Environmental pollution is one of the most significant challenges facing modern societies, particularly water pollution caused by organic substances, dyes, and various chemical compounds. With the increasing need for effective and sustainable technologies to treat these pollutants, photocatalysis has emerged as a promising technique in the field of environmental remediation. Photocatalysis relies on the use of a semiconductor material known as a photocatalyst. When the photocatalyst is exposed to light with sufficient energy, electrons are excited from the valence band (VB) to the conduction band (CB), resulting in the generation of electron–hole pairs. These charge carriers participate in a series of reactions on the surface of the photocatalyst, leading to the formation of reactive oxygen species (ROS), such as hydroxyl radicals (•OH) and superoxide radicals (•O₂⁻). These highly reactive species have a strong oxidation ability and can contribute to the degradation of a wide range of organic pollutants. Among the semiconductor materials that have received considerable attention in photocatalysis research is zinc oxide (ZnO). This is attributed to its favorable optical and electronic properties, relatively low cost, high availability, and relatively low toxicity. ZnO can be used for the degradation of various organic pollutants, including dyes, pharmaceutical compounds, and emerging contaminants. Despite these advantages, ZnO faces several challenges that can limit its photocatalytic performance. One of the major limitations is the rapid recombination of electrons and holes. In addition, its relatively wide band gap restricts its response mainly to ultraviolet light, limiting its utilization of the visible-light region. Therefore, recent research has focused on developing and modifying photocatalysts through different strategies, including metal doping, rare-earth-element doping, composite formation, and heterojunction structures. These approaches aim to improve charge separation, enhance visible-light absorption, and increase photocatalytic efficiency. Photocatalysis has a wide range of potential applications, particularly in wastewater treatment, removal of dyes and organic pollutants, degradation of pharmaceutical contaminants, and purification of water from persistent chemical compounds. It also represents an important research field connecting chemistry, materials science, nanotechnology, and environmental engineering. In light of the rapid development of nanomaterials, research continues to focus on developing photocatalysts with higher efficiency, better stability, and greater potential for practical applications. Photocatalysis therefore represents an important research area that combines chemistry, nanomaterials, and modern environmental technologies, contributing to the development of sustainable approaches for pollutant removal and environmental protection Al-Mustaqbal University — The First University in Iraq