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CuO nanoparticles for degradation of MB and reduction of nitrophenols
Journal Pre-proof Synthesis, characterization and investigation of photocatalytic and catalytic applications of Fe3 O4 /TiO2 /CuO nanoparticles for degradation of MB and reduction of nitrophenols Ali Hossein Kianfar, Mohammad Amin Arayesh
PII:
S2213-3437(19)30763-8
DOI:
https://doi.org/10.1016/j.jece.2019.103640
Reference:
JECE 103640
To appear in:
Journal of Environmental Chemical Engineering
Received Date:
30 November 2019
Revised Date:
19 December 2019
Accepted Date:
25 December 2019
Please cite this article as: Kianfar AH, Arayesh MA, Synthesis, characterization and investigation of photocatalytic and catalytic applications of Fe3 O4 /TiO2 /CuO nanoparticles for degradation of MB and reduction of nitrophenols, Journal of Environmental Chemical Engineering (2019), doi: https://doi.org/10.1016/j.jece.2019.103640
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Synthesis, characterization and investigation of photocatalytic and catalytic applications of Fe3O4/TiO2/CuO nanoparticles for degradation of MB and reduction of nitrophenols Ali Hossein Kianfar1, Mohammad Amin Arayesh
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Department of Chemistry, Isfahan University of Technology, Isfahan, 84156/83111
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Corresponding author Email: [email protected]
Graphical abstract Nanoparticles of Fe3O4 magnetite were prepared using co-precipitation method. Titanium dioxide was then coated on the surface of Fe3O4 by sonicating of TBOT. Finally, Cu(NO3)2.6H2O was loaded over Fe3O4/TiO2 to prepare Fe3O4/TiO2/CuO nanoparticle. The prepared compounds were characterized via FT-IR, DRS, EDAX, XRD, VSM, FE-SEM and TEM. Photocatalytic degradation of methylene blue (MB) was carried out in aqueous
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medium under sun light irradiation. The catalytic activity of the Fe3O4/TiO2/CuO
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nanoparticles was applied in the reduction of para and orthonitrophenol in the presence of NaBH4. The reaction progress of the catalytic and photocatalytic degradation was monitored
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by UV-Vis spectroscopy. In addition, the Fe3O4/TiO2/CuO nanoparticles were separable and recyclable.
Abstract Nanoparticles of Fe3O4 magnetite were prepared using co-precipitation method. Titanium dioxide was then coated on the surface of Fe3O4 by sonicating of TBOT. Finally, Cu(NO3)2.6H2O was loaded over Fe3O4/TiO2 to prepare Fe3O4/TiO2/CuO nanoparticle. The prepared compounds were characterized by FT-IR, DRS, EDX, XRD, XPS, VSM, FE-SEM and TEM. Based on XRD and TEM, titanium dioxide, as the anatase and rutile phases, is coated over Fe3O4 as a core shell structure. Based on the DRS spectra and band gap
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calculation, the band gap energy of Fe3O4/TiO2/CuO was determined as 1.9 eV. Photocatalytic degradation of methylene blue (MB) was carried out in aqueous medium under
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sun light irradiation. The MB was depredated in neutral media (at pH = 7) at about 22 min. more than 99%. The catalytic activity of the Fe3O4/TiO2/CuO nanoparticles was applied in the reduction of para and orthonitrophenol in the presence of NaBH4. The reduction reaction
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was completed at 2 min. The reaction progress of the catalytic and photocatalytic degradation was monitored by UV-Vis spectroscopy. The results show that, the Fe3O4/TiO2/CuO
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nanoparticles can be separable and also recyclable for several times.
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Keyword: Fe3O4, Titanium dioxide, Catalyst, Reduction of nitrophenols, Degradation of MB
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1- Introduction
Water is one of the most important and essential compounds for the survival of creatures. The sources of safe water are limited in the world. On the other hand, the
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development of chemical industries has restricted these sources. Therefore, the environmental pollutants are important in the human society today [1,2,3,4,5]. Toxic materials and dyes are two main groups of hazardous compounds in wastewater [6]. Water pollution by organic compounds has been increasingly attractive in recent decades all over the world [7]. Among the nitroaromatic toxic pollutants [8], nitrogen containing aromatic compounds such as nitrobenzene and nitrophenols are widely used in the industries, e.g. in the production of pesticides and dyes [9, 10]. Among many nitro compounds in the environment, 4-nitrophenol (4-NP) is highly toxic and can damage kidney, blood and the central nervous system [11]. Furthermore, 2-nitrophenol is another nitroaromatic organic compounds widely used in the production of chemical intermediates, fungicides, insecticides, pharmaceuticals, pesticides,
rubber chemicals, synthetic dyes and wood [12]. These water soluble compounds are stable and toxic organic pollutants for industrial wastewater [13]. However, it is difficult to effectively and completely remove the nitrophenol derivatives by conventional wastewater treatment methods [14] including microbial degradation [15], photocatalytic degradation [16], adsorption [17,18] and chemical reduction [19]. Among these methods, the chemical reduction of nitrophenols is the most effective method for the reduction of nitrophenol derivatives [20]. Sodium borohydride (NaBH4) is a general reducing agent applied for the reduction of nitrophenols to aminophenols [21-23]. P-aminophenol is an applicable compound in the preparation of analgesic and febrifuge drugs, antioxidants and dyes. A
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helpful method for the synthesis of 4-AP, which leads to the removal of a nitroaromatic compound is the reduction of nitrophenol. In this method, in addition to sodium borohydride,
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a conventional catalyst is applied to reduce the reaction time. Beside the reaction time, a reproducible and separable catalyst is important in a green reaction [8].
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Disposal of dye pollutants into the water sources inhibits sunlight permeation into the water and decreases the photosynthetic action [24]. In addition, some dyes are carcinogenic
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and toxic and thus their treatment cannot only depend on biodegradation [25,26]. Methylene Blue (MB), an organic and cationic dye used in different industries such as the textile, cosmetics and leather industries, is a wastewater dye, which causes environmental pollution
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[27-29]. Photocatalytic degradation of dyes is one of the most effective methods for water treatment [30]. Moreover, heterogeneous photocatalysis is an excellent technology for the
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destruction of organic dyes [31].
Titanium dioxide (n-type semiconductor), a photocatalyst for the degradation of dyes, is unique because of its chemical stability, non-toxicity, great oxidizing power, and low cost.
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Anatase with 3.2 eV (Rutile 3 eV) band gap energy is the most important phase of titanium dioxide, which absorbs UV-irradiation in photocatalyst degradation reaction of dyes [32]. High band gap and recombination rate of titanium dioxide limit its further applications in the industry [33]. However, many efforts have been made to improve the photocatalytic activity of titanium dioxide by modifying (such as doping and mixing of two semiconductors) the surface or bulk properties of this compound, [20, 34]. Titanium dioxide is applied as a simple and effective compound for the removal of inorganic and organic compounds [32]. In addition to the problems pointed out, the separation of titanium dioxide from the solution is difficult. As an important magnetic compound, Fe3O4 magnetite has high surface redox activity and strong electron transport capability. In addition, titanium dioxide is an
environmentally friendly compound [35, 36]. Fe3O4 is unstable in acidic media and hydrolyzes in acidic solutions [36]. Therefore, the coating of Fe3O4 with a stable solid compound such as titanium dioxide could improve the application of magnetite in acidic solutions. Moreover, this method is important for the separation of titanium dioxide from the solution in photocatalyst applications [37, 38]. Among the catalysts for the reduction of nitrophenol [39] and dyes, a magnetically separable heterogeneous catalyst is the best [40,41]. To improve titanium dioxide as an n-type semiconductor in the absorption of visible light, loading of a p-type transition metal oxide such as CuO and NiO [42, 43] is a simple and suitable method. Thus, the application of a magnetic compound containing titanium dioxide
magnetite is interesting in photocatalytic and catalytic reactions.
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(n-type semiconductor) and a transition metal oxide (P-type semiconductor) supported on
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To achieve a compound with the above properties, in continuation of our studies on the degradation of MB via visible light [44, 45], magnetically separable Fe3O4/TiO2/CuO
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catalyst and photocatalyst was synthesized by co-precipitation technique and characterized via FT-IR, UV-DRS, XRD, XPS, FE-SEM, TEM and VSM. Finally, the reduction of
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nitrophenol and photodegradation of methylene blue were carried out in aqueous solution.
2-1- Materials
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2- Experimental
Chemicals including FeCl3.6H2O, FeCl2.4H2O, sodium hydroxide, Cu(NO3)2, titanium tetrabutoxide (TBOT) and methylene blue were purchased from Sigma Aldrich
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Chemical Company. EtOH, NaBH4, para and orthonitrophenol were purchased from Merck Chemical Company.
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2-2- Preparation of Fe3O4
0.2 g of FeCl3 and 0.08 g of FeCl2 were dissolved in 36 mL of deionized water under
N2 atmosphere and stirred at 50°C for 15 min. Afterwards, 10 mL of NaOH solution (0.1 M) was added dropwise to the reaction mixture until the black color of the solution disappeared (pH = 9). The reaction mixture was then stirred for 1 h at room temperature. The final product was separated by a super magnet and washed with deionized water, ethanol and dried at 60oC in an oven for 1 h [46]. 2-3- Preparation of Fe3O4/TiO2
8 mg of Fe3O4 were dispersed in 30 mL of isopropyl alcohol by ultrasonication for 30 min. [47]. 0.1 mL of (TBOT) was dissolved in ethanol (1 mL) and slowly added into the
mixture [48], which was then stirred for 2 h under N2 gas. The product obtained was washed three times with absolute ethanol, separated by a super magnet and dried at 60°C in an oven for 2 h [49]. 2-4- Preparation of Fe3O4/TiO2/CuO
1 mg of Cu(NO3)2 was dissolved in 10 mL of ethanol and slowly added into 3 mg of Fe3O4/TiO2 dispersed by sonication in 20 mL of absolute ethanol and stirring was continued for 150 min. the product was collected by a super magnet, washed with ethanol and deionized
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water and dried in an oven at 70°C for 6 h [50].
Fig.1. Scheme of synthesis of Fe3O4/TiO2/CuO
2-1- Photocatalytic Activity 2-1-1- Degradation of MB by Fe3O4/TiO2/CuO
For this purpose, 1 mg of Fe3O4/TiO2/CuO was used for degradation of 10 mL of
aqueous solution of MB (10 ppm) with 1 mL of H2O2 (0.1 M) under sunlight irradiation [51]. The reaction progress was followed via UV-Vis spectroscopy. All the photocatalytic experiments were carried out at room temperature. MB was degraded by 99% within 25 min. (with H2O2) and 22 min. (without H2O2). Every 5 min, the product was separated by a super
magnet from the catalyst and the absorption spectra of MB were recorded to follow MB
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degradation [52].
Fig.2. Scheme of mechanism of degradation MB
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2-2- Catalytic Activity 2-2-1- Reduction of 4-NP to 4-AP
An aqueous solution of paranitrophenol (10-4 M, 1 mL) and fresh NaBH4 (10-3 M, 1
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mL) were added into a quartz cell. 3 mg of the catalyst was then added to the mixture to begin the reduction reaction [53,54]. The reaction progress was followed via UV-Vis spectroscopy. 4-NP has a maximum absorption peak at 318 nm. Upon the addition of NaBH4, this peak change to 400 nm due to the formation of phenolate. After reduction of the phenolate ion, the peak at about 400 nm is flattened and the amine peak appears at 300 nm. In order to evaluate the reaction rate, the concentration chart was plotted against the absorption [55].
2-2-2- Reduction of 2-NP to 2-AP
An aqueous solution of orthonitrophenol (10-3 M, 1 mL) and fresh NaBH4 (10-2 M, 1 ml) was added into a quartz cell. 3 mg of the catalyst was then added to the mixture to begin the reduction reaction [54]. The UV-Vis absorption spectra were recorded Orthonitrophenol shows two absorption peaks in the range of 250-500 nm. After the reduction of this compound, the peak at 420 nm was flattened and the amine peak, which overlaps with one of the 2-NP peaks, appeared at 280 nm. In order to evaluate the reaction rate, the concentration
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chart was plotted against the absorption [56].
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Fig.3. Scheme of mechanism of reduction 4-NP
3- Result and discussion
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3-1- FT-IR studies
The FT-IR spectra of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO are shown in (Fig. S1).
The peaks located at 3450 and 1640 cm−1 are ascribed to the H2O stretching and bending vibrations of adsorbed water, respectively [57, 58]. The peaks shown in the 550-653 cm-1 range are attributed to metal-oxygen bonds. In the Fe3O4 spectra, the peak at 559 cm−1 is ascribed to Fe-O bond [50]. The presence of Cu(II) and Ti(IV) metals on the catalyst surface was confirmed by a sharp peak in the range of 1300-1400 cm-1, which were due to the stretching vibrations of Cu-O-Ti [50, 58]. It should be noted that the peak corresponding to the vibrational stretching mode of O-Ti-O was observed in the range of 400-700 [49]. The
stretching vibration of Ti-O located at 500-600 cm-1 could not be recognized due to overlapping with the vibrational stretching of Fe-O in this region [59]. 3-2- DRS
DRS spectra are demonstrated in (Fig. S2). The band gap energies determined by drawing the intercept of the tangent to the graph obtained by plotting the Kubelka-Munk function (ahν = (1-R(hν)) ^.5/2R(hν)) and (hν) are shown Fig 4. [60, 61]. The band gap energies were obtained as 2.1 and 1.9 (eV) for Fe3O4/TiO2 and Fe3O4/TiO2/CuO, respectively (Fig. 4). These results indicate that the reduced energy gap can be due to the p-n heterojunction in the catalyst and addition of CuO to the composite reduced the band gap to
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absorption of sun light [62].
Fig.4. Tauc plot for the determination of band gap
3-3- XRD Studies
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Fig. 5 shows the XRD patterns of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO samples.
The absorption peak at 2θ = 18 is related to the crystal plane in (111), which is ascribed to the layers of titanium dioxide and copper(II) oxide on the surface of the magnetic nanoparticles [63, 64]. The other important peaks at 2θ = 30 (022), 35(113), 57(115), 62(044), 77(335) and 82(155) plane of Fe3O4 are associated with the inverse spinel structure. Titanium dioxide was observed as Rutile(R) at 2θ = 35(011), 43.820(120), 62.330(022), 63.702(130) [65] and anatase(A) at 2θ = 25.156(011), 38.314(110), 47.782(020), 54.753(121) phase [65-66]. (JCPDS file No. 96-900-4143 and 96-900-8216). The presence of Rutile and Anatase in the nanocomposite together enhanced the photocatalytic activity of the nanocomposite [67].
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Fig.5. XRD patterns of room temperature
3-4- XPS analysis
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Fig (S3a) showed the full scan XPS spectra of the magnetic Fe3O4/TiO2/CuO nanoparticles. The C 1s lines (Fig. S3b) displayed three peaks with diff erent intensities,
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which corresponded to different types of carbon. The binding energies of 290.8eV, 291.8eV and 293.9eV were related to C-C, C=C and C=O, respectively [68]. Fig (S3c) showed the XPS spectra of O 1s core level of the sample. The binding energy observed at 535.4, 537.8
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and 537.9 eV could be attributed to –OH of the surface, Ti-O-Ti and Fe-O, respectively [69]. Ti 2p (1/2) and Ti 2p (3/2) binding energy of TiO2 was seen at 471.4 and 464.7 eV (Fig.
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S3d). Binding energy of Cu 2p in Fe3O4/TiO2/CuO was shown in Fig (S3e). The binding energies of CuO and Cu 2p (1/2) and Cu 2p (3/2) were 961.7eV, 948.6eV and 941.2eV, respectively. Finally based on the results the copper(II)oxide was loaded on the surface as CuO. While the titanium dioxide was seen as TiO and TiO2. 3-1- FE-SEM studies
Morphology, surface uniformity and the size of particles can be investigated by FE-
SEM analysis. The FE-SEM images of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO nanoparticles are shown in (Fig. S4). Based on the FE-SEM images, Fe3O4/TiO2/CuO nanoparticles have a spherical morphology, which is confirmed by the good dispersion of the nanoparticles in the structure [49]. The EDX spectra of the prepared Fe3O4/TiO2/CuO nanoparticles are shown in
(Fig. S4). In this spectrum, the presence of Fe, Ti, O, and Cu is confirmed. EDX spectra clearly confirms the formation of nanoparticles as proposed structure [49]. 3-2- TEM studies
TEM was used to characterize the surface morphology of Fe3O4/TiO2/CuO (Fig.6). The scheme represents the spherical shape with proper distribution of the particles. The CoreShell structure of the nanoparticles is confirmed by TEM analysis. According to the TEM analysis, Fe3O4 coating by TiO2 has been performed. In addition, loading of CuO on the surface of Fe3O4/TiO2 has been carried out. From the histogram (Fig.6), the average size of
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the nanoparticles synthesized is about 8 nm.
b)
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d) Fig.6. a, b, c) TEM image and d) histogram curve of Fe3O4/TiO2/CuO
3-3- Magnetic Measurements (VSM)
The S-shaped curve magnetization of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO were shown in Fig.7. This analysis was performed at room temperature. According to the results, the first amount of magnetization saturation of Fe3O4 is 50 emu/g. After coating with TiO2, the saturation magnetization of Fe3O4 reduced to 16 emu/g, indicating that the coating process has been successfully performed [31]. Furthermore, after loading CuO on the surface of Fe3O4/TiO2, the magnetism was reduced to 10 emu/g. This indicated that the copper
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particles were over the surface of the nanoparticles.
Fig.7. Magnetization of Fe3O4, Fe3O4/TiO2, Fe3O4/TiO2/ CuO
3-4- ICP
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To prepare the samples for ICP analysis (Table 1), a certain amount of
Fe3O4/TiO2/CuO nanocatalyst was dissolved in nitric acid (15 M) before and after the reduction reaction of paranitrophenol. This analysis was used to evaluate the weight of copper (II). A solution containing 10 ppm of the sample was prepared for this purpose. The results are as follows.
Table 1. The ICP analysis of Cu(II) in Fe3O4/TiO2/CuO Times of reduction reaction 4-NP
Cu(II) (ppm)
Before reduction reaction
14.12
After first reaction
13.98
After fourth reaction 12.86
4- Photocatalytic activities of Fe3O4/TiO2/CuO for degradation of MB In this study, Fe3O4/TiO2/CuO nanoparticle was applied in the degradation of MB in the presence (Fig. S5) and absence of H2O2 (Fig.8) on sun light irradiation. To study the absorption of MB by the catalyst, a solution containing both MB and the catalyst was placed inside a dark room for 4 h (Fig. S6). Moreover, the degradation of MB was studied in different acidic (pH = 5), neutral (pH = 7) and basic (pH = 9) solutions (Table. 3). The
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reaction progress was followed by UV-Vis spectroscopy in 5 min time intervals (Fig. 8). Based on the results, the degradation in acidic media took 4 or 24 h in the presence and
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absence of H2O2, respectively (Fig. S7). The results show that the shortest photocatalyst degradation was observed in the basic solution (5 min) (Fig. S7). In contrast to the acid
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solution, the degradation time in neutral and basic solutions decreased in the absence of H2O2. MB degradation time in the basic solution is very reasonable and the reaction is
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complete in about 5 min. In basic media the negative sites on the surface are significant. So the interaction of cationic dye’s molecules with the negative sites on nanocomposite is
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significant, leading to higher degradation rate [70,71]. However, the degradation time in the neutral media was 22 min. Considering the environmental contamination and cost issues, neutral media was selected and further studies on the degradation of MB were carried out in
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this media. The reaction was repeated for 5 times and Fe3O4/TiO2/CuO photocatalyst was separated easily by a super magnet (Fig.9). In addition, the degradation time did not change in the next reactions such that the fifth degradation cycle took less than 25 min. (Table 2).
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Furthermore, there are some reported applications on the degradation of organic dyes via magnetic photocatalysts (Table 4), in most of which ultraviolet irradiation was applied as the source of light [52, 72]. In addition, the best reported degradation time was at least 40 min. [52,72]. To refine these parameters, in this study, a separable and reproducible photocatalyst was prepared and applied in the degradation of MB in sun light for 22 min. in neutral media. Eq. (1) is the kinetic equation of degradation of MB. 𝐿𝑛
𝐶 𝐶0
= −𝑘 𝑡
Eq. (1)
where C0 and C are concentrations of MB at t = 0 and at time t, respectively, and k is the rate constant (Fig. 8b). (The ratio C/C0 = A/A0 at 670 nm) [60]. In addition, Eq. (2) shows the degradation of MB. 𝑙=
𝐶0 −𝐶 𝐶0
× 100
Eq. (2)
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In this equation, C0 and C are concentrations of MB at t=0 and t, respectively.
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a)
Time(s)
0
Ln A/A0
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0
500
1000
1500
2000
-1
-2
K = 0.0018 R² = 0.9915
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b) Fig.8. a) degradation of MB 22 min (Without H2O2) and b) Plots of ln(A/A0) vs. time for degradation MB by Fe3O4/TiO2/CuO
Table 2 Recovery of Fe3O4/TiO2/CuO in degradation reaction MB Number of recovery
1
2
3
4
5
Time(s)
1500
1620
1740
1750
1750
Rate constant
18×10-2
2×10-3
1.7×10-3
1.5×10-3
1.3×10-3
0
300
600
900
1200
1500
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Ln A/A0
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Time(s) 0
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Fig.9. The reusability of Fe3O4/TiO2/ CuO in degradation of MB at visible light irradiation
Table 3. Conditions of the photocatalyst reactions H2O2 Without " " With " "
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pH 6.8-7.5 9 5 6.8-7.5 9 5
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Media neutral basic acidic neutral basic acidic
Time(min) 22 5 20hours 25 15 4
Degradation % 99.12 99.78 87< 96 99.04 93
Table 4. Degradation of MB with other catalysts
Catalyst Ag/AgBr/TiO2 Ce-doped MoO3 Ag3PO4 Fe3O4/ PCL Fe3O4/TiO2/Ag Fe3O4/TiO2/CuO
Time(Min) 90 50 10 150 100 22
Concentration 10 ppm 5 ppm 16 ppm 10 ppm 10 ppm 10 ppm
Reference [73] [72] [74] [52] [75] this study
5- Catalytic activities of Fe3O4/TiO2/CuO in the reduction of para and orthonitrophenol The catalytic reduction of para and orthonitrophenol to para and orthoaminophenol using NaBH4 as the reducing agent has been carried out as a model reaction to evaluate the catalytic efficiency of Fe3O4/TiO2/CuO (Fig. 10). UV-Vis spectroscopy was used to monitor the reduction progress. Based on the reported works, the normal conditions for this reaction are 10-4 M 4-NP and 10-2 M NaBH4 [35, 39, 76]. Here, in the presence of Fe3O4/TiO2/CuO, the reaction was complete less than 1 min. Therefore, the reaction was performed using 10-4 M 4-NP and 10-3 M NaBH4 to follow the reaction and determine the rate constant. Under
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these conditions, the reduction reaction was over in 2 min (Fig.10). Eq. (3) is applied to determine the reaction rate (Fig. 10): Eq(3)
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(ln A/A0 = -kt)
0 and time t, respectively, and k is the rate constant.
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where A0 and A are the absorbance values of 4-NP (400 nm) and 2-NP (420 nm) at t =
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The reduction of 4-NP was repeated 4 times (Fig.11) in the presence of Fe3O4/TiO2/CuO catalyst (Table 5). In addition, the last reduction reaction was taking less than 4 min. To compare the reduction reaction of paranitrophenol with other cases, some of
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the reported catalysts are shown in Table 6. Unlike the catalysts reported in the literature for the reduction of paranitrophenol, Fe3O4/TiO2/CuO catalyst is separable and reproducible. In
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addition, the concentration of NaBH4 and the reaction time are less than the reported values. The electronic spectra of pure para and orthoaminophenols (Merck company) (Fig 10. a) and b)) were recorded and compare to electronic spectrum of reaction product to confirm para and
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orthoaminophenols.
c)
Time(S)
0 0
d)
50
100
Time(S) 0
150
0
50
K = 0.0296 R² = 0.9924
-3
-1
-2
K = -0.0206 R² = 0.9691
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-4 -4
150
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100
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Ln A/A0
Ln A/A0
-1
-3
Table 5. 1
Time(S)
120
2.96×10- 3
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Rate constants
Recovery of Fe3O4/TiO2/CuO in reduction reaction
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Number of recovery
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Fig.10. Reduction of a) 4-NP (10 M) and b) 2-NP (10 M), (c and d) Plots of ln(A/A0) vs. time for reduction para and orthnitrophenols with Fe3O4/TiO2/CuO
2
3
4
120-150
150
180
12.6×10-3
11.7×10-3
8×10-3
Time(S)
0
Ln A/A0
0
-1
-2
-3
50
100
150
Fig.11. The reusability of Fe3O4/TiO2/ CuO in reduction 4-NP
Table.6. Reduction of 4-NP with other catalyst Time(S)
180
Catalyst
NaBH4 10-2 M
Rate constant(s-1)
Reference
10
12.8 × 10-3
[53]
1
_
[57]
62.4 × 10-5
[77]
[79]
Pdcomplex on GO-MnFe2O4 Cu/graphene
480
Calcium-AlginateStabilized Ag Nanoparticles
540
CuO-RGO nanocomposite
4
25 × 10-4
600
CuO nanocrystal
4
_
720
AgNP/rGO
10
691 × 10-5
60
Pd/GNS-NH2
300
Cu@GE composite
-
120
Fe3O4/TiO2/CuO
0.1
[79] [54]
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10
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360
1.8
[78]
_
[39]
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0.2
This work
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29.6 × 10-3
6- Conclusion
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Magnetic Fe3O4/TiO2/CuO nanoparticles have been synthesized in this work. Nanoparticles were characterized via different techniques. TiO2 and CuO, as n-type and ptype semiconductors, respectively, have been coated on Fe3O4 as core-shell. The separable
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composite was applied as a photocatalyst in the degradation of MB in sun light. Moreover, the presence of CuO in the composite enables the application of Fe3O4/TiO2/CuO catalyst in the reduction of para and orthonitrophenol. Easy separation, high efficiency, excellent
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stability and recyclability of the catalyst without any loss in its efficiency are the main advantageous of Fe3O4/TiO2/CuO Therefore, it is proposed as a suitable catalyst and photocatalyst for the removal of pollutants from waste waters.
AUTHORS STATEMENT FOR PUBLICATION Component of the research
Author’s number
substantial contribution to conception Ali Hossein Kianfar andofdesign substantial contribution to acquisition Ali Hossein Kianfar Amin substantial contribution to analysis and data Mohammad Arayesh interpretation of data
Mohammad Amin drafting the article Arayesh critically revising the article for important Ali Hossein Kianfar intellectual content final approval of the version to be Ali Hossein Kianfar published
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the
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work reported in this paper
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PII:
S2213-3437(19)30763-8
DOI:
https://doi.org/10.1016/j.jece.2019.103640
Reference:
JECE 103640
To appear in:
Journal of Environmental Chemical Engineering
Received Date:
30 November 2019
Revised Date:
19 December 2019
Accepted Date:
25 December 2019
Please cite this article as: Kianfar AH, Arayesh MA, Synthesis, characterization and investigation of photocatalytic and catalytic applications of Fe3 O4 /TiO2 /CuO nanoparticles for degradation of MB and reduction of nitrophenols, Journal of Environmental Chemical Engineering (2019), doi: https://doi.org/10.1016/j.jece.2019.103640
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Synthesis, characterization and investigation of photocatalytic and catalytic applications of Fe3O4/TiO2/CuO nanoparticles for degradation of MB and reduction of nitrophenols Ali Hossein Kianfar1, Mohammad Amin Arayesh
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Department of Chemistry, Isfahan University of Technology, Isfahan, 84156/83111
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Corresponding author Email: [email protected]
Graphical abstract Nanoparticles of Fe3O4 magnetite were prepared using co-precipitation method. Titanium dioxide was then coated on the surface of Fe3O4 by sonicating of TBOT. Finally, Cu(NO3)2.6H2O was loaded over Fe3O4/TiO2 to prepare Fe3O4/TiO2/CuO nanoparticle. The prepared compounds were characterized via FT-IR, DRS, EDAX, XRD, VSM, FE-SEM and TEM. Photocatalytic degradation of methylene blue (MB) was carried out in aqueous
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medium under sun light irradiation. The catalytic activity of the Fe3O4/TiO2/CuO
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nanoparticles was applied in the reduction of para and orthonitrophenol in the presence of NaBH4. The reaction progress of the catalytic and photocatalytic degradation was monitored
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by UV-Vis spectroscopy. In addition, the Fe3O4/TiO2/CuO nanoparticles were separable and recyclable.
Abstract Nanoparticles of Fe3O4 magnetite were prepared using co-precipitation method. Titanium dioxide was then coated on the surface of Fe3O4 by sonicating of TBOT. Finally, Cu(NO3)2.6H2O was loaded over Fe3O4/TiO2 to prepare Fe3O4/TiO2/CuO nanoparticle. The prepared compounds were characterized by FT-IR, DRS, EDX, XRD, XPS, VSM, FE-SEM and TEM. Based on XRD and TEM, titanium dioxide, as the anatase and rutile phases, is coated over Fe3O4 as a core shell structure. Based on the DRS spectra and band gap
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calculation, the band gap energy of Fe3O4/TiO2/CuO was determined as 1.9 eV. Photocatalytic degradation of methylene blue (MB) was carried out in aqueous medium under
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sun light irradiation. The MB was depredated in neutral media (at pH = 7) at about 22 min. more than 99%. The catalytic activity of the Fe3O4/TiO2/CuO nanoparticles was applied in the reduction of para and orthonitrophenol in the presence of NaBH4. The reduction reaction
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was completed at 2 min. The reaction progress of the catalytic and photocatalytic degradation was monitored by UV-Vis spectroscopy. The results show that, the Fe3O4/TiO2/CuO
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nanoparticles can be separable and also recyclable for several times.
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Keyword: Fe3O4, Titanium dioxide, Catalyst, Reduction of nitrophenols, Degradation of MB
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1- Introduction
Water is one of the most important and essential compounds for the survival of creatures. The sources of safe water are limited in the world. On the other hand, the
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development of chemical industries has restricted these sources. Therefore, the environmental pollutants are important in the human society today [1,2,3,4,5]. Toxic materials and dyes are two main groups of hazardous compounds in wastewater [6]. Water pollution by organic compounds has been increasingly attractive in recent decades all over the world [7]. Among the nitroaromatic toxic pollutants [8], nitrogen containing aromatic compounds such as nitrobenzene and nitrophenols are widely used in the industries, e.g. in the production of pesticides and dyes [9, 10]. Among many nitro compounds in the environment, 4-nitrophenol (4-NP) is highly toxic and can damage kidney, blood and the central nervous system [11]. Furthermore, 2-nitrophenol is another nitroaromatic organic compounds widely used in the production of chemical intermediates, fungicides, insecticides, pharmaceuticals, pesticides,
rubber chemicals, synthetic dyes and wood [12]. These water soluble compounds are stable and toxic organic pollutants for industrial wastewater [13]. However, it is difficult to effectively and completely remove the nitrophenol derivatives by conventional wastewater treatment methods [14] including microbial degradation [15], photocatalytic degradation [16], adsorption [17,18] and chemical reduction [19]. Among these methods, the chemical reduction of nitrophenols is the most effective method for the reduction of nitrophenol derivatives [20]. Sodium borohydride (NaBH4) is a general reducing agent applied for the reduction of nitrophenols to aminophenols [21-23]. P-aminophenol is an applicable compound in the preparation of analgesic and febrifuge drugs, antioxidants and dyes. A
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helpful method for the synthesis of 4-AP, which leads to the removal of a nitroaromatic compound is the reduction of nitrophenol. In this method, in addition to sodium borohydride,
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a conventional catalyst is applied to reduce the reaction time. Beside the reaction time, a reproducible and separable catalyst is important in a green reaction [8].
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Disposal of dye pollutants into the water sources inhibits sunlight permeation into the water and decreases the photosynthetic action [24]. In addition, some dyes are carcinogenic
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and toxic and thus their treatment cannot only depend on biodegradation [25,26]. Methylene Blue (MB), an organic and cationic dye used in different industries such as the textile, cosmetics and leather industries, is a wastewater dye, which causes environmental pollution
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[27-29]. Photocatalytic degradation of dyes is one of the most effective methods for water treatment [30]. Moreover, heterogeneous photocatalysis is an excellent technology for the
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destruction of organic dyes [31].
Titanium dioxide (n-type semiconductor), a photocatalyst for the degradation of dyes, is unique because of its chemical stability, non-toxicity, great oxidizing power, and low cost.
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Anatase with 3.2 eV (Rutile 3 eV) band gap energy is the most important phase of titanium dioxide, which absorbs UV-irradiation in photocatalyst degradation reaction of dyes [32]. High band gap and recombination rate of titanium dioxide limit its further applications in the industry [33]. However, many efforts have been made to improve the photocatalytic activity of titanium dioxide by modifying (such as doping and mixing of two semiconductors) the surface or bulk properties of this compound, [20, 34]. Titanium dioxide is applied as a simple and effective compound for the removal of inorganic and organic compounds [32]. In addition to the problems pointed out, the separation of titanium dioxide from the solution is difficult. As an important magnetic compound, Fe3O4 magnetite has high surface redox activity and strong electron transport capability. In addition, titanium dioxide is an
environmentally friendly compound [35, 36]. Fe3O4 is unstable in acidic media and hydrolyzes in acidic solutions [36]. Therefore, the coating of Fe3O4 with a stable solid compound such as titanium dioxide could improve the application of magnetite in acidic solutions. Moreover, this method is important for the separation of titanium dioxide from the solution in photocatalyst applications [37, 38]. Among the catalysts for the reduction of nitrophenol [39] and dyes, a magnetically separable heterogeneous catalyst is the best [40,41]. To improve titanium dioxide as an n-type semiconductor in the absorption of visible light, loading of a p-type transition metal oxide such as CuO and NiO [42, 43] is a simple and suitable method. Thus, the application of a magnetic compound containing titanium dioxide
magnetite is interesting in photocatalytic and catalytic reactions.
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(n-type semiconductor) and a transition metal oxide (P-type semiconductor) supported on
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To achieve a compound with the above properties, in continuation of our studies on the degradation of MB via visible light [44, 45], magnetically separable Fe3O4/TiO2/CuO
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catalyst and photocatalyst was synthesized by co-precipitation technique and characterized via FT-IR, UV-DRS, XRD, XPS, FE-SEM, TEM and VSM. Finally, the reduction of
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nitrophenol and photodegradation of methylene blue were carried out in aqueous solution.
2-1- Materials
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2- Experimental
Chemicals including FeCl3.6H2O, FeCl2.4H2O, sodium hydroxide, Cu(NO3)2, titanium tetrabutoxide (TBOT) and methylene blue were purchased from Sigma Aldrich
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Chemical Company. EtOH, NaBH4, para and orthonitrophenol were purchased from Merck Chemical Company.
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2-2- Preparation of Fe3O4
0.2 g of FeCl3 and 0.08 g of FeCl2 were dissolved in 36 mL of deionized water under
N2 atmosphere and stirred at 50°C for 15 min. Afterwards, 10 mL of NaOH solution (0.1 M) was added dropwise to the reaction mixture until the black color of the solution disappeared (pH = 9). The reaction mixture was then stirred for 1 h at room temperature. The final product was separated by a super magnet and washed with deionized water, ethanol and dried at 60oC in an oven for 1 h [46]. 2-3- Preparation of Fe3O4/TiO2
8 mg of Fe3O4 were dispersed in 30 mL of isopropyl alcohol by ultrasonication for 30 min. [47]. 0.1 mL of (TBOT) was dissolved in ethanol (1 mL) and slowly added into the
mixture [48], which was then stirred for 2 h under N2 gas. The product obtained was washed three times with absolute ethanol, separated by a super magnet and dried at 60°C in an oven for 2 h [49]. 2-4- Preparation of Fe3O4/TiO2/CuO
1 mg of Cu(NO3)2 was dissolved in 10 mL of ethanol and slowly added into 3 mg of Fe3O4/TiO2 dispersed by sonication in 20 mL of absolute ethanol and stirring was continued for 150 min. the product was collected by a super magnet, washed with ethanol and deionized
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ro
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water and dried in an oven at 70°C for 6 h [50].
Fig.1. Scheme of synthesis of Fe3O4/TiO2/CuO
2-1- Photocatalytic Activity 2-1-1- Degradation of MB by Fe3O4/TiO2/CuO
For this purpose, 1 mg of Fe3O4/TiO2/CuO was used for degradation of 10 mL of
aqueous solution of MB (10 ppm) with 1 mL of H2O2 (0.1 M) under sunlight irradiation [51]. The reaction progress was followed via UV-Vis spectroscopy. All the photocatalytic experiments were carried out at room temperature. MB was degraded by 99% within 25 min. (with H2O2) and 22 min. (without H2O2). Every 5 min, the product was separated by a super
magnet from the catalyst and the absorption spectra of MB were recorded to follow MB
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degradation [52].
Fig.2. Scheme of mechanism of degradation MB
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2-2- Catalytic Activity 2-2-1- Reduction of 4-NP to 4-AP
An aqueous solution of paranitrophenol (10-4 M, 1 mL) and fresh NaBH4 (10-3 M, 1
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mL) were added into a quartz cell. 3 mg of the catalyst was then added to the mixture to begin the reduction reaction [53,54]. The reaction progress was followed via UV-Vis spectroscopy. 4-NP has a maximum absorption peak at 318 nm. Upon the addition of NaBH4, this peak change to 400 nm due to the formation of phenolate. After reduction of the phenolate ion, the peak at about 400 nm is flattened and the amine peak appears at 300 nm. In order to evaluate the reaction rate, the concentration chart was plotted against the absorption [55].
2-2-2- Reduction of 2-NP to 2-AP
An aqueous solution of orthonitrophenol (10-3 M, 1 mL) and fresh NaBH4 (10-2 M, 1 ml) was added into a quartz cell. 3 mg of the catalyst was then added to the mixture to begin the reduction reaction [54]. The UV-Vis absorption spectra were recorded Orthonitrophenol shows two absorption peaks in the range of 250-500 nm. After the reduction of this compound, the peak at 420 nm was flattened and the amine peak, which overlaps with one of the 2-NP peaks, appeared at 280 nm. In order to evaluate the reaction rate, the concentration
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chart was plotted against the absorption [56].
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Fig.3. Scheme of mechanism of reduction 4-NP
3- Result and discussion
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3-1- FT-IR studies
The FT-IR spectra of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO are shown in (Fig. S1).
The peaks located at 3450 and 1640 cm−1 are ascribed to the H2O stretching and bending vibrations of adsorbed water, respectively [57, 58]. The peaks shown in the 550-653 cm-1 range are attributed to metal-oxygen bonds. In the Fe3O4 spectra, the peak at 559 cm−1 is ascribed to Fe-O bond [50]. The presence of Cu(II) and Ti(IV) metals on the catalyst surface was confirmed by a sharp peak in the range of 1300-1400 cm-1, which were due to the stretching vibrations of Cu-O-Ti [50, 58]. It should be noted that the peak corresponding to the vibrational stretching mode of O-Ti-O was observed in the range of 400-700 [49]. The
stretching vibration of Ti-O located at 500-600 cm-1 could not be recognized due to overlapping with the vibrational stretching of Fe-O in this region [59]. 3-2- DRS
DRS spectra are demonstrated in (Fig. S2). The band gap energies determined by drawing the intercept of the tangent to the graph obtained by plotting the Kubelka-Munk function (ahν = (1-R(hν)) ^.5/2R(hν)) and (hν) are shown Fig 4. [60, 61]. The band gap energies were obtained as 2.1 and 1.9 (eV) for Fe3O4/TiO2 and Fe3O4/TiO2/CuO, respectively (Fig. 4). These results indicate that the reduced energy gap can be due to the p-n heterojunction in the catalyst and addition of CuO to the composite reduced the band gap to
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absorption of sun light [62].
Fig.4. Tauc plot for the determination of band gap
3-3- XRD Studies
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Fig. 5 shows the XRD patterns of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO samples.
The absorption peak at 2θ = 18 is related to the crystal plane in (111), which is ascribed to the layers of titanium dioxide and copper(II) oxide on the surface of the magnetic nanoparticles [63, 64]. The other important peaks at 2θ = 30 (022), 35(113), 57(115), 62(044), 77(335) and 82(155) plane of Fe3O4 are associated with the inverse spinel structure. Titanium dioxide was observed as Rutile(R) at 2θ = 35(011), 43.820(120), 62.330(022), 63.702(130) [65] and anatase(A) at 2θ = 25.156(011), 38.314(110), 47.782(020), 54.753(121) phase [65-66]. (JCPDS file No. 96-900-4143 and 96-900-8216). The presence of Rutile and Anatase in the nanocomposite together enhanced the photocatalytic activity of the nanocomposite [67].
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Fig.5. XRD patterns of room temperature
3-4- XPS analysis
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Fig (S3a) showed the full scan XPS spectra of the magnetic Fe3O4/TiO2/CuO nanoparticles. The C 1s lines (Fig. S3b) displayed three peaks with diff erent intensities,
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which corresponded to different types of carbon. The binding energies of 290.8eV, 291.8eV and 293.9eV were related to C-C, C=C and C=O, respectively [68]. Fig (S3c) showed the XPS spectra of O 1s core level of the sample. The binding energy observed at 535.4, 537.8
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and 537.9 eV could be attributed to –OH of the surface, Ti-O-Ti and Fe-O, respectively [69]. Ti 2p (1/2) and Ti 2p (3/2) binding energy of TiO2 was seen at 471.4 and 464.7 eV (Fig.
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S3d). Binding energy of Cu 2p in Fe3O4/TiO2/CuO was shown in Fig (S3e). The binding energies of CuO and Cu 2p (1/2) and Cu 2p (3/2) were 961.7eV, 948.6eV and 941.2eV, respectively. Finally based on the results the copper(II)oxide was loaded on the surface as CuO. While the titanium dioxide was seen as TiO and TiO2. 3-1- FE-SEM studies
Morphology, surface uniformity and the size of particles can be investigated by FE-
SEM analysis. The FE-SEM images of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO nanoparticles are shown in (Fig. S4). Based on the FE-SEM images, Fe3O4/TiO2/CuO nanoparticles have a spherical morphology, which is confirmed by the good dispersion of the nanoparticles in the structure [49]. The EDX spectra of the prepared Fe3O4/TiO2/CuO nanoparticles are shown in
(Fig. S4). In this spectrum, the presence of Fe, Ti, O, and Cu is confirmed. EDX spectra clearly confirms the formation of nanoparticles as proposed structure [49]. 3-2- TEM studies
TEM was used to characterize the surface morphology of Fe3O4/TiO2/CuO (Fig.6). The scheme represents the spherical shape with proper distribution of the particles. The CoreShell structure of the nanoparticles is confirmed by TEM analysis. According to the TEM analysis, Fe3O4 coating by TiO2 has been performed. In addition, loading of CuO on the surface of Fe3O4/TiO2 has been carried out. From the histogram (Fig.6), the average size of
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the nanoparticles synthesized is about 8 nm.
b)
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a)
c)
d) Fig.6. a, b, c) TEM image and d) histogram curve of Fe3O4/TiO2/CuO
3-3- Magnetic Measurements (VSM)
The S-shaped curve magnetization of Fe3O4, Fe3O4/TiO2 and Fe3O4/TiO2/CuO were shown in Fig.7. This analysis was performed at room temperature. According to the results, the first amount of magnetization saturation of Fe3O4 is 50 emu/g. After coating with TiO2, the saturation magnetization of Fe3O4 reduced to 16 emu/g, indicating that the coating process has been successfully performed [31]. Furthermore, after loading CuO on the surface of Fe3O4/TiO2, the magnetism was reduced to 10 emu/g. This indicated that the copper
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particles were over the surface of the nanoparticles.
Fig.7. Magnetization of Fe3O4, Fe3O4/TiO2, Fe3O4/TiO2/ CuO
3-4- ICP
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To prepare the samples for ICP analysis (Table 1), a certain amount of
Fe3O4/TiO2/CuO nanocatalyst was dissolved in nitric acid (15 M) before and after the reduction reaction of paranitrophenol. This analysis was used to evaluate the weight of copper (II). A solution containing 10 ppm of the sample was prepared for this purpose. The results are as follows.
Table 1. The ICP analysis of Cu(II) in Fe3O4/TiO2/CuO Times of reduction reaction 4-NP
Cu(II) (ppm)
Before reduction reaction
14.12
After first reaction
13.98
After fourth reaction 12.86
4- Photocatalytic activities of Fe3O4/TiO2/CuO for degradation of MB In this study, Fe3O4/TiO2/CuO nanoparticle was applied in the degradation of MB in the presence (Fig. S5) and absence of H2O2 (Fig.8) on sun light irradiation. To study the absorption of MB by the catalyst, a solution containing both MB and the catalyst was placed inside a dark room for 4 h (Fig. S6). Moreover, the degradation of MB was studied in different acidic (pH = 5), neutral (pH = 7) and basic (pH = 9) solutions (Table. 3). The
of
reaction progress was followed by UV-Vis spectroscopy in 5 min time intervals (Fig. 8). Based on the results, the degradation in acidic media took 4 or 24 h in the presence and
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absence of H2O2, respectively (Fig. S7). The results show that the shortest photocatalyst degradation was observed in the basic solution (5 min) (Fig. S7). In contrast to the acid
-p
solution, the degradation time in neutral and basic solutions decreased in the absence of H2O2. MB degradation time in the basic solution is very reasonable and the reaction is
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complete in about 5 min. In basic media the negative sites on the surface are significant. So the interaction of cationic dye’s molecules with the negative sites on nanocomposite is
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significant, leading to higher degradation rate [70,71]. However, the degradation time in the neutral media was 22 min. Considering the environmental contamination and cost issues, neutral media was selected and further studies on the degradation of MB were carried out in
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this media. The reaction was repeated for 5 times and Fe3O4/TiO2/CuO photocatalyst was separated easily by a super magnet (Fig.9). In addition, the degradation time did not change in the next reactions such that the fifth degradation cycle took less than 25 min. (Table 2).
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Furthermore, there are some reported applications on the degradation of organic dyes via magnetic photocatalysts (Table 4), in most of which ultraviolet irradiation was applied as the source of light [52, 72]. In addition, the best reported degradation time was at least 40 min. [52,72]. To refine these parameters, in this study, a separable and reproducible photocatalyst was prepared and applied in the degradation of MB in sun light for 22 min. in neutral media. Eq. (1) is the kinetic equation of degradation of MB. 𝐿𝑛
𝐶 𝐶0
= −𝑘 𝑡
Eq. (1)
where C0 and C are concentrations of MB at t = 0 and at time t, respectively, and k is the rate constant (Fig. 8b). (The ratio C/C0 = A/A0 at 670 nm) [60]. In addition, Eq. (2) shows the degradation of MB. 𝑙=
𝐶0 −𝐶 𝐶0
× 100
Eq. (2)
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In this equation, C0 and C are concentrations of MB at t=0 and t, respectively.
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a)
Time(s)
0
Ln A/A0
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0
500
1000
1500
2000
-1
-2
K = 0.0018 R² = 0.9915
-3
b) Fig.8. a) degradation of MB 22 min (Without H2O2) and b) Plots of ln(A/A0) vs. time for degradation MB by Fe3O4/TiO2/CuO
Table 2 Recovery of Fe3O4/TiO2/CuO in degradation reaction MB Number of recovery
1
2
3
4
5
Time(s)
1500
1620
1740
1750
1750
Rate constant
18×10-2
2×10-3
1.7×10-3
1.5×10-3
1.3×10-3
0
300
600
900
1200
1500
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-2
-p
Ln A/A0
-1
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Time(s) 0
-3
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-4
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Fig.9. The reusability of Fe3O4/TiO2/ CuO in degradation of MB at visible light irradiation
Table 3. Conditions of the photocatalyst reactions H2O2 Without " " With " "
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pH 6.8-7.5 9 5 6.8-7.5 9 5
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Media neutral basic acidic neutral basic acidic
Time(min) 22 5 20hours 25 15 4
Degradation % 99.12 99.78 87< 96 99.04 93
Table 4. Degradation of MB with other catalysts
Catalyst Ag/AgBr/TiO2 Ce-doped MoO3 Ag3PO4 Fe3O4/ PCL Fe3O4/TiO2/Ag Fe3O4/TiO2/CuO
Time(Min) 90 50 10 150 100 22
Concentration 10 ppm 5 ppm 16 ppm 10 ppm 10 ppm 10 ppm
Reference [73] [72] [74] [52] [75] this study
5- Catalytic activities of Fe3O4/TiO2/CuO in the reduction of para and orthonitrophenol The catalytic reduction of para and orthonitrophenol to para and orthoaminophenol using NaBH4 as the reducing agent has been carried out as a model reaction to evaluate the catalytic efficiency of Fe3O4/TiO2/CuO (Fig. 10). UV-Vis spectroscopy was used to monitor the reduction progress. Based on the reported works, the normal conditions for this reaction are 10-4 M 4-NP and 10-2 M NaBH4 [35, 39, 76]. Here, in the presence of Fe3O4/TiO2/CuO, the reaction was complete less than 1 min. Therefore, the reaction was performed using 10-4 M 4-NP and 10-3 M NaBH4 to follow the reaction and determine the rate constant. Under
of
these conditions, the reduction reaction was over in 2 min (Fig.10). Eq. (3) is applied to determine the reaction rate (Fig. 10): Eq(3)
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(ln A/A0 = -kt)
0 and time t, respectively, and k is the rate constant.
-p
where A0 and A are the absorbance values of 4-NP (400 nm) and 2-NP (420 nm) at t =
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The reduction of 4-NP was repeated 4 times (Fig.11) in the presence of Fe3O4/TiO2/CuO catalyst (Table 5). In addition, the last reduction reaction was taking less than 4 min. To compare the reduction reaction of paranitrophenol with other cases, some of
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the reported catalysts are shown in Table 6. Unlike the catalysts reported in the literature for the reduction of paranitrophenol, Fe3O4/TiO2/CuO catalyst is separable and reproducible. In
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addition, the concentration of NaBH4 and the reaction time are less than the reported values. The electronic spectra of pure para and orthoaminophenols (Merck company) (Fig 10. a) and b)) were recorded and compare to electronic spectrum of reaction product to confirm para and
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orthoaminophenols.
c)
Time(S)
0 0
d)
50
100
Time(S) 0
150
0
50
K = 0.0296 R² = 0.9924
-3
-1
-2
K = -0.0206 R² = 0.9691
-3
-p
-4 -4
150
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-2
100
ro
Ln A/A0
Ln A/A0
-1
-3
Table 5. 1
Time(S)
120
2.96×10- 3
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Rate constants
Recovery of Fe3O4/TiO2/CuO in reduction reaction
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Number of recovery
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Fig.10. Reduction of a) 4-NP (10 M) and b) 2-NP (10 M), (c and d) Plots of ln(A/A0) vs. time for reduction para and orthnitrophenols with Fe3O4/TiO2/CuO
2
3
4
120-150
150
180
12.6×10-3
11.7×10-3
8×10-3
Time(S)
0
Ln A/A0
0
-1
-2
-3
50
100
150
Fig.11. The reusability of Fe3O4/TiO2/ CuO in reduction 4-NP
Table.6. Reduction of 4-NP with other catalyst Time(S)
180
Catalyst
NaBH4 10-2 M
Rate constant(s-1)
Reference
10
12.8 × 10-3
[53]
1
_
[57]
62.4 × 10-5
[77]
[79]
Pdcomplex on GO-MnFe2O4 Cu/graphene
480
Calcium-AlginateStabilized Ag Nanoparticles
540
CuO-RGO nanocomposite
4
25 × 10-4
600
CuO nanocrystal
4
_
720
AgNP/rGO
10
691 × 10-5
60
Pd/GNS-NH2
300
Cu@GE composite
-
120
Fe3O4/TiO2/CuO
0.1
[79] [54]
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10
of
360
1.8
[78]
_
[39]
-p
0.2
This work
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29.6 × 10-3
6- Conclusion
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Magnetic Fe3O4/TiO2/CuO nanoparticles have been synthesized in this work. Nanoparticles were characterized via different techniques. TiO2 and CuO, as n-type and ptype semiconductors, respectively, have been coated on Fe3O4 as core-shell. The separable
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composite was applied as a photocatalyst in the degradation of MB in sun light. Moreover, the presence of CuO in the composite enables the application of Fe3O4/TiO2/CuO catalyst in the reduction of para and orthonitrophenol. Easy separation, high efficiency, excellent
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stability and recyclability of the catalyst without any loss in its efficiency are the main advantageous of Fe3O4/TiO2/CuO Therefore, it is proposed as a suitable catalyst and photocatalyst for the removal of pollutants from waste waters.
AUTHORS STATEMENT FOR PUBLICATION Component of the research
Author’s number
substantial contribution to conception Ali Hossein Kianfar andofdesign substantial contribution to acquisition Ali Hossein Kianfar Amin substantial contribution to analysis and data Mohammad Arayesh interpretation of data
Mohammad Amin drafting the article Arayesh critically revising the article for important Ali Hossein Kianfar intellectual content final approval of the version to be Ali Hossein Kianfar published
Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the
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work reported in this paper
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