Synthesis, Characterization And Properties Of Metal Organic Skeleton Materials Constructed By Rigid And Three - Way Ligands

Since the 21st century, Environmental problems have become the most serious issue which limits the development of humanbeings. With CO2 being one of the greatest contributors to global warming, there is increasing interest in removing CO2 from the air to combat the greenhouse gas effect. Besides, considerable amount of waste water contenting dyes from many industies has become an urgent problem. Therefore, it is of great importance to find suitable and effective sorbents to capture and separate CO2 and remove dye from water. As a promising class of sorbents, porous metal-organic frameworks (MOFs) have many properties that make them attractive for applications in gas storage, molecular recognition and separation, heterogeneous catalysis, and biomedical area.In this work, two rigid tritopic ligands of H3BTT (1,3,5-tris(2H-tetrazol-5-yl)benzene) and H3BPT (biphenyl-3,4’,5-tricarboxylic acid) were employed to construct seven new MOFs under solvothermal conditions. All compounds were characterized by single-crystal X-ray crystallography, IR spectra, power X-ray diffraction and thermal analyses. Gas storage and separation test were deeply studied by low-pressure and high-pressure sorption measurements. Dye adsorption results were discussed in detail after characterized by UV measurements. Major research results are shown as followed:1. H3BTT was used to construct two nitrogen-rich three-dimensional Cu(Ⅰ)/Cd(Ⅱ) metal-organic frameworks with novel structure. Through the linkage of BTT, linear chains including trinuclear Cu3 and binuclear Cu2 clusters were formed along a axis and b axis, respectively, which were further terminally coordinated by tritopic BTT ligands. Through such connection, a 3D open framework of [NC2H8]4[CuI5(BTT)3]·xG (G=guest molecular) (1), which contains four different sizes channels and giant multi-prismatic nanoscale cage was constructed. Compound [Cd2(BTT)Cl(H2O)2] (2) is a novel three-dimensional framework featuring with three types of connections of the tetrzole ring and two types of octahedral second building units (SBU) of [CdN3OCl2] and [CdN4OCl], respectively. Five isomorphic rare earth-organic frameworks of [Ln(BPT)(DMF)(H2O)]·xG (Ln=La, Gd, Er, Yb) (3-6) were synthesized by using H3BPT and lanthanide nitrate under solvothermal conditions. Each BPT ligand connects three binuclear Ln2 building blocks to form a 3D metal-organic framework with approximately 9.9 A×7.5 A channels.2. Activated sample la was obtained successfully by using solvent-exchanged method. PXRD, TG/DSC and FT-IR measurements indicate that the sample was well activated. Low-pressure gas sorptions isotherm shows a BET surface area and single point adsorption total pore volume are 701 m2 g-1 and 0.302 cm3 g-1, respectively. CO2 uptakes, measured at 273 K and 298 K, reach to the relatively high value benefitting by extensive nitrogen-donor sites. High-pressure gas sorptions isotherm shows a satisfactory storage capacity of CO2 in consideration of its moderate specific surface area. Calculated results from initial slope ratios estimated from Henry’s law and ideal adsorbed solution theory (IAST) indicate that the activated la has high CO2 sorption selectivities towards H2 and N2. The outstanding regeneration and cyclic performance of la makes it to be a promising adsobents in CO2 storage and separation.3. Owing to the existence of gaint nanoscale cage in the water-stable [Cu5IBTTs]4- anion framework of 1, the adsorption capacity towards methylene bule in water phase under different experiment conditions, for example adsorbent dosage, dye solution concentration and pH, etc, were investigated by virtue of UV spectra. Under the same absorption time of 80 min, in comparison with the 20 or 30 mg dosages, the 10 mg one shows the highest adsorption efficiency, i.e. highest dye adsorption amount (mg) per (g) adsorbent. The adsorption capacity and adsorption kinetics of 1 towards MB are dependent on the solution concentrations, which show the maximum values of 7.50×10-4 min-1 and 197.6 mg g-1 at 20 ppm, respectively. However, the MB adsorption capacity of 1 shows similar result even at conditions of acid or weak base. Moreover, the adsorption experiment of 1 toward the anion and neutral dye mixture were also carried out which show the excellent adsorption selectivities.