In Situ Fluorescence Imaging Of Reactive Oxygen Species And Photogenerated Electrons On The Surface Of Photocatalyst Particles

Photocatalysis as an effective method of solar energy collection,conversion and storage has shown great potential in wastewater treatment and carbon dioxide reduction.Therefore,photocatalysis is considered as an effective method to alleviate the existing energy crisis and environmental pollution.The photocatalytic reaction process includes:1)Photocatalyst absorbs light to produce electron-hole pairs.2)Photogenerated electrons and holes are separated and migrated to the surface of the photocatalyst.3)Redox reaction occurs on the photocatalyst surface.In photocatalytic process,the water or oxygen combines with photoinduced carriers to produce highly reactive oxygen species（ROS）.ROS are important intermediates in the process of photocatalysis,they are participated in the catalytic reaction process and affect the efficiency of catalytic reaction.Therefore,it is of great significance to carry on the identification,quantitative and kinetic evaluation.In addition,the generation and transfer of charge carriers on the surface of catalyst particles are the key factors to determine the photocatalytic reaction efficiency.However,the short lifetime of photogenerated electrons and holes,the fast migration and recombination rates,and the fast reaction rates on the surface of the catalyst greatly limit the study of the dynamic behavior of photogenerated electrons and holes on the surface of the photocatalyst and the construction of excellent photocatalysts.Although through transient absorption spectra,photoluminescence spectra,electrochemical impedance and the traditional methods such as X-ray photoelectron spectroscopy can be used to detect the catalytic reactivity,characterization of carrier transfer behavior.The information we obtained is based on the overall level,ignoring the single particle defects on the surface of the photocatalyst,crystal and heterostructure light catalytic activity of the contribution.Therefore,the real-time dynamic study of the photogenerated carrier behavior and ROS production process on the surface of catalyst particles based on single molecule and single particle level is of great significance.Herein single molecule fluorescence imaging is a high sensitivity and high spatial and temporal resolution detection method,widely used in chemical catalysis,electrocatalysis and photocatalysis.Through this method can realize the detection of fluorescence product molecules at the single molecule level,used in the catalyst particle surface reactive oxygen species and photogenerated electrons in situ imaging research.In this paper,the significance and research status of the detection of catalytic reactions at the single molecular level are reviewed,and the research progress of reactive oxygen species detection and carrier detection is described.In addition,single-molecule fluorescence imaging was used to analyze the distribution and generation rate of reactive oxygen species on the photocatalyst surface,and the distribution and transfer process of photogenerated electrons on the photocatalyst surface were deeply explored.The specific research contents of this paper as follows.Firstly,titanium dioxide supported carbon nanotubes（Ti O₂（S）-CNT）photocatalyst was synthesized and a microfluidic flow reaction device was constructed.Then,hydroxyl radical（·OH）species generated on the surface of Ti O₂（S）-CNT catalyst were specifically captured by3’-（p-hydroxyphenyl）fluorescein to collect in situ fluorescence images and monomolecular fluorescence signals of·OH on the surface of Ti O₂（S）-CNT catalyst.Finally,extraction,baseline calibration and threshold screening of the obtained single molecular fluorescence signal were performed to obtain the generation rate of·OH.Based on the collected single molecule fluorescence signal and the innovative high-resolution algorithm,the·OH distribution on the surface of single particle catalyst was visualized from the single molecule level.The photoelectron transfer kinetics of single Ti O₂-tipped CNT was studied in real time at the single molecular level by using in situ monomolecular fluorescence microscopy.The electron transfer process from Ti O₂ to CNT can be clearly observed by single molecule fluorescence imaging.Combined with the adaptive high-resolution algorithm,the spatial resolution of 40 nm was used to reveal the heterogeneity of photogenerated electron transport at different locations of CNT.In summary,in this paper,based on the constructed microfluidic photocatalytic reaction device,combined with the developed high-resolution algorithm,we obtained the fluorescence images of reactive oxygen species and photogenerated electrons on the surface of catalyst particles in situ,and studied their generation,transfer and transfer behaviors.It provides theoretical guidance for understanding the mechanism of catalytic reaction,designing new high efficiency catalyst and improving the reaction efficiency of photocatalysis.