Photoreduction of carbon dioxide and photodegradation of organic pollutants using alkali cobalt oxides MCoO (M = Li or Na) as catalysts.

The recycling of lithium batteries should be prioritized, and the use of discarded alkali metal battery electrode materials as photocatalysts merits research attention. This study synthesized alkali metal cobalt oxide (MCoO, M = Li or Na) as a photocatalyst for the photoreduction of CO and degradation of toxic organic substances. The optimized NaCoO and LiCoO photocatalysts increased the photocatalytic CO-CH conversion rate to 21.0 and 13.4 μmol g h under ultraviolet light irradiation and to 16.2 and 5.3 μmol g h under visible light irradiation, which is 17 times higher than that achieved by TiO P25. The rate constants of the optimized reactions of crystal violet (CV) with LiCoO and NaCoO were 2.29 × 10 and 4.35 × 10 h, respectively. The quenching effect of the scavengers and electron paramagnetic resonance in CV degradation indicated that active O, O, and h play the main role, whereas OH plays a minor role for LiCoO. The hyperfine splitting of the DMPO-OH and DMPO-CH adducts was a = 1.508 mT, a = 1.478 mT and a = 1.558 mT, a = 2.267 mT, respectively, whereas the hyperfine splitting of DMPO was a = 1.475 mT. The quenching effect also indicated that active O and h play the main role and that OH and O play a minor role for NaCoO. The hyperfine splitting of the DMPO-OH and DMPO adducts was a = 1.517 mT, a = 1.489 mT and a = 1.496 mT, respectively. Discarded alkali metal battery electrode materials can be reused as photocatalysts to address environmental pollution.