Shock wave-driven phase transition of iron sulphide for enhanced photocatalytic application: a combined experimental and DFT approach

In the present investigation, we systematically investigate how acoustic shock waves induce a phase transition from FeS to α-Fe₂O₃ and how this transition influences the material's structural, morphological, optical, and photocatalytic properties. The findings from X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet differential reflectance spectroscopy (UV-DRS), and X-ray photoelectron spectroscopy (XPS) studies unequivocally demonstrate a complete phase transition from FeS to α-Fe₂O₃ at 600 shock pulses. The control sample has an uneven morphology. The material exhibits moderate morphological changes but maintains its fundamental FeS phase after 400 shock pulses. On the other hand, the material undergoes a notable structural and morphological change at 600 shock pulses, assuming a distinct needle-like shape that is suggestive of phase transition and improved crystallinity. UV-DRS analysis reveals an increase in optical reflectance and a noticeable blue shift in the energy band gap under 600-shock conditions, further supporting the formation of a new phase with altered electronic structure. Density Functional Theory (DFT) calculations further support these findings, revealing a reduction in the electronic density of states (DOS) near the Fermi level upon phase transition, indicative of the enhanced charge separation crucial for improved photocatalytic performance. As a result, for FeS subjected to 600 shock pulses, transition to α-Fe₂O₃ exhibits superior photocatalytic efficiency and reaction rates compared to the control and other shock-treated samples.