Recent Advances in Urban Planning and Construction
Effects of pH and Bi-functional Groups Modification on Adsorption of
Carbamazepine by Porous Silicas
PATIPARN PUNYAPALAKULa,c,* and THITIKAMON SITTHISORN b,c
a
Department of Environmental Engineering, Chulalongkorn University,
Phayathai Road, Pathumwan, Bangkok, 10330,
Thailand, (email: patiparn.p@eng.chula.ac.th ) (corresponding author)
b
International Postgraduate Programs in Environmental Management,
Graduate School, Chulalongkorn University,
Bangkok 10330, Thailand
c
Center of Excellence for Environmental and Hazardous Waste Management (EHWM),
Bangkok 10330, Thailand
Abstract: - Effects of pH and bi-functional groups modification on adsorption of Carbamazepine (CBZ), by
using hexagonal mesoporous silicates (HMS) as the base porous adsorbent in synthetic wastewater at high
concentration (0.5 – 10 mg/l) was studied. Three different types of surface functional groups which were 3aminopropyltriethoxy- 3-mercaptopropyl- and n-octyldimethyl groups by co-condensation method were applied
in this study. For bi-functional group modified HMSs, 3-aminopropyltriethoxy- and 3-mercaptopropyl- were
grafted in the same surface with three different ratios. Adsorption isotherms on CBZ at 5, 7 and 9 were best
matched with Langmuir isotherm model. At pH 5, all adsorbents performed highest CBZ adsorption capacities,
which might be the effect of hydrogen bonding strength occurred in each pH value.The CBZ adsorption
capacities were related to the ratio of Bi-functional group grafted on HMS. Hydrophobicity and hydrogen
bonding might played a key role on the adsorption mechanisms, while the electrostatic interaction might not
affect the CBZ adsorption capacity.
Key-Words: - Mesoporous silicates; Carbamazepine ; pH; Surface functional group; Adsorption
products and their toxicities have not been
investigated yet. Moreover, photo-fenton process
was applied as pre-treatment to enhance
biodegradation
of
conventional
wastewater
treatment process. However, it takes long retention
time with heavy hydrogen peroxide consumption to
eliminate and/or detoxify the organic compounds in
wastewater.
Hexagonal mesoporous silicate (HMS) having
been studied extensively in adsorption and catalysis
fields has mesoscale pore and silanol as surface
functional group. HMS surface can be modified by
various methods to enhance specific characteristics
(e.g., organic ligand modification). The objective of
this study is to investigate the effects pH on CBZ
adsorption capacities on three functional groups on
HMS. Batch adsorption experiments at high
concentration (05-10 mg/L) were carried out with
various types of surface functional groups of HMS,
comparing with powdered activated carbon
(Shirasagi S-10, Japan EnvironChemecals Ltd.). 3-
1 Introduction
Carbamazepine (CBZ) is a worldwide drug belongs
to epileptic group. It is widely used for remediation
several diseases or symptoms such as alcoholism
[1], opiate withdrawal [2], relieve depressant [3],
and epileptic [4]. CBZ was frequently detected in
the environment including water and soil phase,
particular in the sandy soil. Previous research
reported that no microbial degradation in sandy
sediment [5]. Moreover, several reports indicated
that CBZ cannot be eliminate or partly removed
approximately less than 10% in wastewater
treatment [6]-[8].
Various available physico-chemical treatment
processes have been applied to remove CBZ from
aqueous phase, but their own limitations and effects
could not be neglected. For example, degradation by
UV process required high UV energy and cost [9][11]. Enhancement of pharmaceutical residues
degradation by adding H2O2 during UV process
could reduce UV energy but degradation by-
ISBN: 978-960-474-352-0
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Recent Advances in Urban Planning and Construction
aminopropyltriethoxy, 3- mercaptopropyltrimethoxy
and n-octyldimethyl functional group were
employed to investigate the effects of pH and
physico-chemical characteristics on CBZ adsorption
capacities. Moreover, the study about effects of bifunctional groups (3- aminopropyltriethoxy and 3mercaptopropyltrimethoxy) grafted in same surface
was included in this study.
Octyldimethyl-functional HMS (O-HMS) was
prepared by these following method: drying 5 g of
HMS was put in a 250 ml three-neck round flash
which containing 140 ml of dichloromethane and
stirrer bead. The mixture is stirred, and then 1.8 g of
1-methyl-2-pyrolidine and 3.6 g of n-octyldimethylchlorosilane were added under N2 flow. The mixture
was maintained stirred under reflux at 60°C for 4 hr,
after that, filtrated and wash with 50 ml of
chloroform twice and 50 ml of ethanol. The sample
was drying under vacuum at 40 °C for 4 hr; the ODHMS was obtained.
Preparation of bi-functional group-HMS (BFHMS) was performed by mixing 50 mol of water
with 0.25 mol of dodecylamine and 10.25 mol of
ethanol to form an organic template to HMS.
Tetraethoxysilane (TEOS) of 1.0 mol was added in
the mixture, and were then mixed under vigorous
stirring for 30 min. Then 0.25 mol of 3aminopropyltriethoxysilane
(APTES)
or
3mercaptopropyltrimethoxysilane (MPTES) was
added in the mixture. The molar ratios of APTES
and MPTES for BF-HMS synthesis were 3:7, 5:5
and 7:3 (A3M7, A5M5 and A7M3, respectively).
The reaction mixture was vigorously stirred for 20 h
at ambient temperature and the resulting were
filtered and air-dried on a glass plate for 24 h.
Residual organosilane and organic template were
removed by solvent extraction for 72 h with ethanol.
2 Materials and methods
2.1 Synthesis of Adsorbents
2.1.1 HMS synthesis
HMS was prepared by mixing 29.6 mol of water
with 0.27 mol of dodecylamine and 9.09 mol of
ethanol to form as organic template of HMS. Add
1.0 mol of tetraethoxysilane (TEOS) in the mixture
and were then mixed under vigorous stirring. The
reaction mixture was aged at an ambient
temperature for 18 h. The resulting mixture was
filtered and air-dried on a glass plate. The product
was calcined in air under static condition at 650 ºC
for 4 h to remove organic template.
2.1.2 Synthesis of functionalized HMS
3-aminopropyltriethoxy-functionalized HMS (AHMS) was prepared by mixing 50 mol of water with
0.25 mol of dodecylamine and 10.25 mol of ethanol
to form as organic template of HMS. Add 1.0 mol of
tetraethoxysilane (TEOS) in the mixture and were
then mixed under vigorous stirring for 30 min. Then
0.25 mol of 3-aminopropyltriethoxysilane (APTES)
was added in the mixture. The reaction mixture was
vigorously stirred for 20 h at ambient temperature
and the resulting were filtered and air-dried on a
glass plate for 24 h. Residual organosilane and
organic template were removed by solvent
extraction for 72 h with ethanol. [12]
3-mercaptopropyltrimethoxy-functionalized
HMS (M-HMS) was prepared by mixing 50 mol of
water with 0.25 mol of dodecylamine and 10.25 mol
of ethanol to form as organic template of HMS. Add
1.0 mol of tetraethoxysilane (TEOS) in the mixture
and were then mixed under vigorous stirring for 30
min. Then 0.25 mol of 3-mercaptopropyltrimethoxysilane (MPTMS) was added in the
mixture. The reaction mixture was vigorously
stirred for 20 h at ambient temperature and the
resulting were filtered and air-dried on a glass plate
for 24 h. Residual organosilane and organic
template were removed by solvent extraction for 72
h with ethanol. [12]
ISBN: 978-960-474-352-0
2.2 Characterization of synthetic adsorbents
Surface area, pore volume, and pore size was
calculated from nitrogen adsorption isotherms
measured at 77 K using an Autosorb-1
Quantachrome automatic volumetric sorption
analyzer. Particle diameter was calculated from
Scanning Electron Microscopy (SEM JSM 5800
LV) from ten random obtained particles. The
presence of organo-functional groups on the
synthesized adsorbents’ surface was confirmed by a
Fourier Transform Infrared spectrometer (FTIR)
(Perkin
Elmer
Spectrum
One).
The
hydrophobic/hydrophilic characteristics of the
adsorbent surface were evaluated by measuring the
water contact angle (θ) using a Dataphysics DCAT11 tensiometer in a powder contact angle mode. An
electrophoresis apparatus (Zeta-Meter System 3.0,
Zeta Meter Inc.) was used to measure the surface
charge.
2.3 Adsorption Study of Carbamazepine
(CBZ) on adsorbents
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Recent Advances in Urban Planning and Construction
HMS, M- HMS, PAC, HMS and A-HMS,
respectively. The SEM images of HMS and O-HMS
showed that all adsorbents had spherical
morphology; moreover the particles have slightly
different size between 100 to 300 nm (Fig. 1).
Nitrogen contents of A-HMS was detected as 1.41
% (w/w). Whereas, the sulfur content in M-HMS,
was found to be 9.92%(w/w). Surface charge
densities of synthesized adsorbents vs. pH are
showed in Fig. 2 and summarized total charges in
table 2 . And the ionized surfaces functional groups
depend on pH are listed as following:
Adsorption isotherm was conducted with an initial
CBZ concentration range between 0.5-10 mg/L and
1 g/L of adsorbent. The ionic strength of the
solution was fixed using 0.01 M phosphate buffer at
either pH 5, 7 or 9. The sample was shaken at 220
rpm at 25 oC, and then the supernatant solution was
filtrated through a glass filter (GF/C, pore size 0.45
µm). Adsorption isotherms of CBZ under pH 5,7
and 9 (above and lower pHzpc of the adsorbents)
were investigated and compared. The adsorption
results of synthesized adsorbents were compared
with powdered activated carbon (PAC). The first 10
ml of filtrate was discarded and the rest was
harvested for analysis by using UV-visible
spectrophotometer (GENESYSTM 10S UV Vis).
Experimental data can be analyzed using
adsorption isotherm model. The most widely used
isotherm equation for modeling of the adsorption
data are Langmuir and Freundlich isotherm model
as;
qm K L C e
1 + K LCe
(1)
q = K F C e1 / n
(2)
q=
HMS, SBA-15:
pH < pHzpc: ≡ Si-OH + H+  ≡ Si-OH2+
pH > pHzpc: ≡ Si-OH + OH-  ≡ Si-O- + H2
A-HMS:
pH < pHzpc: ≡ Si-R-NH2 + H+  ≡ Si-R-NH+
pH > pHzpc: ≡ Si-R-NH2 + OH-  ≡ Si-R-NH2OH-
M-HMS:
pH < pHzpc: ≡ Si-R-SH + H+  ≡ Si-R-SH2+
pH > pHzpc: ≡ Si-R-SH + OH-  ≡ Si-R-S-
3.2 CBZ Adsorption isotherms of single
functional grafted HMS
From adsorption kinetic study, the concentrations
CBZ were rapidly reduced in the first 30 minutes
and then reached the saturation stage at evaluated 9
hours for all HMSs and 3 hours for PAC.
The adsorption isotherm studies of CBZ were
conducted at pH 5, 7 and 9 with 0.01 M ionic
strength controlled by phosphate buffer (Fig. 3 (ae)). CBZ, which contain pKa at 2.30 (ketone group)
and 13.90 (amine group) (Yu et al., 2008), had two
different functional groups depending on pH of
solution. Hydrophobicity of synthesized adsirbents
might play a key role on the adsorption. Moreover,
hydrogen bonding between amide groups (-NH2) on
CBZ that can interact with the surface functional
group of adsorbents was mainly responsible for the
adsorption.
Where KL is the adsorption equilibrium constant, qm
is the maximum adsorption capacity (mg/g), qe is
the adsorption capacity at equilibrium (mg/g), K and
n are Freundlich constants.
3.1 Characterization of Synthetic adsorbents
Physico-chemical characteristics of synthesized
adsorbents were summarized in Table 1. Surface
areas of M-HMS and O-HMS did not change
significantly comparing with pristine HMS. But AHMS exhibited the decrease of surface area due to
the collapse of silicate porous structure. Moreover,
sulfur intensity measured by ICP-AES can support
the existence of mercapto functional group on MHNS-SP surface. The contact angle was also shown
in Table 1. The order of hydrophobicity was O-
Table 1 Physico-chemical characteristics of synthesized adsorbents comparing with PAC
HMS
A-HMS-SP
M-HMS-SP
O-HMS-SP
Pore
diameter
(nm)
2.60
3.95
2.48
2.36
BET
Surface
area (m2/g)
712
262
912
477
PAC
1.90
980
Adsorbents
ISBN: 978-960-474-352-0
pHzpc
5.5
8.2
6.2
4.4
9.8
85
Surface
functional
groups
Silanol
Amino
Mercapto
Octyl
Carboxyl
Phenyl
Others
Contact
angle
(θ)
50
45
60
80
58
Hydrophobicity
Hydrophilic
Hydrophilic
Hydrophobic
Hydrophobic
Hydrophobic
Recent Advances in Urban Planning and Construction
Fig. 1 The SEM images of HMS (left) and O-HMS (right).
Fig. 2 Surface charge density of synthesized adsorbents.
Table 2 Charge types of studied adsorbents at different pH
Adsorbents
pHzpc
HMS
A-HMS
M-HMS
OD-HMS
PAC
5.5
8.2
6.2
4.4
9.8
Fig. 3 (a-j) illustrated adsorption capacities of
CBZ at different pH for adsorbents used in this
study. The structure molecule of CBZ was neutral in
thestudied pH range; hence, electrostatic interaction
CBZ might interact with silanol group on HMS
and CBZ might be stronger than hydrogen bonding
interacted with amino functional group on A-HMS
surface. In addition, CBZ can also interact with
mercapto group on M-HMS comparing with the
hydrophobic O-HMS.
ISBN: 978-960-474-352-0
Surface charge
pH 5 pH 7 pH 9
+
+
+
+
+
+
+
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Recent Advances in Urban Planning and Construction
The results of CBZ adsorption capacities of
applied adsorbents at pH 5, 7, and 9 were fitted with
Langmuir and Freundlich isotherm model by linear
regression in order to describe the adsorption
mechanism occurred in this study. It was found that
the obtained experimental data had no relationship
with Freundlich isotherm. On the other hand,
Langmuir isotherm can be fitted to the results with
very high correlation coefficients. The linear
regression data fitted with Langmuir isotherm model
for CBZ adsorption were summarized in Table 3.
Hence, it can be concluded that the adsorption
phenomena of CBZ on all studied adsorbents were
monolayer adsorption.
might not influence the adsorption capacity. From
Figure 3 (e), it was also found that adsorption
capacity of PAC was not impacted by the varying of
pH as well as CIP. The adsorption capacities of
CBZ on HMS, M-HMS and OD-HMS had the
highest capacities at pH 5, comparing to pH 7 and 9.
The strength of hydrogen bonding at different pH
might be responsible for the results. However, AHMS did not perform the adsorption of CBZ in
studied pH range. This might be the results of
hydrogen bonding between CBZ structure and
functional groups on adsorbents, which was not
significantly affected by changing of pH in the
studied range.
HMS
A-HMS
M-HMS
O-HMS
PAC
Fig. 3 Adsorption isotherm of CBZ on synthesized adsorbents
and PAC at pH 5, 7 and 9 (25 oC and IS = 0.01 M).
ISBN: 978-960-474-352-0
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Recent Advances in Urban Planning and Construction
Table 3 Parameters of Langmuir isotherm model for CBZ adsorption on applied adsorbents
Adsorbent
Langmuir
qm
b
R2
5
4.410
0.075
0.922
7
3.913
0.016
0.983
9
3.629
0.009
0.932
5
N/A
N/A
N/A
7
N/A
N/A
N/A
9
N/A
N/A
N/A
5
18.242
0.138
0.989
7
15.711
0.107
0.982
9
12.422
0.099
0.992
15.000
0.051
0.992
pH
HMS
A-HMS
M-HMS
OD-HMS
5
7
12.549
0.037
0.984
9
11.580
0.030
0.958
5
55.426
0.762
0.975
7
51.615
0.777
0.986
9
52.083
0.767
0.971
PAC
The results of kinetic study at pH 7 were found that
the adsorption of CBZ achieved the saturation stage
at 9 hr for synthesized HMSs and PAC. From
adsorption isotherm study, it was found that the
highest adsorption capacities of CBZ was obtained
from M-HMS; however, its capacity was still lower
than PAC. Specific surface area and densities of
surface functional group might play an important
role in the adsorption of CBZ on single- and bifunctional group grafted HMSs. Hydrophobicity and
hydrogen bonding might played a key role on the
adsorption mechanisms, while the electrostatic
interaction might not affect the CBZ adsorption
capacity. Moreover, the effects of pH on adsorption
capacities were determined and found that the
capacities was increased at low pH value (pH = 5)
and lower at high pH (pH = 9), which might be the
effect of hydrogen bonding strength occurred in
each pH value.
3.2 CBZ Adsorption isotherms of single
functional grafted HMS
From obtained results, it was found that M-HMS
still had highest adsorption capacity as can be seen
in Fig.4 and 5. Nevertheless, BF-HMSs provided
very slightly different capacities. As aforementioned
that CBZ tend to be neutral at studied pH,
electrostatic interaction might not be considered as
the main mechanism. The van der Waals interaction
caused by hydrophobic and hydrogen bonding
between amide group of CBZ and functional groups
of adsorbents may responsible for the adsorption
mechanism. However, the strength of hydrogen
bonding of amide group (NH2) of CBZ with
mercapto- functional group of adsorbents might be
higher than with amino group; therefore, BF-HMSs,
which content relatively close of mercapto group
content, resulted in insignificantly different of
adsorption capacities.
4. Conclusions
ISBN: 978-960-474-352-0
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Recent Advances in Urban Planning and Construction
Fig. 4 Adsorption capacities of CBZ on M-HMS, BF-HMSs, and A-HMS
at pH 7 (25 oC and IS = 0.01 M).
Fig. 5 Adsorption capacities in 1 square meter of CBZ on M-HMS, BF-HMSs, and A-HMS
at pH 7 (25 oC and IS = 0.01 M).
through The National Nanotechnology Center
(NANOTEC), The National Science and
Technology Development Agency (NSTDA),
Thailand
(Project
No.
P-11-00985)
of
Chulalongkorn University. This research was also
supported by the Higher Education Research
Promotion and National Research University Project
of Thailand, Office of the Higher Education
Commission (FW1017A). Technical support from
Department of Environmental Engineering, Faculty
of Engineering, Chulalongkorn University, is also
gratefully acknowledged.
5. Acknowledgments
The authors express gratitude to The National
Research Centre for Environmental and Hazardous
Waste Management (NRC-EHWM). This work was
carried out as part of the research cluster “Fate and
Removal of Emerging Micropollutants in
Environment” granted by the Center of Excellence
for Environmental and Hazardous Waste
Management (EHWM) and Special Task Force for
Activating
Research
(STAR),
both
of
Chulalongkorn University. The authors are also
grateful for support from the Research,
Development and Engineering (RD&E) fund
ISBN: 978-960-474-352-0
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Recent Advances in Urban Planning and Construction
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[11] Gagnon C., Lajeunesse A., Cejka P., Gagné F.
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, 30 (2008): 387 - 392.
[12] Punyapalakul P., and Takizawa S., Effect of
organic grafting modification of hexagonal
mesoporous silicate on haloacetic acid removal.
Environmental Engineering Forum. 2004, 44:
p. 247–256.
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