研究目的
To increase the repeatability of H2S gas sensors by fabricating ZnO nanoparticles covered with Cr2O3, addressing the issue of response reduction and saturation in ZnO-based sensors after repeated H2S sensing.
研究成果
The fabrication of ZnO nanoparticles covered with Cr2O3 using spray pyrolysis and thermal evaporation significantly improved the repeatability and sensitivity of H2S gas sensors. The Cr2O3 coating enhanced response at high H2S concentrations without altering operating temperature, and maintained consistent response and recovery times over multiple cycles. Structural analyses confirmed the presence of hexagonal ZnO and Cr2O3 phases, with increased density and smoother surfaces at higher coating thicknesses. This approach effectively mitigates the saturation and degradation issues in bare ZnO sensors, demonstrating high reproducibility and potential for industrial applications in toxic gas detection.
研究不足
The study was conducted under controlled dry air conditions with negligible humidity (less than 3 ppm water vapor), which may not represent real-world environments where humidity could affect sensor performance. The experiments were limited to H2S gas and specific concentration ranges (30-150 ppm) and operating temperatures (up to 350°C), potentially not covering other gases or broader conditions. The coating thickness was varied only up to 60 nm, and further optimization might be needed. Long-term stability and effects of other interfering gases were not extensively studied.
1：Experimental Design and Method Selection:
The study used spray pyrolysis and thermal evaporation techniques to fabricate ZnO nanoparticles covered with Cr2O3. The rationale was to enhance sensor repeatability by protecting ZnO with a Cr2O3 coating.
2：The rationale was to enhance sensor repeatability by protecting ZnO with a Cr2O3 coating.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources: ZnO nanoparticles were synthesized via sol-gel method using zinc acetate and ethanolamine in ethanol, calcined at 500°C. Cr2O3 coating was applied using thermal evaporation deposition with Cr powder, annealed at 300°C. Samples S-40 and S-60 had coating thicknesses of 40 nm and 60 nm, controlled by a quartz crystal.
3：List of Experimental Equipment and Materials:
Equipment included an oven, magnetic stirrer, spray pyrolysis setup, thermal evaporation deposition system, sputtering device for Au electrodes, steel gas chamber, electric hot plate, mass flow controllers (MFC), gas mixer, X-ray diffractometer (Philips XRD X'Pert MPD), scanning electron microscope (SEM), atomic-force microscope (AFM). Materials included zinc acetate, ethanolamine, ethanol, Cr2O3 powder (Sigma-Aldrich, 99.9% purity), Cr powder, tungsten boat, glass substrates, acetone, distilled water, dry air, H2S gas.
4：9% purity), Cr powder, tungsten boat, glass substrates, acetone, distilled water, dry air, H2S gas.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: ZnO synthesis: Dissolve 1M zinc acetate and 1M ethanolamine in ethanol, stir for 90 minutes, evaporate solvent at 250°C, calcine at 500°C. Deposit ZnO on glass substrate via spray pyrolysis at 150°C substrate temperature, 5 ml/min flow rate, anneal at 500°C. Apply Cr2O3 coating via thermal evaporation: Place Cr powder on tungsten boat, deposit at room temperature in oxygen partial pressure of 3×10^-4 Pa, oxidize to Cr2O3, anneal at 300°C for 2 hours. Deposit Au electrodes by sputtering. Gas sensing: Place sensor in gas chamber on hot plate, control temperature with 3°C accuracy, adjust H2S concentration using MFCs and gas mixer with 2 ppm accuracy, measure resistance in air and H2S.
5：2S.
Data Analysis Methods:
5. Data Analysis Methods: Gas response calculated using S(%) = [(R_air - R_gas)/R_air] × 100. XRD data analyzed for phase identification using JCPDS standards, crystallite size determined by Scherer's formula. SEM and AFM used for morphological analysis. Response and recovery times measured from transient curves. Reprodubility tested over ten cycles.
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