Enhanced photocatalytic carbon dioxide reduction over iron tungstate/covalent organic framework heterojunctions by the induced unified adsorption and reduction sites

Inorganic-organic S-scheme heterostructure photocatalysts have demonstrated exceptional potential in boosting charge separation for CO₂ reduction. However, the reduction typically occurs at the inorganic site, resulting in underutilization of high CO₂ adsorption capacity of organic material. To resolve this mismatch, we combined a low conduction band iron tungstate (FeWO₄) with a dioxin-linked covalent organic framework (COF) to construct S-scheme heterojunction, where the COF serve as the reduction photocatalysts and FeWO₄ act as the oxidation photocatalysts, for photocatalytic CO₂ reduction. Density functional theory (DFT) calculations and in-situ spectroscopic analyses confirm that the FeWO₄/COF hybrids steer an S-scheme charge transfer pathway driven by an enhanced internal electric field. Benefiting from the synergy between the strong CO₂ adsorption at the COF cyano site, which aligns with its role as the reduction site, and the unique S-scheme electron transfer, the composites achieve a significantly higher CO yield (55.9 μmol·g⁻¹·h⁻¹) than COF (5.5 μmol·g⁻¹·h⁻¹) with 100 % selectivity and no sacrificial agents or sensitizers. Isotope tracer experiments verify that the CO was from CO₂. In-situ Fourier transform infrared spectroscopy (FT-IR) coupled with two-dimensional correlation spectroscopy (2D-COS) unveils the sequential reduction process of CO₂. This study envisions a harmoniously aligned inorganic/organic S-scheme heterojunction for boosting CO₂ photoreduction.