A water-insoluble viologen-based β-cyclodextrin polymer for selective adsorption toward anionic dyes

The viologen-based β-cyclodextrin polymer (V-CDP) was successfully prepared via a Menshutkin reaction for the first time, and its organic dyes uptake capacities were investigated. The synthesized polymer showed BET surface area of 22 m2 g−1 and exhibited highly charge-selective adsorption of anionic dyes, i.e. congo red and methyl orange. Remarkably, the polymer could efficiently absorb anionic dyes from binary cationic-anionic dye mixtures in a 1:1 mass ratio. The adsorption process of the two anionic dyes on the polymer both followed the pseudo-second-order rate equation and the Langmuir adsorption model. According to the Langmuir isotherm, the maximum adsorption capacity of V-CDP for congo red and methyl orange was calculated to be 323 mg g−1 and 370 mg g−1, respectively. Additionally, the polymer can be easily regenerated and reused at least 5 times with no loss of adsorption efficiency, demonstrating its potential application in dye removal.