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The Aqueous Chemistry of Oxides$
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Bruce C. Bunker and William H. Casey

Print publication date: 2016

Print ISBN-13: 9780199384259

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780199384259.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 24 January 2022

Photochemistry and Excited-State Reactions of Oxides

Photochemistry and Excited-State Reactions of Oxides

(p.371) 13 Photochemistry and Excited-State Reactions of Oxides
The Aqueous Chemistry of Oxides

Bruce C. Bunker

William H. Casey

Oxford University Press

The applied voltages that drive electrochemical processes (see Chapter 11) are only one of many energy sources that can be used to activate reactions in oxide molecules and materials. Another common energy source that drives many environmental and technological oxide reactions is light from the sun. Water plays a key role in many of these reactions. Imagine that you are on vacation floating in a warm ocean bathed by the sun. Many of the phenomena you experience, from your painful sunburn to the photosynthetic growth of the seaweed you see beneath you, are photoactivated processes. In this chapter, we highlight the roles that oxides play in photon-activated solar energy technologies. Also included are reactions stimulated by other nonthermal energy sources, including electrons in high-energy plasmas. Titanium oxide, found in common white paint, is the basis for much of the discussion, because this oxide is used in many photoelectrochemical energy storage technologies. The photochemistry of colloidal manganese- and iron-oxide particles suspended either in atmospheric droplets or in the upper photic zone of the ocean where the sunlight penetrates are discussed in Chapter 18. Such oxide reactions are important globally in the elimination of pollutants. Both industrial and environmental examples illustrate how oxides participate in a wide range of photoactivated chemical reactions, including the catalytic decomposition of water, photoelectrochemistry, and photoactivated dissolution and precipitation reactions. Before exploring excited-state reactions, we need to introduce the energy sources that provide such excitation. In most of this chapter, the excitation source of interest is light. Most of us are familiar with the electromagnetic spectrum, in which the energy of a photon is given by … E=hv=hc/λ=hcω (13.1)… Here, h is Planck’s constant (h = 6.6 ·10 –34 J/second), c is the speed of light (3 ·1010cm/second), ν is the frequency of light (measured in Hertz or per second), λ is the wavelength of light (in centimeters), and ω is the wavelength expressed as wave number (measured per centimeter in infrared spectroscopy).

Keywords:   Beer-Lambert Law, Fermi level, Graetzel cells, X-rays, alpha particles, band bending, conduction band, electromagnetic spectrum, gamma rays, light energy

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