No abstract

The high demand for H2 gas sensors is not just limited to industrial process control and leak detection applications but also extends to the food and medical industry to determine the presence of various types of bacteria or underlying medical conditions. For instance, sensing of H2 at low concentrations (<10 ppm) is essential for developing breath analyzers for the noninvasive diagnosis of some gastrointestinal diseases. However, there are major challenges to overcome in order to achieve high sensitivity and hence low limit of detection (LoD) toward H2. In this study, it is demonstrated that light-assisted amperometric gas sensors employing sensitive layers based on Pd-decorated TiO2 long-range ordered crystals can achieve excellent H2 sensing performance. This unique combination of materials and novel layered structure enables the detection of H2 gas down to 50 ppm with highly promising LoD capabilities. The sensor response profiles revealed that the sensor’s signal-to-noise ratio was higher in the presence of light when operated with a 9 V bias (relative to other conditions used), producing a LoD of only 3.5 ppm at an operating temperature of 33 °C. The high performance of the sensor makes it attractive for applications that require low-level (ppm as opposed to conventional % levels) H2 gas detection. Most importantly, the developed sensor exhibited high selectivity (>93%) toward H2 over other gas species such as CO2, C4H8O, C3H6O, CH3CHO, and NO, which are commonly found to coexist in the environment.

In this report, the gas sensing performance of zinc titanate (ZnTiO3) nanoarrays (NAs) synthesized by coating hydrothermally formed zinc oxide (ZnO) NAs with TiO2 using low-temperature chemical vapor deposition is presented. By controlling the annealing temperature, diffusion of ZnO into TiO2 forms a mixed oxide of ZnTiO3 NAs. The uniformity and the electrical properties of ZnTiO3 NAs made them ideal for light-activated acetone gas sensing applications for which such materials are not well studied. The acetone sensing performance of the ZnTiO3 NAs is tested by biasing the sensor with voltages from 0.1 to 9 V dc in an amperometric mode. An increase in the applied bias was found to increase the sensitivity of the device toward acetone under photoinduced and nonphotoinduced (dark) conditions. When illuminated with 365 nm UV light, the sensitivity was observed to increase by 3.4 times toward 12.5 ppm acetone at 350 °C with an applied bias of 9 V, as compared to dark conditions. The sensor was also observed to have significantly reduced the adsorption time, desorption time, and limit of detection (LoD) when excited by the light source. For example, LoD of the sensor in the dark and under UV light at 350 °C with a 9 V bias is found to be 80 and 10 ppb, respectively. The described approach also enabled acetone sensing at an operating temperature down to 45 °C with a repeatability of >99% and a LoD of 90 ppb when operated under light, thus indicating that the ZnTiO3 NAs are a promising material for low concentration acetone gas sensing applications.

Porous WO3 nanofibers have been synthesized by electrospinning polyvinylpyrrolidone (PVP) nanofibers embedded with semiconducting WO3 nanoparticles followed by annealing in air and have been tested toward acetone.