Fe3O4 nanocomposite using Euphorbia peplus Linn leaf extract and evaluation of its catalytic activity

Accepted Manuscript Green synthesis of Ag/Fe3O4 nanocomposite using Euphorbia peplus Linn leaf extract and evaluation of its catalytic activity Mohaddeseh Sajjadi, Mahmoud Nasrollahzadeh, S. Mohammad Sajadi PII: DOI: Reference:

S0021-9797(17)30200-X http://dx.doi.org/10.1016/j.jcis.2017.02.037 YJCIS 22064

To appear in:

Journal of Colloid and Interface Science

Received Date: Revised Date: Accepted Date:

30 January 2017 10 February 2017 15 February 2017

Please cite this article as: M. Sajjadi, M. Nasrollahzadeh, S. Mohammad Sajadi, Green synthesis of Ag/Fe3O4 nanocomposite using Euphorbia peplus Linn leaf extract and evaluation of its catalytic activity, Journal of Colloid and Interface Science (2017), doi: http://dx.doi.org/10.1016/j.jcis.2017.02.037

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Green synthesis of Ag/Fe3O4 nanocomposite using Euphorbia peplus Linn leaf extract and evaluation of its catalytic activity Mohaddeseh Sajjadi,a Mahmoud Nasrollahzadeh a,b,* and S. Mohammad Sajadic a

Department of Chemistry, Faculty of Science, University of Qom, PO Box 37185-359, Qom, Iran. E-mail: [email protected]; Fax: +98 25 32103595; Tel: +98 25 32850953 b

b

Center of Environmental Researches, University of Qom, Qom, Iran

Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional Government, Iraq

ABSTRACT In this work, the Ag/Fe3O4 nanocomposite was prepared by Euphorbia peplus Linn (L.) leaf extract as a suitable reducing source and stabilizing agent. The green synthesized nanocomposite was characterized using X-ray diffraction analysis (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) images, energy-dispersive X-ray spectroscopy (EDS) and FT-IR spectroscopy. TEM analysis of Ag/Fe3O4 nanocomposite showed the spherical shape nanoparticles (NPs) with an average size of 510 nm. The Ag/Fe3O4 nanocomposite then was used as a magnetically recoverable catalyst for the [2+3] cycloaddition of arylcyanamides and sodium azide in high yields and short reaction times without formation of hydrazoic acid (HN3). Also it can be easily recovered via applying of external magnetic field and reused several times without significant loss of activity. Keywords: Green synthesis, Euphorbia peplus L., Ag/Fe3O4, Arylaminotetrazoles, Heterogeneous catalyst

1. Introduction The extensive ability of tetrazoles in different area of science and industry such as their applications in materials technology and also medicinal and pharmaceutical sciences attracted the interest of many researchers toward this field [1-5]. In addition, tetrazoles can be used as effective materials for the preparation of nitrogen-containing compounds [6]. a

Department of Chemistry, Faculty of Science, University of Qom, Qom 37185-369, Iran. E-mail: [email protected]; Fax: +98

25 32103595; Tel: +98 25 32850953. b

Center of Environmental Researches, University of Qom, Qom, Iran.

c

Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional Government, Iraq.

1

Among tetrazoles, arylaminotetrazoles are the study subject of many researchers interested in the field due to their biological and medicinal applications [1]. These bioactive compounds can be synthesized by different methods such as the diazotation of aminoguanidine derivatives, azidation of cyanamides, benzotriazol-1ylcarboximidamides, thioureas, carbodiimides and aminoiminomethanesulfonic acids, thermal isomerization of 1-substituted-5-amino-1H-tetrazoles in boiling ethylene glycol or melt state (180-200 oC) and addition of amines to tetrazoles containing leaving groups in 5-position [7-20]. The main disadvantage of these methods is harsh reaction conditions, long reaction time, low yield, formation of byproducts, use of expensive and toxic reagents and homogeneous catalysts, difficult to obtain and/or prepare starting materials, use of an excess amount of dangerous and harmful hydrazoic acid, tedious workup procedures and production of the mixture of 5arylamino-1H-tetrazole (A) and 1-aryl-5-amino-1H-tetrazole (B) isomers. The homogeneous catalysts suffer from disadvantages such as high operational costs, short life time, labourintensive and the difficulty of separating from the reaction mixture. These problems affect reaction yields and recycle activity of the catalyst which lead to environmental problems and restrict their application in synthesis due to environmental concerns and industrial processes. According to the points of green chemistry, the use of inexpensive and noncorrosive heterogeneous catalysts presents a promising option, so, due to safety considerations, it is more desirable to develop a more efficient catalytic method for the synthesis of arylaminotetrazoles. As an alternative solution, recently heterogeneous catalysts have been developed in the synthesis of arylaminotetrazoles due to ease of handling, high catalytic activity, simple recovery, recyclability, low toxicity and particularly low price [21-25]. During the past few years silver nanoparticles (Ag NPs) were the hot subject of scientific studies in nanotechnology and one of the most promising and intriguing materials for research and developments in order to prevent its agglomeration and also improve its inherent properties. In fact Ag NPs are well-known for their unique property which makes it potentially applicable in various fields such as biomedicine, biosensors, catalysis, pharmaceuticals, electrical conductivity, and photonics and as the substrates for surface-enhanced Raman spectroscopy (SERS) due to the existence of surface Plasmon. The silver nanoparticles provide high surface energy which promotes surface reactivity but the agglomeration of Ag NPs is inevitable. Therefore, to prevent the agglomeration of Ag NPs during its production and in order to overcome the problems concerning separation, stability and recovery of Ag NPs, a suitable support such as magnetite is necessary to immobilize the Ag NPs onto its surface [26-29]. 2

Among heterogeneous catalysts, magnetic nanocatalysts are attractive candidates as effective catalysts for the highly active and recyclable catalytic systems. The beneficial applications of these catalysts are mainly due to their unique magnetic, electronic, and catalytic properties, excellent chemical stability, low cost, huge industrial applications and large surface area. In addition, these catalysts can be separated from the reaction medium and recovered for using in next reaction cycles easily through an external magnetic field without using any centrifugation or filtration [30]. There are several chemical and physical methods for the preparation of metal/Fe3O4 magnetic nanoparticles [30]. However, these methods have disadvantages such as utilization of organic solvents, harsh reaction conditions (high temperature and pressure) and use of expensive and toxic reducing agents, use of expensive capping agents and organic surfactants, which make them environmentally and economically malignant. Therefore, the development of a simple and environmentally benign method for the preparation of magnetic nanocatalysts has been a major challenge in catalytic systems. Recently, there has been an increasing trend towards using plants extract for the preparation of magnetically recoverable nanocatalysts in order to develop the greener synthetic processes [31-33]. In this direction, we recently synthesized magnetic nanocomposite using plants extract which can efficiently catalyze organic transformations under heterogeneous conditions [31-33]. Biosynthesis of metal NPs and nanocomposites using plants extract provide an environmental friendly, economical, convenient, green and simple method under mild conditions. This method has the advantages of simple methodology, easy work-up, very mild reaction conditions, and use of non-toxic solvents such as water, avoidance of the high temperature and pressure, elimination of toxic and dangerous materials and cost effectiveness [31-34]. The genus Euphorbia (spurges, Euphorbiaceae) is the third largest genus of flowering plants, with almost 2000 species which its exceptional diversity of growth forms and near-cosmopolitan distribution have attracted human interest since ancient times [35,36]. Following a lot of studies on phytochemical content of the Euphorbiaceae family, they have been extremely found as a rich source of various medicinal phytochemicals such as tannins, alkaloids, glycosides, flavonoids and other phenolic compounds on which the presence of phenolics was confirmed in different parts of the Euphorbiaceae plants such as leaves, stems, roots and flowers. Euphorbia peplus L. from the family of Euphorbiaceae is originally native to Europe and North Africa and western Asia which its sap is toxic to rapidly replicating human tissue, and has long been used as a traditional remedy for common skin lesions (Figure 1) [35,36].

3

Figure 1. Images of Euphorbia peplus L.

A survey of literatures about the plant showed the presence of various range of phytochemicals especially diterpenes, sterols, triterpene alcohols, and cerebrosides and also potent antioxidant phenolics such as C- and OGlucosides, dihyroflavonol 3-O-monoglycosides, Rutin, Quercetin, Kaempferol and Myricetininside the plant extract [37,38], which caused to interest us in using the Euphorbia peplus L. extract as a suitable source of natural antioxidants to biosynthesis of nanostructures using those reducing ability. In this paper, we wish to explore Euphorbia peplus L. leaf extract for the generation of the Ag/Fe3O4 nanocomposite as a magnetically recoverable and heterogeneous catalyst without using any surfactant and capping agent to catalyze the [2+3] cycloaddition of arylcyanamides and sodium azide for the synthesis of arylaminotetrazoles in high yields (Scheme 1). To the best of our knowledge, there is no report on the biosynthesis of the Ag/Fe3O4 nanocomposite using Euphorbia peplus L. leaf extract as a stabilizing and reducing agent and its application as magnetically separable nanocatalyst for the preparation of arylaminotetrazoles.

2. Experimental High-purity chemical reagents were purchased from the Merck and Aldrich chemical companies. All materials were of commercial reagent grade. FT-IR spectra were recorded on a Nicolet 370 FT/IR spectrometer (Thermo 4

Nicolet, USA) using pressed KBr pellets. X-ray diffraction (XRD) measurements were carried out using a Philips powder diffractometer type PW 1373 goniometer (Cu Kα = 1.5406 A˚). The scanning rate was 2º/min in the 2θ range from 10 to 80˚. UV-visible spectral analysis was recorded on a double‐beam spectrophotometer (Hitachi, U‐2900) to ensure the formation of nanoparticles. The shape and size of the Ag/Fe3O4 nanocomposite was identified by transmission electron microscope (TEM) using a Philips EM208 microscope operating at an accelerating voltage of 90 kV. Morphology and particle dispersion was investigated by scanning electron microscopy (SEM) (Cam scan MV2300). The chemical composition of the prepared nanostructures was measured by EDS (Energy Dispersive X-ray Spectroscopy) performed in SEM.

Preparation of Euphorbia peplus L. leaf extract 100 g of dried leaf of Euphorbia peplus L. was powdered and refluxed at 80 °C with 500 mL of sterile distilled water for 2 hours. The mixture was allowed to cool to room temperature and then centrifuged at 7500 rpm. The obtained supernatant separated by filtration to use further as extract. Preparation of Ag NPs using Euphorbia peplus L. leaf extract 10 mL of plant extract and 40 ml of 0.003 M aqueous solution of AgNO3 were mixed while stirring at 70 °C. After around 5 min the solution converted to a brown suspension indicating the synthesis of Ag NPs (as monitored by UV-Vis and FT-IR techniques). Then the obtained suspension was centrifuged at 7000 rpm to completely separation and then washed with absolute ethanol and kept under Ar atmosphere to prevent any decomposition and deformation processes. Green synthesis of the Ag/Fe3O4 nanocomposite using Euphorbia peplus L. leaf extract To prepare of the Ag/Fe3O4 nanocomposite, in a 50 ml round-bottomed flask, 1.0 g Fe3O4 and 0.3 g AgNO3 were added in 35 mL aqueous extract of the Euphorbia peplus L. The reaction mixture was stirred for 5 h at 70 ºC. The catalyst was collected by centrifugation, washed with ethanol and distilled water and then dried. General procedure for the preparation of arylaminotetrazoles In a 50 ml round-bottomed flask, a mixture of arylcyanamide (2 mmol), sodium azide (3mmol), DMF (7 mL) and Ag/Fe3O4 nanocomposite (0.03 g) were added and stirred at 110 °C for the appropriate times (Table 2). The reaction was monitored by TLC. After completion of the reaction, the mixture was cooled to room temperature and the catalyst separated using a magnetic separator. Then 25 mL ethyl acetate and 30 mL HCl (2 M) was added to the flask and stirred vigorously. The organic layer was separated, and the aqueous layer was again 5

extracted with 25 mL ethyl acetate. The combined extract was washed with water, concentrated, and washed with ethanol to obtain the pure arylaminotetrazoles. 3. Results and discussion In this study, a valuable green method for preparation of the Ag/Fe3O4 nanocomposite was established via in situ growth of Ag NPs attached on the surface of Fe3O4 NPs as an effective support and using the antioxidant potential of Euphorbia peplus L. leaf extract. The synthesis procedure is a very simple, environmentally friendly and inexpensive method. Additionally, the catalytic activity of biosynthesized Ag/Fe3O4 nanocomposite was evaluated for the synthesis of arylaminotetrazoles via [2+3] cycloaddition of arylcyanamides and sodium azide. Firstly, the preparation of Ag NPs was carried out using the Euphorbia peplus L. leaf extract as a stabilizing and reducing agent. The UV spectrum of leaf extract of the plant (Figure 2) showed bonds around λmax 332 nm (bond Ι) and 240 nm (bond ΙΙ) due to the cinnamoyl and benzoyl systems as the specification of plant phenolics [39].

Figure 2. UV-vis spectrum of Euphorbia peplus L. leaf extract. As shown in Figure 3, the formation of Ag NPs completed after 5 min with appearance the maximum absorbance around 450 nm indicating the effect of surface plasmon resonance phenomenon following the reduction process (Scheme 2). Moreover, the stability of green synthesized Ag NPs was studied during the special time intervals (Figure 3). Furthermore, according the UV-Vis results the synthesized nanoparticles by this method showed no significant variance in the shape, position and symmetry of the absorption peak even after 12 days which confirmed the stability of product.

6

Figure 3. UV-vis spectrum of green synthesized Ag NPs between 5 min to 12 days.

The FT-IR analysis of Euphorbia peplus L. leaf extract (Figure 4A) depicted some considerable peaks around 3500, 1710, 1530, 1350 to 1100 cm-1 for free OH in molecule and OH group forming hydrogen bonds, carbonyl group (C=O), stretching C=C aromatic ring and C-OH stretching vibrations, respectively which indicate the presence of phenolics in the plant extract as responsible agents for the reduction of metal ions to nanoparticles. Furthermore, the FT-IR spectrum of Ag NPs (Figure 4B) shows bands around 3500, 1535 and1680 cm-1 for OH stretching bond and the primary -OH stretching of hydroxyl functional groups, bending vibration of Sp2-carbon groups for aromatics and carbonyl functional group.

7

Figure 4. The FT-IR spectrum of the plant extract (A) and green synthesized Ag NPs (B)

The green synthesized Ag/Fe3O4 nanocomposite was characterized using FT-IR spectroscopy; powder XRD, FESEM, EDS and TEM analyses. Figure 5 demonstrates the FT-IR spectrum of the Ag/Fe3O4 nanocomposite. In the FT-IR spectrum, the peaks at 3408, 1622 and 580 are assigned to the O-H stretching vibration and bending of the H-O-H and stretching vibration of Fe-O in tetrahedral sites.

Figure 5. The FT-IR spectrum of the Ag/Fe3O4 nanocomposite.

8

The green synthesized Ag/Fe3O4 nanocomposite was investigated by the XRD pattern to explain the crystalline nature of the catalyst. Figure 6 displays the XRD pattern of green synthesized Ag/Fe3O4 nanocomposite in which five distinct picks are observed at 38.2°, 44.4°, 64.5°, 77.4° and 81.5° corresponding to (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) planes respectively that could be indexed to face centered cubic (fcc) phase of Ag NPs. The peaks located at 19.1°, 31.4°, 35.7°, 41.2°, 53.6°, 57.6°, 62.9° and 75.3° are assigned to (111), (220), (311), (400), (422), (511), (440) and (533) planes of cubic Fe3O4 (JCPDS 01-1111).

Figure 6. X-Ray diffraction pattern for the Ag/Fe3O4 nanocomposite. FESEM images of the Ag/Fe3O4 nanocomposite are shown in Figure 7. The micrographs demonstrated that the Ag NPs were attached to the surface of the Fe3O4 which displays a good combination between Fe3O4 and Ag NPs.

9

Figure 7. FESEM images of the Ag/Fe3O4 nanocomposite. The green synthesized Ag/Fe3O4 nanocomposite was characterized by EDS analysis to know the elemental composition (Figure 8). In the EDS spectrum, Ag, Fe and oxygen peaks were observed, indicating that the Ag/Fe3O4 nanocomposite was successfully prepared. AgL

5000

4000

3000

2000

AgL

OK 1000

FeK FeL CK FeK keV

0 0

9.329

Figure 8. EDS image of the Ag/Fe3O4 nanocomposite. The TEM images of the Ag/Fe3O4 nanocomposite are shown in Figure 9. The TEM images shown that the Ag nanoparticles were immobilized on the surface of Fe3O4 with no obvious aggregation. It was observed that the Ag/Fe3O4 nanocomposite was composed of Ag and Fe3O4 nanoparticles with spherical morphology and the average size of 5-10 and 60 nm, respectively.

10

Figure 9. TEM images of the Ag/Fe3O4 nanocomposite. The Ag/Fe3O4 nanocomposite was initially assessed for its catalytic activity in the reaction of 4bromophenylcyanamide and sodium azide to form 5-(4-bromophenyl)amino-1H-tetrazole as product (Table 1). As dimethylformamide (DMF) is the solvent of choice for [2+3] cycloaddition reactions in the synthesis of tetrazoles [21-25], it was decided to carry out the reaction in DMF at 110 oC in the presence of the Ag/Fe3O4 nanocomposite as catalyst. The effect of catalyst loading on the synthesis of 5-(4-bromophenyl)amino-1Htetrazole was investigated by carrying out the reaction in the presence of different amounts of catalyst. Results summarized in Table 1 clearly demonstrate that there is no reaction in the absence of the Ag/Fe3O4 nanocomposite (Entry 1). As shown in Table 1, increasing the catalyst amount to 0.03 g leds to an enhancement in reaction yield. The best result was obtained using 0.03 g of the Ag/Fe3O4 nanocomposite in DMF (Entry 4). No significant improvement in reaction yield was observed by further increasing the catalyst concentration (Entry 5).

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Table 1. Optimization of reaction conditions in the reaction of 4-bromophenylcyanamide with sodium azide.a

Entry Ag/Fe3O4 nanocomposite (g) Time (min) Yield (%) b 1 0.00 120 0.0 2 0.01 90 69 3 0.03 70 81 4 0.05 70 81 a Reaction conditions: 4-bromophenylcyanamide (2.0 mmol), NaN 3 (3.0 mmol), DMF (7.0 mL), catalyst, at 110 °C. b Isolated Yield.

The Ag/Fe3O4 nanocomposite also showed excellent catalytic activity for reactions of various arylcyanamides carrying electron-withdrawing and electron-donating substituents with sodium azide (Table 2). Different arylcyanamides possessing electron-withdrawing or electron-donating groups were transformed into the corresponding arylaminotetrazoles in good yields. Generally, it was observed that arylcyanamides with electron-donating groups were more reactive than arylcyanamides with electron-withdrawing groups in the synthesis of arylaminotetrazoles. As shown in Table 2, in contrast with arylcyanamides with electronwithdrawing substituents, reaction of arylcyanamides having the electron-donating groups with sodium azide was completed at 110 ºC in shorter reaction times. Comparing to the reported methods [8,18,23], our method was completely regiospecific (Scheme 2). Results summarized in Table 2 clearly demonstrate that the 5arylamino-1H-tetrazole (A isomer) and 1-aryl-5-amino-1H-tetrazole (B isomer) can be obtained from arylcyanamides carrying electron-withdrawing and electron-donating substituents on the aryl ring, respectively. Also; the [2+3] cycloaddition reaction of 4-nitrophenylcyanamide and sodium azide were involved in this method to produce 5-(4-nitrophenyl)amino-1H-tetrazole (A isomer) in 83% yield (Table 2, entry 12) as a profit in contrast with other reported methods which the mixture of isomers (A + B) or B isomer (1-(4-nitrophenyl)-5amino-1H-tetrazole) were obtained (Scheme 3). In our method, 2-methylphenylcyanamide (Table 2, entry 5) interestingly gave 1-(2-methylphenyl)-5-amino-1H-tetrazole (B isomer), while using the other methods, the mixture of isomers (A + B) or 5-(2-methylphenyl)amino-1H-tetrazole (A isomer) were obtained (Scheme 4).

12

13

Table 2. Preparation of arylaminotetrazoles from arylcyanamides using Ag/Fe3O4 nanocomposite at 110 oC.a Time (min)

Yield%b

1

30

83

2

45

80

3

30

81

4

40

79

5

40

82

6

45

84

7

70

80

8

85

78

9

70

81

10

115

78

11

110

83

12

110

83

13

70

82

14

45

83

15

30

80

Entry

a b

Substrate

Product

Reaction conditions: Cyanamide (2.0 mmol), NaN 3 (3.0 mmol), DMF (7.0 mL), catalyst (0.03 g), at 110 °C. Isolated Yield.

14

According to the previously reported literatures [21-25], we propose a possible mechanism for the synthesis of arylaminotetrazoles as follows (Scheme 5):

To show the advantages of the Ag/Fe3O4 nanocomposite in comparison with other previously reported methods, some results for the [2+3] cycloaddition reaction of 4-nitrophenylcyanamide and sodium azide in the presence of various catalysts are summarized in Table 3, which introduces the Ag/Fe3O4 nanocomposite as the most efficient catalysts, affording the highest yield and requiring the lowest catalyst loading of 0.03 g and shorter time. In addition, in contrast with other catalysts, the Ag/Fe3O4 nanocomposite can be recovered from the reaction mixture by an external magnet and reused several times without significant drop in its catalytic activity. The following items are observed in most of the reported procedures by the literatures for the synthesis of arylaminotetrazoles: 

The use of HN3 (toxic and hazardous substance) (Entry 1);



The use of homogeneous catalysts which cannot be easily recovered and recycled (Entry 4 and 6).



In situ formation of HN3 in reaction mixture (Entry 3 and 9);



The preparation of the mixture of isomers (A + B) (Entry 2);



Low yields of the product (Entry 1);



Difficulties in preparation and availability of the Natrolite zeolite (Entry 7);

In our method, none of the above mentioned disadvantages are observed. In addition, in contrast with reported methods, our method was completely regiospecific and A or B isomer was obtained.

15

Table 3. Comparison of the Ag/Fe3O4 nanocomposite with other previously reported catalysts in the [2+3] cycloaddition reaction of 4-nitrophenylcyanamide and sodium azide.a Entry 1 2 3 4 5 6 7 8 9 a Isolated Yield.

Reaction conditions HN3, xylene, reflux FeCl3-SiO2 (0.1 g), DMF, 110 °C Glacial HOAc (3.0 mL), r.t. ZnCl2 (3.0 mmol), H2O, reflux AlCl3 (0.09 g), DMF, 120 °C ZnO (0.1 g), DMF, 120 °C Natrolite zeolite (0.1 g), DMF, 110-115 °C Rutile TiO2 (0.05 g), DMF, 110 °C Ag/Fe3O4 nanocomposite (0.03 g), DMF, 110 °C

Product B A+ B A+ B A A A A A A

Time 120 min 125 min 24 h 15 h 120 min 120 min 115 min 120 min 110 min

The A and B isomers were characterized by FT-IR, 1H NMR and

13

Yield (%) b 46.2 75 80 80 74 77 80 80 83

Ref. 8 23 18 19 24 25 22 40 This work

CNMR. The disappearance of CN

stretching band and the appearance of an NH stretching signal and also two NH2 stretching bands in the FT-IR spectra provided clear evidence for the formation of A isomer and B isomer, respectively (Figure 10). 1HNMR spectra showed two NH peaks (NH of the amine attached to the aryl group (NHA) and NH of the tetrazole ring (NHT)) for A isomer and one NH2 peak for B isomer (Figure 11).

13

CNMR spectrum of arylaminotetrazoles

showed one peak at 154-158 ppm as indicative of C5 in the tetrazole ring (Figure 12).

16

Figure 10. The FT-IR spectra of the 1-(2,6-dimethylphenyl)-5-amino-1H-tetrazole and 5-(4acetylphenyl)amino-1H-tetrazole.

17

Figure 11. The 1HNMR spectra of the 1-(2,6-dimethylphenyl)-5-amino-1H-tetrazole and 5-(4acetylphenyl)amino-1H-tetrazole.

18

Figure 12. The 13CNMR spectrum of the 1-(2,6-dimethylphenyl)-5-amino-1H-tetrazole.

Catalyst recyclability When the [2+3] cycloaddition reaction of 4-bromophenylcyanamide with sodium azide was completed, the Ag/Fe3O4 nanocomposite could be easily separated from the reaction medium by an external magnet and then washed several times with ethanol and dried in a hot air oven at 100 °C for 2 h. The used catalyst could be recycled many times without significant drop in its catalytic activity. As shown in Figure 13, the catalyst showed consistent activity even after 5 times of recycling. These data demonstrate excellent catalytic activity of the Ag/Fe3O4 nanocomposite in our method. The recyclability of the Ag/Fe3O4 nanocomposite can be attributed to the efficient immobilization of the Ag NPs on the Fe3O4 surface. The EDS spectrum and TEM images of the Ag/Fe3O4 nanocomposite after 5 times of recycling showed that the chemical composition, shape and size have not changed (Figure 14 and 15).

19

AgL 2500

2000

1500

FeK

OK 1000

AgL

FeL

500

CK

FeK keV

0 0

9.329

Figure 14. EDS spectrum of recycled Ag/Fe3O4 nanocomposite.

Figure 15. TEM images of recycled Ag/Fe3O4 nanocomposite.

4. Conclusions

20

In conclusion, a facile, efficient, environmentally benign and green method was developed for the synthesis of the Ag/Fe3O4 nanocomposite as a magnetically recoverable and heterogeneous catalyst using Euphorbia peplus L. leaf extract as a stabilizing and reducing agent without using any hazardous surfactant and capping agent. FTIR spectroscopy demonstrated the presence of polyphenols or flavonoids in the leaf extract of Euphorbia peplus L. as responsible for the reducing Ag+ ions instead of using toxic reducing agents. The catalyst was characterized by SEM, XRD, EDS, TEM and FT-IR. The Ag/Fe3O4 nanocomposite showed high catalytic activity for the preparation of arylaminotetrazoles from arylcyanamides containing either electron-donating or electron-withdrawing groups. Furthermore, the reaction takes much shorter time as compared to some of the conventional methods. The Ag/Fe3O4 nanocomposite could be recovered several times by an external magnet and reused without significant deactivation in its catalytic activity.

Acknowledgments We gratefully acknowledge the Iranian Nano Council and University of Qom for the support of this work.

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Graphical Abstract Green synthesis of Ag/Fe3O4 nanocomposite using Euphorbia peplus Linn leaf extract and evaluation of its catalytic activity Mohaddeseh Sajjadi,a Mahmoud Nasrollahzadeh a,b,* and S. Mohammad Sajadic

a

Department of Chemistry, Faculty of Science, University of Qom, Qom 37185-369, Iran. E-mail: [email protected]; Fax: +98

25 32103595; Tel: +98 25 32850953. b

Center of Environmental Researches, University of Qom, Qom, Iran.

c

Department of Petroleum Geoscience, Faculty of Science, Soran University, PO Box 624, Soran, Kurdistan Regional Government, Iraq.

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Highlights:  Green synthesis of the Ag/Fe3O4 nanocomposite mediated by Euphorbia peplus L. leaf extract.  Preparation of arylaminotetrazoles in good yields.  Characterization of catalyst by TEM, SEM, EDS, XRD and FT-IR techniques.  The catalyst can be recovered by an external magnet and reused several times without significant loss in catalytic activity.

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