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Preparation and characterization of new membranes PSU / PVP for the extraction of cadmium ions from acidic solutions
T. Eljaddi(a)*, A. Benjjar(a), O. Kamal(a), M.Riri(a), L. Lebrun(b), M. Hlaibi (a,b)
a Laboratoire Interface Matériaux et Environnement (LIME), Université Hassan II Faculté des Sciences Aïn Chock, Casablanca, Maroc.
b Laboratoire des Polymères, Biopolymères, Membranes, UMR 6522 du CNRS, Université de Rouen, Faculté des Sciences, Mont-Saint-Aignan, France.
*Corresponding author. E-mail : [email protected]
Received 5 Sept 2014, Revised 24 Sept, Accepted 24 Oct 2014
Abstract
In this work, we developed asymmetric membranes at the base of the PSU / PVP by the phase inversion method and we used Cholic acid (CA) as a carrier, we realized the facilitated transport of cadmium ions in acidic solutions. Macroscopic parameters, permeability P and initial flux J0 related to facilitated transport of these ions were determined, for understanding this process; we have characterized these membranes by various techniques (SEM, angle contact.). To explain this phenomenon of facilitated transport and therefore extraction of these ions in this type of membranes, a mechanism based on the complexation of these ions by the carrier and diffusion of the formed complex through the organic phase has been developed. The experimental results verify this mechanism and we can find the optimum quantity of carrier and determine the microscopic parameters: the association constant Kass and apparent diffusion coefficient D* related to the migration of the complex (Substrate-Carrier) formed through the membrane phase.
Keywords: facilitated extraction; PSU/PVP; cadmium; initial flux; permeability.
1. Introduction
Cadmium is a metal used in many industries such as metallurgy and accumulators, fertilizer [1-2]. It’s known for its toxicity to living beings, and therefore it causes serious problems of environmental pollution especially in the water. Hence, the interest of trying to develop techniques to recover the metal. Membrane techniques are considered among the best techniques to respect the economic, environmental and regulatory requirements. Many researches are conducted to extract cadmium ions by several types of membranes:
supported liquid membrane (SLM) [3], polymer inclusion membrane (PIM)[4], Bulk liquid membrane (BLM)[5], most membranes are synthesized from polymers such as polysulfone PSU. Membranes based on PSU and polyvinyl pyrrolidone (PVP) have better physicochemical properties [6]. In this work we introduced Cholic acid (CA) as a carrier in the matrix of PSU / PVP to study the facilitated transport of cadmium ions through the membrane and we are characterized by SEM, contact angle and using a theoretical model we were able to calculate the parameters for the facilitated transport of cadmium.
471 2 Materials and methods
2.1 Chemicals:
All reagents, solvents and chemicals used in this study are pure commercial products (Aldrich, Fluka and Alpha Aesar). Cadmium ions acids are prepared from solutions of cadmium nitrate hydrate and the pH was adjusted with HCl and NaOH.
2.2 Membrane preparation:
The membrane was prepared by phase inversion method the mixture of polysulfone and polyvinylpyrrolidone (PVP) in NMP as solvent and Cholic acid (CA) as a carrier and as the water bath step of phase inversion at room temperature [7].
2.3 SEM observation:
The samples were fractured in liquid nitrogen and coated with gold–palladium and then observed by a scanning electron microscope (ZEISS EVO40EP).
2.4 Transport experiments:
Transport experiments were performed in a cell that contains two compartments, the source phase and the receiving phase the system is immersed in a thermostatic bath and agitation provided by a multistation magnetic stirring, to follow the evolution the transport of cadmium ions we took samples from the receiving phase as a function of time, and we used Shimadzu atomic absorption spectroscopy to analyze the samples [8].
3 Results and discussion:
3.1 Characterization of the membrane:
We developed under the same conditions three membranes: PSU / PVP / CA, PSU / PVP and PSU alone, and we made the characterization of the three membranes:
3.1.1 Contact Angle:
Analyzing Table 1, we see that the three membranes are in the range of hydrophilicity (thêta <90 °) this shows that all three films are relatively hydrophilic. The character of the hydrophilicity of the synthesized membrane PSU/PVP/CA can be attributed to OH group of Cholic acid added. The thickness of the membrane was measured using the Palmer; it is of the order of 106μm.
Table 1 Contact angle
membrane Contact angle (°)
PSU alone 68,60
PSU/PVP 58,60
PSU/PVP/AC 65,9
3.1.3 Membrane morphology:
The images in Figure 2 show that has asymmetric membranes, the addition of PVP and Cholic acid can create more pores. Membranes are homogeneous and contain cavities of different sizes, communicative
472 through pores. Despite the existence of pores in the membranes only PSU and PSU / PVP we have not observed any passage of cadmium ions through these membranes.
a b c
Figure1. Micrographs of the cross-sections of membranes: (a) PSU alone , (b) PSU/PVP, (c) PSU/PVP/CA
3.2 Facilitated transport of copper ions:
We have transported the cadmium ions using the membrane PSU/PVP/CA at T = 25 ° C and pH = 1 for initial concentrations of 0.0125 M to 0.1 M, we used the calculation model [9-11] to determine the macroscopic parameters (permeability P and initial flux J0) and microscopic parameters (association constant Kass and apparent diffusion coefficient D*).
3.2.1 Macroscopic parameters P and J0:
The Figure 2 shows the evolution of the term -ln (C0-2CR) versus time:
Figure2. Evolution of -ln (C0-2CR) versus time for the facilitated transport of cadmium ions
The Figure 2 shows that the representation of the term -ln (C0-2CR) versus time is a straight line for the concentrations studied, so the kinetic model proposed is verified, then we can calculate the macroscopic parameters P and J0, the values are grouped in Table 2.
Table 2 Macroscopic parameters P and J0 relating to the facilitated transport of cadmium ions
R² = 0.98 R² = 0,99 R² = 0,99 R² = 0,98
2 3 4 5
0 100 200
-Ln(C0-2CR)
Time (min)
0,1M 0,05M 0,025 0,0125M
C0 mol/L P= 107cm2 s-1 J0 105 mmol/s*cm2
0,1 20,10 1,90
0,05 20,87 0,98
0,025 21,64 0,51
0,0125 22,41 0,26
473 Table 2 shows the evolution of the initial flux is in the same direction as the initial concentration of substrate, but the evolution of permeability is the opposite direction. These results are according with the results of other studies [12-13].
3.2.1 Microscopic parameters Kass and D*:
To understand this phenomenon, we proposed a model based on the complexation between the substrate and the carrier, and the diffusion of this complex in the membrane phase. We can used the graphic representation of Lineweaver-burk of 1/J0=f(1/C0), for to confirm this mechanism and to calculate of microscopic parameters Kass and D* (Figure 3):
Figure3. The linweaver-Burk plots for the for the facilitated transport of cadmium ions
The figure 3 shows we get a straight line, which confirms the proposed mechanism based on the complexation of the substrate by the carrier, and kinetically determinate step is the diffusion of the complex substrate-carrier in the membrane phase, model allows us to calculate the microscopic parameters Kass and D*, the results obtained are grouped in table 3 confirm that there is an inverse correlation between these two parameters, when Kass increases the D * decreases and vice versa. The constant Kass gives information about the stability of the complex formed, when Kass is big the stability increases against the value of D* decreases because it gives information on the diffusion of the complex in the membrane phase.
the high values of apparent diffusion coefficient (D*) clearly indicate that the movement within the membrane is not a simple diffusion phenomenon, therefore, the passage of the substrate through the membrane is due to series of reaction (association/dissociation), this result can be explained by the hypothesis of “fixed-site jumping” proposed by Smith [14].
Table 3 Microscopic parameters Kass and D* relating to the facilitated transport of cadmium ions
4 Conclusion:
In this work, we prepared by phase inversion method a new membrane at the base PSU / PVP and Cholic acid as a carrier, we characterized the membrane by SEM and contact angle, and we found that insertion of the Cholic acid in the membrane allows the passage of ions through the cadmium and without Cholic acid membranes are waterproof. On the other hand, we have verified our model calculation and we were able to
y = 0.0464x + 0.0814 R² = 0.9998
0 1 2 3 4
0 30 60 90
1/J0 *10-5 (mmol-1.cm2.s)
1/C0 (mmol-1.cm3)
D* 105 cm².s-1 Kass
2,60 1,75
474 calculate parameters related to facilitated transport of cadmium ions through the membrane prepared and we conclude that the movement in the membrane phase is a jump on the fixed site.
Acknowledgements
All authors wish to acknowledge the AUF “Agence Universitaire de la Francophonie “for financing this project PCSI 6313PS014.
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