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Adsorption of ReO4− ions into polyDMAEMA hydrogels prepared by UV-induced polymerization
REACTIVE & FUNCTIONAL POLYMERS
Reactive & Functional Polymers 59 (2004) 149–154
www.elsevier.com/locate/react
Adsorption of ReO 4 ions into polyDMAEMA hydrogels prepared by UV-induced polymerization Yu Yan a, Min Yi a, Maolin Zhai a,*, Hongfei Ha a, Zhifu Luo b, Xueqin Xiang b a
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China b China Institute of Atomic Energy, Beijing 102413, PR China Received 1 April 2003; received in revised form 1 December 2003; accepted 1 January 2004
Abstract Polydimethylaminaethyl methacrylate (polyDMAEMA) hydrogels with excellent characteristic were prepared by UV-induced polymerization and crosslinking of DMAEMA monomer in aqueous solution, and then the adsorption and enrichment of ReO 4 into polyDMAEMA hydrogels were investigated. Microscopic IR analysis approved the adsorption of ReO into polyDMAEMA hydrogels. A series of adsorption experiments with ReO 4 4 were carried out at different pH, ionic strength, concentration of ReO 4 , the mass of gel and temperature, respectively. It was found that pH 2.0 was the optimum for the adsorption of ReO 4 into polyDMAEMA hydrogels. Isothermal experiment revealed that the adsorption capacity increased linearly with increase of the concentration of ReO 4 in aqueous solution. Adsorption isothermal data could be interpreted well by the Langmuir equation. The adsorption capacity decreased with increase of ionic strength, the mass (size) of gel or temperature. Desorption experiment indicated that more than 90% ReO 4 ions can be desorbed from polyDMAEMA gels. At the same time the adsorbents can be regenerated and also be used again for the adsorption of ReO 4. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Dimethylaminaethyl methacrylate; Hydrogels; UV-induced copolymerization; ReO 4 ; Adsorption
1. Introduction 188
Re is a kind of medical-use radioactive isotopes, with 16.9 h half-life, which fits to prepare radioactive drugs for diagnosis and therapy [1]. However, the specific activity of 188 Re obtained by neutron radiation of natural abundance Re is too *
Corresponding author. Tel.: +86-10-6275-3794; fax: +86-106275-9191. E-mail address: [email protected] (M.L. Zhai).
low to use in radioactive drugs. In recent years, some new methods to obtain 188 Re with high specific activity, such as 188 W–188 Re generator (using 188 WO 4 to prepare 188 ReO 4 ) are much concerned [2,3]. It would be very ideal to improve the specific activity of 188 Re simply from 188 Re obtained by neutron irradiation of natural Re in reactor. Hydrogel has been used widely in adsorption, enrichment and separation process of proteins, enzymes and other biomolecules in aqueous medium [4]. In some special systems, some metal ions may also be
1381-5148/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2004.01.004
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Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154
separated by hydrogels [5]. So in this work polyDMAEMA hydrogels was tried to use in improving the specific activity of 188 Re based on ion-exchanging mechanism. PolyDMAEMA hydrogels possessed tertiary amino-group, which are expected to react with some anions such as 188 ReO 4 resulting in absorption and enrichment of 188 ReO 4 to a higher level of specific activity. The synthesis and characteristic of polyDMAEMA hydrogels were reported in our previous work [6]. In this study, the optimum adsorption and enrichment conditions of ReO 4 into polyDMAEMA hydrogels were investigated and mechanism was discussed.
excess surface water with laboratory tissues. The swelling ratio (R) was calculated as follows: R ¼ We =W0 ;
ð1Þ
where W0 is the initial weight of dried hydrogel; We is the weight of swollen hydrogel at the equilibrium. 2.3.2. Gel fraction The gels were extracted with methanol for 18 h. The samples were dried at 45 °C to constant weight before and after extraction procedure. The gel fraction was calculated as follows: Gels fractionð%Þ ¼ Wg =W0 100;
ð2Þ
where W0 is the initial weight of the dry gel and Wg is the weight of the dry gel after extraction. 2. Experimental 2.4. Measurement of ReO 4 2.1. Materials and instruments DMAEMA was purchased from Acro Co. and purified by decompressed distillation prior to use. N,N0 -Methylene-bisacrylamide (Bis), hydrogen peroxide (30%) and methyl violet were supplied by Beijing Chemical Works. KReO4 was purchased from Switzerland. The photochemical reactor was described in detail in the previous paper [7], the sample could be irradiated uniformly. 2.2. Radiation preparation of polyDMAEMA hydrogels The aqueous solution of DMAEMA, H2 O2 and Bis (crosslinker) was prepared and bubbled with nitrogen for 15 min. Then the quartz tube was sealed and irradiated by UV at room temperature for 3 h. Finally, the hydrogels obtained were cut into cylinders of 3-mm thick and dried in vacuum at 45 °C to constant weight. 2.3. Characteristic of polyDMAEMA hydrogels 2.3.1. Swelling ratio PolyDMAEMA gels dried to constant weight at 45 °C were immersed in distilled water to swollen equilibrium. Then the hydrogels were taken out from the solution and weighed after removing the
Methyl violet can combine with ReO in 4 aqueous solution at pH 4.0 to form a purple complex, which can dissolve in benzene and then was measured at 610 nm [8]. The detailed process of analysis is as follows: first add 1 ml, pH 4.0, buffer solution into a centrifuge tube and then add 2 ml of 0.5% methyl violet solution, ReO 4 solution and distilled water to make the total aqueous solution to be 5 ml, at last add 5 ml benzene. The centrifuge tube is vibrated for 15 min and then centrifuged for 5 min. Take the organic phase and measure the absorbency at 610 nm. 2.5. Adsorption and desorption of ReO 4 The series adsorption experiments of ReO 4 were carried out in different pH, ionic strength, concentration of ReO 4 , the mass of gel and temperature, separately. Put the dry gels into 100 ml KReO4 solution until the equilibrium of adsorption is reached. Then measure the concentration of ReO 4 in solution according to the above method. The adsorption capacity of the gel was calculated as follows: ðC0 Ce ÞV ; ð3Þ Adsorption capacity ðQÞ ¼ W where C0 is the initial concentration of ReO 4 (mol/L); Ce is the equilibrium concentration of
Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154 ReO 4 (mol/L); V is the volume of ReO4 (L); W is the weight of polyDMAEMA dry gel (g). For desorption studies, ReO 4 -laden sample was put into NaOH aqueous solution at pH 12.0. The amount of desorbed ReO 4 was determined after the equilibrium of desorption as before.
2.6. Microscopic IR analysis One piece of dry gels was put into KReO4 solution (0.01 mol/L, pH 2.0), another piece of dry gels was put the solution without KReO4 (pH 2.0). When the gels reached adsorption equilibrium, they were taken out from the solution, and then were freeze-dried and pulverized. Infrared spectra of the gel powder were recorded by MAGNA-IR 750 Nicolet spectrometer.
151
further for obtaining the excellent polyDMAEMA hydrogels. Effect of H2 O2 concentration on the characteristic of the hydrogels was shown in Fig. 1. Both the swelling ratio and gel fraction increased with the concentration of H2 O2 . In following experiments, the concentration of H2 O2 was chosen to be 40 mmol/L for the syntheses of polyDMAEMA hydrogels, which are transparent, elastic and have good swelling behavior. 3.2. Adsorption of ReO into polyDMAEMA 4 hydrogels 3.2.1. The selection of adsorbent condition DMAEMA is a kind of tertiary amine. In acidic condition, DMAEMA can be protonated, so it can combine with ReO 4 shown as þ R3 N þ Hþ þ ReO 4 ! R3 NH ReO4
3. Results and discussion 3.1. Radiation synthesis of polyDMAEMA hydrogels The synthesis and characteristic of polyDMAEMA hydrogels induced by UV radiation have been studied earlier [5]. In this work, the concentration of DMAEMA was chosen to be 25% (W/ V), and Bis was kept at 0.5% of the weight of DMAEMA based on the previous experiment. Here, the concentration of H2 O2 was selected
ð4Þ
According to reaction (4), it can be found that the adsorption of ReO 4 into polyDMAEMA hydrogels belongs mainly to ion adsorption. The adsorption capacity is affected by many factors such as pH, matrix particle size, the nature of the adsorbent, temperature, etc., among which pH is the most important one. In order to investigate pH’s effect, the same dry gels were put into the solutions with different pH and constant concentration of ReO 4 . Fig. 2 showed that there was an optimum pH (pH 2.0) for the adsorption of ReO into polyDMAEMA hydrogels. when 4
18
2.0
94 16
1.5 14
88 12
86 84
10
Q (10-5 mol/g)
90
Swelling ratio
Gel fraction (%)
92
1.0
0.5
82 8
80 20
25
30
35
40
45
50
The concentration of H2O2 (mmol/L)
Fig. 1. Effect of H2 O2 concentration on the swelling ratio and gel fraction of polyDMAEMA hydrogels.
0.0 0
1
2
3
4
5
6
7
8
9
10
11
12
13
pH
Fig. 2. Effect of pH on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 ).
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Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154
gels. Later, pH 2.0 and I ¼ 0:015 were chosen for further adsorption experiments.
1.6
3.2.2. Microscopic IR analysis Curves A and B in Fig. 4 were IR spectra of the gels with ReO 4 and without ReO4 , respectively. Compare with curve A and B it was very obvious that there was a adsorption band at 911 cm1 in curve A. According to [9], ReO 4 has an absorption band at 920 cm1 for Re–O antisymmetric vibration. The results testified further that the adsorption of ReO 4 into polyDMAEMA hydrogels.
-5
Q (10 mol/g)
1.4
1.2
1.0
0.8 0.05
0.10
0.15
0.20
0.25
0.30
Ion strength
Fig. 3. Effect of ionic strength on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0).
pH P 4, the tertiary amine groups of DMAEMA were unprotonated, i.e., in the undissociated state, so the adsorptive capacity of the hydrogels became very low. When pH is 2.0 (I ¼ 0:015), the adsorptive capacity of the hydrogels was larger than that at pH 1.0 (I ¼ 0:15) due to the influence of ionic strength (I). Effect of ionic strength on the adsorption of ReO 4 into polyDMAEMA hydrogels was shown in Fig. 3. The results indicated that the adsorption capacity of the hydrogels decreased with increasing of ionic strength, so pH 2.0 and I ¼ 0:015 were the optimum condition for the adsorption of ReO 4 into polyDMAEMA hydro-
3.2.3. Adsorption kinetics Adsorption kinetics is an important physicochemical parameter, which helps in the evaluation of basic qualities of adsorbents. Simple batch kinetic experiments on the adsorption of ReO 4 into polyDMAEMA hydrogels were carried out here and the adsorption kinetics was showed in Fig. 5. The amount of adsorption increased with the time and reached equilibrium after about 25 h. Adsorption capacity was calculated to be 2.20 105 mol/g and adsorption ratio was 51.6%. 3.2.4. Adsorption isotherms Fig. 6 showed the experimental equilibrium isotherms for the adsorption of ReO 4 into polyDMAEMA hydrogels. The adsorption capacity
A
B 2000
1800
1600
1400
1200
1000
800
-1
Wave numbers (cm ) Fig. 4. IR spectra of polyDMAEMA gels with ReO 4 and without ReO4 .
Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154 250
2.0 200
1.8 1.6
150
1.4 1.2
1/Q
The amount of adsorption (10-5mol/g)
2.2
1.0
100
0.8 50
0.6 0.4
0
0.2 0
5
10
15
20
25
0
30
1
2
4
5
6
7
4
Fig. 5. Adsorption kinetics of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0 and I ¼ 0:015).
Fig. 7. Linearized form of Langmuir isotherm for the adsorption of ReO 4 into polyDMAEMA hydrogels.
Fig. 7 showed that the experimental data fitted well by the Langmuir equation. Correlation coefficient was calculated to be 0.9996, and the values of Qmax and b were calculated to be 0.207 mg/g and 1427.8 L/mg, respectively.
18
15
-5
3
1/Ce (10 )
Time (h)
Q (10 mol/g)
153
12
9
3.2.5. Effect of gel mass (size) Effect of gel size on the adsorption of ReO 4 into polyDMAEMA hydrogels was shown in Fig. 8. Adsorption capacity reduced linearly as the size increased. Because the adsorption of hydrogels including surface and inner adsorption, inner adsorption need ReO 4 ion to diffuse into the
6
3
0 0
1
2
3
4
5
-4
Ce (10 mol/L)
Fig. 6. Adsorption isotherms of ReO 4 into polyDMAEMA hydrogels (pH 2.0 and I ¼ 0:015).
4.0
3.5
-5
Q (10 mol/g)
increased linearly with increase of the concentration of ReO 4 in aqueous solution. The adsorption isothermal data could be well interpreted by Langmuir equation as:
4.5
1 1 1 ¼ þ ; Q Qmax Qmax bCe
ð5Þ
3.0
2.5
where Ce is the equilibrium concentration of ReO 4 , Q is the amount of ReO4 adsorbed per unit weight of polyDMAEMA hydrogels at equilibrium concentration, Qmax is the maximum adsorption at monolayer coverage, and b is the Langmuir adsorption equilibrium constant related to the energy or net enthalpy.
2.0 0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
Mass of hydrogels (g)
Fig. 8. Effect of gel size on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0 and I ¼ 0:015).
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Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154
ReO 4 ions was desorbed from polyDMAEMA gels by treatment with diluted NaOH solution at pH 12.0, and at the same time the adsorbents was regenerated.
2.8
2.4
-5
Q (10 mol/g)
2.6
4. Conclusion
2.2
2.0
1.8 30
35
40
45
50
55
60
Temperature (˚C)
Fig. 9. Effect of temperature on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0 and I ¼ 0:015).
hydrogels. Bigger were gel particles; more difficult was it to reach the center of the gels for ReO 4 ion. So the concentration of obtained ReO had gra4 ded distribution in the gels and the concentration was the lowest in the center of hydrogels. Though the total absorbing amount increased with the increase of the mass of the gel, the adsorption capacity per unit weight would drop down. So smaller gels possessed higher adsorption efficiency and were quicker to reach adsorption equilibrium. 3.2.6. Effect of temperature Fig. 9 showed the relationship between adsorption capacity per unit weight and temperature. The adsorption capacity decreased as the temperature increased and the adsorption was an exothermic reaction. 3.2.7. Desorption studies Desorption studies helps to recover ReO 4 from the adsorbents to elucidate the nature of adsorption process. Moreover, the desorption process regenerates polyDMAEMA gels for reuse. The desorption experiments of ReO from poly4 DMAEMA gels indicated that more than 90%
The adsorption of ReO 4 into polyDMAEMA hydrogels prepared by UV-induced polymerization was carried out. It was found that pH 2.0 was the optimum for the adsorption of ReO 4 into polyDMAEMA hydrogels. Isothermal experiment revealed that the adsorption capacity increased linearly with increase of the concentration of ReO 4 in aqueous solution. Adsorption isothermal data could be well interpreted by the Langmuir equation. The adsorption capacity decreased with increase of ionic strength, the size of gel or temperature. Desorption experiment indicated that more than 90% ReO 4 ions can be desorbed from polyDMAEMA gels and at the same time the adsorbents can be regenerated for reuse.
References [1] K. Hashimoto, S. Bagiawati, M. Izuma, K. Kobayashi, J. Appl. Radiat. Isot. 47 (1996) 195. [2] R.M. Lambrecht, K. Tomiyoshi, T. Sekine, J. Radio. Chim. Acta 77 (1997) 103. [3] F.F. Knapp Jr., A.L. Beets, S. Guhlke, P.O. Zamora, H. Bender, H. Palmedo, H.J. Biersack, J. Anticancer Res. 17 (1997) 1783. [4] O. Guven, M. Sen, E. Karadag, D. Saraydin, Radiat. Phys. Chem. 56 (1999) 381. [5] Y.F. Chen, M. Yi, Radiat. Phys. Chem. 61 (2001) 65. [6] G.L. Jiang, M. Yi, J.B. Zhang, Acta Sci. Nataralium Univ. Pekinensis 35 (1999) 201. [7] M.L. Zhai, Y.F. Chen, M. Yi, H.F. Ha, Polym. Int. 53 (2004) 33. [8] Q. Tan, L. Yu, China Molybdenum Industry 20 (1996) 40. [9] N. Weinstock, H. Schulze, A. M€ uller, J. Chem. Phys. 59 (1973) 5063.
Reactive & Functional Polymers 59 (2004) 149–154
www.elsevier.com/locate/react
Adsorption of ReO 4 ions into polyDMAEMA hydrogels prepared by UV-induced polymerization Yu Yan a, Min Yi a, Maolin Zhai a,*, Hongfei Ha a, Zhifu Luo b, Xueqin Xiang b a
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China b China Institute of Atomic Energy, Beijing 102413, PR China Received 1 April 2003; received in revised form 1 December 2003; accepted 1 January 2004
Abstract Polydimethylaminaethyl methacrylate (polyDMAEMA) hydrogels with excellent characteristic were prepared by UV-induced polymerization and crosslinking of DMAEMA monomer in aqueous solution, and then the adsorption and enrichment of ReO 4 into polyDMAEMA hydrogels were investigated. Microscopic IR analysis approved the adsorption of ReO into polyDMAEMA hydrogels. A series of adsorption experiments with ReO 4 4 were carried out at different pH, ionic strength, concentration of ReO 4 , the mass of gel and temperature, respectively. It was found that pH 2.0 was the optimum for the adsorption of ReO 4 into polyDMAEMA hydrogels. Isothermal experiment revealed that the adsorption capacity increased linearly with increase of the concentration of ReO 4 in aqueous solution. Adsorption isothermal data could be interpreted well by the Langmuir equation. The adsorption capacity decreased with increase of ionic strength, the mass (size) of gel or temperature. Desorption experiment indicated that more than 90% ReO 4 ions can be desorbed from polyDMAEMA gels. At the same time the adsorbents can be regenerated and also be used again for the adsorption of ReO 4. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Dimethylaminaethyl methacrylate; Hydrogels; UV-induced copolymerization; ReO 4 ; Adsorption
1. Introduction 188
Re is a kind of medical-use radioactive isotopes, with 16.9 h half-life, which fits to prepare radioactive drugs for diagnosis and therapy [1]. However, the specific activity of 188 Re obtained by neutron radiation of natural abundance Re is too *
Corresponding author. Tel.: +86-10-6275-3794; fax: +86-106275-9191. E-mail address: [email protected] (M.L. Zhai).
low to use in radioactive drugs. In recent years, some new methods to obtain 188 Re with high specific activity, such as 188 W–188 Re generator (using 188 WO 4 to prepare 188 ReO 4 ) are much concerned [2,3]. It would be very ideal to improve the specific activity of 188 Re simply from 188 Re obtained by neutron irradiation of natural Re in reactor. Hydrogel has been used widely in adsorption, enrichment and separation process of proteins, enzymes and other biomolecules in aqueous medium [4]. In some special systems, some metal ions may also be
1381-5148/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2004.01.004
150
Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154
separated by hydrogels [5]. So in this work polyDMAEMA hydrogels was tried to use in improving the specific activity of 188 Re based on ion-exchanging mechanism. PolyDMAEMA hydrogels possessed tertiary amino-group, which are expected to react with some anions such as 188 ReO 4 resulting in absorption and enrichment of 188 ReO 4 to a higher level of specific activity. The synthesis and characteristic of polyDMAEMA hydrogels were reported in our previous work [6]. In this study, the optimum adsorption and enrichment conditions of ReO 4 into polyDMAEMA hydrogels were investigated and mechanism was discussed.
excess surface water with laboratory tissues. The swelling ratio (R) was calculated as follows: R ¼ We =W0 ;
ð1Þ
where W0 is the initial weight of dried hydrogel; We is the weight of swollen hydrogel at the equilibrium. 2.3.2. Gel fraction The gels were extracted with methanol for 18 h. The samples were dried at 45 °C to constant weight before and after extraction procedure. The gel fraction was calculated as follows: Gels fractionð%Þ ¼ Wg =W0 100;
ð2Þ
where W0 is the initial weight of the dry gel and Wg is the weight of the dry gel after extraction. 2. Experimental 2.4. Measurement of ReO 4 2.1. Materials and instruments DMAEMA was purchased from Acro Co. and purified by decompressed distillation prior to use. N,N0 -Methylene-bisacrylamide (Bis), hydrogen peroxide (30%) and methyl violet were supplied by Beijing Chemical Works. KReO4 was purchased from Switzerland. The photochemical reactor was described in detail in the previous paper [7], the sample could be irradiated uniformly. 2.2. Radiation preparation of polyDMAEMA hydrogels The aqueous solution of DMAEMA, H2 O2 and Bis (crosslinker) was prepared and bubbled with nitrogen for 15 min. Then the quartz tube was sealed and irradiated by UV at room temperature for 3 h. Finally, the hydrogels obtained were cut into cylinders of 3-mm thick and dried in vacuum at 45 °C to constant weight. 2.3. Characteristic of polyDMAEMA hydrogels 2.3.1. Swelling ratio PolyDMAEMA gels dried to constant weight at 45 °C were immersed in distilled water to swollen equilibrium. Then the hydrogels were taken out from the solution and weighed after removing the
Methyl violet can combine with ReO in 4 aqueous solution at pH 4.0 to form a purple complex, which can dissolve in benzene and then was measured at 610 nm [8]. The detailed process of analysis is as follows: first add 1 ml, pH 4.0, buffer solution into a centrifuge tube and then add 2 ml of 0.5% methyl violet solution, ReO 4 solution and distilled water to make the total aqueous solution to be 5 ml, at last add 5 ml benzene. The centrifuge tube is vibrated for 15 min and then centrifuged for 5 min. Take the organic phase and measure the absorbency at 610 nm. 2.5. Adsorption and desorption of ReO 4 The series adsorption experiments of ReO 4 were carried out in different pH, ionic strength, concentration of ReO 4 , the mass of gel and temperature, separately. Put the dry gels into 100 ml KReO4 solution until the equilibrium of adsorption is reached. Then measure the concentration of ReO 4 in solution according to the above method. The adsorption capacity of the gel was calculated as follows: ðC0 Ce ÞV ; ð3Þ Adsorption capacity ðQÞ ¼ W where C0 is the initial concentration of ReO 4 (mol/L); Ce is the equilibrium concentration of
Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154 ReO 4 (mol/L); V is the volume of ReO4 (L); W is the weight of polyDMAEMA dry gel (g). For desorption studies, ReO 4 -laden sample was put into NaOH aqueous solution at pH 12.0. The amount of desorbed ReO 4 was determined after the equilibrium of desorption as before.
2.6. Microscopic IR analysis One piece of dry gels was put into KReO4 solution (0.01 mol/L, pH 2.0), another piece of dry gels was put the solution without KReO4 (pH 2.0). When the gels reached adsorption equilibrium, they were taken out from the solution, and then were freeze-dried and pulverized. Infrared spectra of the gel powder were recorded by MAGNA-IR 750 Nicolet spectrometer.
151
further for obtaining the excellent polyDMAEMA hydrogels. Effect of H2 O2 concentration on the characteristic of the hydrogels was shown in Fig. 1. Both the swelling ratio and gel fraction increased with the concentration of H2 O2 . In following experiments, the concentration of H2 O2 was chosen to be 40 mmol/L for the syntheses of polyDMAEMA hydrogels, which are transparent, elastic and have good swelling behavior. 3.2. Adsorption of ReO into polyDMAEMA 4 hydrogels 3.2.1. The selection of adsorbent condition DMAEMA is a kind of tertiary amine. In acidic condition, DMAEMA can be protonated, so it can combine with ReO 4 shown as þ R3 N þ Hþ þ ReO 4 ! R3 NH ReO4
3. Results and discussion 3.1. Radiation synthesis of polyDMAEMA hydrogels The synthesis and characteristic of polyDMAEMA hydrogels induced by UV radiation have been studied earlier [5]. In this work, the concentration of DMAEMA was chosen to be 25% (W/ V), and Bis was kept at 0.5% of the weight of DMAEMA based on the previous experiment. Here, the concentration of H2 O2 was selected
ð4Þ
According to reaction (4), it can be found that the adsorption of ReO 4 into polyDMAEMA hydrogels belongs mainly to ion adsorption. The adsorption capacity is affected by many factors such as pH, matrix particle size, the nature of the adsorbent, temperature, etc., among which pH is the most important one. In order to investigate pH’s effect, the same dry gels were put into the solutions with different pH and constant concentration of ReO 4 . Fig. 2 showed that there was an optimum pH (pH 2.0) for the adsorption of ReO into polyDMAEMA hydrogels. when 4
18
2.0
94 16
1.5 14
88 12
86 84
10
Q (10-5 mol/g)
90
Swelling ratio
Gel fraction (%)
92
1.0
0.5
82 8
80 20
25
30
35
40
45
50
The concentration of H2O2 (mmol/L)
Fig. 1. Effect of H2 O2 concentration on the swelling ratio and gel fraction of polyDMAEMA hydrogels.
0.0 0
1
2
3
4
5
6
7
8
9
10
11
12
13
pH
Fig. 2. Effect of pH on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 ).
152
Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154
gels. Later, pH 2.0 and I ¼ 0:015 were chosen for further adsorption experiments.
1.6
3.2.2. Microscopic IR analysis Curves A and B in Fig. 4 were IR spectra of the gels with ReO 4 and without ReO4 , respectively. Compare with curve A and B it was very obvious that there was a adsorption band at 911 cm1 in curve A. According to [9], ReO 4 has an absorption band at 920 cm1 for Re–O antisymmetric vibration. The results testified further that the adsorption of ReO 4 into polyDMAEMA hydrogels.
-5
Q (10 mol/g)
1.4
1.2
1.0
0.8 0.05
0.10
0.15
0.20
0.25
0.30
Ion strength
Fig. 3. Effect of ionic strength on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0).
pH P 4, the tertiary amine groups of DMAEMA were unprotonated, i.e., in the undissociated state, so the adsorptive capacity of the hydrogels became very low. When pH is 2.0 (I ¼ 0:015), the adsorptive capacity of the hydrogels was larger than that at pH 1.0 (I ¼ 0:15) due to the influence of ionic strength (I). Effect of ionic strength on the adsorption of ReO 4 into polyDMAEMA hydrogels was shown in Fig. 3. The results indicated that the adsorption capacity of the hydrogels decreased with increasing of ionic strength, so pH 2.0 and I ¼ 0:015 were the optimum condition for the adsorption of ReO 4 into polyDMAEMA hydro-
3.2.3. Adsorption kinetics Adsorption kinetics is an important physicochemical parameter, which helps in the evaluation of basic qualities of adsorbents. Simple batch kinetic experiments on the adsorption of ReO 4 into polyDMAEMA hydrogels were carried out here and the adsorption kinetics was showed in Fig. 5. The amount of adsorption increased with the time and reached equilibrium after about 25 h. Adsorption capacity was calculated to be 2.20 105 mol/g and adsorption ratio was 51.6%. 3.2.4. Adsorption isotherms Fig. 6 showed the experimental equilibrium isotherms for the adsorption of ReO 4 into polyDMAEMA hydrogels. The adsorption capacity
A
B 2000
1800
1600
1400
1200
1000
800
-1
Wave numbers (cm ) Fig. 4. IR spectra of polyDMAEMA gels with ReO 4 and without ReO4 .
Y. Yan et al. / Reactive & Functional Polymers 59 (2004) 149–154 250
2.0 200
1.8 1.6
150
1.4 1.2
1/Q
The amount of adsorption (10-5mol/g)
2.2
1.0
100
0.8 50
0.6 0.4
0
0.2 0
5
10
15
20
25
0
30
1
2
4
5
6
7
4
Fig. 5. Adsorption kinetics of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0 and I ¼ 0:015).
Fig. 7. Linearized form of Langmuir isotherm for the adsorption of ReO 4 into polyDMAEMA hydrogels.
Fig. 7 showed that the experimental data fitted well by the Langmuir equation. Correlation coefficient was calculated to be 0.9996, and the values of Qmax and b were calculated to be 0.207 mg/g and 1427.8 L/mg, respectively.
18
15
-5
3
1/Ce (10 )
Time (h)
Q (10 mol/g)
153
12
9
3.2.5. Effect of gel mass (size) Effect of gel size on the adsorption of ReO 4 into polyDMAEMA hydrogels was shown in Fig. 8. Adsorption capacity reduced linearly as the size increased. Because the adsorption of hydrogels including surface and inner adsorption, inner adsorption need ReO 4 ion to diffuse into the
6
3
0 0
1
2
3
4
5
-4
Ce (10 mol/L)
Fig. 6. Adsorption isotherms of ReO 4 into polyDMAEMA hydrogels (pH 2.0 and I ¼ 0:015).
4.0
3.5
-5
Q (10 mol/g)
increased linearly with increase of the concentration of ReO 4 in aqueous solution. The adsorption isothermal data could be well interpreted by Langmuir equation as:
4.5
1 1 1 ¼ þ ; Q Qmax Qmax bCe
ð5Þ
3.0
2.5
where Ce is the equilibrium concentration of ReO 4 , Q is the amount of ReO4 adsorbed per unit weight of polyDMAEMA hydrogels at equilibrium concentration, Qmax is the maximum adsorption at monolayer coverage, and b is the Langmuir adsorption equilibrium constant related to the energy or net enthalpy.
2.0 0.16
0.18
0.20
0.22
0.24
0.26
0.28
0.30
0.32
Mass of hydrogels (g)
Fig. 8. Effect of gel size on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0 and I ¼ 0:015).
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ReO 4 ions was desorbed from polyDMAEMA gels by treatment with diluted NaOH solution at pH 12.0, and at the same time the adsorbents was regenerated.
2.8
2.4
-5
Q (10 mol/g)
2.6
4. Conclusion
2.2
2.0
1.8 30
35
40
45
50
55
60
Temperature (˚C)
Fig. 9. Effect of temperature on the adsorption of ReO 4 into polyDMAEMA hydrogels (1 104 mol/L KReO4 , pH 2.0 and I ¼ 0:015).
hydrogels. Bigger were gel particles; more difficult was it to reach the center of the gels for ReO 4 ion. So the concentration of obtained ReO had gra4 ded distribution in the gels and the concentration was the lowest in the center of hydrogels. Though the total absorbing amount increased with the increase of the mass of the gel, the adsorption capacity per unit weight would drop down. So smaller gels possessed higher adsorption efficiency and were quicker to reach adsorption equilibrium. 3.2.6. Effect of temperature Fig. 9 showed the relationship between adsorption capacity per unit weight and temperature. The adsorption capacity decreased as the temperature increased and the adsorption was an exothermic reaction. 3.2.7. Desorption studies Desorption studies helps to recover ReO 4 from the adsorbents to elucidate the nature of adsorption process. Moreover, the desorption process regenerates polyDMAEMA gels for reuse. The desorption experiments of ReO from poly4 DMAEMA gels indicated that more than 90%
The adsorption of ReO 4 into polyDMAEMA hydrogels prepared by UV-induced polymerization was carried out. It was found that pH 2.0 was the optimum for the adsorption of ReO 4 into polyDMAEMA hydrogels. Isothermal experiment revealed that the adsorption capacity increased linearly with increase of the concentration of ReO 4 in aqueous solution. Adsorption isothermal data could be well interpreted by the Langmuir equation. The adsorption capacity decreased with increase of ionic strength, the size of gel or temperature. Desorption experiment indicated that more than 90% ReO 4 ions can be desorbed from polyDMAEMA gels and at the same time the adsorbents can be regenerated for reuse.
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