Anchoring and reactivation of single-site Co–porphyrin over TiO2 for the efficient photocatalytic CO2 reduction.

[Display omitted] • Co–TCPP was covalently anchored on TiO 2 surface. • Co–TCPP–TiO 2 photoproduced 13CO at a rate of 17 μmol h−1 g cat −1 from 13CO 2 and H 2. • 13CO formation rate using Co–TCPP–TiO 2 decreased to 12 % after 9 h of photoreaction. • Deactivated Co–TCPP–TiO 2 was reactivated under ethanol and UV–visible light. • Reactivated Co–TCPP–TiO 2 photoproducted 13CO at a rate of 63 μmol h−1 g cat −1. Porphyrin and its derivatives have been often used for electrochemical and photocatalysis combined with first-row transition metals for sustainable applications. Cobalt–tetrakis(4-carboxyphenyl)porphyrin (Co–TCPP) was covalently anchored onto TiO 2. Under CO 2 , H 2 , and UV–visible light irradiation, Co–TCPP anchored on TiO 2 produced CO at a rate of 2.5 μmol h−1 (using 100 mg of catalyst and UV–visible light of 118 mW cm−2) when the Co–TCPP content was 2.5 wt %; however, the CO formation rate dropped to 0.3 μmol h−1 (using 100 mg of catalyst and the same intensity of light). The photoactivity drop to 12 % was solved by removing the hydroxy ligands coordinated to the central Co ions through ethanol treatment for 5 min of the Co–TCPP–TiO 2 photocatalysts. This resulted in an increased CO photoformation rate to 7.3 μmol h−1 (using 100 mg of catalyst and the same intensity of light) because the dispersion of the J- and/or H-aggregates to the isolated Co–TCPP unit proceeded more with ethanol treatment and under UV–visible light. Conversely, to use ethanol as reductant was not effective because it reduced and deactivated Co–TCPP. [ABSTRACT FROM AUTHOR]