Anisochilus carnosus leaf extract mediated synthesis of zinc oxide nanoparticles for antibacterial and photocatalytic activities

Materials Science in Semiconductor Processing 39 (2015) 621–628

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Anisochilus carnosus leaf extract mediated synthesis of zinc oxide nanoparticles for antibacterial and photocatalytic activities M. Anbuvannan a, M. Ramesh b,n, G. Viruthagiri a, N. Shanmugam a, N. Kannadasan a a b

Department of Physics, Annamalai University, Annamalainagar 608002, Tamil Nadu, India Department of Physics, Physics Wing (DDE), Annamalai University, Annamalainagar 608002, Tamil Nadu, India

a r t i c l e i n f o

Keywords: ZnO NPs Optical properties Photodegradation Antibacterial activity

abstract We describe a simple combination reaction between zinc nitrate and leaf extract of Anisochilus carnosus to prepare ZnO nanoparticles. The synthesized NPs subjected to structural, optical, and morphological analyses. The structural analysis demonstrates that the prepared ZnO NPs are crystalline and exhibit hexagonal wurtzite structure. Further, the photocatalytic performance of the ZnO tested against the methylene blue (MB) dye under UV radiation has significant photodegradation. The antibacterial activities of the prepared products analyzed against some selected human pathogens showed excellent results. & 2015 Elsevier Ltd. All rights reserved.

1. Introduction Nanoparticles exhibit atom-like behavior due to a high surface, a large fraction of surface atoms and the wide gap between valence and conduction band when divided to near atomic size [1,2]. Though conventional methods utilize less time for synthesizing large quantities of nanoparticles, they require toxic chemicals as capping agents to maintain stability, thus leading to toxicity in the environment. Green nanotechnology using plants is emerging as an eco-friendly alternative, as plant extract mediated biosynthesis of nanoparticles is cost-effective [3–5] which provides natural capping agents in the form of proteins. The presence of various secondary metabolites, enzymes, proteins and or other reducing agents with electronshuttling compounds usually involved in the synthesis of n

Corresponding author. Tel.: þ91 9976994926. E-mail addresses: [email protected], [email protected] (M. Ramesh). http://dx.doi.org/10.1016/j.mssp.2015.06.005 1369-8001/& 2015 Elsevier Ltd. All rights reserved.

metal nanoparticles by plant components. Synthesis of metal nanoparticles using plant extracts is highly biocompatible and cost efficient and can be suitable for large scale production. Zinc oxide has been a subject of interest to the scientists and the industry for decades. Zinc oxide is a versatile material that has achieved applications in photocatalysts, solar cells, chemical sensors, piezoelectric transducers, transparent electrodes [6,7], electroluminescent devices and ultraviolet laser diodes [8,9]. ZnO NPs exhibit unique characteristics than their bulk-sized materials in terms of the higher proportion of atoms, absorption of light, band gap, and the catalytic and antimicrobial properties [10–12]. Solvo-thermal, hydrothermal, sol–gel [13], micro-emulsion, vapor phase transport process [14], and precipitation [15] are the usually suggested methods for the preparation of nanoparticles. Currently, green synthesis of NPs is gaining importance due to its simplicity, inexpensive and eco-friendly. Previously, biosynthesis of ZnO NPs by plants such as Calotropis procera [16], Aloe barbadensis miller [17], and bacteria [18] were reported.

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Anisochilus carnosus wallich (Karpuravalli), from the family of Lamiaceae and abandoned in the Western Ghats, is selected for the present study. The leaves of A. carnosus are used traditionally in the treatment of gastric ulcers and stomach ache. The most significant active constituents of plants are alkaloids, tannin, flavonoid and phenolic compounds [19,20]. In this study, we demonstrate a green method to synthesize ZnO NPs. For the preparation, zinc nitrate and leaf extract of A. carnosus at different proportions were used. The synthesized NPs were characterized using UV-DRS, PL, FT-IR, XRD, FE-SEM, and TEM. Besides, the photocatalytic and antibacterial activities of the ZnO have also been studied. 2. Materials and methods 2.1. Preparation of the leaf extract Plant leaves of A. carnosus collected from Polur, Thiruvannamalai District (12 1150 N, 79 1070 E), Tamil Nadu, and India. The collected leaves subjected to washing several times with distilled water to remove the dust particles. In the preparation of leaves extract, 20 g of fine cut leaves in 250 mL glass beaker mixed with 100 mL of distilled water. Boiling of the mixture for 20 min changed the color of the aqueous solution from watery to light yellow. After allowing the extract to cool to room temperature, using a Whatman filter paper broth filtration took place. 2.2. Preparation of zinc oxide NPs For the synthesis of ZnO nanoparticles, preferred amount (30, 40, and 50 mL) of A. carnosus leaves extract allowed to boil using a stirrer-heater. Then, 5 g of zinc nitrate added to the above solution as the temperature reached 60 1C. This mixture further boiled until its color changed into a dark yellow. The obtained paste further transformed to the ceramic crucible and annealed at 400 1C for 2 h. The finally arrived light white colored powder consumed for different characterizations.

of MB (10  4 M) with the appropriate amount of catalyst (20 mg) stirred for 30 min in the dark prior to illumination. The progress of the reaction monitored at different time intervals using UV–visible Spectrophotometer. It is obvious that the intensity of blue color of the reaction mixture decreased gradually and turned colorless at last. The absorbance for MB at 665 nm monitored with a UV–vis spectrometer was an indication of the catalytic activity of ZnO particles. 2.5. Antimicrobial assay The synthesized compounds tested for inhibition of the human pathogenic bacteria. Microbial assay carried out by following Kelman et al. disc diffusion method [22]. The pathogens namely Salmonella paratyphi, Vibrio cholerae, Staphylococcus aureus and Escherichia coli, were obtained from Raja Sir Muthaiya Medical College, Annamalai University. About 150 CFU/mL of inoculums was swabbed onto MH-agar plates uniformly and allowed to dry in a sterile environment. Sterile disc of 6 mm (HIMEDIA) were

80

30 mL Leaf extract 40 mL Leaf extract 50 mL Leaf extract

70 60

Reflectance (%)

622

50 40 30 20 10 0 300

400

500

600

700

800

Wavelength (nm)

2.3. Characterization of zinc oxide NPs 35 30 mL Leaf extract 40 mL Leaf extract 50 mL Leaf extract

30 25 20

(α hν)

The UV–vis diffuse reflectance spectra (UV–vis-DRS) recorded in UV140404B model in the wavelength range from 250 to 800 nm in reflectance mode. PL spectra of the samples recorded using a FLUOROLOG-FL3-11 fluorescence spectrometer. The crystalline structure of the samples made use of a PAN analytical X'PERT PRO model X-ray diffractometer. FTIR spectra recorded under identical conditions in the 400–4000 cm  1 region using Fourier Transform Infrared Spectrometer (SHIMADZHU). FE-SEM (JEOL JSM 6701-F) and TEM (JEM-2100) measurements revealed the morphology and size distribution.

15 10 5

2.4. Photocatalytic activity measurement 0

Photocatalytic activities of the ZnO nanoparticles estimated from the degradation of methylene blue (MB) under UV irradiation. Heber multi-lamp photoreactor (HML MP 88) played its role in the study of degradation [21]. The dye

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Photon energy (eV) Fig. 1. (a) UV-DRS spectrum of ZnO NPs synthesized using Anisochilus carnosus leaf extract. (b) Plot of indirect band gap energy for ZnO NPs.

50 mL Leaf extract

(100) (002)

Intensity (a.u)

530

Intensity (a.u)

40 mL Leaf extract

(110)

(102)

471 483

432 447

(103) (200) (112) (201)

50 mL Leaf extract

402

623

(101)

M. Anbuvannan et al. / Materials Science in Semiconductor Processing 39 (2015) 621–628

40 mL Leaf extract

30 mL Leaf extract

30 mL Leaf extract 350

400

450

500

550

Wavelength (nm) Fig. 2. Photoluminescence spectrum of ZnO NPs synthesized using Anisochilus carnosus leaf extract.

loaded with 20 μL of test solution (solvent, leaf extract, and ZnO NPs). Ampicillin (10 mg in 1 mL) was used as positive control. The plates were incubated at 25 1C for 3 days to measure zone of inhibition. Mean was calculated by performing the experiments in triplicates.

10

20

30

40

50

60

70

80

2 Theta (deg) Fig. 3. XRD spectrum of ZnO NPs synthesized using Anisochilus carnosus leaf extract.

50 mL Leaf extract

3. Results and discussion 3.1. Optical studies

Eg ¼

hc

λ

eV; Eg ¼

1240

λ

eV

ð1Þ

Where, Eg is the band gap energy (eV), h is Planck's constant (6.626  10  34 Js), C is the light velocity (3  108 m/s) and λ is the wavelength (nm). From Fig. 1a, the absorption edges are positioned at 359, 354 and 349 nm, respectively for 30, 40 and 50 mL of extract addition. The corresponding band gap values are 3.45, 3.5 and 3.55 eV, which indicates the blue shift of absorption edges with the increase in the amount of extract addition. The increase in the band gap can be ascribed to quantum confinement effect. Usually, the smaller the size of the particle, the greater should be the band gap. The particle size reduction on increased quantum of extract addition can be explained in the X-ray diffraction patterns.

40 mLLeaf extract Transmittance (%)

Fig. 1a depicts the optical absorption spectra of ZnO NPs synthesized by A. carnosus extract. The sample had a clear and strong absorption peak below 400 nm. The band gap energy (Eg) of ZnO obtained from the wavelength value corresponding to the intersection point of the vertical and horizontal part of the spectrum, using the following equations:

30 mL Leaf extract

Leaf

4000 3600 3200 2800 2400 2000 1600 1200

800

400

Wavenumber (cm-1) Fig. 4. FT-IR spectra of leaf extract and ZnO NPs synthesized using Anisochilus carnosus leaf extract.

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Fig. 5. (a, b) FE-SEM images and (c) EDX spectrum of ZnO NPs synthesized using 50 mL of Anisochilus carnosus leaf extract.

3.1.1. Indirect band gap energy (Kubelka–Munk plot) The reflectance spectra were analyzed using the Kubelka–Munk relation (Eq. (2)). To convert the reflectance data into a Kubelka–Munk function (equivalent to the absorption coefficient) F(R), the following relation was used. F ðRÞ ¼

ð1  RÞ2 2R

ð2Þ

where R is the reflectance value. Band gap energy of the sample was estimated from the variation of the Kubelka– Munk function with photon energy. Fig. 1b shows the Kubelka–Munk plots for the ZnO NPs. It was used to determine their band gap energy associated with their indirect transitions. The ZnO exhibits indirect Eg of 3.47, 3.51 and 3.56 eV, respectively for 30, 40, and 50 mL of extract addition.

3.1.2. PL analysis PL measurement is an efficient way to estimate the defects and optical properties of the prepared samples. Fig. 2 exhibits the PL emission properties of the ZnO prepared from different levels of extract addition. As shown in the figure, all the samples have high UV emission at 402 nm. The intense UV emission is the near band edge emission of ZnO originating from the recombination of excitons [23]. Besides, the ZnO derived from 30 and 40 mL of extract addition shows faintly visible emissions at 432 and 443 nm. The faint visible emissions at 432 and 447 nm probably originated from oxygen vacancies or other detects [24]. However, on 50 mL of extract addition, the visible emissions (432, and 447 nm) showed a red-shift (471 and 483 nm) with the creation of a new visible radiation at 530 nm. The origin of green emission at 530 nm ascribed from the single -ionized oxygen vacancies

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625

Fig. 6. (a) TEM image of ZnO NPs synthesized using 50 mL of Anisochilus carnosus leaf extract, (b) corresponding SAED patterns and Particle size histogram (c).

[25–27]. From PL results, it is evident that 50 mL of extract addition creates more oxygen vacancies.

Scherrer's formula. D¼

3.2. XRD analysis XRD patterns of ZnO synthesized for different leaf extract levels (30–50 mL) are shown in the Fig. 3. The diffraction peaks at 2θ ¼31.291, 33.951, 36.031, 47.051, 56.091, 62.361, 65.871, 68.571, 72.051 and 76.461 correspond to (100), (002), (101), (102), (110), (103), (200), (112), (201), (004) and (202), planes respectively. As indicated, all of the diffraction patterns well indexed to pure hexagonal wurtzite structured ZnO. The estimated lattice constants have values a ¼b¼3.25 Å and c¼5.21 Å, which are close to the standard values (JCPDS no. 891397). According to the XRD data, the mean crystalline sizes (D) of the ZnO nanoparticles calculated using Debye

Kλ Å β Cos θ

ð3Þ

Where, λ ¼1.5406 Å is the wavelength of the X-ray radiation used. The term θ is the Bragg diffraction angle and β is the full width at half its maximum intensity of diffraction pattern (FWHM) in radian. The obtained sizes are 56.14, 49.55 and 38.59 nm, respectively for 30, 40, and 50 mL of extract addition. The diffraction results of the present study are in agreement with the earlier report [28]. 3.3. FT-IR analysis Fig. 4 shows the FTIR analysis of both leaf extract and synthesized nanoparticles. The results may address the participatory compounds responsible for bio reduction. The appearance of peaks at 3000–3500 cm  1 ascribed to

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OH stretching vibration of O–H groups in water, alcohol, and phenol. The C–H stretching vibrations of alkanes and O–H stretching of carboxylic acid appeared at 2926 and 2858 cm  1, respectively [29]. The intense band at 1627 cm  1 relates to the C ¼C stretch in aromatic ring, and C¼O stretch in polyphenols compounds [29]. The C ¼O bending of nitro groups gives the band at 1382 cm  1 [30]. Specifically, the strong absorptive peaks at 450 cm  1 attributable to the Zn–O stretching while the bending vibrations are being characteristics of the tetrahedral ZnO4 groups in the compounds [31]. Thus, from the IR spectrum it is obvious that the extract of A. carnosus leaves has a higher quantum of polyphenols, carboxylic acid, polysaccharide, amino acid and proteins [32].

the conduction band performs as reducing agent that reduces the oxygen adsorbed on the surface of ZnO photocatalyst. Further, after irradiation the dye gets excited and the excited dye injected an electron to the conduction band of ZnO and scavenged by pre-adsorbed oxygen, to form active oxygen radicals. These generated active radicals that drove the photodegradation process. The ZnO nanoparticles play an important role as an electron carrier. Such assisted photo processes provide an attractive path for the treatment of dyes under UV light (see Scheme 1). The reasonable mechanism for the photocatalytic degradation of MB dye can be schematically shown as [37–39]

3.4. FE-SEM analysis

3.5. TEM analysis The TEM micrograph of the ZnO (50 mL of broth addition) further confirmed the morphology and size of the synthesized product. Fig. 6 reveals that most of the ZnO NPs are quasi-spherical (Fig. 6a) with sizes in the range of 30 to 40 nm (Fig. 6c). The received SAED patterns (Fig. 6b) also well-matched with the (hkl) values corresponding to the prominent peaks of the XRD profiles.

0 min 30 min 60 min 90 min

0.4

0.3

Abs

The synthesized ZnO nanoparticles from 50 mL addition of broth extract analyzed for their morphology by field-emission scanning electron microscopy (FE-SEM). The images showed the presence of spherical shape with a rough surface (Fig. 5a,b). The diameter of the cluster ZnO NPs found to be in the range of 20–40 nm. The EDX spectrum (Fig. 5c) also confirmed that the components of the products have only zinc and oxygen.

0.5

0.2

0.1

0.0 200

300

400

500

600

700

Wavelength (nm) Fig. 7. UV–visible spectra of methylene blue degradation by 50 mL of Anisochilus carnosus in the presence of ZnO NPs.

3.6. Photocatalytic activity One among the main applications of nanomaterials is their catalytic action. It is well-known that the catalytic activity of NPs is strongly dependent on its composition, size, and shape. Photocatalytic activity of ZnO NPs (50 mL of extract) was investigated by selecting the photocatalytic degradation of methylene blue. However, when the experiment was carried out by the introduction of ZnO NPs; the color of the solution was changed significantly from blue to colorless. Fig. 7 shows the ultraviolet-visible (UV-vis) absorption results of an aqueous solution of methylene blue checked in the presence of ZnO NPs at different time intervals. The absorption peak decreases gradually with the extension of the exposure times, which indicates the photocatalytic degradation [33–36]. 3.6.1. Probable mechanism for photodegradation of methylene blue (MB) using synthesized ZnO NPs When the surface of the ZnO NPs irradiated with light, the electron (e  ) from the valence band of ZnO moves to the conduction band and thereby leaving a hole (h þ ) in the valence band. The holes (h þ ) act as an oxidizing agent and oxidize the pollutant directly, or they may react with water to provide hydroxyl radicals. The electron (e  ) in

Scheme 1. Schematic representation of photodegradation of methylene blue dye using ZnO NPs.

M. Anbuvannan et al. / Materials Science in Semiconductor Processing 39 (2015) 621–628

627

Fig. 8. Antibacterial activity of ZnO NPs synthesized using 50 mL of Anisochilus carnosus leaf extract.

ZnOþhν-e  þhν

ZnOðe  Þ þ  O2 þ H þ -ZnOþ H2 O2

H2Oþhν-OH  þH þ 

þ

ZnO (e  )þH2O2-ZnOþ OHþOH 



OH þh - OH h þ þMB-degradation products

e  þO2 - O2 

MBn þ O2 or  OH or  O2 -degradation products

O2 þH þ - OOH

3.7. Antibacterial activity of ZnO-NPs

MBþhν-MBn n



MB þZnO-MBþZnO (e ) ZnO ðe  Þ þ O2 -ZnOþ O2

The antibacterial activity of green synthesized ZnO NPs (50 mL of extract) towards various human pathogens was tested by disc diffusion methods and was represented in the Fig. 8. The antibacterial activity of leaf mediated ZnO

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was studied against the Gram-negative and the Gram-positive bacteria. As seen in the figure, inhibition zones of 6 mm, 10 mm, 7 mm and 9 mm were obtained from the synthesized ZnO nanoparticles against S. paratyphi, V. cholerae, S. aureus, and E. coli, respectively. In the present study, when compared to leaf extract and solvent, green synthesized ZnO NPs showed a greater significant zone of inhibition. However, when compared to standard tablet, lower antibacterial activity of ZnO NPs was observed in all the bacterial pathogens. The results of the present study are identical with the results reported by other researchers [40–43]. The potential reason for the antibacterial activity of ZnO is that ZnO NPs may attach to the surface of the cell membrane and perturbing the permeability and respiration functions of the cell. Smaller ZnO NPs can have larger surface area available for interaction and may give more antibacterial effect than the larger particles. It is also possible that ZnO NPs not only interact with the surface of membrane, but can also penetrate inside the bacteria. 4. Conclusion We have suggested a simple green synthesis method to prepare the nanoparticles of ZnO using different amounts of A. carnosus leaf extract. The diffraction patterns reveal that the particle size could be controlled by increasing the amount of leaf extract addition. The photocatalytic performance of the green synthesized ZnO showed its enhanced activity against the organic dye methylene blue under UV irradiation. Further, the prepared ZnO nanoparticles showed potential antibacterial activities against the pathogens subjected for analysis. In conclusion, the A. carnosus leaf extract assisted ZnO nanoparticles can open up a new path in controlling the organic pollutants and microbial growth. Acknowledgments The authors are thankful and grateful to Dr. S. Barathan, Professor and Head, Department of Physics, Annamalai University, Tamilnadu 608002, for providing all necessary facilities to carry out the present work successfully. References [1] A.V. Dijiken, E.A. Meulenkamp, D. Vanmaekelbergh, A. Meijerink, J. Lumin. 90 (2000) 123–128. [2] G. Singhal, B. Riju, R.S. Ashish, P.S. Rajendra, Adv. Sci. Eng. Med. 4 (2012) 62–66. [3] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Biotechnol. Prog. 22 (2000) 577–583. [4] S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, J. Colloid Interface Sci. 275 (2004) 496–502. [5] J. Huang, Q. Li, D. Sun, Y. Lu, Y. Su, X. Yang, et al., Nanotechnology 18 (2007) 105104. [6] P. Duran, F. Capel, J. Tartaj, C. Moure, Adv. Mater. 14 (2002) 137–141. [7] C. Bauer, G. Boschloo, E. Mukhtar, A. Hagfeldt, J. Phys. Chem. B 105 (2001) 5585–5588.

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