Efficient Hole Trapping in Carbon Dot/Oxygen‐Modified Carbon Nitride Heterojunction Photocatalysts for Enhanced Methanol Production from CO2 under Neutral Conditions

• Published in: Angewandte Chemie International Edition Vol. 60; no. 38; pp. 20811 - 20816
• Main Authors: Wang, Yiou, Godin, Robert, Durrant, James R., Tang, Junwang
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 13.09.2021; John Wiley and Sons Inc
• Edition: International ed. in English
• Subjects: Absorption spectroscopy; Alcohols; Carbon; Carbon dioxide; carbon dioxide fixation; Carbon dots; Carbon nitride; charge trapping; Electron recombination; Heterojunctions; Methanol; Oxidation; Photocatalysis; Photoelectrons; Photosynthesis; Polymers; Quantum efficiency; Recombination; Selectivity; time-resolved spectroscopy; Trapping
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202105570

Artificial photosynthesis of alcohols from CO2 is still unsatisfactory owing to the rapid charge relaxation compared to the sluggish photoreactions and the oxidation of alcohol products. Here, we demonstrate that CO2 is reduced to methanol with 100 % selectivity using water as the only electron donor on a carbon nitride‐like polymer (FAT) decorated with carbon dots. The quantum efficiency of 5.9 % (λ=420 nm) is 300 % higher than the previously reported carbon nitride junction. Using transient absorption spectroscopy, we observed that holes in FAT could be extracted by the carbon dots with nearly 75 % efficiency before they become unreactive by trapping. Extraction of holes resulted in a greater density of photoelectrons, indicative of reduced recombination of shorter‐lived reactive electrons. This work offers a strategy to promote photocatalysis by increasing the amount of reactive photogenerated charges via structure engineering and extraction before energy losses by deep trapping. A modified carbon nitride with O‐containing linkers decorated with carbon dots selectively produces methanol from CO2 and water with the benchmark quantum yield of ca. 6 %. Transient absorption spectroscopic investigation shows that extraction of holes before trapping by the carbon dots is key for the remarkable performance.