Controlled Synthese?Characterization And Adsorption Properties Of Zeolitic-Imidazolate Frameworks

Zeolitic-imidazolate frameworks?ZIFs?,an novel subclass of metal-organic frameworks?MOFs?and featuring zeolite topologies,are mainly formed by linking transition metals with imidazole linkers.Combining their desirable features,ZIFs possess applications as heterogeneous catalysis,selective gas adsorption,separation and capture due to their promised large surface area,well defined and tunable morphology,uniform pore size and excellent stability.Controlling the size,morphology and phase are at the core of MOFs synthesis because of their important impact on defining material properties and thus relevant functions.Most studies to ZIFs are focused on the specific morphologies/phases and their correlative properties,carefully understanding topotactic phase transformations and corresponding morphologies evolution process of heterostructural ZIFs are also essential for achieving precise morphology controlling strategies and further excellent tunable properties.The aim of this thesis is to synthesize ZIFs and study the corresponding growth mechanism and adsorption behaviors.we investigate mixed solvent?methanol/water?controlled crystal growth method to exploit a series of unprecedented morphologies of well-defined Co-based zeolitic imidazolate frameworks?Co-ZIFs?,including hexapods and tetrapods,and even hierarchical core-shell architectures through mild wet-chemistry process.Topotactic crystal phase associated with their porosity are evolving from a 3D structure go by 3D@2D core-shell structure and then to a 2D layered structure with the increase relative amounts of water in mix-solvent.The findings are very beneficial for exploring the solvent induced structural evolution.The adsorption behaviors of as-prepared ZIFs are studied by the N₂ and CO₂ sorption measurements.With the influence of green gases on global climate change becoming more and more serious,reduction of carbon dioxide emissions has turned into a worldwide problem.Adsorption is considered one of the most appealing options for CO₂ capture,and the key of this technology is searching efficient adsorbent with a high selectivity and adsorbent capacity.With the rapid development of industrialization,people pay much attention to industrial water pollution.In fact,heavy metal ions wastewater is the most dangerous to human health and the environment,so removing heavy metal ions from wastewater is a very important issue.The adsorption of heavy metal Cr???ion in wastewater treatment are investigated by studying the adsorption effect of initial Cr???concentration,adsorption time and varied phase.Study experiments reveal that:?1?The phase evolution of 3D ZIF-67 ?2D ZIF-L is induced by the solvents effect.A serious of novel core-shell unprecedented morphologies are synthesized and defined well.Enough methanol or high concentration 2-MIM for the necessary local ordering to occur to achieve growth of the cages of 3D nanoporous material.The nonframework species,solvent molecules induced different amine hydrogen dissociation constant of 2-MIM and thermodynamic stable phase to determine the final structure of frameworks.This process also applies to synthesis Zn-Co-ZIFs.?2?The adsorption isotherms of CO₂ on Co-ZIFs were measured.Due to the gate-opening effects of ZIF-L,the adsorption isotherms show that the corresponding threshold pressures of the adsorptives control their uptakes and the desorption of the adsorbed molecules.Co-ZIFs exhibit tunable CO₂ adsorption behaviors with the phase evolution and the ZIF-?1:2.5?exhibits the highest CO₂ adsorption amount(1.66 mmol·g^-1)when the presure reaches 100 KPa.The N₂ sorption measurements of as-prepared Co-ZIFs are studied.The porous 3D framework of ZIF-?1:0??i.e.ZIF-67?shows the largest BET surface area of 1880 m2·g^-1 and pore volume of 0.85 m³·g^-1,which exhibits the highest N₂ adsorption amount.?3?Studying indicated that 2D layered structure of ZIF-L show the excellent adsorption rate and the maximum adsorption capacity for Cr???.High-charge at the surface of ZIF-L,which is beneficial to the adsorption of metal ions.The maximum adsorption capacities of Cr???is 33 mg·g^-1.Pseudo-first-order kinetics model and pseudo-second-order kinetics model were employeed to fit the adsorption data of Cr6+ on Co-ZIFs.The results showed that all the adsorption processes fitted well with pseudo-second-order kinetics model and most correlation coefficients were higher than 0.99,indicating the adsorption may include chemical adsorption.Langmuir and Freundlich isothermal adsorption models were used to fit the adsorption of Cr6+ on Co-ZIFs.Compared to Freundlich model,Langmuir model fitted better with experimental results,indicating that the adsorptions of Cr6+ on both adsorbents were mainly a monolayer adsorption.