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Preparation of a novel magnetic resin for effective removal of both natural organic matter and organic micropollutants
Chinese Chemical Letters 24 (2013) 601–604
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Preparation of a novel magnetic resin for effective removal of both natural organic matter and organic micropollutants Meng-Qiao Wang, Qing Zhou *, Man-Cheng Zhang, Chen-Dong Shuang, Yang Zhou, Ai-Min Li State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 26 December 2012 Received in revised form 21 March 2013 Accepted 26 March 2013 Available online 20 May 2013
A novel, bifunctional, hypercrosslinked, magnetic resin W2 was prepared using divinylbenzene (DVB) and glycidyl methacrylate (GMA) as comonomers in three steps (i.e., suspension polymerization, amination and post-crosslinking reactions). To evaluate the adsorption of natural organic matter (NOM) and organic micropollutants (OMPs) on the obtained resin W2, two magnetic resins W1 (the precursor of W2 before post-crosslinking) and W0 (the precursor of W1 before amination) were chosen for comparison. The results indicated that W2 would be a promising material for the removal of both NOM and OMPs from aquatic environments. ß 2013 Qing Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Magnetic resin Adsorption Anion exchange Organic micropollutants Natural organic matter
1. Introduction Nature organic matter (NOM) is ubiquitously present in aquatic environments and can generate potentially harmful disinfection by-products (DBPs) leading to some problems in drinking water production [1,2]. Ion exchange is an efficient method for removing NOM that exists primarily in their anionic form [3]. Recently, magnetic anion exchange resins have been developed for water purification and showed several convenient separation characteristics [4–6]. Humic acid (HA), which is the major component of NOM [7,8], can be removed by the resins successfully [9]. However, magnetic anion exchange resins performed poorly in removing organic micropollutants (OMPs), which are essentially non-ionic matters, such as pesticides, estrogen and some antibiotics. These substances are toxic for aquatic organisms such as fish and invertebrates [4,10]. In order to improve the efficiency of the removal of OMPs by magnetic anion exchange resins, magnetic hypercrosslinked adsorption resins that do not contain any functional groups have been developed to remove OMPs from aquatic environment [11,12]. Although they have large specific surface area and abundant pore structure, these resins also carry some disadvantages. For example, the resins need to be soaked by methanol to ensure that the adsorbates can enter into the hydrophobic internal
* Corresponding author. E-mail address: [email protected] (Q. Zhou).
surface during the adsorption process, which makes the operation process expensive and inconvenient. Also, the removal efficiency of NOM such as HA by these resins was not satisfactory because of their hydrophobic skeleton. The purpose of this work is to prepare a novel magnetic bifunctional, hypercrosslinked resin W2 for the removal of both NOM and OMPs. The resin W2 possessed the advantages of both magnetic anion exchange resins and magnetic hypercrosslinked adsorption resins. In order to evaluate the adsorption behaviors of NOM and OMPs on the obtained resin W2, W1 (the precursor of W2 before post-crosslinking) and W0 (the precursor of W1 before amination) were chosen for comparison. HA and atrazine (AT), were chosen as a representative compound of NOM and OMPs, respectively.
2. Experimental As shown in Scheme 1, the magnetic bifunctional, hypercrosslinked resin (W2) was synthesized using a sequence of polymerization, amination and post-crosslinking reactions. Firstly, 5 g of Fe3O4 was dissolved in 500 mL deionized water in a 1 L threenecked round bottom flask and then deoxygenated for 30 min under a N2 atmosphere at room temperature. Then, 50 mL of ammonia solution (25–28 wt%) and 5 g of oleic acid (OA) dissolved in 25 mL acetone were added and the solution was stirred for 30 min under N2 at 80 8C to obtain the OA-coated Fe3O4. The precursor resin W0 was prepared through a suspension polymerization reaction in the presence of 25 g divinylbenzene (DVB, 80%),
1001-8417/$ – see front matter ß 2013 Qing Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2013.04.021
[(Schem_1)TD$FIG]
602
M.-Q. Wang et al. / Chinese Chemical Letters 24 (2013) 601–604
Scheme 1. Synthetic sequence to produce W2.
25 g glycidyl methacrylate (GMA, >99%) and 5 g OA-coated Fe3O4 particles. Benzoyl peroxide (BPO) 1 g and toluene 100 g were added into the mixture of DVB-co-GMA as an initiator and a porogen, respectively. The reaction was conducted in a 1 L glass flask at 80 8C for 12 h. The following functionalization process was carried out referring to Shuang’s method [13]. W0 were dried at 50 8C and then quaternizated with 350 g of trimethylamine hydrochloride at 80 8C for 12 h to produce W1. Finally, the obtained resin (W1) was fully swollen in 1,2-dichloroethane for 8 h, then the post-crosslinking reaction of pendant vinyl groups was carried out at 50 8C for 12 h using 8 g of FeCl3 as a catalyst. The obtained resins (W2) were rinsed with acetone and deionized water, then dried at 50 8C under vacuum. Hysteresis loop measurement (VSM, EV7, ADE, USA), N2 adsorption–desorption analysis (ASAP-2010C, Micromeritics, USA), Elementary analysis (EA, Vario Micro, Elementar, Germany) and FT-IR spectroscopy (Nexus870, Nicolet, USA) were employed for the characterization of the obtained resins. For adsorption kinetic study, batch experiments at 288 K were conducted at 130 rpm and sampled at different time intervals. TOC analyzer (Aurora 1030D, USA) and high performance liquid
[(Fig._1)TD$IG]
chromatography (Agilent 1200, USA) were used to analyze the concentrations of HA and AT, respectively.
3. Results and discussion Fig. 1 presents the FT-IR spectra of the resins at different stages during the preparation process. The absorption band for W0 at 908 cm 1, corresponding to the epoxide group, weakened after the amination reaction that opened the epoxide ring. The absorption band near 3350 cm 1 corresponding to the amino group demonstrated the success of the amination procedure. Fig. 2 illustrates that no hysteresis exists in the magnetization curve, indicating that the obtained resin W2 is superparamagnetic. With a saturation magnetization of 14.48 emu/g, W2 possessed excellent separating properties. The physicochemical properties of W0, W1 and W2 are presented in Table 1. The BET specific surface area of W2 was 325 m2/g, and the average pore diameter was 5.92 nm. The higher BET specific surface area of W2 than that of the obtained resin W1 confirmed the success of the post-crosslinking reaction. Furthermore, the resin W2 had a greater total working exchange capacity (2.25 mmol/g), demonstrating the presence of abundant ion exchange groups. The increased total working exchange capacity
[(Fig._2)TD$IG]
Fig. 1. FT-IR spectra of (a) W0, (b) W1 and (b) W2.
Fig. 2. Hysteresis loops measured for W2.
[(Fig._3)TD$IG]
M.-Q. Wang et al. / Chinese Chemical Letters 24 (2013) 601–604
603
Fig. 3. Adsorption kinetic curves onto the obtained adsorbents at 288 K (a) 0.05 g resins in 500 mL 200 mg/L HA solution, (b) 0.05 g resins in 500 mL 10 mg/L AT solution.
and N content of W1 compared to the precursor resin W0 also demonstrated the success of the amination process. Fig. 3(a) compares the adsorption kinetics of commercial HA between three adsorbents (W0, W1 and W2) at 288 K. The adsorption behaviors on W1 and W2 were similar, reaching equilibrium at 96 h. The amounts of W2 (116 mg/g) adsorbed at equilibrium were similar to that of W1 (124 mg/g). The functional groups in W2, which were positively charged, could lead to chemical interactions with the negatively charged HA molecule through its carboxyl and hydroxy groups. However, a poor performance of the precursor resin W0 was observed, likely due to the lack of adsorption sites on the surface of W0 containing no functional groups. Fig. 3(b) compares the adsorption kinetics of AT between three adsorbents (W0, W1 and W2) at 288 K. The amounts adsorbed onto the three adsorbents increased over time, and reached an equilibrium at 10 h with equilibrium adsorption capacities of 54, 23 and 38 mg/g, respectively. This result indicated that the adsorption of AT onto the resins primarily depended on the surface area. Similar to most of OMPs, AT is a non-ionic matter in conventional aquatic environment and the functional groups hardly contribute much to the adsorption process. W1 was a resin with functional groups, which could remove ionic matters well. However, functional groups effected the diffusion of AT onto the surface of the resin. In order to improve the adsorption capacity of non-ionic matter, a post-crosslinking reaction was carried out to enhance the surface area. After post-crosslinking, W2 had a larger adsorption capacity of AT than W1 did because its surface area increased. Although its adsorption capacity of AT was slightly lower than that of W0, W2 was more advantageous for the removal of both HA and AT. Therefore, W2 could successfully be used in treating the environmental water, which often contains high concentration of NOM (mg/L levels) and much lower content of OMPs (mg/L levels).
Table 1 Physicochemical properties of the obtained resins. W0 Functional group Total working exchange capacity (mmol/g) N content (%, w/w) BET specific surface area (m2/g) Average pore diameter (nm) Particle size (mm)
– – – 331 7.92 70–150
W1
W2
–N+(CH3)3 3.37
–N+(CH3)3 2.25
1.61 285 7.78 70–150
1.57 325 5.92 70–150
4. Conclusion A novel, bifunctional, hypercrosslinked, magnetic resin W2 was successfully prepared. The results of characterization established the resin structure, and the adsorption experiments confirmed the ability of the resin for the removal of both HA and AT. Due to its functional groups and high BET specific surface area, W2 can adsorb both ionic and non-ionic matters, which makes it a promising material for the removal of both NOM and OMPs from aquatic environments. Moreover, W2 can be used for the treatment of the complex wastewater that contains both ionic and non-ionic contaminants, such as biotreated effluent of chemically contaminated industrial wastewater or surface water contaminated by pesticides. We believe that W2 represents a promising material that can be useful in real world applications. Acknowledgments We gratefully acknowledge generous support provided by Program for Changjiang Scholars Innovative Research Team in University, NSFC (Nos. 51290282 and 51208249), Jiangsu Nature Science Fund for Distinguished Scientists (No. BK2010006) and Joint Innovation Project for Production-Study-Research in Jiangsu Province (No. BY2012155) China. References [1] B. Bolto, D. Dixon, R. Eldridge, Ion exchange for the removal of natural organic matter, React. Funct. Polym. 60 (2004) 171–182. [2] J.N. Wang, Y. Zhou, A.M. Li, et al., Adsorption of humic acid by bi-functional resin JN-10 and the effect of alkali-earth metal ions on the adsorption, J. Hazard. Mater. 176 (2010) 1018–1026. [3] B. Bolto, D. Dixon, R. Eldridge, et al., Removal of natural organic matter by ion exchange, Water Res. 36 (2002) 5057–5065. [4] H. Humbert, H. Gallard, H. Suty, et al., Performance of selected anion exchange resins for the treatment of a high DOC content surface water, Water Res. 39 (2005) 1699–1708. [5] Y. Zhou, C.D. Shuang, Q. Zhou, et al., Preparation and application of a novel magnetic anion exchange resin for selective nitrate removal, Chin. Chem. Lett. 23 (2012) 813–816. [6] C.D. Shuang, P.H. Li, A.M. Li, et al., Quaternized magnetic microspheres for the efficient removal of reactive dyes, Water Res. 46 (2012) 4417–4426. [7] S. Liu, M. Lim, R. Fabris, et al., Removal of humic acid using TiO2 photocatalytic process-fractionation and molecular weight characterisation studies, Chemosphere 72 (2008) 263–271. [8] H.J. Feng, L.F. Hu, Q. Mahmood, et al., Study on biosorption of humic acid by activated sludge, Biochem. Eng. J. 39 (2008) 478–485. [9] C.D. Shuang, F. Pan, Q. Zhou, et al., Magnetic polyacrylic anion exchange resin: preparation, characterization and adsorption behavior of humic acid, Ind. Eng. Chem. Res. 51 (2012) 4380–4387.
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M.-Q. Wang et al. / Chinese Chemical Letters 24 (2013) 601–604
[10] H. Humbert, H. Gallard, H. Suty, et al., Natural organic matter (NOM) and pesticides removal using a combination of ion exchange resin and powdered activated carbon (PAC), Water Res. 42 (2008) 1635–1643. [11] Q. Zhou, M.C. Zhang, C.D. Shuang, et al., Preparation of a novel magnetic powder resin for the rapid removal of tetracycline in the aquatic environment, Chin. Chem. Lett. 23 (2012) 745–748.
[12] Q. Zhou, Z.Q. Li, C.D. Shuang, et al., Efficient removal of tetracycline by reusable magnetic microspheres with a high surface area, Chem. Eng. J. 212 (2012) 350–356. [13] C.D. Shuang, F. Yang, F. Pan, et al., Preparation of magnetic anion exchange resin and their adsorption kinetic behavior of reactive blue, Chin. Chem. Lett. 22 (2011) 1091–1094.
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Preparation of a novel magnetic resin for effective removal of both natural organic matter and organic micropollutants Meng-Qiao Wang, Qing Zhou *, Man-Cheng Zhang, Chen-Dong Shuang, Yang Zhou, Ai-Min Li State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 26 December 2012 Received in revised form 21 March 2013 Accepted 26 March 2013 Available online 20 May 2013
A novel, bifunctional, hypercrosslinked, magnetic resin W2 was prepared using divinylbenzene (DVB) and glycidyl methacrylate (GMA) as comonomers in three steps (i.e., suspension polymerization, amination and post-crosslinking reactions). To evaluate the adsorption of natural organic matter (NOM) and organic micropollutants (OMPs) on the obtained resin W2, two magnetic resins W1 (the precursor of W2 before post-crosslinking) and W0 (the precursor of W1 before amination) were chosen for comparison. The results indicated that W2 would be a promising material for the removal of both NOM and OMPs from aquatic environments. ß 2013 Qing Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Magnetic resin Adsorption Anion exchange Organic micropollutants Natural organic matter
1. Introduction Nature organic matter (NOM) is ubiquitously present in aquatic environments and can generate potentially harmful disinfection by-products (DBPs) leading to some problems in drinking water production [1,2]. Ion exchange is an efficient method for removing NOM that exists primarily in their anionic form [3]. Recently, magnetic anion exchange resins have been developed for water purification and showed several convenient separation characteristics [4–6]. Humic acid (HA), which is the major component of NOM [7,8], can be removed by the resins successfully [9]. However, magnetic anion exchange resins performed poorly in removing organic micropollutants (OMPs), which are essentially non-ionic matters, such as pesticides, estrogen and some antibiotics. These substances are toxic for aquatic organisms such as fish and invertebrates [4,10]. In order to improve the efficiency of the removal of OMPs by magnetic anion exchange resins, magnetic hypercrosslinked adsorption resins that do not contain any functional groups have been developed to remove OMPs from aquatic environment [11,12]. Although they have large specific surface area and abundant pore structure, these resins also carry some disadvantages. For example, the resins need to be soaked by methanol to ensure that the adsorbates can enter into the hydrophobic internal
* Corresponding author. E-mail address: [email protected] (Q. Zhou).
surface during the adsorption process, which makes the operation process expensive and inconvenient. Also, the removal efficiency of NOM such as HA by these resins was not satisfactory because of their hydrophobic skeleton. The purpose of this work is to prepare a novel magnetic bifunctional, hypercrosslinked resin W2 for the removal of both NOM and OMPs. The resin W2 possessed the advantages of both magnetic anion exchange resins and magnetic hypercrosslinked adsorption resins. In order to evaluate the adsorption behaviors of NOM and OMPs on the obtained resin W2, W1 (the precursor of W2 before post-crosslinking) and W0 (the precursor of W1 before amination) were chosen for comparison. HA and atrazine (AT), were chosen as a representative compound of NOM and OMPs, respectively.
2. Experimental As shown in Scheme 1, the magnetic bifunctional, hypercrosslinked resin (W2) was synthesized using a sequence of polymerization, amination and post-crosslinking reactions. Firstly, 5 g of Fe3O4 was dissolved in 500 mL deionized water in a 1 L threenecked round bottom flask and then deoxygenated for 30 min under a N2 atmosphere at room temperature. Then, 50 mL of ammonia solution (25–28 wt%) and 5 g of oleic acid (OA) dissolved in 25 mL acetone were added and the solution was stirred for 30 min under N2 at 80 8C to obtain the OA-coated Fe3O4. The precursor resin W0 was prepared through a suspension polymerization reaction in the presence of 25 g divinylbenzene (DVB, 80%),
1001-8417/$ – see front matter ß 2013 Qing Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2013.04.021
[(Schem_1)TD$FIG]
602
M.-Q. Wang et al. / Chinese Chemical Letters 24 (2013) 601–604
Scheme 1. Synthetic sequence to produce W2.
25 g glycidyl methacrylate (GMA, >99%) and 5 g OA-coated Fe3O4 particles. Benzoyl peroxide (BPO) 1 g and toluene 100 g were added into the mixture of DVB-co-GMA as an initiator and a porogen, respectively. The reaction was conducted in a 1 L glass flask at 80 8C for 12 h. The following functionalization process was carried out referring to Shuang’s method [13]. W0 were dried at 50 8C and then quaternizated with 350 g of trimethylamine hydrochloride at 80 8C for 12 h to produce W1. Finally, the obtained resin (W1) was fully swollen in 1,2-dichloroethane for 8 h, then the post-crosslinking reaction of pendant vinyl groups was carried out at 50 8C for 12 h using 8 g of FeCl3 as a catalyst. The obtained resins (W2) were rinsed with acetone and deionized water, then dried at 50 8C under vacuum. Hysteresis loop measurement (VSM, EV7, ADE, USA), N2 adsorption–desorption analysis (ASAP-2010C, Micromeritics, USA), Elementary analysis (EA, Vario Micro, Elementar, Germany) and FT-IR spectroscopy (Nexus870, Nicolet, USA) were employed for the characterization of the obtained resins. For adsorption kinetic study, batch experiments at 288 K were conducted at 130 rpm and sampled at different time intervals. TOC analyzer (Aurora 1030D, USA) and high performance liquid
[(Fig._1)TD$IG]
chromatography (Agilent 1200, USA) were used to analyze the concentrations of HA and AT, respectively.
3. Results and discussion Fig. 1 presents the FT-IR spectra of the resins at different stages during the preparation process. The absorption band for W0 at 908 cm 1, corresponding to the epoxide group, weakened after the amination reaction that opened the epoxide ring. The absorption band near 3350 cm 1 corresponding to the amino group demonstrated the success of the amination procedure. Fig. 2 illustrates that no hysteresis exists in the magnetization curve, indicating that the obtained resin W2 is superparamagnetic. With a saturation magnetization of 14.48 emu/g, W2 possessed excellent separating properties. The physicochemical properties of W0, W1 and W2 are presented in Table 1. The BET specific surface area of W2 was 325 m2/g, and the average pore diameter was 5.92 nm. The higher BET specific surface area of W2 than that of the obtained resin W1 confirmed the success of the post-crosslinking reaction. Furthermore, the resin W2 had a greater total working exchange capacity (2.25 mmol/g), demonstrating the presence of abundant ion exchange groups. The increased total working exchange capacity
[(Fig._2)TD$IG]
Fig. 1. FT-IR spectra of (a) W0, (b) W1 and (b) W2.
Fig. 2. Hysteresis loops measured for W2.
[(Fig._3)TD$IG]
M.-Q. Wang et al. / Chinese Chemical Letters 24 (2013) 601–604
603
Fig. 3. Adsorption kinetic curves onto the obtained adsorbents at 288 K (a) 0.05 g resins in 500 mL 200 mg/L HA solution, (b) 0.05 g resins in 500 mL 10 mg/L AT solution.
and N content of W1 compared to the precursor resin W0 also demonstrated the success of the amination process. Fig. 3(a) compares the adsorption kinetics of commercial HA between three adsorbents (W0, W1 and W2) at 288 K. The adsorption behaviors on W1 and W2 were similar, reaching equilibrium at 96 h. The amounts of W2 (116 mg/g) adsorbed at equilibrium were similar to that of W1 (124 mg/g). The functional groups in W2, which were positively charged, could lead to chemical interactions with the negatively charged HA molecule through its carboxyl and hydroxy groups. However, a poor performance of the precursor resin W0 was observed, likely due to the lack of adsorption sites on the surface of W0 containing no functional groups. Fig. 3(b) compares the adsorption kinetics of AT between three adsorbents (W0, W1 and W2) at 288 K. The amounts adsorbed onto the three adsorbents increased over time, and reached an equilibrium at 10 h with equilibrium adsorption capacities of 54, 23 and 38 mg/g, respectively. This result indicated that the adsorption of AT onto the resins primarily depended on the surface area. Similar to most of OMPs, AT is a non-ionic matter in conventional aquatic environment and the functional groups hardly contribute much to the adsorption process. W1 was a resin with functional groups, which could remove ionic matters well. However, functional groups effected the diffusion of AT onto the surface of the resin. In order to improve the adsorption capacity of non-ionic matter, a post-crosslinking reaction was carried out to enhance the surface area. After post-crosslinking, W2 had a larger adsorption capacity of AT than W1 did because its surface area increased. Although its adsorption capacity of AT was slightly lower than that of W0, W2 was more advantageous for the removal of both HA and AT. Therefore, W2 could successfully be used in treating the environmental water, which often contains high concentration of NOM (mg/L levels) and much lower content of OMPs (mg/L levels).
Table 1 Physicochemical properties of the obtained resins. W0 Functional group Total working exchange capacity (mmol/g) N content (%, w/w) BET specific surface area (m2/g) Average pore diameter (nm) Particle size (mm)
– – – 331 7.92 70–150
W1
W2
–N+(CH3)3 3.37
–N+(CH3)3 2.25
1.61 285 7.78 70–150
1.57 325 5.92 70–150
4. Conclusion A novel, bifunctional, hypercrosslinked, magnetic resin W2 was successfully prepared. The results of characterization established the resin structure, and the adsorption experiments confirmed the ability of the resin for the removal of both HA and AT. Due to its functional groups and high BET specific surface area, W2 can adsorb both ionic and non-ionic matters, which makes it a promising material for the removal of both NOM and OMPs from aquatic environments. Moreover, W2 can be used for the treatment of the complex wastewater that contains both ionic and non-ionic contaminants, such as biotreated effluent of chemically contaminated industrial wastewater or surface water contaminated by pesticides. We believe that W2 represents a promising material that can be useful in real world applications. Acknowledgments We gratefully acknowledge generous support provided by Program for Changjiang Scholars Innovative Research Team in University, NSFC (Nos. 51290282 and 51208249), Jiangsu Nature Science Fund for Distinguished Scientists (No. BK2010006) and Joint Innovation Project for Production-Study-Research in Jiangsu Province (No. BY2012155) China. References [1] B. Bolto, D. Dixon, R. Eldridge, Ion exchange for the removal of natural organic matter, React. Funct. Polym. 60 (2004) 171–182. [2] J.N. Wang, Y. Zhou, A.M. Li, et al., Adsorption of humic acid by bi-functional resin JN-10 and the effect of alkali-earth metal ions on the adsorption, J. Hazard. Mater. 176 (2010) 1018–1026. [3] B. Bolto, D. Dixon, R. Eldridge, et al., Removal of natural organic matter by ion exchange, Water Res. 36 (2002) 5057–5065. [4] H. Humbert, H. Gallard, H. Suty, et al., Performance of selected anion exchange resins for the treatment of a high DOC content surface water, Water Res. 39 (2005) 1699–1708. [5] Y. Zhou, C.D. Shuang, Q. Zhou, et al., Preparation and application of a novel magnetic anion exchange resin for selective nitrate removal, Chin. Chem. Lett. 23 (2012) 813–816. [6] C.D. Shuang, P.H. Li, A.M. Li, et al., Quaternized magnetic microspheres for the efficient removal of reactive dyes, Water Res. 46 (2012) 4417–4426. [7] S. Liu, M. Lim, R. Fabris, et al., Removal of humic acid using TiO2 photocatalytic process-fractionation and molecular weight characterisation studies, Chemosphere 72 (2008) 263–271. [8] H.J. Feng, L.F. Hu, Q. Mahmood, et al., Study on biosorption of humic acid by activated sludge, Biochem. Eng. J. 39 (2008) 478–485. [9] C.D. Shuang, F. Pan, Q. Zhou, et al., Magnetic polyacrylic anion exchange resin: preparation, characterization and adsorption behavior of humic acid, Ind. Eng. Chem. Res. 51 (2012) 4380–4387.
604
M.-Q. Wang et al. / Chinese Chemical Letters 24 (2013) 601–604
[10] H. Humbert, H. Gallard, H. Suty, et al., Natural organic matter (NOM) and pesticides removal using a combination of ion exchange resin and powdered activated carbon (PAC), Water Res. 42 (2008) 1635–1643. [11] Q. Zhou, M.C. Zhang, C.D. Shuang, et al., Preparation of a novel magnetic powder resin for the rapid removal of tetracycline in the aquatic environment, Chin. Chem. Lett. 23 (2012) 745–748.
[12] Q. Zhou, Z.Q. Li, C.D. Shuang, et al., Efficient removal of tetracycline by reusable magnetic microspheres with a high surface area, Chem. Eng. J. 212 (2012) 350–356. [13] C.D. Shuang, F. Yang, F. Pan, et al., Preparation of magnetic anion exchange resin and their adsorption kinetic behavior of reactive blue, Chin. Chem. Lett. 22 (2011) 1091–1094.