Study On Structures And Properties Of Metal-organic Frameworks (MOF) Constructed From2-amino-1,4-benzenedicarboxylic Acid And Thiophene-2,5-dicarboxylate

Metal-organic frameworks have attracted wide scientific attention in recent years especially as newly developed porous materials. By selecting the appropriate organic ligands and transition-metal ions, our group devotes to build functional MOFs, and study their structure, photocatalytic degradation of X3B, fluorescence and other properties.In chapter1, summarizes the purpose and meaning of our study.In chapter2, solvothermal reactions of NH2bdcH2and N-auxiliary ligands with transition-metal centers (Mn2+/Zn2+/Co2+) have yielded four MOFs based on single crystal X-ray structural, thermo gravimetric (TG), and elemental analyses. Interestingly, crystallographic analysis showed that MOF1is a three-dimensional (3D) porous structure with large channels of size ca.20.5×19.4,17.9×10.9and34.6×10.9A2along the a-, b-and c-directions, respectively. Further examinations reveal that MOF1adopts five interpenetrating4-connected dia net. MOF2is also a3D porous structure and it can be simplified to three interpenetrating4-connected dia net.The individual3D network is "open" with larger hexagonal channels of size ca.23.9×20.7A2, smaller "π"-shaped channels of size ca.20.2×14.2A2and rectangular channels of size ca.13.9×11.0A2(based on Zn…Zn distances) along the c-, a-and b-directions. MOF3its structure is very similar to MOF2. MOF4is a sql net with Schlafli symbol (4462). Sine MOF1crystallizes in the acentric space group Cc that belongs to a polar point group (Cs), it may have ferroelectric behavior. An electric hysteresis loop is clearly observed at room temperature. When we add small amount of nitrobenzene or2-nitrotoluene into methanol solution which contains MOF2, the luminescence emission is significant enhanced. It is very different from the behaviors of luminescent MOFs reported earlier, for which nitro-containing aromatics gave similar quenching profiles. The observed fluorescence enhancement may be attributed to the photo-excited state of MOF2reduction of nitrobenzene or2-nitrotoluene. To evaluate the photocatalytic effectiveness of MOF2, we selected an anionic organic dye X3B, as a model pollutant in aqueous media. We find that MOF2is active for the de composition of X3B under visible-light irradiation. The kinetic data for the degradation of X3B can be well fitted by the apparent first-order rate equation, and the rate constant was found to be0.33h-1. After photocatalysis, MOF2was recycled by filtration and powder XRD demonstrates that MOF2are rather stable during photocatalysis. In addition, the presence of tert-butyl alcohol(TBA, a widely used·OH scavenger) greatly depressed the photodegradation rate of X3B on MOF2, that is, the relevant rate constant for MOF2was sharply decreased to0.027h-1under visible light. The·OH quenching experiment result suggests that the photodegradation of X3B on MOF2is predominately through attack of·OH radicals.In chapter3, five unreported MOFs were obtained under solvothermal conditions based on transition-metal, and we study their photocatalytic performance in hereogeneous system. MOF5, MOF8and MOF9are wave-shaped2D structure; MOF6adopts NaCl-type topology; MOF7presents a3D coordination framework with a (4,6) mixed-connected network topology. It is found that under the visible-light irradiation only MOF7shows high photocatalytic activity. For MOF7, the rate constant under UV-light irradiation was found to be0.84h-1and the rate constant under visible-light irradiation was0.30h-1. In addition, the presence of tert-butyl alcohol(TBA, a widely used·OH scavenger) also greatly depressed the photo degradation rate of X3B on MOF7, the rate constant was sharply decreased to0.074h-1under visible light. It suggests that MOF7has the same mechanism of photocatalytic degradation as MOF2. PXRD shows that MOF7have high stability in photocatalytic process.In the chapter4, we summarize this thesis, put forward the innovation of this thesis and prospect the perspective of MOF as photocatalytic material.