Cu-Based Metal-Organic Framework Nanosheets Synthesized via a Three-Layer Bottom-Up Method for the Catalytic Conversion of S-Nitrosoglutathione to Nitric Oxide

Metal-organic framework nanosheets (MOFNs) are promising materials for heterogeneous catalysis systems where active metal sites are positioned on particle exterior surfaces. The hypothesis that intrapore metal sites are active for catalysis has been disproven for certain systems, and therefore the synthesis of MOF particles with increased external surface area and density of metal active sites is needed. MOFNs provide an increased proportion of metal sites accessible to substrates that experience limited or no diffusion into MOF pores compared to MOF particles with other morphologies such as octahedra. However, developing synthetic methods to generate a variety of MOFNs remains an experimental challenge, particularly for water-stable materials. Herein, we use a three-layer method to synthesize the nanosheet particles of a new MOF, CuBDTri (where H(2)BDTri = 1,4-di(1H-1,2,3-triazol-5-yl)benzene). Scanning electron microscopy (SEM), powder X-ray diffraction (pXRD), Brunauer-Emmett- Teller (BET) analysis, inductively coupled plasma atomic emission spectroscopy (ICP-AES), and acid digestion with time-of-flight mass spectrometry (TOF-MS) were used to characterize the newly synthesized CuBDTri nanosheets. Both the synthetic method and linker identity were shown to impact the anisotropic growth of MOF particles with nanosheet morphologies. Importantly, this is the first report of using the three-layer method to synthesize MOFNs with Cu-N linkages, meaning that the three-layer method is (i) more broadly applicable than previously known (having only been used previously to synthesize nanosheets with Cu-oxo linkages) and (ii) can be used to synthesize water-stable Cu-MOFNs in situ (a key result, given MOFs with Cu-oxo linkages usually exhibit poor water stability). CuBDTri nanosheets are also more catalytically active on a per-total-Cu-atom basis for a standardized test reaction (nitric oxide (NO) generation from S-nitrosoglutathione (GSNO)) than previously studied octahedral particles of the MOF CuBTTri (where H(3)BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), supporting the hypothesis that MOFNs are superior to particles with other morphologies for reactions where catalytic activity is limited to particle exterior surfaces (such as the NO generation reaction).

Automated summary

Metal-organic framework nanosheets (MOFNs) are promising materials for heterogeneous catalysis systems due to their active metal sites positioned on particle exterior surfaces. This study successfully synthesized water-stable CuBDTri nanosheets using a three-layer method. The CuBDTri nanosheets exhibited higher catalytic activity in a standardized test reaction compared to previously studied octahedral particles. This supports the superiority of MOFNs over particles with other morphologies in reactions where catalytic activity is limited to particle exterior surfaces.