Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the exposure of high proportions of ZnO {0001} crystal facets for both these materials. The measured surface area of the flower-like and the grass, or platelet-like ZnO samples were 72.8 and 52.4 m²∙g⁻¹, respectively. Gas sensing results demonstrated that the porous, flower-like ZnO structures exhibited enhanced sensing performance towards NO₂ gas compared with either grass-like ZnO or commercially sourced ZnO nanoparticle samples. The porous, flower-like ZnO structures provided a high surface area which enhanced the ZnO gas sensor response. X-ray photoelectron spectroscopy characterization revealed that flower-like ZnO samples possessed a higher percentage of oxygen vacancies than the other ZnO sample-types, which also contributed to their excellent gas sensing performance.

In this work, 2D WS₂ nanosheets prepared by the exfoliation of WS₂ with Li-intercalation was combined with GO produced by the Hummer method for humidity sensing applications. The GO and WS₂ solutions were mixed with an equal concentration and coated on conductometric transducers. Sensing measurements towards humidity (0–80% RH) at room temperature revealed that the humidity response of hybrid was substantially higher by a factor of 3–9 depending on the RH value compared with those of GO and WS₂. Moreover, no cross sensitivity to common gaseous compounds was observed. Therefore, the GO/2D WS₂ composite is a highly promising humidity sensor.

Interest in nanowires of metal oxide oxides has been exponentially growing in the last years, due to the attracting potential of application in electronic, optical and sensor field. We have focused our attention on the sensing properties of semiconducting nanowires as conductometric and optical gas sensors. Single crystal tin dioxide nanostructures were synthesized to explore and study their capability in form of multi-nanowires sensors. The nanowires of SnO₂ have been used to produce a novel gas sensor based on Pt/oxide/SiC structure and operating as Schottky diode. For the first time, a reactive oxide layer in this device has been replaced by SnO₂ nanowires. Proposed sensor has maintained the advantageous properties of known SiC- based MOS devices, that can be employed for the monitoring of gases (hydrogen and hydrocarbons) emitted by industrial combustion processes.

In this work, we investigate the effect of HNO₃ anodizing solution concentration ranging from 1.5 to 3 M on H₂-sensing performance of 2D WO₃ nanostructures prepared by anodizing sputtered tungsten films. The thickness of WO₃ nanosheets was found to reduce while the crystallinity degraded with increasing HNO₃ concentration. However, the nanosheets anodized in 2 M HNO₃ exhibited the highest response of 43.4 to 1 vol % H₂, which was one order of magnitude larger than those fabricated with other concentrations at the optimal operating temperature of 350 °C. In addition, the optimal nanostructures displayed good H₂ selectivity against NO₂, CH₄, C₂H₂ and C₂H₅OH.

Hybrid SnS₂-SnO_2−x flaked nanostructures were obtained from 2D-SnS₂ flakes deposited as a thin sensing film onto a conductometric transducing platform and annealed in air. The formation of 2D-SnS₂/SnO_2−x mixed phases and the materials morphologies were investigated by in situ Micro-Raman spectroscopy and SEM-EDX analysis. As annealing temperature of the sensitive film increases, the response towards ammonia increases showing a maximum at 250 °C. This behavior can be explained on the basis of the morphological modification and the formation of mixed phases.

The sensor signal of tin disulfide (SnS₂), a two-dimensional (2D) group-IV dichalcogenide, deposited as a film on a conductometric transducer is investigated at 130 °C. The focus is on the detection of the total NO_x concentration. Therefore, the sensor response to NO and NO₂ at ppm- and sub-ppm level at low operating temperature is determined. The results show that the sensing device provides a high sensor signal to NO and NO₂ even at concentrations of only 390 ppb NO_x. Both nitrous components, NO and NO₂, yield the same signal, which offers the opportunity to sense the total concentration of NO_x.