Kinetic and thermodynamic analysis of selective adsorption of Cs(I) by a novel surface whisker-supported ion-imprinted polymer

Desalination 263 (2010) 97–106

Contents lists available at ScienceDirect

Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l

Kinetic and thermodynamic analysis of selective adsorption of Cs(I) by a novel surface whisker-supported ion-imprinted polymer Zulei Zhang a,⁎, Xiaohui Xu b, Yongsheng Yan b a b

School of Biology and Chemical Engineering, Jiaxing University, Jiaxing, PR China 314001 School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, PR China 212013

a r t i c l e

i n f o

Article history: Received 14 March 2010 Received in revised form 8 June 2010 Accepted 22 June 2010 Available online 21 July 2010 Keywords: Surface ion-imprinting Sol–gel technology Cs(I) Kinetic Thermodynamic

a b s t r a c t The surface ion-imprinting concept and chitosan incorporated sol–gel process were applied to the synthesis of a new whisker-supported polymer for selective separation of Cs(I) from aqueous solution. The prepared polymer was characterized with Fourier transform infra-red spectroscopy and X-ray diffraction, and then it was used in the sorption–desorption process. The effect of pH, the sorption rate and the mass of sorbent on the sorption capacity of imprinted polymer were studied. Results showed that sorption equilibrium time was achieved in about 2 h and the kinetic study showed to be well followed the pseudo-second-order kinetic equation in the adsorption process. At the same time, the adsorption isotherms studies indicated that Langmuir isotherm equation for the monolayer adsorption process was fitted well in the adsorption process and the maximum adsorption capacity was 32.9 mg g−1. Selectivity experiments showed that adsorbed amount of Cs(I) ion onto Cs(I) ion-imprinted polymer was higher than all other studied ions and the relative selectivity coefficient (K′) were all greater than 9. The developed method with precision relative standard deviation 1.26% and detection limit (3σ) 0.180 μg L−1, respectively, using inductively coupled plasma atomic emission spectrometry was successfully applied to the determination of trace cesium in different water samples with satisfactory results. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Cesium is important from a radioactive waste viewpoint. It has several radioactive isotopes, the most important of which are 134Cs (t1/2 = 2.06 years), 135Cs (t1/2 = 3.0 × 106 years), and 137Cs (t1/2 = 30.17 years), produced in nuclear fission. Due to their long half-lives, both 135Cs and 137Cs are principal radiocontaminants. Therefore, the determination of trace amounts of cesium is of particular significance in environmental and radioactive studies and its determination in water samples also becomes very important [1,2]. The extraction and determination processes of trace metal ions from different matrices especially water samples are mainly based on the utilization and application of a number of available techniques. The pre-concentration process is an essential step for the accurate measurement and analysis of the various metal species which present in trace level (μg L−1 and ng L−1) in order to match with the detection limits of the major instrumentations [3]. Nowadays, a lot of pre-

⁎ Corresponding author. Tel./fax: +86 573 83640262. E-mail address: [email protected] (Z. Zhang). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.06.044

concentration and separation techniques including liquid–liquid extraction [4], coprecipitation [5], and solid-phase extraction (SPE) [6,7] have been developed for metal ions analysis. Of all these methods, SPE is one of widely used and fast emerging preconcentrative separation techniques due to the following advantages: (1) absence of emulsion; (2) high enrichment factor; (3) flexibility; (4) safety and easy of automation; (5) economical and environmental-friendly; (6) speed and simplicity. Numerous substances have been proposed and applied as SPE sorbents, such as organic chelate resin [8], modified silica gel [9], and carbon nanotubes [10] etc. Nowadays, one of the recently developed sorbents for the selective SPE of trace metals is the ion-selective imprinting polymer prepared by molecular imprinting technique [11,12]. Molecular imprinting is a method for tailor-made preparation of highly selective synthetic polymer receptors for given molecules. The principle of the molecular imprinting is that a target molecule (template) and functional monomers are polymerized with a cross-linking reagent. After removal of the template, the functional groups in the resulting binding sites should be arranged in position suitable for interaction with the template molecule [13,14]. Ion-imprinted polymers are similar to molecular-imprinted polymers (MIPs), besides retaining all

98

Z. Zhang et al. / Desalination 263 (2010) 97–106

the virtues of MIPs they also can recognize metal ions after imprinting. However for traditional ion-imprinting, the template and functional monomers are highly embeded in the polymer and most of these materials are of poor site accessibility to the target analytes. Currently, several studies have reported ion-imprinted polymer based on surface imprinting such as copper [15], cadmium [16] but none is about cesium. Thus, it's more indispensable to propose a new method on the surface imprinting of cesium in order to be ion-selective from complex matrix. Sol–gel technology offers simple and convenient methodology to the production of advanced materials with molecular level uniformity [17,18]. Incorporation of polysaccharide into inorganic network by polysaccharide-manipulated sol–gel process is potentially related to the biomineralization processes [19]. As functional biomaterials, chitosan-based organic–inorganic hybrid materials possess many advantages over conventional cross-linked chitosan materials, e.g., low toxicity and high biocompatibility [20]. In this work we attempt to present a new approach to prepare a new whisker-supported composite sorbent based on surface ionimprinting and polysaccharide incorporated sol–gel coating process for selective separation of Cs(I) ions from aqueous solutions. The effect of pH, the sorption rate and the mass of sorbent on the sorption capacity of imprinted polymer were analysed. The kinetic studies for selective adsorption of Cs(I) were also discussed in detail. Finally, the developed method was applied to the determination of trace cesium in different water samples. 2. Experimental 2.1. Apparatus Vista-MPX inductively coupled plasma atomic emission spectrometry (ICP-AES) (Wollian, USA) was used to determine the concentration of metal ions. And analytical wavelength of determined elements by ICP-AES was Co 238.892 nm, Ni 231.604 nm, Cs 697.327 nm, Ce 418.659 nm, Pb 220.353 nm, Sr 407.771 nm and Zn 213.857 nm. A pHS-3C digital pH meter (Shanghai, Shanghai, China) was used for pH measurements. 802 centrifugal precipitators (Shanghai, Shanghai, China), DHG-9140A Electric thermostat blast oven (Shanghai, Shanghai, China), SHZ-D(III) circulating water pumps (Beijing, Beijing, China) were used. The X-ray diffraction (XRD) (Bruker, Germany) pattern was measured in a D/Max-RA diffractometer with Cu Ka radiation (λ = 1.5406 Å) at 40 kV and 100 mA. 2.2. Reagents Chitosan (CTS), with 98% deacetylation and an average molecular weight of 6 × 104 g mol−1 (Shanghai, China) and cross-linking agent 2,3-epoxy-propoxy-propyltrimethoxysilicane (KH-560) (Wuhan, China) were used. Sodium trititanate whisker (STW) (Shanghai, China) was activated with 3.0 M HNO3. Cs(I) was used in the CsCl·5H2O form (Beijing, China). All the other chemicals used were in analytical grade. Doubly deionized water (DDW) was used throughout this work. Standard stock solution of Cs(I) (1.0 g L−1) was prepared by dissolving the required amounts of the metals in a small volume of concentrated nitric acid. Stock solution was diluted to 1 L with DDW and more dilute standards were prepared daily by dilution of these solution. 2.3. Synthesis of Cs(I) ion-imprinted polymer 0.2 g of CsCl·5H2O and 2 g of CTS was added to 75 mL 0.1 mol L−1 acetic acid aqueous solution. After stirring for 1 h, 12 mL of KH-560 was added to the transparent solution. The mixture was stirred for 4 h and then bathed in an ultrasonic bath for 20 min at power 100 W before 12 g of activated sodium trititanate whisker was added as

powder. After stirring for 1 h, the moist mixture was allowed to evaporate at room temperature and ambient pressure for 24 h to complete the reaction. Then the dry product was grinded thoroughly fine and washed with DDW to remove non-bound Cs(I). The consequent polymer was filtered and treated with 1.0 M HNO3 for 12 h at 25 °C to completely leach the coordinated Cs(I). The acidtreated sorbent was rinsed several times with DDW, 1.0 M NaOH to ensure complete H+ neutralization, and the resulting sorbent with Cs(I) cativities was filtered, washed with DDW, and dried under 50 °C vacuum. Then the product was grounded in a mechanical mortar, and then sized by a 200-mesh sieve and stored for further use. The nonimprinted polymer was prepared as a blank in parallel without the addition of Cs(I). 2.4. Batch experiments The Cs(I) ion-imprinted polymer (0.4 g) was equilibrated with 50 mL of Cs(I) ion solution (10 mg L−1), at 25 °C for 2 h of 50 mL stoppard conical flask. The amount of Cs(I) ion in the solution after and before treatment with imprinted polymer was determined by ICP-AES. The adsorption capacity Q (mg g−1), distribution coefficient (Kd) of Cs(I) with respect to Zn(II), Co(II), Ni(II), Ba(II), Sr(II), Ce(III) and Pb(II), some of which are mid-low radioactive metals, others are familiar metals, the selectivity coefficient (K) and relative selectivity coefficient (K′) were calculated as the following equations: Q =

ðC0  Ce ÞV m

ð1Þ

Kd =

ðC0 −Ce Þ V mCe

ð2Þ

K=

′

K =

KdðCsðIÞÞ

ð3Þ

KdðMÞ Kimprinted Knonimprinted

ð4Þ

where C0 and Ce represent initial concentration of metal ions and the concentration after adsorption, respectively; V is the volume of solution, m is the weight of Cs(I) ion-imprinted polymer. Kd(Cs(I)) is the distribution coefficient of the template metal ion Cs(I) and Kd(M) is the distribution coefficient of the competing metal ions. Kimprinted and Knon-imprinted are the selectivity coefficients of Cs(I) ion-imprinted polymer and non-imprinted polymer respectively. K′ represents the difference of metal adsorption affinity recognition of sites to the imprinted Cs(I) ions between them; the larger the K′, the better the imprinted effect showed. In addition, we payed more attention to the competitive uptake for Cs+ vs K+ which is likely main competitor ion for Cs+ as K+ is ubiquitious in the environment. 2.5. Desorption and reusability experiments After having adsorbed metal ion of Cs(I), the imprinted polymer was treated with 25 mL 1.0 M HNO3 at 50 °C water bath for 6.0 h. And Cs(I) ions concentrations in the solution were determined at different desorption times by ICP-AES. The desorption ratio was calculated from the following expression: Desorption ratio =

  amount of ions desorbed to the elution medium × 100% amount of ions adsorbed onto the sorbent

ð5Þ After each cycle of adsorption–desorption, Cs(I) ion-imprinted polymer was washed with DDW to neutrality and dried at 50 °C for adsorption in the next cycle.

Z. Zhang et al. / Desalination 263 (2010) 97–106

99

3. Results and discussion 3.1. Characterization The FT-IR spectrum (carried out on Nicolte Avatar 205FT-IR spectrometer) for various groups of STW, Cs(I) ion-imprinted polymer before and after leaching, CTS and KH-560 are given in Fig. 1. In Fig. 1a, the main characteristic peak at 3447 cm−1 was O–H stretching vibration. From the FTIR spectrum of CTS (Fig. 1d), it can be seen at 3343–3487 cm− 1 was O–H and N–H stretching vibration, 2873 cm− 1 was C–H stretching vibration integrating with hydroxyls on methyl and methylene, 1659 cm− 1 was C=O of NH–C=O stretching vibration, 1584 cm− 1 was N–H bending vibration and 1069 cm− 1 was C–OH stretching vibration. In KH-560 (Fig. 1e) the bands at 2840 cm−1 and 2945 cm−1 were indicative of the presence of methyl and methylene, and the characteristic absorption band at 1463 cm−1 was methyl or methylene deformation vibration. The characteristic absorption bands at 1075 cm−1 and 783 cm−1 might be ascribed to Si–O stretching vibration. Comparing Cs(I) ion-imprinted polymer after leaching (Fig. 1c) with that before leaching (Fig. 1b), the intensity of absorption bands due to the O–H and N–H stretching vibration (at 3200–3400 cm−1) intensified because of the Cs–N and Cs–O groups destroyed in the leaching process. Compared with CTS, it could be seen the peaks of Cs(I) ion-imprinted polymer after leaching (Fig. 1c) had some changes. It displayed that the –OH and –NH2 groups on the CTS surface underwent a derivative reaction with KH-560 in the preparation. The derivative reaction may be as following chemical equation:

In the mean time, the bands at 2800–2950 cm−1 (methyl and methylene stretching vibration) and 1380 cm−1 (methyl deformation vibration) increased in Cs(I) ion-imprinted polymer. The synthesized polymer (Fig. 1b and c) was lack of the peaks at 1659 cm− 1 (C=O of NH–C=O stretching vibration), but it had a strong adsorption bands at 1109 cm− 1 which ascribed to C–O–C stretching vibration can be connected with the KH-560 reaction with CTS.

Fig. 1. FT-IR spectra of (a) sodium trititanate whisker, (b, c) Cs(I) ion-imprinted polymer before and after leaching, (d) CTS and (e) KH-560.

100

Z. Zhang et al. / Desalination 263 (2010) 97–106

Fig. 2. XRD patterns of CTS (a), sodium trititanate whisker (b), and Cs(I) ion-imprinted polymer (c).

Fig. 2 showed the XRD patterns of pure CTS (a), sodium trititanate whisker (b), and Cs(I) ion-imprinted polymer (c)(measured in a D/Max-RA diffractometer with Cu Ka radiation (λ = 1.5406 Å) at 40 kV and 100 Ma). There was a strong peak in the diffractogram of CTS at 2θ = 21.1° (Fig. 2a). XRD of Cs(I) ion-imprinted polymer (Fig. 2c) mainly showed the characteristic of the matrix sodium trititanate whisker (Fig. 2b). However, a slight shift could be found in Fig. 2b compared with sodium trititanate whisker, indicating the hybridization between CTS and KH-560. To avoid the perturbation of high quantity of sodium trititanate whisker, the coating solution was cast on a clean glass plate and the scraped power was analyzed. 3.2. Effect of pH The effect of pH on the adsorption Cs(I) onto the imprinted polymer and non-imprinted polymer was investigated using the batch procedures at 25 °C. The pH of the solutions was adjusted using diluted hydrochloric acid and sodium hydroxide. The adsorption experiments were triplicated and the results were shown in Fig. 3. As can be seen from Fig. 3, the Cs(I) ion-imprinted polymer for Cs(I) exhibited a low affinity in acidic concentration (pH b 5.0) and a high affinity at pHN 6.0. At pHb 5.0 the concentration of hydrogen ions caused such amino group protonation that the sorption efficiency of Cs(I) was low. At pH N 6.0, concentration of amino group increased and Cs(I) ions in the solution formed as Cs–NH2–R complex and as a result, the sorption efficiency increased. So pH 6.0 was chosen as optimum pH for further experiments. Comparing with the imprinted polymer on the adsorption of Cs(I), non-imprinted polymer had a much lower adsorption efficiency, as in the polymerization process, no cavities were formed and a lot of amino groups had been imbedded. 3.3. Effect of sorbent amount The effect of the imprinted polymer amount on the sorption of Cs(I) was tested utilizing the batch procedures under pH 6.0 and 25 °C conditions. The results were shown in Fig. 4 and they indicated that the sorption efficiency of Cs(I) onto Cs(I) ion-imprinted polymer increased as the sorbent amount increased. When the sorbent added was 0.4 g, the sorption efficiency was above 90%. So 0.4 g of sorbent was chosen for further experiments.

Fig. 3. Effect of pH on the remove of 50 mL 10 mg⋅L−1 Cs(I) onto 0.4 g of the Cs(I) ion-imprinted polymer and non-imprinted polymer for 2.0 h at 25 °C, three parallel determinations.

Z. Zhang et al. / Desalination 263 (2010) 97–106

101

Fig. 4. Effect of sorbent amount on the remove of 50 mL 10 mg L−1 Cs(I) for 2.0 h at pH 6.0, 25 °C, three parallel determinations.

3.4. Adsorption kinetics The adsorption kinetics on the adsorption of Cs(I) onto the imprinted polymer was investigated using 0.4 g sorbent to equilibrate with 150 mg L−1 Cs(I) ion solution at 25 °C and 55 °C using the batch procedures. It is evident from Fig. 5, that the adsorption was initially rapid, and reached equilibrium after approximately 2.0 h, and temperature was found to have an inverse effect on the adsorption capacity of Cs(I). In order to evaluate the kinetic model that fits the adsorption process, pseudo-first-order and pseudo-second-order shown as Eqs. (6) and (7) were employed to interpret the experimental data at 25 °C [21–23]. A good correlation of the kinetic data explains the adsorption mechanism of the metal ions on the solid phase. logðqe  qt Þ = log qe 

k1 t 2:302

      t 1 1 = + t qt qe k2 q2e

ð6Þ ð7Þ

where qe is the experimentally determined adsorbed amount of Cs(I) (mg g−1) under equilibrium conditions; qt is the amount of Cs(I) adsorbed at time t (mg g−1), k1 , k2 are the rate constants. The kinetic parameters for adsorption of Cs(I) are given in Table 1. The experimental qe value is closed to the calculated value using pseudo-second-order, which does not happen with pseudo-first-order kinetic equation. Based on the obtained correlation coefficients, the pseudo-second-order equation was the model that furthered the best fitted for the experimental kinetic data, suggesting chemical adsorption as the rate-limiting step of the adsorption mechanism and no involvement of a mass transfer in solution.

Fig. 5. Effect of contact time on the remove of 50 mL 150 mg L−1 Cs(I) onto 0.4 g sorbent at pH 6.0, 25 °C and 55 °C, three parallel determinations.

102

Z. Zhang et al. / Desalination 263 (2010) 97–106

Table 1 Pseudo-first and second-order kinetic constants determined for Cs(I) adsorption onto Cs(I) ion-imprinted polymer (kinetic studies: 0.4 g sorbent to equilibrate 50 mL of 150 mg L−1 Cs(I) solution at pH 6.0, 25 °C and 55 °C). 32.88 mg g−1

Experimental qe Pseudo-first-order kinetic qe k1 r Pseudo-second-order kinetic (25 °C) qe k2 r Pseudo-second-order kinetic (55 °C) qe k2 r

27.4 mg g−1 0.640 h−1 0.760 33.9 mg g−1 0.540 g (mg h)−1 0.986 31.5 mg g−1 0.650 g−(mg−h)−1 0.992

The pseudo-second-order rate constants could further be used to compute the activation energy (Ea) of adsorption (kJ mol−1) by following equation:     kðT2 Þ Ea 1 1 ln − =− kðT1 Þ

R

T2

T1

ð8Þ

where R is the ideal gas constant (8.314 J K−1), and k(T1) and k(T2) are rate constants under 25 and 55 °C. According to the computed value of k(T1) and k(T2) in Table 1, the computed value of Ea can be 4.99 (kJ mol−1). 3.5. Adsorption isotherm The adsorption isotherm was determined by adding 50 mg Cs(I) ion-imprinted polymer with varying concentrations of Cs(I) (2–500 mg L−1) at pH 6.0 and 25 °C using the batch procedures. After 2 h, the equilibrium concentrations of Cs(I) ions in solution and, consequently, the amounts of the Cs(I) ions bound to the sorbent was determined by ICP-AES. Fig. 6 showed the adsorption equilibrium isotherm obtained for Cs(I) adsorption by the imprinted polymer. It was shown that the adsorption capacity increased with the equilibrium concentration of the metal ion in solution, progressively saturating the sorbent. For interpretation of the adsorption data, the Langmuir, Freundlich isotherm and Dubinin–Radushkevich isotherm models were used [24–26]. Ce 1 C + e = ðqm KL Þ qe qm log qe = log Kf + 2

1 log Ce n

ln qe = Kε + ln qm

ð9Þ

ð10Þ ð11Þ

Fig. 6. Adsorption isotherm of Cs(I) ion-imprinted polymer sorbent (50 mg of Cs(I)-imprinted sorbent to equilibrate with 50 mL of various concentrations of Cs(I) solutions: 2–500 mg L−1, at pH 6.0, 25 °C for 2.0 h, three parallel determinations).

Z. Zhang et al. / Desalination 263 (2010) 97–106

103

Table 2 Langmuir, Freundlich, and Dubinin–Radushkevich isotherm constants (isotherm studies: 50 mg of Cs(I)-imprinted sorbent to equilibrate with 50 mL of various concentrations of Cs(I) solutions: 2–500 mg L−1, at pH 6.0, 25 °C for 2.0 h). Parameter

Adsorption of Cs(I) onto Cs(I) ion-imprinted polymer

Langmuir isotherm qm KL r Freundlich isotherm Kf n r Dubinin–Radushkevich isotherm qm K E r

31.9 mg g−1 0.0270 L mg−1 0.999 0.530 1.23 0.910 31.1 mg g−1 -0.00200 kJ2 (mol2)−1 15.8 kJ mol−1 0.921

  1 ε = RT ln 1 + Ce

ð12Þ

−1 = 2

ð13Þ

E = ð−2KÞ

where qe and Ce are the amount adsorbed (mg g−1) and the adsorbate concentration in solution (mg L−1), both at equilibrium. KL (L mg−1) is the Langmuir constant, K is the Dubinin–Radushkevich constant [kJ2 (mol2)−1], E is the mean adsorption energy (kJ mol−1). The results obtained are shown in Table 2. For the three studied systems, the Langmuir isotherm correlated better (r N 0.98) than Freundlich and Dubinin–Radushkevich isotherm with the experimental data from adsorption equilibrium of Cs(I) ions by the imprinted polymer, suggested a monolayer adsorption. The maximum adsorption value was 31.8 mg g−1, which is very close to the experimentally obtained value (32.9 mg g−1). And the Dubinin–Radushkevich adsorption capacity (qm) was similar to the qm of the Langmuir adsorption (in Table 2). The Langmuir parameters can be used to predict the affinity between the sorbate and the sorbent using the dimensionless separation factor, RL defined by Mckay and Poots [27] as: RL =

1 1 + KL Ce

ð14Þ

The value of RL for adsorption of Cs(I) ions is 0.948. It indicates a highly favourable adsorption (RL b 1). In addition, the mean adsorption energy (E) from the Dubinin–Radushkevich isotherm is involved the transfer of free energy of one mole of solute from infinity (in solution) to the surface of sorbent. The adsorption behavior might be predicted the physical adsorption in the range of 1–8 kJ mol−1 of the mean adsorption energies (E), and the chemical adsorption in more than 8 kJ mol−1 of the mean adsorption energies (E) [28]. The mean adsorption energy (E) of Cs(I) was 15.8 kJ mol−1 reflected that the adsorption was predominant on the chemisorption process. 3.6. Selectivity of Cs(I) ion-imprinted polymer Selectivity of Cs(I) ion-imprinted polymer and non-imprinted polymer were investigated by competitive adsorption of Cs(I), Zn(II), Co(II), Ni(II), Ba(II), Sr(II), Ce(III) and Pb(II) from their mixture. The distribution coefficients (Kd), selectivity coefficients (K) and relative selectivity coefficients (K′) are given in Table 3. As can be seen from Table 3, the imprinting effect was clearly observed, as Cs(I) ion-imprinted polymer had a higher adsorption efficiency of Cs(I) than any other metal ions. It indicated that Cs(I) ion-imprinted polymer had the capability of recognizing Cs(I) with a high affinity and selectivity. Moreover, the relative selectivity coefficients (K′) are greater than 9, and this means that Cs(I) ions can be adsorbed more selective than other ions such as Zn(II), Co(II), Ni(II), Ba(II), Sr(II), Ce(III) and Pb(II). As regards to K+, it can be seen from

Table 3 Adsorption selectivity of Cs(I) ion-imprinted polymer and non ion-imprinted polymer (selectivity studies: equilibrating 0.2 g of the surface imprinted polymer or non ion-imprinted polymer with 50 mL of 4.00 mg L−1 Cs(I), 4.00 mg L−1 Pb(II), 4.00 mg L−1 Ce(III), 4.00 mg L−1 Ba(II), 4.00 mg L−1 Sr(II), 4.00 mg L−1 Ni(II), 4.00 mg L−1 Zn(II) and 4.00 mg L−1 Co (II) mixture solution, at pH 6.0, 25 °C for 2.0 h). Ions

Cs(I) Pb(II) Zn(II) Ce(III) Sr(II) Co(II) Ni(II) Ba(II)

C0 (mg L−1)

4.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00

Cs(I) ion-imprinted polymer

Non-imprinted polymer

K′

Ce(mg L−1)

Kd

K

Ce(mg L−1)

Kd

K

0.0300 0.340 0.350 0.580 2.51 2.57 3.08 0.530

33.1 2.69 2.61 0.1.47 0.148 0.139 0.0747 1.64

–

0.334 0.371 0.232 0.270 0.881 0.433 0.472 0.662

2.74 2.45 4.06 3.45 0.885 2.06 1.87 1.26

– 1.12 0.676 0.795 3.10 1.33 1.47 2.18

12.3 12.7 22.4 223 238 443 20.2

– 11.0 18.8 28.2 71.9 179 301 9.27

104

Z. Zhang et al. / Desalination 263 (2010) 97–106

Table 4 Adsorption selectivity of Cs+ vs K+ by Cs(I) ion-imprinted polymer (selectivity studies: equilibrating 0.2 g of imprinted polymer with 50 mL of 4.00 mg L−1 Cs(I) and 4.00 mg L−1 K(I) mixture solution, at pH 6.0, 25 °C for 2.0 h). Ions

C0 (mg L−1)

Ce (mg L−1)

Kd

K

Cs(I) K(I)

4.00 4.00

0.052 0.364

19.0 2.50

– 7.6

Table 4, the selectivity coefficient (K) 7.6 is far more than 1, and it comes to indicate that the prepared surface imprinted polymer could uptake Cs(I) more effectively and it had good Cs/K selectivity. 3.7. Desorption and reusability After having adsorbed Cs(I) ions, Cs(I) ion-imprinted polymer sorbent was investigated through desorption studies in different concentrations of three acids, and the results showed that by eluting with 25 mL 1.0 M HNO3 at 50 °C water bath for 6.0 h the desorption ratio was determined to be as high as 99% according to the formula described as Eq. (5). The adsorption–desorption process repeated six times, and the adsorption capacity was about 83.7% in the 6th use (in Fig. 7). It indicated that the imprinted polymer can be reused many times without significantly decrease in the adsorption capacity. 3.8. The imprinting mechanism study As shown in the following Fig. 8, the imprinting mechanism of the Cs(I) ion-imprinted polymer mainly contained four steps. Firstly, template Cs(I) coordinated to the –OH and –NH2 from functional monomer CTS, and the complex from CTS–Cs(I) was obtained (Fig. 8a). In the second part, CTS–Cs(I) and KH-560 attended polymeric reaction, and then the cross-linked polymer network was formed. Meanwhile, silanol groups were generated through acid-catalyzed self-hydrolysis of KH-560 (Fig. 8b). Next step is the polymer coated on the surface of sodium trititanate whisker (Fig. 8c). Finally, Cs(I) was leached from the surface of organic–inorganic hybrid polymer leaving behind its impression in the form of a cavity with appropriately oriented functional (Fig. 8d). Then the cavity could form a selective key–lock relationship with the template Cs(I). 3.9. Detection limit and relative standard deviation Under the selected conditions, the linearity of this method was evaluated using a series of Cs(I) stock solution from 0.050 to 10.000 mg L−1. Equation [c] = K1[A] + K0 was selected. A good linear relationship [c] = 8.9736[A] + 0.0863 with squared correlation coefficient (r2) 0.99968 was obtained. The detection limit (3σ) was 0.180 μg L−1. Measuring 1.0 mg L−1 of Cs(I) 10 times, the relative standard deviation for 1.0 mg L−1 Cs(I) was 1.26%. 3.10. Application of the method In order to evaluate the feasibility of the proposed method, it was applied to the analysis of cesium in several water samples. To oxidize organic matter such as humic acid, the sample was digested by oxidizing UV-photolysis in the presence of 1% H2O2 using a low pressure Hg-lamp

Fig. 7. Reusability of Cs(I) ion-imprinted polymer (adsorption: 0.4 g of the Cs(I) ion-imprinted polymer uptake 50 mL 10 mg⋅L−1 Cs(I) for 2 h at 25 °C, desorption: 25 mL 1.0 M HNO3 at 50 °C water bath for 6 h, three parallel determinations).

Z. Zhang et al. / Desalination 263 (2010) 97–106

105

Fig. 8. Scheme of the imprinting mechanism of Cs(I) ion-imprinted polymer towards Cs(I).

Table 5 Determination and recoveries of Cs(I) in environment water samples n = 5 with the proposed method (sample volume: 50 mL, pH 6.0, adsorption: 0.4 g of the Cs(I) ion-imprinted polymer uptake Cs(I) in sample solutions for 2.0 h at 25 °C, desorption: 25 mL 1.0 M HNO3 at 50 °C water bath for 6 h, three parallel determinations). Samples

Cs(I) added (μg L−1)

Determination (μg L−1)

RSD (n = 5) (%)

Recovery (%)

Living sewage

0 5.000 10.000 0 5.000 10.000 0 5.000 10.000 0 5.000 10.000

0.309 ± 0.02 5.321 ± 0.03 10.318 ± 0.03 0.198 ± 0.01 5.205 ± 0.04 10.190 ± 0.02 nd 5.136 ± 0.01 10.128 ± 0.05 0.299 ± 0.02 5.293 ± 0.03 10.301 ± 0.01

2.21 1.60 1.78 1.45 2.11 0.98 – 2.03 1.70 1.38 2.10 1.34

– 100.2 99.8 – 98.6 101.2 – 99.3 100.5 – 100.3 99.9

Pond water

School jade belt river water

Industry waste water

The value following "±" is the standard deviation. The nd stands for not find.

which was integrated in a closed quartz vessel [29]. For the analysis of these water samples, the standard addition method was used. As is shown in Table 5, the recoveries of cesium were in the range of 98.6–101.2%. These results indicated the suitability of this method for selective solidphase extraction and determination of trace Cs(I) in environmental samples.

4. Conclusions In the present work, Cs(I) ion-imprinted polymer synthesized using surface ion-imprinting concept and polysaccharide incorporated sol–gel process was used for selective separation of trace Cs(I) from aqueous solution. Through a series of adsorption experiments educed a high adsorption capacity of 32.88 mg g−1 under the optimum conditions. In addition, the dynamical study showed to be well followed the pseudosecond-order kinetic equation in the adsorption process. Meanwhile, the equilibrium adsorption studies was fitted in three adsorption isotherm models, namely, Langmuir, Freundlich, and Dubinin–Radushkevich to show very good fit in the Langmuir isotherm equation for the monolayer adsorption process. Selectivity experiments showed that adsorbed amount of Cs(I) ion onto Cs(I) ion-imprinted polymer is higher than all other studied ions. The method was successfully applied

to the analysis of trace cesium in water sample solutions. The precision and accuracy of the method are satisfactory. Acknowledgements This work was financially supported by the National Science Foundation of China (no. 20877036), Science and Technology Ministry of China (no. 05C26213100474) and Jiangsu University Talent Foundation (no. 04JDG017). References [1] A.M. El-Kamash, M.R. El-Naggar, M.I. El-Dessouky, J. Hazard. Mater. 136 (2006) 310–316. [2] A.E. Osmanlioglu, J. Hazard. Mater. 137 (2006) 332–335.

106 [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]

Z. Zhang et al. / Desalination 263 (2010) 97–106 M.E. Mahmoud, M.S.M. Al Saadi, Anal. Chim. Acta 450 (2001) 239–246. T. Shimizu, M. Hagiwara, K. Takino, Z. Fresenius, Anal. Chem. 306 (1981) 29–35. Q. Zhang, H. Minami, S. Inoue, I. Atsuya, Anal. Chim. Acta 508 (2004) 99–105. Y. Wang, J.H. Wang, Z.L. Fang, Anal. Chem. 77 (2005) 5396–5401. J.H. Wang, E.H. Hansen, Anal. Chim. Acta 435 (2001) 331–342. Y. Guo, B. Din, Y. Liu, X. Chang, S. Meng, M. Tian, Anal. Chim. Acta 504 (2004) 319–324. E.M. Soliman, M.B. Saleh, S.A. Ahmed, Anal. Chim. Acta 523 (2004) 133–140. P. Liang, Y. Liu, L. Guo, J. Zeng, H. Lu, J. Anal. At. Spectrom. 19 (2004) 1489–1496. C.F. Poole, Trends Anal. Chem. 22 (2003) 362–373. M. Tuzen, M. Soylak, J. Hazard. Mater. 147 (2007) 219–225. K. Haupt, K. Mosbach, Chem. Rev. 100 (2000) 2495–2504. R.S. Praveen, S. Daniel, T.P. Rao, Talanta 66 (2005) 513–520. E. Birlik, A. Ersoz, A. Denizli, R. Say, Anal. Chim. Acta 565 (2006) 145–151. G. Fang, J. Tan, X. Yan, Anal. Chem. 77 (2005) 1734–1737. J.H. Shin, S.W. Weinman, M.H. Schoenfisch, Anal. Chem. 77 (2005) 3494–3501.

[18] Z.H. Zhang, L.H. Nie, S.Z. Yao, Talanta 69 (2006) 435–442. [19] Y.A. Shchipunov, T.Y. Karpenko, Langmuir 20 (2004) 3882–3887. [20] Y. Liu, H.J. Lu, W. Zhong, P.Y. Song, J.L. Kong, P.Y. Yang, H.H. Girault, B.H. Liu, Anal. Chem. 78 (2006) 801–808. [21] Y.S. Ho, G. McKay, Water Res. 34 (2000) 735–742. [22] M. Yurdakoc, Y. Scki, S.K. Yuedakoc, J. Colloid Interface, Sci. 286 (2005) 440–446. [23] F.C. Wu, R.L. Tseng, R.S. Juang, Water Res. 35 (2001) 613–618. [24] C. Niu, W. Wu, Z. Wang, S. Li, J. Wang, J. Hazard. Mater. 141 (2007) 209–214. [25] J.C.Y. Ng, W.H. Cheung, G. McKay, Chemosphere 52 (2003) 1021–1030. [26] S.P. Ramnani, S. Sabharwal, React. Funct. Polym. 66 (2006) 902–909. [27] G. McKay, V.I.P. Poots, J. Chem. Technol. Biotechnol. 30 (1980) 279–292. [28] A.H. Chen, S.C. Liu, C.Y. Chen, C.Y. Chen, J. Hazard. Mater. 154 (2008) 184–191. [29] C. Gueguen, C. Belin, B.A. Thomas, F. Monna, P.Y. Favarger, J. Dominik, Anal. Chim. Acta 386 (1999) 155–159.