Synthesis,Characterization And Photocatalysis Of Pillared-layer Mixed-linker MOFs

In the last two decades,metal–organic frameworks?MOFs?have evoked considerable attention in materials science due to their intriguing structures and properties.Studies on MOFs have been developing at an extraordinary pace,as judged by the exponential growth of novel structures and the constant expansion of its applicability and research scope.Among these studies,pariticular attention has been paid for the design,synthesis and property of MOFs constructed by mixed organic linkers.We mainly focused on the synthesis and photocatalytic properties of mixed-linker MOFs in our research.Because the anthracene-based bipyridine ligand?BPEA?possesses an extended aromatic structure,BPEA shows broad-range visible light absorption.By application of pillared-layer strategy,two MOFs compounds,denoted as NNU-36 and NNU-37,were prepared using BPEA ligand together with the other ligand of 4,4?-biphenyldicarboxylate?BPDC?.The photocatalytic properties of these visible-light-photoactive MOFs for degradation of aqueous pollutants were studied.Details are as follows:1.Wesynthesizedanewmixed-linkermetal-organicframework[Zn₂?BPEA??BPDC?₂]·2DMF?NNU-36?by using pillared-layer strategy.In the structure of NNU-36,Zn?II?ions were coordinated with BPDC ligands to form two-dimensional"layer"structural units,and the visible-light-responsive BPEA ligands coordinate with Zn ions in these Zn-BPDC layers as"pillars"to construct 3D MOF structure.The physicochemical study results showed that NNU-36 is stable in aqueous solution and of broad-range visible light absorption,which is a potential visible light photocatalyst.We have explored the photoreduction of Cr?VI?ions and the photodegradation of organic dyes in aqueous solution using NNU-36 as visible light photocatalyst.The photocatalytic experiments under visible light irradiation reveals that NNU-36 can effectively reduce Cr?VI?ion into Cr?III?species,meanwhile it can be used for efficient degradation of a variety of organic dyes.Furthermore,it has been demonstrated that NNU-36 is stable enough in water where it can maintain high photocatalytic efficiency after cycle experiments.2.By means of the same pillared-layer strategy and identical combination of mixed-linkers,a novel metal-organic framework with a formula of[Co?BPEA??BPDC?]·DMF?NNU-37?was synthesized under solvothermal conditions using cobalt nitrate hexahydrate as the metal source.Spectroscopy measurments manifested that NNU-37 has a broad-band absorption in the visible light region which was ascribed to optical transition of BPEA ligand.NNU-37 exhibits photocatalytic properties for the degradation of the azo dyes?Congo red and methyl orange?.The experimental results illustrate that NNU-37 shows efficient photocatalytic performance for the degradation of Congo Red in aqueous solution.The catalytic reaction could degrade 94.6%Congo Red?50 ppm?within 60 minutes under visible light irradiation.Besides,the photocatalytic degradation of methyl orange using NNU-37 as photocatalyst was also investigated where the degradation reaction showed favorable efficiency.In addition,magnetic measurments indicate that cobalt ions belonging to the dimeric units in the Co-MOF interact antiferromagnetically with each other at low temperature.