Visible‐Light‐Driven Photocatalytic CO2 Reduction to CO/CH4 Using a Metal–Organic “Soft” Coordination Polymer Gel

Abstract

AbstractThe 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 RuII ions results in a Ru‐TPY‐POR coordination polymer gel (CPG), with a nanoscroll morphology. Ru‐TPY‐POR CPG exhibits efficient CO2 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 CO2 to CH4 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 CO2 reduction to CO and CH4 was outlined.