- Email: [email protected]
bentonite composite
International Journal of Biological Macromolecules 115 (2018) 580–589
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac
Simultaneous adsorption of Cu2+ and Acid fuchsin (AF) from aqueous solutions by CMC/bentonite composite Ning Gong 1, Yanping Liu 1, Ruihua Huang ⁎ College of Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi 712100, China
a r t i c l e
i n f o
Article history: Received 22 November 2017 Received in revised form 29 March 2018 Accepted 11 April 2018 Available online 21 April 2018 Keywords: CMC/bentonite composite Binary systems Adsorption Kinetic
a b s t r a c t Carboxymethyl-chitosan (CMC)/bentonite composite was prepared by the method of membrane-forming, and characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The simultaneous adsorption of Cu2+ and Acid fuchsin (AF) applying CMC/bentonite composite as an adsorbent in single or binary systems was investigated. The adsorption study was conducted systematically by varying the ratio of CMC to bentonite, adsorbent dosage, initial pH value, initial Cu2+ (or AF) concentration, contact time and the interaction of two components in binary solutions. The results showed that the presence of Cu2+ hindered the adsorption of AF, while the presence of AF almost had no influence on the adsorption of Cu2+ in binary systems. The adsorption data of Cu2+ and AF were both suitable for Langmuir isotherm model, and the maximum adsorption capacities of CMC/bentonite composite, according to the Langmuir isotherm model were 81.4 mg/g for Cu2+ and 253.2 mg/g for AF at 298 K. The pseudo-second-order model could better describe the adsorption process of Cu2+ and AF. Thermodynamic constant values illustrated that the adsorption of Cu2+ was endothermic, while the adsorption process of AF was exothermic. © 2018 Published by Elsevier B.V.
1. Introduction The treatment of industrial wastewater containing dyes has been a global problem. Their presence, even in small quantities, causes changes in terms of water color and reduces the amount of light that reaches the aquatic environment [1]. The wastewater containing dyes was mainly discharged from these industries such as textile industry, paint industry, paper industry, pharmaceutical industry, printing, leather industry, etc. However, the wastewaters from these industries do not contain only dyes as pollutants; the heavy metals can be also found in significant quantities, especially in textile industry. Copper is an essential element for the human beings, although large acute doses can be harmful and even cause a fatal effect. Its carcinogenic and mutagenic properties lead to health problems such as lung cancer, lesions in the central nervous system [2]. Additionally World Health Organization (WHO) has recommended a maximum acceptable concentration of 1.5 mg/L of Cu2+in drinking water [3]. For these reasons, these pollutants must be removed from industrial effluents before discharging into the environment. Many techniques have been developed for the disposal of both dyes and heavy metals from wastewater such as coagulation, precipitation, ⁎ Corresponding author at: Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi 712100, China. E-mail address: [email protected]. (R. Huang). 1 Both authors contributed equally to this work.
https://doi.org/10.1016/j.ijbiomac.2018.04.075 0141-8130/© 2018 Published by Elsevier B.V.
separation trough membranes [4–6], biological treatments, and adsorption [7–13]. Among these methods, adsorption is considered as a superior technique due to its high efficiency, low cost of implementation, ample availability and simplicity in terms of design. Chitosan derivatives have been extensively investigated as adsorbents and applied in the treatment of wastewater containing both dyes and heavy metals. Among them are chitosan derivatives containing nitrogen, phosphorus and sulfur as heteroatoms, and other derivatives such as quaternized chitosan, carboxymethyl chitosan. Carboxymethyl chitosan (CMC) is a water-soluble chitosan derivative, which contains hydroxyl (OH), carboxyl (COOH) and amine (NH2) groups in the molecule, and makes it possible to offer enough chelate groups for increasing adsorption capacity toward metal ions such as copper ion. Recently, chitosan composites have been developed to adsorb heavy metals and dyes from wastewater. Different kinds of substances have been used to form composite with chitosan such as montmorillonite [14,15], clay [16], bentonite [17–19], polyvinyl alcohol, polyvinylchloride, and perlite. Bentonite, as a mineral clay, has been highlighted for the preparation of chitosan composites because of its high cationic exchange capacity and the possibility of lamellar expansion, which provides greater versatility in the interaction and intercalation of chitosan or its derivatives. These composites have been studied and targeted for environmental applications such as the adsorption of heavy metals, dyes and herbicides. Though the carboxymethyl-chitosan/clay composites as adsorbents have been reported previously, many studies were focused on the adsorption of dyes, heavy metals and pesticides in single systems
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
581
Fig. 1. FTIR spectra of bentonite, CMC/bentonite composite and the CMC/bentonite composite samples after AF and Cu2+ adsorption.
[20,21]. However, as we known, different dyes and heavy metals are often present together in many practical industrial effluents, thus more attention should been paid to the study of their simultaneous adsorption. At present, to the best of our knowledge, only limited data are available for multicomponent adsorption, thus it is of great significance to investigate the simultaneous adsorption of dyes and heavy metals. In this work, CMC/bentonite composite was prepared and characterized by FTIR and XRD techniques. Acid fuchsin (AF) is widely used in dyeing textile fabrics, silk, nylon, wool and leather. Cu2+ and Acid fuchsin (AF) were chosen as model heavy metal and dye pollutants, respectively. To understand the simultaneous removal of AF and Cu2+ as well as their single adsorption from aqueous solution onto this composite, major adsorption factors including the ratio of CMC to bentonite, adsorbent dosage, AF and Cu2+ concentration, pH and contact time were investigated. The corresponding adsorption kinetics and isotherms were also examined. 2. Experimental 2.1. Materials Chitosan (CTS) [weight-average molecular weight (MW) = 100,000 Da, degree of deacetylation (dd) = 90%] was purchased from the Sinopharm Group Chemical Reagent Limited Company (China). Bentonite powder with a particle size of 200-mesh was acquired from the chemical factory of Shentai, Xinyang, Henan, China. Monochloroacetic acid was obtained from Tianjin Chemical Reagent Co., China. The molecular weight of AF (Tianjin Kermel Chemical Reagent Co., China) is 585.54 g/mol. Other agents used were all analytical grade and all solutions were prepared with distilled water.
50 wt% sodium hydroxide solution (50.00 mL) and stirred for 1 h at room temperature, and then frozen overnight. The unfrozen CTS was dipped into 80 mL of isopropanol in a three-necked flask by stirring for 30 min at room temperature, then monochloroacetic acid (6.00 g) was added at three times into the reaction mixture for another 30 min. Then the mixture was heated to 60 °C and allowed to continue for 4 h. Finally, the resultant solution was filtered and the filter cake was washed with 80% (v/v) ethanol for many times and isopropanol once, then dried under vacuum at 60 °C to obtain products.
2.2.2. Preparation of CMC/bentonite composite CMC solution was prepared by dissolving 1.0 g CMC in 50 mL distilled water, and then 1.0 g bentonite was slowly added to CMC solution followed by stirring at room temperature for 6 h to obtain the mixture. The mixture was uniformly coated in petri-dishes, and allowed to stay at 60 °C in an oven to form membranes. Subsequently, these membranes were cross-linked at 60 °C for 5 h with 2.5 wt% glutaraldehyde which was dissolved in anhydrous ethanol. Finally, the cross-linked CMC/bentonite composite was washed using distilled water to remove any free glutaraldehyde and dried in an oven at 60 °C for 24 h. After drying, the composite was ground and sieved. The composite with
2.2. Preparation of CMC/bentonite composite 2.2.1. Preparation of CMC Carboxymethyl chitosan (CMC) was prepared with some modifications according to Sun and Wang [22]. CTS (5.00 g) was added to a
Fig. 2. XRD patterns of bentonite and CMC/bentonite composite.
582
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
The determination of the pHZPC of the sample was determined according to the method described by the solid addition method [23]. 50 mL of 0.1 mol/L NaCl solutions were placed in 150 mL conical flasks. Initial pH of 0.1 mol/L NaCl solutions (pHi) was adjusted from pH 2 to 10 by adding either 0.1 mol/L HCl or 0.1 mol/L NaOH solutions and final pH (pHf) of solution was measured. The difference between the initial and final pH (pHf − pHi) was plotted against the initial pH (pHi) and the point where pHf − pHi = 0 was thought to be the zero point of charge (pHZPC) of adsorbent. 2.4. Batch experiments
Fig. 3. Effect of ratio of CMC to bentonite on Cu2+ and AF adsorption. Adsorption conditions: adsorbent dosage: 0.1 g; at 298 K and natural pH; contact time: 60 min; 50 mg/L Cu2+ and 50 mg/L AF, respectively, in single solution.
100 mesh of particle size was collected and utilized for the batch experiments.
Removal=% ¼
2.3. Characterization FTIR spectra of the samples were characterized using a FTIR Spectrophotometer (Shimadzu 4100) in KBr pellets in the wavenumber range of 400–4000 nm−1. XRD analyses of the powdered samples were measured by an X-ray powder diffractometer (Shimadzu XD3A diffractometer) with Cu target and K∝ radiation (λ = 0.15418 nm) at 40 kV and 30 mA. The scanning rate was 2°/min and the scanning scope of 5–40°. The interlayer of layered silicate and the composite can be calculated by using Bragg's equation: nλ ¼ 2d sinθ
To evaluate the adsorption capacity of CMC/bentonite composite, CMC/bentonite composite was placed in a 250 mL Erlenmeyer flask containing 50 mL aqueous solution of AF and Cu2+. The flask was then shaken at 200 rpm at 25 °C. The factors affecting the adsorption of AF and Cu2+ including adsorbent dosage, initial pollutant concentration, contact time, and pH value were investigated. After shaking for a certain period of time, the suspensions were filtered. The supernatants were then collected and analyzed for Cu2+ concentration with a flame atomic adsorption spectrophotometer (Varian, Spectra AA 240), and for AF with a UV–vis spectrophotometer at 546 nm (754 N, Shanghai, China). The removal for AF (or Cu2+) on adsorbent was calculated according to Eq. (2):
ð1Þ
where n is an integer (n = 1); λ is the wavelength of incident wave (λ = 0.15418 nm); d is the spacing between the planes in the atomic lattice and θ is the angle between the incident ray and the scattering planes.
C 0 −C t 100% C0
ð2Þ
where C0 is the initial concentration (mg/L) and Ct is the concentration (mg/L) at any time, t. The value for qt (mg/g) is the amount of adsorbate adsorbed per amount of adsorbent (mg/g) at any time, t was calculated as follows: qt ¼
ðC 0 −C t Þ V m
ð3Þ
where V was the solution volume and m is the mass of the adsorbent. 2.5. Adsorption isotherms Most adsorption data can be adequately expressed using either the Langmuir or Freundlich models. The Langmuir isotherm is used to describe adsorption phenomena and is based on the assumption that adsorption occurs on a homogenous surface by monolayer sorption
Fig. 4. Effect of adsorbent dosage on Cu2+ and AF adsorption. Adsorption conditions: adsorbent dosage: 0.03–0.15 g; at 298 K and natural pH; contact time: 60 min; 50 mg/L Cu2+ and 50 mg/L AF, respectively, in binary solutions.
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
583
Fig. 5. Effect of initial Cu2+ (or AF) concentration on Cu2+ (or AF) adsorption. Adsorption conditions: adsorbent dosage: 0.08 g; at 298 K and natural pH; contact time: 60 min; Cu2+ and AF concentrations from 50 to 500 mg/L, in single solutions.
without interaction between adsorbed molecules. The linearized Langmuir equation is given as [24]: Ce 1 Ce þ ¼ qe Qb Q
ð4Þ
The Freundlich isotherm model is an empirical equation valid for adsorption on the assumption that this process occurs on heterogeneous surfaces and the solid-phase surfaces possess differing adsorption sites. The linearized Freundlich equation was expressed as [26]: logqe ¼ logK f þ
where Q is the maximum amount of adsorption with complete monolayer coverage on the adsorbent surface (mg/g) and b is the Langmuir constant, which is related to the energy of adsorption (L/mg). The constants Q and b can be determined from the slope and the intercept of the linear plot of Ce/qe against Ce. The essential features of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor (RL) defined by the relationship [25]: RL ¼
1 1 þ bC 0
ð5Þ
1 logC e n
where Kf [(mg/g)(L/mg)1/n] and n are Freundlich constants related to adsorption capacity and heterogeneity factor, respectively. 2.6. Adsorption kinetics In this study, the first-order and pseudo-second-order kinetic models were used to describe the adsorption of AF (or Cu2+) on this adsorbent. The linearized pseudo-first-order kinetic model was given as [27]: logðqe −qt Þ ¼ logqe −
where C0 is the initial pollutant concentration in (mg/L) and b is the Langmuir equilibrium constant (L/mg). The value of the separation factor provides important information about the nature of the adsorption process. The adsorption is said to be irreversible (RL = 0), favorable (0 b RL b 1), linear (RL = 1) or unfavorable (RL N 1).
ð6Þ
k1 t 2:303
ð7Þ
where qe and qt are the amounts (mg/L) of AF (or Cu2+) adsorbed at equilibrium and at time t, respectively, k1 is the pseudo-first-order rate constant (min−1). The k1 and qe were calculated from the slope and intercept of plots of log(qe − qt) versus t, respectively.
Fig. 6. Effect of initial pH on Cu2+ (or AF) adsorption. Adsorption conditions: adsorbent dosage: 0.08 g; at 293 K and natural pH; contact time: 60 min; 100 mg/L Cu2+ and 100 mg/L AF, respectively, in binary solutions.
584
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
Fig. 7. Effect of contact time on Cu2+ (or AF) adsorption. Adsorption conditions: adsorbent dosage: 0.08 g; at 293 K and natural pH; contact time: 0–80 min; Cu2+ concentrations: 100, 150 and 200 mg/L.; AF concentrations: 100, 200 and 300 mg/L.
The pseudo-second-order kinetic model can be expressed by the following equation [28]: t 1 1 ¼ þ t qt k2 qe 2 qe
ð8Þ
where qe (mg/g) and qt (mg/g) are the amounts of adsorbed AF (or Cu2+) at equilibrium and at time t, respectively; k2 (g/mg/min) is the rate constant for the pseudo-second-order model. The values for qe and k2 can be determined from the slope and intercept of the plot of t/qt versus t, respectively. 3. Results and discussions 3.1. FTIR spectra analysis FTIR spectra of bentonite, CMC/bentonite composite and the CMC/ bentonite composite samples after AF and Cu2+ adsorption are shown in Fig. 1. Compared with the FTIR spectrum of bentonite, the one of CMC/bentonite composite showed that the adsorption band at 3454 cm−1, corresponding to\\OH stretching vibration of H2O of bentonite, was strengthened and shifted to a lower wave number (3440 cm−1), suggesting the O\\H and N\\H stretching vibrations in CMC overlapped with \\OH stretching vibration of H2O in bentonite.
The asymmetric stretching vibration of the \\CH3 (2934 cm−1) of CMC was also observed in the FTIR spectrum f CMC/bentonite composite. In addition, the adsorption band at 1644 cm−1, assigned to \\OH bending vibration of H2O of bentonite, was strengthened and shifted to a lower wave number (1628 cm−1), which indicates the \\COO\\ group asymmetric stretching vibration of CMC overlapped with \\OH bending vibration of H2O of bentonite. At the same time, the \\COO\\ group symmetric stretching vibration (1424 cm−1) and the second \\OH group stretching vibration (1090 cm−1) of CMC were observed in the FTIR spectra of CMC/bentonite composite. Besides, the other characteristic peaks of bentonite also appeared in both spectra, i.e., the peak at 521 cm−1 belonged to the angular deformation of Si\\O in the tetrahedral sheet of bentonite; the peaks from 917 to 793 cm−1 corresponded to the octahedral layers of bentonite. The results indicated the forming of CMC/bentonite composite. Comparing to the FTIR spectrum of CMC/bentonite composite, the one of CMC/bentonite composite after Cu2+ adsorption showed the major differences as follows: the absorption band attributed to the asymmetric stretching vibrations of the\\CH3 (2934 cm−1) of CMC was shifted to a lower wave number (2930 cm−1). The absorption band at 1424 cm−1, assigned to the symmetric stretching vibration of \\COO\\ group, was shifted to a lower wave number (1397 cm−1). These results indicates that the \\COO\\ group of CMC was mainly involved in the adsorption process of Cu2+ by CMC/bentonite composite, and the chelation between Cu2+ and
Fig. 8. Interaction of Cu2+ and AF adsorption in binary solutions.
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
585
Fig. 9. Isotherm models for Cu2+ (a and a′) and AF (b and b′) adsorption at different temperatures. (a and b): Langmuir model; (a′ and b′): Freundlich model.
\\COO\\ group in CMC/bentonite composite happened. However, in the spectrum of the CMC/bentonite composite after AF adsorption, the wide absorption band at 3440 cm−1, corresponding to the stretching vibration of NH2 and OH groups, was shifted to a lower wave number (3433 cm−1). The absorption band at 2934 cm−1, assigned to the asymmetric stretching vibrations of \\CH3, showed a shift to lower wave number (2928 cm−1). The absorption band at 1628 cm−1, assigned to the asymmetric stretching vibration of \\COO\\ group, was significantly shifted to a lower wave number (1603 cm−1). These changes indicate that the\\OH and\\COO\\groups in CMC/bentonite composite was involved in the adsorption process of AF.
3.2. X-ray diffraction analysis X-ray diffraction (XRD) is an effective method for the investigation of the intercalation existence of bentonite. Fig. 2 shows that the XRD patterns of bentonite and CMC/bentonite composite. The XRD pattern of bentonite shows a typical diffraction peak at 6.56°, corresponding to a basal spacing of 1.35 nm. After bentonite interacted with CMC, this peak shifted toward a lower angle (6.18°), corresponding to a basal spacing of 1.43 nm. The increasing basal spacing means that CMC had entered into the interlayer of bentonite, and CMC/bentonite composite was obtained.
Table 1 Langmuir and Freundlich isotherm parameters of Cu2+ and AF in single system by CMC/bentonite composite. Isotherms Adsorbates Cu
AF
2+
Langmuir
Freundlich
Temperature (K)
Q (mg/g)
b (L/mg)
R2
RL
Kf (mg/g(L/mg)1/n)
n
R2
298 308 318 298 308 318
81.4 80.7 78.8 253.2 249.4 246.9
0.185 0.183 0.198 0.055 0.056 0.050
0.9996 0.9996 0.9997 0.9996 0.9997 0.9996
0.0133–0.0976 0.0135–0.0985 0.0125–0.0917 0.0351–0.2667 0.0345–0.2632 0.0385–0.2857
35.7 39.6 37.8 29.8 29.4 28.0
6.41 7.55 7.24 2.47 2.47 2.45
0.990 0.996 0.993 0.977 0.961 0.963
586
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
Fig. 10. Kinetic models for Cu2+ (a and a′) and AF (b and b′) adsorption at different temperatures. (a and b): pseudo-first-order kinetic model; (a′ and b′): pseudo-second-order kinetic model.
3.3. Effect of the ratio of CMC to bentonite The effect of the ratio of CMC to bentonite on the removal of AF and Cu2+ is shown in Fig. 3. It is obvious that the amount of CMC is an important factor affecting the adsorption capacity of CMC/bentonite composite. It can be seen that, compared with the single bentonite, CMC/ bentonite composite exhibited higher removal for both AF and Cu2+. The removal for Cu2+ increased with the increase of the ratio of CMC to bentonite till this ratio was 0.3, and increased hardly with further increase of the ratio of CMC to bentonite. It may be explained like this, the amounts of active hydroxyl (\\OH), carboxyl (\\COOH) and amine (\\NH2) groups increased with increasing of the ratio of CMC to
bentonite, which resulted in an increase in the removal of Cu2+ on CMC/bentonite composite due to an increase on the adsorptive sites. However, the removal increased hardly when the ratio exceeded 0.3, which was attributed to the amount of intercalated CMC was saturated. For AF, the removal increased gradually with an increase on the ratio of CMC to bentonite. When introducing CMC, the amount of CMC improved the flocculation capacity of CMC/bentonite composite and facilitated the separation of the adsorbents from the solution [20]. Meanwhile, the increase of active hydroxyl (\\OH), carboxyl (\\COOH) and amine (\\NH2) groups increased when increasing the ratio of CMC to bentonite, which resulted in an increase on the removal of AF by CMC/bentonite composite due to an increase on the adsorptive
Table 2 Kinetic parameters of the adsorption of Cu2+ and AF onto CMC/bentonite composite. Adsorbate
Cu
AF
2+
Concentration (mg/L)
100 150 200 100 200 300
qe (exp)
54.56 63.11 71.06 58.68 109.9 163.3
Pseudo-first-order
Pseudo-second-order
qe (cal)
k1
R2
qe (cal)
k2
R2
20.04 20.32 26.61 9.30 21.93 69.58
0.0760 0.0702 0.0758 0.0610 0.0573 0.0626
0.9867 0.9933 0.9943 0.9923 0.9811 0.9943
55.71 64.27 71.94 59.14 110.9 166.9
0.2004 0.0243 0.0576 0.2007 0.0913 0.0446
0.9998 0.9998 0.9996 0.9999 0.9999 0.9996
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
sites. Considering the removal for AF and Cu2+ and economic cost, the ratio of CMC to bentonite of the composite was selected as 1.
Table 3 Thermodynamic parameters for Cu2+ and AF adsorption onto CMC/bentonite composite. Adsorbate
ΔHθ (kJ/mol)
ΔSθ (kJ/(mol K))
Cu2+ AF
2.811 −3.943
0.0295 0.0162
3.4. Effect of adsorbent dosage The effect of adsorbent dosage, ranging from 0.03 to 0.15 g, on the removal of AF and Cu2+, respectively, is shown in Fig. 4. It can be observed that the removal increased with adsorbent dosage, both for FA and for Cu2+. This was mainly due to an increase in the sorptive surface area and the availability of more active binding sites on the surface of the adsorbent with increase in dosage [29]. This composite shows a sharp increase in Cu2+ removal from 74.3 to 95.8% as the adsorbent dosage increased from 0.03 to 0.05 g. A further increase in adsorbent dosage from 0.05 to 0.15 g had practically an insignificant effect, the removal only increased from 95.8 to 99.5%. For AF, the removal increased sharply from 65.1 to 81.7% as the adsorbent dosage increased from 0.03 to 0.08 g. The removal only increased from 81.7 to 86.3% when increasing in dosage from 0.08 to 0.15 g. However, a reverse trend was obtained as presented in Fig. 4, where a decrease in the adsorption capacity whether for AF or for Cu2+ with increase in adsorbent dosage was recorded. This might be a result of a decrease in the total adsorption surface area available for AF and Cu2+ to bind due to overlapping or aggregation of adsorption sites [30]. Therefore, as the adsorbent dosage increased, the amounts of AF and Cu2+ adsorbed onto a unit mass of CMC/bentonite composite decreased, resulting in the decrease in the adsorption capacity. In the case of the moderate removal for both Cu2+ and AF, 0.08 g of adsorbent dosage was chosen for the following experiments. 3.5. Effect of initial AF (or Cu2+) concentration For this effect, the concentrations of Cu2+ and AF ranging from 50 to 500 mg/L were investigated. The adsorption experiment was conducted for 60 min using 0.08 g of adsorbent dosage at 298 K and 200 pm. The results are shown in Fig. 5. It was observed that the removal for Cu2+ (or AF) decreased with increase in the initial concentration of Cu2+ (or AF). The decrease in removal was due to the fact that all adsorbents have a fixed number of active sites and at higher concentrations the active sites become insufficient. On the other hand, an increase in the adsorption capacity for both Cu2+ and AF with increase in initial concentration was observed as presented in Fig. 5. This results from the increasing concentration gradient which acts like a driving force to overcome the resistance to mass transfer of Cu2+ (or AF) between the adsorbate and adsorbent species [31].
587
ΔGθ (kJ/mol) 298 k
308 k
318 k
−6.31 −8.89
−6.48 −9.23
−6.90 −9.21
3.6. Effect of pH The pH is the most important factor affecting the adsorption process. AF dye is colorless in alkali solution and the hydrolyzation of Cu2+ is prevented, so the range of pH for Cu2+ (or AF) adsorption in this study was selected between 1 and 5. The effect of pH value in the original solution on Cu2+ (or AF) adsorption onto CMC/bentonite composite was investigated and shown in Fig. 6. At the same time, the plot of pHf pHi verse pHi was also presented in Fig. 6. The pHzpc of CMC/bentonite composite was obtained at pH 7.8 or so. When pH value is lower than pHzpc, the surface of CMC/bentonite was positively charged. When the pH value was higher than pHZPC, the surface of CMC/bentonite was negatively charged. As can be observed in Fig. 6, the removal of AF was a little higher at low pH value than those at high pH value, indicating that the adsorption mechanism for AF is influenced by the pH of the solution. It is known that AF, an anionic dye, remained negatively charged throughout the process of testing. At low pH value, the adsorption mechanism of AF was controlled by electrostatic attractions between the positively charged surface of adsorbent, as a result of the protonation process, and the negatively charged AF molecule. With increasing pH values, the number of the negatively charged sites increased, and the number of the positively charged sites decreased, resulting in the reduction of removal for AF at higher pH value. On the contrary, the removal for Cu2+ increased further from 21.6 to 86.2% when pH rose from 1.0 to 4.0. This change can be explained by the competition between H+ and Cu2+ for available adsorption sites at low pH. However, when pH increased, the adsorption of the positively charged Cu2+ through electrostatic attraction was enhanced because of the high negative charge of the surface of CMC/bentonite composite. Moreover, the constant adsorption for both Cu2+ and AF beyond pH 4 was observed. The result suggests the non-electrostatic interactions between the delocalized electrons on the surface of adsorbent and the free electrons in AF molecules were involved in AF adsorption. For Cu2+, the chelation between \\COO\\ and Cu2+ might have a significant contribution to Cu2+ adsorption.
3.7. Effect of contact time
Fig. 11. Plots of lnKL verse 1/T for Cu2+ and AF adsorption.
The contact time between adsorbate and adsorbent is an important parameter in assessing the performance of adsorbents. The shorter the contact time in adsorption process, the lower are the operational costs that recommend the adsorbent for large-scale industrial application. The effect of contact time on AF and Cu2+ adsorption onto CMC/bentonite composite is shown in Fig. 7. It is observed that the removal of AF and Cu2+ from solution was initially rapid and then diminished gradually until an equilibrium time beyond which there was no significant increase in the removal. Equilibrium removal was achieved around 60 min. Hence, a contact time of 60 min was chosen to ensure optimum removal of AF and Cu2+. The initial fast adsorption rate was due to the large number of vacant surface sites available for adsorption in the initial stage of the process. The slow uptake in the later stages was probably attributed to an attachment controlled process caused by less available active sites for adsorption, then, near equilibrium, the available sites for adsorption become difficult to be occupied because of the repulsive forces between the solute molecules on the solid and the solution.
588
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
3.8. Interaction of two components in binary solutions In the multicomponent system, there are three types of effects including synergism, antagonism and non-interaction [32]. 1. Synergism: effect of mixture of component in solution is greater than its individual effect. 2. Antagonism: effect of mixture of component in solution is less than its individual effect. 3. Non-interaction: effect of mixture of component in solution is neither less nor more than that of its individual effect. Interaction of two components in binary mixtures of Cu2+ and AF could be evaluated by the ratio of adsorption capacity of one component in the binary solution (Qmix) to the same component in single solution (Q0) [33]. Qmix/Q0 N 1, synergism; Qmix/Q0 = 1, non-interaction; Qmix/ Q0 b 1, antagonism. In this study, a great number of the values for the ratio of Qmix/Q0 for Cu2+ and AF are presented in Fig. 8. The results showed that the values of Qmix/Q0 for AF were lower than 1 in binary solutions, hence, the presence of Cu2+ showed antagonism effect on the adsorption of AF in the process of adsorption. Besides, the increment of Cu2+ concentrations significantly reduced the uptake of AF in the bi-pollutant system. The antagonism effect became obvious with increasing Cu2+ concentration. However, the values of Qmix/Q0 for Cu2+ were almost 1 or so for all binary systems at tested conditions, suggesting that the adsorption capacity of Cu2+ was not affected by the presence of AF in binary solutions. 3.9. Adsorption isotherm Adsorption isotherm expresses the relationship between the amount of adsorbate removed from the liquid phase by unit mass of adsorbent at a constant temperature. Adsorption isotherms are basic requirements for the design of adsorption systems. The concentrations ranging from 50 to 400 mg/g for Cu 2+ and from 50 to 700 mg/g for AF were tested. Adsorption experiments were performed for 60 min at different temperatures (298, 308 and 318 K). These plots are presented in Fig. 9, and the parameters of isotherm models and correlation coefficients (R2) for Cu 2+ and AF adsorption are depicted in Table 1. As can be seen from Table 1, the values of the correlation coefficient (R2) for Langmuir model are higher than those for Freundlich model. Thus, the Langmuir isotherm gave a better fit to the data than the Freundlich isotherm model for Cu 2+ and AF, suggesting the occurrence of monolayer adsorption by CMC/bentonite composite. Furthermore, for the initial concentration from 50 to 500 mg/g for Cu 2+ and from 50 to 700 mg/g for AF used in this study, the values of RL all ranged from 0 to 1 for both Cu 2+ and AF at three temperatures tested; this indicates a favorable adsorption of Cu2+ and AF onto CMC/bentonite composite. The monolayer adsorption capacity changed from 81.4 to 78.8 mg/g for Cu2+ and from 253.2 to 246.9 mg/g for AF, respectively, when increasing 298 to 318 K. The slight change indicated that the temperature had insignificant effect on the adsorption of Cu2+ and AF onto this adsorbent. It was observed that the adsorption capacity of Cu2+ by CMC/bentonite composite according to Langmuir isotherm was less than that of AF at the same temperature, suggesting CMC/bentonite composite exhibited a stronger binding ability for AF than for Cu2+. 3.10. Adsorption kinetics Adsorption kinetic models were applied to the experimental data in order to analyze the rate of adsorption and possible adsorption mechanism of Cu2+ and AF onto CMC/bentonite composite. Experimental kinetic data of adsorption for Cu2+ using 100, 150, and 200 mg/L solutions and for AF using 100, 200 and 300 mg/L solutions were investigated.
The plots for the kinetic models were illustrated as shown in Fig. 10, and the relative parameters are given in Table 2. From Fig. 10, the experimental data deviated slightly more from the linearity for the pseudo first-order model when compared to the pseudo second-order model, thus the pseudo- second order model provided a good fit to the experimental data of both Cu2+ and AF. This is also indicated by the high values of their linear regression (R2) close to 1. Also when the calculated qe values were compared to those of the experimental qe values, for pseudo first-order model they varied a lot. But in case of the pseudo second-order model both those values almost coincided. Thus the adsorption process followed the pseudo second-order model. 3.11. Adsorption thermodynamic studies The thermodynamic parameters such as the standard free energy change (ΔGθ), enthalpy change (ΔHθ) and entropy change (ΔSθ) were determined based on the following equations: ΔGθ ¼ −RT ln K L ln K L ¼
ΔSθ ΔH θ − R RT
ð9Þ ð10Þ
where KL (L/mol) is the Langmuir constant, R is the universal gas constant, 8.314 J/mol/K, T (K) is the temperature employed in the experiment. The values of ΔHθ and ΔSθ can be obtained from the slope and intercept of a van't Hoff plot of lnKL versus 1 / T. Fig. 11 illustrates the linear relationship between lnKL versus 1 / T and Table 3 shows the parameters of thermodynamics. The values of ΔGθ were all negative at different temperatures, which suggested that the adsorption of Cu2+ and AF onto CMC/bentonite composite could happen spontaneously. Cu2+ had positive ΔHθ values at different temperatures tested, indicating that the reaction was endothermic; while AF had negative ΔHθ values, suggesting that the adsorption process is exothermic. Besides, both Cu2+ and AF maintained positive ΔSθ values, which inferred that the adsorbent had good affinity for Cu2+ and AF. 4. Conclusion CMC/bentonite composite was synthesized by intercalation reaction between CMC and bentonite in distilled water. Simultaneous adsorption tests of Cu 2+ and AF onto CMC/bentonite composite were carried out and the results obtained from this study show that the presence of Cu2+ restrained the adsorption of AF, while the presence of AF hardly affected the adsorption of Cu2+ in binary systems. The kinetic and isotherm studies indicated that the pseudo-second-order model and the Langmuir model well described the adsorption equilibrium of Cu2+ and AF onto CMC/bentonite composite. The maximum adsorption capacities of CMC/bentonite composite were 81.4 mg/g for Cu2+ and 253.2 mg/g for AF at 298 K. Besides, the thermodynamic studies revealed the adsorption of Cu2+ was an endothermic and spontaneous process, while the adsorption of AF was an exothermic and spontaneous process. The results have demonstrated that CMC/bentonite composite could be used as a promising adsorbent and provided a novel method to solve the treatment of Cu2+ and AF. Conflicts of interest The authors declare no conflicts of interests. References [1] G.Z. Kyzas, N.K. Lazaridis, M. Kostoglou, Chem. Eng. J. 248 (2014) 327–336. [2] M.L.P. Dalida, A.F.V. Mariano, C.M. Futalan, C.C. Kan, W.C. Tsai, M.W. Wan, Desalination 275 (2011) 154–159. [3] M.K. Jha, N.V. Nguyen, J.C. Lee, J. Jeong, J.M. Yoo, J. Hazard. Mater. 164 (2009) 948–953. [4] S. Foorginezhad, M.M. Zerafat, Ceram. Int. 43 (17) (2017) 15146–15159.
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589 [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
J. Wang, L. Qin, J. Lin, J. Zhu, B. Van der Bruggen, Chem. Eng. J. 323 (2017) 56–63. X. Wang, Z. Wang, H. Chen, Z. Wu, J. Hazard. Mater. 339 (2017) 182–190. J. He, Y. Li, C. Wang, K. Zhang, J. Liu, Appl. Surf. Sci. 426 (2017) 29–39. H. Peng, P. Gao, G. Chu, B. Pan, B. Xing, Environ. Pollut. 229 (2017) 846–853. P. Tan, Q. Bi, Y. Hu, Z. Fang, J. Cheng, Appl. Surf. Sci. 423 (2017) 1141–1151. Z. Huang, Y. Li, W. Chen, J. Shi, Y. Zhang, Mater. Chem. Phys. 202 (2017) 266–276. A. Shajahan, S. Shankar, A. Sathiyaseelan, K.S. Narayan, S. Ignacimuthu, Int. J. Biol. Macromol. 104 (2017) 1449–1458. I. Belbachir, B. Makhoukhi, J. Taiwan Inst. Chem. Eng. 75 (2017) 105–111. R. Fabryanty, C. Valencia, F.E. Soetaredjo, J.N. Putro, S. Ismadji, J. Environ. Chem. Eng. 5 (6) (2017) 5677–5687. F.A.R. Pereira, K.S. Sousa, G.R.S. Cavalcanti, D.B. França, L.N.F. Queiroga, I.M.G. Santos, M.G. Fonseca, M. Jaber, J. Environ. Chem. Eng. 5 (4) (2017) 3309–3318. C. Hu, G. Li, Y. Wang, F. Li, H. Hu, Int. J. Biol. Macromol. 103 (2017) 751–757. E.M.S. Azzam, G. Eshaq, A.M. Rabie, A.A. Bakr, S.M. Tawfik, Int. J. Biol. Macromol. 89 (2016) 507–517. P.V. Haseena, K.S. Padmavathy, P. Rohit Krishnan, G. Madhu, Procedia Technol. 24 (2016) 733–740. G.L. Dotto, F.K. Rodrigues, E.H. Tanabe, R. Fröhlich, E.L. Foletto, J. Environ, Chem. Eng. 4 (3) (2016) 3230–3239.
589
[19] M.J.C. Calagui, D.B. Senoro, C.C. Kan, J.W.L. Salvacion, M.W. Wan, J. Hazard. Mater. 277 (2014) 120–126. [20] P. Mitra, K. Sarkar, P.P. Kundu, Def. Sci. J. 64 (3) (2014) 198–208. [21] L. Wang, A. Wang, J. Chem. Eng. 143 (2008) 43–50. [22] S. Sun, A. Wang, J. Hazard. Mater. B131 (2006) 103–111. [23] P. Monvisade, P. Siriphannon, Appl. Clay Sci. 42 (2009) 427–431. [24] I. Langmuir, J. Am. Chem. Soc. 40 (1918) 1361–1403. [25] T.S. Anirudan, P.G. Radhakrishnan, J. Chem. Thermodyn. 40 (4) (2008) 702–709. [26] H.M.F. Freundlich, J. Phys. Chem. 57 (1906) 385–471. [27] S. Lagergren, Ksven Vetenskapsakad Hand. 24 (4) (1898) 1–39. [28] Y.S. Ho, G. Mckay, Can. J. Chem. Eng. 76 (1998) 822–827. [29] N. Barka, S. Qourzal, A. Assabbane, A. Nounah, Y. Ait-Ichou, J. Saudi Chem. Soc. 15 (2011) 263–267. [30] N. Barka, M. Abdennouri, M.E. Makhfouk, S. Qouezal, J. Environ. Chem. Eng. 1 (2013) 144–149. [31] F.A. Dawodu, K.G. Akpomie, J. Mater. Res. Technol. 3 (2) (2014) 129–141. [32] B. Agarwal, C. Balomajumder, P.K. Thakur, Chem. Eng. J. 228 (2013) 655–664. [33] B. Agarwal, P.K. Thakur, C. Balomajumder, Chem. Eng. Commun. 200 (2013) 1278–1292.
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: http://www.elsevier.com/locate/ijbiomac
Simultaneous adsorption of Cu2+ and Acid fuchsin (AF) from aqueous solutions by CMC/bentonite composite Ning Gong 1, Yanping Liu 1, Ruihua Huang ⁎ College of Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi 712100, China
a r t i c l e
i n f o
Article history: Received 22 November 2017 Received in revised form 29 March 2018 Accepted 11 April 2018 Available online 21 April 2018 Keywords: CMC/bentonite composite Binary systems Adsorption Kinetic
a b s t r a c t Carboxymethyl-chitosan (CMC)/bentonite composite was prepared by the method of membrane-forming, and characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. The simultaneous adsorption of Cu2+ and Acid fuchsin (AF) applying CMC/bentonite composite as an adsorbent in single or binary systems was investigated. The adsorption study was conducted systematically by varying the ratio of CMC to bentonite, adsorbent dosage, initial pH value, initial Cu2+ (or AF) concentration, contact time and the interaction of two components in binary solutions. The results showed that the presence of Cu2+ hindered the adsorption of AF, while the presence of AF almost had no influence on the adsorption of Cu2+ in binary systems. The adsorption data of Cu2+ and AF were both suitable for Langmuir isotherm model, and the maximum adsorption capacities of CMC/bentonite composite, according to the Langmuir isotherm model were 81.4 mg/g for Cu2+ and 253.2 mg/g for AF at 298 K. The pseudo-second-order model could better describe the adsorption process of Cu2+ and AF. Thermodynamic constant values illustrated that the adsorption of Cu2+ was endothermic, while the adsorption process of AF was exothermic. © 2018 Published by Elsevier B.V.
1. Introduction The treatment of industrial wastewater containing dyes has been a global problem. Their presence, even in small quantities, causes changes in terms of water color and reduces the amount of light that reaches the aquatic environment [1]. The wastewater containing dyes was mainly discharged from these industries such as textile industry, paint industry, paper industry, pharmaceutical industry, printing, leather industry, etc. However, the wastewaters from these industries do not contain only dyes as pollutants; the heavy metals can be also found in significant quantities, especially in textile industry. Copper is an essential element for the human beings, although large acute doses can be harmful and even cause a fatal effect. Its carcinogenic and mutagenic properties lead to health problems such as lung cancer, lesions in the central nervous system [2]. Additionally World Health Organization (WHO) has recommended a maximum acceptable concentration of 1.5 mg/L of Cu2+in drinking water [3]. For these reasons, these pollutants must be removed from industrial effluents before discharging into the environment. Many techniques have been developed for the disposal of both dyes and heavy metals from wastewater such as coagulation, precipitation, ⁎ Corresponding author at: Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi 712100, China. E-mail address: [email protected]. (R. Huang). 1 Both authors contributed equally to this work.
https://doi.org/10.1016/j.ijbiomac.2018.04.075 0141-8130/© 2018 Published by Elsevier B.V.
separation trough membranes [4–6], biological treatments, and adsorption [7–13]. Among these methods, adsorption is considered as a superior technique due to its high efficiency, low cost of implementation, ample availability and simplicity in terms of design. Chitosan derivatives have been extensively investigated as adsorbents and applied in the treatment of wastewater containing both dyes and heavy metals. Among them are chitosan derivatives containing nitrogen, phosphorus and sulfur as heteroatoms, and other derivatives such as quaternized chitosan, carboxymethyl chitosan. Carboxymethyl chitosan (CMC) is a water-soluble chitosan derivative, which contains hydroxyl (OH), carboxyl (COOH) and amine (NH2) groups in the molecule, and makes it possible to offer enough chelate groups for increasing adsorption capacity toward metal ions such as copper ion. Recently, chitosan composites have been developed to adsorb heavy metals and dyes from wastewater. Different kinds of substances have been used to form composite with chitosan such as montmorillonite [14,15], clay [16], bentonite [17–19], polyvinyl alcohol, polyvinylchloride, and perlite. Bentonite, as a mineral clay, has been highlighted for the preparation of chitosan composites because of its high cationic exchange capacity and the possibility of lamellar expansion, which provides greater versatility in the interaction and intercalation of chitosan or its derivatives. These composites have been studied and targeted for environmental applications such as the adsorption of heavy metals, dyes and herbicides. Though the carboxymethyl-chitosan/clay composites as adsorbents have been reported previously, many studies were focused on the adsorption of dyes, heavy metals and pesticides in single systems
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
581
Fig. 1. FTIR spectra of bentonite, CMC/bentonite composite and the CMC/bentonite composite samples after AF and Cu2+ adsorption.
[20,21]. However, as we known, different dyes and heavy metals are often present together in many practical industrial effluents, thus more attention should been paid to the study of their simultaneous adsorption. At present, to the best of our knowledge, only limited data are available for multicomponent adsorption, thus it is of great significance to investigate the simultaneous adsorption of dyes and heavy metals. In this work, CMC/bentonite composite was prepared and characterized by FTIR and XRD techniques. Acid fuchsin (AF) is widely used in dyeing textile fabrics, silk, nylon, wool and leather. Cu2+ and Acid fuchsin (AF) were chosen as model heavy metal and dye pollutants, respectively. To understand the simultaneous removal of AF and Cu2+ as well as their single adsorption from aqueous solution onto this composite, major adsorption factors including the ratio of CMC to bentonite, adsorbent dosage, AF and Cu2+ concentration, pH and contact time were investigated. The corresponding adsorption kinetics and isotherms were also examined. 2. Experimental 2.1. Materials Chitosan (CTS) [weight-average molecular weight (MW) = 100,000 Da, degree of deacetylation (dd) = 90%] was purchased from the Sinopharm Group Chemical Reagent Limited Company (China). Bentonite powder with a particle size of 200-mesh was acquired from the chemical factory of Shentai, Xinyang, Henan, China. Monochloroacetic acid was obtained from Tianjin Chemical Reagent Co., China. The molecular weight of AF (Tianjin Kermel Chemical Reagent Co., China) is 585.54 g/mol. Other agents used were all analytical grade and all solutions were prepared with distilled water.
50 wt% sodium hydroxide solution (50.00 mL) and stirred for 1 h at room temperature, and then frozen overnight. The unfrozen CTS was dipped into 80 mL of isopropanol in a three-necked flask by stirring for 30 min at room temperature, then monochloroacetic acid (6.00 g) was added at three times into the reaction mixture for another 30 min. Then the mixture was heated to 60 °C and allowed to continue for 4 h. Finally, the resultant solution was filtered and the filter cake was washed with 80% (v/v) ethanol for many times and isopropanol once, then dried under vacuum at 60 °C to obtain products.
2.2.2. Preparation of CMC/bentonite composite CMC solution was prepared by dissolving 1.0 g CMC in 50 mL distilled water, and then 1.0 g bentonite was slowly added to CMC solution followed by stirring at room temperature for 6 h to obtain the mixture. The mixture was uniformly coated in petri-dishes, and allowed to stay at 60 °C in an oven to form membranes. Subsequently, these membranes were cross-linked at 60 °C for 5 h with 2.5 wt% glutaraldehyde which was dissolved in anhydrous ethanol. Finally, the cross-linked CMC/bentonite composite was washed using distilled water to remove any free glutaraldehyde and dried in an oven at 60 °C for 24 h. After drying, the composite was ground and sieved. The composite with
2.2. Preparation of CMC/bentonite composite 2.2.1. Preparation of CMC Carboxymethyl chitosan (CMC) was prepared with some modifications according to Sun and Wang [22]. CTS (5.00 g) was added to a
Fig. 2. XRD patterns of bentonite and CMC/bentonite composite.
582
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
The determination of the pHZPC of the sample was determined according to the method described by the solid addition method [23]. 50 mL of 0.1 mol/L NaCl solutions were placed in 150 mL conical flasks. Initial pH of 0.1 mol/L NaCl solutions (pHi) was adjusted from pH 2 to 10 by adding either 0.1 mol/L HCl or 0.1 mol/L NaOH solutions and final pH (pHf) of solution was measured. The difference between the initial and final pH (pHf − pHi) was plotted against the initial pH (pHi) and the point where pHf − pHi = 0 was thought to be the zero point of charge (pHZPC) of adsorbent. 2.4. Batch experiments
Fig. 3. Effect of ratio of CMC to bentonite on Cu2+ and AF adsorption. Adsorption conditions: adsorbent dosage: 0.1 g; at 298 K and natural pH; contact time: 60 min; 50 mg/L Cu2+ and 50 mg/L AF, respectively, in single solution.
100 mesh of particle size was collected and utilized for the batch experiments.
Removal=% ¼
2.3. Characterization FTIR spectra of the samples were characterized using a FTIR Spectrophotometer (Shimadzu 4100) in KBr pellets in the wavenumber range of 400–4000 nm−1. XRD analyses of the powdered samples were measured by an X-ray powder diffractometer (Shimadzu XD3A diffractometer) with Cu target and K∝ radiation (λ = 0.15418 nm) at 40 kV and 30 mA. The scanning rate was 2°/min and the scanning scope of 5–40°. The interlayer of layered silicate and the composite can be calculated by using Bragg's equation: nλ ¼ 2d sinθ
To evaluate the adsorption capacity of CMC/bentonite composite, CMC/bentonite composite was placed in a 250 mL Erlenmeyer flask containing 50 mL aqueous solution of AF and Cu2+. The flask was then shaken at 200 rpm at 25 °C. The factors affecting the adsorption of AF and Cu2+ including adsorbent dosage, initial pollutant concentration, contact time, and pH value were investigated. After shaking for a certain period of time, the suspensions were filtered. The supernatants were then collected and analyzed for Cu2+ concentration with a flame atomic adsorption spectrophotometer (Varian, Spectra AA 240), and for AF with a UV–vis spectrophotometer at 546 nm (754 N, Shanghai, China). The removal for AF (or Cu2+) on adsorbent was calculated according to Eq. (2):
ð1Þ
where n is an integer (n = 1); λ is the wavelength of incident wave (λ = 0.15418 nm); d is the spacing between the planes in the atomic lattice and θ is the angle between the incident ray and the scattering planes.
C 0 −C t 100% C0
ð2Þ
where C0 is the initial concentration (mg/L) and Ct is the concentration (mg/L) at any time, t. The value for qt (mg/g) is the amount of adsorbate adsorbed per amount of adsorbent (mg/g) at any time, t was calculated as follows: qt ¼
ðC 0 −C t Þ V m
ð3Þ
where V was the solution volume and m is the mass of the adsorbent. 2.5. Adsorption isotherms Most adsorption data can be adequately expressed using either the Langmuir or Freundlich models. The Langmuir isotherm is used to describe adsorption phenomena and is based on the assumption that adsorption occurs on a homogenous surface by monolayer sorption
Fig. 4. Effect of adsorbent dosage on Cu2+ and AF adsorption. Adsorption conditions: adsorbent dosage: 0.03–0.15 g; at 298 K and natural pH; contact time: 60 min; 50 mg/L Cu2+ and 50 mg/L AF, respectively, in binary solutions.
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
583
Fig. 5. Effect of initial Cu2+ (or AF) concentration on Cu2+ (or AF) adsorption. Adsorption conditions: adsorbent dosage: 0.08 g; at 298 K and natural pH; contact time: 60 min; Cu2+ and AF concentrations from 50 to 500 mg/L, in single solutions.
without interaction between adsorbed molecules. The linearized Langmuir equation is given as [24]: Ce 1 Ce þ ¼ qe Qb Q
ð4Þ
The Freundlich isotherm model is an empirical equation valid for adsorption on the assumption that this process occurs on heterogeneous surfaces and the solid-phase surfaces possess differing adsorption sites. The linearized Freundlich equation was expressed as [26]: logqe ¼ logK f þ
where Q is the maximum amount of adsorption with complete monolayer coverage on the adsorbent surface (mg/g) and b is the Langmuir constant, which is related to the energy of adsorption (L/mg). The constants Q and b can be determined from the slope and the intercept of the linear plot of Ce/qe against Ce. The essential features of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor (RL) defined by the relationship [25]: RL ¼
1 1 þ bC 0
ð5Þ
1 logC e n
where Kf [(mg/g)(L/mg)1/n] and n are Freundlich constants related to adsorption capacity and heterogeneity factor, respectively. 2.6. Adsorption kinetics In this study, the first-order and pseudo-second-order kinetic models were used to describe the adsorption of AF (or Cu2+) on this adsorbent. The linearized pseudo-first-order kinetic model was given as [27]: logðqe −qt Þ ¼ logqe −
where C0 is the initial pollutant concentration in (mg/L) and b is the Langmuir equilibrium constant (L/mg). The value of the separation factor provides important information about the nature of the adsorption process. The adsorption is said to be irreversible (RL = 0), favorable (0 b RL b 1), linear (RL = 1) or unfavorable (RL N 1).
ð6Þ
k1 t 2:303
ð7Þ
where qe and qt are the amounts (mg/L) of AF (or Cu2+) adsorbed at equilibrium and at time t, respectively, k1 is the pseudo-first-order rate constant (min−1). The k1 and qe were calculated from the slope and intercept of plots of log(qe − qt) versus t, respectively.
Fig. 6. Effect of initial pH on Cu2+ (or AF) adsorption. Adsorption conditions: adsorbent dosage: 0.08 g; at 293 K and natural pH; contact time: 60 min; 100 mg/L Cu2+ and 100 mg/L AF, respectively, in binary solutions.
584
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
Fig. 7. Effect of contact time on Cu2+ (or AF) adsorption. Adsorption conditions: adsorbent dosage: 0.08 g; at 293 K and natural pH; contact time: 0–80 min; Cu2+ concentrations: 100, 150 and 200 mg/L.; AF concentrations: 100, 200 and 300 mg/L.
The pseudo-second-order kinetic model can be expressed by the following equation [28]: t 1 1 ¼ þ t qt k2 qe 2 qe
ð8Þ
where qe (mg/g) and qt (mg/g) are the amounts of adsorbed AF (or Cu2+) at equilibrium and at time t, respectively; k2 (g/mg/min) is the rate constant for the pseudo-second-order model. The values for qe and k2 can be determined from the slope and intercept of the plot of t/qt versus t, respectively. 3. Results and discussions 3.1. FTIR spectra analysis FTIR spectra of bentonite, CMC/bentonite composite and the CMC/ bentonite composite samples after AF and Cu2+ adsorption are shown in Fig. 1. Compared with the FTIR spectrum of bentonite, the one of CMC/bentonite composite showed that the adsorption band at 3454 cm−1, corresponding to\\OH stretching vibration of H2O of bentonite, was strengthened and shifted to a lower wave number (3440 cm−1), suggesting the O\\H and N\\H stretching vibrations in CMC overlapped with \\OH stretching vibration of H2O in bentonite.
The asymmetric stretching vibration of the \\CH3 (2934 cm−1) of CMC was also observed in the FTIR spectrum f CMC/bentonite composite. In addition, the adsorption band at 1644 cm−1, assigned to \\OH bending vibration of H2O of bentonite, was strengthened and shifted to a lower wave number (1628 cm−1), which indicates the \\COO\\ group asymmetric stretching vibration of CMC overlapped with \\OH bending vibration of H2O of bentonite. At the same time, the \\COO\\ group symmetric stretching vibration (1424 cm−1) and the second \\OH group stretching vibration (1090 cm−1) of CMC were observed in the FTIR spectra of CMC/bentonite composite. Besides, the other characteristic peaks of bentonite also appeared in both spectra, i.e., the peak at 521 cm−1 belonged to the angular deformation of Si\\O in the tetrahedral sheet of bentonite; the peaks from 917 to 793 cm−1 corresponded to the octahedral layers of bentonite. The results indicated the forming of CMC/bentonite composite. Comparing to the FTIR spectrum of CMC/bentonite composite, the one of CMC/bentonite composite after Cu2+ adsorption showed the major differences as follows: the absorption band attributed to the asymmetric stretching vibrations of the\\CH3 (2934 cm−1) of CMC was shifted to a lower wave number (2930 cm−1). The absorption band at 1424 cm−1, assigned to the symmetric stretching vibration of \\COO\\ group, was shifted to a lower wave number (1397 cm−1). These results indicates that the \\COO\\ group of CMC was mainly involved in the adsorption process of Cu2+ by CMC/bentonite composite, and the chelation between Cu2+ and
Fig. 8. Interaction of Cu2+ and AF adsorption in binary solutions.
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
585
Fig. 9. Isotherm models for Cu2+ (a and a′) and AF (b and b′) adsorption at different temperatures. (a and b): Langmuir model; (a′ and b′): Freundlich model.
\\COO\\ group in CMC/bentonite composite happened. However, in the spectrum of the CMC/bentonite composite after AF adsorption, the wide absorption band at 3440 cm−1, corresponding to the stretching vibration of NH2 and OH groups, was shifted to a lower wave number (3433 cm−1). The absorption band at 2934 cm−1, assigned to the asymmetric stretching vibrations of \\CH3, showed a shift to lower wave number (2928 cm−1). The absorption band at 1628 cm−1, assigned to the asymmetric stretching vibration of \\COO\\ group, was significantly shifted to a lower wave number (1603 cm−1). These changes indicate that the\\OH and\\COO\\groups in CMC/bentonite composite was involved in the adsorption process of AF.
3.2. X-ray diffraction analysis X-ray diffraction (XRD) is an effective method for the investigation of the intercalation existence of bentonite. Fig. 2 shows that the XRD patterns of bentonite and CMC/bentonite composite. The XRD pattern of bentonite shows a typical diffraction peak at 6.56°, corresponding to a basal spacing of 1.35 nm. After bentonite interacted with CMC, this peak shifted toward a lower angle (6.18°), corresponding to a basal spacing of 1.43 nm. The increasing basal spacing means that CMC had entered into the interlayer of bentonite, and CMC/bentonite composite was obtained.
Table 1 Langmuir and Freundlich isotherm parameters of Cu2+ and AF in single system by CMC/bentonite composite. Isotherms Adsorbates Cu
AF
2+
Langmuir
Freundlich
Temperature (K)
Q (mg/g)
b (L/mg)
R2
RL
Kf (mg/g(L/mg)1/n)
n
R2
298 308 318 298 308 318
81.4 80.7 78.8 253.2 249.4 246.9
0.185 0.183 0.198 0.055 0.056 0.050
0.9996 0.9996 0.9997 0.9996 0.9997 0.9996
0.0133–0.0976 0.0135–0.0985 0.0125–0.0917 0.0351–0.2667 0.0345–0.2632 0.0385–0.2857
35.7 39.6 37.8 29.8 29.4 28.0
6.41 7.55 7.24 2.47 2.47 2.45
0.990 0.996 0.993 0.977 0.961 0.963
586
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
Fig. 10. Kinetic models for Cu2+ (a and a′) and AF (b and b′) adsorption at different temperatures. (a and b): pseudo-first-order kinetic model; (a′ and b′): pseudo-second-order kinetic model.
3.3. Effect of the ratio of CMC to bentonite The effect of the ratio of CMC to bentonite on the removal of AF and Cu2+ is shown in Fig. 3. It is obvious that the amount of CMC is an important factor affecting the adsorption capacity of CMC/bentonite composite. It can be seen that, compared with the single bentonite, CMC/ bentonite composite exhibited higher removal for both AF and Cu2+. The removal for Cu2+ increased with the increase of the ratio of CMC to bentonite till this ratio was 0.3, and increased hardly with further increase of the ratio of CMC to bentonite. It may be explained like this, the amounts of active hydroxyl (\\OH), carboxyl (\\COOH) and amine (\\NH2) groups increased with increasing of the ratio of CMC to
bentonite, which resulted in an increase in the removal of Cu2+ on CMC/bentonite composite due to an increase on the adsorptive sites. However, the removal increased hardly when the ratio exceeded 0.3, which was attributed to the amount of intercalated CMC was saturated. For AF, the removal increased gradually with an increase on the ratio of CMC to bentonite. When introducing CMC, the amount of CMC improved the flocculation capacity of CMC/bentonite composite and facilitated the separation of the adsorbents from the solution [20]. Meanwhile, the increase of active hydroxyl (\\OH), carboxyl (\\COOH) and amine (\\NH2) groups increased when increasing the ratio of CMC to bentonite, which resulted in an increase on the removal of AF by CMC/bentonite composite due to an increase on the adsorptive
Table 2 Kinetic parameters of the adsorption of Cu2+ and AF onto CMC/bentonite composite. Adsorbate
Cu
AF
2+
Concentration (mg/L)
100 150 200 100 200 300
qe (exp)
54.56 63.11 71.06 58.68 109.9 163.3
Pseudo-first-order
Pseudo-second-order
qe (cal)
k1
R2
qe (cal)
k2
R2
20.04 20.32 26.61 9.30 21.93 69.58
0.0760 0.0702 0.0758 0.0610 0.0573 0.0626
0.9867 0.9933 0.9943 0.9923 0.9811 0.9943
55.71 64.27 71.94 59.14 110.9 166.9
0.2004 0.0243 0.0576 0.2007 0.0913 0.0446
0.9998 0.9998 0.9996 0.9999 0.9999 0.9996
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
sites. Considering the removal for AF and Cu2+ and economic cost, the ratio of CMC to bentonite of the composite was selected as 1.
Table 3 Thermodynamic parameters for Cu2+ and AF adsorption onto CMC/bentonite composite. Adsorbate
ΔHθ (kJ/mol)
ΔSθ (kJ/(mol K))
Cu2+ AF
2.811 −3.943
0.0295 0.0162
3.4. Effect of adsorbent dosage The effect of adsorbent dosage, ranging from 0.03 to 0.15 g, on the removal of AF and Cu2+, respectively, is shown in Fig. 4. It can be observed that the removal increased with adsorbent dosage, both for FA and for Cu2+. This was mainly due to an increase in the sorptive surface area and the availability of more active binding sites on the surface of the adsorbent with increase in dosage [29]. This composite shows a sharp increase in Cu2+ removal from 74.3 to 95.8% as the adsorbent dosage increased from 0.03 to 0.05 g. A further increase in adsorbent dosage from 0.05 to 0.15 g had practically an insignificant effect, the removal only increased from 95.8 to 99.5%. For AF, the removal increased sharply from 65.1 to 81.7% as the adsorbent dosage increased from 0.03 to 0.08 g. The removal only increased from 81.7 to 86.3% when increasing in dosage from 0.08 to 0.15 g. However, a reverse trend was obtained as presented in Fig. 4, where a decrease in the adsorption capacity whether for AF or for Cu2+ with increase in adsorbent dosage was recorded. This might be a result of a decrease in the total adsorption surface area available for AF and Cu2+ to bind due to overlapping or aggregation of adsorption sites [30]. Therefore, as the adsorbent dosage increased, the amounts of AF and Cu2+ adsorbed onto a unit mass of CMC/bentonite composite decreased, resulting in the decrease in the adsorption capacity. In the case of the moderate removal for both Cu2+ and AF, 0.08 g of adsorbent dosage was chosen for the following experiments. 3.5. Effect of initial AF (or Cu2+) concentration For this effect, the concentrations of Cu2+ and AF ranging from 50 to 500 mg/L were investigated. The adsorption experiment was conducted for 60 min using 0.08 g of adsorbent dosage at 298 K and 200 pm. The results are shown in Fig. 5. It was observed that the removal for Cu2+ (or AF) decreased with increase in the initial concentration of Cu2+ (or AF). The decrease in removal was due to the fact that all adsorbents have a fixed number of active sites and at higher concentrations the active sites become insufficient. On the other hand, an increase in the adsorption capacity for both Cu2+ and AF with increase in initial concentration was observed as presented in Fig. 5. This results from the increasing concentration gradient which acts like a driving force to overcome the resistance to mass transfer of Cu2+ (or AF) between the adsorbate and adsorbent species [31].
587
ΔGθ (kJ/mol) 298 k
308 k
318 k
−6.31 −8.89
−6.48 −9.23
−6.90 −9.21
3.6. Effect of pH The pH is the most important factor affecting the adsorption process. AF dye is colorless in alkali solution and the hydrolyzation of Cu2+ is prevented, so the range of pH for Cu2+ (or AF) adsorption in this study was selected between 1 and 5. The effect of pH value in the original solution on Cu2+ (or AF) adsorption onto CMC/bentonite composite was investigated and shown in Fig. 6. At the same time, the plot of pHf pHi verse pHi was also presented in Fig. 6. The pHzpc of CMC/bentonite composite was obtained at pH 7.8 or so. When pH value is lower than pHzpc, the surface of CMC/bentonite was positively charged. When the pH value was higher than pHZPC, the surface of CMC/bentonite was negatively charged. As can be observed in Fig. 6, the removal of AF was a little higher at low pH value than those at high pH value, indicating that the adsorption mechanism for AF is influenced by the pH of the solution. It is known that AF, an anionic dye, remained negatively charged throughout the process of testing. At low pH value, the adsorption mechanism of AF was controlled by electrostatic attractions between the positively charged surface of adsorbent, as a result of the protonation process, and the negatively charged AF molecule. With increasing pH values, the number of the negatively charged sites increased, and the number of the positively charged sites decreased, resulting in the reduction of removal for AF at higher pH value. On the contrary, the removal for Cu2+ increased further from 21.6 to 86.2% when pH rose from 1.0 to 4.0. This change can be explained by the competition between H+ and Cu2+ for available adsorption sites at low pH. However, when pH increased, the adsorption of the positively charged Cu2+ through electrostatic attraction was enhanced because of the high negative charge of the surface of CMC/bentonite composite. Moreover, the constant adsorption for both Cu2+ and AF beyond pH 4 was observed. The result suggests the non-electrostatic interactions between the delocalized electrons on the surface of adsorbent and the free electrons in AF molecules were involved in AF adsorption. For Cu2+, the chelation between \\COO\\ and Cu2+ might have a significant contribution to Cu2+ adsorption.
3.7. Effect of contact time
Fig. 11. Plots of lnKL verse 1/T for Cu2+ and AF adsorption.
The contact time between adsorbate and adsorbent is an important parameter in assessing the performance of adsorbents. The shorter the contact time in adsorption process, the lower are the operational costs that recommend the adsorbent for large-scale industrial application. The effect of contact time on AF and Cu2+ adsorption onto CMC/bentonite composite is shown in Fig. 7. It is observed that the removal of AF and Cu2+ from solution was initially rapid and then diminished gradually until an equilibrium time beyond which there was no significant increase in the removal. Equilibrium removal was achieved around 60 min. Hence, a contact time of 60 min was chosen to ensure optimum removal of AF and Cu2+. The initial fast adsorption rate was due to the large number of vacant surface sites available for adsorption in the initial stage of the process. The slow uptake in the later stages was probably attributed to an attachment controlled process caused by less available active sites for adsorption, then, near equilibrium, the available sites for adsorption become difficult to be occupied because of the repulsive forces between the solute molecules on the solid and the solution.
588
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589
3.8. Interaction of two components in binary solutions In the multicomponent system, there are three types of effects including synergism, antagonism and non-interaction [32]. 1. Synergism: effect of mixture of component in solution is greater than its individual effect. 2. Antagonism: effect of mixture of component in solution is less than its individual effect. 3. Non-interaction: effect of mixture of component in solution is neither less nor more than that of its individual effect. Interaction of two components in binary mixtures of Cu2+ and AF could be evaluated by the ratio of adsorption capacity of one component in the binary solution (Qmix) to the same component in single solution (Q0) [33]. Qmix/Q0 N 1, synergism; Qmix/Q0 = 1, non-interaction; Qmix/ Q0 b 1, antagonism. In this study, a great number of the values for the ratio of Qmix/Q0 for Cu2+ and AF are presented in Fig. 8. The results showed that the values of Qmix/Q0 for AF were lower than 1 in binary solutions, hence, the presence of Cu2+ showed antagonism effect on the adsorption of AF in the process of adsorption. Besides, the increment of Cu2+ concentrations significantly reduced the uptake of AF in the bi-pollutant system. The antagonism effect became obvious with increasing Cu2+ concentration. However, the values of Qmix/Q0 for Cu2+ were almost 1 or so for all binary systems at tested conditions, suggesting that the adsorption capacity of Cu2+ was not affected by the presence of AF in binary solutions. 3.9. Adsorption isotherm Adsorption isotherm expresses the relationship between the amount of adsorbate removed from the liquid phase by unit mass of adsorbent at a constant temperature. Adsorption isotherms are basic requirements for the design of adsorption systems. The concentrations ranging from 50 to 400 mg/g for Cu 2+ and from 50 to 700 mg/g for AF were tested. Adsorption experiments were performed for 60 min at different temperatures (298, 308 and 318 K). These plots are presented in Fig. 9, and the parameters of isotherm models and correlation coefficients (R2) for Cu 2+ and AF adsorption are depicted in Table 1. As can be seen from Table 1, the values of the correlation coefficient (R2) for Langmuir model are higher than those for Freundlich model. Thus, the Langmuir isotherm gave a better fit to the data than the Freundlich isotherm model for Cu 2+ and AF, suggesting the occurrence of monolayer adsorption by CMC/bentonite composite. Furthermore, for the initial concentration from 50 to 500 mg/g for Cu 2+ and from 50 to 700 mg/g for AF used in this study, the values of RL all ranged from 0 to 1 for both Cu 2+ and AF at three temperatures tested; this indicates a favorable adsorption of Cu2+ and AF onto CMC/bentonite composite. The monolayer adsorption capacity changed from 81.4 to 78.8 mg/g for Cu2+ and from 253.2 to 246.9 mg/g for AF, respectively, when increasing 298 to 318 K. The slight change indicated that the temperature had insignificant effect on the adsorption of Cu2+ and AF onto this adsorbent. It was observed that the adsorption capacity of Cu2+ by CMC/bentonite composite according to Langmuir isotherm was less than that of AF at the same temperature, suggesting CMC/bentonite composite exhibited a stronger binding ability for AF than for Cu2+. 3.10. Adsorption kinetics Adsorption kinetic models were applied to the experimental data in order to analyze the rate of adsorption and possible adsorption mechanism of Cu2+ and AF onto CMC/bentonite composite. Experimental kinetic data of adsorption for Cu2+ using 100, 150, and 200 mg/L solutions and for AF using 100, 200 and 300 mg/L solutions were investigated.
The plots for the kinetic models were illustrated as shown in Fig. 10, and the relative parameters are given in Table 2. From Fig. 10, the experimental data deviated slightly more from the linearity for the pseudo first-order model when compared to the pseudo second-order model, thus the pseudo- second order model provided a good fit to the experimental data of both Cu2+ and AF. This is also indicated by the high values of their linear regression (R2) close to 1. Also when the calculated qe values were compared to those of the experimental qe values, for pseudo first-order model they varied a lot. But in case of the pseudo second-order model both those values almost coincided. Thus the adsorption process followed the pseudo second-order model. 3.11. Adsorption thermodynamic studies The thermodynamic parameters such as the standard free energy change (ΔGθ), enthalpy change (ΔHθ) and entropy change (ΔSθ) were determined based on the following equations: ΔGθ ¼ −RT ln K L ln K L ¼
ΔSθ ΔH θ − R RT
ð9Þ ð10Þ
where KL (L/mol) is the Langmuir constant, R is the universal gas constant, 8.314 J/mol/K, T (K) is the temperature employed in the experiment. The values of ΔHθ and ΔSθ can be obtained from the slope and intercept of a van't Hoff plot of lnKL versus 1 / T. Fig. 11 illustrates the linear relationship between lnKL versus 1 / T and Table 3 shows the parameters of thermodynamics. The values of ΔGθ were all negative at different temperatures, which suggested that the adsorption of Cu2+ and AF onto CMC/bentonite composite could happen spontaneously. Cu2+ had positive ΔHθ values at different temperatures tested, indicating that the reaction was endothermic; while AF had negative ΔHθ values, suggesting that the adsorption process is exothermic. Besides, both Cu2+ and AF maintained positive ΔSθ values, which inferred that the adsorbent had good affinity for Cu2+ and AF. 4. Conclusion CMC/bentonite composite was synthesized by intercalation reaction between CMC and bentonite in distilled water. Simultaneous adsorption tests of Cu 2+ and AF onto CMC/bentonite composite were carried out and the results obtained from this study show that the presence of Cu2+ restrained the adsorption of AF, while the presence of AF hardly affected the adsorption of Cu2+ in binary systems. The kinetic and isotherm studies indicated that the pseudo-second-order model and the Langmuir model well described the adsorption equilibrium of Cu2+ and AF onto CMC/bentonite composite. The maximum adsorption capacities of CMC/bentonite composite were 81.4 mg/g for Cu2+ and 253.2 mg/g for AF at 298 K. Besides, the thermodynamic studies revealed the adsorption of Cu2+ was an endothermic and spontaneous process, while the adsorption of AF was an exothermic and spontaneous process. The results have demonstrated that CMC/bentonite composite could be used as a promising adsorbent and provided a novel method to solve the treatment of Cu2+ and AF. Conflicts of interest The authors declare no conflicts of interests. References [1] G.Z. Kyzas, N.K. Lazaridis, M. Kostoglou, Chem. Eng. J. 248 (2014) 327–336. [2] M.L.P. Dalida, A.F.V. Mariano, C.M. Futalan, C.C. Kan, W.C. Tsai, M.W. Wan, Desalination 275 (2011) 154–159. [3] M.K. Jha, N.V. Nguyen, J.C. Lee, J. Jeong, J.M. Yoo, J. Hazard. Mater. 164 (2009) 948–953. [4] S. Foorginezhad, M.M. Zerafat, Ceram. Int. 43 (17) (2017) 15146–15159.
N. Gong et al. / International Journal of Biological Macromolecules 115 (2018) 580–589 [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
J. Wang, L. Qin, J. Lin, J. Zhu, B. Van der Bruggen, Chem. Eng. J. 323 (2017) 56–63. X. Wang, Z. Wang, H. Chen, Z. Wu, J. Hazard. Mater. 339 (2017) 182–190. J. He, Y. Li, C. Wang, K. Zhang, J. Liu, Appl. Surf. Sci. 426 (2017) 29–39. H. Peng, P. Gao, G. Chu, B. Pan, B. Xing, Environ. Pollut. 229 (2017) 846–853. P. Tan, Q. Bi, Y. Hu, Z. Fang, J. Cheng, Appl. Surf. Sci. 423 (2017) 1141–1151. Z. Huang, Y. Li, W. Chen, J. Shi, Y. Zhang, Mater. Chem. Phys. 202 (2017) 266–276. A. Shajahan, S. Shankar, A. Sathiyaseelan, K.S. Narayan, S. Ignacimuthu, Int. J. Biol. Macromol. 104 (2017) 1449–1458. I. Belbachir, B. Makhoukhi, J. Taiwan Inst. Chem. Eng. 75 (2017) 105–111. R. Fabryanty, C. Valencia, F.E. Soetaredjo, J.N. Putro, S. Ismadji, J. Environ. Chem. Eng. 5 (6) (2017) 5677–5687. F.A.R. Pereira, K.S. Sousa, G.R.S. Cavalcanti, D.B. França, L.N.F. Queiroga, I.M.G. Santos, M.G. Fonseca, M. Jaber, J. Environ. Chem. Eng. 5 (4) (2017) 3309–3318. C. Hu, G. Li, Y. Wang, F. Li, H. Hu, Int. J. Biol. Macromol. 103 (2017) 751–757. E.M.S. Azzam, G. Eshaq, A.M. Rabie, A.A. Bakr, S.M. Tawfik, Int. J. Biol. Macromol. 89 (2016) 507–517. P.V. Haseena, K.S. Padmavathy, P. Rohit Krishnan, G. Madhu, Procedia Technol. 24 (2016) 733–740. G.L. Dotto, F.K. Rodrigues, E.H. Tanabe, R. Fröhlich, E.L. Foletto, J. Environ, Chem. Eng. 4 (3) (2016) 3230–3239.
589
[19] M.J.C. Calagui, D.B. Senoro, C.C. Kan, J.W.L. Salvacion, M.W. Wan, J. Hazard. Mater. 277 (2014) 120–126. [20] P. Mitra, K. Sarkar, P.P. Kundu, Def. Sci. J. 64 (3) (2014) 198–208. [21] L. Wang, A. Wang, J. Chem. Eng. 143 (2008) 43–50. [22] S. Sun, A. Wang, J. Hazard. Mater. B131 (2006) 103–111. [23] P. Monvisade, P. Siriphannon, Appl. Clay Sci. 42 (2009) 427–431. [24] I. Langmuir, J. Am. Chem. Soc. 40 (1918) 1361–1403. [25] T.S. Anirudan, P.G. Radhakrishnan, J. Chem. Thermodyn. 40 (4) (2008) 702–709. [26] H.M.F. Freundlich, J. Phys. Chem. 57 (1906) 385–471. [27] S. Lagergren, Ksven Vetenskapsakad Hand. 24 (4) (1898) 1–39. [28] Y.S. Ho, G. Mckay, Can. J. Chem. Eng. 76 (1998) 822–827. [29] N. Barka, S. Qourzal, A. Assabbane, A. Nounah, Y. Ait-Ichou, J. Saudi Chem. Soc. 15 (2011) 263–267. [30] N. Barka, M. Abdennouri, M.E. Makhfouk, S. Qouezal, J. Environ. Chem. Eng. 1 (2013) 144–149. [31] F.A. Dawodu, K.G. Akpomie, J. Mater. Res. Technol. 3 (2) (2014) 129–141. [32] B. Agarwal, C. Balomajumder, P.K. Thakur, Chem. Eng. J. 228 (2013) 655–664. [33] B. Agarwal, P.K. Thakur, C. Balomajumder, Chem. Eng. Commun. 200 (2013) 1278–1292.