γ-Fe2O3 nano-composite: Kinetic and equilibrium studies

Materials Science in Semiconductor Processing 40 (2015) 35–43

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The adsorption of basic dye (Alizarin red S) from aqueous solution onto activated carbon/γ-Fe2O3 nano-composite: Kinetic and equilibrium studies Maryam Fayazi a,b, Masoud Ghanei-Motlagh a,b,n, Mohammad Ali Taher a a

Department of Chemistry, Faculty of Sciences, Shahid Bahonar University, Kerman, Iranb Young Researchers Society, Shahid Bahonar University, Kerman, Iran

b

art ic l e i nf o

a b s t r a c t

Article history: Received 12 January 2015 Received in revised form 25 May 2015 Accepted 16 June 2015

The adsorption behavior of Alizarin red S (ARS) from aqueous solution onto magnetic activated carbon (MAC) nano-composite was investigated under various experimental conditions. Characterization of the obtained MAC nano-composite was achieved by FT-IR, BET, FE-SEM, EDX, XRD and VSM techniques. The influence of variables including pH, concentration of the dye, amount of adsorbents and contact time was investigated by the batch method. High maximum adsorption capacity was obtained at 108.69 mg g
1 for ARS. The equilibrium data was evaluated using Langmuir and Freundlich isotherm. The Langmuir model best describes the uptake of ARS dye, which implies that the adsorption of ARS dye onto MAC nano-composite is homogeneous. The kinetic data were analyzed using Lagergren pseudo-first order and pseudo-second equation. The pseudo-second order exhibited the best fit for the kinetic studies (R2 ¼0.9999), which indicates that adsorption of ARS is limited by chemisorption process. This study shows that the as-prepared MAC composite could be utilized as an efficient, magnetically separable adsorbent for the environmental cleanup. & 2015 Elsevier Ltd. All rights reserved.

Keywords: Adsorption Activated carbon Alizarin red S Composite Maghemite

1. Introduction The water bodies contaminated with organic based chemicals have created a serious environmental problem. Industries like textiles, paper, rubber, plastics, leather, cosmetics, food and pharmaceuticals use large quantities of synthetic dyes for coloration of their products and hence, effluents from them contain residues of dyes. It is estimated that more than 10,000 types of dyes and pigments are used and produced annually [1] and among them 10–15% are found in wastewaters [2]. Synthetic dyes have complex aromatic structures which provide them physico-chemical, thermal and optical properties [3,4]. The presence of dye in water is highly visible and affects water transparency, resulting in reduction of light penetration, and gas solubility in water [5]. Many dyes and pigments are toxic in nature with suspected carcinogenic and mutagenic effects [6] that affect aquatic biota and humans [7]. Because of this, industrial effluents containing dyes need to be treated before being delivered to the environment [8,9]. A wide range of physical and chemical processes such as flocculation, coagulation, precipitation, adsorption, membrane filtration, electrochemical techniques, ozonation and fungal decolonization have n

Corresponding author. Fax: þ 98 341 3210051. E-mail address: [email protected] (M. Ghanei-Motlagh).

http://dx.doi.org/10.1016/j.mssp.2015.06.044 1369-8001/& 2015 Elsevier Ltd. All rights reserved.

been investigated extensively for removing dyes from aquatic bodies [10,11]. Among these, liquid phase adsorption has been an attractive and promising option due to the advantages of flexibility and simplicity in design and operation [12–14]. Therefore, design and application of non-toxic, adsorbent able to removal huge amount of dyes molecule in short time via small amount of adsorbent are important requirements. Activated carbon (AC) adsorption has been recognized by United States Environmental Protection Agency (USEPA) as one of the best available control technologies [15,16]. This is due to their extended specific surface area (exceeding 1000 m2 g
1), high total pore volume and the presence of surface functional groups, especially oxygen groups [17]. Activated carbons are materials having complex porous structures with associated energetic as well as chemical in homogeneities. Their structural heterogeneity is a result of existence of micropores, mesopores and macropores of different sizes and shapes. Due to its high surface area, large adsorption capacities and porous structure it can efficiently adsorb pollutants such as dyes and heavy metals [18,19]. However, the application areas suffer from serious problems to separate from treating media. The application of magnetic particle technology to solve environmental problems has received considerable attention in recent years. Magnetic particles can be used to adsorb contaminants

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M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

from aqueous or gaseous effluents and, after adsorption, can be separated from the medium by a simple magnetic process. In the present study, high surface area and high adsorption capacity magnetic nano-composite based on activated carbon/γFe2O3 was prepared and used for the removal of Alizarin red S (ARS). The kinetic and thermodynamic of the dye adsorption on the activated carbon/γ-Fe2O3 composite have been investigated. The resulting magnetic activated carbon (MAC) nano-composite could be utilized as a magnetically separable and efficient adsorbent for dye removal from water.

2. Experimental 2.1. Instruments and reagents All chemicals including AC, FeCl3  6H2O and FeCl2  4H2O, ethanol, NH4OH and ARS with the highest purity available are purchased from Merck (Dermasdat, Germany). The 1000 mg L
1 of ARS solution was prepared by dissolving 100 mg of solid dye in 100 mL of double distilled water. The working solution simply was prepared by its suitable dilution. The pH was adjusted and measured using a 713 pH-mV meter (Metrohm, Switzerland) at the laboratory ambient temperature. The ARS concentration remained in the diluted aqeous phase was determined using a Cary 50 single detector double beam in-time spectrophotometer (Varian, Australia). Infrared (IR) spectra were recorded with KBr pellet on a Bruker tensor 27 Fourier transform infrared (FT-IR) spectrometer with RT-DLATGS detector, in the range (4000–400 cm
1) with a spectral resolution of 4 cm
1 in transmittance mode. The morphology and average particle size of MAC nano-composite was also determined with field emission scanning electron microscope (FESEM, Hitachi S4160), which was equipped with an energy-dispersive X-ray analyzer (EDX). The specific surface area of AC and MAC nano-composite were characterized by the Brunaure–Emett– Teller (BET) method. Magnetizable measurement was performed using a vibration sample magnetometer (VSM) (Model PAR-VSM 155R). X-ray diffraction (XRD) analysis of AC and MAC nanocomposite was performed using a PANalytical X’Pert PRO MPD instrument (PANalytical B.V., Almelo, The Netherlands) equipped with a back monochromator operating at a tube voltage of 40 kV and a tube current of 30 mA using a copper cathode as the X-ray source (λ ¼1.542 Å). The point of zero charge (pHpzc) of MAC nano-composite was determined by the batch equilibration technique according to literature [20]. For this purpose, 0.5 g of adsorbent was mixed with 100 mL electrolyte (NaCl, 0.01 M) in poly(vinyl chloride) (PVC) vessel and pH was adjusted using NaOH or HCl in the range between 2.0 and 12.0. After shaking for 24 h at room temperature, the solution was filtered and the final pH of the solution was determined. The pHpzc of the sample was determined by plotting the initial pH (pHinitial) vs. ΔpH (pHfinal
pHinitial) as the point where ΔpH ¼ 0. 2.2. Preparation of adsorbent MAC nano-composite was synthesized as previously described with some modifications [21]. As a pre-treating step, 20 g of purified activated carbon reacted with 150 mL 5 M nitric acid solution and refluxed for 1 h at 70 °C to achieve treated activated carbon (TAC; BET: 598 m2 g
1). The synthesis procedure for the nanocomposite was as follows: 4.2 g of TAC, 21.6 g of FeCl3  6H2O (99%) and 8.0 g of FeCl2  4H2O (98%) were dissolved in 100 ml of 2 M HCl (37%). Then, NH3H2O (25–30%) solution (4 M) was added dropwise into this solution (250 ml) under vigorous stirring at room temperature for 2 h. The obtained dark brown precipitate was

separated from the reaction medium by magnetic field. After seven times of rinsing the precipitate under deionized water and absolute ethanol (99.9%), it was dried at 70 °C overnight. 2.3. Adsorption of ARS To study the effect of important parameters like the pH, contact time, initial dye concentration and temperature on the adsorptive removal of ARS, batch experiments were conducted. For each experimental run, 10 mL of ARS solution at specified optimum concentration and pH was mixed completely with adsorbent over a fixed time. In this research, in each set all variables were fixed and only one variable over a desirable range was changed of removal was investigated. This mixture was agitated at room temperature controlled shaking water bath at constant speed (150 rpm). After adsorption, the MAC nano-composite was separated by a magnet and the sample absorbance was measured. The percentage removal of ARS was calculated using the following relationship:

⎛C − C ⎞ t Dye Removal (%) = ⎜ 0 ⎟ × 100 ⎝ C0 ⎠

(1)


1

where C0 and Ct (mg L ) are the initial dye concentration and concentration at time t, respectively. All Adsorption experiments were performed in triplicate and the mean of the three are taken for all calculations. Investigation of kinetics of adsorption was carried out by analyzing experimental data of ARS adsorption from aqueous solution at different time intervals. Adsorption isotherms were studied by performing a set of similar experiments according to described optimized procedure at different concentrations of ARS in the range of 50–150 mg L
1, while agitated with 0.01 g of MAC nanocomposite. After equilibrium, the adsorption capacity was calculated from the relationship:

qe =

(C0 − Ce )V W

(2)
1

where qe (mg g ) is the equilibrium adsorption capacity, C0 and Ce (mg L
1) are the initial and equilibrium dye concentrations in aqueous solution, respectively, V (L) is the volume of solution and W (g) is the mass of adsorbent. 2.4. Desorption experiments For the desorption study, 0.01 g of the composite adsorbent was added to 10 mL of dye solution (70 mg L
1) and the mixture was stirred at ambient temperature for 60 min. After the magnetic separation, the supernatant dye solution was discarded and the adsorbent alone was separated. Then, the ARS-adsorbed adsorbent was added into 5 mL of ethanol and stirred for 10 min. The adsorbent was collected by a magnet and reused for adsorption again. The supernatant solutions were analyzed by UV–vis spectra. The cycles of adsorption–desorption processes were successively conducted four times.

3. Results and discussion 3.1. Dye characterization The characteristics of ARS dye are summarized in Table 1. ARS is a water-soluble, widely used anthraquinone dye with pKa value of 4.5. Solubility in water for ARS is reported to be about 77 g L
1 at 20 °C [22].

M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

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Table 1 Characteristics of ARS dye. Characteristics Structure

Synonym Molar mass Color Index Number Color Formula Solubility in water λmax pKa

3,4-Dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt 342.26 g mol
1 58005 Yellow below pH 3.7, yellow to purple between 3.7 and 5.0 and red higher pH 5.0 C14H7NaO7S 1 mg mL
1 (20 °C) 420 nm at pH below 3.7 4.5

Fig. 1. FTIR spectra of (a) AC, (b) γ-Fe2O3 and (c) MAC nano-composite.

3.2. Characterization of adsorbent FTIR spectra of AC, γ-Fe2O3 and MAC nano-composite are shown in Fig. 1. Absorption peaks appearing at 453, 581, 630, 797 and 889 cm
1 in the FTIR spectra are attributed to γ-Fe2O3 nanoparticles existing in the activated carbon. The phenomena could be related to the formation of maghemite nanoparticles inside the pores [23]. The results are in good agreement with the literatures

relating to the magnetic activated carbon nano-composite [24,25]. The FE-SEM/EDX analysis spectra of AC and MAC nano-composite are shown in Fig. 2. As shown in Fig. 2b, it can be seen that maghemite nanoparticles deposited on the surface of AC are uniform with the spherical shape. A typical EDX spectrum of AC is presented in Fig. 2c, and as shown oxygen and carbon can be detected. The quantitative analysis gives weight ratios of C (93.6%) and O (6.4%). The EDX spectrum of MAC nano-composite (Fig. 2d) indicates the presence of iron, oxygen and carbon confirming the formation of iron oxide on the surface of AC. The coated Fe content was determined as 51.3 wt.%. The magnetic hysteresis loops of AC and MAC are illustrated in Fig. 3. The saturation magnetization of the magnetic nano-composite was measured as 29.2 emu g
1. This magnetic susceptibility value is sufficient for this adsorbent to be used in wastewater treatment, which can be used for the magnetic separation (inset in Fig. 3). According to BET theory, the specific surface area was calculated as 347.8 m2 g
1 for MAC nano-composite. The pore size distribution calculated according to the BJH method, the average pore diameter of MAC nano-composite mainly distributed within the mesoporous range of 2–50 nm, which suggests that nanocomposite has potential for catalyst, energy storage, adsorption, and gas sensing applications [26]. The XRD pattern of AC and MAC nano-composite are shown in Fig. 4. The smooth intensity with broad peaks at around 2θ values of 23.98 and 43.79, suggesting that the main structure of AC is amorphous. On the contrary, the XRD pattern of the synthesized MAC nano-composite shows intense reflections indexed to 30.56° (220), 35.94° (311), 43.60° (400), 53.95° (422), 57.64° (511) and 63.19° (440) as cubic spinel structure of maghemite (JCPDS card no. 39-1346). Based on the XRD patterns, it can be postulated that the maghemite nanoparticles are well covered on the AC surface. From the pH initial vs ΔpH plot (Fig. 5), the pHpzc of MAC nanocomposite was found to be  6.8. At this pH value, the total positive charges on the surface of MAC nano-composite are equal to the total negative charges. In other words, the MAC nano-composite surface is positively charged when pH o pHpzc and is negatively charged when pH 4pHpzc.

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M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

Fig. 2. FE-SEM images of (a) AC and (b) MAC nano-composite, EDX spectrums of (c) AC and (d) MAC nano-composite.

Fig. 3. Magnetic hysteresis curves of (a) AC and (b) MAC nano-composite. The bottom inset shows the magnetic separation of the MAC under an external magnetic field.

3.3. Effect of pH value on adsorption The pH of the aqueous solution is the most important parameter for its effect on the adsorption property of adsorbent and adsorbate. Both adsorbent and adsorbate may have functional

Fig. 4. XRD patterns of AC and MAC nano-composite.

groups that can be protonated or deprotonated to produce different surface charges in solutions at different pH, resulting in the electrostatic interactions (attraction or repulsion) between charged adsorbate molecules and adsorbents [27]. Fig. 6 shows the effect of pH on the sorption of ARS on the prepared absorbent. The

M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

Fig. 5. pHpzc of MAC nano-composite.

Fig. 6. Effect of sample's pH on removal efficiency of the dye. Conditions: 10 mL of the dye solution (70 mg L
1); 0.01 g of MAC nano-composite; stirring time ¼ 60 min; stirring speed 150 rpm.

39

Fig. 8. Effect of time on the removal efficiency.

sulfonate groups (–SO3–) that are negatively charged in aqueous solution. Generally, the adsorption of dye anions is highly favored at pH opHpzc [23]. The MAC nano-composite has positive charge until the pH of 6.8. At an acidic pH, the surface of MAC nanocomposite become positive, which are mainly the carboxylic groups (–CO–OH2 þ ), phenolic (–OH2 þ ) and additional active sites (Fe–OH2 þ ) [23]. Maximum removal percentage and adsorption capacity takes place at acidic medium. Therefore, pH ¼2 was selected for all further adsorption experiments. In order to evaluate the stability of MAC nano-composite in terms of iron leaching, leaching test was carried out at optimum pH. Leaching of iron was obtained 17.4 mg g
1 at pH 2 by atomic absorption spectroscopy. After treatment, the MAC nano-composite retained its magnetic sensitivity under a magnet, implying that prepared nano-composite could be used in acidic medium. Furthermore, under experimental condition, it is observed that the dye adsorbed on the surface of MAC nano-composite is not degraded. Since ARS molecule after adsorption dose not undergo structural changes, it can be recovered and reused by suitable desorption methods [28]. 3.4. Effect of adsorbent dose The adsorption of dye on MAC was studied by changing the quantity of adsorbent range of 0.005–0.025 g, with the dye concentration of 70 mg L–1, room temperature (25 71 °C), and pH of 2.0. It is evident (Fig. 7) that the efficiency did not increase linearly with the increase in the adsorbent dosage. As reported [29], with the increase in adsorbent dosage the percentage adsorption also increases up to 99.4% at 0.02 g for for 70 mg L
1 dye solution. After that, even though the adsorbent dosage increases in the

Fig. 7. Effect of adsorbent amounts on removal efficiency of the dye. Conditions: 10 mL of the dye solution (70 mg L
1); sample's pH ¼2.0; stirring time ¼ 60 min; stirring speed 150 rpm.

observed decrease in the uptake values at low pH ( opH 2) was attributed to the decrease in ARS dissociation which led to a lower concentration of the anionic dye species available to interact with the MAC active sites. Above the optimum pH values, the MAC displayed a decrease in the uptake value as pH increased. The mechanisms of the adsorption process of AR on the MAC were due to be the electrostatic attraction of dye with the functional groups of the MAC nano-composite. ARS is an anionic dye due to its

Fig. 9. The effect of initial dye concentration to the adsorption rate of ARS on the MAC nano-composite.

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M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

adsorption system, because of the unavailability of the adsorbate, the percentage adsorption remains constant. 3.5. Effect of shaking time Fig. 8 shows the removal of ARS by magnetic adsorbent as a function of contact time. It is clear that the sorption amount of ARS increases with increasing contact time. The sorption of ARS increases fast in the first 1 h, and then slowed down until the sorption process achieves equilibrium after 4 h. Herein, it is worth noting that the instantaneous time for separating MAC nanocomposite from solution by external magnet can be neglected when testing the total contact time. The fast removal rate during the initial stage may be attributed to the rapid diffusion of ARS from the solution to the external surfaces of activated carbon/γFe2O3 composite. As the sites being gradually occupied, the adsorbed ARS tends to be transported from the bulk phase to the actual sorption sites (i.e., inner-sphere pores of MAC). Such slow diffusion process will decrease the sorption rate of ARS at later stages. Overall, the removal process is quite fast and 1 h is enough to reach equilibrium. 3.6. Effect of initial dye concentration The effects of initial basic dye concentrations on the rate of adsorption by activated carbon/γ-Fe2O3 composite are explored in the range from 50 to 150 mg L
1 (Fig. 9). It is obvious that the removals of the dye by various adsorbents were dependent on the concentration of the dye since the increase in the initial dye concentration increased the amount of the dye adsorbed on the adsorbents. These results suggest that the available sites on the adsorbent are the limiting factor for dye sorption [30]. By increasing the initial dye concentration the percentage of dye removal decreased, although the actual amount of dye adsorbed per unit mass of increased. This increase is due to the decrease in resistance to the uptake of solute from dye solution. The initial concentration provides an important driving force to overcome the mass transfer resistance of dye between the aqueous and the solid phases.

Fig. 10. Pseudo-first-order kinetics (a) and pseudo-second-order kinetics (b) of ARS adsorption on the activated carbon/γ-Fe2O3 nano-composite.

applicability of the model) and by observing the extent to which the experimental adsorption capacity is close to the theoretical value. The Lagergren pseudo-first-order kinetic model is usually used to emphasize the application of a solid adsorbent for the adsorption from an aqueous solution. The Lagergren pseudo-first-order kinetic model can be written as:

3.7. Adsorption kinetic

(

)

ln qe − qt = ln qe − k1t

(3)
1

To explore the potential of using a solid adsorbent such as MAC nano-composite, it is very important to investigate the kinetics of the adsorption. This involves studying the adsorption rate to determine the effects of various factors on the process. This usually occurs through careful monitoring of the experimental conditions that affect the speed of the adsorption process, until it reaches equilibrium. The kinetic data obtained is then used to develop appropriate mathematical models to describe the interactions between the adsorbate molecule and the solid adsorbent [31]. Two of the most widely used kinetic models, i.e. Lagergren pseudofirst-order [32] equation and pseudo-second-order [33] equation were used to research the adsorption kinetic behavior of ARS onto MAC nano-composite. The consistency between the experimental and the model-predicted data was investigated by calculating correlation coefficients (R2 values closer to 1 means more

where qe and qt (mg g ) are the adsorption capacities at equilibrium and at time t, respectively, and k1 is the rate constant of the pseudo-first-order adsorption (min
1). Using this well-known equation, the values of k1 and qe were calculated from the slope and intercept of the plot of ln(qe − qt ) versus t, respectively [34]. Table 2 summarizes the kinetic constants obtained by linear regression for the two models (Fig. 10a). It was found that the correlation coefficient (R2) has low value (o0.97%) and a very large difference exists between qe (experimental, which are the points) and qe (calculated, which are on the straight line), indicating a poor pseudo-first-order fit to the experimental data. In addition, the theoretical and experimental equilibrium adsorption capacities, qe obtained from this kinetic model varied widely at all concentrations. Therefore, it is necessary to fit the experimental data to another model [35]. The adsorption may be described by pseudo-

Table 2 Kinetic parameters for ARS adsorption on the MAC nano-composite. Pseudo-first-order qe,cal (mg g 40.5

Pseudo-second-order
1

)

-1

qe,exp (mg g )

k1 (min

69

0.0755


1

)

R

qe,cal (mg g
1)

k2 (g mg
1 min
1)

R2

0.967

70.4

0.005

0.999

2

M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

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Table 3 Adsorption isotherm parameters for ARS adsorption on the MAC nano-composite. Langmuir isotherm

Freundlich isotherm

kl (L mg
1)

qm (mg g
1)

0.63

108.69

qe =

RL

R2

0.02 0.998

Kf (mg1 þ n/ g Ln) 67.83

n

R2

9.94 0.975

qmklCe 1 + klCe

(5)

Ce 1 1 = + Ce qe klqm qm

(6)

or

where Ce is the equilibrium concentration of the ARS solution (mg L
1), qe is the adsorption capacity at equilibrium (mg g
1), kl is the constant related to free energy of adsorption (L mg
1), and qm is the maximum adsorption capacity at monolayer coverage (mg g
1). The Freundlich isotherm is an empirical equation that assumes heterogeneous adsorbent surface with its adsorption sites at varying energy levels [40]. The corresponding equations are commonly represented by:

qe = kf Ce1/ n

(7)

or

ln qe = ln kf + Fig. 11. Isotherms of ARS adsorption on the MAC nano-composite (temperature: 25 °C; contact time: 60 min).

second-order kinetic model as follows:

t 1 1 = + t qt qe k2qe2

(4)

where k2 is the equilibrium rate constant of pseudo-second-order adsorption (g mg
1 min
1). The slope and intercept of the plot of t /qt versus t were used to calculate the second-order rate constant, k2 (Fig. 10b). The pseudo-second order rate constants, k2, value was obtained as 0.005 g mg
1 min
1 and the equilibrium adsorption capacity was obtained as 70.4 mg g
1. The linear correlation coefficient value (R2) for the pseudo-second-order adsorption model has high value ( 499%) for adsorbent. The best fit of the pseudo-second order kinetic model in the present system shows the adsorption of the dye followed by chemisorption mechanism via electrostatic attraction. 3.8. Adsorption isotherm studies Adsorption properties and equilibrium parameters of each isotherm model indicate the interaction of adsorbent–adsorbate and give comprehensive information about the nature of interaction [36–38]. The adsorption isotherms of ARS on the MAC nanocomposite at different initial concentrations are given in Fig. 11, and the equilibrium adsorption data were analyzed by the wellknown Langmuir and Freundlich isotherm models. The Langmuir isotherm assumes that monolayer adsorption occur at binding sites with homogenous energy levels, no interactions between adsorbed molecules and no transmigration of adsorbed molecules on the adsorption surface [39]. The Langmuir equations can be expressed as:

1þn

1 ln Ce n

(8)

n

Kf (mg /g L ) and n are the Freundlich constants characteristics of the system, indicating the adsorption capacity and the adsorption intensity, respectively. If the value of 1/n is lower than 1, it indicates a normal Langmuir isotherm; otherwise, it is indicative of cooperative adsorption [41]. The corresponding isotherm parameters from both models are listed in Table 3. The adsorption of ARS was well fitted to the Langmuir isotherm model with the higher R2 (0.998). It indicated the adsorption took place at specific homogeneous sites within the adsorbent forming monolayer coverage of ARS at the surface of the absorbent. The Freundlich constant 1/n was smaller than 1, indicating a favorable process (Table 3). The adsorption isotherm process favorability was also checked using the dimensionless separation factor (RL) and the values were calculated using the following equation [42]:

RL =

1 1 + k1C0

(9)

The values of RL determine the favorability of adsorption process. If the value of RL lies between 0 and 1 (0 o RL o1), the adsorption process is favorable. If the value of RL lies beyond one (1 oRL), the adsorption process is not favorable. Whereas if the RL value equals unity (i.e., RL ¼1), then the process is linear and if RL attains a value of zero (RL ¼ 0) then the adsorption process is irreversible in nature [43]. In the study, the value of RL calculated for the initial concentrations of ARS was 0.02. Since the result is within the range of 0–1, the adsorption of ARS onto the adsorbent appears to be a favorable process. The cycles of adsorption–desorption experiments were also carried out, as shown in Fig. 12. The adsorption efficiency decreases for each new cycle after desorption with seven cycles. Meanwhile, after seven cycles of the desorption–adsorption, the MAC nano-composite has high magnetic sensitivity under an

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M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

Table 4 Comparison of various adsorbents for ARS removal. Adsorbents

Adsorption capacity (mg g
1)

Adsorbent dosage (g)

Concentration (mg L
1)

Best fit isotherm

References

Magnetic chitosan AC Cynodon dactylon Mustard husk Gold nanoparticles-AC Multiwalled carbon nanotubes Modified nano-sized silica MAC nano-composite

40.12 o 20 16.32 1.97 123.4 161.29 200 108.69

0.1 1.0 0.6 0.5 0.015 0.02 0.15 0.01

100 50 25 25 35 200 250 70

Langmuir Freundlich Redlich-peterson Freundlich Langmuir Langmuir Langmuir Langmuir

[41] [44] [45] [46] [47] [48] [49] This work

scale-up batch experiments. A comparison of kinetic models on the overall adsorption rate showed that dye/adsorbent system was best described by the pseudo-second-order rate model. The adsorption data fitted well the Langmuir isotherm. The experimental results showed that the MAC nano-composite could be utilized as a magnetically separable and efficient adsorbent for the environmental cleanup.

References

Fig. 12. The removal efficiency during seven repetition usage of MAC nano-composite. Conditions: 10 mL of the dye solution (70 mg L
1); 100 mg of MAC nanocomposite; sample's pH ¼ 2.0; desorption¼ 5 mL of ethanol. Inset in figure shows photographs of aqueous solutions of ARS (a) before adsorption, (b) after adsorption and (c) after seven cycles of desorption–adsorption.

external magnetic field, which can be collected from the solution using a magnet of 4000 Gs (inset in Fig. 12). The results showed that MAC nano-composite can be regenerated by ethanol and reused for at least four successive removal processes with removal efficiency higher than 90% (Fig. 12). Therefore, the MAC nanocomposite can be potentially used as a magnetic adsorbent to remove dye contaminants from water. A comparison was carried out between the results of the performance of proposed sorbent with those reported in previous studies. As can be seen from Table 4, the sorption capacity of MAC nanocomposite is higher than those of magnetic chitosan [41], AC [44], cynodon dactylon [45] and mustard husk [46], comparable with gold nanoparticles-AC [47], but lower than that of multiwalled carbon nanotubes [48] and modified nano-sized silica [49]. Additionally, the inherent magnetic property of MAC nano-composite make it more efficient sorbent for the removal of ARS from aqueous solution.

4. Conclusions In conclusion, the MAC nano-composite with highly efficient adsorption performance has been successfully and directly produced via a simple single-step wet chemical method at room temperature. The resulting composite combined the both features of γ-Fe2O3 and active carbon, and thus exhibited extraordinary removal capacity and fast adsorption rates for ARS dye removal in water. The adsorption kinetic and equilibrium parameters such as kinetic rate constants, the Langmuir and Freundlich constants, maximum capacity of adsorption, were obtained from the adsorption experiments. These parameters are very important for

[1] J.-W. Lee, S.-P. Choi, R. Thiruvenkatachari, W.-G. Shim, H. Moon, Dyes Pigm. 69 (2006) 196–203. [2] H. Abdolmohammad-Zadeh, E. Ghorbani, Z. Talleb, J. Iran. Chem. Soc. 10 (2013) 1103–1112. [3] I.D. Mall, V.C. Srivastava, N.K. Agarwal, I.M. Mishra, Chemosphere 61 (2005) 492–501. [4] P. Janoš, H. Buchtová, M. Rýznarová, Water Res. 37 (2003) 4938–4944. [5] S. Wang, H. Li, J. Hazard. Mater. 126 (2005) 71–77. [6] M. Bahram, S. Asadi, G. Karimnezhad, J. Iran. Chem. Soc. (2014) 1–7. [7] A.R. Gregory, J. Elliott, P. Kluge, J. Appl. Toxicol. 1 (1981) 308–313. [8] F.A. Pavan, S.L.P. Dias, E.C. Lima, E.V. Benvenutti, Dyes Pigm. 76 (2008) 64–69. [9] F.A. Pavan, Y. Gushikem, A.C. Mazzocato, S.L.P. Dias, E.C. Lima, Dyes Pigm. 72 (2007) 256–266. [10] A. Dąbrowski, Adv. Colloid Interface Sci. 93 (2001) 135–224. [11] A.K. Golder, N. Hridaya, A.N. Samanta, S. Ray, J. Hazard. Mater. 127 (2005) 134–140. [12] C. He, X. Hu, Ind. Eng. Chem. Res. 50 (2011) 14070–14083. [13] B.H. Hameed, J. Hazard. Mater. 154 (2008) 204–212. [14] B.H. Hameed, J. Hazard. Mater. 166 (2009) 233–238. [15] R.S. Blackburn, Environ. Sci. Technol. 38 (2004) 4905–4909. [16] G. Crini, Bioresour. Technol. 97 (2006) 1061–1085. [17] A.A. Ahmad, B.H. Hameed, A.L. Ahmad, J. Hazard. Mater. 170 (2009) 612–619. [18] D.M. Ruthven, Principles of Adsorption and Adsorption Processes, Wiley, 1984. [19] L.C.A. Oliveira, R.V.R.A. Rios, J.D. Fabris, V. Garg, K. Sapag, R.M. Lago, Carbon 40 (2002) 2177–2183. [20] S. Lazarević, I. Janković-Častvan, D. Jovanović, S. Milonjić, D. Janaćković, R. Petrović, Appl. Clay Sci. 37 (2007) 47–57. [21] E. Darezereshki, F. Bakhtiari, A.B. Vakylabad, Z. Hassani, Mater. Sci. Semicond. Process. 16 (2013) 221–225. [22] U. Iriarte-Velasco, J.I. Álvarez-Uriarte, M.P. González-Marcos, J.R. GonzálezVelasco, Color. Technol. 130 (2014) 62–72. [23] T. Depci, Chem. Eng. J. 181–182 (2012) 467–478. [24] N. Yang, S. Zhu, D. Zhang, S. Xu, Mater. Lett. 62 (2008) 645–647. [25] L. Ai, H. Huang, Z. Chen, X. Wei, J. Jiang, Chem. Eng. J. 156 (2010) 243–249. [26] E. Darezereshki, F. Tavakoli, F. Bakhtiari, A.B. Vakylabad, M. Ranjbar, Mater. Sci. Semicond. Process. 27 (2014) 56–62. [27] M. Alkan, M. Doğan, Y. Turhan, Ö. Demirbaş, P. Turan, Chem. Eng. J. 139 (2008) 213–223. [28] S. Preethi, A. Sivasamy, S. Sivanesan, V. Ramamurthi, G. Swaminathan, Ind. Eng. Chem. Res. 45 (2006) 7627–7632. [29] K.S. Bharathi, S.T. Ramesh, Appl. Water Sci. 3 (2013) 773–790. [30] F. Çolak, N. Atar, A. Olgun, Chem. Eng. J. 150 (2009) 122–130. [31] M.A. Salam, R.M. El-Shishtawy, A.Y. Obaid, J. Ind. Eng. Chem. 20 (2014) 3559–3567. [32] I. Langmuir, J. Am. Chem. Soc. 40 (1918) 1361–1403. [33] E. Bulut, M. Özacar, İ.A. Şengil, J. Hazard. Mater. 154 (2008) 613–622. [34] J.C. Bellot, J.S. Condoret, Process Biochem. 28 (1993) 365–376. [35] V.C. Srivastava, I.D. Mall, I.M. Mishra, Colloids Surf. A: Physicochem. Eng. Asp. 312 (2008) 172–184. [36] R. Liu, B. Zhang, D. Mei, H. Zhang, J. Liu, Desalination 268 (2011) 111–116. [37] N. Kannan, M.M. Sundaram, Dyes Pigm. 51 (2001) 25–40. [38] I. Langmuir, J. Am. Chem. Soc. 38 (1916) 2221–2295. [39] M.A.K.M. Hanafiah, W.S.W. Ngah, S.H. Zolkafly, L.C. Teong, Z.A.A. Majid, J. Environ. Sci. 24 (2012) 261–268. [40] H. Freundlich, Über die Adsorption in Lösungen, W. Engelmann, 1906.

M. Fayazi et al. / Materials Science in Semiconductor Processing 40 (2015) 35–43

[41] L. Fan, Y. Zhang, X. Li, C. Luo, F. Lu, H. Qiu, Colloids Surf. B: Biointerfaces 91 (2012) 250–257. [42] L. Ai, C. Zhang, Z. Chen, J. Hazard. Mater. 192 (2011) 1515–1524. [43] L. Xiong, Y. Yang, J. Mai, W. Sun, C. Zhang, D. Wei, Q. Chen, J. Ni, Chem. Eng. J. 156 (2010) 313–320. [44] M. Ghaedi, A. Najibi, H. Hossainian, A. Shokrollahi, M. Soylak, Toxicol. Environ. Chem. 94 (2011) 40–48. [45] J. Samusolomon, P. Martin Devaprasath, J. Chem. Pharm. Res. 3 (2011) 478–490.

43

[46] R.K. Gautam, A. Mudhoo, M.C. Chattopadhyaya, J. Environ. Chem. Eng. 1 (2013) 1283–1291. [47] M. Roosta, M. Ghaedi, M. Mohammadi, Powder Technol. 267 (2014) 134–144. [48] M. Ghaedi, A. Hassanzadeh, S.N. Kokhdan, J. Chem. Eng. Data 56 (2011) 2511–2520. [49] D. Li, Q. Liu, S. Ma, Z. Chang, L. Zhang, Adsorpt. Sci. Technol. 29 (2011) 289–300.