An efficient and health-friendly adsorbent N-[4-morpholinecarboximidamidoyl]carboximidamidoylmethylated polyphenylene sulfide for removing heavy metal ions from water

Journal of Molecular Liquids 296 (2019) 111860

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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq

An efficient and health-friendly adsorbent N-[4morpholinecarboximidamidoyl]carboximidamidoylmethylated polyphenylene sulfide for removing heavy metal ions from water Chao-Zhi Zhang*, Hui Sheng, Yan-Xiao Su, Jian-Qiang Xu CICAEET, Jiangsu Key Laboratory of AEMPC, Department of Chemistry, Nanjing University of Information Science & Technology, Nanjing, 210044, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 1 July 2019 Received in revised form 26 September 2019 Accepted 28 September 2019 Available online 12 October 2019

N-[4-morpholinecarboximidamidoyl]carboximidamidoylmethylated polyphenylene sulfide (MCMPPS) was synthesized by grafting moroxydine on cholomethylated polyphenylene sulfide (CMPPS) resin for removing heavy metal ions from water. Polyphenylene sulfide (PPS) is a health-friendly polymer, moreover, the moroxydine is an antiviral drug. The resin MCMPPS exhibited excellent chemical stability under strong acid, basic and oxidative conditions. The maximum adsorption capacity of resin MCMPPS for Pb(II), Cd(II), Cr(III), Cu(II) and Ni(II) ions were 186.92, 189.75, 120.04, 119.33 and 134.05 mg g
1, respectively, moreover, equilibrium time of MCMPPS adsorbing Pb(II), Cr(III), Cu(II) and Cd(II) ions are about 30 min. Therefore, this new sorbent showed a potential application in the removal of heavy metal ions in water owing to its thermal and chemical stability, healthy safety, and efficient adsorption. The FTIR spectra and EA data suggested that heavy metal ions were quickly and effective adsorbed on surfaces of the adsorbent by coordination reaction of heavy metal ions with amino and imino groups. © 2019 Elsevier B.V. All rights reserved.

Keywords: Polyphenylene sulfide Moroxydine Adsorption Water-treatment Mechanism Heavy metal ion

1. Introduction Pollution of heavy metal ions is a serious environmental problem because it is a major contributor to water contamination [1]. Some surface water and groundwater cannot be drunk and irrigate corps due to high toxicity and carcinogenesis of the heavy metal ions [2]. If water containing heavy metal ions was drunk by people, these heavy metal ions could damage nervous system, increase blood pressure, decrease kidney function, etc. [3] Therefore, removal of heavy metal ions from water has been an important issue in water-treatment area. Many methods, such as chemical precipitation [4], membrane filtration [5], coagulation [6], solvent extraction [7] and adsorption [8e11], have been developed to remove heavy metal ions from wastewater. Adsorption is one of the most popular methods for removing heavy metal ions from wastewater due to its high efficiency and convenience [12]. Silica gel [13], carbon nanotubes [14] and polymers [15,16] have been developed as new adsorbents for removing heavy metal ions in wastewater. Adsorption capacity and equilibrium time of adsorbents primarily depend on functional groups on surfaces of the adsorbents [2]. Amino groups are one of the most effective groups

* Corresponding author. E-mail address: [email protected] (C.-Z. Zhang). https://doi.org/10.1016/j.molliq.2019.111860 0167-7322/© 2019 Elsevier B.V. All rights reserved.

for removing heavy metal ions from aqueous solutions [17e21]. For example, Shaaban et al. synthesized an amidoxime chelating resin (PAO-AM) for adsorbing heavy metal ions, which the maximum adsorption capacity of the resin for Pb(II) ions is 235.98 mg g
1 [22]. In general, a good adsorbent for removing heavy metal ions from wastewater should be stable in water and harmless to human being. Active carbon has been employed to remove heavy metal ions from drinking water, however, equilibrium time is too long [23]. Therefore, development of a stable and safe adsorbent for quickly removing heavy metal ions from drinking water is still an important issue. Polyphenylene sulfide (PPS) resin is a kind of popular engineering material with excellent mechanical strength, low toxicity, chemical and thermal stability [24]. Therefore, polyphenylene sulfide derivatives could show excellent stability and be insoluble in aqueous solutions. Moroxydine, an antivirotic medicine, should adsorb heavy metal ions due to coordination reaction of heavy metal ions with amino and imino groups in moroxydine. If moroxydine was grafted on PPS to synthesize a functional polymer, the polymer would be a kind of health-friendly absorbent for removal of heavy metal ions in water, especially, heavy metal ions in drinking water, due to its stability and safety. In this paper, a new adsorbent, N-[4morpholinecarboximidamidoyl]carboximidamidoylmethylated

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C.-Z. Zhang et al. / Journal of Molecular Liquids 296 (2019) 111860

polyphenylene sulfide (MCMPPS) resin, was synthesized by grafting N-[4-morpholinecarboximidamidoyl]carboximidamidoylmethyl moities on PPS for removing heavy metal ions from wastewater [25,26]. Based on powder X-ray diffraction (XRD) spectra, surface area data and scanning electron microscopy (SEM) images, structure of MCMPPS was studied. Functional groups were determined by IR spectra and elemental analysis (EA) data. Thermal stability of MCMPPS was characterized by thermogravimetric analysis (TGA) and differential thermal analysis. Effects of pH values on the adsorption capacity, adsorption kinetics and isotherms of MCMPPS for heavy metal ions were investigated. Based on experimental results, adsorption mechanism of MCMPPS for heavy metal ions was investigated. 2. Experimental 2.1. Materials and methods Elemental analyses (EA) were carried out on a VARIO ELE III elemental analyzer (Germany). IR spectra were recorded on a Brucker Vector 22 spectrophotometer, in which samples were embedded in KBr thin films (Nicolet, USA). XRD spectra were recorded on a XRD-6100 powder diffractometer (Shimadzu, Japan) with Cu Ka radiation (l ¼ 1.5406 Å) operating at a scan rate of 10 min
1 over the 2q range of 10 e50 . Thermal stability of the absorbent was measured by a Labsys Evo thermogravimetric analysis and differential thermal analysis under N2 stream at a heating rate of 10  C min
1 (Setaram, France). Concentrations of heavy metal ions were detected by a 3510 G atomic adsorption spectrophotometer (AAS) (China). SEM morphologies of MCMPPS were taken by scanning electron microscopy performed on a SU1510 SEM tester (Hitachi, Japan). Surface area of resin MCMPPS was determined by a Brunauer-Emmett-Teller (BET) model on an Autosorb-iQ-AG-MP analyzer (Quantachrome, USA). The solid state 13C and 1H nuclear magnetic resonance (13C NMR and 1H NMR) spectra were measured on CPTOSS 5 KHz and 12 KHz NMR spectrometers. The X-ray photoelectron spectroscopy (XPS) spectra were measured on ESCALAB 250XI (Thermo, USA). PPS resin was bought from Zhejiang NHU Co. Ltd., China. Other chemicals were purchased from Sigma-Aldrich. All solvents were purified by standard procedures. 2.2. Synthesis of resin MCMPPS 2.2.1. Synthesis of resin chloromethylated polyphenylene sulfide (CMPPS) CMPPS resin was prepared according to the literature (Scheme 1) [25]. It was acquired as a white powder (Yield: 46.12%). IR spectrum of resin CMPPS is in accordance with that in literature [25]. In CMPPS, 94% of benzyl rings were grafted by chloromethyl groups based on C % in EA data. IR (KBr): y ¼ 1258 (CeH), 706 (CeCl) cm
1; Elem. Anal. (CMPPS): C 54.37%, H 3.25%.

2.2.2. Synthesis of resin MCMPPS Resin MCMPPS was synthesized by a graft reaction of the resin CMPPS with moroxydine. Resin CMPPS (1.53 g) was added into tetrahydrofuran (THF) and stirred for 12 h. Then moroxydine hydrochloride (2.00 g, 9.62 mmol) and K2CO3 (1.38 g, 9.98 mmol) were added into above mixture. The reaction mixture was heated and stirred at 80  C for 48 h. Insoluble solid was separated by filtration, washed by water and dried under vacuum at 50  C to give a yellow powder, MCMPPS (1.98 g, yield: 33.82%). In MCMPPS, 35% of benzyl rings were grafted by N-[4morpholinecarboximidamidoyl]carboximidamidoylmethyl (MCM) groups based on C % in EA data. 13C NMR (5 kHz) d (ppm): 168.87, 160.91, 153.16, 142.79, 127.86, 119.91, 115.10, 41.31, 30.59, 19.61.1H NMR (12 kHz) d (ppm): 6.92 and 5.59 (H in benzene), 3.70 (H in methylene group), 3.43 (H of OeCH2 in morpholine group), 2.83 (H of NeCH2 in morpholine group), 1.35 (H in imino). Elem. Anal. (MCMPPS): C 62.16%, H 4.89%, N 8.30%; IR (KBr): y ¼ 3405 (NeH), 1630 (C]N), 1149 (CeN) cm
1. 2.3. Adsorption experiments Experimental temperature is 25  C. The pH values of solutions were adjusted by an aqueous solution of NaOH or HNO3 (0.1 M). MCMPPS (5.0 mg) was added respectively into aqueous solutions (25 mL) of Pb(NO3)2, Ni(NO3)2, Cu(NO3)2, Cd(NO3)2 and Cr(NO3)3 in distilled water. Each aqueous suspension was stirred for 12 h to obtain adsorption equilibrium. Then, the solids were filtered. Concentrations of heavy metal ions in filtrate were detected by an AAS. 2.3.1. Effect of pH value of aqueous solution on adsorption of resin MCMPPS for heavy metal ions Metal salt Pb(NO3)2 (339.4 mg),Cu(NO3)2$3H2O (950.6 mg), Ni(NO3)2$6H2O (1238.1 mg), Cr(NO3)3$9H2O (1663.5 mg) or Cd(NO3)2$4H2O (685.9 mg) was added into water (250 mL) to get a solution (1000 ppm) containing Pb(II), Cu(II), Ni(II), Cr(III) or Cd(II) ions. An aqueous solution (50 ppm) containing Pb(II), Cu(II), Ni(II), Cr(III) or Cd(II) ions was prepared by further diluting the solution (1000 ppm) with water. The pH values of the solution containing Pb(II) or Cu(II) ions (50 ppm) was adjusted to 2.0, 3.0, 3.5, 4.0, 4.5, 5.0 and 5.5. The pH value of the solution containing Cd(II) or Ni(II) ions (50 ppm) was adjusted to 2.0, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 and 6.0. While pH value of the solution containing Cr(III) ions (50 ppm) was adjusted to 2.0, 3.0, 3.5, 4.0, 4.5 and 5.0. Resin MCMPPS (5.0 mg) was added into an above solution (25 mL) and stirred for 12 h before the resin was separated. Concentration of remanent heavy metal ions in the filtrate was determined by AAS. 2.3.2. Adsorption kinetics Resin MCMPPS (10.0 mg) was added into the aqueous solution (50 mL, 100 ppm) of Pb(II) (pH ¼ 4.5), Cu(II) (pH ¼ 4.5), Ni(II) (pH ¼ 4.5), Cr(III) (pH ¼ 4.0) and Cd(II) (pH ¼ 5.5) ions. After the aqueous suspension was stirred for 1, 2, 3, 5, 10, 20, 30, 50, 80, 140,

Scheme 1. Synthetic route of resin MCMPPS.

C.-Z. Zhang et al. / Journal of Molecular Liquids 296 (2019) 111860

200, 260 min, the resin was filtrated. Concentrations of remanent heavy metal ions in the filtrates were determined by AAS. 2.4. Adsorption isotherms Concentrations (10, 20, 30, 40, 50, 70, 90 and 110 ppm) of aqueous solutions of Pb(II), Cu(II), Ni(II), Cr(III) or Cd(II) ions were prepared by diluting the solution (1000 ppm) containing heavy metal ions with water. Resin MCMPPS (5.0 mg) was added into an above solution (25 mL, 10, 20, 30, 40, 50, 70, 90 or 110 ppm) containing Pb(II) (pH ¼ 4.5), Cu(II) (pH ¼ 4.5), Ni(II) (pH ¼ 4.5), Cr(III) (pH ¼ 4.0) or Cd(II) (pH ¼ 5.5) ions to give a suspension. The suspension was stirred for 12 h before the resin was filtrated. Concentration of remanent heavy metal ions in the filtrate was determined by AAS. Adsorption capacity at equilibrium (qe, mg g
1) was calculated from Equation (1) [27]:

qe ¼

ðC0
Ce ÞV m

(1)

where V is the volume of the solution (L). C0 and Ce are the initial and equilibrium concentrations of heavy metal ions (mg L
1), respectively. W is the weight of resin (g). 2.4.1. Effect of concentration of MCMPPS on the removal rate and adsorption capacity of resin MCMPPS for heavy metal ions Resin MCMPPS (2.5, 5.0, 12.5, 20.0, 25.0, 37.5 or 50.0 mg) was added into an aqueous solution (25 mL; 50 ppm) containing Pb(II) (pH ¼ 4.5), Cu(II) (pH ¼ 4.5), Ni(II) (pH ¼ 4.5), Cr(III) (pH ¼ 4.0) or Cd(II) (pH ¼ 5.5) ions, respectively. The aqueous suspension was stirred for 12 h before the resin was filtrated. Concentration of remanent heavy metal ions in the filtrate was determined by AAS. 2.5. Stability of adsorbent MCMPPS in acid, basic or oxidative aqueous solution Resin MCMPPS (30 mg) was added into an aqueous solution (50 mL) of HNO3 (1 or 5 mol L
1), NaOH (1 or 5 mol L
1) or H2O2 (5 wt% or 10 wt%) to give a suspension. The suspension was stirred for 4 h before the resin was filtrated, washed by water and dried to give treated resin MCMPPS for study on stability of adsorbent MCMPPS in acid, basic and oxidative aqueous solutions. The treated resin MCMPPS (5.0 mg) was added to a solution containing Pb(II) ions (50 mL, 200 ppm, pH ¼ 4.5) and stirred for 30 min, respectively. The treated MCMPPS with adsorbed heavy metal ions was filtered. Concentration of remanent heavy metal ions in the filtrate was determined by AAS. 2.6. Recyclability MCMPPS (20.0 mg) was added to a solution containing Pb(II), Cu(II), Ni(II), Cr(III) or Cd(II) ions (50 mL, 5 ppm) and stirred for 30 min, respectively. Initial pH value of solutions containing Pb(II), Cu(II), Ni(II), Cr(III) or Cd(II) was 4.5, 4.5, 4.5, 4.0 and 5.5, respectively. MCMPPS with adsorbed heavy metal ions was filtered. Then the MCMPPS with adsorbed heavy metal ions was added into HNO3 solution (0.01 M, 50 mL) and stirred for 30 min. The suspension was filter to give regenerated MCMPPS. The regenerated MCMPPS was washed with NaHCO3 solution (0.01 M, 5 mL  3) and distilled water (5 mL  3), dried in a vacuum drying oven at 60  C for 12 h. The regenerated MCMPPS was used to adsorb heavy metal ions again to study its recyclability. After the adsorbent MCMPPS adsorbed and desorbed a kind of heavy metal ions for 5 times, IR spectrum of regenerated adsorbent was performed. Resin MCMPPS (10.0 mg) was added into a solution (50 mL, 200 ppm) of Pb(II) (pH ¼ 4.5) ions. After stirring the aqueous

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suspension for 4 h, the resin was filtered. Concentration of remanent Pb(II) ions in the filtrate was determined by AAS. The resin MCMPPS with adsorbed Pb(II) was added into ethylene diamine tetraacetic acid (EDTA) solution (50 mL, 50 ppm) to give a suspension. After the aqueous suspension was stirred for 12 h, the resin was filtered. Concentration of Pb(II) ions in the filtrate was determined by AAS [28]. The adsorbent MCMPPS adsorbed and desorbed Pb(II) ions for 5 times. 3. Results and discussion 3.1. Structure of resin MCMPPS 3.1.1. Surface images The SEM images of resin MCMPPS were shown in Fig. 1. In SEM images, MCMPPS formed block powder with pores. It could be attributed to the fact that MCMPPS molecules with disorder structures were aggregated to form loose solid. 3.1.2. Distances of particles N2 adsorption and desorption isotherms of resin MCMPPS were shown in the left part of Fig. 2. The adsorption isotherm is close to type-IV according to IUPAC classification [26]. The N2 uptake value increased sharply from 4.25 to 22.00 when pressure of N2 increased from 0.95 to 1.00 atm. Its surface area was about 4.49 m2 g
1. The X-ray diffraction spectra of resins PPS, CMPPS and MCMPPS were shown in the right part of Fig. 2. In XRD spectrum of PPS, a diffraction peak is located at 2q ¼ 20.84 . An average interlayer distance between two adjacent PPS particles is 0.426 nm. In XRD spectrum of CMPPS, a diffraction peak is located at 2q ¼ 20.70 . An average interlayer distance between two adjacent CMPPS particles is 0.428 nm. Area of the diffraction peak of CMPPS is smaller than that of PPS. It suggests that CMPPS molecules had aggregated to disorder structures compared with PPS. In XRD spectrum of MCMPPS, a diffraction peak is located at 2q ¼ 20.52 . An average distance between two adjacent MCMPPS particles is 0.432 nm. Area of the diffraction peak of MCMPPS is smaller than that of PPS. It suggests that MCMPPS molecules had aggregated to very disorder structures compared with PPS. Average distance between two adjacent MCMPPS particles is the longest due to big volumes of moroxydine groups. 3.1.3. Function groups in surfaces of MCMPPS FT-IR spectra of PPS, CMPPS and MCMPPS were shown in Fig. 3. Compared with PPS resin, two new absorption peaks located at 1258 and 706 cm
1 in FT-IR spectrum of resin CMPPS could be attributed to the CeH stretching vibration and CeCl in-plane bending vibration modes of the chloromethyl group, respectively [29]. In FT-IR spectrum of resin MCMPPS, the peaks located at 3405, 1630 and 1149 cm
1 are attributed to NeH, C]N and CeN stretching vibration modes [31]. Moreover, there isn’t an obvious peak located at 706 cm
1, which is due to CeCl in-plane bending vibration modes of the chloromethyl group [31]. It shows that chlorine atoms at the chloromethyl groups in CMPPS had been substituted by moroxydine groups. 3.2. Thermodynamic stability The thermogravimetry (TG) and differential thermogravimetric analysis (DTG) curves of the resin MCMPPS were shown in Fig. 4. In TG curve of MCMPPS, 6% of weight was lost when temperature rose from 25  C to 100  C. It would be attributed to removing adsorbed water from the resin. Twenty three percent of weight of MCMPPS was lost when temperature rose from 200  C to 400  C. It would be attributed to dehydration and breaking of bonds CeN in MCM moieties [32]. According to results of elemental analysis,

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Fig. 1. SEM images of MCMPPS.

Fig. 2. N2 adsorption and desorption isotherms and XRD spectra.

Fig. 4. TG and DTG curves of resin MCMPPS. Fig. 3. FT-IR spectra of PPS, CMPPS and MCMPPS.

there is 8.3% of nitrogen in resin MCMPPS, therefore percent of MCM (C7H14N5O) groups is about 20.3%. Thirty four percent of weight of MCMPPS was lost when temperature rose from 400  C to

600  C. It could be attributed to breaking of carbon skeletons of PPS moieties [32]. Therefore, resin MCMPPS exhibited a good thermal stability.

C.-Z. Zhang et al. / Journal of Molecular Liquids 296 (2019) 111860

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Table 2 Chemical stability of resin MCMPPS. Solution

q1a (mg g-1)

q2a (mg g
1)

q3a (mg g
1)

Dqb (%)

1 mol L
1 HNO3 5 mol L
1 HNO3 1 mol L
1 NaOH 5 mol L
1 NaOH 5% H2O2 10% H2O2

186.92 186.36 181.48 165.61 166.06 165.61

186.77 186.45 181.57 165.87 165.97 165.37

186.93 186.18 181.58 165.47 166.13 165.83

0.03 0.32 2.87 11.38 11.16 11.40

a

Adsorption capacity. Percent of loss of adsorption capacity. The value can be calculated as following method: (Dq ¼ (qmax e (q1 þ q2 þ q3)/3)/qmax  100%). b

Fig. 5. Effect of adsorption time on adsorption capacities of resin MCMPPS for heavy metal ions.

3.3. Adsorption of MCMPPS for heavy metal ions Experiments of MCMPPS adsorbing heavy metal ions in aqueous solution with different pH values were performed to select suitable pH values for adsorption experiments [34] Experimental results (Fig. S1) suggested that suitable pH values of aqueous solutions for adsorption experiments of MCMPPS for Pb(II), Cd(II), Cr(III), Cu(II) and Ni(II) ions are 4.5, 5.5, 4.0, 4.5 and 4.5, respectively. Pseudo-first-order [35,36] and pseudo-second-order [37] adsorption models were used to study adsorption kinetics of MCMPPS adsorbing heavy metal ions (Fig. S2). Correlation coefficient (R2) values of the pseudo-second-order and the pseudo-firstorder models (Table S1) suggested that the pseudo-second-order kinetic model was suitable to study the adsorption kinetics of MCMPPS for heavy metal ions [38,39]. In the initial 20 min (Fig. 5), adsorption capacity of MCMPPS for heavy metal ions increased rapidly. The adsorption capacities of resin MCMPPS for Pb(II), Cr(III), Cu(II) and Ni(II) increased in the initial 30 min. After the initial 30 min, the adsorption capacities didn’t remarkably increase. Therefore, equilibrium time of MCMPPS adsorbing Pb(II), Cr(III), Cu(II) and Cd(II) should be about 30 min. Similarly, equilibrium time of MCMPPS adsorbing Ni(II) should be about 70 min. Therefore, resin MCMPPS may adsorbing heavy metal ions quickly. Langmuir [32] and Freundlich [33] adsorption isotherm models were employed to study adsorption capacities of MCMPPS for heavy metal ions.

Table 1 Parameters of MCMPPS adsorbing heavy metal ions and molar ratios of heavy metal ions to MCM groupc. Metal ion

qmaxa(mg/g)

tb(min)

pHc

Vd

Pb(II) Cd(II) Cr(III) Cu(II) Ni(II)

186.92 189.75 120.04 119.33 134.05

30 30 30 30 30

4.5 5.5 4.0 4.5 4.5

0.54 1.00 1.37 1.11 1.35

: : : : :

1 1 1 1 1

a The maximum adsorption capacity of MCMPPS for heavy metal ions calculated by the Langmuir adsorption isothem model. b Equilibrium time. c The selected pH value for experiments of MCMPPS adsorbing heavy metal ions. d Molar ratio of heavy metal ions to MCM groups. The value can be calculated as following method: (V ¼ (Maximum adsorption capacity/Heavy metal atomic weight): Molar value of MCM groups in 1 g MCMPPS).

Fig. 6. FT-IR spectra of MCMPPS and regenerated MCMPPS.

Table 3 Adsorption capacity and equilibrium time of MCMPPS and popular adsorbents for Pb(II). No.

qmax(mg g
1)

ta(min)

C0(mg L
1)

Ce(mg L
1)

T(oC)

Ref.

ACC LXR AFC ACR MCMPPS

61.16 64.9 243.9 235.98 186.92

e 90 720 40 30

217.4 50 150 1035 50

62.1 5 28 799.0 1.55

25 30 25 25 25

[41] [42] [43] [22] This work

a

Equilibrium time of adsorbent for Pb(II) ions.

Correlation coefficients of the two models suggested that the Langmuir adsorption isotherm model is more suitable to study adsorption of MCMPPS for heavy metal ions. Parameters of MCMPPS adsorbing heavy metal ions and molar ratios of heavy metal ions to MCM groups were collected in Table 1. According to the Langmuir isotherm model, the qmax values of resin MCMPPS for Pb(II), Cd(II), Cr(III), Cu(II) and Ni(II) were 186.92, 189.75, 120.04, 119.33 and 134.05 mg g
1, respectively. Molar ratio of Pb(II), Cd(II), Cr(III), Cu(II) and Ni(II) ions to MCM groups are 0.54, 1.00, 1.37, 1.11 and 1.35, respectively. It suggests that Pb(II), Cd(II), Cr(III), Cu(II) and Ni(II) ions would be adsorbed on surfaces of MCMPPS via coordination of amino and imino groups at MCM moieties with them. It would attributed to the fact that compared with Pb(II), Cd(II), Cu(II) and Ni(II), ionic radius of Cr(III) is the smallest, therefore, a MCM moiety may coordinate with several Cr(III) ions. Moreover, its positive charge value is the largest,

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C.-Z. Zhang et al. / Journal of Molecular Liquids 296 (2019) 111860

Fig. 7. FT-IR spectra of MCMPPS and MCMPPS with adsorbed heavy metal ions (a), and adsorption mechanism of MCMPPS for heavy metal ions (b).

as a result, Cr(III) ions would be easily coordinated with amino, imino groups and H2O molecules to form stable complexes. Therefore, molar ratio of Cr(III) ions to moroxydine groups are the largest. The molar ratio of Pb(II) ions to MCM groups are the smallest due to its large radius. Similarly, the molar ratio of Cd(II) ions to MCM groups are small due to its large radius. In general, heavy metal ions usually coordinate with several ligands, such as amino, imino groups and H2O molecules to form complexes with large radius, which block MCMPPS adsorbing other heavy metal ion. Therefore, the molar ratio values of heavy metal ions to MCM groups would depend on stereo-hindrance generated from the complexes. Atomic weights of Pb and Cd are large, therefore, adsorption capacity of MCMPPS for Pb(II) and Cd(II) are big. 3.4. Stability of MCMPPS in acid, basic and oxidative aqueous solutions The chemical stability of resin MCMPPS in HNO3 (1 or 5 mol L
1), NaOH (1 or 5 mol L
1) and H2O2 (5% or 10%) aqueous solution was studied (Table 2). The experimental data was collected in Table 2. Heavy metal Pb, Cd, Cr, Cu and Ni are transition metals. Interactions between heavy metal ions Pb(II), Cd(II), Cr(III), Cu(II) or Ni(II) and amino or imino groups would be similar modes. Therefore, Pb(II) ions were selected to study chemical stability of resin MCMPPS. Adsorption capacity of resin MCMPPS for Pb(II) ions decreased 0.03% and 0.32%, after MCMPPS was treated by aqueous solutions of 1 or 5 mol L
1 HNO3, respectively. About 2.87% or 11.38% of the adsorption capacity decreased after the resin was treated by aqueous solutions of NaOH (1 or 5 mol L
1), respectively. It could be attributed to the fact that chlorine atoms was replace by hydroxyl groups to give a new resin, which adsorption capacity was smaller than that of MCMPPS. There was a decrease (11.40%) of the adsorption capacity after the resin was treated by an aqueous solution (10%) of H2O2. It could be attributed to an oxidization reaction of amino groups. However, the oxidation resistance of resin MCMPPS was much better than that of the resin Amberlite IRA-400 [40]. Therefore, resin MCMPPS exhibited a good stability in acid, basic and oxidative aqueous solution. 3.5. Recyclability FT-IR spectra of MCMPPS and regenerated MCMPPS were shown in Fig. 6. Recyclability of MCMPPS was investigated by adsorption/ desorption procedures of MCMPPS for Pb(II), Cd(II), Cr(III), Cu(II)

and Ni(II). In FT-IR spectrum of regenerated MCMPPS (Fig. 6), absorption peaks of NeH (3434 cm
1), C]N (1633 cm
1) and CeN (1165 cm
1) stretching vibration modes are in accordance with that of MCMPPS. Other absorption peaks of functional groups at regenerated MCMPPS are same with that of MCMPPS. After MCMPPS with adsorbed Pb(II) was immersed in an aqueous solution of HNO3, adsorbed Pb(II) on surface of MCMPPS was desorbed completely and both amino and imino groups at MCM moieties in MCMPPS reacted with HNO3 to generate amino and imino nitrates. The nitrates reacted with NaHCO3 to recovery amino and imino groups. As a result, adsorbent MCMPPS was regenerated. Consequently, MCMPPS would be a reusable and stable adsorbent for removing heavy metal ions from wastewater. EDTA is a good ligand which may react with Pb(II) ions to form complexes. Therefore, EDTA was employed to desorb heavy metal ions on surfaces of adsorbent [28]. Adsorbed Pb(II) on surface of MCMPPS wasn’t desorbed completely (Table S3), after MCMPPS with adsorbed Pb(II) was immersed in an aqueous solution of EDTA for 4 h. It is contributed to the fact that amino and imino groups at MCM moieties reacted with Pb(II) ions to form stable complexes. Therefore, MCMPPS would be a good adsorbent for removing heavy metal ions from water.

3.6. Adsorption capacity and equilibrium time of MCMPPS and popular adsorbents for Pb(II) Adsorption capacity and equilibrium time of MCMPPS and popular adsorbents were collected in Table 3. Maximum adsorption capacity (qm) value of MCMPPS (186.92 mg g
1) for Pb(II) is bigger than that of lignin xanthate resin (LXR) (64.9 mg g
1) and activated carbon cloth (ACC) (61.16 mg g
1). The qm value of MCMPPS (186.92 mg g
1) for Pb(II) was about 30% smaller than that of amidoxime chelating resin (ACR) (235.98 mg g
1) and amino-functionalized composite (AFC) (243.9 mg g
1). It would be attributed to low mole fraction of amino and imino groups, because 35% of benzene rings in main chains of MCMPPS were grafted by MCM groups according to element analysis values (N, 8.30%). If mole fraction of MCM groups grafted at benzene rings in main chains of MCMPPS were improved, the qm value of resin containing MCM groups would be increased. Equilibrium time (t) of MCMPPS (30 min) adsorbing Pb(II) was shorter than those of LXR (90 min), AFC (720 min) and ACR (40 min). The short t value of MCMPPS should be attributed to primary amine and imino groups on the surface of MCMPPS, which coordinate easily with heavy metal ions [44]. In addition, MCMPPS is easily dispersed

C.-Z. Zhang et al. / Journal of Molecular Liquids 296 (2019) 111860

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Fig. 8. Wide survey XPS spectra of MCMPPS and it with adsorbed Pb(II) (A), Pb 4f spectrum of MCMPPS with adsorbed Pb(II) (B), C 1s spectrum of MCMPPS (C), C 1s spectrum of MCMPPS with adsorbed Pb(II) (D), N 1s spectrum of MCMPPS (E), N 1s spectrum of MCMPPS with adsorbed Pb(II) (F).

in aqueous solution to adsorbing heavy metal ions due to hydrophilicity of the primary amino groups [45]. 3.7. Adsorption mechanism FT-IR spectra of MCMPPS and MCMPPS with adsorbed heavy metal ions, and adsorption mechanism of MCMPPS for heavy metal

ions were shown in Fig. 7. In FT-IR spectrum of MCMPPS, absorption peaks located at 3487, 3405 and 1149 cm
1 are attributed to NeH (3487 and 3405 cm
1) and CeN (1149 cm
1) stretching vibration modes at MCM moieties, respectively (Fig. 7a) [30]. Similarly, in FT-IR spectra of MCMPPS with a kind of adsorbed heavy metal ions, peaks located at 3410 and 1126 cm
1 are due to NeH and CeN stretching vibration modes at

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MCM moieties, respectively (Fig. 7a) [30]. After the amino groups at surfaces of MCMPPS coordinated with heavy metal ion, the absorption peak of NeH stretching vibration shifted to longer wavelength. In the coordination procedure, an empty molecular orbital of a heavy metal ion accepted a lone electron pair at an N atom at amino or imino group to result the red-shift of absorption peaks of NeH and CeN stretching vibrations in FT-IR spectra [46]. In FT-IR spectra of MCMPPS with adsorbed heavy metal ions, a strong peak located at 1383 cm
1 are due to NeO stretching vibration
1 modes of NO
3 groups [47]. Adsorption peak located at 1626 cm are assigned to C]N stretching vibration modes. In summary, adsorption of MCMPPS for heavy metal ions is chemical adsorption via coordination reactions. Based on IR spectra, EA and adsorption data, adsorption mechanism of MCMPPS for heavy metal ions was supposed (Fig. 7b). In the coordination procedure, an empty molecular orbital of a heavy metal ion accepted a lone electron pair of each N atom at an amine or imino group to form a coordination bond, therefore, the N atoms at amino groups would coordinate with heavy metal ions. Consequently, MCMPPS would be an effective absorbent for removing heavy metal ions from water. Chemical composition of MCMPPS and it with adsorbed Pb(II) was examined by XPS (Fig. 8). Compared with XPS spectrum of MCMPPS, new peaks located at (138.18 and 143.03 eV) in the wide survey XPS spectrum of MCMPPS with adsorbed Pb(II) are due to Pb 4f. It suggests that Pb (II) ions were adsorbed on surfaces of MCMPPS Fig. 8 (A). In Fig. 8 (B), the Pb 4f7/2 (138.18 eV) and Pb 4f5/2 (143.03 eV) were attributed to the formation of NHePb2þ and NHePb2þ-NH, respectively [48]. In Fig. 8C, the peaks located at 285.98 and 284.43 eV were attributed to CeOeC and CeC, respectively [48]. In Fig. 8 (D), the binding energies of CeOeC and CeC did not change. It shows that carbon atoms hardly effect on the adsorption of MCMPPS for Pb(II) ions [49]. In Fig. 8 (E), the peaks located at 398.73 and 399.13 eV were attributed to eNH- and ¼NH, respectively. In Fig. 8 (F), the peaks located at 398.83 and 399.83eV was due to eNH- and ¼NH, respectively [48]. The results show that the binding energies of nitrogen atoms at amino and imino groups in MCM moieties were changed due to the coordination reaction between Pb(II) ions and amino and imino groups in MCM moieties of MCMPPS. 4. Conclusion An antiviral drug moroxydine was grafted on health-friendly polymer polyphenylene sulfide to synthesize a new type of adsorbent MCMPPS for removing heavy metal ions from water. The resin MCMPPS exhibited excellent chemical stability in a strong acid, basic or oxidative aqueous solution. The maximum adsorption capacity of resin MCMPPS for Pb(II), Cd(II), Cr(III), Cu(II) and Ni(II) were 186.92, 189.75, 120.04, 119.33 and 134.05 mg g
1, respectively, moreover, equilibrium time of MCMPPS adsorbing Pb(II), Cr(III), Cu(II) and Cd(II) are about 30 min. IR spectra of MCMPPS with adsorbed heavy metal ions suggested that heavy metal ions were adsorbed on surfaces of the adsorbent by coordination reaction of heavy metal ions with amino and imino groups. Therefore, this new resin should be a potential adsorbent for removal of heavy metal ions in water owing to its thermal and chemical stability, healthy safety, and efficient adsorption. Acknowledgements This work was supported by National Natural Science Foundation of China (Grant No. 11305091). Six talent peaks project in Jiangsu Province (R2015L12), the Priority Academic Program Development of Jiangsu Higher Education Institutions.

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molliq.2019.111860. Conflicts of interest The authors declare no conflict of interest. References [1] K.Z. Elwakeel, A.A. El-Bindary, E.Y. Kouta, Guibal Eric, Functionalization of polyacrylonitrile/Na-Y-zeolite composite with amidoxime groups for the sorption of Cu(II), Cd(II) and Pb(II) metal ions, Chem. Eng. J. 332 (2018) 727e736, https://doi.org/10.1016/j.cej.2017.09.091. [2] M. Cegłowski, B. Gierczyk, M. Frankowski, Ł. Popenda, A new low-cost polymeric adsorbents with polyamine chelating groups for efficient removal of heavy metal ions from water solutions, React. Funct. Polym. 131 (2018) 64e74, https://doi.org/10.1016/j.reactfunctpolym.2018.07.006. [3] P.R. Hunt, N. Olejnik, R.L. Sprando, Toxicity ranking of heavy metals with screening method using adult caenorhabditis elegans and propidium iodide replicates toxicity ranking in rat, Food Chem. Toxicol. 50 (2012) 3280e3290, https://doi.org/10.1016/j.fct.2012.06.051. , N. Meunier, R. Hausler, G. Mercier, P. Drogui, Heavy [4] J.F. Blais, C. Montane metals removal from acidic and saline soil leachate using either electrochemical coagulation or chemical precipitation, J. Environ. Eng. 132 (2006) 545e554, https://doi.org/10.1061/(ASCE)0733-9372(2006)132:5(545). [5] J. Rezaniaa, V. Vatanpourb, A. Shockravia, M. Ehsanic, Preparation of novel carboxylated thin-film composite polyamide-polyester nanofiltration membranes with enhanced antifouling property and water flux, React. Funct. Polym. 131 (2018) 123e133, https://doi.org/10.1016/ j.reactfunctpolym.2018.07.012. [6] J.Q. Jiang, The role of coagulation in water treatment, Curr. Opin. Chem. Eng. 8 (2015) 36e44, https://doi.org/10.1016/j.coche.2015.01.008. [7] S. Kafashi, M.R. Yaftian, A.A. Zamani, Binding ability of crown ethers towards Pb(II) ions in binary water/organic solvents using solvent extraction method, J. Solut. Chem. 44 (2015) 1e14, https://doi.org/10.1007/s10953-015-0378-1. [8] A.A. El-Kady, R. Carleer, J. Yperman, J. D’Haen, H.H.A. Ghafar, Kinetic and adsorption study of Pb(II) toward different treated activated carbons derived from olive cake wastes, Desalin. Water Treat. 57 (2016) 8561e8574, https:// doi.org/10.1080/19443994.2015.1020514. [9] A.M. Atta, A.O. Ezzat, S.A. Al-Hussain, H.A. Al-Lohedan, A.M. Tawfeek, A.I. Hashem, New crosslinkedpoly(ionic liquid) cryogels for fast removal of methylene blue from waste water, React. Funct. Polym. 131 (2018) 420e429, https://doi.org/10.1016/j.reactfunctpolym.2018.08.019. [10] M. Yari, M. Rajabi, O. Moradi, A. Yari, M. Asif, S. Agarwal, V.K. Gupta, Kinetics of the adsorption of Pb(II) ions from aqueous solutions by graphene oxide and thiol functionalized graphene oxide, J. Mol. Liq. 209 (2015) 50e57, https:// doi.org/10.1016/j.molliq.2015.05.022. [11] S.F. He, F. Zhang, S.Z. Cheng, W. Wang, Synthesis of sodium acrylate and acrylamide copolymer/GO hydrogels and their effective adsorption for Pb2þ and Cd2þ, ACS Sustain. Chem. Eng. 4 (2016) 3948e3959, https://doi.org/ 10.1021/acssuschemeng.6b00796. [12] S. Babel, T.A. Kurniawan, Low-cost adsorbents for heavy metals uptake from contaminated water: a review, J. Hazard Mater. 97 (2003) 219e243, https:// doi.org/10.1016/s0304-3894(02)00263-7. [13] H.T. Fan, M.X. Liu, S.B. Na, X.T. Sun, Preparation, characterization, and selective adsorption for lead(II) of imprinted silica-supported organic-inorganic hybrid sorbent functionalized with chelating S, N-donor atoms, Monatshefte Chem. 146 (2015) 459e463, https://doi.org/10.1007/s00706-014-1301-y. [14] K. Anitha, S. Namsani, J.K. Singh, Removal of heavy metal ions using a functionalized single-walled carbon nanotube: a molecular dynamics study, J. Phys. Chem. 119 (2015) 8349e8358, https://doi.org/10.1021/ acs.jpca.5b03352. [15] Y. Meng, J.N. Wang, L. Xu, A.M. Li, Fast removal of Pb2þ from water using new chelating fiber modified with acylamino and amino groups, Chin. Chem. Lett. 23 (2012) 496e499, https://doi.org/10.1016/j.cclet.2011.12.019. [16] F.Q. Liu, P.P. Ling, X.S. Jing, C.H. Li, A.M. Li, X.Z. You, Interaction mechanism of aqueous heavy metals onto a newly synthesized IDA-chelating resin: isotherms, thermodynamics and kinetics, Chem. Eng. J. 173 (2011) 106e114, https://doi.org/10.1016/j.cej.2011.07.044. [17] C. McManamon, A.M. Burke, J.D. Holmes, M.A. Morris, Amine-functionalised SBA-15 of tailored pore size for heavy metal adsorption, J. Colloid Interface Sci. 369 (2012) 330e337, https://doi.org/10.1016/j.jcis.2011.11.063. [18] O. Sayar, K. Mehrani, F. Hoseinzadeh, A. Mehrani, O. Sadeghi, Comparison of the performance of different modified graphene oxide nanosheets for the extraction of Pb(II) and Cd(II) from natural samples, Microchim. Acta. 181 (2014) 313e320, https://doi.org/10.1007/s00604-013-1112-6. [19] Z.W. Zhang, F. Wang, W.B. Yang, Z. Yang, A.M. Li, A comparative study on the adsorption of 8-amino-1-naphthol-3,6-disulfonic acid by a macroporous amination resin, Chem. Eng. J. 283 (2016) 1522e1533, https://doi.org/ 10.1016/j.cej.2015.08.010. [20] Y. Zhang, Y.N. Chen, C.Z. Wang, Y.M. Wei, 2014. Immobilization of 5-

C.-Z. Zhang et al. / Journal of Molecular Liquids 296 (2019) 111860

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

aminopyridine-2-tetrazole on cross-linked polystyrene for the preparation of a new adsorbent to remove heavy metal ions from aqueous solution, J. Hazard Mater. 276 (2014) 129e137, https://doi.org/10.1016/j.jhazmat.2014.05.027. H.Y. Shen, Z.X. Chen, Z.H. Li, M.Q. Hu, X.Y. Dong, Q.H. Xia, Controlled synthesis of 2,4,6-trichlorophenol-imprinted amino-functionalized nano-Fe3O4-polymer magnetic composite for highly selective adsorption, Colloids Surf., A 481 (2015) 439e450, https://doi.org/10.1016/j.colsurfa.2015.06.007. A.F. Shaaban, D.A. Fadel, A.A. Mahmoud, M.A. Elkomy, S.M. Elbahy, Synthesis of a new chelating resin bearing amidoxime group for adsorption of Cu(II), Ni(II) and Pb(II) by batch and fixed-bed column methods, J. Environ. Chem. Eng. 2 (2014) 632e641, https://doi.org/10.1016/j.jece.2013.11.001. lu, H. Yilmaz, S.Z. Yildiz, M. Imamoglu, H. S¸ahin, Aydın S¸eyma, F. Tosunog Investigation of Pb(II) adsorption on a novel activated carbon prepared from hazelnut husk by K2CO3 activation, Desalin. Water Treat. 57 (2015) 1e10, https://doi.org/10.1080/19443994.2014.995135. H. Li, G.Y. Lv, G. Zhang, H.H. Ren, X.X. Fan, Y.G. Yan, Synthesis and characterization of novel polyphenylene sulfide (PPS) containing chromophore in the main chain, Polym. Int. 63 (2014) 1707e1714, https://doi.org/10.1002/ pi.4698. J.J. Huang, X. Zhang, L.L. Bai, S.G. Yuan, Polyphenylene sulfide based anion exchange fiber: synthesis, characterization and adsorption of Cr(VI), J. Environ. Sci. 24 (2012) 1433e1438, https://doi.org/10.1016/s1001-0742(11) 60948-0. D. Zhang, H. Yao, D. Zhou, L. Dai, J. Zhang, S. Yuan, Synthesis, characteristics and adsorption properties of polyphenylene sulfide based strong acid ion exchange fiber, Polym. Adv. Technol. 25 (2014) 1590e1595, https://doi.org/ 10.1002/pat.3407. C.-Z. Zhang, Y. Yuan, Z. Guo, Experimental study on functional graphene oxide containing many primary amino groups fast-adsorbing heavy metal ions and adsorption mechanism, Separ. Sci. Technol. 53 (11) (2018) 1666e1677, https://doi.org/10.1016/S1001-0742(11)60948-0. M. Cegłowski, G. Schroeder, Preparation of porous resin with Schiff base chelating groups for removal of heavy metal ions from aqueous solutions, Chem. Eng. J. 263 (2015) 402e411, https://doi.org/10.1016/j.cej.2014.11.047. T. Li, C.-Z. Zhang, X. Fan, Degradation of oxidized multi-walled carbon nanotubes in water via photo-Fenton method and its degradation mechanism, Chem. Eng. J. 323 (2017) 37e46, https://doi.org/10.1016/j.cej.2010.12.048. N. Puviarasan, V. Arjunan, S. Mohany, FT-IR and FT-Raman studies on 3aminophthalhydrazide and N-aminophthalimide, Turk. J. Chem. 26 (2002) 323e333, https://doi.org/10.1016/j.matchemphys.2011.10.025. M.J.S. Dewar, G.P. Ford, Ground states of molecules. 37. MINDO/3 calculations of molecular vibration frequencies, J. Am. Chem. Soc. 99 (6) (1997) 1685e1691, https://doi.org/10.1021/ja00448a001. I. Langmuir, The adsorption of gases on plane surfaces of glass, mica and platinum, J. Am. Chem. Soc. 143 (1918) 1361e1403, https://doi.org/10.1021/ ja02242a004. C.-Z. Zhang, Y. Yuan, T. Li, Adsorption and desorption of heavy metals from water using aminoethyl reduced graphene oxide, Environ. Eng. Sci. 35 (2018) 978e987, https://doi.org/10.1089/ees.2017.0541. L. Qin, L. Yan, J. Chen, T. Liu, H. Yu, B. Du, Enhanced removal of Pb2þ, Cu2þ, and Cd2þ by amino-functionalized magnetite/kaolin clay, Ind. Eng. Chem. Res. 55 (2016) 7344e7354, https://doi.org/10.1021/acs.iecr.6b00657. B. Kumar, K. Smita, E. S anchez, C. Stael, L. Cumbal, Andean sacha inchi (plukenetia volubilis l.) shell biomass as new biosorbents for Pb2þ and Cu2þ ions,

9

Ecol. Eng. 93 (2016) 152e158, https://doi.org/10.1016/j.ecoleng.2016.05.034. [36] L. Cui, Y. Wang, L. Gao, L. Hu, L. Yan, Q. Wei, B. Du, 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. 281 (2015) 1e10, https://doi.org/10.1016/j.cej.2015.06.043. [37] M. Torab-Mostaedi, M. Asadollahzadeh, A. Hemmati, A. Khosravi, Equilibrium, kinetic, and thermodynamic studies for biosorption of cadmium and nickel on grapefruit peel, J. Taiwan Inst. Chem. Eng. 44 (2013) 295e302, https://doi.org/ 10.1016/j.jtice.2012.11.001. [38] A. Hamouz, C.S. Othman, Synthesis and characterization of a novel series of cross-linked (phenol, formaldehyde, alkyldiamine) terpolymers for the removal of toxic metal ions from wastewater, Arabian J. Sci. Eng. 41 (2016) 119e133, https://doi.org/10.1007/s13369-015-1622-0. [39] R. Fu, Y. Liu, Z. Lou, Z. Wang, S.A. Baig, X. Xu, Adsorptive removal of Pb(II) by magnetic activated carbon incorporated with amino groups from aqueous solutions, J. Taiwan Inst. Chem. Eng. 62 (2016) 247e258, https://doi.org/ 10.1016/j.jtice.2016.02.012. [40] V. Neagu, E. Avram, G. Lisa, N-methylimidazolium functionalized strongly basic anion exchanger: synthesis, chemical and thermal stability, React. Funct. Polym. 70 (2010) 88e97, https://doi.org/10.1016/ j.reactfunctpolym.2009.10.009. [41] J.A. Arcibar-Orozco, J.R. Rangel-Mendez, P.E. Diaz-Flores, Simultaneous adsorption of Pb(II)-Cd(II), Pb(II)-phenol, and Cd(II)-phenol by activated carbon cloth in aqueous solution. water. air, Soil Pollut 226 (2015) 1e10, https:// doi.org/10.1007/s11270-014-2197-1. [42] Z. Li, Y. Kong, Y. Ge, Synthesis of porous lignin xanthate resin for Pb2þ removal from aqueous solution, Chem. Eng. J. 270 (2015) 229e234, https://doi.org/ 10.1016/j.cej.2015.01.123. [43] S. Wang, K. Wang, C. Dai, H. Shi, J. Li, Adsorption of Pb2þ on aminofunctionalized core-shell magnetic mesoporous SBA-15 silica composite, Chem. Eng. J. 262 (2015) 897e903. 10.1016/j.cej.2014.10.035. [44] S. Luo, X. Xu, G. Zhou, C. Liu, Y. Tang, Y. Liu, Amino siloxane oligomer-linked graphene oxide as an efficient adsorbent for removal of Pb(II) from wastewater, J. Hazard Mater. 274 (2014) 145e155, https://doi.org/10.1016/ j.jhazmat.2014.03.062. [45] L. Xu, R. Peng, X. Guan, W. Tang, X. Liu, H. Zhang, Preparation, characterization, and application of a new stationary phase containing different kinds of amine groups, Anal. Bioanal. Chem. 405 (2013) 8311e8318, https://doi.org/ 10.1007/s00216-013-7243-0. [46] I. Polowczyk, B.F. Urbano, B.L. Rivas, M. Bryjak, N. Kabay, Equilibrium and kinetic study of chromium sorption on resins with quaternary ammonium and N-methyl-D-glucamine groups, Chem. Eng. J. 284 (2016) 395e404, https://doi.org/10.1016/j.cej.2015.09.018. [47] M. Islam, R. Patel, Nitrate sorption by thermally activated Mg/Al chloride hydrotalcite-like compound, J. Hazard Mater. 169 (2009) 524e531, https:// doi.org/10.1016/j.jhazmat.2009.03.128. [48] H. Xin, W. Dong, X. Zhang, D. Fan, X. Sun, B. Du, Q. Wei, Synthesis of aminofunctionalized magnetic aerobic granular sludgebiochar for Pb(II) removal: adsorption performance and mechanism studies, Sci. Total Environ. 685 (2019) 681e689, https://doi.org/10.1016/j.scitotenv.2019.05.429. [49] M. Li, D. Wei, T. Liu, Y. Liu, L. Yan, Q. Wei, B. Du, W. Xu, EDTA functionalized magnetic biochar for Pb(II) removal: adsorption performance, mechanism and SVM model prediction, Separ. Purif. Technol. 227 (2019) 115696, https:// doi.org/10.1016/j.seppur.2019.115696.