WS2 Gas Sensor Based on Photothermocatalytic Effect for Ammonia Detection With High Response

In this article, four different light sources are utilized to enhance the WS2-based gas sensors properties, and the improvement effects of different light sources on the sensitive characteristics of the sensors are systematically analyzed. First, the WS2 nanomaterials are synthesized by hydrothermal method. In addition, the nanostructures and morphologies are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Finally, the effect of different temperatures and different ammonia concentrations on the sensor response is examined, including darkness, various light illumination (365, 532, 650, and 980 nm). Under dark conditions, the sensor response time is 46 s and recovery time is 55 s in 100-ppm ammonia gas, while the sensor has excellent selectivity for ammonia with a response of up to 81.84 times and only weak response for other gases. The results reveal that the four types of light are capable of reducing the operating temperature where the response value reach the peak. Meanwhile, the maximum response value is effectively increased, from a maximum value of 27 in the dark to a maximum value of 57 under light illumination. The 650-nm light illumination and the 980-nm light illumination exhibit the best effect on improving the response value. Therefore the 180 °C measured by the sensor response curve under 650-nm light conditions is defined as the optimal temperature. At the same time, light illumination can degrade the detection limit of the sensor. Under dark conditions, the ammonia detection limit of the sensor is 100 ppm, while under light illumination conditions, the ammonia detection limit of the sensor is 20 ppm.