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 ∼ 25 % / 75 %. WO₃ samples are functionalized with a nominal thickness of 10 nm Ag layer (∼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.