Controllable Synthesis And Properties Of Magnetic Micro-nano Catalysts Based On MOFs

With the rapid development of economy and technology,people's quality of life has been improved,but at the same time,they need to pay attention to the environmental problems,especially the water environment.Water,which is closely related to our daily life,is an important resource for human beings and animals on earth to survive.In fact,the freshwater resources on the earth are not abundant,the proportion that can be used by human is even less.Coupled with its uneven distribution,about one fifth of the world's population exists the problem of utilizing safe water.In addition,due to the impact of human activities,plenty of untreated industrial,agricultural wastewater and domestic water are discharged into rivers,lakes and seas.And the types of pollutants in the water are becoming more and more diverse and the composition is increasingly complex,which greatly exceeds the self-purification capacity of the water body and can not be decomposed and removed through the metabolism of aquatic organisms,resulting in global water pollution and the crisis of water shortage.Metal-organic frameworks?MOFs?combine inorganic metal ions or ion clusters with organic ligands to produce a kind of crystal microporous materials with unsaturated metal sites,adjustable pore size,super high porosity and huge specific surface area.Its preparation process is simple,raw materials are easy to obtain,and its special structure gives it excellent adsorption performance.Over the past decade,researchers have combined various functional materials with MOFs to form MOFs composite,which not only improves the poor stability of MOFs themselves,but also has the advantages of functional materials?such as optical,electrical,magnetic and catalytic properties?.The strategy of using the synergistic effect of the two to obtain novel MOFs materials with new functions is a research hotspot at present.It is expanding the application field of MOFs,and has broad application prospects in functional and protective coatings,storage,separation,heterogeneous catalysis,sensing and biology fields.In this paper,two kinds of catalysts were synthesized on the basis of MOFs materials.The dye methylene blue in dyeing wastewater and antibiotics in pharmaceutical wastewater were selected as the research objects.The specific research contents and results are as follows:1.Preparation of Pd-loaded magnetic hollow nanoreactor and its catalytic performanceHollow magnetic nanoreactor loaded Pd?HMN/Pd?was constructed by a simple method.First,Fe₃O₄ nanospheres with cavities and large specific surface area were synthesized as the magnetic source by solvothermal method and SiO₂ corrosion.For maximizing the characteristics of MOFs,HMN nanoparticles were synthesized to offer adsorption sites and protect the structure from the external harsh environment.In other words,the stability of the material was improved and the application range of the catalyst in acid,alkali,and other special environments was broadened.Finally,Pd nanoparticles were loaded on HMN through the reduction of PdCl₂ to generate the novel magnetic catalyst named HMN/Pd.Given the notable characteristics of MOFs,nanoparticle agglomeration was no longer an issue.The properties of catalyst were discussed according to the analysis of catalytic reduction of methylene blue?MB?and p-nitrophenol?4-NP?with NaBH₄ as reducer.Compared with other reported catalysts,HMN/Pd exhibited satisfactory performance,it could reduce high concentration MB within 2 min.And owing to its magnetism,the catalyst could be separated and recycled rapidly and easily,which reduced the cost of the application.After 10 times of reuse,the morphology and the loaded amount of Pd nanoparticles of this material had little change.And it could maintain good catalytic performance after placed for a month,which describes its good stability.2.A catalyst based on core-shell MOFs for the degradation of antibiotics in waterA catalyst constructed by Co₃O₄ and carbon nanotubes was prepared based on core-shell MOFs materials by a simple method and applied in the degradation of antibiotics in water.We first synthesized core-shell Zn/Co MOFs materials with specific surface area over 1000 m² g^-1.Next,metallic zinc ions in MOFs would evaporate during the pyrolysis process at 920 ^oC,coupled with the catalytic action of Co ions to promote the formation of carbon nanotubes and internal cavities to produce a catalyst.At the same time,the surface of the catalyst also contained Co nanoparticles that can catalyze the subsequent degradation reaction but is not conducive to the reuse of the catalyst.Therefore,we removed the Co nanoparticles floating on the surface by sulfuric acid,and further oxidized and calcined to produce Co₃O₄.We also found that the catalyst with relatively large specific surface area can activate persulfate and degrade oxytetracycline in water by free radicals.The removal rate of oxytetracycline can reach more than 90%and can be reused effectively.The effects of experimental conditions on catalytic degradation were also investigated.In addition,the magnetic properties of the material itself made it very convenient to separate and recover,which can be achieved through magnets.Through literature review,this work is the first time to apply this material to the degradation of oxytetracycline in aquatic environment,and get a better removal effect,which provides a new direction for the application of this material.