Silver Ion-Facilitated Singular Poulos–Kraut Mechanism of O–O Heterolysis to Enhance the Light Activation of H2O2 over Peroxidase-Mimicking Photonanozymes

The Poulos-Kraut heterolytic O-O cleavage mechanism is essential for natural peroxidases to activate H₂O₂. Current existing peroxidase-mimicking nanozymes, including photonanozymes (PNZs), however, are generally believed to prefer the Fenton-type mechanism of O-O homolysis, which produces ^•OH radicals. Here, Ag⁺ ions are introduced into TiO₂ PNZs to boost the hot hole-driven O-O heterolysis for the expedited H₂O₂ activation in the peroxidase-like photonanozymatic reaction while inhibiting the Fenton-type O-O homolysis. The Ag⁺-facilitated Poulos-Kraut heterolytic O-O cleavage mechanism for H₂O₂ activation is explicated in terms of the speedy capture and exhaustion of photogenerated electrons by Ag⁺ and the dissociation of the peroxo-oxygen bridge in Ti-O-OH promoted by accumulated hot holes. Moreover, the enhanced photonanozymatic activity of TiO₂ PNZs enables the construction of a rapid colorimetric sensing platform for Ag⁺ determination. This work provides valuable insights into the mechanism of H₂O₂ activation and exemplifies a novel photoregulation strategy for controlling reaction pathways in nanozymes.