Urea photosynthesis over a MOF-on-MOF S-scheme heterojunction.

Photocatalytic nitrate reduction reaction coupled carbon dioxide reduction reaction holds great promise for sustainable urea synthesis, the design of photocatalysts with efficient C-N coupling and charge separation is crucial yet challenging. Herein, we report the synthesis of a novel MOF-on-MOF S-scheme heterojunction photocatalyst with interfacial dual active sites for efficient urea production via nitrate reduction reaction coupled carbon dioxide reduction reaction. The integration of semiconducting Zr-MOF and Co-MOF produces interfacial Co and Zr dual sites for NO3- activation and CO2 adsorption, synergistically promoting C-N coupling with reduced energy barriers. Besides, the S-scheme heterojunction enables the strong redox capability and facilitates the charge transfer. Consequently, the rationally designed MOF-on-MOF heterojunction achieves a high urea yield of 3523.4 μg g⁻¹ h⁻¹ and an apparent quantum yield of 1.16% at 365 nm in the absence of sacrificial agents. This work paves the way for the development of high-performance photocatalysts for urea production.