Cu-HEPES Nanosheets with Dual Enzyme-Mimetic Activities for Colorimetric Detection of 2,4-Dichlorophenol

A convenient one-pot strategy was adopted to fabricate Cu-4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) nanosheets through the coordination of HEPES with copper ions under alkaline conditions, and the obtained nanosheets possessed dual laccase-mimetic and oxidase-mimetic activities for phenolic pollutant analysis and show potential for dye decolorization/removal. The Cu-HEPES nanosheets displayed significant dual enzyme-mimetic activities, effectively catalyzing the oxidation conversion for phenolic compounds, specifically 2,4-dichlorophenol (2,4-DCP), to yield quinone imine products characterized by a unique absorption signal at 500 nm. Meanwhile, Cu-HEPES nanosheets also facilitated the conversion of 3,3',5,5'-tetramethylbenzidine to yield a yellow-green substance with a distinctive absorption signal at 458 nm. The Cu-HEPES nanosheets displayed a satisfactory affinity (K_m = 23.2 μM) for 2,4-DCP, facilitating its use in accurately detecting 2,4-DCP (linear range from 3.3 to 16.6 µM) with a detection limit of 0.3 µM. Subsequently, the devised colorimetric sensing platform was applied to measure 2,4-DCP levels in real tap water samples, yielding satisfactory spiked recoveries ranging from 92.7% to 106.9%. Finally, the synthesized Cu-HEPES nanosheets were preliminarily evaluated for the simultaneous decolorization/removal of malachite green and Congo red, suggesting their potential applicability in aqueous systems containing multiple organic dyes.