Synergistic Role of Dual Metal (V) and Non-Metal (N) Doping with Carbon Sensitization in 3D Hierarchical Nb₂O₅ for Highly Selective Visible-Light-Driven CO₂-to-CH₄ Photoreduction

Photocatalytic CO₂ conversion into energy-rich fuels offers a sustainable route to address global energy and environmental challenges. However, achieving high activity and selectivity under visible light remains a key limitation. In this study, a 3D hierarchical Nb₂O₅ nanoflower photocatalyst dual-doped with vanadium (V), nitrogen (N), and sensitized with carbon (designated NVNBOC) is synthesized via a two-step hydrothermal process followed by calcination. The incorporation of dual metal and non-metal dopants, in combination with carbon sensitization, yielded a strong synergistic effect, significantly enhancing both photocatalytic performance and selectivity. Under visible-light irradiation, the NVNBOC catalyst achieved a remarkable methane (CH₄) production rate of 78.32 µmol·g⁻¹·h⁻¹, approximately 12 times higher than that of pristine Nb₂O₅, with an outstanding CH₄ selectivity of 97.10%. In-situ DRIFTS results revealed that the NVNBOC photocatalyst facilitates a stepwise CO₂ reduction pathway, involving key intermediates such as *HCOO⁻, *CHO, and *CH₃O, ultimately leading to full CH₄ generation. These findings demonstrate the pivotal role of dual dopant engineering in enhancing light utilization, charge separation, and intermediate stabilization, providing a promising approach for advancing visible-light-driven photocatalytic CO₂ reduction toward practical clean energy applications.