Novel gas sensor with dual response under CO(g) exposure: Optical and electrical stimuli

Abstract

In this work, a lanthanum (La) doped ceria (CeO 2) film, which depicted a dual gas sensing response (electric and optical) for CO (g) detection, was obtained by the microwave-assisted hydrothermal (HAM) synthesis and deposited by the screen-printing technique, in order to prevent deaths by intoxication with this life-threatening gas. An electric response under CO (g) exposure was obtained, along with an extremely fast optical response for a temperature of 380°C, associated with Ce þ 4 reduction and vacancy generation. A direct optical gap was found to be around 2.31 eV from UV-Vis results, which corresponds to a transition from valence band to 4f states. Due to the anomalous electron configuration of cerium atoms with 4f electrons in its reduced state, they are likely to present an electric conduction based on the small polaron theory with a hopping mechanism responsible for its dual sensing response with a complete reversible behaviour.

Synthesis and defect characterization of hybrid ceria nanostructures as a possible novel therapeutic material towards COVID-19 mitigation

“…2 . It is possible to observe that the CeO 2 crystals grow among the cellulose, with the ceria crystals forming nano-agglomerates throughout the cellulose surface due to their reduced size and strong Van der Waals interaction 34 ⁠. It is worth mentioning that the original micrographs without digital treatments are available in the Supplementary Information.…”

“…Figure 4 illustrates the UV–Vis spectrum of the as-prepared samples synthesized at 100 °C and 120 °C for 8 min by the MAH method. The optical band gap energy (E gap ) was calculated according to the method proposed by Kubelka and Munk, already described elsewhere 34 ⁠. This methodology is based on the transformation of diffuse reflectance measurements to estimate E gap values with good accuracy within the limits of assumptions when modeled in three dimensions 71 ⁠.…”

“…In terms of synthesis routes, several physical/chemical processes have been reported for the preparation of CeO 2 nanoparticles (NPs), such as sol–gel, precipitation, ball milling, hydrothermal decomposition, thermal decomposition, pyrolysis and hydrolysis among others 29 , 30 . Worth mentioning the simple and surfactant-free sonochemical pathway used to prepared pure and copper (Cu)-doped (4 and 40 wt%) CeO 2 nanostructures for hydrogen storage purposes, with the 4 wt% sample depicting a discharge capacity of 5070 mAh/g at 22nd cycle 31 ⁠, as well as the facile and eco-friendly route used to prepare Pr 2 Ce 2 O 7 nanostructures from banana extract 32 ⁠ and the use of grape juice as a novel and green fuel to obtain cobalt ferrite nanocomposites 33 However, none of them enables the preparation of highly crystalline nanostructured materials with low temperature and reaction times (100 °C, 8 min) 34 ⁠ like the microwave-assisted hydrothermal (MAH) synthesis. Besides, common techniques for the preparation of metal oxide-polymer nanocomposites include 35 ⁠: (1) polymerization of monomers in the presence of metal oxide nanoparticles in situ; (2) direct blending of metal oxide nanoparticles and polymers by mixing in a melt or solution; and (3) the sol–gel process.…”

Experimental and ab Initio Studies of Deep-Bulk Traps in Doped Rare-Earth Oxide Thick Films

“…, only presenting electrical changes. Once the gas sensing measurements of the 8wt% La-doped CeO 2 sample depicted a peculiar dual-sensing behavior 20 , not seen in the pure, 4wt% and 12wt% systems, we have focused our attention on this particular system, to specifically study the dependence of rare-earth modification with an AC bias (V) application under vacuum and air (~20% O 2…”

“…The most important properties found on doping CeO 2 with La were the rapid changes in the electrical and optical responses in comparison with the pure CeO 2 , presenting only electrical changes. Once the gas-sensing measurements of the 8 wt % La-doped CeO 2 sample depicted a peculiar dual-sensing behavior, not seen in the pure, 4 wt %, and 12 wt % systems, we have focused our attention on this particular system to specifically study the dependence of rare-earth modification with an ac bias (V) application under vacuum and air (∼20% O 2 ) exposure, differing from the classical Schottky-type semiconductors, to determine the most likely conduction mechanism for nanostructured CeO 2 -based systems.…”