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Abstract A gas sensor based on CuO has been fabricated to detect an ultra-trace H 2 S gas. The CuO samples were characterized by X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The SEM results revealed that CuO exhibited a "grapes" structure made of nanoparticles. Gas-sensing properties of the CuO sensor were also studied. The sensor showed outstanding selectivity and high sensitivity to H 2 S gas, and achieved a ppb level detection limit. In addition, the temperature and humidity was also found to be significantly influential on the sensitivity of the sensor. Graphical abstract Image 1 Highlights • The structure of CuO is "grapes" made of nanoparticles. • The sensor is ultra-highly sensitive to H 2 S with a detective limit lower than 0.1 ppb. • The sensor shows outstanding performance at room temperature. • The sensor shows good selectivity towards H 2 S because of the extraordinary adsorptive capability of CuO to H 2 S. [ABSTRACT FROM AUTHOR]

Pristine SiO 2 , TiO 2 and composite SiO 2 -TiO 2 films of 200 nm thick were coated on surface of quartz acoustic wave (SAW) sensors with sol-gel and spin coating technique. Their performance and mechanisms for sensing NH 3 were systematically investigated. Sensors made with the TiO 2 and SiO 2 -TiO 2 films showed positive frequency shifts, whereas SiO 2 film exhibits a negative frequency shift to NH 3 gas. it is believed that the negative frequency shift was mainly caused by the increase of NH 3 mass loading on the sensitive film while the positive frequency shift was associated to the condensation of the hydroxyl groups (-OH) on the film making the film stiffer and lighter, when exposed to NH 3 gas. It demonstrated that humidity played a significant factor on the sensing performance. Comparative studies exhibited that the sensor based on the composite SiO 2 -TiO 2 film had a much better sensitivity to NH 3 at a low concentration level (1 ppm) with a response of 2 KHz, and also showed fast response and recovery, excellent selectivity, stability and reproducibility. [ABSTRACT FROM AUTHOR]

H 2 S gas sensor based on α-Fe 2 O 3 nanoparticles was fabricated by post-thermal annealing of Fe 3 O 4 precursor which was synthesized using a facile hydrothermal route. The characteristic techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were adopted to characterize the chemical composition and microstructure of the obtained samples. Gas-sensing performance of the sensor was investigated at different operation temperatures from 100 °C to 400 °C. Results showed that the sensor exhibited the best sensitivity, reproducibility and long-term stability for detecting H 2 S gas at an operating temperature of 300 °C. The detection limit towards H 2 S gas was 0.05 ppm, and the response time and recovery time was 30 s and 5 s, respectively. In addition, sensing mechanism of the sensor towards H 2 S was discussed. [ABSTRACT FROM AUTHOR]