Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution

Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution

G Model JIEC 3273 No. of Pages 11 Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx Contents lists available at ScienceDirect Jour...

4MB Sizes 0 Downloads 48 Views

G Model JIEC 3273 No. of Pages 11

Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec

Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution Bei Zhanga , Zhihao Dongb , Dejun Sunb , Tao Wua,b,** , Yujiang Lia,* a Shandong Provincial Key laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science & Engineering, Shandong University, Jinan, 250100, PR China b Key Laboratory of Colloid & Interface Science of Education Ministry, Shandong University, Jinan, 250100, PR China

A R T I C L E I N F O

Article history: Received 8 April 2015 Received in revised form 16 January 2017 Accepted 22 January 2017 Available online xxx Keywords: Adsorption Dyes Organic layered double hydroxides Partition Hydrophobic

A B S T R A C T

The utilization of organo-modified layered double hydroxides with anionic surfactants (organo-LDHs) as adsorbents were successfully carried out to remove various synthetic dyes from aqueous solution. Intercalation of anionic surfactants changed the surface properties of MgAl-LDH from hydrophilic to hydrophobic, and a charge inversion occurred with increasing the length of surfactant chains. Such changes in the surface properties of the organo-LDHs were important. Experimental data shown that the SNS-modified MgAl-LDH could be used as a broad-spectrum adsorbent to effectively remove anionic, non-ionic, and cationic dyes from aqueous solution. © 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Introduction Colored dyes are important water pollutants, which are generated from industries such as textile, rubber, paper, plastics, food, and cosmetics [1]. These industries use dyes or pigments for coloration of the final products [1,2]. The high level of dyes production and extensive use of dyes generate colored wastewater, leading to environmental pollution [2,3]. Because dyes are designed to resist degradation with time and exposure to sunlight, water, soap, and oxidizing agents, they cannot be easily removed [1,2]. Dyes can cause short- and long-term changes in ecosystems [3]. Therefore, it is imperative to develop rapid and effective approaches for the removal of colored dyes from water environment before being discharged into natural water bodies. Because of their complex aromatic structures, dyes are chemically inert and difficult to be biodegraded when discharged into aquatic systems [4–6]. Various physical, chemical and biological treatment methods have been used for the removal of various kinds of dyes. However, these methods have numerous disadvantages such as high operation costs, high capital cost, and secondary sludge disposal problems [7]. The adsorption technique

* Corresponding author. Fax: +86 531 8 8365922. ** Corresponding author. Fax: +86 531 88365437. E-mail addresses: [email protected] (T. Wu), [email protected] (Y. Li).

has been proved to be an excellent method to treat colored effluents, offering numerous advantages over traditional methods especially from energetic and environmental point of view [7–13]. Many adsorbents have been investigated for the removal of dyes in recent years, such as fly ash [14], metal oxides [15,16], natural clay minerals [17,18], and layered double hydroxides [19–21]. Among these inorganic materials, layered double hydroxides (LDHs) have attracted much attention [19–21]. However, because of the hydration of inorganic anions (e.g., Cl, NO3 or CO32) on the exchange sites, LDH particles are hydrophilic in nature. Therefore, LDHs have little or no affinity for hydrophobic non-ionic and cationic dyes. As a result, the adsorption ability of organic dyes on the LDHs is very low. The adsorption properties of LDHs can be improved by modifying the LDH surfaces with anionic surfactants. The replacement of inorganic exchangeable anions with organic anions converts the hydrophilic surface of LDHs to a hydrophobic surface, and the obtained complex is referred to as organo-LDHs [22]. Furthermore, a charge inversion from positive to negative may occur with the intercalation of anionic surfactants. Such changes in the surface properties of the organo-LDHs are important due to their application for organic wastewater purification [23]. Actual dye wastewaters released from factories often contain different types of dyes. Most adsorbents are confirmed to be effective for the removal of single particular dye. However, they are ineffective when different types of dyes co-exist in aqueous

http://dx.doi.org/10.1016/j.jiec.2017.01.029 1226-086X/© 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

2

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

solution. It is necessary to develop a broad-spectrum adsorbent capable of removing multi-dye with high adsorption capacity and rapid adsorption rate. In this work, acid red GR (AR-GR), disperse orange 11 (DO-11), and basic yellow 2 (BY-2) were chosen as the test model pollutants. Sodium hexanesulfonate (SHS), sodium nonanesulfonate (SNS), and sodium dodecanesulfonate (SDS) were used as modifiers and the resulted organo-LDHs were used as adsorbents. The present study is of great importance for the structures, properties, and potential applications of organo-LDHs. Batch adsorption experiments were performed under various operating conditions such as adsorbent dosage, pH, contact time, and temperature. Adsorption isotherms and kinetics data were obtained. In addition, interactions between organo-LDHs and dyes were also discussed. Materials and methods Materials Aluminum chloride hexahydrate (AlCl36H2O, 97%), magnesium chloride hexahydrate (MgCl26H2O, 98%), and ammonia water (NH3H2O, 25–28%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Sodium hexanesulfonate (SHS, >98%), sodium nonanesulfonate (SNS, >98%), and sodium dodecanesulfonate (SDS, >99%) were purchased from Sigma-Aldrich (USA). Acid red GR (AR-GR, >99%) was provided by the Jinan Yuanshou Group (China). Disperse orange 11 (DO-11, >80%), and basic yellow 2 (BY-2, >80%) were purchased from TCI Development Co., Ltd. (Shanghai, China) and used without further purification. The chemical structures of AR-GR, DO-11, and BY-2 are shown in Fig. 1. All other chemical reagents were of analytical grade. Preparation of MgAl-LDH and organo-LDHs Preparation of MgAl-LDH The MgAl-LDH precursor was prepared by following a standard co-precipitation method from metal chlorates [23,24]. Diluted NH3H2O (deionized water: NH3H2O = 5:1, v/v) was slowly added to 2000 mL of a mixed aqueous solution containing 2.0 M MgCl26H2O and 1.0 M AlCl36H2O (Mg/Al molar ratio = 2:1). Temperature (25  C) and pH (10.3  0.1) were kept constant with string during the addition of NH3H2O to the mixed aqueous solution, and then the precipitates were allowed to settle for 1 h at 25  C. The precipitates were filtered and washed several times with deionized water in the filter until no chloride ions were detected in the filtrate (as determined by AgNO3). Then, the filter cake was heated to 80  C for 6 h in an oven to convert the filter cake into MgAl-LDH sol with a concentration of 8 wt.%. Preparation of organo-LDHs The organo-LDHs were prepared by respective dropwise addition of 40 mmol/L SHS, SNS, and SDS solutions to 1.0%

(w/w) MgAl-LDH sol. The reaction mixture was stirred for 24 h at 25  C, and then the mixture was centrifuged and washed several times with deionized in order to remove residual surfactant. Then, the organo-LDHs were dried at 60  C in a vacuum oven.

Characterization of adsorbents The morphology and nanostructure of the MgAl-LDH precursor and organo-LDHs were examined by a JEM-2100 high-resolution transmission electron microscope (HRTEM, JEOL, Japan). The crystal structure of samples was identified by a D/Max-rB power diffractometer (XRD, Riguku, Japan) using Cu-Ka radiation source in the 2u range of 2 –70 with a scanning rate of 2 /min. Any resulting chemical bond and surface functional group changes of the samples were recorded on a Perkin-Elmer 100 Fourier transform infrared spectrometer (FT-IR, Perkin-Elmer, USA) by the KBr pellet technique, and scanned from 400 to 4000 cm1. The zeta potentials of MgAl-LDH and organo-LDHs in the NaCl solution (0.001 M) were determined by a ZetaPALS (Brookhaven, New York, USA) with an average value of three parallel measurements. Adsorption experiments Adsorption experiments were performed using a batch method. Batch adsorption experiments were performed by mixed a required amount of organo-LDHs with 50 mL of varying dye concentration (50–400 mg/L) solutions in a set of 150-mL glass Erlenmeyer flasks. The adsorption of dyes on the organo-LDHs was tested at different pH values (4.0–11.0) for probing the dependence of dyes adsorption on solution pH. The pH was adjusted to the desired values with 0.1 M HCl or 0.1 M NaOH using a pH meter (PB10, Sartorius, Germany). The mixtures were shaken using a thermostatic shaker (SHZ-82, Jintan, China) at 150 rpm and different temperatures (303, 313, 323, and 333 K). At given time intervals, the mixtures were centrifuged at 9000 rpm for 10 min with a centrifuge (LG10-2.4A, Jingli, China). The supernatant was analyzed with a UV–vis spectrophotometer (1601, Shimadzu, Japan) at wavelengths of 525, 506, and 354 nm for AR-GR, DO-11, and BY-2, respectively. The amount of solute adsorbed onto SHS-LDH, SNS-LDH, and SDS-LDH at equilibrium, qe (mg/g), was calculated as follows: V qe ¼ ðC 0  C e Þ W

ð1Þ

where C0 and Ce (mg/L) are the initial and equilibrium liquid phase concentrations of the solute, respectively; V (L) is the volume of the solution and W (g) is the mass of the organo-LDHs used. The percentage removal efficiency, R (%), was calculated as follows: R = (C0  Ce)/C0  100%

(2)

Fig. 1. Chemical structures of (a) AR-GR, (b) DO-11, and (c) BY-2.

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

3

Results and discussion Characterization of adsorbents HRTEM HRTEM was used to determine the morphology and nanostructure of the MgAl-LDH and organo-LDHs are shown in Fig. 2. From the HRTEM image (Fig. 2a), it can be seen that the MgAl-LDH precursor was exhibited regular hexagonal lamellar crystals with an average size in the range of 50–110 nm. Compared to the original MgAl-LDH, the organo-LDHs samples were slightly larger with an average particle size in the range of 80–160 nm and, at the same time, remained crystalline and in hexagonal sheets (Fig. 2b– d). XRD XRD is one of the most useful techniques to probe the structural geometry and texture of MgAl-LDH and organo-LDHs. The XRD pattern of the MgAl-LDH is presented in Fig. 3, which indicates that the as-prepared MgAl-LDH precursor had a layered structure with an interlayer spacing of 7.8 Å. The thickness of MgAl-LDH sheets was about 4.8 Å, so that the gallery height was 3.0 Å. When surfactant molecules intercalated into interlamellar of the MgAlLDH, the interlayer spacing of the SHS-LDH, SNS-LDH, and SDSLDH increased to 20.9, 22.9, and 25.0 Å, respectively. The proposed microstructures of SHS-LDH, SNS-LDH and SDS-LDH were illustrated in Fig. 4(a) and (b). The lengths of the all-trans SHS, SNS, and SDS chains were calculated to be 7.8, 11.5, and 15.3 Å by Chem 3D (Cambridge soft) based on van der Waals radius [24–27], respectively. The computed interlayer spacing for a bilayer was 20.4 Å, considering the length of an all-trans SHS chains as 7.8 Å and the thickness of the MgAl-LDH sheet as 4.8 Å. Comparison of the computed value to the XRD determined value of 20.9 Å indicates a bilayer arrangement of the SHS chains within interlayer space (Fig. 4(a)). For the SNS-LDH and SDS-LDH, the computed interlayer

Fig. 3. LAXRD patterns of MgAl-LDH and different organo-LDHs.

spacing for a tilted bilayer were 22.7 and 24.9 Å, respectively, considering the length of an all-trans SNS and SDS chains as 11.5 and 15.3 Å, respectively, a chain tilt angle of 40–50 , and thickness of the MgAl-LDH sheet of 4.8 Å. Comparison of the computed values to the XRD determined values of 22.9 and 25.0 Å indicates a tilted bilayer arrangement of the intercalated SNS and SDS chains within interlayer space (Fig. 4(b)). Surfactants not only intercalated into the interlayer of LDH layers but also adsorbed on the exterior surface, mainly as a monolayer [24,27–30]. This configuration will enhance the hydrophobicity of the initially hydrophilic particles, leading to the formation of an organic partition medium [24,29]. FT-IR FT-IR analysis is an essential method to obtain information about the functional groups and their bonds [31]. The FT-IR spectra of MgAl-LDH, surfactants, and organo-LDHs are shown in Fig. 5.

Fig. 2. HRTEM images of (a) MgAl-LDH, (b) SHS-LDH, (c) SNS-LDH, and (d) SDS-LDH.

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

4

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

Fig. 4. The illustration of the proposed microstructures of (a) SHS-LDH, and (b) SNS-LDH and SDS-LDH.

From the observed infrared spectra, there are several distinct regions: OH stretching region (3700–3000 cm1), CH stretching region (2900–2800 cm1), HOH bending vibrations region (1700– 1600 cm1), and HCH bending vibration region (1520–1400 cm1) [24,31]. Our discussions mainly focus on the C H,  SO32, and SO C stretching regions. Infrared bands in the region between 2850 and 2922 cm1 are ascribed to the asymmetric g as (CH2) and symmetric g s (CH2) stretching modes of the surfactants. It is observed that the CH2 asymmetric stretching modes of surfactants were found at 2922, 2921 and 2919 cm1, respectively. As the surfactant molecules intercalated into LDH layers, the CH2 asymmetric stretching modes of surfactants shifted to 2930, 2922, and 2916 cm1, respectively. The CH2 symmetric stretching modes were found at 2856, 2851, and 2850 cm1, respectively. After the surfactant molecules intercalated into MgAl-LDH layers, the CH2 symmetric stretching modes significantly shifted to 2857, 2854 and 2852 cm1, respectively. The characteristic peaks corresponding to the out-of-plane bending vibration of the SO32 group of the surfactants were observed at 1054, 1064, and 1064 cm1, respectively. With surfactant molecules intercalated into MgAl-LDH layers, the peaks corresponding

to the  SO32 group shifted to 1051, 1050, and 1049 cm1, respectively. The characteristic peaks corresponding to the stretching vibration of the S O C bond of the surfactants were observed at 795, 798, and 798 cm1, respectively. After the surfactant molecules were intercalated into MgAl-LDH layers, the peaks corresponding to the of S OC bond also shifted to lower wavenumbers of 777, 777, and 788 cm1, respectively. These results showed that the interactions such as electrostatic attraction, hydrogen bonding, and van der Waals forces between the MgAl-LDH layers and surfactant molecules [28–32]. Zeta potential of samples The zeta potential values of MgAl-LDH and organo-LDHs were measured in the NaCl solution (0.001 M) at natural pH, and were listed in Table 1. The results suggested that the high positive charge density on the MgAl-LDH layers. When the anionic surfactants intercalated into MgAl-LDH layers, a charge inversion from positive to negative was observed on the organo-LDHs samples. The charge neutrality also suggested the presence of ion-exchange and electrostatic interactions. A similar result was reported in Ref. [24]. for different concentrations of SDS-modified LDH particles.

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

5

Both the LDH interlayer space and exterior surface are modified by surfactants. An organic medium can be formed and enhanced the hydrophobicity of the LDH particles. This organic medium is very important for the excellent affinity between organo-LDHs and organic pollutants, and is available as a partition medium for contaminants [33].

Dyes removal studies Effect of adsorbent dosage The effect of adsorbent dosage on the removal efficiency of dyes at natural pH is shown in Fig. 6. The initial dye concentration was 100 mg/L and the adsorbent dosage was varied from 0.20 to

Fig. 5. FT-IR spectra of (a) SHS-LDH, (b) SNS-LDH, and (c) SDS-LDH.

Fig. 6. Effect of absorbent dosage on the removal efficiency of (a) AR-GR, (b) DO-11, and (c) BY-2 (Experimental conditions: pH = natural pH, initial dye concentration = 100 mg/L, contact time = 24 h at 303 K).

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

6

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx Table 1 Zeta potential of MgAl-LDH and organo-LDHs in the 0.001 M NaCl solution at 30  C. Samples

Zeta potential (mV)

MgAl-LDH SHS-LDH SNS-LDH SDS-LDH

+39.72 +28.23 +18.49 5.40

4.00 g/L. As observed, SHS-LDH displayed maximum removal efficiency for anionic dye. In contrast, SDS-LDH showed highly removal efficiency for the cationic and non-ionic dyes. However, the removal efficiency of anionic dye by SDS-LDH was significantly lower than that of SHS-LDH. SNS-LDH exhibited excellent removal efficiency for anionic, non-ionic, and cationic dyes compared with SHS-LDH and SDS-LDH. The adsorption behavior of SHS-LDH for anionic dye was partly due to the high positive charge density on the SHS-LDH layers and strong electrostatic attraction between the SHS-LDH and the anionic dye. With further increasing the length of surfactant chains, the zeta potential of organo-LDHs gradually decreases, and then becomes negative. Thus, electrostatic attraction between the SDS-LDH and the oppositely charged cationic dye, which enhances the adsorption of cationic dye onto SDS-LDH. However, the high hydrophobicity of SDS-LDH resulted in poor contact with aqueous solution. At the same time, electrostatic repulsion between the SDS-LDH and the anionic dye. These features result in a lower removal efficiency of SDS-LDH for AR-GR. Intercalation of surfactant molecules can form an effective partition medium within interlayer space, while the partition interactions increased with increasing the length of the surfactant chains. When surfactants intercalated into LDH layers, surfactants mainly adhered to surface sites via electrostatic attraction [31,33]. With further adsorption, dye molecules adhered to the loaded surfactant molecules by van der Waals forces. Therefore, the high removal efficiencies of SNS-LDH for three dyes are complex process that involves a combination of partitioning, hydrogen bonding, electrostatic attraction, and van der Waals forces. SNS-LDH can be used as an effective broad-spectrum adsorbent for the removal of different types of dyes. Effect of pH The initial pH of the dye solutions is an important factor that controls the adsorption process [33,34]. The effect of pH on the adsorption capacities is shown in Fig. 7. The initial pH ranges from 4.0 to 11.0, the adsorption capacities of AR-GR and DO-11 on the organo-LDHs increased with pH until the pH reached 9.0, and then the adsorption capacities of two dyes slightly decreased with further increasing pH. The highest amounts of adsorbed AR-GR and DO-11 were observed at pH 9.0. At low pH values (<5.0), the adsorbents may dissolve, thereby reducing the number of available adsorption sites on the organoLDHs layers, leading to a lower adsorption capacity. The number of positively charged sites on the adsorbent surfaces decreased and the number of negatively charged sites on the adsorbent surfaces increased with increasing solution pH. In this case, the adsorption of the anionic dye onto organo-LDHs is not favored due to electrostatic repulsion. Moreover, the presence of excess hydroxyl ions competed with the dye molecules for the adsorption sites. Therefore, a slight reduction in the adsorption capacities of AR-GR and DO-11 were observed at pH > 9.0. From Fig. 7, maximum adsorption capacity of the cationic dye onto organo-LDHs was achieved at pH 11.0. Adsorption of OH ions from aqueous solution onto organo-LDH surfaces results in a high negative charge density, and thus electrostatic attraction between the cationic dye and the oppositely charged organo-LDHs. It is possible that the

Fig. 7. Effect of pH on the adsorption capacities of (a) AR-GR, (b) DO-11, and (c) BY-2 (Experimental conditions: adsorbent dosage = 1.00 g/L, initial dye concentration = 100 mg/L, contact time = 24 h at 303 K).

electrostatic attraction is a primarily factor in terms of controlling the affinity between cationic dye and organo-LDHs and, at the same time, the loaded surfactants is also an important factor for determining the adsorption mechanism [33–36]. Effect of contact time The effect of contact time on the adsorption capacities of dyes onto organo-LDHs at 303 K is shown in Fig. 8. The adsorbed

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

7

extensive dyes aggregation. As the adsorption further increased, dye molecules adhered to the loaded surfactant molecules by van der Waals forces to form clusters leading to steric hindrance, and these clusters hindered the dye molecules further diffusion and penetration from exterior surface to the interior surface. Therefore, the adsorbed amounts of dyes remained almost the same. Effect of temperature Temperature constitutes another important parameter affecting the adsorption process. The effect of temperature on the adsorption capacities at different temperatures (303, 313, 323 and 333 K) are shown in Fig. 9. The adsorption capacities of AR-GR and DO-11 decreased as the temperature increased, indicating that the adsorption reactions are exothermic. The maximum adsorption capacities of AR-GR and DO-11 onto organo-LDHs occurred at 303 K. Dye molecules firstly adsorbed on the exterior surfaces and interlayer regions of organo-LDHs via partition and electrostatic attraction. With further adsorption, dye molecules adhered to the loaded surfactant molecules via van der Waals forces. However, it was possible that van der Waals forces might significantly decreased with an increase in temperature [28,38–43], meaning that the interactions between the anionic/non-ionic dyes and the loaded surfactant molecules are weak. Moreover, Brownian movement of LDH particles as well as diffusion rate of the dye molecules increased with increasing temperature. In this case, the dye molecules may be unable to build strong bonds with the organic partition medium, resulting in a reduction in the adsorption capacities of AR-GR and DO-11 onto organo-LDHs. In contrast, the results also show that the adsorption capacity of BY-2 onto organo-LDHs increased with increasing temperature, and the reaction was controlled by an endothermic process. The maximum adsorption capacity of BY-2 onto organo-LDHs occurred at 333 K. On the one hand, electrostatic attraction exists between the cationic dye and the organo-LDHs. On the other hand, the surfactant chains formed an organic partition medium in the galleries of MgAl-LDH, and the originally hydrophilic LDH particles become very hydrophobic as the surfactant chains increased from 6 to 12 carbon atoms. This leads to strong hydrophobic interactions between the dye molecules and organo-LDHs, which enhances the adsorption capacity of cationic dye onto organo-LDHs. Experimental results indicate that SHS-modified LDH particles are more effective for the removal of anionic dye. In contrast, SDSmodified LDH particles are more suitable for the removal of nonionic and cationic dyes. In particular, SNS-modified LDH particles can be employed as an effective broad-spectrum adsorbent to remove anionic, non-ionic, and cationic dyes. Partitioning, hydrogen bonding, electrostatic attraction, and van der Waals forces are the main mechanisms controlling the adsorption process.

Fig. 8. Effect of contact time on the adsorption capacities of (a) AR-GR, (b) DO11 and (c) BY-2 (Experimental conditions: pH = natural pH, adsorbent dosage = 1.00 g/L, and initial dye concentration = 100 mg/L at 303 K).

amounts of dyes increased with an increase in contact time and reached complete adsorption equilibrium within 2 h, after which no remarkable changes were observed for longer contact times. Initially, there are abundant vacant adsorbent sites available, and a high concentration gradient between the liquid phase and solid– liquid interface [35–37], and thus the adsorption rates of dyes are rapid. With the adsorption process going, the dye molecules adsorbed on the exterior surfaces and interlayer regions of organLDHs via partition and electrostatic attraction, which caused

Adsorption isotherms The adsorption isotherm plays an important role in the predictive modeling procedure for the analysis and design of adsorption systems [44]. To further understand the behavior and mechanism of the adsorption of dyes onto organo-LDHs, two classical adsorption models, i.e., the Langmuir [45] and Freundlich [46] isotherm models were used to describe the relationship between the amount of dyes adsorbed and their equilibrium concentrations in solution at constant temperature and natural pH. Langmuir isotherm. This model supposes that adsorption occurs at specific homogeneous sites on the surface of the adsorbent, and when a site is occupied by an adsorbate molecule, no further adsorption can occur at this site [47]. The Langmuir isotherm

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

8

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

the solution; and KL (L/mg) is the Langmuir constant that is related to the free energy of adsorption. For the Langmuir isotherm, a method has been adapted to calculate the dimensionless separation factor (RL) [48], which determines the favorability and the shape of the isotherm of the adsorption process by applying the equation: RL ¼

1 1 þ K L C0

ð4Þ

The value of RL indicates whether the isotherm is unfavorable (RL > 1), linear (RL = 1), favorable (0 < RL < 1), or irreversible (RL = 0) [48]. Freundlich isotherm. The Freundlich isotherm model is an empirical equation, and the model is valid for adsorption that occurs on heterogenous surfaces [45,48]. The Freudlich isotherm equation is expressed as: 1

qe ¼ K F C e n

ð5Þ

where KF (L/mg) and n are the Freundlich constants, which are associated with the relative capacity and adsorption intensity, respectively [46,49]. Values of resulting parameters and regression coefficients (R2) are listed in Table 2. According to the experimental data, the regression correlation coefficients of Freundlich model fits better to the adsorption data of dyes than the Langmuir model, suggesting that the Freundlich isotherm was able to describe the adsorption equilibrium well. The KF in the Freundlich equation is related primarily to the capacity of the adsorbent for the adsorbate, and n is a function of the strength of adsorption [49–51]. The KF values of SNS-LDH and SDS-LDH for DO-11 were highest in comparison with that of SHS-LDH. The n values were higher than unity, indicating that dyes were adsorbed favorably by organoLDHs at the temperature studied. The length of the surfactant chains had a great effect on the adsorption. As the length of the surfactant chains increased from 6 to 12 carbon atoms, the surface properties of the organo-LDHs gradually changed from hydrophilic to hydrophobic. Additionally, a charge inversion of the organo-LDHs from positive to negative occurred with increasing the length of the surfactant chains. These features enhance the adsorption capacities of DO-11 and BY-2 onto SNS-LDH and SDS-LDH.

Adsorption kinetics Adsorption kinetics is one of the most important parameters for determining the adsorption mechanism and investigating the efficiency of an adsorbent for the removal of pollutants [52–55]. In

Table 2 Langmuir and Freundlich isotherm parameters for the adsorption of dyes onto organo-LDHs at 303 K. Fig. 9. Effect of temperature on the adsorption capacities of (a) AR-GR, (b) DO-11, and (c) BY-2 (Experimental conditions: pH = natural pH, adsorbent dosage = 1.00 g/L, initial dye concentration = 100 mg/L, and contact time = 24 h).

Dyes

q K L Ce qe ¼ m 1 þ K L Ce

ð3Þ

where qm (mg/g) is the maximum monolayer adsorption capacity of the adsorbent, qe (mg/g) is the amount of dye adsorbed at equilibrium time, Ce (mg/L) is the equilibrium dye concentration in

Freundlich isotherm

qm (mg/g) KL (L/mg) RL ARGR

equation can be represented by the following equation:

Adsorbent Langmuir isotherm rL 2

KF

n

rF 2

SHS-LDH SNS-LDH SDS-LDH

619.45 462.49 424.54

0.044 0.024 0.012

0.054 0.988 42.12 1.60 0.999 0.093 0.988 24.49 1.73 0.994 0.169 0.978 13.96 1.65 0.996

DO-11 SHS-LDH SNS-LDH SDS-LDH

526.96 605.95 650.89

0.030 0.049 0.035

0.076 0.975 34.40 1.78 0.991 0.049 0.988 44.36 1.62 0.999 0.066 0.916 47.55 1.76 0.982

SHS-LDH SNS-LDH SDS-LDH

427.69 698.60 789.62

0.011 0.018 0.016

0.182 0.122 0.138

BY-2

0.974 14.63 1.70 0.988 0.982 24.32 1.51 0.991 0.974 24.05 1.47 0.990

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

this study, the pseudo-first-order and pseudo-second-order models were used to evaluate the experimental data and determine the adsorption kinetics. Pseudo-first-order reaction kinetic. The pseudo-first-order kinetic model [52] is expressed as follows:

9

where qe (mg/g) and qt (mg/g) are the amounts of dyes adsorbed by organo-LDHs at equilibrium conditions and at time t (min), respectively; k1 (1/min) is the equilibrium rate constant [52]. Parameters k1 and qe are determined from the slope and intercept of the plot of ln (qe  qt) versus t, respectively.

ð6Þ

Pseudo-second-order reaction kinetic. The adsorption data were also fitted using the pseudo-second-order kinetic model as

Fig. 10. Pseudo-first-order kinetic model fits for the adsorption of (a) AR-GR, (b) DO-11, and (c) BY-2 onto organo-LDHs (Experimental conditions: initial dye concentration = 100 mg/L, adsorbent dosage = 1.00 g/L, temperature = 303 K at natural pH).

Fig. 11. Pseudo-second-order kinetic model fits for the adsorption of (a) AR-GR, (b) DO-11, and (c) BY-2 onto organo-LDHs (Experimental conditions: initial dye concentration = 100 mg/L, adsorbent dosage = 1.00 g/L, temperature = 303 K at natural pH).

lnðqe  qt Þ ¼ ln qe  k1 t

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

10

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

Table 3 Adsorption parameters of kinetic for the adsorption of 100 mg/L dyes onto organo-LDHs at 303 K. Dyes

Adsorbent

qe,exp (mg/L)

Pseudo-first-order

Pseudo-second-order 3

2

qe1,cal (mg/g)

k1 10 (1/min)

R

qe2,cal (mg/g)

k2  103 (1/min)

R2

AR-GR

SHS-LDH SNS-LDH SDS-LDH

97.00 92.00 84.00

16.01 10.92 11.49

15.92 17.13 18.97

0.9062 0.7473 0.7935

96.90 91.91 84.10

5.54 8.88 8.31

0.9999 0.9999 0.9999

DO-11

SHS-LDH SNS-LDH SDS-LDH

93.00 97.00 98.00

12.25 7.06 4.04

18.57 16.68 12.23

0.7898 0.7236 0.8385

93.02 96.90 97.75

7.86 14.37 21.62

0.9999 0.9999 0.9999

BY-2

SHS-LDH SNS-LDH SDS-LDH

78.00 91.00 92.00

8.05 13.42 9.22

14.19 20.76 19.91

0.7080 0.8729 0.7834

77.70 91.24 92.08

12.21 7.46 10.92

0.9999 0.9999 0.9999

adsorbate–adsorbent take place on the exterior and interior surfaces.

follows: t 1 t ¼ þ qt K 2 qe 2 qe

ð7Þ Dye removal treatment of industrial dye waste

where qe (mg/g) and qt (mg/g) are the amounts of dyes adsorbed by organo-LDHs at equilibrium conditions and at time t (min), respectively; k2 is the equilibrium rate constant (g/mg min). Values of k2 and qe are obtained from the slope and intercept of the plot of t/qt versus t, respectively [56–60]. The straight-line plots of ln(qe  qt) versus t for the pseudo-firstorder (Fig. 10), and t/qt against t for pseudo-second-order model (Fig. 11) of dyes onto organo-LDHs have been tested to obtain the rate parameters at 303 K. The adsorption kinetic parameters under the experimental conditions were calculated from these plots and are shown in Table 3. As shown that the pseudo-first order model does not fit well to the whole range of the contact time. The correlation coefficients values (R2) were applied to determine the relationship between the experimental data and the kinetics in most studies [53]. The R2 values for the pseudo-first-order kinetic model were low. Moreover, the calculated qe values obtained from the pseudo-first-order kinetic model do not give reasonable values, which are too low compared with experimental qe values. This suggests that the adsorption of dyes onto organo-LDHs is not a pseudo-first-order reaction. It is clear to see that the R2 values for the pseudo-second-order kinetic model are much higher than those for the pseudo-firstorder kinetic model. Also, the calculated qe values also agree very well with the experimental data. Therefore, this section indicated that the pseudo-second-order kinetic model was the best choice to describe the adsorption behavior of dyes onto organo-LDHs. It may be concluded that three consecutive steps are involved in the removal of dyes by organo-LDHs from aqueous solution. Firstly, the dye molecules migrate from the bulk phase to the exterior surface of organo-LDH particles. Secondly, the dye molecules partition into interlayer region or organic medium. Finally, the interactions of

Table 4 The characteristics and the treatment results of the industrial dyeing effluents. Sample

Parameter

Effluent

Treated

Removal (%)

1

pH Conductivity (mS/cm) Turbidity (NTU) Point color COD (mg/L)

6.8 10,250 21.5 1100 1080

8.1 11,040 3.6 40 179

– – 83.3 96.3 83.4

2

pH Conductivity (mS/cm) Turbidity (NTU) Point color COD (mg/L)

8.2 9390 19.5 800 890

8.5 9930 4.3 50 194

– – 77.9 93.8 78.2

Actual industrial dye effluents containing different types of dyes and chemical substances from a printing and dyeing factory were used to test the dye removal efficiency. Due to the differences in production process, the amounts of different dyes in the effluents are varying. The SNS-LDH was selected as a broadspectrum adsorbent for treatment of industrial dye effluents. Industrial dye effluents from the equalization pond of the plant during normal production process were used for testing. Industrial effluents which containing various dyes from different workshops were collected in different days and treated with SNS-LDH dosage of 2.2 g/L at original pH. The results of treatment and characteristics of industrial dye effluents are summarized in Table 4. The removal efficiency was 93.8%–96.3% for color matter and 78.2%–83.4% for COD, respectively. The removal efficiency of dye effluents was lower than that of synthetic dye solutions. The reason may be that the industrial effluents are more complex, and the chemical additives in industrial effluents have interfered with the adsorption of dyes onto SNS-LDH. SNS-LDH shows promise as an effective and broad-spectrum dye removal agent. Conclusions Organo-LDHs were prepared by modification of MgAl-LDH with anionic surfactants were successfully employed as adsorbents for the quantitative removal of dyes from aqueous solution. The intercalation of anionic surfactants changed the surface properties of MgAl-LDH from hydrophilic to hydrophobic, and a charge inversion from positive to negative occurred with increasing the length of the surfactant chains. Therefore, this simple modification has been proposed for the improvement adsorption capacity of MgAl-LDH for organic pollutants. HRTEM, XRD, FT-IR and zeta potential measurements showed that the different features in morphology, structure and surface properties of the organo-LDHs. The adsorption process is strongly affected by the initial solution pH and temperature. Freundlich isotherm model fitted well with the experimental data. Kinetics studies showed that the adsorption profiles of all prepared adsorbents followed a pseudo-secondorder kinetic model. Surfactants not only intercalated into the interlayer space but also adsorbed on the exterior surface of LDH particles. Both the LDH interlayer space and exterior surface are modified by surfactants, and forming an effective organic partition medium. Experimental data indicated that SNS-modified MgAlLDH could be used as a broad-spectrum adsorbent for the removal of anionic, non-ionic, and cationic dyes. The long chain SDSmodified MgAl-LDH could be used as an excellent adsorbent for the

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029

G Model JIEC 3273 No. of Pages 11

B. Zhang et al. / Journal of Industrial and Engineering Chemistry xxx (2016) xxx–xxx

removal of non-ionic and cationic dyes. However, the short chain SHS-modified MgAl-LDH could be merely used as an effective adsorbent for the removal of anionic dye. The adsorption mechanism is a complex process that involves a combination of partitioning, hydrogen bonding, electrostatic attraction, and van der Waals forces. Acknowledgment This work was supported by the National Natural Science Foundation of China (Grant nos. 21677087 and 21333005). References [1] L. Wang, A. Wang, J. Hazard. Mater. 147 (2007) 979. [2] E. Clarke, R. Anliker, O. Hutzinger, Handbook of Environmental Chemistry, 3, Springer, Heidelberg, 1980. [3] A.S. Özcan, B. Erdem, A. Özcan, Colloids Surf. A 266 (2005) 73. [4] P. Baskaralingam, M. Pulikesi, D. Elango, V. Ramamurthi, S. Sivanesan, J. Hazard. Mater. 128 (2006) 138. [5] K. Kadirvelu, M. Kavipriya, C. Karthika, M. Radhika, N. Vennilamani, S. Pattabhi, Bioresource Technol. 87 (2003) 129. [6] D. Gusain, S. Dubey, S.N. Upadhyay, C.H. Weng, Y.C. Sharma, J. Ind. Eng. Chem. 33 (2016) 42. lu, Y. Erdog an, A.S. Özcan, J. Hazard. Mater. 140 (2007) 173. [7] A. Özcan, Ç. Ömerog [8] Y. Li, B. Gao, T. Wu, B. Wang, X. Li, J. Hazard. Mater. 164 (2009) 1098. [9] S. Sadri Moghaddam, M. Alavi Moghaddam, M. Arami, J. Hazard. Mater. 175 (2010) 651. [10] H. Liu, X. Ren, L. Chen, J. Ind. Eng. Chem. 34 (2016) 278. [11] T. Esfandiyari, N. Nasirizadeh, M.H. Ehrampoosh, M. Tabatabaee, J. Ind. Eng. Chem. 46 (2017) 35. [12] S.M.d.A.G.U. de Souza, K.A.S. Bonilla, A.A.U. de Souza, J. Hazard. Mater. 179 (2010) 35. [13] K.-H. Goh, T.-T. Lim, Z. Dong, Water Res. 42 (2008) 1343. [14] I.D. Mall, V.C. Srivastava, N.K. Agarwal, I.M. Mishra, Colloids Surf. A 264 (2005) 17. [15] S. Chakma, V.S. Moholkar, J. Ind. Eng. Chem. 37 (2016) 84. [16] C.-C. Wang, L.-C. Juang, T.-C. Hsu, C.-K. Lee, J.-F. Lee, F.-C. Huang, J. Colloid Interface Sci. 273 (2004) 80. [17] R.G. Harris, B.B. Johnson, J.D. Wells, Clays Clay Miner. 54 (2006) 435. _ Demir, M.L. Yola, N. Atar, J. Ind. Eng. Chem. [18] V.K. Gupta, S. Agarwal, A. Olgun, H.I. 34 (2016) 244. [19] R.-r. Shan, L.-g. Yan, Y.-m. Yang, K. Yang, S.-j. Yu, H.-q. Yu, B.-c. Zhu, B. Du, J. Ind. Eng. Chem. 21 (2015) 561. [20] M.-X. Zhu, Y.-P. Li, M. Xie, H.-Z. Xin, J. Hazard. Mater. 120 (2005) 163.

[21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60]

11

L. Lu, J. Li, D.H.L. Ng, P. Yang, P. Song, M. Zuo, J. Ind. Eng. Chem. 46 (2017) 315. L. Zhang, B. Zhang, T. Wu, D. Sun, Y. Li, Colloids Surf. A 484 (2015) 118. P. Wu, T. Wu, W. He, L. Sun, Y. Li, D. Sun, Colloids Surf. A 436 (2013) 726. J. Wang, F. Yang, C. Li, S. Liu, D. Sun, Langmuir 24 (2008) 10054. T. Wu, D. Sun, Y. Li, H. Zhang, F. Lu, J. Colloid Interface Sci. 355 (2011) 198. W. Chen, B. Qu, Chem. Mater. 15 (2003) 3208. Z.-L. Wang, Z.-H. Kang, E.-B. Wang, Z.-M. Su, L. Xu, Inorg. Chem. 45 (2006) 4364. V.V. Naik, S. Vasudevan, J. Phys. Chem. C 115 (2011) 8221. V.V. Naik, R. Chalasani, S. Vasudevan, Langmuir 27 (2011) 2308. L. Mohanambe, S. Vasudevan, J. Phys. Chem. B 110 (2006) 14345. J.A. Smith, P.R. Jaffe, C.T. Chiou, Environ. Sci. Technol. 24 (1990) 1167. K. Lin, J. Pan, Y. Chen, R. Cheng, X. Xu, J. Hazard. Mater. 161 (2009) 231. Y. Chun, G. Sheng, S.A. Boyd, Clays Clay Miner. 51 (2003) 415. L. Zhu, B. Chen, X. Shen, Environ. Sci. Technol. 34 (2000) 468. B. Stephen Inbaraj, C. Chiu, G. Ho, J. Yang, B. Chen, J. Hazard. Mater. 137 (2006) 226. J.A. Smith, A. Galan, Environ. Sci. Technol. 29 (1995) 685. Y.X. Zhang, X.D. Hao, F. Li, Z.P. Diao, Z.Y. Guo, J. Li, Ind. Eng. Chem. Res. 53 (2014) 6966. Y.-T. Fu, H. Heinz, Chem. Matter. 22 (2010) 1595. H. Heinz, R. Vaia, B. Farmer, J. Chem. Phys. 124 (2006) 224713. M. Ahmaruzzaman, D. Sharma, J. Colloid Interface Sci. 287 (2005) 14. H. Heinz, R. Vaia, B. Farmer, J. Chem. Phys. 124 (2006) 224713. H. Christenson, J. Phys. Chem. 97 (1993) 12034. O.L. Manevitch, G.C. Rutledge, J. Phys. Chem. B 108 (2004) 1428. M.S. El-Geundi, Adsorpt. Sci. Technol. 8 (1991) 217. I. Langmuir, J. Am. Chem. Soc. 38 (1916) 2221. H. Freundlich, Z. Phys. 57 (1906) 385. Y. Wu, Z. Ming, S. Yang, Y. Fan, P. Fang, H. Sha, L. Cha, J. Ind. Eng. Chem. 46 (2017) 222. M.E. Mahmoud, G.M. Nabil, N.M. El-Mallah, H.I. Bassiouny, S. Kumar, T.M. Abdel-Fattah, J. Ind. Eng. Chem. 37 (2016) 156. R. Jothirani, P.S. Kumar, A. Saravanan, A.S. Narayan, A. Dutta, J. Ind. Eng. Chem. 39 (2016) 162. A. Košak, A. Lobnik, M. Bauman, Int. J. Appl. Ceram. Technol. 12 (2015) 461, doi: http://dx.doi.org/10.1111/ijac.12180. C. Sarkar, C. Bora, S.K. Dolui, Ind. Eng. Chem. Res. 53 (2014) 16148. Y.S. Al-Degs, M.I. El-Barghouthi, A.A. Issa, M.A. Khraisheh, G.M. Walker, Water Res. 40 (2006) 2645. B. Hameed, A. Ahmad, K. Latiff, Dyes Pigments 75 (2007) 143. M.M. Nassar, Y.H. Magdy, Chem. Eng. J. 66 (1997) 223. M. Arami, N.Y. Limaee, N.M. Mahmoodi, N.S. Tabrizi, J. Colloid Interface Sci. 288 (2005) 371. N. Kannan, M.M. Sundaram, Dyes Pigments 51 (2001) 25. Y.-S. Ho, G. McKay, Chem. Eng. J. 70 (1998) 115. L. Chen, B. Bai, Ind. Eng. Chem. Res. 52 (2013) 15568. S.S. Shenvi, A.M. Isloor, A.F. Ismail, S.J. Shilton, A. Al Ahmed, Ind. Eng. Chem. Res. 4 (2015) 4965. G. Annadurai, M.R.V. Krishnan, Indian J. Chem. Technol. 4 (1997) 213.

Please cite this article in press as: B. Zhang, et al., Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution, J. Ind. Eng. Chem. (2017), http://dx.doi.org/10.1016/j.jiec.2017.01.029