Customized structures of hydrogen-bonded organic frameworks towards photocatalysis

Porous semiconductor photocatalysts have recevied considerable attention to resolve the issues of the current environmental pollution and future energy supply. As a new class of porous crystalline materials, hydrogen-bonded organic frameworks (HOFs) are self-assembled through hydrogen-bonding interactions between organic building blocks. Due to the weak interactions of hydrogen bonds, HOF materials possess more flexible frameworks compared to other porous materials formed via strong bonds (covalent bonds and coordination bonds). Combined with their structural polymorphism and ease of modification, HOFs exhibit multifunctionality in enhancing crystal photoelectric performance and responding to external stimuli such as light, temperature, and pressure, demonstrating their potential under various reaction conditions. Furthermore, their metal-free composition, renewability, and recyclability endow them with excellent biocompatibility and low toxicity, addressing public concerns about environmental issues, reducing waste, and improving economic feasibility. However, currently, strategies to enhance the photocatalytic performance of HOFs by improving stability are relatively scarce. The mechanisms behind their stimulus-responsive behavior also present significant scientific issues that require in-depth exploration. Based on these existing issues, this review focuses on discussing material properties, design principles, synthesis methods, and photocatalytic applications including photocatalytic hydrogen production, CO2 reduction, and H2O2 generation, as well as strategies for enhancing stability and photocatalytic performance. Additionally, this paper highlights the main challenges that need to be addressed and proposes future research directions. This review will help promote the rapid development of HOFs in the field of solar energy conversion.