First principles studies on the structural, electronic, and optical properties of stannite-type quaternary crystal for water treatment

Abstract Stannite-type quaternary crystals have emerged as promising, low-toxicity candidates for photocatalytic water treatment; however, the effectiveness of many conventional photocatalysts is often impeded by their large bandgaps when exposed to visible light. Therefore, there is a need to develop narrow-bandgap materials to maximize photocatalytic activity in the visible spectrum. This study employs first-principles calculations grounded in density functional theory (DFT) to examine the structural, electronic, and optical properties of magnesium (Mg)-doped Ag 2 (Zn)SnS 4 . A sampling mesh of 4 × 4 × 2 k-points was used for the calculations with a cut-off energy of 523 eV and the total energy convergence within 1 × 10 −6 eV atom −1 . The findings reveal that Mg-doping significantly reduces the direct bandgap from 1.153 eV (undoped) to a range of 0.597–0.688 eV, depending on the substitution ratio. This narrowing results in a considerable red shift in optical absorption from the ultraviolet to the visible spectrum. Moreover, Mg-doped structures demonstrate decreased reflectivity and improved conductivity in the visible spectrum compared to their undoped counterparts. These findings reveal that Mg substitution doping effectively enhances the semiconductor properties of Ag 2 (Zn)SnS 4 , making it a highly effective material for visible-light-driven photocatalytic water treatment applications.