RESUMEN
For a long time, chemiresistive gas sensors based on metal oxide semiconductors (MOSs) suffer from higher operating temperatures, resulting in higher energy consumption and instability of the sensors. Generally, a MOS-based chemiresistive gas sensor being able to work at room temperature is considered to be outstanding already. Here, a highly sensitive NO2 gas sensor based on the carbon dots-WO3 heterostructure, which can work below room temperature at -6 °C, is fabricated. At 18, -1, and -6 °C, its detection limits are 200 ppb, 5 ppm, and 20 ppm, respectively, and the corresponding response values (Ra/Rg) are 1.11, 1.04, and 1.13, respectively. The sensor exhibits good selectivity, stability, and linearity between relative humidity and response values too. A peculiar response behavior was observed. Toward oxidizing gas NO2, the resistance of the sensor based mainly on n-type WO3 shows decrease behavior. Its peculiar response behavior and strong gas sensing ability at lower temperatures were elucidated theoretically using the results of first-principles calculations. The reduction of NO2 into NO by surface oxygen vacancies of WO3 and the following adsorption of NO on the surface of WO3 lead to electron transfer from NO to WO3, and the Fermi level shifts toward the conduction band, making the sensor exhibit the peculiar response behavior. The stronger adsorption capability of carbon dots toward NO2 and a synergistic effect of carbon dots and WO3 together make the sensor capable of working at lower temperatures and own higher sensitivity.
Asunto(s)
Carbono , Dióxido de Nitrógeno , Temperatura , Adsorción , Transporte de ElectrónRESUMEN
Asthma is a chronic disease characterized by recurrent attacks of breathlessness and wheezing, which vary in severity and frequency from person to person. H2S is considered as the biomarker of asthma. Here, an ultrasensitive chemiresistive H2S gas sensor based on a γ-Bi2MoO6-CuO heterostructure with a detection limit of 5 ppb has been fabricated. It can distinguish asthmatic patients from healthy people roughly by analyzing the exhaled breaths of 28 asthmatic patients and 28 healthy people, suggesting that the sensor can be used to assist physicians in the diagnosis of asthma. Pathologically, it is discovered by this sensor that with the relief of asthma, the concentration of H2S in one's exhaled breath gradually increases. This subtle concentration variation of H2S can be accurately detected, indicating that this sensor can be used in the asthma severity monitoring too. Physical models have been built by first-principles calculation to reveal the causes of the sensor's ultrasensitivity. The stable adsorption of H2S on the surface of CuO results in massive charge transferring and the appearance of the defect states, which play the major role in the ultrasensitivity of the sensor. Upon integrating this sensor with circuits, the cheap, smart, and portable H2S sensing device can be obtained, which can make asthmatic patients' access to this device easy and make the severity monitoring of asthma convenient, especially for children and the aged.