An anionic Zn-MOF composed of 1D columnar SBUs for highly C2H2/CH4 selective adsorption, dye adsorption and fluorescence sensing.

Abstract

An anionic three-dimensional framework {(Me2NH2)2[Zn8(L)6(ad)4(μ4-O)]·10DMF·11H2O}(Zn-MOF, L2- = 4,4'-(3-aminopyridine-2,5-diyl)dibenzoic acid; ad- = adeninate) with a column-layered structure was synthesized. Structural studies show that the Zn-MOF has octahedral cages [Zn8(ad)4(μ4-O)], the adjacent cages are connected by O atoms to form 1D columnar SBUs, and every four SBUs are connected by L2- to form a square channel 3D framework. Gas adsorption studies show that the BET and Langmuir surface areas of Zn-MOF are 1370.31 and 1478.04 m2 g-1, respectively, and the total pore volume for single-point adsorption is 0.528 cm3 g-1. The surface of the pores of the Zn-MOF is occupied by open metal sites and uncoordinated carboxyl groups, showing good capture ability for C2H2 and good adsorption selectivity for C2H2/CH4. More importantly, the free (CH3)2NH2+ ions present in the pores of the columnar layered Zn-MOF can cation-exchange with MB, MV, and RhB ions in aqueous solution. Therefore, Zn-MOF can not only effectively adsorb the cationic dyes MB, MV, and RhB, but also exhibit particularly selective sorption towards the mixed anion and cation dyes MB/MO and MV/MO. In addition, a series of fluorescence experiments show that Zn-MOF has good fluorescence properties, exhibiting highly selective and sensitive fluorescence detection and recognition performance for Fe3+ ions in aqueous solution with a low detection limit.