Photosensitizer-Anchored 2D MOF Nanosheets as Highly Stable and Accessible Catalysts toward Artemisinin Production

Abstract

2D metal-organic frameworks (2D-MOFs) have recently emerged as promising materials for gas separations, sensing, conduction, and catalysis. However, the stability of these 2D-MOF catalysts and the tunability over catalytic environments are limited. Herein, it is demonstrated that 2D-MOFs can act as stable and highly accessible catalyst supports by introducing more firmly anchored photosensitizers as bridging ligands. An ultrathin MOF nanosheet-based material, Zr-BTB (BTB = 1,3,5-tris(4-carboxyphenyl)benzene), is initially constructed by connecting Zr₆-clusters with the tritopic carboxylate linker. Surface modification of the Zr-BTB structure was realized through the attachment of porphyrin-based carboxylate ligands on the coordinatively unsaturated Zr metal sites in the MOF through strong Zr-carboxylate bond formation. The functionalized MOF nanosheet, namely PCN-134-2D, acts as an efficient photocatalyst for ¹O₂ generation and artemisinin production. Compared to the 3D analogue (PCN-134-3D), PCN-134-2D allows for fast reaction kinetics due to the enhanced accessibility of the catalytic sites within the structure and facile substrate diffusion. Additionally, PCN-134(Ni)-2D exhibits an exceptional yield of artemisinin, surpassing all reported homo- or heterogeneous photocatalysts for the artemisinin production.

Keywords: artemisinin; metal–organic frameworks; photochemical synthesis.

Figure 1

a) Schematic representation showing the one‐pot synthesis of PCN‐134‐3D. b) Stepwise synthesis of PCN‐134‐2D nanosheets with accessible catalytic sites.

Figure 2

a) PXRD patterns of Zr‐BTB sheets produced under different synthetic conditions. The simulated pattern was based on structural models in a hexagonal lattice with P‐31m space group (a = b = 19.595 Å, c = 12.264 Å). b) N₂ adsorption isotherms of Zr‐BTB sheets at 1 bar, 77 K. c) Comparison of BET surface areas and TCPP/BTB ratios of Zr‐BTB sheets synthesized under different conditions.

Figure 3

a) Photographs of PCN‐134‐3D (left) and PCN‐134‐2D (right) dispersed in water, displaying the Tyndall effect. b) AFM image of PCN‐134‐2D nanosheets with corresponding height profiles. c) TEM image of PCN‐134‐2D nanosheets showing a hexagonal lattice. d,e) HR‐TEM images of PCN‐134‐2D nanosheets. f) SEM image of PCN‐134‐2D nanosheets. g) Elemental mapping by SEM/EDX for PCN‐134‐2D. The porphyrin centers are preoccupied by Ni.

Figure 4

a) Proposed binding mode of TCPP in PCN‐134‐2D. b) PXRD of Zr‐BTB and PCN‐134‐2D treated by aqueous solutions with different pH values. c) Stability test of Zr‐BTB modified by TCPP, DCPP, and TPP treated by aqueous solutions with different pH values.

Figure 5

a) UV–vis absorption spectra of DPBF upon visible‐light irradiation with PCN‐134‐2D nanosheets. b) The degradation of DPBF using PCN‐134‐3D and PCN‐134‐2D as monitored by the absorbance decay at 410 nm.