NiWO4 nanocomposites by polymeric capping agents

Journal of Molecular Structure 1157 (2018) 607e615

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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc

Investigation of optical properties and the photocatalytic activity of synthesized YbYO4 nanoparticles and YbVO4/NiWO4 nanocomposites by polymeric capping agents Saeid Pourmasoud a, Ali Sobhani-Nasab b, *, Mohsen Behpour c, Mehdi Rahimi-Nasrabadi d, Farhad Ahmadi e a

Department of Physics, University of Kashan, Kashan, Iran Young Researchers and Elites Club, Arak Branch, Islamic Azad University, Arak, Iran Institute of Nano Science and Nano Technology, University of Kashan, P. O. Box 87317-51167, Kashan, IR, Iran d Department of Chemistry, Faculty of Pharmacy, Baqiyatallah University of Medical Sciences, Tehran, Iran e Department of Medicinal Chemistry, School of Pharmacy-International Campus, Iran University of Medical Sciences, Tehran, Iran b c

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 2 January 2018

YbVO4 nanoparticles YbVO4/NiWO4 nanocomposites were synthesized by simple and new method. The effect of various polymeric capping agents such as Tween 80, Tween 20 and PEG on the shape and size of YbVO4/NiWO4 nanocomposites were investigated. YbVO4/NiWO4 nanocomposites were analyzed through some techniques including, X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM), thermogravimetry differential thermal analysis (TGDTA), transmission electron microscopy (TEM), field emission electron microscopy (FESEM), ultraviolet evisible spectroscopy (UVeVis), and energy-dispersive X-ray spectroscopy (EDX). This attempt is the first study on the photocatalytic performance of the YbVO4/NiWO4 nanocomposites in various conditions such as size of particles and kind of dyes (rhodamine B (Rh B), methylene blue (MB), methyl orange (MO), and phenol red (Ph R)), under visible light. © 2017 Published by Elsevier B.V.

Keywords: YbVO4/NiWO4 Visible light Nanocomposites New method Photocatalytic

1. Introduction At present, due to water pollution, removing disease-causing microorganisms or pathogens, from fresh water has received much attention. When a pollutant enters a water supply including, lakes, rivers, and oceans, it may either accumulate on the bed or floats on the water. As a result, the quality of water decreases [1e4]. Dyes are considered as the most important and carcinogenic substances. They are released into the water from different sources such as paper, paint, plastic, and textile industries. Rhodamine B and methylene blue (MB) are heterocyclic dyes and have various industrial usages. However, they can negatively affect our ecosystem owing to their toxic and mutagenic nature. Also, they collect in the environment. Up to this point, numerous attempts have been conducted for removal of those dyes from water [5e9]. Nowadays Vanadates are being used in different fields such as

* Corresponding author. Tel: þ98 9137290874; Fax: þ98 3155316558. E-mail address: [email protected] (A. Sobhani-Nasab). https://doi.org/10.1016/j.molstruc.2017.12.077 0022-2860/© 2017 Published by Elsevier B.V.

photocatalyst [10], photoluminescence devices [11], lithium ion batteries [12], super capacitors [13,14], antibacterial additives [15], gas sensors [16], catalysts [17], ion-exchange materials [18], and water splittings [19]. YbVO4 nanoparticles are well known for making an appropriate medium in photocatalytic systems. This effort investigates the study of the synthesis of YbVO4/ NiWO4 nanocomposites by the co-precipitation process and their photocatalytic properties under visible light. Up to this point, this is a first report on the preparation of YbVO4/NiWO4 nanocomposites. Using polysorbate 80 (Tween 80), polysorbate 20 (Tween 20), and (PEG) with two metal to polymer molar ratios of (1:1) and (1:2), can be considered as the originality of the preparation of YbVO4/NiWO4 nanocomposites. These nanocomposites are determined through Fourier transforms infrared spectroscopy X-ray diffraction, scanning electron microscopy, cyclic voltammetry, UVevisible absorption, vibrating sample magnetometer, and X ray energy dispersive spectroscopy. We investigated photocatalytic properties of YbVO4/NiWO4 nanocomposities performance in various conditions, such as kind of dyes (rhodamine B (Rh B), methylene blue (MB), methyl orange

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(MO), and phenol red (Ph R)), and particle sizes under visible light (l > 400 nm). Considering these points that YbVO4/NiWO4 nanocomposites reflect an appropriate respond to our photocatalytic experiments, sunlight is composed of 43% visible light (with wavelength 400 through 700 nm) and approximately 7% ultraviolet, and obtaining consistent results with visible spectrum, one can reasonably expect degradation of dyes mentioned above under the light from the sunlight [1,2].

were obtained on LEO-1455VP equipped with an energy dispersive X-ray spectroscopy. The EDX analysis with 20 kV accelerated voltage was done. Transmission electron microscopy (TEM) image was found by a Philips EM208 transmission electron microscope with an accelerating voltage of 200 kV. The diffused reflectance UVevisible spectrum (DRS) of the sample was recorded by a V-670 UVeViseNIR Spectrophotometer (Jasco). 2.4. Photocatalytic measurements

2. Experimental 2.1. Synthesis of pure YbVO4 Firstly, 1 mmol of Yb(NO3).6H2O was dissolved in 20 mL of distilled water to form solution A. Next, to form solution B, 1 mmol of NH3VO4 and 3 mmol of capping agent were mixed and dissolved in 30 mL of water. Afterwards, both solutions were mixed dropwise under constant stirring for 15 min at room temperature. Then, Prior to be washed by distilled water for three times in succession and dried in vacuum at 60  C, the solution was cool down to room temperature and the precipitation was centrifuged, dried and calcined at temperature 500  C for 90 min. 2.2. Synthesis of pure YbVO4/NiWO4 nanocomposite Herein YbVO4/NiWO4 nanocomposites were prepared by coprecipitation method. To do so, YbNO3.6H2O and polymeric capping agents with different molar ratios were dissolved in 30 mL of water according to Table 1 which we called solution A. The solution B was formed by adding 1 mmol of NH4VO3 to 30 mL of water. Next, solution A was added to solution B with vigorous and constant stirring to make solution C. Subsequently, 1 mmol of NiCl2.4H2O and 1 mmol of Na2WO4.H2O solution were constructed individually, and was added to previous solution (solution C) in constant stirring. Finally, the obtained precipitation was washed three times with distilled water, dried, and calcined at temperature 500  C for 90 min. Scheme 1 presents schematic diagram of the formation of the YbVO4/NiWO4 nanocomposites. 2.3. Materials and physical measurements All of the chemicals used in synthesis of YbVO4/NiWO4 nanocomposites including iron ytterbium nitrate pentahydrate, ammonium metavanadate, sodium tungstate, polysorbate 80 (Tween 80), polysorbate 20 (Tween 20), and polyethylene glycol (PEG) were purchased from Merck Company and didn't purify any more. The XRD patterns were recorded by a Philips-X'pertpro, X-ray diffractometer using Ni-filtered Cu Ka radiation. Fourier transform infrared (FT-IR) spectra were recorded on Nicolet Magna- 550 spectrometer in KBr pellets. The electronic spectrum of the sample was taken on PerkineElmer LS-55 luminescence spectrometer. GC2550 TG (Teif Gostar Faraz Company, Iran) were used for all chemical analyses. Scanning electron microscopy (SEM) images

The photocatalytic activities of YbVO4/NiWO4 nanocomposites were tested by different dyes. The degradation reaction was performed in a quartz photocatalytic reactor. The photocatalytic degradation was conducted with 5  105 M of solutions including 0.05 g of nanoparticles, and the mixture was aerated for 30 min to reach adsorption equilibrium. Then, the mixture was located in the photoreactor in which the vessel was 20 cm away from the light source. A 400 W Osram lamp was employed as a visible light source. The experiments were performed at room temperature. Moreover, the pH of the solutions was regulated to 3. The mixture was aliquoted in periodic intervals during the irradiation, and prior to be analyzed with the UVeVis spectrometer, it was centrifuged. The percentage of dyes degradation was computed as the following formula: Degradation rate (%) ¼ 100 (C0- Ct) / C0

(1)

In which C0 and Ct are the absorbance value of solution at 0 and t min, respectively. 3. Results and discussion Production of YbVO4 nanostructures (Fig. 1a) has been shown in the XRD pattern of YbVO4 nanoparticles. It has been obtained from the molar ratio of polymer to metal (1:1). Then, The XRD patterns of YbVO4/NiWO4 nanocomposites with the molar ratio of polymer to metal (1:2) and different capping agents such as Tween 80, Tween 20, and PEG have been displayed in Fig. 1aec respectively. As our findings show, all prepared nanocomposites are pure and have two phases including, the phase of YbVO4 and NiWO4 with crystal structure of tetragonal (JCPDS 17-0338) and space group of I41/amd and monoclinic (JCPDS 15-0755) with space group of P2/c respectively. Considering Fig. 1aec and Scherrer's equation, the crystallite diameter (Dc) of products can be obtained as following [20]: Dc ¼ Kl/bcosq;

(2)

In which K is the so-called shape factor, which commonly takes a value of approximately 0.9, b is the breadth of the noticed diffraction line at its half intensity maximum, and l is the wavelength of X-ray source applied in XRD. The domain sizes of evaluated crystalline have been found out to be 38.2, 31.3, and 22.8 nm, respectively. Therefore, one can conclude that the steric hindrance

Table 1 The preparation conditions of the YbVO4 nanostructures and YbVO4/NiWO4 nanocomposites.

1 2 3 4 5 6 7



Capping agents

Molar ratio (M:Capping Agents)

Temperature C

Product

Figure of SEM images

PEG PEG Tween Tween PEG Tween Tween

(1:1) (1:1) (1:1) (1:1) (1:2) (1:2) (1:2)

500 500 500 500 500 500 500

YbVO4 YbVO4/NiWO4 YbVO4/NiWO4 YbVO4/NiWO4 YbVO4/NiWO4 YbVO4/NiWO4 YbVO4/NiWO4

e Fig3a Fig3b Fig3c Fig4a Fig4b Fig4c

20 80 20 80

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609

Scheme 1. Schematic diagram of preparation of YbVO4/NiWO4 nanocomposites.

of capping agents, increases with the decrease in the size of nanocomposites. The confirmation of the purity of YbVO4/NiWO4 nanocomposites was performed through EDS technique. As illustrated in Fig. 2 (sample No. 7), the YbVO4/NiWO4 nanocomposites are

Fig. 1. XRD pattern of YbVO4/NiWO4 nanocomposites obtained with the molar ratio of polymer to metal (1:2) in the presence of three different capping agents (a) Tween 80, (b) Tween 20, and (c) PEG.

composed of five different elements, Yb, Ni, W, V, and O. Furthermore, no impurity peaks were seen which indicate high purity of as-prepared YbVO4/NiWO4 nanocomposites. Capping agents and surfactants used in inorganic chemistry can de-agglomerate particles by reduce of condensation reaction in liquid phase [21e25]. The effects of some parameters on the morphology of nanocomposites were investigated by various polymers as capping agents with two different molar ratios of polymer to metal. The YbVO4/NiWO4 nanocomposites with the molar ratio of polymer to metal (1:1) in the presence of three different capping agents including, Tween 80, Tween 20, and PEG have been depicted in Fig. 3aec respectively. Moreover, this figure illustrates that with increase in the steric hindrance of capping agents, from PEG toward Tween 80, (three different polymers), the size of final products becomes smaller. Fig. 4aec shows, fabricated nanocomposites with the molar ratio of polymer to metal (1:2) in the presence of Tween 80, Tween 20, and PEG respectively. We reconclude that increase in the steric hindrance of capping agents can lead to smaller particle size. Moreover, enhancement in polymer to metal molar ratio from (1:1) to (1:2) results in smaller and uniform nanocomposites. Schematic 2 shows the effects of capping agents and their different ratio on the size of final product. Based on this scheme, we

Fig. 2. EDS pattern of YbVO4/NiWO4 nanocomposites obtained with the molar ratio of polymer to metal (1:2) in the presence of Tween 80 (Sample No. 7).

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Fig. 3. SEM images of YbVO4/NiWO4 nanocomposites obtained with the molar ratio of polymer to metal (1:1) in the presence of three different capping agents (a) PEG, (b) Tween 20, and (c) Tween 80.

conclude that increase in steric hindrance and molar ratio lead to reduce of particle size. Concerning our findings for XRD and SEM patterns, one can deduce that as-prepared nanocomposites with Tween 80 and molar ratio of (1:2), can lead to production of NiWO4/ YbVO4 nanocomposites with uniform, sphere-like, and smaller particle size. TEM image was conducted to further verification of the morphology of YbVO4/NiWO4 nanocomposites. Based on Fig. 4 d, it was understood that the morphology of YbVO4/NiWO4 nanocomposites gained from sample No.6, is sphere-like nanostructures which were consisted of nanoparticles with average particle size of 50e55 nm. The FT-IR spectrum of the pure YbVO4 nanoparticles (sample No. 1) and YbVO4/NiWO4 nanocomposites (sample No. 7) after calcination at 500  C have been reported in Fig. 5 a and b respectively. Fig. 5a is associated with the sample after calcination. The characterization peaks in the YbVO4 nanoparticles spectrum are 818 cm1 (vibration of atoms intetrahedral oxygen environment; VeO at YbVO4) and 452 cm1 (vibration of ytterbium atoms in the octahedral oxygen environment in YbVO4 nanoparticles.

Fig. 4. SEM images of YbVO4/NiWO4 nanocomposites obtained with the molar ratio of polymer to metal (1:2) in the presence of three different capping agents (a) PEG, (b) Tween 20, c) Tween 80 and d) TEM image of YbVO4/NiWO4 nanocomposites obtained with the molar ratio of polymer to metal (1:2) in the presence of Tween 80 (sample No. 7).

Also, Fig. 5b is linked with the sample after calcination. The characterization peaks in the YbVO4 nanoparticles spectrum are 818 cm1 (vibration of O-V-O) and 453 (vibration of Yb-O) [11]. The characteristic peak at 573 cm1 (O-W-O bending mode) and those at 651 cm1 (Ni-O stretching modes) are the sign of YbVO4/ NiWO4 nanocomposites. The band located in the region 3200 3700 cm1 in the FT-IR spectrum of the as-produced nanostructures connects with the v(OH) stretching vibration of physisorbed water molecules [26]. Fig. 6, shows the TG-DTA curves of YbVO4-NiWO4 nanocomposites in the air atmosphere. The first two curves were endothermic (43-170  C), which were attributed to the elimination of water, dehydration, and gases adsorbed on the powder surface of YbVO4 and NiWO4 respectively. The second two samples were

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Scheme 2. Schematic the effects of capping agents and their different ratio on the size of final product.

exothermic (170-560  C), which may be due to the combustion of the organic material and decomposition of small amount of grafted metal hydroxides of Yb and Ni tungstate respectively. In Fig. 7 the magnetic properties of nanostructures verified at 300 K and nearly saturated nature of our final products at high field have been depicted by the hysteric curve. Our results revealed the magnetic contribution of as-prepared YbVO4/NiWO4 nanocomposites at room temperature. Furthermore, the VSM data validated that as-synthesized products have paramagnetic properties, and the correspondent magnetization value is approximately 0.042 emu/g at room temperature. The optical absorption properties of a semiconductor, which is

related to the electronic structure, can be considered as a key factor to specify the photocatalytic property. UVeVis diffuse reflectance spectra of YbVO4 and YbVO4/NiWO4 nanocomposites have been shown in Fig. 8 a. The optical band gaps of samples can be appraised by the Tauc's formula [27]:

a ¼ a0(hn-Eg)n/hn

(3)

in which a is absorption coefficient, hn is the photon energy, a0 and h are the constants, Eg is the optical band gap of the material, and n depends on the type of electronic transition and can take a value between 1/2 and 3. Band gap was estimated from the linear portion

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Fig. 5. TG/DTG curve of the as-synthesized powders (sample No. 7 before calcination steps).

Fig. 6. FT-IR spectra of (a) YbVO4 nanostructures (Sample No. 1) and (b) YbVO4/NiWO4 nanocomposites (Sample No. 7).

of the (ahn)2 vs. hn plots (Fig. 8b) and the optical band gaps of the heterojunction are calculated to be about 3 and 2.9 eV for YbVO4 and YbVO4/NiWO4 nanocomposites, respectively. The result showed that red shift in the YbVO4/NiWO4 nanocomposites can enhance photocatalytic properties in visible spectrum. Photocatalytic activities of neat YbVO4 and YbVO4/NiWO4 nanocomposites have been verified under visible light irradiation. In respect of Fig. 9 a, nanostructured YbVO4 (sample No. 1) can destruct only 45% of methylene blue pollutant, while destruction of this pollutant in YbVO4/NiWO4 nanocomposities (sample No. 2) can peak at 58%. It was observed that, NiWO4 has notable impact on

catalytic activity of NiWO4 photocatalyst for destruction. Interestingly, YbVO4 nanoparticles can result in a red shift in nanocomposites which leads to reduce in band gap and more adsorption in visible light. Moreover, it is offered that, introducing NiWO4 may give rise to appropriate distribution of YbVO4, facileness of the absorption of methylene blue pollutant and its transition to the active sites on YbVO4, as well as further separation of charge carrier. Therefore, it can bring about the enhancement in destruction efficiency of ytterbium vanadate to methylene blue pollutant. Thus, introducing NiWO4 can increase effectiveness of ytterbium vanadate [27e30]. A photocatalytic test as the blank test has been illustrated in Fig. 9 a. To verify the stability of Rh B under ultraviolet light, the blank test was carried out without catalyst powder. The efficiency of the blank test is 5% resulting in a relatively good stability. In Fig. 9 b, we have displayed the impact of different polymers and molar ratio of these polymers on photocatalytic behavior of the YbVO4/ NiWO4 nanocomposites at the temperature 500  C except for sample No. 1, which is at room temperature. Additionally, compounds with the molar ratio of polymer to metal (2:1), have better photocatalytic degradation. Moreover, fabricated nanocomposites with the polymer Tween 80 and the molar ratio of polymer to metal (2:1) which was sample No. 7 with 5 h calcination and degradation rate of 98%, demonstrated the most appropriate outcome for the photocatalytic test. Photocatalytic degradation of four different dyes as organic pollutant such as rhodamine B (Rh B), methylene blue (MB), methyl orange (MO), and phenol red (Ph R) by YbVO4/NiWO4 nanocomposites was performed under visible irradiation. It is obvious that in Fig. 9 c the photocatalytic activity of nanocomposites in decolouration of Rh B is higher than other dyes. The photocatalytic

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613

0.20 0.16

Magnetization(emu/g)

0.12 0.08 0.04 0.00 -0.04 -0.08 -0.12 -0.16 -0.20 -10000 -8000 -6000 -4000 -2000

0

2000

4000

6000

8000 10000

Applied Field(Oe) Fig. 7. VSM curve of YbVO4/NiWO4 nanocomposites calcined at 500  C (Sample No 6).

efficiencies of Rh B, MB, MO and Ph R are 98%, 91%, 71%, and 65% correspondingly. When the light irradiation excites the sample, electrons from valance band transfer to conduction band. Keeping in mind that visible light has low energy and high wavelength, electrons can be excited and produce electron and holes which require a very long period of time. For this reason, in this attempt more time was applied to explore the degradation of dyes under visible irradiation. In the previous studies, there were reports on the usage of a long induction period of time for visible light photocatalytic activity. This substantial dissimilarity can be ascribed to the point that in this procedure, the anionic contaminant adsorption on YbVO4/ NiWO4 nanocomposites is smaller than the quantity of adsorption of cationic contaminant on it. The electron density of oxygen atoms on the surface of our final products, is significant which stems from the negative charge of YbVO4/NiWO4 nanocomposites which adsorb the cationic contaminants (MB) with positive charge. The offered procedure of photocatalytic degradation of MB may be as following: YbVO4/NiWO4 þ hn / YbVO4/NiWO4 þ e þ hþ

(4)

e þ O2 / O2-

(5)

O2- þ H2O / OOH þ OH

(6)

OOH / O2 þ H2O2

(7)

H2O2 þ O2- / OOH þ OH þ O2

(8)

OH þ Dye / Degradation products

(9)

hþþ Dye / degradation products

Fig. 8. UVevis diffuse reflectance spectrum (a) of the as prepared YbVO4 nanostructures and YbVO4/NiWO4 nanocomposites (sample No. 1) and (b) Tauc plot pattern YbVO4 nanostructures and YbVO4/NiWO4 nanocomposites (sample No. 7).

(10)

The composition procedure of contaminants for the YbVO4/ NiWO4 nanocomposites has been depicted in Scheme 3. These consequences demonstrated a high degree of competence of the YbVO4/NiWO4 nanocomposites (sample No. 7) which can be employed as a suitable, new, and favorable type of photocatalyst

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Fig. 9. (a) The photocatalytic behavior of YbVO4 nanostructures (sample No. 1) and YbVO4/NiWO4 nanocomposites (sample No. 2), (b) Photocatalytic RhB degradation of YbVO4/ NiWO4 nanocomposites under visible light (samples No. 2-7), (c) The photocatalytic behavior of YbVO4/NiWO4 nanocomposites (sample No. 7) on decomposition of various contaminants (cationic and anionic types) and (d) Effect of the reuse of the YbVO4/NiWO4 nanocomposites on the degradation efficiency of RhB (sample No. 7).

Scheme 3. Schematic illustration of charge transfer in a coupled semiconductor system.

under visible light for elimination of cationic contaminants. Moreover, applying of polymers as capping gents for production of nanocomposites is the creativity of this effort. Moreover, changing the capping agent resulted in production of a fine grain size, very homogenous and sphere-like YbVO4/NiWO4 nanocomposites.

Interestingly, to the best of our knowledge, in the literature, there is no report on the study of photocatalytic behavior of YbVO4/NiWO4 nanocomposites. Furthermore, the photocatalytic activity of final products can be affected by various factors such as grain size of YbVO4/NiWO4 nanocomposites and kind of pollutant. The

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outcomes demonstrated that the YbVO4/NiWO4 nanocomposites show considerable possibility to be used as a proper, useful, and innovative kind of photocatalyst under visible light for. As a result, they can erase cationic contaminants. Respecting the production of YbVO4/NiWO4 nanocomposites, one can simply understand the convenience, facileness, and originality of the approach mentioned above [27e30]. In addition, repeated degradation reactions have been conducted to obtain the stability of the YbVO4/NiWO4 nanocomposites. As noticed in Fig. 9 d, the YbVO4/NiWO4 nanocomposites (sample No. 7) did not demonstrate any substantial loss of activity after five consecutive reaction cycles, indicating the high stability of catalyst. The degradation efficiency was reduced to 90% after five cycles. The results of photocatalysis survey clearly disclosed that YbVO4/NiWO4 nanocomposites may be applied as useful and effective photocatalyst under visibile light.

[8]

[9]

[10]

[11] [12]

[13]

4. Conclusions [14]

In summary, a simple co-precipitation process has been carried out for the preparation of the YbVO4/NiWO4 nanocomposites, for the first time. The synthesis of YbVO4/NiWO4 nanocomposites were appraised through different parameters such as type of capping agents (Tween 80, Tween 20 and PEG) with two polymer to metal molar ratios to reach conditions of optimum shape and size. It was found that optimum shape and size can be obtained with the usage of Tween 80, as a capping agent, and the metal to polymer molar ratio of (1:2). In this work, photocatalytic, optical, and magnetic properties of the products were examined. Moreover, the photocatalytic properties of the product were investigated in the presence of different dyes such as methylene blue, methyl-violet, methyl orange, and rhodamine B. The highest and lowest percentages of degradation of dyes were obtained for rhodamine B phenol red dyes with 98% and 65%, respectively. According to the results, one can suggest the high potential of final products for the photocatalytic applications under visible light in degradation of methyl violet dye. Conflicts of interest The authors declare that they have no conflict of interest.

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Acknowledgment [24]

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