Mesoporous SiO2 nanofibers were prepared by electrospinning dispersions of preformed SiO2 nanoparticles and infiltrated with soluble Cu compounds, forming CuO/SiO2 nanocomposites after heat treatment in ambient air. These composites were used as sensor material in H2S dosimeters, which is based on the formation of conductive CuS, allowing for the dosimetric detection of H2S via the significant increase in conductance. The use of CuO/SiO2 nanocomposites targeted the improvement of the morphological stability of CuO nanostructures during the H2S detection, being confined in a rigid nanoscopic scaffold. Also, we aimed at understanding the parameters determining the decrease in sensing performance commonly observed for CuO-based H2S sensors. As a main result, these CuO/SiO2 nanofibers can be used for gas sensing of H2S in a quasi-continuous and dosimetric detection mode for up to 130 cycles for a concentration of 5 ppm, which exceeds the performance of pure CuO materials. As a concentration of 5 ppm is regarded as a level above which H2S is considered to be harmful, the materials show potential for H2S sensors with long-term stability. The deterioration in the sensing properties is attributed to the irreversible formation of CuSO4. Building on these insights, our study indicates strategies to further improve CuO-based sensors for H2S.

Abstract.Copper oxides, such as CuO and Cu 2 O, are promising materials for H 2 S detection because of the reversible reaction with H 2 S to copper sulfides (CuS, Cu 2 S). Along with the phase change, the electrical conductance increases by several orders of magnitude. On CuO x films the H 2 S reaction causes the formation of statistically distributed Cu x S islands. Continuous exposition to H 2 S leads to island growth and eventually to the formation of an electrical highly conductive path traversing the entire system: the so-called percolation path. The associated CuO x / Cu x S conversion ratio is referred to as the percolation threshold. This pronounced threshold causes a gas concentration dependent switch-like behaviour of the film conductance. However, to utilize this effect for the preparation of CuO-based H 2 S sensors, a profound understanding of the operational and morphological parameters influencing the CuS path evolution is needed.Thus, this article is focused on basic features of H 2 S detection by copper oxide films and the influence of structural parameters on the percolation threshold and switching behaviour. In particular, two important factors, namely the stoichiometry of copper oxides (CuO, Cu 2 O and Cu 4 O 3 ) and surface morphology, are investigated in detail. CuO x thin films were synthesized by a radio frequency magnetron sputtering process which allows modification of these parameters. It could be shown that, for instance, the impact on the switching behaviour is dominated by morphology rather than stoichiometry of copper oxide.

TiO2 monoliths were synthesized by a partially hindered sol–gel process. Various synthesis parameters like precursor concentrations and gelation temperature were varied to investigate changes in the macroporosity (being in the range of micrometers) and to determine influences on the macropore formation mechanism. Ionic liquids (ILs) were used as templates to vary the mesopore size independently from the macropore size. Depending on the synthesis parameters, TiO2 monoliths with exclusive mesoporosity or with hierarchical meso-/macropore structure were received, and the range of macropores can be shifted between 100 nm and 10 μm without influencing the mesopore diameter. Pore volumes up to 880 mm3/g were achieved, as determined by mercury intrusion porosimetry. The mesopores’ diameter can be adjusted between 6 and 25 nm by adding different amounts of IL, and surface areas up to 260 m2/g and mesopore volumes of 0.5 cm3/g were obtained, based on N2-physisorption measurements. The monoliths were cladded by polymer, allowing for studying the flow-through properties depending on the macropore size. This precise control for tailored macropores enables the design of optimized TiO2 monoliths with respect to the desired application requirements.

Seit den 1. Oktober 2021 ist sie verbindlich umzusetzen: die Einstufung von Titandioxid‐Pulvern in der CLP‐Verordnung als Krebsverdachtsstoff (Karzinogen, Kategorie 2). Der Einstufungseintrag ist komplex und stellt sowohl Hersteller als auch Verarbeiter von Titandioxid vor neue Herausforderungen.