Porphyrin Supramolecular Nanoassembly/C3N4 Nanosheet S-Scheme Heterojunctions for Selective Photocatalytic CO2 Reduction toward CO

The photocatalytic reduction of CO2 with H2O into valuable chemicals is a sustainable carbon-neutral technology for renewable energy; however, the photocatalytic activity and product selectivity remain challenging. Herein, an S-scheme heterojunction photocatalyst with superior CO2 photoreduction performance─porous C3N4 (CN) nanosheets anchored with zinc(II) tetra(4-cyanophenyl)porphyrin (ZnTP) nanoassemblies (denoted as ZnTP/CN)─was designed and prepared via a simple self-assembly process. The constructed ZnTP/CN heterojunction had rich accessible active sites, improved CO2 absorption capacity, and high charge carrier separation efficiency caused by the S-scheme heterojunction. As a result, the obtained ZnTP/CN catalyst exhibited considerable activity for photocatalytic CO2 reduction, yielding CO with a generation rate of 19.4 μmol g-1·h-1 and a high selectivity of 95.8%, which is much higher than that of pristine CN nanosheets (4.53 μmol g-1·h-1, 57.4%). In addition, theoretical calculations and in situ Fourier transform infrared spectra demonstrated that the Zn sites in the porphyrin unit favor CO2 activation and *COOH formation as well as CO desorption, thereby affording a high CO selectivity. This work provides insight into the design and fabrication of efficient S-scheme heterostructure photocatalysts for solar energy storage.