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Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution
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Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution Guohao Yuan a,1, Mayakrishnan Prabakaran b,1, Sun Qilong c, Jung Soon Lee d, Ill-Min Chung b, Mayakrishnan Gopiraman a, Kyung-Hun Song e, Ick Soo Kim a,∗ a
Nano Fusion Technology Research Group, Division of Frontier Fibers, Institute for Fiber Engineering (IFES), Interdisciplinary Cluster for Cutting Edge Research (ICCER), Shinshu University, Tokida 3-15-1, Ueda, Nagano Prefecture 386-8567, Japan College of Life and Environmental, Department of Applied Bioscience, Konkuk University, 120 Neungdong-ro, Gwangji-gu, Seoul 05029, South Korea c School of Textile and Clothing, Nantong University, Nantong 229016, China d Department of Clothing and Textiles, Chungnam National University, Daejeon 305-764, South Korea e Department of Clothing & Textiles, PaiChai University, Daejeon 302-735, South Korea b
a r t i c l e
i n f o
Article history: Received 20 January 2016 Revised 28 September 2016 Accepted 17 October 2016 Available online xxx Keywords: Cellulose Nanofibers Cyclodextrin Toluene Adsorbent
a b s t r a c t Herein, we report cyclodextrins (CDs)-modified regenerated cellulose nanofibers (CDs/RCNFs) as green adsorbents for the removal of toluene from wastewater. Two different methods, namely, physical mixing and chemical grafting, were opted to combine the CDs with RCNFs. The CDs with three different kinds such as α -, β -, and γ were employed. Initially, various electrospinning parameters were optimized to obtain the better morphology of CDs/RCNFs. Scanning electron microscopy (SEM) results confirmed the good surface morphology of CDs/RCNFs. The effective dispersion and successful chemical modification of RCNFs with CDs were acknowledged by SEM, X-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) analyses. The usefulness of the prepared materials was realized from the higher adsorption rate of toluene. It was found that the chemically modified RCNFs with γ -CDs have a better toluene adsorption rate of 82% after only 180 min. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Owing to the rapid population growth, several industries including small factories are newly opened to fulfill people’s requirements and to improve their life style. On the other hand, the hazardous wastes from the industries and factories have also started creating huge environmental issues [1]. The hazardous industrial wastes, which may be in solid, liquid or gaseous form, may cause risk to health and environment. It is presumed that about 10–15% of wastes produced by industries are hazardous. Particularly, in the last few years, it has raised much and the generation of hazardous wastes is increasing at the rate of 2–5% per year, especially in the developing countries [2]. The contamination of wastewater is also one of the highly problematic environmental issues since the common industrial processes require organic solvents such as toluene, methanol, ethanol, nitromethane, benzene, and dichloromethane [3, 4]. There are several methods such as coagulation, filtration with coagulation, precipitation, ozonation, adsorp∗
Corresponding authors. Fax: +81 268 21 5482. E-mail addresses: [email protected] (I.-M. Chung), [email protected] (K.-H. Song), [email protected], [email protected] (I.S. Kim). 1 Guohao Yuan and Mayakrishnan Prabakaran contributed equally to this work.
tion, ion exchange, reverse osmosis and advanced oxidation processes are developed to remove the organic solvents from wastewater [2]. However, these methods are limited since they often involve relatively high investment and operational cost. Adsorbents are often used as key materials to remove the organic substances from wastewater. The most important properties of the adsorbents are the surface area, wettability, and pore properties [5]. The higher surface area can provide more adsorption sites and therefore enhance the adsorption nature of the materials. Activated carbons (ACs) are the most commonly used materials for the removal of organic solvents [6]. However, the powder form of ACs is difficult to handle and inhaling of ACs may cause health problems. Cyclodextrins (CDs), a family of macrocyclic oligosaccharides linked by α −1,4-glycosidic bonds, have been extensively studied in diverse fields. CDs have toroid-shaped molecular structure in which the inner side is composed of hydrophobic groups and the outside is full of hydrophilic groups, which provides the CDs to adsorb hydrophobic molecules [7]. Therefore, the CDs have been widely applied as an adsorbent for the removal of organic solvents from wastewater. Electrospun nanofibers are demonstrated as enormous potential applications in water filtration, due to its higher surface area, better porous properties, easy handling and lower production cost
http://dx.doi.org/10.1016/j.jtice.2016.10.028 1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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[8]. Particularly, owing to the simple and unique surface modification, cellulose and its composites are often employed for various applications such as energy, catalysis, biomedical, separators and filters [9]. In addition, the solubility of cellulose in various aqueous and organic solvents is nearly zero due to the existence of multiple hydrogen bonds [10]. Very recently Kayaci et al. [11] prepared cyclodextrin modified electrospun polyester nanofibers for the removal of phenanthrene from aqueous solution. They found that the nanofiber composite is effective and easy to handle. Alike, Celebioglu et al. [12] prepared cyclodextrin-grafted electrospun cellulose acetate nanofibers via “Click” reaction for removal of phenanthrene. In our recent course of investigation, we developed a new Prussian blue nanoparticle incorporated polyvinyl alcohol composite nanofiber (c-PBNPs/PVA) [13]. The c-PBNPs/PVA showed nearly 100% adsorption of cesium (Cs) from radioactive wastewater. However, most of the electrospun nanofibers and their composites are physically as well as chemically unstable. Particularly, during the adsorption of organic solvents, the nanofibers are soluble either completely or partially. To overcome this issue, chemical modification or cross-linking methods are often required for electrospun mats. We presumed that the surface modification of cellulose nanofibers with cyclodextrin would show higher adsorption rate toward removal of toluene from wastewater. Moreover, tuning the cellulose acetate electrospun mat to cellulose nanofibers by simple method would assist to obtain a stable adsorbent. Herein, we prepared CDs modified cellulose nanofiber composites (CNFs) by a simple chemical treatment. The prepared materials were completely characterized and tested as an adsorbent for the removal of toluene from wastewater. 2. Materials and methods 2.1. Materials Cellulose acetate (CA, Mw = 30,0 0 0) was purchased from Sigma-Aldrich. N, N-dimethylformamide (DMF), acetone, sodium
hydroxide (NaOH), cyclodextrin (α -CD, β -CD and γ -CD), citric acid, sodium hypophosphite hydrate (SHPI), and toluene, were purchased from Wako Pure Chemicals. All chemicals were used without further purification. 2.2. Preparation of CDs/RCNFs by physical mixing method At first, 19 wt% of CA solution was prepared by dissolving 2.345 g of CA in 10 mL of DMF/acetone [6/4 (w/w)] binary solvent mixture. Subsequently, different weight percentages of CDs/CA solutions were prepared by simply adding CDs (α -CDs, β -CDs and γ -CDs) to the above prepared CA solution under vigorous stirring condition at room temperature. The obtained CDs/CA solutions were electrospun under an electric field of 12 kV at a tipto-collector distance of 15 cm. A metallic Cu wire was used as an anode and a cathode was attached to a rotating metallic collector (RMC). The RMC was wrapped with aluminum foil and used as a collector for the nanofibers. The electrospun CDs/CANFs were dried in air and then dipped in 0.05 M NaOH solution for 48 h. Finally, the nanofibers were washed with distilled water and thoroughly dried [Fig. 1(a)]. 2.3. Preparation of CDs/RCNFs by grafting method The CANFs with 19 wt% was prepared according to our previously reported procedure [14]. The electrospinning condition was same for the both mixing and grafting methods. After preparing CANFs, the electrospun CANFs was dipped in 0.05 M of aqueous NaOH solution for 48 h to obtain RCNFs. For the grafting of CDs on the RCNFs, citric acid was used as a cross-linker [15]. Graft solution was prepared by mixing particular amounts of CDs (α -CDs, β -CDs or γ -CDs), citric acid and SHPI in distilled water under vigorous stirring at 60 °C. Then, the regenerated RCNFs were dipped into the above prepared solution at 60 °C for 4 h. Finally, the samples were washed with distilled water and dried in air for 24 h [Fig. 1(b)].
Fig. 1. Schematic illustration of the preparation of CDs/RCNFs composites; (a) physical mixing method and (b) grafted method.
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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Fig. 2. SEM images of (a), (b) CANFs, (c) α -CANFs/CDs, (d) α -RCNFs/CDs, and (e) the histogram of nanofiber diameter distribution.
2.4. Characterizations The surface morphology of nanofibers was examined by scanning electron microscope (SEM, JSM-6010LA, JEOL, Japan) and field emission scanning electron microscope (FE-SEM, S-50 0 0, Hitachi, Japan). Prior to the analysis, the samples were sputtered with 30 nm Pt/V and ∼50 fibers were chosen from the SEM images to calculate the average fiber diameter. The chemical modification of the nanofibers was investigated by Fourier transform infrared spectrometer (FTIR, IRPrestige-21, Shimadzu Co., Japan), and X-ray photoelectron spectrometer (XPS, Kratos Axis-Ultra DLD, Kratos Analytical). The toluene adsorption rate was performed by using a gas chromatograph analyzer (GC, GC-2014, Shimadzu Co., Japan). Capillary column with 30 m in length and 0.25 mm of inner diameter was used. During the GC analysis, the column kept at a vaporizing chamber temperature of 200 °C and the TCD detector was maintained at the temperature of 280 °C. He was used as a carrier gas. The specific surface area of nanofibers was determined using Brunauer–Emmett–Teller (BET) method [TriStar 30 0 0 (Micromeritics, USA)]. 2.5. Adsorption procedure The performance of prepared nanofiber samples was verified by the toluene adsorption test. In a typical test, the test solution was prepared by adding a 100 mg of toluene in 1 L distilled water (1 L of 100 ppm toluene). Then 10 mL of test solution was injected into a 20 mL vial loaded with 30 mg adsorbents. The vial was rotated at 600 rpm and samples were taken at particular time intervals (60, 120, 180, 240, 300, and 360 min). The samples obtained were centrifuged before the GC analysis. Adsorption rate (A%) was calculated using the following equation.
A = [(Ab − Aa )/Ab ] × 100
(1)
where Ab is the concentration before adsorption test and Aa is the concentration after adsorption test. 3. Results and discussion 3.1. Optimization of electrospinning conditions Two different methods such as mixing and grafting methods were opted to prepare the nanocomposites. At first, the electrospinning conditions were optimized for the mixing method to obtain a better morphology of the nanocomposites. CA solution with
various weight percentages (15, 17, 19, 21 wt%) was prepared and found that 19 wt% is the best concentration since the spinning was continuous without any beads. Fig. 2(a) and (b) shows the SEM images of CANFs. It can be seen that the surface morphology of CANFs was smooth and continuous with fiber diameters ranging from 50 to 600 nm and lengths up to several millimeters. The average diameter of the CANFs was calculated to be 364.5 nm. However, SEM images from Fig. 2(c) and (d) reveal that the surface morphology of the α -CDs incorporated CANFs is rough with several beads. The formation of beads may be due to the aggregation of CDs during the electrospinning process. In order to control the aggregation of CDs, various parameters such as applied voltage (10, 11 and 12 kV), TCD distance (10–15 cm), and CDs concentrations (4, 5, 6 and 7 wt%) were tested. Nevertheless, the expected morphology was not obtained for CDs/CANFs composite from the mixing method. We suspected that the voltage required for the electrospinning process is also one of the main reasons for the aggregation of CDs. Moreover, the diameter of the nanofibers increased about 2 times higher than the pure CANFs. Except the fiber diameter, no big difference in the morphology was observed for CDs incorporated CANFs after deacetylation (Fig. 2d and e). Subsequently, the conditions were optimized for the grafting method to obtain a better morphology of the nanocomposites. A 19 wt% of CA solution was chosen to prepare the nanocomposite. After the preparation, the CANFs were deacetylated using aqueous NaOH (0.05 M) to make regenerated cellulose nanofibers (RCNFs) [16]. The RCNFs was further used for the optimization of the weight percentages of both CDs and citric acid. Various concentrations of CDs (5, 6, 7, 8, 9, and 10%) and citric acid (6, 7, 8, and 10%) were employed. It was found that the optimal concentration of both CDs and citric acid is 7 wt%. The CNFs were dipped into the aqueous mixture containing 7% of citric acid and 7 wt% of CDs to prepare CDs/RCNFs. Since the morphology of the nanofiber composites is very important for any applications, we chosen the nanofiber composites that prepared from grafting method as adsorbents for the removal of toluene. Prior to the test, the nanocomposites were completely characterized by various spectroscopic and microscopic techniques; the results are discussed under the subtitle of microscopic and spectroscopic studies of CDs/RCNFs. 3.2. Microscopic and spectroscopic studies of CDs/RCNFs Initially, the successful generation of RCNFs from CANFs was confirmed by FE-SEM and FT-IR techniques. Fig. 3 shows the FT-IR
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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Fig. 3. (a) FT-IR spectrum of CANFs and RCNFs, and (b) SEM image of CNFs (inset: magnified SEM image of CNFs).
Fig. 4. FE-SEM images of (a) CANFs, (b) CNFs, (c) α -CDs/RCNFs, (d) β -CDs/RCNFs, (e) γ -CDs/RCNFs, and (f) the histogram of nanofiber diameter distribution.
spectra of CANFs and RCNFs, and FE-SEM image of RCNFs. Similar to the CANFs (Fig. 2a), the surface morphology of the RCNFs was fine and continuous but the mean fiber diameter of the CNFs was dramatically decreased from 364.5 to 215.4 nm (Fig. 3). This phenomenon might be caused by the elimination of acetyl group from the CANFs [17]. In Fig. 3, three intense peaks at 1730, 1370 and 1220 cm−1 were observed for CANFs which correspond to the stretching vibration of C=O, C−CH3 , and C–O–C groups, respectively. After the deacetylation process, the strong carbonyl absorption at 1730 cm−1 was completely disappeared. On the other hand, a much broader and stronger hydroxyl (–OH) peak at 3400 cm−1 was observed; the results confirmed the successful regeneration of CNFs from CANFs [18]. In fact, the main reason for the regeneration of cellulose is to improve the solubility of the adsorbent. The nanocomposites (α -CDs/RCNFs, β -CDs/RCNFs, and γ CDs/RCNFs) prepared from grafting method were characterized
in detail by FE-SEM, FT-IR and XPS analysis. Fig. 4 shows FESEM images of CANFs, CNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs. The results confirmed that the surface morphology of CANFs and CNFs is smooth and continuous with narrow fiber diameter distribution and lengths up to several millimeters. However, after the functionalization of CDs, the surface of the α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs (Fig. 4c, d and e) was rough without any significant changes in the diameter and length of the nanofibers (Fig. 4f). This may be due to two main reasons: (1) successful functionalization of CDs with CNFs and (2) the crosslinking between –OH group of CNFs and –COOH of citric acid (Fig. 5b). The mean diameter of the α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs was calculated to be 242.3, 301.3, and 235.2 nm respectively. It was noticed that the mean diameter of the CDs/RCNFs composites are slightly higher than the pure RCNFs. This may be due to the coverage of CDs on RCNFs. To further
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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Fig. 5. (a) FT-IR spectra of RCNFs and CDs/RCNFs composites, and (b) schematic show the crosslinking of citric acid with RCNFs and CDs.
Fig. 6. (a) XPS spectra and (b) magnified C1s peaks of RCNFs (a), α -CDs/RCNFs (b), β -CDs/RCNFs (c) and γ -CDs/RCNFs (d).
confirm the successful functionalization process, XPS and FT-IR were carried out for CANFs, CNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs. Fig. 5 presents the FT-IR spectra of CANFs, RCNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs. The FTIR spectrum of CNFs shows two major peaks at 1100 and 3400 cm−1 correspond to C–C/C=C and –OH respectively. However, after functionalization of CDs, a strong and new peak at 1740 cm−1 was observed, which may be due to the formation of C=O [19]. In addition, the intensity of O–H peak at 3100–3550 cm−1 decreased slightly. The results clearly indicate that the effective crosslinking of citric acid with CDs and RCNFs. XPS spectra of CNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs are presented in Fig. 6. As expected, all the four samples show C 1s and O 1s peaks at 283.2 and 530.5 eV respectively. In Fig. 6b, the binding energy (BE) of the C–C/C=C, C–O–C/C–OH and O–C–O was assigned at 283.5–284 eV, 284.3, and 286.5 eV respectively [20]. When compared to the C 1s XPS spectrum of RCNFs, a dramatic increase in the peak intensity at
284.3 eV (C–O–C/C–OH) was observed for the CDs modified CNFs which indicating the successful functionalization of CDs with CNFs via the crosslinking of citric acid (Fig. 6b). After the complete characterization, the nanocomposites were employed as adsorbents for the removal of toluene from wastewater. 3.3. Surface area of CDs/RCNFs Since the surface properties of the adsorbents are very important, [21] surface area, average pore diameter and pore volume of the RCNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs were determined by BET measurements. The RCNFs has BET surface area of 5.61 m2 /g with average pore size of 15.3 nm. After the immobilization of CDs, the surface area of the CDs/RCNFs was noticed to be slightly decreased which is may be due to the surface irregularities of the CDs/RCNFs. The surface area of α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs was 2.99, 2.03 and 3.27, respectively. Alike, the average pore size of 10.3, 13.2 and 14.7 nm was determined for
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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composites are considerably unstable in organic solvents. Hence, the γ -CDs/RCNFs composite after test was studied by means of SEM (data not shown). The SEM images show the similar morphology to the fresh γ -CDs/RCNFs composite. In addition to the faster adsorption performance and good stability, the γ -CDs/RCNFs composite is green and easy to handle, and therefore, can be used as an adsorbent for the removal of toluene form the wastewater. 4. Conclusions
Fig. 7. Adsorption rates of CDs/RCNFs composites at different time interval.
α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs, respectively. The results showed that the CDs/RCNFs could be a suitable adsorbent. 3.4. Adsorption performance of CDs/RCNFs Fig. 7 shows the toluene adsorption rate of the nanocomposites fabricated by graft method (α -CDs/RCNFs, β -CDs/RCNFs, and γ -CDs/RCNFs). It was noticed that the adsorption rate of pure RCNFs is significantly lower than the CDs grafted RCNFs. The RCNFs showed a maximum adsorption rate of 51.5% only after 300 min. Alike, the α -CDs/RCNFs demonstrated a maximum adsorption rate of 57.4% after 240 min. When β -CDs/RCNFs were used as an adsorbent, the adsorption rate was improved to 69.9% but after the immersion time of 300 min. Among them, the γ -CDs/RCNFs showed a better adsorption rate of 82% after only 180 min. At the immersion of 180 min, the adsorption rate of RCNFs, α -CDs/RCNFs, β -CDs/RCNFs, and γ -CDs/RCNFs was calculated to be 58.9, 55.0, 58.0 and 82% respectively. It is clear that the pore size of the CDs has played significant role on the adsorption rate. The pore size of the α -CDs, β -CDs, and γ -CDs is ∼6, 8 and 10 A˚ [11]. In addition, the molecular size of the toluene is ∼7 A˚ (Fig. 9). The very lower adsorption rate of the α -CDs/RCNFs is may be due to the ˚ than the toluene molecusmaller cavity size of the α -CDs (∼6 A) ˚ is almost same lar size. Since the cavity size of the β -CDs (∼8 A) ˚ the adsorption rate increased to 69.9% but with the toluene (∼7 A), required longer adsorption time of 300 min. Interestingly the adsorption rate of the γ -CDs/RCNFs composite was reached to 82% after 180 min. The faster adsorption rate is mainly due to the bigger cavity size of the γ -CDs. The hydrophilic groups on the outside of CDs would have assisted the toluene to come closer toward the CDs cavities. Subsequently, the inner side of CDs form inclusion complex with the toluene [22,23]. The results conclude that the γ -CDs are the better choice for the removal of toluene from the wastewater. In order to understand the effect of temperature, the adsorption performance of γ -CDs/RCNFs was studied at elevated temperatures (40, 50 and 60 °C). The results showed that there is no significant change in the adsorption rate particularly at 40 and 50 °C. However, at 60 °C, the adsorption rate was observed to be slightly increased to 86%. The results are well comparable with previously reported results. Previously reported adsorbents such as electrospun carbon fibers [24], activated carbons [6], and CDs modified polyester nanofibers [11] are showed good adsorption performance toward the removal of toluene from wastewater. Physical stability of the adsorbent is one of the most important properties. Unlike activated carbons, the electrospun nanofiber
In conclusion, we successfully fabricated CDs-modified RCNFs composites via two different methods, namely, physical mixing and chemical grafting. It was concluded that the grafting method is suitable for the fabrication of CDs/RCNFs. The physicochemical properties of the nanocomposites were investigated by FT-IR, XPS and SEM analyses. The usefulness of the nanocomposites was realized from the higher toluene adsorption rate. It was found that the chemically modified RCNFs with γ -CD has better toluene adsorption rate of 82% after only 180 min. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MOE) (no. 2011 - 0023753). References [1] Foster KL, Fuerman RG, Economy J, Larson SM, Rood MJ. Adsorption characteristics of trace volatile organic compounds in gas streams onto activated carbon fibers. Chem Mat 1992;4:1068–73. [2] Crini G. Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Prog Polym Sci 2005;30:38–70. [3] Gupta VK, Suhas. Application of low-cost adsorbents for dye removal – a review. J Environ Manage 2009;90:2313–42. [4] Weber CT, Collazzo GC, Mazutti MA, Foletto EL, Dotto GL. Removal of hazardous pharmaceutical dyes by adsorption onto papaya seeds. Water Sci Technol 2014;70:102–7. [5] Putra EK, Pranowo R, Sunarso J, Indraswati N, Ismadji S. Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: mechanisms, isotherms and kinetics. Water Res 2009;43:2419–30. [6] Rodenas MAL, Amoros DC, A Solano AL. Benzene and toluene adsorption at low concentration on activated carbon fibres. Adsorption 2011;17:473–81. [7] Szejtli J. Introduction and general overview of cyclodextrin chemistry. Chem Rev 1998;98:1743–54. [8] Gopiraman M, Fujimori K, Zeeshan K, Kim BS, Kim IS. Structural and mechanical properties of cellulose acetate/graphene hybrid nanofibers: Spectroscopic investigations. Express Poly Lett 2013;7:554–63. [9] Gopiraman M, Bang H, Yuan G, Yin C, Song KH, Lee JS, et al. Noble metal/functionalized cellulose nanofiber composites for catalytic applications. Carbohydr Polym 2015;132:554–64. [10] Koga H, Tokunaga E, Hidaka M, Umemura Y, Saito T, Isogai A, et al. Topochemical synthesis and catalysis of metal nanoparticles exposed on crystalline cellulose nanofibers. Chem Commun 2010;46:8567–9. [11] Kayaci F, Aytac Z, Uyar T. Surface modification of electrospun polyester nanofibers with cyclodextrin polymer for the removal of phenanthrene from aqueous solution. J Hazard Mater 2013;261:286–94. [12] Celebioglu A, Demirci S, Uyar T. Cyclodextrin-grafted electrospun cellulose acetate nanofibers via “Click” reaction for removal of phenanthrene. Appl Surf Sci 2014;305:581–8. [13] Bang H, Watanabe K, Nakashima R, Kai W, Song KH, Lee JS, et al. A highly hydrophilic water-insoluble nanofiber composite as an efficient and easily-handleable adsorbent for the rapid adsorption of cesium from radioactive wastewater. RSC Adv 2014;4:59571–8. [14] Khatri Z, Arain RA, Jatoi AW, Gopiraman M, Wei K, Kim IS. Dyeing and characterization of cellulose nanofibers to improve color yields by dual padding method. Cellulose 2013;20:1469–76. [15] Uyar T, Havelund R, Hacaloglu J, Besenbacher F, Kingsport P. Functional electrospun polystyrene nanofibers incorporating α -, β -, and γ -cyclodextrins: comparison of molecular filter performance. ACS Nano 2010;4:5121–30. [16] Khatri Z, Ahmed F, Jhatial AK, Abro ML, Mayakrishnan G, Kim IS. Cold pad-batch dyeing of cellulose nanofibers with reactive dyes. Cellulose 2014;21:3089–95. [17] Deng L, Young RJ, Kinloch IA, Zhu Y, Eichhorn J. Carbon nanofibres produced from electrospun cellulose nanofibres. Carbon 2013;58:66–75. [18] Zhang L, Menkhaus TJ, Fong H. Fabrication and bioseparation studies of adsorptive membranes/felts made from electrospun cellulose acetate nanofibers. J Membr Sci 2008;319:176–84.
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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G. Yuan et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–7 [19] Lojewska J, Miskowiec P, Lojewski T, Proniewicz LM. Cellulose oxidative and hydrolytic degradation: in situ FTIR approach. Polym Degrad Stab 2005;88:512–20. [20] Qaiser AA, Hyland MM, Patterson DA. Surface and charge transport characterization of polyaniline−cellulose acetate composite membranes. J Phys Chem B 2011;115:1652–61. [21] Khatri Z, Gopiraman M, Hirata Y, Wei K, Kim IS. Cationic-cellulose nanofibers: preparation and dyeability with anionic reactive dyes for apparel application. Carbohydr Polym 2013;91:434–43.
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[22] Narayanan G, Gupta BS, Tonelli AE. Enhanced mechanical properties of poly (ε -caprolactone) nanofibers produced by the addition of non-stoichiometric inclusion complexes of poly (ε -caprolactone) and a-cyclodextrin. Polymer 2015;76:321–30. [23] Guo X, Jia X, Du J, Xiao L, Li F, Liao L, et al. Host–guest chemistry of cyclodextrin carbamates and cellulose derivatives in aqueous solution. Carbohydr Polym 2013;98:982–7. [24] Rodenas MAL, Amoro DC, Solano AL. Behaviour of activated carbons with different pore size distributions and surface oxygen groups for benzene and toluene adsorption at low concentrations. Carbon 2005;43:1758–67.
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Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution Guohao Yuan a,1, Mayakrishnan Prabakaran b,1, Sun Qilong c, Jung Soon Lee d, Ill-Min Chung b, Mayakrishnan Gopiraman a, Kyung-Hun Song e, Ick Soo Kim a,∗ a
Nano Fusion Technology Research Group, Division of Frontier Fibers, Institute for Fiber Engineering (IFES), Interdisciplinary Cluster for Cutting Edge Research (ICCER), Shinshu University, Tokida 3-15-1, Ueda, Nagano Prefecture 386-8567, Japan College of Life and Environmental, Department of Applied Bioscience, Konkuk University, 120 Neungdong-ro, Gwangji-gu, Seoul 05029, South Korea c School of Textile and Clothing, Nantong University, Nantong 229016, China d Department of Clothing and Textiles, Chungnam National University, Daejeon 305-764, South Korea e Department of Clothing & Textiles, PaiChai University, Daejeon 302-735, South Korea b
a r t i c l e
i n f o
Article history: Received 20 January 2016 Revised 28 September 2016 Accepted 17 October 2016 Available online xxx Keywords: Cellulose Nanofibers Cyclodextrin Toluene Adsorbent
a b s t r a c t Herein, we report cyclodextrins (CDs)-modified regenerated cellulose nanofibers (CDs/RCNFs) as green adsorbents for the removal of toluene from wastewater. Two different methods, namely, physical mixing and chemical grafting, were opted to combine the CDs with RCNFs. The CDs with three different kinds such as α -, β -, and γ were employed. Initially, various electrospinning parameters were optimized to obtain the better morphology of CDs/RCNFs. Scanning electron microscopy (SEM) results confirmed the good surface morphology of CDs/RCNFs. The effective dispersion and successful chemical modification of RCNFs with CDs were acknowledged by SEM, X-ray photoemission spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) analyses. The usefulness of the prepared materials was realized from the higher adsorption rate of toluene. It was found that the chemically modified RCNFs with γ -CDs have a better toluene adsorption rate of 82% after only 180 min. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Owing to the rapid population growth, several industries including small factories are newly opened to fulfill people’s requirements and to improve their life style. On the other hand, the hazardous wastes from the industries and factories have also started creating huge environmental issues [1]. The hazardous industrial wastes, which may be in solid, liquid or gaseous form, may cause risk to health and environment. It is presumed that about 10–15% of wastes produced by industries are hazardous. Particularly, in the last few years, it has raised much and the generation of hazardous wastes is increasing at the rate of 2–5% per year, especially in the developing countries [2]. The contamination of wastewater is also one of the highly problematic environmental issues since the common industrial processes require organic solvents such as toluene, methanol, ethanol, nitromethane, benzene, and dichloromethane [3, 4]. There are several methods such as coagulation, filtration with coagulation, precipitation, ozonation, adsorp∗
Corresponding authors. Fax: +81 268 21 5482. E-mail addresses: [email protected] (I.-M. Chung), [email protected] (K.-H. Song), [email protected], [email protected] (I.S. Kim). 1 Guohao Yuan and Mayakrishnan Prabakaran contributed equally to this work.
tion, ion exchange, reverse osmosis and advanced oxidation processes are developed to remove the organic solvents from wastewater [2]. However, these methods are limited since they often involve relatively high investment and operational cost. Adsorbents are often used as key materials to remove the organic substances from wastewater. The most important properties of the adsorbents are the surface area, wettability, and pore properties [5]. The higher surface area can provide more adsorption sites and therefore enhance the adsorption nature of the materials. Activated carbons (ACs) are the most commonly used materials for the removal of organic solvents [6]. However, the powder form of ACs is difficult to handle and inhaling of ACs may cause health problems. Cyclodextrins (CDs), a family of macrocyclic oligosaccharides linked by α −1,4-glycosidic bonds, have been extensively studied in diverse fields. CDs have toroid-shaped molecular structure in which the inner side is composed of hydrophobic groups and the outside is full of hydrophilic groups, which provides the CDs to adsorb hydrophobic molecules [7]. Therefore, the CDs have been widely applied as an adsorbent for the removal of organic solvents from wastewater. Electrospun nanofibers are demonstrated as enormous potential applications in water filtration, due to its higher surface area, better porous properties, easy handling and lower production cost
http://dx.doi.org/10.1016/j.jtice.2016.10.028 1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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[8]. Particularly, owing to the simple and unique surface modification, cellulose and its composites are often employed for various applications such as energy, catalysis, biomedical, separators and filters [9]. In addition, the solubility of cellulose in various aqueous and organic solvents is nearly zero due to the existence of multiple hydrogen bonds [10]. Very recently Kayaci et al. [11] prepared cyclodextrin modified electrospun polyester nanofibers for the removal of phenanthrene from aqueous solution. They found that the nanofiber composite is effective and easy to handle. Alike, Celebioglu et al. [12] prepared cyclodextrin-grafted electrospun cellulose acetate nanofibers via “Click” reaction for removal of phenanthrene. In our recent course of investigation, we developed a new Prussian blue nanoparticle incorporated polyvinyl alcohol composite nanofiber (c-PBNPs/PVA) [13]. The c-PBNPs/PVA showed nearly 100% adsorption of cesium (Cs) from radioactive wastewater. However, most of the electrospun nanofibers and their composites are physically as well as chemically unstable. Particularly, during the adsorption of organic solvents, the nanofibers are soluble either completely or partially. To overcome this issue, chemical modification or cross-linking methods are often required for electrospun mats. We presumed that the surface modification of cellulose nanofibers with cyclodextrin would show higher adsorption rate toward removal of toluene from wastewater. Moreover, tuning the cellulose acetate electrospun mat to cellulose nanofibers by simple method would assist to obtain a stable adsorbent. Herein, we prepared CDs modified cellulose nanofiber composites (CNFs) by a simple chemical treatment. The prepared materials were completely characterized and tested as an adsorbent for the removal of toluene from wastewater. 2. Materials and methods 2.1. Materials Cellulose acetate (CA, Mw = 30,0 0 0) was purchased from Sigma-Aldrich. N, N-dimethylformamide (DMF), acetone, sodium
hydroxide (NaOH), cyclodextrin (α -CD, β -CD and γ -CD), citric acid, sodium hypophosphite hydrate (SHPI), and toluene, were purchased from Wako Pure Chemicals. All chemicals were used without further purification. 2.2. Preparation of CDs/RCNFs by physical mixing method At first, 19 wt% of CA solution was prepared by dissolving 2.345 g of CA in 10 mL of DMF/acetone [6/4 (w/w)] binary solvent mixture. Subsequently, different weight percentages of CDs/CA solutions were prepared by simply adding CDs (α -CDs, β -CDs and γ -CDs) to the above prepared CA solution under vigorous stirring condition at room temperature. The obtained CDs/CA solutions were electrospun under an electric field of 12 kV at a tipto-collector distance of 15 cm. A metallic Cu wire was used as an anode and a cathode was attached to a rotating metallic collector (RMC). The RMC was wrapped with aluminum foil and used as a collector for the nanofibers. The electrospun CDs/CANFs were dried in air and then dipped in 0.05 M NaOH solution for 48 h. Finally, the nanofibers were washed with distilled water and thoroughly dried [Fig. 1(a)]. 2.3. Preparation of CDs/RCNFs by grafting method The CANFs with 19 wt% was prepared according to our previously reported procedure [14]. The electrospinning condition was same for the both mixing and grafting methods. After preparing CANFs, the electrospun CANFs was dipped in 0.05 M of aqueous NaOH solution for 48 h to obtain RCNFs. For the grafting of CDs on the RCNFs, citric acid was used as a cross-linker [15]. Graft solution was prepared by mixing particular amounts of CDs (α -CDs, β -CDs or γ -CDs), citric acid and SHPI in distilled water under vigorous stirring at 60 °C. Then, the regenerated RCNFs were dipped into the above prepared solution at 60 °C for 4 h. Finally, the samples were washed with distilled water and dried in air for 24 h [Fig. 1(b)].
Fig. 1. Schematic illustration of the preparation of CDs/RCNFs composites; (a) physical mixing method and (b) grafted method.
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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Fig. 2. SEM images of (a), (b) CANFs, (c) α -CANFs/CDs, (d) α -RCNFs/CDs, and (e) the histogram of nanofiber diameter distribution.
2.4. Characterizations The surface morphology of nanofibers was examined by scanning electron microscope (SEM, JSM-6010LA, JEOL, Japan) and field emission scanning electron microscope (FE-SEM, S-50 0 0, Hitachi, Japan). Prior to the analysis, the samples were sputtered with 30 nm Pt/V and ∼50 fibers were chosen from the SEM images to calculate the average fiber diameter. The chemical modification of the nanofibers was investigated by Fourier transform infrared spectrometer (FTIR, IRPrestige-21, Shimadzu Co., Japan), and X-ray photoelectron spectrometer (XPS, Kratos Axis-Ultra DLD, Kratos Analytical). The toluene adsorption rate was performed by using a gas chromatograph analyzer (GC, GC-2014, Shimadzu Co., Japan). Capillary column with 30 m in length and 0.25 mm of inner diameter was used. During the GC analysis, the column kept at a vaporizing chamber temperature of 200 °C and the TCD detector was maintained at the temperature of 280 °C. He was used as a carrier gas. The specific surface area of nanofibers was determined using Brunauer–Emmett–Teller (BET) method [TriStar 30 0 0 (Micromeritics, USA)]. 2.5. Adsorption procedure The performance of prepared nanofiber samples was verified by the toluene adsorption test. In a typical test, the test solution was prepared by adding a 100 mg of toluene in 1 L distilled water (1 L of 100 ppm toluene). Then 10 mL of test solution was injected into a 20 mL vial loaded with 30 mg adsorbents. The vial was rotated at 600 rpm and samples were taken at particular time intervals (60, 120, 180, 240, 300, and 360 min). The samples obtained were centrifuged before the GC analysis. Adsorption rate (A%) was calculated using the following equation.
A = [(Ab − Aa )/Ab ] × 100
(1)
where Ab is the concentration before adsorption test and Aa is the concentration after adsorption test. 3. Results and discussion 3.1. Optimization of electrospinning conditions Two different methods such as mixing and grafting methods were opted to prepare the nanocomposites. At first, the electrospinning conditions were optimized for the mixing method to obtain a better morphology of the nanocomposites. CA solution with
various weight percentages (15, 17, 19, 21 wt%) was prepared and found that 19 wt% is the best concentration since the spinning was continuous without any beads. Fig. 2(a) and (b) shows the SEM images of CANFs. It can be seen that the surface morphology of CANFs was smooth and continuous with fiber diameters ranging from 50 to 600 nm and lengths up to several millimeters. The average diameter of the CANFs was calculated to be 364.5 nm. However, SEM images from Fig. 2(c) and (d) reveal that the surface morphology of the α -CDs incorporated CANFs is rough with several beads. The formation of beads may be due to the aggregation of CDs during the electrospinning process. In order to control the aggregation of CDs, various parameters such as applied voltage (10, 11 and 12 kV), TCD distance (10–15 cm), and CDs concentrations (4, 5, 6 and 7 wt%) were tested. Nevertheless, the expected morphology was not obtained for CDs/CANFs composite from the mixing method. We suspected that the voltage required for the electrospinning process is also one of the main reasons for the aggregation of CDs. Moreover, the diameter of the nanofibers increased about 2 times higher than the pure CANFs. Except the fiber diameter, no big difference in the morphology was observed for CDs incorporated CANFs after deacetylation (Fig. 2d and e). Subsequently, the conditions were optimized for the grafting method to obtain a better morphology of the nanocomposites. A 19 wt% of CA solution was chosen to prepare the nanocomposite. After the preparation, the CANFs were deacetylated using aqueous NaOH (0.05 M) to make regenerated cellulose nanofibers (RCNFs) [16]. The RCNFs was further used for the optimization of the weight percentages of both CDs and citric acid. Various concentrations of CDs (5, 6, 7, 8, 9, and 10%) and citric acid (6, 7, 8, and 10%) were employed. It was found that the optimal concentration of both CDs and citric acid is 7 wt%. The CNFs were dipped into the aqueous mixture containing 7% of citric acid and 7 wt% of CDs to prepare CDs/RCNFs. Since the morphology of the nanofiber composites is very important for any applications, we chosen the nanofiber composites that prepared from grafting method as adsorbents for the removal of toluene. Prior to the test, the nanocomposites were completely characterized by various spectroscopic and microscopic techniques; the results are discussed under the subtitle of microscopic and spectroscopic studies of CDs/RCNFs. 3.2. Microscopic and spectroscopic studies of CDs/RCNFs Initially, the successful generation of RCNFs from CANFs was confirmed by FE-SEM and FT-IR techniques. Fig. 3 shows the FT-IR
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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Fig. 3. (a) FT-IR spectrum of CANFs and RCNFs, and (b) SEM image of CNFs (inset: magnified SEM image of CNFs).
Fig. 4. FE-SEM images of (a) CANFs, (b) CNFs, (c) α -CDs/RCNFs, (d) β -CDs/RCNFs, (e) γ -CDs/RCNFs, and (f) the histogram of nanofiber diameter distribution.
spectra of CANFs and RCNFs, and FE-SEM image of RCNFs. Similar to the CANFs (Fig. 2a), the surface morphology of the RCNFs was fine and continuous but the mean fiber diameter of the CNFs was dramatically decreased from 364.5 to 215.4 nm (Fig. 3). This phenomenon might be caused by the elimination of acetyl group from the CANFs [17]. In Fig. 3, three intense peaks at 1730, 1370 and 1220 cm−1 were observed for CANFs which correspond to the stretching vibration of C=O, C−CH3 , and C–O–C groups, respectively. After the deacetylation process, the strong carbonyl absorption at 1730 cm−1 was completely disappeared. On the other hand, a much broader and stronger hydroxyl (–OH) peak at 3400 cm−1 was observed; the results confirmed the successful regeneration of CNFs from CANFs [18]. In fact, the main reason for the regeneration of cellulose is to improve the solubility of the adsorbent. The nanocomposites (α -CDs/RCNFs, β -CDs/RCNFs, and γ CDs/RCNFs) prepared from grafting method were characterized
in detail by FE-SEM, FT-IR and XPS analysis. Fig. 4 shows FESEM images of CANFs, CNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs. The results confirmed that the surface morphology of CANFs and CNFs is smooth and continuous with narrow fiber diameter distribution and lengths up to several millimeters. However, after the functionalization of CDs, the surface of the α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs (Fig. 4c, d and e) was rough without any significant changes in the diameter and length of the nanofibers (Fig. 4f). This may be due to two main reasons: (1) successful functionalization of CDs with CNFs and (2) the crosslinking between –OH group of CNFs and –COOH of citric acid (Fig. 5b). The mean diameter of the α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs was calculated to be 242.3, 301.3, and 235.2 nm respectively. It was noticed that the mean diameter of the CDs/RCNFs composites are slightly higher than the pure RCNFs. This may be due to the coverage of CDs on RCNFs. To further
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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Fig. 5. (a) FT-IR spectra of RCNFs and CDs/RCNFs composites, and (b) schematic show the crosslinking of citric acid with RCNFs and CDs.
Fig. 6. (a) XPS spectra and (b) magnified C1s peaks of RCNFs (a), α -CDs/RCNFs (b), β -CDs/RCNFs (c) and γ -CDs/RCNFs (d).
confirm the successful functionalization process, XPS and FT-IR were carried out for CANFs, CNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs. Fig. 5 presents the FT-IR spectra of CANFs, RCNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs. The FTIR spectrum of CNFs shows two major peaks at 1100 and 3400 cm−1 correspond to C–C/C=C and –OH respectively. However, after functionalization of CDs, a strong and new peak at 1740 cm−1 was observed, which may be due to the formation of C=O [19]. In addition, the intensity of O–H peak at 3100–3550 cm−1 decreased slightly. The results clearly indicate that the effective crosslinking of citric acid with CDs and RCNFs. XPS spectra of CNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs are presented in Fig. 6. As expected, all the four samples show C 1s and O 1s peaks at 283.2 and 530.5 eV respectively. In Fig. 6b, the binding energy (BE) of the C–C/C=C, C–O–C/C–OH and O–C–O was assigned at 283.5–284 eV, 284.3, and 286.5 eV respectively [20]. When compared to the C 1s XPS spectrum of RCNFs, a dramatic increase in the peak intensity at
284.3 eV (C–O–C/C–OH) was observed for the CDs modified CNFs which indicating the successful functionalization of CDs with CNFs via the crosslinking of citric acid (Fig. 6b). After the complete characterization, the nanocomposites were employed as adsorbents for the removal of toluene from wastewater. 3.3. Surface area of CDs/RCNFs Since the surface properties of the adsorbents are very important, [21] surface area, average pore diameter and pore volume of the RCNFs, α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs were determined by BET measurements. The RCNFs has BET surface area of 5.61 m2 /g with average pore size of 15.3 nm. After the immobilization of CDs, the surface area of the CDs/RCNFs was noticed to be slightly decreased which is may be due to the surface irregularities of the CDs/RCNFs. The surface area of α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs was 2.99, 2.03 and 3.27, respectively. Alike, the average pore size of 10.3, 13.2 and 14.7 nm was determined for
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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composites are considerably unstable in organic solvents. Hence, the γ -CDs/RCNFs composite after test was studied by means of SEM (data not shown). The SEM images show the similar morphology to the fresh γ -CDs/RCNFs composite. In addition to the faster adsorption performance and good stability, the γ -CDs/RCNFs composite is green and easy to handle, and therefore, can be used as an adsorbent for the removal of toluene form the wastewater. 4. Conclusions
Fig. 7. Adsorption rates of CDs/RCNFs composites at different time interval.
α -CDs/RCNFs, β -CDs/RCNFs and γ -CDs/RCNFs, respectively. The results showed that the CDs/RCNFs could be a suitable adsorbent. 3.4. Adsorption performance of CDs/RCNFs Fig. 7 shows the toluene adsorption rate of the nanocomposites fabricated by graft method (α -CDs/RCNFs, β -CDs/RCNFs, and γ -CDs/RCNFs). It was noticed that the adsorption rate of pure RCNFs is significantly lower than the CDs grafted RCNFs. The RCNFs showed a maximum adsorption rate of 51.5% only after 300 min. Alike, the α -CDs/RCNFs demonstrated a maximum adsorption rate of 57.4% after 240 min. When β -CDs/RCNFs were used as an adsorbent, the adsorption rate was improved to 69.9% but after the immersion time of 300 min. Among them, the γ -CDs/RCNFs showed a better adsorption rate of 82% after only 180 min. At the immersion of 180 min, the adsorption rate of RCNFs, α -CDs/RCNFs, β -CDs/RCNFs, and γ -CDs/RCNFs was calculated to be 58.9, 55.0, 58.0 and 82% respectively. It is clear that the pore size of the CDs has played significant role on the adsorption rate. The pore size of the α -CDs, β -CDs, and γ -CDs is ∼6, 8 and 10 A˚ [11]. In addition, the molecular size of the toluene is ∼7 A˚ (Fig. 9). The very lower adsorption rate of the α -CDs/RCNFs is may be due to the ˚ than the toluene molecusmaller cavity size of the α -CDs (∼6 A) ˚ is almost same lar size. Since the cavity size of the β -CDs (∼8 A) ˚ the adsorption rate increased to 69.9% but with the toluene (∼7 A), required longer adsorption time of 300 min. Interestingly the adsorption rate of the γ -CDs/RCNFs composite was reached to 82% after 180 min. The faster adsorption rate is mainly due to the bigger cavity size of the γ -CDs. The hydrophilic groups on the outside of CDs would have assisted the toluene to come closer toward the CDs cavities. Subsequently, the inner side of CDs form inclusion complex with the toluene [22,23]. The results conclude that the γ -CDs are the better choice for the removal of toluene from the wastewater. In order to understand the effect of temperature, the adsorption performance of γ -CDs/RCNFs was studied at elevated temperatures (40, 50 and 60 °C). The results showed that there is no significant change in the adsorption rate particularly at 40 and 50 °C. However, at 60 °C, the adsorption rate was observed to be slightly increased to 86%. The results are well comparable with previously reported results. Previously reported adsorbents such as electrospun carbon fibers [24], activated carbons [6], and CDs modified polyester nanofibers [11] are showed good adsorption performance toward the removal of toluene from wastewater. Physical stability of the adsorbent is one of the most important properties. Unlike activated carbons, the electrospun nanofiber
In conclusion, we successfully fabricated CDs-modified RCNFs composites via two different methods, namely, physical mixing and chemical grafting. It was concluded that the grafting method is suitable for the fabrication of CDs/RCNFs. The physicochemical properties of the nanocomposites were investigated by FT-IR, XPS and SEM analyses. The usefulness of the nanocomposites was realized from the higher toluene adsorption rate. It was found that the chemically modified RCNFs with γ -CD has better toluene adsorption rate of 82% after only 180 min. Acknowledgment This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MOE) (no. 2011 - 0023753). References [1] Foster KL, Fuerman RG, Economy J, Larson SM, Rood MJ. Adsorption characteristics of trace volatile organic compounds in gas streams onto activated carbon fibers. Chem Mat 1992;4:1068–73. [2] Crini G. Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Prog Polym Sci 2005;30:38–70. [3] Gupta VK, Suhas. Application of low-cost adsorbents for dye removal – a review. J Environ Manage 2009;90:2313–42. [4] Weber CT, Collazzo GC, Mazutti MA, Foletto EL, Dotto GL. Removal of hazardous pharmaceutical dyes by adsorption onto papaya seeds. Water Sci Technol 2014;70:102–7. [5] Putra EK, Pranowo R, Sunarso J, Indraswati N, Ismadji S. Performance of activated carbon and bentonite for adsorption of amoxicillin from wastewater: mechanisms, isotherms and kinetics. Water Res 2009;43:2419–30. [6] Rodenas MAL, Amoros DC, A Solano AL. Benzene and toluene adsorption at low concentration on activated carbon fibres. Adsorption 2011;17:473–81. [7] Szejtli J. Introduction and general overview of cyclodextrin chemistry. Chem Rev 1998;98:1743–54. [8] Gopiraman M, Fujimori K, Zeeshan K, Kim BS, Kim IS. Structural and mechanical properties of cellulose acetate/graphene hybrid nanofibers: Spectroscopic investigations. Express Poly Lett 2013;7:554–63. [9] Gopiraman M, Bang H, Yuan G, Yin C, Song KH, Lee JS, et al. Noble metal/functionalized cellulose nanofiber composites for catalytic applications. Carbohydr Polym 2015;132:554–64. [10] Koga H, Tokunaga E, Hidaka M, Umemura Y, Saito T, Isogai A, et al. Topochemical synthesis and catalysis of metal nanoparticles exposed on crystalline cellulose nanofibers. Chem Commun 2010;46:8567–9. [11] Kayaci F, Aytac Z, Uyar T. Surface modification of electrospun polyester nanofibers with cyclodextrin polymer for the removal of phenanthrene from aqueous solution. J Hazard Mater 2013;261:286–94. [12] Celebioglu A, Demirci S, Uyar T. Cyclodextrin-grafted electrospun cellulose acetate nanofibers via “Click” reaction for removal of phenanthrene. Appl Surf Sci 2014;305:581–8. [13] Bang H, Watanabe K, Nakashima R, Kai W, Song KH, Lee JS, et al. A highly hydrophilic water-insoluble nanofiber composite as an efficient and easily-handleable adsorbent for the rapid adsorption of cesium from radioactive wastewater. RSC Adv 2014;4:59571–8. [14] Khatri Z, Arain RA, Jatoi AW, Gopiraman M, Wei K, Kim IS. Dyeing and characterization of cellulose nanofibers to improve color yields by dual padding method. Cellulose 2013;20:1469–76. [15] Uyar T, Havelund R, Hacaloglu J, Besenbacher F, Kingsport P. Functional electrospun polystyrene nanofibers incorporating α -, β -, and γ -cyclodextrins: comparison of molecular filter performance. ACS Nano 2010;4:5121–30. [16] Khatri Z, Ahmed F, Jhatial AK, Abro ML, Mayakrishnan G, Kim IS. Cold pad-batch dyeing of cellulose nanofibers with reactive dyes. Cellulose 2014;21:3089–95. [17] Deng L, Young RJ, Kinloch IA, Zhu Y, Eichhorn J. Carbon nanofibres produced from electrospun cellulose nanofibres. Carbon 2013;58:66–75. [18] Zhang L, Menkhaus TJ, Fong H. Fabrication and bioseparation studies of adsorptive membranes/felts made from electrospun cellulose acetate nanofibers. J Membr Sci 2008;319:176–84.
Please cite this article as: G. Yuan et al., Cyclodextrin functionalized cellulose nanofiber composites for the faster adsorption of toluene from aqueous solution, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.10.028
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ARTICLE IN PRESS
[m5G;November 1, 2016;15:18]
G. Yuan et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–7 [19] Lojewska J, Miskowiec P, Lojewski T, Proniewicz LM. Cellulose oxidative and hydrolytic degradation: in situ FTIR approach. Polym Degrad Stab 2005;88:512–20. [20] Qaiser AA, Hyland MM, Patterson DA. Surface and charge transport characterization of polyaniline−cellulose acetate composite membranes. J Phys Chem B 2011;115:1652–61. [21] Khatri Z, Gopiraman M, Hirata Y, Wei K, Kim IS. Cationic-cellulose nanofibers: preparation and dyeability with anionic reactive dyes for apparel application. Carbohydr Polym 2013;91:434–43.
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[22] Narayanan G, Gupta BS, Tonelli AE. Enhanced mechanical properties of poly (ε -caprolactone) nanofibers produced by the addition of non-stoichiometric inclusion complexes of poly (ε -caprolactone) and a-cyclodextrin. Polymer 2015;76:321–30. [23] Guo X, Jia X, Du J, Xiao L, Li F, Liao L, et al. Host–guest chemistry of cyclodextrin carbamates and cellulose derivatives in aqueous solution. Carbohydr Polym 2013;98:982–7. [24] Rodenas MAL, Amoro DC, Solano AL. Behaviour of activated carbons with different pore size distributions and surface oxygen groups for benzene and toluene adsorption at low concentrations. Carbon 2005;43:1758–67.
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