Materials Sciences and Applications, 2011, 215-219
doi:10.4236/msa.2011.24027 Published Online April 2011 (http://www.scirp.org/journal/msa)
Characterization and Application of Adsorption
Material with Hematite and Polystyrene
Dewen He1, Yutang Xiao2, Dingmin Liang1, Huannian Zhou1, Lu Du1, Lei Liu1
1School of Metallurgical Science & Engineering, Central South University, Changsha, China; 2School of Environmental Science and
Engineering, Nankai University, Tianjing, China
Received January 30th, 2011; revised February 10th, 2011; accepted February 25th, 2011.
ABSTRACT
In this study, a three-dimensional ordered macroporous hematite was prepared using the polystyrene colloid crystal
templates and characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, and
nitrogen adsorption isotherm. The as-prepared hematite shows a porous structure consisting of the macropores about
200 nm in diameter and the walls about 20 nm in thickness. The adsorption of Pb2+ and Cd2+ ions in aqueous solution
by this hematite was also evaluated. At room temperature, each gram hematite adsorbs 12.5 mg of Pb2+ ions and 7.0
mg of Cd2+ ions. The results suggest that the obtained hematite should be a promising adsorbent to remove Pb2+ and
Cd2+ ions, and other heavy metal ions from aqueous solution.
Keywords: Macroporous, Heavy Metal Ions, Adsorption, Pollution
1. Introduction
With rapid development of economics all over the word,
water pollution becomes a vital problem for people to
survive in the earth because the heavy metal ions are
detrimental to human health. Lead (Pb2+) and cadmium
(Cd2+) ions are toxic heavy metal ions that can enter hu-
man body through inhalation and ingestion from a vari-
ety of sources such as contaminated air and water, soil
and food [1,2]. The deposits of Pb and Cd compounds
are difficult to be absorbed but people can absorb their
soluble salts. Hence, it is very important for us to remove
Pb2+ and Cd2+ ions from water for consideration of the
health of human being. There are many articles discuss
the elimination of Pb2+ [3-5] and Cd2+ [6-8] ions from
aqueous solution. However, few of papers discuss the
effect of three-dimensional ordered macroporous (3DOM)
materials in water treatment.
Three dimensionally ordered macroporous (3DOM)
materials, which consisting of a large number of macro-
pores more than 100 nm in diameter and the walls less
than 100 nm in thickness, have been used as carriers
[9-13], adsorbents [14-17] and electrode materials [18-
23]. As adsorbents, 3DOM materials with a large specific
surface area and porosity are favorable to adsorption of
the heavy metal ions. Because of being available in large
quantity with relatively low cost, α-Fe2O3 (hematite) has
been widely used as an adsorbent to remove heavy metal
ions from water [7,24-28]. However, few people have
investigated the capability of the 3DOM α-Fe2O3 to re-
move Pb2+ and Cd2+ ions from aqueous solution.
Here we report the preparation of a 3DOM α-Fe2O3
material using polystyrene (PS) colloidal crystal template.
Its porous structure was characterized by nitrogen ad-
sorption isotherm plot, scanning electron microscopy (S-
EM) and transmission electron microscopy (TEM) mi-
crographs. Its adsorption capability of Pb2+ and Cd2+ ions
in aqueous solution was investigated as well.
2. Experimental
Polystyrene colloidal crystal spheres were synthesized
according to the method reported in the literature [29]. At
first, 2.8 g polyvinylpyrrolidone (PVP K30, Mw = 30000,
BASF) was dispersed in 200 ml deionized water forming
micelles under mechanical stirring. Subsequently, 0.1 g
K2S2O4 and 21 g styrene were added to the polymeric
solution. The mixed solution was deoxygenated by bub-
bling argon at room temperature for 1 h with gentle stir-
ring, and then polymerized at 70˚C for 24 h in an argon
atmosphere. Finally, the synthesized mono-dispersed PS
spheres were arrayed into the close packed colloidal
crystals by centrifuge (2000 r·min−1) for 24 h, and kept in
air at 50˚C for 48 h to evaporate the remaining water and
alcohol.

Characterization and Application of Adsorption Material with Hematite and Polystyrene
216
To prepare the 3DOM hematite, Fe2O3 needs to be
formed inside the template. First, the PS colloidal crystal
template prepared above was soaked in the solution of
1.5 mol·L−1 FeCl3 in glycol/methanol (3:2, by volume)
fro 8h. Then the solution was removed by filtration and
the template saturated with FeCl3 was dried at 50˚C un-
der vacuum for 10h to form the precursor. After that, the
dried precursor was heated from room temperature to
500˚C at a rate of 0.5˚C·min −1, and calcined at 500˚C for
10h in air. Finally, the porous hematite was obtained with
elimination of the PS template.
Morphology of the prepared Fe2O3 particles was ob-
served by Transmission electron microscope (TEM,
JEOL JEM 2100) and scanning electron microscope
(SEM, JSM-6360L). The crystalline structure was char-
acterized by X-ray diffraction pattern recorded on a Ri-
gaku D/max 2550 X-ray diffractometer. Differential
thermal analysis (DTA) and thermogravimetric analysis
(TGA) curves of the sample were recorded simultane-
ously on SDTQ 600 instrument ranged from ambient
temperature to 750˚C at a heating rate of 10˚C· min −1 un-
der air. The specific area of the obtained Fe2O3 was
measured using a Micromeritics Tristar ASAP 3000 BET
apparatus.
Heavy metal ion adsorption of the prepared hematite
was tested according to the literature [30]. 0.05 g of the
adsorbent were added to a 50 ml aqueous solution of
Pb(NO3)2 and Cd(NO3)2 at 16.4 and 10.6 mg·L−1, respec-
tively. The mixture was stirred for various times and then
centrifuged at 6000 rpm for 15 min. The concentrations
of Pb2+ and Cd2+ ions of the obtained clear solution were
measured using UV–vis spectroscopy after the solution
was adjusted to pH 2. Diphenylthiocarbazone and 1-(2-
pyridinylazo)-2-naohthalenol were used as the chro-
mogenic reagents for Pb2+ and Cd2+ ions, respectively.
3. Results and Discussion
Figure 1 shows the TG and DTA profiles of the precur-
sor. The weak endothermic peak below 100˚C can be
assigned to the evaporation of the remaining methanol
and water. The weight loss from 100˚C to 250˚C is at-
tributed to the evaporation of the remaining glycol in the
samples. The strong endothermic peaks in the tempera-
ture range of 250˚C - 450˚C result from the thermal de-
composition of PS template and the formation of Fe2O3
nanoparticles. No obvious endothermic/exothermic peaks
display above 450˚C suggesting that the PS template
should have decomposed completely and the pure Fe2O3
has formed.
Figure 2 shows the X-ray diffraction pattern of the
Fe2O3. The diffraction peaks of the as-prepared Fe2O3
agree very well with those reported in the literature[31],
where Fe2O3 was indexed as the rhombohedral α-Fe2O3
Figure 1. Differential thermal analysis (DTA) and thermo-
gravimetric analysis (TGA) plots of the precursors at a
heating rate of 10˚C·min−1 under air atmosphere from room
temperature to 700˚C.
[hematite: JCPDS 87-1166]. No other diffraction peaks
of impurities such as Fe3O4 and γ-Fe2O3 were observed.
The high intensities of the diffraction peaks indicate that
the prepared α-Fe2O3 has a perfect crystallization after
heated at 500˚C for 10 h under air atmosphere.
Figure 3 shows the TEM micrographs of the α-Fe2O3
particles. It can be seen that the α-Fe2O3 particles have
the porous structure with uniform pore size and display
3DOM morphology. The porous structure, as shown in
Figure 3, consists of the macropores about 200 nm in
diameter and the walls about 20 nm in thickness.
The nitrogen adsorption isotherm of the 3DOM
α-Fe2O3 is shown in Figure 4. It presents a type IV iso-
therm with hysteresis loop similar to that reported [32].
The specific surface area calculated by the Brunauer-
Emmett-Teller (BET) method and the pore volume de-
termined by the Barrett-Joyner-Halenda (BJH) approach
are 24.14 m2·g−1 and 0.053 cm3·g−1, respectively.
Figure 2. XRD pattern of the three-dimensional ordered
macroporous α-Fe2O3 material.
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Characterization and Application of Adsorption Material with Hematite and Polystyrene 217
Figure 3. TEM (b) micrographs of the three-dimensional
ordered macroporous α-Fe2O3 material.
0.0 0.1 0.2 0.30.4 0.5 0.60.7 0.8 0.9 1.0
0
5
10
15
20
25
30
35
40
Absorbed Volume (cm3 g-1)
R elative Pres sure (p/p0)
Figure 4. Nitrogen adsorption isotherm of the three-dimen-
sional ordered macroporous α-Fe2O3 material.
Figure 5 shows the adsorption rates of Pb2+ (a), Cd2+
(b) ions on the 3DOM α-Fe2O3 material in aqueous solu-
tions after various treatment times at room temperature.
We can see that the concentrations of the metal ions de-
crease quickly after the addition of the 3DOM α-Fe2O3
adsorbent. The adsorption capacities of 3DOM α-Fe2O3
for Pb2+ and Cd2+ ions are 12.5 and 7.0 mg per gram of
adsorbent, respectively. These values are higher than
those of the hematite hollow spindles and microspheres
[7], and similar to those of the ordered macroporous tita-
nium phosphonate materials [33], but lower than those of
the hybrid macroporous materials with thiol functional
groups [15] and the activated carbons with lager specific
surface area [34]. The data suggest that the 3DOM
α-Fe2O3 material needs further improvement before it can
be widely applied as adsorbent to remove the heavy
metal ions from aqueous solution despite of its low cost.
020406080100 120
0.0
0.2
0.4
0.6
0.8
1.0
T ime ( min )
C/C0
Pb2+
(a)
020 40 60 80100120
0.0
0.2
0.4
0.6
0.8
1.0
C/C0
Time (min)
Cd2+
(b)
Figure 5. Adsorption rates of Pb2+ (a), Cd2+ (b) ions on the
three-dimensional ordered macroporous α-Fe2O3 material
after various treatment times at room temperature.
4. Conclusions
The 3DOM α-Fe2O3 material was prepared using the PS
colloid crystal template successfully and showed the po-
rous structure, which is constructed with the 200-nm
sized macropores and the 20-nm thick walls. Due to this
special structure, its adsorption capacities of Pb2+ and
Cd2+ ions in aqueous solution were 12.5 and 7.0 mg per
gram adsorbent at room temperature, respectively. Com-
pared with other adsorbents, the obtained 3DOM α-Fe2O3
material is inexpensive but it needs some further modifi-
cations for its wide application to remove heavy metal
ions from aqueous solution.
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