Photocatalytic reduction of carbon dioxide using Co3O4 nanoparticles under visible light irradiation

Photocatalytic reduction of carbon dioxide under visible light irradiation was carried out with Co₃O₄ powders suspended in water. A Pyrex glass batch reactor of 10mL in volume was used with a 21 W LED lamp of 510 to 620 nm in wave length as light source, and the reaction time was held at 4 h. The major products were formic acid and formaldehyde; the production rates were 4.53 μmol g^?1h^?1 and 0.62 μmol g^?1h^?1 for formic acid and formaldehyde, respectively. Carbon monoxide and methane were detected in trace amounts. The occurrence of the photo-reduction with Co₃O₄ is against the expectation from the valence band edge of Co₃O₄ in the literature. Possible causes for the contradictory result are discussed.