Thermodynamic and Kinetic Studies for Adsorption of Reactive Blue (RB-19) Dye Using Calix[4]arene-Based Adsorbent

Article abstract of DOI:10.1021/acs.jced.9b00223

A current study demonstrates the removal of Reactive Blue 19 (RB-19) from industrial wastewater by synthesizing p-piperdinocalix[4]arene-immobilized silica resin (PASR). The surface morphology and functional group analysis were performed with scanning electron microscopy and Fourier transform infrared spectroscopy. The dye removal efficiency of PASR was analyzed through adsorption studies. Different parameters were optimized such as the pH value of dye, amount of resin, concentration of dye, and effect of electrolyte on adsorption. The adsorption mechanism was analyzed with Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. It was found that experimental data follow the Freundlich isotherm, which suggests multilayer adsorption. The column adsorption study was also evaluated by breakthrough and Thomas models. The Thomas model rate constant k_TH (cm³ mg^-1 min^-1) and maximum solid phase concentration was found to be q_o = 2.702 mg·g^-1. The thermodynamic study reveals that the adsorption process is exothermic and spontaneous in nature. The kinetic study suggests that the adsorption process follows the pseudo-second-order kinetic model.

Full text of DOI:10.1021/acs.jced.9b00223

Article
pubs.acs.org/jced
Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Thermodynamic and Kinetic Studies for Adsorption of Reactive Blue
(RB-19) Dye Using Calix[4]arene-Based Adsorbent
Ranjhan Junejo,† Shahabuddin Memon,† Fakhar N. Memon,‡ Ayaz Ali Memon,*,† Fatih Durmaz,§
Asif Ali Bhatti,∥ and Ashfaque Ali Bhatti†
†National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080, Pakistan
‡Department of Chemistry, University of Karachi, Karachi 75270, Pakistan
§Department of Chemistry, Selcuk University, Konya 42075, Turkey
∥Department of Chemistry, Government College University Hyderabad, Hyderabad 71000, Pakistan
ABSTRACT: A current study demonstrates the removal of
Reactive Blue 19 (RB-19) from industrial wastewater by
synthesizing p-piperdinocalix[4]arene-immobilized silica resin
(PASR). The surface morphology and functional group analysis
were performed with scanning electron microscopy and Fourier
transform infrared spectroscopy. The dye removal efficiency of
PASR was analyzed through adsorption studies. Different
parameters were optimized such as the pH value of dye, amount
of resin, concentration of dye, and effect of electrolyte on
adsorption. The adsorption mechanism was analyzed with
Langmuir, Freundlich, and Dubinin−Radushkevich (D−R)
isotherms. It was found that experimental data follow the
Freundlich isotherm, which suggests multilayer adsorption. The
column adsorption study was also evaluated by breakthrough
and Thomas models. The Thomas model rate constant kTH (cm3 mg−1 min−1) and maximum solid phase concentration was
found to be qo = 2.702 mg·g−1. The thermodynamic study reveals that the adsorption process is exothermic and spontaneous in
nature. The kinetic study suggests that the adsorption process follows the pseudo-second-order kinetic model.
adsorbents have been produced. In this regard, calixarene-
functionalized adsorbents with different solid supports have
been efficiently used for the removal of azo dyes. The
structural frame of calixarene serves as the receptor for a
number of ionic and neutral guest species due to its flexible
shape.18 The upper- or lower-rim calixarene molecule offers an
appropriate place for introducing different functional groups
that can bind with several toxic dyes,19 such as 5,11,17,23-
tetrakis(N-piperidinomethyl)-25,26,27,28-tetrahydroxycalix-
[4]arene, 5,11,17,23-tetrakis(N′-methyl-N-piperazinomethyl)-
25,26,27,28-tetrahydroxycalix[4]arene, and 5,11,17,23-tetrakis-
[(dimethylamino)methyl]-25,26,27,28-tetrahydroxy-calix[4]-
arene, have been applied for the liquid−liquid extraction of
sulfonated dyes such as red-2 (RR-2), acid black (AB), and
(RB-19), respectively.20 Keeping in view of the above
performance of calixarene, in this study, we have synthesized
the p-piperdinomethylcalix[4]arene and immobilized on the
surface of silica to provide a solid support and increase its
surface area for the maximum efficiency of dye removal with a
regenerable property.
1. INTRODUCTION
Synthetic colorants such as azo dyes are used in industries
worldwide.1,2 It is reported that about 7 × 105 tons of dyes are
produced each year and used in the textile, food, and ink
production.3,4 The textile industry is a major cause of water
pollution because of the dye effluent.5,6 About 1000 tons of the
textile waste effluent has been discharged each year into fresh
water, which contains a number of different unreacted azo
dyes.7,8 Reactive dyes are anionic dyes that can be easily
dissolved in water and mainly used for dyeing of cotton rayon,
silk, wool, nylon, etc.9,10 The chemical structure of the dye
molecule is biologically inactive, but degradation by micro-
organisms makes it possible to cleave the azo (NN) group,
which results in the formation of aromatic amines that are toxic
as well as carcinogenic in nature.11,12 Thus, they become
harmful for the aquatic life and cause many environmental
problems.13 Conventionally, different techniques were used for
the removal of azo dyes such as adsorption, photodegradation,
membrane separation, electrolytic chemical treatment, catalytic
processes, and ozone treatment.14 The adsorption process has
got much more attention for the treatment of dye-
contaminated water due to easy application, low cost, higher
efficiency, and reproducibility.15−17 Therefore, different types
of inexpensive, reproducible, and environmentally favorable
Received: March 12, 2019
Accepted: June 12, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.jced.9b00223
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2. EXPERIMENTAL SECTION
Article
and some other possible impurities, the synthesized material
was filtered and washed with 200 mL of each solvent such as
CHCl3, methanol, water, and again CHCl3. To check the
amount of attached p-piperdinomethylcalix[4]arene onto the
silica surface, the gravimetric analysis has been performed, and
it was found that the maximum amount attached onto the silica
surface was 0.396 mmol/g.
2.4. Adsorption Procedure. 2.4.1. Batch Adsorption.
Batch adsorption was carried out in a 25 mL Erlenmeyer flask
containing 0.075 g of adsorbent in 10 mL of RB-19 dye
solution (2 × 10−5 M) and equilibrated at mechanical shaker
with a constant speed of 120 rpm at 25 °C for 60 min. The
adsorbent was filtered off, and the concentration of dye was
analyzed before and after equilibrium by a UV−Vis
spectrophotometer at λmax = 596 nm. The percent (%)
adsorption and adsorption capacity of RB-19 have been
calculated by using the following equations:
2.1. Chemicals. All liquid reagents and solvents used
during the experimental work were of analytical grade. p-
Tertiarybutyl phenol and commercial textile RB-19 was
purchased from Sigma-Aldrich (St. Louis, MO, USA).
Toluene, tetrahydrofuran, dichloromethane, and chloroform
were dried before use. Silica gel (130−270 particle mesh size)
was purchased from Sigma-Aldrich (St. Louis, MO, USA).
Precoated silica gel plates (SiO2, Merck PF254) were used for
analytical TLC. Deionized water was used for the preparation
of solutions. The real wastewater samples were obtained from
textile and dye industries. HCl/NaOH solutions (0.1 M) were
used to maintain the pH of dye solution.
2.2. Instrumentations. FTIR spectra were recorded on a
Thermo Nicolet 5700 FTIR spectrophotometer (WI. 53711,
USA) as KBr pellets. A JSM-6380 instrument was used to
perform scanning electron microscopy (SEM). The concen-
tration of dye was analyzed with a Perkin Elmer (Shelton,
CT06484 USA) Lambda 35 UV−VIS spectrophotometer. The
pH meter (781-pH/Ion meter, Metrohm, Herisau Switzer-
land) with a glass electrode and an internal reference electrode
was used to determine/maintain the pH values of solutions.
The Gallenkamp thermostat automatic mechanical shaker
(model BKS 305−101, UK) was used for the batch adsorption
study.
Ci − Cf
% adsorption =
× 100
Ci
(1)
(Ci − Ce)V
qe =
(2)
m
2.4.2. Dynamic Adsorption Study. The dynamic adsorption
study has been performed using a (6 mm × 10 cm) glass
column containing the optimized quantity of the adsorbent.
The dynamic adsorption capability of the adsorbent was
observed by passing the solution of RB-19 dye at optimized pH
with a flow rate of 2 mL/min using a peristaltic pump. The
efficiency of p-piperdinocalix[4]arene-immobilized silica resin
(PASR) was evaluated by a breakthrough curve, which gives
the exhaustion capacity, and experimental data was fitted to the
Thomas model to calculate the adsorption capacity.
2.3. Synthesis. Compounds 1, 2, and 3 were synthesized
by the reported methods (Scheme 1),21−23 whereas the
immobilization of compound 3 onto silica resin was carried out
according to the following modified method.24
Scheme 1. Syntheses of Calix[4]arene Derivatives: (i)
HCHO/NaOH, (ii) AlCl3/Phenol, and (iii) Piperidine/
HCHO/Acetic Acid
3. RESULTS AND DISCUSSION
3.1. FTIR Analysis. The FTIR spectroscopy analysis helps
to determine the presence of different functionalities in the
compound. Figure 1a represents the pure silica resin spectrum
that indicates a strong absorbance peak at 1094 cm−1 for
asymmetric Si−O−Si. The strong peak in a functional group
region at 3455 cm−1 appeared due to the presence of the −OH
stretching band. The spectrum shown in Figure 1b shows
characteristic bands for p-piperdinomethylcalix[4]arene (3),
and the bands observed at 3400, 3010, 1596, and 1463 cm−1
indicative of OH, CH2, C−C, and C−N stretching,
respectively. Moreover, the attachment of p-
piperdinomethylcalix[4]arene (3) onto silica can be evidenced
in the spectrum shown in Figure 1c. The appearance of some
additional bands of p-piperdinomethylcalix[4]arene at 3445,
2932, 1465, and 1092 cm−1 indicates the presence of OH,
CH2, C−C, and C−N of the calixarene moiety, respectively,
and Si−O groups of silica confirming the immobilization of
compound 3 onto the silica surface.
3.2. Scanning Electron Microscopy Analysis. Scanning
electron microscopy (SEM) is the technique through which
the surface morphology of the adsorbent are analyzed because
the adsorption is a surface phenomenon, and the rate and
degree of adsorption depend upon the surface properties that
include surface area and porosity. SEM micrographs were
obtained in this regard and are very demonstrative. Figure 2
shows the micrograph of pure silica. Figure 2a has smooth
surface morphology; however in Figure 2b, the rough surface
2.3.1. Synthesis of p-Piperdinomethylcalix[4]arene-Immo-
bilized Silica Resin. Five grams of silica was treated with 0.1 M
HCl, filtered, and then neutralized by washing with deionized
water (Scheme 2). Afterwards, the deionized silica sample was
dried at about 120 °C in an oven for 8 h. Then, the dried silica
sample was placed in a round-bottom flask, and 250 mL of 0.1
M SiCl4 solution was added under stirring in CH2Cl2 followed
by 5 mL of triethylamine and kept for 12 h at room
temperature. Consequently, the solvent was removed, and 1.5
g of p-piperdinomethylcalix[4]arene was dissolved in chloro-
form that was then added in treated silica resin followed by an
addition of 3 mL of trimethylamine and refluxed for 72 h.
Immobilization of compound 3 was confirmed by FTIR and
SEM. To remove unattached p-piperdinomethylcalix[4]arene
B
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Scheme 2. Attachment of p-Piperdinomethylcalix[4]arene onto the Silica Surface
Figure 1. FTIR spectra of (a) pure silica, (b) p-piperdinomethylcalix[4]aren-immobilized silica resin (PASR), and (c) p-piperidinomethylcalix-
[4]arene.
of silica can be seen due to the presence of calixarene. This
irregular morphology is very helpful in the adsorption process.
3.3. Optimization of Different Parameters. 3.3.1. Dos-
age Effect. The effect of the adsorbent dosage for the
adsorption (RB-19) was observed by using varying amounts of
adsorbent from 0.025 to 1.50 g with the fixed concentration of
RB-19 (2 × 10−5 M). It can be seen from Figure 3 that the %
adsorption of RB-19 increases by increasing the amount of the
adsorbent. The maximum % adsorption (99% of RB-19) was
observed from 0.125 g of adsorbent. After that, a very slight
increase in % adsorption was detected up to 0.075 g, and it
remains constant at a higher amount of the adsorbent such as
0.075−0.150 g. This may be due to the saturation of the
adsorbent. Further, experiments were carried out using 0.125 g
of adsorbent.
3.3.2. Electrolyte Effect. The effects of different electrolytes
(NaCl, NaOH, Na2CO3, CH3COONa, and NaHCO3) on the
adsorption process have been examined. It is clear in Figure 4
that the adsorption capacity of PASR remains higher than
NaCl, whereas its adsorption capability decreases with the
addition of other electrolytes such as NaOH, Na2CO3,
CH3COONa, and NaHCO3. The electrolytes affect increases
in the order of NaCl < CH3COONa < NaHCO3 < Na2CO3 <
NaOH. It shows that the NaCl increases % adsorption by
C
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Figure 2. SEM images of (a) pure silica and (b) p-piperdinomethylcalix[4]arene-immobilized silica resin PASR.
Figure 3. Effect of the adsorbent dosage 0.025−0.2 g on the %
adsorption of RB-19 dye (60 min of contact time 0.1 M NaCl and 10
mL of dye concentration 2 × 10−5 M).
Figure 5. pH effect on the adsorption of RB-19 (0.05 g PASR) 1 h of
contact time, 0.1 M NaCl and dye concentration of 2 × 10−5 M.
low pH values, H+ ions found in surplus that participate with
the dye molecule for adsorption sites present over the
adsorbent surface. In addition, at higher pH slightly, electro-
static repulsion of negatively charged surface sites does not
favor the adsorption of dye molecules onto the adsorbent
surface; therefore, % adsorption decreases. It can be clearly
observed that the deprotonated amine functionalities of
calix[4]arene moiety show less physical interaction toward
the ions of RB-19 molecules.
3.4. Adsorption Isotherms. Table 1 shows the parameters
calculated from three adsorption isotherms, that is, Langmuir,
Freundlich, and Dubinin−Radushkevich (D−R) at different
temperatures. Adsorption isotherms explain the mechanism as
well as the amount of adsorbate adsorbed onto the surface of
the adsorbent.26 The adsorption isotherm also describes the
adsorption capacity, multilayer or monolayer formation, and
type of interaction in between the adsorbate and adsorb-
ent.26−30 Therefore, in this study, Langmuir, Freundlich, and
D−R adsorption isotherms have been applied to experimental
data under the optimized conditions to assess the adsorption
capacity of the adsorbent. The linear forms of these three
adsorption isotherms are given as follows:
Figure 4. Roles of different electrolytes (concentration: 0.1 M) in the
adsorption of RB-19 dye (concentration: 2 × 10−5 M).
increase salting out itself and neutral behavior. Obviously,
other electrolytes can disturb the pH value of dye solution;
therefore, % adsorption may decrease.
3.3.3. Effect of pH. The role of pH for the ionization of dye
solution is very important due to the nature of functional
groups present on the surface of the adsorbent.25 In this
experiment, pH of dye solution was maintained in a range of
pH 1−11, while the adsorbent dosage was 0.125 g, 1 h contact
time, 0.1 M NaCl, and 10 mL dye solution (2 × 10−5 M). The
maximum adsorption (96%) was observed at pH 4 (Figure 5).
Overall, the acidic pH value remains more favorable for the
adsorption of RB-19. At the basic pH value, it was observed
that % adsorption of RB-19 decreases. The reason behind this
dramatical decrease in % adsorption by increasing the pH value
is due to the deprotonation of the adsorbent and dye molecule.
It may be due to the protonation of nitrogen functionality that
coordinates with negatively charged molecules of RB-19. At
Ce
Cads
Ce
Q
1
Qb
=
+
(3)
1
ln Cads = ln A + ln Ce
(4)
(5)
n
ln Cads = ln Xm − βε2
D
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Table 1. Langmuir, Freundlich, and D−R Adsorption
Isotherm Parameters at Different Temperatures
Langmuir
temperature (K)
Q (mol/g)
b
RL
R2
293
303
313
3.93
5.99
8.62
1203
3391
2247
0.99−0.21
0.99−0.22
0.99−0.12
0.600
0.899
0.891
Fruendlich
A (mg g−1
temperature (K)
)
n
R2
293
303
313
0.0013
0.065
0.042
2.11
1.60
1.87
0.838
0.99
0.99
Figure 7. Freundlich adsorption isotherm (concentration: 1.50 ×
10−10 to 2.00 × 10−5 M, with 60 min shaking time at different
temperatures).
D−R
temperature (K)
Xm (mmol/g)
E (kJ/mol)
R2
293
303
313
14.17
2.70
7.09
10.2
12.5
11.7
0.985
0.685
0.897
i
y
1
Ce
j
j
z
z
ε = RT lnj1 +
z
j
j
z
z
(6)
k
{
Langmuir adsorption isotherm is selective and describes that
only one molecule or ion can bind to each site of the
adsorbent, and there is no interaction in between neighboring
ions, increasing the adsorbate concentration, adsorption
increases.31 The plot of Ce/Cads versus Ce was obtained with
a regression coefficient of R2 = 0.199 (Figure 6). However, the
adsorption process can be reversible or irreversible and that
can be explained by the separation factor RL (RL = 1 + (1/
bCi)).
In above equation, T shows the absolute temperature (K),
whereas R is the ideal gas constant (kJ/mol/K). E shows the
mean adsorption energy mentioned below in eq 7:
1
E =
−2β
(7)
When the values of ε are plotted against ln Cads (mol/g), a
linear graph with a correlation coefficient of R2 = 0.977 was
shown in Figure 8. Table 1 shows the results of D−R
Figure 6. Langmuir adsorption isotherm plot (concentration: 1.50 ×
10−10 to 2.00 × 10−5 M, with 60 min shaking time at different
temperatures).
Figure 8. D−R isotherm (concentration: 1.50 × 10−10 to 2.00 × 10−5
M, with 60 min shaking time at different temperatures).
adsorption models in which the Xm value was found to be
0.343, and the E value 12.9 kJ/mol indicating that the
adsorption process is chemical in nature.
The Freundlich adsorption isotherm model (q 3) is used to
calculate the heterogeneity of the adsorbent surface32 and
describes the multilayer adsorption.33 The graph was plotted
for ln Ce versus ln Cads (Figure 7). From the slop and intercept,
the value of A and n can be calculated. The Freundlich
isotherm model shows good regression coefficient R2 (0.990)
suggesting best fit to experimental data for the adsorption of
RB-19 dye onto PASR. The value of n reveals the favorability
and degree of heterogeneity. Calculated from the Freundlich
model, n > 1 suggests favorable adsorption conditions.17
The Dubinin−Radushkevich (D−R) isotherm model is
applied to describe and distinguish the physical and chemical
adsorption nature of the adsorption mechanism. An important
factor in the D−R model, the polynie potential (ε) can be
calculated as follows:34
3.5. Column Adsorption. The continuous-flow adsorp-
tion experiment was conducted in a glass column, and a
breakthrough curve was observed against time (Figure 9). The
time and shape of the curve were important parameters to
analyze the column operation and response of the column
adsorption. The position of the curve depends upon the flow
rate and concentration of dye solution. The breakthrough
curve can be describe in terms of the inlet dye concentration
(Ci), concentration of dye adsorbed (Cs), and outlet
concentration of dye (Ct) or normalized concentration. It
can be defined as the ratio of the effluent concentration of dye-
to-inlet concentration of dye (Ct/Co) as a function of volume
of the effluent or time. The optimized conditions for the batch
E
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(mLmin−1), A is the quantity of material adsorbed, and Veff
expresses the effluent volume, which can be obtained from the
q 9
V
= Qttotal
(9)
eff
where ttotal stands for the total flow time, Q is the flow rate, and
Veff stands for the effluent volume.
3.5.2. Kinetic Study. Kinetics is an important factor for the
determination of the adsorption mechanism. Experimental data
was fitted to two well-known kinetic models, namely,
Langergren or pseudo-first-order (q 10) that is based on
assumption that the rate-limiting step may be the physical
adsorption, whereas Ho and McKay or the pseudo-second-
order kinetic (q 11) model suggest that the adsorption
mechanism is the rate-controlling step and chemical in
nature35,36
Figure 9. Breakthrough curve of RB-19 dye (concentration: 2.00 ×
10−5 M).
adsorption study were also applied in the dynamic adsorption
at a flow rate of 2 mL min−1 to remove RB-19 (2 × 10−5 M)
from water through PASR (0.125 g). The breakthrough
volume was calculated from the plot of Ct/Ci versus V (mL).
The results show that the column achieved breakthrough at
Ct/Ci = 0.21 RB-19 dye with a bed volume of 5 mL and took
approximately 25 mL to exhaust.
ln(qe − qt) = ln qe − k1t
(10)
i
j
j
j
j
j
j
y
z
i
j
j
j
j
j
j
y
z
z
z
z
z
z
t
qt
1
k2qe
1
qe
z
z
=
+
t
z
2 z
z
(11)
k
{
k
{
3.5.1. Thomas Model. The knowledge of the breakthrough
curve or concentration time profile helps to design the column,
which should be effective and have the maximum removal
capacity of target molecules. Usually, the Thomas model is an
effective tool to evaluate the results of the column adsorption.
The results of dynamic adsorption data were analyzed through
the Thomas model to determine (qo), which is the maximum
solid-phase concentration and the (kTH) Thomas rate constant.
Equation 8 shows the linear form Thomas model, and
constants values were calculated by plotting the graph for
Ci
where k1 and k2 are the adsorption rate constants for pseudo-
first-order and pseudo-second-order kinetics, respectively. The
linear relationship was observed for the pseudo-first-order
kinetic and pseudo-second-order kinetic models as shown in
Figures 11 and 12. The values of k1, k2 (1/min), and qe (mg/g)
ln
− 1 against t (min) at the constant flow rate (igure
(
)
Cr
10). The magnitude of the maximum solid phase concentration
Figure 11. Pseudo-first-order kinetic graph for RB-19 dye (60 min of
contact time, 0.1 M NaCl, and 10 mL of dye with a concentration of 2
× 10−5 M).
were obtained from the slopes and intercepts of the linear plots
and presented in Table 2. Parameters in Table 2 show that the
C0
C
Figure 10. Thomas model graph of ln
(concentration: 2.00 × 10−5 M).
− 1 vs t for RB-19 dye
(
)
of the solute and Thomas model rate constant kTH was found
to be 2.702 with the coefficient of determination (R2 = 0.76)
for RB-19.
i
y
kTHqoA
Q
Ci
Ce
KTH
Q
C
j
z
jln
− 1z =
−
i V
eff
j
z
j
j
z
z
(8)
k
{
Here, Ci and Ce show the initial concentration and effluent
concentration (mg L−1), respectively. Q is the flow rate
Figure 12. Pseudo-second-order graph (60 min of contact time, 0.1
M NaCl, and 10 mL of dye with a concentration of 2 × 10−5 M).
F
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Table 2. Comparison of Kinetic Models
pseudo-first-order kinetic model
pseudo-second-order kinetic model
temperature
K1 (1/min)
qe (mol/g)
R2
K2 (g/mol/min)
qe (mol/g)
R2
303
308
313
0.0001
0.0010
0.0379
0.0700
0.0700
0.0237
0.589
0.297
0.872
16276.3
30185.8
8138.7
2.12 × 10−07
3.43 × 10−07
8.20 × 10−06
0.972
0.999
0.999
kinetic mechanism follows the pseudo-second-order model as
experimental data significantly fitted well with the correlation
coefficient value of R2 = 0.99,
3.5.3. Thermodynamics of Adsorption. Different thermo-
dynamic factors concerning the adsorption method, for
example, ΔH (kJ/mol), ΔS (J/mol/K), and ΔG (kJ/mol)
were estimated from following equations
Table 3. Thermodynamic Parameters for RB-19 onto the
PASR
ΔG (kJ/mol)
ΔH
ΔS
(kJ/mol)
(kJ/mol/K)
303 K
308 K
−4.61
ln Kc = 1.8
313 K
−5.32
ln Kc = 2.0
−0.03
0.115
−3.03
ln Kc = 1.2
−ΔH
ΔS
R
ln KC =
+
(12)
(13)
RT
The negative value of ΔG under applied conditions implies
the spontaneity of the dye adsorption process. Moreover, the
exothermic nature of adsorption observed from the negative
value of ΔH. Additionally, the increase in the value of ln Kc
(1.2, 1.8, and 2.0 at 303, 308, and 313 K, respectively) with the
rise of temperature showed that the RB-19 adsorption onto
PASR was an exothermic process and does not depend on the
temperature. The randomness increases during the adsorption
at the solid/solution, an edge that implies its positive value.
3.5.4. Field Application of PASR. To ensure the PASR as a
competent adsorbent for RB-19, a field study of PASR for real
wastewater samples containing RB-19 dye has also been carried
out. Batch experiments have been performed with PASR
contaminated with RB-19 at the optimized conditions. The
concentration of RB-19 dye was investigated before and after
the treatment of wastewater samples by UV−VIS spectropho-
tometry at its particular wavelength 593 nm. The results are
summarized in Table 4. The lower concentration of RB-19 in
ΔG = −RT ln KC
where ΔH is enthalpy, ΔS is entropy, ΔG is the Gibbs free
energy, and T is the absolute temperature, R is the gas
constant, and KC is the equilibrium constant. The temperature
effect was observed in the range of 293 to 313 K on the
adsorption of RB-19 on PASR under optimum conditions. It
has been observed that increasing the temperature ultimately
increases the adsorption capacity (Figure 13).
Table 4. RB-19 Dye Concentration in the Wastewater
Samples before and after Treatment with the PASR
sample
no.
concentration before
treatment (ppm)
concentration after
treatment (ppm)
% removal
Figure 13. % adsorption curves of RB-19 onto PASR as a function of
different temperatures from 293 to 313 K.
1
2
3
0.836
0.750
0.552
0.0157
0.2306
0.0403
98.12
69.26
92.69
The mathematical values of ΔH and ΔS were calculated
from the plot of ln Kc versus 1/T using eq 12 (Figure 14) and
presented in Table 3.
the wastewater samples after the treatment indicates that PASR
is an efficient adsorbent and could be successfully employed
for the decontamination of RB-19 from the industrial effluent.
A comparative table (Table 5) has been provided to show the
efficiency of PASR with other synthesized material. It can be
observed that PASR has good efficiency along with other
reported materials.
4. CONCLUSIONS
In summary, the work demonstrates the synthesis of p-
piperdinomethylcalix[4]arene-immobilized silica resin (PASR)
and its application for the removal of RB-19 from the industrial
effluent. Experimental results show that the adsorption of RB-
19 is pH dependent, and the adsorption process follows the
Freundlich and Dubinin−Radushkevich (D−R) isotherm
models. Thermodynamic and kinetic studies suggest that the
adsorption process is exothermic and spontaneous in nature
and follow the pseudo-second-order kinetic model. Moreover,
Figure 14. Effect of the temperature on the adsorption of the RB-19
azo dye onto p-piperdinomethycalix[4]arene-immobilized silica resin
(PASR).
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Journal of Chemical & Engineering Data
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Table 5. Comparison of PASR with Other Adsorbents for
the Removal of Azo Dyes
adsorbent
azo dye
acid
orange 7
acid
orange 7
acid
orange 7
pH
% adsorption
31
ref
̈
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̈
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37
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39
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horseradish peroxidase
5.0
7.4
89
75
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(HRP)-immobilized
calcium alginate gel
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RB-19
RB-19
1.0
4.0
98
96
PASR
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AUTHOR INFORMATION
Corresponding Author
*E-mail: ayazmemon33@gmail.com. Phone: +92 (22)
9213430. Fax: +92 (22) 9213431.
■
ORCID
Ayaz Ali Memon: 0000-0002-9018-4856
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are highly thankful to the National Centre of Excellence in
Analytical Chemistry, University of Sindh, Jamshoro, Sindh,
Pakistan for the financial support of this work.
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