Functional Modification Of Metal-organic Frameworks And Their Sensing Applictions For Molecules And Ions

Metal-organic Frameworks?MOFs?,self-assembled from metal ions/clusters and organic ligands,is a newly kind of hybrid porous crystal materials.Owing to the chemical designabilities and tunable pore structures,MOFs exhibited inherent advantages in the field of chemical sensing.In this work,the MOFs based probes were designed by means of prefunctionalization of ligands,post-modification to stable MOFs,and integration of MOFs and other materials.And these probes were applied in chemical sensing for hydrogen sulfide,hypochlorite ion,cadmium ion and ascorbic acid.Moreover,to prepare the MOFs based sensing device,MOFs and conductive polymers were combined to form a composite film,which provided a new avenue for the device application of MOFs material in the field of electrochemical sensing.Compared with organic dyes,fluorescent MOFs probes have the advantages of simple synthesis and low toxicity.A new fluorescence sensing material UiO-66-CH=CH₂ was synthesized by simple reflux method.This nano MOF was coordinated by Zr⁴⁺and vinyl terephthalic acid ligand.UiO-66-CH=CH₂ exhibited excellent water stability,chemical stability and thermal stability.The exposed unsaturated vinyl group on the frameworks of UiO-66-CH=CH₂ provided sensing sites for the reductive hydrogen sulfide.This well-designed probe presented good selectivity,anti-interference,fast response time?15 s?and high sensitivity?6.46?M?to hydrogen sulfide.The MTT analysis also showed this probe had low cytotoxicity and good biocompatibility,proving its potential as hydrogen sulfide biosensor materials.In order to solve the problem of fluorescence-quenching probe,we designed a“turn-on”fluorescence probe ZIF-90-BA,which was prepared by post modification of ZIF-90.Owing to the features of its good water stability and uncoordinated aldehyde group on the framework,ZIF-90-BA was successfully applied for OCl^-turn-on fluorescence detection.The Schiff base groups on the ZIF-90-BA could be easily oxidized by OCl^-and then the flexible alkyl chain would put off,resulting in the turn-on fluorescence behavior.ZIF-90-BA has good water stability,thermal stability and adjustable nano-size.The ratio of schiff base by post-functionalization was calculated quantitatively by ¹H NMR.ZIF-90-BA showed high selectivity over other potentially interfering species,and it exhibited high sensitivity?detection limit:6.25?M?and very fastresponse time?15 s?.It's expected that ZIF-90-BA could be a potential candidate as OCl^-fluorescence probesThe porous structure and chemical designability of MOFs material lead to good diffusion of analytes by the pre-gathering process,which enabled MOFs as ideal electrode modification material with high selectivity and sensitivity during electrochemical detection.3,3'-?pyridine-2,5?benzoic acid and Mn²⁺were used to prepare of a new type of water stable MOFs material ZJU-77 by simple solvethermal methods.ZJU-77 and Nafion composites were dropped onto glassy carbon electrodes to fabricate a modified ZJU-77/Nafion/GCE electrode for electrochemical detection.By introducing recognized nitrogen atoms into frameworks,ZJU-77 displayed excellent sensing performance for Cd²⁺.The detection limit of this modified electrode for Cd²⁺was 0.12 ppb,which was even lower than the standard for Cd²⁺in drinking water.In addition,the new sensor was exploited for Cd²⁺sensing in various real water samples with a high selectivity and sensitivity.It's highly anticipated that this research could offer valuable prospect for the well-designed MOFs materials for electrochemical sensing of heavy metal ions in real environment.In view of the signal transduction limitation caused by the weak conductivity of MOFs,we made use of the porous and chemically designabilities of MOFs materials and prepared the MOF based composite materials by integrating conductive carbon nanotubes.Zn²⁺was firstly immobilized on carboxylate carbon nanotubes,and then the ligand was added to grown ZIF-65 crystal on the surface of carbon nanotubes.The exposed nitro groups on ZIF-65 were used as sensing sites and the CNTs were to accelerate electronic transfer.Combining with sensing advantages of ZIF-65 and the electrochemical activity of carbon nanotubes,ZIF-65/CNTs composites displayed high sensitivity for ascorbic acid?LOD=1.03?M?,wide linear range,excellent anti-interference and time stability.Powder samples displayed some propreties,however,there remained problems such as difficulties in recovery and utilization,large reagent consumption,and easy to fall off from electrodes.To overcome the above problems,we prepared a conductive polypyrrole film bssed on MOFs material.FeCl₃,one of the reactant of polypyrrole,was encapsulated on the framework of MOF-867 by post-modification.And then the monomer and MOF-867@Fe³⁺were used to form a polypyrrole film by interface polymerization.It was proved that the sensing properties of MOF-867@Fe³⁺@PPy film.were better than that of MOF-867 powder,which was attributed to the advantages of electrical conductivity and film device.MOF-867@Fe³⁺@PPy film presented high sensitivity to Cd²⁺(LOD=0.29?g.L^-1)and excellent anti-interference performance,and could be applied in natural water samples,which provided facile and general approach to the device of MOFs based materials for electrochemical sensing.