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Brief introduction of photocatalytic oxidation technology
Photochemical and photocatalytic oxidation are advanced techniques used for the degradation of pollutants. These methods rely on light to initiate chemical reactions that break down organic compounds. In a photochemical reaction, molecules absorb specific wavelengths of light, which excites them to higher energy states. This excitation leads to chemical transformations, either forming new substances or initiating thermal reactions. The energy required for these reactions comes from photons, making photochemical and photovoltaic processes key areas in solar energy research.
Photodegradation refers to the process where organic matter is broken down under light exposure, typically resulting in the formation of carbon dioxide, water, and other ions like nitrate (NO₃â»), phosphate (PO₄³â»), and chloride (Clâ»). This process can be divided into two types: direct and indirect. Direct photodegradation occurs when the organic molecule itself absorbs light and undergoes a chemical change. Indirect photodegradation involves other substances in the environment absorbing light and becoming excited, which then react with the pollutants. This method is especially effective for persistent organic pollutants that are hard to degrade naturally.
Photochemical degradation can be carried out without catalysts or with the help of catalysts. When no catalyst is involved, oxidants like oxygen or hydrogen peroxide are often used under ultraviolet light to break down contaminants. When catalysts are present, the process is known as photocatalytic oxidation. This can be further categorized into homogeneous and heterogeneous catalysis. In homogeneous systems, substances like Fe²⺠or Fe³⺠combined with H₂O₂ are commonly used, as seen in the Photo-Fenton reaction, which generates hydroxyl radicals (·OH) to destroy pollutants.
Heterogeneous photocatalysis is widely applied in environmental remediation. It involves a semiconductor material, such as titanium dioxide, which is activated by light. The excited electrons and holes on the semiconductor surface interact with adsorbed oxygen and water molecules, producing highly reactive species like ·OH. These radicals efficiently oxidize and mineralize organic pollutants through addition, substitution, and electron transfer mechanisms, ultimately breaking them down into harmless byproducts.