Chitosan composite beads

Chitosan composite beads

International Journal of Biological Macromolecules 96 (2017) 459–465 Contents lists available at ScienceDirect International Journal of Biological M...

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International Journal of Biological Macromolecules 96 (2017) 459–465

Contents lists available at ScienceDirect

International Journal of Biological Macromolecules journal homepage:

Research paper

An efficient removal of RB5 from aqueous solution by adsorption onto nano-ZnO/Chitosan composite beads Seda C¸ınar a , Ümit H. Kaynar b , Tülin Aydemir a,∗ , Sermin C¸am Kaynar c , Mehmet Ayvacıklı c a

Manisa Celal Bayar University, Faculty of Science and Arts, Chemistry Department, Manisa, Turkey Manisa Celal Bayar University, Education Faculty, Primary School Science Teaching, Demirci, Manisa, Turkey c Manisa Celal Bayar University, Faculty of Science and Arts, Physics Department, Manisa, Turkey b

a r t i c l e

i n f o

Article history: Received 22 February 2016 Received in revised form 5 December 2016 Accepted 8 December 2016 Available online 21 December 2016 Keywords: Nano-ZnO/Chitosan composite Dye adsorption Isotherms and thermodynamic

a b s t r a c t In this study, the removal of Reactive Black 5 (RB-5) by nano-ZnO/Chitosan composite beads (nanoZnO/CT-CB) from aqueous solution was investigated. ZnO nanoparticles were prepared by the via the microwave-assisted combustion technique. And then nano-ZnO/Chitosan composite beads were prepared by polymerization in the presence of nano-ZnO and chitosan. Characterization of composite beads were conducted using SEM, TEM, FTIR, TGA and XRD. Several important parameters influencing the removal of RB 5 such as contact time, pH and temperature were investigated systematically by batch experiments. At optimum conditions of pH 4 and adsorbent concentration of 0.2 g, dye removal efficiency was found 76%. Langmuir, Freundlich and Temkin adsorption models were used to describe adsorption isotherms and constants. The maximum adsorption capacity (qm ) by Langmuir isotherm has been found to be 189.44 mg/g. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy and entropy of adsorption. The positive value of the enthalpy change (32.7 kJ/mol) indicated that the adsorption is an endothermic process. The obtained results showed that the tested adsorbents are efficient and alternate low-cost adsorbent for removal of dyes from aqueous media. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Chemical industries consumed annually more than 700 000 tons of dye. However, it is reported that 2% of dyes produced annually are discharged in water resources during industrial processing, causing adverse effects on aquatic organisms and human health [1–3]. Most of the used dyes are synthetic dyes which are commonly grouped into acid, reactive (or fibre-reactive), direct, basic and azoic dyes [3]. Moreover, reactive dyes represent an important fraction of the commercialized synthetic dyes used (approximately 12% of the worldwide production) [2]. The main environmental problem associated with the reactive dyes is their low exhaustion. Frequently, the fixation efficiency of these dyes ranges between 60% and 90% consequently substantial amounts of unfixed dyes are released in the wastewater [3]. Different techniques like membrane separation, oxidation or ozonation, electrocoagulation and adsorption have been used for wastewater treatments [4–8]. Recently, hydrogels obtained from

∗ Corresponding author. E-mail address: [email protected] (T. Aydemir). 0141-8130/© 2016 Elsevier B.V. All rights reserved.

bio resources, such as sodium alginate, starch cellulosic materials and chitosan [9–11] are emerging as a potential alternative adsorbents for metal ions and synthetic dyes from aqueous solutions. Chitosan is a cationic biopolymer obtained from alkaline N-deacetylation of chitin, the second most abundant biopolymer in nature and supporting material of crustaceans, insects, etc. Furthermore, chitosan has biological and chemical properties such as non-toxicity, biocompatibility, high chemical reactivity, chirality, anti-bacterial properties, chelation and adsorption properties [12]. Chitosan is well established as an excellent natural adsorbent because its amine (–NH2 ) and hydroxyl (–OH) groups may serve as coordination sites to form complexes with various heavy metal ions. So far, researchers have tested many different types of adsorbents including chitosan, aluminum oxide hydroxide, fly ash, clay, Fe3 O4 etc. In order to remove organic and inorganic pollutants from water and wastewater [13–16]. In recent years, a great number of studies on chitosan-based biosorbents for dye removal have demonstrated. Nanotechnology is nowadays one of the most important trends in material science. The term nanomaterial is normally used to emphasize nanoporous structures in which at least one of its phases has one or more dimensions (length, width or thickness) in the


S. C¸ınar et al. / International Journal of Biological Macromolecules 96 (2017) 459–465









Fig. 1. Structure of Reactive Black 5.

nanometer size range (1–100 nm) [17]. Because of their size, nanomaterials can exhibit an array of novel properties that can be used to develop new technologies and improve existing ones. Characteristics such as large surface area, potential for self-assembly, high specificity, high reactivity, high adsorption capacity, low temperature modification ability and catalytic potential make nanoparticles excellent candidates for water treatment applications [17,18]. Zinc oxide (ZnO) is one of the most important multifunctional oxide materials used for industrial applications. ZnO is a n-type semiconductor with a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV. It has been considered for many applications, for example, ceramics, varistors, piezoelectric transducers, chemical sensors, anti-UV additives, photocatalysts, and microwave absorbers etc. [19]. As an environmental friendly material, ZnO can be used in catalyst industry, electrical and optical devices, gas sensors, solar cell’s chemical, absorbent, etc. [20–22]. Recently, people have found that nanostructured ZnO could efficiently remove heavy metals [23]. It is suggested that nanoporous ZnO powders is suitable as sorbent material for recovery and adsorption of uranium (VI) ions from aqueous solutions [24]. In another study, it was been indicated that nanoporous ZnO was suitable as sorbent material for recovery and adsorption of Th (IV) ions (%97) from aqueous solutions [25]. In the present study, nano-ZnO/CT-CB were used to remove RB5 dyes from aqueous solution by batch adsorption system. The influence of adsorption conditions such as contact time, pH changes, adsorbent dosage, initial concentration of dyes and temperature effect were investigated. The adsorption isotherms of RB5 on nanoZnO/CT-CB was studied to gain a good comparison, accordingly. Surface morphology characterization and structural analysis of adsorbents were done by SEM, TEM and FTIR. Additionally, thermal degradation of beads was observed while performing thermogravimetric measurements. 2. Materials and methods 2.1. Materials Chitosan (CT), sodium triphosphate pentabasic (TPP), acetic acids and Reactive Black 5 (RB5) Mw = 991.8 g/mol; max = 596 nm) were purchased from Sigma–Aldrich Co., USA (Fig. 1). All other chemicals were used in analytical grade. Optical measurements were taken by UV–vis spectrophotometer (Perkin Elmer UV-1601, UV–vis). 2.2. Synthesis of nano-ZnO/CT-CB Zinc nitrate [Zn(NO3 )2 ] and urea [(NH2 )2 CO] were dissolved in high-purity water to form solutions with certain concentrations, respectively. Microwave-assisted combustion synthesis involves the dissolution of zinc nitrate as an oxidizer, and fuel (urea) as reducer in water. The synthesis method used for the nano-ZnO material with microwave-assisted ignition reaction was given in detail in our previous study [24]. In that study, the crystalline structure accuracy and particle size of 52 nm were determined by XRD, SEM and TEM characterizations of the ZnO crystallites [24]. In order to prepare nano-ZnO/CT-CB, chitosan was firstly dissolved in acetic acid solution. The chitosan solution (1.5% w/v)

was prepared by dissolving chitosan powder (1.5 g) in an acetic acid aqueous solution (2% v/v). Then, nano-ZnO powder (0.5 g) was added into the chitosan solution and stirred vigorously for 5 h. Thereafter, the chitosan solution containing ZnO was added drop wise into the TPP with continuous stirring. The obtained beads were immersed in fresh TPP and stirred mechanically for 12 h. Finally, the synthesized nano- ZnO/CT-CB was washed with distilled water several times and then dried in an oven at 70 ◦ C [26] (Scheme 1). 2.3. Characterization of beads The surface morphology of samples was determined by scanning electron microscope (SEM) (XL30-SFEG, FEI/Philips) and Transmission electron microscopy (TEM) (FEI Tecnai G2 Spirit Bio, 120 kV). Fourier transform infrared (FTIR) analysis was accomplished on a Perkin Elmer spectrum BX scanning from 4000 to 400 cm−1 at room temperature. Nano ZnO-chitosan composite beads were mixed with KBr and pressed to plates for measurements. Thermal gravimetric analyses (TGA) were performed on nanoZnO-chitosan composite beads samples using Perkin–Elmer Diamond TA/TGA in the temperature range of 30–1000 ◦ C at a heating rate of 10 ◦ C per minute. X-ray diffraction (XRD) patterns of composites were recorded with an X-ray diffractometer (Model: Rigaku Minifex 600) using Cu-K ␣ radiation (␭ = 0.15418 nm) as source and operated at 45 kV and 40 mA over the range (2◦ of 10–80◦ ). 2.4. Adsorption experiments Adsorption experiments were carried out by batch technique. 0.2 g of nano-ZnO/CT-CB were put in a beaker containing 10 mL of 20 ppm RB5 dye solutions. The shaking was carried out in a thermostated electronic shaker (Labart SH-5) under constant stirring. After decantation, the concentration of dye was analyzed by spectrophotometer at 597 nm. The effect of contact time was studied between 0 and 360 min. The prepared composite beads were investigated to determine the pH effects of the removal of RB5 by adding 0.2 g of adsorbents in 10 mL of 20 ppm dye solutions prepared at different pH. Effect of pH on dye removal was studied over a pH range of 3.0–9.0. pH adjusted by the addition of dilute aqueous solutions of HCl or NaOH (0.1 M) by using a Hanna P211 pH-meter with a combined pH electrode. In order to investigate the effect of temperature on adsorption, experiments were carried out at several temperatures (20, 30 and 40 ◦ C). Isotherm studies were conducted with a constant weight nano-ZnO/CT-CB and varying initial concentrations of RB5 solution in the range of 5–20 ppm. The amount of RB5 adsorbed was calculated according to the following equations (Eq. (1)): q=

(C0 − Ce )xV m


where q is the amount (mg g−1 ) of RB5 adsorbed by nano-ZnO/CTCB, Co is RB5 concentrations (ppm) in the solution initially and Ce is the equilibrium concentration of dye in solution. V is the volume (L) of the solution and m is the mass (g) of adsorbent used. Percentage of adsorption was calculated according to the following equations: (Eq. (2)) A% = (Amountofadsorbeddye/Amountofinitialdye) × 100


Langmuir, Freundlich and Temkin isotherms were used to analyze the adsorption equilibrium. The linearized form of Langmuir equation is: (Eq. (3)) 1 Ce Ce = + qe KL qm qm


where Ce is the equilibrium concentration of dye in the solution (mg/L), qe is the equilibrium capacity of dye on the adsorbent

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Scheme 1. The synthesis methods of the nano-ZnO/CTCB and mechanism of RB5 adsorption.

(mg/g), qm is the maximum adsorption capacity of the adsorbent corresponding to the complete monolayer coverage on the surface (mg/g), and KL is the Langmuir adsorption constant (L/mg) and is related to the free energy of adsorption. The constants qm and KL can be calculated from the intercept and the slope of the linear plot of Ce/qe versus Ce. The linear form of the Freundlich equation is: (Eq. (4)) log qe = logkF +

1 · logCe n


where Kf and 1/n are characteristic constants representing t adsorption capacity and the adsorption intensity of the system respectively. The values of Kf and 1/n are obtained from the linear plot of log qe versus log Ce. Temkin isotherm takes into account adsorbate–adsorbent interactions and assumes that fall in the heat of adsorption is linear rather than logarithmic, as implied in Freundlich equation. The linear form of Temkin relationship can be given as: (Eq. (5)) qe = B ln AT + B ln Ce


where B is constant related to the heat of sorption (J/mol) and AT is Temkin isotherm equilibrium binding constant (L/g). As implied in the equation, its derivation characterized by a uniform distribution of binding energies (up to some maximum binding energy) was fitted by plotting the quantity of sorbent qe against lnCe and the constants were determined from the slope and intercept. The adsorption capacity of the nano-ZnO/CT-CB composite beads spontaneously increased with an increase in the temperature of the system from 293 to 313 K. Thermodynamic parameters including enthalpy change (H◦ ), Gibbs free energy change (G◦ ) and entropy change (S◦ ) can be estimated by using equilibrium constants changing with temperature. According to thermodynamics, the distribution coefficient is related to the enthalpy change (H◦ ) and entropy change (S◦ ) at constant temperature (1/T) by the rearrangement of the Van’t Hoff equation: (Eq. (6)) ln Kd = (S o /R) − (H o /RT )


is the distribution coefficient (L kg−1 ), (S◦ ) is standard

where ln Kd entropy, (H◦ ) is standard enthalpy, T is the absolute temperature (K), R is gas constant (kJ mol−1 K−1 ). The standard free energy value is calculated from: (Eq. (7)) Go = H o − TS o

(7) (H◦ )

and entropy change (S◦ ) The values of enthalpy change were calculated from the slopes and intercepts of linear regression of lnK versus 1/T.

cles in the chitosan was given by SEM images at Fig. 2-b. The surface change in the SEM images of CT indicates the structural changes in the composite before and after the addition nano-ZnO. Nano-ZnO particles in chitosan were observed to be dispersed. Further, transmission electron microscopy (TEM) studies were performed to investigate the nano-ZnO/CT-CB in greater detail, and the results are shown in Fig. 2(c–f). Each nano-ZnO/CT-CB has nano-ZnO particles and the chitosan shell evenly encapsulating the core. TEM image of nano-ZnO/CT-CB sample reveals that number of chitosan–ZnO nanostructures presented within the scale of 50 nm (Fig. 2c–f), and the grain sizes are estimated to be in the range of 20–40 nm. The results obtained in this study are found to be in agreement with the study obtained by other researchers [27]. Thermal stabilities of the ZnO, CT and nano-ZnO/CT-CB have been determined by thermogravimetric studies. This technique reveals the loss of mass of a given substance during the heating process. Thermogravimetric analysis was used to characterize the thermal properties of CT and nano-ZnO/CT-CB and is shown Fig. 3-a. The all thermal decomposition profiles exhibited two main stages, with one starting at around 210 ◦ C and another at 300 ◦ C. The maximum mass loss observed around 300 ◦ C for CT (%40) and nano-ZnO/CT-CB (%29.5). Chitosan’s mass loss was higher than nano-ZnO/CT-CB at the high temperatures. The addition of nano-ZnO particles to chitosan usually made it more resistant to degradation when compared to the chitosan [28]. Fig. 3-b depicts the FTIR spectra of pure CT, nano-ZnO and nanoZnO/CT-CB. The FTIR spectrum of CT exhibits an adsorption band from 3600 to 3200 cm−1 due to OH and NH stretching vibration; at around 2830 cm−1 assigned to CH stretching vibrations in CH and CH2 . The pick at around 1653 cm−1 is due to the amino group bending vibrations in −NH2 .1077 cm−1 is due to C O C in the pyranose ring. Compared with pure CT membrane, a new broad absorption band in the range of 600–450 cm 1 was found in the FTIR spectra of nano-ZnO/CTS composite beads, which were ascribed to the vibration of O Zn O groups. The reason of the above phenomena was the formation of hydrogen bonds between nano-ZnO and chitosan [29]. Fig. 3-c represents the X-ray diffraction pattern of ZnO nanomaterial and further the structure of prepared nano-ZnO/CT-CB composite beads have been characterized by the XRD pattern. It is indicated in the reflecting planes in the patterns, which can be perfectly indexed as a hexagonal phase of ZnO and good agreement with the standard diffraction patterns (01-073-8765). Also, no diffraction peaks corresponding to Zn and other impurities are observed in these patterns.

3. Results and discussion

3.2. Effect of adsorbent dosage

3.1. Characterization of nano-ZnO/CT-CB

The effects of nano-ZnO/CT-CB mass quantity in the range of 0.05–0.2 g on the removal of the RB5 dyes are shown in Fig. 4. The percentage of RB5 removal increased by increasing the adsorbent mass from 67 to 76%. An increase in percentage of removal may be

SEM images of CT and nano-ZnO/CT-CB is shown in Fig. 2-a and b respectively. The direct evidence of the location of nano ZnO parti-


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Fig. 2. SEM (a–b) and TEM (c–f) images analysis of the nano-ZnO/CT-CB.

concluded due to the increase in the adsorbent surface areas and therefore more active functional groups resulting in the availability of more adsorption sites. The absorbance capacity decreased by increasing the amount of adsorbent (Fig. 4) due to the existence of the unsaturated adsorption sites during the adsorption process. In addition, the reduction in absorbance capacity may be due to particle aggregation, resulting from high adsorbent mass. Such aggregation would lead to a decrease in total surface area of the adsorbent and an increase in diffusional path length [30].

3.3. Effect of contact time As can be seen in Fig. 5 RB5 removal yield increased with time until reaching a constant value after 360 min for nano-ZnOchitosan composite beads. Initially, the adsorption of dyes was found to be rapid and then became slow with increased contact time, before reaching equilibrium. These data indicate that adsorp-

tion started immediately upon adding the nano-ZnO-CT-CB to dye solutions. The removal efficiency of RB 5 reached 77.1% after 3 h.

3.4. Effect of pH The influence of solution pH was considered as an important parameter in the adsorption process especially in aqueous solutions. The solution pH can affect the surface charge of the adsorbent and the dissociation of functional groups on the active sites of the adsorbent as well as the structure of the dye molecule. The maximum dye removal efficiency was achieved at the lowest pH values as illustrated in Fig. 6. In acidic conditions, enhancement of adsorption performance can be due to an increase in positive charged sites, which favors the adsorption of anions with electrostatic attractions [31]. The process behavior may become different by varying pH. From Fig. 6 there was the maximum of dye removal (%78) at pH 4. As can

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Fig. 3. TGA (a), FTIR (b) and XRD (c) analysis of the nano-ZnO/CT-CB.





Dye Removal (%)










Dye Removal %

Dye Adsorpon (mg/g)

Dye Adsorpon (mg/g)

66 0


0.1 0.15 Amount of Adsorbent (g)



Fig. 4. Effect of adsorbent dosage on the removal of RB5 by nano-ZnO/CT-CB (for 20 ppm dye concentrarion and 180 min).

be seen from the plot, at low pH the RB5 percentage removal is higher and the maximum removal occurs at pH values of 4.0.

nature of adsorption process. As shown in Table 1, with increasing temperature, there was more efficient adsorption of RB5. 3.6. Adsorption isotherms

3.5. Adsorption thermodynamics The effect of temperature on the sorption of RB 5 onto nanoZnO/CT-CB was studied by performing the adsorption experiments at different temperature (293–313 K). The positive value of H◦ is suggestive of an endothermic nature which favors the adsorption of the RB5 at higher temperature. The positive value of entropy (S◦ ) is suggestive of higher randomness of adsorption in the system and favors the stability of the adsorption. The negative values of G◦ for these processes confirm the feasibility and spontaneous

The adsorption isotherm is essential in understanding the mechanism of adsorption. Important information can be interpreted Table 1 Thermodynamic parameters for removal of RB 5 by nano-ZnO/CT-CB (r2 : 0,99).

RB 5

H◦ (kj mol−1 )

S◦ (jK−1 mol−1 )



G◦ (kj mol−1 ) 293 K

303 K

313 K





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Table 2 Equilibrium isotherm parameters of removal of RB 5 by nano-ZnO/CT-CB (for 313 K). Langmuir



qm (mg g−1 )

KL (L mg−1 )


KF (mg g−1 )

n (gr L−1 )


B (J mol−1 )

AT (L g−1 )













90 10



60 Ce/qe

Dye Adsorpon (%)


50 40

y = 5.2786x + 0.6437 R² = 0.9896

6 4

30 20


10 0 0









0 0



Time (min) Fig. 5. Effect of contact time on the removal of RB5 by nano-ZnO/CT-CB.

based on the adsorption isotherm regarding how the adsorbate molecules distribute between the liquid phase and the solid phase. To evaluate the maximum adsorption capacities, the adsorption isotherm experiments were carried out with varied initial concentrations of RB 5 at pH = 4.0 ± 0.1. The Langmuir, Freundlich and Temkin adsorption models were used to simulate the experimental data of the dye removal on nano-ZnO/CT-CB. It is found that the Langmuir model is more suitable to simulate RB 5 adsorption than the Freundlich model. The equations and parameters of the Langmuir, Freundlich and Temkin adsorption models are listed in Table 2 where the maximum adsorption capacities of RB5 at pH 4.0 and 40 ◦ C are 189.44 mg/g. The correlation coefficient of the Langmuir model for RB5 is about 0.9896, which are consistent with the simulations in Fig. 7. Langmuir, Freundlich and Temkin constants and the coefficient of determination, R, were calculated according to Eqs. (3–6) and the results were listed in Table 2. According to Langmuir, the maximum adsorption capacity was 189.44 mg g−1 for RB5. Freundlich isotherm parameters fits (Table 2) for RB5 removal of nano-ZnO/CTCB yielded isotherms that were in good agreement with observed behavior (R2 ≥0.86 for RB5). Values of Kf and n for RB5 was found to be 9.04 mg g−1 and 3.48; respectively. The Temkin constants are shown in Table 2. Values of AT and B for RB5 was found to be:



Ce (mg/L) Fig. 7. Langmuir isotherm for RB5 adsorption onto nano-ZnO/CT-CB. Table 3 Comparison of adsorption capacity of the nano-ZnO/CT-CB with other adsorbents for RB 5 removal. Adsorbent

Optimum pH

Qm (mg/g)


Chitosan hydrogel beads Silica-polyacrylamide composite Active carbon F400 Pumice AC from walnut wood SiO2 Bone char nano-ZnO/CT-CB

4 2 – 5 5 – – 4

201.90 454.54 176 12.85 19.34 0.67 160 189.44

[32] [33] [34] [35] [35] [36] [37] In this study

160 Lg−1 and 30.1 J mol−1 , respectively, which is an indication of the heat of sorption indicating a physical adsorption process. Accordings to these results, the nano-ZnO/CT-CB can be effectively used for RB5 removal from aqueous solution. The maximum adsorption capacity of other adsorbents investigated for the removal of RB5, as reported in literature are listed in Table 3. Essentially, nano-ZnO/CT-CB shows very good sorption performance for RB5 in comparison with other adsorbents (Active carbon F400, Pumice, AC from walnut wood, SiO2 , bone char) reported in literature (34–37). Also, the advantages of the method are that it has a low cost method of manufacturing high quality capacity and easy to made nano-ZnO/CT-CB. Obtained results in this study will be helpful to improve the adsorbents characteristics and performance by different surface modification such as metal impregnation. In addition nano-ZnO/CT-CB will be useful in analyzing the different mechanisms involved in the uptake process of RB5. 4. Conclusion

Fig. 6. Effect of pH on the adsorption of RB5 by nano-ZnO/CT-CB (C0 = 60 mg L1, adsorbent mass = 0.2 g, temperature 40 ◦ C).

In this study, nano-ZnO/CT-CB were used for the removal of Reactive Black 5 (RB 5) from aqueous solution. The nano-ZnO/CTCB were characterized by SEM, TEM, FTIR, TGA and XRD analysis. RB5 was selected as a model dye to examine the adsorption behavior of the composites. Amounts of 76.0% of RB 5 were adsorbed within 180 min from 25 mg L−1 RB5 solutions at pH = 4.0 by 0.2 g adsorbent dosage. The adsorption process was examined by three adsorption isotherms: Langmuir, Freundlich and Temkin isotherms. The equilibrium adsorption isotherm studies

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