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Copper removal from aqueous solutions using a polyelectrolyte derived from sunflower oil: Physico-chemical aspects
Accepted Manuscript Title: Copper removal from aqueous solutions using a polyelectrolyte derived from sunflower oil: Physico-chemical aspects Authors: Quelen Bulow Reiznautt, Irene Teresinha Santos Garcia, Bruna Girelli Furlanetto, Luiz Mario Angeloni, Dimitrios Samios PII: DOI: Reference:
S2213-3437(17)30540-7 https://doi.org/10.1016/j.jece.2017.10.039 JECE 1949
To appear in: Received date: Revised date: Accepted date:
16-6-2017 6-10-2017 17-10-2017
Please cite this article as: Quelen Bulow Reiznautt, Irene Teresinha Santos Garcia, Bruna Girelli Furlanetto, Luiz Mario Angeloni, Dimitrios Samios, Copper removal from aqueous solutions using a polyelectrolyte derived from sunflower oil: Physico-chemical aspects, Journal of Environmental Chemical Engineering https://doi.org/10.1016/j.jece.2017.10.039 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Copper removal from aqueous solutions using a polyelectrolyte derived from sunflower oil: Physicochemical aspects Quelen Bulow Reiznautt, Irene Teresinha Santos Garcia, Bruna Girelli Furlanetto, Luiz Mario Angeloni and Dimitrios Samios*
Physical Chemistry Department, Institute of Chemistry, Federal University of Rio Grande do Sul, Brazil, e-mail [email protected]
Corresponding author: Dimitrios Samios Physical Chemistry Department, Institute of Chemistry, Federal University of Rio Grande do Sul Av. Bento Gonçalves, 9500, Porto Alegre/RS, CEP 91501-970, Brazil Fax: 55 51 3308 7304. Phone: 5551 33086290. e-mail: [email protected]
Highlights
A safer and cleaner technology to remove copper ions from aqueous media is described. Polyelectrolytes synthesized from renewable raw materials are used for Cu ion removal. The surfactants obtained from sunflower oil in aqueous media are characterized. The copper ion/polyelectrolyte interaction for is studied for wastewater recovery.
Abstract Interactions between polymers and different metal ions represent an interesting field of study due their potential use for wastewater remediation. In turn, polymers with technological applications can be obtained from renewable raw materials. In this work, polyesters weighing 2822 Da were obtained from the reaction of an epoxidized biodiesel from sunflower oil. The polyesters were reacted with aqueous sodium hydroxide solutions to obtain polyelectrolytes. The polyelectrolytes were characterized with respect to their structure by Nuclear Magnetic Resonance Spectroscopy, Infrared Fourier Transform Spectroscopy 1
and Gel Permeation Chromatography; their physicochemical behavior in aqueous media as well as their capacity to remove copper ions were characterized by electrical conductivity (EC) and Static and Dynamic Light Scattering measurements (SLS and DLS). The critical micelle aggregation concentration (CAC) was 1.310-1 g·L-1 polyelectrolyte derived from sunflower oil (PESFO). The polyelectrolyte’s EC abruptly increased when the PESFO concentration increased above the CAC.
PESFO in ionic aqueous media
developed a rigid rod morphology and had a strong interaction with water and ions (up to 5.1 g·L-1). Its capacity to remove copper(II) ions from aqueous media was determined, and the interactions between Cu/PESFO were characterized by FTIR. The polyelectrolyte removed up to 35 mg Cu(II)/g PESFO. Keywords:
sunflower
oil;
heavy
metal
removal;
water
remediation;
polyelectrolyte Introduction
Materials based on heavy metals such as Ni, Cu, Zn, Ru, Os, Rh, Au, Ag, Pd and Pt – widely used in electrodeposition, catalysis, and the industrial manufacturing of electronic components – are serious pollutants for soils, plants and groundwater [1]. Their recovery from aqueous media prevents environmental pollution and is also economically justified. Several processes used for removing metals from waste water are carried out with different types of adsorbents from natural resources. Two wastes from Araucaria angustifolia (named pinhão), one natural (PW) and one loaded with Congo red (CRP), were tested as low-cost adsorbents for Cu(II) removal from aqueous solutions [2]. Electrokinetic (EK) treatments, developed by Wang et. al, can be applied to remove heavy metals from sludge and to reuse wastewater in agriculture [3]. Active carbon has been the most popular adsorbent and is widely used in waste water treatment [4,5]. However, it can cause contamination by introducing polyaromatics. Babel et al. evaluated low cost adsorbents in wastewater treatment, including chitosan, zeolites, oxides and clay [4]. Industrial and agricultural residues have been studied in the removal of arsenic from wastewater [6]. Additionally, nanometric metal oxides, including iron oxides, manganese 2
oxide, and aluminum oxide, among others, provide high surface areas and specific affinities for the adsorption of heavy metals. Although efficient, these oxides tend to aggregate into large particles, lowering their adsorption capacities [7]. Additionally, depending on the system’s pH, these oxides can become solubilized and contaminate the environment. However, the use of renewable resources, such as vegetable oils, has attracted attention due to a great potential to produce new materials that address environmental as well as economic concerns. These materials often present properties comparable to those obtained from petrochemical sources and are capable of replacing them. These raw materials are environmentally friendly, conferring biodegradability to their derivatives, depending on the chemical transformations used [8-11]. Polymers such as oxypolymerized oils, polyesters, polyethers, polyurethanes, polyamides, epoxy resins, polyester amides, and others, produced by the chemical transformation of vegetable oils, have found industrial applications [10-16] and, in recent years, a tendency towards increasing the percentage of "green" raw materials in high value-added application products was observed [11, 17]. Polyesters present a range of structures and properties and are widely used in laminates, molding compounds, coatings, adhesives, and biomaterials for tissue engineering and drug delivery [18-20]. Polyesters produced from vegetable oils have been studied with respect to their thermal, mechanical and chemical properties [21]. Polymers represent an interesting field of study due to their potential use in wastewater remediation [22]. The removal of heavy metals, for example, can be followed by calcination in a vacuum to recover the metal in a reduced oxidation state. Radoiu et. al. obtained polyelectrolytes from the polymerization of acrylamide-acrylic acid under microwave irradiation and investigated their potential for wastewater remediation [23]. Although the synthesis of surfactants from vegetable oils is extensively reported [23-28], there are no studies on the synthesis of polyelectrolytes or even polysurfactants using vegetable oils or their fatty acids as raw materials. In this context, this paper aims to prepare water soluble polyelectrolytes from sunflower oil. In aqueous solution, polyelectrolytes dissociate into a macroion and counterions [29-30] and form organized structures in solution. This self-organizing ability allows the design of many new synthetic 3
architectures with unique properties and important commercial applications. In this work, the conversion of polyester into a polyelectrolyte was followed by FTIR and 1H NMR analysis. The polyelectrolytes were characterized with respect to their structure and physicochemical behavior in aqueous media by using static and dynamic light scattering techniques and conductivity measurements. The polyelectrolyte’s capacity for removing copper ions, as well as the interaction itself, is evaluated by photometry. 2 Methodology 2.1 Materials Sunflower oil was supplied by Farmaquimica (Porto Alegre, Brazil). Materials including triethylamine (99%), cis-1,2-cyclohexanedicarboxylic anhydride (99%) and deuterated chloroform (99.8% with 0.03% w/w tetramethylsilane (TMS)) were purchased from Aldrich Chemical Co. Methanol (99.9%), potassium hydroxide (85%), toluene (99.5%) and formic acid (85%) were purchased from Synth (São Paulo, Brazil). Acetone (99.5%), sodium hydroxide (98.1%) and hydrogen peroxide (29.0% v/v in water) were obtained from Nuclear (Diadema, Brazil), and sulfuric acid (98%) was obtained from Merck. 2.2 Preparation of the polyesters Sunflower oil was chosen as raw material to produce a polyelectrolyte because it is composed of fatty acids rich in linoleic acid, an eighteen-carbon chain with two double bonds [12]. The route to obtain the polyester (PSFO) from sunflower oil, and its subsequent conversion into polyelectrolyte, is shown in Fig. 1. The obtained polyelectrolyte will be referred to as polyelectrolyte derived from sunflower oil (PESFO).
4
Figure 1. Scheme showing the synthesis of the polyelectrolyte from sunflower oil (PESFO). The transesterification, which converts sunflower oil in its biodiesel, and the epoxidation were performed according to Reiznautt et al. [31]. A general scheme for the procedure followed in this work is displayed in Figure 1. The first step includes the transesterification of the sunflower oil. The transesterification was performed according to TDSP — transesterification double step process, as described for Samios et al. [32]. Potassium hydroxide (0.85 g) was dissolved in 50 mL methanol at 25 °C. The alcoholic solution was added, under stirring, to 100 mL of sunflower oil and heathen under reflux at 60 °C, during 1h and after, cooled down to 25 °C. In the second step, 50 mL methanol and 1.5 mL sulfuric acid (98% w/w) were added to the mixture, followed by heating to 60 °C, under stirring, for 1.5 h. After this period, the system is cooled again to 25 °C. The biodiesel phase is separated, washed with cold water and the residual alcohol is removed by evaporation under vacuum.
5
The epoxidation reaction was carried with 100 mL of toluene, 30 g of methyl ester and 10.5 mL of formic acid. Additionally, 225 mL of hydrogen peroxide (H2O2 29% in weight) were added dropwise in to the mixture. The system was maintained at 80 °C, during 10 h. After this time, the organic layer (containing the epoxide) was washed with water to remove residual hydrogen peroxide. The epoxide was concentrated in a rotary evaporator. The epoxy-esters (EE) derived from the sunflower oil biodiesel reacted with cis-1,2 cyclohexane dicarboxylic anhydride (CH), in the presence of a small amount of triethylamine (TEA), at 160 °C for 4 h. A simple 125 mL reactor equipped with reflux and continuous magnetic stirring was used. The compositions used to obtain the polyester are presented in Table 1, in terms of XEE, XCH and XTEA, where X represents the molar fraction. Table I. Molar fraction and molecular weight of epoxy-ester (EE), cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) in the polymerization reaction to produce PSFO. Polymers
XEE
XCH
XTEA10-3
PSFO
0.33
0.67
8.5
Reactant
EE
CH
TEA
Molar fraction
0.33
0.67
8.510-3
310.67(1)
154.17
101.19
Molecular Weight/g.mol-1 (1)
Average molecular weight
The polyester obtained from sunflower oil (PSFO) was purified by fractional precipitation using acetone as a solvent and water as a precipitating agent. The sample was dried under vacuum at 60 °C until it reached a constant weight and was then stored at room temperature. This procedure aimed to purify the polyester. remove the remaining saturated fatty acid methyl esters, which are not useful in the epoxidation reaction and, consequently, in the crosslinking process.
6
2.3 Preparation of the polyelectrolytes To study, by FTIR, the cleavage of the ester bonds, polyelectrolytes were synthesized through the reaction of PSFO with NaOH according to Table 2. To characterized the cleavage of the ester bonds, polyelectrolytes were synthesized through the reaction of PSFO with different amount of NaOH, according to Table 2, and analyzed by FTIR. These reactions were performed in duplicate. PSFO and sodium hydroxide reacted in 40 mL of distilled water under reflux and magnetic stirring. The reaction occurred at room temperature for 30 min. The soluble material (PESFO) was separated from the aqueous medium by precipitation with saturated aqueous NaCl solution. After filtration, the purification process consisted of resolubilizing PESFO in water and reprecipitating it in a saturated aqueous NaCl solution. The purification process was repeated three times until the supernatant reached pH~7. The product was dried at 60 °C until it reached a constant weight and then kept in a desiccator for further analysis. Table II. Methyl ester:sodium hydroxide and carboxylic acid:sodium hydroxide molar ratios used to obtain polyelectrolytes derived from PSFO. nCOOCH3:nNaOH
1:0.5
1:0.75
1:1
1:1.5
1:2
2.4 Structural characterization The precursor polyester, PSFO, was characterized by gel permeation chromatography (GPC), 1H and
13C
NMR and FTIR. The cleavage of the ester
bonds was followed by FTIR. The polyelectrolyte obtained from a 1:1 PSFO:NaOH ratio were characterized by 1H and 13C NMR and FTIR. GPC analyses were performed in a GPC Viscotek VE 2001 equipped with polystyrene/divinylbenzene Styragel Waters Millipore columns and connected to a refractive index detector, Viscotek TDA 302, using tetrahydrofuran as a solvent. The 1H and
13C
NMR spectra were obtained in a 300 MHz Innovate
instrument from Varian. The polyelectrolyte structures and the other compounds were characterized by using D2O and CDCl3 as solvents, respectively, with TMS as reference. A quantitative analysis of the hydrogen present in the signals of 1H NMR spectra were used to determine the average molar mass of the sunflower 7
oil, the conversion degree of the transesterification and epoxidation reactions, and the percent yield of the epoxidation, in accordance to Miyake et al. [32][33]. The FTIR analyses were performed in a Varian 640-IR. The liquid samples were analyzed in a sodium chloride crystal cell and the solid ones with potassium bromide pellets. The spectra were obtained in the transmittance mode, between 4000 and 500 cm−1, with 32 scans. 2.5 Characterization of polyelectrolyte in aqueous media The polyelectrolyte obtained from the 1:1 PSFO:NaOH ratio was characterized in aqueous media. The electrical conductivity measurements were collected with a Metrohm 712 conductivitometer by using an electrochemical cell with constant 0.1 cm -1. The calibration of the electrochemical cell was performed with 10-3 mol·L-1 KCl (146.9 μS·cm-1 at 25 °C). The cell was immersed in PESFO solutions with different concentrations. The average value of three determinations was used for graphic preparation. The Static and Dynamic Light Scattering (SLS and DLS) measurements were carried out with a light scattering spectrophotometer, a Brookhaven Instruments (BI)-9000, at 25 °C. The light source used was a He-Ne laser (λ=632.8 nm) with a power of 30 mW. Thirty-two solutions with concentrations varying from 5.110-4 g·L-1 to 3.500 g·L-1 were filtered with hydrophilic filters of 0.45 µm porosity into optical cuvettes that were free of dust. The SLS measurements took place at 90° and DLS signals were obtained by varying the observation angle for each solution with values of 45, 60, 75, 90, 105, 120, 135 and 145°. The polyelectrolyte’s capacity to remove copper ions was studied by mixing copper sulfate solutions with concentrations varying from 8 to 80 mmol·L -1 with 25 to 150 mg of PESFO at a pH of ~7.5, corresponding to 42 systems. Different volumes (630 uL to 4 mL) of 250 mmol L-1 CuSO4 solutions were used to obtain a final concentration from 8-100 mmol L-1 in a total Volume of 10 mL Also, polyelectrolyte was solubilized and added to the system: to obtain 25 mg to 150 mg PESFO we added 1-6 mL 25 mg/mL PESFO. The CUSO4/PESFO systems were stirred at 25 °C for 24 h in order to attain the equilibrium condition. Then, the systems were centrifuged at 3500 rpm 8
for 20 min. When PESFO and copper sulfate solutions are mixed, flocculation is responsible for a strong light scattering, so the equilibrium condition is important to quantify the copper in solution. To test the effect of the temperature and pH on the removal of copper ions, a test was conducted with the system composed of 100 mmol L -1 CuSO4 and 125 mg PESFO, after the equilibrium condition to be attained, by submitting it to pH 1 and to the temperatures of 40°C and 50°C. The concentration of copper in the solutions were determined by photometry at 810 nm. Photometry measurements were performed on a Shimadzu -UV1601PC Spectrophotometer at 25 °C. The concentration of copper in the solutions were determined by photometry at 810 nm. Photometry measurements were performed on a Shimadzu -UV1601PC Spectrophotometer at 25 °C. The interaction between copper and polyelectrolyte was analyzed by FTIR spectroscopy after the samples were washed, precipitated with distilled water, and dried to a constant weight. 3 Results and discussion This discussion firstly focuses on the structural characterization of the polyesters (PSFO) and polyelectrolytes (PESFO) obtained from sunflower oil; It is demonstrated that the polyelectrolyte obtained with a 1:1 sodium hydroxide:PESFO ratio is the best product for removing copper ions. In the second part, the characteristics of this electrolyte in aqueous media, as well as its copper removal capacity, will be addressed. 3.1 Structural characterization of polyesters and polyelectrolytes The PSFO The molecular weight and polydispersity of PSFO, as determined by GPC are 2820 and 1.7, respectively (GPC chromatogram is displayed in Supplementary Material 1). The sunflower oil is mainly composed of linoleic fatty acids, which has two carbon double bonds (between C9-10 and between C12-13 - see scheme in Figure 1). The epoxidation reaction converts the double bonds into epoxide esters (EE), which are precursors to the polymerization reaction.
9
The steric hindrance from the proximity of the epoxy rings prevents the growth of a polymer chain. Figure 2 shows the 1H NMR spectrum of PSFO obtained in CDCl3. The 1H NMR,
13C
NMR and FTIR spectra of the sunflower oil and its intermediates,
methyl esters and epoxy esters were presented in our previous work [31].
Figure 2.1 ¹H NMR spectrum of PSFO. Peaks situated between δ = 2.95 and 3.10 ppm, corresponding to the hydrogen atoms of the oxirane groups, cannot be observed, which indicates the opening of all the epoxide rings. Signals at δ = 1.51 and 1.72 ppm, present in epoxy esters, are also absent, which indicates the disappearance of the -CH2 groups bonded to the oxirane rings [33, 34] . The peak situated at δ = 0.86 ppm (peak H) corresponds to the terminal methyl groups of the fatty acid from the precursor sunflower oil. The signals at δ = 1.24 (G), 1.58 (F) and 2.29 ppm (D) are similar to that observed for methyl ester groups from fatty acid chains and are attributed to the internal -CH2 groups. At δ = 3.65 ppm, (I) is observed and assigned as the hydrogen signal of the -CH3 from the ester groups, as observed in the spectra of methyl esters and their derived epoxy esters [31]. The signal at δ = 4.97 ppm (N) corresponds to the -CH groups of the methyl ester chains 10
bonded to the anhydride, as suggested in the chemical structure shown in Figure 2; this signal indicates the cleavage of the epoxide ring and the addition of an anhydride to the methyl ester chain to form an internal ester bond. The appearance of two signals at δ = 2.83 ppm (O) and δ = 1.77 and a peak at 2.05 ppm (P) are due to the -CH and -CH2 groups, respectively, of the anhydride cyclohexane rings that were added to the ester chains [33] [34, 35]. This result is confirmed by 13C NMR (see Supplementary Material 12). The behavior of the polyelectrolyte in different solvents differs from that of the precursor PSFO. PSFO is completely soluble in polar organic solvents, such as chloroform, acetone and tetrahydrofuran, but insoluble in water. However, the obtained polyelectrolytes were soluble in water and insoluble in those same polar organic solvents. Figure 3 shows the 1H NMR spectrum of the electrolyte PESFO in D2O. The change of deuterated solvent was responsible for the changes in the values of the chemical shifts. The spectrum of Figure 3 does not show a signal at 3.65 ppm but instead presents a signal at δ=3.47 ppm. The methyl groups of the terminal ester could not be verified; however, a considerable decrease in the signal intensity is observed, which is confirmed by the FTIR analysis. At δ=0.77 ppm, a peak is observed corresponding to the hydrogens of the terminal methyl groups of the fatty acid, whereas the signals between 1.10 and 2.70 ppm correspond to the hydrogens of the internal CH and CH2 groups [35].
11
Figure 3.2 ¹H NMR spectrum of PESFO in D2O. Figure 4 shows the infrared spectrum of polyelectrolytes PESFO compared with its precursor, PSFO.
12
Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and its polyelectrolyte (PESFO). The FTIR spectrum of the polyelectrolyte shows bands at 1562 cm -1 and 1407 cm-1 that are not present in the PSFO spectrum. An intense band at 1562 cm-1 corresponds to the asymmetrical axial deformation of the carboxylate ion (asCOO-), and a weak band, observed at 1407 cm-1, is assigned to the symmetrical axial deformation of the carboxylate ion (sCOO-) [34] [35], which confirms the formation of sodium carboxylate. In the PSFO spectrum, the intense absorption band at approximately 1736 cm-1 is attributed to the C=O of the aliphatic esters. The C–O bands, attributed to the ester groups, are observed in the region between 1300 and 1100 cm -1 [34][35]. These same bands are also observed in the PESFO spectrum. However, these bands are not attributed to the terminal methyl ester groups but to the internal ester bonds instead. The PESFO spectrum (Figure 4) clearly shows a low-intensity, broad band at approximately 3428 cm-1, which can be attributed to the cleavage of the ester bonds. To confirm this interpretation and follow the cleavage of the ester bonds, polyelectrolytes were synthesized with different molar ratios of terminal groups by varying the PSFO:NaOH ratios (see Table 2). In Figure 54 a broad band O-H is observed at approximately 3428 cm -1, which could be attributed to carboxylic acids, alcohols or to the presence of moisture; however, carboxylic acids show a wide, intense band from 3300 to 2500 cm-1, due to the superposition of the C-H from the alquil group with O-H, which was not observed [34][35].
13
Figure 5. FTIR spectra of polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II.
14
Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II. PESFO is the polyelectrolyte with 1/1 ratio. An increase in the intensity of the bands at 3428 cm-1 observed in Figure 54 with the increase of the amount of sodium hydroxide suggests that this band originates from the alcohol formed by the cleavage of the internal ester bonds between the anhydride and the epoxy-ester chain, as proposed in the scheme in
15
Figure
6
5.
Figure 65. Scheme of the polyelectrolyte synthesis in the presence of NaOH (a) and (b) the subproducts formed from an excess of NaOH. Additional sodium hydroxide promotes the cleavage of not only the external ester bonds but also the internal ester groups; however, the hygroscopicity of the product increases with the number of sodium carboxylate groups, and it would be difficult to ensure that the sample does not contain moisture. The increase in the number of the carboxylate ions with the amount of sodium hydroxide used can be confirmed through the band at 1407 cm -1, which is marked in Figure 54 and is due to sCOO-. The intensity of this band increases as the nH3COOC-/nNaOH ratio decreases. A wide band at 34303428 cm-1 is observed for the polyelectrolytes synthesized with more NaOH (1:1, 1:1.5 and 1:2); however, this signal does not appear in the FTIR spectra of the polyelectrolytes synthesized with less NaOH (1:0.5 and 1:0.75). The relative intensities of the two absorption bands at 17341730 cm-1 and 15701562 cm-1 are important to be observe. The band at 17341730 cm-1 is characteristic of C=O from the internal esters of the polyelectrolyte. The band at 15701562 cm-1 is due to the carboxylate anion. As the amount of NaOH increases, I1730/I1562 decreases increases. This behavior indicates that increased 16
amounts of sodium hydroxide promote the cleavage of some internal ester bonds in the polyelectrolyte, between the anhydride and the epoxidized acid chain, to form alcohol groups. This interpretation is confirmed by the band at 34303428 cm-1[35]. Thus, we can conclude that, under mild conditions, i.e., with less NaOH, there was no cleavage of the internal ester linkages and therefore no chain scission was observed. 3.2 Characterization of PESFO in aqueous media for copper removal The polyelectrolyte obtained by mixing polyester and sodium hydroxide in a 1:1 ratio was characterized in aqueous media, at 25 °C, with respect to its physicochemical behavior in aqueous solutions as well as its efficiency for copper ion removal. 3.2.1 Physicochemical behavior of the polyelectrolyte in aqueous media Figure 76 shows the electrical conductivity () as a function of the PESFO concentration. The conductivity only slightly increases for PESFO concentrations below 1.310-1 g·L-1, followed by an abrupt increase at higher concentrations. This behavior differs from that observed for polymer aggregation, which commonly shows a decrease in the slope of the conductivity curves when the concentration exceeds the critical aggregation concentration (CAC) [35, 36][36,37].
17
Figure 76. Electrical conductivity of PESFO aqueous solutions as a function of PESFO concentration at 25 °C. The raw material used to prepare PESFO has approximately 70% w/w linoleic acid, which has two double bonds, allowing it to produce more carboxylate ions per polymer chain. As the electrolyte concentration increases, the effective headgroup area diminishes and the distance of electrostatic repulsion is reduced, which favors aggregation. Polymer aggregation would further decrease the conductivity. The counterion
condensation
theory,
described
by
Manning,
assumes
that counterions can condense onto polyelectrolytes until the charge density is reduced below a certain critical value. This behavior could be responsible for the decrease in the solvation of the polyelectrolytes and, consequently, the increase in ionic mobility [37]. The reason for this abrupt increase of conductivity at higher concentration, is the increasing in the mobility of the ions; as the PESFO concentration increases, the presence of carboxylate ions and counterions disrupted the solvation layer, increasing the mobility of the ions and, consequently, the electrical conductivity. This phenomenon’s effect on the removal of copper ions will be discussed in Section 3.2.2. 18
Fig. 87 displays the scattered light intensities of the aqueous solutions, measured at 90°, as a function of the PESFO concentration. Low intensities of scattered light can be observed for concentrations between 5.110-4 and 1.2101
g·L-1 and vary slightly with concentration. An increase in the light scattered
intensity occurs for concentrations higher than 1.210-1 g·L-1, which is similar to the concentration at which the abrupt increase in the conductivity curve is observed (see Fig. 87). Higher polyelectrolyte concentrations increase the ionic strength of the media, which disrupts the solvation layer and promotes polyelectrolyte aggregation. Similar behavior is observed when Cu +2 and Co+2 were added to the polyelectrolyte solution.
Figure 87. Static light scattering intensity at 90° (I90°) as a function of the PESFO concentration at 25 °C. The gyration radius (Rg) values were determined by SLS using the static intensity dissymmetry method (see Supplementary Material 23). The Rg values for different polyelectrolyte concentrations at 25°C are shown in Table III. Table III. Gyration radius obtained from static light scattering measurements.
19
Concentration of the solution (g·L-1)
Rg (nm) values
0.068
55
0.108
54
0.132
58
0.192
64
0.296
50
Dynamic light scattering (DLS) analyses were performed for eight solutions with 0.07, 0.09, 0.19, 0.39, 0.78, 1.13, 2.43 and 3.50 g·L-1 PESFO. These solutions presented well defined correlation functions and their scaling intensities are higher than 30 kcps at all angles. Concentrations lower than 0.07 g·L-1 could not be used because they did not give correlation functions. Fig. 109 shows the normalized correlation functions for a 0.19 g·L -1 aqueous PESFO solution. As expected, the correlation functions decay faster as the scattering angle increases, as shown in Figure 98. Small scattering angles provide information about the larger features of the structures, and thus slower chain movements are observed. Similar behavior was also observed for the other solutions.
20
Figure 98. Normalized correlation functions, at different angles, for a 0.19 g·L -1 aqueous PESFO solution at 25 °C. The relaxation times were obtained from the correlation functions by fitting two exponential decays that correspond to populations with slow (t 1) and fast (t2) modes. The presence of two populations of light scattering species was observed for all the studied concentrations and scattering angles. These two populations have practically the same contribution for the majority of the solutions. This behavior suggests that, after the micelle formation at the CAC, the micelles continue to grow, i.e., by the addition of molecules at increased concentrations. The relaxation times were used to determine the diffusion coefficients D 1 and D2, which are related to the longer and shorter relaxation times, respectively. The diffusion coefficient and the hydrodynamical radius can be obtained by analyzing the DLS results (see Supplementary Material 34). The diffusion coefficients at infinite dilution were D1,0=1.0110-11 m2·s-1 and D2,0=2.7310-11 m2·s-1, referring to the slow and the fast modes, respectively. The value of Rh calculated for the population with a small diffusion coefficient was 21 nm. The ratio =Rg/Rh, the fractal dimension, compares the hydrodynamic interactions with the geometric dimensions of the molecule and gives different 21
values according to the molecular architecture: for homogeneous spheres, < 1; for microgels, < 0.5; for random coils, 1.5 2.0 and for rigid rods, 2 [38]. The fractal dimension, calculated from the average Rg values shown in Table III and Rh, 2.6, suggests that polyelectrolytes in solution form rigid rods. 3.2.2 Interaction between PESFO and copper ions in solution Figure 109 shows the UV/vis spectra in the region between 200 and 900 nm of the polyelectrolyte and copper sulfate solutions. The absorbance of PESFO, even in concentrations higher than that used in this work, does not interfere in the determination of the copper sulfate concentration at 800810 nm.
Figure 109. UV-VIS spectra of the solutions of (-)CuSO4 (60 mmol·L-1) and (-) PESFO solution (25.0 mg·L-1) at 25°C. When mixed with copper sulfate solution, the polyelectrolyte precipitates. The precipitate is blue, leaving the solution to become colorless (see Figure 1110).
22
23
Figure 1110. Pictures of the: a) PESFO solution, b) copper sulfate solution and c) PESFO/copper sulfate after mixing. A temptation of fitting isotherms as Langmuir, Freundlich or Ships, with ratio between copper removed/PESFO versus CuSO4 equilibrium concentration, did not show correlation. Figure 12-a11-a shows that, independent of the copper coper sulfate concentration, copper is removed in the same quantity the copper ions removal depends linearly on the PESFO amount (Figure 12-b11-b).
24
Figure 121. Copper ions removed as function of copper sulfate concentration (a) and as function of PESFO amount (b), at 25 °C. The number of copper ions removed is proportional to the amount of PESFO added to the system, independent of the copper concentration in the initial solution. In all the concentrations of copper sulfate that were treated with a fixed amount of PEPESFO, approximately the same amount of copper was removed. The time necessary for the conclusion of this process depends of the ion concentration, PESFO concentration, temperature and pH. During the experiments, we observed that the PESFO precipitates immediately after it bonds to copper ions . 25
Figure 12 shows the absorbance of systems composed of 100 mmol L -1 CuSO4/150 mg PESFO after the equilibrium to be attained (after 24 h and centrifuged 20 min at 3500 rpm) for the following conditions: 25 °C and pH 7.5 with: 25°C and pH 1; pH ~7.5, 40 and 50 °C. In acid media PESFO does not present the same efficiency in copper removal, because PESFO is protonated. When the system is submitted to higher temperature, copper is more soluble in aqueous solution and the efficiency in copper removal decreases. Alkaline conditions were not investigated, because, as discussed in previous sessions, the cleavage of the polyelectrolyte chains would produce unreliable results.
0
pH7.5, 25 C 0
pH 1.0, 25 C 0
pH 7.5, 40 C 0
Absorbance
pH 7.5, 50 C
500
600
700
800
900
Wavelength (nm)
Figure 12. Absorbance of 100 mmol L-1 CuSO4/150 mg PESFO after 24 h and centrifuged 20 min at 3500 rpm. The precipitation, as shown above, occurs due to a decrease in the effective headgroup area that reduces the electrostatic repulsion; the electrostatic repulsion is responsible for the stability of the colloidal PESFO in solution. The polymer aggregation is mediated by copper ions. Thus, from the ratio between the quantity of removed ions and the amount PESFO added, it is possible to determine the PESFO’s capacity to remove
26
copper ions. From the average of all the obtained values, it was observed that 1 g of PESFO is able to remove 35 mg Cu+ 2 at 25 °C. Figure 13 shows the spectrum of the polyelectrolyte after absorbing copper ions, i.e., the system which precipitates from the addition of the polyelectrolyte to the copper sulfate solutions. The band at 1558 cm-1, characteristic of sodium carboxylate, shifts to 1618 cm-1 in the polyelectrolyte spectrum. Both bands can be attributed to the asymmetric axial deformation of the carboxylate ions [34][35]. The band at 1618 cm-1 is characteristic of the carboxylate group bound to the metal ion, which confirms the presence of copper in the precipitated system and suggests ionic interactions between the materials [39]. The other FTIR signals are similar to that previously discussed for the ester and polyester oligomer samples. The precipitate was composed of PESFO and copper ions and was found insoluble in water, acetone, chloroform and methanol.
Figure 13. Infrared spectrum of the PESFO/copper precipitate.
27
4 FINAL REMARKSCONCLUSION Polyelectrolytes that are potentially useful for heavy metal removal were obtained from the hydrolysis of polyesters with aqueous sodium hydroxide. The precursor polyester was obtained from biodiesel that was derived from sunflower oil by epoxidation, followed by polymerization with cis-1,2-cyclohexane dicarboxylic anhydride in the presence of triethylamine. The structures of these polyesters were confirmed by FTIR and NMR analyses. PSFO produces polycarboxylates when treated with different amounts of sodium hydroxide. The structures of the polyelectrolytes were confirmed by solubility tests as well as FTIR and NMR analyses. A 1:1 PSFO:NAOH mixture was ideal for promoting the formation of carboxylate anions without breaking internal bonds, which reduced the molecular weight. PESFO analysis showed two populations, one with long and another with short relaxation times. The hydrodynamic radius calculated for the slow population was 21 nm. The obtained fractal dimension, 2.6, suggested the formation of rigid rods, resulting in substantial polyelectrolyte/water interactions. The electrical conductivity of the polyelectrolytes showed an abrupt increase at higher concentrations that was explained by solvation. As the polyelectrolyte concentration increased, the presence of carboxylate ions and counterions disrupted the solvation layer, increasing the mobility of the ions and, consequently, the electrical conductivity. The decreased solvation was in agreement with the observed polyelectrolyte aggregation. PESFO was able to remove copper ions from aqueous solutions at a pH of 7.5. The formation of ionic bonds between the polysurfactant and metal ion was responsible for the removal of up to 35 mg copper/g PESFO. The synthesized polyelectrolytes were able to be used to remove heavy metals from aqueous solutions. Acknowledgements The
authors thank the Brazilian
institution CNPq (Process numbers
405011/2013-0 and 311736/2015-7) for its financial support. statement of novelty This manuscript addresses the recovery of heavy metal ions from aqueous media by using polyelectrolytes synthesized from a renewable raw material, sunflower oil. The novelty of this study is that we can extract ions very efficiently from aqueous media without risking 28
environment contamination, unlike many natural adsorbents and some active carbons, which can lead to pollution by delivering polyaromatics. A new approach for dealing with the problem of heavy metal contamination in wastewater is introduced, and the polyelectrolyte/ion interaction, as well as the physico-chemical properties of the adsorbent in solution, are characterized.
29
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[26] K. Kamalakar, T. Satyavani, Y. Mohini, R.B.N. Prasad, M.S.L. Karuna, Synthesis of thumba, castor and sal fatty ethanolamide-based anionic surfactants, J. Surfact Deterg. 17 (2014) 637-645. [27] T. Fukuoka, S. Ikeda, H. Habe, S. Sato, H. Sakai, M. Abe, D. Kitamoro, K. Sakaki, Synthesis and intefacial properties of monoacyl glyceric acids as a new class of green surfactants, J. Oleo Sci. 61(6) (2012) 343-348. [28] N.A. Negm, A.F.M. El-Farargy, E.A.A. Halim, S. El-lboudy, A.E.S.I. Ahmed, Novel biobased nonionic surfactants: synthesis, surface activity and corrosion inhibition efficiency against aluminum alloy dissolution in acidic media, J Surfact Deterg. 17(6) (2014) 1203-1211. [29] J. Kotz, S. Kosmella, T. Beitz, Self-assembled polyelectrolyte systems, Prog. Polym. Sci. 26 (2001) 1199-1232. [30] A.V. Dobrynin, M. Rubinstein, Theory of polyelectrolytes in solutions and at surfaces, Prog. Polym. Sci. 30 (2005) 1049-1118. [31] Q.B. Reiznautt, I.T.S. Garcia, D. Samios, Oligoesters and polyesters produced by the curing of sunflower oil epoxidized biodiesel with cis-cyclohexane dicarboxylic anhydride: synthesis and characterization, Materials Science and Engineering C. 29 (2009) 2302-2311. [32] D. Samios, F. Pedrotti, A. Nicolau, Q.B. Reiznautt, D.D. Martini, F.M. Dalcin, A Transesterification Double Step Process – TDSP for biodiesel preparation from fatty acids triglycerides, Fuel Processing Technology. 90 (2009) 599-605. [32] [33] Y. Miyake, K. Yokomizo, N. Matsuzaki, Rapid determination of iodine value by 1H nuclear magnetic resonance spectroscopy, J. Amer. Oil. Chem. Soc. 75 (1998) 15-19. [33][34] N.S. Arrieta, A.M. Ilarduya, A. Alla, S.M. Guerra, Poly(ethylene terephthalate) copolymers containing 1,4-cyclohexane dicarboxylate units, European Polymer Journal. 41 (2005) 1493-1501. [34][35] R.M. Silverstein, G.C. Bassler, T.C. Morril, Identificação Espectrometrica de Compostos Organicos, sixth ed., Guanabara Koogan, Rio de Janeiro, 1991. [35][36]
J.
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poly(oxyethylene) and sodium dodecyl sulfate micelles: light scaterring, 32
electrophoresis and dialysis equilibrium studies, J. Phys. Chem. 96 (1992) 68056811. [36][37] K. Chari, The structure of the PVP-SDS complex in water, Colloids Interfaces Science. 151(1) (1992) 294-296. [37]
G.S.
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S.V.
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macromolecular solutions by a combined static and dynamic light scattering technique, International Journal of Thermophysics. 23 (2002) 161-173. [39] C.C. Wang, C.Y. Chang, C.Y. Chen, Study on metal ion absorption of bifunctional chelating/ion-exchange resins, Macromol. Chem. Phys. 202 (2001) 882-890. FIGURE CAPTIONS Figure 1. Scheme showing the synthesis of the polyelectrolyte from sunflower oil (PESFO). Figure 232.¹H NMR spectrum of PSFO. Figure 343. ¹H NMR spectrum of PESFO in D2O. Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and its polyelectrolyte (PESFO). Figure 5. FTIR spectra of polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II. Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II. PESFO is the polyelectrolyte with 1/1 ratio. Figure 65. Scheme of the polyelectrolyte synthesis in the presence of NaOH (a) and (b) the subproducts formed from an excess of NaOH.
33
Figure 76. Electrical conductivity of PESFO aqueous solutions as a function of concentration at 25 °C. Figure 87. Static light scattering intensity at 90° (I90°) as a function of the PESFO concentration at 25 °C. Figure 98. Normalized correlation functions, at different angles, for a 0.19 g·L-1 aqueous PESFO solution at 25 °C. Figure 109. UV-VIS spectra of the solutions of (-)CuSO4 (60 mmol·L-1) and (-) PESFO solution (25.0 mg·L-1) at 25°C. Figure 1110. Pictures of the PESFO solution, copper sulfate solution and PESFO/copper sulfate after mixing and equilibrium be attained. Figure 121. Copper ions removed as function of copper sulfate concentration (a) and as function of PESFO amount (b), at 25 °C and pH 7.5. Figure 12. Absorbance of 100 mmol L-1 CuSO4/150 mg PESFO after 24 h and centrifuged 20 min at 3500 rpm. TABLE CAPTIONS Table I. Molar fraction and molecular weight of epoxy-ester (EE), cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) in the polymerization reaction to produce PSFO. Table II. Methyl ester:sodium hydroxide and carboxylic acid:sodium hydroxide molar ratios used to obtain polyelectrolytes derived from PSFO. Table III. Gyration radius obtained from static light scattering measurements. TABLES Table I. Molar fraction of epoxy-ester (EE), cyclohexane-dicarboxylic anhydride (CH) and triethylamine (TEA) in the polymerization reaction.
34
Polymers
XEE
XCH
XTEA10-3
PSFO
0.33
0.67
8.5
Table II. Methyl ester:sodium hydroxide and carboxylic acid:sodium hydroxide ratios used to obtain polyelectrolytes derived from PSFO. nCOOCH3:nNaOH
1:0.5
1:0.75
1:1
1:1.5
1:2
Table III. Gyration radius obtained from static light scattering measurements. Concentration of the solution (g·L-1)
Rg (nm) values
0.068
55
0.108
54
0.132
58
0.192
64
0.296
50
35
Figure 13. Infrared spectrum of the PESFO/copper precipitate.
36
S2213-3437(17)30540-7 https://doi.org/10.1016/j.jece.2017.10.039 JECE 1949
To appear in: Received date: Revised date: Accepted date:
16-6-2017 6-10-2017 17-10-2017
Please cite this article as: Quelen Bulow Reiznautt, Irene Teresinha Santos Garcia, Bruna Girelli Furlanetto, Luiz Mario Angeloni, Dimitrios Samios, Copper removal from aqueous solutions using a polyelectrolyte derived from sunflower oil: Physico-chemical aspects, Journal of Environmental Chemical Engineering https://doi.org/10.1016/j.jece.2017.10.039 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Copper removal from aqueous solutions using a polyelectrolyte derived from sunflower oil: Physicochemical aspects Quelen Bulow Reiznautt, Irene Teresinha Santos Garcia, Bruna Girelli Furlanetto, Luiz Mario Angeloni and Dimitrios Samios*
Physical Chemistry Department, Institute of Chemistry, Federal University of Rio Grande do Sul, Brazil, e-mail [email protected]
Corresponding author: Dimitrios Samios Physical Chemistry Department, Institute of Chemistry, Federal University of Rio Grande do Sul Av. Bento Gonçalves, 9500, Porto Alegre/RS, CEP 91501-970, Brazil Fax: 55 51 3308 7304. Phone: 5551 33086290. e-mail: [email protected]
Highlights
A safer and cleaner technology to remove copper ions from aqueous media is described. Polyelectrolytes synthesized from renewable raw materials are used for Cu ion removal. The surfactants obtained from sunflower oil in aqueous media are characterized. The copper ion/polyelectrolyte interaction for is studied for wastewater recovery.
Abstract Interactions between polymers and different metal ions represent an interesting field of study due their potential use for wastewater remediation. In turn, polymers with technological applications can be obtained from renewable raw materials. In this work, polyesters weighing 2822 Da were obtained from the reaction of an epoxidized biodiesel from sunflower oil. The polyesters were reacted with aqueous sodium hydroxide solutions to obtain polyelectrolytes. The polyelectrolytes were characterized with respect to their structure by Nuclear Magnetic Resonance Spectroscopy, Infrared Fourier Transform Spectroscopy 1
and Gel Permeation Chromatography; their physicochemical behavior in aqueous media as well as their capacity to remove copper ions were characterized by electrical conductivity (EC) and Static and Dynamic Light Scattering measurements (SLS and DLS). The critical micelle aggregation concentration (CAC) was 1.310-1 g·L-1 polyelectrolyte derived from sunflower oil (PESFO). The polyelectrolyte’s EC abruptly increased when the PESFO concentration increased above the CAC.
PESFO in ionic aqueous media
developed a rigid rod morphology and had a strong interaction with water and ions (up to 5.1 g·L-1). Its capacity to remove copper(II) ions from aqueous media was determined, and the interactions between Cu/PESFO were characterized by FTIR. The polyelectrolyte removed up to 35 mg Cu(II)/g PESFO. Keywords:
sunflower
oil;
heavy
metal
removal;
water
remediation;
polyelectrolyte Introduction
Materials based on heavy metals such as Ni, Cu, Zn, Ru, Os, Rh, Au, Ag, Pd and Pt – widely used in electrodeposition, catalysis, and the industrial manufacturing of electronic components – are serious pollutants for soils, plants and groundwater [1]. Their recovery from aqueous media prevents environmental pollution and is also economically justified. Several processes used for removing metals from waste water are carried out with different types of adsorbents from natural resources. Two wastes from Araucaria angustifolia (named pinhão), one natural (PW) and one loaded with Congo red (CRP), were tested as low-cost adsorbents for Cu(II) removal from aqueous solutions [2]. Electrokinetic (EK) treatments, developed by Wang et. al, can be applied to remove heavy metals from sludge and to reuse wastewater in agriculture [3]. Active carbon has been the most popular adsorbent and is widely used in waste water treatment [4,5]. However, it can cause contamination by introducing polyaromatics. Babel et al. evaluated low cost adsorbents in wastewater treatment, including chitosan, zeolites, oxides and clay [4]. Industrial and agricultural residues have been studied in the removal of arsenic from wastewater [6]. Additionally, nanometric metal oxides, including iron oxides, manganese 2
oxide, and aluminum oxide, among others, provide high surface areas and specific affinities for the adsorption of heavy metals. Although efficient, these oxides tend to aggregate into large particles, lowering their adsorption capacities [7]. Additionally, depending on the system’s pH, these oxides can become solubilized and contaminate the environment. However, the use of renewable resources, such as vegetable oils, has attracted attention due to a great potential to produce new materials that address environmental as well as economic concerns. These materials often present properties comparable to those obtained from petrochemical sources and are capable of replacing them. These raw materials are environmentally friendly, conferring biodegradability to their derivatives, depending on the chemical transformations used [8-11]. Polymers such as oxypolymerized oils, polyesters, polyethers, polyurethanes, polyamides, epoxy resins, polyester amides, and others, produced by the chemical transformation of vegetable oils, have found industrial applications [10-16] and, in recent years, a tendency towards increasing the percentage of "green" raw materials in high value-added application products was observed [11, 17]. Polyesters present a range of structures and properties and are widely used in laminates, molding compounds, coatings, adhesives, and biomaterials for tissue engineering and drug delivery [18-20]. Polyesters produced from vegetable oils have been studied with respect to their thermal, mechanical and chemical properties [21]. Polymers represent an interesting field of study due to their potential use in wastewater remediation [22]. The removal of heavy metals, for example, can be followed by calcination in a vacuum to recover the metal in a reduced oxidation state. Radoiu et. al. obtained polyelectrolytes from the polymerization of acrylamide-acrylic acid under microwave irradiation and investigated their potential for wastewater remediation [23]. Although the synthesis of surfactants from vegetable oils is extensively reported [23-28], there are no studies on the synthesis of polyelectrolytes or even polysurfactants using vegetable oils or their fatty acids as raw materials. In this context, this paper aims to prepare water soluble polyelectrolytes from sunflower oil. In aqueous solution, polyelectrolytes dissociate into a macroion and counterions [29-30] and form organized structures in solution. This self-organizing ability allows the design of many new synthetic 3
architectures with unique properties and important commercial applications. In this work, the conversion of polyester into a polyelectrolyte was followed by FTIR and 1H NMR analysis. The polyelectrolytes were characterized with respect to their structure and physicochemical behavior in aqueous media by using static and dynamic light scattering techniques and conductivity measurements. The polyelectrolyte’s capacity for removing copper ions, as well as the interaction itself, is evaluated by photometry. 2 Methodology 2.1 Materials Sunflower oil was supplied by Farmaquimica (Porto Alegre, Brazil). Materials including triethylamine (99%), cis-1,2-cyclohexanedicarboxylic anhydride (99%) and deuterated chloroform (99.8% with 0.03% w/w tetramethylsilane (TMS)) were purchased from Aldrich Chemical Co. Methanol (99.9%), potassium hydroxide (85%), toluene (99.5%) and formic acid (85%) were purchased from Synth (São Paulo, Brazil). Acetone (99.5%), sodium hydroxide (98.1%) and hydrogen peroxide (29.0% v/v in water) were obtained from Nuclear (Diadema, Brazil), and sulfuric acid (98%) was obtained from Merck. 2.2 Preparation of the polyesters Sunflower oil was chosen as raw material to produce a polyelectrolyte because it is composed of fatty acids rich in linoleic acid, an eighteen-carbon chain with two double bonds [12]. The route to obtain the polyester (PSFO) from sunflower oil, and its subsequent conversion into polyelectrolyte, is shown in Fig. 1. The obtained polyelectrolyte will be referred to as polyelectrolyte derived from sunflower oil (PESFO).
4
Figure 1. Scheme showing the synthesis of the polyelectrolyte from sunflower oil (PESFO). The transesterification, which converts sunflower oil in its biodiesel, and the epoxidation were performed according to Reiznautt et al. [31]. A general scheme for the procedure followed in this work is displayed in Figure 1. The first step includes the transesterification of the sunflower oil. The transesterification was performed according to TDSP — transesterification double step process, as described for Samios et al. [32]. Potassium hydroxide (0.85 g) was dissolved in 50 mL methanol at 25 °C. The alcoholic solution was added, under stirring, to 100 mL of sunflower oil and heathen under reflux at 60 °C, during 1h and after, cooled down to 25 °C. In the second step, 50 mL methanol and 1.5 mL sulfuric acid (98% w/w) were added to the mixture, followed by heating to 60 °C, under stirring, for 1.5 h. After this period, the system is cooled again to 25 °C. The biodiesel phase is separated, washed with cold water and the residual alcohol is removed by evaporation under vacuum.
5
The epoxidation reaction was carried with 100 mL of toluene, 30 g of methyl ester and 10.5 mL of formic acid. Additionally, 225 mL of hydrogen peroxide (H2O2 29% in weight) were added dropwise in to the mixture. The system was maintained at 80 °C, during 10 h. After this time, the organic layer (containing the epoxide) was washed with water to remove residual hydrogen peroxide. The epoxide was concentrated in a rotary evaporator. The epoxy-esters (EE) derived from the sunflower oil biodiesel reacted with cis-1,2 cyclohexane dicarboxylic anhydride (CH), in the presence of a small amount of triethylamine (TEA), at 160 °C for 4 h. A simple 125 mL reactor equipped with reflux and continuous magnetic stirring was used. The compositions used to obtain the polyester are presented in Table 1, in terms of XEE, XCH and XTEA, where X represents the molar fraction. Table I. Molar fraction and molecular weight of epoxy-ester (EE), cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) in the polymerization reaction to produce PSFO. Polymers
XEE
XCH
XTEA10-3
PSFO
0.33
0.67
8.5
Reactant
EE
CH
TEA
Molar fraction
0.33
0.67
8.510-3
310.67(1)
154.17
101.19
Molecular Weight/g.mol-1 (1)
Average molecular weight
The polyester obtained from sunflower oil (PSFO) was purified by fractional precipitation using acetone as a solvent and water as a precipitating agent. The sample was dried under vacuum at 60 °C until it reached a constant weight and was then stored at room temperature. This procedure aimed to purify the polyester. remove the remaining saturated fatty acid methyl esters, which are not useful in the epoxidation reaction and, consequently, in the crosslinking process.
6
2.3 Preparation of the polyelectrolytes To study, by FTIR, the cleavage of the ester bonds, polyelectrolytes were synthesized through the reaction of PSFO with NaOH according to Table 2. To characterized the cleavage of the ester bonds, polyelectrolytes were synthesized through the reaction of PSFO with different amount of NaOH, according to Table 2, and analyzed by FTIR. These reactions were performed in duplicate. PSFO and sodium hydroxide reacted in 40 mL of distilled water under reflux and magnetic stirring. The reaction occurred at room temperature for 30 min. The soluble material (PESFO) was separated from the aqueous medium by precipitation with saturated aqueous NaCl solution. After filtration, the purification process consisted of resolubilizing PESFO in water and reprecipitating it in a saturated aqueous NaCl solution. The purification process was repeated three times until the supernatant reached pH~7. The product was dried at 60 °C until it reached a constant weight and then kept in a desiccator for further analysis. Table II. Methyl ester:sodium hydroxide and carboxylic acid:sodium hydroxide molar ratios used to obtain polyelectrolytes derived from PSFO. nCOOCH3:nNaOH
1:0.5
1:0.75
1:1
1:1.5
1:2
2.4 Structural characterization The precursor polyester, PSFO, was characterized by gel permeation chromatography (GPC), 1H and
13C
NMR and FTIR. The cleavage of the ester
bonds was followed by FTIR. The polyelectrolyte obtained from a 1:1 PSFO:NaOH ratio were characterized by 1H and 13C NMR and FTIR. GPC analyses were performed in a GPC Viscotek VE 2001 equipped with polystyrene/divinylbenzene Styragel Waters Millipore columns and connected to a refractive index detector, Viscotek TDA 302, using tetrahydrofuran as a solvent. The 1H and
13C
NMR spectra were obtained in a 300 MHz Innovate
instrument from Varian. The polyelectrolyte structures and the other compounds were characterized by using D2O and CDCl3 as solvents, respectively, with TMS as reference. A quantitative analysis of the hydrogen present in the signals of 1H NMR spectra were used to determine the average molar mass of the sunflower 7
oil, the conversion degree of the transesterification and epoxidation reactions, and the percent yield of the epoxidation, in accordance to Miyake et al. [32][33]. The FTIR analyses were performed in a Varian 640-IR. The liquid samples were analyzed in a sodium chloride crystal cell and the solid ones with potassium bromide pellets. The spectra were obtained in the transmittance mode, between 4000 and 500 cm−1, with 32 scans. 2.5 Characterization of polyelectrolyte in aqueous media The polyelectrolyte obtained from the 1:1 PSFO:NaOH ratio was characterized in aqueous media. The electrical conductivity measurements were collected with a Metrohm 712 conductivitometer by using an electrochemical cell with constant 0.1 cm -1. The calibration of the electrochemical cell was performed with 10-3 mol·L-1 KCl (146.9 μS·cm-1 at 25 °C). The cell was immersed in PESFO solutions with different concentrations. The average value of three determinations was used for graphic preparation. The Static and Dynamic Light Scattering (SLS and DLS) measurements were carried out with a light scattering spectrophotometer, a Brookhaven Instruments (BI)-9000, at 25 °C. The light source used was a He-Ne laser (λ=632.8 nm) with a power of 30 mW. Thirty-two solutions with concentrations varying from 5.110-4 g·L-1 to 3.500 g·L-1 were filtered with hydrophilic filters of 0.45 µm porosity into optical cuvettes that were free of dust. The SLS measurements took place at 90° and DLS signals were obtained by varying the observation angle for each solution with values of 45, 60, 75, 90, 105, 120, 135 and 145°. The polyelectrolyte’s capacity to remove copper ions was studied by mixing copper sulfate solutions with concentrations varying from 8 to 80 mmol·L -1 with 25 to 150 mg of PESFO at a pH of ~7.5, corresponding to 42 systems. Different volumes (630 uL to 4 mL) of 250 mmol L-1 CuSO4 solutions were used to obtain a final concentration from 8-100 mmol L-1 in a total Volume of 10 mL Also, polyelectrolyte was solubilized and added to the system: to obtain 25 mg to 150 mg PESFO we added 1-6 mL 25 mg/mL PESFO. The CUSO4/PESFO systems were stirred at 25 °C for 24 h in order to attain the equilibrium condition. Then, the systems were centrifuged at 3500 rpm 8
for 20 min. When PESFO and copper sulfate solutions are mixed, flocculation is responsible for a strong light scattering, so the equilibrium condition is important to quantify the copper in solution. To test the effect of the temperature and pH on the removal of copper ions, a test was conducted with the system composed of 100 mmol L -1 CuSO4 and 125 mg PESFO, after the equilibrium condition to be attained, by submitting it to pH 1 and to the temperatures of 40°C and 50°C. The concentration of copper in the solutions were determined by photometry at 810 nm. Photometry measurements were performed on a Shimadzu -UV1601PC Spectrophotometer at 25 °C. The concentration of copper in the solutions were determined by photometry at 810 nm. Photometry measurements were performed on a Shimadzu -UV1601PC Spectrophotometer at 25 °C. The interaction between copper and polyelectrolyte was analyzed by FTIR spectroscopy after the samples were washed, precipitated with distilled water, and dried to a constant weight. 3 Results and discussion This discussion firstly focuses on the structural characterization of the polyesters (PSFO) and polyelectrolytes (PESFO) obtained from sunflower oil; It is demonstrated that the polyelectrolyte obtained with a 1:1 sodium hydroxide:PESFO ratio is the best product for removing copper ions. In the second part, the characteristics of this electrolyte in aqueous media, as well as its copper removal capacity, will be addressed. 3.1 Structural characterization of polyesters and polyelectrolytes The PSFO The molecular weight and polydispersity of PSFO, as determined by GPC are 2820 and 1.7, respectively (GPC chromatogram is displayed in Supplementary Material 1). The sunflower oil is mainly composed of linoleic fatty acids, which has two carbon double bonds (between C9-10 and between C12-13 - see scheme in Figure 1). The epoxidation reaction converts the double bonds into epoxide esters (EE), which are precursors to the polymerization reaction.
9
The steric hindrance from the proximity of the epoxy rings prevents the growth of a polymer chain. Figure 2 shows the 1H NMR spectrum of PSFO obtained in CDCl3. The 1H NMR,
13C
NMR and FTIR spectra of the sunflower oil and its intermediates,
methyl esters and epoxy esters were presented in our previous work [31].
Figure 2.1 ¹H NMR spectrum of PSFO. Peaks situated between δ = 2.95 and 3.10 ppm, corresponding to the hydrogen atoms of the oxirane groups, cannot be observed, which indicates the opening of all the epoxide rings. Signals at δ = 1.51 and 1.72 ppm, present in epoxy esters, are also absent, which indicates the disappearance of the -CH2 groups bonded to the oxirane rings [33, 34] . The peak situated at δ = 0.86 ppm (peak H) corresponds to the terminal methyl groups of the fatty acid from the precursor sunflower oil. The signals at δ = 1.24 (G), 1.58 (F) and 2.29 ppm (D) are similar to that observed for methyl ester groups from fatty acid chains and are attributed to the internal -CH2 groups. At δ = 3.65 ppm, (I) is observed and assigned as the hydrogen signal of the -CH3 from the ester groups, as observed in the spectra of methyl esters and their derived epoxy esters [31]. The signal at δ = 4.97 ppm (N) corresponds to the -CH groups of the methyl ester chains 10
bonded to the anhydride, as suggested in the chemical structure shown in Figure 2; this signal indicates the cleavage of the epoxide ring and the addition of an anhydride to the methyl ester chain to form an internal ester bond. The appearance of two signals at δ = 2.83 ppm (O) and δ = 1.77 and a peak at 2.05 ppm (P) are due to the -CH and -CH2 groups, respectively, of the anhydride cyclohexane rings that were added to the ester chains [33] [34, 35]. This result is confirmed by 13C NMR (see Supplementary Material 12). The behavior of the polyelectrolyte in different solvents differs from that of the precursor PSFO. PSFO is completely soluble in polar organic solvents, such as chloroform, acetone and tetrahydrofuran, but insoluble in water. However, the obtained polyelectrolytes were soluble in water and insoluble in those same polar organic solvents. Figure 3 shows the 1H NMR spectrum of the electrolyte PESFO in D2O. The change of deuterated solvent was responsible for the changes in the values of the chemical shifts. The spectrum of Figure 3 does not show a signal at 3.65 ppm but instead presents a signal at δ=3.47 ppm. The methyl groups of the terminal ester could not be verified; however, a considerable decrease in the signal intensity is observed, which is confirmed by the FTIR analysis. At δ=0.77 ppm, a peak is observed corresponding to the hydrogens of the terminal methyl groups of the fatty acid, whereas the signals between 1.10 and 2.70 ppm correspond to the hydrogens of the internal CH and CH2 groups [35].
11
Figure 3.2 ¹H NMR spectrum of PESFO in D2O. Figure 4 shows the infrared spectrum of polyelectrolytes PESFO compared with its precursor, PSFO.
12
Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and its polyelectrolyte (PESFO). The FTIR spectrum of the polyelectrolyte shows bands at 1562 cm -1 and 1407 cm-1 that are not present in the PSFO spectrum. An intense band at 1562 cm-1 corresponds to the asymmetrical axial deformation of the carboxylate ion (asCOO-), and a weak band, observed at 1407 cm-1, is assigned to the symmetrical axial deformation of the carboxylate ion (sCOO-) [34] [35], which confirms the formation of sodium carboxylate. In the PSFO spectrum, the intense absorption band at approximately 1736 cm-1 is attributed to the C=O of the aliphatic esters. The C–O bands, attributed to the ester groups, are observed in the region between 1300 and 1100 cm -1 [34][35]. These same bands are also observed in the PESFO spectrum. However, these bands are not attributed to the terminal methyl ester groups but to the internal ester bonds instead. The PESFO spectrum (Figure 4) clearly shows a low-intensity, broad band at approximately 3428 cm-1, which can be attributed to the cleavage of the ester bonds. To confirm this interpretation and follow the cleavage of the ester bonds, polyelectrolytes were synthesized with different molar ratios of terminal groups by varying the PSFO:NaOH ratios (see Table 2). In Figure 54 a broad band O-H is observed at approximately 3428 cm -1, which could be attributed to carboxylic acids, alcohols or to the presence of moisture; however, carboxylic acids show a wide, intense band from 3300 to 2500 cm-1, due to the superposition of the C-H from the alquil group with O-H, which was not observed [34][35].
13
Figure 5. FTIR spectra of polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II.
14
Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II. PESFO is the polyelectrolyte with 1/1 ratio. An increase in the intensity of the bands at 3428 cm-1 observed in Figure 54 with the increase of the amount of sodium hydroxide suggests that this band originates from the alcohol formed by the cleavage of the internal ester bonds between the anhydride and the epoxy-ester chain, as proposed in the scheme in
15
Figure
6
5.
Figure 65. Scheme of the polyelectrolyte synthesis in the presence of NaOH (a) and (b) the subproducts formed from an excess of NaOH. Additional sodium hydroxide promotes the cleavage of not only the external ester bonds but also the internal ester groups; however, the hygroscopicity of the product increases with the number of sodium carboxylate groups, and it would be difficult to ensure that the sample does not contain moisture. The increase in the number of the carboxylate ions with the amount of sodium hydroxide used can be confirmed through the band at 1407 cm -1, which is marked in Figure 54 and is due to sCOO-. The intensity of this band increases as the nH3COOC-/nNaOH ratio decreases. A wide band at 34303428 cm-1 is observed for the polyelectrolytes synthesized with more NaOH (1:1, 1:1.5 and 1:2); however, this signal does not appear in the FTIR spectra of the polyelectrolytes synthesized with less NaOH (1:0.5 and 1:0.75). The relative intensities of the two absorption bands at 17341730 cm-1 and 15701562 cm-1 are important to be observe. The band at 17341730 cm-1 is characteristic of C=O from the internal esters of the polyelectrolyte. The band at 15701562 cm-1 is due to the carboxylate anion. As the amount of NaOH increases, I1730/I1562 decreases increases. This behavior indicates that increased 16
amounts of sodium hydroxide promote the cleavage of some internal ester bonds in the polyelectrolyte, between the anhydride and the epoxidized acid chain, to form alcohol groups. This interpretation is confirmed by the band at 34303428 cm-1[35]. Thus, we can conclude that, under mild conditions, i.e., with less NaOH, there was no cleavage of the internal ester linkages and therefore no chain scission was observed. 3.2 Characterization of PESFO in aqueous media for copper removal The polyelectrolyte obtained by mixing polyester and sodium hydroxide in a 1:1 ratio was characterized in aqueous media, at 25 °C, with respect to its physicochemical behavior in aqueous solutions as well as its efficiency for copper ion removal. 3.2.1 Physicochemical behavior of the polyelectrolyte in aqueous media Figure 76 shows the electrical conductivity () as a function of the PESFO concentration. The conductivity only slightly increases for PESFO concentrations below 1.310-1 g·L-1, followed by an abrupt increase at higher concentrations. This behavior differs from that observed for polymer aggregation, which commonly shows a decrease in the slope of the conductivity curves when the concentration exceeds the critical aggregation concentration (CAC) [35, 36][36,37].
17
Figure 76. Electrical conductivity of PESFO aqueous solutions as a function of PESFO concentration at 25 °C. The raw material used to prepare PESFO has approximately 70% w/w linoleic acid, which has two double bonds, allowing it to produce more carboxylate ions per polymer chain. As the electrolyte concentration increases, the effective headgroup area diminishes and the distance of electrostatic repulsion is reduced, which favors aggregation. Polymer aggregation would further decrease the conductivity. The counterion
condensation
theory,
described
by
Manning,
assumes
that counterions can condense onto polyelectrolytes until the charge density is reduced below a certain critical value. This behavior could be responsible for the decrease in the solvation of the polyelectrolytes and, consequently, the increase in ionic mobility [37]. The reason for this abrupt increase of conductivity at higher concentration, is the increasing in the mobility of the ions; as the PESFO concentration increases, the presence of carboxylate ions and counterions disrupted the solvation layer, increasing the mobility of the ions and, consequently, the electrical conductivity. This phenomenon’s effect on the removal of copper ions will be discussed in Section 3.2.2. 18
Fig. 87 displays the scattered light intensities of the aqueous solutions, measured at 90°, as a function of the PESFO concentration. Low intensities of scattered light can be observed for concentrations between 5.110-4 and 1.2101
g·L-1 and vary slightly with concentration. An increase in the light scattered
intensity occurs for concentrations higher than 1.210-1 g·L-1, which is similar to the concentration at which the abrupt increase in the conductivity curve is observed (see Fig. 87). Higher polyelectrolyte concentrations increase the ionic strength of the media, which disrupts the solvation layer and promotes polyelectrolyte aggregation. Similar behavior is observed when Cu +2 and Co+2 were added to the polyelectrolyte solution.
Figure 87. Static light scattering intensity at 90° (I90°) as a function of the PESFO concentration at 25 °C. The gyration radius (Rg) values were determined by SLS using the static intensity dissymmetry method (see Supplementary Material 23). The Rg values for different polyelectrolyte concentrations at 25°C are shown in Table III. Table III. Gyration radius obtained from static light scattering measurements.
19
Concentration of the solution (g·L-1)
Rg (nm) values
0.068
55
0.108
54
0.132
58
0.192
64
0.296
50
Dynamic light scattering (DLS) analyses were performed for eight solutions with 0.07, 0.09, 0.19, 0.39, 0.78, 1.13, 2.43 and 3.50 g·L-1 PESFO. These solutions presented well defined correlation functions and their scaling intensities are higher than 30 kcps at all angles. Concentrations lower than 0.07 g·L-1 could not be used because they did not give correlation functions. Fig. 109 shows the normalized correlation functions for a 0.19 g·L -1 aqueous PESFO solution. As expected, the correlation functions decay faster as the scattering angle increases, as shown in Figure 98. Small scattering angles provide information about the larger features of the structures, and thus slower chain movements are observed. Similar behavior was also observed for the other solutions.
20
Figure 98. Normalized correlation functions, at different angles, for a 0.19 g·L -1 aqueous PESFO solution at 25 °C. The relaxation times were obtained from the correlation functions by fitting two exponential decays that correspond to populations with slow (t 1) and fast (t2) modes. The presence of two populations of light scattering species was observed for all the studied concentrations and scattering angles. These two populations have practically the same contribution for the majority of the solutions. This behavior suggests that, after the micelle formation at the CAC, the micelles continue to grow, i.e., by the addition of molecules at increased concentrations. The relaxation times were used to determine the diffusion coefficients D 1 and D2, which are related to the longer and shorter relaxation times, respectively. The diffusion coefficient and the hydrodynamical radius can be obtained by analyzing the DLS results (see Supplementary Material 34). The diffusion coefficients at infinite dilution were D1,0=1.0110-11 m2·s-1 and D2,0=2.7310-11 m2·s-1, referring to the slow and the fast modes, respectively. The value of Rh calculated for the population with a small diffusion coefficient was 21 nm. The ratio =Rg/Rh, the fractal dimension, compares the hydrodynamic interactions with the geometric dimensions of the molecule and gives different 21
values according to the molecular architecture: for homogeneous spheres, < 1; for microgels, < 0.5; for random coils, 1.5 2.0 and for rigid rods, 2 [38]. The fractal dimension, calculated from the average Rg values shown in Table III and Rh, 2.6, suggests that polyelectrolytes in solution form rigid rods. 3.2.2 Interaction between PESFO and copper ions in solution Figure 109 shows the UV/vis spectra in the region between 200 and 900 nm of the polyelectrolyte and copper sulfate solutions. The absorbance of PESFO, even in concentrations higher than that used in this work, does not interfere in the determination of the copper sulfate concentration at 800810 nm.
Figure 109. UV-VIS spectra of the solutions of (-)CuSO4 (60 mmol·L-1) and (-) PESFO solution (25.0 mg·L-1) at 25°C. When mixed with copper sulfate solution, the polyelectrolyte precipitates. The precipitate is blue, leaving the solution to become colorless (see Figure 1110).
22
23
Figure 1110. Pictures of the: a) PESFO solution, b) copper sulfate solution and c) PESFO/copper sulfate after mixing. A temptation of fitting isotherms as Langmuir, Freundlich or Ships, with ratio between copper removed/PESFO versus CuSO4 equilibrium concentration, did not show correlation. Figure 12-a11-a shows that, independent of the copper coper sulfate concentration, copper is removed in the same quantity the copper ions removal depends linearly on the PESFO amount (Figure 12-b11-b).
24
Figure 121. Copper ions removed as function of copper sulfate concentration (a) and as function of PESFO amount (b), at 25 °C. The number of copper ions removed is proportional to the amount of PESFO added to the system, independent of the copper concentration in the initial solution. In all the concentrations of copper sulfate that were treated with a fixed amount of PEPESFO, approximately the same amount of copper was removed. The time necessary for the conclusion of this process depends of the ion concentration, PESFO concentration, temperature and pH. During the experiments, we observed that the PESFO precipitates immediately after it bonds to copper ions . 25
Figure 12 shows the absorbance of systems composed of 100 mmol L -1 CuSO4/150 mg PESFO after the equilibrium to be attained (after 24 h and centrifuged 20 min at 3500 rpm) for the following conditions: 25 °C and pH 7.5 with: 25°C and pH 1; pH ~7.5, 40 and 50 °C. In acid media PESFO does not present the same efficiency in copper removal, because PESFO is protonated. When the system is submitted to higher temperature, copper is more soluble in aqueous solution and the efficiency in copper removal decreases. Alkaline conditions were not investigated, because, as discussed in previous sessions, the cleavage of the polyelectrolyte chains would produce unreliable results.
0
pH7.5, 25 C 0
pH 1.0, 25 C 0
pH 7.5, 40 C 0
Absorbance
pH 7.5, 50 C
500
600
700
800
900
Wavelength (nm)
Figure 12. Absorbance of 100 mmol L-1 CuSO4/150 mg PESFO after 24 h and centrifuged 20 min at 3500 rpm. The precipitation, as shown above, occurs due to a decrease in the effective headgroup area that reduces the electrostatic repulsion; the electrostatic repulsion is responsible for the stability of the colloidal PESFO in solution. The polymer aggregation is mediated by copper ions. Thus, from the ratio between the quantity of removed ions and the amount PESFO added, it is possible to determine the PESFO’s capacity to remove
26
copper ions. From the average of all the obtained values, it was observed that 1 g of PESFO is able to remove 35 mg Cu+ 2 at 25 °C. Figure 13 shows the spectrum of the polyelectrolyte after absorbing copper ions, i.e., the system which precipitates from the addition of the polyelectrolyte to the copper sulfate solutions. The band at 1558 cm-1, characteristic of sodium carboxylate, shifts to 1618 cm-1 in the polyelectrolyte spectrum. Both bands can be attributed to the asymmetric axial deformation of the carboxylate ions [34][35]. The band at 1618 cm-1 is characteristic of the carboxylate group bound to the metal ion, which confirms the presence of copper in the precipitated system and suggests ionic interactions between the materials [39]. The other FTIR signals are similar to that previously discussed for the ester and polyester oligomer samples. The precipitate was composed of PESFO and copper ions and was found insoluble in water, acetone, chloroform and methanol.
Figure 13. Infrared spectrum of the PESFO/copper precipitate.
27
4 FINAL REMARKSCONCLUSION Polyelectrolytes that are potentially useful for heavy metal removal were obtained from the hydrolysis of polyesters with aqueous sodium hydroxide. The precursor polyester was obtained from biodiesel that was derived from sunflower oil by epoxidation, followed by polymerization with cis-1,2-cyclohexane dicarboxylic anhydride in the presence of triethylamine. The structures of these polyesters were confirmed by FTIR and NMR analyses. PSFO produces polycarboxylates when treated with different amounts of sodium hydroxide. The structures of the polyelectrolytes were confirmed by solubility tests as well as FTIR and NMR analyses. A 1:1 PSFO:NAOH mixture was ideal for promoting the formation of carboxylate anions without breaking internal bonds, which reduced the molecular weight. PESFO analysis showed two populations, one with long and another with short relaxation times. The hydrodynamic radius calculated for the slow population was 21 nm. The obtained fractal dimension, 2.6, suggested the formation of rigid rods, resulting in substantial polyelectrolyte/water interactions. The electrical conductivity of the polyelectrolytes showed an abrupt increase at higher concentrations that was explained by solvation. As the polyelectrolyte concentration increased, the presence of carboxylate ions and counterions disrupted the solvation layer, increasing the mobility of the ions and, consequently, the electrical conductivity. The decreased solvation was in agreement with the observed polyelectrolyte aggregation. PESFO was able to remove copper ions from aqueous solutions at a pH of 7.5. The formation of ionic bonds between the polysurfactant and metal ion was responsible for the removal of up to 35 mg copper/g PESFO. The synthesized polyelectrolytes were able to be used to remove heavy metals from aqueous solutions. Acknowledgements The
authors thank the Brazilian
institution CNPq (Process numbers
405011/2013-0 and 311736/2015-7) for its financial support. statement of novelty This manuscript addresses the recovery of heavy metal ions from aqueous media by using polyelectrolytes synthesized from a renewable raw material, sunflower oil. The novelty of this study is that we can extract ions very efficiently from aqueous media without risking 28
environment contamination, unlike many natural adsorbents and some active carbons, which can lead to pollution by delivering polyaromatics. A new approach for dealing with the problem of heavy metal contamination in wastewater is introduced, and the polyelectrolyte/ion interaction, as well as the physico-chemical properties of the adsorbent in solution, are characterized.
29
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Characterization
of
macromolecular solutions by a combined static and dynamic light scattering technique, International Journal of Thermophysics. 23 (2002) 161-173. [39] C.C. Wang, C.Y. Chang, C.Y. Chen, Study on metal ion absorption of bifunctional chelating/ion-exchange resins, Macromol. Chem. Phys. 202 (2001) 882-890. FIGURE CAPTIONS Figure 1. Scheme showing the synthesis of the polyelectrolyte from sunflower oil (PESFO). Figure 232.¹H NMR spectrum of PSFO. Figure 343. ¹H NMR spectrum of PESFO in D2O. Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and its polyelectrolyte (PESFO). Figure 5. FTIR spectra of polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II. Figure 4. Infrared spectra of the polyester derived from sunflower oil (PSFO) and polyelectrolytes obtained from PSFO using different COOCH3:sodium hydroxide molar ratios, according to Table II. PESFO is the polyelectrolyte with 1/1 ratio. Figure 65. Scheme of the polyelectrolyte synthesis in the presence of NaOH (a) and (b) the subproducts formed from an excess of NaOH.
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Figure 76. Electrical conductivity of PESFO aqueous solutions as a function of concentration at 25 °C. Figure 87. Static light scattering intensity at 90° (I90°) as a function of the PESFO concentration at 25 °C. Figure 98. Normalized correlation functions, at different angles, for a 0.19 g·L-1 aqueous PESFO solution at 25 °C. Figure 109. UV-VIS spectra of the solutions of (-)CuSO4 (60 mmol·L-1) and (-) PESFO solution (25.0 mg·L-1) at 25°C. Figure 1110. Pictures of the PESFO solution, copper sulfate solution and PESFO/copper sulfate after mixing and equilibrium be attained. Figure 121. Copper ions removed as function of copper sulfate concentration (a) and as function of PESFO amount (b), at 25 °C and pH 7.5. Figure 12. Absorbance of 100 mmol L-1 CuSO4/150 mg PESFO after 24 h and centrifuged 20 min at 3500 rpm. TABLE CAPTIONS Table I. Molar fraction and molecular weight of epoxy-ester (EE), cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) in the polymerization reaction to produce PSFO. Table II. Methyl ester:sodium hydroxide and carboxylic acid:sodium hydroxide molar ratios used to obtain polyelectrolytes derived from PSFO. Table III. Gyration radius obtained from static light scattering measurements. TABLES Table I. Molar fraction of epoxy-ester (EE), cyclohexane-dicarboxylic anhydride (CH) and triethylamine (TEA) in the polymerization reaction.
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Polymers
XEE
XCH
XTEA10-3
PSFO
0.33
0.67
8.5
Table II. Methyl ester:sodium hydroxide and carboxylic acid:sodium hydroxide ratios used to obtain polyelectrolytes derived from PSFO. nCOOCH3:nNaOH
1:0.5
1:0.75
1:1
1:1.5
1:2
Table III. Gyration radius obtained from static light scattering measurements. Concentration of the solution (g·L-1)
Rg (nm) values
0.068
55
0.108
54
0.132
58
0.192
64
0.296
50
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Figure 13. Infrared spectrum of the PESFO/copper precipitate.
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