Microfabricated Interdigital Capacitive Sensor and Resonant Sensor Based on PPy/MoO3 Hybrids for Sensitivity-Enhanced Ammonia Detection at Room Temperature

This paper proposes a microwave transduction-based gas sensor based on polypyrrole/molybdenum oxide composite (PPy/MoO3) hybrid material. Optimization of sensing material, measurement platform and fabrication techniques are carried out to achieve excellent ammonia gas real-time detection. Capacitance parameters analysis for the gas sensing response of capacitive sensor is proceeded based on PPy, MoO3, and PPy/MoO3 hybrids at room temperature. The results show that the PPy/MoO3 hybrid material exhibits a sensitivity-enhanced response to ammonia. The PPy/MoO3 capacitive sensor has good linearity (R2=0.987), fast response, and good repeatability within 5-100 ppm ammonia concentration. Frequency parameters analysis for the gas sensing response of microwave resonator sensor is proceeded based on PPy/MoO3 hybrids in the range of 10 ppm to 100 ppm ammonia concentration at room temperature. The proposed microwave sensor has good linearity (R2=0.991), good repeatability with 8 MHz standard deviation, high stability with gas response variation less than 2%, and anti-humidity capacity. Among 100 ppm concentration of isopropanol, acetone, ethanol, methanol and ammonia, ammonia exhibits 97.5 MHz frequency shift, which proves high sensitivity and good step toward selectivity. Therefore, this work could be regarded as a promising candidate in ammonia sensing application based on microwave solution.