Novel polymeric chelating fibers for selective removal of mercury and cesium from water

Article abstract of DOI:10.1021/es0343104

We report here the synthesis and characterization of two new classes of chelating fibers, namely, (1) polymercaptopropylsilsesquioxane (PMPS) and (2) copper(II) ferrocyanide complexed with poly[1-(2-aminoethyl)-3-aminopropyl]silsesquioxane (Cu-FC-PAEAPS) fibers. These fibers were evaluated for selective removal of trace amount of mercury and cesium ions respectively in the presence of competing metal ions from water. The PMPS and Cu-FC-PAEAPS fibers were prepared by coating their corresponding soluble prepolymers, which are derived from mercaptopropyltrimethoxysilane and [1-(2-aminoethyl)-3-aminopropyl]trimethoxysilane monomers, respectively, on a glass fiber substrate, followed by a cross-linking step at 120 °C. The fibers were characterized through infrared spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). These novel materials are extremely efficient in removing low concentrations of mercury and cesium ions from water in the presence of high concentrations of sodium or potassium ions. They were shown to remove trace mercury and cesium contaminants effectively to well below parts per billion concentrations under a variety of conditions.

Full text of DOI:10.1021/es0343104

Environ. Sci. Technol. 2003, 37, 4261-4268
agents must be used to reduce effects of osmotic shock and
Novel Polymeric Chelating Fibers for
Selective Removal of Mercury and
Cesium from Water
to maintain the spherical form of the bead. Furthermore,
environmentally unfriendly solvents used including toluene,
methylene chloride, perchloethylene, and carbon tetrachlo-
ride, etc. are used in the synthesis and carry an added expense
not only in their initial cost but also in the EPA requirements
for handling spent solvents (4, 5).
C H U N Q I N G L I U , YO N G Q I N G H U A N G ,
N A T H A N I E L N A I S M I T H , A N D
J A M E S E C O N O M Y*
In recent years, Economy et al. (6-8) have developed a
new family of polymeric ion-exchange fibers using low-cost
glass fibers as substrate that display a number of important
advantages over conventional ion-exchange beads. These
include simplification of the overall synthesis including faster
more efficient functionalization, elimination of toxic solvents,
and overall process simplification. Another advantage of the
fibers is their ability to be easily fabricated into other
geometries including felts, papers, or fabrics, which exhibit
a greatly improved contact efficiency with the media. This
enhances both the rates of reaction and regeneration.
Additionally, physical and mechanical requirements of
strength and dimensional stability have been achieved by
use of a glass fiber substrate. The ion exchange fibers have
the potential to remove a wide range of contaminant ions
from water such as mercury, cadmium, lead, and cyanide
ions as well as radioactive ions such as cesium and strontium.
However, the ion exchange fibers are not particularly selective
to remove specific toxic ions from water in the presence of
high concentrations of nontoxic ions such as sodium and
potassium.
Recently, a new encouraging branch of research has
evolved on the synthesis of rationally designed materials
capable of specifically removing mercury or cesium from
aqueous systems (9-19). In particular, through the marriage
of ordered mesoporous silica materials with self-assembled
monolayer chemistry, a powerful new class of sorbent
materials functionalized with thiol groups (13) or copper(II)
ferrocyanide groups (19) has been designed for remediation
of mercury and cesium contamination, exhibiting both
excellent binding capacity as well as binding selectivity for
mercury and cesium ions, respectively. However, environ-
mentally hazardous solvents, such as toluene, were used in
the functionalization process of the materials (13, 19).
Furthermore, the final product is generally limited to small
particles, which may require costly containment systems.
Thus exploration of alternate synthesis strategies for prepar-
ing thiol- and copper(II) ferrocyanide-functionalized new
adsorbents may yield more cost-effective preparation tech-
niques.
Department of Materials Science and Engineering, University
of Illinois, 1304 West Green Street, Urbana, Illinois 61801
J O N A T H A N T A L B O T T
Illinois Waste Management and Research Center,
One East Hazelwood Drive, Champaign, Illinois 61820
We report here the synthesis and characterization of two
new classes of chelating fibers, namely, (1) polymer-
captopropylsilsesquioxane (PMPS) and (2) copper(II)
ferrocyanide complexed with poly[1-(2-aminoethyl)-3-
aminopropyl]silsesquioxane (Cu-FC-PAEAPS) fibers. These
fibers were evaluated for selective removal of trace
amount of mercury and cesium ions respectively in the
presence of competing metal ions from water. The PMPS
and Cu-FC-PAEAPS fibers were prepared by coating
their corresponding soluble prepolymers, which are derived
from mercaptopropyltrimethoxysilane and [1-(2-aminoethyl)-
3-aminopropyl]trimethoxysilane monomers, respectively,
on a glass fiber substrate, followed by a cross-linking step
at 120 °C. The fibers were characterized through infrared
spectroscopy, scanning electron microscopy (SEM),
and thermogravimetric analysis (TGA). These novel materials
are extremely efficient in removing low concentrations
of mercury and cesium ions from water in the presence
of high concentrations of sodium or potassium ions. They
were shown to remove trace mercury and cesium
contaminants effectively to well below parts per billion
concentrations under a variety of conditions.
Introduction
Mercury pollution has been identified as a serious problem
at waste-contaminated sites (1). One estimate of the total
annual global input of mercury to the atmosphere from all
sources including natural, anthropogenic, and oceanic
emissions is 5500 tons (2), prompting the establishment of
increasingly stringent government regulations demanding
that levels of this contaminant be lowered. Radioactive cesium
contamination of water is also of serious social and envi-
ronmental concern since it is a significant fraction of the
radioactivity of the liquid waste (3). The separation of mercury
and cesium from various solutions has been done for many
years principally using ion exchange, solvent extraction, or
precipitation processes. However, all of these processes have
some impediments for use in industrial applications. For
example, there are a number of drawbacks associated with
the traditional approach to ion exchange bead synthesis.
During functionalization of the polymeric systems, swelling
In the present study, we designed two new kinds of
chelating fibers that show extremely high selectivity for
mercury and cesium respectively, by coating a low-cost glass
fiber substrate with organosilsesquioxane prepolymers, fol-
lowed by a cross-linking step. The polymeric chelating
materials as fibers do not need complex synthetic procedures
and expensive containment systems, unlike the powder form
of mesoporous organosilica materials.
Experimental Methods
Materials. Mercaptopropyltrimethoxysilane and [1-(2-ami-
noethyl)-3-aminopropyl]trimethoxysilane were purchased
from Gelest Inc. and used without further purification. The
substrate fiber was a nonwoven fiberglass mat, Craneglass
230 (0.015 nominal, fiber diameter of 6.5 µm), made by CRANE
& CO.
Characterization. FTIR spectra of the polymers were
obtained on KBr pellets using a Nicolet Magna IR TM
spectrophotometer 550. A Varian Mercury 400 spectrometer
* Corresponding author phone: (217)333-9260; fax: (217)333-2736;
e-mail: jeconomy@uiuc.edu.
9
10.1021/es0343104 CCC: $25.00
Published on Web 08/19/2003
2003 Am erican Chem ical Society
VOL. 37, NO. 18, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 4 2 6 1

FIGURE 1. Synthesis of PMPS fibers.
operating at 400.2 MHz (1H) and 100.6 MHz was used to
record 1H and 13C NMR spectra. 29Si NMR spectra were
obtained with a Varian Chemagnetics Infinity Plus 500
spectrometer operating at 99.3 MHz. Average molecular
weights (Mn) and distributions were measured using gel
permeation chromatography (GPC) performed in N-meth-
ylpyrolidinone (NMP) with 0.05 M LiBr at 25 °C. GPC was
carried out using a series of three light scattering (7.8 × 300
mm) columns filled with a mixed bed of 10 µm Polymer
Laboratories Pl gel, a Waters 515 HPLC pump, and a Viscotek
model 300 triple detector array. Polystyrene was used as a
standard for the calculation of the Mw. TGA measurements
were performed on a Hi-Res TA Instruments 2950 Thermo-
gravimetric Analyzer. SEM images were acquired using a
Hitachi S4700 scanning electron microscope with an ac-
celeration voltage of 5 kV. Mercury was determined in
adsorption isotherm solutions with a PS Analytical Cold Vapor
Atomic Fluorescence Spectrometer. Sodium was measured
with a Varian 300+ Atomic Absorbance (AA) Spectrometer.
A Thermo Elemental ExCell Inductively Coupled Plasma Mass
Spectrometer (ICP-MS) was used to determine solution
concentrations of Cs, Cr, Zn, Ag, Ba, and Pb.
Synthesis of 1-(2-Am inoethyl)-3-am inopropylsilsesqui-
oxane (AEAPS) Prepolym er. To a stirred 50 mL round-
bottomed flask containing 10.0 g (45 mmol) of [1-(2-
aminoethyl)-3-aminopropyl]trimethoxysilane was added
dropwise a sodium hydroxide aqueous solution (0.03 g (0.75
mmol) of NaOH in 2.43 g (0.14 mol) of water) at room
temperature. The reaction mixture was allowed to stir at 60
°C for 3 h and then at 80 °C for 12 h. All the low molecular
weight components including methanol, water, hydrolyzed
[1-(2-aminoethyl)-3-aminopropyl]trimethoxysilane, etc. were
removed under reduced pressure. Yield: 96%. The resulting
sticky oil was diluted with ethanol to produce two AEAPS
solutions at 10 wt % (AEAPS-10%) and 20 wt % (AEAPS-20%).
Preparation of Thiol-Functionalized Polym ercaptopro-
pylsilsesquioxane (PMPS) Chelating Fibers. A glass fiber
substrate was dip-coated with a MPS-10% (or MPS-20%)
solution for 1 min, and placed on a fine mesh screen. The
coated glass fibers were dried in a hood at room temperature
for 30 min. The dried fibers were cured at 80 °C for 12 h and
then at 120 °C for 48 h in a vacuum oven. The cured fibers
were allowed to cool to room temperature slowly and weighed
immediately. The final thiol-functionalized chelating fibers
prepared from MPS-10% and MPS-20% coating solutions
are designated as PMPS-10% and PMPS-20%, respectively.
Weight gains for the PMPS-10% and PMPS-20% fibers after
coating were 50% and 85%, respectively.
Synthesis of Mercaptopropylsilsesquioxane (MPS) Pre-
polym er. To a stirred 50 mL round-bottomed flask containing
19.6 g (0.1 mol) of mercaptopropyltrimethoxysilane was
added 0.01 g (0.078 mmol) of 30% aqueous hydrochloric acid
at room temperature. The acidified silanes were then
hydrolyzed by the dropwise addition of 5.4 g (0.3 mol) of
water. The reaction mixture was allowed to stir at room
temperature for 2 h and then at 60 °C for 12 h. All the low
molecular weight components including methanol, water,
hydrolyzed mercaptopropyltrimethoxysilane, etc. were re-
moved under reduced pressure. Yield: 94%. The resulting
sticky oil was diluted with ethanol to produce two MPS
solutions with 10 wt % (MPS-10%) and 20 wt % (MPS-20%)
concentrations.
Preparation of Ethylenediam ine-Functionalized Poly-
[1-(2-am inoethyl)-3-am inopropyl]silsesquioxane (PAEAPS)
Chelating Fibers. A glass fiber substrate was dip-coated with
a AEAPS-10% (or AEAPS-20%) solution for 1 min and placed
on a fine mesh screen. The coated glass fibers were dried in
a hood at room temperature for 30 min. The dried fibers
were cured at 80 °C for 12 h and then at 120 °C for 72 h in
a vacuum oven. The cured fibers were allowed to cool to
room temperature slowly and weighed immediately there-
after to determine yield. The final ethylenediamine-func-
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FIGURE 3. FTIR spectra of (a) original Crane-230 glass fiber substrate
and (b) PMPS-10% fiber.
FIGURE 2. 1H NMR spectra of (a) mercaptopropyltrimethoxysilane
and (b) MPS (solvent: ethanol-d6).
tionalized chelating fibers prepared from AEAPS-10% and
AEAPS-20% coating solutions were designated as PAEAPS-
10% and PAEAPS-20%, respectively. Weight gains for the
PAEAPS-10% (from AEAPS-10%) and PAEAPS-20% (from
AEAPS-20%) fibers after coating were 40% and 74%, respec-
tively.
Im m obilization of Copper(II) onto PAEAPS Chelating
Fibers (Cu-PAEAPS). PAEAPS-10% (0.3 g) (or 0.2 g of PAEAPS-
20%) fibers were stirred in a 100 mL aqueous solution of 0.06
M copper(II) chloride for 6 h to produce Cu-PAEAPS-10%
and Cu-PAEAPS-20% fibers, respectively. The metallized
fibers were collected, washed with DI water, washed in
2-propanol, and dried in oven at 80 °C overnight to give
Robin’s egg blue fibers.
Im m obilization of Ferrocyanide onto Cu-PAEAPS-10%
and Cu-PAEAPS-20% Fibers (Cu-FC-PAEAPS). Cu-PAEAPS-
10% (1.0 g) (or 0.5 g of Cu-PAEAPS-20%) in chloride form
was converted to the hexacyanoferrate (II) form by shaking
with a 50 mL solution of 0.25 M Na4Fe(CN)6 for 3 h. The
fibers were thoroughly washed with high purity water to
remove dissolved salts, air-dried, and stored for use. The
final composite fibers were reddish brown in color and
designated as Cu-FC-PAEAPS-10% and Cu-FC-PAEAPS-20%
from Cu-PAEAPS-10% and Cu-PAEAPS-20%, respectively.
Hydrolytic Stability Test of PMPS and PAEAPS Fibers.
The PMPS (or PAEAPS) fibers were mixed with water and
refluxed for 2 days. The fibers were then dried at 80 °C for
12 h in a vacuum oven, allowed to cool to room-temperature
slowly, and weighed.
FIGURE 4. SEM images of (a) original Crane-230 glass fiber substrate
and (b) PMPS-10% fiber.
Equilibration Adsorption Isotherm Experim ents of
PMPS Fibers with Mercury Solutions. Tenth gram samples
of PMPS-10% (or PMPS-20%) fibers were equilibrated with
10 mL solutions containing various concentrations of mercury
at room temperature. After the mixtures were shaken for 2
h, they were filtered through a 0.22 µm Nylon 66 filter and
analyzed by atomic fluorescence for residual metal content.
Mercury Sorption Kinetics. Kinetic experiments were
conducted in the same fashion as the adsorption isotherm
experiments, except that the mixtures were shaken for 1 min,
5 min, 30, 60, and 120 min, respectively, then filtered through
9
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FIGURE 5. Synthesis of PAEAPS fibers.
a 0.22 µm Nylon 66 filter, and analyzed by atomic fluorescence
for residual metal content.
groups into the side chains of cross-linked polysilsesquioxane
coated glass fibers in order to efficiently remove mercury
from contaminated aqueous solutions. Trimethoxysilane with
a thiol group was used to prepare mercaptopropylsilses-
quioxane (MPS). The MPS was synthesized by hydrolysis and
condensation of mercaptopropyltrimethoxysilane in the
presence of hydrochloric acid catalyst (Figure 1). Figure 2
illustrates the 1H NMR spectra of mercaptopropyltrimethoxy-
silane monomer and MPS. The strong sharp peak at 3.5 ppm,
representing methoxyl group hydrogens in the spectrum of
the monomer (Figure 2a), disappears in the spectrum of MPS
(Figure 2b, the weak peak at 3.55 ppm is from EtOD) and
indicates complete hydrolysis of the Si-OCH3 groups.
Moreover, the peaks assigned to Si-CH2, Si-CH2-CH2, and
Si-CH2CH2CH2 in the spectrum of MPS are broad compared
with the sharp peaks in the spectrum of the monomer,
suggesting formation of the prepolymer. MPS has an average
molecular weight (Mn) of 1650 and a polydispersity of 3.4 as
measured by GPC. 29Si NMR shows that it has two charac-
teristic signals of T2 and T3, with a ratio of 45:55.
Regeneration Studies on Mercury-Loaded PMPS Fibers.
Mercury-loaded PMPS-10% fibers were soaked in a con-
centrated HCl (10.1 M) solution for 12 h. The mixture was
filtered, and the mercury concentration in the filtrate was
determined by Atomic Fluorescence Spectrometry. The
leached fibers were rinsed with DI water and oven dried at
60 °C overnight prior to reuse. Tenth gram samples of leached
PMPS-10% fibers were allowed to equilibrate in 10 mL
solutions of 3.0 ppm mercury and 2300 ppm sodium for 2
h with shaking at room temperature. The solution was filtered
through a 0.22 µm Nylon 66 filter and analyzed for mercury
by Atomic Fluorescence Spectrometry and for sodium by
AA.
Equilibrium Adsorption Isotherm Experim ents of Cu-
FC-PAEAPS Fibers with Cesium Solutions. Tenth gram
samples of Cu-FC-PAEAPS-10% (or Cu-FC-PAEAPS-20%)
fibers were allowed to equilibrate at room temperature in 10
mL of solutions containing various concentrations of cesium
for 2 h with shaking. After equilibration the solution was
filtered through a 0.22 µm Nylon 66 filter and analyzed by
ICP-MS for residual metal content.
The thiol-functionalized MPS solution was dip-coated on
a Crane-230 glass fiber substrate, followed by curing to form
an insoluble cross-linked network structure. The FTIR spectra
of the original Crane-230 fiber and PMPS-10% fiber are shown
in Figure 3. It can be seen that there is no apparent absorption
band in the spectrum of the original fiber, while several
absorption bands appear in Figure 3b after coating. An
absorption band displayed in Figure 3b at 2559 cm-1 is
characteristic of a stretching vibration for thiol groups. The
broad band from 3600 to 3100 cm-1 is a conspicuous feature
of an O-H stretching vibration and indicates the existence
of some Si-OH groups on the coated fiber. Additionally, the
typical absorption band at 2930 cm-1 stands for the stretching
vibration for C-H. The strong peak in the region of 1031
cm-1 to 1124 cm-1 is due to the Si-O stretching vibration of
Cesium Sorption Kinetics. Kinetic experiments were
conducted in the same fashion as equilibrium adsorption
isotherm experiments, except that the mixtures were shaken
for 1 min, 5 min, 30, 60, and 120 min, respectively, then
filtered through a 0.22 µm Nylon 66 filter, and analyzed by
ICP-MS for residual metal concentrations.
Results and Discussion
Synthesis and Characterization of Thiol-Functionalized
PMPS Fibers. Thiol functional groups have been recognized
to be efficient chelating ligands for mercury and other heavy
metals such as lead and silver. Here, we incorporate the thiol
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propyl]silsesquioxane (AEAPS) was prepared by hydrolysis
and condensation of [1-(2-aminoethyl)-3-aminopropyl]tri-
methoxysilane using NaOH as a catalyst (Figure 5). The
structure of AEAPS was confirmed by 1H, 13C, and 29Si NMR
1
spectra. It is evident from the H NMR spectrum in Figure
6 that all hydrogen peaks assigned to the monomer broaden
after hydrolysis and condensation. Furthermore, the strong
sharp peak, designated as f in Figure 6a and representing
methoxyl group hydrogens in the monomer, disappears after
condensation and indicates that hydrolysis of the Si-OCH3
groups is complete. GPC measurement revealed that the as-
synthesized AEAPS has a Mn of 1540 and polydispersity of
3.5.
The immobilization of copper ferrocyanide into PAEAPS
fibers was carried out following procedures described
elsewhere (19). Figure 7, after Fryxell et al. (19), illustrates
the synthetic procedures. Figure 8 shows the FTIR spectra
of (a) the original Crane-230 fiber, (b) PAEAPS-10% fiber,
and (c) Cu-FC-PAEAPS-10% fiber. Several absorption bands
evident in Figure 8a,b and representing vibrations of NH
and NH2 groups at 3600 cm-1 to 3100 cm-1, 1665 cm-1 and
928 cm-1, and the stretching vibration of Si-O-Si bonds at
1030-1127 cm-1 appear after the PAEAPS polymer is coated
on the fiber substrate. Moreover, a new strong absorption
peak appears at 2095 cm-1 in Figure 8c. This intense peak
is characteristic of numerous cyanide groups and confirms
successful immobilization of copper ferrocyanide on the
surface of the fibers.
SEM images of the original Crane-230 fiber and of the
PAEAPS-10% fiber are illustrated in Figure 9. By comparing
these two images, it is evident that most of the PAEAPS
polymer is coated on the surface of the fibers rather than
lodging in the void volume between the fibers. As with PMPS-
coated fibers, the void volume facilitates diffusion and access
of metal ions to chelating sites on the surface of the fibers.
TGA results indicate that the PAEAPS fibers are also thermally
stable up to 250 °C. In addition, the weight loss of less than
5% for the PAEAPS coated fibers after refluxing in water for
2 days indicates that the PAEAPS polymer coating on the
fibers is hydrolytically stable.
Equilibrium Adsorption Experim ents for Mercury. The
ability of PMPS fibers to adsorb mercury from contaminated
solutions under a wide range of conditions was investigated.
Table 1 summarizes ion concentrations of several different
contaminated solutions before and after treatment with
PMPS-10% and PMPS-20% fibers. It can be seen from Table
1 that a single treatment with either PMPS-10% or PMPS-
20% fiber reduces the mercury concentration in solution to
well below the U.S. Environmental Protection Agency’s
regulatory limit for this contaminant in hazardous waste and
even below the drinking water standard. Likewise, silver
concentrations were reduced to sub-ppb levels. Lead also
was reduced to below its respective regulatory limit for a
hazardous waste.
The equilibrium adsorption experiments for mercury
shown in Table 1 were performed in the presence of a large
excess of background ions, such as sodium, barium, and
zinc. The adsorption tests show that sodium, barium, and
zinc do not chelate to PMPS and that PMPS materials remain
effective for Hg adsorption in the presence of high concen-
tration of such ions. The selectivity of the PMPS coated fiber
for mercury can be inferred from its distribution coefficient
(Kd) for mercury (Table 1). Kd is a measure of the affinity of
an ion exchanger for a particular ion and an indicator of the
selectivity of the ion exchanger to the particular ion in the
presence of a complex matrix of interfering ions (19). As
indicated from the results in Table 1, the mercury distribution
coefficients for all the equilibrium adsorption experiments
are in excess of 299 900 mL/ g, and some of them are even
significantly in excess of 1 500 000 mL/ g.
FIGURE 6. 1H NMR spectra of (a) [1-(2-aminoethyl)-3-aminopropyl]-
trimethoxysilane and (b) AEAPS (solvent: ethanol-d6).
the Si-O-Si bond. These FTIR results not only confirm that
PMPS has been coated on the glass fiber substrate successfully
but also prove that thiol groups on PMPS remain intact after
curing. Figure 4 shows the SEM images of the original Crane-
230 fiber and the PMPS-10% fiber. It can be concluded by
comparing these two images that, although some bridging
exists, most of the PMPS polymer is coated on the surface
of the fibers rather than occurring randomly within the void
volume between the fibers. The remaining void volume
facilitates diffusion and access of metal ions to thiol groups
on the surface of the fibers. Thermogravimetric analysis (TGA)
revealed that both PMPS-10% and PMPS-20% fibers are
thermally stable up to 250°C. Additionally, the PMPS polymer
coating on the surface of the fibers is hydrolytically stable.
Weight loss of the coated fiber after refluxing in water for 2
days was less than 2%.
Synthesis and Characterization of Cu-FC-PAEAPS Fi-
bers. Based on previous studies by Fryxell and co-workers
(19), it is known that copper ferrocyanide groups are highly
selective for cesium ion. In this work, we synthesized a
polyorganosilsesquioxane containing copper ferrocyanide
groups on a glass fiber matrix. [1-(2-Aminoethyl)-3-amino-
9
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FIGURE 7. Synthesis of Cu-FC-PAEAPS fibers.
sodium (2170 ppm) was tested by the PMPS-10% fibers. It
was observed that the PMPS-10% fibers could selectively
reduce the mercury concentration to 43 ppm with negligible
adsorption of sodium. A mercury loading capacity of 0.16
mmol per gram of PMPS-10% fibers (equivalent to 32 mg/ g)
has been observed.
Equilibrium Adsorption Experim ents for Cesium . The
ability of Cu-FC-PAEAPS fibers to remove cesium from
contaminated solutions also was measured under a wide
range of conditions. Table 2 shows the ion concentrations
of several different contrived solutions before and after
treatment with Cu-FC-PAEAPS-10% and Cu-FC-PAEAPS-20%
fiber materials. The equilibrium results from Table 2 show
that a single treatment with either Cu-FC-PAEAPS-10% or
Cu-FC-PAEAPS-20% fiber material reduces a 2 ppm cesium
solution to below 4 ppb (nearly 100% removed), even at high
concentrations of sodium or potassium from both neutral
and acidic solutions.
The equilibrium adsorption experiments in Table 2 show
that sodium and potassium are not sorbed by Cu-FC-PAEAPS
fibers, and the chelating materials remain effective in the
presence of high concentrations of such ions. The selectivity
of the Cu-FC-PAEAPS fibers for cesium is apparent from its
distribution coefficient (Kd) for this element. Results for Kd
from 56 000 mL/ g to 203 000 mL/ g are reported in Table 2.
Figure 11 shows the sorption kinetics of Cu-FC-PAEAPS-
10% fiber material with cesium in the presence of high
concentrations of sodium. The figure illustrates that Cu-FC-
PAEAPS-10% fibers can reduce a 2.0 ppm cesium solution
to less than 7 ppb within 5 min and to less than 4 ppb within
2 h at a solution-to-solid ratio of 200 mL/ g. While sorption
kinetics of the Cu-FC-PAEAPS fiber material for cesium are
remarkably fast, it is a little bit slower than that of MCM-41
FIGURE 8. FTIR spectra of (a) original Crane-230 glass fiber substrate,
(b) PAEAPS-10% fiber, and (c) Cu-FC-PAEAPS-10% fiber.
Figure 10 shows the sorption kinetics of PMPS-10% fiber
material with mercury in the presence of a high concentration
of sodium. It can be seen from the figure that PMPS-10%
fibers can reduce a 3.0 ppm mercury solution to less than
0.06 ppm within 30 min and to less than 5 ppb within 2 h,
at a solution-to-solid ratio of 200 mL/ g.
In addition to two low initial mercury concentrations (3
and 6 ppm) tested, an initial high concentration of mercury
(109 ppm) in water in the presence of high concentration of
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FIGURE 10. Changes of mercury concentrations as a function of
time in the sorption reaction of PMPS-10%. Initial Hg concentra-
tion: 3.0 ppm in 0.1 M NaNO , 10 mL of solution, and 0.05 g of
3
PMPS-10%.
TABLE 2. Analyzed Concentrations of Cesium in Aqueous
Solutions before and after Treatment with Cu-FC-PAEAPS-10%
and Cu-FC-PAEAPS-20% Fiber Materialsa
Cs concentration (ppb) (K of Cs, mL/g)
d
after treatment after treatment
before
with Cu-FC-
with Cu-FC-
solution
treatment PAEAPS-10% PAEAPS-20%
0.01 M NaNO3
1 M NaNO3
3 M NaNO3
M NaNO3 + 0.1 M HNO3
1 MKNO3
1900
2210
2040
2030
2320
2.0 (94 900)
2.2 (100 354) 1.2 (184 067)
3.6 (56 566)
1.2 (169 067) 1.0 (202 900)
1.5 (154 566)
1.0 (189 900)
a
Ten m illiliters of solution, 0.1 g of Cu-FC-PAEAPS.
FIGURE 9. SEM images of (a) original Crane-230 glass fiber substrate
and (b) PAEAPS-10% fiber.
TABLE 1. Analyzed Concentrations of Metal Contaminants in
Aqueous Solutions before and after Treatment with PMPS-10%
and PMPS-20% Fiber Materialsa
Hg concentration (ppm)
K of Hg
d
solution
Hg
Ag
Cr
Pb
Ba Zn
Na
(mL/g)
Initial Solution
1
2
3.0
6.1
2300
7.4 1.8 2250
0.21 0.59 2.6
after Treatment with PMPS-10%
1′
2′
0.0010
2210 299 900
0.0011 <0.002 0.32 <0.002 6.6 0.47 2270 554 354
after Treatment with PMPS-20%
1′′
2′′
0.0009
2200 333 233
0.00016 <0.002 0.15 0.0105 6.6 1.08 2220 3 812 400
a
Ten m illiliters of solution, 0.1 g of PMPS. Kd ) [(Co-Cf)/Cf]*(V/M),
where Co is the initial concentration of Hg (m g/m L), Cf is the equilibrium
concentration of Hg (m g/m L), V is the volum e of the testing solution
(m L), and M is the am ount of PMPS (g).
FIGURE 11. Changes of cesium concentrations as a function of time
in the sorption reaction of Cu-FC-PAEAPS-10%. Initial Cs concen-
tration: 2.0 ppm in 0.1 M HNO /0.1 M NaNO , 10 mL of solution, and
type mesostructured silicas (19). This may be due to the lack
of mesopores in the Cu-FC-PAEAPS polymer coating on the
glass fibers, which facilitate the diffusion of cesium into the
chelating sites. Additional experiments are in progress to
modify the structure of the Cu-FC-PAEAPS polymer coating
on glass fibers and further improve sorption kinetics of the
material.
Regeneration Study of Mercury-Loaded PMPS Fibers.
The treatment of mercury-loaded PMPS-10% fibers with a
concentrated HCl (10.1 M) solution for 12 h resulted in 100%
3
3
0.05 g of Cu-FC-PAEAPS-10%.
removal of the loaded mercury. The leached PMPS-10% fibers
were then subjected to a second round of mercury adsorption
test. It is shown that the leached fibers were able to remove
99% of mercury from the original 3.0 ppm of mercury aqueous
solution in the presence of a high concentration of sodium.
After a third regeneration cycle, the PMPS-10% fibers were
still able to remove 97% of mercury from the original 1.7
9
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(3) Northrup, C. J.; Jardine, L. J.; Steindler, M. J. IAEA-SM-261/ 31;
International Atomic Energy Agency: Vienna, 1983; p 461.
(4) Pontius, F. W.; Clark, S. W. Water Quality and Treatment, 5th
ppm of mercury in water. It is estimated that five cycles of
regeneration are possible for the PMPS fibers.
The regeneration of the cesium-loaded Cu-FC-PAEAPS
fibers could possibly be realized by the reduction of Fe(III)
back to Fe(II) using hydrazine as the reducing agent (20).
This study is currently in progress.
ed.; Letterman, R. D., Ed.; McGraw-Hill Inc.: 1999; Chapter 1.
(5) U.S. Environmental Protection Agency, Ground Water & Drink-
ing Water. http:/ / www.epa.gov/ safewater/ mcl.html (accessed
June 2003).
(6) Economy, J.; Dominguez, L.; Mangun, C. L. Ind. Eng. Chem.
Res. 2002, 41, 6436-6442.
Conclusions
(7) Dominguez, L.; Benak, K.; Economy, J. Polym. Adv. Technol.
2001, 12 (3-4), 197-205.
(8) Economy, J.; Dominguez, L.; Benak, K. PCT Int. Appl., WO 01/
97973 A1, 2001.
Two new classes of chelating fibers, polymercaptopropyl-
silsesquioxane (PMPS) and copper(II) ferrocyanide com-
plexed poly[1-(2-aminoethyl)-3-aminopropyl]silsesquioxane
(Cu-FC-PAEAPS) fibers, have been synthesized for the
selective removal of trace amounts of mercury and cesium
ions, respectively, from water, in the presence of competing
metal ions. Unlike previous work on these chelating polymers,
these materials are supported on inexpensive glass fibers
that can be manufactured into a variety of structures for
practical applications. The PMPS and Cu-FC-PAEAPS fibers
are rugged and highly selective for and extremely efficient
at removing low concentrations of mercury and cesium from
water in the presence of high concentrations of sodium or
potassium. Sorption kinetics for each of the novel chelating
fibers is relatively fast.
(9) Mercier, L.; Detellier, C. Environ. Sci. Technol. 1995, 29, 1318-
1323.
(10) Izatt, R. M.; Bradshaw, J. S.; Bruening, R. L. Pure Appl. Chem.
1996, 68, 1237-1241.
(11) Bibby, A.; Mercier, L. Chem. Mater. 2002, 14, 1591-1597.
(12) Mercier, L.; Pinnavaia, T. J. Adv. Mater. 1997, 9, 500-503.
(13) Feng, X.; Fryxell, G. E.; Wang, L. Q.; Kim, A. Y.; Liu, J.; Kemner,
K. M. Science 1997, 276, 923-926.
(14) Mercier, L.; Pinnavaia, T. J. Micropor. Mesopor. Mater. 1998, 20,
101-106.
(15) Lim, M. H.; Blanford, C. F.; Stein, A. Chem. Mater. 1998, 10,
467-470.
(16) Mercier, L.; Pinnavaia, T. J. Environ. Sci. Technol. 1998, 32, 2749-
2754.
Acknowledgments
(17) Brown, J.; Mercier, L.; Pinnavaia, T. J. Chem. Commun. 1999,
1, 69-70.
(18) Brown, J.; Richer, R.; Mercier, L. Micropor. Mesopor. Mater. 2000,
37, 41-48.
(19) Lin, Y.; Fryxell, G. E.; Wu, H.; Engelhard, M. Environ. Sci. Technol.
2001, 35, 3962-3966.
This work is supported by the Science and Technology Center
(STC) program of the National Science Foundation (NSF)
under Agreement Number CTS-0120978. We also appreciate
the free fiberglass mat materials provided by CRANE & CO.
(20) Clarke, T. D.; Wai, C. M. Anal. Chem. 1998, 70, 3708-3711.
Literature Cited
(1) U.S. Environmental Protection Agency, Mercury. http:/ /
www.epa.gov/ mercury/ information.htm (accessed June 2003).
(2) U.S. Environmental Protection Agency, Mercury Study Report
to Congress: Overview. http:/ / www.epa.gov/ airprogm/ oar/
mercover.html (accessed June 2003).
Received for review April 6, 2003. Revised manuscript re-
ceived June 26, 2003. Accepted July 14, 2003.
ES0343104
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