Poly(vinyl alcohol) Composite Chelating Fiber

Nov 23, 2015 - Abstract. Abstract Image. The precursor ... Walter Christopher Wilfong , Brian W. Kail , Tracy L. Bank , Bret H. Howard , and McMahan L...
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Polyamidoxime/Poly(vinyl alcohol) Composite Chelating Fiber Prepared by Emulsion Spinning and Its Adsorption Properties for Metal Ions Yongjiao Song, Junfan Li, Guangdou Ye, Jianjun Xu, and Mengjin Jiang* The State Key Laboratory of Polymer Materials and Engineering, Sichuan University, Chengdu, 61006, China S Supporting Information *

ABSTRACT: The precursor polyacrylonitrile/poly(vinyl alcohol) (PAN/PVA) fibers were prepared by emulsion spinning of PAN emulsion with PVA solution. The precursor fibers were then amidoximated to get the polyamidoxime (PAO)/PVA composite chelating fibers. The structures of PAN emulsion particles and composite fiber were studied with a laser mastersizer, scan electronic microscope, Fourier transform infrared spectra, auto-Kjeldahl determination, and X-ray diffraction analysis. Results show that nanosized PAN particles were well-dispersed in PVA fiber matrix through emulsion spinning. Almost all of the PAN particles were amidoximated after treatment. The PAO/PVA fiber has good selectivity to silver ions in a multiple metal ions solution. Its maximum amount of adsorption of silver ions and copper ions were calculated to be 518 and 146 mg g−1 according to the Langmuir model. It also has good mechanical performance with breaking strength, 392.10 MPa, and elongation at break, 30.19%.

1. INTRODUCTION As we know, most of heavy-metal ions are toxic and dangerous to the environment, but at the same time, they are also precious natural resources; therefore, many adsorbents have been developed to remove, separate, or enrich heavy-metals ions for wastewater treatment, water purification, or precious metal recycling and mining.1−6 Chelating fiber is a kind of advanced adsorbent, and their fibrous and high specific surface area structure endows them with extra advantages for adsorption, such as high adsorption capacity, high adsorption/desorption rate, and ease of application in various conditions. Thus, many kinds of chelating fibers have been designed for heavy-metal ions separation, including amidoxime, amine-group,7,8 phosphorus-containing,9,10 and sulfur-containing11,12 samples. Amidoxime chelating fiber is an old type of these fibers, and it has strong selectivity to several heavy-metal ions, especially to uranium ions, which is very promising in application in extraction of uranium from seawater.13 So, the research and development of amidoxime chelating fiber has always been a hot point. There are several types of methods for preparing amidoxime chelating fiber. The most traditional way is to modify polyacrylonitrile (PAN) fiber directly with hydroxylamine,5,14,15 and the cyano groups of PAN are partly changed into amidoxime groups in this modification. The PAN fibers for modification can be normal commercial fiber (for cost control), electrospun nanofibers (for high adsorption performance), or modacrylic fibers (for special selectivity). This method is very simple in operation and can obtain fibers with high amidoxime contents, but it also has an unavoidable disadvantage that the modification process would destroy the super molecular structures of precursor fibers, which would lead to obvious mechanical performance degradation of these fibers, especially when the higher modification degree is expected. To compensate for this disadvantage, grafting methods were © XXXX American Chemical Society

developed. Grafting methods are used to graft acrylonitrile monomers on a natural or chemical fiber and form PAN branches for amidoximation modification.16−18 The fiber bases are stable in the process of amidoxime modification, so the fibers prepared by grafting methods were expected to have better mechanical performance. But, in fact, the grafting processes also have negative effects on the structures of precursor fiber. The grafting methods include chemical grafting and radiation-induced grafting. Chemical grafting requires a large amount of accessible active groups on the fiber base, which may need to partly destroy the fiber’s ordered structure and expose more active groups for reaction. As to radiationinduced grafting, it is an effective way to get fibers with high chelating performance, and it has been attracting much attention in recent years. However, the increase in radiation dose for high grafting ratio is also very destructive to the molecular chains of precursor fiber. The reports about amidoxime chelating fibers are abundant, but seldom are these fibers produced at industrial scale or applied in practice. There are several reasons, such as the high cost of raw materials, the technical difficulties in preparation, and the imbalance between the adsorption performance and the mechanical strength of chelating fibers. Thus, amidoxime chelating fibers with low material costs, easy preparation process, and proper performance still need to be studied and developed for real production and application. In this study, a special fiber structure was designed to easily prepare composite amidoxime fiber with both good chelating performance and good mechanical performance. Different from traditional modification methods, the preparation of the Received: September 2, 2015 Revised: November 23, 2015 Accepted: November 23, 2015

A

DOI: 10.1021/acs.iecr.5b03250 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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together to prepare PAN/PVA composite as-spun fibers through emulsion spinning. Step two: the as-spun fibers were subjected to hot stretching and heat setting to improve the tensile strength. The stretching ratio is 4:1, and the heat setting was conducted at 180 °C for 128 s. Step three: 1 g of PAN/ PVA fiber, 7.92 g of hydroxylamine hydrochloride, 12 g of anhydrous sodium carbonate, and 50 mL of DI water were added into a 100 mL beaker, and then the breaker was sealed with plastic wrap and kept at 70 °C for 2 h. Finally, the obtained PAO/PVA composite chelating fibers were taken out, washed with DI water, and dried at room temperature. 2.4. Characterizations. The particle size of PAN emulsion was analyzed with the laser mastersizer (Mastersizer 2000, Malvern Instruments Ltd., UK). The chemical structure of composite fiber was characterized with a Fourier infrared spectrophotometer (FTIR) (Nicolet FTIP 560, USA). The morphologies of PAN emulsion particles and composite fibers were observed with a JSM- 5900LV scanning electron microscope (SEM) (JEOL). The accelerated voltage of SEM measurements was 20 kV. The composite fibers were analyzed by X-ray diffraction (XRD) with an X’Pert Pro X- ray diffractometer. The instrument works with nickel-filtered Cu Kα radiation (L = 1.54 Å) at 40 kV and the scanning rate was 2° min−1 over a 2θ range from 5° to 40°. The mechanical properties of the composite fibers were tested by the singlefiber tensile tester (Model LLY-06, Laizhou Electron Instrument Co, Ltd., China). Tests were carried out on a single fiber with a crosshead velocity of 20 mm/min and a gauge length of 20 mm. The final mechanical properties were obtained from the results of 10 specimens. The nitrogen contents were measured by Kjeldahl nitrogen determination method with Auto-Kjeldahl determination device (K06A, Shengsheng Automated Analysis Instrument Co., Ltd., Shanghai). The surface element changes of PAO/PVA composite fiber before and after adsorption were analyzed by the X-ray photoelectron spectrum (XPS) (XSAM800 (KRATOS) spectrometer) with mono-Mg Kα radiation. 2.5. Adsorption Characteristics. 2.5.1. Competitive Adsorption. The competitive adsorption experiment was carried out with 25 ± 2 mg fibers in a 25 mL solution with multiple metal ions (Ag+, Cd2+, Cu2+, Ni2+, Pb2+, and Zn2+) at 28 °C for 24 h in a static state. The initial concentration of each metal salt is 25 mg L−1, and the pH value was 5. The concentration of each heavy-metal ion was determined with inductively coupled plasma emission spectrometer (ICP) (ICPS-8100, Shimadzu, Japan). The adsorption amounts of metal ions were calculated according to eq 1

chelating fiber in this study starts from the beginning of spinning. PAN/poly(vinyl alcohol) (PVA) composite precursor fiber was first prepared by the emulsion spinning process with using PAN emulsion and PVA solution. Then the composite precursor fiber was amidoximated to obtain the final polyamidoxime (PAO)/PVA composite chelating fiber. In the composite chelating fiber, the amidoximated PAN particles disperse in the continuous PVA fiber matrix. The continuous PVA fiber matrix could provide composite chelating fiber with good mechanical performance, enough chemical stability, and good wettability, while the amidoximated PAN particles can act as high-efficiency chelating agent. The design of this PAO/PAN composite fiber is shown in Scheme 1. The preparation process, structures, and properties of the PAO/PVA composite chelating fiber are presented in this work. Scheme 1. Preparation Process and Structure Design of PAO/PVA Fibers

2. EXPERIMENTAL SECTION 2.1. Material and Reagents. PVA (DP = 1700 ± 50, alcoholysis degree >99%), industry grade, was supplied by Sinopec Sichuan Vinylon Works. Acrylonitrile (AN), acrylic acid (AA), methyl methacrylate (MMA), potassium persulfate (K2S2O8), hydroxylamine hydrochloride, and anhydrous sodium carbonate were all chemically pure and purchased from Kelong Chemical Reagent Company of Chengdu. All monomers were purified with decompression distillation method. K2S2O8 was purified by the method of recrystallization. Metal salts for adsorption experiments (Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Cd(NO3)2·4H2O, Zn(NO3)2·6H2O, Pb(NO3)2, and AgNO3) were all analytically pure and purchased from Kelong Chemical Reagent Company of Chengdu. Deionized (DI) water was used to prepare all the solutions in the study. 2.2. Preparation of PAN Emulsion. PAN particles were prepared through pre-emulsion copolymerization which was carried out in an oil/water system with sodium dodecyl sulfate (SDS) and Tween-20 as emulsifiers (mSDS:mTween‑20 = 1:4) and K2S2O8 as initiator. First, 3.696 g of emulsifier and 150 g of DI water were poured into the reactor vessel and heated up to 70 °C, with the protection of a continuous N2 environment. Then 40 mL of K2S2O8 solution (0.002 g mL−1) and pre-emulsion were added into the reactor vessel. The pre-emulsion was prepared by dissolving 9.75 g of emulsifier in 65.25 g of DI water, and then the mixture of 45.00 g of AN, 2.25 g of AA, and 1.60 g of MMA were emulsified with the emulsifier solution. The overall emulsion polymerization reaction time was about 9 h. The comonomers AA and MMA were used to reduce the intermolecular force of nitrile groups in PAN chains. 2.3. Preparation of the PAO/PVA Fibers. Step one: PAN emulsion and PVA solution (mPAN:mPVA = 3:7) were blended

Q = (C0 − Ct )V /W −1

(1) −1

where Q (mg g ) is the adsorption capacity, C0 (mg L ) and Ct (mg L−1) are the concentrations of the metal ions in the initial solution and in the solution after adsorption for a certain time t, respectively, V (mL) is the volume of the solution, and W (g) is the weight of the dry PAO/PVA fibers. 2.5.2. Adsorption Isotherm. Dry PAO/PVA fibers (50 ± 5 mg) were immersed in a series of 100 mL beakers containing 50 mL of metal-ion solution at desired concentration (50−1000 mg L−1). The concentration of each solution was measured by ICP, and the adsorption data are fitted by Langmuir (eq 2) and Freundlich (eq 3) isotherm equations:5

qe = B

qmCe 1/kl + Ce

(2) DOI: 10.1021/acs.iecr.5b03250 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 1. (a) FTIR spectrum, (b) particle size, and (c) SEM image of PAN emulsion particles.

qe = k f Ce1/ n

(3)

where qe is the equilibrium amount of adsorbate per unit weight of adsorbent (mg g−1), Ce is the equilibrium concentration of the metal ions in the solution (mg L−1), kl is the adsorption equilibrium constant (L mg−1), qm is the maximum amount of adsorption (mg g−1), kf is a constant representing the adsorption capacity [(mg g−1) (L mg−1)1/n], and n is a constant depicting the adsorption density.

3. RESULTS AND DISCUSSION 3.1. Characterization of PAN Particles. The FTIR spectrum of PAN emulsion particles is given in Figure 1 a. The peak at 2937 cm−1 is due to the −CH2 and −CH3 stretching vibrations. The peak at 2244 cm−1 is attributed to nitrile groups. The peaks at 1730 and 1454 cm−1 belong to the vibration of −CO and −CO−O− of the ester groups of MMA copolymer fragments. The peaks at 3448 and 926 cm−1 belong to the −OH groups of AA fragments in the copolymer. These characteristic peaks prove that the PAN copolymer emulsion is successfully prepared. As shown in Figure 1b, the particle size distribution of PAN emulsion is single and narrow. The medium diameter (D50%) and average volume diameter (D(3, 4)) of PAN emulsion particles are 112 and 118 nm, respectively. The size of the PAN emulsion particle is much smaller than that of the spinneret hole (0.08 mm), which means that the PAN emulsion particles can pass through the spinneret smoothly. The SEM images (Figure 1c and Figure S1a,b of the Supporting Information) of PAN emulsion particles show that the PAN particles are all spherical and have uniform size. The PAN emulsion polymerization is dominated by an aqueous nucleation mechanism. It means that the PAN primary particles form in aqueous phase first and then aggregate to form bigger emulsion particles, so the surfaces of PAN emulsion particles are a bit rough. 3.2. Morphologies of Composite Fibers. SEM images of membrane prepared with composite spinning dope (referring to Figure S1c,d) reveal that PAN emulsion particles are welldistributed in PVA solution, which is beneficial for particles to go through the spinneret holes. The SEM images of the composite fibers at different stages of preparation are shown in Figure 2. The fiber samples are fractured after being frozen by liquid nitrogen to expose their cross sections. It can be seen that the PAN emulsion particles are well-distributed in the PAN/PVA as-spun fibers as in the spinning dope; after stretching and heat setting, the PAN emulsion particles tend to aggregate; after the amidoximation treatment, the emulsion particles in the fiber gathered together obviously. All the fibers

Figure 2. SEM images of composite chelating fibers at different stages of preparation: (a) PAN/PVA as-spun fiber, (b) PAN/PVA fiber after stretching and heat treatment, and (c) PAO/PVA composite fiber.

cross sections are kidney-shaped, which are the same as that of the pure PVA fiber spinned by sodium sulfate wet spinning. The surface of the PAO/PVA fiber is rough and porous, which is good for adsorption. 3.3. Chemical Structure of Composite Fibers. The PAO/PVA fibers were obtained by treating PAN/PVA fiber with hydroxylamine and the FTIR spectra of the fibers before and after the treatment were given in Figure 3. In the spectrum of PAN/PVA fiber, the peak at around 3400 cm−1 is due to the stretching vibration of −OH in PVA molecular chain, and the peaks at 2244 and 1730 cm−1 are attributed to the vibrations of −CN and-CO-OCH3 in the PAN particles, respectively. After amidoximation treatment, the −CN peak disappears, while two

Figure 3. FTIR spectra of composite fibers: (a) PAN/PVA composite fibers, (b) PAO/PVA composite fibers. C

DOI: 10.1021/acs.iecr.5b03250 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research new peaks at 1664 and 918 cm−1 come out, which is attributed to the vibrations of − CN− and − N−O− of the AO groups,16 respectively. The result shows that the PAO/PVA fibers are successfully prepared. The PAN and PAO are all nitrogen-containing compounds, so the nitrogen content in the composite fiber can be considered as a measurement of the PAN or PAO amount in the composite fiber. The results show that the nitrogen content of PAN/PVA fibers is 7.55%. For the PAO/PVA fibers, the measured nitrogen content is 11.70% which is similar to the theoretical content of 12.94% (supposing that all the amidoximated PAN emulsion particles are retained in the fibers and all the nitrile groups have been turned into amidoxime groups), and the result proves that at least 90% nitrile groups have been turned into amidoxime groups. 3.4. XRD Analysis. Figure 4 shows the XRD patterns of PVA fibers, PAN/PVA fibers, and PAO/PVA fibers. The XRD

Figure 5. Stress−strain curves of fibers.

after adsorption may be caused by the metal ions coordination bonds. The PAO/PVA fibers turn to brown and green after the adsorption of Ag+ and Cu2+ ions, respectively (Figure S2a−d), and the strength demonstration of PAO/PVA−Cu fibers is also shown in Figure S2e. The mechanical property of PAO/PVA fiber is quite excellent compared with most other kinds of amidoxime chelating fibers.3,5,20−22 The mechanical strength of this fiber is good enough for most application cases, and the simple preparation process makes it very competitive. 3.6. Adsorption Properties. 3.6.1. Adsorption Selectivity. The adsorptions of different ions on pure PVA fibers, PAN/ PVA fibers, and PAO/PVA fibers are presented in Figure 6. It

Figure 4. XRD patterns of composite fibers: (a) PVA fibers, (b) PAN/ PVA fibers, (c) PAO/PVA fibers, and (d) gray area in the spectrum of PAN/PVA fibers.

patterns show that most diffraction peaks of PAN/PVA fibers are in accordance with those of PVA fibers;19 only the broad peak at 2θ = 16.8° indicatez that there is a little bit of ordered structure of PAN in composite fiber. The peak intensity of PAN/PVA fiber is much weaker than that of pure PVA fiber, which indicates that a large amount of PAN emulsion particles retard the crystallization of PVA. After amidoximation treatment, the peak belonging to PVA is further weakened and the peak of PAN almost disappears, which means that the amidoximation treatment destroys some crystal structure of PVA, and turns almost all PAN in the fiber into PAO. 3.5. Mechanical Properties of Composite Fibers. The mechanical properties of chelating fibers are quite important to their practical applications. One of the main goals of this study is to provide a method for preparing chelating fiber with acceptable mechanical performance. The stress−strain curves of typical PAN/PVA fiber and PAO/PVA fiber before and after adsorption of metal ions are shown in Figure 5. The mechanical properties of composite fibers are shown in Table S1. The breaking strength of PAN/PVA fiber is about 488.95 MPa and the elongation at break is about 28.76%. After amidoximation treatment, the breaking strength of PAO/PVA fiber decreases to 392.10 MPa, and the elongation at break of it increases to 30.19%. The changes of mechanical properties are caused by the structural damage of composite fiber in the amidoximation treatment. The improvement of modulus of PAO/PVA fibers

Figure 6. Competitive adsorption of coexisting ions on PVA fibers, PAN/PVA fibers, and PAO/PVA fibers (C0 = 25 mg/L; pH = 4.0; t = 24 h; T = 28 °C).

shows that the amidoxime modification led to an obvious increase in Ag+ and Cu2+ ions sorption capability. The sorption amount of PAO/PVA fibers toward Ag+ ions is 18.31 mg g−1, which is about 3.6 times that amount of PAN/PVA fibers. On the other hand, the sorption amounts of PAO/PVA fibers toward other ions besides Ag+ and Cu2+ in the multisystem are very low, which means that PAO/PVA fibers have strong selectivity for Ag+ and Cu2+ ions. 3.6.2. XPS Spectra Study. Figure 7 shows the XPS spectra of PAO/PVA fibers before and after adsorption. The peaks at binding energies (BE) of 284.6, 399.3, and 532.0 eV correspond to the C 1s, N 1s, and O 1s spectra, respectively, which exist in all samples. After adsorption of Cu2+, the signals D

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Figure 7. XPS spectra of (a) PAO/PVA fibers, (b) PAO/PVA fibers with Cu2+ adsorption, (c) PAO/PVA fibers with Ag+ adsorption, (d) Ag 3d of PAO/PVA fibers with Ag+ adsorption, and (e) Cu 2p of PAO/PVA fiber with Cu2+ adsorption.

Figure 8. XPS spectra of PAO/PVA fibers before and after the adsorption of metal ions: (a) N 1s; (b) O 1s.

Figure 9. Adsorption isotherms of PAO/PVA fibers: (a) Ag+; (b) Cu2+.

adsorption. The lone pair of electrons in the nitrogen atoms of the amidoxime group is donated to form a coordination bond between Cu2+ and Ag+ and the nitrogen atoms. The O 1s XPS spectra of PAO/PVA fibers can be differentiated into two peaks at the BEs of 531.8 and 532.7 eV (Figure 8b),23 which can be attributed to the oxygen atoms in CH2CH−OH and CN− OH species, respectively. After the adsorption of Cu2+, the peak of CN−OH at 532.7 eV shifts to 532.9 eV, and after the adsorption of Ag+, the peak of CH2CH−OH26 at 531.8 eV shift to 531.9 eV. The results indicate that the oxygen atoms in both CH2CH−OH and CN−OH contribute to the formation of coordinate bonds between composite fiber and metal ions. It also indicates that PVA contributes not only to the mechanical performance of the composite fiber but also to the adsorption performance of the composite fiber. 3.6.3. Adsorption Isotherm. Figure 9 illustrates the adsorption isotherms of Ag+ and Cu2+ onto PAO/PVA fibers at various equilibrium concentrations. The maximum sorption amounts for Ag+ and Cu2+ on PAO/PVA fibers in this system

of Cu 2p3/2 and Cu 2p1/2 at the BEs of 934.7 and 954.6 eV appear in Figure 7b, which is also magnified in Figure 7e.23 After adsorption of Ag+, the peaks at the BE of about 368.1 and 374.5 eV appear in Figure 7c,d, which correspond well with Ag 3d5/2 and Ag 3d3/2.24 These results prove that Cu2+ and Ag+ ions exist in the PAO/PVA fiber after adsorption. To clarify the interaction between metal ions and PAO/PVA composite chelating fiber, the N 1s and O 1s XPS spectra of PAO/PVA fibers before and after adsorption of Cu2+ and Ag+ are analyzed in detail. Figure 8 a presents the N 1s XPS spectra of composite chelating fibers. It shows that the N 1s peak of PAO/PVA fibers can be differentiated into two peaks at the BEs of 399.2 and 399.8 eV, which belong to nitrogen atoms in NH2−C and CN−OH species, respectively.25 After the adsorption of Cu2+, a new peak at BE of 401.3 eV appears in the differentiated peaks of N 1s. Similarly, a peak at BE of 400.3 eV emerges after the adsorption of Ag+. These results confirm that the amidoxime group of the PAO/PVA fibers is the active group which forms coordinate bonds with Cu2+ and Ag+ after E

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were found to be about 355 and 139 mg g−1, respectively. The parameters of isotherm models fitted by Langmuir and Freundlich isotherm equations are summarized in Table 1. It

equation

parameter

Ag+

Langmuir

qm = 518 mg g−1

Freundlich

kf = 4.69 (mg g−1) (L mg−1)1/n qm = 146 mg g−1

Cu2+

Langmuir Freundlich

parameter

R2

kl = 0.003 (L mg−1) n = 1.480

0.9822

kl = 0.011 (L mg−1) −1 kf = 12.219 (mg g ) (L n = 2.724 mg−1)1/n

0.9858

*E-mail: [email protected] (M.J.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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REFERENCES

The financial support of this study was from the Youth Science Foundation of the National Natural Science Foundation of China (NSFC) (Subject No. 51103088). The authors thank all the researchers of the State Key Laboratory of Polymer Materials Engineering (Sichuan University) for their help and efforts in completing this research.

0.9813

0.8425

(1) Fu, F.; Wang, Q. Removal of heavy metal ions from wastewaters: a review. J. Environ. Manage. 2011, 92 (3), 407−18. (2) Ko, Y. G.; Chun, Y. J.; Kim, C. H.; Choi, U. S. Removal of Cu (II) and Cr (VI) ions from aqueous solution using chelating fiber packed column: Equilibrium and kinetic studies. J. Hazard. Mater. 2011, 194, 92−9. (3) Lin, W.; Lu, Y.; Zeng, H. Studies of the preparation, structure, and properties of an acrylic chelating fiber containing amidoxime groups. J. Appl. Polym. Sci. 1993, 47 (1), 45−52. (4) Liu, X.; Chen, H.; Wang, C.; Qu, R.; Ji, C.; Sun, C.; Zhang, Y. Synthesis of porous acrylonitrile/methyl acrylate copolymer beads by suspended emulsion polymerization and their adsorption properties after amidoximation. J. Hazard. Mater. 2010, 175 (1−3), 1014−21. (5) Liu, X.; Liu, H.; Ma, H.; Cao, C.; Yu, M.; Wang, Z.; Deng, B.; Wang, M.; Li, J. Adsorption of the uranyl ions on an amidoxime-based polyethylene nonwoven fabric prepared by preirradiation-induced emulsion graft polymerization. Ind. Eng. Chem. Res. 2012, 51 (46), 15089−15095. (6) Wang, H.-L.; Tian, C.-Y.; Jiang, L.; Wang, L. Remediation of heavy metals contaminated saline soils: a halophyte choice? Environ. Sci. Technol. 2014, 48 (1), 21−22. (7) Deng, S.; Bai, R.; Chen, J. P. Aminated polyacrylonitrile fibers for lead and copper removal. Langmuir 2003, 19 (12), 5058−5064. (8) Wang, J.; Cheng, C.; Yang, X.; Chen, C.; Li, A. A new porous chelating fiber: preparation, characterization, and adsorption behavior of Pb (II). Ind. Eng. Chem. Res. 2013, 52 (11), 4072−4082. (9) George, M.; Funkhouser, G. P.; Terech, P.; Weiss, R. G. Organogels with Fe (III) complexes of phosphorus-containing amphiphiles as two-component isothermal gelators. Langmuir 2006, 22 (18), 7885−7893. (10) Monge, S.; Canniccioni, B.; Graillot, A.; Robin, J. J. Phosphoruscontaining polymers: a great opportunity for the biomedical field. Biomacromolecules 2011, 12 (6), 1973−82. (11) Murray, H.; Garzon, G.; Raptis, R. G.; Mazany, A. M.; Porter, L. C.; Fackler, J. P., Jr Sulfur-containing gold (III) chelates and their use in heterovalent dimer synthesis: crystal structures of AuIII [CH2P (S) Ph2] 2Br,[ AuIII [S2P (OH) Ph] 2] Cl, and AuIII [CH2P (S) Ph2][S2CN (Et) 2] 2. Inorg. Chem. 1988, 27 (5), 836−842. (12) Wen, Y.; Ma, J.; Chen, J.; Shen, C.; Li, H.; Liu, W. Carbonaceous sulfur-containing chitosan−Fe (III): a novel adsorbent for efficient removal of copper (II) from water. Chem. Eng. J. 2015, 259, 372−380. (13) Başarır, S. Ş.; Bayramgil, N. P. The uranium recovery from aqueous solutions using amidoxime modified cellulose derivatives. I. Preparation, characterization and amidoxime conversion of radiation grafted ethyl cellulose-acrylonitrile copolymers. Radiochimica. Acta. 2012, 100 (12), 893−900. (14) Horzum, N.; Shahwan, T.; Parlak, O.; Demir, M. M. Synthesis of amidoximated polyacrylonitrile fibers and its application for sorption of aqueous uranyl ions under continuous flow. Chem. Eng. J. 2012, 213, 41−49.

appears that both Cu2+ and Ag+ adsorption isotherm results of the PAO/PVA fibers can be well-described by the Freundlich equation and the Langmuir equation, but the latter gives a slightly better result than the former. The Langmuir isotherm model assumes that the adsorption takes place on a homogeneous surface by monolayer sorption, suggesting that the adsorption mechanism of Ag+ and Cu2+ on PAO/PVA fibers is mainly monolayer adsorption. In addition, the qm calculated by the Langmuir equation of Ag+ is 518 mg g−1, which is much higher than that of Cu2+ (146 mg g−1). It can be concluded that the PAO/PVA fiber has strong adsorption selectivity to Ag+. Tables S2 and S3 compare the adsorption capacity of the PAO/PVA for Ag+ and Cu2+ with other adsorbents, respectively. The results demonstrated that the adsorption capacity of the PAO/PVA was relatively higher than several other adsorbents.27−45

4. CONCLUSIONS In this study, PAN emulsion was synthesized and mixed with PVA solution to prepare a novel amidoxime chelating fiber by emulsion spinning and amidoximation. The amidoximated PAN emulsion particles serve as highly efficient absorbents and the PVA fiber matrix endows the composite fiber with good mechanical performance. The PAO/PVA composite chelating fiber was successfully prepared as supposed. The fibers have high adsorption capacity and selectivity to Ag+ and Cu2+, and the fibers mechanical performances are quietly good among kinds of amidoxime chelating fibers. The adsorption studies show that, in the composite fibers, the amidoxime groups are the main active groups for adsorption, but the hydroxyl groups of PVA also contribute to the adsorption. The sorption isotherms of the composite fiber to metal ions obey the Langmuir isotherm model. The method in this study gives out an effective and easy way to prepare amidoxime fibers with both high adsorption performance and good mechanical performance, which greatly broaden the potential applications of amidoxime fibers.

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Table 1. Parameter Values of the Freundlich and Langmuir Equations for the Adsorption of Ag+ or Cu2+ on the PAO/ PVA Fibers metal ions

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ASSOCIATED CONTENT

S Supporting Information *

SEM images, photos, tensile strength data, and the adsorption data for Ag+ and Cu2+ onto various adsorbents. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b03250. (PDF) F

DOI: 10.1021/acs.iecr.5b03250 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

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DOI: 10.1021/acs.iecr.5b03250 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX