Advanced Materials Manufacturing & Characterization Vol 6 Issue 1 (2016)
Advanced Materials Manufacturing & Characterization journal home page: www.ijammc-griet.com
THE INTERCALATION OF Zn/Al HDL BY THE DIAMINO DODECYL PHOPHONIC ACID: SYNTHESIS AND PROPERTIES OF ADSORPTION OF CADMIUM Messaadi Mahassenea *; Kaid M’hameda,*; Kadari Mohameda; Mouffok Ben Alia; Didier Villeminb aUniversity
of Djillali Liabes; Laboratoire du synthèse de l’information environnementale; Sidi Bel Abbes; Algeria *aSaida University, Faculty of Sciences, Department of Chemistry,Box 138, Algeria b Université de Caen, Laboratoire de Chimie Moléculaire et Thioorganique, UMR CNRS 6507, INC3M, FR 3038, ENSICAEN & Centre de Recherche, 14050 Caen, France
A B S T R A C T In this paper, Zn/Al double layered hydroxides (ZnAl LDH) were synthesized by chemical co-precipitation method and grafted with Diamino Dodecyl Phosphonic Acid (DDPA) by direct reaction and the obtained solids (ZnAl-DDPA LDH) were characterized by powder X-ray diffraction, infrared spectroscopy, BET and elemental analysis. So, the present research was aimed to study the removal efficiency of Cd2+ by ZnAl-DDPA LDHand investigated all the parameters of adsorption such as the effect of concentration of Cd2+, effect of pH, adsorbent dose, the effect of salt and temperature. The sorption data were analyzed and fitted to linearized equations of the Langmuir and Freundlich. The kinetics of sorption was analyzed by use of pseudo-first-order and pseudosecond order kinetic models. Keywords:Cadmiumremoval,adsorption,Zn-AlLDHs, Diamino Dodecyl Phosphonic Acid.
1.
Introduction
. The presence of metal cations in water could cause serious environmental and human health problems because of their potentially high toxicity [01]. Cadmium (Cd) is a non-essential and toxic heavy metal present in wastewater and polluted soils [02]. The removal of cadmium, Cd(II), ions is gaining wide interest from both environmental and economical viewpoints due to its serious hazardous impacts on humans, animals, and plants. There are several industries that are responsible for polluting the environment with high level of Cd(II) ions [03]. The major sources of cadmium are products of industries such as metal plating, cadmium-nickel batteries, phosphate fertilizers, mining, pigments, stabilizers, metallurgy, ceramics,
photograph, textile printing, lead mining, sewage sludge, alkaline batteries, and electroplating [04]. Layered double-metal hydroxides (LDHs) are known as hydrotalcite compounds (HTlcs) or hydrotalcites. They are layered compounds composed by metal hydroxide sheet with positive charge and interlayer space filled with anion with negative electric charge [05]. LDHs are represented by the general formula [MII1-x MIIIx (OH)2]x+[Anx/n . mH2O]x-. Where MII is a divalent cation (Zn2+ and/or Mg2+, Ni2+, Co2+, Cu2+); MIII is a trivalent cation (Al3+ and/or Fe3+, Cr3+), and A is an anion with charge n (Cl-, OH-, CO32-, NO3-, SO42-). X is MIII/(MIII+MII) and is normally between 0.2 and 0.33. m is the number of mol of cointercalated water per formula weight of compounds and is normally between 0.33 and 0.50 [06]. LDHs possess a welldefined layered structure with unique properties such as adsorption capacity, anion exchange capacity, and mobility of interlayer anions and water molecules. Accordingly, they may be of great value for potential applications as anion-exchange materials, adsorbents or ecological materials [07, 08, 09, 10]. This paper is an extension of our previous work [11]. Where we studied the sorption kinetics and thermodynamics of heavy metals by phosphonic acids (i.e. Zn2+ and Cu2+). The objectives of this work were: (1) to synthesize Zn Al LDH-DDPA by anionic exchange mechanism from layered double hydroxides intercalated by chloride (LDH-Cl); (2) to characterize the Zn Al LDH-DDPA sample by Fourier transform infrared (FTIR) spectroscopy for chemical functional groups, by X-ray powder diffraction (XRD) for chemical composition and BET analysis for surface area and pore size; (3) to study the effects of different parameters on Cd2+ adsorption. such as
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Corresponing author:Messaadi MahasseneE-mail address:
[email protected] Doi:http://dx.doi.org/10.11127/ijammc2016.04.05Copyright@GRIET Publications. All rights reserved.
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contact time, pH, ionic strength, adsorbent dose and temperature; (4) to determine the thermodynamic and kinetics parameters of Cd2+ adsorption on Zn Al LDH-DDPA 2.
Materials and methods
2.1.
Synthesis of the Zn-Al-LDH
A layered double hydroxide of the [Zn-Al-Cl] type with a Zn/Al ratio of 2 was prepared using a co-precipitation method similar to that described by Miyata [12, 13]. 150 ml of an aqueous of the metallic chlorides (0.50 M in ZnCl2 and 0.25 M in AlCl3) was added drop wise to a reactor containing about 100 ml of 1 M Na2SO4, at 25°C and under magnetic stirring. The pH of the reaction mixture was kept constant at 10.5 ± 0.1 by addition of 1.5 M NaOH. After complete addition of the metallic salts, the reaction mixture was left to age at room temperature for 24 h. Then, the precipitate obtained was washed and centrifuged several times and finally dried at room temperature. The composition of the precursor was [Zn0.667Al0.333(OH)2]0.333+[Cl0.333.]1- . 0.667 H2O, leading to a molecular weight of 120.5 gmol-1 and a divalent/trivalent metallic ratio of 2.003.
2.2.
Synthesis of the Zn-Al-LDH-DDPA
Several examples of the intercalation of organic and inorganic compounds in LDHs have been reported in the literature [14]. Zn-Al-LDH-DDPA was synthesized by the direct reaction between DDPA and Zn-Al-Cl LDH obtained at the chosen pH value. 0.01 mol of Zn-Al-Cl LDH Was dispersed in a 500 mL flask containing 50.0 mL deionised water and the slurry was stirred vigorously. After the temperature of the slurry was increased to 50 °C, 50.0 mL of a 0.20 mol/L aqueous solution of DDPA (DDPA/Cl = 1:1) was added drop-wise into the slurry in air and the pH value in the reaction system during the addition process was controlled maintained at 3.5 by adjusting the rate of addition rate of the DDPA solution. The resulting slurry was aged at 100 °C for 6 h, separated by three cycles of centrifugation/washing with a 2:1 (v/v) mixture of deionised water and acetone and dried in air at the room temperature. The acetone was used in order to ensure that excess DDPA was effectively removed.
2.3.
measured from the N2 adsorption and desorption isotherms at 77 K collected from a Quantachrome Autosorb-6 surface area and pore size analyzer. Before measurement, Zn Al-DDPA was first degassed overnight at 110 °C. Elemental analysis was carried out using a Shimadzu ICPS7500 inductive coupled plasma (ICP) emission spectrometer. A UV-2401PC spectrophotometer Schimadzu was used for UV–vis spectral measurements. Arsenazo III (1,8dihydroxynaphthalen-3,6 disulphonic acid-2,7-bis[(azo-2)phenylarsonic acid), a non-specific chromogenic reagent, was selected as the complexing agent for facilitating UV-vis detection. The accuracy and the precision of the method on the instrument were determined by measuring the absorbance at 600 nm against the prepared standards in the concentration range of (10-3 to 10-6 mol/l) [15]. A standard curve for UV-vis measurement demonstrated high degree of accuracy with a coefficient of regression, R2=99.7 %, was used in the calculation of unknown UV-vis concentrations from absorbance readings. 3.
Results and discussion
3.1.
Structure analysis
X-ray diffraction pattern of ZnAl LDH and ZnAl-DDPA LDH are presented in figure 2. The diffraction peaks corresponding to the LDH phase are observed at the 2Ө position 11.8, 23.6, 39.45, 46.9, 60.4 and 61.8 having the respective d-values 7.55, 3.77, 2.28, 1.94, 1.53 and 1.50Å and the respective miller indices are 003, 006, 015, 018, 110 and 113 [16]. The XRD patterns corresponding to the rhombohedral symmetry (space group, R-3m), were indexed in an hexagonal lattice [13]. The a and c lattice parameters were estimated using (110) and (003) reflections, respectively.
3.2.
Elemental analysis
The results of elemental analysis and the calculated structural formula of the ZnAl-Cl LDH precursor and ZnAl-DDPA LDH are listed in Table. 2. The results confirm that each two Cl- anion in the precursor have been replaced by one molecule of DDPA anion. The molar ratio of elements in the layer has little change, indicating that there is no destruction of the layers during the intercalation process.
Characterizations
3.3. Powder X-ray diffraction (XRD) data were collected on a PANAnalytical X'Pert Pro diffractometer in reflection mode at 40 kV and 40 mA using Cu Kα radiation (1.5405980 Å). Scans were recorded from 5°≤2θ≤100° with varying scan speeds and slit sizes. Samples were mounted on stainless steel sample holders. Fourier transform infrared (FTIR) spectra were recorded using a Perkin Elmer 16 PC-FTIR equipped with a thermostat to maintain the temperature of the sample at 25.0 ± 01 °C on KBr pellets in the range of 4000-400 cm-1. Specific surface areas and pore size were analyzed using the Brunauer–Emmett–Teller (BET) method. The samples were
FTIR and BET analysis
The FTIR spectra of the ZnAl LDH and ZnAl-DDPA LDH are shown in figure 1. They present a very intense band around 3458 cm-1, which is due to the stretching vibration of hydroxyl groups of the sheets and water molecules of the interlayer domain. The deformation Vibration of water molecules is responsible for the broad band recorded at 1626 cm-1. Lattice vibrations appear in the 431584 cm-1 range. The weak band at 1363 cm-1 indicates the presence of small amounts of carbonate in the galleries [17]. The peaks located at 1120 and 1020 cm-1 are attributed to the
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bending vibration of adsorbed phosphate P=O, P-O respectivly [18]. Specific surface areas of ZnAl LDH and ZnAl-DDPA LDH were measured and are presented in Table 1. It is evident from the table that the specific surface area (BET) decreased after DDPA intercalation in ZnAl LDH. The BET surface areas of ZnAl LDH was 62.4854 m2 g-1.
Figure 3: Evolution of extraction yield as a function of stirring time. The concentration of Cd++ decreased rapidly during the first 1 h, and then remained nearly constant after 2 h of adsorption. After this equilibrium time, the amount of cadmium adsorbed did not significantly change with time.
Figure 1: FTIR Spectra of ZnAl LDH and ZnAl-DDPA LDH 4.1.2.
The effect of concentration of Cd++
Figure 4:. Effect of the concentration of Cd (II) ions on the extraction. Figure 2: XRD patterns of ZnAl LDH and ZnAl-DDPA LDH 4. Application to cadmium ions (Cd++)
4.1.3.
4.1.
The study of the effect of initial pH of the aqueous phase on the extraction of Cadmium is provided by adding an acid solution (HCl) and adjusts the pH
parametric study
In order to optimize the extraction conditions of Cadmium, the effects of several physico-chemical factors are studied. 4.1.1
Adsorption time
The adsorption time of Cadmium onto the HDL was obtained by monitoring the decrease of metal ion concentration in aqueous solution with time. As shown in figure 3:
The effect of pH
Table 1: Pore properties and specific surface area of the Zn-Al LDHs and Zn-Al LDHs intercalated
BET Surface Area (m2g-1)
Pore volume (cm3g-1)
Average pore size (nm)
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ZnAl LDH
62.4854
0.2908
18.6157
ZnAlDDPA LDH
10.3297
0.009791
3.7912
Table 2: Chemical compositions of ZnAl LDH and ZnAl-DDPA LDH.
Sample compositi on
Znwt %
Al/wt %
Cl/wt %
P/wt %
C/wt %
ZnAl LDH
44.16
9.08
11.98
_
_
ZnAlDDPA LDH
15.48
3.29
_
6.01
22.98
Zn/A l mol ar ratio 2.00 8 1.94 2
Figure 6: The effect of the concentration of HDL on the extraction of cadmium ions. The best adsorption capacity was observed on increasing the adsorbent dose. However, the extraction yield of Cadmium (Cd+2) increase with increase in the dose of adsorbent (Zn-AlDDPA HDL) with vigorous stirring. 4.1.5.
The effect of ionic strength
Adsorption behaviour at different ionic strengths (0.01, 0.1 and 1 mol/L NaNO3) was investigated. As shown in Figure 7 adsorption capacity decreases gradually with the increase of NaNO3 concentration, It is assigned to the common ion effect that lowers the solubility of cadmium salts.
Figure 5: Effect of pH on extraction yield of Cadmium.
Figure 5 shows the variation of cadmium uptake at different pH. It is evident from the figure that the maximum removal was found to be at pH 6 for Cd++ ions. The percentage adsorption was decreased at pH 2; this is probably due to the instability of LDH in the acidic pH. The percentage of extractability is found to be: 17 % at pH=2, 25% at pH: 4 and 28% at pH=6.
Figure 7: Effect of ionic strength on extraction yield of Cadmium.
4.2. Thermodynamic Study 4.1.4.
Effect of adsorbent dose (HDL)
The adsorbent dose (HDL) is important parameters to optimize the amount of HDL for the maximum removal efficiency of Cadmium. The effect of variation of HDL amount on extraction yield of Cadmium is presented in the figure 6:
Thermodynamic data, for example free energy (DG°), enthalpy (DH°), and entropy (DS°), change during adsorption can be evaluated from the equations: ∆G = ∆H − T
(Eq. 1)
∆G = −nR lnKd
(Eq. 2)
From these two equations; it takes the following expression 024
∆𝑆
lnKd =
∆S R
−
T∆H
(Eq. 3)
R
With Kads =
m V
qe( ) m V
(Eq. 4)
[C0−qe ]
The sorption capacity (q) of cadmium by HDL is determined by the following relation: q(mg/g) =
(Co−Ce).V.M m
(Eq. 5)
qe: the sorption capacity at equilibrium. C0 and Ce: The initial and equilibrium concentration of cadmium respectively. V: The volume ofthe solution of cadmiumtreated (10 ml). M: Molecular weight of (Cd(NO3)2,4H2O) = 308.35g/mol. m: The weight of LDHs (0.1 g) R: Ideal gas constant (R= 8.314 J.mol-1 K-1) Kd: Distribution coefficient of Cd++.
5.663 = ⇒ ∆𝑆 = 8.314 × 5.663 = 47.08 J.mol-1.K-1 = 11.29 𝑅 cal .mol-1.K-1 ∆𝑆 = 11.29 cal .mol-1.K-1 ∆𝐻 610 = ⇒ ∆𝐻 =- 610 x 8.314 = - 5.0715 kJ.mol-1= - 1.2162 𝑅 -1 Kcal. mol . ∆𝐻 = −1.2162 K cal.mol-1 Thermodynamic parameters of sorption of cadmium by HDL show the results in table 3. The negative ∆𝐻° value indicates the exothermic nature of adsorption. The DG values obtained in this study for cadmium were < 10 kcal/ mol, which indicates that physical adsorption, is the predominant mechanism in the sorption process and the negative value of ∆S° suggests a decrease in the randomness at the solid/solution interface during adsorption of Cd++ ions on to the adsorbent [19].
-1
4.3.
Figure 8: lnKd depending on the temperature increase. 1 The curve is a straight linear: lnKd = 5.663+ 610 with T correlation coefficient R= 0.994 Then: Langmuir isotherm, BET isotherm, etc. In this work, we will study the Langmuir isotherm and Freundlich isotherm:
-1
Themodynamic ∆H,/kcal.mol-1 ∆S/cal.mol .K ∆G/kcalmo parameters Temperatu 298 308 -318 Valeurs -1.2162 +11.29 -4.580 -4.693 -4.8066
1
Adsorption isotherm
Adsorption is usually described through isotherms, that is, functions which connect the amount of adsorbate on the adsorbent; with its pressure (in the case of gases) or concentration (in the case of liquids). The relation between the amount adsorbed and the concentration is known as the adsorption isotherm [20]. Figure 9 shows the isotherms at temperature 298-338 K. The change of isotherm along with the variation of temperature is just like that of kinetics. This could be attributed to the complex sorption mechanisms of cadmium onto studied ZnAlDDPA LDH. They are in literature several models describing the process of adsorption such as Freundlich isotherm,
Figure 9: Effect of temperature on extraction yield of Cadmium. 4.3.2.
Langmuir isotherm
The Langmuir model admits that the extraction of Cadmium occurs on a homogenous surface by monolayer adsorption without any interaction between adsorbed ions [20].
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Figure 10: Langmuir isotherm model.
Figure 12: Freundlich isotherm model.
The adsorption capacities and Langmuir constant were calculated by the following equation:
The adsorption data found an excellent fit to the Langmuir isotherm and Freundlich isotherm.
1 𝑋/𝑚
=
1 𝑞𝑚.𝑏.𝐶𝑒
+
1 𝑞𝑚
4.4.
(Eq. 6)
Kinetics studies
The kinetic was analyzed using different kinetic models such as pseudo-first order and pseudo-second order. 4.4.2.
Pseudo-first-order
Ln(qe-qt)=ln(qe)-k1t
(Eq. 9)
Where qe and qt refer to the amount of Cadmium adsorbed per unit weight ofZn-Al-DDPA HDL respectively at equilibrium and at any time:
Figure 11: The linearized Langmuir isotherm 𝐶𝑒 𝑞𝑒
=
1 𝑞𝑚𝑎𝑥
𝐶𝑒 +
1 𝐾𝐿 𝑞𝑚𝑎𝑥
(Eq. 7)
In the curve b = 0.018 =
1 𝐾𝐿 𝑞𝑚𝑎𝑥
Where qmax is the monalayer capacity of the adsorbent, and KL is the Langmuir adsorption constant [21,22]. qmax and KL can be determined from the slope and intercept, respectively from the plot of Ce/qe versus Ce in figure 11. 4.3.3.
Freundlich isotherm
Freundlich isotherm is observed if the sites with stronger binding affinities are occupied by the Cadmium ions and the binding strength decreases with the increasing degree of site occupation [23]. The isotherm parameters were calculated using the Freundlich equation; wich is given as (Eq. 8): 1
𝑙𝑛𝑞𝑒 = 𝑙𝑛𝐾𝑓 + 𝑙𝑛𝐶𝑒 𝑛
(Eq. 8)
Figure 13: Pseudo-first-order kinetic model. qe and qt are the amount of cadmium adsorbed at equilibrium and at time t, respectively. The correlation coefficient (R2) which was calculated for the removal Cd++ ion was 0.907. 4.4.3.
Pseudo-second-order
Using the pseudo-second-order equation also, the adsorption process may be described.The differential equation is the following: 𝑡 𝑞𝑡
=
1 (𝑞𝑒2.𝐾)
+
𝑡 𝑞𝑡
(Eq. 10)
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5.
6. 7. 8. 9. 10. Figure 14: Pseudo-second-order kinetic model. The correlation coefficients for the second-order kinetic model obtained were nearly 1 when compared to the pseudo-first-order indicate that the adsorption system studied follows the pseudosecond-order. 5.
11.
12.
Conclusion
Diamino Dodecyl phosphonic acid has been intercalated into a synthesis Zn-Al HDL by ion exchange. After intercalation, the new hybrid compound (Zn-Al-DDPA HDL) was studied for the removal of cadmium from aqueous solution. All parameters, such as, adsorption time, adsorbent dose, solution pH and ionic strength were investigated. The Langmuir and Freundlich isotherms can be used to describe the adsorption equilibria of cadmium onto HDLs grafting with diaminododecylphosphonic acid. It was found that the equilibrium adsorption data were more fitted to the Langmuir isotherm than to the Freundlich model. The kinetics of the adsorption was found to be fitted with pseudo-second-order model.
13. 14. 15. 16.
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