Abstract
Water represents an essential resource for life and for all natural processes. Our existence and our economic activities are totally dependent on this precious resource. It is well known that into the developing countries the main resource of drinkable water is represented by underground waters, so their contamination with arsenic represents a real problem that needs to be solved. To solve the problem of arsenic water pollution, it was necessary to develop a series of chemical, physicochemical and biological methods to reduce arsenic concentrations from water. From all these methods, adsorption offers many advantages including simple and stable operation, easy handling of waste, absence of added reagents, compact facilities and generally lower operation cost. The goal of this paper is to study the sorption properties of a new adsorbent material prepared by impregnating Amberlite XAD7 resin with crown ether (dibenzo-18-crown-6 ether) and loaded with Fe(III) ions. Solvent impregnated resin (SIR) method was used for functionalization. Amberlite XAD7 resin functionalization was evidenced by energy dispersive X-ray analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis and determination of specific surface by the Brunauer, Emmett and Teller (BET) analysis. Equilibrium, kinetic and thermodynamic studies were performed in order to determine the removal efficiency of the studied adsorbent for arsenic removal from water. In order to study the As(V) adsorption mechanism the experimental data were modelled using pseudo-first-order and pseudo-second order kinetic models. Kinetic of adsorption process was better described by pseudo-second-order model. Experimental data were fitted with three non-linear adsorption isotherm models: Langmuir, Freundlich and Sips. Obtained experimental data were better fitted by Sips adsorption isotherm. The values of thermodynamic parameters (ΔG°, ΔH°, ΔS°) showed that the adsorption process was endothermic and spontaneous. The results proved that Amberlite XAD7 resin with crown ether and loaded with Fe(III) is an efficient adsorbent for the As(V) removal from water. The possibility of reuse the adsorbent material through adsorption and desorption cycles was also studied and it was found that the material can be used in five sorption-desorption cycles. Maximum adsorption capacity obtained experimentally being 18.8 μg As(V)/g material.
Introduction
Ever since, drinking water quality has been a marker quality living and consequently a determining factor for human health. Arsenic compounds are known for their toxicity and their presence especially in drinking water represent a serious threat to more than 100 million people worldwide [1], [2].
There have been many documented incidents of arsenic groundwater contamination from worldwide, such as Taiwan, Chile, Argentina, Hungary, Bangladesh, India, Pakistan, Thailand, Vietnam, China and the United States [3], [4]. Arsenic contamination has also triggered various human health issues including skin lesions, diabetes, chronic bronchitis, cardiovascular diseases, peripheral neuropathies and negative effects on reproduction and haematological system [5]. People are susceptible to carcinogenic effects of arsenic, so prolonged exposure to arsenic damages the central nervous system, and is associated with appearance of various types of liver, lung, bladder, and skin cancer [6], [7].
To solve the problem represented by arsenic water pollution, it is necessary to develop a series of chemical, physicochemical and biological methods able to reduce arsenic concentrations from water. From these, the most common are: electrocoagulation [8], adsorption on chemically modified polymers [9], [10], alumina [11], activated mud [12], crystallized ferrihydrite [13], [14], etc.
However, during last years were developed new methods for arsenic removal from water, which are either cheaper, environmentally friendly, or show a higher removal efficiency. Thus, in this paper, following the development of crown ether applications, and the fact that Amberlite XAD resins are generally used for metal ions removal [15], [16] a new material was obtained starting from Amberlite XAD7, which was functionalized by impregnation with crown ether (dibenzo-18-crown-6 ether). Also, knowing the higher affinity of arsenic for iron ions (III), it was necessary for material to be loaded with these ions [17].
It is known the ability of crown ethers to bind metallic ions, whether they are symmetrically or unsymmetrically substituted such as crown ether-5 or crown ether-6 being the most commonly used [18].
The physical-chemical modification of Amberlite XAD7 by impregnation with dibenzo-18-crown-6 and loaded with Fe(III) ions represent a good choice for As(V) removal from aqueous solutions, due to the fact that resin is a relatively inexpensive commercial support and the amount of crown ether necessary for the functionalization is very small, but with representative effect for the adsorption process. This fact will be emphasized in present paper by As(V) adsorption process quantification, and by studying the absorbent performance of the obtained material.
Materials and methods
Preparation and characterization the material
In order to obtain the new adsorbent material, Amberlite XAD7 resin (Rohm and Hass Co., size 0.5–0.7 mm, surface area 380 m2 g−1) was used as solid support. Amberlite XAD 7 was functionalized by impregnation with dibenzo-18-crown-6 ether (Sigma – Aldrich, Merck, purity 98%), which structural formula is represented in Fig. 1.
Structural formula of dibenzo-18-crown-6 ether.
In order to improve the affinity of new adsorbent material for As(V) it is necessary to enrich his surface with Fe(III) ions (Sigma – Aldrich, Merck, purity 99.9%).
The material is prepared by using SIR dry method (Solid Impregnated Resin), when 0.05 g dibenzo-18-crown-6 ether was dissolved in 25 mL nitrobenzene (Sigma – Aldrich, Merck, analytical standard) and mixed with 5 g of Amberlite XAD7 resin, then obtained mixture was kept in contact for 24 h, after which it was filtered and dried at 50°C for 24 h.
To load the new material with iron ions, 25 mL of FeCl3 solution with concentration of 100 mg L−1 were added to the material, left in contact for 24 h, then filtered and dried for 24 h.
Obtained materials were characterized by X-ray dispersion (EDX) using a FEI Quanta FEG 250 instrument, by Fourier Transformed Infrared Spectroscopy (FTIR) using a Bruker Platinum ATR-QL Diamond instrument in the range of 4000–400 cm−1, thermogravimetrical (TG) analysis using a TG 209 F1 Libra (Nietzsche) device and determination of specific surface area by the Brunauer, Emmett and Teller-BET method using a Quantachrome NOVA 1200E instrument.
Adsorption experiments
Several parameters affecting the adsorption of As(V) like contact time, initial concentration and temperature were studied in batch experiments.
To study the influence of contact time and temperature onto the As(V) adsorption process, samples of 0.1 g material were mixed with 25 mL As(V) solution with concentration of 50 μg L−1 for different time periods (30, 60, 120, 180, 240, 300, 360, 420 and 480 min). This experiment was carried out at different temperatures (298 K, 308 K and 318 K) in a thermostatic bath.
For establish the influence of the As(V) initial concentration onto the As(V) adsorption process, samples of 0.1 g material were mixed with 25 mL As(V) solution with concentrations between 10 and 200 μg L−1 for 300 min and 298 K. All studies were made by keeping the pH in interval 7–8, which is the real drinking water.
The stock solutions were prepared by dissolving the adequate amount of H3AsO4 in HNO3 (Merck, 1000 mg As(V) per litter) in distilled water. All adsorption experiments were carried out in a Julabo SW23 thermostatic and shaking water bath with a stirring speed of 200 rpm. After that all samples were filtered and the filtrate was analysed to evaluate the arsenic residual concentration using an Inductively coupled plasma mass spectrometer-ICP-MS Bruker Aurora M90 type.
Sorption/desorption studies
In order to establish the maximum number of adsorption/desorption cycles the As(V) ions were adsorbed and desorbed until the adsorption is not any more possible. Desorption was performed by mixing 1 g polymer containing adsorbed ions with 25 mL NaCl 5%. The mixture was shaken for 2 h at 200 rpm at room temperature. After that the filtered adsorbent material was rinsed with distilled water and dried at room temperature. This step was repeated until the As(V) ions are irreversibly fixed onto the adsorbent material surface, establishing in this way the maximum number of usage cycles. Adsorption/desorption process efficiency was established by counting the adsorbed/desorbed of As(V) quantity.
Results and discussion
Characterization of the obtained material
From the EDX spectra, presented in Fig. 2 can be observed the presence of specific peaks of the Fe(III) ions as well as C and O peaks specific to the resin and crown ether.
EDX spectrum of material obtained by modification of Amberlite XAD7 resin with crown ether and loaded with iron ions.
After that, produced adsorbent material was characterised by recording the FT-IR spectra. In Fig. 3 is depicted the FTIR spectra of Amberlite XAD 7 functionalized with crown ether (dibenzo-18-crown-6 ether) and loaded with Fe(III) ions.
FT-IR spectra of material obtained by modification of Amberlite XAD7 resin with crown ether and loaded with iron ions.
By analysing the FT-IR spectra can observe presence of a specific band located into the range 3200–3000 cm−1, band associated with the presence of O–H bonds [19], while also noticing the presence of a sharp peak located around 1700 cm−1, peak associated with the presence of O–H from water. Presence of the peaks located at 1720 and 1600 cm−1 can be associated with the stretching vibrations of the C=C bond from the aromatic rings [20]. Presence of the band located around 1600 cm−1 can be attributed to the stretching vibrations of C=O bonds from the conjugate groups as could be attributed to the presence of carbonyl groups close to hydroxyl one [20]. Peak located around 1470 cm−1 can be associated with the vibration specific to the C–H groups. Bands characteristic of dibenzo-18-crown-6 ether appear in the range 1550–500 cm−1, the most intense are located at 1100 cm−1 and 1000 cm−1 and they can be attributed to Calphatic-O-Caromatic, respectively Calphatic-O-Calphatic bonds vibrations [17]. At same time, iron surface loading is evidenced by the presence of peaks located near 1037 cm−1, peaks which can be associated with the stretching vibrations of Fe–OH bonds [10].
In order to establish the thermal stability of the new produced adsorbent material, were recorded the TG and DTG curves into the temperature range of 20–1000°C, curves depicted in Fig. 4.
Thermogravimetry (TG) analysis.
Analysing thermogravimetric curves depicted into the Fig. 4 reveal three stages of thermal decomposition of studied adsorbent material. First stage of thermal decomposition is observed into the temperature range between 20 and 200°C, when around 10% of mass was lost, which can be associated with water loss. By further increasing of the temperature can observe that the studied material is stable until the temperature reach the value of 300°C. Second stage of thermal decomposition occurs between 300 and 380°C when 40% of the total mass was lost. This loss can be associated with the degradation of the low molecular mass organic compounds, means with the degradation of crown ethers. Further increase of the temperature reveals no changes until temperature reach 400°C. Third stage of thermal decomposition is taking place between 400 and 500°C, when approximate 50% of the total mass was loss, and which can be associated with the thermal decomposition of Amberlite XAD 7 resin. Total mass loss up 500°C is over 90%, and by increasing temperature until 900°C can observe that final residue mass is less than 1%, so we can confirm that at 900°C the studied product is totally decomposed.
Into the next step was determined the specific surface of the new produced adsorbent material and compared with the one of non-functionalized polymer. So after performing the measurements was observed that the specific surface of the functionalized material has the value of 126 m2 g−1, less than the surface of non-functionalized Amberlite XAD7 resin (300 m2 g−1). Based on that can confirm that the crown ether and irons ions used for functionalization penetrate into the resin pores reducing in this way the specific surface of studied material, reconfirming that the Amberlite XAD 7 resin was functionalized with crown ether and iron ions.
Adsorption of As(V) on the obtained material
In order to better understand the adsorption process of As(V) ions onto the studied material is important to know which species of As(V) ions are presented into the aqueous solution used during experiments.
It is known that in aqueous solutions As(V) exists in the form of four species: H3AsO4, H2AsO4−, HAsO42−, AsO43− (Fig. 5). In our study, the pH of the process was kept in range 7–8, so we can say that the specific species would be H2AsO4− or/and HAsO42− [21], [22], [23].
Diagram of distribution of As(V) species according to pH.
pKa1=2.2; pKa2=6.8; pKa3=11.5; αo – AsO43−; α1 – HAsO42−; α2 – H2AsO4−; α3 – H3AsO4.
Kinetic studies and activation energy
Most important parameters affecting the adsorption process are represented by the contact time and temperature. The effect of contact time and temperature for As(V) adsorption process on the crown ether functionalized Amberlite XAD7 loaded with iron ions are presented in Fig. 6.
Influence of contact time and temperature on the adsorption capacity of the functionalized material.
From experimental data depicted into Fig. 6 can observe that the adsorption capacity increase with the increase of the contact time up to 300 min. Further increase of the contact time lead at no further increase of the adsorption capacity, which remains practically constant, so can conclude that after 300 min contact time is not influencing any more the adsorption process. At same time can observe that the increase of temperature at which was studied the adsorption have an insignificant influence onto the As(V) adsorption capacity. Based on these experimental data can establish the optimal experimental conditions for the As(V) adsorption onto the new produced adsorbent material: contact time 4 h and temperature 298 K. Also, from experimental data was determined the value of the adsorption capacity, ~11 μg As(V) per g of adsorbent material.
The equilibrium adsorption capacity was calculated using eq. 1:
where: Co and Ce are the initial solution concentration and equilibrium concentration (μg/L), V is the volume of the solution (L), and m is the amount of adsorbent material (g).
In order to establish the As(V) adsorption mechanism experimental data were modelled using Lagergren pseudo – first – order kinetic model (model described by eq. 2) [24] and Ho and McKay pseudo – second – order model (described by eq. 3) [25]:
where qe is the adsorption capacity at equilibrium (μg/g) and qt is the adsorption capacity at time t, t is the contact time (min), k1 is the pseudo-first-order rate constant (1/min) and k2 the pseudo-second-order rate constant (g/μg·min).
Based on that were obtained the pseudo – first – order plots and pseudo – second – order one, plots depicted into Figs. 7 and 8.
Pseudo-first order plots for the adsorption of As(V) on the functionalized material.
Pseudo-second order plots for the adsorption of As(V) on the functionalized material.
From linear dependence of ln(qe–qt) versus t, dependence associated with pseudo – first – order model were evaluated the values of rate constant (k1) and the adsorption equilibrium capacity qe,calc. Similar from the linear dependence t/qt versus t, were evaluated the values of rate constant (k2) and the equilibrium adsorption capacity qe,calc. Also, for both models, were determined the correlation coefficients R2, data presented in Table 1.
Kinetic parameters for the adsorption of As(V) on the functionalized material.
| Temperature (K) | q e,exp (μg g−1) | k 1 (min−1) | q e,calc (μg g−1) | R 2 |
|---|---|---|---|---|
| Pseudo-first order | ||||
| 298 | 10.21 | 4.7·10−3 | 4.59 | 0.8284 |
| 308 | 10.70 | 6.1·10−3 | 3.76 | 0.7684 |
| 318 | 10.82 | 6.9·10−3 | 3.63 | 0.8661 |
|
k
2 (g μg−1·min−1)
|
||||
| Pseudo-second order | ||||
| 298 | 10.21 | 48.09 | 11.82 | 0.9984 |
| 308 | 10.70 | 65.73 | 12.25 | 0.9984 |
| 318 | 10.82 | 74.17 | 12.25 | 0.9991 |
Analysing data presented in Table 1 can observe that the correlation coefficient for the pseudo – first – order model is into the range of 0.8284–0.8661, and for pseudo – second – order model is in range of 0.9984–0.9991, values much closer to 1. Also the calculated equilibrium adsorption capacities were around 12, values much closer to the obtained experimental data. Based onto the higher correlation coefficient and due to the smaller differences between experimental and calculated equilibrium adsorption capacities can conclude that the pseudo – second – order model describe better obtained experimental data.
These results confirm literature data according to which the adsorption process depends on the temperature and at the same time the chemical reactions can represent the limiting factor for adsorption process speed [25], [26].
Influence of initial concentration of the As(V)
Also was studied the influence of As(V) initial concentration onto the material adsorption capacity, data depicted in Fig. 9. Analysing data presented in Fig. 11 can observe that the increase of the initial concentration of As(V) leads to an increase of the adsorption capacity until a constant value is reached. Maximum value of the adsorption capacity has a value of 18.8 μg g−1 being reached when the initial concentration has a value of 150 μg L−1, further increase of the initial concentration leads at no further increase of the maximum adsorption capacity.
Influence of the initial concentration of the As(V) solution on adsorption capacity.
Thermodynamic studies
In order to investigate the spontaneity and thermal properties of the As(V) adsorption process on the studied material the influence of temperature on the adsorption capacity of As(V) was investigated by representing the linear dependence of ln k2 versus 1/T (data depicted in Fig. 10).
Arrhenius plot of the adsorption of As(V) on the functionalized material.
Based on the obtained experimental data, and by using the Arrhenius equation (eq. 4) is possible to evaluate the values of the activation energy associated with the As(V) adsorption process onto the produced material. Speed constant used into eq. 4 was determined by modelling the experimental data with pseudo – second – order model.
where k2 is the rate constant (g/min·μg), A is the Arrhenius constant (g·min/μg), E is the activation energy (kJ/mol), R the ideal gas constant (8.314 J/mol·K), and T is the absolute temperature (K).
Based on obtained experimental data was calculated the activation energy value Ea=2.15 KJ/mol and correlation coefficient R2=0.8949. Calculated value of activation energy suggests that the As(V) adsorption onto the studied material is a physical-sorption, but also an endothermic process.
In order to determine how As(V) adsorption process takes place on the surface of the obtained adsorbent material, was calculated the value of free Gibbs energy using the Gibbs-Helmholtz equation (eq. 5) [27].
where ΔS° is the standard entropy change and ΔH° is the standard enthalpy change.
Variations of standard entropy ΔS° and standard enthalpy ΔH° can be calculated from equation (eq. 6) associated with the linear representation of ln Kd function of 1/T (Fig. 11):
Plot of ln Kd vs. 1/T.
where T is the absolute temperature (K) and R the ideal gas constant.
Equilibrium constant Kd is calculated as ratio of equilibrium adsorption capacity – qe – and equilibrium concentration (eq. 7):
Base on linear dependence of ln Kd versus 1/T (depicted in Fig. 11) were calculated the values of thermodynamic parameters associated with the As(V) adsorption process onto the functionalized material (obtained data are presented in Table 2).
Thermodynamic parameters for the adsorption of As(V) on the functionalized material.
| ΔH° (kJ/mol) | ΔS° (J/mol·K) | ΔG° (kJ/mol) |
R 2 | ||
|---|---|---|---|---|---|
| 298 K | 308 K | 318 K | |||
| 15.43 | 55.86 | −1.215 | −1.774 | −2.332 | 0.7913 |
Analysing the data presented in Table 2 can observe that the free Gibbs energy have negative values, which suggests that the As(V) adsorption process onto the functionalized material is a spontaneous and natural process. When the temperature increases can observe that the values of free Gibbs energy becomes more negative, meaning that the adsorption speed increases with temperature increase; this increase of process speed can be attributed to effective growth of the contact surface between adsorbent material and As(V) ions.
Positive value of entropy variation suggests that the adsorption speed increases at adsorbent material/solution interface and the degree of particles clutter increases when the temperature increase. Such behaviour can be attributed to appearance of some changes at material’s surface level. Based on that can affirm that the adsorption of As(V) onto the adsorbent material surface is an endothermic and spontaneous process.
Equilibrium studies
In order to understand the adsorption process mechanism must obtain the adsorption equilibrium data, which can be done by modelling the experimental data using different adsorption isotherms.
Classical adsorption isotherms are represented by Langmuir and Freundlich one; based on these two classical isotherms was developed the non-linear Sips isotherm which represent a combination between classical isotherms.
Obtained experimental data for As(V) adsorption onto the studied adsorbent material were fit using these three non-linear adsorption isotherm models: Langmuir, Freundlich and Sips.
Langmuir isotherm presumes that the adsorption of the adsorbate takes place as a monolayer adsorption on the homogeneous surface of the adsorbent, the activation energy for the adsorption is uniform for all adsorbed molecules, and all adsorption sites are equal. Langmuir non-linear adsorption isotherm is expressed by eq. 8 [28]:
where qe is the equilibrium adsorption capacity (μg/g), Ce is the equilibrium concentration of As(V) in the solution (μg/L), qL the Langmuir maximum adsorption capacity (μg/g), and KL is the Langmuir constant.
Freundlich adsorption isotherm presumes that the surface of the adsorbent is heterogeneous, the distribution of adsorption heat is non-uniform and the adsorption can take place as multilayer. The Freundlich non-linear isotherm is written as in eq. 9 [29]:
where qe is the equilibrium adsorption capacity (μg/g), Ce is the equilibrium concentration of As(V) in the solution (μg/L), KF and nF are characteristic constants.
Sips isotherm represent a combination of the Langmuir and Freundlich isotherms, at adsorbate low concentrations having the characteristics of the Freundlich isotherm, and at high concentrations the characteristics of Langmuir isotherm. The Sips non-linear isotherm is written as in eq. 10 [30]:
where qS (μg/g) is the maximum adsorption capacity, KS is a constant related to the adsorption capacity of the adsorbent, nS is the heterogeneity factor.
Obtained experimental data were modelled using Langmuir, Freundlich and Sips adsorption isotherm. Based on that were obtained the isotherms modelling the adsorption of As(V) ions onto Amberlite XAD7 functionalized with dibenzo – 18 – crown – 6 ether (Fig. 12). Analysing data presented in Fig. 12 can observe that when the initial concentration of As(V) ions increase, as well as the adsorption capacity of studied adsorbent material until an equilibrium concentration (qm,exp) of about 18.8 μ g−1 is reached.
Adsorption isotherm of adsorption As(V) on the functionalized material.
Also, by modelling obtained experimental data with adsorption isotherms were determined the parameters used to describe the adsorption process of As(V) onto functionalized Amberlite XAD7. Obtained parameters are depicted in Table 3.
Parameters of isotherm model for the adsorption of As(V) on the functionalized material.
| q m,exp (μg/g) | K L (L/μg) | q L (μg/g) | R 2 |
|---|---|---|---|
| Langmuir isotherm | |||
| 18.86 | 0.018 | 29.27 | 0.9687 |
| K F (μg/g) | 1/nF | R 2 | |
|
|
|||
| Freundlich isotherm | |||
| 1.50 | 0.552 | 0.9131 | |
| K S | q S (μg/g) | 1/nS | R 2 |
|
|
|||
| Sips isotherm | |||
| 3.31·10−3 | 21.43 | 0.68 | 0.9866 |
Based on data presented in Table 3 can observe that the non – linear Sips adsorption isotherm better describe the adsorption of As(V) ions onto functionalized Amberlite XAD7. From data presented in Table 3 can observe that for Sips model was obtained the highest value for the correlation coefficient, and simultaneously the value of calculated maximum adsorption capacity (qs=21.43 μg g−1) is closer to the obtained experimental value (qm,exp=18.8 μg g−1). Also, from the values of the parameters 1/ns (Sips adsorption isotherm) and 1/nF (Freundlich adsorption isotherm), lower then 1, get confirmation that the studied adsorption process is favourable.
In Table 4 are presented the maximum adsorption capacities obtained when different synthesized of functionalized materials were used as adsorbents for As(V) removal from aqueous solutions. It is well known that Amberlite XAD7 type resins, especially functionalized with pendant groups, present good efficiency for arsenic removal from aqueous solutions through adsorption, fact confirmed also by the data presented in Table 4.
Comparison to other materials for As(V) adsorption.
| Adsorbent | Adsorption capacity, μg As(V) g−1 | Reference |
|---|---|---|
| Copolymer styrene-1% divinylbenzene grafted with phosphonic acid where R=CH3CH2 – (AP1) loaded with iron ion | 10.5 | [31] |
| Copolymer styrene-1% divinylbenzene grafted with phosphonic acid where R=C6H5 – (AP2) loaded with iron | 10.0 | [31] |
| Copolymer styrene-1% divinylbenzene grafted with phosphoric acid where R=CH3CH2 – (AP3) loaded with iron | 6.3 | [31] |
| Copolymer styrene-1% divinylbenzene grafted with phosphoric acid where R=C6H5 – (AP4) loaded with iron | 5.0 | [31] |
| Florisil-dibenzo-18-crown-6 ether-Fe | 2.75 | [17] |
| Amberlite XAD-7-dibenzo-18-crown-6 ether-Fe | 18.8 | Present paper |
Adsorption-desorption studies
One important parameter characterising the efficiency of adsorbent materials into the practical approach is represented by their regenerative capacity, which is translated into possibility to reuse such adsorbent materials. In order to obtain good efficiency (low cost for arsenic removal) is necessary that the regenerative process occurs easy and the metallic ions are desorbed really fast and in higher quantity, so the reuse of adsorbent materials becomes economically feasible.
In present paper was investigated the possibility to reuse the functionalized Amberlite XAD7 used adsorbent by establishing the adsorption/desorption cycles number. Best results for desorption of As(V) were achieved when NaCl 5% was used, and this process has been repeated with significant results for 5 times, as can be observed from data depicted in Fig. 13.
Adsorption/desorption cycles.
Conclusions
In present paper were investigated the adsorbent proprieties of new produced material obtained by functionalization of Amberlite XAD 7 resin with dibenzo – 18 – crown – 6 ether, loaded with iron ions, due to well-known affinity of arsenic ions for iron.
The presence of crown ether (dibenzo-18-crown-6) and iron ions on the functionalized material was proved by energy dispersive X-ray analysis, scanning electron microscopy –SEM, Fourier transform infrared spectroscopy (FTIR), thermogravimetrical (TG) analysis and determination of specific surface area (BET).
The influence of various parameters affecting the adsorption of As(V) like contact time, initial concentration and temperature was studied in batch experiments. Kinetic studies showed that the optimum contact time between As(V) solution and functionalized material was of 300 min and the optimum temperature was 298 K. Obtained experimental data were modelled using the pseudo-first-order and the pseudo-second-order kinetic models. Based on that was observed that the adsorption process is better described by the pseudo-second-order model.
Also, was evaluated the value of the activation energy. The positive value of activation energy (2.15 KJ/mol) suggested that the adsorption process was endothermic, and the mechanism was physical adsorption. Non-linear regression analysis of the equilibrium data was performed using Langmuir, Freundlich, and Sips isotherm models. From all these adsorption isotherms, Sips one is better describing the As(V) adsorption process onto the functionalized Amberlite XAD 7 resin.
Maximum adsorption capacity of the functionalized material was of 18.8 μg As(V) g−1. The values of thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated and showed that the adsorption process was endothermic and spontaneous. The results showed that Amberlite XAD7 functionalized with crown ether (dibenzo-18-crown-6) and loaded with Fe(III) is an effective adsorbent for the removal of As(V) ions from aqueous solutions. The possibility of reuse of the material was studied by adsorption/desorption cycles and it was found that the material can be used for five cycles of adsorption/desorption.
Article note
A collection of papers presented at the 17th Polymers and Organic Chemistry (POC-17) conference held 4–7 June 2018 in Le Corum, Montpelier, France.
Funding source: Universitatea Politehnica Timisoara
Award Identifier / Grant number: PCD-TC-2017
Funding statement: This work was supported by research, Universitatea Politehnica Timisoara, Funder Id: 10.13039/501100007424, grants PCD-TC-2017.
References
[1] S. M. Imdadullah Qureshi, M. Yilmaz. C. R. Chim.13, 1416 (2010).10.1016/j.crci.2010.02.007Search in Google Scholar
[2] E. P. K. Tyrovola, N. Nikolaideis. Environ. Sci. Pollut. Res. Int.2007, 356 (2007).10.1016/j.ejsobi.2007.03.011Search in Google Scholar
[3] D. G. K. P. L. Smedley. Appl. Geochem.17, 517 (2002).10.1016/S0883-2927(02)00018-5Search in Google Scholar
[4] J. M. M. R. T. Nickson, B. Shrestha, T. O. Kyaw-Myin, D. Lowry. Appl. Geochem.20, 55 (2005).10.1016/j.apgeochem.2004.06.004Search in Google Scholar
[5] N. N. R. Council. National Academy Press, Washington DC (1999).Search in Google Scholar
[6] A. H. Hall. Toxicol. Lett.10, 69 (2002).10.1186/rr159Search in Google Scholar PubMed PubMed Central
[7] D. R. G. O. L. Valenzuela, V. H. Borja-Aburto, J. Contreras-Ruiz., G. G. García-Vargas, L. M. Del Razo. Toxicol. Appl. Pharmacol.1, 264 (2007).10.1016/j.taap.2006.12.015Search in Google Scholar PubMed PubMed Central
[8] P. Ratna Kumar, S. Chaudhari, K. C. Khilar, S. P. Mahajan. Chemosphere55, 1245 (2004).10.1016/j.chemosphere.2003.12.025Search in Google Scholar PubMed
[9] M. d. L. Ballinas, E. Rodríguez de San Miguel, M. T. d. J. Rodríguez, O. Silva, M. Muñoz, J. de Gyves. Environ. Sci. Technol.38, 886 (2004).10.1021/es030422jSearch in Google Scholar PubMed
[10] M. Ciopec, A. Negrea, L. Lupa, C. M. Davidescu, P. Negrea. Molecules (Basel, Switzerland)19, 16082 (2014).10.3390/molecules191016082Search in Google Scholar PubMed PubMed Central
[11] Y. Kim, C. Kim, I. Choi, S. Rengaraj, J. Yi. Environ. Sci. Technol.38, 924 (2004).10.1021/es0346431Search in Google Scholar PubMed
[12] H. Genç-Fuhrman, J. C. Tjell, D. McConchie. Environ. Sci. Technol.38, 2428 (2004).10.1021/es035207hSearch in Google Scholar PubMed
[13] W. R. Richmond, M. Loan, J. Morton, G. M. Parkinson. Environ. Sci. Technol.38, 2368 (2004).10.1021/es0353154Search in Google Scholar PubMed
[14] A. Negrea, C. Muntean, I. Botnarescu, M. Ciopec, M. Motoc. Rev. Chim.64, 397 (2013).Search in Google Scholar
[15] M. Ciopec, C. M. Davidescu, A. Negrea, C. Muntean, A. Popa, P. Negrea, L. Lupa. Adsorpt. Sci. Technol.29, 989 (2011).10.1260/0263-6174.29.10.989Search in Google Scholar
[16] A. Negrea, M. Ciopec, L. Lupa, C. M. Davidescu, A. Popa, G. Ilia, P. Negrea. J. Chem. Eng. Data56, 3830 (2011).10.1021/je200476uSearch in Google Scholar
[17] A. Negrea, A. Popa, M. Ciopec, L. Lupa, P. Negrea, C. M. Davidescu, M. Motoc, V. Minzatu. Pure Appl. Chem.86, 1729 (2014).10.1515/pac-2014-0806Search in Google Scholar
[18] M. Ouchi, T. Hakushi. Coord. Chem. Rev.148, 171 (1996).10.1016/0010-8545(96)01208-8Search in Google Scholar
[19] A. M. Puziy, O. I. Poddubnaya, A. Martinez-Alonso, F. Suarez-Garcia, J. M. D. Tascon. Carbon40, 1493 (2002).10.1016/S0008-6223(01)00317-7Search in Google Scholar
[20] H. S. Hassan, M. F. Attallah, S. M. Yakout. J. Radioanal. Nucl. Chem.286, 17 (2010).10.1007/s10967-010-0654-xSearch in Google Scholar
[21] K. Ohe, Y. Tagai, S. Nakamura, T. Oshima, Y. Baba. J. Chem. Eng. Jpn.38, 671 (2005).10.1252/jcej.38.671Search in Google Scholar
[22] M. Pârlea, C. Muntean. Qualitative Analytical Chemistry: Theoretical Aspects. Eurobit, Timişoara (2001).Search in Google Scholar
[23] A. Negrea, M. Ciopec, P. Negrea, L. Lupa, R. Lazau. Buletinul AGIR2, 71 (2011).Search in Google Scholar
[24] S. Lagergren. K. Sven. Vetensk. Akad. Handl. – 189824, 1 (1898).Search in Google Scholar
[25] Y. S. Ho, G. McKay. Process Biochem.34, 451 (1999).10.1016/S0032-9592(98)00112-5Search in Google Scholar
[26] S. N. D. Ramos, A. L. P. Xavier, F. S. Teodoro, M. M. C. Elias, F. J. Goncalves, L. F. Gil, R. P. de Freitas, L. V. A. Gurgel. Ind. Crop. Prod.74, 357 (2015).10.1016/j.indcrop.2015.05.022Search in Google Scholar
[27] P. Atkins, J. de Paula. Atkins’ Physical Chemistry. Oxford University Press, Oxford, UK (2005).Search in Google Scholar
[28] I. Langmuir. J. Am. Chem. Soc.40, 1361 (1918).10.1021/ja02242a004Search in Google Scholar
[29] H. M. F. Freundlich. J. Am. Chem. Soc.57, 385 (1906).Search in Google Scholar
[30] R. Sips. J. Chem. Phys.16, 490 (1948).10.1063/1.1746922Search in Google Scholar
[31] A. Negrea, M. Ciopec, P. Negrea, L. Lupa, A. Popa, M. Davidescu Corneliu, G. Ilia. Open Chem.13, 105 (2014).10.1515/chem-2015-0025Search in Google Scholar
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