Die chemische Rezeption und den elektronischen Transduktionsmechanismus während der Gasdetektion mit kolloidalen Sulfid-Quantenpunkten verstehen
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
For the first time, the sensing characteristics of different metal sulfide nanoparticles were investigated in-operando in the presence of different target gases. It was found that all of the investigated sulfide materials reacted selectively to the oxidizing gases NO2 and (in the case of Bi2S3) O3. It was determined that the sensing mechanism varied from metal sulfide to metal sulfide. For the investigated PbS CQDs, the determined sensing mechanism involved a residual organic ligand from the synthesis process. Oleic acid was the key player in both the aging mechanism and the enhanced sensor response. It was found that oleic acid reacted with NO2 under formation of nonanoic acid and azelaic acid which resulted in an increase in resistance due to the formation of an insulating shell around the CQDs. At the same time, the reaction of oleic acid with NO2 resulted in the production of HNO2 which was responsible for the observed sensor signal in the beginning of the experiments. The further the experiment progressed, the smaller the response was because oleic acid irreversibly reacted with NO2 and less HNO2 was formed. With Bi2S3, the situation was different. Even though an organic ligand was introduced during the synthesis, it did not play a role in the sensing mechanism. The inherent better stability of Bi 2S3 over PbS was also observed for the gas sensors that were investigated. While PbS showed severe and rapid aging when exposed to NO2, Bi2S3 showed a relatively stable sensing behavior over the course of more than 40 days. When the conduction mechanism of Bi2S3 was investigated, it was found that the sensing mechanism was not as straight forward as was initially expected. It was observed that the sensing mechanism changed in dependence of the concentration the sensor was exposed to. For low concentrations, the sulfur vacancies on the defective surface of Bi2S3 played the key role. This changed with higher concentrations where the formation of nitrates became the dominant reaction, both in reception and transduction. The third investigated material was SnS2 and again, the sensing mechanism was found to be influenced by yet another factor, namely the temperature. At room temperature, the resistance increased slightly with O2, but decreased with NO2. At 80 °C, the resistance increased with both O2 and NO2 which was the expected behavior. The reason behind the switch in behavior is not clear as of now. First experiments indicated an electronic effect instead of a change in reaction mechanism. However, additional experiments need to be conducted in order to fully understand the temperature dependent mechanism.
Projektbezogene Publikationen (Auswahl)
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Operando Investigation of the Aging Mechanism of Lead Sulfide Colloidal Quantum Dots in an Oxidizing Background. The Journal of Physical Chemistry C, 125(36), 19847-19857.
Russ, Tamara; Hu, Zhixiang; Junker, Benjamin; Liu, Huan; Weimar, Udo & Barsan, Nicolae
