Synergistic Effect Of Mixed Metal Oxide Prepared Via Layered Double Hydroxides In Gas Sensing

LDHs and its calcined products have a wide range of applications,which have been used in many fields such as catalysis, photosensitive,fire-retardant materials and so on.LDHs with iron-containing as as a single precursor, were used toprepare the mixed metal oxides such as NiFe₂O₄/NiO, MgFe₂O₄/MgO,CoFe₂O₄/Co3O4, MgxNi1-xFe₂O₄/MgO and MgxCo1-xFe₂O₄/MgO aftercalcination at high temperature, and then the gas sensing performance wasdetected.1. NiFe-CO₃LDHs as a single precursor were used to prepareNiFe₂O₄/NiO, and the structure and gas sensing sensor properties werestudied. HR-TEM observation shows that, through the topologicaltransition effect, the （111） facet of NiO and （111） facet of NiFe₂O₄werematched to achieve NiFe₂O₄dispersed in NiO uniformly. The particle sizedistribution of NiFe₂O₄phase is larger as the calcined temperature ishigher. At the same time, the facets of NiO and NiFe₂O₄could becontrolled in regulation.The doping amount of NiFe₂O₄in the NiO phaseis changed by increasing the proportion of Fe in LDHs precursor. Theresults show that when the content of NiFe₂O₄in NiFe₂O₄/NiO is16.7% （mol%）, NiO phase at the same time exposes both （111） and （100） facets,and the particle size distribution for NiFe₂O₄phase is3nm, NiO andNiFe₂O₄demonstrate excellent improvement in gas sensing of ethanol,styrene, xylene and cyclohexane. All of these make an agreement NiO andNiFe₂O₄with the characteristics of lattice-matched via the topologychange of NiFe-CO₃LDHs demonstrate a synergistic effect.2. The structure and gas sensing of MgFe₂O₄/MgO prepared fromMgFe-CO₃LDHs as a single precursor is studied.Both MgO and NiO have the same atomic arrangement in crystalstructure, while both MgFe₂O₄and NiFe₂O₄are inverse spinel structurematerials, and have the same atomic arrangement structure in space. Thestate of MgFe₂O₄dispered in MgO phase is achieved by changing thetemperature of topoly transfer of MgFe-CO₃LDHs, and then two statesare obtained: The generation of MgFe₂O₄is not obvious in MgO phase.And the other is that the selective growth of （111） MgFe₂O₄phaseembedded in a continuous MgO phase with （111） facet exposed obviously.But the gas sensing performance has not been improved, showing asynergistic effect, and it might be related to the electronic structure of theatom itself.3. Extension study of a serious of the iron-containing mixed metal oxidesin gas sensing.As is mentioned above, the advantage of mixed metal oxides with the property of lattice matching via topology change of LDHs were expectedto be applied in other oxides, so CoFe₂O₄/Co₃O₄, MgxNi_1-xFe₂O₄/MgOand MgxCo_1-xFe₂O₄/MgO were prepared by the topology change ofCoFe-CO₃LDHs, MgNiFe-CO₃LDHs and MgCoFe-CO3LDHs. Theresults show that the gas sensitive properties of these materials, only gassensing of MgxCo_1-xFe₂O₄/MgO has been slightly improved, others werenot improved. And the negative synergies related to the mechanism stillneeds further study.