Semiconductor-type SnO2-based NO2 sensors operated at room temperature under UV-light irradiation

Abstract

NO2-sensing properties of typical oxide (SnO2, In2O3, or WO3)-based semiconductor gas sensors were measured at 30°C with and without UV-light irradiation (main wavelength: 365 nm), and effects of noble-metal (Pd or Pt) loading, UV-light intensity (0-134 mW cm −2) and relative humidity in target gas (0-80%RH) on their NO2-sensing properties were investigated in this study. The UV-light irradiation effectively reduced the resistances of all sensors, enhanced their NO2 responses in some cases, and tended to accelerate their response and recovery speeds in dry air, because the UV-light irradiation promoted the adsorption and desorption of NO2-species on the surface. The SnO2 sensor showed the largest NO2 response in dry air, among all the pristine oxide sensors, especially under weak UV-light irradiation (≤ 35 mW cm −2), together with relatively fast response and recovery speeds. The Pd or Pt loading onto SnO2 enhanced the NO2 response of the SnO2 sensor and accelerated their response and recovery speeds in dry air, while XPS analysis indicated that most of the Pd and Pt nanoparticles loaded on the surface were oxidized after heat treatment at 500°C. Among all the sensors, the 0.05 wt% Pd-loaded SnO2 sensor showed the largest NO2 response under weak UV-light irradiation (≤ 35 mW cm −2), together with relatively fast response and recovery speeds. The addition of moisture to the target gas had adverse effects on the NO2 responses and the response speeds of the SnO2 and 0.05 wt% Pd-loaded SnO2 sensors, but the weak UV-light irradiation (7 mW cm −2) largely reduced the dependence of the NO2 response of the 0.05Pd/SnO2 sensor on relative humidity while maintaining the large NO2 response, probably because the weak UVlight irradiation promotes the desorption of physisorbed water molecules and then the effective adsorption of NO2 on the 0.05Pd/SnO2 surface.

Designing SnO2 Nanostructure-Based Sensors with Tailored Selectivity toward Propanol and Ethanol Vapors

“…13−18 An additional second constituent that acts as the energetic material enhances the degree of the redox reaction with the target gases. Hyodo et al 14 reported the gas sensing characteristics of Pd-doped SnO 2 at room temperature for NO 2 under UV light. For a UV light of 7 mW cm –2 , 0.05Pd-doped SnO 2 exhibited an enhanced response toward the gas.…”

Room‐Temperature NO2 Gas Sensing with Ultra‐Sensitivity Activated by Ultraviolet Light Based on SnO2 Monolayer Array Film

“…Generally, thermal‐activated and ultraviolet (UV)‐light driven gas sensors stand for two complementary chemiresistive‐type gas sensing technologies . Even though the thermal‐driven type provided high sensitivity with a rapid response/recovery speed, it would suffer from high operating temperature .…”

Light-Activated Sub-ppm NO2 Detection by Hybrid ZnO/QD Nanomaterials vs. Charge Localization in Core-Shell QD

“…To reduce the power consumption of metal oxide gas sensors, the effective strategies, mainly include surface modification, additive doping and light activation (Wang et al, 2017;Xu and Ho, 2017;Zhu and Zeng, 2017). Most of the publications dealing with the gas sensor properties of semiconductor materials under illumination discussed the effects observed under UV light (Saura, 1994;Mishra et al, 2004;Malagu et al, 2005;De Lacy Costello et al, 2008;Peng et al, 2008Peng et al, , 2009Prades et al, 2009a,b;Carotta et al, 2011;Wang et al, 2011;Cui et al, 2013;Wagner et al, 2013;Klaus et al, 2015;Ilin et al, 2016;Nakate et al, 2016;Saboor et al, 2016;Trawka et al, 2016;Wongrat et al, 2016;Da Silva et al, 2017;Espid and Taghipour, 2017;Hsu et al, 2017;Hyodo et al, 2017;Wu et al, 2018). UV radiation with an energy exceeding the width of the band gap generates electron-hole pairs and thus increases conductivity.…”