Integration of functionalized two-dimensional TaS2 nanosheets and an electron mediator for more efficient biocatalyzed artificial photosynthesis

Abstract

A visible light active photocatalytic system based on two-dimensional (2D) TaS₂ nanosheets with an integrated electron mediator (M) was developed for solar fuel production from CO₂ in a biocatalyzed artificial photosynthesis system. The integration of M to TaS₂ was realized through sequential functionalization by pegylation with lipoic acid conjugated PEG (LA–PEG), surface assembly of graphene (GR), and final integration of M. The photocatalytic activities of the resultant photocatalysts with different degrees of functionalization were evaluated by the photo-regeneration efficiency of NADH from NAD⁺ under visible light irradiation. Compared with non-functionalized TaS₂ nanosheets that could only regenerate 39.7 ± 1.9% of NAD⁺ to NADH in the presence of dispersed M, the wholly integrated photocatalyst termed as TaS₂–PEG–GR–M exhibited significantly improved efficiency with a NADH regeneration yield up to 83.9 ± 2.2%, which was higher than most of the reported values. This NADH photo-regeneration process was then coupled with formate dehydrogenase (FateDH) catalyzed synthesis of formic acid from CO₂. By using TaS₂–PEG–GR–M as a catalyst for NADH photo-regeneration, the formic acid concentration reached 101.4 ± 3.5 mM, which was about 2.5-fold higher than that obtained with the non-functionalized TaS₂ nanosheets. Based on detailed investigations of the photochemical and electrochemical properties, the photo-induced electron transfer mechanism involved in the TaS₂ nanosheets-based artificial photosynthesis system is discussed. The significantly enhanced reaction efficiency of the artificial photosynthesis system using the integrated TaS₂–PEG–GR–M as the photocatalyst was considered to be mainly benefited from the increased hydrophilicity, elimination of electron back-flow and recombination of photogenerated electrons and holes, as well as the shortened distance of electron transfer. The integrated TaS₂–PEG–GR–M photocatalytic system also avoided contamination of M to the reaction system, and allowed reuse of the expensive M. The whole photocatalytic system retained 83% of its original activity after 10 cycles of reuse. The present research highlights the development of a new class of 2D transition metal dichalcogenide-based integrated photocatalysts for the efficient and direct formation of solar fuels and chemicals from CO₂.