Long-Lived Internal Charge-Separated State in Two-Dimensional Metal-Organic Frameworks Improving Photocatalytic Performance

Two-dimensional ( 2D) metal-organic frameworks (MOFs) have attracted great attention in recent years due to their improved photocatalytic performances compared with their bulk counterparts. However, the exact photocatalytic mechanism in 2D MOFs, particularly from the view of charge separation and extraction dynamics, remains unclear. Herein, we examined photocatalytic H-2 evolution activities of bulk manganese-based MOF (Mn-TBAPy-BK) and its exfoliated 2D nanosheets (Mn-TBAPy-NS) and systematically investigated their photoinduced carrier dynamics by using transient absorption (TA) spectroscopy. TA measurement uncovers a long-lived (up to 2 mu s) and largely populated internal charge-separated (ICS) state in Mn-TBAPy-NS. It enables Mn-TBAPy-NS to proceed an efficient electron transfer to Pt cocatalyst with an efficiency of 56%, about 7.9 times higher than the case of Mn-TBAPy-BK, which agrees well with the 7.3 times enhancement of normalized photocatalytic performances. Our result reveals an important dynamic mechanism for the photocatalytic activity in 2D MOFs, providing a new guideline for the rational design of efficient 2D MOF photocatalysts.

Automated summary

Two-dimensional (2D) metal-organic frameworks (MOFs) have attracted great attention for their improved photocatalytic performance compared to bulk counterparts. However, the photocatalytic mechanism of 2D MOFs, particularly in terms of charge separation and extraction dynamics, is still unclear. In this study, transient absorption spectroscopy was used to systematically investigate the photoinduced carrier dynamics of a bulk manganese-based MOF and its exfoliated 2D nanosheets. The results reveal an important dynamic mechanism for the photocatalytic activity in 2D MOFs, providing new guidance for the rational design of efficient 2D MOF photocatalysts.