Heterojunction photocatalysts for solar-driven wastewater treatment: Interfacial design, charge carrier dynamics, and advanced characterization techniques

Photocatalysis offers a promising strategy for wastewater treatment because of its environmental friendliness, non-hazardous nature, and low-energy consumption. Its ability to harness abundant sunlight presents a sustainable alternative to conventional methods, paving the way for cleaner and efficient water purification. Nevertheless, engineering a single photocatalyst that possesses pronounced visible-light absorption, optimal charge-carrier separation, and exceptional stability remains a significant challenge. To address this bottleneck, heterostructure photocatalysts have emerged as a viable solution by offering synergistic advantages that enhance charge carrier dynamics, broaden light absorption, and improve redox efficiency. Herein, we comprehensively summarized the fundamental principles, recent advancements, and design strategies of various heterojunction photocatalysts, including Type-I, Type-II, Type-III, S-scheme, Z-scheme, p-n, and Schottky heterojunctions. The charge migration mechanisms and applications in photocatalytic degradation of an extensive range of organic contaminants are critically reviewed. Furthermore, this review systematically discusses cutting-edge characterization techniques used to elucidate interfacial charge transfer pathways, providing deeper insights for optimizing heterostructure-based photocatalysts. Despite significant progress, major challenges remain, including the development of controlled synthetic strategies for well-defined heterojunctions, gaining a deeper understanding of interfacial charge transfer under realistic operating conditions, and the lack of pilot-scale studies to assess practical performance. Collectively, the insights presented here offer guidance for the rational design of next-generation photocatalytic systems with enhanced efficiency and real-world applicability. • Extensive review of semiconductor heterojunction photocatalysts for dye degradation. • Insights into charge carrier migration mechanisms and heterojunction design. • Key characterization techniques to determine charge carrier migration mechanisms. • Existing challenges and prospects of heterojunction photocatalysts are outlined.