Butyl-methylimidazolium functionalized resorcinol-formaldehyde resins: synthesis, properties, 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 stoechiometry): the crystal structure shows H-bonds between resorcinol and resorcinate, and rarely observed π⁺-π⁻ and C-H -π interactions between imidazolium ring and resorcinate. New RFs presented substantial decreases of the band gap compared to unmodified RF (from 2.0 eV to 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 catalyse the photodegradation of the methylene blue cation, and the post-functionalised resin has excellent adsorption properties for this dye.