetic surface. The band at 570 cm
−1 can be
related to Fe–O–Fe linkage and the bands at 555, 570, 647, and 655 cm
−1 may be
corresponded to γ-Fe 2 O 3 .
The bands at 3509 and 887 cm
−1 disappear in the spectrum (2) corresponding
to c(Ag
+ ) = 1 mg/dm
3 but the intensity of the band near 755 cm
−1 increases. The
bouncing of hydroxyl groups describes the bands at 1150 and 1029 cm
−1 (the σOH linkage in the plane), and the band at 482 cm
−1 (γ-OH out of plane). Probably,
the strong band at 509 cm
−1 is corresponded to α-FeOOH. Disappearance of the
band at 474 cm
−1 may confirm the transition of the nanoparticles from octahedral
to tetrahedral structure. The band at 586 cm
−1 splits into two bands centered at 593
and 582 cm
−1 corresponding to Fe–O linkages in Fe 3 O 4 that were broken due to
argentum interaction, but the band at 674 cm
−1 corresponding to spinel structure is
not changed. At the same time, the band at 628 cm
−1 related to Fe 3 O 4 splits into
three bands at 632, 624, and 613 cm
−1 .
The intensity of the band at 447 cm
−1 is growing in the spectrum 4 (c(Ag
+ )
= 3 mg/dm
3 ) in comparison with spectrum 3 (c(Ag
+ ) = 2 mg/dm
3 ) due to the
reinforcement of the octahedral magnetite structure, and it shifts to 458 cm
−1 on the
spectrum 5 (c(Ag
+ ) = 5 mg/dm
3 ). The vibration of the band at 474 cm
−1 that related
to the surface Fe–O linkages proved on the probable formation of silver shell on the
magnetite surface. The shape of the bands at 460 and 437 cm
−1 points to the changes
of crystalline degree of the samples: from strong (spectrum 2) to weak (spectrum 3)
and back to strong (spectrum 5). The appearance of the bands at 408 and 412 cm
−1
implies the nanocrystalline structure of the samples. Generally, the reduction of silver
on magnetite surface (spectrum 5) leads to the shift of the vibration bands of the Fe–O
linkages to the area of great wave numbers. So, the shift of the band at 570–578 cm
−1
points to the predominance of the M th –M oh structure, whereas the shift of the band
at 586–593 cm
−1 gives the evidence of the magnetite interaction with argentum. The
band at 489 cm
−1 relating to the surface Fe–O vibration disappears but the band
of the OH vibrations at 1018 cm
−1 becomes intensive that points to the formation
of new hydrate coverage. The presence of the bands at 609, 578, and 478 cm
−1
confirms the γ-Fe 2 O 3 increase on the phase interface. The appearance of the band
at 566 cm
−1 points to the inclusion of argentum ions into magnetite structure. The
strong band at 412 cm
−1 appears due to the increase of the particle size. The bands at
794 and 632 cm
−1 relate to the residual of α-FeOOH; the bands at 686 and 721 cm
−1
correspond to γ-Fe 2 O 3 ; the band at 740 and 663 cm
−1 belong to γ-FeOOH; and, the
bands at 505, 458, and 420 cm
−1 can be related to α-Fe 2 O 3 .
O. Lavrynenko et al.
to the Fe–O linkages. The typical bands at 590 and 450 cm
−1 corresponding to the
Fe–O linkages in tetrahedral and octahedral positions of magnetite crystal lattice are
present in spectrum (1) [23]. A band at 1149 cm
−1 points to the presence of oxygen
bridges as well as Fe–OH groups. The bands at 1029, 1164, 759 cm
−1 correspond to
γ-FeOOH and the band at 682 cm
−1 can prove the presence of structural elements
of γ-Fe 2 O 3 . The bands at 674, 628, and 586 cm
−1 are typical for spinel structure and
they characterize the uncoated ferrimagnetic surface. The band at 570 cm
−1 can be
related to Fe–O–Fe linkage and the bands at 555, 570, 647, and 655 cm
−1 may be
corresponded to γ-Fe 2 O 3 .
The bands at 3509 and 887 cm
−1 disappear in the spectrum (2) corresponding
to c(Ag
+ ) = 1 mg/dm
3 but the intensity of the band near 755 cm
−1 increases. The
bouncing of hydroxyl groups describes the bands at 1150 and 1029 cm
−1 (the σOH linkage in the plane), and the band at 482 cm
−1 (γ-OH out of plane). Probably,
the strong band at 509 cm
−1 is corresponded to α-FeOOH. Disappearance of the
band at 474 cm
−1 may confirm the transition of the nanoparticles from octahedral
to tetrahedral structure. The band at 586 cm
−1 splits into two bands centered at 593
and 582 cm
−1 corresponding to Fe–O linkages in Fe 3 O 4 that were broken due to
argentum interaction, but the band at 674 cm
−1 corresponding to spinel structure is
not changed. At the same time, the band at 628 cm
−1 related to Fe 3 O 4 splits into
three bands at 632, 624, and 613 cm
−1 .
The intensity of the band at 447 cm
−1 is growing in the spectrum 4 (c(Ag
+ )
= 3 mg/dm
3 ) in comparison with spectrum 3 (c(Ag
+ ) = 2 mg/dm
3 ) due to the
reinforcement of the octahedral magnetite structure, and it shifts to 458 cm
−1 on the
spectrum 5 (c(Ag
+ ) = 5 mg/dm
3 ). The vibration of the band at 474 cm
−1 that related
to the surface Fe–O linkages proved on the probable formation of silver shell on the
magnetite surface. The shape of the bands at 460 and 437 cm
−1 points to the changes
of crystalline degree of the samples: from strong (spectrum 2) to weak (spectrum 3)
and back to strong (spectrum 5). The appearance of the bands at 408 and 412 cm
−1
implies the nanocrystalline structure of the samples. Generally, the reduction of silver
on magnetite surface (spectrum 5) leads to the shift of the vibration bands of the Fe–O
linkages to the area of great wave numbers. So, the shift of the band at 570–578 cm
−1
points to the predominance of the M th –M oh structure, whereas the shift of the band
at 586–593 cm
−1 gives the evidence of the magnetite interaction with argentum. The
band at 489 cm
−1 relating to the surface Fe–O vibration disappears but the band
of the OH vibrations at 1018 cm
−1 becomes intensive that points to the formation
of new hydrate coverage. The presence of the bands at 609, 578, and 478 cm
−1
confirms the γ-Fe 2 O 3 increase on the phase interface. The appearance of the band
at 566 cm
−1 points to the inclusion of argentum ions into magnetite structure. The
strong band at 412 cm
−1 appears due to the increase of the particle size. The bands at
794 and 632 cm
−1 relate to the residual of α-FeOOH; the bands at 686 and 721 cm
−1
correspond to γ-Fe 2 O 3 ; the band at 740 and 663 cm
−1 belong to γ-FeOOH; and, the
bands at 505, 458, and 420 cm
−1 can be related to α-Fe 2 O 3 .