COMPETITIVE SORPTION OF CU(II), ZN(II) AND CD(II) METAL IONS ONTO SODIUM TRIPOLYPHOSPHATE MODIFIED CHITOSAN MEMBRANES

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1 124 XXV th ARS SEPARATRIA Toruń, Poland 2010 CMPETITIVE SRPTIN F CU(II), ZN(II) AND CD(II) METAL INS NT SDIUM TRIPLYPSPATE MDIFIED CITSAN MEMBRANES Magdalena GIERSZEWSKA-DRUŻYŃSKA, Jadwiga STRWSKA-CZUBENK Chair of Physical Chemistry and Physicochemistry of Polymers, Faculty of Chemistry, Nicolaus Copernicus University Gagarina St. 7, Toruń, Poland Abstract Chitosan/sodium tripolyphosphate (Ch/TPP) membranes were synthesized and used for the adsorption of Cu(II), Zn(II), Cd(II) ions from unary, binary and ternary aqueous solution. The effect of initial p of solution, different initial metal concentrations c o and metal molar ratios were studied. It was found that the amount of metal ion adsorption generally increased with increasing solution p and c o. In binary metal ion solutions Ch/TPP membranes exhibited higher binding ability toward Cu(II) compared to Zn(II) or Cu(II) ions. 1. INTRDUCTIN Chitosan, a natural biopolymer obtained i.a. from seafood wastes, is known as a good ions sorbent [1]. It is a copolymer of β-(1 4)-linked 2-acetamido-2-deoxy-β-D-glucopyranose and 2-amino-2-deoxy-β- D-glucopyranose (Fig. 1a). The high interest of this natural abundant polymer is a consequence of its unique properties [2, 3], i.e. biodegrability, biocompatibility, bioactivity and non-toxicity. Chitosan, as other sorbents, can be used several times in sorption processes after its effective desorption. ne of the well-known method of chitosan regeneration is based on using of acidic solutions as desorption media. It is also well-known that chitosan isn t resistant to acidic p. Among other methods of increasing chitosan s resistance, crosslinking is one of the mostly chosen procedure [1]. Chitosan crosslinking often results in chitosan sorption performance decrease. It is due to the decrease of number of free amino groups that take part in formation of crosslinks. In present work we proposed to use sodium tripolyphosphate, known for its ability to bond heavy metal ions, as a crosslinking agent to overcome the decrease of chitosan sorption performance after its modification. Moreover, chitosan crosslinking with low-molecular phosphate is known as a mild and simple method [4, 5].

2 XXV th ARS SEPARATRIA Toruń, Poland In this work, the adsorption of Cu(II), Zn(II) and Cd(II) from unary, binary and tertiary solutions onto chitosan/tripolyphosphate (Ch/TPP) membranes were studied. All experiments were performed with different initial p, total metal concentrations and molar ratios. 2. EXPERIMENTAL 2.1. Materials Two different commercially available chitosan samples: high molecular weight chitosan (MW-Ch) and medium molecular weight chitosan (MMW-Ch) and sodium tripolyphosphate (TPP, Fig. 1b) were purchased from Sigma-Aldrich (Germany). Acetic acid (Ac), zinc nitrate (Zn(N 3 ) 2 ), copper nitrate (Cu(N 3 ) 2 ), cadmium nitrate (Cd(N 3 ) 2 ), sodium acetate (NaAc), sodium hydroxide (Na), hydrochloric acid (Cl) and nitric acid (N 3 ) were analytical grade and were purchased from PCh (Poland). Chitosan selected for this study varied in their molecular weight, but had similar degree of deacetylation (DDA). Degree of deacetylation of chitosan, determined by potentiometric titration method [6], was equal to 79.5 ± 1.5 (MW-Ch) and 75.7 ± 3.9 (MMW-Ch). The viscosity average molecular weight ( M ), determined by viscosity analysis of chitosan η solutions according to Il`ina and Varlamov [7], was equal to 980 kda (MW-Ch) and 730 kda (MMW-Ch). The details of above measurements have been presented elsewhere [8]. a) b) C 2 C 2 NCC 3 1-DDA N 2 DDA Na P P P Na Na Na Na Fig. 1. Chemical structure of (a) chitosan and (b) sodium tripolyphosphate ydrogel membranes preparation Pure chitosan membranes were obtained by casting and solvent evaporation technique. Filtered, degassed 1 wt.% chitosan solution in 2 wt.% aqueous Ac solution was cast as film on clean glass plate and evaporated to dryness in an oven at 310 K, then further dried under vacuum at the same temperature.

3 126 XXV th ARS SEPARATRIA Toruń, Poland 2010 Chitosan/sodium tripolyphosphate (Ch/TPP) membranes were obtained by dipping pure chitosan membranes in 1.3 wt.% aqueous TPP solution for a defined time period. Conditions of polyelectrolyte complex preparation was as follows: crosllinking time 1h, p of TPP solution 5.5 (adjusted by adding a small amount of concentrated Cl solution), temperature 277 K. The obtained Ch/TPP membranes were additionally thoroughly washed in deionized water and dried similarly as chitosan films. Dried polymer films were stored in a desiccator over P 2 5 at ambient temperature Sorption experiments Aqueous solutions of Cu(II), Zn(II), Cd(II) ions were prepared by dissolving of nitrate salts in deionized water. The total metal (Me(II)) concentration varied from 3.2 mm to 16 mm for unary systems. Solutions of 16 mm total metal concentration and 1:1, 4:1, 1:4 metal molar ratios were used as binary systems and 24 mm metal solution with 1:1:1 metal molar ratio was used as a ternary metal solution. The initial solution p was adjusted in the range by adding a small amount of N 3 or Na. The solution p was selected such that no metal hydroxide precipitations were experimentally found in bulk solutions. In adsorption experiments the mixture of dry Ch/TPP membrane (0.05g) and metal ion solution (75 cm 3 ) were placed in a 0.1 dm 3 glass flask. The flask was shaken and placed in thermostatic bath (T = ± 0.1 K). Time 48h was experimentally found for each system to reach equilibrium. The metal ion concentration in aqueous solution was measured before and after each experiment using an atomic absorption spectrometry. The amount of adsorbed metal q M (mol/kg) was obtained using equation (1): q M ( c c ) 0 M V = (1) m where c 0 and c M are the initial and equilibrium concentrations in aqueous phase (mol/dm 3 ), respectively, V is the volume of the solution (dm 3 ) and m is the weight of dry membrane (kg). Each experiment was triplicate at least in identical conditions. In order to quantify competitive effect, the selectivity factors of metals were calculated using equation (2): q M1 q M2 β M1/M2 = (2) c0(m1) c 0(M2)

XXV th ARS SEPARATRIA Toruń, Poland 2010 127 3. RESULTS AND DISCUSSIN Fig.

Equilibrium adsorption of metal ions from unary 16 mm metal solution onto Ch/TPP membranes.

The former and present literature suggests that observed differences in metal ions sorption onto chitosan and modified chitosan result from sorption mechanism.

4 XXV th ARS SEPARATRIA Toruń, Poland RESULTS AND DISCUSSIN Fig. 2 shows the effect of initial solution p on Cu(II), Zn(II) and Cd(II) ions sorption from unary 16 mm metal solutions onto ionically crosslinked Ch/TPP membranes. Fig. 2. Equilibrium adsorption of metal ions from unary 16 mm metal solution onto Ch/TPP membranes. The obtained results indicate that adsorption capacity of all metal ions strongly depends on the solution p. The former and present literature suggests that observed differences in metal ions sorption onto chitosan and modified chitosan result from sorption mechanism. This mechanism is complicated and probably simultaneously dominated by adsorption, ion exchange and chelation [1, 9, 10]. It is generally accepted that chitosan amine sites are the main reactive groups responsible for the sorption of metal ions, though hydroxyl groups (especially in the C-3 position) may also contribute to the sorption [1]. In chitosan membranes modified with TPP also phosphate groups can act as binding sites [11]. Fig. 3 shows the simplified scheme of changes in bivalence metal ions sorption onto Ch and TPP with changes in p of metal solution.

5 128 XXV th ARS SEPARATRIA Toruń, Poland 2010 Fig. 3. Simplified model of chitosan and TPP sorption mechanism in different p conditions. Simplified mechanism presented schematically in Fig. 3 well agrees with results presented in Fig. 2. Considering results obtained for other initial metal ions concentrations (not shown here), it can be found the best working p intervals with the maximum metal uptake, as presented below: for Cu(II), for Zn(II), for Cd(II). Generally, the Ch/TPP sorption ability towards different metal ions in unary nitrate(v) solutions increases in series Zn 2+ < Cu 2+ < Cd 2+. Fig. 4. Selectivity factor for binary metal systems with 1:1 Me(II) molar ratio.

6 XXV th ARS SEPARATRIA Toruń, Poland In Fig. 4 selectivity factors for binary solutions with 1:1 metal molar ratio were presented. It was found that crosslinked Ch/TPP membranes exhibits high Cu(II) binding ability in binary Cu/Zn and Cu/Cd metal systems. The affinity of Ch/TPP membranes to Zn and Cd metal ions in binary Zn/Cd solutions was comparable. Calculated selectivity factors exhibit the highest values in Cu/Zn and Cu/Cd acidic solutions. 4. CNCLUSINS The results obtained in this study show that chitosan/tripolyphosphate membranes are stable under applied sorption conditions and can be used as an effective materials to remove heavy metal ions from low concentrated salt solutions. The adsorption capacity of Cu(II), Zn(II) and Cd (II) ions strongly depends on solution p and initial metal ion concentration [12]. Chitosan/sodium tripolyphosphate membranes can be used as an effective material to remove copper from low concentrated copper/zinc and copper/cadmium salt binary solutions. The mechanism of interaction of metal ions with Ch/TPP is most probably dominated by chelation. Acknowledgements Scientific work funded by the European Social Fund and the State Budget as part of The Integrated Regional perational Programme, Measure 2.6 Regional Innovation Strategies and transfer of knowledge under a project of the Regional Council of the Kujawsko-Pomorskie Province Scholarships for PhD Students 2008/2009 IRP REFERENCES [1] E. Guibal, Sep. Purif. Technol., 2004, 38, 43. [2] C. Chatelet,. Damour, A. Domard, Biomaterials, 2001, 22, 261. [3] M.. Struszczyk, Polimery (Warsaw), 2002, 47, 396. [4] J. Berger, M. Reist, J.M. Mayer,. Felt, N.A. Peppas, R. Gurny, Eur. J. Pharm. Biopharm., 2004, 57, 19. [5] X. Z. Shu, K. J. Zhu, Eur. J. Pharm. Biopharm., 2002, 54, 235. [6] A. Alagui, M. Vincedou, P. Vottero, Polymer, 2000, 41, [7] A.V. Il ina, V.P. Varlamov, Appl. Biochem. Microbiol., 2004, 40, 300. [8] J. strowska-czubenko, M. Gierszewska-Drużyńska, Carbohydr. Polym., 2009, 77, 590. [9] S.-T. Lee, F.-L. Mi, Y.-J. Shen, S.-S. Shyu, Polymer, 2001, 42, [10] G. Crini, Prog. Polym. Sci., 2005, 30, 38. [11] Y.I. Tarasevich, G.M. Klimova, Appl. Clay Sci., 2001, 19, 95. [12] J. strowska-czubenko, M. Gierszewska-Drużyńska, in preparation.

Katarzyna Zielińska, Alexandre G. Chostenko, Stanisław Truszkowski

ADSORPTION OF CADMIUM IONS ON CHITOSAN MEMBRANES: KINETICS AND EQUILIBRIUM STUDIES Katarzyna Zielińska, Alexandre G. Chostenko, Stanisław Truszkowski Chair of Nuclear and Radiation Chemistry Faculty of