Development of Reduced Graphene Oxide and Zinc Oxide Thin Film Using Spray Coating Method: Application of Nitrogen Dioxide Sensor

다국어 초록 (Multilingual Abstract)

Title: Development of Reduced Graphene Oxide and Zinc Oxide Thin Film Using Spray Coating Method: Application of Nitrogen Dioxide Sensor This research aims to investigate the development process of highly sensitive chemi-resistive gas sensors for detection of nitrogen dioxide using spray coated reduced graphene oxide and zinc oxide thin film. The development of sensitive nitrogen dioxide （NO2） detection platforms has become increasingly critical, as many studies have demonstrated the serious health and environmental risks posed by NO2. Among various sensing methods, chemi-resistive sensors have attracted significant attention because of their simple structure, but the high operating temperature required by pristine metal oxide sensors remains a limitation. In this work, we fabricated a reduced graphene oxide （rGO） and zinc oxide （ZnO） hybrid NO2 sensor via a spray- coating process that can be completed within 1 hours and enables contamination- free, low‑cost deposition. The rGO layer formed a crumpled and porous structure that increased the available gas adsorption sites, while the sequentially coated ZnO nanoparticles provided additional reactive sites and formed a p–n heterojunction with rGO, leading to an enhanced change in resistance upon NO2 exposure. We analyzed the chemical, structural, and electrical properties of the rGO/ZnO films using various characterization techniques to confirm the uniform deposition of ZnO on rGO, and the formation of the heterostructure. As a result, the rGO/ZnO sensor showed a gas response of −44.5 ± 2.2% to 50 ppm NO2 and achieved an excellent limit of detection of 4.88 ppb, while providing a wide detection range from 50 ppm to 10 ppb with selectivity over common interfering gases. The sensor maintained stable sensing performance under various temperature （25°C to 150°C） and humidity （20–80%） conditions and exhibited long-term stability over a month in conductance and response, as well as good repeatability over more than 10 cycles. Finally, we demonstrated the practical applicability of the rGO/ZnO sensor by detecting trace levels of NO2 in cigarette smoke at room temperature, indicating that this spray-coated platform is promising for real-time NO2 monitoring in real environments.

목차 (Table of Contents)

• I. Introduction 1
• 1. Hazardous effect on human health of Nitrogen Dioxide 1
• 2. Overview of Chemi-Resistive Gas sensor 3
• 3. Nanomaterial-Based Approaches for Gas Sensor Development 5
• 4. Reduced Graphene Oxide (rGO) and Zinc Oxide (ZnO) Heterojunction for NO2 Gas Sensing 7
• II. Experimental Methodologies 9
• 1. Reduction of Graphene Oxide and Sensor Fabrication 10
• 2. Characterization of Sensor and Instruments 12
• 3. Gas Sensor Measurement System and Application 14
• III. Results and Discussions 18
• 1. Reduction and Characterization of Graphene Oxide 18
• 2. Surface Morphology and Structural Analysis of rGO and rGO/ZnO Composites 20
• 3. Chemical Characterization of rGO and rGO/ZnO 25
• 4. NO2 Sensing Performance of rGO/ZnO Sensor 32
• 5. Long-Term Stability and Repeatability of rGO/ZnO Sensor 36
• 6. Sensing performance under various environmental conditions and detection of NO2 in cigarette smoke 40
• IV. Conclusion 47
• References 48
• Acknowledgement 56