Functionalized copper metal–organic framework with laccase-like activity for the colorimetric detection of sodium ions in cigarette papers

Abstract

A fast colorimetric approach for the detection of sodium ions (Na⁺) in cigarette papers was developed using a copper-based MOF (Cu-BDC-NH₂). Initially, the prepared Cu-BDC-NH₂ nanosheets functioned as highly effective nanozymes, exhibiting strong laccase-like catalytic activity, which facilitated the chromogenic reaction between 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP). Subsequently, potassium pyroantimonate (PA) ligand could get adsorbed on the Cu-BDC-NH₂ surface to inhibit the laccase-like catalytic activity and cause a decrease in absorbance. The analyte Na⁺ reacted with PA to generate a stable precipitate of [Na₂(PA)], allowing the nanozyme activity to recover and give a deep-red color. A quantitative colorimetric approach was developed for the determination of Na⁺, demonstrating a broad range (8.33 to 6 × 10³ µg L⁻¹), a low limit of detection (3.46 µg L⁻¹), high accuracy (recovery rates ranging from 95.80% to 108.00%), and satisfactory selectivity. Finally, Cu-BDC-NH₂ was employed for the colorimetric determination of Na⁺ in cigarette paper samples, demonstrating its successful practical applicability.