Surface photochemistry probed by two-photon photoemission spectroscopy
Energy & Environmental Science
Two-photon photoemission (2PPE) has been widely used in the study of electronic structure and dynamics of unoccupied electronic states on different types of surfaces and interfaces. Since 2PPE probes electronically excited states, it should be sensitive to surface excited electronic structure changes that accompany surface chemical reactions. Therefore, this method could potentially be used to study the kinetics and dynamics of surface chemical reactions as well as surface photocatalysis. In
... otocatalysis. In this article, we briefly review recent progress made in the study of surface photochemistry and photocatalysis using the time-dependent 2PPE (TD-2PPE) method. A few examples are given to demonstrate the application of this method in probing surface photochemistry and photocatalysis, particularly photocatalysis of methanol on TiO 2 surfaces. Since many problems associated with surface photochemistry and surface photocatalysis are related to energy and environmental issues, the 2PPE technique could have important applications in the study of the fundamental problems in energy and environmental sciences. † Who made similar contributions to this work. Broader context Developing efficient photocatalysts for energy and environmental processes, such as water splitting and photodegradation of environmental contaminants, is an important area of research. Much of the works in this area have been focused on synthesizing and developing new catalysts, while the fundamental study of surface photocatalysis has received much less attention. Developing new and powerful experimental methods to probe the kinetics of surface photocatalytic processes is crucial to understanding these processes at the most fundamental level. This paper provides a brief review on the development of the two-photon photoemission (2PPE) spectroscopy method as a probe for surface photochemistry and photocatalysis. Since 2PPE probes electronically excited states, it is sensitive to surface excited electronic structure changes that accompany surface chemical reactions. We have shown a few examples of photochemistry and photocatalysis studied using the 2PPE method. One particularly interesting example is the kinetic study of photocatalysis of methanol on the TiO 2 (110) surface. The results of these studies show that methanol photocatalysis on TiO 2 (110) occurs mainly on the Ti 5c sites and that defects have a significant effect on the photocatalytic kinetics. These works demonstrate that 2PPE technique can be applied to the study of fundamental mechanisms in many energy and environment related processes.