Preparation And Gas Fluorescence Sensing Properties Of Luminescent Metal-Organic Framework Films

Luminescent metal-organic frameworks?MOFs?,with bright promising in fluorescent sensing and luminescent devices,have intrigued significant interest.Due to their multipul functional units and post-synthesis strategies,it is easy for them to be designed for specific recognition of ions or small molecule.However,most of the MOF-based luminescent sensors can only be operated as powder sample,which severely restricts the actual applications of MOFs.Practical applications of MOF-based sensors rely on the development of film making technology,especially in the field of gas sensing,where films possess severe advantages,such as portable,standable in the blast of gas flux and full contact to analysts.In this thesis,we have developed“in situ sencondary growth”and“spontaneous oxidation of metal substrate”to fabricate new MOF films,which expanded the preparation methods of MOF films.Addtionally,fluospher and react sites were introduced into the MOF films by post-synthesis and linker selection,leading to highly selective and fast response gas fluorescence sensor with novel sensing mechanism.A novel metal-organic framework film MIL-124?In?film was prepared on porous?-Al₂O₃ ceramic plate by in situ synthesizing.After introducing Eu³⁺ions to the free-COOH sites of the ligand,a luminescent MOF film MIL-124?In?@Eu³⁺was obtained and the emissions are unaffected to temperature and humidity.Ammonia exihibits apparent quenching effect to the fluorescence of MIL-124?In?@Eu³⁺film with the limit of dection?LOD?of 26.2 ppm.After sensing process,the fluorescence of MIL-124?In?@Eu³⁺film can be recovered by heating.Based on the chemical reaction between NH₃ and the-COOH,the formation of-COONH₄ which was demonstrated by FT-IR spectrum,which affected the energy absorption efficiency of the ligand,quenching the characteristic emission of MIL-124?In?@Eu³⁺film.In order to improve the sensitivity to harmful gases,we developed“in situ secondary growth”strategy to fabricate an Eu?III?-organic framework film on glass for fluorescence sensing of gaseous SO₂.The UiO-66-NH₂ film was firstly synthesized on glass as a seed layer.Because of their matched components and structures,the Eu-BDC-NH₂ film can be successfully fabricated on the UiO-66-NH₂layer through in situ secondary growth.The Eu-BDC-NH₂ film exhibits strong characteristic Eu³⁺emissions,which can be fast and remarkably quenched by SO₂ gas.The LOD to SO₂ gas is calculated to be 0.65 ppm and the response time is as short as6 s.Further,we reveal that the quenching effect is caused by the intermolecular charge transfer between the ligand and SO₂ molecules,as supported by the luminescence spectra and simulated calculation results.The turn-on detection,in which the interation of the MOFs with analytes can turn a relatively“dark”material into a luminescent one,can avoid the fake detection results caused by common interference factors.We utilized the post-functionalized fluorescent film,MIL-100?In?@Eu³⁺/Cu²⁺film,realizing fluorescence turn-on sensing of gaseous H₂S at room temperature for the first time with the limit of detection as low as 0.535 ppm,which is comparable to some reported fluorescent probes for S^2-ions and semiconductor based H₂S sensors.The sensor was designed due to the strong affinity of H₂S with Cu²⁺.With the formation of CuS,the“antenna effect”between the ligand and Eu³⁺was recovered,resulting in the fluorescence turn-on of Eu³⁺emission.Additionally,we proposed a new method to realize multi-colour anti-counterfeiting patterns with lanthanide ions ink,taking advantage of the extraordinary smooth surface and uncoordinated carboxylate groups within the MIL-100?In?film.The construction of MOF films with remarkable robustness and adhesion between the MOFs crystals and the substrate still remains challenge.We proposed a facile strategy involved in the spontaneous oxidation of metal substrate for the development of robust MOF films.By utilizing the metal substrate as the only metal source,five different MOF films can be synthesized in different ligand solutions,including MOF-5-?OH?₂,ZIF-8,ZIF-67,Zn-BTC and ZJU-66 films.The high quality of the as-obtained MOF films is proved by adhesion examinations through scanning electronic microscopy measurements.It should be noted that even in strong corrosive environments the as-prepared products can be well preserved,ensuring their applications in extreme environment.Among them,ZJU-66 with a newly reported structure,which is constructed by zinc ions and 2-aminoterephthalic acid,was selected as representation to demonstrate its outstanding NO₂ sensing performance due to the strong electron absorption capacity of NO₂.