Accepted Manuscript Title: Evaluation of ethylenediamine-modified nanofibrillated cellulose/chitosan composites on adsorption of cationic and anionic dyes from aqueous solution Author: Kai Liu Lihui Chen Liulian Huang Yaoneng Lai PII: DOI: Reference:
S0144-8617(16)30746-9 http://dx.doi.org/doi:10.1016/j.carbpol.2016.06.071 CARP 11256
To appear in: Received date: Revised date: Accepted date:
24-3-2016 4-6-2016 16-6-2016
Please cite this article as: Liu, Kai., Chen, Lihui., Huang, Liulian., & Lai, Yaoneng., Evaluation of ethylenediamine-modified nanofibrillated cellulose/chitosan composites on adsorption of cationic and anionic dyes from aqueous solution.Carbohydrate Polymers http://dx.doi.org/10.1016/j.carbpol.2016.06.071 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Evaluation of ethylenediamine-modified nanofibrillated cellulose/chitosan composites on adsorption of cationic and anionic dyes from aqueous solution Kai Liu*, Lihui Chen, Liulian Huang, Yaoneng Lai College of Material Engineering, Fujian Agriculture and Forestry University, Fuzhou 350002, China *Corresponding authors: [email protected]
The NFC/CS was prepared by coating chitosan on nanofibrillated cellulose.
An adsorbent was prepared by modifying the NFC/CS with ethylenediamine (E-NFC/CS).
The E-NFC/CS composites can be used to adsorb both cationic and anionic dyes.
Abstract: A multi-functional adsorbent was prepared by modifying nanofibrillated cellulose/chitosan composites with ethylenediamine (E-NFC/CS). The E-NFC/CS was characterized by FTIR and used for adsorption of cationic dye methylene blue (MB) and anionic dye new coccine (NC) from aqueous solution. The FTIR results showed that the E-NFC/CS contained more amino groups than the NFC/CS due to the modification for the NFC/CS with ethylenediamine. The results indicated that the maximum adsorption capacities occurred at pH 4.0 for MB and pH 2.0 for NC, respectively. The adsorption equilibrium time for MB and NC was 30 and 50 min, respectively. In addition, the regenerated E-NFC/CS exhibited excellent adsorption performance for NC. It can keep almost 98% of the adsorption capacity after reused three times. Therefore, the E-NFC/CS can be potentially used as an effective adsorbent of cationic and anionic dyes in industrial effluents. Keywords: Nanofibrillated cellulose; Chitosan; Ethylenediamine; Dye
Introduction Water contamination by dyes from various industries such as textiles, leather, and dyestuffs has attracted more attention, because the dyes in these industrial wastewaters are toxic, carcinogenic, and non-biodegradable (Liu et al. 2015a; Cho et al. 2015). Therefore, a variety of treatment methods such as adsorption, oxidation, membrane, and biological treatment have been developed to remove dyes in the wastewaters (Pei et al. 2013). Among these methods, the adsorption treatment is very simple and effective for removal of different kinds of dyes in aqueous solutions, which was regarded as one of the most common and widespread techniques. For example, Liu et al. (2015a) prepared the magnetic Fe/Ni nanoparticles doped bimodal mesoporous carbon and found the adsorbent was highly effective for the adsorption of cationic dye methylene blue and anionic dye methyl orange. For the adsorption treatment method, a great variety of adsorbents have been used to adsorb dyes from aqueous solutions, such as chitosan, activated carbon, zeolites, and resins (Yao et al. 2015). Among these adsorbents, chitosan, a polymeric substance with a large number of hydroxyl and amino groups, has attracted much interests because of its low-cost and biodegradable properties (Zhou et al. 2010). For example, Yang et al. (2013) prepared the triphenylene-modified chitosan by reacting chitosan with triphenylene aldehyde derivative for the first time and demonstrated that the triphenylene-modified chitosan possessed excellent adsorption capacities for six kinds of cationic and anionic dyes. Moreover, chitosan was often crosslinked with epichlorohydrin or glutaraldehyde in the form of nanoparticles when used to be an
adsorbent. For example, Zhou et al. (2011) prepared the ethylenediamine-modified magnetic chitosan nanoparticles (EMCN) which can be used for the effective adsorption of acid orange 7 and acid orange 10 from aqueous solution. However, the preparation of chitosan adsorbents was very complex, rendered it difficult to carry out in industrial scale. Nanofibrillated cellulose (NFC), disintegrated from wood pulp, possessed flexible and easily entangled properties (Liu et al. 2015b; Kurihara and Isogai 2014; He et al. 2014; Liu et al. 2014; Suzuki et al. 2013). Therefore, the physical or chemical cross-linked NFC aerogels have been used as superabsorbents (Xiao et al. 2015; Yang et al. 2014). In this study, a facile method was proposed to prepare ethylenediamine-modified nanofibrillated cellulose/chitosan composites (E-NFC/CS). The NFC/CS composites were first prepared by coating chitosan on the NFC surface. The ethylenediamine was then used to modify the NFC/CS composites (Hu et al. 2011). The preparation of the E-NFC/CS was shown in Figure 1. The increase of the –NH2 active groups on the surface of the E-NFC/CS can enhance the adsorption capacity for dyes because –NH2 active groups were the main sites for the adsorption of dyes. The E-NFC/CS was characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The adsorption performance of the dyes onto the E-NFC/CS was also studied. Materials and methods Materials Nanofibrillated cellulose (NFC) (1%, w/w) was from Tianjin Hao-jia Cellulose
Co., Ltd. (China). Chitosan (Degree of deacetylation =95%), ethylenediamine, methylene blue (MB), and new coccine (NC) were purchased from Aladdin Reagent Co., Ltd (China). The viscosity of 1% (w/v) chitosan in 1% acetic acid solution at 25 ◦C was 100-200 mPa.s. All other chemicals were analytical grade and used without further purification. Preparation of nanofibrillated cellulose/chitosan composites (NFC/CS) Chitosan solution was prepared by dissolving 2 g of chitosan flakes in 100 mL of 5% (v/v) acetic acid at 30 °C. Then 40 g of 1% (w/w) NFC was added and stirred at 200 rpm. After stirring for 0.5 h, the suspension was centrifuged at 8000rpm for 5 min to obtain the nanofibrillated cellulose/chitosan composites (NFC/CS). Preparation of ethylenediamine-modified nanofibrillated cellulose/chitosan composites (E-NFC/CS) Ten mL of epichlorohydrin was dissolved in 90mL of acetone, the NFC/CS was then added and stirred at 40 °C for 4 h. The solid phase was separated by centrifuging and washed several times with distilled water. The above solid was added into 100mL ethanol/water mixture (1:1, v/v), followed by adding 8 mL of ethylenediamine. The mixture was stirred at 60 °C for 4 h. After reaction, the solid in the mixture was separated by centrifuging and washed several times with distilled water. The final product (labeled as E-NFC/CS) was obtained by freeze-drying. Characterization of ethylenediamine-modified nanofibrillated cellulose/chitosan composites The FTIR spectra of NFC, NFC/CS, and E-NFC/CS were recorded using Fourier
transform infrared spectroscopy (Thermo Nicolet 360) at a resolution of 4 cm−1 in the spectral region of 500-4000 cm−1. The sample was mixed with KBr to form pellet in the preparation. Thermogravimetric analysis (TGA) of NFC, NFC/CS, and E-NFC/CS was performed on a TG−DTA Instruments (Netzsch STA 449F3). Approximately 5 mg of sample was weighed and heated from room temperature to 600 °C at a heating rate of 10 °C/min under a nitrogen flow rate of 20 mL/min. Adsorption experiments All the adsorption experiments were performed in a conical flask with 200 mL dye aqueous solutions on a rotary shaker at 200 rpm and 25 °C. The effect of pH on MB and NC adsorption was investigated in the pH ranges between 1 and 10. The pH of dye solution was adjusted by 1M NaOH or 1M HCl solution. For kinetic studies, 0.1 g of E-NFC/CS was added to 200 mL of dye aqueous solution, the mixture was agitated and 5 mL of solution sample was taken at different time intervals for the analysis of residual dye concentrations. The concentrations of MB and NC in aqueous solution were determined using a UV-vis spectrophotometer (Agilent 8453) at wavelength 663 and 508 nm, respectively. The adsorption capacities were calculated according to Eq. 1.
(C0 −Ce )V W
where qe was the equilibrium adsorption capacity (mmol/g), C0 and Ce were the initial and equilibrium concentrations (mmol/L) of the dyes, respectively. V was the volume (L) of the solution and W was the weight (g) of the adsorbent.
Desorption experiments All the desorption experiments were carried out using 200 mL of NH4OH/NH4Cl (pH 10.0) solution for dyes desorption. After the adsorption, the E-NFC/CS adsorbed with dyes was separated by centrifuging and washed several times with distilled water. The adsorbent was then added to 200 mL of NH4OH/NH4Cl and agitated for 2 h at 25 °C. After desorption, the adsorbent was washed several times with distilled water and then reused for the next cycle of adsorption. Three sequential cycles of adsorption-desorption were performed. Results and discussion FTIR analysis of E-NFC/CS The NFC, NFC/CS, and E-NFC/CS were investigated using FTIR spectroscopy. As seen in Figure 2, for the spectrum of the NFC, the typical bands of cellulose can be observed, such as OH stretching at 3433 cm-1, CH stretching at 2920 cm-1, and CH2 symmetric bending at 1459 cm-1 (Gebald et al. 2011). After coated with chitosan, the spectrum of the NFC/CS showed some characteristic bands of chitosan. For example, the bands at 1632 and 1380 cm-1 came from the primary amine of chitosan, the band at 1065cm−1 was attributed to the combined effects of C–N stretching vibration of primary amines and the C–O stretching vibration from the primary alcohol in chitosan (Mesquita et al. 2010; Liu et al. 2013). After modified with ethylenediamine, the intensity at 1632, 1380, and 1065 cm-1 in the spectrum of the E-NFC/CS increased. This indicated that the E-NFC/CS contained more amino groups than the NFC/CS (Zhou et al. 2009).
Thermal analysis of E-NFC/CS The thermogravimetric (TG) and derivative thermogravimetric (DTG) curves of the NFC, NFC/CS, and E-NFC/CS were shown in Figure 3. It was found that all the samples exhibited three degradation steps. At the first step, there was about 11 wt% degradation for all the samples. This was mainly attributed to water evaporation, which may be from the free water of the samples. At the second step, about 60 wt% degradation for all the samples can be found, but their degradation temperatures were different. From the DTG curves in Figure 3b, the NFC and NFC/CS had a single sharp decomposition peak at 274 and 338 °C, respectively. The degradation temperature of the NFC was lower than that of the NFC/CS, this may be the reason that chitosan had a higher decomposition temperature than the NFC (Stefanescu et al. 2012). In addition, the peak degradation temperature of the E-NFC/CS was 311 °C, showing a decrease in the maximum weight loss temperature in comparison with the NFC/CS. It was very likely that ethylenediamine had a low boiling point, leading to the lower decomposition temperature of the E-NFC/CS compared with the NFC/CS. Effect of pH on dye adsorption The initial pH of solution usually has a great influence on the adsorption of dyes for chitosan-based adsorbents. Therefore, the effect of pH on the adsorption of dyes on the E-NFC/CS has been investigated, and the results were shown in Figure 4. It was found that the adsorption of MB on the E-NFC/CS increased significantly with the increase of pH from 1.0 to 4.0, and the maximum adsorption capacity was 0.067
mmol/g at pH 4.0. Similar trend was also found with the adsorption of acid orange 7 and acid orange 10 with modified chitosan nanoparticles (Zhou et al. 2011). In the case of NC, it can be seen that the adsorption of NC increased with the increase of pH from 1.0 to 2.0, and then decreased with the increase of pH from 2.0 to 5.0. The maximum adsorption capacity of NC was 0.17 mmol/g at pH 2.0. It should be noted that the maximum adsorption capacity of NC was much higher than that of MB. This may be due to the different adsorption mechanism of MB and NC on the E-NFC/CS. The sulfonate groups of NC were converted to anionic dye ions in aqueous solution. Thus the NC can be adsorbed onto the E-NFC/CS according to the ionic interactions of the dye ions with the amino groups of the adsorbent (Zhou et. al, 2011). However, in the case of MB, there was no electrostatic attraction between MB and the E-NFC/CS since MB was a cationic dye (Cho et al. 2015). Therefore, MB was adsorbed onto the E-NFC/CS due to the weak van der waals force. In Figure 4, it was also found that the adsorption capacity of MB was higher than that of NC when the pH was above 4. The possible reason was that the van der waals force became the main adsorption force between dyes and the adsorbent when the pH increased above 4. Kinetic studies The effect of adsorption time on the adsorption capacity of MB and NC on the E-NFC/CS was studied, and the results were shown in Figure 5. The maximum adsorption capacities for MB (0.061 mmol/g ) and NC (0.16 mmol/g) were observed in 30 and 50 min, respectively. After that, the change in the adsorption capacity was
insignificant. In some studies, a long time may be needed to reach adsorption equilibrium for dyes adsorption with other chitosan-based adsorbents (Yang et al. 2013). In this study, the high adsorption rates of MB and NC on the E-NFC/CS may be due to the large surface area and the sufficient exposure of active sites of the E-NFC/CS (Zhou et al. 2011). In addition, the adsorption kinetics of MB and NC on the NFC/CS has been studied under the same conditions. It was found that the maximum adsorption capacities of MB and NC on the NFC/CS were only 0.0047 and 0.012 mmol/g, respectively, which were much lower than that of MB and NC on the E-NFC/CS. This was mainly due to the high content of the amino groups on the E-NFC/CS. Desorption studies The desorption of MB and NC on the E-NFC/CS was carried out with NH4OH/NH4Cl and the results were shown in Figure 6. It can be observed that the adsorption capacity for both MB and NC decreased gradually with the desorption cycles increase, and the regenerated E-NFC/CS exhibited different adsorption performance for MB and NC. In the case of NC, the regenerated adsorbent exhibited excellent adsorption performance. Even after three-time recycles, the E-NFC/CS can keep almost 98% of the adsorption capacity for NC in comparison with the fresh adsorbent. However, The E-NFC/CS showed modest adsorption performance for MB. After three-time recycles, the adsorbent only kept 10% of the adsorption capacity for MB. This may be due to the different adsorption mechanism of MB and NC on the E-NFC/CS.
Conclusions This research focused on a modified composite adsorbent and its application for removal of MB and NC in aqueous solution. The adsorption experiments showed that the maximum adsorption capacities of MB and NC were 0.067 mmol/g at pH 4.0 and 0.172 mmol/g at pH 2.0, respectively. The maximum adsorption capacities of MB and NC were observed in 30 and 50 min, respectively. In addition, the regenerated adsorbent exhibited excellent adsorption performance for NC. Even after three-time recycles, the E-NFC/CS can keep almost 98% of the adsorption capacity for NC in comparison with the fresh adsorbent. Therefore, the modified composite material can be used as a potential multi-functional adsorbent for removal of both cationic and anionic dyes in industrial effluents. Acknowledgments The authors acknowledge the Industrial Technology Key Project of Fujian Province (2014H0001), Natural Science Foundation of Fujian Province (2014J01070), the Forestry Science and Technology Promotion Project of Fujian Province (14-2), the Technology Project of Fujian provincial education department (JB13031), the Science and Technology Cooperation Project of Fuzhou Government and University (2013-G-81), and the Research Fund for Distinguished Young Talents of Fujian Agriculture and Forestry University (XJQ201213) for financial support.
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Figure 1. Preparation scheme of ethylenediamine-modified nanofibrillated cellulose/chitosan composites (E-NFC/CS) Figure 2. FTIR spectra of the NFC, NFC/CS, and E-NFC/CS. Figure 3. TG (a) and DTG (b) curves of the NFC, NFC/CS, and E-NFC/CS. Figure 4. Effect of pH on the MB and NC adsorption of the E-NFC/CS. Figure 5. Effect of adsorption time on the MB and NC adsorption of the E-NFC/CS. Figure 6. Absorption-desorption cycles of the MB and NC by the E-NFC/CS.
(a) First Step
80 Second Step 60 Third Step
40 NFC NFC/CS E-NFC/CS
(b) 0 -2
NFC NFC/CS E-NFC/CS
o 338 C
o 311 C
o 274 C
Temperature ( C)
0.12 0.10 0.08 0.06 0.04 0.02 0.00 0
0.20 0.18 0.16
0.12 0.10 0.08 0.06 0.04 0.02 0.00
Figure 6. 0.19
Number of cycles
Number of cycles