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Synergistic Effect of Mixed Metal Oxide Prepared Via Layered Double Hydroxides in Gas Sensing

Author: XuZiFeng
Tutor: HeJing
School: Beijing University of Chemical Technology
Course: Chemical Engineering and Technology
Keywords: LDHs nanocomposites lattice-matching gas sensing
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 106
Quote: 1
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Abstract


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, MgxNi1-xFe2O4/MgOand MgxCo1-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 MgxCo1-xFe2O4/MgO has been slightly improved, others werenot improved. And the negative synergies related to the mechanism stillneeds further study.

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