Facile Preparation of Novel Ion-Imprinted Polymers for Selective

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Facile preparation of novel ion-imprinted polymers for selective extraction of Br(I) ions from aqueous solution Qi Wang, Xueting Liu, Minghui Zhang, Zhuo Wang, Zhiyong Zhou, and Zhongqi Ren Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 25 Mar 2019 Downloaded from http://pubs.acs.org on March 25, 2019

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Industrial & Engineering Chemistry Research

Facile preparation of novel ion-imprinted polymers for selective extraction of Br(I) ions from aqueous solution Qi Wang, Xueting Liu, Minghui Zhang, Zhuo Wang, Zhiyong Zhou*, and Zhongqi Ren* College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China ABSTRACT: A novel Br(I) ion-imprinted polymer was prepared for selective extraction of Br(I) ions from aqueous solution. Chitosan modified by aluminum nitrate and glutaraldehyde were selected as monomer and cross-linking reagent. Effects of cross-linking reagent dosage, cross-linking time and aluminum nitrate dosage on adsorption performances of prepared polymers were studied. The prepared polymers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and zeta potential. The results confirmed the successful cross-linking and polymerization of both Br(I)-IIPs and non-imprinted polymers. Effects of adsorption conditions like pH, adsorption time and initial Br(I) concentration on adsorption performances of Br(I)IIPs were investigated too. The maximum adsorption capacity of Br(I)-IIPs reached up to 18.89 mg g-1 with the initial Br (I) ion concentration of 100 mg L-1 at pH 4. Freundlich isotherm and pseudo-second-order kinetic models are suitable for describing the adsorption process of Br(I)-IIPs. The prepared Br(I)-IIPs showed high relative selectivity for all Br(I)/competing ions. The prepared polymer also had good reusability. KEYWORDS: Specific binding site; Recognition; Selective recovery; Ion-imprinted 1 ACS Paragon Plus Environment

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polymer; Reusability 1. INTRODUCTION Bromine is one of the important chemical raw materials and bromine industry is the main branch of marine chemical industry. Various bromine compounds, such as inorganic bromides, bromates, and bromine-containing organic compounds, have special values in the development of national economy, science and technology. Bromine and its compounds are widely applied in various fields, such as refrigeration, sterilization, dyeing, flame retardant, and drilling fluid.1,2 Bromine mainly exists in various aqueous solutions, such as underground brine, salt lake brine, and ocean.3-5 Since 99% of the bromine elements exists in seawater, bromine is named as "marine element". With the increasing demand for bromine, the development of efficient extraction method for bromine from seawater has become the research hot topic. Nowadays, various methods have been developed for extracting bromine from seawater, such as gaseous membrane, air blowing, agitated bulb membrane absorption, ion exchange, emulsion liquid membrane, and adsorption, etc.6-10 Among them, the air blowing method was the mainstream method for extracting bromine from seawater. However, this method has the disadvantages of large equipment, high consumptions of energy and fresh seawater resources. In addition, no successful examples of large-scale applications can be found due to various shortcomings of other methods. Therefore, it is urgent to develop a new efficient method for extracting bromine from seawater. To date, adsorption method is known to be one of the most effective and reliable ion 2 ACS Paragon Plus Environment

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separation methods, which can be used for selective and efficient separation of bromine ions from seawater. In terms of adsorption mechanism, chemical adsorption should have better adsorption performance than physical adsorption of bromine from seawater. Hence, it is a correct way to find an adsorbent with excellent performance for directionally chemical adsorption of bromine ions. Molecular imprinting is a technique to synthesize specific polymers with high selectivity toward target template molecule. Molecularly imprinted polymers (MIPs) show some advantages like easy preparation, specific recognition, high selectivity and reusability, which make it have a widely applications.11 Ion imprinting technique can form specific recognition sites for selective separation of various ions.12 Ion-imprinted polymer (IIP) is prepared with anion or cation as template, which interacts with functional monomer by electrostatic and coordination effects. After the cross-linking polymerization, the template ions are removed to obtain a rigid polymer with specific three-dimensional recognized binding cavities, which have similar size and shape for template ions, leading to obtaining high specific selectivity to the target ions.13-15 Nowadays, ion-imprinted polymer as favorable adsorbent is more and more used in the separation and enrichment of metal ions owing to its easy synthesis, thermal and chemical stabilities and high selectivity. Chitosan derived from the deacetylation of chitin is believed to be the second most common polysaccharide after cellulose. Besides, chitosan is also the main constituent of the crusts which consists of some crustacean animals like shrimp and crabs.16 Chitosan is hydrophilic, biodegradable and harmless to organisms. In addition, chitosan 3 ACS Paragon Plus Environment


can be also easily chemically derived and has a variety of amino acids and hydroxyl groups which can chelate heavy metals.17 Therefore, chitosan is a very promising chelating material. However, some disadvantages, such as easy swelling, low solubility under acidic condition and unsatisfactory mechanical properties, greatly limit the application of chitosan as an adsorbent.18 Hence, many studies have focused on chemical modification of chitosan for improving selectivity and mechanical properties for wider use.19 Over the past few decades, ion-implantation technique has been used to prepare cross-linked metal complex chitosan, in which metallization was used as both template and modifier for cross-linking. A large number of metal ion imprinting chitosan material has been synthesized by using Ca2+,20 Cu2+,21 Ni2+,22 Co2+,23 Pb2+,24,25 Hg2+,26 Ru3+,27 and other template ions. Compared with non-imprinted material, it shows better adsorption performance. However, few reports on the preparation of ionimprinted polymers with anion as template ion can be found. This is probably because that anions have relatively large ionic radii and are sensitive to pH.28 Organic anions were mainly used as template ions in preparation of anion-imprinted polymers, such as carboxylic acid root anion, phosphate ion, organic sulfonic acid root anion, and so on.29,30 Only a few kinds of inorganic anions like thiocyanate and its derivatives and chromium anions were used as template ions.31-33 Therefore, the preparation of an ionimprinted polymer with bromide as template ion is a novel idea for recovery of bromine ions from seawater. In this work, Br(I)-IIPs were synthesized with chitosan modified by aluminum nitrate as monomer and glutaraldehyde as cross-linking reagent for extraction of Br(I) 4 ACS Paragon Plus Environment

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ions from aqueous solution. The prepared Br(I)-IIPs were characterized by Fouriertransform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analyzer (TGA) and zeta potential. Effects of adsorption time, initial Br(I) ion concentration and initial pH on adsorption behavior of bromine ions were investigated. In addition, the thermodynamics and kinetics properties of the adsorption process by Br(I)-IIPs were also investigated for exploring the adsorption mechanism. Finally, the reusability and stability of the prepared Br(I)-IIPs were investigated. 2. EXPERIMENTAL SECTION Material. Aluminium nitrate nonahydrate (Al(NO3)3·9H2O), chitosan, potassium bromide (KBr), potassium chloride (KCl) and potassium sulfate (K2SO4) were supplied from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). Potassium iodide (KI), potassium fluoride (KF) and glutaraldehyde were supplied from Macklin Biochemical Co. Ltd (Shanghai, China). Sulfuric acid (H2SO4), 30% hydrogen peroxide and carbon tetrachloride (CCl4) were purchased from Beijing Chemical Works (Beijing, China). All reagents and solvents were analytical grade and used without further purification. Preparation of Br(I)-IIPs. Preparation of Modified Chitosan. 2.0 g chitosan was added to 50 mL aqueous solution containing a certain concentration of Al(NO3)3·9H2O and the mixture was continues stirred at room temperature for 8 h. Then, the obtained product was washed with deionized water and finally dried in vacuum at 50 ℃ for 8 h. Modified chitosan was grinded and screened to 0.05-0.10 mm for reserve. 5 ACS Paragon Plus Environment


Preparation of Ion-Imprinted Polymer. Firstly, 0.1191 g potassium bromide was added to 1000 mL deionized water and then dilute sulfuric acid was added to the mixture until the final pH reached 5.0±0.05. After that, 25 mL of the mixture was taken out and added to a conical flask for dissolving 0.5 g modified chitosan with continuously stirring for 20 min and then glutaraldehyde was added. The reaction system was shaking for a period of time at room temperature. Finally, the obtained polymers were washed with 0.01 mol L-1 sodium hydroxide solution for leaching template ions completely. After that, the obtained product was washed with deionized water and dried in vacuum at 50 ℃ for 24 h. The complete procedure for the preparation of Br(I)-IIPs is shown in Figure 1. As a control, the non-imprinted polymers (NIPs) were prepared by using the same procedure just without the addition of Br(I) ions. Characterization. The FT-IR characterizations of Br(I)-IIPs and NIPs were performed on a Shimadzu 8000-FT-IR Spectrophotometer (Shimadzu, Japan). The particle morphologies of Br(I)-IIPs and NIPs were observed on a S-4700 SEM (Hitachi, Japan). The element compositions of Br(I)-IIPs before and after elution were obtained on a ESCALAB 250XI XPS analyzer (Thermo Fisher, USA). A TG209C analyzer (Netzsch, Germany) was used for analyzing the thermodynamic property of Br(I)-IIPs in a dynamic N2 atmosphere. The zeta potential of Br(I)-IIPs was analyzed on a ZS90 zeta potentiometer (Zetasizer Nano, UK). Adsorption Experiment. The prepared polymer was first added to a 50 mL conical flask containing 20 mL Br(I) ion solution. The pH of the solution was adjusted from 3.0 to 8.0 by adding 0.01 mol L-1 H2SO4 or NaOH solution. Then adsorption 6 ACS Paragon Plus Environment

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experiments were conducted with 210 rpm continues stirring at room temperature. After that, the concentration of Br(I) ions was analyzed by taking out the samples. The adsorption capacity can be calculated using the equation below, 𝑄=

(𝐶0 ― 𝐶e)𝑉

(1)

𝑚

where C0 represents the initial Br(I) concentrations, Ce represents the equilibrium Br(I) concentration, V represents the solution volume, m represents the added dosage of Br(I)-IIPs, Q represents the adsorption capacity of Br(I)-IIPs. The selectivity of Br(I)-IIPs was studied by batch experiments. The mixture of Br(I)/M(I) (M = F, Cl or I) with the same concentrations of Br(I) and M(I) ions was prepared. 20 mg Br(I)-IIPs were added to 20 mL of the mixture containing 80 mg L−1 Br(I)/F(I), Br(I)/Cl(I) or Br(I)/I(I). Then the mixture was continuously stirred for adsorption at 25℃. The distribution ratio Kd and selectivity factor k can be calculated using the equations below, 𝑄

(2)

𝐾d = 𝐶e 𝑘=

𝐾d(Br(I))

(3)

Kd(M) 𝑘(𝐼𝐼𝑃𝑠)

(4)

k′ = 𝑘(𝑁𝐼𝑃𝑠)

Analysis. The Br(I) ion concentration in aqueous solution was determined by UVvisible spectrum (UV-1800, Shimadzu, Japan). The concentrations of the other competing ions were measured on an ICS-1100 ion chromatography spectrometer (Dionex, USA). A FE28 pH meter (Meter, USA) was used for measuring the pH of the aqueous solution. 3. RESULT AND DISCUSSION 7 ACS Paragon Plus Environment


Effects of Preparation Conditions. Effect of Aluminum Nitrate Dosage. The modification of chitosan with aluminum nitrate can increase the amount of –OH group on chitosan molecule, which is conducive to improving the adsorption performance of Br(I)-IIPs. In order to determine the optimum addition amount of aluminum nitrate for modifying chitosan, a group of Br(I)IIPs were prepared under the same conditions except that the addition amounts of aluminum nitrate were 0.03, 0.05, 0.10, 0.20 and 0.30 g, respectively. Effect of addition amount of aluminum nitrate on adsorption performance of imprinted polymers was investigated. It can be seen from Figure 2 that the adsorption capacity of imprinted polymer increases first with increasing addition amount of aluminum nitrate from 0.03 to 0.10 g and then decreases with further increasing addition amount of aluminum nitrate. When the addition amount of aluminum nitrate increases from 0 to 0.1 g, the amount of –OH groups on the surface of chitosan increases, leading to the increase of specific binding sites, which increases the adsorption capacity of Br(I)-IIPs. However, when the addition amount of aluminum nitrate increases from 0.1 g to 0.3 g, excess polar functional monomer groups are randomly distributed throughout the polymer network, which covers some specific binding sites and weakens the specific binding ability of Br(I)-IIPs. Therefore, 0.1 g aluminum nitrate was selected for modifying chitosan in preparation process of the functional monomer. Effect of Cross-Linking Reagent Dosage. The cross-linking reagent is always used to immobilize functional monomer and template ion by forming prepolymers. The rigidity of the polymer can be greatly enhanced after cross-linking process, which can 8 ACS Paragon Plus Environment

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effectively protect the three-dimensional structure of cavities formed during the imprinting process. In order to investigate the effect of cross-linking reagent dosage on adsorption performance of imprinted polymer, the addition amounts of 0.03, 0.06, 0.10, 0.15, 0.20 and 0.30 mL glutaraldehyde were separately added to the mixtures of functional monomers and template ions for cross-linking under the same conditions. Figure 3 shows that the adsorption capacity of imprinted polymer shows a first increase and then decrease tendency with increasing glutaraldehyde dosage. The possible reason is that the cross-linking degree is too low to make the polymer insufficiently rigid when the addition amount of glutaraldehyde is less than 0.10 mL. The insufficient crosslinking can’t supply sufficient imprinting binding sites for Br(I) ions. Therefore, the number of imprinting binding sites per unit mass of the imprinted material increases with the increase of glutaraldehyde dosage from 0 to 0.10 mL, which increases the adsorption capacity of Br(I)-IIPs. However, although excessive cross-linking can increase the rigidity of the polymer, the number of imprinting binding sites per unit mass of the imprinted material would decrease with further increasing the addition amount of glutaraldehyde from 0.10 mL to 0.30 mL, owing to the overlap of some cavities formed during the imprinting process, which decreases the adsorption capacity of Br(I)-IIPs. Therefore, 0.1 mL was selected as the optimal addition amount of glutaraldehyde in the preparation process of Br(I)-IIPs. Effect of Cross-Linking Time. Variation in adsorption capacity of Br(I)-IIPs with crosslinking time (6 h, 8 h, 10 h, 12 h, 14 h or 16 h) was investigated and the results are shown Figure 4. It can be observed that the adsorption performance of the adsorbent 9 ACS Paragon Plus Environment


could be significantly influenced by cross-linking time. The adsorption capacity of imprinted polymer shows a first increase and then decrease tendency with increasing cross-linking time. When cross-linking time is less than 12 h, the cross-linking of bromide ion and chitosan is insufficient, resulting in unstable polymer structure and not enough specific binding sites for Br(I) ions, which decreases adsorption capacity of Br(I)-IIPs. However, when the crosslinking time is larger than 12 h, excessive crosslinking will cover and destroy the structure of the specific binding cavities, resulting in decreasing adsorption capacity of Br(I)-IIPs. Therefore, 12 h was selected as the optimal cross-linking time for preparation of Br(I)-IIPs. Characterization. FT-IR. FT-IR spectroscopy was used for confirmation of successful cross-linking and polymerization of Br(I)-IIPs and NIPs. Figure 5 shows the FT-IR spectra of original chitosan, modified chitosan, Br(I)-IIPs and NIPs. These four spectra have similar backbone curves and retain the basic structure of chitosan. As shown in Figure 5b, the peaks at 1641 and 1384 cm-1 correspond to the bending vibration of –NH2 group and stretching vibration of -NO2 group, respectively. Compared with the unmodified chitosan (Figure 5a), the peak corresponding to the bending vibration of – NH2 group shifts from 1639 cm-1 to 1641 cm-1, which confirms the successful modification of chitosan. As shown in Figure 5b, the characteristic peaks at 3440, 1155 and 1071 cm-1 correspond to the stretching vibration of O-H group, asymmetric stretching vibration of C-O-C group and stretching vibration of C-O group, indicating that chitosan has been successfully cross-linked into the synthesized polymer. 10 ACS Paragon Plus Environment

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Moreover, in Figure 5b, no appearance of characteristic peak of stretching vibration of -NO2 group and an obvious intensity increase of the characteristic peak corresponding to bending vibration of –NH2 group from 1641 cm-1 to 1644 cm-1 could be observed, which is the main structure of Schiff base formed between chitosan and glutaraldehyde by cross-linking. All the above results demonstrated that the cross-linking and polymerization of Br(I)-IIPs and NIPs were successful. SEM. The surface morphologies of Br(I)-IIPs and NIPs were observed by SEM characterization. As shown in Figure 6, obvious porous polymer network structure can be observed on the surface of Br(I) ion-imprinted polymers (Figures. 6a and 6b), which are more irregular and rougher than that of non-imprinted polymers (Figures. 6c and 6d). This is mainly because the elution of template ions makes the surface morphology of Br(I)-IIPs rough and indirectly provide more adsorption binding sites for target ions, which is beneficial to improving the adsorption performance of ion-imprinted polymers. However, since no template ions were added during the preparation of non-imprinted polymers, the elution process had little influence on modification of the surface morphology. XPS. The imprinted polymers before and after elution were characterized by XPS analysis. It can be seen from Figure 7 and Table 1, negligible amount of bromine (0.04%) was found in eluted polymers, indicating that almost all the imprinting sites distributed on the surface of polymers and the elution of polymers was successful. The trace amount of bromine remained in the polymer after elution is mainly due to the fact that very small portion of the imprinted sites were deeply embedded during the imprinting 11 ACS Paragon Plus Environment


process, and it was difficult to elute these residual bromine ions under the elution conditions. In addition, the aluminum content decreases slightly during the elution of bromine ions. TGA. The thermal stability of Br(I)-IIPs was investigated by TGA analysis with the heating rate of 10 ℃ min-1 and temperature ranging from 0 ℃ to 800 ℃. Figure 8 shows that three stages can be observed for the weight loss of imprinted polymer. The first stage is from 40 ℃ to 170 ℃, between which the weight loss of Br(I)-IIPs is about 10%, mainly owing to the volatilization of physical water. Then the weight loss of about 65% can be observed from 170 ℃ to 760 ℃. The weight loss at this stage is mainly attributed to the decomposition of the main body of polymer. Therefore, the prepared Br(I)-IIPs has a good thermal stability when the ambient temperature is below 170 ℃. Zeta Potential. A certain mass of Br(I) ion-imprinted polymers was ultrasonically dispersed in an aqueous solution. H2SO4 or NaOH solution was used to adjust the pH of the solution from 3.0 to 8.0. As shown in Figure 9, it can be observed that the zeta potential of adsorbent surface was significantly influenced by the solution pH. The zeta potential of adsorbent surface decreases with increasing pH of the solution from 3.0 to 8.0 to strengthening the electronegativity of the adsorbent surface. When pH is higher than 4.0, Br(I)-IIPs exhibit electronegativity property, which strengthens significantly with the increase of pH. However, since bromine ion is an anion which is electronegative, the negative charge on the surface of Br(I)-IIPs is not conducive to the adsorption process, due to electrostatic repulsion. Therefore, lower pH may be beneficial to increasing the adsorption capacity of Br(I)-IIPs. 12 ACS Paragon Plus Environment

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Effects of Adsorption Conditions. Effect of pH. Since the prepared polymers can’t be fully dissolved at pH < 4.0, pH value was selected from 4.0 to 8.0. Figure 10 shows that the adsorption capacity of imprinted polymer decreases gradually with increasing pH of the aqueous solution. The protonation degree of amino in the polymer strengthens with the decrease of pH, resulting in strengthening electrostatic attraction effect between the functionalized groups in prepared polymers and bromine ions in aqueous solution. This is consistent with the results of zeta potential analysis. Moreover, Al(III) ion is an amphoteric metal ion which can hydrolyze to yield aluminum hydroxide and hydrogen ion at pH ranging from 4.0 to 6.0.34 Therefore, when the hydrated aluminum ions combine with -NH2 group in chitosan molecule, the hydrolysis of Al(III) ion protonates –NH2 group to become –NH3+. Then Br(I) ions can be adsorbed on chitosan molecule by exchanging with OH- obtained by hydrolysis of Al(III) ion at pH ranging from 4.0 to 6.0. the further adsorption experiments will be carried out at pH 4. Effect of Adsorption Time. Figure 11 shows that the adsorption capacity of imprinted polymer first increases and then remains nearly constant with then increase of adsorption time. As multiple adsorption binding sites are free and can be used for adsorption of Br(I) ions before the adsorption begins, adsorption capacity initially increases rapidly with the increase of adsorption time. Then the increasing rate of adsorption capacity gradually slows down and eventually the adsorption process reaches the equilibrium as the adsorption binding sites become saturated. The maximum value (18.36 mg g-1) of adsorption capacity was reached at 90 min. 13 ACS Paragon Plus Environment


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Then two models, pseudo-first-order and pseudo-second-order kinetic models, were used for investigating the adsorption kinetics properties of Br(I)-IIPs. The two kinetic models are expressed as follows, 𝑘1

ln (𝑄e ― 𝑄t) = ln𝑄e ― 2.30.𝑡 𝑡 𝑄t

1

(5)

𝑡

(6)

= 𝑘 𝑄2 + 𝑄e 2 e

where k1 is the pseudo-first-order kinetic model constant, k2 is the pseudo-second-order rate constant, Qt represents the adsorption amount at time t, Qe represents the adsorption capacity at equilibrium. Figure 12 shows the fitting curves of these two kinetic models for adsorption process by imprinted polymer and the parameters of these two kinetic models are listed in Table 2. The correlation coefficient (R2) obtained by pseudo-second-order kinetic model (0.9879) is higher than that obtained pseudo-first-order kinetic model (0.9187) and the value of Qe (20.09 mg g-1) calculated by pseudo-second-order kinetic model is closer to the experimental value of Qe (18.89 mg g-1) than that calculated by pseudofirst-order kinetic model, which demonstrates that pseudo-second-order kinetic model is more suitable for describing the adsorption behavior of Br(I) ions by Br(I)-IIPs, indicating that chemical adsorption is a control step during adsorption process of imprinted polymer. Effect of Initial Br(I) Ion Concentration. The adsorption isotherm is crucial for the practical application of the adsorbent and deeply understanding the adsorption process. The equilibrium adsorption isotherms of adsorption processes of Br(I)-IIPs and NIPs at 25 °C and pH 4.0 were studied. As shown in Figure 13, both adsorption capacities of 14 ACS Paragon Plus Environment

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imprinted and non-imprinted polymers increase with increasing initial Br(I) ion concentration and both adsorption processes reach equilibrium when the concentration of Br(I) ion is 100 mg L-1. However, the maximum adsorption capacity of imprinted polymer (18.89 mg g-1) is obvious higher than that of non-imprinted polymer (10.38 mg g-1) due to much more specific binding sites on surface of Br(I)-IIPs formed during imprinting process. Moreover, the maximum adsorption capacity of Br(I)-IIPs prepared in this work (18.89 mg g-1) is also much higher than that of Br(I)-IIPs with chitosan modified by lanthanum nitrate as monomer (4.81 mg g-1) reported in previous reference.35 In addition, both polymers exhibit a certain amount of adsorption capacity, which demonstrate the correctness of selection of functional monomer. The interaction between Br(I) ion and adsorbent was further understood by studying the Langmuir, Freundlich and Temkin isothermal properties and these three adsorption isotherm models can be represented as follows, 𝐶e

𝐶e

1

(7)

𝑄e = 𝑄m + 𝑄m𝐾L

( )𝑙𝑛𝐶e +𝑙𝑛𝐾F 𝑄e = ( )ln (𝐾T) + ln (𝐶e) 𝑙𝑛𝑄e =

1

(8)

𝑛

𝑅𝑇

(9)

𝑏T

where KL is the Langmuir isotherm constant, Qm represents the maximum monolayer adsorption capacity, n is a constant depicting the sorption intensity, KF is the Freundlich isotherm constant, R is the universal gas constant (8.315 J K−1mol−1), T is the absolute temperature, kT is the Temkin isotherm constant, bT is a constant related to the heat of adsorption. The fitting of the above three adsorption isotherms models were conducted. Table 15 ACS Paragon Plus Environment


3 shows that the value of R2 obtained by Freundlich model for imprinted polymer (0.984) is higher than that obtained by Langmuir and Temkin models for imprinted polymer (0.982 and 0.957), which indicates that the adsorption behavior of imprinted polymer follows better with Freundlich isotherm model than Langmuir and Temkin isotherm models. However, the R2 value obtained by Temkin model for non-imprinted polymer (0.931) is higher than that obtained by Langmuir and Freundlich models for nonimprinted polymer (0.918 and 0.879), which demonstrates that the experimental data of adsorption process by NIPs agrees better with Temkin isotherm model than Langmuir and Freundlich isotherm models. These results indicate that the adsorption process by Br(I)-IIPs is a multilayer and heterogeneous adsorption process and the adsorption process by NIP occurs on an uneven surface. These two adsorption processes are consistent with different models, which indirectly confirm the success of the imprinting process. Adsorption Selectivity. F(I), Cl(I) and I(I) ions commonly existed in seawater were selected as interfering ions for Br(I) ion. Binary mixture of Br(I)/M(I) (M = F, Cl or I) with both concentrations as 80.0 mg L−1 was prepared for the investigation of the adsorption selectivities of Br(I)-IIPs and NIPs. The distribution ratios of Br(I) and M(I) ions, selectivity factor and relative selectivity factor were calculated using Eqs. (2) (3) and (4). It can be seen that for F(I)、Cl(I) and I(I) ions, Br(I)-IIPs have much stronger adsorption and selective recognition abilities for bromine ions than NIPs, as shown in Table 4. The relative selectivity factors for all Br(I)/M(I) mixture are higher than one. Since the recognition cavities formed during imprinting process are specific for 16 ACS Paragon Plus Environment

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bromide ion, the interfering ion can’t be identified due to its different shape, size and group. Reusability. The regeneration performance of adsorbent is a key factor for industrial application and an important indicator for evaluating its advantages and disadvantages. The desorption experiments of Br(I)-IIPs were conducted with 0.01 mol L-1 NaOH solution as eluent. The imprinted polymers with saturated adsorption of Br(I) ions were eluted several times in a constant temperature oscillator. When Br(I) ions could not be detected, the regeneration process of Br(I)-IIPs was completed. The adsorption-desorption cycle was repeated eight times. Figure 14 shows that the adsorption capacity of imprinted polymer slightly decreases with the increase of regeneration times. However, after eight adsorption-desorption cycles, the adsorption capacity of Br(I)-IIPs still remains about 90% of its initial value, which demonstrates that the three dimensional structure of the imprinted polymer and specific recognition cavities formed during imprinting process could not be destructed by adsorptiondesorption process, indicating that the prepared Br(I)-IIPs has good stability and reusability. 4. CONCLUSION In this work, bulk polymerization was used for papering a new kind of Br(I)-IIP for extraction of bromide ions. Effects of synthesis conditions on adsorption behavior of prepared polymers were investigated. Chitosan modified with 0.1 g aluminum nitrate was selected as functional monomer. 0.1 mL glutaraldehyde and 0.01 mol L-1 sodium hydroxide solution were selected as cross-linking reagent and eluent. FT-IR, TGA, 17 ACS Paragon Plus Environment


SEM and zeta potential were used for characterization of Br(I)-IIPs and NIPs. Effects of adsorption conditions on adsorption behavior of Br(I)-IIPs were also studied. The adsorption process reached equilibrium within 90 min. The maximum adsorption capacity of imprinted polymer (18.89 mg g-1) which was higher than that of nonimprinted polymer (10.38 mg g-1) was obtained with 100 mg L-1 initial Br(I) ion concentration at pH 4.0. The pseudo-second-order kinetic and Freundlich isotherm models could be used for describing the adsorption process of Br(I)-IIPs. The prepared Br(I)-IIPs showed good selectivity for Br(I) ions and the selectivity coefficients for Br(I)/F(I), Br(I)/Cl(I) and Br(I)/I(I) were 7.4076, 2.8003 and 3.4953, respectively. About 90% of the initial adsorption capacity of Br(I)-IIPs could be maintained after eight adsorption-desorption cycles, indicating that the prepared polymer had good reusability and stability. AUTHOR INFORMATION Corresponding Authors *Tel.: +86-10-64433872. E-mail: [email protected]. *Tel.: +86-10-64197101. E-mail: [email protected]. ORCID Zhongqi Ren: 0000-0002-2571-5702 Zhiyong Zhou: 0000-0001-6436-1399 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS 18 ACS Paragon Plus Environment

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This work was supported by the National Natural Science Foundation of China (21576010, 21606009, U1607107 and U1862113), Beijing Natural Science Foundation (2172043) and Fundamental Research Funds for the Central Universities (BUCTRC201515). The authors gratefully acknowledge these grants. REFERENCE (1) Covaci, A.; Harrad, S.; Abdallah, M. A. E.; Ali, N.; Law, R. J.; Herzke, D.; de Wit, C. A. Novel brominated flame retardants: a review of their analysis, environmental fate and behaviour. Environ. Int. 2011, 37, 532-556. (2) Salamova, A.; Hermanson, M. H.; Hites, R. A. Organophosphate and halogenated flame retardants in atmospheric particles from a European Arctic site. Environ. Sci. Technol. 2014, 48, 6133-6140. (3) Ryabtsev, A. D.; Vakhromeev, A. G.; Kotsupalo, N. P. Highly mineralized brines as a promising resourse of bromine and bromine products. J. Min. Sci. 2003, 39, 514522. (4) John, C. Recovery of bromine and iodine from natural brines, US2412390, 1946. (5) Song, P. S.; Li, W.; Sun, B.; Nie, Z.; Bu, L. Z.; Wang, Y. S. Recent development on comprehensive utilization of salt lake resources. Chinese J. Inorg. Chem. 2011, 27, 801-815. (6) Schubert, P. F.; Smith, A. R.; Taube, H. S. D. W. Process for producing bromine from bromide salts, WO1993006039A1, 1993. (7) Eskandari, H. Selective extraction of bromide with liquid organic membrane. Sep. Sci. Technol. 2001, 36, 81-89. 19 ACS Paragon Plus Environment


(8) Liu, Y. F.; Qin, Y. J.; Li, Q.; Wang, Y.; Zhang, Y.; Zhang, L. C.; Liu, L. Q. A reversible absorption-based supported gas membrane process for enriching bromine from brine by using thin PTFE hollow fibers. J. Membrane Sci. 2017, 543, 222-232. (9) Legan, M.; Trochimczuk, A. W. Bis-imidazolium type ion-exchange resin with poly(HIPE) structure for the selective separation of anions from aqueous solutions. Sep. Sci. Technol. 2017, 53, 1163-1177. (10) Guan, R. L.; Wang, H. Z.; Mao, L. L. Preparation of an anion exchange resin/PES blend flat sheet membrane and its application in the enrichment of bromine from aqueous solution. Desalin. Water Treat. 2017, 86, 9-18. (11) Ma, J.; Yuan, L. H.; Ding, M. J.; Wang, S.; Ren, F.; Zhang, J.; Du, S. H.; Li, F.; Zhou, X. M. The study of core-shell molecularly imprinted polymers of 17β-estradiol on the surface of silica nanoparticles. Biosens. Bioelectron. 2011, 26, 2791-2795. (12) Chen, L. X.; Wang, X. Y.; Lu, W. H.; Wu, X. Q.; Li, J. H. Molecular imprinting: perspectives and applications. Chem. Soc. Rev. 2016, 45, 2137-2211. (13) Vlatakis, G.; Andersson, L. I.; Müller, R.; Mosbach, K. Drug assay using antibody mimics made by molecular imprinting. Nature 1993, 361, 645-647. (14) Rao, T. P.; Kala, R.; Daniel, S. Metal ion-imprinted polymers--novel materials for selective recognition of inorganics. Anal. Chim. Acta 2006, 578, 105-116. (15) Chough, S. H.; Park, K. H.; Cho, S. J.; Park, H. R. In situ preparation of powder and the sorption behaviors of molecularly imprinted polymers through the complexation between polymer ion of methyl methacrylate/acrylic acid and Ca++ ion. Anal. Chim. Acta 2014, 841, 84-90. 20 ACS Paragon Plus Environment

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(16) Sarhan, A. A.; Ayad, D. M.; Badawy, D. S.; Monier, M. Phase transfer catalyzed heterogeneous N-deacetylation of chitin in alkaline solution. React. Funct. Polym. 2009, 69, 358-363. (17) Kyzas, G. Z.; Siafaka, P. I.; Pavlidou, E. G.; Chrissafis, K. J.; Bikiaris, D. N. Synthesis and adsorption application of succinyl-grafted chitosan for the simultaneous removal of zinc and cationic dye from binary hazardous mixtures. Chem. Eng. J. 2015, 259, 438-448. (18) Ge, H. C.; Hua, T. T.; Chen, X. D. Selective adsorption of lead on grafted and crosslinked chitosan nanoparticles prepared by using Pb2+ as template. J. Hazard. Mater. 2016, 308, 225-232. (19) Jalal, M. Advances in chitin and chitosan modification through graft copolymerization: a comprehensive review. Iran Polym. J. 2005, 14, 235-265. (20) He, J.; Lu, Y. C.; Luo, G. S. Ca(II) imprinted chitosan microspheres: An effective and green adsorbent for the removal of Cu(II), Cd(II) and Pb(II) from aqueous solutions. Chem. Eng. J. 2014, 244, 202-208. (21) Yoshida, W.; Oshima, T.; Baba, Y.; Goto, M. Cu(II)-imprinted chitosan derivative containing carboxyl groups for the selective removal of Cu(II) from aqueous solution. J. Chem. Eng. Jpn. 2016, 49, 630-634. (22) He, J. N.; Shang, H. Z.; Zhang, X.; Sun, X. R. Synthesis and application of ion imprinting polymer coated magnetic multi-walled carbon nanotubes for selective adsorption of nickel ion. Appl. Surf. Sci. 2018, 428, 110-117. (23) Guo, W. L.; Chen, R.; Liu, Y.; Meng, M. J.; Meng, X. G.; Hu, Z. Y.; Song, Z. L. 21 ACS Paragon Plus Environment


Preparation of ion-imprinted mesoporous silica SBA-15 functionalized with triglycine for selective adsorption of Co(II). Colloid. Surface. A 2013, 436, 693-703. (24) Hande, P. E.; Kamble, S.; Samui, A. B.; Kulkarni, P. S. Chitosan-based lead ionimprinted interpenetrating polymer network by simultaneous polymerization for selective extraction of lead(II). Ind. Eng. Chem. Res. 2016, 55, 3668-3678. (25) Bello, M. P. D.; Lazzoi, M. R.; Mele, G.; Scorrano, S.; Mergola, L.; Del, R. S. A new ion-imprinted chitosan-based membrane with an azo-derivative ligand for the efficient removal of Pd(II). Materials 2017, 10, 1133. (26) Tang, X. J.; Niu, D.; Bi, C. L.; Shen, B. X. Hg2+ adsorption from a lowconcentration aqueous solution on chitosan beads modified by combining polyamination with Hg2+-imprinted technologies. Ind. Eng. Chem. Res. 2013, 52, 13120-13127. (27) Monier, M.; Abdellatif, D. A.; Youssef, I. Preparation of ruthenium (III) ionimprinted beads based on 2-pyridylthiourea modified chitosan. J. Colloid. Interf. Sci. 2017, 513, 266-278. (28) Wu, X. Y. Molecular imprinting for anion recognition in aqueous media. Microchim. Acta 2012, 176, 23-47. (29) Ozkütük, E. B.; Ersöz, A.; Denizli, A.; Say, R. Preconcentration of phosphate ion onto ion-imprinted polymer. J. Hazard. Mater. 2008, 157, 130-136. (30) Alizadeh, T.; Atayi, K. Synthesis of hydrogen phosphate anion-imprinted polymer via emulsion polymerization and its use as the recognition element of graphene/graphite paste potentiometric electrode. Mater. Chem. Phys. 2018, 209, 180-187. 22 ACS Paragon Plus Environment

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(31) Özkütük, E. B.; Özalp, E.; Ersöz, A.; Açıkkalp, E.; Say, R. Thiocyanate separation by imprinted polymeric systems. Microchim. Acta 2010, 169, 129-135. (32) Wang, J. J.; Han, Y. J.; Li, J.; Wei, J. Selective adsorption of thiocyanate anions using straw supported ion imprinted polymer prepared by surface imprinting technique combined with RAFT polymerization. Sep. Purif. Technol. 2017, 177, 62-70. (33) Huang, R. F.; Ma, X. G.; Li, X.; Guo, L. H.; Xie, X. W.; Zhang, M. Y.; Li, J. A novel ion-imprinted polymer based on graphene oxide-mesoporous silica nanosheet for fast and efficient removal of chromium (VI) from aqueous solution. J. Colloid. Interf. Sci. 2017, 514, 544-553. (34) Campbell, P. G. C.; Bisson, M.; Bougie, R.; Tessier, A.; Villeneuve, J. P. Speciation of aluminum in acidic freshwaters. Anal. Chem. 1983, 55, 2246-2252. (35) Wu, H. F.; Qiu, J. H. Adsorption performance for bromine ion using bromide ionlanthanum nitrate modified chitosan imprinted polymer. Anal. Methods 2014, 6, 18901896.

23 ACS Paragon Plus Environment


Table Captions Table 1. Results of XPS analyses of Br(I)-IIPs before and after elution. Table 2. Adsorption kinetic parameters. Table 3. Adsorption isotherms parameters. Table 4. Adsorption selectivity of Br(I)-IIPs for Br(I) ion in the presence of competitive ions.


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Table 1. Results of XPS analyses of Br(I)-IIPs before and after elution. Sample

C(%)

O(%)

Al(%)

Br(%)

Before elution

56.58

36.34

6.11

0.97

After elution

63.02

32.71

4.23

0.04



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Table 2. Adsorption kinetic parameters. Pseudo-first-order

Pseudo-second-order

Qe / Ion

k1 mg

Br -

Qe,cal /

g-1

18.89

k2 / g

Qe,cal /

R2 /min-1

mg g-1

0.0197

9.60

R2 mg−1min−1

mg g-1

0.0041

20.09

0.9187


0.9879

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Table 3. Adsorption isotherms parameters. Qm / mg g-1 Langmuir

KL / L mol-1

R2

IIP

NIP

IIP

NIP

IIP

NIP

42.54

18.52

0.008

0.018

0.982

0.918

KF / mg g−1(L R2

n mol−1)1/n Freundlich IIP

NIP

IIP

NIP

IIP

NIP

1.33

1.98

0.63

1.19

0.984

0.879

KT / L mol−1 Temkin

bT (mg g−1 J mol−1)

R2

IIP

NIP

IIP

NIP

IIP

NIP

0.09

0.17

285.83

605.65

0.957

0.931



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Table 4. Adsorption selectivity of Br(I)-IIPs and NIPs for Br(I) ion in the presence of competitive ions. Br(I)-IIPs

NIPs

Kd(Br(I)) Kd(M(I))

k

Kd(Br(I))

Kd(M(I))

k

k'

Br/F

0.0638

0.0086

7.4076

0.0342

0.0310

1.1032

6.7146

Br/Cl

0.0531

0.0189

2.8003

0.0611

0.0249

2.4538

1.1412

Br/I

0.0360

0.0103

3.4953

0.0380

0.1403

0.2710 12.8974


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Figure Captions Figure 1. Schematic for the preparation of Br(I)-IIP. Figure 2. Effect of aluminum nitrate dosage on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min). Figure 3. Effect of glutaraldehyde dosage on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min). Figure 4. Effect of cross-linking time on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min). Figure 5. FT-IR spectra of (a) original chitosan, (b) modified chitosan, (c) Br(I)-IIPs and (d) NIPs. Figure 6. SEM images of (a, b) Br(I)-IIPs and (c, d) NIPs. Figure 7. XPS spectra of Br(I)-IIPs before and after elution. Figure 8. TGA curve of Br(I)-IIPs. Figure 9. Zeta potential curve of Br(I)-IIPs. Figure 10. Effect of pH on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min). Figure 11. Effect of adsorption time on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution). Figure 12. Fitting curves of pseudo-first-order (a) and pseudo-second-order (b) kinetic models for adsorption process by Br(I)-IIPs. Figure 13. Effect of initial Br(I) ion concentration on adsorption capacities of Br(I)IIPs and NIPs (20 mg adsorbent, 20 mL bromine ion solution, adsorption time = 60 29 ACS Paragon Plus Environment


min). Figure 14. Reusability of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min).


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Figure 1. Schematic for the preparation of Br(I)-IIP.



15

-1

12

Q/mg g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

9 6 3 0 0.00

0.05

0.10 0.15 0.20 0.25 Aluminum nitrate dosage/g

0.30

Figure 2. Effect of aluminum nitrate dosage on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min).


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15 12

-1

9

Q/mg g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


6 3 0 0.00

0.05

0.10

0.15

0.20

0.25

0.30

Glutaraldeyde dosage/mL

Figure 3. Effect of glutaraldehyde dosage on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min).



16

-1

12

Q/mg g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

8

4

0

6

8

10 12 Cross-linking time/h

14

16

Figure 4. Effect of cross-linking time on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min).


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(a) 1639

(b)

Transmittance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1079 3440

1641 1384 1156

(c)

1083

3442

(d)

1664 1155 1071 3440

4000

3500

3000

2500

2000

1500

1000

500

Wavenumber/cm-1

Figure 5. FT-IR spectra of (a) original chitosan, (b) modified chitosan, (c) Br(I)-IIPs and (d) NIPs.



(a)

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(b)

(c)

(d)

Figure 6. SEM images of (a and b) Br(I)-IIPs and (c and d) NIPs.


Page 37 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


O C

before elution

Br

Al

O C after elution

Al

1200

1000

800

600

400

200

Binding Energy(ev)

Figure 7. XPS spectra of Br(I)-IIPs before and after elution.


0


100 80

Weight/%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60 40 20 0

0

100

200

300 400 500 o Temperature/ C

600

Figure 8. TGA curve of Br(I)-IIPs.


700

800

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5 0

Zeta potential/mv

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-5 -10 -15 -20

3

4

5

6

7

pH

Figure 9. Zeta potential curve of Br(I)-IIPs.


8


20 16

-1 Q/mg g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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12 8 4 0

4

5

6

7

8

pH

Figure 10. Effect of pH on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min).


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25 20

-1 Q/mg g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15 10 5 0

0

30

60 90 120 Adsorption time/min

150

180

Figure 11. Effect of adsorption time on adsorption capacity of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution).



2.4

(a) ln(Qe-Qt)

1.6

0.8

0.0

-0.8 0

30

60

90

120

150

t/min

(b)

8

6

t/Qt

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

4

2

0

0

40

80 t/min

120

160

Figure 12. Fitting curves of pseudo-first-order (a) and pseudo-second-order (b) kinetic models for adsorption process by Br(I)-IIPs.


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24

Br(I)-IIPs NIPs

20 16

-1 Q/mg g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


12 8 4 0

0

40

80

120 C0/mg L-1

160

200

Figure 13. Effect of initial Br(I) ion concentration on adsorption capacities of Br(I)IIPs and NIPs (20 mg adsorbent, 20 mL bromine ion solution, adsorption time = 60 min).



20 16

Q/mg g-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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12 8 4 0

1

2

3

4

5

6

7

8

Regeneration times

Figure 14. Reusability of Br(I)-IIPs (20 mg adsorbent, 20 mL 80 mg L-1 bromine ion solution, adsorption time = 60 min).


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For Table of Contents Use Only

A novel Br(I) ion-imprinted polymer was synthesized with chitosan modified by aluminum nitrate for selective extraction of Br(I) ions from aqueous solution.


Facile Preparation of Novel Ion-Imprinted Polymers for Selective

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