Original Article

, Volume: 16( 1)

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Synthesis of Fe2O3 Using Emblica officinalis Extract and its Photocatalytic Efficiency

*Correspondence:

C Malarkodi , Materials Chemistry Group, Department of Chemistry, University of Delhi, Delhi-110007, India, Tel: +254721857685; E-mail: cmalarkodi@chemistry.du.ac.in

Abstract

We identified a green method for the synthesis of Fe2O3 using the plant extract of the fruit E. officinalis. The fresh fruit extract reacted with a solution of ferric chloride at room temperature to form FeOOH initially. Homogeneous Fe2O3 crystallites were obtained after 24 h and were confirmed by the presence of prominent reflections in the PXRD pattern. The presence of various aliphatic amines, alkene and primary amines present in the E. officinalis extract is expected to be responsible for the precipitation of FeOOH and subsequent formation of Fe2O3. The FTIR spectra of Fe2O3 indicated the presence of the bands corresponding to different organic amine and alkene functional groups. The band gap energy of the resultant Fe2O3 investigated by the UV-vis absorption spectroscopy was found to be in the range of 1.97-2.05 eV. The photocatalytic efficiency of Fe2O3 nanoparticles was evaluated by the degradation of Rhodamine 6G (Rh-6G) under visible light irradiation.

Keywords

E. officinalis; Green synthesis; Fe₂O₃ nanoparticles; Photocatalytic activity

Introduction

Metals, bimetallic alloys, binary and ternary metal chalcogenides in nano-size dimensions with well-defined shapes and structures along with unique properties have been widely researched in the past decades because of their vital role in nanotechnology and catalysis [1]. Among the vast majority of materials that are available, Fe₂O₃ deserves special mention because of its easy accessibility with potential applications such as targeted drug delivery, sensors, photo catalysis, and biomedicines and most commonly for water purification etc. [2-7]. The synthesis of Fe₂O₃ in Nano dimensions using naturally occuring reagents available from plants will be significant for special biological related applications. Although many biological based methods are available for the synthesis of magnetic nanoparticles of α-Fe₂O₃ [8], research efforts are continued to find non-toxic, environmental friendly alternate methods [9]. Usually, the reported methods make use of the plant extracts as reagents and some of the previously known plant sources include Hibiscus rosa sinensis, Pisum sativum, Psidium guajava, Emblica officinalis, Aloe vera extract and Piper nigrum [10-15]. Table 1 lists the literature data on the various plant reagents that are used for the synthesis of different metal and metal oxide materials [16-31]. Phyllanthus emblica (Emblica officinalis) commonly known as Indian “gooseberry” or amla, belonging to family Euphorbiaceae is an important herbal drug used in ayurvedic systems of medicine. E. officinalis has been reported to play a beneficial role to treat diseases such as diabetes, ulcer, and anemia and possesses cardio protective properties [32]. E. officinalis fruit extracts contain chemicals including quercetin, ascorbic acid, gallic acid, tannins, flavonoids, and pectin and polyphenolic compounds [33]. The present work reports the investigation of using E. officinalis fruit extracts as a biological reagent for the synthesis of Fe₂O₃. The synthesized Fe₂O₃ has been characterized and explored as a photo catalyst under visible light illumination.

Table 1:  List of nanomaterials obtained using plant sources.

Materials and Methods

Collection and preparation of plant extract

The fruits sample of E. officinalis was collected from the local market near Mayur vihar phase III, New Delhi, India.

Fresh extract

E. officinalis fruit extract was prepared following a procedure reported earlier [13]. E. officinalis fruits were thoroughly washed with water and finely chopped. The E. officinalis fruit pieces were then crushed into the mortar and pestle through the deionized water in a mass to volume ratio 10 g of fruit pieces to 100 ml of water. The mixture was allowed to stand for 10 minutes and passed through the Whatman No.1 filter paper to remove the solids parts. The filtrate was stored at 4°C and was used for the synthesis.

Boiled extract

10 g of finely chopped E. officinalis fruits was weighed and boiled with 100 ml of double distilled water at 60°C-80°C for 10 minutes. After boiling, the solution was filtered through the Whatman No. 1 filter paper and stored at 4°C for further use.

Reflux condition

10 g of E. officinalis fruits were chopped and refluxed with 100 ml of double distilled water for 1 h, followed by filtering and storing at 4°C for further use.

Synthesis of Fe₂O₃ nanoparticles using E. officinalis extracts

Synthesis of Fe₂O₃ nanoparticles was carried out using fresh extract of E. officinalis obtained by boiling and reflux procedures as detailed above. 0.4055 g of FeCl₃ (1 mM) was dissolved in 90 ml of double distilled water. 10 ml of E. officinalis was added separately to this 90 ml of aqueous solution of FeCl₃. The reaction mixtures were stirred for 5 h at room temperature with the formation of brick red color colloidal Fe₂O₃ particles at the bottom of the flask which were allowed to stand for 24 h. The colloidal solution was centrifuged at 2000 rpm for 20 minutes and washed with double distilled water repeatedly to remove any impurities followed by drying in hot air oven at 60°C for 5 h (FIG. 1).

Synthesis of Fe₂O₃ nanoparticles using ascorbic acid

In a typical experiment, 0.4055 g of FeCl₃ (1 mM) was dissolved in 90 ml of double distilled water continuously stirring to form a red solution, and then, 10 ml of 0.4 g ascorbic acid was added to the solution slowly. The reaction mixtures were stirred for 5 h at room temperature with the formation of brick red color colloidal Fe₂O₃ particles at the bottom of the flask which were allowed to stand for 24 h. The colloidal solution was centrifuged at 2000 rpm for 20 minutes and washed with double distilled water repeatedly to remove any impurities followed by drying in hot air oven at 60°C for 5 h.

Characterization

High resolution X’Pert PANanalytical diffractometer equipped with a Xe Propotional detector employing Cu Kα radiation (λ=1.5418 Å) was employed to obtain data with a scan rate of 1.65 s per step and with a step size of 0.04°C at 298 K (DY3813). The SEM micrograph of the sample was recorded using JEOL 6610 LV. TEM was obtained using FEI Technai G2 20 electron microscope operating at 200 kV. Fourier Transform Infra-Red spectroscopy was recorded using a Perkin Elmer 2000 spectrometer using KBr pellet technique. UV-vis diffuse reflectance data were collected over the spectral range 200−800 nm using Perkin-Elmer Lambda 35 (Waltham, MA, USA) scanning double beam spectrometer equipped with a 50 mm integrating sphere. The data were transformed into absorbance with the Kubelka-Munk function for the estimation of the band gap. The synthesized Fe₂O₃ has been characterized and explored as a photocatalyst for the degradation of the cationic dye Rhodamine 6G (Rh-6G) under visible light illumination of a 450 W xenon lamp. The details of the photocatalytic set up have been described earlier [34]. 0.1g of catalyst was added to 50 ml aqueous solution of solution of Rh-6G (10-5 M Concentration). Before the measurements, the suspension was stirred in dark for 30 mins to achieve an adsorption-desorption equilibrium. After shining the light, 4 ml of solution was collected at 1 h intervals and the catalyst was separated using centrifugation. The degradation was followed by monitoring decrease in the λ_max (540 nm) of Rh–6G.

Results and Discussion

The formation of Fe₂O₃ nanoparticles of the filtrate was primarily followed by carefully observing the color change during the reaction. The appearance of brick red color after the treatment of clear yellow FeCl₃ solution with the extract of E. officinalis fruit suggested possible reaction. FIG. 2 (i) shows the digital photographs of the solution of E. officinalis fruit extract with added FeCl₃ solution together with the blank FeCl₃ solution in which fruit extract was not added. The color change from yellow to red was observed within 2-10 mins after mixing and after 6-12 h the suspended particles in the solution got settled down at the bottom of the flask. The stability of the brick red color crystallites after 24 h suggested the formation of Fe₂O₃ possibly from FeOOH that gets precipitated initially. The biomolecule interaction is expected since the hydroxide followed by oxide generation requires change in pH [35]. The PXRD patterns of Fe₂O₃ nanoparticles synthesize using E. officinalis extracts along with Fe₂O₃ synthesized independently using ascorbic acid are shown in FIG. 2 (ii) and (iii).

The observed reflections were indexed in rhombohedral symmetry with lattice parameters a=5.035 (5) Å and c=13.74 (7) Å (S.G. R¯3c) and matched with the reported pattern (JCPDS File No. 86-0550) [36]. The XRD pattern of these peaks reveals that the Fe₂O₃ nanoparticles are crystalline in nature. SEM images coupled with TEM revealed the aggregation of rod shaped of Fe₂O₃ crystallite with diameter ranging between 20 nm to 100 nm (FIG. 3).

Fe₂O₃ nanoparticles synthesized using E. officinalis fresh extracts have more uniform distribution, while boiled and refluxed E. officinalis extracts produced much larger aggregation of the Fe₂O₃ particles. The elemental compositional analysis of the synthesized Fe₂O₃ was also confirmed using EDX. The FTIR spectra of Fe₂O₃ obtained using different E. officinalis extracts indicated the presence of finger print bands corresponding to aliphatic amine, alkene and primary amines (FIG. 4 (i)). The band in the region of 3436 cm^-1 is ascribed to the N-H stretching vibrations of primary amines (R-NH2). The bands at 2934 and 2856 cm^-1 are due to the presence of C-H bonds. Thus, FTIR results confirm the presence of primary amines that are mostly responsible for the formation of Fe₂O₃ particles. The presence of 1056 and 1457 cm^-1 can be assigned to C-O and C-C stretching of alcohols respectively [37,38]. Finally the bands due to Fe-O stretching at 536 and 454 cm^-1 were also observed. The UV-visible diffuse reflectance spectrum consisted of the strong absorption of Fe₂O₃ at 530 nm (FIG. 4 (ii)). The band gap energy was evaluated by plotting the Kubelka-Munk function with photon energy (eV) and was found to vary from 1.97-2.05 eV and these observed values were in close agreement with the earlier reported [39].

The photocatalytic activity of Fe₂O₃ synthesized using fresh, boiled and reflux extract were evaluated for the degradation of aqueous Rh-6G under visible 400 nm<λ>800 nm radiation. The concentration of the dye solution was not decreased in the presence of the catalysts in dark. Also, photolysis of the dye solution under light irradiation was carried out without the addition of the catalysts in order to separate the noticeable degradation due to photo catalysis by the catalysts under visible light irradiation. The fact that only negligible decrease occurred in the concentration of the dye in the absence of the catalyst, suggested that certainly photo catalysis has taken place in the presence of Fe₂O₃ catalyst within four hours under visible light irradiation as shown by the decrease in the absorbance intensity at 540 nm. Appreciable decomposition was noticed only by photocatalysis using Fe₂O₃ under visible light (FIG. 4 (iii)). Further, the Fe₂O₃ obtained using boiled extract showed better photocatalytic abilities as compared to the Fe₂O₃ obtained using the fresh or refluxed E. officinalis extracts (FIG. 4 (iv)).

Conclusion

Fe₂O₃ nanoparticles have been successfully synthesized using the extract obtained from E. officinalis and the formation was confirmed by a variety of analytical techniques. This approach offers a novel ecofriendly and cost effective method probably. The extract containing possibly different stabilizing and capping agents is responsible for the formation of Fe₂O₃ from ferric chloride solution. Fe₂O₃ nanocrystallites are found to be useful to degrade aqueous solution of Rh-6G under visible light irradiation.

Acknowledgements

Authors thank DST (SR/S1/PC-07/2011), DU-DST Purse Grant phase-II and University of Delhi under the “Scheme to Strengthen RandD Doctoral Research Program”. Timely help from Prof. R. Nagarajan for encouragement is profusely acknowledged. CM and VM thank UGC woman PDF and CSIR for SPMF fellowship respectively.

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