Speaker：Pro.Tetsuro Majima,The Institute of Scientific and Industrial Research, Osaka University

Academic Report：Single-Molecule Chemistry of Nanocatalysis for Light Energy Conversion

Time: 15：00p.m., 30th April.

Place: A722 SINANO

Abstract: To design an efficient light energy conversion system, it is important to reveal and understand the molecular interactions and the mechanism of chemical reactions at heterogeneous interfaces. We have been studing the light energy conversion processes occurring on a variety of nanocatalysts using single-molecule fluorescence imaging techniques and gain information related to spatial and temporal heterogeneities in reactions, which are always masked by ensemble averaging.

Single-molecule fluorescence microscopy has been used to investigate photocatalytic reactions at the heterogeneous interface. We synthesized novel fluorogenic probes to selectively observe the catalytic reactions. Such probes are designed to become fluorescent upon the reaction with target species under photoirradiation. The position of individual fluorescent products can be determined with several tens nanometers spatial resolution by two-dimensional Gaussian fitting. In addition, the quantitative analysis of fluorescence intensity trajectory or fluctuation can reveal the underlying properties of individual catalysts.

We prepared nanometer- and micrometer-sized crystals of photoactive metal oxide semiconductors, such as titanium dioxide and bismuth vanadium oxide, and explore the photocatalytic reactions on individual catalysts by single-molecule fluorescence microscopy with newly developed redox-responsive fluorogenic probes. The effects of probe concentration, solvent, pH, and light intensity were examined to optimize the experimental conditions. From the analysis of spatial distribution of reactive sites, the relationship between surface structures and chemical reactivity were elucidated. From the quantitative analysis of on/off duration times, we also determined the turnover frequency of individual catalysts, adsorption and dissociation rates, interfacial electron transfer rates, and temporal fluctuation of reaction efficiency.

The proper understanding of structures and reactions at heterogeneous interfaces can develop the general concept of chemistry and help advance the emerging applications of nanocatalysts for environmentally and economically sustainable uses.