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Novel Gomutra (cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced photocatalytic, photoluminescence and antibacterial studies
Journal Pre-proof Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies S.P. Vinay, Udayabhanu, G. Nagarju, C.P. Chandrappa, N. Chandrasekhar PII:
S2468-2179(19)30212-6
DOI:
https://doi.org/10.1016/j.jsamd.2019.08.004
Reference:
JSAMD 243
To appear in:
Journal of Science: Advanced Materials and Devices
Received Date: 7 April 2019 Revised Date:
18 July 2019
Accepted Date: 10 August 2019
Please cite this article as: S. Vinay, Udayabhanu, G Nagarju, C. Chandrappa, N Chandrasekhar, Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies, Journal of Science: Advanced Materials and Devices, https://doi.org/10.1016/j.jsamd.2019.08.004. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies
Vinay S Pa, Udayabhanub, Nagarju Gb, Chandrappa C Pc, Chandrasekhar Na* a
Research and Development Center, Department of Chemistry, Shridevi Institute of Engineering and Technology, Tumakuru - 572106, India. b Energy Materials Research Laboratory, Department of Chemistry, Siddaganga Institute of Technology, Tumakuru - 572103, India. c Department of Biotechnology, Shridevi Institute of Engineering and Technology, Tumakuru – 572106, India.
*Corresponding authors: E mail: [email protected]
Acknowledgement Dr. Chandrasekhar and Vinay thank Dr. M R Hulinaykar, Managing Trustee, Sri Shridevi Charitable Trust, and Shridevi Institute of Engineering and Technology for encouragement and support for research work. Udayabhanu thanks to CSIR, New Delhi, for Senior Research Fellowship {09/1204(0001)/2018-EMR-1}. Dr. GN Thanks DST Nanomission (SR/NM/NS1262/2013) for financial support. The authors also thank Siddaganga Institute of Technology for providing the lab facilities.
Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies
Abstract This novel work successfully synthesizes silver oxide (Ag2O) nanoparticles (Nps) using cow urine. The presence of different biological components in cow's urine may acts as fuel for the synthesis of Ag2O Nps by combustion method at 500 oC. This is a rapid and environmentally benign procedure, which has added the advantage of shorter response times and better control over size and shape. The synthesized nanoparticles were characterized by XRD, FTIR, UVvis, SEM, EDAX and TEM studies and also these materials have tested for photoluminescence and photocatalytic and biological activities. It is showing good photocatalytic degradation of methylene blue, due to its sensitivity to absorb light with wide band gap energy. Furthermore, we have also examined the photoluminescence studies for the synthesized material and it has given yellow emission for excitation at 436 nm. In addition, it also exhibited good antibacterial activity for both gram-positive and gram-negative bacterial strains by disc diffusion method. In this study, combustion methods will produces nano sized Ag2O with less time, economical and for the large scale synthesis.
Keywords: Silver oxide nanoparticles, Gomutra, Combustion method, Photocatalytic, Photoluminescence, Antibacterial.
1. Introduction Cow urine has significant medicinal drink used for therapeutic purposes in Ayurveda. Nowadays cows are rare to see; in older days in everybody's house we could able to see the cows irrespective of the religion in India. Cows were adopted because of the multiple health benefits, starting with urine, dung, manure, milk, yogurt and ghee products. Human urine received its own medical benefits but was not as popular as cow urine; therefore, cow urine has always been superior and divine [1]. In Hinduism, cows are thought to be sacred and called “KAMADHENU” means the mother of all entities since thousands of years. In India, we use panchagavya (The urine, milk, ghee, curd and dung), obtained from cows are beneficial in different ways as a food supplement, medicine, etc. which holds its own importance in mythological and medicinal aspects. Cow’s urine has promoted as single or in combination with other drugs for medicine and spiritual uses traditionally. The cow is considered as a dwelling place for all God and Goddess. In concern with Gomutra, the spiritual, medicinal and traditional values are higher. Traditionally, Gomutra is being sprinkled in courtyards and home for its holy purposes; it confers the happiness, purity, prosperity, positive health, wealth, etc. [2]. The laboratory analysis of cow’s urine shows that it contains iron, copper, nitrogen, sulphur, manganese, carbolic acid, silicon, chlorine, magnesium, citric, calcium salts, enzymes, mineral salts, vitamins like A, B, C, D, E, creatinine, uric acid, hormones, gold acids, etc. and most interestingly – hip uric acid, which removes toxins through urine, aureum hydroxide, which acts as a germicide and thereby acts as immune-modulatory in increasing immunity if body and build resistance against all minor to major infectious agents.
The above-mentioned contents of Gomutra are found to be very useful in balancing our body constitutes. Thus, whenever we urinate there is a loss of such micro – nutrients, which are well compensated by the daily intake of Gomutra. Paper, dyeing, plastic, and textile industries use color for staining their products and hence consuming a large amount of water to clean, it can lead the formation of wastewater with dye contaminant and it can harmful to human and nature [3-6]. Currently, 100000 various types of dyes produced with an annual production rate of 7×105. Among them, textile industries consume dye about 36000 tons/year, 10 to 20 % of which release dye content waste-water into the environment can lead to polluting the marine life. Hence it is a very important task to reduce the releasing of dye and organic pollutant into the aquatic life. Presently, the photocatalytic degradation has much alarming technique for making free from organic and inorganic toxic pollutants in wastewater [7]. Semiconductor photocatalysis is a favourable technique with various advantages such as air and water purification, water disinfection, and hazardous waste remediation in the environment. Silver oxide assisted photocatalytic degradation is an ideal and excellent technique for degradation of organic pollutants and dye in wastewater [8]. The organics are entirely mineralized into the water, CO2 and corresponding mineral acids without creating any hazardous by-products. This technique has been used for the photo-mineralization of carcinogenic dyes such as methylene blue, direct acid dyes, azo dyes and reactive black [9]. Silver is an important and distinctive inorganic substance, because of its distinctive characteristics and novel applications in various fields of science and technology [10]. Silver oxide has the capacity to exhibit piezoelectric, pyroelectric, optoelectronic, catalysis and semiconducting properties [11]. Due to this, the silver oxide is a multifunctional compound which is used in the field of light emitting diodes, biosensors, spintronic solar cells, transistors and also acts as antioxidants and antibacterial agents [12-14]. Various methods
were discovered for synthesizing the Ag2O Nps namely hydrothermal, direct precipitation, sol-gel and solvothermal methods [15-19]. These methods need costliest starting material, sophisticated laboratory and these are lengthy procedures [20-25]. But the Gomutra assisted combustion method is premier
as it is an easier, less energy and time-consuming method
among all the methods. This technique will reduce the pollution or it is pollution free method and useful materials can be synthesized easily, eco-friendly and reasonable quantities [2630]. The present work reports the synthesis of Ag2O Nps using Gomutra as a reducing agent. The prepared Nps were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared analysis (FTIR), UV-visible spectrum (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the Ag2O Nps.
2. Experimental Materials and Methods Silver nitrate was procured from Merck and used as precursors (without further purification). Gomutra is collected from cow of Tumkur city. 2.1. Preparation of Ag2O nanoparticles Preparation of Ag2O Nps was employed by combustion method using Gomutra as a fuel and silver nitrate as precursor. 1g of Ag(NO3) was dissolved with 15 mL of Gomutra solution. The solution mixture is stirred to obtain a homogeneous solution. This mixture is transferred to a preheated muffle furnace maintained at 500 ºC and subjected for combustion, the smouldering type of the combustion reaction occurs and nano-crystalline Ag2O was formed within 5 minutes. A fine dark brown coloured final product was obtained. The obtained material was stored in an airtight container until supplementary use.
2.2. Characterization Phase and purity of the sample was measured by X-ray diffraction (XRD) recorded by Rigaku Smart Lab XRD. Stretching frequencies of the functional groups in the sample was measured by FTIR analysis using Bruker Alpha-p spectrometer. The morphology of the synthesized nanoparticles was observed using Scanning Electron Microscope (JEOL Model JSM-6390LV). EDAX (OXFORD XMX N) determines the elemental analysis. Shape and size of the Nanoparticles were determined by Transmission Electron Microscopy (TEM) (JEOL/JEM
2100). Photoluminescence studies were recorded using fluorescence
spectrophotometer (Agilent technology Cary Eclipse).
2.3. Photocatalytic degradation of dye The Photo-catalytic activity of the synthesized Ag2O Nps was assessed by considering the dye degradation of Methylene blue (MB) in an aqueous solution at ambient temperature utilizing a 300 W visible light as radiance source. 20 mg of catalyst (Ag2O Nps) was mixed with 100 mL of 5 ppm Methylene blue and the solution was unceasingly stimulated in the dark chamber for about 30 min to attain adsorption-desorption equilibrium. Further, the visible light was switched on. 2 mL of aliquot withdrawn for every 1 h interval. The samples were centrifuged using micro-centrifuge for 10 min in order to segregate Ag2O Nps. Spectrophotometric evaluations were carried out by utilizing a quartz cell having a path length of 0.3 cm. Absorbance was recorded at a fixed wavelength using the UV-vis spectrophotometer [31].
Photodegradation Mechanism Degradation mechanism of dye solution was stated in the following equations Ag2O + hν → Ag2O (h+vb + e-cb)
Ag2O (e-cb) + O2 → Ag2O + O2• H2O → H+ + OH• O2• + H → HO2 Ag2O (e-cb) + HO2 + H+ → H2O2 Ag2O (h+vb) + Dye → Degradation products HO2- + H+ → H2O2 HO2• + e- → HO-2 From the reaction, the hydroxyl radical (•OH), super-oxide radical (O2•) are foremost dependable
for
the
photodegradation
performance
of
the
MB
dye
molecules.
The degradation percentage of the dye has been determined by the following equation. ％ of degradation = (Ci - Cf)/ Ci × 100 ………… (i) where Ci and Cf are the initial and final concentration of the dye.
3. Results and discussion 3.1. XRD Study The XRD pattern of Ag2O Nps showed in Fig. 1. The diffraction peaks at 2θ = 38°, 44°, 64°, and 77° were indexed with the planes (111), (200), (220) and (311) for the resultant particles with cubic phase. The structure of the resultant data is according to the JCPDS card number. 43-0997 [32]. The average crystallite size was calculated using the Debye–Scherrer equation and it was found to be 11 nm. D = Kλ/ β cosθ -----------(ii) Where K value 0.94, λ is wavelength, β is the full width at half maxima and D is the crystallite size.
Intensity (a.u.)
(111)
(220)
(200)
40
(311)
60
80
2θ (degree)
Fig. 1. PXRD pattern of the Ag2O Nps.
3.2. FTIR study The FTIR spectrum of prepared Ag2O nanoparticles was recorded in between 350–4000 cm-1, represented in Fig. 2. A strong peaked appeared at 3396 cm−1 is due to the stretching vibration of -OH, the strong absorption peak at 2916 cm−1 could be assigned to –CH stretching vibrations of –CH3 and –CH2 functional groups, respectively, the peak at 1638 cm−1 is associated with N-H bond and is assigned to the amide-I bond of proteins present in the fuel (reducing agent). The peak at 1376 cm−1 is possibly the N-O symmetry stretching typical of the nitro compound. The band at 1033 cm−1 corresponds to C-F alkyl halide stretch vibration of proteins. The band at 520 cm−1 clearly confirms the formation of silver oxide (Ag–O) [33].
Transmittance (%)
3396
2916
520
1376
1638
1033
1000
2000
3000 -1
Wavenumber (cm )
Fig. 2. FTIR spectrum of Ag2O Nps.
3.3. UV-Visible Study The UV–vis spectrum of the synthesized materials was displayed in Fig. 3a. The spectrum shows a strong absorption peak at the wavelength region of 430 nm (confirming the formation of Ag2O nanoparticles) due to the electron transitions from the valence band to the conduction band. The energy gap (Eg) was found to be around ∼2.74 eV, which is in good agreement with the earlier reported values (Fig. 3b) [34].
430
(a)
(b)
Band gap energy = 2.74 eV
(α .hν )2(eV/cm)2
Absorbance (a.u)
0.9
0.6
0.3
(2.74 eV) 400
600
Wavelength (nm)
1.5
2.0
2.5
hν (eV)
Fig. 3. (a). UV-vis spectrum. (b). Band gap energy of Ag2O Nps.
3.0
3.5
3.4. Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDAX) studies: SEM images of Ag2O nanomaterials are shown in Fig. 4a and b. From the SEM images, it is clearly confirmed that the synthesized material contains a small grain like particles. Those particles are agglomerated to form spherical shaped Motichoor boondi like structures [35]. Fig. 4c shows the EDAX spectrum of Ag2O Nps, which describes the elemental analysis of the material, and obtained spectrum exhibits the strong silver and oxygen peaks.
Fig. 4. (a), (b). SEM images. (c). EDAX spectrum of synthesized Ag2O Nps.
3.5. Transmission Electron Microscopy (TEM) studies: Fig. 5 shows TEM image, HR-TEM image, SAED pattern, and Histogram of synthesized Ag2O nanomaterials. These particles are well dispersed, which acquired the size around 20
nm diameter and these particles are looks like the spherical shape in nature. HR-TEM images give clear information about the d-spacing value of Ag-O material and found to be 0.21 nm, which belongs to (111) plane. The planes at (111), (200), (220) and (311) planes having highest intensity in XRD and which are matched with bright circular fringes in SAED pattern and HR-TEM images [36].
Fig. 5. (a). TEM image. (b). HR-TEM images. (c). SAED pattern and (d). Histogram of Ag2O Nps.
4. Photocatalytic degradation Mechanism: Degradation mechanism of dye solution was stated in the following equations Ag2O + hν → Ag2O (h+vb + e-cb) OH−ads + h+vb → OH•ads (in basic medium) MB + OH•ads → dye degradation Under visible light irradiation, semiconductor absorbs photon energy with equal to or higher than the bandgap of the semiconductors, it generates electrons and holes on the surface of the photocatalyst. If the charge carriers do not recombine, they can migrate on the surface where free electrons from a reduction of oxygen and form peroxide and superoxide radicals, and the generated holes oxidize water and form OH·. This species is highly reactive and unstable. It ultimately acts on organic compounds and oxidizes carcinogenic dyes to CO2, water and inorganic acids. The photocatalytic action of the dye is enhanced by various factors of the photocatalyst, namely, particle size, phase composition, shape, crystallinity, size distribution, surface area, surface hydroxyl group density and band gap [37]. Synthesized Ag2O Nps were used as photocatalysts to investigate the degradation of methylene blue in UV sources [38]. A schematic representation of the degradation of MB using Ag2O superstructure is shown below.
Scheme. 1. Schematic mechanism for the dye degradation.
The absorbance of MB dye solution decreases with increase in time of irradiation in the presence of Ag2O photo-catalyst. The absorbance of MB has been intensely decreased and given 83.63% of degradation in 4 h (Fig. 6) [39].
100
(a)
00 min 1h 2h 3h 4h
(b)
664 nm 75
degradation (%)
Absorbance (a.u.)
0.2
290 nm
0.0
50
25
0 300
450
600
Wavelength (nm)
750
0
2
4
Time (hr)
Fig. 6. (a). Degradation of Methylene blue. (b). Percentage degradation.
5. Photoluminescence (PL) study The PL study is a useful method for determining the efficiency of charge carrier separation in semiconductors [40]. Fig. 7a shows the luminescence spectrum of the synthesized Ag2O nanoparticles recorded at room temperature. The emission spectrum of Ag2O Nps with the excitation wavelength of 436 nm and obtained the emission peaks at 566 and 596 nm, respectively. The corresponding CIE (Commission International De I’Eclairage) color coordinates (x and y) obtained was given in the inset of Fig. 7b. It is cleared from the CIE diagram that pure Ag2O Nps emits yellow light.
Fig. 7. (a). Photoluminescence Emission spectrum of Ag2O Nps: excited at 436 nm. (b). CIE diagram.
6. Antibacterial activity Synthesized Ag2O nanoparticles show significant antibacterial activity against pathogenic bacterial strains (Staphylococcus aureus, Escherichia coli, Pseudomonas desmolyticum, and Klebsiella aerogenes) by disc diffusion process [41]. The zone of inhibition of Ag2O nanoparticles (500µg/µL and 1000µg/µL) with respect to the positive control (Ciprofloxacin) is showing higher significant antibacterial activity on all the 4 bacterial strains and are depicted in Table 1.
Table. 1 Antibacterial activity of Ag2O Nps on pathogenic bacterial strains S. No
Treatment
Escherichia coli (mean ± SE) NA 8.10 ± 0.21
Pseudomonas desmolyticum (mean ± SE) NA 8.47 ± 0.30
Klebsiella aerogenes (mean ± SE) NA 6.50 ± 0.29
Staphylococcus aureus (mean ± SE) NA 5.50 ± 0.29
Control Ag2O Nps (500 µg/µL) 9.73 ± 0.33 10.50 ± 0.30 7.33 ± 0.17 8.50 ± 0.29 Ag2O Nps 3 (1000 µg/µL) Ciprofloxacin 18.36 ± 0.32 19.63 ± 0.17 18.33 ± 0.44 18.17 ± 0.44 4 (5 mg/µL) Values are the mean ± SE of inhibition zone in mm. NA Symbols represent no antibacterial activity was found in this work. 1 2
Table. 2 Comparison of antimicrobial activity with some other synthesized silver and silver oxide nanoparticles. Sl. No
1
2
3
4
Bacterial culture
Samples
Ref.
Ag2O Nps Ag2O Nps Ag2O Nps
Zone of Inhibition (mm) 3 4 5
E-coli Staphylococcus aureus Pseudomonas aeruginosa Staphylococcus aureus Klebsiella aerogenes E-coli E-coli Pseudomonas aeruginosa E-coli Staphylococcus aureus Klebsiella aerogenes Pseudomonas aeruginosa
Ag Nps Ag Nps Ag Nps Ag Nps Ag Nps
4 4.6 6.2 4.2 4.8
[43]
Ag2O Nps Ag2O Nps Ag2O Nps Ag2O Nps
9.7 8.5 7.3 10.5
Present work
[42]
[44]
From Table. 3, the combustion method has more advantages such as (shorter reaction time and enhanced reaction rate, improve the yields and high energy of efficiency) compared with some other preparation methods.
Table. 3 Comparison table for present work and previously reported works. Method
Silver precursor
Reducing agent
Chemical reduction
AgNO3
NaHB4
Physical synthesis Phytochemical reduction (microwave radiation) Phytochemical reduction
AgNO3
Hydrothermal method Combustion method
AgNO3
AgNO3
AgNO3 AgNO3
Stabilizing agent
Size (nm)
Reference
3-28
[45]
14-27
[46]
5-10
[47]
-
20-100
[48]
-
50
[49]
-
20
Present work
Surfactin (a lipopeptide biosurfactant) Electrical are Sodium discharge citrate Ethylene PVP glycol
Abutilon indicum leaf extract Gomutra and Honey Gomutra (Cow urine)
Conclusion In the present research, we have successfully accomplished the one-pot rapid synthesis of spherical shaped Ag2O Nps using Gomutra (cow urine) for the first time. The Ag2O Nps was confirmed by XRD study. The TEM analysis showed spherical shape with 20 nm particle size. It is showing good photocatalytic degradation of methylene blue, due to its sensitivity to absorb light with wide band gap energy. Hence synthesized material is measured as a potent aspirant for the degradation of dye MB. In addition, it also shows the PL spectrum and it will be used for the yellow emitting LED applications. The obtained results confirm that the Ag2O Nps show effective antibacterial activity against foodborne pathogens. This is a rapid and environmentally benign method which has added the advantage of reduced reaction time and better control over size and shape.
Compliance with ethical standards Conflict of interest: The authors declare that they have no conflict of interest.
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39. D. Suresh, P.C. Nethravathi, K. Lingaraju, H. Rajanaika, S.C. Sharma, H. Nagabhushana,
EGCG
assisted
green
synthesis
of
ZnO
nanopowders:
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Hydrothermal assisted biological synthesis of Silver nanoparticles by using honey and gomutra (Cow Urine) for qualitative determination of its antibacterial efficacy against Pseudomonas sp. isolated from contact lenses, Eurasian Journal of Biosciences. 13(1) (2019) 27-33.
S2468-2179(19)30212-6
DOI:
https://doi.org/10.1016/j.jsamd.2019.08.004
Reference:
JSAMD 243
To appear in:
Journal of Science: Advanced Materials and Devices
Received Date: 7 April 2019 Revised Date:
18 July 2019
Accepted Date: 10 August 2019
Please cite this article as: S. Vinay, Udayabhanu, G Nagarju, C. Chandrappa, N Chandrasekhar, Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies, Journal of Science: Advanced Materials and Devices, https://doi.org/10.1016/j.jsamd.2019.08.004. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies
Vinay S Pa, Udayabhanub, Nagarju Gb, Chandrappa C Pc, Chandrasekhar Na* a
Research and Development Center, Department of Chemistry, Shridevi Institute of Engineering and Technology, Tumakuru - 572106, India. b Energy Materials Research Laboratory, Department of Chemistry, Siddaganga Institute of Technology, Tumakuru - 572103, India. c Department of Biotechnology, Shridevi Institute of Engineering and Technology, Tumakuru – 572106, India.
*Corresponding authors: E mail: [email protected]
Acknowledgement Dr. Chandrasekhar and Vinay thank Dr. M R Hulinaykar, Managing Trustee, Sri Shridevi Charitable Trust, and Shridevi Institute of Engineering and Technology for encouragement and support for research work. Udayabhanu thanks to CSIR, New Delhi, for Senior Research Fellowship {09/1204(0001)/2018-EMR-1}. Dr. GN Thanks DST Nanomission (SR/NM/NS1262/2013) for financial support. The authors also thank Siddaganga Institute of Technology for providing the lab facilities.
Novel Gomutra (Cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced Photocatalytic, Photoluminescence and Antibacterial studies
Abstract This novel work successfully synthesizes silver oxide (Ag2O) nanoparticles (Nps) using cow urine. The presence of different biological components in cow's urine may acts as fuel for the synthesis of Ag2O Nps by combustion method at 500 oC. This is a rapid and environmentally benign procedure, which has added the advantage of shorter response times and better control over size and shape. The synthesized nanoparticles were characterized by XRD, FTIR, UVvis, SEM, EDAX and TEM studies and also these materials have tested for photoluminescence and photocatalytic and biological activities. It is showing good photocatalytic degradation of methylene blue, due to its sensitivity to absorb light with wide band gap energy. Furthermore, we have also examined the photoluminescence studies for the synthesized material and it has given yellow emission for excitation at 436 nm. In addition, it also exhibited good antibacterial activity for both gram-positive and gram-negative bacterial strains by disc diffusion method. In this study, combustion methods will produces nano sized Ag2O with less time, economical and for the large scale synthesis.
Keywords: Silver oxide nanoparticles, Gomutra, Combustion method, Photocatalytic, Photoluminescence, Antibacterial.
1. Introduction Cow urine has significant medicinal drink used for therapeutic purposes in Ayurveda. Nowadays cows are rare to see; in older days in everybody's house we could able to see the cows irrespective of the religion in India. Cows were adopted because of the multiple health benefits, starting with urine, dung, manure, milk, yogurt and ghee products. Human urine received its own medical benefits but was not as popular as cow urine; therefore, cow urine has always been superior and divine [1]. In Hinduism, cows are thought to be sacred and called “KAMADHENU” means the mother of all entities since thousands of years. In India, we use panchagavya (The urine, milk, ghee, curd and dung), obtained from cows are beneficial in different ways as a food supplement, medicine, etc. which holds its own importance in mythological and medicinal aspects. Cow’s urine has promoted as single or in combination with other drugs for medicine and spiritual uses traditionally. The cow is considered as a dwelling place for all God and Goddess. In concern with Gomutra, the spiritual, medicinal and traditional values are higher. Traditionally, Gomutra is being sprinkled in courtyards and home for its holy purposes; it confers the happiness, purity, prosperity, positive health, wealth, etc. [2]. The laboratory analysis of cow’s urine shows that it contains iron, copper, nitrogen, sulphur, manganese, carbolic acid, silicon, chlorine, magnesium, citric, calcium salts, enzymes, mineral salts, vitamins like A, B, C, D, E, creatinine, uric acid, hormones, gold acids, etc. and most interestingly – hip uric acid, which removes toxins through urine, aureum hydroxide, which acts as a germicide and thereby acts as immune-modulatory in increasing immunity if body and build resistance against all minor to major infectious agents.
The above-mentioned contents of Gomutra are found to be very useful in balancing our body constitutes. Thus, whenever we urinate there is a loss of such micro – nutrients, which are well compensated by the daily intake of Gomutra. Paper, dyeing, plastic, and textile industries use color for staining their products and hence consuming a large amount of water to clean, it can lead the formation of wastewater with dye contaminant and it can harmful to human and nature [3-6]. Currently, 100000 various types of dyes produced with an annual production rate of 7×105. Among them, textile industries consume dye about 36000 tons/year, 10 to 20 % of which release dye content waste-water into the environment can lead to polluting the marine life. Hence it is a very important task to reduce the releasing of dye and organic pollutant into the aquatic life. Presently, the photocatalytic degradation has much alarming technique for making free from organic and inorganic toxic pollutants in wastewater [7]. Semiconductor photocatalysis is a favourable technique with various advantages such as air and water purification, water disinfection, and hazardous waste remediation in the environment. Silver oxide assisted photocatalytic degradation is an ideal and excellent technique for degradation of organic pollutants and dye in wastewater [8]. The organics are entirely mineralized into the water, CO2 and corresponding mineral acids without creating any hazardous by-products. This technique has been used for the photo-mineralization of carcinogenic dyes such as methylene blue, direct acid dyes, azo dyes and reactive black [9]. Silver is an important and distinctive inorganic substance, because of its distinctive characteristics and novel applications in various fields of science and technology [10]. Silver oxide has the capacity to exhibit piezoelectric, pyroelectric, optoelectronic, catalysis and semiconducting properties [11]. Due to this, the silver oxide is a multifunctional compound which is used in the field of light emitting diodes, biosensors, spintronic solar cells, transistors and also acts as antioxidants and antibacterial agents [12-14]. Various methods
were discovered for synthesizing the Ag2O Nps namely hydrothermal, direct precipitation, sol-gel and solvothermal methods [15-19]. These methods need costliest starting material, sophisticated laboratory and these are lengthy procedures [20-25]. But the Gomutra assisted combustion method is premier
as it is an easier, less energy and time-consuming method
among all the methods. This technique will reduce the pollution or it is pollution free method and useful materials can be synthesized easily, eco-friendly and reasonable quantities [2630]. The present work reports the synthesis of Ag2O Nps using Gomutra as a reducing agent. The prepared Nps were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared analysis (FTIR), UV-visible spectrum (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the Ag2O Nps.
2. Experimental Materials and Methods Silver nitrate was procured from Merck and used as precursors (without further purification). Gomutra is collected from cow of Tumkur city. 2.1. Preparation of Ag2O nanoparticles Preparation of Ag2O Nps was employed by combustion method using Gomutra as a fuel and silver nitrate as precursor. 1g of Ag(NO3) was dissolved with 15 mL of Gomutra solution. The solution mixture is stirred to obtain a homogeneous solution. This mixture is transferred to a preheated muffle furnace maintained at 500 ºC and subjected for combustion, the smouldering type of the combustion reaction occurs and nano-crystalline Ag2O was formed within 5 minutes. A fine dark brown coloured final product was obtained. The obtained material was stored in an airtight container until supplementary use.
2.2. Characterization Phase and purity of the sample was measured by X-ray diffraction (XRD) recorded by Rigaku Smart Lab XRD. Stretching frequencies of the functional groups in the sample was measured by FTIR analysis using Bruker Alpha-p spectrometer. The morphology of the synthesized nanoparticles was observed using Scanning Electron Microscope (JEOL Model JSM-6390LV). EDAX (OXFORD XMX N) determines the elemental analysis. Shape and size of the Nanoparticles were determined by Transmission Electron Microscopy (TEM) (JEOL/JEM
2100). Photoluminescence studies were recorded using fluorescence
spectrophotometer (Agilent technology Cary Eclipse).
2.3. Photocatalytic degradation of dye The Photo-catalytic activity of the synthesized Ag2O Nps was assessed by considering the dye degradation of Methylene blue (MB) in an aqueous solution at ambient temperature utilizing a 300 W visible light as radiance source. 20 mg of catalyst (Ag2O Nps) was mixed with 100 mL of 5 ppm Methylene blue and the solution was unceasingly stimulated in the dark chamber for about 30 min to attain adsorption-desorption equilibrium. Further, the visible light was switched on. 2 mL of aliquot withdrawn for every 1 h interval. The samples were centrifuged using micro-centrifuge for 10 min in order to segregate Ag2O Nps. Spectrophotometric evaluations were carried out by utilizing a quartz cell having a path length of 0.3 cm. Absorbance was recorded at a fixed wavelength using the UV-vis spectrophotometer [31].
Photodegradation Mechanism Degradation mechanism of dye solution was stated in the following equations Ag2O + hν → Ag2O (h+vb + e-cb)
Ag2O (e-cb) + O2 → Ag2O + O2• H2O → H+ + OH• O2• + H → HO2 Ag2O (e-cb) + HO2 + H+ → H2O2 Ag2O (h+vb) + Dye → Degradation products HO2- + H+ → H2O2 HO2• + e- → HO-2 From the reaction, the hydroxyl radical (•OH), super-oxide radical (O2•) are foremost dependable
for
the
photodegradation
performance
of
the
MB
dye
molecules.
The degradation percentage of the dye has been determined by the following equation. ％ of degradation = (Ci - Cf)/ Ci × 100 ………… (i) where Ci and Cf are the initial and final concentration of the dye.
3. Results and discussion 3.1. XRD Study The XRD pattern of Ag2O Nps showed in Fig. 1. The diffraction peaks at 2θ = 38°, 44°, 64°, and 77° were indexed with the planes (111), (200), (220) and (311) for the resultant particles with cubic phase. The structure of the resultant data is according to the JCPDS card number. 43-0997 [32]. The average crystallite size was calculated using the Debye–Scherrer equation and it was found to be 11 nm. D = Kλ/ β cosθ -----------(ii) Where K value 0.94, λ is wavelength, β is the full width at half maxima and D is the crystallite size.
Intensity (a.u.)
(111)
(220)
(200)
40
(311)
60
80
2θ (degree)
Fig. 1. PXRD pattern of the Ag2O Nps.
3.2. FTIR study The FTIR spectrum of prepared Ag2O nanoparticles was recorded in between 350–4000 cm-1, represented in Fig. 2. A strong peaked appeared at 3396 cm−1 is due to the stretching vibration of -OH, the strong absorption peak at 2916 cm−1 could be assigned to –CH stretching vibrations of –CH3 and –CH2 functional groups, respectively, the peak at 1638 cm−1 is associated with N-H bond and is assigned to the amide-I bond of proteins present in the fuel (reducing agent). The peak at 1376 cm−1 is possibly the N-O symmetry stretching typical of the nitro compound. The band at 1033 cm−1 corresponds to C-F alkyl halide stretch vibration of proteins. The band at 520 cm−1 clearly confirms the formation of silver oxide (Ag–O) [33].
Transmittance (%)
3396
2916
520
1376
1638
1033
1000
2000
3000 -1
Wavenumber (cm )
Fig. 2. FTIR spectrum of Ag2O Nps.
3.3. UV-Visible Study The UV–vis spectrum of the synthesized materials was displayed in Fig. 3a. The spectrum shows a strong absorption peak at the wavelength region of 430 nm (confirming the formation of Ag2O nanoparticles) due to the electron transitions from the valence band to the conduction band. The energy gap (Eg) was found to be around ∼2.74 eV, which is in good agreement with the earlier reported values (Fig. 3b) [34].
430
(a)
(b)
Band gap energy = 2.74 eV
(α .hν )2(eV/cm)2
Absorbance (a.u)
0.9
0.6
0.3
(2.74 eV) 400
600
Wavelength (nm)
1.5
2.0
2.5
hν (eV)
Fig. 3. (a). UV-vis spectrum. (b). Band gap energy of Ag2O Nps.
3.0
3.5
3.4. Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray (EDAX) studies: SEM images of Ag2O nanomaterials are shown in Fig. 4a and b. From the SEM images, it is clearly confirmed that the synthesized material contains a small grain like particles. Those particles are agglomerated to form spherical shaped Motichoor boondi like structures [35]. Fig. 4c shows the EDAX spectrum of Ag2O Nps, which describes the elemental analysis of the material, and obtained spectrum exhibits the strong silver and oxygen peaks.
Fig. 4. (a), (b). SEM images. (c). EDAX spectrum of synthesized Ag2O Nps.
3.5. Transmission Electron Microscopy (TEM) studies: Fig. 5 shows TEM image, HR-TEM image, SAED pattern, and Histogram of synthesized Ag2O nanomaterials. These particles are well dispersed, which acquired the size around 20
nm diameter and these particles are looks like the spherical shape in nature. HR-TEM images give clear information about the d-spacing value of Ag-O material and found to be 0.21 nm, which belongs to (111) plane. The planes at (111), (200), (220) and (311) planes having highest intensity in XRD and which are matched with bright circular fringes in SAED pattern and HR-TEM images [36].
Fig. 5. (a). TEM image. (b). HR-TEM images. (c). SAED pattern and (d). Histogram of Ag2O Nps.
4. Photocatalytic degradation Mechanism: Degradation mechanism of dye solution was stated in the following equations Ag2O + hν → Ag2O (h+vb + e-cb) OH−ads + h+vb → OH•ads (in basic medium) MB + OH•ads → dye degradation Under visible light irradiation, semiconductor absorbs photon energy with equal to or higher than the bandgap of the semiconductors, it generates electrons and holes on the surface of the photocatalyst. If the charge carriers do not recombine, they can migrate on the surface where free electrons from a reduction of oxygen and form peroxide and superoxide radicals, and the generated holes oxidize water and form OH·. This species is highly reactive and unstable. It ultimately acts on organic compounds and oxidizes carcinogenic dyes to CO2, water and inorganic acids. The photocatalytic action of the dye is enhanced by various factors of the photocatalyst, namely, particle size, phase composition, shape, crystallinity, size distribution, surface area, surface hydroxyl group density and band gap [37]. Synthesized Ag2O Nps were used as photocatalysts to investigate the degradation of methylene blue in UV sources [38]. A schematic representation of the degradation of MB using Ag2O superstructure is shown below.
Scheme. 1. Schematic mechanism for the dye degradation.
The absorbance of MB dye solution decreases with increase in time of irradiation in the presence of Ag2O photo-catalyst. The absorbance of MB has been intensely decreased and given 83.63% of degradation in 4 h (Fig. 6) [39].
100
(a)
00 min 1h 2h 3h 4h
(b)
664 nm 75
degradation (%)
Absorbance (a.u.)
0.2
290 nm
0.0
50
25
0 300
450
600
Wavelength (nm)
750
0
2
4
Time (hr)
Fig. 6. (a). Degradation of Methylene blue. (b). Percentage degradation.
5. Photoluminescence (PL) study The PL study is a useful method for determining the efficiency of charge carrier separation in semiconductors [40]. Fig. 7a shows the luminescence spectrum of the synthesized Ag2O nanoparticles recorded at room temperature. The emission spectrum of Ag2O Nps with the excitation wavelength of 436 nm and obtained the emission peaks at 566 and 596 nm, respectively. The corresponding CIE (Commission International De I’Eclairage) color coordinates (x and y) obtained was given in the inset of Fig. 7b. It is cleared from the CIE diagram that pure Ag2O Nps emits yellow light.
Fig. 7. (a). Photoluminescence Emission spectrum of Ag2O Nps: excited at 436 nm. (b). CIE diagram.
6. Antibacterial activity Synthesized Ag2O nanoparticles show significant antibacterial activity against pathogenic bacterial strains (Staphylococcus aureus, Escherichia coli, Pseudomonas desmolyticum, and Klebsiella aerogenes) by disc diffusion process [41]. The zone of inhibition of Ag2O nanoparticles (500µg/µL and 1000µg/µL) with respect to the positive control (Ciprofloxacin) is showing higher significant antibacterial activity on all the 4 bacterial strains and are depicted in Table 1.
Table. 1 Antibacterial activity of Ag2O Nps on pathogenic bacterial strains S. No
Treatment
Escherichia coli (mean ± SE) NA 8.10 ± 0.21
Pseudomonas desmolyticum (mean ± SE) NA 8.47 ± 0.30
Klebsiella aerogenes (mean ± SE) NA 6.50 ± 0.29
Staphylococcus aureus (mean ± SE) NA 5.50 ± 0.29
Control Ag2O Nps (500 µg/µL) 9.73 ± 0.33 10.50 ± 0.30 7.33 ± 0.17 8.50 ± 0.29 Ag2O Nps 3 (1000 µg/µL) Ciprofloxacin 18.36 ± 0.32 19.63 ± 0.17 18.33 ± 0.44 18.17 ± 0.44 4 (5 mg/µL) Values are the mean ± SE of inhibition zone in mm. NA Symbols represent no antibacterial activity was found in this work. 1 2
Table. 2 Comparison of antimicrobial activity with some other synthesized silver and silver oxide nanoparticles. Sl. No
1
2
3
4
Bacterial culture
Samples
Ref.
Ag2O Nps Ag2O Nps Ag2O Nps
Zone of Inhibition (mm) 3 4 5
E-coli Staphylococcus aureus Pseudomonas aeruginosa Staphylococcus aureus Klebsiella aerogenes E-coli E-coli Pseudomonas aeruginosa E-coli Staphylococcus aureus Klebsiella aerogenes Pseudomonas aeruginosa
Ag Nps Ag Nps Ag Nps Ag Nps Ag Nps
4 4.6 6.2 4.2 4.8
[43]
Ag2O Nps Ag2O Nps Ag2O Nps Ag2O Nps
9.7 8.5 7.3 10.5
Present work
[42]
[44]
From Table. 3, the combustion method has more advantages such as (shorter reaction time and enhanced reaction rate, improve the yields and high energy of efficiency) compared with some other preparation methods.
Table. 3 Comparison table for present work and previously reported works. Method
Silver precursor
Reducing agent
Chemical reduction
AgNO3
NaHB4
Physical synthesis Phytochemical reduction (microwave radiation) Phytochemical reduction
AgNO3
Hydrothermal method Combustion method
AgNO3
AgNO3
AgNO3 AgNO3
Stabilizing agent
Size (nm)
Reference
3-28
[45]
14-27
[46]
5-10
[47]
-
20-100
[48]
-
50
[49]
-
20
Present work
Surfactin (a lipopeptide biosurfactant) Electrical are Sodium discharge citrate Ethylene PVP glycol
Abutilon indicum leaf extract Gomutra and Honey Gomutra (Cow urine)
Conclusion In the present research, we have successfully accomplished the one-pot rapid synthesis of spherical shaped Ag2O Nps using Gomutra (cow urine) for the first time. The Ag2O Nps was confirmed by XRD study. The TEM analysis showed spherical shape with 20 nm particle size. It is showing good photocatalytic degradation of methylene blue, due to its sensitivity to absorb light with wide band gap energy. Hence synthesized material is measured as a potent aspirant for the degradation of dye MB. In addition, it also shows the PL spectrum and it will be used for the yellow emitting LED applications. The obtained results confirm that the Ag2O Nps show effective antibacterial activity against foodborne pathogens. This is a rapid and environmentally benign method which has added the advantage of reduced reaction time and better control over size and shape.
Compliance with ethical standards Conflict of interest: The authors declare that they have no conflict of interest.
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