Two-Step Preparation of an Amidoxime-Functionalized

Article pubs.acs.org/jced

Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Two-Step Preparation of an Amidoxime-Functionalized Chelating Resin for Removal of Heavy Metal Ions from Aqueous Solution Youning Chen,* Huan Zhao, Yuhong Li, Wei Zhao, Xiaoling Yang, Xiaohua Meng, and Huan Wang

Downloaded via UNIV OF GLASGOW on September 3, 2019 at 19:08:26 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

College of Chemistry and Chemical Engineering, Xianyang Normal University, Xianyang 712000, China ABSTRACT: A novel amidoxime-functionalized chelating resin (PAO-g-PS) was prepared through a two-step method. First, poly (acrylonitrile) was grafted onto chloromethylated polystyrene beads via surface-initiated atom transfer radical polymerization, and then the nitrile group was converted to the amidoxime group by reaction with hydroxylamine. Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy were used to characterize the structure of the resin. The adsorption properties were evaluated with Fe(III), Cr(III), Cd(II), and Pb(II). The maximum adsorption capacities obtained by experiment with Fe(III), Cr(III), Cd(II), and Pb(II) were 3.48, 2.54, 1.33, and 0.89 mmol g−1, respectively. By studying the effects of pH on adsorption, it was found that the adsorption of metal ions was mainly achieved by chelation interaction. The adsorption process conformed to the quasi-second-order dynamic equation. The thermodynamic study of adsorption suggested that the adsorption of PAO-g-PS resins for heavy metal ions was an entropy-driven endothermic chemisorption process. The adsorption of PAO-gPS for heavy metal ions is selective, hardly affected by common coexisting ions such as Na(I), K(I), Ca(II), and Mg(II). The adsorption−desorption cycle indicated that the resin had good reusability and stability. All of these results indicated that the PAO-g-PS resins were suitable for efficient removal of metal ions from aqueous solution.

1. INTRODUCTION Metallurgy, electroplating, tanning, and chemical and mineral processing industries will produce numerous heavy metal wastewaters, and a large amount of industrial wastewater and urban domestic sewage containing heavy metal pollution will be discharged into rivers and lakes.1,2 Heavy metals have a serious impact on animals and plants and human health. In severe cases, it can even lead to heavy metal poisoning death.3−5 Therefore, the treatment and recovery of industrial wastewater have been widely concerned.6−8 The adsorption method is an important physical and chemical method in the treatment of heavy metal-ion industrial wastewater. It has the advantages of low cost, good effect, and strong operability.9,10 The functional groups on the surface of the adsorbent not only affect its adsorption ability but also determine the adsorption mechanism.11,12 Adsorption selectivity and capacity are two important indicators for evaluating the properties of chelating resins.13 Increasing the density of functional groups will increase the adsorption capacity.14 Some ligands with lower molecular weight are commonly used for surface modification of materials. Due to a limited number of reactive sites on the surface of materials, the density of the introduced functional groups is low, resulting in an unsatisfactory increase in adsorption capacity.15 To increase the functional group density, physical methods can be used to introduce macromolecules into the material, but because no chemical bonds are formed between them, macromolecules are easily detached from the surface of the material.16 Polymerization has a promising application in surface modification. By polymer© XXXX American Chemical Society

ization, the polymer chain is covalently bonded to the surface of the material, so that the functional group is firmly attached to the surface of the material.17−19 In recent years, as a new active controllable technology, surface-initiated atom transfer radical polymerization (SIATRP) has been initially applied to the preparation of adsorbing materials such as chromatographic stationary phases, chelation and ion-exchange resins, chelation and ion-exchange adsorption membranes.20−22 In this work, considering that cross-linked polystyrene (PS) resin is a common substrate for the preparation of various adsorbents, we attempted to prepare a novel amidoximefunctionalized chelating resin with high capacity using SIATRP, and its adsorption properties toward Fe(III), Cr(III), Cd(II), and Pb(II) were investigated.

2. EXPERIMENTAL SECTION 2.1. Reagents and Instruments. Chloromethylated cross-linked styrene-divinylbenzene resins (18% Cl, particle size 0.30−0.45 mm) (Sunresin New Materials Co. Ltd., Xi’an, China), acrylonitrile (Tianjin Fuchen Chemical Reagent Factory, China) distilled under normal pressure and stored at 5 °C, copper(I) bromide (Sinopharm, ≥98%), 2,2′-bipyridyl (Sinopharm, ≥99.5%), and hydroxylamine hydrochloride Received: May 5, 2019 Accepted: August 23, 2019

A

DOI: 10.1021/acs.jced.9b00402 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

mol L−1 HCl solution for desorption, then filtered, washed with distilled water, and reused for the next cycle of the adsorption experiment. The stability test of the PAO-g-PS resin is given in ref 23.

(Tianjin Fuchen Chemical Reagent Factory, China) were used. All other chemicals were of analytical purity. 2.2. SI-ATRP of Acrylonitrile on Chloromethylated Polystyrene Beads (PAN-g-PS). The synthesis method of PAN-g-PS is given in ref 23. 2.3. Preparation of PAO-g-PS. The PAN-g-PS resin and aqueous hydroxylamine hydrochloride solution (3% by mass) were mixed and the pH was adjusted to 7.0 with sodium hydroxide solution. The mixture was allowed to react at 80 °C for 6 h. After the reaction, an amidoxime-functionalized chelating resin (PAO-g-PS) was obtained by washing the microspheres repeatedly with acetone and distilled water and drying in a vacuum at 35 °C for 6 h. 2.4. Characterization of the Resin. The surface structure of chloromethylated PS, PAN-g-PS, and PAO-g-PS resins was characterized using a Tensor 27 Fourier-transform infrared (FTIR) spectrophotometer (Bruker Company, Germany) and an X-ray photoelectron spectrometer (XPS, PE, PHI-5400). 2.5. Batch Adsorption. All experiments were carried out in 250 mL conical flasks containing 0.1 g resin and 100 mL of single-metal-ion solution, which were shaken in a 250 rpm thermostatic oscillator at 25 °C except for the temperature experiments. The required pH was adjusted with 0.1 M HNO3 and 0.1 M NaOH solutions. The residual concentration of metal ions in the solution after adsorption was determined by atomic absorption spectrophotometry. The adsorption capacity at equilibrium (Qe, mmol g−1) was calculated by eq 1 Q e = V (C0 − Ce)/m

3. RESULTS AND DISCUSSION 3.1. Preparation of Amidoxime-Functionalized Chelate Resin (PAO-g-PS). The synthetic route of the amidoxime-functionalized chelate resin is shown in Figure 1.

Figure 1. Synthetic route for the preparation of PAO-g-PS resins.

First, PAN was grafted onto the surface of chloromethylated PS beads via SI-ATRP. Ref 23 indicated the effect of the monomer concentration and the reaction time on the degree of grafting. In the second step, amidoxime-functionalized chelating resins were prepared by amine−hydrazine conversion reaction of hydroxylamine and the nitrile group. 3.2. Characterization of the Resin. The PS-CH2Cl, PAN-g-PS, and PAO-g-PS resins were characterized by FTIR and XPS. Figure 2 shows the infrared spectrum of PS-CH2Cl, PAN-gPS, and PAO-g-PS. For the PS-CH2Cl resin (Figure 2a), peaks

(1)

where V is the volume of the solution (L), C0 and Ce are the initial and equilibrium concentrations of metal ions (mmol L−1), respectively, and m is the weight of the resin used (g). To avoid precipitation of metal hydroxide, the adsorption of the above metal ions was investigated at different pH values under acidic conditions by shaking 0.1 g of resin with 100 mL (4 mmol L−1) of metal-ion solution for 12 h. For the adsorption isotherm experiment, 0.1 g of resin was shaken with 100 mL of metal-ion solution at different concentrations (1.0−8.0 mmol L−1) for 12 h. For the adsorption kinetic experiment, 0.1 g of resin was shaken with 100 mL of metal-ion solution at optimum pH and optimum concentration. Samples of 1.00 mL solution were taken out at different time intervals, and the method for analyzing the change of metal-ion concentration was the same as the above. The change of adsorption capacity with temperature was measured at 25, 35, and 45 °C. 2.6. Multicomponent Adsorption. 2.6.1. Competitive Adsorption. The experiments were conducted in 250 mL conical flasks containing 0.1 g of resin and 100 mL of a mixture solution of four metal ions (the concentration of each metal ion was 4.0 mmol L−1), which were shaken in a 250 rpm thermostatic oscillator at 25 °C and the initial pH of 4.0. 2.6.2. Selective Adsorption. A series of binary mixed solutions were obtained by mixing Fe(III), Cr(III), Cd(II), and Pb(II) ions (4.0 mmol L−1) with the coexisting ions such as Na(I), K(I), Ca(II), Mg(II), and Zn(II) (8.0 mmol L−1) respectively. The mixture of 0.1 g of resin and 100 mL of each binary mixture was shaken for 12 h at 25 °C. The selectivity factor can be calculated from the adsorption capacity of metal ions in binary mixtures. 2.7. Recycling and Stability Experiments. The Fe(III), Cr(III), Cd(II), and Pb(II)-loaded resins were placed in 1.0

Figure 2. FTIR spectrum of (a) PS-CH2Cl, (b) PAN-g-PS, and (c) PAO-g-PS resins.

at 2924 and 1450 cm−1 represent the C−H stretching and skeleton vibration of the aromatic ring, respectively. The C−Cl stretching in the −CH2Cl group corresponds to the peaks at 759 and 698 cm−1. For the PAN-g-PS resin (Figure 2b), a characteristic CN stretching vibration at 2240 cm−1 appears, suggesting that PAN was successfully modified to the surface of the PS-CH2Cl resin.24 For PAO-g-PS (Figure 2c), the characteristic absorption peak of CN disappeared at 2240 cm−1 and a new absorption peak appeared at 1660 and 950 cm−1, corresponding to the stretching vibration of CN and NO, respectively. The stretching vibration absorption peak of B



Article

−NH2 appeared at 3300 cm−1. These results indicated that the amidoxime group was formed in the PAO-g-PS resin. The BET surface area, BJH pore volume, and average pore diameter of PAO-g-PS are shown in Table 1. These results indicate that the resin has a mesoporous structure and large pore size, by which it easily transfers metal ions to internal adsorption sites.

To obtain more detailed information on the changes in PAO-g-PS resin surface composition, the peak components of the C 1s peak in the XPS spectra were further analyzed by the core-level spectrum. As shown in Figure 4, the C 1s core-level spectra of the PAO-g-PS resin could be curve-fitted into four peak components. Comparing with PAN-g-PS, two new peaks at 283.8 and 285.2 eV appeared, which were attributed to C− N and CN, indicating the successful conversion of amine− oxime. 3.3. Batch Adsorption. 3.3.1. Effect of pH. Figure 5 shows the effect of solution pH on metal-ion adsorption. As can be

Table 1. Porous Structure Parameters of PAO-g-PS parameters

PAO-g-PS

surface area (m2 g−1) BJH cumulative volume (cm3 g−1) average pore diameter (nm)

43.52 0.19 23.65

From the wide-scan XPS spectrum (Figure 3), it could be seen that the structure of the modified resin had changed. For

Figure 5. Effect of pH on the adsorption of the PAO-g-PS resin for Fe(III), Cr(III), Cd(II), and Pb(II) (initial concentration: 4 mmol L−1; 25 °C; contact time: 12 h; and adsorbent dose: 0.1 g).

seen from Figure 5, the adsorption capacity sharply increased when the pH increased from 1.0 to 3.0 and the platform appeared at pH 4.0. for the four metal ions. The amidoxime has an amphiphilic structure. When the pH is low, the basic amine group in the amidoxime group is highly protonated and has a cationic character, whereas at a higher pH, the acidic hydroxyl group will dissociate, showing the nature of the anion. At lower pH values, the amine group loses its ability to complex with metal ions due to protonation, resulting in low adsorption capacity. The degree of protonation decreases with an increase of the pH value, and the coordination and chelation ability of the amine group with the metal ion are enhanced. Moreover, the degree of dissociation of hydrazine hydroxyl groups is increased, an oxygen anion is generated, and

Figure 3. Wide-scan XPS of (a) PS-CH2Cl, (b) PAN-g-PS, and (c) PAO-g-PS.

the PS-CH2Cl resin (Figure 3a), the peak of N 1s was not found. For the PAN-g-PS resin (Figure 3b), there was N 1s peak emission at approximately 399 eV, indicating that nitrile groups were successfully grafted onto the surface of the resin. For PAO-g-PS (Figure 3c), the peak at 532.3 eV is due to O 1s, suggesting that the amidoxime groups are introduced onto the resin surface via amine−hydrazine conversion reaction.

Figure 4. C 1s core-level spectra of (a) PS-CH2Cl, (b) PAN-g-PS, and (c) PAO-g-PS. C



Article

electrostatic interaction exists between the resin and metal ions. Due to the synergistic effect of electrostatic action and chelation, the metal ions are first attracted to the surface of the resin and then sequestered, so that the adsorption capacity is high. However, heavy metal ions are easily hydrolyzed. When the pH is more than 4.0, the hydrolysis of the metal ions becomes very conspicuous, so that the surface of the resin is covered by the hydrolyzate. These will seriously affect the adsorption performance of the resin, resulting in a decrease in adsorption capacity. In summary, the strong chelation adsorption of resin for metal ions was mainly due to the synergistic effect of electrostatic interaction and coordination chelation. 3.3.2. Adsorption Isotherm. The adsorption isotherms of resin for Fe(III), Cr(III), Cd(II), and Pb(II) at 25 °C are shown in Figure 6. The adsorption isotherm is usually

ln Q e = ln KF +

(3) −1

where Qe is the adsorption capacity, mmol g ; Ce is the equilibrium concentration of metal ions, mmol L−1; Q0 is the saturated adsorption capacity, mmol g−1; KF is an empirical parameter; n is the Freundlich constant; and KF is the binding energy constant, reflecting the affinity of the adsorbents to metal ions. b is the Langmuir adsorption constant, and it is related to the adsorption equilibrium constant between the solid and liquid (aqueous solution), as expressed by the following equation: b = (K C − 1) × M /ρ

(4)

where KC is the adsorption equilibrium constant, which was obtained from the Langmuir isotherm at different temperatures, M and ρ are the molar mass (mg mmol−1) and density (mg L−1) of the solvent, respectively. The fitting results are listed in Table 2. By comparing the R2 values of the Freundlich and Langmuir models, we find that the Langmuir equation fits the experimental data better than the Freundlich equation for the four metal ions. This reflects that the adsorption of metal ions by resin is uniform monolayer adsorption. The maximum adsorption capacities were obtained from the Langmuir fitting results, which were 3.63 mmol g−1 for Fe(III), 2.72 mmol g−1 for Cr(III), 1.55 mmol g−1 for Cd(II), and 1.02 mmol g−1 for Pb(II). 3.3.3. Adsorption Thermodynamics. With the increase of temperature, the adsorption capacity of Fe(III), Cr(III), Cd(II), and Pb(II) on PAO-g-PS resins increased insignificantly (Figure 7), indicating that the adsorption was an endothermic process. Thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) can provide in-depth information about the inherent energy change related to adsorption, which can be calculated respectively using eqs 5−7

Figure 6. Adsorption isotherms and fitting curve of the PAO-g-PS resin on Fe(III), Cr(III), Cd(II), and Pb(II) at 25 °C (pH 4.0; contact time: 12 h; and adsorbent dose: 0.1 g).

ΔG = −RT ln K C

(5)

ΔG = ΔH − T ΔS

(6)

ln K C = −ΔH /RT + ΔS /R

described and analyzed by Langmuir and Freundlich models. The Langmuir isotherm describes the surface as homogeneous, assuming that all of the adsorption sites have equal solute affinity and that adsorption at one site does not affect the adsorption at an adjacent site, whereas the Freundlich isotherm describes the equilibrium on heterogeneous surfaces. The Langmuir equation (eq 2) and Freundlich equation (eq 3) were used to analyze the adsorption experimental data separately. Ce C 1 = e + Qe Q0 Q 0b

1 ln Ce n

(7) −1

−1

where R is the universal gas constant (8.314 J mol K ), T is the absolute temperature (K), and KC is the adsorption equilibrium constant. The results are shown in Table 3. As can be seen from Table 3, the negative values of ΔG indicated the spontaneity of the chelation adsorption process. The positive values of ΔH indicated that chelation adsorption was endothermic chemical adsorption. From the stoichiometric displacement model for adsorption,25 it can be seen that the displacement of adsorbed water molecules by adsorbents can obtain more translation energy than the loss of adsorbed ions, thus allowing the system

(2)

Table 2. Langmuir and Freundlich Constants for the Adsorption of Fe(III), Cr(III), Cd(II), and Pb(II) on PAO-g-PS Resins at 25 °C Langmuir constants

Freundlich constants

metal ions

Q0 (mmol g−1)

b

KC

R2L

KF

1/n

R2F

Fe(III) Cr(III) Cd(II) Pb(II)

3.63 2.72 1.55 1.02

2.30 1.81 1.36 1.08

128.9 101.4 76.3 60.8

0.99023 0.99584 0.99892 0.98945

1.235 1.698 0.894 0.958

0.7567 0.7826 0.7498 0.7658

0.9483 0.95498 0.96876 0.96327

D



Article

Figure 7. Adsorption isotherms of PAO-g-PS resin on (a) Fe(III), (b) Cr(III), (c) Cd(II), and (d) Pb(II) at different temperatures (pH 4.0; contact time:12 h; and adsorbent dose: 0.1 g).

Table 3. Thermodynamic Parameters Estimated for Adsorption of Four Metal Ions on PAO-g-PS Resins ΔG (kJ mol−1) metal ion

ΔH (kJ mol−1)

ΔS (J mol−1 K−1)

25 °C

35 °C

45 °C


68.71 62.0 22.63 15.3

271 246.5 112 85.5

−12.04 −11.44 −10.74 −10.18

−14.78 −13.95 −11.89 −11.02

−17.46 −16.37 −12.98 −11.89

to be random. The release of hydrated water in the process of metal-ion adsorption increases randomly, leading to the positive values of ΔS. In the temperature range studied, TΔS accounted for a large proportion of the total free energy, indicating that the increase of entropy during ion binding was an important factor to promote the interaction between metal ions and amidoxime. 3.3.4. Adsorption Kinetics. As shown in Figure 8, the kinetic curves of the four metal ions increased significantly during the initial phase (90 min) and then the curve gradually became flat. Overall, the adsorption equilibrium was reached for the Pb(II) and Cd(II) ions within 300 min and for the Cr(III) and Fe(III) ions within 480 min.

Figure 8. Adsorption kinetics of PAO-g-PS resins on Fe(III), Cr(III), Cd(II), and Pb(II) (initial concentration: 4 mmol L−1; pH 4.0; 25 °C; and adsorbent dose: 0.1 g).

To study the kinetic mechanism of the adsorption process, three different kinetic models proposed by Weber and Morris,26 Lagergren’s pseudo-first-order kinetic model eq 8, E



Article

Table 4. First-Order and Second-Order Rate Constants equations

parameters

Fe(III)

Cr(III)

Cd(II)

Pb(II)

pseudo-first-order kinetic equation

Qe (mmol g−1) Kads (min−1) R2 Qe (mmol g−1) k (min−1) R2 Kid (mmol g−1 min−1/2) R2

3.13 0.084 0.875 3.84 0.059 0.996 0.325 0.957

2.01 0.064 0.932 2.93 0.082 0.998 0.287 0.948

1.09 0.091 0.895 1.64 0.076 0.998 0.193 0.962

0.76 0.072 0.965 1.18 0.071 0.997 0.125 0.971

pseudo-second-order kinetics

intraparticle diffusion equation

pseudo-second-order kinetic model, eq 9 and intraparticle diffusion model eq 10, were used to explain the kinetic process. lg(Q e − Q t) = lg Q e + t 1 1 = + t 2 Qt Qe kQ e Q t = k idt 0.5

kads t 2.303

(8)

(9) (10)

where t is the adsorption time (min); k is the adsorption rate constant (min−1); Kads is the Lagergren rate constant (min−1) of the adsorption; Kid is the intraparticle diffusion rate constant (mmol g−1 min−1/2), and Qt and Qe are the adsorption amount at given time t and equilibrium time, respectively. The fitting results are listed in Table 4. Obviously, as can be seen from Table 4, R2 values of the second-order kinetics are higher than the first-order kinetics. Therefore, the adsorption behavior of Fe(III), Cr(III), Cd(II), and Pb(II) onto the PAOg-PS chelating resin followed the pseudo-second-order kinetic model. According to Weber and Morris, an adsorption process is divided into three steps: (1) diffusion of the adsorbate from the solution to the surface of the adsorbent; (2) internal diffusion process, usually determined by the pore size of the adsorbent; and (3) adsorption of the adsorbate with the surface active sites in the adsorbent. According to eq 10, if the curve gives a straight line, internal diffusion can be accepted as the only rate-limiting step, but multiple linearities are formed, indicating that two or more stages are involved in metal-ion adsorption.27 As shown in Figure 9, the adsorption process is divided into three stages: (1) rapid transport of metal ions from the solution to the surface of the resin; (2) gradual adsorption stage, where intraparticle diffusion is the rate-limiting step, and (3) final equilibrium stage. Intraparticle diffusion begins to slow down because the concentration of metal ions in the solution is very low and the number of available adsorption sites is small. From the above analysis, we know that intraparticle diffusion is not the only rate-controlling step, which indicates that the adsorption process involves several single kinetic stages. 3.4. Multicomponent Adsorption. 3.4.1. Competitive Adsorption. The competitive adsorption among the four metal ions was investigated (Table 5). As seen in Table 5, compared with the adsorption of single-metal ions, the adsorption capacity of the four metal ions is correspondingly reduced under competitive conditions. The adsorption capacity reduces by 6.90, 22.0, 28.6, and 39.3% for Fe(III), Cr(III), Cd(II), and Pb(II), respectively. In addition, competitive adsorption experiments show that the adsorption of Fe(III) is not significantly affected by other coexisting ions. For four metal

Figure 9. Plot of the Weber−Morris intraparticle diffusion model for the adsorption of metal ions on a chelating resin.

Table 5. Metal Uptake on PAO-g-PS of Competitive and Noncompetitive Adsorption Q (mmol g−1) metal ion

noncompetitive adsorption

competitive adsorption


3.48 2.54 1.33 0.89

3.24 1.98 0.95 0.54

ions, the PAO-g-PS resins had a preferential adsorption of Fe (III) > Cr(III) > Cd(II) > Pb(II). The different adsorption capacity of the same chelating adsorbent to various heavy metal ions depends on the valence electron orbital structure of these heavy metal ions. 3.4.2. Selective Adsorption. The effects of Na(I), K(I), Ca(II), Mg(II), and Zn(II) on the adsorption of Fe(III), Cr(III), Cd(II), and Pb(II) on PAO-g-PS were investigated. As shown in Table 6, the influences of Na(I), K(I), Ca(II), and Mg(II) on the adsorption of Fe(III), Cr(III), Cd(II), and Pb(II) can be ignored, but Zn(II) displayed a minor influence. This phenomenon can be explained based on the HSAB principle.28 3.5. Reusability and Stability of the PAO-g-PS Resin. Desorption of Fe(III), Cr(III), Cd(II), and Pb(II)-loaded resins was conducted by 1.0 mol L−1 HCl aqueous solution. As shown in Figure 10, the desorption efficiency was found to be generally high (more than 96%) within 60 min. To verify the reusability of the resin, 10 adsorption−desorption cycles of metal ions were carried out. As shown in Figure 11, the adsorption capacity of the resin did not change significantly F



Article

3.6. Comparison with Other Adsorbents. Comparing the adsorption capacity of the PAO-g-PS resin with other related adsorbents (Table 7), it was found that the adsorption

Table 6. Effect of Coexisting Metal Ions on the Adsorption Capacity of Fe(III), Cr(III), Cd(II), and Pb(II) (pH 4.0; Contact Time: 12 h; and Adsorbent Dose: 0.1 g) selective coefficients coexisting ions

Fe(III)

Cr(III)

Cd(II)

Pb(II)

K+ Na+ Ca2+ Mg2+ Zn2+

∞ ∞ ∞ ∞ 12.3

∞ ∞ 32.5 45.6 15.8

∞ ∞ 48.9 52.2 17.5

∞ ∞ 50.6 59.8 20.4

Table 7. Comparison of the Adsorption Capacity of Heavy Metal Ions with Various Adsorbents at 25 °C adsorption capacities (mmol g−1) adsorbents

Fe(III) Cr(III)

ZnO nanoflowers magnetic graphite oxide coal fly ash porous pellets titanate nanotubes amino-functionalized magnetic graphene composite material graphitic Fe-embedded ordered mesoporous carbon HZ818-CSIR HZ830-CSIR D301-SIR palygorskite PAO-g-PS resin

Cd(II)

Pb(II)

reference

0.64 0.086

0.56 0.189 0.22

0.25

0.16

29 30 31 32 33

0.44 1.37

0.88

34

0.3 0.28 0.46 3.48

35

2.54

1.33

0.89

36 this work

capacity of the PAO-g-PS resin was significantly higher than those of the reported adsorbent. The stronger the adsorption capacity is, the higher the efficiency for water treatment is. Therefore, based on the principle of sustainability, the PAO-gPS resin should have excellent application value in water treatment.

Figure 10. Desorption curve of the PAO-g-PS resins.

during the adsorption−desorption cycles, indicating that the PAO-g-PS resins showed excellent reusability.

4. CONCLUSIONS In this work, a novel amidoxime-functionalized resin (PAO-gPS) with high capacity was prepared by SI-ATRP of polyacrylonitrile (PAN) and subsequent amine−oxime conversion. FTIR and XPS confirmed the successful grafting of PAN and the formation of the PAO polymer onto the surface of the resin. The PAO-g-PS resin was used to remove Fe(III), Cr(III), Cd(II), and Pb(II) ions from aqueous solution. The adsorption capacity of the PAO-g-PS resin obtained by Langmuir fitting was higher than those of the adsorbent materials reported in the literature. The maximum adsorption capacity could be up to 3.48 mmol g−1 for Fe(III), 2.54 mmol g−1 for Cr(III), 1.33 mmol g−1 for Cd(II), and 0.89 mmol g−1 for Pb(II) at pH 4.0 on the PAO-g-PS resin. The kinetic studies showed that the adsorption process can be described by the pseudo-second-order model, and adsorption thermodynamics indicated the endothermic heat of adsorption and the spontaneous nature of the adsorption process. Competition from common coexisting ions, such as Na(I), K(I), Ca(II), and Mg(II), was negligible, indicating that Fe(III), Cr(III), Cd(II), and Pb(II) can be selectively adsorbed from wastewater. Competitive adsorption among the four metal ions displayed preferential adsorption of Fe (III) > Cr(III) > Cd(II) > Pb(II). The adsorbent exhibited excellent acid−alkali stability. The adsorption−desorption cycles proved that the resin had excellent reusability.

Figure 11. Adsorption capacity of the resin after 10 adsorption− desorption cycles.

As is well known, cross-linked polystyrene resins are usually stable and widely used in water treatment. No weight loss was found after the stability experements of PAO-g-PS resins. No divinylbenzene, vinylbenzene, and other aromatic compounds were detected in the filtered solution by gas chromatography− mass spectrometry analysis, indicating that the harmful compounds were not separated from the resin. These results indicated that PAO-g-PS resins had excellent stability in aqueous solution.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +86 029 33720704. G



Article

ORCID

effective removal of heavy metal ions from model contaminated water. J. Environ. Chem. Eng. 2018, 6, 4623−4633. (16) Ibarra-Rodríguez, D.; Jaime, L. M.; Eduardo, A. L.; Mercedes, T. O. Capacity of ‘nopal’ pectin as a dual coagulant-flocculant agent for heavy metals removal. Chem. Eng. J. 2017, 323, 19−28. (17) Luqman, A. S.; Majid, K.; Rida, J.; Murtaza, S.; Muhammad, S. K.; Abbas, K.; Mohib, U. Superabsorbent polymer hydrogels with good thermal and mechanical properties for removal of selected heavy metal ions. J. Cleaner Prod. 2018, 201, 78−87. (18) Cegłowski, M.; Błażej, G.; Marcin, F.; Łukasz, P. A new lowcost polymeric adsorbents with polyamine chelating groups for efficient removal of heavy metal ions from water solutions. React. Funct. Polym. 2018, 131, 64−74. (19) Abdullah, N.; Yusof, N.; Lau, W. J.; Jaafar, J.; Ismail, A. F. Recent trends of heavy metal removal from water/wastewater by membrane technologies. J. Ind. Eng. Chem. 2019, 76, 17−38. (20) Mahmoudian, M.; Kochameshki, M. G.; Hosseinzadeh, M. Modification of graphene oxide by ATRP: A pH-responsive additive in membrane for separation of salts, dyes and heavy metals. J. Environ. Chem. Eng. 2018, 6, 3122−3134. (21) Mirzaeinejad, M.; Mansoori, Y.; Amiri, M. Amino functionalized ATRP-prepared polyacrylamide-g-magnetite nanoparticles for the effective removal of Cu(II) ions: Kinetics investigations. Mater. Chem. Phys. 2018, 205, 195−205. (22) Yuan, S. J.; Zhang, P.; Yang, Z. Y.; Lv, L.; Tang, S. W.; Liang, B. Successive grafting of poly(hydroxyethyl methacrylate) brushes and melamine onto chitosan microspheres for effective Cu(II) uptake. Int. J. Biol. Macromol. 2018, 109, 287−302. (23) Chen, Y. N.; He, M. F.; Wang, C. Z.; Wei, Y. M. A novel polyvinyltetrazole-grafted resin with high capacity for adsorption of Pb(II), Cu(II) and Cr(III) ions from aqueous solutions. J. Mater. Chem. A 2014, 2, 10444−10453. (24) Wang, C.; Feng, R.; Yang, F. Enhancing the hydrophilic and antifouling properties of polypropylene nonwoven fabric membranes by the grafting of poly (N-vinyl-2-pyrrolidone) via the ATRP method. J. Colloid Interface Sci. 2011, 357, 273−279. (25) Geng, X. D.; Shi, Y. L. A stoichiometric displacement model of solute adsorption in liquid-solid system. Sci. China, Ser. B: Chem. 1989, 32, 11−22. (26) Weber, W. J.; Morris, J. C. Equilibria and capacities for adsorption on carbon. J. Sanit. Eng. Div. 1964, 90, 79−91. (27) Sarıcı-Ö zdemir, C.; Onal, Y. Equilibrium, kinetic and thermodynamic adsorptions of the environmental pollutant tannic acid onto activated carbon. Desalination 2010, 251, 146−152. (28) Pearson, R. G. Hard and Soft Acids and Bases. J. Am. Chem. Soc. 1963, 85, 3533−3539. (29) Kataria, N.; Garg, V. K. Optimization of Pb (II) and Cd (II) adsorption onto ZnO nanoflowers using central composite design: isotherms and kinetics modelling. J. Mol. Liq. 2018, 271, 228−239. (30) Ghasemabadi, S. M.; Baghdadi, G. M.; Safari, E.; Ghazban, F. Investigation of continuous adsorption of Pb(II), As(III), Cd(II), and Cr(VI) using a mixture of magnetic graphite oxide and sand as a medium in a fixed-bed column. J. Environ. Chem. Eng. 2018, 6, 4840− 4849. (31) Papandreou, A. D.; Stournaras, C. J.; Panias, D.; Paspaliaris, I. Adsorption of Pb(II), Zn(II) and Cr(III) on coal fly ash porous pellets. Miner. Eng. 2011, 24, 1495−1501. (32) Liu, W.; Wang, T.; Borthwick, A. G. L.; Wang, Y. Q.; Yin, X. C.; Li, X. Z.; Ni, J. R. Adsorption of Pb2+, Cd2+, Cu2+ and Cr3+ onto titanate nanotubes: Competition and effect of inorganic ions. Sci. Total Environ. 2013, 456-457, 171−180. (33) Guo, X. Y.; Du, B.; Wei, Q.; Yang, J.; Hu, L. H.; Yan, L. G.; Xu, W. Y. Synthesis of amino functionalized magnetic graphenes composite material and its application to remove Cr(VI), Pb(II), Hg(II), Cd(II) and Ni(II) from contaminated water. J. Hazard. Mater. 2014, 278, 211−220. (34) Li, K. Q.; Zhou, Y.; Li, J.; Liu, J. M. Soft-templating synthesis of partially graphitic Fe-embedded ordered mesoporous carbon with rich

Youning Chen: 0000-0002-6084-725X Huan Wang: 0000-0002-7813-7408 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by “Cyanine Talent” of Xianyang Normal College (no. XSYQL201710) and University students innovation and entrepreneurship base team (project) (no. XSYC201922).

■

REFERENCES

(1) Mohammad, K. U. A review on the adsorption of heavy metals by clay minerals, with special focus on the past decade. Chem. Eng. J. 2017, 308, 438−462. (2) Pandey, S. A comprehensive review on recent developments in bentonite-based materials used as adsorbents for wastewater treatment. J. Mol. Liq. 2017, 241, 1091−1113. (3) Fu, F. L.; Wang, Q. Removal of heavy metal ions from wastewaters: A review. J. Environ. Manage. 2011, 92, 407−418. (4) Wu, Y. H.; Pang, H. W.; Liu, Y.; Wang, X. X.; Yu, S. J.; Fu, D.; Chen, J. R.; Wang, X. K. Environmental remediation of heavy metal ions by novel-nanomaterials: A review. Environ. Pollut. 2019, 246, 608−620. (5) Du, Y.; Chen, L.; Ding, P.; Liu, L. L.; He, Q. C.; Chen, B. Z.; Duan, Y. Y. Different exposure profile of heavy metal and health risk between residents near a Pb-Zn mine and a Mn mine in Huayuan county, South China. Chemosphere 2019, 216, 352−364. (6) Chen, S. H.; Li, Y. X.; Li, P. H.; Xiao, X. Y.; Jiang, M.; Li, S. S.; Zhou, W. Y.; Yang, M.; Huang, X. J.; Liu, W. Q. Electrochemical spectral methods for trace detection of heavy metals: A review. TrAC, Trends Anal. Chem. 2018, 106, 139−150. (7) Yang, D. X.; Li, L. F.; Chen, B. L.; Shi, S. X.; Nie, J.; Ma, G. P. Functionalized chitosan electrospun nanofiber membranes for heavymetal removal. Polymer 2019, 163, 74−85. (8) Baydarashvili, M.; Shrednik, N.; Spasovskaia, A. Detection Method of Pollution with Heavy Metals Ions of the Soil. Procedia Eng. 2017, 189, 630−636. (9) Kyzas, G. Z.; George, B.; Ramonna, I. K.; Eleni, K. E.; Evangelos, P. F.; Margaritis, K.; Athanasios, C. M. Nanobubbles effect on heavy metal ions adsorption by activated carbon. Chem. Eng. J. 2019, 356, 91−97. (10) Cao, D. Q.; Song, X.; Fang, X. M.; Yang, W. Y.; Hao, X. D.; Iritani, E.; Katagiri, N. Membrane filtration-based recovery of extracellular polymer substances from excess sludge and analysis of their heavy metal ion adsorption properties. Chem. Eng. J. 2018, 354, 866−874. (11) Peng, W. J.; Li, H. Q.; Liu, Y. Y.; Song, S. X. A review on heavy metal ions adsorption from water by graphene oxide and its composites. J. Mol. Liq. 2017, 230, 496−504. (12) Liu, Q.; Li, F.; Lu, H.; Li, M.; Liu, J.; Zhang, S. L.; Sun, Q. J.; Xiong, L. Enhanced dispersion stability and heavy metal ion adsorption capability of oxidized starch nanoparticles. Food Chem. 2018, 242, 256−263. (13) Liu, X. Y.; Liu, M. Y.; Zhang, L. Co-adsorption and sequential adsorption of the co-existence four heavy metal ions and three fluoroquinolones on the functionalized ferromagnetic 3D NiFe2O4 porous hollow microsphere. J. Colloid Interface Sci. 2018, 511, 135− 144. (14) Ma, J. C.; Shen, J. W.; Wang, Z.; Wei, Y. M. Preparation of dual-function chelating resin with high capacity and adjustable adsorption selectivity to variety of heavy metal ions. J. Taiwan Inst. Chem. Eng. 2018, 91, 532−538. (15) Hojamberdiev, M.; Shahlo, S. D.; Zukhra, C. K.; Khasan, T. S.; Felix, M.; Masashi, H. Ligand-immobilized spent alumina catalyst for H



Article

micropores from bayberry kernel and its adsorption for Pb(II) and Cr(III). J. Taiwan Inst. Chem. Eng. 2018, 82, 312−321. (35) Liu, J. S.; Gao, X. Z.; Liu, C.; Guo, L.; Zhang, S. X.; Liu, X. Y.; Li, H. M.; Liu, C. P.; Jin, R. C. Adsorption properties and mechanism for Fe(III) with solvent impregnated resins containing HEHEHP. Hydrometallurgy 2013, 137, 140−147. (36) Middea, A.; Fernandes, T. L. A. P.; Neumann, R.; Gomes, O. F. M.; Spinelli, L. S. Evaluation of Fe(III) adsorption onto palygorskite surfaces. Appl. Surf. Sci. 2013, 282, 253−258.

I


Two-Step Preparation of an Amidoxime-Functionalized

Recommend Documents