NO2 sensing properties of WO3-decorated In2O3 nanorods and In2O3-decorated WO3 nanorods

Bumhee Nam,Tae-Kyoung Ko,Soong-Keun Hyun,Chongmu Lee

doi:10.1186/s40580-019-0205-2

Abstract

In2O3 nanoparticle (NP)-decorated WO3 nanorods (NRs) were prepared using sol–gel and hydrothermal methods. The In2O3 NRs and WO3 NPs were crystalline. WO3 NP-decorated In2O3 NRs were also prepared using thermal evaporation and hydrothermal methods. The NO2 sensing performance of the In2O3 NP-decorated WO3 NR sensor toward NO2 was compared to that of the WO3 NP-decorated In2O3 NR sensor. The former showed a high response to NO2 due to a significant reduction of the conduction channel width upon exposure to NO2. In contrast, the latter showed a far less pronounced response due to limited reduction of the conduction channel width upon exposure to NO2. When the sensors were exposed to a reducing gas instead of an oxidizing gas (NO2), the situation was reversed, i.e., the WO3 NP-decorated In2O3 NR exhibited a stronger response to the reducing gas than the In2O3 NP-decorated WO3 NR sensor. Thus, a semiconducting metal oxide (SMO) with a smaller work function must be used as the decorating material in decorated heterostructured SMO sensors for detection of oxidizing gases. The In2O3 NP-decorated WO3 NR sensor showed higher selectivity for NO2 compared to other gases, including reducing gases and other oxidizing gases, as well as showed high sensitivity to NO2.

Highlights

Despite the numerous merits of semiconducting metal oxides (SMOs) as sensor materials there are still certain limitations, such as their relatively low response to gases at room temperature and dissatisfactory selectivity [1]
The scanning electron microscopy (SEM) images of the pristine and WO3 NP-decorated In2O3 NRs are exhibited in Fig. 1c, d
The In2O3-decorated WO3 nanorod sensor fabricated in this study showed higher response to N O2 than other gases at 300 °C because of the higher dissociation rate of N O2 at the surface of In2O3 and WO3 at the temperature, but it might show higher responses to other gases than N O2 at different temperatures [17,18,19,20,21,22]

Summary

Introduction

Despite the numerous merits of semiconducting metal oxides (SMOs) as sensor materials there are still certain limitations, such as their relatively low response to gases at room temperature and dissatisfactory selectivity [1]. To address the dissatisfactory sensing properties, various strategies have been attempted, including noble metal catalyst doping, heterojunction formation, and radiationassisted treatment with energetic particles including ion beams, electrons, and ultraviolet (UV) lights [2,3,4]. Of these techniques, heterostructure formation is plausibly most widely studied and is used for the fabrication of chemiresistive nanostructured gas sensors. This study focuses on, decorated n–n heterostructures. Nam et al Nano Convergence (2019) 6:40 of In2O3 NP-decorated WO3 nanorods (NRs), W O3 NPdecorated In2O3 NRs, pristine WO3 NRs, and pristine In2O3 NRs are compared and the differences in the sensing properties of these four nanostructures are analyzed and the origin of the differences is discussed in detail

Methods

Results

Conclusion