Kinetics of the Photoelectron-Transfer Process Characterized by Real-Time Single-Molecule Fluorescence Imaging on Individual Photocatalyst Particles

Abstract

Uncovering the underlying kinetics mechanism of the charge carrier during the transfer process is of fundamental importance in pursuing outstanding photocatalytic activity. However, it still remains a challenge owing to the rapid reaction rate of the charge carrier on the surface of photocatalysts. Here, in situ single-molecule fluorescence microscopy is employed to study the photoelectron-transfer kinetics in real time for an individual TiO2-tipped carbon nanotube (TiO2-tipped CNT) using a redox-responsive fluorogenic probe. A visual transport process for electron transfer from TiO2 nanoparticles to CNT is obviously observed via single-molecule fluorescence imaging. Based on the fluorescent product formation rate, the kinetics information of the photoelectron-transfer process can be obtained. The kinetics analysis results show that heterogeneity of catalytic activity caused by the photoelectron reactive sites exists in an individual TiO2-tipped CNT heterostructure, which is always masked in the ensemble measurement. After applying an adaptive high-resolution algorithm, which considers temporal and spatial factors into consideration simultaneously, the dynamic heterogeneity of special location on CNT within the TiO2-tipped CNT heterostructure in product formation is revealed with 40 nm spatial resolution. Moreover, we prove that the photoelectron-transfer distance on CNT can be up to 16.82 μm. These results give a deep insight into the kinetics information of the photoelectron-transfer process and a policy toward designing better photocatalysts.

In Situ Imaging of Catalytic Reactions on Tungsten Oxide Nanowires Connects Surface–Ligand Redox Chemistry with Photocatalytic Activity

“…Single-molecule localization microscopy can overcome the limitations of ensemble-averaging to identify both inter- and intraparticle heterogeneity in the reactivity of nanostructured catalysts. − This super-resolution optical technique uses fluorogenic probes that are chemically activated into their fluorescence state to monitor catalytic turnover events in situ at the single-molecule and single-particle scales. However, a limitation of single-molecule imaging is that the fluorogenic probes used to visualize reaction events do not directly report on the chemical properties that lead to nanoscale variations in activity.…”

Nanoscale Luminescence Imaging/Detection of Single Particles: State-of-the-Art and Future Prospects

“…The authors determined the photocatalytic activity of single catalysts by monitoring the nanobubble growth kinetics in an operando imaging manner. Very recently, Tang and colleagues explored the photoelectron-transfer kinetics of a typical heterostructure photocatalyst, TiO 2 -tipped CNTs, on an individual particle level by applying a real-time single molecule FLM . This work provides deep insights (theoretical basis) into the photoelectron-transfer processes (kinetics information and behaviors) and guide for designing high performance photocatalysts.…”

Single-Molecule Imaging of Reactive Oxygen Species on a Semiconductor Nano-Heterostructure for Understanding Photocatalytic Heterogeneity in Aqueous

“…This strategy was also used in our previous study, which showed this corrected threshold screening can successfully filter off the background signal. 28 A unique fluorescent blinking pattern was captured (Figure 3A), indicating the signal was collected at a singlemolecule level, which facilitated our localization of every •OH distribution in the subsequent investigation.…”

“…The produced e – quickly transfers onto the MWCNT, whereas the freshly generated h + on the TiO 2 surface exhibits a strong oxidation potential. In the aqueous phase, a ROS was produced, including the reduction of O 2 with e – and the oxidation of H 2 O with h + . − Indeed, •OH is considered the most effective ROS intermediate in the photocatalytic reaction because its oxidation potential is higher than those of other ROS . Therefore, understanding •OH production during the photocatalyst process is crucial for clarifying the photocatalytic mechanism and improving the efficiency of artificial photochemical reactions …”

“…Figure S5A shows a typical time trajectory of a single-molecule fluorescence burst on point “a” in Figure C. The •OH production rate ν was calculated according to the formula ν = 1/τ off , where τ off is the average interval of a single-molecule fluorescence burst. − , The •OH production rate ν of every pixel along the red line in Figure C is explored (Figure A). The average rate of production of •OH was 0.58 s –1 .…”