Synthesis And Properties Of MOFs Derived Iron-based Composites

With the rapid development of human economic activities and production,a large amount of non-renewable energy sources were consumed,and a large amount of waste gases and soot are discharged into the atmosphere,which seriously affects the quality of the atmospheric environment,especially in densely populated cities and industrial areas.There are many kinds of air pollutants,which can be divided into two categories:granular pollutants and gaseous pollutants.Gaseous pollutants are mainly sulfur compounds,carbon oxides,nitrogen compounds,hydrocarbons and halogen compounds.At present,there are more than 100 kinds of air pollutants known.Nitrogen oxides,sulfur compounds and carbon oxides are the three major gaseous pollutants.The detection of them has great practical value and commercial prospects in gas sensing and other related fields.Since the MOFs materials were firstly synthesized in the 1990s,they have gradually become the main research direction of many branches of chemistry(inorganic chemistry and organic chemistry,etc.).Due to their excellent properties such as porosity,high specific surface area and polymetallic sites,MOFs have many applications in the fields of chemistry and chemical industry,such as gas storage,molecular separation,catalysis,drug delivery,and many similar applications.Owing to their high specific surface area and high pore structure,the oxide semiconductors calcined in air have a strong ability to adsorb gas molecules and are conducive to the diffusion of gas molecules.In terms of gas sensing detection,compared with bulk gas sensing materials,MOFs material derivatives have lower gas sensing detection limit,higher gas sensing response value and shorter response time.Based on the understanding of the relationship between the structure and properties of MOFs-derived metal oxides,a series of gas sensing materials based on MOFs template are designed and synthesized in this thesis.These MOFs-derived metal oxides with unique structures have high gas sensing performance and high stability at room temperature.The main contents of this thesis are as follows:(1)Fe2O3/Co3O4 composites were synthesized by using Co-MOFs as templates.Firstly,Fe/Co-MOFs composites were synthesized at room temperature,and then Fe2O3/Co3O4 composites were obtained by calcinated under Ar atmosphere at 500?.The composite gas sensors based on Fe/Co-MOFs composites were fabricated to detect NOx gas at room temperature.It was found that the gas sensing responses of Fe2O3/Co3O4 composite to NOx gas were significantly higher than that of pure Co3O4.Among them,Fe2O3/Co3O4-10 composite gas sensor has the minimum detection to 0.97 ppm for NOx at room temperature,the response to 97.0 ppm NOx was 2.5404,and the response time was 153 s.The Fe2O3/Co3O4-10 composites sensor has good gas sensing performance to NOx,and it has little response to H2S,NH3,SO2,CHCl3 and HCHO.(2)Gamma-ferric oxide/reduced graphene oxide composites(?-Fe2O3/rGO)were prepared by a two-step method.MIL-88/rGO composites were synthesized at 100?,and then calcined at 500? under Ar.?-Fe2O3/rGO composites were obtained and used as detect the gas sensor at room temperature.MIL-88 derived ?-Fe2O3 octahedron was highly dispersed on the reduced graphene oxide to form the ?-Fe2O3/rGO composites.Compared with the pure ?-Fe2O3 sensor,the ?-Fe2O3/rGO composites sensors show significantly enhanced gas-sensing performance.The ?-Fe2O3/rGO-20 composites show exceptional H2S gas response(Rair/Rgas=520.73 to 97 ppm)and have lower response to NOx,SO2,NH3,CHCl3 and HCHO.Mott-Schottky and EIS measurements show that the carrier density of ?-Fe2O3/rGO composites was higher than that of pure?-Fe2O3,which leads the easy capture of electrons from the conduction band and rapid migration.Compared with pure ?-Fe2O3,which was realized as gas detection based on the bulk resistance effect of materials,the gas-sensing mechanism of ?-Fe2O3/rGO composites were mainly surface-controlled due to the good conductivity of rGO and their two-dimensional planar structure,which can provide more active sites.Therefore,the prepared metal-organic framework drived ?-Fe2O3/rGO composites sensors show excellent performance in H2S detection at room temperature.