Single Atomically Anchored Cobalt on Carbon Quantum Dots as Efficient Photocatalysts for Visible Light-Promoted Oxidation Reactions

Abstract

Generation of efficient light-induced charge separation inside the photocatalyst is an essential factor for a high catalytic efficiency. The usual immobilization of metal or metal oxide particles on semiconductor photocatalysts offers an uncontrolled assembly of active sites during the reaction. The introduction of single metal atoms on photocatalysts can lead to extremely high atomic utilization and precise active sites. However, this approach is limited because of the lack of suitable photosensitizers for single atom immobilization. Here, we have designed photocatalytic carbon quantum dots with anchoring sites for single cobalt atoms in a defined Co–N4 structure via facile pyrolysis of vitamin B12. Carbon dots functioned as both light-harvesting antenna and support for the cobalt atom with high atom loadings up to 3.27 wt %. This new photocatalytic material demonstrated enhanced visible light absorption, efficient charge separation, and reduced electrochemical impedance, while single Co atoms acted as the active site with strong oxidative ability. As a result, the photocatalysts showed excellent visible light-promoted photocatalytic efficiency with oxygen evolution rates up to 168 μmol h–1 g–1 via water oxidation, imine formation with high conversion (∼90%) and selectivity (>99%), and complete photodegradation of organic dyes.

Precursor-dependent structural diversity in luminescent carbonized polymer dots (CPDs): the nomenclature

“…The single Co atom was stabilized by a defined Co−N 4 structure inherited from VB12 (Fig. 3c) 59 . reversible fluorescence properties.…”

Single-Atom Photocatalysts for Emerging Reactions

“… 91 , 92 In recent work, Wang et al fabricated single-atom Co dispersed on carbon quantum dots (CoSAS@CD) for selective photocatalytic oxidation of benzylamine together with a range of its derivatives to yield imines in the presence of O 2 using visible light illumination ( Figure 5 a). 93 CoSAS@CD was fabricated through pyrolyzing vitamin B12 followed by hydrolysis in NaOH solution. CoSAS@CD was treated with an acid to yield the acid-treated CoSAS@CD (CoSAS@CD-acid).…”

“…(f) The reaction conversion and selectivity of oxidative photocatalytic coupling of benzylamines on CoSAS@CD using visible light over 4 repeating cycles. Reproduced with permission from ref ( 93 ) (with CC-BY license). Copyright 2020 American Chemical Society.…”

Anion-Exchange-Mediated Internal Electric Field: Boosting Photogenerated Carrier Separation and Utilization

“…The average luminescence lifetimes are 3.68 ns for BOH, 3.17 ns for BOH-Cl, 2.63 ns for BOH-Br and 1.96 ns for BOH-I. A shorter PL lifetime indicates that the photo-excitons are more prone to separate rather than to recombine [36][37][38][39] .…”