Adsorption of Cationic Dyes on a Cellulose-Based Multicarboxyl

Article pubs.acs.org/jced

Adsorption of Cationic Dyes on a Cellulose-Based Multicarboxyl Adsorbent Yanmei Zhou,* Min Zhang, Xiaoyi Hu, Xinhai Wang, Jingyang Niu,* and Tongsen Ma Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, P. R. China ABSTRACT: A novel adsorbent based on cellulose (CGD) was prepared via modifying with glycidyl methacrylate (GMA) and diethylenetriamine pentaacetic acid (DTPA), characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential thermogravimetry (DTA/TGA). Malachite green (MG) and basic fuchsine (BF) were used to resemble cationic dyes in wastewaters. The influences of several parameters (contact time, pH, temperature, initial concentration) were evaluated to determine the best adsorption conditions. Langmuir adsorption isotherm items explained MG adsorption well, while BF was fitted well with the Freundlich model. The maximum adsorption capacities were greater than some other reports, 1155.76 mg·g−1 for a BF internal concentration of 2000 mg·L−1 and 458.72 mg·g−1 for MG in theory. Kinetics and thermodynamics were adopted to explain in-depth information associated with the adsorption process. The adsorption processes of dyes were both feasible spontaneous and well-described by the pseudosecond-order model. The dynamic adsorption/desorption experiments, with saturated sodium bicarbonate solution as the eluent, show that the adsorbent could be reused for five cycles or four cycles, keeping the adsorption rate above 85 % and 90 % for BF and MG, respectively.

1. INTRODUCTION Annually, millions of tons of cationic dyes are consumed by the textile, rubber, paper, and plastic industries. The cationic dyes, released together with the industry effluents, have a high toxicity, poor degradability, and great solubility in water, for most of them are aromatic compounds.1,2 These hazardous dyes can cause numerous environmental issues, such as breaking the ecological balance and affecting crop growth.1 More seriously, they cause human health, such as teratogenetic, carcinogenic, and mutagenic, problems as well as affect marine lives through the biological enrichment material cycle. Hence, it is obligatory to remove it from the discharged effluent. The inherent properties of the dyes make it difficult to remove from wastewater. Conventional sewage treatment methods, such as chemical precipitation,4 chemical oxidation/reduction,3 ion exchange,6,7 reverse osmosis,1 and adsorption5 have been available for the dyes removal. Particularly, adsorption techniques represent a popular technology for its easy handling and high efficiency. Activated carbon as an adsorbent has been commercial, but its higher production cost and regeneration difficulty prohibits its extensive use.8 If adsorbents are readily available and inexpensive, adsorption techniques will be a more promising technology, which motivates scientists to spend great attention on developing cheaper and more efficient adsorbents.3,4 The chemically modified with functional groups on the surface of biological wastes, such as polymer blends,9 bagasse,10 cellulosic wastes,7 chitosan,11 eggshell,12 and waste tea13 have been widely studied for pollutant removal from water. Among the materials, cellulose has some prominent advantages such as © 2013 American Chemical Society

biodegradability, low cost, good mechanical properties, no toxicity, and high stability to most organic solvents.14 In addition, they have a high density of hydroxyl groups on which different reactions can be carried out according to their needs. There have been some reports about cellulose-based adsorbents,5,6,15 such as those modified with amino, carboxyl, sulfo group, cyclodextrin, oximido, and olefine to adsorb specific pollutant. According to refs 16 to 18, cellulose modified with carboxyl was used to adsorb metal ions and dyes, while diethylenetriamine pentaacetic acid (DTPA) is a strong complexing agent with five carboxyl groups, widely used in basic research, makes decolorizing liquid and is also used in medicine. DTPA introduced into cellulose would provide more active binding sites complexing with cationic dyes.19,20 Since the adsorption mainly takes place on the adsorbent surface, increasing the adsorption active sites on the surface would be an effective pathway to enhance the adsorption capacity.21,22 A survey of literature in our research showed no work has been done so far on an adsorbent with so many carboxyl groups. The objective of this study was to determine the effectiveness originated from the molecular design of the new adsorbent CGD. The structure of CGD in Figure 1 is quite different from previous studies.17,18 The novel low-cost adsorbent displayed a high efficiency to adsorb dyes from aqueous solution and was evaluated in view of the sorption kinetic, thermodynamic, and Received: October 20, 2012 Accepted: December 21, 2012 Published: January 9, 2013 413

dx.doi.org/10.1021/je301140c | J. Chem. Eng. Data 2013, 58, 413−421

Journal of Chemical & Engineering Data

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Figure 2. FTIR spectra of (a) CGD; (b) epoxy cellulose.

stirred for 3 h at room temperature to turn the COO−Na+ to COOH, and then filtered, taking the filtrate 50 mL in triplicate to make sure the standard deviations are less than 5.0 %, using sodium hydroxide solution (0.005 M) to titrate, respectively. Calculating the concentration of the carboxylic group follows eq 1: (C0 − Ct )V ·1000 (1) W −1 where C0 (mol·L ) is the initial concentration of HCl solution; Ct (mol·L−1) is the end concentration of HCl solution; V (mL) is the volume of HCl; W (g) is the mass of CGD. 2.4. Characterization of CGD. The intermediate product and the final adsorbent were measured on a Fourier transform infrared (FTIR) spectrometer (Thermo Nicolet Avatar 360 FTIR) in transmittance mode by the use of KBr pellets. Measurements were taken in the wavelength range from 400 cm−1 to 4000 cm−1. Scanning electron microscopes of samples were recorded using a Jeol JSM5600LV scanning electron microscope. Thermogravimetric analysis (TGA) and the differential thermal analysis (DTA) were acquired by Mettler-Toledo DTA/TGA instrument. The test temperature was from (323 to 1273) K at the heat rate of 283 K·min−1 with nitrogen protection in the course of testing with alumina as a reference. X-ray diffractograms were recorded by an X-Pert Pro X-ray diffract meter equipped with Cu Kα radiation at wavelength λ = 0.15406 nm and the generator working at 40 kV and 40 mA. Diffractograms were collected in a 2θ range of 10° to 40° at the rate of 0.08 deg·s−1. 2.5. Adsorption Experiments. A sample of 25 mg of dry adsorbent was added into 100 mL conical flask, and then 25 mL of dye solution of a certain concentration was added. As the natural pH of dye solution was faintly acid, the pH of the synthetic wastewater was adjusted by hydrochloric acid (0.01 mol·L−1) and caustic soda solution (0.01 mol·L−1) point by point to keep the volume changes as small as possible and measured by pH meter, and it was put into the shaker at 190 rpm for the scheduled time. At last, filtered and measured dye concentration of the filter liquor with TU-1900 recording spectrophotometer (TU-1900, Beijing Purkinje General Instrument. Co., Ltd. Beijing, China) at the wavelength of maximum absorbance, 618 nm for MG, 520 nm for BF. The concentration of dyes was calculated from the equivalent standard curves of the dyes at different pH values. The amount of dye absorbed by the CGD at adsorption equilibrium, qe (mg·g−1), was calculated according to eq 2. C=

Figure 1. Structures of BF, MG, and CGD.

isotherm models, as well as the reuse of adsorbents. The information for the research shows that CGD was really a potential adsorbent based on cellulose and prospectively used in practical applications dealing with dye-containing effluents.

2. MATERIALS AND METHODS 2.1. Materials. The cellulose was provided by Henan Xiren Cellulose Co., Ltd. (Henan, China). Glycidyl methacrylate (> 99 %, GMA) was obtained from Shangqiu Shengyuan Industrial Assistant Co. Ltd. (Henan, China). Basic fuchsin, malachite green, sodium bicarbonate, and sodium hydroxide were all provide by Enterprise Group of Chemical Reagent Co., Ltd. (Henan, China). Diethylenetriamine pentaacetic acid (DTPA) was purchased from Chemical Reagent Co. Ltd. (Shanghai, China). All of these chemicals were all analytical grade and used without any purification. All aqueous solutions and standards were prepared using distilled water. 2.2. Synthesis of CGD. The cellulose was modified with GMA to get epoxy cellulose according to the methodology described by our previous work.23 DTPA was pretreated with sodium hydroxide to form DTPANa,21,24,25 and 3 g of sodium hydroxide and 2.5 g of DTPA were dissolved in 100 mL of distilled water, stirring for 30 min at room temperature in nitrogen gas atmosphere. Then 1.63 g of epoxy cellulose was added, and the temperature of the system was kept at 383 K for 20 h under constant stirring.9,26,27 The result mixture was leached, washed with hot distilled water to remove the DTPANa that did not react, dried at 353 K for 12 h at last, and stored in desiccators. 2.3. Carboxyl Content Determination. The concentration of carboxylic functions per gram of CGD was determined by the titration method. Specific steps as follows: 50 mg of adsorbents was added to 300 mL of hydrochloric acid (0.01 M),

qe = 414

(C0 − Ce)V W

(2)



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Figure 3. Morphology contrast of (A) cellulose magnification 1000×; (B) epoxy cellulose magnification 1000×; (C) CGD magnification 1000×; (D) CGD magnification 2000×.

where C0 (mg·L−1) is the initial concentration of dye; Ce (mg·L−1) is the equilibrium concentration of the dye; V (L) is the volume of dye solution; W (g) is the quantity of CGD. 2.6. Adsorption Kinetics, Thermodynamics, and Isotherm Model. The pseudofirst-order (PFO) and pseudosecond-order (PSO) equations were employed to elucidate the adsorption kinetics. The linear equation of PFO compiles as eq 3, and the linear equation of PSO compiles as eq 4. ln(qe − qt ) = ln qe − k1t t 1 1 = + t 2 qt qe k 2qe

ln(Kc) =

ΔG 0 = −RT ln Kc −1

(7) (8)

−1

where R (8.314 J·mol ·K ) is the ideal gas constant; T (K) is the absolute temperature; K (L·mol−1) is the Langmuir adsorption constant. The isotherm linear equations of Langmuir, Freundlich, and Temkin are compiled as eqs 9, 10, and 11, respectively:

(3)

Ce C 1 = + e qe qmbL qm

(4)

When t → 0, the adsorption rate can be defined as h, calculated following eq 5; h = k 2qe 2

ΔS 0 ΔH 0 − R RT

ln qe = ln KF +

(5)

qe =

where k1 (g·mg−1·min−1) is the speed constant of PFO during the adsorption progress; qe is the adsorption capacity at adsorption equilibrium; k2 is the speed constant of PSO; qt (mg·g−1) is the adsorption capacity at t min; t (min) is adsorption time; qe and k1 were calculated through the slope and intercept of eq 3. The exothermic nature of the adsorption of dyes onto CGD could be explained on the basis of thermodynamic parameters such as the change in Gibbs free energy (ΔG0), enthalpy (ΔH0), and entropy (ΔS0). They were defined as eqs 6, 7, and 8 for adsorptive reactions: q Kc = e Ce (6)

1 ln Ce nF

RT RT ln AT + ln Ce bT bT

(9)

(10)

(11)

−1

where qe (mg·g ) is the equation adsorption capacity; qm (mg·g−1) is the maximum adsorption capacity; Ce (mg·L−1) is the equilibrium concentration of dye in solution. bL (L·mg−1) in eq 9 is the parameter related to the adsorption energy. KF and nF in eq 10 represent the maximum adsorption capacity and the adsorption affinity of the adsorbent for adsorbate. In eq 11, R (8.314 J·mol−1·K−1) is the gas constant, T (K) is the absolute temperature; AT (mL·mg−1) and bT (J·mol−1) are the isotherm constant and Temkin−Pyzhev constant, respectively. 2.7. Desorption and Reusability Behaviors of the Adsorbent CGD. A glass column was used to pack 25 mg of 415



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Figure 6. (A) The adsorption rate variation with contact time at room temperature, ▲, MG; ●, BF. (B) Pseudosecond-order kinetics linear fit of adsorbate on CGD, ▲, MG; ●, BF.

The sharp peak at 1560 cm−1 and 1379 cm−1 could be assigned to stretching vibrations of COO− groups of CGD.28 The characteristic spectra of epoxy group at 759 cm−1, 844 cm−1, and 902 cm−1 disappeared, and the representative spectra of allyl glycidyl ether at 3000 cm−1 disappeared, too. The moderate strength peak at 1269 cm−1 could confirm the existence of tertiary amine of DTPANa,29 which shows that DTPANa should have been modified on cellulose as expected. 3.3. SEM Analysis. Figure 3A shows that the cellulose surface was smoother than the others, had no crack, and expressed fibrous characteristics,30 against adsorption from the appearance shape. But the epoxy cellulose surface in Figure 3B appeared rougher than A’s, the fiber had swelled and had a small amount of fracture; the fibrous structure of cellulose degenerated little after the GMA modified, presenting many small convex impressions. However, the CGD surface in Figure 3C and D was the most rough, swelling most severely in them. Microcracks caused an increase in surface area, which resulted from the opening of epoxide ring when DTPANa was grafted to epoxy cellulose.6 The changes of physical characteristics observed would positively have a greater adsorption capacity than natural cellulose or epoxy cellulose and provided proofs for grafting. 3.4. DTA/TGA Analysis. To examine the thermal stability, DTA/TGA was completed. The results are shown in Figure 4. The decomposition of cellulose leaded to the lost weight of 90 % in the range 393 K to 723 K forming into large amounts of volatiles and solid char. For epoxy cellulose, the split of GMA polymer from the cellulose leaded to weight loss about 24 % at 503 K and the 68 % weight loss at 633 K leaving behind solid char.23 For CGD, the evaporation of approximately 7 % residual water leaded to the first phase weight loss at temperature below 573 K.31,32 Two other obvious weightlessness temperature ranges were 523 K to 573 K and 623 K to 693 K, which resulted from the thermal decomposition between epoxy cellulose and DTPANa,7 and the pyrolytic decomposition of cellulose subunits, respectively.23 The DTA curves of CGD appeared

Figure 4. TGA/DTA curves of a series of products: (a) cellulose; (b) epoxy cellulose; (c) CGD.

Figure 5. X-ray diffraction of (a) CGD; (b) cellulose.

adsorbent, and then 25 mL of dye solution (50 mg·L−1) was added, dynamicly absorbing at a rate of 0.5 mL·min−1. After that, 25 mL of saturated sodium bicarbonate solution was added for desorption at the same rate. The procedure was repeated like this until the adsorption rate decreased rapidly, investigating the reusability.

3. RESULTS AND DISCUSSION 3.1. Determination of Carboxyl Content. Calculating the content of carboxyl groups following the method in 2.3 above, the content of carboxyl groups was 5.7 mmol·g−1. 3.2. FTIR Spectra Analysis. Figure 2 shows a comparison of FTIR spectra between the epoxy cellulose and CGD. 416



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Table 1. Kinetic Parameters of Two Models (PFO and PSO) parameters qe adsorbate MG

kinetic model

mg·g

PFO PSO PFO PSO

BF

k1 −1

k2

−1

−1

g·mg ·min

50.79 49.17 48.23 48.38

5.07·10

g·mg ·min

−1

−1

mg·g ·min−1

−4

0.1290

7.756

0.0064

14.874

1.07·10−2

Figure 7. Adsorption rate variation with pH: ▲, MG; ●, BF. Conditions for MG: C0 = 50 mg·L−1; T = 303 K; t = 2 h. Conditions for BF: C0 = 50 mg·L−1; T = 303 K; t = 3.5 h.

BF

MG

283 293 303 313 323 ΔH0/(kJ·mol−1) ΔS0/(J·mol−1·K−1)

−7.70 −7.63 −7.03 −7.04 −7.19 −12.45 −16.93

−6.20 −6.13 −6.49 −6.68 −7.06 2.27 28.76

0.4940 0.9999 0.7438 0.9990

through the crystallinity.11,34 The crystalline index (χc %) was estimated by Rabek’s method, as follows from eq 12; χc =

ΔG0/(kJ·mol−1) of adsorbate

T/K

R2

Figure 9. Adsorption rate of GM variation with initial concentration. Conditions: at 303 K, pH 6.0, shaking for 120 min.

Table 2. Result of Related Parameters of Adsorption Thermodynamics parameters

h

−1

Sc Sc + Sa

(12)

where Sc is the areas of crystal diffraction peaks of samples; where Sa is the amorphous diffraction peaks of samples. The crystallinity of CGD calculated at last was 25 %, and there was a greater decline in comparison with native cellulose (χc = 77.22 %),23 which indicated that the structure changed. 3.6. Contact Time Effect. After changing the shaking time from 30 min to 420 min, the result was shown in Figure 6A. The dye could be adsorbed rapidly in the first 30 min; the adsorption rate had reached 90 % at least. The time achieved maximum adsorption capacity was about one hour. To ensure a better adsorption result we choose 120 min for MG and 210 min for BF. Before bonded with the active sites of CGD, the dye molecules must over come three stages.35,36 First, the molecules of dyes migrated through the solution onto the surface of the adsorbent. Second, some molecules of the dyes were adsorbed on the adsorbent surface though the van der Waals force.37 At last, strong electrostatic interactions took place when cation dye molecules were close enough to CGD. The strong electrostatic interactions played a main role during the adsorption progress.7,38 As shown in Figure 6A, with the lapse of time the remaining vacant sites were difficult to be occupied by dyes, and adsorption reached equilibrium. qe and k2 were calculated through the slope and intercept of eq 4. Kinetic parameters are shown in Table 1, and the linear fitting is shown in Figure 6B. It was observed in Table 1 that the adsorption kinetics of BF and GM on CGD were well-represented by the PSO kinetic model, and the rate of adsorption was proportional to the square of the number unoccupied ligands, which suggested BF and GM adsorption onto CGD to be occurred by internal and external mass transfer mechanisms.36 3.7. pH Effect of Sorption. The ranges of pH for BF and GM were confirmed as 2 to 8 and 3 to 8, respectively,

Figure 8. Adsorption rate of BF variation with initial concentration. Conditions: at 303 K, pH 6.5, shaking for 210 min.

as a big slow peak, which indicated a continuous endothermic process. 3.5. X-ray Diffraction Spectrogram Analysis. Figure 5 shows the comparison results of cellulose and CGD. The diffraction peaks of cellulose at 2θ values of 14.5°, 16.3°, and 22.5° stated that it was primitive cellulose.33 The peaks in the range of 13° to 18° changed slightly, and a new diffraction peak at 28.54° appeared in diffraction spectra compared to cellulose. In this study, the structure change was investigated mainly 417



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Figure 10. Fitting curve of (A) Freundlich and (B) Tempkin for

▲,

MG; ●, BF; fitting curve of Langmuir for (C) MG and (D) BF.

Table 3. Isotherm Models for the Adsorption of BF and MG parameters qm adsorbate BF

MG

isotherm model Langmuir Freundlich Temkin Langmuir Freundlich Temkin

mg·g

bL −1

1375.52

L·mg

KF −1

L·g

−1

nF

bT −1

L·mg

J·mol−1

−3

2.50·10

15.96 458.72

AT

1.62 0.09

13.45

3.94

28.81

2.68·10−1 93.65

2.23

R2 0.8377 0.9892 0.8619 0.9934 0.9151 0.9623

So the temperature was determined at 303 K in consideration of convenience. The values of ΔH0 and ΔS0 were determined from the slopes (−ΔH0/R) and the intercepts (ΔS0/R) of the plots of ln(qe/Ce) toward 1/T shown in eq 7. As shown in the Table 2, ΔG0 was negative at the investigated temperature in this study, which meant a spontaneous process for BF and MG adsorption. Generally, if the free energy change is from −20 to 0 (kJ·mol−1), it means physical adsorption. The numerical values of ΔG0 for the dyes were in the range from −20 to 0, which proved the mechanism physical adsorption depending on electrostatic interaction.27 The ΔH0 for the adsorption of MG on the adsorbent was positive, indicating that the process was endothermic in nature, while for BF, the opposite result was obtained, and it was an exothermic progress for the adsorption of BF on CGD. Besides, the positive ΔS0 value for MG on CGD implied increasing randomness at the adsorbent−solution interface during the adsorption process. On the contrary, the negative ΔS0 value for BF on CGD revealed the decrease of randomness.13,34,40 3.9. Initial Concentration Effect. The best conditions were found from the above experiments. The adsorption rate variation with initial concentration was shown in Figures 8 and 9. It was obvious that the adsorption rate for BF increased rapidly when the concentration was less than 1000 mg·L−1 and then increased less slowly when the concentration further

to prevent itself from degeneration. The dye uptake rate variation of different pH values is shown in Figure 7, and the adsorption rate changed obviously at the beginning, from 13 % at pH 2.0 to 90 % at pH 3.0 for BF, from 37 % at pH 3.0 to 96 % at pH 4.0 for GM. With a further increase of pH to 4 to 8, the adsorption rate of the two dyes was kept invariant. The pH 6.0 and 6.5 were selected as the optimum pH of all subsequent adsorption experiments for MG and BF, respectively. The reason could be explained as follows. These functional groups COO−Na+ are dissociated at various pH values. At low pH (less than 4.0), carboxyl groups retain their protons (COOH) due to protonation,7,12 which weakens the interaction between negatively charged groups (COO−) and positively charged dye ions because a hydrogen ion in the solution could compete with cation dyes for active sites on the CGD surface.10 With an increase in pH of the solution, these functional groups became deprotonated (COO−), which resulted in an increase in the negative charge density on the adsorbent surface and facilitated the binding of cation dyes.39 Hence, the dye ions binding to the adsorbent mainly involved electrostatic interaction between cationic dyes and negatively charged COO− groups, and the mechanism of the adsorption process is physical adsorption depending on electrostatic interaction.17 3.8. Temperature Influence. At different temperatures, the adsorption rate variation with temperature was inconspicuous. 418



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all of the adsorption sites were energetically identical. The Langmuir parameter qm values were obtained. 3.10. Desorption and Regeneration. The performance of reuse was an important index for the absorbent value. In this investigation, successive sorption/desorption cycles were done to test the suitability and stability of the adsorbent.44,45 The results are shown in Figure 11; the sorption capacity for dyes appeared significantly sated after four cycles for MG and after five cycles for BF. The mechanism of desorption could be thought as the rat race between COO− and HCO3−. A good deal of HCO3− was disadvantageous for the adsorption of dyes onto adsorbent, because of the existence of stronger electrostatic interaction between HCO3− and cationic dyes.46,47 After several cycles, rudimental dyes grains on CGD mainly depended on the complexation reaction, difficult for desorption.45,48 3.11. Comparisons with Other Adsorbents. The Langmuir parameter qm values of MG and the maximum adsorption capability of BF obtained in the experiment compared with other results reported in literature appear in Table 4. It can be Table 4. Adsorption Capacities of Various Low-Cost Adsorbents Reported Previously for Cationic Dyes

Figure 11. Adsorption rate of (A) GM and (B) BF after several successive desorption/adsorption cycles. Conditions: 50 mg·L−1 dye, 25 mL; saturated sodium bicarbonate solution as eluent, 25 mL.

increased, which could be seen clearly through the slope of the lines. For GM in Figure 9, the adsorption rate increased rapidly before the concentration reached 450 mg·L−1 and appeared a platform above 450 mg·L−1. A high initial dye concentration led to an increase in the mass gradient between the solution and the adsorbent CGD, which was functioned as the driving force for the transfer of dye ions from the bulk solution to the adsorbent surface.41 The well-known Langmuir, Freundlich, and Temkin adsorption isotherms were employed to discuss the progress in this study. After calculating qm and bL through the slope and intercept of Langmuir isotherm linear equation (eq 9), the fitting curves are shown in Figure 10.32 Similarly, other related parameters are calculated. The fitting results of the adsorption isotherm models are shown in Table 3. For BF, the correlation coefficient (R2 = 0.9892) of the Freundlich isotherm was the best in the three isotherm models. The Freundlich isotherm model better fit the experimental results, which meant that the adsorption of BF onto the CGD was multilayer adsorption.42 According to the Freundlich theory, nF reveals whether the adsorption is favorable, when nF < 1, it is unfavorable adsorption; when nF = 1, it is linear adsorption; when nF > 1, it is favorable adsorption. The value of nF was above 1, which meant the adsorption process was favorable.27 For MG, as shown in Table 3, the correlation coefficient (R2 = 0.9934) of the Langmuir isotherm was the highest in the three isotherm models, which meant the adsorption process fitted well with the Langmuir isotherm model.43 This indicated that the MG adsorption was monolayer, the adsorption took place at specific homogeneous sites within the adsorbent, and

qm/(mg·g−1) pH

adsorbents

dye

Ashoka leaf powder bivalve shell (BS)-Zea mays L. Husk leaf (ZHL) eggshells oxalic acid modified rice husk (MRH) natural rice husk (NRH) graphite oxide (GO) CGD sizania-latifolia activated carbons (ZLAC) ZLAC-Fe ZLAC-Mn deoiled soya bottom ash cellulose-maleic anhydride (CM) CGD

MG MG

83.3 81.5

6.0 6.0

8 41

refs

MG MG MG MG MG BF

56.76 54.02 28.00 248.1 458.7 135.14

9.0 7.0 7.0 4.3 6.0 8.0

12 51 51 50 this study 49

BF BF BF BF BF BF

212.77 238.10 13.48 7.16 31.92 1155.8

8.0 8.0 9.0 9.0 6.5 6.5

49 49 21 21 34 this study

seen from the table that CGD showed a greater adsorption capability with respect to other adsorbents, including activated carbon and some other low-cost adsorbents. The results indicated that the CGD can be considered a promising adsorbent for the removal of BF and MG from aqueous solutions.

4. CONCLUSION In this study, a novel low-cost, environmentally friendly, greater adsorption capacity adsorbent was prepared by grafting DTPANa and GMA onto cellulose without the presence of organic solvent. The grafted function group DTPANa with GMA as a link arm allowed us to obtain a cellulose based anion adsorbent with more carboxyl groups. Batch adsorption experiments were performed to evaluate the efficiency of CGD toward cationic dyes. The Langmuir isotherm model explained MG adsorption well and calculated the maximum theory absorbance of 458.72 mg·g−1, while BF was fitted well with the Freundlich isotherm model, increasing the initial concentration as much as possible to get a maximum absorbance of 1155 mg·g−1 in the laboratory. Additionally, adsorption thermodynamics revealed 419



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that the adsorbent processes were spontaneous. The adsorption of them both fitted the pseudosecond-order kinetic model. In the sorption−desorption experiments, the absorbent did well during the first several cycles, where could be reused four times at least. Thus, the technically feasible, cost-effective, and highly efficient adsorbent has great potential. Further study is needed to excavate the potential of CGD for removing metal ions from real industry wastewater and groundwater samples.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-378-2868633-3422. Fax: +86-378-3881589. E-mail address: [email protected] (Y.M.Z.), [email protected]. cn (J.Y.N.). Funding

The authors are grateful for the Key Scientific and Technological Project of Henan province (Nos. 112102310360, 122300410260), the natural science research project of Henan province education department (No. 2011A610005), and the financial support of the foundation of International Scientific and Technological Cooperation of the Henan province (No. 124300510012) in China. Notes

The authors declare no competing financial interest.

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REFERENCES

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Adsorption of Cationic Dyes on a Cellulose-Based Multicarboxyl

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