Synthesis and characterization of ion-imprinted resin for selective removal of UO2(II) ions from aqueous medium

Article abstract of DOI:10.1002/jmr.2445

In this work, uranyl ion-imprinted resin based on 2-(((4-hydroxyphenyl)amino)methyl)phenol was synthesized by condensation polymerization of its uranyl complex in presence of resorcinol and formaldehyde cross-linkers. Numerous instrumental techniques incl

Full text of DOI:10.1002/jmr.2445

Research Article
Received: 23 July 2014,
Revised: 29 September 2014,
Accepted: 27 October 2014,
Published online in Wiley Online Library: 8 March 2015
(wileyonlinelibrary.com) DOI: 10.1002/jmr.2445
Synthesis and characterization of ion-
imprinted resin for selective removal of
UO2(II) ions from aqueous medium
M. Moniera,b*, Raedah A. S. Alatawic and D. A. Abdel-Latifa,b
In this work, uranyl ion-imprinted resin based on 2-(((4-hydroxyphenyl)amino)methyl)phenol was synthesized by
condensation polymerization of its uranyl complex in presence of resorcinol and formaldehyde cross-linkers. Numer-
1
ous instrumental techniques including elemental analysis, Fourier transform infrared spectroscopy, ultraviolet, H
along with 13C nuclear magnetic resonance spectroscopy have been employed for complete characterization of
the synthesized ligand and its uranyl complex. Additionally, the obtained ion-imprinted and non-imprinted resins
were investigated using scanning electron microscope and Fourier transform infrared spectroscopy. The effects of
various essential parameters such as pH, temperature and contact time on removal of uranyl ions have been exam-
ined, and the results indicated that the obtained resin exhibited the optimum activity at pH 5. Furthermore, the ad-
sorption process was spontaneous at all studied temperatures and followed the second-order kinetics model. Also,
Langmuir adsorption isotherm exhibited the best fit with the experimental results with maximum adsorption capac-
ity 139.3 mg/g. Moreover, the selectivity studies revealed that the ion-imprinted resin exhibited an obvious affinity
toward the uranyl ions in presence of other metal ions compared with the non-imprinted resin. Copyright © 2015
John Wiley & Sons, Ltd.
Keywords: ion-imprinting; phenol resin; heavy metals
and modification of comparatively novel and smart materials
known as ion-imprinted polymers (IIPs), which are capable of se-
INTRODUCTION
Because of their participation in nuclear applications,
uranium is regarded as one of the most terrifying heavy
metals. Despite the fact that uranium is a poor radioactive
element that emits alpha particles, it can be applied to
generate clean electrical energy for centuries without worry-
ing about CO2 productions, which are responsible for global
warming problems (Milja, et al., 2011; Monreal and
Diaconescu, 2010). Several studies have been conducted
regarding the removal and recovery of uranium from its
environmental sources including rocks and soils as well as
from contaminated ground or surface water (Jackson, et al.,
2005; Donia, et al., 2009; Smith, et al., 2007; Xie, et al.,
2009; Liu, et al., 2010).
Recently, numerous strategies have been employed for heavy
metal removal including chemical precipitation where the metal
ions sediment in form of salts, membranes where the metal ions
can be extracted via membranes–metal-ion interaction and also
ion exchangers in which the metal ions adsorbed via coordination
with specific functional groups inserted onto the adsorbent (Devi
and Fingermann, 1995; Chanda and Rempel, 1997; Reed, et al.,
1997; Beuvais and Alexandratos, 1998; George, et al., 1999; Rivas,
et al., 2001; Wu and Li, 2003; Kara, et al., 2004; Hoai, et al., 2010).
Although the earlier mentioned strategies are extensively used
for industrial non-selective metal ion removal, the lake of selectiv-
ity regarded as a serious downside limits the application for spe-
cific metal-ion extraction (Devi and Fingermann, 1995).
lectively removing a single target metal ion in presence of others
(Rao, et al., 2004; Rajabi, et al., 2013). IIPs provide excellent char-
acteristics such as high selectivity, high surface area, ease of
preparation and reusability (Liu, et al., 2011). Various IIPs were
prepared for selective removal of metal ions such as mercury
(Monier and Abdel-Latif, 2013a), copper (Shamsipur and
Besharati-Seidani, 2011), uranyl (Monier and Abdel-Latif, 2013b;
Zhang, et al., 2013) and nickel (Vatanpour, et al., 2011). Usually,
the IIPs are synthesized in three consecutive steps: (i) coordina-
tion of the target metal ion with suitable polymerizable ligand;
(ii) polymerization of the obtained complex in presence of a suit-
able cross-linker; and (iii) leaching the template metal ion from
the three-dimensional cross-linked network leaving specific co-
ordination cavities that relatively match with the template metal
* Correspondence to: M. Monier, Chemistry Department, Deanery of Academic
Services, Taibah University, Yanbu Branch, Yanbu El-Bahr, KSA.
E-mail: monierchem@yahoo.com
a M. Monier, D. A. Abdel-Latif
Chemistry Department, Deanery of Academic Services, Taibah University,
Yanbu Branch, Yanbu El-Bahr, KSA
b M. Monier, D. A. Abdel-Latif
Chemistry Department, Faculty of Science, Mansoura University, Mansoura
35516, Egypt
The selective extraction is required if we need to separate cer-
tain components from multi-component mixtures (Soleimani,
et al., 2012). Many recent studies were conducted for preparation
c R. A. S. Alatawi
Department of Chemistry, Faculty of Science, University of Tabuk, Tabuk
71421, KSA
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ION-IMPRINTING PHENOL RESIN HEAVY METALS
ion over other structurally related components (Shamsipur and
Besharati-Seidani, 2011; Shamsipur, et al., 2014).
20 mL uranyl ion solution (2 mmol). The mixture was refluxed for
about 3 h and then allowed to stand. The appeared brown pre-
cipitate was filtered, washed with water then ethanol and finally
dried in vacuum.
The present study deals with the synthesis and characteriza-
tion of highly selective uranyl ion-imprinted resin through
base-catalyzed polycondensation of uranyl complex with the
previously prepared 2-(((4-hydroxyphenyl)amino)methyl)phenol
(H2PAP) ligand, resorcinol and formaldehyde. The prepared li-
gand, uranyl complex and polymeric resin before and after tem-
plate uranyl removal were fully characterized. Also, the effect of
various parameters such as pH, temperature and contact time
on the rebinding of uranyl, in addition to selectivity studies, were
examined and discussed.
Polymerization of the uranyl complex
The U-HAPF ion-imprinted resin was prepared through the con-
densation polymerization of the previously prepared uranyl
complex with resorcinol and formaldehyde. In a 250-mL round-
bottom flask, 5 g of the previously prepared [UO2(HPAP)2] com-
plex was dissolved in 20 mL dimethylformamide (DMF) until
clear solution, to which 10 mL 20% (w/v) resorcinol/DMF solution
was added, and the mixture was stirred for about 1 h. Then,
20 mL 37% formaldehyde solution and 20 mL 1 M NaOH solution
were added, and the mixture was refluxed with constant stirring
in an oil bath at about 120°C for approximately 3 h. A dark brown
gel was formed, separated and dried in an oven for 24 h. The
dried resin was then crushed and grounded to particle size rang-
ing 100–150 μm and then washed several times with DMF to re-
move the impurities and unreacted substances. The template
uranyl ion elimination from the cross-linked polymer was carried
out by stirring the resin in 300 mL 0.5 M HNO3 solution for 6 h
and repeating the process until the solution became free of ura-
nyl ions. The resin was then washed several times with distilled
water for neutralization. Finally, the obtained U-HAPF ion-
imprinted resin was dried under vacuum in a desiccator to be
used in the subsequent extraction studies. For comparison rea-
sons, non-imprinted polymer (NI-HAPF) was prepared by the
same procedure in absence of uranyl ions and treated in the
same manner. The ion-imprinting process is schematically
shown in Scheme 2.
EXPERIMENTAL
Materials
Salicyaldehyde, p-aminophenol, sodium borohydride, formalde-
hyde and UO2(NO3)2.6H2O were all purchased from Sigma-Aldrich
(St. Louis, MO, USA). All the reagents and chemicals used were of
analytical grade.
Preparation of uranyl ion-imprinted resin
The synthetic procedures of the uranyl ion-imprinted resin (U-
HAPF) were performed in the following consecutive steps: (i) syn-
thesis of p-aminophenol salicyaldehyde Schiff base; (ii) reduction
of the resulted Schiff base using NaBH4 to produce the ligand
2+
H2PAP; (iii) complex formation between UO2 and H2PAP; (iv)
condensation terpolymerization of the resulted complex with
formaldehyde and resorcinol; and (v) removal of the template
2+
UO2 ions from the three-dimensional cross-linked network.
Synthesis of the H2PAP ligand
Characterization of samples
The first step involves the formation of a p-aminophenol-
salicyaldehyde Schiff base through the condensation of p-
aminophenol and salicyaldehyde (1 : 1 M ratio) in ethanol. Briefly,
1 g of p-aminophenol was dissolved in 20 mL ethanol. Then, 1.2 g
salicyaldehyde was added and the mixture was refluxed for 6 h
after adding 1 mL piperidine. The brown solution was then
cooled in ice bath to produce the intermediate Schiff base. In
the subsequent step, the Schiff base was reduced using 0.4 g
NaBH4, the brown color was gradually discharged. After 1 h, the
mixture was acidified using acetic acid and the solution was con-
centrated to half of its volume. The resulted amine was extracted
using diethyl ether, filtered, washed several times with ether and
finally stored in a desiccator. The synthetic process was pre-
sented in Scheme 1.
The elemental analysis of the ligand H2PAP and uranyl complex
[UO2(HPAP)2] were performed using a PerkinElmer 240 C Ele-
mental Analytical Instrument (Waltham, MA, USA). Fourier trans-
form infrared (FTIR) spectra of both ligand and complex were
obtained with a PerkinElmer spectrum. The samples were mixed
with KBr and pressed in the form of disks. The 1H and 13C nuclear
magnetic resonance (NMR) spectra were recorded in DMSO-d6
using an Oxford NMR instrument (Model Unity Inova 500 MHz,
USA). The electronic spectrum of the ligand and its uranyl com-
plex were recorded in DMF solution on a Unicam UV2-UV–visible
spectrometer, in the range 200–900 nm.
The surface morphologies of the polymeric resin samples were
examined using a FEI Quanta 200 scanning electron microscope
(FEI Company, Eindhoven, the Netherlands) operating at a typi-
cal accelerating voltage of 20 kV. The samples were sputter-
coated with gold for 40 s at 15 mA prior to the observation.
The specific surface area was measured by N2 adsorption iso-
therm using an ASAP 2010 Micromeritics instrument (Norcross,
GA, USA) and by Brunauer–Emmett–Teller method, using the
software of Micromeritics.
Synthesis of uranyl complex
The uranyl complex was prepared by mixing 20 mL hot ethanolic
solution of the previously prepared H2PAP ligand (4 mmol) with
Uranyl ions adsorption studies
The experiments were carried out using both U-HAPF ion-
imprinted and NI-HAPF non-imprinted resin. In most of the ex-
periments, 0.03 g of the studied resins were placed in 100-mL
2+
glass bottles containing 30-mL UO2 aqueous solution with
Scheme 1. Synthesis of H2PAP ligand.
main concentration 100 mg/L (except in cases of adsorption
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M. MONIER ET AL.
Scheme 2. Schematic presentation of the ion-imprinting process.
isotherm studies where the initial uranyl ion concentration
ranged between 10 and 400 mg/L and thermodynamic studies
where the concentration was 30 mg/L), at pH 5 (except for effect
of pH studies in which the pH ranged between 1 and 5 using
KCl/HCl for pH 1, 2, and 3; CH3COOH/CH3COONa for pH 4 and
5), at 30°C (except for the temperature effect where the temper-
ature ranged between 20°C and 40°C) and for 3 h (except for the
kinetic studies where the contact time changed from 10 to
120 min). All the batches were equilibrated utilizing a shaker ad-
justed at 150 rpm. Then, the resins were removed and the resid-
ual metal ion content was estimated using atomic absorption.
For all experiments, the following equations were utilized for
determination of the adsorption values:
D ¼ ½ðCi ꢀ CeÞ=CeꢁV=W
(4)
The influence of the ion-imprinting process on the selectivity
of the prepared U-HAPF resin can be evaluated using relative se-
lectivity coefficient βr, which can be calculated using the follow-
ing equation (Monier and Abdel-Latif, 2013a):
βr ¼ βimprint=βnon-imprint
(5)
where βimprint and βnon-imprint are the selectivity coefficients of U-
HAPF and NI-HAPF resins, respectively.
Desorption and reusability experiments
qe ¼ ðCi ꢀ CeÞV=W
(1)
Desorption and regeneration experiments were performed utiliz-
ing HNO3 solution. After loading the studied resin with uranyl
ions, the resin was immersed in a 100 mL 0.5 M HNO3 solution,
and the batches were continuously shaken for 4 h at 30°C. The re-
where qe (mg/g) adsorption capacity; Ci (mg/L) and Ce (mg/L) ini-
tial and equilibrated metal ion concentrations, respectively, V (L)
volume of added solution and W(g) the mass of the adsorbent
(dry).
2+
leased UO2 ions were then estimated and the resin was
removed and reused for five consecutive adsorption–desorption
cycles.
Percent removal ð%Þ ¼ ðCi ꢀ CeÞ x 100 =Ci
(2)
RESULTS AND DISCUSSION
Selective adsorption studies
Samples characterization
The selectivity of the prepared U-HAPF ion-imprinted resin to-
ward uranyl ions compared with the non-imprinted NI-HAPF
was anticipated using the selectivity coefficient, which can be
estimated by equilibrating 0.3 g of the studied resin with
The elemental analysis outcomes displayed in Table 1 tend to be
in accordance with that computed from the proposed [UO2
(HPAP)2] complex structure.
As a way to take into account the coordination manner of the
uranyl complex, the FTIR spectra of the prepared uranyl complex
[UO2(HPAP)2] was compared with that of the free H2PAP ligand.
300 mL multi-component solution mixture containing VO2+
,
Cd2+, Cu2+, and Hg2+ in addition to UO22+, each metal with initial
concentration 20 mg/L. The selectivity coefficient can be esti-
mated according to the following equation (Singh and Mishra,
2009):
Table 1. Elemental analysis of H2PAP and [UO2(HPAP)2]
2þ
2þ
nþ
βUO2 =Mnþ ¼ DUO2 =DM
(3)
Found (calc.) (%)
where DUO22+ and DMn+ can be defined as the distribution coef-
ficient of the UO2 ions and the other metal ion exist in the
2+
Compound
C
H
N
batch system, respectively.
The distribution coefficient (D) was also determined using the
following equation:
H2PAP
[UO2(HPAP)2]
72.4 (72.5)
44.7 (44.5)
5.9 (6.04)
3.2 (3.4)
6.7 (6.5)
4.1 (4.02)
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ION-IMPRINTING PHENOL RESIN HEAVY METALS
Table 2 lists the characteristic peaks of the free ligand, which are
supposed to undertake diagnostic alterations upon coordination
with uranyl ions. The ligand demonstrated two peaks at 3387
and 3350 cmꢀ1, which can be associated with the stretching vi-
brations of the two phenolic O–H groups, powerful peaks at
about 3150 and 1550 cm-1 as a result of N–H stretching and
bending vibrations, respectively, besides the intensive peaks at
around 1270 and 1130 cmꢀ1 corresponding to C–O and C–N
stretching vibrations, respectively. In the uranyl complex, the ab-
sence of one of the phenolic O–H peak at 3350 cmꢀ1, lower shifts
associated with v(N–H), v(C–N), and v(C–O), as well as the ap-
pearance of the characteristic v(O¼U¼O) bands at 880 and
912 cmꢀ1 (Brancatelli, et al., 2013) recommend the coordination
of the ligand to uranyl ions through the deprotonated phenolic
O–H group and the amine nitrogen atom in order to create a
six-membered ring as demonstrated in Scheme 2. The suggested
mode of coordination was in agreement with previous reports
(Brancatelli, et al., 2013; Kianfar and Dostani, 2011).
The electronic spectra of the prepared [UO2(HPAP)2] complex
present a band 250–276 nm, which can be linked to the π → π*
of the aromatic rings. Moreover, other bands at about 570 and
430 nm were also observed, which could be related to the
1Σ+g → 2π4 transition of OUO and charge transfer n → π*,
respectively.
The 1HNMR spectra associated with both H2PAP and its uranyl
complex had been conducted in d6-DMSO. The H2PAP spectra
(Figure 1a) showed singlet peaks at 4.45 ppm and 7.35 ppm re-
lated to the –CH2- aliphatic protons and the 20 amine proton –
NH-, respectively. The multiplet signals observed between 6.6
and 7.12 ppm tend to be designated for the aromatic protons.
In addition, both singlet signals at 9.44 and 9.58 ppm correspond
to the two protons of the two phenolic –OH groups. Alternatively,
the 1HNMR spectrum associated with [UO2(HPAP)2] complex
(Figure 1b) displayed the 20 amine –NH- proton at 7.2 ppm,
Table 2. Characteristic infrared bands (cmꢀ1) of the uranyl complexes
Compound
v(O–H)a
v(O–H)b
v/δ(N–H)
v(C–O)
v(C–N)
v(O¼U¼O)
H2PAP
[UO2(HPAP)2]
3387
3385
3350
—
3150, 1550
3127, 1530
1270
1236
1130
1112
—
880, 912
Figure 1. 1H nuclear magnetic resonance spectra of (a) H2PAP, (b) [UO2(HPAP)2].
J. Mol. Recognit. 2015; 28: 306–315
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M. MONIER ET AL.
Figure 2. 13C nuclear magnetic resonance spectra of (a) H2PAP, (b) [UO2(HPAP)2].
additionally, the disappearance of the singlet peak corresponding
The optimized structures of the H2PAP ligand and its complex
2+
to the phenolic –OH proton at 9.58 ppm give an evidence for the
participation of both the 20 amine nitrogen atom and the
deprotonated phenolic group in the coordination with uranyl ions.
Furthermore, 13C NMR spectra examinations associated with both
ligand and complex (Figure 2a,b) indicated obvious shifts of both C–
O and C–N signals after coordination, revealing that the aforemen-
tioned groups participated in the complexation with uranyl ions.
Accordingly, it’s obvious from the previously mentioned studies
utilizing elemental analysis, FTIR, electronic 1H NMR and 13C NMR
spectra that the H2PAP ligand coordinates with uranyl ions
according to the proposed structure displayed in Scheme 2.
For more evaluation of the conformational changes of the li-
gand H2PAP and upon coordination to uranyl ion, the structures
of the free ligand and its uranyl complex [UO2(HPAP)2] were
drawn using HyperChem program version 8.03 (Hearne, Victoria,
Australia) implemented on a Dell core i5 personal computer
(Round Rock, TX, USA). Geometry optimizations of the free ligands
and its complex with UO22+ carried out using MM+ force field.
with UO2 ion are presented in Structures 1 and 2. As can be
seen, the coordination of the two H2PAP molecules around the
central uranyl ion can form a symmetrical structure, which can
easily perform the condensation polymerization around the phe-
nolic –OH groups as presented in Scheme 2.
The surface morphological structures regarding both uranyl
ion-imprinted U-HPAF and non-imprinted NI-HPAF were analyzed
using SEM, and the photos were displayed in Figure 3. As can be
seen, the ion-imprinted resin demonstrated an irregular and po-
rous surface compared to the non-imprinted resin; this could be
explained as a result of uranyl ions template leaching from the
cross-linked network upon treatment with HNO3 solution.
Structure 1. Molecular modeling of the free ligand H2PAP.
Structure 2. Molecular modeling of the uranyl complex [UO2(HPAP)2].
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ION-IMPRINTING PHENOL RESIN HEAVY METALS
Figure 3. SEM photos of (a) NI-HPAF (b) U-HAPF.
The surface-area measurements of the prepared polymeric
samples have been estimated using the Brunauer–Emmett–
Teller technique, and the outcomes suggested that the surface
area of both U-HPAF and NI-HPAF were 75.45 and 28.23 m2/g, re-
spectively. The comparatively low surface area of the prepared
resins most likely gives a proof for the chemical adsorption of
ions from the cross-linked network. Also, the presence of the C–N
characteristic peaks at about 3150 and 1550 cmꢀ1 indicated that
the active H2PAP ligand moieties are kept intact in the polymeric
matrix network after uranyl ions leaching.
Metal ions uptake studies
2+
UO2 ions on the functional groups of the resin.
Effect of pH on adsorption
The infrared spectra of U-HPAF before and after template uranyl
ion removal, beside that of NI-HPAF resins have been examined
and the spectra are displayed in Figure 4. As can be noticed, the
three studied resins exhibited nearly identical infrared spectra
confirming the identical polymeric backbone of the resin. The
unleashed U-HPAF spectra (Figure 4b) presented a lower shift of
the characteristic peaks corresponding to v(N–H), v(C–N), and v
(C–O) in addition to the appearance of O¼U¼O special diagnostic
peaks at 880 and 912 cmꢀ1, suggesting the coordination according
to the previously mentioned coordination mode (Structure 2). Also,
the absence of these peaks in the spectra of the leashed U-HPAF
(Figure 4c) confirms the complete removal of the template uranyl
The initial pH is one of the essential parameters managing the
metal ion removal process (Shin, et al., 2011; Sun and Wang,
2006). The adsorption capacities of both ion-imprinted and non-
imprinted resins have been examined as a function of the initial
pH and the results are presented in Figure 5. As can be noticed,
the adsorption capacity of both U-HPAF and NI-HPAF exhibited
an understandable increase by raising the pH value. In an acidic
medium, the functional groups implemented in the polymeric net-
work matrix can be easily protonated due to the high availability of
the H+ ions; this protonation will consequently reduce the capabil-
ities of these functional groups to coordinate with the uranyl ions.
Figure 4. Fourier transform infrared spectra of (a) NI-HPAF, (b) U-HPAF befor uranyl leaching, and (c) U-HAPF after uranyl leaching.
J. Mol. Recognit. 2015; 28: 306–315
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M. MONIER ET AL.
adsorption presents an evident decrease by elevating tempera-
ture, which signifies the exothermic character of the uranyl-re-
moval process.
The earlier mentioned thermodynamic functions have been
assessed according to the following series of equations (Reddad,
et al., 2002):
100
80
60
40
20
0
KC ¼ Cad=Ce
(6)
where KC is the equilibrium constant, Cad is the concentration of
uranyl ions adsorbed on the resin at equilibrium (mg/g) and Ce is
the equilibrium concentration of uranyl ions in the solution (mg/L).
To calculate the free energy of the adsorption (ΔGoads), the fol-
lowing equation was employed:
1
2
3
4
5
pH
ΔGo ¼ ꢀRT ln KC
(7)
ads
2+
Figure 5. Effect of pH on the uptake of UO2 ions by U-HPAF and NI-
HPAF (initial concentration 100 mg/L; adsorbent. 1 g/L; contact time 3 h;
shaking rate 150 rpm, 30°C).
Eq. (8), allows evaluating the standard enthalpy (ΔHoads) and en-
tropy (ΔSoads) of the adsorption by plotting lnKC versus 1/T (Figure 6).
lnKC ¼ ΔSoads=R ꢀ ΔHoads=RT
where R (8.314 J/molK) is the gas constant.
(8)
Furthermore, it is apparent that the adsorption capacity exhibited
by the ion-imprinted U-HPAF seemed to be definitely greater than
that displayed by the non-imprinted NI-HPAF resin; this can be ex-
plained possibly due to of the higher surface area offered by U-
HPAF because of the porous morphological structure (Figure 3)
as well as the imprinting process, which often generates selective
UO22+ ions adsorption sites.
The computed thermodynamic functions for the uranyl ions
removal utilizing both U-HPAF and NI-HPAF had been displayed
ads
in Table 3. As can be observed, the negative ΔGo values give
an indication for the spontaneous nature of the adsorption pro-
cess. In addition, the calculated negative ΔHoads as well as ΔSaods
values confirm that the adsorption is definitely an exothermic
process associated with entropy decrease. Similar observations
were previously reported (Monier, et al., 2010).
Adsorption thermodynamics
Regarding the assessment of the thermodynamic parameters in-
cluding Gibbs free energy (ΔG°), enthalpy (ΔH°) as well as entropy
change (ΔS°), the adsorption of uranyl ions on both U-HPAF ion-
imprinted and NI-HPAF non-imprinted resin had been measured
in the temperature range 20–40°C. In both resin types, the
Adsorption kinetics
For more evaluation of the adsorption mechanism, the kinetics of
the uranyl removal was examined by estimation of the amount of
uranyl adsorbed using both NI-HPAF and U-HPAF as a function of
the adsorption time and the results are presented in Figure 7.
Both pseudo-first-order along with pseudo-second-order
models have been utilized for treatment of the obtained experi-
mental data in order to anticipate the mechanism that controls
the entire adsorption process. The mathematical expressions as-
sociated with both pseudo-first-order and pseudo-second-order
models are presented by Eq. (9) and (10), respectively (Monier
and Abdel-Latif, 2013b; Monier, et al., 2010).
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
1=qt ¼ k1=qet þ 1=qe
(9)
where k1 is the pseudo-first-order rate constant (minꢀ1) of ad-
sorption and qe and qt (mg/g) are the amounts of metal ion
adsorbed at equilibrium and time t (min), respectively. The value
of 1/qt was calculated from the experimental results and plotted
against 1/t (minꢀ1). The linear form of pseudo-second-order
equation can be written as
4.0
0.00320 0.00325 0.00330 0.00335 0.00340 0.00345
1/T (K-1)
Figure 6. Plot of lnKC as a function of reciprocal of temperature (1/T) for
the adsorption of UO22+ by U-HPAF and NI-HPAF resin.
Table 3. Thermodynamic parameters for the adsorption of UO22+ on U-HPAF and NI-HPAF resins
System
Kc
ꢀΔGo (kJ/mol)
ΔHo
ΔSo
ads
ads
ads
(kJ/mol)
(J/mol K)
293K
298K
303K
308K
313K
293K
298K
303K
308K
313K
U-HPAF
NI-HPAF
2999
235.2
1249
201.7
628.3
176.5
374
153.6
332.0
141.5
19.5
13.3
17.7
13.1
16.5
13.0
15.4
12.91
15.1
12.8
ꢀ89.53
ꢀ20.04
ꢀ240.56
ꢀ23.10
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ION-IMPRINTING PHENOL RESIN HEAVY METALS
100
90
80
70
60
50
40
30
20
ion-imprinted modified carboxymethyl cellulose.
Adsorption isotherm studies
Intended for additional comprehension of the adsorbate–adsor-
bent interactions, it is essential to accomplish the adsorption iso-
therm studies by calibrating the amount adsorbed as a function
of the equilibrium adsorbate concentration. In this study, a range
of initial uranyl ions concentration between 10 and 400 mg/L
was examined and following the equilibration for 3 h, the equi-
librium concentrations were plotted against the amount of ura-
nyl ion adsorbed (Figure 8). As can be seen, for both U-HPAF
and NI-HPAF resins, it is obvious that the amount of uranyl ions
adsorbed exhibited a spectacular increase as the initial concen-
tration increases prior to the saturation of the adsorbent resin.
The obtained experimental results were fitted with the widely
used Langmuir (Eq. (11)) and Freundlich (Eq. (12)) isotherm
models (Langmuir, 1918; Freundlich, 1906).
0
20
40
60
80
100
120
Time (min.)
Figure 7. Effect of contact time on the uptake of UO22+ ions by U-HPAF
and NI-HPAF resin (initial concentration 150 mg/L, adsorbent 1 g/L,
pH 5.0, shaking rate 150 rpm, 30°C).
1n qe ¼ 1n KF þ 1=nð1n CeÞ
Ce=qe ¼ ð1=KLqmÞ þ ðCe=qmÞ
(11)
(12)
2
t=qt ¼ 1=k2qe þ ð1=qeÞt
(10)
where k2 is the pseudo-second-order rate constant of adsorption
(g/(mg min)).
where KF and n were Freundlich constants, which affect the ad-
The kinetic parameters estimated from the aforementioned
models were collected in Table 4. Both correlation coefficients
(R2) and standard deviation were employed to investigate the
most appropriate model that fit with the obtained experimental ki-
netic data. As can be observed, the second-order model exhibited
the higher R2 values and lower standard deviation. Furthermore,
the calculated amounts adsorbed (qe) using the second-order
model was much more close to the experimental values. Accord-
ingly, the pseudo-second-order model is the most appropriate
model for treatment of the experimental kinetic data in case of
both ion-imprinted U-HPAF and non-imprinted NI-HAPF revealing
that the chemical adsorption step is the rate-determining step
without involvement of a mass transfer in the solution (Yurdakoç,
et al., 2005).
sorption process, such as adsorption capacity and intensity of
140
120
100
80
60
40
20
0
0
50
100
150
200
250
300
350
The pseudo-second-order kinetic model was also the most ap-
propriate for treatment of the kinetic adsorption data in the studies
performed by Donia et al. (2009), where uranyl was removed using
glycidyl methacrylate chelating resins; Xie et al. (2009), in which
uranyl ions were removed using hematite; Liu et al (2010), where
uranyl was adsorbed using ion-imprinted chitosan/polyvinyl
alcohol (PVA) cross-linked hydrogel and Monier and Abdel-Latif
(2013b), where uranyl ions were selectively adsorbed using surface
Ce (mg/L)
Figure 8. Adsorption isotherms of UO22+ ions by U-HPAF and NI-HPAF
resin (initial concentration 10–400 mg/L, adsorbent 1 g/L, pH 5.0, shaking
rate 150 rpm, 30°C).
2+
Table 5. Parameters for UO2 ions adsorption by U-HPAF
and NI-HPAF resins according to different equilibrium models
Table 4. Kinetic parameters for UO22+ adsorption by U-HPAF
Resin
Langmuir isotherm
constants
and NI-HPAF resins
Resin
First-order model
k1 (minꢀ1
qe1(mg/g)
KL(L/g)
qm(mg/g)
R2
)
R2
U-HPAF
NI-HPAF
Resin
20.7 × 10ꢀ2
11.3 × 10ꢀ2
139.3
86.5
0.9989
0.9999
U-HPAF
NI-HPAF
Resin
8.768
6.456
95
60
3
4
0.9334
0.8988
Freundlich isotherm
constants
Second-order model
k2 (g/(mg min))
qe2 (mg/g)
R2
KF
sn
R2
U-HPAF
NI-HPAF
5.3 × 10ꢀ3
4.1 × 10ꢀ3
98
59
1
1
0.9998
0.9987
U-HPAF
NI-HPAF
22.212
13.435
2.879
4.212
0.8988
0.1987
J. Mol. Recognit. 2015; 28: 306–315
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/jmr

M. MONIER ET AL.
Table 6. Selactive adsorption of UO2(II) from multicompo-
nent mixtures by U-HPAF and NI-HPAF resins (initial concen-
tration 20 mg/L, adsorbent 1 g/L, shaking rate 150 rpm,
solution pH 5.0, 30°C)
Table 7. Repeated adsorption of UO22+ ions by U-HPAF (ini-
tial concentration 100 mg/L, U-HPAF 1 g/L, pH 5.0, contact
time 3 h, shaking rate 150 rpm, 30°C)
Cycle number
Adsorption capacity (%)
Metal
Distribution
ratio (L/g)
Selectivity
Relative
selectivity
coefficient βr
1
2
3
4
5
100
99.3
99
98.5
97.2
coefficient
2+ n+
/M
βUO2
U-HPAF NI-HPAF U-HPAF NI-HPAF
UO22+
396.34
11.34
—
—
VO2+
Cd2+
Cu2+
Hg2+
5.23
7.67
8.56
4.87
11.05
9.78
10.54
5.76
75.78
51.67
43.15
81.39
1.02
1.16
1.07
1.97
74.3
44.54
40.33
41.31
Separation selectivity
The uranyl selective separation studies had been conducted
using both U-HPAF and NI-HPAF resins in presence of VO2+
,
Cd2+, Cu2+ and Hg2+ ions, which are chosen as competitive
ions because of the similar charge and coordination mode
with uranyl ion. The selectivity coefficient and the other
parameters were listed in Table 6. It is obvious that the uranyl
ion-imprinted U-HPAF resin exhibits a higher selectivity toward
the uranyl ions compared with the rest of the competitive
ions. These results could be attributed to the formation of
the complementary recognition sites in the ion-imprinted
resin, which match the charge, coordination and geometry of
the uranyl ions.
adsorption, respectively. Freundlich isotherm parameters were
estimated by plotting lnqe versus lnCe. qm (mg/gꢀ1) and KL were
Langmuir parameters associated with the monolayer adsorption
capacity and energy of adsorption, respectively.
The estimated Langmuir parameters along with Freundlich pa-
rameters combined with the correlation coefficients were gath-
ered in Table 5. It is apparent from the correlation coefficient
values that, in both resin types, Langmuir adsorption isotherm
model is the most appropriate model describing the experi-
mental adsorption data, indicating monolayer adsorption pat-
tern on energetically homogeneous surface. The maximum
adsorption capacities for both U-HPAF and NI-HPAF were
139.3 and 86.5 mg/g. The higher capacity provided by the
ion-imprinted compared with the non-imprinted resin could
be explained as a result of both the higher surface area
and the imprinting effect.
The suitability of the adsorption process could be evaluated
by calculating the separation factor constant (RL): RL >1.0, unsuit-
able; RL =1, linear; 0 < RL <1, suitable; RL =0, irreversible (Zhou,
et al., 2012). The RL value can be estimated according to the fol-
lowing equation:
Desorption and reusability studies
A 0.5-M HNO3 solution was utilized for desorption and regen-
eration experiments of the ion-imprinted U-HPAF resin and
the results are presented in Table 7. As can be noticed, after
five adsorption–desorption cycles, the resin still maintain
about 97% of its original efficiency, which indicate that the
prepared resin is promising, with high adsorption efficiency
and high economic value for selective and fast removal of
uranyl ions.
CONCLUSIONS
In the present study, U-HAPF ion-imprinted resin has been syn-
thesized by condensation polymerization of uranyl complex with
H2PAP and resorcinol in the presence of a formaldehyde cross-
linker. The ion-imprinted resin exhibited high adsorption ability
toward the template uranyl ions particularly at pH 5. The adsorp-
tion process follows the pseudo-second-order kinetics model.
Furthermore, the adsorption isotherm can be well described by
the Langmuir model with maximum capacity of 139.3 mg/g. Ad-
ditionally, the ion-imprinted resin showed a high selectivity to-
ward uranyl ions in presence of VO2+, Cd2+, Cu2+ and Hg2+ as
competitive metal ions.
RL ¼ 1=ð1 þ C0KLÞ
(13)
where KL is the Langmuir equilibrium constant and C0 (10–400 mg/L)
is the initial concentration of the UO2(II) ions. The values of RL
lie between 0.0119 and 0.326, indicating the suitability of the
imprinted resin as adsorbents for UO2(II) from an aqueous
solution.
Langmuir adsorption isotherm model showed the best fit in
some other previous studies including Donia et al. (2009), where
uranyl was removed using glycidyl methacrylate chelating resins;
Xie et al. (2009), in which uranyl ions were removed using hema-
tite; Liu et al. (2010) where uranyl was adsorbed using ion-
imprinted chitosan/PVA cross-linked hydrogel; and Monier and
Abdel-Latif (2013b), where uranyl ions were selectively adsorbed
using surface ion-imprinted modified carboxymethyl cellulose,
which are in agreement with our study.
Acknowledgements
The authors are grateful to Dr S. Das and Dr M. Shamma for the
great support regarding the instrumental analysis particularly
scanning electron microscope and NMR spectra.
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