- Email: [email protected]
Magnetic field assisted adsorption of methyl blue onto organo-bentonite
Applied Clay Science 55 (2012) 177–180
Contents lists available at SciVerse ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Note
Magnetic field assisted adsorption of methyl blue onto organo-bentonite Xiaolong Hao ⁎, He Liu, Guangsheng Zhang, Hua Zou, Yibo Zhang, Minmin Zhou, Yuchen Gu Laboratory of Lake Ecology and Environment, School of Environmental and Civil Engineering, Jiangnan University, Wuxi 214122, China
a r t i c l e
i n f o
Article history: Received 24 November 2010 Received in revised form 21 November 2011 Accepted 21 November 2011 Available online 10 December 2011 Keywords: Magnetic exposure Organo-bentonite Methyl blue Adsorption
a b s t r a c t The influence of adsorbent dosage, initial dye concentration, pH value, intensity of magnetic field and exposure types of the magnetic field on the adsorption of methyl blue were examined. The optimum condition was pH 7.0–8.0, magnetic exposure at the bottom due to the action of Lorentz force at an adsorbent dosage of 1.0 g/L and initial MB concentration 100 mg/L. The adsorption data were fitted by Freundlich model. The magnetic field improved the adsorption coefficient (Kads.) of the Freundlich model by 49%. The pseudosecond order rate constant (k2) of the adsorption kinetics was increased by 143%. The application of magnetic field enhanced the adsorption ability and obviously affected the adsorption behavior of the organo-bentonite. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Effluents from numerous dyeing industries and terminal users of dyes and pigments not only cause damage to aquatic life, but also to human by mutagenic and carcinogenic effects. For solving this problem, bentonite is used as an absorbent for the removal of various organic compounds, metal ions and basic dyes. Bentonite modified by organic cations (organo-bentonite) is widely utilized in the decolorization of dyes from industrial effluents (Baskaralingam et al., 2006; Khenifi et al., 2007). There are many reports about the modified bentonites, such as organo-bentonite, inorganic-organo-bentonite and organophilic-bentonite, which showed outstanding performance on the separation and removal of dyes (Li et al., 2007; Shen et al., 2009; Yue et al., 2007) and metal ions (Andini et al., 2006; Gitipour et al., 1998; Marsal et al., 2009; Shakir et al., 2008; Yıldız et al., 2005; Zhu and Zhu, 2007). Magnetic field-exposed methods have gradually drawn attention to improving the adsorption and separation. Some researchers described the impacts of magnetic exposure on nonmagnetic colloidal particles in aqueous solutions and the comparison of physiochemical properties before and after magnetic exposure (Higashitani et al., 1995; Zhang et al., 2004, 2005). In addition, an interest was focused on utilizing magnetic materials (such as magnetite and magnetitesilica composites) to separate metal ions in aqueous solution for wastewater treatment (Ebner et al., 2001). On the other hand, magnetic exposure on the water changed water properties and the interface between water and solid surface by magnetic-field-induced
⁎ Corresponding author. Tel./fax: + 86 510 85326571. E-mail address: [email protected] (X. Hao). 0169-1317/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2011.11.019
adsorption and desorption (MAD) (Otsuka and Ozeki, 2006; Ozeki et al., 1996). However, until recently, there is some lack of knowledge about magnetic effects on adsorption and the mechanism of magnetic exposure on adsorption characteristics of organic compounds on clay minerals, especially the organo-bentonite. In this study, methyl blue (MB) as a typical dye was used to evaluate the effect of a magnetic field on the adsorption. Static magnetization is convenient, simple, of little cost, and may be an alternative to improve the adsorption. This paper aims to provide basic experimental findings of magnetic assisted adsorption and to guide the application of the magnetic chemistry on adsorption process and wastewater treatment. 2. Experimental 2.1. Materials The organobentonite (HFGEL-110) was bought from Zhejiang Feng Hong Clay Chemical Co., Ltd (Zhejiang, China), which was modified by using bentonite as a matrix and organic ammonium salt as the modifying agent in the hydrothermal process. It contained about 95% bentonite with the chemical composition of 60.12% SiO2, 14.81% Al2O3, 1.88% CaO, 2.14% MgO, 7.93% Fe2O3, 1.53% Na2O, 1.09% K2O by XPS. The grains size of the bentonite was about 200 mesh size (≥97.0), mass loss after calcination was 35.5%, apparent density was about 0.44 g/cm 3, and the true density was approximately 1.70 g/cm 3. Its cation exchange capacity (CEC) was 0.65 meq/g of bentonite measured by the methylene blue method (Kahr and Madsen, 1995). The BET surface area of this organo-bentonite was 8.6 m 2/g by N2. The basal spacing value of this organo-bentonite was 2.03 nm. Methyl blue (MB, Fig. 1) (high purity > 96%) was supplied by Shanghai Biaoben Model Co., Ltd (Shanghai, China). The
178
X. Hao et al. / Applied Clay Science 55 (2012) 177–180
3. Results and discussion 3.1. Optimization of experimental conditions
Fig. 1. Structure of methyl blue.
plate stone magnates with various surface magnetic intensities were bought from Wuxi Hardware Co., Ltd (Jiangsu, China).
To select the optimal adsorption condition without magnetic field, we varied the concentration of methyl blue from 50 mg/L to 150 mg/ L, pH from 4 to 10, and the range of the organo-bentonite content from 0.05 g/L to 1.5 g/L. We found the following optimal experimental conditions: initial MB concentrations approximately 100 mg/L, pH 7.0–8.0, initial adsorbent content of 1.0 g/L. The optimal pH values can be explained as follows (Dentel et al., 1995): The electrophoretic mobility of the organo-bentonite particles at pH 3 to 11 was positive, confirming an excess of positive charges. In alkaline solution the number of the positive charges is reduced, thus decreasing the adsorption of the dye anions. Protonation of the NH groups of the dye decreasing the negative charge of the dye anions also reduces the adsorption in acidic medium.
3.2. Influence of the magnetic field on the MB adsorption 2.2. Adsorption experiments Adsorption experiments were conducted at 25 ± 3°C. The experimental diagram is depicted in Fig. 2. Each experiment was conducted in a 200 mL beaker with a cooling water jacket. The organo-bentonite was dispersed in distilled water before methyl blue solution was added. The samples were agitated in a rotary shaker at 200 rpm. Every 10 min, we removed 2.0 mL of the solution, and separated the organo-bentonite by centrifugation. The intensity of the magnetic field was 0 T, about 0.08 T (weak magnetic field) and about 0.32 T (strong magnetic field), respectively. The magnetic field intensity was measured at the center of dispersion by a magnetic field meter (CLASS TOUCHSTONE-10). Each experiment was conducted in triplicate. The average values were reported. The absorbance of methyl blue was measured at 600 nm with the spectrophotometer 721 (Jiangshu, China). MB removal rate (η) is expressed by: η ¼ ð1−C t =C 0 Þ 100%
ð1Þ
where Ct is the concentration of MB at time t (mg/L), C0 the initial concentration (mg/L).The adsorption (qt) is calculated as: ð2Þ
where qt is the adsorption at time t (mg/g), Ct the concentration of MB in the solution at time t (mg/L), and Cads. the adsorbent content (mg/L). 1 2
1 2 3 4 5 6
(a)
3 4 5 6
(b)
1. Flat bottom beaker; 2. Mechanical agitation; 3. Cooling water; 4. Water jacket; 5. Magnetic lines of force; 6. Magnet plate. Fig. 2. Different modes of magnetic exposure: (a) magnetic exposure at the two sides for bipolar repulsion or attraction; and (b) magnetic exposure at the bottom.
No magnetic field With magnetic exposure from the bottom With magnetic exposure by bipolar repulsion With magnetic exposure by bipolar attraction
100
Methyl blue concentrion (mg/L)
qt ¼ ðC 0 −C t Þ=C ads:
3.2.1. Effect of the orientation magnetic field When the magnetic field was directed perpendicular to the bottom of the vessel, the time to reach the adsorption equilibrium was shorter than for an arrangement with the field parallel to the bottom but the equilibrium amount of dye adsorbed was only slightly changed (Fig. 3). The orientation of the dye molecules may promote the penetration into the pores of the organo-bentonite accelerating the adsorption process. The bipolar attraction on two sides of the solution is not favorable for MB adsorption in contrast to the bipolar mutual repulsion (Fig. 3). When MB molecules have negative charges and move clockwise, the Lorentz force is directed inward or outward twice a round under bipolar repulsive exposure according to Lorentz Force Law (Naletova et al., 2005), which will draw the MB molecules away or back from the organo-bentonite twice, and the MB molecules move counter-clockwise, vice versa (Fig. 4(1)). However, under bipolar attractive exposure, the MB molecules are drawn away or back once for a cycle, which is one time longer than under repulsive magnetic exposure, and it makes MB molecules easily desorbed from the organo-bentonite (Fig. 4(2)). When the magnetic field is directed perpendicular to the bottom, the direction of the movement of MB molecules is vertical to the magnetic lines of force, and the Lorentz force always draws MB molecules onto the organo-bentonite surface at a direction, which benefits MB molecules adsorption.
80
60
40
20
0 0
20
40
60
80
100
120
Fig. 3. Influence of the direction of the magnetic field on the adsorption of MB. (pH 7.0±0.2; adsorbent content 1.0 g/L; initial dye concentration 100 mg/L.).
X. Hao et al. / Applied Clay Science 55 (2012) 177–180
179
parameters were calculated from linear and nonlinear curve fits by the OriginLab 8.0 software (Table 1). Langmuir equation: qe ¼
qm bC e 1 þ bC e
ð3Þ
Freundlich equation: 1
qe ¼ K ads: C e
(2) Bipolar attraction
(1) Bipolar repulsion Magnetic line of force
Movement track of bentonite particle
Bentonite particle
Dye molecule
Lorentz force inward and vertical to paper plane
Lorentz force outward and vertical to paper plane
Under magnetic field exposure, the properties of adsorbate and adsorbent would change, e.g. magnetized water (Higashitani and Oshitani, 1998), and the surface morphology of the adsorbents may become less homogeneous under magnetic exposure (Bel'chinskaya et al., 2009) which would increase the surface area of organobentonite particles to enhance the adsorption of MB dye. On the other hand, the exposure to the magnetic field could influence more the organo-bentonite particles than the MB molecules, because of some components in the bentonite, such as Fe2O3, were magnetic sensitive, which would enhance the adsorption of the MB molecules under magnetic field exposure. 3.2.2. Effect of the intensity of the magnetic field Increasing the magnetic field intensity, the MB adsorption was improved (Fig. 5). Therefore, a high intensity of the magnetic field is an important factor for further application of magnetic field assisted adsorption on wastewater treatment.
3.3.1. Adsorption isotherms The adsorption data were fitted by the Langmuir, Freundlich and Redlich-Peterson models (Bokova et al., 2004; Faria et al., 2005; Sánchez-Polo and Rivera-Utrilla, 2003), and the corresponding
Methyl blue concentration (mg/L)
aC e 1 þ bC ne
ð5Þ
where qe is the amount of adsorbed dye at equilibrium (mg/g), Ce the absorbent content (mg/L) and Kads. the adsorption affinity coefficient (mg g − 1 (L mg − 1) 1/n). The correlation coefficients (R 2) for the Freundlich model were the highest values. The magnitude of the dimensionless exponent n reflects the surface heterogeneity of the adsorbent, and values between 1 and 10 indicate beneficial adsorption (Anbia and Hariri, 2010). The adsorption coefficient (Kads.) of 51.3 under influence of the magnetic field was higher than in the absence of the magnetic field (46.6). The value of qm of the Langmuir model and of a of the Redlich-Peterson model also indicated the positive influence of the magnetic field. 3.3.2. Adsorption kinetics The pseudo first-order and second-order kinetic models have the following forms (Anbia and Hariri, 2010): dqt =dt ¼ k1 ðqe −qt Þ
ð6Þ
2
dqt =dt ¼ k2 ðqe −qt Þ
ð7Þ
These differential equations were converted to linear kinetic equations (Baskaralingam et al., 2006):
3.3. Adsorption isotherms and kinetics
With no magnetic exposure With weak magnetic exposure With strong magnetic exposure
100
ð4Þ
Redlich-Peterson equation: qe ¼
Fig. 4. Schematic Explanation of the direction of the magnetic field on the MB adsorption.
=n
80
logðqe −qt Þ ¼ logqe −ðk1 =2:303Þt
ð8Þ
2 t=qt ¼ 1= k2 qe þ ð1=qe Þt
ð9Þ
where qt is the amount of adsorbed dye (mg/g) at time t (min), qe the amount of adsorbed dye at equilibrium (mg/g), k1 the equilibrium rate constant of the pseudo first-order model (min–1), and k2 the equilibrium rate constant of the pseudo second-order model (g mg− 1 min–1). The correlation coefficients (R 2) >0.99 for the pseudo secondorder model were higher than for the pseudo first-order kinetics
60 Table 1 Langmuir, Freundlich and Redlich-Peterson constants for adsorption of MB on the organo-bentonite.
40
20
Isotherms
Parameters
No magnetic exposure
Magnetic exposure
Langmuir
qm (mg g− 1) b (L mg− 1) R2 Kads. (mg g− 1 (L mg− 1)1/n) n R2 a b n R2
92.96 3.42 0.9789 46.62 3.46 0.9982 89.54 2.96 × 10− 2 78.53 × 10− 2 0.9602
98.15 5.67 0.9852 51.32 2.67 0.9913 183.00 4.76 × 10− 2 79.75 × 10− 2 0.9522
Freundlich
0 0
20
40
60
80
100
120
Time (min) Fig. 5. Effect of the intensity of the magnetic field perpendicular to the bottom on the adsorption of MB. (pH 7.0 ± 0.2; adsorbent content 1.0 g/L; initial dye concentration 100 mg/L.).
Redlich-Peterson
180
X. Hao et al. / Applied Clay Science 55 (2012) 177–180
Acknowledgments
(a)
1.2
Without magnetic exposure With magnetic exposure
1.0
We really appreciate the partial financial supports from the Selfdetermined Research Program of Jiangnan University (No. 20091102), the National Natural Science Foundation of China (Nos. 21107034 and 20707007), and the Fundamental Research Funds for the Central Universities (No. JUSRP31105).
0.8
log (qe-qt)
0.6 0.4 0.2
References
0.0 -0.2 -0.4 -0.6 0
10
20
30
40
50
60
70
80
90
Time (min) 1.0
(b)
t/qt (min g mg-1)
0.8
0.6
0.4
0.2
Without magnetic exposure With magnetic exposure
0.0 0
10
20
30
40
50
60
70
80
90
Time (min) Fig. 6. The pseudo first-order kinetics (A) and pseudo second-order kinetics (B) for the adsorption of MB onto organo-bentonite. (pH 7.0 ± 0.2; adsorbent content 1.0 g/L; initial dye concentration 100 mg/L.).
(Fig. 6). The pseudo-second coefficient (k2) was 6.089 × 10 − 3 without magnetic field and 1.479 × 10 − 2 under magnetic exposure (Table 2).
4. Conclusions The optimum conditions for the methyl blue (MB) adsorption on the organo-bentonite under the influence of a magnetic field were pH = 7.0–8.0, adsorbent content 1.0 g/L, MB concentration 100 mg/L. The Freundlich isotherm model showed the best fit with the experimental data. The rate constants of the pseudo second-order model indicated that the adsorption increased with increasing magnetic intensity. Table 2 The pseudo first-order and pseudo second-order rate constants. First-order kinetic model R2
qe k1 (mg g− 1) (min–1) No magnetic 89.99 exposure Magnetic 94.30 exposure
Second-order kinetic model qe k2 R2 (mg g− 1) (g mg− 1 min–1)
2.95 × 10− 2 0.9744 90.25 4.06 × 10
−2
0.9690 94.88
6.089 × 10− 3
0.9998
−2
0.9999
1.479 × 10
Anbia, M., Hariri, S.A., 2010. Removal of methylene blue from aqueous solution using nanoporous SBA-3. Desalination 261, 61–66. Andini, S., Cioffi, R., Montagnaro, F., Pisciotta, F., Santoro, L., 2006. Simultaneous adsorption of chlorophenol and heavy metal ions on organophilic bentonite. Applied Clay Science 31, 126–133. Baskaralingam, P., Pulikesi, M., Elango, D., Ramamurthi, V., Sivanesan, S., 2006. Adsorption of acid dye onto organobentonite. Journal of Hazardous Materials 128, 138–144. Bel'chinskaya, L.I., Khodosova, N.A., Bityutskaya, L.A., 2009. Adsorption of formaldehyde at mineral nanoporous sorbents exposed to a pulse magnetic field. Protection of Metals and Physial Chemistry of Surfaces 45 (2), 203–206. Bokova, M., Decarne, C., Abi-Aad, E., Pryakhin, A., Lunin, V., Aboukaïs, A., 2004. Effects of ozone on the catalytic combustion of carbon black. Applied Catalysis B: Environmental 54 (1), 9–17. Dentel, S.K., Bottero, J.Y., Khatib, K., Demougeot, H., Duguet, J.P., Anselme, C., 1995. Sorption of tannic acid, phenol, and 2,4,5-trichlorophenol on organoclays. Water Research 29, 1273–1280. Ebner, A.D., Ritter, J.A., Navratil, J.D., 2001. Adsorption of cesium, strontium and cobalt ions on magnetite and magnetite-silica composite. Industrial and Engineering Chemistry Research 40, 1615–1623. Faria, P.C.C., Órfão, J.J.M., Pereira, M.F.R., 2005. Mineralisation of coloured aqueous solutions by ozonation in the presence of activated carbon. Water Research 39 (8), 1461–1470. Gitipour, S., Bowers, M.T., Huff, W., Bodocsi, A., 1998. The efficiency of modified bentonite clays for removal of aromatic organics from oily liquid wastes. Spill Science and Technology Bulletin 3, 155–164. Higashitani, K., Oshitani, J., 1998. Magnetic Effects on thickness of adsorbed layer in aqueous solutions evaluated directly by atomic force microscope. Journal of Colloid and Interface Science 204, 363–368. Higashitani, K., Iseri, H., Okuuhara, K., Kage, A., Hatade, S., 1995. Magnetic effects on zeta potential and diffusivity of nonmagnetic colloidal particles. Journal of Colloid and Interface Science 172, 383–388. Kahr, G., Madsen, F.T., 1995. Determination of the cation exchange capacity and the surface area of bentonite, illite and kaolinite by methylene blue adsorption. Applied Clay Science 9, 327–336. Khenifi, A., Bouberka, Z., Sekrane, F., Kameche, M., Derriche, Z., 2007. Adsorption study of an industrial dye by an organic clay. Adsorption 13, 149–158. Li, Q., Yue, Q.Y., Su, Y., Gao, B.Y., Fu, L., 2007. Cationic polyelectrolyte/bentonite prepared by ultrasonic technique and its use as adsorbent for Reactive Blue K-GL dye. Journal of Hazardous Materials 147, 370–380. Marsal, A., Bautista, E., Ribosa, I., Pons, R., García, M.T., 2009. Adsorption of polyphenols in wastewater by organo-bentonites. Applied Clay Science 44, 151–155. Naletova, V.A., Turkov, V.A., Tyatyushkin, A.N., 2005. Spherical body in a magnetic fluid in uniform electric and magnetic fields. Journal of Magnetism and Magnetic Materials 289, 370–372. Otsuka, I., Ozeki, S., 2006. Does magnetic treatment of water change its properties? The Journal of Physical Chemistry. B 110, 1509–1512. Ozeki, S., Miyamoto, J., Ono, S., Wakai, C., Watanabe, T., 1996. Water-solid interactions under steady magnetic fields: Magnetic-field-induced adsorption and desorption of water. Journal of Physical Chemistry A 100, 4205–4212. Sánchez-Polo, M., Rivera-Utrilla, J., 2003. Effect of the ozone–carbon reaction on the catalytic activity of activated carbon during the degradation of 1,3,6-naphthalenetrisulphonic acid with ozone. Carbon 41 (2), 303–307. Shakir, K., Ghoneimy, H.F., Elkafrawy, A.F., Beheir, S.G., Refaat, M., 2008. Removal of catechol from aqueous solutions by adsorption onto organophilic-bentonite. Journal of Hazardous Materials 150, 765–773. Shen, D.Z., Fan, J.X., Zhou, W.Z., Gao, B.Y., Yue, Q.Y., Kang, Q., 2009. Adsorption kinetics and isotherm of anionic dyes onto organo-bentonite from single and multisolute systems. Journal of Hazardous Materials 172, 99–107. Yıldız, N., Gönülşen, R., Koyuncu, H., Çalımlı, A., 2005. Adsorption of benzoic acid and hydroquinone by organically modified bentonites. Colloids and Surfaces A: Physicochemical and Engineering Aspects 260, 87–94. Yue, Q.Y., Li, Q., Gao, B.Y., Wang, Y., 2007. Kinetics of adsorption of disperse dyes by polyepicholorohydrin-dimethylamine cationic polymer/bentonite. Separation and Purification Technology 54, 279–290. Zhang, G.K., Yang, X., Liu, Y., Jia, Y.Y., Yu, G.W., Ouyang, S.X., 2004. Copper(II) adsorption on Ca-rectorite, and effect of static magnetic field on the adsorption. Journal of Colloid and Interface Science 278, 265–269. Zhang, G.K., Liu, Y., Xie, Y., Yang, X., Hu, B., Ouyang, S.X., Liu, H.X., Wang, H.Y., 2005. Zinc adsorption on Na-rectorite and effect of static magnetic field on the adsorption. Applied Clay Science 29, 15–21. Zhu, L.Z., Zhu, R.L., 2007. Simultaneous sorption of organic compounds and phosphate to inorganic–organic bentonites from water. Separation and Purification Technology 54, 71–76.
Contents lists available at SciVerse ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Note
Magnetic field assisted adsorption of methyl blue onto organo-bentonite Xiaolong Hao ⁎, He Liu, Guangsheng Zhang, Hua Zou, Yibo Zhang, Minmin Zhou, Yuchen Gu Laboratory of Lake Ecology and Environment, School of Environmental and Civil Engineering, Jiangnan University, Wuxi 214122, China
a r t i c l e
i n f o
Article history: Received 24 November 2010 Received in revised form 21 November 2011 Accepted 21 November 2011 Available online 10 December 2011 Keywords: Magnetic exposure Organo-bentonite Methyl blue Adsorption
a b s t r a c t The influence of adsorbent dosage, initial dye concentration, pH value, intensity of magnetic field and exposure types of the magnetic field on the adsorption of methyl blue were examined. The optimum condition was pH 7.0–8.0, magnetic exposure at the bottom due to the action of Lorentz force at an adsorbent dosage of 1.0 g/L and initial MB concentration 100 mg/L. The adsorption data were fitted by Freundlich model. The magnetic field improved the adsorption coefficient (Kads.) of the Freundlich model by 49%. The pseudosecond order rate constant (k2) of the adsorption kinetics was increased by 143%. The application of magnetic field enhanced the adsorption ability and obviously affected the adsorption behavior of the organo-bentonite. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Effluents from numerous dyeing industries and terminal users of dyes and pigments not only cause damage to aquatic life, but also to human by mutagenic and carcinogenic effects. For solving this problem, bentonite is used as an absorbent for the removal of various organic compounds, metal ions and basic dyes. Bentonite modified by organic cations (organo-bentonite) is widely utilized in the decolorization of dyes from industrial effluents (Baskaralingam et al., 2006; Khenifi et al., 2007). There are many reports about the modified bentonites, such as organo-bentonite, inorganic-organo-bentonite and organophilic-bentonite, which showed outstanding performance on the separation and removal of dyes (Li et al., 2007; Shen et al., 2009; Yue et al., 2007) and metal ions (Andini et al., 2006; Gitipour et al., 1998; Marsal et al., 2009; Shakir et al., 2008; Yıldız et al., 2005; Zhu and Zhu, 2007). Magnetic field-exposed methods have gradually drawn attention to improving the adsorption and separation. Some researchers described the impacts of magnetic exposure on nonmagnetic colloidal particles in aqueous solutions and the comparison of physiochemical properties before and after magnetic exposure (Higashitani et al., 1995; Zhang et al., 2004, 2005). In addition, an interest was focused on utilizing magnetic materials (such as magnetite and magnetitesilica composites) to separate metal ions in aqueous solution for wastewater treatment (Ebner et al., 2001). On the other hand, magnetic exposure on the water changed water properties and the interface between water and solid surface by magnetic-field-induced
⁎ Corresponding author. Tel./fax: + 86 510 85326571. E-mail address: [email protected] (X. Hao). 0169-1317/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2011.11.019
adsorption and desorption (MAD) (Otsuka and Ozeki, 2006; Ozeki et al., 1996). However, until recently, there is some lack of knowledge about magnetic effects on adsorption and the mechanism of magnetic exposure on adsorption characteristics of organic compounds on clay minerals, especially the organo-bentonite. In this study, methyl blue (MB) as a typical dye was used to evaluate the effect of a magnetic field on the adsorption. Static magnetization is convenient, simple, of little cost, and may be an alternative to improve the adsorption. This paper aims to provide basic experimental findings of magnetic assisted adsorption and to guide the application of the magnetic chemistry on adsorption process and wastewater treatment. 2. Experimental 2.1. Materials The organobentonite (HFGEL-110) was bought from Zhejiang Feng Hong Clay Chemical Co., Ltd (Zhejiang, China), which was modified by using bentonite as a matrix and organic ammonium salt as the modifying agent in the hydrothermal process. It contained about 95% bentonite with the chemical composition of 60.12% SiO2, 14.81% Al2O3, 1.88% CaO, 2.14% MgO, 7.93% Fe2O3, 1.53% Na2O, 1.09% K2O by XPS. The grains size of the bentonite was about 200 mesh size (≥97.0), mass loss after calcination was 35.5%, apparent density was about 0.44 g/cm 3, and the true density was approximately 1.70 g/cm 3. Its cation exchange capacity (CEC) was 0.65 meq/g of bentonite measured by the methylene blue method (Kahr and Madsen, 1995). The BET surface area of this organo-bentonite was 8.6 m 2/g by N2. The basal spacing value of this organo-bentonite was 2.03 nm. Methyl blue (MB, Fig. 1) (high purity > 96%) was supplied by Shanghai Biaoben Model Co., Ltd (Shanghai, China). The
178
X. Hao et al. / Applied Clay Science 55 (2012) 177–180
3. Results and discussion 3.1. Optimization of experimental conditions
Fig. 1. Structure of methyl blue.
plate stone magnates with various surface magnetic intensities were bought from Wuxi Hardware Co., Ltd (Jiangsu, China).
To select the optimal adsorption condition without magnetic field, we varied the concentration of methyl blue from 50 mg/L to 150 mg/ L, pH from 4 to 10, and the range of the organo-bentonite content from 0.05 g/L to 1.5 g/L. We found the following optimal experimental conditions: initial MB concentrations approximately 100 mg/L, pH 7.0–8.0, initial adsorbent content of 1.0 g/L. The optimal pH values can be explained as follows (Dentel et al., 1995): The electrophoretic mobility of the organo-bentonite particles at pH 3 to 11 was positive, confirming an excess of positive charges. In alkaline solution the number of the positive charges is reduced, thus decreasing the adsorption of the dye anions. Protonation of the NH groups of the dye decreasing the negative charge of the dye anions also reduces the adsorption in acidic medium.
3.2. Influence of the magnetic field on the MB adsorption 2.2. Adsorption experiments Adsorption experiments were conducted at 25 ± 3°C. The experimental diagram is depicted in Fig. 2. Each experiment was conducted in a 200 mL beaker with a cooling water jacket. The organo-bentonite was dispersed in distilled water before methyl blue solution was added. The samples were agitated in a rotary shaker at 200 rpm. Every 10 min, we removed 2.0 mL of the solution, and separated the organo-bentonite by centrifugation. The intensity of the magnetic field was 0 T, about 0.08 T (weak magnetic field) and about 0.32 T (strong magnetic field), respectively. The magnetic field intensity was measured at the center of dispersion by a magnetic field meter (CLASS TOUCHSTONE-10). Each experiment was conducted in triplicate. The average values were reported. The absorbance of methyl blue was measured at 600 nm with the spectrophotometer 721 (Jiangshu, China). MB removal rate (η) is expressed by: η ¼ ð1−C t =C 0 Þ 100%
ð1Þ
where Ct is the concentration of MB at time t (mg/L), C0 the initial concentration (mg/L).The adsorption (qt) is calculated as: ð2Þ
where qt is the adsorption at time t (mg/g), Ct the concentration of MB in the solution at time t (mg/L), and Cads. the adsorbent content (mg/L). 1 2
1 2 3 4 5 6
(a)
3 4 5 6
(b)
1. Flat bottom beaker; 2. Mechanical agitation; 3. Cooling water; 4. Water jacket; 5. Magnetic lines of force; 6. Magnet plate. Fig. 2. Different modes of magnetic exposure: (a) magnetic exposure at the two sides for bipolar repulsion or attraction; and (b) magnetic exposure at the bottom.
No magnetic field With magnetic exposure from the bottom With magnetic exposure by bipolar repulsion With magnetic exposure by bipolar attraction
100
Methyl blue concentrion (mg/L)
qt ¼ ðC 0 −C t Þ=C ads:
3.2.1. Effect of the orientation magnetic field When the magnetic field was directed perpendicular to the bottom of the vessel, the time to reach the adsorption equilibrium was shorter than for an arrangement with the field parallel to the bottom but the equilibrium amount of dye adsorbed was only slightly changed (Fig. 3). The orientation of the dye molecules may promote the penetration into the pores of the organo-bentonite accelerating the adsorption process. The bipolar attraction on two sides of the solution is not favorable for MB adsorption in contrast to the bipolar mutual repulsion (Fig. 3). When MB molecules have negative charges and move clockwise, the Lorentz force is directed inward or outward twice a round under bipolar repulsive exposure according to Lorentz Force Law (Naletova et al., 2005), which will draw the MB molecules away or back from the organo-bentonite twice, and the MB molecules move counter-clockwise, vice versa (Fig. 4(1)). However, under bipolar attractive exposure, the MB molecules are drawn away or back once for a cycle, which is one time longer than under repulsive magnetic exposure, and it makes MB molecules easily desorbed from the organo-bentonite (Fig. 4(2)). When the magnetic field is directed perpendicular to the bottom, the direction of the movement of MB molecules is vertical to the magnetic lines of force, and the Lorentz force always draws MB molecules onto the organo-bentonite surface at a direction, which benefits MB molecules adsorption.
80
60
40
20
0 0
20
40
60
80
100
120
Fig. 3. Influence of the direction of the magnetic field on the adsorption of MB. (pH 7.0±0.2; adsorbent content 1.0 g/L; initial dye concentration 100 mg/L.).
X. Hao et al. / Applied Clay Science 55 (2012) 177–180
179
parameters were calculated from linear and nonlinear curve fits by the OriginLab 8.0 software (Table 1). Langmuir equation: qe ¼
qm bC e 1 þ bC e
ð3Þ
Freundlich equation: 1
qe ¼ K ads: C e
(2) Bipolar attraction
(1) Bipolar repulsion Magnetic line of force
Movement track of bentonite particle
Bentonite particle
Dye molecule
Lorentz force inward and vertical to paper plane
Lorentz force outward and vertical to paper plane
Under magnetic field exposure, the properties of adsorbate and adsorbent would change, e.g. magnetized water (Higashitani and Oshitani, 1998), and the surface morphology of the adsorbents may become less homogeneous under magnetic exposure (Bel'chinskaya et al., 2009) which would increase the surface area of organobentonite particles to enhance the adsorption of MB dye. On the other hand, the exposure to the magnetic field could influence more the organo-bentonite particles than the MB molecules, because of some components in the bentonite, such as Fe2O3, were magnetic sensitive, which would enhance the adsorption of the MB molecules under magnetic field exposure. 3.2.2. Effect of the intensity of the magnetic field Increasing the magnetic field intensity, the MB adsorption was improved (Fig. 5). Therefore, a high intensity of the magnetic field is an important factor for further application of magnetic field assisted adsorption on wastewater treatment.
3.3.1. Adsorption isotherms The adsorption data were fitted by the Langmuir, Freundlich and Redlich-Peterson models (Bokova et al., 2004; Faria et al., 2005; Sánchez-Polo and Rivera-Utrilla, 2003), and the corresponding
Methyl blue concentration (mg/L)
aC e 1 þ bC ne
ð5Þ
where qe is the amount of adsorbed dye at equilibrium (mg/g), Ce the absorbent content (mg/L) and Kads. the adsorption affinity coefficient (mg g − 1 (L mg − 1) 1/n). The correlation coefficients (R 2) for the Freundlich model were the highest values. The magnitude of the dimensionless exponent n reflects the surface heterogeneity of the adsorbent, and values between 1 and 10 indicate beneficial adsorption (Anbia and Hariri, 2010). The adsorption coefficient (Kads.) of 51.3 under influence of the magnetic field was higher than in the absence of the magnetic field (46.6). The value of qm of the Langmuir model and of a of the Redlich-Peterson model also indicated the positive influence of the magnetic field. 3.3.2. Adsorption kinetics The pseudo first-order and second-order kinetic models have the following forms (Anbia and Hariri, 2010): dqt =dt ¼ k1 ðqe −qt Þ
ð6Þ
2
dqt =dt ¼ k2 ðqe −qt Þ
ð7Þ
These differential equations were converted to linear kinetic equations (Baskaralingam et al., 2006):
3.3. Adsorption isotherms and kinetics
With no magnetic exposure With weak magnetic exposure With strong magnetic exposure
100
ð4Þ
Redlich-Peterson equation: qe ¼
Fig. 4. Schematic Explanation of the direction of the magnetic field on the MB adsorption.
=n
80
logðqe −qt Þ ¼ logqe −ðk1 =2:303Þt
ð8Þ
2 t=qt ¼ 1= k2 qe þ ð1=qe Þt
ð9Þ
where qt is the amount of adsorbed dye (mg/g) at time t (min), qe the amount of adsorbed dye at equilibrium (mg/g), k1 the equilibrium rate constant of the pseudo first-order model (min–1), and k2 the equilibrium rate constant of the pseudo second-order model (g mg− 1 min–1). The correlation coefficients (R 2) >0.99 for the pseudo secondorder model were higher than for the pseudo first-order kinetics
60 Table 1 Langmuir, Freundlich and Redlich-Peterson constants for adsorption of MB on the organo-bentonite.
40
20
Isotherms
Parameters
No magnetic exposure
Magnetic exposure
Langmuir
qm (mg g− 1) b (L mg− 1) R2 Kads. (mg g− 1 (L mg− 1)1/n) n R2 a b n R2
92.96 3.42 0.9789 46.62 3.46 0.9982 89.54 2.96 × 10− 2 78.53 × 10− 2 0.9602
98.15 5.67 0.9852 51.32 2.67 0.9913 183.00 4.76 × 10− 2 79.75 × 10− 2 0.9522
Freundlich
0 0
20
40
60
80
100
120
Time (min) Fig. 5. Effect of the intensity of the magnetic field perpendicular to the bottom on the adsorption of MB. (pH 7.0 ± 0.2; adsorbent content 1.0 g/L; initial dye concentration 100 mg/L.).
Redlich-Peterson
180
X. Hao et al. / Applied Clay Science 55 (2012) 177–180
Acknowledgments
(a)
1.2
Without magnetic exposure With magnetic exposure
1.0
We really appreciate the partial financial supports from the Selfdetermined Research Program of Jiangnan University (No. 20091102), the National Natural Science Foundation of China (Nos. 21107034 and 20707007), and the Fundamental Research Funds for the Central Universities (No. JUSRP31105).
0.8
log (qe-qt)
0.6 0.4 0.2
References
0.0 -0.2 -0.4 -0.6 0
10
20
30
40
50
60
70
80
90
Time (min) 1.0
(b)
t/qt (min g mg-1)
0.8
0.6
0.4
0.2
Without magnetic exposure With magnetic exposure
0.0 0
10
20
30
40
50
60
70
80
90
Time (min) Fig. 6. The pseudo first-order kinetics (A) and pseudo second-order kinetics (B) for the adsorption of MB onto organo-bentonite. (pH 7.0 ± 0.2; adsorbent content 1.0 g/L; initial dye concentration 100 mg/L.).
(Fig. 6). The pseudo-second coefficient (k2) was 6.089 × 10 − 3 without magnetic field and 1.479 × 10 − 2 under magnetic exposure (Table 2).
4. Conclusions The optimum conditions for the methyl blue (MB) adsorption on the organo-bentonite under the influence of a magnetic field were pH = 7.0–8.0, adsorbent content 1.0 g/L, MB concentration 100 mg/L. The Freundlich isotherm model showed the best fit with the experimental data. The rate constants of the pseudo second-order model indicated that the adsorption increased with increasing magnetic intensity. Table 2 The pseudo first-order and pseudo second-order rate constants. First-order kinetic model R2
qe k1 (mg g− 1) (min–1) No magnetic 89.99 exposure Magnetic 94.30 exposure
Second-order kinetic model qe k2 R2 (mg g− 1) (g mg− 1 min–1)
2.95 × 10− 2 0.9744 90.25 4.06 × 10
−2
0.9690 94.88
6.089 × 10− 3
0.9998
−2
0.9999
1.479 × 10
Anbia, M., Hariri, S.A., 2010. Removal of methylene blue from aqueous solution using nanoporous SBA-3. Desalination 261, 61–66. Andini, S., Cioffi, R., Montagnaro, F., Pisciotta, F., Santoro, L., 2006. Simultaneous adsorption of chlorophenol and heavy metal ions on organophilic bentonite. Applied Clay Science 31, 126–133. Baskaralingam, P., Pulikesi, M., Elango, D., Ramamurthi, V., Sivanesan, S., 2006. Adsorption of acid dye onto organobentonite. Journal of Hazardous Materials 128, 138–144. Bel'chinskaya, L.I., Khodosova, N.A., Bityutskaya, L.A., 2009. Adsorption of formaldehyde at mineral nanoporous sorbents exposed to a pulse magnetic field. Protection of Metals and Physial Chemistry of Surfaces 45 (2), 203–206. Bokova, M., Decarne, C., Abi-Aad, E., Pryakhin, A., Lunin, V., Aboukaïs, A., 2004. Effects of ozone on the catalytic combustion of carbon black. Applied Catalysis B: Environmental 54 (1), 9–17. Dentel, S.K., Bottero, J.Y., Khatib, K., Demougeot, H., Duguet, J.P., Anselme, C., 1995. Sorption of tannic acid, phenol, and 2,4,5-trichlorophenol on organoclays. Water Research 29, 1273–1280. Ebner, A.D., Ritter, J.A., Navratil, J.D., 2001. Adsorption of cesium, strontium and cobalt ions on magnetite and magnetite-silica composite. Industrial and Engineering Chemistry Research 40, 1615–1623. Faria, P.C.C., Órfão, J.J.M., Pereira, M.F.R., 2005. Mineralisation of coloured aqueous solutions by ozonation in the presence of activated carbon. Water Research 39 (8), 1461–1470. Gitipour, S., Bowers, M.T., Huff, W., Bodocsi, A., 1998. The efficiency of modified bentonite clays for removal of aromatic organics from oily liquid wastes. Spill Science and Technology Bulletin 3, 155–164. Higashitani, K., Oshitani, J., 1998. Magnetic Effects on thickness of adsorbed layer in aqueous solutions evaluated directly by atomic force microscope. Journal of Colloid and Interface Science 204, 363–368. Higashitani, K., Iseri, H., Okuuhara, K., Kage, A., Hatade, S., 1995. Magnetic effects on zeta potential and diffusivity of nonmagnetic colloidal particles. Journal of Colloid and Interface Science 172, 383–388. Kahr, G., Madsen, F.T., 1995. Determination of the cation exchange capacity and the surface area of bentonite, illite and kaolinite by methylene blue adsorption. Applied Clay Science 9, 327–336. Khenifi, A., Bouberka, Z., Sekrane, F., Kameche, M., Derriche, Z., 2007. Adsorption study of an industrial dye by an organic clay. Adsorption 13, 149–158. Li, Q., Yue, Q.Y., Su, Y., Gao, B.Y., Fu, L., 2007. Cationic polyelectrolyte/bentonite prepared by ultrasonic technique and its use as adsorbent for Reactive Blue K-GL dye. Journal of Hazardous Materials 147, 370–380. Marsal, A., Bautista, E., Ribosa, I., Pons, R., García, M.T., 2009. Adsorption of polyphenols in wastewater by organo-bentonites. Applied Clay Science 44, 151–155. Naletova, V.A., Turkov, V.A., Tyatyushkin, A.N., 2005. Spherical body in a magnetic fluid in uniform electric and magnetic fields. Journal of Magnetism and Magnetic Materials 289, 370–372. Otsuka, I., Ozeki, S., 2006. Does magnetic treatment of water change its properties? The Journal of Physical Chemistry. B 110, 1509–1512. Ozeki, S., Miyamoto, J., Ono, S., Wakai, C., Watanabe, T., 1996. Water-solid interactions under steady magnetic fields: Magnetic-field-induced adsorption and desorption of water. Journal of Physical Chemistry A 100, 4205–4212. Sánchez-Polo, M., Rivera-Utrilla, J., 2003. Effect of the ozone–carbon reaction on the catalytic activity of activated carbon during the degradation of 1,3,6-naphthalenetrisulphonic acid with ozone. Carbon 41 (2), 303–307. Shakir, K., Ghoneimy, H.F., Elkafrawy, A.F., Beheir, S.G., Refaat, M., 2008. Removal of catechol from aqueous solutions by adsorption onto organophilic-bentonite. Journal of Hazardous Materials 150, 765–773. Shen, D.Z., Fan, J.X., Zhou, W.Z., Gao, B.Y., Yue, Q.Y., Kang, Q., 2009. Adsorption kinetics and isotherm of anionic dyes onto organo-bentonite from single and multisolute systems. Journal of Hazardous Materials 172, 99–107. Yıldız, N., Gönülşen, R., Koyuncu, H., Çalımlı, A., 2005. Adsorption of benzoic acid and hydroquinone by organically modified bentonites. Colloids and Surfaces A: Physicochemical and Engineering Aspects 260, 87–94. Yue, Q.Y., Li, Q., Gao, B.Y., Wang, Y., 2007. Kinetics of adsorption of disperse dyes by polyepicholorohydrin-dimethylamine cationic polymer/bentonite. Separation and Purification Technology 54, 279–290. Zhang, G.K., Yang, X., Liu, Y., Jia, Y.Y., Yu, G.W., Ouyang, S.X., 2004. Copper(II) adsorption on Ca-rectorite, and effect of static magnetic field on the adsorption. Journal of Colloid and Interface Science 278, 265–269. Zhang, G.K., Liu, Y., Xie, Y., Yang, X., Hu, B., Ouyang, S.X., Liu, H.X., Wang, H.Y., 2005. Zinc adsorption on Na-rectorite and effect of static magnetic field on the adsorption. Applied Clay Science 29, 15–21. Zhu, L.Z., Zhu, R.L., 2007. Simultaneous sorption of organic compounds and phosphate to inorganic–organic bentonites from water. Separation and Purification Technology 54, 71–76.