Removing Trypan blue dye using nano-Zn modified Luffa sponge

SAA-14638; No of Pages 7 Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2016) xxx–xxx

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Removing Trypan blue dye using nano-Zn modified Luffa sponge Hayrunnisa Nadaroglu a,b,⁎, Semra Cicek b,c, Azize Alayli Gungor b,d a

Ataturk University, Erzurum Vocational Training School, Department of Food Technology, 25240 Erzurum, Turkey Ataturk University, Faculty of Engineering, Department of Nano-Science and Nano-Engineering, 25240 Erzurum, Turkey c Ataturk University, Faculty of Agriculture, Department of Agricultural Biotechnology, 25240 Erzurum, Turkey d Ataturk University, Erzurum Vocational Training School, Department of Chemical Technology, 25240 Erzurum, Turkey b

a r t i c l e

i n f o

Article history: Received 7 December 2015 Received in revised form 19 August 2016 Accepted 26 August 2016 Available online xxxx Keywords: Luffa sponge Zinc nanoparticles Green synthesis Trypan blue dye

a b s t r a c t This study has presented specific features that are examined to remove the Trypan blue dye from the waste using Luffa sponge (LS) and modified Luffa sponge with zinc nanoparticles (ZnNPs). Peroxidase enzyme was obtained from Euphorbia amygdaloides plant and it was used with the green synthesis of Zn nanoparticles. Luffa sponge was used to be a support material for immobilized nanoparticles and it also used in remediation work. The obtained membrane forms, fibrous materials, (LS, ZnNPs-LS) were characterized with SEM and XRD. LS and ZnNPs-LS were employed as adsorbent to be used for the removal of Trypan blue dye from aqueous via batch studies. Measurements were made for the equilibrium, pH, temperature, concentration of dye with UV–visible spectrometer (590 nm; for Trypan blue dye). The optimum removal of Trypan blue dye was found at pH 7, the equilibrium was attained within 30 min. The thermodynamic properties ΔG0, ΔH 0, and ΔS0 showed that adsorption of Trypan blue dye onto LS and ZnNPs-LS were spontaneous and endothermic. The equilibrium isotherm data were analyzed using Langmuir and Freundlich models and the sorption process was described by the Langmuir isotherm with maximum monolayer adsorption capacity of 45.32 and 47.3 mg/g for LS and LS-ZnNPs at 303 ± 1 °K, respectively. © 2016 Published by Elsevier B.V.

1. Introduction Nanoparticles are a general name given to unit changing sizes ranged from 0.1 nm to 100 nm. Nanoparticles have great benefits in many areas with their great surface areas. They consent to both increasing the capability and reducing the procedure time appreciations to their great surface area/mass ratio mainly related to surface such as adsorption [1,2]. Recently, the number of studies investigating production use of nanoparticles in water remediation has been increasing progressively [3–6]. Possible presentations of zinc nanomaterials contain nanolasers, solar cells, gas sensors, optoelectronics, antibacterial products, coating and paints, and health-related applications [7]. ZnO nanoparticles (ZnO NPs) with their great visual, influential adsorption, piezoelectric belongings and catalytic action are among nanoparticles explored the accessibility of water remediation studies [8,9]. There are numerous methods such as template-assisted, sol–gel, sonochemical, aerosol, thermal decomposition and laser exposer to be used for the production of metal nanoparticles. These procedures

⁎ Corresponding author at: Atatürk University, Department of Food Technology, Erzurum Vocational Training School, 25240 Erzurum, Turkey. E-mail address: [email protected] (H. Nadaroglu).

regularly required several processing steps, well-ordered temperature, pressure, pH and contaminated chemicals. Also these methods produce numerous by-products that are poisonous to the environment. Therefore, in this study, it has been aimed to synthesize ZnNPs, perform an enzymatical production of ZnNPs and use these NPs [7]. Treatment of nanoparticles without being immobilized on a support material for removal of azo dyes from water comes with pollution and contrary effects (AgNPs due to antimicrobial activity eliminate of balance of microbial flora, the increase of nanoparticles in water, etc.). Consequently, use of immobilization materials in water remediation works to be done with use of nanoparticle is vital to eliminate these difficulties. Luffa sponge (Luffa aegyptica Mill syn. L. cylindrica) is one of the organic tools which is suitable for ecological and commercial relationships. Fibro-vascular (venous) reticulated configuration including open form web of random cross-section of thin birdcage by very high permeability (79–93%), has very low bulk (0.02–0.04 g/cm3) and high specific hole capacity (21–29 cm3/g), and it is an appropriate transporter ZnNPs immobilization. Luffa sponge is particularly lightweight, it has total specific gravity of 0.92 g/cm3, the surface space of 850 m2/m3, 92% void volume and has recyclability and biodegradability [10–12]. The number of studies conducted on Luffa sponge is increasing due to its properties (low cost, light weight, etc.). These researches have presented that it can be used as an alternate material for packaging and water absorption [13–14], wastewater usage [12,15].

http://dx.doi.org/10.1016/j.saa.2016.08.052 1386-1425/© 2016 Published by Elsevier B.V.

Please cite this article as: H. Nadaroglu, et al., Removing Trypan blue dye using nano-Zn modified Luffa sponge, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2016), http://dx.doi.org/10.1016/j.saa.2016.08.052

2

H. Nadaroglu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2016) xxx–xxx

or 0.1 M of NaOH. All the chemicals used had analytical grade without any further purification. Distillated water was used for all the tests performed (GFL 2004).

Table 1 General characteristics of Tripan blue dye. Tripan blue (TB) Chemical formula Chemical structure

Molar mass (g mol−1) λmax (nm)

C34H24N6O14S4Na4

2.2. Zn NPs synthesis

960.81 607

Industrial events organized to improve the existing standards of mankind have also affected the environment and indirectly the living creatures. Increasing use of azo dyes in numerous industries (health, cosmetics, textiles, leather, plastics, etc.) has led to growing problem of azo dyes of resulting wastewater. Trypan Blue is one of these azo dyes used for the preparation of color staining solutions, staining histological sample materials of human origin, e.g. (Table 1). Release of this wastewater without treatment negatively affect the visual appearance of water resources, destructs the aquatic lifecycle, and results in serious problems such as carcinogenicity and toxicology in human lives [16–19]. Consequently, remediation mechanisms of water quality are one of the main requirements for human lives and these mechanisms have great significance all around the world. In this study, it was investigated that Luffa Sponge (LS) and Luffa Sponge with modified nano zinc (ZnNPs) for the removal of Trypan blue dye from water. ZnO nanoparticles were obtained by using peroxidase enzyme from Euphorbia amygdaloides plants. Two membrane forms (native-LS, ZnNPs-LS) were obtained with Luffa sponge that was used as a support material. It is a significant application, which immobilized nanoparticles that were used in the remediation works as a support material for avoidance of the second contamination in relation with environmental contamination. It has been aimed to demonstrate the effective membrane form for removed of Trypan blue azo dye from water.

Zn NPs was obtained by green synthesis. The method reported by Gungor et al., [20] was used for the peroxidase enzyme from Euphorbia (Euphorbia amygdaloides). The peroxidase enzymes were used to reduce from ZnCl2 to Zn NPs [21]. The Zn NPs were characterized with instrumental analysis [22]. Then, Zn NPs obtained were immobilized on fiber of Luffa sponge and they were used in remediation studies for removing Trypan blue azo dye. Briefly, 0.25 g Luffa sponge was taken and added to 100 mL, 100 ppm ZnO NPs solution. And, this mixture was incubated in the ultrasonic bath during 30 min. Then, LS was separated and the filtrate was lyophilized applying vacuum and the amount of linked ZnO NPs onto LS was calculated. Obtained LS was used all removal of TB process. 2.3. Collection and preparation of Luffa sponge TB dye was removed from aqueous solution using the Luffa sponge modified with Zn nanoparticles. Luffa sponge, which is fruit of Luffa cylindrical, was obtained from a local spice store in Erzurum, Turkey and it was identified with the help of taxonomists. Dried Luffa sponge material was cut into small pieces and was autoclaved for 20 min to soften the fibrous structure. Then, it was transformed into dough using blender. The dough was incubated for 4 h with 1 N NaOH at 80 °C. Then, the fibers were collected and were thoroughly washed with distilled water until NaOH was resolved. 0.1% hypochlorite was used for decoloration of washed fibers and then, they were washed with distilled water removal process. Fibers that have a length of 10–50 μm were collected and dispersed with distilled water to form a suspension form. The suspension was filtered under aseptic conditions using filter paper and Luffa sponge fibers were dried on filter paper at 40 °C for 4 h [23]. The Luffa sponge modified with Zn nano-particles was used for removal of TB dye from aqueous solution.

2. Experimental 2.4. Adsorption study 2.1. Chemicals and reagents CH3COONa, NaHCO3, Na2HPO4, ZnCl2 and Trypan blue dye were purchased from Sigma-Aldrich. The chemical properties of TB are summarized in Table 1. The pH of the solution was adjusted as 0.1 M of HCl

Synthetic wastewater was prepared by dissolving TB dye. A calibration curve was prepared in within the range 0–40 ng/cm3 of TB dye. The reaction mixture was prepared by adding LS-ZnNPs into flasks containing 50 mL of TB dye solution. The samples were taken out from the flasks

Fig. 1. The SEM images of LS-Zn-NPs (A) and loaded LS-Zn-NPs with TB dye (B).

Please cite this article as: H. Nadaroglu, et al., Removing Trypan blue dye using nano-Zn modified Luffa sponge, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2016), http://dx.doi.org/10.1016/j.saa.2016.08.052

H. Nadaroglu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2016) xxx–xxx

60

002

Lufaa s.

40

101101 A

30000

B

040 (100)

20000

C

qe (mg/L)

40000

10000

20

0

0 10

20

30

40

50

60

0

70

10

20 30 40 Contact time (min)

2θ

Fig. 2. XRD pattern of (A) LS and (B) LS-Zn-NPs and (C) loaded LS-Zn-NPs with TB dye.

periodically with a micropipette and were centrifuged at 5000 rpm for 10 min. The supernatant solutions were filtered with 0.45 μm filters. Then, the concentration of TB was measured with a UV/VIS spectrophotometer (Epoch Nanodrop spectrophotometer) at λ = 590 nm. Amounts of the dyes adsorbed onto LS or LS-ZnNPs (qe in mg/g) were calculated from the equation: qe ¼

Lufaa s.+Zn

50000

(002)

Relative Intensity (a.u.)

60000

3

ðC o −C e Þ  V m

ð1Þ

where, Co and Ce are the initial and equilibrium concentrations of dye in solution (mg/L); V is the volume of solution (L) and m is the mass of adsorbent (g). 2.5. Material (ZnNPs-LS and ZnNPs-LS-TB) characterization Scanning electron microscopy (SEM) was used to examine the surface of the adsorbents before and after dye adsorption (JEOL JSM-6400 SEM). Before SEM examinations, the surface of samples was coated with a thin layer (20 nm) of gold to obtain a conductive surface and to avoid electrostatic charging during examination. 3. Results and discussion 3.1. SEM and XRD analysis The SEM images of LS-ZnNPs and dye-loaded LS-ZnNPs were shown in Fig. 1A and B. The LS-ZnNPs displays rough, fibrous and porous surface, which is one of the factors increasing adsorption capacity (Fig. 1A). After adsorption, the surface has become smoother (Fig. 2B). 60

Luffa s

50

60

Fig. 4. Effect of contact time on adsorption of TB by the LS and LS-ZnNPs (initial TB concentration: 1 mg/mL, adsorbent dose: 1 g/50 mL, stirring speed: 500 rpm temperature: 303 ± 1 K).

This is suggesting that upon adsorption of the Trypan blue dye (TB), the surface morphology of adsorbent structure has been changed [24]. Initially, ZnNPs were seen on fiber of LS presented in Fig. 1A. After applying TB dye, most of them contact to fiber of LS modified with ZnNPs (B). This can be clearly seen from Fig. 1A and B. XRD shows the decrease of the peak intensity of LS-ZnNPs phase in case of colored LS-ZnNPs indicates that the removal process is mainly accompanied by an adsorption reaction which occurred between the dye molecules and the dissolved portion of the LS-ZnNPs (Fig. 2). The ZnNPs modified LS display the typical XRD pattern of cellulose as shown in Fig. 2 with main diffraction signals at 2θ = 14.43°, 16.4°, 22.19° and 33.69° assigned to (101), (101), (002) and (040) diffraction planes, respectively [25]. The diffraction peaks located at 30.36° and 34.77° have been keenly indexed as hexagonal wurtzite phase of ZnO NPs. After TB dye removal using LS-ZnNPs no significant alteration of the XRD Luffa sponge pattern can be noted suggesting that the reaction occurred predominantly on the surface without affecting in a great extent the internal structure of the material. 3.2. Effect of pH The pH of the solution is an important factor in the adsorption process because it affects the surface charge of the adsorbent and the degree of ionization and the specificity of the adsorbate [26]. In order to establish the influence of pH on the adsorption of the dye, batch equilibrium studies were conducted at pH 3–10 and the results are presented in Fig. 3. The pH significantly affected the adsorption of TB onto LSZnNPs at neutral pHs. Maximum removal occurred was observed at pH 7.0 for LS and LS-ZnNPs adsorbents. 60

Luffa s. + Zn

Luffa s.

Luffa s. + Zn

40

qe (mg/L)

qe (mg/g)

50

30 20

40

20

10

0

0 3

5

7 pH

9

11

Fig. 3. Adsorption of TB on LS and LS-Zn-NPs at different pH values (TB concentration: 1 mg/mL, adsorbent dose: 1 g/50 mL, stirring speed: 500 rpm, temperature: 293 ± 1 K).

10

30

50 Temperature (oC)

70

90

Fig. 5. Effect of temperature on TB dye adsorption by the original LS and LS-ZnNPs (initial TB concentration: 1 mg/mL, adsorbent dose: 1 g/50 mL, stirring speed: 500 rpm).

Please cite this article as: H. Nadaroglu, et al., Removing Trypan blue dye using nano-Zn modified Luffa sponge, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2016), http://dx.doi.org/10.1016/j.saa.2016.08.052

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60

Luffa

Table 2 Langmuir and the Freundlich constants for the adsorption isotherms.

Luffa s. + Zn

Langmuir adsorption model

qe(mg/L)

40

20

0 1E-15 0.2 0.4 Adsorbent dosage (g)

-0.2

0.6

LS

LS-ZnNPs

Freundlich constants

LS

LS-ZnNPs

qmax (mg/g) b (L/mg) R2

114.94 0.999 0.9977

129.87 0.999 0.9993

KF (mg/g) n R2

38.16 3.17 0.9756

7.81 0.930 0.9686

equilibrium of 30 min was 45.32 and 47.3 mg/g for LS and LSZnNPs, respectively. 3.4. Effect of temperature

Fig. 6. Influence of adsorbent dosage on the adsorption of TB dye on LS and LS-ZnNPs (initial dye concentration: 1 mg/mL, stirring speed: 500 rpm, temperature: 303 ± 1 °K).

LS-ZnNPs have almost completely removed TB from wastewater. Furthermore, LS-ZnNPs were more efficient adsorbents than the original LS. High adsorption rates for TB were observed at neutral pH values on LS and LS-ZnNPs. In the surface of LS and LS-ZnNPs, ionic changes which was occurred in acidic or basic pHs could make steric shielding for removal of TB. So, it was considered that the highest amount removal of TB was occurred in neutral pH. It is suggested that \\OH groups in the surface of LS and LS-ZnNPs interacted with NH\\, \\OH and S\\ of dye molecules thereby increased the amount of dye adsorbed [27,28].

3.3. Equilibrium time The equilibrium time between adsorbent and adsorbate species is significant for the removal of pollutants from water and wastewater by means of adsorption at a particular temperature and pH. Fast removal of dye pollutants and establishment of equilibrium in a short period of time signifies the efficiency of the adsorbent for its use in wastewater treatment [28]. For determination of the optimum contact time, samples were spectrophotometrically measured between 0 and 60 min with 15 min intervals and the results are shown in Fig. 4. The adsorption capacity of the LS and LS-ZnNPs for TB dye increased considerably during the initial adsorption stage and then, it was continued to increase at a relatively slow rate with contact time until equilibrium was established after 30 min. This suggests that a large number of sites were available for adsorption at the initial stage, and after a lapse of time, the remaining sites were not easily accessible due to repulsive forces between solute molecules on the solid and bulk phases [29]. The maximum adsorption efficiency of TB dye at

1

Freundlich adsorption model

Langmuir constants

Temperature affects the adsorption rate by modifying the molecular interactions and the solubility of adsorbate [30]. In order to observe the effect of temperature on the adsorption of TB onto LS and LS-ZnNPs batch, adsorption experiments were conducted within the range from 10 to 80 °C (Fig. 5). Maximum adsorption of TB dye was observed at 20 °C as 45.3 and 48.95 mg/mL for LS and LSZnNPs, respectively. 3.5. Effect of adsorbent dosage The adsorbent dose determines the capacity of adsorbent for a given initial concentration of dye solution [31]. The effect of adsorbent dose on the dye removal is shown in Fig. 6. Initially, dye adsorption was very fast and then slowly reached equilibrium point. The maximum amount of TB removal attained with an adsorbent dose of 1 g/L was 45.6 and 49.8 mg/g for LS and LS-ZnNPs, respectively. Adsorption of TB was increased with the increase in the amount of mesoporous adsorbent and remained almost constant up to a certain limit. This can be attributed to increased adsorbent surface area and availability of additional adsorption sites [32–34]. 3.6. Adsorption isotherms 3.6.1. Langmuir adsorption isotherm model The Langmuir isotherm assumes that adsorption occurs at specific homogenous sites on the adsorbent. The linear form of the Langmuir isotherm equation is:

qe ¼

q max K L C e 1 þ K L  Ce

Luffa s.

ð2Þ

Luffa s.

6

Luffa s. + Zn

5

y = 0.3145x + 3.6418 R² = 0.9756

Ce/qe

lnqe

Luffa s. + Zn y = 0.0087x + 0.0722 R² = 0.9977

0.75

4 3

0.5

2

y = 0.0077x + 0.02 R² = 0.9993

1

0.25

y = 0.5698x + 2.0556 R² = 0.9686

0 -6

0 0

20

40

60

80

100

-4

-2

0 -1 lnCe

2

4

6

Ce Fig. 7. Langmuir isotherm model for the adsorption of TB on natural LS and LS-ZnNPs.

Fig. 8. Freundlich isotherm model for the adsorption of TB on natural LS and LS-ZnNPs.

Please cite this article as: H. Nadaroglu, et al., Removing Trypan blue dye using nano-Zn modified Luffa sponge, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2016), http://dx.doi.org/10.1016/j.saa.2016.08.052

H. Nadaroglu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy xxx (2016) xxx–xxx 10 mg/L (Luffa s.) -(R2:0,9191)

10 mg/L (Luffa s.) -(R2:0,983) 25 mg/L (Luffa s.)-(R2:0,9916) 50 mg/L (Luffa s.)-(R2:0,9781) 10 mg/L (Luffa s. + Zn)-(R2:0,9241) 25 mg/L (Luffa s. + Zn)-(R2:0,9916) 50 mg/L (Luffa s. + Zn)-(R2:0,8266)

4

3

5

25 mg/L (Luffa s.)-(R2:0,9937)

10

50 mg/L (Luffa s.)-(R2:0,9718) 10 mg/L (Luffa s. + Zn)-(R2:0,9583) 8

25 mg/L (Luffa s. + Zn)-(R2:0,9975) 50 mg/L (Luffa s. + Zn)-(R2:0,9843)

2

t/qt

log (qe-qt)

6

4

1 2

0

0 0

20

40

60

0

80

10

20

30 40 Time (Min)

50

60

70

Time (Min)

-1

Fig. 10. Pseudo-second-order reaction for TB dye adsorption onto LS and LS-ZnNPs adsorbents at different concentrations. Fig. 9. Pseudo-first-order model for TB adsorption onto LS and LS-ZnNPs at different concentrations.

where, qmax (mg/g) is the maximum adsorption capacity and KL is Langmuir adsorption constant. They are determined from the linear form of Eq. (2): Ce 1 1 ¼ þ Ce qe q max  K L q max

ð3Þ

Dye concentration varied from 10 mg/L to 200 mg/L. The values of Q max and b were calculated from the slope and the intercept of the plot of Ce versus Ce/Q e (Fig. 7) and the Langmuir parameters are presented in Table 2. The isotherm was linear throughout the entire concentration range examined and it has given high coefficients of determination (R2 = 0.9977 and 0.9993 for LS and LS-ZnNPs, respectively), suggesting that the Langmuir model adequately fits the data in both cases. 3.6.2. Freundlich adsorption isotherm model The Freundlich isotherm model is an empirical relationship describing the adsorption of solutes from a liquid to a solid surface, which assumes that adsorption sites with different adsorption energies are involved. It is described by the following equation: q max ¼ K F C e 1=n

ð4Þ

where, KF is the empirical Freundlich constants related to the absorption capacity of the adsorbent (mg/g) and n is the energy of adsorption. They can be calculated from the linear form of Eq. (2):

lnqe ¼ ln K F þ

1 ln C e n

ð5Þ

KF and n values were calculated from the intercept and slope of the Freundlich plot (Fig. 8). The calculated values of the Freundlich parameters are listed in Table 2. The corresponding R2 for the adsorption of TB onto LS and LS-ZnNPs adsorbents were 0.9686 and 0.9756, respectively showing that the Freundlich model adequately fits the data in both cases. The Langmuir and Freundlich isotherm models describe the equilibrium adsorption of TB onto LS and LS-ZnNPs sufficiently. These models show that the adsorption process is the monolayer coverage of the dye on the surface of both materials [35]. 3.6.3. The pseudo-first-order kinetic model The linear form of pseudo-first-order kinetic model can be written as [36]: logðqe −qt Þ ¼ logqe −

1 k1 t ¼ qt 2; 303

ð6Þ

where, k1 is the pseudo-first-order rate constant (min−1) and qt and qe are the amounts of dye adsorbed at time t and at equilibrium (mg/g), respectively. At different dye concentrations, the correlation coefficients and the k1 values were calculated for dye adsorption from the linear plots of log (qe − qt) versus t for the original clinoptilolite and LMC (Fig. 9). For the pseudo-first-order model, the coefficients of determination (R2) for LS and LS-Zn-NPs adsorbents ranged from 0.9781 to 0.9916 and from 0.8266 to 0.9941, respectively (Table 3). The high R2 values suggest that the pseudo-first-order model sufficiently describes the TB removal by both LS and LS-ZnNPs. 3.6.4. The pseudo-second-order kinetic model The linear form of the pseudo-second-order kinetic model is [36]: t 1 t ¼ þ qt k2 qe 2 qe

ð7Þ

Table 3 Inetic parameters for the adsorption of TB on LS and LS-ZnNPs. Pseudo-first-order rate equation

Pseudo-second-order rate equation k2

qe-cal (mg/g)

R2

0.9830 0.9916 0.9781

2.99.10−3 4.40.10−2 3.25.10−4

8.62 20.49 44.33

0.9191 0.9937 0.9718

0.9241 0.9916 0.8266

4.46.10−3 1.40.10−3 7.16.10−4

9.71 24.09 46.91

0.9583 0.9975 0.9843

Initial TB concentration (mg/L)

qe-exp (mg/g)

k1

qe-cal (mg/g)

R

LS 10 25 50

9.42 16.20 41.50

3.56.10−2 2.97.10−2 2.99.10−2

9.270 14.30 40.65

LS-ZnNPs 10 25 50

9.48 18.60 48.10

3.40.10−2 3.29.10−2 3.67.10−2

9.11 17.48 47.44

2

Please cite this article as: H. Nadaroglu, et al., Removing Trypan blue dye using nano-Zn modified Luffa sponge, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2016), http://dx.doi.org/10.1016/j.saa.2016.08.052

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at equilibrium (mg/L), T is the temperature (°K), and R is the gas constant. The influence of temperature on the thermodynamics of TB adsorption by LS and LS-ZnNPs adsorbents is illustrated in Fig. 11, and the thermodynamic parameters are listed in Table 4. The positive value of ΔG0 suggests that the adsorption of TB was not spontaneous within the range of temperatures studied and the adsorption requires energy to convert reactants into products [37]. The negative values of ΔH0 further confirm the exothermic nature of the adsorption and the negative ΔS0 values suggest an increase in adsorbate concentration in the solid-liquid interface there by indicating an increase in adsorbate concentration onto the solid phase. It also confirms the increased randomness at the solid-liquid interface during adsorption. This is the normal consequence of the physical adsorption process, which takes place through electrostatic interactions [37].

Luffa s.

4.5

Luffa s. + Zn

y = 7830.2x - 22.843 R² = 0.9931

ln KL

3 y = 7690.5x - 23.971 R² = 0.9998 1.5

0 3.15E-033.20E-033.25E-033.30E-033.35E-033.40E-033.45E-03 1/T Fig. 11. Influence of temperature on the thermodynamics of adsorption of TB dye.

where, k2 is the equilibrium rate constant of the pseudo-second-order model (g mol−1 min−1). This equation has been applied to the present study. At different dye concentrations, the correlation coefficients, qe and k2 for dye adsorption on the clinoptilolite and LMC were calculated from the linear plots of t/qt versus t (Fig. 10). For the pseudo-secondorder models, the coefficient of determination (R2) values range from 0.9191 to 0.9718 and from 0.9583 to 0.9843 for the natural LS and LSZnNPs adsorbents, respectively. The high R2 values suggest that the pseudo-second-order model also sufficiently describes TB removal by natural LS and LS-Zn-NPs. The R2 values of the pseudo-second-order model are closer to unity and the Q e values calculated from the pseudo-second-order equation show very good agreement with experimental values. This indicates that the pseudo-second-order kinetic model is more suitable for adsorption of TB dye onto the natural LS and LS-ZnNPs adsorbents. 3.7. Adsorption thermodynamics It is necessary to consider the thermodynamic properties of the adsorption to infer if the process is spontaneous or not [36]. In this study, the adsorption capacity was increased with an increase in temperature from 293 K to 313 K. The change in free energy (ΔG0, kJ mol−1), enthalpy (ΔH0, kJ mol−1) and entropy (ΔS0, J/K mol) were determined from the following equations: KL ¼

Cs Ce

ð8Þ

ΔG0 ¼ RT 1n K L lnK L ¼

ΔS0 R

ð9Þ

! þ

ΔH 0 RT

! ð10Þ

where, KL is the equilibrium constant, Cs is the concentration of the solid phase at equilibrium (mg/L), Ce is the concentration of the liquid phase Table 4 Thermodynamic parameters for the RB5 adsorption on natural LS and LS-ZnNPs. Temperature (K)

Thermodynamic parameters ΔG0 (kJ mol−1)

ΔH0 (kJ mol−1)

ΔS0 (J mol−1)

LS 293 303 313

58.32 60.32 62.32

−63.94

−199.295

LS-ZnNPs 293 303 313

55.58 57.48 59.38

−65.1

−189.92

4. Conclusion In this study, the adsorption of TB dye by LS and LS-ZnNPs from aqueous solution was investigated in batch mode. The equilibrium data obtained by the Langmuir isotherm model had higher R2 value compared to the Freundlich isotherm model. The sorption process could be better described by the pseudo-second order kinetic model. The thermodynamic parameters ΔG0, ΔH0 and ΔS0 indicate nonspontaneous, exothermic adsorption of TB dye on LS from aqueous solutions. The results of the present investigation indicate that LSZnNPs, a low-cost adsorbent could be employed as an alternative to commercial adsorbents for removal of TB from aqueous solutions. Acknowledgments The SEM and FTIR study of this research was carried out in the Ataturk University, Faculty of Science, Department of Chemistry and XRD study of this research was carried out in Ataturk University, the Faculty of Engineering, and Department of Mechanical Engineering. So, the authors thank the Prof. Dr. Umit DEMIR and Prof. Dr. Yasar Totik, respectively. This research was performed under the project numbered 115Z810 and supported by the Scientific and Technical Research Council of Turkey (TUBITAK). The authors acknowledge the support of TUBITAK, Turkey for this work. References [1] S.R. Chowdhury, K.Y. Ernest, R.P. Allen, Arsenic removal from aqueous solutions by mixed magnetite-maghemite nanoparticles, Environ. Earth Sci. 64 (2) (2010) 411–423. [2] I. Percin, V. Karakoc, S. Akgol, E. Aksoz, A. Denizli, Poly(hydroxyethylcmethacrylate) based magnetic nanoparticles for plasmid DNA purification from Escherichia coli lysate, Mater. Sci. Eng. C 32 (2012) 1133–1140. [3] C. Su, R.W. Puls, T.A. Krug, M.T. Watling, S.K. O'Hara, J.W. Quinn, N.E. Ruiz, A two and half-year-performance evaluation of a field test on treatment ofsource zone tetrachloroethene and its chlorinated daughter products using emulsified zero valent iron nanoparticles, Water Res. 46 (2012) 5071–5084. [4] K. Choi, W. Lee, Enhanced degradation of trichloroethylene in nano-scalezero-valent iron Fenton system with Cu(II), J. Hazard. Mater. 211-212 (2012) 146–153. [5] S. Shirin, V.K. Balakrishnan, Using chemical reactivity to provide insightsinto environmental transformations of priority organic substances: the Fe0-mediated reduction of Acid Blue. 129, Environ. Sci. Technol. 45 (2011) 10369–10377. [6] S. Luo, P. Qin, J. Shao, L. Peng, Q. Zeng, J.D. Gu, Synthesis of reactive nanoscalezero valent iron using rectorite supports and its application for Orange II removal, Chem. Eng. J. 223 (2013) 1–7. [7] R. Raliya, J.C. Tarafdar, ZnO nanoparticle biosynthesis and its effect on phosphorousmobilizing enzyme secretion and gum contents in Clusterbean (Cyamopsis tetragonoloba L.), Agric. Res. 2 (1) (2013) 48–57. [8] D. Sharma, S. Sharma, B.S. Kaith, J. Rajput, M. Kaur, Synthesis of ZnO nanoparticles using surfactant free in-air and microwave method, Appl. Surf. Sci. 257 (2011) 9661–9672. [9] X. Wang, J. Lu, M. Xu, B. Xing, Sorption of pyrene by regular and nanoscaled metal oxide particles: influence of adsorbed organic matter, Environ. Sci. Technol. 42 (2008) 7267–7272. [10] M.J. John, S. Thomas, Biofibres and biocomposites, Carbohydr. Polym. 71 (2008) 343–364.

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Please cite this article as: H. Nadaroglu, et al., Removing Trypan blue dye using nano-Zn modified Luffa sponge, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2016), http://dx.doi.org/10.1016/j.saa.2016.08.052