Enhanced acetone detection performance of mechanically-mixed WO3:ZnO composites

Abstract

In recent years, the potential use of mixed metal oxide WO3:ZnO is widely sought in photocatalytic application due to its excellent electrical and optical properties, but is less explored for chemiresistive sensor. The heterojunction effect in WO3:ZnO is of particular interest to eradicate common issues suffered by the pristine metal oxide sensors, such as limited sensitivity, poor selectivity, and high operating temperature. In addition, the acetone detection study based on heterostructured WO3:ZnO is quite limited. Herein, we demonstrate that the mechanically-mixed WO3:ZnO sensor exhibits comparable reducing gas sensing performance as other doped WO3:ZnO and relative improvement compared with the undoped composites, without the need of catalyst. In this work, WO3:ZnO thin-film based chemiresistive sensors were fabricated through straightforward methods comprising mechanical mixing and drop casting of sensor materials onto gold interdigitated alumina substrates. Structural and morphological properties of the prepared WO3, ZnO, and WO3:ZnO composites were examined through the X-ray diffraction (XRD), Raman spectroscopy, photoluminescence spectroscopy (PL), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX) analyses, respectively. Sensor performance parameters including operating temperature and response were determined. The sensing properties of WO3:ZnO composites with different weight compositions (1:1, 1:2, and 1:3) were evaluated against the pristine ZnO and WO3. The weight ratio of 1:2 was the optimal composition for the WO3:ZnO composite to achieve the highest sensor response of 53.8 % towards 300 ppm acetone at 200 ºC compared to the pristine ZnO with a response of 23.5 %. The WO3:ZnO (1:2) thin film displayed granular morphology with uniform particle dispersion and porosity, enhancing the gas diffusion. The WO3:ZnO (1:2) thin-film composite sensor exhibited improved sensing performance and good repeatability towards acetone compared with that of ZnO and WO3. The enhanced response to acetone was possibly contributed by the development of n-n heterojunctions, porous morphology, and surface defects in the WO3:ZnO composite. The underlying sensing mechanism of WO3:ZnO composite is also discussed extensively with the aid of energy band diagrams. This study presents a foundation for future development of cost-effective acetone sensors through mechanical mixing with great potential for practical and scalable implementation in various industries.