Characterization and Application of Adsorption Material with Hematite and Polystyrene

doi:10.4236/msa.2011.24027

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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

E-mail: [email protected]

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.

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

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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