Synthesis And Application Of Metal-organic Frameworks And Their Derivatives

Porous crystalline materials that organize molecular components into periodicnetworks can be considered as interconnected compartments regularly aligned in threedimensions. The desirable properties and numerous functionalities of these materials areusually originated from these interconnected compartments with open channels and largecavities. Metal-organic frameworks are constructed by joining metal-containing units withorganic linkers, using strong bonds (reticular synthesis) to create open crystallineframeworks with permanent porosity. However, the uniformity of the compartments willconsequently restrain the multi-functionalization of these topological frameworks. Arational approach to overcome these limitations is to construct their structures with differentfunctional groups.The preparation of highly functionalized MOFs has become both an active area ofresearch and an important tool for exploiting and expanding their unique properties. Thisfunctionality can be incorporated by modifying an organic ligand with specific substituents,by changing the chemical or structural properties of the metal node, or by encapsulating ofactive species into metal-organic frameworks. Compared with the traditional syntheticmethods, mechanochemical method is more widely used as a simple, green and efficientsynthesis strategy. By using ball-milling method, we successfully prepared compounds inwhich POMs are enclosed in the cages of ZIFs, materials with bimetallic-center MOFs, anda highly stable metal-and nitrogen-doped nanocomposite derived from bimetallic-centerMOFs. The properties of the composites were further studied. The main results are asfollows:(1) We embark on a new yet simple one-pot method to synthesize POMs enclosed inthe MOFs nanoparticles, and expand such nanocomposites into ZIFs. Specifically thesystematic variation of POM species and quantities in the mechanochemical synthesis ofthese nanocomposites, afforded five distinct compounds, H3PW12O40ZIF-8(BIT-1),H4SiW12O40ZIF-8(BIT-2), H3PMo12O40ZIF-8(BIT-3), BIT-4(H4PMo11VO40ZIF-8)and BIT-5(H5PMo10V2O40ZIF-8. All members of these series haveintact ZIF-8crystalline structures with permanent porosity and appear as homogeneousnanoparticles. The POM cages are intentionally ‘trapped’ inside the well-defined cages ofZIF-8. The composites can serve as hydrophobic open channels that allow the guest molecules diffuse in and out, whereas the domains that consisted of compartments withPOMs in it renders the hydrophilic nature to the accessible surface. More importantly, thesenovel nanocomposites show the highest uptake capacity (810mg/g) and excellentcontrolled release performance for typical biomolecules, methylene blue (MB). Notably,these nanocomposites can pick and capture dye molecules (such as MB) from a mixture ofdifferent dyes with unprecedented high selectivity. Furthermore, controlled release of MBand5-FU from BIT-1is achieved in a simulated body fluid,80%releasing over32days and93%releasing over50hours for MB and5-FU, respectively. BIT-1can be fully recoveredand easily reused without losing its uptake capacity. These characteristics make thesePOMs ZIF nanocomposites promising candidates for strategies aimed at selective capture,storing and controlled delivery of biologically active molecules for critical applications inbio-imaging and pain relieving.(2) We developed a facile strategy to introduce active Ni metal centers into ZIFs viamechanochemical method under liquid assisted grinding (LAG) conditions. Both BIT-11and-11b adopt ZIF-8topology with Ni partially substituting the ZnN4in the backbone;nevertheless, the coordination modes of Ni in these two frameworks are distinct from eachother. The Ni ions are distorted six-coordinated in BIT-11, whereas they are tetrahedrallycoordinated in BIT-11b with enhanced stability. Meta-stable framework BIT-11in greencolor can easily transform to violet BIT-11b triggered by small polar solvent molecules thatcan enter the narrow apertures of BIT-11(i.e. MeOH, H2O, EtOH etc.) and undergo achemical-induced de-coordination. This transformation process can be utilized toselectively and precisely sensing and detecting different alcohol molecules in atime-resolved manner in both vapor and liquid phase. BIT-11b with photoactive Ni centersand open channels exhibits outstanding photocatalytic activity under visible light. Thefindings explored a simple yet powerful way to incorporate metal ions into the backbonesof open framework materials without losing their activity. This may shed light ondeveloping new complex metal-organic frameworks for energy and environmentalapplications as catalysis, photochemical and electrochemical materials.(3) We have demonstrated a facile one-step synthetic strategy for the fabrication ofmetal-and N-doped porous composite from pyrolysis of a nickel-substituted zeoliticimidazolate framework with pores in the micro-, meso-pore ranges. A high CO2adsorptionuptake of4.25mmol g-1CO2at273K is obtained for the composite of Zn/Ni-ZIF-8-1000prepared from Zn/Ni-ZIF-8at1000°C. The results demonstrate that Zn/Ni-ZIF-8-1000can serve as an alternative to conventional porous solids with significantly enhanced CO2capacity and thermal stability. The high CO2adsorption performance is presumably causedby the presence of N basic groups together with active metal sites.The initial slopes and Ideal Adsorption Solution Theory (IAST) were used in theseparation of CO2/N2å'ŒCO2/CH4. This, combined with the extraordinary high stability andease of regeneration, may serve as a starting point to develop novel adsorbents based onopen framework materials and explore the potential industrial applications in carboncapture and gas purifications.