Recent advances in photocatalytic overall production of hydrogen peroxide from metal-free photocatalysts

Hydrogen peroxide (H 2 O 2 ) has been recognized as a green and nonpolluting multifunctional oxidant with extensive applications in environmental protection, metal etching, textile printing and dyeing, chemical synthesis and food processing. However, over 90 % of industrial H 2 O 2 is currently produced through the multi-step anthraquinone oxidation process, which suffers from a process with some drawbacks such as complex, high-energy consumption, and toxic byproducts emissions. Compared to the traditional anthraquinone method, artificial photosynthesis of H 2 O 2 using semiconductor photocatalysts has emerged as a sustainable alternative due to its use of water and O 2 as the clean reactants and sole energy as the driving force. In recent years, metal-free photocatalysts mainly including covalent organic frameworks (COFs), covalent triazine frameworks (CTFs) and carbon nitrile (g-C 3 N 4 ) have garnered significant interest due to their superior thermal and chemical stability, diverse synthesis methods, tunable functionality, light weight nature and non-toxicity. These materials also exhibit adjustable band structure and unique photoelectric properties. Sustainable efforts have been made to advance metal-free photocatalysts for artificial photosynthesis of H 2 O 2 , however, a comprehensive summary of current research status on metal-free-based photocatalytic overall H 2 O 2 production remain scarce. This review outlines recent process in overall H 2 O 2 photosynthesis based on metal-free photocatalysts. First, we introduced the fundamental concepts of photocatalytic overall H 2 O 2 production. Then, we analyze representative studies on photocatalytic overall H 2 O 2 synthesis using metal-free materials. Finally, we discuss the challenges and future perspectives in this field to guide the design and synthesis of metal-free systems for H 2 O 2 generation. Metal-free organic/polymeric materials have demonstrated great potential as efficient photocatalysts for solar H 2 O 2 generation due to their unique and designable structural features. This review summarizes the recent advances in photocatalytic overall H 2 O 2 generation based on metal-free photocatalysts including C 3 N 4 , CTFs and COFs, also discusses the prospects and challenges in this research field.