| With the development and progress of society,the monitoring of pollutant gases in industrial and agricultural production and daily life has become an important challenge and a topic that needs to be studied in depth.The sensitive materials used in gas sensors directly determine the performance of the sensors.Metal oxide semiconductor materials have become the research hotspot and focus of gas sensors due to their low cost and good stability.Many researches are devoted to finding new synthesis techniques and methods to obtain more efficient sensitive materials to break through the technical bottlenecks such as poor selectivity,weak anti-interference and high working temperature.In this thesis,metal-organic frameworks(MOFs)are used as precursors to prepare metal oxides with larger porosity to achieve effective control of the microstructure and composition of the materials.On the one hand,the paper choosed Prussian blue iron-based metal-organic framework(PB-MOF)as the precursor to synthesize multi-metal oxide composite materials SnO2/α-Fe2O3 andα-MoO3/α-Fe2O3,and use them as gas sensing materials to study their gas selective sensitivity to acetone and triethylamine,respectively.On the other hand,multi-component spinel ferrite(Cu,Zn)Fe2O4 nanospheres were prepared by self-template and thermal annealing strategy,and its gas-sensitivity response to triethylamine gas was studied.The specific works are as follows:(1)Using surface Sn2+ ion deposition and pyrolysis methods,Sn2+ions are loaded on the surface of Fe4(Fe(CN)6)3(PB-MOF)cubes and then pyrolyzed,and SnO2/α-Fe2O3 porous nano-cage composite material with cubic morphology was successfully obtained.Compared with pure α-Fe2O3,the heterostructure has enhanced acetone gas sensing performance.Under the condition of Sn:Fe=1.5,the response value of SnO2/α-Fe2O3(Ra/Rg=9.3)to 200 ppm acetone gas is 6.6 times higher than that of pure α-Fe2O3(Ra/Rg=1.4).The response and recovery times of SnO2/α-Fe2O3(6 s/7 s)is 1/2 and 1/5 smaller than that of pure α-Fe2O3(12 s/36 s).This strategy provides a new way to control the preparation of multi-metal oxide gas sensing materials with hierarchical structure.(2)Using PB-MOF as the precursor,combined with ion exchange method and pyrolysis method to obtain the α-MoO3/α-Fe2O3 composite materials with a loose internal hierarchical structure.PB-MOF was an important precursor for ion exchange with Na2MoO4,including two-step ion exchange processes,[Fe(CN)6]34--OH-and MoO42--[Fe(CN)6]34-.First,the OHions produced by the hydrolysis of Na2MoO4 was replaced by the[Fe(CN)6]34-ions in PB-MOF,and the MoO42-ions were deposited on the surface of PB-MOF and further occurred the ion exchange with[Fe(CN)6]34-.Then the α-MoO3/α-Fe2O3 heterostructures were obtained by heat treatment at 550℃ for 6 h,which retained the cubic structure of PB-MOF and had hollow porous structure inside.The α-MoO3/α-Fe2O3 heterostructures showed an excellent choice for triethylamine gas and had good stability for at least 20 days.This work provides an important experimental idea for the preparation of other multi-metal oxide-based gas sensing materials with hierarchical structures.(3)Through a simple self-template solvothermal method combined with annealing strategy,the multi-element(Cu,Zn)Fe2O4 spinel nanospheres with adjustable hollow internal structure were successfully synthesized,including solid,core-shell and yolk-shell structures.The formation of the internal structures of(Cu,Zn)Fe2O4 nanospheres are closely related to the thermal annealing rates of the precursors.Among them,the(Cu,Zn)Fe2O4 nanospheres with yolk-shell structure showed high responsiveness to triethylamine gas,and had excellent selectivity(STEA/Sx=1.86)at the working temperature of 160℃,fast response and recovery speeds(58 s/136 s)and excellent gas sensitivity stability.This work also discussed the influence of the solid,core-shell and yolk-shell internal structures on the triethylamine gas sensing properties of(Cu,Zn)Fe2O4 nanospheres in detail. |
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