Visible-Light-Driven Photocatalytic CO 2 Reduction to CO/CH 4 Using a Metal-Organic "Soft" Coordination Polymer Gel.

The self-assembly of a well-defined and astutely designed, low-molecular weight gelator (LMWG) based linker with a suitable metal ion is a promising method for preparing photocatalytically active coordination polymer gels. Here, we report the design, synthesis, and gelation behaviour of a tetrapodal LMWG based on a porphyrin core connected to four terpyridine units (TPY-POR) through amide linkages. The self-assembly of TPY-POR LMWG with Ru II ions results in a Ru-TPY-POR coordination polymer gel (CPG), with a nanoscroll morphology. Ru-TPY-POR CPG exhibits efficient CO 2 photoreduction to CO (3.5 mmol g -1  h -1 ) with >99 % selectivity in the presence of triethylamine (TEA) as a sacrificial electron donor. Interestingly, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH) with TEA as the sacrificial electron donor, the 8e - /8H + photoreduction of CO 2 to CH 4 is realized with >95 % selectivity (6.7 mmol g -1  h -1 ). In CPG, porphyrin acts as a photosensitizer and covalently attached [Ru(TPY) 2 ] 2+ acts as a catalytic center as demonstrated by femtosecond transient absorption (TA) spectroscopy. Further, combining information from the in situ DRIFT spectroscopy and DFT calculation, a possible reaction mechanism for CO 2 reduction to CO and CH 4 was outlined.