Porous Organic Polymers (POPs) represent an emerging class of porous organic materials which mainly comprising with organic building blocks, interconnected via strong covalent bonds thereby offering highly cross-linked frameworks with...
Post-combustion CO2 capture, storage, and separation have garnered colossal research interest in the energy industry, although realistic implementation of the available porous adsorbents is restricted owing to their cost competitiveness, stability, and scalability issues. The integration of heteroatom functionalities (N, O, or S) at the molecular level into the organic skeleton of porous framework materials endowed them with superior CO2 adsorbents to mitigate greenhouse gases. In this work, we have successfully introduced triazine–thiophene (Tt) groups to the nanoporous organic polymer (POP) skeleton by Friedel–Craft alkylation of Tt (as a monomer) with a series of cross-linking agents including formaldehyde dimethyl acetal, 1,4-bis(bromomethyl)benzene (BMB), and 4,4′-bis(bromomethyl)biphenyl, which contained methylene, bis-methylene benzene, and bis-methylene biphenyl moieties in each linker unit, respectively. The precise skeleton engineering with the variation of organic cross-linking agents at the molecular level leads to the development of Tt-POP-1, Tt-POP-2, and Tt-POP-3, having nanorod-, nanocoral-, and nanocloud-like morphologies, respectively. In particular, at 273 K, Tt-POP- 1, Tt-POP- 2, and Tt-POP-3 exhibited CO2 uptake capacities of about 33.04, 40.06, and 34.12 cm3/g, respectively, up to 1 bar pressure. Interestingly, Tt-POP-2 bearing a BMB linker exhibited enhanced CO2 uptake capacity both at 298 and 273 K in comparison with the other Tt-POP-1 and Tt-POP-3, respectively. An in-depth study of the CO2 adsorption mechanism by density functional theory calculations showed that the benzyl rings of linker units in Tt-POP-2 and Tt-POP-3 play a pivotal role in CO2 uptake. The more polarized interaction of CO2 with the thiophenyl and benzyl rings compared to the N and S atoms in Tt-POP-2 results in enhanced CO2 uptake capacity with respect to the others.
Porous organic polymers (POPs) continue to garner immense attention for CO 2 capture and sequestration (CCS) as well as CO 2 fixation to generate useful chemicals for alleviating global warming. Functionally engineered, visible light responsive organic photopolymers with extended π-conjugation and abundant heteroatoms enable photogenerated charge carriers, enhancement in visible light absorption, higher charge separation, and reduction in charge recombination during photocatalysis. In this work, we have explored the construction of a chemically stable, pyridine-equipped, and imine-linked porous organic polymer (Py-POP) by template-free Schiff base condensation of 1,3,5-tris(4aminophenyl) benzene (APB) and 2,6-pyridinedicarboxaldehyde (PDC). This donor−acceptor Py-POP with extensive π-conjugations enables photocatalytic fixation of CO 2 with styrene epoxide (STE) under visible light illumination. We have achieved an impressive conversion of STE to styrene carbonate (STC) (∼99%) under optimized reaction conditions using tert-butyl ammonium bromide (TBAB) as a promoter. Both the efficient CO 2 adsorption and activation for photocatalytic fixation reaction are enabled by the existence of both imine and pyridine moieties in Py-POP. The interaction between Py-POP and CO 2 is further illustrated by density functional theory (DFT) calculations that show that all the POP-CO 2 interactions are favorable and exergonic. Using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization techniques, we elucidate the mechanistic pathways of active key surface species in CO 2 photofixation with Py-POP. Our results provide mechanistic insight into the effectiveness of efficient, sustainable porous organic photocatalysts in visible light-driven CO 2 conversion for various energy applications.
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