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.

Recently, photobiocatalysis with oxidoreductases, inspired by natural photosynthesis, has drawn increasing attention due to its high catalytic efficiency and selectivity. However, although an important cofactor for the activation of redox enzymes, nicotinamide adenine dinucleotide (NADH) suffers from the drawbacks of cost and limited stability. Moreover, the design of an effective NADH regeneration system remains a huge challenge. Here, we report a visible light-driven conjugated microporous polymer DBTS-CMP1 for the heterogeneous photocatalytic regeneration of NADH. Thanks to various improved properties, such as extended visible light absorption, adequate fluorescence lifetime, enhanced wettability, and rapid charge separation and transfer, an NADH regeneration efficiency of 84% in 45 min was achieved with DBTS-CMP1. In addition, the small molecule model compound DBTS-Ph2, which shares similar structural motifs, was also designed to further study the photoinduced electron transfer process. The strong coordination interaction between dibenzo-[b,d]­thiophene sulfone and the Rh metal center, as reflected in fluorescence quenching, cyclic voltammetry, and Fourier-transform infrared spectroscopy measurements, plays an essential role in electron transfer from the photocatalyst to the Rh complex, thus endowing DBTS-CMP1 with a high reaction conversion and selectivity (100%) for 1,4-NADH regeneration. Finally, a photobiocatalytic system was constructed by incorporating NADH-dependent alcohol dehydrogenase for the reduction of formaldehyde into methanol. A total amount of 2.23 mM methanol with a turnover number of 2.23 mmol g–1 was obtained after 95 min in the photobiocatalytic system, indicating the high photostability and biocompatibility of our DBTS-CMP1 photocatalyst.

Graphene quantum dots with switchable phase transfer for photocatalytic imine synthesis under visible light.

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