THE STUDY OF ION SORPTION PERFORMANCES OF STOICHIOMETRIC AND NON-STOICHIOMETRIC POLYELECTROLYTE COMPLEXES.

THE STUDY OF ION SORPTION PERFORMANCES OF STOICHIOMETRIC AND NON-STOICHIOMETRIC POLYELECTROLYTE COMPLEXES. Pha-sita Plengplung a and Stephan T. Dubas *,a,b a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand b Center of Excellence on Petrochemical and Materials Technology, Bangkok, Thailand Keywords: Polyelectrolyte complexes, Adsorption, Methyl orange, Methylene blue ABSTRACT In this study, the ion sorption performance of polyelectrolyte complexes (PECs) were observed by using negatively-charged dye and positively-charged dye. PECs were prepared in both stoichiometric and non-stoichiometric system with different concentration of salt and different ratio of poly(diallyldimethylammonium chloride) (PDADMAC), polycation, and poly(sodium-p-styrenesulfonate) (PSS), polyanion. After obtaining PECs, compression molding was used to compress PECs into films. The films were characterized by fourier transformed infrared spectrometer (FTIR) andscanning electron micoscopic (SEM). Moreover, the amount of PDADMAC and PSS in the films were measured by the intensity of FTIR peaks. Sorption experiments were studied with methylene blue (MB), as positively-charged dye, and methyl orange (MO), as negatively-charged dye, in both singlesolute and multisolute system. The concentration of dyes during the sorption experiments were determined via UV-vis spectrophotometry and the swelling of films before and after sorption experiments was also observed. The results showed that non-stoichiometric PECs were likely to transformed to stoichiometric PECs when the salt concentration was increased and non-stoichiometric PECs can be prepared when the concentration of salt is between 0.5 and 2.0 M NaCl. Non-stoichiometric PEC films with excess PDADMAC content are excellent sorbents for MO. Meanwhile, PEC films with excess PSS content are excellent for MB sorbents. * stephan.d@chula.ac.th INTRODUCTION The removal of organic dyes from waste water is important because these dyes are toxic to aquatic life and harm human health. Presently, there are various conventional methods to removal organic dyes such as coagulation/flocculation, membrane filtration, chemical oxidation and adsorption. The adsorption method has several advantages over other methods; for example, simple processing and high efficiency (Guo et al., 2014). Polyelectrolyte complexes (PECs) are formed by exposing polycations to polyanions. The concentration of salt within the PECs controls the physical appearance of PECs, because salt can break physical crosslinks between oppositely charged polymers and this phenomena can be reversed. Salt affects the physical appearances of PECs by changing from tough complexes to viscous, liquid-like coacervates, and dissolve solutions (Kelly et al., 2015). Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1

The aim of this work is to study the use of stoichiometric and non-stoichiometric PECs as organic sorbents. The characteristics of stoichiometric and non-stoichiometric PECs were studied by preparing PECs in different salt concentrations (0.5, 1.0 and 2.0M) and in different ratios of poly(diallydimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS). After PECs fabrication, the amount of PDADMAC and PSS were determined by the intensity of FTIR peaks. Moreover, the ion sorption performances of stoichiometric and non-stoichiometric PECs were studied using dye absorption using methylene blue (MB), as positively-charged dye, and methyl orange (MO), as negativelycharged dye, in both single-solute and multisolute system. EXPERIMENTAL A. Materials. Poly(diallydimethylammonium chloride) (PDADMAC; Sigma-Aldrich; average M w 200,000-350,000), poly(sodium 4-styrenesulfonate) (PSS; Sigma-Aldrich; average M w ~ 70,000), sodium chloride (NaCl; Lobal Chemie), Methyl Orange (MO; Carlo Erba Reagents), Methylene Blue (MB; Carlo Erba Reagents). B. Equipment. Field Emission Scanning Electron Microscopy (FE-SEM), Hitachi S-4800, Fourier Transform Infrared Reflection (FT-IR), Thermo Scientific, Nicolet is5 ATR-FTIR spectrometer, UV-Vis spectrophotometry, Avantes, AvaSpec-2048, micrometer C. PEC Sorbents Preparation. Polyelectrolyte complexes (PECs) sorbents are produced by mixing between PDADMAC (polycation) and PSS (polyanion) together. For the stoichiometric and non-stoichiometric PECs, PECs were prepared in different salt concentrations (0.5, 1.0 and 2.0M) and in different ratio of PDADMAC and PSS (Table 1.). After obtaining PECs, compression molding was used to compress PECs into films. Table 1. Ratio between PDADMAC and PSS in PECs preparation. PDADMAC : PSS 2:1 1.5:1 1:1 1:1.5 1:2 Stoichiometric C. Characterizations. The morphology of PEC membranes was characterized by using Scanning electron microscopy (SEM). Fourier transform infrared reflection (FT-IR) was used to detect functional groups in PEC membranes. The FT-IR spectrums of these samples were recorded in the region of 650-4,000 cm -1. The thickness of PEC membranes was measured by a micrometer. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2

D. Adsorption Experiments. Dye concentration during the adsorption experiment was determined via UV-Vis spectrophotometry, calibration curve of dye was built by using standard solutions of known concentration. Single-Solute System: Methyl Orange Adsorption Study. In this study, PEC sorbents were cut into 2 2 cm and weighed. These sorbents were added to 10 ml of 10 ppm MO solution. After resting for 2 h, at a temperature of 27±1, sorbents were removed. The concentration of MO solutions before and after the adsorption experiment was determined by using UV-Vis spectrophotometer base on calibration curve at a wavelength corresponding to the maximum absorbance, 464 nm. The adsorbed amount (q e ) of MO on PEC sorbents were calculated as q e = V (C 0 -C e )/m (i) where C 0 is the initial concentration (ppm), C e is the equilibrium concentration (ppm), V is the volume of the solution (L) and m is the amount of PEC sorbents (g) (Mouzdahir et al., 2010) Single-Solute System: Methylene Blue Adsorption Study. The adsorption study of MB was carried out in the same method as the MO adsorption study and in MB concentration of 10 ppm, at a temperature of 27±1. The concentration of MB solutions before and after adsorption experiment were determined by using UV-Vis spectrophotometer base on calibration curve at a wavelength corresponding to the maximum absorbance, 663 nm. The adsorbed amount of MB on PEC sorbents were calculated as equation (i). Multisolute System Adsorption Study: Mixed Dye solution. The 100 ml mixed dye solution of MO/MB was prepared by mixing between 50 ml of 20 ppm MO solution and 50 ml of 10 ppm of MB solution. This experiment was carried out in the same method as single-solute system, at a temperature of 27±1. The concentration of MO and MB in mixed dye solution before and after adsorption experiment were determined by using UV-Vis spectrophotometer base on calibration curve at a wavelength corresponding to the maximum absorbance, 464 and 663 nm. The adsorbed amount of MO and MB on PEC sorbents were calculated as equation (i). The separation efficiency (S) is used for showing the separation ability between MO and MB in multisolute system adsorption. Separation efficiency (%S) were calculated as S MO (%) = q e (MO)/[q e (MO) + q e (MB)] S MB (%) = q e (MB)/[q e (MO) + q e (MB)] (ii) (iii) RESULTS AND DISCUSSION A. Stoichiometric and non-stoichiometric PECs in different salt concentration. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3

After fabricated, the amount of PDADMAC and PSS in PECs were measured by the intensity of FTIR peaks (peak height). Peak position of PDADMAC and PSS are 1473 and 1126-1182 cm -1 (Shin et al., 2014). Table 2. shows the PDADMAC peak height/pss peak height values of every samples and slope of trend lines in different salt concentration. Table 2. PDADMAC peak height/pss peak height values of every samples and slope of trend lines in different salt concentration. Concentration of NaCl (M) PDADMAC : PSS 0.5 1.0 2.0 2:1 0.2416 0.2897 0.2923 1.5:1 0.2330 0.2641 0.2880 1:1 0.2453 0.3043 0.2791 1:1.5 0.2130 0.2364 0.2518 1:2 0.1951 0.2451 0.2414 Slope of trend line (m) 0.0113 0.0117 0.0138 From Table 2., the slope of trend line of all samples showed little variation. These results showed that the concentration of salt between 0.5-2.0 M can be used to prepared stable stoichiometric and non-stoichiometric PECs since the ionic strength was not too high (Zhang et al., 2015). B. Adsorption Experiments. Single-Solute System: Methyl Orange Adsorption Study. From MO adsorption study, only at ratios 2:1, 1.5:1 and 1:1 between PDADMAC and PSS can adsorb MO on the surface of PEC sorbents. However, the ratios 1:1.5 and 1:2 can adsorb lower amount of MO (lower than 0.03 mg/g). A B Figure 1. The adsorbed amount of dyes on PEC sorbents: A. the adsorbed amount of MO on PEC sorbents at ratio of 2:1, 1.5:1 and 1:1; B. the adsorbed amount of MB on PEC sorbents at ratio of 1:1.5 and 1:2. Figure 1.A represents the adsorbed amount of MO on PEC sorbents at ratio of 2:1, 1.5:1 and 1:1 between PDADMAC and PSS in 0.5, 1.0 and 2.0 M concentration of NaCl. The highest adsorption efficiency was at ratio of 1.5:1 due to the excess amount of PDADMAC. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4

Thus, the PECs surface was dominated by the positively charged PDADMAC which interacts with the negatively charged MO dye via electrostatic forces (Morais et al., 2007). Furthermore, 0.5 M salt provided highest amount adsorbed i.e. 1.57 mg/g. Figure 2.A shows the PEC sorbents after MO adsorption experiment, the color of PEC sorbents changed from transparent to orange only at the ratios 2:1, 1.5:1 and 1:1. Single-Solute System: Methylene Blue Adsorption Study. From MB adsorption study, MB can be adsorbed on PEC sorbents only at ratio 1:1.5 and 1:2 between PDADMAC and PSS. Figure 1.B shows the adsorbed amount of MB on PEC sorbent at ratios of 1:1.5 and 1:2 in 0.5, 1.0 and 2.0 M NaCl. Similarly, due to the excess of PSS in PEC sorbents that affected to adsorption performance between MB and PEC sorbents. MB is a positively-charged dye that can interacted with PSS (polyanion) via electrostatic forces. From this experiment, at ratio of 1:1.5 were provided high adsorption efficiency, especially in 2.0 M NaCl, 1.51 mg/g. A. B. Figure 2. The PEC sorbents after single-solute system adsorption experiments: A. MO adsorption experiment; B. MB adsorption experiments. Multisolute System Adsorption Study: Mixed Dye solution. Table 3. The separation efficiency (%S) of PEC sorbents. [NaCl] PDADMAC:PSS (M) 2:1 1.5:1 1:1 1:1.5 1:2 S MO S MB S MO S MB S MO S MB S MO S MB S MO S MB 0.5 100 0 100 0 100 0 6.23 93.77 7.81 92.19 1.0 100 0 100 0 100 0 3.24 96.76 6.36 93.64 2.0 100 0 100 0 100 0 7.72 92.28 19.18 80.82 Table 3. represents the separation efficiency (S), at ratios of 2:1, 1.5:1 and 1:1 had 100% in S MO as a result from PDADMAC excess, it showed that these PEC sorbents were as applicable as MO sorbent in mixed dye system. While, at ratios 1:1.5 and 1:2 showed the high S MB values. Thus, the high separation efficiency was from PSS excess. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5

0.5 Figure 3. The color of mixed dye before (Ref.) and after multisolute system adsorption experiment. Figure 3. shows the color of mixed dyes before and after adsorption experiments, due to the removal MO from mixed dye solution the color was changed from green to light sea green at the ratio of 2:1, 1:5 and 1:1. On the other hand, at ratio of 1:1.5 and 1:2 were had excess PSS. Hence the color was changed from green to yellowish green. The PEC sorbents after adsorption experiments were shown in Figure 4. The PEC with excess PDADMAC and stoichiometric changed color from transparent to orange and PECs with excess PSS changed its color from transparent to light blue or aquamarine. Figure 4. The PEC sorbents after multisolute system adsorption experiment. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6

CONCLUSIONS For studied stoichiometric and non-stoichiometric PECs, PECs were prepared in different salt concentrations. From FTIR results, the concentration of NaCl between 0.5-2.0 M were suitable for preparing stable stoichiometric and non-stoichiometric PECs. The ion sorption performances of stoichiometric and non-stoichiometric PECs were studied with MO and MB dyes, in both single-solute and multisolute systems. Results from single-solute system showed that at ratio between PDADMAC and PSS in 1.5:1, 0.5 M NaCl (1.57 mg/g) was the best formula to be used as MO sorbent and in 1:1.5, 2.0 M NaCl (1.51 mg/g) was the best formula for use as MB sorbent. For the multisolute system, at ratios of 2:1, 1.5:1 and 1:1 in every salt concentrations were suitable to be used as selective sorbent for the removal of MO from mixed dye solution. Meanwhile, for the removal of MB from mixed dye solution, the ratios of 1:1.5 and 1:2 were suitable, especially the ratio of 1:1.5. ACKNOWLEDGEMENTS This research is financially supported by the Petroleum and Petrochemical College, Center of Excellence on Petrochemucals and Materials Technology, Chulalongkorn University, Thailand. REFERENCES Guo, Y., Hou, W., Liang, J. and Liu, J. (2014). Sorbent Concentration Effect on Adsorption of Methyl Orange on Chitosan Beads in Aqueous Solutions. Chem. Res. Chin. Univ., 30(5), 837-843. Kelly, K.D. and Schlenoff, J.B. (2015). Spin-Coated Polyelectrolyte Coacervate Films. ACS Applied Materials & Interfaces, 7, 13980-13986. Morais, W.A., Fernandes, A.L.P., Dantas, T.N.C., Pereira, M.R. and Fonseca, J.L.C. (2007). Sorption studied of model anionic dye on crosslinked chitosan. Colloids and Surfaces A: Physicochem. Eng., 310, 20-31. Mouzdahir, Y. E., Elmchaouri, A., Mahboub, R., Gil, A. and Korili, S.A. (2010). Equilibrium modeling for the adsorption of methylene blue from aqueous solutions on activated clay minerals. Desalination, 250, 335-338. Shin, Y., Cheung, W.H., Ho, T. T.M., Bremmell, K. E. and Beattie, D. A. (2014). Insights into hydrophobic molecule release from polyelectrolyte multilayer films using in situ and ex situ techniques. The Royal Society of Chemistry, 16, 22409-22417. Zhang, Y., Yildirim, E., Antila, H. S., Valenzuela, L. D., Sammalkorpi, M. and Lutkenhaus, J. L. (2015). The influence of ionic strength and mixing ratio on the colloidal stability of PDAD/PSS polyelectrolyte complexes. The Royal Society of Chemistry, 11, 7392-7401. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7