Journal of Environmental Management 132 (2014) 107e112
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Cysteine-grafted nonwoven geotextile: A new and efficient material for heavy metals sorption e Part A M. Vandenbossche a, M. Casetta a, *, M. Jimenez a, S. Bellayer a, b, M. Traisnel a a Unité Matériaux et Transformations (UMET), Ingénierie des Systèmes Polymères (ISP), CNRS-UMR 8207, ENSCL, Université Lille Nord de France, 59652 Villeneuve d’Ascq Cedex, France b Service Microsonde Electronique, ENSCL, Université Lille Nord de France, 59652 Villeneuve d’Ascq Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 March 2013 Received in revised form 23 October 2013 Accepted 28 October 2013 Available online 27 November 2013
Cysteine is an interesting biomolecule in the heavy metals trapping field, thanks to its amino, thiol and carboxylic groups. This amino acid is indeed present in some natural chelating agents: glutathione, phytochelatins and metallothioneins. However, cysteine has never been used in remediation processes. When immobilized on a polypropylene nonwoven (PP) geotextile, an innovative and eco-friendly material is obtained, with potential use in drainage and filtration of wastewaters and sediments. PP was first functionalized with acrylic acid using a low pressure cold plasma process to bring reactive carboxylic functions onto the surface (PP-g-AA). Cysteine was then covalently grafted on this modified PP. The cysteine grafting on PP-g-AA was optimized using response surface methodology, which allowed concluding that the best conditions of immersion without heating consist in: a solution containing 0.229 mol/L of cysteine for 28 h. The materials were characterized by Scanning Electron Microscopy, InfraRed Spectroscopy and X-ray Photoelectron Spectroscopy: evidence of covalent cysteine grafting was given. Preliminary sorption tests at 20 C and pH ¼ 4.5 with artificially polluted solutions give promising results for divalent heavy metal ions: 95 mg Cu (II) (CuSO4 solution), 104 mg Cu (II) and 135 mg Pb(II) (with NO 3 counter-ion) per gram of PP are trapped. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Polypropylene nonwoven Cysteine Cold plasma process Heavy metals Remediation
1. Introduction Massive amounts of sediments are dredged in order to maintain the depth of the navigational waterways, harbors and estuaries worldwide. Land disposal of these dredged materials may affect the surrounding environment due to the presence of harmful components such as organic compounds and heavy metals (Singh et al., 1998). In some harbors, a lot of sediments and sludge can be dredged, but nobody can use them further because of their high concentration in heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn (Gouzy and Ducos, 2008). All these metals can be found in sediments from seas (Lopez-Sanchez et al., 1996) or from rivers (Louriño-Cabana et al., 2011). To recover sediments and sludge, heavy metals must be removed. Numerous synthetic and natural molecules can trap these heavy metals. For example, poly(dimethylaminoethyl methacrylate e cross linked pregelled starch graft copolymers), also written poly(DMAEM-CPS), can be used to trap Cu(II), Cd(II), Hg(II) or Pb(II)
* Corresponding author. Tel.: þ33 (0)3 20 33 63 11. E-mail address: [email protected] (M. Casetta). 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.10.027
by putting it into the polluted solution followed by a filtration step (Mostafa et al., 2011). Poly(2-hydroxyethyl methacrylate-n-vinyl imidazole), or poly(HEMA-VIM), can also be used to trap Cu(II), Pb(II), Zn(II) and Cd(II) when it is in cryogel form (Tekin et al., 2011). These polymers are synthetic, but natural polymers such as cellulose and alginate, under beads form, can trap heavy metals like Cu(II), Pb(II) and Zn(II) when beads are stirred up into the polluted solution (Lai et al., 2010). Geotextile is a common material consisting in a permeable structure that possesses filtration and draining capacities. When the geotextile is grafted with some biomolecules, it can trap heavy metals from polluted effluent. For example, a chitosan/acrylic acidgrafted-polypropylene nonwoven can trap Cu(II) from an artificially polluted solution (Vandenbossche et al., 2013). The efficiency of the functionalized geotextile depends on the grafted biomolecule and this is why the choice of the biomolecule is crucial. The best way to find out the most efficient biomolecules is to look at the natural living organisms able to trap heavy metals. For example, some unicellular organisms can chelate heavy metals to protect themselves: when Cd(II) or Cu(II) enters Chlorella vulgaris, phytochelatin synthase is activated and forms phytochelatins from glutathione. The phytochelatins then remove the heavy
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metals from the cytosol (Cobbett, 2000; Zenk, 1996). In the same way, Saccharomyces cerevisiae and other animal cells are able to chelate heavy metals thanks to metallothioneins (Klaassen et al., 1999; Maret et al., 1997). The interesting point is that phytochelatins and metallothioneins are both cysteine-rich proteins. Cysteine is an amino-acid, and it is known that amino acids are excellent metal complexing agents forming chelates through their amino and carboxylate groups (Yamauchi et al., 2002). In addition to these two types of groups, cysteine also possesses a thiol group, which is an important metal binding site. This explains why cysteine can be efficient at different pH conditions: between pH ¼ 2 and pH ¼ 4.5 an oxygen-sulfur chelation is mainly observed, whereas between pH ¼ 6 and pH ¼ 9 a nitrogen-sulfur chelation is mainly observed (Palackova et al., 2007). Thus, cysteine could be used as biosorbent of heavy metals for the depollution of water, sediments and sludge. Some studies on the sorption of heavy metals using L-cysteine or poly-L-cysteine were carried out. Holcombe and co-workers demonstrated that polypeptides such as poly-L-cysteine are able to chelate metal ions such as Cd(II), Pb(II), Ni(II) and Cu(II) (Howard et al., 1999; Johnson and Holcombe, 2004; Jurbergs and Holcombe, 1997; Xiao et al., 2006). However, biohomopolymers are prohibitively expensive and difficult to manufacture on large scale. To overcome these problems, some scientists used monomeric amino acids as well as polypeptides covalently attached to a substrate, like for example, glassy carbon microspheres (Xiao et al., 2006) or bentonite (Faghihian and Nejati-Yazdinejad, 2009). Cysteine was adsorbed on bentonite in order to trap Cd(II) and Pb(II) and the sorption capacity of this new material was enhanced compared to the unmodified bentonite. The Langmuir isotherm explained well the sorption process, showing that there were specific sites at the surface for the trapping of heavy metals with a maximum sorption capacity of 0.503 and 0.525 mmol/g for Pb(II) and Cd(II) respectively in a 7.0 mmol/dm3 artificially polluted solution at pH 4e5 and 25 C. Two steps were proposed to explain the sorption mechanism: first there was probably an ion exchange step, followed by a complexation step (Faghihian and Nejati-Yazdinejad, 2009). Another study also shows the ability of spherical beads of cysteine-graftedchitosan to trap Hg(II). The adsorption capacity was approximately 8.0 mmol Hg per gram dry beads at pH 7 (Merrifield et al., 2004). The aim of this study is to functionalize a geotextile with cysteine in order to decontaminate fluvial or marine wastewater. The chosen biosorbent, i.e. cysteine, has to be grafted onto the polypropylene nonwoven without altering its ability to trap heavy metals. Polypropylene nonwovens are often used as geotextiles because of the polypropylene chemical stability (Müller et al., 2009). However, polypropylene is a hydrophobic inert material and consequently it is not easy to directly graft a molecule on it. First, a cold plasma treatment is used to bring active functional groups on the sample surface. Then, grafting of acrylic acid by cold plasma treatment is possible, and finally the immobilization of cysteine can be carried out. The same methodology was already carried out in previous studies (Degoutin et al., 2012; Vandenbossche et al., 2013). Cysteine can be grafted on polypropylene nonwoven either by the amino group or by the acid group which leads to two possible reaction pathways. In this study, as acrylic acid is first grafted on polypropylene nonwoven, some acidic groups are present at the sample surface. Thus, cysteine can be immobilized on PP-g-AA thanks to a coupling reaction between the amino group of cysteine and the acidic group of acrylic acid. An experimental design has been carried out in order to optimize the cysteine grafting on the acrylic acid-grafted polypropylene. The material grafted with the highest amount of cysteine was then characterized using different techniques (SEM, FTIR-ATR, XPS). To evaluate the
efficiency of the grafted materials, sorption tests have been realized using artificially polluted solutions containing Cu(II), Pb(II), Cr(III) and Cr(VI). 2. Materials and methods 2.1. Samples preparation Squares (5*5 cm2) were cut from polypropylene nonwoven INTN50 (50 g/m2, provided by PGI nonwovens, France). To remove any contaminant, the squares were first washed as it was already described in another paper (Vandenbossche et al., 2013). 2.2. Modification of the polypropylene nonwoven The modification of the polypropylene nonwoven was already described in detail in another paper (Vandenbossche et al., 2013): (1) activation of the sample by an argon low pressure cold plasma process (Europlasma apparatus CD1200-400 COMBI MC, Radio Frequency generator Dressler, 13.56 MHz); (2) immersion of the sample in an acrylic acid solution; (3) removal of the excess solution with a roll-padder; (4) grafting and polymerization using the low pressure argon cold plasma process; (5) washing of the textile; and (6) drying of the sample under vacuum. The PP-g-AA was thus obtained. 2.3. Cysteine immobilization L-Cysteine (>97%, provided by SigmaeAldrich) was chemically grafted on the PP-g-AA thanks to a carbodiimide which can make the carboxylic group more reactive: the N-(3Dimethylaminopropyl)-N0 -ethylcarbodiimide hydrochloride (EDC) (provided by SigmaeAldrich) (Vandenbossche et al., 2013). The textile was immersed for 1 h in a bath of EDC (1 g in 100 mL of distilled water at 4 C). Then, the textile was removed from this bath to be put into a bath of cysteine (2 g in 100 mL distilled water with 10 mL of 1 M NaOH) for 24 h. Finally, the textile was washed for 1 h in an ultrasonic bath, and then, for 6 h in a Soxhlet extractor with distilled water. The samples were dried under vacuum leading to the PP-g-AA-Cysteine material.
2.4. Experimental design The optimization of the cysteine grafting on PP-g-AA was carried out using response surface methodology. The influence of two main parameters was studied: the concentration of cysteine and the immersion time in the cysteine bath. A central composite design (CCD), consisting in 10 experimental runs, was used, including: a full factorial design, containing 4 experiments; four star points at a distance a ¼ 1.414 from the design center; two replicates of the center point. Experiments were conducted randomly to provide protection against the extraneous factors, which could affect the measured response. For statistical calculations, the variables Ui were coded as Xi according to the following transformation:
Xi ¼ ðUi Ui0 Þ=DUi
(1)
where Xi is the dimensionless coded value of the variable Ui, Ui0 represents the value of Ui at the center point and DUi is the step change. The experimental values associated with the coded levels of the different variables are given in Table 1. A second-order polynomial equation was used to express the response as a function of the independent variables:
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C1s CeC at 285 eV. The C1s peaks were decomposed using GaussianeLorentzian peak shapes and the full-width at half maximum (fwhm) of each line shape was maintained below 1.3 eV.
Table 1 Coded and real values of experimental parameters used for the CCD. Coded variable
Parameter
X1
U1 cysteine concentration in the bath (mol/L) U2 immersion time (h)
X2
Levels a 0.12 12.66
1 0.15 16
þ1
0 0.225 24
y ¼ b0 þ b1 X1 þ b2 X2 þ b12 X1 X2 þ b11 X12 þ b22 X22
0.30 32
þa 0.33 35.33
(2)
where y is response variable, b0 is the value of the fitted response at the center point, bi, bii and bij correspond respectively to the linear, quadratic and interaction terms of the model. Modde 7.0 software developed by Umetrics was used to determine the coefficients of the model and for the graphical analysis of the obtained experimental data. The statistical significance of the main, quadratic and interaction effects of the variables was determined by analysis of variance (ANOVA) and a multiple regression analysis was performed to fit the experimental data to the secondorder polynomial equation. The determination coefficients R2 and R2Adjusted respectively describe the fraction of variation of the response explained by the model and the fraction of variation of the response explained by the model adjusted for degrees of freedom. The coefficient of prediction Q2 describes the fraction of variation of the response that can be predicted by the model. To evaluate the efficiency of cysteine immobilization, only one criterion has been considered and taken as a response for the composite design. The sample has been weighed before plasma activation (Wi in mg) and after immobilization of cysteine followed by washing and drying step (Wf in mg). It allowed the calculation of the grafting rate, using the following equation:
. Wi % ¼ 100 Wf Wi
109
(3)
2.6. Heavy metals trapping tests 2.6.1. Preparation of the artificially polluted solutions Five artificially polluted solutions have been prepared at a concentration of 1000 mg/L each. The first one is a copper (II) sulfate solution of final pH 4.3. The second one is a copper (II) nitrate solution also of pH ¼ 4.3. The third solution contains lead (II) nitrate and its pH is 4.8. The fourth one is a chromium (III) nitrate solution with a final pH of 2.7. And finally, the fifth solution containing chromium (VI) has been prepared by dilution of a 10 g/L K2Cr2O7 solution, with a final pH of 8.3. The pH of these solutions was adjusted to 4.5 with NaOH 1 M or HCl 1 M for the heavy metals sorption test in order to compare the obtained results. 2.6.2. Heavy metals sorption Cysteine-grafted polypropylene samples were immersed in 100 mL of the different artificially polluted solutions at 20 C for 24 h. The textiles were then washed in 50 mL of ultrapure water, and the surfaces were digested with 10 mL sulfuric acid (purity of 95%) and 20 mL hydrochloric acid (purity of 37%) to remove copper, lead, and chromium. 70 mL of ultrapure water was added to the solution and the heavy metal concentration of this final solution was determined by flame atomic absorption using the standard addition method (Thermo Solaar S4 AA Spectrometer, Thermo S Series, Multi-elements combined coded hollow-cathods lamp for CreCueMneNi, Thermo Scientific and Mono-elements coded hollow-cathods lamp for Pb, Thermo Scientific). 3. Results and discussion 3.1. Cysteine immobilization
2.5. Surface characterization 2.5.1. SEM The samples were observed using a Scanning Electron Microscope Hitachi S4700 at an accelerating voltage of 6 kV and a current of 15 mA. All images were taken at 1500 magnification to ensure good comparison between all the samples. This method allows determining the surface morphology and the quality of the coating. 2.5.2. FTIR/ATR The samples were analyzed thanks to a FTIR/ATR spectrometer (Thermo Scientific Nicolet 380 FT-IR Spectrometer) in the range of 800e2500 cm1 (16 scans) to determine the presence of acrylic acid and/or cysteine. 2.5.3. XPS XPS analyses were performed on an Axis ultra DLD (Kratos analytical) using a monochromatic Al KR X-ray source (hn ¼ 1486.6 eV). The emission voltage and the current of this source were set to 15 kV and 10 mA, respectively. The pressure in the analyzing chamber was maintained at 107 Pa during analysis, and the area analyzed was 300 700 mm2, with a depth of 10 nm. Survey (0e1300 eV) and high-resolution (C1s) spectra were recorded at pass energies of 20 eV with a step of 0.05 eV (the surveys were recorded at pass energies of 160 eV with a step of 1 eV). Data treatment and peak-fitting procedures were performed using Casa XPS software. Obtained spectra were rescaled by shift of
3.1.1. Preliminary results Prior to the experimental design, a rapid evaluation of the influence of cysteine concentration and immersion time in the cysteine containing bath has been realized in order to adjust the limits of each parameter. 3.1.1.1. Influence of cysteine concentration. The immersion time was fixed at 24 h. Four cysteine concentrations were tested: 0.075 mol/ L, 0.15 mol/L, 0.30 mol/L and 0.45 mol/L and the grafting rates respectively obtained are 1.5%, 2.7%, 3.0% and 3.3%. The grafting rate seems to increase when the cysteine concentration increases. 3.1.1.2. Influence of immersion time. The cysteine concentration was fixed at 0.15 mol/L. Three immersion times were tested: 4 h, 24 h, and 72 h. The following grafting rates were obtained: 0.5%, 2.7%, and 8.3%, respectively. It was observed that for 72 h of immersion, there was a cysteine homopolymerisation phenomenon. As a consequence, the maximum immersion time used in the experimental design is around 35 h. 3.1.2. Experimental design As the preliminary studies showed the influence of cysteine concentration and immersion time on the grafting, an experimental design was set up in order to improve cysteine immobilization on PP-g-AA. All PP samples were first grafted with acrylic acid using the protocol described in the experimental part, and were then chemically activated thanks to EDC.
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Table S1 details the experimental conditions applied to the 10 experiments and also the experimental results obtained for the response. The determination coefficients obtained for the response show that the regression model fits the experimental data correctly. In fact, R2 value is 98%, indicating that 2% of the total variation is not explained by the model. The value of the adjusted determination coefficient is also high (R2Adjusted ¼ 94.6%), showing a high significance of the model. The grafting is also well predicted by the model as the coefficient of prediction Q2 is 77%. The second-order polynomial equation associated to the response is:
y ¼ 3:05 þ 0:2202X1 þ 0:4225X2 0:25X1 X2 0:8617X12 0:3962X22
(4)
This model allows plotting the evolution of the predicted grafting rate as a function of cysteine concentration and immersion time (Fig. 1). Thus the sample must be immersed in a solution containing 0.229 mol/L of cysteine for 28 h to reach the best grafting rate, namely 3.16%. A new experiment has been realized using a 0.229 mol/L cysteine concentration and an immersion time of 28 h. An experimental grafting rate close to the predicted one i.e. 3.2 0.5% has been obtained, thus validating the experimental design procedure.
3.2. Surface characterization 3.2.1. SEM Textiles were grafted according to the protocol described in the experimental part. A previous paper (Vandenbossche et al., 2013) detailed the homogeneity of the acrylic acid coating. To confirm the presence of cysteine, SEM was carried out on fibers after cysteine grafting. Several samples obtained from the experimental design and corresponding to various grafting rates have been characterized (Fig. 2). The coating obtained after cysteine grafting is strongly dependent on the grafting rate: for experiment 3 (Fig. 2A), corresponding to a grafting rate of 2.1%, the coating is observed on and between the fibers, but this coating seems very thin and fragile; for experiment 4 (Fig. 2B), corresponding to a grafting rate of 0.9%, cysteine is only slightly visible between fibers; for experiment 8 (Fig. 2C), corresponding to a grafting rate of 3%, the coating is homogeneous and is observed both on and between the fibers; and
finally, for experiment 10 (Fig. 2D) and for the optimized conditions (Fig. 2E), both corresponding to a grafting rate of 3.2%, a thick coating is visible around and between fibers. 3.2.2. FTIR/ATR Infrared spectroscopy (FTIR-ATR) was used to detect the presence of characteristic chemical groups on the geotextile surface (Fig. 3). The presence of acrylic acid is evidenced by the peak of asymmetric elongation of the carboxylic function at 1715 cm1. The grafting of cysteine is shown by two different peaks: scissoring deformation of the NeH of the amide group at 1566 cm1 and asymmetric elongation of the carboxylic function of cysteine at 1640 cm1 (Pawlukojc et al., 2005). Presence of the peak of amide scissoring deformation evidence the grafting of cysteine on PP-gAA: a coupling reaction between the carboxylic group of acrylic acid and the amine group of cysteine has occurred. 3.2.3. XPS XPS analyses were carried out on PP, PP-g-AA and the optimized PP-g-AA-cysteine samples. An evolution of the surface atomic percentages is observed. Indeed, with XPS, only the extreme surface (w10 nm depth) is analyzed. Thus, when a new layer is grafted on the textile, the underlying layer is less visible. The different atomic percentages are summarized in Table 2. Virgin polypropylene contains mainly carbon. The small amount of oxygen observed by XPS is due to manufacturing process of the nonwoven. When acrylic acid is grafted on PP, there is an increase of the oxygen atomic percentage, and the ratio [O1s]/[C1s] is important: more than 1/5 atoms in the extreme surface is an oxygen. Finally, when cysteine is grafted on PP-g-AA, presence of nitrogen and sulfur is also observed, but with small atomic percentages. There is also an increase of the oxygen atomic percentage, and the ratio [O1s]/[C1s] is more important than the one obtained for PP-g-AA (more than 1/ 3 atoms in the extreme surface is an oxygen). Fig. S1 presents the C1s peak obtained for Cysteine and PP-g-AAcysteine. The decomposition of Cysteine C1s peak gives information about the important group of Cysteine, and these results can then be used to decompose PP-g-AA-cysteine C1s peak. The C1s peak of cysteine can be decomposed into 3 peaks: one peak at 285.4 eV (fwhm ¼ 1.3), which corresponds to CeS bonds; one peak at 286.2 eV (fwhm ¼ 1.3), corresponding to CeN bonds; and another peak at 288.2 eV (fwhm ¼ 1.3), which corresponds to the O]CeO bonds. From these observations, the C1s peak of PP-g-AA-cysteine can be decomposed. An important peak at 285.0 eV (fwhm ¼ 1.3) is observed, corresponding to CeC bonds. Evidence of the grafting of acrylic acid is given by the peak at 286.4 eV (fwhm ¼ 1.3), which corresponds to the ether group formed between PP and acrylic acid (Vandenbossche et al., 2013), and can also correspond to the CeN bond in cysteine. Two other peaks can be observed: one at 288.3 eV (fwhm ¼ 1.3), corresponding to the contribution of acrylic acid, polyacrylic acid and cysteine (OeC]O), and also corresponding to the amide group (NeC]O) formed during the grafting of cysteine on PP-g-AA, and the other one a peak at 285.2 eV (fwhm ¼ 1.3), corresponding to the thiol group of cysteine (CeSH). Thus, according to FTIR and XPS results, cysteine is proven to be covalently grafted on PP-g-AA. The amide groups formed are due to the linkages between the acidic groups of acrylic/polyacrylic acid and the amine groups of cysteine. 3.3. Heavy metals trapping tests
Fig. 1. Contour plot showing the evolution of the cysteine grafting a function of cysteine concentration (X1) and immersion time (X2).
3.3.1. Heavy metals sorption The sorption capacity of the textile depends on the heavy metals oxidation degree. Fig. 4 describes the amount (in mg heavy metal per gram of textile) of different heavy metals [Cu(II), Pb(II), Cr(III)
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Fig. 2. SEM images of fibers coming from PP-g-AA-cysteine samples: (A) from experiment 3; (B) from experiment 4; (C) from experiment 8; (D) from experiment 10; and (E) optimized grafting conditions.
and Cr(VI)] trapped by the nonwovens using solutions containing 1000 mg/L of heavy metals. It can be observed that PP-g-AAcysteine is more efficient for the trapping of divalent cations than other metals with oxidation degrees. At 20 C for 24 h (in 1000 mg/ L heavy metal solution) PP-g-AA-cysteine adsorbs 95 mg of copper
(from CuSO4 solution), 104 mg of copper (from Cu(NO3)3 solution), 135 mg of lead per gram PP whereas the same sample adsorbs only 21 mg Cr (III) per gram PP, and does not adsorb any Cr (VI) at all. Atomic radii of copper and chromium are respectively about 135 pm and 140 pm, with respective electronegativities of 1.9 and 1.66. The slight differences between these parameters cannot explain the differences obtained in terms of copper and chromium adsorption. Thus, oxidation degree can play an important role in heavy metals trapping. Moreover, what is interesting to notice is that the textile becomes immediately yellow when put in contact with the chromium (VI) containing solution. But, as soon as the textile is rinsed with water, this yellow color disappears and not any or only a slight remaining amount of chromium is detected by atomic absorption. It means that some weak interactions are probably involved in the trapping of chromium, e.g. hydrogen bonds between oxygen from Cr2 O2 7 and the thiol or carboxylic acid groups of PP-g-AA-cysteine. But this chromium is easily released in water during the rinsing step. Table 2 Quantification by XPS of various elements at the surface of the textiles.
Fig. 3. FTIR-ATR spectra of the virgin-polypropylene (PP), acrylic-acid-grafted polypropylene (PP-g-AA), cysteine/acrylic-acid-grafted-polypropylene (PP-g-AA-cysteine), optimized cysteine/acrylic-acid-grafted-polypropylene (PP-g-AA-Cys optimum) and cysteine powder.
Samples
%C1s
%O1s
%N1s
%S2p
[O1s]/ [C1s]
[N1s]/ [C1s]
[S2p]/ [C1s]
PP PP-g-AA PP-g-AA-cysteine
97.4 82.1 68.9
2.6 17.9 25.1
0 0 3.7
0 0 2.3
2.7 22 36
0 0 5.4
0 0 3.3
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Up-Tex Competitiveness Cluster and all DEPOLTEX partners for helpful collaboration and discussion. Finally, the authors acknowledge M. Yann CHIPAN for assistance for the experiments, and M. Arnaud Beaurain (Plateforme régionale d’analyse des surfaces, Université Lille Nord de France) for the XPS analyses. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2013.10.027. References
Fig. 4. Amount of heavy metals trapped by PP-g-AA-cysteine in solutions containing 1000 ppm of heavy metals.
From Fig. 4, it can also be noticed that the amount of lead adsorbed (135 mg/g textile) is more important than the amount of copper adsorbed (104 mg/g textile). However, lead is heavier than copper, and consequently the molar amount of lead trapped is less important than the molar amount of copper: 6.6 104 mol/g of lead (from a Pb(NO3)2 solution) and 16 104 mol/g of copper (from a Cu(NO3)2 solution). Consequently, more copper than lead is trapped by PP-g-AA-cysteine. This result could be explained by the different atomic radii. Indeed, the atomic radius of lead is about 180 pm whereas atomic radius of copper is about 135 pm: copper being smaller than lead, it can thus be more easily trapped by PP-g-AAcysteine. 2 Finally, the importance of the counter-ion (NO 3 or SO4 ) was studied in the case of copper adsorption: no significant difference between these two experiments is observed. If the molar amount is considered, an amount of 16 104 mol Cu (from Cu(NO3)2 solution) and 15 104 mol Cu (from Cu(SO4) solution) is trapped by PP-g-AA-cysteine samples. 4. Conclusion In this paper, cysteine was successfully grafted on PP using a cold plasma treatment. The use of the experimental design technique allowed determining the best condition for the grafting of cysteine on PP-g-AA: a cysteine concentration of 0.229 mol/L and an immersion time of 28 h. The covalent grafting of cysteine on polypropylene nonwoven was evidenced using different characterization techniques (SEM, FTIR/ATR, and XPS). Sorption studies were carried out with copper (II), lead (II), chromium (III) and chromium (VI). Very promising results are obtained for the trapping of divalent heavy metals. A further study (Part B) will be published on the efficiency of this textile to trap heavy metals, completed with kinetic studies at 20 C, varying the pH and ionic strength effect. Acknowledgments The authors gratefully acknowledge the support of FEDER (Fonds Européen de Développement Régional), Nord-Pas-de-Calais region, and FUI (Fonds Unique Interministériel) for funding this work .We also would like to deeply acknowledge the support of the
Cobbett, C.S., 2000. Phytochelatins and their roles in heavy metal detoxification. Plant Physiol. 123, 825e832. Degoutin, S., Jimenez, M., Casetta, M., Bellayer, S., Chai, F., Blanchemain, N., Neut, C., Kacem, I., Traisnel, M., Martel, B., 2012. Anticoagulant and antimicrobial finishing of non-woven polypropylene textiles. Biomed. Mat 7, 1e13. Faghihian, H., Nejati-Yazdinejad, M., 2009. Sorption performance of cysteinemodified bentonite in heavy metals uptake. Russ. Source 74, 833e843. Gouzy, A., Ducos, G., 2008. La connaissance des éléments-traces métalliques: un défi pour la gestion de l’environnement. Air Pur 75, 6e10. Howard, M., Jurbergs, H.A., Holcombe, J.A., 1999. Comparison of silica-immobilized poly(L-cysteine) and 8-hydroxyquinoline for trace metal extraction and recovery. J. Anal. At. Spectrom. 14, 1209e1214. Johnson, A.M., Holcombe, J.A., 2004. Poly(l-cysteine) as an electrochemically modifiable ligand for trace metal chelation. Anal. Chem. 77, 30e35. Jurbergs, H.A., Holcombe, J.A., 1997. Characterization of immobilized poly(lcysteine) for cadmium chelation and preconcentration. Anal. Chem. 69, 1893e1898. Klaassen, C.D., Liu, J., Choudhuri, S., 1999. Metallothionein: an intracellular protein to protect against cadmium toxicity. Annu. Rev. Pharmacol. Toxicol. 39, 267e294. Lai, Y.-L., Thirumavalavan, M., Lee, J.-F., 2010. Effective adsorption of heavy metal ions (Cu2þ, Pb2þ, Zn2þ) from aqueous solution by immobilization of adsorbents on Ca-alginate beads. Toxicol. Environ. Chem. 92, 697e705. Lopez-Sanchez, J.F., Rubio, R., Samitier, C., Rauret, G., 1996. Trace metal partitioning in marine sediments and sludges deposited off the coast of Barcelona (Spain). Water Res. 30, 153e159. Louriño-Cabana, B., Lesven, L., Charriau, A., Billon, G., Ouddane, B., Boughriet, A., 2011. Potential risks of metal toxicity in contaminated sediments of Deûle river in Northern France. J. Hazard. Mater. 186, 2129e2137. Maret, W., Larsen, K.S., Vallee, B.L., 1997. Coordination dynamics of biological zinc “clusters” in metallothioneins and in the DNA-binding domain of the transcription factor Gal4. Proc. Natl. Acad. Sci. 94, 2233e2237. Merrifield, J.D., Davids, W.G., MacRae, J.D., Amirbahman, A., 2004. Uptake of mercury by thiol-grafted chitosan gel beads. Water Res. 38, 3132e3138. Mostafa, K.M., Samarkandy, A.R., El-Sanabary, A.A., 2011. Preparation of poly(DMAEM)-cross linked pregelled starch graft copolymer and its application in waste water treatments. Carbohydr. Polym. 86, 491e498. Müller, W.W., Jakob, I., Li, C.S., Tatzky-Gerth, R., 2009. Durability of polyolefin geosynthetic drains. Geosynth. Int. 16, 28e42. Palackova, H., Vinklarek, J., Holubova, J., Cisarova, I., Erben, M., 2007. The interaction of antitumor active vanadocene dichloride with sulfur-containing amino acids. J. Organomet. Chem. 692, 3758e3764. Pawlukojc, A., Leciejewicz, J., Ramirez-Cuesta, A.J., Nowicka-Scheibe, J., 2005. LCysteine: neutron spectroscopy, Raman, IR and ab initio study. Spectrochim. Acta Part A 61, 2474e2481. Singh, S.P., Tack, F.M.G., Verloo, M.G., 1998. Land disposal of heavy metal contaminated dredged sediments: a review of environmental aspects. Land Contam. Recl 6, 149e158. Tekin, K., Uzun, L., Sahin, C.A., Bektas, S., Denizli, A., 2011. Preparation and characterization of composite cryogels containing imidazole group and use in heavy metal removal. React. Funct. Polym. 71, 985e993. Vandenbossche, M., Jimenez, M., Casetta, M., Bellayer, S., Beaurain, A., Bourbigot, S., Traisnel, M., 2013. Chitosan-grafted nonwoven geotextile for heavy metals sorption in sediments. React. Funct. Polym. 73, 53e59. Xiao, L., Wildgoose, G.G., Crossley, A., Knight, R., Jones, J.H., Compton, R.G., 2006. Removal of toxic metal-ion pollutants from water by using chemically modified carbon powders. Chem. e Asian J. 1, 614e622. Yamauchi, O., Odani, A., Takani, M., 2002. Metal-amino acid chemistry. Weak interactions and related functions of side chain groups. J. Chem. Soc. Dalton Trans., 3411e3421. Zenk, M.H., 1996. Heavy metal detoxification in higher plants e a review. Gene 179, 21e30.
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Cysteine-grafted nonwoven geotextile: A new and efficient material for heavy metals sorption e Part A M. Vandenbossche a, M. Casetta a, *, M. Jimenez a, S. Bellayer a, b, M. Traisnel a a Unité Matériaux et Transformations (UMET), Ingénierie des Systèmes Polymères (ISP), CNRS-UMR 8207, ENSCL, Université Lille Nord de France, 59652 Villeneuve d’Ascq Cedex, France b Service Microsonde Electronique, ENSCL, Université Lille Nord de France, 59652 Villeneuve d’Ascq Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 March 2013 Received in revised form 23 October 2013 Accepted 28 October 2013 Available online 27 November 2013
Cysteine is an interesting biomolecule in the heavy metals trapping field, thanks to its amino, thiol and carboxylic groups. This amino acid is indeed present in some natural chelating agents: glutathione, phytochelatins and metallothioneins. However, cysteine has never been used in remediation processes. When immobilized on a polypropylene nonwoven (PP) geotextile, an innovative and eco-friendly material is obtained, with potential use in drainage and filtration of wastewaters and sediments. PP was first functionalized with acrylic acid using a low pressure cold plasma process to bring reactive carboxylic functions onto the surface (PP-g-AA). Cysteine was then covalently grafted on this modified PP. The cysteine grafting on PP-g-AA was optimized using response surface methodology, which allowed concluding that the best conditions of immersion without heating consist in: a solution containing 0.229 mol/L of cysteine for 28 h. The materials were characterized by Scanning Electron Microscopy, InfraRed Spectroscopy and X-ray Photoelectron Spectroscopy: evidence of covalent cysteine grafting was given. Preliminary sorption tests at 20 C and pH ¼ 4.5 with artificially polluted solutions give promising results for divalent heavy metal ions: 95 mg Cu (II) (CuSO4 solution), 104 mg Cu (II) and 135 mg Pb(II) (with NO 3 counter-ion) per gram of PP are trapped. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Polypropylene nonwoven Cysteine Cold plasma process Heavy metals Remediation
1. Introduction Massive amounts of sediments are dredged in order to maintain the depth of the navigational waterways, harbors and estuaries worldwide. Land disposal of these dredged materials may affect the surrounding environment due to the presence of harmful components such as organic compounds and heavy metals (Singh et al., 1998). In some harbors, a lot of sediments and sludge can be dredged, but nobody can use them further because of their high concentration in heavy metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn (Gouzy and Ducos, 2008). All these metals can be found in sediments from seas (Lopez-Sanchez et al., 1996) or from rivers (Louriño-Cabana et al., 2011). To recover sediments and sludge, heavy metals must be removed. Numerous synthetic and natural molecules can trap these heavy metals. For example, poly(dimethylaminoethyl methacrylate e cross linked pregelled starch graft copolymers), also written poly(DMAEM-CPS), can be used to trap Cu(II), Cd(II), Hg(II) or Pb(II)
* Corresponding author. Tel.: þ33 (0)3 20 33 63 11. E-mail address: [email protected] (M. Casetta). 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.10.027
by putting it into the polluted solution followed by a filtration step (Mostafa et al., 2011). Poly(2-hydroxyethyl methacrylate-n-vinyl imidazole), or poly(HEMA-VIM), can also be used to trap Cu(II), Pb(II), Zn(II) and Cd(II) when it is in cryogel form (Tekin et al., 2011). These polymers are synthetic, but natural polymers such as cellulose and alginate, under beads form, can trap heavy metals like Cu(II), Pb(II) and Zn(II) when beads are stirred up into the polluted solution (Lai et al., 2010). Geotextile is a common material consisting in a permeable structure that possesses filtration and draining capacities. When the geotextile is grafted with some biomolecules, it can trap heavy metals from polluted effluent. For example, a chitosan/acrylic acidgrafted-polypropylene nonwoven can trap Cu(II) from an artificially polluted solution (Vandenbossche et al., 2013). The efficiency of the functionalized geotextile depends on the grafted biomolecule and this is why the choice of the biomolecule is crucial. The best way to find out the most efficient biomolecules is to look at the natural living organisms able to trap heavy metals. For example, some unicellular organisms can chelate heavy metals to protect themselves: when Cd(II) or Cu(II) enters Chlorella vulgaris, phytochelatin synthase is activated and forms phytochelatins from glutathione. The phytochelatins then remove the heavy
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metals from the cytosol (Cobbett, 2000; Zenk, 1996). In the same way, Saccharomyces cerevisiae and other animal cells are able to chelate heavy metals thanks to metallothioneins (Klaassen et al., 1999; Maret et al., 1997). The interesting point is that phytochelatins and metallothioneins are both cysteine-rich proteins. Cysteine is an amino-acid, and it is known that amino acids are excellent metal complexing agents forming chelates through their amino and carboxylate groups (Yamauchi et al., 2002). In addition to these two types of groups, cysteine also possesses a thiol group, which is an important metal binding site. This explains why cysteine can be efficient at different pH conditions: between pH ¼ 2 and pH ¼ 4.5 an oxygen-sulfur chelation is mainly observed, whereas between pH ¼ 6 and pH ¼ 9 a nitrogen-sulfur chelation is mainly observed (Palackova et al., 2007). Thus, cysteine could be used as biosorbent of heavy metals for the depollution of water, sediments and sludge. Some studies on the sorption of heavy metals using L-cysteine or poly-L-cysteine were carried out. Holcombe and co-workers demonstrated that polypeptides such as poly-L-cysteine are able to chelate metal ions such as Cd(II), Pb(II), Ni(II) and Cu(II) (Howard et al., 1999; Johnson and Holcombe, 2004; Jurbergs and Holcombe, 1997; Xiao et al., 2006). However, biohomopolymers are prohibitively expensive and difficult to manufacture on large scale. To overcome these problems, some scientists used monomeric amino acids as well as polypeptides covalently attached to a substrate, like for example, glassy carbon microspheres (Xiao et al., 2006) or bentonite (Faghihian and Nejati-Yazdinejad, 2009). Cysteine was adsorbed on bentonite in order to trap Cd(II) and Pb(II) and the sorption capacity of this new material was enhanced compared to the unmodified bentonite. The Langmuir isotherm explained well the sorption process, showing that there were specific sites at the surface for the trapping of heavy metals with a maximum sorption capacity of 0.503 and 0.525 mmol/g for Pb(II) and Cd(II) respectively in a 7.0 mmol/dm3 artificially polluted solution at pH 4e5 and 25 C. Two steps were proposed to explain the sorption mechanism: first there was probably an ion exchange step, followed by a complexation step (Faghihian and Nejati-Yazdinejad, 2009). Another study also shows the ability of spherical beads of cysteine-graftedchitosan to trap Hg(II). The adsorption capacity was approximately 8.0 mmol Hg per gram dry beads at pH 7 (Merrifield et al., 2004). The aim of this study is to functionalize a geotextile with cysteine in order to decontaminate fluvial or marine wastewater. The chosen biosorbent, i.e. cysteine, has to be grafted onto the polypropylene nonwoven without altering its ability to trap heavy metals. Polypropylene nonwovens are often used as geotextiles because of the polypropylene chemical stability (Müller et al., 2009). However, polypropylene is a hydrophobic inert material and consequently it is not easy to directly graft a molecule on it. First, a cold plasma treatment is used to bring active functional groups on the sample surface. Then, grafting of acrylic acid by cold plasma treatment is possible, and finally the immobilization of cysteine can be carried out. The same methodology was already carried out in previous studies (Degoutin et al., 2012; Vandenbossche et al., 2013). Cysteine can be grafted on polypropylene nonwoven either by the amino group or by the acid group which leads to two possible reaction pathways. In this study, as acrylic acid is first grafted on polypropylene nonwoven, some acidic groups are present at the sample surface. Thus, cysteine can be immobilized on PP-g-AA thanks to a coupling reaction between the amino group of cysteine and the acidic group of acrylic acid. An experimental design has been carried out in order to optimize the cysteine grafting on the acrylic acid-grafted polypropylene. The material grafted with the highest amount of cysteine was then characterized using different techniques (SEM, FTIR-ATR, XPS). To evaluate the
efficiency of the grafted materials, sorption tests have been realized using artificially polluted solutions containing Cu(II), Pb(II), Cr(III) and Cr(VI). 2. Materials and methods 2.1. Samples preparation Squares (5*5 cm2) were cut from polypropylene nonwoven INTN50 (50 g/m2, provided by PGI nonwovens, France). To remove any contaminant, the squares were first washed as it was already described in another paper (Vandenbossche et al., 2013). 2.2. Modification of the polypropylene nonwoven The modification of the polypropylene nonwoven was already described in detail in another paper (Vandenbossche et al., 2013): (1) activation of the sample by an argon low pressure cold plasma process (Europlasma apparatus CD1200-400 COMBI MC, Radio Frequency generator Dressler, 13.56 MHz); (2) immersion of the sample in an acrylic acid solution; (3) removal of the excess solution with a roll-padder; (4) grafting and polymerization using the low pressure argon cold plasma process; (5) washing of the textile; and (6) drying of the sample under vacuum. The PP-g-AA was thus obtained. 2.3. Cysteine immobilization L-Cysteine (>97%, provided by SigmaeAldrich) was chemically grafted on the PP-g-AA thanks to a carbodiimide which can make the carboxylic group more reactive: the N-(3Dimethylaminopropyl)-N0 -ethylcarbodiimide hydrochloride (EDC) (provided by SigmaeAldrich) (Vandenbossche et al., 2013). The textile was immersed for 1 h in a bath of EDC (1 g in 100 mL of distilled water at 4 C). Then, the textile was removed from this bath to be put into a bath of cysteine (2 g in 100 mL distilled water with 10 mL of 1 M NaOH) for 24 h. Finally, the textile was washed for 1 h in an ultrasonic bath, and then, for 6 h in a Soxhlet extractor with distilled water. The samples were dried under vacuum leading to the PP-g-AA-Cysteine material.
2.4. Experimental design The optimization of the cysteine grafting on PP-g-AA was carried out using response surface methodology. The influence of two main parameters was studied: the concentration of cysteine and the immersion time in the cysteine bath. A central composite design (CCD), consisting in 10 experimental runs, was used, including: a full factorial design, containing 4 experiments; four star points at a distance a ¼ 1.414 from the design center; two replicates of the center point. Experiments were conducted randomly to provide protection against the extraneous factors, which could affect the measured response. For statistical calculations, the variables Ui were coded as Xi according to the following transformation:
Xi ¼ ðUi Ui0 Þ=DUi
(1)
where Xi is the dimensionless coded value of the variable Ui, Ui0 represents the value of Ui at the center point and DUi is the step change. The experimental values associated with the coded levels of the different variables are given in Table 1. A second-order polynomial equation was used to express the response as a function of the independent variables:
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C1s CeC at 285 eV. The C1s peaks were decomposed using GaussianeLorentzian peak shapes and the full-width at half maximum (fwhm) of each line shape was maintained below 1.3 eV.
Table 1 Coded and real values of experimental parameters used for the CCD. Coded variable
Parameter
X1
U1 cysteine concentration in the bath (mol/L) U2 immersion time (h)
X2
Levels a 0.12 12.66
1 0.15 16
þ1
0 0.225 24
y ¼ b0 þ b1 X1 þ b2 X2 þ b12 X1 X2 þ b11 X12 þ b22 X22
0.30 32
þa 0.33 35.33
(2)
where y is response variable, b0 is the value of the fitted response at the center point, bi, bii and bij correspond respectively to the linear, quadratic and interaction terms of the model. Modde 7.0 software developed by Umetrics was used to determine the coefficients of the model and for the graphical analysis of the obtained experimental data. The statistical significance of the main, quadratic and interaction effects of the variables was determined by analysis of variance (ANOVA) and a multiple regression analysis was performed to fit the experimental data to the secondorder polynomial equation. The determination coefficients R2 and R2Adjusted respectively describe the fraction of variation of the response explained by the model and the fraction of variation of the response explained by the model adjusted for degrees of freedom. The coefficient of prediction Q2 describes the fraction of variation of the response that can be predicted by the model. To evaluate the efficiency of cysteine immobilization, only one criterion has been considered and taken as a response for the composite design. The sample has been weighed before plasma activation (Wi in mg) and after immobilization of cysteine followed by washing and drying step (Wf in mg). It allowed the calculation of the grafting rate, using the following equation:
. Wi % ¼ 100 Wf Wi
109
(3)
2.6. Heavy metals trapping tests 2.6.1. Preparation of the artificially polluted solutions Five artificially polluted solutions have been prepared at a concentration of 1000 mg/L each. The first one is a copper (II) sulfate solution of final pH 4.3. The second one is a copper (II) nitrate solution also of pH ¼ 4.3. The third solution contains lead (II) nitrate and its pH is 4.8. The fourth one is a chromium (III) nitrate solution with a final pH of 2.7. And finally, the fifth solution containing chromium (VI) has been prepared by dilution of a 10 g/L K2Cr2O7 solution, with a final pH of 8.3. The pH of these solutions was adjusted to 4.5 with NaOH 1 M or HCl 1 M for the heavy metals sorption test in order to compare the obtained results. 2.6.2. Heavy metals sorption Cysteine-grafted polypropylene samples were immersed in 100 mL of the different artificially polluted solutions at 20 C for 24 h. The textiles were then washed in 50 mL of ultrapure water, and the surfaces were digested with 10 mL sulfuric acid (purity of 95%) and 20 mL hydrochloric acid (purity of 37%) to remove copper, lead, and chromium. 70 mL of ultrapure water was added to the solution and the heavy metal concentration of this final solution was determined by flame atomic absorption using the standard addition method (Thermo Solaar S4 AA Spectrometer, Thermo S Series, Multi-elements combined coded hollow-cathods lamp for CreCueMneNi, Thermo Scientific and Mono-elements coded hollow-cathods lamp for Pb, Thermo Scientific). 3. Results and discussion 3.1. Cysteine immobilization
2.5. Surface characterization 2.5.1. SEM The samples were observed using a Scanning Electron Microscope Hitachi S4700 at an accelerating voltage of 6 kV and a current of 15 mA. All images were taken at 1500 magnification to ensure good comparison between all the samples. This method allows determining the surface morphology and the quality of the coating. 2.5.2. FTIR/ATR The samples were analyzed thanks to a FTIR/ATR spectrometer (Thermo Scientific Nicolet 380 FT-IR Spectrometer) in the range of 800e2500 cm1 (16 scans) to determine the presence of acrylic acid and/or cysteine. 2.5.3. XPS XPS analyses were performed on an Axis ultra DLD (Kratos analytical) using a monochromatic Al KR X-ray source (hn ¼ 1486.6 eV). The emission voltage and the current of this source were set to 15 kV and 10 mA, respectively. The pressure in the analyzing chamber was maintained at 107 Pa during analysis, and the area analyzed was 300 700 mm2, with a depth of 10 nm. Survey (0e1300 eV) and high-resolution (C1s) spectra were recorded at pass energies of 20 eV with a step of 0.05 eV (the surveys were recorded at pass energies of 160 eV with a step of 1 eV). Data treatment and peak-fitting procedures were performed using Casa XPS software. Obtained spectra were rescaled by shift of
3.1.1. Preliminary results Prior to the experimental design, a rapid evaluation of the influence of cysteine concentration and immersion time in the cysteine containing bath has been realized in order to adjust the limits of each parameter. 3.1.1.1. Influence of cysteine concentration. The immersion time was fixed at 24 h. Four cysteine concentrations were tested: 0.075 mol/ L, 0.15 mol/L, 0.30 mol/L and 0.45 mol/L and the grafting rates respectively obtained are 1.5%, 2.7%, 3.0% and 3.3%. The grafting rate seems to increase when the cysteine concentration increases. 3.1.1.2. Influence of immersion time. The cysteine concentration was fixed at 0.15 mol/L. Three immersion times were tested: 4 h, 24 h, and 72 h. The following grafting rates were obtained: 0.5%, 2.7%, and 8.3%, respectively. It was observed that for 72 h of immersion, there was a cysteine homopolymerisation phenomenon. As a consequence, the maximum immersion time used in the experimental design is around 35 h. 3.1.2. Experimental design As the preliminary studies showed the influence of cysteine concentration and immersion time on the grafting, an experimental design was set up in order to improve cysteine immobilization on PP-g-AA. All PP samples were first grafted with acrylic acid using the protocol described in the experimental part, and were then chemically activated thanks to EDC.
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Table S1 details the experimental conditions applied to the 10 experiments and also the experimental results obtained for the response. The determination coefficients obtained for the response show that the regression model fits the experimental data correctly. In fact, R2 value is 98%, indicating that 2% of the total variation is not explained by the model. The value of the adjusted determination coefficient is also high (R2Adjusted ¼ 94.6%), showing a high significance of the model. The grafting is also well predicted by the model as the coefficient of prediction Q2 is 77%. The second-order polynomial equation associated to the response is:
y ¼ 3:05 þ 0:2202X1 þ 0:4225X2 0:25X1 X2 0:8617X12 0:3962X22
(4)
This model allows plotting the evolution of the predicted grafting rate as a function of cysteine concentration and immersion time (Fig. 1). Thus the sample must be immersed in a solution containing 0.229 mol/L of cysteine for 28 h to reach the best grafting rate, namely 3.16%. A new experiment has been realized using a 0.229 mol/L cysteine concentration and an immersion time of 28 h. An experimental grafting rate close to the predicted one i.e. 3.2 0.5% has been obtained, thus validating the experimental design procedure.
3.2. Surface characterization 3.2.1. SEM Textiles were grafted according to the protocol described in the experimental part. A previous paper (Vandenbossche et al., 2013) detailed the homogeneity of the acrylic acid coating. To confirm the presence of cysteine, SEM was carried out on fibers after cysteine grafting. Several samples obtained from the experimental design and corresponding to various grafting rates have been characterized (Fig. 2). The coating obtained after cysteine grafting is strongly dependent on the grafting rate: for experiment 3 (Fig. 2A), corresponding to a grafting rate of 2.1%, the coating is observed on and between the fibers, but this coating seems very thin and fragile; for experiment 4 (Fig. 2B), corresponding to a grafting rate of 0.9%, cysteine is only slightly visible between fibers; for experiment 8 (Fig. 2C), corresponding to a grafting rate of 3%, the coating is homogeneous and is observed both on and between the fibers; and
finally, for experiment 10 (Fig. 2D) and for the optimized conditions (Fig. 2E), both corresponding to a grafting rate of 3.2%, a thick coating is visible around and between fibers. 3.2.2. FTIR/ATR Infrared spectroscopy (FTIR-ATR) was used to detect the presence of characteristic chemical groups on the geotextile surface (Fig. 3). The presence of acrylic acid is evidenced by the peak of asymmetric elongation of the carboxylic function at 1715 cm1. The grafting of cysteine is shown by two different peaks: scissoring deformation of the NeH of the amide group at 1566 cm1 and asymmetric elongation of the carboxylic function of cysteine at 1640 cm1 (Pawlukojc et al., 2005). Presence of the peak of amide scissoring deformation evidence the grafting of cysteine on PP-gAA: a coupling reaction between the carboxylic group of acrylic acid and the amine group of cysteine has occurred. 3.2.3. XPS XPS analyses were carried out on PP, PP-g-AA and the optimized PP-g-AA-cysteine samples. An evolution of the surface atomic percentages is observed. Indeed, with XPS, only the extreme surface (w10 nm depth) is analyzed. Thus, when a new layer is grafted on the textile, the underlying layer is less visible. The different atomic percentages are summarized in Table 2. Virgin polypropylene contains mainly carbon. The small amount of oxygen observed by XPS is due to manufacturing process of the nonwoven. When acrylic acid is grafted on PP, there is an increase of the oxygen atomic percentage, and the ratio [O1s]/[C1s] is important: more than 1/5 atoms in the extreme surface is an oxygen. Finally, when cysteine is grafted on PP-g-AA, presence of nitrogen and sulfur is also observed, but with small atomic percentages. There is also an increase of the oxygen atomic percentage, and the ratio [O1s]/[C1s] is more important than the one obtained for PP-g-AA (more than 1/ 3 atoms in the extreme surface is an oxygen). Fig. S1 presents the C1s peak obtained for Cysteine and PP-g-AAcysteine. The decomposition of Cysteine C1s peak gives information about the important group of Cysteine, and these results can then be used to decompose PP-g-AA-cysteine C1s peak. The C1s peak of cysteine can be decomposed into 3 peaks: one peak at 285.4 eV (fwhm ¼ 1.3), which corresponds to CeS bonds; one peak at 286.2 eV (fwhm ¼ 1.3), corresponding to CeN bonds; and another peak at 288.2 eV (fwhm ¼ 1.3), which corresponds to the O]CeO bonds. From these observations, the C1s peak of PP-g-AA-cysteine can be decomposed. An important peak at 285.0 eV (fwhm ¼ 1.3) is observed, corresponding to CeC bonds. Evidence of the grafting of acrylic acid is given by the peak at 286.4 eV (fwhm ¼ 1.3), which corresponds to the ether group formed between PP and acrylic acid (Vandenbossche et al., 2013), and can also correspond to the CeN bond in cysteine. Two other peaks can be observed: one at 288.3 eV (fwhm ¼ 1.3), corresponding to the contribution of acrylic acid, polyacrylic acid and cysteine (OeC]O), and also corresponding to the amide group (NeC]O) formed during the grafting of cysteine on PP-g-AA, and the other one a peak at 285.2 eV (fwhm ¼ 1.3), corresponding to the thiol group of cysteine (CeSH). Thus, according to FTIR and XPS results, cysteine is proven to be covalently grafted on PP-g-AA. The amide groups formed are due to the linkages between the acidic groups of acrylic/polyacrylic acid and the amine groups of cysteine. 3.3. Heavy metals trapping tests
Fig. 1. Contour plot showing the evolution of the cysteine grafting a function of cysteine concentration (X1) and immersion time (X2).
3.3.1. Heavy metals sorption The sorption capacity of the textile depends on the heavy metals oxidation degree. Fig. 4 describes the amount (in mg heavy metal per gram of textile) of different heavy metals [Cu(II), Pb(II), Cr(III)
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111
Fig. 2. SEM images of fibers coming from PP-g-AA-cysteine samples: (A) from experiment 3; (B) from experiment 4; (C) from experiment 8; (D) from experiment 10; and (E) optimized grafting conditions.
and Cr(VI)] trapped by the nonwovens using solutions containing 1000 mg/L of heavy metals. It can be observed that PP-g-AAcysteine is more efficient for the trapping of divalent cations than other metals with oxidation degrees. At 20 C for 24 h (in 1000 mg/ L heavy metal solution) PP-g-AA-cysteine adsorbs 95 mg of copper
(from CuSO4 solution), 104 mg of copper (from Cu(NO3)3 solution), 135 mg of lead per gram PP whereas the same sample adsorbs only 21 mg Cr (III) per gram PP, and does not adsorb any Cr (VI) at all. Atomic radii of copper and chromium are respectively about 135 pm and 140 pm, with respective electronegativities of 1.9 and 1.66. The slight differences between these parameters cannot explain the differences obtained in terms of copper and chromium adsorption. Thus, oxidation degree can play an important role in heavy metals trapping. Moreover, what is interesting to notice is that the textile becomes immediately yellow when put in contact with the chromium (VI) containing solution. But, as soon as the textile is rinsed with water, this yellow color disappears and not any or only a slight remaining amount of chromium is detected by atomic absorption. It means that some weak interactions are probably involved in the trapping of chromium, e.g. hydrogen bonds between oxygen from Cr2 O2 7 and the thiol or carboxylic acid groups of PP-g-AA-cysteine. But this chromium is easily released in water during the rinsing step. Table 2 Quantification by XPS of various elements at the surface of the textiles.
Fig. 3. FTIR-ATR spectra of the virgin-polypropylene (PP), acrylic-acid-grafted polypropylene (PP-g-AA), cysteine/acrylic-acid-grafted-polypropylene (PP-g-AA-cysteine), optimized cysteine/acrylic-acid-grafted-polypropylene (PP-g-AA-Cys optimum) and cysteine powder.
Samples
%C1s
%O1s
%N1s
%S2p
[O1s]/ [C1s]
[N1s]/ [C1s]
[S2p]/ [C1s]
PP PP-g-AA PP-g-AA-cysteine
97.4 82.1 68.9
2.6 17.9 25.1
0 0 3.7
0 0 2.3
2.7 22 36
0 0 5.4
0 0 3.3
112
M. Vandenbossche et al. / Journal of Environmental Management 132 (2014) 107e112
Up-Tex Competitiveness Cluster and all DEPOLTEX partners for helpful collaboration and discussion. Finally, the authors acknowledge M. Yann CHIPAN for assistance for the experiments, and M. Arnaud Beaurain (Plateforme régionale d’analyse des surfaces, Université Lille Nord de France) for the XPS analyses. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2013.10.027. References
Fig. 4. Amount of heavy metals trapped by PP-g-AA-cysteine in solutions containing 1000 ppm of heavy metals.
From Fig. 4, it can also be noticed that the amount of lead adsorbed (135 mg/g textile) is more important than the amount of copper adsorbed (104 mg/g textile). However, lead is heavier than copper, and consequently the molar amount of lead trapped is less important than the molar amount of copper: 6.6 104 mol/g of lead (from a Pb(NO3)2 solution) and 16 104 mol/g of copper (from a Cu(NO3)2 solution). Consequently, more copper than lead is trapped by PP-g-AA-cysteine. This result could be explained by the different atomic radii. Indeed, the atomic radius of lead is about 180 pm whereas atomic radius of copper is about 135 pm: copper being smaller than lead, it can thus be more easily trapped by PP-g-AAcysteine. 2 Finally, the importance of the counter-ion (NO 3 or SO4 ) was studied in the case of copper adsorption: no significant difference between these two experiments is observed. If the molar amount is considered, an amount of 16 104 mol Cu (from Cu(NO3)2 solution) and 15 104 mol Cu (from Cu(SO4) solution) is trapped by PP-g-AA-cysteine samples. 4. Conclusion In this paper, cysteine was successfully grafted on PP using a cold plasma treatment. The use of the experimental design technique allowed determining the best condition for the grafting of cysteine on PP-g-AA: a cysteine concentration of 0.229 mol/L and an immersion time of 28 h. The covalent grafting of cysteine on polypropylene nonwoven was evidenced using different characterization techniques (SEM, FTIR/ATR, and XPS). Sorption studies were carried out with copper (II), lead (II), chromium (III) and chromium (VI). Very promising results are obtained for the trapping of divalent heavy metals. A further study (Part B) will be published on the efficiency of this textile to trap heavy metals, completed with kinetic studies at 20 C, varying the pH and ionic strength effect. Acknowledgments The authors gratefully acknowledge the support of FEDER (Fonds Européen de Développement Régional), Nord-Pas-de-Calais region, and FUI (Fonds Unique Interministériel) for funding this work .We also would like to deeply acknowledge the support of the
Cobbett, C.S., 2000. Phytochelatins and their roles in heavy metal detoxification. Plant Physiol. 123, 825e832. Degoutin, S., Jimenez, M., Casetta, M., Bellayer, S., Chai, F., Blanchemain, N., Neut, C., Kacem, I., Traisnel, M., Martel, B., 2012. Anticoagulant and antimicrobial finishing of non-woven polypropylene textiles. Biomed. Mat 7, 1e13. Faghihian, H., Nejati-Yazdinejad, M., 2009. Sorption performance of cysteinemodified bentonite in heavy metals uptake. Russ. Source 74, 833e843. Gouzy, A., Ducos, G., 2008. La connaissance des éléments-traces métalliques: un défi pour la gestion de l’environnement. Air Pur 75, 6e10. Howard, M., Jurbergs, H.A., Holcombe, J.A., 1999. Comparison of silica-immobilized poly(L-cysteine) and 8-hydroxyquinoline for trace metal extraction and recovery. J. Anal. At. Spectrom. 14, 1209e1214. Johnson, A.M., Holcombe, J.A., 2004. Poly(l-cysteine) as an electrochemically modifiable ligand for trace metal chelation. Anal. Chem. 77, 30e35. Jurbergs, H.A., Holcombe, J.A., 1997. Characterization of immobilized poly(lcysteine) for cadmium chelation and preconcentration. Anal. Chem. 69, 1893e1898. Klaassen, C.D., Liu, J., Choudhuri, S., 1999. Metallothionein: an intracellular protein to protect against cadmium toxicity. Annu. Rev. Pharmacol. Toxicol. 39, 267e294. Lai, Y.-L., Thirumavalavan, M., Lee, J.-F., 2010. Effective adsorption of heavy metal ions (Cu2þ, Pb2þ, Zn2þ) from aqueous solution by immobilization of adsorbents on Ca-alginate beads. Toxicol. Environ. Chem. 92, 697e705. Lopez-Sanchez, J.F., Rubio, R., Samitier, C., Rauret, G., 1996. Trace metal partitioning in marine sediments and sludges deposited off the coast of Barcelona (Spain). Water Res. 30, 153e159. Louriño-Cabana, B., Lesven, L., Charriau, A., Billon, G., Ouddane, B., Boughriet, A., 2011. Potential risks of metal toxicity in contaminated sediments of Deûle river in Northern France. J. Hazard. Mater. 186, 2129e2137. Maret, W., Larsen, K.S., Vallee, B.L., 1997. Coordination dynamics of biological zinc “clusters” in metallothioneins and in the DNA-binding domain of the transcription factor Gal4. Proc. Natl. Acad. Sci. 94, 2233e2237. Merrifield, J.D., Davids, W.G., MacRae, J.D., Amirbahman, A., 2004. Uptake of mercury by thiol-grafted chitosan gel beads. Water Res. 38, 3132e3138. Mostafa, K.M., Samarkandy, A.R., El-Sanabary, A.A., 2011. Preparation of poly(DMAEM)-cross linked pregelled starch graft copolymer and its application in waste water treatments. Carbohydr. Polym. 86, 491e498. Müller, W.W., Jakob, I., Li, C.S., Tatzky-Gerth, R., 2009. Durability of polyolefin geosynthetic drains. Geosynth. Int. 16, 28e42. Palackova, H., Vinklarek, J., Holubova, J., Cisarova, I., Erben, M., 2007. The interaction of antitumor active vanadocene dichloride with sulfur-containing amino acids. J. Organomet. Chem. 692, 3758e3764. Pawlukojc, A., Leciejewicz, J., Ramirez-Cuesta, A.J., Nowicka-Scheibe, J., 2005. LCysteine: neutron spectroscopy, Raman, IR and ab initio study. Spectrochim. Acta Part A 61, 2474e2481. Singh, S.P., Tack, F.M.G., Verloo, M.G., 1998. Land disposal of heavy metal contaminated dredged sediments: a review of environmental aspects. Land Contam. Recl 6, 149e158. Tekin, K., Uzun, L., Sahin, C.A., Bektas, S., Denizli, A., 2011. Preparation and characterization of composite cryogels containing imidazole group and use in heavy metal removal. React. Funct. Polym. 71, 985e993. Vandenbossche, M., Jimenez, M., Casetta, M., Bellayer, S., Beaurain, A., Bourbigot, S., Traisnel, M., 2013. Chitosan-grafted nonwoven geotextile for heavy metals sorption in sediments. React. Funct. Polym. 73, 53e59. Xiao, L., Wildgoose, G.G., Crossley, A., Knight, R., Jones, J.H., Compton, R.G., 2006. Removal of toxic metal-ion pollutants from water by using chemically modified carbon powders. Chem. e Asian J. 1, 614e622. Yamauchi, O., Odani, A., Takani, M., 2002. Metal-amino acid chemistry. Weak interactions and related functions of side chain groups. J. Chem. Soc. Dalton Trans., 3411e3421. Zenk, M.H., 1996. Heavy metal detoxification in higher plants e a review. Gene 179, 21e30.
