Abstract
Certain nano-scale metal oxides exhibiting the intrinsic enzyme-like reactivity had been used for environment monitoring. Herein, we evaluated the oxidase-mimicking activity of environmentally relevant nano-MnO2 and its sensitivity to the presence of metal ions, and particularly, the use of MnO2 nanozyme to potentially detect Cu2+, Zn2+, Mn2+, and Fe2+ in water. The results indicated the oxidase-like activity of nano-MnO2 at acidic pH-driven oxidation of 2,6-dimethoxyphenol (2,6-DMP) via a single-electron transfer process, leading to the formation of a yellow product. Notably, the presence of Cu2+ and Mn2+ heightened the oxidase-mimicking activity of nano-MnO2 at 25°C and pH 3.8, showing that Cu2+ and Mn2+ could modify the reactive sites of nano-MnO2 surface to ameliorate its catalytic activity, while the activity of MnO2 nanozyme in systems with Zn2+ and Fe2+ was impeded probably because of the strong affinity of Zn2+ and Fe2+ toward nano-MnO2 surface. Based on these effects, we designed a procedure to use MnO2 nanozyme to, respectively, detect Cu2+, Zn2+, Mn2+, and Fe2+ in the real water samples. MnO2 nanozyme-based detecting systems achieved high accuracy (relative errors: 2.2–26.1%) and recovery (93.0–124.0%) for detection of the four metal ions, respectively. Such cost-effective detecting systems may provide a potential application for quantitative determination of metal ions in real water environmental samples.
Highlights
In recent years, considerable attention has been paid to the applications of artificial nanomaterials as nanozymes in mimicking the intrinsic catalytic function of natural enzymes due to their unique structural, electrical, and optical properties, as well as remarkable catalytic activities [1,2,3]
E role of dissolved O2 in the oxidation of 2,6-DMP was evaluated by purging the reaction solution with N2, resulting in a decrease on the oxidase-like activity of nanoMnO2. is revealed that dissolved O2 acted as an electron acceptor in the catalytic reactions [14, 29]. is result is in agreement with an earlier report that indicated the oxidation of a substrate in the absence of H2O2 via bovine
Nano-MnO2 was used as an oxidase mimetic to catalyze the chromogenic reaction of 2,6-DMP in citratephosphate buffer solution (C-PBS) buffer
Summary
Considerable attention has been paid to the applications of artificial nanomaterials as nanozymes in mimicking the intrinsic catalytic function of natural enzymes due to their unique structural, electrical, and optical properties, as well as remarkable catalytic activities [1,2,3]. Chromogenic reactions by nano-MnO2 have been developed using dissolved O2 as the oxidant, avoiding the use of H2O2 [14], providing easy and rapid detecting systems for quantitative analysis of any substances that can serve either as the accelerator or inhibitor of the chromogenic reactions [15, 16]. Such systems could be used for real environmental
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