A high-response ethanol gas sensor based on one-dimensional TiO₂/V₂O₅branched nanoheterostructures

Abstract

Hierarchical nanostructures with much increased surface-to-volume ratio have been of significant interest for prototypical gas sensors. Herein we report a novel resistive gas sensor based on TiO2/V2O5 branched nanoheterostructures fabricated by a facile one-step synthetic process, in which well-matched energy levels induced by the formation of effective heterojunctions between TiO2 and V2O5, a large Brunauer-Emmett-Teller surface area and complete electron depletion for the V2O5 nanobranches induced by the branched-nanofiber structures are all beneficial to the change of resistance upon ethanol exposure. As a result, the ethanol sensing performance of this device shows a lower operating temperature, faster response/recovery behavior, better selectivity and about seven times higher sensitivity compared with pure TiO2 nanofibers. This study not only confirms the gas sensing mechanism for performing enhancement of branched nanoheterostructures, but also proposes a rational approach to the design of nanostructure-based chemical sensors with desirable performance.

ZnO Coated Anodic 1D TiO2 Nanotube Layers: Efficient Photo‐Electrochemical and Gas Sensing Heterojunction

“…The work function of ZnO is higher than that of TiO 2 , thus, electrons from the conduction band of ZnO are transferred to TiO 2. The migration of electrons to align the two Fermi levels resulting in an energy barrier, which creates depletion and accumulation layers at the interface, causes the band bending between ZnO and TiO 2 , shown in Figure b. The adsorption of oxygen (discussed earlier) and formation of negatively charged ions results in upward bending of ZnO.…”

“…The sensing mechanism of the ZnO coated TiO 2 nanotube layers follows the surface depletion model . Under an atmospheric ambient, the initial resistance of the ZnO coated TiO 2 nanotube layers is high because the oxygen molecules are adsorbed on the structure surface and form chemisorbed oxygen species (O 2 ‐ for <150 °C; O ‐ , and O 2‐ for ≥150 °C) by capturing electrons from the conduction band …”

“…Upon removal of ethanol, the increase in energy barrier height widens the depletion region, hence the electrons are confined and increased resistance is recorded. In addition, the heterojunction serves as additional active sites for ethanol adsorption, as well as the reaction of ethanol with surface‐adsorbed oxygen ions for improved sensing responses …”

“…This deduction is substantiated by the sensing response at 200 °C (Figure b), where the available active reaction sites of the heterostructure are more readily utilized for the interactions with electrons from ethanol, which rendered saturation response. Moreover, elevated sensing temperature initiates higher dehydrogenation rate of ethanol, and enables the formation of specific type of adsorbed oxygen species, that is, O ‐ and O 2‐ to release the adsorbed electrons . All in all, these factors intensify the sensitivity and reduce the response time at 200 °C.…”

The Role of Nb Addition in TiO2 Nanoparticles: Phase Transition and Photocatalytic Properties

“…In past decades, the titanium dioxide (TiO 2 ) is one of the most investigated SMO due to its unique physical and chemical properties as well as potential applications in photocatalysis, dye sensitized solar cells, and chemiresistors . In particular, TiO 2 has been widely applied as a photocatalyst because of its high chemical stability, low toxicity, and UV–visible sensitivity …”