One-Pot Synthesis of a Hierarchical-Octahedral NiSe₂ as a Co-Catalyst for Enhanced CO₂ Photoreduction Under Full-Spectrum Light Irradiation

Excess carbon dioxide emission accompanied by gross fossil fuel consumption has worsened the global warming crisis in recent decades. The photocatalytic conversion of CO₂ into hydrocarbons is a potential solution to mitigate both energy and environmental problems. However, conventional photocatalysts suffer low efficiency in CO₂ conversion with C1 and/or C2 products. Nanostructured perovskite oxides (titanates) have emerged as a class of high-performance photocatalytic materials because of their nontoxic nature, adequate chemical stability, tunable crystal structures, band gaps, and surface energies. Two-dimensional (2D) transition metal dichalcogenides (TMDs) are another emerging group of materials that got high attention due to their light absorption, high conductivity, low cost, and non-toxic properties. The design and fabrication of layered transition metal chalcogenides with high exposure of crystal layer edges is one of the key paths to achieving distinctive performances in their catalysis and electrochemistry applications. Nevertheless, the photocatalytic performance and CO₂ reduction efficiencies are still low due to severe charge recombination and sluggish kinetics. Therefore, the rational design and preparation of dissimilar dimensional materials have been extensively investigated for use to effectively increase photocatalytic performance.<br/>In this study, we report an effective strategy to synthesize a unique octahedron-shape NiSe₂ nanoparticles from a one-dimensional (1D) NiTiO₃ nanofibers (NFs) precursor. Firstly, the 1D NiTiO₃ NFs are prepared by electrospinning and then combined with Se powder through the solvothermal method. The 1D NiTiO₃ NFs acted bi-functionally, as both the Ni source and the substrate. The combined effect of NiTiO₃ NFs and NiSe₂ has been optimized by varying the loading amounts of Se powder. The varying amounts of Se powder play a vital role in optimizing the photocatalytic behavior of the NiTiO₃ NFs/NiSe₂. Among different NiTiO₃/NiSe₂ products, 0.09 wt.% loading of Se powder shows superior photocatalytic performance because of the unique octahedron-like morphology and enhanced active sites. The as-synthesized sample exhibits lower charge recombination, higher current densities, and outstanding photocatalytic conversion of CO₂ into CO, and CH₄ shows 90% selectivity. This enhanced photocatalytic performance should be attributed to its higher light absorption, efficient charge separation, and transfer as well as a relatively large number of surface-active sites. The structure and morphology of the octahedra with more surfaces endow the NiSe₂ favorable for more chemical reactions with exposed active sites. NiSe₂ acted as a novel cooperative co-catalyst to trap the electrons and improve charge separation efficiency. Hence, we presume that the synthesized one-dimensional NiTiO₃ NFs precursor-derived NiSe₂ nanoparticles have excellent potential to replace the noble-metal-based photocatalyst for enhanced photocatalytic activity.