Cation Exchange Properties of a Terpolymer: Synthesis and Characterization

Transcription

1 July 2010, Volume 1, No. 1 International Journal of Chemical and Environmental Engineering Cation Exchange Properties of a Terpolymer: Synthesis and Characterization M. Riswan Ahamed 1, R. Azarudeen 1, M. Karunakaran 2, T. Karikalan 1, R. Manikandan 1, A. Burkanudeen 1 * 1 PG & Research Department of Chemistry, Jamal Mohamed College (Autonomous) Tiruchirappalli , Tamil Nadu, India 2 Department of Science and Humanities, P.A. College of Engineering and Technology, Pollachi , Tamil Nadu, India *Corresponding author: a_deen@rediffmail.com Abstract 4-hydroxybenzoic acid - thiourea - formaldehyde (4-HBTUF) terpolymer has been prepared by polycondensation technique in 2:3:5 mole ratio using 2M H 2 SO 4 as a catalyst was proved to be a selective chelation ion-exchange for certain metals. The characterization and the structural elucidation of the prepared terpolymer were confirmed by elemental analysis, FTIR and 1 H-NMR spectral studies. The morphological feature of the 4-HBTUF tepolymer was established by scanning electron microscopy (SEM). The gel permeation chromatography (GPC) was used to determine the average molecular weight of the terpolymer resin. The cation-exchange properties of the terpolymer were determined by batch equilibrium method. The method involves ion-exchange behavior of the terpolymer with specific cations like Cd, Mg, Fe 3+, Cu, and UO 2 in various electrolytes, wide ph ranges and different time intervals. The results of the ion-exchange studies reveal that the 4-HBTUF terpolymer was found to be an excellent cation-exchanger for selective metal ions. Hence the resin can be used to recover metal ions from waste solutions and used for the purpose of purification of waste water and for the removal of iron from boiler water. The ion-exchange capacity of the terpolymer has also been compared with the other commercial resins. Keywords: Terpolymer, FTIR, Morphology, Gel Permeation Chromatography, Chelation Ion-exchange Study. 1. Introduction Over the past few decades, significant research work has been done on enhancing the properties of new synthesized ion-exchange terpolymers for the treatment of waste water and pollution control. Ion-exchange may be defined as the reversible exchange of ions between the substrate and surrounding medium. The removal of heavy metal ions from industrial wastewater has been given much attention in the last decade, as the heavy metals released into the environment pose potential threat, because of their tendency to accumulate in living organisms. The necessity to reduce the amount of heavy metal ions pollution in wastewater streams has led to an increasing interest in ion-exchange terpolymers [1-6]. Therefore, attempt has been made to synthesize terpolymer and to evaluate the ion-exchange properties. Various combinations of thiourea based terpolymers like 8-hydroxyquinoline-5-sulfonic acid thiourea - formaldehyde, ortho-nitro phenol thiourea paraformaldehyde and anthranilic acid thiourea - paraformaldehyde have been synthesized by condensation polymerization and reported for their chelation ionexchange properties toward selective metal ions [7-9]. Ion-exchange terpolymer derived from 2, 2- dihydroxybiphenyl-urea-formaldehyde has been reported as an effective ion-exchanger against certain transition metal ions [10]. The chelating behavior of the synthesized resin was studied using metal ions Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) and the sorption capacities of the resin follows the order Pb(II)<Zn(II)<Cd(II)<Cu(II)<Ni(II) [11]. Cation-exchange behavior of a reported terpolymer show higher selectivity for Cu (II), Zn (II) and Co (II) as compared to Ni (II), Pb (II) and Cd (II) metal ions [12]. p- Cresol and oxamide with formaldehyde terpolymer was a selective chelating ion-exchange resin for Fe 3+, Cu, Ni, Co, Zn, Cd and Pb ions [13]. Ion-exchange technique can be used to remove traces of ionic impurities from water/process liquors and gives out a product of ultra pure quality in a simple efficient and techno-economically viable manner. Hence, the present article describes the preparation, characterization and ion-exchange properties of 4-hydroxybenzoic acid and thiourea with formaldehyde terpolymer. 2. Experimental 2.1 Chemicals and Reagents 4-hydroxybenzoic acid (SRL, Mumbai) and thiourea

2 (Merck, India) were purified by rectified spirit. Formaldehyde (37%), metal nitrates of chosen metals (AR grade, Merck) was used as received. All the other chemicals, solvents and the indicators were of analytical grade procured from Qualigens fine chemicals, Mumbai, India. Standardized Na 2 EDTA was used as a titrant for all the complex metric titrations. Double distilled water was used for all the experiments. 2.2 Terpolymerization The terpolymer resin was synthesized by the condensation reaction of 4-hydroxybenzoic acid (0.2 mol), thiourea (0.3 mol) and formaldehyde ( mol) using 2M H2SO4 as the reaction medium and refluxed with occasional shaking at 140 ± 2 C for 4 h [8-13]. The reaction mixture was then cooled, poured into crushed ice with constant stirring and left. OH COOH 4-Hydroxybenzoic acid Thiourea Formaldehyde OH COOH + H 2 N C 2M H 2 SO 4 H 2 C NH C S S NH ± 2 C 4 h NH + CH 2 O H 2 C 4-HBTUF Terpolymer Scheme 1. Reaction route of 4-HBTUF terpolymer OH COOH Overnight. The dark brown coloured resin separated out was washed with warm water and methanol. It was then filtered off to remove the unreacted monomers. Finally, the terpolymer was air dried. The dried sample was then dissolved in 8% NaOH and regenerated using 1:1(v/v) HCl/water. It was filtered off and cured in an air oven at 75 C for 24 h. The yield of the terpolymer was found to be 83% and the reaction route is shown in Scheme Spectral analysis The FTIR spectrum of the synthesized terpolymer had been scanned in KBr pellets on a Bruker (Model Tensor 27) spectrophotometer to identify the linkages and the functional groups. The proton NMR spectrum of the terpolymer was recorded in DMSO-d 6 solvent using Bruker 400 MHz. 2.4 Surface analysis and GPC n The average molecular weight of the 4-HBTUF terpolymer was determined by gel permeation chromatography in Shimadzu using DMSO column. The surface analysis of the 4-HBTUF terpolymer was examined by scanning electron microscope Hitachi (Model S-3000H). 2.5 Ion-exchange characteristics The cation-exchange properties of 4-HBTUF terpolymer were studied by batch equilibrium method. The finely ground terpolymer was used to determine the metal ion uptake capacity of the metal ions like Cd, Mg, Fe 3+, Cu, and UO 2 in the form of their aqueous metal nitrate solutions. Metal ion binding capacity for the terpolymer was studied in various electrolytes with different concentrations, ph ranges and time intervals. 2.6 Effect of metal ion uptake in different electrolytes with variation in concentrations The prepared 4-HBTUF terpolymer (25 mg) was taken in a pre-cleaned glass bottles and each of the electrolytes (25 ml) such as NaCl, NaNO 3, NaClO 4, and Na 2 SO 4 in different concentrations viz. 0.1, and M. The ph of the suspension was adjusted to the required value either by adding 0.1 M HCl or 0.1 M NaOH. This suspension was mechanically stirred for 24 h at 25 C for the swelling of the terpolymer. To this suspension 2 ml of 0.1 M of specific metal ion solution was added and vigorously stirred for 24 h at 25 C. It was then filtered off and washed with distilled water. The filtrate and the washings were collected and then the amount of metal ion was estimated by titrating against standard Na 2 EDTA solution. A blank experiment was also performed following the same procedure without the polymer sample. The amount of metal ions taken up by the polymer in the presence of a given electrolyte can be calculated from the difference between the actual titre value and that of from the blank. The chelating mechanism of the terpolymer resin is as follows. (Res.A - )B + + C + (solution) (Res.A - )C + + B + (solution) (1) where, Res., A -, B +, and C + represents the polymeric resin, the anion attached to the polymeric framework, the active or mobile cation, and the metal ion respectively. 2.7 Effect of the distribution of metal ions at various ph The distribution of each one of the metal ions at various ph ranging from 3 to 5.5 between the polymer phase and the aqueous phase were determined in the presence of 1 M NaNO 3 at 25 ºC. The distribution ratio K D, may be defined as Weight (in mg) of metal ions taken up by 1 g of the resin sample K D = (2) Weight (in mg) of metal ions present in 1 ml of the solution 2.8 Effect of rate of metal ion uptake 8

3 A series of experiments were carried out to determine the amount of metal ion adsorbed by the terpolymer at specific time intervals. 25 mg of the polymer sample was mechanically stirred with 25 ml of 1 M NaNO 3 to allow the polymer to swell. The ph of the suspension was adjusted to the required value by adding either 0.1 M HCl or 0.1 M NaOH. It is assumed that under the given experimental conditions the state of equilibrium is established within 24 h at 25 ºC. The rate of metal ion uptake is expressed as the percentage of the metal ion uptake after a specific time related to that of the state of equilibrium. It is given as, Amount of metal ion adsorbed Metal ion uptake = (3) Amount of metal ion adsorbed at equilibrium 3. Result and discussion The 4-hydroxybenzoic acid and thiourea with formaldehyde (4-HBTUF) terpolymer was soluble in solvents like N,N-dimethylformamide (DMF), tetrahydrofuran (THF), dimethylsulphoxide (DMSO), and aqueous sodium and potassium hydroxide solutions. 3.1Physicochemical and Elemental Analysis The physicochemical parameters such as moisture content, solid percentage, void volume fraction, true density and sodium exchange capacity of the 4-HBTUF terpolymer are shown in Table I. The results of the elemental analysis of the terpolymer are presented in Table 2. Based on the analytical data, the empirical formula of the terpolymer is found to be C 19 H 20 N 2 O 6 S which is in good agreement with the calculated values of C, H, N and S. 3.2 Spectral Studies The recorded FTIR spectrum of the 4-HBTUF terpolymer is shown in Fig. 1 and the important IR bands along with their assignments appeared in the spectrum is presented in Table 3. The spectrum shows a strong band at 3479 cm -1 due to the ν (O-H) stretching of Ar-OH group. The band appeared at 2640 cm -1 is due to aromatic ν (C-H) stretching group. The weak band at 2872 cm -1 is due to the ν (C-H) stretching of methylene group. The band at 1672 cm -1 may be assigned to ν (C=O) stretching of ketonic group of acid. The band appeared at 3376 cm -1 is due to ν NH-stretching vibrations. Table 1.Physicochemical characteristics of 4-HBTUF Terpolymer Properties Moisture (%) Solid (%) True density (dry resin) g/cm 3 Void volume fraction Sodium exchange capacity ( mmol/g dry resin) Value (SD) 10.4 ± ± ± ± ± 0.40 The band appeared at 1299 cm -1 and 916 cm -1 may be due to ν C=S stretching and bending vibration respectively. The band clearly appeared around 1116 cm -1 9 may be assigned due to the ν C-N stretching vibration. The tetra substitution in the benzene ring is established by the presence of the medium bands at 1022 and 758 cm -1 are assumed ν (C-H) bending vibrations [14-17]. Table 2.Elemental analysis of 4-HBTUF Terpolymer Sample name 4-HBTUF terpolymer Analysis (%) Calculated (Found) C H N S (55.21) 4.86 (4.21) 6.81 (6.34) Fig.1 FTIR spectrum of 4-HBTUF terpolymer 7.79 (7.41) 1 H NMR spectrum of 4-HBTUF terpolymer is depicted in Fig. 2 and the spectral data are presented in Table 4. The NMR spectrum reveals that the signal around 3.3 δ is due to the methylene proton of the Ar- CH 2 -N linkage. The multiple signals observed in the range of δ indicate the presence of aromatic protons. The signal displayed at 8.4 δ may be due to the carboxylic proton of Ar-COOH group. The signal in the region of 8.7 δ is assigned to the OH of Ar-OH group. An intense signal appeared in the region of 5.5 δ is assigned to the NH protons of in the terpolymer [18]. Table. 3 FTIR Spectral data of 4-HBTUF Terpolymer Vibrational mode -OH of Ar-OH group Methylene(-CH 2) stretching >C=O stretching (carboxylic ketone) 1,2,3,5-substituted benzene ring (C-N) stretching Aromatic ring stretching (C-H) NH bridge C=S stretching & bending Frequency (cm -1 ) Reported Observed & & 916.6

4 Table 4. 1 H NMR Spectral data of 4-HBTUF Terpolymer Assigned protons Aromatic proton (Ar-H) Protons of NH bridge Ar-COOH group Expected chemical shift (δ) ppm Observed chemical shift (δ) ppm Fig.2 1 H NMR spectrum of 4-HBTUF terpolymer 3.3 Surface analysis and molecular weight measurements The average molecular weight of the 4-HBTUF terpolymer is determined by gel permeation chromatography. The number average molecular weight ( Mn ) and weight average molecular weights ( Mw ) are 5575 and 5764 respectively. The polydispersity index ( Mw / Mn ) is found to be 33. The average molecular weight ( Mz ) of the terpolymer is The polydisperstiy ( Mz / Mn ) is 66. The data obtained from molecular weight measurements are presented in Table Morphological studies The typical microphotograph at 6000 magnification from SEM of 4-HBTUF is shown in Fig. 3. The SEM image shows the surface feature of the sample. The photograph clearly shows that the terpolymer has deep shallow pits with more amorphous character and less close packed surface. Further, it is interesting to note that the high porosity and less close packed nature of the terpolymer provide enough space for the metal ions of specific size to be accommodated in the pores. Hence, these kinds of polymers can act as effective ionexchangers. Compound Table. 5 GPC for molecular weight measurements Mn Mw Mz Polydispersity Mw / Mn Polydispersity Mz / Mn Phenolic (Ar-OH) Ar-CH 2- moiety Ar-CH 2-N moiety Effect of metal ion uptake in different electrolytes with variation in concentrations The chelation ion-exchange property of the 4-HBTUF terpolymer was measured by batch equilibrium method involving Cd, Mg, Fe 3+, Cu, and UO 2 metal ions in various electrolytes viz. NaCl, NaNO 3, NaClO 4, and Na 2 SO 4 in different concentrations such as 0.1,, and M. The results are presented in Table 6. Table 6. Effect of metal ion uptake by 4-HBTUF Terpolymer Metal ions Electrolyte concentrations (mol.l -1 ) Fe Cd Weight of metal ion uptake in presence of electrolytes (mg) NaCl NaNO 3 NaClO 4 Na 2SO HBTUF terpolymer Cu UO Mg M (NO 3) 2 = 0.1 M; volume = 2 ml; volume of electrolyte = 25 ml; weight of resin = 25 mg; time = 24 h; temperature = 25 ºC. Fig.3 SEM photograph of 4-HBTUF terpolymer 10 From the data it is observed that the amount of metal ion taken up by the terpolymer depends on the nature and concentrations of the electrolytes. The increase in the

5 metal ion uptake with the increase in concentration may be explained on the basis of the stability constants of the complexes. From the results, it is observed that the amount of metal ion taken up by the terpolymer increases with the increasing concentration of Cl -, NO 3 -, and ClO 4 - and decreases with the increasing concentration of SO 4 2- ion. This may be due to the sulphate ion forming strong chelates with metal ions, while other anions form weak chelates. The amount of uptake of Fe 3+ and Cu ions by the terpolymer is comparatively higher than that of the other metal ions such as UO 2, Cd, and Mg [19]. This may be due to the Fe 3+ and Cu ions form weak chelates with the anions of the electrolytes compared to the other metal ions. Further, the polymer is amorphous in nature and has porosity in its structure; hence they can accommodate metal ions of specific size, easily into its cavities. The metal binding property of the 4-HBTUF terpolymer is found to be higher than that of the other polymeric resins reported earlier [13]. 3.6 Effect of distribution of metal ions at various ph The distribution of each one of the metal ions such as Cd, Mg, Fe 3+, Cu, and UO 2 between polymer phase and the aqueous phase was determined at 25 C in the presence of 1 M NaNO 3 at various ph ranging from 3 to 5.5. The study was restricted up to maximum ph of 5.5, due to the precipitation of metal ions at higher ph. The formations of metal hydroxide also interfere with the ionexchange process. The amount of the metal ion which remained in the aqueous phase was estimated. If the original metal ion concentration is known, the metal ion adsorbed by the resin can be calculated. The effect of ph on the amount of metal ions reveals that the uptake of metal ions by the terpolymer at equilibrium increases with increasing ph (Table 7). It is perceived that the equilibrium state is attained in 24 h at 25 ºC under the given conditions. Table 7.Effect of distribution ratios (K D), as a function of ph by 4- HBTUF Terpolymer Distribution ratio (K D) of the metal ions Metal ph of the medium ions It is also observed that the terpolymer takes up Fe 3+ ions more effectively than other ions under study at all ph values. Among the other ions taken up for the study, Cu and UO 2 shows selective uptake of the metal ions under moderate ph values. Further, Cd and Mg ions have lower distribution ratio over the ph ranges from 3 to 5.5. This can be explained as the weak stabilization energy of the metal chelates formed from these ions. In the present investigation it is observed that the order of the distribution ratio of the metal ions are Fe 3+ > Cu > UO 2 > Cd > Mg for the ph ranges from 3 to 5.5. The values of the distribution ratio and the order at different ph depend on the nature of the polymeric resin and its structure. 3.7 Effect of rate of metal ion uptake The rate refers to the change in the concentration of the metal ions in the aqueous solution, which is in contact with the terpolymer. Perusal of the Table 8 reveals that the time taken for the uptake of the different metal ions at a given stage depends on the nature of the metal ion and its ionic size. The rate of metal ion uptake follows the order Fe 3+ > Cu > UO 2 > Cd > Mg for the 4- HBTUF terpolymer. 3.8 Comparative study for resin The ion-exchange capacity of the terpolymer resin was compared with the commercially available resins. The metal ion uptake capacity for the 4-HBTUF resin was found to be 5.58 mmol/g for Fe 3+ ion. Futher the ionexchange capacity of the terpolymer is comparable to the commercially available ion-exchange resins for the other metal ions also under study. This shows that the PUF resin has higher uptake capacity for the ion-exchange process than commercial phenolic and polystyrene ionexchange resins (Table 9). Metal ions Table 8 Effect of rate of metal ion uptake by 4-HBTUF Terpolymer Equilibrium attainment (%) Time (h) Fe Fe Cu Cu UO UO Cd Cd Mg Mg M (NO 3) 2 = 0.1 M; volume = 2 ml; NaNO 3 = 1 M; volume = 25 ml; weight of resin = 25 mg; temperature = 25 ºC. M (NO 3) 2 = 0.1 M; volume = 2 ml; NaNO 3 = 1 M; volume = 25 ml; weight of resin = 25 mg; time = 24 h; temperature = 25 ºC. 11

6 Table 9.Comparative study of the various Ion exchange resins Trade Name Amberlite IR-120 Polymer Matrix Ion-Exchange capacity (mmol/g) [5] O. Szabadka, E. Varga, and L. Nagy, Determination of protonation and metal complex stability constants for a chelating monomer and its immobilized in polymer resin, Talanta., vol. 59, pp , Duolite C-3 Amberlite IRC-50 Duolite ES-63 Dowex 1 Phenolic Methacrylic [6] Q. Rong-jun, J. Chun-nuan, S. Yan-zhi, L. Zhong-fang, C. Guoxiang, and S. Ren-feng, Syntheses and adsorption properties of phenol-formaldehyde-type chelating resins bearing the functional group of tartaric acid, Chinese J. Polym. Sci., vol. 22(5), pp , Amberlite IRA-45 Dowex 3 4-HBTUF Resin Phenolic [7] V.D. Mane, N.J. Wahane, and W.B. Gurnule, Copolymer resin. VII. 8-hydroxyquinoline-5-sulfonic acid thiourea formaldehyde copolymer resins and their ion-exchange properties, J. Appl. Polym. Sci., vol. 111, pp , Conclusion A terpolymer (4-HBTUF) was prepared from 4- hydroxybenzoic acid and thiourea with formaldehyde in sulphuric acid medium by condensation polymerization technique. From the elemental analysis, FTIR, and NMR spectral studies the proposed structure of the terpolymer was confirmed. In the ion-exchange studies, the resin was highly selective for Fe 3+ > Cu > UO 2 > Cd > Mg ions which may be due to the presence of S and N atoms. The sulfur atom plays the key role in binding the metal ions and nitrogen helps in chelation. The highly amorphous nature of the 4-HBTUF terpolymer confirmed by SEM studies further proves that the terpolymer can act as an effective ion-exchanger. The exchange capacity of the chosen metal ions is comparable to the commercial resins. ACKNOWLEDGMENT The authors thank the Management & Principal of Jamal Mohamed College, Tiruchirappalli, Tamil Nadu and Dr. D. Jeyakumar, Scientist, Central Electrochemical Research Institute, Karaikudi, Tamil Nadu for their support and encouragement. REFERENCES [1] A.A. Elassar, O.A. Al-Fulaij, and A.E.M. El-Sayed, Novel synthesis of poly (N1,N3 - diacryloylmalonohydrazide): characterization, complexation, ion selectivity, thermogravimetry, swelling, morphology and biological activity, J. Polym. Res. vol. 17, pp , [2] S.D. Alexandratos, C.A. Shelley, E.P. Horwitz, and R. Chiarizia, A mechanism for enhancing ionic accessibility into selective ion exchange resins, Solv. Extr. Ion Exch., vol. 16(4), pp , [3] A. Singh, and S.K. Saraf, Synthesis, characterization and ionexchanging properties of a novel ion-exchange resin, part II, Int. J. Polym. Mater., vol. 58(10), pp , [4] E.P. Michael Pratik, J.M. Barbe, H.D. Juneja, and L.J. Paliwal, Synthesis, characterization and thermal degradation of 8- hydroxyquinoline guanidine formaldehyde terpolymer, Eur. Polym. J., vol. 43, pp , [8] A. Burkanudeen, and M. Karunakaran, Chelation ion-exchange properties of ortho nitrophenol-thiourea-paraformaldehyde terpolymer, Orient. J. Chem., vol. 18, pp , [9] M. Karunakaran, and A. Burkanudeen, Synthesis and ionexchange characteristics of anthranilic acid-thioureaparaformaldehyde resins, Orient. J. Chem., vol. 18, pp , [10] M.M. Jadhao, L.J. Paliwal, and N.S. Bhave, Resin I: synthesis and characterization of 2,2-dihydroxybiphenyl urea formaldehyde terpolymers, J. Appl. Polym. Sci., vol. 96, pp , [11] P.M. Shah, A.V. Shah, and B.A. Shah, Metal ions uptake by chelating resin derived from o-substituted benzoic acid and its synthesis, characterization and properties, Macromol. Symp. vol. 274, pp , [12] V.V. Hiwase, A.B. Kalambe, K.M. Khedkar, and S.D. Deosarkar, Ion exchange properties of resins derived from p- hydroxybenzaldehyde, resorcinol and formaldehyde, E. J. Chem., vol. 7(1), pp , [13] R.N. Singru, and W.B. Gurnule, Chelating ion-exchange properties of copolymer resins derived from p-cresol, oxamide and formaldehyde, Iran. Polym. J., vol. 9(3), pp , [14] R.S. Azarudeen, M.A. Riswan Ahamed, D. Jeyakumar, and A.R. Burkanudeen, An eco-friendly synthesis of a terpolymer resin: characterization and chelation ion-exchange property, Iran. Polym. J., vol. 18(10), pp , [15] M.A. Riswan Ahamed, R.S. Azarudeen, M. Karunakaran, and A.R. Burkanudeen, Metal ion binding properties of a terpolymer resin: synthesis, characterization and its applications, Iran. Polym. J., in press. [16] J.A. Raj, C. Vedhi, A. Burkanudeen, P. Arumugam, and P. Manisankar, Synthesis and characterization of novel nano-size polyreactive yellow 107, Ionics., vol. 16, pp , [17] K. Nakanishi, Infrared Absorption Spectroscopy, 2 nd ed., Nankodo Co. Ltd: Japan, [18] R.M. Silverstein, and F.X. Webster, Spectrometric Identification of Organic Compounds, 6 th ed., John Wiley: New York, [19] A. Vogel, Text Book of Quantitative Chemical Analysis, 5 th ed., Longman group: UK,