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.