Visible‐Light‐Driven Photocatalytic CO<sub>2</sub> Reduction to CO/CH<sub>4</sub> Using a Metal–Organic “Soft” Coordination Polymer Gel
Parul Verma, Faruk Ahamed Rahimi, Debabrata Samanta, Arup Kundu, Jyotishman Dasgupta, Tapas Kumar Maji
Abstract
Abstract 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.