Shape-Controlled Metal-Free Catalysts: Facet-Sensitive Catalytic Activity Induced by the Arrangement Pattern of Noncovalent Supramolecular Chains

Metal-free catalytic materials have
recently received broad attention
as promising alternatives to metal-involved catalysts. This is owing
to their inherent capability to overcome the inevitable limitations
of metal-involved catalysts, such as high sensitivity to poisoning,
the limited reserves, high cost and scarcity of metals (especially
noble metals), etc. However, the lack of shape-controlled metal-free
catalysts with well-defined facets is a formidable bottleneck limiting
our understandings on the underlying structure–activity relationship
at atomic/molecular level, which thereby restrains their rational
design. Here, we report that catalytically active crystals of a porphyrin,
5,10,15,20-tetrakis­(pentafluorophenyl)­porphyrin, could be shaped into
well-defined cubes and sheet-like tetradecahedrons (TDHD), which are
exclusively and predominantly enclosed by {101} and {001} facets,
respectively. Fascinatingly, compared to the cubes, the TDHDs display
substantially enhanced catalytic activity toward water decontamination
under visible-light irradiation, although both the architectures have
identical crystalline structure. We disclose that such interesting
shape-sensitive catalytic activity is ascribed to the distinct spatial
separation efficiency of photogenerated electrons and holes induced
by single-channel and multichannel charge transport pathways along
noncovalent supramolecular chains, which are arranged as parallel-aligned
and 2D network patterns, respectively. Our findings provide an ideal
scientific platform to guide the rational design of next-generation
metal-free catalysts of desired catalytic performances.