Hyperbranched Poly(ether amine) (hPEA) - American Chemical Society

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Hyperbranched Poly(ether amine) (hPEA)/Poly(vinyl alcohol) (PVA) Interpenetrating Network (IPN) for Selective Adsorption and Separation of Guest Homologues Peng Zhang, Jie Yin, and Xuesong Jiang* School of Chemistry & Chemical Engineering, State Key Laboratory for Metal Matrix Composite Materials, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China S Supporting Information *

ABSTRACT: We here reported that hyperbranched poly(ether amine) (hPEA) and poly(vinyl alcohol) (PVA) interpenetrating network (hPEA/PVA-IPN) can be used for the selective adsorption and separation of guest homologues. A series of hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks (hPEA/PVA-IPNs) were fabricated by introducing poly(vinyl alcohol) chains into network of hyperbranched poly(ether amine), in which two independent networks of hyperbranched poly(ether amine) and poly(vinyl alcohol) were cross-linked through photodimerization of coumarin groups of hyperbranched poly(ether amine) and aldol condensation reaction between hydroxyl groups of poly(vinyl alcohol) and glutaraldehyde, respectively. The mechanical strength of interpenetrating networks can be enhanced by the introduction of poly(vinyl alcohol), and the tensile strength of interpenetrating networks increased with tens of times in compared with the pure hyperbranched poly(ether amine) network. The adsorption behavior of seven fluorescein dyes sharing with the same backbone and charge state onto hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks was then investigated in detail. Regardless of their charge states, these interpenetrating networks exhibited the quick adsorption to Rose Bengal (RB), Erythrosin B (ETB), Eosin B (EB), 4′,5′-dibromofluorescein (DBF), and 4,5,6,7-tetrachlorofluorescein (TCF), with high adsorption capacity (Qeq) and very low adsorption of Calcein (Cal) and fluorescein (FR). The adsorption process was found to follow the pseudo-second-order kinetics, and the introduction of poly(vinyl alcohol) has no obvious effect on the adsorption behavior in this study. The big difference in the adsorption is indicative of the selective adsorption of hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating networks to fluorescein dyes. Based on the unique selective adsorption, the separation of several mixtures of fluorescein dyes such as RB/Cal, RB/FR, ETB/FR, and ETB/Cal was achieved by using hPEA/ PVA-IPN as adsorbent.

1. INTRODUCTION The amphiphilic polymer materials with selective adsorption has been attracting much attention because it can be widely used in the applications such as water treatment,1−4 smart separation,5,6 temporally controlled release of drug,7,8 and sensor.9,10 For example, the recovery of valuable chemicals in the treatment of industrial wastewater can be realized by these polymer materials with the unique ability of selective adsorption.11−18 The selective adsorption of guest molecules is generally resulted from the difference in the interaction between the host polymer materials and different guest molecules. The fundamental investigation on the interaction between the host polymer materials and guest molecules reveals that the selective adsorption is usually determined by several main factors such as electrostatic interaction,19−21 hydrophobic interaction,22,23 π−π stacking,24−27 and topology structure.28−30 Based on these fundamental investigations, a series of host polymer materials such as unimolecular micelles, nano- and microgels, and hydrogels with the high selectivity have been developed. The Haag,31 Thayumanavan,32,33 and Wan34 groups reported amphiphilic polymer as supramolecular host for transferring various guest molecules from the aqueous phase to the organic phase with selectivity. Maskos prepared the © XXXX American Chemical Society

amphiphilic poly(organosiloxane) nanoparticles, in which the hydrophilic dyes can be loaded selectively depending on their charge and size.35 In addition to these nanomaterials, macroscale hydrogels and polymer network with selective adsorption have been also developed very recently, which are very potential in practical separation. Molina fabricated the urease−poly(ethylene oxide) hybrid matrix and found that it can adsorb selectively and separate anionic orange II from its mixture with cationic methylene blue (MB) in water.36 Broer groups reported a novel nanoporous polymer network prepared from smectic liquid crystals, which possesses the charge and size-selective adsorption to the hydrophilic dyes.37 Smith developed a versatile supramolecular hydrogel which demonstrates selective adsorption of dyes with opposite charge from aqueous solution.38 In these studies, the selective adsorption and separation is based on the difference in charge and size of guest molecules. Because of the same charge and similar structure, however, it is very challenging to prepare polymer Received: July 20, 2014 Revised: September 14, 2014

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dx.doi.org/10.1021/la502869n | Langmuir XXXX, XXX, XXX−XXX

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in Table 1. The introduction of PVA to form the IPN is expected to enhance the mechanical strength of hPEA network.

materials with ability to adsorb selectively and separation of guest homologues. Recently, we reported that the responsive microgel prepared from hyperbranched poly(ether amine) (hPEA-mGel) exhibited the unique selective adsorption to fluorescein dyes with the same charge and similar structure.16 The hydrophobic interaction, rather than electrostatic interaction, was found to determine the interaction between hPEA-mGel and fluorescein dyes, resulting in the selectivity to these guest homologues. To extend these hPEA-based polymer materials into application of separation, we here designed hyperbranched poly(ether amine) and poly(vinyl alcohol) interpenetrating network (hPEA/PVAIPN), in which two independent network of hPEA and PVA can be cross-linked by the photodimerization of coumarin moieties and aldol condensation reaction, respectively (Scheme 1). The introduction of PVA independent network to form IPN

Table 1. Composition and Mechanical Properties of hPEA/ PVA-IPNs sample

composition hPEA/PVA (wt)

tensile stress (MPa)

elongation at break (%)

elasticity modulus (MPa)

hPEA/PVA-1/0-IPN hPEA/PVA-4/1-IPN hPEA/PVA-2/1-IPN hPEA/PVA-1/1-IPN SA-hPEA/PVA-1/1-IPN

1:0 4:1 2:1 1:1 1:1

2.0 4.2 9.7 17.3 41.1

220 8.4 6.2 4.5 24

1.3 91.2 154.8 580.6 581.9

The reason to choose PVA as reinforcement is that PVA is an inexpensive material and has a good mechanical strength. More importantly, PVA has no obvious effect on the unique selective adsorption of poly(ether amine) materials to guest molecules.17 Two types of hyperbranched poly(ether amine)s (hPEA-EC and SA-hPEA-EC, Scheme 1) were used for fabrication of IPNs. The introduction of carboxyl groups (SA) is beneficial for understanding the effect of electrostatic interaction on the adsorption of the obtained IPNs to guest molecules. The presence of coumarin moieties provides the ability to formation of hPEA cross-linked network through UV-lightinduced dimerization. The process of photodimerization of coumarin moieties in hPEA was traced by UV−vis spectra. As shown in Figure 1a, upon the exposure of 365 nm UV light, the peak ascribed to the adsorption of coumarin decreased gradually, suggesting the dimerization of coumarin. After formation of the first hPEA network, the film of hPEA/PVA was then immersed in acetone solution of GA. The formation of the second PVA network in the presence of GA was

Scheme 1. (a) Chemical Structure of Coumarin-Capped Hyperbranched Poly(ether amine)s: hPEA-EC and SAhPEA-EC; (b) Strategy for Fabrication of hPEA/PVA-IPN through Photodimerization of Coumarin Groups and Adol Condensation Reaction

is expected to enhance the mechanical strength of hPEA network,39,40 which is of importance in practical application. The resulting hPEA/PVA-IPN exhibited the enhanced mechanical strength, which was increased with tens of times in comparison to the single network of hPEA. The adsorption behavior of fluorescein dyes onto hPEA/PVA-IPN was then investigated systematically. Interestingly, hPEA/PVA-IPN possesses the ability of selective adsorption to fluorescein dyes and can be used in the separation of their mixtures in aqueous solution.

2. RESULTS AND DISCUSSION Fabrication and Characterization of hPEA/PVA-IPN. The whole strategy for fabrication of hPEA/PVA-IPN is shown in Scheme 1. hPEA/PVA-IPN is composed of two independent cross-linked networks of hPEA and PVA. The first network of hPEA was fabricated through the photodimerization of coumarin moieties of hPEA under UV-irradiation, while the second network of PVA was cross-linked chemically through aldol condensation reaction of hydroxyl groups of PVA and aldehyde groups of GA. Through this way, five hPEA/PVAIPNs with different compositions were prepared and are listed

Figure 1. To trace cross-linking process of hPEA/PVA-1/1-IPN. (a) UV−vis absorption spectra of hPEA-EC photodimerization kinetics at different irradiation times by 365 nm UV light and (b) FT-IR spectra of hPEA/PVA-1/1 network cross-linked with 100 mM GA in the acetone at 25 °C. B


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confirmed by FT-IR. As shown in Figure 1b, the intensity of two peaks at 2870 and 1135 cm−1 assigned to the stretching C−H and C−O−C from cyclic ether,41 respectively, increases with the increasing immersing time. The appearance of these two peaks provides an obvious evidence for the formation of acetal bridges, indicating that PVA chains were cross-linked. The resulting hPEA/PVA-IPNs are hydrophilic and can be swelled in water, but not soluble in water. There is no weight loss after immersion in water for 24 h, suggesting that two independent networks of hPEA and PVA were well crosslinked. The internal morphology of hPEA/PVA-IPN before and after swelling in water checked by SEM (Figure S2), which revealed that there are many pores with different sizes formed in hPEA/PVA-IPN after swelling. The occurrence of pores makes it easy to transport small molecules such as water and dyes across the networks. XRD measurements were performed to further analyze the state of the hPEA/PVA-IPNs (Figure S3). The pure cross-linked network of pure PVA exhibits a semicrystalline structure with a large peak at 2θ = 19.2°, while with the increasing content of hPEA only amorphous peak at 2θ = 22.3° appears in XRD spectra of hPEA/PVA-IPNs. This result indicates that two independent networks of hPEA and PVA mixed homogeneously, which was further supported by the following differential scanning calorimeter (DSC) analysis. Figure 2 presents DSC curves of the resulting hPEA/PVAIPNs as well as the cross-linked single networks of hPEA and

Figure 3. Typical stress−strain curves of hPEA/PVA-IPNs and SAhPEA/PVA-IPN.

PVA second independent network, the tensile strength of hPEA/PVA-IPNs was enhanced obviously. The tensile strength increases to 17.3 MPa with the increasing content of PVA from hPEA/PVA-4/1-IPN to hPEA/PVA-1/1-IPN, suggesting that the second PVA network dominated the strength of hPEA/ PVA-IPNs. The elongation at break decreases from hPEA/ PVA-4/1-IPN to hPEA/PVA-1/1-IPN. For convenient comparison, the values of stresses, elongation at break, and elasticity modulus are summarized in Table 1. It should be noted that both tensile strength and elongation of SA-hPEA/PVA-1/1IPN are 41.1 MPa and 22%, respectively, much higher than that of hPEA/PVA-1/1-IPN. This might be due to the introduction of SA groups, which leads to the strong interaction between two independent networks of hPEA and PVA via hydrogen bond between carboxyl and hydroxyl groups, consequently resulting in the enhanced mechanical performance. Such enhanced mechanical strength by the introduction of PVA network is beneficial for the stability of hPEA/PVA-IPNs in the following experiments of adsorption and separation of guest molecules. Selective Adsorption Behavior of Fluorescein Dyes. The adsorption behavior of the obtained hPEA/PVA-IPNs to a family of hydrophilic fluorescein dyes was studied. As shown in Scheme 2, seven hydrophilic fluorescein dyes were chosen as the guest homologues because they share the same backbone and are all negative-charged in aqueous solution.42,43 The adsorption experiments were conducted in aqueous solution, in which the initial concentration of dyes and hPEA/PVA-IPN adsorbents were fixed at 100 μM and 1.0 mg mL−1, respectively. After addition of hPEA/PVA-1/1 for 24 h, the color of the solutions of RB, ETB, EB, TCF, and DBF turned obviously colorless, and the adsorbents turned colored accordingly, indicating that hPEA/PVA-1/1-IPN can adsorb these fluorescein dyes (Figure S4). On the contrast, the color of the solutions of FR and Cal did not change as significantly, suggesting that only a small part of FR and Cal in solution was adsorbed by hPEA/PVA-1/1-IPN. Taking ETB and Cal as examples, it can be seen with the naked eye that most of the ETB was adsorbed by hPEA/PVA-1/1, but Cal still stayed in solution (Figure 4). UV−vis spectra of fluorescein dye solution before and after addition of hPEA/PVA-1/1-IPN for 24 h were recorded for the adsorption of dyes. Nearly 100% ETB was adsorbed by hPEA/PVA-1/1-IPN, while less than 30% Cal was adsorbed. The adsorption capacities of the interpenetrating networks toward seven fluorescein dyes were determined by the UV−vis spectra of dye’s solution before and after adsorption. The saturated adsorption capacities (Qeq), which is one of the

Figure 2. DSC thermograms of hPEA/PVA-IPNs and cross-linked PVA as reference. The scans were run at a heating rate of 10 °C/min.

PVA as references. The pure hPEA network takes a glass transition (Tg) at low temperature around −0.3 °C, while PVA network cross-linked by GA exhibits the high Tg around 55.0 °C. As for all hPEA/PVA-IPNs, only one obvious glass transition can be founded in DSC curves, suggesting that the resulting interpenetrating network is homogeneous, and both hPEA and PVA chains can intersperse with each other in a molecular scale. Meanwhile, the introduction of PVA chain leads to a remarkable improvement in the glass transition temperature of hPEA/PVA-IPNs. With the increasing content of PVA from 0 to 50 wt %, Tg of hPEA/PVA-IPNs increased from −0.3 to 27.8 °C. It should be noted that SA-hPEA/PVA1/1-IPN exhibits a higher glass transition of 33.4 °C than that hPEA/PVA-1/1-IPN (27.8 °C). This might be ascribed to the hydrogen-bond interaction between hPEA and PVA independent networks caused by the introduction of carboxyl groups. Tensile strength tests were performed to investigate the mechanical properties of the resulting hPEA/PVA-IPNs. As shown in Figure 3, the tensile strength of pure hPEA crosslinked network is very low (∼2.0 MPa). After introduction of C


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Scheme 2. Structure and Abbreviation of Seven Fluorescein Dyes

Figure 4. UV−vis spectra of ETB (a) and Cal (b) before and after adsorption by hPEA/PVA-1/1-IPN for 24 h. Inset pictures are photos of solution of ETB and Cal before and after adsorption by hPEA/PVA-1/1-IPN for 24 h. (c) Saturated adsorption capacities of hPEA/PVA-1/1-IPN, hPEA/ PVA-2/1-IPN, hPEA/PVA-4/1-IPN, and SA-hPEA/PVA-1/1-IPN for fluorescein dyes at 25 °C.

hPEA/PVA containing amino groups which is more positively charged, indicating that the interaction between the host hPEA/PVA-IPN and guest fluorescein dyes is independent of the electrostatic interaction. The adsorption behavior of SAhPEA/PVA-IPN to seven fluorescein dyes is different from hPEA/PVA-IPN: it exhibits strong adsorption to ETB and RB with high Qeq, while it possesses low Qeq to EB, TCF, DBF, FR, and Cal. This indicated that the adsorption behavior of hPEA/ PVA-IPN to fluorescein dyes can be tuned by introducing functional groups to hPEA. The different selective adsorption caused by the introduction of SA provides hPEA/PVA-IPNs more opportunity in separation of guest molecules. To further understand the interaction between the interpenetrating networks and dyes, adsorption kinetics of seven

important parameters for adsorbents in practical applications, were measured when the adsorptions reached equilibrium. As shown in Figure 4c, hPEA/PVA-1/1-IPN membrane exhibited high Qeq toward RB, ETB, and EB, while they possessed low Qeq to FR and Cal. The similar adsorption behavior of hPEA/ PVA-2/1-IPN and hPEA/PVA-4/1-IPN to these seven fluorescein dyes was also observed. The experiments proved that hPEA/PVA-IPN exhibits strong interactions with RB, ETB, and EB but weak interactions with FR and Cal even though they have similar structures. The large difference in Qeq suggests that hPEA/PVA-IPN can adsorb the fluorescein dyes selectively regardless of their charge state and similar structure. Compared with other six fluorescein dyes, Cal has more negative charges, but it shows a weaker interaction with the D


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fluorescein dyes by hPEA/PVA-1/1-IPN and SA-hPEA/PVA1/1-IPN were investigated in aqueous solution (Figure 5). For

onto hPEA/PVA-IPN conducted in the solution under different pH 5, 7.2, and 8 (Figure S5). No significant influence of pH on dye adsorption for RB can be observed even in the wide pH range from 5 to 8. Taking the structures of fluorescein dyes into consideration, halogen substituents on the fluorescein backbone may play an important role, which might be explained by the increasing hydrophobic structure which is helpful for the interaction with IPN. Therefore, we proposed that the hydrophobic interaction may play key roles in the interaction between hPEA/PVA-IPN and fluorescein dyes. A pseudo-second-order equation was used to analyze the adsorption kinetics to further investigate the adsorption mechanism of dyes onto the interpenetrating networks. It was found that pseudo-second-order equations fitted well to the whole range of the contact time, and the correlation coefficient (R2) is very high (Figure S6 and Table S1). The value of Qeq,exp is closed to that of Qeq,cal, further indicating that the pseudosecond-order model applied to the adsorption of dyes onto IPNs. By comparing the Qeq of dyes with high adsorption capacity, it might be concluded that Qeq can reflect the strength of interaction between interpenetrating networks and dyes: large Qeq means a strong affinity. The big difference in Qeq implied that hPEA/PVA-IPNs possess the unique selective adsorption to several of fluorescein dyes. We further conducted an isotherm study to investigate how hPEA/PVA-IPNs interact with the hydrophilic dyes and estimate the characteristics of the adsorption system. Three dyes, RB, FR, and Cal, and two IPNs, hPEA/PVA-1/1-IPN and SA-hPEA/PVA-1/1-IPN, were chosen for the isotherm study because the hPEA/PVA-1/1-IPN and SA-hPEA/PVA-1/1-IPN exhibited a completely different affinity toward RB and Cal, RB, and FR, respectively. The Langmuir and Freundlich isotherm models were used to analyze the equilibrium adsorption data (Figure S7 and Table S2). As shown in Figure S7, it can be seen clearly that the Langmuir model is suitable for describing the adsorption equilibrium of RB by the two IPNs, suggesting that charge state has no obvious effect on interaction between IPNs and dyes. It can be also found that the adsorption of Cal with low Qeq appropriates for the Freundlich model. Based on the above isotherm study results, it can be concluded that the

Figure 5. Adsorption capacity Qt versus time curves for the adsorption of seven dyes: (a) hPEA/PVA-1/1-IPN; (b) SA-hPEA/PVA-1/1-IPN.

the dyes with high Qeq such as RB, ETB, EB, DBF, TCF (Figure 5a) and RB, ETB (Figure 5b), the adsorption capacity increased rapidly initially and then continued to increase with the contact time at a relatively slow rate. In contrast, the adsorption rate and capacity of Cal by the two IPNs are much lower regardless of its more negative charges, indicating that the electrostatic interaction between dyes and IPNs has no obvious effect on the adsorption kinetics. This is consistent with the experiments of the saturated adsorption capacity (Qeq), and it can be further supported by the adsorption experiments of RB

Figure 6. One-pot separation of mixed dyes RB-Cal in aqueous solution. (a) Photograph of RB-Cal before and after separation for 36 h by using hPEA/PVA-1/1-IPN at 25 °C. (b) UV−vis spectra of RB-Cal during separation experiment. (c) Dye concentration of [RB] and [Cal] and dye concentration ratio of the mixed dyes in solution ([RB]/[Cal]) vs time. E


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Figure 7. One-pot separation of mixed dyes RB-FR in aqueous solution. (a) Photograph of RB-FR and before and after separation for 36 h by using SA-hPEA/PVA-1/1 IPN at 25 °C. (b) UV−vis spectra of RB-FR during separation experiment. (c) Dye concentration of [RB] and [FR] and dye concentration ratio of the mixed dyes in solution ([RB]/[FR]) vs time.

orange became yellow of FR and the SA-hPEA/PVA-1/1-IPN immersed in solution turned red, suggesting that SA-hPEA/ PVA-1/1 IPN adsorbed RB selectively from the mixture RB-FR (Figure 7a). As shown in Figure 7b,c, the concentration of FR kept almost unchanged with the increasing contact time, while the concentration of RB in solution decreased obviously from the initial 10 μM to about 0.4 μM. In other words, the purity of Cal in the solution increased from the initial 50% to 96% after separation for 36 h. The separation of other mixtures of dyes such as ETB-Cal and ETB-FR was also achieved through the same approach by using hPEA/PVA-1/1-IPN and SA-hPEA/PVA-1/1 IPN, respectively (Figures S8 and S9). These experiments suggest that the fluorescein dyes with similar structures can be separated in the presence of hPEA/PVA-IPN by one-pot separation. The introduction of SA groups changes the selectivity of hPEA/PVA-IPN to fluorescein dyes and broadens the scope of the guest homologues which they can separate. In brief, these works might expand range of application of hPEA materials in separation and purification. Finally, the reusability of the hPEA/PVA-IPNs was demonstrated because of its significance in practical application. Immersed in NaOH aqueous solution (2 mg mL−1) and dialyzed for 48 h, the dyes can be removed from hPEA/PVA-1/1-IPN separation agents, and hPEA/PVA-1/1-IPN get to regenerate, which is convenient for their regeneration (Figure 8). It is notable the shapes of the IPNs can always be kept in the complete separation−regeneration tests due to their good mechanical performance.

chemisorption dominates in the adsorption of RB with a strong affinity onto the IPNs regardless of charge state.44 Separation of the Mixture of Dyes. The characteristics of unique selective, enhanced mechanical strength, and crosslinked structure resistance to solvent provide the hPEA/PVAIPNs in the separation of guest homologues. Fluorescein dyes with high Qeq can be adsorbed by hPEA/PVA-IPNs from aqueous solution, while dyes with low Qeq are expected to stay in solution. Because of the big difference in Qeq of RB and Cal, the mixture of RB-Cal was first separated by using hPEA/PVA1/1-IPN as adsorbent. The separation experiments were conducted by adding 10 mg hPEA/PVA-1/1-IPN into 10 mL solution of RB-Cal mixture (concentrations of RB and Cal are 10.0 μM). As shown in Figure 6a, the color of solution gradually turned from red to yellow with the contact time increasing. After 36 h, the color of the solution became yellow of Cal, while hPEA/PVA-1/1-IPN immersed in solution turned red of RB, suggesting that hPEA/PVA-1/1-IPN adsorbed RB selectively from the mixed solution of RB and Cal. UV−vis spectra were used to trace the whole separation process to check the change of dye’s concentration in solution. As shown in Figure 6b,c, the concentration of Cal kept nearly unchanged with the increasing contact time, while the concentration of RB in solution decreased obviously from the initial 10 μM to almost zero. In other words, the purity of Cal in the solution increased from the initial 50% to 100% after separation for 36 h. Through the same approach, the other mixture of RB-Cal can be also separated in the presence of hPEA/PVA-1/1-IPN. By using hPEA/PVA-1/1-IPN as absorbent, however, it is incapable of separating RB and FR from their mixture solution because hPEA/PVA-1/1-IPN possess the similar adsorption behavior to RB and FR. As the introduction of SA groups causes the big difference in Qeq between RB and FR (Qeq,RB and Qeq,FR are 5.59 and 0.37 μmol/L, respectively), we proposed that SA-hPEA/PVA-1/1-IPN allows for separation of RB-FR mixture, which cannot be done by hPEA/PVA-1/1-IPN. To verify this idea, the separation of RB−FR mixture is conducted through the same approach in the presence of SA-hPEA/PVA1/1-IPN. After addition of SA-hPEA/PVA-1/1-IPN for 36 h, the color of the mixture solution of RB and FR turns from

Figure 8. Regeneration for hPEA/PVA-1/1-IPN absorbing ETB through dialysis in NaOH aqueous solution for 48 h. F


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Differential scanning calorimetry (DSC, Model 6200, Seiko, Japan) was used to measure the glass transition temperature of the samples. Tensile stress−strain measurements of IPNs were conducted at room temperature with an Instron 4465 instrument at a cross-head speed of 6 mm/min. The samples were cut into strips of 30 mm × 4 mm with a razor blade, and five strips were measured for each sample. Adsorption Experiments. Seven fluorescein dyes with similar structures were chosen for the adsorption experiments. Their structures are shown in Figure S3. The initial concentration of all dyes was 100 μM; 10 mg of four dried absorbents (hPEA/PVA-1/1IPN, hPEA/PVA-2/1-IPN, hPEA/PVA-4/1-IPN, SA-hPEA/PVA-1/1IPN) was added into 10 mL of the solution of dyes in buffered aqueous media at pH 7.2 for 24 h to reach their adsorption equilibrium at 25 °C. The equilibrium adsorption capacity (Qeq) of dyes is defined as follows:47

3. CONCLUSION In this work, we demonstrated that hyperbranched poly(ether amine) (hPEA) and poly(vinyl alcohol) (PVA) interpenetrating network (hPEA/PVA-IPN) possess ability for the selective adsorption and separation of guest homologues. By introducing PVA chains into network of hPEA, a series of hPEA/PVA-IPNs were fabricated in which two independent networks of hPEA and PVA were cross-linked through photodimerization of coumarin groups of hPEA and aldol condensation reaction between hydroxyl groups of PVA and GA, respectively. The mechanical strength of hPEA/PVA-IPNs can be enhanced by the introduction of PVA, and the tensile strength of hPEA/ PVA-1/1-IPN increased to tens of times. The detailed investigation on adsorption behavior of hPEA/PVA-IPNs to seven fluorescein dyes revealed that hPEA/PVA-IPNs possess the unique selective adsorption to fluorescein dyes regardless of their charge states, and the adsorption process follows the pseudo-second-order kinetics. The hydrophobic interaction may play key roles in the interaction between IPNs and fluorescein dyes. Based on the unique selective adsorption, the separation of several mixtures of fluorescein dyes such as RB/ Cal, RB/FR, ETB/FR, and ETB/FR was achieved in the presence of hPEA/PVA-1/1-IPNs as adsorbent. The introduction of carboxyl groups into hPEA changes the selective adsorption of hPEA-PVA-IPNs and broadens the scope of the fluorescent dyes which they can separate. In addition, hPEAPVA-IPNs are easily regenerated and can keep the shapes during the complete separation−regeneration tests. It is believed that hPEA-PVA-IPNs provide a novel alternative in separation and purification of guest homologues.

Q eq =

C0 − Ceq M

V

(1)

where Qeq (μmol/g) is the amount adsorbed per gram of interpenetrating networks at equilibrium, C0 is the initial concentration of dyes in the solution (μmol/L), Ceq is the concentration of dyes at equilibrium (μmol/L), V is the volume of the solution (L), and M is the mass of interpenetrating networks used (g). For the adsorption kinetics tests, the initial concentration of dyes was 20 μM, and the volume of the solution of dyes is 4 mL. 10 mg absorbents including hPEA/PVA-1/1-IPN and SA-hPEA/PVA-1/1IPN were added into the prepared solution of dyes. UV−vis spectra were used to trace the adsorption behaviors and evaluated the adsorption capacity at different absorption times. The concentration of dye was calculated by absorption at maximum absorption wavelength (λmax). Separation Experiments. The separation experiments were carried out in mixture of RB-Cal, ETB-Cal, RB-FR, and ETB-FR in buffered aqueous media at pH 7.2. The initial concentrations of both dyes and IPN adsorbents were fixed at 10 μM and 1.0 mg mL−1, respectively. UV−vis spectra were used to trace and determine the concentration of dyes in the solution at 25 °C.

4. EXPERIMENTAL SECTION

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Fabrication of hPEA/PVA-IPNs. The coumarin-capped hyperbranched poly(ether amine)s (hPEA-EC and SA-hPEA-EC) used for fabrication of hPEA/PVA-IPNs were synthesized according to our previous report (Scheme S1 and Figure S1).45,46 The hPEA/PVAIPNs were prepared based on a solution casting method. The hPEAEC or SA-hPEA-EC was dispersed into PVA aqueous solution with the designed feed. The total solid content of hPEA-EC and PVA was kept at about 0.033 g/mL. The solution was then added several drops of hydrochloric acid and then stirred for 24 h to form homogeneous hPEA/PVA solution. Then, the prepared hPEA/PVA solution were cast onto a plastic Petri dish (70 mm × 70 mm) and dried at 30 °C for 24 h in a drying oven to obtain hPEA/PVA membrane. The membrane was first photo-cross-linked by irradiation of 365 nm UV light for 10 h and then was immersed in 100 mL acetone solution with 0.1 M glutaraldehyde (GA) and 0.01 N HCl for 24 h for the second cross-linking. The obtained IPNs were washed by acetone several times and dried at 30 °C for 24 h in a drying oven. Characterization. 1H NMR spectra were acquired by a Varian Mercury Plus 400 MHz spectrometer, using DMF as the solvent and using TMS as an internal standard at room temperature. UV−vis spectra were recorded on a UV-2550 spectrophotometer (Shimadzu, Japan) at room temperature. The samples at different irradiation times were prepared by spinning hPEA/PVA solution onto a quartz plate whose diffuse reflectance UV−vis spectrum was collected as the background. Fourier transform infrared spectroscopy (FT-IR) spectra were recorded on a PerkinElmer Paragon1000 FT-IR spectrometer. Scanning electron microscopy (SEM) was carried out on a JSM7401F electron microscope (JEOL, Japan) at 5 kV, which showed the sizes and images of the interpenetrating network. All the samples were coated with gold particles for observation. X-ray diffraction (XRD) patterns were recorded on a D/max-220 0/ PC (Japan Rigaku Corp.) using Cu Kα radiation (λ = 1.5418 Å).

ASSOCIATED CONTENT

S Supporting Information *

Experimental details; Figures S1−S9 and Tables S1, S2. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel +86-21-54743268; Fax +86-21-54747445; e-mail [email protected] (X.J.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Nature Science Foundation of China (21174085, 21274088, and 51373098), Education Commission of Shanghai Municipal Government (12ZZ020), for their financial support. X. S. Jiang is also supported by the NCET-123050 Project.

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REFERENCES

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Hyperbranched Poly(ether amine) (hPEA) - American Chemical Society

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