Silica Nanospheres with Three- Dimensional

Article pubs.acs.org/IECR

Polyacrylonitrile/Silica Nanospheres with Three- Dimensional Interpenetrating Network Structure and Their Application for Removal of Pb(II) from Water Qingchun Zhao* and Tian Cao Department of Material Science and Engineering, Anhui Institute of Architecture & Industry, Hefei 230022 Anhui, PR China ABSTRACT: Polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure have been synthesized via emulsion polymerization method using 0.08 g azobisisbutyronitrile (AIBN) as initiator, 5 g acrylonitrile, and 5 g γ-methacryloxypropyl trimethoxy silane as monomer, 0.85 g dodecylbenzene sulfate as emulsifier at 60 °C for 10 h. The composition and morphology of the obtained nanospheres were investigated by infrared spectrum, thermogravimetric analysis, and scanning electron microscopy, respectively. The obtained polyacrylonitrile/silica nanospheres were used to investigate adsorption Pb(II) from aqueous solutions. The research results display that composite material has high adsorption capacity at optimum pH = 5. The maximum adsorption capacity was 0.108 mmol/g within 300 min at 25 °C. The pseudo-first-order equation and the pseudo-second-order equation are applied to analyze the experimental data. Adsorption behavior for Pb(II) onto nanospheres belongs to the pseudo-second-order kinetic model, and the adsorption process is a chemical process.

1. INTRODUCTION Heavy metal pollution has become more serious with the rapid development of global industry. Typically, these heavy metal ions cannot be biodegraded and easily accumulate in human body and induce various diseases. 1−3 Many treatment processes, such as chemical precipitation, electrodialysis, and adsorption, are currently used. Among these methods, adsorption is highly effective and economical, and is a promising and widely applied method. Consequently, many effective adsorbents with strong affinity and high loading capacity for heavy metal ions were subsequently prepared (such as activated carbon,4,5 clay,6 zeolite,7 resin,8 and so on). Till now, people found chelating resins with three-dimensional network structure that contain chelating functional groups are insoluble in water and other solvents. Among chelating resins, the nitrogen-type chelating resins using nitrogen atoms as ligating atoms have excellent adsorption property for heavymetal ions and are applied widely in separation, enrichment, and removing of heavy-metal ions.9−11 But, thermal and mechanical stabilities of those chelating resins are poor. Recently, composite materials have been a significant concern because they are engineered materials formed two or more constituent materials with significantly different physical or chemical properties. Among composite materials, polymer− inorganic composite materials offer very interesting and potential applications and may have prominent properties in areas such as adsorbents,12 optics,13 and electronics.14,15 The silica matrix has received great attention since it shows excellent swelling resistance in different solvents and good mechanical, thermal, and chemical stabilities. Polymers with functional group are grafted on the silica formed inorganic−organic composite materials. This can overcome polymers shortcomings of being toxic and soluble in water. Such kinds of composite materials have received a great deal of attention recently because of their excellent performance in the field of adsorption16−20 and catalysis.21 But, synthetic processes of © 2012 American Chemical Society

these composite materials are complicated and difficult. Synchronously, polymers with functional groups are grafted on the silica. The silica surface area will be reduced. These will reduce silica high loading capacity for heavy metal ions. Hydrogels are slightly cross-linked hydrophilic polymers with excellent three-dimensional networks consisting of flexible chains fast adsorption rate, high adsorption capacity, easy separation, wide pH application range, and mild regeneration. However, the pure organic hydrogel shows a higher swelling degree which is not beneficial for practical applications. In recent years, preparation of organic−inorganic three-dimensional network composites have attracted a great deal of attention due to their low production cost, higher mechanical resistance, and extensive applications.22−25 Although molecular chains of polymers are incorporated in the composite materials, they still retain their purification properties for water treatment.26,27 Interpenetrating network structure inorganic− organic composite nanospheres not only increase the adsorption capacity but also enhance the adsorption rate, leading the adsorption process completing within a few minutes.28 In the present work, polyacrylonitrile/silica nanospheres with three-dimensional network structure were synthesized via emulsion polymerization method. The sorption properties of the obtained composite materials were tested for Pb(II). This will offer a facile method to prepare adsorbent with threedimensional interpenetrating network structure in the material field. Received: Revised: Accepted: Published: 4952

January 5, 2012 March 11, 2012 March 17, 2012 March 18, 2012 dx.doi.org/10.1021/ie3000024 | Ind. Eng. Chem. Res. 2012, 51, 4952−4957

Industrial & Engineering Chemistry Research

Article

2. EXPERIMENTAL SECTION 2.1. Materials. Acrylonitrile, γ-methacryloxypropyl trimethoxy silane, and plumbum nitrate were reagent grade and used without further purification obtained from Shanghai Chemical Co. N,N′-Methylene-bis-acrylamide, dodecylbenzene sulfate, and dimethylbenzene were purchased from by Nanjing Shuguang Chemicals Co. Water was distilled once. 2.2. Preparation Polyacrylonitrile/Silica Nanospheres. Polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure were prepared via emulsion polymerization method using 0.08 g azobisisbutyronitrile (AIBN) as initiator, and acrylonitrile and γ-methacryloxypropyl trimethoxy silane as monomer. In a flask, 5 g acrylonitrile, 5 g γmethacryloxypropyl trimethoxy silane, 0.85 g dodecylbenzene sulfate as emulsifier, 0.01 g N,N′-methylene-bis-acrylamide as cross-linker, 30 g water, and 18 g dimethylbenzene were mixed. The mixture was bubbled with N2 for 40 min to eliminate oxygen before it was sealed with a magnetic stirring and heating at 60 °C for 10 h. The system was then allowed to cool to room temperature. The final products were collected by filtration, washed with deionied water and alcohol to remove any possible ionic remnants and, then, dried at 60 °C for 24 h. Experimental result indicates that well-defined polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure can be obtained under the present experimental conditions. These processes are described in Scheme 1.

mL of solution containing different concentrations of Pb(II) ions at pH = 5 for different hours. Meanwhile, the adsorption isotherm was conducted by changing the solution concentration ranging from 10.0 to 50.0 mg L−1 at room temperature (25 °C) for 6 h at pH = 5. After centrifugation, 5 mL residues solution was taken out and put in a tube, and distilled with water until the whole volume was 25 mL. The concentrations of Pb(II) ion solution were determined on a GBC-932 atomic adsorption spectrophotometer. Adsorption amount (Q) was calculated according to eq 1 Q (mmol/g) = (C0 − C)V /MW

(1)

Where C0 and C are the concentration of Pb(II) ions before and after sorption (mg/L), respectively; V is the volume of the solution used for sorption (L); M is atomic weight of the Pb(II); and W is the weight of the polyacrylonitrile/silica nanospheres.

3. RESULTS AND DISCUSSION 3.1. Preparation and Characterization of the Polyacrylonitrile/Silica Nanospheres. The SEM (Figure 1a) micrograph reveals that optimization of the experimental parameters allows macroscopic preparation of polyacrylonitrile/silica nanospheres. From Figure 1a, SEM observation shows that the products consist of a large quantity of nanospheres with an average diameter 160 nm. Examining

Scheme 1. Preparation Process for Polyacrylonitrile/Silica Nanospheres with Three-Dimensional Interpenetrating Network Structure: (A) Globelet Formed by Azobisisbutyronitrile (AIBN), Acrylonitrile, γMethacryloxypropyl Trimethoxy Silane, Dimethylbenzene, and N,N′-Methylene-bis-acrylamide; (B) Copolymer Nanospheres; (C) Polyacrylonitrile/Silica Nanospheres with Three-Dimensional Interpenetrating Network Structure

2.3. Instruments. The synthesized products were characterized by scanning electron microscopy (SEM) (JEOL JSM6300), The infrared spectrum was acquired on a Bruker FT-IR Vector-22. The thermal decomposition measurements were performed using a Perkin-Elmer STA409PC thermogravimetric analyzer. The sample pans are a ceramic (alumina, Al2O3) crucible. A 10−20 mg portion of polyacrylonitrile/silica nanospheres were put in a pan with heating rate was 2 °C min−1. The temperature range was 15−600 °C. The samples were studied under air atmosphere with a flow rate of 100 mL min−1. 2.4. Adsorption Procedure. Adsorption experiments were carried out using a batch method. A 0.02 g portion of the polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure were immersed in with 50

Figure 1. (a) SEM image of obtained polyacrylonitrile/silica nanospheres. (b) SEM image of obtained SiO2 quantum dots. 4953

dx.doi.org/10.1021/ie3000024 | Ind. Eng. Chem. Res. 2012, 51, 4952−4957


Article

numerous SEM images of the polyacrylonitrile/silica nanospheres prepared at 60 °C for 10 h experimental results indicates that well-defined polyacrylonitrile/silica nanospheres can be obtained under the present experimental conditions. In order to investigate colloid of silica that was produced between molecular chains of the copolymer and formed threedimensional interpenetrating network structure, polyacrylonitrile/silica nanospheres were heated to 600 °C in air for 25 h. The copolymers were degradated, oxidized, and volatilized by high temperature, and oxygen and SiO2 nanoparticles were obtained. From Figure 1b, we can see that a large quantity of SiO2 quantum dots were obtained. The experimental result indicates that the colloid of SiO2 quantum dots was produced between molecular chains of the copolymer and formed a three-dimensional interpenetrating network structure. A key question here is why did the adsorbents formed nanospheres with interpenetrating three-dimensional network structure. The most likely mechanism to explain nanospheres with interpenetrating three-dimensional network structure may be the control of the network of the molecule chains of copolymer. In the globelet formed by azobisisbutyronitrile (AIBN), acrylonitrile, and γ-methacryloxypropyl trimethoxy silane, acrylonitrile and γ-methacryloxypropyl trimethoxy silane were initiated by free-radicals that were produced by decomposing AIBN. Cross-linking copolymer nanospheres were synthesized. When copolymers were hydrolyzed, a colloid of silica was produced between molecular chains of the copolymer and formed interpenetrating three-dimensional network structure.29 3.2. FT−IR Spectra. A typical infrared spectrum of the obtained polyacrylonitrile/silica nanospheres is shown in Figure 2a. The spectrum of pure PAN contains prominent peaks at 2930, 2240, and 1460 cm−1 due to stretching vibration of methylene (−CH2−), stretching vibration of nitrile groups (−CN), and bending vibration of methylene, respectively.16 Peaks at about 1720 and 1375 cm−1, which were assigned to the vibration of the CO bonds and stretching vibration of methyl (−CH3), respectively.30 These results testify acrylonitrile and γmethacryloxypropyl trimethoxy silane have copolymerized. Composite nanospheres present a peak with relatively high intensity around 1100 cm−1, which is the characteristic Si−O− Si vibrational mode peaks.27 Polyacrylonitrile/silica nanopheres also show characteristic bending mode peaks at 790 and 935 cm−1. It is also seen that the peak at 3400 cm−1, which is the characteristic band of O−H (Si−OH) group. This can be attributed to the stretching vibrations involving the hydroxyl group. These results confirmed that (γ-methacryloxypropyl trimethoxy silane) has been successfully copolymerized with acrylonitrile and hydrolyzed resulting in the desired high degree Si−O−Si network. Figure 2b is infrared spectrum of the products obtained by heated copolymer nanospheres to 600 °C in air for 25 h. Peaks at about 3435 cm−1 and at 1636 cm−1can be attributed to the vibration mode of Si−OH. The peak at around 1103 cm−1 is related to the Si−O−Si asymmetric stretching mode.27 Peaks at 796 and 481 are related to the vibrations of SiO2 (∼790 cm−1), SiOx (∼460 cm−1), respectively. No Si−Si, Si−H, and C−H peaks were detected in our samples, which testify that the copolymer was entirely removed and silica was obtained. 3.3. Thermogravimetric Analysis. To examine the composition of the above-prepared polyacrylonitrile/silica nanospheres, the weight loss of polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network

Figure 2. (a) Infrared spectrum of obtained polyacrylonitrile/silica nanospheres. (b) Infrared spectrum of the silica obtained by heated copolymer nanospheres to 600 °C in air for 25 h.

structure at the first stage ranging between room temperature and 200 °C may be attributed to the emitted water (it starts at approximately 50 °C) and volatile materials (starts at approximately 200 °C). The second stage of weight loss starts at about 200 °C and continues up to 350 °C due to the degradation of grafted functional groups. The last stage begins from 350 to 430 °C, and weight loss of the polyacrylonitrile/ silica nanospheres is around 50%. The copolymer were degradated, volatilized, and oxidized by high temperature and oxygen. From 430 to 600 °C, weight loss of the remainder is slowness and it may belong to oxidation of the remaining carbon. Finally, about 20% weight white solid (less remaining black solid) was obtained (Figure 3). The result further testifies

Figure 3. Thermo-analytical curve of the obtained polyacrylonitrile/ silica nanospheres. 4954



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that γ-methacryloxypropyl trimethoxy silane has been successfully copolymerized with acrylonitrile. 3.4. Adsorption Kinetics and Isothermal Adsorption for Pb(II). The adsorption kinetics of polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure for Pb(II) at room temperature is shown in Figure 4.

Table 1. Comparison of Pseudo-First- and Pseudo-SecondOrder Rate Constants Calculated from Experimental Data pseudo-first-order model qe(exp) (mmol/ g) 0.108

0.025

0.220

R

2

0.943

pseudo-second-order model K2 (g/ mmol min) 7.5 × 10

−4

qe(cal) (mmol g)

R2

0.13

0.994

with the data for R2 = 0.994. In addition, the theoretical qe(cal) values were closer to the experimental qe(exp) (0.108 mmol/g). It can be said that the pseudo-second-order kinetic model provided a good correlation for the adsorption of Pb(II) onto nanospheres in contrast to the pseudo-first-order model. Therefore, the adsorption behavior of Pb(II) onto nanospheres belonged to the pseudo-second-order kinetic model and the adsorption process was a chemical process. The saturated adsorption capacity of obtained polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure is higher than that of silica grafted polyacrylonitrile.16 The high adsorption capacity may be caused by the three-dimensional interpenetrating network structure. The interpenetrating network structure formed by SiO2 quantum dots and polyacrylonitrile may provide convenient diffusion channel for Pb(II) ions into the interior of the copolymer beads when it was used in adsorption of Pb(II) ions in aqueous solution. The isotherms revealed that the adsorption capacities increased with equilibrium concentration and that isothermal experiments are needed. To examine the effect of contact time on the adsorption of Pb(II) at different initial concentrations, kinetics experiments were carried out by adding 0.020 g polyacrylonitrile/silica nanospheres to 50.0 mL solution containing 10.0, 20.0, 30.0, and 40.0 mg/L Pb(II) at pH = 5, T = 25 °C, respectively. The results were shown in Figure 5.

Figure 4. Kinetics studies of Pb(II) adsorption onto polyacrylonitrile/ silica nanospheres (pH = 5, initial concentration of Pb(II) = 10.0 mg/ L, 0.020 g sorbent, T = 25 °C).

From Figure 4, we can see the adsorption rate was quick at the beginning and, then, slow. The adsorption equilibrium was established in about 300 min, and it could reach the saturation adsorption capacity 0.108 mmol/g within 300 min. The nitrogen atoms that have chelating effects with metal ions mostly gather on the surface of the nanospheres, which is favorable for quick adsorption. To evaluate the adsorption kinetics of Pb(II) ions, two different kinetic models were applied for the experimental data:29 The pseudo-first-order equation is ln(qe − qt ) = ln qe − k1t

K1 (1/ min)

qe(cal) (mmol/ g)

(2)

The pseudosecond-order equation is t /qt = 1/k2qe2 + t /qe

(3)

The terms qe (mmol/g) and qt (mmol/g) are adsorption capacity at equilibrium and the adsorption amount at time t (min), respectively. Values of qe calculated from the intercept of the plot of ln(qe − qt) vs t and the slope of t/qt vs t are defined as theoretical qe(cal) values of the pseudo-first- and pseudosecond-order models, respectively. Also, k1 (1/min) and k2 (1/ gmmol min) are pseudo-first- and pseudo-second-order rate constants of adsorption, respectively. The pseudo-first-order model is rendered as the rate of occupation of the adsorption sites which is proportional to the number of unoccupied sites; the pseudo-second-order kinetic model is assumed for the chemical reaction mechanisms. The idea that the adsorption rate is controlled by chemical adsorption through sharing or exchange of electrons between the adsorbrate and adsorbent is also assumed. On the basis of the experimental data of qt, t, and qe, k1, k2, and the correlation coefficient can be determined, respectively, Parameters of two kinetic models are given in Table 1. The best-fit model was selected based on both linear regression correlation coefficient and the theoretical qe(cal) value (0.13 mmol/g). The pseudosecond-order rate equation for adsorption of Pb(II) ions onto nanospheres agreed well

Figure 5. Adsorption isotherms of Pb(II) onto nanospheres at different initial concentrations (pH = 5, 0.020 g sorbent, T = 25 °C).

While changing the concentration of the solution from 10.0 to 40.0 mg/L, the absolute amount of Pb(II) ions per unit of adsorbent increased from 0.108 to 0.1270 mmol/g at 25 °C. A study of the effect of contact time on the adsorption of Pb(II) on polyacrylonitrile/silica nanospheres at 25, 30, 35, and 40 °C are shown in Figure 6. The curves indicated that the adsorption amount of Pb(II) ion increases with the rising of temperature, and the influence of temperature on the 4955



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When pH is lower than 5, it is not propitious for Pb(II) ions to react with silanol groups. Pb(II) ions hydrolyze in aqueous solutions as in the following equations: Pb2 + + H2O ↔ Pb(OH)+ , Pb(OH)2 , Pb(OH)3− , Pb (OH)4 2 − + H+

(2)

When pH > 5, the hydrolysis of Pb(II) ions has become obvious (the first-order hydrolysis constant of Pb(II) ion is K1 = 6.3 × 10−8), and the nanosphere surfaces will be covered with the hydrolysis product.16 This will badly affect the adsorption property of the solid adsorbent and lead to the decline of the adsorption capacity. Our results are agreement with the previous report.31 3.5. Desorption. The adsorption−desorption cycle was repeated 10 times using the same nanospheres. Analysis of the influence of pH on the removal efficiency showed that it was expected that acid would be an effective agent for desorption. The results indicated that Pb(II) ions could be desorbed completely by 3 min of sonication in the presence of 0.1 mol/L HCl. In addition, the adsorption capacity of regenerated polyacrylonitrile/silica nanospheres was increased little. Figure 8 showed the relationship between the time for reuse and the

Figure 6. Adsorption isotherms of Pb(II) onto nanospheres an different temperature (pH = 5, initial concentration of Pb(II) = 10.0 mg/L, 0.020 g sorbent).

adsorption amount is greater. The saturated adsorption amount at 40 °C is 0.131 mmol/g, which is far greater than 0.108 mmol/g of the saturated adsorption amount at 25 °C. The fact that the adsorption amount of Pb(II) increases with the rising temperature implies that the adsorption Pb(II) on polyacrylonitrile/silica nanospheres is an endothermic process. By varying the pH value of the medium, the isothermal adsorption experiments of nanospheres of polyacrylonitrile/ silica for Pb(II) ions at different pH values were carried out, respectively, and Figure 7 presents the adsorption isotherms of

Figure 8. Relationship between the cycle times and adsorption capacity of the regenerated polyacrylonitrile/silica nanospheres.

adsorption capacity of the regenerated polyacrylonitrile/silica nanospheres. From Figure 8, we can see that after 8 sorption− desorption cycles, the adsorption capacity of regenerated polyacrylonitrile/silica nanospheres increased from 1.08 to 1.1 mmol/g. These results suggest that few CN groups change into CONH2 or COOH.32 The schematic representation of conversion of CN groups to CO NH2 or COOH groups is shown in Scheme 2. Solubility of the polyacrylonitrile is less than polyacryamide and poly(acrylic acid). There are more −NH2 and −COOH groups chelated with Pb(II) in aqueous solutions. This will induce adsorption capacity of regenerated polyacrylonitrile/ silica nanospheres to increase.

Figure 7. Effect of pH value on adsorption property of polyacrylonitrile/silica nanospheres (initial concentration of Pb(II) = 10.0 mg/L, 0.020 g sorbent, T = 25 °C).

polyacrylonitrile/silica nanospheres for the Pb(II) ion at different pH values. From Figure 7, we can see that the pH value of solution is less than 5 and the adsorption capacity of polyacrylonitrile/silica nanospheres increases with increasing pH value: when pH = 5, the adsorption capacity gets up to a maximum; when pH is over 5, the adsorption capacity turns to decline with further increase of the pH value. The ion-exchange reaction on the silica gel surface is accomplished through the substitution of protons of the surface silanol groups by the metal ions from solution as follows31 Mn + + χ(SiOH) ↔ M(SiO)x(n − x) + + χH+

Scheme 2. Conversion of CN Groups to CONH2 or COOH Groups

(1) 4956



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(14) Finlayson, C. E.; Russell, D. M.; Ramsdale, C. M.; Ginger, D. S.; Silva, C.; Greenham, N. C. amplified Spontaneous Emission in ClosePacked Films of Semiconductor nanocrystals using picosecond excitation. Adv. Funct. Mater. 2002, 12, 537−540. (15) Jun, F.; Alex, M.; Phil, A.; Michael, E. H.; Calvin, C.; David, G. Self-assembly of photoactive TiO2−cyclodextrin wires. J. Am. Chem. Soc. 2005, 127 (43), 14968−14969. (16) Gao, B.; Gao, Y.; Li, Y. Preparation and chelation adsorption property of composite chelating material poly(amidoxime)/SiO2 towards heavy metal ions. J. Chem. Eng. 2010, 158, 542−549. (17) Kumar, G. P.; Kumar, P. A.; Chakraborty, S.; Ray, M. Uptake and desorption of copper ion using functionalized polymer coated silica gel in aqueous environment. Sep. Purif. Technol. 2007, 57, 47−56. (18) Yin, P.; Xu, Q.; Qu, R.; Zhao, G.; Sun, Y. Adsorption of transition metal ions from aqueous solutions onto a novel silica gel matrix inorganic−organic composite material. J. Hazard. Mater. 2010, 173, 710−716. (19) An, F.; Gao, B. Chelating adsorption properties of PEI/SiO2 for plumbum ion. J. Hazard. Mater. 2007, 145, 495−500. (20) Shintaro, M.; Namazuda, K.; Shitoka, S.; Noriko, K.; Haruka, K.; Yoshitsugu, H.; Nakano, Y. Temperature-swing adsorption of proteins in water using cationic copolymer-grafted silica particles. Ind. Eng. Chem. Res. 2011, 50, 12358−12365. (21) Kisch, H.; Weiß, H. Tuning photoelectrochemical and photocatalytic properties through electronic semiconductor−support interaction. Adv. Func. Mater. 2002, 12, 483−488. (22) Wang, Q.; Mynar, J. L.; Yoshida, M.; Lee, E.; Lee, M.; Okuro, K.; Kinbara, K.; Aida, T. High-water-content mouldable hydrogels by mixing clay and a dendritic molecular binder. Nature 2010, 463, 339− 343. (23) Bulut, Y.; Akcay, G.; Elma, D.; Serhatlı, I. E. Synthesis of claybased superabsorbent composite and its sorption capability. J. Hazard. Mater. 2009, 171, 717−723. (24) Zheng, Y.; Wang, A. Preparation and ammonium adsorption properties of biotite-based hydrogel composites. Ind. Eng. Chem. Res. 2010, 49, 6034−6041. (25) Zheng, Y.; Xie, Y.; Wang, A. Rapid and wide pH-independent ammonium-nitrogen removal using a composite hydrogel with threedimensional networks. J. Chem. Eng. 2012, 179, 90−98. (26) Miller, S. A.; Hong, E. D.; Wright, D. Rapid and efficient enzyme encapsulation in a dendrimer silica nanocomposite. Macromol. Biosci. 2006, 6, 839−845. (27) Michael, A.; Dimitris, T. Organic/inorganic hybrid nanospheres based on hyperbranched poly(ethyleneimine) encapsulated into silica for the sorption of toxic metal ions and polycyclic aromatic hydrocarbons from water. J. Hazard. Mater. 2009, 170, 35−42. (28) Kasgő z, H.; Durmus, A. Dye removal by a novel hydrogel-clay nanocomposite with enhanced swelling properties. Polym. Adv. Technol. 2008, 19, 838−845. (29) Zhao, Q.; Chen, W.; Zhu, Q. Preparation of nanoporous SiOx materials via interpenetrating polymer network method. Mater. Lett. 2003, 57, 3606−3608. (30) Liu, J.; Ma, Y.; Xu, T.; Shao, G. Preparation of zwitterionic hybrid polymer and its application for the removal of heavy metal ions from water. J. Hazard. Mater. 2010, 178, 1021−1029. (31) Tran, H. H.; Roddick, F. A.; O’Donnell, J. A. Copparison of chromatography and desiccant silica gels for the adsorption of metal ions-I adsorption and kinetics. Wat. Res. 1999, 33 (13), 2992−3000. (32) Zhang, W. B.; Xie, S. X. Study on simultaneous hydrolysis and sulfonation of acrylonitriles-styrenen copolymer by sulfuric acid. Oilfield chem. 1994, 11 (3), 190−193.

4. CONCLUSION Polyacrylonitrile/silica nanospheres with three-dimensional interpenetrating network structure have been synthesized via an emulsion polymerization method. The obtained polyacrylonitrile/silica nanospheres were used to investigate adsorption Pb(II) ion from aqueous solutions. Research results displayed that composite material has higher adsorption capacity than . Adsorption behavior of Pb(II) onto nanospheres belonged to the pseudo-second-order kinetic model, and the adsorption process was a chemical process.

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AUTHOR INFORMATION

Corresponding Author

*E-mail addresses: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Project 1040606M43 supported by the Anhui province Natural Science Foundation

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REFERENCES

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Silica Nanospheres with Three- Dimensional

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