Co3O4 quantum dots-polyoxometalate nanocomposites as visible light photoelectrocatalysts for selective oxidation of benzyl alcohol

Abstract

Highly efficient visible-light photoelectrocatalysts were developed for mild oxidation of benzyl alcohol and its derivatives to related aldehydes with air as a safe and environmental friendly oxidant. The photoelectrocatalysts were designed by electrostatic association of the amino acids and [PMo12O40]3- for achieving (amino acid)3PMA followed by covalent attachment to Co3O4-QDs. The prepared Co/(ABA)3PMA and Co/(gly)3PMA nanocomposites were immobilized on charcoal using an alternate electrophoretic approach. Interestingly, the formation of nanocomposite structures remarkably enhanced the photo-generated charge separation and photoelectrocatalytic performance. Comparison of the results of photoelectrocatalytic oxidation of benzyl alcohol with that of photocatalytic and catalytic ones revealed that no reaction occurred during the catalytic tests, while the photocatalytic performance was positively affected by the utilization of a small bias (0.9 V vs. saturated calomel electrode). The Co3O4-QDs increases the visible light absorption and H3PMo12O40 with appropriate energy levels increases the charge mobility in nanocomposites structures. A plausible mechanism for the photoelectrocatalytic oxidation was suggested and illustrated using the results of scavenger tests and energy level determination.