Advances in visible light photocatalysis for harmful algal bloom mitigation from mechanistic understanding to sustainable application

Harmful algal blooms (HABs) have become an increasing global environmental problem, threatening aquatic ecosystems, drinking water quality, and public health. Conventional methods like physical, chemical, and biological methods often suffer from limited efficiency, secondary pollution, high operational costs, or poor scalability, creating an urgent need for sustainable mitigation technologies. Visible-light-driven semiconductor photocatalysis has emerged as a promising approach because it utilizes solar energy to generate reactive oxygen species (ROS) capable of inducing oxidative damage to algal cell membranes, photosynthetic systems, proteins, and nucleic acids, resulting in efficient algal inactivation. This review critically examines recent advances in visible-light-responsive photocatalysts for HAB mitigation, with emphasis on photocatalytic mechanisms, ROS-mediated algal inactivation, material design strategies, heterojunction engineering, and reactor development. In addition, the influence of environmental factors, including water chemistry, natural organic matter, salinity, catalyst stability, recyclability, and scalability, is comprehensively discussed to evaluate the practical feasibility of photocatalytic technologies under real environmental conditions. Unlike previous reviews that primarily focus on photocatalytic materials or pollutant degradation, this review integrates catalyst design, mechanistic understanding, environmental constraints, and engineering considerations into a unified framework for HAB mitigation. Overall, this review highlights the current progress, key challenges, and practical considerations associated with visible-light-responsive photocatalytic systems, providing a comprehensive foundation for their future development and implementation in sustainable harmful algal bloom control.