| Metal-organic frameworks(MOFs)are crystalline porous materials composed of metal nodes or metal clusters and organic connectors.Due to their advantages of large specific surface area,high porosity and flexible structure and function,MOFs have been widely used in various fields,such as drug carriers,catalysis,gas storage and luminescent materials.The metal ions and organic ligands that constitute MOFs play a decisive role in the properties of MOFs.At present,the MOFs reported are mainly composed of transition metals such as Ti,Cr,Zr,Fe as the central atom,while the main group metals are rarely involved.The main group metal bismuth is green and non-toxic metal with abundant reserves and flexible coordination.Moreover,many bismuth based materials have high photoactivity and have been widely used in the field of photocatalysis,such as Bi2O3,BiOX(X=Cl Br I),Bi2CO3,BiVO4.Based on the above background,we believe that bismuth-based MOFs should also have potential application in the field of photocatalysis.Therefore,this paper focuses on the application of bismuth-based MOFs in the field of photocatalysis.The classical method to construct MOFs with high stability is to improve the coordination bond strength between metal ions and organic ligands according to the hard and soft acid-base theory.Therefore,selecting appropriate organic ligands is an effective method to construct MOFs with high stability.The currently reported bismuth based MOFs are mainly composed of-COOH or-SH containing organic ligands,and MOFs are constructed by the coordination between oxygen atoms in-COOH and sulfur atoms in-SH with bismuth.According to the hard and soft acid-base theory,oxygen atoms in phenolic hydroxyl groups belorg to soft base,and Bi3+ close to soft acid.Therefore the coordination between the oxygen atoms of phenolic hydroxyl and bismuth is more stable.Therefore,theoretically speaking,bismuth-based MOFs composed of organic ligands containing phenolic hydroxyl groups have high stability and great potential application.In this paper,two organic ligands containing phenolic hydroxyl groups,baicalin and ellagic acid,were selected to construct Bi-MOFs respectively,and their applications in photocatalysis were explored respectively.In addition,we unexpectedly found that MOFs constructed with ellagic acid and bismuth showed great potential for light-controlled release of drug molecules.In the second chapter,baicalin(BAI)was used as the organic ligand to construct bismuth-based MOFs(Bi-BAI).Baicalin is a flavonoid compound extracted and separated from the root of scutellaria baicalensis and it has antibacterial and diuretic properties,which endows baicalin high medicinal value,such as diminish inflammation and spasmolysis effect.Baicalin contains two phenolic hydroxyl groups.Therefore,we choose baicalin as organic ligand to construct MOFs with bismuth.Baicalin and bismuth acetate were stirred at room temperature for 48h in acetic acid to obtain the MOFs(Bi-BAI).We first characterized the structure by XRD,SEM,TGA,BET and other characterizations,and then we characterized the photophysical properties by DRS and PL spectra.It was found that Bi-BAI displays obvious absorption in the visible region from the DRS spetrum.Then,we carried out photoelectric test and found that Bi-BAI had good photoelectrical response,indicating that Bi-BAI is a potential photocatalyst.Further photocatalytic performance proved that Bi-BAI is able to efficiently degrade Rhodamine B and selectively oxidize benzyl alcohol to benzaldehyde under the action of visible light,and demonstrates good cyclic stability as well.However,unfortunately,we have not obtained the single crystal structure of Bi-BAI.In the third chapter,we chose a bismuth-based MOFs(SU-101)whose crystal structure has been reported in literature.The organic ligand of SU-101 is ellagic acid containing phenolic hydroxyl which is similar to baicalin.Ellagic acid,and it is also a natural ingredient extracted from plants and has anti-cancer and anti-oxidation effects.According to the reported literature,SU-101 was successfully synthesized.XRD,TAG,F T-IR,SEM,TEM,DRS and PL test were used to characterize the structure and photophysical properties of SU-101.The photoelectric properties show that SU-101 exhibites good photoelectric response,and we speculated that SU-101 might have photocatalytic activity.However,rhodamine B degradation experiment found that SU-101 could not degrade rhodamine B under light irradiation.On the contrary,the adsorbed rhodamine B is released under light.So we changed our idea and investigated the potential of SU-101 as a light-controlled drug carrier.We were pleasantly to find that SU-101 has an efficient drug delivery capability for ciprofloxacin(CIP)and light illumination is able to control the release of CIP from SU-101.After exploring the mechanism of drug loading and photocontrolled release,it was found that hydrogen bond between the hydroxyl group of CIP and the carbonyl group of SU-101 is responsible for above behavior,which is broken under light irradiation via regulating the electronic structure of SU-101.Therefore,the drug is released under the action of light.Further study found that SU-101 has good loading ability and photocontrolled release ability for other drugs containing hydroxyl,which indicates that SU-101 has universal applicability as photocontrolled drug carrier.In the last chapter,we make a brief summary of this theisis,emphasizing the main innovations and shortcomings of this paper,and also point out the ideas for the follow-up research work. |
