Tuning Of Host-guest Interactions In Metal-Organic Frameworks And Their Contaminant Adsorption/Separation Performance

Porous metal-organic frameworks(MOFs)represent a new type of functional materials and have been found to exhibit great potential in various applications such as gas storage/separation,luminescence,catalysis,magnetism,gas storage/separation etc.Applying the crystal engineering strategy,this dissertation details the design of host-guest architecture,investigation of porous MOFs for guest molecules capture in water,including organic dyes and heavy metal ions.Firstly,this thesis evaluates porous MOFs as promising candidates for cationic organic capture.A new organic linker was designed and synthesized to construct an anionic microporous MOF:the large organic backbone of this organic linker enforces the construction of large pore spaces to encapsulate methylene blue molecules;while the free-COOH groups on the pore surfaces generate their strong interactions with methylene blue molecules.To our surprise,the resulting MOF(ZJU-24 series)not only exhibits the highest methylene blue(MB)removal capacity of 902 mg/g,but can also completely remove the methylene blue from its aqueous solution.Single-crystal X-ray diffraction reveals the rotation of benzene ring and the stretch of the exposed-COOH groups caused by the electrostatic attraction between the exposed carboxyl group and MB for the first time.This research put forword a new method for the design of new MOFs which can be applied for adsorption of cationic contaminant.Then,elimination of Cr2O72-with robust porous MOFs was studied.A cationic Zr-MOF(ZJU-101)which not only exhibits the highest Cr2O72-removal capacity of245 mg/g,but can also selectively removes the Cr2O72-from its aqueous solution within a very short period of time was elaborated.Such a cationic MOF strategy will be further explored for the capture and encapsulation of anionic guest molecules.This work put forword an effective and universal strategy for the developing of cationic MOFs for ellimination of anionic contaminant.Furthermore,3D mesoporous MIL-101(Cr)s in variable surface charge states by incorporating different functional groups were engineered,leading to charge-based separation of both positively and negatively charged organic molecules and an extraordinary reusable adsorption capacity of 1.27 g/g for Methylene Blue,the highest for any adsorbent materials ever reported.At the same time,the relationship among functional group,surface charge states and host-guest interactions are revealed,which will benefit the design and preparation of targeted host-guest system in crystal engineering.At last,a series of isostructural,highly stable,porous molecular sieves named MIL-140s that possess 1D microporous channels and the systematic study of organic molecule sieving following a charge-and size-based recognition of organics strategy were introduced.By modifying the pore size and chemical environment in pore with the isostructural MIL-140s,both size-and charge-based sieving of organics was realized.The affinities and joint influence of crystal structure,surface charge states,functional groups and host-guest interactions finally,revealed by both experimental and simulation methods,indicated that MIL-140s can be potentially utilized for the organic molecular sieving.This work comes up with an unprecedented multi-level recognition strategy,which will contribute to the task-specific design of MOFs for recognition and separation of molecules in water.