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Removal of NO3− ions from water using bioadsorbent based on gum tragacanth carbohydrate biopolymer
Carbohydrate Polymers 227 (2020) 115367
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Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Removal of NO3− ions from water using bioadsorbent based on gum tragacanth carbohydrate biopolymer
T
⁎
Maryam Shojaipoura, Mousa Ghaemya, , Seyed Mojtaba Amininasabb a b
Polymer Research Laboratory, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran Laboratory of Polymer Chemistry, Faculty of Science, University of Kurdistan, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Bioadsorbent Gum tragacanth carbohydrate Quaternary ammonium salt NO3− removal
In this study, functionalized hydrogel bioadsorbents were produced from gum tragacanth (GT) carbohydrate and quaternary ammonium salt (TMSQA) as a crosslinker. The prepared bioadsorbents were used for the removal of NO3− ions from water through the electrostatic and ion exchange mechanism and antibacterial activity. The effect of quaternary ammonium content on the adsorption capacity was studied. The bioadsorbents were characterized by using FE-SEM, energy dispersive X-Ray (EDX), FT-IR, and TGA techniques. The equilibrium time and the most effective pH value for maximum NO3− removal (20 mg g−1) were 21 min and 7, respectively. A series of isotherms and kinetics models were undertaken and the obtained data were fitted well to the Langmuir isotherm and pseudo-second-order rate kinetic. The thermodynamic study confirmed the suitability of NO3− removal by the as-prepared bioadsorbent at room temperature, and also the negative value of ΔGº = −89.1 kJ mol−1 demonstrating the spontaneous nature of adsorption.
1. Introduction Water is an essential component for the life of living organisms on the earth and the groundwater is the most important source of sweetened water in the world. In recent years, growth of the population along with the rising industrial and agricultural activities have increased the pollution due to the presence of contaminants such as inorganic ions, heavy metals, organic contaminants, and synthetic chemicals (Ali, 2012; Ediagbonya et al., 2015). Nitrate is one of the most important inorganic anions of major water pollutant in many areas of the world which has caused much concern about the quality of drinking water. The pervasive use of artificial fertilizer in agriculture, disposal of untreated municipal and animal waste, changes in land use, and industrial activities have often enrich the amount of nitrate in soil and limits the direct use of the groundwater resources (Chauhan et al., 2016; Mohseni-Bandpi, Elliott, & Zazouli, 2013). The presence of high concentrations of nitrate in drinking water can cause stomach cancer with an extensive variety of tumors, blue baby syndrome and shortness of breath, and will also be a serious threat to the life of fish, animals and the destruction of water supplies (Ashok & Hait, 2015; Nur, Shim, Loganathan, Vigneswaran, & Kandasamy, 2015). According to the world health organization (WHO) and other environmental regulatory agencies, the maximum allowable concentration of nitrate in drinking water is 45–50 mg/L (10–11.3 mg/L N-NO3−) (Ward et al., 2018). ⁎
Nitrates can be removed by chemical, physical, and biological methods from aqueous environments (Alighardashi, Kashitarash Esfahani, Najafi, Afkhami, & Hassani, 2018) These methods include reduction by enzymes and catalytic, biological and chemical, denitrification, nanofiltration (NF), electrodialysis, ion exchange, reverse osmosis, and adsorption method (Mohseni-Bandpi et al., 2013; Shrimali & Singh, 2001). Among these various techniques, adsorption or ion exchange is the most simple, efficient, ease of operation, relatively low cost, and renewable method which is generally considered for removal of pollutants from water (Bhatnagar & Sillanpää, 2011). In recent years, the use of natural biopolymers such as gum tragacanth (GT) (Sahraei, Sekhavat Pour, & Ghaemy, 2017), chitosan (Kim, Balathanigaimani, & Moon, 2015), alginate (Swain, Patnaik, & Dey, 2013), cellulose (Kanmani, Aravind, Kamaraj, Sureshbabu, & Karthikeyan, 2017), starch (Chauhan, Kaur, Kumari, Kumari, & Chauhan, 2015) and rice husk (Masoumi, Hemmati, & Ghaemy, 2016) as adsorbent for the removal of pollutants has been developed due to their availability, biocompatibility, biodegradability, chemical stability, specific structure and easy modification (Crini, 2005; Kanmani et al., 2017). GT is an abundant natural biocompatible polymer which is available in many Middle Eastern countries. Although GT hydrogels have been used before for water purification but has never been used as an ion exchange resin for the removal of nitrate ion. It has recently been demonstrated that quaternary ammonium functionalized adsorbents with the anion
Corresponding author. E-mail address: [email protected] (M. Ghaemy).
https://doi.org/10.1016/j.carbpol.2019.115367 Received 8 July 2019; Received in revised form 14 September 2019; Accepted 20 September 2019 Available online 24 September 2019 0144-8617/ © 2019 Elsevier Ltd. All rights reserved.
Carbohydrate Polymers 227 (2020) 115367
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that the adsorption was complete after 20 min, then the adsorbent was separated from the solution by centrifuging. The equilibrium concentration of NO3− was determined by the addition of 0.4 mL HCl (1 N) using UV–vis spectrophotometer at wavelengths 220 and 275 nm (A(NO3− ) = A(220nm) −2 A(275nm)), according to the reported procedure (Rashidi Nodeh, Sereshti, Zamiri Afsharian, & Nouri, 2017). The concentration of the residual NO3− ions (the equilibrium concentration) after centrifugation was determined by using a standard curve obtained from standard concentrations of NO3− ions. All experiments were carried out twice and the given adsorbed concentrations were the means of duplicate experimental results. The removal percentage (R%) and the equilibrium adsorption capacity (Qe, mg g−1) of NO3− ions were calculated according to Eqs. (1) and (2), respectively:
exchangeability and antibacterial activity can be useful for the removal of nitrate ion from contaminated water (Makvandi, Jamaledin, Jabbari, Nikfarjam, & Borzacchiello, 2018; Palko, Oyarzun, Ha, Stadermann, & Santiago, 2018). However, the quaternary ammonium salts have never been used as a cross-linker and an anionic exchanger at the same time in a natural carbohydrate polymer for the removal of nitrate ions from water. In the present study, the objective was to prepare a biopolymerbased hydrogel adsorbent from GT functionalized with a synthesized quaternary ammonium chloride which has also acted as a crosslinker. The quaternary ammonium salt (TMSQA) was obtained from the reaction between N-(trimethylsilyl) imidazole (NTMSI) and (3-chloropropyl) trimethoxysilane (CPTS). The prepared hydrogel bioadsorbent was characterized by using 1HNMR, FE-SEM, X-Ray (EDX), FT-IR, and TGA techniques and then used to the removal of NO3− ions from water through the electrostatic and ion exchange mechanism. The various absorption parameters such as contact time, adsorbent dosage, and concentration of NO3− ions, pH, and temperature were also investigated to determine the best absorption conditions. The kinetics and isothermal parameters for the removal of NO3− from water by the prepared bioadsorbent was investigated.
R (%) =
Qe =
C0 − Ce × 100 C0
C0 − Ce ×V m
(1) (2)
2. Experimental section
Where C0 and Ce are the initial and equilibrium concentration of NO3− ions in solution, respectively; m is the amount of adsorbent (g); V is the volume of the solution (L); qe is the absorption capacity (mg g−1) and R (%) is adsorption percent.
2.1. Materials
3. Results and discussion
N-(Trimethylsilyl)imidazole (NTMSI), (3-chloropropyl)trimethoxysilane (CPTS), potassium nitrate, acetic acid, toluene and ethanol, Silver nitrate, were purchased from Merck Co. (Germany). All the chemicals were of reagent grade and used without any further purification. Gum tragacanth (GT) was purchased from a local pharmaceutical shop (Sanandaj, Kurdistan, Iran). The synthetic methods of trimethoxysilane functionalized quaternary ammonium salt (TMSQA) as a crosslinker and bioadsorbent, and devices used for analysis are described in section S1 (From supplementary data).
3.1. Preparation and characterization of bioadsorbent hydrogel Modification of the chemical and physical properties of natural and synthetic polymers is a well-known method. In this study, the macromolecular structure of a natural carbohydrate polymer, GT, has been modified by graft polymerization using TMSQA acting also as a crosslinker. Therefore, the main properties of the ion exchange function are kept in the quaternary ammonium salt. One of the main properties of carbohydrate polymers is biodegradability which is preserved to some extent in the crosslinked bioadsorbent hydrogels. The bioadsorbent has been synthesized in two steps that are illustrated in schematic form in Scheme 1. In the first step, the quaternary ammonium salt was synthesized from the substitution reaction between CPTS and NTMSI in toluene as described in section S1.1. Quaternization of the nitrogen atom in imidazole ring with chlorine improves the ionic character. In the second step, the bioadsorbent was obtained from the reaction between hydroxyl groups on the macromolecular chains of GT and trimethoxysilane groups of the crosslinker TMSQA in a mixture of ethylene and acidic acid. The amount of TMSQA required as crosslinker which affected the gel content and also the adsorption process has been investigated here to obtain materials with reasonable adsorption. As can be seen in Table 1S, the gel content increased with increasing TMSQA content in the range of 33–66 wt %. It can be concluded that the increase in the gel content may be due to the increase in the diffusion rate of the crosslinker into the bulk of GT macromolecular chains. To determine the gel content, a certain amount of composite was placed in a soxhlet system and refluxed in distilled water for 72 h. Eq. (3) was used to determine the amount of dried gel remained after extraction and the results are reported in Table 1S (from Supplementary data).
2.2. Antibacterial activity Antibacterial activity of the synthesized composites were evaluated by using Kirby-Bauer technique against the Gram-negative bacterium Escherichia coli (E. coli) and the Gram-positive bacterium Bacillus subtilis (B. subtilis) (Pourshab, Asghari, & Mohseni, 2018). Gentamicin and chloramphenicol as Standard antibacterial drug were used in the method that are considered a benchmark for comparing their antibacterial activity with synthesized composites (GT/TMSQA: 1/2, 1/1 and 2/1) and the results of this study are reported in the Table 4S and Fig. 3S. (From supplementary data) 2.3. Adsorption experiments Adsorption of NO3− ions onto prepared bioadsorbent was carried out with batch experiments. The stock nitrate solution was prepared by dissolving an accurate quantity of KNO3 in distilled water (1000 mg/L). The required concentrations of the NO3− ions (20, 30, 40, 50 and 60 ppm) was prepared by serial dilution of stock solution in room temperature and then filtered. The adsorption behavior of NO3− ions onto the hydrogel bioadsorbent was investigated in 20 mL aqueous solution at different temperatures (298–318°K), and by varying the effective parameters including adsorbent dosage (5–40 mg), pH medium (3–11), contact time (5–30 min), and initial NO3− concentration (20–60 ppm) to achieve the best conditions with the highest adsorption capacity and understand the mechanism of the adsorption process. pH was adjusted to the desired level with 0.1 M NaOH or 0.1M HCl solutions. All other variables were kept constant while a particular variable was under verification. Experiments were mainly carried out with the initial adjustment of the pH and the preliminary tests showed
Gel fraction(%) =
Wg W0
× 100
(3)
Where W0 and Wg are the weight of the initial dry material and after the process of soxhlet extraction, respectively (Sadat Hosseini, Hemmati, & Ghaemy, 2016). The results show that the gel content as a result of crosslinking reaction and networking increased from 31.5 wt % to 72.8 wt% when the amount of TMSQA increased from 33 wt% to 66 wt %. The swelling behavior of the bioadsorbent was investigated at different times. The results of this study are fully documented in Table 1S 2
Carbohydrate Polymers 227 (2020) 115367
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Scheme 1. Schematic presentation for synthesis of biopolymer adsorbent.
absorption bands at 1622 and 1745 cm−1 in Fig. 1b corresponds to carboxylic acid or carboxylate groups of d-galacturonic acid in GT structure. The absorption bands in the region 1100–1200 cm−1 can demonstrate the stretching vibrations of CeO bond in ether and alcohol groups of GT and also the absorption bands at 2927 and 3432 cm−1 related to the stretching vibrations of aliphatic CeH and OeH groups in GT, respectively (Sadat Hosseini et al., 2016). As can be seen in the FTIR spectrum of bioadsorbent (GT/TMSQA:1/2((Fig. 1c), it is quite clear that the emergence of a new peak at 2855 cm−1 is assigned to the CeH bond in imidazole and new band at 1747 cm−1 is related to carbonyl groups in GT. Furthermore, there are both peaks at 1030 and 1094 cm−1 that indicate Si-O-C that overlap with CeO and CeOH bonds. The presence of these peaks confirms successfully synthesis of biopolymer composites. The FESEM images were exploited to investigate the surface morphology and size of the particles. The FESEM images of GT and the adsorbent (GT/TMSQA:1/2) are shown in Fig.2. The morphology of GT displayed a regular and almost smooth surface (Fig. 2a). In contrast, the FESEM image of the crosslinked bioadsorbent (Fig. 2b) shows much rough surface and heterogeneous structure which can be indicative of the cross-linking reaction between GT and TMSQA. Comparison between these surfaces in Fig. 2a and b, it can be concluded that the layered structure in GT has changed to the spherical form in the hydrogel bioadsorbent as a result of crosslinking reaction. Moreover, the results of the EDX analysis for GT in Fig. 2c and hydrogel bioadsorbent in Fig. 2d demonstrate that the bioadsorbent contains Si and Cl in the structure. The chlorine ion (9%) could be carried out in the ion exchange process for NO3− ions removal. The TGA curves of GT, TMSQA, and bioadsorbent with the weight ratios of 1:1, 1:2 and 2:1 of GT/TMSQA have been investigated from room temperature to 600 °C and the results are shown in Fig. 3, also that explanation is given in section S3 (from Supplementary data).
Fig. 1. FT-IR spectra of ammonium salt (a), GT (b), bioadsorbent (GT/ TMSQA:1/2((c).
and section S4 (from Supplementary data). Due to gelation and insolubility of bioadsorbent hydrogel, 1H NMR analysis was used only for the quaternary ammonium TMSQA. The 1H NMR spectrum analysis of TMSQA has been given in the supplementary and in Fig. 1S. Also, the XRD spectrum for both GT and bioadsorbent hydrogels have been given in the supplementary and shown in Fig. 2S which confirms the synthesis of this compound. The chemical structure of the as-prepared bioadsorbent has been confirmed by using different techniques such as such as FT-IR, XRD, FE-SEM, TGA, and energy dispersive X-Ray (EDX). The FT-IR spectrum of TMSQA, GT and bioadsorbent are shown in Fig. 1. The quaternary ammonium salt (Fig. 1a) shows the absorption bands at 1031 and 758 cm−1 related to the SieOeC stretching vibration, and also the strongly absorbing band at 1108 cm−1 is attributed to the vibration mode of C-Si. The bending bands at 1377 and 1569 cm−1 are ascribed to C]N and C]C in imidazole rings. The CeH stretching vibration is shown at 2854 and 2923 cm−1 and OeH stretching vibration at 3435 cm−1 related to the absorption of surface water. The
3.2. Adsorption study One of the most important methods to separate anions such as nitrate from aqueous solution by polymeric adsorbent hydrogels is the ion exchange process. The capacity of the ion exchange adsorbent towards the nitrate ions depends on several factors and the important ones are pH of the solution, adsorption time, nitrate ion concentration, 3
Carbohydrate Polymers 227 (2020) 115367
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Fig. 2. FESEM image of GT (a) and hydrogel adsorbent) GT/TMSQA:1/2((b). EDX data of GT (c) and hydrogel adsorbent) GT/TMSQA:1/2)(d).
efficiency is the adsorbent dosage. This determines the capacity of the ion exchanging in an initial concentration of the adsorbent under processing conditions (Xu, Gao, Yue, Zhong, & Zhan, 2010). Therefore, to evaluate the effect of bioadsorbent dosage on the adsorption of NO3− ions, various amounts (5–40 mg) of bioadsorbent (GT/TMSQA:1/1) were used under conditions: 20 mL solution containing 30 ppm NO3− ion at pH 7 tested for 20 min at room temperature. As can be seen in Fig. 4b, the adsorption capacity increased with increasing the bioadsorbent content from 5 mg to 30 mg. After that, increasing the amount of bioadsorbent dosage up to 30 mg has not changed the absorption capacity due to the saturation of active sites (Rashidi Nodeh et al., 2017). Therefore, 30 mg bioadsorbent was used as the optimal amount for further experiments. 3.2.2. Effect of solution pH The pH of the solution is one of the effective parameters on the absorption efficiency because it affects the chemical properties, surface characteristics of adsorbents, and ionization/dissociation of the adsorbate molecules. In order to study this effect, 30 mg bioadsorbent (GT/TMSQA: 1/1) in 20 mL nitrate solution (30 ppm) was mixed during 20 min and the pH of the solution was adjusted in the range of 3–11 by HCl and NaOH (0.1M), the results are shown in Fig. 4c. As can be seen, the removal percentage increased from 80% to almost 100% with increasing the pH of the solution from 3 to 7. Then the removal percentage started to decrease with further increase in pH up to 11. Therefore, the bioabsorbent shows the best possible performance in the neutral condition (pH 7). The NO3− removal efficiency in the alkaline environment is reduced due to the competition of hydroxyl ions with the NO3− ions and electrostatic repulsion between negative ions. In the acidic environment, the nitrate removal percentage decreases owing to hydration of the hydroxyl group of the GT. Therefore, the adsorbent was more effective in the neutral conditions due to the presence of chlorine exchange groups and the formation of hydrogen bonding between hydroxyls of GT and nitrate.
Fig. 3. TGA curves of GT, quaternary ammonium salt (TMSQA), and bioadsorbent.
adsorbent dosage, adsorbent composition, and temperature. Batch experiments were carried out to investigate the effect of these factors on the adsorption process. The composition (GT/TMSQA: 2/1, 1/1, 1/2) influence on the removal efficiency of nitrate ion was studied at room temperature using 20 mL aqueous solution containing 30 ppm of NO3− ions and 30 mg adsorbent. As the results show in Fig. 4a, adsorbent composition with GT/TMSQA ratio of 1/1 and 1/2 have a higher adsorption capacity than the other. Therefore, sample 1/1 with the highest degree of swelling after 24 h and sufficient ion exchanging functionality exhibited the maximum removal efficiency for NO3− ions. In the following, the effect of different parameters such as bioadsorbent dosage, solution pH, initial NO3− ion concentration, contact time, and temperature in the adsorption capacity of the prepared bioadsorbent was investigated.
3.2.3. Effect of temperature Fig. 4d shows the effect of temperature ranging from 25 to 45 °C on the absorption. The experiments were performed with 30 mg bioadsorbent in 20 mL solution containing 30 ppm NO3− ions at pH 7. As can
3.2.1. Effect of bioadsorbent dosage One of the important parameters which affect the adsorption 4
Carbohydrate Polymers 227 (2020) 115367
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Fig. 4. Effects of bioadsorbent composition (a), bioadsorbent (GT/TMSQA: 1/1) dosage (b), pH (c), temperature (d), initial NO3− concentration (f), and contact time (e) on the removal of NO3− ions.
using 20 mL solution contained 30 mg L−1 NO3− ions at pH 7, at room temperature, and by 30 mg bioadsorbent for different times (5, 10, 15, 20, 25 and 30 min). The concentration of the remaining NO3− ions in the solution was analyzed by UV–vis spectrophotometer after removing the adsorbent. As is evident from the figure, the removal efficiency increased with increasing the contact time from 5 min to 20 min. According to the experimental data, 20 min was the optimum time to remove 98% of the NO3− ion and the adsorption capacity reached an equilibrium level of 20 mg g−1. Further increase in the contact time did not change the absorption capacity significantly and this is due to the decrease in NO3− ion concentration and also the exhaustion of free adsorptive sites. Therefore, it is indicated that the time of equilibrium of NO3− ion absorption is considered to be 20 min by this bioadsorbent. To clarify the adsorption mechanism, the experimental data were tested by using different kinetics methods such as pseudo-first-order (Eq. (4), the most reliable kinetics equation for the rapid initial phase), pseudosecond-order (Eq. (5), for adsorption with chemical sorption as a ratecontrolling step), Elovich (Eq. (6), this implies a multilayer adsorption), and Weber–Morris intraparticle diffusion (Cheung, Porter, & McKay, 2000; Inyinbor, Adekola, & Olatunji, 2016; Tsibranska & Hristova, 2011) (Eq. (7)), binding of targets to the surface of adsorbent is influenced by the mass transfer resistance. The calculated kinetic parameters are listed in Table 1.
be seen in the figure, the adsorption capacity decreased significantly with increasing temperature from 25 to 45 °C. In fact, this observation proves that NO3− ions uptake by this bioabsorbent is an exothermic process. The adsorption capacity and the removal percentage were 19.65 mg g−1 and 98.2%, respectively, at room temperature (25 °C). The thermodynamic parameters of this study (ΔH°, ΔS°, and ΔG°) are shown in Table 2S and section S5 (from Supplementary data). 3.2.4. Effect of initial nitrate concentration In order to investigate the effect of initial NO3− ions concentration, the testing was carried out with 30 mg bioadsorbent in 20 mL solution using various NO3− ions concentrations from 20 to 60 ppm at pH 7. The results in Fig. 4e clearly show that the adsorption capacity enhanced with increasing the initial concentration of NO3− ions. The adsorption capacity increased from ∼13.18 mg g−1 for an initial concentration of 20 ppm to 19.65 mg g−1 when the initial concentration was 30 ppm. With increasing the initial concentration of NO3− ions, the number of ions transported from the solution to the bulk of the adsorbent increases and facilitates the interaction between NO3− ions and active sites of the hydrogel bioadsorbent. The adsorption of NO3− ions by the present bioadsorbent (GT/TMSQA: 1/1) has reached the maximum of Q = 19.65 mg g−1 (∼98%) and then remained unchanged when the concentration of nitrate increased to 60 ppm. According to the obtained results, the percentage of nitrate removal reduced at higher concentrations due to the lack of quaternary ammonium ions with exchangeable chlorine ions at high concentrations of nitrate. This is actually due to the higher competition between chlorine ions and NO3− for quaternary ammonium sites on the composite (Li et al., 2012). Therefore, 30 ppm is the optimum concentration of nitrate for adsorption by this bioadsorbent.
log(Qe − Qt ) = logQe − 1 1 t = + t Qt Qe k2 Qe2 Qt =
3.2.5. Effect of contact time The effect of contact time was evaluated as an effective factor in efficient uptake. Fig. 4f shows the relationship between the time of the adsorption process and the efficiency of nitrate removal by the prepared bioadsorbent. This effect was measured in various times (5–30 min) by
1 1 ln(αβ ) + lnt β β 1
Qt = Kp t 2 + C
k1 t 2.303
(4)
(5)
(6) (7)
−1
where Qt (mg g ) is the adsorption capacity at time t. k2, α, β, C, and Kp are the constants of the equations that are predicted by calculating the slopes and intercepts of the linear plots between log(Qe−Qt) and t 5
Carbohydrate Polymers 227 (2020) 115367
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the experimental Qe. Therefore, chemical sorption is the main mechanism and controls the adsorption rate of NO3− ions on the bioadsorbent. According to the correlation coefficient (R2 > 0.9) of the Morris model, the intraparticle diffusion model is also part of the absorption mechanism.
Table 1 Parameters and coefficients of determination of the linearized kinetic models for nitrate removal. kinetic model
parameter
mount
pseudo-first-order model
k1 ( min−1 ) Qe, cal (mg g−1) 2 R k2 (g mg−1 min−1) Qe, cal (mg g−1) Qe, exp (mg g−1) R2 Kdiff (g mg−1 min −1/2) C (mg g−1) R2 A (mg g−1 min−1) B (g mg−1) R2
0.13 6.44 0.40 0.026 21.05 19.7 0.999 1.3 13.19 0.91 406.94 0.330 0.96
pseudo-second-order model
Morris-Weber
Elovich
3.2.6. Adsorption isotherms Adsorption isotherms show the adsorption equilibrium distribution function in terms of the concentration of the adsorbing material in a solution at a constant temperature. Isotherms describe how interactions between NO3− ions and active sites of the adsorbent are, as well as have a fundamental function in optimizing adsorption conditions. When adsorption equilibrium occurs, the amount of NO3− ions adsorbed at the adsorbent surface is equal to the amount of NO3− ions released from its. In the present work the Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich isotherm models were studied. The Langmuir model (Eq. (8)) describes monolayer adsorption on the homogeneous surface where the adsorption sites are identical and energetically equivalent. The Freundlich model (Eq. (10)) explains multilayer adsorption on a reversible heterogeneous surface (Öztürk & Bektaş, 2004; Zhan, Lin, & Zhu, 2011). Temkin isotherm model (Eq. (11)) describes indirect interactions between adsorbent and adsorbate on the adsorption isotherms (Inyinbor et al., 2016). Dubinin–Radushkevich isotherm (Eq. (13)) is a general model where the mechanism of adsorption is based on a heterogeneous surface with Gaussian energy distribution (Ayawei, Ebelegi, & Wankasi, 2017). The experimental data and the results obtained from these isotherm models were collected in Table 2.
Table 2 Parameters values in isotherm models for adsorption of NO3− ions. Model
Parameters
Langmuir
Freundlich
Temkin
Dubinin–Radushkevich
Mount at temperature (°K)
−1
Qm (mg g ) qm exp. (mg g−1) KL (L g−1) R2L KF (L g−1) n 1/n R2F B KT (L g−1) bT (kJ mol−1) R2T KDR (mol2 kJ−2) qm (mg g−1) E (kJ mol−1) R2DR
298
303
313
21.01 21.22 4.53 0.99 17.05 14.56 0.0687 0.60 1.1613 3.2 2.13 0.62 0.02 21.01 5 0.89
20.45 20.66 3.19 0.99 15.38 12.02 0.083 0.86 1.4017 0.025 1.79 0.88 0.04 20.7 3.54 0.96
20.04 19.3 0.46 0.98 13.06 11.17 0.089 0.67 1.4042 0.011 1.85 0.66 0.04 16.78 3.54 0.41
Ce 1 C = + e Qe KL Qm Qm RL =
1 1 + KL C0
log Qe = log KF +
(9)
1 log Ce n
Qe = B lnKT + B lnCe
B=
(8)
RT bT
(10) (11)
(12)
lnQe = lnQm − KDR ε 2
(13)
1⎞ ε = RT ln ⎛1 + C e⎠ ⎝
(14)
1 2KDR
(15)
⎜
E=
⎟
Where Qe and Ce represent the amount and the concentration of nitrate adsorbed at the time of equilibrium and Qm is the maximum adsorption capacity (mg g−1). KL is the Langmuir constant and is obtained with Qm from plotting Ce/Qe vs Ce. KF and n constants associate with the adsorption capacity (mg g−1) and its intensity, respectively, and are obtained from plotting logQe vs logCe. The dimensionless equilibrium factor (RL) indicating a favorable adsorption process is determined via Eq. (9). The RL value between 0–1 and > 1 demonstrate favorable and unfavorable adsorption, respectively. The value of 1/n between 0–1 represents the desirable sorption (Öztürk & Bektaş, 2004). bT (J mol−1) and KT (L g−1) are constants related to the heat of adsorptions that are obtained by plotting Qe versus LnCe and from the Eq. (12) (Inyinbor et al., 2016). KDR and ε are the isotherm constants; KDR is obtained by plotting LnQe vs ε2 and sorption energy E (kJ/mol) is determined from Eqs. (13–15) (Ayawei et al., 2017). The results in Table 2 show that the absorption capacity is reduced with increasing temperature, which confirmed the suitability of absorption at room temperature. At the temperature range of 298–313 ºK, the correlation coefficient (R2) of the linear form of isotherm equation for NO3− ions is closer to unity for the
Fig. 5. Competition adsorption of different ions onto bioadsorbent (GT/ TMSQA: 1/1).
(Eq. (4)), t/(Qt) and t (Eq. (5)), Qt and lnt (Eq. (6)), and Qt and t1/2 (Eq. (7)). Coefficients of determination (R2) were calculated to determine the conformity of the models with the experimental data. Comparing the results of different kinetic models applied to the uptake of nitrate (Table 1), the highest correlation coefficient (R2 > 0.99) for NO3− ions adsorption on this bioadsorbent is shown to be the pseudo-second-order kinetic model. The Qe,cal value of this kinetic model is much closer to 6
Carbohydrate Polymers 227 (2020) 115367
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Table 3 Competition of NO3− ions adsorption with other adsorbents. Adsorbent
Qe (mg/g)
Contact time (min)
Weight
Ref.
Relite A490 Duolite A7 ALR-AE resin Pumice SBA-15 biomass Amberlite IRA Bioadsorbent GT/TMSQA
13.02 6.51 40.5 15.6 12.3 11.2 14.8 19.95
360
0.6 g
Nujic, Milinkovic, & Habuda-Stanic (2017)
10 250 100 150 60 20
0.1 g –
Xu et al. (2012) Kim et al. (2015)
5 g/L 1.25 g/L 0.03 g
Kilpimaa, Runtti, Kangas, Lassi, & Kuokkanen (2015) Cha, bani, Amrane, & Bensmaili (2006) Present work
Langmuir (0.99 < RL2 < 0.98) and at the temperature of 303 K, the correlation coefficient fit Dubinin–Radushkevich model (RDR2 = 0.96). The maximum adsorption capacity calculated from both Langmuir model (Qm,cal = 21.01, 20.45, 20.04 mg g−1) at the range 298–313 ºK and Dubinin–Radushkevich model at 303°K (Qm,cal = 20.07 mg g−1) were close to the experimental values (Qm,exp = 21.22, 20.66, 19.3) which confirm that Langmuir model has better conformity with the experimental data. Accordingly, the adsorption capacity (Qe) of the hydrogel exceeds to 21.22 mg g−1 for nitrate ions. Therefore, the ideal absorption was achieved on the homogeneous surface of the bioadsorbent.
conducting antibacterial studies in this project. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.carbpol.2019.115367. References Ali, I. (2012). New generation adsorbents for water treatment. Chemical Reviews, 112(10), 5073–5091. https://doi.org/10.1021/cr300133d. Alighardashi, A., Kashitarash Esfahani, Z., Najafi, F., Afkhami, A., & Hassani, N. (2018). Development and application of graphene Oxide/Poly-Amidoamines dendrimers (GO/PAMAMs) nano-composite for nitrate removal from aqueous solutions. Environmental Processes, 5(1), 41–64. https://doi.org/10.1007/s40710-017-0279-y. Ashok, V., & Hait, S. (2015). Remediation of nitrate-contaminated water by solid-phase denitrification process—A review. Environmental Science and Pollution Research International, 22(11), 8075–8093. https://doi.org/10.1007/s11356-015-4334-9. Ayawei, N., Ebelegi, A. N., & Wankasi, D. (2017). Modelling and interpretation of adsorption isotherms. Journal of Chemistry, 2017, 1–11. https://doi.org/10.1155/2017/ 3039817. Bhatnagar, A., & Sillanpää, M. (2011). A review of emerging adsorbents for nitrate removal from water. Chemical Engineering Journal, 168(2), 493–504. https://doi.org/ 10.1016/j.cej.2011.01.103. Chabani, M., Amrane, A., & Bensmaili, A. (2006). Kinetic modelling of the adsorption of nitrates by ion exchange resin. Chemical Engineering Journal, 125(2), 111–117. https://doi.org/10.1016/j.cej.2006.08.014. Chauhan, K., Kaur, J., Kumari, A., Kumari, A., & Chauhan, G. S. (2015). Efficient method of starch functionalization to bis-quaternary structure unit. International Journal of Biological Macromolecules, 80, 498–505. https://doi.org/10.1016/j.ijbiomac.2015.07. 011. Chauhan, K., Kaur, J., Singh, P., Sharma, P., Sharma, P., & Chauhan, G. S. (2016). An efficient and regenerable quaternary starch for removal of nitrate from aqueous solutions. Industrial & Engineering Chemistry Research, 55(9), 2507–2519. https://doi. org/10.1021/acs.iecr.5b03923. Cheung, C. W., Porter, J. F., & McKay, G. (2000). Elovich equation and modified second‐order equation for sorption of cadmium ions onto bone char. Journal of Chemical Technology & Biotechnology, 75(11), 963–970. https://doi.org/10.1002/10974660(200011)75:11< 963:: AID-JCTB302&3.0.CO;2-Z. Crini, G. (2005). Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Progress in Polymer Science (Oxford), 30(1), 38–70. https://doi.org/10.1016/j.progpolymsci.2004.11.002. Ediagbonya, T. F., Nmema, E., Nwachukwu, P. C., Teniola, O. D., Ediagbonya, T. F., Nmema, E., ... Teniola, O. D. (2015). Identification and quantification of heavy metals, coliforms and anions in water bodies using enrichment factors. J. Environ. Anal. Chem, 2(146), 2380–2391. https://doi.org/10.4172/2380-2391.1000146. Inyinbor, A. A., Adekola, F. A., & Olatunji, G. A. (2016). Kinetics, isotherms and thermodynamic modeling of liquid phase adsorption of Rhodamine B dye onto Raphia hookerie fruit epicarp. Water Resources and Industry, 15, 14–27. https://doi.org/10. 1016/j.wri.2016.06.001. Kanmani, P., Aravind, J., Kamaraj, M., Sureshbabu, P., & Karthikeyan, S. (2017). Environmental applications of chitosan and cellulosic biopolymers: A comprehensive outlook. Bioresource Technology, 242, 295–303. https://doi.org/10.1016/j.biortech. 2017.03.119. Kilpimaa, S., Runtti, H., Kangas, T., Lassi, U., & Kuokkanen, T. (2015). Physical activation of carbon residue from biomass gasification: Novel sorbent for the removal of phosphates and nitrates from aqueous solution. Journal of Industrial and Engineering Chemistry, 21, 1354–1364. https://doi.org/10.1016/j.jiec.2014.06.006. Kim, J. Y., Balathanigaimani, M. S., & Moon, H. (2015). Adsorptive removal of nitrate and phosphate using MCM-48, SBA-15, chitosan, and volcanic pumice. Water, Air, and Soil Pollution, 226(12), 431–442. https://doi.org/10.1007/s11270-015-2692-z. Li, W., Mo, W., Kang, C., Zhang, M., Meng, M., & Chen, M. (2012). Adsorption of nitrate from aqueous solution onto modified cassava (Manihot esculenta) straw. Ecological Chemistry and Engineering S, 19(4), 629–638. https://doi.org/10.2478/v10216-0110045-4. Makvandi, P., Jamaledin, R., Jabbari, M., Nikfarjam, N., & Borzacchiello, A. (2018). Antibacterial quaternary ammonium compounds in dental materials: A systematic
3.2.7. Effect of competitive adsorption Anions such as chloride (Cl−), phosphate (PO43−), bicarbonate (HCO3−), and sulfate (SO42−) are common with NO3− ions in the polluted water resources. These anions can compete with the NO3− ions for the exchangeable ion in the adsorption sites. The effect of the competitive ions on the NO3− adsorption (in Fig. 5) and the data in Table 3S in section S6 are described in more details in the supplementary data. The sorption capacity of other synthetic adsorbents was investigated for NO3− ions removal from aqueous solution. As shown in Table 3, the as-prepared bioadsorbent based on GT carbohydrate polymer showed suitable absorption capacity compared to other reported adsorbents. 4. Conclusion In this study, bioadsorbents were prepared in the form of antibacterial hydrogel from GT carbohydrate polymer and a new quaternary ammonium ion exchanger as crosslinker and employed for the removal of NO3− ions from water. The bioadsorbent showed 98.26% removal of NO3− ions under optimum adsorption conditions (contact time = 20 min, adsorbent dosage = 30 mg, pH = 7, and initial nitrate concentration = 30 mg L−1). The adsorption process followed the pseudo-second-order rate kinetic and the experimental data were fitted well with the Langmuir isotherm with the maximum monolayer adsorption capacity of 21 mg g−1 at 298 K. The thermodynamic parameters, ΔGº = −89.1 kJ mol−1, showed that the adsorption was spontaneous and exothermic in nature. The presence of competitive anions such as Cl−, PO43−, HCO3−, and SO42− reduced the NO3− ions adsorption efficiency slightly. The main mechanism of NO3− ions adsorption by the bioadsorbent can be anionic exchange and electrostatic interaction. Good antibacterial activity was obtained against E. coli, confirming that quaternary ammonium molecules were dispersed within the hydrogel matrix effectively. Therefore, the high performance of the prepared low-cost bioadsorbent hydrogels suggests their potential for water purification applications as well as using in the separation column. Acknowledgment The authors would like to thank Dr. Mojtaba Mohseni (Department of Microbiology, University of Mazandaran, Babolsar, Iran) for 7
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on tragacanth gum biopolymer and investigation of swelling and drug delivery. International Journal of Biological Macromolecules, 82, 806–815. https://doi.org/10. 1016/j.ijbiomac.2015.09.067. Sahraei, R., Sekhavat Pour, Z., & Ghaemy, M. (2017). Novel magnetic bio-sorbent hydrogel beads based on modified gum tragacanth/graphene oxide: Removal of heavy metals and dyes from water. Journal of Cleaner Production, 142, 2973–2984. https:// doi.org/10.1016/j.jclepro.2016.10.170. Shrimali, M., & Singh, K. P. (2001). New methods of nitrate removal from water. Environmental Pollution, 112(3), 351–359. https://doi.org/10.1016/S0269-7491(00) 00147-0. Swain, S. K., Patnaik, T., & Dey, R. K. (2013). Efficient removal of fluoride using new composite material of biopolymer alginate entrapped mixed metal oxide nanomaterials. Desalination and Water Treatment, 51(22–24), 4368–4378. https://doi.org/10. 1080/19443994.2012.749426. Tsibranska, I., & Hristova, E. (2011). Comparison of different kinetic models for adsorption of heavy metals onto activated carbon from apricot stones. Bulgarian Chemical Communications, 43(3), 370–377. Ward, M. H., Jones, R. R., Brender, J. D., de Kok, T. M., Weyer, P. J., Nolan, B. T., ... van Breda, S. G. (2018). Drinking water nitrate and human health: An updated review. International Journal of Environmental Research and Public Health, 15(7), 1557–1588. https://doi.org/10.3390/ijerph15071557. Xu, X., Gao, B. Y., Yue, Q. Y., Zhong, Q. Q., & Zhan, X. (2010). Preparation, characterization of wheat residue based anion exchangers and its utilization for the phosphate removal from aqueous solution. Carbohydrate Polymers, 82(4), 1212–1218. https:// doi.org/10.1016/j.carbpol.2010.06.053. Xu, X., Gao, B., Zhao, Y., Chen, S., Tan, X., Yue, Q., ... Wang, Y. (2012). Nitrate removal from aqueous solution by Arundo donax L. Reed based anion exchange resin. Journal of Hazardous Materials, 203, 86–92. https://doi.org/10.1016/j.jhazmat.2011.11.094. Zhan, Y., Lin, J., & Zhu, Z. (2011). Removal of nitrate from aqueous solution using cetylpyridinium bromide (CPB) modified zeolite as adsorbent. Journal of Hazardous Materials, 186(2–3), 1972–1978. https://doi.org/10.1016/j.jhazmat.2010.12.090.
review. Dental Materials, 34(6), 851–867. https://doi.org/10.1016/j.dental.2018.03. 014. Masoumi, A., Hemmati, K., & Ghaemy, M. (2016). Low-cost nanoparticles sorbent from modified rice husk and a copolymer for efficient removal of Pb(II) and crystal violet from water. Chemosphere, 146, 253–262. https://doi.org/10.1016/j.chemosphere. 2015.12.017. Mohseni-Bandpi, A., Elliott, D. J., & Zazouli, M. A. (2013). Biological nitrate removal processes from drinking water supply - A review. Journal of Environmental Health Science & Engineering, 11(1), 35–46. https://doi.org/10.1186/2052-336X-11-35. Nujic, M., Milinkovic, D., & Habuda-Stanic, M. (2017). Nitrate removal from water by ion exchange. Croatian Journal of Food Science and Technology, 9(2), 182–186. https:// doi.org/10.17508/CJFST.2017.9.2.15. Nur, T., Shim, W. G., Loganathan, P., Vigneswaran, S., & Kandasamy, J. (2015). Nitrate removal using Purolite A520E ion exchange resin: Batch and fixed-bed column adsorption modelling. International Journal of Environmental Science and Technology, 12(4), 1311–1320. https://doi.org/10.1007/s13762-014-0510-6. Öztürk, N., & Bektaş, T. E. (2004). Nitrate removal from aqueous solution by adsorption onto various materials. Journal of Hazardous Materials, 112(1–2), 155–162. https:// doi.org/10.1016/j.jhazmat.2004.05.001. Palko, J. W., Oyarzun, D. I., Ha, B., Stadermann, M., & Santiago, J. G. (2018). Nitrate removal from water using electrostatic regeneration of functionalized adsorbent GRAPHICAL ABSTRACT. Chemical Engineering Journal, 334, 1289–1296. https://doi. org/10.1016/j.cej.2017.10.161. Pourshab, M., Asghari, S., & Mohseni, M. (2018). Synthesis and antibacterial evaluation of novel Spiro [indole‐pyrimidine] ones. Journal of Heterocyclic Chemistry, 55(1), 173–180. https://doi.org/10.1002/jhet.3021. Rashidi Nodeh, H., Sereshti, H., Zamiri Afsharian, E., & Nouri, N. (2017). Enhanced removal of phosphate and nitrate ions from aqueous media using nanosized lanthanum hydrous doped on magnetic graphene nanocomposite. Journal of Environmental Management, 197, 265–274. https://doi.org/10.1016/j.jenvman.2017.04.004. Sadat Hosseini, M., Hemmati, K., & Ghaemy, M. (2016). Synthesis of nanohydrogels based
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Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol
Removal of NO3− ions from water using bioadsorbent based on gum tragacanth carbohydrate biopolymer
T
⁎
Maryam Shojaipoura, Mousa Ghaemya, , Seyed Mojtaba Amininasabb a b
Polymer Research Laboratory, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran Laboratory of Polymer Chemistry, Faculty of Science, University of Kurdistan, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Bioadsorbent Gum tragacanth carbohydrate Quaternary ammonium salt NO3− removal
In this study, functionalized hydrogel bioadsorbents were produced from gum tragacanth (GT) carbohydrate and quaternary ammonium salt (TMSQA) as a crosslinker. The prepared bioadsorbents were used for the removal of NO3− ions from water through the electrostatic and ion exchange mechanism and antibacterial activity. The effect of quaternary ammonium content on the adsorption capacity was studied. The bioadsorbents were characterized by using FE-SEM, energy dispersive X-Ray (EDX), FT-IR, and TGA techniques. The equilibrium time and the most effective pH value for maximum NO3− removal (20 mg g−1) were 21 min and 7, respectively. A series of isotherms and kinetics models were undertaken and the obtained data were fitted well to the Langmuir isotherm and pseudo-second-order rate kinetic. The thermodynamic study confirmed the suitability of NO3− removal by the as-prepared bioadsorbent at room temperature, and also the negative value of ΔGº = −89.1 kJ mol−1 demonstrating the spontaneous nature of adsorption.
1. Introduction Water is an essential component for the life of living organisms on the earth and the groundwater is the most important source of sweetened water in the world. In recent years, growth of the population along with the rising industrial and agricultural activities have increased the pollution due to the presence of contaminants such as inorganic ions, heavy metals, organic contaminants, and synthetic chemicals (Ali, 2012; Ediagbonya et al., 2015). Nitrate is one of the most important inorganic anions of major water pollutant in many areas of the world which has caused much concern about the quality of drinking water. The pervasive use of artificial fertilizer in agriculture, disposal of untreated municipal and animal waste, changes in land use, and industrial activities have often enrich the amount of nitrate in soil and limits the direct use of the groundwater resources (Chauhan et al., 2016; Mohseni-Bandpi, Elliott, & Zazouli, 2013). The presence of high concentrations of nitrate in drinking water can cause stomach cancer with an extensive variety of tumors, blue baby syndrome and shortness of breath, and will also be a serious threat to the life of fish, animals and the destruction of water supplies (Ashok & Hait, 2015; Nur, Shim, Loganathan, Vigneswaran, & Kandasamy, 2015). According to the world health organization (WHO) and other environmental regulatory agencies, the maximum allowable concentration of nitrate in drinking water is 45–50 mg/L (10–11.3 mg/L N-NO3−) (Ward et al., 2018). ⁎
Nitrates can be removed by chemical, physical, and biological methods from aqueous environments (Alighardashi, Kashitarash Esfahani, Najafi, Afkhami, & Hassani, 2018) These methods include reduction by enzymes and catalytic, biological and chemical, denitrification, nanofiltration (NF), electrodialysis, ion exchange, reverse osmosis, and adsorption method (Mohseni-Bandpi et al., 2013; Shrimali & Singh, 2001). Among these various techniques, adsorption or ion exchange is the most simple, efficient, ease of operation, relatively low cost, and renewable method which is generally considered for removal of pollutants from water (Bhatnagar & Sillanpää, 2011). In recent years, the use of natural biopolymers such as gum tragacanth (GT) (Sahraei, Sekhavat Pour, & Ghaemy, 2017), chitosan (Kim, Balathanigaimani, & Moon, 2015), alginate (Swain, Patnaik, & Dey, 2013), cellulose (Kanmani, Aravind, Kamaraj, Sureshbabu, & Karthikeyan, 2017), starch (Chauhan, Kaur, Kumari, Kumari, & Chauhan, 2015) and rice husk (Masoumi, Hemmati, & Ghaemy, 2016) as adsorbent for the removal of pollutants has been developed due to their availability, biocompatibility, biodegradability, chemical stability, specific structure and easy modification (Crini, 2005; Kanmani et al., 2017). GT is an abundant natural biocompatible polymer which is available in many Middle Eastern countries. Although GT hydrogels have been used before for water purification but has never been used as an ion exchange resin for the removal of nitrate ion. It has recently been demonstrated that quaternary ammonium functionalized adsorbents with the anion
Corresponding author. E-mail address: [email protected] (M. Ghaemy).
https://doi.org/10.1016/j.carbpol.2019.115367 Received 8 July 2019; Received in revised form 14 September 2019; Accepted 20 September 2019 Available online 24 September 2019 0144-8617/ © 2019 Elsevier Ltd. All rights reserved.
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that the adsorption was complete after 20 min, then the adsorbent was separated from the solution by centrifuging. The equilibrium concentration of NO3− was determined by the addition of 0.4 mL HCl (1 N) using UV–vis spectrophotometer at wavelengths 220 and 275 nm (A(NO3− ) = A(220nm) −2 A(275nm)), according to the reported procedure (Rashidi Nodeh, Sereshti, Zamiri Afsharian, & Nouri, 2017). The concentration of the residual NO3− ions (the equilibrium concentration) after centrifugation was determined by using a standard curve obtained from standard concentrations of NO3− ions. All experiments were carried out twice and the given adsorbed concentrations were the means of duplicate experimental results. The removal percentage (R%) and the equilibrium adsorption capacity (Qe, mg g−1) of NO3− ions were calculated according to Eqs. (1) and (2), respectively:
exchangeability and antibacterial activity can be useful for the removal of nitrate ion from contaminated water (Makvandi, Jamaledin, Jabbari, Nikfarjam, & Borzacchiello, 2018; Palko, Oyarzun, Ha, Stadermann, & Santiago, 2018). However, the quaternary ammonium salts have never been used as a cross-linker and an anionic exchanger at the same time in a natural carbohydrate polymer for the removal of nitrate ions from water. In the present study, the objective was to prepare a biopolymerbased hydrogel adsorbent from GT functionalized with a synthesized quaternary ammonium chloride which has also acted as a crosslinker. The quaternary ammonium salt (TMSQA) was obtained from the reaction between N-(trimethylsilyl) imidazole (NTMSI) and (3-chloropropyl) trimethoxysilane (CPTS). The prepared hydrogel bioadsorbent was characterized by using 1HNMR, FE-SEM, X-Ray (EDX), FT-IR, and TGA techniques and then used to the removal of NO3− ions from water through the electrostatic and ion exchange mechanism. The various absorption parameters such as contact time, adsorbent dosage, and concentration of NO3− ions, pH, and temperature were also investigated to determine the best absorption conditions. The kinetics and isothermal parameters for the removal of NO3− from water by the prepared bioadsorbent was investigated.
R (%) =
Qe =
C0 − Ce × 100 C0
C0 − Ce ×V m
(1) (2)
2. Experimental section
Where C0 and Ce are the initial and equilibrium concentration of NO3− ions in solution, respectively; m is the amount of adsorbent (g); V is the volume of the solution (L); qe is the absorption capacity (mg g−1) and R (%) is adsorption percent.
2.1. Materials
3. Results and discussion
N-(Trimethylsilyl)imidazole (NTMSI), (3-chloropropyl)trimethoxysilane (CPTS), potassium nitrate, acetic acid, toluene and ethanol, Silver nitrate, were purchased from Merck Co. (Germany). All the chemicals were of reagent grade and used without any further purification. Gum tragacanth (GT) was purchased from a local pharmaceutical shop (Sanandaj, Kurdistan, Iran). The synthetic methods of trimethoxysilane functionalized quaternary ammonium salt (TMSQA) as a crosslinker and bioadsorbent, and devices used for analysis are described in section S1 (From supplementary data).
3.1. Preparation and characterization of bioadsorbent hydrogel Modification of the chemical and physical properties of natural and synthetic polymers is a well-known method. In this study, the macromolecular structure of a natural carbohydrate polymer, GT, has been modified by graft polymerization using TMSQA acting also as a crosslinker. Therefore, the main properties of the ion exchange function are kept in the quaternary ammonium salt. One of the main properties of carbohydrate polymers is biodegradability which is preserved to some extent in the crosslinked bioadsorbent hydrogels. The bioadsorbent has been synthesized in two steps that are illustrated in schematic form in Scheme 1. In the first step, the quaternary ammonium salt was synthesized from the substitution reaction between CPTS and NTMSI in toluene as described in section S1.1. Quaternization of the nitrogen atom in imidazole ring with chlorine improves the ionic character. In the second step, the bioadsorbent was obtained from the reaction between hydroxyl groups on the macromolecular chains of GT and trimethoxysilane groups of the crosslinker TMSQA in a mixture of ethylene and acidic acid. The amount of TMSQA required as crosslinker which affected the gel content and also the adsorption process has been investigated here to obtain materials with reasonable adsorption. As can be seen in Table 1S, the gel content increased with increasing TMSQA content in the range of 33–66 wt %. It can be concluded that the increase in the gel content may be due to the increase in the diffusion rate of the crosslinker into the bulk of GT macromolecular chains. To determine the gel content, a certain amount of composite was placed in a soxhlet system and refluxed in distilled water for 72 h. Eq. (3) was used to determine the amount of dried gel remained after extraction and the results are reported in Table 1S (from Supplementary data).
2.2. Antibacterial activity Antibacterial activity of the synthesized composites were evaluated by using Kirby-Bauer technique against the Gram-negative bacterium Escherichia coli (E. coli) and the Gram-positive bacterium Bacillus subtilis (B. subtilis) (Pourshab, Asghari, & Mohseni, 2018). Gentamicin and chloramphenicol as Standard antibacterial drug were used in the method that are considered a benchmark for comparing their antibacterial activity with synthesized composites (GT/TMSQA: 1/2, 1/1 and 2/1) and the results of this study are reported in the Table 4S and Fig. 3S. (From supplementary data) 2.3. Adsorption experiments Adsorption of NO3− ions onto prepared bioadsorbent was carried out with batch experiments. The stock nitrate solution was prepared by dissolving an accurate quantity of KNO3 in distilled water (1000 mg/L). The required concentrations of the NO3− ions (20, 30, 40, 50 and 60 ppm) was prepared by serial dilution of stock solution in room temperature and then filtered. The adsorption behavior of NO3− ions onto the hydrogel bioadsorbent was investigated in 20 mL aqueous solution at different temperatures (298–318°K), and by varying the effective parameters including adsorbent dosage (5–40 mg), pH medium (3–11), contact time (5–30 min), and initial NO3− concentration (20–60 ppm) to achieve the best conditions with the highest adsorption capacity and understand the mechanism of the adsorption process. pH was adjusted to the desired level with 0.1 M NaOH or 0.1M HCl solutions. All other variables were kept constant while a particular variable was under verification. Experiments were mainly carried out with the initial adjustment of the pH and the preliminary tests showed
Gel fraction(%) =
Wg W0
× 100
(3)
Where W0 and Wg are the weight of the initial dry material and after the process of soxhlet extraction, respectively (Sadat Hosseini, Hemmati, & Ghaemy, 2016). The results show that the gel content as a result of crosslinking reaction and networking increased from 31.5 wt % to 72.8 wt% when the amount of TMSQA increased from 33 wt% to 66 wt %. The swelling behavior of the bioadsorbent was investigated at different times. The results of this study are fully documented in Table 1S 2
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Scheme 1. Schematic presentation for synthesis of biopolymer adsorbent.
absorption bands at 1622 and 1745 cm−1 in Fig. 1b corresponds to carboxylic acid or carboxylate groups of d-galacturonic acid in GT structure. The absorption bands in the region 1100–1200 cm−1 can demonstrate the stretching vibrations of CeO bond in ether and alcohol groups of GT and also the absorption bands at 2927 and 3432 cm−1 related to the stretching vibrations of aliphatic CeH and OeH groups in GT, respectively (Sadat Hosseini et al., 2016). As can be seen in the FTIR spectrum of bioadsorbent (GT/TMSQA:1/2((Fig. 1c), it is quite clear that the emergence of a new peak at 2855 cm−1 is assigned to the CeH bond in imidazole and new band at 1747 cm−1 is related to carbonyl groups in GT. Furthermore, there are both peaks at 1030 and 1094 cm−1 that indicate Si-O-C that overlap with CeO and CeOH bonds. The presence of these peaks confirms successfully synthesis of biopolymer composites. The FESEM images were exploited to investigate the surface morphology and size of the particles. The FESEM images of GT and the adsorbent (GT/TMSQA:1/2) are shown in Fig.2. The morphology of GT displayed a regular and almost smooth surface (Fig. 2a). In contrast, the FESEM image of the crosslinked bioadsorbent (Fig. 2b) shows much rough surface and heterogeneous structure which can be indicative of the cross-linking reaction between GT and TMSQA. Comparison between these surfaces in Fig. 2a and b, it can be concluded that the layered structure in GT has changed to the spherical form in the hydrogel bioadsorbent as a result of crosslinking reaction. Moreover, the results of the EDX analysis for GT in Fig. 2c and hydrogel bioadsorbent in Fig. 2d demonstrate that the bioadsorbent contains Si and Cl in the structure. The chlorine ion (9%) could be carried out in the ion exchange process for NO3− ions removal. The TGA curves of GT, TMSQA, and bioadsorbent with the weight ratios of 1:1, 1:2 and 2:1 of GT/TMSQA have been investigated from room temperature to 600 °C and the results are shown in Fig. 3, also that explanation is given in section S3 (from Supplementary data).
Fig. 1. FT-IR spectra of ammonium salt (a), GT (b), bioadsorbent (GT/ TMSQA:1/2((c).
and section S4 (from Supplementary data). Due to gelation and insolubility of bioadsorbent hydrogel, 1H NMR analysis was used only for the quaternary ammonium TMSQA. The 1H NMR spectrum analysis of TMSQA has been given in the supplementary and in Fig. 1S. Also, the XRD spectrum for both GT and bioadsorbent hydrogels have been given in the supplementary and shown in Fig. 2S which confirms the synthesis of this compound. The chemical structure of the as-prepared bioadsorbent has been confirmed by using different techniques such as such as FT-IR, XRD, FE-SEM, TGA, and energy dispersive X-Ray (EDX). The FT-IR spectrum of TMSQA, GT and bioadsorbent are shown in Fig. 1. The quaternary ammonium salt (Fig. 1a) shows the absorption bands at 1031 and 758 cm−1 related to the SieOeC stretching vibration, and also the strongly absorbing band at 1108 cm−1 is attributed to the vibration mode of C-Si. The bending bands at 1377 and 1569 cm−1 are ascribed to C]N and C]C in imidazole rings. The CeH stretching vibration is shown at 2854 and 2923 cm−1 and OeH stretching vibration at 3435 cm−1 related to the absorption of surface water. The
3.2. Adsorption study One of the most important methods to separate anions such as nitrate from aqueous solution by polymeric adsorbent hydrogels is the ion exchange process. The capacity of the ion exchange adsorbent towards the nitrate ions depends on several factors and the important ones are pH of the solution, adsorption time, nitrate ion concentration, 3
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Fig. 2. FESEM image of GT (a) and hydrogel adsorbent) GT/TMSQA:1/2((b). EDX data of GT (c) and hydrogel adsorbent) GT/TMSQA:1/2)(d).
efficiency is the adsorbent dosage. This determines the capacity of the ion exchanging in an initial concentration of the adsorbent under processing conditions (Xu, Gao, Yue, Zhong, & Zhan, 2010). Therefore, to evaluate the effect of bioadsorbent dosage on the adsorption of NO3− ions, various amounts (5–40 mg) of bioadsorbent (GT/TMSQA:1/1) were used under conditions: 20 mL solution containing 30 ppm NO3− ion at pH 7 tested for 20 min at room temperature. As can be seen in Fig. 4b, the adsorption capacity increased with increasing the bioadsorbent content from 5 mg to 30 mg. After that, increasing the amount of bioadsorbent dosage up to 30 mg has not changed the absorption capacity due to the saturation of active sites (Rashidi Nodeh et al., 2017). Therefore, 30 mg bioadsorbent was used as the optimal amount for further experiments. 3.2.2. Effect of solution pH The pH of the solution is one of the effective parameters on the absorption efficiency because it affects the chemical properties, surface characteristics of adsorbents, and ionization/dissociation of the adsorbate molecules. In order to study this effect, 30 mg bioadsorbent (GT/TMSQA: 1/1) in 20 mL nitrate solution (30 ppm) was mixed during 20 min and the pH of the solution was adjusted in the range of 3–11 by HCl and NaOH (0.1M), the results are shown in Fig. 4c. As can be seen, the removal percentage increased from 80% to almost 100% with increasing the pH of the solution from 3 to 7. Then the removal percentage started to decrease with further increase in pH up to 11. Therefore, the bioabsorbent shows the best possible performance in the neutral condition (pH 7). The NO3− removal efficiency in the alkaline environment is reduced due to the competition of hydroxyl ions with the NO3− ions and electrostatic repulsion between negative ions. In the acidic environment, the nitrate removal percentage decreases owing to hydration of the hydroxyl group of the GT. Therefore, the adsorbent was more effective in the neutral conditions due to the presence of chlorine exchange groups and the formation of hydrogen bonding between hydroxyls of GT and nitrate.
Fig. 3. TGA curves of GT, quaternary ammonium salt (TMSQA), and bioadsorbent.
adsorbent dosage, adsorbent composition, and temperature. Batch experiments were carried out to investigate the effect of these factors on the adsorption process. The composition (GT/TMSQA: 2/1, 1/1, 1/2) influence on the removal efficiency of nitrate ion was studied at room temperature using 20 mL aqueous solution containing 30 ppm of NO3− ions and 30 mg adsorbent. As the results show in Fig. 4a, adsorbent composition with GT/TMSQA ratio of 1/1 and 1/2 have a higher adsorption capacity than the other. Therefore, sample 1/1 with the highest degree of swelling after 24 h and sufficient ion exchanging functionality exhibited the maximum removal efficiency for NO3− ions. In the following, the effect of different parameters such as bioadsorbent dosage, solution pH, initial NO3− ion concentration, contact time, and temperature in the adsorption capacity of the prepared bioadsorbent was investigated.
3.2.3. Effect of temperature Fig. 4d shows the effect of temperature ranging from 25 to 45 °C on the absorption. The experiments were performed with 30 mg bioadsorbent in 20 mL solution containing 30 ppm NO3− ions at pH 7. As can
3.2.1. Effect of bioadsorbent dosage One of the important parameters which affect the adsorption 4
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Fig. 4. Effects of bioadsorbent composition (a), bioadsorbent (GT/TMSQA: 1/1) dosage (b), pH (c), temperature (d), initial NO3− concentration (f), and contact time (e) on the removal of NO3− ions.
using 20 mL solution contained 30 mg L−1 NO3− ions at pH 7, at room temperature, and by 30 mg bioadsorbent for different times (5, 10, 15, 20, 25 and 30 min). The concentration of the remaining NO3− ions in the solution was analyzed by UV–vis spectrophotometer after removing the adsorbent. As is evident from the figure, the removal efficiency increased with increasing the contact time from 5 min to 20 min. According to the experimental data, 20 min was the optimum time to remove 98% of the NO3− ion and the adsorption capacity reached an equilibrium level of 20 mg g−1. Further increase in the contact time did not change the absorption capacity significantly and this is due to the decrease in NO3− ion concentration and also the exhaustion of free adsorptive sites. Therefore, it is indicated that the time of equilibrium of NO3− ion absorption is considered to be 20 min by this bioadsorbent. To clarify the adsorption mechanism, the experimental data were tested by using different kinetics methods such as pseudo-first-order (Eq. (4), the most reliable kinetics equation for the rapid initial phase), pseudosecond-order (Eq. (5), for adsorption with chemical sorption as a ratecontrolling step), Elovich (Eq. (6), this implies a multilayer adsorption), and Weber–Morris intraparticle diffusion (Cheung, Porter, & McKay, 2000; Inyinbor, Adekola, & Olatunji, 2016; Tsibranska & Hristova, 2011) (Eq. (7)), binding of targets to the surface of adsorbent is influenced by the mass transfer resistance. The calculated kinetic parameters are listed in Table 1.
be seen in the figure, the adsorption capacity decreased significantly with increasing temperature from 25 to 45 °C. In fact, this observation proves that NO3− ions uptake by this bioabsorbent is an exothermic process. The adsorption capacity and the removal percentage were 19.65 mg g−1 and 98.2%, respectively, at room temperature (25 °C). The thermodynamic parameters of this study (ΔH°, ΔS°, and ΔG°) are shown in Table 2S and section S5 (from Supplementary data). 3.2.4. Effect of initial nitrate concentration In order to investigate the effect of initial NO3− ions concentration, the testing was carried out with 30 mg bioadsorbent in 20 mL solution using various NO3− ions concentrations from 20 to 60 ppm at pH 7. The results in Fig. 4e clearly show that the adsorption capacity enhanced with increasing the initial concentration of NO3− ions. The adsorption capacity increased from ∼13.18 mg g−1 for an initial concentration of 20 ppm to 19.65 mg g−1 when the initial concentration was 30 ppm. With increasing the initial concentration of NO3− ions, the number of ions transported from the solution to the bulk of the adsorbent increases and facilitates the interaction between NO3− ions and active sites of the hydrogel bioadsorbent. The adsorption of NO3− ions by the present bioadsorbent (GT/TMSQA: 1/1) has reached the maximum of Q = 19.65 mg g−1 (∼98%) and then remained unchanged when the concentration of nitrate increased to 60 ppm. According to the obtained results, the percentage of nitrate removal reduced at higher concentrations due to the lack of quaternary ammonium ions with exchangeable chlorine ions at high concentrations of nitrate. This is actually due to the higher competition between chlorine ions and NO3− for quaternary ammonium sites on the composite (Li et al., 2012). Therefore, 30 ppm is the optimum concentration of nitrate for adsorption by this bioadsorbent.
log(Qe − Qt ) = logQe − 1 1 t = + t Qt Qe k2 Qe2 Qt =
3.2.5. Effect of contact time The effect of contact time was evaluated as an effective factor in efficient uptake. Fig. 4f shows the relationship between the time of the adsorption process and the efficiency of nitrate removal by the prepared bioadsorbent. This effect was measured in various times (5–30 min) by
1 1 ln(αβ ) + lnt β β 1
Qt = Kp t 2 + C
k1 t 2.303
(4)
(5)
(6) (7)
−1
where Qt (mg g ) is the adsorption capacity at time t. k2, α, β, C, and Kp are the constants of the equations that are predicted by calculating the slopes and intercepts of the linear plots between log(Qe−Qt) and t 5
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the experimental Qe. Therefore, chemical sorption is the main mechanism and controls the adsorption rate of NO3− ions on the bioadsorbent. According to the correlation coefficient (R2 > 0.9) of the Morris model, the intraparticle diffusion model is also part of the absorption mechanism.
Table 1 Parameters and coefficients of determination of the linearized kinetic models for nitrate removal. kinetic model
parameter
mount
pseudo-first-order model
k1 ( min−1 ) Qe, cal (mg g−1) 2 R k2 (g mg−1 min−1) Qe, cal (mg g−1) Qe, exp (mg g−1) R2 Kdiff (g mg−1 min −1/2) C (mg g−1) R2 A (mg g−1 min−1) B (g mg−1) R2
0.13 6.44 0.40 0.026 21.05 19.7 0.999 1.3 13.19 0.91 406.94 0.330 0.96
pseudo-second-order model
Morris-Weber
Elovich
3.2.6. Adsorption isotherms Adsorption isotherms show the adsorption equilibrium distribution function in terms of the concentration of the adsorbing material in a solution at a constant temperature. Isotherms describe how interactions between NO3− ions and active sites of the adsorbent are, as well as have a fundamental function in optimizing adsorption conditions. When adsorption equilibrium occurs, the amount of NO3− ions adsorbed at the adsorbent surface is equal to the amount of NO3− ions released from its. In the present work the Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich isotherm models were studied. The Langmuir model (Eq. (8)) describes monolayer adsorption on the homogeneous surface where the adsorption sites are identical and energetically equivalent. The Freundlich model (Eq. (10)) explains multilayer adsorption on a reversible heterogeneous surface (Öztürk & Bektaş, 2004; Zhan, Lin, & Zhu, 2011). Temkin isotherm model (Eq. (11)) describes indirect interactions between adsorbent and adsorbate on the adsorption isotherms (Inyinbor et al., 2016). Dubinin–Radushkevich isotherm (Eq. (13)) is a general model where the mechanism of adsorption is based on a heterogeneous surface with Gaussian energy distribution (Ayawei, Ebelegi, & Wankasi, 2017). The experimental data and the results obtained from these isotherm models were collected in Table 2.
Table 2 Parameters values in isotherm models for adsorption of NO3− ions. Model
Parameters
Langmuir
Freundlich
Temkin
Dubinin–Radushkevich
Mount at temperature (°K)
−1
Qm (mg g ) qm exp. (mg g−1) KL (L g−1) R2L KF (L g−1) n 1/n R2F B KT (L g−1) bT (kJ mol−1) R2T KDR (mol2 kJ−2) qm (mg g−1) E (kJ mol−1) R2DR
298
303
313
21.01 21.22 4.53 0.99 17.05 14.56 0.0687 0.60 1.1613 3.2 2.13 0.62 0.02 21.01 5 0.89
20.45 20.66 3.19 0.99 15.38 12.02 0.083 0.86 1.4017 0.025 1.79 0.88 0.04 20.7 3.54 0.96
20.04 19.3 0.46 0.98 13.06 11.17 0.089 0.67 1.4042 0.011 1.85 0.66 0.04 16.78 3.54 0.41
Ce 1 C = + e Qe KL Qm Qm RL =
1 1 + KL C0
log Qe = log KF +
(9)
1 log Ce n
Qe = B lnKT + B lnCe
B=
(8)
RT bT
(10) (11)
(12)
lnQe = lnQm − KDR ε 2
(13)
1⎞ ε = RT ln ⎛1 + C e⎠ ⎝
(14)
1 2KDR
(15)
⎜
E=
⎟
Where Qe and Ce represent the amount and the concentration of nitrate adsorbed at the time of equilibrium and Qm is the maximum adsorption capacity (mg g−1). KL is the Langmuir constant and is obtained with Qm from plotting Ce/Qe vs Ce. KF and n constants associate with the adsorption capacity (mg g−1) and its intensity, respectively, and are obtained from plotting logQe vs logCe. The dimensionless equilibrium factor (RL) indicating a favorable adsorption process is determined via Eq. (9). The RL value between 0–1 and > 1 demonstrate favorable and unfavorable adsorption, respectively. The value of 1/n between 0–1 represents the desirable sorption (Öztürk & Bektaş, 2004). bT (J mol−1) and KT (L g−1) are constants related to the heat of adsorptions that are obtained by plotting Qe versus LnCe and from the Eq. (12) (Inyinbor et al., 2016). KDR and ε are the isotherm constants; KDR is obtained by plotting LnQe vs ε2 and sorption energy E (kJ/mol) is determined from Eqs. (13–15) (Ayawei et al., 2017). The results in Table 2 show that the absorption capacity is reduced with increasing temperature, which confirmed the suitability of absorption at room temperature. At the temperature range of 298–313 ºK, the correlation coefficient (R2) of the linear form of isotherm equation for NO3− ions is closer to unity for the
Fig. 5. Competition adsorption of different ions onto bioadsorbent (GT/ TMSQA: 1/1).
(Eq. (4)), t/(Qt) and t (Eq. (5)), Qt and lnt (Eq. (6)), and Qt and t1/2 (Eq. (7)). Coefficients of determination (R2) were calculated to determine the conformity of the models with the experimental data. Comparing the results of different kinetic models applied to the uptake of nitrate (Table 1), the highest correlation coefficient (R2 > 0.99) for NO3− ions adsorption on this bioadsorbent is shown to be the pseudo-second-order kinetic model. The Qe,cal value of this kinetic model is much closer to 6
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Table 3 Competition of NO3− ions adsorption with other adsorbents. Adsorbent
Qe (mg/g)
Contact time (min)
Weight
Ref.
Relite A490 Duolite A7 ALR-AE resin Pumice SBA-15 biomass Amberlite IRA Bioadsorbent GT/TMSQA
13.02 6.51 40.5 15.6 12.3 11.2 14.8 19.95
360
0.6 g
Nujic, Milinkovic, & Habuda-Stanic (2017)
10 250 100 150 60 20
0.1 g –
Xu et al. (2012) Kim et al. (2015)
5 g/L 1.25 g/L 0.03 g
Kilpimaa, Runtti, Kangas, Lassi, & Kuokkanen (2015) Cha, bani, Amrane, & Bensmaili (2006) Present work
Langmuir (0.99 < RL2 < 0.98) and at the temperature of 303 K, the correlation coefficient fit Dubinin–Radushkevich model (RDR2 = 0.96). The maximum adsorption capacity calculated from both Langmuir model (Qm,cal = 21.01, 20.45, 20.04 mg g−1) at the range 298–313 ºK and Dubinin–Radushkevich model at 303°K (Qm,cal = 20.07 mg g−1) were close to the experimental values (Qm,exp = 21.22, 20.66, 19.3) which confirm that Langmuir model has better conformity with the experimental data. Accordingly, the adsorption capacity (Qe) of the hydrogel exceeds to 21.22 mg g−1 for nitrate ions. Therefore, the ideal absorption was achieved on the homogeneous surface of the bioadsorbent.
conducting antibacterial studies in this project. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.carbpol.2019.115367. References Ali, I. (2012). New generation adsorbents for water treatment. Chemical Reviews, 112(10), 5073–5091. https://doi.org/10.1021/cr300133d. Alighardashi, A., Kashitarash Esfahani, Z., Najafi, F., Afkhami, A., & Hassani, N. (2018). Development and application of graphene Oxide/Poly-Amidoamines dendrimers (GO/PAMAMs) nano-composite for nitrate removal from aqueous solutions. Environmental Processes, 5(1), 41–64. https://doi.org/10.1007/s40710-017-0279-y. Ashok, V., & Hait, S. (2015). Remediation of nitrate-contaminated water by solid-phase denitrification process—A review. Environmental Science and Pollution Research International, 22(11), 8075–8093. https://doi.org/10.1007/s11356-015-4334-9. Ayawei, N., Ebelegi, A. N., & Wankasi, D. (2017). Modelling and interpretation of adsorption isotherms. Journal of Chemistry, 2017, 1–11. https://doi.org/10.1155/2017/ 3039817. Bhatnagar, A., & Sillanpää, M. (2011). A review of emerging adsorbents for nitrate removal from water. Chemical Engineering Journal, 168(2), 493–504. https://doi.org/ 10.1016/j.cej.2011.01.103. Chabani, M., Amrane, A., & Bensmaili, A. (2006). Kinetic modelling of the adsorption of nitrates by ion exchange resin. Chemical Engineering Journal, 125(2), 111–117. https://doi.org/10.1016/j.cej.2006.08.014. Chauhan, K., Kaur, J., Kumari, A., Kumari, A., & Chauhan, G. S. (2015). Efficient method of starch functionalization to bis-quaternary structure unit. International Journal of Biological Macromolecules, 80, 498–505. https://doi.org/10.1016/j.ijbiomac.2015.07. 011. Chauhan, K., Kaur, J., Singh, P., Sharma, P., Sharma, P., & Chauhan, G. S. (2016). An efficient and regenerable quaternary starch for removal of nitrate from aqueous solutions. Industrial & Engineering Chemistry Research, 55(9), 2507–2519. https://doi. org/10.1021/acs.iecr.5b03923. Cheung, C. W., Porter, J. F., & McKay, G. (2000). Elovich equation and modified second‐order equation for sorption of cadmium ions onto bone char. Journal of Chemical Technology & Biotechnology, 75(11), 963–970. https://doi.org/10.1002/10974660(200011)75:11< 963:: AID-JCTB302&3.0.CO;2-Z. Crini, G. (2005). Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Progress in Polymer Science (Oxford), 30(1), 38–70. https://doi.org/10.1016/j.progpolymsci.2004.11.002. Ediagbonya, T. F., Nmema, E., Nwachukwu, P. C., Teniola, O. D., Ediagbonya, T. F., Nmema, E., ... Teniola, O. D. (2015). Identification and quantification of heavy metals, coliforms and anions in water bodies using enrichment factors. J. Environ. Anal. Chem, 2(146), 2380–2391. https://doi.org/10.4172/2380-2391.1000146. Inyinbor, A. A., Adekola, F. A., & Olatunji, G. A. (2016). Kinetics, isotherms and thermodynamic modeling of liquid phase adsorption of Rhodamine B dye onto Raphia hookerie fruit epicarp. Water Resources and Industry, 15, 14–27. https://doi.org/10. 1016/j.wri.2016.06.001. Kanmani, P., Aravind, J., Kamaraj, M., Sureshbabu, P., & Karthikeyan, S. (2017). Environmental applications of chitosan and cellulosic biopolymers: A comprehensive outlook. Bioresource Technology, 242, 295–303. https://doi.org/10.1016/j.biortech. 2017.03.119. Kilpimaa, S., Runtti, H., Kangas, T., Lassi, U., & Kuokkanen, T. (2015). Physical activation of carbon residue from biomass gasification: Novel sorbent for the removal of phosphates and nitrates from aqueous solution. Journal of Industrial and Engineering Chemistry, 21, 1354–1364. https://doi.org/10.1016/j.jiec.2014.06.006. Kim, J. Y., Balathanigaimani, M. S., & Moon, H. (2015). Adsorptive removal of nitrate and phosphate using MCM-48, SBA-15, chitosan, and volcanic pumice. Water, Air, and Soil Pollution, 226(12), 431–442. https://doi.org/10.1007/s11270-015-2692-z. Li, W., Mo, W., Kang, C., Zhang, M., Meng, M., & Chen, M. (2012). Adsorption of nitrate from aqueous solution onto modified cassava (Manihot esculenta) straw. Ecological Chemistry and Engineering S, 19(4), 629–638. https://doi.org/10.2478/v10216-0110045-4. Makvandi, P., Jamaledin, R., Jabbari, M., Nikfarjam, N., & Borzacchiello, A. (2018). Antibacterial quaternary ammonium compounds in dental materials: A systematic
3.2.7. Effect of competitive adsorption Anions such as chloride (Cl−), phosphate (PO43−), bicarbonate (HCO3−), and sulfate (SO42−) are common with NO3− ions in the polluted water resources. These anions can compete with the NO3− ions for the exchangeable ion in the adsorption sites. The effect of the competitive ions on the NO3− adsorption (in Fig. 5) and the data in Table 3S in section S6 are described in more details in the supplementary data. The sorption capacity of other synthetic adsorbents was investigated for NO3− ions removal from aqueous solution. As shown in Table 3, the as-prepared bioadsorbent based on GT carbohydrate polymer showed suitable absorption capacity compared to other reported adsorbents. 4. Conclusion In this study, bioadsorbents were prepared in the form of antibacterial hydrogel from GT carbohydrate polymer and a new quaternary ammonium ion exchanger as crosslinker and employed for the removal of NO3− ions from water. The bioadsorbent showed 98.26% removal of NO3− ions under optimum adsorption conditions (contact time = 20 min, adsorbent dosage = 30 mg, pH = 7, and initial nitrate concentration = 30 mg L−1). The adsorption process followed the pseudo-second-order rate kinetic and the experimental data were fitted well with the Langmuir isotherm with the maximum monolayer adsorption capacity of 21 mg g−1 at 298 K. The thermodynamic parameters, ΔGº = −89.1 kJ mol−1, showed that the adsorption was spontaneous and exothermic in nature. The presence of competitive anions such as Cl−, PO43−, HCO3−, and SO42− reduced the NO3− ions adsorption efficiency slightly. The main mechanism of NO3− ions adsorption by the bioadsorbent can be anionic exchange and electrostatic interaction. Good antibacterial activity was obtained against E. coli, confirming that quaternary ammonium molecules were dispersed within the hydrogel matrix effectively. Therefore, the high performance of the prepared low-cost bioadsorbent hydrogels suggests their potential for water purification applications as well as using in the separation column. Acknowledgment The authors would like to thank Dr. Mojtaba Mohseni (Department of Microbiology, University of Mazandaran, Babolsar, Iran) for 7
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