Abstract
During the last two decades, various pathways describing photoexcitation of small molecules’ surface reactions at the wide band gap metal oxides and halides (Eg>3eV) have been recognized. Photogeneration of excitons and free charge carriers may occur in bands of: i) fundamental absorption; ii) extrinsic and intrinsic defect absorption, including those related to surface states; and iii) in UV-induced color centers. Considerable red shifts relative to the fundamental absorption threshold of wide band gap solids have been observed for the spectral limits of surface photoreactions induced in extrinsic absorption bands. This allows thinking about the wide band gap solids as a potential competitors for the relatively narrow band gap photocatalysts. This review discusses the concept of surface photoadsorption (photocatalytic) center while differentiating active and inactive states of the center. Electronically excited defect, surface self-trapped or bound exciton, and the surface defect with trapped photo carrier are considered as the active states of photoadsorption (photocatalytic) centers of different types. The decay pathway of active state determines the lifetime of a photocatalytic center, and in this connection the Langmuir-Hinshelwood kinetic approach is discussed.
Highlights
SUMMARYThis review will discuss selected topics related to photoinduced chemical reactions in gas/solid heterogeneous systems
The heterogeneous photocatalysis can be defined as “Photocatalysis taking place at the interfacial boundary between two phases” [1]
For both above mentioned mechanisms the F(F+) intrinsic defect looks like renewable “self-sensitizing” agent for electrons and holes photo generation via two step absorption of photons below the fundamental threshold of wide band gap solid
Summary
This review will discuss selected topics related to photoinduced chemical reactions in gas/solid heterogeneous systems. The photoadsorption and photocatalytic (photo assisted) reactions of small molecules at the surface of wide band gap solids mainly will be examined. From the chemical point of view, photoadsorption can be considered as the simplest process induced by photons at gas/solid or liquid/solid interface. The variety of photophysical events preceding chemical stages of photocatalytic reaction are often similar (if not the same) to the events characteristic of small molecules photoadsorption. The special emphasis will be on the photoexcitation of solids which precedes the chemical interaction of molecules at illuminating solid surface during photoadsorption and photocatalysis. The concept of surface photoadsorption (photocatalytic) center will be considered in more details in connection with the photoexcitation of a photocatalysts
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
