Heterostructured NiO/ZnO Nanorod Arrays with Significantly Enhanced H2S Sensing Performance

Abstract

H2S gas sensors were fabricated using p-n heterojunctions of NiO/ZnO, in which the ZnO nanorod arrays were wrapped with NiO nanosheets via a hydrothermal synthesis method. When the H2S gas molecules were adsorbed and then oxidized on the ZnO surfaces, the free electrons were released. The increase in the electron concentration on the ZnO boosts the transport speed of the electrons on both sides of the NiO/ZnO p-n junction, which significantly improved the sensing performance and selectivity for H2S detection, if compared with sensors using the pure ZnO nanorod arrays. The response to 20 ppm of H2S was 21.3 at 160 °C for the heterostructured NiO/ZnO sensor, and the limit of detection was 0.1 ppm. We found that when the sensor was exposed to H2S at an operating temperature below 160 °C, the resistance of the sensor significantly decreased, indicating its n-type semiconductor nature, whereas when the operating temperature was above 160 °C, the resistance significantly increased, indicating its p-type semiconductor nature. The sensing mechanism of the NiO/ZnO heterostructured H2S gas sensor was discussed in detail.

Significantly enhancement of sunlight photocatalytic performance of ZnO by doping with transition metal oxides

“…In all of cases, the band gap of TMO-doped ZnO are smaller in comparison to pure ZnO, being the smallest for the CoO/ZnO sample (2.46 eV). These results are in agreement with other works such as NiO/ZnO nanorods 43 and CoO/ZnO nanofibers 44 . As a consequence of the coupling of MTO and ZnO in the heterojunction more electrons are freely transferred from M n+ of the TMO (with higher Fermi level) to ZnO (with lower level), promoting the separation of holes and electrons and, then, effective heterojunctions are formed 43 .…”

“…These results are in agreement with other works such as NiO/ZnO nanorods 43 and CoO/ZnO nanofibers 44 . As a consequence of the coupling of MTO and ZnO in the heterojunction more electrons are freely transferred from M n+ of the TMO (with higher Fermi level) to ZnO (with lower level), promoting the separation of holes and electrons and, then, effective heterojunctions are formed 43 . Therefore, the band gap closing can facilitate stepping electrons from the valence band to the conduction band as that reported in the literature for CuO-ZnO nanocomposites 45 .…”

Nickel Oxide-Carbon Soot-Cellulose Acetate Nanocomposite for the Detection of Mesitylene Vapour: Investigating the Sensing Mechanism Using an LCR Meter Coupled to an FTIR Spectrometer

“…Furthermore, both the Ni 2P spectra have satellite peaks occurring at approximately 861 eV (Ni 2p 3/2 ) and 878.8 eV (Ni 2p 1/2 ). The positioning of the main and satellite peaks indicates the presence of Ni 2+ in both NiO and NiO-CNPs-CA composite [ 24 , 25 , 26 , 27 ].…”

Synthesis of ZnO Hierarchical Structures and Their Gas Sensing Properties

“…Meanwhile, metal oxide (MO) materials gas sensors, such as ZnO [7,8,9], CuO [10,11], In 2 O 3 [12,13], WO 3 [14,15], CeO 2 [16], SnO 2 [17,18], etc., have attracted extensive attention. Besides, MO materials exhibit outstanding sensing properties in the detection of H 2 S gas [19,20,21,22]. Kaur et al [23] prepared In 2 O 3 whiskers by the carbothermal method and the In 2 O 3 whiskers exhibited excellent sensing properties toward H 2 S gas.…”