A photocatalytic reactor is a specialized device designed to facilitate chemical reactions under light irradiation, typically using a semiconductor catalyst such as titanium dioxide or other photoactive materials. Its structure is carefully engineered to maximize light utilization, catalyst contact, and reactant flow, ensuring efficient degradation of pollutants or production of valuable chemical products. Although reactor designs vary depending on the application, most share several key structural components.At the core of the reactor is the reaction chamber, which serves as the main space where the photocatalytic process occurs. This chamber is usually made of transparent or semi-transparent materials such as quartz or glass when ultraviolet or visible light must reach the catalyst surface. In some designs, the chamber may be constructed from corrosion-resistant metals or lined with reflective coatings to improve durability and light distribution. The internal shape of the chamber can be cylindrical, annular, flat-plate, or tubular, depending on whether the reactor is intended for batch operation or continuous flow.A critical structural element is the light source system. Photocatalytic reactors may rely on natural sunlight or artificial lamps, such as UV lamps, LED arrays, or xenon lamps. The light source is positioned so that photons can evenly illuminate the catalyst and minimize shadowed regions. In many reactors, lamps are placed either inside the reaction zone, surrounded by protective sleeves, or outside the transparent reactor wall. The arrangement is chosen to optimize photon penetration while controlling heat generation.Another major component is the photocatalyst support or bed. The catalyst may be suspended as fine particles in a liquid, immobilized on a substrate, or coated on structured surfaces. If the catalyst is in slurry form, the reactor usually includes agitation or recirculation to prevent sedimentation and maintain uniform exposure to light. If the catalyst is immobilized, the structure often features plates, meshes, foams, beads, or membranes that provide a large surface area for reaction while simplifying separation after treatment.The fluid handling system is also essential. It includes inlet and outlet ports, pumps, valves, and channels that control the flow of gas, liquid, or mixed-phase reactants through the reactor. For water treatment applications, the reactor may be designed to circulate contaminated water continuously over the catalyst surface. For gas-phase reactions, the structure may incorporate distributors or packed sections to enhance contact between the gas and the illuminated catalyst.To improve performance, many reactors include auxiliary structural features such as cooling jackets, temperature sensors, reflective panels, and mixing devices. Cooling systems help maintain stable reaction conditions and prevent overheating of the catalyst or light source. Reflective surfaces increase photon efficiency by redirecting unused light back into the reaction zone. Mixing components, such as magnetic stirrers or impellers, ensure that reactants are evenly distributed and that mass transfer limitations are reduced.In summary, the structure of a photocatalytic reactor is defined by the integration of a light delivery system, a reaction chamber, a catalyst arrangement, and a fluid management system. Each part plays a specific role in enhancing light absorption, improving catalyst utilization, and ensuring effective reaction performance. A well-designed reactor balances optical, chemical, and mechanical requirements to achieve high efficiency in photocatalytic applications.