Preparation And Properties Of Ce-Based Metal-Organic Frameworks And Derivatives

Environmental pollution and energy shortage are seriously restricting our country’s economic development.Photocatalytic technology has attracted extensive research interest due to its low energy consumption,easy operation,and low secondary pollution.Photocatalysts are the core of photocatalytic technology.Therefore,the development of functional materials with excellent photocatalytic properties is important to the development of the photocatalytic field.In recent years,metal-organic frameworks（MOFs）have attracted extensive attention of researchers due to their porosity and tunable structures.Among them,Ce-MOFs have attracted much attention due to their excellent redox ability of Ce³⁺/Ce⁴⁺and the unique 4f orbital of lanthanides.However,most Ce-MOFs have wide band gaps and can only respond under ultraviolet light.Therefore,it is important to design Ce-MOFs with efficient visible light photocatalytic performance.Dielectric barrier discharge（DBD）low-temperature plasma technology is a fast,simple and environmentally friendly method for material synthesis.In this paper,three aspects of preparation method,bimetallic MOFs and MOFs derivative composites are designed,aiming to obtain Ce-MOFs with excellent visible light photocatalytic performance.A series of low crystallinity bimetallic Fe/Ce-MOFs were synthesized by DBD technique and used for photocatalytic degradation of methyl orange.The photocatalytic performance of bimetallic Fe/Ce-MOFs was significantly better than that of single metal Ce-MOFs.The introduction of Fe affected the coordination structure of Ce-MOFs,resulting in the low crystallinity of the samples.Fe/Ce-MOFs with low crystallinity could exhibit abundant active sites and abundant oxygen defects.Furthermore,the introduction of Fe could significantly reduce the band gap and suppress the photogenerated electron-hole recombination.Fe/Ce-MOFs-2,prepared under the discharge voltage of 8.4 k V,the discharge time of 90 min,the metal to ligand ratio of 2:1,the molar ratio between Fe/Ce of 1:2,and the reactant concentration of 22g/L,exhibited excellent visible light photocatalytic performance.After 36 min of visible light irradiation,the degradation rate of methyl orange solution reached 99.8%.Using Fe/Ce-MOFs as precursors,a series of metal oxide/MOFs composites（MO@Fe/Ce-MOFs）were synthesized by partial pyrolysis using a partial framework conversion strategy for visible-light photocatalytic nitrogen fixation.Compared with Ce-MOFs derivatives,the introduction of Fe could transform the samples into nanosheet structures with lower crystallinity,exposing more active sites and generating more oxygen defects.Furthermore,the introduction of Fe could significantly reduce the band gap and the recombination efficiency of photogenerated charge carriers.MO@Fe/Ce-MOFs-2,prepared at the discharge voltage of 8.4 k V,the discharge time of 90 min,the ratio between metal and ligand of 2:1,the calcination atmosphere of air,the calcination temperature of 150℃,the calcination time of 3 h,and the molar ratio between Fe/Ce of 1:3,showed the best photocatalytic nitrogen fixation effect.The photocatalytic nitrogen fixation efficiency could reach 54.24μmol·g^-1·h^-1.Compared with Fe/Ce-MOFs,the construction of MO@Fe/Ce-MOFs composites could promote the electronic interfacial transfer,improving the photocatalytic nitrogen fixation performance of the samples effectively.