research article aminoalkylated merrifield resins reticulated ...deta-tcep resin (f), and...
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Research ArticleAminoalkylated Merrifield Resins Reticulated byTris-(2-chloroethyl) Phosphate for Cadmium, Copper, andIron (II) Extraction
Mokhtar Dardouri, Fayçel Ammari, and Faouzi Meganem
Laboratory of Organic Synthesis, Faculty of Sciences of Bizerte, University of Carthage, Zarzouna, 7021 Bizerte, Tunisia
Correspondence should be addressed to Fayçel Ammari; [email protected]
Received 4 February 2015; Revised 1 April 2015; Accepted 2 April 2015
Academic Editor: Cun-Yue Guo
Copyright © 2015 Mokhtar Dardouri et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.
We aimed to synthesize novel substituted polymers bearing functional groups to chelate heavy metals during depollutionapplications. Three polyamine functionalized Merrifield resins were prepared via ethylenediamine (EDA), diethylenetriamine(DETA), and triethylenetetramine (TETA) modifications named, respectively, MR-EDA, MR-DETA, and MR-TETA. Theaminoalkylated polymers were subsequently reticulated by tris-(2-chloroethyl) phosphate (TCEP) to obtain new polymeric resinscalled, respectively, MR-EDA-TCEP,MR-DETA-TCEP, andMR-TETA-TCEP.The obtained resins were characterized via attenuatedtotal reflectance Fourier transform infrared spectroscopy (ATR-FTIR), elemental analysis (EA), and thermogravimetric (TGA),thermodynamic (DTA), and differential thermogravimetric (DTG) analysis. The synthesized resins were then assayed to evaluatetheir efficiency to extract metallic ions such as Cd2+, Cu2+, and Fe2+ from aqueous solutions.
1. Introduction
Recently, the solid phase extraction (SPE) has been shown tobe an excellent separation technique due to immiscibility ofresins with aqueous phase, low rate of physical degradation,minimum release of toxic organic solvents, and recyclingoptions [1, 2]. In SPE, the organic extractants are eithersorbed or anchored to an inert polymeric support [3, 4].In this context, grafted resins have been used in separationof hazardous metallic ions in industrial effluents [5, 6]. Infact, many polymers were reported to contain functionalchelating groups; (i) morin (2,3,4,5,7-pentahydroxyflavone)which was covalently attached to Merrifield’s resin and usedin metal sorption and recognition [7], (ii) chelating ionexchange which was prepared by functionalizing Merrifieldresin with 2,2-pyridylimidazole and used to selectivelyadsorb and separate nickel from other base metal ions insynthetic sulfate solutions [8], and (iii) polymer-supportedtriazoles were used to extract metals such as Cd, Fe, Mg,Ni, and Co from aqueous solutions [9]. Indeed, it hasbeen reported that adsorption properties and selectivity for
metallic ions depend on the molecular structure of adsorp-tionmaterials, particularly, polyamine functional groups, andnitrogen atoms [10–13]. Besides, other resins modified bythe organophosphorus reagents such as polyethylene iminemethylene phosphonic acid have also been performed toremove copper ions from aqueous media [14]. In fact, thereare many research articles describing the synthesis procedureof chloromethylated polystyrene or Merrifield resin attachedwith polyamine groups and employed them as adsorbent forheavy metals removal from aqueous solutions [15–18].
In the present paper we attempt to investigate modifiedMerrifield resins functionalized by polyamines and phospho-rus derivatives to adsorb metallic ions in an aqueous phase.
2. Experimental
2.1. Materials. Merrifield resin (MR reticulated by 2% divin-ylbenzene, 200–400 mesh, 2.1mmol Cl⋅g−1, Fluka), ethylene-diamine (EDA), diethylenetriamine (DETA), triethylenete-tramine (TETA), and Tris-(2-chloroethyl) phosphate (TCEP)were purchased from Sigma-Aldrich. Tetrahydrofuran (THF)
Hindawi Publishing CorporationInternational Journal of Polymer ScienceVolume 2015, Article ID 782841, 6 pageshttp://dx.doi.org/10.1155/2015/782841
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DMF
H2N(CH2CH2NH)nH
CH2Cl CH2NH(CH2CH2NH)nHMR
n = 1, MR-EDA; n = 2, MR-DETA; n = 3, MR-TETA
80∘C
Figure 1: Proposed synthesis of MR-EDA, MR-DETA, and MR-TETA resins.
and dimethylformamide (DMF)were purchased fromSigma-Aldrich. Absolute ethanol, triethylamine (TEA), and diethylether were purchased from Prolabo. Iodide potassium (KI),CdCl2⋅H2O, FeCl
2⋅4H2O, and CuCl
2⋅6H2O were purchased
from Fluka.
2.2. Instrumental Analyses. Infrared analysis was carried outby using the attenuated total reflectance technique (ATR-FTIR), with a Nicolet FTIR 200 spectrophotometer (ThermoScientific). Elemental analysis of C, H, and N was performedby Perkin Elmer analyzer CHN Series II 2400. Elementalanalysis of P was performed by ICP-OES analysis on aHORIBA Scientific. DTA, TGA, and DTG analyses werecarried out with a Mettler Toledo TGA/DSC 1 Star System(power 400 Watts). The amount of remaining metal ionsin solution was evaluated by flame atomic absorption spec-troscopy (FAAS) analysis on a Perkin-Elmer PinAAcle 900 T.The detection limits for Cd2+, Cu2+, and Fe2+ are 0.8, 1.5, and5mg⋅L−1, respectively, and the corresponding wavelengthsfor the studied metals are 228.8, 324.75, and 248.33 nm,respectively.
2.3. Extraction Procedure of Metal Cations. The synthesizedpolymers (0.1 g) were incubated with 20mL of aqueoussolution of metal ion at 25∘C for 24 h. Aqueous monometallicsolutions of CdCl
2⋅H2O, FeCl
2⋅4H2O, and CuCl
2⋅6H2Owere
prepared at a concentration of 2.10−4mol⋅L−1 in relation witheach metal ion in distilled water (pH = 6-7). The suspensionwas filtrated on filter paper (previously washed several timeswith distilled water until disappearance of conductivity inwashing water). The amount of remaining metal ions wasevaluated by FAAS analysis of the filtrate. The extractionpercentage (%) was calculated using the following equation:
%Extraction = ((𝐶
𝑖− 𝐶
𝑓)
𝐶
𝑖
) × 100,(1)
where 𝐶𝑖and 𝐶
𝑓are the concentrations of the metal ion in
initial and final solutions, respectively.
2.4. Synthesis of Merrifield Resin with Ethylenediamine Group(MR-EDA). MR-EDA was prepared according to the litera-ture [16] with some modification. The synthesis procedure
was performed according to Figure 1. First, commerciallyavailable Merrifield resin was suspended in DMF for 10 hfollowed by the addition of EDA.The amine is used in excessto act as the base and increase the rate of reaction. Then, thereaction mixture was stirred at room temperature for 1.5 hand then for 24 h at 70–80∘C. After completing the reaction,the resin was washed several times with deionized water andthenwith absolute ethanol. After, the obtained resinwas driedunder vacuum at 50∘C for 48 h.
2.5. Synthesis of Merrifield Resin with DiethylenetriamineGroup (MR-DETA). The reaction involved MR, DMF, andexcess of DETA.The reaction conditions of the product weresimilar to that of MR-EDA (see Figure 1).
2.6. Synthesis of Merrifield Resin with TriethylenetetramineGroup (MR-TETA). The reaction involved MR, DMF, andexcess TETA. The reaction conditions of the product weresimilar to that of MR-EDA (see Figure 1).
2.7. Synthesis of MR-EDA Reticulated by Tris-(2-chloroethyl)Phosphate (MR-EDA-TCEP). The synthesis procedure wasperformed according to Figure 2.MR-EDAwas suspended inTHF followed by the addition of certain amount of TCEP, asmall amount of KI used as catalysts. Then, a certain amountof TEA used as base was added to the flask. The reactionmixture was heated at 70∘C for 72 h. The cooled mixturewas filtered and washed with distilled water and with diethylether. After, the obtained resin was dried in a vacuum at 50∘Cfor 48 h.
2.8. Synthesis of MR-DETA Reticulated by Tris-(2-chloroethyl)Phosphate (MR-DETA-TCEP). The reaction medium con-tained MR-DETA, THF, KI, TCEP, and TEA. The reactionconditions of the product were similar to that of MR-EDA-TCEP (see Figure 2).
2.9. Synthesis of MR-TETA Reticulated by Tris-(2-chloroethyl)Phosphate (MR-TETA-TCEP). The reaction medium con-tained MR-TETA, THF, KI, TCEP, and TEA. The reactionconditions of the product were similar to that of MR-EDA-TCEP (see Figure 2).
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CH2NH(CH2CH2NH)nH
THF
Tris-(2-chloroethyl) phosphateKI, Et3N
O OP
n = 1: MR-EDA-TCEP; n = 2: MR-DETA-TCEP; n = 3: MR-TETA-TCEP
3
(NHCH2CH2)n
NHCH2
70∘C
Figure 2: Proposed synthesis of MR-EDA-TCEP, MR-DETA-TCEP, and MR-TETA-TCEP resins.
4000 3500 3000 2500 2000 1500 1000 500
16051456
3330
3320
2937
285929383044
1673
1673(d)
(c)
(b)
(a)
696
3332 1673
1265
Tran
smitt
ance
(%)
Wavenumber (cm−1)
Figure 3: ATR-FTIR ofMR resin (a),MR-EDA resin (b),MR-DETAresin (c), and MR-TETA resin (d).
3. Results and Discussion
3.1. Characterization
3.1.1. ATR-FTIR Analysis. The structures of synthetic chelat-ing resins MR-EDA, MR-DETA, and MR-TETA can beconfirmed by comparing the ATR-FTIR spectra of Merrifieldresin before and after reaction with polyamines as shownin Figure 3. The spectra showed the disappearance of the 𝛿CH2-Cl band which appears at 1265 cm−1 from theMerrifield
resin [15] and the appearance of new bands at 3320 cm−1and a broad peak at 1670 cm−1, which could be attributedto the stretching vibration and deformation vibration of N-H, respectively, accounting for NH/NH
2introduced groups.
These findings agree with the literature [16]. The proposedsynthesis route to the prepared resins is presented schemati-cally in Figure 1.
On the other hand the ATR-FTIR spectra of the resinsMR-EDA-TECP, MR-DETA-TECP, and MR-TETA-TCEP(Figure 4) showed the appearance of new bands of symmet-rical and asymmetrical stretching vibration characteristics ofP-O-C observed at, respectively, 1030 and 1076 cm−1. Indeed,new peak appeared at 1221 cm−1 and could be attributed tothe stretching vibration of P=O. These findings confirmedthe functionalization of the resins by the tris-(2-chloroethyl)phosphate group. The proposed synthesis route to the newlyprepared resins is presented schematically in Figure 2.
4000 3500 3000 2500 2000 1500 1000 500
6961670
3329
3340
3317 1076
1076
1221
1221
1030
1030
12211076
1030
(g)
(f)
(e)
Tran
smitt
ance
(%)
Wavenumber (cm−1)
Figure 4: ATR-FTIR ofMR-EDA-TCEP resin (e),MR-DETA-TCEPresin (f), and MR-TETA-TCEP resin (g).
Table 1: Elemental analysis results of MR-EDA, MR-DETA, andMR-TETA resins.
Sample name C (%) H (%) N (%)MR-EDA 78.15 5.18 4.23MR-DETA 72.50 7.25 5.03MR-TETA 72.90 7.86 6.80
3.1.2. Elemental Analysis. Table 1 presented the N percent-age in chelating resins determined by elemental analyses.Obtained results showed that the content of nitrogen in MR-EDA, MR-DETA, and MR-TETA were 4.24, 5.03, and 6.80%,respectively. These findings suggest that the resin structure,particularly polyamine chain length and nitrogen atomscomposition, influences the N content. Besides, elementalanalysis showed also that the P content in MR-EDA-TCEP,MR-DETA-TCEP, and MR-TETA-TCEP resins was 1.47, 1.44,and 1.52%, respectively, which confirm the grafting of TCEPgroups on the aminoalkylated resins. In fact, the polyaminegroups (EDA, DETA, and TETA) loading in MR-EDA, MR-DETA, and MR-TETA are 9.07, 12.24, and 17.69% by weight,respectively. In addition, TCEP group loading in MR-EDA-TCEP,MR-DETA-TCEP, andMR-TETA-TCEP is 27.64, 27.08,and 28.58% by weight, respectively.
3.1.3. TGA,DTA, andDTGAnalyses. Thecharacteristic TGA,DTA, and DTG curves of MR, MR-EDA, MR-DETA, MR-TETA, MR-EDA-TECP, MR-DETA-TECP, and MR-TETA-TECP were presented in Figures 5, 6, and 7, showing
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0 100 200 300 400 500 600
0
20
40
60
80
100(g)(f)(e)
(d)(c)(b)(a)W
eigh
t los
s (%
)
Temperature (∘C)
Figure 5: TGA curves of MR resin (a), MR-EDA resin (b), MR-DETA resin (c), MR-TETA resin (d), MR-EDA-TCEP resin (e), MR-DETA-TCEP resin (f), and MR-TETA-TCEP resin (g) heated withthe temperature increment rate 5∘C min−1 in air.
0 100 200 300 400 500 600−100−50
050
100150200250300350400450500550600650700
305 330509
Exo
(g)
(f)
(e)
(d)(c)
(b)
(a)
HF
(mw
)
Tg = 184∘C
Tg = 163∘C
Tg = 204∘C
Tg = 196∘C
Tg = 215∘C
Tg = 200∘C
Temperature (∘C)
Figure 6: DTA curves of MR resin (a), MR-EDA resin (b), MR-DETA resin (c), MR-TETA resin (d), MR-EDA-TCEP resin (e), MR-DETA-TCEP resin (f), and MR-TETA-TCEP resin (g) heated withthe temperature increment rate 5∘C min−1 in air.
the complexity of the thermal decomposition for chemicallymodified resins. The thermal stability of MR resin wasdivided into three regions: 190–325∘C, 325–425∘C, and above600∘C. In fact, the exothermic peak which appears nearlyto 320∘C was detected, in TGA, by a weight loss up to28.8% in the temperature range 190–325∘C that can explainthe elimination of chloromethylated group CH
2Cl [19]. In
addition, the exothermic phenomena that corresponded toa weight loss up to 23% in the temperature range between325∘C and 425∘C may suggest the thermal degradation ofthe cross-linked structure of MR resin and the polymerseems to be decomposed completely at 600∘C [20]. The DTAcurves (Figure 6) ofMR resin showed three exothermic peaksobserved at 305, 330, and 509∘C. This data may suggestthat the decomposition of the resin took place in steps.
50 100 150 200 250 300 350 400 450 500 550 600
(g)
(f)(e)
(d)(c)
(b)
(a)
dW
/dT
Temperature (∘C)
302∘C 328∘C 511∘C
Figure 7: DTG curves of MR resin (a), MR-EDA resin (b), MR-DETA resin (c), MR-TETA resin (d), MR-EDA-TCEP resin (e), MR-DETA-TCEP resin (f), and MR-TETA-TCEP resin (g) heated withthe temperature increment rate 5∘C min−1 in air.
The DTA curves of MR-EDA, MR-DETA, MR-TETA, MR-EDA-TCEP, MR-DETA-TCEP, and MR-TETA-TCEP showedthat the glass transition temperature (𝑇
𝑔) was, respectively,
184, 163, 204, 196, 215, and 200∘C. Besides, all resins presenttwo exothermic peaks that could indicate their decompo-sition. The substitution at the benzene ring of polystyrenedetermined three degradation stages with different weightlosses depending on the chemical structure of the substituent(Table 2). Hence, we have considered the weight losses (𝑤 <10%), up to 250∘C as insignificant, representing the solventand water retained in the sample. From Figure 7 and Table 2one can see that the thermal stability of the studied com-pounds decreases in the following order: MR-EDA > MR-TETA >MR-DETA >MR-EDA-TCEP >MR-TETA-TCEP >MR-DETA-TCEP = MR.
3.2. Metal Ions Extraction by the Synthesized Polymers.Table 3 showed that the order of adsorption capacity ofthe chelating resins against Cd2+, Cu2+, and Fe2+ ions was,respectively, MR-TETA > MR-DETA > MR-EDA, whichagree with the other investigation [16]. This increase inadsorption percentage could be explained by the highercontent of nitrogen atoms in functional groups and thusimposed more coordination with metallic ions.
The orders of adsorption capacity for Cd2+ are asfollows: MR-DETA-TCEP > MR-EDA-TCEP > MR-TETA-TCEP, MR-EDA-TCEP > MR-EDA, MR-DETA-TCEP >MR-DETA, and MR-TETA > MR-TETA-TCEP. Besides, theorders of adsorption capacity for Cu2+ are as follows:MR-TETA-TCEP >MR-DETA-TCEP >MR-EDA-TCEP andMR-EDA-TCEP > MR-EDA and MR-DETA-TCEP > MR-DETA and MR-TETA-TECP > MR-TETA. In addition, theorders of adsorption capacity for Fe2+ are as follows: MR-EDA-TCEP > MR-DETA-TCEP > MR-TETA-TCEP andMR-EDA-TCEP > MR-EDA and MR-DETA > MR-DETA-TCEP and MR-TETA > MR-TETA-TCEP. Hence, it appears
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International Journal of Polymer Science 5
Table 2: TGA data for Merrifield resin and its substituted derivatives.
Sample Weight loss (𝑊, %) and temperature range (Δ𝑇,∘C)
Step I Step II Step III
MR Δ𝑇I = 190–325∘C
𝑊I = 28.83%Δ𝑇II = 325–420
∘C𝑊II = 23.89%
Δ𝑇III = 420–550∘C
𝑊III = 45.90%
MR-EDA Δ𝑇I = 50–250∘C
𝑊I = 6.4%Δ𝑇II = 250–425
∘C𝑊II = 45.79%
Δ𝑇III = 425–580∘C
𝑊III = 46.07%
MR-DETA Δ𝑇I = 50–220∘C
𝑊I = 7.6%Δ𝑇II = 220–425
∘C𝑊II = 47.60%
Δ𝑇III = 425–600∘C
𝑊III = 43.50%
MR-TETA Δ𝑇I = 50–240∘C
𝑊I = 5.57%Δ𝑇II = 240–435
∘C𝑊II = 52.33%
Δ𝑇III = 435–600∘C
𝑊III = 40.63%
MR-EDA-TCEP Δ𝑇I = 50–215∘C
𝑊I = 3.6%Δ𝑇II = 215–430
∘C𝑊II = 43.29%
Δ𝑇III = 430–600∘C
𝑊III = 46.33%
MR-DETA-TCEP Δ𝑇I = 50–190∘C
𝑊I = 3.94%Δ𝑇II = 190–425
∘C𝑊II = 35.10%
Δ𝑇III = 425–600∘C
𝑊III = 46.20%
MR-TETA-TCEP Δ𝑇I = 50–200∘C
𝑊I = 4.85%Δ𝑇II = 200–430
∘C𝑊II = 45.13%
Δ𝑇III = 430–600∘C
𝑊III = 47.56%
Table 3: Extraction percentage results of metal ions by the synthesized polymers.
Extraction percentage (% ± standard deviation)Metals ions MR-EDA MR-DETA MR-TETA MR-EDA-TECP MR-DETA-TECP MR-TETA-TCEPCd2+ 50 ± 0.7 57 ± 0.5 69 ± 0.7 69 ± 0.9 73 ± 0.8 63 ± 0.7Cu2+ 68 ± 1.1 71 ± 1.2 94 ± 1.5 90 ± 1.1 93 ± 1.3 95 ± 1.3Fe2+ 69 ± 1.7 70 ± 1.6 96 ± 1.4 70 ± 1.5 66 ± 1.3 61 ± 1.3Note: each result is the mean from three determinations ± standard deviation.
that MR-TETA-TECP and MR-TETA resins exhibited goodadsorption selectivity for Fe(II) and Cu(II), respectively.
This high adsorption selectivity could be explained bythe high affinity of Fe(II) and Cu(II) ions to the polyamineand organophosphate groups in studied resins. On the basisof hard-soft acid-base (HSAB) theory, Fe(II) and Cu(II)were classified as intermediate ions. Therefore, they haveaffinities to two types of soft ligands which contain nitrogenatoms of polyamine groups and hard ones which containoxygen atoms of organophosphate groups. The deference ofadsorption capacity of metallic ions such as Cd2+, Cu2+,and Fe2+ by the three synthesized polymers MR-EDA-TCEP,MR-DETA-TCEP, and MR-TETA-TCEP can be explainedessentially by the compatibility factor between the cationssize and the ligands cavity size in polymer matrix, whichwas probably influenced by the cross-linking degree. Thelength of amine chain and the cross-linking by the TCEP isdirectly proportional. However, the active sites are less readilyavailable and efficiency of the resin is reduced. In fact, for Fe2+
which has a less size than Cu2+, the adsorption percentageincreases in the sense: MR-EDA-TCEP, MR-DETA-TCEP,and MR-TETA-TCEP. But, for Cu2+, which has a higher sizethan Fe2+, the same phenomena decreases in the same sense.In the case of Cd2+, which has a higher size than the twocations Cu2+ and Fe2+, the adsorption percentage is better inMR-DETA-TCEP than in the two resins MR-EDA-TECP andMR-TETA-TCEP. In fact, in MR-DETA-TCEP, the Cd2+ wassimply incorporated in the complex sites compared to the two
other resins. It can be explained by the high compatibilitybetween the Cd2+ cations size and the ligands cavity size inMR-DETA-TCEP polymer matrix.
4. Conclusions
In the present paper, three chelating resins were synthesizedvia chemical grafting of polyamine groups on Merrifieldresin, leading to resin polymers namedMR-EDA,MR-DETA,and MR-TETA. In fact, these chelating resins are reticulatedby tris-(2-chloroethyl) phosphate (TCEP) to access to newpolymers, calledMR-EDA-TECP,MR-DETA-TECP, andMR-TETA-TECP, respectively. These synthesized polymers werecharacterized by ATR-FTIR, EA, TGA, DTA, and DTGanalysis and were tested for their ability to extract metallicions from aqueous solutions, particularly for Cu2+, Fe2+,and Cd2+. The obtained results show that MR-DETA-TECPexhibited good efficiency towards Cd2+ (73%) while MR-TETA-TCEP andMR-TETAwere efficient against Cu2+ (95%)and Fe2+ (96%), respectively. However, further approachesare still required in order to highlight and understand theinvolvement of polymermodifications and their mechanismsfor metallic extractions, as well as their application in envi-ronmental conditions.
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper.
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Acknowledgment
The authors would like to thank the Tunisian Ministry(Research Unit: 05/UR/12-05) which financed this project.
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