Contrastive study for coadsorption of copper and two dihydroxybenzene isomers by a multi-amine modified resin

Coadsorption of Cu(II) and two dihydroxybenzene isomers (hydroquinone, HQ and catechol, CAT) onto a multi-amine modified resin (CEAD) were comparatively studied. The presence of Cu(II) promoted adsorption of both HQ and CAT by a maximum of 25.8% and 41.6%, respectively. However, two diphenols exerted a very different influence on Cu(II) uptake. Higher concentrations of HQ consistently suppressed Cu(II) adsorption while the coexistence of CAT facilitated it, especially at lower CAT concentrations. The interactions among solutes and adsorbents were revealed by means of kinetic tracking, sequential adsorption experiments, and characterizations/calculations (FTIR, XPS, MINTEQ and DFT). Cu(II) and HQ/CAT competed for amine sites with the order of adsorption affinity as HQ > Cu(II) > CAT. The bridging effect of Cu(II) forming ternary complexes (amine-Cu-CAT/HQ) on the resin phase was the dominant mechanism for the enhanced adsorption of diphenols. The [Cu-CAT] complex species showed a lower affinity to bind directly to amine sites compared with free Cu²⁺. Instead, the complex could be attracted by the polyphenyl matrix of CEAD, contributing to the increase of Cu(II) adsorption. Additionally, Cu(II) and diphenols were successively recovered, and CEAD could be stably reused. The findings will guide adsorbent applications and the environmental fate of concurrent heavy metals and phenolic compounds.