Photochemistry can be used to efficiently degrade persistent organic pollutants POPs in contaminated air or water bodies through a process called photocatalysis. Photocatalysis involves the use of light energy to activate a catalyst, which then accelerates the degradation of pollutants. The most common photocatalyst used for this purpose is titanium dioxide TiO2 .Here are the steps to degrade POPs using photochemistry:1. Choose an appropriate photocatalyst: As mentioned earlier, TiO2 is the most commonly used photocatalyst due to its high efficiency, stability, and non-toxic nature. Other photocatalysts, such as zinc oxide ZnO and cadmium sulfide CdS , can also be used.2. Expose the photocatalyst to light: The photocatalyst must be exposed to light, preferably ultraviolet UV light, to activate it. This can be achieved using natural sunlight or artificial UV lamps.3. Create a reaction environment: The contaminated air or water must be brought into contact with the activated photocatalyst. This can be done by dispersing the photocatalyst in the water or by using a photocatalytic reactor for air treatment.4. Degradation of POPs: When the photocatalyst is exposed to light, it generates reactive oxygen species ROS , such as hydroxyl radicals OH and superoxide radicals O2- . These ROS are highly reactive and can break down the POPs into less harmful by-products.5. Removal of by-products: The by-products formed during the degradation process can be removed through various methods, such as adsorption, filtration, or sedimentation.Possible by-products that may form during the photochemical degradation of POPs include:1. Smaller organic molecules: The breakdown of POPs can result in the formation of smaller organic molecules, such as alcohols, aldehydes, ketones, and carboxylic acids. These by-products are generally less toxic and more biodegradable than the original POPs.2. Inorganic ions: The degradation of POPs containing halogens e.g., chlorinated or brominated compounds can produce inorganic ions, such as chloride Cl- or bromide Br- , which can be removed through filtration or other water treatment processes.3. Carbon dioxide and water: Complete mineralization of POPs can result in the formation of carbon dioxide CO2 and water H2O as the final by-products.It is essential to monitor the by-products formed during the photochemical degradation process to ensure that they do not pose any environmental or health risks. Further treatment may be required to remove or neutralize these by-products before releasing the treated air or water back into the environment.