Green synthesis, characterization and catalytic activity of 4-nitrophenol reduction and formation of benzimidazoles using bentonite supported zero valent iron nanoparticles

Materials Science for Energy Technologies 2 (2019) 298–307

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Green synthesis, characterization and catalytic activity of 4-nitrophenol reduction and formation of benzimidazoles using bentonite supported zero valent iron nanoparticles Kallepally Sravanthi, Dasari Ayodhya ⇑, Parikabandla Yadagiri Swamy ⇑ Department of Chemistry, Osmania University, Hyderabad, Telangana State 500007, India

a r t i c l e

i n f o

Article history: Received 20 December 2018 Revised 28 February 2019 Accepted 28 February 2019 Available online 16 March 2019 Keywords: Zero-valent iron nanoparticles Eucalyptus leaf extract Green catalyst 4-Nitrophenol Benzimidazoles

a b s t r a c t In this work, we report the green synthesis and characterization of a green catalyst by the immobilization of zero-valent iron nanoparticles (ZVIN) on the surface of bentonite clay using Eucalyptus leaf extract as both reducing and stabilizing agent and it is abbreviated as ZVIN. As-synthesized B-ZVIN catalyst was characterized by Fourier transformed infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy with energy-dispersive X-ray analysis (SEMEDX) and Brunauer-Emmett-Teller (BET) techniques for the investigation of optical, structural and surface morphology properties. The size and surface area of synthesized B-ZVIN were observed around less than 50 nm and 62.47 m2/g by the TEM and BET analysis, respectively. Afterward, the catalytic activity of the synthesized catalyst was tested for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in an aqueous medium with remarkable results. The reduction reaction of 4-NP in water follows the pseudo-first order kinetics. B-ZVIN was also used as a catalyst for the synthesis of benzimidazoles in various solvents and solvent-free conditions. Ó 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction The immense growth of nanotechnology assents extensive challenges and opportunities in catalysis for the degradation of dyes and reduction of 4-NP, which is the driving force of the chemical industry [1–4]. Over the last two decades, metal-based nanoparticles prepared through green synthesis route without any surfactant are widely applied in both homogeneous and heterogeneous catalysis due to their exclusive structures and properties [5,6]. Among them, metal nanoparticles (MNP) have ample attraction into the field of catalysis due to their enhanced surface to volume ratio, quantum size effect, quantum tunnel effect and solubility in various solvents [5]. While acting as a catalyst in organic reactions, MNP are majorly suffering from the decrease in surface area due to agglomeration and some loss in the amount of catalyst on recollection after completion of the reaction. However, the above mentioned problems are solved by the immobilization of MNP on certain supports. Immobilized metal nanoparticles on supporting materials such as clays, zeolites, activated carbon, graphene, metal

⇑ Corresponding authors. E-mail addresses: [email protected] (D. Ayodhya), parikabandla@gmail. com (P.Y. Swamy).

oxides, etc., have been used as heterogeneous catalysts due to their special structures and properties [5–8]. In organic synthesis, the new methodologies are invented for the preparation of heterogeneous catalysts. However, metal nanoparticles immobilized on clay mineral supports are of great interest in green chemistry due to their natural abundance, low cost, eco-friendliness and high specific surface area [9–11]. Chemically clay minerals are hydrous aluminium, silicon, calcium (rarely Mg or Fe) oxides which are in a micro-crystalline form [12–13] and most of these minerals have layered structure which attracts them into the field of heterogeneous catalysis. Different arrangements of sheets of octahedral and tetrahedral units are responsible for general clay mineral-structure. Generally, the smectite class of clay minerals, one octahedral sheet sandwiched between two tetrahedral sheets [14]. Recently, the green catalysts are designed and prepared using bentonite clay as promising support due to its ordered structure, high safety, high exchange capacity, low-cost, high specific surface area, thermal, chemical and mechanical stability [15]. In the last decade, ZVIN and immobilized ZVIN on various supports including clays, resins, activated carbon, zeolites or biomaterials are widely used in environmental remediation due to good adsorption and degradation efficiency of ZVIN towards pollutants such as heavy metals, sulphates, nitrates, textile dyes, drug resi-

https://doi.org/10.1016/j.mset.2019.02.003 2589-2991/Ó 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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dues, PCB, organic matter etc. [16–26]. Furthermore, ZVIN is non toxic, environmentally compatible and inexpensive than the precious Ag, Au, Pt and Pd metallic nanoparticles, etc. [27]. Previously bentonite supported ZVIN are prepared by liquid phase reduction method, using sodium borohydride as a reducing agent [28–30] and used for removal of methyl orange [31], cobalt (II) [32], pchlorophenol [33], and chromium (VI) [34] from wastewater. However, a little work has been published on the preparation of a green catalyst by the immobilization of ZVIN on bentonite clay using plant extract. The comparative catalytic activity of ZVIN is less reported over environmental remediation but described with advanced Fenton process [35–36], which inspired us to synthesize a new nanocatalyst B-ZVIN. It was used to synthesize some benzimidazoles which are important bioactive intermediates in organic synthesis due to their pharmacological properties [37]. Many anthelmintic drugs or antihelminthics like albendazole, mebendazole, triclabendazole etc., and some antibacterial, antibiotics, antiulceretics, anti-inflammatory, fungicides, antidiabetic, and antihypertensive agents [38–44] are compounds which have benzimidazole nucleus. Benzimidazoles are also used as organic solderability preservatives in printed circuit board manufacturing [45] and substrates for the synthesis of some dyes [46]. In addition, it shows the significant activity against the functions of various viruses like HIV and HSV-1 [47,48]. Herein, we report a new and green method for the synthesis of B-ZVIN. At this point, eco-friendly, inexpensive, non-toxic and reproducible Eucalyptus leaf extract was used as both reducing and stabilizing agent instead of sodium borohydride. In the synthesis of B-ZVIN, the hazardous materials were neither used and nor produced. As synthesized B-ZVIN was characterized by XRD, FTIR, SEM, TEM and N2 adsorption-desorption (BET method) techniques for the confirmation of B-ZVIN. The reduction of 4-NP was used as a model reaction to examine the catalytic activity of BZVIN and further more B-ZVIN was used to synthesize some benzimidazoles which are important bioactive intermediates in organic synthesis due to their pharmacological properties. 2. Materials and methods 2.1. Materials All reagents and solvents are purchased from Merck and SigmaAldrich and used as such. Ferric nitrate nona hydrate (Fe(NO3)3
9H2O), bentonite clay, p-nitrophenol and sodium borohydride chemicals are AR grade and purchased from Sigma Aldrich. The fresh leaves of Eucalyptus collected from Osmania University, Hyderabad, India. Double distilled water was used for preparing the solutions. 2.2. Collection of Eucalyptus leaf extract Fresh leaves of Eucalyptus were collected, washed several times with distilled water and dried. The dried leaves were cut into small pieces, ground finely and then 2 g weight of ground leaves added to 100 mL of double-distilled water. This mixture was boiled for 10 min, allowed to cool and filtered by Whatman’s no.1 filter paper thrice to get the clear extract. The extract thus obtained had pale green color. 2.3. Preparation of bentonite supported ZVIN In this typical process, 0.1 M solution (100 mL) was prepared by dissolving Fe(NO3)3
9H2O in double distilled water and it was further added into 7.5% (7.5 g/100 mL) of bentonite clay. The formed reaction mixture was stirred for 1 h on a magnetic stirrer, then

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an equal volume of Eucalyptus leaf extract which acts as both reducing and stabilizing agent was added and further stirred for 3 h. The resultant mixture centrifuged and B-ZVIN solid substance was collected. It was washed several times with 1:1 ethanol-water and oven dried at 60 °C for 12 h. The previous reports were shown that the Eucalyptus leaf extract contains water-soluble non-toxic polyphenols and they are responsible for the formation and stabilization of ZVIN [49,50]. These polyphenols form a complex with ferric ions and then reduce them into ZVIN. The entire procedure for the synthesis of bentonite clay supported ZVIN was illustrated in Scheme 1. Finally, the formed B-ZVIN product was used for further analysis. 2.4. Characterization techniques The UV–visible analysis was performed in the range of 200– 800 nm using UV-3600 spectrophotometer with step scan of 2 nm. The crystal structure of the samples was investigated using X-ray diffraction (XRD; Philips X’pert Pro Advance X-ray diffractometer) with Cu Ka radiation over the range of 2h = 10–80° with the acceleration voltage and applied current were 40 kV and 40 mA, respectively. Particle dispersion and morphology were examined by Scanning Electron Microscope with energydispersive X-ray analysis (SEM-EDX) using a Zeiss evo18 scanning electron microscope. The Fourier-transformed infra-red (FT-IR) spectral analysis was recorded by Shimadzu spectrophotometer in the range of wavenumber 400–4000 cm1. The specific surface areas were calculated by a standard multipoint BrunauerEmmett-Teller (BET) method using adsorption values in the range P/P0 = 0.01–0.1 using an ASAP 2020 surface area and porosity analyzer. The total pore volume and pore distribution were calculated based on the Barrett-Joyner-Halenda (BJH) model using N2 adsorption isotherm. Transmission electron microscopy (TEM) characterization was carried out on Technai G2 microscope operated at 200 kV applied voltage. SIL G/UV 254 Silica gel polygram plates are used for thin layer chromatography (TLC). 2.5. Catalytic reduction of 4-NP The catalytic activity of synthesized B-ZVIN was tested with the reduction of 4-NP as a model reaction. In this typical process, 10 mg/L of the B-ZVIN was mixed with 30 mL aqueous solution of 4-NP (0.2 mM) in a glass beaker and stirred vigorously for 2 min on a magnetic stirrer. To the above mixture, 30 mL of freshly prepared aqueous sodium borohydride (0.2 M) solution was added and stirred until the reaction mixture became colorless. During the reduction process, 3 mL of the aliquot samples were withdrawn from the reaction mixture in equal time intervals, filtered with 0.22 lm pore size membrane filters to remove the catalyst and the concentration of 4-NP in the residual solution was determined on UV–visible spectrophotometer. 2.6. Catalytic synthesis of benzimidazoles In a typical process for the synthesis of benzimidazoles, 200 mg (1.33 mmol) of aldehydes and 87 mg (1.599 mmol) of orthophenylenediamine were added to different amounts of synthesized bentonite supported nano scale iron in the various solvents and the reaction mixture was stirred at required temperature using magnetic stirrer. The reaction progress was monitored by thin-layer chromatography technique (TLC). After the completion of the reaction, the product was extracted into organic phase. The separated solid catalyst was washed with ethanol-water and used for other cycles. As best of our knowledge, these benzimidazole products were synthesized by different types of catalysts and reported. The boiling points, melting points, and spectral analysis of synthe-

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Scheme 1. The schematic representation of the synthesis of bentonite supported ZVIN.

sized products have been carried out and confirmed with comparison of previous data. 3. Results and discussion 3.1. XRD analysis The XRD (X-ray diffraction) measurements were done to see the crystalline or amorphous nature of the synthesized ZVIN particles. The XRD pattern of bentonite and B-ZVIN was displayed in Fig. 1 to determine the crystal structure of green synthesized B-ZVIN. In both the XRD patterns, the broad peaks at 2H values below 26.5° correspond to characteristic peaks of bentonite clay [51]. However in the XRD pattern of B-ZVIN, the diffraction peaks at 2h value of 44.9°, 63.99° indicate the presence of zero-valent iron [52] and low-intensity diffraction peaks at 2h value of 35.6°, 54.59°, 72.3° reveal that iron was slightly oxidized in bentonite [53]. These experimental results reveal that the Eucalyptus leaf extract act as an efficient reducing and stabilizing agent in the reduction of ferric ions to ZVIN. The estimated range of the particle size of the ZVIN is from 15 ± 1.2 to 45 ± 1.5 nm by using the Debye-Scherrer equation. 3.2. FTIR analysis The FTIR analysis of bentonite clay which was used as supporting material and synthesized B-ZVIN carried out in the range of

Fig. 1. XRD patterns of (a) bentonite and (b) B-ZVIN.

4000–400 cm1 (Fig. 2). In the figure deep bands positioned at 3625 cm1, 1636 cm1 and 1034 cm1 correspond to Al-O-H bands, stretching vibration bands of H-O-H of the water molecule in bentonite which was held by the surface of Si-O with weak hydrogen bond and Si-O stretching bands in a tetrahedral sheet of Si-O-Si groups respectively [54]. The bands at 910 cm1 and 1100 cm1 are due to the bending vibration of Al-O and Si-O vibrations respectively [55]. The bands at 524 cm1 and 470 cm1 represent the bending vibrations of Si-O-Al and Si-O-Si respectively [56]. In addition, in the FTIR spectrum of B-ZVIN the slight shifting of bands from 524 cm1, 470 cm1 and 910 cm1 to 530 cm1, 468 cm1 and 912 cm1, respectively were due to Fe-O stretching vibrations [57]. However, from spectral data, it was clear that the basic chemical composition of bentonite was not changed by the immobilization of the ZVIN and also no additional bands corresponding to the iron complex of ferric ion with chemical components of leaf extract are noticed.

3.3. SEM analysis SEM analysis was carried out for the determination of morphology of both bentonite and B-ZVIN and the distribution of ZVIN particles on the surface of bentonite. The high-resolution SEM images of bentonite and ZVIN were displayed in Fig. 3(a–c). The SEM image of bentonite (Fig. 3a) reveals that it has smooth and gleamy

Fig. 2. FTIR spectra of (a) bentonite, and (b) B-ZVIN.

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layers with a large number of gorges which make it a good supporting material for ZVIN. However, the SEM image of B-ZVIN (Fig. 3(b–c)) shows that ZVIN were well dispersed on the bentonite surface, as a result, the less agglomeration of ZVIN and increases the surface area. Based on the SEM results, the large surface area of ZVIN is responsible for the excess active sites for the catalytic reduction of 4-NP. Fig. 3(d) shows the EDX spectra of the bentonite supported ZVIN for the estimation of elemental analysis. In EDX reveals the intense peaks of C (5.68 wt%), O (38.28 wt%), Mg (1.06 wt%), Al (10.08 wt%), Si (14.77 wt%), and Fe (20.13 wt%), confirming the existence of Fe. The C and O signals are attributed to Eucalyptus leaf extract contains water-soluble non-toxic polyphenols and other Mg, Al, and Si signals are attributed to bentonite clay. 3.4. TEM analysis The size and morphology of synthesized B-ZVIN were assessed with transmission electron microscopy (TEM). Fig. 4 shows different magnifications of TEM images of B-ZVIN, which provides the information that the ZVIN are well dispersed on the surface of bentonite clay without any aggregation. In addition, the TEM image clearly exhibits a transparent organic layer coating around the ZVINs, which was due to the surrounding phytochemicals that serve as a capping agent to prevent agglomeration. The sizes of dispersed ZVIN are within the range 10–60 nm. The TEM image of the ZVIN shows that the particles have cubic crystalline phase and

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irregular shape of individual particles with an average diameter is less than 50 nm. The large sizes of particles are in good agreement with the results of XRD characterization. 3.5. BET analysis BET analysis provides the evaluation of a precise specific surface area of materials by nitrogen multilayer adsorption measured as a function of relative pressure using a fully automated analyzer. The technique encompasses external area and pore area evaluations to determine the total specific surface area yielding important information in studying the effects of surface porosity and the particle size in many applications. The surface area measurements were carried with high purity nitrogen at 77 K. Nitrogen adsorptiondesorption isotherm and pore size distribution (BJH) plot of BZVIN is as shown in Fig. 5. The N2 adsorption-desorption isotherm of B-ZVIN reveals that the samples have a typical IV curve of the N2 adsorption-desorption isotherm with H1 hysteresis loop, which indicates that the samples have spherical mesopores [58]. The results reveal that the BET surface area, average pore width and total pore volume of B-ZVIN were 62.47 m2/g, 51.87 Å and 0.0891 cm3/g respectively. 3.6. Catalytic reduction of 4-NP The catalytic reduction of 4-NP to 4-AP in the presence of NaBH4 as a reducing agent was taken as a model reaction to eval-

Fig. 3. SEM images of (a) bentonite and (b-c) B-ZVIN and (d) EDX results showing the presence of ZVIN.

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Fig. 4. (a–b) TEM images of B-ZVIN.

Fig. 5. N2 adsorption-desorption isotherm and BJH pore size distribution of the B-ZVIN.

uate the catalytic activity of as-synthesized nano green catalyst BZVIN and the progress of the reaction was monitored by UV–visible absorption spectroscopy at given intervals as shown in Fig. 6. Initially, 4-NP shows its original absorption peak at 318 nm, after the addition of NaBH4 solution the formation of 4-nitrophenolate ions takes place and the absorption peak shifts to 400 nm. After the addition of a catalyst, the percentage of conversion of 4-NP to 4-aminophenol was observed for every 2 min with the decrease in the intensity of absorption peak at 400 nm and after 20 min the peak was completely disappeared (Fig. 6). It is noted that without the addition of NaBH4 there is no conversion of 4-NP to 4aminophenol even after 24 h time period also. The recovered catalyst can be reused with almost all same catalytic activity for several times. The excess NaBH4 is used to maintain alkaline condition and reduce the degradation of borohydride ions. The catalytic reduction of 4-NP using the synthesized green catalyst (B-ZVIN) in the presence of excess NaBH4 can be fitted to a pseudo-first-order kinetic equation given by the following equation:

ln

Ct At ¼ ln ¼ kt C0 A0

where C0 is the initial concentration of 4-NP, Ct is the concentration of 4-NP at a reaction time t, A0 is the absorbance at time t = 0 sec

Fig. 6. The reduction of 4-NP using synthesized B-ZVIN by NaBH4: in the graph (a) denotes to absorption maxima of 4-NP, and (b) conversion of 4-nitrophenolate ion to 4-amino phenol with respect to time (0–20 min.)

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K. Sravanthi et al. / Materials Science for Energy Technologies 2 (2019) 298–307 Table 1 The comparative study of 4-NP reduction in the presence of NaBH4 as a reducing agent with various catalysts as well as present study. Catalyst

Conc. of NaBH4

Calcium Alginate-stabilized Au NPs Au-Ag bimetallic nanoparticles Au/SiO2 NPs Xanthan gum stabilized Pd NPs Ag NPs-chitosan TiO2 Starch supported-Au NPs Chitosan-Guar gum blend AgNPs Tulsi leaves-Ag NPs Bentonite clay supported Fe NPs

0.1 M 0.01 M 102 M 15 mM 0.1 mM 0.7 g 0.01 M 0.2 M 0.2 M

Conc. of catalyst 1.2 g/L 20 mL/1mg 5 mg 10 mL 50 mg/L 20 mg 0.3 mg 10 mL 10 mg/L

Conc. of 4-NP 4

1.0  10 104 M 0.005 M 0.2 mM 0.1 mM 1 mM 2 mM 0.005 M 0.2 mM

M

Reaction time 45 min 30 min 20 min 24 min 120 min 13 min 3 min 30 min 20 min

Rate constant 5

1

0.14  10 min 2.85  102 min1 1.98  102 min1 0.18309 min1 0.0422 min1 0.0218 min1 – 2.048 min1 0.1409 min1

Conversion, (%)

Refs.

92.2 99.1 98.4 99.1 99.0 100 75 100 96.8

[59] [60] [61] [62] [63] [64] [65] [66] This work

Scheme 2. The possible mechanism of 4-NP to 4-AP conversion using green synthesized B-ZVIN.

and At is the absorbance at time t. The linear plot of ln CC0t against

time (Fig. 7) gives the rate constant (k) value 0.1409 min1, which is very near to the rate of conversion with the reaction time was reported by noble metals and which are expensive when compared with B-ZVIN and results are summarized in Table 1.

Scheme 3. The solvent and solvent free synthesis of benzimidazoles using green synthesized B-ZVIN.

3.7. Possible mechanism for the reduction of 4-NP

Fig. 7. The rate equation plot of the reduction of 4-NP using synthesized B-ZVIN by NaBH4.

Recently, the reaction of sodium borohydride with metal surfaces in the presence of metal nanoparticles as a catalyst is an interesting area of research due to its potential application in catalysis [67]. Metal NPs exhibit excellent catalytic properties owing to the high rate of surface adsorption and high surface area to volume ratio. The mechanism of reduction of 4-nitrophenol to 4aminophenol by NaBH4 in the presence of silver nanoparticles is discussed in terms of the Langmuir-Hinshelwood (LH) model [67]. Esumi et al. have proposed that the catalytic reduction of 4NP proceeded in two steps: (1) diffusion and adsorption of 4-NP to the catalyst surface and (2) electron transfer mediated by the catalyst surface from BH4 to 4-NP [68]. Therefore, enhancing both the adsorption ability and electron transfer property of the catalyst is important for the reduction of 4-NP. In this work, it is well known that the catalytic reduction process of 4-NP to 4-AP occurs on the Fe surface and can be described by general mechanism of heterogeneous catalysis i.e. diffusion of reactants (borohydride ion and 4-NP) on to the Fe surface; adsorption of reactants on to the Fe surface; electron transfer from donor (borohydride ion) to acceptor (4-NP); and finally desorption of products (4-AP) from the surface of catalyst. The possible mechanism of the 4-NP reduction using the green synthesized B-ZVIN by NaBH4 as a reducing agent and it is represented in Scheme 2.

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Scheme 4. The synthesis of benzimidazoles using green synthesized B-ZVIN under solvent free conditions.

Table 2 The various amounts of synthesized B-ZVIN as catalyst in the preparation of benzimidazoles. S. No.

Catalyst, (wt%)

Time, (min.)

Yield, (%)

1 2 3 4 5

0 mg 05 mg 10 mg 20 mg 30 mg

180 10 10 10 5

0 58 ± 1.2 76 ± 0.7 88 ± 1.1 95 ± 0.8

Table 3 The catalytic determination of percentage of benzimidazoles yield using synthesized B-ZVIN under solvent and solvent free conditions. Entry

Solvent

Time

Temperature, (oC)

Yield, (%)

1 2 3 4 5 6 7 8 9

C2H5OH C2H5OH PEG PEG CH2Cl2 CH2Cl2 DMF DMF solvent-free

12 h 6h 12 h 6h 12 h 6h 12 h 6h 5 min

25 60 25 60 25 60 25 60 120

50 ± 1.1 47 ± 0.9 55 ± 0.5 51 ± 0.8 60 ± 1.1 58 ± 1.2 80 ± 0.7 79 ± 1.1 95 ± 0.8

3.8. Catalytic activity of B-ZVIN in the synthesis of benzimidazoles The comprehensive study of the synthesis of benzimidazoles under solvent and solvent-free conditions (Schemes 3 and 4) was carried out for more intelligible information of catalytic activity using B-ZVIN. In order to know the optimum conditions of the reaction, primary studies were carried out for the synthesis of benzimidazoles by varying the weight of catalyst (5–30 mg) (Table 2) and the polarity of solvents (Table 3). It was observed that no reaction occurs without catalyst and among all conditions of the reaction; solvent-free condition gives best results (Table 4). The recovered catalyst was washed with ethanol and water and it was used for five successive cycles for the standard reaction of synthesized benzimidazoles (Scheme 4). It is noticed that the catalytic activity of B-ZVIN remains unchanged even after running of successive five cycles (Fig. 8).

4. Conclusions In this paper, we have developed the green synthesis and characterizations of B-ZVIN using Eucalyptus leaf extract as both reducing and stabilizing agent for the reduction of 4-NP to 4-AP by NaBH4 as a reducing agent. The characterization techniques were

Table 4 The preparation of various benzimidazoles by different substrates using synthesized B-ZVIN under solvent free conditions. Entry

Substrate H

1

Product N

O

O

Yield, (%)

N H

O

95 ± 1.1

O O

O

2

95 ± 0.8

H

N N H

O

3

O

H

H N

Cl

Cl

O 4

N

H

H

H N

O N

+

O

O 5

96 ± 0.7

F

-

+

N

O

N H N

N

97 ± 0.6

F

O

96 ± 1.2

O

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K. Sravanthi et al. / Materials Science for Energy Technologies 2 (2019) 298–307 Table 4 (continued) Entry

Substrate

6

H

Product

Yield, (%)

H N

CH3

CH3

O 7

N

H

H N

OH

H

N

Cl

H N

O N

+

94 ± 0.8

O

O

-

96 ± 0.9 +

N

H N

H

O

-

N

O 10

Cl

N

O 9

97 ± 1.0

OH

O 8

96 ± 0.5

H

H N

O

96 ± 1.1

N

reduction of 4-NP by NaBH4 and it was more efficient in the synthesis of benzimidazoles. The prepared B-ZVIN is a stable and more efficient catalyst for the reduction of 4-NP and synthesis of benzimidazoles after five successive cyclic experiments under similar conditions. Moreover, B-ZVIN was environmental compatible, magnetically separable and prepared by green synthetic methods. Competing interest The authors declare that they have no competing interests. Funding Not applicable. Acknowledgement

Fig. 8. The reusability of synthesized B-ZVIN in the preparation of benzimidazoles.

Authors are thankful to the Head, Department of Chemistry, Osmania University, Hyderabad for providing the necessary facilities. References

revealed by the successful formation of B-ZVIN. The FTIR analysis notifies that the polyphenols present in the leaf extract are responsible for the formation of B-ZVIN. XRD analysis reveals that the iron nanoparticles immobilized on bentonite clay are majorly ZVIN. SEM and TEM images showed that iron nanoparticles are well dispersed on the bentonite surface and have the irregular shape with an average size in the range of 40 nm. The BET surface area, average pore width and total pore volume of B-ZVIN were 62.47 m2/g, 51.87 Å and 0.0891 cm3/g, respectively were determined by the surface area measurements. The green synthesized B-ZVIN possessed comparable catalytic activity with noble metals in the

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