Construction Of Three Metal-Organic Frameworks And Their Gas Adsorption Separation And Fluorescence Sensing Properties

Environmental toxicants have caused serious potential harm to the ecosystem because of its easy migration and difficulty to remove,and the development of efficient detection methods is crucial to manage the hazards of these pollutants.Meanwhile,the storage and low-energy separation of light hydrocarbon energy gases such as C2H2 and C3H6 are also a major challenge for the industry,and there is an urgent need to develop corresponding new materials and technologies to solve them.In this paper,two nitrogen-containing heterocyclic polycarboxylate ligands with Nd(Ⅲ),Cd(Ⅱ),Eu(Ⅲ)and Tb(Ⅲ)as the central ions were designed and four structurally novel metal-organic frameworks were constructed by the solvothermal method.The structure and stability of the metal-organic frameworks were characterized by single-crystal X-ray diffraction structural analysis,powder X-ray diffraction,Fourier-IR spectroscopy,and thermogravimetric analysis.The fluorescence temperature sensing of metal-organic frameworks,the fluorescence sensing of environmental toxic substances such as tetracycline(TC),4-(phenylazo)aniline(AnY)and PF6-,and the storage and separation of energy gases such as light hydrocarbons were also investigated on this basis.Related work is as follows:1.A novel metal-organic framework was constructed using[4,4’-(4,4’-bipyridine-2,6-diyl)dibenzoic acid](H2L1)as a ligand under solvothermal reaction conditions:{[Cd(L1)(DMF)2]·2.5H2O}n(1).The fluorescence temperature sensing experiments investigated the temperature sensing performance of(1)in the physiological interval(298-358 K)and the physiological high temperature interval(298-478 K),and it was found that the emission intensity of(1)exhibited a good linear relationship with temperature in the low temperature band 313-333 K and the high temperature band 338-403 K,with the correlation coefficients R2 of 0.9949 and 0.9973.And the direct transition from 313-413 K low temperature to high temperature band also showed good linearity with R2=0.9937 and calculated relative sensitivity Sr=0.76%K-1(413 K).There are more reports of fluorescent temperature sensing materials covering the low temperature to physiological temperature interval,while the high temperature region is less reported.The above analysis indicates that(1)can be used for temperature sensing and also provides a feasible idea for the preparation of higher temperature sensing materials.Meanwhile,(1)can efficiently detect TC and AnY through fluorescence quenching pathway;the detection limits are 0.49 μM(0.21 ppm)and 0.098 μM(19.33 ppb),respectively.Competition and cycle experiments show that(1)has good anti-interference ability and recyclability to the corresponding sensed objects,which indicates that(1)can be used as a fluorescent probe for the detection of TC and AnY.2.A novel heterometallic organic-framework with a "pillared-layer" structure was constructed under solvothermal reaction conditions using[4,4’-(pyridazine-3,6-diyl)dibenzoic acid](H2L2)as the ligand,H2ODA as the co-ligand:｛[Nd3(ODA)3(L2)3HNa2]·1.8H2O·5DMF}n(2).The gas adsorption performance of(2)was investigated.77 K N2 adsorption experiments showed that the BET specific surface area of(2)was 1062 m2 g-1.Also,(2)showed good adsorption capacity for C2H2 and C3H4 at atmospheric pressure:The adsorption capacities were 138.32 cm3 g-1 and 103.78 cm3 g-1(273K/298K,STP)for C2H2 and 135.99 cm3 g-1 and 120.27 cm3 g-1(273K/298K,STP)for C3H4,respectively,while the adsorption capacities of(2)for CO2 and for C3H6,which were significantly smaller than those for C2H2 and C3H4.It has more significant adsorption differences for light hydrocarbon gases and has the potential to separate C2H2/CO2 and C3H4/C3H6.IAST shows that(2)has a good theoretical separation capacity for C2H2/CO2 and C3H4/C3H6(4.07,4.30,10/90 v/v),and dynamic breakthrough tests further demonstrate that(2)is a porous crystalline material that can be used for the separation of C2H2/CO2 and C3H4/C3H6.3.Based on(2),two Na-Ln heterometallic organic-frameworks were continued to be constructed:{[Eu3(ODA)3(L2)3Na(H2O)]·H2O·DMF}n(3),{[Tb3(ODA)3(L2)3Na(H2O)]·2.75H2O·2DMF}n(4).Fluorescence sensing studies revealed that(3)and(4)can efficiently detect PF6-with corresponding detection limits of 1.34 ppm(3)and 0.42 ppm(4).The competition and cycle detection experiments showed that(3)and(4)have good anti-interference ability and recyclability for the above analytes.Meanwhile,77 K N2 adsorption experiments showed that the BET specific surface areas of(3)and(4)are 848 m2 g-1 and 816 m2 g-1,respectively.Gas adsorption experiments showed that(3)and(4)have a good adsorption capacity for C2H2(106.87 cm3 g-1,97.55 cm3 g-1,298 K).Ideal adsorption and dissolution theory(IAST)show that(3)has a good theorcetical separation capacity for C2H2/CH4(18.70,50/50 v/v).These analyses indicate that(3)can be used not only as a storage material for C2H2,but also has the ability to separate C2H2/CH4 at ambient temperature and pressure.