Heterogeneous photocatalytic water treatment: From scientific advances to real-world implementation

Over the past three decades, photocatalytic technology has attracted extensive research interest, resulting in thousands of publications and significant scientific advances. Despite these efforts, the transition of this technology from laboratory studies to real-world applications, particularly in water treatment, remains limited and uncertain. Most research has focused on the development of increasingly sophisticated photocatalytic materials and the investigation of fundamental mechanisms, while comparatively less attention has been devoted to reactor engineering, process integration, scalability, and practical implementation under realistic operating conditions. As a result, photocatalysis is often presented as a standalone alternative to conventional treatment technologies, overlooking its actual potential as a complementary process within multi-stage treatment schemes. In this review, the current status of heterogeneous photocatalytic water treatment is critically examined, with emphasis on both its advantages and inherent limitations. Particular attention is given to the technological, thermodynamic, kinetic, and regulatory challenges that continue to hinder large-scale implementation. In addition, emerging strategies based on process intensification, hybrid systems, and pilot-scale engineering are discussed as promising pathways to improve the practical feasibility of photocatalytic technologies. Finally, this review positions heterogeneous photocatalytic water purification as a complementary advanced oxidation process (AOP) for tertiary treatment within integrated multi-stage water purification systems. A clearer understanding of these aspects is essential to bridge the persistent gap between academic research and industrial implementation.