Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water

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Original Article

Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water Reza Mohassel a , Mahnaz Amiri b,c , Ali Kareem Abbas d , Azam Sobhani e , Mahdi Ashrafi a , Hossein Moayedi f,∗ , Masoud Salavati-Niasari a,∗ a

Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box. 87317–51167, Iran Neuroscience Research Center, Institute of Neuropharmacology, Kerman University of Medical Science, Kerman, Iran c Cell Therapy and Regenerative Medicine Comprehensive Center, Kerman University of Medical Science, Kerman, Iran d Department of Chemistry, College of Applied Medical Sciences, University of Kerbala, Kerbala, Iraq e Department of Chemistry, Kosar University of Bojnord, Bojnord, Iran f Institute of Research and Development, Duy Tan University, Da Nang, 550000, Viet Nam b

a r t i c l e

i n f o

a b s t r a c t

Article history:

Gd2 NiMnO6 (GNMO NSs) nanostructures were synthesized via a Pechini method using

Received 10 October 2019

propylene glycol (PG) as alkaline agent and various acid solutions as stabilizing agents.

Accepted 2 December 2019

Effect of temperature, time and stabilizing agent was investigated in order to reach the finest

Available online xxx

nanostructures. The morphology, structure and magnetic property of nanostructures examined by XRD, SEM, HRTEM, FTIR, BET and VSM techniques. The photocatalytic degradation

Keywords:

ability of GNMO NSs for the removal of different dyes from wastewater was reported. The

Gd2 NiMnO6

obtained adsorbent with porous structure not only displayed fast rate adsorption, greater

Pechini

capacity adsorption, and promising selectivity adsorption to various dyes but also presented

Stabilizing agent

convenient magnetic separation characteristic. Rapid decomposition of dye observed with

Photocatalytic property Nanostructures

a rate of degradation, more than 90 % within the initial 105 min, which is qualified to the ˜ porous structure, great surface area (6.1735 m2 g−1 ), narrow of pore size (106.09 nm) assessed

Dye degradation.

from adsorption-desorption isotherms analysis of N2 as well as outstanding electron accepting structures of the planned porous nanoparticles. Consequently, prepared nanocomposite indicated the great potential to be considered as an active and rapid magnetic adsorbent for the dye removal from wastewater. © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

∗

Corresponding author. E-mails: [email protected] (H. Moayedi), [email protected] (M. Salavati-Niasari). https://doi.org/10.1016/j.jmrt.2019.12.003 2238-7854/© 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/). Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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1.

Introductions

Considerable attention has been focused on double perovskite oxides with formula A2 BB’O6 (A = rare earth, B and B’ = metal transition elements) which B is partially filled, and B is empty eg the orbital, or contrariwise [1]. The double perovskites possess 180◦ super-exchange communications among B’ and B cations by the oxygen ions [2–5] which suggests ferromagnetic insulators and provide a unique opportunity for promoting multiferroic behavior [1]. The ordering among B site cations causes misrepresentation of the sites of metal, leaning of the octahedral and lowering of perovskite symmetry as well [2]. The magnetical and electric nature of A2 BB O6 ceramics could be altered by differences in B –O– B angle and bond length associated in the tilting, besides changing orbital overlap within BO6 sublattices [2]. Both presence of magnetic-caloric and electronic-caloric properties, with multi-caloric connection in A2 BB O6 motivated the double perovskites role in solid state cooling usage. Two factors of 1) magnetic moment and 2) room temperature magnetocaloric effect of Gd, Gd2 BB’O6 ceramics caused noteworthy research attention among all the rare earth elements. Gd and Ni based alloys, are essential because of their ferromagnetic insulating behavior and ferroelectric characteristics, magnetoresistance, magnetocaloric, magnetodielectric effects and technological applications, etc. [6–10]. Studies on GNMO oxides are relatively limited based on the new physical properties and synthetic methods that are of great interest. Moreover, these nanostructures have been synthesized previously [1,11]. In GNMO, spin moments of Gd3+ and Mn3+ are 7/2 and 2, respectively, wherever the maximum employed state stands the individual busy eg orbital that is a split because of Jahn-Teller interface [12]. Rapid development not solitary donates to important enhancement on economic activities but similarly effects in thoughtful pollution problems of environmental for instance wastewater pollution. These Organic dyes, that have been widely applied in industrial applications, considered the main wastewater impurities meanwhile bit dyes amount may cause thoughtful mutagen and carcinogen properties on ecology [13]. Consequently, it is critical to eliminate dyes from waste water beforehand settling them in the aquatic location. Till nowadays, numerous methods [14–17] for wastewater have been applied for dyes removing. Amongst them, method of adsorption due to ease of design, simplicity of the process, widespread suitability as well as low cost is observed as the greatest talented method [18]. Activated carbon adsorbents normally, indicated some properties similar to low capacity, slow rate, reusability and selectivity of adsorption. Consequently, considerable care is needed for developing of efficient adsorbents which instantaneously have high rate and capacity, superior selectivity as well as promising reusage. The present research is the first attempt on the GNMO synthesis in the existence of various acids via a Pechini method. The effect of calcination temperature, time reaction and different acids (as stabilizing agent) on morphology and size of GNMO NSs were examined, and the photocatalytic activity of synthesized nanostructures studied as well. Compared with the previously reported adsorbents, the synthesized adsor-

bent in the present work was anticipated to display collective merits that not only indicates greater adsorption behavior to dyes but also shows simplistic magnetic separation ability.

2.

Experimental

2.1.

Materials

All the materials used in these experiments, counting gadolinium nitrate (Gd(NO3 )3 ), nickel nitrate (Ni(NO3 )2 ), manganese nitrate hexahydrate (Mn(NO3 )2 .6H2 O), maleic acid, citric acid, 1,3,5-benzenetricarboxylic acid, succinic acid and PG were of analytical grade, purchased from Merck Company and used without further purification.

2.2.

Characterizations

FE-SEM and TEM images were obtained by TESCAN Mira3 FESEM and Philips EM208 transmission electron (200 kV voltage) microscopes, respectively. The XRD pattern was done by a diffractometer of Philips Company with X’PertPro monochromatized Cu K␣ radiation. EDS analysis was carried out by XL30, Philips microscope. A Nicolet Magna- 550 spectrophotometer was used to record the Fourier transform infrared spectrum (FT-IR). The specific surface area was determined using BET method, by BELsorp mini II instrument (Japan). A Shimadzu UV-1800 was used to carry out the absorption measurements. A vibrating sample magnetometer (VSM, Meghnatis Kavir Kashan Co., Kashan, Iran) was used for determination of the samples magnetic properties at room temperature.

2.3.

Synthesis of Gd2 NiMnO6 nanostructures

For the synthesis of GNMO, as shown in Scheme 1, at first the aqueous solutions of Gd(NO3 )3 , Ni(NO3 )2 and Mn(NO3 )2 .6H2 O with 2:1:1 molar ratio was prepared. The maleic acid, citric acid, 1,3,5-benzenetricarboxylic acid and succinic acid as stabilizing agents were added to the mixed solution composed of nitrate salts separately. Finally, PG was added under stirring. After the evaporation of the solvent the formed gel dried in an oven at 75 ◦ C and calcined at various temperatures (800–1000 ◦ C). Effect of the stabilizing agent, temperature and time of calcination on the morphology, particle size and product phase was examined. Table 1 indicates the reaction conditions for the synthesis of GNMO NSs.

2.4.

Photocatalytic tests

The degradation of three dyes under UV light irradiation (a 125 W mercury lamp) was investigated for photocatalytic ability evaluation of as-synthesized GNMO NSs. 50 mg of GNMO NSs was suspended in 50 mL of 5 ppm solution of various dyes (methyl violet (MV), erythrosine (ES), eriochrome black T (EBT) and methyl orange (MO)). The solutions using a magnetic stirrer were stirred in the dark for 30 min to reach adsorption/desorption equilibrium. The photocatalytic degradation was happened by irradiating the UV light at a distance of 50 cm to the suspension solution. Then the final solution was

Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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Scheme 1 – Diagram illustrating the formation and characterization of GNMO NSs.

centrifuged for removing the NSs. The dyes concentration in the solution was measured using a UV–Vis spectrophotometer. The degradation efficiency of dyes was determined as follows: Degradation % = {(A0 – A)/A0 } × 100; where A0 is the initial absorbance of dye solution, and A is the dye solution absorbance after irradiation at a certain reaction time [19].

2.5.

Statistical analysis

Statistical analysis was performed using SPSS. Significance among groups was evaluated by Student’s t-test and analysis of variances. The probability level of p < 0.05 was considered as statistical significance.

3.

Results and discussion

3.1.

SEM microscopy

The size and morphology of the prepared samples were investigated by scanning electron microscopy and reported in Figs. 1 and 2 respectively. Figs. 1 and 2 display the SEM images of GNMO NSs obtained in the presence of the different stabilizing agents. It is obvious that nanoparticles with under 10 nm diameter are formed in the presence of all four stabilizing agents.The agglomerated nanoparticles with irregular shape and different size are formed when succinic acid (Fig. 1a, b), maleic acid (Fig. 1c, d) and citric acid (Fig. 2a, b) are

Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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Table 1 – The reaction conditions of GNMO NSs synthesized in this work. Morphology

Time (h)

Calcination Temperature(◦C)

Acid:PG

Stabilizing agent

Effect

Sample

Nanostructures with irregular shapes and different sizes Nanostructures with irregular shapes and different sizes Nanostructures with irregular shapes and different sizes Semi-spherical nanostructures with almost same diameters Agglomerated nanoparticles Agglomerated nanoparticles Agglomerated nanoparticles

9

900

1:1.2

Citric acid

9

900

1:1.2

Maleic acid

9

900

1:1.2

Succinic acid

S900-9

9

900

1:1.2

1,3,5Benzenetricarboxylicacid

B900-9

5

900

1:1.2

B900-5

5

800

1:1.2

5

1000

1:1.2

1,3,5Time Benzenetricarboxylicacid 1,3,5Temperature Benzenetricarboxylicacid 1,3,5Benzenetricarboxylicacid

C900-9

Stabilizing agent

M900-9

B800-5 B1000-5

Fig. 1 – SEM images of GNMO NSs at 900 ◦ C for 9 h, in the presence of different stabilizing agents: (a, b) succinic acid, (c, d) maleic acid.

Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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Fig. 2 – SEM images of GNMO NSs at 900 ◦ C for 9 h, in the presence of different stabilizing agents: (a, b) citric acid, (c, d) 1, 3, 5-benzenetricarboxylic acid.

used. In the presence of 1,3,5-benzenetricarboxylic acid, semispherical nanostructures with almost similar diameters are formed (Fig. 2c, d). The structure of samples synthesized in the presence of dissimilar stabilizing agents have been revealed in Scheme 1. Generally, the presence of two or three carboxyl functional groups produces barriers in order to protect nanoparticles from additional aggregation and show a significant character in the nanostructured formation. The succinic acid and 1,3,5-benzenetricarboxylic acid possess symmetrical structures that cause the formation of the nanostructures with smaller sizes, due to better morphology and smaller nanostructure size, the 1,3,5-benzenetricarboxylic acid was selected as the optimum stabilizing agent. In the continuation of the work, the effect of calcination time and temperature on the morphology and structure of the products was examined as well, while the stabilizing agent was nominated to be 1, 3, 5benzenetricarboxylic acid. By decreasing the calcination time from 9 h (Fig. 2c and d) to 5 h (Fig. 3a and b), the agglomeration of the nanoparticles increased obviously. In the case of calcination time, the diameters of the nanoparticles prepared in the presence of 1, 3, 5-benzenetricarboxylic acid after 5 h were different, as shown in Fig. 3a and b. Fig. 3 displays

SEM of nanostructures while increasing the temperature from 800 ◦ C (Fig. 3c and d) to 900 ◦ C (Fig. 3a and b) and then 1000 ◦ C (Fig. 3e and f), that illustrates agglomeration of the nanoparticles remains nearly constant that means, temperature only effects on the size increases. Generally, agglomeration may be attributed to the dipole-dipole magnetic interaction between neighboring particles that are basically the same as those consequences of under micrometer magnetite besides ferrite of manganese nanocrystal clusters [20]. However, it is renowned that magnetic nanoparticles have a tendency to agglomerate, because of not solitary their robust magnetic interactions but similarly their great surface energy. Consequently, the magnetic properties are more professionally studied by making the samples in the form of nanocomposites due to fundamental then applied investigations, that is, by separating the magnetic particles in inert matrixes comparable polymers, resins and etc., that are mutual and often used [21].

3.2.

TEM microscopy

The morphology of the best product was also studied by TEM at various magnifications for better understanding. Fig. 4 demon-

Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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Fig. 3 – SEM images of GNMO NSs in the presence of 1, 3, 5-benzenetricarboxylic acid at different temperatures, for 5 h: (a, b) 900 ◦ C, (c, d) 800 ◦ C, (e, f) 1000 ◦ C.

strates TEM images of B900-9 prepared in the presence of 1, 3, 5-benzenetricarboxylic acid at 900 ◦ C. The sizes and typical structure of nanospheres with narrow size distribution are clearly seen in TEM images, which is in consistent with the above-mentioned SEM analysis. Fig. 4 confirms SEM results in Fig. 2c and d that indicates the formation of the nanoparticles with diameters <10 nm and also formation of agglomerated

semi-spherical nanostructures. High-resolution transmission electron microscopy (HRTEM) analysis was done on randomly selected regions of the nanoparticles. The HRTEM image of GNMO NSs in Fig. 4d expressions that the nanostructures have crystalline nature and distance between the two adjacent planes is measured to be 0.125 nm.

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Fig. 4 – (a–c) TEM and (d) HRTEM images of GNMO NSs (B900-9).

3.3.

XRD analysis

The XRD pattern of the products prepared in the presence of the dissimilar stabilizing agents is shown in Fig. 5. The sharp and intense diffraction peaks propose that the obtained products are well crystallized. The crystallite diameters (Dc) of nanostructures obtained using the Scherrer equation, since D = K␭/␤cos␪, where ␤ is the breadth of the observed diffraction line at its half intensity maximum, the so-called shape factor is K, which usually takes a value of about 0.9, and ␭ is the wavelength of X-ray source used in XRD [22]. The sample prepared in the presence of citric acid (Fig. 5a) is God, GdO and Gd2 O3 . Fig. 5b indicate the formation of Gd2 NiMnO6 along with Gd2 O3 as impurity for the sample organized in the presence of maleic acid. Fig. 5c and d display XRD patterns of Gd2 NiMnO6 and GdNiO3 prepared in the presence of 1, 3, 5-benzenetricarboxylic acid at 900 and 1000 ◦ C, respectively. No notable diffraction picks of other phases such as God, GdO, Gd2O3 or other compounds observed in Fig. 5c. Consequently, based on the structural and morphological information, it can be detected that the use of 1,3,5-benzenetricarboxylic acid at 900 ◦ C is promising for the preparation of uniform

semi-spherical GNMO NSs with a pure orthorhombic crystal system.

3.4.

EDS analysis

For better understanding of the elemental composition of the as-synthesized GNMO NSs, the EDS analysis was done. The EDS patterns in Fig. 6 demonstrates the presence of Gd, Ni, Mn and O elements in chemical composition of the samples that was produced in the presence of 1,3,5-benzenetricarboxylic acid and maleic acid.

3.5.

FTIR investigation

Fig. 7a displays the FT-IR spectrum of product prepared in the presence of 1, 3, 5-benzenetricarboxylic acid at 1000 ◦ C. The appeared bands at 3449.77 and 1636.57 cm−1 are belonging to O H stretching and H O H bending vibrations of wastewater absorbed on GNMO NSs [23,24]. The bands at 596.96 and 467.07 cm−1 in Fig. 7a are corresponding to the vibrations of M O (M = metal). BET method was applied to determine the

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Fig. 6 – EDS patterns of GNMO NSs: (a) B1000-5, (b) M900-9.

Fig. 5 – XRD patterns of GNMO NSs prepared in the presence of: (a) citric acid at 900 ◦ C (C900-9), (b) maleic acid at 900 ◦ C (M900-9), (c) 1, 3, 5-benzenetricarboxylic acid at 900 ◦ C (B900-5), (d) 1, 3, 5-benzenetricarboxylic acid at 1000 ◦ C (B1000-5).

specific surface area and characteristic’ s porosity of GNMO NSs.

3.6.

Adsorption–desorption investigation

N2 adsorption–desorption isotherm of B1000-5 has been shown in Fig. 7b. According to the IUPAC classification, B10005 is a type III isotherm with a type H3 hysteresis loop. This hysteresis type is usually found on solids through aggregated or agglomerated particles forming slit shaped pores, without a uniform shape or size [25]. The SEM images of B1000-5 sample in Fig. 3e and f presented formation of agglomerated nanoparticles as well as the presence of pores that confirmed with BET results. Fig. 7b and c display the pore volume and size distribution of the nanospheres, analyzed from adsorption-desorption

of N2 based on the Barrett-Joyner-Halenda model. From the figures, it can be understood that the porous nanospheres own high surface area with large pore volume, besides narrow pore size distribution that are evaluated from N2 adsorptiondesorption isotherms analysis. At high P/P0 between 0.5 and 1.0, the samples display a type H1 hysteresis loop (IUPAC classification) representing the porous nature of nanostructures. The pore size distribution of B1000-5 was calculated using Barrette Joynere Halenda (BJH) method (Fig. 7c) of the N2 isotherm. The pore size distribution of the B1000-5 was around 106.09 nm. The specific surface area was found to be 6.1735 m2 /g with the corresponding volume of 2.6907 cm3 /g. Therefore, the pores found on the spheres obviously certify that the surface is highly porous, which also has been verified by the TEM and SEM observation.

3.7.

DRS analysis

The semiconducting behavior of GNMO NSs ascertained by UV–vis absorption spectrum (Fig. 8). In Fig. 8a absorption peaks in ranging 200–400 nm can be detected that are related to the charge transfers from d-d transitions of the Jahn-Teller splittings and also 2pO orbital to 3dTM (TM = transition metal) orbital [12]. Optical band gap (Eg) is estimated based on the optical absorption spectrum by means of the following equation [26]: ␣h = k (h − Eg) n/2 . In this equation ␣ is absorption

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Fig. 7 – (a) FT-IR spectrum, (b) N2 adsorption-desorption isotherm and (c) pore size distribution curve of GNMO NSs prepared in the presence of 1,3,5-benzenetricarboxylic acid at 1000 ◦ C.

coefficient, h is the photon energy (in eV), Eg is gap energy, k and h are constants. The Eg value of GNMO NSs is obtained over extrapolating the linear section of the plot of (␣h)2 against h to a point (␣h)2 = 0 (Fig. 8b). The Eg value of GNMO NSs prepared in the presence of 1, 3, 5-benzenetricarboxylic acid at 1000 ◦ C estimated to be 2.9 eV. Fig. 8b appearances a direct transition for the NSs. From the calculated Eg value, asproduced GNMO NSs may be employed as the photocatalyst.

3.8.

VSM analysis

Fig. 9 displays M−H hysteresis for GNMO NSs prepared in the presence of 1,3,5-benzenetricarboxylic acid at 1000 ◦ C, which have been measured at 300 K, in a magnetic field ranging from −10 kOe to 10 kOe. The figure indicates a weak ferromagnetic (FM) behavior. Gd and Gd-based alloys are extensively used along with application in low temperature magnetic refrigerant materials, automotive air-conditioning and etc. ˜ K [1]. [27]. GNMO displays a magnetic transition (TN) at 125 The A2 BB O6 shows both FM and antiferromagnetic (AFM) interactions (↑↑↓↓) [5]. The AFM interaction in GNMO NSs is because of super-exchange interaction between B2+ −O2− −B2+ and B4+ −O2− −B4+ in the perovskites crystal [11]. The FM in A2 BB O6 is due to B3+ −O2− −B3+ super-exchange interactions [4]. Both existence of FM and AFM states in rare earth double perovskites is regular. The meta-magnetism is recognized to the competition among these two magnetic interactions,

between the nearest-neighbor (B2+ −B4+ ) and the next-nearest neighbor exchange interaction (B2+ −B2+ and B4+ − B4+ ). Correspondingly, the A site’s ions and temperature have crucial effects on metamagnetic effect. In metamagnetic systems, the magnetic field is critical for the appearance of metamagnetism [28]. Gan et al. synthesized La2 NiMnO6 ceramics by ultra-high pressure sintering and measured magnetic property as-prepared ceramics at 10 K and 300 K [26]. The ceramics synthesized by Gan displayed a paramagnetic behavior at 300 K, with very unimportant Ms and a FM behavior at 10 K [29]. Similarly, Oh et al. displayed a FM behavior with a weak magnetic hysteresis for Gd2 NiMnO6 at 5 K [30]. They investigated temperature effect on magnetic property of the Gd2 NiMnO6 . Organic dyes decompose to carbon dioxide, wastewater and other nontoxic or less toxic residuals [31]. There are more researches on the magnetic nanostructures for photocatalytic applications [32–34].

3.9.

Photocatalytic investigation

The photocatalytic decomposition mechanism of contaminants can be assumed as: GNMO → GNMO(e− CB +h+ VB ) GNMO(h+ VB ) + H2 O → GNMO + H+ +OH◦

Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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Fig. 9 – M−H hysteresis at 300 K for GNMO NSs prepared in the presence of 1, 3, 5-benzenetricarboxylic acid at 1000 ◦ C.

Fig. 8 – (a) DRS spectrum and (b) curve of (␣h)2 against h for the GNMO NSs (B1000-5).

GNMO(e− CB ) + O2 → GNMO + O2 ◦− O2 ◦− +H+ → HO2◦ Dye + OH◦ → degradation Dye + h+ VB → oxidation Dye + e− CB → reduction The photocatalytic behavior of GNMO NSs under UV light for the degradation of MV, ES, EBT and MO was examined. Figs. 10 and 11 represent the obtained results in the dye degradation field. Both cationic and anionic dyes have been designated in this investigation. MV, ES, EBT and MO degradation efficiencies calculated using Eq. (1) and were about 95 %, 83 %, 77 % and 56 %, respectively, in the presence of B1000-

5 sample after 105 min irradiation of UV light, as exposed in Fig. 10a. This figure demonstrates a better photocatalytic performance of B1000-5 for degradation of MV than that of ES, EBT and MO. MV is a cationic contaminant with a positive charge. It can be adsorbed by GNMO NSs owing to the presence of the oxygen atoms with a high surface electron density on the surface of these nanostructures [35–45]. Therefore, in our experimental conditions, the most amount of photocatalytic decomposition is for MV. Fig. 10b spectacles that degradation percentages of MV, ES, EBT and MO in the presence of B900-9 sample that calculated degradation of dye value is 98.16 %, 85.57 %, 80.49 % and 62.11 %, respectively. This figure displays a better photocatalytic performance of B900-9 for degradation of MV than other dyes. Accordingly, both B10005 and B900-9 display more photocatalysis efficiencies in the presence of MV, as shown in Figs. 10a and 10b.The MV dye degradation percent was improved with the growing exposed time and practically all dyes were disintegrated more than 50 % in the initial 40 min over the photocatalyst. Mutually, these outcomes present nanospheres as hopeful photocatalyst for photocatalytic degradation of MV dye. Figs. 11 (a–d) expose the photocatalytic performance of the synthesized GNMO NSs on various dyes. Fig. 11a expressions that the degradation efficiencies of MV in the presence of B1000-5 and B900-9 are about 95.49 % and 98.15 %, respectively. From the figures, it is obvious that the photocatalytic performance of B1000-5 in the presence of MV is weaker than B900-9. The photocatalytic activities of B1000-5 and B900-9 for the degradation of ES, EBT and MO have been compared in Figs. 11b-d, respectively. The obtained results from these figures are similar to the results of Fig. 11a. The catalysis efficiency of B900-9 is more than that of B1000-5 in the presence ES, EBT and

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Fig. 10 – (a)Photocatalytic activity of GNMO NSs (B1000-5) and (b) GNMO NSs (B900-9) for degradation of MV, ES, EBT and MO.

MO. According to the obtained results, it is decided that the photocatalytic activity of GNMO NSs is increased with decreasing the reaction temperature and time. The enhanced photocatalytic performance at low temperatures and longer times can be attributed to the effective separation of the photogenerated electron–hole pairs of the nanostructures. To assess the adsorbent regeneration possibility, five cycles of adsorption–desorption tests were achieved. The adsorption capacities decline for each new cycle afterward desorption. Meanwhile nanostructures adsorbent possess magnetic sensitivity underneath an external magnetic field, hence it was simply separated, recycled continually and reused for a number of times.

4.

Conclusions

Semi-spherical GNMO NSs successfully produced by a simple Pechini method. Based on the morphological and structural characterization. 1,3,5-benzenetricarboxylic acid at 900 ◦ C is a promising agent for the preparation of uniform semi-spherical

GNMO NSs with a pure orthorhombic crystal structure. The effect of temperature, time and stabilizing agent on the particle size, purity of the phase, morphology and photocatalytic behavior of the products was investigated as well. The nanostructures displayed optical property by UV–vis and the calculated band gap was to be about 2.9 eV. Investigation of the photocatalytic ability of optimum GNMO NSs (B900-9) for organic dye degradation indicated a higher performance in photodegradation of MV compared to other dyes, where can be described due to the presence of positive charge of MV. The engineered nanostructures confirmed rapid and wellorganized MV dye decomposition with a degradation rate of 50 % in initial 40 min and more than 90 % within the 105 min, owed to the porous nature, great specific surface area and outstanding electron accepting features of the nanospheres. The current study offers a low-cost, rapid and convenient approach for the degradation of MV for wastewater purification and optoelectronic application. As a consequence, GNMO NSs can be considered as a promising and effective adsorbent for the dye removal researches.

Please cite this article in press as: Mohassel R, et al. Pechini synthesis using propylene glycol and various acid as stabilizing agents and characterization of Gd2 NiMnO6 ceramic nanostructures with good photocatalytic properties for removal of organic dyes in water. J Mater Res Technol. 2019. https://doi.org/10.1016/j.jmrt.2019.12.003

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Fig. 11 – Photocatalytic activity of B1000-5 and B900-9 for degradation of (a) MV, (b) ES, (c) EBT, (d) MO.

Conflict of interest [4]

The authors declare that there are no conflicts of interest regarding the publication of this manuscript.

Acknowledgment Authors are grateful to the council of Iran National Science Foundation (97017837) and University of Kashan for supporting this work by Grant No (159271/8990).

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