A double-layered neutral cadmium-organic framework for selective adsorption of cationic organic dyes through electrostatic affinity

The treatment of dyeing wastewater has been a major issue of environmental pollution at present. Adsorption is one of the more feasible methods, Metal-organic frameworks (MOFs) as a class of emerging porous materials have been widely utilized in adsorptive removal of organic dyes. Herein, we designed and synthesized a Cd-MOF {[Cd2(BPTC)(H2O)6]·2H2O}n (H4BPTC ​= ​3,3′,5,5′-biphenyl tetracarboxylic acid) to investigate the correlation of size-exclusion and charge-matching effect between MOFs adsorbents and dye molecules. X-ray single crystal diffraction indicated that Cd-MOF exhibits a unique double-layered helical coordination framework with tetramer water moieties accommodated in the open channels. Zeta-potential of Cd-MOF revealed it a negative charged framework that preferred electrostatic interactions with cationic dye particles, which endorsed Cd-MOF good adsorption capacities to cationic dyes especially methylene blue (MB) with the highest adsorption capacity of 595.4 ​mg ​g–1 at pH ​= ​7.