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Magnetic Fe3O4@C nanoparticles as adsorbents for removal of amoxicillin from aqueous solution Babak Kakavandi, Ali Esrafili, Anoushiravan Mohseni-Bandpi, Ahmad Jonidi Jafari and Roshanak Rezaei Kalantary
ABSTRACT In the present study, powder activated carbon (PAC) combined with Fe3O4 magnetite nanoparticles (MNPs) were used for the preparation of magnetic composites (MNPs-PAC), which was used as an adsorbent for amoxicillin (AMX) removal. The properties of magnetic activated carbon were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunaeur, Emmett and Teller and vibrating sample magnetometer. The operational factors affecting adsorption such as pH, contact time, adsorbent dosage, initial AMX concentration and temperature were studied in detail. The high surface area and saturation magnetization for the synthesized adsorbent were found to be 671.2 m2/g and 6.94 emu/g, respectively. The equilibrium time of the adsorption process was 90 min. Studies of adsorption equilibrium and kinetic models revealed that the adsorption of AMX onto MNPs-PAC followed Freundlich and Langmuir isotherms and pseudosecond-order kinetic models. The calculated values of the thermodynamic parameters, such as ΔG , W
ΔH and ΔS demonstrated that the AMX adsorption was endothermic and spontaneous in nature. It W
W
could be concluded that MNPs-PAC have a great potential for antibiotic removal from aquatic media. Key words
| activated carbon, adsorption, amoxicillin, Fe3O4 magnetic nanoparticle, thermodynamic
Babak Kakavandi Department of Environmental Health Engineering, School of Health, Ahvaz, Jundishapur University of Medical Sciences, Ahvaz, Iran Ali Esrafili Ahmad Jonidi Jafari Roshanak Rezaei Kalantary (corresponding author) Department of Environmental Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran E-mail: [email protected] Anoushiravan Mohseni-Bandpi Department of Environmental Health Engineering, School of Public Health, Shahid Beheshti University of Medical Sciences, Tehran, Iran Roshanak Rezaei Kalantary Center for Water Quality Research (CWQR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran
INTRODUCTION The presence of antibiotics in aquatic media is a major source of environmental pollution. Most antibiotics have high water solubility, low biodegradability and high toxicity (RiveraUtrilla et al. ) and some are reported to have mutagenic and carcinogenic characteristics (Bendesky et al. ). In conventional wastewater treatment processes, only 60–90% of antibiotics can be removed (Liu et al. ). Little is known about the fate of pharmaceuticals in the environment. Amoxicillin (AMX) is a broad-spectrum aminopenicillin antibiotic, widely used in veterinary medicine for the treatment or prevention of bacterial infections encountered in gastro-intestinal and systemic infections (Putra et al. ). It is also known to be non-biodegradable and an inhibitor of the photosynthesis mechanism of the algae Synechocystis sp. (Pan et al. ). Several methods are available for the removal of AMX from aqueous media, including adsorption (Homem et al. ), ozonation technology (Baciogliu & Otker ), membrane filtration (Li et al. ), advanced oxidation processes (Trovo et al. ) and biological methods (Xu et al. ). AMX doi: 10.2166/wst.2013.568
is resistant to biodegradation due to a beta-lactam ring with toxic properties for microorganisms, thus biological methods seem to be inefficient for removal of this pollutant. Among these methods, adsorption is more popular due to its simplicity of operation, effectiveness even at very low concentrations, and easy operation (Iram et al. ). Recently, several adsorbents such as carbon nanotubes, zeolite and bentonite have been used to remove antibiotics from aqueous media (Putra et al. ; Xu et al. ). Powder activated carbon (PAC) is the most commonly used adsorbent for the removal of organic contaminants due to its high surface area, porous structure and total pore volume. In the case of AMX Putra et al. , reported that bentonite had a good potential for adsorption, but activated carbon was shown to have more adsorption capacity. The removal efficiency of AMX from real wastewater by activated carbon was found to be 94.67% (Putra et al. ). The main disadvantage of PAC is difficult application in process engineering due to the small particle size, dispersion
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in the medium, and separation and filtration problems (Ai et al. ). Therefore, it is necessary to use an adsorbent that does not generate secondary pollution and can be easily used on an industrial scale. Combining the advantages of magnetic nanoparticles (MNPs) separation and PAC to fabricate an adsorbent seems to be an opportunity to achieve desirable adsorption and effective separation by an external magnetic field. The presence of MNPs, mainly Fe3O4, in an adsorbent may provide better kinetics for the adsorption of pollutants due to the basic properties of activated carbon, extremely small size and high surface-area-to-volume ratio (Shariati et al. ). The micro-sized overall structure of MNPs-PAC provides the necessary mechanical resistance against wear and tear and the nano-structure provides the high surface area (Iram et al. ). The other advantage of MNPs-PAC is that it can be employed in situ, and thus is suitable for online separation. However, the possibility of a decrease in surface area of PAC after incorporating MNPs needs to be taken into consideration. The aim of the present study was to synthesise MNPs-PAC for the removal of AMX from aqueous media by the adsorption process under varying conditions and to investigate the equilibrium isotherms, kinetics and thermodynamics.
MATERIALS AND METHODS Chemicals AMX was supplied by the Razi Pharmaceutical Co. (Tehran, Iran). All other chemicals including nitric acid (65%), ferric nitrate and PAC were purchased from Merck (Merck, Darmstadt, Germany).
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by the Brunaeur, Emmett and Teller (BET) method (Quantachrome, NOVA 2000) using N2 adsorption–desorption isotherms at 77.3 K. Adsorption experiments study The stock of synthetic AMX solution at a concentration of 1,000 mg/L was prepared by dissolving the required amount in deionized water. The adsorption experiments were carried out using the batch equilibrium technique in aqueous solutions under the following conditions: contact time, 0–180 min; pH 3–11; at room temperature. After the optimization of pH and contact time, the adsorption isotherms were determined with initial concentrations of AMX and MNPs-PAC in the range of 50–300 mg/L and 1–5 g/L respectively. The adsorption thermodynamic was also studied in the range of 20–50 C. The pH of the solutions was adjusted by using 0.1 mol L1 HCl or 0.1 mol L1 NaOH. After a certain time, MNPs-PAC was separated from the solution by using an external magnetic field with an intensity of 1.3 T in 40–50 seconds. The AMX remaining concentrations were measured using UV-Visible spectrophotometer (CE CECIL 7400) at the appropriate wavelength corresponding to the maximum absorbance of AMX, 228 nm. The amount of AMX adsorbed (qe, mg/g) onto the adsorbent was calculated using the following equation: W
qe ¼
(C0 Ce )v m
(1)
where, C0 and Ce are the initial and the equilibrium concentrations of AMX (mg L1), m is the mass of adsorbent (g), and v is the volume of solution (L). All the experiments were done in triplicate.
Synthesis and characterization of MNPs-PAC The MNPs were synthesized by a chemical co-precipitation method using a reactor according to our previous work (Kakavandi et al. ). The size and morphology of MNPs-PAC was estimated by scanning electron microscopy (SEM, PHILIPS, XL-30) and transmission electron microscopy (TEM, PHILIPS, EM 208). An X-ray diffractometer (XRD, Quantachrome, NOVA 2000) was used for an X-ray diffraction pattern of a powder of MNPs-PAC at 25 C. The magnetic properties of the adsorbent were investigated with a vibrating sample magnetometer (VSM, Lakeshare, USA 7400) at room temperature. The specific surface area and pore volume of MNPs-PAC were measured W
RESULTS AND DISCUSSION Properties of synthesized MNPs-PAC In order to characterize the crystal phase of iron oxide particles, the MNPs-PAC was analyzed by XRD in the 2θ in the region of 10–70 at 25 C (λ ¼ 1.54 Å). Figure 1(a) shows the XRD pattern for the adsorbent. According to JCPDS No. 01-088-0866 the highest peak of 35.5 corresponds to 511 planes confirming the presence of Fe3O4 particle crystals with a cubic structure. The pores with different sizes and shapes in Figure 1(b) indicate that W
W
W
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Figure 1
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(a) XRD pattern of Fe3O4-loaded PAC, (b) SEM image of MNPs-PAC and (c) TEM image of Fe3O4 particles.
their distribution on the surface of the adsorbent was approximately uniform. The TEM micrograph of MNPsPAC shows the iron oxide particles with an average diameter of 30–80 nm; see Figure 1(c). Figure 2(a) shows the VSM magnetization curve of the prepared adsorbent at 25 C in the magnetic field of ±10 kOe. Maximum saturation of magnetization was about 6.94 emu/g which exhibits super-paramagnetic characteristic (Depci ). These results also indicated that the MNPs-PAC showed an excellent magnetic response to a magnetic field. Therefore, it could be separated easily and rapidly due to this high magnetic sensitivity. W
The N2 adsorption–desorption isotherms, volume and pore size distribution for MNPs-PAC after application of the BET method are shown in Figure 2(b), (c). According to Figure 2(c) the average pore size was 3.5 nm. On the basis of IUPAC classification (micropores (d < 2 nm), mesopores (2 < d < 50 nm) and macropores (d > 50 nm), it could be classified into mesopores group (Huang et al. ). The total pore volume obtained at p/p0 ¼ 0.99 by BET and BJH were 4.87 cc/g and 3.7 cc/g respectively. The results of the BET analysis also indicated that the highest surface area of adsorbent was 671.2 m2/g, which is slightly less than that of PAC (733 m2/g) (Do
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Figure 2
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(a) VSM magnetization curve of MNPs-PAC, (b) the nitrogen adsorption–desorption isotherms and (c) volume and pore size distribution for MNPs-PAC.
et al. ). This could be due to the filling of pores of PAC by MNPs. Effect of solution pH The variation of the adsorption capacity with pH follows a bell-shape pattern in the pH range of 3–9, and then it remains relatively flat up to pH11; see Figure 3(a). The highest adsorption capacity was obtained at pH 5. By increasing the pH from 2 to 5, the carboxyl functional groups (–COOH) present in the AMX molecules are readily dissociated to carboxylate ions (–COO) and subsequently the electrostatic attraction between the AMX molecules and the PAC surface increases (Putra et al. ; Moussavi et al. ). However, at higher pH, the
PAC surface is negatively charged, therefore the electrostatic repulsion between the negatively charged adsorbed ions and negatively charged adsorbent surface lead to the reduction of the AMX adsorption onto MNPs-PAC. In alkaline solution a shift from cationic to anionic species may occur, so the electrostatic (hydrophobic) interactions may play a major role in the adsorption of AMX on MNPs-PAC surface at pH 5 (Xu et al. ). To take all the above mentioned matters into consideration, pH 5 was selected as the optimum pH for the future adsorption experiments. It is worth noting that the optimum pH in the range of 5–6 was reported by the other researchers studying AMX adsorption on different adsorbents as well (Moussavi et al. ).
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Figure 3
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Magnetic Fe3O4@C nanoparticles for amoxicillin removal
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The effect of (a) pH and (b) contact time on AMX adsorption by MNPs-PAC, T ¼ 20 C, C0 ¼ 50 mg/L and m ¼ 1 g/L; and (c) the effect of adsorbent dosage (1–5 g/L) and AMX initial concentration (50–300 mg/L) on the removal efficiency of AMX by MNPs-PAC, T ¼ 20 C, pH ¼ 5 and t ¼ 90 min. W
W
Effect of contact time The contact time between adsorbate and adsorbent is the other important parameter that affects the performance of the adsorption process. The effect of contact time on the adsorption capacity of MNPs-PAC for AMX is shown in Figure 3(b). The results indicate that the adsorption capacity increases rapidly during the first 20 min and then keeps increasing at a relatively slow rate by increasing contact time and finally reaches the equilibrium point after 90 min. There were almost no significant changes in the adsorption capacity from 90–180 min. This can be due to the reduced availability of AMX molecules to active sites on the MNPs-
PAC surface, which is in agreement with the phenomenon noted by other researchers in the study of some antibiotic removal (Wang et al. ). In the study of AMX adsorption on activated carbon, the equilibrium time of 100 min was reported (Moussavi et al. ). The main reason for the fast absorption rate was attributed to a large surface area on MNPs-PAC that could supply a large number of active sites available for AMX (Naghizadeh et al. ). Impact of adsorbent dose and initial AMX concentration Figure 3(c) shows the effect of adsorbent dose and initial AMX concentration on the uptake of AMX by MNPs-PAC
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under the optimum condition (pH ¼ 5, t ¼ 90 min). According to the Figure 3(c), it can be seen that the removal efficiency was increased with enhancement of the adsorbent dose from 1 to 5 g/L. This observation arises from the increasing adsorbent surface area and the availability of AMX molecules to adsorption active sites. Figure 3(c) also shows that with the rise in initial concentration from 50 to 300 mg/L, at adsorbent dosage of 1 g/L, the removal efficiency decreased from 95.26 to 44.22%. In the study of aniline adsorption on the MNPs-PAC reported that the rise in the adsorption capacity is also relevant to the rise in initial pollution concentration gradient (Kakavandi et al. ).
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Table 1
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ln(qe qt ) ¼ ln qe k1 t
(2)
where, qe and qt (mg/g) are the amounts of AMX adsorbed at equilibrium at a given time t (min) respectively, and k1 (min1) is the pseudo-first-order rate constant. The pseudo-second-order kinetic model can be expressed as follows (Naghizadeh et al. ): t 1 1 ¼ þ t qt k2 q2e qe
(3)
where, k2 (g mg1 min1) is the rate constant of the pseudosecond-order adsorption. The intra-particle diffusion equation can be expressed as follows: qt ¼ ki t0:5 þ Ci
(4)
where, both ki (mg/g min0.5) and Ci (mg/g) represent the boundary layer effects. In Equation (4), if Ci is equal to zero, intra-particle diffusion will be the only controlling step. By contrast, the values of C ≠ 0 suggest that the adsorption process is partly complex and involves more than one diffusive resistance (Rodríguez et al. ). Kinetic constants obtained by the linear regressions of the three models are depicted in Table 1. The calculated amount of qe derived from the pseudo-first-order model
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Kinetic model parameters for AMX adsorption onto the MNPs-PAC
Kinetic models
Constants
qe,exp (mg/g)
47.8
qe,cal (mg/g) K1 (min1)
15.06 0.04
Pseudo-first-order
R2
0.656
Pseudo-second-order qe,cal K2 (g/mg)(min)1 R2
50 0.009 0.999
ki (mg/g min0.5) Ci (mg/g) R2
0.784 39.02 0.878
Intraparticle diffusion
Adsorption kinetic studies To investigate the mechanism of AMX adsorption on the MNPs-PAC, three kinetic models (pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetic models) were considered in order to find the best fitted model for the experimental data. The pseudo-first-order model is expressed by the following equation (Zhu et al. ):
|
is not coherent with the experimental data. But good agreement is obtained when qe has been calculated according to pseudo-second-order model. In addition, the suitability of data deducted from the pseudo-secondorder confirms that the rate-limiting step in adsorption of AMX by MNPs-PAC might be coming from electrostatic attraction phenomenon (Budyanto et al. ). As observed in Table 1, the value of Ci was measured 39.02 mg/g, indicating that intra-particle diffusion is not the only controlling step for AMX adsorption and the process is controlled by boundary layer diffusion to some degree (Zhu et al. ). Adsorption equilibrium studies The adsorption isotherm is important for the design of adsorption system. It expresses the relationship between adsorbate and adsorbent at constant temperature. In this study, Langmuir, Freundlich and Temkin isotherms were used to describe the equilibrium between the adsorbed amounts of AMX on the MNPs-PAC (qe) and AMX concentration in the solution (Ce). The Langmuir adsorption isotherm assumes that the reaction has a constant freeenergy change (ΔG ads) for all sites and each site is also assumed to be capable of binding to one molecule of adsorbate. The linear form of the Langmuir isotherm equation is: W
Ce Ce 1 ¼ þ qe q0 k L q0
(5)
where q0 (mg/g) is the maximum adsorbent-phase concentration of adsorbate when the surface site is saturated with
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adsorbate and kL (L mg1) is the Langmuir adsorption constant. The dimensionless constant (separation factor, RL) expresses the characteristics of the Langmuir isotherm as follows:
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Table 2
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Parameters of adsorption equilibrium isotherms for adsorption of AMX onto the MNPs-PAC at different temperatures T (K)
Isotherm models
293
308
323
qm (mg/g)
142.85
135.13
123.45
KL (L/mg)
0.08
0.05
0.043
0.994
0.9825
0.9813
0.04–0.2
0.062–0.285
0.072–0.317
Langmuir
1 RL ¼ 1 þ kL C0
(6)
where C0 is the initial solute concentration. The adsorption will be favorable if the RL is between 0 and 1. The RL > 1 values indicate unfavorable adsorption and for RL of 1 and 0, the adsorptions are linear and irreversible, respectively (Kakavandi et al. ). The Freundlich isotherm is an empirical equation that assumes that the adsorption process occurs on heterogeneous surfaces with non-uniform distribution of adsorption heat. The linear form of Freundlich isotherm equation is as follows: 1 ln qe ¼ ln kF þ ln Ce n
RL Freundlich KF (mg/g(L mg)1/n)
40
32.4
27.34
n
4.45
3.87
3.71
R2
0.996
0.9901
0.9928
4.564
2.03
1.352
Temkin kT
117.06
bT R2
12.64
0.946
137.08
0.9435
0.954
(7)
where kF is a Freundlich adsorption capacity parameter (mg/g) (L/mg)1/n and 1/n is the Freundlich adsorption intensity parameter (relating to the heterogeneity factor), which is unitless. The values of n indicate that the type of adsorption is favorable in the range of 2–10, moderate in the range of 1–2 and poor if n < 1 (Hameed et al. ). The Temkin isotherm model proposed the impact of some indirect adsorbent–adsorbate interactions on adsorption isotherms (Li et al. ). The linear form of the Temkin isotherm model is as follows: qe ¼ B ln kT þ B ln (Ce )
R
2
indicating that the adsorption of AMX on the MNPsPAC had a favorable Langmuir isotherm fit too, but the adsorption isotherm models were fitted into the data in the order of: Freundlich > Langmuir > Temkin isotherm. Putra et al. reported that the Langmuir and Freundlich isotherm models were the best isotherm for AMX adsorption on activated carbon (Putra et al. ). Figure 4(a) also suggests that equilibrium data from AMX adsorption experiments are in high accordance with the Langmuir and Freundlich equilibrium isotherms. The effect of temperature and adsorption thermodynamic studies
(8)
where kT is the equilibrium binding constant corresponding to the maximum binding energy, B ¼ RT/bT, bT (J/mol) is the Temkin constant related to the heat of adsorption, R (8.314 J/mol K) is the universal gas constant and T (K) is solution temperature. The values of equilibrium model parameters presented in Table 2 show that the equilibrium adsorption data were well described by Freundlich and Langmuir isotherms compared to the Temkin isotherm based on R 2. The Freundlich adsorption heterogeneity factors (n values) were in the range of 4.28–3.71, at 293–323 K, indicating that AMX was favorably adsorbed by MNPsPAC. The values of RL also were between 0 and 1,
As shown in Figure 4(b), the AMX adsorption by MNPsPAC decreases with an increase in the temperature from 20–50 C, which is similar to the results obtained by other researchers (Homem et al. ; Xu et al. ). The relationship of the thermodynamic parameters such as change in free energy (ΔG ), enthalpy (ΔH ), and entropy (ΔS ) is expressed according to the following Equation 9 (Kakavandi et al. ): W
W
W
W
ΔS ΔH R RT W
ln kd ¼
W
(9)
where, kd (L/mg) is the distribution coefficient, i.e., the ratio of equilibrium concentration of AMX on adsorbent
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5.6 kJ/mol for the temperature range 20–50 C. The negative values of ΔG demonstrate the spontaneous nature of the adsorption process. The negative ΔG values also determine that the reaction rate decreases with an increase in the temperature. Furthermore, the ΔG values become greater as the temperature increases from 20 to 50 C, which suggests that the adsorption process is not favorable at higher temperatures. The ΔS value was found to be 63.21 J/mol.K. This value suggests the drop in the degree of freedom by the adsorbed species. It also indicates that there is no structural change at solid–liquid interface and the adsorption process looks stable (Kamari & Ngah ). W
W
W
W
W
W
CONCLUSION The present study demonstrated that the AMX removal using MNPs-PAC increases as both the adsorbent dosage and contact time increase, and it decreases when the initial concentration of AMX and the temperature are increased. The optimum conditions obtained for the adsorption are as follows: pH5, contact time of 90 min, adsorbent dosage of 1 g/L and a temperature of 20 C. According to the Langmuir model, the maximum adsorption capacity was 142.85 mg/g. Studying Freundlich and Langmuir equilibrium isotherms at different temperatures showed that the adsorption of AMX on the MNPs-PAC went very well, following both models with a fairly good coefficient correlation (R 2 > 0.98). Having applied a large amount of PAC for the removal of contaminants from aqueous solutions, we magnetized it with the aim of accelerating the separation process and also avoiding filtration. W
Figure 4
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The adsorption isotherms (a) and (b) the effect of solution temperature on the adsorption of AMX by MNPs-PAC, m ¼ 1 g/L, pH ¼ 5 and t ¼ 90 min.
(mg/g) to that in solution (mg/L). The parameters ΔH and ΔS can be computed from the intercept and slope of vant Hoff plots of ln Kd versus 1/T, respectively. The standard free energy (ΔG ) can be calculated using the equation: W
W
W
ΔG ¼ RT ln kd W
(10)
The values of ΔH for AMX adsorption on MNPs-PAC were determined as 26.01 kJ/mol. This indicates that the adsorption process was exothermic in nature. The calculated ΔG values were found to be in the range of 7.49 to W
W
REFERENCES Ai, L., Zhou, Y. & Jiang, J. Removal of methylene blue from aqueous solution by montmorillonite/CoFe2O4 composite with magnetic separation performance. Desalination 266, 72–77. Baciogliu, I. A. & Otker, M. Treatment of pharmaceutical wastewater containing antibiotics by O3 and O3/H2O2 processes. J. Chemosphere 50, 85–95. Bendesky, a., Menéndez, D. & Ostrosky-Wegman, P. Is metronidazole carcinogenic? Mutat. Res-Rev. Mutat. 511, 133–144. Budyanto, S., Soedjono, S., Irawati, W. & Indraswati, N. Studies of adsorption equilibria and kinetics of amoxicillin from simulated wastewater using activated carbon and natural bentonite. J. Environ. Prot. Sci. 2, 72–80.
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B. Kakavandi et al.
|
Magnetic Fe3O4@C nanoparticles for amoxicillin removal
Depci, T. Comparison of activated carbon and iron impregnated activated carbon derived from Golbaş ı lignite to remove cyanide from water. J. Chem. Eng. 181–182, 467–478. Do, M. H., Phan, N. H. & Nguyen, T. D. Activated carbon/ Fe3O4 nanoparticle composite: Fabrication, methyl orange removal and regeneration by hydrogen peroxide. J. Chemosphere 85, 1269–1279. Hameed, B. H., Mahmoud, D. K. & Ahmad, A. L. Equilibrium modeling and kinetic studies on the adsorption of basic dye by a low-cost adsorbent: coconut (Cocos nucifera) bunch waste. J. Hazard. Mater. 158, 65–72. Homem, V., Alves, A. & Santos, L. Amoxicillin removal from aqueous matrices by sorption with almond shell ashes. Int. J. Environ. Analyt. Chem. 90, 1063–1084. Huang, L., Sun, Y., Wang, W., Yue, Q. & Yang, T. Comparative study on characterization of activated carbons prepared by microwave and conventional heating methods and application in removal of oxytetracycline (OTC). J. Chem. Eng. 171, 1446–1453. Iram, M., Guo, C., Guan, Y., Ishfaq, A. & Liu, H. Adsorption and magnetic removal of neutral red dye from aqueous solution using Fe3O4 hollow nanospheres. J. Hazard. Mater. 181, 1039–1050. Kakavandi, B., Jonidi, A., Rezaei, R., Nasseri, S., Ameri, A. & Esrafily, A. Synthesis and properties of Fe3O4-activated 3 carbon magnetic nanoparticles for removal of 4 aniline from aqueous solution: equilibrium, kinetic 5 and thermodynamic studies. Iran. J. Environ. Heal. Sci. Eng 10, 1–9. Kamari, A. & Ngah, W. S. W. Isotherm, kinetic and thermodynamic studies of lead and copper uptake by H2SO4 modified chitosan. Colloids Surf. B: Biointerfaces 73, 257–266. Li, S., Li, X. & Wang, D. Membrane (RO-UF) filtration for antibiotic wastewater treatment and recovery of antibiotics. J. Sep. Puri. Tech 34, 109–114. Li, K., Zheng, Z., Huang, X., Zhao, G., Feng, J. & Zhang, J. Equilibrium, kinetic, thermodynamic studies on the adsorption of 2-nitroaniline onto activated carbon prepared from cotton stalk fibre. J. Hazard. Mater. 166, 213–220. Liu, H., Liu, W., Zhang, J., Zhang, C., Ren, L. & Li, Y. Removal of cephalexin from aqueous solutions by original and Cu(II)/Fe(III) impregnated activated carbons developed from lotus stalks Kinetics and equilibrium studies. J. Hazard. Mater. 185, 1528–1235. Moussavi, G., Alahabadi, A., Yaghmaeian, K. & Eskandari, M. Preparation, characterization and adsorption potential
Water Science & Technology
|
69.1
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of the NH4Cl-induced activated carbon for the removal of amoxicillin antibiotic from water. J. Chem. Eng. 217, 119–128. Naghizadeh, A., Nasseri, S., Rashidi, A. H., Rezaei, R., Nabizadeh, R. & Mahvi, A. H. Adsorption kinetics and thermodynamics of hydrophobic Natural Organic Matters (NOMs) removal from aqueous solution by multi-wall carbon nanotubes. J. Water Sci. Tech: Water Sup 13 (2), 273–285. Pan, X., Deng, C., Zhang, D., Wang, J., Mu, G. & Chen, Y. Toxic effects of amoxicillin on the photosystem II of Synechocystis sp. characterized by a variety of in vivo chlorophyll fluorescence tests. Aquat. Toxicol. 89, 207–213. Putra, E. K., Pranowo, R., Sunarso, J., Indraswati, N. & Ismadji, S. Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: mechanisms, isotherms and kinetics. J. Water Res. 43, 2419–2430. Rivera-Utrilla, J., Prados-Joya, G., Sánchez-Polo, M., Ferro-García, M. A. & Bautista-Toledo, I. Removal of nitroimidazole antibiotics from aqueous solution by adsorption/ bioadsorption on activated carbon. J. Hazard. Mater. 170, 298–305. Rodríguez, A., García, J., Ovejero, G. & Mestanza, M. Adsorption of anionic and cationic dyes on activated carbon from aqueous solutions: equilibrium and kinetics. J. Hazard. Mater. 172, 1311–1320. Shariati, S., Faraji, M., Yamini, Y. & Rajabi, A. A. Fe3O4 magnetic nanoparticles modified with sodium dodecyl sulfate for removal of safranin O dye from aqueous solutions. Desalination 270, 160–165. Trovo, A. G., Pupo Nogueira, R. F., Aguera, A., Fernandez-Alba, A. R. & Malato, S. Degradation of the antibiotic amoxicillin by photo-Fenton process – Chemical and toxicological assessment. J. Wat. Res 45, 1394–1402. Wang, G., Wu, T., Li, Y., Sun, D., Wang, Y., Huang, X., Zhang, G. & Liu, R. Removal of ampicillin sodium in solution using activated carbon adsorption integrated with H2O2 oxidation. J. Chem. Tech. Biotech. 87, 623–628. Xu, L., Dai, J., Pan, J., Li, X., Huo, P., Yan, Y., Zou, X. & Zhang, R. Performance of rattle-type magnetic mesoporous silica spheres in the adsorption of single and binary antibiotics. J. Chem. Eng. 174, 221–230. Zhu, H-Y., Jiang, R., Xiao, L. & Li, W. A novel magnetically separable γ-Fe2O3/crosslinked chitosan adsorbent: Preparation, characterization and adsorption application for removal of hazardous azo dye. J. Hazard. Mater. 179, 251–257.
First received 27 May 2013; accepted in revised form 25 September 2013. Available online 24 October 2013
© IWA Publishing 2014 Water Science & Technology
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Magnetic Fe3O4@C nanoparticles as adsorbents for removal of amoxicillin from aqueous solution Babak Kakavandi, Ali Esrafili, Anoushiravan Mohseni-Bandpi, Ahmad Jonidi Jafari and Roshanak Rezaei Kalantary
ABSTRACT In the present study, powder activated carbon (PAC) combined with Fe3O4 magnetite nanoparticles (MNPs) were used for the preparation of magnetic composites (MNPs-PAC), which was used as an adsorbent for amoxicillin (AMX) removal. The properties of magnetic activated carbon were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunaeur, Emmett and Teller and vibrating sample magnetometer. The operational factors affecting adsorption such as pH, contact time, adsorbent dosage, initial AMX concentration and temperature were studied in detail. The high surface area and saturation magnetization for the synthesized adsorbent were found to be 671.2 m2/g and 6.94 emu/g, respectively. The equilibrium time of the adsorption process was 90 min. Studies of adsorption equilibrium and kinetic models revealed that the adsorption of AMX onto MNPs-PAC followed Freundlich and Langmuir isotherms and pseudosecond-order kinetic models. The calculated values of the thermodynamic parameters, such as ΔG , W
ΔH and ΔS demonstrated that the AMX adsorption was endothermic and spontaneous in nature. It W
W
could be concluded that MNPs-PAC have a great potential for antibiotic removal from aquatic media. Key words
| activated carbon, adsorption, amoxicillin, Fe3O4 magnetic nanoparticle, thermodynamic
Babak Kakavandi Department of Environmental Health Engineering, School of Health, Ahvaz, Jundishapur University of Medical Sciences, Ahvaz, Iran Ali Esrafili Ahmad Jonidi Jafari Roshanak Rezaei Kalantary (corresponding author) Department of Environmental Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran E-mail: [email protected] Anoushiravan Mohseni-Bandpi Department of Environmental Health Engineering, School of Public Health, Shahid Beheshti University of Medical Sciences, Tehran, Iran Roshanak Rezaei Kalantary Center for Water Quality Research (CWQR), Institute for Environmental Research (IER), Tehran University of Medical Sciences, Tehran, Iran
INTRODUCTION The presence of antibiotics in aquatic media is a major source of environmental pollution. Most antibiotics have high water solubility, low biodegradability and high toxicity (RiveraUtrilla et al. ) and some are reported to have mutagenic and carcinogenic characteristics (Bendesky et al. ). In conventional wastewater treatment processes, only 60–90% of antibiotics can be removed (Liu et al. ). Little is known about the fate of pharmaceuticals in the environment. Amoxicillin (AMX) is a broad-spectrum aminopenicillin antibiotic, widely used in veterinary medicine for the treatment or prevention of bacterial infections encountered in gastro-intestinal and systemic infections (Putra et al. ). It is also known to be non-biodegradable and an inhibitor of the photosynthesis mechanism of the algae Synechocystis sp. (Pan et al. ). Several methods are available for the removal of AMX from aqueous media, including adsorption (Homem et al. ), ozonation technology (Baciogliu & Otker ), membrane filtration (Li et al. ), advanced oxidation processes (Trovo et al. ) and biological methods (Xu et al. ). AMX doi: 10.2166/wst.2013.568
is resistant to biodegradation due to a beta-lactam ring with toxic properties for microorganisms, thus biological methods seem to be inefficient for removal of this pollutant. Among these methods, adsorption is more popular due to its simplicity of operation, effectiveness even at very low concentrations, and easy operation (Iram et al. ). Recently, several adsorbents such as carbon nanotubes, zeolite and bentonite have been used to remove antibiotics from aqueous media (Putra et al. ; Xu et al. ). Powder activated carbon (PAC) is the most commonly used adsorbent for the removal of organic contaminants due to its high surface area, porous structure and total pore volume. In the case of AMX Putra et al. , reported that bentonite had a good potential for adsorption, but activated carbon was shown to have more adsorption capacity. The removal efficiency of AMX from real wastewater by activated carbon was found to be 94.67% (Putra et al. ). The main disadvantage of PAC is difficult application in process engineering due to the small particle size, dispersion
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in the medium, and separation and filtration problems (Ai et al. ). Therefore, it is necessary to use an adsorbent that does not generate secondary pollution and can be easily used on an industrial scale. Combining the advantages of magnetic nanoparticles (MNPs) separation and PAC to fabricate an adsorbent seems to be an opportunity to achieve desirable adsorption and effective separation by an external magnetic field. The presence of MNPs, mainly Fe3O4, in an adsorbent may provide better kinetics for the adsorption of pollutants due to the basic properties of activated carbon, extremely small size and high surface-area-to-volume ratio (Shariati et al. ). The micro-sized overall structure of MNPs-PAC provides the necessary mechanical resistance against wear and tear and the nano-structure provides the high surface area (Iram et al. ). The other advantage of MNPs-PAC is that it can be employed in situ, and thus is suitable for online separation. However, the possibility of a decrease in surface area of PAC after incorporating MNPs needs to be taken into consideration. The aim of the present study was to synthesise MNPs-PAC for the removal of AMX from aqueous media by the adsorption process under varying conditions and to investigate the equilibrium isotherms, kinetics and thermodynamics.
MATERIALS AND METHODS Chemicals AMX was supplied by the Razi Pharmaceutical Co. (Tehran, Iran). All other chemicals including nitric acid (65%), ferric nitrate and PAC were purchased from Merck (Merck, Darmstadt, Germany).
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by the Brunaeur, Emmett and Teller (BET) method (Quantachrome, NOVA 2000) using N2 adsorption–desorption isotherms at 77.3 K. Adsorption experiments study The stock of synthetic AMX solution at a concentration of 1,000 mg/L was prepared by dissolving the required amount in deionized water. The adsorption experiments were carried out using the batch equilibrium technique in aqueous solutions under the following conditions: contact time, 0–180 min; pH 3–11; at room temperature. After the optimization of pH and contact time, the adsorption isotherms were determined with initial concentrations of AMX and MNPs-PAC in the range of 50–300 mg/L and 1–5 g/L respectively. The adsorption thermodynamic was also studied in the range of 20–50 C. The pH of the solutions was adjusted by using 0.1 mol L1 HCl or 0.1 mol L1 NaOH. After a certain time, MNPs-PAC was separated from the solution by using an external magnetic field with an intensity of 1.3 T in 40–50 seconds. The AMX remaining concentrations were measured using UV-Visible spectrophotometer (CE CECIL 7400) at the appropriate wavelength corresponding to the maximum absorbance of AMX, 228 nm. The amount of AMX adsorbed (qe, mg/g) onto the adsorbent was calculated using the following equation: W
qe ¼
(C0 Ce )v m
(1)
where, C0 and Ce are the initial and the equilibrium concentrations of AMX (mg L1), m is the mass of adsorbent (g), and v is the volume of solution (L). All the experiments were done in triplicate.
Synthesis and characterization of MNPs-PAC The MNPs were synthesized by a chemical co-precipitation method using a reactor according to our previous work (Kakavandi et al. ). The size and morphology of MNPs-PAC was estimated by scanning electron microscopy (SEM, PHILIPS, XL-30) and transmission electron microscopy (TEM, PHILIPS, EM 208). An X-ray diffractometer (XRD, Quantachrome, NOVA 2000) was used for an X-ray diffraction pattern of a powder of MNPs-PAC at 25 C. The magnetic properties of the adsorbent were investigated with a vibrating sample magnetometer (VSM, Lakeshare, USA 7400) at room temperature. The specific surface area and pore volume of MNPs-PAC were measured W
RESULTS AND DISCUSSION Properties of synthesized MNPs-PAC In order to characterize the crystal phase of iron oxide particles, the MNPs-PAC was analyzed by XRD in the 2θ in the region of 10–70 at 25 C (λ ¼ 1.54 Å). Figure 1(a) shows the XRD pattern for the adsorbent. According to JCPDS No. 01-088-0866 the highest peak of 35.5 corresponds to 511 planes confirming the presence of Fe3O4 particle crystals with a cubic structure. The pores with different sizes and shapes in Figure 1(b) indicate that W
W
W
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Figure 1
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(a) XRD pattern of Fe3O4-loaded PAC, (b) SEM image of MNPs-PAC and (c) TEM image of Fe3O4 particles.
their distribution on the surface of the adsorbent was approximately uniform. The TEM micrograph of MNPsPAC shows the iron oxide particles with an average diameter of 30–80 nm; see Figure 1(c). Figure 2(a) shows the VSM magnetization curve of the prepared adsorbent at 25 C in the magnetic field of ±10 kOe. Maximum saturation of magnetization was about 6.94 emu/g which exhibits super-paramagnetic characteristic (Depci ). These results also indicated that the MNPs-PAC showed an excellent magnetic response to a magnetic field. Therefore, it could be separated easily and rapidly due to this high magnetic sensitivity. W
The N2 adsorption–desorption isotherms, volume and pore size distribution for MNPs-PAC after application of the BET method are shown in Figure 2(b), (c). According to Figure 2(c) the average pore size was 3.5 nm. On the basis of IUPAC classification (micropores (d < 2 nm), mesopores (2 < d < 50 nm) and macropores (d > 50 nm), it could be classified into mesopores group (Huang et al. ). The total pore volume obtained at p/p0 ¼ 0.99 by BET and BJH were 4.87 cc/g and 3.7 cc/g respectively. The results of the BET analysis also indicated that the highest surface area of adsorbent was 671.2 m2/g, which is slightly less than that of PAC (733 m2/g) (Do
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Figure 2
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Magnetic Fe3O4@C nanoparticles for amoxicillin removal
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(a) VSM magnetization curve of MNPs-PAC, (b) the nitrogen adsorption–desorption isotherms and (c) volume and pore size distribution for MNPs-PAC.
et al. ). This could be due to the filling of pores of PAC by MNPs. Effect of solution pH The variation of the adsorption capacity with pH follows a bell-shape pattern in the pH range of 3–9, and then it remains relatively flat up to pH11; see Figure 3(a). The highest adsorption capacity was obtained at pH 5. By increasing the pH from 2 to 5, the carboxyl functional groups (–COOH) present in the AMX molecules are readily dissociated to carboxylate ions (–COO) and subsequently the electrostatic attraction between the AMX molecules and the PAC surface increases (Putra et al. ; Moussavi et al. ). However, at higher pH, the
PAC surface is negatively charged, therefore the electrostatic repulsion between the negatively charged adsorbed ions and negatively charged adsorbent surface lead to the reduction of the AMX adsorption onto MNPs-PAC. In alkaline solution a shift from cationic to anionic species may occur, so the electrostatic (hydrophobic) interactions may play a major role in the adsorption of AMX on MNPs-PAC surface at pH 5 (Xu et al. ). To take all the above mentioned matters into consideration, pH 5 was selected as the optimum pH for the future adsorption experiments. It is worth noting that the optimum pH in the range of 5–6 was reported by the other researchers studying AMX adsorption on different adsorbents as well (Moussavi et al. ).
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Figure 3
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Magnetic Fe3O4@C nanoparticles for amoxicillin removal
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The effect of (a) pH and (b) contact time on AMX adsorption by MNPs-PAC, T ¼ 20 C, C0 ¼ 50 mg/L and m ¼ 1 g/L; and (c) the effect of adsorbent dosage (1–5 g/L) and AMX initial concentration (50–300 mg/L) on the removal efficiency of AMX by MNPs-PAC, T ¼ 20 C, pH ¼ 5 and t ¼ 90 min. W
W
Effect of contact time The contact time between adsorbate and adsorbent is the other important parameter that affects the performance of the adsorption process. The effect of contact time on the adsorption capacity of MNPs-PAC for AMX is shown in Figure 3(b). The results indicate that the adsorption capacity increases rapidly during the first 20 min and then keeps increasing at a relatively slow rate by increasing contact time and finally reaches the equilibrium point after 90 min. There were almost no significant changes in the adsorption capacity from 90–180 min. This can be due to the reduced availability of AMX molecules to active sites on the MNPs-
PAC surface, which is in agreement with the phenomenon noted by other researchers in the study of some antibiotic removal (Wang et al. ). In the study of AMX adsorption on activated carbon, the equilibrium time of 100 min was reported (Moussavi et al. ). The main reason for the fast absorption rate was attributed to a large surface area on MNPs-PAC that could supply a large number of active sites available for AMX (Naghizadeh et al. ). Impact of adsorbent dose and initial AMX concentration Figure 3(c) shows the effect of adsorbent dose and initial AMX concentration on the uptake of AMX by MNPs-PAC
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under the optimum condition (pH ¼ 5, t ¼ 90 min). According to the Figure 3(c), it can be seen that the removal efficiency was increased with enhancement of the adsorbent dose from 1 to 5 g/L. This observation arises from the increasing adsorbent surface area and the availability of AMX molecules to adsorption active sites. Figure 3(c) also shows that with the rise in initial concentration from 50 to 300 mg/L, at adsorbent dosage of 1 g/L, the removal efficiency decreased from 95.26 to 44.22%. In the study of aniline adsorption on the MNPs-PAC reported that the rise in the adsorption capacity is also relevant to the rise in initial pollution concentration gradient (Kakavandi et al. ).
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Table 1
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ln(qe qt ) ¼ ln qe k1 t
(2)
where, qe and qt (mg/g) are the amounts of AMX adsorbed at equilibrium at a given time t (min) respectively, and k1 (min1) is the pseudo-first-order rate constant. The pseudo-second-order kinetic model can be expressed as follows (Naghizadeh et al. ): t 1 1 ¼ þ t qt k2 q2e qe
(3)
where, k2 (g mg1 min1) is the rate constant of the pseudosecond-order adsorption. The intra-particle diffusion equation can be expressed as follows: qt ¼ ki t0:5 þ Ci
(4)
where, both ki (mg/g min0.5) and Ci (mg/g) represent the boundary layer effects. In Equation (4), if Ci is equal to zero, intra-particle diffusion will be the only controlling step. By contrast, the values of C ≠ 0 suggest that the adsorption process is partly complex and involves more than one diffusive resistance (Rodríguez et al. ). Kinetic constants obtained by the linear regressions of the three models are depicted in Table 1. The calculated amount of qe derived from the pseudo-first-order model
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Kinetic model parameters for AMX adsorption onto the MNPs-PAC
Kinetic models
Constants
qe,exp (mg/g)
47.8
qe,cal (mg/g) K1 (min1)
15.06 0.04
Pseudo-first-order
R2
0.656
Pseudo-second-order qe,cal K2 (g/mg)(min)1 R2
50 0.009 0.999
ki (mg/g min0.5) Ci (mg/g) R2
0.784 39.02 0.878
Intraparticle diffusion
Adsorption kinetic studies To investigate the mechanism of AMX adsorption on the MNPs-PAC, three kinetic models (pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetic models) were considered in order to find the best fitted model for the experimental data. The pseudo-first-order model is expressed by the following equation (Zhu et al. ):
|
is not coherent with the experimental data. But good agreement is obtained when qe has been calculated according to pseudo-second-order model. In addition, the suitability of data deducted from the pseudo-secondorder confirms that the rate-limiting step in adsorption of AMX by MNPs-PAC might be coming from electrostatic attraction phenomenon (Budyanto et al. ). As observed in Table 1, the value of Ci was measured 39.02 mg/g, indicating that intra-particle diffusion is not the only controlling step for AMX adsorption and the process is controlled by boundary layer diffusion to some degree (Zhu et al. ). Adsorption equilibrium studies The adsorption isotherm is important for the design of adsorption system. It expresses the relationship between adsorbate and adsorbent at constant temperature. In this study, Langmuir, Freundlich and Temkin isotherms were used to describe the equilibrium between the adsorbed amounts of AMX on the MNPs-PAC (qe) and AMX concentration in the solution (Ce). The Langmuir adsorption isotherm assumes that the reaction has a constant freeenergy change (ΔG ads) for all sites and each site is also assumed to be capable of binding to one molecule of adsorbate. The linear form of the Langmuir isotherm equation is: W
Ce Ce 1 ¼ þ qe q0 k L q0
(5)
where q0 (mg/g) is the maximum adsorbent-phase concentration of adsorbate when the surface site is saturated with
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adsorbate and kL (L mg1) is the Langmuir adsorption constant. The dimensionless constant (separation factor, RL) expresses the characteristics of the Langmuir isotherm as follows:
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Table 2
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Parameters of adsorption equilibrium isotherms for adsorption of AMX onto the MNPs-PAC at different temperatures T (K)
Isotherm models
293
308
323
qm (mg/g)
142.85
135.13
123.45
KL (L/mg)
0.08
0.05
0.043
0.994
0.9825
0.9813
0.04–0.2
0.062–0.285
0.072–0.317
Langmuir
1 RL ¼ 1 þ kL C0
(6)
where C0 is the initial solute concentration. The adsorption will be favorable if the RL is between 0 and 1. The RL > 1 values indicate unfavorable adsorption and for RL of 1 and 0, the adsorptions are linear and irreversible, respectively (Kakavandi et al. ). The Freundlich isotherm is an empirical equation that assumes that the adsorption process occurs on heterogeneous surfaces with non-uniform distribution of adsorption heat. The linear form of Freundlich isotherm equation is as follows: 1 ln qe ¼ ln kF þ ln Ce n
RL Freundlich KF (mg/g(L mg)1/n)
40
32.4
27.34
n
4.45
3.87
3.71
R2
0.996
0.9901
0.9928
4.564
2.03
1.352
Temkin kT
117.06
bT R2
12.64
0.946
137.08
0.9435
0.954
(7)
where kF is a Freundlich adsorption capacity parameter (mg/g) (L/mg)1/n and 1/n is the Freundlich adsorption intensity parameter (relating to the heterogeneity factor), which is unitless. The values of n indicate that the type of adsorption is favorable in the range of 2–10, moderate in the range of 1–2 and poor if n < 1 (Hameed et al. ). The Temkin isotherm model proposed the impact of some indirect adsorbent–adsorbate interactions on adsorption isotherms (Li et al. ). The linear form of the Temkin isotherm model is as follows: qe ¼ B ln kT þ B ln (Ce )
R
2
indicating that the adsorption of AMX on the MNPsPAC had a favorable Langmuir isotherm fit too, but the adsorption isotherm models were fitted into the data in the order of: Freundlich > Langmuir > Temkin isotherm. Putra et al. reported that the Langmuir and Freundlich isotherm models were the best isotherm for AMX adsorption on activated carbon (Putra et al. ). Figure 4(a) also suggests that equilibrium data from AMX adsorption experiments are in high accordance with the Langmuir and Freundlich equilibrium isotherms. The effect of temperature and adsorption thermodynamic studies
(8)
where kT is the equilibrium binding constant corresponding to the maximum binding energy, B ¼ RT/bT, bT (J/mol) is the Temkin constant related to the heat of adsorption, R (8.314 J/mol K) is the universal gas constant and T (K) is solution temperature. The values of equilibrium model parameters presented in Table 2 show that the equilibrium adsorption data were well described by Freundlich and Langmuir isotherms compared to the Temkin isotherm based on R 2. The Freundlich adsorption heterogeneity factors (n values) were in the range of 4.28–3.71, at 293–323 K, indicating that AMX was favorably adsorbed by MNPsPAC. The values of RL also were between 0 and 1,
As shown in Figure 4(b), the AMX adsorption by MNPsPAC decreases with an increase in the temperature from 20–50 C, which is similar to the results obtained by other researchers (Homem et al. ; Xu et al. ). The relationship of the thermodynamic parameters such as change in free energy (ΔG ), enthalpy (ΔH ), and entropy (ΔS ) is expressed according to the following Equation 9 (Kakavandi et al. ): W
W
W
W
ΔS ΔH R RT W
ln kd ¼
W
(9)
where, kd (L/mg) is the distribution coefficient, i.e., the ratio of equilibrium concentration of AMX on adsorbent
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5.6 kJ/mol for the temperature range 20–50 C. The negative values of ΔG demonstrate the spontaneous nature of the adsorption process. The negative ΔG values also determine that the reaction rate decreases with an increase in the temperature. Furthermore, the ΔG values become greater as the temperature increases from 20 to 50 C, which suggests that the adsorption process is not favorable at higher temperatures. The ΔS value was found to be 63.21 J/mol.K. This value suggests the drop in the degree of freedom by the adsorbed species. It also indicates that there is no structural change at solid–liquid interface and the adsorption process looks stable (Kamari & Ngah ). W
W
W
W
W
W
CONCLUSION The present study demonstrated that the AMX removal using MNPs-PAC increases as both the adsorbent dosage and contact time increase, and it decreases when the initial concentration of AMX and the temperature are increased. The optimum conditions obtained for the adsorption are as follows: pH5, contact time of 90 min, adsorbent dosage of 1 g/L and a temperature of 20 C. According to the Langmuir model, the maximum adsorption capacity was 142.85 mg/g. Studying Freundlich and Langmuir equilibrium isotherms at different temperatures showed that the adsorption of AMX on the MNPs-PAC went very well, following both models with a fairly good coefficient correlation (R 2 > 0.98). Having applied a large amount of PAC for the removal of contaminants from aqueous solutions, we magnetized it with the aim of accelerating the separation process and also avoiding filtration. W
Figure 4
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The adsorption isotherms (a) and (b) the effect of solution temperature on the adsorption of AMX by MNPs-PAC, m ¼ 1 g/L, pH ¼ 5 and t ¼ 90 min.
(mg/g) to that in solution (mg/L). The parameters ΔH and ΔS can be computed from the intercept and slope of vant Hoff plots of ln Kd versus 1/T, respectively. The standard free energy (ΔG ) can be calculated using the equation: W
W
W
ΔG ¼ RT ln kd W
(10)
The values of ΔH for AMX adsorption on MNPs-PAC were determined as 26.01 kJ/mol. This indicates that the adsorption process was exothermic in nature. The calculated ΔG values were found to be in the range of 7.49 to W
W
REFERENCES Ai, L., Zhou, Y. & Jiang, J. Removal of methylene blue from aqueous solution by montmorillonite/CoFe2O4 composite with magnetic separation performance. Desalination 266, 72–77. Baciogliu, I. A. & Otker, M. Treatment of pharmaceutical wastewater containing antibiotics by O3 and O3/H2O2 processes. J. Chemosphere 50, 85–95. Bendesky, a., Menéndez, D. & Ostrosky-Wegman, P. Is metronidazole carcinogenic? Mutat. Res-Rev. Mutat. 511, 133–144. Budyanto, S., Soedjono, S., Irawati, W. & Indraswati, N. Studies of adsorption equilibria and kinetics of amoxicillin from simulated wastewater using activated carbon and natural bentonite. J. Environ. Prot. Sci. 2, 72–80.
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B. Kakavandi et al.
|
Magnetic Fe3O4@C nanoparticles for amoxicillin removal
Depci, T. Comparison of activated carbon and iron impregnated activated carbon derived from Golbaş ı lignite to remove cyanide from water. J. Chem. Eng. 181–182, 467–478. Do, M. H., Phan, N. H. & Nguyen, T. D. Activated carbon/ Fe3O4 nanoparticle composite: Fabrication, methyl orange removal and regeneration by hydrogen peroxide. J. Chemosphere 85, 1269–1279. Hameed, B. H., Mahmoud, D. K. & Ahmad, A. L. Equilibrium modeling and kinetic studies on the adsorption of basic dye by a low-cost adsorbent: coconut (Cocos nucifera) bunch waste. J. Hazard. Mater. 158, 65–72. Homem, V., Alves, A. & Santos, L. Amoxicillin removal from aqueous matrices by sorption with almond shell ashes. Int. J. Environ. Analyt. Chem. 90, 1063–1084. Huang, L., Sun, Y., Wang, W., Yue, Q. & Yang, T. Comparative study on characterization of activated carbons prepared by microwave and conventional heating methods and application in removal of oxytetracycline (OTC). J. Chem. Eng. 171, 1446–1453. Iram, M., Guo, C., Guan, Y., Ishfaq, A. & Liu, H. Adsorption and magnetic removal of neutral red dye from aqueous solution using Fe3O4 hollow nanospheres. J. Hazard. Mater. 181, 1039–1050. Kakavandi, B., Jonidi, A., Rezaei, R., Nasseri, S., Ameri, A. & Esrafily, A. Synthesis and properties of Fe3O4-activated 3 carbon magnetic nanoparticles for removal of 4 aniline from aqueous solution: equilibrium, kinetic 5 and thermodynamic studies. Iran. J. Environ. Heal. Sci. Eng 10, 1–9. Kamari, A. & Ngah, W. S. W. Isotherm, kinetic and thermodynamic studies of lead and copper uptake by H2SO4 modified chitosan. Colloids Surf. B: Biointerfaces 73, 257–266. Li, S., Li, X. & Wang, D. Membrane (RO-UF) filtration for antibiotic wastewater treatment and recovery of antibiotics. J. Sep. Puri. Tech 34, 109–114. Li, K., Zheng, Z., Huang, X., Zhao, G., Feng, J. & Zhang, J. Equilibrium, kinetic, thermodynamic studies on the adsorption of 2-nitroaniline onto activated carbon prepared from cotton stalk fibre. J. Hazard. Mater. 166, 213–220. Liu, H., Liu, W., Zhang, J., Zhang, C., Ren, L. & Li, Y. Removal of cephalexin from aqueous solutions by original and Cu(II)/Fe(III) impregnated activated carbons developed from lotus stalks Kinetics and equilibrium studies. J. Hazard. Mater. 185, 1528–1235. Moussavi, G., Alahabadi, A., Yaghmaeian, K. & Eskandari, M. Preparation, characterization and adsorption potential
Water Science & Technology
|
69.1
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of the NH4Cl-induced activated carbon for the removal of amoxicillin antibiotic from water. J. Chem. Eng. 217, 119–128. Naghizadeh, A., Nasseri, S., Rashidi, A. H., Rezaei, R., Nabizadeh, R. & Mahvi, A. H. Adsorption kinetics and thermodynamics of hydrophobic Natural Organic Matters (NOMs) removal from aqueous solution by multi-wall carbon nanotubes. J. Water Sci. Tech: Water Sup 13 (2), 273–285. Pan, X., Deng, C., Zhang, D., Wang, J., Mu, G. & Chen, Y. Toxic effects of amoxicillin on the photosystem II of Synechocystis sp. characterized by a variety of in vivo chlorophyll fluorescence tests. Aquat. Toxicol. 89, 207–213. Putra, E. K., Pranowo, R., Sunarso, J., Indraswati, N. & Ismadji, S. Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: mechanisms, isotherms and kinetics. J. Water Res. 43, 2419–2430. Rivera-Utrilla, J., Prados-Joya, G., Sánchez-Polo, M., Ferro-García, M. A. & Bautista-Toledo, I. Removal of nitroimidazole antibiotics from aqueous solution by adsorption/ bioadsorption on activated carbon. J. Hazard. Mater. 170, 298–305. Rodríguez, A., García, J., Ovejero, G. & Mestanza, M. Adsorption of anionic and cationic dyes on activated carbon from aqueous solutions: equilibrium and kinetics. J. Hazard. Mater. 172, 1311–1320. Shariati, S., Faraji, M., Yamini, Y. & Rajabi, A. A. Fe3O4 magnetic nanoparticles modified with sodium dodecyl sulfate for removal of safranin O dye from aqueous solutions. Desalination 270, 160–165. Trovo, A. G., Pupo Nogueira, R. F., Aguera, A., Fernandez-Alba, A. R. & Malato, S. Degradation of the antibiotic amoxicillin by photo-Fenton process – Chemical and toxicological assessment. J. Wat. Res 45, 1394–1402. Wang, G., Wu, T., Li, Y., Sun, D., Wang, Y., Huang, X., Zhang, G. & Liu, R. Removal of ampicillin sodium in solution using activated carbon adsorption integrated with H2O2 oxidation. J. Chem. Tech. Biotech. 87, 623–628. Xu, L., Dai, J., Pan, J., Li, X., Huo, P., Yan, Y., Zou, X. & Zhang, R. Performance of rattle-type magnetic mesoporous silica spheres in the adsorption of single and binary antibiotics. J. Chem. Eng. 174, 221–230. Zhu, H-Y., Jiang, R., Xiao, L. & Li, W. A novel magnetically separable γ-Fe2O3/crosslinked chitosan adsorbent: Preparation, characterization and adsorption application for removal of hazardous azo dye. J. Hazard. Mater. 179, 251–257.
First received 27 May 2013; accepted in revised form 25 September 2013. Available online 24 October 2013
