Preparation and Cationic Dye Adsorption of Novel Fe3O4

Article pubs.acs.org/jced

Preparation and Cationic Dye Adsorption of Novel Fe3O4 Supermagnetic/Thiacalix[4]arene Tetrasulfonate Self-Doped/ Polyaniline Nanocomposite: Kinetics, Isotherms, and Thermodynamic Study Moslem Mansour Lakouraj,* Rafieh-Sadat Norouzian, and Soheila Balo Polymer Chemistry Research Laboratory, Department of Organic Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar 47416-95447, Iran S Supporting Information *

ABSTRACT: In this study, a novel magnetically separable nanoadsorbent, namely, Fe3O4@PAmABAmPD-TCAS consisting of a magnetite core and conductive terpolymer of aniline/m-aminobenzoicacid/m-phenilendiamine shell which was self-doped by protonic acid of thiacalixarene tetrasulfonate pendent groups has been synthesized in a three step procedure. Adsorption features of the magnetic nanoadsorbent were evaluated by using methylene blue (MB) and malachite green (MG) as adsorbates. The isotherms, kinetics, and thermodynamics of the adsorption of MB and MG onto Fe3O4@PAmABAmPD-TCAS nanoadsorbent have been studied in various experimental conditions, i.e., initial dye concentration, contact time, solution pH, adsorbent dosage, and temperature. The obtained results fitted well to the Langmuir model and the kinetics of the adsorption process were found to follow the pseudo-second-order kinetics. The synthesized nanoadsorbent revealed improvements in terms of adsorption capacity for the dyes as a result of its high surface area and large amount of functional groups. The thermodynamic study was conducted by calculating a number of thermodynamic parameters such as the standard Gibbs energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) changes. The high sensitivity of the magnetic nanoadsorbent to external magnetic field culminates in its efficient and easy separation.

1. INTRODUCTION As a result of physiological effects of color on human beings, the use of versatile colors and coloring techniques for textile and goods has become an important marketing tool. On the other hand, increasing population density and expanding coloring industries are putting pressure on the environment especially in rapid developing countries. In order to protect the public health and the natural environment, millions of dollars is given through the World Bank as loans to support the governments in reducing the agglomeration of pollution in major cities.1,2 Dye pollution, besides being aesthetically displeasing, can cause serious harm to aquatic life and living organisms on a short period of exposure. Dyes which are utilized in the industry for numerous applications such as textile, leather, paper, printing, food, cosmetics, dyestuff, pigments, and pharmaceutical industries can find their way into water streams which must have the color removed prior to discharge in order to facilitate recycling and reuse of the water.3 Dyes are extensively grouped as anionic, cationic, and nonionic regarding the ionic charge on the dye molecule. Methylene blue (MB) and malachite green (MG) are two basic dyes which on their exposure to natural streams can pose a destructive impact on the environment. MB is a substance commonly used for coloring paper, dying cotton wool and silk, temporary hair © XXXX American Chemical Society

colorant, and coating for paper stock. MB can cause eye burn and on inhalation can cause increased heart rate, vomiting, cyanosis, jaundice, quadriplegia, mental confusion, and tissue necrosis in humans.4 MG is widely used as a biocide in aquaculture, a dye in the textile industry, and a food coloring agent and is also applied as a biological staining agent for microscopic analysis. Consuming fish contaminated with MG poses a significant threat to human health by its adverse effect on the immune and reproductive system and its carcinogenic, mutagenic, genotoxic, and teratogenic properties.5 While traditional dye treatment by physical, chemical, and biological methods such as activated carbon and oxidation may be efficient in terms of dye removal from wastewater, costs and residual chemistry can quickly become an issue. The adsorption process is capable of providing color removal with a minimum footprint, low initial cost, ease of operation, insensitivity to toxic substances and a simplistic design.6,7 Meanwhile, the choice of a suitable adsorbent is a great challenge for environmental management. To overcome the limitation of conventional adsorbents such as high cost, low Received: January 24, 2015 Accepted: July 13, 2015

A

DOI: 10.1021/acs.jced.5b00080 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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characterized via Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermo gravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The efficiency of absorbance was assessed via isotherm models (by Langmuir and Freundlich equations), kinetic models (by pseudo-first-order and pseudo-second-order), and thermodynamic parameters for the removal of cationic MB and MG dyes.

sorption efficiency, and problems with regeneration extensive research has been under-taken to produce alternative and economical adsorbents. A number of nonconventional sorbents have been introduced in the literature so far with innovative characters, i.e., high sorption capacity8 natural resources from low cost waste byproducts,9−12 easy separable solids after adsorption,13 and nanosize distribution.14 The most reported material for dye removal, include activated carbon, zeolite, clay polymer, etc., and an extensive list of dye sorbents has been accumulated recently by Crini,15 Babel and Kurniawan,16 Mall et al.,17 and Bailey et al.18 but still a lack of sorbent with a combined virtue character seems to be visible. Therefore, some innovative, economical, generable, easily available, and highly efficient sorbents are still under investigation. An expanding desire in the use of conductive polymers for the removal of dyes is evident in the literature which among them polyaniline (PANI) with its amine functional group has drawn considerable attention.19−21 PANI has good stability, high conductivity, and low cost which gives it numerous potential applications22 but the key problem for the possible commercial application of polyaniline is its processability. To overcome this limitation, various approaches have been pursued including (1) copolymerization with substituted aniline,23 (2) addition of pendent groups such as dopants to the polymer backbone, or redoping polyaniline with various functionalized protonic acid,24 and (3) making composites or blends of conducting polymers.25 Along these, (1) the copolymerization of aniline with various substituted aniline maintaining different functional groups has been reported.26 An accurate choice of the substituted monomer can not only help the processability of the PANI but also serve as a stock for the addition of desired pendent groups. (2) Thiacalix[4]arene tetrasulfonate (TCAS) is a protonic acid of the macrocycle thiacalix[4]arene (TCA[4]) from the classical calixarene family. Calix[n]arenes are a group of supramolecular compounds which are extensively studied in the field of molecular recognition, metal sorption, sensors, and macrocyclic chemistry for their incorporation properties. The uniqueness of thiacalix[n]arenes is that (a) they are easily synthesized by a onestep procedure, (b) they have sulfide bridged segments which are capable of coordinating cations, they also exist in multiple conformations that can provide adjustable binding sites in desired spatial orientations for “guests”, and (c) the upper and lower rims of the supramolecule can be modified by various functional groups. Thus, the sulfonation of the upper rim can give the desired protonic dopant of PANI and the lower rim is ready for an appropriate interaction with the substituted aniline to serve as a pendent internal dopant. Various attempts have been undertaken to incorporate calixarenes into different polymers.27−30 (3) The separation of the adsorbent after dye sorption is of high importance in the industrialization of adsorbents. Recently, there has been a growing interest with the objective of using nanocomposites with magnetic nanoparticles (MNPs) for the removal of water waste contaminates with respect to their high adsorption capacity, rapid adsorption equilibrium and easy magnetic separation of solids after adsorption.31 Maintaining these issues in mind, the present investigation was carried out with the aim of synthesizing novel supermagnetic nanocomposite consisting of Fe3O4 core and polyaniline− aminobenzoic acid−phenylenediamine terpolymer shell functionalized with thiacalix[4]arene tetrasulfonate as the internal dopant (Fe3O4@AmABAmPD[4]TCAS). Structural, morphological, and magnetic properties of the nano composite were

2. EXPERIMENTAL SECTION 2.1. Chemicals. Aniline (Merck, Germany) was doubly distilled in the presence of zinc dust in order to eliminate possible oxidation impurities. Meta-aminobenzoic acid (mABA), metaphenylenediamine (mPD), ferric chloride (FeCl3·6H2O), ferrous chloride (FeCl2·4H2O), ammonium persulfate (APS), N,N′diisopropylcarbodiimide (DIC), and the solvents employed in the present research were purchased from Merck (Germany) and were used without further purification. The applied TCAS was synthesized according to the literature by ipso sulfonation of thiacalix[4]arene in concentrated sulfuric acid media.32 2.2. Synthesis of Poly(aniline-co-m-aminobenzoicacidco-m-phenylenediamine) (PAmABAmPD) Terpolymer. PAmABAmPD terpolymer was synthesized via radical oxidation polymerization in 1:3:1 molar ratio of Ani to mABA to mPD at room temperature. A solution of 0.93 g (0.01 mol) of aniline, 4.11 g (0.03 mol) of mABA, 1.08 g (0.01 mol) of mPD, and 50 mL of HCl (1M) was prepared in a 100 mL Erlenmeyer flask under sonication. Polymerization was initiated through the addition of 25 mL of APS to the HCl solution; the latter solution was added over 20 min in order to avoid heating of the reaction mixture. Polymerization was carried out over 24 h at room temperature. The dark green powder was filtered and washed several times with distilled water and methanol until the filtrate became colorless. The polymers were further dried in a vacuum oven at 50 °C for 24 h. 2.3. Synthesis of TCAS Functionalized Poly(aniline-com-aminobenzoicacid-co-m-phenylenediamine) Terpolymer (PAmABAmPD-TCAS). In a round-bottomed flask, about 6.0 g of the synthesized terpolymer, 2.55 g of TCAS, and 0.37 mL of DIC as a coupling reagent were mixed in 150 mL of dry DMSO. The mixture was continuously agitated by a magnetic stirrer (at 1500 rpm) for 3 days under N2 atmosphere. The resulting mixture was filtered, and the filter cake was dried in a vacuum oven for 3 h at 45 ◦C to give TCAS nanocomposite in 64.5 % yield. 2.4. Synthesis of Superparamagnetic Fe3O4@ PAmABAmPD-TCAS Nanocomposites. Superparamagnetic iron oxide nanocomposite was synthesized from a fine mixture of Fe(II) and Fe(III) salts and doped copolymers as a solution via in situ coprecipitation method. Briefly, 0.66 g of FeCl2·4H2O and 1.3 g of FeCl3·6H2O were dissolved in 30 mL of deionized water at room temperature. Then 0.2 g of copolymer was added to the above solution, and the mixture was stirred at 50 °C for 15 min under nitrogen gas. 10 mL of NH4OH (25 %) was added in 1 mL per minute into the reaction mixture until the pH reached 10. After 45 min, the mixture was exposed to ultrasound for 10 min, and then the black precipitate was magnetically separated and washed several times with deionized water. Finally, the Fe3O4@ PAmABAmPD-TCAS nanocomposite was dried at 80 °C under vacuum overnight. 2.5. Characterization. FTIR analysis was conducted through a Bruker Tensor 27 spectrometer (Bruker, karlsrohe, B



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Scheme 1. Schematic Representative of the Synthesis Route, Dye Sorption and Magnetic Separation of Fe3O4@PAmABAmPDTCAS Nanoadsorbent

In the above equation, C0 and Ce are the initial and equilibrium concentration (mg·L−1) of dye solutions, respectively. The adsorption isotherm of the supermagnetic nanocomposite was further studied by analyzing its adsorption behavior in a 0.01 g/10 mL Fe3O4@PANI-AmAzoTCA[4] nanoadsorbant in dye solution with the initial concentration of dye solution to be (5−50) mg·L−1 at 298 K. The pH was maintained at a constant value during adsorption, and the equilibrium time was 180 min. Following the filtration, a UV−vis spectrophotometer (Cecil 5503) at a wavelength of 665 nm for MB and 618 nm for MG was used to measure the dye concentration in the filtrate solution spectrophotometrically. The equilibrium adsorption capacity qe (mg·g−1) was determined according to eq 2:

Germany). X-ray diffraction (XRD) patterns were recorded using a Rigaku D/Max-2550 powder diffractometer in the 2θ range of 10°−80° and a scanning rate of 5° min−1 at room temperature. The field emission scanning electron microscopy (FESEM) images were recorded on a Hitachi S4160 instrument. TEM micrographs were taken by the evaporation of their aqueous dispersion onto a Cu support grid and further recorded using a Philips EM 208 (100 kV) transmission electron microscope. VSM measurement was obtained through a vibrating sample magnetometer, Daghigh Kavir Corporation. The external field for magnetization measurements was adjusted up to 15 kOe at room temperature. Sonication agitation was performed on a Soner 220H Ultrasonic Cleaner, AC110 V, 60 Hz (Taiwan). 2.6. Adsorption Procedure. The content of adsorption from dyes solutions was measured in batch experiments through shaking the flasks on a horizontal bench shaker at 200 rpm for a constant period of time. The effect of adsorbent dose ((100− 220) mg·L−1), pH (4.0−10.0), kinetics time ((30−240) min), and temperature ((298−328) K) of MB and MG cationic dyes were studied for the novel nanoadsorbent. Subsequently the results obtained from each batch study were used to calculate the dye removal in terms of percentage by applying the mass balance relationship in eq 1: ⎛ C − Ce ⎞ %dye removal = ⎜ 0 ⎟ · 100 ⎝ C0 ⎠

qe =

(C0 − Ce)V m

(2)

wherein the above equation V is the dye solution volume (L) and m is the mass of adsorbent added in each batch (g). The same path was used for kinetic studies of the dye solutions at the initial dye concentration of 20 mg·L−1. The mixtures were thoroughly shaken and at predetermined time intervals samples were separated by magnetic decantation. The adsorption capacity at time t, qt (mg·g−1), was calculated by eq 3: qt =

(C0 − Ct )V m

(3)

in which Ct is the concentration of dye solution at any time (mg· L−1). Each adsorption experiment was conducted three times

(1) C



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terpolymer, in which a broad and strong vibration bond at about (3521−3100) cm−1 represents the overlapping of stretching vibrational bands of phenolic OH of TCAS and those of the magnetite surface and the peak at 642 resembles the Fe−O−Fe stretching mode of Fe3O4. Other characteristic absorption bands of TCAS ((1161 and 1140) cm−1) and PAmABAmPD ((1639, 1425, and 1045) cm−1) are also evident in the spectrum of Fe3O4@PAmABAmPD-TCAS nanocomposite. 3.2. Morphological Study. The XRD patterns of TCAS macrocycle, PAmABAmPD terpolymer, PAmABAmPD-TCAS doped nanocomposite, and Fe3O4@PAmABAmPD-TCAS magnetic nanoadsorbent are presented in Figure 2. According to the

and afterward the results were averaged. The standard deviation was measured to be less than 5 %.

3. RESULTS AND DISCUSSION The core−shell nanoadsorbent with Fe3O4 core and conductive terpolymer of polyaniline doped by a TCAS shell was synthesized according to Scheme 1 and characterized as follows. 3.1. Structural Characterization. The FTIR spectra of PAmABAmPD terpolymer, PAmABAmPD-TCAS doped conductive polymer, and Fe3O4@PAmABAmPD-TCAS magnetic nanoadsorbent are presented in Figure 1. PAmABAmPD is

Figure 1. FTIR spectra of PAmABAmPD terpolymer, PAmABAmPDTCAS doped conductive polymer, and Fe3O4@PAmABAmPD-TCAS magnetic nanoadsorbent.

characterized with stretching vibrations of N−H bond at 3478 cm−1 which is submerged with the carboxylic acid−OH vibration, stretching vibration of the acidic CO group at 1720 cm−1, stretching vibration modes of quinoid and benzenoid rings respectively at (1645 and 1578) cm−1, and C―N and CN stretching vibrations at (1145 and 1319) cm−1.33 The PAmABAmPD-TCAS showed a shift of the CO group peak from (1720 to 1771) cm−1 that provided evidence for the completion of acid to ester conversion. The stretching vibration of −OH bonds of TCAS is assigned by a broad peak at around (3432−3620) cm−1, and the characteristic bands of −SO3 in the TCAS macrocycle were observed by the split doublets at (1166 and 1143) cm−1.34 The FT-IR spectra of the Fe3O4@PAmABAmPD-TCAS nanocomposite contained characteristic peaks of the self-doped

Figure 2. XRD patterns of (a) TCAS macrocycle, (b) PAmABAmPD terpolymer, (c) PAmABAmPD-TCAS doped nanocomposite, and (d) Fe3O4@PAmABAmPD-TCAS magnetic nanoadsorbent.

literature TCAS reveals a crystalline nature32 which is also observed in the XRD pattern in Figure 2a; on the other hand, the XRD pattern for the terpolymer shows peaks at 2θ = 5.9°, 15.2°, 19.1°, 21.3°, and 27.4° corresponding to its amorphous character. As seen in Figure 2c, PAmABAmPD-TCAS shows a semicrystalin nature with diffraction peaks at 2θ = 9.8°, 18.7°, 28.9°, 34.6°, 45.1°, 55.6°, and 61.2°. It seems that the insertion of TCAS macrocycles improves the crystalline nature of the nanocomposite probably due to the regular interaction of TCAS in the terpolymer backbone and the self-assembly D



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3.4. Magnetic Property. The magnetic aptitude of Fe3O4@ PAmABAmPD-TCAS nanoadsorbent was studied by Vibrating sample magnetometer (VSM), which displays the magnetic property of the nanoadsorbent as a function of magnetic field.38 The typical magnetic curves of pristine Fe3O4 nanoparticle and Fe3O4@PAmABAmPD-TCAS nanoadsorbent at room temperature are illustrated in Figure 5. The remanence (Mr) and coercivity (Hc) of both samples equal to nearly ziro in the absence of external magnetic field, which confirms their supermagnetic property. However, Fe3O4@PAmABAmPDTCAS nanoadsorbant shows a smaller Hc and Mr compared to bare Fe3O4 nanoparticles which reveal that the presence of a conductive polymer adsorbent layer on the surface of Fe3O4 can inhibit agglomeration of magnetic nanoparticles. As seen from Figure 5 the saturated magnetization (Ms) of bare magnetic nanoparticle is 52 emu/g, while for the Fe3O4@ PAmABAmPD-TCAS nanoadsorbent is about 38 emu/g. The decrease of Ms was because of the adsorbent coating around MNPs which results in quenching of surface moments. In addition, the decrease of Ms can be a result of decreased core size of magnetite as the saturation magnetization of nanoparticles consistently increases with the size of the magnetic core.39 Generally, the synthesis of polymeric-adsorbent coated supermagnetic nano composite was confirmed which is capable of magnetic field separation from any solution. 3.5. Adsorption Studies. The surface characteristic, size distribution and extent of functional groups in an adsorbent are the key factor governing the efficiency of adsorption.40 The Fe3O4@PAmABAmPD-TCAS nanoadsorbent with a porous surface and nanosize distribution of the adsorbent together with the presence of diverse functional groups is predicted to have a high sorption capacity. The adsorption procedure can be conducted by the Host−guest character of TCAS which enables the capture of dyes by its flexible cavity and through the π−π interactions between its aromatic cavity and hydrophobic residues of dyes, and the electrostatic interactions between the −SO3 group on the upper rim of TCAS or −OH and −NH groups at the lower rim and the polymer backbone respectively with the cationic dyes. Scheme 2 shows the suggested adsorption mechanism between the Fe3O4@PAmABAmPD-TCAS host

property of the thiacalixarenes. The XRD pattern of superparamagnetic Fe3O4@PAmABAmPD-TCAS nanoadsorbent depicts a crystalline morphology with the mean diameter of nano particles to be 82 nm which was calculated according to the scherrer equation.35 The morphology of the nanoadsorbent and its core−shell structure were characterized by SEM and TEM imaging (Figure 3). The SEM image shows spherical self-doped nanocomposites

Figure 3. Microscopic images of Fe3O4@PAmABAmPD-TCAS magnetic nanoadsorbent (a) SEM and (b) TEM.

with a heterogeneous size distribution on phase separated plates of TCAS. The size of the magnetic nanocomposite was measured to be as small as 39 nm. The TEM image of the spherical magnetic nanoadsorbent clearly shows the dark iron core with a thin layer of polymeric shell capable of accelerated sorption capacity. 3.3. Thermal Property. TGA curve of Fe3O4@PAmABAmPD-TCAS magnetic nanocomposite in nitrogen is shown in Figure 4. A three step weight loss is observed for the magnetic nanocomposite. The first stage shows a 3 % weight loss located between (35 and 150) °C which corresponds to moisture evaporation, solvent volatilization, and adsorbed HCl loss.36 The next stage (4 % weight-loss) between (175 and 300) °C can be a result of thermal dedoping of the nanocomposite and simultaneous evolution of CO2.37 The last step of weight-loss (10 %) which occurred between (300 and 600) °C is probably due to final degradation of the copolymer.36

Figure 4. TGA and DTGA of Fe3O4@PAmABAmPD-TCAS magnetic nanoadsorbent. E



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Figure 5. Magnetic response of pure Fe3O4 and Fe3O4@ PAmABAmPD-TCAS nanoadsorbent in the applied field.

effect in the adsorption of ionic dyes in acidic and basic media. In the acidic media where the pH value is low, sulfonate (SO3) sites are in its protonated form, which results in an electrostatic repulsion with cationic dyes, in addition, there is also a competition between H+ and dye cations for the chelating groups, i.e., amine (NH) and hydroxyl (OH) sites, at low pH where proton concentration surpasses that of the dyes and induces an adsorption capacity decrease. As the alkalinity of solution increases, the proton concentration decreases and active chelating sites of the adsorbent (sulfonate, amine and phenoxide) can form electrostatic interaction with iminium site of MB and MG. 3.5.3. Effect of Contact Time. Among various parameters governing the adsorption rate structural property and morphology of adsorbent, amount of adsorbent stirring rate, and initial concentration of dyes are the most prominent.44 The extent of dye removal versus time is plotted in Figure 6c. As can be seen the adsorption efficiency increases with time up to 90 % (for MB) and 92 % (for MG) and remains almost constant after 3 h. The high removal efficiency can be a result of the high surface area of Fe3O4@PAmABAmPD-TCAS nanocomposite which has a nanosize distribution. 3.5.4. Effect of Initial Dye Concentration. The removal efficiency of each dye as a function of initial dye concentration ((5−50) mg·L−1) is observed in Figure 6d. As the initial dye concentration increases the adsorption efficiency of MB and MG tends to decrease from 98 and 99.8 to 50.57 and 60.9 respectively. As the concentration of each dy increases more active sites of Fe3O4@PAmABAmPD-TCAS adsorbent get involved in the chelating phenomena, and as a result of its saturation a decrease in dye adsorption can be observed. 3.6. Adsorption Isotherm. In the isotherm study the interaction between an adsorbate and adsorbent at a given temperature under equilibrium conditions is described. The adsorption isotherm can be expressed as the equation between the amount of dye adsorbed on the solid adsorbent (qe, mg·g−1) and the concentrations of dye in the bulk solution (Ce, mg·L−1) when both phases are in equilibrium. The adsorption of MB and MG with initial concentrations ranging from (5 to 50) mg·L−1

Scheme 2. Cationic Dye Adsorption Mechanism on to Fe3O4@PAmABAmPD-TCAS Nanoadsorbent

segments and dyes which makes it capable to be used as a membrane or solid phase of fixed separating column.41 In order to better describe the adsorption mechanism sorption was investigated from isotherm, kinetic, and thermodynamic point of view. 3.5.1. Effect of Adsorbent Dosage. The amount of adsorbent required to treat per unit volume of solution is defined as a function of the extent of its reactive groups and the aspect ratio of adsorbent which directly affects the cost of adsorption.42 The plot of equilibrium adsorption capacity versus adsorbent dosage of Fe3O4@PAmABAmPD-TCAS is shown in Figure 6a. As observed, for either dyes the equilibrium adsorption capacity increases with increasing the amount of adsorbent which is a result of accelerated nanoadsorbent surface area and the increasing availability of adsorption sites. 3.5.2. Effect of pH. The adsorption of ionic dyes on any specific and nonspecific adsorbents are pH dependent which is a result of the chemistry of dyes in the solution and the ionization state of the functional groups of the sorbent.43 In order to assess the effect of initial pH on the adsorption of MB and MG dyes by Fe3O4@PAmABAmPD-TCAS, batch adsorption was conducted at the pH range of 4−10. Figure 6b clearly displays the pH dependency of dye removal where the removal reaches a maximum of 83.15 and 92.45 for MB and MG, respectively, at pH 8. Accordingly, electrostatic interactions have a predominant F



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Figure 6. Effect of adsorbent dose (a), solution pH (b), adsorbent/adsorbate contact time (c), and initial dye concentration (d) on the adsorption.

Figure 7. Adsorption isotherms of Fe3O4@PAmABAmPD-TCAS nanadsorbent for MB and MG dyes at 30 °C, pH 8.0, initial dye concentration (5−50) ppm and time 180 min.

were studied at pH 8, with an adsorption time t = 180 min, and temperature T = 30 °C (Figure 7). In order to find the best suited model for each dye adsorption, experimental isotherm data were fitted to Langmuir and Freundlich isotherm models and further analyzed through isotherm constants. The Langmuir isotherm model suggests that monolayer coverage of sorbate on the surface of sorbent exists; whereas the Freundlich isotherm model assumes that the heterogeneity of the sorbent surface and multilayer formation takes place.45 The nonlinier Langmuir model is described as eq 4:

qe =

qmKLCe 1 + KLCe

(4)

where qe is the equilibrium adsorption capacity of dye on the adsorbent (mg·g−1); qm, is the maximum capacity of the adsorbent (mg·g−1); KL, is the Langmuir adsorption constant (L·mg−1); and Ce, is the equilibrium concentration of dyes in solution. The isotherm constants were calculated from the linear plot between Ce/qe and Ce (S1a). The empirical Freundlich model is expressed as eq 5: qe = K f Ce1/ n G

(5) DOI: 10.1021/acs.jced.5b00080 J. Chem. Eng. Data XXXX, XXX, XXX−XXX


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are calculated from the slope and intercept of log (qe − qt) versus t linear plots (Figure 8a) and are tabulated in Table 2.

where equilibrium values of qe and Ce are defined as above, Kf is the Freundlich constant (L·mg−1) which indicates the adsorption capacity, and 1/n is related to the heterogeneity factor and indicates the adsorption capacity. The constant, n, reveals the extent of nonlinearity in which if n = 1 the adsorption is linear, if n < 1 the adsorption approves a chemisorption, and if n > 1 it favors the physisorption. The isotherm constants were predicted from the ln qe versus ln Ce linear plot (S1b). The calculated values of the Langmuir and Freundlich equations parameters are given in Table 1. The comparison of

Table 2. . Kinetic Models and Other Statistical Parameters of Fe3O4@PAmABAmPD-TCAS Adsorbent at 30 °C, pH 8.0, Initial Dye Concentration = 20 ppm and Time = (10−60) min dye solution (500 mg/L) kinetic model pseudo-first-order Equation

Table 1. Isotherms and Their Statistical Parameters of Fe3O4@PAmABAmPD-TCAS Nanoadsorbent at 30 °C MB

pseudo-second-order equation

MG

isotherm model

parameter

R2

parameter

R2

Langmuir

qm =31.64 KL = 1.25 KF = 12.78 n = 2.98

0.9991

qm = 29.069 KL = 7.48 KF = 17.14 n = 4.42

0.9999

Freundlich

0.9450

parameters Kad (min‑1) qe, cal (mg·g−1) R2 K (g·mg−1·min−1) × 10−3 qe, cal (mg·g−1) R2 qe, exp (mg·g−1)

MB

MG

0.008 7.91 0.9102 0.0032

0.0087 14.39 0.9769 0.001

18.05 0.9889 18.33

20.44 0.9816 19.7

0.8687

On the other hand, the pseudo-second-order model proposes that chemisorption is the rate-limiting step and that adsorption occurs on localized sites where no interactions between adsorbates take place. This equation is expressed as eq 7: t 1 t = + qt qe K 2qe 2 (7)

determination coefficients (R2) of MB and MG cationic dyes indicates that sorption onto Fe3O4@PAmABAmPD-TCAS super magnetic adsorbent can be better depicted by the Langmuir isotherm equation which suggests the monolayer coverage of adsorbates on the surface of sorbent. In addition, the n value gained from the Freundlich isotherm was larger than unity; this marks that the interaction force between the dyes and Fe3O4@PAmABAmPD-TCAS adsorbent is strong. 3.7. Adsorption Kinetics. The adsorption of dye on to the Fe3O4@PAmABAmPD-TCAS nanoadsorbent was further studied in terms of kinetic models via Lagergren pseudo-first-order and pseudo-second-order equations. The first-order kinetic model of Lagergren is extensively applied for the adsorption of any solute from solution by the common exchange procedure which is fast and is mainly controlled by diffusion.46 The equation is given by eq 6: K ad log(qe − qt) = logqe − t (6) 2.303

where K2 is the rate constant of second-order adsorption (g·(mg· min)−1). The values K2 and qe can be calculated from the slope and intercept of the plot of t/qt versus t as shown in Figure 8b. As obviate in Table 2 the R2 values of the second-order kinetic model for either dyes were closer to unity than the first-order adsorption model. Accordingly, MG and MB adsorption onto Fe3O4@PAmABAmPD-TCAS nanoadsorbent follows the pseudo-second-order kinetic model. Also, a comparison between the calculated (qcal) and experimental (qexp) adsorption capacities reveals the high applicability of the pseudo-second-order model to describe the sorption process. These results suggest that adsorption takes place through a chemical process in which the valence forces proceed through sharing or exchanging electrons between the cationic dyes and the Fe3O4@PAmABAmPD-TCAS nanocomposites. 3.8. Adsorption Thermodynamics. The effect of temperature fluctuation on the adsorption capacity of MB and MG dyes by Fe3O4@PAmABAmPD-TCAS nanoadsorbent is shown in

where qt is the adsorption capacity (mg·g−1) at time, t (min), and Kad is the Lagergren rate constant for the first-order adsorption (min−1). The rate constant, Kad, and determination coefficients

Figure 8. Kinetic models for the adsorption of MB (blue diamonds) and MG (green circles) on to Fe3O4@PAmABAmPD-TCAS nanoadsorbent (a) pseudo-first-order and (b) pseudo-second-order diffusion model. (Temperature = 30 °C, C0 = 20 mg·L −1, adsorbent dosage = 1 mg, pH 8.) H



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Figure 9. Effect of temperature on (a) capacity of adsorption and (b) Van’t Hoff plot for adsorption of MB and MG onto Fe3O4@PAmABAmPD-TCAS nanoadsorbent.

at equilibrium must increase with increasing temperature. The calculated value of ΔH° is also positive in the temperature range of (298 to 328) K, which again indicates the adsorption process is endothermic and that chemisorption is taking place. eventually, the positive value of ΔS° resembles a good affinity of MB and MG for the magnetic nanoadsorbent and also confirms thatan increase in the randomness takes place at the solid solution interface through the adsorption process.49 It seems that by raising the temperature the mobility of the dye molecules increases and the rate of diffusion of adsorbate molecules across the surface of the nanoadsorbent rises, which leads to an increase in the adsorption capacity of [email protected],46

Figure 9. The experiments were carried out at (298, 308, 318, and 328) K. As observed in Figure 9a, the adsorption capacity increases from 15 to 17.2 for MB and 13.6 to 15 for MG with the increase of temperature. It is apparent that the adsorption of MB and MG on the magnetic nanoadsorbent is an endothermic process implying a chemical adsorption process.47 In order to provide fluctuation information on the energetic changes associated with adsorption process, thermodynamic parameters such as standard Gibbs energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were studied. The thermodynamic parameters for the adsorption process were obtained using the following equations:48 q Kd = e Ce (8) ΔG◦ = −RT ln Kd

4. CONCLUSION In conclusion, a novel magnetically separable adsorbent, namely, Fe3O4@PAmABAmPD-TCAS magnetic nanoadsornent, has been prepared by a three step chemical process; oxidation terpolymerization of aniline/m-aminobenzoicacid/m-phenilendiamine, functionalization with TCAS protonic acid dopant, and in situ precipitation with Fe3O4 nanoparticles. Adsorption characteristics of the supermagnetic nanoadsorbent were considered by using methylene blue (MB) and malachite green (MG) as adsorbates. The isotherms, kinetics, and thermodynamics were determined by batch experiments. The equilibrium data was better depicted by the Langmuir model with the adsorption capacity of [32 (MB) and 29 (MG)] mg·g−1. The kinetic studies reveal that the adsorption process follows the pseudosecond-order kinetic model. The ΔH° value for each dye is positive in the temperature range of (298 to 328) K. The ΔG° values are negative at the same temperature range which indicates the spontaneous nature of MB and MG adsorption onto the magnetic nanoadsorbent. The ΔS° value is positive which suggests the good affinity of MB and MG toward the magnetic nanoadsorbent during the adsorption process. In addition, regarding VSM results the prepared supermagnetic nanocomposite has a relatively high magnetic sensitivity on external magnetic field exposure, which results in an easy and efficient way of separation from aqueous solution. The introduction of this supermagnetic thiacalix based high capacity dye adsorbent can open new horizons for safe and easy water reclamation.

(9)

⎛ ΔS◦ ⎞ ⎛ ΔH ◦ ⎞ ⎟−⎜ ⎟ Kd = ⎜ ⎝ R ⎠ ⎝ RT ⎠

(10)

where Kd is the distribution coefficient, T is the temperature, and R is the gas constant, respectively. The ΔH° and ΔS° values were determined experimentally from the slope and intercept of van’t Hoff plots, i.e., ln Kd versus 1/T (Figure 9b) and the calculated values are presented in Table 3. The negative value of ΔG° at various temperatures for either cationic dye remarks their spontaneous nature of adsorption onto the magnetic nanocomposite. The negative value increases at higher temperatures which confirm that the amount adsorbed Table 3. Thermodynamic Parameters for the Adsorption of MB and MG onto Fe3O4@PAmABAmPD-TCAS Magnetic Nanoadsorbents temperature

ΔG°

ΔH°

ΔS°

K

KJ·mol−1

KJ·mol−1

KJ·mol−1·K‑1

298 308 318 328

MB

MG

−5.3 −6.4 −8.4 −9.0

−3.6 −4.2 −4.5 −5.4

MB

MG

MB

MG

19.71

7.96

0.075

0.003

I



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ASSOCIATED CONTENT

S Supporting Information *

Linear plots of Langmuir and Freundlich isotherm models. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b00080.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +98 112 5342350. Fax: +98 112 5342350. Notes

The authors declare no competing financial interest.

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