Design,Synthesis And Fluorescence Sensing Properties Of D¹⁰ Grouped Transition Metal Organic Frameworks

In today’s society,pollution,both anionic and cationic,poses a great challenge to our environment and ecosystem.For example,Fe³⁺is essential in many life processes,and it not only promotes immune responses,but also activates enzymes,thus performing their unique physiological functions.As another example,Cr₂O₇^2-exists in different occupational environments,and once the Cr₂O₇^2-in the environment exceeds a certain limit,it can pose serious hazards.In order to effectively detect these ionic contaminations,d¹⁰subgroup transition metal organic framework materials（MOFs）are considered as an ideal sensor.MOFs have the advantages of adjustable luminescence characteristics,high selectivity,good sensitivity,short response time,easy operation,and visualization,which have wide application prospects.In this paper,two examples of d¹⁰subgroup transition metal organic framework materials,which we call:Cd-BIPA and SXU-120,were constructed from the design considerations of both metal and organic ligands to achieve the sensitive detection of Fe³⁺and Cr₂O₇^2-.The details of the study are as follows:（1）Three-dimensional Cd-BIPA was synthesized by using d¹⁰transition metal Cd（Ⅱ）and organic ligand 4,6-bis（1H-1,2,4-triazole-1-ethyl）isophthalic acid（H₂BIPA）to detect Fe³⁺.The structure of Cd-BIPA was analyzed by single-crystal X-ray diffraction combined with elemental analysis.It is worth noting that the K_svvalue of Fe³⁺quenching of Cd-BIPA fluorescence was 1.3171×10⁴M^-1.The detection limit of Fe³⁺LOD is1.3681×10^-6M.Other metal ions(such as Al³⁺,Cd²⁺,Li⁺,Mg²⁺,In³⁺,etc.)do not interfere with the detection of Fe³⁺.After five regenerations for Fe³⁺detection,the fluorescence emission intensity of Cd-BIPA only slightly decreased,which indicates that Cd-BIPA is a fluorescent detection material that can be regenerated for many times.The quenching mechanism was investigated,and it was found that the absorption spectra of Fe³⁺to Cd-BIPA overlapped,and the quenching of Cd-BIPA fluorescence was caused by the competitive absorption of excitation light.（2）An example of 1,3,5-triazine ringμ₃-bridged neutral Cu（I）-MOF SXU-120 was synthesized by using metal Cu（Ⅱ）and ammeline as ligands.SXU-120 can be stable in different solvents,such as boiling water,acid solution（0.01 M nitric acid）,potassium hydroxide base solution（10 M）,etc.SXU-120 has very high stability.SXU-120 can detect Fe³⁺and Cr₂O₇^2-very sensitively,the quenching constant K_svof Fe³⁺is 1.0208×10⁴M^-1and the detection limit of Fe³⁺LOD is 1.0×10^-6M.The quenching constant K_svof Cr₂O₇^2-is 3.7188×10⁴M^-1and the detection limit of Cr₂O₇^2-LOD is 1.236×10^-6M.Mechanistic investigation showed that the UV-vis absorption spectra of Fe³⁺and Cr₂O₇^2-had the largest overlap with SXU-120 MOF,producing a significant SXU-120 was able to maintain a sensitive response to Fe³⁺and Cr₂O₇^2-after several regenerations.