Single Molecule Photocatalysis on TiO₂ Surfaces

Heterogeneous photocatalysis has been widely applied in various fields, such as photovoltaic cell, solar water splitting, photocatalytic pollutant degradation, and so on. Therefore, the reaction mechanisms involved in these important photocatalytic processes, especially in TiO₂ photocatalysis, have been extensively investigated by various surface science techniques in the past decade. In this review, we highlight the recent progress that provides fundamental insights into TiO₂ photocatalysis through direct tracking the evolution of single molecule photochemistry on TiO₂ single crystal surfaces using a combination of scanning tunneling microscopy (STM) and other surface science techniques. Insight into the structures of various TiO₂ surfaces is discussed first, which provides a basic concept on TiO₂. Afterward, the details of the single molecule photocatalysis of several important molecules (water, alcohols, and aldehydes) on the model TiO₂ surfaces are presented, which are trying to probe bond cleavages and the roles of adsorption sties and adsorption states in TiO₂ photocatalysis step-by-step. Last, challenges and opportunities in single molecule photocatalysis on TiO₂ are discussed briefly.