Confining Molecular Photosensitizer and Catalyst in MOF toward Artificial Photosynthesis: Validating Electron Transfer by <i>In Situ</i> DRIFT Study
Sneha Raj V. Parambil, Sanchita Karmakar, Faruk Ahamed Rahimi, Tapas Kumar Maji
Abstract
Exploration of different chemical systems for photocatalytic CO 2 reduction by using sunlight en route to the achievement of artificial photosynthesis stems from global warming and the energy crisis. In this work, we have covalently grafted the molecular photosensitizer (PS) [Ru(MBA)(bpy) 2 ]Cl 2 (bpy: 2,2′-bipyridine) and the catalyst [Mn(MBA)(CO) 3 Br] inside the Zr-MOF-808 ( Zr-MOF ) nanopore postmodified with 2-(5′-methyl-[2,2′-bipyridine]-5-yl)acetic acid (H-MBA) and developed a single integrated system named Zr-MBA-Ru/Mn-MOF for the CO 2 reduction reaction (CO 2 RR). Zr-MBA-Ru/Mn-MOF is found to be active toward CO 2 -to-CO conversion, with a maximum production of 1027 μmol g –1 after 26 h of reaction having >99% selectivity in the aqueous medium without any additional hole scavenger. The catalyst with direct sunlight in the aqueous medium is equally active for CO production, thus mimicking the natural photosynthetic process. We have performed an in situ diffuse reflectance Fourier transform infrared spectroscopy (FTIR) (DRIFT) study to unveil the electron transfer from the PS to the catalytic center during CO 2 reduction by monitoring the changes in the carbonyl stretching frequency in the [Mn(MBA)(CO) 3 Br] center and correlated with the density functional theory (DFT) calculations. Additionally, we have performed in situ DRIFT spectroscopy to understand the reaction mechanism for the CO 2 -to-CO conversion.