Studies on the synthesis and physico-chemical properties of the new polymeric ion exchangers with sulphur groups

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1 15th Ukrainian-Polish Symposium Studies on the synthesis and physico-chemical properties of the new polymeric ion exchangers with sulphur groups Adsorption Science & Technology 2017, Vol. 35(5 6) ! The Author(s) 2017 DOI: / journals.sagepub.com/home/adt Beata Podkościelna Department of Polymer Chemistry, Maria Curie-Sklodowska University, Lublin, Poland Małgorzata Gil Laboratory of Optical Fibre Technology, Faculty of Chemistry, Maria Curie-Sklodowska University, Lublin, Poland Andrzej Bartnicki and Karolina Fila Department of Polymer Chemistry, Maria Curie-Sklodowska University, Lublin, Poland Abstract In this paper, new styrene microspheres with pendant methylenethiol or sulphonic groups are presented. The copolymer was obtained by the emulsion suspension polymerization of aromatic tetrafunctional monomer 1,1 0 -bis[4-(2-hydroxy-3-acryloiloxypropoxy)phenyl] cyclohexane (C.DA) with styrene. This process was performed at constant mole ratio of C.DA to styrene (1:1 w/w). In order to introduce sulphur groups on the surface of the microspheres, the multistage modification was carried out. After modification very attractive methylenethiol ( CH 2 SH) and sulphonic ( SO 3 H) groups were introduced into the structure of microspheres. Elemental analysis and the spectroscopic method (attenuated total reflectance-fourier transform infrared spectroscopy) were used to confirm the modification reaction. Thermal stabilities and degradation behaviours of the obtained copolymers were characterized by using thermogravimetry/differential scanning calorimetry/quadrupole mass spectrometry analyses. Keywords Emulsion suspension, ion exchanger, microspheres, polymer, spectroscopy Submission date: 28 November 2016; Acceptance date: 16 January 2017 Corresponding author: Małgorzata Gil, Faculty of Chemistry, Uniwersytet Marii Curie-Sklodowskiej, Maria Curie-Sklodowska Sq 5, Lublin , Poland. malgorzata.gil@poczta.umcs.lublin.pl Creative Commons CC-BY: This article is distributed under the terms of the Creative Commons Attribution 3.0 License ( which permits any use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (

2 414 Adsorption Science & Technology 35(5 6) Introduction Heavy metals are used in many industrial areas particularly in power and transport industries. Their occurrence in the natural environment is an undesirable phenomenon. The most dangerous heavy metal ions for living organisms are: Cr(II), Hg(II), Cd(II), Pb(II), As(II), etc. Purification of the environment from toxic metals is very important problem. Ion exchangers with sulphur groups on the surface are used for the removal of toxic metals. These groups exhibit great affinity for heavy metal ions, particularly for mercury ions (Dujardin et al., 2000; Podkos cielna and Kolodyn ska, 2013; Podkos cielna et al., 2016). Ion exchange is a process in which mobile ions of one substance are replaced by similarly charged ions of another substance that are electrostatically bound to the functional groups present in a solid matrix. This process is reversible and stoichiometric. Ion exchangers such as high molecular weight acids or bases, as a result of ion exchange, are converted to their corresponding salts. Depending on the type of the functional group, ion exchangers are called anionic if they exchange negative ions (e.g. CrO 4 2, SO 4 2, NO 3, Cl ) and cationic if they exchange positive ions (Fe þ3, Pb þ2, Cd þ2, Ca þ2, NH 4 þ ). Ion exchangers are widely used in laboratories and in the industry. They are used, for example, for softening and demineralization of water for power industry, separation of ions of the valuable metals in metallurgy, catalyzing a chemical processes, the removal of heavy metal ions from aqueous solutions, isolation of antibiotics and the separation of aminoacids in the pharmaceutical industry. Ion exchange is one of the basic chromatographic analytical techniques (ion exchange chromatography) (Wheaton and Anderson, 1958). In this article synthesis of sulphur-containing microspheres are presented. Copolymerization was performed using 1,1 0 -bis[4-(2-hydroxy-3-acryloiloxypropoxy) phenyl] cyclohexane (C.DA) (Podkos cielny and Bartnicki, 2000), styrene, a,a 0 -Azoiso-bisbutyronitrile (AIBN) (initiator) and pore forming diluents (toluene and decan-1-ol). In the first stage of modification chloromethyl derivative was obtained with paraformaldehyde in the presence of hydrochloric acid at about 100 C. Then chloromethyl groups reacted with thiourea resulting in the formation of isothiouranium salt, which was hydrolysed with the NaOH solution and acidified with hydrochloric acid. In the final stage, the microspheres containing methylenethiol groups on its surface ( CH 2 SH) were synthesized. The sulphonic groups ( SO 3 H) were obtained by the reaction between C.DA and sulphuric acid for 3 h at temperature range of C. The course of the modification was controlled by elemental analysis and the spectroscopic methods. This work was first presented at the 15th Ukrainian Polish Symposium on Theoretical and Experimental Studies of Interfacial Phenomena and their Technological Applications, Lviv, Ukraine, September Experimental Reagents for copolymerization Styrene, bis(2-ethylhexyl)sulphosuccinate sodium salt (DAC,BP) and decan-1-ol were from Sigma-Aldrich (Buchs, Switzerland). C.DA was obtained from Department of Polymer Chemistry (UMCS Lublin, Poland). AIBN was obtained from Merck (Darmstadt, Germany). Toluene was from POCh (Gliwice, Poland).

3 Podkościelna et al. 415 Figure 1. Chemical structures of monomers used for copolymerization: (a) 1,1 0 -bis[4-(2-hydroxy-3- acryloiloxpropoxy)phenyl]-cyclohexane (C.DA) and (b) styrene (St). Copolymerization One hundred fifty millilitres of redistilled water and 1.5 g of bis(2-ethylhexyl)sulphosuccinate sodium salt were stirred for 0.5 h at 80 C in a three-necked flask fitted with a stirrer, a water condenser and a thermometer. Then, 10 g of C.DA and 2.03 g of styrene were dissolved in a mixture of solvents (10 ml toluene/10 ml decan-1-ol). To the resulting solution 1% AIBN (initiator) was added and then transferred to a flask containing an aqueous phase. Copolymerization was performed for 18 h at 80 C. The obtained copolymers were filtered off, washed with distilled hot water, dried and extracted in a Soxhlet apparatus (firstly with acetone, next with methanol). Chemical structures of monomers used for synthesis of microspheres are shown in Figure 1. Modifications Modification I with sulphuric acid. In a 500 ml round-bottomed three-necked flask, equipped with a mechanical stirrer, thermometer and condenser, 50 g of C.DA-St microspheres were placed and then 300 ml of sulphuric acid was added dropwise slowly (for about 1.5 h at 50 C). Then the content of the flask was heated to C, this temperature was kept constant for 3 h and after switching off the heating, stirring was continued for 15 h. The obtained modified microspheres with SO 3 H groups on the surface were cooled. The sulphuric acid was washed by decantation, and then filtered on a Buchner funnel by washing with distilled water. Modification II. Step 1: To a 250 ml three-necked flask equipped with mechanical stirrer, thermometer and condenser, 10 g of polymer microspheres C.DA-St, 15 g of paraformaldehyde and 100 ml of concentrated hydrochloric acid were added. The mixture was heated using a heating mantle for 22 h, maintaining the temperature at about 100 C. The obtained modified microspheres with CH 2 Cl groups on the surface were cooled, washed with distilled water, filtered off and extracted in a Soxhlet apparatus with boiling acetone and toluene. Next, the product was dried in air.

4 416 Adsorption Science & Technology 35(5 6) Step 2: In a 250 ml round-bottomed three-necked flask, equipped with mechanical stirrer, thermometer and condenser, 10 g of chloromethylated microspheres, 15 g of thiourea and 100 ml of 1,4-dioxane were placed. The mixture was heated for 9 h at a temperature of about 100 C. After cooling, the contents of the flask were filtered and washed with hot water to remove excess thiourea. The modified microspheres were placed in a Soxhlet apparatus and washed precisely with methanol by continuous extraction. Step 3: In a 250 ml round-bottomed three-necked flask, equipped with a mechanical stirrer, thermometer and condenser, 25 g of NaOH dissolved in 75 ml of H 2 O and then 20 g of microspheres containing thiourea groups on its surface were added. The mixture was heated at 80 C for 2 h. After cooling the flask, modified microspheres were filtered and washed with distilled water. Then the filtered product was placed in a glass beaker (250 ml) and concentrated hydrochloric acid (40 ml HCl þ 50 ml H 2 O) was added and this mixture was stirred at periodic intervals. After about 0.5 h microspheres were filtered, washed with distilled water and dried. Finally, microspheres with CH 2 SH groups on their surface were obtained. Chemical structures of the microspheres obtained by modifications I and II are presented in Figure 2. Characterization Elemental analysis of the modified microspheres was carried out using the Perkin-Elmer CHNS 2400 apparatus and elemental analyser Vario EL III Elementar (S). Porous structure of copolymers was investigated by nitrogen adsorption at 77 K using the adsorption analyzer ASAP 2405 (Micrometrics Inc., USA). Attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR) spectra were obtained using a Bruker FTIR spectrophotometer TENSOR 27 in the Department of Polymer Chemistry UMCS. The spectra were acquired in the spectral region of cm 1. Thermal analysis of the modified samples was carried out on a STA 449 Jupiter F1, Netzsch (Selb, Germany) under the following operational conditions: heating rate 10 C min 1, dynamic atmosphere of helium (50 ml min 1 ) in the temperature range of C, sample mass of about 5 mg and sensor thermocouple type S thermogravimetry differential scanning calorimetry (TG DSC). The identification of gas composition coming out during decomposition (degradation) was detected and analyzed by quadrupole mass spectrometer QMS 403 C Ae olos (Germany) coupling on-line to STA instrument. Scanning electon microscopic (SEM) photos of microspheres were obtained by means of an optical microscope Morphologie G3 Malvern (UK). Figure 2. Microspheres with SO 3 H and CH 2 SH groups on their surface.

5 Podkościelna et al. 417 Results and discussion In Table 1 elemental analysis of modified microspheres was presented. The highest sulphur content (7.55%) for the polymer C.DA-St-SO 3 H was obtained. The results of elementary analysis show a good efficiency modification process, particularly in the case of sulphonic groups. Specific surface areas (S BET ) and total pore volumes (V tot ) are in the range of 6 20 m 2 /g and cm 3 /g, respectively. Their values are not too high, but the ion exchange takes place on the thiol and sulphonic functional groups present on the surface of the microspheres. The data obtained from the ATR-FTIR spectra of the parent (C.DA-St) and modified copolymers (C.DA-St-CH 2 SH and C.DA-St-SO 3 H) are shown in Table 2. An analysis of these data confirms the differences in the structure of the copolymers obtained in the modification reactions. In the spectra of the studied microspheres, C H stretching vibrations of the aromatic ring backbone methyl group are observed at 2929 and 2925 cm 1, respectively. The vibrations of the OH group are visible at about 3349 cm 1 for C.DA-St-SO 3 H. The carbonyl group gives a shape signal at 1605 cm 1 and 1702 cm 1 for C.DA St CH 2 SH and at 1707 cm 1 for C.DA-St-SO 3 H. The aromatic skeletal absorption is observed at about 1505 cm 1 for C.DA St CH 2 SH and at 1492 cm 1 for C.DA-St-SO 3 H. In the spectra of the copolymer C.DA-St-CH 2 SH the signal of the CH 2 S group occurs approximately at 1415 cm 1, which is characteristic for this compound. In turn, the spectrum of the copolymer C.DA St-SO 3 H shows a signal at 1121 cm 1, which is associated with the presence of SO 3 H groups in the structure of the obtained microspheres. The results of swellability coefficient (B) (Podkos cielna and Kolodyn ska, 2013) are summarized in Table 3. From these data, one can see that all copolymers do not have a tendency to swell (B ¼ 0%) in distilled water. The solvents copolymerized with SO 3 H Table 1. The results of elemental analysis of modified microspheres. (wt.%) Sample N C S H C.DA-St-SO 3 H C.DA-St-CH 2 SH Table 2. The ATR-FTIR analysis of copolymers. C.DA-St Group O H C H arom C¼O C C arom Ar C Wavelength C.DA-St-CH 2 SH Group C H arom C¼O C C arom CH 2 S Ar C Wavelength l; C.DA-St-SO 3 H Group O H C H arom C¼O C C arom SO 3 H Ar C Wavelength

6 418 Adsorption Science & Technology 35(5 6) Table 3. Swellability coefficient results. B (%) Solvent C.DA-St C.DA-St-SO 3 H C.DA-St-CH 2 SH Chlorobenzene Tetrahydrofuran Acetone Acetonitrile Methanol Distilled water Table 4. Thermal stabilities of all samples. Mass loss DTG max 1 wt.% 50 wt.% I o II o Residual mass/wt.% C.DA-St 265 C 433 C 300 C 430 C 8.1 C.DA-St-SO 3 H 190 C 430 C 270 C 426 C 13.3 C.DA-St-CH 2 SH 184 C 423 C 214 C 422 C 9.6 Figure 3. Thermogravimetric/differential scanning calorimetric/quadrupole mass spectrometric (TG/DTG/ DSC) curves.

7 Podkościelna et al. 419 Figure 4. Mass spectrometric (MS) curves. Figure 5. Scanning electon microscopic (SEM) photos of microspheres.

8 420 Adsorption Science & Technology 35(5 6) groups have largest swellability coefficients. In polar methanol, the highest tendencies to swell were observed in the range %. For the physio-chemical studies coupled thermal (TG, DSC) and spectroscopic (MS) methods were chosen. Using these methods, full thermal and spectroscopic characterization were obtained by increasing the temperature. In Table 4 all thermal properties were summarized and Figure 3 presents the TG/DTG/DSC curves obtained at a heating rate of 10 C min 1 under helium atmosphere. The mass loss, which appears for all samples below 140 C (TG), is directly related to the elimination of the water from the samples. This conclusion is confirmed by quadrupole mass spectrometer (QMS) analysis (Figure. 4) where ion 17 and 18 appeared in discussed temperature range and this is further confirmed by DSC curves (Figure 3) where endothermic effects can be observed. A 1 wt.% of mass loss shows that the sample is thermally stable. Based on obtained data we can conclude that the sample C.DA-St-CH 2 SH has the lowest thermal resistance. It can be seen that 1 wt.% of mass loss for this sample was observed at about 185 C, while for sample C.DA-St-SO 3 H the mass loss was observed at 190 C, and for C.DA-St at 265 C. Before the main decomposition stage, a small gap in mass was observed. The temperature ranges for samples C.DA-St and C.DA-St-SO 3 H are C and C, respectively. Based on QMS spectra (Figure 4) it can be seen that it is related to the presence of ions 17 and 18 (water). For C.DA-St-CH 2 SH sample the mass loss is observed between 184 C and 320 C and based on QMS spectra (Figure 4) it is related to the presence of ions 17,18 (water), 91 and 92 (benzyl group). For all tested samples the temperature at which 50 wt.% of mass loss was observed was very similar about 430 C. Based on TG/DTG/DSC data it was concluded that the main decomposition stage for samples C.DA-St and C.DA-St-SO 3 H starts at about 320 C and for sample C.DA-St-CH 2 SH at about 290 C. The maximum of these processes (DTGmax II o ) is about 425 C. Above this temperatures ions 17, 18 (water), 40 (C 3 H 4 ), 50, 51, 52, 76, 77, 78, 79 (phenyl group) and 91, 92 (benzyl group) was registered by QMS apparatus (Figure 4). The residual mass at 1000 C after degradation process for sample C.DA-St is about 8.1 wt.% for sample C.DA-St-SO 3 H 13.3 wt.% (and is the highest) and for the sample C.DA-St-CH 2 SH is 9.6 wt.%. In Figure 5 the photos of the microspheres are presented. After modification some partial destruction of the surface of C.DA-St-SO 3 H is visible. Conclusion. Polymer microspheres are obtained as a result of the copolymerization reaction of C.DA with styrene.. Modifications of the copolymer results in the formation microspheres with CH 2 SH and SO 3 H groups on their surface;. By elemental analysis the percentage elemental composition of the obtained copolymers was determined and it confirmed the correct course of the modification reaction to form a 7.55% (for the SO 3 H) and 2.30% sulphur (for CH 2 SH), respectively.. ATR spectra analysis confirmed the presence of characteristic signals derived from the groups that are included in structure of these compounds in the C.DA-St-CH 2 SH and C.DA-St-SO 3 H copolymers.. In the next stage the obtained modified microspheres will be tested as polymeric ion exchangers.

9 Podkościelna et al Based on TG/DTG/DSC/QMS studies it was concluded that the sample C.DA-St have the highest thermal resistance. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: People Programme (Marie Curie Actions) of the European Union s Seventh Framework Programme FP7/ / under REA grant agreement n PIRSES-GA References Dujardin MC, Caze C and Vroman I (2000) Ion-exchange resins bearing thiol groups to remove mercury: Part 1: Synthesis and use of polymers prepared from thioester supported resin. React Funct Polym 43: 123. Podkos cielna B and Kolodyn ska D (2013) A new type of cation-exchange polymeric microspheres with pendant methylenethiol groups. Polym Adv Technol 24: 866. Podkos cielna B, Kolodyn ska D, Hubicki Z, et al. (2016) Synthesis, characterization, and application of a new methylenethiol resins for heavy metal ions removal. Sep Sci Technol 51: Podkos cielny W and Bartnicki A (2000) New acrylic esters, derivatives of some diglycidyl ethers as main components of lacquer compositions. Mol Cryst Liq Cryst 354: 35. Wheaton RM and Anderson RE (1958) Industrial applications of ion exchange resins. J Chem Educ 35(2): 59.