Design And Synthesis Of Metal-organic Frameworks And Their Applications In Heavy Metal Ions Detection

Metal-organic frameworks are a new type of porous crystal materials,which have received widespread attentions in the past two decades due to their large specific surface area,rich adsorption sites,superior designability,and various functional modification of the surface chemical environment.Among them,the UiO-series metal-organic framework materials have stable chemical structure and luminescent properties,and can be functionally modified through ligand design,post-modification,or introduction of guest molecules.Therefore,UiO-series can be explored to be fluorescent probe for the sensing of solvents,pH,ions and small molecules in aqueous environment.In addition,MOFs materials have good electrical conductivity,high porosity and rich active adsorption sites for heavy metal ions.Therefore,MOFs materials are rational electrode modification materials and are widely used for the electrochemical sensing and detection of heavy metal ions and small molecules.Nanoscale MOFs UiO-66-NH2 was synthesized as the precursor by solvothermal method,which has an octahedral structure.After post-synthetic modification(PSM),the fluorescent probe UiO-66-N=CH2 was prepared and its performance for fluorescent detection towards cadmium ions was explored.The MOFs probe UiO-66-N=CH2 displayed a sensitive fluorescence enhancement effect in aqueous environments by the addition of Cd2+.The fluorescence intensity of this probe increased with the increasing of Cd2+ concentration in the range of 0-500 ?M,with a sensitivity(Ksv)of 3.81 × 103 M-1 and a detection limit(LOD)of 0.336 ?M(37.8 ppb).This is because Cd2+ can interact with the C=N group to form weak coordination bonds thus affect the energy transfer and non-radiative transitions of the ligands,resulting in enhanced luminescence of the ligands.This work indicates that the design of imine-functionalized nano-MOFs probe via PSM method has an important guiding significance for the fluorescence detection of heavy metal ions(HMIs).Considering the superior stability,good conductivity and rich adsorption sites towards HMIs,UiO-66-NH2 was used to modify the glassy carbon electrode(GCE)and applicated in electrochemical detection of HMIs.Based on the modified electrode,trace detection of 0.1-3.0 ?M cadmium(Cd2+)and 0.1-2.0 ?M lead(Pb2+)were determined by square wave anodic stripping voltammetry(SWASV)with good linear correlation.The sensitivity of detecting Cd2+ was 14.72 ?A/?M,and the detection limit reached 0.411 ppb.The sensitivity of detecting Pb2+ was 19.92 ?A/?M with a detection limit of 0.678 ppb.Furthermore,the sensor has good anti-interference ability and repeatability.According to the coordination diversity of the rare earth elements,ZJU-27 was designed and synthesed by the ligand H3BTB and Yb3+ ions in DMF/water mixed solvent,which was further applicated in electrochemical detection of HMIs.Trinuclear clusters and nonanuclear clusters are two kinds of secondary building units of Yb3+,which were further bridged with H3BTB and self-assembled into a three-dimensional framework of hexagonal plate crystal ZJU-27.The electrochemical sensor based on ZJU-27 modified GCE electrode has good conductivity with charge transfer resistance(Rct)of 700 ?.Using square wave anodic stripping voltammetry(SWASV),the sensor can detect Zn2+,Cd2+,Pb2+ and Cu2+ respectively,with the highest sensitivity for Pb2+.The sensitivity for the detection of Cd2+ and Pb2+ were 30.26 ?A/?M and 53.10 ?A/?M,respectively,and the calculated LOD were 0.129 ppb and 0.228 ppb,respectively.The sensor can detect Cd2+ and Pb2+ simultaneously with a decrease in sensitivity,which indicates the competition of adsorption sites between Cd2+ and Pb2+ on the electrode surface.In addition,the sensor is capable to be used in real water samples for ion detection,showing its good anti-interference performance and value for practical use.