Modifying polymer flocculants for the removal of inorganic phosphate from water

Article abstract of DOI:10.1016/j.tetlet.2011.07.130

Due to strong hydrogen bonding interactions, thiourea has been shown to have a high affinity for anions such as inorganic phosphate. The interaction between phosphate and thiourea has been used to develop technologies that can detect and even remove phosp

Full text of DOI:10.1016/j.tetlet.2011.07.130

Tetrahedron Letters 52 (2011) 5241–5244
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Modifying polymer flocculants for the removal of inorganic phosphate
from water
Timothy S. Goebel a,b, ,à, Kevin J. McInnes a, , Scott A. Senseman a, , Robert J. Lascano b,à, Lucas S. Marchand c,§
,
Todd A. Davis c,
⇑
a Department of Soil and Crop Sciences, Texas A&M University, 2474 TAMU, College Station, TX 77843 2474, USA
b USDA Wind, Erosion, and Water Conservation Unit, 3810 4th Street, Lubbock, TX 79415, USA
c Department of Chemistry, Idaho State University, 921 8th Ave., Pocatello, ID 83209, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 4 August 2011
Due to strong hydrogen bonding interactions, thiourea has been shown to have a high affinity for anions
such as inorganic phosphate. The interaction between phosphate and thiourea has been used to develop
technologies that can detect and even remove phosphate from water. This research investigates the use of
thiourea derivatized polymer flocculants for the sequestering of inorganic phosphate from water. The
study presented herein describes the development of a thiourea based monomer that was used to create
a bi-functional polymer that flocculates suspended solid material as well as sorbs phosphate, removing
both from water. The new polymer removed more than 60% of the phosphate from a simulated wastewa-
ter sample. The addition of a thiourea trapping group to the polymer more than doubled the amount of
phosphate removed from solution compared to control polymers.
Ó 2011 Elsevier Ltd. All rights reserved.
Introduction
H2O).13 To display the utility of these trapping groups, Kugimiya
showed that thiourea molecular imprinted polymers can be used
Inorganic phosphate contamination leads to a variety of envi-
ronmental problems with water resources including increased algal
blooms, bacterial contaminations, and eutrophication.1 Phosphate
contamination can be attributed to a variety of factors including
runoff from agricultural fields, land application of wastewater from
confined animal feeding operations, and municipal wastewater. To
help alleviate these adverse effects of phosphate on the environ-
ment, methods for the removal of inorganic phosphate from water
are needed.
Thiourea/urea derived organic molecules have been used exten-
sively in the area of molecular recognition for a variety of anions.2–13
Due to the hydrogen bonding ability of urea/thiourea, these mole-
cules have been used as molecular hosts for carboxylates, halogens,
lactones, sulfur, and phosphorous containing anions. Recently, Gun-
nlaugsson and co-workers showed that strategically adding a third
hydrogen-bonding moiety to a urea molecular host can greatly in-
crease anion binding in a variety of solvents such as acetonitrile.
Althougha hydrogen bonding interaction was observed in non-polar
and polar aprotic solvents, binding was completely reversible and
the complex disseminated in highly polar solvents (methanol and
for the removal of inorganic phosphate from water.14 In a simulated
wastewater study the thiourea imprinted polymer was able to re-
move up to 75% of the inorganic phosphate.15 The successful utiliza-
tion of hydrogen bonding capabilities of thiourea in these diverse
applications suggested that a derivatized polymer flocculant should
increase its sorption capacity for phosphate. Polymer flocculants are
routinely used to remove solid material from water. These polymers
interact with the surface of suspended solids, organizing the individ-
ual particles into larger structures called flocs. The flocs then settle
out of solution faster as the flocs have a larger diameter than the
individual particles. The addition of the thiourea group to a polymer
flocculent should increase the sorption capacity for phosphate,
while maintaining the ability to remove sorbed phosphate through
settling of suspended materials. Although polymer flocculants are
generally used for the removal of solid material from solution, this
is the first example of their modification with a thiourea-trapping
group for the removal of inorganic phosphate (H2POÀ) in solution.
4
Results and discussion
The synthesis of the thiourea monomers was conducted using a
modified method developed by Elsabee and co-workers.16 For the
synthesis of the substituted thioureas (1 and 2); acroyl chloride
was reacted with ammonium thiocyanate followed by aniline (1)
or o-phenylenediamine (2). The yields for these reactions were
excellent proceeding in 88% yield for (1) and 75% for (2) (Scheme 1).
⇑
Corresponding author. Tel.: +208 221 5657; fax: +208 282 4373.
E-mail addresses: tim.goebel@usda.ars.gov (T.S. Goebel), k-mcinnes@tamu.edu
(K.J. McInnes), davitodd@isu.edu (T.A. Davis).
Tel.: +979 845 5986; fax: +979 845 0456.
Tel.: +806 749 5560; fax: +806 723 5272.
Tel.: +208 282 2668; fax: +208 282 4373.
à
§
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.07.130

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T. S. Goebel et al. / Tetrahedron Letters 52 (2011) 5241–5244
inorganic phosphate, while the remaining shows an increase in
1. N
S-+NH4
H2POÀ from 0.5–2.0 equiv (Fig. 1). As observed in the NMR spectra
Acetone
4
an increase in H2POÀ concentration leads to a significant decrease
4
°
0 C
N2
in both of the thiourea (11.60 and 12.65 ppm, Ha and Hb) signals
O
S
O
indicating a hydrogen bonding interaction between the monomer
and H2POÀ.
N
H
N
H
Cl
2.
4
Figure 2 displays the 1H NMR of the three-point monomer (2)
NH2
88%
(1)
with increasing levels of H2POÀ (0.0, 0.5, 1.0, 2.0 equiv). The thio-
4
urea protons are once again labeled Ha (11.90 ppm), Hb
(11.52 ppm), and the amino moiety Hc (5.00 ppm). Similar results
were observed with the three-point thiourea (2) upon the addition
of H2POÀ. As the concentration of H2POÀ increases, a significant
1. N
S-+NH4
Acetone
4
4
°
0 C
N2
decrease in the thiourea proton signal (Ha and Hb) is observed
(Fig. 2). The major difference in the two- (1) versus three-point
(2) monomer is the decrease in the amino (labeled Hc) signal.
The decrease in the amino proton signal indicates a third site for
O
S
O
N
H
N
H
75%
Cl
2.
NH2
NH2
NH2
hydrogen bonding to H2POÀ. Based on the NMR studies, two- and
4
(2)
three-point thioureas were pursued as our trapping groups for
the polymer flocculent studies and their possible removal of inor-
ganic phosphate from water.
Scheme 1. Preparation of two- and three-point thiourea trapping groups.
Thiourea monomers (1 and 2) were polymerized with acrylam-
ide and [2-(acryloyloxy)ethyl] trimethylammonium chloride utiliz-
ing AIBN as the initiator (Scheme 2).
Once the modified polymers were prepared, experiments were
conducted to test the sorption of phosphate to the polymer (Table
1). To test the sorption of phosphate on the polymers an aqueous
suspension of solid material was prepared. The solid material used
was kaolinite (1:1 aluminosilicate) that was weighed and added to
To test the affinity of the two- and three-point hydrogen bond-
ing thiourea monomers (1 and 2) 1H NMR studies were performed.
1H NMR studies were conducted at room temperature using each
monomer individually and increasing amounts of tetra-n-butyl
ammonium phosphate (0, 0.5, 1.0, and 2.0 equiv). The first NMR
spectrum contains the two-point thiourea (1) without any
O
S
O
S
N
H
O
N
H
O
-
+ H2PO4
N
N
Ha Hb
P
HO OH
-
0.0 equiv. H2PO4
a
b
-
0.5 equiv. H2PO4
-
1.0 equiv. H2PO4
-
2.0 equiv. H2PO4
Figure 1. 1H NMR (DMSO-d6) of two-point thiourea monomer (1) and increasing concentrations of H2POÀ4 . NMR’s were run at 7.40 Â 10À3 M concentration based on (1).

T. S. Goebel et al. / Tetrahedron Letters 52 (2011) 5241–5244
5243
O
S
P
O
S
N
H
O
N
H
O
-
+ H2PO4
N
N
N
Ha Hb
H
H
NH2c
HO
O
H
-
0.0 equiv. H2PO4
b
c
a
-
0.5 equiv. H2PO4
-
1.0 equiv. H2PO4
-
2.0 equiv. H2PO4
Figure 2. 1H NMR (DMSO-d6) of three-point thiourea monomer (2) and increasing concentrations of H2POÀ4 . NMR’s were run at 7.40 Â 10À3 M concentration based on (2).
Polymer Synthesis
Cl-
N
S
AIBN
N
O
O
O
O
O
O
R
°
H
NH
45 C
(1 or 2)
+
N
+
Cl-
CH3CN
O
NH2
n
NH2
(3 & 4)
(3) R=H
(4) R=-NH2
Scheme 2. Preparation of modified polymer flocculants.
The resulting clear solution above the flocculated material was
sampled and tested for phosphate using ion chromatography (IC).
Controls containing phosphate and clay were tested to check
the level of sorption of phosphate to clay (Clay, Fig. 3). Several dif-
ferent polymers were tested for an interaction with phosphate.
Magnifloc 494C was tested as a control with 10% positive charge
density and 90% acrylamide (Mag C, Fig. 3). The polymer C40-00
was made according to the U.S. patent 5,945,494 as a control with
40% positive charge density and 60% acrylamide, C40-20(2-pt) was
made modifying the same patent (appendix) with 40% positive
charge density, 20% two-point thiourea (1), and 40% acrylamide.
C40-20(3-pt) (2) was made with 40% positive charge density, 20%
three-point thiourea, and 40% acrylamide.
Table 1
Mole percent of monomers for individual modified polymers
Monomer
C-40-00 C-40-20 (2-pt) C-40-20 (3-pt)
Acrylamide
60
40
40
40
N/A
20
Trimethyl ammonium chloride 40
40
Thiourea (2-pt) (1)
Thiourea (3-pt) (2)
N/A
N/A
20
N/A
a known volume of water. NaH2PO4 was then added from an inter-
mediate standard to create an aqueous suspension with a 5 mg/L
phosphate concentration. The polymers tested were then added
to the suspension and vortexed for 5 s. The suspension was left
for 20 min to allow the flocs to form and settle out of solution.
The results from the polymer sequestration experiment
(Fig. 3A) show that kaolinite was able to sorb 30% of the phosphate

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T. S. Goebel et al. / Tetrahedron Letters 52 (2011) 5241–5244
Conclusion
A
It has been discovered that substituted thiourea with two- and
three-points of hydrogen bonding displays a high affinity for inor-
ganic phosphate. 1H NMR studies indicate that not only can deriv-
atized thiourea molecules bind phosphate, but also the addition of
neighboring amino moiety can induce a three point hydrogen
bonding interaction.
Based on the high affinity of derivatized thiourea for inorganic
phosphate, polymer flocculants were substituted with a thiourea-
trapping group and sequestration studies discovered that up to
60% of inorganic phosphate could be removed from the solution.
The polymer flocculants were able to remove the phosphate sorbed
to the kaolinite through the flocculation event as well as remove an
additional portion from the solution. These newly derived thiourea
polymer flocculants worked up to 45% better than currently avail-
able commercial products in the removal of inorganic phosphate
from water.
B
Acknowledgments
T.A.D. would like to thank the Department of Chemistry, Office
of Research, and the College of Arts & Sciences at Idaho State Uni-
versity for generous start-up funds. DSC-TGA-MS was purchased
through funding from NSF (NSF CHE-1048714). T.S.G. would like
to thank Dr. Casey Carrothers for insightful input.
‘‘Mention of trade names or commercial products in this publi-
cation is solely for the purpose of providing specific information
and does not imply recommendation or endorsement by the U.S.
Department of Agriculture.’’
‘‘The U.S. Department of Agriculture (USDA) prohibits discrimi-
nation in all its programs and activities on the basis of race, color,
national origin, age, disability, and where applicable, sex, marital
status, familial status, parental status, religion, sexual orientation,
genetic information, political beliefs, reprisal, or because all or part
of an individual’s income is derived from any public assistance
program.’’
Figure 3. (A) Phosphate (H2POÀ) removed by polymers with an initial phosphate
concentration of 5 mg/L, and (B) the same results with the phosphate removed by
kaolinite partitioned to examine the portion removed by the polymers.
4
from the solution. To further examine the results from the polymer
treatment in this experiment the amount of phosphate removed by
kaolinite was partitioned and removed to look at what portion of
the phosphate left in solution bound to the polymers (Fig. 3B). Fig-
ure 3B suggests that the addition of Magnifloc 494C did not de-
crease the amount of phosphate in the solution. Comparing the
results from Magnifloc 494C and C40-00 shows a decrease in phos-
phate concentration related to increasing the positive charge den-
sity on the polymer from 10% to 40%, suggesting that a positively
charged quaternary ammonium group is interacting with the phos-
phate in the solution. Comparing the amount of phosphate re-
moved from the solution when C40-00 was added to the addition
of C40-20(2-pt) suggests that the addition of the thiourea group in-
creased the polymers’ sorption of phosphate. C40-20(3-pt) showed
little improvement over the control C40-00.
While the monomers of the two-point and three-point thio-
ureas displayed similar bonding to phosphate in the NMR studies,
the polymer studies showed a difference in the amount of phos-
phate removed from the solution (2-pt vs 3-pt). The difference
likely lies in the interaction of the thiourea (2-pt or 3-pt) portion
of the polymer with the solid material present (kaolinite). The
two-point thiourea polymer would likely not interact with the neg-
atively charged clay surface as strongly as the three-point thiourea.
The three-point thiourea polymer has an additional site (free
amine) for interaction with the solid material thus decreasing the
availability of the trapping group for the phosphate in the solution.
Due to the higher affinity of the three-point thiourea polymer with
the surface, the amount of phosphate removed through the floccu-
lation event is decreased. These experiments are currently under
investigation and will be reported in due course.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.07.130.
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