14 research outputs found
ZnO@ZIF-8: Gas sensitive core-shell hetero-structures show reduced cross-sensitivity to humidity
A ‘lawn-like’ distribution of interconnected zinc oxide nanorods, coated with a metal-organic compound based on zeolitic imidazolate frameworks – ZIF-8 was prepared on microstructured thin-film interdigitated Pt-electrodes forming ZnO@ZIF-8 core-shell heterostructures and investigated as gas sensor material in relation to the identical, but uncovered pure ZnO-layer. This composite combines the gas sensing properties of the metal oxide ZnO with the specific properties of the metal-organic framework material which result in a distinct change of the conditions of gas sensing at the ZnO/ZIF-8-interface. Herein, for the first time it is reported that as prepared ZnO@ZIF-8 composite material is an attractive choice to reduce the cross-sensitivity to water vapour (humidity) in the gas sensing response towards propene and ethene. The observed change of sensitivity in relation to uncovered ZnO is discussed to be due to (i) the specific interaction of the ZIF-8 at the interface with the ZnO taking influence on the gas reaction processes, (ii) the diffusivity of ZIF-8 for the different gas components, and (iii) the sorption behaviour of the used gases at the ZnO interface and inside the ZIF-8 material
High-temperature CO / HC gas sensors to optimize firewood combustion in low-power fireplaces
In order to optimize firewood combustion in low-power firewood-fuelled fireplaces, a novel combustion airstream control concept based on
the signals of in situ sensors for combustion temperature, residual oxygen
concentration and residual un-combusted or partly combusted pyrolysis gas
components (CO and HC) has been introduced. A comparison of firing experiments
with
hand-driven and automated airstream-controlled furnaces of the same type
showed that the average CO emissions in the high-temperature phase of the batch
combustion can be reduced by about 80 % with the new control concept.
Further, the performance of different types of high-temperature CO / HC sensors
(mixed-potential and metal oxide types), with reference to simultaneous
exhaust gas analysis by a high-temperature FTIR analysis system, was
investigated over 20 batch firing experiments (∼ 80 h).
The distinctive sensing behaviour with respect to the characteristically varying flue
gas composition over a batch firing process is discussed. The calculation of
the
Pearson correlation coefficients reveals that mixed-potential sensor signals
correlate more with CO and CH4; however, different metal oxide sensitive layers correlate with different gas species:
1 % Pt / SnO2 designates the presence of CO and 2 % ZnO / SnO2 designates the presence of hydrocarbons. In the case of a TGS823 sensor
element,
there was no specific correlation with one of the flue gas components observed.
The stability of the sensor signals was evaluated through repeated exposure
to mixtures of
CO, N2 and synthetic air after certain numbers of firing
experiments and exhibited diverse long-term signal instabilities
In situ high-temperature gas sensors: continuous monitoring of the combustion quality of different wood combustion systems and optimization of combustion process
The sensing characteristics and long-term stability of different
kinds of CO ∕ HC gas sensors (non-Nernstian mixed potential type) during
in situ operation in flue gas from different types of low-power
combustion systems (wood-log- and wood-chip-fuelled) were investigated. The
sensors showed representative but individual sensing behaviour with respect to
characteristically varying flue gas composition over the combustion process.
The long-term sensor signal stability evaluated by repeated exposure to
CO ∕ H2 ∕ N2 ∕ synthetic air mixtures showed no sensitivity loss
after operation in the flue gas. Particularly for one of the sensors
(Heraeus GmbH), this high signal stability was observed in a field
test experiment even during continuous operation in the flue gas of the
wood-chip firing system over 4Â months. Furthermore, it was experimentally
shown that the signals of these CO ∕ HC sensing elements yield important
additional information about the wood combustion process. This was
demonstrated by the adaptation of an advanced combustion airstream control
algorithm on a wood-log-fed fireplace and by the development of a combustion
quality monitoring system for wood-chip-fed central heaters