{"paper_id":"08c93bc3-547f-42cc-9cc8-e72687510f47","body_text":"Fabrication and Characterization of Graphene, Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel Nanomaterials Using Horizontal Vapor Phase Growth Technique for Formaldehyde Gas Detection | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Fabrication and Characterization of Graphene, Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel Nanomaterials Using Horizontal Vapor Phase Growth Technique for Formaldehyde Gas Detection Arturo Salvador, Gil Nonato Santos This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4269893/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Toxic gases, such as formaldehyde, pose serious health risks and can lead to a range of illnesses, including cancer and damage to the nervous system. Formaldehyde is a common air pollutant found in indoor environments due to its release from various sources, such as building materials, furniture, and cleaning products. The development of gas sensors that can effectively detect and monitor formaldehyde levels is important to ensure the safety and well-being of individuals in these environments. Nickel Oxide, Graphene-Nickel Oxide, and Graphene-Nickel nanomaterials were synthesized using the Horizontal Vapor Phase Growth (HPVG) technique and fabricated as sensor substrates. The nanomaterials were characterized morphologically using Scanning Electron Microscopy (SEM) and underwent gold sputtering using the JEOL JFC-1200 Fine coater. Elemental composition analysis was conducted using Energy Dispersive X-ray (EDX). Chronoamperometry technique was employed for the electrical characterization, utilizing the Biologic SP-150 instrument. The sensors were exposed to various concentrations of formaldehyde, ranging from 0.95 ppm to 4.77 ppm. The current measurement of the gas sensors was recorded at different input voltages, ranging from 0.25 volts to 2 volts, both when exposed to air and the target gas. Results showed that the Graphene-Nickel sensor showed the highest sensing performance in both input voltages of 0.50V and 2V with sensor response of 420% and 84.64% respectively and in both concentrations gap from low and high with sensitivity of 52.63 and 131.7 respectively. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction The field of nanotechnology offers great potential in various industries, including the development of sensors with improved capabilities in terms of accuracy, sensitivity, and selectivity [1]. One important application of nanotechnology is in gas sensing, where nanomaterials can be used as effective substrates to detect and monitor the presence of harmful gases, such as formaldehyde [2]. Formaldehyde, a volatile organic compound, is a common air pollutant released from industrial processes and various household materials. Prolonged exposure to formaldehyde can lead to serious health problems, including increased risk of leukemia and other cancers [3]. Additionally, formaldehyde is often used as a preservative in food products, particularly in the preservation of vegetables and agricultural goods. While controlled amounts of formaldehyde are acceptable, excessive ingestion can have adverse effects on human health [4]. Therefore, it is crucial to have efficient detection methods to monitor the formaldehyde content in food and ensure the safety of consumers. Various techniques, such as High-Performance Liquid Chromatography (HPLC), colorimetric sensors, and fluorescence spectroscopy, have been used for formaldehyde detection [5,6,7]. Gas sensors have also been developed using different sensing materials, including colorimetric reagents, carbon nanotubes, and metal oxide materials such as zinc oxide, nickel oxide, and tin oxide [8,9,10,11]. Additionally, graphene-based materials have shown promise in gas sensing applications, as they exhibit interactions between gas molecules and the graphene layer to detect toxic gases [12,13]. In this study, horizontal vapor phase growth (HVPG) technique was utilized to fabricate graphene, nickel, and nickel oxide nanomaterials as sensing materials for formaldehyde gas detection. The conductance change of these materials upon exposure to formaldehyde gas was measured to examine their sensing properties. By investigating the response of these nanomaterials to different concentrations of formaldehyde, we aim to develop efficient gas sensors that can accurately detect and monitor formaldehyde levels in a range of applications. 2. Methodology The fabrication process of the nickel oxide, graphene-nickel oxide, graphene-nickel nanomaterial-based gas sensor involves a sequence of five steps as shown in Fig1: the preparation of graphene, nickel, and nickel oxide raw bulk materials, synthesis of nanomaterials, characterization of the resulting materials, the assembly of the gas sensor with varying sensor materials based on the indicated proportion of graphene, nickel, and nickel oxide, and the subsequent detection of formaldehyde at varying low concentrations. Various combinations of graphene, nickel oxide, and nickel materials were utilized to fabricate the gas sensor. In Tube 1, a composition of 50 mg pure graphene was employed. Tube 2 consisted of 50 mg nickel (II) oxide, while Tube 3 contained a combination of 10 mg graphene and 40 mg nickel (II) oxide. Lastly, Tube 4 is comprised of 10 mg graphene and 40 mg nickel. These different compositions enabled the investigation of the impact of varying material ratios on the gas sensing performance of the nanomaterials, specifically in detecting formaldehyde. The aim was to determine the most efficient composition that would result in a gas sensor with high sensitivity and selectivity towards formaldehyde gas. The synthesis process involved several steps as shown in Fig2. Firstly, one end of the quartz tube was sealed using a blowtorch fueled by Liquefied Petroleum Gas (LPG) and Oxygen. The tube was then cleaned in a Branson ultrasonic cleanser for 30 minutes to remove any impurities. After drying, the precursor powder, a combination of graphene, nickel, and nickel oxide in various ratios, was introduced into the tube. Different compositions were explored to optimize the density and composition of the resulting nanomaterials. The sealed tube was then subjected to controlled pressurization to 1.5 × 10-6 torr using a high vacuum system. This ensured the creation of a high vacuum state within the tube, facilitating the Horizontal Vapor Phase Growth (HVPG) technique. The tube was further heated in a horizontal tube furnace at a maximum temperature of 1400°C for 12 hours. This temperature gradient within the furnace allowed for the vaporization and subsequent condensation of the precursor materials, leading to the synthesis of nanomaterials. The samples grown within the cracked tubes undergo a gold coating process using a fine coater, with a time duration of 30 seconds and a current of 50 milliamperes. This gold coating enhances the surface conductivity of the grown samples, ensuring improved characterization of their morphology when subjected to SEM analysis. The elemental composition and density are determined using Energy Dispersive X-ray Spectroscopy (EDX), building upon the information captured by SEM. A specific point from the SEM image is examined to analyze the elemental composition of the samples. The sensing material substrate is connected to the Biologic SP-150 and configured as an ammeter, and a two-point probe is employed to measure the change in current across the entire sensing layer. Five vials with formaldehyde solutions (0.95 ppm, 1.91 ppm, 2.86 ppm, 3.82 ppm, and 4.78 ppm) were prepared, stored for 24 hours to allow formaldehyde particle evaporation, and then characterized with I-V measurements using different input voltages ( -2v to +2v, -1v to 1v, -0.50v to +0.50v, -0.25v to +0.25v) for 60 seconds each. The application of varying input voltages allowed the measurement of current responses in both ambient air and formaldehyde-containing vials from the average of 600 data points. The sensor's response (S R ) value is quantified based on the current of the material in both ambient air and the target gas, expressed as ∆I/I₀ = (I A - I G ) / I A if I A >I G for reducing gases and (I G – I A ) / I G if I G >I A for oxidizing gases, where I A is the current of the sensor in air, and I G is the current of the sensor in the presence of the target gas. Furthermore, Sensitivity (S), as the slope of the calibration curve, representing the sensor's ability to discern different concentrations, is measured by [S R (c+ h) - S R (c)] / h where S R is the sensor response to specific concentration c and h denotes the difference between the two concentrations under comparison [14]. 3. Results and Discussion Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis was performed to determine the composition of the deposited nanomaterials in the quartz silica tube. In Fig3, Tube 1 exhibited limited structural formation and a less defined morphology, as observed in the SEM analysis. The EDX analysis revealed an atomic composition consisting of 61.08% oxygen (O), 34.30% silicon (Si), and 4.62% carbon (C). The presence of silicon indicates the contribution from the quartz silica tube, while the carbon signifies the incorporation of carbon from the graphene powder in the synthesized structures although it only consists of 2.78% of the entire weight indicating that only a very small percentage of graphene was deposited. In Tube 2 and 3, an agglomeration of different structures was observed, including web-like formations, cloud-like structures, and tiny blocks. The EDX analysis of Tube 2 revealed an atomic composition primarily consisting of nickel (Ni) at 87.52% total weight percentage and a little portion of oxygen (O), and silicon (Si), which aligns with the presence of pure nickel oxide in this tube while Tube 3 showed atomic composition including oxygen (O), silicon (Si), carbon (C), and nickel (Ni). The additional presence of carbon indicates the incorporation of graphene, which was part of the composition in this tube with a combination of graphene and nickel (II) oxide. In Tube 4, there was a lesser formation of structures indicative of high weight percentage of (Si) pertaining to the quartz silica tube. The EDX analysis of Tube 4 displayed a similar atomic composition as Tube 3, with oxygen (O), silicon (Si), carbon (C), and nickel (Ni). However, in Tube 4, the presence of nickel indicates the utilization of pure nickel rather than nickel oxide in the nanomaterial synthesis. Fig4 shows the gas current responses (IG) of Nickel Oxide (NiO), Graphene Nickel Oxide (GNiO), and Graphene Nickel (GNi) sensors at a voltage of 0.25 volts, focusing on the formaldehyde concentrations ranging between 1.91 ppm and 2.86 ppm. Nickel Oxide Sensor exhibits a decrease in current response from 0.53 nA to 0.39 nA as the formaldehyde concentration increases within the specified range. Similarly, the Graphene Nickel Oxide Sensor shows a decline in current response, dropping from 0.66 nA to 0.47 nA under the same conditions. These observations align with expectations of reduced sensor response with increasing formaldehyde concentrations, indicative of the sensors' sensitivity to the target gas. Unexpectedly, the Graphene Nickel Sensor displays a similar behavior although reaching a negative current measurement with its response decreasing from -0.02 nA to -0.1 nA. Fig5 shows the sensor response (SR) of Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel sensors at a voltage of 0.50 volts, focusing on formaldehyde concentrations ranging from 2.86 ppm to 4.77 ppm. Initially, the Nickel Oxide Sensor demonstrates a moderate increase in sensor response, rising from 25.91% to 34.29% as the formaldehyde concentration escalates within the specified range. This observed increment aligns with expectations of heightened sensor response to higher concentrations of the target gas, reflecting the sensor's ability to detect and respond to increasing levels of formaldehyde. In contrast, the Graphene Nickel Oxide Sensor exhibits a substantial surge in sensor response, escalating from 40.00% to 82.99% under the same conditions. This pronounced increase suggests a heightened sensitivity of the Graphene Nickel Oxide Sensor to formaldehyde, potentially attributed to the unique properties of graphene in enhancing sensing capabilities. Remarkably, the Graphene Nickel Sensor displays an exceptional response, surging from 93.33% to 420.00%. This exponential increase reflects the sensor's remarkable responsiveness to formaldehyde concentrations, surpassing the responses of the other two sensors by a significant margin. In addition to the previous analysis, the examination of sensor response to formaldehyde gas was extended to include a higher input voltage of 2V, providing further insights into sensor behavior. The presented figure (Fig6) illustrates the Sensor Response (SR) at 2 volts for Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel Sensors across formaldehyde concentrations from 0.96 ppm to 4.77 ppm. Nickel Oxide Sensor demonstrates a moderate increase in response, from 49.19% to 54.07%, indicative of its responsiveness to formaldehyde within this concentration range. In contrast, the Graphene Nickel Oxide Sensor exhibits a higher increase in response from 7.39% to 37.14%, highlighting its enhanced responsiveness compared to the Nickel Oxide Sensor under similar conditions. Interestingly, the Graphene Nickel Sensor again displays exceptional performance, with its response reaching from 40.63% to 84.64%. This remarkable increase reaffirms the sensor's superior responsiveness to formaldehyde, consistent with previous observations. Fig7 shows the overview of the sensitivity (S) of both nickel oxide (NiO) and graphene nickel (GNi) sensors at an input voltage of 0.25 volts, highlighting their performance across low and high concentration gaps of formaldehyde. In this context, a low concentration gap pertains to the gas concentration of formaldehyde between 2.86 ppm and 1.91 ppm, while a high concentration gap encompasses gas concentrations between 4.77 ppm and 1.91 ppm. NiO sensor demonstrates a notable increase in sensitivity from 1 to 3.33 from low to high concentration gap, indicating its enhanced sensitivity to subtle variations in formaldehyde concentration within this range. However, the GNi sensor exhibits a substantially higher sensitivity range, escalating from 52.63 to 131.70 from low to high concentration gap. This significant increase shows the remarkable sensitivity of the GNi sensor to even minor fluctuations in formaldehyde concentration, showcasing its potential for precise and accurate detection within narrow concentration ranges. 4. Conclusion The SEM-EDX analysis revealed diverse structural formations of nanomaterials in quartz silica tubes, with Tubes 2, 3, and 4 exhibiting compositions conducive to gas sensing applications, particularly highlighting the incorporation of graphene, nickel oxide, and nickel. However, Tube 1, which exclusively contained pure graphene, exhibited minimal deposition of structures. This limited deposition was indicative of carbon, constituting only a small fraction (2-5%) of the overall weight composition which is unsuitable for effective gas sensing application. The analyses across various sensor types and conditions consistently highlight the superior performance of graphene-based sensors, particularly Graphene Nickel and Graphene Nickel Oxide, compared to traditional Nickel Oxide sensors. The addition of graphene to nickel and nickel oxide configurations significantly enhances sensing capabilities, as evidenced by their heightened sensitivity and superior sensor responses across formaldehyde concentration ranges. Moreover, the Graphene Nickel sensor emerges as particularly exceptional, exhibiting superior sensitivity to Nickel Oxide sensors across both low and high formaldehyde concentration gaps. The observations underscore the general trend wherein gas current responses of sensors decrease with increasing formaldehyde concentrations, with the Graphene Nickel sensor displaying an ideal decreasing line of gas current response, further emphasizing its enhanced performance compared to Graphene Nickel Oxide and Nickel Oxide sensors. 5. Declarations This study was funded by Deparment of Science and Technology – Science Education Institute (DOST-SEI). The authors have no conflicts of interest to declare that are relevant to the content of this article. 6. References Noah, N. M., & Ndangili, P. M. (2019). Current Trends of Nanobiosensors for Point-of-Care Diagnostics. Journal of Analytical Methods in Chemistry, 2019, 1–16. Bouchikhi, B., Chludziński, T., Saidi, T., Smulko, J., Bari, N. E., Wen, H., & Ionescu, R. (2020). Formaldehyde detection with chemical gas sensors based on WO3 nanowires decorated with metal nanoparticles under dark conditions and UV light irradiation. Sensors and Actuators B: Chemical, 320, 128331. Beane Freeman, L.E.; Blair, A.; Lubin, J.H.; Stewart, P.A.; Hayes, R.B.; Hoover, R.N.; Hauptmann, M. Mortality from lymphohematopoietic malignancies among workers in formaldehyde industries: the National Cancer Institute cohort. J. Natl. Cancer Inst. 2009, 101, 751–761. Guzman, J.M.C., Tayo, L., Liv. C.C., Wang, Y, N., (2017). Rapid microfluid paper-based platform for low concentration formaldehyde detection. Kumar, R., Avasthi, D. K., & Kaur, A. (2017). Fabrication of chemiresistive gas sensors based on multistep reduced graphene oxide for low parts per million monitoring of sulfur dioxide at room temperature. Sensors and Actuators B: Chemical, 242, 461–468. Feng, L., Musto, C. J., Kemling, J. W., Lim, S. H., & Suslick, K. S. (2010). A colorimetric sensor array for identification of toxic gases below permissible exposure limits. Chemical Communications, 46(12), 2037. Huang, X., Guo, Q., Zhang, R., Zhao, Z., Leng, Y., Lam, J. W. Y., Xiong, Y., & Tang, B. Z. (2020). AIEgens: An emerging fluorescent sensing tool to aid food safety and quality control. Comprehensive Reviews in Food Science and Food Safety, 19(4), 2297–2329. Suzuki Y., Nakano N., Suzuki K. Portable sick house syndrome gas monitoring system based on novel colorimetric reagents for the highly selective and sensitive detection of formaldehyde. Environ. Sci. Technol. 2003;37:5695–5700. Xie H., Sheng C., Chen X., Wang X., Li Z., Zhou J. Multi-wall carbon nanotube gas sensors modified with amino-group to detect low concentration of formaldehyde. Sens. Actuators B Chem. 2012;168:34–38. Zhang L., Zhao J., Lu H., Gong L., Li L., Zheng J., Li H., Zhu Z. High sensitive and selective formaldehyde sensors based on nanoparticle-assembled ZnO micro-octahedrons synthesized by homogeneous precipitation method. Sens. Actuators B Chem. 2011;160:364–370. Castro-Hurtado I., Herrán J., Mandayo G.G., Castaño E. Studies of influence of structural properties and thickness of NiO thin films on formaldehyde detection. Thin Solid Film. 2011;520:947–952. Pandey, P. A., Wilson, N. R., & Covington, J. A. (2013). Pd-doped reduced graphene oxide sensing films for H2 detection. Sensors and Actuators B: Chemical, 183, 478–487. Hu, J., Zou, C., Su, Y., Li, M., Hu, N., Ni, H., Yang, Z., & Zhang, Y. (2017). Enhanced NO2 sensing performance of reduced graphene oxide by in situ anchoring carbon dots. Journal of Materials Chemistry C, 5(27), 6862–6871. Tonezzer, M., & Van Duy, L. (2023). Gas sensors. In Elsevier eBooks (pp. 185–208). Additional Declarations No competing interests reported. Supplementary Files DATA.xlsx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-4269893\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":293315806,\"identity\":\"f8aa0a3b-0798-4c14-8ec0-0adc563d3763\",\"order_by\":0,\"name\":\"Arturo 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Nanomaterials Using Horizontal Vapor Phase Growth Technique for Formaldehyde Gas Detection\",\"fulltext\":[{\"header\":\"1.\\tIntroduction\",\"content\":\"\\u003cp\\u003eThe field of nanotechnology offers great potential in various industries, including the development of sensors with improved capabilities in terms of accuracy, sensitivity, and selectivity [1]. One important application of nanotechnology is in gas sensing, where nanomaterials can be used as effective substrates to detect and monitor the presence of harmful gases, such as formaldehyde [2]. Formaldehyde, a volatile organic compound, is a common air pollutant released from industrial processes and various household materials. Prolonged exposure to formaldehyde can lead to serious health problems, including increased risk of leukemia and other cancers [3].\\u003c/p\\u003e\\n\\u003cp\\u003eAdditionally, formaldehyde is often used as a preservative in food products, particularly in the preservation of vegetables and agricultural goods. While controlled amounts of formaldehyde are acceptable, excessive ingestion can have adverse effects on human health [4]. Therefore, it is crucial to have efficient detection methods to monitor the formaldehyde content in food and ensure the safety of consumers. Various techniques, such as High-Performance Liquid Chromatography (HPLC), colorimetric sensors, and fluorescence spectroscopy, have been used for formaldehyde detection [5,6,7]. Gas sensors have also been developed using different sensing materials, including colorimetric reagents, carbon nanotubes, and metal oxide materials such as zinc oxide, nickel oxide, and tin oxide [8,9,10,11]. Additionally, graphene-based materials have shown promise in gas sensing applications, as they exhibit interactions between gas molecules and the graphene layer to detect toxic gases [12,13].\\u003c/p\\u003e\\n\\u003cp\\u003eIn this study, horizontal vapor phase growth (HVPG) technique was utilized to fabricate graphene, nickel, and nickel oxide nanomaterials as sensing materials for formaldehyde gas detection. The conductance change of these materials upon exposure to formaldehyde gas was measured to examine their sensing properties. By investigating the response of these nanomaterials to different concentrations of formaldehyde, we aim to develop efficient gas sensors that can accurately detect and monitor formaldehyde levels in a range of applications.\\u003c/p\\u003e\"},{\"header\":\"2.\\tMethodology\",\"content\":\"\\u003cp\\u003eThe fabrication process of the nickel oxide, graphene-nickel oxide, graphene-nickel nanomaterial-based gas sensor involves a sequence of five steps as shown in Fig1: the preparation of graphene, nickel, and nickel oxide raw bulk materials, synthesis of nanomaterials, characterization of the resulting materials, the assembly of the gas sensor with varying sensor materials based on the indicated proportion of graphene, nickel, and nickel oxide, and the subsequent detection of formaldehyde at varying low concentrations.\\u003c/p\\u003e\\n\\u003cp\\u003eVarious combinations of graphene, nickel oxide, and nickel materials were utilized to fabricate the gas sensor. In Tube 1, a composition of 50 mg pure graphene was employed. Tube 2 consisted of 50 mg nickel (II) oxide, while Tube 3 contained a combination of 10 mg graphene and 40 mg nickel (II) oxide. Lastly, Tube 4 is comprised of 10 mg graphene and 40 mg nickel. These different compositions enabled the investigation of the impact of varying material ratios on the gas sensing performance of the nanomaterials, specifically in detecting formaldehyde. The aim was to determine the most efficient composition that would result in a gas sensor with high sensitivity and selectivity towards formaldehyde gas.\\u003c/p\\u003e\\n\\u003cp\\u003eThe synthesis process involved several steps as shown in Fig2. Firstly, one end of the quartz tube was sealed using a blowtorch fueled by Liquefied Petroleum Gas (LPG) and Oxygen. The tube was then cleaned in a Branson ultrasonic cleanser for 30 minutes to remove any impurities. After drying, the precursor powder, a combination of graphene, nickel, and nickel oxide in various ratios, was introduced into the tube. Different compositions were explored to optimize the density and composition of the resulting nanomaterials. The sealed tube was then subjected to controlled pressurization to 1.5 \\u0026times; 10-6 torr using a high vacuum system. This ensured the creation of a high vacuum state within the tube, facilitating the Horizontal Vapor Phase Growth (HVPG) technique. The tube was further heated in a horizontal tube furnace at a maximum temperature of 1400\\u0026deg;C for 12 hours. This temperature gradient within the furnace allowed for the vaporization and subsequent condensation of the precursor materials, leading to the synthesis of nanomaterials.\\u003c/p\\u003e\\n\\u003cp\\u003eThe samples grown within the cracked tubes undergo a gold coating process using a fine coater, with a time duration of 30 seconds and a current of 50 milliamperes. This gold coating enhances the surface conductivity of the grown samples, ensuring improved characterization of their morphology when subjected to SEM analysis. The elemental composition and density are determined using Energy Dispersive X-ray Spectroscopy (EDX), building upon the information captured by SEM. A specific point from the SEM image is examined to analyze the elemental composition of the samples. The sensing material substrate is connected to the Biologic SP-150 and configured as an ammeter, and a two-point probe is employed to measure the change in current across the entire sensing layer. Five vials with formaldehyde solutions (0.95 ppm, 1.91 ppm, 2.86 ppm, 3.82 ppm, and 4.78 ppm) were prepared, stored for 24 hours to allow formaldehyde particle evaporation, and then characterized with I-V measurements using different input voltages ( -2v to +2v, -1v to 1v, -0.50v to +0.50v, -0.25v to +0.25v) for 60 seconds each. The application of varying input voltages allowed the measurement of current responses in both ambient air and formaldehyde-containing vials from the average of 600 data points. The sensor\\u0026apos;s response (S\\u003csub\\u003eR\\u003c/sub\\u003e) value is quantified based on the current of the material in both ambient air and the target gas, expressed as ∆I/I₀ = (I\\u003csub\\u003eA\\u003c/sub\\u003e - I\\u003csub\\u003eG\\u003c/sub\\u003e) / I\\u003csub\\u003eA\\u0026nbsp;\\u003c/sub\\u003eif I\\u003csub\\u003eA\\u003c/sub\\u003e\\u0026gt;I\\u003csub\\u003eG\\u0026nbsp;\\u003c/sub\\u003efor reducing gases and (I\\u003csub\\u003eG\\u003c/sub\\u003e \\u0026ndash; I\\u003csub\\u003eA\\u003c/sub\\u003e) / I\\u003csub\\u003eG\\u0026nbsp;\\u003c/sub\\u003eif I\\u003csub\\u003eG\\u003c/sub\\u003e\\u0026gt;I\\u003csub\\u003eA\\u0026nbsp;\\u003c/sub\\u003efor oxidizing gases, where I\\u003csub\\u003eA\\u003c/sub\\u003e is the current of the sensor in air, and I\\u003csub\\u003eG\\u003c/sub\\u003e is the current of the sensor in the presence of the target gas. Furthermore, Sensitivity (S), as the slope of the calibration curve, representing the sensor\\u0026apos;s ability to discern different concentrations, is measured by [S\\u003csub\\u003eR\\u003c/sub\\u003e(c+ h) - S\\u003csub\\u003eR\\u003c/sub\\u003e(c)] / h where S\\u003csub\\u003eR\\u003c/sub\\u003e is the sensor response to specific concentration c and h denotes the difference between the two concentrations under comparison [14].\\u003c/p\\u003e\"},{\"header\":\"3.\\tResults and Discussion\",\"content\":\"\\u003cp\\u003eScanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis was performed to determine the composition of the deposited nanomaterials in the quartz silica tube. In Fig3, Tube 1 exhibited limited structural formation and a less defined morphology, as observed in the SEM analysis. The EDX analysis revealed an atomic composition consisting of 61.08% oxygen (O), 34.30% silicon (Si), and 4.62% carbon (C). The presence of silicon indicates the contribution from the quartz silica tube, while the carbon signifies the incorporation of carbon from the graphene powder in the synthesized structures although it only consists of 2.78% of the entire weight indicating that only a very small percentage of graphene was deposited. In Tube 2 and 3, an agglomeration of different structures was observed, including web-like formations, cloud-like structures, and tiny blocks. The EDX analysis of Tube 2 revealed an atomic composition primarily consisting of nickel (Ni) at 87.52% total weight percentage and a little portion of oxygen (O), and silicon (Si), which aligns with the presence of pure nickel oxide in this tube while Tube 3 showed atomic composition including oxygen (O), silicon (Si), carbon (C), and nickel (Ni). The additional presence of carbon indicates the incorporation of graphene, which was part of the composition in this tube with a combination of graphene and nickel (II) oxide. In Tube 4, there was a lesser formation of structures indicative of high weight percentage of (Si) pertaining to the quartz silica tube. The EDX analysis of Tube 4 displayed a similar atomic composition as Tube 3, with oxygen (O), silicon (Si), carbon (C), and nickel (Ni). However, in Tube 4, the presence of nickel indicates the utilization of pure nickel rather than nickel oxide in the nanomaterial synthesis.\\u003c/p\\u003e\\n\\u003cp\\u003eFig4 shows the gas current responses (IG) of Nickel Oxide (NiO), Graphene Nickel Oxide (GNiO), and Graphene Nickel (GNi) sensors at a voltage of 0.25 volts, focusing on the formaldehyde concentrations ranging between 1.91 ppm and 2.86 ppm. \\u0026nbsp;Nickel Oxide Sensor exhibits a decrease in current response from 0.53 nA to 0.39 nA as the formaldehyde concentration increases within the specified range. Similarly, the Graphene Nickel Oxide Sensor shows a decline in current response, dropping from 0.66 nA to 0.47 nA under the same conditions. These observations align with expectations of reduced sensor response with increasing formaldehyde concentrations, indicative of the sensors\\u0026apos; sensitivity to the target gas. Unexpectedly, the Graphene Nickel Sensor displays a similar behavior although reaching a negative current measurement with its response decreasing from -0.02 nA to -0.1 nA.\\u003c/p\\u003e\\n\\u003cp\\u003eFig5 shows the sensor response (SR) of Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel sensors at a voltage of 0.50 volts, focusing on formaldehyde concentrations ranging from 2.86 ppm to 4.77 ppm. Initially, the Nickel Oxide Sensor demonstrates a moderate increase in sensor response, rising from 25.91% to 34.29% as the formaldehyde concentration escalates within the specified range. This observed increment aligns with expectations of heightened sensor response to higher concentrations of the target gas, reflecting the sensor\\u0026apos;s ability to detect and respond to increasing levels of formaldehyde.\\u003c/p\\u003e\\n\\u003cp\\u003eIn contrast, the Graphene Nickel Oxide Sensor exhibits a substantial surge in sensor response, escalating from 40.00% to 82.99% under the same conditions. This pronounced increase suggests a heightened sensitivity of the Graphene Nickel Oxide Sensor to formaldehyde, potentially attributed to the unique properties of graphene in enhancing sensing capabilities. Remarkably, the Graphene Nickel Sensor displays an exceptional response, surging from 93.33% to 420.00%. This exponential increase reflects the sensor\\u0026apos;s remarkable responsiveness to formaldehyde concentrations, surpassing the responses of the other two sensors by a significant margin.\\u003c/p\\u003e\\n\\u003cp\\u003eIn addition to the previous analysis, the examination of sensor response to formaldehyde gas was extended to include a higher input voltage of 2V, providing further insights into sensor behavior. The presented figure (Fig6) illustrates the Sensor Response (SR) at 2 volts for Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel Sensors across formaldehyde concentrations from 0.96 ppm to 4.77 ppm. Nickel Oxide Sensor demonstrates a moderate increase in response, from 49.19% to 54.07%, indicative of its responsiveness to formaldehyde within this concentration range. In contrast, the Graphene Nickel Oxide Sensor exhibits a higher increase in response from 7.39% to 37.14%, highlighting its enhanced responsiveness compared to the Nickel Oxide Sensor under similar conditions. Interestingly, the Graphene Nickel Sensor again displays exceptional performance, with its response reaching from 40.63% to 84.64%. This remarkable increase reaffirms the sensor\\u0026apos;s superior responsiveness to formaldehyde, consistent with previous observations.\\u003c/p\\u003e\\n\\u003cp\\u003eFig7 shows the overview of the sensitivity (S) of both nickel oxide (NiO) and graphene nickel (GNi) sensors at an input voltage of 0.25 volts, highlighting their performance across low and high concentration gaps of formaldehyde. In this context, a low concentration gap pertains to the gas concentration of formaldehyde between 2.86 ppm and 1.91 ppm, while a high concentration gap encompasses gas concentrations between 4.77 ppm and 1.91 ppm.\\u003c/p\\u003e\\n\\u003cp\\u003eNiO sensor demonstrates a notable increase in sensitivity from 1 to 3.33 from low to high concentration gap, indicating its enhanced sensitivity to subtle variations in formaldehyde concentration within this range. However, the GNi sensor exhibits a substantially higher sensitivity range, escalating from 52.63 to 131.70 from low to high concentration gap. This significant increase shows the remarkable sensitivity of the GNi sensor to even minor fluctuations in formaldehyde concentration, showcasing its potential for precise and accurate detection within narrow concentration ranges.\\u003c/p\\u003e\"},{\"header\":\"4.\\tConclusion\",\"content\":\"\\u003cp\\u003eThe SEM-EDX analysis revealed diverse structural formations of nanomaterials in quartz silica tubes, with Tubes 2, 3, and 4 exhibiting compositions conducive to gas sensing applications, particularly highlighting the incorporation of graphene, nickel oxide, and nickel. However, Tube 1, which exclusively contained pure graphene, exhibited minimal deposition of structures. This limited deposition was indicative of carbon, constituting only a small fraction (2-5%) of the overall weight composition which is unsuitable for effective gas sensing application.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003eThe analyses across various sensor types and conditions consistently highlight the superior performance of graphene-based sensors, particularly Graphene Nickel and Graphene Nickel Oxide, compared to traditional Nickel Oxide sensors. The addition of graphene to nickel and nickel oxide configurations significantly enhances sensing capabilities, as evidenced by their heightened sensitivity and superior sensor responses across formaldehyde concentration ranges. Moreover, the Graphene Nickel sensor emerges as particularly exceptional, exhibiting superior sensitivity to Nickel Oxide sensors across both low and high formaldehyde concentration gaps. The observations underscore the general trend wherein gas current responses of sensors decrease with increasing formaldehyde concentrations, with the Graphene Nickel sensor displaying an ideal decreasing line of gas current response, further emphasizing its enhanced performance compared to Graphene Nickel Oxide and Nickel Oxide sensors.\\u003c/p\\u003e\"},{\"header\":\"5.\\tDeclarations\",\"content\":\"\\u003cp\\u003eThis study was funded by Deparment of Science and Technology \\u0026ndash; Science Education Institute (DOST-SEI). The authors have no conflicts of interest to declare that are relevant to the content of this article.\\u003c/p\\u003e\"},{\"header\":\"6.\\tReferences\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003eNoah, N. M., \\u0026amp; Ndangili, P. M. (2019). Current Trends of Nanobiosensors for Point-of-Care Diagnostics. Journal of Analytical Methods in Chemistry, 2019, 1\\u0026ndash;16.\\u003c/li\\u003e\\n\\u003cli\\u003eBouchikhi, B., Chludziński, T., Saidi, T., Smulko, J., Bari, N. E., Wen, H., \\u0026amp; Ionescu, R. (2020). Formaldehyde detection with chemical gas sensors based on WO3 nanowires decorated with metal nanoparticles under dark conditions and UV light irradiation. Sensors and Actuators B: Chemical, 320, 128331. \\u003c/li\\u003e\\n\\u003cli\\u003eBeane Freeman, L.E.; Blair, A.; Lubin, J.H.; Stewart, P.A.; Hayes, R.B.; Hoover, R.N.; Hauptmann, M. Mortality from lymphohematopoietic malignancies among workers in formaldehyde industries: the National Cancer Institute cohort. J. Natl. Cancer Inst. 2009, 101, 751\\u0026ndash;761.\\u003c/li\\u003e\\n\\u003cli\\u003eGuzman, J.M.C., Tayo, L., Liv. C.C., Wang, Y, N., (2017). Rapid microfluid paper-based platform for low concentration formaldehyde detection.\\u003c/li\\u003e\\n\\u003cli\\u003eKumar, R., Avasthi, D. K., \\u0026amp; Kaur, A. (2017). Fabrication of chemiresistive gas sensors based on multistep reduced graphene oxide for low parts per million monitoring of sulfur dioxide at room temperature. Sensors and Actuators B: Chemical, 242, 461\\u0026ndash;468. \\u003c/li\\u003e\\n\\u003cli\\u003eFeng, L., Musto, C. J., Kemling, J. W., Lim, S. H., \\u0026amp; Suslick, K. S. (2010). A colorimetric sensor array for identification of toxic gases below permissible exposure limits. Chemical Communications, 46(12), 2037.\\u003c/li\\u003e\\n\\u003cli\\u003eHuang, X., Guo, Q., Zhang, R., Zhao, Z., Leng, Y., Lam, J. W. Y., Xiong, Y., \\u0026amp; Tang, B. Z. (2020). AIEgens: An emerging fluorescent sensing tool to aid food safety and quality control. Comprehensive Reviews in Food Science and Food Safety, 19(4), 2297\\u0026ndash;2329. \\u003c/li\\u003e\\n\\u003cli\\u003eSuzuki Y., Nakano N., Suzuki K. Portable sick house syndrome gas monitoring system based on novel colorimetric reagents for the highly selective and sensitive detection of formaldehyde. Environ. Sci. Technol. 2003;37:5695\\u0026ndash;5700. \\u003c/li\\u003e\\n\\u003cli\\u003eXie H., Sheng C., Chen X., Wang X., Li Z., Zhou J. Multi-wall carbon nanotube gas sensors modified with amino-group to detect low concentration of formaldehyde. Sens. Actuators B Chem. 2012;168:34\\u0026ndash;38.\\u003c/li\\u003e\\n\\u003cli\\u003eZhang L., Zhao J., Lu H., Gong L., Li L., Zheng J., Li H., Zhu Z. High sensitive and selective formaldehyde sensors based on nanoparticle-assembled ZnO micro-octahedrons synthesized by homogeneous precipitation method. Sens. Actuators B Chem. 2011;160:364\\u0026ndash;370.\\u003c/li\\u003e\\n\\u003cli\\u003eCastro-Hurtado I., Herr\\u0026aacute;n J., Mandayo G.G., Casta\\u0026ntilde;o E. Studies of influence of structural properties and thickness of NiO thin films on formaldehyde detection. Thin Solid Film. 2011;520:947\\u0026ndash;952.\\u003c/li\\u003e\\n\\u003cli\\u003ePandey, P. A., Wilson, N. R., \\u0026amp; Covington, J. A. (2013). Pd-doped reduced graphene oxide sensing films for H2 detection. Sensors and Actuators B: Chemical, 183, 478\\u0026ndash;487. \\u003c/li\\u003e\\n\\u003cli\\u003eHu, J., Zou, C., Su, Y., Li, M., Hu, N., Ni, H., Yang, Z., \\u0026amp; Zhang, Y. (2017). Enhanced NO2 sensing performance of reduced graphene oxide by in situ anchoring carbon dots. Journal of Materials Chemistry C, 5(27), 6862\\u0026ndash;6871.\\u003c/li\\u003e\\n\\u003cli\\u003eTonezzer, M., \\u0026amp; Van Duy, L. (2023). Gas sensors. In Elsevier eBooks (pp. 185\\u0026ndash;208). \\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":true,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true},\"keywords\":\"\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-4269893/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-4269893/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eToxic gases, such as formaldehyde, pose serious health risks and can lead to a range of illnesses, including cancer and damage to the nervous system. Formaldehyde is a common air pollutant found in indoor environments due to its release from various sources, such as building materials, furniture, and cleaning products. The development of gas sensors that can effectively detect and monitor formaldehyde levels is important to ensure the safety and well-being of individuals in these environments. Nickel Oxide, Graphene-Nickel Oxide, and Graphene-Nickel nanomaterials were synthesized using the Horizontal Vapor Phase Growth (HPVG) technique and fabricated as sensor substrates. The nanomaterials were characterized morphologically using Scanning Electron Microscopy (SEM) and underwent gold sputtering using the JEOL JFC-1200 Fine coater. Elemental composition analysis was conducted using Energy Dispersive X-ray (EDX). Chronoamperometry technique was employed for the electrical characterization, utilizing the Biologic SP-150 instrument. The sensors were exposed to various concentrations of formaldehyde, ranging from 0.95 ppm to 4.77 ppm. The current measurement of the gas sensors was recorded at different input voltages, ranging from 0.25 volts to 2 volts, both when exposed to air and the target gas. Results showed that the Graphene-Nickel sensor showed the highest sensing performance in both input voltages of 0.50V and 2V with sensor response of 420% and 84.64% respectively and in both concentrations gap from low and high with sensitivity of 52.63 and 131.7 respectively.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Fabrication and Characterization of Graphene, Nickel Oxide, Graphene Nickel Oxide, and Graphene Nickel Nanomaterials Using Horizontal Vapor Phase Growth Technique for Formaldehyde Gas Detection\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2024-04-29 13:20:24\",\"doi\":\"10.21203/rs.3.rs-4269893/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"3157e1f7-0eef-4957-ad04-aedcbeb5e830\",\"owner\":[],\"postedDate\":\"April 29th, 2024\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2024-07-15T12:32:26+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2024-04-29 13:20:24\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-4269893\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-4269893\",\"identity\":\"rs-4269893\",\"version\":[\"v1\"]},\"buildId\":\"qtupq5eGEP_6zYnWcrvyt\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}