Principles of Heterogeneous Photocatalysis

Abstract

At the turn of 1970s, the photo-response of solid materials became a constant subject of intensive research for possible application in modern technologies. Heterogeneous photocatalysis has evolved in a unique way giving rise to various applications for alternative energy, organic synthesis and environmental treatment. Semiconducting compounds have thrived as the most suitable materials for these applications. Towards achieving the maximum potential benefits of semiconductor photocatalysis and to make remarkable impact, the fundamental concept as well as application has been extensively and rigorouslyexplored. We therefore detail herein the basic formalism of semiconductor photocatalysis from band models through the generation of oxidants to the light harvesting processes. The key imperfections in semiconductor oxides and their consequences on the extrinsic semiconductivity are outlined. The advances being made regarding the role of oxidising species in photocatalytic degradation are rationally discussed. Finally, the reader is referred to some 'must read' articles in heterogeneous photocatalysis by semiconductor solids.

Assessing the Role of Pt Clusters on TiO2 (P25) on the Photocatalytic Degradation of Acid Blue 9 and Rhodamine B

“…The transferred electrons in the Pt clusters may support different reactions determining the fate of the electrons. Pt is not only well known as an H 2 evolution catalyst by reducing H + with the collected electrons , but is also shown to readily adsorb O 2 on its surface. , The reduction of adsorbed O 2 to O 2 –* superoxide radical by the collected electrons would positively influence the photocatalytic activity for pollutant degradation improving the generation of ROS . Therefore, photocatalytic degradation experiments using different environments, such as dispersions saturated with O 2 and Ar atmosphere, would give insight into the influence of adsorbed O 2 on the photocatalytic activity of Pt:P25.…”

“…18,20 The reduction of adsorbed O 2 to O 2 − * superoxide radical by the collected electrons would positively influence the photocatalytic activity for pollutant degradation improving the generation of ROS. 9 Therefore, photocatalytic degradation experiments using different environments, such as dispersions saturated with O 2 and Ar atmosphere, would give insight into the influence of adsorbed O 2 on the photocatalytic activity of Pt:P25. Excluding O 2 from the reaction medium will block the generation of superoxide O 2 * − radicals via the consumption of the CB electrons.…”

“…According to this mechanism for the photocatalytic degradation of organic pollutants, three different events lead to the degradation of the pollutant: , The creation of superoxide radicals (O 2 *– ) from the CB electrons and dissolved oxygen leads to the formation of OH* radicals which oxidize the pollutant subsequently to CO 2 and H 2 O: The creation of OH* radicals from the reaction of H 2 O or −OH groups at the surface with the VB holes which subsequently oxidize the pollutant: Generated holes in the VB directly oxidize the pollutant: …”

“…According to this mechanism for the photocatalytic degradation of organic pollutants, three different events lead to the degradation of the pollutant: 4,9 (1) The creation of superoxide radicals (O 2 * − ) from the CB electrons and dissolved oxygen leads to the formation of OH* radicals which oxidize the pollutant subsequently to CO 2 and H 2 O:…”

Perovskite Structure Associated with Precious Metals: Influence on Heterogenous Catalytic Process

“…Nonetheless, the applications of semiconductor photocatalysts are not limited to degradation of dyes and other potential pollutants that are harmful to human health and the environment. Its application also involves the production of hydrogen, purification of air, and antibacterial activity [12,[26][27][28][29][30]. The evolution of photocatalysis progressed in parallel to advances in researches on the investigation of TiO 2 properties applied to photoelectrochemical reactions.…”