Green-based synthesis of mixed-phase silver nanoparticles as an effective photocatalyst and investigation of their antibacterial properties

Journal Pre-proof Green-based synthesis of mixed-phase silver nanoparticles as an effective photocatalyst and investigation of their antibacterial properties

Niloufar Khandannasab, Zahra Sabouri, Samaneh Ghazal, Majid Darroudi PII:

S0022-2860(19)31520-0

DOI:

https://doi.org/10.1016/j.molstruc.2019.127411

Reference:

MOLSTR 127411

To appear in:

Journal of Molecular Structure

Received Date:

21 July 2019

Accepted Date:

11 November 2019

Please cite this article as: Niloufar Khandannasab, Zahra Sabouri, Samaneh Ghazal, Majid Darroudi, Green-based synthesis of mixed-phase silver nanoparticles as an effective photocatalyst and investigation of their antibacterial properties, Journal of Molecular Structure (2019), https://doi. org/10.1016/j.molstruc.2019.127411

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Journal Pre-proof

Green-based synthesis of mixed-phase silver nanoparticles as an effective photocatalyst and investigation of their antibacterial properties

Niloufar Khandannasaba, Zahra Sabouria, Samaneh Ghazalb, Majid Darroudic,d,* aNeurogenic

Inflammation Research Center, Mashhad University of Medical Sciences, Mashhad, Iran

bNanotechnology

Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical

Sciences, Mashhad, Iran cNuclear

Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran

dDepartment

of Medical Biotechnology & Nanotechnology, Faculty of Medicine, Mashhad University of

Medical Sciences, Mashhad, Iran

Abstract Ag/Ag2O nanoparticles (Ag/Ag2O-NPs) have attracted the attention of many due to exhibiting excellent photocatalytic activity within the UV region. In this work, Ag/Ag2O-NPs were prepared with the employment of sol-gel procedure and the usage of gelatin as a polymerization agent at various temperatures. The obtained Ag/Ag2O-NPs were identified by the means of FT-IR, XRD, UV-Vis, and FESEM/EDX/PSA techniques. XRD results have confirmed the synthesis of Ag/Ag2O-NPs with the face-centered cubic phase (FCC), while the formation of agglomerated spherical nanoparticles has been approved through the FESEM images. The photocatalytic test of Ag/Ag2O-NPs has been assessed for methylene blue (MB) degradation. The degradation percentages of MB dye by Ag/Ag2O-NPs in the optimum conditions was about 93% (pH = 9.0, irradiation time = 360 min, solution temperature = 55 °C, CMB=1.0 mg.L-1, and photocatalyst concentration was 10 mg.L-1). Also, the antimicrobial activity of Ag/Ag2O-NPs was checked in regards to gram-positive bacteria Staphylococcus Aureus and Bacillus subtilis, as well as gram-negative bacteria Escherichia Coli and Pseudomonas aeruginosa. The obtained results showed that Escherichia Coli was more susceptible relative to Staphylococcus aureus, which can be stated in other words that Staphylococcus aureus has displayed resistance towards Ag/Ag2O-NPs. Keywords: Ag/Ag2O nanoparticles, Gelatin, Photocatalytic degradation; Antibacterial

*Corresponding author: Email: [email protected], [email protected] (M. Darroudi). Tel.: +98 5138002286 Fax: +98 513 8002

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Journal Pre-proof 1. Introduction Nanoparticles have been developed through discovering a significant new progress by applying the rules of ‘‘Green Chemistry’’ to different nanotechnology fields [1]. Recently, there has been a lot of interest in the production of metal and metal oxide nanoparticles due to their large surface areas [2]. Green protocols have invested their attention in the synthesis of nanoparticles since they have proved to be eco-friendly, fast, and cheap [3]. Recently many dangerous organic contaminants have gained access into the surrounding environment through different industries, in which organic dyes are included as one of these pollutants [4, 5]. Organic dyes, which are extensively used in textile industries and cosmetic devices, are known to be harmful and cause serious environmental pollutions [6]. The byproducts of these organic dyes can be deadly for human health due to hydrolysis and oxidation in the sewerage [7, 8]. Photocatalysis is one of the methods that is often used to remove the organic colors of watery environments [9], in which the combination of photochemistry and catalyst are applied to target the degradation of organic pigments [10]. In addition, this phenomenon involves the utilization of light and catalyst, which fundamentally increase the speed of thermodynamical transformations. Considering how researchers have exerted catalysts to remove the hazardous chemicals of different resources, therefore catalysts can be indicated as useful green knowledge for water usage and the removal of toxic chemicals from the environment [11, 12]. Metal nanoparticles or metal oxides, such as silver, titanium [13, 14], copper, gold, iron oxide, and silver oxide, have been used in the fields of medicine, pharmacy, and biology throughout the recent years [15]. On the other hand, mineral nanoparticles are utilized in a larger range of applications due to their sustainability and safety when compared to the organic nanoparticles. Ag/Ag2O-NPs are p-type semiconductors with a band gap energy observed in the limit of 3.3 to 4.0 eV [16, 17], which are extensively utilized in electronic, optical, drug delivery [18], antimicrobial, and catalytic [19, 20] due to their unique physical and chemical properties. Since

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Journal Pre-proof microbial infections are increasing, it is necessary to develop the robust antibacterial materials [21]. Ag/Ag2O-NPs are one of the broadest nanoparticles with antibacterial properties and are considered toxic to disease agents [22] which is due to the effect of surface enhancement that results in increasing the reactivity of nanocrystalline materials [23]. When nanoparticles are in the nanometer range, their microbial properties increase by more than 99%, to the extent that they can be used to improve the designated damage and infections [23, 24]. Examinations have shown that the antibacterial results of Ag/Ag2O-NPs were related to shape, size, and functional groups in nanoparticles [25]. Recently, the usage of biopolymer in the preparation of nanomaterials has received much attention due to its low cost and environmental compatibility, as well as the lack of pollutants and toxic substances [26]. Although many researchers have synthesized Ag/Ag2O-NPs, yet there are no reports throughout scientific resources on their utilization as a photocatalyst or on examining their effective parameters on the removal of organic dyes from the aquatic environment. Therefore, the aim of this study is to develop an eco-friendly and economical procedure for the biosynthesis of Ag/Ag2O-NPs through the application of gelatin as the stabilizing agent to prevent the aggregation of nanoparticles, as well as investigating their photocatalytic activity on eliminating the MB dye of aqueous environments and achieve a higher degradation efficiency (93 %). Furthermore, we have assessed the antibacterial activity of Ag/Ag2O-NP versus gram-positive bacteria Staphylococcus Aureus and Bacillus subtilis, as well as gram-negative bacteria Escherichia Coli and Pseudomonas aeruginosa. As the last step, the structural properties of the obtained nanoparticles, such as phases, crystalline size, morphology, and specific surface area, have been examined by the means of modern spectroscopic techniques.

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Journal Pre-proof 2. Experimental section 2. 1. Substances and Apparatus The chemical materials and solvents employed in the experiment have been used without purification. Silver nitrate (AgNO3, 99.99%) has been procured from Germany Merck and the gelatin polymer has been purchased from Sigma Aldrich Company. UV-Vis spectrophotometer has been exerted to measure the adsorption, UVA-11W lamp as the light source throughout the photocatalyst test, and magnetic stirrer has been used to stir the solutions. 2. 2. Synthesis of Ag/Ag2O nanoparticles For the biosynthesis of Ag/Ag2O-NPs in this research, AgNO3 were applied as the precursor of silver, while gelatin was used as the stabilizing agent. To begin, 5.0 g of gelatin powder was solved in 50 mL of H2O, while the solution of silver nitrate (0.5 M) was slowly added to the mixture under constant stirring. Afterward, the obtained solution was stirred at 80 °C for 6 h and then, the achieved gel was dried at a temperature of 100 °C for 12 h. In the following the gel was calcinated at the temperatures of 400, 500, and 600 °C for 2 h, which resulted in obtaining Ag/Ag2O-NPs. 2. 3. Characterization of Ag/Ag2O nanoparticles The characterization of Ag/Ag2O-NPs was carried out with different analyzing methods to confirm the synthesis of nanoparticles. The powder was measured by FT-IR spectra (FT-IR 8400-SHIMADZU made in Germany) to identify the bonds and functional groups that existed in the range of 4000-400 cm-1. XRD analysis (D8-Advance Bruker made in Germany) was carried out by the usage of Cu Kα radiation (k = 1.5418 Å) in the Bragg range of 80> 2θ> 10 to determine the phases and detect the crystalline structure of nanoparticles. The morphology of Ag/Ag2O-NPs had to be ascertained by FESEM and EDX analyzes (TESCAN BRNO-Mira3

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Journal Pre-proof LMU made in Germany), while their optical properties was investigated through UV-Vis spectroscopy (UV-Vis 2550-SHIMADZU Made in the USA).

3. Result and Discussion 3. 1. XRD Patterns The XRD pattern of Ag/Ag2O-NPs in 2θ = 20- 80° at the temperatures of 400, 500, and 600 °C is presented in Fig. 1. The detected peaks of Ag2O-NPs at 2θ values 30.00°, 38.48°, and 64.58° are related to the crystal planes (111), (200), and (311) that accurately match with the reference card [17, 19, 27]. Also, the observed peaks at 2θ values 44.28° and 77.24° are indicative of AgNPs, which are related to the crystal planes (220) and (222). By comparing the XRD pattern of

Ag/Ag2O-NPs with the pattern of standard sample diffraction (JCPDS No. 41-1104), it can be concluded that Ag/Ag2O-NPs has been synthesized in the cubic geometry [19, 27-29]. The size of nanoparticles was calculated via the employment of Debye-Scherrer equation (Eq. 1) [30]. 𝒟=

kλ βcos θ

(1)

Where D stands as the particle size (nm), k = 0.9 would be a crystallized form factor, λ is the wavelength of radiation (nm), β would be the maximum peak width at half of the height, and θ represents an angle of diffraction (degree). The nanoparticles size at 400, 500, and 600 °C were about 22, 34, ad 36 nm, respectively. Therefore, the calcinated sample at 400 °C was observed to be in arrangements with the results that were obtained from the FESEM (42.6 nm) images [31]. Table 1 exhibits the average size of Ag/Ag2O-NPs at the temperatures of 400, 500, and 600 °C. 3. 2. FT-IR Analysis The FT-IR spectrum of Ag/Ag2O-NPs in the limit of 4000-400 cm-1 at various temperatures 400, 500, and 600 °C are demonstrated in Fig. 2. The detected stretch in 3419 cm-1 is apparently

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Journal Pre-proof assigned to the O-H bond of H2O molecules and the band that had appeared at 1430 cm-1 was associated with the absorbed water bending vibration. Also, the band that had been observed at 1618 cm-1 was correlated to the CO2 stretching vibration from the atmosphere, and the bands detected in the range of 400-620 cm-1 were assigned to the stretching vibration of Ag and AgO-Ag [32, 33]. 3. 3. FESEM /EDX/PSA Images The shape and distribution of synthesized Ag/Ag2O-NPs at the temperature of 400 °C has been investigated through the FESEM/EDX/PSA images, which is presented in Fig. 3 (a, b, c). As it can be perceived, the nanoparticles are grown relatively uniformly and have an almost spherical morphology, while their dimensions are at nano-scale [34]. The achieved results that were obtained from the FESEM images were in correspondence to the XRD pattern. The obtained results of EDX analysis have confirmed the presence of Ag and O elements within the Ag/Ag2O-NPs [35]. 3. 4. UV-Visible Spectrophotometry The UV-Vis chart and gap band of Ag/Ag2O-NPs is illustrated in Fig. 4 (a. b), which displays a band of about 354 nm in the visible limit that indicates the formation of Ag/Ag2O-NPs. The bandgap energy (Eg) was estimated based on the maximum absorbance band of plots (αhν)2 beside photon energy (hν) and had been obtained by following Eq. 2 [36, 37]. (𝛼ℎ𝜈)𝑛 = 𝐴(ℎ𝜈 ― 𝐸𝑔)

(2)

Where, 𝐸𝑔 is the gap band energy, hv (eV) would be the photon energy, α stands for the absorbance coefficient, A represents a constant, and n = 2 in direct transition whereas n = 1/2 in regards to indirect transition. The gap band energy of nanoparticles was observed to be

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Journal Pre-proof enhanced from 5.74 to 5.93 eV with an increased temperature of 400 to 600 °C [38]. The energy band gap of Ag/Ag2O-NPs is displayed in Table 2. < Tab. 2>

4. Applications of Ag/Ag2O nanoparticles 4. 1. Determine the antimicrobial effect 4. 1. 1. Preparation of Microbial Suspension Initially, 4 mL of physiological serum was put in four test tubes and had them sterilized. Thereafter, the colonies of bacteria that had been isolated from clinical specimens were inoculated in separate tubes to have an opacity similar to 0.5 McFarland. 4. 1. 2. Determine the antimicrobial effect of Ag/Ag2O-NPs The antibacterial activity of Ag/Ag2O-NPs has been evaluated through an agar diffusion method against gram-positive bacteria Staphylococcus Aureus and Bacillus subtilis as well as gram-negative bacteria Escherichia Coli and Pseudomonas aeruginosa. First, the stock solution has been prepared from Ag/Ag2O-NPs and diluted in 9 tubes that each of them contained 4 mL of distilled water. We had about 4 mL of each dilution added to each of the plates that contained the agar culture medium, resulting in plates that were prepared with various concentrations (including concentrations of 10, 5, 2.5, 1.25, 0.625, 0.312, 0.156, 0.078, and 0.039 mM). Then, we used a sterile swab to place the bacterial suspension of each bacteria in four different locations of the plates and had them incubated at 37 °C for 24 h. According to the results, none of the bacteria showed any sign of growth at the concentrations of 5 and 10 mM, which can be stated in other words that the bacteria were sensitive to nanoparticles. Furthermore, Staphylococcus Aureus bacteria were observed to grow at a concentration of 2.5 mM and also, Escherichia Coli has displayed a bit of growth at concentrations that were less

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Journal Pre-proof than 1.25 mM, which indicates that nanoparticles did not have much effect on bacterial elimination and had allowed the bacteria to grow. 4. 1. 3. Antibacterial evaluation of Ag/Ag2O nanoparticles The antimicrobial evaluation of Ag/Ag2O-NPs has been performed through the agar diffusion method against gram-positive bacteria Staphylococcus Aureus and Bacillus subtilis and gramnegative bacteria Escherichia Coli and Pseudomonas aeruginosa. The findings of this experiment has suggested that an increase in the concentration of nanoparticles can cause a reduction in the population of bacteria [39]. On the other hand, a decrease in the size of nanoparticles can induce alterations in their structural features, since a size reduction provides them with an easy access to living organisms and consequently increase their destructive power. Reducing the size and increasing the surface-to-volume ratio as a factor can enhance the reactivity of nanoparticle, which is listed as the essential factor in increasing their toxicity [40-42]. Results have shown that Escherichia Coli was more susceptible relative to Staphylococcus aureus. In other words, Staphylococcus aureus was detected to display resistance towards Ag/Ag2O-NPs. The obtained results of Ag/Ag2O-NPs antibacterial activity are shown in Fig. 5.

4. 2. Photocatalytic Test The photocatalytic efficiency of Ag/Ag2O-NPs has been determined by the means of MB dye at ~ 663 nm [43]. First, a photocatalytic test was performed in the absence of UVA light, while the degradation percentage was calculated through the application of Eq. 3, which was about 9%. The results are presented in Fig. 6a. Then, the photocatalysis experiment has been carried out under UVA light irradiation. In this regard, 10 mg (~ 10-3 M) gelatin-stabilized Ag/Ag2ONPs were immersed in 50 mL solution that contained 3 mg (10-5 M and pH=9) of MB. As the solution was being stirred, it was exposed to the UVA light that was irradiated with 11 W

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Journal Pre-proof power. In the following, to determine the amount of dye degradation, 2 mL of the solution was removed every 60 min, while the UV-Vis spectrum was taken and repeated for up to 360 min. In all of the cases, the volume of solution was kept constant. The percentage of degradation was calculated by the usage of Eq. 3 [44].

Degradation(%) =

A0 ― At A0

× 100

(3)

Whereas 𝐴0 is the absorption of solution ago radiation and 𝐴𝑡stands for the absorption at time t. The percentage of MB degradation was about 93%. Figure. 6 (b) illustrates the MB degradation efficiency that had been obtained through the utilization of Ag/Ag2O-NPs calcination at 400 °C under UVA light. To determine the kinetics of photocatalytic test overall this manner, the time has been discussed as a variable agent in the ranges of 0, 60, 120, 180, 240, 300, 360 min. The Photodegradation of color has established a pseudo-first-order kinetic, which is demonstrated in Eq. 4.

()

𝐿𝑛

𝐶𝑡

𝐶0

= 𝐾𝑜𝑏𝑠𝑡

(4)

Where, 𝐶0would be the concentration of solution ago light,𝐶𝑡 is the concentration of solution at time t, andKobs is the apparent rate constant. According to Fig. 7, the photodegradation of MB on Ag/Ag2O-NPs has displayed a pseudo-first-order kinetic. The reaction rate constant (k) has been measured for the dye degradation reaction, following a pseudo-first-order, which was observed to be 0.0015 min-1 [45, 46]. 4. 2. 1. Photocatalytic mechanism Subsequent to placing Ag/Ag2O-NPs under UV light, the existing 𝐴𝑔 + in Ag/Ag2O-NPs could be decomposed to metallic Ag. Consequently, a high number of oxygen atoms would be created through the decomposition of Ag2O. In addition, it has been proved that the oxygen atoms can

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Journal Pre-proof also provide the photocatalysis of Ag2O by producing H2O2 through the following reactions (Eq. 5 and 6) [47]. 𝐴𝑔2𝑂 + 2ℎ + + 2𝑒 ― →𝑂 + 2𝐴𝑔

(5)

𝑂 + 𝐻2𝑂→𝐻2𝑂2

(6)

The existing metallic Ag on the surface of Ag2O can function as an electron transfer agent and in result with light irradiation, the electrons become excited from the valence band (VB) towards the conduction band (CB) that creates holes (h+) on the area of Ag2O. Usually, a réaction happens among 𝑒 ― and ℎ + on the semiconductor surfaces. Electrons (e ― ) can reduce O2 to °𝑂2― or H2O2, and ℎ + reaction by H2O or OH ― and manufacture°OH. In this among, h + , H2O2, °O2― ,

°OH, and O2 have displayed a significant manner of functioning during

photocatalytic reactions. The mechanism of MB photocatalytic degradation via Ag2O-NPs is presented in Fig. 8 [48]. The appropriate reactions have been expressed as the following (Eq. 7-14) [48]. ℎ𝑣(𝑈𝑉) + 𝐴𝑔2𝑂→𝐴𝑔 + + ℎ + + 𝑒 ―

(7)

𝐴𝑔 + + 𝑒 ― →𝐴𝑔

(8)

𝑂2 + 𝑒 ― →𝑂°2 ―

(9)

𝑂°2 ― + 𝐻 + →𝐻𝑂°2

(10)

𝐻𝑂°2 + 𝐻2𝑂→𝑂𝐻° + 𝐻2𝑂2

(11)

𝐷𝑦𝑒 + 𝑂𝐻°→𝐷𝑒𝑔𝑟𝑎𝑑𝑎𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

(12)

𝐷𝑦𝑒 + ℎ + →𝑂𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

(13)

𝐷𝑦𝑒 + 𝑒 ― →𝑅𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

(14)



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4.2.2. Different parameters on MB photodegradation using UV-A in Ag/Ag2O system To determine the optimum state of MB photodegradation by Ag/Ag2O-NPs, experiments have been performed at different concentrations of photocatalyst (Ag/Ag2O-NPs: 10, 5, and 2.5 mg L-1), different concentrations of dye (MB: 1, 2, and 4 mg L-1), various temperatures (25, 35, 45, 55 °C), and different values of pH (4, 7, 9). 4.2.2.1. pH The pH is one of the chief factors that can cause effects on photocatalytic degradation; therefore, the optimization of pH factor has been studies in this research. For this purpose, the pH in ranges of 4, 7, and 9 via MB solution (10-5 M) and the photocatalyst value (10 mg) has been used, while the suspension was put to UV-A light at a time interval of 0, 60, 120, 180, 240, 300, and 360 min. The adsorption rate was read by utilizing a spectrophotometer and thereafter, the dye degradation performance was calculated by following Eq. 3. The outcomes of MB degradation at various pH have been illustrated in Fig. 9 (a). The percentages of MB degradation in the pH values of 9, 7, and 4 were about 93, 84, and 53 %, respectively. [49]. The increasing rate of MB degradation that was caused by heightening the pH is apparently due to a rise in the value of OH ― that results in the further formation of hydroxyl radicals. As a consequence, the reactions among OH° and MB molecules follow more rapidly [50, 51]. In conclusion, the MB dye (C16H18N3S+) decomposes to CO2 gas, nitrogen, and sulfur [52]. 4.2.2.2. Photocatalyst amount To achieve the optimal value of photocatalyst, several investigations have been done in numerous concentrations of this material. The standard solution has been composed at optimal pH = 9 and the MB value that equaled to 1 mg at different levels of photocatalyst (10, 5, and 2.5 mg L-1), which was put under UVA light at the time intervals of 0, 60, 120, 180, 240, 300,

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Journal Pre-proof and 360 min The adsorption rate was read by the usage of a spectrophotometer and thereafter, the dye degradation efficiency was determined through Eq. 3. Based on the results that were obtained, it was found that by increasing the concentrations of photocatalyst (2.5, 5, and, 10 mg L-1), the degradation efficiency of MB would face an increase as well (79, 88, and 93%) respectively. The results of MB degradation at several concentrations of photocatalyst have been displayed in Fig. 9 (b), which includes a raise in the amount of photocatalyst. The observed increase in reaction speed was associated with the induced increase in the active positions on photocatalyst surface and the increase in photons [53, 54]. 4.2.2.3. Dye amount The results of influences that were caused by the different concentrations of MB (1, 2, and 4 mg L-1) at pH= 9 and photocatalyst concentration that had been equivalent to 10 mg L-1 is represented in Fig. 9 (c) The findings has shown that by increasing the MB concentration (1, 2, and, 4 mg L-1) the degradation efficiency of MB (93, 88, and 78%) faced a decrease respectively. The reduction in dye decomposition at high concentrations could be caused by the reducing photocatalyst active locations, which is induced for adsorption and manufacture of hydroxyl radicals (°𝑂𝐻) so that by rising the dye concentration, dye molecules would be attracted on the level of nanoparticles and inhibit the making of hydroxyl radicals [55]. Furthermore, throughout the high concentrations of dyes, a significant value of ultraviolet radiation could be absorbed on dye molecules and reduce the amount of radiation that is exhibited by photocatalyst nanoparticles and in the end, the efficiency of photocatalytic degradation reaction faces a reduction that is caused by the occurrence of a decrease in the concentration of °𝑂𝐻 , O2―° radicals [56, 57]. 4.2.2.4. Temperature effect The ultimate solution has been achieved at the optimal conditions of pH= 9, photocatalyst concentration that equaled to 10 mg L-1, and CMB= 1.0 mg L-1 at various temperatures (25, 35, 12

Journal Pre-proof 45, and 55 °C). The solution was put below UVA light at the time intervals of 0, 60, 120, 180, 240, 300, and 360 min. The absorbance has been ascertained with the application of a spectrophotometer and in the following, the yield was calculated by Eq. 3. Based on the findings that were obtained, by increasing the reaction temperature (25, 35, 45, and 55 °C) the degradation efficiency of MB (85, 94, 98, and 99%) increases as well respectively. In accordance with Fig. 9 (d), which displays the outcomes of MB degradation at several temperatures, the degradation percent of MB was enhanced as the temperature was increased [58, 59]. Increasing the temperature results in faster molecular movements and consequently heightens the effective interactions between methylene blue molecules and silver oxide adsorbents, which can increase the possibility of color molecules adsorption on the adsorbent. Enhancing the temperature causes a rise in the hole volume and porosity of absorbent level and consequently, the active positions on photocatalyst level become easily available to dye molecules, which increases the possibility of their adsorption on photocatalyst [60, 61]. < Fig. 9 >

5. Conclusion In this work, Ag/Ag2O-NPs have been synthesized through the usage of gelatin as a stabilizer agent at different temperatures. The synthesized nanoparticles have been identified by the application of FT-IR, UV-Vis, XRD, FESEM / EDX/PSA techniques. The bandgap energy of the samples has been measured through the UV-Visible spectroscopy, while the optical research has displayed that the samples had contained a bandgap of about 5.74 to 5.93 eV. The photocatalytic results have indicated that Ag/Ag2O-NPs had been approved as a photocatalyst in the degradation of MB dye under UVA light irradiation. The percentage of MB degradation by Ag/Ag2O-NPs in optimum conditions has been about 93% (pH = 9, t = 360 min, and T = 55 °C, the photocatalyst concentration = 10 mg.L-1, and the initial concentration of MB = 1.0 mg.L-1). Also, the antibacterial evaluation of Ag/Ag2O-NPs has been examined versus gram-

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Journal Pre-proof positive bacteria Staphylococcus Aureus and Bacillus subtilis, as well as Gram-negative bacteria Escherichia Coli and Pseudomonas aeruginosa. The results have suggested that Escherichia Coli had been more susceptible relative to Staphylococcus aureus, which can be stated in other words that Staphylococcus aureus has shown resistance towards Ag/Ag2O-NPs.

Conflict of interest The authors declare that they have no conflict of interest.

Acknowledgment The research reported in this publication has been supported by the Elite Researcher Grant Committee under award number [No. 986096] from the National Institutes for Medical Research Development (NIMAD), Tehran, Iran.

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Figure captions Fig. 1. The XRD patterns of Ag/Ag2O-NPs prepared using gelatin at different temperatures. Fig. 2. The FTIR spectra of Ag/Ag2O-NPs prepared using gelatin at different temperatures. Fig. 3. The FESEM image (a), Particle size (b) and EDX analysis (c) of Ag/Ag2O-NPs prepared using gelatin at 400 °C. Fig. 4. The UV-vis spectra of Ag/Ag2O-NPs (a) and the band gap of Ag/Ag2O-NPs prepared using gelatin (b). Fig. 5. Antibacterial evaluation of different concentration of Ag/Ag2O-NPs. Fig. 6. Decomposition of MB, over time, using Ag/Ag2O-NPs in the absence of UV-A light irradiation (a) under UV-A light irradiation (b). Fig. 7. The curve of determination the pseudo-first-order kinetic photocatalytic reaction of Ag/Ag2ONPs. Fig. 8. Schematic plan of the Ag/Ag2O-NPs photocatalytic mechanism. Fig. 9. Influence of pH on MB removal with UV/Ag/Ag2O-NPs system (a), The effect of photocatalyst concentration on MB removal with UV/ Ag2O system (b), The effect of the amount of dye on MB removal with UV/Ag/Ag2O-NPs system (c), and effect of solution temperature on MB removal with UV/ Ag/Ag2O-NPs - system (d). Tab. 1. Comparison of particles size of as-synthesized Ag/Ag2O-NPs. Tab. 2. The UV-Vis spectra of Ag/Ag2O-NPs.

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Graphical Abstract

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Fig. 1. M. Darroudi et al., 2019.

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Fig. 2. M. Darroudi et al., 2019.

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Fig. 3. M. Darroudi et al., 2019.

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Fig. 4. M. Darroudi et al., 2019.

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Fig. 5. M. Darroudi et al., 2019.

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Fig. 6. M. Darroudi et al., 2019.

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Fig. 7. M. Darroudi et al., 2019.

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Fig. 8. M. Darroudi et al., 2019.

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Fig. 9. M. Darroudi et al., 2019.

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Journal Pre-proof Table. 1. M. Darroudi et al., 2019. Temp. (°C)

2θ (deg.)

FWHM (rad.)

Diameter (nm)

Identification

400

38.17

0.371

22.68

fcc (Ag/Ag2O)

500

38.11

0.248

33.97

fcc (Ag/Ag2O)

600

38.13

0.234

36

fcc (Ag/Ag2O)

Table. 2. M. Darroudi et al., 2019. Parameters

Temperature / °C 400

500

600

Wavelength /nm

317

349

355

Absorbance

0.041

0.127

0.233

Energy gap / eV

5.93

5.87

5.74

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Journal Pre-proof CRediT author statement N. Khandannasab: Methodology. Z. Sabouri: Conceptualization, Formal analysis, Writing- Reviewing and Editing. S. Ghazal: Investigation, Investigation. M. Darroudi: Supervision.

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Highlights 1. Green-based synthesis of Ag2O nanoparticles. 2. Ag2O nanoparticles as a great photocatalyst for degradation of azo dyes. 3. Investigating effective factors in degradation of dyes. 4. Investigation of antibacterial properties of Ag2O nanoparticles.