Zhu, Yiyun; (2021) Aerosol-Assisted Chemical Vapour Deposition (AACVD) of Silver Nanoparticle Decorated Tungsten Oxide Nanoneedle for Use in Oxygen Gas Sensing. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Semiconducting metal oxides (SMOX) gas sensors, such as tungsten oxide (WO3), have been developed in depth for use in toxic gas detection, such as nitrogen oxides (NOx). With the addition of catalytic nanoparticles, like Ag, Pt, Pd and etc., the sensing properties, the three ‘S’ (sensitivity, selectivity and stability), can be significantly improved. This thesis details a two-step synthesis method for the fabrication of Ag nanoparticle decorated WO3 nanoneedle by using different silver metal precursors, including silver nitrate (AgNO3), silver 2-aminoethanol (Ag-EA), silver 1-aminopropan-2-ol (Ag-AP) and silver 2-methyl-2-aminopropan-1-ol (Ag-AMP), in a vapour deposition process. A series of experiments were conducted to investigate the parameters that affect the growth of the materials microstructure including deposition temperature, deposition time, flow rate of N2 carrier gas and concentration of precursor solution. Physical property characterization techniques including UV/Vis, XRD, XPS, SEM and TEM, have been systematically applied for all WO3 and Ag-decorated WO3 samples and sensor materials. Oxygen sensors’ have been considered as the critical component of Engine Management System for several decades. Gas sensing performance was carried out toward different O2 concentration between 1 and 20% at various operating temperatures. The sensing response revealed that the decoration of Ag nanoparticle on WO3 sensors significantly improved sensing properties as compared to undecorated WO3 sensors. An optimal gas response with silver-decorated WO3 is enhanced 400% compared to an undecorated WO3 sensor at an optimum operating temperature at 350 °C towards 20% oxygen at a relative humidity level ~ 85% by using AgNO3 as a precursor. An enhancement was also observed for the Ag decorated WO3 sensors fabricated using organometallic silver precursors, with a dramatically increasing in baseline resistance for these Ag@WO3 sensors. Sensing mechanisms, are proposed to explain the enhancement in sensing response.

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