GO decorated ZnO

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

Contents lists available at ScienceDirect

Journal of the Mechanical Behavior of Biomedical Materials journal homepage: www.elsevier.com/locate/jmbbm

Removal of hexavalent chromium by electrospun PAN/GO decorated ZnO M.M. Abdel-Mottaleb

a,∗∗

, Alaa Khalil

b,c,∗

d

, T.A. Osman , A. Khattab

T

d

a

Production Engineering and Printing Technology Department, Akhbar El-Youm Academy, 12655, Giza, Egypt Egypt Nanotechnology Center, EGNC, Cairo University, 12613, Giza, Egypt Mechanical Engineering Department, Candian International College, Fifth Settlement, New Cairo, Egypt d Mechanical Design and Production Engineering Department, Cairo University, 12613, Giza, Egypt b c

A R T I C LE I N FO

A B S T R A C T

Keywords: Adsorption Nanofibers Graphene oxide Zinc oxide Kinetics Electrospinning Hexavalent chromium

A novel composite nanofibers material have fabricated by using electrospinning technique followed by chemical cross-linking with zinc oxide (ZnO). The surface sensitization and morphology changes of the fabricated composite nanofibers were studied by using X-Ray Diffraction (XRD) analysis, Scanning Electron Microscopy (SEM) and transmission electron microscope (TEM). The effect of operating parameters includes the amount of ZnO, initial solution PH, and hexavalent chromium concentration on adsorption were investigated. The maximum adsorption capacity was found to be 690 mg/g at pH 6, which is much higher than most of the reported adsorbents. The adsorption equilibrium reached within 25 and 180 min as the initial solution concentration increased from 10 to 300 mg/L, and the data fitted well using nonlinear pseudo first order model with determination coefficient (R2) in between 0.97 and 0.99. Adsorption isotherms correlate the data on equilibrium adsorption with different mathematical models to describe the behaviour of an adsorption process and provide valuable information for optimizing the design of an adsorption system.

1. Introduction Industry is a huge source of water pollution, it produces pollutants that can lead to serious human and animal health problems as well as widespread destruction of the natural world (Abolhasani et al., 2017; Abdel-Mottaleb et al., 2019; Khalil et al., 2019). The removal of toxic contaminants has become a huge challenge for industrial and municipal wastewaters as the deterioration of global environment is increasing (Adeosun et al., 2015; Mohamed et al., 2016a; Yazdi et al., 2018; Kameda et al., 2011; Saleh and Gupta, 2014). Chromium occurs in the environment largely in two forms: trivalent chromium Cr(III), which is found in many vegetables, fruits, meats, grains, and yeast, and hexavalent chromium Cr(VI), which is the most toxic form of the element (Al-Sabahi et al., 2016; An et al., 2014; Saleh and Gupta, 2012; Gupta et al., 2011; Khani et al., 2010). Hexavalent chromium is genotoxic carcinogenic to humans and animals when its concentration is above 0.05 mg/l and can cause irritation and corrosion of human skin, metal finishing, textile industries, electroplating, dyeing, wood preservation, painting, fertilizing, and photographying (Asif et al., 2014; Saravanan et al., 2016; Ghaedi et al., 2015). A variety of approaches have been in use for the treatment of chromium containing wastewater, including ion exchange,

∗

photoreduction, chemical or electrochemical reduction, membrane filtration, precipitation, etc (Anirudhan and Deepa, 2017; Apul and Karanfil, 2015; Arenas et al., 2017; Rajendran et al., 2016). However, most of these experimental techniques need complicated instrumentation, large quantity of chemicals and also it can produce the secondary wastes during the removal process. For recent decades, the adsorption process shows many advantages, such as high efficiency, low cost, and effective for the treatment of Cr(VI) (Atchison and Schauer, 2011; Salama et al., 2017; Mohammadi et al., 2011). As one of the most promising adsorbent, zinc oxide (ZnO) has been successfully used in the pollutant degradation, removal of heavy metal ions and air purification (Atchudan et al., 2016; Barzegar et al., 2015; Aboamera et al., 2018; Saravanan et al., 2014). The high efficiency of ZnO in heterogeneous adsorption reaction requires a suitable architecture that minimizes electron loss during excitation state and maximizes photon absorption. In order to further improve the immigration of photo-induced charge carriers during excitation state, considerable effort has to be exerted for increasing hydroxyl groups on the surface of ZnO. Xu et al. (2017) reported that the ZnO–graphene composite improved adsorption performance of the organic dye as compared with pure ZnO. While graphene acts as an excellent electron-acceptor/ transport material to effectively facilitate the migration of photo-

Corresponding author. Membrane Technology Department, Institute of Functional Interfaces (IFG-MT), Karlsruhe Institute of Technology, 76344, Germany. Corresponding author. E-mail addresses: [email protected] (M.M. Abdel-Mottaleb), [email protected] (A. Khalil).

∗∗

https://doi.org/10.1016/j.jmbbm.2019.06.025 Received 31 May 2019; Received in revised form 19 June 2019; Accepted 26 June 2019 Available online 27 June 2019 1751-6161/ © 2019 Elsevier Ltd. All rights reserved.

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

nanofibers to ZnO was carried out as follows: PAN/GO composite nanofibers was immersed into the crosslinking medium containing 2.5 wt. % Glutaraldehyde (GA), and kept shaking for 24 h at room temperature. After that washed and dried, then 2 ml of an aqueous dispersion of ZnO was added to the composite nanofibers and kept shaking for 24 h. The crosslinked composite nanofibers were washed out with deionized water and ethanol, and then dried. Glutaraldehyde, a bifunctional cross-linking reagent, was used for fixing primarily the surface of the fibers and creates a polymeric network that hinders the further crosslinking of the interstitium of the fibers. The concentration of Cr(VI) in the solution was measured using UV–vis/NIR spectrophotometer. Field emission scanning electron microscopy (SEM, FEI Quanta FEG 250, Czech Republic) was used to observe withdrawn fiber, and the average diameters of the fibers and Transmission Electron Microscopy (TEM, JEM-2100F, Joel USA, Inc) was used to study the structure of the fiber surface. X-ray diffraction (XRD, Bruker D8 Advance, USA) using a CuKα radiation (λ = 1.5406 Å) was used to study the crystal structure of the nanofibers.

induced electrons and hinder the charge recombination in electrontransfer processes due to the electronic interaction between ZnO and graphene, which enhances the adsorption performance of ZnO (Ghaedi et al., 2015; Gautam et al., 2016; Yousef et al., 2018). In this work, graphene oxide powder was selected and used not only to increase the surface area but also to enhance apparent quantum efficiency owing to their high aspect ratio and unique electrical properties. The objective of this work is to chemically crosslinking ZnO to electrospun PAN/GO nanofibers in order to increase the adsorption efficiency. The structure and functional groups of the dye determines the effectiveness of adsorption activity for the adsorption of Cr(VI) in aqueous solutions. The effect of operating parameters includes initial solution pH, the amount of ZnO, and Cr(VI) concentration on the adsorption reduction of Cr(VI) were investigated. Furthermore, the adsorption kinetics, isotherms, and thermodynamic were investigated by fitting the experimental data with different models. 2. Experimental 2.1. Materials

2.3. Adsorption of Cr(VI) experiments

Potassium dichromate (K2Cr2O7), Zink oxide (ZnO) with average particle size < 100 nm, Polyacrylonitrile (PAN), homopolymer, average molecular weight MW = 150,000. purchased from Sigma Aldrich. GA, Glitaric dialdehyde, 50% in water C5h8O2 liquid colorless to light yellow soluble in water soluble in benzene, ethanol and organic solvent science lab, Houston, Texas USA. N,N - dimethylformamide (DMF), Alfa Aser Co. Ltd., Massachusetts, USA. Graphene oxide powder (796034 Aldrich), 15–20 sheets, 4–10% edge-oxidized were brought from Sigma Aldrich Co. Ltd, Saint Louis, USA. pH of the solution was adjusted with Hydrochloric acid (HCl), disulfonic acid disodium salt.

The adsorption of Cr(VI) in aqueous solution experiments were performed in the laboratory by using 50 × 50 mm2 of PAN/GO–ZnO nanofibers placed into the beaker containing Cr(VI) solution (50 mL) in an incubated shaker with varying concentration from 10 to 300 ppm. The effect of ZnO loading, pH, time of shaking and initial concentration were studied by taking 2 mL of the dye solution from the reservoir at a fixed interval of time. The pH value of the dye solution was adjusted between 3 and 9 by the addition HCl solution. The adsorption of the Cr (VI) was measured using a UV–vis/NIR spectrophotometer. The equilibrium adsorption capacity (qe) was calculated using equation (1), while the Cr(VI) removal percentage was determined using equation (2).

2.2. Preparation and characterization of photocatalytic based nanofibers PAN powder was added into a DMF solvent with a weight ratio of 10 wt% and then stirred at 35 °C in a water bath to get the PAN electrospinning solution for 8 h. Then, 1 wt.% of GO was slowly dispersed to the PAN solution at 35 °C and stirring was continued for 24 h to ensure complete dissolution and then sonicated for 4 h (Karim et al., 2018). The dissolution also reduces the viscosity to a level at which spinning becomes possible. It has been proven that continuous and smooth fibers cannot be obtained in very low viscosity. The PAN/GO solutions were extruded using a syringe pump into a 3 ml plastic syringe. Adjusting the electrospinning parameters as follows: DC voltage of 25 kV, with a tip of the needle-collector distance of 15 cm and a feeding rate of 0.5 mL/h was applied to fabricate the photocatalytic based nanofibers (Aboamera et al., 2017). The crosslinking mechanism between PAN/GO composite

qe =

(c0 − ce ) × V m

(1)

c − ce ⎞ × 100 Cr(VI)removal% = ⎛ 0 ⎝ c0 ⎠ ⎜

⎟

(2)

Where, C0 is the initial chromium concentration (mg/L) and Ce is the chromium concentration in the aqueous solution at equilibrium (mg/L), V is the total aqueous volume (L), and m is the mass of the composite nanofibers (g). Thermodynamic parameters such as ΔH°, ΔS°, ΔG ° were also evaluated from equilibrium data. All experiments were duplicated to assure the consistency and reproducibility of the results.

Fig. 1. (A) TEM and (B) SEM of the adsorption based nanofibers PAN/GO–ZnO. 206

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

Fig. 2. XRD of PAN/GO and PAN/GO–ZnO nanofibers.

3. Results and discussion

Fig. 3. Effect of solution pH on the percentage adsorption of Cr(VI) for the PAN/GO-ZnO composite nano fibers at (Cr(VI) = 20 ppm, and 20 mg of ZnO content).

3.1. Characterization of nanocomposites Fig. 1a and b shows the TEM and SEM images of the fabricated fibers respectively. It is clearly observed in Fig. 1b that ZnO nanoparticles are well dispersed on the surface of nanofibers without forming apparent aggregation, which confirm that ZnO nanoparticles attached to the surface due to the crosslinking mechanism. Fig. 1a shows clearly that ZnO nanoparticles are well attached and decorated on the surface of graphene oxide. The morphology of PAN/GO-ZnO nanofibers as depicted in Fig. 1a and b shows clearly fine, smooth, and uniform composite nanofibers with an average diameter about 150 ± 10 nm. The X-ray diffraction XRD patterns of the PAN/GO and PAN/GOZnO composite nanofibers are shown in Fig. 2. In the diffraction pattern for both types of the photocatalytic based nanofibers GO exhibits a major diffraction peak centered at 2θ = 10.9° this peak was associated with the (002) facet of GO (Ferrari, 2007). The X-ray diffraction of PAN shows typical diffraction peaks at 2ϴ = 17° and 28°, respectively, corresponding to (100) and (110) planes of PAN (Kim et al., 2014). The spectrum of PAN/GO-ZnO exhibits several diffraction peak at 31°, 34°, 36°, and 56° crossbonding to (100), (002), (101), and (110) planes which confirms the presence of ZnO in the composite nanofibers (Sagadevan et al., 2017; Karim et al., 2019).

Fig. 4. Effect of ZnO loading on the percentage adsorption of Cr(VI) for the PAN/GO-ZnO composite nano fibers at (Cr(VI) = 20 ppm, and pH 6).

3.2. Effect of pH value on the adsorption performance

capacity is attributed to the larger surface area and more adsorption sites that introduced by increasing the number of adsorbent particles results in more metals attached with the weight of adsorbent increasing (Mohamed et al., 2019; Uheida et al., 2019). Addition of excess of ZnO above 25 mg did not significantly enhance the degradation as shown in Fig. 4. This is due to aggregation of ZnO particles, which reduce the interfacial area between Cr(VI) solution and fiber surface.

The pH level of the solution is an important factor affecting the adsorption performance of the PAN/GO-ZnO nanofibers (Choi et al., 2018; Salama et al., 2018). Therefore, the role of photocatalytic performance was examined at different pH conditions as shown in Fig. 3. It has been observed that the adsorption performance increases with the increase of pH exhibiting maximum rate of adsorption at pH 6 this can be explained by the present of the acidity medium (H+) in the solution which competes Cr(VI) active sites on the adsorbents surface thus lesser adsorption was observed (Mohamed et al., 2018). Maximum removal efficiency reached 82% at pH between 5 and 7.

3.4. Adsorption kinetics The adsorption kinetics is one of the most important characteristics that control and describe the adsorption efficiency (Fellahi et al., 2016). In the present work the kinetics of removal Cr(VI) from aqueous solution was carried out to study the adsorption behaviour and equilibrium time for the adsorption reaction of the prepared PAN/GO-ZnO composite nanofibers. The adsorption kinetics of the Cr(VI) was analyzed using two kinetic models, linear and nonlinear pseudo first order and pseudo second order kinetic model. The linear pseudo first order kinetic equation is expressed as following (Alipour et al., 2016; Mohamed et al., 2016b):

3.3. Effect of ZnO loading on the adsorption performance The amounts of Cr(VI) adsorbed by different amount of ZnO loading in the PAN/GO- ZnO composite nanofibers are shown in Fig. 4. It is obvious that there is a progressive gradually increase in adsorptions percentage of Cr(VI) with the increase of ZnO loading. With the increase of ZnO from 10 to 30 mg at pH 6 the adsorptions percentage of Cr (VI) increase from 60% to 98.8%. The initial increase in adsorption 207

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

dqt = k1 (qe − qt ) dt

(3)

Log-linearization version of Eq. (3):

log(qe − qt ) = log qe −

k1 t 2.303

(4)

Where qt and qe are the adsorption capacities (mg/g) of Cr(VI) at time t (min) and at equilibrium time, respectively, and k1 is the linear pseudo first order adsorption constant (min−1). The linear pseudo second order kinetic equation is expressed as following:

dqt = k2 (qe − qt )2 dt

(5)

Log-linearization version of Eq. (5):

t 1 1 = + t qt qe k2 qe2

(6)

Fig. 6. Nonlinear pseudo first order and second order for the adsorption of Cr (VI) using PAN/GO-ZnO (pH = 6 and temperature = 25°).

Where k2 is the linear pseudo-second-order rate constant of adsorption (mg/g). The nonlinear pseudo-first-order and second-order kinetic equation are expressed by Eqs. (7) and (8) respectively.

qt = qe (1 − e−k3 t )

qt =

qt = kid t 1/2 + c

Where C is the intercept and kid is the intra-particle diffusion rate constant (mg/g/min1/2), which can be fitted with the results as shown in Fig. 7. It can be observed that the intra-particle diffusion is involved from the linear trend between qt versus the square root of time (t 1/2 ). The adsorption plot of Cr(VI) lines pass through the origin concluded that intra-particle diffusion was rate the controlling step. As shown in Table 1 the intra-particle diffusion rate constant kid increase from 1.15 to 56.5 mg/g/min1/2 with the increase in initial concentration from 10 to 300 ppm indicates that composite nanofibers exhibits fast removal of Cr(VI) from aqueous solutions. The adsorption kinetics constants, determination coefficient values (R2), and the theoretical value of adsorption capacity at equilibrium time qe are given in Table 1 for all adsorption kinetics models. The experimental data fitted well into the nonlinear pseudo first order model with determination coefficient (R2) in between 0.97 and 0.99. Also, the theoretical value qe,cal was very close to the experimental results in all Cr(VI) concentration experiments. Therefore, it can be concluded from these results that the nonlinear pseudo first order model is applicable for the adsorption process (Mohamed et al., 2017a).

(7)

k 4 qe2 t 1 + k 4 qe t

(9)

(8)

Where k3 is the rate constant of nonlinear pseudo first order adsorption (min−1), and k 4 is the rate constant of nonlinear pseudo second order rate constant (g/mg min). The linear and nonlinear pseudo-first-order and pseudo-second-order kinetic are shown in Fig. 5 and 6 respectively. It is obvious from Figs. 5 and 6 that pseudo first order equations expressed a poor connection to experimental data on the other hand pseudo second order equations expressed a good connection to the experimental results as shown in Table 1. As shown in Fig. 6 that the Cr(VI) adsorption capacity of PAN/GOZnO increases gradually with time until an equilibrium was established. The removal of Cr(VI) reached adsorption equilibrium within 30 min for 10 ppm, while for 300 ppm it takes 150 min to reach adsorption equilibrium. The diffusion mechanism could not be identified using pseudo model but it can be analyzed by using the intra-particle diffusion (IPD) model. The initial rate of intra-particle diffusion is calculated by linearization of equation (9)

Fig. 5. Adsorption kinetics of Cr(VI) using PAN/GO-ZnO (a) linear pseudo first order and (b) linear pseudo second order (pH = 6 and temperature = 25°). 208

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

Table 1 Kinetics parameters for Cr(VI) adsorption using PAN/GO-ZnO nanofibers. C0 (mg/L)

parameters

qe,exp (mg/g) Linear pseudo first order

Linear pseudo second order

Nonlinear pseudo first order

Nonlinear pseudo second order

Intra-particle diffusion

K1 (l/min) qe,cal (mg/g) R2 K2 (g/mg min) qe,cal (mg/g) R2 K3 (l/min) qe,cal (mg/g) R2 K4 (g/mg min) qe,cal (mg/g) R2 Kid (mg/g/min1/2) C R2

10

20

30

50

80

100

200

300

24.9

49.9

74.7

124

200

248

465

697

−0.04 25 0.98 0.04 25.6 0.99 0.11 24.8 0.99 0.007 26.8 0.97 1.15 13 0.45

−0.04 50 0.91 0.02 52.6 0.99 0.08 49.5 0.98 0.002 54.2 0.98 2.6 23 0.56

−0.01 39 0.87 0.01 78 0.99 0.06 71.2 0.98 0.001 79.3 0.99 4.2 27 0.67

-.02 100 0.92 1E-3 166 0.96 0.03 127 0.97 2E-4 150 0.93 9.2 22 0.72

−0.01 186 0.9 0.004 255 0.99 0.03 195 0.99 2E-4 231 0.98 13.9 36 0.83

-.01 195 0.93 3E-3 333 0.99 0.03 243 0.98 2E-4 293 0.97 17.8 35 0.84

−0.01 575 0.93 0.002 662 0.95 0.01 487 0.98 2E-5 652 0.97 37.5 −14 0.93

−0.01 955 0.93 .0001 1012 0.96 0.01 762 0.99 1E-5 965 0.98 56.5 −18 0.93

log qe = log kf +

1 log ce n

qe = kf ce1/ n

(12) (13)

Where Kf and 1/n are Freundlich constants related to the adsorption capacity (mg/g) and intensity of adsorption, respectively. The obtained kinetic parameters are summarized in Table 2. The plots for linear and nonlinear Freundlich isotherm for adsorption of Cr(VI) are shown in Fig. 9. Furthermore, Temkin isotherm model is used to evaluate the sorption potential of the sorbent for Cr(VI), and assumes that the fall in the heat of sorption is linear rather than logarithmic, as implied in the Freundlich equation. The Temkin isotherm has generally been applied in the following form (Mohamed et al., 2016b):

qe = Fig. 7. Intra-particle diffusion of Cr(VI) by PAN/GO-ZnO (pH = 6 and temperature = 25°).

To study the adsorption mechanism of PAN/GO-ZnO nanofibers, the equilibrium adsorption isotherms were investigated at three temperatures (25, 40, and 60 °C) with fixed initial concentration of Cr(VI). The adsorption experimental data were fitted with two commonly used isotherms models, linear and nonlinear Langmuir and Freundlich. This isotherm shows a limiting sorption capacity (Mohamed et al., 2017b) and is expressed by the following equations, (10), and (11) for linear and nonlinear Langmuir model, respectively.

q k a ce qe = m 1 + k a ce

(14)

Where bT is the Temkin constant related to the heat of adsorption (kJ/mol), R is the universal gas constant (8.314 J/mol/K) and T is the absolute temperature (K). Temkin model presented as shown in Fig. 10. The results indicate that the adsorption capacity increase as the temperature increases which confirms that the adsorption process is endothermic. The high values of correlation coefficients (R2) indicate that the Freundlich model fitted well the isotherm data better than the Langmuir and Temkin models confirms the multilayer adsorption of Cr (VI) onto the composite surface. In addition, Table 3 provide a comparison of adsorption activities of materials used for removal of different pollutants.

3.5. Adsorption isotherms

ce 1 c = + e qe qm ka qm

RT ln (AT Ce ) bT

3.6. Thermodynamic study (10) In any adsorption process, both energy and entropy considerations must be taken into account in order to determine what process will occur spontaneously. Values of thermodynamic parameters are the actual indicators for practical application of a process. The thermodynamic parameters such as change in free energy ( ΔG°) , Cr(VI) adsorption diffusion coefficient is expressed as a function of temperature by the following Arrhenius type relation (Mohamed et al., 2017b, 2017d):

(11)

Where qm (mg/g) is the maximum adsorption capacity and ka (L/mg) is the Langmuir constant related to the energy of adsorption, and Ce is the equilibrium concentration (mg/L). The plots for linear and nonlinear Langmuir isotherm for adsorption of Cr(VI) are shown in Fig. 8. Unlike the Langmuir model, the Freundlich model assumes that adsorption occurs on a multilayer heterogeneous surface with a nonuniform distribution of the heat over the surface and is expressed by the following equations, (12), and (13) for linear and nonlinear Freundlich model, respectively (Gurunathan et al., 2003).

Di = D0 e

−Ea

RT

(15)

Enthalpy (ΔH °) , and entropy (ΔS°) are calculated using the following equations: 209

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

Fig. 8. a) linear Langmuir isotherm b) nonlinear Langmuir isotherm for adsorption of Cr(VI) by PAN/GO-ZnO (pH = 6).

Table 2 Langmuir, Freundlich, and Temkin Isotherm constants parameters for the adsorption of Cr(VI) using PAN/GO-ZnO nanofibers. Model

Parameters

Langmuir

Freundlich

Temkin

ln kd =

kd =

qMax. (mg/g) KL (L/mg) R2 n Kf (mg.g) R2 AT (L/g) bT (kJ/mol) R2

ΔS° −ΔH + R RT

(c0 − ce ) V mce

Linear

Nonlinear

Temperature (°C)

Temperature (°C)

25

40

60

25

40

60

525 0.0019 0.87 4 0.46 0.95 130 49 0.05

548 0.0017 0.9 4.4 0.41 0.95 194 36 0.57

567 0.0017 0.94 4.6 0.39 0.99 270 33 0.61

610.5 0.035 0.9 2.08 55.4 0.96 – – –

706 0.037 0.93 2.18 72.4 0.97 – – –

645 0.07 0.87 2.98 130.5 0.91 – – –

Fig. 10. Temkin isotherm model for adsorption of Cr(VI) by PAN/GO-ZnO (pH = 6).

(16)

ΔG° = −RT ln kd

(17)

Fig. 9. a) linear Frundlich isotherm b) nonlinear Frundlich isotherm for adsorption of Cr(VI) by PAN/GO-ZnO (pH = 6). 210

(18)

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

Table 3 Comparison of adsorption activities of materials used for removal of different pollutants. Material

Model Type

Model concentration (PPM)

Adsorption capacity (mg/g)

Ref

PAN/PPy core/shell nanofiber PAN-CNT/TiO2-NH2 PPy-PANI nanofibers Fe_PhB_A_CNF PAN/Go-ZnO

Cr Cr Cr Cr Cr

200 300 100 150 300

43 732 100 41 690

Wang et al. (2013) Mohamed et al. (2017c) Bhaumik et al. (2012) Talreja et al. (2014) This work

(VI) (VI) (VI) (VI) (VI)

contact time and temperature. The adsorption of Cr(VI) was endothermic in nature with the removal capacity increasing with increasing temperature. The experimental data fitted well into the nonlinear pseudo first order model with determination coefficient (R2) in between 0.97 and 0.99. Also, the theoretical value qe,cal was very close to the experimental results in all Cr(VI) concentration experiments. Therefore, it can be concluded from these results that the nonlinear pseudo first order model is applicable for the adsorption process. Moreover, PAN/GO-ZnO nanofibers, could be applied as a promising adsorbent with a high adsorption capacity and fast adsorption rate.

Table 4 Thermodynamic parameters for the adsorption of Cr(VI) using PAN/GO-ZnO nanofibers. T (°C)

ΔH ° (kJ/mol)

ΔS° (kJ/mol)

ΔG° (kJ/mol)

25 40 60

41 41 41

113 113 113

4 3.5 0.9

Conflicts of interest The authors declare that they have no conflict of interest. References Abdel-Mottaleb, M.M., Khalil, A., Karim, S., Osman, T.A., Khattab, A., 2019. High performance of PAN/GO-ZnO composite nanofibers for photocatalytic degradation under visible irradiation. J. Mech. Behav. Biomed. Mater. 96, 118–124. Aboamera, N.M., Mohamed, A., Salama, A., Osman, T.A., Khattab, A., 2017. Characterization and mechanical properties of electrospun cellulose acetate/graphene oxide composite nanofibers. Mech. Adv. Mater. Struct. 1–5. Aboamera, N.M., Mohamed, A., Salama, A., Osman, T.A., Khattab, A., 2018. An effective removal of organic dyes using surface functionalized cellulose acetate/graphene oxide composite nanofibers. Cellulose. Abolhasani, M.M., Shirvanimoghaddam, K., Naebe, M., 2017. PVDF/graphene composite nanofibers with enhanced piezoelectric performance for development of robust nanogenerators. Compos. Sci. Technol. 138, 49–56. Adeosun, S.O., Oyetunji, A., Akpan, E.I., 2015. Strength and ductility of forged 1200 aluminum alloy reinforced with steel particles. Niger. J. Technol. 34 (4), 710. Al-Sabahi, J., Bora, T., Al-Abri, M., Dutta, J., 2016. Controlled defects of zinc oxide nanorods for efficient visible light photocatalytic degradation of phenol. Materials 9 (4). Alipour, D., Keshtkar, A.R., Moosavian, M.A., 2016. Adsorption of thorium(IV) from simulated radioactive solutions using a novel electrospun PVA/TiO 2/ZnO nanofiber adsorbent functionalized with mercapto groups: study in single and multi-component systems. Appl. Surf. Sci. 366, 19–29. An, S., Joshi, B.N., Lee, M.W., Kim, N.Y., Yoon, S.S., 2014. Electrospun graphene-ZnO nanofiber mats for photocatalysis applications. Appl. Surf. Sci. 294, 24–28. Anirudhan, T.S., Deepa, J.R., 2017. Nano-zinc oxide incorporated graphene oxide/nanocellulose composite for the adsorption and photo catalytic degradation of ciprofloxacin hydrochloride from aqueous solutions. J. Colloid Interface Sci. 490, 343–356. Apul, O.G., Karanfil, T., 2015. Adsorption of synthetic organic contaminants by carbon nanotubes: a critical review. Water Res. 68, 34–55. Arenas, C.N., Vasco, A., Betancur, M., Martínez, J.D., 2017. Removal of indigo carmine (IC) from aqueous solution by adsorption through abrasive spherical materials made of rice husk ash (RHA). Process Saf. Environ. Protect. 106, 224–238. Asif, S.A., Khan, S.B., Asiri, A.M., 2014. Efficient solar photocatalyst based on cobalt oxide/iron oxide composite nanofibers for the detoxification of organic pollutants. Nanoscale Res. Lett. 9 (1), 510. Atchison, J.S., Schauer, C.L., 2011. Fabrication and characterization of electrospun semiconductor nanoparticle-polyelectrolyte ultra-fine fiber composites for sensing applications. Sensors 11 (11), 10372–10387. Atchudan, R., Edison, T., Perumal, S., Karthikeyan, D., Lee, Y.R., 2016. Facile synthesis of zinc oxide nanoparticles decorated graphene oxide composite via simple solvothermal route and their photocatalytic activity on methylene blue degradation. J. Photochem. Photobiol., B 162, 500–510. Barzegar, F., Bello, A., Fabiane, M., Khamlich, S., Momodu, D., Taghizadeh, F., Dangbegnon, J., Manyala, N., 2015. Preparation and characterization of poly(vinyl alcohol)/graphene nanofibers synthesized by electrospinning. J. Phys. Chem. Solids 77, 139–145. Bhaumik, M., Maity, Arjun, Srinivasu, V.V., Onyango, Maurice S., 2012. Removal of hexavalent chromium from aqueous solution using polypyrrole-polyaniline nanofibers. Chem. Eng. J. 181–182, 323–333. Choi, D., Ham, S., Jang, D.-J., 2018. Visible-light photocatalytic reduction of Cr(VI) via carbon quantum dots-decorated TiO 2 nanocomposites. J. Environ. Chem. Eng. 6

Fig. 11. Van't Hoff plot for the adsorption of Cr(VI) by PAN/GO-ZnO (pH = 6) at various temperature. The ΔG value decreases from 4 to 0.9 kJ/mol when the temperature increases from 25 to 60 °C (Table 4), suggesting the more adsorbable of Cr(VI) species with increasing temperature.

ΔG° = ΔH ° − TΔS°

(19)

Where R is the universal gas constant (8.314 J/mol K), T is the absolute temperature (K), m is the adsorbent dose (g), and Kd is the thermodynamic equilibrium constant (L/mol). The values of ΔH ° and ΔS° were obtained from the slope and intercept of the plot of ln Kd versus 1/T as shown in Fig. 11 and Table 3. The positive values ΔH ° indicate the presence of an energy barrier in the adsorption and endothermic process (Mohamed et al., 2017b). The positive value of entropy change ΔS° reflects good affinity of Cr(VI) ions towards the sorbent and the increasing randomness at the solid-solution interface during the adsorption process. 3.7. Adsorbent stability The reuse of the adsorbent is important and have an economic necessity. The composite nanofibers were used in sequential adsorption process to estimate the durability of the composite nanofibers. After each process, the composite nanofibers were washed several times by distilled water and then dried in air to reuse it in other experiments. The adsorption capacity of the composite nanofibers remained stable during the four five sequential cycles. 4. Conclusions This study investigated the equilibrium and the dynamics of the adsorption of Cr(VI) onto PAN/GO-ZnO nanofibers prepared by electrospinning. The adsorption was found to be strongly dependent on pH, 211

Journal of the Mechanical Behavior of Biomedical Materials 98 (2019) 205–212

M.M. Abdel-Mottaleb, et al.

Mohamed, A., Yousef, S., Ali Abdelnaby, M., Osman, T.A., Hamawandi, B., Toprak, M.S., Muhammed, M., Uheida, A., 2017d. Photocatalytic degradation of organic dyes and enhanced mechanical properties of PAN/CNTs composite nanofibers. Separ. Purif. Technol. 182, 219–223. Mohamed, A., Salama, A., Nasser, W.S., Uheida, A., 2018. Photodegradation of Ibuprofen, Cetirizine, and Naproxen by PAN-MWCNT/TiO2–NH2 nanofiber membrane under UV light irradiation. Environ. Sci. Eur. 30 (1), 47. Mohamed, A., Ghobara, M.M., Abdelmaksoud, M.K., Mohamed, G.G., 2019. A novel and highly efficient photocatalytic degradation of malachite green dye via surface modified polyacrylonitrile nanofibers/biogenic silica composite nanofibers. Separ. Purif. Technol. 210, 935–942. Mohammadi, N., Khani, H., Gupta, V.K., Amereh, E., Agarwal, S., 2011. Adsorption process of methyl orange dye onto mesoporous carbon material–kinetic and thermodynamic studies. J. Colloid Interface Sci. 362 (2), 457–462. Rajendran, S., Khan, M.M., Gracia, F., Qin, J., Gupta, V.K., Arumainathan, S., 2016. Ce3+-ion-induced visible-light photocatalytic degradation and electrochemical activity of ZnO/CeO2 nanocomposite. Sci. Rep. 6, 31641. Sagadevan, S., Pal, K., Chowdhury, Z.Z., Foley, M., 2017. Controllable synthesis of Graphene/ZnO-nanocomposite for novel switching. J. Alloy. Comp. 728, 645–654. Salama, A., Mohamed, A., Aboamera, N.M., Osman, T.A., Khattab, A., 2018. Photocatalytic degradation of organic dyes using composite nanofibers under UV irradiation. Appl. Nanosci. Salama, A., Mohamed, A., Aboamera, N.M., Osman, T., Khattab, A., 2017;al., Khattab. Characterization and mechanical properties of cellulose acetate/carbon nanotube composite nanofibers. Adv. Polym. Technol n/a-n/a. Saleh, T.A., Gupta, V.K., 2012. Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide. J. Colloid Interface Sci. 371 (1), 101–106. Saleh, T.A., Gupta, V.K., 2014. Processing methods, characteristics and adsorption behavior of tire derived carbons: a review. Adv. Colloid Interface Sci. 211, 93–101. Saravanan, R., Gupta, V.K., Mosquera, E., Gracia, F., 2014. Preparation and characterization of V2O5/ZnO nanocomposite system for photocatalytic application. J. Mol. Liq. 198, 409–412. Saravanan, R., Sacari, E., Gracia, F., Khan, M.M., Mosquera, E., Gupta, V.K., 2016. Conducting PANI stimulated ZnO system for visible light photocatalytic degradation of coloured dyes. J. Mol. Liq. 221, 1029–1033. Talreja, N., Kumar, Dinesh, Verma, Nishith, 2014. Removal of hexavalent chromium from water using Fe-grown carbon nanofibers containing porous carbon microbeads. J. Water Process Eng. 3, 34–45. Uheida, A., Mohamed, A., Belaqziz, M., Nasser, W.S., 2019. Photocatalytic degradation of Ibuprofen, Naproxen, and Cetirizine using PAN-MWCNT nanofibers crosslinked TiO2NH2 nanoparticles under visible light irradiation. Separ. Purif. Technol. 212, 110–118. Wang, J., Pan, Kai, He, Qiwei, Cao, Bing, 2013. Polyacrylonitrile/polypyrrole core/shell nanofiber mat for the removal of hexavalent chromium from aqueous solution. J. Hazard Mater. 244 (245), 121–129. Xu, S., Song, J., Zhu, C., Morikawa, H., 2017. Graphene oxide-encapsulated Ag nanoparticle-coated silk fibers with hierarchical coaxial cable structure fabricated by the molecule-directed self-assembly. Mater. Lett. 188, 215–219. Yazdi, M.G., Ivanic, M., Mohamed, A., Uheida, A., 2018. Surface modified composite nanofibers for the removal of indigo carmine dye from polluted water. RSC Adv. 8 (43), 24588–24598. Yousef, S., Mohamed, A., Tatariants, M., 2018. Mass production of graphene nanosheets by multi-roll milling technique. Tribol. Int. 121, 54–63.

(1), 1–8. Fellahi, O., Barras, A., Pan, G.H., Coffinier, Y., Hadjersi, T., Maamache, M., Szunerits, S., Boukherroub, R., 2016. Reduction of Cr(VI) to Cr(III) using silicon nanowire arrays under visible light irradiation. J. Hazard Mater. 304, 441–447. Ferrari, A.C., 2007. Raman spectroscopy of graphene and graphite: disorder, electron–phonon coupling, doping and nonadiabatic effects. Solid State Commun. 143 (1–2), 47–57. Gautam, A., Kshirsagar, A., Biswas, R., Banerjee, S., Khanna, P.K., 2016. Photodegradation of organic dyes based on anatase and rutile TiO2 nanoparticles. RSC Adv. 6 (4), 2746–2759. Ghaedi, M., Hajjati, S., Mahmudi, Z., Tyagi, I., Agarwal, S., Maity, A., Gupta, V.K., 2015. Modeling of competitive ultrasonic assisted removal of the dyes – methylene blue and Safranin-O using Fe3O4 nanoparticles. Chem. Eng. J. 268, 28–37. Gupta, V.K., Jain, R., Nayak, A., Agarwal, S., Shrivastava, M., 2011. Removal of the hazardous dye—tartrazine by photodegradation on titanium dioxide surface. Mater. Sci. Eng. C 31 (5), 1062–1067. Gurunathan, K., Amalnerkar, D.P., Trivedi, D.C., 2003. Synthesis and characterization of conducting polymer composite (PAn/TiO2) for cathode material in rechargeable battery. Mater. Lett. 57 (9–10), 1642–1648. Kameda, T., Fubasami, Y., Yoshioka, T., 2011. Kinetics and equilibrium studies on the treatment of nitric acid with Mg–Al oxide obtained by thermal decomposition of NO3–intercalated Mg–Al layered double hydroxide. J. Colloid Interface Sci. 362 (2), 497–502. Karim, S.A., Mohamed, A., Abdel-Mottaleb, M.M., Osman, T.A., Khattab, A., 2018. Mechanical properties and the characterization of polyacrylonitrile/carbon nanotube composite nanofiber. Arabian J. Sci. Eng. 43, 4697–4702. Karim, S.A., Mohamed, A., Abdel-Mottaleb, M.M., Osman, T.A., Khattab, A., 2019. Visible light photocatalytic activity of PAN-CNTs/ZnO-NH2 electrospun nanofibers. J. Alloy. Comp. 772, 650–655. Khalil, A., Aboamera, N.M., Nasser, W.S., Mahmoud, W.H., Mohamed, G.G., 2019. Photodegradation of organic dyes by PAN/SiO2-TiO2-NH2 nanofiber membrane under visible light. Separ. Purif. Technol. 224, 509–514. Khani, H., Rofouei, M.K., Arab, P., Gupta, V.K., Vafaei, Z., 2010. Multi-walled carbon nanotubes-ionic liquid-carbon paste electrode as a super selectivity sensor: application to potentiometric monitoring of mercury ion(II). J. Hazard Mater. 183 (1), 402–409. Kim, S., Kuk, Y.-S., Chung, Y.S., Jin, F.-L., Park, S.-J., 2014. Preparation and characterization of polyacrylonitrile-based carbon fiber papers. J. Ind. Eng. Chem. 20 (5), 3440–3445. Mohamed, A., El-Sayed, R., Osman, T.A., Toprak, M.S., Muhammed, M., Uheida, A., 2016a. Composite nanofibers for highly efficient photocatalytic degradation of organic dyes from contaminated water. Environ. Res. 145, 18–25. Mohamed, A., Osman, T.A., Toprak, M.S., Muhammed, M., Yilmaz, E., Uheida, A., 2016b. Visible light photocatalytic reduction of Cr(VI) by surface modified CNT/titanium dioxide composites nanofibers. J. Mol. Catal. A Chem. 424, 45–53. Mohamed, A., Osman, T.A., Toprak, M.S., Muhammed, M., Uheida, A., 2017a. Surface functionalized composite nanofibers for efficient removal of arsenic from aqueous solutions. Chemosphere 180, 108–116. Mohamed, A., Nasser, W.S., Osman, T.A., Toprak, M.S., Muhammed, M., Uheida, A., 2017b. Removal of chromium (VI) from aqueous solutions using surface modified composite nanofibers. J. Colloid Interface Sci. 505, 682–691. Mohamed, A., Nasser, W.S., Osman, T.A., Toprak, M.S., Muhammed, M., Uheida, A., 2017c. Removal of chromium (VI) from aqueous solutions using surface modified composite nanofibers. J. Colloid Interface Sci. 505, 682–691.

212