Rapid colorimetric detection of trace-level catechol and hydroquinone using a robust, highly active δ-MnO2 nanoflower nanozyme synthesized under mild conditions.

The colorimetric discrimination and detection of catechol (CC) and hydroquinone (HQ) remain a challenge due to their highly similar physicochemical properties. Herein, pure-phase δ-MnO2 nanoflower nanozyme (δ-MnO2-NF) was synthesized at a mild temperature of 80°C. The as-obtained material exhibits dual laccase- and oxidase-like activities, favorable substrate affinity and accelerated maximum reaction velocity, with its specific activity more than 11.77 times higher than previously reported nanozymes. Additionally, it features robust stability across broad ranges of pH (2-10), temperature (10-80°C), NaCl concentration (0-300 mM), and organic solvent content (0-80%). These properties are attributed to the amorphous nanoflower structure of δ-MnO2-NF, which provides rich active sites owing to its large specific surface area, abundant oxygen vacancies and hydroxyl groups, and exhibits high robustness due to its strong structural integrity. δ-MnO2-NF was successfully utilized to construct a colorimetric sensing system for the discrimination and detection of CC and HQ. The system achieves low detection limits of 0.189 and 0.0089 μM, respectively, along with high anti-interference capability and a fast response time of 1 min, significantly outperforming previously reported colorimetric methods. This facile, pretreatment-free colorimetric system, based on the robust and remarkably active δ-MnO2-NF prepared under energy-saving conditions, shows promising potential for low-cost, on-site rapid screening of real environmental water samples.