Efficient UV–Vis–NIR Responsive CO₂ Reduction Photocatalyst with Black Pinecone-Shaped Carbon Nitride Loaded with Lanthanum Oxide

Photothermal catalysis combines the advantages of photocatalysis and thermal activation, which provides a new research angle for CO₂ catalytic reduction. In this study, Black carbon nitride with a three-dimensional (3D) pinecone-shaped structure (BPCN) was prepared by a simple solvothermal method using melamine as a precursor without the aid of a template. Lanthanum oxide doping on the BPCN catalysts (BPCN-La) was achieved by ultrasonic impregnation. This unique pinecone-shaped structure consists of self-assembled and interlaced carbon nitride rods (by SEM). The lanthanum element was distributed on the surface of the CN framework in the form of La₂O₃ (by XPS). The chemical structures of the samples were characterized by solid-state ¹³C nuclear magnetic resonance (¹³C NMR) and elaborated by density functional theory (DFT) analysis. This black carbon nitride expanded the light absorption band edge into the near-infrared (NIR) (300-1400 nm, by UV-vis absorption spectra) and had excellent photothermal conversion activity. La atom doping can significantly boost photogenerated electron excitation (by photocurrent test) and promote carrier separation and transfer (by PL). Upon incorporation of La atoms into BPCN, the highest occupied molecular orbital (HOMO) orbital is more concentrated on the oxygen atoms of La₂O₃. BPCN-La considerably narrowed the band gap width, exhibited an exceptional photothermal effect, and provided a large surface area, which significantly enhanced the photocatalytic reduction of CO₂ reactions. The yields of CO reached 58.2 and 104.9 μmol·h^-1·g^-1 for BPCN and BPCN-La, respectively, with GCN as the control (6.3 μmol·h^-1·g^-1). Theoretical reaction pathways and selectivity for the photoreduction of CO₂ on BPCN and BPCN-La were studied by DFT simulation. This work provides a new vision for the design of photothermal synergistic without extra-thermal input and full spectral response photocatalysts with high efficiency.