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. 2020 Aug 3;5(32):19920–19927. doi: 10.1021/acsomega.9b03405

Preparation of a Hydrogel-Based Adsorbent for Metal Ions through High Internal Phase Emulsion Polymerization

Jing Chen 1, Xuyang Jiang 1, Dezhong Yin 1,*, Wei Zhang 1
PMCID: PMC7439275  PMID: 32832746

Abstract

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In this work, a porous hydrogel-based adsorbent for metal ions was prepared through the copolymerization of acrylic acid and 2-hydroxyethyl methacrylate using a high internal phase emulsion (HIPE) method. Stretched molecular chains in the hydrogel ensure the excellent accessibility of functional sites by the metal ions. A highly open cellular structure endows the P(AANa-co-HEMA) gel with high transport rates as a promising adsorbent. Adsorption properties were investigated by three isotherm models and two kinetic models. X-ray photoelectron spectroscopy analysis proved a chelating interaction between −COO– and metal ions. The adsorption capacity reached 630 mg·g–1 for Pb2+ under 303 K and a 400 μg·mL–1 initial concentration. The results show that the as-prepared PolyHIPE-based P(AANa-co-HEMA) gel possesses an open cellular structure, high adsorption capacity, and high selectivity for Pb2+.

1. Introduction

With the advancement of industrialization, many heavy metal ions are discharged into the environment. Water pollution caused by the toxic heavy metal ions is a serious environmental problem. Various techniques, such as chemical precipitation,1 ion exchange,2 membrane separation,3 and adsorption,4 have been committed to the removal of the metal ions in wastewater. At present, the adsorption method is considered to be an effective and economic one because of its relative simplicity, high efficiency, and recyclability.

The amount and accessibility of functional sites are crucial for an ideal adsorbent for metal ion removal from water. For a common solid material, only the functional sites on the surface can interact with the metal ions in the water. Hydrogels are polymeric materials in a three-dimensional network structure with high water retention and a stretched molecular structure. The functional groups in their network structures, such as carboxyl (−COOH), hydroxyl (−OH), and amine (−NH2), can provide the necessary chelating sites for the heavy metal ions. Moreover, the molecular chains are highly stretched in the captured water, which ensures an excellent accessibility of chelating sites by the metal ions. All these make hydrogels a promising material in scavenging of heavy metals with high sorption capacities and excellent recyclability.

Another factor influencing the adsorption is the porous structure of the adsorbent. Ideally, materials with interconnecting channels show great advantages in achieving high transport rates as a promising adsorbent. To obtain an interconnecting channel, polymerized high internal phase emulsion (PolyHIPE) was considered as a simple, quick, and economical method.5−7 HIPEs are generally defined as very concentrated emulsions in which the internal phase has a volume fraction greater than 74% with a maximum up to 99%.8−11 Polymerizing the continuous phase will produce an open cellular porous structure with the interconnecting windows on the wall. Yang et al.12 synthesized an interconnected macroporous foam by templating an oil-in-water HIPE solely stabilized by lignin particles. They exhibited an excellent adsorption capacity for Cu(II) ions in aqueous solutions. Liu and Wang13 prepared chitosan scaffolds with hierarchical macroporous structures for recyclable adsorption of Cu(II) ions by templating from Pickering HIPEs for the first time. Wang et al.10 prepared a series of magnetic hydroxypropyl cellulose-g-acrylic porous spheres via O/W Pickering high internal phase emulsion (HIPE)-integrated precipitation polymerization. They had good adsorption capacity for Cu2+ and Cd2+ ions.

Herein, a hydrophilic hydrogel with an open cellular PolyHIPE structure was prepared through polymerizing an oil-in-water (O/W) HIPE with an aqueous solution of acrylic acid and 2-hydroxyethyl methacrylate as the continuous phase. A PolyHIPE with a hydrophilic skeleton presents advantages in terms of accessibility of functional groups and high transport rates. The metal ions can be transported into the inner part of the hydrogel skeleton and interact freely with the functional sites. The effects of monomer content, internal phase ratio, oil phase composition, and acrylic acid content on the pore structure were investigated. In addition, we also investigated the adsorption capacity of the obtained P(AANa-co-HEMA) gel for metal ions.

2. Experimental Section

2.1. Materials

Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (F68) and 2-hydroxyethyl methacrylate (HEMA, 97%) were purchased from Adamas-beta (Shanghai, China). N,N,N′,N′-Tetramethylethylenediamine (TEMED, 99%), acrylic acid (AA, 99%), Pb(NO3)2 (99%), and NaOH were purchased from Xiya Reagent (Chengdu, China). N,N′-Methylene bisacrylamide (MBAA, 99%) was purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Toluene (TL, 99.5%), (NH4)2S2O8 (APS, 98%), cyclohexane (CYH, 99%), acetone, and ethanol (absolute) were purchased from Chengdu Kelon Chemical Reagent (Chengdu, China).

2.2. Preparation of the P(AA-co-HEMA) Gel

In a typical polymerization reaction, AA and HEMA were charged into a 150 mL beaker along with H2O, the cross-linker MBAA (18 wt % based on the total mass of AA and HEMA), and F68 (15 wt % based on the water phase) and stirred at 400 rpm for 10 min. Then, a mixture of cyclohexane and toluene was added dropwise under stirring. Once all the oil phases were added, the initiator APS (2 wt % monomer, dissolved in 1 mL of water) was added, and the mixture was then stirred at 3000 rpm for 8 min using a homogenizer. Next, the catalyst TEMED (20 μL) was added, and stirring was continued for 2 min to obtain a viscous milky O/W HIPE. The emulsion was then transferred to a glass test tube and polymerized in a 50 °C water bath for 10 h. The obtained monolith was cut into small pieces and purified by Soxhlet extraction with ethanol. The internal structure and morphology were determined on a FEI-Verios G4 scanning electron microscope (SEM). Pore properties were determined on an AutoPore IV 9500 mercury porosimeter. The backbone component of the P(AA-co-HEMA) gel was determined on a TENSOR 27 infrared spectrometer. Each element’s information was determined by X-ray photoelectron spectroscopy (XPS; Kratos, AXIS Ultra DLD). The zero charge point of the adsorbent was determined by the method in refs (14) and (15).

2.3. Adsorption Experiments

The P(AA-co-HEMA) gel was changed to the P(AANa-co-HEMA) gel by NaOH solution (0.1 M) before the adsorption experiment. The adsorption experiments were carried out by a batch method. In a constant temperature oscillator, 50 mL of Pb2+ solution was brought into contact with 20 mg of the adsorbent for 3 h. The residual Pb2+ in the solution was traced using atomic adsorption spectroscopy (AAS). The adsorption capacity Qe was calculated by eq 1.

2.3. 1

where C0 and Ce are the Pb2+concentration in the solution before and after the adsorption process, respectively, V is the volume of the Pb2+ solution, and m is the mass of the P(AANa-co-HEMA) gel used (g).

2.4. Regeneration Experiment

After the adsorption, the P(AANa-co-HEMA) gel adsorbent was regenerated through a desorption procedure. First, the adsorbent was desorbed in 50 mL of HCl solution (0.1 M) for 2 h at 303 K, and the desorption procedure was repeated three times. Second, the desorbed adsorbent was soaked with NaOH (0.1 M) to change the P(AA-co-HEMA) gel to P(AANa-co-HEMA) gel. Third, the P(AANa-co-HEMA) gel was washed with deionized water.

3. Results and Discussion

3.1. Pore Structure of P(AA-co-HEMA) Gel

By polymerizing the continuous phase of the HIPE, an open cellular PolyHIPE structure was prepared extensively, especially for a hydrophobic skeleton. Herein, an oil-in-water (O/W) HIPE was employed to achieve a hydrophilic hydrogel where the molecular chains were in a status of fully stretching. To obtain a PolyHIPE-based P(AA-co-HEMA) gel with high interconnectivity, the effects of the monomer content, internal phase ratio, oil phase composition, and acrylic acid content on the pore structure were investigated (Figure 1 and Figures S1–S3). Typical open cellular PolyHIPE structures prepared with different AA contents are presented and summarized in Table 1.

Figure 1.

Figure 1

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SEM images of P(AA-co-HEMA) gels prepared with different AA contents. (A1) Monomer only AA. (A2) AA content of 75%. (A3) AA content of 50%. (A4) AA content of 25%.

Table 1. Pore Parameters of P(AA-co-HEMA) Gel Prepared with Different AA Contents.

sample VAA/VHEMA monomer (%) internal phase (%) VTL/VCYH porosity (%) pore diameter (nm) pore area (m2·g–1)
A1 4:0 32 75 2:2 a a a
A2 3:1 32 75 2:2 62.4 7575 1.33
A3 2:2 32 75 2:2 75.5 4098 4.81
A4 1:3 32 75 2:2 84.7 1124 17.00
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a

Large portion of closed voids.

In the O/W HIPE, the monomer was dissolved in water and polymerized into a hydrogel skeleton of PolyHIPE. We started the experiment with AA as solely the monomer to achieve a high density of functional groups for heavy metals. The prepared PAA gel presented a large portion of closed voids (Figure 1A1). We speculate that this is ascribed to the poor stability of the emulsion caused by the high polarity of AA. Targeted on the polarity, HEMA was copolymerized, and a highly interconnecting P(AA-co-HEMA) gel was achieved, as shown in Figure 1 and summarized in Table 1. The content of AA has a significant effect on the pore structure. As the VAA/VHEMA decreased from 3:1 to 1:3, the porosity of the P(AA-co-HEMA) gel increased from 62.4 to 84.7%, and the P(AA-co-HEMA) gel contained abundant windows and a highly open cellular structure.

3.2. Characterization of Adsorbent Materials

FTIR (Fourier transform infrared spectroscopy) and XPS were used to confirm the successful preparation of the P(AANa-co-HEMA) gel. Figure 2 shows the FITR spectra of P(AA-co-HEMA) and P(AANa-co-HEMA) gels. For the P(AA-co-HEMA) gel, special peaks around 3400 cm–1 (wide peak) and 1719 cm–1 are attributed to νO–H (including alcoholic hydroxyl groups and carboxyhydroxy groups of HEMA) and νC=O, respectively. In the P(AANa-co-HEMA) gel, two new peaks appear at 1565 and 1400 cm–1. They are assigned to the asymmetric and symmetric stretching vibrations of the carboxylate anion −CO2–, respectively.16,17 XPS was performed to determine the chemical composition of the adsorbent surface. The C 1s, N 1s, and O 1s peaks were detected at 284, 397, and 531 eV, respectively, in the P(AA-co-HEMA) gel XPS spectra (Figure 3a). In Figure 3b, a new peak attributed to Na 1s appears at 1069 eV.

Figure 2.

Figure 2

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FTIR spectra of the (a) P(AA-co-HEMA) and (b) P(AANa-co-HEMA) gel.

Figure 3.

Figure 3

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XPS spectra of the (a) P(AA-co-HEMA) and (b) P(AANa-co-HEMA) gel.

3.3. Adsorption of the Metal Ion by P(AANa-co-HEMA) Gel

3.3.1. Adsorption Mechanism

We employed the original P(AA-co-HEMA) gel as an adsorbent for Pb2+ and found that the P(AA-co-HEMA) gel had almost zero adsorption capacity for Pb2+. After being treated with NaOH, the P(AA-co-HEMA) gel transformed into the P(AANa-co-HEMA) gel and presented good adsorption performance. These results indicated that the adsorption originated from the −COO– group of P(AANa-co-HEMA).

In order to further explore the mechanism of adsorption, this study used X-ray photoelectron spectroscopy to analyze the hydrogel before and after adsorption. The high-resolution XPS spectra of the P(AANa-co-HEMA) gel and P(AANa-co-HEMA) gel–Pb2+ for C 1s, O 1s, and Pb 4f are presented in Figure 4. Three group peaks of the P(AANa-co-HEMA) gel and P(AANa-co-HEMA) gel–Pb2+ in Figure 4a are attributed to the C–C, C–N, and C=O binding energies of C 1s, respectively. Obviously, all the binding energies of C 1s increased slightly a little after adsorption of Pb2+ due to the reaction between the adjacent N or O atoms and Pb2+. Two group peaks of the P(AANa-co-HEMA) gel and P(AANa-co-HEMA) gel–Pb2+ in Figure 4b are attributed to the C=O and C–O binding energies of O 1s, respectively. It can be seen that the binding energy of C–O significantly increased from 530.19 to 533.11 eV after adsorption of Pb2+, which indicates that there is a strong combination between the absorbent −COO– and Pb2+. Therefore, it was speculated that the reaction between −COO– and Pb2+ was via chelation.15,18,19

Figure 4.

Figure 4

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High-resolution XPS spectra of the P(AANa-co-HEMA) gel and P(AANa-co-HEMA) gel–Pb2+ for (a) C 1s, (b) O 1 s, and (c) Pb 4f.

3.3.2. Effect of the Solution pH

The pH plays an important role in the adsorption behavior because the pH can have an effect not only on the surface charge density of the adsorbent but also on the existing form of the adsorbate.20−22 As shown in Figure 5, the adsorption of Pb2+ shows a great pH-dependent property. The adsorption capacity Qe increases remarkably with the increase in pH from 2 to 4 then retains a high Qe at pH 4–6. The pH value at zero point charge (pHPZC) of the P(AANa-co-HEMA) hydrogel is about 8.86 (Figure S4). At pH < pHPZC, the adsorbent is highly positively charged, and the electrostatic repulsion counts against the adsorption of positive metal ions.23,24 As the pH increases, the protonation reaction (−COO– + H+ → −COOH) decreases, leading to an increase in Qe. When pH increases to 5, Pb2+ becomes a priority over H+ when competing for the adsorption site (-–COO–), and the Qe reached a maximum. At pH > pHPZC, the adsorbent becomes deprotonated, which promotes the adsorption of heavy metal ions. However, at this pH condition, Pb2+ forms hydroxide precipitates. According to the solubility product constant of Pb(OH)2 (4.8 × 10–20), the pH value beginning to form hydroxide precipitates was calculated to be 5.8.19

Figure 5.

Figure 5

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Effect of pH on the adsorption capacity (T = 303 K, C0 = 200 μg·mL–1).

3.3.3. Adsorption Capacity and Regeneration of the Material

Adsorption capacities of P(AANa-co-HEMA) gel A1, A2, A3, and A4 were investigated under 303 K and different Pb2+ initial concentrations. The results are shown in Figure 6. Under 200 μg·mL–1 of Pb2+ concentration, Qe increased from 130 to 480 mg·g–1 as the AA content increased from 25% (A4) to 100% (A1). Under 400 μg·mL–1 Pb2+, the Qe of the A2 hydrogel reached 527 mg·g–1, and the maximum adsorption capacity reached 630 mg·g–1 for the A1 hydrogel. Our results reveal that the as-prepared hydrogel has relatively larger adsorption capacities than similar hydrogel adsorbents published previously (Table 2).

Figure 6.

Figure 6

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Different AA contents of P(AANa-co-HEMA) gel adsorbed Pb2+ (T = 303 K, pH 5).

Table 2. Comparison of Metal Ion Adsorption among Different Hydrogel Adsorbents.
hydrogel adsorbents metal ion Qe (mg·g–1) references
P(AMPS-co-IA) Pb2+ 360 Çavuş et al. (2009)25
m-chitosan/PVA/CCNFs Pb2+ 171 Zhou et al. (2014)26
m-chitosan/PVA Pb2+ 117 Zhou et al. (2014)26
Gg-cl-P(AAm-co-AN) Pb2+, Cu2+ 385, 204 Mittal et al. (2015)27
P(AANa-co-AM)/GO Pb2+, Cd2+ 452, 196 He et al. (2016)19
CTS-g-PAA Cu2+, Pb2+ 300, 600 Zhu et al. (2016)9
Jute/PAA Cd2+, Pb2+ 401, 542 Zhou et al. (2017)28
CMC/PAM composite hydrogel Pb2+, Cd2+ 312, 256 Godiya et al. (2019)29
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Regeneration of the adsorbent has an important significance for the application of the adsorbent. The adsorption efficiency of the P(AANa-co-HEMA) gel at different cycle times is shown in Figure 7. After five times adsorption–desorption processes, adsorption of Pb2+ by the P(AANa-co-HEMA) gel preserves more than 95% of the initial adsorption amount, indicating that the as-prepared porous hydrogel is a high-performance recyclable adsorbent for metal ions.

Figure 7.

Figure 7

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Recyclability of the P(AANa-co-HEMA) gel for Pb2+ adsorption (T = 303 K, C0 = 200 μg·mL–1, pH 5 for Pb2+).

3.3.4. Isothermal Adsorption

The adsorption isotherms of the prepared absorbent at three different temperatures are represented in Figure 8. The initial ion concentration provides the necessary driving force to overcome mass transfer resistance until the maximum adsorption capacity is reached.30 As a result, the adsorption capacity increased significantly during the initial stage until the adsorption is almost at equilibrium. The Qe increases from 481 mg·g–1 at 293 K to 606 mg·g–1 at 313 K, indicating that the adsorption is an endothermic process.

Figure 8.

Figure 8

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Effect of the initial concentration on the adsorption reaction (pH 5 for Pb2+).

Three isotherm adsorption models were employed to fit the adsorption process (Figure S7). The calculated parameters and correlation coefficients are listed in Table 3. A higher R2 for the Freundlich equation indicates a multilayer adsorption model rather than a monolayer model.31,32 This is consistent with our hypothesis that the metal ion can intrude into the stretched molecular chains.

Table 3. Parameters of Langmuir, Freundlich, and D–R Isotherm Adsorption Models.
  Langmuir isotherm adsorption model
 Freundlich isotherm adsorption model
 D–R isotherm adsorption model
T (K) Qm (mg·g–1) KL (L·mg–1) R2 KF ((mg·g–1)·(L·mg–1)1/n) 1/n R2 Qm (mg·g–1) E (kJ·mol–1) R2
293 505 0.0528 0.988 87.4 0.318 0.996 917 13.8 0.981
303 552 0.0682 0.988 110 0.297 0.995 948 15.0 0.983
313 617 0.122 0.989 168 0.247 0.997 1025 16.8 0.988
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3.3.5. Adsorption Kinetics

The porous structure of the P(AANa-co-HEMA) gel can diminish the diffusion limitation during the adsorption, shortening the adsorption time to reach adsorption equilibrium. As shown in Figure 9, the P(AANa-co-HEMA) gel adsorbs Pb2+ rapidly in 45 min and reaches equilibrium in 1 h. Pseudo-first-order and pseudo-second-order models were used to fit the experimental data, as described by the following equations

3.3.5. 2
3.3.5. 3

where Qe and Qt are the adsorption amounts (mg·g–1) at equilibrium and time t, respectively, and kf (min–1) and ks (g·(mg·min)−1) are primary and secondary constants, respectively.

Figure 9.

Figure 9

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(a) Variation of the adsorption amount at different times. (b) Fitted pseudo-first-order and (c) pseudo-second-order model (T = 303 K, C0 = 200 μg·mL–1, pH 5 for Pb2+).

The fitting curves are presented in Figure 9, and the calculated parameters are listed in Table 4. A higher correlation coefficient shows that the pseudo-second-order model can be used for the whole adsorption process. This result indicates that the adsorption rate of Pb2+ by the P(AANa-co-HEMA) gel is controlled by chemical processes.33,34

Table 4. Parameters Fitted from Pseudo-First-Order and Pseudo-Second-Order Models.
  pseudo-first-order model
 pseudo-second-order model
temperature Qe (mg·g–1) kf (min–1) R2 Qe (mg·g–1) ks (g·(mg·min)−1) R2
303 K 548 0.0526 0.945 437 1.19 × 10–4 0.994
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3.3.6. Selective Adsorption

The selectivity of adsorbents for heavy metals has an important impact in practical industrial applications. Highly selective adsorbents are suitable for wastewater treatment with a single heavy metal ion, while low selectivity is more effective for treating wastewater containing multiple heavy metal ions. In a constant temperature oscillator, 50 mL of a mixed solution containing 50 μg·mL–1 Pb2+, Cu2+, and Zn2+ was brought into contact with 20 mg of the adsorbent for 3 h. The results of selective adsorption of the P(AANa-co-HEMA) gel on the same concentration of three metal-ion-mixed solutions are shown in Figure 10. Under 50 μg·mL–1 of ions, the adsorption ratios of Pb2+, Cu2+, and Zn2+ by the P(AANa-co-HEMA) gel were 93.7, 77.7, and 52.3%, respectively. Under a higher concentration of the metal ion mixture, a similar tendency of the adsorption ratio was achieved (Pb2+ > Cu2+ > Zn2+). From the results of adsorption of a single heavy metal ion, the P(AANa-co-HEMA) gel can achieve a nearly 100% adsorption rate for Pb2+. The adsorption of Pb2+ by the P(AANa-co-HEMA) gel was slightly affected in competitive adsorption experiments in binary metal ion systems. The adsorption capacity of the P(AANa-co-HEMA) gel for different heavy metals is mainly due to the difference in the binding ability of functional groups to heavy metal ions. The experimental results show that the adsorbent can efficiently treat wastewater containing Pb2+.

Figure 10.

Figure 10

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Selective adsorption of the P(AANa-co-HEMA) gel on different heavy metal ions (T = 303 K, pH 5 for Pb2+).

4. Conclusions

In this study, an open cellular PolyHIPE hydrogel was prepared by polymerizing HIPE with acrylic acid and 2-hydroxyethyl methacrylate as monomers. SEM images confirm that the as-prepared porous hydrogel monolith shows a good open cellular framework structure, and the pore structure can be adjusted by changing the polymerization parameters, such as acrylic acid content, monomer content, internal phase ratio, and oil phase composition. This open cellular hydrogel presents faster adsorption kinetics and a high adsorption capacity for Pb2+ and has potential to be a highly effective adsorbent for the enrichment of metal ions from the aqueous solution.

Acknowledgments

This work has been sponsored by the National Key Research and Development Program of China (2016YFC0301302), the Natural Science Foundation of Shaanxi Province (2017JM5080), and the Innovation and Entrepreneurship Training Program for College Students (S201910699188).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.9b03405.

  • Table S1: pore parameters of the P(AA-co-HEMA) gel prepared under different monomer contents; Figure S1: SEM images of the P(AA-co-HEMA) gel prepared under different monomer contents; Table S2: pore parameters of the P(AA-co-HEMA) gel prepared under different internal phase ratios; Figure S2: SEM images of the P(AA-co-HEMA) gel prepared under different internal phase ratios; Table S3: pore parameters of the P(AA-co-HEMA) gel prepared under different oil phase compositions; Figure S3: SEM image of the P(AA-co-HEMA) gel composed of different oil phases; Figure S4: zero point charge of P(AANa-co-HEMA) at different pH solutions; Figure S5: photograph of the adsorbent before (left) and after (right) water absorption; Table S4: ESR of hydrogels with different AA contents; Figure S6: compressive nominal stress–strain curves with compressive strain; Figure S7: Langmuir, Freundlich, and Dubinin–Radushkevish isotherm adsorption models; and Table S5: parameters of Langmuir, Freundlich and D–R isotherm adsorption models (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao9b03405_si_001.pdf (997KB, pdf)

References

  1. Vereda F.; de Vicente J.; Hidalgo-Álvarez R. Influence of a magnetic field on the formation of magnetite particles via two precipitation methods. Langmuir 2007, 23, 3581–3589. 10.1021/la0633583. [DOI] [PubMed] [Google Scholar]
  2. Wong C.-W.; Barford J. P.; Chen G.; McKay G. Kinetics and equilibrium studies for the removal of cadmium ions by ion exchange resin. J. Environ. Chem. Eng. 2014, 2, 698–707. 10.1016/j.jece.2013.11.010. [DOI] [Google Scholar]
  3. Zhu L.; Xue Q.; Li X.; Wu T.; Jin Y.; Xing W. C2N: an excellent two-dimensional monolayer membrane for He separation. J. Mater. Chem. A 2015, 3, 21351–21356. 10.1039/C5TA05700K. [DOI] [Google Scholar]
  4. Cui L.; Wang Y.; Gao L.; Hu L.; Yan L.; Wei Q.; Du B. EDTA functionalized magnetic graphene oxide for removal of Pb (II), Hg (II) and Cu (II) in water treatment: Adsorption mechanism and separation property. Chem. Eng. J. 2015, 281, 1–10. 10.1016/j.cej.2015.06.043. [DOI] [Google Scholar]
  5. Zhu Y.; Wang W.; Zhang H.; Ye X.; Wu Z.; Wang A. Fast and high-capacity adsorption of Rb+ and Cs+ onto recyclable magnetic porous spheres. Chem. Eng. J. 2017, 327, 982–991. 10.1016/j.cej.2017.06.169. [DOI] [Google Scholar]
  6. Lu T.; Zhu Y.; Wang W.; Qi Y.; Wang A. Interconnected superporous adsorbent prepared via yeast-based Pickering HIPEs for high-efficiency adsorption of Rb+, Cs+ and Sr2+. Chem. Eng. J. 2019, 361, 1411–1422. 10.1016/j.cej.2018.11.006. [DOI] [Google Scholar]
  7. Yin D.; Ma L.; Liu J.; Zhang Q. Pickering emulsion: A novel template for microencapsulated phase change materials with polymer-silica hybrid shell. Energy 2014, 64, 575–581. 10.1016/j.energy.2013.10.004. [DOI] [Google Scholar]
  8. Zhu Y.; Wang W.; Zheng Y.; Wang F.; Wang A. Rapid enrichment of rare-earth metals by carboxymethyl cellulose-based open-cellular hydrogel adsorbent from HIPEs template. Carbohydr. Polym. 2016, 140, 51–58. 10.1016/j.carbpol.2015.12.003. [DOI] [PubMed] [Google Scholar]
  9. Zhu Y.; Zheng Y.; Wang F.; Wang A. Monolithic supermacroporous hydrogel prepared from high internal phase emulsions (HIPEs) for fast removal of Cu2+ and Pb2+. Chem. Eng. J. 2016, 284, 422–430. 10.1016/j.cej.2015.08.157. [DOI] [Google Scholar]
  10. Zhu Y.; Zheng Y.; Zong L.; Wang F.; Wang A. Fabrication of magnetic hydroxypropyl cellulose-g-poly (acrylic acid) porous spheres via Pickering high internal phase emulsion for removal of Cu2+ and Cd2+. Carbohydr. Polym. 2016, 149, 242–250. 10.1016/j.carbpol.2016.04.107. [DOI] [PubMed] [Google Scholar]
  11. Lu T.; Zhu Y.; Qi Y.; Kang Y.; Wang A. Tunable superporous magnetic adsorbent prepared via eco-friendly Pickering MIPEs for high-efficiency adsorption of Rb+ and Sr2+. Chem. Eng. J. 2019, 368, 988–998. 10.1016/j.cej.2019.03.040. [DOI] [Google Scholar]
  12. Yang Y.; Wei Z.; Wang C.; Tong Z. Lignin-based Pickering HIPEs for macroporous foams and their enhanced adsorption of copper (II) ions. Chem. Commun. 2013, 49, 7144–7146. 10.1039/c3cc42270d. [DOI] [PubMed] [Google Scholar]
  13. Liu H.; Wang C. Chitosan scaffolds for recyclable adsorption of Cu (II) ions. RSC Adv. 2014, 4, 3864–3872. 10.1039/C3RA45088K. [DOI] [Google Scholar]
  14. Sepehr M. N.; Kazemian H.; Ghahramani E.; Amrane A.; Sivasankar V.; Zarrabi M. Defluoridation of water via Light Weight Expanded Clay Aggregate (LECA): Adsorbent characterization, competing ions, chemical regeneration, equilibrium and kinetic modeling. J. Taiwan Inst. Chem. Eng. 2014, 45, 1821–1834. 10.1016/j.jtice.2014.02.009. [DOI] [Google Scholar]
  15. Chu L.; Liu C.; Zhou G.; Xu R.; Tang Y.; Zeng Z.; Luo S. A double network gel as low cost and easy recycle adsorbent: Highly efficient removal of Cd (II) and Pb (II) pollutants from wastewater. J. Hazard. Mater. 2015, 300, 153–160. 10.1016/j.jhazmat.2015.06.070. [DOI] [PubMed] [Google Scholar]
  16. Kong W.; Yue Q.; Li Q.; Gao B. Adsorption of Cd2+ on GO/PAA hydrogel and preliminary recycle to GO/PAA-CdS as efficient photocatalyst. Sci. Total Environ. 2019, 668, 1165–1174. 10.1016/j.scitotenv.2019.03.095. [DOI] [PubMed] [Google Scholar]
  17. Alizadehgiashi M.; Khuu N.; Khabibullin A.; Henry A.; Tebbe M.; Suzuki T.; Kumacheva E. Nanocolloidal Hydrogel for Heavy Metal Scavenging. ACS Nano 2018, 12, 8160–8168. 10.1021/acsnano.8b03202. [DOI] [PubMed] [Google Scholar]
  18. Irani M.; Ismail H.; Ahmad Z.; Fan M. Synthesis of linear low-density polyethylene-g-poly (acrylic acid)-co-starch/organo-montmorillonite hydrogel composite as an adsorbent for removal of Pb (ΙΙ) from aqueous solutions. J. Environ. Sci. 2015, 27, 9–20. 10.1016/j.jes.2014.05.049. [DOI] [PubMed] [Google Scholar]
  19. He S.; Zhang F.; Cheng S.; Wang W. Synthesis of sodium acrylate and acrylamide copolymer/GO hydrogels and their effective adsorption for Pb2+ and Cd2+. ACS Sustainable Chem. Eng. 2016, 4, 3948–3959. 10.1021/acssuschemeng.6b00796. [DOI] [Google Scholar]
  20. Yu Z.; Zhang X.; Huang Y. Magnetic chitosan–iron (III) hydrogel as a fast and reusable adsorbent for chromium (VI) removal. Ind. Eng. Chem. Res. 2013, 52, 11956–11966. 10.1021/ie400781n. [DOI] [Google Scholar]
  21. Yang S.; Hu J.; Chen C.; Shao D.; Wang X. Mutual effects of Pb (II) and humic acid adsorption on multiwalled carbon nanotubes/polyacrylamide composites from aqueous solutions. Environ. Sci. Technol. 2011, 45, 3621–3627. 10.1021/es104047d. [DOI] [PubMed] [Google Scholar]
  22. Zhao D.; Sheng G.; Hu J.; Chen C.; Wang X. The adsorption of Pb (II) on Mg2Al layered double hydroxide. Chem. Eng. J. 2011, 171, 167–174. 10.1016/j.cej.2011.03.082. [DOI] [Google Scholar]
  23. Zhou G.; Liu C.; Tang Y.; Luo S.; Zeng Z.; Liu Y.; Xu R.; Chu L. Sponge-like polysiloxane-graphene oxide gel as a highly efficient and renewable adsorbent for lead and cadmium metals removal from wastewater. Chem. Eng. J. 2015, 280, 275–282. 10.1016/j.cej.2015.06.041. [DOI] [Google Scholar]
  24. Zhou G.; Luo J.; Liu C.; Chu L.; Ma J.; Tang Y.; Zeng Z.; Luo S. A highly efficient polyampholyte hydrogel sorbent based fixed-bed process for heavy metal removal in actual industrial effluent. Water Res. 2016, 89, 151–160. 10.1016/j.watres.2015.11.053. [DOI] [PubMed] [Google Scholar]
  25. Çavuş S.; Gürdaǧ G. Noncompetitive removal of heavy metal ions from aqueous solutions by poly [2-(acrylamido)-2-methyl-1-propanesulfonic acid-co-itaconic acid] hydrogel. Ind. Eng. Chem. Res. 2009, 48, 2652–2658. 10.1021/ie801449k. [DOI] [Google Scholar]
  26. Zhou Y.; Fu S.; Zhang L.; Zhan H.; Levit M. V. Use of carboxylated cellulose nanofibrils-filled magnetic chitosan hydrogel beads as adsorbents for Pb (II). Carbohydr. Polym. 2014, 101, 75–82. 10.1016/j.carbpol.2013.08.055. [DOI] [PubMed] [Google Scholar]
  27. Mittal H.; Maity A.; Sinha Ray S. The adsorption of Pb2+ and Cu2+ onto gum ghatti-grafted poly (acrylamide-co-acrylonitrile) biodegradable hydrogel: isotherms and kinetic models. J. Phys. Chem. B 2015, 119, 2026–2039. 10.1021/jp5090857. [DOI] [PubMed] [Google Scholar]
  28. Zhou G.; Luo J.; Liu C.; Chu L.; Crittenden J. Efficient heavy metal removal from industrial melting effluent using fixed-bed process based on porous hydrogel adsorbents. Water Res. 2018, 131, 246–254. 10.1016/j.watres.2017.12.067. [DOI] [PubMed] [Google Scholar]
  29. Godiya C. B.; Cheng X.; Li D.; Chen Z.; Lu X. Carboxymethyl cellulose/polyacrylamide composite hydrogel for cascaded treatment/reuse of heavy metal ions in wastewater. J. Hazard. Mater. 2019, 364, 28–38. 10.1016/j.jhazmat.2018.09.076. [DOI] [PubMed] [Google Scholar]
  30. Srivastava V. C.; Swamy M. M.; Mall I. D.; Prasad B.; Mishra I. M. Adsorptive removal of phenol by bagasse fly ash and activated carbon: equilibrium, kinetics and thermodynamics. Colloids Surf., A 2006, 272, 89–104. 10.1016/j.colsurfa.2005.07.016. [DOI] [Google Scholar]
  31. Freundlich H., Über die Adsorption in Lösungen. Habilitationsschrift durch welche... zu haltenden Probevorlesung″ Kapillarchemie und Physiologie″ einladet Dr. Herbert Freundlich. W. Engelmann: 1906. [Google Scholar]
  32. Langmuir I. The constitution and fundamental properties of solids and liquids. Part I. Solids. J. Am. Chem. Soc. 1916, 38, 2221–2295. 10.1021/ja02268a002. [DOI] [Google Scholar]
  33. Ho Y.-S.; McKay G. Sorption of dye from aqueous solution by peat. Chem. Eng. J. 1998, 70, 115–124. 10.1016/S0923-0467(98)00076-1. [DOI] [Google Scholar]
  34. Kadirvelu K.; Faur-Brasquet C.; Cloirec P. L. Removal of Cu (II), Pb (II), and Ni (II) by adsorption onto activated carbon cloths. Langmuir 2000, 16, 8404–8409. 10.1021/la0004810. [DOI] [Google Scholar]

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