Confining charge-transfer complex in a metal-organic framework for photocatalytic CO2 reduction in water

Abstract

In the quest for renewable fuel production, the selective conversion of CO2 to CH4 under visible light in water is a leading-edge challenge considering the involvement of kinetically sluggish multiple elementary steps. Herein, 1-pyrenebutyric acid is post-synthetically grafted in a defect-engineered Zr-based metal organic framework by replacing exchangeable formate. Then, methyl viologen is incorporated in the confined space of post-modified MOF to achieve donor-acceptor complex, which acts as an antenna to harvest visible light, and regulates electron transfer to the catalytic center (Zr-oxo cluster) to enable visible-light-driven CO2 reduction reaction. The proximal presence of the charge transfer complex enhances charge transfer kinetics as realized from transient absorption spectroscopy, and the facile electron transfer helps to produce CH4 from CO2. The reported material produces 7.3 mmol g−1 of CH4 under light irradiation in aqueous medium using sacrificial agents. Mechanistic information gleans from electron paramagnetic resonance, in situ diffuse reflectance FT-IR and density functional theory calculation.

Pore-Confined π-Chromophoric Tetracene as a Visible Light Harvester toward MOF-Based Photocatalytic CO2 Reduction in Water

“…A clear bathochromic shift for absorbance and emission bands was observed when TET was encapsulated inside Zr-MOF compared to its solution state. This significant redshift can be surmised with the aggregation of the TET molecules inside the MOF nanopore as a result of the confinement effect. , In addition, the comparison of the time-resolved photoluminescence (TRPL) decay of TET in the solution state and the MOF encapsulated state revealed a significant difference in the average excited-state lifetime (Figure a). The average excited-state lifetime of TET in DMF was obtained as 4.33 ns, whereas Zr-MBA-TET-MOF displayed an enhanced lifetime of 12.79 ns.…”

“…Regulating molecular packing and controlling their self-assembly becomes the possible lane for molding them as a suitable material for organic optoelectronic and light-harvesting applications . Confining such chromophores inside rigid scaffolds like MOFs, covalent organic frameworks, and metal–organic cages can result in drastic changes in their photophysical properties, including excited-state dynamics, reaction kinetics, and electronic structure, which in turn affect the absorption/emission maxima, quantum yield, and excited-state lifetime in comparison to the unrestricted state of the chromophore. − In addition, the intermolecular locking can suppress the molecular motion-induced nonradiative transition, thereby benefiting the cumulation and utilization of excited-state electrons. , MOFs have emerged as appreciable host systems with tunable pore sizes and surface areas for loading guest molecules via both postsynthetic modifications and in situ ensnaring in the pores. − Moreover, MOFs decorated with suitable functional moieties can provide a well-defined nanospace for confining the molecules and regulating their orientation . In addition, the confinement can eliminate the self-quenching in absorption and emission of the molecules and thereby enhance the light response of the system .…”

“…29−33 Moreover, MOFs decorated with suitable functional moieties can provide a well-defined nanospace for confining the molecules and regulating their orientation. 34 In addition, the confinement can eliminate the self-quenching in absorption and emission of the molecules and thereby enhance the light response of the system. 35 Herein, we have explored the feasibility of utilizing the light-harvesting nature of a π-chromophoric molecule, TET, toward CO 2 photoreduction by confining them in a MOF nanopore having the proximity of covalently grafted catalytic center to facilitate the fast electron transfer aiding the appreciable CO 2 reduction reaction.…”

Modular Gating of Ion Transport by Postsynthetic Charge Transfer Complexation in a Metal–Organic Framework

“…The pore size distribution was calculated from the non-local density functional theory (NLDFT) method, which illustrates the presence of two types of pores in the framework, micropores situated at 1.6 nm, and mesopores located in the range of 2–10 nm (Figure S10). The origin of mesoporosity in MOF-808 can be attributed to missing linker and cluster defects in the MOF secondary building units (SBUs), as reported earlier. − The 1.6 nm micropore of MOF-808 was consistent with the lattice fringe spacing calculated from the HRTEM images (Figure e). Moreover, HRTEM images of MOF-808 depicted uniformly distributed micro- and mesopores (Figure e, inset).…”

Defect-containing metal–organic framework materials for sensor applications

“…Sanchita Karmakar et al 105 utilized the SALE method to synthesize defective MOF-808-PBA. This intricate integration of methyl viologen generated a sophisticated donor–acceptor composite, akin to an artificial “special pair” at the molecular level (Fig.…”