Metal oxide semiconductor (MOS) gas sensors have the advantages of high sensitivity, short response-recovery time and long-term stability. However, the shortcoming of poor discriminability of homogeneous gases limits their applications in gas sensors. It is well-known that the MOS materials have similar gas sensing responses to homogeneous gases such as CO and H₂, so it is difficult for these gas sensors to distinguish the two gases. In this paper, simple sol–gel method was employed to obtain the ZnO–xNiO composites. Gas sensing performance results illustrated that the gas sensing properties of composites with x > 0.425 showed a p-type response to both CO and H₂, while the gas sensing properties of composites with x < 0.425 showed an n-type response to both CO and H₂. However, it was interesting that ZnO–0.425NiO showed a p-type response to CO but an discriminable response (n-type) to H₂, which indicated that modulating the p-type or n-type semiconductor concentration in p-n composites could be an effective method with which to improve the discriminability of this type of gas sensor regarding CO and H₂. The phenomenon of the special gas sensing behavior of ZnO–0.425NiO was explained based on the experimental observations and a range of characterization techniques, including XRD, HRTEM and XPS, in detail.

Here SnO₂/LaFeO_3−XN_X composite was fabricated using a wet chemical method and was applied to pollutants degradation and gas sensing for the first time. The composite exhibits high performance for photocatalytic degradation of Rhodamine B (RhB) dye and selectivity sensing of various gases. On the basis of the completed experiments, the improved RhB degradation and selective gas sensing performance resulted from the extended optical absorption via N₂ incorporated surface states and enhanced charge separation via coupling SnO₂. Using the scavengers trapping experiments, the superoxide radical (O₂^•−) was investigated as the major scavenger involved in the degradation of RhB over SnO₂/LaFeO_3−XN_X composite. In this paper, the probable reaction steps involved in the RhB dye degradation over SnO₂/LaFeO_3−XN_X composite are proposed. This work will provide reasonable strategies to fabricate LaFeO₃-based proficient and stable catalysts for environmental purification. In addition, the result of the selectivity of gas performance is also presented.

In this work, we have successfully fabricated Sr-doped porous LaFeO₃ samples via sol–gel method. The results reveal that Sr²⁺ cation is effectively doped into LaFeO₃ crystal lattice substituting La³⁺ cation. The visible light catalytic performance of the materials was evaluated by the degradation of 2,4-dichlorophenol (2,4-DCP) and Rhodamine B (RhB). The amount-optimized Sr-doped porous LaFeO₃ sample exhibited outstanding visible-light catalytic performance for the degradation of the model pollutants compared to the porous LaFeO₃ alone. The enhanced performance was accredited to the enlarged surface area, absorption extension via the surface states of the introduced Sr²⁺ below the conduction band bottom of LaFeO₃, and promoted charge carrier’s separation as confirmed by various experiments. Experiments of radical trapping reveal that •OH species are dominant intermediate oxidants involved in the oxidation of 2,4-DCP and RhB over the optimized sample. This research will provide new routes for environmental remediation based on the LaFeO₃ semiconductor.