Imidazolium Ionic Liquid Assisted Synthesis Of Hierarchically Structured ?-Fe₂O₃ Nanomaterials And Theirs Gas-sensing Properties

The emission of gaseous pollutants destroys our living and working environment and threatens the human health.Gas sensors play an important role in the supervision and detection of flammable,explosive,toxic and harmful gases.Therefore,research and development of low cost,high performance gas-sensitive materials,the preparation of green gas sensor have become one of the current hot topics.The ionic liquids(ILs)have been used as solvents,structural templates,precursors,stabilizers,and surfactants to prepare nanometrials with special phase and morphology because of their unique physical and chemical properties.The reported investigations were focused on the effect of ILs on the size,shape and architecture controllable synthesis of pure metal oxides and the ILs were removed completely by subsequent calcination.However,the influence of residuial ILs on the product performance was less discussed.Therefore,hierarchical ?-Fe₂O₃ nanomaterials were designed and prepared by various ionic liquids here,the morphology and structure were characterized by the modern instrument analysis methods such as X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM)and N2 adsorption-desorption analyses(BET).The ?-Fe₂O₃ mesoporous nanomaterials with appropriate ionic liquid residual could be easily obtained by controlling the calcination temperature.It might be helpful to improve the gas sensing performance of metal oxides.The main contents of the thesis are as follows:(1)?-Fe₂O₃ hollow ellipsoid precursor was prepared via hydrothermal synthetic method in which ferric chloride was used as reactants and ionic liquid 1-dodecyl-3-methylimidazolium hexafluorophosphate([C₁₂mim][PF4])was used as assisted reagent.The average diameter and the length of the ?-Fe₂O₃ precursor are estimated to be about 400-600 nm and 200-400 nm,respectively.After being calcined at 300 °C,the sensors based on the ?-Fe₂O₃ hollow ellipsoid exhibit excellent gas sensing properties to different carbon chain lengths of alcohols at 217 °C,especially the fast response time,high sensitivity,good anti-humidity and long term stability to butanol.(2)Single-crystalline ?-Fe₂O₃ mesoporous nanospheres were sythesized via hydrothermal synthetic method in which Fe Cl3·6H2O and Na OH were used as raw materials and ionic liquid 1-dodecyl-3-methylimidazolium tetrafluoroborate([C₁₂mim][BF4]).The diameter of the ?-Fe₂O₃ microspheres is about 100 nm which are assembled by nanorpaticles with a particle size of 3-15 nm.And hierarchical ?-Fe₂O₃ mesoporous nanospheres were obtained after subsequent calcinationin in air at 300 °C and 600 °C for 2 h,repectively.The products calcined at 300 °C have uniform distribution of mesoporous structure and large specific surface area.It is demonstrated that [C₁₂mim][BF4] is not only used as an additive to bedeck ?-Fe₂O₃ particles and reduce their surface energy,but also as a template to control and stabilize inorganic nanomaterial with novel and hierarchical architectures.The sensors based on such single-crystalline ?-Fe₂O₃ nanospheres,calcined at 300 °C,show better acetone sensing properties,including good selectivity,fast response,and low detection limit.They also have good anti-interference of ethanol and humidity,implying their potential application in the detection of breath acetone in type-? diabetic patients.(3)The precursor of well-aligned ?-Fe OOH nanorod arrays was in-situ deposited on the ceramic tubes by ionic liquid 1-dodecyl-3-methylimidazolium bromide([C₁₂mim][Br])assisted hydrothermal reaction in which Fe Cl3·6H2O and urea were employed.The average diameter and the length of the nanorods are estimated to be about 30 nm and 200 nm,respectively,which are assembled by nanoparticles.?-Fe₂O₃ nanorods arrays were obtained after the precursors being calcined in air at 250,400 and 600°C for 2 h,repectively.The products calcined at 250 °C have uniform distribution of mesoporous structure and large specific surface area.Such in-situ assembled ?-Fe₂O₃ mesoporous nanorod arrays sensor exhibites good sensing performance to gaseous amines at 217 °C,especially good selectivity,long stability and low detection limit to trimethylamine(TMA).[C₁₂mim][BF4] has not only an important effect on the ordered formation of ?-Fe₂O₃ nanorod arrays,but also good adsorption action to the TMA gas,and can be used as a non-destructive measurement in monitoring fish freshness.