Abstract
We prepared 0.1 wt%–30 wt% Pd-loaded Co3O4 by a colloidal mixing method and investigated the sensing properties of a Pd-loaded Co3O4 sensor element, such as the sensor response, 90% response time, 90% recovery time, and signal-to-noise (S/N) ratio, toward low nitric oxide (NO) gas levels in the range from 50 to 200 parts per billion. The structural properties of the Pd-loaded Co3O4 powder were investigated using X-ray diffraction analysis and transmission electron microscopy. Pd in the powder existed as PdO. The sensor elements with 0.1 wt%–10 wt% Pd content have higher sensor properties than those without any Pd content. The response of the sensor element with a 30 wt% Pd content decreased markedly because of the aggregation and poor dispersibility of the PdO particles. High sensor response and S/N ratio toward the NO gas were achieved when a sensor element with 10 wt% Pd content was used.
Highlights
Human breath contains many main gases such as N2, CO2, O2 and minor gases such as inflammable gases (CO, CH4, and H2), and volatile organic compounds (VOCs) [1,2,3,4,5]
We have reported the nitric oxide (NO) and NO2 sensing (0.5–5 ppm in air) properties of a p-type Co3O4 gas sensor [13]
The obtained sample powders were characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM)
Summary
Human breath contains many main gases such as N2, CO2, O2 and minor gases such as inflammable gases (CO, CH4, and H2), and volatile organic compounds (VOCs) [1,2,3,4,5]. Some biomarker gases in human breath are present at very low concentrations in the range from several parts per billion (ppb) to parts per million (ppm). The Co3O4-based gas sensor showed a low sensor response, even at 0.5 ppm NO and could not accurately detect NO concentrations in several hundred ppb. Pd-loaded Co3O4 was prepared by a colloidal mixing method [17] to improve the gas-sensing properties, and the sensor response, response time, recovery time, and signal-to-noise (S/N) ratio toward low NO concentration were investigated. To study the possibility of breath analysis using a 10 wt% Pd-loaded Co3O4 sensor, the sensor responses to 25 and 100 ppm H2 in air were investigated as an initial evaluation
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