Synthesis And Gas Sensing Properties Of AB₂O₄ Spinel Type Metal Oxide Semiconductors

Recent years,many kinds of volatile organic compounds?VOCs?are widely applied in serious fields.However,most of VOCs exhibit inflammability,explosion hazard and nocuity,the leakage of VOCs might cause incalculable harm and danger.Therefore,the detection of different VOC gases is becoming more and more necessary.This article introduces the synthesis and gas sensing application of two different AB2O4 spinel type metal oxide semiconductor materials,including porous javelin-like NiFe2O4 nanorods and porous ZnFe2O4 nanospindles.For the first study,H₂BDC was used as organic-ligand and reacted with Ni?NO₃?₂·6H₂O and Fe?acac?₃,to prepare Ni/Fe bimetallic MOFs.The products were annealed in air to get porous javelin-like NiFe2O4 nanorods.For the second study,fumaric acid was used as organic-ligand and reacted with Zn?NO₃?₂·6H₂O and Fe?NO₃?₂·9H₂O,to prepare Zn/Fe bimetallic MOFs.The products were annealed in air to get porous spindle-like ZnFe2O4 nanoparticles.In order to analyze the characteristic of as-fabricated materials and prepare for the gas sensing testing,the samples were characterized by SEM,TEM,XRD,BET,XPS and so on.As n-type semiconductors,NiFe₂O₄ and ZnFe₂O₄ in the article could make oxygen in the air adsorbed on the surface at appropriate working temperatures,and the adsorbed oxygen species will capture electrons from materials,causing the increasing of resistance.While the materials are exposed to reducing gases,the adsorbed oxygen on the surface will react with reducing gas molecules and the captured electrons will return to the surface,which causing the decreasing of resistance.XPS analyze was experimented and surface-adsorbed oxygen species were found from the XPS survey spectrums of these two samples,which verifies the correctness of this gas sensing mechanism.Thereout,the gas sensing performances of these two materials were measured and them all behaved the highest sensitivity at ultralow working temperature?120°C?toward different VOCs.Porous javelin-like NiFe2O4 nanorods exhibited excellent selectivity,sensitivity?120 response value to 200 ppm n-propanol?,stability and short response/recover time?19 s,42 s?.Porous spindle-like ZnFe2O4 nanoparticles obtained from the annealing treatment at 450°C showed the most outstanding gas sensing performance with 223response value to 200 ppm ethanol,rapid response speed?10 s?,good selectivity and stability.