In situ construction of Fe substituted palygorskite/FeS2 heterostructure for full-spectrum photocatalytic nitrogen fixation

Highlights: • Cost-effective photocatalyst constructed by 1-D natural palygorskite. • Fe substitution reduced the band gap of Pal with structure unchanged. • In situ precipitated FeS₂ harvested the near infrared light. • Sulfur vacancies and Fe species contributed to activation of nitrogen. • Z-scheme FeS₂/Fe-Pal preserved high charge potential for N₂ reduction. -- Abstract: The innovation of cost-effective ammonia synthesis under mild condition to replace traditional Haber-Bosch process remains a grand challenge. In this work, partial cations in one-dimensional clay palygorskite (Pal) were substituted by Fe ions to achieve lattice reconstruction, followed by in situ precipitation of FeS₂ nanoparticles using a microwave hydrothermal method. The band gap of Fe-modified Pal was largely reduced with the perseverance of its original crystal structure. As the Fe content exceeded 20 wt%, excess Fe ions on the surface of Fe-Pal reacted with sulfide ions to form iron sulfide (FeS₂), which owned narrow bandgap (1.3 eV) responsive in near infrared (NIR) light. The presence of abundant sulfur vacancies (S_v) as well as Fe species served as nitrogen adsorption and activation center, which promoted the adsorption of N₂ and weakened the NN triple bond. A Z-scheme heterostructure can be formed between Fe-Pal and FeS₂ intermediated by S_v, improving the adsorption range of solar light and enhancing the redox potential for N₂ reduction. The optimized 40 wt% Fe-Pal exhibited remarkable N₂ fixation ability in a wide spectrum, providing a new perspective for cost-effective photocatalytic nitrogen fixation.