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

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 À 1 h À 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 À /8H + photoreduction of CO 2 to CH 4 is realized with > 95 % selectivity (6.7 mmol g À 1 h À 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.

Photocatalytic CO2 Conversion Using Metal-Containing Coordination Polymers and Networks: Recent Developments in Material Design and Mechanistic Details

“…Self-assembly was proven by HR-TEM and powder X-ray diffraction (XRD) studies. The porphyrin-based monomers self-assembled together with Ru(II) ions to a fully coordinated polymer gel (Ru-TPY-POR CPG) ( Figure 6 a) [ 54 ]. Ru(II) was chosen due to its well-studied photocatalytic activity [ 55 ].…”

“…A high production rate of 3500 μmol g −1 h −1 with a selectivity of over 99% over CH 4 was observed when using TEA as SA ( Figure 6 b). Furthermore, the catalyst was stable without losing its performance for more than six cycles [ 54 ]. Previous research showed that the addition of BNAH was beneficial for photoreduction due to lower oxidation potential in comparison to TEA [ 56 ].…”

“…This regeneration step could not be shown in the presence of BNAH. When BNAH was oxidized, deprotonation and further dimerization to BNA 2 was induced [ 54 ]. The reduction potential of the BNA 2 dimer exceeded the one of BNAH, facilitating the quenching of the photosensitizer [ 56 ].…”

“…Final proton-coupled electron transfer released CH 4 and [Ru II (TPY •− )(TPY)] + was regenerated. These mechanistic insights revealed that covalent linkage of the photosensitizer and the catalyst could be a key factor for high performances and the choice of SA is critical for product selectivity [ 54 ].…”

Bis-Pyridine-Based Organogel with AIE Effect and Sensing Performance towards Hg2+

“…In the past thirty years, supramolecular chemistry has become even more sophisticated and quickly developed due to its applications in a variety of disciplines and fields [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. As a typical supramolecular material, low-molecular-weight gels (LMWGs) are a kind of soft material between a solid and liquid which have been developed rapidly and widely used in electrolyte materials [ 12 ], sensors [ 13 , 14 ], drug delivery systems [ 15 ], liquid crystal [ 16 ], supramolecular chirality [ 17 , 18 , 19 ], light-harvesting systems [ 20 , 21 ], surfactants [ 22 ] and other fields [ 23 , 24 , 25 , 26 , 27 , 28 ]. Organic molecules can be self-assembled into organogel or hydrogel under the driving force of noncovalent interactions, such as a hydrogen bond, metal coordination, π–π stacking, hydrophobic effect, electrostatic force and van der Waals force [ 29 , 30 , 31 , 32 , 33 ].…”