Strategic Design of Mg-Centered Porphyrin Metal–Organic Framework for Efficient Visible Light-Promoted Fixation of CO₂ under Ambient Conditions: Combined Experimental and Theoretical Investigation

Abstract

The sunlight-driven fixation of CO 2 into valuable chemicals constitutes a promising approach toward environmental remediation and energy sustainability over traditional thermal-driven fixation. Consequently, in this article, we report a strategic design and utilization of Mg-centered porphyrin-based metal− organic framework (MOFs) having relevance to chlorophyll in green plants as a visible light-promoted highly recyclable catalyst for the effective fixation of CO 2 into value-added cyclic carbonates under ambient conditions. Indeed, the Mg-centered porphyrin MOF showed good CO 2 capture ability with a high heat of adsorption (44.5 kJ/mol) and superior catalytic activity under visible light irradiation in comparison to thermal-driven conditions. The excellent light-promoted catalytic activity of Mg−porphyrin MOF has been attributed to facile ligand-to-metal charge transfer transition from the photoexcited Mg−porphyrin unit (SBU) to the Zr 6 cluster which in turn activates CO 2 , thereby lowering the activation barrier for its cycloaddition with epoxides. The in-depth theoretical studies further unveiled the detailed mechanistic path of the light-promoted conversion of CO 2 into high-value cyclic carbonates. This study represents a rare demonstration of sunlight-promoted sustainable fixation of CO 2 , a greenhouse gas into value-added chemicals.

Photo-Responsive Signatures in a Porous Organic Polymer Enable Visible Light-Driven CO2 Photofixation

“…The overall negative stabilization energy indicates that the conversion from STE to STC is energetically feasible. Based on the above experiments, we suggest the mechanistic pathway for light-irradiated CO 2 cycloaddition reaction to cyclic carbonates, where the Py-POP acts as a photocatalyst that can harvest light and activate the CO 2 molecule, as shown in Figure b . First, the Zn 2+ cocatalyst triggers the epoxide ring-opening via an O–Zn 2+ interaction followed by a Br – ( TBAB ) attack at the epoxide ring.…”

“…•− by taking photoexcited electrons from the conduction band (CB) after irradiation of light on the photocatalyst. 57,58 Thus, from previous reports, it is well established that activation of the epoxide ring is crucial and can be controlled by changing the electron density in the epoxide ring. The EWG and EDG play a crucial role that can reduce or increase the electron density in the epoxide ring, respectively.…”

“…Recently, Wang and co-workers demonstrated the photocatalytic cycloaddition of CO 2 to epoxides based on an S-scheme photocatalysis where the styrene epoxide ( STE ) is oxidized to STE + by photogenerated holes from the valence band (VB) of the π-conjugated electron-rich photocatalyst . The CO 2 molecule is reduced to CO 2 •– by taking photoexcited electrons from the conduction band (CB) after irradiation of light on the photocatalyst. , Thus, from previous reports, it is well established that activation of the epoxide ring is crucial and can be controlled by changing the electron density in the epoxide ring. The EWG and EDG play a crucial role that can reduce or increase the electron density in the epoxide ring, respectively.…”

Nanocage-Based Tb3+-Organic Framework for Efficiently Catalyzing the Cycloaddition Reaction of CO2 with Epoxides and Knoevenagel Condensation

“…Furthermore, the results were consistent with previous literature reports: electron-withdrawing groups (−F, −CF 3 , −Cl, −CC) had a positive effect on the reaction (entries 2–4 and 6). − The molecular sizes of all epoxy derivatives are shown in Table S5. In addition, compared with various newly reported nanochannel-based MOF catalysts such as UiO-66-Gua0.2(s), 2, and Rh-PMOF-1 (Table ), − NUC-58a owns a more efficient catalytic activity, which should be due to the satisfactory structural merits from nanoporous channels, enough Lewis acidic sites from {Tb 4 } clusters, plentiful basic sites of N pyridine atoms, and μ 2 –OH groups.…”

Nanochannel-Based Heterometallic {CoIITbIII}-Organic Framework for Fluorescence Recognition of Tryptophan and Catalytic Cycloaddition of Epoxides with CO2

“…As shown in Table S5, the catalytic activity of these components is lower than that of the NUC-31 framework. Moreover, compared with MOF-based catalysts reported in recent literature, − NUC-31 shows excellent catalytic performance (Table S6), which can be attributed to the high CO 2 concentration around the hollow channel of the NUC-31 main framework due to the active metal sites (Co II and Tb III ), unmatched pyridine, free carboxyl oxygen atoms, and undisturbed void space in its structure.…”