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REACTIVE
Reactive & Functional Polymers 64 (2005) 63–73
&FUNCTIONALPOLYMERS
www.elsevier.com/locate/react
Adsorption of resorcinol and catechol from aqueoussolution by aminated hypercrosslinked polymers
Yue Sun *, Jinlong Chen, Aimin Li, Fuqiang Liu, Quanxing Zhang
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University,
Nanjing 210093, PR China
Received 20 October 2004; received in revised form 7 March 2005; accepted 17 March 2005
Available online 22 June 2005
Abstract
A series of aminated hypercrosslinked polymers (AH-1, AH-2 and AH-3) were prepared on the basis of the conven-
tional chloromethylated low-crosslinked macroporous styrene–divinylbenzene copolymers by controlling the post-
crosslinking reaction and surface modification with dimethylamine. Adsorption behaviour of resorcinol and catechol
from aqueous solution onto the above aminated hypercrosslinked polymers and the hypercrosslinked polymeric adsor-
bent NDA-100 without amino groups was compared. It was found that the aminated hypercrosslinked polymers had
higher adsorption capacities than NDA-100 due to the Lewis acid–base interaction between the phenolic compounds
and the tertiary amino groups on the polymer matrix. Specific surface area and micropore structure of the adsorbent, in
company with tertiary amino groups on the polymer matrix mutually affect the adsorption performance towards the
both phenolic compounds. Additionally, more catechol is adsorbed than resorcinol due to the affinity towards water
and position of the hydroxyl group on the benzene ring of the compound. Besides, thermodynamic study was carried
out to interpret the adsorption mechanism. Kinetic study testified that the tertiary amino groups on the polymer matrix
could decrease the adsorption rate and increase the adsorption apparent activation energy.
� 2005 Elsevier B.V. All rights reserved.
Keywords: Hypercrosslinked polymer; Resorcinol; Catechol; Adsorption; Thermodynamics; Kinetics
1. Introduction
Phenol and its derivatives are versatile raw
materials in chemical industry. As a result, they
1381-5148/$ - see front matter � 2005 Elsevier B.V. All rights reserv
doi:10.1016/j.reactfunctpolym.2005.03.004
* Corresponding author.
are widely found in the effluence of their manu-
facture and subsequent usage. Because of their
high toxicity, high oxygen demand and low bio-
degradability, phenolic compounds are consid-
ered as primary pollutants in wastewater [1,2].Consequently, the removal or destruction of phe-
nols from such streams has become significant
ed.
64 Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73
environmental concern. During the past decades,
resin adsorption technology as a method of
recovery of resource has been widely adopted
for the treatment of effluents containing phenolic
compounds [3–5]. In comparison with such classi-cal adsorbents as silica gels, aluminas and acti-
vated carbons, polymeric adsorbents are of
particular interest for their high chemical stabil-
ity, easy regeneration, excellent selectivity and
longevity. Among them, the commercial resin
Amberlite XAD-4 has ever been considered the
best one for the removal of phenolic compounds
from wastewater [3,6]. Subsequently, the hyper-crosslinked polymers developed by Davankov
were discovered better contact with aqueous
phase and larger adsorption capacities towards
aromatic organics, especially the phenols with
limited solubility such as 2-naphthol [7–9]. How-
ever, they appear to possess much lower adsorp-
tion capabilities towards organic compounds
that exhibit a strong affinity towards water [10].Consequently, there is a clear need for new poly-
functional adsorption materials to efficiently re-
move these strongly hydrophilic compounds
from aqueous media. Thus, some scientists have
made more efforts on chemical modification of
polymeric adsorbents to improve their adsorption
properties owing to the presence of some special
interactions between adsorbates and adsorbents[11–14]. In the present study, three aminated
hypercrosslinked polymeric adsorbents (AH-1,
AH-2 and AH-3) were prepared from the conven-
tional chloromethylated low-crosslinked macro-
porous styrene–divinylbenzene copolymers by
controlling the post-crosslinking reaction and sur-
face modification with dimethylamine expectantly
to remove hydrophilic phenolic compounds. Twoderivatives of phenol, namely resorcinol and cat-
echol, are chosen as the target solutes since both
of them have high toxicity, high solubility and
further, widely exist in the effluents of many
industries such as textile, paper, pulp, steel, petro-
chemical, petroleum refinery, rubber, dyes, plas-
tics, pharmaceutical and so on [15]. The focus
of this work is to compare the adsorption ofthe two phenolic compounds from aqueous solu-
tion onto the aminated hypercrosslinked resins
(AH-1, AH-2, AH-3) and the hypercrosslinked
resin (NDA-100). The adsorption thermodynam-
ics and kinetics were further discussed.
2. Experimental
2.1. Materials
Resorcinol and catechol were purchased from
Shanghai Chemical Reagent Plant (Shanghai
City, China) and dissolved in deionized water in
adsorption tests without pH adjustment. The
chloromethylated low-crosslinked macroporousstyrene–divinylbenzene copolymers (the DVB
content 6% and the chlorine content 19.5%),
1,2-dichloroethane, zinc chloride, ethanol and
aqueous dimethylamine (40 wt%) were all sup-
plied by Langfang Electrical Resin Co. Ltd. (He-
bei Province, China).
2.2. Synthesis of adsorbents
2.2.1. Post-crosslinking
In a 100 mL three-necked round-bottomed flask
equipped with a mechanical stirrer, a thermometer
and a reflux condenser, 10 g of chloromethylated
low-crosslinked macroporous styrene–divinylben-
zene copolymer beads were swollen in 60 mL 1,2-
dichloroethane. Under mechanical stirring,weighted zinc chloride was added at 298 K. The
mixture was further stirred at 388 K for 2–12 h
to get post-crosslinked polymer beads with differ-
ent residual chloride content. Then the polymer
beads were filtered and extracted with ethanol
for 8 h in a Soxhlet apparatus and dried under vac-
uum at 333 K.
2.2.2. Chemical modification of the post-crosslinked
polymers
In a 100 mL three-necked round-bottomed flask
equipped with a mechanical stirrer, a thermometer
and a reflux condenser, 10 g of the post-cross-
linked polymer beads of a known residual chloride
content were swollen in 60 g of aqueous dimethyl-
amine (40 wt%). Under mechanical stirring, theamination reaction continued for 12 h at 318 K.
Finally, the reaction mixture was filtered and the
modified adsorbents AH-1, AH-2 and AH-3 were
Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73 65
extracted with ethanol for 8 h in a Soxhlet appara-
tus and then dried under vacuum at 333 K.
2.3. Characterization of adsorbents
Chlorine content of the polymers was mea-
sured using the Volhard method [16]. Tertiary
amino group content of the aminated polymers
was measured according to the literature [3].
Specific surface area and pore structure of the
resins were measured with an ASAP-2010C
Micromeritics Instrument (Micromeritics Instru-
ment Corp., Norcross, GA, USA) with nitrogenas the adsorbate following the BET method.
Infrared spectra of the polymeric adsorbents
were obtained using a Nicolet 170 SX IR spec-
trometer (Nicolet Instrument Corp., Madison,
WI, USA) employing a pellet of powdered
potassium bromide and resin.
2.4. Static adsorption
Static adsorption of resorcinol and catechol on
the adsorbents at three temperatures (283, 298 and
313 K) was conducted as follows: 0.100 g of dry re-
sin was introduced into a flask and 100 mL of
aqueous solution of resorcinol or catechol was
added into each flask. The initial concentrations
(C0) of the solutions ranged from 100 to1000 mg/L. The flasks were completely sealed
and placed in a constant temperature shaker (Taic-
ang Guangming Experimental Instrument Co.
Ltd., Jiangsu Province, China) at a pre-settled
temperature and shaken at 200 rpm for 24 h to en-
sure the adsorption process reaching equilibrium.
The equilibrium concentration (Ce) of resorcinol
and catechol was determined using a Helious Betra
CH CH2 CH CH2
CH2 CH2Cl+ NH CH3
CH3
Fig. 1. Scheme of am
UV–VIS spectrometer (Unicam, Cambridge, UK).
The corresponding equilibrium adsorption capac-
ity Qe (mmol/g) was calculated via the following
equation:
Qe ¼ V ðC0 � CeÞ=WM ; ð1Þwhere V is the volume of solution (L), W is the
mass of dry resin (g) and M is the molecular
weight of resorcinol or catechol.
2.5. Kinetic adsorption
Kinetic adsorption of resorcinol and catechol
onto the resins NDA-100, AH-1, AH-2 and AH-
3 was carried out in the way similar to the static
adsorption tests, except for that the initial concen-
tration of each adsorbate was settled at 1000 mg/L
in all cases at 298 and 313 K. The instantaneous
adsorbate uptakes on the resins were calculated
by measuring the concentration of adsorbate insolution at different contact time.
3. Results and discussion
3.1. Characteristics of the polymeric adsorbents
Three post-crosslinked polymers were preparedfrom the chloromethylated low-crosslinked macro-
porous polymer beads by controlling the residual
chloride content, and then the hypercrosslinked
resins AH-1, AH-2 and AH-3 containing tertiary
amino groups were obtained by the amination of
these post-crosslinked polymers with dimethyl-
amine. The amination reaction scheme is shown
in Fig. 1. The hypercrosslinked resin NDA-100without amino groups was prepared in the way
CH CH2 CH CH2
CH2 CH2N(CH3)2
ination process.
Table 1
Characteristics of the four adsorbents
Property NDA-100 AH-1 AH-2 AH-3
Structure St-DVBa St-DVB St-DVB St-DVB
Hypercrosslinked Amine-modified Amine-modified Amine-modified
Hypercrosslinked Hypercrosslinked Hypercrosslinked
Polarity Weak polar Moderate polar Moderate polar Moderate polar
BET surface area (m2/g) 934 819 726 483
Micropore area (r 6 1 nm, m2/g) 561 463 394 261
Micropore volume (r 6 1 nm, cm3/g) 0.25 0.21 0.18 0.12
Tertiary amino group (mmol/g) 0 1.51 2.10 2.75
Average pore diameter (nm) 2.4 2.4 2.6 3.0
Average particle size (mm) 0.4–0.6 0.4–0.6 0.4–0.6 0.4–0.6
Chlorine content before amination (%) 6.02 6.02 8.10 10.50
Chlorine content after amination (%) 0.85 0.76 0.84
Colour Brown Brown Yellow Yellow
a Abbreviated form of styrene–divinylbenzene.
66 Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73
similar to AH-1, AH-2 and AH-3, but without
chemical modification process.
The characteristics of the tested adsorbents are
presented in Table 1. It can be seen from Table 1
that the post-crosslinked polymers can be ami-
nated by dimethylamine effectively, and the resid-
ual chlorine content is very low after amination.
The hypercrosslinked resin NDA-100 has the larg-est surface area, micropore area and micropore
volume among the four resins but without tertiary
amino groups on the matrix. The content of ter-
tiary amino groups of AH-1, AH-2 and AH-3 in-
creases in turn but all the specific surface area,
Fig. 2. IR spectr
micropore area and micropore volume accordingly
decrease. The presence of tertiary amino groups on
the aminated hypercrosslinked polymers was fur-
ther supported by the absorbance bands at 2772
and 1347 cm�1 in IR spectra from Fig. 2.
3.2. Static equilibrium adsorption
Fig. 3 shows the equilibrium adsorption iso-
therms of resorcinol and catechol on the adsor-
bents at 283 K. The data were analyzed using the
empirical Freundlich equation [17]:
logQe ¼ logKF þ 1=n logCe; ð2Þ
a of AH-1.
0 2 4 6 8 100.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6 (a)
Qe (
mm
ol/g
)
Ce (mmol/L)
0 2 4 6 80.00.20.40.60.81.01.21.41.61.82.02.2 (b)
Qe (
mm
ol/g
)
Ce (mmol/L)
Fig. 3. Adsorption isotherms of: (a) resorcinol and (b) catechol onto (e) NDA-100, (h) AH-1, (n) AH-2 and (·) AH-3 at 283 K.
Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73 67
where Qe is the equilibrium adsorption capacity of
adsorbent (mmol/g); Ce is the equilibrium concen-
tration of adsorbate (mmol/L), KF and n are the
characteristic constants. All the isotherm parame-
ters could be determined from the experimental
data by plotting log Qe against log Ce on the basisof the above equation. The Freundlich isotherms
parameters KF, n, and the square of the correlative
coefficients R2 are listed in Table 2.
All the equations are reliable because of the
square of all the correlative coefficients R2 > 0.98.
The values of KF, a relative indicator of adsorption
capacity from Freundlich theory [17], indicate that
the aminated hypercrosslinked polymers AH-1,AH-2 and AH-3 have more effective adsorption
sites than NDA-100. The exponent n is larger than
one in all cases, an indication of favorable pro-
cesses. The adsorption capacities (Qe) on the
adsorbents calculated with Freundlich equations
corresponding to the same residual concentration
Table 2
Freundlich isotherms parameters for adsorption of resorcinol and ca
Adsorbate Adsorbent KF
Resorcinol NDA-100 0.4441
Resorcinol AH-1 0.5937
Resorcinol AH-2 0.6909
Resorcinol AH-3 0.6653
Catechol NDA-100 0.5109
Catechol AH-1 1.015
Catechol AH-2 1.145
Catechol AH-3 1.024
a Calculated by isotherm equations when Ce = 4.0 mmol/L.
(Ce) of 4.0 mmol/L are also listed in Table 2. At
283 K, when Ce = 4.0 mmol/L, the adsorption
capacities of AH-1, AH-2 and AH-3 are 25.6%,
47.7%, 42.2% towards resorcinol and 54.7%,
70.9%, 60.6% for catechol higher than those of
NDA-100, respectively.Generally speaking, surface area, micropore
structure, as well chemical surface heterogeneity
of a hypercrosslinked polymer usually put much
influence on its adsorption capacity [13,14,18].
All the specific surface area, micropore area and
micropore volume of NDA-100 are the largest
among the tested resins, but its capacity is the low-
est, thus the significant difference in adsorptioncapacity is not only related to the specific surface
area or micropore structure. It is reasonable that
the higher adsorption capacities of the aminated
hypercrosslinked polymers are attributed to the
presence of tertiary amino group on their net-
works. According to Lewis acid–base theory, the
techol on the adsorbents
n R2 Qe(mmol/g)a
2.286 0.9846 0.8144
2.547 0.9866 1.023
2.499 0.9926 1.203
2.503 0.9909 1.158
2.028 0.9955 1.012
3.245 0.9987 1.556
3.357 0.9970 1.730
3.001 0.9988 1.625
68 Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73
benzene ring of aromatic-based resin and the ter-
tiary amino groups on it can be viewed as Lewis
bases, while phenolic compounds can be viewed
as Lewis acids [12]. Therefore, the Lewis acid–base
interaction may occur between phenolic com-pounds and the benzene ring as well as the tertiary
amino group of the resins, which leads to the for-
mation of a hydrogen bonded complex. The inter-
action can be interpreted qualitatively in terms of
the Lewis acidity and basicity [19,20]. The solvato-
chromic parameters a and b for resorcinol and cat-
echol are given in Table 3. For the values of
benzene ring and tertiary amino group on resinsare not available, they are approximated by the
values of the close homologues, namely, benzene
and triethyl amine, respectively. A larger a corre-
sponds to a greater ability of a molecule, or actu-
ally of the functional group to accept electrons or
serve as a Lewis acid in an association complex.
Conversely, a larger b corresponds to a greater
ability of a molecule or group, to donate electronsor serve as a Lewis base. From Table 3, it will be
found that both resorcinol and catechol can serve
as a Lewis acid and also a Lewis base. The fact
that triethyl amine has a larger value of b than
benzene, indicates that tertiary amino group on
the resin network acts as a stronger Lewis base
than benzene ring of the resin, which leads to a
stronger Lewis acid–base interaction between theboth phenolic compounds and tertiary amino
group than that between them and benzene ring.
This is probably the primary reason for the in-
creased adsorption capacity of the aminated
hypercrosslinked polymers over that of NDA-
100. In addition, the adsorption capacity towards
resorcinol and catechol on AH-2 with moderate
content of tertiary amino groups is highest amongthe three aminated hypercrosslinked polymers but
not AH-3, which has the most tertiary amino
groups. It is because that all the specific surface
Table 3
Acidity and basicity parametersa
Solute Resorcinol Catechol Benzene Triethyl amine
a 1.10 0.85 0 0
b 0.58 0.52 0.14 0.71
a Taken from [19,20].
area, micropore area and micropore volume of
the polymers decrease with increasing content of
tertiary amino groups. In a word, specific surface
area, micropore structure and content of tertiary
amino groups together dominate the adsorptionproperty of the aminated hypercrosslinked
polymers.
Resorcinol has a larger value of a than catechol
indicating a stronger Lewis acid–base interaction
between it and the tertiary amino group on the re-
sin, but as is evident from Table 2, the adsorption
capacity of catechol is larger than that of resor-
cinol onto the aminated resins. The difference inadsorbability can be explained in terms of the sol-
ubility and polarity of adsorbate and the position
of hydroxyl group on the benzene ring. The solu-
bility of resorcinol in water is much higher than
that of catechol (229 and 46 wt%, respectively
[21]), thus it shows stronger affinity towards water.
This may be one of the possible reasons for its
lower adsorption capacity. In addition, the match-ing of polarity between adsorbent and adsorbate is
also an important factor affecting adsorption of
phenolic compounds. The tertiary amino nitrogen
on the resins has a large dipole moment, and the
dipole moment of catechol is larger than that of
resorcinol (2.620 and 2.071 D, respectively [22]),
therefore, the interaction between the resins and
catechol is expected to be stronger than that be-tween the resins and resorcinol. Furthermore,
some researches revealed that the same functional
group but at the ortho position greatly enhances
the adsorption energy of such compound as cate-
chol used in the present study [15]. Thus cumula-
tive effects of solubility and position of the
hydroxyl group at the ortho position may probably
account for higher adsorbability of catechol thanresorcinol onto not only aminated hypercross-
linked polymers but also NDA-100.
3.3. Thermodynamics of resorcinol and catechol
adsorbed onto NDA-100, AH-1, AH-2 and AH-3
As discussed above, the aminated hypercross-
linked polymers demonstrated excellent adsorp-tion capabilities towards resorcinol and catechol.
Comparing with NDA-100, the thermodynamic
study of AH-1, AH-2 and AH-3 was thus carried
Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73 69
out to explore the adsorption mechanism. The
isosteric enthalpy change of adsorption herein
was calculated by Van�t Hoff equation [23].
logð1=CeÞ ¼ logKe þ ð�DH=2.303RT Þ; ð3Þ
where Ce is the equilibrium concentration of solute
in mol/L at the absolute temperature T; DH is the
isosteric enthalpy change in adsorption and R is
the gas constant. Ce was obtained from the well-
suited isotherms corresponding to a definite Qe va-
lue at different temperatures (283, 298 and 313 K).
DH was then calculated from the slope of the lineplotted by log (1/Ce) versus 1/T, and some of the
plotted lines are shown in Fig. 4.
The adsorption free energy change was calcu-
lated from the Freundlich isotherm by employing
the Gibbs equation [1,23]:
DG ¼ �nRT ; ð4Þ
0.0031 0.0032 0.0033 0.0034 0.0035 0.00362.2
2.4
2.6
2.8
3.0
3.2
3.4(a)
log
(1/C
e(mol
/L))
1/T (K)
Fig. 4. Determination of isosteric enthalpy changes of adsorption towa
1, (m) AH-2 and (d) AH-3 at adsorption capacity Qe = 0.5 mmol/g.
Table 4
Calculated thermodynamic parameters for adsorption of resorcino
(Qe = 0.5 mmol/g)
Adsorbate Adsorbent DH (kJ/mol) DG (kJ/mol)
283 K 2
Resorcinol NDA-100 �24.93 �5.38 �Resorcinol AH-1 �31.37 �5.99 �Resorcinol AH-2 �31.17 �5.88 �Resorcinol AH-3 �30.27 �5.89 �Catechol NDA-100 �25.31 �4.77 �Catechol AH-1 �33.76 �7.64 �Catechol AH-2 �33.26 �7.90 �Catechol AH-3 �36.72 �7.06 �
where n is the parameter of the Freundlich equa-
tion and DG is the free energy change in an adsorp-
tion process.
The adsorption entropy change then could be
calculated via the Gibbs–Helmholtz relationship[23]:
DS ¼ ðDH � DGÞ=T . ð5ÞWhen the equilibrium adsorption capacity is
determined as 0.5 mmol/g adsorbent, the values
of the isosteric enthalpy change (DH, kJ/mol), free
energy change (DG, kJ/mol) and entropy change(DS, J/mol K) calculated from the data obtained
in the present study were thoroughly presented in
Table 4.
From Table 4, exothermic adsorption processes
are testified by the negative values of all the isos-
teric enthalpy changes. The larger absolute values
of adsorption isosteric enthalpy changes of AH-1,
0.0031 0.0032 0.0033 0.0034 0.0035 0.00362.4
2.8
3.2
3.6
4.0
4.4(b)
log
(1/C
e(m
ol/L
))
1/T (K)
rds: (a) resorcinol and (b) catechol onto (.) NDA-100, (n) AH-
l and catechol within the temperature range of 283–313 K
DS (J/mol K)
98 K 313 K 283 K 298 K 313 K
4.97 �4.66 �69.08 �66.98 �64.76
5.74 �5.99 �89.68 �86.01 �81.09
5.75 �5.25 �89.36 �85.30 �82.81
5.17 �5.20 �86.15 �84.23 �80.10
4.54 �4.12 �72.58 �69.70 �67.70
7.71 �6.96 �92.30 �87.42 �85.62
7.93 �7.60 �89.61 �85.00 �81.98
6.88 �6.56 �104.81 �100.13 �96.36
70 Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73
AH-2 and AH-3 mean the interactions between the
two phenolic compounds and the aminated hyper-
crosslinked resins are stronger than that between
them and NDA-100 due to the Lewis acid–base
interaction. The adsorption free energy changesare always negative proving that the adsorption
processes of resorcinol and catechol on adsorbent
surface are all spontaneous. In addition, the abso-
lute values of adsorption free energy changes of
the aminated hypercrosslinked resins are larger
than that of NDA-100, suggesting that the adsorp-
tion of resorcinol and catechol is easier onto the
former resins. The entropy changes during theadsorption of resorcinol and catechol on all
the employed adsorbents are negative, indicating
that the activity of adsorbate molecules on the
adsorbents is weaker than those in the aqueous
solution. In comparison with NDA-100, the abso-
lute values of the adsorption entropy changes of
AH-1, AH-2 and AH-3 are large, which indicates
that the adsorbate molecules are more tight and
0 50 100 150 200 2500.0
0.2
0.4
0.6
0.8
1.0
1.2 (a)
Q (
mm
ol/g
)
t (min)
0 50 100 150 200 2500.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6(c)
Q (
mm
ol/g
)
t (min)
Fig. 5. Effect of contact time on the uptake of: (n) resorcinol at 313 K
298 K onto: (a) NDA-100; (b) AH-1; (c) AH-2; (d) AH-3 (C0 = 1000
ordered on the aminated hypercrosslinked resins.
Furthermore, the fact that the absolute values of
the isosteric enthalpy change, free energy change
and entropy change of adsorption on the aminated
hypercrosslinked resins towards catechol are alllarger than those for resorcinol, indicates the bet-
ter adsorbed property of the former. This is con-
sistent with the conclusion made in the static
equilibrium adsorption study.
3.4. Kinetics of resorcinol and catechol adsorbed
onto NDA-100, AH-1, AH-2 and AH-3
Kinetic sorption of resorcinol and catechol
onto NDA-100, AH-1, AH-2 and AH-3 was car-
ried out to explore the feasibility of this type of
resins in the removal of the two phenolic com-
pounds from water stream. The influence of con-
tact time on the uptake of resorcinol and catechol
onto NDA-100, AH-1, AH-2 and AH-3 was
shown in Fig. 5.
0 50 100 150 200 2500.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6 (b)
Q (
mm
ol/g
)
t (min)
0 50 100 150 200 2500.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6(d)
Q (
mm
ol/g
)
t (min)
; (·) resorcinol at 298 K; (n) catechol at 313 K; (s) catechol at
mg/L).
Table 5
Kinetic parameters for adsorption of resorcinol and catechol onto NDA-100, AH-1, AH-2 and AH-3
Adsorbate Adsorbent Temperature (K) ln (1 � Qt/Qe) = �k t Ea (kJ/mol)
k (min�1) R2
Resorcinol NDA-100 298 0.0343 0.9848 22.50
Resorcinol NDA-100 313 0.0530 0.9895
Resorcinol AH-1 298 0.0303 0.9905 24.21
Resorcinol AH-1 313 0.0484 0.9952
Resorcinol AH-2 298 0.0224 0.9934 32.62
Resorcinol AH-2 313 0.0421 0.9908
Resorcinol AH-3 298 0.0180 0.9806 34.67
Resorcinol AH-3 313 0.0352 0.9910
Catechol NDA-100 298 0.0258 0.9806 24.82
Catechol NDA-100 313 0.0417 0.9851
Catechol AH-1 298 0.0238 0.9839 26.19
Catechol AH-1 313 0.0395 0.9881
Catechol AH-2 298 0.0187 0.9899 32.70
Catechol AH-2 313 0.0352 0.9939
Catechol AH-3 298 0.0148 0.9874 35.13
Catechol AH-3 313 0.0292 0.9833
Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73 71
The adsorption rate constants for the removal
of resorcinol and catechol by the resins were deter-
mined using the pseudo first-order kinetic expres-
sion [24]:
lnð1� Qt=QeÞ ¼ �kt; ð6Þwhere Qt is the uptake (mmol/g) of adsorbate attime t; Qe is the equilibrium uptake (mmol/g); k
and t are the rate constant and time, respectively.
The kinetic data obtained within 80 min were plot-
ted relating ln (1 � Qt/Qe) with the contact time t
at 298 and 313 K, respectively, and k was therefore
obtained from the slope of the linear relationship.
The apparent activation energy was calculated via
the Arrhenius equation:
k ¼ k0 expð�Ea=RT Þ; ð7Þ
where k is the rate constant (1/min); k0 is a param-
eter related to temperature (1/min); Ea is the
apparent activation energy (J/mol); R is the gas
constant (8.314 J/mol K); and T is the absolute
temperature (K). The values of the rate constantsand the square of the correlation coefficients along
with the apparent activation energy are listed in
Table 5.
Fig. 5 shows the sorption equilibrium com-
pleted within about 3 h of contact time with the
initial resorcinol or catechol concentration C0 of
1000 mg/L and the higher temperature is favor-
able to attaining equilibrium but leads to lower
sorption uptake. From Table 5, it will be found
that the adsorption of the two phenolic com-
pounds onto the resins conformed to be the
first-order process because the square of all the
correlation coefficients (R2) are higher than 0.98.
Under the same temperature, for both adsor-bates, the values of rate constant k decrease in
the following order: AH-3 < AH-2 < AH-
1 < NDA-100. Some researchers have studied
the effect of chemical surface heterogeneity on
the adsorption of dissolved aromatic compounds
on activated carbon and found that water adsorp-
tion happened on the hydrophilic, polar oxygen
groups and then water clusters were built up onthese groups by hydrogen-bonding interaction
[25]. The water clusters can effectively reduce
the width of the pores and then the diffusion rate
will slow down. Similarly it may occur on AH-1,
AH-2 and AH-3 for the presence of tertiary ami-
no group on the resin matrix and then water
adsorption can happen to slow down the adsorp-
tion rate [26]. The order of apparent activationenergy required for the adsorption of both resor-
cinol and catechol onto the resins is: NDA-
100 < AH-1 < AH-2 < AH-3. This may also be
attributed to the Lewis acid–base interaction.
72 Y. Sun et al. / Reactive & Functional Polymers 64 (2005) 63–73
4. Conclusions
Post-crosslinking reaction and surface modifi-
cation of the conventional chloromethylated
low-crosslinked macroporous polymers werestudied and three aminated hypercrosslinked res-
ins AH-1, AH-2 and AH-3 were obtained. The
adsorption capacities of both resorcinol and cate-
chol on the aminated hypercrosslinked resins
AH-1, AH-2 and AH-3 are higher than on the
hypercrosslinked resin NDA-100 without amino
groups. Specific surface area, micropore structure
and content of tertiary amino groups play acombined role during the adsorption of the both
compounds onto the aminated hypercrosslinked
polymers.
Negative values of the isosteric enthalpy
changes indicate that the adsorption towards res-
orcinol and catechol on the tested resins is exother-
mic. The negative values of adsorption free energy
changes demonstrate the spontaneous processes.The entropy changes are negative, indicating
the weaker activity of adsorbate molecules on the
adsorbents than in the aqueous solution. The
absolute values of the above three thermodynamic
parameters of AH-1, AH-2 and AH-3 are all larger
than those of NDA-100 indicating that the ami-
nated hypercrosslinked resins exhibited better
adsorption abilities towards resorcinol andcatechol.
Kinetic sorption study of resorcinol and cate-
chol onto NDA-100, AH-1, AH-2 and AH-3 indi-
cates a first-order kinetic behaviour. The aminated
hypercrosslinked resins show a lower adsorption
rate than NDA-100 for the presence of water clus-
ters. Furthermore, the values of apparent activa-
tion energy required for the adsorption increasewith the rising content of tertiary amino groups
on the resin matrix for Lewis acid–base
interaction.
Acknowledgements
The authors thank the National Natural Sci-ence Foundation of China (No. 20274017). We
are grateful to the Analytical Center at Jiangsu
Polytechnic University for the measurement of
the specific surface area and pore structure, and
the State Key Laboratory for Coordination
Chemistry at Nanjing University for the IR
data.
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