Preparation And Application Of In(?)-Based Metal-Organic Frameworks(In-MOFs) With Pyridine Carboxylate Ligand

In this paper,a pyridinecarboxylic acid ligand 2-(4-pyridyl)terephthalic acid(H2pta)with Lewis base active site was selected to synthesize a multifunctional metal-organic framework(MOF)in the existence of the main group metal In(?)ion under solvothermal conditions.Based on the structural analysis and characterization,the fluorescence sensing and gas adsorption properties of the MOF have been explored.The main contents are as follows:1.The combination of 2-(4-pyridyl)terephthalic acid(H2pta)ligand and metal In(?)center leads to a case of indium metal-organic framework material H3O[In3(pta)4(OH)2]·10H2O(MOF 1).Structural analysis shows that MOF 1 is composed of linear In3(COO)4(OH)2 clusters to form a three-dimensional framework.There is a one-dimensional open channel in the framework.The channel cross section is 11.6 A × 13.4 A,and the effective porosity is 33.5%.The topology symbol of the MOF is described to be(43)2(418624 83).There are two types of pta2-connectors in MOF 1.The pyridyl N atom in one of the two coordination modes is not related to the In(?)ion and located at the inner side of the channel to be a functional site.Thermal analysis results show that the decomposition temperature of MOF 1 is 350??indicating that MOF 1 represents excellent thermostability.2.The network of MOF 1 remains stable not only in water for 5 days,but also in the acid-base solutions with pH from 1 to 13 for one day,demonstrating that MOF 1 has good water stability and chemical stability.Fluorescent experiments display that MOF 1 performs strong solid-state fluorescence emission and can be considered as a sensor to detect Fe3+ions through fluorescence quenching effect.The calculated quenching constant Ksv is of 12205 M-1.More importantly,MOF 1 can be recycled up to 5 times.As a result,MOF 1 is a promising fluorescent sensor that can be employed as a highly selective and recyclable material for detecting Fe3+ions.3.Based on the stractural characteristics of the MOF,the gas adsorption has been investigated.At 77 K and 1 atm,the maximal adsorption capacity of N2 is measured to be 170 cm3/g.MOF 1 is indicative of not only a reversible type ? adsorption behavior,but also a significant hysteresis during the desorption process,which is probably due to the relatively narrow pores preventing the escape of the gas.In order to further develop the potential application of MOF 1 in gas capture and separation,the adsorption isotherms of CO2 and CH4 are recorded at 273 and 298 K,respectively.For MOF 1,the adsorption capacities are 94.45 cm3/g for CO2 and 24.25 cm3/g for CH4 at 273 K,as well as 45.75 cm3/g for CO2 and 4.85 cm3/g for CH4 at 298 K,respectively.Ideal adsorbed solution theory(IAST)can be used to calculate the separation selectivity of the CO2/CH4 binary mixture at 298 K.The simulated selectivity of the CO2/CH4 mixture is observed from 10 to 60 which is superior to that of the known MOFs.Moreover,the Qst values of CO2 and CH4 are respectively calculated to be 38.6 and 33.8 kJ·mol-1,implying a strong interaction between the MOF 1 skeleton and gas molecules.The results of this work provide both theoretical and practical supports for the development of high-performant multifunctional materials.