MXenes,
two-dimensional transition metal carbides or nitrides,
have recently shown great promise for gas sensing applications. We
demonstrate that the sensitivity of intrinsically metallic Ti3C2T
x
MXene can be considerably
improved via its partial oxidation in air at 350 °C. The annealed
films of MXene sheets remain electrically conductive, while their
decoration with semiconducting TiO2 considerably improves
their chemiresistive response to organic analytes at low-ppm concentrations
in dry air, which was used to emulate practical sensing environments.
We demonstrate that partially oxidized MXene has a faster and a qualitatively
different sensor response to volatile analytes compared to pristine
Ti3C2T
x
. We fabricated
multisensor arrays of partially oxidized Ti3C2T
x
MXene devices and demonstrate that
in addition to their high sensitivity they enable a selective recognition
of analytes of nearly the same chemical nature, such as low molecular
weight alcohols. We investigated the oxidation behavior of Ti3C2T
x
in air in a wide
temperature range and discuss the mechanism of sensor response of
partially oxidized MXene films, which is qualitatively different from
that of pristine Ti3C2T
x
.
Reliable environmental monitoring requires cost effective but highly sensitive and selective gas sensors. While the sensitivity of the sensors is improved by reducing the characteristic dimensions of the gas-sensing material, the selectivity is often approached by combining the sensors into multisensor arrays. The development of scalable methods to manufacture such arrays based on low-dimensional structures offers new perspectives for gas sensing applications. Here we examine an approach to produce multisensor array chips based on the TiOx nanotube layers segmented by multiple Pt strip electrodes. We study the sensitivity and selectivity of the developed chip at operating temperatures up to 400 °C towards organic vapors in the ppm range. The results indicate that the titania nanotubes are a promising material platform for novel cost-effective and powerful gas-analytical multisensor units.
Bottom-up synthesized quasi-2D Co3O4 nanoflakes demonstrate a remarkable chemiresistive response towards chemically akin alcohol vapors in a mixture with air.
Information
about the surrounding atmosphere at a real timescale
significantly relies on available gas sensors to be efficiently combined
into multisensor arrays as electronic olfaction units. However, the
array’s performance is challenged by the ability to provide
orthogonal responses from the employed sensors at a reasonable cost.
This issue becomes more demanded when the arrays are designed under
an on-chip paradigm to meet a number of emerging calls either in the
internet-of-things industry or in situ noninvasive diagnostics of
human breath, to name a few, for small-sized low-powered detectors.
The recent advances in additive manufacturing provide a solid top-down
background to develop such chip-based gas-analytical systems under
low-cost technology protocols. Here, we employ hydrolytically active
heteroligand complexes of metals as ink components for microplotter
patterning a multioxide combinatorial library of chemiresistive type
at a single chip equipped with multiple electrodes. To primarily test
the performance of such a multisensor array, various semiconducting
oxides of the p- and n-conductance
origins based on pristine and mixed nanocrystalline MnO
x
, TiO2, ZrO2, CeO2, ZnO, Cr2O3, Co3O4,
and SnO2 thin films, of up to 70 nm thick, have been printed
over hundred μm areas and their micronanostructure and fabrication
conditions are thoroughly assessed. The developed multioxide library
is shown to deliver at a range of operating temperatures, up to 400
°C, highly sensitive and highly selective vector signals to different,
but chemically akin, alcohol vapors (methanol, ethanol, isopropanol,
and n-butanol) as examples at low ppm concentrations
when mixed with air. The suggested approach provides us a promising
way to achieve cost-effective and well-performed electronic olfaction
devices matured from the diverse chemiresistive responses of the printed
nanocrystalline oxides.
We discuss the fabrication of gas-analytical multisensor arrays based on ZnO nanorods grown via a hydrothermal route directly on a multielectrode chip. The protocol to deposit the nanorods over the chip includes the primary formation of ZnO nano-clusters over the surface and secondly the oxide hydrothermal growth in a solution that facilitates the appearance of ZnO nanorods in the high aspect ratio which comprise a network. We have tested the proof-of-concept prototype of the ZnO nanorod network-based chip heated up to 400 °C versus three alcohol vapors, ethanol, isopropanol and butanol, at approx. 0.2–5 ppm concentrations when mixed with dry air. The results indicate that the developed chip is highly sensitive to these analytes with a detection limit down to the sub-ppm range. Due to the pristine differences in ZnO nanorod network density the chip yields a vector signal which enables the discrimination of various alcohols at a reasonable degree via processing by linear discriminant analysis even at a sub-ppm concentration range suitable for practical applications.
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