Composition and particle size of electrolytic copper powders prepared in water-containing dimethyl sulfoxide electrolytes

Article abstract of DOI:10.1134/S0036024417070226

The possibility of the electroprecipitation of copper powder via the cathodic reduction of an electrolyte solution containing copper(II) nitrate trihydrate and dimethyl sulfoxide (DMSO) is shown. The effect electrolysis conditions (current density, concen

Full text of DOI:10.1134/S0036024417070226

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2017, Vol. 91, No. 7, pp. 1332–1336. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © Aigul’ Mamyrbekova, B.S. Abzhalov, Aizhan Mamyrbekova, 2017, published in Zhurnal Fizicheskoi Khimii, 2017, Vol. 91, No. 7, pp. 1232–1236.
COLLOID CHEMISTRY
AND ELECTROCHEMISTRY
Composition and Particle Size of Electrolytic Copper Powders
Prepared in Water-containing Dimethyl Sulfoxide Electrolytes
Aigul’ Mamyrbekovaa,*, B. S. Abzhalovb, and Aizhan Mamyrbekovab
aAuezov South Kazakhstan State University, Shymkent, 160012 Kazakhstan
bAkhmet Yassawi University, Turkestan, 161200 Kazakhstan
*e-mail: aizhan.mamyrbekova@ayu.edu.kz, aigul_akm@mail.ru
Received May 25, 2016
Abstract—The possibility of the electroprecipitation of copper powder via the cathodic reduction of an
electrolyte solution containing copper(II) nitrate trihydrate and dimethyl sulfoxide (DMSO) is shown.
The effect electrolysis conditions (current density, concentration and temperature of electrolyte) have
on the dimensional characteristics of copper powder is studied. The size and shape of the particles of the
powders were determined by means of electron microscopy; the qualitative composition of the powders,
with X-ray diffraction.
Keywords: dimethyl sulfoxide, copper(II) nitrate trihydrate, electroconductivity, electrolysis, copper powder,
X-ray diffraction
DOI: 10.1134/S0036024417070226
INTRODUCTION
erol, and ethylene glycol have been used as amphi-
protic solvents [6, 7]; pyridine, formamide, dimethyl-
formamide, dimethylethanolamine, and dimethyl
sulfoxide (DMSO) have been used as protophilic sol-
vents [8]; and acetonitrile, tartaric, citric, sulfosali-
cylic acid, and propylene carbonate have been used as
additives [9]. Copper sulfate, acetate, monochoride,
dichloride, and dibromide were used as electrolytes.
Electrolytic method is easy to use, does not require
expensive equipment, and allows obtaining chemi-
cally pure copper powders that have unique and sta-
ble properties (dendrite shape, dense texture of the
particles). The main advantage of these method is the
possibility of controlling a powder’s structure and
properties by varying the parameters of electrochem-
ical synthesis. This enables us to adjust the structure,
size, shape, and chemical composition of the pow-
ders [10, 11].
Among the developing areas of modern research,
fine powders whose microstructure gives them a num-
ber of valuable properties and the possibility of wide
application in catalysis, medicine, ecology, and tribol-
ogy, are of particular interest. In recent years, fine
copper powders have been of great importance, since
they have special properties (anti-friction, high elec-
tric conductivity) that allow their use in engineering
and as composite materials [1, 2].
Developing new ways of the electrochemical syn-
thesis of fine copper powders is thus a topic of great
interest. Metal reduction on a cathode without the
concomitant (parallel) hydrogen evolution reaction
that is characteristic of electrolysis in aqueous solu-
tions can be conducted using solvents with greater
electrochemical stability than water. Aprotic organic
solvents that do not contain labile hydrogen and are
reduced at relatively high cathode potentials are the
best in this respect [3, 4]. In this work, dimethyl sulf-
oxide (CH3)2SO, a cationtropic compound character-
Despite such a long list of nonaqueous solvents in
which the possibility of copper electroextraction has
been demonstrated, there are few works on the elec-
ized by high dissolving and ionizing power (ε = 47) was trodeposition of copper from electrolytes based on
selected as a solvent. The high adsorption activity of DMSO or mixtures of it and other compounds.
DMSO on copper metal/electrolyte interface is also Among the solvents mentioned above, such aprotic
well known [5].
solvents as DMSO have attracted much attention of
researchers [12–14]. Dipolar organic solvents are able
to form complexes with some ds metals and exhibit
high adsorptivity toward metals. Molecules of
(CH3)2SO, like their cationtropic counterparts, form
fairly stable complexes with ions of copper(II). Anal-
ysis of the electronic structure of the (CH3)2SO mol-
A review of the literature data showed that a con-
siderable number of works have been devoted to study-
ing the possible electrodeposition of copper from non-
aqueous media. Acetic acid has been used as a proto-
genic solvent; acetone, acetonitrile, methanol,
ethanol, propanol, isopropanol, tert-butanol, glyc-
1332

COMPOSITION AND PARTICLE SIZE OF ELECTROLYTIC COPPER POWDERS
1333
ecules and features of copper’s metal lattice allows us as the reference electrode [16], the potential of which
to conclude that the orientation of the adsorbed was measured relative to a saturated mercury sulfate
DMSO molecules with oxygen atoms toward the electrode (Hg/Hg2SO4, 1 N H2SO4). It was +0.3 V,
metal is the one most probable. The electrolyte pro-
posed in this work, which is obtained by dissolving
copper nitrate trihydrate Cu(NO3)2 · 3H2O in
relative to hydrogen.
RESULTS AND DISCUSSION
DMSO, has a simple composition and, due to the
presence of a surfactant and the complexing proper-
As was shown in studying the bulk and transport
properties of copper(II) nitrate trihydrate solutions in
DMSO, the maximum of electrical conductivity is
observed in a 0.4 M copper(II) nitrate solution in
DMSO at 15°C, which shifts to 0.6 M at higher tem-
peratures [17]. An 0.1–0.6 M interval of copper salt
concentrations was therefore chosen to study the pos-
sible electrodeposition of copper powder from
DMSO. In solutions with 0.5 M (and higher) concen-
trations of copper salts in DMSO, viscosity grew con-
siderably and the mobility of the metal ions was
reduced.
−
ties of Cu2+ and
ions with solvents, does not
NO3
require other additives that affect the kinetics of the
copper reduction.
The aim of this work was to obtain fine powders of
copper from dimethyl sulfoxide aqueous solutions
with particle sizes of up to 50 μm, and to study their
physicochemical properties.
EXPERIMENTAL
The electrocrystallization of copper powder was
conducted in solutions of copper(II) nitrate trihydrate
in DMSO. Copper nitrate was synthesized according
to the procedure described in [15] and purified by
recrystallization from aqueous solution. DMSO of
chemically pure grade was subjected to vacuum distil-
25
Copper(II)
ions,
nitrate
ions,
[Cu(DMSO)4(H2O)2]2+ solvate complexes, and
[(CH3)2SO · NO3]– ion adducts that provide the con-
ductivity of the solution probably form in the electro-
lyte used to obtain copper powder as a result of inter-
action between its components [18]. The effect
DMSO has on the electrocrystallization of copper
powder is obviously associated with its surfactant and
complexing properties.
lation (
= 1.4816). Prior to electrolysis, the pre-
nD
pared electrolyte solutions were held for at least a day
to achieve ionic equilibrium.
The electrodeposition of the copper powder was
conducted in the galvanostatic mode without forced
stirring in a thermostatted glass cell equipped with a
polyvinyl chloride cap with parallel fixed anodes.
A cylindrical steel rod placed in the center of the cap
was used as a cathode. Plates made of electrolytic cop-
per were used as soluble anodes. One advantage of
using soluble anodes is that electrolysis can be con-
ducted for a fairly long time. After electrolysis, the
resulting precipitate was repeatedly rinsed with bidis-
tilled water to the constant value of conductivity of the
rinsing water and dried to a constant mass.
The kinetics of cathodic processes of electrochem-
ical copper deposition was studied in the potentiody-
namic mode in a 0.4 M solution of Cu(NO3)2 · 3H2O
in DMSO in the temperature range of 25–55°C.
At 25°C, two distinct current maxima are observed on
voltammograms (Fig. 1), indicating a two-step dis-
charge of solvate complexes of copper(II)
[Cu(DMSO)4(H2O)2]2+ on the electrode. This can be
presented schematically as
Cu2+ + е– = Cu+, Е = –0.1…–0.2 V,
Cu+ + e– = Cu0, Е = –0.3…–0.5 V.
(1)
(2)
The size and shape of the powder particles were
determined via electron microscopy. We used a JSM
6490 LA scanning electron microscope at a magnifi-
cation of ×2000. An LS 13320 particle laser analyzer
equipped with an aqueous liquid module equipped
with an ultrasonic probe was used to examine the size
distribution of the copper powder. The range of parti-
cle size measurement ranged from 0.020 to 200 μm.
XRD analysis of electrolytic copper powders was per-
formed using a DRON-2.0 unit with CuKα mono-
chromatic radiation. The rate of detector rotation was
2 deg/min.
The formation of dimethyl sulfoxide complexes of
copper(II) leads to certain inhibition of reduction pro-
cess, and shifts the reduction potential of copper(II)
ion to a more negative region (E = –0.5 V). At 35–
55°C, there is a third wave in the polarization curves
(Fig. 2) at more negative potential range. This maxi-
mum likely corresponds to the reduction of nitrate
ions:
NO3− + H2O + 2e− = NO2− + 2OH–,
(3)
Е = –1.2…–1.3 V.
Raising the temperature to 35°C and higher obvi-
ously contributes to the partial desorption of the sol-
vent and the breaking of hydrogen bonds between H2O
Polarization was measured in the potentiodynamic
mode using a PI-50-1 potentiostat. The sweep rate was
5 mV/s. The working electrode was a platinum wire,
preliminarily coated with a copper layer 18–20 μm and (CH3)2SO molecules, resulting in the decomposi-
thick, electrodeposited under standard conditions.
Ag/0.01 M AgNO3 silver electrode in DMSO was used
tion of heteronuclear complexes, and structural fluc-
tuations associated with nitrate complexes decompo-
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 7 2017

1334
I, µA
MAMYRBEKOVA et al.
I, µA
100
100
2
3
2
1
50
50
1
0
1'
0
0.2
0.4
0.6
1.2
1.4
E, V
2'
3'
−50
Fig. 2. Cathodic polarization curves of copper reduction
from 0.4 M copper(II) nitrate trihydrate solution in
DMSO at 35°C.
0.4
0
−0.4
−0.8
E, V
2+
Fig. 1. Cyclic voltammograms of Cu in 0.4 M solution of
Cu(NO ) · 3H O in DMSO at 25°C. The background
reduction of copper(II) ions in DMSO is a two-stage
process requires detailed investigation and additional
polarization studies.
3 2
2
electrolyte is 0.5 M LiClO in DMSO: (1) 0.05, (2) 0.05,
4
and (3) 0.1 V/s.
The compositions of electrolytes and conditions of
electrolysis used for the deposition of the dispersed
copper are given in Table 2. The sizes and shapes of the
powders’ particles were determined from micrographs
taken with a JSM 6490 LA scanning electron micro-
scope. For each preparation of the copper powder,
several micrographs were taken to determine the par-
ticle-size distribution of the dispersion powder
(Table 3). The data suggest that DMSO plays a role in
the formation of fine particles. The maximum amount
of powder particles with sizes of 20–60 μm was
obtained at 0.4 M copper nitrate trihydrate concentra-
tion.
sition. These processes consequently favor the reduc-
tion of nitrate ions less solvated with the molecules of
the organic solvent, improving their reactivity as the
temperature rises.
Upon increasing the concentration of copper(II)
salt, the cathodic potential in the organic solvent shifts
to more electronegative values, resulting in lower val-
ues of the maxima and values of the cathodic currents.
This is explained by the increased viscosity of the solu-
tion, which reduces the degree of copper(II) salt dis-
sociation in DMSO and lowers the diffusion coeffi-
cient of copper ions. In solutions with higher concen-
trations (>0.6 M), ionic association is enhanced,
resulting in increased viscosity, lower permittivity, and
a drop in conductivity, all of which were established in
[19].
Table 1. Transfer coefficients (α) of the discharge of cop-
per(II) ions in dimethyl sulfoxide
The transfer coefficients of copper ions (α) were
calculated voltammetry data (Table 1). As can be seen
from the table, increasing the potential sweep rate
gradually reduces the value of α1 at temperatures of
25–35°C to 0.20–0.24, which is typical of irreversible
processes. The values of α2 for the second stage of the
discharge of copper(I) ions at the same temperatures
display greater irreversibility of the process at the
higher sweep rates, as the difference between the ratios
at low and high scan rates increases.
The low values of the transfer coefficients of cop-
per(II) ions discharge allow us to conclude that the
second stage of electron transfer is appreciably slower.
However, the conclusion drawn in this work that the
v, V/s
t, °C
0.02
0.05
0.10
0.20
First stage (α1)
25
35
0.34
0.41
0.27
0.24
0.25
0.20
0.24
0.29
Second stage (α2)
0.13
25
35
0.37
0.45
0.15
0.23
0.08
0.15
0.13
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COMPOSITION AND PARTICLE SIZE OF ELECTROLYTIC COPPER POWDERS
1335
Table 2. Composition of the electrolytes and conditions of
electrolytic deposition of the copper powder (the volume of
DMSO is <1 L)
Our data show that during the electrolysis of a
dilute solution of copper nitrate in DMSO, low tem-
peratures (up to 25°C) favor the formation of high
quality powders. Under these conditions, the main
cathodic process proceeds according to Eqs. (1) and
(2). Upon raising the temperature to 35°C and higher,
hydrogen bonds break in the electrolyte, complicating
the physicochemical phenomena and gain fluctua-
tions in the solution. As a result of the decomposition
of nitrate ions complexes with DMSO, the overvoltage
is reduced, facilitating their reduction according to
Eq. (3). As a consequence, the rate of nitrate ion
reduction grows substantially, the pH of the near-
cathode volume rises, the current yield of metal falls,
and the quality of the powder deteriorates sharply. In
the near-cathode electrolyte layer, the probability of
the formation of poorly soluble compounds of cop-
per(I) (CuOH and Cu2O) captured by the growing
precipitate grows, coloring the resulting powder some-
i, A/m2
No. c, mol/L
T, °C
d, μm
I, %
0.1
400
500
1
2
3
4
5
6
7
8
25
30
35
40
25
30
25
25
30
30
40
40
40
30
30
30
96.8
95.7
94.5
93.6
96.6
96.2
98.7
98.7
0.15
0.2
600
0.25
0.3
700
800
0.35
0.4
900
1000
1100
0.45
c is the concentration of copper(II) nitrate trihydrate, i is the
cathodic current density, d is the size of the powder particles, and what.
I is the current yield.
CONCLUSIONS
Table 3. Particle size distribution at 0.4 M concentration of
Cu(NO3)2 ⋅ 3H2O in DMSO
Fine copper powders with particle sizes of 50 μm
were obtained from dimethyl sulfoxide aqueous solu-
tions via electrochemical synthesis, and their physico-
chemical properties were studied. It was found that the
powders obtained from 0.1–0.4 M solutions of
Cu(NO3)2 · 3H2O in DMSO contained the maximum
amount of particles with sizes of 30–40 μm. According
to XRD measurements, the resulting powders contain
Cu and Cu2O phases.
d, μm
N
c, %
459
121
33
67.30
17.74
4.84
7.33
20–39
40–59
60–79
80–99
50
100–120
19
2.79
N is the number of the particles and c is fraction.
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