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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. 

Synthesis of nitrogen doped mesoporous graphitic carbon spheres with dispersed metal oxide nanoparticles using a single temperature treatment step serves as one of the big challenges in materials research. To date only a few reports have been published on the soft-templating synthesis of mesoporous graphitic carbons. The preparation of graphitic carbons with dispersed Fe 2 O 3 using a single carbonization step at relatively low temperatures is yet to be explored. The first phase of this work shows the potential of graphitization of polyvinylpyrrolidine (PVP) stabilized cubic Prussian blue nanoparticles (CPB) in phenolic resin spheres to produce graphitic carbon spheres through a facile Stöber-like method. In the second phase, the Pluronic F127 soft template was used along with PVP stabilized Prussian blue nanoparticles (PB) in carbon spheres to generate mesopores and graphitic domains with uniformly dispersed Fe 2 O 3 nanoparticles in these spheres. Due to the presence of graphitic layers, doped N species and Fe 2 O 3 nanoparticles in the carbon matrix, the yielded carbon spheres feature a high surface area and magnetic properties. Moreover, these graphitic spheres exhibited excellent capacitive behavior with rectangular cyclic voltammetry (CV) profiles and large capacitance up to 247 F g −1 at 1 mV s −1 scan rate in 6 M KOH solution.