Lattice Engineering in Hydroxyapatite Enables Direct Photocatalytic Synthesis of C₄ Products from CO₂

Amid the burst of carbon dioxide (CO₂) capture and conversion technologies, research prioritizing industrially feasible catalysts is vital to minimize climate change effects. In the present work, permanently polarized hydroxyapatite-based biphasic systems have been strategically designed through vacancy engineering and a thermally stimulated polarization (TSP) process, achieving a 15% selectivity toward C₃-C₄ products through a single-step CO₂ continuous-flow reaction (CO₂-to-C₃₊) under solar light irradiation and mild reaction conditions. To elucidate the underlying catalytic mechanism, extensive experimental characterization has been performed in combination with theoretical density functional theory (DFT) calculations. More specifically, Raman spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy have been used for structural characterization, and electrochemical impedance spectroscopy studies have been performed to determine charge conduction customization. On the other hand, DFT calculations have been employed to determine the photocatalytic contribution by determining the density of states and band diagrams. The results have been further supported by UV-vis experimental measurements, facilitating the elucidation of the mechanisms behind the photoexcited electrons through band gap trap state generation. Finally, additional adsorption energy studies, combined with Bader charge analysis and Nudge elastic band calculations, have allowed the identification of the binding sites responsible for C₃₊ molecule growth as far as the CO₂ dissociation pathway and respective energy barrier. These results highlight the role of the crystal lattice vacancies in the CO₂ bond-cleavage process and represent a huge step toward the design of efficient and scalable catalysts for CO₂-to-C₃₊ production.