Photoelectrochemical Oxidation

Photochemical oxidation methods for the degradation of pollutants include processes involving both catalytic and non-catalytic photochemical oxidation. The former often utilize oxygen and hydrogen peroxide as oxidants and rely on ultraviolet (UV) light to initiate the oxidation and decomposition of pollutants. The latter, known as photocatalytic oxidation, can generally be categorized as homogeneous and heterogeneous catalysis.

In heterogeneous photocatalytic degradation, a certain amount of photosensitive semiconductor material is introduced into the polluted system, combined with a certain amount of light radiation. This results in the excitation of “electron-hole” pairs on the photosensitive semiconductor surface under light exposure. Dissolved oxygen, water molecules, and other substances adsorbed on the semiconductor interact with these “electron-hole” pairs, storing excess energy. This allows the semiconductor particles to overcome thermodynamic reaction barriers and act as catalysts in various catalytic reactions, generating highly oxidative radicals such as •HO. These radicals then facilitate the degradation of pollutants through processes such as hydroxyl addition, substitution, and electron transfer.

Photochemical oxidation methods encompass photosensitized oxidation, photoexcited oxidation, and photocatalytic oxidation. Photochemical oxidation combines chemical oxidation and radiation to enhance the rate and oxidative capacity of oxidation reactions compared to individual chemical oxidation or radiation treatment. Ultraviolet light is commonly used as the radiation source in photocatalytic oxidation.

Additionally, a predetermined amount of oxidants like hydrogen peroxide, ozone, or certain catalysts must be introduced into the water. This method is highly effective for the removal of small organic molecules, such as dyes, that are difficult to degrade and possess toxicity. Photochemical oxidation reactions generate numerous highly reactive radicals in the water, which readily disrupt the structure of organic compounds.