Effects of Alkali and Alkaline‐earth Cations on the Removal of Reactive Dyes with Cucurbituril

The sorption of reactive (textile) dyes onto cucurbituril, a cyclic polymer with hydrophobic cavity, was studied. Dye sorption is strongly enhanced by Ca²⁺ or Sr²⁺ concentrations up to 100 mmol/L for all studied dyes. Mg²⁺ and alkaline ions had similar effects for only one dye (Reactive Red 120), and only at higher concentrations. Concentrations above 100 mmol/L – depending on cation and dye – dissolve cucurbituril and prevent dye removal. As shown in previous studies by our group loadings obtained under suitable conditions (calcium concentration between 2 and 100 mmol/L, total salt concentration not exceeding 100 mmol/L) are 1 to 1.7 mol/mol or 0.9 to 1.8 g/g. The chemical mechanism responsible for the ionic influences is still under investigation. Generally, cucurbituril is a potent sorbent for reactive dyes. However, the technical application is still limited by the lack of a support material that would allow use in fixed bed filters.