a special case of photochemical oxidation (PCO). Photochemical oxidation entails the generation of radical species that enable oxidation reactions, with or without the electrochemical interactions involved in semiconductor-catalyzed systems, which occur in photoelectrochemical oxidation. Applications PECO may be useful in treating both air and water, as well as producing hydrogen as a source of renewable energy. Water Treatment PECO has shown promise for water treatment of both stormwater and wastewater. Currently, water treatment methods like the use of biofiltration technologies are widely used. These technologies are effective at filtering out pollutants like suspended solids, nutrients, and heavy metals, but struggle to remove herbicides. Herbicides like diuron and atrazine are commonly used, and often end up in stormwater, posing potential health risks if they are not treated before reuse. PECO is a useful solution to treating stormwater because of its strong oxidation capacity. Investigating different mechanisms for herbicide degradation in stormwater, like PECO, photocatalytic oxidation (PCO), and electro-catalytic oxidation (ECO), researchers determined that PECO was the best option, demonstrating complete mineralization of diuron in one hour. Further research into this use for PECO is needed, as it was only able to degrade 35% of atrazine in that time, however it is a promising solution moving forward. Air Treatment PECO has also shown promise as a means of air purification. For people with severe allergies, air purifiers are important to protect them from allergens within their own homes. However, some allergens are too small to be removed by normal purification methods. Air purifiers using PECO filters are able to remove particles as small as 0.1 nm. These filters work as photons excite a photocatalyst, creating hydroxyl free radicals, which are extremely reactive and oxidize organic material and microorganisms that cause allergy symptoms, forming harmless products like carbon dioxide and water. Researchers testing this technology with patients suffering from allergies drew promising conclusions from their studies, observing significant reductions in total symptom scores (TSS) for both nasal (TNSS) and ocular (TOSS) allergies after just 4 weeks of using the PECO filter. This research demonstrates strong potential for impactful health improvements who suffer from severe allergies and asthma. Hydrogen Production Possibly the most exciting potential use for PECO is producing hydrogen to be used as a source of renewable energy. Photoelectrochemical oxidation reactions that take place within PEC cells are the key to water splitting for hydrogen production. While the main concern with this