Coordination-driven assembly of a ferrocene-functionalized lead iodide framework with enhanced stability and charge transfer for photocatalytic CO2-to-CH3OH conversion

Abstract

Hybrid lead halides are promising photocatalysts due to their high structural tunability and excellent photophysical properties, but their ionic structures suffer from instability in polar environments and suppressed charge transfer between lead halide units and organic components. Herein, we successfully incorporated a ferrocene-based light-harvesting antenna into a lead iodide framework by coordination-driven assembly. The π-conjugated Pb²⁺-carboxylate linkage affords synergistic interactions between [Pb₂I₂]²⁺ chains and ferrocene linkers, achieving broad visible absorption up to 612.7 nm and efficient ligand-to-metal charge transfer for spatial charge separation. This ultrastable framework combines strong visible-light absorption of ferrocene centers with excellent charge transport of lead halide units, achieving 6e^- CO₂ photoreduction to CH₃OH coupled with ethanol oxidation. Mechanistic studies reveal that ferrocene photoexcitation followed by linker-to-metal charge transfer significantly enhances carrier accumulation, accelerating CH₃O* intermediate formation as indicated by in situ spectroscopy and theoretical calculations.

Fig. 1. (Top) Synthetic scheme and crystallographic view of (FMTMA)PbI₃, including a single [PbI₃]⁻ chain with FMTMA⁺ cations and the overall structure of (FMTMA)PbI₃. (Bottom) Synthetic scheme and crystallographic views of TJU-26, including a single [Pb₂I₂]²⁺ chain coordinated with Fcdc²⁻ ligands and the overall structure of TJU-26.

Fig. 2. (a) PXRD patterns of TJU-26 before and after 24 h treatment in different organic solvents. (b) The PXRD patterns of TJU-26 and (FMTMA)PbI₃ after light irradiation (300 W Xe lamp, AM 1.5G) for 48 h and 24 h, respectively. (c) Normalized UV-vis diffuse reflectance spectroscopy of TJU-26 and (FMTMA)PbI₃. (d) Tauc plots of TJU-26 and (FMTMA)PbI₃. (e) Band alignment of TJU-26 and (FMTMA)PbI₃. (f) Calculated band structure and DOS of TJU-26.

Fig. 3. (a) Photoluminescence decay of H₂Fcdc, (FMTMA)PbI₃ and TJU-26 at room temperature. (b) SPV spectra of TJU-26 and (FMTMA)PbI₃. (c) Two-dimensional pseudo-color TA plot of TJU-26. (d) TA kinetics of TJU-26. (e) Extracted exciton binding energies of TJU-26. (Inset) Temperature-dependent PL spectra of TJU-26 with an excitation wavelength of 355 nm. (f) Extracted exciton binding energies of (FMTMA)PbI₃. (Inset) Temperature-dependent PL spectra of (FMTMA)PbI₃ with an excitation wavelength of 350 nm. (g) Schematic presentation showing the photoexcitation, photoinduced LMCT and carrier transport of TJU-26 (left) and the suppressed photoinduced LMCT in (FMTMA)PbI₃ (right).

Fig. 4. (a) Time courses of CH₃OH, CH₄ and CO evolution for photocatalytic CO₂ reduction by TJU-26 in EtOH (AM1.5G simulated sunlight). (b) The control experiments of photocatalytic CO₂ reduction performance over TJU-26 and (FMTMA)PbI₃. (c) ¹³C NMR results of ¹³CH₃OH produced over TJU-26 from the ¹³CO₂ isotope experiment. (d) Wavelength-dependent AQEs of photocatalytic CO₂ reduction on TJU-26. Error bars represent the deviations of monochromatic light wavelengths. (e) Time courses of CH₃OH production over 20 mg of TJU-26 in 10 mL of EtOH for four consecutive cycles. (f) Schematic diagram for photocatalytic CO₂ reduction by TJU-26.

Fig. 5. (a) In situ DRIFTS spectra for the photocatalytic CO₂ reduction process by TJU-26. (b) Free energy diagram of photocatalytic CO₂-to-CH₃OH transformation on the (001) facet of TJU-26. (c) Contact angle measurement of TJU-26 with water. (d) Vapor adsorption isotherms of TJU-26 at 298 K.