Amide-functionalized ionic indium–organic frameworks for efficient separation of organic dyes based on diverse adsorption interactions

Abstract

By varying the solvents, two ionic indium–organic frameworks (1 and 2) were achieved. Both MOFs are constructed from the same indium monomer building units and amide-functionalized linker, but they present distinct topologies along with varied channel sizes and shapes. Importantly, the adsorption potential of the two anionic frameworks towards organic dyes with different charges and sizes was thoroughly examined. Both frameworks exhibited highly selective adsorption of the cationic dye methylene blue (MB) based on preferential electronic affinity and the size-exclusion effect. Besides MB, 1 and 2 also exhibited uptake of cationic dyes rhodamine B (RhB) and rhodamine 6G (R6G) but an inert reaction to the cationic dye crystal violet (CV), and thus additional hydrogen-bonding interactions of the amide groups and dyes during adsorption were suggested. The results also revealed that the adsorption capacity and kinetic constant of 1 are greater than those of 2, showing the importance of porosity and pore structure during adsorption. The adsorption capacity of 1 towards MB is as high as 281 mg g⁻¹ and thus it can potentially serve as a column-chromatographic filler for separating dye molecules.