A stable metal cluster-metalloporphyrin MOF with high capacity for cationic dye removal

Abstract

A metalloporphyrin Cu₅-cluster based MOF (metal–organic framework), [Cu_4.5((H₄TZPP)(TZPP)Cl₂)(H₂O)_0.5]·CH₃NH₂CH₃·7EtOH·8H₂O (LIFM-WZ-3) was synthesized from the tetrapodal ligand 5,10,15,20-tetrakis[4-(2,3,4,5-tetrazolyl)phenyl]porphyrin (H₆TZPP) and copper chloride. LIFM-WZ-3 exhibits a rare 2D + 3D → 3D interpenetration topology, of which the frl-type 3D MOF and a layered 2D HOF (hydrogen bond organic framework) are intertwined, leading to an anionic framework with 1D spindle-like channels. Powder X-ray diffraction analysis reveals that the framework is stable in acid, base and various organic solvent environments. LIFM-WZ-3 exhibits moderately high separation performances for CO₂/CH₄, CO₂/N₂, C₃H₆/CH₄, C₂H₆/CH₄, and C₂H₄/CH₄ at room temperature. Specifically, the anionic framework in LIFM-WZ-3 containing dimethylamine cations can selectively adsorb cationic organic dyes from aqueous pollutants for recycle purpose. The high adsorption capacity for methylene-blue (MB⁺, 983 mg g⁻¹) and crystal violet (CV⁺, 713.5 mg g⁻¹) ranks the highest among those MOFs ever reported.