Layered double hydroxide Zn/(Al + Fe) with a molar ratio of 3:(0.85 + 0.15), designated as ZAF-HT, was synthetized by co-precipitation. Its calcined product CZAF was obtained by heat treatment of ZAF-HT at 500°C. The calcined and uncalcined materials were used to remove the acid dyes indigo carmine (IC) and green bezanyl-F2B (F2B) from water in batch mode. The synthetized materials were characterized by X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller analysis, Fourier transform infra-red spectroscopy and thermogravimetric/differential thermal analysis. The sorption kinetic data fitted a pseudo-second-order model. The adsorbed amounts of the calcined material were much larger than ZAF-HT. The maximum adsorption capacity of CZAF was found to be 617.3 mg g−1 for IC and 1,501.4 mg g−1 for F2B. The isotherms showed that the removal of IC and F2B by ZAF-HT and CZAF could be described by a Langmuir model. The thermodynamic parameters were also calculated. The negative values of standard free energy ΔG° indicate the spontaneity of sorption process. The reuse of CZAF was studied for both dyes and the calcined material showed a good stability for four thermal cycles.

INTRODUCTION

Synthetic dyes have long been used in various industries, such as textiles, cosmetics, paper, leather, pharmaceuticals and foods (Yuan et al. 2009). During and after the dyeing process, huge amounts of dyes are released as industrial discharges into the environment causing serious problems. They are aesthetic pollutants, and the coloration of water by dyes reduces the penetration of light which affects photochemical activities (McMullan et al. 2001). As a result, the aquatic ecosystem is destroyed. Moreover, it has been reported that many dyes are toxic, carcinogenic and mutagenic for aquatic organisms, even at very low doses, and may cause severe damage to human beings, such as dysfunction of the kidneys, reproductive system, liver, brain and central nervous system (Mittal & Gupta 1996).

Chemical, electrochemical and photochemical methods, reverse osmosis, coagulation and aerobic and anaerobic biodegradation have been used to remove dye compounds from water and wastewater (Zhu et al. 2005; El Gaini et al. 2009). However, photodegradation methods may not fully mineralize synthetic dyes, due to their resistance, and also may produce persistent degradation products which are toxic and carcinogenic for aquatic organisms (Lourenco et al. 2001). Furthermore, treatment of dyes in water by chemical or electrochemical methods, reverse osmosis and coagulation is not widely applicable because of economic considerations (Zhu et al. 2005; El Gaini et al. 2009). However, the adsorption process has widely been used to remove different types of dye from water using less expensive adsorbents. This process has several advantages over others, such as high efficiency, no harmful by-products and simplicity of operation.

Layered double hydroxides (LDHs), also known as hydrotalcite-like materials or anionic clay, can be good adsorbents for removal of organic and inorganic pollutants because of their high capacity for anion exchange and high layer charge densities (Extremera et al. 2012; González et al. 2015). LDHs are scarce in nature, but can be prepared easily and in large quantities in the laboratory using inexpensive precursors (Seftel et al. 2008). Their general formula is [ (OH)2] (A)x/n mH2O, where M2+ and M3+ are di- and trivalent metal cations, An is an exchangeable organic or inorganic anion with negative charge n, m is the number of interlayer water molecules and x = M3+/ (M2+ + M3+) is the layer charge density of the LDH (Kameda et al. 2015). LDHs can be used to remove pollutants by anionic exchange with the original interlayer anions. However, the latter process is not always feasible, especially when the initial interlayer anions have a strong affinity toward the LDH layers, e.g. carbonates ions.

Calcination transforms LDHs into mixed metal oxides with high specific areas and homogeneous dispersion of metal cations (Ni et al. 2007). The calcined-LDHs (CLDHs) are also used as adsorbents to remove anionic contaminants from water via a specific property called ‘memory effect’. The CLDHs regain their original structure by the intercalation of anionic species such as acid dyes (Lv et al. 2006).

In the present study, ZAF-HT LDH was synthesized by co-precipitation and calcined at 500 °C (CZAF). The adsorptive performances of the calcined and the uncalcined materials were tested on the uptake of two anionic dyes, indigo carmine (IC) and green bezanyl-F2B (F2B), from aqueous solution in batch mode. The effect of various sorption factors, such as kinetics, solution pH, isotherms and temperature, was investigated. The thermodynamic parameters of change in standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated. The reusability study of CZAF for both dyes for four thermal cycles was also studied.

METHODS

Materials and reagents

IC (purity 99%) was produced by Ciba Society (Zurich, Switzerland) and F2B, was provided by the company Soitex, Tlemcen, Algeria. The dyes were used as received. Dye solutions were prepared by dissolving an accurately known amount of dye (1 g L−1) in distilled water and subsequently diluting to required concentrations. Aluminium chloride hexahydrate (purity 99%) and urea (purity 98%) were obtained from Sigma-Aldrich, Germany. Zinc chloride (purity 98%, Paureac, Spain) and ferric chloride (purity 99%, Chemopharma, Austria) were used as received.

Synthesis of ZAF-HT and CZAF

Zn/(Al + Fe) DLH with a molar ratio of 3/(0.85 + 0.15) was synthesized by co-precipitation according to the literature with some modifications (Mantilla et al. 2010). A mixture of 0.06 moles of ZnCl2, 0.017 moles of AlCl3.6H2O and 0.003 moles of FeCl3 was dissolved in 200 mL of deionized water. The latter solution was added dropwise to a glass reactor vessel containing 100 ml of urea solution (20% w/v) as precipitant agent, with vigorous stirring. The pH of the suspension was adjusted to 10.5 by using 2 M NaOH. The resulting precipitate was vigorously stirred for 4 h at room temperature and then heated at 90 °C under reflux for 36 h. The material obtained was separated by centrifugation, washed thoroughly with deionized water several times until the precipitate was free from Cl (AgNO3 test) and air-dried at 100 °C overnight. This material, designated as ZAF-HT, was ground and sieved to obtain a particle size of <0.250 mm. A portion of ZAF-HT was calcined in air at 500°C for 4 h and designated as CZAF.

Characterization of the materials

The samples were characterized by several physical and chemical techniques. Powder X-ray diffraction (XRD) patterns were recorded using a Phillips X'Pert MPD diffractometer with monochromatic CuKα = 1.5418 Å (40 kV, 30 mA). Fourier transform infra-red (FTIR) spectra were obtained in a transmission mode on a Nicolet Avatar 330 FTIR spectrometer by using KBr disks containing 1wt% samples. The spectra were recorded with 2 cm−1 resolution in the range 4,000–400 cm−1. Thermogravimetric analysis (TGA) of solid samples was conducted using a NETZSCH STA 409 PC/PG simultaneous thermal analyser, heated from 20 to 900 °C at a heating rate of 10°C/min under a N2 flow rate of 50 mL/min. The Brunauer–Emmett–Teller (BET) specific surface areas and pore sizes of the samples were determined by N2 adsorption–desorption isotherms using a Micromeritics ASAP (2010). The particle morphologies of ZAF-HT and CZAF were observed by scanning electron microscopy (SEM) using a Hitachi S-2600N variable pressure scanning electron microscope.

Adsorption equilibrium experiments

The removal of IC and F2B was studied in batch mode at room temperature and at atmospheric pressure. The effects of contact time, solution pH, initial concentration of the dyes and temperature on the adsorption process were investigated. A suspension containing 25 mg of ZAF-HT or CZAF was added to 50 ml of IC or F2B solution with initial concentrations of 250 and 750 mg L−1, respectively. The suspensions were stirred for various time intervals (0.5–24 h) without adjusting the initial pH of solution. To study the effect of pH, the suspension pH was adjusted in the range 5.0–9.5 by adding 1 N HCl or 1 N NaOH. Samples were stirred during equilibration and then centrifuged. The concentrations of dyes in the supernatant were determined by visible spectrophotometry on a HACH DR/4000 U spectrophotometer at 610 nm and at 646 nm for IC and F2B, respectively. The equilibrium sorption amount Qe (mg g−1) (Equation (1)) and the removal percentage of the dyes (R %) (Equation (2)) were calculated using the following equations: 
formula
1
 
formula
2
where Ci (mg L−1) and Ce (mg L−1) are the initial and the equilibrium concentration of dyes, respectively, Ct (mg L−1) is the concentration of the dye solution at time t, V (L) is the solution volume and m (g) is the adsorbent mass.

Temperature effect

The temperature effect was studied on suspensions of CZAF in IC and F2B solutions with initial dye concentration of 260 and 800 mg.L−1, respectively (solid/solution ratio = 0.5 g L−1). The suspensions were stirred during the equilibrium time at three constant temperatures (25, 35 and 45 °C) and then centrifuged, and the residual concentrations were determined as above.

Reusability study

The regeneration of CZAF was based on a thermal recycling method. After the adsorption of dyes (IC or F2B), the material was recovered and calcined at 500°C for 4 h, and then the calcined product was dispersed into a known concentration of dye solution. The residual concentration of dye was determined as above. This procedure was repeated three times.

RESULTS AND DISCUSSION

Characterization of materials

The XRD patterns of ZAF-HT, CZAF before and after sorption experiments are shown in Figure 1. The XRD pattern of the original LDH showed sharp and symmetrical peaks with some asymmetrical peaks at a high angle, indicating good crystallinity (You et al. 2002). The interlayer distance of ZAF-HT at 003 reflection was 7.645 Å (d003), which is higher than value reported by Mantilla et al. (2009). The XRD spectra of the calcined sample (CZAF) at 500°C confirmed that the layered structure was destroyed where the carbonates anions and water molecules of the interlayer space had decomposed. New diffraction lines appeared (Figure 1(d)) which can probably be associated with the presence of the mixed metal oxides as seen in Mantilla et al. (2010). After the retention of IC and F2B by CZAF, a new peak was observed at weak 2θ. However, the intensity of the peaks (003) and (006) decreased slightly indicating some reductions in the crystallinity after calcination and rehydration (Zhu et al. 2005). Moreover, the interlayer distance was increased from 7.645 Å in ZAF-HT to 18.652 Å after the adsorption of IC and to 19.031 Å after the uptake of F2B. These values may suggest that the dye molecules were inserted vertically into the interlayer space (Chen et al. 2012).
Figure 1

XRD patterns: ZAF-HT (a), ZAF-IC (b), ZAF-F2B (c) and CZAF (d).

Figure 1

XRD patterns: ZAF-HT (a), ZAF-IC (b), ZAF-F2B (c) and CZAF (d).

The intercalation of IC and F2B was also shown by FTIR spectra (Figure 2). The ZAF-HT spectra showed an intense broad band at 3,460 cm−1 corresponding to the stretching vibration of the metal hydroxide layer and interlayer water molecules. The shoulder near 3,200 cm−1 is associated with the H-bond stretching vibration of the interaction between CO32− and water molecules in the interlayer space (Dula et al. 2002). The weak peak at 1,637 cm−1 can be attributed to the H2O bending vibration of interlayer water (Chen et al. 2012). The strong peak observed at 1,362 cm−1 was assigned to the ν3 vibration of the interlayer carbonate anions (Yuan et al. 2009). The bands in the range 500–700 cm−1 probably were due to metal–oxygen–metal vibrations.
Figure 2

FTIR spectra: (a) ZAF-HT; (b) CZAF; (c) IC; (d) ZAF-IC; (e) F2B; (f) ZAF-F2B.

Figure 2

FTIR spectra: (a) ZAF-HT; (b) CZAF; (c) IC; (d) ZAF-IC; (e) F2B; (f) ZAF-F2B.

The retention of IC by CZAF was demonstrated by the appearance of new peaks at 681 cm−1, attributed to the C–C single vibration; at 1,614 cm−1, assigned to the double bonding of the ethylenic band; and the bands at 1,473–1,399 cm−1, which are probably due to the double bonding of the aromatic ring system (El Gaini et al. 2009). The C = O vibration band was also present at 1,640 cm−1 and the S–O vibration bands appeared at 1,153 and 1,199 cm−1. The band assigned to ν(S = O) at 1,104 cm−1 was shifted to 1,110 cm−1 (El Gaini et al. 2009). The intensity of vibration bands decreased after the fixation of the IC dye. The FTIR spectra of F2B and ZAF-F2B showed the presence of many common peaks indicating the uptake of F2B dye by CZAF. The FTIR results were consistent with the XRD patterns.

Nitrogen adsorption–desorption isotherms of uncalcined and calcined samples are shown in Figure 3. The data were presented in arbitrary units, showing only the form of the isotherm and not its real values. According to IUPAC classification, ZAF-HT and CZAF followed by type IV isotherm with H3 hysteresis corresponds to mesoporous solids with slit-shaped irregular pores (Parida & Mohapatra 2012). The surface area for ZAF-HT was 28.59 m2/g, while for CZAF it was almost double (53.29 m2/g). SEM images of ZAF-HT and CZAF are shown in Figure 4(a) and 4(b), respectively. It can be seen that ZAF-HT has a planar structure with particles of various sizes. Upon calcination, the structure of hydrotalcite crumbled as the planar forms become fragile and the size of the particles becomes smaller; this change can be attributed to the formation of mixed metal oxide.
Figure 3

N2 adsorption–desorption curves of uncalcined and calcined material.

Figure 3

N2 adsorption–desorption curves of uncalcined and calcined material.

Figure 4

SEM images: (a) ZAF-HT; (b) CZAF.

Figure 4

SEM images: (a) ZAF-HT; (b) CZAF.

Figure 5 shows the thermoanalytical measurements of ZAF-HT to evaluate the different transformations of the sample during the heat treatment. At temperature range 80–220°C, a small endothermic peak was observed and related to dehydration of water molecules from the internal gallery and the external non-gallery surfaces. In the second region from 220 to 400°C, about 11% of weight was lost due to the dehydroxylation and the beginning of carbonate decomposition (Seftel et al. 2008).
Figure 5

TGA and differential thermal analysis (DTA) of ZAF-HT.

Figure 5

TGA and differential thermal analysis (DTA) of ZAF-HT.

Effect of contact time and kinetic modelling

The contact time between the pollutants and the adsorbent is an important parameter in treatment by adsorption. Figure 6(a) shows the time effect on the sorption of IC and F2B by CZAF: the adsorbed amount increased with contact time, and remained almost constant after 4 h and 20 h for IC and F2B, respectively, indicating an equilibrium state. The adsorption capacity of the material at the equilibrium was 488.9 mg g−1 for IC and 1,487.9 mg g−1 for F2B. El Gaini et al. (2009) studied the removal of IC by calcined Mg-Al-CO3 where the equilibrium time was found to be 20 min. However, Bouraada et al. reported that the sorption of F2B by Mg-Al-SDS takes 2 h to reach the equilibrium state (Bouraada et al. 2009). Thus, the equilibrium time depends closely on the nature of the adsorbent (structure and chemical composition) and the dye structure.
Figure 6

(a) Effect of contact time on removal of IC and F2B by CZAF; (b) pseudo-second-order plots for the sorption of IC and F2B by CZAF.

Figure 6

(a) Effect of contact time on removal of IC and F2B by CZAF; (b) pseudo-second-order plots for the sorption of IC and F2B by CZAF.

Adsorption kinetics models were used in order to explain the possible adsorption mechanism. Pseudo-first-order (Equation (3)) and pseudo-second-order (Equation (4)) are the most used models (Mantilla et al. 2009), and they were applied to the experimental data of the uptake of IC and F2B by CZAF material. 
formula
3
 
formula
4
where Qt and Qe are the adsorbed amount at time t and at equilibrium state, respectively (mg g−1), k1: the pseudo-first-order rate constant of adsorption (h−1), and k2: the pseudo-second-order rate constant of adsorption (g mg−1 h−1).

The kinetic parameters of the models were calculated and are reported in Table 1. Based on the values of determination coefficient R2, the sorption of the dyes was better expressed by a pseudo-second-order kinetic model (Figure 6(b)). Several studies reported that the adsorption of acid dyes by anionic clay was described by a pseudo-second-order model (Ni et al. 2007; Bouraada et al. 2009; El Gaini et al. 2009; Ahmed & Gasser 2012).

Table 1

Parameters of pseudo-first- and the pseudo-second-order models for sorption of IC and F2B by CZAF

Dyes Ci (mg L−1Qexp (mg g−1k1 (h−1Q1 (mg g−1R12 k2 (mg g−1 h−1Q2 (mg g−1R22 
IC 250 488.94 0.803 207.06 0.926 0.0124 500 0.999 
F2B 750 1,487.9 0.140 1,107.6 0.965 5.5 × 10−4 1,538.2 0.993 
Dyes Ci (mg L−1Qexp (mg g−1k1 (h−1Q1 (mg g−1R12 k2 (mg g−1 h−1Q2 (mg g−1R22 
IC 250 488.94 0.803 207.06 0.926 0.0124 500 0.999 
F2B 750 1,487.9 0.140 1,107.6 0.965 5.5 × 10−4 1,538.2 0.993 

Effect of initial pH

The variation of the sorption capacity of CZAF at different initial pH solution is presented in Figure 7. This figure showed that the sorption amount was almost constant in the studied pH range (5.0–9.5) for both dyes. These results are consistent with previous reports (El Gaini et al. 2009). Thus, it was decided for the rest of this study to carry out the sorption experiments without pH adjustment (pHi of IC equal 6.10 and pHi of F2B equal 5.01).
Figure 7

Effect of pH on adsorption capacity of IC and F2B by CZAF.

Figure 7

Effect of pH on adsorption capacity of IC and F2B by CZAF.

Sorption isotherms

Sorption isotherms of IC and F2B by CZAF and ZAF-HT are shown in Figure 8. The sorption capacities of CZAF were higher than those of ZAF-HT for both dyes. The adsorption amount of F2B by CZAF was about a hundred times greater than that of ZAF-HT. On the other hand, the mixed oxides metals CZAF regained their original structure by the intercalation of the dye molecules into interlayer space. Moreover, the sorption capacity of F2B by CZAF was three times greater than that of IC. This is probably related to the chemical structure of the dyes and their affinity towards the calcined material. These results suggest that calcined LDHs may be good adsorbents for removal of a wide range of anionic dyes from wastewater (You et al. 2002).
Figure 8

Sorption isotherms of IC and F2B by (a) ZAF-HT and (b) CZAF.

Figure 8

Sorption isotherms of IC and F2B by (a) ZAF-HT and (b) CZAF.

The experimental isotherm data were investigated with the most frequently used isotherm models: Langmuir and Freundlich. The linearized formula of Langmuir model (Equation (5)) and Freundlich (Equation (6)) (Zhu et al. 2005; Bouraada et al. 2009) are expressed by the following equations: 
formula
5
 
formula
6
where Ce (mg L−1) is the equilibrium concentration of dyes, Qe is the amount adsorbed at equilibrium, Qmax is the maximum monolayer adsorption capacity (mg g−1), KL is the Langmuir constant refers to energy of adsorption and KF is the Freundlich isotherm constant (L g−1) related to the adsorption capacity. 1/n is the heterogeneity factor that could be obtained from the slope of the plot lnQe versus ln Ce.
The parameter values of Freundlich and Langmuir models are reported in Table 2. The sorption of both dyes by ZAF-HT and CZAF fitted very well to the Langmuir isotherm model (Figure 9) with determination coefficient values R2 very close to 1. The maximum adsorption capacity of the calcined material was found to be 617.3 and 1,501.4 mg g−1 for IC and F2B, respectively. These values were compared with other studies (Zhu et al. 2005; Ni et al. 2007; Bouraada et al. 2009, 2014; Ahmed & Gasser 2012) and are shown in Table 3; it can be seen that the negative charges number of the dye has no significant effect on the maximum adsorption capacity. This allows us to conclude that the nature of the adsorbent and the structure of the adsorbed have a significant influence on the adsorbed amount. Moreover, CZAF material showed a strong ability to remove a huge quantity of dyes.
Table 2

Langmuir, Freundlich parameters and determination coefficient R2 for the uptake of IC and F2B by CZAF and ZAF-HT

    Langmuir
 
Freundlich
 
 Qexp (mg g−1Qmax (mg g−1KL (L mg−1R2 n KF (L g−1R2 
CZAF-IC 488.9 617.3 0.86 0.991 41.15 488.97 0.754 
CZAF-F2B 1,487.9 1,501.4 20.75 151.58 1,459.28 0.908 
ZAF-IC 41.1 41.41 157.29 60.97 39.58 0.794 
ZAF-F2B 28.4 28.9 20.84 0.998 8.92 22.07 0.752 
    Langmuir
 
Freundlich
 
 Qexp (mg g−1Qmax (mg g−1KL (L mg−1R2 n KF (L g−1R2 
CZAF-IC 488.9 617.3 0.86 0.991 41.15 488.97 0.754 
CZAF-F2B 1,487.9 1,501.4 20.75 151.58 1,459.28 0.908 
ZAF-IC 41.1 41.41 157.29 60.97 39.58 0.794 
ZAF-F2B 28.4 28.9 20.84 0.998 8.92 22.07 0.752 
Table 3

Comparison of the maximum monolayer sorption capacities (Qmax) of some dyes on various calcined LDH

LDH nature Dye Negative charges number Qmax (mg g−1References 
CZAF IC 617.3 This work 
CZAF F2B Unknown 1,501.4 This work 
Zn-Al Methyl orange 200.0 Ni et al. (2007)  
Mg-Al Brilliant blue R 613.6 Zhu et al. (2005)  
Mg-Al Yellow thiazole 222.2 Bouraada et al. (2014)  
Mg-Al Evans blue 107.5 Bouraada et al. (2014)  
Mg-Fe Congo red 104.6 Ahmed & Gasser (2012)  
LDH nature Dye Negative charges number Qmax (mg g−1References 
CZAF IC 617.3 This work 
CZAF F2B Unknown 1,501.4 This work 
Zn-Al Methyl orange 200.0 Ni et al. (2007)  
Mg-Al Brilliant blue R 613.6 Zhu et al. (2005)  
Mg-Al Yellow thiazole 222.2 Bouraada et al. (2014)  
Mg-Al Evans blue 107.5 Bouraada et al. (2014)  
Mg-Fe Congo red 104.6 Ahmed & Gasser (2012)  
Figure 9

Langmuir adsorption isotherms of IC and F2B by (a) CZAF and (b) ZAF-HT.

Figure 9

Langmuir adsorption isotherms of IC and F2B by (a) CZAF and (b) ZAF-HT.

Effect of the temperature

The sorption of IC and F2B by CZAF was studied at different temperatures (25, 35 and 45°C) to evaluate the variation of the adsorbed amount. The thermodynamic parameters such as change in standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were estimated using Equations (7) and (8): 
formula
7
 
formula
8
where T is the absolute temperature (in K), R is the gas constant (8.314 J mol−1 K−1), and Kd (cm3 g−1) is distribution coefficient of adsorbates between liquid and solid phase. Kd was calculated using Equation (9): 
formula
9
Figure 10 shows the plots of ln Kd versus 1,000/T. The high values of the determination coefficient indicate the good linearity of the plots (R2 > 0.995). The calculated values of ΔG°, ΔH° and ΔS° are shown in Table 4. The negative values of standard free energy indicate the spontaneity of the sorption process, which means a high affinity of CZAF material toward anionic dyes. It was seen also that the value of ΔH° was positive (endothermic) in the sorption of IC, but it was negative (exothermic) for the removal of F2B. These results showed that for IC higher adsorption occurs at higher temperature, whereas for F2B less adsorption occurs at higher temperature. Positive values of ΔS° showed a high affinity of the material towards the dye molecules and the increasing of the randomness during sorption process (Qiuhong et al. 2007).
Table 4

Thermodynamic parameters for the sorption of IC and F2B by CZAF at several temperatures

  ΔS° (Kj.   ΔG° (Kj mol−1)
 
 mol−1.K−1ΔH° (Kj.mol−1298 K 308 K 318 K 
ZAF-IC 0.146 14.360 − 29.267 − 30.731 − 32.195 
ZAF-F2B 0.020 − 19.273 − 25.233 − 25.433 − 25.633 
  ΔS° (Kj.   ΔG° (Kj mol−1)
 
 mol−1.K−1ΔH° (Kj.mol−1298 K 308 K 318 K 
ZAF-IC 0.146 14.360 − 29.267 − 30.731 − 32.195 
ZAF-F2B 0.020 − 19.273 − 25.233 − 25.433 − 25.633 
Figure 10

Van't Hoff plot of the sorption by CZAF of IC and F2B.

Figure 10

Van't Hoff plot of the sorption by CZAF of IC and F2B.

Reusability of CZAF

Several researchers have studied the possibility of CLDH regeneration by thermal recycling method. The heat treatment of the used CLDHs at around 500 °C can completely decompose the adsorbed organic pollutants and transform the CLDHs for reuse (Shin et al. 1996; Crepaldi et al. 2002). Figure 11 showed the reusability study of CZAF for both dyes (IC and F2B) for four cycles. The results showed that CZAF exhibits a good stability after four thermal cycles: the adsorption capacities decreased slightly for both dyes and attained 385.7 and 1,365.6 mg g−1 for IC and F2B, respectively for the fourth cycle. After calcination and rehydration, the CLDH crystallinity reduced affecting on the adsorption capacity (Zhu et al. 2005). Furthermore, some dye molecules can be presumably interfered with the mixed metal oxides during the heat treatment of CLDHs affecting also their crystallinity.
Figure 11

Reuse of CZAF for the uptake of IC and F2B for four thermal cycles.

Figure 11

Reuse of CZAF for the uptake of IC and F2B for four thermal cycles.

CONCLUSIONS

In this study, ZAF-HT and CZAF were synthetized and characterized by several experimental techniques (XRD, BET, FTIR spectroscopy and SEM). The material was used to take up IC and F2B from water in a batch mode. The adsorption capacities of CZAF were found to be 488.94 and 1,487.91 mg g−1 for IC and F2B, respectively. The sorption of IC and F2B does not depend on the pH of the solution. The kinetic data of both dyes fitted the pseudo-second-order kinetic model well, and the isotherm sorption data were described by the Langmuir model. The thermodynamic parameters were calculated and showed that the sorption process was spontaneous in nature. The reusability study of CZAF for the removal of IC and F2B for four cycles showed that the efficiency of the calcined material decreased slightly.

ACKNOWLEDGEMENTS

The authors would like to thank Professor Jersy Zajac, Director of Laboratory AIME-UMR, University of Montpellier, France, for the acceptance in his laboratory allowing us to achieve our characterizations of materials and for inspiring discussions and helpful comments. We would like also to thank all the co-workers cited in the references below for their valuable contributions to the work described here. This work was financially supported by the CNEPRU-Algeria, Project E02220120028.

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