Synthesis of cadmium complex sulfides nanoparticles by thermal decomposition

Article abstract of DOI:10.1007/s10973-005-0799-y

The paper presents the conditions of synthesis and results in the characterization (chemical analysis, thermal analysis, kinetic of decomposition) for two complex compounds of cadmium: [Cd(S₂O ₃)phen]×H₂O and [Cd(S₂

Full text of DOI:10.1007/s10973-005-0799-y

Journal of Thermal Analysis and Calorimetry, Vol. 81 (2005) 399–405
SYNTHESIS OF CADMIUM COMPLEX SULFIDES NANOPARTICLES BY
THERMAL DECOMPOSITION*
A. Dumbrava1**, V. Ciupina2, B. Jurca3, G. Prodan2, E. Segal3 and M. Brezeanu
1Department of Chemistry, Faculty of Physics and Chemistry, ‘Ovidius’ University, 124 Mamaia Street, Constanta, Romania
2Department of Physics, Faculty of Physics and Chemistry, ‘Ovidius’ University, 124 Mamaia Street, Constanta, Romania
3Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest, 4–12 Elisabeta Blvd., Bucharest, Romania
The paper presents the conditions of synthesis and results in the characterisation (chemical analysis, thermal analysis, kinetic of de-
composition) for two complex compounds of cadmium: [Cd(S2O3)phen]·H2O and [Cd(S2O3)phen2]⋅2H2O. The obtained complexes
were used as precursors for complex sulfides by controlled thermal decomposition. On the basis of transmission electron micros-
copy (TEM) the complex sulfides may be included in the nanomaterials category.
Keywords: cadmium, complex sulfide, nanoparticles, phenanthroline, thermal analysis, thiosulfate
Introduction
From this system there were separated two com-
pounds, [Cd(S2O3)phen]⋅H2O and [Cd(S2O3)phen2]
⋅2H2O. By thermooxidative degradation of these com-
plexes there were obtained nanoparticles of two com-
In last years nanomaterials have received a great at-
tention for their potential applications (biology,
chemical technology, medicine, etc.). The chemical
and physical properties of nanostructured materials
(which are characterised by at least one dimension in
nanometre range) can significantly differ from those
of the atomic molecular and the bulk materials with
the same composition [1, 2].
plex
sulfides,
[Cd2(phen)2(S)]SO4
and
[Cd2(phen)4(S)]SO4.
Experimental
Materials
Complex compounds which contain ligands hav-
ing sulfur as donor atom and especially complex sul-
fides are interesting because: (i) can be used as model
compounds, (ii) have interesting stereochemistry, (iii)
can be used as catalysers and (iv) have biological im-
portance. A general procedure for the synthesis of
metal–sulfur complexes does not exist. However,
such very different reagents, for instance, H2S, S8,
Sx2– , SCN–, S2O23– , RNSNR or RSH, may be the pre-
cursors of sulfide ligands. Very little is known about
the reaction pathways [3]. Complex sulfides can be
obtained by different methods from complexes that
have ligands with sulfur as atom donor [4, 5].
The aim of our study is to obtain nanoparticles of
complex sulfides by thermal decomposition of cad-
mium complexes having coordinated thiosulfate as
generator of sulfide ion.
All the chemicals used for the present study were pur-
chased from commercial sources and used without
further purification.
Syntheses
Synthesis of the complex [Cd(S2O3)phen]⋅H2O (1)
Complex 1 was obtained as follows: 0.99 g (5 mmol)
1,10-phenanthroline⋅H2O and 2.48
g (10 mmol)
Na2S2O3⋅5H2O were added into an aqueous solution con-
taining 1.33 g (5 mmol) Cd(CH3COO)2⋅2H2O in 100 cm3
water and the resulted solution was heated under continu-
ous stirring for two hours. It was separated a yellowish
powder, which was filtered and washed with hot water.
Anal. Found: Cd, 26.22; S, 15.47; N, 7.51. Calc. for
CdC12H10N2S2O4: Cd, 26.54; S, 15.16; N, 6.63.
In order to obtain complex compounds which
can be precursors for complex sulfides of cadmium, it
was studied the system:
Synthesis of the complex [Cd(S2O3)phen2]⋅2H2O (2)
Complex 2 was obtained as follows: 0.99 g (5 mmol)
1,10-phenanthroline⋅H2O and 6.20 g (25 mmol) Na2S2O3
Cd(CH3COO)2:Na2S2O3:1,10-phenanthroline (phen)
*
In the memory of academician Maria Brezeanu
**
Author for correspondence: adumbrava@univ-ovidius.ro
1388–6150/$ 20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2005 Akadémiai Kiadó, Budapest

DUMBRAVA et al.
⋅5H2O were added into an aqueous solution containing
The study of above system had in view the con-
tribution at the nature of synthesised compounds of
parameters like: molar ratio of components, tempera-
ture, time, value of pH and order of reactants adding.
The conditions were established for obtaining the
compounds:
1.33 g (5 mmol) Cd(CH3COO)2⋅2H2O in 100 cm3 water
and the resulted solution was heated under continuous
stirring for two hours. It was separated a yellowish pow-
der, which was filtered and washed with hot water.
Anal. Found: Cd, 18.24; S, 10.01; N, 9.62. Calc. for
CdC24H20N4S2O5: Cd, 18.06; S, 10.32; N, 9.03.
1
2
[Cd(S2O3)phen]⋅H2O
[Cd(S2O3)phen2]⋅2H2O
Synthesis of the complex [Cd2(phen)2(S)]SO4 (3)
Complex 1 is known in literature [15] but: (i) it was
Complex 3 was obtained as follows: 2.11 g (5 mmol)
of 1 were heated in an oven at 551 K and kept for
15 min at this temperature. The resulted powder was
cooled in the exsiccator. Anal. Found: Cd, 31.54;
S, 9.23; N, 8.61. Calc. for Cd2C24H16N4S2O4:
Cd, 31.46; S, 8.99; N, 7.86.
obtained using a different method than the method pre-
sented in this paper; (ii) it was not studied the capacity
of complex to be a precursor for complex sulfide.
The results proved that the nature of obtained
compound is the same, independent of the reaction
conditions that were changed, in a large range. This
behaviour indicates a great stability of the complex.
The chemical analysis of compounds proved that it
does not occur hydrolysis of both (at room tempera-
ture or high temperature).
The compounds obtained from the studied sys-
tem were characterised by chemical analysis, DTA-TG
and IR methods.
The second step of research was the synthesis of
complex sulfides by thermooxidative degradation.
The compounds obtained by thermooxidative degra-
dation were characterised by chemical analysis, IR
spectra and TEM.
Synthesis of the complex [Cd2(phen)4(S)]SO4 (4)
Complex 4 was obtained as follows: 3.1 g (5 mmol) of
2 were heated in an oven at 510 K and kept for 15 min
at this temperature. The resulted powder was cooled
in the exsiccator. Anal. Found: Cd, 20.69; S, 6.67;
N, 10.97. Calc. for Cd2C48H32N8S2O4: Cd, 20.89;
S, 5.97; N, 10.45.
The elemental chemical analyses were per-
formed by usual micromethods.
Physical measurements
The IR spectra of pellets with KBra were recorded on
Bruker Vector 22 spectrometer, in the range of
400–4000 cm–1. The DTA-TG curves have been re-
corded using a Paulik–Paulik–Erdey Q 1500 D
derivatograph, in static air atmosphere, with α-Al2O3
as an inert reference compound, at various heating
rates (from 1.25 to 10 K min–1), in the range
293–1273 K. The sample masses were between
90–100 mg. The thermoanalytical data have been
used in order to evaluate the decomposition kinetic
parameters by three integral methods: Coats–Red-
fern [6, 7], Flynn–Wall [8, 9] (for constant heating
rate) and Urbanovici–Segal [10, 11] who modified
Coats–Redfern method. For automatic processing of
the data the Versatile program was used [12–14]. The
TEM was made on the Phillips CM 120 ST transmis-
sion electron microscope using an accelerating volt-
age of 100 kV, with 2 Å resolution.
Thermal decomposition and kinetic studies
Thermal decomposition of complex [Cd(S2O3)phen]
⋅H2O (1) in the temperature range 293–1273 K, at a
heating rate of 10, 5, 2.5, respectively, 1.25 K min–1,
occurs through four steps (Fig. 1):
Results and discussion
The first step of our research was the synthesis of new
cadmium complexes having thiosulfate anion and
1,10-phenanthroline as ligands, which can be used as
precursors for complex sulfides.
Fig. 1 TG, DTG and DTA curves for complex
[Cd(S2O3)phen]⋅H2O (1) at a heating rate of 5 K min–1
400
J. Therm. Anal. Cal., 81, 2005

SYNTHESIS OF CADMIUM COMPLEX SULFIDES NANOPARTICLES
Table 1 Kinetic parameters value for reaction (4) in ther-
mal decomposition of complex 1
• the first step (in the temperature range of 313–423 K)
is endothermic and consists in elimination of uncoor-
dinated water molecule:
Method
CR
FW
US
Z/s–1
E/kJ mol–1
1.14⋅1021
340
6.10⋅1021
336
2.42⋅1021
345
418 K
[Cd(S2O3)phen]⋅H2O(s)⎯⎯⎯→
[Cd(S2O3)phen](s)+H2O(g)
(1)
n
r
1.6
1.6
1.6
Δmcalc.=4.26%; Δmfound=4.04%;
–0.9951
–0.9954
–0.9952
The temperature written above the arrow corre-
sponds to the maximum decomposition rate as shown
by the DTG curve;
Z – pre-exponential factor, E – activation energy,
n – apparent order, r – correlation coefficient of the
linear regression; CR – Coats–Redfern,
FW – Flynn–Wall, US – Urbanovici–Segal
• the second step (in the temperature range of
518–573 K) is exothermic and consists in changing
thiosulfate ions into sulfide and sulfate ions. This
kind of thermal decomposition for sulfate ion is
known from literature [16].
is the Neper number and Tp is the peak temperature
from the DTG curve. For the first complex ΔS≠=
142.0 J mol–1 K–1. The positive value of ΔS≠ shows that
the activated complex is less organized than the reagent.
According to the formulas:
551K
2[Cd(S2O3)phen](s)+O2(g)⎯⎯⎯→
Cd2(phen)2(S)(SO4)(s)+2SO2(g)
(2)
ΔH≠=E–RTp
Δmcalc.=11.37%; Δmfound=12.97%;
and
• the third step (in the temperature range of
617–699 K) is endothermic and consists in loosing
of a phenanthroline molecule:
ΔG≠=ΔH≠–TpΔS≠
the values of ΔH≠ (333.7 kJ mol–1) and ΔG≠
(225.2 kJ mol–1) were calculated respectively at the
peak temperature Tp [18, 19].
666K
Cd2(phen)2(S)(SO4)(s)⎯⎯⎯→
Cd2(phen)(S)(SO4)(s)+phen(g)
(3)
• the fifth step (in the temperature range of
1135–1250 K) consists in decomposition of cad-
mium sulfate and cadmium oxide (which is instable
at temperatures above 1223 K), with formation of
metallic cadmium:
Δmcalc.=21.33%; Δmfound=19.87%;
• the fourth step (in the temperature range of
699–825 K) is strongly exothermic and consists in
oxidation of phenanthroline and obtaining of cad-
mium sulfide and cadmium sulfate. Above 717 K
cadmium sulfide is decomposed in elements and me-
tallic cadmium can be oxidised to cadmium oxide.
In the presence of SO2 is possible the reaction [17]:
1243K
2CdO(s)+CdSO4(s)⎯⎯⎯→3Cd(s)+SO2(g)+2O2(g) (5)
Δmcalc.=10.11%; Δmfound=11.23%.
The decomposition of thiosulfate ion with for-
mation coordinated sulfide ion, confirms the coordi-
nation of thiosulfate through sulfur atom in
[Cd(phen)(S2O3)]⋅H2O.
CdS+2SO2⎯⎯→CdSO4+2S
Elemental sulfur can be oxidised to SO2.
The thermal decomposition of complex
[Cd(S2O3)phen2]⋅2H2O (2) in the temperature range
of 293–1273 K, at the heating rate of 5 K min–1, oc-
curs through four steps:
The most probable reaction in these conditions is:
764K
3/2Cd2(phen)(S)(SO4)(s)+26O2(g)⎯⎯⎯→2CdO(s)+
CdSO4(s)+18CO2(g)+6H2O(g)+3NO2(g)2SO2(g) (4)
• the first step (in the temperature range of 343–408 K)
consists of elimination uncoordinated water mole-
cules, in an endothermic process:
Δmcalc.=26.38%; Δmfound=25.56%.
The values of kinetic parameters obtained for the
reaction (4) are presented in Table 1.
Using the equations of Arrhenius and Eyring si-
multaneously, the values of change of entropy for the
activated complex formation from the reagent (ΔS≠)
can be calculated according to the formula:
[Cd(phen)2(S2O3)]⋅2H2O(s)⎯⎯→
[Cd(phen)2(S2O3)](s)+2H2O(g)
(6)
Δmcalc.=5.82%; Δmfound=5.61%;
Zh
ΔS = R ln
χekBTp
• the second step (in the temperature range of
477–532 K), exothermic, consists in changing thio-
sulfate ions into sulfide and sulfate ions:
where χ is the transmission factor, which is unity for
monomolecular reaction, kB is the Boltzmann con-
stant, h is the corresponding Plank constant, e=2.7183
510K
2Cd(phen)2(S2O3)(s)+O2(g)⎯⎯⎯→
Cd2(phen)4(S)(SO4)(s)+2SO2(g)
(7)
J. Therm. Anal. Cal., 81, 2005
401

DUMBRAVA et al.
IR spectra
Δmcalc.=7.74%; Δmfound=7.24%.
The presence of coordinated sulfide ion is a
proof of thiosulfate coordination through sulfur atom;
• the third step (in the temperature range of
572–668 K), endothermic, consists in loosing of
two phenanthroline molecules, without burning:
IR spectra for compounds 1–4 in the range of
400–4000 cm–1 were discussed according to the liter-
ature data [20, 21].
From the examination of IR data (Table 2) the
following conclusions result:
634K
Cd2(phen)4(S)(SO4)(s)⎯⎯⎯→
• in spectra of complexes 1 and 2 are found bands as-
signed of thiosulfate ion and phenanthroline. In
spectra of complexes 3 and 4 are found bands as-
signed to phenanthroline. The fact that bands as-
signed to thiosulfate are not found in spectra of 3
and 4 is due to disappearance of thiosulfate anion;
• the movement of bands assigned to the vibration
mode ν(C=N) to higher energies suggests that
phenanthroline is coordinated through nitrogen at-
oms in both complexes;
Cd2(phen)2(S)(SO4)(s)+2phen(g)
(8)
Δmcalc.=29.03%; Δmfound=29.59%;
• the fourth step (in the temperature range of
668–820 K) is strongly exothermic and consists in
oxidation of phenanthroline:
761K
3/2Cd2phen2(S)(SO4)(s)+50O2(g)⎯⎯⎯→2CdO(s)+
+CdSO4(s)+36CO2(g)+12H2O(g)+6NO2(g)+2SO2(g) (9)
• the band νs(SO3) is moved to lower energy and the
bands νa(SO3) are split in two components in spec-
tra of compounds 1 and 2. This fact suggests that
thiosulfate ion is coordinated as chelating bidentate
ligand or bridging bidentate ligand through sulfur
and oxygen [22, 23];
Δmcalc.=31.47%; Δmfound=30.53%;
• the fifth step (in the temperature range of
1147–1244 K), consists in decomposing of cad-
mium sulfate and cadmium oxide and obtaining of
metallic cadmium:
• the new band at about 1100 cm–1, the most intense
in spectra of complexes 3 and 4 can be assigned to
2CdO(s)+CdSO4(s)⎯⎯→3Cd(s)+SO2(g)+2O2(g) (10)
Δmcalc.=8.58%; Δmfound=9.08%.
The final product resulted from thermal decom-
position of complex 2 is metallic cadmium.
According the results of thermal decomposition,
compounds 3 and 4 were obtained by controlled heat-
ing of complex 1 at 551 K, respective of complex 2 at
510 K. On the basis of chemical analysis the minimal
formula for 3 is [Cd2(phen)2(S)]SO4 and for 4 is
[Cd2(phen)4(S)](SO4). The presence of uncoordinated
sulfate ion in both compounds is proved by IR spectra.
the vibration mode ν3(SO2– ) of sulfate ion. The
4
presence of uncoordinated sulfate ion is confirmed
by the band at about 620 cm–1 assigned to vibration
mode ν4(SO2– );
4
• in spectra of complexes 1 and 2 a strong, broad
band at about 3400 cm–1 reveals presence of water
molecules as coordination and/or crystallisation
water. The presence of water is also confirmed by
the band at about 1600 cm–1 due to the vibration
mode δ(H2O) in spectra of complexes 1 and 2.
For complex [Cd(phen)(S2O3)]⋅H2O (1) can be
proposed the most probable formula as in Fig. 3, in
which the thiosulfate anion is a chelating ligand. The
presence of water molecule as hydration water, not as
coordination water, as in [15], is demonstrated by
thermal analysis.
On the basis of all chemical and physico-chemi-
cal data, the most probable formula for complex
[Cd(S2O3)phen2]⋅2H2O (2) is shown in Fig. 4.
For complex ions in compounds 3 and 4 the most
probable formulas are shown in Figs 5 and 6, respec-
tively.
Fig. 2 DTA-TG curves for complex [Cd(S2O3)phen2]·2H2O
(2) at a heating rate of 5 K min–1
Fig. 3 The most probable formula proposed for complex
[Cd(phen)(S2O3)]·H2O (1)
402
J. Therm. Anal. Cal., 81, 2005

SYNTHESIS OF CADMIUM COMPLEX SULFIDES NANOPARTICLES
Table 2 IR frequencies of phen⋅H2O, Na2S2O3⋅5H2O, [Cd(S2O3)phen]⋅H2O (1), [Cd(S2O3)phen2]⋅2H2O (2),
[Cd2(phen)2(S)]⋅SO4 (3) and [Cd2(phen)4(S)]⋅SO4 (4) (in cm–1)
phen⋅H2O
Na2S2O3⋅5H2O
1
2
3
4
Assignments
–
428 m
544 s
–
421 w
541 m
–
417 w
539 w
–
419 s
418 w
ν(S–S)
δs(SO3)
–
–
619 s
–
–
620 s
–
–
622 m
–
ν4(SO2–
)
4
–
638 vs
–
637 m
ν(C–C)
δa(SO3)
668 s
647 m
666 m
–
–
736 vs
777 w
850 vs
–
–
724 s
781 w
850 s
1004 vs
1100 m
–
727 vs
777 w
845 s
996 vs
1096 m
–
727 vs
778 w
850 s
–
730 s
779 w
851 s
–
ν(C–H)
ν(C–H)
ν(C–H)
νs(SO3)
β(C–H)
–
–
1003 s
1089 m
–
–
–
1055 m
1116 vs
–
1054 m
1116 vs
–
ν3(SO2–
)
4
–
1123 s
1167 s
1135 vs
1153 vs
1182 vs
1120 vs
1141 vs
1185 vs
νa(SO3)
1128 m
1228 w
–
–
–
–
–
–
–
–
ν(C–H)
ν(C–N)
aromatic
–
1221 vw
1336 w
1420 vs
–
–
–
1344 w
1427 m
1344 w
1428 s
1344 vw
1427 s
1344 vw
1427 s
ν(C–C)
Ring vibrations
ν(C=N)
1503 s
1550 w
1591 m
1515 m
1576 w
1514 m
1576 w
1591 w
1515 m
1574 w
1589 w
1515 m
1573 w
1589 w
1614 w
1648 m
1657 m
–
1619 w
3049 w
1620 w
–
–
δ(H2O)
ν(C–H)
2983 w
3024 w
3068 m
2990 vw
3048 w
3066 vw
3054 m
3052 m
3418 s, broad
3452 vs, broad
3447 m, broad
3423 s, broad
–
–
ν(O–H)
vs - very strong; s - strong; m - medium; w - weak, vw - very weak.
Electron microscopy
Figures 7a and 8a depict the bright field TEM
micrographs of [Cd2(phen)2(S)]SO4 (3) and
[Cd2(phen)4(S)]SO4 (4), respectively. The figures in-
dicate that most particles are nearly uniform, fine and
spherical.
Particle sizes can be measured directly from
TEM images. From Figs 7b and 8b it can be seen that,
for both complexes size distribution of particles is
narrowly dispersed with medium diameter of 5.59 nm
The size of primary nanoparticles can be determined
from imaging by TEM. This technology is more direct
than X-ray line broadening and less likely to be af-
fected by experimental errors and/or other properties
of the particles such as strain or a distribution in the
size of lattice parameter [24].
Fig. 5 The most probable formula proposed for complex ion
in [Cd2(phen)2(S)]SO4 (3)
Fig. 4 The most probable formula proposed for complex
[Cd(S2O3)phen2]·2H2O (2)
J. Therm. Anal. Cal., 81, 2005
403

DUMBRAVA et al.
for [Cd2(phen)2(S)]SO4 (3) and 7.64 nm for
[Cd2(phen)4(S)]SO4 (4). Medium diameter of particle
is evaluated by arithmetic mean of diameters mea-
sured at different angle (0, 15, 30, …180°), assuming
lognormal distribution of nanoparticles. Experimental
diameter measured from TEM micrograph was fitted
with function given by:
ln 2 (x/ xc)
2w 2
y = y0 + Ae
where A is a constant strongly related to particle
count, xc position of maximum, and w dispersion.
There were obtained values of 5.27 nm for
[Cd2(phen)2(S)]SO4 (3) and respective 7.20 nm for
[Cd2(phen)4(S)]SO4 (4) around of which there are dis-
tributed the medium diameters of particles.
Fig. 6 The most probable formula proposed for complex ion in
[Cd2(phen)4(S)]SO4 (4)
Fig. 8 a – The TEM image of [Cd2(phen)4(S)]SO4 (4);
b – Mean particle size and particle distribution for
[Cd2(phen)4(S)]SO4 (4)
Fig. 7 a – The TEM image of [Cd2(phen)2(S)]SO4 (3);
b – Mean particle size and particle distribution for
[Cd2(phen)2(S)]SO4 (3)
404
J. Therm. Anal. Cal., 81, 2005

SYNTHESIS OF CADMIUM COMPLEX SULFIDES NANOPARTICLES
chemical analysis, IR spectra, TEM and HRTEM
analyses.
The resulted complex sulfides of cadmium may
be included in nanomaterials category, on the basis of
medium diameter (5.59 nm for [Cd2(phen)2(S)]SO4
and 7.64 nm for [Cd2(phen)4(S)]SO4).
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Conclusions
There were synthesised two new complex compounds
of cadmium with 1,10-phenathroline and thiosulfate
ion, having formulas [Cd(S2O3)phen]⋅H2O (1), respec-
tive [Cd(S2O3)phen2]⋅2H2O (2). The both compounds
were characterised by chemical analysis, DTA-TG and
IR methods. The authors proposed mechanism of de-
composition for obtained complex compounds.
On the basis of the results of thermal decomposi-
tion, the complexes were used as precursors for com-
plex sulfides. Thus, by thermooxidative degradation
were obtained complexes [Cd2(phen)2(S)]SO4 (3) and
[Cd2(phen)4(S)]SO4 (4), which were characterised by
Received: October 2, 2004
In revised form: March 21, 2005
DOI: 10.1007/s10973-005-6528-8
J. Therm. Anal. Cal., 81, 2005
405