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Reactive orange 5 removal from aqueous solution using hydroxyl
ammonium ionic liquids/layered double hydroxides intercalation composites
Qingqing Zhou(School of Chemistry and Chemical Engineering, Wuhan Textile University)
Abstract: A series of hydroxyl ammonium ionic liquids/layered double
hydroxides intercalation composites (ILs/LDHs) were synthesized and
adopted to study the adsorption process of anionic dye reactive
orange 5 from aqueous solutions. The ILs/LDHs and LDHs were
characterized by infrared spectroscopy (IR), X-ray diffractometry
(XRD), thermogravimetric analysis (TG), total organic carbon (TOC)
analyzer and BET surface area measurement. The successful
intercalation of the anion of ILs (2-hydroxyethylammonium acetate)
into the interlayer space of LDHs was confirmed. The effects of
contact time, temperature, adsorbent dosage and solution pH on the
adsorption experiments were investigated. The experimental results
showed that the maximum adsorption capability of ILs/LDHs reached
up to 300.9 mg/g, which was obviously higher than that of LDHs. The
adsorption isotherms were well described by Freundlich model in the
presence of the LDHs and ILs/LDHs. The adsorption kinetics followed
the pseudo-second order kinetic model. The negative value of ΔG0 and
the positive value of ΔH0 indicated spontaneous and endothermic
nature of reactive orange 5 adsorption. For ILs/LDHs(b), desorption
percentages were 57.91%, 46.67%, and 37.34% in each cycle,
respectively. This innovative approach, using ILs/LDHs, was more
efficient and could be envisaged as a promising process for reducing
the pollution of the textiles manufacturing.
Keywords:2-Hydroxyethylammonium acetate (ILs); Intercalation;
Layered double hydroxides; Adsorption; Reactive orange 5
0 IntroductionTextile industry is one of the fast growing industries and
significantly contributes to the economic growth in china. However,
the textile dyeing industry consumes large quantities of water and
produces large volumes of wastewater. The major pollutant of textile
wastewater comes from the dyes which are not dyed or washed down
after dyeing[1]. From the point of view of production practice, ten to
twenty percent of dyes are poured into the dyeing-printing
wastewater during the dyeing and printing process[2]. Unfortunately,
on account of the complex and stable chemical structure, most of
these dyes are toxic and poor biodegradation, and dyeing wastewater
discharge is able to reduce aquatic diversity by blocking the passage
of sunlight through the water and affect human health.
At present, many methods, such as coagulation or flocculation,
chemical oxidation, biological treatment, membrane filtration,
photodegradation, adsorption and etc[3–8], have been studied in order
to remove the dyes from the textile wastewater. Among the above
treatment techniques, the adsorption method is regarded as one of
the most economical and effective way to deal with the dyed
wastewater[9,10]. For example, activated carbon has been used as the
adsorbent in some industrial water treatment devices to remove the
dyes from the wastewater. In recent years, a lot of attention has been
focused on preparing the adsorption material with low-cost and high
adsorption capacity, like clay minerals, polymers, nano materials,
silica and so forth[11–14].
Layered double hydroxides (LDHs), known as the anionic clay,
have become an important kind of adsorbents for treating the
wastewater owing to its efficient adsorption and reusability. In brief,
hydrotalcites are referred to as layered double hydroxide with the
general formula [M1−xⅡMxⅢ(OH)2]x+[An-]x/n·mH2O, where MⅡ and MⅢ stand
for a divalent and a trivalent cation[15,16], respectively, An - is the
interlayer anion, such as CO32-, Cl-, NO3- and etc, which is located in
the interlayer and the lamellar surface. Due to their anionic exchange
capacity, LDHs are suitable for sorption of anionic species[17].
Moreover, the adsorption capacity of LDH is largely influenced by the
anion.
Nowadays, LDHs have been modified in various forms in order
to improve their adsorption capacity[18–20], such as calcination and the
organic modification. Zaghouane-Boudiaf et al.[21] investigated the
adsorption of methyl orange on calcined MgNiAl LDHs and their
precursor and found a much higher adsorption on calcined MgNiAl
LDHs than their precursor without heat treatment. Miranda et al. [22]
used dodecylsulfate (DS) and dodecylbenzenesulfonate (DSB) anionic
surfactants to modify hydrotalcite-iron oxide magnetic so as to
improve the adsorption efficiency of the LDHs, and the removal
percentages of methylene blue (MB) dye had increased by 81% and
73%, respectively. Liu et al.[23] even used LDHs-bacteria aggregates to
enhance the decolourisation of methylene blue. In a word, utilization
of LDHs and derivations could bring great economical and
environmental benefits to dyeing wastewater industries.
In recent years, room temperature ionic liquids (ILs) have
become the research emphasis in consequence of their unique
properties, such as extremely low vapor pressures, fine stability and
outstanding solubility. Accordingly, ILs can certainly be used as dye
extractant to achromatize aqueous solution[24,25]. However, such kind
of green material is difficult to have a role in the dyes wastewater
treatment because of high price, low liquidity and unsatisfactory mass
transfer efficiency. Facing these problems, immobilization of ILs on
solid supports may improve their applicability in industrial processes.
Gao et al.[26] had synthesized a functional ionic liquid cross-linked
polymer to adsorb anionic azo dyes, the experimental results showed
that the performance of it is superior to other adsorbents and
adsorption capacity could reach 547–925 mg/g for different anionic
azo dyes. Ghaedi et al.[27] and Absalan et al.[28] had immobilized ILs on
inorganic materials to improve the adsorption properties of these
materials.
As mentioned above, both LDHs and immobilized ILs are
promising class of sorbents. However, to the best of our knowledge,
the combination of LDHs and ILs has not been reported in literature.
Therefore, the objectives of our work are to prepare a series of
hydroxyl ammonium ionic liquids/layered double hydroxides
composites (ILs/LDHs), which used as adsorbent for the removal of
anionic dye reactive orange 5 from aqueous solution. The effects of
various factors such as solution pH, and adsorbent dosage on
adsorption have been investigated. Kinetic and isotherm models have
also been discussed. The experimental results show that the
adsorption capacity and performance of LDHs have improved
significantly after inserting the ILs in their interlamination. This study
can provide a reference for the dyes wastewater treatment using
inexpensive and easily-obtained the intercalation composites.
1 Experimental
1.1 Materials
Ethanolamine, 2-(2-aminoethoxy) ethanol, triethanolamine, formic
acid, ethanoic acid, lactic acid, ethyl alcohol, aluminum nitrate
nonahydrate, magnesium nitrate hexahydrate, sodium hydroxide and
sodium carbonate were all AR grade and purchased from Sinopharm
Chemical Reagent Co., Ltd. reactive orange 5 was purchased from
Jiangsu Shenxin Dyestuff Chemicals Co., Ltd. All reagents were used
without further purification.
1.2 Sample preparation
Hydroxyl ammonium ionic liquids were synthesized according to
the procedures described in literature[29].
The co-precipitation method was adopted for the preparation of
ILs/LDHs intercalation composites. The reaction was conducted in a
500 mL four neck round bottom flask with a magnetic stirrer, two
dropping funnel and a reflux condenser. 20 mL ILs and 35 mL water
were mixed up uniformly and put into the flask. The mixture was
heated to 90℃ in a thermostat water bath. A solution was prepared
by mixing Mg(NO3)2·6H2O and Al(NO3)3·9H2O (Mg2+/Al3+ molar ratio of 2
and Mg2+ concentration is 0.6 M) in 100 mL of deionized water. This
solution and the aqueous solution of 0.8 M NaOH were simultaneously
added dropwise into a flask under vigorous stirring. Meanwhile, the pH
value of the mixed suspension liquid should be controlled at about 10
during the dropping process. Afterwards, the samples should be
acutely stirred for 3 h at 90℃ and then aged at 100℃ for 24 h. The
precipitate was separated by suction filtration, washed with deionized
water and dried in an oven at 80℃ for 12 h.
1.3 Characterization of the prepared materials
X-ray diffraction (XRD) patterns of the samples were obtained by
Bruker D8 Advance, using filtered CuKα radiation (λ = 0.154 nm). 2θ
angle of the diffractometer was stepped from 3° to 80° at a scan rate
of 10°/min. FT-IR spectra were recorded on a Tensor 27 IR
spectrometer (Bruker, Germany) using KBr disc technique. Thermal
decomposition of LDHs and ILs/LDHs were evaluated by
thermogravimetric analysis (TG) carried out on Diamond TG/DTA
instrument under nitrogen atmosphere at 10℃/min from room
temperature up to 700℃. The proportion of ILs(b) containing in
ILs/LDHs(b) composite was analyzed by total organic carbon (TOC)
analyzer (VarioTOC, Elernentar, Germany) at 950℃. The pore
structures of the LDH and ILs/LDHs were analyzed by N2 adsorption–
desorption at 77 K on an Automatic specific surface and porosity
analysis physical adsorption instrument (ASAP 2020-M, Micromeritics,
USA).
1.4 Adsorption
1.4.1 Effect of initial pH
This effect was studied on suspensions of adsorption material
in 180 mg·L-1 of reactive orange 5 dye solutions (solid/solution ratio =
0.5 g·L - 1). The initial pH (the values varied from 4 to 11) of dye
solutions was adjusted with 0.1 M Na2CO3 and 0.1 M ethanoic acid
solutions (used to adjust pH in dyeing and printing industry). The
suspensions were stirred at 25℃ during equilibrium times and then
centrifuged. The dye equilibrium concentration in the supernatants
was measured by visible spectrophotometer on METASH (V-5600) UV–
vis spectrophotometer at 478 nm.
1.4.2 Effect of LDHs and ILs/LDHs dose
The effect was studied on suspension of LDHs or ILs/LDHs
(solid/solution ratio varied from 0.1 to 0.9 g·L-1) in 60 or 180 mg·L-1 of
reactive orange 5 dye solution at natural pH of the dye (6.48). The
suspensions were stirred during equilibrium times and then
centrifuged. The dye equilibrium concentration in the supernatants
was determined as above.
1.4.3 Kinetic study
Kinetic studies were conducted to find out the equilibrium time
and the kinetic models of reactive orange 5 sorption by LDHs and
ILs/LDHs. In the experiment, the solid (LDHs and ILs/LDHs) /solution
ratio was 0.5 g·L-1, the initial concentration of reactive orange 5 was
180 mg·L-1. Suspensions were stirred for different time interval (5 min
to 8 h) at 25℃ and then centrifuged.
1.4.4 Sorption isotherms
The sorption isotherms were established using LDHs and
ILs/LDHs suspension in reactive orange 5 dye solutions (solid/solution
ratio = 0.5 g·L - 1) at different concentrations (80–250 mg·L - 1). The
suspensions were stirred in a thermostatic reciprocating shaker bath
at 25℃ during equilibrium times and then centrifuged. The dye
equilibrium concentration in the supernatants was determined as
above.
1.4.5 Adsorption thermodynamics
In order to evaluate the effect of temperature on the
adsorption process, the experiments were studied on suspensions of
LDHs and ILs/LDHs (solid/solution ratio = 0.5 g·L - 1) in 50 and 200
mg·L - 1 of Reactive orange 5 dye solution, respectively. The
suspensions were stirred in thermostatic reciprocating shaker bath at
30, 45 and 60℃ during equilibrium time and then centrifuged. The
dye equilibrium concentration in the supernatants was determined as
above.
The adsorption capacity qe (mg of reactive orange 5 per g of
sorbent) was calculated using the following equation:
(1)
where C0 is the initial dye concentration (mg·L - 1) in the
solution; Ce is the dye concentration (mg·L-1) at equilibrium; V is the
initial volume (L) of the dye solution and m is the mass of LDHs or
ILs/LDHs (g).
1.4.6 Desorption study
The process of desorption of ILs/LDHs for the adsorption of
reactive orange 5 was studied for consecutive three cycles. In each
cycle, 0.5 g·L-1 of the adsorbents was added in the 180 mg·L-1 of the
reactive orange 5 solution (pH = 6.0, 25℃) and shaken in the water
bath for 2.5 h. Then, the adsorbent/adsorbed was separated from the
dye solution and added to 15 mL of solution (pH = 11.0, 35℃) and
shaken for 4 h. The adsorbents were separated by centrifugal and the
amount of adsorbed dye was determined through the same method
used in the adsorption experiments. After each cycle of desorption,
the adsorbents were washed with deionized water several times until
the residual water coloration was not significant. The amount of
desorbed dye was calculated from the concentration of desorbed dye
in the liquid phase.
1.4.7 Statistical analysis
All experiments were conducted in triplicate under identical
conditions and statistically analyzed by F test. When Fc > 10Fα(n, n-p
-1), α = 0.005, the results were statistically highly significant.
2 Results and discussion
2.1 Characterizations of ILs/LDHs and LDHs
The XRD patterns of ILs/LDHs and LDHs are shown in Fig. 1. The
XRD patterns of LDHs show sharp and symmetric peaks which give
clear indication the sample is well crystallized, the peaks
corresponding to (003), (006), (009), (015), (018), (110) and (113)
planes are characteristic of hydrotalcite with a layered structure [30].
The peak at about 11° is assigned to the (003) reflections and can be
calculate the basal spacing between the layers. For convenience, the
LDHs inserted with different ILs are designated as ILs/LDHs(a),
ILs/LDHs(b) and ILs/LDHs(c), and so on. The results are shown in
Table1 and Fig. 1. As shown in Fig. 1, the intercalation of ILs
containing formate into the interlayer of the LDHs causes the
disappearance of (006) plane. And using ILs containing lactate as
guest molecules, the broadened peaks for intercalation composites
are mainly owing to its less ordered layer stacking. The crystal
structure of ILs/LDHs(b) is the best among the synthesized
intercalation composites, and the adsorption capability is in
agreement with the crystallinity of intercalation composites, which
maybe due to larger specific surface area. So ILs/LDHs(b) will be
chosen for the further detailed adsorption study.
Table 1 Synthesized ILs intercalated into the interlayer of the LDHs, and the maximum
adsorption amount of reactive orange 5 onto each ILs/LDHs.
Synthesized ILs composites Intercalated qe
2-hydroxyethylammonium formate (ILs(a)) ILs/LDHs(a) -- 165
2-hydroxyethylammonium acetate (ILs(b)) ILs/LDHs(b) √ 320
2-hydroxyethylammonium lactate (ILs(c)) ILs/LDHs(c) -- 54
tri-(2-hydroxyethyl)ammonium formate
(ILs(d))
ILs/LDHs(d) -- 156
tri-(2-hydroxyethyl)ammonium acetate (ILs(e)) ILs/LDHs(e) -- 105
tri-(2-hydroxyethyl)ammonium lactate (ILs(f)) ILs/LDHs(f) √ 280
2-(2-hydroxyethoxy)ammonium formate
(ILs(g))
ILs/LDHs(g) -- 128
2-(2-hydroxyethoxy)ammonium acetate
(ILs(h))
ILs/LDHs(h) √ 233
2-(2-hydroxyethoxy)ammonium lactate (ILs(i)) ILs/LDHs(i) -- 60
Note: -- the anion of ILs did not intercalate into the interlayer of the LDHs or
intercalation composites have less ordered layer stacking. qe (mg•L-1) is the
equilibrium adsorbing capacity of the sorbents, solid/solution ratio = 0.5 g•L-1, 25℃,
dye solution concentration = 180 mg•L-1, natural pH (6.48) of dye solution.
Fig. 1 XRD patterns of the synthesized ILs/LDHs and pure LDHs samples.
The position of diffraction peaks (003), (006) and (009) of
ILs/LDHs(b) moved to small angle integrally corresponding to the
increase of interlayer spacing (Fig. 1). The d003 of pure LDHs, which
corresponds to an adjacent distance of hydroxide layers, is
determined to be 0.7644 nm. The interlayer spacing of ILs/LDHs(b) is
enlarged to 1.229 nm. It can be concluded that the acetate radical of
ILs has successfully intercalated into the gallery of LDHs. And, cation
of ILs is spread outside of laminates of LDHs, which will increase the
adsorption by electrostatic repulsion force between the –SO3− group of
dye molecule and cation of ILs.
From the results of total organic carbon (TOC) analyzer, the
proportion of ILs(b) containing in ILs/LDHs(b) composite was 6.9128
wt%.
To further verify the above conclusion, the prepared samples are
characterized by FTIR. Fig. 2 presents the FTIR spectra of LDHs and
ILs/LDHs(b) intercalation compounds. For LDHs, the broad peak is
found at 3488 cm - 1 ( - OH stretching vibration), caused by the
interlayer water molecules and hydroxyl groups in the brucite-like
layers. The weak band around 1642 cm-1 region(δ-HOH) is due to the
H2O from the interlay water. The 1381 cm-1 peak corresponds to the
carbonate group[31]. Following the ionic exchange of carbonate by
ILs(b), several characteristic bands are observed at 1559 cm -1, 1410
cm - 1 and 1168 cm - 1. The weak absorption peak at 1168 cm - 1 is
assigned to CN stretching vibration. The corresponding bands at 1559
cm- 1 and 1410 cm-1 are ascribable to antisymmetric and symmetric
vibrations of - COO - groups. In addition, characteristic absorption
peak of the carbonate group can still be observed, which partially
overlaps with -COO- groups[32]. These data indicate that the acetate
radical of ILs has successfully intercalated into the gallery of LDHs and
replace part of the carbonate group.
Fig. 2 FI-IR patterns of the synthesized ILs/LDHs(b) and pure LDHs samples.
The TG thermograms of ILs/LDHs(b) intercalation compounds
are shown in Fig. 3, with ILs(b) and neat LDHs as the controls. The
sharp weight loss of ILs(b) started from 110℃, and it lost all the
weight at 190℃. LDHs exhibit two-step degradation at 50–210℃ and
250–610℃. A first weight loss of 10.1% is observed from about 50 to
210℃ and is caused by the elimination of adsorbed and interlayer
water[33]. A second weight loss of approximately 37.1% in the
temperature range of 250–610℃, corresponding to the decomposition
of carbonate anion in the brucite-like layers and the deeper
decomposition of brucite layer anions OH - [34]. The ILs/LDHs(b)
intercalation compounds mainly exhibited two weight losses at about
90–321 and 321–520℃. A first step of weight loss is owing to the
degradation of ILs(b) and the elimination of interlayer water.
Compared with pure ILs(b), the degradation of intercalated ILs(b) in
the LDHs gallery is obviously delayed, because of the protection from
the inorganic layers and electrostatic bonding with the layers[35]. The
second step of degradation can be attributed to the decomposition of
residual carbonate anion. Because most part of the carbonate group is
replaced by ILs(b), decomposition temperature of ILs/LDHs(b) is lower
than pure LDHs.
Fig. 3. TG thermograms of ILs(b), LDHs and ILs/LDHs(b)
The N2 adsorption–desorption isotherms for LDHs and
ILs/LDHs(b) are revealed in Fig. 4. LDHs and ILs/LDHs(b) show the
isotherm of type IV according to IUPAC classification, characteristic of
mesoporous solids. H3-type hysteresis loop, is observed for the LDHs
sample, which is characteristic solids with slit-shaped irregular
pores[15]. The isotherm of ILs/LDHs(b) is of type IV with a broad H2-type
hysteresis loop, which also indicated that mesoporous in ILs/LDHs(b)
can be classified as regular and large[36]. The specific surface area of
LDHs and ILs/LDHs(b), as derived from the adsorption data using a
BET equation, are 81.6 and 96.7 m2/g, respectively. It has been found
that many organic compounds have a strong affinity to the surface of
clay minerals. Clearly, a large specific surface area can be an
important factor in the adsorption of colored species by the sorbents.
Fig. 4 N2 adsorption-desorption curves of the synthesized ILs/LDHs(b) and pure LDHs samples.
2.2 Study of reactive orange 5 removal with LDHs and ILs/LDHs(b)
2.2.1 Effect of initial pH
The solution pH is one of the most important parameters in the
adsorption process, which can affect the chemical properties of both
the dye molecule and the adsorbent. The influence of pH values on
the adsorption of reactive orange 5 on the two adsorbents is
investigated and illustrated in Fig. 5. It is obviously that the sorption
capacity of the two adsorbents decreased gradually with the
increasing of solution pH. Reactive orange 5 contains negatively
charged sulfonate group. The adsorption capacity is related to the pH
values of the solution, which may be due to the electrostatic
attraction negatively charged dye molecule and adsorbents. At the
lower solution pH, a large amount of H+ causes hydroxyl groups
became protonated (-OH+2) in the surface of the adsorbents, which
promoted the electrostatic attraction between the surface of the
adsorbents and the - SO3- group of reactive orange 5. The uptake
decreased with the increase of OH - in solutions, indicating that high
pH is not in favor of the adsorption of reactive orange 5. At the higher
solution pH, the surfaces of adsorbents had negative charges, which
cause the electrostatic repulsion between the negatively charged
surface sites and -SO3- group of dyes. Meanwhile, the competition
between OH- excess in the solution and -SO3- of the dyes was fierce
with the increase of pH.
Fig. 5 Effect of initial pH on reactive orange 5 adsorption on LDHs and bILs/LDHs.
2.2.2 Effect of LDHs and ILs/LDHs(b) dose
The effect of the dosage of LDHs and ILs/LDHs(b) on the
removal of reactive orange 5 is examined by varying dosages from
0.1 to 1.0 g ·L-1. Fig. 6 shows that the percentage removal increased
sharply from 14.6% to 73.0% and 17.6% to 98.6% with increasing
adsorbent dosage from 0.1 to 0.9 g·L - 1 for LDHs and ILs/LDHs(b),
respectively. The equilibriums removal percentage are both obtained
at absorbent dose 1.0 g·L - 1 for LDHs and ILs/LDHs(b). It is also
observed from Fig. 6 that the adsorption capacity decreased with
increase in adsorbent dosage. This can be explained that the low
adsorbent dosage causes the dispersion of sorbent grains in aqueous
solution, all types of sites of the adsorbent surface are entirely
exposed which would facilitate saturated quickly, and a large number
of sites are accessible to the dye molecules. Furthermore, because
the probability of collision between solid particles and particle
aggregations increased, the higher particle concentrations cause an
increase in diffusion path length and a decrease in the total surface
area[21], and overdosing adsorbent dosage will result in high cost.
Furthermore, confirming as expected, the adsorbed amount on
ILs/LDHs(b) is much higher than on LDHs, which can be explained by
the larger specific surface area of ILs/LDHs(b) which could lead the
adsorption more available.
Fig. 6 Effect of adsorbent dose on reactive orange 5 adsorption on LDHs and ILs/LDHs(b).
2.3 Adsorption kinetics
Kinetic modeling of sorption process provides a prediction of
sorption rates and allows determination of suitable rate expression
characteristic for possible sorption mechanisms. In this study, three
kinetic models are used for the analysis of the adsorption kinetic
process: the pseudo-first order model, the pseudo-second order model
and the Weber and Morris intra-particle diffusion model[37].
The pseudo-first order model is expressed by the following
equation:
The pseudo-first order model is expressed by the following
equation: (2)
The pseudo-second order kinetic model can be expressed as:
(3)
The mathematical expression of the intra-particle diffusion model is:
(4)
where qe and qt (mg·L-1) are the adsorption amount of reactive
orange 5 at equilibrium and at the time t, respectively. K1(min-1)
represents the first-order rate constant, K2 (g(mg·min) -1) is the
second-order adsorption rate constant, and Ki (mg·g-1·min-0.5) is the
intra-particle diffusion rate constant, C is the adsorption constant.
These statistical parameters (R2) and the non-linear regression
coefficients were obtained and shown in Table 2. The results are
plotted in Fig. 7.
Table 2 Kinetic parameters for reactive orange 5 adsorption by LDH and ILs/LDHs(b).Models Parameters LDHs bILs/LDHs
qe (exp) (mg·g-1) 56.82 253.01
Pseudo-first order qe (cal) (mg·g-1) 52.88 238.12
K1(min-1) 0.0169 0.1122
R2 0.9782 0.9182
Fc 54.53 66.83
10F0.005 38.8 38.8
Pseudo-second order qe (cal) (mg·g-1) 61.56 249.47
K2(g (mg·min)-1) 3.24×10-4 8.21×10-4
R2 0.9905 0.9897
Fc 311.58 273.51
10F0.005 38.8 38.8
Intra-particle diffusion model
Ki(g (mg·min0.5)-1) 2.43 4.35
C(mg·g-1) 10.16 175.14
R2 0.9142 0.7524
Fc 18.14 15.65
10F0.005 38.8 38.8
Fig. 7 Adsorption kinetics of reactive orange 5 on LDHs and ILs/LDHs(b) fitted with pseudo-first order, pseudo-second order and intra-particle diffusion models.
The adsorption of reactive orange 5 on the LDHs and
ILs/LDHs(b) might be described by intra-particle diffusion model,
which is a process involving migration of dye into layer of LDHs
and ILs/LDHs(b). The values calculated from the intra-particle
diffusion model obtained values of statistical parameters R2=0.91
and R2=0.75 for LDHs and ILs/LDHs(b), respectively, which
suggests that the intra-particle diffusion model does not
appropriately describe the adsorption processes. It means that
intra-particle diffusion has not played the key role in this the
adsorption process.
The values calculated from the pseudo-first order kinetic
model obtained values of statistical parameters R2 = 0.978 and R2
= 0.918 for LDHs and ILs/LDHs(b), respectively. And, relatively
great differences between experimental (qe(exp)) and calculated
(qe(cal)) are observed, especially with ILs/LDHs(b) as adsorbent. It
can be concluded that the pseudo-first order kinetic model does
not appropriately describe the adsorption processes.
The plots of the non-linearized form of the pseudo-second
order model for the adsorption are showed in Fig. 7. The R2 are
much greater in this case, confirming a very good agreement with
experimental data. It is also obviously, for the pseudo-second
order kinetic model, the values of the Fc for both materials are
much higher than others. In addition, the results of qe which
calculated from the pseudo-second order rate model are
consistent with the experimental values. Therefore, we consider
that the pseudo-second order kinetic model is the most suitable
model in describing the adsorption kinetic of reactive orange 5 on
LDHs and ILs/LDHs(b).
2.4 Sorption isotherm
In order to research the characteristics of the adsorption
isotherms, the Langmuir, the Sips and Freundlich isotherm models are
studied to analyze the equilibrium adsorption data.
The non-linearized form of Langmuir isotherm model are
expressed as the following equation:
(5)
where KL(L·mg - 1) is the Langmuir adsorption constant which is
related to the energy of adsorption, Ce (mg·L - 1) is the equilibrium
concentration of the dye, qe and qmax (mg·g-1) are the equilibrium and
maximum adsorption capacity.
The non-linearized form of Freundlich isotherm model can be
described as the following equation:
(6)
where KF is the Freundlich constant related to adsorption
capacity, n is related to the intensity of adsorption.
The Sips isotherm model is obtained by introducing a power
law expression of the Freundlich isotherm into the Langmuir isotherm.
The non-linearized form of Sips isotherm model can be given as
follows:
(7)
where Ks is the Sips isotherm constant representing the energy of adsorption, and m is the empirical constant.
Sips isotherm equation is characterized by the heterogeneity
factor, m. and it can be employed to describe the heterogenous
system. qmax is the maximum adsorption capacity. When m=1, Sips
isotherm equation reduces to the Langmuir equation and it implies a
homogeneous adsorption process.
The adsorption isotherms of reactive orange 5 onto LDHs and
ILs/LDHs(b) are shown in Fig. 8, and the fitted parameters for the
three models are given in Table 3. As can be seen, the values of R2
and Fc for the Freundlich model were much higher than other models,
indicating that the equilibrium data for the adsorption of reactive
orange 5 onto both sorbents can be well described by the Freundlich
isotherm model. This is indicative of the heterogeneity of the
adsorption sites on the LDHs and ILs/LDHs(b). The value of n (>1)
which was calculated from the Freundlich equations indicated a
favorable adsorption process[38,39]. The high KF (20.12,250.73) values
indicate that both adsorbents, LDHs and ILs/LDHs(b), have high
adsorption capacity and affinity by dye molecules.
Fig. 8. Adsorption isotherm of reactive orange 5 on LDHs and ILs/LDHs(b) fitted with Langmuir, Freundlich and Sips models.
Table 3 Isotherm constants for reactive orange 5 adsorption by LDH and ILs/LDHs(b).Models Parameters LDHs bILs/LDHs
Langmuir isotherm model Qmax (mg·g-1) 53.83 300.91
KL (L·mg-1) 0.14 16.16
R2 0.9595 0.9548
Fc 57.97 12.01
10F0.005 70.1 56.6
Freundlich isotherm model KF (mg1-1/n·L1/n·g-1) 20.12 250.73
1/n 0.2060 0.0554
R2 0.9922 0.9955
Fc 278.17 223.57
10F0.005 70.1 56.6
Sips isotherm model Qmax (mg·g-1) 53.09 315.94
Ks((L·mg-1)m) 0.1975 3.6544
m 0.6827 0.5988
R2 0.8304 0.9177
Fc 9.13 12.93
10F0.005 83.8 62.3
A comparison of the dyes removal performance between the
ILs/LDHs(b) in this study and other sorbents reported in literature was
given in Table 4. It is found that the ILs/LDHs(b) in this work has a
relatively higher adsorption capacity, which makes it to be used as
potential efficient adsorbent for the anionic dyes removal from
aqueous solutions.Table 4 A comparison between the performance of the ILs/LDHs composites in this
study and other sorbents reported in literature.Material Adsorbate q (mg·g-1) Contact time
(min)Reference
GO/CS/ETCH Reactive congo red 121.48 600 [8]
Mg-Fe-CO3-LDH Reactive congo red 104.6 30 [18]
Mg/Fe-CLDH Orang G 128.6 540 [42]
Mg/Fe-CLDH Acid brown 14 369 250 [15]
Mg/Al-CLDH Orange acid 10 303 300 [44]
RR-Fe4O3/Mg/Al-LDH Reactive red (RR) 101 30 [45]
ILs/LDH(b) Reactive orange 5 320 150 This study
2.5 Adsorption thermodynamics
The study of the temperature effect on reactive orange 5
adsorption on LDHs and ILs/LDHs(b) enabled us to determine the
thermodynamic parameters (Gibbs free energy ΔG0, enthalpy ΔH0 and
entropy ΔS0), which can be calculated by the following equations[40]:
(8)
(9)
where R is the ideal gas constant, T is the temperature (K), Kd
is the distribution coefficient. The plot of lnKd against 1000/T gives a
straight line for both of sorbents, the slope and the intercept
correspond to ΔHo/R and ΔSo/R, respectively. Values of ΔGo at different
temperatures can be calculated by the following equation: (10)
The results of the thermodynamic parameters are summarized
in Table 5. Generally, the change in adsorption enthalpy for
physisorption is in the range of −20 to 40 kJ/mol, but chemisorption is
between −400 and 80 kJ/mol[43]. The positive ΔH0 values (16.36 and
38.23 kJ/mol) reveal that the adsorptions on LDHs and ILs/LDHs(b) are
endothermic and physical in nature. The positive values of ΔS0, which
indicate an increase of randomness at the interface
adsorbent/adsorbate during adsorption process, suggest that the
removal of dye by LDHs gives a less ordered system than by
ILs/LDHs(b). Furthermore, the negative values of ΔG0 indicate that the
adsorptions onto LDHs and ILs/LDHs(b) is spontaneous.Table 5 Thermodynamic parameters for the adsorption of reactive orange 5 on
LDHs and ILs/LDHs(b).
Sorbents So
(Jmol-1K-1)Ho
(kJmol-1) Go (kJmol-1)
303.15K 318.15K 333.15KLDHs 151.34 38.23 -7.65 -9.92 -12.19
ILs/LDHs(b) 66.87 16.36 -3.96 -4.91 -5.92
2.6 Adsorption mechanisms
To elucidate adsorption mechanisms between reactive orange 5
and ILs/LDHs(b), FT-IR analyses are conducted. The FT-IR spectra (Fig.
9) of ILs/LDHs(b) before and after adsorption of dyes are recorded and
compared each other in the range of 400–2000 cm - 1. As it can be
seen from the spectra of after adsorption, there are new adsorption
peaks, which are due to the functional groups of dyes. the peaks at
1190 cm - 1 and 1047 cm - 1 are mainly attributed to symmetric
vibrations and antisymmetric of sulfate S = O bond, the peak at 782
cm - 1 was due to the stretching vibration of S - O, and the peak at
1139 cm-1 corresponds to stretching vibration of -C-O from phenol.
Through the FT-IR of ILs/LDHs(b) before and after adsorption of dyes,
it is clear that the dye is successfully adsorbed into ILs/LDHs(b).
Moreover, it can be seen that a weakening in the relative intensity of
1559 cm- 1 (corresponding to the -COO stretching from the interlay
anions) suggesting that part of species of dye replace the interlayer
anions. In other words, the ion exchange is occurred between
interlayer anions and dye species.
Fig.9. FI-IR patterns of the synthesized ILs/LDHs(b) before and after the adsorption of reactive orange 5.
The adsorption behavior is affected by the functional groups of
the adsorbent and adsorbate. Considering the groups of ILs/LDHs(b)
(C=O,-CN, -OH) and reactive orange 5 ( -SO3- ,C-O,N-H), the
adsorption of reactive orange 5 onto ILs/LDHs(b) may occur through
electrostatic attraction (O - H+/ - SO3- ) under acidic conditions and
hydrogen bond (C=O/N-H, O-H/C-O) interactions. As mentioned,
the adsorption capacity significantly decreased with increasing pH
value, the results indicate that the electrostatic interaction is the main
responsible. In addition, van der Waals interactions may also occur.
The process of dyes adsorption onto ILs/LDHs(b) is the combination of
these factors.
2.7 Desorption analysis
Desorption experiments of reactive orange 5 were performed to
evaluate the recyclable availability. The experimental results show
that the desorption percentages were 57.91%, 46.67%, and 37.34% in
each cycle, respectively (in Fig.10) As it was described before, an
increment in the solution pH favors reducing the interaction with dye
and sorbents, and the behavior of desorption sustains the results
obtained in the previous adsorption at different pH experiment, and it
also could be concluded that the principal interaction force that lead
the adsorption onto ILs/LDHs(b) is the ionic interaction between -SO3
- of dye and ILs/LDHs(b)[44].
Fig.10. Performance of ILs/LDHs(b) by three cycles of adsorption/desorption reactive orange 5.
3 Conclusions
In this study, 2-hydroxyethylammonium acetate is successfully
intercalated into the hydrotalcite (LDHs) by co-precipitation method,
which is proven by the marked increase in interlayer spacing of host
structure and presentation of the - COO - group characteristic
vibration peaks in the FT-IR spectrum of the intercalation composites
(ILs/LDHs(b)). The BET surface of ILs/LDHs(b) is larger than that of
LDHs. LDHs and ILs/LDHs(b) are applied to remove anionic dye
reactive orange 5 from aqueous solutions. The experimental factors
such as adsorbent dosage and pH to affect the adsorption were
measured. The pseudo-second order model accurately described the
reactive orange 5 adsorption kinetic for LDHs and ILs/LDHs(b). The
adsorption isotherm data are in agreement with the Freundlich model.
Thermodynamic data indicated reactive orange 5 adsorptions were
spontaneous and endothermic nature. The maximum adsorption
capacity of reactive orange 5 onto ILs/LDHs(b) was 300.9 mg/g, which
was higher than that of pure LDHs(53.9 mg/g). The process of dyes
adsorption onto ILs/LDHs(b) is the combination of ion exchange,
electrostatic attraction, hydrogen bond interactions and van der
Waals interactions. The desorption percentages were 57.91%,
46.67%, and 37.34% in each cycle, respectively. On the basis of
above results, ILs/LDHs(b) could be used as potential adsorbent for
reactive orange 5 removal from aqueous solutions.
References:[1] Y.L. Pang and A.Z. Abdullah, Current status of textile industry wastewater
management and research progress in Malaysia: A review, Clean-Soil. Air. Water.
41, 2013, 751–764.
[2] G.M. Walker, L. Hansen, J.A. Hanna and S.J. Allen, Kinetics of a reactive dye
adsorption onto dolomitic sorbents, Water Res. 37, 2003, 2081–2089.
[3] C.Z. Liang, S.P. Sun, F.Y. Li, Y.K. Ong and T.S. Chung, Treatment of highly
concentrated wastewater containing multiple synthetic dyes by a combined
process of coagulation/flocculation and nanofiltration, J. Membr. Sci. 469, 2014,
306–315.
[4] O. Turgay, G. Ersoz, S. Atalay, J. Forss and U. Welander, The treatment of azo
dyes found in textile industry wastewater by anaerobic biological method and
chemical oxidation, Sep. Purif. Technol. 79, 2011, 26–33.
[5] B. Bonakdarpour, I. Vyrides and D.C. Stuckey, Comparison of the performance
of one stage and two stage sequential anaerobic–aerobic biological processes for
the treatment of reactive-azo-dye-containing synthetic wastewaters, Int.
Biodeterior. Biodegr. 65, 2011, 591–599.
[6] Y. Zheng, G. Yao, Q. Cheng, S. Yu, M. Liu and C. Gao, Positively charged thin-
film composite hollow fiber nanofiltration membrane for the removal of cationic
dyes through submerged filtration, Desalination 328, 2013, 42–50.
[7] L. Karimi, S. Zohoori and M.E. Yazdanshenas, Photocatalytic degradation of
azo dyes in aqueous solutions under UV irradiation using nano-strontium titanate
as the nanophotocatalyst, J. Saudi. Chem. Soc. 18, 2014, 581–588.
[8] Q. Du, J. Sun, Y. Li, X. Yang, X. Wang, Z. Wang and L. Xia, Highly enhanced
adsorption of congo red onto graphene oxide/chitosan fibers by wet-chemical
etching off silica nanoparticles, Chem. Eng. J. 245, 2014, 99–106.
[9] X. Zhuang, Y. Wan, C.M. Feng, Y. Shen and D.Y. Zhao, Highly efficient
adsorption of bulky dye molecules in wastewater on ordered mesoporous carbons,
Chem. Mater. 21, 2009, 706–716.
[10] Q.H. Hu, S.Z. Qiao, F. Haghseresht, M.A. Wilson and G.Q. Lu, Adsorption study
for removal of basic red dye using bentonite, Ind. Eng. Chem. Res. 45, 2006, 733–
738.
[11] J.C. Hu, Z. Song, L.F. Chen, H.J. Yang, J.L. Li and R. Richards, Adsorption
properties of MgO(111) nanoplates for the dye pollutants from wastewater, J.
Chem. Eng. Data 55, 2010, 3742–3748.
[12] M.M.F. Silva, M.M. Oliveira, M.C. Avelino, M.G. Fonseca, R.K.S. Almeida and
E.C. Silva, Filho, Adsorption of an industrial anionic dye by modified-KSF-
montmorillonite: evaluation of the kinetic, thermodynamic and equilibrium data,
Chem. Eng. J. 203, 2012, 259–268.
[13] C. Wang, J. Li, L. Wang, X. Sun and J. Huang, Adsorption of dye from
wastewater by zeolites synthesized from fly ash: kinetic and equilibrium studies,
Chin. J. Chem. Eng. 17, 2009, 513–521.
[14] N.M. Mahmoodi, B. Hayati, M. Arami and F. Mazaheri, Single and binary
system dye removal from colored textile wastewater by a dendrimer as a
polymeric nanoarchitecture: equilibrium and kinetics, J. Chem. Eng. Data 55,
2010, 4660–4668.
[15] Y. Guo, Z. Zhu, Y. Qiu and J. Zhao, Enhanced adsorption of acid brown 14 dye
on calcined Mg/Fe layered double hydroxide with memory effect, Chem. Eng. J.
219, 2013, 69–77.
[16] E.D. Isaacs-Paez, R. Leyva-Ramos, A. Jacobo-Azuara, J.M. Martinez-Rosales
and J.V. Flores-Cano, Adsorption of boron on calcined AlMg layered double
hydroxide from aqueous solutions. Mechanism and effect of operating conditions,
Chem. Eng. J. 245, 2014, 248–257.
[17] M. Bouraada, M. Lafjah, M.S. Ouali and L.C. de Menorval, Basic dye removal
from aqueous solutions by dodecylsulfate- and dodecyl benzene sulfonate-
intercalated hydrotalcite, J. Hazard. Mater. 153, 2008, 911–918.
[18] I.M. Ahmed and M.S. Gasser, Adsorption study of anionic reactive dye from
aqueous solution to Mg–Fe–CO3 layered double hydroxide (LDH), Appl. Surf. Sci.
259, 2012, 650–656.
[19] Y.M. Zheng, N. Li and W.D. Zhang, Preparation of nanostructured
microspheres of Zn–Mg–Al layered double hydroxides with high adsorption
property, Colloid. Surf. A Physicochem. Eng. Asp. 415, 2012, 195–201.
[20] N. Drici, N. Setti and Z. Jouini, Derriche, Sorption study of an anionic dye –
benzopurpurine 4B – on calcined and uncalcined Mg–Al layered double
hydroxides, J. Phys. Chem. Solids 71, 2010, 556–559.
[21] H. Zaghouane-Boudiaf, M. Boutahala and L. Arab, Removal of methyl orange
from aqueous solution by uncalcined and calcined MgNiAl layered double
hydroxides (LDHs), Chem. Eng. J. 187, 2012, 142–149.
[22] L.D.L. Miranda, C.R. Bellato, M.P.F. Fontes, M.F. de Almeida, J.L. Milagres and
L.A. Minim, Preparation and evaluation of hydrotalcite-iron oxide magnetic
organocomposite intercalated with surfactants for cationic methylene blue dye
removal, Chem. Eng. J. 254, 2014, 88–97.
[23] J. Liu, X. Li, J. Luo, C. Duan, H. Hu and G. Qian, Enhanced decolourisation of
methylene blue by LDH-bacteria aggregates with bioregeneration, Chem. Eng. J.
242, 2014, 187–194.
[24] X. Chen, F. Li, C. Asumana and G. Yu, Extraction of soluble dyes from
aqueous solutions with quaternary ammonium-based ionic liquids, Sep. Purif.
Technol. 106, 2013, 105–109.
[25] A.M. Ferreira, J.A.P. Coutinho, A.M. Fernandes and M.G. Freire, Complete
removal of textile dyes from aqueous media using ionic-liquid-based aqueous two-
phase systems, Sep. Purif. Technol. 128, 2014, 58–66.
[26] H. Gao, T. Kan, S. Zhao, Y. Qian, X. Cheng, W. Wu, X. Wang and L. Zheng,
Removal of anionic azo dyes from aqueous solution by functional ionic liquid
cross-linked polymer, J. Hazard. Mater. 261, 2013, 83–90.
[27] M. Ghaedi, D. Elhamifar, M. Roosta and R. Moshkelgosha, Ionic liquid based
periodic mesoporous organosilica: an efficient support for removal of sunset
yellow from aqueous solutions under ultrasonic conditions, J. Ind. Eng. Chem. 20,
2014, 1703–1712.
[28] G. Absalan, M. Asadi, S. Kamran, L. Sheikhian and D.M. Goltz, Removal of
reactive red-120 and 4-(2-pyridylazo) resorcinol from aqueous samples by Fe3O4
magnetic nanoparticles using ionic liquid as modifier, J. Hazard. Mater. 192, 2011,
476–484.
[29] X.L. Yuan, S.J. Zhang and X.M. Lu, Hydroxyl ammonium ionic liquids:
synthesis, properties, and solubility of SO2, J. Chem. Eng. Data 52, 2007, 596–
599.
[30] H.Y. Zeng, F. Zhen, X. Deng and Y.Q. Li, Activation of Mg-Al hydrotalcite
catalysts for transesterification of rape oil, Fuel 87, 2008, 3071–3076.
[31] H.Y. Zeng, X. Deng, Y.J. Wang and K.B. Liao, Preparation of Mg-Al hydrotalcite
by urea method and its catalytic activity for transesterification, AIChE J. 55, 2009,
1229–1235.
[32] M.F. Chiang and T.M. Wu, Intercalation of γ-PGA in Mg/Al layered double
hydroxides: an in situ WAXD and FTIR investigation, Appl. Clay Sci. 51, 2011, 330–
334.
[33] M.G. Alvarez, A.M. Segarra, S. Contreras, J.E. Sueiras, F. Medina and F.
Figueras, Enhanced use of renewable resources: transesterification of glycerol
catalyzed by hydrotalcite-like compounds, Chem. Eng. J. 161, 2010, 340–345.
[34] F.F. Chen, G.H. Wang, W. Li and F. Yang, Glycolysis of Poly(ethylene
terephthalate) over Mg−Al mixed oxides catalysts derived from hydrotalcites, Ind.
Eng. Chem. Res. 52, 2013, 565–571.
[35] H. Hu, J.C. Martin, M. Xiao, C.S. Southworth, Y.Z. Meng and L.Y. Sun,
Immobilization of ionic liquids in layered compounds via mechanochemical
intercalation, J. Phys. Chem. C 115, 2011, 5509–5514.
[36] K.M. Parida and L. Mohapatra, Carbonate intercalated Zn/Fe layered double
hydroxide: a novel photocatalyst for the enhanced photo degradation of azo dyes,
Chem. Eng. J. 179, 2012, 131–139.
[37] P.P. Wu, T. Wu, W.W. He, L.L. Sun, Y.J. Li and D.J. Sun, Adsorption properties
of dodecylsulfate-intercalated layered doublehydroxide for various dyes in water,
Colloid. Surf. A Physicochem. Eng. Asp. 436, 2013, 726–731.
[38] K. Yang, L.G. Yan, Y.M. Yang, S.J. Yu, R.R. Shan, H.Q. Yu, B.C. Zhu and B. Du,
Adsorptive removal of phosphate by Mg–Al and Zn–Al layered double hydroxides:
kinetics, isotherms and mechanisms, Sep. Purif. Technol. 124, 2014, 36–42.
[39] L.G. Yan, K. Yang, R.R. Shan, T. Yan, J. Wei, S.J. Yu, H.Q. Yu and B. Du, Kinetic,
isotherm and thermodynamic investigations of phosphate adsorption onto core–
shell Fe3O4@LDHs composites with easy magnetic separation assistance, J.
Colloid Interface Sci. 448, 2015, 508–516.
[40] N.B.H. Abdelkader, A. Bentouami, Z. Derriche, N. Bettahar and L.C. de
Menorval, Synthesis and characterization of Mg–Fe layer double hydroxides and
its application on adsorption of orange G from aqueous solution, Chem. Eng. J.
169, 2011, 231–238.
[41] R. Extremera, I. Pavlovic, M.R. Pérez, C. Barriga, Removal of acid orange 10
by calcined Mg/Al layered double hydroxides from water and recovery of the
adsorbed dye, Chem. Eng. J. 213, 2012, 392-400.
[42] R.R. Shan, L.G. Yan, K. Yang, S.J. Yu, Y.F. Hao, H.Q. Yu, B. Du, Magnetic
Fe3O4/MgAl-LDH composite for effective removal of three red dyes from aqueous
solution, Chem. Eng. J. 252, 2014, 38-46.
[43] L.L. Lian, L.P. Guo and C.J. Guo, Adsorption of Congo red from aqueous
solutions onto Ca-bentonite, J. Hazard. Mater. 161, 2009, 126–131.
[44] J.A. González, M.E. Villanueva, L.L. Piehl and G.J. Copello, Development of a
chitin/graphene oxide hybrid composite for the removal of pollutant dyes:
adsorption and desorption study, Chem. Eng. J. 280, 2015, 41–48.
项目来源:2015 年湖北省自然科学基金面上项目(B2015304) 作者简介:周青青(1990.07-),女,主要研究方向:染整清洁生产工艺。