From waste CO2 to high-value chemicals: a novel copper-based metal-organic framework material powers tandem using inexhaustible sunlight

Photocatalysis is an attractive way to convert carbon dioxide into useful chemicals under mild conditions. But most photocatalytic CO₂ reduction systems still stop at making low-value C₁ products such as carbon monoxide, formic acid or methane. Upgrading those simple products into more valuable chemicals remains a major challenge.

In a new study, researchers report a copper-based metal-organic framework, or MOF, that pushes CO₂ conversion a step further. The material not only reduces CO₂ to carbon monoxide under light irradiation, but also uses that intermediate in a second reaction to produce N-formamides, a class of higher-value compounds widely used in pharmaceuticals, fine chemicals and functional materials. Conventional routes to N-formamides often rely on carbon monoxide, precious-metal catalysts, high temperatures and pressurized conditions. The new system offers a simpler and potentially greener alternative. It uses light as the only driving force and does not require palladium catalysts, external heating or added pressure.

The material, called CuPzC-tbo, is built from two different copper motifs linked within one porous framework. One is a trinuclear Cu₃ cluster and the other is a dinuclear Cu₂ paddlewheel unit. According to the researchers, combining these two copper sites in one structure gives the MOF several useful properties at once, including broad light absorption, efficient charge separation, strong affinity for CO and photothermal conversion. Under visible light, the MOF produced CO from CO₂ at a rate of 3448 micromoles per gram per hour with 85.6% selectivity. The same material also promoted N-formylation of amines, giving up to 93% yield with n-butylamine as a model substrate. The system worked for a broad range of amines, including aliphatic, cyclic and aromatic substrates.

The team then combined both reactions in a two-chamber tandem setup. In one chamber, CO₂ was reduced to CO. In the other, the in situ generated CO was immediately used to form N-formamides. Under visible light alone, the integrated system delivered product yields of up to 88%, with carbon utilization efficiency as high as 83%. Isotope-labeling experiments confirmed that the carbonyl carbon in the final products came from external CO₂.

The researchers say the work provides a new strategy for moving CO₂ photocatalysis beyond low-value C₁ products. By integrating light harvesting, intermediate generation and downstream upgrading in one MOF platform, the study offers a new route for sustainable CO₂ valorization without noble metals or external heating.

---

---