Lead citrate precursor route to synthesize nanostructural lead oxide from spent lead acid battery paste

Article abstract of DOI:10.1016/j.materresbull.2013.01.031

Nanostructural lead oxides were prepared by the decomposition of a new type of lead citrate precursor (Pb₃(C₆H₅O ₇)₂·3H₂O), which was synthesized through leaching of spent lead acid battery paste in citrate salt aqueous system and more economical compared with former precursor (Pb(C₆H ₆O₇)·H₂O). The products were characterized by thermogravimetric-differential thermal analysis, scanning electron microscopy and X-ray diffraction. The results show that when lead citrate of columnar-shape crystals are calcined in N₂ gas, orthorhombic β-PbO is the main product containing small amount of Pb and C. On combusting the citrate in air, a mixture of orthorhombic β-PbO, tetragonal α-PbO and Pb with the particle size of 100-200 nm is obtained, with β-PbO as the major product. And the cyclic voltammetry measurements of lead oxides present different electrochemical redox potentials because of the different structure of lead oxide obtained from Pb₃(C ₆H₅O₇)₂·3H₂O.

Full text of DOI:10.1016/j.materresbull.2013.01.031

Materials Research Bulletin 48 (2013) 1700–1708
Contents lists available at SciVerse ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Lead citrate precursor route to synthesize nanostructural lead oxide from
spent lead acid battery paste
a
a
a,b
a
a
a
c
Lei Li , Yuchen Hu , Xinfeng Zhu , Danni Yang , Qin Wang , Jianwen Liu , R. Vasant Kumar ,
a,
Jiakuan Yang *
a
School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road, Wuhan, Hubei 430074, PR China
b
Henan University of Urban Construction, Pingdingshan, Henan 467000, PR China
c
Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK
A R T I C L E I N F O
A B S T R A C T
Article history:
Nanostructural lead oxides were prepared by the decomposition of a new type of lead citrate precursor
Received 22 November 2012
Received in revised form 28 December 2012
Accepted 7 January 2013
(
Pb
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O), which was synthesized through leaching of spent lead acid battery paste in citrate
O). The
salt aqueous system and more economical compared with former precursor (Pb(C
6
H
6
O
7
)ꢀH
2
products were characterized by thermogravimetric–differential thermal analysis, scanning electron
microscopy and X-ray diffraction. The results show that when lead citrate of columnar-shape crystals are
Available online 23 January 2013
calcined in N
combusting the citrate in air, a mixture of orthorhombic
particle size of 100–200 nm is obtained, with -PbO as the major product. And the cyclic voltammetry
measurements of lead oxides present different electrochemical redox potentials because of the different
structure of lead oxide obtained from Pb (C O.
ꢀ3H
2
gas, orthorhombic
b
-PbO is the main product containing small amount of Pb and C. On
Keywords:
b
-PbO, tetragonal -PbO and Pb with the
a
A. Nanostructures
b
B. Chemical synthesis
C. Thermogravimetric analysis
C. X-ray diffraction
3
6
H
5
O
7
)
2
2
D. Electrochemical properties
Crown Copyright ß 2013 Published by Elsevier Ltd. All rights reserved.
1
. Introduction
was roasted at 110–500 8C, to produce PbO nanostructures. The
research results from Cruz et al. [6] showed that
were prepared by spray pyrolysis of aqueous solutions of
Pb(CH COO) O and deposited onto a lead substrate. The
ꢀ3H
a-PbO thin films
Recently, the synthesis of nanostructural oxide materials has
attracted considerable attention of chemists and metallurgists [1–
]. Lead oxide has many crystalline forms, such as PbO ( ),
Pb , Pb , and PbO ). Lead dioxide (PbO ), which is used
3
2
2
ꢁ
1
3
a
,
b
battery cell maintained a discharge capacity of 100 mAh g of
positive plate (40 wt% of the theoretical value) upon extensive
cycling. Karami et al. [7,8] synthesized a uniform nano-structured
lead oxide via sonochemical method. The electrochemical tests
showed that a large discharge capacity and excellent cycle
characteristics of the nanostructural powder were obtained.
In previous study, the synthesis process of nano-structured lead
oxide is more or less complex because of the utilization of
sonochemical technology. And the starting materials are lead
2
O
3
3
O
4
2
(
a,
b
2
as a positive active material in lead acid battery, has been
extensively studied. In lead acid batteries, PbO is the starting paste
material for both anode and cathode, which is then converted to
2
active Pb and PbO during cell formation stage. There is a big
interest to improve lead oxide characteristics to obtain more
discharge capacity and long cycle-life. It is expected that the lead
oxide in form of nano-particulates can deliver more electrical
energy at discharge process due to its large specific surface area
and good reversible property. Wang et al. [3] prepared nano
crystalline lead oxide through two-step chemical reactions.
Salavati-Niasari et al. [4] reported that synthesis of nano-size
lead oxide powder with an average particle size of 35 nm could be
made by decomposing lead oxalate at 500 8C. Sadeghzadeh et al.
compounds, such as Pb(NO
3
)
2
, Pb(CH
3
COO)
2
ꢀ3H
2
O, which are
expensive as pure chemical reagents. Citrate precursor route has
been used in the preparation of nano-structured materials widely
[9–11]. This route contains two steps: one is the synthesis of citrate
precursors, and the second is the decomposition of citrate
precursors. And different structured precursors can obtain
different nano-structured materials. However, there is little report
about synthesis of nanostructural lead oxide using citrate
precursor route. The lead citrate precursor can be readily converted
to PbO (containing some Pb) for directly making lead acid battery
pastes with controllable degree of metallization by a combustion–
calcination process [12–14].
[
5] used 2-pyridinecarboxylic acid, lead acetate and sodium nitrite
to synthesize one-dimensional structure of Pb (II) chelate, which
*
Corresponding author. Tel.: +86 27 87792207; fax: +86 27 87792101.
E-mail addresses: jkyang@mail.hust.edu.cn, yjiakuan@hotmail.com (J. Yang).
0025-5408/$ – see front matter. Crown Copyright ß 2013 Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2013.01.031

L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
1701
Table 1
In our previous research [15], the lead citrate (Pb(C
6
H
6
O
7
)ꢀH
2
O)
Chemical composition of spent lead acid battery paste.
was synthesized from spent lead acid battery pastes in citric acid
system, and nano lead oxide with particle size of 100–200 nm was
obtained from calcination–combustion. The precursor, with
Constituent
PbSO
56.8
4
PbO
32.4
2
PbO
4.2
Pb
Others
1.1
Percentage (%)
5.5
formula of Pb(C
6
H
6
O
7
)ꢀH
2
O, was generated in the 3–4 pH range
in citric acid system. Due to the various types of citrate ions
ꢁ
2ꢁ
3ꢁ
) and lead’s effective interac-
(C
6
H
7
O
7
, C
tions with organic molecules, some other Pb-citrate types, such as
Pb (C O, can be synthesized in this citric acid system by
ꢀ3H
changing the reaction conditions. Unlike the former lead citrate
Pb(C O), Pb (C O has a different morphology
6
H
6
O
7
and C
6
H
5
O
7
2. Experimental
3
6
H
5
O
7
)
2
2
2.1. Materials
(
6
H
6
O
7
)ꢀH
2
3
6
H
5
O
7
)
2
ꢀ3H
2
The samples of spent lead acid battery pastes were provided by
Hubei Jinyang Metallurgical Co. Ltd., China, where the waste lead
pastes are treated to recover lead metal using a conventional
smelting process. The chemical composition of the spent lead acid
battery pastes is shown in Table 1.
and its crystals particle can grow up to some extent, which could
improve filtration performance of lead citrate. Moreover, the ratio
of lead to citrate of Pb(C
in Pb (C O is 3:2. It is indicated that the consumption of
ꢀ3H
citrate ions in the synthesis of Pb (C O with per mol
ꢀ3H
is less than the consumption in the synthesis of
O. Even though Pb (C O is of advantages
6
H
6
O
7
)ꢀH
2
O is 1:1, whereas the ratio of that
3
6
H
5
O
7
)
2
2
3
6
H
5
O
7
)
2
2
Trisodium citrate hydrate (Na
used as the desulfating agent and organic ligand during leaching
spent lead battery pastes. Anhydrous acetic acid (CH COOH, 99.5%
purity) was used to leaching and keeping balance of pH. Hydrogen
peroxide (H , 30%, w/v) was used as the reductant.
3
C
6
H
5
O
7
2
ꢀ2H O, >99% purity) was
2+
Pb
Pb(C
6
H
6
O
7
)ꢀH
2
3
6
H
5
O
7
)
2
ꢀ3H
2
3
in the lead citrate precursor route to synthesize nanostructural
lead oxide, there is a lack of knowledge about the decomposition
2 2
O
process of Pb
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O and the characteristics of decom-
position products. In this work, as shown in Fig. 1, the
nanostructural lead oxide was prepared via a low temperature
2.2. Synthesis of lead citrate precursor
calcination process both in N
2
gas and air, by using a new lead citrate
The reaction in this leaching system can be represented by the
following equations [(1)–(3)].
type (Pb (C O) as a precursor. The decomposition
3
H O ) ꢀ3H
6 5 7 2 2
process and the characteristics of nanostructural lead oxide have
been discussed in detail. By controlling the calcination process of
lead citrate, it is possible to obtain variation in the microstructure
from nano to micro scale, and nano-powders are attractive for future
development work in advanced lead acid batteries.
3PbO þ 6CH
3
COOH þ 2Na
3
ðC
6
H
5
O
7
Þ ꢀ 2H
2
O
! Pb ðC H O Þ ꢀ3H O þ 6CH COONa þ 4H O
3
6
5
7
2
2
3
2
(1)
(2)
(3)
3
3
PbO
2
þ 6CH
3
COOH þ 3H
ꢀ3H
2
O
2
þ 2Na
3
ðC
6
H
5
O
7
Þ ꢀ 2H
2
O
!
Pb
3
ðC
6
H
5
O
7
Þ
2
2
O þ 6CH
3
COONa þ 3O
2
þ 7H
2
O
Spent lead pastes
3
CH COOH
PbSO
4
þ 2Na
SO
3
ðC
6
H
6
O
7
Þ ꢀ 2H
2
O
ꢁ! Pb
3
ðC
6
H
5
O
7
Þ2 ꢀ 3H
2
O
þ 3Na
2
4
Leaching and
crystal growth
In this leaching experiment, 10 g of spent lead battery paste was
added to trisodium citrate and anhydrous acetic acid and 30%
peroxide hydrogen solution with a solid/liquid mass ratio of 1/5.
The calculated and actual dosages of each leaching reagents are
shown in Table 2. In order to transform all lead compounds in spent
lead battery paste into lead citrate, the actual dosage of
New precursor Pb (C H O ) ·3H O
3
6
5
7 2
2
Na
both twice of calculated dosage. The actual dosage of H
.6 mL (a quadruple calculated dosage). The pH of the solution was
3
C
6
H
5
O
7
ꢀ2H
2
O was 14.4 g and CH
3
COOH was 6.6 g, which were
2 2
O
was
5
TG-FTIR
TG-DTA
Thermal analyses
in a range of 5–6. Leaching was carried out under magnetic stirring
at speed of 650 rpm to maintain full suspension of the slurry for 5 h
at room temperature (25 8C). During leaching, lead citrate began to
crystallize from the solution at the room temperature. After
leaching, the reaction vessel with lead citrate slurry was left in
homoeothermic water bath at 55 8C for 8 h. The lead citrate
crystals grown up, then the resulting crystals were washed with
distilled water; vacuum filtrated and dried at 45 8C. The
concentration of lead ion in the left solution was analyzed with
atomic absorption spectrometry (WFX-100, Beifen-Ruili, China).
Calcination process
in N and in air
2
Nanostructural lead oxide
2
.3. Thermal analyses of lead citrate
XRD
Characterization
SEM/EDX
CV
Thermal analyses of the lead citrate were performed in
corundum crucible by thermogravimetric–differential thermal
Table 2
Potential active materials for
high-performance battery
The calculated and actual dosages of each leaching reagents.
Leaching reagents
Na C H O ꢀ2H O (g) CH COOH (g) H O (30%) (mL)
3
6
5
7
2
3
2
2
Calculated dosages
Actual dosages
7.2
3.3
6.6
1.4
5.6
Fig. 1. The procedure of preparing nanostructural lead oxide by the decomposition
14.4
of a new lead citrate precursor (Pb
3
(C
H
6 5
O
)
7 2
ꢀ3H
2
O).

1
702
L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
analysis (TG–DTA), in different atmospheres using TA Instruments
Diamond TG-DTA, Platinum-Selmer Equipment Co. Ltd., Shanghai),
(
3
ꢁ1
with air or nitrogen gas under a flow rate of 100 cm min by
ꢁ1
heating up to 800 8C at heating rate of 5 8C min . Thermogravi-
metric–Fourier Transform Infrared Spectroscopy (TG-FTIR) was used
to analyze the tail gas. When the tail gas was generated during
decomposition of lead citrate in the thermogravimetric instrument,
it was sent directly to the connected Fourier Transform Infrared
Spectroscopyinstrumentto analyze. The experiment was carried out
by using TA Instrument (STA 409, NETZSCH Scientific Instrument Co.
Ltd., Germany) and FTIR Instrument (EQUINOX 55, Bruker corpora-
tion, Germany), both in air and nitrogen gas under a flow rate of
(a)
3
ꢁ1
ꢁ1
7
9 cm min by heating up to 600 8C at heating rate of 5 8C min
.4. Calcination of lead citrate
The calcination behaviors of lead citrate were investigated in a
.
(b)
2
0
10
20
30
40
θ (˚)
50
60
70
80
tubular atmosphere furnace in different atmospheres. In nitrogen
gas, the lead citrate powders of 2 g were calcined at 295 8C, 335 8C,
2
3
1
1
50 8C, 400 8C and 450 8C for 2 h, respectively, at heating rate of
0 8C min . In the air, the citrate powders of 2 g were calcined at
20 8C, 300 8C, 350 8C, 370 8C, 415 8C, 450 8C and 550 8C for 1 h,
Fig. 2. XRD patterns of (a) crystals obtained from spent lead acid battery pastes and
(b) lead citrate Pb (C H O ) ꢀ3H O from Alfa Aesar China (Tianjin) Co., Ltd. (CAS:
ꢁ1
3
6
5
7
2
2
6107-83-1).
respectively. The lead citrate powders of 2 g were also calcined
isothermally at 350 8C with variation of time, such as 5 min,
1
0 min, 15 min, 20 min, 40 min and 60 min in air. The weight loss
the mass of lead in the spent solution, which was to be 96.0 wt%.
The XRD pattern of the resulting crystals are shown in Fig. 2,
compared with the XRD pattern of lead citrate. None of the original
lead phases are observed in the XRD patterns (a), indicating that
the reaction undergone completely. The pattern of XRD almost
was measured for each set of the experiments. Calcination
temperature was determined based on TG–DTA data.
2.5. Characterization of materials
matches with lead citrate structural data of Pb
which was purchased from Alfa Aesar China (Tianjin) Co., Ltd. (CAS
number: 6107-83-1). Thus, it can be indicated that the leaching
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O
X-ray diffraction (XRD) data were collected from powder
samples using a X’Pert PRO XRD (Philips, PAN alytical B.V., Holland)
˚
with Cu K
a
radiation and
l
= 1.5418 A at scanning rate of 0.288 per
product is Pb
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O. The photograph of the lead citrate
second for 2
u
in the range from 58 to 758. In order to identify new
(C O purchased from Alfa
ꢀ3H
product is shown in Fig. 3(a). Lead citrate precursor is white, which
is different from the brown color of spent lead acid battery paste
samples. Morphology of the lead citrate is shown in Fig. 3(b). The
lead citrate is columnar shaped with length of 5–50
diameter of 2–50
leaching solution.
lead citrate precursor, Pb
3
6
H
5
O
7
)
2
2
Aesar China (Tianjin) Co., Ltd. (CAS number: 6107-83-1) was used
as the reference in XRD analysis. Morphology studies were carried
out with scanning electron microscopy (Sirion 200SEM, FEI,
Holland) operated at 10 kV after coating the samples with gold.
EDX spectra of the calcined products were collected on an ultra-
thin window (UTW) X-ray detector equipped with Sirion 200 SEM.
m
m and
mm. These crystals are easy to filter out of the
3.2. Thermal analyses results
2
.6. Characterization of lead oxide with electrochemical
Thermal decomposition of lead citrate was identified with
thermal analysis. The TG–DTA curves of the lead citrate in two
different atmospheres are shown in Fig. 4. In the pure nitrogen
atmosphere, decomposition of the citrate is supposed to takes
place through pyrolysis. From patterns (a), when the temperature
is in the range of 20–350 8C, there are three obvious stages of
measurements
Cyclic voltammetry (CV) was employed to investigate the
electrochemical behavior of the lead oxide. The CV curves were
determined with a typical three-electrode system. The working
electrode (WE) was prepared from platinum microelectrode which
was filled with lead oxide. PbO in contact with concentrated
sulfuric acid was converted into PbSO
electrochemically active precursor in the electrode for formation of
PbO via oxidation. A double platinum electrode was used as the
counter electrode while Hg/Hg SO /K SO (sat.) was, employed as
the reference electrode. Sulfuric acid solution at concentration of
2
weight loss in the TG curve in N , which corresponds to
endothermic peaks in the DTA curve. The mass loss at 200 8C is
approximately 5.3% that is most likely due to dehydration. Then
lead citrate decomposes at 295 8C and 335 8C, respectively. It has
been reported that [16] PbO could be reduced to Pb metal by
carbon above 370 8C in N gas. As shown in Fig. 4(a), the mass loss
2
keeps increasing slowly when temperature rises from 350 8C to
800 8C. This may be reasoned from the reduction of PbO by carbon.
4
which then acted as the
2
2
4
2
4
ꢁ1
3
mol L was used as electrolyte. CV was performed for 7 cycles at
room temperature (22 8C) using electrochemical workstation
It shows that thermal decomposition of Pb
3
(C
6
H
5
O
7
)
2
ꢀ3H
2 2
O in N
ꢁ
1
(VMP-2, Princeton, USA), with a scanning speed of 20 mV s in
can be completed around and above 350 8C with a total weight loss
about 32 wt%. Therefore, the temperature for decomposing lead
citrate in nitrogen can be selected progressively near the three
stages of weight loss, i.e. 295 8C, 335 8C, 350 8C and 400 8C, 450 8C.
The FTIR spectrums of tail gas generated during the pyrolysis of
a potential range of 0 V to +1.5 V.
3
. Results and discussion
3
.1. Crystallization of lead citrate
lead citrate in N
spectral range of 2400–2250 cm and 3950–3500 cm shows
that CO and H O are the main gas products in the temperature
range of 250–400 8C.
2
are shown in Fig. 5(a). The absorption in the
ꢁ
1
ꢁ1
After leaching, the spent solution was diluted in the 1000 mL
2
2
volumetric flask. Recovery of lead was calculated by subtracting

L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
1703
100
90
80
70
60
(
a)
b)
(
50
40
30
20
10
0
(
a)
(b)
100
200
300
400
500
600
700
800
T ( C)
Fig. 4. TG–DTA curves of lead citrate in different atmospheres: (a) in nitrogen gas
and (b) in air.
Fig. 3. Photograph and SEM image of lead citrate product: (a) photograph of lead
citrate after filtering and (b) SEM image.
Thermal analysis patterns (b) show that the thermal behavior is
more complex in air. The first stage of weight loss in 200 8C is due
to dehydration. In the following stages, weight loss takes place in
the temperature range 270–450 8C, which is ascribed to combus-
tion of the citrate. This process is accompanied by four somewhat
overlapping exothermic peaks in DTA curve around 300 8C, 345 8C,
3
70 8C and 415 8C. Exothermic peaks observed in the DTA curve are
ascribed to the oxidation of both C and H from the citrate. When
temperature is above 450 8C, both weight loss and heat flow
remain constant up to 800 8C. The calcination–combustion
temperatures for the citrate can be selected progressively
corresponding to the exothermic peaks, at 120 8C (for confirming
dehydration reaction in the decomposition process), 300 8C,
3
50 8C, 370 8C, 415 8C, 450 8C and 550 8C. The FTIR spectrums of
tail gas are shown in Fig. 5(b). As the same in N , CO and H O are
2
2
2
the main gas products during the decomposition of lead citrate in
the range of 250–400 8C.
According to Fig. 4, when temperature is under 350 8C, the TG
curve in air is similar to TG in N
curve in air is identical to the results in N
range of 350–450 8C, the TG curve in air shows a slope, while TG
curve in N is an approximately flat line. It can be inferred that
2
, and the peak temperatures of DTA
2
. When temperature is in
Fig. 5. FTIR spectrums of tail gas generated during decomposition of lead citrate in
2
different atmospheres: (a) in nitrogen gas and (b) in air.

1
704
L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
35
30
25
20
15
10
5
0
Massicot -PbO
Lead Pb
(a)
(b)
(c)
0
295
335
350
400
450
500
Temperature ( C)
(d)
2
Fig. 6. Effects of calcination temperatures on weight loss of lead citrate in N .
1
0
20
30
40
50
60
70
there are two stages taking place in the calcination of
Pb (C O in air. One stage is decomposition of citrate
ꢀ3H
which is alike of pyrolysis of citrate in N , accompanying by a little
of oxidation of C and H; second stage is violent combustion of C and
H when the temperature is higher than 350 8C.
3
6
H
5
O
7
)
2
2
2 ( )
2
Fig. 7. XRD patterns of decomposition products from lead citrate at different
temperature for 2 h in N : (a) 295 8C, (b) 335 8C, (c) 350 8C, and (d) 450 8C.
2
2
Fig. 8. SEM images of products decomposed at different temperatures in N : (a) 295 8C, (b) 350 8C, and (c) 450 8C.

L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
1705
4
5
4
0
3
5
3
0
2
5
2
0
1
5
1
0
5
0
0
120 300 350 370 415 450 550
Temperature ( C)
Fig. 10. Effects of calcination temperatures on weight loss after calcinations in air
1 h).
(
study, a mixture of PbO, Pb and C is obtained and CO
the main gas products during the thermal decomposition of
Pb (C O in inert atmosphere.
ꢀ3H
2 2
with H O are
3
6
H
5
O
7
)
2
2
3.4. Calcination in air
In air, lead citrate was calcined respectively for 1 h at 120 8C,
300 8C, 350 8C, 370 8C, 415 8C, 450 8C and 550 8C to remove all
carbon and hydrogen. The effect of temperature on weight loss of
the citrate precursor was investigated. Fig. 10 shows that the
weight loss increases with an increase in temperature from 120 8C
to 370 8C and then it keeps relatively stable at 38 wt% in the
temperature range 370–450 8C. The weight loss of around 5% at
2
Fig. 9. EDX spectra of calcination product at 450 8C for 1 h in N .
3
.3. Calcination in nitrogen gas
Massicot -PbO
Litharge -PbO
Plumbonacrite Pb (CO ) (OH) O
1
0
3
6
6
The samples of lead citrate were heated respectively in a tube
furnace under nitrogen atmosphere at 295 8C, 335 8C, 350 8C,
00 8C and 450 8C for 2 h to investigate the thermal decomposition.
O Lead Pb
(a)
4
The effect of the calcination temperature on weight loss of the
citrate precursor is shown in Fig. 6. The weight loss increases with
an increase in calcination temperature from 295 8C to 335 8C and it
appears to be a plateau above 335 8C. The weight loss at 335 8C is
(
b)
3
0 wt%.
The phase transformation of the calcination products shown
in Fig. 7 was examined with X-ray diffraction technique. The
XRD demonstrates that the crystalline contains massicot (
b
-
(c)
PbO) and lead metal in temperature from 295 8C to 450 8C. The
SEM images of products decomposed at different temperature
are shown in Fig. 8. The products show similar morphology as
the temperature increased. The EDX spectrum of product
calcined at 450 8C is shown in Fig. 9. Some carbon is identified
in calcination product by the EDX spectra. Therefore, the
observed mass loss of 30% in nitrogen gas is about 7% less
than the stoichiometric mass loss of 36.5% in the decomposition
(d)
(e)
Pb
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O to PbO because of the formation of carbon in
the decomposition products.
1
0
20
30
40
( )
50
60
70
Brown [17] studied the thermal decomposition of lead citrate
Pb
3
(C
6
H
5
O
7
)
2
ꢀ2H
2 2
O in N , and the results at temperature (305–
2
3
25 8C) in his report showed that the pyrophoric metallic lead and
carbon particles were produced. The presence of Pb can be
reasoned from the reduction of PbO by carbon. However, in this
Fig. 11. XRD patterns of calcination–combustion products at different temperatures
for 1 h in air: (a) 300 8C, (b) 350 8C, (c) 415 8C, (d) 450 8C, and (e) 550 8C.

1
706
L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
Fig. 12. SEM images of calcination–combustion products at different temperature for 1 h in air: (a) 300 8C, (b) 350 8C, and (c) 450 8C, and (d) EDX spectra of spherical substance
in product at 350 8C.
1
20 8C is consistent with the crystallization water content of
lead citrate precursor (Pb (C O). It is indicated that
ꢀ3H
a dehydration reaction occurs in the temperature range of
the main components in the gas products. Therefore, the
decomposition can be shown approximately as Eq. (4). The
stoichiometric weight loss in Eq. (4) is 36.5%.
3
6
H
5
O
7
)
2
2
1
20–300 8C.
If air supply is sufficient, PbO is the final product. According to
Pb
3
ðC
6
H
5
O
7
Þ
2
ꢀ3H
2
O þ 9O
2
! 3PbO þ 12CO
2
þ 8H
2
O
(4)
2 2
the FTIR spectrums of tail gas (shown in Fig. 5(b)), CO and H O are

L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
1707
If the air is insufficient, Pb is the final product. The
decomposition can be shown as Eq. (5). The stoichiometric weight
loss in Eq. (5) is 41.0%.
4
40
5
3
3
2
5
0
5
Pb
3
ðC
6
H
5
O
7
Þ
2
ꢀ3H
2
O þ 7:5O
2
! 3Pb þ 12CO
2
þ 8H
2
O
(5)
The weight loss in the calcination experiments in air is around
3
8%, which is between 36.5% and 41.0%. It is indicated that the
product is composed of PbO and Pb. The XRD patterns of products
20
(
Fig. 11) also demonstrate the composition of PbO and Pb.
Fig. 11 presents the XRD patterns of the calcination products in
1
1
5
0
5
0
air at different temperature. The combustion products are
-PbO and metallic lead at 300 8C, 350 8C, 415 8C and 450 8C, with
some intermediate phases which is Pb10(CO (OH) O at 300 8C.
This results suggest that Pb (C O can be fully calcined
b-PbO,
a
3
)
6
6
3
6
H
5
O
7
)
2
ꢀ3H
2
in air at and above 350 8C. Additionally, the XRD patterns show that
the diffraction peak for metallic Pb decreases as calcination
temperature is increased.
0
5
10
15
20
40
60
Time (min)
Based on the results as mentioned above, it can be confirmed
that there are two sequential stages taking place in the calcination
Fig. 13. Effects of the calcination time on weight loss in air at 350 8C.
of Pb
lead citrate is decomposed and transformed into crystalline phases
of -PbO, -PbO, Pb and small amount of intermediate containing
C and H. The decomposition of this stage is alike of pyrolysis of lead
citrate in N . Compared with calcination products in N (shown in
Fig. 7), the difference is that metallic Pb are mostly oxidized to
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O in air. When temperature is under 350 8C,
3 6 6
compound Pb10(CO ) (OH) O can be seen at time of 15 min.
b
a
However, the peak of the intermediate disappears after 20 min of
calcination. Additionally, the XRD patterns show that the diffrac-
tion peak for metallic Pb decreases as calcination time is increased,
that is, more metallic Pb is oxidized in air. This result suggests that
the level of Pb oxidation can be adjusted by control of calcination
atmosphere or oxidation potential to achieve a desirable PbO/Pb
ratio.
2
2
a
-
PbO in air. As temperature is higher than 350 8C, C and H in the
intermediate combusted violently, accompanied with intense
exothermic phenomenon and generation of CO
temperature of 350 8C leads to producing -PbO,
of metallic Pb, and weight loss is 38 wt%. If temperature is higher
than 488 8C, -PbO will be transformed into -PbO [18]. As it
shown in Fig. 11(e), -PbO is only crystal phase in the product.
2
2
and H O. The
b
a
-PbO and a little
By contrast with the Pb(C
more economical and its crystal particle can grow up to the 5–
50 m length range. On the one hand, larger crystals can be
6
H
6
O
7
)ꢀH
2
O, the Pb
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O is
a
b
m
b
filtrated easily. On the other hand, the mass transfer of oxygen
becomes less efficient during the decomposition of big lead citrate
particles. Thus, the calcination requires higher temperature in
order to obtain pure products which contained only PbO and Pb,
but high temperature will aggravate the agglomeration of the lead
oxide products, which is resulting the decomposition temperature
as a dilemma factor.
Salavati-Niasari et al. [4] prepared PbO nanocrystals via
decomposition of lead oxalate in air. He reported that a mixture
of
proportion of
and Gao [19] synthesized single crystalline
through a hydrothermal processing of Na
Pb(CH COO) O. With lead citrate, formation of
ꢀ3H
than -PbO was observed, in both air (by combustion) and N
a
-PbO and
b
b
-PbO nanocrystals was obtained at 235 8C, and the
-PbO increased as the temperature increased. Jia
-PbO nanorods
ꢀ2H O and
-PbO rather
(by
b
3
C
6
H
5
O
b
7
2
3
2
2
a
2
Massicot PbO
Litharge PbO
(OH)6
decomposition). These results are consistent to the data in this
paper.
Plumbonacrite Pb10(CO
)
O
3
6
The SEM images of the products from the citrate calcined at
different temperatures are shown in Fig. 12. The results show that
the morphology of products converts from porous columnar to
spherical structure with increasing temperature. As shown in
Fig. 12(a) at larger magnification, the products are agglomerated
by ultrafine particles with the size of approximately in the range of
O Lead Pb
(a)
1
00–200 nm. When calcination temperature increases up to 350 8C
and above, shown in Fig. 12(b), particulates agglomerate and grow
larger. Furthermore, the morphology transforms from porous
columnar into spherical structure at higher temperature as shown
in Fig. 12(c). The spherical substance is also identified as the
mixture of PbO and Pb by EDX spectra in Fig. 12(d). This indicates
that the appearance of spherical structure could be attributed to
the agglomeration and partial-melt of particles at higher calcina-
tion temperatures.
(b)
In order to determine the influence of calcination time, the
citrate was calcined at 350 8C for 5–60 min in air respectively. The
effect of calcination time on weight loss is shown in Fig. 13. The
weight loss remains constant at 37.5 wt% for a calcination time of
(c)
70
10
20
30
40
( )
50
60
1
5 min and more. This phenomenon suggests that the reactions
2
during calcination–combustion are fast. The XRD patterns of
combustion product at different calcination time are shown in
Fig. 14. A small peak for intermediate which is organic lead
Fig. 14. XRD patterns of calcination–combustion products at 350 8C with different
calcination times in air: (a) 15 min, (b) 20 min, and (c) 40 min.

1
708
L. Li et al. / Materials Research Bulletin 48 (2013) 1700–1708
0
0
0
0
0
.012
.009
.006
.003
.000
lead oxide with porous columnar shape are not integrity. It is
indicated that microstructure of nanostructural lead oxide can
influence on its electrochemical performance.
4. Conclusions
(a)
(b)
Preparation of nano-structural lead oxide has been investigated
by decomposition of lead citrate in inert (nitrogen) and air
atmospheres. The lead citrate (Pb
was synthesized from spent lead acid battery pastes in citrate salt
system. The citrate particle is in columnar shaped with length of 5–
3
(C
6
H
5
O
7
)
2
ꢀ3H
2
O), a precursor,
-0.003
5
0
m
m and diameter of 2–50
nitrogen gas, the major decomposition products are orthorhombic
phase -PbO, metallic Pb and elemental C.
mm. If the calcination is carried out in
0
0
0
0
.03
.02
.01
.00
(2)
b
When the calcination–combustion is performed in air, lead
citrate can be calcined completely at 350 8C for 20 min. The
morphology of products converts from porous columnar to
spherical structure with increasing temperature. Nano size
product from calcination–combustion is achieved with particle
(1)
size of around 100–200 nm. It is found to compose mainly of
with a small part of -PbO and Pb. Both in air and N
decomposition, CO and H O are the main gas products. The CV
curves of nanostructural lead oxide with spherical structure show
good reversible ability.
b-PbO
-
0.01
a
2
-0.02
(
3)
2
2
0
.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Ewe (V)
Acknowledgements
Fig. 15. Last three cyclic voltammograms of nanostructural lead oxide with 7 cycles
of scanning. (a) The sample with porous columnar shape was synthesized at 350 8C
for 1 h in air. (b) The sample with spherical structure was synthesized at 450 8C for
The authors would like to express thanks to the National
Science Council of China (NSC 50804017) for the financial support
and New Century Excellent Talents Project of Ministry of Education
1
h in air.
(
NCET-09-0392). And the authors would like to appreciate
3
.5. Characterization of lead oxide with electrochemical technique–
financial supports of the Wuhan Planning Project of Science and
Technology (20120321100) and the Key Program of Hubei
Provincial Natural Science Foundation for Distinguished Young
Scholars (2011CDA083). The authors would also like to extend the
thanks to Analytical and Testing Center of Huazhong University of
Science and Technology (HUST), which supplied the facilities for
materials analysis.
cyclic voltammetry
The lead oxide product with nano-size particulate will be used
as anode material of lead acid battery. The properties of this kind of
products were examined with electrochemical technique–cyclic
voltammetry (CV) [20]. In the current research, the electrochemi-
cal technique was employed to determine the property of different
nano-size lead oxide produced from the citrate precursor. Fig. 15
shows last three CV curves for 7 cycles of lead oxide. The lead
oxides were synthesized at 350 8C and 450 8C respectively in air.
They are of same crystal phase, but are different in microstructure
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