Adsorption Mechanism of Aromatic Sulfonates onto Resins with

Sep 8, 2007 - In this study, acrylic ester resin YWB was prepared and utilized as adsorbent to investigate the adsorption mechanism of aromatic sulfon...
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Ind. Eng. Chem. Res. 2007, 46, 6971-6977

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SEPARATIONS Adsorption Mechanism of Aromatic Sulfonates onto Resins with Different Matrices Weiben Yang,†,‡,§ Aimin Li,*,†,§ Chang’e Fu,‡ Jun Fan,†,§ and Quangxing Zhang†,§ State Key Laboratory of Pollution Control and Resource Reuse, School of the EnVironment, Nanjing UniVersity, Nanjing, People’s Republic of China, 210093, Nanjing College of Chemical Technology, Nanjing, People’s republic of China 210048, and Jiangsu Engineering & Technology Research Center for Organic Toxicant Control and Resource Reuse, Nanjing, People’s republic of China 210038

In this study, acrylic ester resin YWB was prepared and utilized as adsorbent to investigate the adsorption mechanism of aromatic sulfonate onto it. For comparison, the commercial resins XAD-7, D-301, and XAD-4 were also employed along with YWB. Different adsorption and desorption behaviors of these resins showed that the matrices of resins and functional groups on their surface significantly affected the adsorption mechanism. The adsorption mechanism of acrylic ester resin with surfactant and dye, two kinds of aromatic sulfonates, were examined using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), which provided valuable information regarding the adsorption mechanism of adsorbate onto acrylic ester resin YWB. The changes of spectrum after adsorption were mainly attributed to the formation of hydrogen bonding, electrostatic attraction forces, and the formation of the oxonium group, although the hydrophobic interactions played an important role in binding aromatic sulfonate onto the resin surface from the solutions. The results indicated that the oxygen atoms of ester functional groups made a contribution to the adsorption mechanism. 1. Introduction Safety, health, and environmental concerns are challenging traditional wastewater treatment techniques, and particularly, heightened public attention is driving efforts to recover toxic organic substances from aquatic systems. Aromatic sulfonates, widely used as industrial intermediates and consumer detergent products, are of especial interest because of their good solubility in water and negative impacts on the environment once discharged into the receiving water system with industrial waste streams.1 It is therefore important in environmental processes to effectively recover and reuse them from the aquatic system. Adsorption is one of the most extensively used technologies to remove these organic contaminants from aqueous streams in water treatment, and various adsorbents, including activated carbon, resins, chitosan, and silica, have been used in the literature.1-7 In principle, adsorption offers great potential for separations because adsorbents can be designed with binding sites with high selectivity. Such binding selectivity is important especially when adsorption is being used for the large-scale separation of an organic species from dilute aqueous mixtures.8 To achieve high selectivity, it is necessary to understand and control the mechanism responsible for adsorption. However, many of the adsorbents are nonspecific and of limited capabilities for binding selectivity. * To whom correspondence should be addressed. Tel.: (86)-2585560233. Fax: (86)-25-85572627. E-mail: [email protected]. † Nanjing University. ‡ Nanjing College of Chemical Technology. § Jiangsu Engineering & Technology Research Center for Organic Toxicant Control and Resource Reuse.

One promising approach involves the use of selective adsorption resin, which has homogeneous surface chemistry offering the potential for limiting adsorption forces to specific mechanistic interactions. Now, we have focused on an acrylic ester adsorbent, which has oxygen heteroatoms permitting adsorption through interactions between its ester functional groups and polar groups of benzene sulfonate. Moreover, acrylic ester adsorbents are inexpensive and offer surface areas and mechanical properties appropriate for large-volume, bulk chemical separations.9 Payne and co-workers investigated adsorption mechanisms of various solutes onto acrylic ester resin from nonaqueous system through a hydrogen-bonding mechanism.8-12 These observations do not offer mechanistic information of the binding interactions by spectroscopy despite providing typically phenomenological evidence and thermodynamic data. So far, there is limited understanding about interactions between aromatic sulfonate adsorbate and acrylic ester resin adsorbent in aqueous systems. The adsorption mechanisms for aqueous systems remain largely unknown. Historically, Amberlite XAD resins were widely used in adsorbing organic matters mainly through hydrophobic or hydrophilic interactions. For example, the Van der Waals force plays a dominant role for solute adsorbing onto a hydrophobic resin XAD-4. However, XAD-7, a typical commercial acrylic ester resin with many of ester functional groups on its matrix, is a more polar or less hydrophobic adsorbent than styrene polymer XAD-4.13-16 In the present study, we investigate the adsorption mechanism between acrylic ester resin and aromatic sulfonates. Acrylic ester resin YWB, which was prepared in our laboratory presenting similar chemical properties to that of XAD-7, was employed as adsorbent along with macroporous

10.1021/ie0615281 CCC: $37.00 © 2007 American Chemical Society Published on Web 09/08/2007

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Figure 1. Structures of the adsorbates in this study.

weak base anion exchanger D-301, hydrophobic resin XAD-4, and XAD-7 for comparison. The adsorbates selected in this study are surfactant sodium 6-dodecyl benzenesulfonate (6NaDBS) and dye reactive brilliant blue KN-R (Figure 1). These two chemicals, which are extensively used in developing countries like China due to their lower cost, can lead to potential sources of pollution because of their resistance to biodegradation in an aqueous environment.17-19 The purpose of our work is to investigate the adsorption mechanism of these two adsorbates onto acrylic ester resin by employing Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). 2. Materials and Methods 2.1. Materials. Sodium 6-dodecyl benzenesulfonate, methanol, sodium sulfate, methylbenzene, xylene, dodecylbenzene, methyl acrylate, Dimethyl acrylate glycol ester, hydroxyethyl cellulose, dibenzoyl peroxide, sulfuric acid, and dye reactive brilliant blue KN-R (abbreviated as KN-R) were all obtained from Shanghai Chemical Reagent Plant (Shanghai, PRC). Trimethylolpropane trimethacrylate (TRIM) was purchased from Minguang Co. (Anhui Province, PRC). Amberlite XAD-4 and XAD-7 (Rohm and Haas Co., Ltd., Philadelphia, PA), were purchased from Kanglin Corporation (Beijing, PRC). Macroporous weakly basic exchanger resins D-301 were kindly provided by Jiangsu N&G Environmental Technology Co. Ltd. (China). The resin D-301 was washed with 4% aqueous HCl and 4% NaOH solution alternatively twice and finally sufficiently washed with distilled water. All the resins used in this study were extracted with ethanol in a Soxhlet apparatus for 8 h and then dried under vacuum at 333 K for 8 h. The resultant beads with the fractions ranging from 30 to 50 meshes were adopted for the study. Chemicals were used without any further purification. 2.2. Synthesis of YWB Resin. Resins beads were prepared by suspension polymerization. First, an aqueous phase (450 g) comprised of 0.2% (0.9 g) of hydroxyethyl cellulose, an organic phase (150 g overall mass) comprised of the monomer such as methyl acrylate, dimethyl acrylate glycol ester, and trimethylolpropane trimethacrylate (TRIM) at a 1:2:7 weight ratio, and 75 g porogen such as methylbenzene, xylenes, and dodecylbenzene at a 6:1:3 weight ratio were formulated separately. Dibenzoyl peroxide (1 wt % relative to monomer) was then introduced into the organic phase. After that, the aqueous phase was added to a 1000 mL parallel-sided flanged gastight glass vessel fitted with a metal stirrer carrying two impellers, and then, the organic phase was added. The stirring speed was set to be 250 rpm, and the polymerization was allowed to proceed at 348 K for 10 h. At the end of the reaction, the mixture was cooled down to room temperature and the beads were filtered using a 75 µm sieve. The filtered polymer was rinsed three times with hot water, extracted with methanol in a Soxhlet apparatus for 8 h, and then dried under vacuum at 333 K for 8 h. The specific surface area and the porosity measurements of adsorbents were carried out by the nitrogen adsorption and

desorption method using a Micrometics ASAP-2000 automatic surface area analysis instrument (Micromeritics Instruments, Norcros, GA). Infrared spectra of resins were obtained with a Nexus 870 FTIR spectrometer. The elemental analysis of the resins was performed using a Perkin-Elmer 240 C elemental analytical instrument (Wellesley, MA). The IR spectra and the content of the element imply that the structure of YWB resin is in agreement with that of the acrylic ester resin XAD-7. 2.3. Adsorption Assay. The equilibrium experiments of resins were carried out at a temperature of 298 K. A 0.100 g portion of resin was introduced into a series of 150 mL conical flasks containing 100 mL aqueous solution of 6-NaDBS or KN-R with different initial concentrations (C0): 100, 200, 400, 600, 800, 1000, 1200, 1400 and 1600 mg‚L-1. Additionally, the practical wastewater of aromatic sulfonate is acidic, and the pH value of the solution before adsorption was therefore adjusted to 1. The flasks were then completely sealed and placed in a model G25 incubator shaker (New Brunswick Scientific) at 298 K with a shaking speed of 130 rpm for 48 h, ensuring adsorption equilibrium. After the equilibrium, the concentrations of 6-NaDBS and KN-R in solutions (Ce) were determined with spectrophotometric measurements on a 722 ultraviolet and visible spectrometer at its maximum absorbance wavelength, which is 261 nm for 6-NaDBS and 602 nm for KN-R, respectively. The adsorption capacity qe (mmol‚g-1) was calculated using eq 1:

qe ) V(C0 - Ce)/MW

(1)

where V is the volume of solution (L), W is the weight of dry resin (g), C is the mass concentration, and M is the molecular weight of 6-NaDBS or KN-R. 2.4. Desorption. To obtain desorption data and to determine the suitable eluent required for different adsorbate and adsorbent, 100 mL of 1600 mg‚L-1 6-NaDBS or KN-R solutions at 298 K was introduced into a series of 150 mL conical flasks and shaken with 0.1 g resin for 48 h. After adsorption, 0.1 g of the resin with adsorbate was placed into 100 mL elutant aqueous solutions with different amounts of NaOH and ethanol. The amounts of adsorbate eluted were estimated by measuring absorbance at its maximum absorbance wavelength, respectively. 2.5. FTIR and XPS. FTIR and XPS analysis of the acrylic ester resin YWB before and after adsorption was carried out. Infrared spectra of YWB resin were collected with a Nexus 870 FTIR spectrometer. The samples of resins were ground into powder and blended with KBr and pressed into discs. The spectra were recorded under ambient conditions. The X-ray photoelectron spectroscopy (XPS) study was carried out on a VG ESCALAB MKII spectrometer equipped with Mg KR X-ray source (1253.6 eV protons). The X-ray source was run at a reduced power of 150 W, and the pressure in the analysis chamber was maintained at less than 10-8 Torr during each measurement. Detailed regional scans were obtained for elements C and O. A software package, Scalab, was used to fit the spectra.

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Figure 2. Equilibrium adsorption isotherms for 6-NaDBS and KN-R on four resins at 298 K. Table 1. Salient Properties of Polymeric Adsorbents resin matrix pore volume (cm3/g) BET surface area (m2/g) average pore diameter (nm)

YWB acrylic ester 1.0067

XAD-7 acrylic ester 0.9448

XAD-4 styrene 1.0005

D-301 styrene 0.283

609.6

510.9

880.2

31.8

7.8

7.3

5.8

16.6

3. Results and Discussion 3.1. Adsorption Behavior. In general, adsorption can be defined as a process of molecules accumulating from a bulk solution onto the exterior and interior surface of an adsorbent, involving various interactions such as hydrophobic, electrostatic attraction, and hydrogen bonding.20 A matrix of adsorbent and functional groups on its surface can play an important role in determining states and equilibrium of adsorption. Four resins with different physicochemical properties were selected as adsorbents. Their properties are presented in Table 1. The adsorption isotherms of 6-NaDBS and KN-R on YWB, XAD-7, XAD-4, and D-301 at 298 K are depicted in Figure 2. From these figures, it can be seen that the studied systems show different characteristics for different adsorbates. The equilibrium adsorption capacity of 6-NaDBS on XAD-4 is larger than that on the other three resins, while the equilibrium adsorption amount of KN-R on YWB is largest in the four resins. The equilibrium adsorption amount of ion exchanger resin D-301 is the lowest when the adsorbate is 6-NaDBS, whereas its equilibrium adsorption amount to KN-R is only less than that of acrylic ester resin YWB. The equilibrium adsorption amount of YWB is always bigger than that of XAD-7 in two different adsorption processes, which can be ascribed to the same matrix and the bigger BET surface area of YWB. The different characteristics of adsorption behavior observed for four resins might be due to the different adsorption mechanism between adsorbates and adsorbents. As we know, 6-NaDBS and KN-R molecules are all made up of the hydrophobic alkyl moiety and hydrophilic sulfonate moiety. The relative contribution of each part to the overall interactions is central to the adsorption behavior. The polystyrene resin XAD-4 is strongly hydrophobic because of its hydrocarbon structure, and there is no functional group on its matrix. Its BET surface area is the largest among the four resins. Hence, the adsorption capacity of XAD-4 should be significantly affected by the hydrophobic part of the adsorbate. The largest equilibrium

adsorption amount of 6-NaDBS and the least equilibrium adsorption amount of KN-R on XAD-4 indicate that the hydrophobic alkyl moiety of 6-NaDBS plays a more important role to the adsorption capacity of XAD-4 than KN-R. The weak base anion exchanger D-301 is a hydrophilic polymer as there are many ion groups on its surface. Its BET surface area is the least among four resins. Therefore, the ion exchange mechanism and electrostatic interactions are essential to the adsorption behavior of 6-NaDBS and KN-R onto D-301. The contrbution of the ion functional group of KN-R to the adsorption capacity of D-301 is especially important, which leads to the equilibrium adsorption amount of KN-R on D-301 being larger than that on XAD-4. In short, the hydrophobic moiety of the 6-NaDBS molecule and the hydrophilic moiety of KN-R molecules are the essential parts to the adsorption process. This difference may be important to explore the adsorption mechanism of aromatic sulfonate onto acrylic ester resin. Compared to XAD-4 and D-301 resins, acrylic ester resins YWB and XAD-7 are partially hydrophobic and partially hydrophilic due to the presence of polymer carbon chain and the polar ester functional groups. Additionally, their BET surface areas are also comparatively large which are important to the adsorption capacity of resin. In general, Van der Waals forces are normally predominant in the adsorption of adsorbate molecules from an aqueous phase onto a hydrophobic adsorbent. However, in some cases, electrostatic attraction and hydrogen bonding are also important for molecules with certain functional groups.3 Hydrophobic interaction and other mechanisms such as polar or electrostatic forces or hydrogen bonding can play similarly important roles to the adsorption mechanisms of acrylic ester resins. Because the hydrophobic part of the 6-NaDBS molecule makes a stronger contribution to the adsorption behavior, the equilibrium adsorption amount of 6-NaDBS on YWB is less than that on XAD-4. To the adsorption behavior of KN-R on four resins, the cooperation of hydrophobic and hydrophilic interactions contributes the largest to the equilibrium adsorption amount of YWB in four resins. However, further investigations are necessary to elucidate the adsorption mechanism of aromatic sulfonate onto acrylic ester resin. 3.2. Desorption. In general, the structures and properties of both adsorbate and adsorbent significantly impact the adsorbate uptake rate. The high adsorption potential and the high affinity of the resin matrix for the adsorbate may render adsorbate elution from the resins very difficult.21 It is worthwhile to investigate desorption behavior of the adsorbates from the resins and the possibility of recycled use of the resins. The ideal

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Figure 3. Influence of eluent on the elution of adsorbates from adsorbent. (a) Elution of 6-NaDBS adsorbed on YWB and XAD-4 resins with 4% (mass percent concentration) NaOH aqueous solution containing various contents of ethanol. (b) Elution of KN-R adsorbed on YWB and D-301 resins with various contents of NaOH aqueous solution.

adsorbent should be sufficiently porous to allow easy diffusion into and out of the resin matrix, and it is of practical and research interest to examine the regeneration behaviors of these resins. For comparison, we selected two resins with larger adsorption amounts to investigate their desorption behaviors and get a suitable eluting solvent. Figure 3 show the influence of eluent on the desorption of adsorbates from adsorbent. As seen from Figure 3a, the degree of elution increases with increasing ethanol content in alkaline solution. Desorption of 6-NaDBS from YWB resin is 93.5% when the eluent is NaOH 4% solutions containing ethanol of 40 vol %, while desorption of 6-NaDBS from XAD-4 is 73.0% under the same condition. When the eluting agent is NaOH 4% without ethanol, only 18.7% and 7.8% 6-NaDBS is eluted from two resins. On the other hand, the adsorbate KN-R on YWB and D-301 can be easily eluted with alkaline solution. In particular, the elution rate of KN-R on YWB resin is 83% when the elution solution is NaOH 4%, while the desorption rate of KN-R on D-301 resin is 56% under the same condition. The investigation of desorption may be related to the interfering effect of ethanol and alkali on hydrophobic and other interactions. Likely, the role played by ethanol in the eluant system is that of displacing adsorbates bearing specific chemical groups which are preferentially adsorbed on the active centers of the solid surface.22 Meanwhile, the existance of ethanol in aromatic sulfonate solution may decrease the hydrophobicity of the solute, which results in the decrease of hydrophobic interaction between adsorbate and adsorbent. Therefore, ethanol is important to the elution processes of 6-NaDBS and KN-R from two resins. Additionally, having the alkali in aromatic sulfonate solution, which has adsorbate molecules dissociated, results in the disappearance of hydrogen bonding, electrostatic attraction, and the oxonium functional group and leads to the desorption of adsorbates from two resins. The different eluting efficiency of adsorbates from adsorbents may be ascribed to the different contributions of hydrophobic and other interactions to the adsorption process. According to certain adsorbents, a complete recovery of adsorbate can be achieved in a simple way by suitably choosing the eluting solvent systems. The phenomenological evidence indicates that YWB is an ideal adsorbent in this study which has better adsorption and eluting

properties than other resins. We will further investigate the adsorption mechanism of aromatic sulfonate on acrylic ester resin YWB by spectroscopy. 3.3. FTIR and XPS. FTIR spectra have been a useful tools to identify the presence of certain functional groups on a solid surface because each specific chemical bond often shows a unique energy adsorption band.23 In this study, FTIR analysis was utilized to examine the changes of carbonyl and ester groups on acrylic ester resin YWB so that the adsorption mechanism can be identified. The typical FTIR results of resins before and after adsorption are shown in Figure 4. The main peaks of acrylic ester resin before adsorption can be assigned as follows (Figure 4A): 1735.6 cm-1 (CdO stretching), 1639.2 cm-1 (COOH stretching), 1467.6 cm-1 (CH blending), 1388.5 cm-1 (symmetric blending of CH3 in CCH3), 1149.4 and 1263.2 cm-1 (Cs O stretching), 586.3 cm-1 (CdO twisting).24-26 After adsorption, the obvious changes of the wavenumber for the peak at 1735.6 and 1149.4 cm-1 due to aromatic sulfonate adsorption are observed in Figure 4B-E, which are attributed to the attachment of the sulfonate ions on the CdO and CsOsC groups affecting the stretching vibration frequency of these surface chemical groups. The infrared peak of CdO shifting from 1735.6 to about 1729 cm-1 indicates that the interaction mechanism between the carbonyl groups of the resin and the functional groups of the two adsorbates is similar. In general, the shift of peaks depends on the extent of lone pair electron transfer.27 As the amount of sulfonate groups increases, more negative charges are withdrawn from the carbonyl oxygen lone pair electrons, resulting in a lower peak of the carbonyl group. Similarly, the peak shift at a wavenumber of 1149.4 cm-1 indicates that there are interactions between the functional groups of the adsorbate and the oxygen atoms of sCsOsCs and the existence of oxonium groups. The trends of peak shift of ester functional groups after adsorption are different between two types of adsorbate: one shift from 1149.4 to 1155.2 (B) and 1157.2 cm-1 (C) and the other shift from 1149.4 to 1146.46 (D) and 1143.5 cm-1 (E), respectively. X-ray photoelectron spectroscopy (XPS) has found increasing applications in studying the interactions between an adsorbate and the active groups on the surface of adsorbent in the adsorption process. This is due to the fact that the creation of

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Figure 4. FTIR spectra of YWB before and after adsorption: (A) before adsorption; (B) the equilibrium adsorption concentration of 6-NaDBS on YWB is 0.194 mmol‚L-1; (C) the equilibrium adsorption concentration of 6-NaDBS on YWB is 0.735 mmol‚L-1; (D) the equilibrium adsorption concentration of KN-R on YWB is 0.145 mmol‚L-1; (E) the equilibrium adsorption concentration of KN-R on YWB is 0.338 mmol‚L-1.

chemical bonds during adsorption will change the distribution of the electrons around the corresponding atoms. As a consequence, the binding energy of the electrons can be shifted to a lower or higher level, which will provide information on the adsorption mechanism.28-29 To investigate the interactions between aromatic sulfonates and acrylic ester resin YWB and the adsorption mechanism of adsorbate on adsorbent, XPS studies of resin YWB before and after adsorption with different adsorption amounts of adsorbate on resins were conducted. The spectra of the YWB resin under various conditions are shown in Figure 5. The C 1s spectrum can be fitted with three peaks of binding energies at 285.0 (peak a), 287.15 (peak b), and 288.85 eV (peak c), respectively. Peak a is for the C-C or C-H carbon atoms in the polymer chain; peak b is for methylene carbon atoms bound to one oxygen (-CH2-O-), and peak c is for the carbonyl carbon atoms (-CO-O-).29 The area ratios of peaks c/b are found to increase with the increase of the adsorption amounts of adsorbate on resins. Before adsorption, the areas of peaks for b and c are similar, and the area ratio of b/c is 0.99. After adsorption, the areas of peaks for b and c changed significantly as described in Figure 5B-E, which should be attributed to the changes of the different forms of carbon atoms in carbonyl and ester functional groups on resin surfaces. When sulfonate ions of adsorbate are incorporated with the oxygen atoms of carbonyl or ester functional groups on adsorbent surfaces, electrons from these groups are drawn or pushed from the sulfonate functional groups, which change the intensity of the binding energy for the C 1s in 288.85 eV (peak of carbon atoms in -CO-O-) and C 1s in 287.15 eV (peak of carbon atoms in -CH2-O-). The changes of spectroscopy show that the functional groups on YWB surface make a contribution to the adsorption process. 3.4. Mechanism of Adsorption. The adsorption mechanisms of aromatic sulfonates onto XAD-4 and D-301 are evident according to the investigations mentioned above. Hydrophobic interactions and the ion exchange mechanism play prominent roles in their adsorption process, respectively. On the other hand, the conclusion can be made according to the adsorption behavior and the characterization of spectroscopy that the combination of both hydrophobic and other interactions are responsible for the adsorption mechanism of aromatic sulfonates onto acrylic ester resins. There are at least three different adsorption

mechanisms between ester functional groups and sulfonate groups, such as hydrogen bonding, electrostatic attraction, and ion exchange of the positively charged oxonium group. The adsorption mechanism between adsorbate and acrylic ester resin was generally understood as hydrophobic interactions, hydrogen bonding, and electrostatic attraction, which are thought to be important to the adsorption process.3,14-16,30 Little attention is paid to the formation and existence of the oxonium group in the adsorption process of acrylic ester resins. In fact, there are many discussions about the effect of the oxygen atom of the carbonyl group (sCdO), while the oxygen atom of the ester group (sCsOsC) is often neglected in argument.8-12,31-33 Corcia et al. observed that the graphitic structure of the Carbopack surface was contaminated by an oxygen complex having a chromenelike structure, which, in the presence of acidified water, was promptly rearranged to form benzpyrylium salts, the so-called oxonium group. These groups bearing positive charges enabled Carbpack to act as an anion exchanger as well as a nonspecific adsorbent.34-35 Altenbach and Giger also studied the existence of the oxonium group in a later paper.36 In fact, both oxygen atoms of carbonyl and ester groups have a lone pair or lone pairs of electrons that can bind a proton ion through an electron pair sharing to form a complex.28 Because of the strong attraction of the lone pair of electrons to the nucleus in an oxygen atom, in acidified solution, the hydrogen atoms will have a tendency to donate the lone pair of electrons for sharing with oxygen atoms to form oxonium groups. In a word, the adsorption mechanism of aromatic sulfonate onto acrylic ester resin may be ascribed to the combination of hydrophobic interaction and the forces between ester functional groups and the functional group of adsorbate. 4. Conclusions The acrylic ester resin YWB, which has a similar structure to that of XAD-7, was utilized as adsorbent to investigate the adsorption mechanism along with XAD-7, XAD-4, and D-301. The adsorption and elution behavior indicate that the matrix of the adsorbent and the structure of the adsorbate have an important effect on the adsorption capacity. The adsorption

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Figure 5. C 1s XPS of acrylic ester resin YWB: (A) before adsorption without adsorbate; (B) 6-NaDBS is adsorbate, and the adsorption amount is 0.95 mmol‚L-1; (C) 6-NaDBS is adsorbate, and the adsorption amount is 1.55 mmol‚L-1; (D) KN-R is adsorbate, and the adsorption amount is 0.44 mmol‚L-1; (E) KN-R is adsorbate, and the adsorption amount is 0.64 mmol‚L-1.

capacity of XAD-4 is significantly affected by the hydrophobic part of the adsorbate while the contrbution of the ion functional group of KN-R to the adsorption capacity of D-301 is especially important. Hydrophobic interaction and other mechanisms such as polar or electrostatic forces or hydrogen bonds play similarly important roles to the adsorption mechanisms of acrylic ester resins. FTIR and IR studies showed that oxygen atoms of carbonyl and ester groups make contributions to the adsorption process and the existence of oxonium groups is necessary to the adsorption mechanism of aromatic sulfonate onto acrylic ester resin.

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ReceiVed for reView November 28, 2006 ReVised manuscript receiVed July 25, 2007 Accepted July 26, 2007 IE0615281