Fluorogenic Reaction Probes Defect Sites on Titanium Dioxide Nanoparticles

Abstract Titanium dioxide nanoparticles (TiO₂ NPs) have traditionally been utilized as industrial catalysts, finding widespread application in various chemical processes due to their exceptional stability and minimal toxicity. However, quantitatively assessing the reactive sites on TiO₂ NPs remains a challenge. In this study, we employed a fluorogenic reaction to probe the apparent reactivity of TiO₂ NPs. By manipulating the number of defect sites through control of hydrolysis speed and annealing temperature, we determined that the Ti(III) content is positively correlated with the reactivity of TiO₂ NPs. Additionally, these Ti(III) sites could be introduced by reducing commercial TiO₂ NPs using NaBH₄. Our findings suggest that fluorogenic oxidation of Amplex Red is an effective method for probing defect site densities on TiO₂ NPs. Utilizing single‐molecule fluorescence imaging, we demonstrated the ability to map defect site density within TiO₂ nanowires. Achieving sub‐nanoparticle spatial resolution, we observed significant intraparticle and interparticle variations in the defect site distribution, leading to substantial reactivity heterogeneity.