Metal-Free, Light Assisted Integrated Co2 Reduction Coupled with Selective Oxidation of Alcohols under Visible Light Irradiation

An integrated CO2 photoreduction to CO by photo-induced electrons coupled with selective oxidation of aromatic alcohols to carbonyl compounds by photo-generated holes using metal-free anthraquinone (AQ) as an organo-photocatalyst under visible illumination is described. The maximum conversion of benzyl alcohol to benzaldehyde was 65.6% with a selectivity of 98 %, accompanied with the CO yield in gaseous phase 8.67 μmol h−1 g.−1 DFT calculations indicated that initial binding of benzyl alcohol with AQ formed an intermediate IM1 that subsequently interacted with CO2 to give CO2 anion with a free energy change of 0.24 eV. Further, the reduction of CO2 accompanied with the oxidation of benzyl alcohol provided CO and benzaldehyde, respectively along with the release of a water molecule. This concerted metal-free photocatalytic system offers the efficient use of electron-hole pairs for organic synthesis coupled with the CO2 conversion in a cost-effective and sustainable manner.