Visible Light Responsive Ni‐Doped Hierarchical SnS ₂ Nanoflowers for Photocatalytic Removal of Atmospheric NO _x Gas

Abstract Efficient removal of nitrogen oxides (NO _x ) from urban air is a pressing environmental need. Here, Ni‐doped SnS ₂ nanoflowers are synthesized via a microwave‐assisted solvothermal method and their visible‐light‐driven NO _x abatement performance is evaluated. X‐ray diffraction and Raman confirm phase‐pure hexagonal SnS ₂ , while X‐ray photoelectron spectroscopy verifies successful Ni ² ⁺ incorporation without secondary phases. Ni doping slightly distorts the marigold flower‐like morphology observed in pristine SnS ₂ and narrows the bandgap (UV–vis), enhancing visible‐light absorption and charge separation. Photoluminescence spectra reveal suppressed carrier recombination, with 5 wt% Ni‐doped SnS ₂ showing the lowest emission intensity. Photocatalytic tests demonstrate that this composition achieves the highest NO _x removal efficiency (14.2%) within 60 min, 1.6× higher than pristine SnS ₂ , while maintaining 70% activity after ten cycles. Theoretical calculations reveal Ni‐3 d /S‐p hybridization and the introduction of mid‐gap states, which lower the optical transition threshold and support the experimentally observed bandgap narrowing and enhanced light harvesting. A mechanism involving Ni‐induced electron trapping and reactive oxygen species generation is proposed to explain the enhanced activity. This work establishes Ni doping as an effective strategy to tailor the structural, optical, and electronic properties of SnS ₂ , delivering a low‐cost, stable, and highly active photocatalyst for sustainable NO _x mitigation.