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A chelating resin containing S, N and O atoms: Synthesis and adsorption properties for Hg(II)
EUROPEAN POLYMER JOURNAL
European Polymer Journal 42 (2006) 188–194
www.elsevier.com/locate/europolj
A chelating resin containing S, N and O atoms: Synthesis and adsorption properties for Hg(II) Changmei Sun a,b, Rongjun Qu a,b,*, Chunnuan Ji a, Qun Wang a, Chunhua Wang a, Yanzhi Sun a, Guoxiang Cheng b a
School of Chemistry and Materials Science, Yantai Normal University, Shandong 264025, PR China b School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China Received 2 February 2005; received in revised form 15 June 2005; accepted 23 June 2005 Available online 2 August 2005
Abstract A novel chelating resin containing S, N and O atoms (PSME–EDA) was synthesized by using poly(2-hydroxyethylmercaptomethylstyrene) (PSME) and diethanolamine (EDA) as materials. Its structure was characterized by elemental analysis, Fourier transform-infrared spectra (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The adsorption of the resin for Hg2+ was investigated. The saturated adsorption capacity of PSME–EDA for Hg2+ could reach to about 1.1 mmol/g at 25 C when the initial Hg2+ concentration was 0.02 mol/l. Some factors affecting the adsorption such as temperature, reaction time and ion concentration were also studied. The results showed that adsorption was controlled by liquid film diffusion. The increasing of temperature was beneficial to adsorption. The Langmuir model was better than the Freundlich model to describe the isothermal process. The values of DG, DH, and DS calculated at 25 C were 7.99 kJ mol1, 22.5 kJ mol1 and 34.4 J mol1 K1, respectively. The adsorption mechanism of PSME–EDA resin for Hg(II) was confirmed by X-ray photoelectron spectroscopy (XPS). 2005 Elsevier Ltd. All rights reserved. Keywords: Chelating resin containing S, N, O atoms; Synthesis; Adsorption; Hg(II)
1. Introduction The selective and quantitative separation of metal ions related to water pollution problems has received increasing importance in recent years. The ion exchange resins have shown excellent metal ion separation and are widely used for removing heavy metal ions from waste * Corresponding author. Address: School of Chemistry and Materials Science, Yantai Normal University, Shandong 264025, PR China. Tel.: +86 5356673982; fax: +86 5356672574. E-mail addresses: [email protected], qurongjun@eyou. com (R. Qu).
water and for concentrating and retrieving noble metal ions [1–4]. The trace metal ions of Hg(II) represent a serious environmental problem. Mercury is used in a wide variety of industries such as electrical, paints, fungicides, chlor-alkali, paper and pulp, pharmaceutical, etc. [5]. Out of these, the chlor-alkali industry is the largest consumer of mercury and the single largest source of mercury pollution. Hg(II) has a strong affinity towards S, N and O atoms containing ligands [6] and many efforts have ever been made to synthesize the chelating resins to remove mercury [7–10]. There are two O atoms and one N atom in a diethanolamine (EDA) molecule and
0014-3057/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2005.06.024
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
(XRD) patterns of the resins were recorded on an X-ray diffractometer (D/max-2500VPC, Rigaku Corporation), test conditions: CuKa radiation, 40 kV voltage, and 200 mA current. The range of diffraction angles (2h) was 10–50, and the scanning speed was 4 (2h/ min).
the poly(2-hydroxyethylmercaptomethylstyrene) (PSME) resin contains S atoms. If EDA were introduced to PSME resin, the novel resin obtained containing simultaneously S, N and O atoms would be expected to have excellent adsorption ability for Hg(II). On the other hand, the two hydroxyl groups in EDA would improve the novel resin have better hydrophilicity. Therefore, we synthesized a novel chelating resin by using EDA and PSME as materials and studied the adsorption properties for Hg(II) in this paper.
2.3. Preparation of the resin PSME–EDA Scheme 1 showed the synthesis route of the resin PSME–EDA. The PSME beads (10.00 g) were swollen in the solution of 70 ml CCl4, 50 ml benzene and 80 ml pyridine in a three-neck flask for more than 2 h. With magnetically stirring, 65 ml benzene sulfonyl chloride was added dropwise within 1 h at 15 C. After 18 h, the temperature of water-bath was raised to 25 C for 3 h and then to 95 C for 18 h. The product was filtered, washed with distilled water, ethanol, acetone and finally with hydrochloric acid. After washing, the product was moved to a SoxhletÕs extraction apparatus for reflux–extraction in 95% ethanol for 10 h and then was dried under vacuum at 50 C over 48 h. The product obtained was benzene sulphonic acid ester of PSME and was abbreviated to be PSME–SO3ph in this paper. Elemental analysis (%): S, 17.95. The OH conversion calculated according to the result of elemental analysis is 92.8%. 5.00 g of PSME–SO3ph was swollen in 30 ml tetrahydrofuran for 24 h and then 30 ml EDA was added with magnetically stirring after the mixture was cooled in ice waterbath. After 4 h, the temperature of the water-bath was raised to 50 C for 18 h and then to 80 C for 8 h. When the mixture cooled down to room temperature, 5 g NaOH and proper quantities of distilled water were added. After 2 h, the resulting yellow–green resin was filtered and washed with distilled water repeatedly. After washing, it was moved to a SoxhletÕs extraction apparatus for reflux–extraction in 95% ethanol for 10 h and then was dried under vacuum at 50 C over 48 h. Elemental analysis (%): S, 2.80; N, 3.45.
2. Experimental 2.1. Materials PSME resin beads were provided by the central laboratory of polymer materials of Yantai Normal University, 4.95 mmol –SC2H4OH g1 resin. Other reagents were analytical-grade chemical products and used without any further purification. Aqueous solutions of Hg(II) at various concentrations (102–103 M) were prepared from Hg(NO3)2 and the concentrations were determined by titration with a standard EDTA solution. The pH of the solutions was adjusted with hexamethylenetetramine–HNO3 (5.4) buffer solution. 2.2. Instruments Infrared spectra were recorded on a Nicolet MAGNA-IR 550 (series II) spectrophotometer; test conditions: potassium bromide pellets, scanning 32 times, resolution are 4 cm1. The content of S and N elementary analyses were carried out by central laboratory of Shandong University. The shapes and surface morphology of the resins were examined on a scanning electron microscope, JSF5610LV, JEOL. XPS spectra were collected on PHI 1600ESCA system, Perkin–Elmer Co., USA, test conditions: MgKa (1253.6 eV), power 200.0 W, resolution 187.85 Ev. The X-ray diffraction
CH2SCH2CH2OH
phSO2Cl N
,
, CCl4
PSME
CH2SCH2CH2SO3ph
PSME-SO3ph
CH2CH2OH HN CH2CH2OH
189
CH2CH2OH CH2SCH2CH2N CH2CH2OH
O
PSME-EDA Scheme 1. The synthesis route of PSME–EDA.
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C. Sun et al. / European Polymer Journal 42 (2006) 188–194
2.4. Adsorption procedure 2.4.1. Adsorption kinetics Batch tests were performed to determine adsorption kinetics. A typical procedure is: 50-ml Pyrex glass tubes were prepared with the desired amounts of reagent solution and were placed in a thermostat-cum-shaking assembly. When the desired temperature was reached, a known amount resin (about 0.1 g) was added into each tube, and the mixed solutions were mechanical shaken. At pre-decided intervals of time, the solutions in the specified tubes were separated from the adsorbent and determined the concentration of Hg2+ by titration method. The adsorption amounts were calculated according to the following Eq. (1): Q¼
ðC 0 CÞV W
ð1Þ
where Q is the adsorption amount, mmol/g; C0 and C, the initial and concentrations of Hg2+ in solution when the contact time is t respectively, mmol/ml; V, the volume, ml; W, the weight of PSME–EDA beads, g. 2.4.2. Isothermal adsorption The isothermal adsorption was investigated also by batch studies. A typical procedure is: a series of 50-ml test tubes were employed. Each test tube was filled with 10 ml of metal ion solution of varying concentrations and adjusted to the desired pH and temperature. A known amount of resin (about 0.1 g) was added into each test tube and agitated intermittently for the desired time periods, up to a maximum of about 12 h. The
adsorption capacities were calculated also by using Eq. (1), where C is the equilibrium concentrations of Hg2+ in solution.
3. Results and discussion 3.1. Characterization of the resins by FTIR Fig. 1 showed the infrared spectra of PSME, PSME– SO3ph and PSME–EDA. By comparison with the curve of PSME, the characteristic peaks of O@S@O appeared at 1194 cm1 and 1130 cm1 in the curve of PSME– SO3ph, indicating that esterification reaction occurred and –SO3ph groups had been introduced to PSME successfully. While in the curve of PSME–EDA as could be seen, the characteristic peaks of O@S@O at 1194 cm1 and 1130 cm1 disappeared, which implied that –SO3ph groups in PSME–SO3ph were replaced by EDA. 3.2. SEM observations of the resins The SEM images in Fig. 2 visually showed the morphological differences of the surface of PSME, PSME– SO3ph and PSME–EDA resins. Compared with the PSME resin, the pore space on the surface of PSME– SO3ph increased because of the introduction of the –SO3ph groups to the PSME resin. After the reaction of EDA with PSME–SO3ph resin, as could be seen in Fig. 2(C), there were abundant pores evenly distributed on the surface of the PSME–EDA resin, implying that the macroporous structures of PSME resin had not been
Fig. 1. FTIR spectra of PSME, PSME–SO3ph and PSME–EDA.
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
191
3.3. XRD analysis of the resins The X-ray diffraction patterns of the resins were shown in Fig. 3. There was no sharp peak appeared in the three patterns, implying that all the three resins were amorphous. Namely, the introduction of several kinds of polar groups did not change the crystalline state of resins. 3.4. Adsorption kinetics Fig. 4 showed adsorption kinetics of PSME–EDA for Hg2+ at different temperature. The contact time and other conditions were selected on the basis of the preliminary experimental results in Fig. 4, which demonstrated that the equilibrium was established in 7 h. Equilibration, for longer times, that was between 7 and 10 h gave practically the same adsorption capacity. Therefore the contact period was 8 h in all equilibrium tests. Also it could be seen from Fig. 4 that temperature affected the adsorption capacities significantly, that is,
8000 Intensity (CPS)
A 6000
C B
4000 2000 0 0
10
20 30 Two-Theta (deg)
40
50
Fig. 3. X-ray diffraction patterns of (A) PSME, (B) PSME– SO3ph and (C) PSME–EDA.
1.3
Fig. 2. The SEM images of (A) PSME, (B) PSME–SO3ph and (C) PSME–EDA.
damaged after the reaction and those pores which collapsed before the reaction reopened after the polar groups –N(CH2CH2OH)2 were introduced into the polymer matrix. The existence of macropores would provide convenient diffusion channels for metal ions into the interior of PSME–EDA resin when it was used in adsorption of metal ions in aqueous solution.
Q(mmol/g)
1.1
0.9
5 ºC 15 ºC
0.7
25 ºC 0.5
35 ºC 0
4 t(h)
8
12
Fig. 4. The adsorption kinetics of PSME–EDA for Hg2+ (pH = 5.4, [Hg2+] = 0.02 mol/l).
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the adsorption capacities increased with the increasing of temperature. The possible explanations for this were: (1) the PSME–EDA resin was swollen more completely at higher temperature, which made mercury ions diffused more easily into the inside of resin; (2) the adsorption was an endothermal process and high temperature was of benefit to the adsorption. Analyzed the data in Fig. 4 by the procedure given by Reichenberg [11] and Helfferich [12]. The following equations were used: 1 6 X 1 Di tp2 n2 F ¼1 2 ð2Þ p n¼1 n2 r20 or F ¼1
1 6 X 1 exp½n2 Bt 2 p n¼1 n2
ð3Þ
where F is the fractional attainment of equilibrium at time t and is obtained by the expression F ¼
Qt ; Q0
ð4Þ
where Qt is the amount of adsorbate taken up at time t and Q0 is the maximum equilibrium uptake and B¼
p2 Di ¼ time constant r20
ð5Þ
where Di is the effective diffusion coefficient of ion in the adsorbent phase; r0 is the radius of the adsorbent particle, assumed to be spherical; and n is an integer that defines the infinite series solution. Bt values were obtained for each observed value of F from ReichenbergÕs table [11] and the results were plotted in Fig. 5. The linearity test of Bt vs. time plots was employed to distinguish between the film diffusion and particle diffusion controlled adsorption [13]. If the plot of Bt vs. time (having slope B) is a straight line passing through the origin, then the adsorption rate is governed
by particle diffusion mechanism otherwise it is governed by film diffusion. From Fig. 5 it could be seen that the four straight lines under different temperature did not pass through the origin, indicating the rate controlling step not to be particle diffusion, but film diffusion. The linear equations and correlation coefficients R2 were listed in Table 1. 3.5. Isothermal adsorption The adsorption isotherms of the Hg2+ were presented in Fig. 6 at four different temperatures. Analyzed the data in Fig. 6 with Langmuir (6) and Freundlich (7) equations respectively, Figs. 7 and 8 were obtained. C 1 C ¼ þ Q bQ0 Q0 ln Q ¼ ln K F þ
ð6Þ 1 ln C n
ð7Þ
where Q is the adsorption capacity, mmol/g; C the equilibrium concentration of metal ions, mmol/ml; Q0, the saturated adsorption capacity, mmol/g; b, an empirical parameter; n, the Freundlich constant; KF, the binding energy constant reflecting the affinity of the resin to metal ions. Freundlich and Langmuir parameters were given in Table 2. The correlation coefficients showed Table 1 The Bt vs. time linear equations, correlation coefficient R2 and intercept error Temperature (C)
Linear equation
Correlation coefficient, R2
Intercept error
5 15 25 35
Bt = 0.4765t + 0.1758 Bt = 0.4612t + 0.2368 Bt = 0.5477t + 0.1850 Bt = 0.5294t + 0.1872
0.9962 0.9930 1.0000 0.9976
0.017 0.022 0.001 0.018
1.8
3.5 3.0
1.4 Q(mmol/g)
2.5
Bt
2.0 5 ºC
1.5
15 ºC 1.0
5 ºC 15 ºC
0.6
25 ºC 35 ºC
25 ºC
0.5 0.0
1.0
35 ºC
0.2 0
0
2
4 Time (h)
Fig. 5. Bt vs. time plots at different temperature.
6
0.002
0.004 0.006 C(mol/L)
0.008
0.01
Fig. 6. Adsorption isotherms of PSME–EDA for Hg2+ at pH = 5.4.
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
193
1.2
0.009
1.0
15 ºC
0.8
Q(mmol/g)
0.006
5 ºC
C/Q
25 ºC 35 ºC
Langmuir 0.6
Experimental
0.4
Freundlich
0.003 0.2 0.0 0
0 0
0.005
Fig. 9. Comparison of theoretical isotherms of PSME–EDA for Hg2+ at 15 C.
Fig. 7. The Langmuir isotherms of PSME–EDA for Hg2+.
0.4
0.8
0.2
0.6 LgD
lnQ
5 ºC 15 ºC 25 ºC
0.0
35 ºC 0.2 -9
0.01
C(moL/L)
C(mmol/mL)
0.4
0.005
0.01
-8
-7 LnC
-6
-5
y = -1176.5x + 4.1323 2 R = 0.9181
-0.2 0.0030
0.0032
0.0034
0.0036
0.0038
-1
1/T(K )
Fig. 8. The Freundlich isotherms of PSME–EDA for Hg2+.
Fig. 10. lg D vs. 1/T plots for the adsorption of PSME–EDA for Hg2+.
that the Langmuir model fitted the results better than the Freundlich model, indicating that all adsorption processes could be described by Langmuir formula. The theoretical isotherms can be obtained from Eqs. (6) and (7) for Langmuir and Freundlich analysis. At 15 C, the theoretical results were compared with the experimental results in Fig. 9. Obviously, the Langmuir equation is much better than Freundlich equation to fit the experimental results. Fig. 10 was the curve of lg D vs. 1/T, where D is the distribution ratio, D = Q/C, Q and C are adsorption
capacity and the concentration of free metal ion at the equilibrium adsorption, respectively. The result revealed that the distribution ratio increased with the increase of temperature. This meant that the adsorption process was an endothermal process. From Fig. 10, it could be drawn that the linear slope was 1176.5 and the correlation coefficient is 0.9181. According to the lg D = DH/(2.303RT) + DS/R, DH and DS could be calculated 22.5 kJ mol1 and 34.4 J mol1 K1. The DH
Table 2 Freundlich and Langmuir constants for Hg2+ adsorption on PSME–EDA resin at different temperature Temperature (C)
5 15 25 35
Freundlich parameters
Langmuir parameters
KF
1/n
R2F
Q0
b · 103
R2L
0.536 0.517 0.839 0.870
0.185 0.184 0.118 0.103
0.9368 0.8553 0.9714 0.9080
1.269 1.086 1.529 1.404
2.626 1.841 6.539 7.120
0.9916 0.9817 0.9986 0.9957
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C. Sun et al. / European Polymer Journal 42 (2006) 188–194
Table 3 The binding energy (eV) of the adsorption of PSME–EDA for Hg2+ N1s
O1s
S2p
C1s
Protonized PSME–EDA
399.53 401.24
531.42 532.82
163.88 168.25
PSME–EDA–Hg2+
399.74 401.76 406.88 407.10 [14]
531.40 532.80
163.94 169.01
284.75 286.67 288.39 284.75 286.67 288.39
Hg(NO3)2
being positive value justified that the adsorption of PSME–EDA for Hg2+ was endothermal process, which was fitted to the deduction obtained from the adsorption kinetics. According to the DG = DH TDS, the DG at 298 K could be calculated 7.99 kJ mol1. The DG being negative value implied that the adsorption of PSME– EDA for Hg2+ was a spontaneous process. 3.6. Adsorption mechanism of PSME–EDA for Hg2+ The data listed in Table 3 showed that the binding energies of N1s and S2p in PSME–EDA-Hg2+ both increased obviously in contrast to those in protonized PSME–EDA, which indicated that both N and S atoms were electron donors. Also it should be noticed that the binding energy of O1s almost had no change after adsorption, meaning that O atom did not take part in the coordination with Hg2+ and the existence of it only increased the hydrophilicity of PSME–EDA resin. The binding energy of Hg4f decreased (about 2 eV) after adsorbed by PSME–EDA, implying that Hg2+ was an electron acceptor. In the meantime, a new peak of N1s appeared at 406.88 eV and it was almost the same as that in Hg(NO3)2, which demonstrated that Hg was adsorbed by PSME–EDA in the form of Hg(NO3)2 molecule.
4. Conclusions A novel chelating resin containing O, N and S atoms (PSME–EDA) were synthesized using poly(2-hydroxyethylmercaptomethylstyrene) (PSME) and diethanolamine (EDA) as materials. Elemental analysis, FTIR, SEM, XRD were employed to character its structure. The adsorption of the resin for Hg2+ was investigated. The results showed that the adsorption was controlled by liquid film diffusion. The increasing of temperature was beneficial to adsorption. The Langmuir model was a little better than the Freundlich model to describe the isothermal process. The values of DG, DH, and DS calculated at 25 C were 7.99 kJ mol1, 22.5 kJ mol1 and 34.4 J mol1 K1, respectively. The XPS results
Hg4f
101.89
104.0 [15]
showed that N and S atoms were the main electron donors to coordinate with Hg(NO3)2 molecule.
Acknowledgements The authors are grateful for the financial support by the Postdoctoral Science Foundation of China (No. 2003034330), the Science Foundation for mid-youth elite of Shandong Province, the Nature Science Foundation of Shandong Province (No. Q99B15) and the National Nature Science Foundation of China (No. 29906008).
References [1] Gong BL, Li XQ, Wang FR, Chang XJ. Talanta 2000;52: 217. [2] Beauvais RA, Alexandratos SD. React Funct Polym 1998;36:113. [3] Chen YY, Lu BX, Chen XW. J Macromol Sci Chem 1998;A25:1443. [4] Chen YY, Yuan XZ. React Funct Polym 1994;23:65. [5] Dines M, Gupta VK, Srivastava SK, Chander S. Colloid Surface B 2002;17:161. [6] Shriver DF, Atkins PW, Langford CH. Inorganic chemistry. second ed. Oxford: Oxford University Press; 1994. p. 432. [7] Meng LZ, Gong SL, Yin YH, Chen YY, Wang YW. J Appl Polym Sci 2003;87:1445. ¨ zkan G, Arica MY. J Appl Polym Sci 2000;78: [8] Denizli A, O 81. [9] Sreedhar MK, Anirudhan TS. J Appl Polym Sci 2000;75: 1261. [10] Lezzi A, Cobianco S, Roggero A. J Polym Sci A Polym Chem 1994;32:1877. [11] Reichenberg D. J Am Chem Soc 1953;75:589. [12] Helfferich F. Ion-exchange. New York: McGraw-Hill; 1962. [13] Dines M, Gupta VK, Srivastava SK, Chander S. Colloid Surface A 2001;177:169. [14] Liu SH, Wang DH, Pan CH. X-ray electron spectra analysis. Beijing: Science press; 1988. p. 300. [15] Liu SH, Wang DH, Pan CH. X-ray electron spectra analysis. Beijing: Science press; 1988. p. 180.
European Polymer Journal 42 (2006) 188–194
www.elsevier.com/locate/europolj
A chelating resin containing S, N and O atoms: Synthesis and adsorption properties for Hg(II) Changmei Sun a,b, Rongjun Qu a,b,*, Chunnuan Ji a, Qun Wang a, Chunhua Wang a, Yanzhi Sun a, Guoxiang Cheng b a
School of Chemistry and Materials Science, Yantai Normal University, Shandong 264025, PR China b School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China Received 2 February 2005; received in revised form 15 June 2005; accepted 23 June 2005 Available online 2 August 2005
Abstract A novel chelating resin containing S, N and O atoms (PSME–EDA) was synthesized by using poly(2-hydroxyethylmercaptomethylstyrene) (PSME) and diethanolamine (EDA) as materials. Its structure was characterized by elemental analysis, Fourier transform-infrared spectra (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The adsorption of the resin for Hg2+ was investigated. The saturated adsorption capacity of PSME–EDA for Hg2+ could reach to about 1.1 mmol/g at 25 C when the initial Hg2+ concentration was 0.02 mol/l. Some factors affecting the adsorption such as temperature, reaction time and ion concentration were also studied. The results showed that adsorption was controlled by liquid film diffusion. The increasing of temperature was beneficial to adsorption. The Langmuir model was better than the Freundlich model to describe the isothermal process. The values of DG, DH, and DS calculated at 25 C were 7.99 kJ mol1, 22.5 kJ mol1 and 34.4 J mol1 K1, respectively. The adsorption mechanism of PSME–EDA resin for Hg(II) was confirmed by X-ray photoelectron spectroscopy (XPS). 2005 Elsevier Ltd. All rights reserved. Keywords: Chelating resin containing S, N, O atoms; Synthesis; Adsorption; Hg(II)
1. Introduction The selective and quantitative separation of metal ions related to water pollution problems has received increasing importance in recent years. The ion exchange resins have shown excellent metal ion separation and are widely used for removing heavy metal ions from waste * Corresponding author. Address: School of Chemistry and Materials Science, Yantai Normal University, Shandong 264025, PR China. Tel.: +86 5356673982; fax: +86 5356672574. E-mail addresses: [email protected], qurongjun@eyou. com (R. Qu).
water and for concentrating and retrieving noble metal ions [1–4]. The trace metal ions of Hg(II) represent a serious environmental problem. Mercury is used in a wide variety of industries such as electrical, paints, fungicides, chlor-alkali, paper and pulp, pharmaceutical, etc. [5]. Out of these, the chlor-alkali industry is the largest consumer of mercury and the single largest source of mercury pollution. Hg(II) has a strong affinity towards S, N and O atoms containing ligands [6] and many efforts have ever been made to synthesize the chelating resins to remove mercury [7–10]. There are two O atoms and one N atom in a diethanolamine (EDA) molecule and
0014-3057/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2005.06.024
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
(XRD) patterns of the resins were recorded on an X-ray diffractometer (D/max-2500VPC, Rigaku Corporation), test conditions: CuKa radiation, 40 kV voltage, and 200 mA current. The range of diffraction angles (2h) was 10–50, and the scanning speed was 4 (2h/ min).
the poly(2-hydroxyethylmercaptomethylstyrene) (PSME) resin contains S atoms. If EDA were introduced to PSME resin, the novel resin obtained containing simultaneously S, N and O atoms would be expected to have excellent adsorption ability for Hg(II). On the other hand, the two hydroxyl groups in EDA would improve the novel resin have better hydrophilicity. Therefore, we synthesized a novel chelating resin by using EDA and PSME as materials and studied the adsorption properties for Hg(II) in this paper.
2.3. Preparation of the resin PSME–EDA Scheme 1 showed the synthesis route of the resin PSME–EDA. The PSME beads (10.00 g) were swollen in the solution of 70 ml CCl4, 50 ml benzene and 80 ml pyridine in a three-neck flask for more than 2 h. With magnetically stirring, 65 ml benzene sulfonyl chloride was added dropwise within 1 h at 15 C. After 18 h, the temperature of water-bath was raised to 25 C for 3 h and then to 95 C for 18 h. The product was filtered, washed with distilled water, ethanol, acetone and finally with hydrochloric acid. After washing, the product was moved to a SoxhletÕs extraction apparatus for reflux–extraction in 95% ethanol for 10 h and then was dried under vacuum at 50 C over 48 h. The product obtained was benzene sulphonic acid ester of PSME and was abbreviated to be PSME–SO3ph in this paper. Elemental analysis (%): S, 17.95. The OH conversion calculated according to the result of elemental analysis is 92.8%. 5.00 g of PSME–SO3ph was swollen in 30 ml tetrahydrofuran for 24 h and then 30 ml EDA was added with magnetically stirring after the mixture was cooled in ice waterbath. After 4 h, the temperature of the water-bath was raised to 50 C for 18 h and then to 80 C for 8 h. When the mixture cooled down to room temperature, 5 g NaOH and proper quantities of distilled water were added. After 2 h, the resulting yellow–green resin was filtered and washed with distilled water repeatedly. After washing, it was moved to a SoxhletÕs extraction apparatus for reflux–extraction in 95% ethanol for 10 h and then was dried under vacuum at 50 C over 48 h. Elemental analysis (%): S, 2.80; N, 3.45.
2. Experimental 2.1. Materials PSME resin beads were provided by the central laboratory of polymer materials of Yantai Normal University, 4.95 mmol –SC2H4OH g1 resin. Other reagents were analytical-grade chemical products and used without any further purification. Aqueous solutions of Hg(II) at various concentrations (102–103 M) were prepared from Hg(NO3)2 and the concentrations were determined by titration with a standard EDTA solution. The pH of the solutions was adjusted with hexamethylenetetramine–HNO3 (5.4) buffer solution. 2.2. Instruments Infrared spectra were recorded on a Nicolet MAGNA-IR 550 (series II) spectrophotometer; test conditions: potassium bromide pellets, scanning 32 times, resolution are 4 cm1. The content of S and N elementary analyses were carried out by central laboratory of Shandong University. The shapes and surface morphology of the resins were examined on a scanning electron microscope, JSF5610LV, JEOL. XPS spectra were collected on PHI 1600ESCA system, Perkin–Elmer Co., USA, test conditions: MgKa (1253.6 eV), power 200.0 W, resolution 187.85 Ev. The X-ray diffraction
CH2SCH2CH2OH
phSO2Cl N
,
, CCl4
PSME
CH2SCH2CH2SO3ph
PSME-SO3ph
CH2CH2OH HN CH2CH2OH
189
CH2CH2OH CH2SCH2CH2N CH2CH2OH
O
PSME-EDA Scheme 1. The synthesis route of PSME–EDA.
190
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
2.4. Adsorption procedure 2.4.1. Adsorption kinetics Batch tests were performed to determine adsorption kinetics. A typical procedure is: 50-ml Pyrex glass tubes were prepared with the desired amounts of reagent solution and were placed in a thermostat-cum-shaking assembly. When the desired temperature was reached, a known amount resin (about 0.1 g) was added into each tube, and the mixed solutions were mechanical shaken. At pre-decided intervals of time, the solutions in the specified tubes were separated from the adsorbent and determined the concentration of Hg2+ by titration method. The adsorption amounts were calculated according to the following Eq. (1): Q¼
ðC 0 CÞV W
ð1Þ
where Q is the adsorption amount, mmol/g; C0 and C, the initial and concentrations of Hg2+ in solution when the contact time is t respectively, mmol/ml; V, the volume, ml; W, the weight of PSME–EDA beads, g. 2.4.2. Isothermal adsorption The isothermal adsorption was investigated also by batch studies. A typical procedure is: a series of 50-ml test tubes were employed. Each test tube was filled with 10 ml of metal ion solution of varying concentrations and adjusted to the desired pH and temperature. A known amount of resin (about 0.1 g) was added into each test tube and agitated intermittently for the desired time periods, up to a maximum of about 12 h. The
adsorption capacities were calculated also by using Eq. (1), where C is the equilibrium concentrations of Hg2+ in solution.
3. Results and discussion 3.1. Characterization of the resins by FTIR Fig. 1 showed the infrared spectra of PSME, PSME– SO3ph and PSME–EDA. By comparison with the curve of PSME, the characteristic peaks of O@S@O appeared at 1194 cm1 and 1130 cm1 in the curve of PSME– SO3ph, indicating that esterification reaction occurred and –SO3ph groups had been introduced to PSME successfully. While in the curve of PSME–EDA as could be seen, the characteristic peaks of O@S@O at 1194 cm1 and 1130 cm1 disappeared, which implied that –SO3ph groups in PSME–SO3ph were replaced by EDA. 3.2. SEM observations of the resins The SEM images in Fig. 2 visually showed the morphological differences of the surface of PSME, PSME– SO3ph and PSME–EDA resins. Compared with the PSME resin, the pore space on the surface of PSME– SO3ph increased because of the introduction of the –SO3ph groups to the PSME resin. After the reaction of EDA with PSME–SO3ph resin, as could be seen in Fig. 2(C), there were abundant pores evenly distributed on the surface of the PSME–EDA resin, implying that the macroporous structures of PSME resin had not been
Fig. 1. FTIR spectra of PSME, PSME–SO3ph and PSME–EDA.
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
191
3.3. XRD analysis of the resins The X-ray diffraction patterns of the resins were shown in Fig. 3. There was no sharp peak appeared in the three patterns, implying that all the three resins were amorphous. Namely, the introduction of several kinds of polar groups did not change the crystalline state of resins. 3.4. Adsorption kinetics Fig. 4 showed adsorption kinetics of PSME–EDA for Hg2+ at different temperature. The contact time and other conditions were selected on the basis of the preliminary experimental results in Fig. 4, which demonstrated that the equilibrium was established in 7 h. Equilibration, for longer times, that was between 7 and 10 h gave practically the same adsorption capacity. Therefore the contact period was 8 h in all equilibrium tests. Also it could be seen from Fig. 4 that temperature affected the adsorption capacities significantly, that is,
8000 Intensity (CPS)
A 6000
C B
4000 2000 0 0
10
20 30 Two-Theta (deg)
40
50
Fig. 3. X-ray diffraction patterns of (A) PSME, (B) PSME– SO3ph and (C) PSME–EDA.
1.3
Fig. 2. The SEM images of (A) PSME, (B) PSME–SO3ph and (C) PSME–EDA.
damaged after the reaction and those pores which collapsed before the reaction reopened after the polar groups –N(CH2CH2OH)2 were introduced into the polymer matrix. The existence of macropores would provide convenient diffusion channels for metal ions into the interior of PSME–EDA resin when it was used in adsorption of metal ions in aqueous solution.
Q(mmol/g)
1.1
0.9
5 ºC 15 ºC
0.7
25 ºC 0.5
35 ºC 0
4 t(h)
8
12
Fig. 4. The adsorption kinetics of PSME–EDA for Hg2+ (pH = 5.4, [Hg2+] = 0.02 mol/l).
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the adsorption capacities increased with the increasing of temperature. The possible explanations for this were: (1) the PSME–EDA resin was swollen more completely at higher temperature, which made mercury ions diffused more easily into the inside of resin; (2) the adsorption was an endothermal process and high temperature was of benefit to the adsorption. Analyzed the data in Fig. 4 by the procedure given by Reichenberg [11] and Helfferich [12]. The following equations were used: 1 6 X 1 Di tp2 n2 F ¼1 2 ð2Þ p n¼1 n2 r20 or F ¼1
1 6 X 1 exp½n2 Bt 2 p n¼1 n2
ð3Þ
where F is the fractional attainment of equilibrium at time t and is obtained by the expression F ¼
Qt ; Q0
ð4Þ
where Qt is the amount of adsorbate taken up at time t and Q0 is the maximum equilibrium uptake and B¼
p2 Di ¼ time constant r20
ð5Þ
where Di is the effective diffusion coefficient of ion in the adsorbent phase; r0 is the radius of the adsorbent particle, assumed to be spherical; and n is an integer that defines the infinite series solution. Bt values were obtained for each observed value of F from ReichenbergÕs table [11] and the results were plotted in Fig. 5. The linearity test of Bt vs. time plots was employed to distinguish between the film diffusion and particle diffusion controlled adsorption [13]. If the plot of Bt vs. time (having slope B) is a straight line passing through the origin, then the adsorption rate is governed
by particle diffusion mechanism otherwise it is governed by film diffusion. From Fig. 5 it could be seen that the four straight lines under different temperature did not pass through the origin, indicating the rate controlling step not to be particle diffusion, but film diffusion. The linear equations and correlation coefficients R2 were listed in Table 1. 3.5. Isothermal adsorption The adsorption isotherms of the Hg2+ were presented in Fig. 6 at four different temperatures. Analyzed the data in Fig. 6 with Langmuir (6) and Freundlich (7) equations respectively, Figs. 7 and 8 were obtained. C 1 C ¼ þ Q bQ0 Q0 ln Q ¼ ln K F þ
ð6Þ 1 ln C n
ð7Þ
where Q is the adsorption capacity, mmol/g; C the equilibrium concentration of metal ions, mmol/ml; Q0, the saturated adsorption capacity, mmol/g; b, an empirical parameter; n, the Freundlich constant; KF, the binding energy constant reflecting the affinity of the resin to metal ions. Freundlich and Langmuir parameters were given in Table 2. The correlation coefficients showed Table 1 The Bt vs. time linear equations, correlation coefficient R2 and intercept error Temperature (C)
Linear equation
Correlation coefficient, R2
Intercept error
5 15 25 35
Bt = 0.4765t + 0.1758 Bt = 0.4612t + 0.2368 Bt = 0.5477t + 0.1850 Bt = 0.5294t + 0.1872
0.9962 0.9930 1.0000 0.9976
0.017 0.022 0.001 0.018
1.8
3.5 3.0
1.4 Q(mmol/g)
2.5
Bt
2.0 5 ºC
1.5
15 ºC 1.0
5 ºC 15 ºC
0.6
25 ºC 35 ºC
25 ºC
0.5 0.0
1.0
35 ºC
0.2 0
0
2
4 Time (h)
Fig. 5. Bt vs. time plots at different temperature.
6
0.002
0.004 0.006 C(mol/L)
0.008
0.01
Fig. 6. Adsorption isotherms of PSME–EDA for Hg2+ at pH = 5.4.
C. Sun et al. / European Polymer Journal 42 (2006) 188–194
193
1.2
0.009
1.0
15 ºC
0.8
Q(mmol/g)
0.006
5 ºC
C/Q
25 ºC 35 ºC
Langmuir 0.6
Experimental
0.4
Freundlich
0.003 0.2 0.0 0
0 0
0.005
Fig. 9. Comparison of theoretical isotherms of PSME–EDA for Hg2+ at 15 C.
Fig. 7. The Langmuir isotherms of PSME–EDA for Hg2+.
0.4
0.8
0.2
0.6 LgD
lnQ
5 ºC 15 ºC 25 ºC
0.0
35 ºC 0.2 -9
0.01
C(moL/L)
C(mmol/mL)
0.4
0.005
0.01
-8
-7 LnC
-6
-5
y = -1176.5x + 4.1323 2 R = 0.9181
-0.2 0.0030
0.0032
0.0034
0.0036
0.0038
-1
1/T(K )
Fig. 8. The Freundlich isotherms of PSME–EDA for Hg2+.
Fig. 10. lg D vs. 1/T plots for the adsorption of PSME–EDA for Hg2+.
that the Langmuir model fitted the results better than the Freundlich model, indicating that all adsorption processes could be described by Langmuir formula. The theoretical isotherms can be obtained from Eqs. (6) and (7) for Langmuir and Freundlich analysis. At 15 C, the theoretical results were compared with the experimental results in Fig. 9. Obviously, the Langmuir equation is much better than Freundlich equation to fit the experimental results. Fig. 10 was the curve of lg D vs. 1/T, where D is the distribution ratio, D = Q/C, Q and C are adsorption
capacity and the concentration of free metal ion at the equilibrium adsorption, respectively. The result revealed that the distribution ratio increased with the increase of temperature. This meant that the adsorption process was an endothermal process. From Fig. 10, it could be drawn that the linear slope was 1176.5 and the correlation coefficient is 0.9181. According to the lg D = DH/(2.303RT) + DS/R, DH and DS could be calculated 22.5 kJ mol1 and 34.4 J mol1 K1. The DH
Table 2 Freundlich and Langmuir constants for Hg2+ adsorption on PSME–EDA resin at different temperature Temperature (C)
5 15 25 35
Freundlich parameters
Langmuir parameters
KF
1/n
R2F
Q0
b · 103
R2L
0.536 0.517 0.839 0.870
0.185 0.184 0.118 0.103
0.9368 0.8553 0.9714 0.9080
1.269 1.086 1.529 1.404
2.626 1.841 6.539 7.120
0.9916 0.9817 0.9986 0.9957
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Table 3 The binding energy (eV) of the adsorption of PSME–EDA for Hg2+ N1s
O1s
S2p
C1s
Protonized PSME–EDA
399.53 401.24
531.42 532.82
163.88 168.25
PSME–EDA–Hg2+
399.74 401.76 406.88 407.10 [14]
531.40 532.80
163.94 169.01
284.75 286.67 288.39 284.75 286.67 288.39
Hg(NO3)2
being positive value justified that the adsorption of PSME–EDA for Hg2+ was endothermal process, which was fitted to the deduction obtained from the adsorption kinetics. According to the DG = DH TDS, the DG at 298 K could be calculated 7.99 kJ mol1. The DG being negative value implied that the adsorption of PSME– EDA for Hg2+ was a spontaneous process. 3.6. Adsorption mechanism of PSME–EDA for Hg2+ The data listed in Table 3 showed that the binding energies of N1s and S2p in PSME–EDA-Hg2+ both increased obviously in contrast to those in protonized PSME–EDA, which indicated that both N and S atoms were electron donors. Also it should be noticed that the binding energy of O1s almost had no change after adsorption, meaning that O atom did not take part in the coordination with Hg2+ and the existence of it only increased the hydrophilicity of PSME–EDA resin. The binding energy of Hg4f decreased (about 2 eV) after adsorbed by PSME–EDA, implying that Hg2+ was an electron acceptor. In the meantime, a new peak of N1s appeared at 406.88 eV and it was almost the same as that in Hg(NO3)2, which demonstrated that Hg was adsorbed by PSME–EDA in the form of Hg(NO3)2 molecule.
4. Conclusions A novel chelating resin containing O, N and S atoms (PSME–EDA) were synthesized using poly(2-hydroxyethylmercaptomethylstyrene) (PSME) and diethanolamine (EDA) as materials. Elemental analysis, FTIR, SEM, XRD were employed to character its structure. The adsorption of the resin for Hg2+ was investigated. The results showed that the adsorption was controlled by liquid film diffusion. The increasing of temperature was beneficial to adsorption. The Langmuir model was a little better than the Freundlich model to describe the isothermal process. The values of DG, DH, and DS calculated at 25 C were 7.99 kJ mol1, 22.5 kJ mol1 and 34.4 J mol1 K1, respectively. The XPS results
Hg4f
101.89
104.0 [15]
showed that N and S atoms were the main electron donors to coordinate with Hg(NO3)2 molecule.
Acknowledgements The authors are grateful for the financial support by the Postdoctoral Science Foundation of China (No. 2003034330), the Science Foundation for mid-youth elite of Shandong Province, the Nature Science Foundation of Shandong Province (No. Q99B15) and the National Nature Science Foundation of China (No. 29906008).
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