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Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Novel Gomutra (cow urine) mediated synthesis of silver oxide nanoparticles and their enhanced photocatalytic, photoluminescence and antibacterial studies S.P. Vinay a, Udayabhanu b, G. Nagaraju b, C.P. Chandrappa c, N. Chandrasekhar a, * a b c Research and Development Center, Department of Chemistry, Shridevi Institute of Engineering and Technology, Tumakuru, 572106, India Energy Materials Research Laboratory, Department of Chemistry, Siddaganga Institute of Technology, Tumakuru, 572103, India Department of Biotechnology, Shridevi Institute of Engineering and Technology, Tumakuru, 572106, India a r t i c l e i n f o a b s t r a c t Article history: Received 7 April 2019 Received in revised form 18 July 2019 Accepted 10 August 2019 Available online 16 August 2019 This work successfully synthesizes silver oxide (Ag2O) nanoparticles (Nps) using cow urine. The presence of different biological components in cow's urine may act as fuel for the synthesis of Ag2O Nps by a combustion method at 500
C. This is a rapid and environmentally benign procedure, which has the added advantage of shorter response times and better control over size and shape. The synthesized nanoparticles were characterized by means of XRD, FTIR, UV-vis, SEM, EDAX and TEM and have been tested for photoluminescence and for photocatalytic and biological activities. They show good photocatalytic degradation of methylene blue, due to their sensitivity to absorb light with a wide band gap energy. Furthermore, we have examined the photoluminescence properties of the synthesized material and found that it has a yellow emission for excitation at 436 nm. In addition, the synthesized material exhibits a good antibacterial activity for both gram-positive and gram-negative bacterial strains by the disc diffusion method. It is shown that these combustion methods produce nano sized Ag2O within less time suited for a large scale synthesis in an economic way. © 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). 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 be 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” which means the mother of all entities since thousands of years. In India, we use panchagavya (urine, milk, ghee, curd and dung), which is obtained from cows an is beneficial in different ways as a food supplement, medicine, etc. holding its own importance in mythological and medicinal aspects. Cow's urine has * Corresponding author. E-mail address: chandruharshu@gmail.com (N. Chandrasekhar). Peer review under responsibility of Vietnam National University, Hanoi. 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 e 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 e nutrients, which are well compensated by the daily intake of Gomutra. https://doi.org/10.1016/j.jsamd.2019.08.004 2468-2179/© 2019 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). S.P. Vinay et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 Paper, dyeing, plastic, and textile industries use different colours for staining their products and hence consume a large amount of water for cleaning. It leads to wastewater with dye contaminant and which can be harmful to human and nature [3e6]. Currently, hundred thousand various types of dyes are produced with an annual production rate of 7  105 per year. Among them, textile industries consume dye for about 36000 tons/year, 10e20% of which is released as dye content waste-water into the environment which can lead to a pollution of marine life. Hence, it is a very important task to reduce the release of dye and other organic pollutants into the aquatic life. Presently, photocatalytic degradation is an alarming technique for making wastewater free from organic and inorganic toxic pollutants [7]. Semiconductor photo-catalysis is a favourable technique with various advantages such as air and water purification, water disinfection and the remediation of hazardous waste 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 organic pollutants are entirely mineralized into the water, into CO2 and into corresponding mineral acids without creating any hazardous byproducts. This technique has been used for the photomineralization 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 these capacities, silver oxide is a multifunctional compound which is used in the field of light emitting diodes, biosensors, spintronic solar cells and transistors and which also acts as antioxidant and antibacterial agent [12e14]. Various methods were discovered for synthesizing the Ag2O Nps viz hydrothermal, direct precipitation, solegel and solvothermal methods [15e19]. These methods need costliest starting materials, sophisticated laboratories and these require lengthy procedures [20e25]. In contrast, the Gomutra assisted combustion method is favourable as it is an easier, less energy- and time-consuming method among all the other methods. This technique will reduce the pollution or is even a pollution free method. Useful materials can be synthesized easily, eco-friendly and in reasonable quantities [26e30]. 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 Silver nitrate was procured from Merck and used as precursor (without further purification). Gomutra is collected from cows of the Tumkur city. The preparation of Ag2O Nps was employed by the combustion method using Gomutra as a fuel and silver nitrate as precursor. One gram 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
C and subjected for combustion resulting in a smouldering type of the combustion reaction in which nano-crystalline Ag2O was formed within 5 min. A fine dark brown-coloured final product was obtained. The obtained 393 material was stored in an airtight container until supplementary use. 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 were measured by a FTIR analysis using a 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 a fluorescence spectrophotometer (Agilent technology Cary Eclipse). 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. Twenty 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 the adsorptionedesorption equilibrium. Further, the visible light was switched on. Two mL of aliquot were withdrawn for every 1 h interval. The samples were centrifuged using a micro-centrifuge for 10 min in order to segregate the Ag2O Nps. Spectrophotometric evaluations were carried out by utilizing a quartz cell having a path length of 0.3 cm. The absorbance was recorded at a fixed wavelength using the UV-vis spectrophotometer [31]. Degradation mechanism of the dye solution was stated in the following equations Ag2 O þ hv/Ag2 O hvb þ þ ecb 
Ag2 Oðecb  Þ þ O2 /Ag2 O þ O$2 H2 O / Hþ þ OH$ O$2 þ H/HO2 Ag2 Oðecb  Þ þ HO2 þ Hþ /H2 O2
Ag2 O hvb þ þ Dye/Degradation products HO2  / Hþ þ H2 O2 HO$2 / e þ HO2  From the reaction, the hydroxyl radical (OH) and the superoxide 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. Percentage of degradation ¼ (CiCf)/Ci  100 (1) 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 is shown in Fig. 1. The diffraction peaks at 2q ¼ 38
, 44
, 64
, and 77
were indexed with the planes 394 S.P. Vinay et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 calculated using the DebyeeScherrer equation and was found to be 11 nm. D ¼ Kl/b cosq (2) where K value 0.94, l is wavelength, b is the full width at half maxima and D is the crystallite size. 3.2. FTIR study Fig. 1. PXRD pattern of the Ag2O Nps. The FTIR spectrum of the prepared Ag2O nanoparticles, recorded between 350 and 4000 cm1, is represented in Fig. 2. The strong peaked that appeared at 3396 cm1 is due to the stretching vibration of eOH, the strong absorption peak at 2916 cm1 could be assigned to eCH stretching vibrations of eCH3 and eCH2 functional groups, the peak at 1638 cm1 is associated with a NeH bond and is assigned to the amide-I bond of the proteins present in the fuel (reducing agent). The peak at 1376 cm1 is possibly due to the NeO symmetry stretching that is typical for the nitro compound. The band at 1033 cm1 corresponds to the CeF alkyl halide stretch vibration of proteins. The band at 520 cm1 clearly confirms the formation of silver oxide (AgeO) [33]. 3.3. UV-visible study The UVevis spectrum of the synthesized materials is 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 electronic 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]. 3.4. Scanning electron microscopy (SEM) and energy-dispersive Xray (EDAX) studies Fig. 2. FTIR spectrum of Ag2O Nps. (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 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 small grain-like particles. Those particles are agglomerated to form spherical-shaped Motichoorboondi-like structures [35]. Fig. 4c shows the EDAX spectrum of Ag2O Nps, which describes the elemental analysis of the material. Theobtained spectrum exhibits strong silver and oxygen peaks. 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 Fig. 3. (a). UV-vis spectrum. (b). Band gap energy of Ag2O Nps. S.P. Vinay et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 395 Fig. 4. (a), (b). SEM images. (c). EDAX spectrum of synthesized Ag2O Nps. well dispersed, with an acquired size around 20 nm diameter, and are looking like the spherical shape in nature. HR-TEM images give clear information about the d-spacing value of the AgeO material which is found to be 0.21 nm, and belong to the (111) plane. The (111), (200), (220) and (311) planes have the highest intensity in XRD and are matched with the bright circular fringes in the SAED pattern and the HR-TEM images [36]. 4. Photocatalytic degradation action of the dye is enhanced by various factors of the photocatalyst, viz 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]. The absorbance of the MB dye solution decreases with increase in time of the irradiation in the presence of the Ag2O photocatalyst. The absorbance of MB is decreased to 83.63% of degradation in 4 h (Fig. 6) [39]. Mechanism: Degradation mechanism of dye solution was stated in the following equations 5. Photoluminescence (PL) study Ag2 O þ hv/Ag2 O hvb þ þ ecb  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 reveals emission peaks at 566 and 596 nm. The corresponding CIE (Commission International De I'Eclairage) colour coordinates (x and y) are given in the inset of Fig. 7b. It is clear from the CIE diagram that pure Ag2O Nps emits yellow light.
OHads  þ hvb þ /OHads $ ðin basic mediumÞ MB þ OHads $ /dye degradation Under visible light irradiation, a semiconductor absorbs photon energy with equal to or higher than the bandgap of the semiconductors and 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, which is shown in Scheme 1. The photocatalytic 6. Antibacterial activity Synthesized Ag2O nanoparticles show significant antibacterial activities against pathogenic bacterial strains (Staphylococcus aureus, Escherichia coli, Pseudomonas desmolyticum, and Klebsiella aerogenes) by the disc diffusion process [41]. The zone of inhibition 396 S.P. Vinay et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 Fig. 5. (a). TEM image. (b). HR-TEM images. (c). SAED pattern and (d). Histogram of Ag2O Nps. Scheme 1. Schematic mechanism for the dye degradation. of Ag2O nanoparticles (500 mg/mL and 1000 mg/mL) 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. From Tables 2 and 3 clearly shows that, 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. S.P. Vinay et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 397 Fig. 6. (a). Degradation of Methylene blue. (b). Percentage degradation. Fig. 7. (a). Photoluminescence Emission spectrum of Ag2O Nps: excited at 436 nm. (b). CIE diagram. Table 1 Antibacterial activity of Ag2O Nps on pathogenic bacterial strains. S. No Treatment Escherichia coli (mean ± SE) Pseudomonas desmolyticum (mean ± SE) Klebsiella aerogenes (mean ± SE) Staphylococcus aureus (mean ± SE) 1 2 3 4 Control Ag2O Nps (500 mg/mL) Ag2O Nps (1000 mg/mL) Ciprofloxacin (5 mg/mL) NA 8.10 ± 0.21 9.73 ± 0.33 18.36 ± 0.32 NA 8.47 ± 0.30 10.50 ± 0.30 19.63 ± 0.17 NA 6.50 ± 0.29 7.33 ± 0.17 18.33 ± 0.44 NA 5.50 ± 0.29 8.50 ± 0.29 18.17 ± 0.44 Values are the mean ± SE of inhibition zone in mm. NA Symbols represent no antibacterial activity was found in this work. Table 2 Comparison of antimicrobial activity with some other synthesized silver and silver oxide nanoparticles. Sl. No Bacterial culture Samples Zone of Inhibition (mm) Ref. 1 E-coli Staphylococcus aureus Pseudomonas aeruginosa Staphylococcus aureus Klebsiella aerogenes E-coli E-coli Pseudomonas aeruginosa E-coli Staphylococcus aureus Klebsiella aerogenes Pseudomonas aeruginosa Ag2O Nps Ag2O Nps Ag2O Nps Ag Nps Ag Nps Ag Nps Ag Nps Ag Nps Ag2O Nps Ag2O Nps Ag2O Nps Ag2O Nps 3 4 5 4 4.6 6.2 4.2 4.8 9.7 8.5 7.3 10.5 [42] 2 3 4 [43] [41] Present work 398 S.P. Vinay et al. / Journal of Science: Advanced Materials and Devices 4 (2019) 392e399 Table 3 The comparative results of the present work and previously reported works. Method Silver precursor Reducing agent Stabilizing agent Size (nm) Reference Chemical reduction Physical synthesis Phytochemical reduction (microwave radiation) Phytochemical reduction Hydrothermal method Combustion method AgNO3 AgNO3 AgNO3 AgNO3 AgNO3 AgNO3 NaHB4 Electrical are discharge Ethylene glycol Abutilon indicum leaf extract Gomutra and Honey Gomutra (Cow urine) Surfactin (a lipopeptide biosurfactant) Sodium citrate PVP e e e 3e28 14e27 5e10 20e100 50 20 [44] [45] [46] [47] [48] Present work 7. Conclusion In the present research, we have, for the first time, successfully accomplished the one-pot rapid synthesis of spherical shaped Ag2O Nps using Gomutra (cow urine). The Ag2O Nps were confirmed by a XRD study. The TEM analysis showed spherical shaped particles with 20 nm particle size. They show a good photocatalytic degradation of methylene blue, due to their sensitivity to absorb light with a wide band gap energy. Hence, the synthesized material is measured as a potent aspirant for the degradation of dye MB. In addition, they can be used for the yellow emitting LED applications as shown by the PL spectrum. The obtained results confirm that the produced Ag2O Nps show an effective antibacterial activity against foodborne pathogens. This is a rapid and environmentally benign method which has the added advantage of reduced reaction time and better control over size and shape. Conflict of interest The authors declare that they have no conflict of interest. Acknowledgements Udayabhanu thanks to CSIR, New Delhi, for Senior Research Fellowship {09/1204(0001)/2018-EMR-1}. 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 the research work. Dr. GN thanks DST Nanomission (SR/NM/NS-1262/2013) for the financial support. 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