Superabsorbent CelluloseâClay Nanocomposite Hydrogels for Highly

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Superabsorbent Cellulose-Clay Nanocomposite Hydrogels for High Efficient Removal of Dye in Water Na Peng, Danning Hu, Jian Zeng, Yu Li, Lei Liang, and Chunyu Chang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02178 • Publication Date (Web): 05 Oct 2016 Downloaded from http://pubs.acs.org on October 11, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Superabsorbent Cellulose-Clay Nanocomposite Hydrogels for High Efficient Removal of Dye in Water Na Peng, †,‡ Danning Hu, † Jian Zeng, ‡ Yu Li, ‡ Lei Liang, ‡ Chunyu Chang*, †,‡

†

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072,

China ‡

Guangzhou Sugarcane Industry Research Institute, Guangzhou 510316, China

Corresponding author: Chunyu Chang (Email: [email protected])

KEYWORDS: cellulose, clay, nanocomposite, superabsorbent hydrogels, dye removal

ABSTRACT The toxic dyes have threaten human health through the consumption of polluted water, so removal of dyes from wastewater has become a hot topic in both academic and industrial fields. Herein, we reported a kind of cellulose-clay hydrogels with superabsorbent properties, superior mechanical performance, and high dye removal efficiency. The main strategy for the preparation of superabsorbent hydrogels was chemical cross-linking of cellulose, carboxymethyl cellulose (CMC), and the intercalated clay in NaOH/urea aqueous solution. The as-prepared hydrogels exhibited high absorption capacity for methylene blue (MB) solution through spontaneous physic-sorption process which fitted well with pseudo second order and Langmuir

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

isotherm models. The maximum removal efficiencies of hydrogel samples for MB solution with concentration of 10 mg L-1 and 100 mg L-1 were 96.6% and 98%, respectively. These results demonstrated that cellulose-clay nanocomposite hydrogels were effective adsorbents for removal of MB dyes, which would provide a new platform for dye decontamination.

INTRODUCTION Over 10,000 commercially available dyes are inevitably used in many industries such as dyestuffs, textile, paper, plastics, rubber, tannery, paints, and cosmetics.1 More than 7×105 tons of dyes are produced annually worldwide, and approximately 12% of dyes are lost during manufacturing and processing operations, where about 20% of these lost dyes enter industrial wastewaters and cause environmental pollution problems.2 The removal of dye pollutants from wastewater has attracted considerable attention in recent years, since many dyes are toxic, carcinogenic, mutagenic, and hazard to aquatic living organisms,3 which also bring health risks to humans through the consumption of polluted water.4 Owing to dyes are recalcitrant, resistant to aerobic digestion, stable to oxidizing agents, and unsolvable with low concentration, wastewater containing dyes are very difficult to treat,5 so various techniques including coagulation, flocculation, chemical oxidation, membrane separation, catalytic degradation, biodegradation, and activation carbon adsorption, are proposed to removal dyes from contaminated media.6,7 Amongst the numerous methods, adsorption gives the best results as it is inexpensive, easy to perform, insensitive to toxic substances, and effective for different types of dyes.8 After activated carbon


Page 2 of 31

Page 3 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


were commonly used as sorbent to remove dyes, metal-organic framework (MOF),9 graphene oxide,10 porous carbon materials,11 magnetic nanoparticles,12 and their composites were developed to remove dye from effluent, which usually exhibited high adsorption capacity and efficiency. However, the practical application of these high performance adsorbents was limited by their high cost. So it is still a major challenge to develop simple, cheap, and efficient adsorbents. Montmorillonite clay possesses a layered structures with large surface area and high cationic exchange capacity, whose current market price is considered to be 20 times cheaper than that of activated carbon.13 Clay exhibited a strong affinity for both cationic and anionic dyes, whereas the sorption capacity for basic dye was much higher than for acidic dye because of the negative charge on the structure of clay.1 On the other hand, clay could participate in the design of polymeric hydrogels through in situ polymerization, which displayed excellent mechanical properties and optical transparency.14-16 In contrast, great attention has been paid towards the hydrogels composed of clay and acrylic acid-/acrylamide-based polymers or copolymers, which exhibited improved properties such as oxygen barrier, flame retardant, thermal stability, and adsorption capacity for industry, healthcare, and agriculture applications.17-20 However, these polyolefin based hydrogels were usually non-biodegradable, which may also cause the environmental problem and resulted in “white pollution”. Cellulose is a kind of abundant, low cost, renewable, and biodegradable natural polymers, which were widely used to construct hydrogels.21,22 Combination of the distinguishing features of clay and cellulose, it is feasible to



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

design superabsorbent cellulose/clay hydrogels for dye removal, which contain high specific area networks plugged by a lot of water. In our previous work, we reported a class of superabsorbent hydrogels which were prepared by chemical cross-linking cellulose and carboxyl cellulose in NaOH/urea aqueous solution, which was “green” solvent for cellulose.23 The characteristics of the superabsorbent hydrogels were high swelling ratio in water (1000 g/g,) and low organic content (～0.1 wt%), which could achieve controllable release of bovine serum albumin. Despite the superabsorbent hydrogels were self-standing because of the introduction of unsubstituted cellulose in the hydrogel networks, their mechanical properties (such as compressive strength) were still very low, which limited their further application. To enhance the mechanical performance of these hydrogels, we incorporated clay nanosheets into cellulose networks in this work. These novel superabsorbent hydrogels from low cost cellulose and intercalated clay were also applied for the removal of methylene blue in the water. Moreover, we characterized the structure and properties of cellulose/clay composite hydrogels, discussed the influence of state and content of clay on the properties of hydrogels, investigated the effect of time, temperature, and pH on the adsorption capacity of hydrogels for methylene blue (MB), and clarified the mechanism of MB adsorption onto hydrogels.

EXPERIMENTAL Materials


Page 4 of 31

Page 5 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The cellulose samples (cotton linter pulps) were supplied by Hubei Chemical Fiber Co. Ltd. (Xiangfan, China). Its weight-average molecular weight (Mw) was determined by static laser light scattering (DAWN DSP, Wyatt Technology Co.) to be 9.2×104. Sodium carboxymethylcellulose (CMC, 2.4×104) was analytical-grade reagent purchased from Shanghai Chemical Agents Co. Ltd. The degree of carboxymethyl substitution (DS) is 0.7, which is the number of substituent per sugar ring. Inorganic clay (Montmorillonite) (cation exchange capacity = 100 meq/100 g) was supplied by Hongyu Clay Company (Zhejiang, China). Epichlorohydrin (ECH) (1.18 g/mL) and methylene blue trihydrate (C16H18ClN3S·3H2O) were purchased from Sinopharm chemical Reagent Co. Ltd. (China). Preparation of cellulose/clay nanocomposite hydrogels The 3 wt% cellulose solution was prepared as follows: 3 g cellulose was dissolved into 97 g of 7 wt% NaOH/12 wt% urea/81 wt% water mixture at -12 °C, while CMC was dissolved in the same solvent at room temperature to obtain a 3 wt% polymer concentration. A desired amount of modified or unmodified clay was added into the mixture of CMC and cellulose solutions with weight ratio of 9:1 under stirring. ECH was dropped into the mixture as cross-linker with stirring at 0 °C until form a homogeneous solution, and then the reaction was conducted at 60 °C for 12 h to obtain gels which were finally dialyzed in distilled water to remove NaOH, urea, and unreacted ECH. For the modification of clay, 2,3-epoxypropyltrimethylammonium chloride (EPTAC) was used to exchange the cation of clay. 1.0 g clay was dispersed into 99 g



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

distilled water, and excess EPTAC was added into the clay suspension. The mixture was stirred for 2 h at 80 °C under nitrogen atmosphere. Afterwards, the clay was filtrated, washed with distilled water, and dried. The above procedure was repeated until the weight of clay constant, which indicated clay was completely modified. The hydrogels prepared with modified clay were named as Gel M-5, Gel M-10, and Gel M-15, according to content of clay, while the hydrogels composed of unmodified clay were coded as Gel U-5, Gel U-10, and Gel U-15, respectively. Characterization TEM observation of cellulose-clay nanocomposite hydrogels was carried out on a JEM-2010 FEF (UHR) transmission electron microscope (JEOL TEM, Japan). Samples were embedded into epoxy resin and sliced for ultrathin section before measurement. Rheology experiments of the samples were performed on HR-2 hybrid rhometer (TA instruments, USA) under cone and plate model with cone diameter of 40 mm and truncation of 24 µm. The mixture of cellulose and CMC solution, clay, and epichlorohydrin was stirred to form a homogeneous solution, which was quickly transferred into rheometer for testing. By using a deformation of 10% (in the linear viscoelastic zone) and a constant shear frequency (1 Hz), a time sweep was conducted on each sample at 60 °C to record the elastic stored modulus (G’) and viscous loss modulus (G’’) for the investigation of the hydrogel samples. The compressive strengths of hydrogels were measured on a universal testing machine (CMT6503, Shenzhen SANS Test Machine Co. Ltd., China) with compression clamp under a speed of 1 mm min-1. The disk shaped samples were 2 cm-1 × 1 cm-1 (diameter


Page 6 of 31

Page 7 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


×height). The gravimetric method was employed to measure the equilibrium swelling ratio of the hydrogels in the distilled water at 25 °C. The equilibrium swelling ratio was calculated according to Equation 1.

=

(1)

where Ws (g) was the weight of swollen gel after equilibrium at 25 °C, and Wd (g) was the weight of dried gel. The freeze-dried hydrogels and methylene blue trihydrate were ground into powder and analyzed in KBr disks with FTIR (Perkin Elmer Specturm one, USA) in the region of 400-4000 cm-1. The methylene blue solution before and after absorption were detected ESI-Q-TOF(III)-MS (Bruker, Germany). The parameters for the measurement were as follows: positive mode, capillary voltage of 4500 V, TOF voltage of 2032.5 V. Dye Adsorption The efficiency of adsorption of methylene blue (MB) on samples was performed by batch methods. Kinetic experiments were measured with an initial concentration of MB of 10 mg L-1at room temperature. At desired time intervals, the remaining amount of dye in the aqueous solution was then determined by UV-Vis measurement. To evaluate the thermodynamic properties, adsorption isotherms were determined by varying concentration of MB from 10 to 200 mg L-1 at 303K, 313K, and 323K, respectively. The effect of pH for adsorption of MB was investigated by a series of experiments where the initial concentration of MB was maintained constant (100 mg L-1) at different pH (1～11).



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 31

All tests were conducted in 10 mL polyethylene tubes by taking about 0.5 g hydrogel sample with 8 mL MB solution, where tubes were fixed in a temperature controlled shaker at 100 rpm for the desired time (except the sample for photograph). The concentration of MB in aqueous solution was determined by UV-Vis spectrophotometer at 664 nm, and the hydrogel samples did not exhibit any absorbance at this wavelength. The calibration curve was reproducible and linear over the concentration range used in this work. The amount of MB adsorbed on sample was described as adsorption capacity (qe) and calculated by Equation 2.

=

×

(2)

where c0 (mg L-1) and ce (mg L-1) are the initial and equilibrium concentration of MB, respectively, W (g) is the weight of dried sample, and V (L) is the volume of solution. Parallel studies of adsorption were carried out three times and the mean value was used for calculation. The removal efficiency of hydrogel samples for MB aqueous solution were carried out by immersing 1.5 g hydrogels in 8 mL MB aqueous solution with concentration of 10 mg L-1 and 100 mg L-1, respectively. The removal efficiency (%) was calculated by Equation 3. (%) =

(3)

where W0 (g) was the initial weight of MB in the aqueous solution, and We (g) was the weight of MB in the aqueous solution after adsorption equilibrium. Besides UV-vis measurement, the removal efficiency was also determined by the total organic carbon analyzer (Vario TOC, Elementar, Germany). Here, we emphasized that the samples


Page 9 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


used in all dye absorption experiments were swollen hydrogel which reached swelling equilibrium in in distilled water.

RESULTS AND DISCUSSION Preparation and structure of cellulose-clay nanocomposite hydrogels Cellulose-clay

nanocomposite

hydrogels

were

fabricated

by

chemical

cross-linking cellulose and carboxyl cellulose (CMC) with epichlorohydrin in presence of clay nanosheets. The schematic representations of cellulose-clay hydrogel networks containing unmodified clays and intercalated clays is shown in Figure 1. To prepare conventional hydrogels, clay without any modification was incorporated into cellulose hydrogel networks, where cellulose or CMC chains could not enter the galleries of clays (Figure 1a). For intercalated nanocomposite hydrogels, clays were first modified by 2,3-epoxypropyltrimethylammonium chloride (EPTAC) through cationic exchange. Then, the modified clays took part in the formation of hydrogel networks, where the epoxy group of EPTAC between in the clay layers could react with the hydroxyl groups of cellulose and CMC as well as epichlorohydrin (Fig. 1b). In this case, cellulose or CMC chains entered the galleries, but the clay nanosheets remained stacked.24



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Synthesis schemes of cellulose-clay nanocomposite hydrogels. (a) Hydrogel network containing unmodified clay. (b) Epoxidized clay (modified clay) cross-linked in the hydrogel networks.

To confirm that clay was successfully modified by EPTAC, we compared the TGA curves of clay samples (Figure S1). The mass loss around 300 °C of modified clay which was absence in the curve of unmodified clay could be attributed to the loss of EPTAC, indicating that EPTAC has been introduced into clay layers by cationic exchange. Furthermore, XRD patterns of Gel U-10 and Gel M-10 (Figure S2) showed the maximum peak of Gel U-10 could be observed at 2θ = 7.1 °, whereas the obvious diffraction peak of Gel M-10 was detected at 6.3 °, which were assigned to the crystal structure of clays in the hydrogel networks. The changes of peak positions indicated that the clays modified by EPTAC altered their structure, suggesting that the increase of the distance between the tetrahedral sheets led to the intercalated structure of clays.25 For direct observation of the architecture of clays in hydrogel networks, the TEM images of nanocomposite hydrogels are shown in Figure 2, where the platelets of the montmorillonite clays appeared as the dark and thin lines. For Gel U-15


Page 10 of 31

Page 11 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(Figure 2a), the aggregated clay layers could be observed in the cellulose matrix, due to high content of clays (15 %) in the hydrogel. After the clays were modified by EPTAC, their dispersity in the hydrogel networks was greatly improved, and the clay nanosheets could be homogenously dispersed in the matrix of Gel M-15 (Figure 2b). We should emphasize that intercalation and homogenous dispersion of clays by EPTAC in the hydrogels were essential for increase of the effective surface area which might benefit the removal efficiency of dyes. In the TEM images with higher magnification, we can find the original clay structure in Gel U-15 (Figure 2c), and intercalated clay in Gel M-15 (Figure 2d).

Figure 2. The morphology of cellulose-clay nanocomposite hydrogels: TEM images of Gel U-15 (a, c) and Gel M-15 (b, d) with different magnifications.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Properties of cellulose-clay nanocomposite hydrogels The gelation time of cellulose-clay hybrid systems were monitored by rheological technology. Figure 3a presents the time sweep measurement for viscoelastic properties of each system at 60 °C. All hybrid systems behaved as viscous liquid at initial time (G’＜G”), then G’ increased more rapidly than G” with prolonging time, and finally G’ exceeded G” where the system behaved as gel state. The crossover (G’=G”) of two curves was defined as gel point (t=tgel), indicating the sol-gel translation of such system and formation of the cross-linked networks.26 The gelation time of different systems significantly shortened with the increasing of clay content (Figure 3b), revealing that clay might destroy the stability of the hybrid system and promote the formation of hydrogel networks. Moreover, the hybrid system containing clay exchanged with EPTAC showed shorter gelation time than that containing unmodified clay with the same content, such as 20.9 min for M-5 and 27.7 min for U-5. These results indicated that modified clay introduced epoxy groups into the system which greatly enhanced the opportunity of chemical cross-linking reaction, resulting in fast formation of hydrogel networks. The storage modulus of hybrid system at 60 min for full development of cross-linked hydrogel networks was selected to evaluate the mechanical properties of hydrogels. As shown in Figure 3c, the G’ of M-5 (11.3 Pa) was higher than that of U-5 (6.5 Pa) and the same rule could also be observed in the system with clay content of 10 wt% or 15 wt%, G’ (M-10) ＞G’(U-10), and G’(M-15) ＞G’(U-15). This tendency suggested that the modified clay containing EPTAC could increase the


Page 12 of 31

Page 13 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


cross-linking density of hydrogel networks, leading to higher G’ in comparison with unmodified clay hybrid system. On the other hand, the G’ value increased as clay contents changed from 5 wt% to 15 wt%, which was consistent with the finding of Haraguchi et al. in poly(N-isopropylacrylamide)-clay nanocomposite hydrogels.27 The unexpected result that G’ (U-5) ＞G’(U-10) could be attributed to the error of measurement where the hydrogel network was considered as complete formation. To further understand the mechanical properties of nanocomposite hydrogels, the compressive stress–strain curves are shown in Figure 3d. The compressive strength of hydrogels increased markedly with increasing clay contents, which did not sacrifice the extensibility of the samples. It should be noted that the nanocomposite hydrogels with modified clay not only showed much superior compressive strength, but also exhibited larger fracture strain compared to the hydrogel samples containing unmodified clay. For example, the compressive strength of M-5 (4.7 KPa) was approximate 16 times as high as that of U-5 (0.3 KPa), while the facture strain of M-5 (51%) was still larger than that of U-5 (43%). These results revealed that the modified clay in the hydrogel networks formed intercalated architecture and more cross-linking points, resulting in higher toughness. The photographs of M-5 in as-prepared state and after reaching swelling equilibrium in distilled water are presented in Figure 3e. From the outstanding change in volume of M-5 after swelling in water, it can be seen that the cellulose-clay nanocomposite hydrogel exhibited very high equilibrium swelling ratio in distilled water. Moreover, the swelling ratio of all hydrogel samples was determined to be 691



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

to 1443 g/g, indicating their superabsorbent properties (Figure 3f). This result was related our previous findings that the electrostatic repulsion of negative charges (ionization of carboxyl groups of CMC) expanded the hydrogel networks, leading to high swelling ratio.28 When a small amount of clay (5%) was added into hydrogel networks, clay nanosheets could be uniform dispersed, which also participated in electrostatic interactions owing to their surface contained negative charges. So the swelling ratio of U-5 were higher than that of cellulose-based superabsorbent hydrogel (~1000 g/g).23 However, the swelling ratio of hydrogels decreased as the clay contents increased from 5% to 15%, indicating that the clay nanosheets aggregated in the conventional hydrogel networks and high cross-linking density formed in the intercalated hydrogel networks, which has been observed in the TEM images above. The hydrogels prepared by using modified clays showed lower swelling ratio in comparison with samples prepared with unmodified clays, suggesting that the cationic exchange of clays enhanced the numbers of functional groups (epoxy groups) which could react with cross-linker and the cross-linking density of hydrogel networks was significantly raised, leading to the decrease of swelling ratio.


Page 14 of 31

Page 15 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Properties of cellulose-clay nanocomposite hydrogels. (a) The time dependence of storage modulus (G’) and loss modulus (G”) for different gelation system at 60 °C. The data are shifted along the Y axis to avoid overlapping. (b) Gelation time. (c) Storage modulus at 1 h. (d) Compressive-strain curves. (e) Photographs of M-5. (f) Swelling ratio in distilled water.

Adsorption of MB on cellulose-clay nanocomposite hydrogels Removal of dye were performed by batch experiments to investigate the effects of various parameters such as contact time, temperature, solution pH, and initial dye



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 31

concentration on the adsorption of dye MB onto superabsorbent hydrogels. The adsorption amount of MB on hydrogels as function of time and the photographs of the adsorption process of the dyes are shown in Figure 4a. To accurate understand the adsorption kinetics of MB onto hydrogels, we carried out the experiment by using a low concentration MB (10 mg L-1). The initial appearance of dye solution was blue and Gel M-10 in the solution was almost invisible. The adsorption of MB was fast in the beginning and then reached equilibrium after 40 h. Finally, the blue color of MB almost faded from the solution, and the transparent hydrogel became blue due to the adsorption of MB. Kinetics of adsorption of MB onto Gel M-10 were analyzed by the pseudo second order kinetic models as expressed in Equation 4. !

=

" #$ $

+

(4)

where qe (mg g-1) and qt (mg g-1) were the amount of adsorption at equilibrium and time t, respectively, k2 (g mg-1 h-1) was the equilibrium rate constant of pseudo second order adsorption, which can be calculated by the plot of t/qt versus t as shown in Figure S3. The calculated qe (50.02 mg g-1) was close to the experimental qe (47.39 mg g-1), and the correlation coefficient ( && ) of pseudo second order kinetic was approximately 0.9981, demonstrating that the kinetic data fitted well with the pseudo second order model. The similar results have been reported for absorption of MB on cellulose beads29 and chitin hydrogels.30


Page 17 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Adsorption of MB on cellulose-clay nanocomposite hydrogels. (a) Effect of contact time on the MB adsorption into Gel M-10 at room temperature. (b) Adsorption isotherms of MB onto Gel M-10 at 303, 313, and 323K. (c) Effect of solution pH on the MB adsorption onto Gel 0, Gel U-10, and Gel M-10 at room temperature. (d) Efficiency of Gels for removing MB from aqueous solution with concentration of 10 and 100 mg L-1.

Figure 4b shows the adsorption isotherms of MB onto Gel M-10 at different temperature (303, 313, and 323 K). qe values increased with an increase of equilibrium concentration of dye solution (ce). To quantify the effect of temperature on the sorption of MB on hydrogel samples, both Langmuir and Freundlich isotherm models were adopted to describe the relationships between adsorption amount of MB



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 31

onto hydrogels and its equilibrium concentration in water at 303, 313, and 323 K, respectively. Langmuir isotherm adsorption equation was expressed as Equation 5. '

=

'

+

()*

" ()* +

(5)

where qe (mg g-1) was the amount of adsorption at equilibrium, ce (mg L-1) was the equilibrium MB concentration, qmax (mg g-1) was the maximum adsorption at monolayer coverage, and b (L mg-1) was the Langmuir adsorption equilibrium constant related to the free energy of adsorption, respectively. Freundlich isotherm model was applicable to a heterogeneous adsorption surfaces with mutilayer adsorption as shown in Equation 6. "

= ln. + / ln0

(6)

where k (mg g-1) was the Freundlich constant, indicating the adsorption capacity, and n was the dimensionless exponent of the Freundlich equation. The MB adsorption on hydrogels were fitted well by the Langmuir isotherm model with large && values (＞0.99) compared to Freundlich isotherm model (Table S1), indicating that MB was adsorbed on hydrogel as a monolayer adsorption. The qmax values obtained by calculation and experiment were 1065 and 782.9 mg g-1, respectively. Table 1 lists the qmax values of relevant materials for various dyes, where all hydrogels showed high absorption capability for dyes. The qmax value of cellulose-clay nanocomposite hydrogel was higher than that of most hydrogels31-38and comparable with that of nickel sulphide nanoparticles incorporated gum karaya-polyacrylamide composite hydrogel,39 revealing that the incorporation of intercalated clay in the cellulose hydrogel networks led to their super high adsorption


Page 19 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


capacity for MB in the aqueous solution.

Table 1. The maximum absorption capability of relevant materials obtained by calculation and experiment. qmax (mg g-1) Hydrogels

Dye

References Cal./Exp.

Poly(AA-co-AMPS)/MMT

Methylene blue

192.3/215

(31)

Poly(methacrylic acid)/Zeolite

Basic yellow

180/--

(32)

259/144.4

(33)

28 Chitosan-MMT

Nitrazine Yellow

Gum karaya-poly(acrylic acid)/SiC

Malachite

757.6/--

(34)

nanoparticles

green

497.5/--

(34)

Erichrome

--/520

(35)

black T

--/407

(35)

Rhodamine B Chitosan/polyacrylamide

Reactive blue 2 Cellulose nanocrystal /alginate

Methylene blue

256.4/--

(36)

Collagen-g-poly(acrylamide-co-maleic

Crystal Violet

439/--

(37)

anhydride)/MMT

Methylene

155/--

(37)

green



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 31

Poly(sodium

Congo red

172/--

(38)

acrylate-co-HEMA)/sodium alginate

Methyl violet

120/--

(38)

Gum karaya-polyacrylamide

Rhodamine 6G

1244.7/--

(39)

Methylene blue

1065/782.9

This work

/NiS/Ni3S4 nanoparticles Cellulose/MMT

AA: acrylic acid; AMPS: 2-acryamido-2-methylpropanesulfonic acid; MMT: montmorillonite; HEMA: hydroxyethyl methacrylate.

Furthermore, the standard enthalpy (∆H0), standard entropy (∆S0), and Gibbs free energy change (∆G0) for adsorption of MB on hydrogels were calculated by Equations 7 and 8.

12 =

∆3 4

−

∆6

(7)

47

∆8 9 = ∆: 9 − ; ∆ 9

(8)

where Kd , the distribution coefficient of absorbent at temperature T (K), was equal to qe/ce, R (8.314 J mol-1 K-1) was the universal gas constant. ∆H0 and ∆S0 were determined by the slope and intercept of linear plot of lnKd versus 1/T (Fig. A4) to be 14.41 kJ mol-1 and 75.17 J mol-1 K-1, respectively. The positive values of ∆H0 and ∆S0 revealed that the adsorption was endothermic and random at the solid-solution surface, whereas the value of ∆H0 was less than 40 kJ mol-1, showing that the adsorption was physic-sorption feature.40 Next, the negative values of Gibbs energy changes for adsorption of MB on hydrogels (∆G0 was -8.366, -9.118, and -9.870 kJ mol-1, at 303, 313, and 323 K, respectively) were obtained, suggesting that adsorption of MB on


Page 21 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydrogel samples was spontaneous. The increase of absolute values of ∆G0 as a function of temperatures indicated that the adsorption was favorable at high temperature. The influence of solution pH on the removal of MB by hydrogels was investigated to gain further insight into the adsorption process. Figure 4c shows the qe of Gel 0, Gel U-10, and Gel M-10 in various pH solutions. The absorption capacity of Gel 0 for MB was much lower than that of composite hydrogels (Gel U-10 and Gel M-10), reflecting that clay in the hydrogel networks could promote the absorption of hydrogels for MB. While the qe values of Gel M-10 were greater than those of Gel U-10 in the range of pH 1～11, indicating that the surface of intercalated clays exposed more negative charges in the hydrogels networks, which benefited their electrostatic attraction with the cationic species of MB, leading to higher qe values. On the other hand, the qe values of hydrogels slightly increased with the raise of solution pH, which also could be explained by the electrostatic interaction of positive charges of MB with the negative charges of hydrogel network (including the clay and CMC) which were enhanced at higher pH values, leading to greater qe values. The adsorption was not drastically affected by pH, suggesting the presence of other interactions (such as hydrophobic interaction) between MB and hydrogels. Since the superabsorbent hydrogel incorporated with intercalated clays exhibited superior MB removal capacity, the effect of clay contents in the Gel M series on the removal efficiency of MB was also studied (Figure 4d). Compared to Gel0, hydrogel samples containing intercalated clays showed high removal efficiency for MB



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

aqueous solution with concentration of 10 and 100 mg L-1. And it could be seen that the removal efficiency for MB increased with the clay contents of hydrogel networks, indicating that intercalated clay was important component for the absorption of MB. Gel M-15 exhibited high removal efficiency for MB with different concentration, especially, its removal efficiency for 10 mg L-1 MB was still as high as 97%. The above results calculated by the concentration of MB obtained from UV-Vis measurement were also verified by the total organic carbon content method. Furthermore, the results of ESI-Q-TOF MS indicated that no degradation during the treatment of MB solution with hdyrogels (Figure S5). To understand the mechanism of the interaction between hydrogel and dye, FT-IR spectra of samples are shown in Figure 5. The sharp absorption peaks at about 3450 cm-1 were assigned to the O-H bond stretching vibration of the hydroxyl group of hydrogel networks and bound water of MB. Some absorption peaks around 2932 cm-1 of hydrogel sample before absorbing MB could be attributed to the C-H stretching vibration of methylene groups of in the hydrogel networks, whereas the peaks around 2921 cm-1 observed in the spectrum of MB were assigned to C-H stretching vibration of methyl groups. However, the corresponding absorption peaks in the spectrum of hydrogel absorbed MB almost disappeared, indicating that the presence of strong hydrophobic interaction between hydrogel network and MB limited the mobility of methylene groups of hydrogel and methyl groups of MB. Therefore, our finding revealed that hydrophobic interaction was also a main driving force for MB absorption in this work, besides electrostatic attraction.


Page 22 of 31

Page 23 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. FT-IR spectra of cellulose-clay nanocomposite hydrogels before (a) and after MB dye absorption (b), and MB dye.

CONCLUSION We have fabricated a series of novel cellulose-clay nanocomposite hydrogels by chemical cross-linking of natural polymers (cellulose and carboxymethyl cellulose) and clay (epoxidized montmorillonite) with epichlorohydrin in NaOH/urea aqueous solution. The modified clays participated in the formation of hydrogel networks, leading to their homogeneous dispersion in the cellulose matrix. These hydrogels exhibited superabsorbent properties in distilled water, superior mechanical performance compared to the hydrogel containing unmodified clays, and great ability for removal of methylene blue (MB) from wastewater. The adsorption of MB onto hydrogels was spontaneous monolayer adsorption through physical process, which



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

could be well described by pseudo second order and Langmuir isotherm models. With these findings, this work may promote the development of new absorbents for the removal of dye from wastewater.

ASSOCIATED CONTENT

Supporting Information. The detail of TGA and XRD measurements in this work, TGA and XRD results, the plot of t/qt versus t for adsorption kinetic, Langmuir and Freundlich isotherms parameters, and the plot of lnKd versus 1/T in Isothermal adsorptions could be found in Supporting Information. AUTHOR INFORMATION Corresponding Author Email: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by Pearl River S&T Nova Program of Guangzhou (201506010101), Guangzhou science and technology project (201510010221), Hubei Province Science Foundation for Youths (2015CFB499), the National Natural Science Foundation of China (21304021), and Jiangsu Province Science Foundation for


Page 24 of 31

Page 25 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Youths (BK20150382). Authors also thank Prof. Bin Hu and Dr. Beibei Chen for their kindly supporting on the ESI-Q-TOF MS measurements.

References (1) Crini, G. Non-conventional low-cost adsorbents for dye removal: A review. Bioresour. Technol. 2006, 97 (9), 1061-1085. (2) Demirbas, A. Agricultural based activated carbons for removal of dyes from aqueous solution: A review. J. Hazard. Mater. 2009, 167 (1-3), 1-9. (3) Sun, H.; Cao, L.; Lu, L. Magnetite/reduced graphene oxide nanocomposites: on step solvothermal synthesis and use as a novel platform for removal of dye pollutants. Nano Research 2011, 4 (6), 550-562. (4) Leung, W. H.; Lo, W. H.; Chan, P. H. Amyloid fibrils as rapid and efficient nanobiosorbents for removal of dye pollutants. RSC Adv. 2015, 5 (109), 90022-90030. (5) Crini, G.; Badot, P. M. Application of chisosan, a natural amnopolysaccharide, for dye removal from aqueous solutions by adsorption process using batch studies: a review of recent literature. Prog. Polym. Sci. 2008, 33 (4), 399-447. (6) Gong, R.; Li, M.; Yang, C.; Sun, Y.; Chen, J. Removal of cationic dyes from aqueous solution by adsorption on peanut hull. J. Hazard. Mater. 2005, 121 (1-3), 247-250. (7) Chen, W.; Lu, W.; Yao, Y.; Xu, M. Highly efficient decomposition of organic dyes by aqueous-fiber phase transfer and in situ catalytic oxidation using fiber-supported cobalt phthalocyamine. Environ. Sci. Technol. 2007, 41 (17), 6240-6245.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

(8) Gil, A.; Assis, F. C. C.; Albeniz, S.; Korili, S. A. Removal of dyes from wastewater by adsorption on pillared clays. Chem. Eng. J. 2011, 168 (3), 1032-1040. (9) Zhao, X.; Liu, S.; Tang, Z.; Niu, H.; Cai, Y.; Meng, W.; Wu, F.; Giesy, J. P. Synthesis of magnetic metal-organic framework (MOF) for efficient removal of organic dyes from water. Sci. Rep. 2015, 5, 11849. (10) Robati, D.; Mirza, B.; Rajabi, M.; Moradi, O.; Tyagi,

I.; Agarwal, S.; Gupta, V.

K. Removal of hazardous dyes-BR 12 and methyl orange using graphene oxide as an adsorbent from aqueous phase. Chem. Eng. J. 2016, 284, 687-697. (11) Alatalo, S. M.; Mäkilä, E.; Repo, E.; Heinonen, M.; Salonen, J.; Kukk, E.; Sillanpaa, M.; Titicici, M. M. Meso- and microporous soft templated hydrothermal carbons for dye removal from water. Green Chem. 2016, 18 (4), 1137-1146. (12) Wang, Z.; Guo, J.; Ma, J.; Shao, L. Highly regenerable alkali-resistant magnetic nanoparticles inspired by mussels for rapid selective dye removal offer high-efficiency environmental remediation. J. Mater. Chem. A 2015, 3 (39) 19960-19968. (13) Babel, S.; Kurniawan, T. A. Low-cost adsorbents for heavy metals uptake from contaminated water: a review. J. Hazard. Mater. 2003, 97 (1-3), 219-243. (14)

Haraguchi,

K.;

Takehisa,

T.

Nanocomposite

hydrogels:

a

unique

organic-inorganic networks structure with extraordinary mechanical, optical, and swelling/deswelling properties. Adv. Mater. 2002, 14 (16), 1120-1124. (15) Haraguchi, K.; Li, H. J. Mechanical properties and structure of polymer-clay nanocomposite gels with highly clay content. Macromolecules 2006, 39 (5),


Page 27 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1898-1905. (16) Tameuse, S.; Ohtani, M.; Yamada, K.; Ishida, Y.; Spruell, J. M.; Lynd, N. A.; Hawker, C. J.; Aida, T. Linear versus dendritic molecular binders for hydrogel network formation with clay nanosheets: studies with ABA triblock copolyethers carrying guandinium ion pendants. J. Am. Chem. Soc. 2013, 135 (41), 15650-15655. (17) Li, A.; Wang, A. Synthesis and properties of clay-based superabsorbent composite. Eur. Polym. J. 2005, 41 (7), 1630-1637. (18) Partra, S. K.; Swain, S. K. Swelling study of superabsorbent PAA-co-PAM/clay nanohydrogel. J. Appl. Polym. Sci. 2011, 120 (3), 1533-1538. (19) Bulut, Y.; Akçay, G.; Elma, D.; Serhatlı, I. E. Synthesis of clay-based superabsorbent composite and its sorption capability. J. Hazard. Mater. 2009, 171 (1-3), 717-723. (20) Li, A.; Zhang, J.; Wang, A. Utilization of starch and clay for the preparation of superabsorbent composite. Bioresour. Technol. 2007, 98 (2), 327-332. (21) Chang, C.; Zhang, L. Cellulose-based hydrogels: present status and application prospects. Carbohydr. Polym. 2011, 84 (1), 40-53. (22) Sannino, A.; Demitri, C.; Madaghiele, M. Biodegradable cellulose-based hydrogels: design and applications. Materials 2009, 2 (2), 353-373. (23) Chang, C.; Duan, B.; Cai, J.; Zhang, L. Superabsorbent hydrogels based on cellulose for smart swelling and controllable delivery. Eur. Polym. J. 2010, 46 (1), 92-100. (24) Chen, B.; Evans, J. R. G.; Greenwell, H. C.; Boulet, P.; Coveney, P. V.; Bowden,



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 31

A. A.; Whiting, A. A critical appraisal of polymer-clay nanocomposites. Chem. Soc. Rev. 2008, 37 (3), 568-594. (25)Wang, C. C.; Juang, L. C.; Hsu, T. C.; Lee, C. K.; Lee, J. F.; Huang, F. C. Adsorption of basic dyes onto montmorillonite. J. Colloid Interf. Sci. 2004, 273 (1), 80-86. (26) Chang, C.; Duan, B.; Zhang, L. Fabrication and characterization of novel macroporous cellulose-alginate hydrogels. Polymer 2009, 50 (23), 5467-5473. (27) Haraguchi, K.; Takehisa, T.; Fan, S. Effect of clay content on the properties of nanocomposite hydrogels composed of poly(N-isopropylacrylamide) and clay. Macromolecules 2002, 35 (27), 10162-10171. (28) Chang, C.; He, M.; Zhang, L.; Zhou, J. Swelling behaviors of pH- and salt-responsive cellulose based hydrogels. Macromolecules 2011, 44 (6), 1642-1648. (29) Luo, X.; Zhang, L. High effective adsorption of organic dyes on magnetic cellulose beads entrapping activated carbon. J. Hazard. Mater. 2009, 171 (1-3), 340-347. (30) Tang, H.; Zhou, W.; Zhang, L. Adsorption isotherm and kinetics studies of malachite green on chitin hydrogels. J. Hazard. Mater. 2012, 209, 218-225. (31)

Hosseinzadeh,

H.;

Khoshnood,

N.

Removal

of

cationic

dyes

by

poly(AA-co-AMPS)/montmorillonite nanocomposite hydrogel. Desalin. Water Treat. 2016, 57, 6372-6383.


Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(32) Panic, V. V.; Velickovic, S. J. Removal of model dye by adsorption onto poly(methyacrylic acid)/zeolite hydrogel composites: Kinetics, equilibrium study and image analysis. Sep. Purif. Technol. 2014, 122, 384-394. (33) Ngwabeghoh, A. F.; Erdem, A.; Yildiz U. Synergistic removal of Cu (II) and nitrazine yellow dye using an eco-friendly chitosan-montmorillonite hydrogel: Optimization by response surface methodology. J. Appl. Polym. Sci. 2016, 43664. (34) Mittal, H.; Maity, A.; Ray, S. S. Gum karaya based hydrogel nanocomposites for the effective removal of cationic dyes from aqueous solutions. Appl. Surf. Sci. 2016, 364, 917-930. (35) Oladipo, A. A.; Gazi, M.; Yilmaz, E. Single and binary adsorption of azo and anthraquinone dyes by chitosan-based hydrogel: Selectivity factor and Box-behnken process design. Chem. Eng. Res. Des. 2015, 104, 264-279. (36) Mohammed, N.; Grishkewich, N.; Berry, R. M.; Tam, K. C. Cellulose nanocrystal-alginate hydrogel beads as novel adsorbent for organic dyes in aqueous solutions. Cellulose 2015, 22, 3725-3738. (37) Marandi, G. B.; Kermani, Z. P.; Kurdtabar M. Fast and efficient removal of cationic dyes from aqueous solution by collagen-based hydrogel nanocomposites. Polym-Plast. Technol. 2013, 52, 310-318. (38) Mandal, B.; Ray S. K. Synthesis of interpenetrating network hydrogel from poly(acrylic acid-co-hydroxyethyl methacrylate) and sodium alginate: Modeling and kinetics study for removal of synthetic dyes from water. Carobohyd. Polym. 2013, 98, 257-269.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(39) Kumar, N.; Mittal, H.; Parashar, V.; Ray, S. S.; Ngila J. C. Efficient removal of rhodamine 6G aqueous solution using nickel sulphide incorporated polyacrylamide grafted gum karaya bionanocomposite hydrogel. RSC Adv. 2016, 6, 21929. (40) Hameed, B. H. Equilibrium and kinetics studies of 2,4,6-trichlorophenol adsorption onto activated clay. Colloid Surface. A 2007, 307 (1-3), 45-52.


Page 30 of 31

Page 31 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Superabsorbent Cellulose-Clay Nanocomposite Hydrogels for High Efficient Removal of Dye in Water Na Peng, †,‡ Danning Hu, † Jian Zeng, ‡ Yu Li, ‡ Lei Liang, ‡ Chunyu Chang*, †,‡ †

College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072,

China ‡

Guangzhou Sugarcane Industry Research Institute, Guangzhou 510316, China

Corresponding author: Chunyu Chang (Email: [email protected])

Superabsorbent hydrogels prepared from low cost, renewable cellulose and clay exhibited high efficiency for removal of methylene blue.


Superabsorbent CelluloseâClay Nanocomposite Hydrogels for Highly

Recommend Documents

Superabsorbent CelluloseâClay Nanocomposite Hydrogels for Highly