Pure
and 3–12 at. % Pr-doped In2O3 macroporous
spheres were fabricated by ultrasonic spray pyrolysis and their acetone-sensing
characteristics under dry and humid conditions were investigated to
design humidity-independent gas sensors. The 12 at. % Pr-doped In2O3 sensor exhibited approximately the same acetone
responses and sensor resistances at 450 °C regardless of the
humidity variation, whereas the pure In2O3 exhibited
significant deterioration in gas-sensing characteristics upon the
change in the atmosphere, from dry to humid (relative humidity: 80%).
Moreover, the 12 at. % Pr-doped In2O3 sensor
exhibited a high response to acetone with negligible cross responses
to interfering gases (NH3, CO, benzene, toluene, NO2, and H2) under the highly humid atmosphere. The
mechanism for the humidity-immune gas-sensing characteristics was
investigated by X-ray photoelectron and diffuse reflectance infrared
Fourier transform spectroscopies together with the phenomenological
gas-sensing results and discussed in relation with Pr3+/Pr4+ redox pairs, regenerative oxygen adsorption, and
scavenging of hydroxyl groups.
The chemiresistive sensing characteristics of metal oxide gas sensors depend closely on ambient humidity. Herein, we report that gas sensors using Tb-doped SnO yolk-shell spheres can be used for reliable acetone detection, regardless of the variations in humidity. Pure SnO and Tb-doped SnO yolk-shell spheres were prepared via ultrasonic spray pyrolysis and their chemiresistive sensing characteristics were studied. The sensor resistance and gas response of the pure SnO yolk-shell spheres significantly changed and deteriorated upon exposure to moisture. In stark contrast, the Tb-doped SnO yolk-shell spheres exhibited similar gas responses and sensor resistances in both dry and humid [relative humidity (RH) 80%] atmospheres. In addition, the Tb-doped SnO yolk-shell sensors showed a high gas response (resistance ratio) of 1.21 to the sub-ppm-levels (50 ppb) of acetone with low responses to the other interference gases. The effects of Tb oxide and the chemical interactions among the Tb oxide, SnO, and water vapor on this humidity-independent gas sensing behavior of the Tb-doped SnO yolk-shell sensors were investigated. This strategy can provide a new road to achieve highly sensitive, selective, and humidity-independent sensing of acetone, which will facilitate miniaturized and real-time exhaled breath analysis for diagnosing diabetes.
Metal–organic
frameworks (MOFs) with high surface area,
tunable porosity, and diverse structures are promising platforms for
chemiresistors; however, they often exhibit low sensitivity, poor
selectivity, and irreversibility in gas sensing, hindering their practical
applications. Herein, we report that hybrids of Cu
3
(HHTP)
2
(HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) nanoflakes
and Fe
2
O
3
nanoparticles exhibit highly sensitive,
selective, and reversible detection of NO
2
at 20 °C.
The key parameters to determine their response, selectivity, and recovery
are discussed in terms of the size of the Cu
3
(HHTP)
2
nanoflakes, the interaction between the MOFs and NO
2
, and an increase in the concentration and lifetime of holes facilitated
by visible-light photoactivation and charge-separating energy band
alignment of the hybrids. These photoactivated MOF–oxide hybrids
suggest a new strategy for designing high-performance MOF-based gas
sensors.
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