Tinospora cordifolia mediated facile green synthesis of cupric oxide nanoparticles and their photocatalytic, antioxidant and antibacterial properties

Materials Science in Semiconductor Processing 33 (2015) 81–88

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Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/mssp

Tinospora cordifolia mediated facile green synthesis of cupric oxide nanoparticles and their photocatalytic, antioxidant and antibacterial properties Udayabhanu a, P.C. Nethravathi a, M.A. Pavan Kumar b, D. Suresh a,n, K. Lingaraju c, H. Rajanaika c, H. Nagabhushana d, S.C Sharma e,f a

Department of Studies and Research in Chemistry, Tumkur University, Tumkur, Karnataka 572103, India Department of Studies and Research in Biochemistry, Tumkur University, Tumkur, Karnataka 572103, India c Department of Studies and Research in Environmental Science, Tumkur University, Tumkur, Karnataka 572103, India d Prof. C. N. R. Rao Centre for Advanced Materials, Tumkur University, Tumkur, Karnataka 572103, India e Department of Mechanical Engineering, Siddaganga Institute of Technology, Tumkur, Karnataka 572103, India f Chattisgarh Swami Vivekanand Technical University, Bhilai, Chattisgarh, India b

a r t i c l e i n f o

Keywords: CuO Nanoparticles Tinospora cordifolia Antioxidant Antimicrobial

abstract The study reports a facile method for the green synthesis of copper oxide nanoparticles (CuO Nps) by a solution combustion method using Tinospora cordifolia water extract. The Nps were characterized by XRD, SEM, TEM and UV–visible studies. XRD data indicates the formation of pure monoclinic crystallite structures of CuO Nps. SEM images show that the particles have sponge like structure with large surface area and the average crystallite sizes were found to be
6–8 nm. These observations were confirmed by TEM analysis. Photocatalytic activity studies of CuO Nps reveal that they act as very good catalyst for the effective degradation of methylene blue (MB) in the presence of UV and Sun light. Also, the degradation of MB was found to be pH dependent. The Nps found to inhibit the activity of 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radicals effectively. CuO Nps exhibit significant bactericidal activity against Klebsiella aerogenes, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus. The study reveals a simple, ecofriendly and robust method for the synthesis of multifunctional CuO nanoparticle employing underutilized medicinal plants. & 2015 Elsevier Ltd. All rights reserved.

1. Introduction Industrial dyestuff contain one of the largest groups of organic compounds that lead to discoloration of water and cause great loss of aquatic life. The elimination of these colors and other organic materials is a priority for ensuring a safe and clean environment [1]. Advanced oxidation processes

n

Corresponding author. Tel.: þ91 9886465964. E-mail address: [email protected] (D. Suresh).

http://dx.doi.org/10.1016/j.mssp.2015.01.034 1369-8001/& 2015 Elsevier Ltd. All rights reserved.

(AOPs) have been used during the last decade to degrade dyes in aqueous media without the formation of harmful byproducts [2]. AOPs are based on the generation of very reactive species such as hydroxyl radicals (OH) that oxidize a broad range of pollutants quickly. Irradiation sources have a vital role in enhancing the activity of catalysts, and UV radiation sources are widely used but they are also expensive and polluting [3]. CuO is one of the most important catalysts used to eliminate industrial effluents in the environment. Earlier studies indicate that the catalytic reaction is apparently a structure sensitive process and the oxygen surface lattice of

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CuO is involved in the reaction [4]. Catalytic reactivity of CuO nanostructures depends on the shape and the exposed crystal planes. Hence the architectural shape-controlled synthesis of CuO structures may be helpful for designing novel structures with preferred improved performance [5]. In the last few years, synthesis of metal oxide nanostructures with desired architecture has received significant attention due to their unique properties and applications [6,7]. Among metal oxides, cupric oxide (CuO) is a p-type semiconductor with a bandgap of 1.2 eV [8]. The synthesis and application of CuO Nps are of practical and fundamental importance. CuO is used in numerous applications like gas sensors [9], solar energy conversion [10], electrode material in lithium ion batteries [11], as field emitter [12] and as a heterogeneous catalyst [13]. Due to the versatile properties and diverse applications, various kinds of CuO nanostructures e.g. nanorods, nanosheets, and nanodendrites as well as honeycomb-like, urchin-like and dumbbell-like structures [14–17]. They have been synthesized using a variety of fabrication techniques including the chemical bath method, sol–gel method, gas phase oxidation, micro-emulsion, and many other techniques [18–21]. Recently, there have been several attempts to synthesize functional materials through greener approaches for achieving materials with variety of properties. Also, these methods avoid the extensive use of hazardous chemicals for the synthesis. Additionally, solution combustion synthesis is one of the best and easy methods for the synthesis approach towards the uniform mixing with combustible fuel. This is an exothermic reaction between oxidizing and reducing agents. Usually metal nitrates are used because of their unique solubility to form homogeneous solution. Metal nitrates act as oxidizer agents and fuel acts as reducing agents for the synthesis of CuO nano crystals [22,23]. In this paper, we report the green synthesis of CuO Nps via solution combustion synthesis using Tinospora cordifolia leaf extract of water for the first time. T. cordifolia commonly named as “Guduchi” in Sanskrit belongs to the family Menispermaceae. It is a genetically diverse, deciduous climbing shrub with greenish yellow typical flowers found at higher altitude [24,25]. It mainly contains alkaloids, diterpenoid lactones, glycosides, steroids, sesquiterpenoid, phenolics, aliphatic compounds and polysaccharides [26,27]. T. cordifolia leaf extract is extensively used in various herbal preparations which have anti-periodic, anti-spasmodic, anti-microbial, antiosteoporotic, anti-inflammatory, anti-arthritic, anti-allergic and anti-diabetic properties [28]. Various components present in leaves of T. cordifolia (Fig. 1) are antioxidants and may act as good fuels for the preparation of Nps. Therefore, this study attempts to exploit T. cordifolia extract as fuel for the synthesis of CuO Nps. The procedure involves a self-sustained reaction in homogeneous solution of Copper nitrate and T. cordifolia extract.

2. Materials and methods T. cordifolia leaves were sourced from Tumkur University Campus, Tumkur, Karnataka, India. The plant material was shade dried and powdered into 100 mesh size and stored at room temperature in an airtight container.

Fig. 1. Leaves of Tinospora cordifolia.

2.1. Preparation of the extract The coarsely powdered plant material was mixed with water (1:10 proportion) and extracted at 100 1C with a reflux arrangement for 5 h. The extract was filtered and centrifuged to eliminate any un-dissolved material. It was then concentrated, dried using roto evaporator and stored in airtight bottles at 4 1C. 2.2. Synthesis of nanoparticles CuO Nps were prepared by eco-friendly green combustion route using T. cordifolia plant leaf extract as fuel [29,30]. The Copper nitrate trihydrate was procured from Sigma-Aldrich (AR) and used without further purification. Exactly 1.205 g of Cu(NO3)2  3H2O was dissolved with 0.2 g of T. cordifolia leaf extract in 10 ml of distilled water. The mixture was kept in a pre-heated muffle furnace at 400 710 1C and subjected for combustion. The reaction was completed within 5 min. A fine black colored material was obtained. The synthesis of Nps was repeated with different concentrations of the plant extract such as 0.3, 0.4, and 0.5 g keeping copper nitrate concentration constant at 1.205 g. The obtained product was stored in airtight container until further use. 2.3. Structural and morphological studies Optical properties of CuO Nps were measured using an UV–visible spectrophotometer (Thermo Scientific Evolution – 220). The sample was sonicated for uniform dispersion and the aqueous component was subsequently analyzed at room temperature for optical band gap (Eg) determination. The morphology of the Nps was assessed by Scanning Electron Microscopy (Hitachi – 7000 Table top) and TEM (TECNAIF-30). Phase purity and grain size were determined by using X-ray diffraction analysis using Shimadzu – 7000 with monochromatized Cu-Kα radiation. All experiments were performed in triplicates and the data

Udayabhanu et al. / Materials Science in Semiconductor Processing 33 (2015) 81–88

was analyzed using Origin 8.0 software (Orgin Lab Corporation, USA). The phase compositions of the CuO Nps were studied by X-ray diffraction. The XRD patterns were compared to standards compiled by the Joint Committee on Powder Diffraction and Standards (JCPDS). The crystallite sizes were calculated using the Debye Sherrer formula: D¼

0:89λ β cos θ

ð1Þ

2.4. Photocatalytic degradation of dye Photocatalytic degradation experiments were carried out with the help of a batch reactor which has the dimensions of 150  75 mm2 [31]. A catalytic load of 50 mg Nps in 100 ml of 5 ppm dye was prepared. The dye solution and catalyst were placed in the reactor and magnetically stirred with simultaneous exposure to Sun light/UV-light. Then 3 ml of slurry was drawn at specific intervals (30 min), centrifuged to remove the intervention of the catalyst and assessed using a spectrophotometer for rate of degradation. The photo-degradation efficiency of methylene blue by CuO Nps was calculated using the following equation: % of degradation ¼

Ci Cf  100 Ci

ð2Þ

83

bacteria Staphylococcus aureus (SA). Nutrient agar plates were prepared and swabbed using sterile L-shaped glass rod with 100 ml of 24 h mature broth culture of individual bacterial strains. Wells (6 mm) were made in each petriplate using the sterile cork borer. Different concentrations of Nps (500 and 1000 mg/well) were used to assess the bactericidal activity of the compounds. The material was prepared in sterile water and added into the wells by using sterile micropipettes. Simultaneously the standard antibiotics (as positive control) was tested against the pathogens. Ciprofloxacin (Hi Media, Mumbai, India) was used as positive control. Then the plates were incubated at 37 1C for 48 h. After the incubation period, the zone of inhibition of each well was measured and the values were noted. The studies were conducted in triplicates and the average values were calculated for the ultimate antibacterial activity.

3. Results and discussion The X-ray diffraction pattern of the CuO Nps synthesized using T. cordifolia leaf extract with different concentrations is shown in Fig. 2. The XRD peak positions were consistent with the Copper oxide and sharp peaks of XRD indicate the crystalline structure. These are in good agreement with those in the JCPDS Card (Joint Committee on Powder Diffraction Standards, Card No. 89-1397). The presence of (110), (111) and (202) planes in XRD indicates

where Ci is the original concentration and Cf is the residual concentration of methylene blue dye in solution. The experiment was carried out by varying experimental parameters such as dye concentration, catalytic load, pH and nature of light (UV and Sun light).

0.5 g

2.5. Antioxidant activity

0.4 g

Intensity (a.u.)

Antibacterial activity was screened by agar well diffusion method [33] against four bacterial strains namely Gram  ve bacteria Klebsiella aerogenes (KA), Escherichia coli (EC), Pseudomonas desmolyticum (PD) and Gram þ ve

20

30

40

50

60

2θ (degrees) Fig. 2. XRD patterns of CuO nanoparticles.

(004)

(311)

(113)

2.6. Antibacterial studies

(202)

0.2 g (202)

(110)

0.3 g

(111)

Antioxidant activity was carried out by DPPH assay using the Brand–Williams method [32]. DPPH (oxidized form) is a stable free radical with purple color having absorption maximum at 520 nm. Its activity is inhibited due to donation of electron by an antioxidant molecule. This results in change in absorbance at 520 nm. 39.4 mg of DPPH was dissolved in 100 ml of methanol to get 0.14 mM concentration of DPPH in the assay. Ascorbic acid was used as standard in the concentration range of 2–10 mg/ml for calibration plot. 140 ml of 1 mM DPPH was mixed with 860 ml of test sample and incubated at 37 1C for 30 min. The absorbance was measured at 520 nm against 50% methanol blank using the spectrophotometer. The antioxidant activity was measured with reference to the standard ascorbic acid absorbance values. The actual absorbance was taken as the absorbance difference of the control and the test sample and IC50 value was determined.

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the formation of pure monoclinic structure of CuO Nps. No peaks were observed due to impurities, which infers that high purity of CuO Nps were synthesized by this method. The strong intensity and narrow width of CuO diffraction peaks indicate that the resulting products were of highly crystalline in nature. By using the Scherrer formula, average crystallite size was found to be 6.5, 6.4, 6.47 and 8.47 nm for the extract concentrations of 0.2, 0.3, 0.4 and 0.5 g respectively. Hence we can conclude that fuel has played profound role in controlling particle size. Fig. 3 shows the room temperature UV–visible spectra of CuO Nps synthesized using T. cordifolia leaf extract with different concentrations. The CuO NPs were dispersed in water with a concentration of 0.1 wt%, sonicated for uniform dispersion of CuO Nps then subjected for UV–visible spectrophotometric measurements. The spectrum reveals a characteristic absorption peak of CuO at wavelength of 275 and 372 nm. This pattern of absorption spectrum can be assigned to the intrinsic band-gap absorption of CuO due to the electron transitions from the valence band to the conduction band [34,35]. The band gap of the CuO thin film was calculated from this absorption spectrum using Tauc equation [36] αhν ¼ Dðhν Eg Þn

Fig. 4. SEM image of CuO NPs synthesized using water extract of Tinospora cordifolia leaves.

ð3Þ

where h is the energy of the photon, Eg is the band gap of the material and D is a constant. The transition data provides the best linear fit in the band edge region for n ¼1/2. The band gap was found to be 4.480 and 3.330 eV which is greater than that of the bulk CuO. This band gap enhancement arises due to the size effect of the Nps. In addition, this sharp peak indicates that the particles are in nanosize, and the particle size distribution is narrow. A normal way to obtain the band gap from absorbance spectra is to get the first derivative of the absorbance with respect to photon energy and find the maximum in the derivative spectrum at the lower energy sides [37,38].

372 nm

Intensity (a.u)

0.5 g 0.4 g

0.3 g

0.2 g 275 nm

300

400

500

600

700

Wavelength (nm) Fig. 3. UV–visible spectra of CuO nanoparticles.

800

Fig. 5. TEM image of CuO NPs synthesized using water extract of Tinospora cordifolia leaves.

The Scanning Electron Microscopy images of the as prepared CuO Nps are shown in Fig. 4. The images depict the formation of crystalline phase in the sample. The SEM micrographs show that the morphology comprises of voids and pores, the cause of which can be traced to the large amounts of hot gases that escape out of the reaction mixture during a combustion process. Through the pores of various sizes and shapes that the crystallites are interlinked to one another, it is significant that the agglomerated crystallites are uniformly spherical in shape. The results were confirmed by the TEM analysis as shown in Fig. 5. The effect of photodegradative activity of fixed amount of CuO Nps was evaluated against increasing concentrations of dye. Fig. 6 shows the consequence of dye

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% degradation

Udayabhanu et al. / Materials Science in Semiconductor Processing 33 (2015) 81–88

40 30 20

5 ppm 10 ppm 15 ppm 20 ppm

10 0

85

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5 ppm 10 ppm 15 ppm 20 ppm

20 10 0

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Time (min)

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Fig. 6. Percentage degradation of (a) UV-light and (b) Sun light in presence of CuO nanoparticles synthesized using water extract of Tinospora cordifolia leaves.

concentration on the photocatalytic activity of CuO Nps. Various concentrations of methylene blue dye such as 5, 10, 15, and 20 ppm/100 ml were tested with fixed catalytic level of 50 mg. It was witnessed that the photodegradation efficiency of methylene blue is inversely proportional to its concentration, which means, the lower is the dye concentration, the higher efficiency of the dye photodegradation at fixed concentrations of catalyst. Increasing the dye concentration from 5 to 20 ppm decreases the photodegradation efficiency of Nps in both the cases of exposure. The photodegradation efficiency depends on the formation of hydroxyl radicals, which is the critical species in the degradation process. Due to static concentration of the catalyst there are only fewer active sites for adsorption of HO  so the generation of HO will be reduced. Moreover, as the concentration of methylene blue increases with constant intensity of light and illumination, the path length of photons entering the solution becomes lesser, so only fewer photons reach the catalyst surface. As a result, the productions of holes or hydroxyl radicals that can attack the methylene blue becomes lesser. Therefore, the relative HO number attaching the compound decreases and hence the photodegradation efficiency drops [39,40]. So, the optimal initial dye concentration is 5 ppm with 80% degradation. The effect of catalyst load on the photodegradation efficiency of methylene blue was assessed by taking different amounts of catalyst such as 50, 100, 150, and 200 mg/100 ml of 5 ppm dye solution at pH 7. The results are depicted in Fig. 7. These results indicate that with increase of catalytic load the photodegradation efficiency of methylene blue increases. Further increase in catalytic load did not show any effect on the photodegradation efficiency. This leads to increased number of active sites available on the catalyst surface for the reaction due to enhanced catalyst load, which in turn increased the number of holes and hydroxyl radicals. When the catalyst load increased beyond 200 mg, the photodegradation efficiency abruptly decreased due to accumulation and sedimentation of the catalyst particles which causes an increase in the particle size and decrease in specific surface area which lead to decrease in the number of surface

active sites [41]. Also at high level of catalyst, turbidity of the suspension, the opacity and light scattering of catalyst particles increased. This leads to decrease in the passage of irradiation through the sample [42]. Therefore, the effective photodegradation for methylene blue was observed with catalytic-load of 200 mg. Effect of pH on photocatlytic degradation of methylene blue was studied at fixed levels of dye and catalyst by changing pH from 2 to 12. The results are depicted in Fig. 8. The results revealed that the photodegradation efficiency decreases with increase in pH. At low pH value (pH¼2) the photodegradation efficiency was 91.23%. When the pH value of methylene blue dye solution increased from 2 to 4, the photodegradation efficiency of methylene blue almost increased to 96.93% and then the photodegradation efficiency decreased with further increase in pH. This is due to the fact that the methylene blue is negatively charged in acidic medium, whereas CuO is positively charged around pH 12 which is reported as pH of zero point charge for CuO [43]; therefore the increase in pH value leads to change in the charge on CuO to negative charge by adsorbing HO  ions, which favors the formation of HO [44] and thus the photocatalytic activity decreased due to the increase of the electrostatic repulsion between CuO and anionic methylene blue dye. In addition, the increase of pH may increase e  /h þ recombination rate and subsequently decrease the photocatalytic activity [45]. The best pH value for the efficient photodegradation of methylene blue is 4 at which the positively charged CuO and negatively charged methylene blue molecules attract each other and photocatalytic oxidation occurs very effectively. DPPH, a stable free radical with a characteristic absorption at 517–520 nm, was used to study the radical scavenging activity of CuO Nps prepared by using T. cordifolia leaf extracts. The decrease in absorption is considered as a measure of the extent of radical scavenging. The radical-scavenging activity (RSA) values were expressed as the ratio of percentage of sample absorbance decrease and the absorbance of DPPḢ solution in the absence of extract at 520 nm (Fig. 9). The CuO Nps were evidenced to be potent at inhibiting the DPPH free radical scavenging activity with IC50 value of 566 mg/ml.

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100 100 80

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2 pH 4 pH 6 pH 8 pH 10 pH 12 pH

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% degradation

Fig. 7. Percentage degradation of MB under with different catalytic loads (50, 100, 150, 200 mg) upon exposure to (a) UV-light and (b) Sun light in presence of CuO nanoparticles synthesized using water extract of Tinospora cordifolia leaves.

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2 pH 4 pH 6 pH 8 pH 10 pH 12 pH

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The antibacterial activity of the CuO Nps was assessed against Gram ve E. coli, K. aerogenes, P. desmolyticum and Gram þve bacteria S. aureus using the agar well diffusion method. CuO Nps showed significant antibacterial activity on all the four bacterial strains tested as shown in Fig. 10 for the NPs concentration of 400 and 800 mg. Table 1 illustrates the statistical observations of bacterial inhibitions of CuO Nps. A variety of active components derived from the plant like alkaloids, steroids, diterpenoids, lactones, aliphatics and glycosides [27] have been isolated form the leaves of the plant by extracting with suitable solvents. The extract is enriched with selective components. These natural components are very well known for their health beneficial properties especially antioxidant activity. When such an extract is employed for the combustion synthesis of metal nitrates, they effectively yield metal oxide Nps due to the process of reduction. Our results reveal that water extract of T. cordifolia leaves has shown to have very significant antioxidant activity and the same has

% Inhibition

Fig. 8. Percentage degradation of MB under (a) UV-light and (b) Sun light in presence of CuO nanoparticles synthesized using water extract of Tinospora cordifolia leaves.

50

IC50 of CuO = 566 μg/mL

0 0

200

400

600

800

1000

1200

1400

Concentration ( μg) Fig. 9. Antioxidant activity of CuO nanoparticles synthesized using water extract of Tinospora cordifolia leaves.

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Fig. 10. Zone of inhibition of (a) K. aerogenes (b) E. coli (c) P. aeruginous and (d) S. aureus. Table 1 Antibacterial activity of CuO nanoparticles on pathogenic bacterial strains. Treatment Standard (5 mg/50 ml) CuO (400 mg/40 ml)A CuO (800 mg/80 ml)A1

K. aerogenes (B1) (mean 7 SE) n

13.6770.33 2.3370.33 8.6770.33n

E. coli (B2) (mean 7SE) n

12.677 0.33 1.337 0.33n 2.007 0.00

P. aeruginous (B3) (mean 7 SE)

S. aureus (B4) (mean 7 SE)

10.00 70.00 5.6770.33n 8.6770.33n

11.677 0.33n 5.007 0.00 7.677 0.33n

Values are the mean 7 SE of inhibition zone in mm. *Symbols represent statistical significance. n Po 0.01 as compared with the control group.

been used for the synthesis of CuO Nps. Therefore, various components of wide variety of plants which are rich in these kinds of antioxidants could act as potential reducing agents to obtain functionally superior Nps for various applications. Our study successfully demonstrates utilization of environment friendly solvent such as water to obtain phytochemical enriched extracts from underutilized natural resources for the effective synthesis of Nps which could aid in various applications. In view of the potential beneficial activities of CuO Nps

prepared by T. cordifolia leaf extract assistance, they can be further developed to use them as antimicrobials, antioxidants and effective photodegradative agents. 4. Conclusion Copper oxide nanoparticles were synthesized by a solution combustion method using T. cordifolia water extract. Powder XRD, SEM, TEM and UV–visible techniques

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were utilized to characterize the as formed nanoparticles. XRD data suggests that pure monoclinic crystallite structures of CuO nanoparticles were formed. SEM and TEM images reveal that nanoparticles possess sponge like structures with large surface area. The average crystallite sizes were found to be
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