Lead sulphide colloidal quantum dots for room temperature NO2 gas sensors

Abstract

colloidal quantum dots (cQDs) have been recently investigated as promising building blocks for low-cost and high-performance gas sensors due to their large effective surface-to-volume ratio and their suitability for versatile functionalization through surface chemistry. in this work we report on lead sulphide cQDs based sensors for room temperature no 2 detection. the sensor response has been measured for different pollutant gases including NO 2 , cH 4 , co and co 2 and for different concentrations in the 2.8-100 ppm range. For the first time, the influence of the QDs film thickness on the sensor response has been investigated and optimized. Upon 30 ppm NO 2 release, the best room temperature gas response is about 14 Ω/Ω, with response and recovery time of 12 s and 26 min, respectively. A detection limit of about 0.15 ppb was estimated from the slope of the sensor response and its electric noise. the gas sensors exhibit high sensitivity to no 2 , remarkable selectivity, repeatability and full recovery after exposure. Nitrogen dioxide (NO 2) is an important air pollutant since it contributes to the formation of the photochemical smog, the acid rains and it is also central to the formation of fine particles (PM) as well as affecting tropospheric ozone 1,2. Besides natural sources (volcanoes, oceans, biological decay, forest fires), a significant amount of NO 2 results from human activities such as combustion of fossil fuels welding, explosives, refining of petrol and metals, commercial manufacturing, and food manufacturing 3. These activities can generate high local concentration of NO 2 that produces significant impacts on human health, especially breathing problems since NO 2 inflames the lining of the lungs thus reducing immunity to lung infections 4,5. Therefore, reliable detection of NO 2 , even at low concentration, is critical in many different sectors such as industrial plants, indoor and outdoor air quality assurance, automotive and so on, and it is an enabling technology for automatic systems capable of taking necessary measures to reduce unsafe concentrations through ventilation, filtering or catalytic breakdown 6. At present, accurate measurement of air quality is possible only by means of large monitoring equipment or laboratory instruments, unsuitable for pervasive monitoring purposes. Alternative low-cost, small-size, ultralow-power gas sensor platforms have been developed during the last two decades, mainly in the form of components for experimental sensor networks, with promising superior performance in terms of sensitivity, selectivity, minimal drift, fast time response, compactness and low energy consumption 7,8. In particular, systems that meet the following characteristics would be of great interest: miniaturization and compatibility with the development of sensor arrays integration with temperature and humidity sensors, simple production techniques and process transferability towards innovative printing techniques. Today, commercially available gas sensors are mainly based on nanostructured me...

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