Ionic Liquid-Modified Resorcinol Formaldehyde Resins: Synthesis and Applications to Methylene Blue Removal

Two new imidazolium-functionalized resorcinol-formaldehyde resins RFs were synthesized, using butyl-methyl imidazolium resorcinate [C₁C₄Im][Res] as a new precursor or using a post-functionalization method. During its synthesis, [C₁C₄Im][Res] spontenaously co-crystallizes with resorcinol (in a 1: 1 stoichiometry): the crystal structure shows H-bonds between resorcinol and resorcinate, and rarely observed π⁺-π^- and C-H - π interactions between the imidazolium ring and resorcinate. New RFs presented substantial decreases of the band gap compared to unmodified RF (2.0-1.72 eV). The use of [C₁C₄Im][Res] significantly improves particle size uniformity compared to unmodified RF, whereas the post-functionalization method partially degrades their structure. As RF, the two new resins efficiently catalyze the photodegradation of the methylene blue cation, and the post-functionalized resin has excellent adsorption properties for this dye.