Efficient Adsorption of Methyl Orange Using a Modified Chitosan

Article pubs.acs.org/jced

Efficient Adsorption of Methyl Orange Using a Modified Chitosan Magnetic Composite Adsorbent Dezhi Yang,† Lingbing Qiu,‡ and Yaling Yang*,† †

Faculty of Life Science and Technology, Kunming University of Science and Technology, Yunnan Province 650500, Kunming, China Central Monitoring Center of Kunming City, Yunnan Province 650228, Kunming City, China

‡

ABSTRACT: Glutaraldehyde cross-linked chitosan-coated Fe3O4 nanocomposites (MCNPs) were successfully synthesized for the removal of methyl orange (MO) from wastewater. Experimental conditions such as the pH, cation surfactant dosage, nanoadsorbent dosage, and ionic strength were also investigated. Kinetics date was better fit by a pseudosecond-order model, indicating that adsorption was the ratelimiting step. The Freundlich models (R2 = 0.9794) fit the experimental data better than the Langmuir models, and the theoretical maximum adsorption capacity was 758 mg g−1. The values of the Gibbs free energy (ΔG° = −7.27 kJ mol−1), enthalpy (ΔH° = 0.001 kJ mol−1), and entropy (ΔS° = 23.58 J mol−1) indicated the spontaneous and endothermic process of MO adsorption. The prepared MCNPs showed 96−98% adsorption of MO by adding 0.2 mg of cationic surfactant cetyltrimethylammonium bromide (CTAB) to form mixed hemimicelles and can be easily regenerated with a 0.1 mol L−1 HCl solution. secondary pollution.12 In this regard, the combination of chitosan and magnetic compounds exhibits excellent separation performance and a high adsorption capacity, and this property can be used to overcome those problems. Moreover, a crosslinking agent can be applied to enhance the acid resistance of chitosan, which can dissolve below pH 5.5.13 Hemimicelles and admicelles combined with magnetic nanoparticles, in recent years, have received more and more attention and are widely employed for the treatment of wastewater because they are easy to use, exhibit rapid adsorption, are inexpensive, and exhibit strong superparamagnetic behavior.14,15 Hemimicelles and admicelles are formed by the adsorption of ionic surfactants on the surface of nanoparticles. Thus, hemimicelles were applied to enhance the adsorption capacity of magnetic nanoparticles through hydrophobic interactions and electrostatic attraction.16 In this work, glutaraldehyde cross-linked magnetic chitosan nanocomposites (MCNPs) were synthesized and developed as an efficient nanoadsorbent for the removal of methyl orange (MO) from industrial wastewater. To further increase the adsorption capacity of MCNPs, CTAB was used to form mixed hemimicelles on nanoparticles and increase the dispersity of MCNPs. TEM, XRD, and FT-IR spectroscopy were applied to characterize the nanocomposites. The adsorption properties of MCNPs under different experimental conditions such as adsorbent dosage, contact time, pH, regeneration cycles,

1. INTRODUCTION Dyes in many industries such as textiles, varnishes, leather, and plastics are widely used to color products. Dye wastewater discharged from factories is almost always toxic and has serious carcinogenic and mutagenic effects on humans and aquatic animals.1 Dye molecules are particularly stable and do not easily decompose under natural conditions. Therefore, it is necessary to remove dyes before discharging into sewage. Nowadays, many methods have been reported for dyeing effluent, including adsorption, chemical coagulation, biological degradation,2 and oxidation. However, treatments that dye effluent by using chemical and biological methods are technically complex and expensive. Among these methods, adsorption as a widely available and highly efficiency method is promising for the treatment of wastewater, and it is often used to eliminate different dyes in water.3−6 Many efficient adsorbents have been used to remove dyes from wastewater. In order not to cause secondary pollution, adsorbents should be ecofriendly, nontoxic, highly effective, and inexpensive. Adsorbents containing natural polymers and biopolymers are also attracting more and more attention because of their biodegradability, biocompatibility, and renewability. Chitosan as the product of the deacetylation of chitin is the most abundant nitrogen biopolymer in nature and is harmless to humans. Because of its amino and hydroxyl functional groups, it is often used to as a bioadsorbent and exhibits a high adsorption capacity toward dyes.7−9 In practical applications, using traditional separation methods such as filtration and sedimentation makes it difficult to separate chitosan from the treated solution10,11 and may cause © XXXX American Chemical Society

Received: August 7, 2016 Accepted: October 21, 2016

A

DOI: 10.1021/acs.jced.6b00706 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

solution of known MO concentration and then shaken at 250 rpm for 2 min and held for 25 min at 25 °C. After the completion of adsorption, the MCNPs were separated with an external magnet. The supernatant was filtered using 0.45 μm Millipore membrane filters, and the concentration of residual MO was analyzed at λmax = 464 nm. The adsorption rate (η) and the adsorption capacity of the MCNPs (qe, mg g−1) were calculated on the basis of the following equations

temperature, and CTAB dosage were studied. Moreover, the equilibrium isotherms, thermodynamics, and kinetics of the MCNP process were also investigated.

2. EXPERIMENTAL SECTION 2.1. Chemicals. Iron(III) chloride hexahydrate (FeCl3· 6H2O), iron(II) chloride tetrahydrate (FeCl2·4H2O), and glutaraldehyde (50% in H2O) were obtained from Aladdin Industrial Corporation (Shanghai, China). Chitosan was supplied by Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). Methyl orange was purchased from the Tianjin Chemical Reagent Six Factory Three Branch (Tianjin, China). Sodium chloride, sodium nitrate, anhydrous trisodium phosphate, sodium carbonate, sodium hydroxide, and hexadecyl trimethylammonium bromide (CTAB) were all provided by Tianjin Chemical Reagent Technology Co., Ltd. (Tianjin, China). Hydrochloric acid (36−38%) was a product of Shandian Pharmaceutical Co. Ltd. (Yunnan, China). All reagents were analytical reagent grade and used without further purification. 2.2. Instrumentation. Fourier transform infrared (FT-IR) spectra of the samples were obtained by infrared spectrometer TENSOR27 (Germany, Bruker) in the range of 4000−400 cm−1. The magnetic properties of MCNPs were detected by using a vibrating sample magnetometer (Shanghai, China). The morphology of the composite materials was investigated by transmission electron microscope Tecnai G2 TF30 (TEM; FEI, Holland). The XRD measurement was studied by powder X-ray diffraction (Rigaku, D/Max 2200, America) with Cu Kα radiation (γ = 1.540510 A) and a scanning range of 5−90° (2θ). A Shimadzu UV−vis 2550 spectrophotometer (Japan), a vortex mixer (Jintan Guo Wang Instrument Factory, Jiangsu, China), and an ultrasonic cleaner (Kunshan ultrasonic instrument plant, Jiangsu, China) were used in the experiment. A pH meter (Sartorius PB20, Gttingen, Germany) and a vacuum drying oven (BPZ-5033, Shanghai, China) were used to detect the pH value of solution and dry nanoparticles, respectively. Deionized water was provided by a Milli-Q system (USA). 2.3. Preparation of MCNPs. MCNPs were synthesized by the modified chemical coprecipitation method. Briefly, 2.5 g of FeCl3·6H2O and 1.05 g of FeCl2·4H2O were dissolved in 20 mL of deionized water, and then 50 mL of chitosan solution (1 g in 50 mL of 1% HCl) was added. The mixed solution was vigorously stirred for 40 min to form a homogeneous solution, resulting in a yellow solution. The solution was heated to 80 °C under an N2 atmosphere, followed by the addition of 22 mL of a NaOH (2 mol L−1) solution, prompting black precipitate materials. After that, 5 mL of a glutaraldehyde solution (50%) was slowly dispersed into the mixture, and the solution was stirred continuously for 4 h at 80 °C and then cooled to room temperature. Finally, black products were collected by the aid of a neodymium magnet and washed with deionized water, ethanol, and acetone. After being washed with acetone several times, the obtained precipitate was dried under vacuum at room temperature. 2.4. Adsorption Experiments. The investigation of MO adsorption was conducted in a batch experiment, and the influence of different parameters, such as adsorbent dosage, pH, temperature, coexisting anions, and adsorption kinetics, was studied. Typically, 5 mg of NPs and 0.2 mg of CTAB were added to a series of 100 mL glass flasks containing 20 mL of

η=

C0 − Ce × 100% C0

qe =

V (C0 − Ce) m

(1)

(2)

where V (L) is the volume of solution and m (g) is the weight of adsorbents. C0 (mg L−1) and Ce (mg L−1) are the initial and equilibrium concentrations of MO in solution, respectively. To ensure the reliability of the results, the correlation coefficients (R2) and the χ2 parameter were used for statistical analysis. The model parameters and constants were analyzed by linear regression using Origin 7.5. χ2 is calculated by n 2

χ =

∑ i=1

(qe,exp − qe,cal)2 qe,cal

(3)

where n is the number of data points and qe,exp and qe,cal are the observation from the experiment and the calculation from the models, respectively. 2.5. Desorption and Regeneration Studies. The desorption studies were carried out in Erlenmeyer flasks and were similar to adsorption experiments. After the completion of the adsorption, saturated load adsorbents were collected with an external magnet and washed with deionized water to clean out unadsorbed MO. Then, 20 mL of HCl or NaOH (0.1 mol L−1) was introduced into Erlenmeyer flasks, and the saturated load adsorbents were vortex mixed for 1 min at 25 °C. After that, the adsorbents were magnetically separated and washed with deionized water to remove excessive acidity/alkalinity and then dried for reuse. The concentration of MO in the eluent was analyzed by a UV spectrophotometer. To detect the regeneration times, adsorption was repeated several times by using the same adsorbent. The eluent of each cycle was used to detect the MO concentration.

3. RESULTS AND DISCUSSION 3.1. Characterization of MCNPs. The FT-IR spectra of Fe3O4 and MCNPs are shown in Figure 1a. As seen from the MCNPs spectrum, the peak appearing at 3442 cm−1 is attributed to the stretching vibration of O−H overlapped with the N−H bonds that might be related to the cross-linked chitosan.17 Abundant amino and hydroxyl groups indicate that the MCNPs have an efficient adsorbent rate for dyes.7−9 The peak appearing at 535 cm−1 is related to the O−Fe stretching bonds.18 The weak peaks at 2921 and 1047 cm−1 are ascribed to the stretching of the C−H and C−N bonds in the spectrum of MCNPs, respectively. In particular, the overlapped characteristic at 1627 cm−1 corresponds to the stretching vibration of the CN stretching band and N−H stretching,19 indicating that chitosan has been successfully coated on Fe3O4 by using glutaraldehyde as a cross-linking agent. Figure 2 shows the TEM microstructures of MCNPs. It could be observed that the diameters of the MCNPs are in the B



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Figure 3a shows the magnetic properties of MCNPs. The saturation magnetization values of Fe3O4 (64.5 emu g−1) and

Figure 1. FT-IR spectra of Fe3O4 and MCNPs (a). XRD patterns of MCNPs (b).

Figure 3. Magnetization curve of MCNPs (a), photographs of MCNPs dispersed in solution (b), the MO aqueous solution (c), and the separation of MCNPs for the removal of MO (d).

range of 3−8 nm with a generally homogeneous size, indicating that MCNPs have a huge specific surface area. The TEM images showed that the MCNPs were mostly homogeneous, porous structures that play an important role in dispersion. However, it is obviously observed that chitosan was successfully coated on the side walls of Fe3O4.

MCNPs (34.89 emu g−1) indicated that the adsorbent has a relatively strong magnetic response to the magnetic field. The result (Figure 3b) also shows that the adsorbent exhibited good dispersion that was favored for adsorption. Moreover, MCNPs could be quickly and completely separated from MO solution within 20 s through an external magnet (Figure 3d).

Figure 2. TEM images of MCNPs. C



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Figure 1b shows the XRD pattern of the MCNPs. The characteristic diffraction peaks of MCNPs at 2θ = 30.31, 35.72, 44.52, 57.36, and 63.12° were ascribed to the cubic spinel structure of this inorganic magnetite, indicating that MCNPs contained iron oxide particles and the glutaraldehyde crosslinked chitosan adsorbents were well prepared.20 3.2. Investigation of the Removal Ability of the MCNPs in Aqueous Solution. 3.2.1. Effect of Adsorbent Dosage. To compare the different adsorbent capacities for MO and find the optimum amount of adsorbent, the MCNPs and Fe3O4 were all used to remove MO from aqueous solution, and the result of the experiment is presented in Figure 4. A certain Figure 5. Effect of solution pH on MO adsorption (C0 = 100 mg L−1, MCNPs = 5 mg, CTAB = 0.2 mg, T = 298 K, and contact time = 25 min).

heads.23,24 At pH >10, OH− ions competed with MO anions, causing a decrease in the MO removal rate in alkaline solution.25,26 3.2.3. Effect of Coexisting Anions. The inorganic salts in textile effluent were also an important parameter because of their effect on the adsorbent active sites.27 The experiments on the effect of coexisting anions were carried out with different inorganic salts, including NaCl, NaNO3, Na3PO4, and Na2CO3. The influence of salt concentration was also studied by adding different concentrations of salt (0.01, 0.05, 0.1, 0.15, 0.2, 0.5, and 1 mol L−1). As can be seen in Figure 6, the MO adsorption

Figure 4. Effect of dosage on MO adsorption (C0 = 100 mg L−1, pH 7, CTAB = 0.2 mg, T = 298 K, and contact time = 25 min).

amount of each adsorbent (1−100 mg) was dispersed into 20 mL of MO aqueous solution (100 mg L−1) for 25 min at 25 °C, and the result shows that the removal percentage of MO increased from 0.981 to 8.289% as the amount of Fe3O4 increased because of the surface of Fe3O4 containing a small amount of hydroxyl. Compared to the capacity of Fe3O4, the removal percentage of MCNPs increased from 70.32 to 93.22%, indicating that the introduction of chitosan can obviously improve the capacity of adsorbents. Because of the greater number of adsorbent active sites, the removal efficiency will increase with the dosage increase and then will reach equilibrium. Therefore, 5 mg of NPs was selected as the optimum amount of adsorbent. 3.2.2. Effect of pH. The pH as an important parameter in the adsorption process can significantly affect the adsorption capacity. In the study, the effect of pH was changed in the range of 2−12 and adjusted with 0.1 mol L−1 HCl or NaOH, and the results are shown in Figure 5. It is obviously observed that the pH of the aqueous solution in the range of 6−10 has no significant effect on the MO adsorption and the removal efficiency reached about 95%, which might be due to the strong electrostatics. However, at pH 10, the removal percent was reduced to about 66%. In this study, the optimum pH was selected to be around 6−10. Under strongly acidic conditions, there is electrostatic repulsion between protonated MO and the positively charged active site. At a pH of 6−10, MO molecules were negatively charged and ionic surfactants can attach to the charged surfaces of MCNPs by strong electrostatics to form hemimicelles and admicelles,21,22 and adsorption is driven by both hydrophobic interactions and electrostatic attraction. The obtained material therefore exhibits a high extraction efficiency for anionic organic pollutants because of the dual functions of the hydrocarbon tail groups and the positively charged hydrophilic

Figure 6. Effect of coexisting anions on MO adsorption (C0 = 100 mg L−1, MCNPs = 5 mg, CTAB = 0.2 mg, pH 7, T = 298 K, and contact time = 25 min).

capacity obviously decreased with the increasing concentrations of NaCl and NaNO3, which might be due to the competition of coexisting anions with dye anions. In addition, Na3PO4 and Na2CO3 will be hydrolyzed in solution, thus affecting the pH value, to further reduce the MO adsorption capacity. 3.2.4. Effect of CTAB Dosage. The relationship between the CTAB dosage and the adsorption efficiencies was also investigated. The result shows that the adsorption efficiencies (Figure 7) increased with the amount of CTAB (0, 1, 5, 10, 20, 40, 60, and 80 mg L−1), reaching about 98%. Therefore, the CTAB concentration of 10 mg L−1 (0.2 mg) was selected as the optimum amount of cation surfactant. 3.3. Kinetics of Adsorption. The process of adsorption involves the mass transfer of solutes from the liquid phase to the surface of the adsorbent.11 To investigate the mechanism of MO adsorption onto MCNPs, two kinetic models (the pseudofirst-order and pseudo-second-order models) were applied to fit D



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equations of Langmuir (5) and Freundlich (6) are expressed as the following equations 1 1 1 = + qe qmax qmax KLCe

(6)

1 ln Ce n

(7)

ln qe = ln KF + −1

where Ce (mg L ) is the MO concentration at equilibrium. KL (L mg−1) and KF ((mg g−1)/ (mg L−1) 1/n) are the Langmuir constant related to the affinity of binding sites and the Freundlich constant indicating the adsorption capacity, respectively. qmax (mg g−1) is the theoretical maximum adsorption capacity, and qe (mg g−1) is the adsorption capacity of MO adsorbed at equilibrium. 1/n is the constant related to the adsorption density. Figure 8 shows the adsorption isotherms of MO on MCNPs, and the corresponding data are listed in Table 2. The regression coefficient (R2) values obtained by adsorption isotherms suggested that the Freundlich isotherm (R2 = 0.9794) fit the experimental data well. In comparing the value of χ2 for the two models, it also could be concluded that MO adsorption onto MCNPs was best fit to the Langmuir isotherms. This reveals that adsorption takes place at the homogeneous sites on the surface of the adsorbent. From the Langmuir isotherms, the maximum adsorption capacity (qmax) of MO on MCNPs was 758 mg g−1. Moreover, 1/n indicates the degree of suitability of the adsorbent, and when 0.1 < 1/n ≤ 1, MO can be easily adsorbed. In this study, the 1/n value was 0.74, indicating that MO could be easily adsorbed on MCNPs. Because the electrostatic attractions are the main interactions between the adsorbents and dyes, dyes mainly interact with CTAB on the adsorbents. It is estimated that one MO ion might be adsorbed by approximately one CTAB, showing a higher removal efficiency for MO because the dyes’ adsorption behavior of MCNPs follows a homogeneous chemisorption process based on the analysis of the adsorption isotherms and the adsorption kinetics. 3.5. Thermodynamic Studies of Adsorption. The adsorption experiments were carried out in the range of 298−318 K to investigate the influence of temperature on MO adsorption. Thermodynamic parameters such as the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were determined from the following equations: q Kc = e Ce (8)

Figure 7. Effect of CTAB dosage on MO adsorption (C0 = 100 mg L−1, MCNPs = 5 mg, pH 7, T = 298 K, and contact time = 25 min).

the experimental date. Pseudo-first-order eq 3 and pseudosecond-order eq 4 may be expressed as follows11,28,29 log(qe − qt ) = log qe −

k1t 2.303

(4)

t 1 t = + 2 qt q k 2qe e

(5) −1

where qe and qt are the amounts of MO adsorbed (mg g ) at equilibrium and time t (min), respectively; k1 and k2 are the rate constant of the pseudo-first-order kinetic model (min−1) and the rate constant (mg g−1 min−1) of the pseudo-second-order kinetic model for adsorption, respectively. Table 1 shows the different kinetic parameters of MO onto MCNPs. The adsorption kinetics of MCNPs for MO were examined in different concentrations of MO (50 and 100 mg L−1). Adsorption equilibrium (data not given) is achieved in 25 min. According to the correlation coefficients (R2) and χ2 in Table 1, R2 values of the pseudo-second-order model are high and the values of χ2 are low, indicating that the pseudo-secondorder model was more suitable for describing the adsorption kinetics of MO adsorption. It indicates that the rate-controlling step might be chemical adsorption. For the adsorbent-dye system, the values of the pseudo-second-order rate constant, K2, exhibited a decrease with the increase in the initial dye concentration. It indicates that chemisorption is the ratecontrolling mechanism in the adsorption of anionic dyes onto both magnetic adsorbents, which is fully consistent with that drawn from adsorption isotherm analysis. 3.4. Equilibrium Isotherm of Adsorption. In this study, two classic adsorption models (Langmuir and Freundlich) were used to analyze the experimental data to evaluate the adsorption properties of MCNPs. The Langmuir model assumes that uniform adsorption occurs at definite localized sites on the surface of adsorbents. The Freundlish models refers to a multilayer adsorption that was widely applied to the adsorption for organic compounds.30,31 The adsorption

ΔG◦ = −RT ln Kc

ln Kc = −

(9)

1 ΔS + RT R

(10) −1

R is the gas constant (8.314 J mol K), T is the absolute temperature (in Kelvin), Kc is the thermodynamic equilibrium constant, Ce (mg L−1) and qe (mg L−1) are the remaining MO

Table 1. Kinetic Parameters of MO Adsorption onto MCNPs for Two Dye Concentrations (n = 6) Lagergren first-order kinetic model −1

−1

−1

−1

C0 (mg L )

qe,exp (mg g )

K1 (min )

qe,cal(mg g )

R

50 100

622.05 545.21

0.7368 0.6215

514.63 434.35

0.6633 0.7173

pseudo-second-order kinetic model χ

2

2

17.5813 21.4521 E

−1

K2 (g mg

min−1)

0.6183 0.5724

qe,cal (mg g−1)

R2

χ2

658.32 530.34

0.9531 0.9763

2.4121 0.5434



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Table 3. Thermodynamic Parameters for MO Adsorption onto MCNPs thermodynamic parameters T (K)

ΔG° (kJ mol−1)

ΔH° (kJ mol−1)

ΔS° (J mol−1)

298 308 318

−6.92 −7.27 −7.60

0.001

23.58

3.6. Regeneration. The regeneration and reusability of an adsorbent play important roles in practical applications to reduce the overall cost of the adsorbent. In this study, desorption experiments were performed to use 0.1 mol L−1 HCl and 0.1 mol L−1 NaOH as the eluents, and Figure 9 shows

Figure 9. Adsorption capability of MO in each of five regeneration cycles (C0 = 100 mg L−1, MCNPs = 5 mg, CTAB = 0.2 mg, pH 7, T = 298 K, and contact time = 25 min).

the removal efficiency of adsorbents in each regeneration cycle. It can be seen that the regeneration efficiencies of HCl and NaOH were about 85% and 70%, respectively, implying that 0.1 mol L−1 HCl can be chosen as the optimum eluent. The adsorption capacity of the MCNPs decreased slowly as the number of regeneration cycles increased. However, the percentage adsorption for MO is still higher than 80% after four cycles and remained about at 60% for the six regeneration cycles, indicating that the MCNPs as the adsorbent could be easily reused by using 0.1 mol L−1 HCl. 3.7. Real Sewage Applications. To investigate the validity of the proposed method, nine samples taken from different chemical plant at different times were used to examine the adsorption performance of MCNPs (Kunming, China). All of the sample measurements were performed in triplicate. After the previous treatment, the initial concentrations of MO in wastewater were detected by using the national standard, and then the materials of MCNPs were applied to remove the MO. The detail data are listed in Table 4. As can be seen clearly, the recovery is in the range of 85.9−95.6%, and the relative standard deviation is in the range of 1.8−5.3%. 3.8. Comparison with Other Adsorbents. Table 5 shows some parameters compared to those of other adsorbents. The result shows that the MCNPs have a high MO adsorption

Figure 8. (a) Adsorption isotherms of MO on MCNPs. (b) Langmuir and (c) Freundlich model fitting for the adsorption.

concentration in the solution at equilibrium and the MO concentration on the adsorbent at equilibrium. ΔH° and ΔS° are calculated from the slope and intercept of the linear plot of ln Kc versus 1/T. Table 3 shows the values of enthalpy (ΔH°) and entropy (ΔS°). The positive values of ΔH° (0.001) implied that the adsorption process was endothermic. The positive value of ΔS° for the adsorption of MO onto MCNPs indicated that the adsorption was favored under vigorous stirring. The negative values (−6.92, −7.27, and −7.60 kJ mol−1) of ΔG° indicated the spontaneous process of MO adsorption at 298, 308, and 318 K.

Table 2. Langmuir and Freundlich Adsorption Isothermal Parameters, Correlation Coefficients, and the Adsorption Capacities of MCNPs for MO (n = 7) Langmuir −1

Freundich −1

adsorption models

KL (L mg )

qmax (mg g )

R

isotherm constant

0.02

758.00

0.9661

−1

−1

χ

KF ((mg g )/(mg L )1/n)

1/n

R2

χ2

3.5463

−3.92

0.74

0.9794

1.8627

2

2

F



■

Table 4. Removal Performance of MO by MCNPs from Real Sewage (n = 6) samples Hao Feng wastewater Shang Pin wastewater Peng Yu wastewater

1 2 3 1 2 3 1 2 3

equilibrium concentration (mg L−1)

recovery %

RSD %

51.41 23.64 13.20 104.34 85.77 122.17 32.35 43.70 25.60

3.08 1.16 1.44 8.95 5.84 7.32 2.54 1.89 3.59

94.0 95.1 89.1 91.4 93.1 94.0 92.1 95.6 85.9

2.1 1.8 2.3 4.8 2.7 4.7 4.9 5.3 3.6

Corresponding Author Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The work was supported by the Kunming University of Science and Technology.

■

M-CS/γ-Fe2O3/MWCNTs chitosan/Al2O3/magnetite nanoparticles mesoporous γ-Fe2O3/SiO2 activated carbon/Fe3O4 MCNPs a

contact time (min)

reuse times a

reference

31.44 417

100 14

nd nda

11 32

476 384.62 758

20 200 25

nda 5 5

33 34 this study

REFERENCES

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Table 5. Adsorption Capacities of MO on Different Adsorbents qm (mg g−1)

AUTHOR INFORMATION

*E-mail: [email protected].

initial concentration (mg L−1)

adsorbent

Article

Not detected.

efficiency and can be easily reused many times compared to the other magnetic materials. In addition, MCNPs could reach adsorption equilibrium within 25 min.

4. CONCLUSIONS Glutaraldehyde cross-linked chitosan magnetic nanocomposites as a low-cost adsorbent were synthesized by a simple method. And MCNPs combined with the ionic surfactants (CTAB) were developed as a highly efficient nanoadsorbent for the removal of methyl orange (MO) from industrial aqueous wastewater. The main advantages of MCNPs are that they are easy to separate from aqueous solution by using an external magnet and they can be reused. In addition, CTAB can attach to the surfaces of MCNPs to form mixed hemimicelles. Thus, the adsorption capacity of MCNPs can be obviously increased. On the basis of the adsorption isotherms, the Freundlich isotherm (R2 = 0.9794) fit the experimental date well, and the MCNP adsorbents have a high adsorption capacity for MO with the addition of a small amount of CTAB, reaching a Langmuir maximum of 758 mg g−1 at a contact time of 25 min at the optimum pH (6−10). The result shows that the pseudofirst-order model best fit the experimental date. The negative values of ΔG° and positive values of ΔH° indicate that the process of MO adsorption was spontaneous and endothermic. To increase the capacity of MCNPs, adsorption was favored under vigorous stirring. The MCNPs can be reused five times and regenerated with a 0.1 mol L−1 HCl solution followed by vigorous agitation. Overall, these factors, including low cost, high MO capacity, and the reuse of the MCNP adsorbent, make them promising, and they can be used as an environmentally friendly and economical bioadsorbent. G



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Efficient Adsorption of Methyl Orange Using a Modified Chitosan

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