Spinel-typed Metal Oxides Based VOCs Gas Sensing Materails:Morphology Controllable Synthesis And Application

During the past few years,high-quality spinel-typed metal oxides have received intense concerns and present lots of enhanced properties in many areas,such as energy storage and transformation,catalysis,medicinal chemistry and so on.Especially in the field of VOCs gas detection,spinel-typed compounds often have many advantages over the traditional single metal oxides in the aspect of working temperature and gas selectivity.Benefits from these facts,an increasing number of scholars have launch their research focusing on the enhancement of sensing properties of spinel oxides,and some phased research results have been reported.This paper adopts a facile route combining hydro-/solvothermal method with high-temperature treatment to controllably prepare three spinel-typed oxides with uniform morphologies,namely Co3O4,ZnCo2O4 and ZnFe2O4,to improve gas sensor's performance.The main work in paper is illustrated as bellow.Spinel Co3O4 compound with needle-shaped microspheres was prepared by a facile PVP-assisted hydrothermal process and applied into gas detection.After observations from SEM and TEM images,we found that the hierarchical needle-shaped microspheres had a relatively uniform diameter of 1.5 ?m.The results also indicated that this 3-D needle-shaped microsphere was constructed by numerous ordered nano-needles growing from inside to outside and presenting an urchin-like morphology.Gas test indicated that needle-shaped Co3O4 microspheres based gas sensor displayed a high response to ethanol at 170 ?.And the selectivity and stability is also comparable to the recent reports.Next,porous ZnCo2O4 hollow microspheres with 1.3 ?m at diameter were successfully synthesized by a cost-effective method coupling solvothermal with a post-annealing treatment.Based on observation and analysis,we noticed that these hollow microspheres were well-dispersed and self-assembled by many fine nanoparticles.In experiment,we explored the formation conditions of the hollow microsphere and obtained the final and optimal synthetic solvothermal condition.The formation evolution of this structure was also explored by a time-dependent experiment.Gas test indicated that porous ZnCo2O4 hollow microspheres based gas sensor displayed a good sensing performance(R=18.6)to ethanol at 200 ? and a good selectivity and cyclic stability.And then,ZnFe2O4 compound with bead-like morphology was obtained by a facile method coupling solvothermal with a post-annealing treatment.After characterized in detail,we noticed that each bead-like microsphere had a diameter of-850 nm and has an open structure.And we also fabricated a gas sensor based on the sample to test sensing performance.Gas test reflected that this sensor showed a good response performaace to 10×10-6 ethanol at 180?and the response is ca.6.8.Also,a fast response/recovery speed,good gas selectivity and stability were achieved in test.