Tin Oxide Based Nanomaterials for Gas/VOC Sensing

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Gupta, Ritu
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Indian Institute of Technology Jodhpur
Extensive usage of toxic, flammable, and explosive Volatile Organic Compounds (VOCs)/ gases in industry induces tremendous environmental pollution leading to a threat to living organisms. Therefore, there is a requirement for continuous monitoring of VOCs/gases using cost-effective, highly selective, sensitive, environmentally stable sensors. So, our work focuses on different approaches to modify the SnO2 for developing low-temperature operable humidity tolerant VOCs/gases sensors. NO2, the most common toxic gas, induces various respiratory diseases even for short-term exposure at a low concentration of 5 ppm. Thus SnO2-rGO is synthesized at optimized conditions by the solvothermal method. In the SnO2-rGO nanohybrid device identified through a combinatorial approach, optimum morphology and structure along with the intrinsic Sn-C bond exhibited a significant response of ~3 to a low concentration of 80 ppm NO2 at room temperature operation and fluctuating humidity (20-50% RH) at much faster speeds ~5.6 s and recovered quickly in 14.1 s without heating. Xylene, one of the components of cigarette smoke, is a major contributor to indoor pollution and induces various respiratory diseases. We synthesized Sn-SnO2 as a sensing material with unique mesoporous nano-spherical morphology, providing a high specific surface area for Volatile Organic Compounds (VOCs)/gases adsorption. The sensor exhibits a repeatable response of 255% at 60 ppm xylene at room temperature with unprecedented ultrafast response and recovery time of 1.5 s and 40 s, respectively. The concentration of NH3 in the exhaled breath of healthy persons is about 0.4–1.8 ppm, while that in end-stage renal disease patients is around 0.8–14.7 ppm. Hence, disease state monitoring and environmental exposure assessment applications demand highly sensitive, faster, and more selective NH3 sensors that can operate under various environmental conditions. In our study, we synthesized SnO2 nanosheets using a solvothermal method and carefully optimized the pH conditions of the precursor solution for tuning the size, crystallinity, and thickness. The sensors fabricated using these samples exhibited a selective response to ammonia at 25 ºC and relative humidity (RH) of 70%. The pH 14 device demonstrated the highest sensitivity to ammonia (150% at 100 ppm) with fast response (8 s) and recovery kinetics (55 s). A theoretical LOD of 64 ppt implies superior sensitivity to all previously reported SnO2-based chemiresistive sensors. Triethylamine becomes explosive at concentrations above 10 ppm in the air and can induce headaches and difficulty breathing as well. The optimized substitutional fluorine doping in SnO2 film results in high conductivity, hydrophobicity, transparency, reduction in oxygen defects, and excellent electrochemical stability. Consequently, the fabricated F-SnO2 sensor showed a humidity-resistant nature with the highest response of 52% towards triethylamine at a relatively low operating temperature. Thus, the gas and VOC sensors developed in this work can be deployed for real-time sensing after miniaturization and integration with the AIoT platform.
Mohit. (2023).Tin Oxide Based Nanomaterials for Gas/VOC Sensing (Doctor's thesis). Indian Institute of Technology Jodhpur, Jodhpur.