Micro-hotplate gas sensor based on tungsten trioxide (WO3) nanoflakes for detecting chemical warfare agent simulants

Abstract

In this study, micro-hotplate chemiresistive gas sensors based on pristine, and silver (Ag) loaded tungsten trioxide (WO3) nanoflakes are developed and comparatively evaluated for detecting chemical warfare agent (CWA) simulants. WO3 nanoflakes are synthesized directly on a platinum (Pt) micro-hotplate platform via hydrothermal method. X-Ray diffraction (XRD) results show the orthorhombic phase of WO3. Scanning electron microscopy (SEM) analysis proves the dense nanoflake morphology of WO3, while Energy dispersive spectroscopy (EDS) analysis proves the formation of WO3 with atomic ratio of W/O similar to 25 % / 75 %. WO3 samples are functionalized with a nominal thickness of 10 nm Ag layer (similar to 2.5 % wt.) using RF magnetron sputtering. The fabricated sensors are tested against CWA simulants, including hydrogen cyanide (HCN), hydrogen sulfide (H2S), 2-chloroethyl ethyl sulfide (2-CEES), dimethyl methylphosphonate (DMMP), dipropylene glycol monomethyl ether (DPGME), and trimethyl phosphate (TMP). Ag loading enhances sensitivity and selectivity toward HCN, achieving a response of 27.70 at 1 ppm compared to 6.93 for pristine WO3, while the response time is observed as 112 s. The improved performance is attributed to specific interaction between HCN molecules and Ag sites on the WO3 surface, providing a distinct response mechanism. Compared to previous studies that have reported broad or non-specific responses toward toxic gases, this work demonstrates for the first time a sharp enhancement in HCN selectivity through Ag nanoparticle decoration, making it highly suitable as a targeted CWA detection. These results highlight the impact of Ag loading on gas selectivity, offering a strategic approach for designing WO3 based sensors tailored for specific gas detection applications and emphasizing its potential for real-time CWA detection.