Abstract
Photocatalytic oxidation (PCO) of organic contaminants is a promising air and water quality management technique which offers energy and cost savings compared to thermal catalytic oxidation (TCO). The most widely used photocatalyst, anatase TiO2, has a wide band gap (3.2 eV) requiring UV photons to activate it. Solar radiation consists of ~4-6% UV and 45% visible light at the Earth’s surface. Therefore, catalysts capable of utilizing these visible photons need to be developed to make PCO approaches more efficient, economical, and safe. Many approaches have been taken to make TiO2 visible-light-active (VLA) with varied degrees of success. Strategies attempted thus far fall into three categories based on their electrochemical mechanisms: 1) photosensitizing TiO2 with Dyes; 2) altering the band gap of TiO2; and 3) coupling TiO2 with a narrow band gap semiconductor. There are diverse technical approaches to implement each of these strategies. This paper presents a brief review of these approaches and their outcomes in terms of the photocatalytic activity and photonic efficiency of the resulting products under visible light. Although resulting visible-light-responsive (VLR) photocatalysts show promise, there is very few comparative studies on the performance of unmodified TiO2 under UV and the modified TiO2 under visible light. It was found that the UV-induced catalytic activity of unmodified TiO2 is much greater than the visible-light-induced catalytic activity of the VLR catalyst at the current state of technology. Furthermore, VLR-catalysts have much lower quantum efficiency than UV-catalysts. This stresses the need for continuing research in this area.
Published Version
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