| Metal-organic frameworks(MOFs)are a class of porous crystalline materials constructed from metal centers with organic linkers,creating three dimensional ordered frameworks.The framework topologies and pore size of MOFs can be designed via choosing various metal centers and organic linkers.Their chemical properties can be modified by chemical functionalization of linkers and post modification.These unique characteristics make MOFs one of the research hot spots in many fields and showing potential applications in various research areas.Zirconium-terephthalate-based MOF UiO-66(UiO = University of Oslo)has remarkable hydrothermal stability,highly resistant to acidic/basic environment and mechanical pressure.UiO-66 is one of the most popular and important MOFs.Herein,we are focus on the modulated synthesis of UiO-66 with crystal size varying from nanometer scale to micrometer scale,as well as the functionalization of UiO-66 by foreign metal doping.The main contents and conclusions are as follows:(1)HF was employed as a modulator in the solvothermal synthesis of UiO-66,the influence of HF on the crystal growth was studied.In the presence of HF,UiO-66 crystals with various sizes between 150 nm and 7 μm can be obtained.By optimizing the concentration of the reactants,the crystal morphology of micron-sized UiO-66 can be changed from a truncated cube to a cuboctahedron.Due to the strongest electronegativity of fluorine,fluorine ions directly bond to zirconium in the SBUs.The bonding of fluorine ions and zirconium competes with the H2BDC linkers to coordinate with the Zr6 clusters,thereby controlling the processes of nucleation and growth of UiO-66 crystals.In comparison with the small UiO-66 crystals,the structure stability and gas adsorption capacity of the UiO-66 crystals in micrometer scale exhibit remarkable enhancements.(2)A novel method was presented to prepare high quality UiO-66 in nanometer scale by using Cu20 as the additive.Well-dispersed nanometer scale UiO-66 crystals with mean size of 40 nm can be easily synthesized by the addition of Cu2O.Cu2O additive plays a role of rate controller of the growth of UiO-66 crystals by their competitive coordination behavior with zirconium.This generates a depleted Zr6 clusters concentration for constructing the UiO-66 framework,which favors the production of small crystals.The as-synthesized nanometer scale UiO-66 crystals have a pure crystal structure with high crystallinity and superior porosity.The structures of the nano-sized UiO-66 contain both Zr6 cluster defects and H2BDC linker defects,and the defects increase with the decrease of the crystal size.(3)Titanium in different amount was successfully doped into UiO-66 via an in situ synthesis method,resulting in a series of hybrid UiO-66-nTi MOFs.These materials maintain a relatively high crystallinity and excellent structural stability.The addition of titanium has a significant effect on the crystal size and morphology of UiO-66.The UiO-66-nTi MOFs exhibit a sphere-like crystal morology with smaller crystal size and a rougher surface compared to the octahedral UiO-66 crystals.The framework order and porosity of the UiO-66-nTi MOFs slightly decrease due to titanium doping.The Ui0-66-nTi MOFs were studied as adsorbents for removal of an organic dye from water.The results demonstrate that these hybrid materials have enhanced adsorption capacity for the organic dye Conge red in comparison with the parent UiO-66.UiO-66-2.7Ti with 2.7 wt%titanium doping shows the highest adsorption capacity of 979 mg·g-1,which is three times higher than that of the parent UiO-66.The strong electrostatic attraction between the positively charged surface of UiO-66-nTi MOFs and the negatively charged Congo red molecules was identified as the main driving force for the high adsorption capacity. |
