Magnetizing Calixarene: Azo Dye Removal from Aqueous Media by

Article pubs.acs.org/jced

Magnetizing Calixarene: Azo Dye Removal from Aqueous Media by Fe3O4 Nanoparticles Fabricated with Carboxylic-Substituted Calix[4]arene Asif Ali Bhatti,†,‡ Mehmet Oguz,†,§ and Mustafa Yilmaz*,† †

Department of Chemistry, and §Department of Advanced Material and Nanotechnology, Selcuk University, Konya, 42031, Turkey National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, 76080, Pakistan

‡

S Supporting Information *

ABSTRACT: Calix[4]arene was reacted with isonipecotic acid to synthesize the Mannich base derivative, and Fe3O4 magnetic nanoparticles were bonded to the lower rim of the calix[4]arene derivative through ether linkage to obtain carboxylic calix[4]arene magnetic nanoparticles (CCMN). After characterization with transmission electron microscopy and Fourier transform infrared spectroscopy, adsorption studies were carried out for the removal of azo dyes (Evans Blue and Chicago Sky Blue 6 B). Adsorption parameters such as effects of pH, dosage, concentration, temperature, and time were optimized. Results showed that adsorption equilibrium was achieved within 15 min, and maximum % adsorption was calculated as 95% for both dyes at pH 2.5. An equilibrium isotherm study suggests that the adsorption mechanism follows a chemical ion exchange process with an adsorption capacity value of 13.9 and 17.5 mmol g−1 for Evans Blue and Chicago Sky Blue 6 B, respectively. The adsorption kinetic follows pseudosecond-order kinetics as anticipated from R2 values, whereas thermodynamic parameters suggest an endothermic reaction that can also be evident from ΔG° values, which decreased with an increase in temperature suggesting a spontaneous reaction. In addition, the dye removal efficiency of CCMN was hardly effected after 10 consecutive cycles. The study suggests that the magnetically retrievable calix[4]arene is a promising adsorbent for removal of azo dyes from aqueous solution. have gained attention.23 In this regard “supramolecular chemistry” provides important possibilities for producing sophisticated molecules that may have the proper orientation of functional groups demarcating the binding site.24,25 In this field, calix[n]arenes have gained greater importance because of their simplicity and ease of production.26 Calix[n]arenes conformations and complexation properties make them unique over many synthetic and natural hosts.27,28 Moreover, nanostructured metal oxides are gaining much attention owing to their outstanding chemical and catalytic properties. Among various metal oxides, the nanoparticles of iron oxide (Fe3O4) are of great interest due to their easy synthesis, low cost, good stability, and high magnetic permeability.29−32 Because of these unique properties, these nanomaterials efficiently remove organic as well as inorganic contaminants from aqueous media.29,33,34 The purpose of this work is to synthesize the wide rim derivative of calix[4]arene via the Mannich reaction using

1. INTRODUCTION The significant inflation of synthetic dyes usage has been observed worldwide with an annual production of over 150 000 to 200 000 tons per year. Extensive usage and enormous production of synthetic dyes are the main cause for water pollution.1,2 Among them azo dyes are frequently being used in various industries such as plastic, paper, textile, leather and cosmetic industry.3 However, their manufacturing or processing operation releases large amounts of effluents directly into the aquatic environment which causes turbidity, eutrophication, and aggravation of aquatic life.4 Most of the azo dyes are carcinogenic, mutagenic, and nonbiodegradable, making them the main cause of water pollution.5−7 For this, significant efforts have been made to detoxify the effects of contamination before the dye is discharged to main streams by using different methods, such as the Fenton process, in conjunction with ultrasound technology,8 flocculation/coagulation,9 oxidation− ozonation,10,11 electrochemical process,12−14 membrane filtration,15,16 and photocatalysis,17,18 solid phase extraction,19−22 Among these, solid phase extraction has been very economical and is easy to model. In recent years, new solid phase extraction materials with enhanced recycling and economical properties at industrial level © 2017 American Chemical Society

Special Issue: Memorial Issue in Honor of Ken Marsh Received: February 2, 2017 Accepted: June 1, 2017 Published: June 9, 2017 2819

DOI: 10.1021/acs.jced.7b00128 J. Chem. Eng. Data 2017, 62, 2819−2825

Journal of Chemical & Engineering Data

Article

Figure 1. Synthesis of carboxylic calix[4]arene Fe3O4 magnetic nanoparticles (CCMN): (i) isonipecotic acid/CH3CO2H/H2CO/THF, (ii) EPPTMS-MN/K2CO3/ACN.

Figure 2. Comparative FTIR spectra of 2, EPPTMS, and CCMN.

had been passed through a Millipore Milli-Q Plus water purification system (ELGA Model CLASSIC UVF, UK). 2.2. Instrumentation. A pH meter (Thermo scientific Orion star 410A+) with glass electrode and internal reference electrode was used for pH measurements. 1HNMR spectra were referenced to tetramethylsilane (TMS) at 0.00 ppm as the internal standard solution and recorded on a Varian 400 MHz spectrometer at room temperature (25 ± 1 °C). Fourier transform infrared (FTIR) spectra were recorded by Bruker Vertex ATR-FTIR spectrometer for characteristic functional group analysis. UV−vis spectra were obtained with a Shimadzu 1700 UV−visible double beam spectrophotometer using standard 1.00 cm quartz cells for the determination of concentration of dyes in aqueous solution. Analytical TLC was performed on precoated silica gel plates (SiO2, Merck

isonipecotic acid, and subsequently bond the derivative on Fe3O4 to obtain carboxylic calix[4]arene magnetic nanoparticles (CCMN). Solid phase extraction studies were carried out for the separation of azo dyes such as Evans Blue and Chicago Sky Blue 6 B by optimizing different parameters.

2. EXPERIMENTAL SECTION 2.1. Chemicals. All chemicals were of reagent grade and used without further purification. Evans Blue (EB) and Chicago Sky Blue 6 B (CSB) were obtained from Sigma. A standard solution of dyes with a concentration of 1.0 M was prepared, and calibration was carried out by diluting the standard solution. The pH of dyes was adjusted by 0.1 M (HCl/KOH). All aqueous solutions were prepared with deionized water that 2820



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Figure 3. TEM images: (A) Pure Fe3O4 nanoparticles; (B) CCMN.

PF254). All glassware were washed and soaked overnight in 3 M HNO3, and rinsed with deionized water before use. 2.3. Syntheses. Carboxylic calix[4]arene and EPPTMS magnetic nanoparticles (EPPTMNPs) were synthesized as described previously (Figure 1),29 whereas the immobilization of calix[4]arene on EPPTMNPs nanoparticles was carried out through the literature method with little modification.35 2.4. Fabrication of EPPTMNPs with CCMN. Compound 2 (1.5 g) was mixed with (0.3 g) potassium carbonate in acetonitrile (50 mL) and stirred for 30 min. EPPTMS-MN (1.5 g) was added, and the mixture was refluxed for 72 h. Modified magnetic particles were separated with the help of a magnet, and an excess amount of compound 2 was removed by washing the mixture with DMF and then with water and then drying under vacuum. The amount of compound 2 immobilized was calculated by measuring the concentration of compound 2 in the remaining solution through aspectroscopic method. It was found to be 34%. 2.5. Characterization. FTIR and transmission electron microscopy (TEM) techniques were used to characterize the prepared materials. Figure 2 shows the comparative FTIR spectra, in which the presence of a carbonyl moiety (CO) at 1706 cm−1 along with an aromatic CC band at 1481 cm−1 in CCMN confirms the successful fabrication of compound 2 on EPPTMS (Figure 2). On the other hand TEM micrographs (Figure 3) show a difference in the morphology of particles, being spherical and aggregated after fabrication of compound 2. 2.6. Adsorption Procedure. The batch method was used for the adsorption of dyes (Figure 4) on newly synthesized CCMN. Typically, 5 mL of dye solution (1 × 10−5 mol· L−1) was taken in a 25 mL Erlenmeyer flask and 5 mg of CCMN was added with mechanical shaking for 30 min. After magnetic separation, the concentration of dye was evaluated using a UV− visible spectrophotometer, and % adsorption and adsorption capacity was calculated using eq 1 and 2, respectively. All the measurements were carried out in triplicate and values presented are the average. % Adsorption =

C i − Cf × 100 Ci

Figure 4. Structure of azo dyes.

qe =

(C i − Ce)V m

(2)

where qe (mmol·g−1) represents adsorption capacity, Ci (mol· L−1) and Cf (mol·L−1) are initial and final concentrations of dyes, respectively, V is the volume (mL) of dyes solution, and m is the mass (g) of adsorbent.

3. RESULTS AND DISCUSSION 3.1. Preparation of Effective Material for Azo Dyes. The aim of this work was to prepare an effective material for the removal of azo dyes. In this regard calixarene was immobilized on magnetic iron oxide nanoparticles and used in solid phase extraction for the removal of azo dyes. The idea behind the immobilization of calix[4]arene on magnetic iron oxide nanoparticles was not only to ease separation and reduce the separation time of adsorbent after adsorption process but also to enhance the surface binding sites at the nanolevel. In the literature, many calixarene derivatives have been immobilized on natural and synthetic polymer materials to increase the surface area, but these polymeric materials only increase the

(1) 2821



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surface area not the specific active binding sites that can bind guest molecules at the nanolevel.6,36,37 So the immobilized compound 2 on iron oxide nanoparticles certainly increases the binding sites for guest molecules and decreases the amount of adsorbent material used for high adsorption of contaminants present in aqueous media.38 Immobilization of compound 2 was confirmed by FTIR and TEM analysis. The FTIR spectra of CCMN (Figure 2) indicated the presence of different bands at 1700 cm−1 corresponding to the CO stretching vibration in carboxylate and the peak at 570 cm−1 resulting from the characteristic absorption of Fe−O bond stretching vibration. The TEM images demonstrated CCMN tended to aggregate in aqueous solution because of the small size effect caused by hydrophilic units of compound 2 on the iron nanoparticles and lack of any repulsive force between Fe3O4 nanoparticles. 3.2. Effect of Adsorbent Dosage and Concentration. Accomplishment of absorbent efficiency at initial concentration for adsorbate can be examined by changing adsorbent dosage. The optimum amount of adsorbent for dyes (CSB and EB) of particular concentration (1 × 10−5 mol·L−1) was established by using different quantities of CCMN (1−6 mg). The plot for the amount of CCMN vs % adsorption is shown in Figure 5. It was

Figure 6. Concentration effect on adsorption capacity (5 mg of CCMN, 5 mL dye and 30 min shaking time).

Figure 7. Influence of pH on the percent removal (5 mg CCMN, 5 mL dye with 1 × 10−5 mol·L−1, 30 min shaking time).

evaluated through different equilibrium isotherms. Langmuir, Freundlich, and D-R models were fitted to experimental data for thorough understanding of adsorbate behavior. Equations 3−5 present the linear forms of these equations.40−42

Figure 5. Influence of amount of adsorbent (5 mL, 1 × 10−5 mol·L−1, 30 min shaking time).

observed that more than 80% adsorption was achieved by using only 5 mg of the adsorbent, that is, CCMN for both dyes. The high % adsorption for this amount of adsorbent occurs because of the availability of a large number of adsorption sites at the nanolevel. The carboxylic calix[4]arene provides the Fe3O4 nanoparticles with extra efficiency to accommodate foreign guests by providing extra binding sites on the cage-like shape to hold large molecules inside the ring, whereas increasing the concentration of dyes while maintaining a fixed amount of adsorbent decreases the efficiency of CCMN to bind the dyes (Figure 6). The curves observed in Figure 6 are the reflection of a decrease in adsorption efficiency, because saturation of the binding sites occurs. 3.3. Adsorption Dependency on pH. The adsorption of dyes to the surface of CCMN is greatly affected by the solution pH. The calix[4]arene derivative used here contains soft binding sites which are ideal for binding different ionic species. In the acidic solution, the protonation of SO3− groups could shift the SO3Na of a dye molecule to form SO3H, resulting in the formation of NH+SO3− with the amine group of calix[4]arene through electrostatic interaction. As a result, enhanced physical affinity at lower pH occurs.39 This behavior explains the high adsorption capacity of CCMN for both dyes at pH 2.5 (Figure 7). 3.4. Adsorption Isotherms. The feasibility of adsorption and mechanism of adsorbate−adsorbent interaction can be

Ce C 1 = + e Cads Qb Q ln Cads = ln A +

(3)

1 ln Ce n

ln Cads = ln X m − βε

2

(4) (5)

where Q in eq 3 represents monolayer sorption capacity and b indicates enthalpy of reaction. In eq 4, A is the Freundlich isotherm constant adsorption capacity and 1/n is energy or adsorption intensity. Xm is the total adsorption capacity in eq 5; b is the activity coefficient, having dimensions of energy, and ε is the Polanyi potential. Different parameters were obtained (Table 1) from slope and intercept by fitting experimental data in these equations. (Figures S2−S4). R2 of these plots favors the Langmuir isotherm, which assumes the sorption takes place at specific homogeneous sites within the adsorbent and the dye is chemically adsorbed. This suggests the adsorption process is a monolayer surface coverage with equal and independent sites. The favorability of the isotherm can be evaluated by the separation factor RL = 1 + (1/bCi) that defines the type of isotherm.43,44 The RL values, found between 0.999 and 0.982, were in range (0 < RL < 1). The 1/n values were lower than 1 suggesting a favorable adsorption process and confirming the high bonding intensity. 2822



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Table 1. Langmuir, Freundlich, and D-R Isotherm Parametersa for Adsorption of Dyes on CCMN Langmuir isotherm

dye

mol·g

−1

−1

L·mol

0.0139 ± 0.02 0.0175 ± 0.03

CSB EB

Freundlich isotherm

b × 104

Q

391.491 116.011

D-R isotherm

A R

2

L mol

Xm −1

0.143 ± 0.09 0.278 ± 0.012

0.997 0.996

2

1/n

R

0.541 0.598

0.979 0.967

mol·g

E −1

0.451 ± 0.072 0.515 ± 0.087

kJ·mol−1

R2

12.30915 11.95

0.993 0.986

a Notation: Q, adsorption saturation capacity; b, enthalpy of sorption; A, multilayer adsorption capacity; Xm, maximum adsorption capacity; E, mean free energy; R2, regression coefficient.

Table 2. Pseudo-first-order and Pseudo-second-order Kinetic Parametersa for for Adsorption of Dyes on CCMN pseudo-first-order

pseudo-second-order

k1

qe

k2

qe

dye

T

min−1

mol·g−1

R2

g·mmol−1min−1

mmol·g−1

R2

CSB

303 308 313 303 308 313

0.1351 0.211 0.1072 0.064 0.136 0.126

0.067 0.089 0.059 0.038 0.039 0.030

0.959 0.947 0.979 0.970 0.937 0.959

3311.724 4806.061 3132.163 3653.733 6994.273 8061.825

0.225 0.223 0.225 0.221 0.218 0.222

0.999 0.999 0.999 0.998 0.999 0.999

EB

a

Notation: k1 and k2 represent rate constants; qe, amount of dye adsorbed at equilibrium, T is the working temperature; R2 is the regression coefficient.

Table 3. Thermodynamic Parametersa for Adsorption of Dyes on CCMN ΔH

a

ΔG°/kJ·mol−1

ΔS −1

−1

−1

kJ·mol ·K

dye

kJ·mol

EB

−108.23

0.387

CSB

−48.65

0.188

303/K

308/K

313/K

−6.8410 ln Kc = 2.72 −8.2976 ln Kc = 3.30

−8.4948 ln Kc = 3.32 −8.6904 ln Kc = 3.40

−10.7248 ln Kc = 4.12 −10.1971 ln Kc = 3.92

Notation: ΔH, change in enthalpy; ΔS change in entropy, and ΔG° change in free energy.

parameters were calculated from these plots and presented in Table 2. The regression coefficient R2 values were above 0.99 providing an adequate fitting of pseudo-second-order kinetics rather than pseudo-first-order kinetics for both dyes. The pseudo-second-order kinetic model follows the initial period of the adsorption process suggesting that heterogeneity of the adsorbent and transfer of adsorbate along with the chemical reaction happen instantaneously. 3.6. Thermodynamics of Adsorption. Thermodynamic considerations of an adsorption process are necessary to conclude whether the process is spontaneous or not. Thermodynamic parameters ΔH (kJ·mol−1), ΔS (kJ·mol· K−1), and ΔG° (kJ·mol−1) of adsorption were evaluated using the Van’t Hoff equation (eq 9) and free energy equation (eq 10) by plotting ln kc versus T−1 (Figure S6).

From Dubinin−Radushkevich, (D-R) isotherm (eq 5) the mean free energy E (kJ mol−1) of adsorption process can be evaluated using eq 6, which is interpreted as physio-sorption (0−8) kJ·mol−1 or chemo-sorption (8−16) kJ·mol−1. The E values were found to be 12.30 and 11.95 kJ·mol− for CSB and EB, respectively, which appear to indicate a chemical adsorption process.

E=

1 −2β

(6)

3.5. Adsorption Kinetics. To get insights into the reaction pathways and mechanism, a sorption kinetic study was carried out, which can define the adsorption rate and controls the sorbate removed at the solid−solution interface that are vital for the proposal of suitable sorption treatment plants. In this study Lagergren and pseudo-second-order rate equations were applied to evaluate the adsorption kinetics (eqs 7 and 8)45,46 by observing the % adsorption at different time intervals with 1.0 × 10−6 mol·L−1, 5 mg of CCMN per 5 mL of adsorbate (Figures S5, S6). ln(qe − qt ) = ln qe − k1t

(7)

⎛ ⎞ t 1 ⎟ ⎛⎜ 1 ⎞⎟ = ⎜⎜ + ⎜ ⎟t 2⎟ qt ⎝ k 2qe ⎠ ⎝ qe ⎠

(8)

ln kc =

−ΔH ΔS + RT R

ΔG° = −RT ln kc

(9) (10)

Adsorption capacity increases with elevation in temperature (Figure S5−S6). The negative value of ΔG° indicates the feasibility of the adsorption process, and a decrease in ΔG° values with temperature indicates the spontaneity adsorption process at elevated temperatures (Table 3). The negative value of ΔH endorses the exothermic process, and ΔS indicates good affinity for the dyes adsorption on CCMN.

where k1 and k2 represent rate constants, qe is amount of dye adsorbed at equilibrium, and t is the time of saturation. Kinetic 2823



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3.7. Reusability of Resin. The regeneration of CCMN shows its efficiency and economical property. CCMN was regenerated by using 0.1 N NaOH and reused for a number of cycles for its adsorption efficacy. Results show that the adsorption ability is hardly affected after 10 uses, that is, only 13−15% decrease (Figure 8). The nanoscale adsorbent can

Article

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00128. 1 HNMR spectrum and different isotherms (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Mustafa Yilmaz: 0000-0003-2904-160X Funding

We would like to thank The Research Foundation of Selcuk University (BAP) for their financial support of this work. Notes

The authors declare no competing financial interest.

■

REFERENCES

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Figure 8. Reusability of CCMN (10 mg of adsorbent, 10 mL of dye 1 × 10−5 mol·L−1, pH 2.5, and T = 30 °C, regenerated by using 0.1 N NaOH).

have a number of sites to accommodate a foreign guest molecule. The adsorption rate was also high due to the likelihood of many binding sites such as acetate and amino groups which play an important part in binding guest molecules at suitable pH values. 3.8. Comparison with Other Materials. In our previous studies, different materials were used to remove Chicago Sky Blue 6 B and Evans Blue azo dyes. Table 4 shows the results of those materials and CCMN for the removal of these dyes. The organo-magnetic materials are efficient and always perform well in the removal of pollutants from aqueous media. CCMN shows a good ability to remove dyes at low pH with less amount of material required.

4. CONCLUSION It could be anticipated that the calix[4]arene derivative fabricated on Fe3O4 (CCMN) has proved to be good adsorbent material for the removal of pollutants at low level. The method was developed to achieve the maximum % adsorption at optimized condition such as pH, amount, concentration, time, as well as temperature. The results are promising, and hopefully this economical material will find its applicability in many fields. Table 4. Comparison of CCMN with Other Adsorbents adsorbent calix copolymer β-cyclodextrin-based polymers. cyclodextrin-Fe3O4 CCMN

a

dye

pH

% adsorption

qe (mmol/g)a

EB CSB EB CSB EB CSB EB CSB

2.0

70

N/A

25

3

2.0

96 94 99 99 94 95

9.58 10.59 N/A

25

7

25

34

3.0 2.5

17.5 13.9

dosage (mg)

5.0

ref

present study

N/A: not available. 2824



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Magnetizing Calixarene: Azo Dye Removal from Aqueous Media by

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