Adsorption of dye from wastewater using chitosan–CTAB modified bentonites

Journal of Colloid and Interface Science 382 (2012) 61–66

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Journal of Colloid and Interface Science www.elsevier.com/locate/jcis

Adsorption of dye from wastewater using chitosan–CTAB modified bentonites Jianzhong Guo a,⇑, Shunwei Chen b, Li Liu a, Bing Li a, Ping Yang a, Lijun Zhang a, Yanlong Feng a,⇑ a b

Department of Chemistry, College of Science, Zhejiang A & F University, Lin’an, 311300 Zhejiang, China Zhejiang Provincial Key of Biological and Chemical Utilization of Forest Resources, Zhejiang Forestry Academy, Hangzhou, 310023 Zhejiang, China

a r t i c l e

i n f o

a b s t r a c t

Article history: Received 26 January 2012 Accepted 23 May 2012 Available online 31 May 2012

Dyeing wastewater removal is important for the water treatment, and adsorption is an efficient treatment process. In this study, three modified bentonites, chitosan modified bentonite (CTS-Bent), hexadecyl trimethyl ammonium bromide (CTAB) modified bentonite (CTAB-Bent), and both chitosan and hexadecyl trimethyl ammonium bromide modified bentonite (CTS–CTAB-Bent) were prepared and characterized by FTIR and XRD analysis. Batch experiments were conducted to evaluate the adsorptive removal of weak acid scarlet from aqueous phase using modified bentonites under different conditions. The results show that the adsorption capacity of weak acid scarlet onto natural bentonite was low (4.9%), but higher for 1CTS-Bent and 1CTS–10CTAB-Bent. The optimal conditions for weak acid scarlet adsorption were 1% chitosan, 10% CTAB, at 80 °C and reaction time 2.5 h. The best removal efficiency was 85%, and the adsorption capacity of weak acid scarlet was around 102.0 mg g1, much higher than that of commercial activated carbon (27.2 mg g1). These results suggest that 1CTS–10CTAB-Bent is an excellent adsorbent for effective weak acid scarlet removal from water. The adsorption isotherms of weak acid scarlet were investigated. It was found that Langmuir and Temkin models fitted the data very well (R2 > 0.99). Ó 2012 Elsevier Inc. All rights reserved.

Keywords: Modified bentonite Chitosan Hexadecyl trimethyl ammonium bromide Adsorbent Weak acid scarlet Adsorption isotherm

1. Introduction The dyeing industry is one of the biggest wastewater producing industries. The wastewater is characterized by high organic pollutant content, deep color, and significant impact on water quality. Color is recognized as the first contaminant in wastewater, because a very small amount of dyes in water is highly visible and undesirable. The discharge of dyeing wastewater to rivers and basins pose a potential risk to local resident’s health and ecosystem. Therefore, the effective treatment of dyeing wastewater becomes a task of top priority to government. Currently, the dyeing wastewater treatment has been widely investigated, and several technologies have been developed including adsorption, oxidation, super filter film, and coagulation [1,2]. Adsorption using low-cost adsorbents is one of the most economically and viable method for dyeing wastewater decontamination. A large variety of conventional and nonconventional adsorbent materials have been proposed and studied for their ability to remove dyes. However, all of these adsorbents have various drawbacks. Activated carbons have the advantages of high adsorption capacity and selectivity for dyestuff removal but it is difficult to regenerate, which makes its application for dyeing wastewater restricted. It is now recognized that adsorption using low-cost adsorbents, naturally occurring adsorbents is an ⇑ Corresponding authors. Fax: +86 571 63732772. E-mail (Y. Feng).

addresses:

[email protected]

(J.

Guo),

[email protected]

0021-9797/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2012.05.044

effective and economic method for removing contaminants from wastewater. Recently, the use of natural mineral adsorbents for wastewater treatment increasingly attracts attention because of their abundance and low price [3,4]. Naturally, bentonite exhibits strong adsorption capability due to its large surface area and surface energy. However, the presence of surface negative charge and large amount of exchangeable positive ions result in the cover of a layer of water molecule on the mineral surface, which makes natural bentonite exhibit strong hydrophilicity, and therefore, it is not an effective adsorbent for organic pollutants. Chitosan is a type of amino homogeneous state polysaccharide and no risk to environment, which can be bio-synthesized or biodegraded. Because of containing large numbers of –OH and –NH2 functional groups, it is widely applied in organic wastewater treatment [5–8]. Moreover, the occupation of exchange sites on the bentonite surface by organic cations (such as cationic surfactants, quaternary ammonium surfactants) will change the surface properties from hydrophilic to hydrophobic. Therefore, there has been much interest in the use of modified bentonites as adsorbents to prevent and remediate environmental organic contamination. Previous studies showed that chitosan and organic modified bentonites have been widely used to adsorb heavy metals [9–14], dyes [15–17], organic pollutants such as phenol [18,19], catechol [20], benzoic acids [21,22], and other environmental pollutants [23,24]. The main objective of this study is to evaluate the feasibility of using different modified bentonites to remove weak acid scarlet from dyeing wastewater. Three adsorbents, chitosan modified

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bentonite (CTS-Bent), hexadecyl trimethyl ammonium bromide modified bentonite (CTAB-Bent), and both chitosan and hexadecyl trimethyl ammonium bromide modified bentonite (CTS–CTABBent) were synthesized. The synthesized modified bentonites were characterized by Fourier Transform Infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The adsorption performance of modified bentonites in weak acid scarlet wastewater was also investigated by batch experiments. 2. Experimental 2.1. Materials

2.2. Preparation of modified bentonites The chitosan with a deacetylation degree of 85% was kept at 1.0% throughout the experiment. First, chitosan solution was prepared with 1.0% acetic acid in a three-neck flask with constant stirring and bubbling of nitrogen gas at room temperatures. A predetermined bentonite (5.0 g) was added into 200 mL of deionized water. A certain volume of quaternary ammonium salt solution (0.02 mol L1) was added in the above mixture with strongly stirring for 2 h. Then, 1.0% chitosan solution was added step by step under certain temperature. The mixture was stirred for 2 h and then cooled down to the room temperature. Then, the sample was filtered under reduced pressure and washed with deionized water until no bromide ion detected by silver nitrate solution. The filter cake is dried at 80 °C overnight and ground. The modified bentonite was obtained and sieved to 150–200 mesh for use. The prepared modified bentonites were designated as xCTS–yCTAB-Bent, where x denotes the loading amount of CTS (wt% of the substrate) and y denotes the loading amount of CTAB (wt% of the substrate). 2.3. Adsorption experiments Distilled water was used to prepare dye solutions with the desired concentration. The calibration curve of weak acid scarlet solution was obtained by measuring the absorbance of different predetermined concentrations of the samples at a wavelength of 507 nm using the 722 visible spectrophotometers. A predetermined amount of dry modified bentonite (0.05 g) was placed in a 250 mL flask, followed by adding 40 mL certain concentration weak acid scarlet solution. The adsorption test was performed in a gas bath constant temperature oscillator under room temperature for certain time, then centrifugal separation at 3000 rpm for 10 min. The weak acid scarlet concentration of the filtrate solution was measured with the 722 visible spectrophotometers. Removal efficiency (%) and adsorption capacity q (mg g1) were calculated according to the formula:

c0  ct  100%; c0

FTIR spectra were used to characterize the modified bentonites using a Nicolet 6700 instrument. Typically, 100 scans were collected at 4 cm1 spectral resolution in the range of 4000– 400 cm1. X-ray diffraction patterns (XRD) of the prepared samples were performed with X-ray diffractometer in XRD2600 (SHIMADZU, Japan) equipment using nickel-filtered Cu Ka radiation operated at 40 kV and 30 mA. All XRD patterns were obtained with a scan speed of 2°/min.

2.5. Regeneration studies

Sodium bentonite used in this study was purchased from the Zhejiang Huate New material Co., Ltd. (Lin’an, Zhejiang Province, China). Chitosan (Degree of deacetylation >85%) was purchase from Jinan Haidebei Marine Bioengineering Co., Ltd. (Jinan, Shandong Province, China). Hexadecyl trimethyl ammonium bromide (CTAB), Hexadecylpyridinium chloride monohydrate (CPC), HCl, NaOH, Acetic acid were all of analytical grade and obtained from Sinopharm Chemical Reagent Beijing Co., Ltd., China.

R¼

2.4. Characterization

q¼

For re-use of modified bentonite, desorption and regeneration experiments were performed with NaOH aqueous solution. Desorption experiment was performed by placing used 1CTS– 10CTAB-Bent (0.05 g) in 100 mL beaker with 30 mL 0.25 mol L1 NaOH under shaking at room temperature on gas bath constant temperature oscillator for 5 h. Then, neutralized with 0.2 mol L1 HCl. The regenerated chitosan-CTAB modified bentonite was tested for further adsorption of weak acid scarlet under same adsorption condition. Adsorption and desorption experiments were followed for three cycles.

3. Results and discussion 3.1. Characterization of bentonites The FTIR spectra of natural Na-bentonite, 10CTAB-Bent, 1CTSBent, and 1CTS–10CTAB-Bent in the range of 4000–400 cm1 were shown in Fig. 1. The band at 3650–3622 cm1 in the spectra showed H–O–H hydrogen bond of water molecule. The intensive band at around 1030 cm1 was assigned to Si–O stretching vibrations. The Si–O– Al and Si–O–Si bending vibrations appeared at 525 and 462 cm1, respectively [21,25]. The small band at 1634 cm1 was corresponded to the dSiO–H deformation vibration. From Fig. 1b and d, it can be seen that the bands at 2930 and 2850 cm1 were correspond to the CH2 asymmetric stretching mode (vs(CH2)) and the symmetric stretching mode (vs(CH2)), respectively. The results indicated that the CTAB molecule was impregnated into the interlayer space of the bentonite. A new band at 1564 cm1 was related to the NH2 vibration mode of the chitosan (Fig. 1c and d), which

ðc0  ct Þ  V ðmg g1 Þ m

where c0 (mg L1) is the initial concentration of adsorbate; ct (mg L1) is the concentration of adsorbate by adsorbents; V (L) is the volume of adsorbate; m (g) is the mass of adsorbents; qt (mg g1) is the adsorbed amount at certain time; qe (mg g1) is the adsorbed amount at equilibrium.

Fig. 1. FTIR spectra of natural bentonite (a), 10CTAB-Bent (b), 1CTS-Bent (c), and 1CTS–10CTAB-Bent (d).

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indicated that the chitosan molecule was inserted into the interlayer space of the bentonite. X-ray diffraction (XRD) was performed on Bent, 1CTS-Bent, 10CTAB-Bent, and 1CTS–10CTAB-Bent, as shown in Table 1. The 2h of the 001 face diffraction of bentonite moved gradually from original 6.25° to 3.23°. From the Bragg equation: 2d sinh = nk (where d is the spacing between the planes, h is the incident angle, n is the order, k is the X-ray wave length), it is observed that the spacing of d001 of natural bentonite was 1.41 nm. After chitosan and hexadecyl trimethyl ammonium bromide exchange, the d001 value increased to 1.96 nm and 2.31 nm, respectively. For the 1CTS–10CTAB-Bent, the d001 value increased to 2.74 nm, which is larger than that of CTS-Bent and CTAB-Bent. These results showed that chitosan and hexadecyl trimethyl ammonium bromide molecules are inserted into the layers of bentonite. 3.2. The effect of preparation condition 3.2.1. The type of quaternary ammonium salt The adsorption performances of Na-bentonite modified with different quaternary ammonium salt are presented in Table 2. The adsorption performance of natural bentonite is poor, only 3.9 mg g1. Whereas the adsorption performance was obviously increased after pretreatment with quaternary ammonium salt and chitosan. On the 1CTS-Bent and 5CTAB-Bent, the removal efficiency of weak acid scarlet increased from 4.9% to 48.5% and 52.1%, respectively. The removal efficiency and adsorption capacity improved to 61.9% and 49.5 mg g1 on the 1CTS–5CTAB-Bent, while, which is only 53.3% and 42.6 mg g1 on 1CTS-5CPC-Bent. The results indicated that the effect of CTAB is better than CPC, so the CTAB was chosen as the modifying agent for further experiment. 3.2.2. Effect of preparation temperature Effect of preparation temperature is presented in Table 3. With the increasing of temperature, the adsorption capacity of adsorbent maintained relatively constant. The results showed that the effect of preparation temperature on the adsorption performance is insignificant. 3.2.3. Effect of modifying agent dosage Table 4 shows the effect of modifying agent dose on the adsorption performance. With the increasing of chitosan content from 0.5% to 1.5%, the adsorption capacity increased gradually from 48.7 to 49.9 mg g1. However, as the dose of CTAB increased from 5% to 10%, the adsorption capacity of the adsorbent increased obviously from 49.5 to 62.3 mg g1. The results indicated that the addition of CTAB significantly improved the adsorption performance of adsorbent. 3.2.4. Orthogonal test analysis Orthogonal experiment results are presented in Table 5. The significant level of influencing factors is as follows: CTAM > chitosan > reaction time > reaction temperature. CTAB is the dominant factor, which affects the adsorption. Best reaction condition for preparation of adsorbent is the addition of 1% chitosan and 10% CTAM at 80 °C and 2.5 h. The adsorbent is marked as 1CTS–10CTAB-Bent.

Table 2 The adsorption performance of modified bentonites.a,b Adsorbents

Removal efficiency (%)

Adsorption capacity (mg g1)

Bent 1CTS-Bent 5CTAB-Bent 1CTS–5CTAB-Bent 1CTS–5CPC-Bent

4.9 48.5 52.1 61.9 53.3

3.9 38.8 41.7 49.5 42.6

b

Adsorption condition: modified bentonites 0.05 g, 100 mg L1 weak acid scarlet 40 mL, contact time 2 h, room temperature. a Preparation condition: 60 °C, reaction temperature 2 h.

Table 3 Effect of preparation temperature.a Temperature (°C)

Removal efficiency (%)

Adsorption capacity (mg g1)

60 70 80

56.5 56.8 56.8

45.2 45.4 45.4

a Adsorption condition: modified bentonites 0.05 g, 100 mg L1 weak acid scarlet 40 mL, contact time 2 h, room temperature.

Table 4 Effect of modifying agent loading amount.a Adsorbents

Removal efficiency (%)

Adsorption capacity (mg g1)

0.5CTS–5CTAB-Bent 1CTS–5CTAB-Bent 1.5CTS–5CTABBent 1CTS–7CTAB-Bent 1CTS–10CTAB-Bent

60.9 61.9 62.4

48.7 49.5 49.9

70.0 77.9

56.0 62.3

a Adsorption condition: modified bentonites 0.05 g, 100 mg L1 weak acid scarlet 40 mL, contact time 2 h, room temperature.

3.3. The effect of contact time The adsorption of weak acid scarlet increased with contact time and reached equilibrium at 300 min with a fixed 60 mL, 100 mg L1 weak acid scarlet solution, and 0.05 g of adsorbent (Fig. 2). The final removal efficiency was higher than 85%, and qe was 102 mg g1 onto 1CTS–10CTAB-Bent, suggesting that 1CTS– 10CTAB-Bent is an excellent adsorbent for effective removal of weak acid scarlet from wastewater. 3.4. The compare of adsorption properties of different adsorbents Table 6 shows the adsorption capacities of natural bentonite, activated carbon, and 1CTS–10CTAB-Bent for the adsorption of weak acid scarlet under the same conditions. The adsorption capability of natural bentonite is lowest, which is only 4.0 mg g1. It increased to 102.0 mg g1 for 1CTS–10CTAB-Bent, which is much higher than activated carbon (27.2 mg g1). It is shown that the 1CTS–10CTAB-Bent adsorbent has predominant adsorption capabilities and is a feasible adsorbent for the weak acid scarlet wastewater. 3.5. Reuse and regeneration of adsorbent

Table 1 The diffraction angle (2h) and interlayer spacing (d001) of Bent and modified-Bent. Samples

Bent

1CTS-Bent

10CTAB-Bent

1CTS–10CTAB-Bent

2h (°) d001 (nm)

6.28 1.41

4.51 1.96

3.82 2.31

3.23 2.74

The adsorption experiments were performed with fresh and regenerated 1CTS–10CTAB-Bent to determine the effect of regeneration process on the adsorption capacity. Regeneration experiments were performed with 0.25 mol L1 NaOH solution and the adsorption results are shown in Table 7. The adsorption

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Table 5 Orthogonal experiment of L9(34).a

1 2 3 4 5 6 7 8 9 Average 1 Average 2 Average 3 Range

CTAB (%)

Temperature (°C)

Reaction time (h)

Adsorption capacity (mg g1)

0.5 0.5 0.5 1.0 1.0 1.0 1.5 1.5 1.5 57.1 58.9 59.1 2.0

5 7 10 5 7 10 5 7 10 55.8 57.1 62.2 6.4

60 70 80 70 80 60 80 60 70 57.6 58.5 59.1 1.5

1.5 2.0 2.5 2.5 1.5 2.0 2.0 2.5 1.5 57.4 58.7 58.9 1.5

52.8 56.3 62.2 57.0 57.4 62.3 57.6 57.6 62.1

Adsorption condition: modified bentonites 0.05 g, 100 mg L1 weak acid scarlet 40 mL, contact time 2 h, room temperature.

Removal efficiency (%)

100

120

A

Adsorption capacity (mg/g)

a

Chitosan (%)

90 80 70 60 50 40

0

60

120

180

240

300

B

110 100 90 80 70 60 50 40

0

Contact time (min)

60

120

180

240

300

Contact time (min)

Fig. 2. Effect of contact time on the adsorption of weak acid scarlet solution onto 1CTS–10CTAB-Bent, removal efficiency (A), and adsorption capacity (B).

Table 6 Adsorption properties of different adsorbents for weak acid scarlet solution.a Adsorbents

Removal efficiency (%)

Adsorption capacities (mg g1)

Natural bentonite Activated carbon 1CTS–10CTAB-Bent

3.3 22.7 85.0

4.0 27.2 102.0

a

Adsorption condition: adsorbent 0.05 g, 100 mg L1 dyeing solution 40 mL, contact time 3 h, room temperature.

capacity of used adsorbent slightly decreases than fresh 1CTS– 10CTAB-Bent. After three cycles, the removal efficiency of weak acid scarlet on 1CTS–10CTAB-Bent decreased from 85.0% to 76.2%. This indicates that used adsorbent can be regenerated by the alkali treatment. Even though a gradual decrease in adsorption capacity of 1CTS–10CTAB-Bent, considering the chances of loss of some amount of adsorbent during filtration and washing after every cycle, the regenerated 1CTS–10CTABBent showed greater affinity toward weak acid scarlet, and hence chitosan-CTAB modified bentonite was thought as potential adsorbent for weak acid scarlet removal in wastewater treatment.

Table 7 Three cycles of weak acid scarlet adsorption–desorption on 1CTS–10CTAB-Bent with NaOH as desorbing agent.a No. of cycles

Removal efficiency (%)

Adsorption capacities (mg g1)

Fresh 1 2 3

85.0 82.1 80.2 76.2

102.0 98.5 96.2 91.4

a Adsorption condition: adsorbent 0.05 g, 100 mg L1 dyeing solution 40 mL, contact time 3 h, room temperature.

The Henry, Langmuir, Freundlich, Temkin, and Dubinin– Radushkevich equations expressed in Eqs. (1)–(5) were used to model the adsorption data.

qe ¼ kce qe ¼

bqm ce 1 þ bce

qe ¼ K F ce1=n 3.6. Adsorption isotherms Based on the above optimized conditions, the adsorption isotherms of weak acid scarlet by the two modified bentonites were studied at room temperature (298 K), and the results are shown in Fig. 3.

qe ¼

ð1Þ 1 1 1 1 ¼  þ qe bqm ce qm ln qe ¼ ln K F þ

ð2Þ

1 ln ce n

ð3Þ

RT RT ln ce þ ln AT bT bT

ln qe ¼ ln qm  be2

ð4Þ 

e ¼ RT ln 1 þ

1 ce

 ð5Þ

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Fig. 3. Henry (A), Langmuir (B), Freundlich (C), Temkin (D), and Dubinin–Radushkevich (E) adsorption isotherm fit of weak acid scarlet adsorption onto 1CTS-Bent and 1CTS– 10CTAB-Bent.

3.0

1CTS-Bent 1CTS-10CTAB-Bent

2.5 2.0

ln (qe /ce )

The fitted parameters are summarized in Table 8. The R2 values obtained from Langmuir and Temkin models were both above 0.99, indicating a very good agreement with the data. Temkin equation is the correction of Langmuir equation, which introduces the influence of temperature on the adsorption based on Langmuir model. Therefore, the adsorptions of weak acid scarlet onto 1CTS-Bent and 1CTS–10CTAB-Bent are monolayer uniform adsorption. As illustrated in Table 8, the calculated qm and Kf followed the order of

1.5 1.0

Table 8 Constants and correlation coefficients of adsorption isotherms for the adsorption of weak acid scarlet onto 1CTS-Bent and 1CTS–10CTAB-Bent. Model

Parameter

Henry equation

Kh R2 1

CTSBent 1.232 0.947

2.017 0.889

102.041 0.067 0.992

175.439 0.132 0.994

qm (mg g ) b (L mg1) R2

Freundlich equation

Kf n R2

12.257 1.986 0.990

37.483 2.586 0.979

Temkin equation

bT AT R2

25.649 0.492 0.991

39.869 1.136 0.997

Dubimin–Radushkevich equation

b (g2/KJ2) qm (mg g1) R2

0.000 66.109 0.801

0.000 131.013 0.815

K0

0.0 0

CTS–CTABBent

Langmuir equation

DG0 (kJ mol1)

0.5

2.15

3.70

1.90

3.24

20

40

60

80 100 120 140 160 180 200

qe (mg· g -1) Fig. 4. Plots of ln(qe/ce) vs. qe for the adsorption of weak acid scarlet on 1CTS-bent and 1CTS–10CTAB-Bent.

1CTS–10CTAB-Bent > 1CTS-Bent. All isotherms showed a similar shape and were nonlinear over a wide range of aqueous equilibrium concentrations in Fig. 3. Thermodynamic parameters for the adsorption were calculated from the variations of the thermodynamic equilibrium constant K0 and are given in Table 8. K0 for the sorption reactions was determined by plotting ln(qe/ce) vs. qe and extrapolating to zero qe (Fig. 4) [26]. The standard free energy change DG0 was calculated with following equation:

DG0 ¼ RT ln K 0

ð6Þ

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The thermodynamic parameters are listed in Table 8. The negative value of DG0 indicates that the adsorptions of weak acid scarlet onto 1CTS-Bent and 1CTS–10CTAB-Bent are spontaneous. 4. Conclusions In this study, three modified bentonites, CTS-Bent, CTAB-Bent, and CTS–CTAB-Bent, were prepared and applied to remove weak acid scarlet from aqueous solution. The effect of quaternary ammonium salt, preparation temperature, modifying agent dose, and contact time were also investigated. The adsorption capacity of weak acid scarlet onto natural bentonite is very low. It significantly enhanced its adsorption capacity after modification using chitosan and quaternary ammonium salt. Optimal preparation and adsorption conditions for the adsorption of 100 mg L1 weak acid scarlet solution were 1% chitosan and 10% CTAM at 80 °C and 2.5 h. Aqueous weak acid scarlet solution with the concentration of 100 mg L1 was adsorbed by 1CTS–10CTAB-Bent, and the final removal efficiency was higher than 85%, and adsorption capacity reached 102.0 mg g1. Regeneration of the chitosan-CTAB modified bentonite adsorbent is easily performed with 0.25 mol L1 NaOH, and the adsorbent can be effectively reused for three cycles consecutively. These results suggest that 1CTS–10CTAB-Bent is excellent adsorbent for effective removal of weak acid scarlet from wastewater. Both the Langmuir and Temkin models described the adsorption isotherm data well (R2 > 0.99). Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 51103136), Zhejiang Provincial Natural Science Foundation of China (Nos. Y5090179, Y4100206), Zhejiang Provincial Municipal Science and Technology Project (No. 2008C12055), Innovation Research Team of Young Teachers of Zhejiang A & F University (No. 2010RC02), The Open Fund for Zhejiang Provincial Key of Biological, and Chemical Utilization of Forest Resources for financial supports of this research.

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