Colorimetric detection of chromium(<scp>vi</scp>) using copper-based porphyrin organic framework materials and 8-hydroxyquinoline <i>via</i> a ‘signal inhibition-target activation’ response mode

Chromium(VI) ions (Cr(VI)) are highly toxic heavy metal pollutants, and their rapid detection holds significant importance for environmental protection. In this study, a colorimetric detection platform was developed using a copper-based porphyrin metal-organic framework (CuTCPP) with peroxidase-like (POD) activity. 8-Hydroxyquinoline (8-HQ) was used to inhibit the color-forming reaction. Upon the addition of the target analyte, Cr(VI), the colorimetric response was restored, since Cr(VI) can preferentially form a chelate with 8-HQ. Results showed that the detection system exhibited a linear range from 50 nM to 10 μM (<i>R</i>² = 0.999) with a low detection limit (LOD) of 22.3 nM, demonstrating excellent selectivity even in the presence of multiple interfering ions. The proposed intelligent response mechanism provided a visual, rapid, and user-friendly solution for on-site monitoring of Cr(VI) contamination, showing promising application potential in environmental analysis.