- Email: [email protected]
Synthesis and characterization of a composite polymeric material including chelating agent for adsorption of uranyl ions
Accepted Manuscript Title: Synthesis and Characterization of a Composite Polymeric Material Including Chelating Agent for Adsorption of Uranyl Ions Authors: Selc¸uk S¸ims¸ek, Zeynep Mine S¸enol, Halil ˙Ibrahim Ulusoy PII: DOI: Reference:
S0304-3894(17)30418-1 http://dx.doi.org/doi:10.1016/j.jhazmat.2017.05.059 HAZMAT 18618
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
30-12-2016 30-5-2017 31-5-2017
Please cite this article as: Selc¸uk S¸ims¸ek, Zeynep Mine S¸enol, Halil ˙Ibrahim Ulusoy, Synthesis and Characterization of a Composite Polymeric Material Including Chelating Agent for Adsorption of Uranyl Ions, Journal of Hazardous Materialshttp://dx.doi.org/10.1016/j.jhazmat.2017.05.059 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.
Synthesis and Characterization of a Composite Polymeric Material Including Chelating Agent for Adsorption of Uranyl Ions Selçuk ŞİMŞEK1,#, Zeynep Mine ŞENOL2, Halil İbrahim ULUSOY3 1
Cumhuriyet University, Faculty of Science, Department of Chemistry, 58140 SIVAS, TURKEY
2
Cumhuriyet University, Zara Vocational School, Department of Food Technology, 58140 SIVAS, TURKEY
3
Cumhuriyet University, Faculty of Pharmacy, Department of Analytical Chemistry, 58140 SIVAS, TURKEY
Highlights
A new adsorbent including a powerful chelating was developed for effective uranyl. Characterization was carried out by FTIR, EDX, SEM, UV-VIS-NIR, and PZC technical. As we know, this is the first application for grafting of CCA to a polymeric matrix. CCA-g-PAA can be used as potential adsorbent for removal or pre-concentration of uranyl.
Abstract In this study, a versatile polymeric material was synthezed by grafting Calcon Carboxylic Acid (CCA), which is known as a chelating agent for some metal ions, to polyacrylamide (PAA) structure. Thus, the adsorptive properties of inert PAA polymer were significantly improved owing to this procedure. The obtained new material, CCA-g-PAA, was characterized by point zero charge (PZC), FTIR, SEM, and UV-VIS-NIR analysis. The adsorption properties of new material were investigated comprehensively and experimental variables were optimized such as pH, temperature, time, and concentration. Experimental data were evaluated by using therotical adsorption models. The maximum adsorption capacity of material was calculated as 0.079 mol kg-1 by considering Langmuir equation. The constants calculated from Freundlich and DR model were found as 6.98 and 0.441, respectively. Adsorption kinetic was also explained with pseudo second order and intra particular diffusion models. Experimental studies were showed that adsorption was endothermic and occured spontaneously. The developed material has important advantages such as reusability, cost-effective synthesis procedure, high adsorption capacity, and selectivity. Keywords: Uranyl; adsorption; polyacrylamide; calcon carbocylic acid 1. Introduction Needs for new energy sources have a vital importance in the developing countries since industrial evaluation. Conventional energy sources including crude oil cause seriously
environmental problems. So, important of various alternatives sources such as wind, sun, nuclear energy is increasing every day. Among these sources, nuclear energy is preferred as a clean energy and it is primer source in a lot of developed country. Uranium is the most used elements as a radioactive source. But it is difficult to obtain it due to limited reserves and expensive costs. So, it is generally produced from seawater, wastes of nuclear plants by recovery and preconcentration. For example, seawater includes 3.3 ppb uranium and this is important amount for recovery studies [1]. By increasing usage of radioactive elements including uranium as energy source causes spreading of toxic and dangerous chemicals to environment. The main reasons of this contamination are leaks from nuclear plants, accidents, and natural sources. This circumstance threats both human health and environment. A lot of study showed that uranium species mainly exist as uranyl form (UO22+) in the aquatic medium [2]. These ions can accumulate at organs and tissues by forming stable complexes with various biochemical molecules in the huma body. In addition, it causes a lot of negative circumstances like cancer, organ failure, and finally death. So, removal of uranium species is very important and attracts great attention due to their negative effects on the human health [3]. Most used conventional methods for recovery or pre-concentration of uranium species are adsorption [4], precipitation [5], membrane filtration [6] and biological accumulation [7]. Among these approaches, adsorption is mostly preferred in last decades owing to positive advantages. In the adsorption, ion or molecules in the solution or gas phase are retained on a solid surface through physical or chemical interaction. Mechanism of adsorption is fairly complex, but it is very useful method with easy applications. Especially, if the concentration of target species is very low and so recovery of these species is so expensive and laborious with conventional methods, the adsorption is first preference method with simplicity, cost effectivity, and environmental friendly. So, it is one of the most studied research areas for removal of toxic species. The first step of adsorption studies is focused on developing a suitable, accessible, reusable, and cost-effective adsorbent for target species. Kinetic of adsorption should be fast in order to shorten recovery time. The most used adsorbents are carbon [8, 9], zeolite [10], clay [11], composites [12] and natural polymers [13] and synthetic polymers [14,15]. Polymers are mainly preferred owing to changeable structural properties according to target species. Selectivity of polymer adsorbents can be increased by using specific molecules having functional groups. Chelating groups having high affinity for metal ions can be grafted to a
polymeric sturucture by a physical or chemical way. So, a useful material is obtained for selective adsorption of some target ions. This approach is one of the popular research area at last decades. Moreover, this method is not limited only with metal ions. There are a lot of studies about development of selective and effective material for organic molecules such as dyes, pesticides, and drugs [16]. The aim of this study is to develop a new material for selective and effective removal of uranyl ions. Calcon carboxylic acid molecule having potential for strong complex formation was grafted to polyacrylamide structure which is an inert material for uranyl ions. CCA [1-(2hydroxy-4-sulfo-1-naphtylazo)-3-naphtolic acid] can coordinate with uranyl ions through its azo-nitrogen and phenolic oxygen sites. 2. Experimental 2.1 Reagents All chemicals used were of analytical reagent grade. Calcon carboxylic acid, acrylamide monomer, N,N’-methylenebisacrylamide (Bis–AA) , N,N,N’,N’-tetramethyl ethylenediamine (TEMED) and 4-(2-pyridylazo) resorcinol (PAR) were purchased from Sigma (St. Loius, MO, USA). UO2 (NO3)2.6H2O and the remaining of the chemicals were obtained from Merck (Germany). Ultra-pure water with a resistivity of 18.2 MΩ cm was used during all experiments produced by a Labcanco water purification system. All experiments were performed in duplicates and within ±5% experimental error limit. 2.2. Characterization and Instrumentations The fourier transform infrared spectroscopy (FTIR) analysis were done to study the functional groups in the range of 400-4000 cm-1 using modified FTIR spectrophotometer (Bruker, Tensor II) in KBR pellets. The concentration of uranyl ions was determined using modified spectrometric method mentioned at section 2.4 by means of a UV-VIS spectrophotometer (Shimadzu, Japan). This spectrophotometer has a wavelength accuracy of ±0.2 nm and a bandwidth of 2 nm in the wavelength range of 190–1100 nm. A pH meter with a glass-calomel electrode (Selecta, Spain) was used to measure the pH values. A centrifuge (Hettich Universal) was used to accelerate the phase separation. A thermostated water bath (Nuve NT 120, Turkey) was used in order to keep constant the temperature. 2.3. Preparation of new composite, CCA-g-PAA
For synthesis of CCA-g-PAA, 10 g of acrylamide (AA) monomer and 0.2 g of cross linker (N,N’-methylenebisacrylamide) were weighed and dissolved in 10 mL of water. 400 mg of CCA was added onto this mixture and stirred on a magnetic stirrer. Then, 300 mg of ammonium persulphate was added as starter agent. Polymerization reaction was sustained by adding 200 μL of N,N,N’,N’-tetramethylethylenediamine at room temperature. The obtained new composite was washed with ultrapure water and the ethanol for several times in order to remove non-grafted reagents. After then, it was dried, ground, and sieved by obtaining a homogene material. 2.4. Determination of uranyl ions in the solution The concentration of uranyl ions was determined by using the modified PAR method as spectrophotometrically [17]. In this method, uranyl ions are formed a selective complex with PAR (4-(2-pyridylazo) resorcinol) at pH 8.5. For this purpose, 3.5×10 -3 mol L-1 of PAR was prepared in Tris/HCl buffer (pH 8.5). Then, 50 µL of sample solution was added to 3 mL of PAR solution and the absorbance of the formed complex was followed at 530 nm. After a calibration graph was plotted, the concentration of uranyl ions was determined in the supernatants. 2.5. Adsorption studies Adsorptive
features of the developed adsorbent were investigated for UO 22+ ions. For this
purpose, 0.1 g of the adsorbent were equilibrated with 10 mL of UO 22+ in the concentration range of (0.37 - 3.70) ×10-3 mol L-1. The adsorbent–solution systems were equilibrated for 24 h at 298 K in a thermostatic water-bath and equilibrium solutions aqueous phase were obtained by centrifuging at 2.500 rpm for 5 min. The concentration of uranyl ions was determined as explained in section 2.4. 2.6. Point of zero charge and pH dependence of adsorption The determination of point of zero charge (PZC) was done to investigate the surface charge and acidic-basic character of adsorbent. For that 0.1 mol L-1 KNO3 solution was prepared and its initial pH was adjusted in the range of 1-12 by NaOH and HCl. Then 10 mL of KNO3 and 0.100 g adsorbent were interacted in test tubes. The samples were kept at 25 ºC for 24 hours and the final pH of solutions was measured by using a pH meter. The graph was plotted using initial versus final pHs and point of zero charge was determined by the obtained experimental results.
3. Result and Discussion 3.1. Characterization of new material The characterization of new material was carried out by ATR, UV-VIS-NIR, SEM, and EDX technicals.
S0304-3894(17)30418-1 http://dx.doi.org/doi:10.1016/j.jhazmat.2017.05.059 HAZMAT 18618
To appear in:
Journal of Hazardous Materials
Received date: Revised date: Accepted date:
30-12-2016 30-5-2017 31-5-2017
Please cite this article as: Selc¸uk S¸ims¸ek, Zeynep Mine S¸enol, Halil ˙Ibrahim Ulusoy, Synthesis and Characterization of a Composite Polymeric Material Including Chelating Agent for Adsorption of Uranyl Ions, Journal of Hazardous Materialshttp://dx.doi.org/10.1016/j.jhazmat.2017.05.059 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.
Synthesis and Characterization of a Composite Polymeric Material Including Chelating Agent for Adsorption of Uranyl Ions Selçuk ŞİMŞEK1,#, Zeynep Mine ŞENOL2, Halil İbrahim ULUSOY3 1
Cumhuriyet University, Faculty of Science, Department of Chemistry, 58140 SIVAS, TURKEY
2
Cumhuriyet University, Zara Vocational School, Department of Food Technology, 58140 SIVAS, TURKEY
3
Cumhuriyet University, Faculty of Pharmacy, Department of Analytical Chemistry, 58140 SIVAS, TURKEY
Highlights
A new adsorbent including a powerful chelating was developed for effective uranyl. Characterization was carried out by FTIR, EDX, SEM, UV-VIS-NIR, and PZC technical. As we know, this is the first application for grafting of CCA to a polymeric matrix. CCA-g-PAA can be used as potential adsorbent for removal or pre-concentration of uranyl.
Abstract In this study, a versatile polymeric material was synthezed by grafting Calcon Carboxylic Acid (CCA), which is known as a chelating agent for some metal ions, to polyacrylamide (PAA) structure. Thus, the adsorptive properties of inert PAA polymer were significantly improved owing to this procedure. The obtained new material, CCA-g-PAA, was characterized by point zero charge (PZC), FTIR, SEM, and UV-VIS-NIR analysis. The adsorption properties of new material were investigated comprehensively and experimental variables were optimized such as pH, temperature, time, and concentration. Experimental data were evaluated by using therotical adsorption models. The maximum adsorption capacity of material was calculated as 0.079 mol kg-1 by considering Langmuir equation. The constants calculated from Freundlich and DR model were found as 6.98 and 0.441, respectively. Adsorption kinetic was also explained with pseudo second order and intra particular diffusion models. Experimental studies were showed that adsorption was endothermic and occured spontaneously. The developed material has important advantages such as reusability, cost-effective synthesis procedure, high adsorption capacity, and selectivity. Keywords: Uranyl; adsorption; polyacrylamide; calcon carbocylic acid 1. Introduction Needs for new energy sources have a vital importance in the developing countries since industrial evaluation. Conventional energy sources including crude oil cause seriously
environmental problems. So, important of various alternatives sources such as wind, sun, nuclear energy is increasing every day. Among these sources, nuclear energy is preferred as a clean energy and it is primer source in a lot of developed country. Uranium is the most used elements as a radioactive source. But it is difficult to obtain it due to limited reserves and expensive costs. So, it is generally produced from seawater, wastes of nuclear plants by recovery and preconcentration. For example, seawater includes 3.3 ppb uranium and this is important amount for recovery studies [1]. By increasing usage of radioactive elements including uranium as energy source causes spreading of toxic and dangerous chemicals to environment. The main reasons of this contamination are leaks from nuclear plants, accidents, and natural sources. This circumstance threats both human health and environment. A lot of study showed that uranium species mainly exist as uranyl form (UO22+) in the aquatic medium [2]. These ions can accumulate at organs and tissues by forming stable complexes with various biochemical molecules in the huma body. In addition, it causes a lot of negative circumstances like cancer, organ failure, and finally death. So, removal of uranium species is very important and attracts great attention due to their negative effects on the human health [3]. Most used conventional methods for recovery or pre-concentration of uranium species are adsorption [4], precipitation [5], membrane filtration [6] and biological accumulation [7]. Among these approaches, adsorption is mostly preferred in last decades owing to positive advantages. In the adsorption, ion or molecules in the solution or gas phase are retained on a solid surface through physical or chemical interaction. Mechanism of adsorption is fairly complex, but it is very useful method with easy applications. Especially, if the concentration of target species is very low and so recovery of these species is so expensive and laborious with conventional methods, the adsorption is first preference method with simplicity, cost effectivity, and environmental friendly. So, it is one of the most studied research areas for removal of toxic species. The first step of adsorption studies is focused on developing a suitable, accessible, reusable, and cost-effective adsorbent for target species. Kinetic of adsorption should be fast in order to shorten recovery time. The most used adsorbents are carbon [8, 9], zeolite [10], clay [11], composites [12] and natural polymers [13] and synthetic polymers [14,15]. Polymers are mainly preferred owing to changeable structural properties according to target species. Selectivity of polymer adsorbents can be increased by using specific molecules having functional groups. Chelating groups having high affinity for metal ions can be grafted to a
polymeric sturucture by a physical or chemical way. So, a useful material is obtained for selective adsorption of some target ions. This approach is one of the popular research area at last decades. Moreover, this method is not limited only with metal ions. There are a lot of studies about development of selective and effective material for organic molecules such as dyes, pesticides, and drugs [16]. The aim of this study is to develop a new material for selective and effective removal of uranyl ions. Calcon carboxylic acid molecule having potential for strong complex formation was grafted to polyacrylamide structure which is an inert material for uranyl ions. CCA [1-(2hydroxy-4-sulfo-1-naphtylazo)-3-naphtolic acid] can coordinate with uranyl ions through its azo-nitrogen and phenolic oxygen sites. 2. Experimental 2.1 Reagents All chemicals used were of analytical reagent grade. Calcon carboxylic acid, acrylamide monomer, N,N’-methylenebisacrylamide (Bis–AA) , N,N,N’,N’-tetramethyl ethylenediamine (TEMED) and 4-(2-pyridylazo) resorcinol (PAR) were purchased from Sigma (St. Loius, MO, USA). UO2 (NO3)2.6H2O and the remaining of the chemicals were obtained from Merck (Germany). Ultra-pure water with a resistivity of 18.2 MΩ cm was used during all experiments produced by a Labcanco water purification system. All experiments were performed in duplicates and within ±5% experimental error limit. 2.2. Characterization and Instrumentations The fourier transform infrared spectroscopy (FTIR) analysis were done to study the functional groups in the range of 400-4000 cm-1 using modified FTIR spectrophotometer (Bruker, Tensor II) in KBR pellets. The concentration of uranyl ions was determined using modified spectrometric method mentioned at section 2.4 by means of a UV-VIS spectrophotometer (Shimadzu, Japan). This spectrophotometer has a wavelength accuracy of ±0.2 nm and a bandwidth of 2 nm in the wavelength range of 190–1100 nm. A pH meter with a glass-calomel electrode (Selecta, Spain) was used to measure the pH values. A centrifuge (Hettich Universal) was used to accelerate the phase separation. A thermostated water bath (Nuve NT 120, Turkey) was used in order to keep constant the temperature. 2.3. Preparation of new composite, CCA-g-PAA
For synthesis of CCA-g-PAA, 10 g of acrylamide (AA) monomer and 0.2 g of cross linker (N,N’-methylenebisacrylamide) were weighed and dissolved in 10 mL of water. 400 mg of CCA was added onto this mixture and stirred on a magnetic stirrer. Then, 300 mg of ammonium persulphate was added as starter agent. Polymerization reaction was sustained by adding 200 μL of N,N,N’,N’-tetramethylethylenediamine at room temperature. The obtained new composite was washed with ultrapure water and the ethanol for several times in order to remove non-grafted reagents. After then, it was dried, ground, and sieved by obtaining a homogene material. 2.4. Determination of uranyl ions in the solution The concentration of uranyl ions was determined by using the modified PAR method as spectrophotometrically [17]. In this method, uranyl ions are formed a selective complex with PAR (4-(2-pyridylazo) resorcinol) at pH 8.5. For this purpose, 3.5×10 -3 mol L-1 of PAR was prepared in Tris/HCl buffer (pH 8.5). Then, 50 µL of sample solution was added to 3 mL of PAR solution and the absorbance of the formed complex was followed at 530 nm. After a calibration graph was plotted, the concentration of uranyl ions was determined in the supernatants. 2.5. Adsorption studies Adsorptive
features of the developed adsorbent were investigated for UO 22+ ions. For this
purpose, 0.1 g of the adsorbent were equilibrated with 10 mL of UO 22+ in the concentration range of (0.37 - 3.70) ×10-3 mol L-1. The adsorbent–solution systems were equilibrated for 24 h at 298 K in a thermostatic water-bath and equilibrium solutions aqueous phase were obtained by centrifuging at 2.500 rpm for 5 min. The concentration of uranyl ions was determined as explained in section 2.4. 2.6. Point of zero charge and pH dependence of adsorption The determination of point of zero charge (PZC) was done to investigate the surface charge and acidic-basic character of adsorbent. For that 0.1 mol L-1 KNO3 solution was prepared and its initial pH was adjusted in the range of 1-12 by NaOH and HCl. Then 10 mL of KNO3 and 0.100 g adsorbent were interacted in test tubes. The samples were kept at 25 ºC for 24 hours and the final pH of solutions was measured by using a pH meter. The graph was plotted using initial versus final pHs and point of zero charge was determined by the obtained experimental results.
3. Result and Discussion 3.1. Characterization of new material The characterization of new material was carried out by ATR, UV-VIS-NIR, SEM, and EDX technicals.
The characteristic peaks of PAA and CCA were shown in the Figure 1a. When it was analysed the Attenuated Total Reflection (ATR) spectra belong to PAA, CCA, and CCA-gPAA structures, it can be seen that the desired CCA-g-PAA material was obtained successfully. More detailed comments about PAA material were presented in our previous study [18]. By considering this study, if it was focused on the ATR spectrum of CCA-g-PAA, a new peak can be seen at 1050 cm-1. In addition, the intensities of peaks at 1120 and 1190 cm-1 was became equal while they had different intensity in PAA structure. This change is also one of the evidences for grafting of CCA to PAA structure. Because, a change occurred in the chemical bonds of PAA during synthesis process. UV-VIS-NIR measurments were also used for more detailed characterization. It can be seen in the Figure 1b that all of PAA, CCA, and CCA-g-PAA structures have high reflectance intensity. Uranyl adsorbed CCA-g-PAA was also compared in order to see the change of reflectance intensity in UV-VIS region. Because, the color of new material is changed when it adsorps uranyl ions. So, it can be said that it works as a sensor. The reflectance of PAA and CCA-g-PAA shows difference significantly. At this region, the reflectance of CCA-g-PAA decreases while PAA’s reflectance is high still. The colors of CCA and PAA are pink and white, respectively. After CCA was grafted to PAA structure, the color of new material, CCA-g-PAA, turns to more dark and its reflectance decreases. Lighther color means more reflectance. The color of CCA-g-PAA is darker when it adsorps uranyl ions. All of these evidences showed that grafting of CCA to PAA structure and adsorption of uranyl ion by this material were performed successively. [19]
EDX and SEM instruments were also used for more detailed structural analysis of CCAg-PAA and results were shown in Figure 2. SEM view at seconder electron mode was presented at Figure 2a. It is clearly seen that there are distinctive changes in the images at back scattered electron mode (BSE, Figure 2b). The brightness is increased in some zone due to high atomic
mass of uranium and this provides the existing of uranium in the structure after adsorption. The obtained EDX diagram which presents the elemental composition of surface was given in the Figure 2c. The characteristic peak of uranium (Mα 3.17) can be seen next to gold peak which is used for plating of material. Moreover, the elemental composition of surface was also given in Table 1. In addition, as a result of EDX analysis, red points are demonstrated the zones where uranyl was adsorbed in the material (Figure 2d). This also provides adsorption of uranyl ions. 3.2. Influnce of pH to adsorption A series solutions having different pH in the range of 1-7 were prepared by using diluted HCl and NaOH. Test tubes including 50 mg of CCA-g-PAA and 100 mg L-1 uranyl ion were treated with these solutions. pH is one of the main parameters effecting the achievement of adsorption process. Because, both surface charge of adsorbent and ionic charges of species in the medium are depend on pH. The mobility of the other ions in the medium is affected by concentration of H + ions. Moreover, it also affects interest and capacity of adsorbent for target species. There is always a competition between H+ ions and target species depending on pH in the medium [20]. Espicially, if there are polyanionic or polycationic species in there solution, interactions are fairly affected by pH of medium. As a results of this experiments, it was observed that the adsorption of uranyl ions on surface of CCA-g-PAA was low at acidic pHs and then increased by pH (Figure 3a). This circumstance can be explained by two ways. Firstly, the charge of surface is changed by pH. Point of zero electric charge (PZC) experiments also showed that surface charge of adsorbent is negative beyond pH 5.5 and positive the pHs below 5.5 (Figure 3b) [21]. So, surface charge is going to negative by increasing pH. Then, as expected, adsorption of cationic uranyl ions increased in these pH values. Uranyl ions can precipitate at alkaline pHs as expected. So, it was not studied pHs beyond 7.0. Secondly, a lot of study showed that uranyl ions exist as hexavalent UO22+ ions at low pHs. This cationic ion can competite with H + ions and this competition is more at low pHs. This affect decreases with increasing pH. Initial pH of uranyl solutions used in adsorption studies was measured in range of 4-6.
mass of uranium and this provides the existing of uranium in the structure after adsorption. The obtained EDX diagram which presents the elemental composition of surface was given in the Figure 2c. The characteristic peak of uranium (Mα 3.17) can be seen next to gold peak which is used for plating of material. Moreover, the elemental composition of surface was also given in Table 1. In addition, as a result of EDX analysis, red points are demonstrated the zones where uranyl was adsorbed in the material (Figure 2d). This also provides adsorption of uranyl ions.