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Nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass: Photocatalytic activity for degradation of an azo textile dye F3B
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JIEC-1335; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
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Nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass: Photocatalytic activity for degradation of an azo textile dye F3B Mohammad Hossein Habibi *, Amir Hossein Habibi Nanotechnology Laboratory, Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Islamic Republic of Iran
A R T I C L E I N F O
Article history: Received 25 February 2013 Accepted 9 April 2013 Available online xxx Keywords: ZnFe2O4–FeFe2O4–ZnO Nanostructure Doctor blade Reactive Red 195
A B S T R A C T
An efficient and scalable one-pot synthetic method to prepare nanostructure composite of ZnFe2O4– FeFe2O4–ZnO (ZFZ) has been investigated. This method is based on thermal decomposition of iron(III) acetate and zinc acetate in monoethanolamine (MEA) as a capping agent. Moreover, thermogravimetric analysis (TG-DTG) was performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. ZFZ was immobilized on glass using doctor blade method and calcinated at different temperatures. The properties of the ZFZ nanocomposite have been examined by different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance (DRS). FESEM shows that nanocomposite is monocrystallines and a narrow dispersion in size of 48 nm. XRD confirms that the prepared nanocomposite is composed of franklinite, ZnFe2O4 (54%), magnetite, FeFe2O4 (8%) and wurtzite, ZnO (48%). Photocatalytic activity of ZFZ immobilized on glass was carried out by choosing an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation with homemade photocatalytic apparatus and the results indicated that ZFZ exhibited good photocatalytic activity. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Azo textile dyes are the main chemical class of dyes due to their stability and the range of colors available compared to natural dyes. More than 60% of all textile dyes contains azo dyes which making them the largest group of synthetic colorants released into the environment [1–3]. Nanostructure zinc oxide with a large exciton binding energy and wide band gap has received growing interest in the application of photocatalysis [4–8]. Nanostructure zinc oxides show more advantages than titanium dioxide with lower cost and higher quantum yields [9–12]. Nanoparticles of photocatalysts must be separated and reused after application which may encounter technological problems [13]. The immobilization of nano-size photocatalyst overcomes the difficulties in separation and recycle of photocatalyst [14–18]. There are some reports on immobilization of the nano-size photocatalysts on different supports but the problem is lower efficiency of the immobilized photocatalyst compared with nanoparticles suspensions [19–24]. This can be done by application of nanostructured photocatalyst with more active sites, higher surface-to-volume ratio and less electron–hole recombination is needed [25–27]. However, to our best knowledge, there are no report about the
nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass and their use as photocatalyst for degradation of an azo textile dye F3B. In continuation of our research in semiconductor metal oxide thin film [6,28–30], in the present work, we report for the first time the preparation and characterization of nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass. The nanostructure coating was characterized in detail by means of XRD, SEM and DRS. We have applied the coatings for photocatalytic decoloration of a textile dye (F3B) (Fig. 1) as an aquatic environmental pollutant. 2. Experimental 2.1. Materials Borosilicate glass was used as a support of the ZnFe2O4– FeFe2O4–ZnO (ZFZ) nanocomposite. Zinc acetate dihydrate, Zn(CH3COO)22H2O, iron(III) acetate, Fe(CH3COO)2, monoethanolamine and isopropanol were used without any further purification. Double-distilled water was used in all the experiments. 2.2. Preparation of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite
* Corresponding author. Tel.: +98 311 7932707; fax: +98 311 6689732. E-mail addresses: [email protected], [email protected] (M.H. Habibi).
To the solution of isopropyl alcohol, 30 ml as a solvent, monoethanolamine, 0.63 ml as a complexing agent, zinc acetate
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.04.025
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Fig. 1. Chemical structure of Reactive Red 195 (F3B) as a textile dye.
dihydrate, Zn(CH3COO)22H2O (2.304 g), was added while stirring at 60 8C for 1 h to achieve a transparent solution (Sol A). Iron(III) acetate, Fe(CH3COO)3 (1.826 g) was dissolved in the mixture of isopropyl alcohol, 30 ml and monoethanolamine, 0.63 ml while stirring at 60 8C for 1 h (Sol B). Sol A was added to Sol B with continuous stirring for 10 min at room temperature and aged for 2 days. The solution was heated to 80 8C with formation of a gel. Dried gel was annealed at 700 8C to obtain the ZnFe2O4–FeFe2O4– ZnO (ZFZ) nanocomposite. A schematic diagram of the process is presented in Fig. 2. 2.3. Preparation of ZnFe2O4–FeFe2O4–ZnO paste (ZFZP) ZnFe2O4–FeFe2O4–ZnO powders (0.60 g) was grinded in a mortar with 1 mL of acetic acid at 5 min. Double distilled water (1 mL) was added with stirring for 1 min (5 times). Ethanol (1 mL) was added and stirred for 1 min (15 times). Ethanol (2.5 mL) was added and grinded in the mortar for 1 min (6 times). The paste was
Fig. 3. Absorption spectra of F3B taken at different photocatalytic degradation times using ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite coated on glass as photocatalysts.
transferred to a 300 mL beaker with addition of 100 mL ethanol. The sample was sonicated for 1 min. Terpineol (20 mg) was added and the paste solution was sonicated. A solution of ethyl cellulose in ethanol was sonicated the solvent was evaporated in a rotary evaporator. It was found that ZnFe2O4–FeFe2O4–ZnO/ethyl cellulose/terpineol paste is helpful to increase the powder loading and make it possible to produce ZnFe2O4–FeFe2O4–ZnO films with higher surface uniformity and particle density after sintering process. 2.4. Coating of ZnFe2O4–FeFe2O4–ZnO paste on glass by doctor blade (ZFZPC) The paste was coated on a glass slide by doctor blade method and the thin film annealed at 550 8C for 2 h. Microscope slides were carefully cleaned by ethanol and dried in an oven. ZnFe2O4– FeFe2O4–ZnO paste immobilized on glass substrates were fabricated using the doctor blade method [31,32]. The area of the ZnFe2O4–FeFe2O4–ZnO coated glass was 11.25 cm2, length 7.5 cm and width 1.5 cm. The ZFZPC coated glass was air dried, annealed at 550 8C and cooled [33,34]. 2.5. Characterization
Fig. 2. Flow chart for preparation ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite paste.
The thermoanalytical measurements (TG-DTG) study for the thermal decomposition of precursors were carried out with a using a Mettler TA4000 system from 20 to 700 8C at a heating rate of 5 8C min 1. ZnFe2O4–FeFe2O4–ZnO paste on glass by doctor blade was characterized by XRD analysis using X-ray diffractometer (D8 Advance, BRUKER) in the diffraction angle range 2u = 20–608, using Cu Ka radiation. The crystallite size D of the sample was estimated using the Scherer’s equation, (0.9l)/(b cos u), by measuring the line broadening of main intensity peak, where l is the wavelength of Cu Ka radiation, b is the full width at half-maximum, and u is the brag’s angle. Field emission scanning electron microscopy (FESEM, Hitachi, model S-4160) was used to observe the surface morphology of the ZnFe2O4 photocatalyst. Diffuse reflectance spectra (DRS) were collected with a V-670, JASCO spectrophotometer and transformed to the absorption spectra according to the Tach relationship. FT-IR absorption spectra of selected samples were obtained using KBr disks on a FT-IR 6300. A UV-Spectrophotometer (Varian Cary 500 Scan) was used to measure F3B azo textile dye concentrations at various time intervals during the reactions at wavelength 563 nm (Fig. 3).
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the loss of residual moisture in the powder. The second weight loss step in the peak temperature of 350 8C is associated with the combustion of acetates. A small weight loss was observed about 640 8C, implying the presence of nanocomposite oxides.
Fig. 4. Photooxidation set up (a) oxygen cylinder; (b) power supply; (c) lamps; (d) photoreactor with aluminum foil as reflector for a full irradiate of catalyst; (e) fan; (f) magnetic stirrer; (g) 2 l Pyrex beaker; (h) photooxidation cell; (i) water thermostat Haake model F-122.
2.6. Experimental procedure for photocatalytic degradation of F3B azo textile dye The experiments were conducted under a 250 W Hg lamp placed 5 cm above the solutions using a Petri Dish with 20 ml of F3B azo textile dye and the ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide using by doctor blade method. Three milliliter dye solution about was withdrawn periodically to monitor the absorbance spectra. The degradation process of Reactive Red 2 was monitored by the absorbance at 563 nm. The UV light was turned off during the absorbance monitoring process. Aqueous solution was poured into the testing container (Fig. 4). 3. Results and discussion 3.1. Characterization of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite 3.1.1. Thermogravimetric analysis TG-DTG curves of synthesized ZFZ nanocomposite are shown in Fig. 5. The TG curve exhibits two distinct weight loss steps. The first weight loss step in the peak temperature of 250 8C, arises due to
3.1.2. XRD analysis The crystal structure of the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite has been analyzed via X-ray powder diffraction measurements. Diffraction patterns show the characteristic Bragg peaks expected for ZnFe2O4, FeFe2O4 and ZnO. The calculated cell parameters are in agreement with the typical value for the ferrite spinels and zinc oxide wurtzite. The sizes of the nanoparticles synthesized were calculated by the Debye–Schrerrer formula using the diffraction patterns, being the diameter similar with those calculated by analyzing FESEM images. Fig. 6a shows the XRD patterns of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite sample annealed at 500 8C. The detected diffraction peaks could be attributed to the characteristic peaks of ZnFe2O4 (31.7%), FeFe2O4 (13.8%) and ZnO (54.5%) (Table 1). This composition ratio was supported by EDS measurements. The peaks centered at 31.78, 34.48, 36.28 and 47.58 in Fig. 6a are corresponded to (1 0 0), (0 0 2), (1 0 1) and (1 0 2) of zinc oxide with the hexagonal wurtzite structure (space group: P63mc), respectively [4,35]. The diffraction patterns in Fig. 6a show characteristic peak for FeFe2O4 at 43.1 (4 0 0) [36]. This finding indicates that the composite consists of FeFe2O4 crystals with spinel structures [36–38]. The diffraction peaks (2 2 0), (3 1 1), (4 0 0), (5 1 1) and (4 4 0) at 2u of 30.18, 348, 438, 568, and 628 in the XRD spectra are corresponding to ZnFe2O4 franklinite phase respectively [39,40]. Fig. 6b shows the XRD patterns of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite sample annealed at 600 8C. The detected diffraction peaks could be attributed to the characteristic peaks of ZnFe2O4 (50.2%), FeFe2O4 (11.0%) and ZnO (38.9%). Fig. 6c shows the XRD patterns of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite sample annealed at 700 8C. The detected diffraction peaks could be attributed to the characteristic peaks of ZnFe2O4 (54.2%), FeFe2O4 (7.3%) and ZnO (38.6%). The results from the XRD spectra in Fig. 6a–c showed that the increase of annealing temperature increases the amounts of ZnFe2O4 phase. 3.1.3. Morphology characterization Fig. 7 shows the typical FESEM image of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite. With an average size of the sphere-like and square-like nanoparticles around 46 nm, close to the XRD analysis [41–43]. 3.1.4. Diffuse reflectance (DRS) spectroscopic analysis for determination of band gap A Tauc plot is used to determine the band gap of ZnFe2O4– FeFe2O4–ZnO (ZFZ) nanocomposite. A Tauc plot shows the quantity hn (the energy of the light) on the abscissa and the quantity (ahv)n on the ordinate, where a is the absorption coefficient of the material and n = 2 for indirect allowed transitions [44–46]. The band gap of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite is shown in Fig. 8. The energy band gap of films was found to be 2.07 eV. Fig. 9 shows the band gaps obtained for ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite using Kubelka–Munk plot [47]. 3.2. Photocatalytic degradation of F3B azo textile dye using ZnFe2O4– FeFe2O4–ZnO (ZFZ) nanocomposite coated on glass by doctor blade (ZFZPC)
Fig. 5. TG-DTG of ZnFe2O4–FeFe2O4–ZnO dried sol.
The photocatalytic activity of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite coated on glass is evaluated by choosing azo textile dye, Reactive Red 195 (F3B) as a model and the results are presented in Fig. 10. The F3B degradation kinetics data were
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Fig. 6. (a) XRD patterns for the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 500 8C. (b) XRD patterns for the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 600 8C. (c) XRD patterns for the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C. Table 1 Effect of annealing temperature on relative intensities of different phases found in the XRD analysis using zinc acetate and iron acetate. Mol. ratio
Temp. (8C)
ZnO (%, w/w)
ZnFe2O4 (%, w/w)
FeFe2O4 (%, w/w)
1:1 1:1 1:1
500 600 700
54.5 38.9 38.6
31.7 50.2 54.2
13.8 11.0 7.2
Fig. 7. FESEM image of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C.
examined using a first-order reaction kinetics. The first order rate constant k is obtained by plotting ln(C0/Ct) vs. time (min). As shown, the effect of light on increasing decolorization rate of the azo textile of F3B is evident and the decolorization percentages under light conditions are found to be about 60%. The light-induced decolorization of azo textile of F3B on the ZnFe2O4–FeFe2O4–ZnO particles is contributed to the following possible mechanism. The rate of valence electrons excited to the conduction band, occurring
Fig. 8. Tauc plot ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C.
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(54%), magnetite, FeFe2O4 (8%) and wurtzite, ZnO (48%). Photocatalytic activity of ZFZ immobilized on glass was carried out by choosing an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation with homemade photocatalytic apparatus and the results indicated that ZFZ exhibited good photocatalytic activity. Acknowledgment The authors wish to thank the University of Isfahan for financially supporting this work. References
Fig. 9. Munk plot ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C.
Fig. 10. ln C0/Ct vs. time for photocatalytic degradation of an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation using ZnFe2O4– FeFe2O4–ZnO paste on glass by doctor blade (ZFZPC) immobilized on glass.
at the ZnFe2O4–FeFe2O4–ZnO particles surface, is accelerated by irradiation. The photo-generated holes are scavenged by azo textile of F3B. A photolysis test was conducted in the presence of Reactive Red 2 (F3B) without ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide as photocatalysts but with the UV lamp turned on. The direct photolysis of Reactive Red 2 (F3B) by UVC, UVA and 250 W Hg lamps was negligible. The UV applied alone was not sufficient without the presence of the photocatalysts for the oxidation of Reactive Red 2. Photodegradation of Reactive Red 2 (F3B) with UVA, UVC and 250 W Hg lamps with ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide are compared. The photoactivity with UVC and UVA using ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide are very close. However, using 250 W Hg lamp the photoactivity was slightly higher due to higher intensity. 4. Conclusions Nanostructure composite of ZnFe2O4–FeFe2O4–ZnO (ZFZ) was prepared using thermal decomposition of iron(III) acetate and zinc acetate. ZFZ composite was immobilized on glass using doctor blade method. The properties of the ZFZ nanocomposite was examined by XRD, FESEM and DRS. XRD confirms that the prepared nanocomposite is composed of franklinite, ZnFe2O4
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JIEC-1335; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2013) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass: Photocatalytic activity for degradation of an azo textile dye F3B Mohammad Hossein Habibi *, Amir Hossein Habibi Nanotechnology Laboratory, Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Islamic Republic of Iran
A R T I C L E I N F O
Article history: Received 25 February 2013 Accepted 9 April 2013 Available online xxx Keywords: ZnFe2O4–FeFe2O4–ZnO Nanostructure Doctor blade Reactive Red 195
A B S T R A C T
An efficient and scalable one-pot synthetic method to prepare nanostructure composite of ZnFe2O4– FeFe2O4–ZnO (ZFZ) has been investigated. This method is based on thermal decomposition of iron(III) acetate and zinc acetate in monoethanolamine (MEA) as a capping agent. Moreover, thermogravimetric analysis (TG-DTG) was performed to determine the temperature at which the decomposition and oxidation of the chelating agents took place. ZFZ was immobilized on glass using doctor blade method and calcinated at different temperatures. The properties of the ZFZ nanocomposite have been examined by different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and diffuse reflectance (DRS). FESEM shows that nanocomposite is monocrystallines and a narrow dispersion in size of 48 nm. XRD confirms that the prepared nanocomposite is composed of franklinite, ZnFe2O4 (54%), magnetite, FeFe2O4 (8%) and wurtzite, ZnO (48%). Photocatalytic activity of ZFZ immobilized on glass was carried out by choosing an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation with homemade photocatalytic apparatus and the results indicated that ZFZ exhibited good photocatalytic activity. ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Azo textile dyes are the main chemical class of dyes due to their stability and the range of colors available compared to natural dyes. More than 60% of all textile dyes contains azo dyes which making them the largest group of synthetic colorants released into the environment [1–3]. Nanostructure zinc oxide with a large exciton binding energy and wide band gap has received growing interest in the application of photocatalysis [4–8]. Nanostructure zinc oxides show more advantages than titanium dioxide with lower cost and higher quantum yields [9–12]. Nanoparticles of photocatalysts must be separated and reused after application which may encounter technological problems [13]. The immobilization of nano-size photocatalyst overcomes the difficulties in separation and recycle of photocatalyst [14–18]. There are some reports on immobilization of the nano-size photocatalysts on different supports but the problem is lower efficiency of the immobilized photocatalyst compared with nanoparticles suspensions [19–24]. This can be done by application of nanostructured photocatalyst with more active sites, higher surface-to-volume ratio and less electron–hole recombination is needed [25–27]. However, to our best knowledge, there are no report about the
nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass and their use as photocatalyst for degradation of an azo textile dye F3B. In continuation of our research in semiconductor metal oxide thin film [6,28–30], in the present work, we report for the first time the preparation and characterization of nanostructure composite ZnFe2O4–FeFe2O4–ZnO immobilized on glass. The nanostructure coating was characterized in detail by means of XRD, SEM and DRS. We have applied the coatings for photocatalytic decoloration of a textile dye (F3B) (Fig. 1) as an aquatic environmental pollutant. 2. Experimental 2.1. Materials Borosilicate glass was used as a support of the ZnFe2O4– FeFe2O4–ZnO (ZFZ) nanocomposite. Zinc acetate dihydrate, Zn(CH3COO)22H2O, iron(III) acetate, Fe(CH3COO)2, monoethanolamine and isopropanol were used without any further purification. Double-distilled water was used in all the experiments. 2.2. Preparation of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite
* Corresponding author. Tel.: +98 311 7932707; fax: +98 311 6689732. E-mail addresses: [email protected], [email protected] (M.H. Habibi).
To the solution of isopropyl alcohol, 30 ml as a solvent, monoethanolamine, 0.63 ml as a complexing agent, zinc acetate
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.04.025
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Fig. 1. Chemical structure of Reactive Red 195 (F3B) as a textile dye.
dihydrate, Zn(CH3COO)22H2O (2.304 g), was added while stirring at 60 8C for 1 h to achieve a transparent solution (Sol A). Iron(III) acetate, Fe(CH3COO)3 (1.826 g) was dissolved in the mixture of isopropyl alcohol, 30 ml and monoethanolamine, 0.63 ml while stirring at 60 8C for 1 h (Sol B). Sol A was added to Sol B with continuous stirring for 10 min at room temperature and aged for 2 days. The solution was heated to 80 8C with formation of a gel. Dried gel was annealed at 700 8C to obtain the ZnFe2O4–FeFe2O4– ZnO (ZFZ) nanocomposite. A schematic diagram of the process is presented in Fig. 2. 2.3. Preparation of ZnFe2O4–FeFe2O4–ZnO paste (ZFZP) ZnFe2O4–FeFe2O4–ZnO powders (0.60 g) was grinded in a mortar with 1 mL of acetic acid at 5 min. Double distilled water (1 mL) was added with stirring for 1 min (5 times). Ethanol (1 mL) was added and stirred for 1 min (15 times). Ethanol (2.5 mL) was added and grinded in the mortar for 1 min (6 times). The paste was
Fig. 3. Absorption spectra of F3B taken at different photocatalytic degradation times using ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite coated on glass as photocatalysts.
transferred to a 300 mL beaker with addition of 100 mL ethanol. The sample was sonicated for 1 min. Terpineol (20 mg) was added and the paste solution was sonicated. A solution of ethyl cellulose in ethanol was sonicated the solvent was evaporated in a rotary evaporator. It was found that ZnFe2O4–FeFe2O4–ZnO/ethyl cellulose/terpineol paste is helpful to increase the powder loading and make it possible to produce ZnFe2O4–FeFe2O4–ZnO films with higher surface uniformity and particle density after sintering process. 2.4. Coating of ZnFe2O4–FeFe2O4–ZnO paste on glass by doctor blade (ZFZPC) The paste was coated on a glass slide by doctor blade method and the thin film annealed at 550 8C for 2 h. Microscope slides were carefully cleaned by ethanol and dried in an oven. ZnFe2O4– FeFe2O4–ZnO paste immobilized on glass substrates were fabricated using the doctor blade method [31,32]. The area of the ZnFe2O4–FeFe2O4–ZnO coated glass was 11.25 cm2, length 7.5 cm and width 1.5 cm. The ZFZPC coated glass was air dried, annealed at 550 8C and cooled [33,34]. 2.5. Characterization
Fig. 2. Flow chart for preparation ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite paste.
The thermoanalytical measurements (TG-DTG) study for the thermal decomposition of precursors were carried out with a using a Mettler TA4000 system from 20 to 700 8C at a heating rate of 5 8C min 1. ZnFe2O4–FeFe2O4–ZnO paste on glass by doctor blade was characterized by XRD analysis using X-ray diffractometer (D8 Advance, BRUKER) in the diffraction angle range 2u = 20–608, using Cu Ka radiation. The crystallite size D of the sample was estimated using the Scherer’s equation, (0.9l)/(b cos u), by measuring the line broadening of main intensity peak, where l is the wavelength of Cu Ka radiation, b is the full width at half-maximum, and u is the brag’s angle. Field emission scanning electron microscopy (FESEM, Hitachi, model S-4160) was used to observe the surface morphology of the ZnFe2O4 photocatalyst. Diffuse reflectance spectra (DRS) were collected with a V-670, JASCO spectrophotometer and transformed to the absorption spectra according to the Tach relationship. FT-IR absorption spectra of selected samples were obtained using KBr disks on a FT-IR 6300. A UV-Spectrophotometer (Varian Cary 500 Scan) was used to measure F3B azo textile dye concentrations at various time intervals during the reactions at wavelength 563 nm (Fig. 3).
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the loss of residual moisture in the powder. The second weight loss step in the peak temperature of 350 8C is associated with the combustion of acetates. A small weight loss was observed about 640 8C, implying the presence of nanocomposite oxides.
Fig. 4. Photooxidation set up (a) oxygen cylinder; (b) power supply; (c) lamps; (d) photoreactor with aluminum foil as reflector for a full irradiate of catalyst; (e) fan; (f) magnetic stirrer; (g) 2 l Pyrex beaker; (h) photooxidation cell; (i) water thermostat Haake model F-122.
2.6. Experimental procedure for photocatalytic degradation of F3B azo textile dye The experiments were conducted under a 250 W Hg lamp placed 5 cm above the solutions using a Petri Dish with 20 ml of F3B azo textile dye and the ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide using by doctor blade method. Three milliliter dye solution about was withdrawn periodically to monitor the absorbance spectra. The degradation process of Reactive Red 2 was monitored by the absorbance at 563 nm. The UV light was turned off during the absorbance monitoring process. Aqueous solution was poured into the testing container (Fig. 4). 3. Results and discussion 3.1. Characterization of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite 3.1.1. Thermogravimetric analysis TG-DTG curves of synthesized ZFZ nanocomposite are shown in Fig. 5. The TG curve exhibits two distinct weight loss steps. The first weight loss step in the peak temperature of 250 8C, arises due to
3.1.2. XRD analysis The crystal structure of the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite has been analyzed via X-ray powder diffraction measurements. Diffraction patterns show the characteristic Bragg peaks expected for ZnFe2O4, FeFe2O4 and ZnO. The calculated cell parameters are in agreement with the typical value for the ferrite spinels and zinc oxide wurtzite. The sizes of the nanoparticles synthesized were calculated by the Debye–Schrerrer formula using the diffraction patterns, being the diameter similar with those calculated by analyzing FESEM images. Fig. 6a shows the XRD patterns of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite sample annealed at 500 8C. The detected diffraction peaks could be attributed to the characteristic peaks of ZnFe2O4 (31.7%), FeFe2O4 (13.8%) and ZnO (54.5%) (Table 1). This composition ratio was supported by EDS measurements. The peaks centered at 31.78, 34.48, 36.28 and 47.58 in Fig. 6a are corresponded to (1 0 0), (0 0 2), (1 0 1) and (1 0 2) of zinc oxide with the hexagonal wurtzite structure (space group: P63mc), respectively [4,35]. The diffraction patterns in Fig. 6a show characteristic peak for FeFe2O4 at 43.1 (4 0 0) [36]. This finding indicates that the composite consists of FeFe2O4 crystals with spinel structures [36–38]. The diffraction peaks (2 2 0), (3 1 1), (4 0 0), (5 1 1) and (4 4 0) at 2u of 30.18, 348, 438, 568, and 628 in the XRD spectra are corresponding to ZnFe2O4 franklinite phase respectively [39,40]. Fig. 6b shows the XRD patterns of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite sample annealed at 600 8C. The detected diffraction peaks could be attributed to the characteristic peaks of ZnFe2O4 (50.2%), FeFe2O4 (11.0%) and ZnO (38.9%). Fig. 6c shows the XRD patterns of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite sample annealed at 700 8C. The detected diffraction peaks could be attributed to the characteristic peaks of ZnFe2O4 (54.2%), FeFe2O4 (7.3%) and ZnO (38.6%). The results from the XRD spectra in Fig. 6a–c showed that the increase of annealing temperature increases the amounts of ZnFe2O4 phase. 3.1.3. Morphology characterization Fig. 7 shows the typical FESEM image of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite. With an average size of the sphere-like and square-like nanoparticles around 46 nm, close to the XRD analysis [41–43]. 3.1.4. Diffuse reflectance (DRS) spectroscopic analysis for determination of band gap A Tauc plot is used to determine the band gap of ZnFe2O4– FeFe2O4–ZnO (ZFZ) nanocomposite. A Tauc plot shows the quantity hn (the energy of the light) on the abscissa and the quantity (ahv)n on the ordinate, where a is the absorption coefficient of the material and n = 2 for indirect allowed transitions [44–46]. The band gap of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite is shown in Fig. 8. The energy band gap of films was found to be 2.07 eV. Fig. 9 shows the band gaps obtained for ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite using Kubelka–Munk plot [47]. 3.2. Photocatalytic degradation of F3B azo textile dye using ZnFe2O4– FeFe2O4–ZnO (ZFZ) nanocomposite coated on glass by doctor blade (ZFZPC)
Fig. 5. TG-DTG of ZnFe2O4–FeFe2O4–ZnO dried sol.
The photocatalytic activity of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite coated on glass is evaluated by choosing azo textile dye, Reactive Red 195 (F3B) as a model and the results are presented in Fig. 10. The F3B degradation kinetics data were
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Fig. 6. (a) XRD patterns for the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 500 8C. (b) XRD patterns for the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 600 8C. (c) XRD patterns for the ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C. Table 1 Effect of annealing temperature on relative intensities of different phases found in the XRD analysis using zinc acetate and iron acetate. Mol. ratio
Temp. (8C)
ZnO (%, w/w)
ZnFe2O4 (%, w/w)
FeFe2O4 (%, w/w)
1:1 1:1 1:1
500 600 700
54.5 38.9 38.6
31.7 50.2 54.2
13.8 11.0 7.2
Fig. 7. FESEM image of ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C.
examined using a first-order reaction kinetics. The first order rate constant k is obtained by plotting ln(C0/Ct) vs. time (min). As shown, the effect of light on increasing decolorization rate of the azo textile of F3B is evident and the decolorization percentages under light conditions are found to be about 60%. The light-induced decolorization of azo textile of F3B on the ZnFe2O4–FeFe2O4–ZnO particles is contributed to the following possible mechanism. The rate of valence electrons excited to the conduction band, occurring
Fig. 8. Tauc plot ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C.
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(54%), magnetite, FeFe2O4 (8%) and wurtzite, ZnO (48%). Photocatalytic activity of ZFZ immobilized on glass was carried out by choosing an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation with homemade photocatalytic apparatus and the results indicated that ZFZ exhibited good photocatalytic activity. Acknowledgment The authors wish to thank the University of Isfahan for financially supporting this work. References
Fig. 9. Munk plot ZnFe2O4–FeFe2O4–ZnO (ZFZ) nanocomposite annealed at 700 8C.
Fig. 10. ln C0/Ct vs. time for photocatalytic degradation of an azo textile dye, Reactive Red 195 (F3B) as a model pollutant under UV irradiation using ZnFe2O4– FeFe2O4–ZnO paste on glass by doctor blade (ZFZPC) immobilized on glass.
at the ZnFe2O4–FeFe2O4–ZnO particles surface, is accelerated by irradiation. The photo-generated holes are scavenged by azo textile of F3B. A photolysis test was conducted in the presence of Reactive Red 2 (F3B) without ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide as photocatalysts but with the UV lamp turned on. The direct photolysis of Reactive Red 2 (F3B) by UVC, UVA and 250 W Hg lamps was negligible. The UV applied alone was not sufficient without the presence of the photocatalysts for the oxidation of Reactive Red 2. Photodegradation of Reactive Red 2 (F3B) with UVA, UVC and 250 W Hg lamps with ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide are compared. The photoactivity with UVC and UVA using ZnFe2O4–FeFe2O4–ZnO paste coated on glass slide are very close. However, using 250 W Hg lamp the photoactivity was slightly higher due to higher intensity. 4. Conclusions Nanostructure composite of ZnFe2O4–FeFe2O4–ZnO (ZFZ) was prepared using thermal decomposition of iron(III) acetate and zinc acetate. ZFZ composite was immobilized on glass using doctor blade method. The properties of the ZFZ nanocomposite was examined by XRD, FESEM and DRS. XRD confirms that the prepared nanocomposite is composed of franklinite, ZnFe2O4
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