Transition metal doping effects on the structural, mechanical, electronic, and optical properties of α-NiS for photocatalysis applications via DFT + U insights

Abstract Understanding and engineering material properties at the atomic level is critical for developing efficient photocatalysts. In this work, we systematically investigated the effects of transition metal (TM) including Co, Cu, Fe, Mn, and Zn doping on the structural, mechanical, electronic, magnetic, and optical properties of α-NiS using the DFT + U method and explores its potential in photocatalytic applications. A 25% substitution of Ni atoms with each TM dopant was modeled. The structural analysis reveals that TM doping increases lattice constants and bond lengths attributed to the atomic radius differences between dopants and the host Ni atom. Mechanical stability, ductility, and ionic bonding characteristics are preserved across all doped systems. Electronic structure calculations show that doping modulates the indirect bandgap, ranging from 1.10 eV to 2.57 eV, with partial density of states analyses highlighting the orbital contributions from dopants. Doping also introduces magnetic behavior and mid-gap states, absent in undoped α-NiS, which may enhance photocatalytic activity by facilitating charge separation and reducing recombination rates. Optical property evaluations indicate improved visible-light absorption in doped materials, further supporting their potential for photocatalytic applications. Effective mass and carrier concentration calculations reveal that Fe and Co doping drastically enhance charge carrier mobility and separation in α-NiS, underscoring their superior potential for visible-light-driven photocatalysis. This theoretical study provides a fundamental understanding of TM doped α-NiS systems and offers valuable insights for guiding future experimental work in photocatalyst design.