Photochemical reduction of carbon dioxide

Photochemical reduction of carbon dioxide harnesses solar energy to convert CO2 into higher-energy products.

Environmental interest in producing artificial systems is motivated by recognition that CO2 is a greenhouse gas.

To harness the sun's energy, the photosensitizer must be able to absorb light within the visible and ultraviolet spectrum.

[1] Molecular sensitizers that meet this criterion often include a metal center, as the d-orbital splitting in organometallic species often falls within the energy range of far-UV and visible light.

[2] Common donors in photochemical reduction include triethylamine (TEA), triethanolamine (TEOA), and 1-benzyl-1,4-dihydronicotinamide (BNAH).

[5][6] When paired with methylviologen, cobalt, and nickel-based catalysts, carbon monoxide and hydrogen gas are observed as products.

An example of photoexcitation using Ru(bpy) 3 and triethylamine. The net result is a lone electron, originating from the metal, residing in the aromatic bipyridine moiety of Ru(bpy) 3 .
An example of a supramolecular complex capable of photochemical reduction. Notice the photosensitizer on left tethered to the catalytic complex on the right. [ 3 ]
A reaction scheme for the catalytic reduction of CO 2 by Re(bpy)CO 3 Cl. CT is an abbreviation for Charge-Transfer. [ 9 ]