Design and Synthesis of Nanomaterials Based on Solution Process Techniques for High Performance NOGas Sensors


Student thesis: Doctoral Thesis

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Awarding Institution
Award date18 May 2021


Nitrogen dioxide (NO2) is a prominent air pollutant that is harmful to both the environment and human health. In the recent years, there has been a growing demand for real-time analysis of NO2 in air, especially with the rapidly increasing health and environmental concerns due to NO2 emission from the combustion of fossil fuels. The development of nanotechnology has created a huge potential for building highly sensitive, selective, low power, and portable gas sensors.

Solution-process techniques such as hydrothermal, liquid phase exfoliation, and sol-gel have been used for preparation of nanostructured materials. These methods have obvious advantages as they are facile, in many cases green, and low cost, which have been widely used for preparing gas sensing materials of various morphologies. Despite the remarkable progress made on NO2 gas sensor materials, there is plenty of room for the rational design and controllable synthesis of NO2 gas sensor materials with better performance. In this thesis, the design and synthesis of high performance NO2 gas sensing materials based on solution process techniques are presented. In order to provide a theoretical basis for performance optimization, the NO2 gas sensing mechanism has also been explored in detail. Results suggest that large surface area, appropriate defect density, and formation of heterojunction are the main contributors to performance enhancement. The main contents of the dissertation can be summarized as follows:

In chapter two, a highly sensitive and selective NO2 sensor based on 3D molybdenum disulfide (MoS2)/reduced graphene oxide (rGO) composites were synthesized using self-assembly/hydrothermal method, enabling a significant reduction of MoS2 agglomeration. Gas sensing characterization confirmed highly sensitive and selective detection of NO2. Especially, the fabricated sensor showed a response of 2483 % toward 10 ppm of NO2 at 80 oC. The proposed NO2 sensor achieved an ultra-low detection limit of 27.9 ppb.

In chapter three, an ultra-sensitive and selective NO2 sensor based on black phosphorous (BP) nanosheets were synthesized by liquid-phase exfoliation. The unique combination of probe sonication and ice-water bath sonication can produce BP nanosheets of various controllable sizes. NO2 sensing characterization shows the drop casted BP nanosheet based sensor exhibits a large sensing response of 88%, a high selectivity, a full recovery towards 100 ppb NO2 gas at room temperature, which represent a substantial improvement over reported prototype.

In chapter four, an ultra-fast NO2 gas sensor is fabricated based on nanohybrid of SnS2 and MXene derived TiO2 synthesized by hydrothermal. The 2D structure of MXene derived TiO2 provides a unique platform for SnS2 decoration. The specific surface area is significantly increased, contributing to enhanced gas sensing properties. Under room temperature operation, the fabricated nanohybrid based sensor exhibits a large response of 115 toward 1000 ppm NO2 gas and an ultra-fast recovery of 10 s.

In chapter five, conclusion and comments on future work are given.