Selective Adsorption of Metal Ions to Surface-Templated Resins

Chapter 18

Selective Adsorption of Metal Ions to SurfaceTemplated Resins Prepared by Emulsion Polymerization Using a Functional Surfactant 1

1

2

2

Downloaded by STANFORD UNIV GREEN LIBR on July 31, 2012 | http://pubs.acs.org Publication Date: May 7, 1998 | doi: 10.1021/bk-1998-0703.ch018

Yoshifumi Koide , Hideto Shosenji , Mizuo Maeda , and Makoto Takagi 1

Department of Applied Chemistry, Faculty of Engineering, Kumamoto University, Kurokami, Kumamoto 860, Japan Department of Applied Chemistry, Faculty of Engineering, Kyushu University, Hakozaki, Fukuoka 860, Japan 2

Monomer-type surfactants which can function as a ligand, 10-(p -vinylphenyl)decanoicacid (Rac) and 2-(p-vinylbenzylamino)alkanoic acids (R NAc), have been used as emulsifiers for the preparation of surface-templated resins. The surfactants adsorb at the oil-water interface and emulsify divinylbenzene-styrene monomers. Emulsion polymerization using a potassium persulfate initiator or by irradiation with y-rays gave fine particles which were 200—300 nm in diameter. The metal-imprinted resins prepared with Rac were 1.8 times more effective than the unimprinted resins for adsorption of Cu(II) and Zn(II)-imprinted resins showed highly effective adsorption of Zn(II). Such surface-template effects were also seen for metal-imprinted resins prepared with R NAc, but the effect was sensitive to the alkyl chain length. The R NAc resin was the most effective. The Cu(II)/Zn(II) ratio in competitive sorption was 3.7 for the Cu(II)-imprinted resins prepared with Rac and 4.2 with R NAc n

n

18

18

Molecular imprinting methods (1-3) have been used for selective recovery of specific chemical species, such as organic compounds (4-5) and metal ions (6-8). However, the techniques reported so far lack generality, especially for water-soluble guests. Since host monomers bound to specific guest molecules are chemically solidified with matrix monomers by crosslinking polymerization, the host-guest complexes must be soluble in the matrix monomers. When the target molecules are polar, the complexes will usually have low solubility in the matrix monomers. Moreover, the resulting molecular-imprinted resins must be ground and sieved to produce finely divided resins, since most of the imprinted sites are formed in the inner portions of the bulk resins. For the same reason, the resins may require long times for the separation of guest species. Some surface-templated resins have been developed to reduce such problems (9-15). A technique which utilizes the orientation of a surfactant is an efficient method for the preparation of surface-templated resins (16). A functional surfactant (emulsifier) that is capable of binding metal ions and functions as a vinyl monomer must orient at the interface between the matrix monomers and water, and emulsify these solutions. The surfactant will be polymerized with the matrix

264

©1998 American Chemical Society

In Molecular and Ionic Recognition with Imprinted Polymers; Bartsch, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

265 monomers in the form of a metal complex. Thus, a functional surfactant should make the surface imprinting easy and reliable. However, imprinting sites on the resins will be influenced by the hydrophilic lipophilic balance (HLB) of the surfactant and the surface-template effect, i.e. the metal ion selectivity should be affected by the location of the templated sites. In this chapter, monomer-type surfactants which can function ligands, lQ-(pvinylphenyl)decanoic acid (Rac), 2-(/?-vinylbenzylamino)alkanoic acids (R NAc), and N-alkyl 2-(p-vinylbenzylamino)dodecanoic acid derivatives (RR NAc), have been used as emulsifiers for the preparation of surface-templated resins. Effects of interfacial phenomena on the imprinting effect are probed. n


n

Functional Surfactants for the Preparation of Surface-Templated Resins A monomer-type surfactant called New Frontier A-229ER, which is a phosphonic ester of acrylate oligomer (Dai-Ichi Kogyo Seiyaku Co., Ltd.), has been used as an emulsifier in emulsion polymerization by Yamasaki et al. (17). However, surfaceimprinting was not attempted. In this study, the monomer-type surfactants (Rac, R NAc, and RR NAc) have been synthesized and used as functional surfactants for the preparation of surface-templated resins. n

n

Functional Surfactants. The monomer-type surfactant Rac with mp 55-57 °C was obtained in 16 % yield by a procedure (Figure 1) analogous to that reported by Freedman et al. (18-21) for the synthesis of branched 10-(p-vinylphenyl)undecanoic acids. IR (KBr): 3200 (OH); 1690 (C=0) cm' . ' H - N M R (CC1 ): 8 = 1.25 (14H, -CH2-), 2.15 (2H, -CH2Ac), 2.43 (2H, -CH2-Ar), 4.94-5.11 (1H, trans CH=CAr), 5.49-5.73 (1H, cis CH=CAr), 6.49-6.73 (1H, C=CHAr), 7.15 (4H, ArH), 10.38 (COOH). Calculated for C H 0 : C, 78.80; H , 9.55. Found: C, 78.10; H , 9.00. R NAc and RR NAc were obtained by a procedure analogous to that employed by Freeman et al. (22-24) for the preparation of A^-(vinylbenzyUmino)diacetic acid. The precursor 2-bromoalkanoic acids were synthesized from the corresponding alkanoic acids and converted into 2-aminoalkanoic acids or 2-alkylaminoalkanoic acids by the reaction with ammonia water or an alkylamine, respectively. By reaction with /7-chloromethylstyrene, R NAc and RR NAc were produced in 6-30 % yields (Figure 2). R NAc: mp 206-207 °C. IR (KBr): 3400 (NH), 2970 (OH), 1590 ( C = 0 ) c m . ' H - N M R (CD OD, NaOD): 8 = 0.94 (3H, - C H , 1.06-1.76 (10H, -CH -), 3.24 (1H, >CHN-), 3.52-3.85 (2H, -NCH -), 5.18 (1H, trans CH=CAr), 5.73 (1H, cis CH=CAr), 6.71 (1H, C=CHAr), 7.04-7.67 (4H, ArH). Calculated for C H N 0 : C, 74.18; H , 9.09; N , 5.09. Found: C, 74.16; H , 8.92; N , 4.62. R NAc: mp 172-175 °C. IR (KBr): 3400 (NH), 2970 (OH), 1590 (C=0) c m . H N M R (CD3OD, NaOD): 8 = 0.92 (3H,-CH3), 1.11-1.82 (10H, -CH2-), 3.22 (1H, >CHN-), 3.54-3.93 (2H, -NCH2-), 5.24 (1H, trans CH=CAr), 5.73 (1H, cis CH=CAr), 6.72 (1H, C=CHAr), 7.04-7.72 (4H, ArH). Calculated for C H N 0 : C, 78.07; H , 10.84; N , 3.37. Found: C, 77.76; H , 10.65; N , 3.23. RR NAc: viscous oil. IR (KBr): 3000 (OH), 1590 (C=0) cm' . *H N M R (CD OD): 8 = 0.87 (6H, -CH ), 1.12-1.84 (26H, -CH -), 2.99, -CH NCHN-), 4.26 (2H, -NCH Ar), 5.28 (1H, trans CH=CAr), 5.84 (1H, cis CH=CAr), 6.73 (1H, C=CHAr), 7.25-7.71 (4H, ArH). Calculated for C H N 0 * 1 / 2 H 0 : C, 74.62; H , 10.82; N , 3.29. Found: C, 76.95; H , 10.97; N , 3.17. RR NAc: viscous oil. IR (KBr): 3000 (OH), 1590 (C=0) cm' . ' H - N M R (CH OD): 8 = 0.91 (6H, -CH3), 1.12-2.02 (38H, -CH2-), 2.97 (2H, - C H 2 N O , 3.56 (1H, >CHN-), 4.25 (2H, NCH2Ar), 5.28 (1H, trans CH=CAr), 5.84 (1H, cis CH=CAr), 6.73 (1H, 1

4

1 8

n

2 6

2

n

n

n

8

l

3

3

2

1 7

2

2 5

2

1

!

18

2 7

4 5

6

1

3

3

2

2

2

27

45

2

2

12

1

3


2

266

1) Zn/Hg ^ 2) C H

H0 C(CH ) C0 H 2

2

8

2

6

/ = = v

7

n

,

0-CO(CH ) C0 H 2

8

Q-(CH ) C0 I1

2

2


AICI3 CH3I

CH3COCI

\J-(

C H

2)9C0 CH 2

CII CO-Q-(CN ) C0 CH3

3

3

2

9

2

1) (CH ) CHOH AI[OCH(CH ) ] 3

CH CH(OH)^Q-(CH ) C0 CH 3

2

9

2

2

I

3

2) O H " 1) KHSO4

2

3

2

10-phenyldecanoic acid

/=x

KHC^

9

6

3

f j TV " - ^ 2 (CH ) C0 II N

2

9

2

Rac

Figure 1. Preparation of Rac.

CH3(CH ) 2

M+I

COOH J ^ H ( C H ) 3

2

M

CHCOOH

PCI3

^

r

CH (CH ) CHCOOH 3

2

m

NH NH

CH (CH ) (piCOOII

3

3

2

m

NII

C I C H - £ } - CH=CH 2

CH

2

R

*m=5

2

1 2

I

V

J

R NAc m=15 18

CH=CH CH (CH ) COOII 3

2

^

10

CH (CH ) CHCOOH ^ 3

2

R

CH (CH ) (J:HCOOH 3

2

9

CH (CH ) N 3

C H

3

( C H

2

) NH N

2

ciI (CH ) C H C O O H C 1 C H H Q - C H = C H 3

2

9

2

CH (CH ) NH 3

2

N

2

9

2

N

RR NAc 6

M

=

5

2

~~

fj

RR12NAC 1

y^ m=ll CH=CH 2

Figure 2. Preparations of RnNAcand R R N A c . n


267 C=CHAr), 7.24-7.71 (4H, ArH). Calculated for C H N 0 » 1 / 3 H 0 : C, 78.41; H , 11.41; N , 2.77. Found: C, 78.61; H , 11.48; N , 2.64. 33

57

2

2

Surface Activities of the Functional Surfactants. As measured by a Wilhelmy surface tension balance, an alkaline solution of Rac had a surface tension of Ycmc = 41 mN m" and cmc = 1.25 x 10~ M at pH 12. The cross-sectional area of the molecule, as calculated from the Gibbs adsorption equilibrium, is 0.57 nm . Thus the cmc of Rac is lower than those of C H C O O N a (above 1 x 10 mol dm~ ), C H C O O K (6 x 10" M)(25), and C H C O O N a (3.2 x 10" M at 52 °C)(25). Based on the cmc values, the hydrophobicity of Rac should nearly correspond to that of C H C O O N a . Hydrophobicity of a phenyl group is known to be equivalent to about three and one-half methylene groups (26). Therefore, the sum of the carbon numbers for Rac is estimated to be C (C H COONa or C H C O O N a ) . The monomer-type surfactant Rac is easily polymerized by heating, and an alkaline solution of the resultant polymer (polysoap) shows a lowering of the curve for the surface tension without a break point for the cmc (y = 47 rnNrn" at 2.5 x 10~ M ) . A mixture of toluene and water (1:1) containing 0.2 mol % of Rac (as the sodium salt) was emulsified by vigorous stirring. The volume (height) of the resulting emulsion at time intervals of five minutes, compared with those for 0.2 mol % of sodium dodecyl sulfate (DS) and some sodium alkanoates was: hexadecanoate > tetradecanoate > Rac > DS > dodecanoate » octadecanoate. Therefore, the chain length of Rac seems to correspond to the alkyl chain of 13 carbon number for a sodium alkanoate. This is shorter than the carbon number of 15.5-16 estimated from the cmc values and the calculation. The smaller oleophilicity (larger hydrophilicity) on emulsification is ascribed to the large partitioning of the vinylbenzene moiety between the two liquid phases, since styrene is sparingly soluble in water. R NAc and RR„NAc (5.0 x 10 M in toluene) were also emulsified by stirring in a toluene-water mixture (1:1). The order of emulsifying ability for the mixture of toluene-water at pH 5.5 is R NAc > R NAc > RR NAc = RR NAc, and that for toluene-Cu(H) solutions (1.0 x 10 M at pH 5.5) is R NAc > R^NAc > R R N A c = RR NAc. Emulsification is correlated with the interfacial tension. The interfacial tensions of the toluene-water or toluene-Cu(II) solutions (1.0 x 10 M at pH 5.5), measured with a Du Nouy type surface tension meter, are shown in Table I. R N Ac 1

3

2

2

n


13

3

27

15

3

23

3

15

31

31

1 2 + 3 5

15

31

16

33

1

3

2

n

18

8

6

12

2

8

6

12

2

18

exhibits the lowest interfacial tension (ycmc) in water and the lowering by R N A c has the lowest interfacial tension in the aqueous Cu(II) solution. 8

Table I.

Lowering of Interfacial Tension by R NAc and R R N A c cmc (mM) ycmcCmN-nr ) toluene/aqueous phase water 4.3 0.22 0.14 3.7 Cu(II) solution R NAc water 3.5 0.18 0.32 Cu(II) solution 4.0 RR NAc water 0.32 5.0 0.50 Cu(II) solution 5.0 RR NAc water 0.35 5.0 0.63 Cu(II) solution 5.0 n

n

1

Surfactant R NAc 8

18

6

12

Preparation of Surface-Templated Resins The monomer-type surfactants (Rac, R NAc, and RR NAc) orient at the interface between the matrix monomers and water, and emulsify these solutions. Metaln

n


268 imprinted resins were obtained by both suspension and emulsion polymerization using Rac, R NAc, or RR NAc.


n

n

Metal Ion-Imprinted Resins. The preparative method was as follows. The monomer-type surfactant Rac was dissolved in 80 mL of aqueous Cu(II) solution (pH 6.0) containing 1 wt % of polyvinyl alcohol) (n= ca. 1500, Wako Pure Chemicals). Then, the Cu(II) solution was added to a divinylbenzene:styrene (DVB-ST) (10:1) solution with stirring at 300-400 rpm. The emulsion was heated to 75 °C under nitrogen atmosphere and potassium persulfate was added as the initiator. The monomers in the emulsion gradually polymerized and the polymer (resin) was left in the mixture for 6 hours. After decantation, the white solid resin was separated by filtration with a sintered-glass filter (No. 5). The resin was washed with hot water (90 °C) and then treated with 0.1 M nitric acid for 1 hour to remove the metal ions from the resin (Figure 3). The resin was washed with cold water and dried under vacuum. The monomer-type surfactants R„NAc and RR NAc were dissolved in the DVBST solution and added to the Cu(II) solution (pH 5.5) and the mixture was polymerized with potassium persulfate initiator at 80 °C. Removal of the imprinting Cu from the Cu(II)-imprinted resins prepared with R NAc or RR NAc was accomplished by treatment with 5 M HC1. Polymerization at room temperature was accomplished by irradiating the emulsion n

n

4

n

1

with 1.25 x 10 C K g of ^Co y-rays. Surface-Templated Resins Orientation of the surfactants at the interface is affected by the hydrophilic lipophilic balance (HLB) and interfacial phenomena should be influenced. The surface-template effect of the resulting resins, i.e. the metal ion sorption selectivity, should be highly affected by the orientation and the location of the template sites. The resins were evaluated in batch metal ion sorption experiments. Resins prepared with Rac, R NAc, or RR NAc were added to a Cu(II) solution (pH 5.0 and 6.0) and the suspension was stirred for 2 hours. The resin in the solution was filtered and treated with 0.1 M HC1 for desorption of the metal ions. After washing with water, the resins could be reused for metal ion sorption. n

n

Preparation by Suspension Polymerization. Monomer-type surfactants in the matrix monomers (DVB+ST) adsorb at the monomers-Cu(II) solution interface and form the Cu(II) complex. The polymer (resin) formed from these monomers by suspension polymerization will have the same cavitiesat the surface as the structures of the Cu(II) complexes. Conditions of the resin preparation with Rac are summarized in Table II. Excess DVB (10 times the ST) was copolymerized with ST and Rac to prepare resins of tight structure which should prevent the carboxyl groups from moving. Suspension polymerization gave fine resin beads of about 0.08 mm (0.04-0.16 mm) diameter in 31-66 % yields, while polymerization without Rac give coarser resin beads with diameters of approximately 0.4 mm in 70-80 % yields. The monomertype surfactant Rac produced finely divided particles because Rac lowers the interfacial tension. After the incorporated Cu(II) was removed from the surface-template resins, the readsorption of Cu(II) on the resins at pH 5-6 reaches equilibrium in 2 hours. The amounts of adsorbed metal ions (mmol/g-resin) increase with enhancement of the molar ratio of Rac, as shown in Figure 4. The amounts of Rac at the interface should increase with the addition of Rac at the time of polymerization. However, the relative amount of Rac at the interface is larger than those in the two liquids when Rac is polymerized at the lower concentration, and smaller when at a higher concentration because of dissolution of Rac in the two liquids in the form of an



269

Figure 3. Preparation of Metal Ion-Imprinted Resins.

0.006

•3 ^

0 0.1 0.2 0.3 0.4 Ratio of Rac to monomers(St+DVB+Rac)/ mol%

Figure 4. Adsorption of Cu(II) and Zn(II) on the Cu-Imprinted Resins Prepared by Suspension Polymerization. Initial concentrations of Cu(Et) and Zn(II) = 5 x 10' M , 50 mL, pH 6.0. Resin = 1.0 g. Cu 7Cu-imp = adsorption of Cu(II) on Cu-imprinted resin; C u = adsorption on unimprinted resin, Zn 7Cu-imp = adsorption of Zn(II) on Cu-imprinted resin; and Zrr = adsorption on unimprinted resins. 5

2

2+

2

+


270 Table II. Preparation of Cu(II)-Imprinted Resins by Suspension Polymerization Yield Rac/(DVB+ST), mol % % grams Rac, mol Cu(H)/Rac 0.04 41 0.92 7.3xl0" 0.5 1.7x10-5 0.08 1.68 60 2 0.19 1.56 65 2 3.5xl01.8x10-5 0.30 44 1 0.35 3.6x10-5 0.33 48 0.68 2 1.9x10-5 0.34 0.22 31 1 1.8x10-5 0.39 31 1 0.19 0.04 66 1.47 7.3xl0" 0 1.5x10-5 0.17 44 0 0.49 1.9x10-5 0.25 45 0.47 0 1.7x10-5 0.30 31 0 0.23 1.8x10-5 0.39 0.15 25 0 Conditions of suspension polymerization: DVB/ST = 10 (mol/mol); initiator, benzoyl peroxide (BPO), 1 wt %; P V A , 2.5 wt %; Cu(II) solution, 80 mL, pH 6.0; stirring of the mixture at 300-400 rpm at 85 °C for 6 hours. 8

6


5

6

aggregate, micelle, etc. The influence of additional Rac decreases at high concentra tion. Thus, the adsorbed Cu(II) on the resins is 0.021 mmol-g^mol % at 0.04 mol % of Rac, 0.019 mmolg^mol %' at 0.08 mol % of Rac, 0.014 mmol-g'mol at 0.19-0.30 mol % of Rac, and 0.013 m m o l g mol at 0.39 mol % of Rac. Figure 4 also shows that the amount of Cu(II) adsorbed on the Cu(II)-imprinted resin is larger than that on the unimprinted resins. Moreover, the adsorption of Zn(II) on the Cu(II)-imprinted resins is a Utile larger than that on the unimprinted resins in the range of 0.04-0.25 mol % of Rac. Fixation of Rac at the interface is effective during the polymerization in the presence of Cu(II) because of the orientation of the carboxyl groups toward the Cu(II) solution, and much of the Zn(II) is also adsorbed on the resin at the lower concentration by cation exchange. The size and the coordination number of the imprinted metal ions should change the conformation of the metal complex at the interface. Therefore, a large adsorption of Cu(II) is brought about by template effects at the surface. However, the resin particles are too large for use in metal ion separations and the amounts of Cu(II) adsorbed per gram of resin are not high. Moreover, lower resin yields may weaken the template effect, since the conformation during the polymerization is variable. 1

1

Prepared by Emulsion Polymerization. Emulsion polymerization is expected to produce finer resin particles. Rac functions as an emulsifier and gives stable emulsions upon agitation at 300-400 rpm. Three monomers (DVB+ST+Rac) in metal-ion solutions were copolymerized with initiation by the water-soluble initiator potassium persulfate or by irradiation with y-rays. Conditions for the resin preparations are shown in Table IE. The resins prepared with 0.04-0.33 mol % of Rac were hard, but those with 1.0 mol % of Rac were rubber-like polymers. Polymerization with 0.25 mol % of Rac gave fine particles and the size of resin beads was 200-300 nm in diameter, which is similar to that usually obtained by emulsion polymerization. However, the C u - imprinted resins were obtained in the lowest yields. The polymerization yields were about 3 % for the Cu(II)-imprinted resin, 37 % for the Zn(II)-imprinted resin, 15 % for the Ni(II)-imprinted resin, and 32 % for the unimprinted resin. It is proposed that


271

Table III.

Preparation of Metal Ion-Imprinted Resins by Emulsion Polymerization with Rac Rac Metal Initiator (DVB+St) Rac, imprinting MOD K S 0 , y-ray, mol% mol ion Rac mg CKg 0.25 2.0 x 10" Cu(H) 1 20 0.25 2.0 x 10" Zn(II) 1 20 0.25 2.0 x 10 Ni(II) 1 20 0.25 2.0 x 10" none 0 20 0.33 3.6 x l O Cu(E) 1 31 0.33 2.7 x 10' Zn(n) 1 21 0.33 1.8 x 10" Ni(II) 1 14 0.33 3.6 x l O " none 0 31 1.0 4.0 x l O " Cu(H) 1 10 1.0 4.0 x l O " Zn(n) 1 10 1.0 4.0 x 10" Ni(II) 1 10 1.0 4.0 x l O ' none 0 10 0.04 3.7 x l O Cu(H) 1 " 1.25 x 10 0.04 3.7 x l O " Ni(II) 1 1.25 x 10 0.04 3.7 x 10 none 0 1.25 x 10 Conditions of emulsion polymerization: DVB/ST = 10 (mol/mol); metal solution = 80 mL, pH 6.0; initiator = K S 0 at 75 °C or y-rays at 15-20 °C. a

2

2

8

1

5

5

5

5

5


5

5

5

5

5

5

5

6

4

6

4

6

4

2

2

8

radicals of the initiator are inactivated by the Cu(II) because of the high reduction potential •OS0 + Cu 3

2+

—> S 0

2 4

+ Cu

+

Metal-imprinted resins of RnNAcand R R N A c were prepared in the presence of Cu(II) or Zn(II) solution. The resins prepared by emulsion polymerization using R NAc and RR NAc are shown in Table IV. The resin beads after the desorption of Cu(H) with 5 M H Q were spherical and the size was 0.2-0.8 pm in diameter, which is usual for emulsion polymerization. The Cu(II) would form a complex with a composition of Cu(II)(surfactant) in a yield of 70-100 % when the Cu(H) is one half the amount of surfactant and a complex of Cu(II)(surfactant) in 45-54% yield when the ratio of Cu(II) to surfactant is two. A blue-green Cu(H)-imprinted resin means that the complexes are formed in the interior and at the surface of the resin. Complexation at the surface is in following order: R NAc > R N A c > R R N A c > R R N A c . Since the lipophilic surfactants would be in the bulk monomers, this should reduce complexation at the surface of the resin. n

n

n

2

8

18

6

12

Adsorption of Metal Ions. The Cu(II) adsorbed on 1.0 gram of the resins from emulsion polymerization is 50-100 times as much as that on resins prepared by suspension polymerization (see Figure 4 and Table V). The metal ions are combined with the carboxyl groups on the wider surface of the finer resins. Moreover, the amounts of Cu(II) adsorbed at pH 6.0 are much higher than those at pH 5.0. The monomer-type surfactant Rac must dissociate at pH 4-5 and should complex more easily with Cu(II) at pH 6.0, since the acid dissociation of hexanoic acid is 4.63 at 25 °C (/= 0.1) (27). The adsorption sites on the unimprinted resins are still unsaturated with the metal ions under the conditions described in Table V because of the increased amount of Cu(II)-sorption at the high concentration. The adsorption of Cu(II) on the Cu(II)-imprinted resins is 1.2-4.5 times (mean = 1.88) higher than that on the unimprinted resins. The Zn(II)- and the Ni(II)-imprinted resins also show high


272 Table IV.

Preparation of Metal-Imprinted Resins by Emulsion Polymerization with R NAc or RR NAc Ratio of Yield Color Amount of M m ) x lO^.mol-g' surface, Surfactant Imprinting ion (%) % of resin Inner Surface Surfactant: Metal Ion = 1:0.5 59 Cu(II) 5.7 4.0 48 Yellow-Green R NAc Zn(H) 1.0 29 52 White 2.0 None 63 White -— — — n

n

1


8

R NAc 18

RR NAc 6

RR NAc 12

3.3 0.4

31 12

—

—

4.4 0.5

29 10

—

—

7.8 4.6

3.0 0.5

28 8

—

—

—

5.8 3.0

20.7 2.0

78 40

Cu (n) Zn(II) None

48 68 63

Cu (II) Zn (II) None

42 61 63

Green White White

9.6 4.5

Cu (II) Zn(II) None

58 68 65

Green White White

Blue-Green White White

7.5 2.9

Surfactant: Metal Ion = 1:2 R NAc Cu (II) 52 Yellow-Green Zn (II) 76 White 8

R NAc

Cu (II) Zn(II)

30 61

Blue-Green White

10.1 2.8

27.5 1.0

73 25

RR NAc

Cu (II) Zn(II)

28 70

Yellow-Blue White

12.6 4.3

30.4 1.2

71 21

RR NAc

Cu (II) Zn (II)

62 65

Gray-Green White

8.0 4.3

13.5 0.7

63 14

18

6

12

adsorption for Zn(II) and Ni(II), respectively. In addition to the high adsorption, the Zn(II)-imprinted resins show more effective adsorption for Zn(II) than of Cu(II) and Ni(II). Thus 1.0 gram of Zn(II)-imprinted resin prepared with 0.25 mol % of Rac adsorbs 0.062 mmol of Cu(II), 0.138 mmol of Zn(II), and 0.095 mmol of Ni(II) at pH 5. Such template effects are also seen for the Cu(II)- and Ni(II)-imprinted resins. The highly effective adsorption of the imprinted metal ions clearly indicates the surface-template effect based on the orientation of Rac, and the surface-template effects exceed those of the interior-templated resins (1.3-1.5 times) reported by Nishide et al. (6). Orientation of Rac during polymerization by potassium persulfate may be disordered by the high temperature for chemical initiation (75 °C). Resins prepared at room temperature to minimize disorder of the oriented Rac were obtained in greater than 90 % yield by irradiation with 1.25 x 10 C Kg" y-rays. The resins also have similar surface-template effects (see the lower portion of Table V). However, the particles are slightly larger (below 500 nm in diameter) because ofthe lack of the agitation. Therefore, the metal ion-sorption efficiencies are not as high as those for resins prepared by initiation with potassium persulfate. The resins prepared with RnNAcand R R N A c also adsorb Cu(II), as shown in Figure 5. The Cu(II)-imprinted resins sorb more Cu(II) than the Zn(II)-imprinted 4

1

n


273

1

.s •

0.5 Surfactant : M

2

+

= 1 : 0.5

1 :2

0.4 2 +

l!*\ Cu -inip Downloaded by STANFORD UNIV GREEN LIBR on July 31, 2012 | http://pubs.acs.org Publication Date: May 7, 1998 | doi: 10.1021/bk-1998-0703.ch018

s

"o E m

0.3

Zn

2 +

+

^tmjj\^ -

i m

P %

2

o

"•••• o Zn +-imp Unimprinted \

UnimpriSeri ®% V"""4 K

X

0.2

c

.2

^itiiitiiitft iii^iiiMtintiwiX

Q

%

b

0.1

b

a

o

0

Selective Adsorption of Metal Ions to Surface-Templated Resins

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