Rapid adsorption of binary dye pollutants onto the nanostructred mesoporous alumina

Article abstract of DOI:10.1016/j.molliq.2014.08.023

In this study ordered mesoporous alumina (OMA) with pore size of about 5 nm has been used for removal of dye pollutants from binary systems including methyl orange+ bromothymol blue, methyl orange + reactive yellow and methyl orange + methyl violet. Deriv

Full text of DOI:10.1016/j.molliq.2014.08.023

MOLLIQ-04403; No of Pages 8
Journal of Molecular Liquids xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
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Rapid adsorption of binary dye pollutants onto the nanostructred
mesoporous alumina
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Q1 Bahareh Yahyaei, Saeid Azizian ⁎
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Department of Physical Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan, Iran
5
a r t i c l e i n f o
a b s t r a c t
OOF
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1
Article history:
Received 22 July 2014
Received in revised form 14 August 2014
Accepted 18 August 2014
Available online xxxx
In this study ordered mesoporous alumina (OMA) with pore size of about 5 nm has been used for removal of dye 16
pollutants from binary systems including methyl orange + bromothymol blue, methyl orange + reactive yellow 17
and methyl orange + methyl violet. Derivative spectrophotometry was used for simultaneous determination of 18
the dyes concentrations. The results show that OMA is a good adsorbent for rapid removal of dyes (especially 19
anionic ones) from aqueous solution. Characterization of OMA has been performed by TEM and XRD techniques. 20
The adsorption kinetic data of binary dye mixtures follows the competitive statistical rate theory (SRT) model well. 21
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Keywords:
Dye pollutants
Rapid adsorption
Binary solutions
Ordered mesoporous alumina
©
2014 Published by Elsevier B.V. 22
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1. Introduction
aluminas to remove copper from aqueous solution. Lee et al. [13] used 50
MA to remove fluoride from water. Inumaru et al. [14] used alkyl- 51
grafted mesoporous alumina to remove alkylphenols and alkylanilines 52
from water. In our recent work we have used OMA to remove single 53
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Many kinds of synthetic dyes have been used in food, pharmaceuti-
cal and textile industries. The discharge of the waste water of these
industries has harmful effects on to the human health and the environ-
ment. Thus, removal of dye pollutants from aqueous solutions is neces-
sary. Within various methods for removal of pollutants from aqueous
solutions, such as ion exchange, membrane filtration, etc., adsorption
is the most common method. Many kinds of adsorbents such as activat-
ed carbons [1], biological adsorbents [2], polymeric adsorbents [3], etc.
have been used for dye removal from aqueous solutions. Among these
adsorbents, the mesoporous materials are effective adsorbents for dye
removal from aqueous solutions, due to their unique properties such
as similar pore size, high surface area and tunable structures [4]. Many
types of mesoporous materials were synthesized by different methods
and were used for different purposes [5–9]. For example the biological
application of mesoporous silica (MS) [4], the optical and electronic
applications of mesoporous WO
of pollutant from water by MA [10] and mesoporous carbon [8] have
been reported previously.
Although alumina was used extensively as adsorbent [11], the
specific structure of ordered mesoporous alumina which makes it better
adsorbent than alumina has been considered by many researchers. For
example Rengaraj et al. [12] used aminated and protonated mesoporous
dye pollutants from aqueous solution [15].
54
Although the removal of individual dyes from water has been 55
studied by many researches [16–18], the industrial wastewater usually 56
consists of the mixture of dyes. Thus, the removal of dye mixtures from 57
industrial wastewater is too important.
58
Spectrophotometry is the common way to determine the concentra- 59
tions of dyes, but in some cases, the spectra of dyes in the binary mix- 60
tures overlap. In this situation the determination of dyes concentration 61
for adsorption studies is limited. Derivative spectrophotometry is the 62
way to solve this limitation [19]. This method is based on the analysis 63
of derivative spectra generated from the UV–vis absorption spectra of 64
zero order [20,21]. Thus, in the present study we have used the deriva- 65
tive spectroscopy to determinate simultaneous concentration of dyes 66
3
–TiO
2
composites [4] and the removal
in binary mixtures during the adsorption process.
67
Different methods such as double hydrolysis route [22], sol–gel pro- 68
cess [23] and spin coating method [24] have been used to synthesize 69
MA. In the present study OMA has been synthesized according to Grant 70
et al.'s [25] method, using aluminum iso-propoxide as aluminum source, 71
F127 triblock copolymer as a pore directing agent and ethanol as a sol- 72
vent. The synthesized OMA has been used for removal of dye pollutants 73
from binary systems including methyl orange (MO) with bromothymol 74
blue (BTB), reactive yellow (RY) and methyl violet (MV). The adsorption 75
process was followed by UV–vis spectroscopy and the proper wave- 76
UNCORRECTED PR
⁎
Corresponding author. Tel.: +98 8118282807; fax: +98 8118380709.
E-mail address: sazizian@basu.ac.ir (S. Azizian).
lengths were determined from second derivative spectra.
77
http://dx.doi.org/10.1016/j.molliq.2014.08.023
167-7322/© 2014 Published by Elsevier B.V.
0
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B. Yahyaei, S. Azizian / Journal of Molecular Liquids xxx (2014) xxx–xxx
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2. Experimental
2.1. Materials
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Aluminum iso-propoxide (for synthesis), ethanol (99.8%), methyl
violet (MV) and nitric acid (65%) were purchased from Merck Co. and
Pluronic F127 (MW = 12600) from Sigma-Aldrich. Methyl orange
(MO), reactive yellow (RY) and bromothymol blue (BTB) were
purchased from Fluka, Alvan Sabet Co. (Iran) and BDH companies,
respectively.
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2.2. Instruments
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0
1
UV–vis spectrophotometer (PG-T80) was used to obtain UV–vis
spectra. The X-ray diffraction pattern of ordered mesoporous alumina
was gained by a Phillips apparatus “PW 1710” with Cu-Kα radiation.
Transmission electron microscope Philips CM120 was used for TEM
image.
9
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2.3. Preparation and characterization of OMA
Fig. 2. The TEM images of the obtained OMA along [1 1 0] and [0 0 1] directions. The scale-bar
represents 50 nm. The ordered hexagonal pore openings along [0 0 1] direction are shown by
a hexagonal image.
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OMA was synthesized according to Grant et al.'s [25] method. Briefly
the ethanolic solution of F127 was prepared by dissolving 0.75 g F127 in
40 ml absolute ethanol. The obtained solution was stirred at room
temperature for 4 h. After that 1.0213 g of aluminum iso-propoxide
and 0.85 ml HNO 65% were added to the solution. The stirring of the
3
obtained mixture was continued at room temperature for another 5 h.
2.4. Batch adsorption experiments
116
The final mixture was oven dried at 60 °C for 48 h. The calcination of
Batch adsorption experiments were performed at concentration of 117
0 mg/l for each binary solution. In each experiment a series of 5 ml 118
00 the obtained specimen was carried out in a quartz tube furnace under
01 atmospheric air by heating at 1 °C/min to 400 °C and keeping at
02 400 °C for 4 h.
1
of dye binary solutions with 3 mg of OMA was placed in a shaker 119
150 rpm and 25 °C) and at the proper time intervals the adsorbent 120
(
03
Characterization of the microscopic features of the synthesized OMA
was separated from solution by centrifuge and the absorption spectra 121
of the each solutions have been obtained. The amount of adsorbed dye 122
per unit mass of OMA at time t was calculated by Eq. (1):
04 has been performed using XRD patterns and TEM images. Fig. 1 shows
05 the XRD pattern of the obtained OMA. Broad peaks at the ranges of
06 10° to 40° and 50° to 80° [13,26] and the strong peak around 1.0°,
07 which is shown in the inset of Fig. 1, prove the formation of OMA with
08 amorphous wall. The strong peak around 1.0° identifies the p6mm
09 hexagonal symmetry [22]. The TEM image proves the mentioned
10 structure too (Fig. 2).
123
ðC −C Þ
0
t
qt ¼
V
ð1Þ
W
11
The highly ordered hexagonal pore openings along [0 0 1] direc-
where C
any time, V is the solution volume and W is the mass of adsorbent.
To determine the maximum adsorption capacity (q ) of each dye, 126
0 t
is the initial concentration of each dye, C is its concentration at 125
12 tion and the cylindrical pores along [1 1 0] direction [13,26] are
13 shown by the TEM image (Fig. 2) of the obtained OMA. Also the
14 p6mm hexagonal symmetry for the synthetized OMA has been
15 approved in Fig. 2.
m
5 ml of individual dye solution with high concentration (120 mg/l) and 127
3 mg of OMA were placed in a shaker (150 rpm and 25 °C) for 24 h. 128
Fig. 1. XRD pattern of the prepared OMA. The inset shows the high intensity peaks at low angle regions.
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B. Yahyaei, S. Azizian / Journal of Molecular Liquids xxx (2014) xxx–xxx
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29
The amount of q
m
was calculated by Eq. (2):
According to Eq. (3), to determine the concentrations of RY at its 147
proper wavelength, the molar absorptivities of MO and RY at 415 are 148
required. These values have been specified by using Beer–Lambert law 149
and are 0.0548 (mg/l) cm and 0.0243 (mg/l) cm , respectively. 150
The concentration of BTB was measured at 433 nm, where the BTB 151
derivative signal value is higher than the signal for MO. Therefore the 152
total absorbance at the selected wavelength can be described as Eq. (4). 153
ðC −C Þ
0
e
qm
¼
V
ð2Þ
−1
−1
−1
−1
W
131
where C
.5. Derivative spectrophotometric method
The absorption spectra for both MO–RY and MO–BTB binary systems
e
is the concentration of dye after 24 h.
2
A
¼ AMO ð433 nmÞ þ ABTB ð433 nmÞ
ð4Þ
Tð433 nmÞ
1
1
1
1
1
1
1
1
1
1
1
1
1
32
33 overlap (Figs. 3a and 4a, respectively). Thus 2nd derivative spectra of
34 the mentioned binary systems were plotted against the wavelength
35 (λ) to select the appropriate wavelength to determinate the concentra-
36 tions of individual dyes in the binary systems (Figs. 3b and 4b).
where AT (433 nm), AMO (433 nm) and ABTB (433 nm) correspond to the total 155
absorbance for the mixture, MO and BTB at 433 nm, respectively.
The molar absorptivities of MO and BTB at 433 nm have been deter- 156
−
1
−1
−1
−1
mined as 0.0626 (mg/l) cm and 0.0374 (mg/l) cm , respectively. 157
The absorption spectra of MO and MV in the MO–MV binary solution 158
are partially overlapped. In this binary solution the 2nd-derivative 159
method has been used to select the λ values of MO and MV in the binary 160
solution too. The wavelengths of 402 nm and 590 nm have been select- 161
ed for determining the MO and MV concentrations in the MO–MV 162
37
According to the 2nd-derivative spectra, the wavelengths of 534 nm
38 and 550 nm have been selected for determining the MO concentrations
39 in the MO–RY and MO–BTB binary solutions, respectively, where the
40 signal of RY or BTB is near to zero. Determination of RY concentrations
41 in the MO–RY binary solution has been performed at 415 nm, where
42 the RY derivative signal value is higher than the signal of MO. Therefore
43 the total absorbance of RY at the selected wavelength can be described
44 as Eq. (3) [19].
binary solution, respectively.
163
OOF
2.6. Calibration curves
164
A
¼ AMO ð415 nmÞ þ ARY ð415 nmÞ
ð3Þ
Tð415 nmÞ
To obtain the calibration curve for MO at its proper wavelengths, 2nd 165
derivatives of the spectra of a series of solutions with different MO 166
concentrations and the constant concentration of RY, BTB or MV have 167
been plotted against the concentration of MO. The same procedure 168
1
46 where AT (415 nm), AMO (415 nm) and ARY (415 nm) correspond to the total
absorbance for the mixture, MO and RY at 415 nm, respectively.
UNCORRECTED PR
Fig. 3. (a) Zero order absorption spectra and (b) second order derivative spectra for single MO, RY and binary MO–RY solutions.
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B. Yahyaei, S. Azizian / Journal of Molecular Liquids xxx (2014) xxx–xxx
Fig. 4. (a) Zero order absorption spectra and (b) second order derivative spectra for MO, BTB and MO–BTB binary solution.
1
1
69 has been performed to obtain the calibration curve for RY at 415 nm,
70 BTB at 433 nm and MV at 590 nm.
Fig. 5 shows the time dependency of the adsorption of RY and MO 184
from binary solution at initial concentration of 10 mg/l for each dye. 185
The removal percentages of MO and RY by OMA are more than 50% 186
and 40% only after 30 s. Thus, it is clear that the dye removal by OMA 187
1
1
71 3. Results and discussions
72 3.1. MO–RY binary solution
is too fast and has been performed within few minutes.
188
Pseudo-first-order and pseudo-second-order kinetic models [27] 189
have been used for modeling the adsorption data of single component 190
systems, extensively. These models are not suitable for kinetic modeling 191
of competitive adsorption. Recently, we have proposed a new kinetic 192
model for competitive adsorption at solid/solution interface based on 193
statistical rate theory (SRT) [28]. Eqs. (5) and (6) express the rate 194
1
1
1
1
1
1
1
1
1
1
1
73
Different kinds of adsorbents were used to remove the individual
74 dyes from aqueous solutions. Since the industrial wastewater usually
75 consists of mixture of dyes, an efficient adsorbent with the high rate of
76 adsorption must be used to remove the mixture of dyes from water.
equations of competitive adsorption based on SRT model [28].
195
77
Fig. 3a shows the zero order spectra of single MO, RY and binary
196
78 MO–RY systems.
79
The MO calibration equation based on 2nd order derivative at
dθA
dt
C ð1−θ −θ Þ
θA
A
A
B
80 534 nm is given in Table 1.
¼ kaðAÞ
−kdðAÞ
ð5Þ
ð6Þ
θ
C ð1−θ −θ Þ
A
A
A
B
81
Fig. 3b shows the 2nd-derivative spectra of MO–RY binary solution
1
1
98
99
82 versus the wavelength to select the λ values for determining the
83 concentrations of individual dyes in the binary system.
dθB
dt
C ð1−θ −θ Þ
θB
C ð1−θ −θ Þ
B
A
B
¼
k
−kdðBÞ
aðBÞ
θ
B
B
A
B
t1:1
t1:2
Table 1
Second order derivative equations for the dyes.
where C
the adsorption and desorption rate constants and θ
surface coverage. The qi,t, is the amount of i ad-species per unit mass 202
of adsorbent at any time and q is the total maximum adsorption 203
capacity (i.e. q = qm,A + qm,B) [28]. The qm,A and qm,B values for MO 204
and RY are 76 and 110 mg/g, respectively. 205
i
is the bulk concentration of i species at any time, k
a
and k
d
are 201
t1:3
t1:4
Dye
MO
λ (nm)
Calibration equations
r2
i
= qi,t/q
m
is the
d A/d λ = −3 × 10 C − 10−5
2
2
−5
1.000
0.997
0.997
0.998
534
2
2
−5
−5
5
4
50
02
d A/d λ = −2 × 10 C − 3 × 10
m
2
2
−5
−5
−4
d A/d λ = 1.33 × 10 C − 3.04 × 10
m
2
2
−4
t1:5
MV
590
d A/d λ = 1.15 × 10 C − 0.08 × 10
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B. Yahyaei, S. Azizian / Journal of Molecular Liquids xxx (2014) xxx–xxx
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Table 3
t3:1
t
The q (mg/g) values of the individual dye solutions and binary solutions at 0.5 min and t3:2
30 min.
Solutions
0.5 min
30 min
t3:3
RY
MO
BTB
MV
16.90
10.78
12.30
–
31.88
22.45
24.00
–
t3:4
t3:5
t3:6
t3:7
t3:8
MO–RY
RY
9.32
9.33
1.85
11.08
4.20
6.22
13.92
11.33
5.45
13.55
4.28
MO
BTB
MO
MV
MO
MO–BTB
MO–MV
t3:9
t3:10
7.95
The effect of pH on removal percentage of dyes by OMA has also 224
been investigated. The results show that the removal percentage of RY 225
Fig. 6) and MO [15] remains almost unchanged at different pH. 226
The pH of point of zero charge (pHpzc) for OMA was determined by 227
Faria et al.'s method [32] and is about 7.8 [15]. 228
concentrations of dyes as a 229
function of pH have been obtained by Eqs. (7) and (8) [33]. 230
(
0
i
The molecular (C
e
) and
OOF
ionize
d (C
e
)
231
0
Ce
Ce
¼
ð7Þ
ð8Þ
þ 10ðpH−pKaÞ
1
233
ꢀ
ꢁ
234
Fig. 5. Experimental kinetic data for the adsorption of (a) RY and (b) MO from MO–RY
i
e
1
þ 10
binary solution by OMA at the initial concentration of 10 (mg/l). The solid lines present
the predicted values of q based on SRT model as a function of time.
t
C
¼ Ce 1− 1
ðpH−pKa
Þ
where C
MO (pK
and ionized concentrations of RY at different pH are shown in Fig. 7 237
and for MO were reported elsewhere [15]. 238
Fig. S1 reveals the molecular structure of RY. In the acidic medium 239
the sulfonate groups of the RY were almost protonated [34] so RY 240
molecules exist in the molecular form as shown in Fig. S1, while in the 241
basic medium the ionic form is dominant. The surface charge of OMA is 242
different below and above of pHpzc = 7.8; since the removal percentage 243
e
is the RY or MO concentration and K
a
is the acidity constant of 236
= 3.4) or RY (pK = 5.3). The results of calculated molecular
a
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
06
The experimental kinetic data for competitive adsorption were fitted
a
07 to the Eqs. (5) and (6) using stochastic numerical simulation. For
08 stochastic numerical simulation the CKS package from IBM, which was
09 developed by Houle and Hinsberg [29], was used. We have used this
10 method for numerical solution of SRT rate equations successfully [28,
11 30,31].
12
As shown in Fig. 5 the kinetic data of RY and MO are in the good
13 agreement with the predicted values of q
14 results of fitting are listed in Table 2.
15
16 SRT model as a function of time.
17
To compare the difference between the removal of individual of RY
18 and MO from water and their removal from binary solution, an adsorp-
19 tion experiment has been performed at concentration of 20 mg/l for
t
20 each dye. The q values of MO and RY in single and binary solutions
t
based on SRT model. The
of RY by OMA remains unchanged at different pH (Fig. 7), it is suggested 244
−
that the RY molecules are not adsorbed through ionic \SO
3
groups.
245
t
The solid lines in Fig. 5 represent the predicted values of q based on
It seems that MO molecules, like RY molecules, are not adsorbed 246
−
through ionic \SO
3
group [15]. This result is based on the removal 247
percentage of MO by OMA at different pH and MO structure in acidic 248
and basic mediums (Fig. S2). 249
Although OMA removes both dyes from binary solution as well as 250
individual dyes in the aqueous solution, the amount of adsorbed dyes 251
from the binary solution is less than the amount removed from the 252
21 are listed in Table 3. The results show that the amount of dyes removed
22 from the binary solution is less than the amount removed from the
23 solution of each dye at the same time which will be discussed later.
UNCORRECTED PR
t2:1
t2:2
t2:3
Table 2
The obtained constants of SRT kinetic model for adsorption of RY, BTB and MO onto the
OMA from different binary solutions.
t2:4
Solution
SRT
k
a
(g/mg min)
d
k (mg/g min)
t2:5
t2:6
t2:7
MO–RY
MO
RY
1.24 × 10−
5.61 × 10−
4
0.494
0.487
3
t2:8
t2:9
MO–BTB
MO
BTB
t2:10
t2:11
4.70
0.140
0.480
4.93 × 10−
6
Fig. 6. Effect of pH on the removal percentage of RY by OMA.
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B. Yahyaei, S. Azizian / Journal of Molecular Liquids xxx (2014) xxx–xxx
binary solution according to Fig. 4b. The MO calibration equation at 266
50 nm is given in Table 1. 267
The time dependency of the adsorption of BTB and MO from binary 268
5
solution by OMA at initial concentration of 10 mg/l of each dye has 269
been shown in Fig. 8. The removal percentages of MO and BTB by 270
OMA are more than 70% and 20% only after 30 s. Thus, both dyes have 271
been removed too fast from binary solution by OMA.
272
The kinetic adsorption data of the MO–BTB binary solution were 273
fitted with SRT rate equation (Eqs. (5) and (6)) with qm,A and qm,B values 274
of 93 and 33 mg/g for MO and BTB, respectively. The solid lines in Fig. 8 275
present the predicted values of q
function of time. Fig. 8 shows that the kinetic data of BTB and MO are in 277
the good agreement with the predicted values of q based on competi- 278
tive SRT model. The obtained rate constants for this system are listed 279
in Table 2. 280
t
based on competitive SRT model as a 276
t
Fig. 7. Calculated molecular and ionized concentrations of RY at different pH (right axes).
The dye removal percentages are presented on left axes too.
To compare the removal of individual BTB and MO molecules from 281
water with the removal of dyes from binary solution, an adsorption 282
experiment has been performed at the concentration of 20 mg/l for 283
2
2
2
2
2
53 solution of each dye at the same time. This is due to the competition
54 between MO and RY molecules for adsorption sites of OMA. Since the
55 steric hindrance of RY molecules is more than that of MO molecules it
56 may cause the RY molecules to be adsorbed from the binary solution
57 slower than MO molecules (Table 3).
t
each dye. The q values for individual and binary MO and BTB systems 284
are listed in Table 3. The results of this experiment show that the 285
amount of MO removed from the binary solution is more than the 286
amount removed from the individual MO solution while the amount 287
of BTB removed from the binary mixture is less than the amount 288
removed from the individual BTB solution at the same time, which 289
will be discussed later.
290
2
58 3.2. MO–BTB binary solution
The effect of pH on the removal of MO and BTB by OMA has been 291
studied in our previous work [15]. The results of this study suggest 292
2
2
2
2
2
2
2
59
Fig. 4a shows the zero order spectra of MO, BTB and MO–BTB binary
−
that MO molecules are not adsorbed through ionic \SO
3
group. In 293
60 systems. The absorption spectra for the MO–BTB binary system are
61 overlapping too.
62
63 used for wavelength selection (Fig. 4b).
64
Wavelengths of 550 nm and 433 nm have been selected for deter-
the case of BTB, the high removal percentage of BTB by OMA in acidic 294
solution is due to attractive interaction between the positive surface of 295
OMA and molecular BTB and the strong repulsive interaction between 296
the anionic form of BTB and the negative surface of OMA causes the 297
Therefore a similar method as for MO–RY binary system has been
drastic decrease of removal percentage in the basic solution [15].
298
65 mining the MO and BTB concentrations, respectively, in the MO–BTB
In the acidic solution, MO and BTB exist in the ionic and molecular 299
forms, respectively, and the surface of OMA is positive. The results 300
(Table 3) show that OMA removes MO faster than BTB from MO–BTB 301
binary solution due to the strong interaction between the positive 302
surface of OMA and ionic MO. The occupation of OMA adsorption sites 303
by MO and BTB molecules and the steric hindrance of adsorbed mole- 304
cules causes the amount of dyes removed from the binary solution be 305
less than the amount removed from the solution of each dye after 306
30 min.
307
3.3. MO–MV binary solution
308
As shown in Fig. 9 (the zero order spectra of MO, MV and MO–MV 309
binary system), the absorption spectra of MO and MV in the MO–MV 310
binary solution are partially overlapped. According to the 2nd- 311
derivative spectra of MO–MV binary solution, the wavelengths of 312
Fig. 8. Experimental kinetic data for the adsorption of (a) BTB and (b) MO from MO–BTB
binary solution by OMA at the initial concentration of 10 (mg/l). The solid lines present the
predicted values of q
t
based on SRT model as a function of time.
Fig. 9. Zero order absorption spectra for MO, MV and MO–MV binary solution.
Please cite this article as: B. Yahyaei, S. Azizian, J. Mol. Liq. (2014), http://dx.doi.org/10.1016/j.molliq.2014.08.023

B. Yahyaei, S. Azizian / Journal of Molecular Liquids xxx (2014) xxx–xxx
7
Fig. 10. Experimental kinetic data for the adsorption of (a) MV and (b) MO from MO–MV
binary solution by OMA at the initial concentration of 10 (mg/l).
Fig. 12. The proposed mechanism of the adsorption of MV in the presence of MO onto the
surface of OMA.
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13 402 nm and 590 nm have been selected for determining the MO and MV
14 concentrations in the MO–MV, respectively. The calibration equations of
15 MO and MV at their proper wavelength are listed in Table 1.
hindrance of adsorbed molecules causes the amount of MO removed 343
from the binary solution be less than the amount removed from the 344
individual MO solution after 30 min. The proposed mechanism of the 345
16
The time dependency of the adsorption of MV and MO from binary
adsorption of MV in the presence of MO has been schematically 346
OOF
17 solution at initial concentration of 10 mg/l of each dye, has been
18 shown in Fig. 10. The removal percentages of MO and MV by OMA are
19 more than 40% and 30% only after 30 s. Thus, both dyes have been
20 removed too fast from binary solution by OMA.
shown in Fig. 12.
347
4. Conclusion
348
21
The experimental data for the adsorption of MV from MO–MV bina-
Ordered mesoporous alumina is an interesting adsorbent that can 349
remove dye pollutants from binary mixture as well as single systems. 350
Although OMA can remove anionic dyes perfectly from aqueous solu- 351
tions, it cannot remove cationic dye from aqueous solution. In the 352
MO–RY binary solution the competition between MO and RY molecules 353
for adsorption sites of OMA causes the amount of adsorbed dyes from 354
the binary solution be less than the amount removed from the solution 355
of each dye at the same time. The strong interaction between the posi- 356
tive surface of OMA and ionic MO causes OMA to remove MO faster 357
than BTB from MO–BTB binary solution. Although OMA cannot remove 358
MV from the aqueous solution, the attractive interaction between the 359
anionic MO and cationic MV may cause the removal of MV by OMA in 360
the binary solution. The experimental kinetic data of MO–RY and MO– 361
BTB binary systems follow the competitive SRT kinetic model well. 362
The results of kinetic studies of the mentioned binary dye mixtures 363
show that the fast removal of anionic dye mixture also cationic and 364
anionic one which is important for practical applications is possible by 365
using OMA as a proper adsorbent for dye mixtures. Finally, since the 366
rate of dye removal by the prepared OMA is very high, this adsorbent 367
22 ry solution which are shown in Fig. 10, reveal that the adsorption of MV
23 on to the surface of OMA has reached to the equilibrium state only after
24 30 s. Since it is not possible to catch the kinetic data below 30 s, and all of
25 the obtained data for MV are in equilibrium, the fitting to the kinetic
26 models for this system is impossible.
27
The adsorption experiment with OMA for individual MO and MV
28 solution shows that OMA removes MO from aqueous solution very
29 fast [15], but cannot remove MV from the acidic and basic aqueous solu-
30 tion. The molecular structure of MV is shown in Fig. S3.
31
Fig. 11 shows that most of MV molecules exist in the ionic form in
32 both acidic and basic mediums. The absence of sorption at acidic medi-
33 um is because of the repulsive interaction between the cationic MV and
34 the positive surface of OMA while in the basic medium may be attribut-
35 ed to the difference in the molecular size of the MV molecules and the
36 pore size of OMA (5 nm).
37
Although OMA cannot remove MV from the aqueous solution but in
38 the binary solution of MO and MV, it happens (Table 3). The removal of
39 MV by OMA from the binary solution may occur due to the attractive
40 interaction between the anionic MO and cationic MV. Thus, MV mole-
41 cules have been removed from the binary mixture by OMA when the
42 MO molecules have been absorbed on the surface of OMA. The steric
can be suggested as a potential adsorbent for flow systems.
368
Acknowledgment
369
The authors acknowledge the financial support of Bu-Ali Sina 370
University. The authors acknowledge Dr. H. Bashiri from Kashan 371
University (Iran) for performing the numerical simulations.
372
Appendix A. Supplementary data
UNCORRECTED PR
373
Supplementary data to this article can be found online at http://dx. 374
doi.org/10.1016/j.molliq.2014.08.023.
375
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