Pt nanoparticles modified single-atoms nanozymes with tunable metal valence for rapid chlorpyrifos colorimetric detection.

The rational design and synthesis of nanozymes with tunable peroxidase-like (POD-like) catalytic activity remain challenging. By coupling metal single-atom and nanoparticle catalytic active sites, catalysts can drive complex catalytic systems, enhance reaction selectivity, and enable synergistic catalysis. On this basis, the effect of the metal oxidation state on POD-like catalytic activity can be clarified and the highly active nanozymes can be designed reasonably. This insight motivated us to develop a temperature-regulated strategy for synthesizing Pt nanoparticles and single-atom loaded porous carbon spheres (Pt/Pt-NC) nanozymes with tunable Pt valence, thereby enabling precise regulation of POD-like activity. The experimental results demonstrated that the nanozyme under the pyrolysis temperatures of 800 °C had the highest ratio of Pt/Pt during different pyrolysis temperatures (750 °C, 800 °C, 850 °C). The Pt/Pt-NC nanozymes displayed superior POD-like catalytic activity with the specific activity of 110.76 U mg of Pt/Pt-NC-800. Subsequently, the Pt/Pt-NC-800 was applied to detect pesticides under low concentrations (2-10 mg L) based on enzyme inhibition which displayed an excellent response of chlorpyrifos with the limit of detection of 0.81 mg L. The temperature-regulated synthesis strategy and valence regulation approach provide a new direction for the rational design and regulation of POD-like catalytic activity.