Photothermal-assisted full solar spectrum-driven CO₂ reduction by an azapentacene-based copper MOF

Photocatalytic CO₂ reduction is currently one of the most attractive researched topics, however, most photocatalysts to date can only utilize the energy from the ultraviolet and visible light spectrum, wasting the infrared light spectrum which occupies half of the solar spectrum energy. Herein, a novel full solar spectrum responsive metal-organic framework material based on azapentacene, named CDN-1, was designed and constructed. Its absorption profile covered the entire spectrum from 250 nm to 1500 nm. As a result, CDN-1 demonstrated remarkable photothermal properties, with a rapid temperature increase up to 140 °C within 60 s upon 808 nm laser irradiation. Electrochemical studies proved the potential of CDN-1 for CO₂ photoreduction. With photothermal synergy, CDN-1 displayed a CO₂ reduction rate of 656.8 μmol g^-1h^-1 for formic acid formation under white LED light, representing the highest performance among all copper-based metal-organic frameworks so far. Surprisingly, CDN-1 also showed a reaction rate of 454.9 μmol g^-1h^-1 under natural sunlight. Ultrafast spectroscopic analysis of CDN-1 indicated the presence of a photoinduced ligand-to-metal charge-transfer process, which was confirmed by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and assisted by DFT calculations. This photoinduced electron transfer pathway was found to be responsible for CDN-1’s full solar spectrum absorption, excellent photothermal properties, and efficient photocatalytic CO₂ reduction performance.