Enhanced Solar CO₂ Photoreduction to Formic Acid by Platinum Immobilization on Bipyridine Covalent Triazine Framework with Defects

The immobilization and structural analysis of platinum nanoparticles on a nitrogen-rich, bipyridine-containing covalent triazine framework (bpyCTF) having structural defects are disclosed by taking advantage of ¹⁵N solid-state nuclear magnetic resonance measurements at natural ¹⁵N isotope abundance and X-ray photoelectron spectroscopic analyses. The photocatalyst (Pt@bpyCTF) with structural defects reduces CO₂ to formic acid (FA) at a rate of 152 µmol h⁻¹g⁻¹ and a selectivity higher than 95% over CO and H₂ in water under simulated solar light. The presence of amine defects and the immobilization of Pt cause improvement in the photocurrent density and CO₂ capture capacity (≈8% by weight) despite the moderate surface area (0.54 cm³ g⁻¹)of the photocatalyst. Theoretical models and density functional theory calculations are employed to investigate the possible CO₂ reduction reaction (CO₂RR) mechanisms. Considering the exceptional CO₂ capture capacity and high FA production using only CO₂-bubbled water, this work highlights the great potential of nitrogen-rich CTFs for photocatalyzed CO₂RRs under green conditions.