Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5, 3309-3320 2025 Publisher: Learning Gate DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate © 2025 by the author; licensee Learning Gate History: Received: 21 March 2025; Revised: 16 May 2025; Accepted: 19 May 2025; Published: 31 May 2025 * Correspondence: ameerib7771@gmail.com Chemical bath deposition-produced Ag2O nanoparticles synthesis and characterization for NO2 gas sensing applications Ameer I. Khudadad1* 1The General Directorate of Education in the Province of Baghdad/Rusafa-2 Ministry of Education, Baghdad, Iraq; ameerib7771@gmail.com (A.I.K.). Abstract: Deposition of thin films of silver oxide Ag2O of a nanoscopic nature, which are highly sensitive to NO2 gas, on quartz glass bases using the chemical bath deposition technique. Then conduct tests for pH values at the time of deposition at 75oC. In this work, AgNO3 was used. Through XRD examinations, the results showed that all the thin films are polycrystalline. Peaks of silver oxides such as Ag2O and AgO also appeared, with an average particle size ranging from 31.9 to 46 nm, depending on the sedimentation parameters. Also, through the use of (FESEM) electron microscopy technology, images of the samples used and the arrangement and distribution of the particles are shown. Using an atomic force microscope (AFM), the samples showed that the thin films were homogeneous with different surface roughness, and the particle size ranged from 55.57 to 87.1 nm. It was noted that Ag2O films have a high sensitivity of approximately 71.58 to NO2 gas at an operating temperature of 75oC. The study showed that it is possible to manufacture high-quality and efficient gas sensors from silver oxide nanoparticles. Keywords: Ag2O, Chemical bath, XRD, SEM, AFM, Gas sensors. 1. Introduction Ag2O is a semiconductor that has an energy gap ranging from 1.3 to 3.6 eV [1]. Then silver oxides were used as gas sensors, as it turned out to be a good sensor for gases, especially NO2 gas. It is also characterized by its non-toxic properties and is often low in cost and other advantages of Ag2O [2, 3]. Silver oxides are used in photoelectronic applications [4, 5]. The oxygen vacancies present in silver oxide Ag2O have a very important role in the conduction mechanism [6]. Therefore, the choice for Ag2O thin films is a good conductive oxide group that is transparent to P-type thin films. Nitrogen dioxide (NO2) is a toxic gas present in the atmosphere as well as in laboratories. Due to the danger of this gas, many researchers have sought to find means to protect against this gas [7-9]. Through several techniques, thin films of Ag2O can be created [10]. Among these techniques are: technique [11] is considered one of the simplest methods for obtaining thin films of silver oxide. The chemical bath deposition technique properties can also be controlled by changing the deposition time, working temperature, and solution pH. In this work, silver oxide was deposited on quartz glass bases at a different pH as well as a different dipping time. Then verify its structural properties and gas sensing. 2. Experimental Work Quartz glass bases were used before precipitating Ag2O. Then make scratches on the bases using 25% chromic acid with water for 24 hours. After that, it is cleaned with a detergent solution using ultrasonic waves. Dissolve solid silver nitrate weighing 0.887 g in 5 ml of distilled water. Then add triethanolamine (C6H15NO3), which is considered a complexing agent. Then add drop by drop and with continuous stirring in order to obtain a colorless solution so that the volume of the solution becomes approximately 41 ml with 0.02 M. The pH also increases after adding nitric acid drip. After that, the https://orcid.org/0000-0002-1629-1936 tel:1.3 tel:3.6 3310 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate samples are placed in a beaker, vertically with a bath, at a constant temperature of 75oC. The immersion times in the bath are different, (30, 40 and 50) min, and the pH values are also different, (10, 11 and 12). Then, the coated samples are taken out of the bath and using distilled water, the samples are rinsed and dried with hot air, then the thickness of the thin films is measured by optical interference. Using XRD technology, the grain size and crystalline structure of the samples were determined (Philips PW 1050 Å Target: Cu-Kα, Current: 20 mA, Voltage: 40 KV, Wavelength: 1.541874 Å). Topography and roughness of the surface of the deposited films were determined by atomic force microscope AFM (SPM-AA3000 Angstrom Advanced Inc). Gas sensing calculations were made for the samples by measuring the change in electrical resistance at about 450 ppm of NO2 gas, with different working temperatures and also different pH values of the solution. Table 1. The sample number with preparation conditions of the prepared nano-silver oxide thin films at 75°C Sample pH value Deposition Time (t min) Thickness (nm) a 10 40 299.8 b 11 40 250.6 c 12 40 214.7 3. Result and Discussion Through XRD examination of the samples used in this work, we show that the thin films are polycrystalline based on the appearance of many peaks for (Ag2O, Ag3O4 and AgO). Silver oxide is a cubic structure at level (200), which is compatible with card No. (43-0997). While we note that AgO is a single structure with level (023) according to card No. (43-1038). We believe that the pH of 11 and at the peak has increased significantly for all oxides sample (b) and also the increase in deposition time for sample (c). From Fig (1), it is possible that this is due to the nucleation of Ag2O, which has an effect on the crystallization process. The average particle size was calculated using the relationship [7]. D= Kλ 𝛽𝑐𝑜𝑠𝜃 (1) Where k is a constant with a value of (0.9), which is usually called the (shape factor). λ is the wavelength of the x-rays. β is the diffraction peak. 2θ represents the diffraction angle in degrees. The grain size ranges from (33.21 to 38.11) nm. as shown in Table (2). tel:200 tel:023 tel:0.9 tel:33.21 tel:38.11 3311 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate Figure 1. The XRD patterns of the deposited nano-silver oxide thin films. Figure 2 is showed the results of FESEM examinations of the surface morphology of the samples used showed that the Ag2O particles formed a nanostructure arranged in a geometric manner and in the form of layers on top of each other. Upon further magnification, it was observed that the grain size ranged from (31.9 to 41) nm, and this corresponds to the XRD examination of the samples that were examined. Note that there are interstitial distances between the nanoparticles and these distances are very large when conducting a gas sensing test on samples[12]. tel:31.9 3312 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate 3313 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate 3314 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate Figure 2. FESEM images of Ag2O structures deposited on quartz glass. When conducting an AFM examination of Ag2O nano-silver oxide samples and the particle size distribution. It was noted that the surface roughness and particle size that made up the surface of the thin films were primarily dependent on the parameters that were adopted in preparing the samples, which are pH and time t. Through Table 2 which displays the RMS surface roughness as well as the average particle size, it ranged from (57.1 to 87.54) nm. Depending on the deposition parameters, we notice a change in roughness for the thin films of pure Ag2O nanoparticles between smooth and rough, which is related to the movement and growth of the thin films. Such thin films can be used in many fields, such as gas sensing, for example sample (c), as well as in the field of electronic applications, for example smooth sample (a) [13]. 3315 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate Figure 3. AFM images of silver oxide thin films at different preparation parameters. 3316 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate Table 2. XRD and AFM measurements of the prepared silver oxide films. XRD AFM Sample Crystallite size (nm) Ra (nm) RMS (nm) Average grain size (nm) a 38.11 0.91 0.94 57.1 b 36.43 4.07 4.71 73.23 c 33.21 3.17 3.55 87.54 3.1. Gas Sensor Characterization The sensitivity of samples prepared from Ag2O nanoparticles to 450 ppm of NO2 gas was measured according to the equation... 𝑆 = 𝑅𝑎 − 𝑅𝑔 𝑅𝑎 𝑥100% (2) Where Ra is the air resistance and Rg is the gas resistance, respectively. From Figure (4), we notice the change in sensitivity over time from samples that have a high response due to the change in the pH solution. The sensitivity, response time and recovery time with temperature were recorded and determined for the operating sensor and for all prepared samples. As shown in Table 3 From Figure (4) and Table 3 we can notice that the thin films of Ag2O did not respond to 450 ppm of NO2 gas when the temperature was 25oC, that is, at room temperature. But on the other hand, we see that the sensitivity has increased well at 50oC. The explanation for this is that the sensors operate at low temperatures and have good sensitivity values. The change in good sensitivity is due to the change in the pH of the solution, which is related to the surface morphology, as well as the particle size and also the thickness of the thin films. Given that the sensitivity is a function of the particle size. Therefore, a decrease in particle size will lead to an increase in surface sensitivity. This increase is important because it leads to an increase in adsorption. For this reason, the sensors prepared for this work showed very good performance. According to the source [14] the good sensitivity obtained for the Ag2O gas sensor was due to the grain size, which was rather small. We note that sample (b) had a low response time (0.93) sec and also had a low recovery time (0.97) sec. This may be due to its good compositional properties. tel:450 tel:450 3317 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate Figure 4. Sensitivity of the optimal Ag2O thin film with different operating time. 3.2. Values at 450 ppm NO2 gas. Table 3. Values of sensitivity, response and recovery time with respect to temperature at 450 ppm NO2 gas. Sample Temp (°C) Sensitivity Response Time Recovery Time (sec) (sec) 25 0.00 0.00 0.00 50 7.11 1.70 0.92 a 75 72.20 11.01 1.09 100 8.11 1.83 1.57 25 0.00 0.00 0.00 50 66.70 0.93 0.97 b 75 10.30 11.89 2.09 100 1.80 1.85 0.88 25 0.00 0.00 0.00 50 1200 9.00 1.50 c 75 10.75 11.89 4.44 100 0.45 2.55 10.01 From Figure 5 we notice the variation of operating temperatures with the sensitivity value. It can be noted that sample (b) works at pH, which is equal to 11, and at a somewhat low temperature, which is equal to 50oC with high sensitivity. While it can be observed that sample (c), which was prepared at a 3318 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate pH of 12, works with a low sensitivity value at a temperature of 50oC. For this reason, we believe that the best bathing condition for obtaining the best gas sensor is when the pH is 11, the bathing temperature is 75oC, and the immersion time is 40 min. The mechanism of sensing the action of silver oxide Ag2O includes trapping oxygen in the form of O- or O-2 on the roof. This leads to an increase in resistance relative to the oxygen surface. When NO2 gas interacts with the surface of Ag2O or with the absorbed oxygen electrons that are released from the oxide surface, we notice that there is an increase as follows [9]. (3) (4) Figure 5. Changing of the sensitivity with temperature at different pH values at 450 ppm NO2 gas. The reaction requires activation energy in order to continue, and therefore thermal energy must be provided. For this reason, we note that silver oxide nanoparticles do not have a response at room temperature. If the temperature is not increased. We note that the maximum degree of response to the gas is achieved when good and actual thermal energy is given to the reaction, and we also note despite this. There is a decrease in responsiveness when there is an increase in operating temperature. There is absorption and adsorption of oxygen on the surface of the sensor [15, 16]. 3319 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate 4. Conclusions In this work, thin films of Ag2O nanoparticles were prepared using (Chemical bath deposition). XRD examination showed that the thin films had different compositions of (Ag2O, Ag3O4 and Ag2O). The average grain size as well as the average crystallite size measured by XRD and AFM are within the nanometer range. The Ag2O nanomembranes had good sensing properties for NO2 gas at 50°C, which is somewhat close to room temperature. Noting that there is a high and good gas sensing value and a low response time and recovery time. From these results, we can see the possibility of using Ag2O nano thin films in many applications, including gas sensors as well as electro-optical applications. Transparency: The author confirms that the manuscript is an honest, accurate, and transparent account of the study; that no vital features of the study have been omitted; and that any discrepancies from the study as planned have been explained. This study followed all ethical practices during writing. Acknowledgement: Thanks, and appreciation to the Department of Physics at the College of Education at (Mustansiriya University), Baghdad, Iraq for supporting this work. Copyright: © 2025 by the author. This open-access article is distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). References [1] A. Nwanya, P. Ugwuoke, B. Ezekoye, R. Osuji, and F. Ezema, "Structural and optical properties of chemical bath deposited silver oxide thin films: role of deposition time," Advances in Materials Science and Engineering, vol. 2013, no. 1, p. 450820, 2013. https://doi.org/10.1155/2013/450820 [2] G. Bhanjana, G. R. Chaudhary, N. Dilbaghi, M. Chauhan, K.-H. Kim, and S. Kumar, "Novel electrochemical sensor for mononitrotoluenes using silver oxide quantum dots," Electrochimica Acta, vol. 293, pp. 283-289, 2019. https://doi.org/10.1016/j.electacta.2018.10.042 [3] M. M. Rahman, S. B. Khan, A. Jamal, M. Faisal, and A. M. Asiri, "Highly sensitive methanol chemical sensor based on undoped silver oxide nanoparticles prepared by a solution method," Microchimica Acta, vol. 178, pp. 99-106, 2012. https://doi.org/10.1007/s00604-012-0817-2 [4] K. Z. Yahia, "Study optoelectronic properties of ag2o heterojunction prepered by thermal oxidation technique," Engineering and Technology Journal, vol. 26, no. 5, pp. 570-578, 2008. https://doi.org/10.30684/etj.29.5.10 [5] Y. Ida et al., "Direct electrodeposition of 1.46 eV bandgap silver (I) oxide semiconductor films by electrogenerated acid," Chemistry of Materials, vol. 20, no. 4, pp. 1254-1256, 2008. https://doi.org/10.1021/cm702865r [6] U. Brink and A. Subrahmanyam, "Electrical and optical properties of silver oxide (ag~ 2o) thin films prepared by reactive electron beam evaporation," in Proceedings-Spie The International Society For Optical Engineering. 2002. International Society for Optical Engineering, 1999. [7] M. Navaneethan et al., "Sensitivity enhancement of ammonia gas sensor based on Ag/ZnO flower and nanoellipsoids at low temperature," Sensors and Actuators B: Chemical, vol. 255, pp. 672-683, 2018. https://doi.org/10.1016/j.snb.2017.08.015 [8] M. Wagh, G. Jain, D. Patil, S. Patil, and L. Patil, "Modified zinc oxide thick film resistors as NH3 gas sensor," Sensors and Actuators B: Chemical, vol. 115, no. 1, pp. 128-133, 2006. https://doi.org/10.1016/j.snb.2005.08.030 [9] E. Vinoth and N. Gopalakrishnan, "Effect of temperature on NH3 sensing by ZnO: Mg thin film grown by radio frequency magnetron sputtering technique," presented at the AIP Conference Proceedings. 2018. AIP Publishing, 2018. [10] N. L. Yong, A. Ahmad, and A. W. Mohammad, "Synthesis and characterization of silver oxide nanoparticles by a novel method," Int. J. Sci. Eng. Res, vol. 4, no. 4, 2013. https://doi.org/10.1166/jap.2013.1058 [11] H. R. Abed, A. I. Khudadad, and F. M. Oleiwi, "Influence of the distance between nozzle and substrate on the structural, photoluminescence, and detector characteristics of p-NiO/n-Si hetero-junction deposited by spray pyrolysis method," Optical and Quantum Electronics, vol. 54, no. 8, p. 482, 2022. https://doi.org/10.1007/s11082-022- 03833-2 https://creativecommons.org/licenses/by/4.0/ https://doi.org/10.1155/2013/450820 https://doi.org/10.1016/j.electacta.2018.10.042 https://doi.org/10.1007/s00604-012-0817-2 https://doi.org/10.30684/etj.29.5.10 https://doi.org/10.1021/cm702865r https://doi.org/10.1016/j.snb.2017.08.015 https://doi.org/10.1016/j.snb.2005.08.030 https://doi.org/10.1166/jap.2013.1058 https://doi.org/10.1007/s11082-022-03833-2 https://doi.org/10.1007/s11082-022-03833-2 3320 Edelweiss Applied Science and Technology ISSN: 2576-8484 Vol. 9, No. 5: 3309-3320, 2025 DOI: 10.55214/25768484.v9i5.7691 © 2025 by the author; licensee Learning Gate [12] A. I. Khudadad, A. A. Yousif, and H. R. Abed, "Effect of heat treatment on WO3 nanostructures based NO2 gas sensor low-cost device," Materials Chemistry and Physics, vol. 269, p. 124731, 2021. https://doi.org/10.1016/j.matchemphys.2021.124731 [13] J. López-García, J. Montero, C. Maffiotte, C. Guillén, and J. Herrero, "Crystallization of wide-bandgap CuAlSe2 thin films deposited on antimony doped tin oxide substrates," Journal of Alloys and Compounds, vol. 648, pp. 104-110, 2015. [14] J. Wang et al., "Hydrothermally grown oriented ZnO nanorod arrays for gas sensing applications," Nanotechnology, vol. 17, no. 19, p. 4995, 2006. https://doi.org/10.1088/0957-4484/17/19/037 [15] H. Al-Jumaili and M. Jasim, "Preparation and characterization of zno: Sno2 nanocomposite thin films on porous silicon as h2s gas sensor," J. Ovonic Res, vol. 15, pp. 81-87, 2019. https://doi.org/10.1021/acsanm.3c06279.s001 [16] I. K. Jasim, I. M. Ibrahim, and M. K. Alyas, "In2O3-ZnO pyramids like structure prepared by spray-pyrolysis Technique for gas Sensing Applications," Iraqi Journal of Science, pp. 67-74, 2018. https://doi.org/10.24996/ijs.2018.59.1a.9 https://doi.org/10.1016/j.matchemphys.2021.124731 https://doi.org/10.1088/0957-4484/17/19/037 https://doi.org/10.1021/acsanm.3c06279.s001 https://doi.org/10.24996/ijs.2018.59.1a.9