Studies On Post-synthetic Modification Of Metal-Organic Framework And Fluorescent Properties

Metal-organic frameworks?MOFs?are excellent candidates for chemical sensing due to their outstanding fluorescence properties,diverse chemical properties,permanent porosity,and high surface areas.To date,a series of fluorescent probes based on MOFs have been used to recognize guest targets including ions,organic small molecules,gases,biomolecules,pH and temperature.It is a hot spot to design high performance MOFs-based sensors to achieve high sensitivity and selectivity.To introduce appropriate recognition sites benefits to provide chemically specific receptor-target interactions.The interactions should be reversible and should not destroy the structural integrity of MOFs.Therefore,the choice and incorporation of functional groups are essentially important.Post-synthetic modification?PSM?is a valuable alternative to introduce functional groups into MOFs and will not affect their frameworks.The combination of MOFs and PSM endows MOFs-based sensors with synergistic merits of three-dimensional networks architecture,uniform nanoscale cavities,and recognition sites,which greatly benefits the sensing ability and expands their applications.In this work,2,3,4-trihydroxybenzaldehyde?THBA?and carboxylatocalix[4]arene?CC[4]A?were selected as the functional materials to modify MOFs to detect free bilirubin and hippuric acid in complex samples,respectively.The specific investigation is divided into two parts:1.We reported the synthesis of a novel fluorescent material UIO-66-PSM based on the aldimine condensation reaction of UIO-66-NH₂ and THBA.UIO-66-PSM exhibited good day-to-day fluorescence stability within 2 weeks.The abundant unsaturated metal sites,hydroxyl groups,and?electrons of UIO-66-PSM made it tend to interact with free bilirubin.The fluorescence of UIO-66-PSM could be effectively quenched by free bilirubin via a fluorescent resonant energy transfer process,thus achieving its recognition of free bilirubin.The developed sensor exhibited fast response time,outstanding sensitivity,and high selectivity toward free bilirubin without suffering from the interference of other biomolecules and metal ions.Moreover,the sensor was successfully employed to detect free bilirubin in human serum samples.The obtained recovery values were in the range of 96%–107%with relative standard deviations less than 3.0%.2.CC[4]A@MIL-53-NH₂?Al?was prepared based on the covalent attachment of MIL-53-NH₂?Al?and CC[4]A via a PSM strategy.The introduced CC[4]A could not only enhance the fluorescence performance and the recognition ability of the probe,but also sustain the high stability under UV light and moisture conditions.A method based on the as-synthesized CC[4]A@MIL-53-NH₂?Al?probe was established for rapid and highly selective sensing hippuric acid.Over the concentration range of0.005–3 mg/mL,the calibration curve was obtained with a satisfactory linearity?R²=0.993?.The detection limit was determined to be as low as 3.7?g/mL.The method was used for direct monitor of hippuric acid in human urine,recovery values were obtained in the range of 95%–104%with relative standard deviations less than 4.0%.